Diverse activity of human secretory phospholipases A2 on the migration of human vascular smooth muscle cells

OBJECTIVE

Investigation of the diversity of human secretory phospholipases A2 (sPLA2) on the migration of human vascular smooth muscle cells (VSMC).

MATERIAL

We investigated the impact of sPLA2 IIA, V, and X and of oleic acid, linoleic acid and lysophosphatidylcholine on the migration of human VSMC.

METHODS

Recombinant human sPLA2's and Boyden's chamber method were applied.

RESULTS

sPLA2, IIA but not V or X enhanced migration of VSMC in a dose/time dependent manner. Oleic and linoleic acids, and lysophosphatidylcholine markedly enhanced migration.

CONCLUSIONS

These results imply that sPLA2 IIA, which is known to be present in the arterial wall in the vicinity of VSMC, as well as products of lipid hydrolysis induced by sPLA2, enhance the migration of VSMC, and thus may contribute to atherogenic process.

A comparative study of the lipids of chylomicron membrane and fat core and of the lymph serum of dogs

Thoracic lymph was collected from 13 dogs fed corn oil and butterfat. The chylomicrons were isolated by centrifugation. The lipid composition of the fat core and the membrane of the chylomicron was compared to that of the surrounding lymph serum. The fat cores contained 90-96% triglyceride, 0.7-1.9% free cholesterol, 0.2-0.5% steryl ester, 0.9-3.5% free fatty acid and 1.4-6.1% diglyceride, but no phospholipid. The lipids of the membranes contained 58-75% phospholipid, 20-35% triglyceride, 2-5% free cholesterol, 1-2% free fatty acid, and 2-3% diglyceride, but little or no steryl ester. The membrane phospholipids were made up of 70-90% lecithin, 5-20% phosphatidyl ethanolamine, and 1-3% each of lysolecithin and sphingomyelin. The lymph serum contained 24-47% of total lipid as phospholipid, of which 70-92% was lecithin; the phosphatidyl ethanolamine, lysolecithin and sphingomyelin also present contributed 1-10% each. The neutral lipids of the lymph serum contained 49-75% triglyceride, 2-15% free cholesterol, 6-23% esterified cholesterol, 10-33% free fatty acid and 1-6% diglyceride.Alterations in dietary fat, or plant sterol supplementation led to lesser changes in the lipids of the chylomicron membranes than in the lipids of any other lymph fraction. The least variation was seen in the phospholipids.

A comparative study of the lipids of globule membrane and fat core and of the milk serum of cows

Nine samples of fresh raw cow's milk were separated into fat globules and milk serum by centrifugation. After destabilization by freezing and thawing, the milk fat globules were resolved into membranes and fat cores. The lipid composition of these structures was compared to that of the surrounding milk serum. Of the total milk fat, 95-98% was in the fat cores, 0.5-1% in the globule membranes and the rest (1.5-4%) in the milk serum. The fat cores contained 88-93% triglyceride, 5.2-9.8% diglyceride, 1.5-7.3% free fatty acid and 0.2-0.4% cholesterol, but no phospholipid. The lipids of the membrane contained 21-44% phospholipid, made up of about equal proportions of phosphatidyl ethanolamine, phosphatidyl choline, and sphingomyelin. The other lipids of the membrane (56-79%) consisted of 83-88% triglyceride, 5.1-10.7% diglyceride, 1-5.1% free fatty acid and 0.4-1.9% cholesterol. The milk serum contained 30-45% phospholipid divided about equally among phosphatidyl ethanolamine, phosphatidyl choline and sphingomyelin. The rest (55-70%) of the milk serum lipids was made up of 71-83% triglycerides, 4.3-10.1% diglycerides, 8.7-15.7% free fatty acids, and 1.2-8.4% cholesterol. Corresponding phospholipid classes of milk serum and globule membranes had identical fatty acid compositions. The triglycerides and diglycerides of the globule membranes possessed increased proportions of palmitic and stearic acids in comparison to the glycerides of the fat cores.

Hydrolysis of minor glycerophospholipids of plasma lipoproteins by human group IIA, V and X secretory phospholipases A2

We investigated the hydrolysis of the minor glycerophospholipids of human HDL(3), total HDL and LDL using human group IIA, V and X secretory phospholipases A(2) (sPLA(2)s). For this purpose we employed the enzyme and substrate concentrations and incubation times optimized for hydrolysis of phosphatidylcholine (PtdCho), the major glycerophospholipid of plasma lipoproteins. In contrast to PtdCho, which was readily hydrolyzed by group V and X sPLA(2)s, and to a lesser extent by group IIA sPLA(2), the minor ethanolamine, inositol and serine glycerophospholipids exhibited marked resistance to hydrolysis by all three sPLA(2)s. Thus, when PtdCho was hydrolyzed about 80%, the ethanolamine and inositol glycerophospholipids reached a maximum of 40% hydrolysis. The hydrolysis of phosphatidylserine (PtdSer), which was examined to a more limited extent, showed similar resistance to group IIA, V and X sPLA(2)s, although the group V sPLA(2) attacked it more readily than group X sPLA(2) (52% versus 39% hydrolysis, respectively). Surprisingly, the group IIA sPLA(2) hydrolysis remained minimal at 10-15% for all minor glycerophospholipids, and was of the order seen for the PtdCho hydrolysis by group IIA sPLA(2) at the 4-h digestion time. All three enzymes attacked the oligo- and polyenoic species in proportion to their mole percentage in the lipoproteins, although there were exceptions. There was evidence of a more rapid destruction of the palmitoyl compared to the stearoyl arachidonoyl glycerophospholipids. Overall, the characteristics of hydrolysis of the molecular species of the lipoprotein-bound diradyl GroPEtn, GroPIns and GroPSer by group V and X sPLA(2)s differed significantly from those observed with lipoprotein-bound PtdCho. As a result, the acidic inositol and serine glycerophospholipids accumulated in the digestion residues of both LDL and HDL, and presumably increased the acidity of the residual particles. An accumulation of the ethanolamine glycerophospholipids in the sPLA(2) digestion residues also had not been previously reported. These results further emphasize the diversity in the enzymatic activity of the group IIA, V and X sPLA(2)s. Since these sPLA(2)s possess comparable tissue distribution, their combined activity may exacerbate their known proinflammatory and proatherosclerotic function.

Differential hydrolysis of molecular species of lipoprotein phosphatidylcholine by groups IIA, V and X secretory phospholipases A2

Human groups IIA, V and X secretory phospholipases A2 (sPLA2s) were incubated with human HDL3, total HDL and LDL over a range of enzyme and substrate concentrations and exposure times. The residual phosphatidylcholines (PtdChos) were assayed by high performance liquid chromatography with electrospray ionization mass spectrometry (LC/ESI-MS). The enzymes varied markedly in their rates of hydrolysis of the different molecular species and in the production of lysoPtdCho. The sPLA2s were compared at a concentration of 1 microg/ml and an incubation time of 4 h, when all three enzymes showed significant activity. The groups V and X sPLA2 were up to 20 times more reactive than group IIA sPLA2. Group X sPLA2 hydrolyzed arachidonate and linoleate containing species preferentially, while group V hydrolyzed the linoleates in preference to polyunsaturates. In all instances, the arachidonoyl and linoleoyl palmitates were hydrolyzed in preference to the corresponding stearates by group X sPLA2. The group IIA enzyme appeared to hydrolyze randomly all diacyl molecular species. The minor alkylacyl and alkenylacyl glycerophosphocholines (GroPChos) were poor substrates for groups V and X sPLA2s and these phospholipids tended to accumulate. The present study demonstrates a preferential release of arachidonate from plasma lipoprotein PtdCho by group X sPLA2, as well as a relative resistance of polyunsaturated PtdChos to hydrolysis by group V enzyme, which had not been previously documented. The use of lipoprotein PtdCho as substrate with LC/ESI-MS identification of hydrolyzed molecular species eliminates much of the uncertainty about sPLA2 specificity arising from past analyses of fatty acid release from unknown or ill-defined sources.

