Paracetamol (acetaminophen) cytotoxicity in rat type II pneumocytes and alveolar macrophages in vitro

Paracetamol (acetaminophen, APAP) liver and kidney cytotoxicity is associated with bioactivation by P450 and/or prostaglandin H synthetase (PGHS) to a reactive metabolite, which depletes GSH, covalently binds to proteins, and leads to oxidative stress. Although APAP may also damage the lung, little is known about the mechanism by which this occurs. We studied the in vitro toxicity of APAP and its effect on the intracellular GSH level in rat type II pneumocytes (freshly isolated or 24-hr-old) and alveolar macrophages. Cytotoxicity was evaluated by changes in membrane integrity (lactate dehydrogenase, [LDH] assay) as well as by mitochondrial metabolic activity (reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide, MTT), following a 20-hr incubation with APAP (1-20 mM). APAP caused a concentration-related decrease in MTT reduction and LDH retention in the fraction of attached cells, which was associated with an increase in LDH activity in the medium and in the fraction of non-attached cells. The order of susceptibility was: freshly isolated type II pneumocytes > alveolar macrophages > 24-hr-old type II pneumocytes. A time- and concentration-dependent decrease in intracellular GSH occurred in freshly isolated type II pneumocytes and alveolar macrophages exposed to subtoxic (less than or equal to 1 mM) APAP concentrations. In 24-hr-old type II pneumocytes, there were no changes in intracellular GSH concentration after APAP exposure. Potassium ethyl xanthate (a P450 inhibitor) and indomethacin (a PGHS inhibitor) significantly decreased APAP-induced GSH depletion in freshly isolated type II pneumocytes and alveolar macrophages, suggesting that P450 and/or PGHS are involved in APAP bioactivation in these cells. BIOCHEM PHARMACOL 59;11:1467-1475, 2000. (C) 2000 Elsevier Science Inc.