Growth hormone isoforms, segments/fragments: Does a link exist with multifunctionality?

Oral Supplementation Using Gamma-Aminobutyric Acid and Whey Protein Improves Whole Body Fat-Free Mass in Men After Resistance Training

Background

Oral gamma-aminobutyric acid (GABA) supplementation increases growth hormone (GH) serum levels and protein synthesis. Therefore, post-exercise supplementation using GABA and protein may help enhance training-induced muscle hypertrophy. We evaluated whether GABA with whey protein enhanced muscular hypertrophy in men after progressive resistance training.

Methods

Twenty-one healthy men (26 - 48 years) were randomized to receive whey protein (WP; 10 g) or whey protein + GABA (WP + GABA; 10 g + 100 mg) daily for 12 weeks. Both groups performed resistance training twice per week (three sets of 12 repetitions at 60% of maximal strength; leg press, leg extension, leg curl, chest press, and pull down). Body composition was assessed using dual-energy X-ray absorptiometry.

Results

In the WP + GABA group, resting plasma GH concentrations were significantly elevated at 4 and 8 weeks, compared to baseline. However, resting plasma GH concentrations in the WP group were only significantly elevated at 8 weeks. After 12 weeks, the WP + GABA group exhibited significantly greater increase in whole body fat-free mass than the WP group.

Conclusions

The GABA and whey protein combination was more effective for increasing whole body fat-free mass; daily GABA supplementation may help enhance exercise-induced muscle hypertrophy.

Human Placental Growth Hormone Variant in Pathological Pregnancies

Growth hormone (GH), an endocrine hormone, primarily secreted from the anterior pituitary, stimulates growth, cell reproduction, and regeneration and is a major regulator of postnatal growth. Humans have two GH genes that encode two versions of GH proteins: a pituitary version (GH-N/GH1) and a placental GH-variant (GH-V/GH2), which are expressed in the syncytiotrophoblast and extravillous trophoblast cells of the placenta. During pregnancy, GH-V replaces GH-N in the maternal circulation at mid-late gestation as the major circulating form of GH. This remarkable change in spatial and temporal GH secretion patterns is proposed to play a role in mediating maternal adaptations to pregnancy. GH-V is associated with fetal growth, and its circulating concentrations have been investigated across a range of pregnancy complications. However, progress in this area has been hindered by a lack of readily accessible and reliable assays for measurement of GH-V. This review will discuss the potential roles of GH-V in normal and pathological pregnancies and will touch on the assays used to quantify this hormone.

Nanoparticle technology: amplifying the effective sensitivity of biomarker detection to create a urine test for hGH

Several clinical-grade immunoassays exist for the specific measurement of hGH or its isoforms in blood but there is an urgent need to apply these same reliable assays to the measurement of hGH in urine as a preferred 'non-invasive' biofluid. Unfortunately, conventional hGH immunoassays cannot attain the sensitivity required to detect the low concentrations of hGH in urine. The lowest limit of sensitivity for existing hGH immunoassays is >50 pg/mL, while the estimated concentration of urinary hGH is about 1 pg/m-50 times lower than the sensitivity threshold. We have created novel N-isopropylacrylamide (NIPAm)-based hydrogel nanoparticles functionalized with an affinity bait. When introduced into an analyte-containing solution, the nanoparticles can perform, in one step, (1) complete harvesting of all solution phase target analytes, (2) full protection of the captured analyte from degradation and (3) sequestration of the analyte, effectively increasing the analyte concentration up to a hundredfold. N-isopropylacrylamide nanoparticles functionalized with Cibacron Blue F3GA bait have been applied to raise the concentration of urinary hGH into the linear range of clinical grade immunoassays. This technology now provides an opportunity to evaluate the concentration of hGH in urine with high precision and accuracy.

Detection of doping with recombinant human growth hormone

Detection of doping with recombinant human growth hormone is one of the challenges for antidoping analysis. This review focuses on the most important relevant publications that provide insight into the laboratory measurement of human growth hormone (hGH), antibodies and standards, the isoform approach and the biomarker approach. The isoform approach monitors the changes of hGH molecular isoform composition in serum and was applied at the Olympic Games in Athens in 2004, Turin in 2006 and Beijing in 2008. The markers approach detects a formula score, which reflects the changes in concentration of IGF-1 and P-III-P. All these methodologies measure the concentrations of growth hormone and its isoforms for isoform approach, or the concentrations of IGF-1 and P-III-P. All factors that affect these measurements should be taken into account for the development of methods to detect doping with recombinant hGH.

CHO-recombinant human growth hormone as a protease sensitive reporter protein

Protein-free media are gaining more and more interest in mammalian cell culture technology. However, the range of commercially available protein-free media is wide, but lack of serum causes the lack of various substances (Keenan et al. in Cytotechnology, 50(1-3):49-56, 2006) which must be substituted case by case. Details on the composition of protein-free media are often unavailable or inaccessible in some cases, and as a consequence, there is an obvious need for testing procedures in order to evaluate the various commercialised products for their performance. Additionally, negative effects of tryptic meat digests on product quality have been reported in the literature (Gu et al. in Biotech Bioeng 56 (4):353-341, 1997). In the present studies of comparing various protein-free media for their suitability in propagation of recombinant CHO cells expressing human growth hormone (hGH), we have found somatotropin to be an excellent candidate for detection of protease activity. Somatotropin contains protease recognition sites for numerous proteases located around amino-acid residues 134-150. In this study, we demonstrate highly specific cleavage of recombinant hGH during batch cultivation. Analysis of the digested molecule was then performed by convergent methods like SDS-PAGE, HPLC and mass spectroscopy, and the results indicate hGH to be an ideal candidate for media and component screening in mammalian cell culture.