Regiospecific determination of short-chain triacylglycerols in butterfat by normal-phase HPLC with on-line electrospray-tandem mass spectrometry

This study uses normal-phase HPLC with on-line positive ion electrospray mass spectrometry (ESI-MS) to obtain quantitative compositional data on both synthetic and butterfat short-chain TAG. The product ion tandem MS of standards averaged 11.1 times lower in abundance of the ion formed by cleavage of FA from the sn-2-position for the pairs of regioisomers in the TAG classes: L/L/S-L/S/L and L/S/S-S/L/S, where L denotes long and S short acyl chain (C2-C6). The molar correction factors, determined for 42 regioisomeric pairs of short-chain TAG of 20 randomized mixture of standards, differed by 1.4-80% as the ratios varied between 0.217 and 5.847. Butterfat TAG were resolved into four fractions on short flash chromatography grade silica gel columns. Pairs of regioisomers in the TAG classes L/S/S-S/L/S with predominance of L/S/S isomers and the sole regioisomers in the TAG classes L/L(M)/S were identified by tandem MS, where M denotes either 8:0 or 10:0 acyl chain. The total proportion of L/L(M)/S isomers was estimated at 34.7 and that of L/S/S-S/L/S at 1.0 mol%, including a small proportion of S/S/S. In contrast to previous work, the present data indicate the presence of a small proportion of butyric and caproic acids in the sn-1-position. The overall distribution of the FA in the short-chain TAG of butterfat, calculated from direct MS measurements, was consistent with the results of indirect determinations based on stereospecific analyses of total butterfat.

Analysis of diastereomeric DAG naphthylethylurethanes by normal-phase HPLC with on-line electrospray MS

Normal-phase HPLC resolution of sn-1,2(2,3)- and x-1,3-DAG generated by partial Grignard degradation from natural TAG was carried out with both (R)-(-) and (S)-(+)-1-(1-naphthyl)ethylurethane derivatives. The diastereomeric sn-1,2- and sn-2,3-DAG derivatives were resolved using two Supelcosil LC-Si (5 microm, 25 cm x 4.6 mm i.d.) columns in series and an isocratic elution with 0.37% isopropanol in hexane at a flow rate of 0.7 mL/min. The DAG were detected by UV absorption at 280 nm and were identified by electrospray ionization MS in the positive ion mode following postcolumn addition of chloroform/methanol/30% ammonium hydroxide (75:24.5:0.5, by vol) at 0.6 mL/min. Application of the method to a stereospecific analysis of the molecular species of TAG of rat VLDL showed that the TAG composition of VLDL circulating under basal conditions differs markedly from that of VLDL secreted by the liver during inhibition of serum lipases. The inhibition of serum lipases resulted in a significant proportional decrease in 16:0 and PUFA and an increase in 18:0 and oligoenoic FA in the sn-1-position, whereas the FA compositions in the sn-2- and sn-3-positions were much less affected.

Software algorithm for automatic interpretation of mass spectra of glycerolipids

A new software algorithm for automatic interpretation of mass spectra of glycerolipids has been developed. The algorithm utilizes a user-specified list of parameters needed to process the spectra. The compounds in mass spectra are identified according to range of measured m/z values, after which the spectra are automatically corrected by the content of naturally occurring isotopes and ion intensities of identified compounds by response correction factors. Automatic processing of the spectra was shown to be accurate and reliable by testing with numerous spectra of glycerophospholipids obtained by liquid chromatography/electrospray ionization mass spectrometry and by comparing the results with manual interpretation of the spectra. If quantitative analysis using internal standards is performed, all the identified compounds in the sample are quantified automatically. A dilution factor may be defined for each sample and is applied to correct the alterations in sample concentration during sample preparation. Processing of several replicate spectra simultaneously produces mean results with standard deviations. The software may also be used to subtract the results of two analyses and to calculate the mean result of replicate subtractions. The algorithm was shown to save time and labor in repetitive processing of mass spectra of similar type. It may be applied to processing of spectra obtained by various mass spectrometric methods.

Analysis of molecular species of peroxide adducts of triacylglycerols following treatment of corn oil with tert-butyl hydroperoxide

We recently demonstrated that exposure of synthetic mono- and diunsaturated triacylglycerols to tert-butylhydroperoxide (TBHP) leads to formation of stable adducts of the oxidizing agent and the unsaturated esters (Sjövall, O., Kuksis, A., and Kallio, H., Reversed Phase High-Performance Liquid Chromatographic Separation of tert-Butyl Hydroperoxide Oxidation Products of Unsaturated Triacylglycerols, J. Chromatogr. A 905, 119-132, 2001). In the present study we isolated and identified the TBHP adducts of corn oil triacylglycerols. The much wider range of molecular species available in the corn oil permitted us to demonstrate that the yield of the adducts varies with the degree of unsaturation of the triacylglycerol. The highest yields were obtained for the linoleate (20%, of linoleoyl-containing residual triacylglycerols) and the lowest ones for the oleate (5% of oleoyl-containing residual triacylglycerols) triacylglycerols, whereas the saturated triacylglycerols did not give TBHP adducts in readily detectable amounts. Normal-phase thin-layer chromatography along with reversed-phase high-performance liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization was used to isolate and separate the major molecular species of polyunsaturated triacylglycerols and corresponding TBHP adducts. As an extreme example, the dilinoleoylmonooleoylglycerol was identified as the mono-, di-, tri-, tetra-, and penta-TBHP adduct. LC/MS with electrospray ionization at elevated capillary exit voltage (pseudo tandem mass spectrometry) was used to confirm structures of the [M-RCOOH]+ ions and the absence of TBHP adducts of [M-RCOOH]+. It is concluded that stable adduct formation is an unavoidable complication of preparation of oxotriacylglycerols by oxidation with concentrated TBHP solutions and care must be taken to resolve the adducts from the desired oxidation product.

Plasma non-cholesterol sterols

Increased levels of plasma sterols other than cholesterol can serve as markers for abnormalities in lipid metabolism associated with clinical disease. Premature atherosclerosis and xanthomatosis occur in two rare lipid storage diseases, Cerebrotendinous xanthomatosis (CTX) and sitosterolemia. In CTX, cholestanol is present in all tissues. In sitosterolemia, dietary campesterol and sitosterol accumulate in plasma and red blood cells. Plasma accumulation of oxo-sterols is associated with inhibition of bile acid synthesis and other abnormalities in plasma lipid metabolism. Inhibition of cholesterol biosynthesis is associated with plasma appearance of precursor sterols. The increases in non-cholesterol sterols, while highly significant, represent only minor changes in plasma sterols, which require capillary gas-liquid chromatography and MS for effective detection, identification and quantification.

Regiospecific analysis of neutral ether lipids by liquid chromatography/electrospray ionization/single quadrupole mass spectrometry: validation with synthetic compounds

A reversed-phase high-performance liquid chromatography (HPLC) method with on-line electrospray ionization/collision-induced dissociation/mass spectrometry (ESI/CID/MS) is presented for the regiospecific analysis of synthetic reference compounds of neutral ether lipids. The reference compounds were characterized by chromatographic retention times, full mass spectra, and fragmentation patterns as an aid to clarify the regiospecificity of ether lipids from natural sources. The results clearly show that single quadrupole mass spectroscopic analysis may elucidate the regiospecific structure of neutral ether lipids. Ether lipid reference compounds were characterized by five to six major ions in the positive ion mode. The 1-O-alkyl-sn-glycerols were analyzed as the diacetoyl derivative, and showed the [M - acetoyl](+) ion as an important diagnostic ion. The diagnostic ions of directly analyzed 1-O-alkyl-2-acyl-sn-glycerols and 1-O-alkyl-3-acyl-sn-glycerols were the [M - alkyl](+), [M + H - H(2)O](+) and [M + H](+) ions. Regiospecific characterization of the fatty acid position was evident from the relative ion intensities, as the sn-2 species had relatively high [M + H](+) ion intensities compared with [M + H - H(2)O](+), whereas the reverse situation characterized the sn-3 species. Furthermore, corresponding sn-2 and sn-3 species were separated by the chromatographic system. However, loss of water was promoted as fatty acid unsaturation was raised, which may complicate interpretation of the mass spectra. The diagnostic ions of directly analyzed 1-O-alkyl-2,3-diacyl-sn-glycerols were the [M - alkyl](+), [M - sn-2-acyl](+) and [M - sn-3-acyl](+) ions. Regiospecific characterization of the fatty acid identity and position was evident from the relative ion intensities, as fragmentation of the sn-2 fatty acids was preferred to the sn-3 fatty acids; however, loss of fatty acids was also promoted by higher degrees of unsaturation. Therefore, both structural and positional effects of the fatty acids affect the spectra of the neutral ether lipids. Fragmentation patterns and optimal capillary exit voltages are suggested for each neutral ether lipid class. The present study demonstrates that reversed-phase HPLC and positive ion ESI/CID/MS provide direct and unambiguous information about the configuration and identity of molecular species in neutral 1-O-alkyl-sn-glycerol classes.

