Major human plasma lipid classes determined by quantitative high-performance liquid chromatography, their variation and associations with phospholipid fatty acids

Extracellular Vesicles in Liquid Biopsies: Potential for Disease Diagnosis

Liquid biopsy is conducted through minimally invasive or noninvasive procedures, and the resulting material can be subjected to genomic, proteomic, and lipidomic analyses for early diagnosis of cancers and other diseases. Extracellular vesicles (EVs), one kind of promising tool for liquid biopsy, are nanosized bilayer particles that are secreted by all kinds of cells and that carry cargoes such as lipids, proteins, and nucleic acids, protecting them from enzymatic degradation in the extracellular environment. In this review, we provide a comprehensive introduction to the properties and applications of EVs, including their biogenesis, contents, sample collection, isolation, and applications in diagnostics based on liquid biopsy.

UPLC-ELSD Analysis of Algal Lipid Classes and Derivatization of Bound and Free Fatty Acids and Sterols for GC-MS Methods

Constituents of microalgae and sample preparation for UPLC-ELSD and GC-MS analyses are described. Bound fatty acids from acylglycerols, alkylacylglycerols, galactosyldiacylglycerols, glycerophospholipids, and sterol esters are derivatized by using transesterification with sodium methoxide to form fatty acid methyl esters. Compounds containing free hydroxyl groups, either present originally or formed during previous step, like free fatty acids, sterols, α-tocopherol, phytol, and nonesterified alkoxyglycerols, are trimethylsilylated. The compounds in algal lipid extract are subsequently derivatized by these two steps.

Fast LC-ESI-MS/MS analysis and influence of sampling conditions for gut metabolites in plasma and serum

In the past few years, the gut microbiome has been shown to play an important role in various disorders including in particular cardiovascular diseases. Especially the metabolite trimethylamine-N-oxide (TMAO), which is produced by gut microbial metabolism, has repeatedly been associated with an increased risk for cardiovascular events. Here we report a fast liquid chromatography tandem mass spectrometry (LC-MS/MS) method that can analyze the five most important gut metabolites with regards to TMAO in three minutes. Fast liquid chromatography is unconventionally used in this method as an on-line cleanup step to remove the most important ion suppressors leaving the gut metabolites in a cleaned flow through fraction, also known as negative chromatography. We compared different blood matrix types to recommend best sampling practices and found citrated plasma samples demonstrated lower concentrations for all analytes and choline concentrations were significantly higher in serum samples. We demonstrated the applicability of our method by investigating the effect of a standardized liquid meal (SLM) after overnight fasting of 25 healthy individuals on the gut metabolite levels. The SLM did not significantly change the levels of gut metabolites in serum.

Quantification of Lipids: Model, Reality, and Compromise

Lipids are key molecules in various biological processes, thus their quantification is a crucial point in a lot of studies and should be taken into account in lipidomics development. This family is complex and presents a very large diversity of structures, so analyzing and quantifying all this diversity is a real challenge. In this review, the different techniques to analyze lipids will be presented: from nuclear magnetic resonance (NMR) to mass spectrometry (with and without chromatography) including universal detectors. First of all, the state of the art of quantification, with the definitions of terms and protocol standardization, will be presented with quantitative lipidomics in mind, and then technical considerations and limitations of analytical chemistry's tools, such as NMR, mass spectrometry and universal detectors, will be discussed, particularly in terms of absolute quantification.

Chemical Profiling and Bioactivity of Body Wall Lipids from Strongylocentrotus droebachiensis

