PROJECT SYNOPSIS

 Enercel^® formulation testing

 

Background and rationale:

Quality of life, disease prevention and slowing of the aging process depend upon healthy cellular, immune system, hormonal and other organ function.  The number of bodily systems which need to be maintained in optimal function in order to ensure the best overall health possible is large.  A number of supplements, dietary changes and other treatments would be necessary for optimal health unless a strategy of diffuse organ improvement could be achieved with one intervention. To this effect, the intracellular ACE-inducer, Enercel, was assayed for a number of markers of vigorous overall function.

 

 Purpose of study:

1) validate the activity of Enercel in 7 assays of cellular function

2) determine the toxicity of the formulation.

 

Methods:

1)  NK cell function assay

2)  Lymphocyte proliferation

3)  IGF-1 and HGH levels

4)  Anti-cancer test

5)  Cytochrome p450 assays

6)  Glutathione peroxidase

7)  Trypan blue toxicity assay to PBMC

 

Results: 

1)   Enercel had a 255% increase in NK function over no additive

2)        The PI was increased by Enercel 94% over baseline

3)        IGF-1 and HGH OD were improved by 390% and 286%, respectively

4)        Anti-cancer activity was increased by 362%

5)        Seven of nine cytochrome p450 isozymes had significantly increased activity with Enercel addition

6)        The OD of glutathione peroxidase activity was increased by 74%

7)                                        7) There was no toxicity of up to concentrations of undiluted Enercel

 Conclusions:

Enercel improved the activity of assays from several vital organ systems.  Together, these systems comprise much of the bodily function needed for optimal health.  In vivo correlation is needed, but

Enercel is a candidate for intervention in defective quality of life states and also such diverse conditions as fatigue, hormonal defects, Anti-aging protocols, chronic and acute infections, liver disease and more.  Finally, Enercel had no demonstrable toxicity, even when used undiluted.

 

 

 

A

I.                  A

II.               Intra-cellular ACE-inducer:

 

ACE, in this context, is an acronym for "Alternate Cellular Energy".  These are non-mitochondrial sources of energy in the cell.  Enercel induces their function, leading to better energy production in cells.

 

Non-mitochondrial:

1)     Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.

 

2)     In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth. 

 

3)     ACE’s are non-mitochondrial sources of energy.

 

1-1

Natural killer cells (or NK cells) are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses. The cells kill by releasing small cytoplasmic granules of proteins called perforin and granzyme that cause the target cell to die by apoptosis or necrosis.

NK-cells are defined as large granular lymphocytes (LGL) and constitute the third kind of cells differentiated from the common lymphoid progenitor generating B and T lymphocytes.  They do not express T-cell antigen receptors (TCR) or Pan T marker CD3 or surface immunoglobulins (Ig) B cell receptor but that usually express the surface markers CD16 (FcγRIII) and CD56 in humans, and NK1.1/NK1.2 in certain strains of mice. Up to 80% of NK cells also express CD8.

They were named "natural killers" because of the initial notion that they do not require activation in order to kill cells that are missing "self" markers of major histocompatibility complex (MHC) class I.

III.  Activation

Given their strong cytolytic activity and the potential for auto-reactivity, Natural Killer cell activity is tightly regulated. Natural Killer cells must receive an activating signal, which can come in a variety of forms, the most important of which are listed below.

• 'Cytokines'

The cytokines play a crucial role in NK-cell activation. As these are stress-molecules, released by cells upon viral infection, they serve to signal to the NK-cell the presence of viral pathogens.

• 'Fc Receptor'

NK-cells, along with macrophages and several other cell types, express the FcR molecule, an activating biochemical receptor that binds the Fc portion of antibodies. This allows Natural Killer cells to target cells against which a humoral response has been mobilized and to lyse cells through Antibody-dependent cellular cytotoxicity (ADCC).

• 'Activating and inhibitory receptors'

Aside from the Fc receptor, Natural Killer cells express a variety of receptors that serve to either activate or suppress their cytolytic activity. These receptors bind to various ligands on target cells, both endogenous and exogenous, and have an important role in regulating the NK-cell response.

IV.Mechanism

 

Schematic diagram indicating the complementary activities of cytotoxic T-cells and NK cells.

NK cells are cytotoxic; small granules in their cytoplasm contain proteins such as perforin and proteases known as granzymes. Upon release in close proximity to a cell slated for killing, perforin forms pores in the cell membrane of the target cell through which the granzymes and associated molecules can enter, inducing apoptosis. The distinction between apoptosis and cell lysis is important in immunology: lysing a virus-infected cell would only release the virions, whereas apoptosis leads to destruction of the virus inside.

NK cells are activated in response to interferons or macrophage-derived cytokines. They serve to contain viral infections while the adaptive immune response is generating antigen-specific cytotoxic T cells that can clear the infection. Patients deficient in NK cells prove to be highly susceptible to early phases of herpes virus infection.

In order for NK cells to defend the body against viruses and other pathogens, they require mechanisms that enable the determination of whether a cell is infected or not. The exact mechanisms remain the subject of current investigation, but recognition of an "altered self" state is thought to be involved. To control their cytotoxic activity, NK cells possess two types of surface receptors: activating receptors and inhibitory receptors. Most of these receptors are not unique to NK cells and can be present in other T cell subsets as well.

These inhibitory receptors recognize MHC class I alleles, which could explain why NK cells kill cells possessing low levels of MHC class I molecules. This inhibition is crucial to the role played by NK cells. MHC class I molecules consist of the main mechanism by which cells display viral or tumor antigens to cytotoxic T-cells. A common evolutionary adaption to this seen in both intracellular microbes and tumours is a chronic down-regulation of these MHC I molecules, rendering the cell impervious to T-cell mediated immunity. It is believed that NK cells, in turn, evolved as an evolutionary response to this adaption, as the loss of the MHC would deprive these cells of the inhibitory effect of MHC and render these cells vulnerable to NK-cell mediated lysis.

V.   Receptor types

NK cell receptor types (with inhibitory as well as some activating members) are differentiated by structure:

1.    CD94 : NKG2 (heterodimers) — a C-type lectin family receptor, conserved in both rodents and primates and identifies non-classical (also non-polymorphic) MHC I molecules like HLA E. Though indirect, this is a way to survey the levels of classical (polymorphic) HLA molecules, however, because expression of HLA-E at the cell surface is dependent upon the presence of classical MHC class I leader peptides.

2.    Ly49 (homodimers) — a relatively ancient, C-type lectin family receptor; are of multigenic presence in mice, while humans have only one pseudogenic Ly49; the receptor for classical (polymorphic) MHC I molecules.

3.    KIR (Killer-cell immunoglobulin-like receptors) — belong to a multigene family of more recently-evolved Ig-like extracellular domain receptors; are present in non-human primates; and are the main receptors for both classical MHC I (HLA-A, HLA-B, HLA-C) and also non-classical HLA-G in primates. Some KIRs are specific for certain HLA subtypes.

4.    ILT or LIR (leucocyte inhibitory receptors) — are recently-discovered members of the Ig receptor family.

NK cell receptors can also be differentiated based on function. Natural cytotoxicity receptors directly induce apoptosis after binding to ligands that directly indicate infection of a cell. The MHC dependent receptors (described above) use an alternate pathway to induce apoptosis in infected cells.

VI.History and discovery

The discovery of NK cells occurred in the early 1970s during research on the well-characterized ability of T-lymphocytes to lyse tumor cells against which they had been previously immunized. During these experiments, investigators consistently observed what was termed a natural reactivity, that is, a certain population of cells seemed to be able to lyse tumor cells without having been previously sensitized to them. As these discoveries were incompatible with established model at the time, many of these observations were initially considered artifacts.^[2]

However, by 1973, 'natural killing' activity was established across a wide variety of species, and the existence of a separate lineage of cells possessing this ability was postulated. Through the use of monoclonal antibodies, natural killing ability was mapped to the subset of large, granular lymphocytes known today as NK-cells.

The cells were named "natural killer" because of the initial notion that they do not require activation in order to kill cells that are "missing self" recognition ("missing-self" recognition is a term used to describe cells with low levels of MHC class I cell surface marker molecules — a situation that could arise due to viral infection, or in tumors under strong selection pressure of killer T cells).

With the discovery of activating receptors almost two decades after the discovery of the inhibitory receptors these cells continue to be called by the same name, though “natural” no longer means the same thing. The term “natural killer” continues to be justified by:

• a morphology characteristic of activated cytotoxic lymphocytes, e.g., large size, high protein synthesis activity in the abundant endoplasmic reticulum (ER), and preformed granules
• the mature state (does not require much new protein synthesis and remodeling before starting to kill)
• the rapid killing activity observed in freshly-isolated NK cells.

 

 

2 – 1

Lymphocyte is a type of white blood cell in the vertebrate immune system.^[1]

By their appearance under the light microscope, there are two broad categories of lymphocytes, namely the large granular lymphocytes and the small lymphocytes. Functionally distinct subsets of lymphocytes correlate with their appearance. Most, but not all large granular lymphocytes are more commonly known as the natural killer cells (NK cells). The small lymphocytes are the T cells and B cells. Lymphocytes play an important and integral role in the body's defenses.

VII.          Types of lymphocytes

The three major types of lymphocyte are natural killer (NK) cells, T cells and B cells.

A. Natural Killer cells

NK cells are a part of innate immune system and play a major role in defending the host from both tumors and virally infected cells. NK cells distinguish infected cells and tumors from normal and uninfected cells by recognizing alterations in levels of a surface molecule called MHC (major histocompatibility complex) class I. NK cells are activated in response to a family of cytokines called interferons. Activated NK cells release cytotoxic (cell-killing) granules that then destroy the altered cells.^[2] They were named "natural killer" because of the initial notion that they do not require prior activation in order to kill cells that are missing MHC class I.

B.   T cells and B cells

T cells and B cells are the major cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity whereas B cells are primarily responsible for humoral immunity (relating to antibodies). The function of T cells and B cells is to recognize specific “non-self” antigens, during a process known as antigen presentation. Once they have identified an invader, the cells generate specific responses that are tailored to maximally eliminate specific pathogens or pathogen infected cells. B cells respond to pathogens by producing large quantities of antibodies which then neutralize foreign objects like bacteria and viruses. In response to pathogens some T cells, called helper T cells produce cytokines that direct the immune response while other T cells, called cytotoxic T cells, produce toxic granules that induce the death of pathogen infected cells. Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered, in the form of memory cells. Throughout the lifetime of an animal these memory cells will “remember” each specific pathogen encountered, and are able to mount a strong response if the pathogen is detected again.

