Measurement of human growth hormone by immunoassays: current status, unsolved problems and clinical consequences

Tackling access and payer barriers for growth hormone therapy in Saudi Arabia: a consensus statement for the Saudi Working Group for Pediatric Endocrinology

Prompt diagnosis and early treatment are key goals to optimize the outcomes of children with growth hormone deficiency (GHD) and attain the genetically expected adult height. Nonetheless, several barriers can hinder prompt diagnosis and treatment of GHD, including payer-related issues. In Saudi Arabia, moderate-to-severe short stature was reported in 13.1 and 11.7 % of healthy boys and girls, respectively. Several access and payer barriers can face pediatric endocrinologists during the diagnosis and treatment of GHD in Saudi Arabia. Insurance coverage policies can restrict access to diagnostic tests for GHD and recombinant human growth hormone (rhGH) due to their high costs and lack of gold-standard criteria. Some insurance policies may limit the duration of treatment with rhGH or the amount of medication covered per month. This consensus article gathered the insights of pediatric endocrinologists from Saudi Arabia to reflect the access and payer barriers to the diagnostic tests and treatment options of children with short stature. We also discussed the current payer-related challenges endocrinologists face during the investigations of children with short stature. The consensus identified potential strategies to overcome these challenges and optimize patient management.

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.

Prevalence of refractoriness when testing growth hormone levels in children

OBJECTIVE

Late night spontaneous growth hormone (GH) pulses may influence the pituitary GH response to provocation tests. We evaluated GH response during arginine-insulin-tolerance test (AITT) after a GH peak during a short spontaneous nocturnal profile (SSNP) in children with short stature or low growth velocity.

DESIGN

Using SSNP and subsequent AITT, we examined 257 children 4-18 years old (138 (53.7%) males) recruited from three hospitals. Medical records were reviewed retrospectively. Refractory children were defined as a GH peak ≥7 μg/L during SSNP but no GH peak ≥7 μg/L during AITT.

RESULTS

In total, 201/257 children had a GH peak ≥7 μg/L at SSNP and/or AITT. Of these, 21.9% were refractory. The proportion of males (p = 0.033) and body mass index (BMI) standard deviation score (SDS) (p = 0.037) were higher in the refractory group than in children with a GH peak ≥7 μg/L during AITT. The median period between last GH peak ≥7 μg/L during SSNP and GHmax at AITT was 210 (30-390) minutes. The GHmax at AITT occurred 30 min earlier for children without a peak ≥7 μg/L during the SSNP (p = 0.004). The number of refractoriness differed somewhat between the hospitals (p = 0.025).

CONCLUSIONS

Many children with short stature were refractory at testing; among them we found few clinical characteristics. Refractoriness might be influenced by some differences in procedure, but needs to be considered when evaluating GH response in children.

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.

Sparse Deconvolution of Pulsatile Growth Hormone Secretion in Adolescents

Growth hormone (GH) is secreted by cells in the anterior pituitary on two time scales: discrete pulses over minutes that occur within a 24-hr pattern. Secretion reflects the balance of stimulatory and inhibitory inputs from the hypothalamus and is influenced by gonadal steroids, stress, nutrition, and sleep/wake states. We propose a novel approach for the analysis of GH data and use this approach to quantify (i) the timing, amplitude and the number of GH pulses and (ii) GH infusion, clearance and basal secretion (i.e., time invariant) rates, using serum GH sampled every 10 minutes during an 8-hour sleep study in 18 adolescents. In our method, we approximate hormonal secretory events by deconvolving GH data via a two-step coordinate descent approach. The first step utilizes a sparse-recovery approach to estimate the timing and amplitude of GH secretory events. The second step estimates physiological parameters. Our method identifies the timing and amplitude of GH pulses and system parameters from experimental and simulated data, with a median R2 of 0.93, among experimental data. Recovering GH pulses and model parameters using this approach may improve the quantification of GH parameters under different physiological and pathological conditions and the design and monitoring of interventions.

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.

Sex steroid priming in short stature children unresponsive to GH stimulation tests: Why, who, when and how

Despite decades of experience, the diagnosis of growth hormone deficiency (GHD) remains challenging, especially in peripubertal children. Failure to respond to GH stimulation tests (GHSTs) is needed to confirm GHD, but long-standing controversies regarding the number of tests needed and the interpretation of GH peaks are still a matter of debate worldwide. Diagnostic workup is even more problematic in short children with slow growth and delayed sexual development: they often exhibit low GH peaks under GHST, which often normalize as puberty progresses. Consequently, this transient suboptimal response to GHST may result in GH overtreatment, carrying both health and economic concerns. Considering the complex and bound link between GH axis and sex steroids, the use of sex steroid priming prior to GHST might be helpful in peripubertal setting. However, its use is still controversial. There is no consensus regarding patient selection, timing, dose, and preparation of sex steroids. In this review, we aim to overview the use of sex steroid priming in clinical practice, highlighting the need to develop appropriate guidelines in order to overcome diagnostic pitfalls in peripubertal age.

Soluble Alpha Klotho in Acromegaly: Comparison With Traditional Markers of Disease Activity

CONTEXT

Soluble alpha klotho (sαKL) has been linked to growth hormone (GH) action, but systematic evaluation and comparisons with traditional biomarkers in acromegaly are lacking.

OBJECTIVE

To evaluate the potential of sαKL to aid classification of disease activity.

METHODS

This retrospective study at 2 academic centers included acromegaly patients before surgery (A, n = 29); after surgery (controlled, discordant, or uncontrolled) without (B1, B2, B3, n = 28, 11, 8); or with somatostatin analogue treatment (C1, C2, C3, n = 17, 11, 5); nonfunctioning pituitary adenomas (n = 20); and healthy controls (n = 31). sαKL was measured by immunoassay and compared with traditional biomarkers (random and nadir GH, insulin-like growth factor I [IGF-I], IGF binding protein 3). Associations with disease activity were assessed.

RESULTS

sαKL was correlated to traditional biomarkers, particularly IGF-I (rs=0.80, P <0.0001). High concentrations before treatment (A, median, interquartile range: 4.04 × upper limit of normal [2.26-8.08]) dropped to normal after treatment in controlled and in most discordant patients. A cutoff of 1548 pg/mL for sαKL discriminated controlled (B1, C1) and uncontrolled (B3, C3) patients with 97.8% (88.4%-99.9%) sensitivity and 100% (77.1%-100%) specificity. sαKL was below the cutoff in 84% of the discordant subjects. In the remaining 16%, elevated sαKL and IGF-I persisted, despite normal random GH. Sex, age, body mass index, and markers of bone and calcium metabolism did not significantly affect sαKL concentrations.

CONCLUSION

Our data support sαKL as a biomarker to assess disease activity in acromegaly. sαKL exhibits close association with GH secretory status, large dynamic range, and robustness toward biological confounders. Its measurement could be helpful particularly when GH and IGF-I provide discrepant information.

Provocative growth hormone testing in children: how did we get here and where do we go now?

OBJECTIVES

Provocative growth hormone (GH) tests are widely used for diagnosing pediatric GH deficiency (GHD). A thorough understanding of the evidence behind commonly used interpretations and the limitations of these tests is important for improving clinical practice.

CONTENT

To place current practice into a historical context, the supporting evidence behind the use of provocative GH tests is presented. By reviewing GH measurement techniques and examining the early data supporting the most common tests and later studies that compared provocative agents to establish reference ranges, the low sensitivity and specificity of these tests become readily apparent. Studies that assess the effects of patient factors, such as obesity and sex steroids, on GH testing further bring the appropriateness of commonly used cutoffs for diagnosing GHD into question.

