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      Rosiglitazone Inhibits Early Stage of Glucolipotoxicity-Induced Beta-Cell Apoptosis

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          Aim: We investigated whether rosiglitazone protects β-cells from glucolipotoxicity directly. Methods: INS-1 cells were incubated with 25 m M glucose and 0.5 m M palmitate in the absence or presence of 2.5 µ M rosiglitazone. We evaluated caspase-3 expression and nuclear DAPI staining. An in vivo study was performed, in which 18-week-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats were treated with rosiglitazone (4 mg/kg/day, n = 6) and with placebo (n = 6) for 10 weeks. At 28 weeks of age, an oral glucose tolerance test, insulin sensitivity test, TUNEL assay and histologic examination were performed. Results: Rosiglitazone attenuated glucolipotoxicity-induced nuclear change and caspase-3 expression for 8 h after treatment, but this effect was not observed at 12 h in INS-1 cells. Rosiglitazone treatment decreased β-cell apoptosis, preserved β-cell mass and improved glucose tolerance in OLETF rats. Conclusion: The present in vitro findings suggest that rosiglitazone can inhibit the early stage of glucolipotoxicity-induced β-cell apoptosis. Our results suggest that the antidiabetic action of rosiglitazone is, at least in part, related to a direct effect on β-cells rather than simply an indirect effect of improving insulin sensitivity.

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          Most cited references 22

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          PPAR-gamma: adipogenic regulator and thiazolidinedione receptor.

          The past several years have seen an explosive increase in our understanding of the transcriptional basis of adipose cell differentiation. In particular, a key role has been illustrated for PPAR-gamma, a member of the nuclear hormone receptor superfamily. PPAR-gamma has also been recently identified as the major functional receptor for the thiazolidinedione class of insulin-sensitizing drugs. This review examines the evidence that has implicated this transcription factor in the processes of adipogenesis and systemic insulin action. In addition, several models are discussed that may explain how a single protein can be involved in these related but distinct physiological actions. I also point out several important areas where our knowledge is incomplete and more research is needed. Finally, I discuss how advances in our understanding of nuclear receptor function, particularly the docking of cofactors in a ligand-dependent fashion, should lead to improved drugs that utilize the PPAR-gamma system for the treatment of insulin resistance.
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            Spontaneous long-term hyperglycemic rat with diabetic complications. Otsuka Long-Evans Tokushima Fatty (OLETF) strain.

             T Natori,  K Kawano,  S Mori (1992)
            A spontaneously diabetic rat with polyuria, polydipsia, and mild obesity was discovered in 1984 in an outbred colony of Long-Evans rats, which had been purchased from Charles River Canada (St. Constant, Quebec, Canada) in 1982. A strain of rats developed from this rat by selective breeding has since been maintained at the Tokushima Research Institute (Otsuka Pharmaceutical, Tokushima, Japan) and named OLETF. The characteristic features of OLETF rats are 1) late onset of hyperglycemia (after 18 wk of age); 2) a chronic course of disease; 3) mild obesity; 4) inheritance by males; 5) hyperplastic foci of pancreatic islets; and 6) renal complication (nodular lesions). Histologically, the changes of pancreatic islets can be classified into three stages: 1) an early stage (6-20 wk of age) of cellular infiltration and degeneration; 2) a hyperplastic stage (20-40 wk of age); and 3) a final stage (at > 40 wk of age). These clinical and pathological features of disease in OLETF rats resemble those of human NIDDM.
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              Saturated fatty acids synergize with elevated glucose to cause pancreatic beta-cell death.

              We have proposed the "glucolipotoxicity" hypothesis in which elevated free fatty acids (FFAs) together with hyperglycemia are synergistic in causing islet beta-cell damage because high glucose inhibits fat oxidation and consequently lipid detoxification. The effects of 1-2 d culture of both rat INS 832/13 cells and human islet beta-cells were investigated in medium containing glucose (5, 11, 20 mM) in the presence or absence of various FFAs. A marked synergistic effect of elevated concentrations of glucose and saturated FFA (palmitate and stearate) on inducing beta-cell death by apoptosis was found in both INS 832/13 and human islet beta-cells. In comparison, linoleate (polyunsaturated) synergized only modestly with high glucose, whereas oleate (monounsaturated) was not toxic. Treating cells with the acyl-coenzyme A synthase inhibitor triacsin C, or the AMP kinase activators metformin and 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside that redirect lipid partitioning to oxidation, curtailed glucolipotoxicity. In contrast, the fat oxidation inhibitor etomoxir, like glucose, markedly enhanced palmitate-induced cell death. The data indicate that FFAs must be metabolized to long chain fatty acyl-CoA to exert toxicity, the effect of which can be reduced by activating fatty acid oxidation. The results support the glucolipotoxicity hypothesis of beta-cell failure proposing that elevated FFAs are particularly toxic in the context of hyperglycemia.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                September 2008
                29 July 2008
                : 70
                : 3
                : 165-173
                aDepartment of Internal Medicine, bBrain Korea 21 for Medical Science, and cInstitute of Endocrine Research, Yonsei University College of Medicine, dInstitute for Cancer Research, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, eDepartment of Endocrinology, Ajou University School of Medicine, fLaboratory of Endocrinology, Institute for Medical Science, Ajou University School of Medicine, Suwon, South Korea
                137662 Horm Res 2008;70:165–173
                © 2008 S. Karger AG, Basel

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                Page count
                Figures: 7, Tables: 1, References: 30, Pages: 9
                Original Paper


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