The Role of Free Radicals in Paraquat-Induced Corneal Lesions

Paraquat is a synthetic bipyridylium salt widely used as herbicide and defoliant. Enzyme-catalyzed redox-cycling of paraquat generates oxygen radicals. The toxic, even lethal, effects of paraquat are due to free radical-mediated tissue injury. Ocular lesions, sometimes quite severe, have been observed following accidental splashing of paraquat solutions onto the eyes.These studies were designed to document the generation of paraquat free radicals in corneal tissue, and to describe the histological nature of the corneal injuries in experimental animals (rabbits and monkeys). The EPR spectrum of rabbit corneas, 30 min. after intrastromal injection of paraquat, showed the signal of the free radical of paraquat. Ultrastructural studies of corneas 8 days after intrastromal injections (100μl) of paraquat solutions showed that the initial lesions occur at the epithelium/basement membrane interface. In rabbit cornea, dose dependent lesions were observed, i.e. whereas 50 mM paraquat caused only minimal damage to t...