Up-regulation of heme oxygenase-1 as a resistance mechanism against MPP⁺ induced cytotoxicity in Raw 264.7 macrophages

To elucidate the effects of heme oxygennase-1 (HO-1) on a neurotoxic substance, 1-methyl-4-phenylpyridinium (MPP⁺), induced cytotoxicity in immune cells, cell death, and the production of reactive oxygen species (ROS) were studied using Raw 264.7 macrophages. HO-1 is induced by harmful stimuli including oxidative stress, and it exerts a protective effect against cytotoxicity in immune cells. Using Western blotting analysis, we have evaluated the expression of HO-1 in Raw 264.7 macrophages treated with MPP⁺. Via a WST assay and flow cytometric analysis, we have also evaluated the cytoprotective effect of HO-1 induction against the cytotoxicity induced by exposure to MPP⁺. In Raw 264.7 macrophage exposed MPP⁺ cells, HO-1 expression evidenced a rapid increase, peaking at 12 h. The increment of cell death and ROS production due to MPP⁺ exposure were aggravated further by treatment with Tin protoporphyrin-IX (SnPP-IX, HO-1 inhibitor). The increased cell death and ROS production induced by MPP ⁺ exposure were recovered to a significant degree by treatment with Cobalt protoporphyrin-IX (CoPP-IX, HO-inducer). According to these results, HO-1 induction exerts a cytoprotective effect on MPP⁺-induced cytotoxicity, which is related to ROS production.