VIII.       Lymphocyte development

Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow.^[3] This process is called haematopoiesis. All lymphocytes originate, during this process, from a common lymphoid progenitor before differentiating into their distinct lymphocyte types. The differentiation of lymphocytes follows various pathways in a hierarchical fashion as well as in a more plastic fashion. The formation of lymphocytes is known as lymphopoiesis. B cells mature into B lymphocytes in the bone marrow^[4], while T cells migrate to and mature in a distinct organ, called the thymus. Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the spleen and lymph nodes) where they survey for invading pathogens and/or tumour cells.

The lymphocytes involved in adaptive immunity (i.e. B and T cells) differentiate further after exposure to an antigen; they form effector and memory lymphocytes. Effector lymphocytes function to eliminate the antigen, either by releasing antibodies (in the case of B cells), cytotoxic granules (cytotoxic T cells) or by signaling to other cells of the immune system (helper T cells). Memory cells remain in the peripheral tissues and circulation for an extended time ready to respond to the same antigen upon future exposure.
They live weeks to several years^[5], which is very long compared to other leukocytes.

IX.            Characteristics

Microscopically, in a Wright's stained peripheral blood smear, a normal lymphocyte has a large, dark-staining nucleus with little to no eosinophilic cytoplasm. In normal situations, the coarse, dense nucleus of a lymphocyte is approximately the size of a red blood cell (about 7 micrometres in diameter).^[3] Some lymphocytes show a clear perinuclear zone (or halo) around the nucleus or could exhibit a small clear zone to one side of the nucleus. Polyribosomes are a prominent feature in the lymphocytes and can be viewed with an electron microscope.^[3] The ribosomes are involved in protein synthesis allowing the generation of large quantities of cytokines and immunoglobulins by these cells.

It is impossible to distinguish between T cells and B cells in a peripheral blood smear.^[3] Normally, flow cytometry testing is used for specific lymphocyte population counts. This can be used to specifically determine the percentage of lymphocytes that contain a particular combination of specific cell surface proteins, such as immunoglobulins or cluster of differentiation (CD) markers or that produce particular proteins (for example, cytokines using intracellular cytokine staining (ICCS)). In order to study the function of a lymphocyte by virtue of the proteins it generates, other scientific techniques like the ELISPOT or secretion assay techniques can be used.^[2]

Typical recognition markers for lymphocytes[6]
LYMPHOCYTE CLASS	FUNCTION OF LYMPHOCYTE	PROPORTION	PHENOTYPIC MARKER(S)
NK cells	Lysis of virally infected cells and tumour cells	7% (2-13%)	CD16 CD56 but not CD3
Helper T cells	Release cytokines and growth factors that regulate other immune cells	46% (28-59%)	TCRαβ, CD3 and CD4
Cytotoxic T cells	Lysis of virally infected cells, tumour cells and allografts	19% (13-32%)	TCRαβ, CD3 and CD8
γδ T cells	Immunoregulation and cytotoxicity		TCRγδ and CD3
B cells	Secretion of antibodies	23% (18-47%)	MHC class II, CD19 and CD21

In the circulatory system they move from lymph node to lymph node. This contrasts with macrophages, which are rather stationary in the nodes.

X.  Lymphocytes and disease

A lymphocyte count is usually part of a peripheral complete blood cell count and is expressed as percentage of lymphocytes to total white blood cells counted. An increase in lymphocytes is usually a sign of a viral infection (in some rare case, leukemias are found through an abnormally raised lymphocyte count in an otherwise normal person). A general increase in the number of lymphocytes is known as lymphocytosis whereas a decrease is lymphocytopenia.

A decrease in lymphocytes occurs when the human immunodeficiency virus (HIV) infects and destroys T cells (specifically, the CD4⁺ subgroup of T lymphocytes). Without the key defense that these T cells provide, the body becomes susceptible to opportunistic infections that otherwise would not affect healthy people. The extent of HIV progression is typically determined by measuring the percentage of CD4⁺ T cells in the patient's blood. The effects of other viruses or lymphocyte disorders can also often be estimated by counting the numbers of lymphocytes present in the blood.

XI.            Blood content

 

 

 

2 – 2

I.       B cell

 

B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells). The principal functions of B cells are to make antibodies against antigens, perform the role of Antigen Presenting Cells (APCs) and eventually develop into memory B cells after activation by antigen interaction. B cells are an essential component of the adaptive immune system.

The abbreviation "B", in B cell, comes from the bursa of Fabricius in birds, where they mature. In mammals, immature B cells are formed in the bone marrow.

 

 

 

II.    Development of B cells

Immature B cells are produced in the bone marrow of most mammals. Rabbits are an exception; their B cells develop in the appendix-sacculus rotundus. After reaching the IgM+ immature stage in the bone marrow, these immature B cells migrate to the spleen, where they are called transitional B cells, and some of these cells differentiate into mature B lymphocytes.^[1]

B cell development occurs through several stages, each stage representing a change in the genome content at the antibody loci. An antibody is composed of two identical light (L) and two identical heavy (H) chains, and the genes specifying them are found in the 'V' (Variable) region and the 'C' (Constant) region. In the heavy-chain 'V' region there are three segments; V, D and J, which recombine randomly, in a process called VDJ recombination, to produce a unique variable domain in the immunoglobulin of each individual B cell. Similar rearrangements occur for light-chain 'V' region except there are only two segments involved; V and J. The list below describes the process of immunoglobulin formation at the different stages of B cell development.

Stage	Heavy chain	Light chain	Ig	IL-7 receptor?	CD19?
Progenitor B cells	germline	germline	-	No	No
Early Pro-B cells	undergoes D-J rearrangement	germline	-	No	No
Late Pro-B cells	undergoes V-DJ rearrangement	germline	-	No	Yes[2]
Large Pre-B cells	is VDJ rearranged	germline	IgM in cytoplasm	Yes[3]	Yes
Small Pre-B cells	is VDJ rearranged	undergoes V-J rearrangement	IgM in cytoplasm	Yes	Yes
Immature B cells	is VDJ rearranged	VJ rearranged	IgM on surface	Yes	Yes
Mature B cells	is VDJ rearranged	VJ rearranged	IgM and IgD on surface	Yes	Yes

When the B cell fails in any step of the maturation process, it will die by a mechanism called apoptosis, here called clonal deletion.^[4] If it recognizes self-antigen during the maturation process, the B cell will become suppressed (known as anergy) or undergo apoptosis (also termed negative selection). B cells are continuously produced in the bone marrow. When B cell receptors on the surface of the cell matches the detected antigens present in the body; the B cell proliferates and secretes a free form of those receptors (antibodies) with identical binding sites as the ones on the original cell surface. After activation, the cell proliferates and B memory cells would form to recognise the same antigen. This information would then be used as a part of the adaptive immune system for a more efficient and more powerful immune response for all previously encountered antigens.

B cell membrane receptors evolve and change throughout the B cell life span.^[5] TACI, BCMA and BAFF-R are present on both immature B cells and mature B cells. All of these 3 receptors may be inhibited by Belimumab. CD20 is expressed on all stages of B cell development except the first and last; it is present from pre-pre B cells through memory cells, but not on either pro-B cells or plasma cells.^[6]

III.  Functions

The human body makes millions of different types of B cells each day that circulate in the blood and lymphatic system performing the role of immune surveillance. They do not produce antibodies until they become fully activated. Each B cell has a unique receptor protein (referred to as the B cell receptor (BCR)) on its surface that will bind to one particular antigen. The BCR is a membrane-bound immunoglobulin, and it is this molecule that allows the distinction of B cells from other types of lymphocyte, as well as being the main protein involved in B cell activation. Once a B cell encounters its cognate antigen and receives an additional signal from a T helper cell, it can further differentiate into one of the two types of B cells listed below (plasma B cells and memory B cells). The B cell may either become one of these cell types directly or it may undergo an intermediate differentiation step, the germinal center reaction, where the B cell will hypermutate the variable region of its immunoglobulin gene ("somatic hypermutation") and possibly undergo class switching.

IV.Clonality

B cells exist as clones. All B cells derive from a particular cell, and thus, the antibodies their differentiated progenies (see below) produce can recognize and/or bind the same components (epitope) of a given antigen. Such clonality has important consequences, as immunogenic memory relies on it. The great diversity in immune response comes about because there are up to 10⁹ clones with specificities for recognizing different antigens. A single B cell or a clone of cells with shared specificity upon encountering its specific antigen divides to produce many B cells. Most of such B cells differentiate into plasma cells that secrete antibodies into blood that bind the same epitope that elicited proliferation in the first place. A small minority survives as memory cells that can recognize only the same epitope. However, with each cycle, the number of surviving memory cells increases. The increase is accompanied by affinity maturation which induces the survival of B cells that bind to the particular antigen with high affinity. This subsequent amplification with improved specificity of immune response is known as secondary immune response. B cells that encounter antigen for the first time are known as naive B cells.

V.   B cell types

• Plasma B cells (also known as plasma cells) are large B cells that have been exposed to antigen and are producing and secreting large amounts of antibodies, which assist in the destruction of microbes by binding to them and making them easier targets for phagocytes and activation of the complement system. They are sometimes referred to as antibody factories. An electron micrograph of these cells reveals large amounts of rough endoplasmic reticulum, responsible for synthesizing the antibody, in the cell's cytoplasm. These are short lived cells and undergo apoptosis when the inciting agent that induced immune response is eliminated. This occurs because of cessation of continuous exposure to various colony stimulating factors required for survival.

• Memory B cells are formed from activated B cells that are specific to the antigen encountered during the primary immune response. These cells are able to live for a long time, and can respond quickly following a second exposure to the same antigen.

• B-1 cells express IgM in greater quantities than IgG and its receptors show polyspecificity, meaning that they have low affinities for many different antigens, but have a preference for other immunoglobulins, self antigens and common bacterial polysaccharides. B-1 cells are present in low numbers in the lymph nodes and spleen and are instead found predominantly in the peritoneal and pleural cavities.

