Impact of GHBP interference on estimates of GH and GH pharmacokinetics

The effect of miR-23b-3p on regulating GH by targeting POU1F1 in Yanbian yellow cattle

This study aimed to evaluate the effect of miR-23b-3p on growth hormone (GH) in pituitary cells of Yanbian yellow cattle. The mRNA and protein levels of GH and miR-23b-3p target genes were measured by real time fluorescence quantitative PCR (qPCR) and Western blot, respectively. The target relationship of miR-23b-3p was validated by double luciferase reporter gene system. The results showed that GH mRNA and protein levels in pituitary cells of Yanbian yellow cattle were significantly lower in the miR-23b-3p-mi group than in the NC group (P<0.01), while GH mRNA and protein levels were higher in the miR-23b-3p-in group than in the iNC group (P<0.05). The result of bioinformatics analysis and double luciferase reporter gene system validation proved that miR-23b-3p targeted 3'UTR of pituitary specific transcription factor 1 (POU1F1). POU1F1 mRNA and protein levels were lower miR-23b-3p-mi group than in the NC group (P<0.01), while POU1F1 mRNA and protein levels were higher in the miR-23b-3p-in group than in the iNC group (P<0.01). These results demonstrated that miR-23b-3p could regulate GH expression in pituitary cells by regulating POU1F1 gene.

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.

Impact of body mass index on growth hormone stimulation tests in children and adolescents: a systematic review and meta-analysis

Peak stimulated growth hormone (GH) levels are known to decrease with increasing body mass index (BMI), possibly leading to overdiagnosis of GH deficiency (GHD) in children with overweight and obesity. However, current guidelines do not guide how to interpret the peak GH values of these children. This systematic review and meta-analysis aimed to study the effect of the BMI standard deviation score (SDS) on stimulated peak GH values in children, to identify potential moderators of this association, and to quantify the extent to which peak GH values in children with obesity are decreased. This systematic review was performed by the PRISMA guidelines. Medline, Embase, Cochrane, Web of Science, and Google Scholar databases were searched for studies reporting the impact of weight status on peak GH in children. Where possible, individual participant data was extracted and/or obtained from authors. Quality and risk of bias were evaluated using the Scottish Intercollegiate Guidelines Network (SIGN) checklists. The primary outcome was the association between peak GH values and BMI SDS. The pooled correlation coefficient r, 95% confidence interval (CI), and heterogeneity statistic I² were calculated under a multilevel, random-effects model. In addition, exploratory moderator analyses and meta-regressions were performed to investigate the effects of sex, pubertal status, presence of syndromic obesity, mean age and mean BMI SDS on the study level. For the individual participant dataset, linear mixed-models regression analysis was performed with BMI SDS as the predictor and ln(peak GH) as the outcome, accounting for the different studies and GH stimulation agents used. In total, 58 studies were included, providing data on n = 5135 children (576 with individual participant data). Thirty-six (62%) studies had high, 19 (33%) medium, and 3 (5%) low risks of bias. Across all studies, a pooled r of -0.32 (95% CI -0.41 to -0.23, n = 2434 patients from k = 29 subcohorts, I² = 75.2%) was found. In meta-regressions, larger proportions of males included were associated with weaker negative correlations (p = 0.04). Pubertal status, presence of syndromic obesity, mean age, and mean BMI SDS did not moderate the pooled r (all p > 0.05). Individual participant data analysis revealed a beta of -0.123 (95% CI -0.160 to -0.086, p < 0.0001), i.e. per one-point increase in BMI SDS, peak GH decreases by 11.6% (95% CI 8.3-14.8%). To our knowledge, this is the first systematic review and meta-analysis to investigate the impact of BMI SDS on peak GH values in children. It showed a significant negative relationship. Importantly, this relationship was already present in the normal range of BMI SDS and could lead to overdiagnosis of GHD in children with overweight and obesity. With the ever-rising prevalence of pediatric obesity, there is a need for BMI (SDS)-specific cutoff values for GH stimulation tests in children. Based on the evidence from this meta-analysis, we suggest the following weight status-adjusted cutoffs for GH stimulation tests that have cutoffs for children with normal weight of 5, 7, 10, and 20 µg/L: for overweight children: 4.6, 6.5, 9.3, and 18.6 µg/L; and for children with obesity: 4.3, 6.0, 8.6, and 17.3 µg/L.

The effect of miR-6523a on growth hormone secretion in pituitary cells of Yanbian yellow cattle

Yanbian yellow cattle breeding is limited by its slow growth. We previously found that the miRNA miR-6523a is differentially expressed between Yanbian yellow cattle and Han Yan cattle, which differ in growth characteristics. In this study, we evaluated the effects of miR-6523a on growth hormone (GH) secretion in pituitary cells of Yanbian yellow cattle. Bioinformatics analyses using TargetScan and RNAhybrid, as well as dual luciferase reporter assays, showed that miR-6523a targets the 3′ untranslated region of somatostatin receptor 5 (SSTR5). We further found that the mRNA and protein expression levels of GH in pituitary cells were significantly higher in cells treated with miR-6523a mimic than in the control group (P = 0.0082 and P = 0.0069). The GH mRNA and protein expression levels were lower in cells treated with miR-6523a inhibitor than in the control group, but the difference was not significant (P = 0.064 and P = 0.089). SSTR5 mRNA and protein levels were inhibited by miR-6523a mimic compared with the control group (P = 0.0024 and P = 0.0028) and were elevated slightly by miR-6523a inhibitor (P = 0.093 and P = 0.091). These results prove that miR-6523a regulates GH secretion in pituitary cells by SSTR5. More broadly, these findings provide a basis for studies of the roles of miRNAs in animal growth and development.

