Growth Hormone Isoforms Research Articles

Simultaneous quantification of the 22-kDa isoforms of human growth hormone 1 and 2 in human plasma by multiplexed immunocapture and LC-MS/MS

An LC-MS/MS method is presented for the simultaneous quantification of two structurally closely related protein biomarker isoforms, the 22-kDa isoforms of human growth hormone 1 and human growth hormone 2, in human plasma. It is based on multiplexed immunocapture using two monoclonal antibodies immobilized on magnetic beads, tryptic digestion and quantification of two specific signature peptides plus an additional peptide for estimation of total growth hormone related concentrations. A full validation according to international guidelines was performed across the clinically relevant concentration ranges of 0.5 to 50 ng/mL for growth hormone 1, and 2 to 50 ng/mL for growth hormone 2 and demonstrated satisfactory method performance in terms of accuracy, precision, stability and absence of interference. The method’s applicability for routine analysis and its ability to effectively distinguish between GH1 and GH2 was demonstrated by the analysis of plasma samples from pregnant individuals to study the changes in growth hormone levels during pregnancy.

A combined top-down and bottom-up LC-HRMS/MS method for the quantification of human growth hormone in plasma and serum

ObjectiveThe precise and accurate quantification of human growth hormone (GH) in plasma/ serum is crucial for the diagnosis and treatment of diseases like GH deficiency or acromegaly. However, the ligand-binding assays (LBAs) currently used for routine testing show considerable methodological variability. Here, we present a complementary, combined top-down and bottom-up LC-MS-based method to quantify (intact) GH in plasma and serum, which concurrently provides a basis for a MS-based analysis of GH in doping controls. DesignExtraction of GH from plasma/ serum was accomplished by protein precipitation, followed by an immunocapture step using protein A-coupled magnetic beads and a polyclonal anti-GH antibody. The intact protein was subsequently analyzed top-down on a 2D-LC-HRMS/MS system. In addition, sample extracts were digested with trypsin and analyzed for signal peptides corresponding to ‘total’, 22 kDa and 20 kDa GH (bottom-up). Both assays were validated according to current guidelines and compared to the GH isoform differential immunoassay used in routine doping control analysis. GH concentrations in serum samples of healthy adults, patients with acromegaly, and in samples obtained after administration of recombinant GH were analyzed as proof-of-principle. ResultsThe intact monomeric 22 kDa isoform of GH was selectively quantified in a representative working range of 0.5 to 10 ng/ml by top-down LC-HRMS/MS. Subsequent bottom-up analysis provided additional data on ‘total’ and 20 kDa GH. Top-down and bottom-up assay results for the 22 kDa isoform correlated well with the corresponding immunoassay results (R2 > 0.95). For a possible application of the method in an anti-doping context, the ratio between 22 kDa and ‘total’ GH was evaluated, indicating differences between the various donor groups, but only with limited significance. ConclusionThe top-down and bottom-up LC-HRMS/MS method developed here presents a valuable tool for the quantification of GH in plasma/ serum complementary to established LBAs used at present in clinical measurements. Albeit the examination of the GH isoform proportions by the LC-MS method does not yet allow for the assessment of GH abuse, the obtained findings provide an important basis to enable LC-MS-based GH analysis of doping control samples in the future.

Selective quantification of the 22-kDa isoform of human growth hormone 1 in serum and plasma by immunocapture and LC–MS/MS