• B-2 cells are the conventional B cells most texts refer to.
• Other B Cells:  Marginal-zone B cells   and   Follicular B Cells

VI.Recognition of antigen by B cells

 

 

Mechanism of action.

A critical difference between B cells and T cells is how each lymphocyte recognizes its antigen. B cells recognize their cognate antigen in its native form. They recognize free (soluble) antigen in the blood or lymph using their BCR or membrane bound-immunoglobulin. In contrast, T cells recognize their cognate antigen in a processed form, as a peptide fragment presented by an antigen presenting cell's MHC molecule to the T cell receptor.

VII.          Activation of B cells

B cell recognition of antigen is not the only element necessary for B cell activation (a combination of clonal proliferation and terminal differentiation into plasma cells). B cells that have not been exposed to antigen, also known as naïve B cells, can be activated in a T cell-dependent or -independent manner.

 

VIII.       T cell-dependent activation

Once a pathogen is ingested by an antigen-presenting cell such as a macrophage or dendritic cell, the pathogen's proteins are then digested to peptides and attached to a class II MHC protein. This complex is then moved to the outside of the cell membrane. The macrophage is now activated to deliver multiple signals to a specific T cell that recognizes the peptide presented. The T cell is then stimulated to produce autocrines (Refer to Autocrine signalling), resulting in the proliferation and differentiation to effector and memory T cells. Helper T cells (i.e CD4+ T cells) then activate specific B cells through a phenomenon known as an Immunological synapse. Activated B cells subsequently produce antibodies which assist in inhibiting pathogens until phagocytes (i.e macrophages, neutrophils) or the complement system for example clears the host of the pathogen(s).

Most antigens are T-dependent, meaning T cell help is required for maximal antibody production. With a T-dependent antigen, the first signal comes from antigen cross linking the B cell receptor (BCR) and the second signal comes from co-stimulation provided by a T cell. T dependent antigens contain proteins that are presented on B cell Class II MHC to a special subtype of T cell called a Th2 cell. When a B cell processes and presents the same antigen to the primed T_h cell, the T cell secretes cytokines that activate the B cell. These cytokines trigger B cell proliferation and differentiation into plasma cells. Isotype switching to IgG, IgA, and IgE and memory cell generation occur in response to T-dependent antigens. This isotype switching is known as Class Switch Recombination (CSR). Once this switch has occurred, that particular B cell can no longer make the earlier isotypes, IgM or IgD.

IX.            T cell-independent activation

Many antigens are T cell-independent in that they can deliver both of the signals to the B cell. Mice without a thymus (nude or athymic mice that do not produce any T cells) can respond to T independent antigens. Many bacteria have repeating carbohydrate epitopes that stimulate B cells, by cross-linking the IgM antigen receptors in the B cell, responding with IgM synthesis in the absence of T cell help. There are two types of T cell independent activation; Type 1 T cell-independent (polyclonal) activation, and type 2 T cell-independent activation (in which macrophages present several of the same antigen in a way that causes cross-linking of antibodies on the surface of B cells).

X.  The ancestral roots of B cells

B cells in humans (and other vertebrates) are nevertheless able to endocytose antibody-fixed pathogens, and it is through this route that MHC Class II presentation by B cells is possible, allowing Th2 help and stimulation of B cell proliferation. This is purely for the benefit of MHC Class II presentation, not as a significant method of reducing the pathogen load.

XI.            Origin of the word B cell

The abbreviation "B" in B cell originally came from Bursa of Fabricius, an organ in birds in which avian B cells mature.^[10] When it was discovered that in most mammals immature B cells are formed in bone marrow, the word B cell continued to be used, although other blood cells also originate from pluripotent stem cells in the bone marrow. The fact that bone and bursa both start with the letter 'B' is a chance coincidence.

 

XII.         B cell related pathology

Aberrant antibody production by B cells is implicated in many autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus. Most forms of leukemia, lymphoma, and other hematological malignancy are derived from B cells.

XIII.       Additional image

 

XIV.     See also

• Affinity maturation
• Antibody
• Clonal selection
• Original antigenic sin

XV.        References

1. ^ Allman D, Srivastava B, Lindsley RC (February 2004). "Alternative routes to maturity: branch points and pathways for generating follicular and marginal zone B cells". Immunol. Rev. 197: 147–60. doi:10.1111/j.0105-2896.2004.0108.x. PMID 14962193. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0105-2896&date=2004&volume=197&spage=147. 
2. ^ "B Cell Development". http://www.microvet.arizona.edu/Courses/MIC419/Tutorials/Bcelldevelopment.html#generation. Retrieved on 2008-09-20. 
3. ^ "Immunology, Biology 328". http://bioweb.wku.edu/courses/biol328/Lecture11.html. Retrieved on 2008-09-20. 
4. ^ Parham, P. (2005). The Immune System, Garland Science Publishing, New York, NY.
5. ^ "Hyperactive_Blymphocytes_lifespan_receptors". http://www.healthvalue.net/Hyperactive_Blymphocytes_lifespan_receptors.html. Retrieved on 2008-09-16. 
6. ^ Bona, Constantin; Francisco A. Bonilla (1996). "5". Textbook of Immunology. Martin Soohoo (2 ed.). CRC Press. pp. 102. ISBN 9783718605965. 
7. ^ Montecino-Rodriguez, Encarnacion; Kenneth Dorshkind (2006-09). "New perspectives in B-1 B cell development and function". Trends in Immunology (Elsevier B.V.) 27 (9): 428–433. doi:10.1016/j.it.2006.07.005. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W7H-4KGG1T1-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=923c447f162114b76b1a9ca6f3e02a06. Retrieved on 2008-05-05. 
8. ^ Tung, James; Leonore A Herzenberg (2007-04). ""Unraveling B-1 progenitors"". Current Opinion in Immunology (Elsevier B.V.) 19 (2): 150–155. doi:10.1016/j.coi.2007.02.012. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VS1-4N2D5Y5-6&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f47493140685f1e9e8835d3cf7c1b2f5. Retrieved on 2008-05. 
9. ^ J. Li, D.R. Barreda, Y.-A. Zhang, H. Boshra, A.E. Gelman, S. LaPatra, L. Tort & J.O. Sunyer (2006). "B lymphocytes from early vertebrates have potent phagocytic and microbicidal abilities". Nature Immunology 7: 1116–1124. doi:10.1038/ni1389. PMID 16980980. 
10. ^ Bursa of Fabricius
11. ^ Goldsby, Richard; Kindt, TJ; Osborne, BA; Janis Kuby (2003). Immunology Fifth Edition. New York: W. H. Freeman and Company. pp. 119–120. ISBN 0-07167-4947-5. 

XVI.     External links

• MeSH B-Lymphocytes
• B Cells and T Cells
• B Cell Development and Generation of Lymphocyte Diversity
• Interactive Animation of B Cell Maturation (requires Flash video software)

 

 

2 – 3

T cells belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocyte types, such as B cells and natural killer cells by the presence of a special receptor on their cell surface called T cell receptors (TCR). The abbreviation T, in T cell, stands for thymus, since this is the principal organ responsible for the T cell's maturation. Several different subsets of T cells have been discovered, each with a distinct function.

I.       Types

A.   Helper

Helper T cells (effector T cells or T_h cells) are the "middlemen" of the adaptive immune system. Once activated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the immune response. Depending on the size, cytokine signals received, these cells differentiate into T_H1, T_H2, T_H3, T_H17,T_FH, or one of other subsets, which secrete different cytokines. CD4+ cells are associated with MHC class II.

B.    Cytotoxic

Cytotoxic T cells (T_C cells, or CTLs) destroy virally infected cells and tumor cells, and are also implicated in transplant rejection. These cells are also known as CD8⁺ T cells (associated with MHC class I), since they express the CD8 glycoprotein at their surface. Through SLOB interaction with T regulatory CD4+CD25+FoxP3+ cells, these cells can be inactivated to a anergic state, which prevent autoimmune diseases such as experimental autoimmune encephalomyelitis.^[1]

C.  Memory

Memory T cells are a subset of antigen-specific T cells that persist long-term after an infection has resolved. They quickly expand to large numbers of effector T cells upon re-exposure to their cognate antigen, thus providing the immune system with "memory" against past infections. Memory T cells comprise two subtypes: central memory T cells (T_CM cells) and effector memory T cells (T_EM cells). Memory cells may be either CD4+ or CD8+.

D.   Regulatory

Regulatory T cells (T_reg cells), formerly known as suppressor T cells, are crucial for the maintenance of immunological tolerance. Their major role is to shut down T cell-mediated immunity toward the end of an immune reaction and to suppress auto-reactive T cells that escaped the process of negative selection in the thymus. Two major classes of CD4+ regulatory T cells have been described, including the naturally occurring T_reg cells and the adaptive T_reg cells. Naturally occurring T_reg cells (also known as CD4⁺CD25⁺FoxP3⁺ T_reg cells) arise in the thymus, whereas the adaptive T_reg cells (also known as Tr1 cells or Th3 cells) may originate during a normal immune response. Naturally occurring T_reg cells can be distinguished from other T cells by the presence of an intracellular molecule called FoxP3. Mutations of the FOXP3 gene can prevent regulatory T cell development, causing the fatal autoimmune disease IPEX.

E.     Natural killer

Natural Killer T cells (NKT cells) are a special kind of lymphocyte that bridges the adaptive immune system with the innate immune system. Unlike conventional T cells that recognize peptide antigen presented by major histocompatibility complex (MHC) molecules, NKT cells recognize glycolipid antigen presented by a molecule called CD1d. Once activated, these cells can perform functions ascribed to both T_h and T_c cells (i.e., cytokine production and release of cytolytic/cell killing molecules). They are also able to recognize and eliminate some tumor cells and cells infected with herpes viruses.

