Variability in growth hormone stimulation tests

Response to growth hormone according to provocation test results in idiopathic short stature and idiopathic growth hormone deficiency

PURPOSE

To investigate growth response in children with either idiopathic short stature (ISS) or growth hormone (GH) deficiency (GHD).

METHODS

The data of prepubertal GHD or ISS children treated using recombinant human GH were obtained from the LG Growth Study database. GHD children were further divided into partial and complete GHD groups. Growth response and factors predicting growth response after 1 and 2 years of GH treatment were investigated.

RESULTS

This study included 692 children (98 with ISS, 443 partial GHD, and 151 complete GHD). After 1 year, changes in height standard deviation score (ΔHt-SDS) were 0.78, 0.83, and 0.96 in ISS, partial GHD, and complete GHD, respectively. Height velocity (HV) was 8.72, 9.04, and 9.52 cm/yr in ISS, partial GHD, and complete GHD, respectively. ΔHt-SDS and HV did not differ among the 3 groups. Higher initial body mass index standard deviation score (BMI-SDS) and midparental height standard deviation score (MPH-SDS) were predictors for better growth response after 1 year in ISS and the partial GHD group, respectively. In the complete GHD group, higher Ht-SDS and BMI-SDS predicted better growth response after 1 year. After 2 years of GH treatment, higher BMI-SDS and MPH-SDS predicted a better growth outcome in the partial GHD group, and higher MPH-SDS was a predictor of good growth response in complete GHD.

CONCLUSION

Clinical characteristics and growth response did not differ among groups. Predictors of growth response differed among the 3 groups, and even in the same group, a higher GH dose would be required when poor response is predicted.

GH Replacement in the Elderly: Is It Worth It?

Growth hormone (GH), once the age of linear growth is completed, continues to play a fundamental role for the human body. In adulthood, GH contributes to regulate muscle, cardiovascular and bone metabolism. The same happens in old age, although there is less data on the effect of GH in the elderly. Regardless the age of onset, a reduced quality of life (QoL), an increased cardiovascular risk and an accelerated age-related decline in physical strength have been demonstrated in the elderly with GH deficiency (EGHD). In adults with GH deficiency (AGHD), recent studies suggest a role of GH replacement therapy (GHrt) in improving lean/fat mass ratio, blood pressure, lipid profile, bone metabolism and QoL. Despite these recent studies, there is still a lack of randomized controlled trials proving these positive effects in EGHD. Moreover, the lack of a long-term positive outcome on mortality, and the cost of GHrt could often impact on treatment decision-making and lead to postpone or avoid the prescription. The aim of this mini-review is to summarize the available data on GHrt in EGHD, in order to highlight its weaknesses and strengths and to provide directions to clinicians that will help in the management of this specific set of patients.

Idiopathic Short Stature Phenotypes among Korean Children: Cluster Analysis

Idiopathic short stature (ISS) is a heterogeneous group and their responsiveness to growth hormone treatment varies among individuals. The aim of this study was to identify homogeneous phenotypes to better assess response before the initiation of treatment. We focused on person-centered approaches using a latent profile analysis. Clinical data of 218 children (127 boys and 91 girls) aged 4-15 years were obtained from the "LG Growth Study" which is a non-interventional Korean multicenter registry for growth hormone treatment. Growth hormone dose, first-year difference in height standard deviation score (Δheight SDS), mid-parental height SDS, and initial bone age were inputted into the model. The distribution of scatter plot was clearly distinguished at the chronological age of 8.83 years, Δheight SDS of 0.82 and mean GH dose of 0.36 mg/kg/week. The latent profile analysis revealed three distinct phenotypes names as follows: younger good responder (n = 56), older good responder (n = 111), and older poor responder (n = 51) groups. Despite more than twice the mean growth hormone dose, the older poor responder group showed the least improvement in the mean Δheight SDS. The pretreatment height velocity and peak growth hormone level were lower for the older poor responder group compared with those of the older good responder group. The statistically optimal cutoff point for predicting poor response was 3.41 cm/year for pretreatment height velocity and 9.18 ng/mL for peak growth hormone level. This study offers a new multidimensional approach to enable personalized growth hormone treatment optimization according to ISS phenotypes.

