Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects

A novel leprechaunism mutation, Cys807Arg, in an Arab infant: a rare cause of hypoglycaemia

Leprechaunism is a rare autosomal recessive disorder which is usually fatal in early infancy or childhood. There is a paucity of genetic data on leprechaunism in the Arab population. A 4-month-old boy presented with jaundice, asymptomatic hypoglycaemia and growth retardation with features of leprechaunism. A novel Cys807Arg was identified, which could facilitate antenatal diagnosis for families in the Middle East.

Insulin-like growth factor receptor inhibitors: baby or the bathwater?

The success of targeted therapies for cancer is undisputed; strong preclinical evidence has resulted in the approval of several new agents for cancer treatment. The type I insulin-like growth factor receptor (IGF1R) appeared to be one of these promising new targets. Substantial population and preclinical data have all pointed toward this pathway as an important regulator of tumor cell biology. Although early results from clinical trials that targeted the IGF1R showed some evidence of response, larger randomized phase III trials have not shown clear clinical benefit of targeting this pathway in combination with conventional strategies. These disappointing results have resulted in the discontinuation of several anti-IGF1R programs. However, the conduct of these trials has brought to the forefront several important factors that need to be considered in the conduct of future clinical trials. The need to develop biomarkers, a clearer understanding of insulin receptor function, and defining rational combination regimens all require further consideration. In this commentary, the current state of IGF1R inhibitors in cancer therapy is reviewed.

The insulin-like growth factors in adipogenesis and obesity

Adipose tissue has been recognized as a major target of growth hormone (GH) action. GH was shown to inhibit adipocyte differentiation but stimulated preadipocyte proliferation in vitro. GH acts directly via its receptor or via upregulating insulin-like growth factor (IGF)-I, which is a critical mediator of preadipocyte proliferation, differentiation, and survival. Results from clinical studies on GH treatment in patients with GH deficiency or GH insensitivity syndrome can be used to dissect GH and IGF as well as IGF-binding protein (IGFBP) actions in vivo. In this article, changes of the GH/IGF system during adipocyte differentiation in vitro as well as related signaling pathways and their impact on adipose tissue growth and function are discussed. Clinical considerations include the effects of GH and IGF-I on adipose tissue during treatment of GH deficiency, differences in the IGF system between visceral and subcutaneous adipose tissue depots as well as the recently emerging role for adipose tissue in the regulation of glucose homeostasis.

Hormone replacement therapy and physical function in healthy older men. Time to talk hormones?

Improving physical function and mobility in a continuously expanding elderly population emerges as a high priority of medicine today. Muscle mass, strength/power, and maximal exercise capacity are major determinants of physical function, and all decline with aging. This contributes to the incidence of frailty and disability observed in older men. Furthermore, it facilitates the accumulation of body fat and development of insulin resistance. Muscle adaptation to exercise is strongly influenced by anabolic endocrine hormones and local load-sensitive autocrine/paracrine growth factors. GH, IGF-I, and testosterone (T) are directly involved in muscle adaptation to exercise because they promote muscle protein synthesis, whereas T and locally expressed IGF-I have been reported to activate muscle stem cells. Although exercise programs improve physical function, in the long-term most older men fail to comply. The GH/IGF-I axis and T levels decline markedly with aging, whereas accumulating evidence supports their indispensable role in maintaining physical function integrity. Several studies have reported that the administration of T improves lean body mass and maximal voluntary strength in healthy older men. On the other hand, most studies have shown that administration of GH alone failed to improve muscle strength despite amelioration of the detrimental somatic changes of aging. Both GH and T are anabolic agents that promote muscle protein synthesis and hypertrophy but work through separate mechanisms, and the combined administration of GH and T, albeit in only a few studies, has resulted in greater efficacy than either hormone alone. Although it is clear that this combined approach is effective, this review concludes that further studies are needed to assess the long-term efficacy and safety of combined hormone replacement therapy in older men before the medical rationale of prescribing hormone replacement therapy for combating the sarcopenia of aging can be established.

GH activity and markers of inflammation: a crossover study in healthy volunteers treated with GH and a GH receptor antagonist

INTRODUCTION

The GH/IGF1 axis may modulate inflammatory processes. However, the relationship seems complicated as both pro- and anti-inflammatory effects have been demonstrated.

METHODS/DESIGN

Twelve healthy volunteers (mean age 36, range 27-49 years) were treated in random order with increasing doses of GH for 3 weeks (first week 0.01  mg/kg per day, second week 0.02  mg/kg per day, and third week 0.03  mg/kg per day) or a GH receptor antagonist (pegvisomant; first week 10  mg/day and last two weeks 15  mg/day), separated by 8 weeks of washout. Circulating levels of the pro-inflammatory cytokines tumor necrosis factor α (TNFα (TNFA)), interleukin 6 (IL6), and IL1β (IL1B) and the acute phase proteins (APPs) C-reactive protein (CRP), haptoglobin, orosomucoid, YKL40 (CHI3L1), and fibrinogen were measured.

RESULTS

During GH treatment, IGF1 (median 131 (Inter-quartile range (IQR) 112-166) vs 390 (322-524) μg/l, P=0.002) increased together with TNFα (0.87 (0.74-1.48) vs 1.27 (0.80-1.69) ng/l, P=0.003), IL6 (1.00 (0.83-1.55) vs 1.35 (0.80-4.28) ng/l, P=0.045), and fibrinogen (9.2 (8.8-9.6) vs 11.1 (9.4-12.4) μM, P=0.002). By contrast, orosomucoid decreased (18.0 (15.5-24.3) vs 15.0 (15.0-17.0) μM, P=0.018). CRP, YKL40, and haptoglobin were unchanged. During pegvisomant treatment, IGF1 decreased (139 (117-171) vs 91 (78-114) ng/ml, P=0.005). Orosomucoid (21.0 (16.3-23.8) vs 22.0 (17.0-29.3) μM, P=0.036) and CRP (1.00 (0.62-1.77) vs 1.43 (0.71-3.29) mg/l, P=0.074) increased without an increase in pro-inflammatory cytokines.

CONCLUSIONS

GH/IGF1 action appears to modulate the initial stage of the inflammatory response as well as downstream processes elucidated by levels of APPs. The data suggest a complicated relationship not allowing any simple conclusions as to whether GH/IGF1 actions have mainly pro- or anti-inflammatory effects in vivo.

Growth hormone-induced JAK2 signaling and GH receptor down-regulation: role of GH receptor intracellular domain tyrosine residues

GH receptor (GHR) mediates important somatogenic and metabolic effects of GH. A thorough understanding of GH action requires intimate knowledge of GHR activation mechanisms, as well as determinants of GH-induced receptor down-regulation. We previously demonstrated that a GHR mutant in which all intracellular tyrosine residues were changed to phenylalanine was defective in its ability to activate signal transducer and activator of transcription (STAT)5 and deficient in GH-induced down-regulation, but able to allow GH-induced Janus family of tyrosine kinase 2 (JAK2) activation. We now further characterize the signaling and trafficking characteristics of this receptor mutant. We find that the mutant receptor's extracellular domain conformation and its interaction with GH are indistinguishable from the wild-type receptor. Yet the mutant differs greatly from the wild-type in that GH-induced JAK2 activation is augmented and far more persistent in cells bearing the mutant receptor. Notably, unlike STAT5 tyrosine phosphorylation, GH-induced STAT1 tyrosine phosphorylation is retained and augmented in mutant GHR-expressing cells. The defective receptor down-regulation and persistent JAK2 activation of the mutant receptor do not depend on the sustained presence of GH or on the cell's ability to carry out new protein synthesis. Mutant receptors that exhibit resistance to GH-induced down-regulation are enriched in the disulfide-linked form of the receptor, which reflects the receptor's activated conformation. Furthermore, acute GH-induced internalization, a proximal step in down-regulation, is markedly impaired in the mutant receptor compared to the wild-type receptor. These findings are discussed in the context of determinants and mechanisms of regulation of GHR down-regulation.

