Molecular Species Of Sphingomyelin Research Articles

Edible insects as a novel source of lecithin: Extraction and lipid characterization of black soldier fly larvae and yellow mealworm

Edible insects with high fat and phosphorus content are a potential novel source of lecithin, however, studies on their minor lipids are limited. In this study, lecithin was extracted from black soldier fly larvae and yellow mealworm. Herein, the effects of lecithin extraction method, matrix and ultrasound pretreatment were explored based on the fatty acid composition and phospholipid profile with soy lecithin as a reference. The use of a wet matrix and ultrasound pretreatment increased the extraction efficiency of total PLs from both insects. Insect lecithin contained a considerable amount of sphingomyelin compared to soy lecithin. In insect lecithin, a total of 47 glycerophospholipid and sphingomyelin molecular species, as well as four molecular species of fatty acyl esters of hydroxy fatty acid, were detected. This study is the first comprehensive investigation of insects as a new source of lecithin with applications in food, cosmetics and in the pharmaceutical industry.

Screening of Phospholipids in Plasma of Large-Artery Atherosclerotic and Cardioembolic Stroke Patients With Hydrophilic Interaction Chromatography-Mass Spectrometry.

Ischemic stroke (IS) is a deadly and debilitating disease with a high incidence and recurrence rate in elderly people worldwide. Large-artery atherosclerotic (LAA) and cardioembolic (CE) stroke are two leading subtypes and require different management. As a complementary biochemistry method for current diagnostic techniques, a sensitive and accurate phospholipid (PL) targeted lipidomic method was developed in this study. Plasma PLs were selectively extracted with titanium dioxide/fibrous silica nanosphere material, then characterized and quantified with hydrophilic interaction chromatography-mass spectrometry. A total of 31 molecular species of PLs were determined and ten biomarkers including seven molecular species of sphingomyelins (SM d18:1/18:1, d18:1/18:0, d18:1/24:1, d18:1/16:1, d18:1/22:1, d18:1/24:2, and d18:1/16:0) and three molecular species of phosphatidylcholines (16:0/18:1, 16:0/18:2 and 16:0/22:6) showed significant differences in LAA, CE, and healthy control (HC) groups. The independent diagnostic capabilities of these PL biomarkers were successfully evaluated and validated with receiver operating characteristic curves. Additionally, the oleic acid-enriched SMs, which can result in atherogenic lipoprotein aggregation, were proved to be positively related to IS and may perform as the potential risk factors in the future. Meanwhile, valuable suggestions for dietary interventions as an essential source of endogenous PLs could be obtained from this study.

Lactational changes in phospholipid classes and molecular species concentration in human milk

Concentrations of five phospholipid (PL) classes and their respective molecular species were determined in mature milk samples from a cohort of Chinese mothers over an eight month lactational period. Although changes were not statistically significant, average total PL concentrations increased over the mature milk period from a one month low of 193 mg L−1 to a high of 246 mg L−1 at eight months lactation. Phosphatidyl ethanolamine (37% of total PLs) was the most abundant phospholipid class throughout the mature milk period, followed by sphingomyelin (32%), phosphatidyl choline (22%), phosphatidyl serine (4%) and phosphatidyl inositol (3%). The molecular species 36:2 was identified as the most abundant for the glycerophospholipids, ranging from 37% to 64% of the total molecular species intensities, and lactational changes in this molecular species dominated the overall lactational changes in proportions of molecular species. At 20.6%, the molecular species d40:1 was the major sphingomyelin molecular species identified.

