2-Hexanone potentiation of [ 14C]chloroform hepatotoxicity: Covalent interaction of a reactive intermediate with rat liver phospholipid

Abstract

Rats were treated with [ 14C]chloroform ( 14CHCl 3) 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- 14CHCl 3 administration, and glutathione (GSH) content, irreversible binding of 14CHCl 3-derived radiolabel, and phospholipid composition were determined. The combination of 2-HX + CHCl 3 reduced GSH content to 21% of control (CO + CO) 1 hr after CHCl 3 administration. No significant rebound of GSH was observed 24 hr post-CHCl 3 administration. In contrast, GSH was not altered by administration of CHCl 3 to CO-pretreated rats. Although 14CHCl 3-derived radiolabel was irreversibly bound to hepatic macromolecules of both CO- and 2-HX-pretreated rats, total irreversibly bservation 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- 14CHCl 3 administration and was distributed 52% in protein, 41% in lipid, and 7% in acid soluble fractions 6 hr post- 14CHCl 3 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 14CHCl 3 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 durkng 2-hexanone + 14CHCl 3 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 model studies, 12% phosgene in toluene was reacted with liver phosphatidylethanolamine for 6 hr at 37°C. Two reaction products were formed, further substantiating that phosphatidylethanolamine (PE) may react with [ 14C]phosgene in liver. Although the data presented here are insufficient to conclude that the depletion of PE is a major mechanism in CHCl 3 hepatotoxicity, documented studies in which altered phospholipid composition modified cellular function suggest the possibility that PE depletion may contribute to phosgene-induced liver injury.