SUMMARY AND OUTLOOK

Despite the widely recognized poor performance of provocative GH tests in distinguishing GH sufficiency from deficiency, limited progress has been made in improving them. New diagnostic modalities are needed, but until they become available, clinicians can improve the clinical application of provocative GH tests by taking into account the multiple factors that influence their results.

Insulin-Like Growth Factor-1 (IGF-1) and Its Monitoring in Medical Diagnostic and in Sports

Insulin-like growth factor-1 (IGF-1) is the principal mediator of growth hormone (GH), plays a crucial role in promoting cell growth and differentiation in childhood and continues to have an anabolic effect in adults. IGF-1 is part of a wide network of growth factors, receptors and binding proteins involved in mediating cellular proliferation, differentiation and apoptosis. Bioavailability of IGF-1 is affected by insulin-like growth factor binding proteins (IGFBPs) which bind IGF-1 in circulation with an affinity equal to or greater than that of the IGF-1 receptor (IGF-1R). The six IGFBPs serve as carrier proteins and bind approximately 98% of all circulating IGF-1. Other proteins known to bind IGF-1 include ten IGFBP-related proteins (IGFBP-rPs), albeit with lower affinities than the IGFBPs. IGF-1 expression levels vary in a number of clinical conditions suggesting it has the potential to provide crucial information as to the state of an individual’s health. IGF-1 is also a popular doping agent in sport and has featured in many high-profile doping cases in recent years. However, the existence of IGFBPs significantly reduces the levels of immunoreactive IGF-1 in samples, requiring multiple pre-treatment steps that reduce reproducibility and complicates interpretation of IGF-1 assay results. Here we provide an overview of the IGF network of growth factors, their receptors and the entirety of the extended family of IGFBPs, IGFBP-rPs, E peptides as well as recombinant IGF-1 and their derivatives. We also discuss issues related to the detection and quantification of bioavailable IGF-1.

Case Report: A Clinical and Genetic Analysis of Childhood Growth Hormone Deficiency With Familial Hypercholesterolemia

BACKGROUND

Growth hormone deficiency (GHD) is a developmental disorder in children characterized by low growth hormone (GH), short stature and unfavorable lipid profiles. Familial hypercholesteremia (FH) is an inborn disorder of low-density lipoprotein cholesterol (LDL-C) metabolism which results in premature cardiovascular events. The co-occurrence of GHD and FH, which may aggravate the hypercholesteremic condition in the affected individuals, had rarely been discussed in previous publication.

METHODS

This work reports two cases of GHD with FH, and explores the lipid profiles of GHD children and their therapeutic response to recombinant human growth hormone (rhGH). The diagnosis of GHD is based on low peak GH level (<7 ng/mL) in GH provocation test. FH is diagnosed by high LDL-C level (≥ 4 mmol/L) and confirmed genetic mutations in the LDL-C metabolic pathway. We also searched all previously published metabolic studies on GHD children as of December 31, 2020. Information on their LDL-C, duration and dose of rhGH treatment were retrieved and summarized.

RESULTS

The first case was a 5.3 year-old boy. His height was 103.6 cm (SDS = -2.29) and his peak GH in provocative test was 6.37 ng/mL. Additionally, his LDL-C was 4.80 mmol/L and he harbored a heterozygous mutation for the apolipoprotein B (APOB) gene (c.10579 C > T). The second case was a 9-year-old girl at the height of 117.3 cm (SDS = -2.91). Her GH peaked at 4.99 ng/mL in insulin-induced hypoglycemic test and 2.80 ng/mL in L-dopa test. Her LDL-C was 6.16 mmol/L, and she carried a mutated copy of the low-density lipoprotein receptor (LDLR) gene (c.809 G > A). Literature review indicated that GHD children suffered from higher baseline LDL-C, but it was significantly reduced after rhGH treatment.

CONCLUSIONS

FH should be considered if a GHD child has remarkably elevated LDL-C that cannot be attributed to low GH level alone. Genetic mutations in the LDL-C metabolic pathway prevent the body from effectively metabolizing lipids, thereby resulting in early-onset hypercholesteremia and probably playing a negative role in children's growth.

The Cut-off Limits of Growth Hormone Response to the Insulin Tolerance Test Related to Body Mass Index for the Diagnosis of Adult Growth Hormone Deficiency

INTRODUCTION

The diagnosis of growth hormone deficiency (GHD) in adults is based on a reduced GH response to provocative tests, such as the insulin tolerance test (ITT) and the GH-releasing hormone (GHRH) + arginine (ARG) test. However, the cut-off limits of peak GH response in lean subjects are not reliable in obese patients; this is noteworthy since adult GHD is often associated with obesity. To date, there are no ITT cut-offs related to body mass index (BMI).

OBJECTIVE

We aimed to evaluate the diagnostic cut-offs of GH response to the ITT in the function of BMI.

METHODS

The GH response to the ITT was studied in 106 patients with a history of hypothalamic-pituitary disease, a mean age of 48.2 ± 12.4 years, and a mean BMI of 26.8 ± 6.1 kg/m2). Patients were divided into lean, overweight, and obese groups according to their BMI. The lack of GH response to GHRH + ARG test was considered the gold standard for the diagnosis of GHD. The best GH cut-off in the ITT, defined as the one with the best sensitivity (SE) and specificity (SP), was identified using receiver-operating characteristics curve (ROC) analysis.

RESULTS

The best GH cut-off in the ITT was 3.5 μg/L in lean subjects (SE 82.1%; SP 85.7%), 1.3 μg/L in overweight subjects (SE 74.1%; SP 85.7%), and 2.2 μg/L in obese subjects (SE 90.0%; SP 50.0%). The diagnostic accuracy was 97.2, 76.5, and 76.7%, respectively.

CONCLUSIONS

Our data show that the ITT represents a reliable diagnostic tool for the diagnosis of adult GHD in lean subjects if an appropriate cut-off limit is assumed. Overweight and obesity strongly reduce the GH response to the ITT, GH BMI-related cut-off limits, and the diagnostic reliability of the test.

Discordant biological parameters of remission in acromegaly do not increase the risk of hypertension or diabetes: a study with the Liege Acromegaly Survey database

PURPOSE

Acromegaly is a rare disease due to growth hormone (GH)-secreting pituitary adenoma. GH and IGF-1 levels are usually congruent, indicating either remission or active disease; however, a discrepancy between GH and IGF-1 may occur. We aimed to evaluate the outcome of diabetes mellitus (DM) and hypertension (HT) in acromegalic patients with congruent GH and/or IGF-1 levels vs. discordant biochemical parameters.

METHODS

Retrospective analysis of the data of 3173 patients from the Liege Acromegaly Survey (LAS) allowed us to include 190 patients from 8 tertiary referral centers across Europe, treated by surgery, with available data concerning DM and HT both at diagnosis and at the last follow-up (LFU). We recorded the number of anti-HT and anti-DM drugs used at the first evaluation and at LFU for every patient.

RESULTS

Ninety-nine patients belonged to the REM group (concordant parameters), 65 patients were considered as GH_dis (high random GH/controlled IGF-1), and 26 patients were considered as IGF-1_dis (high IGF-1/controlled random GH). At diagnosis, 72 patients (37.8%) had HT and 54 patients had DM (28.4%). There was no statistically significant difference in terms of the number of anti-HT and anti-DM drugs at diagnosis versus LFU (mean duration: 7.3 ± 4.5 years) between all three groups.

