Effects of Thioredoxin on Apoptosis-Inducing Neuronal Cell Injury

ABSTRACT

PURPOSE: Thioredoxin is an endogenous antioxidant. It regulates the activities of transcriptional factors such as NF-kB(nuclear factor kappa B)and AP-1(activator protein-1) and it increases the synthesis of cytokines, preventing cellular proliferation and apoptosis. The aim of this study was to clarify the role of thioredoxin on apoptosis-inducing neuronal cell injury. We investigated the protective effects of thioredoxin against apoptosis-inducing neuronal cell injury through intracellular mechanism by 6-hydroxydopamine and serum deprivation. METHODS: PC 12 cells were cultured in RPMI 1640 media containing 10% fetal calf serum and subcultured in 96-well plates. Each well contained 30,000 cells. Cells were treated with hydrogen peroxide, diamide or 6-hydroxydopamine 30 minutes after thioredoxin treatment and then incubated for 24 hours. Cytotoxicity and cellular viability were assessed by measuring lactate dehydrogenase(LDH) release and MTT reduction. RESULTS: Thioredoxin increased cytotoxicity of PC cells treated with 6-hydroxydopamine by increasing LDH release and decreasing MTT reduction. In the serum deprivation condition, thioredoxin increased cytotoxicity of PC cells by increasing LDH release. CONCLUSION: Thioredoxin potentiates oxidative injury through intracellular mechanisms by 6-hydroxydopamine and serum deprivation instead of protecting. The cytotoxicity of thioredoxin may be mediated by decreasing the activity of NF-kB, which has been reported recently to protect against cellular apoptosis. Evidence suppors that the cytotoxic effect was not increased in the presence of serum in this study. Therefore, we found that the antioxidant effects of thioredoxin depended on mechanisms of injuries.