Serum IGF1 and insulin levels in girls with normal and precocious puberty

OBJECTIVE

IGF1 plays an important role in growth and metabolism during puberty. IGF1 levels are increased in girls with central precocious puberty (CPP). However, the relationship with insulin before and during gonadal suppression is unknown. In addition, the influence of the exon 3-deleted GH receptor gene (GHRd3) on IGF1 levels was evaluated.

DESIGN

Nine hundred and eleven healthy and 23 early pubertal girls (15 with CPP) participated and were evaluated by dual-energy X-ray absorptiometry (DXA) scans, fasting and oral glucose-stimulated insulin levels, IGF1 levels, and GHR genotyping. Fifteen girls with early puberty (13 with CPP) were treated with GNRH agonists and reevaluated after 3 and 12 months.

RESULTS

IGF1 and insulin levels were higher in girls with CPP compared with healthy controls after adjustment for age, bone age, and breast development (all P≤0.02). IGF1 levels were only significantly positively correlated with insulin levels in girls with CPP at baseline (P≤0.03). During gonadal suppression, changes in IGF1 levels were inversely associated with changes in insulin levels (P=0.04). The GHRd3/d3 genotype was associated with significantly higher IGF1 levels (P=0.01) but not with earlier pubertal timing in healthy girls. The distribution of the GHRd3 genotypes among girls with CPP did not differ significantly from healthy girls (P=0.2).

CONCLUSION

The increased IGF1 and insulin levels in girls with CPP may be causally interrelated. In addition, the GHRd3 allele positively influences IGF1 levels in a copy number-response relationship but not pubertal timing in healthy girls.

Profound hypoglycemia in starved, ghrelin-deficient mice is caused by decreased gluconeogenesis and reversed by lactate or fatty acids

When mice are subjected to 7-day calorie restriction (40% of normal food intake), body fat disappears, but blood glucose is maintained as long as the animals produce ghrelin, an octanoylated peptide that stimulates growth hormone secretion. Mice can be rendered ghrelin-deficient by knock-out of the gene encoding either ghrelin O-acyltransferase, which attaches the required octanoate, or ghrelin itself. Calorie-restricted, fat-depleted ghrelin O-acyltransferase or ghrelin knock-out mice fail to show the normal increase in growth hormone and become profoundly hypoglycemic when fasted for 18-23 h. Glucose production in Goat(-/-) mice was reduced by 60% when compared with similarly treated WT mice. Plasma lactate and pyruvate were also low. Injection of lactate, pyruvate, alanine, or a fatty acid restored blood glucose in Goat(-/-) mice. Thus, when body fat is reduced by calorie restriction, ghrelin stimulates growth hormone secretion, which allows maintenance of glucose production, even when food intake is eliminated. In humans with anorexia nervosa or kwashiorkor, ghrelin and growth hormone are known to be elevated, just as they are in fat-depleted mice. We suggest that these two hormones prolong survival in starved humans as they do in mice.

The association between IGF-I and insulin resistance: a general population study in Danish adults

OBJECTIVE

IGF-I has an almost 50% amino acid sequence homology with insulin and elicits nearly the same hypoglycemic response. Studies showed that low and high IGF-I levels are related to impaired glucose tolerance and to a higher risk of type 2 diabetes. The aim of the current study was to evaluate the association between IGF-I level and insulin resistance in a Danish general population.

RESEARCH DESIGN AND METHODS

Included were 3,354 adults, aged 19-72 years, from the cross-sectional Health2006 study. The homeostasis model assessment of insulin resistance (HOMA-IR) was used as the index to estimate insulin resistance. Serum IGF-I levels were determined by an immunoassay and grouped into quintiles (Q1-Q5). Linear or multinomial logistic regression analyses were performed.

RESULTS

In the study population, 520 subjects (15.5%) had increased HOMA-IR values above 2.5. After adjustment for age, sex, physical activity, and waist-to-height ratio, a U-shaped association between IGF-I and HOMA-IR was found. Low IGF-I (Q1: odds ratio [OR] 1.65 [95% CI 1.16-2.34], P < 0.01) as well as high IGF-I (Q5: 1.96 [1.38-2.79], P < 0.01) levels were related to a higher odds of increased HOMA-IR values compared with subjects with intermediate (Q3) IGF-I levels. These associations remained statistically significant after the exclusion of subjects with type 2 diabetes and by using the updated computer HOMA2-IR model.

CONCLUSIONS

Low- and high-normal IGF-I levels are both related to insulin resistance. The biological mechanism of this complex phenomenon has to be elucidated in more detail for future risk stratification.

Fat content in liver and skeletal muscle changes in a reciprocal manner in patients with acromegaly during combination therapy with a somatostatin analog and a GH receptor antagonist: a randomized clinical trial

CONTEXT

Pegvisomant is a GH antagonist, which is used for the treatment of acromegalic patients. It effectively blocks the hepatic and peripheral effects of GH, but transient elevations in circulating liver enzymes of unknown pathogenesis may occur, which seems to be more prevalent when the treatment is combined with a somatostatin analog (SA). Accumulation of intrahepatic lipid is a known cause of elevated liver enzymes, and there is evidence to suggest that GH impacts lipid content in liver and skeletal muscle.

OBJECTIVE

Our objective was to measure lipid content in liver and skeletal muscle in acromegalic patients before and after cotreatment with pegvisomant and SA as compared with SA monotherapy.

DESIGN

Eighteen acromegalic patients well controlled on SA monotherapy were randomized in a parallel study over 24 wk to 1) unchanged SA monotherapy, or 2) cotreatment with pegvisomant (15-30 mg twice a week) and SA (half the usual dosage).

SETTING

This was an investigator-initiated study in a single tertiary referral center.

MAIN OUTCOME MEASURES

Intrahepatic lipid (IHL) and intramyocellular lipid (IMCL) was assessed by ¹H magnetic resonance spectroscopy.

RESULTS

IHL increased in the cotreatment group compared with SA only (P = 0.002). The increase was positively correlated to weekly pegvisomant dose (r² = 0.52; P = 0.01). By contrast, IMCL decreased in the cotreatment group compared with SA only (P = 0.01). These changes related neither to insulin sensitivity nor inflammatory markers.

CONCLUSION

Cotreatment with pegvisomant and a reduced SA dose increase IHL and decrease IMCL compared with SA monotherapy. The clinical implications remain unclear, but increased IHL may be causally linked to the transient elevations in liver enzymes observed during pegvisomant treatment.

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.

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSIONS

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

Plasma dehydroepiandrosterone sulphate and insulin-like growth factor I levels in obstructive sleep apnoea syndrome

CONTEXT

We aimed to assess whether obstructive sleep apnoea syndrome (OSAS) affects plasma IGF-1 and dehydroepiandrosterone sulphate (DHEA-S) levels in men, factors implicated in the development of age-related metabolic disorders.