Qualitative distribution of endogenous phosphatidylcholine and sphingomyelin in serum using LC-MS/MS based profiling

PCs and SMs are the major types of glycerophospholipids and sphingophospholipids, the two main categories of phospholipids (PLs). To study the qualitative distribution of serum phosphatidylcholine (PC) and sphingomyelin (SM) in human and three rodent species, liquid chromatography-Orbitrap mass spectrometry (LC-Orbitrap-MS/MS) was used to identify them comprehensively through the accurate mass measurement of both precursor ions and their corresponding product ions. Based on the fragmentation rules of standards, the product ions at m/z 184.0733 were filtered to maximally screen possible PC and SM molecules. For PC, the fatty acid at sn-1 and sn-2 of the glycerol backbone was identified based on the product ions in negative mode. A total of 91 PCs and 31 SMs molecular species, consisting of 166 PCs and 39 SMs regioisomers, were detected in human serum, which is the most comprehensive identification of PC and SM species in serum. The qualitative distributions of PC in rat and SM in golden hamster, respectively, were more similar with that of human from an overall perspective. Those results provided guidance regarding to the animal model selection for mimicking lipid related-syndromes or diseases in human.

Composition and variability of phospholipids in Chinese human milk samples

Using gas chromatography and HPLC–MS/MS, 28 fatty acids and 74 molecular species of phospholipid were identified in 90 mature (96–180 days) human milk samples from three regions of China (Zhengzhou, Wuhan and Harbin). There were obvious differences in the content of some phospholipid fatty acids from three regions. The differences in fatty acid composition of human milk phospholipids in different individuals were mainly reflected in the contents of unsaturated fatty acids. The molecular species with the highest content of glycerophospholipids in human milk samples tested were 36:2. The molecular species of sphingomyelin in human milk from the three regions differed greatly, but the glycerophospholipid composition did not differ significantly. Compared with glycerophospholipid, the contents of molecular species in human milk sphingomyelin from different individuals had a higher coefficient of variation (33.14%).

High-Performance Thin-Layer Chromatography Coupled with Electrospray Ionization Tandem Mass Spectrometry for Identifying Neutral Lipids and Sphingolipids in Complex Samples.

High-performance thin-layer chromatography was directly combined with electrospray mass spectrometry (ESI-MS) for structural identification issues below the level of lipid classes in complex samples through a portable, automated, elution-based interface. For samples as diverse as biodiesel and human plasma, separation conditions using Automated Multiple Development were selected in each case to provide lipid classes as zones narrow enough to ensure a direct transfer of them to ESI-MS. The respective zone of interest can be selected at will. ESI+ spectra of neutral lipids and sphingolipids showed sodium adducts when recorded from the plate. By using the described technique and ion-trap technology, the respective sodium adducts were fragmented. Sodium remained as the charge of the fragment ions and, thus, was useful for their structural identification through MSn. In this way, composition profiles of each class by ESI+-MS, and further identification of individual lipids and the molecular species belonging to each of them, were obtained by MS/MS and/or high-resolution MS. Thus, mono and diacylglycerides in ESI+ and fatty acids (in ESI-) were identified as low-concentration impurities in a fatty acid methyl ester-based biodiesel sample. Likewise, molecular species of sphingomyelins and globotriaosylceramides were unequivocally identified in human plasma samples.

Profiling of phospholipids molecular species from different mammalian milk powders by using ultra-performance liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry

Phospholipids (PLs) are increasingly considered as nutrients with putative health benefits. Mammalian milk is a prominent source of phospholipids. In this study, PLs from different mammalian milk powders (buffalo, camel, bovine, goat, and ewe) purchased from supermarkets were enriched by solid-phase extraction cartridges, and subsequently separated and analyzed with ultra-performance liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry (UPLC-ESI-Q-TOF-MS). Phospholipid classes were separated using hydrophilic interaction liquid chromatography (100×1mm, 1.7μm particle size BEH column) by gradient elution with acetonitrile/ammonium formate as a mobile phase. 22 molecular species of phosphatidylcholine (PC) were detected in the five types of milk powders, and PC (C16:0–C18:1) was the most abundant species with relative abundances of 10.93, 9.35, 9.35, 12.92, and 11.14%, respectively. While, 15 molecular species of phosphatidylethanolamine (PE) were detected, and PE (C18:0–C18:2) was the most abundant species making up 32.70, 16.45, 31.39, 29.88, and 27.24%, respectively. Furthermore, 9 molecular species of sphingomyelin (SM) were also detected, and the predominant species was SM (d18:1/16:0). This method of analysis was rapid, sensitive and precise for the identification of milk PLs. Also, it can be suggested as an application for studying specific technology markers in the dairy processing industry, and exploring novel applications of milk phospholipids.

