Pyruvate inhibits zinc-mediated pancreatic islet cell death and diabetes

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.

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.

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.

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.