The key mechanism for acetaminophen hepatotoxicity is cytochrome P450 (CYP)-dependent formation of N-acetyl-p-benzoquinone imine, a potent electrophile that forms protein adducts. Previous studies revealed the fundamental role of glutathione, which binds to and detoxifies N-acetyl-p-benzoquinone imine. Glutathione is synthesized from cysteine in the liver, and N-acetylcysteine is used as a sole antidote for acetaminophen poisoning. Here, we evaluated the potential roles of transsulfuration enzymes essential for cysteine biosynthesis, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CTH), in acetaminophen hepatotoxicity using hemizygous (Cbs+/- or Cth+/-) and homozygous (Cth-/-) knockout mice. At 4h after intraperitoneal acetaminophen injection, serum alanine aminotransferase levels were highly elevated in Cth-/- mice at 150mg/kg dose, and also in Cbs+/- or Cth+/- mice at 250mg/kg dose, which was associated with characteristic centrilobular hepatocyte oncosis. Hepatic glutathione was depleted while serum malondialdehyde accumulated in acetaminophen-injected Cth-/- mice but not wild-type mice, although glutamate-cysteine ligase (composed of catalytic [GCLC] and modifier [GCLM] subunits) became more activated in the livers of Cth-/- mice with lower Km values for Cys and Glu. Proteome analysis using fluorescent two-dimensional difference gel electrophoresis revealed 47 differentially expressed proteins after injection of 150mgacetaminophen/kg into Cth-/- mice; the profiles were similar to 1000mgacetaminophen/kg-treated wild-type mice. The prevalence of Cbs or Cth hemizygosity is estimated to be 1:200-300 population; therefore, the deletion or polymorphism of either transsulfuration gene may underlie idiosyncratic acetaminophen vulnerability along with the differences in Cyp, Gclc, and Gclm gene activities.
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