Glucose-lowering effects of orally administered superoxide dismutase in type 2 diabetic model rats

Superoxide dismutase (SOD) is an enzyme found in most food sources, might be a candidate to reduce oxidative damage to intestinal barrier, thereby ameliorating the vicious circle between hyperglycemia and the oxidative damage. Here we report the oral administration of SOD, liposome-embedded SOD (L-SOD), and SOD hydrolysate to type 2 diabetic model rats to confirm this hypothesis. Oxidative damage severity in model rat intestine was indicated by malondialdehyde level, GSSG/GSH ratio, and antioxidant enzyme activity. The damage was significantly repaired by L-SOD. Furthermore, blood glucose and related indexes correlated well not only with oxidative damage results but also with indexes indicating physical intestinal damage such as colon density, H&E staining, immunohistochemical analysis of the tight junction proteins occludin and ZO-1 in the colon, as well as lipopolysaccharide and related inflammatory cytokine levels. The order of the magnitude of the effects of these SOD preparations was L-SOD > SOD > SOD hydrolysate. These data indicate that orally administered SOD can exhibit glucose-lowering effect via targeting the intestine of diabetic rats and systemic lipopolysaccharide influx.