The Experimental Study Of Triglycerides-Induced Lipotoxicity In Primary Cultured Rat Islet Cells

Objectives : Type 2 diabetes mellitus is characterized by hypertriglyceridemia . Several studies show that HTG is an independent risk factor for type 2 diabetes mellitus . Using islet cells of SD rats in primary culture , the study was to investigate TGs-induced lipotoxicity by observing cellular TG accumulation , determining cell function , intracellular free calcium concentration and mitochondria activity.Methods: (1) Isolated pancreatic islet cells from SD rats were cultured in monolayer and were treated with different concentrations of TGs for 72 h . Using radioimmunoassay , insulin level in the cell culture media was measured after glucose load test . Mitochondria activity was determined by MTT assay . (2) After Oil Red O-staining techniques cellular TG accumulation and other morphologic changes of islet cells were observed by light microscope and electron microscope . (3) The Flou-3/AM was applied to probe intracellular free calcinm concentration and the fluorescent intensity was detected using laser confical microscopy.Results: (1) No effect was observed after a 72 h incubation with different concentration of TGs at low glucose level(2.8 mmol/L) . Glucose-induced insulin secretion was inhibited by highter concentration of TG and not inhibited by lower concentration of TG at high glucose level(27.8 mmol/L). (2) Insulin secreation was no significantly affected after a 72 h incubation with 5.0 mmol/L TG or 27.8 mmol/ L glucose or 5.0 mmol/L TG plus 27.8mmol/L glucose at the low glucose stimulation , while insulin secreation was reduced at the high glucose stimulation . (3) Following exposure of islet cells to different concentratin of TGs for 72 h , the cell activity was remarkably decreased . (4) By Oil-Red O staining TG accumulation and morphological changes were found in culturing islet cells with TGs , especially high levels of TGs . In electron micrograph numerous cells exhibited gray cytoplasmic lipid droplets and ultrastructure features of cell injury after 72 h of exposure to 5 mmol/L TG . (5) The fluorescent intensity in TG groups was significantly higher than that of control group , while the fluorescent intensity in TG groups was in no remarkable differences .Conclusions: (1) The study confirmed that TGs had inhibitory effects on function of rat islet cells in primary culture . Highter concentration of TGs could inhibit insuln secreation at 27.8 mmol/L glucose stimulation . High concentrations of TGs and Glu had synergistic effects on impairing function of islet cells . (2) TGs could damage directly islet cells through deceasing the cell viability . (3) Exposure of islet cells to TGs resulted in cytoplasmic lipid accumulations and led to morphological changes of islet cells. 4. The result showed that TGs induced intracellular free calcium elevation in primary cultured islet cells from normal rats and suggested that long-term exposure of islet cells to TGs was toxic to islet cells .