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Type 2 diabetes is caused by chronic insulin resistance and progressive decline in beta-cell function. Optimal beta-cell function and mass is essential for glucose homeostasis and beta-cell impairment leads to the development of diabetes. Elevated levels of circulating fatty acids (FAs) and disturbances in lipid metabolism regulation are associated with obesity, and they are major factors influencing the increase in the incidence of type 2 diabetes. Chronic free FA (FFA) treatment induces insulin resistance and beta-cell dysfunction; therefore, reduction of elevated plasma FFA levels might be an important therapeutic target in obesity and type 2 diabetes. Lipid signals via receptors, and intracellular mechanisms are involved in FFA-induced apoptosis. In this paper, we discuss lipid actions in beta cells, including effects on metabolic pathways and stress responses, to help further understand the molecular mechanisms of lipotoxicity-induced type 2 diabetes.

Background: Conjugated linoleic acid (CLA) has strong chemoprotective properties in experimental animal models. The insulin-like growth factor (IGF) system has been implicated as a risk factor for the development of bladder cancer. The present study examined CLA regulation of TSU-Pr1 bladder cancer cell proliferation and apoptosis and the influence of CLA on IGF-I receptor (IGF-IR) signaling., Materials and Methods: TSU-Pr1 cells were cultured in serum-free medium with 0, 2, 5, or 10 microM CLA and/or 10 nM IGF-I. [3H]Thymidne incorporation, DNA laddering, FACS analysis, immunoprecipitation and Western blotting were performed., Results: CLA decreased DNA synthesis and induced apoptosis in TSU-Pr1 cells dose-dependently. Exogenous IGF-I alone increased viable cell numbers but did not counteract growth inhibition induced by CLA. CLA decreased IGF-IR and insulin receptor substrate (IRS)-1 protein levels. In addition, CLA decreased IGF-I-induced phosphorylation of IGF-IR and IRS-1, recruitment of the p85 subunit of phosphoinositide 3-kinase to IRS-1 and phosphorylation of Akt and extracellular signal-regulated kinase-1/2., Conclusion: These results suggest that CLA inhibits cell proliferation and stimulates apoptosis of TSU-Pr1 cells via its inhibition of the IGF-IR signaling pathway.