Altered neuroregulation of GH secretion in viscerally obese premenopausal women

Once upon a time: the glucagon stimulation test in diagnosing adult GH deficiency

PURPOSE

The clinical features of adult GH deficiency (GHD) are nonspecific, and its diagnosis is established through GH stimulation testing, which is often complex, expensive, time-consuming and may be associated with adverse side effects. Moreover, diagnosing adult GHD can be challenging due to the influence of age, gender, and body mass index on GH peak at each test. The insulin tolerance test (ITT), GHRH + arginine test, glucagon stimulation test (GST), and, more recently, testing with macimorelin are all recognized as useful in diagnosing adult GHD. To date GST is still little used, but due to the unavailability of the GHRH all over the world and the high cost of macimorelin, in the next future it will probably become the most widely used test when ITT is contraindicated. The aim of the present review is to describe the current knowledge on GST.

METHODS

Narrative review.

RESULTS

In the last years several studies have suggested some changes in the original GST protocol and have questioned its diagnostic accuracy when the classic GH cut-point of 3 μg/L is used, suggesting to use a lower GH cut-point to improve its sensitivity and specificity in overweight/obese patients and in those with lower pretest GHD probability.

CONCLUSION

This document provides an update on the utility of GST, summarizes how to perform the test, shows which cut-points should be used in interpreting the results, and discusses its drawbacks and caveats referring to the most recent studies.

Anterior Pituitary Transcriptomics Following a High-Fat Diet: Impact of Oxidative Stress on Cell Metabolism

Anterior pituitary cell function requires a high level of protein synthesis and secretion which depend heavily on mitochondrial adenosine triphosphate production and functional endoplasmic reticula. Obesity adds stress to tissues, requiring them to adapt to inflammation and oxidative stress, and adding to their allostatic load. We hypothesized that pituitary function is vulnerable to the stress of obesity. Here, we utilized a 10- to 15-week high-fat diet (HFD, 60%) in a thermoneutral environment to promote obesity, testing both male and female FVB.129P mice. We quantified serum hormones and cytokines, characterized the metabolic phenotype, and defined changes in the pituitary transcriptome using single-cell RNA-sequencing analysis. Weight gain was significant by 3 weeks in HFD mice, and by 10 weeks all HFD groups had gained 20 g. HFD females (15 weeks) had increased energy expenditure and decreased activity. All HFD groups showed increases in serum leptin and decreases in adiponectin. HFD caused increased inflammatory markers: interleukin-6, resistin, monocyte chemoattractant protein-1, and tumor necrosis factorα. HFD males and females also had increased insulin and increased TSH, and HFD females had decreased serum prolactin and growth hormone pulse amplitude. Pituitary single-cell transcriptomics revealed modest or no changes in pituitary cell gene expression from HFD males after 10 or 15 weeks or from HFD females after 10 weeks. However, HFD females (15 weeks) showed significant numbers of differentially expressed genes in lactotropes and pituitary stem cells. Collectively, these studies reveal that pituitary cells from males appear to be more resilient to the oxidative stress of obesity than females and identify the most vulnerable pituitary cell populations in females.

Relationships between longitudinal changes in body composition and bone mineral density in middle-to-older aged Australians

There are limited longitudinal data regarding relationships between changes in body composition and bone mineral density (BMD). In 3671 participants aged 46-70 years at baseline, ∆lean mass was a stronger determinant than ∆fat mass of ∆BMD over 6 years. Maintained or increased lean mass may slow down age-related bone loss.

PURPOSE

There are limited longitudinal data regarding relationships between changes in body composition and bone mineral density (BMD) with ageing. We examined these in the Busselton Healthy Ageing Study.

METHODS

We studied 3671 participants (2019 females) aged 46-70 years at baseline with body composition and BMD assessments by dual-energy x-ray absorptiometry at baseline and after ~6 years. Relationships between changes in total body mass (∆TM), lean mass (∆LM) and fat mass (∆FM) with ∆BMD at total hip, femoral neck and lumbar spine were evaluated using restricted cubic spline modelling (accounting for baseline covariates) and mid-quartile least square means were compared.

RESULTS

∆TM was positively associated with ∆BMD of total hip and femoral neck in both sexes, and spine in females; in females but not males, associations plateaued at ∆TM above ~5kg for all sites. In females, ∆LM was positively associated with ∆BMD of all three sites with plateauing of the relationship at ∆LM above ~1kg. Women in the highest quartile of ∆LM (Q4, mid-quartile value +1.6 kg) had 0.019-0.028 g/cm2 less reduction in BMD than those in the lowest quartile (Q1, -2.1 kg). In males, ∆LM was positively associated with ∆BMD of total hip and femoral neck; men in Q4 (+1.6 kg) had 0.015 and 0.011 g/cm2 less bone loss, respectively, compared with Q1 (-2.7 kg). ∆FM was positively associated with ∆BMD of total hip only in both sexes.

CONCLUSION

∆LM is a stronger determinant than ∆FM of ∆BMD. Maintained or increased LM is associated with less age-related bone loss.

Growth Hormone Cut-Off Post Glucagon Stimulation Test in an Indian Cohort of Overweight/Obese Hypopituitary Patients for the Diagnosis of Adult Growth Hormone Deficiency

Obesity has been associated with reduced growth hormone (GH) secretion, which might lead to the over diagnosis of adult GH deficiency (GHD) in overweight (OW)/obese hypopituitary patients. Currently, there are no body mass index (BMI)-specific peak GH cut-offs for the glucagon stimulation test (GST) for assessing adult GHD in India, given the BMI cut-offs vary for Asians. The study's main objective was to determine a peak GH cut-off level for the diagnosis of adult GHD in overweight (OW)/obese individuals utilizing the GST. Forty OW/obese subjects were studied in two groups of 20 each. The first group included 20 OW/obese hypopituitary adults and the second group included 20 control subjects. The intervention consisted of a 3 h GST. The main outcome measured was the peak GH level on GST. The mean age of control subjects was lower (33.15 ± 7.67 v/s. 42.10 ± 13.70 years; P = 0.017) in comparison with hypopituitary adults. The mean BMI (27.93 ± 1.63 v/s. 25.81 ± 1.66 kg/m2; P < 0.001), mean IGF1 (272.81 ± 38.57 v/s. 163.75 ± 42.42; P < 0.001, and mean HOMA IR (11.8 ± 9.7 v/s. 6.02 ± 3.14; P = 0.02) was greater in OW/obese controls. The mean GH peak was significantly higher in control subjects (5.41 ± 3.59 ng/mL v/s. 1.49 ± 1.25 ng/mL; P < 0.001) compared to hypopituitary subjects. ROC curve analysis demonstrated a GH cut-off of 3.3 ng/mL with a moderate sensitivity of 70% and high specificity of 95%, with an AUC of 0.838 (P < 0.001; 95% confidence interval [CI] of 0.710-0.965) for the diagnosis of GHD in overweight/obese hypopituitary adults. This study demonstrates that a cut-off of 3.3 ng/mL would diagnose GHD in Indian overweight/obese hypopituitary adults.

IGF-1 is positively associated with BMI in patients with acromegaly

PURPOSE

Acromegaly is a disorder characterized by IGF-1 excess due to autonomous GH secretion. In individuals without acromegaly, IGF-1 is not only influenced by GH secretion but is also sensitive to other factors including nutritional status, as evidenced by the inverted U-shaped association between BMI and IGF-1; in low-weight individuals (BMI < 18.5 kg/m²) and those who are obese, IGF-1 levels may be frankly low. It is not known if this same relationship between BMI and IGF-1 is also observed in acromegaly.

METHODS

Retrospective study including patients who underwent resection of a pituitary adenoma (n = 197) for either acromegaly (n = 32) or a nonfunctioning adenoma (NFPA, n = 165) at a large academic medical center between 1/1/2015 and 5/31/2021.

RESULTS

Median BMI in acromegaly was 30.8 kg/m² (range 20.9-42.6 kg/m²). Percent upper limit of normal (%ULN) IGF-1 was 228.2% [159.0, 271.4] in acromegaly versus 32.2% [18.5, 50] in NFPA (p < 0.0001). There was a significant positive association between BMI and %ULN IGF-1 (R = 0.35, p < 0.05) in acromegaly. In contrast, there was no association between BMI and %ULN IGF-1 in the NFPA group as a whole (p = 0.22), but a significant inverse association between BMI and %ULN IGF-1 in NFPA patients with a BMI ≥ 35 kg/m² (rho =  - 0.39, p = 0.02).

CONCLUSION

In contrast to individuals without acromegaly, BMI is significantly and positively associated with IGF-1 in acromegaly across the weight spectrum. Future studies are needed to determine if obese patients with acromegaly experience more significant symptoms related to their disease, or if patients with a low BMI may require different diagnostic criteria.

Metabolic actions of the growth hormone-insulin growth factor-1 axis and its interaction with the central nervous system

The growth hormone/insulin growth factor-1 axis is a key endocrine system that exerts profound effects on metabolism by its actions on different peripheral tissues but also in the brain. Growth hormone together with insulin growth factor-1 perform metabolic adjustments, including regulation of food intake, energy expenditure, and glycemia. The dysregulation of this hepatic axis leads to different metabolic disorders including obesity, type 2 diabetes or liver disease. In this review, we discuss how the growth hormone/insulin growth factor-1 axis regulates metabolism and its interactions with the central nervous system. Finally, we state our vision for possible therapeutic uses of compounds based in the components of this hepatic axis.

The GH/IGF-1 Axis Is Associated With Intrahepatic Lipid Content and Hepatocellular Damage in Overweight/Obesity

CONTEXT

Obesity is a state of relative growth hormone (GH) deficiency, and GH has been identified as a candidate disease-modifying target in nonalcoholic fatty liver disease (NAFLD) because of its lipolytic and anti-inflammatory properties. However, the GH/IGF-1 axis has not been well characterized in NAFLD.

OBJECTIVE

We aimed to investigate serum GH and IGF-1 levels in relation to intrahepatic lipid content (IHL) and markers of hepatocellular damage and fibrosis in NAFLD.

METHODS

This cross-sectional study included 102 adults (43% women; age 19-67; BMI ≥ 25 kg/m2) without type 2 diabetes. IHL was measured by magnetic resonance spectroscopy; NAFLD was defined by ≥ 5% IHL. Peak-stimulated GH in response to GH releasing hormone and arginine was assessed as was serum IGF-1 (LC/MS).

