Separation of neutral lipids by high-performance liquid chromatography: quantification by ultraviolet, light scattering and fluorescence detection

Cholesterol determination in foods: Comparison between high performance and ultra-high performance liquid chromatography

Analytical methods for cholesterol evaluation in foods are crucial since this compound was closely related with cardiovascular disease. In the present study, two chromatographic methods were implemented and validated, in order to achieve the ideal analytical method for the quantification of cholesterol in food matrices. The developed methods were applied to different foodstuffs, sour cream, egg, egg yolk and chicken nuggets. Both HPLC and UHPLC methods are rapid, specific, sensitive, precise (RSD<2.5%) and accurate. The achieved LOD and LOQ for UHPLC were 0.7 and 2.4μg/mL, respectively, while for HPLC were 3 and 11μg/mL. UHPLC method allowed reduction of the organic solvents consumption (8 times lower) and decreased analysis time in 4min, being more eco-friendly, than conventional HPLC methods. Moreover, it will be very useful for the quality control of cholesterol content in food matrices and can be easily adopted by analytical laboratories.

Prenatal ethanol exposure increases brain cholesterol content in adult rats

Fetal alcohol syndrome is the most severe expression of the fetal alcohol spectrum disorders (FASD). Although alterations in fetal and neonate brain fatty acid composition and cholesterol content are known to occur in animal models of FASD, the persistence of these alterations into adulthood is unknown. To address this question, we determined the effect of prenatal ethanol exposure on individual phospholipid class fatty acid composition, individual phospholipid class mass, and cholesterol mass in brains from 25-week-old rats that were exposed to ethanol during gestation beginning at gestational day 2. While total phospholipid mass was unaffected, phosphatidylinositol and cardiolipin mass was decreased 14 and 43 %, respectively. Exposure to prenatal ethanol modestly altered brain phospholipid fatty acid composition, and the most consistent change was a significant 1.1-fold increase in total polyunsaturated fatty acids (PUFA), in the n-3/n-6 ratio, and in the 22:6n-3 content in ethanolamine glycerophospholipids and in phosphatidylserine. In contrast, prenatal ethanol consumption significantly increased brain cholesterol mass 1.4-fold and the phospholipid to cholesterol ratio was significantly increased 1.3-fold. These results indicate that brain cholesterol mass was significantly increased in adult rats exposed prenatally to ethanol, but changes in phospholipid mass and phospholipid fatty acid composition were extremely limited. Importantly, suppression of postnatal ethanol consumption was not sufficient to reverse the large increase in cholesterol observed in the adult rats.

Rapid detection and quantification of triacylglycerol by HPLC-ELSD in Chlamydomonas reinhardtii and Chlorella strains

Triacylglycerol (TAG) analysis and quantification are commonly performed by first obtaining a purified TAG fraction from a total neutral lipid extract using thin-layer chromatography (TLC), and then analyzing the fatty acid composition of the purified TAG fraction by gas chromatography (GC). This process is time-consuming, labor intensive and is not suitable for analysis of small sample sizes or large numbers. A rapid and efficient method for monitoring oil accumulation in algae using high performance liquid chromatography for separation of all lipid classes combined with detection by evaporative light scattering (HPLC–ELSD) was developed and compared to the conventional TLC/GC method. TAG accumulation in two Chlamydomonas reinhardtii (21 gr and CC503) and three Chlorella strains (UTEX 1230, CS01 and UTEX 2229) grown under conditions of nitrogen depletion was measured. The TAG levels were found to be 3–6 % DW (Chlamydomonas strains) and 7–12 % DW (Chlorella strains) respectively by both HPLC–ELSD and TLC/GC methods. HPLC–ELSD resolved the major lipid classes such as carotenoids, TAG, diacylglycerol (DAG), free fatty acids, phospholipids, and galactolipids in a 15-min run. Quantitation of TAG content was based on comparison to calibration curves of trihexadecanoin (16:0 TAG) and trioctadecadienoin (18:2 TAG) and showed linearity from 0.2 to 10 μg. Algal TAG levels >0.5 μg/g DW were detectable by this method. Furthermore TAG content in Chlorella kessleri UTEX 2229 could be detected. TAG as well as DAG and TAG content were estimated at 1.6 % DW by HPLC–ELSD, while it was undetectable by TLC/GC method.

