Injury of rat thymocytes caused by exogenous peroxyl radicals in vitro

The aim of this study was to investigate oxidative cell injury in rat thymocytes under conditions of radical generation exterior to the cell utilizing the thermolabile azocompound 2,2'-azobis(2-amidinopropane) dihydrochloride to generate peroxyl radicals at a constant and reproducible rate. This initiator, being water-soluble and endowed with a positive charge, is suitable for studies on oxidative damage of biomembranes induced in the external water environment. The relationship between cell viability, lipid and thiol oxidation and chain-breaking antioxidant depletion was studied. During the first hour of treatment cell viability decreased slightly, protein sulfhydryl groups were consumed slowly and no significant production of conjugated dienes occurred. After 90 min of incubation, when thymocyte permeability started to increase, the concentration of alpha-tocopherol decreased gradually, significant changes of polyunsaturated fatty acids occurred and a rapid phase of thio oxidation commenced. It can be concluded that, under conditions of an exogenous oxidant challenge, initially the cell membrane provides a physical barrier to the entrance of radicals to the thymocyte. When peroxyl radicals gain access to the membrane and the molecular barrier begins to disorganize, the oxidizable cellular components become susceptible to massive attack.