Comparison of ELISA and HPLC-MS methods for the determination of exenatide in biological and biotechnology-based formulation matrices

The development of biotechnology-based active pharmaceutical ingredients, such as GLP-1 analogs, brought changes in type 2 diabetes treatment options. For better therapeutic efficiency, these active pharmaceutical ingredients require appropriate administration, without the development of adverse effects or toxicity. Therefore, it is required to develop several quantification methods for GLP-1 analogs products, in order to achieve the therapeutic goals, among which ELISA and HPLC arise. These methods are developed, optimized and validated in order to determine GLP-1 analogs, not only in final formulation of the active pharmaceutical ingredient, but also during preclinical and clinical trials assessment. This review highlights the role of ELISA and HPLC methods that have been used during the assessment for GLP-1 analogs, especially for exenatide.

Secretory tumors of the pituitary gland: a clinical biochemistry perspective

The pituitary gland is responsible for the production and/or secretion of various hormones that play a vital role in regulating endocrine function within the body. Secretory tumors of the anterior pituitary predominantly, pituitary adenomas, collectively account for 10%–25% of central nervous system tumors requiring surgical treatment. The most common secretory tumors are prolactinomas, which can be diagnosed by basal prolactin levels. Acromegaly can be diagnosed by basal insulin growth-like factor 1 levels and the failure of growth hormone (GH) to suppress during an oral glucose tolerance test. Cushing disease can be diagnosed by demonstrating hypercortisolemia evidenced by increased salivary cortisol levels in the evening, increased urine free cortisol excretion and failure of plasma cortisol to suppress following oral dexamethasone given overnight (1.0 mg). We also discuss the diagnosis of the rarer thyroid-stimulating hormone and gonadotrophin secretory tumors. Morbidity is associated with tumor occurrence, clinical sequelae as well as the related medical, surgical and radiological management. This review focuses on the pathogenesis of secretory tumors of the anterior pituitary with emphasis on molecular mechanisms associated with tumorigenesis and the major role of the clinical chemistry laboratory in diagnosis and management of these tumors.

The timing of administration of exogenous glucocorticoid affects 24hour growth hormone secretion in children

Exogenous glucocorticoids may suppress linear growth by affecting the diurnal secretory rhythm of GH.

OBJECTIVE

To assess whether the timing of exogenous glucocorticoid administration affects GH secretion in children.

DESIGN

Four girls and four boys aged 10.6 to 15.8 (mean 13.2) years with normal weight and height and pubertal stages I-IV were studied in an open randomized 2-period cross-over trial, with a 1-day un-in, and two 4-day periods of 5mg prednisolone in the morning or in the evening, respectively, separated by a 3-week washout period. At run-in and on the last day of each treatment period serum was collected every 20min for 24h for assessment of GH. Secondary analyses were serum levels of IGF-I and IGFBP-3 (measured every 8h), and IGFBP-1, insulin, and collagen markers PICP, PINP, ICTP and PIIINP (measured every 2h).

RESULTS

Evening prednisolone suppressed 24hour GH secretion (P=0.016), overnight GH secretion (P=0.023) and IGF-I (P=0.024) when compared to morning prednisolone, but not when compared to run-in. Evening prednisolone also increased nocturnal insulin levels as compared to run-in (P=0.010). Irrespective of time of day, prednisolone increased serum collagen markers PICP, PIINP, ICTP and PINP (all P<0.05).

CONCLUSIONS

Short-term prednisolone 5mg administered in the morning may alleviate nocturnal GH suppression as compared to evening administration. In analogy, growth rates are less affected by morning as compared to evening administration of exogenous glucocorticoids. In contrast, collagen markers and metabolic indices were not affected by the timing of prednisolone administration.

Growth hormone binding protein - physiological and analytical aspects

A significant proportion of total circulating growth hormone (GH) is bound to a high affinity growth hormone binding protein (GHBP). Several low affinity binding proteins have also been described. Significant differences between species exist with respect to origin and regulation of GHBP, but generally it resembles the extracellular domain of the GH receptor. Concentrations are associated with GH status, body composition and other factors. Although the clinical relevance of GHBP is not fully understood it is suggested that concentrations indirectly reflect GH receptor status. This is supported by cases of Laron's syndrome where a molecular defect in the extracellular domain of the GH receptor is associated with low or unmeasurable GHBP concentrations. Methods to measure GHBP have evolved from chromatographic, activity based procedures to direct immunoassays. In clinical practice, measurement of GHBP can be helpful to differentiate between GH deficiency and GH insensitivity, particularly if GHBP is absent.