Apolipoprotein A-I promotes the formation of phosphatidylcholine core aldehydes that are hydrolyzed by paraoxonase (PON-1) during high density lipoprotein oxidation with a peroxynitrite donor

High density lipoprotein (HDL) is rich in polyunsaturated phospholipids that are sensitive to oxidation. However, the effect of apolipoprotein A-I and paraoxonase-1 (PON-1) on phosphatidylcholine oxidation products has not been identified. We subjected native HDL, trypsinized HDL, and HDL lipid suspensions to oxidation by the peroxynitrite donor, 3-morpholinosydnonimine. HDL had a basal level of phosphatidylcholine mono- and di-hydroperoxides that increased to a greater extent in HDL, compared with either trypsinized HDL or HDL lipid alone. Phosphatidylcholine core aldehydes, which were present in small amounts, increased 10-fold during oxidation of native HDL, compared with trypsinized HDL (p = 0.004), and 4-fold compared with HDL lipid suspensions (p = 0.0021). In addition, the content of lysophosphatidylcholine increased 300% during oxidation of native HDL, but only 80 and 25%, respectively, during oxidation of trypsinized HDL and HDL lipid suspensions. Phosphatidylcholine isoprostanes accumulated in comparable amounts during the oxidation of all three preparations. Incubation of apolipoprotein A-I with 1-palmitoyl-2-linoleoyl glycerophosphocholine proteoliposomes in the presence of 3-morpholinosydnonimine or apoAI with phosphatidylcholine hydroperoxides resulted in a significant increase in phosphatidylcholine core aldehydes with no formation of lysophosphatidylcholine. We propose that apolipoprotein A-I catalyzes a one-electron oxidation of alkoxyl radicals. Purified PON-1 hydrolyzed phosphatidylcholine core aldehydes to lysophosphatidylcholine. We conclude that, upon HDL oxidation with peroxynitrite, apolipoprotein AI increases the formation of phosphatidylcholine core aldehydes that are subsequently hydrolyzed by PON1.

Determination of stereochemical configuration of the glycerol moieties in glycoglycerolipids by chiral phase high-performance liquid chromatography

This study reports a simple and sensitive method for determining the absolute configuration of the glycerol moieties in glycoglycerolipids. The method is based on chiral phase high-performance liquid chromatography (HPLC) separations of enantiomeric di- and monoacylglycerols released from glycosyldi- and monoacylglycerols, respectively, by periodate oxidation followed by hydrazinolysis. The released di- and monoacylglycerols were chromatographed as their 3,5-dinitrophenylurethane (3,5-DNPU) and bis(3,5-DNPU) derivatives, respectively. The derivatives were separated on two chiral phases of opposite configuration, (R)- and (S)-1-(1-naphthyl)ethylamine polymers for diacylglycerols and N-(R)- -(1-naphthyl)ethylaminocarbonyl-(S)-valine and N-(S)-1 -(1-naphthyl)ethylamino-carbonyl-(R)-valine for monoacylglycerols. Clear enantiomer separations, which permit the assignment of the glycerol configuration, were achieved for sn-1,2(2,3)-diacyl- and sn-1(3)-monoacylglycerols generated from linseed oil triacylglycerols by partial Grignard degradation on all the chiral stationary phases employed. Using the method, we have determined the glycerol configuration in the glycosyldiacylglycerols (monogalactosyl-, digalactosyl-, and sulfquinovosyldiacylglycerols) and glycosylmonoacylglycerols (monogalactosyl-, digalactosyl-, and sulfoquinovosylmonoacylglycerols) isolated from spinach leaves and the coralline red alga Corallina pilulifera. The results clearly showed that the glycerol moieties in all the glycoglycerolipids examined have S-configuration (sn-1,2-diacyl- and sn-1-monoacylglycerols). The new method demonstrates that chiral phase HPLC provides unambiguous information on the configuration of the glycerol backbone in natural glycosyldi- and monoacylglycerols, and that the two-step liberation of the free acylglycerols does not compromise glycerol chirality.

Mitogenic effect of lipoproteins on human vascular smooth muscle cells: the impact of hydrolysis by gr II A phospholipase A(2)

Multifactorial interaction among lipoproteins, vascular wall cells, and inflammatory mediators has been recognized as the basis of atherogenesis. In the arterial wall high-density lipoprotein (HDL) and human secretory phospholipase A(2) (sPLA(2)) colocalize with vascular smooth muscle cells and concentrate in the atherosclerotic lesions. It has been shown that gr IIA sPLA(2) hydrolyzes lipoproteins, altering their structure and releasing active agents such as lyso-phosphatidylcholine (PtdCho) and free fatty acids. We investigated the impact of normal HDL(3) (NHDL(3)), acute phase HDL(3) (APHDL(3)), and low-density lipoprotein (LDL), both unhydrolyzed and sPLA(2)-hydrolyzed, and some products of hydrolysis, such as lyso-PtdCho, oleic and linoleic acid, on [(3)H] thymidine incorporation by DNA of cultured human vascular smooth muscle cells (VSMC). NHDL(3) markedly enhanced mitogenic activity of VSMC in a dose- and time-dependent manner. Doubling of thymidine incorporation was usually achieved by 40 microg/ml of NHDL(3) after 4 hours of incubation. APHDL(3) had invariably a stronger inducing effect on the mitogenic activity than NHDL(3); 40 microg/ml more than tripled [(3)H] thymidine incorporation after 4 hours of incubation. NHDL(3) preincubated with human apo serum amyloid A apolipoprotein-induced higher mitogenic activity in VSMC than NHDL(3) alone. Hydrolysis of NHDL(3), APHDL(3), or LDL by gr IIA sPLA(2) markedly enhanced mitogenic activity of VSMC as compared with unhydrolyzed lipoproteins. sPLA(2) concentrations that can be found in atherosclerotic vascular walls markedly enhanced lipoprotein-induced mitogenic activity of VSMC. sPLA(2) per se did not affect thymidine incorporation and VSMC did not release sPLA(2) into the medium. There was no evidence for hydrolysis of the wall of VSMC by gr IIA sPLA(2). The presence of the products of hydrolysis of lipoproteins such as oleic and linoleic acids and lyso-PtdCho or their combinations with NHDL(3) explains in part markedly enhanced mitogenic activity of VSMC. It is conceivable that sPLA(2,) which is known to colocalize with lipoproteins in the vascular wall in the domain of VSMC, is capable of induction of the mitogenic activity in these cells in vivo and should be considered as a proatherogenic enzyme.

