Increase of NAD(P)H:quinone reductase by dietary antioxidants: possible role in protection against carcinogenesis and toxicity.

2(3)-tert-Butyl-4-hydroxyanisole (BHA) is one of several widely used antioxidant food additives that protect against chemical carcinogenesis and toxicity. The present report concerns the enhancement of dicoumarol-inhibited NAD(P)H:quinone reductase [NAD(P)H dehydrogenase (quinone); NAD(P)H:(quinone acceptor) oxidoreductase, EC 1.6.99.2] activity in mouse tissues in response to dietary administration of BHA. Cytosolic quinone reductase specific activity was increased significantly in 10 of 15 tissues examined from BHA-fed mice. The greatest proportionate increase, to 10 times control levels, was observed in liver. BHA also increased the quinone reductase activities of kidney, lung, and the mucosa of the upper small intestine severalfold. The increases of quinone reductase activities in liver and digestive tissues in response to BHA were comparable to the increases previously observed in glutathione S-transferase (EC 2.5.1.18) and epoxide hydratase (EC 3.3.2.3) activities. Quinones are among the toxic products of oxidative metabolism of aromatic hydrocarbons. NAD(P)H:quinone reductase exhibits broad specificity for structurally diverse hydrophobic quinones and may facilitate the microsomal metabolism of quinones to readily excreted conjugates. The protective effects of BHA appear to be due, at least in part, to the ability of this antioxidant to increase the activities in rodent tissues of several enzymes involved in the nonoxidative metabolism of a wide variety of xenobiotics.