Werner F. Blum

Insulin and Cortisol Promote Leptin Production in Cultured Human Fat Cells

The aim of this study was to investigate the regulation of leptin expression and production in cultured human adipocytes using the model of in vitro differentiated human adipocytes. Freshly isolated human preadipocytes did not exhibit significant leptin mRNA and protein levels as assessed by reverse transcriptase (RT)-polymerase chain reaction (PCR) and radioimmunoassay (RIA). However, during differentiation induced by a defined adipogenic serum-free medium, cellular leptin mRNA and leptin protein released into the medium increased considerably in accordance with the cellular lipid accumulation. In fully differentiated human fat cells, insulin provoked a dose-dependent rise in leptin protein. Cortisol at a near physiological concentration of 10−8 mol/l was found to potentiate this insulin effect by almost threefold. Removal of insulin and cortisol, respectively, was followed by a rapid decrease in leptin expression, which was reversible after readdition of the hormones. These results clearly indicate that both insulin and cortisol are potent and possibly physiological regulators of leptin expression in human adipose tissue.

Contribution of androgens to the gender difference in leptin production in obese children and adolescents.

Recent studies demonstrated significantly higher serum leptin concentrations in females as compared with males, even after correction for differences in body fat mass. The aim of our study was to measure serum leptin concentrations in a large group of obese children and adolescents to determine the possible role of sex steroid hormones on both leptin serum concentrations and production in human adipocytes. Obese girls were found to have significantly higher leptin concentrations than boys at the same degree of adiposity (25.2+/-14.1 vs. 17.2+/-12.6 ng/ml, P < 0.001). In a multiple regression analysis with age and body mass index (percent body fat) as fixed variables, it turned out that testosterone had a potent negative effect on serum leptin in boys, but not in girls. In vitro experiments using newly developed human adipocytes in primary culture showed that both testosterone and its biologically active metabolite dihydrotestosterone are able to reduce leptin secretion into the culture medium by up to 62%. Using a semiquantitative reverse transcriptase-PCR method, testosterone was found to suppress leptin mRNA to a similar extent. These results suggest that, apart from differences in body fat mass, the higher androgen concentrations in obese boys are responsible for the lower leptin serum concentrations compared with obese girls.

The ratio between serum levels of insulin-like growth factor (IGF)-I and the IGF binding proteins (IGFBP-1, 2 and 3) decreases with age in healthy adults and is increased in acromegalic patients

OBJECTIVE Several in‐vitro studies have suggested that the biological actions of IGF‐I can be modified by the presence of specific IGF binding proteins. In man, the 24‐hour serum levels of IGF‐I and IGFBP‐3 remain constant, but short‐term changes in the IGF‐l/IGFBP‐3 ratio have been described following GH administration. Serum levels of IGF‐I and IGFBP‐3 decrease with age in normal adults and are elevated In active acromegaly due to excessive GH secretion. However, the Individual ratios between serum levels of IGF‐I and IGFBP‐3 in acromegalic and healthy adults have not been described previously.

Growth hormone resistance and inhibition of somatomedin activity by excess of insulin-like growth factor binding protein in uraemia

Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) were studied in children with end-stage renal failure (ESRF,n=31) and chronic renal failure (n=11) with residual glomerular filtration. Somatomedin bioactivity in patient sera was found to be decreased while IGF-I and IGF-II levels by radio-immunoassay (RIA) were normal. In contrast, IGFBP-1 and IGFBP-3 levels (measured by RIA) were markedly increased in uraemia. Excess IGFBP was shown to be able to bind IGF by determination of the free IGF binding capacity. Using high-performance liquid chromatography a shift of the IGFBP-3 profile to low molecular weight components could be demonstrated in ESRF. Affinity crosslinking experiments showed that these low molecular weight IGFBP-3 immunoreactive forms are biologically active. In normal urine only IGFBP-3 forms smaller than 60 kDa were detected with a major peak at 12–20 kDa. Removal of excessive IGFBP from patient sera by affinity chromatography on an IGF-II Sepharose column resulted in a significant increase in somatomedin bioactivity. Model calculations on the interaction of IGF and IGFBP using empirical data suggested a reduction of IGF secretion in uraemia by an order of magnitude. It is concluded: (1) that renal failure causes an accumulation of low molecular weight IGFBP, (2) that the resulting excess of IGFBP acts as a somatomedin inhibitor, and (3) that in uraemia there is a relative growth hormone resistance with respect to IGF production.

