Increasing dietary lipid and iron content decreases manganese superoxide dismutase activity in colonic mucosa

Manganese superoxide dismutase (MnSOD) is an important mitochondrial antioxidant. Alteration in the regulation of MnSOD activity has been proposed to play a critical role in the development of many types of tumors. Colorectal cancer is one of the most common human malignancies and has been shown to be influenced by dietary factors. Two such dietary factors include lipid and iron. Lipid and iron are also potential modulators of MnSOD activity. This study examined lipid and iron influence on MnSOD activity in colonic mucosa. Fischer rats were fed one of eight test diets for six weeks. Four of the diets included AIN-76A-based formulas containing 5% corn oil or 20% lipid from corn oil, menhaden oil, or beef tallow. Four additional diets included identical formulations with iron supplemented to a level of 140 mg/kg. Results showed that iron supplementation decreased MnSOD activity in animals fed the 5% corn oil diet. An increase in dietary lipids from 5% to 20% also decreased MnSOD activity in colonic mucosa. The lipid and iron variables used in this study decreased MnSOD activity without affecting manganese status or other antioxidant mechanisms in this tissue.