Molecular species of cholesteryl esters formed via plasma lecithin: Cholesterol acyltransferase in fish oil supplemented dogs

Abstract

Effects of a dietary supplement containing n-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), on molecular species of cholesteryl ester (CE) formed via the plasma lecithin: cholesterol acyltransferase (LCAT; EC 2.3.1.43) reaction was studied. A commercially available basal diet was initially fed to 18 normal adult dogs for 10 days prior to supplementing the dogs, divided into two groups of nine, using either menhaden fish (MHO) or safflower (SAF) oil capsules for a 22 day period. Fatty acid compositions of plasma phospholipid (PL) and CE were measured at days 0, 10 and 32. Characterization of the plasma LCAT-derived reaction products formed in vitro was performed using a radiolabeled cholesterol substrate and molecular species formed were separated by argentation thin-layer chromatography. Significant differences in PL EPA, DHA, and docosapentaenoic acid (DPA) were found in the MHO group. The CE fatty acid distributions revealed a greater than 20-fold elevation in EPA and a nearly 6-fold increase in DHA after MHO supplements. However, DPA was not detected in any CE fatty acid samples suggesting that this fatty acid is not a substrate for cholesterol esterification. The CE molecular species in plasma and those formed via the plasma LCAT reaction in vitro support the possibility that LCAT is responsible, at least in part, for the plasma CE fatty acid distribution. Ratios of selected plasma CE and LCAT derived CE n-6 and n-3 fatty acids using the MHO group data resulted in 3-fold elevations of both DHA/EPA and DHA/AA in the LCAT-derived in vitro CE fraction compared to CE in whole plasma. It is concluded that while both EPA and DHA are suitable substrates for CE formation, relatively lower amounts of plasma CE-DHA compared to the LCAT derived CE-DHA indicates that this fatty acid may be selectively taken up by the tissues compared to CE-EPA and AA.