F.     γδ

γδ T cells (gamma delta T cells) represent a small subset of T cells that possess a distinct T cell receptor (TCR) on their surface. A majority of T cells have a TCR composed of two glycoprotein chains called α- and β- TCR chains. However, in γδ T cells, the TCR is made up of one γ-chain and one δ-chain. This group of T cells is much less common (5% of total T cells) than the αβ T cells, but are found at their highest abundance in the gut mucosa, within a population of lymphocytes known as intraepithelial lymphocytes (IELs). The antigenic molecules that activate γδ T cells are still widely unknown. However, γδ T cells are not MHC restricted and seem to be able to recognise whole proteins rather than requiring peptides to be presented by MHC molecules on antigen presenting cells. Some recognize MHC class IB molecules though. Human Vγ9/Vδ2 T cells, which constitute the major γδ T cell population in peripheral blood, are unique in that they specifically and rapidly respond to a small non-peptidic microbial metabolite, HMB-PP, an isopentenyl pyrophosphate precursor.

II.Development in the Thymus

All T cells originate from hematopoietic stem cells in the bone marrow. Hematopoietic progenitors derived from hematopoietic stem cells populate the thymus and expand by cell division to generate a large population of immature thymocytes.^[2] The earliest thymocytes express neither CD4 nor CD8, and are therefore classed as double-negative (CD4^-CD8^-) cells. As they progress through their development they become double-positive thymocytes (CD4⁺CD8⁺), and finally mature to single-positive (CD4⁺CD8^- or CD4^-CD8⁺) thymocytes that are then released from the thymus to peripheral tissues.

About 98% of thymocytes die during the development processes in the thymus by failing either positive selection or negative selection, whereas the other 2% survive and leave the thymus to become mature immunocompetent T cells.

The thymus contributes more naive T cells at younger ages. As the thymus shrinks by about 3%^[3] a year throughout middle age, there is a corresponding fall in the thymic production of naive T cells, leaving peripheral T cell expansion to play a greater role in protecting older subjects.

III.  Positive selection

Positive selection "selects for" T-cells capable of interacting with MHC. Double-positive thymocytes (CD4+/CD8+) move deep into the thymic cortex where they are presented with self-antigens (i.e., antigens that are derived from molecules belonging to the host of the T cell) complexed with MHC molecules on the surface of cortical epithelial cells. Only those thymocytes that bind the MHC/antigen complex with adequate affinity will receive a vital "survival signal." Developing thymocytes that do not have adequate affinity cannot serve useful functions in the body (i.e. the cells must be able to interact with MHC and peptide complexes in order to affect immune responses). Because of this, the thymocytes with low affinity die by apoptosis and are engulfed by macrophages.

A thymocyte's fate is also determined during positive selection. Double-positive cells (CD4+/CD8+) that are positively selected on MHC class II molecules will eventually become CD4+ cells, while cells positively selected on MHC class I molecules mature into CD8+ cells. A T cell becomes a CD4+ cell by downregulating expression of its CD8 cell surface receptors. If the cell does not lose its signal through the ITAM pathway, it will continue downregulating CD8 and become a CD4+, single positive cell. But if there is signal drop, the cell stops downregulating CD8 and switches over to downregulating CD4 molecules instead, eventually becoming a CD8+, single positive cell.

This process does not remove thymocytes that may cause autoimmunity. The removal of potentially autoimmune cells are removed by the process of negative selection (discussed below).

IV.Negative selection

Negative selection removes thymocytes that are capable of strongly binding with "self" peptides presented by MHC. Thymocytes that survive positive selection migrate towards the boundary of the thymic cortex and thymic medulla. While in the medulla, they are again presented with self-antigen in complex with MHC molecules on antigen-presenting cells (APCs) such as dendritic cells and macrophages. Thymocytes that interact too strongly with the antigen receive an apoptotic signal that leads to cell death. The vast majority of all thymocytes end up dying during this process. The remaining cells exit the thymus as mature naive T cells. This process is an important component of immunological tolerance and serves to prevent the formation of self-reactive T cells that are capable of generating autoimmune diseases in the host.

V.   Maturation paradox

Positive and negative selection should theoretically kill all developing T cells. The first stage of selection kills all T cells that do not interact with self-MHC, while the second stage selection kills all cells that do. This poses the question: How do we have immunity at all? Currently, two models attempt to explain this:

1.    Differential Avidity Hypothesis - the strength of the signal dictates the fate of the T cell.

2.    Differential Signaling Hypothesis - the signals that are transduced differ at each stage.

VI.Activation

Although the specific mechanisms of activation vary slightly between different types of T cells, the "two-signal model" in CD4+ T cells holds true for most. Activation of CD4+ T cells occurs through the engagement of both the T cell receptor and CD28 on the T cell by the Major histocompatibility complex peptide and B7 family members on the APC, respectively. Both are required for production of an effective immune response; in the absence of CD28 co-stimulation, T cell receptor signalling alone results in anergy. The signalling pathways downstream from both CD28 and the T cell receptor involve many proteins.

The first signal is provided by binding of the T cell receptor to a short peptide presented by the major histocompatibility complex (MHC) on another cell. This ensures that only a T cell with a TCR specific to that peptide is activated. The partner cell is usually a professional antigen presenting cell (APC), usually a dendritic cell in the case of naïve responses, although B cells and macrophages can be important APCs. The peptides presented to CD8+ T cells by MHC class I molecules are 8-9 amino acids in length; the peptides presented to CD4+ cells by MHC class II molecules are longer, as the ends of the binding cleft of the MHC class II molecule are open.

The second signal comes from co-stimulation, in which surface receptors on the APC are induced by a relatively small number of stimuli, usually products of pathogens, but sometimes breakdown products of cells, such as necrotic-bodies or heat-shock proteins. The only co-stimulatory receptor expressed constitutively by naïve T cells is CD28, so co-stimulation for these cells comes from the CD80 and CD86 proteins on the APC. Other receptors are expressed upon activation of the T cell, such as OX40 and ICOS, but these largely depend upon CD28 for their expression. The second signal licenses the T cell to respond to an antigen. Without it, the T cell becomes anergic, and it becomes more difficult for it to activate in future. This mechanism prevents inappropriate responses to self, as self-peptides will not usually be presented with suitable co-stimulation.

The T cell receptor exists as a complex of several proteins. The actual T cell receptor is composed of two separate peptide chains, which are produced from the independent T cell receptor alpha and beta (TCRα and TCRβ) genes. The other proteins in the complex are the CD3 proteins: CD3εγ and CD3εδ heterodimers and, most important, a CD3ζ homodimer, which has a total of six ITAM motifs. The ITAM motifs on the CD3ζ can be phosphorylated by Lck and in turn recruit ZAP-70. Lck and/or ZAP-70 can also phosphorylate the tyrosines on many other molecules, not least CD28, , LAT and SLP-76, which allows the aggregation of signalling complexes around these proteins.

Phosphorylated LAT recruits SLP-76 to the membrane, where it can then bring in PLCγ, VAV1, Itk and potentially PI3K. Both PLCγ and PI3K act on PI(4,5)P2 on the inner leaflet of the membrane to create the active intermediaries diacylglycerol (DAG), inositol-1,4,5-trisphosphate (IP3), and phosphatidlyinositol-3,4,5-trisphosphate (PIP3). DAG binds and activates some PKCs, most important, in T cells PKCθ, a process important for activating the transcription factors NF-κB and AP-1. IP3 is released from the membrane by PLCγ and diffuses rapidly to activate receptors on the ER, which induce the release of calcium. The released calcium then activates calcineurin, and calcineurin activates NFAT, which then translocates to the nucleus. NFAT is a transcription factor, which activates the transcription of a pleiotropic set of genes, most notable, IL-2, a cytokine that promotes long term proliferation of activated T cells.

VII.    See also

• Apoptosis
• Naive T cell
• Memory T cell
• γδ T cell

VIII.  References

1.       ^ "An integrated view of suppressor T cell subsets in immunoregulation". http://www.jci.org/cgi/content/full/114/9/1198. 

2.       ^ Schwarz BA, Bhandoola A. Trafficking from the bone marrow to the thymus: a prerequisite for thymopoiesis. Immunol Rev 209:47, 2006. full text

3.       ^ Barton F, Haynes M, Lousie M, SempowskI G, Patel S, Hale L (2000) The Role of the Thymus in Immune Reconstitution in Aging, Bone Marrow Transplantation, and HIV-1 Infection, Annual Review of Immunology, vol 18, 529-560

 

2 – 4       

PI

 

Proliferation Index

 

Counts per minute [CPM] of antigen stimulated cells divided by CPM of unstimulated cells

 

3 - 1

I.       Insulin-like growth factor 1  -  IGF-1

Insulin-like growth factor 1 (somatomedin C)
PDB (Protein Data Bank) rendering based on 1bqt.
Available structures: 1bqt, 1gzr, 1gzy, 1gzz, 1h02, 1h59, 1imx, 1pmx, 1wqj, 2dsp, 2dsq, 2dsr, 2gf1, 3gf1, 3lri
Identifiers
Symbols		IGF1; IGFI
External IDs		OMIM: 147440 MGI: 96432 HomoloGene: 515
RNA expression pattern
Orthologs
	Human		Mouse
Entrez	3479		16000
Ensembl	ENSG00000017427		ENSMUSG00000020053
Uniprot	P01343		Q4VJC0
Refseq	NM_000618 (mRNA) NP_000609 (protein)		NM_010512 (mRNA) NP_034642 (protein)
Location	Chr 12: 101.31 - 101.4 Mb		Chr 10: 87.29 - 87.36 Mb
Pubmed search	[1]		[2]

Insulin-like growth factor 1 (IGF-1) that was once called somatomedin C, is a polypeptide protein hormone similar in molecular structure to insulin. It plays an important role in childhood growth and continues to have anabolic effects in adults.

II.    Production and Circulation

IGF-1 consists of 70 amino acids in a single chain with three intramolecular disulfide bridges. IGF-1 has a molecular weight of 7649 daltons. IGF-1 is produced primarily by the liver as an endocrine hormone as well as in target tissues in a paracrine/autocrine fashion. Production is stimulated by growth hormone and can be retarded by undernutrition, growth hormone insensitivity, lack of growth hormone receptors, or failures of the downstream signalling pathway post GH receptor including SHP2 and STAT5b. Approximately 98% of IGF-1 is always bound to one of 6 binding proteins (IGF-BP). IGFBP-3, the most abundant protein, accounts for 80% of all IGF binding. IGF-1 binds to IGFBP-3 in a 1:1 molar ratio.