Protein-based matrix interferences in ligand-binding assays

An adequate bioanalytical support for a typical biotherapeutic requires a number of assays, including those to measure drug concentration and to assess induction of specific immune responses. Ligand-binding assays are the most commonly used platform in bioanalysis of biotherapeutics. Ligand-binding assays are frequently designed to detect appropriate analytes in complex biological matrices with limited or no sample pretreatment steps. The complex composition of the test matrix is highly diverse and varies from normal to disease populations. Additional post-treatment changes are often observed, including induction of antidrug antibodies. Due to potential interaction of biological matrix components, for example, rheumatoid factors, heterophilic antibodies and human anti-animal antibodies, with the test analyte or assay reagents, ligand-binding assays are often subjected to various degrees of matrix interferences that lead to an erroneous under- or over-reporting of the analyte concentration. Impact of various matrix components and practical means designed to mitigate interferences are discussed in this Review.

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.

Principles and pitfalls of free hormone measurements

The free hormone hypothesis states that a hormone's physiological effects depend on the free hormone concentration, not the total hormone concentration. Although the in vivo relationship between free hormone and protein-bound hormone is complex, most experts have applied this view to the design of assays used to assess the free hormone concentration in the blood sampled for testing in vitro. The history of the measurement of free thyroxine, probably the most frequently requested free hormone determination, offers a good example of the approaches that have been taken. Methods that require physical separation of the free hormone from the protein-bound hormone must address both the potential disturbance in the equilibrium between the two, as well as the challenge of quantifying small levels of hormone accurately and precisely. The implementation of mass spectrometry in the clinical laboratory has helped to develop proposed reference measurement procedures. These must be utilized to standardize the variety of immunoassay approaches that currently represent options commercially available to the routine clinical laboratory. Practicing endocrinologists should discuss the details of the free hormone assays offered by the clinical laboratory they utilize for patient result reporting, and clinical laboratories should implement the recommendations of published guidelines to ensure that free hormone results using commercially available immunoassays are as accurate and precise as possible.

Gaps in the Traceability Chain of Human Growth Hormone Measurements

BACKGROUND

Human growth hormone (hGH) is measured for the diagnosis of secretion disorders. These measurements fall under the EU Directive 98/79/EC on in vitro diagnostic medical devices requiring traceability of commercial calibrator values to higher-order reference materials or procedures (Off J Eur Communities 1998 Dec 7;L 331:1–37). External quality assessment schemes show large discrepancies between results from different methods, even though most methods provide results traceable to the recommended International Standard (IS 98/574). The aim of this study was to investigate possible causes for these discrepancies.

METHODS

We investigated the commutability and recovery of hGH in reconstituted IS 98/574. We tested different reconstitution protocols and used 4 different serum matrices for spiking. These IS preparations were measured together with serum samples. We quantified hGH by 5 different methods in 4 different laboratories.

RESULTS

Results from the different methods correlated well for the serum samples. Mean discrepancies between results from different methods were ≤20%. None of the IS preparations was commutable for all the method comparisons. The recovery of hGH in preparations of IS 98/574 depended on the reconstitution protocol (&gt;10-fold differences) and BACKGROUND matrix (relative differences ≤17% for different serum matrices).

CONCLUSIONS

The use of different protocols for reconstitution and spiking of hGH reference preparations affects quantification by immunoassays, potentially leading to a bias between commercial methods, despite the use of calibrators with values claimed to be traceable to the same higher-order reference material.

Detecting and solving the interference of pregnancy serum, in a GH immunometric assay

BACKGROUND

High homology of GH with placental GH (pGH) and hPL frequently resulted in falsely high GH levels in competitive immunoassays during pregnancy. However, in immunometric assays, falsely high or low GH levels can result from GH-like molecules binding to both or only one monoclonal antibody. Since our GH-IFMA assay detected GH suppression in both normal and acromegalic pregnancies, we evaluated potential negative interference of pregnancy serum in the assay.

METHODS

GH was measured in samples from acromegalic patients with and without the addition of normal pregnancy serum using a sensitive in-house two-step GH-IFMA (no crossreactivity with pGH, Prolactin or hPL). Standard GH assay curves were run with and without pGH (20 and 22 K). Pegvisomant, a GH-antagonist with high homology to GH, was also tested for cross-reactivity.

RESULTS

Addition of pregnancy serum to acromegaly serum resulted in marked decrease in GH, but addition of pGH did not change GH measurements. Redesign of the routine assay by switching the positions of the antibodies ("inverted" assay) completely abrogated the interference of pregnancy serum. GH by both routine and inverted assays declined progressively throughout pregnancy in controls, with higher nadir levels in the "inverted" assay (median 0.03 μg/L vs 0.50 μg/L, P<0.05). GH suppression during acromegalic pregnancy previously found with the routine assay was not observed in the "inverted" assay. Pegvisomant does not cross-react with GH in the "inverted" assay.

CONCLUSIONS

GH measurements in pregnancy by immunometric assays must be made after exclusion of pregnancy serum interference by dilutional tests. Redesigning a two-step immunometric GH assay by switching the positions of the antibodies can be a successful strategy to abrogate such interference.

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.