Genotypes and phenotypes in children with short stature: clinical indicators of SHOX haploinsufficiency

Background: Short stature affects approximately 2% of children, representing one of the more frequent disorders for which clinical attention is sought during childhood. Despite assumed genetic heterogeneity, mutations or deletions of the short stature homeobox-containing gene (SHOX) are found quite frequently in subjects with short stature. Haploinsufficiency of the SHOX gene causes short stature with highly variable clinical severity, ranging from isolated short stature without dysmorphic features to Léri-Weill syndrome, and with no functional copy of the SHOX gene, Langer syndrome. Methods: To characterise the clinical and molecular spectrum of SHOX deficiency in childhood we assessed the association between genotype and phenotype in a large cohort of children of short stature from 14 countries. Results: Screening of 1608 unrelated individuals with sporadic or familial short stature revealed SHOX mutations or deletions in 68 individuals (4.2%): complete deletions in 48 (70.6%), partial deletions in 4 (5.9%) and point mutations in 16 individuals (23.5%). Although mean height standard deviation score (SDS) was not different between participants of short stature with or without identified SHOX gene defects (–2.6 vs –2.6), detailed examination revealed that certain bone deformities and dysmorphic signs, such as short forearm and lower leg, cubitus valgus, Madelung deformity, high-arched palate and muscular hypertrophy, differed markedly between participants with or without SHOX gene defects (p<0.001). Phenotypic data were also compared for 33 children with Turner syndrome in whom haploinsufficiency of SHOX is thought to be responsible for the height deficit. Conclusion: A phenotype scoring system was developed that could assist in identifying the most appropriate subjects for SHOX testing. This study offers a detailed genotype-phenotype analysis in a large cohort of children of short stature, and provides quantitative clinical guidelines for testing of the SHOX gene.

Leptin levels in patients with anorexia nervosa are reduced in the acute stage and elevated upon short-term weight restoration

Circulating leptin concentrations are known to be low in acute anorexia nervosa (AN), which is characterized by low weight, amenorrhea and specific psychopathological features. In this study plasma leptin concentrations were determined during inpatient treatment of 23 adolescent females with AN using a sensitive radioimmunoassay (RIA) and set into relationship to leptin levels of females matched for age, body mass index (BMI; kg m−2) and/or percent body fat. At referral patients had leptin concentrations well below the female controls. Weight gains led to steep increases of leptin levels which peaked at values well in excess of those observed in controls matched for BMI. In patients who reached the final treatment stage and who were followed-up after discharge, levels subsequently fluctuated and finally dropped into or below the control range. The low leptin levels at referral are likely to be involved in the pathogenesis of amenorrhea and the reduced metabolic state of acutely ill patients. Peak leptin levels reached after weight gain are possibly the cause of increased energy expenditure during this stage of the disorder.

Growth-stimulating effects of recombinant human growth hormone in children with end-stage renal disease

Because patients with uremia have evidence for growth hormone resistance, we investigated whether this resistance can be overcome by administration of recombinant human growth hormone in supraphysiologic doses in children with severe uremia. Nine stunted children with end-stage renal disease (median age 5.8 years, median bone age 2.7 years) were treated with recombinant human growth hormone, 4 IU/m2/day subcutaneously, for a period of 1 year. Median height velocity was increased from 4.4 cm/yr before therapy to 8.0 cm/yr during treatment. Negative values for height velocity standard deviation scores for chronologic age were improved from a median of -2.6 to +1.5 without advancing bone age more than chronologic age. The growth hormone-insulin-like growth factor I resistance may be explained in part by the increased serum concentration of the high molecular weight insulin-like growth factor binding protein despite normal insulin-like growth factor I serum concentration. Treatment with recombinant human growth hormone improved the ratio between the serum concentrations of insulin-like growth factor I and its binding protein, and normalized the somatomedin bioactivity in the growth cartilage bioassay.

Leptin suppresses semi-starvation induced hyperactivity in rats: implications for anorexia nervosa

Semi-starvation induced hyperactivity (SIH) occurs in rodents upon caloric restriction. We hypothesized that SIH is triggered by the decline in leptin secretion associated with food restriction. To test this hypothesis, rats, which had established a stable level of activity, were treated with leptin or vehicle via implanted minipumps concomitantly to initiation of food restriction for 7 days. In a second experiment treatment was initiated after SIH had already set in. In contrast to the vehicle-treated rats, which increased their baseline activity level by 300%, the development of SIH was suppressed by leptin. Furthermore, leptin was able to stop SIH, after it had set in. These results underscore the assumed major role of leptin in the adaptation to semi-starvation. Because SIH has been viewed as a model for anorexia nervosa, we also assessed subjective ratings of motor restlessness in 30 patients with this eating disorder in the emaciated state associated with hypoleptinemia and after increments in leptin secretion brought upon by therapeutically induced weight gain. Hypoleptinemic patients ranked their motor restlessness higher than upon attainment of their maximal leptin level during inpatient treatment. Thus, hypoleptinemia might also contribute to the hyperactivity frequently associated with anorexia nervosa.

