Serum choline plasmalogens—those with oleic acid in sn− 2—are biomarkers for coronary artery disease

Hetero-Diels-Alder Cycloaddition Reaction of Vinyl Ethers Enables Selective Fluorescent Labeling of Plasmalogens in Human Plasma Lipids

Plasmalogens (Pls) are vinyl ether-containing glycerophospholipids of broad biological interest. Their abnormal levels are associated with neurological disorders and cardiovascular diseases. The intricacy of analyzing Pls in lipid samples arises from the wide variety of other coexisting lipid species, which underscores the urgent need for a Pls-specific labeling reaction. To address this challenge, we report an efficient hetero-Diels-Alder cycloaddition reaction between nonterminal vinyl ethers of Pls and o-quinolinone quinone methide probes under mild conditions. On the basis of this mechanism, a selective fluorescent labeling method for Pls is developed. The application of this method permits the exclusive derivatization of Pls over other human plasma lipids. The process also imparts labeled Pls with distinct fluorescence emission and chromatographic retention properties. By integrating this method with high-performance liquid chromatography, we are able to identify individual chromatographic signatures of Pls from 10 different human plasma samples. This Pls signature analytical technique, empowered by the Pls-specific labeling reaction, is cost-effective and simple in terms of instrumentation, suggesting its promising potential for the early screening and diagnosis of diseases linked to Pls abnormalities.

Marine Plasmalogens: A Gift from the Sea with Benefits for Age-Associated Diseases

Aging increases oxidative and inflammatory stress caused by a reduction in metabolism and clearance, thus leading to the development of age-associated diseases. The quality of our daily diet and exercise is important for the prevention of these diseases. Marine resources contain various valuable nutrients, and unique glycerophospholipid plasmalogens are found abundantly in some marine invertebrates, including ascidians. One of the major classes, the ethanolamine class (PlsEtn), exists in a high ratio to phospholipids in the brain and blood, while decreased levels have been reported in patients with age-associated diseases, including Alzheimer's disease. Animal studies have shown that the administration of marine PlsEtn prepared from marine invertebrates improved PlsEtn levels in the body and alleviated inflammation. Animal and human studies have reported that marine PlsEtn ameliorates cognitive impairment. In this review, we highlight the biological significance, relationships with age-associated diseases, food functions, and healthcare materials of plasmalogens based on recent knowledge and discuss the contribution of marine plasmalogens to health maintenance in aging.

Baseline Elevations of Leukotriene Metabolites and Altered Plasmalogens Are Prognostic Biomarkers of Plaque Progression in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is associated with an increased incidence of acute and chronic cardiovascular disease as compared to the general population. This study uses a comprehensive metabolomic screen of baseline sera from lupus patients to identify metabolites that predict future carotid plaque progression, following 8–9 years of follow-up. Nine patients had SLE without plaque progression, 8 had SLE and went on to develop atherosclerotic plaques (SLE^PP), and 8 patients were controls who did not have SLE. The arachidonic acid pathway metabolites, leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE), and the oxidized lipids 9/13-hydroxyoctodecadienoic acid (HODE) were found to be significantly altered (p < 0.05 and fold-change >2) in SLE^PP patients compared to SLE patients without plaque progression. SLE^PP patients also exhibited significantly altered levels of branched chain amino acid (BCAA) metabolites and plasmalogens compared to the non-SLE controls. Taken together with the rich literature on these metabolites, these findings suggest that the identified metabolites may not only be prognostic of cardiovascular disease development in SLE patients, but they may also be active drivers of atheroma formation. Early identification of these high risk SLE patients may help institute preventive measures early in the disease course.

