Serum choline plasmalogens, particularly those with oleic acid in sn-2, are associated with proatherogenic state

Abstract

Serum plasmalogens (Pls) (1-O-alk-1'-enyl-2-acyl glycerophospholipids) are of particular interest for studies on metabolic disorders associated with oxidative stress and chronic inflammation. Serum levels of Pls are known to correlate positively with HDL-cholesterol (HDL-C); however, few studies have examined serum Pls molecular species in association with pathophysiological conditions and their clinical significance. To clarify these, we determined serum levels of individual ether glycerophospholipids in Japanese asymptomatic cohorts (n = 428; 362 male and 66 female subjects) by LC/MS/MS, and examined their correlations with clinical parameters. We found that the proportion of choline Pls (PlsCho) among total serum phospholipids was significantly lower in the male group over 40 years old and was associated with multiple risk parameters more strongly than HDL-C. The abundance of serum PlsCho with oleic acid (18:1) in sn-2 exhibited the strongest positive correlation with serum concentrations of adiponectin and HDL-C, while being inversely associated with waist circumference and the serum levels of TG and small dense LDL-cholesterol. The characterization of serum ether glycerophospholipids verified the specificity of PlsCho, particularly the ones with 18:1 in sn-2, as a sensitive biomarker for the atherogenic state. Serum plasmalogens (Pls) (1-O-alk-1'-enyl-2-acyl glycerophospholipids) are of particular interest for studies on metabolic disorders associated with oxidative stress and chronic inflammation. Serum levels of Pls are known to correlate positively with HDL-cholesterol (HDL-C); however, few studies have examined serum Pls molecular species in association with pathophysiological conditions and their clinical significance. To clarify these, we determined serum levels of individual ether glycerophospholipids in Japanese asymptomatic cohorts (n = 428; 362 male and 66 female subjects) by LC/MS/MS, and examined their correlations with clinical parameters. We found that the proportion of choline Pls (PlsCho) among total serum phospholipids was significantly lower in the male group over 40 years old and was associated with multiple risk parameters more strongly than HDL-C. The abundance of serum PlsCho with oleic acid (18:1) in sn-2 exhibited the strongest positive correlation with serum concentrations of adiponectin and HDL-C, while being inversely associated with waist circumference and the serum levels of TG and small dense LDL-cholesterol. The characterization of serum ether glycerophospholipids verified the specificity of PlsCho, particularly the ones with 18:1 in sn-2, as a sensitive biomarker for the atherogenic state. Plasmalogens (Pls) are a subclass of glycerophospholipids; they are characterized by the presence of a vinyl-ether bond and an ester bond at the sn-1 and sn-2 positions, respectively, of the glycerol backbone. On the basis of their polar head groups at the sn-3 position, Pls are mainly classified into either choline Pls (PlsCho) or ethanolamine Pls (PlsEtn); the former are localized in a few tissues such as cardiac muscle and blood plasma, whereas the latter belong to a predominant class distributed in a wide variety of cells and tissues (1Braverman N.E. Moser A.B. Functions of plasmalogen lipids in health and disease.Biochim. Biophys. Acta. 2012; 1822: 1442-1452Crossref PubMed Scopus (644) Google Scholar). Serum Pls levels are associated with diverse clinical manifestations (2Brites P. Waterham H.R. Wanders R.J.A. Functions and biosynthesis of plasmalogen in health and disease.Biochim. Biophys. Acta. 2004; 1636: 219-231Crossref PubMed Scopus (302) Google Scholar). For instance, some patients with peroxisomal disorders were found to exhibit the systemic reduction of Pls, which was explained by the fact that the first two steps of Pls biosynthesis occur exclusively in peroxisomes (3Wanders R.J.A. Waterham H.R. Peroxisomal disorders: The single peroxisomal enzyme deficiencies.Biochim. Biophys. Acta. 2006; 1763: 1707-1720Crossref PubMed Scopus (207) Google Scholar). In addition, because Pls are abundant in the brain and play essential roles in neuronal functions and myelin formation, defects in Pls contents represent a pathological factor for a number of neurodegenerative disorders such as Alzheimer's disease (AD) (4Han X. Holtzman D.M. Jr. McKeel D.W. Plasmalogen deficiency in early Alzheimer's disease subjects and in animal models: molecular characterization using electrospray ionization mass spectrometry.J. Neurochem. 2001; 77: 1168-1180Crossref PubMed Scopus (387) Google Scholar). Goodenowe et al. (5Goodenowe D.B. Cook L.L. Liu J. Lu Y. Jayasinghe D.A. Ahiahonu P.W. Heath D. Yamazaki Y. Flax J. Krenitsky K.F. et al.Peripheral ethanolamine plasmalogen deficiency: a logical causative factor in Alzheimer's disease and dementia.J. Lipid Res. 2007; 48: 2485-2498Abstract Full Text Full Text PDF PubMed Scopus (203) Google Scholar) also reported that the serum level of PlsEtn containing DHA (22:6) could be a useful biomarker for the early detection and long-term follow-up of AD. Recently, particular attention has been paid to the involvement of Pls in metabolic diseases associated with oxidative stress and chronic inflammation (6Wallner S. Schmitz G. Plasmalogens the neglected regulatory and scavenging lipid species.Chem. Phys. Lipids. 