Exposure to the carcinogen benzopyrene depletes tissue vitamin a: β‐carotene prevents depletion

Abstract

Evidence in humans and laboratory animals supports a cancer‐protective effect of vitamin A, but the mechanism remains unclear. While vitamin A deficiency causes squamous metaplasia, and lung cancer patients have lower vitamin A status, their serum vitamin A levels are not indicative of deficiency. We hypothesize that local enzymatic degradation of vitamin A can be induced by exposure to carcinogens such as benzopyrene found in cigarette smoke. This study was designed to determine if benzopyrene exposure depletes tissue vitamin A and whether β‐carotene might prevent the depletion. Weanling male Fischer rats were fed a nutritionally complete purified diet, supplemented with or without benzopyrene at 400 mg/kg feed or β‐carotene at 2 g/kg feed. Vitamin A content of the liver, small intestine, and serum was determined by high‐performance liquid chromatography. There was no effect of benzopyrene feeding on serum retinol levels through four weeks. However, there was a decline in tissue retinol in the liver and small intestine by two weeks, with a 30% decline by four weeks (p < 0.05). In rats fed β‐carotene, there was no effect of benzopyrene on tissue vitamin A level. These results indicate that exposure to benzopyrene induces a local tissue vitamin A depletion despite a vitamin A‐sufficient diet and maintenance of serum vitamin A levels. A high intake of β‐carotene prevented the vitamin A depletion effect of benzopyrene exposure. Further studies appear warranted to determine whether some of the adverse effects of environmental carcinogens, as found in cigarette smoke, charcoal‐broiled meats, and industrial wastes, might be alleviated by dietary intervention.