Transfer and Enzyme-Mediated Metabolism of Oxidized Phosphatidylcholine and Lysophosphatidylcholine between Low- and High-Density Lipoproteins

Oxidized low-density lipoprotein (oxLDL) and oxidized high-density lipoprotein (oxHDL), known as risk factors for cardiovascular disease, have been observed in plasma and atheromatous plaques. In a previous study, the content of oxidized phosphatidylcholine (oxPC) and lysophosphatidylcholine (lysoPC) species stayed constant in isolated in vivo oxLDL but increased in copper-induced oxLDL in vitro. In this study, we prepared synthetic deuterium-labeled 1-palmitoyl lysoPC and palmitoyl-glutaroyl PC (PGPC), a short chain-oxPC to elucidate the metabolic fate of oxPC and lysoPC in oxLDL in the presence of HDL. When LDL preloaded with d13-lysoPC was mixed with HDL, d13-lysoPC was recovered in both the LDL and HDL fractions equally. d13-LysoPC decreased by 50% after 4 h of incubation, while d13-PC increased in both fractions. Diacyl-PC production was abolished by an inhibitor of lecithin-cholesterol acyltransferase (LCAT). When d13-PGPC-preloaded LDL was incubated with HDL, d13-PGPC was transferred to HDL in a dose-dependent manner when both LCAT and lipoprotein-associated phospholipase A2 (Lp-PLA2) were inhibited. Lp-PLA2 in both HDL and LDL was responsible for the hydrolysis of d13-PGPC. These results suggest that short chain-oxPC and lysoPC can transfer between lipoproteins quickly and can be enzymatically converted from oxPC to lysoPC and from lysoPC to diacyl-PC in the presence of HDL.

Platelet-activating factor receptor (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is an ether phospholipid mediator associated with platelet coagulation, but also subserves inflammatory roles. The PAF receptor (provisional nomenclature recommended by NC-IUPHAR [37]) is activated by PAF and other suggested endogenous ligands are oxidized phosphatidylcholine [73] and lysophosphatidylcholine [96]. It may also be activated by bacterial lipopolysaccharide [89].

Oxidized lipids: not just another brick in the wall

Over the past decade, there has been intense investigation in trying to understand the pathological role that oxidized phospholipids play in cardiovascular disease. Phospholipids are targets for oxidation, particularly during conditions of excess free radical generation. Once oxidized, they acquire novel roles uncharacteristic of their precursors. Oxidized phosphatidylcholines have an important role in multiple physiological and pathophysiological conditions including atherosclerosis, neurodegenerative diseases, lung disease, inflammation, and chronic alcohol consumption. Circulating oxidized phosphatidylcholine may also serve as a clinical biomarker. The focus of this review, therefore, will be to summarize existing evidence that oxidized phosphatidylcholine molecules play an important role in cardiovascular pathology.

Abstract 17341: Novel Lipid Markers of Calcific Aortic Valve Stenosis

Introduction: Calcific aortic valve stenosis (CAVS) is the most prevalent cardiac valvular pathology, leading to a high incidence of morbidity and mortality if left untreated. The exact pathophysiology of CAVS is largely undefined. Genetic studies have shown a strong correlation of the Lp(a) gene to developing CAVS. Lp(a) is known to be the carrier of plasma Oxidized Phosphatidylcholine and results in Lysophosphatidic acid (LPA) accumulation. The focus of the present study was to determine if OxPC and LPA in calcific human aortic valves relate with echocardiographic markers of CAVS. Methods: Aortic valves (n=98) were obtained from patients undergoing AVR. OxPC and LPA were extracted from pulverized aortic valves and analyzed using a targeted mass spectrometry approach. Lipid values are represented relative to an internal standard and normalized by homogenate and leaflet weights. The severity of calcification and aortic stenosis were measured anatomically by Echocardiographic calcification (ECC) score and hemodynamically by mean AV pressure gradient. Results: One-palmitoyl-2-(9-oxo)-nonanoyl- sn- glycero-3-phosphocholine (PONPC) was the most abundant OxPC among 58 OxPC molecules detected (49.3±3.8ng), in AV tissue. When valves were graded by ECC score, scores of 1 (no calcification) had observably attenuated amounts of mean total OxPC’s (135.3±39.3ng) compared to those with a score of 4 (severe calcification) (310.1±34.8 ng). Total valvular OxPC increased linearly with increased ECC score. Total non-fragmented OxPC’s were also significantly lower in valves with ECC scores of 1 and 2 compared to a score of 4 ( P =0.03). Six LPA species were also identified with 16:0 and 18:1 being the most prevalent. Mean AV pressure gradient had a significant, positive correlation with Total LPA amounts (r 2 =0.580, p <0.001), suggesting that elevated LPA concentrations in CAVS tissue is associated with disease severity. Conclusions: Our study is the largest lipidomics study of human aortic valve tissue demonstrating that OxPC and LPA molecules play a significant role in the etiology of CAVS and provides a novel therapeutic target for mitigating disease progression.

Phosphokinome Analysis of Barth Syndrome Lymphoblasts Identify Novel Targets in the Pathophysiology of the Disease

Barth Syndrome (BTHS) is a rare X-linked genetic disease in which the specific biochemical deficit is a reduction in the mitochondrial phospholipid cardiolipin (CL) as a result of a mutation in the CL transacylase tafazzin. We compared the phosphokinome profile in Epstein-Barr-virus-transformed lymphoblasts prepared from a BTHS patient with that of an age-matched control individual. As expected, mass spectrometry analysis revealed a significant (>90%) reduction in CL in BTHS lymphoblasts compared to controls. In addition, increased oxidized phosphatidylcholine (oxPC) and phosphatidylethanolamine (PE) levels were observed in BTHS lymphoblasts compared to control. Given the broad shifts in metabolism associated with BTHS, we hypothesized that marked differences in posttranslational modifications such as phosphorylation would be present in the lymphoblast cells of a BTHS patient. Phosphokinome analysis revealed striking differences in the phosphorylation levels of phosphoproteins in BTHS lymphoblasts compared to control cells. Some phosphorylated proteins, for example, adenosine monophosphate kinase, have been previously validated as bonafide modified phosphorylation targets observed in tafazzin deficiency or under conditions of reduced cellular CL. Thus, we report multiple novel phosphokinome targets in BTHS lymphoblasts and hypothesize that alteration in the phosphokinome profile may provide insight into the pathophysiology of BTHS and potential therapeutic targets.