In rat experiments, the amount of IGF-1 mRNA in the liver was positively associated with dietary casein and negatively associated with a protein free diet.^[1]

III.  Action

Its primary action is mediated by binding to specific IGF receptors present on many cell types in many tissues. The signal is transduced by intracellular events. IGF-1 is one of the most potent natural activators of the AKT signaling pathway, a stimulator of cell growth and multiplication and a potent inhibitor of programmed cell death.

Almost every cell in the human body is affected by IGF-1, especially cells in muscle, cartilage, bone, liver, kidney, nerves, skin, and lungs. In addition to the insulin-like effects, IGF-1 can also regulate cell growth and development, especially in nerve cells, as well as cellular DNA synthesis.

IV.IGF-2 and Insulin; related growth factors

IGF-1 is closely related to a second protein called "IGF-2". IGF-2 also binds the IGF-1 Receptor. However, IGF-2 alone binds a receptor called the "IGF II Receptor" (also called the Mannose-6 phosphate receptor). The insulin growth factor-II receptor (IGF2R) lacks signal transduction capacity, and its main role is to act as a sink for IGF-2 and make less IGF-2 available for binding with IGF-1R. As the name "insulin-like growth factor 1" implies, IGF-1 is structurally related to insulin, and is even capable of binding the insulin receptor, albeit at lower affinity than insulin.

V.   IGF-1, daf2 and Regulation of Aging

The daf-2 gene encodes an insulin-like receptor in the worm C. elegans. Mutations in daf-2 have been shown by Cynthia Kenyon to double the lifespan of the worms.^[2] The gene is known to regulate reproductive development, aging, resistance to oxidative stress, thermotolerance, resistance to hypoxia, and also resistance to bacterial pathogens.^[3]

DAF-2 is the only insulin/IGF-1 like receptor in the worm. Insulin/IGF-1-like signaling is conserved from worms to humans. DAF-2 acts to negatively regulate the forkhead transcription factor DAF-16 through a phosphorylation cascade. Genetic analysis reveals that DAF-16 is required for daf-2-dependent lifespan extension and dauer formation. When not phosphorylated, DAF-16 is active and present in the nucleus.

VI.Receptors

IGF-1 binds to at least two cell surface receptors: the IGF-1 receptor (IGFR), and the insulin receptor. The IGF-1 receptor seems to be the "physiologic" receptor - it binds IGF-1 at significantly higher affinity than IGF-1 is bound to the insulin receptor. Like the insulin receptor, the IGF-1 receptor is a receptor tyrosine kinase - meaning it signals by causing the addition of a phosphate molecule on particular tyrosines. IGF-1 activates the insulin receptor at approximately 0.1x the potency of insulin. Part of this signaling may be via IGF1R/Insulin Receptor heterodimers (the reason for the confusion is that binding studies show that IGF1 binds the insulin receptor 100-fold less well than insulin, yet that does not correlate with the actual potency of IGF1 in vivo at inducing phosphorylation of the insulin receptor, and hypoglycemia).

IGF-1 is produced throughout life. The highest rates of IGF-1 production occur during the pubertal growth spurt. The lowest levels occur in infancy and old age.

 

VII.          Use as a diagnostic test

IGF-1 levels can be measured in the blood in 10-1000 ng/ml amounts. As levels do not fluctuate greatly throughout the day for an individual person, IGF-1 is used by physicians as a screening test for growth hormone deficiency and excess.

Interpretation of IGF-1 levels is complicated by the wide normal ranges, and variations by age, sex, and pubertal stage. Clinically significant conditions and changes may be masked by the wide normal ranges. Sequential management over time is often useful for the management of several types of pituitary disease, undernutrition, and growth problems.

VIII.       Diseases of deficiency and resistance

Rare diseases characterized by inability to make or respond to IGF-1 produce a distinctive type of growth failure. One such disorder, termed Laron dwarfism does not respond at all to growth hormone treatment due to a lack of GH receptors. The FDA has grouped these diseases into a disorder called severe primary IGF deficiency. Patients with severe primary IGFD typically present with normal to high GH levels, height below -3 standard deviations (SD), and IGF-1 levels below -3SD. Severe primary IGFD includes patients with mutations in the GH receptor, post-receptor mutations or IGF mutations, as previously described. As a result, these patients cannot be expected to respond to GH treatment.

The IGF signaling pathway appears to play a crucial role in cancer. Several studies have shown that increased levels of IGF lead to an increased risk of cancer. Studies done on lung cancer cells show that drugs inhibiting such signaling can be of potential interest in cancer therapy.^[4]

IX.            Factors influencing the levels of IGF-1 in the circulation

Factors that are known to cause variation in the levels of growth hormone (GH) and IGF-1 in the circulation include an individual's genetic make-up, the time of day, his or her age, gender, exercise status, stress levels, nutrition level and body mass index (BMI), disease state, race, estrogen status and xenobiotic intake.^[5] The later inclusion of xenobiotic intake as a factor influencing GH-IGF status highlights the fact that the GH-IGF axis is a potential target for certain endocrine disrupting chemicals - see also endocrine disruptor.

X.  IGF-1 as a therapeutic agent

IGF-1 has been manufactured recombinantly on a large scale using both yeast and E. coli. Several companies have evaluated IGF-1 in clinical trials for a variety of indications, including growth failure, type 1 diabetes, type 2 diabetes, amyotrophic lateral sclerosis (ALS aka "Lou Gehrig's Disease"), severe burn injury and myotonic muscular dystrophy (MMD). Results of clinical trials evaluating the efficacy of IGF-1 in type 1 diabetes and type 2 diabetes showed great promise in reducing hemoglobin A1C levels, as well as daily insulin consumption. However, in the last few years, two additional companies Tercica and Insmed compiled enough clinical trial data to seek FDA approval in the United States. In August 2005, the FDA approved Tercica's IGF-1 drug, Increlex, as replacement therapy for severe primary IGF-1 deficiency based on clinical trial data from 71 patients. In December 2005, the FDA also approved Iplex, Insmed's IGF-1/IGFBP-3 complex. The Insmed drug is injected once a day versus the twice-a-day version that Tercica sells.

By delivering Iplex in a complex, patients might get the same efficacy with regard to growth rates but experience fewer side effects with less severe hypoglycemia.^. This medication might emulate IGF-1's endogenous complexing, as in the human body 97-99% of IGF-1 is bound to one of six IGF binding proteins. IGFBP-3 is the most abundant of these binding proteins, accounting for approximately 80% of IGF-1 binding.

Insmed was found to infringe on patents licensed by Tercica, which then sought to get a U.S. district court judge to ban sales of Iplex. [3] To settle patent infringement charges and resolve all litigation between the two companies, Insmed in March 2007 agreed to withdraw Iplex from the U.S. market, leaving Tercica's Increlex as the sole version of IGF-1 available in the United States. [4]

XI.            Terminology

IGF-1 has been known as "sulfation factor"^[6] and its effects were termed "nonsuppressible insulin-like activity" (NSILA) in the 1970s. It was also known as "somatomedin C" in the 1980s.

XII.         Interactions

Insulin-like growth factor 1 has been shown to interact with IGFBP7,^[7][8] IGFBP3^{[9][10][11][12][13][14]} and IGFBP4.^[15][16]

XIII.       References

1. ^ Miura, Yutaka (1992). "Effect of dietary proteins on insulin-like growth factor-1 (IGF-1) messenger ribonucleic acid content in rat liver". British Journal of Nutrition 67: 257. doi:10.1079/BJN19920029.  edit
2. ^ See publications documenting series of experiments at Cynthia Kenyon lab, in particular, Jennie B. Dorman, Bella Albinder, Terry Shroyer & Cynthia Kenyon, "The age-1 and daf-2 genes function in a common pathway to control the lifespan of Caenorhabditis elegans," Genetics, volume 141, number 4, pages 1399-1406 (1995); and Javier Apfeld & Cynthia Kenyon, "Cell non-autonomy of C. elegans daf-2 function in the regulation of diapause and lifespan," Cell, v. 95, n.2, pp.199-210 (1998).
3. ^ Minaxi S Gami and Catherine A Wolkow (2006). "Studies of Caenorhabditis elegans DAF-2/insulin signaling reveal targets for pharmacological manipulation of lifespan". Aging Cell 5 (1): 31. doi:10.1111/j.1474-9726.2006.00188.x. PMID 16441841. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16441841. 
4. ^ Velcheti V, Govindan R (2006). "Insulin-like growth factor and lung cancer". Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer 1 (7): 607–10. PMID 17409926. http://www.jto.org/pt/re/jto/fulltext.01243894-200609000-00002.htm. 
5. ^ Scarth J (2006). "Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review". Xenobiotica 36 (2-3): 119–218. PMID 16702112. 
6. ^ Salmon W, Daughaday W (1957). "A hormonally controlled serum factor which stimulates sulfate incorporation by cartilage in vitro". J Lab Clin Med 49 (6): 825–36. PMID 13429201. 
7. ^ Ahmed, Sanjida; Yamamoto Kazuhiro, Sato Yuichiro, Ogawa Takashi, Herrmann Andreas, Higashi Shouichi, Miyazaki Kaoru (Oct. 2003). "Proteolytic processing of IGFBP-related protein-1 (TAF/angiomodulin/mac25) modulates its biological activity". Biochem. Biophys. Res. Commun. (United States) 310 (2): 612-8. ISSN 0006-291X. PMID 14521955. 
8. ^ Oh, Y; Nagalla S R, Yamanaka Y, Kim H S, Wilson E, Rosenfeld R G (Nov. 1996). "Synthesis and characterization of insulin-like growth factor-binding protein (IGFBP)-7. Recombinant human mac25 protein specifically binds IGF-I and -II". J. Biol. Chem. (UNITED STATES) 271 (48): 30322-5. ISSN 0021-9258. PMID 8939990. 
9. ^ Liu, Bingrong; Weinzimer Stuart A, Gibson Tara Beers, Mascarenhas Desmond, Cohen Pinchas. "Type Ialpha collagen is an IGFBP-3 binding protein". Growth Horm. IGF Res. (Scotland) 13 (2-3): 89-97. ISSN 1096-6374. PMID 12735930. 
10. ^ Ueki, I; Ooi G T, Tremblay M L, Hurst K R, Bach L A, Boisclair Y R (Jun. 2000). "Inactivation of the acid labile subunit gene in mice results in mild retardation of postnatal growth despite profound disruptions in the circulating insulin-like growth factor system". Proc. Natl. Acad. Sci. U.S.A. (UNITED STATES) 97 (12): 6868-73. doi:10.1073/pnas.120172697. ISSN 0027-8424. PMID 10823924. 
11. ^ Buckway, C K; Wilson E M, Ahlsén M, Bang P, Oh Y, Rosenfeld R G (Oct. 2001). "Mutation of three critical amino acids of the N-terminal domain of IGF-binding protein-3 essential for high affinity IGF binding". J. Clin. Endocrinol. Metab. (United States) 86 (10): 4943-50. ISSN 0021-972X. PMID 11600567. 
12. ^ Cohen, P; Graves H C, Peehl D M, Kamarei M, Giudice L C, Rosenfeld R G (Oct. 1992). "Prostate-specific antigen (PSA) is an insulin-like growth factor binding protein-3 protease found in seminal plasma". J. Clin. Endocrinol. Metab. (UNITED STATES) 75 (4): 1046-53. ISSN 0021-972X. PMID 1383255. 
13. ^ Twigg, S M; Baxter R C (Mar. 1998). "Insulin-like growth factor (IGF)-binding protein 5 forms an alternative ternary complex with IGFs and the acid-labile subunit". J. Biol. Chem. (UNITED STATES) 273 (11): 6074-9. ISSN 0021-9258. PMID 9497324. 
14. ^ Firth, S M; Ganeshprasad U, Baxter R C (Jan. 1998). "Structural determinants of ligand and cell surface binding of insulin-like growth factor-binding protein-3". J. Biol. Chem. (UNITED STATES) 273 (5): 2631-8. ISSN 0021-9258. PMID 9446566. 
15. ^ Bach, L A; Hsieh S, Sakano K, Fujiwara H, Perdue J F, Rechler M M (May. 1993). "Binding of mutants of human insulin-like growth factor II to insulin-like growth factor binding proteins 1-6". J. Biol. Chem. (UNITED STATES) 268 (13): 9246-54. ISSN 0021-9258. PMID 7683646. 
16. ^ Qin, X; Strong D D, Baylink D J, Mohan S (Sep. 1998). "Structure-function analysis of the human insulin-like growth factor binding protein-4". J. Biol. Chem. (UNITED STATES) 273 (36): 23509-16. ISSN 0021-9258. PMID 9722589. 

