Reduced levels of catalase activity potentiate MPP +-induced toxicity: comparison between MN9D cells and CHO cells

Abstract

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to be toxic by inducing oxygen free radicals in the mammalian nervous system, especially in the nigrostriatal dopaminergic system. The present study was designed to compare the toxic effects of MPP +, the active metabolite of MPTP, in MN9D neuronal cells that exhibit relatively low levels of catalase activity, as compared to CHO cells, which exhibit high levels of catalase activity. The survival of the MN9D cells in the presence of 250 μM MPP + was less than 10%, whereas CHO cells exhibited 70% survival at the same concentration of MPP +. The ED 50 values of MPP + in MN9D and CHO cell lines were 60–600 μM, respectively. MN9D cells contain less catalase, an enzyme believed to be involved in the detoxification of free radicals compared to CHO cells. The catalase activity was 2 Units/mg protein in MN9D cells and 30 U/mg protein in CHO cells. The catalase activity in CHO cells increased with increasing MPP + concentrations from 100–500 μM, however, it decreased at 1 mM MPP +. In contrast, catalase activity in MN9D remained the same at all MPP + concentrations. When the CHO cells were pre-treated with 10–25 mM 3-aminotriazole (3-AT), which inhibits catalase activity, and exposed to MPP + at various concentrations, they became susceptible to MPP +. It is evident from these data that the differential susceptibility to MPP + in these two cell lines are due to differences in catalase activity. In addition, the inhibition of constituentive catalase activity in CHO cells by 3-AT treatment enhances their susceptibility. In conclusion, the study demonstrates that catalase activity represents an important defence mechanism in MPTP-induced toxicity.