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In vivo murine studies on the biochemical mechanism of acetaminophen cataractogenicity
Abstract:
C57BL/6 and DBA/2 mice are, respectively, susceptible and resistant both to the induction of aryl hydrocarbon hydroxylase (cytochrome P450 1A1, or CYP1A1) and to the cataractogenicity of acetaminophen, which may involve its bioactivation to a toxic reactive intermediate, catalysed by P450 and (or) prostaglandin H synthase (PHS). Following induction of P450 using beta-naphthoflavone, the cataractogenicity of acetaminophen (400 mg/kg ip) in C57BL/6 mice was reduced by pretreatment with the P450 inhibitors SKF 525A and metyrapone, the glutathione precursor N-acetylcysteine, the antioxidant vitamin E, and the free radical spin trapping agent alpha-phenyl-N-t-butylnitrone (p < 0.05). Acetaminophen (200 mg/kg) cataractogenicity was enhanced by pretreatment with the glutathione depletor diethyl maleate (DEM) and the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine (BSO) (p < 0.05). No significant effect on acetaminophen cataractogenicity was observed using the PHS cyclooxygenase inhibitors aspirin or naproxen, or the glutathione reductase inhibitor 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Accordingly, acetaminophen cataractogenicity in C57BL/6 mice does not appear to be dependent upon bioactivation by PHS. In DBA/2 mice treated with beta-naphthoflavone, a high dose of acetaminophen (750 mg/kg ip) was not cataractogenic, even after pretreatment with DEM, BSO, or BCNU. The resistance of DBA/2 mice to acetaminophen cataractogenesis, despite concomitant pretreatments with an inducer of P450 and several agents that interfere with glutathione-dependent detoxifying pathways, suggests differences in this strain involving cytoprotective pathways subsequent to acetaminophen bioactivation and detoxification of the cataractogenic reactive intermediate. These results indicate that acetaminophen cataractogenicity in C57BL/6 mice results from P450-catalysed bioactivation of acetaminophen to a reactive intermediate, possibly a benzoquinone imine and (or) a free radical, the toxicity of which is reduced by glutathione-dependent reactions.
Insights
Acetaminophen causes cataracts in mice through a P450-catalyzed process, but this effect is reduced by antioxidants and glutathione. DBA/2 mice are resistant, suggesting different protective pathways.
Area of Science:
- Toxicology
- Pharmacology
- Biochemistry
Background:
- Acetaminophen can cause cataracts, potentially via bioactivation to toxic intermediates.
- Mouse strain differences (C57BL/6 vs. DBA/2) exist in susceptibility to acetaminophen toxicity and cytochrome P450 induction.
Purpose of the Study:
- To investigate the role of P450 and prostaglandin H synthase (PHS) in acetaminophen-induced cataracts.
- To explore the involvement of glutathione and oxidative stress in acetaminophen cataractogenicity.
- To compare acetaminophen cataractogenicity between C57BL/6 and DBA/2 mice.
Main Methods:
- Acetaminophen cataractogenicity was assessed in C57BL/6 mice pretreated with P450 inducers/inhibitors, glutathione modulators, antioxidants, and free radical scavengers.
- The role of PHS was examined using cyclooxygenase inhibitors.
- Experiments were also conducted in DBA/2 mice with various pretreatments.
Main Results:
- In C57BL/6 mice, P450 inhibitors, N-acetylcysteine, vitamin E, and alpha-phenyl-N-t-butylnitrone reduced acetaminophen cataractogenicity.
- Glutathione depletors (DEM, BSO) enhanced cataract formation.
- PHS inhibitors did not affect cataractogenicity, suggesting PHS is not involved.
- DBA/2 mice were resistant to acetaminophen-induced cataracts, even with glutathione depletion.
Conclusions:
- Acetaminophen cataractogenicity in C57BL/6 mice is mediated by P450-catalyzed bioactivation to a reactive intermediate.
- Glutathione-dependent pathways play a crucial role in detoxifying this intermediate.
- DBA/2 mice possess inherent resistance mechanisms against acetaminophen-induced cataracts.