Automated 22-kD growth hormone-specific assay without interference from Pegvisomant

BACKGROUND

Large variability exists among different growth hormone (GH) assays owing to differences in calibration, antibody specificity, isoform recognition, and interference from GH binding protein (GHBP). The GH receptor antagonist Pegvisomant presents a new challenge because Pegvisomant interferes with many GH assays. A recent consensus conference established criteria for standardization and evaluation of GH assays. Following consensus recommendations, we developed a new GH assay on an automated analyzer (IDS-iSYS, Immunodiagnostic Systems).

METHODS

A monoclonal antibody not cross-reacting with Pegvisomant was combined with a monoclonal antibody specific for 22-kD GH. Isoform specificity and interference from GHBP was tested and compared to that seen in 2 existing automated GH assays (Siemens Immulite, Diasorin Liaison). We also compared GH concentrations measured by the 3 assays for healthy volunteers and patients with acromegaly receiving different treatments. Using the iSYS assay, we also established nadir GH values during oral glucose load and analyzed changes in endogenous GH during Pegvisomant treatment.

RESULTS

Analytical and functional sensitivities were 0.01 μg/L and 0.04 μg/L, with a dynamic range from 0.04 to 100 μg/L. Intraassay CVs were 2%-4%, whereas interassay CVs were 5%-7% at GH concentrations between 1.7 and 27.5 μg/L. The assay was specific for 22-kD GH and not affected by GHBP. The presence of Pegvisomant, which leads to a negative bias on the Immulite and dramatic overestimation of GH on the Liaison, had no impact on the iSYS GH assay.

CONCLUSIONS

The new assay fulfils recent consensus recommendations and presents a useful new tool for reliable measurement of GH.

Quantification of the GH/IGF-axis components: lessons from human studies

Originally, the circulating bioactivity of IGF-I was estimated by bioassays measuring the ability of serum to stimulate uptake of labeled sulfate or thymidine in cultures of costal cartilage or by the ability of serum to stimulate the uptake of glucose in fat tissue cultures. However, because of their laborious and unspecific nature, the original bioassays were quickly abandoned with the development of the first RIA for IGF-I in 1977. Consequently, for the past three decades the endogenous IGF-I bioactivity has been almost exclusively estimated by the use of immunoassays. Beyond any doubt, the immunoassays have provided an extensive insight into IGF-I physiology and pathophysiology. However, immunoassays ignore the presence of the IGFBPs, which are important regulators of IGF-I action in vivo. In addition, immunoassays do not consider the presence of IGF-II, which also interacts with the IGF-I receptor (IGF-IR). This aroused our interest to reintroduce the bioassay; therefore, we established a cell-based kinase receptor activation (KIRA) assay based on cells transfected with the human IGF-IR. The output signal of the KIRA assay is IGF-IR phosphorylation, and, as such, it is highly specific. Further, because detection of phosphorylated IGF-IRs is based on modern immunoassay techniques, the overall performance of the assay is close to that of a traditional IGF-I immunoassay. The first part of this review comprises a short description of the bioassay, and a more in-depth presentation of the data that have been obtained so far. It will be demonstrated that the bioassay is indeed able to yield novel information on the IGF system, most likely because it is able to integrate the different components of the IGF system into one signal: IGF-IR activation. As IGF-I, circulating GH is bound to larger proteins, the far most important GH-binding protein (GHBP) is identical to the extracellular domain of the GH receptor (GHR). Because of its origin, GHBP binds GH with the same affinity as GHR and, consequently, GHBP may affect GH bioactivity as well as pharmacokinetics. To improve our knowledge on the complex interaction between GH and GHBP in vivo, we found it of interest to develop a method for determination of free GH. To this end, we developed an ultrafiltration assay that enabled isolation of free GH in undiluted serum during approached in vivo-like conditions. The last part of this review presents our current data on free GH and its interaction with GHBP.

The effect of prolonged fasting on levels of growth hormone-binding protein and free growth hormone

OBJECTIVE

There are limited data on growth hormone-binding protein (GHBP) and free GH levels during the physiological challenge of a prolonged fast. Our aim was to explore the relationships between GHBP, free GH, total GH and non-esterified fatty acid (NEFA) levels during overnight and 24-hour fasts in healthy young adults.

DESIGN

We measured nocturnal levels of GHBP at three time-points (22:00, 03:00, 08:00), NEFA every 60 min and ultra-filtered free GH and total GH at 15-minute intervals for 10 h (22:00-08:00) during an overnight and a 24-hour fast in 7 female and 4 male normal-weight subjects aged 24.8 years (range: 22.8-26.9) with BMI 22.5 kg/m² (range: 18-27).

RESULTS

Spontaneous free and total GH levels were closely related during the overnight and 24-hour fasts (r=0.99, p<0.0001 and r=0.99, p<0.0001 respectively). 24 h of fasting led to an increase in levels of basal free GH (p=0.03), mean free GH (p=0.04), mean total GH (p=0.04) and NEFA (p<0.0001) whilst GHBP levels remained similar (p=0.8). Percentage free (over total) GH was similar during the overnight and prolonged fasts (p=0.3). There were no associations between levels of NEFA and free (r=0.24, p=0.5) or total GH (r=0.20, p=0.6).