RESULTS

There was no difference in mean age, BMI, or sex distribution in NAFLD vs controls. Mean (± SD) IHL was higher in NAFLD vs controls (21.8 ± 13.3% vs 2.9 ± 1.1%, P < 0.0001). Mean peak-stimulated GH was lower in NAFLD vs controls (9.0 ± 6.3 vs 15.4 ± 11.2 ng/mL, P = 0.003), including after controlling for age, sex, visceral adipose tissue, and fasting glucose. In a stepwise model, peak-stimulated GH predicted 14.6% of the variability in IHL (P = 0.004). Higher peak-stimulated GH was also associated with lower ALT. Higher serum IGF-1 levels were associated with lower risk of liver fibrosis by Fibrosis-4 scores.

CONCLUSION

Individuals with NAFLD have lower peak-stimulated GH levels but similar IGF-1 levels as compared to controls. Higher peak-stimulated GH levels are associated with lower IHL and less hepatocellular damage. Higher IGF-1 levels are associated with more favorable fibrosis risk scores. These data implicate GH and IGF-1 as potential disease modifiers in the development and progression of NAFLD.

Growth Hormone and Insulin-Like Growth Factor 1 Regulation of Nonalcoholic Fatty Liver Disease

Patients with obesity have a high prevalence of nonalcoholic fatty liver disease (NAFLD), representing a spectrum of simple steatosis to nonalcoholic steatohepatitis (NASH), without and with fibrosis. Understanding the etiology of NAFLD is clinically relevant since NAFLD is an independent risk factor for diabetes and cardiovascular disease. In addition, NASH predisposes patients to the development of cirrhosis and hepatocellular carcinoma, and NASH cirrhosis represents the fastest growing indication for liver transplantation in the United States. It is appreciated that multiple factors are involved in the development and progression of NAFLD. Growth hormone (GH) and insulin-like growth factor 1 (IGF1) regulate metabolic, immune, and hepatic stellate cell function, and alterations in the production and function of GH is associated with obesity and NAFLD/NASH. Therefore, this review will focus on the potential role of GH and IGF1 in the regulation of hepatic steatosis, inflammation, and fibrosis.

In premenopausal women with idiopathic osteoporosis, lower bone formation rate is associated with higher body fat and higher IGF-1

We examined serum IGF-1 in premenopausal IOP, finding relationships that were opposite to those expected: higher IGF-1 was associated with lower bone formation and higher body fat, and lower BMD response to teriparatide. These paradoxical relationships between serum IGF-1, bone, and fat may contribute to the mechanism of idiopathic osteoporosis in premenopausal women.

INTRODUCTION

Premenopausal women with idiopathic osteoporosis (IOP) have marked deficits in bone microarchitecture but variable bone remodeling. We previously reported that those with low tissue-level bone formation rate (BFR) are less responsive to teriparatide and have higher serum IGF-1, a hormone anabolic for osteoblasts and other tissues. The IGF-1 data were unexpected because IGF-1 is low in other forms of low turnover osteoporosis-leading us to hypothesize that IGF-1 relationships are paradoxical in IOP. This study aimed to determine whether IOP women with low BFR have higher IGF-1 and paradoxical IGF-1 relationships in skeletal and non-skeletal tissues, and whether IGF-1 and the related measures predict teriparatide response.

METHODS

This research is an ancillary study to a 24 month clinical trial of teriparatide for IOP. Baseline assessments were related to trial outcomes: BMD, bone remodeling.

SUBJECTS

 Premenopausal women with IOP(n = 34); bone remodeling status was defined by baseline cancellous BFR/BS on bone biopsy.

MEASURES

 Serum IGF-1 parameters, compartmental adiposity (DXA, CT, MRI), serum hormones, and cardiovascular-risk-markers related to fat distribution.

RESULTS

As seen in other populations, lower BFR was associated with higher body fat and poorer teriparatide response. However, in contrast to observations in other populations, low BFR, higher body fat, and poorer teriparatide response were all related to higher IGF-1: IGF-1 Z-score was inversely related to BFR at all bone surfaces (r =  - 0.39 to - 0.46; p < 0.05), directly related to central fat (p = 0.05) and leptin (p = 0.03). IGF-1 inversely related to 24 month hip BMD %change (r =  - 0.46; p = 0.01).

CONCLUSIONS

Paradoxical IGF-1 relationships suggest that abnormal or atypical regulation of bone and fat may contribute to osteoporosis mechanisms in premenopausal IOP.

Early overnutrition sensitizes the growth hormone axis to the impact of diet-induced obesity via sex-divergent mechanisms

In addition to its essential role in the physiological control of longitudinal growth, growth-hormone (GH) is endowed with relevant metabolic functions, including anabolic actions in muscle, lipolysis in adipose-tissue and glycemic modulation. Adult obesity is known to negatively impact GH-axis, thereby promoting a vicious circle that may contribute to the exacerbation of the metabolic complications of overweight. Yet, to what extent early-overnutrition sensitizes the somatotropic-axis to the deleterious effects of obesity remains largely unexplored. Using a rat-model of sequential exposure to obesogenic insults, namely postnatal-overfeeding during lactation and high-fat diet (HFD) after weaning, we evaluated in both sexes the individual and combined impact of these nutritional challenges upon key elements of the somatotropic-axis. While feeding HFD per se had a modest impact on the adult GH-axis, early overnutrition had durable effects on key elements of the somatotropic-system, which were sexually different, with a significant inhibition of pituitary gene expression of GH-releasing hormone-receptor (GHRH-R) and somatostatin receptor-5 (SST5) in males, but an increase in pituitary GHRH-R, SST2, SST5, GH secretagogue-receptor (GHS-R) and ghrelin expression in females. Notably, early-overnutrition sensitized the GH-axis to the deleterious impact of HFD, with a significant suppression of pituitary GH expression in both sexes and lowering of circulating GH levels in females. Yet, despite their similar metabolic perturbations, males and females displayed rather distinct alterations of key somatotropic-regulators/ mediators. Our data document a synergistic effect of postnatal-overnutrition on the detrimental impact of HFD-induced obesity on key elements of the adult GH-axis, which is conducted via mechanisms that are sexually-divergent.

Early versus late initiation of GH replacement in adult-onset hypopituitarism

INTRODUCTION

Adult-onset growth hormone deficiency (AGHD) is usually the last deficiency to be substituted in hypopituitarism. In children with documented GH deficiency, treatment without delay is crucial for achieving optimal effects on growth and development. In adults, it is not known whether a delay in treatment initiation influences biochemical response and the favourable physiological effects resulting from GH replacement therapy (GHRT).

METHODS

A total of 1085 GH-deficient adults from KIMS (Pfizer International Metabolic Database) were included, adequately replaced with all pituitary hormones except for GH at baseline. Patients were stratified by sex and age (20-50 years and ≥50 years) and subsequently divided into two groups below and above the median duration of unsubstituted AGHD for that subgroup. The median time of unsubstituted GHD for the total cohort was 2.53 years (P5 = 0.35, P95 = 24.42).

RESULTS

Beneficial effects of 4 years of GHRT were observed on lipids and quality of life in all subgroups. A decrease in waist circumference was observed only in older (>50 years) patients. There was no difference in IGF-I SDS and in GH dose required to normalize IGF-I in patients with a duration of unsubstituted AGHD above or below the median. No relevant differences were found between the groups for anthropometric measures, cardiovascular risk factors and quality of life scores.

CONCLUSION

In contrast to GHD in children and adolescents, no difference could be established in treatment response between early or late initiation of GHRT in AGHD in terms of required GH dose, IGF-I, metabolic health and quality of life.

Sitagliptin Decreases Visceral Fat and Blood Glucose in Women With Polycystic Ovarian Syndrome

CONTEXT

Women with polycystic ovarian syndrome (PCOS) have decreased growth hormone (GH), which can result in increased visceral adiposity (VAT) and impaired vascular function. GH-releasing hormone, a dipeptidyl peptidase-4 (DPP4) substrate, stimulates GH secretion.

OBJECTIVE

We tested the hypothesis that DPP4 inhibition increases GH and improves glucose levels and vascular function in women with PCOS.

METHODS

Eighteen women with PCOS participated in a double-blind, crossover study. They received sitagliptin either 100 mg or placebo daily for 1 month, with crossover treatments separated by an 8-week washout. During each treatment, women underwent a 75-gram oral glucose tolerance test (OGTT) and assessments of vascular function and body composition. Overnight GH secretion was assessed via venous sampling every 10 minutes for 12 hours and analyzed using an automated deconvolution algorithm.

RESULTS

During OGTT, sitagliptin increased glucagon-like peptide-1 (P < 0.001), early insulin secretion (from mean [± SD] insulinogenic index 1.9 ± 1.2 to 3.2 ± 3.1; P = 0.02), and decreased peak glucose (mean -17.2 mg/dL [95% CI, -27.7 to -6.6]; P < 0.01). At 1 month, sitagliptin decreased VAT (from 1141.9 ± 700.7 to 1055.1 ± 710.1 g; P = 0.02) but did not affect vascular function. Sitagliptin increased GH half-life (from 13.9 ± 3.6 to 17.0 ± 6.8 min, N = 16; P = 0.04) and interpulse interval (from 53.2 ± 20.0 to 77.3 ± 38.2 min, N = 16; P < 0.05) but did not increase mean overnight GH (P = 0.92 vs placebo).

CONCLUSIONS

Sitagliptin decreased the maximal glucose response to OGTT and VAT. Sitagliptin did not increase overnight GH but increased GH half-life and the interpulse interval.

CLINICAL TRIAL REGISTRATION

This study was registered at www.clinicaltrials.gov as NCT02122380 prior to enrollment of the first participant.

AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS AND AMERICAN COLLEGE OF ENDOCRINOLOGY GUIDELINES FOR MANAGEMENT OF GROWTH HORMONE DEFICIENCY IN ADULTS AND PATIENTS TRANSITIONING FROM PEDIATRIC TO ADULT CARE

Objective: The development of these guidelines is sponsored by the American Association of Clinical Endocrinologists (AACE) Board of Directors and American College of Endocrinology (ACE) Board of Trustees and adheres with published AACE protocols for the standardized production of clinical practice guidelines (CPG). Methods: Recommendations are based on diligent reviews of clinical evidence with transparent incorporation of subjective factors, according to established AACE/ACE guidelines for guidelines protocols. Results: The Executive Summary of this 2019 updated guideline contains 58 numbered recommendations: 12 are Grade A (21%), 19 are Grade B (33%), 21 are Grade C (36%), and 6 are Grade D (10%). These detailed, evidence-based recommendations allow for nuance-based clinical decision-making that addresses multiple aspects of real-world care of patients. The evidence base presented in the subsequent Appendix provides relevant supporting information for the Executive Summary recommendations. This update contains 357 citations of which 51 (14%) are evidence level (EL) 1 (strong), 168 (47%) are EL 2 (intermediate), 61 (17%) are EL 3 (weak), and 77 (22%) are EL 4 (no clinical evidence). Conclusion: This CPG is a practical tool that practicing endocrinologists and regulatory bodies can refer to regarding the identification, diagnosis, and treatment of adults and patients transitioning from pediatric to adult-care services with growth hormone deficiency (GHD). It provides guidelines on assessment, screening, diagnostic testing, and treatment recommendations for a range of individuals with various causes of adult GHD. The recommendations emphasize the importance of considering testing patients with a reasonable level of clinical suspicion of GHD using appropriate growth hormone (GH) cut-points for various GH-stimulation tests to accurately diagnose adult GHD, and to exercise caution interpreting serum GH and insulin-like growth factor-1 (IGF-1) levels, as various GH and IGF-1 assays are used to support treatment decisions. The intention to treat often requires sound clinical judgment and careful assessment of the benefits and risks specific to each individual patient. Unapproved uses of GH, long-term safety, and the current status of long-acting GH preparations are also discussed in this document. LAY ABSTRACT This updated guideline provides evidence-based recommendations regarding the identification, screening, assessment, diagnosis, and treatment for a range of individuals with various causes of adult growth-hormone deficiency (GHD) and patients with childhood-onset GHD transitioning to adult care. The update summarizes the most current knowledge about the accuracy of available GH-stimulation tests, safety of recombinant human GH (rhGH) replacement, unapproved uses of rhGH related to sports and aging, and new developments such as long-acting GH preparations that use a variety of technologies to prolong GH action. Recommendations offer a framework for physicians to manage patients with GHD effectively during transition to adult care and adulthood. Establishing a correct diagnosis is essential before consideration of replacement therapy with rhGH. Since the diagnosis of GHD in adults can be challenging, GH-stimulation tests are recommended based on individual patient circumstances and use of appropriate GH cut-points. Available GH-stimulation tests are discussed regarding variability, accuracy, reproducibility, safety, and contraindications, among other factors. The regimen for starting and maintaining rhGH treatment now uses individualized dose adjustments, which has improved effectiveness and reduced reported side effects, dependent on age, gender, body mass index, and various other individual characteristics. With careful dosing of rhGH replacement, many features of adult GHD are reversible and side effects of therapy can be minimized. Scientific studies have consistently shown rhGH therapy to be beneficial for adults with GHD, including improvements in body composition and quality of life, and have demonstrated the safety of short- and long-term rhGH replacement. Abbreviations: AACE = American Association of Clinical Endocrinologists; ACE = American College of Endocrinology; AHSG = alpha-2-HS-glycoprotein; AO-GHD = adult-onset growth hormone deficiency; ARG = arginine; BEL = best evidence level; BMD = bone mineral density; BMI = body mass index; CI = confidence interval; CO-GHD = childhood-onset growth hormone deficiency; CPG = clinical practice guideline; CRP = C-reactive protein; DM = diabetes mellitus; DXA = dual-energy X-ray absorptiometry; EL = evidence level; FDA = Food and Drug Administration; FD-GST = fixed-dose glucagon stimulation test; GeNeSIS = Genetics and Neuroendocrinology of Short Stature International Study; GH = growth hormone; GHD = growth hormone deficiency; GHRH = growth hormone-releasing hormone; GST = glucagon stimulation test; HDL = high-density lipoprotein; HypoCCS = Hypopituitary Control and Complications Study; IGF-1 = insulin-like growth factor-1; IGFBP = insulin-like growth factor-binding protein; IGHD = isolated growth hormone deficiency; ITT = insulin tolerance test; KIMS = Kabi International Metabolic Surveillance; LAGH = long-acting growth hormone; LDL = low-density lipoprotein; LIF = leukemia inhibitory factor; MPHD = multiple pituitary hormone deficiencies; MRI = magnetic resonance imaging; P-III-NP = procollagen type-III amino-terminal pro-peptide; PHD = pituitary hormone deficiencies; QoL = quality of life; rhGH = recombinant human growth hormone; ROC = receiver operating characteristic; RR = relative risk; SAH = subarachnoid hemorrhage; SDS = standard deviation score; SIR = standardized incidence ratio; SN = secondary neoplasms; T3 = triiodothyronine; TBI = traumatic brain injury; VDBP = vitamin D-binding protein; WADA = World Anti-Doping Agency; WB-GST = weight-based glucagon stimulation test.

Differences in Trabecular Plate and Rod Structure in Premenopausal Women Across the Weight Spectrum

CONTEXT

Premenopausal women with anorexia nervosa (AN) and obesity (OB) have elevated fracture risk. More plate-like and axially aligned trabecular bone, assessed by individual trabeculae segmentation (ITS), is associated with higher estimated bone strength. Trabecular plate and rod structure has not been reported across the weight spectrum.

OBJECTIVE

To investigate trabecular plate and rod structure in premenopausal women.

DESIGN

Cross-sectional study.

SETTING

Clinical research center.

PARTICIPANTS

A total of 105 women age 21 to 46 years: (i) women with AN (n = 46), (ii) eumenorrheic lean healthy controls (HCs) (n = 29), and (iii) eumenorrheic women with OB (n = 30).

MEASURES

Trabecular microarchitecture by ITS.

RESULTS

Mean age (±SD) was similar (28.9 ± 6.3 years) and body mass index differed (16.7 ± 1.8 vs 22.6 ± 1.4 vs 35.1 ± 3.3 kg/m2; P < 0.0001) across groups. Bone was less plate-like and axially aligned in AN (P ≤ 0.01) and did not differ between OB and HC. After controlling for weight, plate and axial bone volume fraction and plate number density were lower in OB vs HC; some were lower in OB than AN (P < 0.05). The relationship between weight and plate variables was quadratic (R = 0.39 to 0.70; P ≤ 0.0006) (i.e., positive associations were attenuated at high weight). Appendicular lean mass and IGF-1 levels were positively associated with plate variables (R = 0.27 to 0.67; P < 0.05). Amenorrhea was associated with lower radial plate variables than eumenorrhea in AN (P < 0.05).

CONCLUSIONS

In women with AN, trabecular bone is less plate-like. In women with OB, trabecular plates do not adapt to high weight. This is relevant because trabecular plates are associated with greater estimated bone strength. Higher muscle mass and IGF-1 levels may mitigate some of the adverse effects of low weight or excess adiposity on bone.

A framework for selection of blood-based biomarkers for geroscience-guided clinical trials: report from the TAME Biomarkers Workgroup

Recent advances indicate that biological aging is a potentially modifiable driver of late-life function and chronic disease and have led to the development of geroscience-guided therapeutic trials such as TAME (Targeting Aging with MEtformin). TAME is a proposed randomized clinical trial using metformin to affect molecular aging pathways to slow the incidence of age-related multi-morbidity and functional decline. In trials focusing on clinical end-points (e.g., disease diagnosis or death), biomarkers help show that the intervention is affecting the underlying aging biology before sufficient clinical events have accumulated to test the study hypothesis. Since there is no standard set of biomarkers of aging for clinical trials, an expert panel was convened and comprehensive literature reviews conducted to identify 258 initial candidate biomarkers of aging and age-related disease. Next selection criteria were derived and applied to refine this set emphasizing: (1) measurement reliability and feasibility; (2) relevance to aging; (3) robust and consistent ability to predict all-cause mortality, clinical and functional outcomes; and (4) responsiveness to intervention. Application of these selection criteria to the current literature resulted in a short list of blood-based biomarkers proposed for TAME: IL-6, TNFα-receptor I or II, CRP, GDF15, insulin, IGF1, cystatin C, NT-proBNP, and hemoglobin A1c. The present report provides a conceptual framework for the selection of blood-based biomarkers for use in geroscience-guided clinical trials. This work also revealed the scarcity of well-vetted biomarkers for human studies that reflect underlying biologic aging hallmarks, and the need to leverage proposed trials for future biomarker discovery and validation.

Effects of dietary restriction on adipose mass and biomarkers of healthy aging in human

In developing countries the rise of obesity and obesity-related metabolic disorders, such as cardiovascular diseases and type 2 diabetes, reflects the changes in lifestyle habits and wrong dietary choices. Dietary restriction (DR) regimens have been shown to extend health span and lifespan in many animal models including primates. Identifying biomarkers predictive of clinical benefits of treatment is one of the primary goals of precision medicine. To monitor the clinical outcomes of DR interventions in humans, several biomarkers are commonly adopted. However, a validated link between the behaviors of such biomarkers and DR effects is lacking at present time. Through a systematic analysis of human intervention studies, we evaluated the effect size of DR (i.e. calorie restriction, very low calorie diet, intermittent fasting, alternate day fasting) on health-related biomarkers. We found that DR is effective in reducing total and visceral adipose mass and improving inflammatory cytokines profile and adiponectin/leptin ratio. By analysing the levels of canonical biomarkers of healthy aging, we also validated the changes of insulin, IGF-1 and IGFBP-1,2 to monitor DR effects. Collectively, we developed a useful platform to evaluate the human responses to dietary regimens low in calories.

GH administration decreases subcutaneous abdominal adipocyte size in men with abdominal obesity

OBJECTIVE

To investigate the effects of short-term GH administration on abdominal subcutaneous adipocyte size and CT attenuation in men with abdominal obesity.

DESIGN

6-week, randomized, double-blind, placebo-controlled study of GH (starting dose 2μg/kg/d) vs placebo of 15 abdominally obese men (mean age: 34±6years; mean BMI: 37.7±6.1kg/m², mean IGF-1 SDS: -1.9±0.5) who underwent abdominal subcutaneous adipose tissue (SAT) aspirations to determine adipocyte size, CTs for body composition and measures of glucose tolerance at baseline and 6weeks. GH dosing was titrated to target IGF-1 levels in the upper normal age-appropriate range.