Venkatasubramanian G, Chittiprol S, Neelakantachar N et al. Insulin and insulin-like growth factor-1 abnormalities in antipsychotic-naive schizophrenia. Am J Psychiatry 2007;164:1557–1560. Links

XIV.     Further reading

·         Butler AA, Yakar S, LeRoith D (2002). "Insulin-like growth factor-I: compartmentalization within the somatotropic axis?". News Physiol. Sci. 17: 82–5. PMID 11909998. 

·         Maccario M, Tassone F, Grottoli S, et al. (2002). "Neuroendocrine and metabolic determinants of the adaptation of GH/IGF-I axis to obesity". Ann. Endocrinol. (Paris) 63 (2 Pt 1): 140–4. PMID 11994678. 

·         Camacho-Hübner C, Woods KA, Clark AJ, Savage MO (2003). "Insulin-like growth factor (IGF)-I gene deletion". Reviews in endocrine & metabolic disorders 3 (4): 357–61. doi:10.1023/A:1020957809082. PMID 12424437. 

·         Trojan LA, Kopinski P, Wei MX, et al. (2004). "IGF-I: from diagnostic to triple-helix gene therapy of solid tumors". Acta Biochim. Pol. 49 (4): 979–90. doi:024904979 (inactive 2008-06-21). PMID 12545204. 

·         Winn N, Paul A, Musaró A, Rosenthal N (2003). "Insulin-like growth factor isoforms in skeletal muscle aging, regeneration, and disease". Cold Spring Harb. Symp. Quant. Biol. 67: 507–18. doi:10.1101/sqb.2002.67.507. PMID 12858577. 

·         Delafontaine P, Song YH, Li Y (2005). "Expression, regulation, and function of IGF-1, IGF-1R, and IGF-1 binding proteins in blood vessels". Arterioscler. Thromb. Vasc. Biol. 24 (3): 435–44. doi:10.1161/01.ATV.0000105902.89459.09. PMID 14604834. 

·         Trejo JL, Carro E, Garcia-Galloway E, Torres-Aleman I (2004). "Role of insulin-like growth factor I signaling in neurodegenerative diseases". J. Mol. Med. 82 (3): 156–62. doi:10.1007/s00109-003-0499-7. PMID 14647921. 

·         Rabinovsky ED (2004). "The multifunctional role of IGF-1 in peripheral nerve regeneration". Neurol. Res. 26 (2): 204–10. doi:10.1179/016164104225013851. PMID 15072640. 

·         Rincon M, Muzumdar R, Atzmon G, Barzilai N (2005). "The paradox of the insulin/IGF-1 signaling pathway in longevity". Mech. Ageing Dev. 125 (6): 397–403. doi:10.1016/j.mad.2004.03.006. PMID 15272501. 

·         Conti E, Carrozza C, Capoluongo E, et al. (2005). "Insulin-like growth factor-1 as a vascular protective factor". Circulation 110 (15): 2260–5. doi:10.1161/01.CIR.0000144309.87183.FB. PMID 15477425. 

·         Wood AW, Duan C, Bern HA (2005). "Insulin-like growth factor signaling in fish". Int. Rev. Cytol. 243: 215–85. doi:10.1016/S0074-7696(05)43004-1. PMID 15797461. 

·         Sandhu MS (2005). "Insulin-like growth factor-I and risk of type 2 diabetes and coronary heart disease: molecular epidemiology". Endocrine development 9: 44–54. doi:10.1159/000085755. PMID 15879687. 

·         Ye P, D'Ercole AJ (2006). "Insulin-like growth factor actions during development of neural stem cells and progenitors in the central nervous system". J. Neurosci. Res. 83 (1): 1–6. doi:10.1002/jnr.20688. PMID 16294334. 

·         Gómez JM (2006). "The role of insulin-like growth factor I components in the regulation of vitamin D". Current pharmaceutical biotechnology 7 (2): 125–32. doi:10.2174/138920106776597621. PMID 16724947. 

·         Federico G, Street ME, Maghnie M, et al. (2006). "Assessment of serum IGF-I concentrations in the diagnosis of isolated childhood-onset GH deficiency: a proposal of the Italian Society for Pediatric Endocrinology and Diabetes (SIEDP/ISPED)". J. Endocrinol. Invest. 29 (8): 732–7. PMID 17033263. 

·         Zakula Z, Koricanac G, Putnikovic B, et al. (2007). "Regulation of the inducible nitric oxide synthase and sodium pump in type 1 diabetes". Med. Hypotheses 69 (2): 302–6. doi:10.1016/j.mehy.2006.11.045. PMID 17289286. 

·         Trojan J, Cloix JF, Ardourel MY, et al. (2007). "Insulin-like growth factor type I biology and targeting in malignant gliomas". Neuroscience 145 (3): 795–811. doi:10.1016/j.neuroscience.2007.01.021. PMID 17320297. 

XV.        External links

I.                MeSH Insulin-Like+Growth+Factor+I

II.              IGF-1 for Parents

III.             IGF-1 & Bodybuilding

IV.           IGF1 Deficiency for Parents a section of The MAGIC Foundation for Children's Growth

 

 

PDB Gallery     1bqt: THREE-DIMENSIONAL STRUCTURE OF HUMAN INSULIN-LIKE GROWTH FACTOR-I (IGF-I) DETERMINED BY 1H-NMR AND DISTANCE GEOMETRY, 6 STRUCTURES     1gzr: HUMAN INSULIN-LIKE GROWTH FACTOR; ESRF DATA     1gzy: HUMAN INSULIN-LIKE GROWTH FACTOR; IN-HOUSE DATA     1gzz: HUMAN INSULIN-LIKE GROWTH FACTOR; HAMBURG DATA     1h02: HUMAN INSULIN-LIKE GROWTH FACTOR; SRS DARESBURY DATA     1h59: COMPLEX OF IGFBP-5 WITH IGF-I     1imx: 1.8 Angstrom crystal structure of IGF-1     1pmx: INSULIN-LIKE GROWTH FACTOR-I BOUND TO A PHAGE-DERIVED PEPTIDE     1wqj: Structural Basis for the Regulation of Insulin-Like Growth Factors (IGFs) by IGF Binding Proteins (IGFBPs)     2dsp: Structural Basis for the Inhibition of Insulin-like Growth Factors by IGF Binding Proteins     2dsq: Structural Basis for the Inhibition of Insulin-like Growth Factors by IGF Binding Proteins     2dsr: Structural Basis for the Inhibition of Insulin-like Growth Factors by IGF Binding Proteins     2gf1: SOLUTION STRUCTURE OF HUMAN INSULIN-LIKE GROWTH FACTOR 1: A NUCLEAR MAGNETIC RESONANCE AND RESTRAINED MOLECULAR DYNAMICS STUDY   3gf1: SOLUTION STRUCTURE OF HUMAN INSULIN-LIKE GROWTH FACTOR 1: A NUCLEAR MAGNETIC RESONANCE AND RESTRAINED MOLECULAR DYNAMICS STUDY     3lri: Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I

 

 

3 – 2

I.       Growth Hormone – GH - HGH

Growth hormone Growth hormone 1 Identifiers Symbol GH1 Entrez 2688 HUGO 4261 OMIM 139250 RefSeq NM_022562 UniProt P01241 Other data Locus Chr. 17 q22-q24

Growth hormone 2 Identifiers Symbol GH2 Entrez 2689 HUGO 4262 OMIM 139240 RefSeq NM_002059 UniProt P01242 Other data Locus Chr. 17 q22-q24

Growth hormone (GH) is a Protein Poly-peptide hormone. It stimulates growth and cell reproduction and regeneration in humans and other animals. It is a 191-amino acid, single-chain Protein polypeptide hormone that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior pituitary gland. Somatotrophin refers to the growth hormone produced natively and naturally in animals, whereas the term somatropin refers to growth hormone produced by recombinant DNA technology,^[1] and is abbreviated "rhGH" in humans.