DESIGN

We conducted a cross-sectional and longitudinal clinical study.

PATIENTS AND SETTING

We measured plasma IGF-1 and DHEA-S levels in 191 non-drug-treated Japanese men (34 primary snorers (PS), 88 patients with mild-to-moderate OSAS and 69 patients severe OSAS ).

RESULTS

Plasma IGF-1 and DHEA-S were negatively correlated with age. Plasma IGF-1 was also negatively correlated with plasma glucose, HOMA-IR and systolic blood pressure and apnoea parameters such as the apnoea-hypopnea index, minimum oxygen saturation and slow-wave sleep (SWS) time. Plasma DHEA-S was associated with plasma glucose, HbA1c and free fatty acid and was negatively correlated with SWS time. To eliminate the influence of age, PS, patients with mild-to-moderate OSAS and severe OSAS were divided into three groups by age: young (<40 years), middle-aged (40-59 years) and elderly (≥ 60 years). Patients with severe OSAS aged <40 or <60 years had lower plasma IGF-1 or DHEA-S levels, respectively, than did the corresponding snorers and mild-to-moderate OSAS groups. Continuous positive airway pressure therapy for generally 16-18 months increased plasma IGF-1 levels in patients with severe OSAS aged <40 years (n = 18). Plasma DHEA-S levels were increased in patients with severe OSAS aged <60 years, whose DHEA-S level was below the mean value for that age (n = 23/41).

CONCLUSION

Severe OSAS could reduce plasma IGF-1 and DHEA-S levels in younger, but not elderly Japanese men, which is potentially associated with the development of metabolic abnormalities.

GH/IGF-I axis and matrix adaptation of the musculotendinous tissue to exercise in humans

Exercise is not only associated with adaptive responses within skeletal muscle fibers but also with induction of collagen synthesis both in muscle and adjacent connective tissue. Additionally, exercise and training leads to activation of the systemic growth hormone/insulin-like growth factor I axis (GH/IGF-I), as well as increased local IGF-I expression. Studies in humans with pathologically high levels of GH/IGF-I, and in healthy humans who receive either weeks of GH administration or acute injection of IGF-I into connective tissue, demonstrate increased expression and synthesis of collagen in muscle and tendon. These observations support a stimulatory effect of GH/IGF-I on the connective tissue in muscle and tendon, which appears far more potent than the effect on contractile proteins of skeletal muscle. However, GH/IGF-I may play an additional role in skeletal muscle by regulation of stem cells (satellite cells), as increased satellite cell numbers are found in human muscle with increased GH/IGF-I levels, despite no change in myofibrillar protein synthesis. Although advanced age is associated with both a reduction in the GH/IGF-I axis activity, and in skeletal muscle mass (sarcopenia) as well as in tendon connective tissue, there is no direct proof linking age-related changes in the musculotendinous tissue to an impaired GH/IGF-I axis.

Oral contraception enhances growth hormone responsiveness to hyper- and hypoglycaemia

AIMS

Plasma glucose levels influence growth hormone concentrations. Oral contraceptives are known to affect circulating growth hormone levels and glucose metabolism. While growth hormone plays an important role in hypoglycaemia counter-regulation, it has been shown that oral contraceptives increase growth hormone concentrations. In this context, we tested if serum growth hormone concentrations display a differential response on glycaemic variations in healthy women using oral contraceptives and those not using contraceptives.

METHODS

Fifteen healthy women with oral contraceptive treatment and 10 without participated in a stepwise hyper- and hypoglycaemic glucose clamp procedure. Serum growth hormone concentrations were measured at euglycaemic baseline and subsequently at plasma glucose plateaus of 8.8, 6.8, 4.8 and 2.8 mmol/l.

RESULTS

Growth hormone values were significantly higher in women using oral contraceptives throughout the experiments (P = 0.001). Hyperglycaemia decreased growth hormone concentrations in women using oral contraceptives (P = 0.009), but not in those who were not using oral contraceptives (P = 0.241). Hypoglycaemia significantly elevated growth hormone concentrations in women using oral contraceptives (P = 0.009), but not in those not using oral contraceptives (P = 0.094). Maximum growth hormone values were reached at the end of the hypoglycaemic plateau, with significantly higher concentrations in the group using oral contraceptives than in the group not using oral contraceptives (P = 0.016).

CONCLUSION

Healthy women on oral contraceptive treatment display an increased responsiveness of growth hormone to hypoglycaemic, as well as hyperglycaemic conditions and generally higher serum growth hormone concentrations than women without oral contraceptives. Given the known boosting effects of growth hormone on hypoglycaemic hormonal counter-regulation, oral contraceptives may thus be a pharmacological candidate contributing to combat hypoglycaemia unawareness in women with diabetes in the future.

CXCL14-like immunoreactivity in growth hormone-containing cells of urodele pituitaries

Immunohistochemical techniques were employed to investigate the distribution of a chemokine, namely, CXCL14-like immunoreactivity in the axolotl (Ambystoma mexicanum) and Japanese black salamander (Hynobius nigrescens) pituitaries. CXCL14-immunoreactive cells concentrated at an area of the pars distalis adjacent to the pars intermedia. We found that these cells correspond to the cells immunoreactive to an antibody against rat growth hormone (GH). Immunoelectron microscopy indicated that the CXCL14-like substance and GH coexisted on the secretory granules in the axolotl pituitary. Western blot analysis of axolotl pituitary extracts revealed the anti-human CXCL14 antibody labeled an approximately 16.6-kDa band that was not labeled by the anti-GH antibody. The CXCL14-like substance in the pars distalis may participate in GH functions in these species.

Tesamorelin: a review of its use in the management of HIV-associated lipodystrophy

Tesamorelin (Egrifta™) is a synthetic analogue of human growth hormone-releasing hormone (also known as growth hormone-releasing factor) that stimulates the synthesis and release of endogenous growth hormone. It is the first and, so far, only treatment indicated for the reduction of excess abdominal fat in patients with HIV-associated lipodystrophy. This article reviews the pharmacological properties, clinical efficacy and tolerability of tesamorelin in patients with HIV-associated central fat accumulation. Subcutaneous tesamorelin was effective in reducing visceral adipose tissue (VAT), but did not affect subcutaneous adipose tissue to a clinically significant extent in two 26-week, well designed, clinical trials in patients with HIV-associated central fat accumulation. This reduction in VAT was maintained in the longer term in patients who continued to receive tesamorelin until week 52 in the extension phases of the two trials. However, discontinuation of therapy during this period resulted in the reaccumulation of VAT. Tesamorelin therapy was also associated with significant improvements in other body composition measures (e.g. trunk fat and waist circumference) and improvements were generally seen in some body image parameters (e.g. belly image distress). Tesamorelin was generally well tolerated, with treatment-emergent serious adverse events occurring in <4% of patients during 26 weeks of therapy. Most of these events were injection-site reactions or events known to be associated with growth hormone therapy (e.g. arthralgia, headache and peripheral oedema). Although long-term clinical experience is needed to further assess the benefits and risks of therapy, current evidence suggests that tesamorelin may be useful for reducing visceral adiposity in patients with HIV-associated lipodystrophy, thereby potentially improving self image.

