Leptin suppression of insulin secretion and gene expression in human pancreatic islets: implications for the development of adipogenic diabetes mellitus.
Previously we demonstrated the expression of the long form of the leptin receptor in rodent pancreatic beta-cells and an inhibition of insulin secretion by leptin via activation of ATP-sensitive potassium channels. Here we examine pancreatic islets isolated from pancreata of human donors for their responses to leptin. The presence of leptin receptors on islet beta-cells was demonstrated by double fluorescence confocal microscopy after binding of a fluorescent derivative of human leptin (Cy3-leptin). Leptin (6.25 nM) suppressed insulin secretion of normal islets by 20% at 5.6 mM glucose. Intracellular calcium responses to 16.7 mM glucose were rapidly reduced by leptin. Proinsulin messenger ribonucleic acid expression in islets was inhibited by leptin at 11.1 mM, but not at 5.6 mM glucose. Leptin also reduced proinsulin messenger ribonucleic acid levels that were increased in islets by treatment with 10 nM glucagon-like peptide-1 in the presence of either 5.6 or 11.1 mM glucose. These findings demonstrate direct suppressive effects of leptin on insulin-producing beta-cells in human islets at the levels of both stimulus-secretion coupling and gene expression. The findings also further indicate the existence of an adipoinsular axis in humans in which insulin stimulates leptin production in adipocytes and leptin inhibits the production of insulin in beta-cells. We suggest that dysregulation of the adipoinsular axis in obese individuals due to defective leptin reception by beta-cells may result in chronic hyperinsulinemia and may contribute to the pathogenesis of adipogenic diabetes. (+info)
DEF-1, a novel Src SH3 binding protein that promotes adipogenesis in fibroblastic cell lines.
The Src homology 3 (SH3) motif is found in numerous signal transduction proteins involved in cellular growth and differentiation. We have purified and cloned a novel protein, DEF-1 (differentiation-enhancing factor), from bovine brain by using a Src SH3 affinity column. Ectopic expression of DEF-1 in fibroblasts resulted in the differentiation of a significant fraction of the culture into adipocytes. This phenotype appears to be related to the induction of the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma), since DEF-1 NIH 3T3 cells demonstrated augmented levels of PPARgamma mRNA and, when treated with activating PPARgamma ligands, efficient induction of differentiation. Further evidence for a role for DEF-1 in adipogenesis was provided by heightened expression of DEF-1 mRNA in adipose tissue isolated from obese and diabetes mice compared to that in tissue isolated from wild-type mice. However, DEF-1 mRNA was detected in multiple tissues, suggesting that the signal transduction pathway(s) in which DEF-1 is involved is not limited to adipogenesis. These results suggest that DEF-1 is an important component of a signal transduction process that is involved in the differentiation of fibroblasts and possibly of other types of cells. (+info)
Low calorie diet enhances renal, hemodynamic, and humoral effects of exogenous atrial natriuretic peptide in obese hypertensives.
The expression of the natriuretic peptide clearance receptor is abundant in human and rat adipose tissue, where it is specifically inhibited by fasting. In obese hypertensives, plasma atrial natriuretic peptide (ANP) levels were found to be lower than in obese normotensives. Therefore, the increased adipose mass might influence ANP levels and/or its biological activity. The aim of the present study was to evaluate whether the humoral, hemodynamic, and renal effects of exogenous ANP in obese hypertensives might be enhanced by a very low calorie diet. Eight obese hypertensives received a bolus injection of ANP (0.6 mg/kg) after 2 weeks of a normal calorie/normal sodium diet, and blood pressure (BP), heart rate, ANP, cGMP, plasma renin activity, and aldosterone were evaluated for 2 hours before and after the injection. Diuresis and natriuresis were measured every 30 minutes. The patients then started a low calorie/normal sodium diet (510 kcal/150 mmol/d) for 4 days, and then the ANP injection protocol was repeated. The low calorie diet induced a slight weight loss (from 90.6+/-1.1 to 87. 7+/-1.2 kg; P<0.01), which was accompanied by increase of cGMP excretion (from 146.0+/-10.1 to 154.5+/-9.5 nmol/24 h; P<0.05) together with a reduction of BP (P<0.01 versus basal levels). ANP injection after diet was followed by an increase of ANP levels similar to that observed before diet, but plasma cGMP, diuresis, and natriuresis increased significantly only after diet. Similarly, the decrease of BP after ANP administration was significantly higher after diet (change in mean arterial pressure, -6.4+/-0.7 versus -4. 0+/-0.6 mm Hg; P<0.05) as well as that of aldosterone (P<0.01). These data show that a low calorie diet enhances the humoral, renal, and hemodynamic effects of ANP in obese hypertensives and confirm the importance of caloric intake in modulating the biological activity of ANP, suggesting that the natriuretic peptide system can play a role in the acute changes of natriuresis and diuresis associated with caloric restriction. (+info)
Relation between obesity and breast cancer in young women.
This study was conducted to assess the relation between body size and risk of breast cancer among young women. A case-control study was conducted among women aged 21-45 years living in three counties in Washington State. Cases were women born after 1944 with invasive or in situ breast cancer that was diagnosed between January 1, 1983, and April 30, 1990. Controls were selected using random digit dialing and were frequency-matched to cases on the basis of age and county of residence. Interviews took place between 1986 and 1992. Body size was evaluated using indices from several different time periods. After adjustment for confounders, a decreased risk of breast cancer was found for women in the highest quintile of body mass index (weight (kg)/height (m)2) as compared with the lowest quintile (for maximum lifetime body mass index, odds ratio = 0.69, 95% confidence interval (CI) 0.51-0.94). Age modified the relation between body size and risk of breast cancer. The odds ratio for women in the highest quintile of maximum body mass index who were aged 21-35 years was 0.29 (95% CI 0.16-0.55), as compared with an odds ratio of 1.5 for women aged 36-45 years (95% CI 0.9-2.5) (p for interaction = 0.003). This study supports prior research showing a decreased risk of breast cancer associated with increased body size among premenopausal or young women. More detailed analysis in this study found a strong effect that was limited to the youngest age group (< or = 35 years). (+info)
Obesity induces expression of uncoupling protein-2 in hepatocytes and promotes liver ATP depletion.