RESULTS

GH administration decreased subcutaneous abdominal adipocyte size compared to placebo. Adipocyte size was positively associated with 120-min glucose and HOMA-IR and inversely associated with peak-stimulated GH and CT attenuation. CT attenuation of SAT was inversely associated with 120-min glucose and HOMA-IR and increased following GH administration.

CONCLUSION

In men with abdominal obesity, subcutaneous abdominal adipocyte size is positively associated with measures of impaired glucose tolerance and administration of GH at doses that raise IGF-1 levels within the normal range, decreases abdominal subcutaneous adipocyte size, suggesting that GH administration improves the health of adipose tissue. Clinical trials number: NCT00131378.

A two-step deconvolution-analysis-informed population pharmacodynamic modeling approach for drugs targeting pulsatile endogenous compounds

Pharmacodynamic modeling of pulsatile endogenous compounds (e.g. growth hormone [GH]) is currently limited to the identification of a low number of pulses. Commonly used pharmacodynamic models are not able to capture the complexity of pulsatile secretion and therefore non-compartmental analyses are performed to extract summary statistics (mean, AUC, C_max). The aim of this study was to develop a new quantification method that deals with highly variable pulsatile data by using a deconvolution-analysis-informed population pharmacodynamic modeling approach. Pulse frequency and pulse times were obtained by deconvolution analysis of 24 h GH profiles. The estimated pulse times then informed a non-linear mixed effects population pharmacodynamic model in NONMEM V7.3. The population parameter estimates were used to perform simulations that show agonistic and antagonistic drug effects on the secretion of GH. Additionally, a clinical trial simulation shows the application of this method in the quantification of a hypothetical drug effect that inhibits GH secretion. The GH profiles were modeled using a turnover compartment in which the baseline secretion, k_out, pulse secretion width, amount at time point 0 and pulse amplitude were estimated as population parameters. Population parameters were estimated with low relative standard errors (ranging from 2 to 5%). Total body water (%) was identified as a covariate for pulse amplitude, baseline secretion and the pulse secretion width following a power relationship. Simulations visualized multiple gradients of a hypothetical drug that influenced the endogenous secretion of GH. The established model was able to fit and quantify the highly variable individual 24 h GH profiles over time. This pharmacodynamic model can be used to quantify drug effects that target other endogenous pulsatile compounds.

Benefits of resistance exercise in lean women with fibromyalgia: involvement of IGF-1 and leptin

Background

Chronic pain and fatigue improves by exercise in fibromyalgia (FM) but underlying mechanisms are not known. Obesity is increased among FM patients and associates with higher levels of pain. Symptom improvement after aerobic exercise is affected by body mass index (BMI) in FM. Metabolic factors such as insulin-like growth factor 1 (IGF-1) and leptin may be involved. In this study, the aim was to evaluate the role of metabolic factors in lean, overweight and obese women during resistance exercise, in relation to symptom severity and muscle strength in women with FM.

Methods

Forty-three women participated in supervised progressive resistance exercise, twice weekly for 15-weeks. Serum free and total IGF-1, IGF-binding protein 3 (IGFBP3), adiponectin, leptin and resistin were determined at baseline and after 15-weeks. Level of current pain was rated on a visual analogue scale (0–100 mm). Level of fatigue was rated by multidimensional fatigue inventory (MFI-20) subscale general fatigue (MFIGF). Knee extension force, elbow flexion force and handgrip force were assessed by dynamometers.

Results

Free IGF-1 (p = 0.047), IGFBP3 (p = 0.025) and leptin (p = 0.008) were significantly decreased in lean women (n = 18), but not in the overweight (n = 17) and the obese (n = 8). Lean women with FM benefited from resistance exercise with improvements in current pain (p= 0.039, n = 18), general fatigue (MFIGF, p = 0.022, n = 18) and improved elbow-flexion force (p = 0.017, n = 18). In overweight and obese women with FM there was no significant improvement in pain or fatigue but an improvement in elbow flexion (p = 0.049; p = 0.012) after 15 weeks of resistance exercise.

Conclusion

The clearest clinical response to resistance exercise was found in lean patients with FM. In these individuals, individualized resistance exercise was followed by changes in IGF-1 and leptin, reduced pain, fatigue and improved muscular strength. In overweight and obese women FM markers of metabolic signaling and clinical symptoms were unchanged, but strength was improved in the upper limb. Resistance exercise combined with dietary interventions might benefit patients with FM and overweight.

Trial registration

The trial was registered 21 of October 2010 with ClinicalTrials.gov identification number: NCT01226784.

The Association Between IGF-1 Levels and the Histologic Severity of Nonalcoholic Fatty Liver Disease

Objectives:

The mechanisms responsible for the development of nonalcoholic fatty liver disease (NAFLD) and progression to nonalcoholic steatohepatitis (NASH) are incompletely understood. Growing evidence suggests that growth hormone (GH) and insulin-like growth factor-1 (IGF-1) may have roles in the development and progression of NAFLD. We hypothesized that lower serum IGF-1 levels would be associated with increased liver fat accumulation, inflammation, and fibrosis in a group of meticulously phenotyped obese subjects with liver biopsies.

Methods:

A retrospective, cross-sectional study was performed at Massachusetts General Hospital, Boston, MA, USA and St. Mary's Hospital, Richmond, VA, USA. Liver biopsies were performed in 142 subjects during NAFLD work-up or bariatric surgery and were graded by a single, blinded pathologist. Main outcome measures included liver histology and serum IGF-1.

Results:

Mean age was 52±10 years and body mass index (BMI) was 43±9 kg/m². Mean serum IGF-1 was lower in subjects with lobular inflammation (112±47 vs. 136±57 ng/ml, P=0.01), hepatocyte ballooning (115±48 vs. 135±57 ng/ml, P=0.05), higher fibrosis stage (stage 2–4 vs. 0–1; 96±40 vs. 125±51 ng/ml, P=0.005), and NASH (109±45 vs. 136±57 ng/ml, P=0.002). All results remained significant after controlling for age, BMI, and a diagnosis of diabetes, and all but hepatocyte ballooning (trend, P=0.06) remained significant after excluding individuals with cirrhosis. Steatosis was not significantly associated with mean serum IGF-1 levels.

Conclusions:

Low serum IGF-1 levels are associated with increased histologic severity of NAFLD when rigorously controlled for age, BMI, the presence of diabetes, and after the exclusion of subjects with cirrhosis. Further investigation is warranted to determine the differential effects of GH and IGF-1 on the development and progression of NAFLD, which could further elucidate pathophysiology and identify therapeutic targets.

Diabetes and Bone Marrow Adiposity

PURPOSE OF REVIEW

This study aims to describe bone marrow fat changes in diabetes and to discuss the potential role of marrow fat in skeletal fragility.

RECENT FINDINGS

Advances in non-invasive imaging have facilitated marrow fat research in humans. In contrast to animal studies which clearly demonstrate higher levels of marrow fat in diabetes, human studies have shown smaller and less certain differences. Marrow fat has been reported to correlate with A1c, and there may be a distinct marrow lipid saturation profile in diabetes. Greater marrow fat is associated with impaired skeletal health. Marrow fat may be a mediator of skeletal fragility in diabetes. Circulating lipids, growth hormone alterations, visceral adiposity, and hypoleptinemia have been associated with greater marrow fat and may represent potential mechanisms for the putative effects of diabetes on marrow fat, although other factors likely contribute. Additional research is needed to further define the role of marrow fat in diabetic skeletal fragility and to determine whether marrow fat is a therapeutic target.

Multiple Effects of Growth Hormone in the Body: Is it Really the Hormone for Growth?

In this review, we analyze the effects of growth hormone on a number of tissues and organs and its putative role in the longitudinal growth of an organism. We conclude that the hormone plays a very important role in maintaining the homogeneity of tissues and organs during the normal development of the human body or after an injury. Its effects on growth do not seem to take place during the fetal period or during the early infancy and are mediated by insulin-like growth factor I (IGF-I) during childhood and puberty. In turn, IGF-I transcription is dependent on an adequate GH secretion, and in many tissues, it occurs independent of GH. We propose that GH may be a prohormone, rather than a hormone, since in many tissues and organs, it is proteolytically cleaved in a tissue-specific manner giving origin to shorter GH forms whose activity is still unknown.

What Can We Learn from Interventions That Change Fat Distribution?

Epidemiological studies have illustrated convincingly that fat distribution is associated with cardiometabolic risk. Fat deposition preferentially in the lower body, commonly seen in premenopausal women, is associated with lower risk, while central obesity in men and postmenopausal women is associated with higher risk. Studies of the physiology and the tissue and cellular characteristics of different adipose tissue depots, visceral and abdominal, gluteal, and femoral subcutaneous, corroborate this idea. In this report, we chose to focus on interventions-surgical, hormonal, lifestyle, and pharmacological-that directly or indirectly affect fat distribution, seeking further evidence for its pathophysiological significance.

Growth Hormone Dynamics in Healthy Adults Are Related to Age and Sex and Strongly Dependent on Body Mass Index

BACKGROUND

Studies on 24-hour growth hormone (GH) secretion are rare. The influences of sex, age, and adiposity are well recognized but generally derived from specific, selected subject groups, not spanning sexes, many age decades, and a range of body weights.

OBJECTIVE

Our goal was to investigate GH dynamics in a group of 130 healthy adult subjects, both men and women, across 5 age decades as well as a 2.5-fold range of body mass index (BMI) values.

METHODS

GH was measured by a sensitive immunofluorometric assay. Secretion parameters were quantified by automated deconvolution and relative pattern randomness by approximate entropy (ApEn).

RESULTS

The median age was 40 years (range 20-77). The median BMI was 26 (range 18.3-49.8). Pulsatile 24-hour GH secretion was negatively correlated with age (p = 0.002) and BMI (p < 0.0001). Basal GH secretion negatively correlated with BMI (p = 0.003) but not with age. The sex- dependent GH secretion (greater in women) was no longer detectable after 50 years of age. Insulin-like growth factor (IGF)-1 levels were lower in women over 50 years of age compared with men of a similar age. ApEn showed an age-related increase in both sexes and was higher in premenopausal and postmenopausal women than in men of comparable age (p < 0.0001). A single fasting GH measurement is not informative of 24-hour GH secretion.

CONCLUSIONS

BMI dominates the negative regulation of 24-hour GH secretion across 5 decades of age in this up till now largest cohort of healthy adults who underwent 24-hour blood sampling. Sex also impacts GH secretion before the age of 50 years as well as its regularity at all ages. Differences in serum IGF-1 partly depend on the pre- or postmenopausal state. Finally, a single GH measurement is not informative of 24-hour GH secretion.