CONCLUSION

The long-term outcome of DM and HT in acromegaly does not tend to be more severe in patients with biochemical discordance in comparison with patients considered as in remission on the basis of concordant biological parameters, suggesting that patients with biochemical discordance do not require a closer follow-up.

Deciphering short stature in children

Short stature is a common reason for referral to pediatric endocrinologists. Multiple factors, including genetic, prenatal, postnatal, and local environmental factors, can impair growth. The majority of children with short stature, which can be defined as a height less than 2 standard deviation score below the mean, are healthy. However, in some cases, they may have an underlying relevant disease; thus, the aim of clinical evaluation is to identify the subset of children with pathologic conditions, for example growth hormone deficiency or other hormonal abnormalities, Turner syndrome, inflammatory bowel disease, or celiac disease. Prompt identification and management of these children can prevent excessive short stature in adulthood. In addition, a thorough clinical assessment may allow evaluation of the severity of short stature and likely growth trajectory to identify the most effective interventions. Consequently, appropriate diagnosis of short stature should be performed as early as possible and personalized treatment should be started in a timely manner. An increase in knowledge and widespread availability of genetic and epigenetic testing in clinical practice in recent years has empowered the diagnostic process and appropriate treatment for short stature. Furthermore, novel treatment approaches that can be used both as diagnostic tools and as therapeutic agents have been developed. This article reviews the diagnostic approach to children with short stature, discusses the main causes of short stature in children, and reports current therapeutic approaches and possible future treatments.

Auxological characteristics of pediatric patients with permanent or transient isolated growth hormone deficiency. Response to treatment and final height

INTRODUCTION

Treatment with recombinant human growth hormone (rhGH) has been shown to improve adult height in pediatric patients with GH deficiency (GHD). However, reassessment of patients after they reach their final height shows some of them have permanent GH deficiency (PGHD), while others had a transient deficiency (TGHD). The study objective was to assess, in a cohort of pediatric patients with GHD, potential differences in response to treatment with rhGH depending on whether deficiency is permanent or transient.

MATERIALS AND METHODS

A retrospective study of 89 patients with GHD, who were monitored from diagnosis to adult height. Clinical, auxological, radiographic and laboratory variables were collected at diagnosis, after the first year of treatment, and when they had reached their adult height.

RESULTS

PGHD was found in 28% of patients. Initial height was -2.46 ± 0.86 SD and -2.24 ± 0.68 SD in subjects with PGHD and TGHD respectively. Peak GH level at diagnosis was 4.26 ± 2.78 and 6.20 ± 2.01 ng/mL (p < 0.01) in the PGHD and TGHD groups respectively. After the first year of treatment, increase in growth velocity was greater in the PGHD group: 4.33 ± 3.53 SD vs. 2.95 ± 2.54 SD in the PGHD group (p = 0.043). Final height was -0.81 ± 0.87 SD in the PGHD and -0.95 ± 0.83 SD in the TGHD group (p = 0.47).

CONCLUSIONS

Patients with PGHD had a better short- and long-term response to rhGH. They also showed lower GH levels in stimulation tests at diagnosis, as previously reported.

Obese adolescents exhibit a constant ratio of GH isoforms after whole body vibration and maximal voluntary contractions

BACKGROUND

Growth hormone (GH) is a heterogeneous protein composed of several molecular isoforms, the most abundant ones being the 22 kDa- and 20 kDa-GH. Exercise-induced secretion of GH isoforms has been extensively investigated in normal-weight individuals due to antidoping purposes, particularly recombinant human GH (rhGH) abuse. On the other hand, the evaluation of exercise-induced responses in GH isoforms has never been performed in obese subjects.

METHODS

The acute effects of whole body vibration (WBV) or maximal voluntary contraction (MVC) alone and the combination of MVC with WBV (MVC + WBV) on circulating levels of 22 kDa- and 20 kDa-GH were evaluated in 8 obese male adolescents [mean age ± SD: 17.1 ± 3.3 yrs.; weight: 107.4 ± 17.8 kg; body mass index (BMI): 36.5 ± 6.6 kg/m²; BMI standard deviation score (SDS): 3.1 ± 0.6].

RESULTS

MVC (alone or combined with WBV) significantly stimulated 22 kDa- and 20 kDa-GH secretion, while WBV alone was ineffective. In particular, 22 kDa- and 20 kDa-GH peaks were significantly higher after MVC + WBV and MVC than WBV. In addition, 22 kDa-GH (but not 20 kDa-GH) peak was significantly higher after MVC + WBV than MVC. Importantly, the ratio of circulating levels of 22 kDa- to 20 kDa-GH was constant throughout the time window of evaluation after exercise and similar among the three different protocols of exercise.

CONCLUSIONS

The results of the present study confirm the ability of MVC, alone and in combination with WBV, to stimulate both 22 kDa- and 20 kDa-GH secretion in obese patients, these responses being related to the exercise workload. Since the ratio of 22 kDa- to 20 kDa-GH is constant after exercise and independent from the protocols of exercise as in normal-weight subjects, hyposomatotropism in obesity does not seem to depend on an unbalance of circulating GH isoforms. Since the present study was carried out in a small cohort of obese sedentary adolescents, these preliminary results should be confirmed in further future studies enrolling overweight/obese subjects with a wider age range.

A Consensus Statement on acromegaly therapeutic outcomes

The 11th Acromegaly Consensus Conference in April 2017 was convened to update recommendations on therapeutic outcomes for patients with acromegaly. Consensus guidelines on the medical management of acromegaly were last published in 2014; since then, new pharmacological agents have been developed and new approaches to treatment sequencing have been considered. Thirty-seven experts in the management of patients with acromegaly reviewed the current literature and assessed changes in drug approvals, clinical practice standards and clinical opinion. They considered current treatment outcome goals with a focus on the impact of current and emerging somatostatin receptor ligands, growth hormone receptor antagonists and dopamine agonists on biochemical, clinical, tumour mass and surgical outcomes. The participants discussed factors that would determine pharmacological choices as well as the proposed place of each agent in the guidelines. We present consensus recommendations highlighting how acromegaly management could be optimized in clinical practice.

Growth hormone: isoforms, clinical aspects and assays interference

The measurement of circulating concentrations of growth hormone (GH) is an indispensable tool in the diagnosis of both GH deficiency and GH excess. GH is a heterogeneous protein composed of several molecular isoforms, but the physiological role of these different isoforms has not yet been fully understood. The 22KD GH (22 K-GH) is the main isoform in circulation, followed by 20KD GH (20 K-GH) and other rare isoforms. Studies have been performed to better understand the biological actions of the different isoforms as well as their importance in pathological conditions. Generally, the non-22 K- and 20 K-GH isoforms are secreted in parallel to 22 K-GH, and only very moderate changes in the ratio between isoforms have been described in some pituitary tumors or during exercise. Therefore, in a diagnostic approach, concentrations of 22 K-GH accurately reflect total GH secretion. On the other hand, the differential recognition of GH isoforms by different GH immunoassays used in clinical routine contributes to the known discrepancy in results from different GH assays. This makes the application of uniform decision limits problematic. Therefore, the worldwide efforts to standardize GH assays include the recommendation to use 22 K-GH specific GH assays calibrated against the pure 22 K-GH reference preparation 98/574. Adoption of this recommendation might lead to improvement in diagnosis and follow-up of pathological conditions, and facilitate the comparison of results from different laboratories.