The human growth hormone GH1 (22 kDa) is a commonly measured biomarker for diagnosis and during treatment of growth disorders, but its quantification by ligand binding assays may be compromised by the occurrence of a number of isoforms. These can interfere in the assays and lead to differences in results between laboratories and potentially even in the treatment of patients. We present an LC–MS/MS method that is able to distinguish the major growth hormone isoform (GH1, 22 kDa) from other isoforms and quantify it without any interference across the clinically relevant concentration range of 0.5 to 50 ng/mL. Analysis involves purification of a 100-µL serum sample by immunocapture using an anti-GH-directed antibody, tryptic digestion, and LC–MS/MS quantification of an isoform-specific signature peptide for GH1 (22 kDa). A tryptic peptide occurring in all GH isoforms is monitored in the same 16-min analytical run as a read-out for total GH. Stable-isotope-labeled forms of these two peptides are included as internal standards. Full validation of the method according to recent guidelines, against a recombinant form of the analyte in rat plasma calibrators, demonstrated intra-assay and inter-assay imprecision below 6% across the calibration range for both signature peptides and recoveries between 94 and 102%. An excellent correlation was found between nominal and measured concentrations of the WHO reference standard for GH1 (22 kDa). Addition of up to 1000 ng/mL biotin or the presence of a 100-fold excess of GH binding protein did not affect the measurement. Equivalent method performance was found for analysis of GH in serum, EDTA, and heparin plasma. Analyte stability was demonstrated during all normal sample storage conditions. Comparison with the IDS-iSYS GH immunoassay showed a good correlation with the LC–MS/MS method for the isoform-specific signature peptide, but a significant positive bias was observed for the LC–MS/MS results of the peptide representing total GH. This seems to confirm the actual occurrence of other GH isoforms in serum. Finally, in serum from pregnant individuals, no quantifiable GH1 (22 kDa) was found, but relatively high concentrations of total GH.Graphical abstract

Growth hormone isoform testing in capillary dried blood spots: Results from single and multiple dose administration studies and large-scale field collections.

A multiphase study was designed to examine the detectability of human growth hormone (GH) use in capillary dried blood spots (DBS). First, 13 subjects self-injected a single, 2-mg dose of somatropin and collected capillary DBS samples for 24 h. Next, nine subjects self-injected 2-mg somatropin, six times over the course of 11 days; DBS were collected intermittently following dosing. Finally, a nondrug, large-scale field study involved DBS collections from an athlete and staff population over 3 years. All DBS samples were self-collected using the Tasso M20 device and were analyzed for the presence of GH using the WADA-approved GH isoforms test. Following the single dose, positive detection within 12 h of dosing was 86% and 56% sensitive on Kits 1 and 2, respectively. In the multidose study, detection within 12 h was 85% and 69% sensitive on Kits 1 and 2, respectively. No positives were detected outside the 12-h window following a single dose, wherein detection was 5.6% sensitive at 24-h in the multidose study. Combining the 12-h windows from both studies, 100% of samples had measurable recombinant (REC) and pituitary (PIT) GH concentrations above the assay LoD, 0.041 ng/ml. Finally, 1213 samples were collected in the large-scale field study: 189 showed REC and PIT concentrations above the LoD; none returned positive results. GH is detectable in capillary DBS using the isoforms method for 12-24 h following use. While detection is short lived, transitioning to a DBS self-collection method can allow more frequent testing and increase deterrence to GH abuse.

Different isoforms of growth hormone (20 kD-GH and 22 kD-GH) shows different biological activities in mesenchymal stem cell (MSC)

ABSTRACT There are two main types of growth hormone (GH) in the circulatory system. One is 22 kD-GH, which is the predominant isoform in the circulating system, 90% GH is present as a 22 kD protein, and 10% of GH is present as a 20 kD protein. Amino acid sequences are identical between 20 kD-GH and 22 kD-GH protein, except that 20 kD-GH lacks 15 amino acid residues 32 to 46. Studies have shown that GH has many important biological effects on mesenchymal stem cells (MSCs). However, so far, the cellular characteristics of the two types of GH have not been studied in BM-MSCs. Furthermore, the biological activity of 20 kD-GH has not been explored in BM-MSCs. For this, in the current work, BM-MSCs were used as in vitro cell model. We have carried out the current research using a series of experimental techniques (such as Western-blot and indirect immunofluorescence). Firstly, we explored the cell behavior of two types of GH in the Bm-MSC model and found that they showed different biological characteristics; Secondly, we investigated the biological characteristics of 20 kD-GH and 22 kD-GH, and results showed that 22 kD-GH and 20 kD-GH exhibited different signaling profiles; Thirdly, we found that the 20 kD-GH and 22 kD-GH Gexhibited different regulatory effects on the osteogenic differentiation of BM-MSCs. The current research lays a solid foundation for further studies on the regulatory effects of GH on MSCs.

