Removal of xenobiotic dichlorostearic acid from phospholipids and neutral lipids in cultured human cell lines by B-oxidation and secretion of dichloromyristic acid.

Abstract

Chlorinated fatty acids represent a recently discovered group of potentially hazardous organochlorine pollutants in the environment. The ability of human cells to incorporate and metabolise this type of fatty acids has never been investigated. The aim of the present study was, therefore, to investigate if two human cell lines, INT 407 and SH-SY5Y, incorporate and metabolise extracellular dichlorostearic acid. Cells were incubated with 9,10-dichlorostearic acid for 24 hr, and the amounts of chlorinated fatty acids in cells and culture medium analysed every two days for up to 6 or 10 days. Lipids were separated by solid phase extraction, transesterified to fatty acid methyl esters, and analysed by gas chromatography in combination with a halogen specific detector (GC/XSD). Dichlorostearic acid, dichloropalmitic acid and dichloromyristic acid were found in phospholipids and in neutral lipids of the INT 407 cells. Both cell lines secreted considerable amounts of dichloromyristic acid into the culture medium. Cellular or secreted metabolites shorter than dichloromyristic acid were not found. Taken together, the results suggest that human cells may (1) incorporate chlorinated fatty acids into membrane lipids and storage lipids, (2) metabolise cellular dichlorostearic acid to dichloropalmitic acid and dichloromyristic acid by B-oxidation; but that further metabolism is hindered, possibly because of the chlorine atoms, and (3) remove formed dichloromyristic acid by secretion. The removal of cellular dichloromyristic acid might represent an important cellular defence mechanism and deserves further investigations.