Chem Biol Interact. 1998 Nov 6;116(1-2):123-41.  

Interindividual variability in P450-dependent generation of neoantigens in
halothane hepatitis.

Eliasson E, Gardner I, Hume-Smith H, de Waziers I, Beaune P, Kenna JG.

Department of Molecular Toxicology, Imperial College School of Medicine at St
Mary's, London, UK. erieli@ki.se

Halothane hepatitis occurs because susceptible patients mount immune responses
to trifluoroacetylated protein antigens, formed following cytochrome
P450-mediated bioactivation of halothane to trifluoroacetyl chloride. In the
present study, an in vitro approach has been used to investigate the cytochrome
P450 isozyme(s) which catalyze neoantigen formation and to explore the
protective role of non-protein thiols (cysteine and reduced glutathione).
Significant levels of trifluoroacetyl protein antigens were generated when human
liver microsomes, and also microsomes from livers of rats pre-treated with
isoniazid, phenobarbital or beta-naphtoflavone, were incubated with halothane
plus a nicotinamide adenine dinucleotidephosphate (NADPH) generating system.
Immunoblotting studies revealed that the major trifluoroacetyl antigens
expressed in vitro exhibited molecular masses of 50-55 kDa and included 60 and
80 kDa neoantigens recognized by antibodies from patients with halothane
hepatitis. Much lower concentrations of halothane were required to produce
maximal antigen generation in isoniazid-induced rat microsomes, as compared with
phenobarbital or isosafrole-induced microsomes (0.5 vs 12.5 microl/ml). In
isoniazid-induced microsomes, antigen generation was inhibited > 90% by the
nucleophiles cysteine and glutathione and by the CYP2E1-selective inhibitors
diallylsulfide and p-nitrophenol, but was unaffected by inhibitors of other P450
isozymes (furafylline, sulfaphenazole or triacetyloleandomycin). Neoantigen
formation in six human liver microsomal preparations was inhibited in the
presence of diallylsulfide, but not by furafylline, sulfaphenazole or
triacetyloleandomycin, and exhibited marked variability which correlated with
CYP2E1 levels. These results suggest that the balance between metabolic
bioactivation by CYP2E1 and detoxication of reactive metabolites by cellular
nucleophiles could be an important metabolic risk factor in halothane hepatitis.

PMID: 9877205 [PubMed - indexed for MEDLINE]