Ruthenium red protects HepG2 cells overexpressing CYP2E1 against acetaminophen cytotoxicity

We studied the mechanisms of acetaminophen (APAP) cytotoxicity in HepG2 cells overexpressing cytochrome p4502E1, particularly the role of oxidative/nitrosative stress and ryanodine Ca²⁺ channel. Cells were grown for 24 h with APAP in the presence or absence of 4-methylpyrazole (4MP), l-arginine methyl ester (L-NAME), superoxide dismutase (SOD), or ruthenium red (RuR). Drug cytotoxicity was also tested in cells pretreated overnight with V-PYRRO/NO. APAP was without effect on empty vector-transfected cells, but damaged CYP2E1-transfected cells and this was abolished by RuR, reduced by 4MP, or V-PYRRO/NO but affected by L-NAME or SOD. APAP increased microsomal [³H]-ryanodine binding, while microsomal Ca²⁺ uptake was significantly lowered. RuR increased net microsomal Ca²⁺ uptake and normalized cytosolic Ca²⁺ levels. We can conclude that neither oxidative nor nitrosative stress is relevant to APAP cytotoxicity in cultured HepG2 cells, but our results point to ryanodine receptors as a potential crucial protein in the early stages of APAP cytotoxicity.