Molecular heterogeneity of human GH: from basic research to clinical implications

Interpreting growth hormone and IGF-I results using modern assays and reference ranges for the monitoring of treatment effectiveness in acromegaly

Standard treatment for acromegaly focuses on the achievement of target absolute levels of growth hormone (GH) and insulin-like growth factor (IGF-I). The appropriateness of these targets when measured using modern assay methods is not well defined. This paper reviews biochemical status assessed using methods available at the time and associated clinical outcomes. GH measurements were shown to provide an indication of changes in tumor size, and failure of GH suppression after glucose stimulation is associated with tumor recurrence. IGF-I levels were more closely associated with changes in symptoms and signs. Reduced GH and IGF-I concentrations were shown to be associated with increased longevity, although the degree of increase has only been analyzed for GH. Lowering of GH and IGF-I has consistently been associated with improved outcomes; however, absolute levels reported in previous studies were based on results from methods and reference ranges that are now obsolete. Applying previously described absolute thresholds as targets (e.g. "normal" IGF-I level) when using current methods is best applied to those with active acromegaly symptoms who could benefit from further lowering of biochemical markers. In asymptomatic individuals with mild IGF-I or GH elevations, targeting biochemical "normalization" would result in the need for combination pharmacotherapy in many patients without proven benefit. Measurement of both GH and IGF-I remains an essential component of diagnosis and monitoring the effectiveness of treatment in acromegaly; however, treatment goals based only on previously identified absolute thresholds are not appropriate without taking into account the assay and reference ranges being employed. Treatment goals should be individualized considering biochemical improvement from an untreated baseline, symptoms of disease, risks, burdens and costs of complex treatment regimens, comorbidities, and quality of life.

Lung proliferative lesion-promoting effects of left pulmonary ligation in A/J female mice

This present study was conducted in an attempt to examine proliferative lesion‐promoting effect in the lung by compensatory lung growth after left pulmonary ligation. To examine a strong proliferative lesion‐promoting effect in the lung, the effects of left pulmonary ligation on lung proliferative lesions induced by 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK) were examined for 12 weeks. The number of proliferative lesions induced by NNK in the right lung after left pulmonary ligation increased significantly after 12 weeks, indicated by an increase in the weight of the right lung. In addition, several messenger RNA (mRNA) markers, including insulin growth factor 1, were highly expressed in the right lung on the seventh day after left ligation. These experiments demonstrated the clear proliferative lesion‐promoting effects of pulmonary ligation on the induction of the expression of mRNAs related to the cell cycle, cell division and mitosis. However, the proliferative lesion‐promoting effects were not strong enough to allow a shortened experimental period for the establishment of the lung bioassay model. The results also indicated the necessity to pay attention to the possibility of a recurrence of lung cancer in the residual lung after resection in humans.

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.

Human Pituitary Adenoma Proteomics: New Progresses and Perspectives

Pituitary adenoma (PA) is a common intracranial neoplasm that impacts on human health through interfering hypothalamus-pituitary-target organ axis systems. The development of proteomics gives great promises in the clarification of molecular mechanisms of a PA and discovery of effective biomarkers for prediction, prevention, early-stage diagnosis, and treatment for a PA. A great progress in the field of PA proteomics has been made in the past 10 years, including (i) the use of laser-capture microdissection, (ii) proteomics analyses of functional PAs (such as prolactinoma), invasive and non-invasive non-functional pituitary adenomas (NFPAs), protein post-translational modifications such as phosphorylation and tyrosine nitration, NFPA heterogeneity, and hormone isoforms, (iii) the use of protein antibody array, (iv) serum proteomics and peptidomics, (v) the integration of proteomics and other omics data, and (vi) the proposal of multi-parameter systematic strategy for a PA. This review will summarize these progresses of proteomics in PAs, point out the existing drawbacks, propose the future research directions, and address the clinical relevance of PA proteomics data, in order to achieve our long-term goal that is use of proteomics to clarify molecular mechanisms, construct molecular networks, and discover effective biomarkers.

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.

