Probucol Protects Neuronal Cells Against Peroxide-Induced Damage and Directly Activates Glutathione Peroxidase-1

Experimental evidence has shown that probucol, a hypocholesterolemic agent, is also able to increase glutathione peroxidase (GPx) activity. However, there is a lack of knowledge about the mechanism(s) involved in this event. In this study, in vitro experiments with purified GPx1 from bovine erythrocytes and cultured SH-SY5Y neuroblastoma cells, as well as in silico studies with GPx1, were performed in order to elucidate mechanisms mediating the stimulatory effect of probucol on GPx activity and to investigate the relevance of this event in terms of susceptibility against peroxide-induced cytotoxicity. In vitro experiments with purified GPx1 showed a direct stimulatory effect of probucol on the activity of GPx1, which was related to an increase in V_max with no changes in K_M. Probucol also increased GPx activity in cultured SH-SY5Y neuroblastoma cells, while the levels of GPx1 expression were not changed, corroborating the results found with the purified enzyme. In addition, probucol rendered SH-SY5Y cells more resistant to hydroperoxide-induced cytotoxicity, and this event was abolished in GPx1 knocked-down cells. In silico studies with GPx1 pointed to a potential binding site for probucol at the close vicinity of the GSH pocket. Collectively, the results presented herein indicate that GPx1 plays a central role in the probucol-induced protective effects against peroxide toxicity. This highlights a novel target (GPx1) and a new mechanism of action (direct activation) for an "old drug." The relevance of such results for in vivo conditions deserves further investigation.