Tumor necrosis faсtor-alpha - potential target for neuroprotector dimebon

Dimebon (Dimebolin) is an antihistamine drug which has been used in Russia since 1983. Recently Dimebolin has attracted renewed interest after being shown to have positive effects on persons suffering from Alzheimer's disease. Animal studies have shown that dimebon acts through multiple mechanisms, both blocking the action of neurotoxic beta-amyloid peptides and inhibiting L-type calcium channels, modulating the action of AMPA and NMDA glutamate receptors. Our experiments with cell culture L929 and mice have shown that dimebon may exert its neuroprotective effect by blocking cytotoxic signals induced by proinflammatory cytokines such as TNF-a which are believed to play a central role in Alzheimer's disease. Dimebon (10 mg/ml) protected mouse fibroblasts L929 against the toxic action of TNF-a. Our study included 65 male mice. TNF-a (10 mg per mouse), dimebon (0,2 mg/kg) and their combination were injected intraperitonealy. Changes in the level of molecular species of sphingomyelin and galactosyl ceramide in hippocampus, cerebellum and cerebral cortex within 30 min, 2 h, 4 h, and 24 h after injection were detected by chromato-mass-spectrometry. Maximal changes in sphingomyelin and galactosyl ceramides contents of different molecular species after single TNF-a administration were found in the hippocampus, and were less expressed in the cerebral cortex and cerebellum after 24 h. Dimebon itself did not induce changes in the sphingolipid spectrum in brain sections, but protected them against disorders induced by TNF-a in the brain. Modern strategies in the search of new therapeutic approaches are based on the multitarget properties of new drugs. According to our results TNF-a may serve as a new target for dimebon.

Histological analyses by matrix-assisted laser desorption/ionization-imaging mass spectrometry reveal differential localization of sphingomyelin molecular species regulated by particular ceramide synthase in mouse brains

Sphingomyelin (SM) is synthesized by SM synthase (SMS) from ceramide (Cer). SM regulates signaling pathways and maintains organ structure. SM comprises a sphingoid base and differing lengths of acyl-chains, but the importance of its various forms and regulatory synthases is not known. It has been reported that Cer synthase (CerS) has restricted substrate specificity, whereas SMS has no specificity for different lengths of acyl-chains. We hypothesized that the distribution of each SM molecular species was regulated by expression of the CerS family. Thus, we compared the distribution of SM species and CerS mRNA expression using molecular imaging. Spatial distribution of each SM molecular species was investigated using ultra-high-resolution imaging mass spectrometry (IMS). IMS revealed that distribution of SM molecular species varied according to the lengths of acyl-chains found in each brain section. Furthermore, a combination study using in situ hybridization and IMS revealed the spatial expression of CerS1 to be associated with the localization of SM (d18:1/18:0) in cell body-rich gray matter, and CerS2 to be associated with SM (d18:1/24:1) in myelin-rich white matter. Our study is the first comparison of spatial distribution between SM molecular species and CerS isoforms, and revealed their distinct association in the brain. These observations were demonstrated by suppression of CerS2 using siRNA in HepG2 cells; that is, siRNA for CerS2 specifically decreased C22 very long-chain fatty acid (VLCFA)- and C24 VLCFA-containing SMs. Thus, histological analyses of SM species by IMS could be a useful approach to consider their molecular function and regulative mechanism.