Growth hormone stimulates transcription of the fibroblast growth factor 21 gene in the liver through the signal transducer and activator of transcription 5

Fibroblast growth factor 21 (FGF21) is a recently discovered metabolic regulator. Interestingly, FGF21 is also known to inhibit Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) signaling from the GH receptor in the liver, where FGF21 mRNA is predominantly expressed. In this study, we tested the hypothesis that FGF21 gene expression in the liver is controlled by GH through STAT5. We found that GH injection to cattle increased FGF21 mRNA expression in the liver. Mapped by a 5'-rapid amplification of cDNA ends assay, transcription of the FGF21 gene in the bovine liver was mainly initiated from a nucleotide 24 bp downstream of a TATA box. The bovine FGF21 promoter contains three putative STAT5-binding sites. EMSA confirmed the ability of them to bind to liver STAT5 protein from GH-injected cattle. Chromatin immunoprecipitation assays demonstrated that GH administration increased the binding of STAT5 to the FGF21 promoter in the liver. Cotransfection analyses showed that GH induced reporter gene expression from the FGF21 promoter in a STAT5-dependent manner. GH also stimulated FGF21 mRNA expression in cultured mouse hepatocytes. These data together indicate that GH directly stimulates FGF21 gene transcription in the liver, at least in part, through STAT5. This finding, together with the fact that FGF21 inhibits GH-induced JAK2-STAT5 signaling in the liver, suggests a novel negative feedback loop that prevents excessive JAK2-STAT5 signaling from the GH receptor in the liver.

Essential roles of growth hormone (GH) and insulin-like growth factor-I (IGF-I) in the liver

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) play essential roles in growth in childhood, and continue to have important metabolic actions in adults. Adult growth hormone deficiency (AGHD) is characterized by increased visceral adiposity, abnormal lipid profiles, premature atherosclerosis, decreased quality of life, and increased mortality. Recently, case reports and several clinical studies suggest that GHD state in adults is associated with an increased prevalence of nonalcoholic fatty liver disease (NAFLD) and progression to nonalcoholic steatohepatitis (NASH) or liver cirrhosis. As a mechanistic insight, growing evidence has revealed that GH as well as IGF-I play essential roles in the liver. Further investigation is necessary to clarify the precise mechanisms by which GH and IGF-I exert their effects in the liver; however, it should be noted that NAFLD/NASH has emerged as an important comorbidity in AGHD.

Incidence of diabetes mellitus and evolution of glucose parameters in growth hormone-deficient subjects during growth hormone replacement therapy: a long-term observational study

OBJECTIVE

Growth hormone (GH) deficiency is associated with insulin resistance and diabetes. The aim of the current study was to determine incidence of diabetes during GH replacement therapy (GHRT) and the effect of GHRT on fasting plasma glucose concentrations and HbA(1c) in adult patients with GH deficiency.

RESEARCH DESIGN AND METHODS

A total of 5,143 GH-deficient patients (male 49.9%; mean age ± SD, 49 ± 13 years; BMI 29.1 ± 5.9 kg/m(2)) were analyzed. Mean observation period was 3.9 years (range 0.01-13). Total number of patient-years was 20,106. Observed number of cases (O) was compared with expected number of cases (E). Reference rates were from Sweden, three additional European regions, and one U.S. region.

RESULTS

Patients who developed diabetes (n = 523) were older; had higher BMI, waist circumference, triglyceride concentrations, and blood pressure; and had lower HDL-cholesterol concentrations (P < 0.0001) than those who did not develop diabetes. Diabetes incidence was 2.6 per 100 patient-years, equal in both sexes, and significantly increased compared with the Swedish reference (O/E = 6.02; P < 0.0001) as well as with the four other populations (O/E = 2.11-5.22). O/E increased with BMI and decreased with duration of GHRT (P < 0.0001). There was no significant association with GH dose (P = 0.74) or IGF-I SDS (P = 0.47). In subjects not developing diabetes, plasma glucose concentrations increased from 84.4 ± 0.9 mg/dL to 89.5 ± 0.8 mg/dL (0.70 mg/dL/year) and HbA(1c) increased from 4.74 ± 0.04% to 5.09 ± 0.13% (0.036%/year) after 6 years of GHRT.

CONCLUSIONS

Diabetes incidence appears to be increased in GH-deficient patients receiving GHRT and exhibiting an adverse risk profile at baseline. Therefore, glucose homeostasis parameters should be monitored carefully in these patients.

Targeted loss of GHR signaling in mouse skeletal muscle protects against high-fat diet-induced metabolic deterioration

Growth hormone (GH) exerts diverse tissue-specific metabolic effects that are not revealed by global alteration of GH action. To study the direct metabolic effects of GH in the muscle, we specifically inactivated the growth hormone receptor (ghr) gene in postnatal mouse skeletal muscle using the Cre/loxP system (mGHRKO model). The metabolic state of the mGHRKO mice was characterized under lean and obese states. High-fat diet feeding in the mGHRKO mice was associated with reduced adiposity, improved insulin sensitivity, lower systemic inflammation, decreased muscle and hepatic triglyceride content, and greater energy expenditure compared with control mice. The obese mGHRKO mice also had an increased respiratory exchange ratio, suggesting increased carbohydrate utilization. GH-regulated suppressor of cytokine signaling-2 (socs2) expression was decreased in obese mGHRKO mice. Interestingly, muscles of both lean and obese mGHRKO mice demonstrated a higher interleukin-15 and lower myostatin expression relative to controls, indicating a possible mechanism whereby GHR signaling in muscle could affect liver and adipose tissue function. Thus, our study implicates skeletal muscle GHR signaling in mediating insulin resistance in obesity and, more importantly, reveals a novel role of muscle GHR signaling in facilitating cross-talk between muscle and other metabolic tissues.

Inhibitory GH receptor extracellular domain monoclonal antibodies: three-dimensional epitope mapping

GH receptor (GHR) mediates the anabolic and metabolic effects of GH. We previously characterized a monoclonal antibody (anti-GHR(ext-mAb)) that reacts with subdomain 2 of the rabbit GHR extracellular domain (ECD) and is a conformation-specific inhibitor of GH signaling in cells bearing rabbit or human GHR. Notably, this antibody has little effect on GH binding and also inhibits inducible metalloproteolysis of the GHR that occurs in the perimembranous ECD stem region. In the current study, we demonstrate that anti-GHR(ext-mAb) inhibits GH-dependent cellular proliferation and also inhibits hepatic GH signaling in vivo in mice that adenovirally express rabbit GHR, as assessed with our noninvasive bioluminescence hepatic signaling assay. A separate monoclonal antibody (anti-GHR(mAb 18.24)) is a sister clone of anti-GHR(ext-mAb). Here, we demonstrate that anti-GHR(mAb 18.24) also inhibits rabbit and human GHR signaling and inducible receptor proteolysis. Further, we use a random PCR-generated mutagenic expression system to map the three-dimensional epitopes in the rabbit GHR ECD for both anti-GHR(ext-mAb) and anti-GHR(mAb 18.24). We find that each of the two antibodies has similar, but nonidentical, discontinuous epitopes that include regions of subdomain 2 encompassing the dimerization interface. These results have fundamental implications for understanding the role of the dimerization interface and subdomain 2 in GHR activation and regulated GHR metalloproteolysis and may inform development of therapeutics that target GHR.

