Plasma concentrations of lysolecithin and other phospholipids in the healthy population and in men suffering from atherosclerotic diseases

An Updated Review of Pro- and Anti-Inflammatory Properties of Plasma Lysophosphatidylcholines in the Vascular System

Lysophosphatidylcholines are a group of bioactive lipids heavily investigated in the context of inflammation and atherosclerosis development. While present in plasma during physiological conditions, their concentration can drastically increase in certain inflammatory states. Lysophosphatidylcholines are widely regarded as potent pro-inflammatory and deleterious mediators, but an increasing number of more recent studies show multiple beneficial properties under various pathological conditions. Many of the discrepancies in the published studies are due to the investigation of different species or mixtures of lysophatidylcholines and the use of supra-physiological concentrations in the absence of serum or other carrier proteins. Furthermore, interpretation of the results is complicated by the rapid metabolism of lysophosphatidylcholine (LPC) in cells and tissues to pro-inflammatory lysophosphatidic acid. Interestingly, most of the recent studies, in contrast to older studies, found lower LPC plasma levels associated with unfavorable disease outcomes. Being the most abundant lysophospholipid in plasma, it is of utmost importance to understand its physiological functions and shed light on the discordant literature connected to its research. LPCs should be recognized as important homeostatic mediators involved in all stages of vascular inflammation. In this review, we want to point out potential pro- and anti-inflammatory activities of lysophospholipids in the vascular system and highlight recent discoveries about the effect of lysophosphatidylcholines on immune cells at the endothelial vascular interface. We will also look at their potential clinical application as biomarkers.

Lysophosphatidylcholines inhibit human eosinophil activation and suppress eosinophil migration in vivo

Eosinophils are important multifaceted effector cells involved in allergic inflammation. Following allergen challenge, eosinophils and other immune cells release secreted phospholipases, generating lysophosphatidylcholines (LPCs). LPCs are potent lipid mediators, and serum levels of LPCs associate with asthma severity, suggesting a regulatory activity of LPCs in asthma development. As of yet, the direct effects of LPCs on eosinophils remain unclear. In the present study, we tested the effects of the major LPC species (16:0, 18:0 and 18:1) on eosinophils isolated from healthy human donors. Addition of saturated LPCs in the presence of albumin rapidly disrupted cholesterol-rich nanodomains on eosinophil cell membranes and suppressed multiple eosinophil effector responses, such as CD11b upregulation, degranulation, chemotaxis, and downstream signaling. Furthermore, we demonstrate in a mouse model of allergic cell recruitment, that LPC treatment markedly reduces immune cell infiltration into the lungs. Our observations suggest a strong modulatory activity of LPCs in the regulation of eosinophilic inflammation in vitro and in vivo.

Metabolomic profiles of current cigarette smokers

Smoking-related biomarkers for lung cancer and other diseases are needed to enhance early detection strategies and to provide a science base for tobacco product regulation. An untargeted metabolomics approach by ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UHPLC-Q-TOF MS) totaling 957 assays was used in a novel experimental design where 105 current smokers smoked two cigarettes 1 h apart. Blood was collected immediately before and after each cigarette allowing for within-subject replication. Dynamic changes of the metabolomic profiles from smokers' four blood samples were observed and biomarkers affected by cigarette smoking were identified. Thirty-one metabolites were definitively shown to be affected by acute effect of cigarette smoking, uniquely including menthol-glucuronide, the reduction of glutamate, oleamide, and 13 glycerophospholipids. This first time identification of a menthol metabolite in smokers' blood serves as proof-of-principle for using metabolomics to identify new tobacco-exposure biomarkers, and also provides new opportunities in studying menthol-containing tobacco products in humans. Gender and race differences also were observed. Network analysis revealed 12 molecules involved in cancer, notably inhibition of cAMP. These novel tobacco-related biomarkers provide new insights to the effects of smoking which may be important in carcinogenesis but not previously linked with tobacco-related diseases. © 2016 Wiley Periodicals, Inc.