Bioassay-directed fractionation for discovery of bioactive neutral lipids guided by relative mass defect filtering and multiplexed collision-induced dissociation

We report a synergistic method using bioassay-directed liquid chromatography fractionation and time-of-flight mass spectrometry to guide and accelerate bioactive compound discovery. To steer purification and assays toward anticipated neutral lipid activators of a constitutive androstane receptor splice variant, a relative mass defect filter was calculated, based on the ratio of the mass defect to the measured ion mass, and used to reduce the number of candidate ion masses. Mass measurements often lack sufficient accuracy to provide unambiguous assignments of elemental compositions, and since the relative mass defect reflects fractional hydrogen content of ions, this value is largely determined by the hydrogen content of a compound's biosynthetic precursors. A relative mass defect window ranging from 600-1000 ppm, consistent with an assortment of lipids, was chosen to assess the number of candidate ions in fractions of fetal bovine serum. This filter reduced the number of candidate ion m/z values from 1345 to 892, which was further reduced to 21 by intensity and isotope filtering. Accurate mass measurements from time-of-flight mass spectrometry and fragment ion masses generated using nonselective collision-induced dissociation suggested dioctyl phthalate as one of few neutral lipid constituents in the active fraction. The identity of this compound was determined to be di(2-ethylhexyl) phthalate using GC/MS, and it was ranked as a promising candidate for reporter assay screening.

Lipid profiling of rat peritoneal surface layers by online normal- and reversed-phase 2D LC QToF-MS

An online, two-dimensional (2D) liquid chromatography (LC) quadrupole time-of-flight mass spectrometry (QToF-MS) method was developed for lipid profiling of rat peritoneal surface layers, in which the lipid classes and species could be simultaneously separated in one injection with a significantly increased sensitivity. Different lipid classes were separated on a normal-phase column in the first dimension and lipid molecular species were separated on a reversed-phase column in the second dimension, so that the ion suppression effects were reduced while the detection sensitivity was improved. Identified were 721 endogenous lipid species from 12 lipid classes, in which 415 structures were confirmed using tandem mass spectra, and the other 306 lipid molecular species were identified by accurate masses. The linearity, limit of detection, and repeatability were all satisfactory. The method was applied to the investigation of the lipid changes in rat peritoneal surface layer after peritoneal dialysis, and 32 potential lipid biomarkers were identified, as their concentrations in the dosed group were 2.2-12.5 times of those in the control group. The results revealed that this 2D LC-MS system was a promising tool for lipid profiling of complex biological samples.

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.

Interest of fluorescence derivatization and fluorescence probe assisted post-column detection of phospholipids: a short review

Phospholipids are essential constituents of all living cell membranes. There are many analytical methods available for the quantitative and qualitative determination of phospholipids, but since these molecules lack chromophores, common absorbance based methods are of limited use. Beside mass spectrometry, some less specific approaches that are routinely used are evaporative light scattering detection or fluorescence, which exhibit sufficient sensitivity. Here, we focus on fluorescence, which remains an interesting way to quantify phospholipids. Two ways of detecting phospholipids by fluorescence are possible coupled with separation techniques such as thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE): firstly, pre-column derivatization procedures and secondly, probe assisted post-column detection with suitable fluorescence reagents. In both cases, the common purpose is to increase the detection sensitivity. It is shown that, whereas pre-column derivatization is characterized by selectivity due to the chemical functionality of the analyte involved in the derivatization process, in supramolecular post-column derivatization, the selectivity only proceeds from the capacity of the lipid to involve supramolecular assemblies with a fluorescence probe. The aim of this review is to summarize available experiments concerning fluorescence detection of phospholipids. The interest and limitation of such detection approaches are discussed.

Evaporative light scattering detection: trends in its analytical uses

Evaporative light scattering detection (ELSD) is widely recognized as a universal tool for liquid and supercritical chromatographies. In addition, this detection technique is fully compatible with continuous-flow systems. In fact, the combination of continuous non-chromatographic techniques and ELSD affords the design of simple, reliable systems for extracting qualitative information. This paper reviews instrumental innovations regarding the miniaturization of evaporative light scattering detectors and their uses in micro and capillary liquid chromatography; also, it discusses their increasingly important role in the development of vanguard configurations for sample screening and the determination of total indices without the need for chromatographic separation. Moreover, it compares them with other types of chromatographic detectors in terms of performance. Finally, the potential of ELSD for solving real-life analytical problems arising from the need to meet (bio)chemical information needs is illustrated with various selected applications.

