Tissue vitamin A repletion is impaired by exposure to carcinogen

Vitamin A appears to exert a protective effect against certain cancers. Epithelial cancers, such as those of the skin, bladder, oropharynx and respiratory tract, have the strongest association with vitamin A. These same cancers are causally associated with exposure to carcinogens such as benzo(alpha)pyrene (BP), a product of combustion found in cigarette smoke and charbroiled meat. This study was designed to determine whether BP exposure affects tissue vitamin A nutriture. Female Sprague-Dawley rats were randomized to purified diets, sufficient or deficient in vitamin A, and with or without 200 mg BP/kg feed. Rats were killed after 4 or 6 weeks. Serum, liver and lungs were assessed for vitamin A levels; trachea, stomach, small intestine and bladder were examined for histologic change. Lack of dietary vitamin A resulted in a profound decrease in vitamin A in the serum, liver and lungs (p less than .005). No histologic changes were evident in any tissues examined. Serum vitamin A was not affected by dietary BP. In vitamin-A-sufficient rats, dietary BP caused a significant decline in hepatic and lung vitamin A. In rats fed vitamin-A-deficient diets, dietary BP had no effect on tissue vitamin A. We conclude that chronic exposure to the carcinogen BP leads to tissue depletion of vitamin A, despite a vitamin-A-sufficient diet. We postulate that BP impairs tissue repletion by metabolizing incoming vitamin A rather than in situ vitamin A, since BP had no effect on tissue vitamin A levels in rats fed a diet devoid of vitamin A. This BP-induced vitamin depletion may eventually have a deleterious effect on epithelial tissue health, and may help to explain the association between vitamin A and cigarette-smoke-related cancers.