Oxidised guanosines induce mitochondrial dysfunction and loss of viability in β-cells

The production of reactive oxygen species and oxidative stress promote β-cell dysfunction and impair insulin secretion, thereby contributing to the pathogenesis of type 2 diabetes mellitus (T2DM). The nucleobase guanine is highly sensitive to oxidation, which results in the formation of 8-oxoguanosine (8oxoG) and 8-oxodeoxyguanosine (8oxodG). The urinary excretion of 8oxoG is associated with the risk of mortality in people with T2DM, including from diabetic complications such as cardiovascular disease. However, the cellular mechanisms responsible for this association are poorly defined. Therefore, in this study, we examined the effect of 8oxoG, 8oxodG and other oxidized guanosine derivatives, on the INS-1E β-cell line. Exposure of INS-1E cells to 8oxoG and 8oxodG decreased metabolic activity and promoted cell death by apoptosis. The change in cell viability was similar to that induced by treatment of INS-1E cells with the inflammatory cytokines interleukin 1β (Il-1β) and tumour necrosis factor α (TNFα). Changes in mitochondrial membrane permeability and superoxide radical formation were also observed with 8oxoG, but there was no significant change in the oxidation state of mitochondrial cytochromes or hydrogen peroxide levels in the INS-1E cells. Interestingly, exposure to 8oxoG and 8-oxodG also increased the mRNA expression of stress response genes, including NADPH dehydrogenase quinone 1 (NQO1), and thioredoxin-interacting protein (TXNIP). Together, these results support a potential role of oxidized guanosine derivatives in the induction of β-cell dysfunction, which could be relevant to the pathogenesis of T2DM.