Analysis of triacylglycerol and fatty acid isomers by low-temperature silver-ion high performance liquid chromatography with acetonitrile in hexane as solvent: Limitations of the methodology

Silver ion HPLC (Ag-HPLC), utilizing columns containing silver ions bonded to a silica substrate and acetonitrile in hexane as solvent, has proven to be a powerful technology for the analysis of geometric (cis or trans) or positional fatty acids, fatty acid ester (primarily methyl ester; FAME), or triacylglycerol (TAG) isomers. Previous studies had demonstrated that, unlike gas chromatography, samples eluted more rapidly at lower temperatures (at 20 degrees C versus 40 degrees C, for example). A low-temperature bath [dual-column Ag-HPLC; isocratic solvent systems of 0.3 to 0.7% acetonitrile (ACN) in hexane] was utilized to study the application of this system at low (below 0 degrees C) temperatures for analysis of FAME (zero to six double bonds) and TAG [SSS, OOO and LLL, where S=stearic acid (18:0), O=oleic acid (9c-18:1), and L=linoleic acid (9c, 12c-18:2)] standards. While FAME elution times continued to decrease from 0 degrees C to -10 degrees C, they began to increase at -20 degrees C. A similar situation was noted for the TAG isomers, except that retention times began to increase below 0 degrees C. The lower temperature limit of the Ag-HPLC/ACN in hexane system is thus ca. -25 degrees C. Increasing sample elution times and pump head pressures upon sample injection were noted at temperatures of -25 degrees C to -40 degrees C. Equilibration times at each temperature could be reduced to ca. 15 min without loss of resolution and with retention times of +/-2%. Temperature, rather than solvent composition, can therefore be utilized with the Ag-HPLC/ACN in hexane solvent system to optimize elution times and resolution(s) of FAME and TAG isomers.

Brain neutral lipids mass is increased in alpha-synuclein gene-ablated mice

Because alpha-synuclein (Snca) has a role in brain lipid metabolism, we determined the impact that Snca deletion had on whole brain lipid composition. We analysed masses of individual phospholipid (PL) classes and neutral lipid mass as well as PL acyl chain composition in brains from wild-type and Snca-/- mice. Although total brain PL mass was not altered, cardiolipin and phosphatidylglycerol mass decreased 16% and 27%, respectively, in Snca-/- mice. In addition, no changes were observed in plasmalogen or polyphosphoinositide mass. In ethanolamine glycerophospholipids and phosphatidylserine, docosahexaenoic acid (22 : 6n-3) was decreased 7%, while 16 : 0 was increased 1.1-fold and 1.4-fold, respectively. Surprisingly, brain cholesterol, cholesteryl ester, and triacylglycerol mass were increased 1.1-fold, 1.6-fold, and 1.4-fold, respectively in Snca-/- mice. In isolated myelin, cholesterol mass was also increased 1.3-fold, but because there was also a net increase in myelin PL mass, the cholesterol to PL ratio was unaltered. No changes in the expression of cholesterogenic enzymes were observed, suggesting these did not account for the observed changes in cholesterol. These data extend our previous results in astrocytes and kinetic studies in vivo demonstrating a role for Snca in brain lipid metabolism and demonstrate a clear impact on brain neutral lipid metabolism.

Deposition of iron and beta-amyloid plaques is associated with cortical cellular damage in rabbits fed with long-term cholesterol-enriched diets

Hypercholesterolemia is a potential trigger of Alzheimer's disease, and is thought to increase brain levels of beta-amyloid (Abeta) and iron. However, animal models to address the mechanisms by which Abeta and iron accumulation may cause neuronal damage are poorly defined. To address this question, we fed adult rabbits a 1% cholesterol-enriched diet for 7 months. This diet was associated with increased regional deposition of both iron and Abeta peptide in the brain. Iron preferentially accumulated around Abeta plaques in the adjacent cortex, but was not found in the hippocampus. Co-localization of iron and Abeta was accompanied by apoptosis, DNA damage, blood-brain barrier (BBB) disruption, as well as dysregulation in the level of the iron-regulatory proteins, ferritin and heme-oxygenase-1. We further demonstrate that the cholesterol diet-induced apoptosis is mediated by the activation of the endoplasmic reticulum stress pathway, involving the down-regulation of the endoplasmic reticulum chaperones, calreticulin, grp78 and grp94, and the activation of the growth and arrest DNA damage protein, gadd153. Our results suggest that BBB damage and disturbances in iron metabolism may render the cortex more vulnerable than the hippocampus to the cholesterol-induced cellular stress.