Menthol Smokers: Metabolomic Profiling and Smoking Behavior

BACKGROUND

The use of menthol in cigarettes and marketing is under consideration for regulation by the FDA. However, the effects of menthol on smoking behavior and carcinogen exposure have been inconclusive. We previously reported metabolomic profiling for cigarette smokers, and novelly identified a menthol-glucuronide (MG) as the most significant metabolite directly related to smoking. Here, MG is studied in relation to smoking behavior and metabolomic profiles.

METHODS

This is a cross-sectional study of 105 smokers who smoked two cigarettes in the laboratory one hour apart. Blood nicotine, MG, and exhaled carbon monoxide (CO) boosts were determined (the difference before and after smoking). Spearman correlation, χ2, and ANCOVA adjusted for gender, race, and cotinine levels for menthol smokers assessed the relationship of MG boost, smoking behavior, and metabolic profiles. Multivariate metabolite characterization using supervised partial least squares-discriminant analysis (PLS-DA) was carried out for the classification of metabolomics profiles.

RESULTS

MG boost was positively correlated with CO boost, nicotine boost, average puff volume, puff duration, and total smoke exposure. Classification using PLS-DA, MG was the top metabolite discriminating metabolome of menthol versus nonmenthol smokers. Among menthol smokers, 42 metabolites were significantly correlated with MG boost, which linked to cellular functions, such as of cell death, survival, and movement.

CONCLUSIONS

Plasma MG boost is a new smoking behavior biomarker that may provide novel information over self-reported use of menthol cigarettes by integrating different smoking measures for understanding smoking behavior and harm of menthol cigarettes.

IMPACT

These results provide insight into the biological effect of menthol smoking. Cancer Epidemiol Biomarkers Prev; 26(1); 51-60. ©2016 AACR.

Plasma Lipids and Lipoproteins in Friedreich's Ataxia and Familial Spastic Ataxia — Evidence for an Abnormal Composition of High Density Lipoproteins

A systematic study of plasma lipids and lipoproteins was carried out in II cases of Friedreich's ataxia and 6 cases of familial spastic ataxia (Charlevoix-Saguenay disease) using II healthy normolipidemic volunteers of comparable age and sex as controls. No differences were noted in the fatty acid profile of the total lipid fraction, in the total cholesterol and phospholipids or in the percentage distribution of the individual phospholipid classes. The triglycerides were significantly higher in Friedreich's ataxia, but remained within the normal range. Although no systematic abnormalities could be detected in the electrophoretic pattern of plasma lipoproteins or in the apolipoprotein profile on polyacrylamide gel electrophoresis, major differences were found in the high density lipoprotein (HDL) fraction. Their total amount was reduced and their composition was abnormal in both neurological diseases. In Friedreich patients, the relative proportion of cholesterol and triglycerides was increased while the relative protein content was greatly reduced. In Charlevoix disease, a similar abnormality was seen except for the excess of triglycerides. The proportion of phospholipids in HDL was the same in the three groups of patients. In addition, the low density lipoprotein (LDL) fraction was slightly reduced in both diseases. This anomaly of the HDL fraction could indicate that the HDL apolipoprotein moiety has a greater affinity for cholesterol and triglycerides in Friedreich's ataxia than its normal counterpart.

An enzymatic assay for lysophosphatidylcholine concentration in human serum and plasma

OBJECTIVES

Several methods for measuring lysophosphatidylcholine (LPC) concentrations have been reported. However, these methods are not practical because they are either too complicated and/or too time-consuming for LPC determinations in human serum and plasma.

DESIGN AND METHODS

We have developed a new enzymatic LPC assay, which uses lysophospholipase, glycerophosphorylcholine phosphodiesterase and choline oxidase, and which determines the quantities of hydrogen peroxide generated in the presence of peroxidase using an oxidative chromogenic reagent and 4-aminoantipyrine.