Growth Hormone Research Society perspective on biomarkers of GH action in children and adults

OBJECTIVE

The Growth Hormone Research Society (GRS) convened a Workshop in 2017 to evaluate clinical endpoints, surrogate endpoints and biomarkers during GH treatment of children and adults and in patients with acromegaly.

PARTICIPANTS

GRS invited 34 international experts including clinicians, basic scientists, a regulatory scientist and physicians from the pharmaceutical industry.

EVIDENCE

Current literature was reviewed and expert opinion was utilized to establish the state of the art and identify current gaps and unmet needs.

CONSENSUS PROCESS

Following plenary presentations, breakout groups discussed questions framed by the planning committee. The attendees re-convened after each breakout session to share the group reports. A writing team compiled the breakout session reports into a document that was subsequently discussed and revised by participants. This was edited further and circulated for final review after the meeting. Participants from pharmaceutical companies were not part of the writing process.

CONCLUSIONS

The clinical endpoint in paediatric GH treatment is adult height with height velocity as a surrogate endpoint. Increased life expectancy is the ideal but unfeasible clinical endpoint of GH treatment in adult GH-deficient patients (GHDA) and in patients with acromegaly. The pragmatic clinical endpoints in GHDA include normalization of body composition and quality of life, whereas symptom relief and reversal of comorbidities are used in acromegaly. Serum IGF-I is widely used as a biomarker, even though it correlates weakly with clinical endpoints in GH treatment, whereas in acromegaly, normalization of IGF-I may be related to improvement in mortality. There is an unmet need for novel biomarkers that capture the pleiotropic actions of GH in relation to GH treatment and in patients with acromegaly.

Gender has to be taken into account in diagnosing adult growth hormone deficiency by the GHRH plus arginine test

OBJECTIVE

Data on the effect of gender on the interpretation of the GHRH plus arginine stimulation test (GHRH+ARG test) is controversial. We validated the GHRH+ARG stimulation test in control subjects and patients with organic or idiopathic pituitary disease and a suspicion of adult growth hormone deficiency (AGHD) using the Immulite 2000 XPi GH assay.

DESIGN

We studied 126 apparently healthy adults (median age 38.8years) and 34 patients with a suspicion of AGHD (median age 42.2years). Identification of AGHD with the GHRH+ARG test was investigated with commonly accepted BMI-related consensus cut-off limits for peak GH concentrations. Serum samples collected during the GHRH+ARG test were analysed for GH in 2014-2015. Serum IGF-1 concentrations were studied as a reference.

RESULTS

In 14 of 65 (22%) control males the GH peak value was below the BMI-related cut-off limits for GH sufficiency indicating a false diagnosis of AGHD. All control females had a normal GHRH+ARG response. Median peak GH response was significantly (p<0.001) higher in female (39.3μg/L) than in male controls (21μg/L). According to consensus cut-offs all but one young female patient had a deficient response compatible with a diagnosis of AGHD.

CONCLUSIONS

The GH response to stimulation by GHRH+ARG is gender-dependent, being lower in healthy males than in females. Gender should be considered when defining cut-off limits for peak GH concentrations in the GHRH+ARG test. The presently used BMI-related cut-off levels will lead to a significant misclassification of males as GH deficient.

Physiology and role of irisin in glucose homeostasis

Irisin is a myokine that leads to increased energy expenditure by stimulating the 'browning' of white adipose tissue. In the first description of this hormone, increased levels of circulating irisin, which is cleaved from its precursor fibronectin type III domain-containing protein 5, were associated with improved glucose homeostasis by reducing insulin resistance. Consequently, several studies attempted to characterize the role of irisin in glucose regulation, but contradictory results have been reported, and even the existence of this hormone has been questioned. In this Review, we present the current knowledge on the physiology of irisin and its role in glucose homeostasis. We describe the mechanisms involved in the synthesis, secretion, circulation and regulation of irisin, and the controversies regarding the measurement of irisin. We also discuss the direct effects of irisin on glucose regulatory mechanisms in different organs, the indirect effects and interactions with other hormones, and the important open questions with regard to irisin in those organs. Finally, we present the results from animal interventional studies and from human clinical studies investigating the association of irisin with obesity, insulin resistance, type 2 diabetes mellitus and the metabolic syndrome.

Anthropometric factors have significant influence on the outcome of the GHRH-arginine test: establishment of normative data for an automated immunoassay specifically measuring 22 kDa human growth hormone

CONTEXT

Adult growth hormone (GH) deficiency (GHD) is diagnosed by provocative testing of GH secretion.

OBJECTIVE

To improve the diagnostic accuracy of GH-releasing hormone (GHRH) plus arginine (GARG) testing, we evaluated the influence of age, BMI and sex and established normative data for an automatic immunoassay specifically measuring 22 kDa human GH.

DESIGN/SETTING

Prospective multicenter study.

PARTICIPANTS

Eighty-seven patients with hypothalamic-pituitary disease and 200 healthy controls. Patients were classified according to the number of pituitary hormone deficiencies (PHD). GHD was assumed when ≥2 PHD (in addition to GH) were present (n = 51); 36 patients with <2 PHD were considered GH sufficient (GHS). ROC analysis identified cutoffs with ≥95% specificity for GHD. Controls were prospectively stratified for sex, age and BMI.

INTERVENTIONS

All participants received GHRH and l-arginine.

MAIN OUTCOME MEASURES

GH was measured by immunoassay (iSYS, IDS).

RESULTS

In controls, multiple stepwise regression analysis showed that BMI (21%, P < 0.0001), sex (20%, P < 0.0001) and age (5%, P < 0.001), accounted for 46% of GH peak level variability during GARG. Comparison of peak GH during GARG (GHD vs GHS + controls) revealed an overall cutoff of 3.9 ng/mL (sensitivity 86%, specificity 95%). After adjustment for BMI and sex, optimal cutoffs (male vs female) were 6.5 vs 9.7 ng/mL in lean, 3.5 vs 8.5 ng/mL in overweight and 2.2 vs 4.4 ng/mL in obese subjects respectively.

CONCLUSION

BMI and sex account for most of the variability of peak GH levels during GARG. Consequently, diagnostic accuracy of the GARG test is significantly improved by use of adjusted cutoffs.

Biochemical investigations in diagnosis and follow up of acromegaly

Measurements of human growth hormone (GH) and insulin-like growth-factor I (IGF-I) are cornerstones in the diagnosis of acromegaly. Both hormones are also used as biochemical markers in the evaluation of disease activity during treatment. Management of acromegaly is particularly challenging in cases where discordant information is obtained from measurement of GH concentrations following oral glucose load and from measurement of IGF-I. While in some patients biological factors can explain the discrepancy, in many cases issues with the analytical methods seem to be responsible. Assays used by endocrine laboratories to determine concentrations of GH and IGF-I underwent significant changes during the last decades. While generally leading to more sensitive and reproducible methods, these changes also had considerable impact on absolute concentrations measured. This must be reflected by updated decision limits, cut-offs and reference intervals. Since different commercially available assays do not agree very well, method specific interpretation of GH and IGF-I concentrations is required. This complexity in the interpretation of hormone concentrations is not always appropriately reflected in laboratory reports, but also not in clinical guidelines reporting decision limits not related to a specific analytical method. The present review provides an overview about methodological and biological variables affecting the biochemical assessment of acromegaly in diagnosis and follow up.