Elevated GH/IGF-I, due to somatotrope-specific loss of both IGF-I and insulin receptors, alters glucose homeostasis and insulin sensitivity in a diet-dependent manner

A unique mouse model was developed with elevated endogenous GH (2- to 3-fold) and IGF-I (1.2- to 1.4-fold), due to somatotrope-specific Cre-mediated inactivation of IGF-I receptor (IgfIr) and insulin receptor (Insr) genes (IgfIr,Insr(rGHpCre), referred to as HiGH mice). We demonstrate that the metabolic phenotype of HiGH mice is diet dependent and differs from that observed in other mouse models of GH excess due to ectopic heterologous transgene expression or pituitary tumor formation. Elevated endogenous GH promotes lean mass and whole-body lipid oxidation but has minimal effects on adiposity, even in response to diet-induced obesity. When caloric intake is moderated, elevated GH improves glucose clearance, despite low/normal insulin sensitivity, which may be explained in part by enhanced IGF-I and insulin output. However, when caloric intake is in excess, elevated GH promotes hepatic lipid accumulation, insulin resistance, hyperglycemia, and ketosis. The HiGH mouse model represents a useful tool to study the role endogenous circulating GH levels play in regulating health and disease.

Diabetes mellitusin a cohort of patients with acromegaly

OBJECTIVES: To evaluate the presence of diabetes mellitus (DM) in a cohort of patients with acromegaly. METHODS: This was a cross sectional study. RESULTS: Fifty-eight acromegalic patients were assessed. Only 29% met the criteria for cure, and 27% had the disease controlled. Twenty-two had DM; HbA1c was equal to 7.34 ± 2.2%. Most of the diabetic patients (18 out of 22, 82%) did not meet criteria for cure. They were more often hypertensive [16/22 (73%) vs. 17/36 (46%), p = 0.04], and used statins more frequently [14/22 (64%) vs. 8/36 (21%), p = 0.004]. After regression analysis, hypertension was associated with diabetes [odds ratio (OR): 9.28 (95% CI: 1.59 - 54.00), p = 0.01], and cured/ controlled acromegaly was associated with protection against the presence of diabetes [OR: 0.17 (95% CI: 0.03 - 0.78), p = 0.02]. CONCLUSIONS: The presence of DM was associated with active acromegaly and presence of hypertension. However, absolute levels of GH and IGF-1 did not differ between patients with and without diabetes.

Biochemical markers of bone turnover in tibia fracture patients randomly assigned to growth hormone (GH) or placebo injections: Implications for detection of GH abuse

CONTEXT

It has been argued that increased levels of bone remodelling markers are not suitable indicators of GH abuse, as bone injuries per se increase the expression levels of these markers.

OBJECTIVE

To investigate the impact of a recovering tibia fracture on circulating bone markers in subjects receiving placebo or GH treatment.

DESIGN AND SETTING

A randomised, double-blind, placebo-controlled trial of up to 16weeks GH treatment, followed by a 16-week washout.

PARTICIPANTS AND INTERVENTION

Subjects (406 adult males and females) with a tibia fracture were randomly allocated within three days after surgery, to either placebo or GH treatment (15, 30 or 60μg/kg daily) until fracture healing or 16weeks after treatment initiation.

MAIN OUTCOME MEASURES

IGF-I, serum C-terminal telopeptide of type I collagen (CTX), osteocalcin (OST) and bone-specific alkaline phosphatase (BAP) were measured during and after treatment.

RESULTS

Dose-dependent increases were observed in groups receiving GH, and mean levels in the highest GH dose group peaked at eight (IGF-I, CTX) or 12weeks (OST) after treatment initiation. Statistically significant differences between GH treatment and placebo were seen for IGF-I, CTX and OST in all GH dose groups throughout the treatment period, and persisted until eight (CTX) or 12 (OST) weeks after cessation of treatment.

CONCLUSION

IGF-I, CTX and OST are suitable candidate markers of prolonged, illicit administration of GH. Furthermore, CTX and OST have potentials to serve as markers also after cessation of GH administration.

Differential effects of growth hormone versus insulin-like growth factor-I on the mouse plasma proteome

The GH/IGF-I axis has both pre- and postpubertal metabolic effects. However, the differential effects of GH and/or IGF-I on animal physiology or the plasma proteome are still being unraveled. In this report, we analyzed several physiological effects along with the plasma proteome after treatment of mice with recombinant bovine GH or recombinant human IGF-I. GH and IGF-I showed similar effects in increasing body length, body weight, lean and fluid masses, and organ weights including muscle, kidney, and spleen. However, GH significantly increased serum total cholesterol, whereas IGF-I had no effect on it. Both acute and longer-term effects on the plasma proteome were determined. Proteins found to be significantly changed by recombinant bovine GH and/or recombinant human IGF-I injections were identified by mass spectrometry (MS) and MS/MS. The identities of these proteins were further confirmed by Western blotting analysis. Isoforms of apolipoprotein A4, apolipoprotein E, serum amyloid protein A-1, clusterin, transthyretin, and several albumin fragments were found to be differentially regulated by GH vs. IGF-I in mouse plasma. Thus, we have identified several plasma protein biomarkers that respond specifically and differentially to GH or IGF-I and may represent new physiological targets of these hormones. These findings may lead to better understanding of the independent biological effects of GH vs. IGF-I. In addition, these novel biomarkers may be useful for the development of tests to detect illicit use of GH or IGF-I.

Prolonged exposure to GH impairs insulin signaling in the heart

Acromegaly is associated with cardiac hypertrophy, which is believed to be a direct consequence of chronically elevated GH and IGF1. Given that insulin is important for cardiac growth and function, and considering that GH excess induces hyperinsulinemia, insulin resistance, and cardiac alterations, it is of interest to study insulin sensitivity in this tissue under chronic conditions of elevated GH. Transgenic mice overexpressing GH present cardiomegaly and perivascular and interstitial fibrosis in the heart. Mice received an insulin injection, the heart was removed after 2  min, and immunoblotting assays of tissue extracts were performed to evaluate the activation and abundance of insulin-signaling mediators. Insulin-induced tyrosine phosphorylation of the insulin receptor (IR) was conserved in transgenic mice, but the phosphorylation of IR substrate 1 (IRS1), its association with the regulatory subunit of the phosphatidylinositol 3-kinase (PI3K), and the phosphorylation of AKT were decreased. In addition, total content of the glucose transporter GLUT4 was reduced in transgenic mice. Insulin failed to induce the phosphorylation of the mammalian target of rapamycin (mTOR). However, transgenic mice displayed increased basal activation of the IR/IRS1/PI3K/AKT/mTOR and p38 signaling pathways along with higher serine phosphorylation of IRS1, which is recognized as an inhibitory modification. We conclude that GH-overexpressing mice exhibit basal activation of insulin signaling but decreased sensitivity to acute insulin stimulation at several signaling steps downstream of the IR in the heart. These alterations may be associated with the cardiac pathology observed in these animals.

