Effects Of Supraphysiologic Concentrations Of Glucose And Palmitate On Intracellular Triglyceride Content And FAT/CD36 Gene Expression In Pancreatic β-Cells.

【Objective】We study the effects of supraphysiologic levels of glucose and palmitate on intracellular triglyceride content and fatty acid translocase (FAT/CD36) gene expression in pancreaticβ-cells, so as to explore the role of FAT/CD36 in cellular triglyceride accumulation andβ-cells dysfunction.【Methods】1. The mice insulinoma cell lines NIT-1 were incubated with various concentrations of glucose(5 mmol/L,10 mmol/L,15 mmol/L,20 mmol/L,25 mmol/L,30 mmol/L) or palmitinic acid(0 mmol/L,0.125 mmol/L,0.25 mmol/L,0.5 mmol/L)for 24 hours , reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the levels of FAT/CD36 gene expression. Then according to the results of RT-PCR, we choosed appropriate levels of glucose (25 mmol/L) and palmitate (0.25 mmol/L) to further study. 2. NIT-1 cells were cultured in the presence of 0.25mmol/L palmitate with (GP group) or without (HP group) 25 mmol/L glucose and 25 mmol/L glucose along (HG group) for 24 hours. Control group was provided by cells cultured at 5 mmol/L glucose. Based on the colorimetric determination of glycerol produced by hydrolysis of neutral lipids, intracellular triglyceride (TG) content was determined. Insulin levels after glucose load test in the cell were measured with radioimmunoassay and FAT/CD36 mRNA expression was detected by RT-PCR.【Results】1. Following exposure of NIT-1 cells to increasing concentrations of glucose for 24 hours, FAT/CD36 mRNA expression was gradually augmented as the glucose levels were enhanced. A significant maximal effect was observed at 25 mmol/L glucose. But palmitate had no effect on FAT/CD36 mRNA levels at any concentrations.2. Compared with NC group, a 24-hour period of culture with supraphysiologic concentrations of glucose or/and palmitate promoted intracellular TG content, but inhibited glucose-stimulated insulin secretion (GSIS). A most significant change of TG and GSIS was observed in GP group (P<0.01).And in comparison with GP group, a significant difference of TG and GSIS was also apparent in HG (P<0.05) and HP groups (P<0.01).3. In the presence of elevated glucose levels,FAT/CD36 mRNA expression was significantly enhanced in both HG and GP groups compared with NC group(P<0.01), but palmitate did not show any effect on the expression of FAT/CD36 mRNA at either 5 mmol/L or 25 mmol/L glucose.【Conclusion】1. Glucose promotes FAT/CD36 mRNA expression ofβ-cells in a dose-dependent manner, but palmitate shows no effect on the levels of FAT/CD36 mRNA at any concentrations.2. In the presence of elevated palmitate levels, prolonged exposure ofβ-cells to supraphysiologic glucose concentration could further increase intracellular triglyceride content and inhibit GSIS. The upregulation of FAT/CD36 gene expression induced by high glucose maybe one of important mechanisms. Glucose and palmitate have synergistic effects onβ-cells dysfunction.