Reversed-phase high-performance liquid chromatographic separation of tert.-butyl hydroperoxide oxidation products of unsaturated triacylglycerols

Triacylglycerols containing monounsaturated fatty acids are known to be relatively resistant to autoxidation and require long periods of exposure to dilute oxidants. Use of concentrated solutions of synthetic hydroperoxides, however, yields in addition to the hydroperoxides also unidentified oxidation by-products. In the present study we have employed synthetic triacylglycerols containing one (18:0/18:1/18:0 and 18:1/16:0/16:0) and two (18:0/18:0/18:2 and 18:1/18:1/18:0) double bonds per molecule to reinvestigate the formation of oxotriacylglycerols using tert.-butyl hydroperoxide as an oxidant. Reversed-phase HPLC was used to separate and tentatively identify the oxidation products based on relative retention times of standards and the estimated elution factors for functional groups and their positional distribution. Hydroperoxides, diepoxides and hydroxides were the major components of the oxidation mixtures (50-95% of total). Previously unidentified peroxide-bridged tert.-butyl adducts were present in significant amounts (5-50% of total oxidation products) in all preparations. In several instances more than one functional group was present on a single fatty chain. The tentative reversed-phase chromatographic identification of the adducts was confirmed by determination of the molecular mass of each component by on-line LC with electrospray MS. The oxidation products were quantified by HPLC with light scattering detection.

High-performance liquid chromatographic resolution of reverse isomers of 1,2-diacyl-rac-glycerols as 3,5-dinitrophenylurethanes

The resolution of reverse isomers remains a major unsolved problem in glycerolipid chromatography. We have investigated the separation of the reverse isomers of 1,2-diacyl-rac-glycerols under a variety of high-performance liquid chromatography (HPLC) conditions. The reverse isomers of diacylglycerols having various pairs of acyl groups including short and highly unsaturated chains, which were prepared by partial Grignard degradation of the corresponding triacylglycerols, were chromatographed as 3,5-dinitrophenylurethanes. Excellent resolution was achieved for the reverse isomers of very different pairs of acyl groups, such as acetate-palmitate and docosahexaenoate-palmitate, by chiral-phase HPLC on columns containing (R)- and (S)-1-(1-naphthyl)ethylamine polymeric phases, reversed-phase HPLC on a highly efficient C18 column (4 microm particle size) and silver ion HPLC on a silver loaded cation-exchange column. The chiral-phase HPLC also permitted complete enantiomer resolution for all the reverse isomers examined. No satisfactory resolution by any of the HPLC methods, however, was obtained for the reverse isomers possessing minor differences in chain lengths and degree of unsaturation, such as laurate-palmitate and oleate-linoleate. The limitations of resolution and characteristics of elution are described.

The effect of low alpha-linolenic acid diet on glycerophospholipid molecular species in guinea pig brain

The changes in guinea pig brain (cerebrum) glycerophospholipid molecular species resulting from a low-alpha linolenic acid (ALA) diet are described. Two groups of six guinea pigs were raised from birth to 16 wk of age on either an n-3 deficient diet containing 0.01 g ALA/100 g diet or n-3 sufficient diet containing 0.71 g ALA/100 g diet. Molecular species of diradyl glycerophosphoethanolamine (GroPEtn), glycerophosphocholine, glycerophosphoserine, and glycerophosphoinositol were analyzed by high-performance liquid chromatography with on-line electrospray ionization mass spectrometry (HPLC/ESI/MS). Alkenylacyl GroPEtn species were determined by comparing spectra before and after mild acid treatment while diacyl- and alkylacyl species were distinguished by HPLC/ESI/MS. The proportions of phospholipid classes and of the diradyl GroPEtn subclasses were not altered by diet changes. The main polyunsaturated molecular species of diradyl GroPEtn subclasses and of phosphatidyl choline and phosphatidylserine (PtdSer) contained 16:0, 18:0, or 18:1 in combination with docosahexaenoic acid (DHA, 22:6n-3), docosapentaenoic (DPA, 22:5n-6), or arachidonic acid (ARA, 20:4n-6). A significant proportion of DPA containing species were present in both diet groups, but in n-3 fatty acid deficiency, the proportion of DPA increased and DHA was primarily replaced by DPA. The combined value of main DHA and DPA containing species in the n3 deficient group ranged from 91-111% when compared with the n-3 sufficient group, indicating a nearly quantitative replacement. The n-3 fatty acid deficiency did not lower the content of ARA containing molecular species of PtdSer of the guinea pig brain as reported previously for the rat brain. The molecular species of phosphatidylinositol were not altered by n-3 fatty acid deficiency. The present data show that the main consequence of a low ALA diet is the preferential replacement of DHA-containing molecular species by DPA-containing molecular species in alkenylacyl- and diacyl GroPEtn and PtdSer of guinea pig brain.

Comparative analysis of lipid composition of normal and acute-phase high density lipoproteins

In the acute-phase response and in diseases with prolonged acute phases, normal HDL (NHDL) is converted into acute-phase HDL (APHDL) and becomes proinflammatory and unable to protect LDL against oxidative modification. Earlier work had demonstrated that these changes are associated with alterations in apolipoprotein composition and enzymatic activity of APHDL, but the effect of the acute-phase condition on the lipid composition of APHDL had remained obscure. The present study shows marked quantitative differences in lipid composition between NHDL and APHDL. Specifically, APHDL contained 25% less total lipid per milligram of protein. Up to 50% of cholesteryl ester in the lipid core of APHDL was replaced by triacylglycerol; however, the total phospholipid/total neutral lipid ratios were the same as in NHDL, both lipoproteins giving similar calculated lipid core radii. Furthermore, the phosphatidylcholine/sphingomyelin ratio in APHDL was nearly double that in NHDL, indicating a relative loss of sphingomyelin. A decrease was also seen in diacyl and alkenylacyl glycerophosphatidylethanolamine as well as in phosphatidylinositol of APHDL when compared with NHDL. APHDL contained proportionally more saturated and less polyunsaturated and isoprostane-containing species of phosphatidylcholine, as well as more saturated than unsaturated cholesteryl esters. APHDL also contained significantly more free fatty acids, lysophosphatidylcholine, and free cholesterol. These changes in the lipid composition of HDL are consistent with the alterations in the apoprotein composition and enzymatic activity of APHDL and indicate proinflammatory and proatherogenic roles for APHDL.

Glucosylated glycerophosphoethanolamines are the major LDL glycation products and increase LDL susceptibility to oxidation: evidence of their presence in atherosclerotic lesions

Glycation of both protein and lipid components is believed to be involved in LDL oxidation. However, the relative importance of lipid and protein glycation in the oxidation process has not been established, and products of lipid glycation have not been isolated. Using glucosylated phosphatidylethanolamine (Glc PtdEtn) prepared synthetically, we have identified glycated diacyl and alkenylacyl species among the ethanolamine phospholipids in LDL. Accumulation of these glycation products in LDL incubated with glucose showed a time- and glucose concentration-dependent increase. LDL specifically enriched with Glc PtdEtn (25 nmol/mg protein) showed increased susceptibility to lipid oxidation when dialyzed against a 5-micromol/L Cu(2+) solution. The presence of this glucosylated lipid resulted in a 5-fold increase in production of phospholipid-bound hydroperoxides and 4-fold increase in phospholipid-bound aldehydes. Inclusion of glucosylated phosphatidylethanolamine in the surface lipid monolayer of the LDL resulted in rapid loss of polyunsaturated cholesteryl esters from the interior of the particle during oxidation. Glycated ethanolamine phospholipids were also isolated and identified from atherosclerotic plaques collected from both diabetic and nondiabetic subjects. The present findings provide direct evidence for the previously proposed causative effect of lipid glycation on LDL oxidation.

