Zinc deficiency affects insulin secretion and alters insulin-regulated metabolic signaling in rats.

ABSTRACT

BACKGROUND: The essential trace element zinc is important in stabilizing pancreatic insulin secretion. Zinc not only influences the synthesis of insulin but also affects its activity. Insulin not only exerts a hypoglycemic effect but also regulates glucose and lipid metabolisms in insulin target organs. In this study, we aimed to determine changes to pancreatic ß cells and insulin secretion induced by different zinc concentrations and to evaluate the effect of zinc deficiency on glucose intolerance, insulin resistance, and insulin target organs via changing insulin levels. METHODS: We set up two experimental trials. In the first trial, male Sprague Dawley (SD) rats were divided into three groups. Group one (ZnC) received a standard diet, group two (ZnF) was given a zinc-free diet, and group three (ZnFC) was initially fed a zinc-free diet followed by a reversion to the standard diet. After sacrifice, we observed changes in blood parameters, including insulin, and examined alterations in pancreatic tissue using immunostaining, with focus on the localization of pancreatic ß-cells. In the second trial, male SD rats were split into two groups, with one receiving a standard diet and the other a zinc-free diet. Oral glucose tolerance and insulin tolerance tests were then performed. After sacrifice, we evaluated changes in lipid and glucose metabolism within insulin target organs using quantitative polymerase chain reaction. RESULTS: In the first trial, blood insulin levels and the area of insulin-positive staining in pancreatic ß-cells decreased in the ZnF compared to the ZnC group. The ZnFC group did not show recovery in either blood insulin levels or the area of insulin-positive staining in pancreatic ß-cells. In the second trial, no differences were observed in glucose tolerance or insulin resistance between the ZnC and ZnF groups. However, changes in the expression of insulin target genes were noted in the liver and adipose tissue in the ZnF group. CONCLUSION: We reveal that dietary zinc concentrations not only affect the concentration of insulin in the blood but also impact the localization of pancreatic ß-cells involved in insulin production. Furthermore, our results suggest that changes in blood insulin levels, induced by different zinc concentrations, could cause metabolic alterations in insulin target organs such as the liver and adipose tissue. This study sheds more light on the role of zinc in insulin-regulated metabolic diseases.