Positive Health Online

Abstract

BAKER and colleagues, Department of Pharmacology and Toxicology, College of Pharmacy, and Department of Chemistry, University of Arizona, Tucson, Arizona 85721-0207 USA write that recent intervention trials reported that smokers given dietary beta-carotene supplementation demonstrated an increased risk of lung cancer and overall mortality . Beta-carotene has been proposed to promote lung cancer by acting as a prooxidant in the smoke-exposed lung.

Background

Methodology

The authors examined the interactions of cigarette smoke with beta-carotene in model systems.

Results

Both whole smoke and gas-phase smoke oxidised beta-carotene in toluene to several products, which included carbonyl-containing polyene chain cleavage products and beta-carotene epoxides. A major reaction product was 4-nitro-beta-carotene, both cis and all-trans isomers, formed by nitrogen oxides in smoke. The hypothesis that smoke-driven beta-carotene auto-oxidation exerts prooxidant effects was tested in a liposome system. Lipid peroxidation in liposomes exposed to gas-phase smoke was modestly inhibited by the incorporation of 0.1 mol % beta-carotene. Both the lipid soluble antioxidant alpha-tocopherol and the water soluble antioxidant ascorbate were oxidised more slowly by gas-phase smoke exposure in liposomes containing beta-carotene.,

Conclusion

These data demonstrate that beta-carotene exerts weak antioxidant effects against smoke-induced oxidative damage in vitro. It is unlikely that a prooxidant effect of beta-carotene occurs under biologically relevant conditions or is responsible for the increased lung cancer incidence in the smokers who consumed beta-carotene supplements.

References

Baker DL et al. Reactions of beta-carotene with cigarette smoke oxidants. Identification of carotenoid oxidation products and evaluation of the prooxidant/antioxidant effect. Chemical Research in Toxicology 12(6): 535-43. Jun 1999.

Comment

One more piece of the puzzle in the ongoing saga of beta-carotene and cigarette smoke.