PPARalpha activation increases triglyceride mass and adipose differentiation-related protein in hepatocytes

Adipose differentiation-related protein (ADRP) is a lipid droplet-associated protein that is expressed in various tissues. In mice treated with the peroxisome proliferator-activated receptor alpha (PPARalpha) agonist Wy14,643 (Wy), hepatic mRNA and protein levels of ADRP as well as hepatic triglyceride content increased. Also in primary mouse hepatocytes, Wy increased ADRP expression and intracellular triglyceride mass. The triglyceride mass increased in spite of unchanged triglyceride biosynthesis and increased palmitic acid oxidation. However, Wy incubation decreased the secretion of newly synthesized triglycerides, whereas apolipoprotein B secretion increased. Thus, decreased availability of triglycerides for VLDL assembly could help to explain the cellular accumulation of triglycerides after Wy treatment. We hypothesized that this effect could be mediated by increased ADRP expression. Similar to PPARalpha activation, adenovirus-mediated ADRP overexpression in mouse hepatocytes enhanced cellular triglyceride mass and decreased the secretion of newly synthesized triglycerides. In ADRP-overexpressing cells, Wy incubation resulted in a further decrease in triglyceride secretion. This effect of Wy was not attributable to decreased cellular triglycerides after increased fatty acid oxidation because the triglyceride mass in Wy-treated ADRP-overexpressing cells was unchanged. In summary, PPARalpha activation prevents the availability of triglycerides for VLDL assembly and increases hepatic triglyceride content in part by increasing the expression of ADRP.

Fatty acid incorporation is decreased in astrocytes cultured from alpha-synuclein gene-ablated mice

Because alpha-synuclein may function as a fatty acid binding protein, we measured fatty acid incorporation into astrocytes isolated from wild-type and alpha-synuclein gene-ablated mice. alpha-Synuclein deficiency decreased palmitic acid (16:0) incorporation 31% and arachidonic acid [20:4 (n-6)] incorporation 39%, whereas 22:6 (n-3) incorporation was unaffected. In neutral lipids, fatty acid targeting of 20:4 (n-6) and 22:6 (n-3) (docosahexaenoic acid) to the neutral lipid fraction was increased 1.7-fold and 1.6-fold, respectively, with an increase in each of the major neutral lipids. This was consistent with a 3.4- to 3.8-fold increase in cholesteryl ester and triacylglycerol mass. In the phospholipid fraction, alpha-synuclein deficiency decreased 16:0 esterification 39% and 20:4 (n-6) esterification 43% and decreased the distribution of these fatty acids, including 22:6 (n-3), into this lipid pool. alpha-Synuclein gene-ablation significantly decreased the trafficking of these fatty acids to phosphatidylinositol. This observation is consistent with changes in phospholipid fatty acid composition in the alpha-synuclein-deficient astrocytes, including decreased 22:6 (n-3) content in the four major phospholipid classes. In summary, these studies demonstrate that alpha-synuclein deficiency significantly disrupted astrocyte fatty acid uptake and trafficking, with a marked increase in fatty acid trafficking to cholesteryl esters and triacylglycerols and decreased trafficking to phospholipids, including phosphatidylinositol.

Fluorescence probe assisted post-column detection for lipid analysis in microbore-LC

A general approach, still few exploited so far and never associated with microbore-LC, consisting of detection of various lipid classes (i.e. phospholipids, triglycerides, ceramides and glycosphingolipids) by non-covalent association with 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence probe is developed. This mode of detection was coupled with non-aqueous reversed-phase microbore-LC (C18) by using classical post-column fluorescence detection. The classical LC system was first adapted to microbore-chromatography (internal diameter 1 mm) without apparatus miniaturization of the solvent delivery system and the detection cell. For this purpose, the detection parameters (probe concentration, post-column flow rate, post-column reactor length and post-column system temperature) were optimized by a central composite design (CCD) using a mixture of phosphatidylcholine (PC) species as a lipid model and DPH (lambda(ex) = 350 nm, lambda(em) = 430 nm) as a fluorescence probe. The optimal conditions of detection for the various molecular species of PC were determined for a DPH concentration of 3.35 micromol/L, a post-column flow rate of 0.5 mL/min, a reactor length of 1.4 m and a temperature of 35 degrees C. The fluorescence response was linear over a wide range of PC species from 5 microg/mL to 100 microg/mL and the lower limit of detection (signal/noise = 3) was about 1 microg/mL, that is equivalent to evaporative light scattering detection (ELSD). Others molecular species of various classes of lipids, i.e. triglycerides, ceramides and glycosphingolipids were also easily detected. Thus, this study demonstrated the versatility of the proposed system of detection which was shown to be sensitive, easy to perform, non-destructive and allowed, in contrast to ELSD, for a linear response with various polarity lipid classes.