Analytical considerations and general diagnostic and therapeutic ramifications of milk hormones during lactation

In this review, we will discuss the changes that occur in the mammary gland from pregnancy to lactation and the issues surrounding the analysis of circulating and milk hormones during the stages of lactogenesis. There is a cascade of events that must occur to achieve milk synthesis, milk ejection, and successful transfer to the breastfeeding infant. The adequacy and success of this process is no small measure and the assessment of milk production, the hormones involved in this process and the ability to properly diagnose conditions and causes of low milk supply are critical for the health and well-being of the mother-infant breastfeeding dyad. The normative data that have been amassed in past decades suggest that there are certain values or circulating concentrations of milk hormones, that if lacking or low, could explain low milk supply status. Yet, in looking more closely at the tests themselves, the certainly of what constitutes "normal" can vary depending on the preanalytical conditions that the blood or milk sample were obtained, the methods used in obtaining circulating or milk concentrations, and the standardization of how that result is expressed. The standardization of these aspects of breast milk physiology are essential for providing important normative data to health care professionals and researchers and will result in more consistent findings across multi-disciplinary platforms.

Metabolic differences between short children with GH peak levels in the lower normal range and healthy children of normal height

OBJECTIVE

Severe growth hormone deficiency (GHD) leads to several metabolic effects in the body ranging from abnormal body composition to biochemical disturbances. However, less is known regarding these parameters in short children with GH peak levels in the lower normal range during provocation tests. Our aim was to study the metabolic profile of this group and compare it with that of healthy children of normal height.

DESIGN

Thirty-five pre-pubertal short children (<-2.5 SDS) aged between 7 and 10years, with peak levels of GH between 7 and 14μg/L in an arginine insulin tolerance test (AITT), were compared with twelve age- and sex-matched children of normal height. The metabolic profile of the subjects was analysed by blood samples, DEXA, frequently sampled intravenous glucose tolerance test, microdialysis and stable isotope examinations of rates of glucose production and lipolysis.

RESULTS

There were no overall significant metabolic differences between the groups. However, in the subgroup analysis, the short children with GH peaks <10μg/L had significantly lower fasting insulin levels which also correlated to other metabolic parameters.

CONCLUSION

The short pre-pubertal children with GH peak levels between 7 and 14μg/L did not differ significantly from healthy children of normal height but subpopulations within this group show significant metabolic differences.

Current practice in diagnosis and treatment of growth hormone deficiency in childhood: a survey from Turkey

OBJECTIVE

Approaches to diagnosis and treatment of growth hormone deficiency (GHD) in children vary among countries and even among centers in the same country. This survey, aiming to facilitate the process of preparing the new consensus on GHD by the Turkish Pediatric Endocrinology and Diabetes Society, was designed to evaluate the current practices in diagnosis and treatment of GHD in different centers in Turkey.

METHODS

A questionnaire covering relevant items for diagnosis and treatment of GHD was sent out to all pediatric endocrinology centers.

RESULTS

Twenty-four centers returned the questionnaire. The most frequently used GH stimulation test was L-dopa, followed by clonidine. Eighteen centers used a GH cut-off value of 10 ng/mL for the diagnosis of GHD; this value was 7 ng/mL in 4 centers and 5 ng/mL in 2 centers. The most frequently used assay was immunochemiluminescence for determination of GH, insulin-like growth factor-1 and insulin-like growth factor binding protein-3 concentrations. Sex steroid priming in both sexes was used by 19 centers. The most frequently used starting dose of recombinant human GH (rhGH) in prepubertal children was 0.025-0.030 mg/kg/day and 0.030-0.035 mg/kg/day in pubertal children. Growth velocity was used in the evaluation for growth response to rhGH therapy in all centers. Anthropometric measurements of patients every 3-6 months, fasting blood glucose, bone age and thyroid panel evaluation were used by all centers at follow-up. Main indications for cessation of therapy were decreased height velocity and advanced bone age. Fourteen centers used combined treatment (rhGH and gonadotropin-releasing analogues) to increase final height.

CONCLUSION

Although conformity was found among centers in Turkey in current practice, it is very important to update guideline statements and to modify, if needed, the approach to GHD over time in accordance with new evidence-based clinical studies.