The lipids from gonads and polyhydroxynaphthoquinone pigments from body walls of sea urchins are intensively studied. However, little is known about the body wall (BW) lipids. Ethanol extract (55 °C) contained about equal amounts of saturated (SaFA) and monounsaturated fatty acids (MUFA) representing 60% of total fatty acids, with myristic, palmitic and eicosenoic acids as major SaFAs and MUFAs, respectively. Non-methylene-interrupted dienes (13%) were composed of eicosadienoic and docosadienoic acids. Long-chain polyunsaturated fatty acids (LC-PUFA) included two main components, n6 arachidonic and n3 eicosapentaenoic acids, even with equal concentrations (15 μg/mg) and a balanced n6/n3 PUFA ratio (0.86). The UPLC-ELSD analysis showed that a great majority of the lipids (80%) in the ethanolic extract were phosphatidylcholine (60 μg/mg) and phosphatidylethanolamine (40 μg/mg), while the proportion of neutral lipids remained lower than 20%. In addition, alkoxyglycerol derivatives-chimyl, selachyl, and batyl alcohols-were quantified. We have assumed that the mechanism of action of body wall lipids in the present study is via the inhibition of MAPK p38, COX-1, and COX-2. Our findings open the prospective to utilize this lipid fraction as a source for the development of drugs with anti-inflammatory activity.

Daily Intake of Milk Enriched with n-3 Fatty Acids, Oleic Acid, and Calcium Improves Metabolic and Bone Biomarkers in Postmenopausal Women

OBJECTIVE

Nutritional strategies can be effective for the prevention of menopause-related diseases, such as osteoporosis and cardiovascular disease. Our aim was to evaluate the effects of a dairy product enriched in polyunsaturated fatty acids, calcium, oleic acid, and vitamins on cardiovascular markers and bone metabolism in postmenopausal women with moderate cardiovascular risk.

METHODS

One hundred seventeen healthy postmenopausal women (aged 45 ± 7.7 years) were allocated to 2 groups: the intervention group (IG; n = 63), who consumed 0.5 L/day of a low-lactose skimmed milk enriched with 40 mg/100 mL of eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA), 0.54 g/100 mL oleic acid, and vitamins, and the control group (CG; n = 54), who consumed 0.5 L/day of semiskimmed milk 0.5 L/day enriched with vitamins A and D.

RESULTS

After 12 months, in the IG there was an improvement in lipid profile: a -5.78% decrease in total cholesterol (p = 0.010), -9.79% (p = 0.004) in low-density lipoprotein (LDL) cholesterol, -9.56% (p < 0.001) in total cholesterol (TC)/high-density lipoprotein (HDL) ratio, and -3.38% in LDL/HDL ratio (p < 0.001). No changes were observed in the CG. In the IG we observed a decrease of -28.20% in high-sensitivity C-reactive protein (hs-CRP; p = 0.012). There was no effect on bone turnover markers or serum osteoprotegerin (OPG) in either of the study groups. In the IG, receptor activator of nuclear factor κB ligand (RANKL) was reduced -17.64% (p = 0.003), with no effect in the CG.

CONCLUSION

In postmenopausal women with moderate cardiovascular risk, dietary supplementation with a dairy drink enriched with fatty acids (EPA+DHA), oleic acid, minerals, and vitamins induces a positive effect on cardiovascular risk and parameters of bone metabolism. Its regular consumption may be a useful nutritional support for postmenopausal women.

Determination of the fatty acid profile of neutral lipids, free fatty acids and phospholipids in human plasma

BACKGROUND

Knowledge of the fatty acid composition of lipid classes in human plasma is an important factor in the investigation of human metabolism. Therefore, a method for the analysis of neutral lipid (NL), phospholipid (PL) and free fatty acids (FFA) in human plasma has been developed and validated.

METHODS

Separation of lipid classes was carried out by solid phase extraction of the lipid extract. The fractions were transesterified and the resulting fatty acid methyl esters were determined by GC/FID. For the method to be validated, precision, detection and quantification limits, as well as recovery, were determined for combined lipid extraction, solid phase extraction and GC analysis.

RESULTS

The lipid extraction was miniaturized and simplified by application of an ultrasound ‘Sonotrode’. The resolution of lipid classes was optimized with appropriate standards added to a representative plasma sample. In addition, a rapid derivatization procedure using trimethylsulfoniumhydroxide was established. Low determination limits (1.5, 0.2 and 1.3 μg/g plasma for NL, PL and FFA, respectively) indicate that the method’s sensitivity is sufficient to quantify even minor components. Furthermore, recovery for NL and PL fatty acids was found to range from 80% to 110%. The results were similar for FFA apart from more polar free fatty acids due to their higher solubility in water. Repetitive measurements showed very good precision apart from the long chain PUFA for which the coefficients of variation were significantly higher.