Multipathway modulation of exercise and glucose stress effects upon GH secretion in healthy men

OBJECTIVE

Exercise evokes pulsatile GH release followed by autonegative feedback, whereas glucose suppresses GH release followed by rebound-like GH release (feedforward escape). Here we test the hypothesis that age, sex steroids, insulin, body composition and physical power jointly determine these dynamic GH responses.

METHODS

This was a prospectively randomized glucose-blinded study conducted in the Mayo Center for Advancing Translational Sciences in healthy men ages 19-77 years (N=23). Three conditions, fasting/rest/saline, fasting/exercise/saline and fasting/rest/iv glucose infusions, were used to drive GH dynamics during 10-min blood sampling for 6h. Linear correlation analysis was applied to relate peak/nadir GH dynamics to age, sex steroids, insulin, CT-estimated abdominal fat and physical power (work per unit time).

RESULTS

Compared with the fasting/rest/saline (control) day, fasting/exercise/saline infusion evoked peak GH within 1h, followed by negative feedback 3-5h later. The dynamic GH excursion was strongly (R(2)=0.634) influenced by (i) insulin negatively (P=0.011), (ii) power positively (P=0.0008), and (iii) E2 positively (P=0.001). Dynamic glucose-modulated GH release was determined by insulin negatively (P=0.0039) and power positively (P=0.0034) (R(2)=0.454). Under rest/saline, power (P=0.031) and total abdominal fat (P=0.012) (R(2)=0.267) were the dominant correlates of GH excursions.

CONCLUSION

In healthy men, dynamic GH perturbations induced by exercise and glucose are strongly related to physical power, insulin, estradiol, and body composition, thus suggesting a network of regulatory pathways.

Associations between body mass index, lean and fat body mass and bone mineral density in middle-aged Australians: The Busselton Healthy Ageing Study

Low BMI is a risk factor for osteoporosis, but it is not clear if relationships between BMI, lean mass (LM), fat mass (FM) and BMD are consistent across different levels of BMI. We studied 1929 Caucasian participants (1014 females) aged 45-66years in the Busselton Healthy Ageing Study in Western Australia. Body composition and BMD of total body, lumbar spine, total hip and femoral neck were measured using DXA. From generalized additive models, the positive relationships between BMI and BMD were weaker at high BMI, particularly at the spine and in males. In the entire cohort, adjusting for relevant covariates, LM and FM were significant predictors of all BMD measures in both genders. In men, analysis by tertiles of BMI showed that LM and FM (in kg) were positively associated with BMD (in mg/cm(2)) in tertile 1 except for LM and spine BMD (LM β: 5.18-6.80, FM β: 3.38-9.24, all P<0.05), but not in the middle or upper tertiles (LM β: -3.12-3.07, FM β: -4.75-1.82, P>0.05). In women, LM was positively associated with BMD in each tertile of BMI, except for spine BMD in the upper tertile, with regression coefficients lower in the upper tertile (β: 5.16-9.95, 5.76-9.56 and 2.80-5.78, respectively, all P<0.05). FM was positively associated with total body, spine and total hip BMD in women in BMI tertile 1 (β: 2.86-6.68, P<0.05); these associations were weaker or absent in the middle and upper tertiles. In conclusion, in middle-aged adults the positive relationships between lean or fat mass with BMD among those with higher BMI are absent in males and weaker in females.

Whole-body insulin sensitivity rather than body-mass-index determines fasting and post-glucose-load growth hormone concentrations

Background

Obese, non-acromegalic persons show lower growth hormone (GH) concentrations at fasting and reduced GH nadir during an oral glucose tolerance test (OGTT). However, this finding has never been studied with regard to whole-body insulin-sensitivity as a possible regulator.

Methods

In this retrospective analysis, non-acromegalic (NonACRO, n = 161) and acromegalic (ACRO, n = 35), non-diabetic subjects were subdivided into insulin-sensitive (IS) and –resistant (IR) groups according to the Clamp-like Index (CLIX)-threshold of 5 mg·kg⁻¹·min⁻¹ from the OGTT.

Results

Non-acromegalic IS (CLIX: 8.8±0.4 mg·kg⁻¹·min⁻¹) persons with similar age and sex distribution, but lower (p<0.001) body-mass-index (BMI = 25±0 kg/m², 84% females, 56±1 years) had 59% and 70%, respectively, higher (p<0.03) fasting GH and OGTT GH area under the curve concentrations than IR (CLIX: 3.5±0.1 mg·kg⁻¹·min⁻¹, p<0.001) subjects (BMI = 29±1 kg/m², 73% females, 58±1 years). When comparing on average overweight non-acromegalic IS and IR with similar anthropometry (IS: BMI: 27±0 kg/m², 82% females, 58±2 years; IR: BMI: 27±0 kg/m², 71% females, 60±1 years), but different CLIX (IS: 8.7±0.9 vs. IR: 3.8±0.1 mg·kg⁻¹·min⁻¹, p<0.001), the results remained almost the same. In addition, when adjusted for OGTT-mediated glucose rise, GH fall was less pronounced in IR. In contrast, in acromegalic subjects, no difference was found between IS and IR patients with regard to fasting and post-glucose-load GH concentrations.

Conclusions

Circulating GH concentrations at fasting and during the OGTT are lower in non-acromegalic insulin-resistant subjects. This study seems the first to demonstrate that insulin sensitivity rather than body-mass modulates fasting and post-glucose-load GH concentrations in non-diabetic non–acromegalic subjects.

The complex relationship between obesity and the somatropic axis: the long and winding road

Despite the considerable body of evidence pointing to a possible relationship between the state of the adipose tissue depots and regulation of the somatotropic axis, to date the relationship between obesity and low growth hormone (GH) status remains incompletely understood. The low GH status in obesity is mainly considered as a functional condition, largely reversible after a sustained weight loss. Moreover, due to the effects of the adiposity on the regulation of the somatotropic axis, the application of GH stimulation tests in obesity may also lead to an incorrect diagnosis of GH deficieny (GHD). On the other hand, similar to patients with GHD unrelated to obesity, the reduced GH response to stimulation testing in obese individuals is associated with increased prevalence of cardiovascular risk factors and detrimental alterations of body composition, which contribute to worsening their cardio-metabolic risk profile. In addition, the reduced GH secretion may result in reduced serum insulin-like growth factor (IGF)-1 levels, and the concordance of low peak GH and low IGF-1 identifies a subset of obese individuals with high cardiovascular risk. Furthermore, after weight loss, the normalization of the GH response and IGF-1 levels may or may not occur, and in patients undergoing bariatric surgery the persistence of a low GH status may affect the post-operative outcomes. In this review, we will provide an overview on some clinically relevant aspects of the relationship between obesity axis and the somatotropic axis in the light of the recently published research.

Overweight/Obese adults with pituitary disorders require lower peak growth hormone cutoff values on glucagon stimulation testing to avoid overdiagnosis of growth hormone deficiency

CONTEXT

Obesity is associated with diminished GH secretion, which may result in the overdiagnosis of adult GH deficiency (GHD) in overweight/obese pituitary patients. However, there are no body mass index (BMI)-specific peak GH cutoffs for the glucagon stimulation test (GST), the favored dynamic test for assessing adult GHD in the United States.

OBJECTIVE

The objective of the study was to determine a peak GH cutoff level for the diagnosis of adult GHD in overweight/obese individuals using the GST.

DESIGN

This was a retrospective, cross-sectional study.

SETTING

The study was conducted at Massachusetts General Hospital and Oregon Health and Science University.

METHODS

A total of 108 subjects with a BMI ≥ 25 kg/m(2) were studied: healthy controls (n = 47), subjects with total pituitary deficiency (TPD) (n = 20, ≥ 3 non-GH pituitary hormone deficiencies), and subjects with partial pituitary deficiency (PPD) (n = 41, 1-2 non-GH pituitary hormone deficiencies).

INTERVENTION

The intervention consisted of a standard 4-hour GST.

MAIN OUTCOME MEASURES

The main outcome measure was peak GH level on GST.

RESULTS

Using the standard peak GH cutoff of 3 ng/mL, 95% of TPD cases (19 of 20), 80% of PPD (33 of 41), and 45% of controls (21 of 47) were classified as GHD. In receiver-operator characteristic curve analysis (controls vs TPD), a peak GH value of 0.94 ng/mL provided the greatest sensitivity (90%) and specificity (94%). Using a peak GH cutoff of 1 ng/mL, 6% of controls (3 of 47), 59% of PPDs (24 of 41), and 90% of TPDs (18 of 20) were classified as GHD. BMI (R = -0.35, P = .02) and visceral adipose tissue (R = -0.32, P = .03) negatively correlated with peak GH levels in controls.

CONCLUSION

A large proportion of healthy overweight/obese individuals (45%) failed the GST using the standard 3 ng/mL GH cutoff. Overweight/obese pituitary patients are at risk of being misclassified as GHD using this cutoff level. A 1-ng/mL GH cutoff may reduce the overdiagnosis of adult GHD in overweight/obese patients.

Energy homeostasis targets chromosomal reconfiguration of the human GH1 locus

Levels of pituitary growth hormone (GH), a metabolic homeostatic factor with strong lipolytic activity, are decreased in obese individuals. GH declines prior to the onset of weight gain in response to excess caloric intake and hyperinsulinemia; however, the mechanism by which GH is reduced is not clear. We used transgenic mice expressing the human GH (hGH) gene, GH1, to assess the effect of high caloric intake on expression as well as the local chromosome structure of the intact GH1 locus. Animals exposed to 3 days of high caloric intake exhibited hyperinsulinemia without hyperglycemia and a decrease in both hGH synthesis and secretion, but no difference in endogenous production of murine GH. Efficient GH1 expression requires a long-range intrachromosomal interaction between remote enhancer sequences and the proximal promoter region through "looping" of intervening chromatin. High caloric intake disrupted this interaction and decreased both histone H3/H4 hyperacetylation and RNA polymerase II occupancy at the GH1 promoter. Incorporation of physical activity muted the effects of excess caloric intake on insulin levels, GH1 promoter hyperacetylation, chromosomal architecture, and expression. These results indicate that energy homeostasis alters postnatal hGH synthesis through dynamic changes in the 3-dimensional chromatin structure of the GH1 locus, including structures required for cell type specificity during development.

