Phospholipase Action of Platelet-activating Factor Acetylhydrolase, but Not Paraoxonase-1, on Long Fatty Acyl Chain Phospholipid Hydroperoxides

Abstract

Phospholipid hydroperoxide (PLOOH) degrading activity of high density lipoprotein (HDL)-derived paraoxonase-1 (PON1) was investigated, using peroxidized 1-palmitoyl-2-oleoyl phosphatidylcholine (PCOOH) as substrate and high performance thin layer chromatography for quantitative peroxide analysis. Incubation of PCOOH with PON1 resulted in decay of the latter and reciprocal buildup of oleic acid hydroperoxide (OAOOH) at rates unaffected by GSH or other reductants. A serine esterase inhibitor blocked this activity and a recombinant PON1 was devoid of it, raising the possibility that the activity represents platelet-activating factor acetylhydrolase (PAF-AH), an esterase that co-purifies with PON1 from HDL. This was verified by showing that a recombinant PAF-AH recapitulates the ability of natural PON1 to hydrolyze PCOOH and release OAOOH while having essentially no effect on parental PC. Furthermore, recombinant PAF-AH and natural PON1 were shown to have similar K m values for PCOOH hydrolysis. Finally, we found that recombinant PAF-AH, but not PON1, catalyzes PLOOH hydrolysis in peroxidized low density lipoprotein. We conclude from this study that PON1 is neither a PLOOH peroxidase nor hydrolase and that the phospholipase A 2 -like activity previously attributed to PON1 in natural enzyme preparations was actually due to novel PLOOH hydrolytic activity of contaminating PAF-AH.

Effect of Probucol on Antioxidant Properties of HDL in Patients with Heterozygous Familial Hypercholesterolemia

“…By contrast, PON1 and PAF-AH are weakly reactive towards LOOH 36) . Moreover, accumulating data question the ability of PON1 to hydrolyze oxidized phospholipids and suggest that PAF-AH, rather than PON-1, is the hydrolase for oxidized phospholipids in HDL [36][37][38] ; however, our data suggest the importance of PON1 rather than PAF-AH against LDL oxidation. Recent proteomic studies have identified multiple proteins that are co-isolated with human HDL 20) .…”

“…Levels of specific HDL proteins, including PON1, correlated with the potent capacity of HDL3 to protect LDL from oxidation 20) . PON1 has several different catalytic activities involving different residues and that its physiologic substrate (s) have not yet been defined 38) . Another study indicated that the two histidine residues required for the lactonase activity of PON1 are also essential for protecting LDL against oxidative modification 39) ; therefore, the antioxidative properties of HDL may be unrelated to its capacity to inactivate LOOH, but rather may involve its major activity as a lactonase through a still unknown pathway upstream of the regulation of systemic oxidative stress 36) .…”

Functionality of HDL: Antioxidation and Detoxifying Effects

“…Finally, the trypanosome lytic factor present in very high-density subpopulations of human HDL exhibits a peroxidase-like activity (Molina Portela et al 2000) that may provide a minor contribution to LOOH-inactivating properties of HDL. With respect to PON1, PAF-AH and LCAT, these are weakly reactive towards LOOH (Goyal et al 1997;Kriska et al 2007;Teiber et al 2004). HDL-associated PON1, which has been attributed a major antioxidant role in HDL (see Sect.…”

“…2.1 for further discussion of PON1). It is more probable that PAF-AH, rather than PON1, represents the hydrolase for PLOOH in HDL (Kriska et al 2007). LCAT may equally hydrolyse PLOOH generated during lipoprotein oxidation (Goyal et al 1997).…”

Protection against Oxidative Stress-induced Hepatic Injury by Intracellular Type II Platelet-activating Factor Acetylhydrolase by Metabolism of Oxidized Phospholipids in Vivo

“…Recently it has been reported that oxidatively modified phospholipids such as esterified F 2 -isoprostanes (24) and phospholipid hydroperoxides (25) are good substrates for plasma PAF-AH, suggesting that residue length is not the only factor involved in substrate recognition. In animal models recombinant plasma PAF-AH was effective in treating acute pancreatitis (26), asthma (27), and anaphylactic shock (28).…”