CONCLUSIONS

A 24-hour fast led to parallel increases in free and total GH levels whilst there was no discernable change in GHBP levels or the fraction of free GH. This suggests that GHBP plays a role in limiting variations of circulating free GH levels. NEFA levels increased during the prolonged fast but they were not correlated with free or total GH levels.

Harmonization of growth hormone measurements with different immunoassays by data adjustment

BACKGROUND

The aim of our study was to evaluate the between-assay variability of commercially available immunoassays for the measurement of human growth hormone (hGH). In addition, we asked whether the comparability of the diagnosis of childhood onset growth hormone deficiency could be improved by adjusting hGH results by statistical methods, such as linear regression, conversion factors, and quantile transformation.

METHODS

In archived sera from 312 children and adolescents (age: 17 days-17 years) hGH values between 0.01 and 16.5 ng/mL were determined by using the following immunoassays: AutoDELFIA (PerkinElmer), BC-IRMA (Beckman-Coulter), ELISA (Mediagnost), IMMULITE 2000 (Siemens), iSYS (IDS), Liaison (DiaSorin), UniCel DxI 800 Access (BeckmanCoulter) and "In house"-RIA (Tübingen).

RESULTS

The assays differed in median hGH concentrations by as much as 5.44 ng/mL (Immulite), and as little as 2.67 ng/mL (BC-IRMA). The mean difference between assays ranged from 0.35 to 2.71 ng/mL, whereas several samples displayed differences up to 11.4 ng/mL. The best correlation (r=0.992) was found between AutoDELFIA and Liasion, the lowest (r=0.864) was between an in-house RIA and iSYS. The between-assay CV (mean ± SD) of values within the cut-off range was 24.3% ± 7.4%, resulting in an assay-dependent diagnosis of growth hormone deficiency (GHD) in more than 27% of patients. Yet, adjustment of this data by linear regression or a conversion factor reduced the CV below 14%, and the ratio of assay-dependent diagnoses below 8%. Using quantile transformation, the CV and ratio were reduced to 11.4% and <1%, respectively.

CONCLUSIONS

hGH measurements using different assays vary significantly. Linear regression, conversion factors, or particularly quantile transformation are useful tools to improve comparability in the diagnostic procedure for the confirmation of GHD in childhood and adolescence.

Biotherapeutic bioanalysis: a multi-indication case study review

A thorough understanding of the structure and biology of a biotherapeutic is crucial to defining a suitable strategy for pharmacokinetic characterization in proof-of-concept disease models, toxicology species as well as the healthy and disease indication patient populations. This manuscript summarizes parameters that impact bioanalytical strategy for over 50 biotherapeutics indicated for the treatment of oncology, rheumatoid arthritis, allergy, multiple sclerosis, hematology, metabolism and infectious disease. We have addressed numerous therapeutic modalities including chimeric, humanized and fully human monoclonal antibodies, replacement proteins, peptides and fusion proteins, including polyethylene glycol and Fc fusions, as well as antibody–drug conjugates. With the rapid evolution of biotherapeutics over the last 20 years and the contraction of the pharmaceutical and biotechnology labor force, efficient workflow management becomes a crucial bioanalytical component. Thus, we have also addressed new technologies that have demonstrated either increased throughput or enhanced characterization, including Meso Scale Discovery, Gyrolab and affinity MS.

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

Measuring the concentration of growth hormone (GH) in blood samples taken during dynamic tests represents the basis for diagnosis of growth hormone related disorders, namely growth hormone deficiency and growth hormone excess. Today, a wide spectrum of immunoassays are in use, enabling rapid and sensitive determination of growth hormone concentrations in routine diagnostics. From a clinical point of view several difficulties exist with the use and interpretation of GH assay results in the assessment of GH related disorders: Many physiological factors such as fat mass, age and gender influence the outcome of dynamic tests, overall leading to significant inter-individual differences in GH responses. However, in addition to the physiological variability, considerable variability exists in GH assay results obtained by different immunoassays. Unfortunately, all the new technical advances in the field of GH measurement techniques have not reduced this methodological variability. To a large extent, the actual values reported for the GH concentration in a sample depend on the method used by the respective laboratory. Obviously, such discrepancies limit the applicability of consensus guidelines on diagnosis and treatment in clinical practice. This review summarizes current practices for GH measurement with respect to the methods used, their limitations and the clinical consequences of the existing heterogeneity in GH immunoassay results.

Different growth hormone sensitivity of target tissues and growth hormone response to glucose in HIV-infected patients with and without lipodystrophy

