Glucagon plays an important role in the modification of insulin secretion by leptin.

Obese people show marked hyerinsulinemia, but the exact mechanism has not been clarified. Hyperleptinemia is one of possible candidates, although there is an obvious difference in the effect of leptin on insulin secretion between isolated pancreatic islets and ß-cell line. Since glucagon may modulate the effect of leptin on insulin secretion, we determined the influences of glucagon in the leptin effect on insulin secretion. The influences of glucagon in the leptin effect on insulin secretion for 10 minutes were determined by using isolated mouse islets and HIT-T 15 cells. The influences of 3-isobutyl-1- methylxanthine (IBMX), forskolin, and dibutyryl cyclic AMP were investigated in the leptin effect on insulin secretion. Leptin-inhibited insulin and glucagon secretion in isolated mouse pancreatic islets. In contrast, leptin stimulated insulin secretion in isolated mouse islets previously incubated with monoclonal anti-glucagon antibodies for 18 hours. In HIT-T 15 cells, leptin dose-dependently increased insulin secretion, but this effect was attenuated by the addition of glucagon. The stimulatory effect of leptin on insulin secretion was attenuated by 48 hour pre-incubation with glucagon. In the presence of 100 mM IBMX, leptin decreased insulin secretion from HIT-T 15 cells. Leptin also reduced insulin secretion in the presence of 1mM forskolin or 1mM dibutyryl cyclic AMP. The leptin effects on insulin secretion were affected by the existence of glucagon. Intracellular cyclic AMP concentrations may determine the leptin effects on insulin secretion in pancreatic ß-cells.

Fasting concentrations of nesfatin-1 are negatively correlated with body mass index in non-obese males.

BACKGROUND: We recently identified a novel anorexigenic protein, nesfatin-1, which is processed from nesfatin/nucleobindin-2 (NUCB2). However, the clinical importance of this protein has not been determined. OBJECTIVE: To investigate its clinical significance in humans, we have established a new specific enzyme-linked immunosorbent assay (ELISA) for human nesfatin-1 in peripheral blood and measured its circulating concentration in healthy subjects. DESIGN: The new sandwich-type ELISA method was validated and then used to measure nesfatin-1 levels in plasma samples, under overnight fasting conditions, followed by oral glucose tolerance and meal tests. PATIENTS AND MEASUREMENTS: A total of 43 nonobese males (age: 24.5 ± 0.6, body mass index (BMI); 21.1 ± 0.3 kg/m(2)) were recruited to the study for evaluating fasting concentrations of nesfatin-1. In those, fifteen subjects underwent a 75- g oral glucose tolerance test (OGTT) and another 15 underwent a meal test. In addition, fasting concentrations of nesfatin-1 were measured in nine males with high BMI (age: 32.4 ± 3.7, BMI; 37.3 ± 3.8 kg/m(2)). RESULTS: Peripheral concentrations of nesfatin-1 showed a significant negative correlation with BMI, percentage body fat, body fat weight and blood glucose (P < 0.05). Nesfatin-1 concentrations were not significantly changed during OGTT and meal tests. Fasting nesfatin-1 levels were significantly lower in subjects with high BMI compared to nonobese subjects (P < 0.05). CONCLUSIONS: A new specific and sensitive ELISA for nesfatin-1 was established. Further accumulation of clinical observations is necessary to clarify the role of circulating nesfatin-1 in various metabolic disorders.

The role of CHOP messenger RNA expression in the link between oxidative stress and apoptosis.

