In vivo production of different chloroform metabolites: effect of phenobarbital and buthionine sulfoximine pretreatment.

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Abstract
The regioselective attack on microsomal phospholipid (PL) polar heads (PH) and fatty acyl chains (FC) demonstrated in vitro has been exploited for the selective quantitation in vivo of the biochemical damages produced by the oxidation and reduction products of CHCl3 metabolism. Five hours after CHCl3 injection (60 mg/kg body weight, ip) to control Sprague-Dawley rats, most of the label covalently bound in the liver was associated to PH, indicating a predominant production of COCl2. The levels of radioactivity bound to both PL moieties increased proportionally when 180 mg/kg body weight 14CHCl3 was administered. Buthionine sulfoximine (BSO) pretreatment resulted in a further increase of binding either to PH or FC. The pretreatment of rats with phenobarbital (PB) reduced the PH/FC binding ratio to 3.4, still indicating the predominance of the oxidative metabolism, but giving some indication of the simultaneous presence of CHCl3 reduction. When reduced glutathione (GSH) was depleted by BSO in PB-induced animals prior to 14CHCl3 administration, only the level of radioactivity associated with oxidative intermediates was increased six times. The present results confirmed that GSH is able to exert an efficient protection mainly toward 14CHCl3 oxidation intermediates. Furthermore, they indicate that in the liver of the Sprague-Dawley rat the major pathway of CHCl3 biotransformation is its oxidation and that pretreatment of rats with a GSH-depleting agent (such as BSO) is more relevant than PB induction in enhancing the biochemical damages produced by CHCl3.