Tissue-dependent alterations in lipid mass in mice lacking glycerol kinase

Glycerol kinase (ATP:glycerol-3-phosphotransferase, EC 2.7.1.30, glycerokinase) (Gyk) has a central role in plasma glycerol extraction and utilization by tissues for lipid biosynthesis. Gyk deficiency causes various phenotypic changes ranging from asymptomatic hyperglycerolemia to a severe metabolic disorder with growth and psychomotor retardation. To better understand the potential role of Gyk in tissue lipid metabolism, we determined phospholipid (PL), cholesterol (Chol), and triacylglycerol (TG) mass in a number of tissues from mice lacking Gyk. We report a tissue-dependent response to Gyk gene deletion. Tissues with elevated total PL mass (brain, kidney, muscle) were characterized by the increased mass of ethanolamine glycerophospholipids (EtnGpl), choline glycerophospholipids, and phosphatidylserine (PtdSer). In heart, lipid changes were characterized by a reduction in total PL, including decreased EtnGpl, phosphatidylinositol, and PtdSer mass and decreased TG and FFA mass. In parallel with tissue PL alterations, tissue Chol was also changed, maintaining a normal Chol/PL ratio. Under conditions of Gyk deficiency, we speculate that glycerol-3-phosphate and lipid production is maintained via alternative biosynthesis, including glycolysis, glyceroneogenesis, or by direct acylation of glycerol in brain, muscle, kidney, and liver, but not in heart.

Analysis of triglyceride isomers by silver-ion high-performance liquid chromatography

Silver ion chromatography (Ag-HPLC), utilizing columns packed with silver ions bonded to a silica or similar substrate, has proven to be a powerful technique for the analytical separation of cis and trans geometric and positional fatty acid methyl ester (FAME) and triacylglycerol (TAG) isomers. In this manuscript, we utilize an HPLC column chiller/heater to study the effects of Ag-HPLC column temperatures on elution rates of FAME and TAG isomers. Two Varian ChromSpher lipids columns connected in series and isocratic solvent systems of 1.0% or 1.5% acetonitrile (ACN) in hexane were used to analyze FAMEs (zero to six double bonds; cis/trans isomers), TAGs (homogeneous (triacetyl-, tristearoyl-, trioleoyl-, trilinoeyl- and trilinolenoyl-glycerols) and positional (1,3-distearoyl,2-monolinolenoyl- and 1,2-distearoyl, 3-monolinolenoylglycerol, etc.)) mixtures at four different temperatures (10 degrees C, 20 degrees C, 30 degrees C or 40 degrees C). Unexpectedly, the unsaturated FAME and TAG samples were found to elute more slowly at higher temperatures, a result just the opposite to the usual temperature effect (where samples elute more rapidly at higher temperatures) noted in gas and most liquid (reversed-phase or silica gel substrates) chromatography systems. This effect in Ag-HPLC may be limited to hexane-based solvent systems (it does not seem to occur with chlorinated hydrocarbon-based solvents); its magnitude is directly related to the total number of double bonds in the sample. It is also more evident with cis than with trans double bonds.

Migration of lubricants from food packagings

A normal-phase high-performance liquid chromatography (NP-HPLC) method is introduced for the identification and quantitative estimation of 12 lipid classes (paraffin, wax esters, cholesterol esters, fatty acid methyl esters, triacyl glycerols, fatty alcohols, free fatty acids, cholesterol, 1,3-diacyl glycerols, 1,2-diacyl glycerols, monoacyl glycerols and fatty acid amide) used as lubricantsin food packaging materials. The HPLC separation is carried out on a LiChrospher Diol (100 A, 5 microm, 125 mm x 3 mm) column with gradient elution (isooctane/0.1% acetic acid in tert-butyl methyl ether) and evaporative light scattering detection (ELSD). The method has been calibrated with representatives of each class in working ranges of about 5-150 mg/l, depending on the lipid class. Intra-day variance for all representatives range from 1.9 to 5.1%, inter-day variances from 7.0 to 26.5% and the limits of detection from 0.79 to 3.65 mg/l (except for two classes). A simple sample preparation could be established for the determination of migrating lubricants obtained from packaging materials containing external or internal lubricants. Since the detector response depends on the chain length and the degree of saturation, the quantification of a lipid class with unknown composition is only semi-quantitative. The amount of migrating lubricants from an epoxy-based can coating could be estimated with 0.3 mg/dm2 and from a light weight container with 5.5 mg/dm2.