Glycated phosphatidylethanolamine promotes macrophage uptake of low density lipoprotein and accumulation of cholesteryl esters and triacylglycerols

Non-enzymatic glycation of low density lipoprotein (LDL) has been suggested to be responsible for the increase in susceptibility to atherogenesis of diabetic individuals. Although the association of lipid glycation with this process has been investigated, the effect of specific lipid glycation products on LDL metabolism has not been addressed. This study reports that glucosylated phosphatidylethanolamine (Glc-PtdEtn), the major LDL lipid glycation product, promotes LDL uptake and cholesteryl ester (CE) and triacylglycerol (TG) accumulation by THP-1 macrophages. Incubation of THP-1 macrophages at a concentration of 100 micrograms/ml protein LDL specifically enriched (10 nmol/mg LDL protein) with synthetically prepared Glc-PtdEtn resulted in a significant increase in CE and TG accumulation when compared with LDL enriched in non-glucosylated PtdEtn. After a 24-h incubation with LDL containing Glc-PtdEtn, the macrophages contained 2-fold higher CE (10.11 +/- 1.54 micrograms/mg cell protein) and TG (285.32 +/- 4.38 micrograms/mg cell protein) compared with LDL specifically enriched in non-glucosylated PtdEtn (CE, 3.97 +/- 0.95, p < 0.01 and TG, 185.57 +/- 3.58 micrograms/mg cell protein, p < 0.01). The corresponding values obtained with LDL containing glycated protein and lipid were similar to those of LDL containing Glc-PtdEtn (CE, 11.9 +/- 1.35 and TG, 280.78 +/- 3.98 micrograms/mg cell protein). The accumulation of both neutral lipids was further significantly increased by incubating the macrophages with Glc-PtdEtn LDL exposed to copper oxidation. By utilizing the fluorescent probe, 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate (DiI), a 1.6-fold increase was seen in Glc-PtdEtn + LDL uptake when compared with control LDL. Competition studies revealed that acetylated LDL is not a good competitor for DiI Glc-PtdEtn LDL (5-6% inhibition), whereas glycated LDL gave an 80% inhibition, and LDL + Glc-PtdEtn gave 93% inhibition of uptake by macrophages. These results indicate that glucosylation of PtdEtn in LDL accounts for the entire effect of LDL glycation on macrophage uptake and CE and TG accumulation and, therefore, the increased atherogenic potential of LDL in hyperglycemia.

Rapid complexing of oxoacylglycerols with amino acids, peptides and aminophospholipids

We prepared model Schiff bases from 2-[9-oxo]nonanoyl glycerol (2-MAG-ALD) and various amino compounds. 2-MAG-ALD was obtained by pancreatic lipase hydrolysis of trioleoyl glycerol and reductive ozonolysis of the resulting 2-monooleoyl glycerol. The reaction products were purified by thin-layer chromatography. Schiff bases were synthesized in greater than 50% yield by reacting 2-MAG-ALD with twofold molar excess of valine, Nalpha-acetyl-L-lysine methyl ester and the tripeptides glycyl-glycyl-glycine, glycyl-glycyl-histidine, and glycyl-histidyl-lysine in aqueous methanol and with 1-palmitoyl-2-stearoyl glycerophosphoethanolamine (PE) in chloroform/methanol for 16 h at room temperature. Prior to analysis the bases were reduced with sodium cyanoborohydride in methanol for 30 min at 4 degrees C. Reaction products were analyzed by high-performance liquid chromatography/electrospray ionization/mass spectrometry (HPLC/ESI/MS). Reduced Schiff bases of 2-MAG-ALD with PE and amino acids were analyzed by normal-phase HPLC/ESI/MS and those with peptides by reversed-phase HPLC/ESI/MS. Single adducts were obtained in all cases and both the alpha-amino group of valine and the epsilon-amino group of Nalpha-acetyl-L-lysine methyl ester were reactive. Molecular ions of reaction products were the only detected ions in the negative ionization mode, whereas in the positive ion mode sodiated molecular ions were also detected. The present study suggests that 2-MAG-ALD may form Schiff base adducts with amino compounds in other aqueous media, such as the intestinal lumen and in the hydrophobic environment of cell membranes.

Lipoproteins are substrates for human secretory group IIA phospholipase A2: preferential hydrolysis of acute phase HDL

Group IIA secretory phospholipase A2 is an acute phase enzyme, co-expressed with serum amyloid A protein. Both are present in atherosclerotic lesions. We report that human normal and acute phase high density lipoproteins and low density lipoprotein are effective substrates for human group IIA phospholipase A2. The enzyme hydrolyzed choline and ethanolamine glycerophospholipids at the sn -2 position resulting in an accumulation of the corresponding lysophospholipids, including the unhydrolyzed alkyl and alkenyl ether derivatives. The hydrolysis of acute phase high density lipoprotein was 2- to 3-fold more rapid and intensive than of normal high density lipoprotein. The hydrolysis of lipoproteins was noted at enzyme concentration as low as 0.05 microgram/mg protein, which was within the range observed in the circulation in acute and chronic inflammatory diseases. The enzyme hydrolyzed the different molecular species of the residual glycerophospholipids in proportion to their mass, showing no preference for the release of arachidonic acid. Group IIA phospholipase A2 preferentially attacked the hydroxy and hydroperoxy linoleates and possibly other oxygenated fatty acids, which were released from the glycerophospholipids at early times of incubation. There was no effect on the content or molecular species composition of the sphingomyelins or neutral lipids of the lipoproteins. In conclusion, human plasma lipoproteins are the first reported natural biological substrates for human group IIA phospholipase A2. The enhanced hydrolysis of acute phase high density lipoproteins is probably due to its association with serum amyloid A protein, which enhances the activity of the enzyme and may promote its penetration to the lipid monolayer. As sPLA2-induced hydrolysis of the lipoproteins leads to accumulation of lysophosphatidylcholine and potentially toxic oxygenated fatty acids, overexpression of this enzyme may be proatherogenic.

Fas-induced apoptosis in rat thecal/interstitial cells signals through sphingomyelin-ceramide pathway

Of the ovarian follicles that develop during reproductive life, more than 99% do not ovulate and are eliminated from the ovary by follicular atresia. Atresia is achieved by the self destruction of thecal and granulosa cells that comprise the follicle, by the process of apoptosis. The objective of this study was to determine if activation of the Fas receptor could enact apoptosis of thecal cells, and to explore the signal transduction pathway involved. Primary cultures of thecal/interstitial cells isolated from immature rat ovaries were treated with anti-Fas monoclonal antibody (anti-Fas mAb) (2.5 microg/ml). Morphological changes indicative of apoptosis, such as, condensation of chromatin, nucleoplasmic segmentation and formation of apoptotic bodies, were observed by fluorescence microscopy following nucleic acid staining with Hoechst 33342 dye and propidium iodide. DNA analysis of cells after 10 h of treatment with anti-Fas mAb showed that DNA had been cleaved into fragments that were multiples of 180-300 bp in length; biochemical evidence of apoptosis. The sphingomyelin (N-acylsphingosine-1-phosphocholine, SM) pathway that is initiated by the hydrolysis of SM to ceramide (Cer) has been shown previously to be activated by the Fas ligand/receptor system in a number of different cell types. It was therefore possible that the intracellular transduction of Fas receptor activation of thecal/interstitial cells could also involve the SM-Cer pathway. Hence, we have measured the SM levels in control and treated thecal/interstitial cells. Extracts of untreated thecal/interstitial cells contained six major species of SM identified as d18:1/16:0 (sphingosine base/fatty acid), d18:1/18:0, d18:1/20:0, d18:1/22:0, d18:1/24:1, d18:1/24:0 by normal phase high performance liquid chromatography interfaced with electrospray mass spectrometry. Treatment with anti-Fas mAb (2.5 microg/ml) for 30 min caused significant hydrolysis of only two of the SM species, d18:1/16:0 and d18:1/24:1. The involvement of ceramide, the central lipid in this phospholipid second messenger system, was tested using the synthetic cell permeable Cer analog (N-acetyl-N-sphingosine, C2-Cer). C2-Cer (10 microM). This analog induced both morphological and biochemical changes in thecal/interstitial cells, that were characteristic of apoptosis, and the same as those induced by anti-Fas mAb. C2-dihydroceramide (10 microM), an inactive analog of C2-Cer, failed to induce apoptosis of thecal/interstitial cells. In conclusion, the sphingomyelin-ceramide cycle that can lead to cell suicide by apoptosis is functional and activated through the Fas ligand/receptor signal transduction pathway, not only in the immune system, but also in thecal/interstitial cells of the ovarian follicle.

