Lung Cancer Promotion by -Carotene and Tobacco Smoke: Relationship to Suppression of Retinoic Acid Receptor- and Increased Activator Protein-1?

A considerable number of epidemiologic studies conducted in the 1970s and 1980s indicated that an inverse relationship exists between estimated intakes of �-carotene and the risk of developing various types of cancer, especially lung cancer. These studies have led to the suggestion that dietary �-carotene can reduce human cancer rates (1,2). Subsequent observational cohort and nested case–control studies based on measurement of carotenoids in blood and tissues showed consistent inverse association between blood �-carotene and risk of lung cancer (1). Initially, it was thought that the conversion of �-carotene to retinol (1,3) is the mechanism of its cancer preventive effects. However, the inability to demonstrate a consistent negative association between plasma retinol levels and cancer risk has led to the proposal that �-carotene itself might exert chemopreventive effects. Several mechanisms have been proposed for such