Growth hormone isoforms in acromegalic patients before and after treatment with octreotide LAR

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.

Exon 3-deleted growth hormone receptor isoform is not related to worse bone mineral density or microarchitecture or to increased fracture risk in acromegaly

PURPOSE

Acromegaly is a cause of secondary osteoporosis and is associated with increased risk of vertebral fractures (VFs). The influence of exon 3-deleted isoform of growth hormone receptor (d3-GHR) on bone microarchitecture has not been studied in acromegaly.

AIM

The aim of this study was to analyze the associations between d3-GHR isoform and bone mineral density (BMD), bone microarchitecture, and VFs in acromegaly patients.

METHODS

Consecutive acromegaly patients treated at a single reference center were included. BMD was analyzed using dual-energy X-ray absorptiometry (DXA) and bone microarchitecture was analyzed by high-resolution peripheral quantitative computed tomography (HR-pQCT). The presence of moderate to severe VFs was assessed by thoracic and lumbar X-ray. GHR genotyping was analyzed by PCR, and full-length isoform of GHR (fl-GHR) was represented by a 935-bp fragment and d3-GHR by a 532-bp fragment.

RESULTS

Eighty-nine patients were included [56 females; median age at diagnosis: 43 years (17-78)]. Disease was uncontrolled in 63% of patients. At least one d3-GHR allele was present in 60% of patients. Frequency of active disease (p = 0.276) and hypogonadism (p = 1.000) was not different between patients with fl-GHR and those with at least one d3-GHR. There was no difference in any DXA or HR-pQCT parameters between patients with fl-GHR and those with d3-GHR. Significant VFs were observed in 14% of patients, but there was no difference in frequency between patients with fl-GHR and those with at least one d3-GHR allele (p = 0.578).

CONCLUSIONS

Presence of d3-GHR was not associated with worse BMD or bone microarchitecture or with higher frequency of significant VFs.

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

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

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.

MANAGEMENT OF ENDOCRINE DISEASE: Acromegaly and pregnancy: a contemporary review

Although fertility is frequently impaired in women with acromegaly, pregnancy is apparently becoming more common due to improvement in acromegaly treatment as well as in fertility therapy. As a result, several studies on pregnancy in patients with acromegaly have been published in recent years adding new and relevant information to the preexisting literature. Also, new GH assays with selective specificities and the knowledge of the expression of the various GH genes have allowed a better understanding of somatotrophic axis function during pregnancy. In this review, we show that pregnancy in women with acromegaly is generally safe, usually with tumoral and hormonal stability. Although the paucity of data limits evidence-based recommendations for preconception counseling and pregnancy surveillance, controlling tumor size and hormonal activity before pregnancy is highly recommended to ensure better outcomes, and surgical control should be attempted when feasible. Treatment interruption at pregnancy confirmation has also proven to be safe, as drugs are not formally allowed to be used during pregnancy. Drug exposure (somatostatin analogs) during early or whole pregnancy might increase the chance of a lower birth weight. Aggressive disease is uncommon and may urge individual decisions such as surgery or drug treatment during pregnancy or lactation.

Experience with pegvisomant treatment in acromegaly in a single Brazilian tertiary reference center: efficacy, safety and predictors of response

Objective

To describe the safety and efficacy of pegvisomant therapy and the predictors of treatment response in acromegaly patients at a single tertiary reference center in Brazil.

Materials and methods

We retrospectively reviewed the clinical, hormonal and radiological data of acromegaly patients treated with pegvisomant in our center. We also evaluated the presence of the d3 isoform of the growth hormone receptor (d3GHR).

Results

Twenty-seven patients were included (17 women). Pegvisomant was used in combination with octreotide LAR in 20 patients (74%), in combination with cabergoline in one (4%) and as monotherapy in six (22%). IGF-I normalization was achieved in 23 patients (85%). Mild and transitory elevation of liver enzymes was observed in two patients (7.4%), tumor growth in one (3.4%) and lipodystrophy in two (7.4%). One patient stopped the drug due to headaches. The GHR isoforms were evaluated in 14 patients, and the presence of at least one d3GHR allele was observed in 43% of them, but it was not a predictor of treatment response. Only pre-treatment IGF-I level was a predictor of treatment response.

Conclusion

Pegvisomant treatment was highly effective and safe in our series of Brazilian patients. A better chance of disease control can be expected in those with lower pre-pegvisomant IGF-I levels.

Growth hormone receptor exon 3 isoforms may have no importance in the clinical setting of multiethnic Brazilian acromegaly patients

BACKGROUND

Acromegaly is associated with significant morbidity and increased mortality, but has a variable severity phenotype. The presence of the exon 3-deleted isoform of the growth hormone receptor (d3-GHR) may influence the disease phenotype and treatment outcomes, including the frequency of biochemical discordance after medical treatment.

AIMS

The objective of this study was to analyze the influence of the d3-GHR isoform on clinical and biochemical characteristics and in the treatment outcomes of Brazilian multiethnic acromegaly patients.

METHODS

We retrospectively analyzed our acromegaly outpatient clinic databank and collected demographic, clinical, biochemical and treatment outcome data from those patients who agreed to participate in the study. A blood sample was collected from all patients, the DNA was extracted and the GHR isoforms were evaluated by PCR, with the full length (fl)-GHR represented by a 935-bp fragment and the d3-GHR represented by a 532-bp fragment.

RESULTS

A total of 121 patients were included. Fifty-six patients (46.3 %) were full-length homozygous (fl/fl), 48 (39.7 %) were heterozygous (fl/d3) and 17 (14.0 %) were d3-GHR homozygous (d3/d3). There was no difference between patients homozygous for the fl isoform and those harboring at least one d3-GHR allele in the demographic, clinical and biochemical data or in the treatment outcomes, including somatostatin receptor ligands (SRL) monotherapy, combination therapy with SRL and cabergoline and pegvisomant treatment. There was also no difference between the groups for the frequency of GH and IGF-I discordance after medical treatment.

CONCLUSION

GHR exon 3 genotyping appears to have no clinical significance, at least in Brazilian acromegaly patients.

Pitfalls of insulin-like growth factor-i and growth hormone assays

Accurate measurement of growth hormone (GH) and insulin-like growth factor-I (IGF-I) are the key to correct diagnosis of acromegaly and GH deficiency. Unfortunately, there is much variation involved when these hormones are measured at different sites and using different assay methods. There is an ongoing global effort to standardize the measurement process to obtain more comparable results in the future. This review discusses common pitfalls in the measurement of GH and IGF-I and guides laboratories in their analyses of these hormones.

Octreotide long-acting repeatable for acromegaly

Acromegaly remains a therapeutic challenge for the endocrinologist. Among the available therapeutic options, octreotide long-acting repeatable (Sandostatin(®) LAR(®), Novartis) plays a chief role, both as a primary therapy and as an adjuvant treatment after unsuccessful surgery. A plethora of papers and a meta-analysis have demonstrated its efficacy in: control of clinical picture; achievement of safe growth hormone and normal age-matched IGF-I levels (both factors associated with restoration of normal life expectancy) in 60-70% of patients; control of tumor volume (with real shrinkage in over half of cases); and halt or reversal of most acromegaly-associated comorbidities. Treatment is well tolerated in most patients and can be safely prolonged for many years if required.