Simultaneous HPLC analysis of alpha-tocopherol and cholesterol in fresh pig meat

A method has been developed for simultaneously determining alpha-tocopherol and cholesterol in fresh pig meat by HPLC. It allows a reduction in the number of analyses and brings savings in time and materials. The unsaponifiable fraction is extracted following the modified method of Liu et al. (Liu, Q.; Scheller, K. K.; Schaefer, D. M. Technical note: A simplified procedure for vitamin E determination in beef muscle. J. Anim. Sci. 1996, 74, 2406-2410). The modifications introduced are the use of nitrogen atmosphere during the extraction, the addition of an antioxidant in the organic extraction phase, and the use of alpha-tocopherol itself as an internal standard. There is then a chromatographic analysis which allows the separation of the two compounds in question. To identify and quantify, two different detectors are used in series: the first is a fluorescence detector (alpha-tocopherol), and the second is a light-scattering detector (cholesterol). The technique shows sufficient sensitivity to determine the normal levels of alpha-tocopherol and cholesterol in meat, with recovery percentages of 78% and 97%, respectively. The average amount of alpha-tocopherol and cholesterol in samples from pig Longissimus dorsi muscle analyzed using this method is 1.8 and 620 mg/kg of fresh meat, respectively.

Targeted disruption of peroxisomal proliferator-activated receptor beta (delta) results in distinct gender differences in mouse brain phospholipid and esterified FA levels

The peroxisomal proliferator-activated receptor beta (delta) (PPARbeta) is a nuclear hormone receptor that is ubiquitously expressed and that regulates the transcription of genes involved in lipid metabolism. A homozygous PPARbeta-null mouse has been developed in which the ligand-binding domain of the PPARbeta receptor is disrupted. Analysis of brains from these animals shows that female null mice have 24 and 17% increases in plasmenylethanolamine and phosphatidylserine and a 9% decrease in the level of phosphatidylinositol when compared to controls. The phospholipid changes found in female null mice were associated with increased levels of esterified 18:1n-9, 20:1n-9, 20:4n-6, and 22:5n-3 FA in plasmenylethanolamine, 20:1n-9 in phosphaticlylinositol, and 18:0, 18:1n-9, 18:3n-6, 20:1 n-9, and 20:4n-6 in phosphatidylserine. Increased levels of esterified 18:1n-9, 18:2n-6, 18:3n-6, and 20:1n-9 were also found in the phosphatidylethanolamine fraction despite its cellular content remaining unchanged. Brain phospholipid content in male PPARbeta-null mice did not differ from controls, but increased levels of 20:1n-9 in the phosphatidylinositol and 18:1n-9 in the phosphatidylserine fractions were observed. No changes were found in the content of brain cholesterol, TAG, and FFA in either female or male PPARbeta-null mice. These data suggest that PPARbeta is involved in maintaining FA and phospholipid levels in adult female mouse brain and provide strong evidence that suggests a role for PPARbeta in brain peroxisomal acyl-CoA utilization.

Quantitative determination of fat emulsion using 1,6-diphenyl-1,3,5-hexatriene as fluorescence probe: application to the compounding of all-in-one parenteral nutrition admixtures

The potential contamination of binary bags by traces of fat emulsion stemmed from ternary bags prepared just before, led us to determine traces of lipids into the line set of the automated compounder MM23. Diphenylhexatriene (DPH) was chosen as fluorescence probe due to its strong fluorescence enhancement in a lipid environment. Optimization of experimental conditions (i.e. DPH amounts, pH of fat emulsion samples, ultrasounds use, light, temperature and contact duration) for fluorescence measurement and validation of analytical method were performed. This method was linear over 0.5-8.0 mg l(-1) (r=0.999) of fat emulsion. The intra-day and inter-day precisions were inferior to 2% for the 2.0 and 8.0 mg l(-1) standards. Under optimized conditions, the detection limit and quantitation limit were 0.10 and 0.29 mg l(-1) of lipids respectively. Compared to the colorimetric method using sodium dichromate, it is at least 100 times more sensitive. The proposed method permitted to rapidly measure fat emulsion traces in automated compounder line set for parenteral nutrition solutions and thus, to assess the risk of contamination of binary bags by lipids. At last, this method was shown to be conveniently applied to the analysis of fat emulsion in the final total parenteral nutrition bag.

