Changes in linoleic acid metabolism and membrane fatty acids of LLC-PK cells in culture induced by 5 alpha-cholestane-3 beta,5,6 beta-triol.

The aim of this study was to investigate the effect of the oxysterol 5 alpha-cholestane-3 beta,5,6 beta-triol (triol) on the metabolism of linoleic acid (18:2n-6) to arachidonic acid (20:4n-6) and on the cell membrane fatty acid composition. Porcine kidney cells were incubated in medium with or without 10 microgram(s)/mL of triol for 24 h, then incubated for 1, 6, or 12 h in a medium which contained 50 muM of either [14C] linoleic acid or unlabeled linoleic acid. The cellular uptake of [14C] linoleic acid was significantly higher in the triol-treated cells than in control cells. After 1- and 6-h incubations despite the increase of [14C] linoleic acid pool size in the triol-treated cells, neither total n-6 polyunsaturated fatty acids (PUFA) metabolites nor arachidonic acid were increased in the triol-treated cells as compared to the control cells, but trienoic acids accumulated to a greater extent in the triol-treated cells. Therefore, the ratios of n-6 PUFA metabolites vs. pool size of linoleic acid and of tetraenoic acids vs. dienoic acids were significantly decreased in triol-treated cells as compared to the control cells. The cellular fatty acid composition also showed that linoleic acid percentage was significantly increased while arachidonic acid percentage was significantly decreased in the triol-treated cells, and that the accumulation of trienoic acids (18:3n-6 + 20:3n-6) observed from the [14C] linoleic acid experiment was due solely to increased 20:3n-6 content. This latter finding indicates that a decrease of elongase activity by triol is unlikely. Our results also showed that the triol-treated cells had a lower level of free cholesterol but higher levels of phospholipid and triol in their membranes, suggesting that triol displaced free cholesterol from the cell membrane.