The effect of combined antioxidant supplementation (b-carotene, ascorbic acid and a-tocopherol) on the expression of CMO1 and CMO2 in smoke-exposed ferrets.

A132

Contrary to the results of observational studies showing a beneficial effect of increased intakes of fruits and vegetables high in b-carotene (BC) on lung cancer, intervention trials using high dose BC supplements in heavy smokers demonstrated either a harmful or no effect of BC on the relative risk of lung cancer. Some evidence suggests that the increase in carcinogenesis may be due to a disruption in carotenoid metabolism and retinoid signaling associated with BC dosage and/or increased instability of the BC molecule in the antioxidant-poor environment of the smoke-exposed lung. a-Tocopherol (AT) and ascorbic acid (AA) are able to regenerate BC from the BC free radical cation, thus protecting BC from oxidation. b, b-carotene-15,15'-monooxygenase (CMO1) is the key enzyme in the oxidative cleavage of BC to vitamin A. b-carotene-9,10'-monooxygenase (CMO2) is an alternative enzyme that also plays a role in carotenoid metabolism and retinoid homeostasis. The specific aim of this study was to evaluate the influence of BC dosage and antioxidant combinations (AA+AT) on expression of CMO1 and CMO2 in the lungs and liver of cigarette smoke-exposed ferrets. We evaluated the effects of BC at both a physiologic dose [low dose LBC, equivalent to an intake of 6.7 mg/d in a human] and a pharmacological dose [high dose HBC, equivalent to 33.6 mg/d in a human] in the presence or absence of AA [equivalent to 210 mg/d in a human] and AT [equivalent to 100 mg/d in a human] on the expression of CMO1 and CMO2 in the lung and liver of the male adult ferret. Ferrets were exposed to smoke (SM), equivalent to 1.5 packs of cigarettes a day in humans, for 6 weeks. Previously, we have shown that lung BC concentrations increase in a dose-dependent manner in the BC supplemented groups. However, lung BC levels were significantly lower in the presence of AA and AT. Lung RA concentrations remained at control levels in the SM+LBC and SM+HBC groups yet were significantly increased in the SM+HBC+AA+AT group. Liver RA concentrations increased in a dose-dependent manner in BC supplemented groups. In the current analysis, we show that lung CMO1 expression increases in a dose-dependent manner in the BC alone groups. In contrast, CMO1 expression decreases to control levels with BC supplementation in the presence of AA and AT. BC supplementation increased lung CMO2 expression in dose-dependent manner independent of AA+AT presence. Expression of CMO1 and CMO2 in the liver was not significantly affected by BC supplementation or AA+AT presence. We conclude that BC supplementation in the presence of AA and AT is able to regulate ferret CMO1 expression in an organ specific manner through local regulation of RA, whereas lung CMO2 is regulated independently of CMO1 regulatory mechanisms.