Comparison of two immunoassays in the determination of IGF-I levels and its correlation with oral glucose tolerance test (OGTT) and with clinical symptoms in acromegalic patients

The aim of our study was to evaluate two different methodologies in IGF-I levels determination, its correlation with GH nadir in OGTT <1 and <0.4 ng/ml and with clinical symptoms in acromegalic patients. We analyzed 37 patients. Sixteen patients had not undergone any kind of treatment (Group 1). Twenty-one patients underwent surgery as primary treatment, and after that, some of them another kind of treatment (except pegvisomant) (Group 2). Serum IGF-I levels were measured by Immulite-1000 (IMM) and by an immunoradiometric assay (DSL) and, GH by immunochemiluminometric assay. IGF-I levels by IMM and by DSL showed a significant difference. When we analyzed in both groups the concordance by crosstabs-Kappa coefficients, between different parameters, GH nadir <1 and <0.4 ng/ml with IGF-I by DSL and IMM showed concordance in group 1, but in group 2 only GH nadir <1 and <0.4 ng/ml had a weak concordance with IGF-I by IMM. When we analyzed clinical symptoms in the patients and, GH nadir <1 and <0.4 ng/ml and IGF-I levels by both methodologies, more than 90% of clinically active patients had abnormal GH response or/and elevated IGF-I levels in group 1, but less than 70% in group 2. In the 8 patients under medical treatment, GH nadir was higher than 0.4 ng/ml in all patients, and IGF-I levels were elevated in 8/8 by DSL and in 6/8 by IMM. In conclusion, discrepant GH and IGF-I levels in the diagnosis and follow-up of patients with acromegaly requires consideration of many factors that influence these parameters.

O-Glycosylated 24 kDa human growth hormone has a mucin-like biantennary disialylated tetrasaccharide attached at Thr-60

MS was used to characterize the 24 kDa human growth hormone (hGH) glycoprotein isoform and determine the locus of O-linked oligosaccharide attachment, the oligosaccharide branching topology, and the monosaccharide sequence. MALDI-TOF/MS and ESI-MS/MS analyses of glycosylated 24 kDa hGH tryptic peptides showed that this hGH isoform is a product of the hGH normal gene. Analysis of the glycoprotein hydrolysate by high-performance anion-exchange chromatography with pulsed amperometric detection and HPLC with fluorescent detection for N-acetyl neuraminic acid (NeuAc) yielded the oligosaccharide composition (NeuAc(2), N-acetyl galactosamine(1), Gal(1)). After beta-elimination to release the oligosaccharide from glycosylated 24 kDa hGH, collision-induced dissociation of tryptic glycopeptide T6 indicated that there had been an O-linked oligosaccharide attached to Thr-60. The sequence and branching structure of the oligosaccharide were determined by ESI-MS/MS analysis of tryptic glycopeptide T6. The mucin-like O-oligosaccharide sequence linked to Thr-60 begins with N-acetyl galactosamine and branches in a bifurcated topology with one appendage consisting of galactose followed by NeuAc and the other consisting of a single NeuAc. The oligosaccharide moiety lies in the high-affinity binding site 1 structural epitope of hGH that interfaces with both the growth hormone and the prolactin receptors and is predicted to sterically affect receptor interactions and alter the biological actions of hGH.

Prevalence of discordant GH and IGF-I levels in acromegalics at diagnosis, after surgical treatment and during treatment with octreotide LAR

BACKGROUND

Acromegalic patients are considered "discordant" if their insulin-like growth factor type I (IGF-I) levels are increased for their age with "safe" growth hormone (GH) levels or if their IGF-I levels are normal for their age with "unsafe" GH levels. The prevalence of discordance in acromegalics has been described to vary from 9.4% to 39%, and it may be observed at diagnosis or during the follow up.

OBJECTIVE

To evaluate the prevalence of discordant levels of IGF-I and GH in our acromegalic population.

METHODS

Hormonal evaluation was made with an oral glucose tolerance test (OGTT) with the IGF-I being assessed in the basal sample at diagnosis and after 3 months of the adenomectomy. During treatment with octreotide LAR, a GH curve (for the calculation of mean GH) and IGF-I assessment were made every 3 months.

