Molecular cytotoxic mechanisms of chlorpromazine in isolated rat hepatocytes.
Chlorpromazine (CPZ), a member of the largest class of first-generation antipsychotic agents, is known to cause hepatotoxicity in the form of cholestasis and hepatocellular necrosis in some patients. The mechanism of CPZ hepatotoxicity is unclear, but is thought to result from reactive metabolite formation. The goal of this research was to assess potential cytotoxic mechanisms of CPZ using the accelerated cytotoxicity mechanism screening (ACMS) technique with freshly isolated rat hepatocytes. This study identified CPZ cytotoxicity and inhibition of mitochondrial membrane potential (MMP) to be concentration-dependent. Furthermore, inhibition of cytochrome P450s (CYPs), including CYP2D1 and 1A2, delayed CPZ cytotoxicity, suggesting a role for CYP activation of CPZ to a toxic metabolite(s) in this model. Metabolism studies also demonstrated glucuronide and glutathione (GSH) requirement for CPZ detoxification in hepatocytes. Inactivating the 2-electron reduction pathway, NAD(P)H quinone oxidoreductase (NQO1), caused a significant increase in hepatocyte susceptibility to CPZ, indicating quinoneimine contribution to CPZ cytotoxicity. Nontoxic concentrations of peroxidase/H(2)O(2) (inflammatory model) increased cytotoxicity in CPZ-treated hepatocytes and caused additional mitochondrial toxicity. Inflammation further depleted GSH and increased oxidized glutathione (GSSG) levels. Results suggest activation of CPZ to reactive metabolites by 2 pathways in hepatocytes: (i) a CYP-catalyzed quinoneimine pathway, and (ii) a peroxidase-catalyzed oxidation of CPZ to CPZ radicals.
Department of Pharmaceutical Science, Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, ON M5S 3M2, Canada.
Stephanie L
SL
MacAllister
Cheryl
C
Young
Anna
A
Guzdek
Nickholas
N
Zhidkov
Peter J
PJ
O'Brien
D000429:Alcohol Oxidoreductases / Q000037:antagonists & inhibitors; D000818:Animals; D014150:Antipsychotic Agents / Q000378:metabolism / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002746:Chlorpromazine / Q000378:metabolism / Q000633:toxicity*; D019388:Cytochrome P-450 CYP1A2; D000072467:Cytochrome P450 Family 2; D003580:Cytochromes / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D005978:Glutathione / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D008658:Inactivation, Metabolic; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley
D014150:Antipsychotic Agents; D003580:Cytochromes; D000429:Alcohol Oxidoreductases; C017170:Cyp1a2 protein, rat; C504568:Cyp2d1 protein, rat; D019388:Cytochrome P-450 CYP1A2; D000072467:Cytochrome P450 Family 2; D005978:Glutathione; D002746:Chlorpromazine