Critical illness is associated with low circulating concentrations of insulin-like growth factors-i and -ii, alterations in insulin-like growth factor binding proteins, and induction of an insulin-like growth factor binding protein 3 protease

OBJECTIVES To describe the sequential changes in the circulating concentrations of insulin-like growth factor-I, insulin-like growth factor-II, and insulin-like growth factor binding proteins in critically ill patients. To determine whether critical illness is associated with induction of a specific protease directed against insulin-like growth factor binding protein 3 and to relate these changes to outcome. DESIGN Prospective, descriptive study. SETTING Intensive care unit (ICU) of a university hospital. PATIENTS Eighteen heterogeneous critically ill patients, requiring ventilatory support. INTERVENTIONS Serial daily blood samples were collected until death or discharge from the ICU. In five patients, samples were also obtained on the ward before discharge from the hospital. MEASUREMENTS AND MAIN RESULTS Serum concentrations of insulin-like growth factor-I, insulin-like growth factor-II, and insulin-like growth factor binding proteins 1, 2, and 3 were measured by radioimmunoassay. After 5 days, insulin-like growth factor binding protein 3 concentrations were measured on alternate days. Alterations in binding of insulin-like growth factor-I to insulin-like growth factor binding protein 3 and the presence of protease activity directed against insulin-like growth factor binding protein 3 were investigated by Western ligand blotting. Circulating concentrations of insulin-like growth factor-I and insulin-like growth factor-II were low and remained low throughout the 7-day study period. Insulin-like growth factor binding protein 1 concentrations were initially increased to within the fasting range, but subsequently decreased. There was considerable variability in insulin-like growth factor binding protein 2 concentrations, but generally, concentrations were at the upper end of the normal range throughout. Insulin-like growth factor binding protein 3 concentrations were consistently low and Western ligand blotting at the nadir of the insulin-like growth factor-I concentration demonstrated the presence of a protease directed against insulin-like growth factor binding protein 3. The last recorded concentrations of insulin-like growth factor-I and insulin-like growth factor binding protein 3 were higher in survivors than in nonsurvivors (p < .05). Two patients were also studied for a prolonged period. In one patient, a survivor, insulin-like growth factor-I and insulin-like growth factor binding protein 3 were low initially, but later increased in association with recovery and cessation of protease activity over a period of 33 days. In another patient, a nonsurvivor, insulin-like growth factor-I and insulin-like growth factor binding protein 3 remained low and protease activity persisted until the patient died 38 days after admission to the ICU. CONCLUSIONS Critical illness is associated with low circulating concentrations of insulin-like growth factor-I, insulin-like growth factor-II, and insulin-like growth factor binding protein 3 and these low values are associated with induction of protease activity specifically directed against insulin-like growth factor binding protein 3. In survivors, recovery is associated with increasing insulin-like growth factor-I and insulin-like growth factor binding protein 3 concentrations and cessation of protease activity. The therapeutic effects of exogenous growth factors are likely to be influenced by these changes.

Dexamethasone Impairs Growth Hormone (GH)-Stimulated Growth by Suppression of Local Insulin-Like Growth Factor (IGF)-I Production and Expression of GH- and IGF-I-Receptor in Cultured Rat Chondrocytes1

Growth depression as a side effect of glucocorticoid therapy in childhood is partially mediated by alterations of the somatotropic hormone axis. The mechanisms of interaction between glucocorticoids and somatotropic hormones on the cellular and molecular level are poorly understood. In an experimental model of primary cultured rat growth plate chondrocytes, basal as well as GH (40 ng/ml) or insulin-like growth factor (IGF)-I (60 ng/ml)-stimulated growth was suppressed dose dependently (10−12–10−7 m) by dexamethasone (Dexa). An IGF-I antibody specifically and dose dependently inhibited the GH- but not the basic fibroblast growth factor (bFGF)-stimulated cell proliferation. GH increased the IGF-I concentration in conditioned serum-free culture medium; this was reversed by concomitant Dexa. Dexa time dependently suppressed the transcription of GH receptor (GHR) messenger RNA (mRNA) and down-regulated the basal and GH-stimulated expression of GHR. Whereas no suppressive effect on basal type I IGF-receptor (IG...