Palmitate induces fat accumulation by activating C/EBPß-mediated G0S2 expression in HepG2 cells.

AIM: To determine the role of G0/G1 switch gene 2 (G0S2) and its transcriptional regulation in palmitate-induced hepatic lipid accumulation. METHODS: HepG2 cells were treated with palmitate, or palmitate in combination with CCAAT/enhancer binding protein (C/EBP)ß siRNA or G0S2 siRNA. The mRNA expression of C/EBPß, peroxisome proliferator-activated receptor (PPAR)γ and PPARγ target genes (G0S2, GPR81, GPR109A and Adipoq) was examined by qPCR. The protein expression of C/EBPß, PPARγ, and G0S2 was determined by Western blotting. Lipid accumulation was detected with Oil Red O staining and quantified by absorbance value of the extracted Oil Red O dye. Lipolysis was evaluated by measuring the amount of glycerol released into the medium. RESULTS: Palmitate caused a dose-dependent increase in lipid accumulation and a dose-dependent decrease in lipolysis in HepG2 cells. In addition, palmitate increased the mRNA expression of C/EBPß, PPARγ, and PPARγ target genes (G0S2, GPR81, GPR109A, and Adipoq) and the protein expression of C/EBPß, PPARγ, and G0S2 in a dose-dependent manner. Knockdown of C/EBPß decreased palmitate-induced PPARγ and its target genes (G0S2, GPR81, GPR109A, and Adipoq) mRNA expression and palmitate-induced PPARγ and G0S2 protein expression in HepG2 cells. Knockdown of C/EBPß also attenuated lipid accumulation and augmented lipolysis in palmitate-treated HepG2 cells. G0S2 knockdown attenuated lipid accumulation and augmented lipolysis, while G0S2 knockdown had no effects on the mRNA expression of C/EBPß, PPARγ, and PPARγ target genes (GPR81, GPR109A and Adipoq) in palmitate-treated HepG2 cells. CONCLUSION: Palmitate can induce lipid accumulation in HepG2 cells by activating C/EBPß-mediated G0S2 expression.

[Pancreatic ß-cell Dysfunction and Apoptosis Induced by Elevated Free Fatty Acids Synergize with Hyperglycemia].

OBJECTIVES: To analysis the effects of glucoxicity and lipotoxicity on the function and apoptosis of pancreatic ß-cells. METHODS: The levels of circulating glucose and free fat acids (FFAs) were elevated by infusion dextrose and fat emulsion in high-fat obese rats. The insulin resistance model obese rats were divided into four gourp: obese group with saline infusion (OB-NS group, n=7), obese group with glucose infusion (OB-GS group, n=9), obese group with Lipid emulsion infusion (OB-FFA group, n=8), obese group with glucose and lipid emulsion infusion (OB-FG group, n=9). Five rats fed with general diet were taken as normal group (NC group).Plasma FFAs and ß-hydroxybutyric acid (ß-HBA) concentrations were determined by an enzymatic colorimetric method. An intravenous glucose tolerance test (IVGTT) was performed to examine the glucose-stimulated insulin secretion in vivo and immunohistochemical staining to detect the storage volume of insulin. FFA and ß-HBA concentrations were measured at baseline and post-infusion. The apoptosis of pancreatic ß-cell was detected byin situ end labeling technique (TUNEL). RESULTS: Glucose infusion rate (GIR) of obese rats was significantly lower than that in NC group [(10.82±1.8) mg/(kg·min) vs. (25.21±1.7) mg/(kg·min), P<0.05], confirming insulin resistance rat model successfully established. The insulin secretion peak load time of OB-FG group rats delayed, and the serum insulin level was significantly lower than that of NC group and OB-NS group during IVGTT. The differences were statistically significant ( P<0.05). Compared with OB-NS and NC groups, storage volume of insulin of OB-GS group reduced, and ß cell apoptosis rate elevated significantly. CONCLUSIONS: Glucolipotoxicity could induce ketone overproduction, insulin resistance and defective insulin secretion.

[Alpha-linolenic acid improves insulin sensitivity in obese patients].

OBJECTIVE: To explore the effects of α-linolenic acid on insulin sensitivity in obese patients. METHODS: From October 2011 to April 2012, 16 patients received an oral dose of α-linolenic acid for 8 weeks.Oral glucose tolerance test (OGTT) and insulin releasing test were performed before and after treatment. Homeostasis model assessment insulin resistance (HOMA-IR) index and area under curve of insulin (AUCI) were calculated to evaluate the insulin sensitivity. The levels of serum triglyceride, free fatty acids (FFA), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were measured after an overnight fast. RESULTS: Obese patients had significantly elevated serum insulin, triglyceride, FFA, IL-6 and TNF-α versus the subjects in normal control group (all P < 0.05). Obese patients were also more insulin-resistant than normal subjects based on a higher HOMA-IR (P < 0.05). Decreased serum insulin, triglyceride, FFA, IL-6 and TNF-α were observed after treatment. With the administration of α-linolenic acid, HOMA-IR and AUCI significantly decreased in obese patients (HOMA-IR: 1.8 ± 0.2 vs 1.2 ± 0.3, P < 0.05; AUCI: 1151 ± 505 vs 768 ± 347, P < 0.05). CONCLUSION: α-linolenic acid increases peripheral insulin sensitivity in obese patients and it may aid the prevention and treatment of type 2 diabetes mellitus and atherosclerotic vascular diseases.

[Role of apoptosis and mitochondrial apoptotic pathway in glucolipotoxicity-induced islet beta-cell dysfunction].

OBJECTIVE: To investigate the mechanism of beta-cell dysfunction induced by glucolipotoxicity in high fat-fed obese rats. METHODS: Eighteen high-fat obese male Wistar rats were assigned into 3 groups and underwent 48-hour infusion through the jugular vein with normal saline (n=6), 20% intralipid + heparin (FFA group, n=6), or 25%glucose +20% intralipid + heparin (GS-FFA group, n=6). The plasma beta-hydroxybutyric acid (beta-HBA) was measured before and at the end of the infusion. After the infusion, the rats were sacrificed following an intravenous glucose tolerance test (IVGTT) to remove the tail of the pancreas for detection of apoptotic islet cells using TUNEL method. Immunohistochemical staining was performed to detect the expression of cytochrome c (cyt c), apoptosis-inducing factor (AIF), caspase-9 and caspase-3 in the islet cells. RESULTS: At the end of the infusion, all the rats exhibited increased plasma beta-HBA levels, which was the highest in the GS-FFA group (P<0.05). IVGTT performed after the infusion showed a significantly lower insulinogenic index in GS-FFA group than that in NS and FFA groups. Greater number of apoptotic islet cells was found in the GS-FFA group than in the FFA and NS groups (P<0.05), and the islets had significantly higher levels of cyt c, AIF, caspase-9 and caspase-3 in the former group than in the latter two groups (P<0.05). CONCLUSIONS: Hyperglycemia and high free fatty acid level synergistically impair insulin secretions to cause ketone overproduction in high fat-fed obese rats. The beta-cell dysfunction due to glucolipotoxicity is associated with increased beta-cell apoptosis and activation of mitochondrial apoptotic pathway.