Tumor necrosis factor-alpha is a potential target for the neuroprotector Dimebon

Since 1983, Dimebon (Dimebolin) is used clinically in Russia as an antihistamine drug. Recent interest in Dimebolin is associated with its therapeutic effect in patients with Alzheimer’s disease. Animal studies have shown that Dimebon activity is realized via multiple mechanisms. Our experiments performed on the fibroblast cell culture L929 and C57Bl mice have been shown that Dimebon may block cytotoxic signals induced by the proinflammatory cytokines, tumor necrosis factor α (TNFα). Dimebon (10 μg/mL) protected mouse fibroblast cells L929 against toxic action of TNFα. Pretreatment of mice with Dimebon prevented development of changes in molecular species of sphingomyelins and galactosylceramides induced by a single dose administration of TNAα. Dimebon itself did not induce changes in sphingolipids of the investigated brain structures.

Structural characterization of the pulmonary innate immune protein SPLUNC1 and identification of lipid ligands.

The short palate, lung and nasal epithelial clone 1 (SPLUNC1) protein is a member of the palate, lung, and nasal epithelium clone (PLUNC) family, also known as bactericidal/permeability-increasing (BPI) fold-containing protein, family A, member 1 (BPIFA1). SPLUNC1 is an abundant protein in human airways, but its function remains poorly understood. The lipid ligands of SPLUNC1 as well as other PLUNC family members are largely unknown, although some reports provide evidence that lipopolysaccharide (LPS) could be a lipid ligand. Unlike previous hypotheses, we found significant structural differences between SPLUNC1 and BPI. Recombinant SPLUNC1 produced in HEK 293 cells harbored several molecular species of sphingomyelin and phosphatidylcholine as its ligands. Significantly, in vitro lipid-binding studies failed to demonstrate interactions between SPLUNC1 and LPS, lipoteichoic acid, or polymyxin B. Instead, one of the major and most important pulmonary surfactant phospholipids, dipalmitoylphosphatidylcholine (DPPC), bound to SPLUNC1 with high affinity and specificity. We found that SPLUNC1 could be the first protein receptor for DPPC. These discoveries provide insight into the specific determinants governing the interaction between SPLUNC1 and lipids and also shed light on novel functions that SPLUNC1 and other PLUNC family members perform in host defense.

Surface Behavior of Sphingomyelins with Very Long Chain Polyunsaturated Fatty Acids and Effects of Their Conversion to Ceramides

Molecular species of sphingomyelin (SM) with nonhydroxy (n) and 2-hydroxy (h) very long chain polyunsaturated fatty acids (n- and h-28:4, 30:5, and 32:5) abound in rat spermatogenic cells and spermatozoa. These SMs are located on the sperm head, where they are converted to the corresponding ceramides (Cer) after the completion of the acrosomal reaction, as induced in vitro. The aim of this study was to look into the surface properties of these unique SM species and how these properties change by the SM → Cer conversion. After isolation by HPLC, these SMs were organized in Langmuir films and studied alone, in combination with different proportions of Cer, and during their conversion to Cer by sphingomyelinase. Compression isotherms for all six SMs under study were compatible with a liquid-expanded (LE) state and showed large molecular areas. Only the longest SMs (n-32:5 and h-32:5 SM) underwent a phase transition upon cooling. Interestingly, the abundant h-28:4 Cer exhibited a highly compressible liquid-condensed (LC) phase compatible with a high conformational freedom of Cer molecules but with the characteristic low diffusional properties of the LC phase. In mixed films of h-28:4 SM/h-28:4 Cer, the components showed favorable mixing in the LE phase. The monolayer exhibited h-28:4 Cer-rich domains both in premixed films and when formed by the action of sphingomyelinase on pure h-28:4 SM films. Whereas the SMs from sperm behaved in a way similar to that of shorter acylated SMs, the corresponding Cers showed atypical rheological properties that may be relevant to the membrane structural rearrangements that take place on the sperm head after the completion of the acrosomal reaction.

