Elsevier

Biochemical Pharmacology

Volume 41, Issue 8, 15 April 1991, Pages 1111-1117
Biochemical Pharmacology

The killing of cultured hepatocytes by N-acetyl-p-benzoquinone imine (NAPQI) as a model of the cytotoxicity of acetaminophen

https://doi.org/10.1016/0006-2952(91)90648-OGet rights and content

Abstract

The killing of isolated hepatocytes by N-acetyl-p-benzoquinone imine (NAPQI), the major metabolite of the oxidation of the hepatotoxin acetaminophen, has been studied previously as a model of liver cell injury by the parent compound. Such studies assume that the toxicity of acetaminophen is mediated by NAPQI and that treatment with exogenous NAPQI reproduces the action of the endogenously produced product. The present study tested these assumptions by compairing under identical conditions the toxicity of acetaminophen and NAPQI. The killing of hepatocytes by acetaminophen was mediated by oxidative injury. Thus, it depended on a cellular source of ferric ion; was potentiated by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase; and was sensitive to antioxidants. By contrast, the cytotoxicity of NAPQI was not prevented by chelation of ferric iron; was unaffected by BCNU; and was insensitive to antioxidants. Thus, the killing of cultured hepatocytes by NAPQI occurs by a mechanism different from that of acetaminophen. The killing by NAPQI was preceded by a collapse of the mitochondrial membrane potential and a depletion of ATP. Monensin potentiated the cell killing, and extracellular acidosis prevented it. These manipulations are characteristic of the toxicity of mitochondrial poisons, and are without effect on the depletion of ATP and the loss of mitochondrial energization. Thus, mitochondrial de-energization by a mechanism unrelated to oxidative stress is a likely basis of the cell killing by NAPQI. It is concluded that treatment of cultured hepatocytes with NAPQI does not model the cytotoxicity of acetaminophen in these cells.

References (28)

Cited by (33)

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    Although only a small fraction (5%-10%) of acetaminophen is converted by CYP2E1 into NAPQI (90% is excreted as conjugates of glucuronide and sulfate16), acute overdose may overwhelm glutathione stores that normally inactivate NAPQI, resulting in the reported toxic effects to the liver.17 A later study, however, provided plausible evidence that while acetaminophen-mediated hepatotoxicity may be from oxidative injury, NAPQI may kill hepatocytes by a different mechanism.18 Although acetaminophen hepatotoxicity was sensitive to antioxidants and was potentiated by BCNU (carmustine; Bristol Meyers Squibb Oncology/Immunology Division, Princeton, NJ)—an inhibitor of glutathione reductase—NAPQI liver cytotoxicity was insensitive to antioxidants and was unaffected by BCNU.

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This work was performed during the tenure of a sabbatical leave from the Department of Pharmacology, University of Western Australia, Nedlands, Western Australia.

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