ROLE OF TISSUE ANTIOXIDANT DEFENSE IN THYROID CANCERS

Reactive oxygen species (ROS), consisting mainly of superoxide, hydrog en peroxide and hydroxyl radical, have been implicated in many disease s including cancer. ROS have been known to play an important role in t he initiation and promotion of multistage carcinogenesis. The cellular antioxidant defence plays a crucial role in neoplastic disease. Howev er, very little is known about the tissue antioxidant defence in thyro id cancers. We therefore undertook a study to assess the role of ROS i n the pathogenesis of thyroid cancers, Our samples consisted of post-o perated thyroid tissues (normal, goiters, follicular adenomas, follicu lar carcinomas and papillary carcinomas). The parameters studied were lipid peroxidation (LP), antioxidant enzymes superoxide dismutase (SOD ), catalase (CAT) and glutathione peroxidase (GPx) - and non-protein t hiols (GSH). Compared to normal thyroid no changes were seen in goiter s. LP was significantly higher in adenomas (16%) and carcinomas (60-69 %). SOD was decreased by 15% in adenomas while in carcinomas it increa sed by 9-12%. GPx was raised in carcinomas by 10-21%. Follicular carci nomas showed a 4% increase in CAT activity while GSH was raised in ade nomas and papillary carcinomas by 17%. Thus, in adenomas (initial stag e) involvement of superoxide radicals and in carcinomas (later stage) hydrogen peroxide and, possibly, hydroxyl radical involvement cannot b e ruled out. These ROS may be responsible for elevated LP observed in adenomas and carcinomas.