GH administration rescues fatty liver regeneration impairment by restoring GH/EGFR pathway deficiency

GH pathway has been shown to play a major role in liver regeneration through the control of epidermal growth factor receptor (EGFR) activation. This pathway is down-regulated in nonalcoholic fatty liver disease. Because regeneration is known to be impaired in fatty livers, we wondered whether a deregulation of the GH/EGFR pathway could explain this deficiency. Hepatic EGFR expression and triglyceride levels were quantified in liver biopsies of 32 obese patients with different degrees of steatosis. We showed a significant inverse correlation between liver EGFR expression and the level of hepatic steatosis. GH/EGFR down-regulation was also demonstrated in 2 steatosis mouse models, a genetic (ob/ob) and a methionine and choline-deficient diet mouse model, in correlation with liver regeneration defect. ob/ob mice exhibited a more severe liver regeneration defect after partial hepatectomy (PH) than methionine and choline-deficient diet-fed mice, a difference that could be explained by a decrease in signal transducer and activator of transcription 3 phosphorylation 32 hours after PH. Having checked that GH deficiency accounted for the GH signaling pathway down-regulation in the liver of ob/ob mice, we showed that GH administration in these mice led to a partial rescue in hepatocyte proliferation after PH associated with a concomitant restoration of liver EGFR expression and signal transducer and activator of trnascription 3 activation. In conclusion, we propose that the GH/EGFR pathway down-regulation is a general mechanism responsible for liver regeneration deficiency associated with steatosis, which could be partially rescued by GH administration.

Effects of growth hormone administration for 6 months on bone turnover and bone marrow fat in obese premenopausal women

PURPOSE

Abdominal adiposity is associated with low BMD and decreased growth hormone (GH) secretion, an important regulator of bone homeostasis. The purpose of our study was to determine the effects of a short course of GH on markers of bone turnover and bone marrow fat in premenopausal women with abdominal adiposity.

MATERIALS AND METHODS

In a 6-month, randomized, double-blind, placebo-controlled trial we studied 79 abdominally obese premenopausal women (21-45 y) who underwent daily sc injections of GH vs. placebo. Main outcome measures were body composition by DXA and CT, bone marrow fat by proton MR spectroscopy, P1NP, CTX, 25(OH)D, hsCRP, undercarboxylated osteocalcin (ucOC), preadipocyte factor 1 (Pref 1), apolipoprotein B (ApoB), and IGF-1.

RESULTS

GH increased IGF-1, P1NP, 25(OH)D, ucOC, bone marrow fat and lean mass, and decreased abdominal fat, hsCRP, and ApoB compared with placebo (p<0.05). There was a trend toward an increase in CTX and Pref-1. Among all participants, a 6-month increase in IGF-1 correlated with 6-month increase in P1NP (p=0.0005), suggesting that subjects with the greatest increases in IGF-1 experienced the greatest increases in bone formation. A six-month decrease in abdominal fat, hsCRP, and ApoB inversely predicted 6-month change in P1NP, and 6-month increase in lean mass and 25(OH)D positively predicted 6-month change in P1NP (p≤0.05), suggesting that subjects with greatest decreases in abdominal fat, inflammation and ApoB, and the greatest increases in lean mass and 25(OH)D experienced the greatest increases in bone formation. A six-month increase in bone marrow fat correlated with 6-month increase in P1NP (trend), suggesting that subjects with the greatest increases in bone formation experienced the greatest increases in bone marrow fat. Forward stepwise regression analysis indicated that increase in lean mass and decrease in abdominal fat were positive predictors of P1NP. When IGF-1 was added to the model, it became the only predictor of P1NP.

CONCLUSION

GH replacement in abdominally obese premenopausal women for 6 months increased bone turnover and bone marrow fat. Reductions in abdominal fat, and inflammation, and increases in IGF-1, lean mass and vitamin D were associated with increased bone formation. The increase in bone marrow fat may reflect changes in energy demand from increased bone turnover.

Discordance of IGF-1 and GH stimulation testing for altered GH secretion in obesity

OBJECTIVE

To investigate the concordance/discordance of IGF-1 and peak stimulated GH in identifying subjects with reduced GH secretion and to determine the physiological significance of any discordance in obese subjects.

DESIGN, PATIENTS AND METHODS

95 obese and 43 normal weight men and women underwent measurement of IGF-1 and GH stimulation testing with GH releasing hormone (GHRH)-arginine. Reduced IGF-1 and GH secretion were defined using pre-determined cut-points. Cardiovascular disease risk was determined by measuring carotid intima-media thickness (cIMT). In a second study, IGF-1 was measured in 52 obese men and women who underwent GH stimulation testing and overnight frequent blood sampling. The association of IGF-1 and peak stimulated GH with parameters of endogenous GH secretion was assessed.

RESULTS

60% of obese subjects had normal IGF-1 and peak stimulated GH while 8.4% of obese subjects had reduced IGF-1 and GH secretion. Discordance rate for IGF-1 and peak GH was 31.6%. Subjects with both low IGF-1 and low peak GH had the highest cIMT, while subjects with both normal IGF-1 and peak GH had the lowest cIMT. Subjects with reduction in either IGF-1 or peak GH, had intermediate cIMT (P=0.02). IGF-1 and peak stimulated GH were associated with maximum and mean overnight serum GH and GH AUC as well as maximum peak mass and median pulse mass. Peak stimulated GH, but not IGF-1, was also associated with nadir overnight serum GH concentration and basal GH secretion.

CONCLUSION

Peak stimulated GH and IGF-1 demonstrate significant discordance in identification of subjects with reduced GH secretion in obesity. Subjects with reduction of either IGF-1 or peak GH had higher cIMT compared to subjects with both normal IGF-1 and peak GH. Subjects with reductions in both IGF-1 and peak GH had the highest cIMT. Peak GH, compared to IGF-1, has broader associations with various parameters of endogenous GH secretion which support its utility in identifying those with reduced GH secretion.

The effects of tesamorelin on phosphocreatine recovery in obese subjects with reduced GH

CONTEXT

Few studies have assessed the relationship between GH and mitochondrial function.

OBJECTIVE

The objective of this study was to determine the effects of improving IGF-I using a GHRH analog, tesamorelin, on mitochondrial function assessed by phosphocreatine (PCr) recovery using (31)P magnetic resonance spectroscopy in obese adults with reduced GH.

DESIGN

A total of 39 obese men and women with reduced GH secretion as determined by GHRH-arginine stimulation tests underwent magnetic resonance spectroscopy as part of a 12-month, double-blind, randomized, placebo-controlled trial comparing tesamorelin vs placebo. PCr recovery after submaximal exercise was assessed at baseline and at 12 months.

RESULTS

At baseline, there were no differences in age, sex, race/ethnicity, and GH or PCr parameters between tesamorelin and placebo. After 12 months, tesamorelin treatment led to a significantly greater increase in IGF-I than did placebo treatment (change, 102.9±31.8 μg/L vs 22.8±8.9 μg/L, tesamorelin vs placebo; P=.02). We demonstrated a significant positive relationship between increases in IGF-I and improvements in PCr recovery represented as ViPCr (R=0.56; P=.01). The association between IGF-I and PCr recovery was even stronger among subjects treated with tesamorelin only (ViPCr: R=0.71; P=.03). This association remained significant after controlling for age, sex, race, ethnicity, and parameters of body composition and insulin sensitivity (all P<.05).

CONCLUSIONS

Increases in IGF-I from 12 months of treatment with tesamorelin were significantly associated with improvements in PCr recovery parameters in obese men and women with reduced GH secretion, suggestive of improvements in mitochondrial function.

Effects of GH on body composition and cardiovascular risk markers in young men with abdominal obesity

CONTEXT

Visceral adiposity is associated with increased cardiometabolic risk and decreased GH secretion.

OBJECTIVE

Our objective was to determine the effects of GH administration in abdominally obese young men on body composition, including liver fat, mitochondrial function, and cardiovascular (CV) risk markers.

DESIGN AND PARTICIPANTS

This was a 6-month, randomized, double-blind, placebo-controlled study with 62 abdominally obese men (IGF-1 below the mean, no exclusion based on GH level), 21 to 45 years of age.

MAIN OUTCOME MEASURES

We evaluated abdominal fat depots, thigh muscle and fat (computed tomography), fat and lean mass (dual-energy x-ray absorptiometry), intramyocellular and intrahepatic lipids (proton magnetic resonance spectroscopy), mitochondrial function (dynamic phosphorous magnetic resonance spectroscopy), CV risk markers, carotid intimal-medial thickness, and endothelial function.

RESULTS

GH administration resulted in a mean IGF-1 SD score increase from -1.9 ± 0.08 to -0.2 ± 0.3 in the GH group and a decrease in visceral adipose tissue (VAT), VAT/sc adipose tissue, trunk/extremity fat, intrahepatic lipids, high-sensitivity C-reactive protein and apolipoprotein B/low-density lipoprotein vs placebo after controlling for the increase in weight observed in both groups. There were inverse associations between change in IGF-1 levels and change in VAT, VAT/sc adipose tissue, trunk fat, trunk/extremity fat, high-sensitivity C-reactive protein, and apolipoprotein B. Mitochondrial function improved in the GH group compared with placebo after controlling for change in glucose. There was no change in thigh fat, muscle mass, intramyocellular lipids, cholesterol, fibrinogen, intimal-medial thickness, or endothelial function. There was no increase in fasting glucose or hemoglobin A1c in the GH vs placebo group, although glucose during the 2-hour oral glucose tolerance test increased slightly.

CONCLUSION

GH replacement in abdominally obese men improves body composition, including liver fat, mitochondrial function, and markers of CV risk. Although fasting glucose was unchanged, a slight increase in 2-hour glucose during an oral glucose tolerance test was noted.

Approach to testing growth hormone (GH) secretion in obese subjects

Identification of adults with GH deficiency (GHD) is challenging because clinical features of adult GHD are not distinctive and because clinical suspicion must be confirmed by biochemical tests. Adults are selected for testing for adult GHD if they have a high pretest probability of GHD, ie, if they have hypothalamic-pituitary disease, if they have received cranial irradiation or central nervous system tumor treatment, or if they survived traumatic brain injury or subarachnoid hemorrhage. Testing should only be carried out if a decision has already been made that if deficiency is found it will be treated. There are many pharmacological GH stimulation tests for the diagnosis of GHD; however, none fulfill the requirements for an ideal test having high discriminatory power; being reproducible, safe, convenient, and economical; and not being dependent on confounding factors such as age, gender, nutritional status, and in particular obesity. In obesity, GH secretion is reduced, GH clearance is enhanced, and stimulated GH secretion is reduced, causing a false-positive result. This functional hyposomatotropism in obesity is fully reversed by weight loss. In conclusion, GH stimulation tests should be avoided in obese subjects with very low pretest probability.