Lymphatic Absorption of Microbial Plasmalogens in Rats

Plasmalogens, functional glycerophospholipids with biological roles in the human body, are associated with various diseases. Although a variety of saturated and/or unsaturated fatty acids in plasmalogens are presumed to have different functions in the human body, there are limited reports validating such functions of plasmalogens. In this study, we focused on the bacterial plasmalogen derived from Selenomonas ruminantium subsp. lactilytica (NBRC No. 103574) with different main species of hydrocarbon chains at the sn-1 position and shorter fatty acids at the sn-2 position than animal plasmalogens. Optimum culture conditions of S. ruminantium for high-yield production of plasmalogens, such as pH and the concentration of caproic acid, were investigated under anaerobic conditions using a 2-L scale jar fermenter. The obtained plasmalogen mainly consisted of the ethanolamine plasmalogen (PlsEtn). The molar ratios of PlsEtn species obtained from S. ruminantium, at sn-1/sn-2 positions, were p16:1/14:0 (68.4%), p16:1/16:1 (29.2%), p16:1/16:0 (0.7%), p16:1/15:0 (0.3%), and p17:1/14:0 (0.3%). Subsequently, duodenal infusion of the emulsion carrying the lipid extracted from S. ruminantium was carried out in lymph duct-cannulated rats. In the lymphatic plasmalogen of rats, the level of PlsEtns with molar ratios p16:1/14:0 and p16:1/16:1, the main species of plasmalogens from S. ruminantium, increased gradually until 3–4 h after lipid injection and then gradually decreased. In addition, the level of PlsEtns with p16:1/20:4 and p16:1/22:6 rapidly increased, peaking at 1–1.5 h and 1.5–2 h after lipid injection, respectively. The increase in the number of PlsEtns with p16:1/20:4 and p16:1/22:6 suggested that 20:4 and 22:6, the main fatty acids at the sn-2 position in the rat lymphatic plasmalogen, were preferentially re-esterified at the sn-2 position, regardless of the types of hydrocarbon chains at the sn-1 position. Thus, we showed that bacterial PlsEtns with “unnatural” structures against rats could be absorbed into the lymph. Our findings provide insights into the association between the chemical structure of plasmalogens and their biological functions in humans.

Destruction of polyunsaturated alkyl/acyl and alkenyl/acyl glycerophosphocholine of plasma lipoproteins during incubation with group V and X secretory phospholipase A2 s

Plasma lipoproteins are carriers of various glycerophospholipids including diacyl, alkenyl/acyl, and alkyl/acyl glycerophosphocholines (GPCs), which become distributed among cells and tissues during metabolism. For metabolic function, these phospholipids require hydrolysis by phospholipases, but the responsible enzymes have not been identified. We had previously shown that after complete digestion of lipoprotein diacyl- and oxo-diacyl-GPCs, degradation of residual alkyl/acyl and alkenyl/acyl GPCs continues, despite the fact that ether lipids are resistant to hydrolysis by Ca²⁺ -activated secretory PLA₂ s and require the presence of the Ca²⁺ -independent PLA₂ . In the course of further investigation, we came across a report by Khaselev and Murphy in which the autoxidative degradation of plasmalogens in the presence of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) proceeded beyond the formation of dihydroperoxides, hydroxides and epoxides, and led to an attack on the enyl bond of the plasmalogen, resulting in formation of 1-OH/2-20:4-GPC and 1-formyl/2-20:4-GPC. Our preliminary investigation indicated that lipoprotein 16:0p/20:4ω6-GPC yielded the same autoxidation products as those reported for synthetic 16:0p/20:4ω6-GPC in the presence of AAPH. Such autoxidative degradation of lipoprotein plasmalogens had not been previously reported with or without AAPH. Subsequent study led to the conclusion that this reaction was not limited to arachidonates, but extended to other polyunsaturated eicosanoids, docosanoids, and tetracosanoids, as well as oligounsaturated octadecanoids. These observations led to a hypothesis that the autoxidative cleavage of the lipoprotein plasmalogens proceeded under the influence of apo-protein-derived free radicals as intermediates of oxidative processes.

Identification of Potential Metabolic Markers of Hypertension in Chinese Children

Background

Studies in adults have shown that several metabolites across multiple pathways are strongly associated with hypertension. However, as yet, to our knowledge, no study has investigated such association in childhood. We, therefore, compared the serum metabolite profile of children with normal and elevated blood pressure (BP) to identify potential metabolic markers and pathways that could be useful for the assessment of pediatric hypertension.

