Lipoprotein-associated phospholipase A2, platelet-activating factor acetylhydrolase, generates two bioactive products during the oxidation of low-density lipoprotein: use of a novel inhibitor

Abstract

A novel and potent azetidinone inhibitor of the lipoprotein-associated phospholipase A2 (Lp-PLA2), i.e. platelet-activating factor acetylhydrolase, is described for the first time. This inhibitor, SB-222657 (Ki=40+/-3 nM, kobs/[I]=6. 6x10(5) M-1.s-1), is inactive against paraoxonase, is a poor inhibitor of lecithin:cholesterol acyltransferase and has been used to investigate the role of Lp-PLA2 in the oxidative modification of lipoproteins. Although pretreatment with SB-222657 did not affect the kinetics of low-density lipoprotein (LDL) oxidation by Cu2+ or an azo free-radical generator as determined by assay of lipid hydroperoxides (LOOHs), conjugated dienes and thiobarbituric acid-reacting substances, in both cases it inhibited the elevation in lysophosphatidylcholine content. Moreover, the significantly increased monocyte chemoattractant activity found in a non-esterified fatty acid fraction from LDL oxidized by Cu2+ was also prevented by pretreatment with SB-222657, with an IC50 value of 5.0+/-0.4 nM. The less potent diastereoisomer of SB-222657, SB-223777 (Ki=6.3+/-0.5 microM, kobs/[I]=1.6x10(4) M-1.s-1), was found to be significantly less active in both assays. Thus, in addition to generating lysophosphatidylcholine, a known biologically active lipid, these results demonstrate that Lp-PLA2 is capable of generating oxidized non-esterified fatty acid moieties that are also bioactive. These findings are consistent with our proposal that Lp-PLA2 has a predominantly pro-inflammatory role in atherogenesis. Finally, similar studies have demonstrated that a different situation exists during the oxidation of high-density lipoprotein, with enzyme(s) other than Lp-PLA2 apparently being responsible for generating lysophosphatidylcholine.

The inhibition of lipoprotein-associated phospholipase A2 exerts beneficial effects against atherosclerosis in LDLR-deficient mice

“…3.1.1.47), is a Ca 2+ -independent, 45 kDa secreted protein that associates with lipoproteins and circulates within the plasma in active form [7] . Lp-PLA2 can be up-regulated by the oxidized phospholipids in oxLDL [8] and in turn acts upon those oxidized phospholipids to produce two pro-inflammatory mediators, lysophosphatidylcholines (lysoPCs) and oxidized nonesterified fatty acids (oxNEFAs) [9] . Research suggests that the regulatory roles of these two products, especially lysoPCs, are in the promotion of atherosclerotic plaque formation.…”

Amelioration of atherosclerosis in apolipoprotein E-deficient mice by inhibition of lipoprotein-associated phospholipase A2

“…An interesting target for cardiovascular drug development is lipoprotein-associated phospholipase A2 (Lp-PLA 2 , also termed platelet-activating factor acetylhydrolase, PAFAH). Lp-PLA 2 is an enzyme that plays an atherogenic role by hydrolyzing platelet activating factor (PAF) and oxidized phospholipids, resulting in the generation of two bioactive lipid mediators, lysophosphatidylcholine (LPC) and oxidized non-esteri ed fatty acid (oxNEFA), both of which play key roles in atherosclerosis [1][2][3][4][5]. Epidemiological studies have supported Lp-PLA2 as a cardiovascular risk marker independent of traditional risk factors [6][7][8][9].…”

Platelet-Activating Factor Acetylhydrolase Is Mainly Associated With Electronegative Low-Density Lipoprotein Subfraction

“…1 However, hydrolysis of PAF-like molecules produces lysophosphatidylcholine (LPC) and oxidized or fractionated nonesterified fatty acids (NEFA), which are also well-known inflammation mediators. 3 Furthermore, plasma levels of lipoprotein-associated PLA 2 appeared to be an independent risk factor for coronary artery disease in normolipemic and hypercholesterolemic subjects. 4,5 The observation that PAF-AH inhibition in rabbits slows atherosclerosis progression provided further evidence of the relationship between PAF-AH and atherogenesis.…”