Short Stature Diagnosis and Referral

The "360° GH in Europe" meeting, which examined various aspects of GH diseases, was held in Lisbon, Portugal, in June 2016. The Merck KGaA (Germany) funded meeting comprised three sessions entitled "Short Stature Diagnosis and Referral," "Optimizing Patient Management," and "Managing Transition." Each session had three speaker presentations, followed by a discussion period, and is reported as a manuscript, authored by the speakers. The first session examined current processes of diagnosis and referral by endocrine specialists for pediatric patients with short stature. Requirements for referral vary widely, by country and by patient characteristics such as age. A balance must be made to ensure eligible patients get referred while healthcare systems are not over-burdened by excessive referrals. Late referral and diagnosis of non-GH deficiency conditions can result in increased morbidity and mortality. The consequent delays in making a diagnosis may compromise the effectiveness of GH treatment. Algorithms for growth monitoring and evaluation of skeletal disproportions can improve identification of non-GH deficiency conditions. Performance and validation of guidelines for diagnosis of GH deficiency have not been sufficiently tested. Provocative tests for investigation of GH deficiency remain equivocal, with insufficient information on variations due to patient characteristics, and cutoff values for definition differ not only by country but also by the assay used. When referring and diagnosing causes of short stature in pediatric patients, clinicians need to rely on many factors, but the most essential is clinical experience.

Exploiting Nanobodies in the Detection and Quantification of Human Growth Hormone via Phage-Sandwich Enzyme-Linked Immunosorbent Assay

BACKGROUND

Monitoring blood levels of human growth hormone (hGH) in most children with short stature deficiencies is crucial for taking a decision of treatment with extended course of daily and expensive doses of recombinant hGH (rhGH or Somatropin^®). Besides, misusing of rhGH by sportsmen is banned by the World Anti-Doping Agency and thus sensitive GH-detecting methods are highly welcome in this field. Nanobodies are the tiniest antigen-binding entity derived from camel heavy chain antibodies. They were successfully generated against numerous antigens including hormones.

METHODS

A fully nanobody-based sandwich ELISA method was developed in this work for direct measurement of GH in biological samples.

RESULTS

Two major characteristics of nanobody were exploited for this goal: the robust and stable structure of the nanobody (NbGH04) used to capture hGH from tested samples, and the great ability of tailoring, enabling the display of the anti-GH detector nanobody (NbGH07) on the tip of M13-phage. Such huge, stable, and easy-to-prepare phage-Nb was used in ELISA to provide an amplified signal. Previously, NbGH04 was retrieved on immobilized hGH by phage display from a wide "immune" cDNA library prepared from a hGH-immunized camel. Here, and in order to assure epitope heterogeneity, NbGH07 was isolated from the same library using NbGH04-captured hGH as bait. Interaction of both nanobodies with hGH was characterized and compared with different anti-GH nanobodies and antibodies. The sensitivity (~0.5 ng/ml) and stability of the nanobody-base sandwich ELISA were assessed using rhGH before testing in the quantification of hGH in blood sera and cell culture supernatants.

CONCLUSION

In regard to all advantages of nanobodies; stability, solubility, production affordability in Escherichia coli, and gene tailoring, nanobody-based phage sandwich ELISA developed here would provide a valuable method for hGH detection and quantification.

Preparation of soluble isotopically labeled human growth hormone produced in Escherichia coli

Isotopically labeled proteins have been used as internal standards for mass spectrometry (MS)-based absolute protein quantification. Although this approach can provide highly accurate analyses of proteins of interest within a complex mixture, one of the major limitations of this method is the difficulty in preparing uniformly labeled standards. Human growth hormone (hGH) is one of the most important hormones that circulate throughout the body, and its measurement is primarily of interest in the diagnosis and treatment of growth disorders. In order to provide a useful internal standard for MS-based hGH measurement, we describe an efficient strategy to produce a potentially valuable, stable isotope-labeled hGH with high purity and yield. The strategy involves the following steps: solubilization of hGH under labeling conditions, detection of stable isotope incorporation, large-scale purification, analysis of the labeled protein, and assessment of the labeling efficiency. We show that the yield of soluble hGH under selective isotopic labeling conditions can be greatly increased by optimizing protein expression and extraction. Our efficient method for generating isotopically labeled hGH does not influence the structural integrity of hGH. Finally, we assessed the efficiency of stable isotope labeling at the intact protein level, and the result was further verified by amino acid analysis. These results clearly indicate that our labeling approach allows an almost complete incorporation of ¹³C₆¹⁵N₄-arginine into the hGH expressed in E.coli without detectable isotope scrambling.

Continuing efforts to standardize measured serum growth hormone values in Japan

Determination of serum growth hormone (GH) levels is mandatory for diagnosis of GH deficiency and excess. In the present study, we, the Study Committee for GH and Its Related Factors, The Foundation for Growth Science, Japan measured GH values in serum samples using all the commercially available kits in Japan. Significant discrepancies in the GH values were observed among the kits in spite of using the unified recombinant human GH-based standards. To deal with the discrepancies, we established a formula using a linear structural relationship model and were able to standardize the GH values. We propose to use the formula to diagnose GH deficiency and excess in Japan.

Mass spectrometry - an alternative in growth hormone measurement

Growth hormone (GH) constitutes a set of closely related protein isoforms. In clinical practice, the disagreement of test results between commercially available ligand-binding assays is still an ongoing issue, and incomplete knowledge about the particular function of the different forms leaves an uncertainty of what should be the appropriate measurand. Mass spectrometry is promising to be a way forward. Not only is it capable of providing SI-traceable reference values for the calibration of current GH-tests, but it also offers an independent approach to highly reliable mass-selective quantification of individual GH-isoforms. This capability may add to reliability in doping control too. The article points out why and how.

Growth Hormone Concentrations in Different Body Fluids Before and After Moderate Exercise

BACKGROUND

Growth hormone (GH) has many direct and indirect actions and roles including substrate regulation and priming of some cells of the immune system, and the expected aspects of growth and repair. Different concentrations in human body fluids reflect the exercise-induced growth hormone response (EIGR) after exercise. In populations such as elite athletes, the invasive nature of venous sampling is poorly accepted. Thus, this study examines possible viable alternatives such as urine and saliva samples and the GH concentration.

METHODS

A heterogeneous group of 11 males (age 26.0 ± 5.0 years; body mass 76.5 ± 9.3 kg; VO2peak 57.0 ± 6.0 mL kg-1 min-1) ran for 40 min on a treadmill at 5 % below their individually indentified lactate threshold pace. Samples of urine, saliva and blood were collected immediately pre- and post-test and at 30 and 60 min post-test.

RESULTS

Salivary GH was correlated with serum pre- and post-exercise (p < 0.001); urinary GH was correlated with serum (p < 0.05). However, despite being significantly correlated, it is clear from the large differences in absolute concentration in the three media that the appearance of serum GH due to exercise is different from that of the appearance of salivary and urinary GH. This aspect of compartmental exchanges is very difficult to define and to investigate. Differences in any analyte concentration in different compartments are to be expected between different media, and hence the same medium should be used where the same 'pattern of response' can be tracked.

CONCLUSIONS

The results suggest that urinary and saliva sampling cannot substitute for venous sampling with respect to exercise-induced changes in GH concentration. The use of the analyses in these three areas may be appropriate for further investigation.