Methods

The study included 26 hypertensive children (age range, 6-11 years) and 26 age- and sex-matched ones with normal BP, who were recruited from the baseline survey of the Huantai Childhood Cardiovascular Health Cohort Study. Ultrahigh-performance liquid chromatography-quadrupole time-of-flight-mass spectrometry was performed to assess the serum metabolite profile. Logistic regression analysis was used to select significant metabolites associated with hypertension after adjustment for body mass index, waist circumference, and lipid profile. Kyoto Encyclopedia of Genes and Genomes (KEGG) and MetaboAnalyst were utilized to search for the potential pathways of metabolites.

Results

A total of 45 and 34 metabolites were preliminarily screened in positive and negative modes, respectively (variable importance in the projection (VIP) > 1.0 and P < 0.05). After adjustment for the false discovery rate, 7 and 1 differential metabolites in the positive and negative modes, respectively, remained significant (VIP > 1.0 and q < 0.05). These metabolites were mainly involved in amino acid metabolism and glycerophospholipid metabolism. Among these, two significant metabolites including ethanolamine and 2-methyl-3-hydroxy-5-formylpyridine-4-carboxylate displayed an area under the curve value of 0.820 (95% confidence interval, 0.688-0.951), with a sensitivity of 0.846 and a specificity of 0.769.

Conclusion

The untargeted metabolomics approach effectively identified the differential serum metabolite profile in children with and without hypertension. Notably, two metabolites including ethanolamine and 2-methyl-3-hydroxy-5-formylpyridine-4-carboxylate exhibited a good discriminative ability to identify children with hypertension, providing new insights into potential mechanisms of pediatric hypertension.

Cardiac phospholipidome is altered during ischemia and reperfusion in an ex vivo rat model

Acute myocardial infarction (AMI) is the leading cause of death, morbidity, and health costs worldwide. In AMI, a sudden blockage of blood flow causes myocardial ischemia and cell death. Reperfusion after ischemia has paradoxical effects and may exacerbate the myocardial injury, a process known as ischemic reperfusion injury. In this work we evaluated the lipidome of isolated rat hearts, maintained in controlled perfusion (CT), undergoing global ischemia (ISC) or ischemia followed by reperfusion (IR). 153 polar lipid levels were significantly different between conditions. 48 features had q < 0.001 and included 8 phosphatidylcholines and 4 lysophospholipids, which were lower in ISC compared to CT, and even lower in the IR group, suggesting that IR induces more profound changes than ISC. We observed that the levels of 16 alkyl acyl phospholipids were significantly altered during ISC and IR. Overall, these data indicate that myocardial lipid remodelling and possibly damage occurs to a greater extent during reperfusion. The adaptation of cardiac lipidome during ISC and IR described is consistent with the presence of oxidative damage and may reflect the impact of AMI on the lipidome at the cellular level and provide new insights into the role of lipids in the pathophysiology of acute myocardial ischemia/reperfusion injury.

Structural changes of ethanolamine plasmalogen during intestinal absorption

Considerable attention has been paid to the absorption mechanisms of plasmalogen (Pls) because its intake has been expected to have preventive effects on brain-related diseases. Possible structural changes of Pls during absorption (i.e., preferential arachidonic acid re-esterification at the sn-2 position and base conversion of ethanolamine Pls (PE-Pls) into choline Pls (PC-Pls)) have previously been proposed. Since the physiological functions of Pls differ according to its structure, further elucidation of such structural changes during absorption is important to understand how Pls exerts its physiological effects in vivo. Hence, the absorption mechanism of Pls was investigated using the lymph-cannulation method and the everted jejunal sac model, with a focus on Pls molecular species. In the lymph-cannulation method, relatively high amounts of PE-Pls 18:0/20:4 and PC-Pls 18:0/20:4 were detected from the lymph even though these species were minor in the administered emulsion. Moreover, a significant increase of PE-Pls 18:0/20:4 and PC-Pls 18:0/20:4 in the intestinal mucosa was also confirmed by the everted jejunal sac model. Therefore, structural changes of PE-Pls in the intestinal mucosa were strongly suggested. The results of this study may provide an understanding of the relationship between intestinal absorption of Pls and exertion of its physiological functions in vivo.

