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Reduction of cytochrome c by oral mucosa of patients with oropharyngeal cancer.

Superoxide radicals and other reactive oxygen products are likely to play a role in the development of mouth cancer since they are able to convert penultimate carcinogens present in cigarette smoke into ultimate carcinogens. Those radicals can be generated, e.g., by phagocytes infiltrating inflamed mucosa or by semiquinone radicals present in cigarette tar. We therefore measured the ability of oral mucosa of patients with oropharyngeal tumors to reduce cytochrome c. All patients were heavy smokers and drinkers. It was found that patient mucosa had by far more reducing power than control mucosa. Within the control group, smokers' mucosa was most active. When tested, the cytochrome c reduction was not inhibitable by superoxide dismutase or copper(II)3,5-diisopropylsalicylate. We hypothesize that reduction of cytochrome c by oral mucosa of smokers and patients with mouth cancer is primarily due to residues of cigarette tar containing conjugated quinones of mixed oxidative states which are strong reductants as well as producers of oxygen-centered radicals.