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.

Macimorelin (AEZS-130)-stimulated growth hormone (GH) test: validation of a novel oral stimulation test for the diagnosis of adult GH deficiency

CONTEXT

In the absence of panhypopituitarism and low serum IGF-I levels, the diagnosis of adult GH deficiency (AGHD) requires confirmation with a GH stimulation test. Macimorelin is a novel, orally active ghrelin mimetic that stimulates GH secretion.

OBJECTIVE

The objective of the study was to determine the diagnostic efficacy and safety of macimorelin in AGHD.

DESIGN

This was a multicenter open-label study comparing the diagnostic accuracy of oral macimorelin with that of arginine+GHRH in AGHD patients and healthy, matched controls. After 43 AGHD patients and 10 controls were tested, the GHRH analog Geref Diagnostic [GHRH(1-29)NH2] became unavailable in the United States. The study was completed by testing 10 additional AGHD patients and 38 controls with macimorelin alone.

MAIN OUTCOME MEASURE

Peak GH area under the receiver operating characteristic curve after macimorelin was measured.

RESULTS

Fifty AGHD subjects and 48 controls were evaluated. Peak GH levels in AGHD patients and controls after macimorelin were 2.36 ± 5.69 and 17.71 ± 19.11 ng/mL, respectively (P < .0001). With macimorelin, the receiver operating characteristic analysis yielded an optimal GH cut point of 2.7 ng/mL, with 82% sensitivity, 92% specificity, and 13% misclassification rate. For subjects receiving both tests, macimorelin showed discrimination comparable with arginine+GHRH (area under the receiver operating characteristic curve 0.99 vs 0.94, respectively, P = .29). Obesity (body mass index > 30 kg/m(2)) was present in 58% of subjects, and peak GH levels were inversely associated with body mass index in controls (r = -0.37, P = .01). Using the separate cut points of 6.8 ng/mL for nonobese and 2.7 for obese subjects reduced the misclassification rate to 11%. Only 1 drug-related serious adverse event, an asymptomatic QT interval prolongation on the electrocardiogram, was reported.

CONCLUSION

Oral macimorelin is safe, convenient, and effective in diagnosing AGHD with accuracy comparable with the arginine+GHRH test.

Heat stress activates the Akt/mTOR signalling pathway in rat skeletal muscle

AIM

It is well known that various stimuli, such as mechanical stress and nutrients, induce muscle hypertrophy thorough the Akt/mTOR signalling pathway, which is a key mediator of protein synthesis and hypertrophy in skeletal muscle. It was recently reported that heat stress also induces an increase in muscle weight and muscle protein content. In addition, heat stress enhances Akt/mTOR signalling after one bout of resistance exercise. However, it remains unclear whether increased temperature itself stimulates the Akt/mTOR signalling pathway.

METHODS

Forty-two male Wistar rats (279.5 ± 1.2 g) were divided into a control group (CON) or one of five thermal stress groups at 37, 38, 39, 40 or 41 °C (n = 7 each group). After overnight fasting, both legs were immersed in different temperatures of hot water for 30 min under sodium pentobarbital anaesthesia. The soleus and plantaris muscles were immediately removed from both legs after the thermal stress.

RESULTS

The phosphorylation of mTOR or 4E-BP1 and heat shock protein (HSP) expression levels were similar among groups in both the soleus and plantaris muscles. However, Akt and p70S6K phosphorylation significantly increased at 41 °C in the soleus and plantaris muscles. Moreover, we observed a temperature-dependent increase in Akt and p70S6K phosphorylation in both muscles.

CONCLUSION

Our data indicate that the altered temperature increased phosphorylation in a temperature-dependent manner in rat skeletal muscle and may itself be a key stimulator of Akt/mTOR signalling.

The effect of in vivo growth hormone treatment on blood gene expression in adults with growth hormone deficiency reveals potential biomarkers to monitor growth hormone therapy

OBJECTIVE

Growth hormone (GH) replacement therapy is presently utilized in the treatment of adult GH deficiency (AGHD). Adult responses to GH treatment are highly variable and, apart from measurement of IGF-I, few tools are currently available for monitoring GH treatment progress. As GH receptors are expressed in certain blood cell types, changes in gene expression in peripheral blood can reflect perturbations induced as a result of GH therapy.

