Oxidative and antioxidative mechanisms in oral cancer and precancer: a review.

Development of cancer in humans is a multistep process. Complex series of cellular and molecular changes participating in cancer development are mediated by a diversity of endogenous and exogenous stimuli and important amongst this is generation of reactive oxygen species (ROS). Reactive radicals and non-radicals are collectively known as ROS. These can produce oxidative damage to the tissues and hence are known as oxidants in biological system. Many researchers have documented the role of ROS in both initiation and promotion of multistep carcinogenesis. To mitigate the harmful effects of free radicals, all aerobic cells are endowed with extensive antioxidant defence mechanisms. Lowered antioxidant capacity or the oxidant-antioxidant imbalance can lead to oxidative damage to cellular macromolecules leading to cancer. Oral cavity cancer is an important cancer globally and tobacco is the primary etiological factor in its development. Tobacco consumption exposes the oral epithelium to toxic oxygen and nitrogen free radicals that can affect host antioxidant defence mechanisms. Elevated levels of ROS and Reactive Nitrogen Species (RNS) and lowered antioxidants are found in oral precancer and cancer. Protection can be provided by various antioxidants against deleterious action of these free radicals. Treatment with antioxidants has the potential to prevent, inhibit and reverse the multiple steps involved in oral carcinogenesis. This review is an attempt to understand the interesting correlation between ROS and RNS mediated cell damage and enzymatic and non-enzymatic defence mechanisms involved in oral cancer development and its progression and the use of antioxidants in oral cancer prevention and treatment.