Abstract
The mechanisms by which human recombinant Cu-Zn superoxide dismutase prevents cultured rat hepatocytes from tert-butylhydroperoxide (TBHP) cytotoxicity were investigated. Both liposome-encapsulated human recombinant Cu-Zn superoxide dismutase (LSOD) and free (not liposome-encapsulated) human recombinant Cu-Zn superoxide dismutase (FSOD) were uptaken by cultured rat hepatocytes and prevented TBHP-induced cell killing dose-dependently. The 50%-effective final concentrations of FSOD for its cytoprotection and cellular internalization were approximately 9-and 6-fold higher than those of LSOD, respectively. Whereas the pretreatment of cultured rat hepatocytes with each of 5 different blockers of the endocytosis abolished both cellular uptake and cytoprotection of FSOD, the same treatment did not affect those of LSOD. The present results indicate that LSOD prevents TBHP-induced killing of cultured rat hepatocytes more efficiently than dose FSOD and suggest that the endocytosis-independent mechanism by which cultured rat hepatocytes uptake LSOD participates in the cytoprotection of such an enzyme.