Fast and Specific Screening of EPA/DHA-Enriched Phospholipids in Fish Oil Extracted from Different Species by HILIC-MS

Eicosapentaenoic acid- and docosahexaenoic acid-enriched phospholipids (PL_EPA/DHA) have versatile health-beneficial functions and can be well absorbed in the intestine. Herein, a precursor ion scan-driven hydrophilic interaction chromatography mass spectrometry (PreIS-HILIC-MS) method with the fatty acyl moieties of m/z 301.6 and 327.6 locked was established to specifically and selectively screen PL_EPA/DHA in different fish oil samples, including saury, grass carp, hairtail, and yellow croaker. Taking saury oil as an example, a total of 24 PL_EPA/DHA were successfully identified and quantified, including 20 PC_EPA/DHA and 4 PE_EPA/DHA. Finally, this method was validated in terms of sensitivity (limit of detection ≤ 4.15 μg·mL^-1), linearity (≥0.9979), precision (RSD_intraday ≤ 4.65%), and recovery (≥78.6%). The performance of the PreIS-HILIC-MS method was also compared with that of the traditional full-scan mode, and the former demonstrated its unique superiority in targeted screening of PL_EPA/DHA in fish oils.

Dual mass spectrometry as a tool to improve annotation and quantification in targeted plasma lipidomics

INTRODUCTION

High quality data, based on reliable quantification and clear identification of the reported lipid species, are required for the clinical translation of human plasma lipidomic studies.

OBJECTIVE

Lipid quantification can be efficiently performed on triple quadrupole (QqQ) mass spectrometers in targeted multiple reaction monitoring (MRM) mode. However, a series of issues can be encountered when aiming at unambiguous identification and accurate quantification, including (i) resolving peaks of polyunsaturated species, (ii) discriminating between plasmanyl-, plasmenyl- and odd chain species and (iii) resolving the isotopic overlap between co-eluting lipid species.

METHODS

As a practical tool to improve the quality of targeted lipidomics studies, we applied a Dual MS platform by simultaneously coupling a reversed-phase liquid chromatography separation to a QqQ and a quadrupole-time of flight (Q-ToF) mass spectrometers. In one single experiment, this platform allows to correctly identify, by high-resolution MS and MS/MS, the peaks that are quantified by MRM.

RESULTS

As proof of concept, we applied the platform on glycerophosphocholines (GPCs) and sphingomyelins (SMs), which are highly abundant in human plasma and play crucial roles in various physiological functions. Our results demonstrated that Dual MS could provide a higher level of confidence in the identification and quantification of GPCs and SMs in human plasma. The same approach can also be applied to improve the study of other lipid classes and expanded for the identification of novel lipid molecular species.

CONCLUSIONS

This methodology might have a great potential to achieve a better specificity in the quantification of lipids by targeted lipidomics in high-throughput studies.

Unique Distribution of Diacyl-, Alkylacyl-, and Alkenylacyl-Phosphatidylcholine Species Visualized in Pork Chop Tissues by Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry Imaging

Phosphatidylcholine (PC) is the major phospholipid in meat and influences meat qualities, such as healthiness. PC is classified into three groups based on the bond at the sn-1 position: Diacyl, alkylacyl, and alkenylacyl. To investigate their composition and distribution in pork tissues, including longissimus thoracis et lumborum (loin) spinalis muscles, intermuscular fat, and transparent tissues, we performed matrix-assisted laser desorption/ionization–mass spectrometry imaging (MALDI–MSI). Eleven diacyl-, seven alkylacyl-, and six alkenylacyl-PCs were identified using liquid chromatography (LC)-tandem MS (MS/MS) analysis. Despite many alkylacyl- and alkenylacyl-PC species sharing identical m/z values, we were able to visualize these PC species using MALDI–MSI. Diacyl- and alkylacyl- and/or alkenylacyl-PC species showed unique distribution patterns in the tissues, suggesting that their distribution patterns were dependent on their fatty acid compositions. PCs are a major dietary source of choline in meat, and the amount was significantly higher in the muscle tissues. Consumption of choline mitigates age-related memory decline and neurodegenerative diseases; therefore, the consumption of pork muscle tissues could help to mitigate these diseases. These results support the use of MALDI–MSI analysis for assessing the association between PC species and the quality parameters of meat.

