The role of calcium in paracetamol (acetaminophen) cytotoxicity in PC12 cells transfected with CYP4502E1.

Paracetamol-induced toxicity is mainly due to the accumulation of its CYP450-mediated N-hydroxylation product - N-acetylimidoquinone. We examined cell viability, proliferation rates and intracellular calcium in PC12 cells and in a PC12 cell line transfected with cytochrome P4502E1 exposed to paracetamol. This drug had a concentration-related effect on cell survival and a LD(50) which was significantly different between both cell types. A 48% decrease of PC12 cells was found following application of 5 mmol/L paracetamol for 48 h. A total 73% decrease in cell numbers was found in cells metabolizing the drug. Culture protein levels were diminished in a similar manner. Paracetamol increased intracellular calcium (by 662%) only in CYP4502E1-transfected cells. The protective role of EGTA and verapamil modulating calcium homeostasis was more evident in CYP4502E1-transfected cells. These results suggest that biotransformation of paracetamol by CYP2E1 increases its cytotoxicity and that a calcium imbalance may have a key role in the initiation of cell injury.