Growth hormone (GH)-secretion in HIV-lipodystrophy is impaired; however, GH-sensitivity of GH-target tissues remains to be evaluated. We measured overnight fasting concentrations of GH-sensitive insulin-like growth-factor-I (IGF-I) and IGF binding protein-3 (IGFBP-3) including GH binding protein (GHBP), a marker of GH-receptor sensitivity, in antiretroviral treated HIV-infected patients with (LIPO) and without lipodystrophy (NONLIPO) and antiretroviral naive HIV-infected patients (NAIVE). Three h GH-suppression tests using oral glucose were undertaken to determine dynamics of GH-secretion. IGF-I and IGFBP-3 were increased in LIPO compared with NONLIPO (p <0.05), but did not differ significantly between NONLIPO and NAIVE. Area under the curve of GH (AUC-GH) during the GH-suppression test was decreased in LIPO compared with NONLIPO (p <0.05). Ratio of limb to trunk fat, which was decreased in LIPO compared to NONLIPO and NAIVE (p <0.001), correlated positively with AUC-GH and rebound-GH (p <0.05). All groups displayed suppression of GH during the suppression test (p <0.05) and all groups, except LIPO, displayed a rebound of GH (p <0.05), which probably is explained by persistently increased plasma glucose in LIPO compared with NONLIPO and NAIVE (p <0.01). GHBP was inversely correlated with AUC-GH (p <0.01). Our data suggest that GH-target tissues in LIPO are at least as GH-sensitive as in HIV-infected patients without lipodystrophy.

Increased levels of human placental growth hormone in the amniotic fluid of pregnancies affected by Down syndrome

OBJECTIVE

To evaluate the concentrations of human placental growth hormone (hPGH) in amniotic fluid (AF) at gestational mid-trimester in normal pregnancies and in pregnancies complicated by Down's syndrome.

DESIGN

AF samples from 21 women with Down's syndrome pregnancies were analyzed retrospectively. About 47 AF samples from women with singleton, uncomplicated pregnancies, who gave birth to healthy neonates with birth weight appropriate for gestational age were used as controls. All AF samples were obtained during amniocentesis for fetal karyotyping at 16-23 weeks' gestation. hPGH levels were measured by a solid phase immunoradiometric assay using two different epitopes.

RESULTS

The mean hPGH values in the AF of the Down's syndrome-affected pregnancies were significantly higher (P<0.05) compared to those of normal pregnancies, at 16-23 weeks' gestation: mean-value+/-SD in the AF was 1.96+/-1.35 microg/l vs. 0.82+/-0.67 microg/l.

CONCLUSIONS

Higher hPGH levels in AF were found in pregnancies affected by Down's syndrome as compared to normal pregnancies at gestational mid-trimester. hPGH was detected in all AF samples, and it provides evidence that this pregnancy-specific hormone enters the fetal compartment and is not limited to the maternal circulation. The physiological role and effect of hPGH on fetal growth in normal and pathological pregnancies needs further investigation.

High-sensitivity chemiluminescence immunoassays for detection of growth hormone doping in sports

BACKGROUND

Recombinant human growth hormone (rhGH) is abused in sports, but adequate routine doping tests are lacking. Analysis of serum hGH isoform composition has been shown to be effective in detecting rhGH doping. We developed and validated selective immunoassays for isoform analysis with potential utility for screening and confirmation in doping tests.

METHODS

Monoclonal antibodies with preference for pituitary hGH (phGH) or rhGH were used to establish 2 pairs of sandwich-type chemiluminescence assays with differential recognition of rhGH (recA and recB) and phGH (pitA and pitB). We analyzed specimens from volunteers before and after administration of rhGH and calculated ratios between the respective rec- and pit-assay results.

RESULTS

Functional sensitivities were <0.05 microg/L, with intra- and interassay imprecision < or =8.4% and < or =13.7%, respectively. In 2 independent cohorts of healthy subjects, rec/pit ratios (median range) were 0.84 (0.09-1.32)/0.81 (0.27-1.21) (recA/pitA) and 0.68 (0.08-1.20)/0.80 (0.25-1.36) (recB/pitB), with no sex difference. In 20 recreational athletes, ratios (median SD) increased after a single injection of rhGH, reaching 350% (73%) (recA/pitA) and 400% (93%) (recB/pitB) of baseline ratios. At a moderate dose (0.033 mg/kg), mean recA/pitA and recB/pitB ratios remained significantly increased for 18 h (men) and 26 h (women). After high-dose rhGH (0.083 mg/kg), mean rec/pit ratios remained increased for 32 h (recA/pitA) and 34 h (recB/pitB) in men and were still increased after 36 h in women.

CONCLUSIONS

Using sensitive chemiluminescence assays with preferential recognition of phGH or rhGH, detection of a single injection of rhGH was possible for up to 36 h.

Problems with GH assays and strategies toward standardization

Disorders affecting GH secretion--either GH deficiency or GH excess (acromegaly)--are biochemically defined through peak or nadir concentrations of human GH in response to dynamic tests. Immunoassays employing polyclonal or monoclonal antibodies are routinely used for the analysis of GH concentrations, and many different assays are available on the market today. Unfortunately, the actual value reported for the GH concentration in a specific patient's sample to a large extent depends on the assay method used by the respective laboratory. Variability between assay results exceeds 200%, limiting the applicability of consensus guidelines in clinical practice. Reasons for the heterogeneity in GH assay results include the heterogeneity of the analyte itself, the availability of different preparations for calibration, and the interference from matrix components such as GH-binding protein. Furthermore, the reporting of results in mass units or international units together with the application of variable conversion factors led to confusion. International collaborations proposed measures to improve the comparability of assay results, recommending the use of a single, recombinant calibrator for all assays and reporting only in mass units as first steps. However, because of the differences in epitope specificity of antibodies used in different assays, method-specific cut-off levels for dynamic tests might remain necessary to correctly interpret and compare results from different laboratories.

