Skin-tumour-promoting activity of processed bidi tobacco in hairless S/RV Cri-ba mice

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Abstract
Workers engaged in processing tobacco for the manufacture of bidis, the most popular smoking devices in India, are exposed to tobacco dust, volatile components and flakes via nasopharyngeal and cutaneous routes. In order to evaluate the risk of occupational tobacco exposure, the complete carcinogenic action of an aqueous extract of bidi tobacco (ATE), its ability to initiate and promote skin papillomas and to convert these to carcinomas, was tested in hairless S/RV Cri-ba mice using the skin tumorigenesis protocol. Epidermal cell kinetics and tissue alterations were recorded after a single or multiple applications of ATE to 7,12-dimethylbenz[a]-anthracene(DMBA)-initiated mouse skin. While ATE did not exhibit complete carcinogenic, initiating or progressor activity, it effectively promoted skin papilloma formation in DMBA-initiated mice. An increase in papilloma yield per mouse above the control was noted only after 30 weeks of promotion, and at week 40 of promotion with 5 mg and 50 mg ATE it was significantly higher than that in the control mice (9.69±1.30 and 11.73±1.38 compared to 4.70±1.01;P<0.01). Mild epidermal hyperplasia, increase in mitotic activity and dermal thickness induced by a single application of ATE persisted upon multiple treatment and correlated well with its tumour-promoting activity. The findings indicate that occupational exposure to bidi tobacco may pose a cancer risk among workers in the bidi industry.