Seasonal regulation of the growth hormone-insulin-like growth factor-I axis in the American black bear (Ursus americanus)

The American black bear maintains lean body mass for months without food during winter denning. We asked whether changes in the growth hormone/insulin-like growth factor-I (GH-IGF-I) axis may contribute to this remarkable adaptation to starvation. Serum IGF-I levels were measured by radioimmunoassay, and IGF-binding proteins (IGFBPs) were analyzed by ligand blotting. Initial studies in bears living in the wild showed that IGF-I levels are highest in summer and lowest in early winter denning. Detailed studies in captive bears showed that IGF-I levels decline in autumn when bears are hyperphagic, continue to decline in early denning, and later rise above predenning levels despite continued starvation in the den. IGFBP-2 increased and IGFBP-3 decreased in early denning, and these changes were also reversed in later denning. Treatment with GH (0.1 mg·kg(-1)·day(-1) × 6 days) during early denning increased serum levels of IGF-I and IGFBP-3 and lowered levels of IGFBP-2, indicating that denning bears remain responsive to GH. GH treatment lowered blood urea nitrogen levels, reflecting effects on protein metabolism. GH also accelerated weight loss and markedly increased serum levels of free fatty acids and β-hydroxybutyrate, resulting in a ketoacidosis (bicarbonate decreased to 15 meq/l), which was reversed when GH was withdrawn. These results demonstrate seasonal regulation of GH/IGF-I axis activity in black bears. Diminished GH activity may promote fat storage in autumn in preparation for denning and prevent excessive mobilization and premature exhaustion of fat stores in early denning, whereas restoration of GH/IGF activity in later denning may prepare the bear for normal activity outside the den.

Clinical and biochemical characteristics of acromegalic patients with different abnormalities in glucose metabolism

To determine the prevalence of diabetes, glucose intolerance and impaired fasting glucose in Mexican patients with acromegaly and establish associations with clinical, anthropometric and biochemical variables. 257 patients with acromegaly were evaluated by a 75 g-oral glucose tolerance test with measurements of both GH and glucose (0, 30, 60, 90 120 min) as well as baseline IGF-1. Normal glucose tolerance (NGT), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and diabetes (DM) were defined based on the 2003 ADA criteria. NGT, IFG, IGT and DM were found in 27.6, 8.9, 31.6 and 31.9% of the subjects, respectively; 42 of the DM patients were unaware of the diagnosis. Patients with diabetes were older than subjects in the other 3 categories (P = 0.001), and the proportion of women was significantly higher in the DM (74%) and IGT (68%) groups than in the NGT group (52%) (P = 0.004). Odds ratio for the development of DM was 3.29 (95% CI 3.28-3.3). GH and IGF-1 levels were comparable among the different groups. In a multivariable analysis DM was significantly associated with age, presence of a macroadenoma, disease duration and a basal GH > 30 μg/dl. DM and probably IGT are more prevalent in acromegaly than in the general Mexican population. DM was more frequent in females of all ages, in subjects with severely elevated GH concentrations, in patients with macroadenomas, and long-standing disease duration. The odds ratio for DM in our subjects with acromegaly is more than 3 times higher than in the general population.

Esterase 1 is a novel transcriptional repressor of growth hormone receptor gene expression: a unique noncatalytic role for a carboxyesterase protein

The pleiotropic actions of GH result from its engagement with the GH receptor (GHR). GHR expression is regulated by free fatty acids (FFA). A cDNA phage expression library was screened to identify a phage clone expressing esterase 1 (ES1) binding to the FFA-response element (FARE), L2-D1, in the murine GHR promoter. Ectopically expressed ES1 inhibited GHR promoter activity via effects at two FARE, L2-D1 and L2-A2. Chromatin immunoprecipitation experiments demonstrated specific association of ES1 with the FARE. Catalytically inactive ES1 retained inhibitory activity on the GHR promoter and excluded the possibility that the effect on the GHR promoter was an indirect effect secondary to ES1's actions on the intracellular metabolism of FFA. Ectopically expressed ES1 inhibited the endogenous GHR mRNA and protein expression in 3T3-F442A preadipocytes. Subcellular fractionation and confocal microscopy established that ES1 localizes both to the cytoplasm and the nucleus. Experiments demonstrated chromosome region maintenance 1-dependent nuclear export and the presence of a functional nuclear export signal in ES1. The domain of ES1 responsible for the effect on the GHR promoter was localized to the C-terminal portion of the protein. The in vivo significance of ES1's effect on GHR expression was suggested by decreased liver GHR mRNA expression in mice on a high-fat diet correlating with increased steady-state abundance of liver ES1 mRNA. Our results identify and characterize ES1 as a novel transcriptional regulator of GHR gene expression, thereby establishing a unique nonenzymatic role for a carboxyesterase and expanding the potential biological roles of this protein superfamily.

Growth hormone (GH)-induced insulin resistance is rapidly reversible: an experimental study in GH-deficient adults

CONTEXT

It is clinically relevant and of physiological interest to investigate whether GH-induced insulin resistance depends on the timing of GH exposure relative to when insulin sensitivity is assessed.

HYPOTHESIS

GH-induced insulin resistance is rapidly reversible.

DESIGN AND PARTICIPANTS

Eight male GH-deficient patients underwent a 6-h euglycemic-hyperinsulinemic glucose clamp thrice in a randomized crossover design receiving either no GH (study 0), a 7-h GH infusion (0.2-0.3 mg in total) that terminated 5 h before the clamp (study 1), or a similar GH infusion timed to continue during the first hour of the clamp (study 2). A muscle biopsy was obtained 30 min into the clamp. The patients were compared with eight healthy untreated control subjects (study c).

MAIN OUTCOME MEASURES

The glucose infusion rate, indirect calorimetry, and free fatty acid metabolism were assessed. In muscle biopsies, protein phosphorylation of signal transducer and activator of transcription 5, Akt, and Akt substrate 160 (phospho-Akt substrate signal) and gene expression of IGF-I and SOCS1-3 were assessed.

RESULTS

Insulin sensitivity differed significantly between the GH-deficiency studies (P = 0.005) with distinct insulin resistance in study 2 and increased insulin sensitivity in study 0 [area under the glucose infusion rate curve (mg/kg · min): 1663 ± 151 (study 0) vs. 1482 ± 166 (study 1) vs. 1123 ± 136 (study 2) vs. 1492 ± 229 (control group)]. Free fatty acid levels and lipid oxidation were elevated in response to GH exposure but became suppressed during the clamp. IGF-I and SOCS3 gene expression was increased in study 2.

CONCLUSIONS

Very-low-dose GH exposure evokes acute insulin resistance that subsides after 5 h. This time-dependent reversibility should be considered when assessing the impact of GH on glucose homeostasis.

A high protein diet during pregnancy affects hepatic gene expression of energy sensing pathways along ontogenesis in a porcine model

In rodent models and in humans the impact of gestational diets on the offspring's phenotype was shown experimentally and epidemiologically. The underlying programming of fetal development was shown to be associated with an increased risk of degenerative diseases in adulthood, including the metabolic syndrome. There are clues that diet-dependent modifications of the metabolism during fetal life can persist until adulthood. This leads to the hypothesis that the offspring's transcriptomes show short-term and long-term changes depending on the maternal diet. To this end pregnant German landrace gilts were fed either a high protein diet (HP, 30% CP) or an adequate protein diet (AP, 12% CP) throughout pregnancy. Hepatic transcriptome profiles of the offspring were analyzed at prenatal (94 dpc) and postnatal stages (1, 28, 188 dpn). Depending on the gestational dietary exposure, mRNA expression levels of genes related to energy metabolism, N-metabolism, growth factor signaling pathways, lipid metabolism, nucleic acid metabolism and stress/immune response were affected either in a short-term or in a long-term manner. Gene expression profiles at fetal stage 94 dpc were almost unchanged between the diets. The gestational HP diet affected the hepatic expression profiles at prenatal and postnatal stages. The effects encompassed a modulation of the genome in terms of an altered responsiveness of energy and nutrient sensing pathways. Differential expression of genes related to energy production and nutrient utilization contribute to the maintenance of development and growth performance within physiological norms, however the modulation of these pathways may be accompanied by a predisposition for metabolic disturbances up to adult stages.

