THE EFFECT OF BORAGE OIL CONSUMPTION ON HUMAN PLASMA-LIPID LEVELS AND THE PHOSPHATIDYLCHOLINE AND CHOLESTEROL ESTER COMPOSITION OF HIGH-DENSITY-LIPOPROTEIN

The effect of consuming an enriched source of gamma-linolenic acid (GLA, 18:3 n-6) in the form of borage oil on the plasma lipid levels of human volunteers and the fatty acid composition of high density lipoprotein (HDL)-phosphatidylcholine (PC) and HDL- cholesterol ester (CE) was examined. Furthermore, an estimation was made of the relative utilization of GLA and dihomo-gamma-linolenic acid (DGLA, 20:3 n-6) by the plasma lecithin: cholesterol acyltransferase (LCAT) reaction. For this purpose, six healthy male subjects consumed encapsulated borage oil (21.8 wt % GLA) so as to provide an average intake of 5.23 g GLA/person/day for 42 consecutive days followed by a wash-out period of an additional 42 days. Analysis of plasma lipids (triglycerides, total cholesterol, HDL-cholesterol, low density lipoprotein (LDL)-cholesterol) and the plasma HDL-cholesterol:total cholesterol ratio indicated no significant change in any of the latter arising from the supplementation. Consumption of the borage oil supplement was found to produce marked alterations in the fatty acid compositions of HDL-PC and HDL-CE. Whereas only a moderate accumulation in PC (up to 0.6 mol %) of GLA was found with supplementation, a more dramatic rise in DGLA (by 3.9 mol %) and arachidonic acid (AA, 20:4 n-6) (by 3.3 mol %) was found. These changes were reversible by day 64. In contrast to the HDL-PC, the GLA accumulation in HDL-CE exceeded that of DGLA such that the net rise was 1.8 mol % as compared to only 0.8 mol % for DGLA. Positional analysis of the HDL-PC from subjects at day 43 revealed GLA and DGLA to reside almost exclusively in the 2-position (> 98 %). Dividing the percentages of unsaturated fatty acids in the HDL-CE relative to their levels in the corresponding 2-position of PC provided the following estimated order of fatty acid selectivity for the plasma LCAT reaction: GLA > linoleic acid (LA, 18:2 n-6) > oleic acid (OA, 18:1 n-9) > AA > DGLA greater-than-or-equal-to docosahexaenoic acid (DHA, 22:6 n-3).