Determination of free growth hormone

CONTEXT

Approximately 50% of circulating GH is bound to the high-affinity GH-binding protein (GHBP), which is known to affect the pharmacokinetics, bioactivity, and quantitative determination of GH. Nevertheless, the presence of GHBP is rarely taken into account in the clinical use of GH measurements.

OBJECTIVE

Our objective was to develop an assay for free GH in serum.

METHODS

We used ultrafiltration by centrifugation. Due to the small molecular difference between GH and GHBP, the size of GHBP and GHBP-GH complexes was increased by preincubation of serum with a monoclonal GHBP antibody (MAb 263).

RESULTS

The ultrafiltration membrane almost completely retained all GHBP (>98.5%) and allowed free passage of unbound GH (>98.4%). Addition of increasing concentrations of GHBP reduced free GH dose dependently, and measured and calculated levels of free GH changed in parallel. During an insulin-tolerance test, free and total GH changed in parallel in all individuals (n = 11) and their peak values as well as area under the curve values were positively correlated (r = 0.89; P < 0.001 and r = 0.92; P < 0.001, respectively). Of note, the relative levels of free GH (calculated as the area under the curve of free to total GH) was inversely correlated with GHBP (r = -0.94; P < 0.001).

CONCLUSION

It is possible to measure free GH in human serum. Free GH correlated positively with total GH and inversely with GHBP. Measurement of free GH may be a helpful future tool in the management of GH disorders and in studies of GH-GHBP interrelationships.

Differential regulation of membrane associated-growth hormone binding protein (MA-GHBP) and growth hormone receptor (GHR) expression by growth hormone (GH) in mouse liver

Growth hormone (GH) binding to GH receptor (GHR) is the initial step that leads to the physiological functions of the hormone. Proteolytical cleavage of the GHR in humans and rabbits and alternative processing of the GHR transcript in rodents generates circulating growth hormone binding protein (GHBP). Moreover, other GHR truncated forms that result from alternative processing of the GHR mRNA transcript have been described. These GHR short forms are inserted in the plasma membrane but they are unable to transduce the signal. In rodents, membrane associated-GHBP (MA-GHBP), which accounts for a significant proportion of liver GH binding capacity, represents the main GHR short form found in membranes, and may therefore function as a negative form of the receptor. In the present study, GHR and MA-GHBP content in liver were analyzed using mutant and transgenic mice expressing different concentrations of growth hormone to evaluate the correlation between GH levels, body weight (BW), GHR and MA-GHBP expression. It was found that GH deficiency was associated with diminished BW, GHR and MA-GHBP expression, while increased GH concentration led to increased BW, GHR and MA-GHBP expression, but MA-GHBP upregulation was more pronounced than the observed increase in GHR expression. Since GHR and MA-GHBP both contribute to liver GH binding capacity, GH-induced enrichment of the dominant negative form would represent a compensatory mechanism triggered by high levels of the hormone. This attempt to attenuate the effects of supraphysiological concentrations of GH may be critical to reduce or prevent their plausible damaging effects on the organism.

What endocrinologists should know about growth hormone measurements

Determination of human growth hormone (GH) concentration in serum plays a key role in the diagnosis of GH deficiency and GH excess (acromegaly). Methods of measuring GH still lack standardization and show considerable between-method variability. Therefore, correct interpretation of GH test results requires knowledge of measurement techniques and awareness of potential problems in applying recommendations for cut-off values given in the literature. This article focuses on the molecular, structural, and methodologic background of the heterogeneity of assay results and on possible next steps toward standardization.

Growth hormone assays: current methodologies and their limitations

Measurement of circulating growth hormone (GH) concentrations is essential in diagnosis of either GH deficiency or GH excess. The invention of immunoassays for the measurement of peptide hormones was a major breakthrough, enabling the routine analysis of GH concentrations in larger series of samples. Over the last few decades, measurement technology has evolved from less sensitive, mainly radioactive assays based on polyclonal antisera to the latest generations of highly sensitive chemiluminescence methods employing monoclonal antibodies. Unfortunately, the development of newer assays did not lead to better agreement among the results obtained by different assay methods. On the contrary, the differences tended to increase when monoclonal antibody based assays became more popular. The actual value reported for the GH concentration in a specific patient's sample still mainly depends on the method used by the respective laboratory, limiting the applicability of international consensus guidelines in clinical practice. The heterogeneity of the analyte itself, the availability of different reference preparations for calibration and the interference from matrix components such as GH binding protein are among the reasons why standardizing GH assays is difficult. An additional challenge arose from the availability of a GH receptor antagonist for the treatment of acromegaly, which is basically a mutated form of GH and therefore interferes in many GH assays. This review provides an overview on GH assays used in clinical practice, their limitations and the potential next steps towards standardization.

Aspects of placental growth hormone physiology

Placental growth hormone (PGH) has been known for 20 years. Nevertheless, its physiology is far from understood. In this review, basal aspects of PGH physiology are summarised and put in relation to the highly homologous pituitary growth hormone (GH). During normal pregnancy, PGH progressively replaces GH and reach maximum serum concentrations in the third trimester. A close relationship to insulin-like growth factor (IGF)-I and -II levels is observed. Furthermore, PGH levels are positively associated to fetal growth. The potential importance of growth hormone receptors and binding protein for PGH effects is discussed. Finally, the review outlines current knowledge of PGH in pathological pregnancies.