GH1 C.291 + 34G>C in a Growth Hormone Deficient Pedigree

Background: Heterozygous loss of function mutations in GH1 are a cause of autosomal dominant isolated growth hormone deficiency (GHD) or IGHD type II. However, this condition is rare and a genotype/phenotype association is often based on single case or pedigree reports. Clinical Case: The male proband was born at 38 weeks following an uncomplicated pregnancy, birthweight 2585 gm (˗1.3SD), length 43 cm (˗2.7SD). At 20 months old: length ˗3.2SD, weight/length 16%. Peak growth hormone (GH) levels 4.42 ng/mL and 3.2 ng/mL following clonidine and arginine stimulation, respectively; cortrosyn-stimulated cortisol was 41.4 mcg/dL. Prolactin was 61.2 ng/mL (reference range 2.6 to 13.1 ng/mL); T4 and TSH levels were normal. Magnetic resonance imaging showed a flattened anterior pituitary gland, consistent with empty sella, with normal bright spot. He has had an intermittent and variable response to GH treatment due to noncompliance; recent recorded height was ˗3.6SD at 13.9 and he was early pubertal. Father had a history of childhood growth hormone treatment and is 151 cm tall, 2 paternal aunts did not receive treatment and are 145 cm tall, 3 children of these aunts are diagnosed with GHD. There is no maternal family history of GHD; mother is 155 cm. Proband testing revealed heterozygous GH1 c.291 + 34G>C (EGL Genetics), classified as a variant of unknown significance; father was also found to have this variant, mother was negative. Genetic testing for of additional family members is under consideration. Conclusion: Nine of 96 heterozygous GH1 variants are located in intron 3. Two have been classified as pathogenic and are predicted to cause exon skipping. Our proband’s variant cannot be considered a canonical splice site or in a mutational hot spot but has extremely low frequency in population databases. Functional studies clan clarify if our proband’s variant results in a 17.5 kDa GH isoform and dominant negative effect on full length GH production with potential detrimental effects on other anterior pituitary hormones. We present the second GHD pedigree with GH1 c.291 + 34G>C mutation. As in the previous report (1), no other hormone deficiencies are identified, despite the appearance of an empty sella for our proband. Reference: (1) Cho SY, Ki, CS, Park, HD, et al. Genetic investigation of patients with undetectable peaks of growth hormone after two provocation tests. Clin Endocrinol 2013; 78: 317-20.

Doping and GH

Abuse of growth hormone (GH) in sport is evidenced by customs and police, and more recently through testing in anti-doping laboratories. The popularity of GH among cheaters contrasts to the difficulty to prove performance-enhancing effects in controlled studies. Earlier results from replacement therapy in GH deficient adults indicated effects on muscle strength, which were not confirmed in meta-analyses. Even less evidence is available from healthy, trained adults. Obviously, it is impossible to mimic doses used by dopers in controlled studies. Changes in body composition induced by GH lipolytic actions could be helpful in some disciplines. Biochemical detection of doping with recombinant GH remained impossible for decades because of the short half-life in circulation and the similarity of pharmaceutical preparations to endogenous GH. The “marker method” uses changes in GH dependent biomarkers with longer half-lives, and some athletes have been banned because concentrations of IGF-I or P-III-P (a marker of bone and collagen turnover) were grossly elevated. High inter- and intra-individual variability of the biomarkers remains problematic. The “isoform-method” detects changes in molecular isoforms of GH occurring after administration of recombinant GH. This consists of the 22 kD isoform only, while the pituitary secretes a wide spectrum of GH isoforms. A respective change in circulating GH isoforms can be measured by specific assays. Window of detection is limited, but targeted out of competition testing continuously detects cheating athletes. Associated sanctions have been upheld in front of the court of arbitration is sports, and the method is widely implemented today.

Growth Hormone and Insulin-like Growth Factor-I Molecular Weight Isoform Responses to Resistance Exercise Are Sex-Dependent.

