Pyruvate inhibits zinc-mediated pancreatic islet cell death and diabetes

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Abstract
Aims/hypothesis We have shown that zinc ion (Zn2+) in secretory granules of pancreatic beta cells could act as a paracrine death effector in streptozotocin-induced diabetes. As Zn2+ has been reported to perturb glycolysis, we studied if pyruvate could inhibit Zn2+-mediated islet cell death in vitro and streptozotocin-induced diabetes in vivo by normalizing intracellular energy metabolism. Methods Cell death was measured by quantitative viable cell staining and Hoechst/propidium iodide staining. ATP was measured by bioluminescence determination. Pyruvate was infused through the tail vein 1 h before streptozotocin administration. Beta-cell volume was measured by point counting of the insulin-containing cells. Results Zn2+ induced classical necrosis on MIN6N8 insulinoma cells which was associated with a rapid decline of intracellular ATP levels. Pyruvate inhibited Zn2+-induced necrosis of insulinoma cells and depletion of intracellular ATP by Zn2+. Pyruvate did not inhibit other types of necrosis or apoptosis. Energy substrates such as oxaloacetate, α-ketoglutarate and succinic acid dimethylester also attenuated Zn2+-induced insulinoma cell death. Methylpyruvate that does not generate NAD+ in the cytoplasm or α-ketoisocaproate that stimulates ATP generation exclusively in mitochondria also protected insulinoma cells from Zn2+-induced necrosis. Pyruvate infusion inhibited the development of diabetes by protecting beta-cell mass after streptozotocin administration. Conclusion/interpretation These results indicate that pyruvate inhibits Zn2+-induced necrosis of beta cells in vitro by protecting intracellular ATP levels and also streptozotocin-induced diabetes in vivo where Zn2+ has been reported to act as a paracrine death effector.