Choline and Ethanolamine Plasmalogens Prevent Lead-Induced Cytotoxicity and Lipid Oxidation in HepG2 Cells

Plasmalogens derived from dietary phospholipids are considered to be potential protectors against oxidation-related disorders, while lead (Pb) is an environmental contaminant worldwide and is known to induce oxidative stress. However, the protective and antilipid oxidative effects of individual plasmalogen species against Pb damage have received little attention. In this study, six plasmalogen species (with either choline or ethanolamine as the headgroup and p16:0/18:1, p16:0/18:2, or p16:0/20:5 as the side chains) were evaluated in human hepatoma cells. Plasmalogen species showed a remarkable recovery in cell viability as well as elimination of reactive oxygen species and suppressed the accumulation of phosphatidylcholine hydroperoxides (from 63.6 ± 1.8% to 80.3 ± 2.9%) and phosphatidylethanolamine hydroperoxides (from 25.7 ± 9.3% to 76.1 ± 3.7%). Moreover, plasmalogens significantly upregulated the gene expression levels of a series of antioxidant enzymes that are regulated via the Nrf-2-dependent pathway. This study suggested that choline and ethanolamine plasmalogens could prevent Pb-induced cytotoxicity and lipid oxidation in HepG2 cells.

Composition of plasmalogens in serum lipoproteins from patients with non-alcoholic steatohepatitis and their susceptibility to oxidation

BACKGROUND

Plasmalogens are ether phospholipids (PL) with an alkenyl group including vinyl ether bound at the sn-1 position and a polyunsaturated fatty acid bound at the sn-2 position, and are susceptible to oxidation. To date, there are no reports on the relationship between plasmalogen in serum lipoproteins and non-alcoholic steatohepatitis (NASH), caused by multiple factors including oxidative stress. Here, we have investigated the distribution of plasmalogens in serum lipoproteins isolated from NASH patients and healthy volunteers.

METHODS

Serum lipoproteins were separated by gel-filtration chromatography, and analyzed for ethanolamine and choline plasmalogens using liquid chromatography-mass spectrometry.

RESULTS

Both plasmalogen levels were higher in HDL than in VLDL or LDL. The plasmalogens/PL ratio was significantly lower in NASH than controls, for all lipoprotein fractions. Ethanolamine plasmalogens containing 20:4 and 22:6 at the sn-2 position and choline plasmalogens containing 16:0 at the sn-1 position were predominant in each group. In oxidation test using LDL from healthy serum, both types of plasmalogens were decreased during the early stages of oxidation.

CONCLUSION

Plasmalogens could be a potential biomarker for evaluating the early stages of oxidation in NASH.

Phosphatidylcholine and phosphatidylethanolamine plasmalogens in lipid loaded human macrophages

Background

Plasmalogens are either phosphatidylcholine (PC P) or phosphatidylethanolamine (PE P) glycerophospholipids containing a vinyl ether moiety in sn-1-position and an esterified fatty acid in sn-2 position. Multiple functions have been proposed, including reservoir of precursors for inflammatory mediators, modulation of membrane fluidity, and anti-oxidative properties. They could therefore play a role under conditions of metabolic stress. Especially enzymatically modified LDL (eLDL) and oxidatively modified LDL (oxLDL) represent modifications of LDL that are taken up by macrophages in atherosclerotic plaques. The aim of this study was to analyze plasmalogen related effects of eLDL and oxLDL in human monocyte derived macrophages, as well as the effects of HDL₃ mediated deloading.

Methods

Elutriated monocytes from nine healthy donors were differentiated in vitro for four days. Macrophages were then loaded with native LDL, eLDL and oxLDL for 24h and subsequently deloaded with HDL₃ for another 24h. Lipidomic and transcriptomic profiles were obtained.