Purpose: To determine if acute resistance exercise-induced increases in growth hormone (GH) and insulin-like growth factor-I (IGF-I) were differentially responsive for one or more molecular weight (MW) isoforms and if these responses were sex-dependent.Methods: College-aged men (n = 10) and women (n = 10) performed an acute resistance exercise test (ARET; 6 sets, 10 repetition maximum (10-RM) squat, 2-min inter-set rest). Serum aliquots from blood drawn Pre-, Mid-, and Post-ARET (0, +15, and +30-min post) were processed using High Performance Liquid Chromatography (HPLC) fractionation and pooled into 3 MW fractions (Fr.A: >60; Fr.B: 30–60; Fr.C: <30 kDa).Results: We observed a hierarchy of serum protein collected among GH fractions across all time points independent of sex (Fr.C > Fr.A > Fr.B, p ≤ 0.03). Sex × time interactions indicated that women experienced earlier and augmented increases in all serum GH MW isoform fraction pools (p < 0.05); however, men demonstrated delayed and sustained GH elevations (p < 0.01) in all fractions through +30-min of recovery. Similarly, we observed a sex-independent hierarchy among IGF-I MW fraction pools (Fr.A > Fr.B > Fr.C, p ≤ 0.01). Furthermore, we observed increases in IGF-I Fr. A (ternary complexes) in men only (p ≤ 0.05), and increases in Fr.C (free/unbound IGF-I) in women only (p ≤ 0.05) vs. baseline, respectively.Conclusions: These data indicate that the processing of GH and IGF-I isoforms from the somatotrophs and hepatocytes are differential in their response to strenuous resistance exercise and reflect both temporal and sex-related differences.

MON-LB014 Autosomal Dominant Growth Hormone Deficiency Due to a Novel c.178g&amp;gt;A Mutation in the GH1 Gene Is Caused by Alternative Splicing to Produce a Small GH Isoform

Introduction: Growth hormone (GH) plays a vital role in human physiology. Mutations in GH1 cause isolated growth hormone deficiency (GHD). The most frequent cause of familial growth hormone deficiency is Type II autosomal dominant GHD (isolated GHD type II) due to several heterozygous GH1 mutations. These mutations have been shown to (a) produce shorter isoforms of GH that do not bind to growth hormone receptors, (b) cause diminished secretion of GH, or (c) result in misfolded GH protein. Methods: Genomic DNA from patients with familial GHD was enriched for the coding exons using hybrid capture technology, and GH1 was sequenced using Next Generation Sequencing technology. The p.A34T mutant protein was expressed in bacteria, and binding to GHR was studied by surface plasmon resonance technology. Computational prediction of transcription indicated that alternative splicing is likely to produce a shorter GH variant with skipping of exon 3 in GH1. Mammalian cell-based studies incorporating transfection of whole GH1 gene containing exons/introns were used to study transcriptional effects. RNA was isolated from cells transfected with WT and mutant GH1 gene and analyzed by RT PCR using primers in the second and fifth exons of GH1 that could identify all possible isoforms of GH1 mRNA. Results: GHD was identified in three female siblings aged 3.25-6.33 years (Ht SDS -3.21 to -1.13, peak GH 2.9-6.6 ng/mL); their mother had previously been diagnosed with GHD at age 12.33 years (Ht SDS -3.44, GH peak < 2 ng/mL). Sequencing of GH1 identified a novel heterozygous variant (c.178G>A; p.Ala34Thr) not found in the Broad ExAc dataset representing >60,000 children without the severe childhood-onset disease. Functional studies using whole gene transfection showed that the c.178G>A mutation leads to alternate splicing resulting in increased production of the shorter 17.5kD isoform of GH due to exon 3 skipping. Results were confirmed by quantitative RT-PCR as well as GH secretion assays, which showed a lower level of GH production from cells transfected with the GH1 gene containing the c.178G>A mutation. The SPR based receptor binding assay and cell proliferation assay using bacterially expressed proteins showed that once produced, the GH protein with the A34T mutation behaves similar to WT GH protein. All these results confirm that the cause of GHD due to the c.178G>A mutation in GH1 is due to altered transcription leading to the production of the shorter 17.5 kD isoform of GH protein and not due to the amino acid change A34T that is caused by the mutation. Conclusion: The presence of a heterozygous GH1 variant (c.178G>A, p.Ala34Thr) in four individuals with GHD suggests that this is a novel cause of IGHD type II. Production of the smaller 17.5 kD GH isoform results in reduced overall GH secretion and loss of binding to GHR due to competition with the normal GH protein, explaining the dominant-negative phenotype.