Chronic exogenous insulin and chronic carbohydrate supplementation increase de novo VLDL triglyceride fatty acid production in rats

We have investigated hepatic de novo lipogenesis and the ratio of apoB-48/apoB-100 during chronic carbohydrate supplementation with or without administration of exogenous insulin in rats. Two groups received chronic (2 weeks) carbohydrate supplementation either as 10% glucose or 10% fructose (wt/v) in their drinking water. Two other groups received exogenous insulin chronically, in addition to the monosaccharides above. The insulin was given for 2 weeks as daily human ultralente insulin injections in increasing doses up to 6 units per day. A fifth group of rats (normal control) received only chow and water. The fractional synthetic rate (FSR), the fraction of very low density lipoprotein triglyceride (VLDL-TG) palmitate that was newly made during an 8-h infusion with sodium [1-13C]acetate, was evaluated. The glucose and fructose groups had a 4-fold (0.60%/h) and 7.5-fold (1.13%/h) increase in FSR from baseline, respectively, compared to chow-fed controls (0.15%/h). Chronic exogenous insulin administration resulted in a 11.5 (1.73%/h) and 11.0 (1.65%/h)-fold increase over baseline in the synthesis of newly made VLDL-TG palmitate in the glucose and fructose groups, respectively. The ratio of apoB-48/apoB-100, i.e. apoB-48 enrichment, in VLDL was positively correlated with insulin levels (r = 0.41, P < 0.01) and with FSR (r = 0.39, P < 0.01). The present study shows that carbohydrate supplementation significantly increases the FSR of newly made VLDL-TG palmitate and that this increase is further augmented by chronic hyperinsulinemia.

Reassessment of stereochemical configuration of natural phosphatidylglycerols by chiral-phase high-performance liquid chromatography and electrospray mass spectrometry

Using chiral-phase high-performance liquid chromatography (HPLC) and electrospray ionization-mass spectrometry (ESI/MS), we have redetermined the stereochemical configuration of some natural and synthetic phosphatidylglycerols (PG). For this purpose, the synthetic and natural PG were converted to their bis-3,5-dinitrophenylurethanes (DNPU), which were separated by HPLC using two columns having chiral phases of opposite configuration, (R)-(+)- and (S)-(-)-1-(1-naphthyl)ethylamine polymers. The molecular species were identified by on-line negative-ion ESI/MS. Absolute configurations of the resolved peaks were assigned by comparison with the elution order of the corresponding 1(3)-monoacyl-sn-glycerol enantiomers as bis-DNPU derivatives on the same column. The results clearly showed that the PG from cabbage leaf lipids and soybean phospholipids consisted of single R,S isomers (1,2-diacyl-sn-glycero-3-phospho-1'-sn-glycerols), despite the presence of nonstereospecific phospholipase D in the tissues. On the other hand, the PG derived from egg yolk phosphatidylcholine and glycerol by transphosphatidylation with cabbage phospholipase D was a mixture of 45% R,S isomers (1, 2-diacyl-sn-glycero-3-phospho-1'-sn-glycerols) and 55% R,R isomers (1,2-diacyl-sn-glycero-3-phospho-3'-sn-glycerols). The PG from Escherichia coli lipids was a mixture of 89% R,S and 11% R,R isomers. The present study demonstrates that chiral-phase HPLC and negative-ion ESI/MS provide direct and unambiguous information about the configuration, identity, and quantity of molecular species in natural and synthetic PG.

Elution factors of synthetic oxotriacylglycerols as an aid in identification of peroxidized natural triacylglycerols by reverse-phase high-performance liquid chromatography with electrospray mass spectrometry

Selected elution factors were determined for model oxotriacylglycerols as an aid in identification of the peroxidation products of natural triacylglycerols by reverse-phase high-performance liquid chromatography (HPLC) with electrospray mass spectrometry (LC/ES/MS). For this purpose synthetic triacylglycerols of known structure were converted to hydroperoxides, hydroxides, epoxides, and core aldehydes and their dinitrophenylhydrazones by published procedures. The oxotriacylglycerols were resolved by normal-phase thin-layer chromatography and reverse-phase HPLC, and the identities of the oxotriacylglycerols confirmed by LC/ES/MS. Elution factors of oxotriacylglycerols were determined in relation to a homologous series of saturated triacylglycerols, ranging from 24 to 54 acyl carbons, and analyzed by reverse-phase HPLC, using a gradient of 20-80% isopropanol in methanol as eluting solvent and an evaporative light-scattering detector. It was shown that the elution times varied with the nature of the functional group and its regiolocation in the triacylglycerol molecule. A total of 31 incremental elution factors were calculated from chromatography of 33 oxygenated and nonoxygenated triacylglycerol species, ranging in carbon number from 36 to 54 and in double-bond number from 0 to 6.

Evidence that apolipoprotein A-IMilano has reduced capacity, compared with wild-type apolipoprotein A-I, to recruit membrane cholesterol

Human carriers of apolipoprotein (apo) A-IMilano are heterozygous for an Arg173-->Cys substitution in the apoA-I primary sequence; despite severe reductions in HDL cholesterol concentrations, affected individuals do not develop coronary heart disease, suggesting that apoA-IMilano may possess antiatherogenic properties. As the beneficial effects of wild-type apoA-I are linked to its role in HDL cholesterol transport, we examined the capacity of apoA-IMilano to recruit cell cholesterol and activate lecithin:cholesterol acyltransferase (LCAT) (two key events in the antiatherogenic reverse cholesterol transport pathway). ApoA-IMilano and wild-type apoA-I were expressed in Chinese hamster ovary cells, and their ability to recruit membrane phospholipid and cholesterol for the assembly of nascent HDL was compared. Both clonal cell lines exhibited similar levels of apolipoprotein accumulation in serum-free medium (approximately 2 micrograms/mg cell protein per 24 hours), and 15% of each apolipoprotein was associated with membrane lipids to form nascent HDL (d = 1.063 to 1.21 g/mL). SDS-PAGE showed that a majority (66 +/- 12%) of the lipidated apoA-IMilano was in the homodimer form. Compositional analyses revealed that apoA-IMilano nascent HDL had a significantly lower (P < .001) unesterified cholesterol/phospholipid mole ratio (0.47 +/- 0.10) than wild-type apoA-I complexes (1.29 +/- 0.14), indicating that apoA-IMilano had a reduced capacity to recruit cell cholesterol. In addition to the reduced unesterified cholesterol/phospholipid ratio, apoA-IMilano nascent HDL consisted mostly of small 7.4-nm particles compared with wild-type apoA-I, in which 11- and 9-nm particles predominated. Despite these changes in nascent HDL particle size and composition, apoA-IMilano activated LCAT normally. We conclude that, even though apoA-IMilano is a normal activator of LCAT, it is less efficient that wild-type apoA-I in recruiting cell cholesterol, suggesting that the putative antiatherogenic properties attributed to apoA-IMilano may be unrelated to the initial stages of reverse cholesterol transport.

Preparation of Schiff base adducts of phosphatidylcholine core aldehydes and aminophospholipids, amino acids, and myoglobin

We have prepared Schiff base adducts of the core aldehydes of phosphatidylcholine and aminophospholipids, free amino acids, and myoglobin. The Schiff bases of the ethanolamine and serine glycerophospholipids were obtained by reacting sn-1-palmitoyl(stearoyl)-2-[9-oxo]nonanoyl-glycerophosphocholine (PC-Ald) with a twofold excess of the aminophospholipid in chloroform/methanol 2:1 (vol/vol) for 18 h at room temperature. The Schiff bases of the amino acids and myoglobin were obtained by reacting the aldehyde with an excess of isoleucine, valine, lysine, methyl ester lysine and myoglobin in aqueous methanol for 18 h at room temperature. Prior to isolation, the Schiff bases were reduced with sodium cyanoborohydride in methanol for 30 min at 4 degrees C. The reaction products were characterized by normal-phase high-performance liquid chromatography and on-line mass spectrometry with electrospray ionization. The amino acids and aminophospholipids yielded single adducts. A double adduct was obtained for myoglobin, which theoretically could have accepted up to 23 PC-Ald groups. The yields of the products ranged from 12 to 44% for the aminophospholipids and from 15-57% for the amino acids, while the Schiff base of the myoglobin was estimated at 5% level. The new compounds are used as reference standards for the detection of high molecular weight Schiff bases in lipid extracts of natural products.