CONCLUSIONS

The present method is applicable to the quantitation of fatty acids in lipid classes of human plasma including several minor components.

Identifying analytics for high throughput bioprocess development studies

In recent years, high throughput screening (HTS) studies have been increasingly employed as an integral element of bioprocess development activities. These studies are often limited by an analytical bottleneck; they generate multiple samples for analysis and the available analytical methods cannot always cope with the added analytical burden. A potential solution to this challenge is offered by the deployment of appropriate analytics. This article outlines features of analytical methods that affect their fit to high throughput (HT) applications. These are discussed for a range of analytics frequently used in bioprocess development studies of monoclonal antibodies. It then outlines how these features need to be considered in order to classify analytical methods in terms of their particular application in high throughput scenarios.

Analysis of phospholipids in infant formulas using high performance liquid chromatography-tandem mass spectrometry

Phospholipids have been used widely in the food industry as emulsifiers, but it is their biological and nutritional function that has been the focus over recent years. The recognition of the importance of phospholipids and sphingomyelin for infant development has led to an increase in the number of infant formulas claiming to contain these complex lipid components. Therefore, the ability to measure these lipids in infant formulas and dairy-derived complex lipid ingredients for fortification purposes is important. A high-performance liquid chromatography-tandem mass spectrometry method that quantifies phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin found in infant formulas and dairy-derived complex lipid ingredients is described. The method uses external standards of similar fatty acid profile for calibration. The recovery of phospholipids ranged from 92% to 102% with a method repeatability coefficient of variation of 6-10%. In addition to the specificity and selectivity of the method, details of the molecular species in the individual phospholipid classes are available using this method.

Application of HPLC with ELSD Detection for the Assessment of Azelaic Acid Impurities in Liposomal Formulation

In the course of research and development of a new pharmaceutical formulation of azelaic acid in the liposomal form, we developed a rapid and accurate method for the detection of impurities using high-performance liquid chromatography. A chromatographic column from Merck (Purospher Star RP C18, 250–4 mm (5 μm) was used in the assay, and the mobile phase gradient consisted of three phases: A—methanol : water (5 : 95) + 1.5% (v/v) acetic acid; B—water : methanol (5 : 95) + 1.5% (v/v) acetic acid; and C—chloroform. Detection of the impurities and the active substance was performed by an evaporative light-scattering detector. The method was validated for selectivity, system precision, method precision, limit of detection, and response rates. The proposed method can be used to detect impurities in the liposomal formulation of azelaic acid. The method enables separation of azelaic acid from the identified and unidentified impurities and from the excipients used in the drug form.

A hyphenated microLC-Q-TOF-MS platform for exosomal lipidomics investigations: application to RCC urinary exosomes

Urinary exosomes are released from every renal epithelial cell type facing the urinary space and therefore, they may carry molecular markers of renal dysfunction and structural injury. Here, we present a hyphenated microLC-Q-TOF-MS platform for lipidomics studies applied to investigate the urinary exosome lipid repertoire. Lipids were separated by reversed-phase chromatography using a linear gradient of formic acid 0.2% and tetrahydrofuran, in 40 min of analysis. Features (m/z with associated own retention time) were extracted by MarkerLynx(TM) (Waters) and processed, demonstrating good analytical performance in terms of repeatability and mass accuracy of the microLC Q-TOF MS platform. In particular, a stable retention time (RSD less than 4%) and relative intensity (RSD from 2.9% to 11%) were observed. Moreover, the method takes advantages by the use of a lock spray interface (Waters) that allows readjusting the m/z data after acquisition, obtaining inaccuracy below 6 ppm in measuring the m/z value of the reference compound during chromatographic run. The method was employed in a preliminary application to perform comparative analysis from healthy control subjects and renal cell carcinoma (RCC) patients, in order to possibly highlight differences in lipid composition to be exploited as potential tumor biomarker. Differential lipid composition in RCC urinary exosomes was achieved and tentatively identified by accurate mass, providing a preliminary indication of a relationship between lipid composition of urinary exosomes and RCC disease. Among the total features significantly different in RCC exosomes, the ion at m/z 502.3 was taken as an example for molecular confirmation by MS/MS fragmentation analysis.