Glucose homeostasis in patients with acromegaly treated with surgery or somatostatin analogues

OBJECTIVE

Long-acting somatostatin analogues (SSA) are widely used for the treatment of acromegaly; however, they also alter β-cell function by inhibiting insulin secretion. In this study, we assess the effect of SSA on glucose homeostasis in patients with acromegaly treated with SSAs, compared to patients treated with surgery.

DESIGN

We studied four groups of patients with acromegaly: at the time of diagnosis (group I, n = 53), after successful transsphenoidal surgery (TSS, group II, n = 30) and under successful SSA treatment (group III, n = 20); 22 patients were studied only before treatment, 19 only post-treatment, while 31 patients (group IV) were studied before and after the treatment.

MEASUREMENTS

Patients underwent an oral glucose tolerance test. Insulin sensitivity and β-cell insulin secretion were estimated using appropriate mathematical models.

RESULTS

Control of acromegaly with either TSS or SSA improved insulin sensitivity as evident by significantly lower fasting and postglucose insulin levels and HOMA-IR. In addition, patients of group III compared to patients of group II demonstrated significantly lower HOMA-β% (52·5 ± 10·9 vs 189·6 ± 86·7, P < 0·05) and lower first and second phase insulin release (443 ± 83·5 vs 1077 ± 140·8, P < 0·05 and 150 ± 18·2 vs 285 ± 33·3, P < 0·05), respectively. Also, lower fasting glucose levels and a lower prevalence of diabetes were noted in group II compared to group III (5·1 ± 0·2 vs 6·2 ± 0·2 mm, P < 0·05, and 13·3%vs 40%, P < 0·0031, respectively). CONCLUSIONS; Control of acromegaly with SSA seems to exhibit a negative effect on pancreatic β-cell function. Whether this has long-term clinical implications remains to be established. Nevertheless, careful monitoring of glucose metabolism in patients under SSA is beneficial for their optimal management.

Growth hormone-stimulated insulin-like growth factor-1 expression in rainbow trout (Oncorhynchus mykiss) hepatocytes is mediated by ERK, PI3K-AKT, and JAK-STAT

Growth hormone (GH) initiates many of its growth-promoting actions by binding to GH receptors (GHR) and stimulating the synthesis and secretion of insulin-like growth factor-1 (IGF-1) from the liver and other sites. In this study, we used hepatocytes isolated from rainbow trout as a model system in which to determine the molecular signaling events of GH in fish. GH directly stimulated the phosphorylation of ERK, protein kinase B (Akt), a downstream target of phosphatidylinositol 3-kinase (PI3K), JAK2, and STAT5 in hepatocytes incubated in vitro. Activation of ERK, Akt, JAK2, and STAT5 was rapid, occurring within 5–10 min, and was concentration dependent. GH-induced ERK activation was completely blocked by the ERK pathway inhibitor, U0126, and the JAK2 inhibitor, 1,2,3,4,5,6-hexabromocyclohexane (Hex), and was partially blocked by the PI3K inhibitor LY294002. GH-stimulated Akt activation was completely blocked by LY294002 and Hex, but was not affected by U0126; whereas, STAT5 activation by GH was blocked only by Hex, and was not affected by either U0126 or LY294002. GH stimulated hepatic expression of IGF-1 mRNA as well as the secretion of IGF-1, effects that were partially or completely blocked by U0126, LY294002, and Hex. These results indicate that GHR linkage to the ERK, PI3K/Akt, or STAT pathways in trout liver cells requires activation of JAK2, and that GH-stimulated IGF-1 synthesis and secretion is mediated through the ERK, PI3K/Akt, and JAK-STAT pathways.

Growth hormone and adipose tissue: beyond the adipocyte

The last two decades have seen resurgence in research focused on adipose tissue. In part, the enhanced interest stems from an alarming increase in obesity rates worldwide. However, an understanding that this once simple tissue is significantly more intricate and interactive than previously realized has fostered additional attention. While few would argue that growth hormone (GH) radically alters fat mass, newer findings revealing the complexity of adipose tissue requires that GH's influence on this tissue be reexamined. Therefore, the objective of this review is to describe the more recent understanding of adipose tissue and to summarize our current knowledge of how GH may influence and contribute to these newer complexities of this tissue with special focus on the available data from mice with altered GH action.

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.

New onset diabetes associated with bovine growth hormone and testosterone abuse in a young body builder

Case: A 33-year-old male presented to the emergency department with complaints of polydipsia, polyuria, nausea, headaches, blurry vision and malaise. Lab work revealed a serum glucose level of 1166 mg/dl (64.8 mmol/L). The patient admitted to completing a cycle of androgenic anabolic steroids (AASs) for bodybuilding. His regimen consisted of supraphysiologic intramuscular injections of a bovine growth hormone, trenbolone acetate and testosterone. The patient received intravenous fluids and insulin to restore metabolic balance. Previously healthy with a non-contributory family history, he was diagnosed with new onset diabetes. Discussion: It has been demonstrated that AAS use, specifically growth hormone, can affect glucose homeostasis through increasing cellular insulin resistance and reducing glucose uptake. Excess growth hormone has been shown to cause symptoms of acromegaly which predisposes up to 40% of patients to diabetes. As trenbolone acetate is not indicated for human use and athletes are known to use supraphysiologic doses of this underground, performance enhancing drug, the correlation of the timing of events and the use of this veterinary growth hormone likely exacerbated an underlying condition or caused this new onset diabetes. Conclusion: We report a case of a young bodybuilder with no significant past medical history who was diagnosed with new onset diabetes associated with supraphysiologic self-injections of the bovine growth hormone, trenbolone acetate, combined with testosterone. AAS have the potential to induce or exacerbate diabetic conditions due to decreased glucose tolerance and increased insulin resistance.

Diabetes, growth hormone-insulin-like growth factor pathways and association to benign prostatic hyperplasia

Diabetes significantly increases the risk of benign prostatic hyperplasia (BPH) and low urinary tract symptoms (LUTS). The major endocrine aberration in connection with the metabolic syndrome is hyperinsulinemia. Insulin is an independent risk factor and a promoter of BPH. Insulin resistance may change the risk of BPH through several biological pathways. Hyperinsulinemia stimulates the liver to produce more insulin-like growth factor (IGF), another mitogen and an anti-apoptotic agent which binds insulin receptor/IGF receptor and stimulates prostate growth. The levels of IGFs and IGF binding proteins (IGFBPs) in prostate tissue and in blood are associated with BPH risk, with the regulation of circulating androgen and growth hormone. Stromal-epithelial interactions play a critical role in the development and growth of the prostate gland and BPH. Previously, we have shown that the expression of c-Jun in the fibroblastic stroma can promote secretion of IGF-I, which stimulates prostate epithelial cell proliferation through activating specific target genes. Here, we will review the epidemiologic, clinical, and molecular findings which have evaluated the relation between diabetes and development of BPH.

Insulin and GH signaling in human skeletal muscle in vivo following exogenous GH exposure: impact of an oral glucose load

INTRODUCTION

GH induces acute insulin resistance in skeletal muscle in vivo, which in rodent models has been attributed to crosstalk between GH and insulin signaling pathways. Our objective was to characterize time course changes in signaling pathways for GH and insulin in human skeletal muscle in vivo following GH exposure in the presence and absence of an oral glucose load.

