2-hexanone potentiation of [14C]chloroform hepatotoxicity: covalent interaction of a reactive intermediate with rat liver phospholipid.

Rats were treated with [14C]chloroform (14CHCl3) in corn oil (CO) or corn oil alone 18 hr following pretreatment with 2-hexanone (2-HX) in corn oil or corn oil alone. Livers were removed, homogenized 1,2, and 6 hr post-14CHCl3 administration, and glutathione (GSH) content, irreversible binding of 14CHCl3-derived radiolabel, and phospholipid composition were determined. The combination of 2-HX + CHCl3 reduced GSH content to 21% of control (CO + CO) 1 hr after CHCl3 administration. No significant rebound of GSH was observed 24 hr post-CHCl3 administration. In contrast, GSH was not altered by administration of CHCl3 to CO-pretreated rats. Although 14CHCl3-derived radiolabel was irreversibly bound to hepatic macromolecules of both CO- and 2-HX-pretreated rats, total irreversibly bound 14C was significantly enhanced in 2-HX-pretreated rats at all time points. The latter observation was consistent with the decrease in GSH of 2-HX-pretreated rats. Total 14C binding in 2-HX-pretreated rats reached a plateau 2 hr post-14CHCl3 administration and was distributed 52% in protein, 41% in lipid, and 7% in acid soluble fractions 6 hr post-14CHCl3 administration. 2-HX enhanced 14C binding to protein and lipid at each time point. Radiolabel was not detected in neutral lipids of control or 2-hexanone-treated animals, but was enhanced 33-fold in phospholipids of 2-hexanone-treated animals. Phospholipid fatty acid methyl ester derivatives did not contain 14C indicating the radiolabel was most likely associated with phospholipid polar head groups. Two dimensional thin layer chromatographic analysis of phospholipid from treated animals demonstrated that 87% of the total radiolabel was associated with a specific phospholipid (14C-PL) which had a 1:1 molar ratio of phosphate to 14C. The latter indicates that the 14C-PL was a monophospholipid derivative of 14CHCl3 reactive intermediate, generally thought to be phosgene. Concurrent decrease in phosphatidylethanolamine content from 23% of total phospholipid to 7%, accumulation of 14C-PL to 2.6% of total phospholipid, and increase in lysophosphatidylethanolamine from 1 to 7% of total phospholipid during 2-hexanone + 14CHCl3 treatment indicated that the amine moiety of phosphatidylethanolamine polar head groups was the probable target of phosgene-lipid interaction, and that a degradative pathway existed which removed the abnormal phospholipid from hepatic membranes. No phospholipid other than phosphatidylethanolamine was depleted. During models studies, 2% phosgene in toluene was reacted with liver phosphatidylethanolamine for 6 hr at 37 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)