Effect of dietary oxidized tyrosine products on insulin secretion via the oxidative stress-induced mitochondria damage in mice pancreas

Abstract

Oxidized tyrosine products (OTPs) have been detected in commercial food and have been demonstrated to induce oxidative damage in vivo. The pancreas plays an important role in glucose metabolism, but its antioxidant capacity is low. The present study investigates the potential impact of dietary OTPs on the pancreatic function. Sprague Dawley (SD) rats (8 rats per group) were fed a diet containing OTPs for 24 weeks, and the blood glucose and plasma insulin levels were then measured. Elevated fasting blood glucose and decreased plasma insulin levels indicated dysfunction of the pancreatic islets. The rats fed the OTPs-containing diet also exhibited pancreatic oxidative stress, accompanied by inflammation. Furthermore, the expression of genes involved in the Nrf2/ARE pathway was down-regulated in the OTPs-treated groups. In addition, supplementation with lipoic acid (LA) significantly remitted the OTPs induced oxidative stress of the pancreas, and mitigated the effects of OTPs on the blood glucose and insulin synthesis. A gavage experiment was performed to explore whether dityrosine (Dityr), a major component of OTPs, was responsible for the injury induced by OTP. The OTPs, including Dityr, induced mitochondrial defects in cultured mice insulinoma MIN-6 cells and mice pancreas, as evidenced by less ATP production, loss of mitochondrial membrane potential, mitochondrial DNA (mtDNA) depletion, and alteration of the mRNA levels of genes involved in mitochondrial function. Moreover, the apoptosis of pancreatic islets and MIN-6 cells increased after exposure to OTPs/Dityr. The findings suggest that decreased insulin secretion triggered by OTPs may be mediated by oxidative stress and mitochondrial damage in pancreatic β cells.