Inhibition of lecithin:cholesterol acyltransferase activity by synthetic phosphatidylcholine species containing eicosapentaenoic acid or docosahexaenoic acid in the sn-2 position.

Phospholipids isolated from the plasma of monkeys fed a diet enriched in fish oil were poor substrates for cholesteryl ester (CE) synthesis by the 1ecithin:cholesterol acyltransferase (LCAT) reaction relative to those from animals fed a lard con- taining diet when the phospholipids were used for the prepara- tion of recombinant particles by cholate dialysis (Parks, J. S., B. C. Bullock, and L. L. Rudel. 1989. J. Biol. Chem. 264: 2545-2551). The purpose of the present study was to directly test the influence of eicosapentaenoic acid (20:5 n-3) and docosahex- aenoic acid (22:6 n-3) in the sn-2 position of phosphatidylcholine (PC) on the activity of LCAT. PC species containing l-palmitoyl- 2-oleoyl PC (POPC), 1-palmitoyl-2-linoleoyl PC (PLPC), 1- palmitoyl-2-arachidonoyl PC (PAPC), 1-palmitoyl-2-eicosa- pentaenoyl PC (PEPC), or 1-palmitoyl-2-docosahexaenoyl PC (PDPC) were purchased or synthesized and made into recom- binant particles of uniform size and composition with (*4C)cho- lesterol and apoA-I using the cholate dialysis procedure. The recombinant particles (PC:cholesterol:apoA-I molar ratio = 42:1.9:1) exhibited the following order of reactivity towards purified human LCAT in vitro: POPC > PLPC > PEPC = PAPC >PDPC. The apparent V,,,JKm for recombinant parti- cles containing PEPC and PDPC was 17% and 7% that of parti- cles containing POPC, respectively. There was a linear decrease in CE formation when the percentage of PEPC or PDPC was increased from 0 to 100% relative to POPC in recombinant par- ticles with a constant PC:cholesterol:apoA-I molar ratio, suggest- ing that the PEPC and PDPC were competitive inhibitors of the LCAT reaction. The phospholipase activity of LCAT was mea- sured on monolayers of POPC, PEPC, and PDPC at a constant surface pressure of 25 mN/m using a zero order reaction trough. The hydrolysis rates for POPC, PEPC, and PDPC by LCAT were 2.5, 1.1, and 0 nmol/ml LCAT preparation per min (n = 2), respectively, and were inversely related to the mean molecular area Bt the argon-water interface of the PC species (72, 79, and 86 A2 per molecule, respectively). We conclude from these studies that PEPC and PDPC were less reactive with LCAT than POPC or PLPC. The decreased reactivity of PEPC and PDPC with LCAT appears related to the increased molecu- lar surface area and/or conformation of these molecules. The data also suggest that PEPC and PDPC are competitive inhibi- tors of the phospholipase A2 half of the LCAT reaction. The studies suggest that enrichment of plasma phospholipids with n-3 fatty acids may result in decreased plasma CE synthesis by l-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine; PLPC, l-palmitoyl-2- linoleoyl-m-glycero-3-phosphocholine; PAPC, 1-palmitoyl-2-arachidonoyl- sn-glycero-3-phosphocholine; PEPC, 1-palmitoyl-2-eicosapentaenoyl-sn- glycero-3-phosphocholine; PDPC, 1-palmitoyl-2-docosahexaenoyl-sn- glycero-3-phosphocholine. 'To whom correspondence should be addressed.