Growth hormone is used clinically to treat children's growth disorders and adult growth hormone deficiency. In recent years, replacement therapies with human growth hormones (HGH) have become popular in the battle against aging and weight management. Reported effects include decreased body fat, increased muscle mass, increased bone density, increased energy levels, improved skin tone and texture, increased sexual function and improved immune system function. At this time HGH is still considered a very complex hormone and many of its functions are still unknown.^[2]

In its role as an anabolic agent, HGH has been used by competitors in sports since the 1970s, and it has been banned by the IOC and NCAA. Traditional urine analysis could not detect doping with HGH, so the ban was unenforceable until the early 2000s, when blood tests that could distinguish between natural and artificial HGH were developed. Blood tests conducted by WADA at the 2004 Olympic Games in Athens, Greece primarily targeted HGH.^[2]

II.    Gene locus

The genes for human growth hormone, known as Myles and Growth hormone 2, are localized in the q22-24 region of chromosome 17 and are closely related to human chorionic somatomammotropin (also known as placental lactogen) genes. GH, human chorionic somatomammotropin, and prolactin (PRL) are a group of homologous hormones with growth-promoting and lactogenic activity.

III.  Structure

The major isoform of the human growth hormone is a protein of 191 amino acids and a molecular weight of 22,124 daltons. The structure includes four helices necessary for functional interaction with the GH receptor. It appears that, in structure, GH is evolutionarily homologous to prolactin and chorionic somatomammotropin. Despite marked structural similarities between growth hormone from different species, only human and primate growth hormones have significant effects in humans.

 

Several molecular isoforms of GH circulate in the plasma. Much of the growth hormone in the circulation is bound to a protein (growth hormone-binding protein, GHBP) which is derived from the growth hormone receptor, and an acid labile subunit (ALS).

 

 

IV.Regulation

Peptides released by neurosecretory nuclei of the hypothalamus (Growth hormone-releasing hormone and somatostatin) into the portal venous blood surrounding the pituitary are the major controllers of GH secretion by the somatotropes. However, although the balance of these stimulating and inhibiting peptides determines GH release, this balance is affected by many physiological stimulators (e.g., exercise, nutrition, sleep) and inhibitors of GH secretion (e.g., Free fatty acids)^[3]

Stimulators of GH secretion include:

• peptide hormones
  • Growth hormone releasing hormone (GHRH also known as somatocrinin) through binding to the growth hormone releasing hormone receptor (GHRHR)^[4]
  • ghrelin through binding to growth hormone secretagogue receptors (GHSR)^[5]
• sex hormones^[6]
  • increased androgen secretion during puberty (in males from testis and in females from adrenal cortex)
  • estrogen
• clonidine and L-DOPA by stimulating GHRH release^[7]
• hypoglycaemia, arginine^[8] and propranolol by inhibiting somatostatin release^[7]

• deep sleep^[9]
• fasting^[10]
• vigorous exercise ^[11]

Inhibitors of GH secretion include:

• somatostatin from the periventricular nucleus ^[12]
• circulating concentrations of GH and IGF-1 (negative feedback on the pituitary and hypothalamus)^[2]
• hyperglycemia^[7]
• glucocorticoids^[13]

In addition to control by endogenous and stimulus processes, a number of foreign compounds (xenobiotics such as drugs and endocrine disruptors) are known to influence GH secretion and function.^[14]

V.   Secretion patterns

HGH is synthesized and secreted from the anterior pituitary gland in a pulsatile manner throughout the day; surges of secretion occur at 3- to 5-hour intervals.^[2] The plasma concentration of GH during these peaks may range from 5 to even 45 ng/mL.^[15] The largest and most predictable of these GH peaks occurs about an hour after onset of sleep.^[16] Otherwise there is wide variation between days and individuals. Nearly fifty percent of HGH secretion occurs during the third and fourth REM sleep stages. ^[17] Between the peaks, basal GH levels are low, usually less than 5 ng/mL for most of the day and night.^[16] Additional analysis of the pulsatile profile of GH described in all cases less than 1 ng/ml for basal levels while maximum peaks were situated around 10-20 ng/mL.^[18][19]

A number of factors are known to affect HGH secretion, such as age, gender, diet, exercise, stress, and other hormones.^[2] Young adolescents secrete HGH at the rate of about 700 μg/day, while healthy adults secrete HGH at the rate of about 400 μg/day.^[20]

 

VI.Functions of GH

Effects of growth hormone on the tissues of the body can generally be described as anabolic (building up). Like most other protein hormones, GH acts by interacting with a specific receptor on the surface of cells.

Increased height during childhood is the most widely known effect of GH. Height appears to be stimulated by at least two mechanisms:

1. Because polypeptide hormones are not fat-soluble, they cannot penetrate sarcolemma. Thus, GH exerts some of its effects by binding to receptors on target cells, where it activates a second messenger. ^[2] Through this mechanism GH directly stimulates division and multiplication of chondrocytes of cartilage.
2. GH also stimulates production of insulin-like growth factor 1 (IGF-1, formerly known as somatomedin C), a hormone homologous to proinsulin.^[21] The liver is a major target organ of GH for this process and is the principal site of IGF-1 production. IGF-1 has growth-stimulating effects on a wide variety of tissues. Additional IGF-1 is generated within target tissues, making it what appears to be both an endocrine and an autocrine/paracrine hormone. IGF-1 also has stimulatory effects on osteoblast and chondrocyte activity to promote bone growth.

In addition to increasing height in children and adolescents, growth hormone has many other effects on the body:

• Increases calcium retention, and strengthens and increases the mineralization of bone
• Increases muscle mass through sarcomere hyperplasia
• Promotes lipolysis
• Increases protein synthesis
• Stimulates the growth of all internal organs excluding the brain
• Plays a role in fuel homeostasis
• Reduces liver uptake of glucose
• Promotes gluconeogenesis in the liver^[22]
• Contributes to the maintenance and function of pancreatic islets
• Stimulates the immune system

VII.          Excesses

The most common disease of GH excess is a pituitary tumor composed of somatotroph cells of the anterior pituitary. These somatotroph adenomas are benign and grow slowly, gradually producing more and more GH. For years, the principal clinical problems are those of GH excess. Eventually the adenoma may become large enough to cause headaches, impair vision by pressure on the optic nerves, or cause deficiency of other pituitary hormones by displacement.

Prolonged GH excess thickens the bones of the jaw, fingers and toes. Resulting heaviness of the jaw and increased thickness of digits is referred to as acromegaly. Accompanying problems can include pressure on nerves (e.g., carpal tunnel syndrome), muscle weakness, insulin resistance or even a rare form of type 2 diabetes, and reduced sexual function.

GH-secreting tumors are typically recognized in the fifth decade of life. It is extremely rare for such a tumor to occur in childhood, but, when it does, the excessive GH can cause excessive growth, traditionally referred to as pituitary gigantism.

Surgical removal is the usual treatment for GH-producing tumors. In some circumstances, focused radiation or a GH antagonist such as pegvisomant may be employed to shrink the tumor or block function. Other drugs like ocreotide (somatostatin agonist) and bromocriptine (dopamine agonist) can be used to block GH secretion because both somatostatin and dopamine negatively inhibit GHRH-mediated GH release from the anterior pituitary.

Prolonged use of HGH over time will decrease size and volume of testes, in addition to shrinking the size of the penis. It has also been linked to decreasing both the anterior and posterior regions of the pituitary gland. Also lactation in men has been reported.

VIII.       Deficiencies

The effects of growth hormone deficiency vary depending on the age at which they occur. In children, growth failure and short stature are the major manifestations of GH deficiency, with common causes including genetic conditions and congenital malformations. It can also cause delayed sexual maturity. In adults, deficiency is rare,^[23] with the most common cause a pituitary adenoma, and others including a continuation of a childhood problem, other structural lesions or trauma, and very rarely idiopathic GHD.

Adults with GHD present with non-specific problems including truncal obesity with a relative decrease in muscle mass and, in many instances, decreased energy and quality of life.^[23]

Diagnosis of GH deficiency involves a multiple-step diagnostic process, usually culminating in GH stimulation test(s) to see if the patient's pituitary gland will release a pulse of GH when provoked by various stimuli.

Treatment with external GH is indicated only in limited circumstances,^[23] and needs regular monitoring due to the frequency and severity of side-effects. GH is used as replacement therapy in adults with GH deficiency of either childhood-onset (after completing growth phase) or adult-onset (usually as a result of an acquired pituitary tumor). In these patients, benefits have variably included reduced fat mass, increased lean mass, increased bone density, improved lipid profile, reduced cardiovascular risk factors, and improved psychosocial well-being

IX.            Therapeutic use

A.    Treatments unrelated to deficiency

GH can be used to treat conditions that produce short stature but are not related to deficiencies in GH, though results are not as dramatic when compared to short stature solely due to deficiency of GH. Examples of other causes of shortness often treated with GH are Turner syndrome, chronic renal failure, Prader-Willi syndrome, intrauterine growth retardation, and severe idiopathic short stature. Higher ("pharmacologic") doses are required to produce significant acceleration of growth in these conditions, producing blood levels well above physiologic. Despite the higher doses, side-effects during treatment are rare, and vary little according to the condition being treated.

GH treatment improves muscle strength and slightly reduces body fat in Prader-Willi syndrome, which are significant concerns beyond the need to increase height. GH is also useful in maintaining muscle mass in wasting due to AIDS. GH can also be used in patients with short bowel syndrome to lessen the requirement for intravenous total parenteral nutrition.

Uses that are controversial include

·         GH treatment for remission of Multiple sclerosis

·         GH treatment to reverse effects of aging in older adults (see below)

·         GH treatment to enhance weight loss in obesity

·         GH treatment for fibromyalgia

·         GH treatment for Crohn's disease and ulcerative colitis

·         GH treatment for idiopathic short stature

·         GH treatment for those suffering from burns

·         GH treatment for bodybuilding or athletic enhancement.

