Methapyrilene hepatotoxicity is associated with oxidative stress, mitochondrial disfunction and is prevented by the Ca2+ channel blocker verapamil.
Methapyrilene (MP) is an unusual hepatotoxin in that it causes periportal necrosis in rats. The mechanism of acute methapyrilene hepatotoxicity has, therefore, been investigated in cultured male rat hepatocytes. Addition of methapyrilene to rat hepatocytes resulted in a time- and dose-dependent loss in cell viability between 4 and 8 h of incubation as judged by cellular enzyme leakage. The cytochrome P450 (CYP) inhibitor metyrapone protected against methapyrilene-mediated toxicity suggesting that MP is metabolised by CYP for toxicity. The concentration-dependent protection from methapyrilene toxicity afforded by metyrapone correlated with an inhibition of microsomal CYP2C11-associated androstenedione 16alpha hydroxylase activity, and hepatocytes prepared from hypophysectomised rats (containing reduced levels of microsomal immunodetectable CYP2C11 and associated androstenedione 16alpha hydroxylase activity) showed resistance to the toxic effects of methapyrilene. These data suggest that the toxicity of methapyrilene is predominantly dependent on the CYP2C11 isoform. Treatment of hepatocytes with a toxic concentration of MP caused oxidative stress as indicated by increases in NADP+ levels within 2 h and cellular thiol oxidation as evidenced by a reduction--but not complete loss--in glutathione levels. Methapyrilene hepatotoxicity was associated with an early loss in mitochondrial function, as indicated by mitochondrial swelling and significant losses in cellular ATP within 2 h. Co-incubation of methapyrilene-treated hepatocytes with inhibitors of inner mitochondrial transition permeability pore opening--cyclosporin A or the thiol reductant dithiothreitol--abrogated cell death suggesting that pore opening and loss of mitochondrial Ca2+ homeostasis play a significant role in methapyrilene-mediated cell death. Co-incubation of methapyrilene-treated hepatocytes with the phenylalkylamine calcium channel blocker verapamil--but not by treating cells in a nominally calcium-free medium--also abrogated cell death, suggesting that if Ca2+ is involved in cell killing then it is dependent on an intracellular Ca2+ pool. Pre-treatment of hepatocytes for 1 h with verapamil--to inhibit intracellular Ca2+ pool filling--increased the potency of verapamil protection against methapyrilene toxicity by approximately 100-fold. Taken together, these data indicate that methapyrilene intoxication leads to mitochondrial disfunction and suggest a critical role for a loss of mitochondrial Ca2+ homeostasis in this model of hepatocyte death.
Ratra
G S
GS
Department of Toxicology, St Bartholomew's and the Royal London School of Medicine and Dentistry, UK.
Morgan
W A
WA
Mullervy
J
J
Powell
C J
CJ
Wright
M C
MC
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects / Q000473:pathology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D000072467:Cytochrome P450 Family 2; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006634:Histamine H1 Antagonists / Q000737:chemistry / Q000633:toxicity*; D007016:Hypophysectomy; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008701:Methapyrilene / Q000737:chemistry / Q000633:toxicity*; D008797:Metyrapone / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000201:enzymology; D018384:Oxidative Stress / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D006634:Histamine H1 Antagonists; D000255:Adenosine Triphosphate; D003577:Cytochrome P-450 Enzyme System; D008701:Methapyrilene; D014700:Verapamil; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; D005978:Glutathione; D008797:Metyrapone