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One of the unique features of β-cells is their relatively low expression of many antioxidant enzymes. This could render β-cells susceptible to oxidative damage but may also provide a system that is sensitive to reactive oxygen species as signals. In isolated mouse islets and INS-1(832/13) cells, glucose increases intracellular accumulation of H₂O₂. In both models, insulin secretion could be stimulated by provision of either exogenous H₂O₂ or diethyl maleate, which raises intracellular H₂O₂ levels. Provision of exogenous H₂O₂ scavengers, including cell permeable catalase and N-acetyl-l-cysteine, inhibited glucose-stimulated H₂O₂ accumulation and insulin secretion (GSIS). In contrast, cell permeable superoxide dismutase, which metabolizes superoxide into H₂O₂, had no effect on GSIS. Because oxidative stress is an important risk factor for β-cell dysfunction in diabetes, the relationship between glucose-induced …