Lipidomic investigations for the characterization of circulating serum lipids in multiple sclerosis

Multiple Sclerosis (MS) is a neurodegenerative autoimmune demyelinating disease affecting young adults. The aetiology still remains a mystery and diagnosis is impaired by the lack of defined molecular markers. Autoimmune response remains the main topic under investigation and recent studies suggest additional non-proteic mediators of brain inflammation such as lipids. We carried out an LC-MS based lipidomics approach to highlight serum lipids profiling in MS. Method was optimised and applied in a preliminary clinical cross-sectional investigation of MS patients vs Healthy Controls (HC) and patients with Other Neurological Diseases (OND). Ten significant metabolites were highlighted and tentatively identified by accurate mass and MS/MS experiments. Our most relevant data show altered level of lyso-glycerophosphatidylcholine (lysoPC) and glycerophosphatidylcholine (PC) species. Total lysoPC/PC ratio showed significant decrease in pathological groups (MS, OND) and, in addition, MS subjects had a relevant decrease of this ratio also in respect to OND. These findings suggest that there may be an altered phospholipid metabolism in MS that can be evaluated in serum. Some of these features are distinctive and may be considered specific for MS. Our lipidomics data show, for the first time, evidence in serum of a relationship between LysoPC/PC ratio and MS.

An ultraperformance liquid chromatography method for the normal-phase separation of lipids

An ultraperformance liquid chromatography method using normal-phase solvents, a silica column, and evaporative light-scattering detection is presented. The method is based on a quaternary gradient profile and is capable of resolving the major neutral and polar lipids present in plasma and animal tissue in under 5 min, with a total cycle time of 11 min. Limits of quantitation for 7 different lipid classes were on the order of 200 ng of material on column which enables an accurate analysis from as little as 20 μL of plasma or 50 mg of tissue for typical samples. Intraday and interday precision for the determination of the major lipid classes in human plasma ranged from 3.6 to 10.5% CV with a variability in retention time of less than 6%. The utility of the method is demonstrated through the separation and quantitation of lipids in mouse plasma, liver, and heart tissue.

Interactions between the consumption of a high-fat diet and fasting in the regulation of fatty acid oxidation enzyme gene expression: an evaluation of potential mechanisms

The consumption of high-fat diets (HFDs) and fasting are known to increase the expression of enzymes involved in fatty acid oxidation (FAO). However, it has been reported that the ability of physiological stressors to induce enzymes of FAO in skeletal muscle is blunted with obesity. In this regard, we sought to explore the effects and potential mechanisms of an HFD on the expression of FAO enzymes in the fed and fasted state. The consumption of an HFD increased the mRNA expression or protein content of medium-chain acyl-CoA dehydrogenase (MCAD), uncoupling protein-3 (UCP3), and pyruvate dehydrogenase kinase 4 (PDK4) in the fed state. Fasting increased the mRNA expression of PDK4, MCAD, and UCP-3, and the protein content of UCP-3 in chow but not HFD rats. HFDs did not increase carnitine palmitoyl transfer-1 (CPT-1) mRNA levels in the fed state and the effects of fasting were markedly reduced compared with chow-fed rats. The expression of peroxisome-proliferator-activated receptor-γ coactivator-1β (PGC-1β) was increased in muscle from HFD rats in the fed state, while PGC-1-related coactivator (PRC) was increased with fasting in chow-fed but not HFD rats. Plasma fatty acid levels were elevated in the fed state from HFD rats but not increased further with fasting, whereas fasting increased plasma fatty acids in chow-fed animals. Fasting-mediated increases in plasma epinephrine, and the activation of PKA and AMPK in skeletal muscle were similar between chow and HFD rats. p38 MAPK phosphorylation was increased with fasting in chow-fed but not HFD rats. Our findings suggest that a blunted effect of fasting on the induction of PDK4, MCAD, and UCP3 in skeletal muscle from HFD rats is likely a result of already elevated levels of these enzymes, the induction of which is associated with increases in plasma fatty acid and PGC-1β. On the other hand, a blunted induction of PRC and CPT-1 mRNA may be explained by decreases in p38 MAPK signaling.

