Dietary influences on rat hepatic and intestinal DT-diaphorase activity.

DT-diaphorase (DTD) is a flavoprotein that catalyses the two-electron reduction of various redox dyes and quinones such as menadione and phylloquinone. It has been proposed that this enzyme may have a protective effect against cancer, as the two-electron reduction prevents the formation of toxic oxygen metabolites that may be generated as a result of the one-electron reduction catalysed by enzymes such as NADPH-cytochrome P-450 reductase. The effects of a purified diet supplemented with either 25% Brussels sprouts, phylloquinone (2.5 or 25 ppm) or 250 ppm indole-3-carbinol on hepatic and intestinal DTD activity in adult male Sprague-Dawley rats have been determined. One group was fed on the purified diet and dosed with 3-methylcholanthrene (20 mg/kg), 24 hr before being killed. Hepatic DTD activity was increased 3-fold in the indole-3-carbinol group, 4.4-fold in the sprouts-fed animals and 8.2-fold in the 3-methylcholanthrene-treated animals. Neither level of phylloquinone affected hepatic DTD activity. Intestinal DTD activity was increased 2.1-fold in the indole-3-carbinol group, 3.7-fold in the sprouts-fed animals and 4.3-fold in the 3-methylcholanthrene group. In animals given 25 ppm phylloquinone, intestinal enzyme activity was 60% of the control level, while no effect was noted in those given 2.5 ppm phylloquinone. Although increases in the activities of intestinal xenobiotic-metabolizing enzymes resulting from dietary influences are well documented, the increase in hepatic DTD activity seen in response to vegetable consumption has not been reported. The significance of these results in relation to the possible protective effects of dietary cruciferous vegetables against cancer is discussed.