Oxidation products of cholesteryl linoleate are resistant to hydrolysis in macrophages, form complexes with proteins, and are present in human atherosclerotic lesions

Accumulation of the insoluble lipid-protein complex, ceroid, is a characteristic of atherosclerotic plaques. To determine whether deficient processing of cholesteryl esters in oxidized (ox) low density lipoprotein (LDL) contributes to ceroid formation, we studied the hydrolysis of internalized [3H] cholesteryl linoleate (CL) in oxLDL by mouse peritoneal macrophages (MPM). The hydrolysis by MPM of [3H]CL incorporated into oxLDL or LDL did not differ, suggesting that products of lipid and/or apoB oxidation had no impact on the lysosomal hydrolysis of [3H]CL. To evaluate the hydrolysis of oxCL by MPM, we subjected extensively ox[3H]CL to fractionation by TLC. The predominant fraction (D) consisted of sterols and oxysterols esterified to scission products of oxidized fatty acids containing terminal carbonyl groups, i.e., lipid core aldehydes. The extent of hydrolysis of [3H]-fraction D by MPM cultures, as well as by MPM extracts at pH 4.0, was significantly reduced when compared to the hydrolysis of intact [3H]CL. Fraction D also formed complexes with serum proteins, and the purified core aldehyde, cholesteryl 9-oxononanoate reacted with epsilon-amino group of lysines. Finally, several cholesteryl ester aldehydes were detected in lipid extracts of human atheroma. These results suggest that decomposition products of extensively oxidized cholesteryl linoleate that are also present in atherosclerotic lesions, are not adequately degraded by mouse peritoneal macrophage lysosomes and could interact with proteins to form ceroid.

Lipid structure of rat adipocyte plasma membranes following dietary lard and fish oil

We have determined the changes in the lipid structure of the adipocyte plasma membranes of rats receiving lard or fish oil in their diet. For this purpose, mature Wistar rats were fed 20% (w/w) lard or fish oil diets for 22 days, when the plasma membranes of the epididymal and perirenal adipocytes were prepared. Detailed analysis of the membrane lipids by chromatographic methods showed that dietary fat exerted a major effect on the lipid class and molecular species composition of the phospholipids. As a result of fish oil feeding, significant increases in the 20:5(n-3), 22:5(n-3) and 22:6(n-3) were detected in all glycerophospholipid classes, while the 18:1(n-9) and 18:2(n-6) and to a lesser extent 20:4(n-6) decreased. Incorporation of n-3 fatty acids increased the phosphatidylcholine/sphingomyelin ratio without changing the total phospholipid or free cholesterol content of the membrane. Fish oil feeding also caused a marked increase in the proportion of 24:1 in sphingomyelins, which occurred mainly at the expense of 18:0 and 24:0. New n-3 fatty acid-containing species appeared in the choline and ethanolamine glycerophospholipids, when compared to membrane lipids from lard-fed rats. Membranes from fish oil fed rats also had moderately higher levels of ether lipids. Few differences were seen between the membranes of the epididymal and perirenal adipocytes. It is concluded that dietary fish oils modify the lipid structure of rat adipocyte plasma membranes by increasing the ratio of phosphatidylcholine to sphingomyelin and by increasing the proportion of molecular species with polyunsaturated fatty acids, which would be anticipated to increase the fluidity of the lipid bilayer of adipocyte plasma membranes.

Isolation and identification of glycated aminophospholipids from red cells and plasma of diabetic blood

Glycosylation is a major pathway for posttranslational modification of tissue protein and begins with nonenzymatic addition of carbohydrate to the primary amino groups. Excessive glycation of tissue protein has been implicated in the pathogenesis of diabetes and ageing. While glycation of aminophospholipids has also been postulated, glycated aminophospholipids have not been isolated. Using normal phase HPLC with on-line electrospray mass spectrometry we found glycated ethanolamine phospholipids to make up 10-16% of the total phosphatidylethanolamine (PE) of the red blood cells and plasma of the diabetic subjects. The corresponding values for glycated PE of control subjects were 1-2%.

Stereospecific analysis of triacylglycerols rich in long-chain polyunsaturated fatty acids

Six oils of marine, algal, and microbial origin were analyzed for stereospecific distribution of component fatty acids. The general procedure involved preparation of sn-1,2-(2,3)-diacylglycerols by partial deacylation with ethylmagnesium bromide or pancreatic lipase, separation of X-1,3- and sn-1,2(2,3)-diacylglycerols by borate thin-layer chromatography, resolution of the sn-1,2- and sn-2,3-enantiomers by chiral phase high-performance liquid chromatography following preparation of dinitrophenylurethane derivatives, and determination of the fatty acid composition by gas chromatography. Unexpected complications arose during a stereospecific analysis of triacylglycerols containing over 33% of either 20:4 or 22:6 fatty acids. The sn-1,2(2,3)-diacylglycerols made up of two long-chain polyunsaturated acids migrated with the X-1,3-diacylglycerols and required separate chiral phase resolution. Furthermore, the enzymatic method yielded sn-1,2(2,3)-diacylglycerols, overrepresenting the polyenoic species due to their relative resistance to lipolysis, but prolonged digestion yielded correct composition for the 2-monoacylglycerols. The final positional distribution of the fatty acids was established by pooling and normalizing the data from subfractions obtained by normal- and chiral-phase separation of diacylglycerols. The molecular species of X-1,3-, sn-1,2- and sn-2,3-diacylglycerol dinitrophenylurethanes were identified by chiral-phase liquid chromatography/mass spectrometry with electrospray ionization, which demonstrated a preferential association of the paired long-chain acids with the sn-1,2- and sn-2,3-diacylglycerol isomers.

Contribution of de novo fatty acid synthesis to very low density lipoprotein triacylglycerols: evidence from mass isotopomer distribution analysis of fatty acids synthesized from [2H6]ethanol

A detailed comparison of the structures of plasma very low density lipoprotein (VLDL) and liver triacylglycerols (TG) (Yang et al. 1995. J. Lipid Res. 36: 125-136) has demonstrated that a minimum of 60% of the secreted TG could have been derived from partial lipolysis and reesterification of stored TG and a maximum of 40% could have been derived from direct secretion of newly made TG. To investigate the processes involved in the transfer of TG to VLDL in vivo, we have determined the distribution of deuterium among the molecular species of the liver-TG and VLDL-TG during the infusion of perdeuterated ethanol along with fructose or glucose and during the provision of either glucose or fructose in the drinking water for 2 weeks. The deuterium labeling (percent excess and percent replacement) of the total fatty acids was determined by GC/MS of the methyl esters while the labeling of the glycerol and the glycerol plus fatty acids of the enantiomeric diacylglycerol moieties of TG was determined by LC/MS with on-line mass spectrometry. Supplementation of the diet for 2 weeks with either glucose and fructose stimulated the synthesis of TG containing new fatty acids and glycerol. The proportion of the newly made to preexisting TG differed in VLDL from that in the liver. The 2H % replacement in glycerol and in total fatty acids was greater in VLDL-TG than in the liver-TG. On the basis of the mass isotopomer distribution analysis it was estimated that a maximum of 30% of the VLDL-TG could have been derived directly from TG that was made de novo and did not equilibrate with the liver-TG stores. The transfer of the stored TG to VLDL was best accounted for by a degradation to 2-monoacylglycerols and resynthesis via the 2-monoacylglycerol pathway with addition of an excess of newly synthesized fatty acids to the resynthesized TG.