RESULTS

Among the 51 patients evaluated at diagnosis, the prevalence of discordance was 13.7% (7/51). Among the 58 patients evaluated after the surgical procedure, eight (13.8%) had discordant GH and IGF-I levels. Among the 42 patients evaluated during treatment with octreotide LAR, the prevalence of discordant GH and IGF-I levels was 33.3% (14/42). Using 1 microg/L as a cut off level for "safe" GH, the prevalence of discordance was 3.9%, 8.6% and 28.6% at diagnosis, after surgery and during treatment with octreotide LAR, respectively. No difference of sex, age or treatment modality was observed among discordant and concordant patients with any GH cut off level.

CONCLUSION

We observed a prevalence of discordance similar to that previously described in the literature. We believe that studies evaluating morbidity and mortality in discordant patients are also necessary and will enlighten the true impact of this condition in the follow up of acromegaly.

Abuse of growth hormone among young athletes

The underground abuse of growth hormone (GH) among young athletes presents a challenge to medical professionals. Health care professionals providing knowledgeable guidance regarding healthy ways to improve performance and appearance, as well as accurate information regarding substances' perceived benefits, risks, and unknown qualities, is invaluable to the young athlete. Further research focused on the profile and motivation of young people who use GH is essential to understanding and intervening better with those who use these substances.

Ensaios para a medida de hormônio do crescimento (GH) e IGF-I: aspectos metodológicos e suas implicações no diagnóstico e seguimento da acromegalia

A dosagem do GH no soro é essencial para confirmar ou excluir o seu excesso. Na acromegalia, a ausência de critérios clínicos suficientemente sensíveis para monitorizar o sucesso do tratamento faz com que o GH sérico seja o procedimento de escolha e, para isso, é essencial que a sua dosagem seja realizada de forma confiável, capaz de permitir interpretações uniformes. Vários critérios hormonais têm sido propostos para caracterizar remissão da acromegalia, incluindo níveis séricos de GH randômico inferior a 2,5 µg/l, nadir de GH durante o teste de tolerância oral a glicose inferior a 1,0 µg/l e IGF-I normal para sexo e idade. A importância do tratamento adequado consiste na possibilidade de reverter a mortalidade prematura da acromegalia através da diminuição dos níveis de GH para valores menores que 2,5 µg/l. Com o surgimento de ensaios ultra-sensíveis para medida do GH, tornaram-se necessários critérios mais estritos para determinar cura ou remissão da doença. Nesta revisão, descreveremos aqui as modificações decorrentes da evolução dos ensaios, as conseqüências nos resultados de GH e os pontos de corte propostos na literatura para caracterização da atividade e remissão da acromegalia.

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.

Separation of proteins with a molecular mass difference of 2 kDa utilizing preparative double-inverted gradient polyacrylamide gel electrophoresis under nonreducing conditions: Application to the isolation of 24 kDa human growth hormone

A method for separating proteins with a molecular mass difference of 2 kDa using SDS-PAGE under nonreducing conditions is presented. A sample mixture containing several human growth hormone (hGH) isoforms was initially separated on a weak anion-exchange column. Fractions rich in 24 kDa hGH as determined by analytical SDS-PAGE were pooled and further separated by cation-exchange chromatography. The fractions pooled from the cation-exchange chromatography contained two hGH isoforms with a 2 kDa molecular mass difference according to SDS-PAGE analysis, 22 and 24 kDa hGH. The 22 and 24 kDa hGH were separated using continuous-elution preparative double-inverted gradient PAGE (PDG-PAGE) under nonreducing conditions. The preparative electrophoresis gel was composed of three stacked tubular polyacrylamide matrices, a 4% stacking gel, a 13-18% linear gradient gel, and a 15-10% linear inverted gradient gel. Fractions containing purified 24 kDa hGH were pooled and Western blot analysis displayed immunoreactivity to antihGH antibodies. PDG-PAGE provides researchers with an electrophoretic technique to preparatively purify proteins under nonreducing conditions with molecular mass differences of 2 kDa.