Uncoupling protein 2 (UCP2) uncouples respiration from oxidative phosphorylation and may contribute to obesity through effects on energy metabolism. Because basal metabolic rate is decreased in obesity, UCP2 expression is predicted to be reduced. Paradoxically, hepatic expression of UCP2 mRNA is increased in genetically obese (ob/ob) mice. In situ hybridization and immunohistochemical analysis of ob/ob livers demonstrate that UCP2 mRNA and protein expression are increased in hepatocytes, which do not express UCP2 in lean mice. Mitochondria isolated from ob/ob livers exhibit an increased rate of H+ leak which partially dissipates the mitochondrial membrane potential when the rate of electron transport is suppressed. In addition, hepatic ATP stores are reduced and these livers are more vulnerable to necrosis after transient hepatic ischemia. Hence, hepatocytes adapt to obesity by up-regulating UCP2. However, because this decreases the efficiency of energy trapping, the cells become vulnerable to ATP depletion when energy needs increase acutely. (+info)
Descriptive analysis of eating regulation in obese and nonobese children.
Bite rate, sip rate, and concurrent activities of six 7-yr-old children, three obese and three nonobese, were observed at lunchtime over a six-month period. A procedure for decreasing bite rate, putting eating utensils down between bites, was implemented in a multiple-baseline across-subjects design. Sip rates and concurrent activities were observed to assess behavioral covariations. In addition, bite rate and amount of food completed were computed over six food categories to analyze food preferences. Results indicated the control of bite rate acorss all subjects, with a significant reduction in amount of food consumed. Correlations between the response classes indicated they were at least partially independent. Differences in eating behavior of obese and nonobese subjects were observed for breadstuffs and milk drinking. (+info)
Divergent effects of intracerebroventricular and peripheral leptin administration on feeding and hypothalamic neuropeptide Y in lean and obese (fa/fa) Zucker rats.
Leptin inhibits feeding and decreases body weight. It may act partly by inhibiting hypothalamic neurons that express neuropeptide Y, a powerful inducer of feeding and obesity. These neuropeptide Y neurons express the Ob-Rb leptin receptor and are overactive in the fatty (fa/fa) Zucker rat. The fa mutation affects the extracellular domain of the leptin receptor, but its impact on leptin action and neuropeptide Y neuronal activity is not fully known. We compared the effects of three doses of leptin given intracerebroventricularly and three doses of leptin injected intraperitoneally on food intake and hypothalamic neuropeptide Y mRNA, in lean and fatty Zucker rats. In lean rats, 4-h food intake was reduced in a dose-related fashion (P<0.01) by all intracerebroventricular leptin doses and by intraperitoneal doses of 300 and 600 microg/kg. Neuropeptide Y mRNA levels were reduced by 28% and 21% after the highest intracerebroventricular and intraperitoneal doses respectively (P<0. 01 for both). In fatty rats, only the highest intracerebroventricular leptin dose reduced food intake (by 22%; P<0. 01). Neuropeptide Y mRNA levels were 100% higher in fatty rats than in lean animals, and were reduced by 18% (P<0.01) after the highest intracerebroventricular leptin dose. Intraperitoneal injection had no effect on food intake and neuropeptide Y mRNA. The fa/fa Zucker rat is therefore less sensitive to leptin given intracerebroventricularly and particularly intraperitoneally, suggesting that the fa mutation interferes both with leptin's direct effects on neurons and its transport into the central nervous system. Obesity in the fa/fa Zucker rat may be partly due to the inability of leptin to inhibit hypothalamic neuropeptide Y neurons. (+info)
No association between the -308 polymorphism in the tumour necrosis factor alpha (TNFalpha) promoter region and polycystic ovaries.
The tumour necrosis factor (TNF)2 allele appears to be linked with increased insulin resistance and obesity, conditions often found in overweight patients with polycystic ovary syndrome (PCOS). The significance of TNFalpha polymorphism in relation to the clinical and biochemical parameters associated with PCOS was investigated in 122 well-characterized patients with polycystic ovaries (PCO). Of these, 84 had an abnormal menstrual cycle and were classified as having PCOS, while the remaining 38 had a normal menstrual cycle and were classified as having PCO. There were a further 28 individuals without PCO (non-PCO) and 108 individuals whose PCO status was undetermined (reference population). The promoter region of the TNFalpha gene was amplified by polymerase chain reaction (PCR), and the presence or absence of the polymorphism at -308 was determined by single-strand conformational polymorphism (SSCP) analysis. The less common TNF allele (TNF2) was found as TNF1/2 or TNF2/2 in 11/38 (29%) of PCO subjects, 25/84 (30%) of PCOS subjects, 7/28 (25%) of non-PCO subjects, and 45/108 (42%) of the reference population. There was no significant difference in the incidence of the TNF2 allele between the groups. The relationship of TNF genotype to clinical and biochemical parameters was examined. In both the PCO group and the PCOS group, the presence of the TNF2 allele was significantly associated with lower glucose values obtained from the glucose tolerance testing (P<0.05). The TNF genotype was not significantly associated with any clinical or biochemical parameter measured in the PCO, PCOS or non-PCOS groups. Thus, the TNFalpha -308 polymorphism does not appear to strongly influence genetic susceptibility to polycystic ovaries. (+info)