RESULTS

Various samples were mixed with LPC assay reagents, and their changes in absorbance were measured. The present method produced a linear calibration line between LPC concentration and absorbance change. It also measured only LPC, and not other phospholipids such as phosphatidylcholine, sphingomyelin and lysophosphatidic acid. The within-run and between-run coefficients of variation were 0.3-0.7% and 0.7%, respectively. The recovery of exogenous LPC added to control serum was 99.5-102.1%. The correlation coefficient obtained in a comparison with a method for analyzing fatty acids was 0.9122.

CONCLUSIONS

The present method is simple, specific for LPC, and can be applied with an automatic analyzer. It may also be useful for further studies of the biological functions of LPC as well as clinical applications in various disorders.

Levels of cholesteryl esters and other lipids in the plasma of patients with end-stage renal failure

BACKGROUND

The importance of plasma lipid abnormalities in chronic renal failure (CRF) is well recognized, but surprisingly little attention has been given to the study of some plasma lipid fractions, including cholesteryl esters (CE) and phospholipids, which might be expected to be important factors in the pathogenesis of the disease.

MATERIALS AND METHODS

Fasting blood samples were taken from 25 control subjects and 53 CRF patients (29 predialysis and 24 on hemodialysis). Samples were analyzed for urea nitrogen, creatinine, triacylglycerols, total and individual phospholipids, total and free cholesterol, as well as cholesterol bound to very low-, low- and highdensity lipoproteins (VLDL, LDL and HDL). Plasma CE was calculated and expressed as a percentage of total cholesterol.

RESULTS

Over half of the patients had CE levels more than two standard deviations below the control value. In this subgroup of low CE patients, total, LDL- and HDL-cholesterol levels were also significantly lower than for controls, while levels of phosphatidylcholine and lysophosphatidylcholine were decreased and increased, respectively. In patients with high CE, no significant lipid abnormalities were observed.

CONCLUSION

In this study, CE was an excellent marker for lipid disturbances--if CE was high, then the other lipid fractions were normal, but if CE was low, most other lipid fractions were abnormal. The changes noted appear to be consequences of or related to deficiency of the plasma enzyme lecithin-cholesterol acyltransferase.

Elevated levels and altered fatty acid composition of plasma lysophosphatidylcholine(lysoPC) in ovarian cancer patients

Lysophosphatidylcholine (lysoPC), a product of phosphatidylcholine (PC) hydrolysis via phospholipase A activity, has been proposed to activate cells from a number of lineages. Here, we demonstrate that lysoPC levels are significantly elevated (by 43% overall, relative to normal controls) in the plasma of ovarian cancer patients. This does not appear to be common to all cancers as 5 out of 6 leukemia patients tested had markedly lower (less than one-half of normal) plasma lysoPC. In the plasma of ovarian cancer patients, the percentages of palmitoyl- and stearoyl-lysoPC species were significantly higher, whereas oleoyl and particularly linoleoyl-lysoPC were significantly lower than in control subjects. The molar ratios of lysoPC/PC and palmitoyl-lysoPC/linoleoyl-lysoPC were also significantly elevated in the plasma of ovarian cancer patients compared with those of control subjects. Furthermore, the calculated value of plasma (lysoPC/ PC) x (palmitoyl-lysoPC/linoleoyl-lysoPC) was markedly higher in patients compared with controls.

The phospholipase activities present in preheparin mouse plasma are inhibited by antiserum to hepatic lipase

1. Preheparin plasma from mice, but not rats or man, contains high levels of phospholipase A and lysophospholipase activities which are distinct from lecithin:cholesterol acyltransferase (LCAT). 2. Neither the phospholipase A nor the lysophospholipase activities in preheparin plasma are inhibited by incubation in the presence of protamine sulphate or high salt concentrations. 3. When mouse plasma is incubated in the presence of an antiserum specific for rat hepatic triacylglycerol lipase (HTGL), the phospholipase activities are abolished. 4. These observations suggest that the phospholipase activities are attributable to the action of HTGL, which, in the mouse appears to be a freely circulating enzyme, whereas for other species this enzyme only appears in the blood following administration of heparin.

