Use of the micronucleus test to monitor the effect of vitamin A, beta‐carotene and canthaxanthin on the buccal mucosa of betel nut/tobacco chewers

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Abstract
The frequency of exfoliated cells with micronuclei in buccal swabs was used to estimate the protective effect of vitamin A, beta-carotene and canthaxanthin (4,4''-diketobeta-carotene) on the buccal mucosa of betel (areca) nut/tobacco chewers. Micronuclei were scored on exfoliated cells taken by swabbing and stained with the Feulgen reaction and fast green. The betel (areca) nut/tobacco chewers served as their own controls. Prior to the administration of vitamin A and beta-carotene, the examined betel quid chewers had elevated frequencies of micronucleated buccal mucosa cells, averaging 4.03% .+-. 1.24 sd (n = 26) and 3.43% .+-. 1.22 sd (n = 25), respectively. The frequency of micronucleated buccal mucosa cells in non-chewers and non-smokers was 0.51% (n = 52). Following a 9-wk ingestion of vitamin A (150,000 IU/wk) and beta-carotene (180 mg/wk in 6 capsules), the frequency of micronucleated cells decreased significantly (P < 0.001) to 1.70% and 1.16%, respectively. No significant shift in the frequencies of micronucleated cells was observed following the intake of canthaxanthin (180 mg/wk in 6 capsules) for 9 wk or that of a placebo. The lack of protective activity of canthaxanthin, which is a good trapper of oxygen singlets but cannot be converted into vitamin A, suggests that vitamin A and beta-carotene exert their inhibitory effect on the formation of micronuclei by a mechanism not involving the scavenging of free radicals. The efficacy of beta-carotene as an inhibitor of micronucleated cell formation, the lack of toxicity, and its availability from a multitude of dietary sources should focus attention on this carotenoid as a promising chemopreventive agent. [Micronuclei, which result mainly from chromatid or chromosome fragments, seem to provide an excellent marker for genotoxic damage in tissues from which oral carcinomas develop.].