2011; 164: 573-589Crossref PubMed Scopus (217) Google Scholar). Pls may be involved in the etiology of both T1D and T2D through oxidative stress. Patients with T1D exhibit absolute insulin deficiency due to autoimmune destruction of insulin-producing pancreatic β cells. In a longitudinal study, children who developed T1D were later found to have reduced serum levels of ether type choline glycerophospholipids (ChoGpl), including PlsCho at birth and consistently throughout medical follow-ups (7Oresic M. Simell S. Sysi-Aho M. Näntö-Salonen K. Seppänen-Laakso T. Parikka V. Katajamaa M. Hekkala A. Mattila I. Keskinen P. et al.Dysregulation of lipid and amino acid metabolism precedes islet autoimmunity in children who later progress to type 1 diabetes.J. Exp. Med. 2008; 205: 2975-2984Crossref PubMed Scopus (360) Google Scholar). Pls deficiency may cause enhanced susceptibility of pancreatic β cells to oxidative damage and trigger progression to diabetes. Oxidative stress may also be associated with T2D and related cardiovascular diseases. Notably, decreased PlsEtn levels and increased lipid peroxidation were found in LDL particles from obese patients with metabolic syndrome (MetS) and patients with T2D (8Colas R. Sassolas A. Guichardant M. Cugnet-Anceau C. Moret M. Moulin P. Lagarde M. Calzada C. LDL from obese patients with the metabolic syndrome show increased lipid peroxidation and activate platelets.Diabetologia. 2011; 54: 2931-2940Crossref PubMed Scopus (59) Google Scholar), which may be a risk factor for atherosclerosis. Plasma Pls may be a good marker for inferring the level of oxidative stress and predicting cardiovascular mortality in patients with end-stage renal disease (9Stenvinkel P. Diczfalusy U. Lindholm B. Heimbürger O. Phospholipid plasmalogen, a surrogate marker of oxidative stress, is associated with increased cardiovascular mortality in patients on renal replacement therapy.Nephrol. Dial. Transplant. 2004; 19: 972-976Crossref PubMed Scopus (66) Google Scholar). Plasma concentration of Pls also decreases with hypertension (10Graessler J. Schwudke D. Schwarz P.E. Herzog R. Shevchenko A. Bornstein S.R. Top-down lipidomics reveals ether lipid deficiency in blood plasma of hypertensive patients.PLoS ONE. 2009; 4: e6261Crossref PubMed Scopus (259) Google Scholar), as well as with age and chronic inflammatory-related diseases such as atherosclerosis and AD (11Farooqui A.A. Ong W.Y. Horrocks L.A. Inhibitors of brain phospholipase A2 activity: their neuropharmacological effects and therapeutic importance for the treatment of neurologic disorders.Pharmacol. Rev. 2006; 58: 591-620Crossref PubMed Scopus (300) Google Scholar, 12Lessig J. Fuchs B. Plasmalogens in biological systems: their role in oxidative processes in biological membranes, their contribution to pathological processes and aging and plasmalogen analysis.Curr. Med. Chem. 2009; 16: 2021-2041Crossref PubMed Scopus (151) Google Scholar). Pls function as reservoirs for precursor fatty acids, such as arachidonic acid and DHA, which generate bioactive lipid mediators. Eicosanoids derived from arachidonic acid play an important role in the regulation of vascular tone and possibly link Pls with hypertension via blood pressure regulation. Studies have postulated that Pls serve as endogenous antioxidants and protect membrane lipids and lipoprotein particles from excessive oxidation by scavenging reactive oxygen species via the vinyl-ether moiety (13Zoeller R.A. Lake A.C. Nagan N. Gaposchkin D.P. Legner M.A. Lieberthal W. Plasmalogens as endogenous antioxidants: somatic cell mutants reveal the importance of vinyl ether.Biochem. J. 1999; 338: 769-776Crossref PubMed Scopus (183) Google Scholar, 14Hahnel D. Thiery J. Brosche T. Engelmann B. Role of plasmalogens in the enhanced resistance of LDL to copper-induced oxidation after LDL apheresis.Arterioscler. Thromb. Vasc. Biol. 1999; 19: 2431-2438Crossref PubMed Scopus (27) Google Scholar, 15Maeba R. Ueta N. Ethanolamine plasmalogens prevent the oxidation of cholesterol by reducing the oxidizability of cholesterol in phospholipid bilayers.J. Lipid Res. 2003; 44: 164-171Abstract Full Text Full Text PDF PubMed Scopus (65) Google Scholar). To date, however, available data regarding the relationship between serum Pls and clinical disease entities are still limited, and the association of Pls molecular species with preclinical pathophysiological conditions is yet to be clarified. Previously, we performed an advanced comprehensive analysis of serum ether glycerophospholipids, including Pls, by LC/MS/MS, which has allowed the accurate quantification of each molecular species (16Nishimukai M. Yamashita M. Watanabe Y. Yamazaki Y. Nezu T. Maeba R. Hara H. Lymphatic absorption of