Effects of intestinal microflora on superoxide dismutase activity in the mouse cecum.

In the antioxidant defense system, superoxide dismutase (SOD) catalyzes the breakdown of superoxide into hydrogen peroxide and oxygen. In the cecum, the influence of intestinal microflora on SOD activity is unknown. In this study, we used germ-free (GF) mice to examine the effect of intestinal microflora on SOD activity in the cecum, and SOD activity was compared between GF and conventional (CV) mice. The activity of CuZnSOD and MnSOD was determined using the SOD Assay Kit-WST. Expressions of CuZnSOD mRNA and protein were determined by real-time PCR and western blot analyses, respectively. The activities of CuZnSOD and MnSOD were significantly higher in the ceca of GF IQI and FVB/N strain mice than in CV mice (P<0.01-0.05). The gene expressions of CuZnSOD mRNA in the ceca of GF mice were significantly higher than those in CV mice (P<0.05), and CuZnSOD protein expression showed similar tendencies. Consistent with the abovementioned results, the total SOD activity in conventionalized mice decreased to the level of total SOD activity observed in the ceca of CV mice. Furthermore, no differences between GF and CV mice were observed in the SOD activities in the liver and thymus. Our results suggest that the antioxidant defense system in the mouse cecum is influenced by the intestinal microflora that downregulate SOD activity.