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

An HPLC method with evaporative light-scattering detection (ELSD) was optimized and validated for the simultaneous quantitation of cholesteryl esters (CEs), triacylglycerols (TGs), free cholesterol (FC) and phosphatidylcholine (PC) in human plasma. The separation of CEs from TGs, the most variable plasma lipid class, was improved by speeding up the gradient steps and by increasing the re-equilibration time between runs. The calibrations were made at levels of 0.14-14 microg lipid/injection. The intra- and inter-day precision values of the method ranged between 1.9 and 4.5 and 2.3-7.2% (RSD, n=6), respectively, including determinations at two concentration levels. In comparison to other lipid classes, quantitation of PC proved to be equally repeatable despite its lowest detector response. The relative recoveries varied from 97.0 to 110.3%, showing good accuracy of the method. The methodological variation of the lipid classes covered 0.6-3.1% of their total variation in the study population (n=48). The CE/FC ratio showed an even closer relationship with phospholipid linoleic acid (18:2n-6; r=0.65, P<0.001) than with serum cholesterol levels, while eicosapentaenoic acid (20:5n-3) was significantly associated with PC (r=0.41, P<0.01). The CE/FC ratio increased (P<0.01) during soyabean oil substitution and the level of PC increased (P<0.01) during cold-pressed rapeseed oil substitution.

Liver and intestinal fatty acid-binding protein expression increases phospholipid content and alters phospholipid fatty acid composition in L-cell fibroblasts

Although fatty acid-binding proteins (FABP) differentially affect fatty acid uptake, nothing is known regarding their role(s) in determining cellular phospholipid levels and phospholipid fatty acid composition. The effects of liver (L)- and intestinal (I)-FABP expression on these parameters were determined using stably transfected L-cells. Expression of L- and I-FABP increased cellular total phospholipid mass (nmol/mg protein) 1.7- and 1.3-fold relative to controls, respectively. L-FABP expression increased the masses of choline glycerophospholipids (ChoGpl) 1.5-fold, phosphatidylserine (PtdSer) 5.6-fold, ethanolamine glycerophospholipids 1.4-fold, sphingomyelin 1.7-fold, and phosphatidylinositol 2.6-fold. In contrast, I-FABP expression only increased the masses of ChoGpl and PtdSer, 1.2- and 3.1-fold, respectively. Surprisingly, both L- and I-FABP expression increased ethanolamine plasmalogen mass 1.6- and 1.1-fold, respectively, while choline plasmalogen mass was increased 2.3- and 1.7-fold, respectively. The increase in phospholipid levels resulted in dramatic 48 and 33% decreases in the cholesterol-to-phospholipid ratio in L- and I-FABP expressing cells, respectively. L-FABP expression generally increased polyunsaturated fatty acids, primarily by increasing 20:4n-6 and 22:6n-3, while decreasing 18:1n-9 and 16:1n-7. I-FABP expression generally increased only 20:4n-6 proportions. Hence, expression of both I- and L-FABP differentially affected phospholipid mass, class composition, and acyl chain composition. Although both proteins enhanced phospholipid synthesis, the effect of L-FABP was much greater, consistent with previous work suggesting that these two FABP differentially affect lipid metabolism.

Phospholipid composition and levels are altered in Down syndrome brain

Phospholipid composition (mol %) and levels (nmol/mg protein) were determined in postmortem frontal cortical and cerebellar gray matter from older Down Syndrome (DS) patients (age range 38-68 years) and from control subjects. Neither DS nor control tissue exhibited any age-dependent alteration in phospholipid composition or levels. Total phospholipid content was significantly reduced approximately 20% in DS frontal cortex and cerebellum relative to these regions in control tissue. Individual phospholipid levels were also reduced in DS frontal cortex and cerebellum, including a specific 37% decrease in phosphatidylinositol (PtdIns) and a nearly 35% decrease in ethanolamine plasmalogen. Because of the large decrease in phospholipid content in DS brain, the cholesterol/phospholipid ratio was calculated for each group. There was no significant difference in this ratio between groups, indicative of compensatory changes to keep the cholesterol/phospholipid ratio constant. Despite the large changes in DS brain phospholipid levels, significant changes in composition were limited to a 18% decrease in PtdIns mol % and a 22% increase in the mol % of sphingomyelin. These results suggest either a decrease in membrane phospholipids due to a loss of dendrites and dendritic spines, or a general defect in brain lipid metabolism in older DS subjects. The proportionally greater alterations in PtdIns and PlsEtn levels, indicate that the metabolism of these two phospholipids was affected to a greater extent than the other phospholipids. Further, because these changes are found in both the frontal cortical and cerebellar gray matter, they likely are related to the Down syndrome condition rather than to Alzheimer neuropathology.