choline plasmalogen is much higher than that of ethanolamine plasmalogen in rats.Eur. J. Nutr. 2011; 50: 427-436Crossref PubMed Scopus (22) Google Scholar, 17Hui S.P. Chiba H. Kurosawa T. Liquid chromatography-mass spectrometric determination of plasmalogens in human plasma.Anal. Bioanal. Chem. 2011; 400: 1923-1931Crossref PubMed Scopus (25) Google Scholar). The present study provides the reference data from 428 Japanese asymptomatic subjects on their serum levels of individual ether glycerophospholipid species. By analyzing the correlation of each molecular species with clinical parameters or biochemical measurements, we found that PlsCho with 18:1 in the sn-2 position strongly correlated with a wide range of risk factors for atherosclerosis and MetS. Our findings suggest that serum PlsCho, like HDL-cholesterol (HDL-C), may serve as a sensitive antiatherogenic biomarker. Asymptomatic subjects (n = 428; 362 male and 66 female subjects; age, 22–66 years old) who were for a health were in the was from and the studies were by the of of and were from blood in a blood containing by at for and an was concentration of and concentration of 1 by at of waist and blood pressure were were to health of with to their medical as well as their and Serum lipids were by after the serum was 1 of including and and was to the serum and for of was to each and for the at for the were and the was was and the was The including were with glycerophospholipids, including Pls, in lipids were by and of each PlsCho and as well as and were to generate a for individual molecular species of ether glycerophospholipids also to the and of the as S.P. Chiba H. Kurosawa T. Liquid chromatography-mass spectrometric determination of plasmalogens in human plasma.Anal. Bioanal. Chem. 2011; 400: 1923-1931Crossref PubMed Scopus (25) Google Scholar). The of and for PlsCho and respectively, as well as was (n = of of phospholipids from to from the by choline to ethanolamine was to generate a for molecular species. The concentrations of individual molecular species of ether glycerophospholipids were determined using for PlsCho and and for PlsEtn and The of molecular species were and for each class of and Pls, respectively, of which were determined by was a (16Nishimukai M. Yamashita M. Watanabe Y. Yamazaki Y. Nezu T. Maeba R. Hara H. Lymphatic absorption of choline plasmalogen is much higher than that of ethanolamine plasmalogen in rats.Eur. J. Nutr. 2011; 50: 427-436Crossref PubMed Scopus (22) Google Scholar). was performed using an with a at and a of of containing while of was at at decreased to at to at and to at and at for 1 being to The analysis was performed using a with an in positive The conditions were as a of and and of and was as both the and was as the at a pressure of The was for and PlsCho, for and for was performed with for each class of Pls and molecular species are in and PlsEtn was to the by and ionization mass of plasmalogen 2004; PubMed Scopus Google Scholar). In at and were for the of the sn-1 position of PlsEtn containing and and PlsCho, by derived from as well as sn-1 and sn-2 were using a at the of each molecular species by by derived from sn-1 and fatty derived from the sn-2 was using a at the of each molecular species by C. B. A. P. of phospholipids in brain using chromatography-mass 2009; 44: PubMed Scopus Google Scholar). The presence of Pls was by the of the treatment with Serum concentrations of HDL-C, total phospholipids blood acid and were determined with an and dense was using the was by a was using the adiponectin was determined using a analysis was performed using with the are as or and were by for data and as well as for among were with ether parameters of the subjects classified by age and Pls are and range of among groups was by with were to be and a are significantly of between and was by ether glycerophospholipids; PlsCho PlsEtn in a between the serum levels of PlsCho molecular species and parameters. represent from a correlation by for over male subjects (n = the of which is to be with between the serum levels of Pls molecular species and HDL-C. represent from a correlation by for over male subjects (n = the of which is to be with of the correlations with parameters among PlsCho, and data from over 40 years old (n = data from over 40 years old (n = data from over 40 years old (n = data from over 40 years old (n = represent correlation by blood blood data from over 40 years old (n = in a of the correlations with parameters for male subjects over 40 years old among individual class or subclass of glycerophospholipids containing oleic acid in and sn-2 sn-2 sn-2 sn-2 sn-2 sn-2 in serum represent correlation by and the over are to be with and quantification of individual ether glycerophospholipid molecular species were performed with the as in the molecular species were using the mass as for of molecular species. of each and were for a to individual molecular species. in a are and range of among groups was by with were to be and a are significantly of between and was by ether glycerophospholipids; PlsCho PlsEtn represent correlation