Simple chromatographic method for simultaneous analyses of phosphatidylcholine, lysophosphatidylcholine, and free fatty acids

This study describes a simple chromatographic method for the simultaneous analyses of phosphatidylcholine (PC) and its hydrolytic degradation products: lysophosphatidylcholine (LPC) and free fatty acids (FFA). Quantitative determination of PC, LPC, and FFA is essential in order to assure safety and to accurately assess the shelf life of phospholipid-containing products. A single-run normal-phase high-performance liquid chromatography (HPLC) with evaporative light scattering detector has been developed. The method utilizes an Allsphere silica analytical column and a gradient elution with mobile phases consisting of chloroform: chloroform-methanol (70:30%, v/v) and chloroform-methanol-water-ammonia (45:45:9.5:0.5%, v/v/v/v). The method adequately resolves PC, LPC, and FFA within a run time of 25 min. The quantitative analysis of PC and LPC has been achieved with external standard method. The free fatty acids were analyzed as a group using linoleic acid as representative standard. Linear calibration curves were obtained for PC (1.64-16.3 μg, r(2) = 0.9991) and LPC (0.6-5.0 μg, r(2) = 0.9966), while a logarithmic calibration curve was obtained for linoleic acid (1.1-5.8 μg, r(2) = 0.9967). The detection and quantification limits of LPC and FFA were 0.04 and 0.1 μg, respectively. As a means of validating the applicability of the assay to pharmaceutical products, PC liposome was subjected to alkaline hydrolytic degradation. Quantitative HPLC analysis showed that 97% of the total mass balance for PC could be accounted for in liposome formulation. The overall results show that the HPLC method could be a useful tool for chromatographic analysis, stability studies, and formulation characterization of phospholipid-based pharmaceuticals.

Increased lipid peroxidation in LDL from type-2 diabetic patients

Increased oxidative stress is associated with type-2 diabetes and related cardiovascular diseases, but oxidative modification of LDL has been partially characterized. Our aim was to compare the lipid and fatty acid composition as well as the redox status of LDL from diabetic patients and healthy subjects. First, to ensure that isolation of LDL by sequential ultracentrifugation did not result in lipid modifications, lipid composition and peroxide content were determined in LDL isolated either by ultracentrifugation or fast-protein liquid chromatography. Both methods resulted in similar concentrations of lipids, fatty acids, hydroxy-octadecadienoic acid (HODE) and malondialdehyde (MDA). Then, LDLs were isolated by ultracentrifugation from eight type-2 diabetic patients and eight control subjects. Compared to control LDL, diabetic LDL contained decreased cholesteryl esters and increased triglyceride concentrations. Ethanolamine plasmalogens decreased by 49%. Proportions of linoleic acid decreased in all lipid classes, while proportions of arachidonic acid increased in cholesteryl esters. Total HODE concentrations increased by 56%, 12- and 15-hydroxy-eicosatetraenoic acid by 161 and 86%, respectively, and MDA levels increased by twofold. alpha-Tocopherol concentrations, expressed relative to triglycerides, were lower in LDL from patients compared to controls, while gamma-tocopherol did not differ. Overall, LDL from type-2 diabetic patients displayed increased oxidative stress. Determination of hydroxylated fatty acids and ethanolamine plasmalogen depletion could be especially relevant in diabetes.