Kinetics and secretion of placental growth hormone around parturition

OBJECTIVE

During pregnancy, placental growth hormone (PGH) is secreted into the maternal circulation, replacing pituitary GH. It is controversial whether PGH levels decline during vaginal birth. After placental expulsion, PGH is eliminated from the maternal blood. GH binding protein (GHBP) and body mass index (BMI) influence GH kinetics, but their impact on PGH kinetics is unknown. The present study was undertaken to define the kinetics of PGH during vaginal delivery and Caesarian section and to relate these kinetics to GHBP and BMI.

DESIGN

A short term, prospective cohort study.

METHODS

Twelve women had repeated blood samples drawn during vaginal delivery. From 26 women undergoing planned Caesarian delivery (CS) repeated blood samples were withdrawn before, during and after the CS, allowing PGH half-life determination.

RESULTS

During vaginal delivery, median PGH values did not change before expulsion of the placenta, although individual fluctuations were seen. Clearance of PGH from the maternal circulation was best described by a two-compartment model. The initial half-life of serum PGH was (mean +/- s.d.) 5.8 +/- 2.4 min, and the late half-life was (median) 87.0 min (range: 25.1-679.6 min). The late half-life was correlated to the pre-gestational BMI (r = 0.39, P = 0.047), but not to the serum GHBP concentration.

CONCLUSIONS

Serum PGH did not decrease significantly during vaginal delivery. Elimination of PGH fitted a two-compartment model, with an estimated initial half-life of 5.8 min. The late phase serum half-life of PGH was related to BMI, suggesting a role for maternal fat mass in PGH metabolism.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

Effect of sex and assay method on serum concentrations of growth hormone in patients with acromegaly and in healthy controls

BACKGROUND

Diagnosis and follow-up of acromegaly is based on measurements of serum growth hormone (GH) concentrations during an oral glucose tolerance test (OGTT). A nadir value <1 microg/L is commonly used to define a normal response, but some authors suggest lower cutoff values.

METHODS

To compare the results and subsequent patient classification obtained with 3 GH assays, we obtained basal serum samples from 78 apparently healthy adult controls (43 women and 35 men; median age, 32.5 years) and from 71 treated (44 women and 27 men; median age, 55.2 years) and 7 untreated acromegaly patients (4 women and 3 men; median age, 54.6 years), and OGTT was performed on all patients and on 72 of the 78 controls. GH was determined by 2 immunometric assays-a double monoclonal (AutoDELFIA; Wallac) and a monopolyclonal (Immulite 2000; DPC) assay-and in a limited set of samples by an RIA (Spectria RIA; Orion).

RESULTS

There was a strong correlation (r = 0.995; P < 0.001) between the 2 immunometric methods, but the results obtained with the Immulite 2000 were, on average, 1.4-fold higher than those obtained with the AutoDELFIA. At concentrations around the cutoff (1 microg/L), however, the difference was approximately 2-fold. Overall, the Orion RIA method also showed a good correlation (r = 0.951-0.959) with the other methods, but it did not measure concentrations <2 microg/L. Women had higher basal and OGTT nadir GH concentrations than men.

CONCLUSION

Reference intervals should be determined separately for each method, and the need for establishing sex-specific reference values should be investigated.

Problematic determination of serum growth hormone: experience from external quality assurance surveys 1998-2003

The objective of the present study was to start a new external quality assurance survey (EQAS) for the determination of serum growth hormone (GH) using pooled serum specimens as quality-assurance samples. To give good coverage of multiple forms of GH, the specimens included sera from GH-deficient and acromegalic patients as well as from persons showing a normal response in GH provocation tests. In one survey the quality-control specimens were spiked with exogenous 22-kD GH to obtain some idea of the specificity and GH recovery of the assays. The EQA surveys of 1998-2003 were organized by Labquality of Helsinki in cooperation with three university hospital laboratories in Finland. The number of participating laboratories ranged from 8 to 14. During 1998-2003, gratifying methodological harmonization occurred in the participating group, as the participants switched to the immunometric detection principle, the number of method applications decreasing from 7 to 3. In 1998 the 14 participating laboratories reported five different conversion factors (from microg/l to mU/l), whereas in 2003 7 of the 8 participants reported the same factor. Despite the harmonization trend among participating laboratories, further efforts are needed, because marked method-based differences still exist. This dialogue should include kit manufacturers, laboratory experts, EQA organizations and clinicians using the test results.

Pharmacokinetics and acute lipolytic actions of growth hormone. Impact of age, body composition, binding proteins, and other hormones

The biologic actions of endogeneous growth hormone (GH) depend on its secretion and clearance rates as well as sensitivity at the receptor level. Aberrations in GH pharmacokinetics and pharmacodynamics may occur with increasing age, and have been implicated in diseases such as obesity, diabetes mellitus, and critical illness. In this review, recent insights into the association between GH metabolism and age, body composition, binding proteins and other hormones are discussed.