Phospholipid composition and levels are not altered in fibroblasts bearing presenilin-1 mutations

Lipid alterations have been reported in brain regions affected by Alzheimer disease (AD). The mechanisms causing these changes are poorly understood because it is difficult to study dynamic, biochemical processes in post-mortem brain. Fibroblasts derived from AD patients offer an alternative model to study disease-related alterations in lipid metabolism. Therefore, we measured the phospholipid levels and composition of fibroblasts from individuals bearing two different presenilin-1 mutations and compared these values to appropriate control fibroblasts. There were no differences between groups in phospholipid composition or in individual phospholipid levels, including the plasmalogens. Cholesterol levels and the cholesterol/phospholipid ratio were not different between presenilin-1 mutation bearing and control fibroblasts. Although these presenilin-1 mutation bearing fibroblasts have a number of biochemical changes related to AD, the absence of a change in phospholipid levels suggests that under these conditions, these cells are not useful in studying the mechanisms underlying the alterations in brain phospholipid levels associated with AD. However, these results do not preclude the possible use of other fibroblasts bearing AD-related mutations, e.g., APP mutations, to examine AD-related changes in brain lipid metabolism, or of these fibroblasts under different conditions.

Sterol carrier protein-2 mediated cholesterol esterification in transfected L-cell fibroblasts

The relative function of the 15 and 13.2 kDa forms of SCP-2 in cholesterol trafficking and metabolism was assessed using L-cell fibroblasts permanently transfected with the cDNA encoding for either the mouse 15 kDa or 13.2 kDa SCP-2. Expression of the 15 kDa, but not the 13.2 kDa SCP-2 increased [3H]cholesteryl ester formation from medium derived cholesterol by 30% compared to control cells. In both SCP-2 expressing cell lines, sphingomyelinase treatment increased the initial rate of [3 H]cholesteryl ester formation from plasma membrane derived cholesterol more than 11-fold and elevated [3H]cholesteryl ester levels 1.5-fold compared to control cells. Expression of both proteins resulted in nearly a 1.5-fold increase in [3H]oleic acid esterification into cholesteryl esters, although [3H]oleic acid esterification into triacylglycerols was also increased in the 13.2 kDa SCP-2 expressing cells relative to control. In both transfected cell lines, the cholesteryl ester mass was increased nearly 2-fold compared to control cells, consistent with increased cholesteryl ester synthesis. Similarly, triacylglycerol levels were increased 1.3-fold in the 13.2 kDa SCP-2 expressing cells which is consistent with the increased [3H]oleic acid esterification into triacylglycerol. In the 15 kDa SCP-2 expressing cells, triacylglycerol levels were decreased 60%, but free cholesterol levels were increased 1.2-fold relative to control cells. Thus, only the 15 kDa expression product, containing the putative targeting sequence, specifically enhanced cholesteryl ester formation from either plasma membrane or medium-derived cholesterol. In contrast, the 13.2 kDa expression product, lacking the putative targeting sequence, stimulated an increase in [3H]oleic acid esterification into both cholesterol and triacylglycerol pools, suggesting a non-specific stimulation of fatty acid esterification.

Intestinal fatty acid-binding protein expression stimulates fibroblast fatty acid esterification

The effect of intestinal fatty acid binding protein (I-FABP) expression on cell growth and cell lipid content is not known. Therefore, mouse L-cell fibroblasts were transfected with the cDNA encoding for I-FABP. The high expression clones expressed 0.35% of the total cytosolic proteins as I-FABP. Mock transfected L-cells did not differ from control L-cells in any properties tested. Neither the growth rate, maximal cell density, nor [3H]oleic acid uptake differed in I-FABP expressing as compared to control cells. In contrast, I-FABP expression increased triacylglycerol and cholesteryl ester mass (nmol/mg protein) by 63% and 25%, respectively. Phospholipid mass was unchanged in I-FABP expressing cells. The initial [3H]oleic acid esterification into triacylglycerols and cholesteryl esters was increased 3.9- and 2.5-fold in I-FABP expressing cells. Although, the initial [3H]oleic acid esterification into total phospholipids was unchanged, within the phospholipid fraction the initial [3H]oleic acid esterification into phosphatidylethanolamine was increased 70% and decreased 50% in phosphatidylcholine in I-FABP expressing cells. These observed differences suggest a distinct role for I-FABP in stimulating net formation, and not just turnover, of triacylglycerides and cholesteryl esters in transfected L-cell fibroblasts.