SUN-LB62 Differential Regulation of 22 kDa and 20 kDa Growth Hormone Isoforms in Response to Acute Glucose Load and Moderate Intensity Exercise

Background: Among growth hormone (GH) isoforms, the 22kDa (22kD) is the most abundant (~90%), followed by 20 kDa GH ((20kD) ~10%). 22kD has known diabetogenic potential by increasing insulin resistance. Although of equal somatotropic activity, 20kD has been suggested to be less diabetogenic. Under physiological conditions, both isoforms are largely secreted in parallel, but data on regulation of both isoforms in the context of glucose load and utilization are scarce. Methods: We measured 20- and 22kD GH in fasted healthy adult females during two scenarios: (A) Premenopausal females (n = 25; age (mean (range)) 27.8 (22-52), body mass index (BMI) (kg/m2) 21.8 (18.2-27.3), insulin sensitivity index (ISI) 7.9 (3.2-19.7) underwent an oral glucose tolerance test (OGTT, 75g, sampling at baseline, 30, 60, 90, 120 and 180 minutes (min); (B) Premenopausal females within 1 year postpartum (n=28, age 36 (29-44), BMI 23.7 (19.4-41.3), ISI (7.2- (2.4-13.2)) performed moderate intensity exercise (fixed workload 60% VO2max, sampling at -15, -10, -5, 0, 3, 6, 10, 15, 20, 30 and 45 min and after 5, 10 and 15 min of resting). 20- and 22kD were measured by specific immunoassays (22kD: IDS-iSYS GH CLIA, limit of quantification (LoQ) 0.05 ng/mL; 20kD: in-house immunofluorometric assay (IFMA), LoQ 0.025 ng/mL), and the 20/22kD ratio was calculated. Results: As expected, both, 22kD and 20kD concentrations decreased after glucose load. However, the 20/22kD ratio increased significantly (Friedman test, P = 0.04, Kendall’s W 0.69, Conover’s post test: 0 vs. 60, 90 and 120 min; P = 0.018, 0.032 and 0.018, respectively. After 120 min, 20/22kD returned to baseline.With exercise, both, 20- and 22kD increased. In contrast to glucose load, the 20/22kD ratio significantly decreased (Friedman test, P = 0.025, Kendall’s W 0.59, Conover’s post test: -10 vs. 10 and 20 min; P = 0.015 and 0.022, respectively), reaching a nadir at 10 min and returning to the baseline after cessation of exercise (20 vs. 50, 55 and 60 min; P = 0.02, 0.005 and 0.016, respectively. Conclusion: Glucose load and exercise lead to opposite changes in the 20/22kD ratio, suggesting a tight regulation by glucose demands. We speculate that the putative less diabetogenic isoform (20kD) is preferentially secreted during situations of glucose excess, while the opposite happens during exercise, when increased energy demands are associated with predominant upregulation of the more diabetogenic 22kD GH.

Longitudinally monitoring of P-III-NP, IGF-I, and GH-2000 score increases the probability of detecting two weeks' administration of low-dose recombinant growth hormone compared to GH-2000 decision limit and GH isoform test and micro RNA markers.