Hormone replacement therapy in children: The use of growth hormone and IGF-I

Recombinant human GH (rhGH) has been available since 1985. This article gives an overview, what has been achieved over the past 30 years in respect to optimization of rhGH treatment for the individual child with GH deficiency and what are the safety issues concerned with this treatment. In the last twenty years significant scientific progress has been made in the diagnosis of GH deficiency, the genetic disorders that are associated with pituitary GH deficiency and the genetics that influence growth in general. On the other hand rhGH is not only used in states of GH deficiency but also various conditions without a proven GH deficiency by classical standards. Clinical studies that investigated both the genetics of growth and the individual responses to rhGH therapy in these patient populations were able to refine our concept about the physiology of normal growth. In most patients under rhGH treatment there is a considerable short-term effect, however the overall gain in growth obtained by a long-term treatment until final height still remains a matter of debate in some of the conditions treated. Also first studies on the long-term safety risks of rhGH treatment have raised the question whether this treatment is similarly safe for all the patient groups eligible for such a treatment. Therefore even in the face of a longstanding safety record of this drug replacement therapy the discussion about the right cost and risk to benefit ratio is continuing. Consequently there is still a need for carefully conducted long-term studies that use modern anthropometric, genetic, and laboratory techniques in order to provide the necessary information for clinicians to select the patients that will benefit best from this valuable treatment without any long term risk.

Failure to achieve disease control in acromegaly: cause analysis by a registry-based survey

CONTEXT

Disease control is a prime target in acromegaly treatment. This should be achievable in the vast majority of patients by available treatment options. For unknown reasons, however, a significant number of patients do not achieve disease control.

OBJECTIVE

To investigate reasons for failure to achieve disease control in long-standing acromegaly.

DESIGN AND METHODS

Survey based on the German Acromegaly Registry database (1755 patients in 57 centres). Questionnaires were sent to 47 centres treating 178 patients with elevated disease markers (IGF1 and GH) at the last documented database visit out of 1528 patients with a diagnosis dated back ≥2 years. Thirty-three centres returned anonymised information for 120 patients (recall rate 67.4%).

RESULTS

Median age of the 120 patients (58 females) was 57 years (range 17-84). Ninety-four patients had at least one operation, 29 had received radiotherapy and 71 had been previously treated medically. Comorbidities were reported in 67 patients. In 61 patients, disease activity had been controlled since the last documented database visit, while 59 patients still had biochemically active disease. Reasons were patients' denial to escalate therapy (23.3%), non-compliance (20.6%), fluctuating insulin-like growth factor 1 (IGF-1) and growth hormone (GH) levels with normal values at previous visits (23.3%) and modifications in pharmacotherapy (15.1%). Therapy resistance (9.6%), drug side effects (4.1%) and economic considerations (4.1%) were rare reasons.

CONCLUSIONS

Main reasons for long-standing active acromegaly were patients' lack of motivation to agree to therapeutic recommendations and non-compliance with medical therapy. Development of patient education programmes could improve long-term control and thus prognosis of acromegalic patients.

A pilot study of growth hormone administration in boys with predicted adult short stature and near-ending growth

CONTEXT

The growth-promoting effect of starting recombinant human growth hormone (rhGH) at the time of near-ending growth has not been studied in sexually mature boys who will have idiopathic short stature (ISS) as adults because it is believed that such an advanced stage of puberty would preclude favorable results.

OBJECTIVES

1) To explore the effects of starting rhGH administration at time of near-ending growth in boys with ISS. 2) To search for predictors of response to rhGH.

SUBJECTS

Fifteen boys aged 15.5 ± 1 years terminating puberty were growing at a rate < 2 cm/6 months towards a predicted adult height (PAH) <-2.5 SDS.

METHODS

Participants received 0.50 ± 0.06 mg/kg · wk of rhGH according to a target-to-treat protocol. When growth became less than 0.5 cm in 3 months or when height has reached 169 cm, rhGH was ceased. Testosterone, growth velocity (GV), height, serum IGF-1, bone age (BA) at hand-wrist and knee score were measured at onset; IGF-1 and height were monitored every 3 months. A formula for PAH was developed. Height increment (HI, adult height-starting height) and height gain (HG, adult height-PAH) were calculated.

RESULTS

Following rhGH administration for 11.1 ± 4.8 months, GV-SDS increased from -2.5 ± 1.7 to 3.5 ± 4.3 (P = 2 × 10(-4)), HI = 8.5 ± 3.7 cm, HG = 6.8 ± 4.8 cm and adult height was -1.8 ± 0.9 SDS, compared to a PAH of -2.9 ± 0.6 SDS (P = 4 × 10(-4)). Knee score (P = 2 × 10(-3)), GV at rhGH onset (P = 8 × 10(-3)) and rhGH dose (P = 8 × 10(-3)) were identified as predictors of HI and HG, but BA was not.

CONCLUSIONS

Our study suggests that 1) a short period of rhGH administration can increase true adult height significantly in boys with ISS at time of near-ending growth; and 2) knee score rather than BA should be used to identify rhGH responders. These preliminary observations await confirmation by larger randomized trials.

The impact of immunohistochemical markers of Ki-67 and p53 on the long-term outcome of growth hormone-secreting pituitary adenomas: A cohort study

BACKGROUND AND OBJECTIVES

The tumoral biomarkers have a rather well known effect upon the tumor control period of several types of malignant lesions. The aim of this study was to evaluate the impact of immunohistochemical (IHC) markers of Ki-67 and p53 on the long-term outcome of growth hormone (GH)-secreting pituitary adenomas treated surgically.

MATERIALS AND METHODS

We conducted and followed a cohort of 47 consecutive patients with GH-secreting pituitary adenomas referred to our department during a 4 year period for trans-sphenoidal microsurgical adenomectomy. The expression levels of Ki-67 and p53 were determined by IHC study of the tissue samples. Periodical pituitary magnetic resonance imaging (MRI), visual field studies and hormonal evaluations (GH and insulin-like growth factor-1 [IGF-1]) performed during the follow-up period were the outcome measures.

RESULTS

The level of Ki-67 expression was higher among patients with postoperative residual tumor (3.5 vs. 1.7%) and those with a hormonal recurrence (4.3 vs. 1.6%). The p53 expression level was remarkably higher in patients with radiological recurrence (18 vs. 6.3%). Patients with invasive features (i.e. cavernous sinus and suprasellar invasion) had significantly higher p53 and Ki-67 values and higher IGF-1 levels during the follow-up period. The patients younger than 30 years of age and those with mixed GH-prolactin secreting adenomas had significantly higher hormonal remission and lower radiological recurrence rates.

CONCLUSION

Each of the biomarkers, Ki-67 and p53, along with patient's age and mixed GH-prolactin secretion showed a kind of correlation with each of aspects of the clinical, hormonal and radiologic outcome of GH-secreting pituitary adenomas in this series.

Discordance between growth hormone and insulin-like growth factor-1 after pituitary surgery for acromegaly: a stepwise approach and management

INTRODUCTION

Follow-up management of patients with acromegaly after pituitary surgery is performed by conducting biochemical assays of growth hormone (GH) and insulin-like growth factor-1 (IGF1). Despite concordant results of these two tests in the majority of cases, there is increasing recognition of patients who show persistent or intermittent discordance between GH and IGF1 (normal GH and elevated IGF1 or vice versa).

METHOD

In this narrative review, the last three decades materials on the issue of discrepancy between GH and IGF1 were thoroughly assessed.

