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 l inoleic acid (18:2n-6) to arachidonic acid (20:4n-6) and on the cell m embrane fatty acid composition. Porcine kidney cells were incubated in medium with or without 10 mu g/mL of triol for 24 h, then incubated f or 1, 6, or 12 h in a medium which contained 50 mu M of either [C-14] linoleic acid or unlabeled linoleic acid. The cellular uptake of [C-14 ]linoleic acid was significantly higher in the triol-treated cells tha n in control cells. After 1- and 6-h incubations despite the increase of [C-14] linoleic acid poor size in the triol-treated cells, neither total n-6 polyunsaturated fatty acids (PUFA) metabolites nor arachidon ic acid were increased in the triol-treated cells as compared to the c ontrol cells, but trienoic acids accumulated to a greater extent in th e triol-treated cells. Therefore, the ratios of n-6 PUFA metabolites v s. pool size of linoleic acid and of tetraenoic acids vs. dienoic acid s were significantly decreased in triol-treated cells as compared to t he control cells. The cellular fatty acid composition also showed that linoleic acid percentage was significantly increased while arachidoni c acid percentage was significantly decreased in the triol-treated cel ls, and that the accumulation of trienoic acids (18:3n-6 + 20:3 n-6) o bserved from the [C-14]linoleic acid experiment was due solely to incr eased 20:3n-6 content. This latter finding indicates that a decrease o f elongase activity by triol is unlikely. Our results also showed that the triol-treated cells had a lower level of free cholesterol but hig her levels of phospholipid and triol in their membranes, suggesting th at triol displaced free cholesterol from the cell membrane.