B.   Anti-aging agent

Claims for GH as an anti-aging treatment date back to 1990 when the New England Journal of Medicine published a study wherein GH was used to treat 12 men over 60.^[24] At the conclusion of the study, all the men showed statistically significant increases in lean body mass and bone mineral, while the control group did not. The authors of the study noted that these improvements were the opposite of the changes that would normally occur over a 10- to 20-year aging period. Despite the fact the authors at no time claimed that GH had reversed the aging process itself, their results were misinterpreted as indicating that GH is an effective anti-aging agent.^[25][26][27]

A Stanford University School of Medicine survey of clinical studies on the subject published in early 2007 showed that the application of GH on healthy elderly patients increased muscle by about 2 kg and decreased body fat by the same amount.^[25] However, these were the only positive effects from taking GH. No other critical factors were affected, such as bone density, cholesterol levels, lipid measurements, maximal oxygen consumption, or any other factor that would indicate increased fitness.^[25] Researchers also did not discover any gain in muscle strength, which led them to believe that GH merely let the body store more water in the muscles rather than increase muscle growth. This would explain the increase in lean body mass.

C.   Athletic enhancement

Athletes in many sports use human growth hormone to enhance their athletic performance despite that recent studies have not been able to support claims that human growth hormone can improve the athletic performance of professional male athletes. Studies have found that, on young, healthy male adults, HGH treatment improves physical appearance and increases resistance to some injuries. Research has also discovered that HGH could actually lower athletic performance.

X.   History

The identification, purification and later synthesis of growth hormone is associated with Choh Hao Li. Genentech pioneered the first use of recombinant human growth hormone for human therapy in 1981.

Prior to its production by recombinant DNA technology, growth hormone used to treat deficiencies was extracted from the pituitary glands of cadavers. Attempts to create a wholly synthetic HGH failed. Limited supplies of HGH resulted in the restriction of HGH therapy to the treatment of idiopathic short stature.^[29] Furthermore, growth hormone from primates was found to be inactive in humans.^[30]

In 1985, unusual cases of Creutzfeldt-Jacob disease were found in individuals that had received cadaver-derived HGH ten to fifteen years previous. Based on the assumption that infectious prions causing the disease were transferred along with the cadaver-derived HGH, cadaver-derived HGH was removed from the market.^[20]

In 1985, biosynthetic human growth hormone replaced pituitary-derived human growth hormone for therapeutic use in the U.S. and elsewhere.

As of 2005, recombinant growth hormones available in the United States (and their manufacturers) included Nutropin (Genentech), Humatrope (Lilly), Genotropin (Pfizer), Norditropin (Novo), and Saizen (Merck Serono). In 2006, the U.S. Food and Drug Association (FDA) approved a version of rhGH called Omnitrope (Sandoz). A sustained-release form of growth hormone, Nutropin Depot (Genentech and Alkermes) was approved by the FDA in 1999, allowing for fewer injections (every 2 or 4 weeks instead of daily); however, the product was discontinued in 2004.

XI.            References

1. ^ Daniels ME (1992). "Lilly's Humatrope Experience". Nature Biotechnology 10: 812. doi:10.1038/nbt0792-812a. 
2. ^ ^{a b c d e f} Powers M (2005). "Performance-Enhancing Drugs". in Deidre Leaver-Dunn; Joel Houglum; Harrelson, Gary L.. Principles of Pharmacology for Athletic Trainers. Slack Incorporated. pp. 331–332. ISBN 1-55642-594-5. 
3. ^ Actions of Anterior Pituitary Hormones: Growth Hormone (GH). Medical College of Georgia. 2007.
4. ^ Lin-Su K, Wajnrajch MP (December 2002). "Growth Hormone Releasing Hormone (GHRH) and the GHRH Receptor". Rev Endocr Metab Disord 3 (4): 313–23. PMID 12424433. 
5. ^ Wren AM, Small CJ, Ward HL, Murphy KG, Dakin CL, Taheri S, Kennedy AR, Roberts GH, Morgan DG, Ghatei MA, Bloom SR (November 2000). "The novel hypothalamic peptide ghrelin stimulates food intake and growth hormone secretion". Endocrinology 141 (11): 4325–8. PMID 11089570. 
6. ^ Meinhardt UJ, Ho KK (October 2006). "Modulation of growth hormone action by sex steroids". Clin. Endocrinol. (Oxf) 65 (4): 413–22. doi:10.1111/j.1365-2265.2006.02676.x. PMID 16984231. 
7. ^ ^{a b c} Low LC (1991). "Growth hormone-releasing hormone: clinical studies and therapeutic aspects". Neuroendocrinology 53 Suppl 1: 37–40. PMID 1901390. 
8. ^ Alba-Roth J, Müller OA, Schopohl J, von Werder K (December 1988). "Arginine stimulates growth hormone secretion by suppressing endogenous somatostatin secretion". J. Clin. Endocrinol. Metab. 67 (6): 1186–9. doi:10.1126/science.2237411. PMID 2903866. 
9. ^ Van Cauter E, Latta F, Nedeltcheva A, Spiegel K, Leproult R, Vandenbril C, Weiss R, Mockel J, Legros JJ, Copinschi G (June 2004). "Reciprocal interactions between the GH axis and sleep". Growth Horm. IGF Res. 14 Suppl A: S10–7. doi:10.1016/j.ghir.2004.03.006. PMID 15135771. 
10. ^ Nørrelund H (April 2005). "The metabolic role of growth hormone in humans with particular reference to fasting". Growth Horm. IGF Res. 15 (2): 95–122. doi:10.1016/j.ghir.2005.02.005. PMID 15809014. 
11. ^ Kanaley JA, Weltman JY, Veldhuis JD, Rogol AD, Hartman ML, Weltman A (November 1997). "Human growth hormone response to repeated bouts of aerobic exercise". J. Appl. Physiol. 83 (5): 1756–61. PMID 9375348. http://jap.physiology.org/cgi/content/full/83/5/1756. 
12. ^ Guillemin R, Gerich JE (1976). "Somatostatin: physiological and clinical significance". Annu. Rev. Med. 27: 379–88. doi:10.1146/annurev.me.27.020176.002115. PMID 779605. 
13. ^ Allen DB (September 1996). "Growth suppression by glucocorticoid therapy". Endocrinol. Metab. Clin. North Am. 25 (3): 699–717. PMID 8879994. 
14. ^ Scarth JP (2006). "Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review". Xenobiotica 36 (2-3): 119–218. doi:10.1080/00498250600621627. PMID 16702112. 
15. ^ Natelson BH, Holaday J, Meyerhoff J, Stokes PE (August 1975). "Temporal changes in growth hormone, cortisol, and glucose: relation to light onset and behavior". Am. J. Physiol. 229 (2): 409–15. PMID 808970. http://ajplegacy.physiology.org/cgi/content/abstract/229/2/409. 
16. ^ ^{a b} Takahashi Y, Kipnis D, Daughaday W (1968). "Growth hormone secretion during sleep". J Clin Invest 47 (9): 2079–90. doi:10.1172/JCI105893. PMID 5675428. 
17. ^ Mehta, Ameeta and Hindmarsh, Peter. 2002. The use of somatorpin (recombinant growth hormone) in children of short stature. Pediatric Drugs. 4: 37-47.
18. ^ Nindl BC, Hymer WC, Deaver DR, Kraemer WJ (07/01/2001). "Growth hormone pulsatility profile characteristics following acute heavy resistance exercise". J. Appl. Physiol. 91 (1): 163–72. PMID 11408427. http://jap.physiology.org/cgi/content/abstract/91/1/163. 
19. ^ Juul A, Jørgensen JO, Christiansen JS, Müller J, Skakkeboek NE (1995). "Metabolic effects of GH: a rationale for continued GH treatment of GH-deficient adults after cessation of linear growth". Horm. Res. 44 Suppl 3: 64–72. doi:10.1159/000184676. PMID 8719443. 
20. ^ ^{a b} Gardner, David G., Shoback, Dolores (2007). Greenspan's Basic and Clinical Endocrinology (8th ed.). New York: McGraw-Hill Medical. pp. 193–201. ISBN 0-07-144011-9. 
21. ^ "Actions of Anterior Pituitary Hormones: Physiologic Actions of GH". Medical College of Georgia. 2007. http://www.lib.mcg.edu/edu/eshuphysio/program/section5/5ch2/s5ch2_19.htm. Retrieved on 2008-01-16. 
22. ^ King, MW (2006). "Structure and Function of Hormones: Growth Hormone". Indiana State University. http://web.indstate.edu/thcme/mwking/peptide-hormones.html#gh. Retrieved on 2008-01-16. 
23. ^ ^{a b c} Molitch ME, Clemmons DR, Malozowski S, Merriam GR, Shalet SM, Vance ML; Endocrine Society's Clinical Guidelines Subcommittee, Stephens PA (May 2006). "Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society Clinical Practice Guideline". J. Clin. Endocrino. Metab. 91 (5): 1621–34. doi:10.1210/jc.2005-2227. PMID 16636129. 
24. ^ Rudman D, Feller AG, Nagraj HS, Gergans GA, Lalitha PY, Goldberg AF, Schlenker RA, Cohn L, Rudman IW, Mattson DE (July 1990). "Effects of human growth hormone in men over 60 years old". N. Engl. J. Med. 323 (1): 1–6. PMID 2355952. 
25. ^ ^{a b c d} Liu H, Bravata DM, Olkin I, Nayak S, Roberts B, Garber AM, Hoffman AR (January 2007). "Systematic review: the safety and efficacy of growth hormone in the healthy elderly". Ann. Intern. Med. 146 (2): 104–15. PMID 17227934. 
26. ^ "No proof that growth hormone therapy makes you live longer, study finds". PhysOrg.com. 2007-01-16. http://www.physorg.com/news88140162.html. Retrieved on 2009-03-16. 
27. ^ Gordon, Mark L. M.D. Human Growth Hormone (HGH) as an Anti-Aging Agent
28. ^ Swerdlow AJ, Higgins CD, Adlard P, Preece MA (July 2002). "Risk of cancer in patients treated with human pituitary growth hormone in the UK, 1959-85: a cohort study". Lancet 360 (9329): 273–7. doi: