High iron consumption has been proposed to relate to an increase in the risk of colon cancer, whereas high levels of supplemental sodium phytate effectively reduce iron-induced oxidative injury and reverse iron-dependent augmentation of colorectal tumorigenesis. However, the protective role of intrinsic dietary phytate has not been determined. In this study, we examined the impact of removing phytate present in a corn-soy diet by supplemental microbial phytase on susceptibility of pigs to the oxidative stress caused by a moderately high dietary iron intake. Thirty-two weanling pigs were fed the corn-soy diets containing two levels of iron (as ferrous sulfate, 80 or 750 mg/kg diet) and microbial phytase (as Natuphos, BASF, Mt. Olive, NJ, 0 or 1200 unitslkg). Pigs fed the phytase-supplemented diets did not receive any inorganic phosphorus to ensure adequate degradation of phytate. After 4 months of feeding, liver, colon, and colon mucosal scrapings were collected from four pigs in each of the four dietary groups. Colonic lipid peroxidation, measured as thiobarbituric acid reacting substances (TBARS), was increased by both the high iron (P< 0.0008) and phytase (P < 0.04) supplementation. Both TBARS and F,-isoprostanes, an in vivo marker of lipid peroxidation, in colonic mucosa were affected by dietary levels of iron (P < 0.03).Mean hepatic TBARS in pigs fed the phytase-supplemented, high iron diet was 43%-65% higher than that of other groups although the differences were nonsignificant.Moderately high dietary iron induced hepatic glutathione peroxidase activity (P = 0.06) and protein expression, but decreased catalase (P < 0.05) in the colonic mucosa. In conclusion, intrinsic phytate in corn and soy was protective against lipid peroxidation in the colon associated with a moderately high level of dietary iron. [P.S.E.B.M. 1999[P.S.E.B.M. , Vol 2211 he importance of iron in human nutrition and health is well documented ( 1 4 ) . High dietary intakes of T iron may enhance the risk of colon cancer, due to the ability of iron to generate free radicals in \,ivo (5). Because colon cancer is a prevalent disease (average rate 42.U 100,000) with a high mortality rate (average rate 15.7/ Dr. Jes65 M. Porres is funded by a fellowship from NATO. and this project 17 also supported in part by an NIH grant (DK53018 to XCL)
2016-12-23T18:52:10
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