To detect doping with growth hormone (GH), GH isoform and biomarkers tests are available. Both methods use population-based decision limits. Future testing in anti-doping is progressing toward individual-based reference ranges, and it is possible that with such an approach the sensitivity to detect GH doping may increase. In addition to monitoring different proteins, the use of miRNAs as future GH biomarkers has been discussed. Here we have longitudinally studied the serum concentrations of IGF-I, P-III-NP and the different GH isoforms in nine healthy men prior to, during and after two weeks' administration with low doses (1 and 4IU/day) of recGH. Moreover, three putative miRNAs were analyzed. The results show that 80% of the participants were identified as atypical findings using the GH isoform test. However, the participants were only positive 1.5-3hours directly after an injection. Only one of the participants reached a GH-2000 score indicative of doping when a population-based decision limit was applied. When IGF-I and P-III-NP were longitudinally monitored, 88% of the participants were identified above an individual upper threshold arbitrarily calculated as three standard deviations above the mean values of four baseline samples. The miRNA levels displayed large intra-subject variations that did not change in relation to recGH administration. Our results show that the GH isoform test is very sensitive in detecting low doses of recGH but with a short detection window. Moreover, longitudinally monitoring of IGF-I and P-III-NP may be a promising future approach to detect GH doping.

Cellular internalization and trafficking of 20 KDa human growth hormone

Twenty kilodalton human growth hormone (20K-GH) is the second most abundant GH isoform after the twenty-two kilodalton human growth hormone (22 K-GH) isoform. 20K-GH exhibits similar but not identical physiological activities as that of 22K-GH. The cell behaviour of 22K-GH has been extensively studied, but little or no information has been reported regarding 20K-GH. Here, we focussed on the internalization of 20K-GH. We found that the internalization of 20K-GH is rapid and occurs in a time- and dose-dependent manner. 20K-GH internalization is mediated by GHR. It appears that the internalization of 20K-GH and GHR into the cytoplasm is mediated by clathrin and/or caveolin. The current study indicates that 20K-GH can internalize into the cytoplasm and suggests that the internalized 20K-GH may exhibit different functions from those of 22K-GH.

Human growth hormone (GH) isoforms during oral glucose tolerance test in patients with acromegaly and in healthy subjects

Human growth hormone (GH) isoforms during oral glucose tolerance test in patients with acromegaly and in healthy subjects

Growth hormone isoform-differential massspectrometry for doping control purposes.

Mass spectrometry (MS) allows for monitoring growth hormone (GH) isoform compositions at high specificity. It is demonstrated that this capability can be used to reliably detect alterations as elicited by (putative) doping with 22kDa-GH. Sample treatment consists of enzymatic protein cleavage, followed by 2-step liquid chromatography clean-up, prior to analysis by MS. The protocol does not depend on antibodies for analyte extraction at any stage. Therefore, MS opens an opportunity for independent confirmation, if combined with the antibody-based isoform differential test presently used in practice. To check the fitness-for-purpose of this concept, GH-free serum was spiked with pure 22kDa- and 20kDa-GH covering a representative range of concentrations (0.5-9.4μg/L), while the 22kDa fraction was within a range of 80%-85%, or at 100%, the latter simulating an administration of 22kDa-GH. Mean deviation of 22kDa-fractions found was within less than 3% for samples with total GH>= 1 μg/L . Beyond this, results by antibody-free isoform-differential MS, as described, were in line with those of the World Anti-Doping Agency-approved antibody-based test for 18 native sera and 3 positive controls. In this context, relating 22kDa-GH to total-GH rather than 22kDa+20kDa was considered as an alternative strategy to earlier approaches. However, 20kDa-GH as an additional measurand, next to 22kDa- and total-GH, provides useful extra information, as it directly indicates the presence or absence of a non-22kDa-GH form.

Report on an anti-doping operation in Guadeloupe: High number of positive cases and inferences about doping habits.