RESULTS

Various studies have obtained different discordance rates, ranging from 5.4 to 39.5%. At present, despite the use of current sensitive assays and more stringent criteria to define remission, the rate of discordance still remains high. A number of mechanisms have been proposed to explain the postoperative discordance of GH and IGF1 including; altered dynamics of the GH secretion after surgery, early postoperative hormone assay, inaccurate or less sensitive tests and laboratory errors, too high cut-off point for GH suppression in the GH assays, GH nadir values not adjusted to age, sex, and body mass index, the influence of concomitant medication, co-existing physiologic and pathologic conditions, and many other proposed reasons. Nevertheless, the underlying mechanisms are still far from clear, and the solution continues to evade complete elucidation. Similarly, the impacts of such a discrepancy over mortality and morbidity and the risk of biochemical and/or clinical recurrence are unclear.

CONCLUSION

As a challenging clinical problem, a stepwise evaluation and management of these patients appears to be more rational.

Clinical evidence-based cutoff limits for GH stimulation tests in children with a backup of results with reference to mass spectrometry

CONTEXT

Cutoff limits of GH stimulation tests to diagnose GH deficiency (GHD) in children and adolescents are not sufficiently validated by clinical studies due to discrepancies in the performance of GH immunoassays and lack of available study populations.

OBJECTIVE

We aimed to establish new cutoff limits for GH stimulation tests based on clinical evidence and compared these immunoassay-based values with an antibody-independent mass spectrometric method.

DESIGN AND SETTING

In a retrospective study, GH cutoff limits for eight different immunoassays and isotope dilution mass spectrometry (ID-MS) were calculated from hGH peak concentrations of short-statured children with and without GHD.

PATIENTS

We compared the serum GH peak concentrations at GH stimulation test of 52 short-statured children and adolescents, who have normal GH secretion at initial workup and normal growth in the follow-up, with the serum GH peak concentrations of 44 GHD patients in the same age range, in order to optimize the cutoff limit calculation.

RESULTS

Discriminant analysis of re-measured GH led to a new cutoff limit of 7.09 μg/l using the iSYS assay (IDS) and the limits for the other seven hGH assays varied between 4.32 and 7.77 μg/l. For ID-MS, cutoffs of 5.48 μg/l (22k GH) and 7.43 μg/l (total GH) were ascertained.

CONCLUSION

The establishment of method-specific clinical evidence-based GH cutoff limits is of importance to ensure adequate clinical diagnosis and treatment of children and adolescents with GHD. ID-MS may become an important tool for providing both reliable and sustainable SI traceability of GH measurements in the future.

Generation and characterization of nanobodies against rhGH expressed as sfGFP fusion protein

Growth hormone (GH) deficiencies are diagnosed in most children with short stature and treated with a long course of administrating expensive and daily doses of recombinant human GH (rhGH or Somatropin®). This work describes for the first time the production of several GH specific nanobodies with great potential in the field of GH production and detection. Nanobodies are the smallest intact antigen binders derived from heavy chain-only antibodies (HCAbs) of camelids. They are very stable, highly soluble and are produced as recombinant proteins in Escherichiacoli at an affordable cost for various biotechnological applications. To increase its solubility and immunogenicity, GH was produced as fusion with superfolder green fluorescent protein (sfGFP) and was used in this form to successfully immunize an adult camel. The active involvement of HCAbs in the specific camel immune response encouraged the preparation of large nanobody "immune" library. Phage display biopanning of this library against GH resulted in the isolation of five interesting and different nanobodies, referred to as NbGH01, 02, 03, 04 and 06. All nanobodies were able to recognize GH in its fusion and free formats and the detection sensitivity ranged from 0.5 to 10 ng/ml in sandwich ELISA. Pure rhGH was successfully purified by affinity chromatography, using immobilized NbGH06, from the cleavage reaction of fusion proteins with the tobaccos etch virus (TEV) protease. These specific molecular binders, especially NbGH06, provide valuable tools for rhGH diagnostic as well as for production purposes.

Isolated growth hormone deficiency (GHD) in childhood and adolescence: recent advances

The diagnosis of GH deficiency (GHD) in childhood is a multistep process involving clinical history, examination with detailed auxology, biochemical testing, and pituitary imaging, with an increasing contribution from genetics in patients with congenital GHD. Our increasing understanding of the factors involved in the development of somatotropes and the dynamic function of the somatotrope network may explain, at least in part, the development and progression of childhood GHD in different age groups. With respect to the genetic etiology of isolated GHD (IGHD), mutations in known genes such as those encoding GH (GH1), GHRH receptor (GHRHR), or transcription factors involved in pituitary development, are identified in a relatively small percentage of patients suggesting the involvement of other, yet unidentified, factors. Genome-wide association studies point toward an increasing number of genes involved in the control of growth, but their role in the etiology of IGHD remains unknown. Despite the many years of research in the area of GHD, there are still controversies on the etiology, diagnosis, and management of IGHD in children. Recent data suggest that childhood IGHD may have a wider impact on the health and neurodevelopment of children, but it is yet unknown to what extent treatment with recombinant human GH can reverse this effect. Finally, the safety of recombinant human GH is currently the subject of much debate and research, and it is clear that long-term controlled studies are needed to clarify the consequences of childhood IGHD and the long-term safety of its treatment.

The harmonisation of growth hormone measurements: taking the next steps

For over 20 years differences in results of growth hormone (GH) measurement have been recognised as being significant enough to lead to misdiagnosis and inappropriate management of patients with GH-related disorders. Whilst issues of method standardisation, variable antibody specificity, use of different reporting units with different conversion factors, and interference from GH binding protein have been acknowledged as contributing to the discrepancies, inconsistent approaches to method harmonisation have hampered opportunities to enhance the evidence base for GH measurements. Amongst the first steps to be taken, international collaboratives recommended the universal adoption of the International Standard 98/547 and the reporting of results in mass units. Whilst inter-method variability may have improved over the last 10 years, clinically significant differences remain. A more recently recognised issue contributing to the discrepancies may be the differences in the matrix materials used by kit manufacturers to assign values to their calibrants. The establishment of an international harmonisation oversight group is recommended: its key roles to include identification of a commutable matrix reference material, assessing the clinical significance of assay interferents, the evaluation of liquid chromatography-mass spectrometry as a reference measurement procedure and the provision of acceptance criteria for the clinical application of GH methods.

Growth hormone values after an oral glucose load do not add clinically useful information in patients with acromegaly on long-term somatostatin receptor ligand treatment

The optimal method of assessing GH status in acromegalic patients receiving medical therapy with somatostatin analogs (SSA) has been matter of debate. The aim of the study has been to investigate whether OGTT may add information in patients with discordant random GH (GHr) and IGF values. Moreover, we evaluated the association of GH nadir with the prevalence of co-morbidities observed in acromegalic patients on SSA therapy. We evaluated 130 patients with proven diagnosis of acromegaly on SSA. The patients were subdivided in three groups: patients with controlled disease (both safe random GH and normal IGF-I, group A, 20.0 %), patients with uncontrolled disease (both high random GH and IGF-I, group B, 34.6 %), and patients with discordant random GH and IGF-I values (group C, 35.4 %). A high concordance rate for GH nadir with random GH and IGF-I was observed in group B, while a significant reduced concordance rate has been observed in group A (100 % sensitivity, 64.5 % specificity). By contrast, in group C, we observed concordant results between GH nadir and IGF-I only in 14/59 patients. In group A, the prevalence of diabetes was lower than in group B or C. Safe random GH was the only single criteria associated with a lower prevalence of diabetes. Discrepant IGF-I and either GH nadir or random GH values are frequently observed in acromegalic patients treated with SSA. Concordant IGF-I and random GH may influence the prevalence of metabolic complications. GH nadir measurement may help to interpret discrepancies between random GH and IGF-I data only in few cases.