METHODS

Eight young men were studied in a single-blinded randomized crossover design on 3 occasions: 1) after an intravenous GH bolus 2) after an intravenous GH bolus plus an oral glucose load (OGTT), and 3) after intravenous saline plus OGTT. Muscle biopsies were taken at t = 0, 30, 60, and 120. Blood was sampled at frequent intervals for assessment of GH, insulin, glucose, and free fatty acids (FFA).

RESULTS

GH increased AUC(glucose) after an OGTT (p<0.05) without significant changes in serum insulin levels. GH induced phosphorylation of STAT5 independently of the OGTT. Conversely, the OGTT induced acute phosphorylation of the insulin signaling proteins Akt (ser(473) and thr(308)), and AS160.The combination of OGTT and GH suppressed Akt activation, whereas the downstream expression of AS160 was amplified by GH. WE CONCLUDED THE FOLLOWING: 1) A physiological GH bolus activates STAT5 signaling pathways in skeletal muscle irrespective of ambient glucose and insulin levels 2) Insulin resistance induced by GH occurs without a distinct suppression of insulin signaling proteins 3) The accentuation of the glucose-stimulated activation of AS 160 by GH does however indicate a potential crosstalk between insulin and GH.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00477997.

[The importance of early diagnosis in acromegaly]

The authors review the historical and epidemiological aspects, clinical features and complications of acromegaly while emphasizing the importance of the early diagnosis and treatment. Acromegaly is a rare and mostly sporadic disorder due to excessive production of growth hormone. It is characterized by progressive somatic disfigurement (mainly involving the face and extremities) and systemic manifestations. The prevalence is estimated between 40 and 125 cases/million. Generally, it is diagnosed in middle-aged adults (mean age 40 years, men and women equally affected). Due to its insidious onset and slow progression, acromegaly is often diagnosed 7 to more than 10 years after its onset. The disease has cardiovascular, rheumatological, respiratory and metabolic consequences which highly determine its prognosis. Acromegaly is associated with a number of complications resulting in a two- or four-fold increase of mortality and a decrease of life expectancy by about 10 years. The major causes of death include cardiovascular and cerebrovascular events, respiratory diseases and malignancies. The duration of the disease before the introduction of effective therapy may be a major predictor of increased mortality mainly due to complications . The early diagnosis is important for timely commencement of treatment and for prevention of serious complications of the disease.

Fasting vs dietary restriction in cellular protection and cancer treatment: from model organisms to patients

The dietary recommendation for cancer patients receiving chemotherapy, as described by the American Cancer Society, is to increase calorie and protein intake. Yet, in simple organisms, mice, and humans, fasting--no calorie intake--induces a wide range of changes associated with cellular protection, which would be difficult to achieve even with a cocktail of potent drugs. In mammals, the protective effect of fasting is mediated, in part, by an over 50% reduction in glucose and insulin-like growth factor 1 (IGF-I) levels. Because proto-oncogenes function as key negative regulators of the protective changes induced by fasting, cells expressing oncogenes, and therefore the great majority of cancer cells, should not respond to the protective signals generated by fasting, promoting the differential protection (differential stress resistance) of normal and cancer cells. Preliminary reports indicate that fasting for up to 5 days followed by a normal diet, may also protect patients against chemotherapy without causing chronic weight loss. By contrast, the long-term 20 to 40% restriction in calorie intake (dietary restriction, DR), whose effects on cancer progression have been studied extensively for decades, requires weeks-months to be effective, causes much more modest changes in glucose and/or IGF-I levels, and promotes chronic weight loss in both rodents and humans. In this study, we review the basic as well as clinical studies on fasting, cellular protection and chemotherapy resistance, and compare them to those on DR and cancer treatment. Although additional pre-clinical and clinical studies are necessary, fasting has the potential to be translated into effective clinical interventions for the protection of patients and the improvement of therapeutic index.

Regulation of whole body energy homeostasis with growth hormone replacement therapy and endurance exercise

We hypothesized that network analysis is useful to expose coordination between whole body and myocellular levels of energy metabolism and can identify entities that underlie skeletal muscle's contribution to growth hormone-stimulated lipid handling and metabolic fitness. We assessed 112 metabolic parameters characterizing metabolic rate and substrate handling in tibialis anterior muscle and vascular compartment at rest, after a meal and exercise with growth hormone replacement therapy (GH-RT) of hypopituitary patients (n = 11). The topology of linear relationships (| r | ≥ 0.7, P ≤ 0.01) and mutual dependencies exposed the organization of metabolic relationships in three entities reflecting basal and exercise-induced metabolic rate, triglyceride handling, and substrate utilization in the pre- and postprandial state, respectively. GH-RT improved aerobic performance (+5%), lean-to-fat mass (+19%), and muscle area of tibialis anterior (+2%) but did not alter its mitochondrial and capillary content. Concomitantly, connectivity was established between myocellular parameters of mitochondrial lipid metabolism and meal-induced triglyceride handling in serum. This was mediated via the recruitment of transcripts of muscle lipid mobilization (LIPE, FABP3, and FABP4) and fatty acid-sensitive transcription factors (PPARA, PPARG) to the metabolic network. The interdependence of gene regulatory elements of muscle lipid metabolism reflected the norm in healthy subjects (n = 12) and distinguished the regulation of the mitochondrial respiration factor COX1 by GH and endurance exercise. Our observations validate the use of network analysis for systems medicine and highlight the notion that an improved stochiometry between muscle and whole body lipid metabolism, rather than alterations of single bottlenecks, contributes to GH-driven elevations in metabolic fitness.

Time-course effects of physiological free fatty acid surges on insulin sensitivity in humans

AIM

Physiological elevations of free fatty acids (FFAs) occur in bell-shaped surges lasting some hours, observed nocturnally, during exercise and inflammation. The time-course effects of such FFA surges on insulin sensitivity are unknown. We therefore aimed to define the effects of a graded 4-h FFA elevation intended to mimick physiological excursions.

METHODS

Eight lean, healthy men were studied on two occasions: (1) control (saline) and (2) 4 h graded infusion of intralipid (20%)/heparin. Insulin sensitivity was continuously assessed by isotope dilution (3H-glucose) during an 8 h hyperinsulinemic-euglycaemic clamp (0.5 mU kg(-1) min(-1) ). Phosphorylation of Akt and ERK1/2 was measured in muscle biopsies taken at 0 and 120 min. Inflammatory cytokines were assessed with a Luminex Suspension Array System.

RESULTS

Infusion of intralipid caused a bell-shaped increase in FFA levels reaching peak levels ~1.9 mmol L(-1) and markedly impairing insulin sensitivity. Impairment of insulin sensitivity was apparent (P>0.05) 120 min after initiation of FFA infusion, significant after 270 min (P < 0.001) and peaked after 360 min. FFA induced insulin resistance prevailed 210 min after cessation of FFA infusion. No effect was observed on Akt and ERK1/2 phosphorylation.

CONCLUSIONS

(1) Physiological FFA elevations require at least 120 min to induce insulin resistance, (2) that insulin resistance peaks 360 min after initiation of FFA exposure and (3) ceases 210 min after termination of the FFA infusion. These observations add to our understanding of FFA induced insulin resistance in relation to circadian variations, exercise, generalized inflammation and exposure to stress hormones such as growth hormone.