The involvement of reactive oxygen species in oral cancers of betel quid/tobacco chewers

Abstract

Most biological reactions, including carcinogenesis, are complex processes involving thousands of compounds, their metabolites and intermediates. The separation of events which form part of a direct chain leading to neoplastic transformation from those which are mere by-products is a herculean task. In this study, we focused on the pros and cons of reactive oxygen species (ROS) being involved in the development of oral cancer among chewers of tobacco and areca nuts. The results revealed that bursts of ROS generation occur at different stages of carcinogenesis, and are cauesed by different mechanisms. This observation may be conderable practical implications. Different strategies will be required in the administration of chemopreventive agents in order to trap ROS formed in the alkaline (due to the addition of slaked lime) chewing mixture within the saliva of a chewer, to scavenge ROS within mucosal cells exposeed to an array of tobacco- or nut-related carcinogens or tumour promoters, and to inhibit the action of ROS released from ROS-generating white cells during lymphocytic infiltration of the oral mucosa at a precancerous stage. The remission of oral leukoplakoias following the administration of vitamin A (200,000 IU/ week) or vitamin A (100,000 IU/week) plus β-carotene (180 mg/week) for 6 months, the inhibition of new leukoplakias during this trial period, and reduction of micronucleated oral mucosal cells in chewers treated with β-carotene or vitamin A are indeed promising results. However, a better understanding og the role of ROS in various stages of carcinogenesis will provide the basis for selection of the proper chemopreventive agents and the design of a treatment regime which may either prevent the formation of precancerous lesions, induce their remission, or inhibit the progression of precancerous lesions into malignant cancers.