Heat acclimation decreases the growth hormone response to acute constant-load exercise in the heat

OBJECTIVE

The major objective of this study was to elucidate the effect of heat acclimation on blood growth hormone (GH) response to moderate intensity exhausting exercise in the heat. In addition, the potential relationship between inter-individual differences in GH response to exercise and variability in exercise-induced sweat loss was investigated.

DESIGN

Twenty young men completed three exercise tests on a treadmill: H1 (walk at 60% VO₂peak until exhaustion at 42 °C), N (walk at 22 °C; duration equal to H1) and H2 (walk until exhaustion at 42 °C after a 10-day heat acclimation program). Core temperature (T(c)) was recorded continuously and venous blood samples were taken before, during and after each exercise test. Exercise-induced sweat production was calculated on the basis of body mass change taking into account water intake and the volume of blood samples drawn.

RESULTS

Lower pre-exercise T(c), lower rate of rise in T(c) during exercise, and prolonged time to exhaustion in H2 compared with H1 revealed that the subjects successfully achieved an acclimated state. Overall, serum GH level was higher in H1 compared with both N and H2 (p<0.001) but did not differ between the two latter trials (p>0.05). T(c) correlated with serum GH concentration (r=0.615, p<0.01). Analysis of the individual data revealed a group (n=9) possessing a threshold-like pattern of the relationship between T(c) and blood GH response, whereas a plateau-like pattern was evident in the rest of the subjects (n=11). Both sweat production (r=0.596; p<0.001) and the rate of sweat production (r=0.457; p<0.001) correlated with the growth hormone area under the curve.

CONCLUSION

Heat acclimation decreases the GH response to moderate intensity exhausting exercise in the heat. GH may have a modest stimulating effect on whole-body sweat production during exercise.

Short-term administration of pegvisomant improves hepatic insulin sensitivity and reduces soleus muscle intramyocellular lipid content in young adults with type 1 diabetes

CONTEXT

Data on the metabolic effects of GH derived from studies using GH suppression by pharmacological agents may not reflect selective actions.

OBJECTIVE

The purpose of this study was to evaluate the effects of GH antagonism on glucose and lipid metabolism using pegvisomant, a selective GH receptor antagonist in patients with type 1 diabetes (T1D).

DESIGN AND PARTICIPANTS

In a randomized, placebo-controlled, crossover study, 10 young adults with T1D were evaluated at baseline and after 4 weeks of treatment with either 10 mg of pegvisomant or placebo. The assessments included an overnight euglycemic steady state followed by a hyperinsulinemic euglycemic clamp and used glucose and glycerol cold stable isotopes.

OUTCOME MEASURES

Hepatic and peripheral insulin sensitivity (IS), lipid turnover, and intramyocellular lipid (IMCL) were measured.

RESULTS

Compared with placebo, pegvisomant treatment resulted in lower IGF-I levels (P < .001). During the overnight steady state, insulin requirements for euglycemia (P = .019), insulin levels (P = .008), and glucose production rates (Ra) (P = .033) were reduced. During the clamp study, glucose infusion rates (P = .031) increased and glucose Ra (P = .015) decreased whereas glucose disposal rates were unchanged. Free fatty acid levels were similar during the steady state but were lower during the clamp (P = .040) after pegvisomant. Soleus muscle IMCL decreased after treatment (P = .024); however, no change in tibialis anterior muscle was observed.

CONCLUSIONS

The study demonstrates that GH antagonism in T1D results in improved hepatic insulin sensitivity. Lack of consistent changes in free fatty acid levels may suggest a direct effect of GH on IS. Unchanged peripheral IS despite reductions in IMCL indicate that GH-induced alterations in IMCL may not be causally linked to glucose metabolism.

Reevaluation of Acromegalic Patients in Long-Term Remission according to Newly Proposed Consensus Criteria for Control of Disease

Acromegaly guidelines updated in 2010 revisited criteria of disease control: if applied, it is likely that a percentage of patients previously considered as cured might present postglucose GH nadir levels not adequately suppressed, with potential implications on management. This study explored GH secretion, as well as hormonal, clinical, neuroradiological, metabolic, and comorbid profile in a cohort of 40 acromegalic patients considered cured on the basis of the previous guidelines after a mean follow-up period of 17.2 years from remission, in order to assess the impact of the current criteria. At the last follow-up visit, in the presence of normal IGF-I concentrations, postglucose GH nadir was over 0.4 μg/L in 11 patients (Group A) and below 0.4 μg/L in 29 patients (Group B); moreover, Group A showed higher basal GH levels than Group B, whereas a significant decline of both GH and postglucose GH nadir levels during the follow-up was observed in Group B only. No differences in other evaluated parameters were found. These results seem to suggest that acromegalic patients considered cured on the basis of previous guidelines do not need a more intensive monitoring than patients who met the current criteria of disease control, supporting instead that the cut-off of 0.4 mcg/L might be too low for the currently used GH assay.

Measuring growth hormone and insulin-like growth factor-I in infants: what is normal?

The role of growth hormone (GH) and insulinlike growth factor-I (IGF-I) change through early childhood. Whereas poor growth is a later presenting feature, infants with isolated GH deficiency have a normal birth weight and length, and often present with hypoglycemia. IGF-I plays an important role antenatally and post-natally in somatic and brain growth. In order to evaluate the GH/IGF-I axis in infancy, an understanding of the normal physiology is required. Measurements of GH and IGF-I in this population should be interpreted in the context of the assays used, as well as their limitations. In this review, we summarize our current understanding of normal GH and IGF-I secretion in children under 18 months of age, and describe variations in the reported assay-specific measurements.

Basal luteinizing hormone and follicular stimulating hormone: is it sufficient for the diagnosis of precocious puberty in girls?

PURPOSE

A gonadotropin-releasing hormone stimulation test (GnRHST) is the gold standard in diagnosing central precocious puberty (CPP). The aim of this study was to investigate the diagnostic accuracy of basal gonadotropin levels for girls with suspected precocious puberty and to evaluate the factors affecting positive results of the GnRHST.

METHODS

Korean girls with early pubertal development who visited the clinic during 2010-2012 were included. Auxological and biochemical tests were evaluated and a standard GnRHST was performed. A peak luteinizing hormone (LH) level of ≥5 IU/L was considered a positive response during the GnRHST.

RESULTS

A total of 336 girls were included. The positive responses were observed in 241 girls (71.7%), and negative responses were found in 95 girls (28.3%). In the logistic regression analysis, the coefficient of the basal LH and basal LH/follicular stimulating hormone (FSH) ratio was 4.23 (P<0.001) and 21.28 (P<0.001), respectively. Receiver operating characteristic analysis showed that the basal LH/FSH ratio is a better predictor of the pubertal result after the GnRHST than the basal LH (area under the curve was 0.745 and 0.740, respectively; P=0.027). Among 189 girls with a basal LH of <0.1 IU/L, 105 (55.6%) had positive responses.

CONCLUSION

An elevated level of the basal LH and basal LH/FSH ratio was a significant predicting factor of positive responses during the GnRHST. However a GnRHST was still necessary for diagnostic confirmation of CPP because more than half of the girls with a basal LH level below the detection limit revealed to have CPP.