In addition to the ascertained efficacy as antidiabetic drug, metformin is increasingly being used as weight-loss agent in obesity, and as insulin sensitizer in nonalcoholic fatty liver disease (NAFLD). However, the mechanisms underlying these effects are still incompletely understood. Emerging evidence suggest metformin as leptin sensitizer to mediate the weight-loss effect in the brain. In this study, we investigated effects of metformin on expression of leptin receptors in liver and kidney in mice. C57BL/6 mice were fed with chow diet (CD) or high-fat diet (HF) for 5months. Afterward, mice were treated with metformin (50mg/kg or 200mg/kg) for 15days. Metabolic parameters and hepatic gene expression were analyzed at the end of the treatment. We also tested the effects of metformin on plasma-soluble leptin receptor (sOB-R) levels in newly diagnosed type 2 diabetes mellitus (T2DM) patients, and assessed its effect on hepatosteatosis in mice. Results showed that metformin upregulates the expression of leptin receptors (OB-Ra, -Rb, -Rc, and -Rd) in liver but not kidney. The stimulation effect is dose-dependent in both chow and HF mice. Upregulation of OB-Rb, long signaling isoform, needs a relatively higher dose of metformin. This effect was paralleled by increased sOBR levels in mice and T2DM patients, and decreased hepatic triglyceride (TG) content and lipogenic gene expression, including sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthase (FAS) and acetyl-CoA carboxylase-1 (ACC-1). Taken together, these data identify hepatic leptin receptor as target gene being upregulated by metformin which may enhance leptin sensitivity in liver to alleviate steatosis.

Oxidative stress is a major cause of islet injury and dysfunction during isolation and transplantation procedures. Cyanidin-3-O-glucoside (C3G), which is present in various fruits and vegetables especially in Chinese bayberry, shows a potent antioxidant property. In this study, we determined whether C3G could protect neonatal porcine islets (NPI) from reactive oxygen species (H₂O₂)-induced injury in vitro and promote the function of NPI in diabetic mice. We found that C3G had no deleterious effect on NPI and that C3G protected NPI from damage induced by H₂O₂. Significantly higher hemeoxygenase-1 (HO1) gene expression was detected in C3G-treated NPI compared to untreated islets before and after transplantation (P < 0.05). Western blot analysis showed a significant increase in the levels of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3K/Akt) proteins in C3G-treated NPI compared to untreated islets. C3G induced the nuclear translocation of nuclear erythroid 2-related factor 2 (NRF2) and the significant elevation of HO1 protein. Recipients of C3G-treated NPI with or without C3G-supplemented drinking water achieved normoglycemia earlier compared to recipients of untreated islets. Mice that received C3G-treated islets with or without C3G-supplemented water displayed significantly lower blood glucose levels at 5–10 weeks post-transplantation compared to mice that received untreated islets. Mice that received C3G-treated NPI and C3G-supplemented drinking water had significantly (P < 0.05) lower blood glucose levels at 7 and 8 weeks post-transplantation compared to mice that received C3G-treated islets. These findings suggest that C3G has a beneficial effect on NPI through the activation of ERK1/2- and PI3K/AKT-induced NRF2-mediated HO1 signaling pathway.

Prostaglandin (PGE) 2 is the most common prostanoid and plays an important role in female reproduction. The aim of this study was to examine the expression and regulation of microsomal (m) PGE synthase (PGES)-1 and cytosolic (c) PGES in the mouse ovary during sexual maturation, gonadotropin treatment and luteal development by in situ hybridization and immunohistochemistry. Both mPGES-1 mRNA signals and immunostaining were localized in the granulosa cells, but not in the thecal cells and oocytes. cPGES mRNA signals were localized in both granulosa cells and oocytes, whereas cPGES immunostaining was exclusively localized in the oocytes. In our superovulated model of immature mice, there was a basal level of mPGES-1 mRNA signals in the granulosa cells at 48 h after equine chorionic gonadotropin (eCG) treatment. mPGES-1 mRNA level was induced by human chorionic gonadotropin (hCG) treatment for 0.5 h, whereas mPGES-1 immunostaining was slightly induced at 0.5 h after hCG treatment and reached a maximal level at 3 h after hCG treatment. eCG treatment had no obvious effects on either cPGES mRNA signals or immunostaining. A strong level of cPGES immunostaining was present in both unstimulated and eCG-treated groups. Both mPGES-1 mRNA signals and immunostaining were highly detected in the corpus luteum 2 days post-hCG injection and declined from days 3 to 7 post-hCG injection. cPGES immunostaining was at a basal level or not detectable from days 1 to 7 after hCG injection and was highly expressed in the corpus luteum from days 9 to 15 post-hCG injection. PGE2 biosynthesized through the mPGES-1 pathway may be important for follicular development, ovulation and luteal formation.