20K-GH and its use in detecting GH abuse

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

OBJECTIVE

The 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.

DESIGN

Extraction 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.

RESULTS

The 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.

CONCLUSION

The 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.

The biochemical diagnosis of acromegaly: revising the role of measurement of IGF-I and GH after glucose load in 5 questions

INTRODUCTION

Acromegaly is a rare disorder characterized by the excessive secretion of growth hormone (GH), mostly caused by pituitary adenomas. While in full-blown cases the diagnosis is easy to establish, milder cases are more challenging. Additionally, establishing whether full cure after surgery is reached may be difficult.

AREAS COVERED

In this article, we will review the challenges posed by the variability in measurements of GH and its main effector insulin-like growth factor I (IGF-I) due to both biological changes, co-morbidities, and assays variability.

EXPERT OPINION

Interpretation of GH and IGF-I assays is important in establishing an early diagnosis of acromegaly, in avoiding misdiagnosis, and in establishing if cure is achieved by surgery. Physicians should be familiar with the variables that affect measurements of these 2 hormones, and with the performance of the assays available in their practice.

Laboratory investigations in the diagnosis and follow-up of GH-related disorders

In addition to auxiological, clinical and metabolic features measurements of growth hormone (GH) and insulin-like growth factor I (IGF-I) complement our tools in diagnosis and follow-up of GH-related disorders. While comparably robust during the pre-analytical phase, measurement and interpretation of concentrations of both hormones can be challenging due to analytical issues and biological confounders. Assay methods differ in terms of antibody specificity, interference from binding proteins, reference preparations and sensitivity. GH assays have different specificity towards different GH-isoforms (e.g. 20 kDa GH, placental GH) and interference from the GH antagonist Pegvisomant. The efficacy to prevent binding protein interference is most important in IGF-I assays. Methodological differences between assays require that reference intervals and diagnostic cut-offs are assay-specific. Among biological variables, pubertal development and age are most relevant for IGF-I, making detailed reference intervals mandatory for interpretation. GH has pulsatile secretion and short half-life. Its concentration is modified by acute factors such as stress, exercise and sleep, but also by intake of oral estrogens and anthropometric factors (e.g. BMI). Other GH dependent biomarkers such as free IGF-I, IGF binding protein 3 (IGFBP 3) and acid labile subunit (ALS) have been proposed. Their concentrations largely mirror the information obtained through measurement of IGF-I, but their measurement can be helpful in particular situations. In this review, we describe the evolution of analytical methods to measure biomarkers of GH action, the impact of the methodological changes on laboratory results and the need to include biological variables in their interpretation. Arch Endocrinol Metab. 2019;63(6):618-29.

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.

Implementation of a SPR immunosensor for the simultaneous detection of the 22K and 20K hGH isoforms in human serum samples

We have implemented a Surface Plasmon Resonance (SPR) immunosensor based on a sandwich assay for the simultaneous detection of the two main hGH isoforms, of 22 kDa (22K) and 20 kDa (20K). An oriented-antibody sensor surface specific for both hormone isoforms was assembled by using the biotin-streptavidin system. The immunosensor functionality was checked for the direct detection of the 22K hGH isoform in buffer, which gave high specificity and reproducibility (intra and inter-assay mean coefficients of variation of 8.23% and 9% respectively). The selective determination of the 22K and 20K hGH isoforms in human serum samples in a single assay was possible by using two specific anti-hGH monoclonal antibodies. The detection limit for both hormone isoforms was 0.9 ng mL(-1) and the mean coefficient of variation was below 7.2%. The excellent reproducibility and sensitivity obtained indicate the high performance of this immunosensor for implementing an anti-doping test.

Hormones as doping in sports

Though we may still sing today, as did Pindar in his eighth Olympian Victory Ode, "… of no contest greater than Olympia, Mother of Games, gold-wreathed Olympia…", we must sadly admit that today, besides blatant over-commercialization, there is no more ominous threat to the Olympic games than doping. Drug-use methods are steadily becoming more sophisticated and ever harder to detect, increasingly demanding the use of complex analytical procedures of biotechnology and molecular medicine. Special emphasis is thus given to anabolic androgenic steroids, recombinant growth hormone and erythropoietin as well as to gene doping, the newly developed mode of hormones abuse which, for its detection, necessitates high-tech methodology but also multidisciplinary individual measures incorporating educational and psychological methods. In this Olympic year, the present review offers an update on the current technologically advanced endocrine methods of doping while outlining the latest procedures applied-including both the successes and pitfalls of proteomics and metabolomics-to detect doping while contributing to combating this scourge.