by blood blood represent correlation by and the over are to be with and quantification of individual ether glycerophospholipid molecular species were performed with the as in the molecular species were using the mass as for of molecular species. of each and were for a to individual molecular species. parameters and serum biochemical of the subjects were classified by age or over 40 years old) and The data that male subjects over 40 years old exhibited in clinical and biochemical including waist and blood blood the serum levels of and as well as the atherogenic of plasma as To that subjects to the at serum concentrations of and adiponectin were The data of male subjects years old that they were the or lower of a serum that male subjects over 40 years old are associated with The serum concentrations of each class of Pls PlsCho and and and with their class and and their in total phospholipids total and total were to and age The show that while the serum levels of PlsCho and PlsEtn were the serum concentrations of were much lower than of In addition, the for the male group was significantly lower than for whereas the and total were higher among the and female The of age groups were by factors such as and the in some of factors were among age factors effects on parameters. than significantly higher serum concentrations of were related to the of among groups The proportion of female subjects in the study was the in study be We also determined the serum levels of each molecular species of ether glycerophospholipids and examined their molecular fatty and were in the sn-1 position of ether was the predominant fatty species among the choline class of both and Pls, whereas among the ethanolamine species were distributed acid the fatty acid in the sn-2 position, was in ether In addition, DHA was among the ethanolamine and acid was in The among serum ether glycerophospholipids is in positive correlation was between the serum concentrations of and = because they a The of PlsEtn from to be by both the positive correlation between their serum levels = and the between their molecular the of PlsCho is to be derived from from and biological functions of Biophys. Acta. PubMed Scopus Google Scholar, K. in ether lipid PubMed Scopus Google Scholar). the correlation between the serum levels of PlsCho and PlsEtn = was higher than that between PlsCho and = the molecular of PlsCho and PlsEtn were from each that a of serum PlsCho species may have than serum ether of molecular species in the sn-1 and sn-2 of ether represent the of the serum concentrations of fatty in sn-1 and fatty in sn-2 of individual ether glycerophospholipids of over subjects (n = male and female We found that the was significantly associated with multiple risk factors for the atherogenic and that correlations were at or levels than of In addition, we found that among PlsCho PlsCho with 18:1 and in sn-2 correlated positively with the serum adiponectin concentration = and inversely with waist circumference = and the serum concentrations of TG = and = and and = and In species of or PlsEtn with parameters The correlations with parameters were among or of glycerophospholipids containing 18:1 in sn-2 The that among the glycerophospholipids, PlsCho correlations with of parameters. In choline and ethanolamine glycerophospholipids with 18:1 in sn-2, as well as total 18:1 lipids in correlated positively with and In addition, we that the proportion of PlsCho with in total serum phospholipids correlated with age also suggest that both of Pls with acid in sn-2 are associated with the of = = whereas total lipids in exhibited correlation the serum levels of both of Pls molecular species were found to correlate with the serum as R. T. M. K. H. J. N. Y. D. T. et in human serum positively correlate with lipoprotein and with Thromb. 2007; PubMed Scopus Google Scholar). The of correlation among molecular species in the male subjects (n = that the of serum PlsCho with 18:1 in the sn-2 position correlated strongly with the concentration = Notably, the levels of both of Pls with acid or in sn-2 were also found to be associated with the we for the first that the was significantly lower in the male group also correlations with multiple antiatherogenic parameters than In addition, serum PlsCho with 18:1 or in the sn-2 position also correlations with a wide range of risk such as age the susceptibility of their vinyl-ether moiety to oxidation O. 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M.A. Goodenowe D.B. plasmalogen and cholesterol a PubMed Scopus Google Scholar). suggest the of serum Pls to the important functions of including studies are to the involvement of Pls in metabolism and In characterization of serum ether glycerophospholipids that PlsCho with 18:1 or in the sn-2 position may serve as a sensitive biomarker for the atherogenic state. with Alzheimer's disease atherogenic of plasma choline glycerophospholipid HDL-cholesterol metabolic syndrome fatty disease choline ethanolamine phospholipid plasmalogen choline plasmalogen ethanolamine plasmalogen choline cholesterol small dense acid