Covalent binding of oxidative biotransformation reactive intermediates to protein influences halothane-associated hepatotoxicity in guinea pigs.

Halothane (CF3CBrClH; H) biotransformation by cyt P-450 produces reactive intermediates along both oxidative (acyl chloride) and reductive (free radical) pathways that ultimately generate the metabolites trifluoroacetic acid and F-, respectively. Inhibiting oxidative metabolism with deuterated halothane (d-H) reduces resultant injury in our guinea pig model of acute H hepatoxicity. To elucidate whether covalent binding of reactive intermediates to proteins (oxidative pathway) or lipids (reductive pathway) is a mechanism of necrosis, male outbred Hartley guinea pigs (600-725 g), N = 8, were exposed to either 1% (v/v) H or d-H at either 40% or 10% O2 for 4 hr. One-half of the animals were killed immediately after exposure for binding studies; the remainder at 96 hr post for evaluation of hepatotoxicity. Covalent binding of halothane intermediates to liver protein or lipid was determined by measuring the fluoride content of the bound moieties. The use of d-H and/or 10% O2 during exposure led to 63-88% reductions (p less than 0.01) in plasma trifluoroacetic acid concentrations (H-40% O2 = 546; 73 mM, N = 8) which were accompanied by 33-60% decreases (p less than 0.01) in binding to liver proteins (H-40% O2 = 1.36; 0.26 nmoles bound F-/mg protein, N = 4), 78-84% decreases (p less than 0.05) in 48 hr plasma ALT levels (H-40% O2 = 308; 219, control = 23 + 3, N = 4) and a total amelioration of centilobular necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)