Influence of hypoxanthine and other purines on the lecithin:cholesterol acyltransferase reaction in the plasma of rat and other species

1. Esterification of radiolabelled cholesterol in the plasma of rat, mouse, pig, ox and, to a lesser extent, guinea pig was partially inhibited by hypoxanthine, xanthine and guanine; esterification in human plasma and in plasma from 12 other vertebrate species was unaffected by purines. 2. Esterification of endogenous cholesterol and the formation of lysolecithin in rat plasma were decreased in the presence of purines indicating that it was the lecithin:cholesterol acyltransferase (LCAT) reaction that was inhibited rather than the isotopic equilibration of labelled cholesterol with the endogenous substrate lipoproteins. 3. Maximum inhibition of the LCAT reaction in rat plasma occurred at 1.4 mM hypoxanthine or xanthine; inhibition was not dependent upon the concentration of LCAT or plasma lipoproteins but increased with the amount of lipoprotein depleted rat plasma (LDRP) present in the incubation mixture. 4. Partial inhibition of the LCAT reaction in rat or mouse plasma by purines had no significant effect on the fatty acyl composition of the cholesteryl esters (CE) formed by LCAT. 5. In the presence of heated rat plasma, LDRP or, to a lesser extent, rat high density lipoproteins (HDL) prepared from heated plasma, the LCAT reaction in human plasma was inhibited by hypoxanthine. 6. Rat HDL and LDRP prepared from plasma pre-incubated at 37 degrees C for 4 hr before heating increased and decreased, respectively, the inhibitory effect of hypoxanthine on human plasma LCAT compared with HDL and LDRP prepared from unincubated rat plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of lysophosphatidylcholine on coronary and renal circulation in the rabbit

It has been shown that different lysophosphatidylcholines (LPC) possess relaxing properties in vascular strips. We report on the effect of intraatrial injection of LPC micelles into white New Zealand rabbits. Changes in renal and coronary flow were determined by radioactive microspheres. Coronary blood flow increased significantly following administration of LPC, while no significant changes were observed in renal blood flow, cardiac output and myocardial contractility. Coronary, renal and total vascular resistance, as well as mean arterial pressure, dropped significantly. Cardiac arrhythmia and hemolysis were not noted. The results demonstrate the vasorelaxant effect of LPC in vivo.

Lecithin: cholesterol acyltransferase and lysolecithin in coronary atherosclerosis

Of 100 arteriographically examined, hospitalized, male patients, those without myocardial infarctions were divided into the following categories: zero-, one-, two-, and three-vessel disease; patients diagnosed with myocardial infarction were classified separately. The fasting plasma samples from these patients were examined for concentrations of triglycerides and total cholesterol, lipoprotein profile, lecithin: cholesterol acyltransferase (LCAT) activity, and lysolecithin (LPC) concentration. Those parameters in this group which are commonly determined were consistent with the clinical classification of these patients. Of those remaining parameters, the LCAT activity was increased as the severity of coronary atherosclerosis increased and the changes in the activity of this enzyme were appropriately reflected by increases in LPC concentration and decreases in the proportion of the plasma cholesterol unesterified. The results of this study suggest that increased, rather than decreased, plasma LCAT activity and increased LPC concentrations are characteristic of coronary atherogenesis. The plasma concentrations of LPC observed in these atherosclerotic patients are more than sufficient to qualify this substance for its previously proposed roles of mediator of transmembrane diffusion of LDL and as an inhibitor of platelet aggregation.