Small chicken growth hormone (scGH) variant in the neural retina

A novel variant of chicken growth hormone (cGH) that is severely truncated has recently been discovered in the neural retina. It is, however, unknown whether this protein binds to GH receptors (GHRs) and has biological activity. This possibility has therefore been addressed by homology modeling, using human (h)GH as a template because it is the only GH molecule with a crystal structure and because hGH binds to cGH receptors (cGHRs). Most of the residues of the small (s)cGH model fitted the hGH template, apart from two restricted regions from Ser 12 to Gln 20 and from Ser 55 to Val 58. The scGH model differs, however, from hGH in structure: hGH is composed of a four-helix bundle, whereas scGH has three main helices. Helices 2, 3, and 4 of hGH correspond to helices 1, 2, and 3 of scGH, but they are longer by one, four, and one residues, respectively. The secondary structure of the C-terminus of scGH is therefore similar to C-terminal hGH. The N-terminus of scGH is, however, severely truncated, lacking the residues of the full-length molecule derived from exons 1, 2, and 3. The N-terminus of scGH also includes 20 residues derived from intron C of full-length cGH. The predicted structure of its N-terminus has no classical secondary structure (alpha-helix or beta-sheet), whereas the N-terminus of hGH is composed of helix 1 and two mini-helices located between helix 1 and 2. This difference in ribbon structure results in a difference in the overall shape of the scGH model and hGH. The possibility that scGH could bind to a GHR dimer was assessed by examining the primary and hypothetical tertiary structure of scGH. hGH binds the extracellular domain (ECD) of two GHRs sequentially at its binding site 1 (or high affinity site) then at its binding site 2 (or low affinity site). Sequence alignment of scGH with hGH demonstrates that scGH lacks three key residues (of 14) at site 1 and nine residues (of 15) at site 2. It is therefore unlikely that tight binding of ECD1 to the site 1 of scGH could occur. scGH also lacks most of the site 2 residues, suggesting that it is unlikely that ECD2 would bind to the scGH model. In summary, we have developed a novel, structural model of scGH, with implications for its putative actions through classical GHRs.

Growth hormone isoform responses to GABA ingestion at rest and after exercise

Oral administration of the amino acid/inhibitory neurotransmitter gamma aminobutyric acid (GABA) reportedly elevates resting serum growth hormone (GH) concentrations.

PURPOSE

To test the hypothesis that GABA ingestion stimulates immunoreactive GH (irGH) and immunofunctional GH (ifGH) release at rest and that GABA augments the resistance exercise-induced irGH/ifGH responses.

METHODS

Eleven resistance-trained men (18-30 yr) participated in this randomized, double-blind, placebo-controlled, crossover study. During each experimental bout, participants ingested either 3 g of GABA or sucrose placebo (P), followed either by resting or resistance exercise sessions. Fasting venous blood samples were acquired immediately before and at 15, 30, 45, 60, 75, and 90 min after GABA or P ingestion and were assayed for irGH and ifGH.

RESULTS

At rest, GABA ingestion elevated both irGH and ifGH compared with placebo. Specifically, peak concentrations of both hormones were elevated by about 400%, and the area under the curve (AUC) was elevated by about 375% (P < 0.05). Resistance exercise (EX-P) elevated time-point (15-60 min) irGH and ifGH concentrations compared with rest (P < 0.05). The combination of GABA and resistance exercise (EX-GABA) also elevated the peak, AUC, and the 15- to 60-min time-point irGH and ifGH responses compared with resting conditions (P < 0.05). Additionally, 200% greater irGH (P < 0.01) and 175% greater ifGH (P < 0.05) concentrations were observed in the EX-GABA than in the EX-P condition, 30 min after ingestion. GABA ingestion did not alter the irGH to ifGH ratio, and, under all conditions, ifGH represented approximately 50% of irGH.

CONCLUSIONS

Our data indicate that ingested GABA elevates resting and postexercise irGH and ifGH concentrations. The extent to which irGH/ifGH secretion contributes to skeletal muscle hypertrophy is unknown, although augmenting the postexercise irGH/ifGH response may improve resistance training-induced muscular adaptations.

New preparations comprising recombinant human growth hormone: deliberations on the issue of biosimilars

Manufactured recombinant human GH (rhGH) has been available for more than 25 years. In the meantime, the GH produced by various manufacturers has been approved for application in replacement therapy in children and adults with GH deficiency or a number of disorders involving small stature in children. Until recently approval for each individual diagnosis was only granted after extensive studies on the long-term efficacy (e.g. adult height reached) and safety of the various products. Meanwhile, the European approving agency, the European Medicines Evaluation Agency (EMEA), has relinquished this restrictive stance. Thus, new rhGH preparations can count on gaining approval for existing indications even without conducting standard clinical studies of their efficacy and safety for each of these indications. The EMEA's reconsideration is apparently based on the rationale that recombinant GH can, in effect, be considered equivalent to the tried and tested preparations in wide use, provided certain specifications are met. The term 'biosimilars' was coined to denote the similarities between the products rather than their parity, as is the case with generics for instance. The higher complexity of biopharmaceuticals relates not only to the substances themselves but also to the manufacturing process. It is generally believed that modifications to a manufacturing process - which are a prerequisite for a patent - may cause modifications of the active substance which then may lead to different long-term effects. Thus, the term 'biosimilar' does not indicate that complex biopharmaceuticals deriving from the same substance are entirely identical, nor does the approval of a 'biosimilar' ensure this. The factual information provided here is offered towards clarification of some uncertainties and as a contribution towards resolving open questions relating to the topic of biosimilars. The final choice of product to be prescribed must be made by the informed, independent physician.