Proteomics analysis of growth hormone isoforms in the human pituitary

In order to elucidate the roles of human growth hormone (hGH) in the normal (control) pituitary and in adenomas, the hGH isoforms in the human pituitary were analyzed with two-dimensional gel electrophoresis, immobilized metal affinity column (Ga(+3)) chromatography, mass spectrometry (MS), and bioinformatics. Twenty-four hGH-containing proteins, with significantly different expression proportions of their isoforms were found. The proportions of isoforms were as follows: isoform 1 (87.5%) > isoform 2 (8.1%) > isoform 3 (3.3%) > isoform 4 (1.1%). Deamidation of asparagine to aspartate was identified with matrix-assisted laser desorption/ionization-time of flight MS. Tandem mass spectrometry data demonstrated that hGH is a phosphoprotein (spot 6); phosphorylation was found at Ser-77 in the tryptic peptide (68)YSFLQNPQTSLCFSESIPTPSNR(90), at Ser-176 in the tryptic peptide (172)FDTNSHNDDALLK(184), and at Ser-132 in the peptide (126)SLVYGASDSNVYDLLK(141). The phosphorylation sites at Ser-77 and Ser-176 were consistent with computer-program predictions (NetPhos). These results provide novel clues for further studies of the functions, and mechanisms of action, of hGH in the human pituitary and in growth hormone-related diseases.

Extraordinarily stable disulfide-linked homodimer of human growth hormone

Although a 22-kDa human growth hormone (hGH) is the predicted protein product of the hGH-N gene, a pleiotropic collection of uncharacterized molecular weight and charge isoforms is also produced. Using chromatography and preparative SDS-PAGE under reducing conditions we isolated an unusually stable mercaptoethanol-resistant (MER) 45-kDa hGH. A 5-h incubation at 100 degrees C in the presence of 2-mercaptoethanol was required to convert approximately 90% of MER-45-kDa hGH into a 22-kDa hGH. Other reductants were not as effective in splitting MER-45-kDa hGH. After fracturing MER-45-kDa hGH, the 22-kDa hGH fragments would spontaneously reassociate if the reductant was removed; however, alkylation of cysteine residues prevented their reassociation. Identical amino acid sequences for the first six N-terminal residues were obtained for MER-45-kDa hGH and its 22-kDa hGH cleavage product. Structural identity of MER-45-kDa hGH and 22-kDa hGH was demonstrated by MALDI-TOF mass spectrometry of tryptic digests. MER-45-kDa hGH did not break up upon incubation with EDTA and EGTA. The significance of this work to our understanding of the structure of hGH isoforms is that it demonstrates that MER-45-kDa hGH is not a single chain polypeptide but is instead a homodimer of 22-kDa hGH monomers. The MER-45-kDa hGH dimer is held together by interchain disulfide bonds and not by divalent metal cation bridges. Additionally, MER-45-kDa hGH's interchain disulfide links are exceptionally resistant to reducing agents and thus confer extreme stability to the homodimer.

Diagnóstico e tratamento da acromegalia no Brasil

Acromegalia é uma doença debilitante e desfigurante que, se não controlada adequadamente, reduz a expectativa de vida do paciente. Complicações cardiovasculares e respiratórias representam as principais causas de morte nos acromegálicos. Atualmente, o diagnóstico é realizado de acordo com as diretrizes do consenso de 2000: ausência de supressão do GH para um valor <1ng/mL e IGF-1 elevado. Avanços em todas as modalidades terapêuticas têm ocorrido, propiciando o controle bioquímico da doença em um número cada vez maior de pacientes. Estudos prévios mostraram que a obtenção de níveis seguros de GH (GH médio <2,5ng/mL) e de IGF-1 normal reduz a taxa de mortalidade para o normal. Em 2002, foram publicadas diretrizes para o manejo da acromegalia, o qual envolve, muitas vezes, uma abordagem multidisciplinar. Neste artigo, fazemos uma avaliação crítica do que dispomos no Brasil para seguirmos as diretrizes estabelecidas nos consensos sobre diagnóstico e tratamento da acromegalia.