Exercise and obesity in fibromyalgia: beneficial roles of IGF-1 and resistin?

Introduction

Severe fatigue is a major health problem in fibromyalgia (FM). Obesity is common in FM, but the influence of adipokines and growth factors is not clear. The aim was to examine effects of exercise on fatigue, in lean, overweight and obese FM patients.

Methods

In a longitudinal study, 48 FM patients (median 52 years) exercised for 15 weeks. Nine patients were lean (body mass index, BMI 18.5 to 24.9), 26 overweight (BMI 25 to 29.9) and 13 obese. Fatigue was rated on a 0 to 100 mm scale (fibromyalgia impact questionnaire [FIQ] fatigue) and multidimensional fatigue inventory (MFI-20) general fatigue (MFIGF). Higher levels in FIQ fatigue and MFIGF indicate greater degree of fatigue. Free and total IGF-1, neuropeptides, adipokines were determined in serum and cerebrospinal fluid (CSF).

Results

Baseline FIQ fatigue correlated negatively with serum leptin (r = -0.345; P = 0.016) and nerve growth factor (NGF; r = -0.412; P = 0.037). In lean patients, baseline MFIGF associated negatively with serum resistin (r = -0.694; P = 0.038). FIQ Fatigue associated negatively with CSF resistin (r = -0.365; P = 0.073). Similarly, FIQ fatigue (r = -0.444; P = 0.026) and MFIGF correlated negatively with CSF adiponectin (r = -0.508; P = 0.01). In lean patients, FIQ fatigue (P = 0.046) decreased after 15 weeks. After 30 weeks, MFIGF decreased significantly in lean (MFIGF: P = 0.017), overweight (MFIGF: P = 0.001), and obese patients (MFIGF: P = 0.016). After 15 weeks, total IGF-1 increased in lean (P = 0.043) patients. ∆Total IGF-1 differed significantly between lean and obese patients (P = 0.010). ∆Total IGF-1 related negatively with ∆MFIGF after 15 weeks (r = -0.329; P = 0.050). After 30 weeks, ∆FIQ fatigue negatively correlated with ∆NGF (r = -0.463; P = 0.034) and positively with ∆neuropeptide Y (NPY) (r = 0.469; P = 0.032). Resistin increased after 30 weeks (P = 0.034). ∆MFIGF correlated negatively with ∆resistin (r = -0.346; P = 0.031), being strongest in obese patients (r = -0.815; P = 0.007). In obese patients, ∆FIQ fatigue after 30 weeks correlated negatively with ∆free IGF-1 (r = -0.711; P = 0.032).

Conclusions

Exercise reduced fatigue in all FM patients, this effect was achieved earlier in lean patients. Baseline levels of resistin in both serum and CSF associated negatively with fatigue. Resistin was increased after the exercise period which correlated with decreased fatigue. Changes in IGF-1 indicate similar long-term effects in obese patients. This study shows reduced fatigue after moderate exercise in FM and indicates the involvement of IGF-1 and resistin in these beneficial effects.

Trial registration

ClinicalTrials.gov: NCT00643006

Pathophysiology of human visceral obesity: an update

Excess intra-abdominal adipose tissue accumulation, often termed visceral obesity, is part of a phenotype including dysfunctional subcutaneous adipose tissue expansion and ectopic triglyceride storage closely related to clustering cardiometabolic risk factors. Hypertriglyceridemia; increased free fatty acid availability; adipose tissue release of proinflammatory cytokines; liver insulin resistance and inflammation; increased liver VLDL synthesis and secretion; reduced clearance of triglyceride-rich lipoproteins; presence of small, dense LDL particles; and reduced HDL cholesterol levels are among the many metabolic alterations closely related to this condition. Age, gender, genetics, and ethnicity are broad etiological factors contributing to variation in visceral adipose tissue accumulation. Specific mechanisms responsible for proportionally increased visceral fat storage when facing positive energy balance and weight gain may involve sex hormones, local cortisol production in abdominal adipose tissues, endocannabinoids, growth hormone, and dietary fructose. Physiological characteristics of abdominal adipose tissues such as adipocyte size and number, lipolytic responsiveness, lipid storage capacity, and inflammatory cytokine production are significant correlates and even possible determinants of the increased cardiometabolic risk associated with visceral obesity. Thiazolidinediones, estrogen replacement in postmenopausal women, and testosterone replacement in androgen-deficient men have been shown to favorably modulate body fat distribution and cardiometabolic risk to various degrees. However, some of these therapies must now be considered in the context of their serious side effects. Lifestyle interventions leading to weight loss generally induce preferential mobilization of visceral fat. In clinical practice, measuring waist circumference in addition to the body mass index could be helpful for the identification and management of a subgroup of overweight or obese patients at high cardiometabolic risk.

Metabolic effects of a growth hormone-releasing factor in obese subjects with reduced growth hormone secretion: a randomized controlled trial

CONTEXT

Obesity is associated with reduced GH secretion and increased cardiovascular disease risk.

OBJECTIVE

We performed this study to determine the effects of augmenting endogenous GH secretion on body composition and cardiovascular disease risk indices in obese subjects with reduced GH secretion.

DESIGN, PATIENTS AND METHODS

A randomized, double-blind, placebo-controlled study was performed involving 60 abdominally obese subjects with reduced GH secretion. Subjects received tesamorelin, a GHRH(1-44) analog, 2 mg once daily, or placebo for 12 months. Abdominal visceral adipose tissue (VAT) was assessed by abdominal computed tomography scan, and carotid intima-media thickness (cIMT) was assessed by ultrasound. Treatment effect was determined by longitudinal linear mixed-effects modeling.

RESULTS

VAT [-16 ± 9 vs.19 ± 9 cm(2), tesamorelin vs. placebo; treatment effect (95% confidence interval): -35 (-58, -12) cm(2); P = 0.003], cIMT (-0.03 ± 0.01 vs. 0.01 ± 0.01 mm; -0.04 (-0.07, -0.01) mm; P = 0.02), log C-reactive protein (-0.17 ± 0.04 vs. -0.03 ± 0.05 mg/liter; -0.15 (-0.30, -0.01) mg/liter, P = 0.04), and triglycerides (-26 ± 16 vs. 12 ± 8 mg/dl; -37 (-67, -7) mg/dl; P = 0.02) improved significantly in the tesamorelin group vs. placebo. No significant effects on abdominal sc adipose tissue (-6 ± 6 vs. 3 ± 11 cm(2); -10 (-32, +13) cm(2); P = 0.40) were seen. IGF-I increased (86 ± 21 vs. -6 ± 8 μg/liter; 92 (+52, +132) μg/liter; P < 0.0001). No changes in fasting, 2-h glucose, or glycated hemoglobin were seen. There were no serious adverse events or differences in adverse events between the groups.

CONCLUSION

Among obese subjects with relative reductions in GH, tesamorelin selectively reduces VAT without significant effects on sc adipose tissue and improves triglycerides, C-reactive protein, and cIMT, without aggravating glucose.

Body composition and skeletal health: too heavy? Too thin?

The relationship between body composition and skeletal metabolism has received growing recognition. Low body weight is an established risk factor for fracture. The effect of obesity on skeletal health is less well defined. Extensive studies in patients with anorexia nervosa and obesity have illuminated many of the underlying biologic mechanisms by which body composition modulates bone mass. This review examines the relationship between body composition and bone mass through data from recent research studies throughout the weight spectrum ranging from anorexia nervosa to obesity.

Negative regulation of human growth hormone gene expression by insulin is dependent on hypoxia-inducible factor binding in primary non-tumor pituitary cells

Insulin controls growth hormone (GH) production at multiple levels, including via a direct effect on pituitary somatotrophs. There are no data, however, on the regulation of the intact human (h) GH gene (hGH1) by insulin in non-tumor pituitary cells, but the proximal promoter region (nucleotides -496/+1) responds negatively to insulin in transfected pituitary tumor cells. A DNA-protein interaction was also induced by insulin at nucleotides -308/-235. Here, we confirmed the presence of a hypoxia-inducible factor 1 (HIF-1) binding site within these sequences (-264/-259) and investigated whether HIF-1 is associated with insulin regulation of "endogenous" hGH1. In the absence of primary human pituitary cells, transgenic mice expressing the intact hGH locus in a somatotroph-specific manner were generated. A significant and dose-dependent decrease in hGH and mouse GH RNA levels was detected in primary pituitary cell cultures from these mice with insulin treatment. Increasing HIF-1α availability with a hypoxia mimetic significantly decreased hGH RNA levels and was accompanied by recruitment of HIF-1α to the hGH1 promoter in situ as seen with insulin. Both inhibition of HIF-1 DNA binding by echinomycin and RNA interference of HIF-1α synthesis blunted the negative effect of insulin on hGH1 but not mGH. The insulin response is also sensitive to histone deacetylase inhibition/trichostatin A and associated with a decrease in H3/H4 hyperacetylation in the proximal hGH1 promoter region. These data are consistent with HIF-1-dependent down-regulation of hGH1 by insulin via chromatin remodeling specifically in the proximal promoter region.

The association of macro- and micronutrient intake with growth hormone secretion

CONTEXT

Growth hormone (GH) is known to be nutritionally regulated, but the effect of dietary composition on detailed GH secretion parameters has not previously been comprehensively evaluated.

OBJECTIVE

The objective of the study was to determine whether specific macro- and micronutrients are associated with discrete parameters of GH secretion among subjects with wide ranges of body mass index.

DESIGN

Detailed macro- and micronutrient intake was assessed by 4-day food records while GH secretion was assessed by standard stimulation testing in 108 men and women in one study (Study 1), and by overnight frequent blood sampling in 12 men in another study (Study 2).