Results

Loading of macrophages with eLDL and oxLDL led to a transient but strong elevation of lysophosphatidylcholine (LPC) most likely through direct uptake. Only eLDL induced increased levels of total PC, presumably through an induction of PC synthesis. On the other hand treatment with oxLDL led to a significant increase in PC P. Analysis of individual lipid species showed lipoprotein and saturation specific effects for LPC, PC P and PE P species. Membrane fluidity was decreased by the large amount of FC contained in the lipoproteins, as indicated by a lower PC to FC ratio after lipoprotein loading. In contrast the observed changes in the saturated to mono-unsaturated fatty acid (SFA to MUFA) and saturated to poly-unsaturated fatty acid (SFA to PUFA) ratios in PE P could represent a cellular reaction to counteract this effect by producing more fluid membranes. Transcriptomic analysis showed considerable differences between eLDL and oxLDL treated macrophages. As a common feature of both lipoproteins we detected a strong downregulation of pathways for endogenous lipid synthesis as well as for exogenous lipid uptake. Deloading with HDL₃ had only minor effects on total lipid class as well as on individual lipid species levels, most of the time not reaching significance. Interestingly treatment with HDL₃ had no effect on membrane fluidity under these conditions, although incubation with HDL₃ was partially able to counteract the oxLDL induced transcriptomic effects. To investigate the functional effect of lipoprotein treatment on macrophage polarization we performed surface marker flow cytometry. Under our experimental conditions oxLDL was able to partially shift the surface marker pattern towards a pro-inflammatory M1-like phenotype. This is consistent with the consumption of arachidonic acid containing PE P species in oxLDL treated cells, presumably for the synthesis of inflammatory mediators.

Summary

Our findings provide novel data on the lipoprotein induced, lipidomic and transcriptomic changes in macrophages. This can help us better understand the development of metabolic, inflammatory diseases as well as improve our background knowledge on lipid biomarkers in serum.

Serum Ethanolamine Plasmalogen and Urine Myo-Inositol as Cognitive Decline Markers

Recent studies have suggested that metabolic disorders, particularly type 2 diabetes mellitus (T2DM), and dementia, including Alzheimer's disease (AD), were linked at the clinical and molecular levels. Brain insulin deficiency and resistance may be key events in AD pathology mechanistically linking AD to T2DM. Ethanolamine plasmalogens (PlsEtns) are abundant in the brain and play essential roles in neuronal function and myelin formation. As such, PlsEtn deficiency may be pathologically relevant in some neurodegenerative disorders such as AD. Decreased brain PlsEtn associated with dementia may reflect serum PlsEtn deficiency. We hypothesized that myo-inositol plays a role in myelin formation through its facilitation of PlsEtn biosynthesis. Excessive urinary myo-inositol (UMI) loss would likely result in PlsEtn deficiency potentially leading to demyelinating diseases such as dementia. Accordingly, measurement of both serum PlsEtn and baseline UMI excretion could improve the detection of cognitive impairment (CI) in a more specific and reliable manner. To verify our hypothesis, we conducted a clinical observational study of memory clinic outpatients (MCO) and cognitively normal elderly (NE) for nearly 4.5years. We demonstrated that serum PlsEtn concentration associated with UMI excretion was useful for predicting advancing dementia in patients with mild CI. Because hyperglycemia and associated insulin resistance might be a leading cause of increased baseline UMI excretion, serum PlsEtn quantitation would be useful in detecting CI among the elderly with hyperglycemia. Our findings suggest that myo-inositol is a novel candidate molecule linking T2DM to AD.