Anti-doping controls in non-major events are relatively infrequent and athletes that compete only in these events are less likely to be controlled. The French Anti-Doping Agency carried out an anti-doping operation during a regional cycling competition in Guadeloupe. The urine and serum samples were analysed by the French anti-doping laboratory. Out of 42 athletes, 7 were positive for one or more substances prohibited by the World Anti-Doping Agency. Four serum samples contained continuous erythropoietin receptor activator (CERA) and one a recombinant erythropoietin. However, no traces were found in the corresponding urines. One of the athletes positive for CERA was also positive for growth hormone (GH), identified using the GH isoform test. The same serum was negative with the GH biomarkers test, probably because of the brief interval between injection and control (less than a day). The stimulants heptaminol and dimethylbutylamine, as well as the glucocorticoid prednisone and its metabolite prednisolone, were also found. Strikingly, 16.6% of the controlled athletes were using one or more prohibited drugs. These findings indicate that doping is widespread in athletes competing regionally and that CERA is still a popular drug for endurance sports. They underline the need for more controls, particularly blood sampling during non-major competitions. Copyright © 2017 John Wiley & Sons, Ltd.

Autocrine/paracrine proliferative effect of ovarian GH and IGF-I in chicken granulosa cell cultures

It is known that growth hormone (GH) and its receptor (GHR) are expressed in granulosa cells (GC) and thecal cells during the follicular development in the hen ovary, which suggests GH is involved in autocrine/paracrine actions in the female reproductive system. In this work, we show that the knockdown of local ovarian GH with a specific cGH siRNA in GC cultures significantly decreased both cGH mRNA expression and GH secretion to the media, and also reduced their proliferative rate. Thus, we analyzed the effect of ovarian GH and recombinant chicken GH (rcGH) on the proliferation of pre-hierarchical GCs in primary cultures. Incubation of GCs with either rcGH or conditioned media, containing predominantly a 15-kDa GH isoform, showed that both significantly increased proliferation as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, proliferating cell nuclear antigen (PCNA) quantification and (3H)-thymidine incorporation (3H-T) assays in a dose response fashion. Both, locally produced GH and rcGH also induced the phosphorylation of Erk1/2 in GC cultures. Furthermore, GH increased IGF-I synthesis and its release into the GC culture incubation media. These results suggest that GH may act through local IGF-I to induce GC proliferation, since IGF-I immunoneutralization completely abolished the GH-induced proliferative effect. These data suggest that GH and IGF-I may play a role as autocrine/paracrine regulators during the follicular development in the hen ovary at the pre-hierarchical stage.

Exploration of Molecular Network Variations in Different Subtypes of Human Non-functional Pituitary Adenomas.

Exploration of Molecular Network Variations in Different Subtypes of Human Non-functional Pituitary Adenomas.

Unaltered ratio of circulating levels of growth hormone/GH isoforms in adults with Prader–Willi syndrome after GHRH plus arginine administration

Human growth hormone (GH) is a heterogeneous protein hormone consisting of several isoforms, the most abundant being 22kDa- and 20kDa-GH. The availability of analytical methods to measure these GH isoforms might represent a valuable diagnostic tool to investigate GH hyposecretory states, including Prader–Willi syndrome (PWS), one of the most common causes of syndromic obesity. The aim of the present study was to measure circulating levels of 22kDa- and 20kDa-GH in PWS adults (n=14; M/F: 5/9; genotype DEL15/UPD15: 12/2; age: 19.0±3.7years; BMI: 29.9±8.7kg/m2) after combined GH releasing hormone (GHRH) plus arginine (ARG) administration. The results were analysed subdividing the study population in obese vs. nonobese (6/8) and GH deficient vs. nonGH deficient (GHD) (6/8) subjects, according to appropriate BMI-related diagnostic cut-off limits of GH peak response to the provocative test. Circulating levels of 22kDa-GH were measured by a chemiluminescent method based on a detection monoclonal antibody targeting an epitope in the loop connecting helix 1 and 2 of GH, which is missing in 20kDa-GH; the 20kDa-GH was measured using a time resolved fluorescence assay based on two monoclonal antibodies with no cross-reactivity to 22-kDa GH.GHRH plus ARG significantly stimulated the secretions of 22kDa- and 20kDa-GH in nonobese (at 30, 45, 60 and 90min and at 45, 60, 90 and 120min vs. 0min, p<0.05, with GH peaks of 15.8±10.3ng/ml and 2.7±1.2ng/ml, respectively) and in nonGHD PWS (at 30, 45 and 60min and at 45, 60 and 90min vs 0min, p<0.05, with GH peaks of 12.5±9.0ng/ml and 2.0±1.8ng/ml, respectively). No significant GHRH plus ARG-induced changes in 22kDa- and 20kDa-GH were observed in obese or GHD PWS patients, the only exception being the increase of 22kDa-GH (p<0.05) 60min after the stimulus administration in GHD group (with GH peaks of 6.9±4.7ng/ml and 0.8±0.6ng/ml in obese subjects and 8.5±6.0ng/ml and 1.2±1.0ng/ml in GHD subjects for 22kDa- and 20kDa-GH, respectively). The GH responses for both isoforms were significantly higher in nonobese than in obese PWS patients (at 45 and 60min for 22kDa-GH and at 45, 60, 90 and 120min for 20kDa-GH, p<0.05), while no differences were detected between GHD vs. nonGHD groups. As previously reported in healthy subjects, the ratios of circulating levels of 22kDa- to 20kDa-GH remained constant after GHRH plus ARG both in obese/non-obese and GHD/non-GHD groups, thus suggesting the preservation of a normal balance in GH isoforms in PWS.