DESIGN/PATIENTS

We have carried out a pilot study to identify GH-responsive genes in blood, and have assessed the utility of GH-responsive genes in monitoring GH therapy in AGHD. Blood was collected from ten women diagnosed with AGHD syndrome both before and 4 weeks after initiation of GH substitutive therapy. RNA was extracted from peripheral blood mononuclear cells (PBMCs) and changes in response to GH were detected using microarray-based gene analysis.

RESULTS

All patients responded to GH replacement therapy, with serum levels of IGF-I increasing by an average of 307% (P = 0.0003) while IGFBP-3 increased by an average of 182% (P = 0.0002). Serum levels of triglycerides, LDL-C, HDL-C, APOA1 or APOB did not change after 1 month of GH treatment. By contrast, we detected an increase in Lp(a) serum levels (P = 0.0149). Using a stringent selection cutoff of P <or= 0.05, paired analysis identified a set of transcripts that correlated with GH administration. We applied the multivariate statistical technique PLS-DA to the changes in gene expression, demonstrating their utility in differentiating untreated patients and those undergoing GH replacement therapy.

CONCLUSION

This study shows that GH-dependent effects on gene expression in PBMCs can be detected by microarray-based gene analysis, and our results establish a foundation for the further exploration of peripheral blood as a surrogate to detect exposure to GH therapy.

Effect of hyperthermia and physical activity on circulating growth hormone

The aim of this study was to differentiate the effects of hyperthermia and physical activity on circulating growth hormone (GH) secretion. Nine healthy volunteer adults performed two 40 min exercise trials and two 50 min passive standing trials. The exercise was performed in either thermo-neutral (N-Ex: air temperature 18 °C, air humidity 40%, and wet bulb globe temperature (WBGT) 17.7 °C) or hot environmental conditions (H-Ex: air temperature 33 °C, air humidity 30%, and WBGT 34.6 °C). The passive exposure trials were also performed in either a comfortable (N-P: air temperature 18 °C, air humidity 40%, and WBGT 17.7 °C) or a hot climatic chamber (H-P: air temperature 40 °C, air humidity 100%, and WBGT 97.1 °C). Plasma GH, plasma volume (PV), tympanic temperature (Tty), and body mass loss (BML) were measured before and after each trial. The decrease in PV was significantly higher during H-Ex and H-P sessions than during N-Ex and N-P sessions. Comparisons showed significantly lower BML in the N-Ex session (1.5% ± 0.3%) than in the H-Ex and H-P sessions (2.1% ± 0.3% and 1.9% ± 0.2%, respectively) (p < 0.001). The rise in Tty was significantly higher during the H-P session (2.9 ± 0.4 °C) (p < 0.001) when compared with the other sessions. Plasma GH concentration increased significantly during all the trials, particularly during the H-Ex session (45 ± 7 ng·mL–1) (p < 0.01). Both exercise and heat exposure, separately, are sufficient to increase significantly the plasma GH concentration, and their combined effect induced a highly synergistic rise in GH.

Growth hormone status in morbidly obese subjects and correlation with body composition

Morbidly obese subjects are characterized by multiple endocrine abnormalities and these are paralleled by unfavorable changes in body composition. In obese individuals, either 24-h spontaneous or stimulated GH secretion is impaired without an organic pituitary disease and the severity of the secretory defect is proportional to the degree of obesity. The GHRH+arginine (GHRH+ARG) test is likely to be the overall test of choice in clinical practice to differentiate GH deficiency (GHD) patients. Similarly to other provocative tests, GHRH+ARG is influenced by obesity per se. Therefore, a new cut-off limit of peak GH response of 4.2 microg/l in obese subjects has been recently assumed. The aim of the present study was to investigate the reciprocal influence between decreased GH secretion and body composition in a group of 110 morbidly obese subjects, using the new cut-off limit of peak GH response to GHRH+ARG test for these subjects. In our study, GHD was identified in 27.3% of the obese subjects, without gender difference. In GDH obese subjects body mass index (BMI), waist circumference, waist-to-hip ratio (WHR), fat mass (FM), and resistance (R) were higher while reactance (Xc), phase angle, body cell mass (BCM), IGF-I, or IGF-I z-scores were lower than in normal responders (p<0.001). In all obese subjects, GH peak levels showed a negative correlation with age, BMI, waist circumference and FM, and a positive correlation with IGF-I. In the stepwise multiple linear regression, waist circumference and FM were the major determinants of GH peak levels and IGF-I. In conclusion, using the new cut-off limit of peak GH response to GHRH+ARG test for obese subjects, about 1/3 morbidly obese subjects were GHD. GHD subjects showed a significantly different body composition compared with normal responders, and the secretory defect was correlated to different anthropometric variables with waist circumference and FM as the major determinants.