Molecular cloning, heterologous expression, and enzymatic characterization of lysoplasmalogen-specific phospholipase D from Thermocrispum sp

Lysoplasmalogen (LyPls)‐specific phospholipase D (LyPls‐PLD) is an enzyme that catalyses the hydrolytic cleavage of the phosphoester bond of LyPls, releasing ethanolamine or choline, and 1‐(1‐alkenyl)‐sn‐glycero‐3‐phosphate (lysoplasmenic acid). Little is known about LyPls‐PLD and metabolic pathways of plasmalogen (Pls). Reportedly, Pls levels in human serum/plasma correlate with several diseases such as Alzheimer's disease and arteriosclerosis as well as a variety of biological processes including apoptosis and cell signaling. We identified a LyPls‐PLD from Thermocrispum sp. strain RD004668, and the enzyme was purified, characterized, cloned, and expressed using pET24a(+)/Escherichia coli with a His tag. The enzyme's preferred substrate was choline LyPls (LyPlsCho), with only modest activity toward ethanolamine LyPls. Under optimum conditions (pH 8.0 and 50 °C), steady‐state kinetic analysis for LyPlsCho yielded K_m and k_cat values of 13.2 μm and 70.6 s⁻¹, respectively. The ORF of LyPls‐PLD gene consisted of 1005 bp coding a 334‐amino‐acid (aa) protein. The deduced aa sequence of LyPls‐PLD showed high similarity to those of glycerophosphodiester phosphodiesterases (GDPDs); however, the substrate specificity differed completely from those of GDPDs and general phospholipase Ds (PLDs). Structural homology modeling showed that two putative catalytic residues (His46, His88) of LyPls‐PLD were highly conserved to GDPDs. Mutational and kinetic analyses suggested that Ala55, Asn56, and Phe211 in the active site of LyPls‐PLD may participate in the substrate recognition. These findings will help to elucidate differences among LyPls‐PLD, PLD, and GDPD with regard to function, substrate recognition mechanism, and biochemical roles.

Data Accessibility

Thermocrispum sp. strain RD004668 and its 16S rDNA sequence were deposited in the NITE Patent Microorganisms Depositary (NPMD; Chiba, Japan) as NITE BP‐01628 and in the DDBJ database under the accession number AB873024. The nucleotide sequences of the 16S rDNA of strain RD004668 and the LyPls‐PLD gene were deposited in the DDBJ database under the accession numbers AB873024 and AB874601, respectively.

Enzyme

EC number EC 3.1.4.4

Measurement of Ether Phospholipids in Human Plasma with HPLC-ELSD and LC/ESI-MS After Hydrolysis of Plasma with Phospholipase A1

Ethanolamine ether phospholipid (eEtnGpl) and choline ether phospholipid (eChoGpl) are present in human plasma or serum, but the relative concentration of the ether phospholipids in plasma is very low as compared to those in other tissues. Nowadays, measurement of ether phospholipids in plasma depends on tandem mass spectrometry (LC/MS/MS), but a system for LC/MS/MS is generally too expensive for usual clinical laboratories. Treatment of plasma with phospholipase A₁ (PLA1) causes complete hydrolysis of diacylphospholipids, but ether phospholipids remain intact. After the treatment of plasma with PLA1, both eEtnGpl and eChoGpl are detected as independent peaks by high-performance liquid chromatography with evaporative light scattering detection (HPLC–ELSD). The same sample used for HPLC–ELSD can be applied to detect eEtnGpl and eChoGpl with electrospray ionization mass spectrometry. Presence of alkylacylphospholipids in both eChoGpl and eEtnGpl in human plasma was indicated by sequential hydrolysis of plasma with PLA1 and hydrochloric acid.

Changes in Plasma Lipids during Exposure to Total Sleep Deprivation

STUDY OBJECTIVES

The effects of sleep loss on plasma lipids, which play an important role in energy homeostasis and signaling, have not been systematically examined. Our aim was to identify lipid species in plasma that increase or decrease reliably during exposure to total sleep deprivation.

DESIGN

Twenty individuals underwent sleep deprivation in a laboratory setting. Blood was drawn every 4 h and mass spectrometry techniques were used to analyze concentrations of 263 lipid species in plasma, including glycerolipids, glycerophospholipids, sphingolipids, and sterols.

SETTING

Chronobiology and Sleep Laboratory, Duke-NUS Graduate Medical School.

PARTICIPANTS

Healthy ethnic-Chinese males aged 21-28 y (n = 20).