RESULTS

Peak stimulated GH was positively associated with vitamin C (r=+0.29; P=0.003), dietary fiber (r=+0.27; P=0.004), arachidic acid (r=+0.25; P=0.008), and behenic acid (r=+0.30; P=0.002) intake in univariate analysis. Controlling for age, gender, race/ethnicity, visceral fat, HOMA-IR, total caloric intake and these four dietary factors in step-wise multivariate modeling, peak GH remained significantly associated with vitamin C and visceral fat (both P<0.05). In addition, vitamin C intake was associated with various parameters of endogenous GH secretion including basal GH secretion (r=+0.95; P<0.0001), GH half-life (r=+.75; P=0.005), total GH production (r=+0.76; P=0.004), GH area-under-the-curve (r=+0.89; P=0.0001), mean log(10) GH pulse area (r=+0.67; P=0.02), and overnight maximum (r=+0.62; P=0.03), nadir (r=+0.97; P<0.0001), and mean GH secretion (r=+0.89; P=0.0001).

CONCLUSIONS

These results suggest that certain micronutrients such as vitamin C intake are strongly and uniquely associated with stimulated and endogenous spontaneous GH secretion.

Effects of GH in women with abdominal adiposity: a 6-month randomized, double-blind, placebo-controlled trial

OBJECTIVE

Abdominal adiposity is associated with increased cardiovascular risk and decreased GH secretion. The objective of our study was to determine the effects of GH on body composition and cardiovascular risk markers in abdominally obese women.

MATERIALS AND METHODS

In this randomized, double-blind, placebo-controlled study, 79 obese premenopausal women received GH vs placebo for 6 months. Primary endpoints were i) total abdominal (total abdominal adipose tissue, TAT) fat by computed tomography (CT) (body composition) and ii) high-sensitivity C-reactive protein (hsCRP) (cardiovascular risk marker). Body composition was assessed by CT, dual-energy X-ray absorptiometry, and proton MR spectroscopy. Serum cardiovascular risk markers, carotid intima-media thickness, and endothelial function were measured.

RESULTS

Mean 6-month GH dose was 1.7±0.1 mg/day, resulting in a mean IGF1 SDS increase from -1.7±0.08 to -0.1±0.3 in the GH group. GH administration decreased TAT and hsCRP compared with placebo. In addition, it increased thigh muscle mass and lean body mass and decreased subcutaneous abdominal and trunk fat, tissue plasminogen activator, apoB, and apoB/low-density lipoprotein compared with placebo. Visceral adipose tissue (VAT) decreased and intramyocellular lipid increased within the GH group. Six-month change in IGF1 levels was negatively associated with 6-month decrease in TAT and VAT. One subject had a 2 h glucose >200 mg/ml at 3 months; four subjects, three of whom were randomized to GH, had 2 h glucose levels >200 mg/ml at the end of the study.

CONCLUSION

GH administration in abdominally obese premenopausal women exerts beneficial effects on body composition and cardiovascular risk markers but is associated with a decrease in glucose tolerance in a minority of women.

Does the pituitary somatotrope play a primary role in regulating GH output in metabolic extremes?

Circulating growth hormone (GH) levels rise in response to nutrient deprivation and fall in states of nutrient excess. Because GH regulates carbohydrate, lipid, and protein metabolism, defining the mechanisms by which changes in metabolism alter GH secretion will aid in our understanding of the cause, progression, and treatment of metabolic diseases. This review will summarize what is currently known regarding the impact of systemic metabolic signals on GH-axis function. In addition, ongoing studies using the Cre/loxP system to generate mouse models with selective somatotrope resistance to metabolic signals will be discussed, where these models will serve to enhance our understanding of the specific role the somatotrope plays in sensing the metabolic environment and adjusting GH output in metabolic extremes.

Determinants of bone mineral density in obese premenopausal women

Despite being a risk factor for cardiovascular disease and diabetes mellitus, obesity has been thought to protect against osteoporosis. However, recent studies have demonstrated a differential impact of specific fat compartments on bone mineral density (BMD) with visceral adipose tissue (VAT) having potential detrimental effects on BMD. Visceral obesity is also associated with dysregulation of the GH/IGF-1 axis, an important regulator of bone homeostasis. The purpose of our study was to evaluate the differential effects of abdominal fat depots and muscle, vitamin D, and hormonal determinants, including insulin-like growth factor-1 (IGF-1), testosterone, and estradiol, on trabecular BMD of the lumbar spine. We studied 68 healthy obese premenopausal women (mean BMI, 36.7±4.2 kg/m(2)). Quantitative computed tomography (QCT) was used to assess body composition and lumbar trabecular BMD. There was an inverse association between BMD and VAT, independent of age and BMI (p=0.003). IGF-1 correlated positively with BMD and negatively with VAT and, in stepwise multivariate regression modeling, was the strongest predictor of BMD and procollagen type 1 amino-terminal propeptide (P1NP). Thigh muscle cross sectional area (CSA) and thigh muscle density were also associated with BMD (p<0.05), but 25-hydroxyvitamin D [25(OH)D], testosterone, free testosterone, and estradiol levels were not. 25(OH)D was associated inversely with BMI, total, and subcutaneous abdominal adipose tissue (p<0.05). These findings support the hypothesis that VAT exerts detrimental effects, whereas muscle mass exerts positive effects on BMD in premenopausal obese women. Moreover, our findings suggest that IGF-1 may be a mediator of the deleterious effects of VAT on bone health through effects on bone formation.

Rapid suppression of growth hormone concentration by overeating: potential mediation by hyperinsulinemia

CONTEXT

The very low GH concentration in obesity is commonly attributed to high body fat mass; however, the influence of overeating on GH secretion is not clear.

OBJECTIVE

The aim of the study was to examine the effects of 2 wk of overeating on changes in GH secretion.

SETTING

Subjects were admitted to the hospital and stayed within the Michigan Clinical Research Unit throughout the entire 2-wk overeating period.

PARTICIPANTS

We studied seven healthy, nonobese men (body mass index, 24 ± 1 kg/m(2); age, 25 ± 1 yr).

INTERVENTION

Subjects ate standardized meals containing 70 kcal/kg fat free mass/d (∼4000 kcal/d) for 2 wk.

MAIN OUTCOME MEASURES

Twenty-four-hour plasma concentrations of GH (every 20 min) and insulin (every 2 h) were measured before overeating (baseline), on d 3, and after 2 wk of overeating.

RESULTS

Compared with baseline, average 24-h plasma GH concentration declined nearly 80% by d 3 of overeating (1.30 ± 0.18 vs. 0.36 ± 0.09 ng/ml; P = 0.01). This marked suppression of GH secretion occurred in the absence of an increase in body weight (77.0 ± 2.2 vs. 76.4 ± 2.4 kg). At the same time, average 24-h insulin concentration doubled (16.6 ± 2.1 vs. 31.7 ± 5.8 μU/ml; P = 0.009). After 2 wk, body weight significantly increased (79.0 ± 2.1 kg; P < 0.001), and body fat increased by more than 10% (P = 0.002). However, this did not induce a further suppression in plasma GH concentration (0.33 ± 0.08 ng/ml).

CONCLUSION

Only a few days of overeating markedly suppressed GH secretion before any measurable weight gain and was accompanied by chronic hyperinsulinemia. Increased body weight and body fat by 2 wk of overeating did not further suppress GH secretion.

Vertebral bone marrow fat is positively associated with visceral fat and inversely associated with IGF-1 in obese women

Recent studies have demonstrated an important physiologic link between bone and fat. Bone and fat cells arise from the same mesenchymal precursor cell within bone marrow, capable of differentiation into adipocytes or osteoblasts. Increased BMI appears to protect against osteoporosis. However, recent studies have suggested detrimental effects of visceral fat on bone health. Increased visceral fat may also be associated with decreased growth hormone (GH) and insulin-like growth factor 1 (IGF-1) levels which are important for maintenance of bone homeostasis. The purpose of our study was to assess the relationship between vertebral bone marrow fat and trabecular bone mineral density (BMD), abdominal fat depots, GH and IGF-1 in premenopausal women with obesity. We studied 47 premenopausal women of various BMI (range: 18-41 kg/m², mean 30 ± 7 kg/m²) who underwent vertebral bone marrow fat measurement with proton magnetic resonance spectroscopy (1H-MRS), body composition, and trabecular BMD measurement with computed tomography (CT), and GH and IGF-1 levels. Women with high visceral fat had higher bone marrow fat than women with low visceral fat. There was a positive correlation between bone marrow fat and visceral fat, independent of BMD. There was an inverse association between vertebral bone marrow fat and trabecular BMD. Vertebral bone marrow fat was also inversely associated with IGF-1, independent of visceral fat. Our study showed that vertebral bone marrow fat is positively associated with visceral fat and inversely associated with IGF-1 and BMD. This suggests that the detrimental effect of visceral fat on bone health may be mediated in part by IGF-1 as an important regulator of the fat and bone lineage.

Gender, age, body mass index, and IGF-I individually and jointly determine distinct GH dynamics: analyses in one hundred healthy adults

BACKGROUND

GH secretion is quantifiable as mean, peak, and nadir GH concentrations; degree of irregularity (approximate entropy); and spikiness (brief staccato-like fluctuations).

HYPOTHESIS

Distinct GH dynamics reflect relatively distinct (combinations of) subject variables, such as gender, age, body mass index (BMI), and IGF-I concentrations.

LOCATION

The study took place at a clinical translational research unit.

SUBJECTS

Subjects included 100 healthy adults ages 20-77 yr (59 women and 41 men), BMI 18-42 kg/m(2), and IGF-I 9.2-38 nmol/liter.

MEASURES

Immunofluorometric GH assay was done on 10-min samples collected for 24 h.

RESULTS

Stepwise forward-selection multivariate regression analysis revealed that mean GH concentrations were simultaneously determined (overall r = 0.36; P < 0.001) by gender (higher in women, P < 0.001), BMI (negatively, P < 0.001), and IGF-I (positively, P < 0.001). Peak GH levels were influenced (r = 0.28) by both BMI (P < 0.001) and IGF-I (P = 0.001). Nadir GH values were jointly affected by gender (higher in women, P = 0.005) and BMI (negatively, P = 0.001). GH approximate entropy was triply defined (r = 0.29) by gender (greater irregularity in women, P < 0.001), age (P = 0.022), and BMI (P = 0.008) and dually (r = 0.25) by gender (P = 0.0001) and BMI (P = 0.017) if sex steroids were included. GH spikiness was determined (r = 0.29) by gender (higher in women, P = 0.0016) and BMI (positively, P = 0.0002).

CONCLUSION

In healthy adults, combinations of gender, age, BMI, and IGF-I specify distinct GH dynamics, thus requiring balanced representation of these variables in comparative GH studies.