Evidence that lysolecithin is an important causal agent of atherosclerosis

We examine the hypothesis of Portman et al. (1970) that lysolecithin is a causal agent of atherosclerosis. Four lines of argument support this hypothesis. (1) Lysolecithin is present, taken up and can act. Large amounts of lysolecithin are formed in plasma concomitant with triglyceride transport and it is readily taken up by arteries and retained for some time. Lysolecithin in aortic intima increases several-fold early in the induction of atherosclerosis in animals. From model system studies it is plausible that physiological doses of lysolecithin have physiologically significant effects. (2) At least one plausible mechanism of action can be formulated: stimulation of smooth muscle cell division due to lysolecithin-increased Ca2+ uptake. (3) The hypothesis is consistent with, and rationalizes, many literature observations in that inferred lysolecithin levels or production rates are appropriately correlated with a variety of positive and negative risk factors to a degree highly unlikely by chance. We found no data contradicting the hypothesis and only one piece weakening it. (4) A mechanism is outlined showing that low density lipoprotein receptor deficiency, the severest known risk factor, should cause the delivery of very high lysolecithin doses to artery walls. We conclude that the evidence, although indirect, is strong enough to give direct tests a high priority.

Alterations of cell membrane composition during prolonged fasting in lizards

Male lizards fasted for 35 days showed significant alterations in the lipid composition of membranes isolated from a variety of organs and tissues. Unesterified cholesterol was significantly increased in membranes from kidney, skeletal muscle, small intestine, testis and heart but not in those from lung, brain and liver; cholesterol/phospholipid molar ratio was also significantly increased in membranes from all organs except brain and liver. Membrane total phospholipids were reduced for all tissues except brain and liver, whilst significant reductions in the molar ratio of membrane phosphatidylcholine to sphingomyelin occurred in kidney, muscle, testis, intestine and liver. Similar alterations in lipid composition were found in plasma and significant correlations between plasma and membrane cholesterol/phospholipid and phosphatidylcholine/sphingomyelin molar ratios were found for those organs in which significant lipid changes occurred during fasting. Lizards fasted for 35 days and then refed a natural diet, such that they started to regain weight, had normal membrane lipid compositions. These observations suggest that during prolonged fasting certain tissues of the lizard are unable to maintain a normal membrane lipid composition and that abnormal plasma lipoproteins may be involved in this process.

Relationships between cholesterol and phospholipid concentrations in the serum of humans, calves, rabbits and chickens

In humans, calves and rabbits very strong correlations were found between the concentrations of serum total cholesterol and phospholipids; in these species more than 70% of the variance in the level of serum phospholipids is accounted for by the variance in the serum cholesterol concentration. The regression coefficients in the equations relating the concentration of serum cholesterol to that of phospholipids were almost identical in humans and rabbits, but differed from those observed in calves and chickens. It is suggested that the rabbit is a suitable model animal for studying the relation between cholesterol and phospholipids in human serum.

Serum lipids and lipoprotein concentrations during the acute phase of myocardial infarction

The concentrations of serum lipids and lipoprotein cholesterol were measured serially during the acute phase (14 days) following myocardial infarction (MI) in 13 male survivors. All patients were re-examined at least two months after discharge from hospital. A significant increase in serum triglyceride (TG) concentration occurred during the acute phase, with values returning to baseline two months after recovery. No changes in the concentrations of the other lipids or lipoprotein cholesterol were observed.

Plasma lipid concentrations for some Brazilian lizards

1. Plasma concentrations of cholesterol, cholesteryl esters, phospholipids and triglycerides were determined for ten species of Brazilian lizards, Iguana iguana, Tropidurus torquatos and T. semitaeniatus (Iguanidae), Tupinambis teguixin, Ameiva ameiva and Cnemidophorus ocellifer (Teiidae), Mabuya maculata (Scincidae), Hemidactylus mabouia (Gekkonidae), Amphisbaenia vermicularis and Leposternon polystegum (Amphisbaenidae). 2. Considerable inter- and intra-species variations in plasma lipid concentrations were observed. 3. The percentage of total cholesterol esterified and the individual phospholipid composition of plasma were relatively constant for each species. 4. Over 60% of the cholesteryl esters present in plasma from three species each of iguanid and teiid lizards were polyenoic.