Growth hormone response to arginine test distinguishes multiple system atrophy from Parkinson's disease and idiopathic late-onset cerebellar ataxia

OBJECTIVE

Multiple system atrophy (MSA) is difficult to distinguish from idiopathic Parkinson's disease (PD) and idiopathic late-onset cerebellar ataxia (ILOCA). This study aimed to evaluate GH response to three different GH stimulation tests in order to establish a reliable test to differentiate these degenerative disorders.

DESIGN

Twelve patients with MSA, 10 with PD, eight with ILOCA and 30 healthy controls entered the study. They were submitted to clonidine, arginine, and GH-releasing-hormone (GHRH) + arginine tests in a random manner on three different nonconsecutive days. The peak serum GH response was used as a primary variable for analysis of stimulation tests. By ROC analysis, the optimum cut-off level was considered as the cut-off with the maximal sum of sensitivity and specificity.

RESULTS

After clonidine administration, GH peak was significantly lower in patients with MSA than in those with ILOCA (P < 0.05) and in the controls (P < 0.001). At the optimum cut-off level of 5 mU/l, the clonidine test distinguished patients with MSA from those with PD with a sensitivity and specificity of 78%. Moreover, this test distinguished patients with MSA from those with ILOCA with a sensitivity of 100% and a specificity of 75% at a cut-off level of 5 mU/l, and with a sensitivity of 75% and a specificity of 100% at the cut-off level of 7.6 mU/l. After arginine administration, the GH peak was significantly lower in patients with MSA than in those with ILOCA (P = 0.001) and in controls (P < 0.001). At the optimum cut-off level of 5 mU/l, the arginine test distinguished patients with MSA from those with PD with a sensitivity and a specificity of 100%. At a GH peak cut-off value of 3.6 mU/l the arginine test distinguished patients with MSA from those with ILOCA with a sensitivity and specificity of 100%. After GHRH + arginine administration, a significant GH increase was found in all groups of patients and controls.

CONCLUSIONS

The GH response to arginine administration is impaired in MSA. Therefore, the arginine test showed the highest diagnostic accuracy to distinguish MSA from both PD and ILOCA, and could be used in the clinical practice of these neurodegenerative diseases.

Insulin-Like Growth Factor I Levels and the Diagnosis of Adult Growth Hormone Deficiency

The current guidelines state that, within the appropriate clinical context, the diagnosis of adult growth hormone (GH) deficiency must be made biochemically using provocative tests. Measurement of insulin-like growth factor I (IGF-I) and binding protein 3 (IGFBP-3) levels cannot always distinguish between healthy and GH-deficient individuals. In particular, IGFBP-3 as a marker of GH status is clearly less sensitive than IGF-I and there is general agreement that its measurement does not provide useful diagnostic information. However, the diagnostic value of measuring IGF-I levels has been revisited recently. It has been confirmed that normal IGF-I levels do not rule out severe GH deficiency (GHD) in adults, in whom the diagnosis has therefore to be based on the demonstration of severe impairment of the peak GH response to provocative tests. It has also been emphasized that very low IGF-I levels in patients with high suspicion of GHD could be considered to be definite evidence for severe GHD. This assumption particularly applies to patients with childhood-onset, severe GHD or with multiple hypopituitary deficiencies acquired in adulthood. In addition, the use of IGF-I levels to monitor the efficacy and adequacy of recombinant human GH replacement remains widely accepted.