Low expression of antioxidant enzymes makes pancreatic beta-cells susceptible to cell damage by oxidative stress. Pancreatic beta-cell loss caused by endoplasmic reticulum stress is associated with the onset of diabetes mellitus. The present studies were undertaken to investigate a possible involvement of proapoptotic gene CHOP in pancreatic beta-cells damage by oxidative stress. The induction of CHOP messenger RNA and apoptosis were investigated in betaHC-9 cells after the oxidative stress by hydrogen peroxide and ribose. Latter was examined after the suppression of CHOP by small interfering RNA. For in vivo study, the pancreatic beta-cells were examined in CHOP-knockout (KO) mice after multiple low-dose streptozotocin (MLDS) administration. In betaHC-9 cells, both hydrogen peroxide and ribose obviously increased apoptotic cells, accompanied with enhanced CHOP messenger RNA expression. However, the number of apoptotic cells by those stimulations was significantly reduced by the addition of small interfering RNA against CHOP. In vivo study also showed that CHOP-KO mice were less susceptible to diabetes after MLDS administration. Although the oxidative stress marker level was similar to that of MLDS-treated wild type, the pancreatic beta-cell area was maintained in CHOP-KO mice. The present studies showed that CHOP should be important in pancreatic beta-cell injury by oxidative stress and indicate that CHOP may play a role in the development of pancreatic beta-cell damage on the onset of diabetes mellitus.

Chop-deficient mice showed increased adiposity but no glucose intolerance.

OBJECTIVE: CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP)-10/growth arrest and DNA damage 153 is a dominant-negative member of the C/EBP transcription family and inhibits adipogenesis in vitro. The study was undertaken to determine the role of CHOP in obesity in vivo. RESEARCH METHODS AND PROCEDURES: Changes in daily food consumption and body weight were measured. The weight of white and brown adipose tissue was compared between Chop(+/+) and (-/-) mice fed normal chow or a high-fat diet. Glucose and insulin tolerance tests were done, and serum adipocytokine was measured to determine their metabolic state. Fat cell size of subcutaneous and mesenteric adipose tissue was microscopically observed. C/EBP expression in white adipose tissue was examined by Western blot. RESULTS: Female Chop(-/-) mice had significantly greater body weight and adiposity than Chop(+/+) mice, although daily food intake and rectal temperature did not differ. In comparison with Chop(+/+) mice, glucose tolerance and insulin sensitivity did not differ in female Chop(-/-) mice, but levels of plasma leptin and adiponectin were higher. High-fat diet feeding resulted in obesity in female Chop(+/-) and (-/-) mice, although caloric intake did not differ from that of Chop(+/+) mice. Fat cell area was larger in mesenteric fat but not in subcutaneous fat in Chop(-/-) mice fed a high-fat diet. C/EBPbeta and the 30-kDa form of C/EBPalpha expressions were increased in parametrial fat of Chop(-/-) mice, but the 42-kDa form of C/EBPalpha expression was lower than in Chop(+/+) mice. DISCUSSION: CHOP deficiency causes obesity in female animals without severe metabolic disorders, and C/EBP's expression may be considered to participate in the process.

HGF ameliorates a high-fat diet-induced fatty liver.

Hepatocyte growth factor (HGF) has various effects especially on epithelial cells. However, the precise role of HGF on lipogenesis is still not fully understood. A high-fat diet was administered to HGF transgenic mice and wild-type control mice in vivo. Furthermore, recombinant human HGF (rhHGF) was administered to HepG2 cell line in vitro. We performed an analysis regarding the factors relating to lipid metabolism. An overexpression of HGF dramatically ameliorates a high-fat diet-induced fatty liver. HGF transgenic mice showed an apparently reduced lipid accumulation in the liver. The activation of microsomal triglyceride transfer protein (MTP) and apolipoprotein B (ApoB) accompanying higher triglyceride levels in the serum were found in HGF transgenic mice on a normal diet. Interestingly, this upregulation of the MTP activation became more apparent in the high-fat diet. In addition, the administration of rhHGF stimulated MTP and ApoB expression while reducing reduced the intracellular lipid content in HepG2 cell line. However, this induction of MTP and ApoB by HGF was clearly inhibited by PD98059 (MAPK inhibitor). In conclusion, the data presented in this study indicated that HGF ameliorates a high-fat diet-induced fatty liver via the activation of MTP and ApoB.