Asbestos and benzo[a]pyrene act synergistically to induce squamous metaplasia and incorporation of [3H]thymidine in hamster tracheal epithelium

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Abstract
When exposed to either crocidolite asbestos (single 1-h exposure to 0.4 mg/ml medium) or the polycyclic aromatic hydrocarbon, benzo [a]pyrene (BaP) (≤2.5 μg/ml medium, 1x weekly for 4 weeks), the epithelium of hamster tracheal explants exhibits insignificant amounts of squamous metaplasia, an atypical lesion, in comparison to amounts observed in untreated tissues. Incorporation of [3H]thymidine, an indication of DNA synthesis by epithelial cells, likewise is unchanged. However, the extent of squamous metaplasia and numbers of labeled basal and suprabasal cells are increased substantially when BaP and asbestos are added in combination. These results suggest an important mechanism of co-carcinogenesis involving chemical and physical carcinogens and support epidemiologic observations documenting an increased risk of bronchogenic carcinoma in asbestos workers who smoke.