Elevated plasma fibrinogen caused by inadequate alpha-linolenic acid intake can be reduced by replacing fat with canola-type rapeseed oil

The effects of canola-type rapeseed oil (RSO) on serum lipids, plasma fibrinogen, lipid oxidation and fatty acids were studied in three groups of subjects, two of which had not been consuming fish in their habitual diets. Forty-two volunteers (35 women, 7 men, 16-62 years) replaced fat with RSO for 6 weeks in a parallel design. The average cholesterol and fibrinogen concentrations were 5.0 mmol/l and 2.6 g/l, respectively. The intake of alpha-linolenic acid (alpha-LLA) was doubled. Efficient competitive inhibition by alpha-LLA was seen as a decrease in long-chain (LC) n-6 PUFA at 3 weeks. Elevated fibrinogen (2.6-3.9 g/l) decreased by 0.95 g/l at 6 weeks. Docosahexaenoic acid (22:6n-3) in plasma phospholipids increased at low fibrinogen levels only. The associations and changes in plasma C18 and LC PUFA followed the competitive and metabolic principles of the body, and especially in the case of n-3 PUFA according to the recycling pathway.

Separation and identification of neutral cereal lipids by normal phase high-performance liquid chromatography, using evaporative light-scattering and electrospray mass spectrometry for detection

A novel method was developed for the analysis of molecular species in neutral lipid classes, using separation by normal phase high-performance liquid chromatography, followed by detection by evaporative light-scattering and electrospray ionization tandem mass spectrometry. Monoacid standards, i.e. sterol esters, triacylglycerols, fatty acids, diacylglycerols, free sterols and monoacylglycerols, were separated to baseline on microbore 3 microm-silica gel columns. Complete or partial separation of molecular species in each lipid class permitted identification by automatic tandem mass spectrometry of ammonium adducts, produced via positive electrospray ionization. After optimization of the method, separation and identification of molecular species of various lipid classes was comprehensively tested by analysis of neutral lipids from the free lipid extract of maize flour.

Determination of total cholesterol in serum by high-performance liquid chromatography with electrochemical detection

A simple and sensitive HPLC method that does not require derivatization for determining cholesterol has been developed. Investigation of voltammetric behavior of cholesterol showed that cholesterol could be oxidized on a glassy carbon electrode in non-aqueous solvents. This was applied to the development of a method by HPLC with electrochemical detection (HPLC-ED). The HPLC-ED was optimized using the separation of cholesterol and oxysterols including 26-hydroxycholesterol and 24S-hydroxycholesterol. The separation was carried out with a Develosil C30-UG-3 column; acetonitrile-2-propanol (9:1, v/v) containing 50mM LiClO(4) as a mobile phase; and an applied potential at 1.9V versus Ag/AgCl. The current peak height was linearly related to the amount of cholesterol injected from 0.5-100 microM (r>0.999). The detection limit (S/N=3) of cholesterol was 0.36 microM (1.8 pmol). Cholesterol at 100 microM was directly detected with a relative standard deviation (RSD) of less than 1.0% (n=8). Total cholesterol and free cholesterol in control human serum were determined by the present method with the recovery of more than 90% and the RSD (n=6) of less than 3.0%.

Serum phospholipid fatty acids, adipose tissue, and metabolic markers in obese adolescents

OBJECTIVE

Fatty acid (FA) composition has a role in adipogenesis. The objective was to study serum phospholipid (PL) FAs in adolescents and their relation to abdominal adipose tissue (AT) compartments and metabolic markers.

RESEARCH METHODS AND PROCEDURES

Abdominal AT was measured by magnetic resonance imaging and FA pattern was determined in serum PL of 10 obese adolescents (5 females), median age 12.0 years (range, 10.4 to 16.4) and BMI 30.7 (26.8 to 40.4), and 15 lean control subjects (9 females), median age 12.6 years (range, 11.3 to 15.4), and BMI 19.5 (17.1 to 23.4).