Growth hormone variants: a potential avenue for a better diagnostic characterization of growth hormone deficiency in children

Human GH (hGH) is a heterogeneous protein hormone consisting of several isoforms. This heterogeneity is the consequence of multiple hGH genes, mRNA splicing, post-translational modifications, and peripheral metabolism, and it represents one important reason for the disparity among GH assay results from different laboratories. However, other factors are involved: a) interference from endogenous GH binding proteins; b) different specificities of anti- GH (monoclonal and polyclonal) antibodies; c) different matrix effects among the calibrators; d) the use of different calibrators. The measurement of GH levels in response to provocative testing is an essential part of the diagnosis of GH deficiency. For this purpose, an accurate, reproducible and universally valid GH measurement would be highly desirable, but, despite a huge number of efforts in clinical biochemistry, this goal remains elusive.

Ghrelin stimulation of growth hormone isoforms: parallel secretion of total and 20-kDa growth hormone and relation to insulin sensitivity in healthy humans

CONTEXT

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.

OBJECTIVE

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.

DESIGN AND SETTING

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.

RESULTS

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.

CONCLUSION

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.

Immunological screening and characterization of highly specific monoclonal antibodies against 20 kDa hGH

Background: hGH has been widely abused as a doping agent in sports for many years. There are some important approaches for the detection of hGH doping, and the ratio of 22:20 kDa GH was considered one of the most suitable detection indicators of GH abuse. Currently, effective anti-GH antibodies and related reagents are needed to develop a detection method, in particular, highly specific anti-20 kDa hGH monoclonal antibodies are a prerequisite. Herein we constructed the expression vector of 20 kDa hGH and prepared the corresponding antibodies by the immunization of the recombinant human 20 kDa into mice. Positive clones that can specifically recognize 20 kDa hGH were screened and characterized by enzyme immunoassay, Dot-ELISA and surface plasmon resonance. In total, 14 specific monoclonal cell lines were screened out. Results: By a series of characterization, it was found that the 6C8, 44H3, 12G7 and 33Y19 clones were showing much higher specificity and affinity to 20 kDa hGH, and P3H9 could recognize both 20 and 22 kDa hGH isoforms. 6C8 and 44H3 matched well with P3H9 in the surface plasmon resonance testing. The 12G7 clone had the best surface properties with an association constant of 3.4 × 109 M-1 and a dissociation constant of 2.95 × 1010 M. Conclusion: Highly specific monoclonal antibodies against 20 kDa hGH were generated, and also two paired antibodies (P3H9 and 6C8 or P3H9 and 44H3) were characterized, which can serve as the potential components for 22:20 kDa detection kit.

Growth hormone doping in sports: a critical review of use and detection strategies

GH is believed to be widely employed in sports as a performance-enhancing substance. Its use in athletic competition is banned by the World Anti-Doping Agency, and athletes are required to submit to testing for GH exposure. Detection of GH doping is challenging for several reasons including identity/similarity of exogenous to endogenous GH, short half-life, complex and fluctuating secretory dynamics of GH, and a very low urinary excretion rate. The detection test currently in use (GH isoform test) exploits the difference between recombinant GH (pure 22K-GH) and the heterogeneous nature of endogenous GH (several isoforms). Its main limitation is the short window of opportunity for detection (~12-24 h after the last GH dose). A second test to be implemented soon (the biomarker test) is based on stimulation of IGF-I and collagen III synthesis by GH. It has a longer window of opportunity (1-2 wk) but is less specific and presents a variety of technical challenges. GH doping in a larger sense also includes doping with GH secretagogues and IGF-I and its analogs. The scientific evidence for the ergogenicity of GH is weak, a fact that is not widely appreciated in athletic circles or by the general public. Also insufficiently appreciated is the risk of serious health consequences associated with high-dose, prolonged GH use. This review discusses the GH biology relevant to GH doping; the virtues and limitations of detection tests in blood, urine, and saliva; secretagogue efficacy; IGF-I doping; and information about the effectiveness of GH as a performance-enhancing agent.