Detecting growth hormone misuse in athletes

Athletes have been misusing growth hormone (GH) for its anabolic and metabolic effects since the early 1980s, at least a decade before endocrinologists began to treat adults with GH deficiency. Although there is an ongoing debate about whether GH is performance enhancing, recent studies suggest that GH improves strength and sprint capacity, particularly when combined with anabolic steroids. The detection of GH misuse is challenging because it is an endogenous hormone. Two approaches have been developed to detect GH misuse; the first is based on the measurement of pituitary GH isoforms and the ratio of 22-kDa isoform to total GH. The second is based on the measurement of insulin like growth factor-I (IGF-I) and N-terminal propeptide of type III procollagen (P-III-NP) which increase in a dose-dependent manner in response to GH administration. Both methodologies have been approved by the World Anti-Doping Agency (WADA) and have led to the detection of a number of athletes misusing GH.

Ghrelin Stimulation of Growth Hormone Isoforms: Parallel Secretion of Total and 20-kDa Growth Hormone and Relation to Insulin Sensitivity in Healthy Humans

The 20-kDa human GH (hGH) is produced in the pituitary by alternative splicing of the hGH-N gene. The 20-kDa hGH promotes growth similarly to 22-kDa or total hGH, the predominant form in circulation, but the relative effects of these isoforms on glucose metabolism have been debated. To investigate the effect of ghrelin on 20-kDa and total hGH secretion in healthy, nonobese subjects. We also studied associations between basal GH concentration and fasting glucose and insulin as well as between dynamic GH secretion and insulin sensitivity. Synthetic human acyl ghrelin (0.2 or 0.6 nmol/kg · h) or saline was infused in random order in 14 healthy subjects (six males, eight females; age 27.7 ± 6.3 yr; body mass index 22.0 ± 2.7 kg/m(2), mean ± SEM) on 3 separate days. Ghrelin was infused for 45 min to achieve steady-state levels and continued through a 3-h frequently sampled i.v. glucose tolerance test. Insulin sensitivity index was quantified using the minimal model of glucose kinetics. Basal 20-kDa and total GH concentrations were 0.4 ± 0.1 and 2.2 ± 0.4 ng/ml, respectively, with a 20-kDa to total GH ratio of 0.13 ± 0.02. Females had significantly higher baseline GH levels. Ghrelin administration increased 20-kDa and total GH levels in a parallel and dose-dependent fashion, with no significant change in the ratio of the isoforms. Basal 20-kDa and total GH levels were negatively correlated with fasting glucose, insulin, and homeostasis model assessment of insulin resistance. During the frequently sampled iv glucose tolerance test, GH secretion was positively correlated with insulin sensitivity index with saline infusion. Ghrelin dose-dependently increases endogenous 20-kDa and total GH secretion in a parallel fashion in healthy subjects. Both basal and stimulated levels of the different GH isoforms were positively associated with insulin sensitivity in this cohort of healthy men and women.