Apolipoprotein A-I deficiency. Biochemical and metabolic characteristics

Familial HDL deficiencies are associated with variable susceptibility to premature coronary heart disease, but the mechanism underlying this association remains poorly understood. Three homozygotes with isolated complete apo A-I deficiency caused by an autosomal codominant apo A-I Q[-2]X mutation and one heterozygote developed coronary heart disease before age 40 years. We characterized the effects of this mutation on lipoprotein metabolism. LDL FC, phospholipid, and apo B were all significantly higher in homozygotes than in heterozygotes. The HDLs of the heterozygotes were apo A-I poor relative to apo A-II. Lecithin-cholesterol acyltransferase activity was 59% lower in homozygotes than in normal subjects or heterozygotes. Cholesteryl ester transfer activity was increased in a homozygote compared with a normolipidemic control subject. Postprandial lipid metabolism was studied in one homozygote and one heterozygote. Post-prandial TG response in the homozygote was significantly exaggerated, while residual plasma HDL level remained unaffected. The homozygote also had delayed clearance of retinyl ester, a marker of chylomicron remnant metabolism. Thus, homozygosity and heterozygosity for apo A-I Q[-2]X are associated with qualitative, as well as quantitative, disturbances in plasma HDLs, LDLs, lipid-modifying enzyme activities, and postprandial retinyl ester metabolism. The observed elevation of atherogenic lipoproteins and reduction in antiatherogenic lipoproteins in the affected members of the apo A-I Q[-2]X kindred are consistent with the primary deficiency in apo A-I having pleiotropic effects that markedly enhance susceptibility for coronary heart disease.

Determination of lipid ester ozonides and core aldehydes by high-performance liquid chromatography with on-line mass spectrometry

Unsaturated triacylglycerols (TG) and choline (PC) and ethanolamine (PE) phosphatides of known structure were subjected to ozonization and reduction with triphenylphosphine to yield the corresponding lipid ester core aldehydes. Mono- and di-C9 aldehyde palmitoylglycerols were prepared from oleoyldipalmitoyl and oleoyllinoleoylpalmitoyl glycerols, respectively, while egg yolk PC and PE provided the mono-C5 and mono-C9 aldehydes of palmitoyl-and stearoyl glycerophospholipids. The aldehydes were isolated in the free form and as the dinitrophenylhydrazone (DNPH) derivatives by thin-layer chromatography (TLC). The intermediate ozonides, free aldehydes and hydrazones were identified by reversed phase high performance liquid chromatography (HPLC) with on-line negative ion thermospray and normal phase HPLC with on-line positive ion electrospray mass spectrometry (LC-MS). The synthetic aldehydes were used as carriers during isolation from natural sources and as reference compounds in quantitative analyses.

Preparation and characterization of glucosylated aminoglycerophospholipids

Natural aminophospholipids were isolated from egg yolk and from human red blood cells. Glucosylated ethanolamine and serine phosphatides were prepared by exposing synthetic and natural aminophospholipids to glucose for 3-18 h at pH 7.4. The glucosylation products were resolved from parent phospholipids by normal-phase high-performance liquid chromatography and were identified by on-line mass spectrometry with an electrospray interface. The soft ionization method allowed us to detect the glucosylation products as molecular ions of the Schiff bases. The Schiff bases could be stabilized by sodium cyanoborohydride reduction. The molecular species of the ethanolamine and serine phosphatides reacted in proportion to their molar concentration in the mixtures. The yields of the glucosylation products varied with time of reaction and the concentration of glucose in the medium. At 50 mM glucose and 0.6 mg/mL phosphatidylethanolamine, 20% of the aminophospholipid was glycated in 18 h at 37 degrees C.

General strategies in chromatographic analysis of lipids

Lipid extracts of natural sources contain a large number of lipid classes and molecular species. Completely reproducible samples are obtained only with great care and skill. Analytical methods other than chromatography and/or mass spectrometry are of little use for resolution and identification of lipid molecules even in simple mixtures. The analytical information desired governs the selection of the chromatographic and mass spectrometric method, which determine the sample preparation and derivative needed. Usually a combination of chromatographic methods is necessary to identify specific species of lipids. The recent development of soft ionization techniques, that are readily interfaced with mass spectrometers, have greatly simplified the sample preparation and have largely eliminated the need for derivatization. Because these techniques require expensive equipment and dedicated operators, the methods selected must be consistent with the true analytical needs and the available resources. Although personal preference cannot be eliminated entirely, the general strategies outlined below should help to reduce the number of possibilities facing a lipid analyst to a few practical choices.

Application of tandem mass spectrometry for the analysis of long-chain carboxylic acids

The application of MS-MS for the analysis of long-chain carboxylic acids and their esters has proved enormously successful but expensive. It is discussed mainly on basis of results obtained with different instruments with lesser attention to principles of the method, which have been adequately reviewed elsewhere. The use of electrospray ionization (ESI) has greatly increased the sensitivity of the method and has permitted assay of total lipid extracts. The combination of HPLC with electrospray and single quadrupole mass spectrometry, LC-ESI-CID-MS, rivals the triple quadrupole MS-MS application in many instances at considerably lower cost. However, LC-ESI-MS-MS remains the most desirable system at the present time for lipid ester analyses.

Comparison of Helicobacter mustelae and Helicobacter pylori adhesion to eukaryotic cells in vitro

BACKGROUND & AIMS

Bacterial adhesion to mucosal surfaces is an important pathogenic mechanism for Helicobacter-induced gastritis. The aims of this study were to compare binding of selected Helicobacter mustelae and Helicobacter pylori strains to lipids extracted from HEp-2, Chinese hamster ovary, human embryonic lung cells, and ferret gastrointestinal tissues as well as to intact tissue culture cells and to analyze the fatty acids of the receptor.

METHODS

Thin-layer chromatography overlay binding and a receptor-based immunoassay detected adhesion of bacteria to commercial lipids and to individual species within the lipid extracts. H. mustelae binding to tissue culture cells was performed by whole cell bacterial adhesion assay.

RESULTS

H. mustelae and H. pylori both bound to phosphatidylethanolamine and lysophosphatidylethanolamine. Adhesion of H. mustelae to intact eukaryotic cells correlated with the amount of phosphatidylethanolamine. Binding of helicobacters was greater to lipids derived from ferret antrum compared with colon (P < 0.05). Biochemical analysis suggested that heterogeneity in fatty acid composition of phosphatidylethanolamine could influence the degree of Helicobacter binding.

CONCLUSIONS

Adhesion of Helicobacter strains correlates with the quantity of phosphatidylethanolamine present in the epithelial cell and with the differences in the fatty acid profile of the lipid.

Lipid ester-bound aldehydes among copper-catalyzed peroxidation products of human plasma lipoproteins

We have isolated the core aldehydes (aldehydes still bound to parent molecules) of phosphatidylcholine (PC) and cholesteryl esters (CE) from copper-catalyzed peroxidation of human plasma low (LDL) and high (HDL) density lipoproteins. The aldehydes were isolated by extraction with acidified chloroform-methanol containing 2,4-dinitrophenylhydrazine. The 2,4-dinitrophenylhydrazone (DNPH) derivatives formed were resolved by reversed phase high performance liquid chromatography (HPLC) and identified by on-line quadrupole mass spectrometry (LC/MS). The major PC core aldehydes from oxidized LDL and HDL were identified as 1-palmitoyl-(1-stearoyl) 2-(9-oxononanoyl)-, 1-palmitoyl-(1-stearoyl) 2-(8-oxooctanoyl)-, and 1-palmitoyl-(1-stearoyl) 2-(5-oxovaleroyl)-sn-glycerols after phospholipase C digestion of the DNPH derivatives of the phospholipids. The major aldehydes from peroxidation of cholesteryl esters were the 9-oxononanoyl, 8-oxooctanoyl, and 5-oxovaleroyl esters of cholesterol and 7-ketocholesterol. The core aldehydes were estimated to account for a minimum of 1-2% of the consumed linoleate and arachidonate esters. A relatively smaller yield of the PC core aldehydes from LDL compared to HDL was attributed to the presence of greater amounts of phospholipases in LDL than in HDL. More comparable yields of PC core aldehydes were obtained in the presence of phenylmethylsulfonylfluoride, which inhibits phospholipases. We conclude that peroxidation of LDL and HDL results in formation of detectable amounts of cholesteryl and glycerophospholipid esters containing aldehyde functions. The yield of PC aldehydes varies with the activity of the platelet activating factor (PAF) acetyl hydrolase.