INTERVENTIONS

Subjects were kept awake for 40 consecutive hours.

MEASUREMENTS AND RESULTS

Each metabolite time series was modeled as a sum of sinusoidal (circadian) and linear components, and we assessed whether the slope of the linear component differed from zero. More than a third of all individually analyzed lipid profiles exhibited a circadian rhythm and/or a linear change in concentration during sleep deprivation. Twenty-five lipid species showed a linear and predominantly unidirectional trend in concentration levels that was consistent across participants. Choline plasmalogen levels decreased, whereas several phosphatidylcholine (PC) species and triacylglycerides (TAG) carrying polyunsaturated fatty acids increased.

CONCLUSIONS

The decrease in choline plasmalogen levels during sleep deprivation is consistent with prior work demonstrating that these lipids are susceptible to degradation by oxidative stress. The increase in phosphatidylcholines and triacylglycerides suggests that sleep loss might modulate lipid metabolism, which has potential implications for metabolic health in individuals who do not achieve adequate sleep.

Hydrolysis of plasmalogen by phospholipase A1 from Streptomyces albidoflavus for early detection of dementia and arteriosclerosis

OBJECTIVES

To obtain an ethanolamine plasmalogen (PlsEtn)-hydrolyzing enzyme and to develop an assay that would help determine PlsEtn concentrations in human serum as an indicator of Alzheimer-type dementia and of arteriosclerosis.

RESULTS

Phospholipase A1s, SaPLA1 and SvPLA1 from, respectively, Streptomyces albidoflavus NA297 and S. avermitilis JCM5070-but not phospholipase B from Streptomyces sp. NA684, PLA2-Nagase from S. avermitilis, PLA2IIL from S. violaceoruber nor LIPOMOD 699L (porcine phospholipase)-hydrolyzed choline plasmalogen (PlsCho) and PlsEtn (PlsCho preferred over PlsEtn). Using a combination of SaPLA1, lysoplasmalogen-specific phospholipase D (LyPls-PLD), with amine oxidase, an end-point assay was developed for measuring serum PlsEtn concentration. The standard curve, generated using various amounts of PlsEtn in this assay, was linear between 0 and 0.2 mM. PlsEtn concentrations in forty-seven serum samples, determined independently by this enzyme-based assay and (125)I-HPLC method, exhibited a linear relationship, indicating that the assay is suitable for fast and accurate measurement of serum PlsEtn concentration.

CONCLUSIONS

An assay, developed using SaPLA1, LyPls-PLD, and AOX, selectively measured PlsEtn levels in blood samples. This assay could be a useful diagnostic tool for early stage detection of diseases such as Alzheimer-type dementia and arteriosclerosis.

Update on ischemic heart disease and intensive cardiac care

This article summarizes the main developments reported in 2014 on ischemic heart disease, together with the most important innovations in intensive cardiac care.

Plasma/Serum Plasmalogens: Methods of Analysis and Clinical Significance

Age-related diseases, such as atherosclerosis and dementia, are associated with oxidative stress and chronic inflammation. Peroxisome dysfunction may be related to aging and age-related pathologies, possibly through the derangement of redox homeostasis. The biosyntheses of plasmalogens (Pls), a subclass of glycerophospholipids, are primarily regulated by peroxisomes. Thus, plasma Pls may reflect the systemic functional activity of peroxisomes and serve as potential biomarkers for diseases related to oxidative stress and aging. Recently, we have established three promising analytical methods for plasma/serum Pls using high-performance liquid chromatography with radioactive iodine, liquid chromatography-tandem mass spectrometry, and enzymatic assay. These methods were validated and used to obtain detailed molecular information regarding these molecules. In cross-sectional studies on asymptomatic, coronary artery disease, and elderly dementia individuals, we found that serum choline Pls, particularly those containing oleic and linoleic acid in the sn-2 position of the glycerol backbone, may serve as reliable antiatherogenic biomarkers. Furthermore, we also found that serum ethanolamine Pls were effective in discriminating cognitive impairment. These results support our hypothesis and further studies are clearly needed to elucidate Pls pathophysiologic significance.