RESULTS

Obese adolescents had relatively higher levels of saturated FA (SFA) and nervonic acid compared with controls. Serum PL concentration of n-3 polyunsaturated fatty acids (PUFA) was lower in the obese vs. lean females (p = 0.01), including docosahexaenoic acid (DHA) (p = 0.01). The ratios of arachidonic acid to DHA and total n-6/n-3 FA were increased in obese children (p = 0.02 and 0.01, respectively). n-3 PUFAs were inversely correlated to all subcutaneous AT compartments except visceral AT. The homeostasis model assessment index of beta-cell function related inversely to DHA concentration (p = 0.03). All changes were more marked in the females.

DISCUSSION

Serum FA pattern in obese adolescents differed significantly from that in age-matched lean controls, reflecting a decrease in n-3 PUFA, especially DHA, and an increase in SFA. The subcutaneous AT, but not visceral AT, correlated to the changes in PUFA and SFA, suggesting an abnormal essential FA metabolism in obese adolescents.

A review of chromatographic methods for the assessment of phospholipids in biological samples

Phospholipids are important constituents of all living cell membranes. Lipidomics is a rapidly growing field that provides insight as to how specific phospholipids play roles in normal physiological and disease states. There are many analytical methods available for the qualitative and quantitative determination of phospholipids. This review provides a summary of the methods that were historically used such as thin layer chromatography, gas chromatography and high-performance liquid chromatography. In addition, an introduction to applications of interfacing these traditional chromatographic techniques with mass spectrometry is provided.

Quantification of major lipid classes in human triacylglycerol-rich lipoproteins by high-performance liquid chromatography with evaporative light-scattering detection

Triacylglycerol-rich lipoproteins (TRL), comprising chylomicrons (CM) and very-low-density lipoproteins (VLDL), have been associated with cardiovascular disease. The lipid class content in the remnant particles of these lipoproteins is a determinant for the accumulation of lipids in macrophages and their transformation into foam cells. We have optimized a method for the simultaneous determination of cholesteryl esters (CE), triacylglycerols (TG), free cholesterol (FC), monoacylglycerols (MG), and phospholipids (PL) by HPLC coupled to a light-scattering detector (ELSD). A diol column and a ternary gradient of hexane, 2-propanol, and methanol were applied to CM and VLDL of human origin (n = 10), with excellent precision in terms of repeatability of peak areas and retention times. All peaks were baseline resolved although the resolution of CE and TG was compromised for the sake of simplicity of the solvent gradient. The ELSD response was fitted to second-order equations, with correlation coefficients (r2) higher than 0.999 for a wide range of concentrations (0.25-10 microg of lipid injected). TG were the major lipid class detected in human TRL, accounting for 62% in CM obtained 2 h after the oil intake. In addition we recorded a depletion of TG and CE in CM obtained 2 h after the oil intake of about 60%. We conclude that the method reported here is suitable for a rapid and precise determination of lipid classes in human TRL and, therefore, may be a useful tool for investigations on the atherogenicity of these lipoproteins.

Separation and quantification of chicken and bovine growth plate cartilage matrix vesicle lipids by high-performance liquid chromatography using evaporative light scattering detection

Matrix vesicles (MV) are lipid bilayer-enclosed nanoscale structures that initiate extracellular mineral formation in most vertebrate species. Little attention has been given to differences between species in membrane lipid composition or to how new mineral is formed in MV. To explore more precisely the lipids of MV isolated from avian and bovine species, we developed a new high-performance liquid chromatography (HPLC) method used in combination with evaporative light scattering detection (ELSD) to quantify their lipid composition. HPLC analyses were performed on a Lichrosorb silica column using separate binary gradient elution systems for analyzing polar and nonpolar lipids. Standard mixtures of both phospholipids and nonpolar lipids were used to prepare calibration curves for each lipid, which were analyzed mathematically by polynomial regression for accurate quantitation. This new methodology provides high-resolution separations and quantitation of both the polar and the nonpolar lipids typically present in biological membranes, including lyso- (monoacyl-) phospholipids. We have applied this method to quantitate the phospholipid and nonpolar lipid composition of MV isolated from chicken and bovine growth plate cartilage. We also compared the ability of these MV to induce mineral formation. While the ability to induce mineralization and the lipid composition were generally similar, some significant differences between MV from these two disparate species were seen.