Lipid Polarity Is Maintained in Absence of Tight Junctions

The role of tight junctions (TJs) in the establishment and maintenance of lipid polarity in epithelial cells has long been a subject of controversy. We have addressed this issue using lysenin, a toxin derived from earthworms, and an influenza virus labeled with a fluorescent lipid, octadecylrhodamine B (R18). When epithelial cells are stained with lysenin, lysenin selectively binds to their apical membranes. Using an artificial liposome, we demonstrated that lysenin recognizes the membrane domains where sphingomyelins are clustered. Interestingly, lysenin selectively stained the apical membranes of epithelial cells depleted of zonula occludens proteins (ZO-deficient cells), which completely lack TJs. Furthermore, the fluorescent lipid inserted into the apical membrane by fusion with the influenza virus did not diffuse to the lateral membrane in ZO-deficient epithelial cells. This study revealed that sphingomyelin-cluster formation occurs only in the apical membrane and that lipid polarity is maintained even in the absence of TJs.

Liquid Chromatography–Tandem Mass Spectrometry for the Determination of Sphingomyelin Species from Calf Brain, Ox Liver, Egg Yolk, and Krill Oil

In this study, molecular species of sphingomyelin (SM) in egg yolk, calf brain, ox liver, and krill oil were investigated. Classes of phospholipids (PLs) were purified, identified, and quantified by normal phase semipreparative high-performance liquid chromatography (HPLC) combined with evaporative light scattering detectors (ELSD). For SM molecular species identification, pure SM collected through a flow splitter was loaded to HPLC-electrospray ionization-tandem mass spectrometry (LC-ESI-MS(2)), with 100% methanol containing 5 mM ammonium formate as mobile phase. In addition to classes of PLs, the used approach allowed the determination of profiles of SM species in egg yolk, ox liver, and calf brain, whereas krill oil turned out not to contain any SM. It also allowed the separation and identification of SM subclasses, as well as tentative identification of species with the same molecular mass, including isomers. The results showed that egg yolk contained the highest proportion of (d18:1-16:0)SM (94.1%). The major SM molecular species in ox liver were (d18:1-16:0)SM (25.5%), (d18:1-23:0)SM (19.7%), (d18:1-24:0)SM (13.2%), and (d18:1-22:0)SM (12.5%). Calf brain SM was rich in species such as (d18:1-18:0)SM (40.7%), (d18:1-24:1)SM (17.1%), and (d18:1-20:0)SM (10.8%).

MALDI imaging MS of phospholipids in the mouse lung

Lipid mediators are important in lung biochemistry and are derived from the enzymatic oxidation of arachidonic and docosahexaenoic acids, which are PUFAs that are present in phospholipids in cell membranes. In this study, MALDI imaging MS was used to determine the localization of arachidonate- and docosahexaenoate-containing phospholipids in mouse lung. These PUFA-containing phospholipids were determined to be uniquely abundant at the lining of small and large airways, which were unequivocally identified by immunohistochemistry. In addition, it was found that the blood vessels present in the lung were characterized by sphingomyelin molecular species, and lung surfactant phospholipids appeared evenly distributed throughout the lung parenchyma, indicating alveolar localization. This technique revealed unexpected high concentrations of arachidonate- and docosahexaenoate-containing phospholipids lining the airways in pulmonary tissue, which could serve as precursors of lipid mediators affecting airways biology.

Thematic Review Series: Sphingolipids. Biodiversity of sphingoid bases (“sphingosines”) and related amino alcohols

“Sphingosin” was first described by J. L. W. Thudichum in 1884 and structurally characterized as 2S,3R,4E-2-aminooctadec-4-ene-1,3-diol in 1947 by Herb Carter, who also proposed the designation of “lipides derived from sphingosine as sphingolipides.” This category of amino alcohols is now known to encompass hundreds of compounds that are referred to as sphingoid bases and sphingoid base-like compounds, which vary in chain length, number, position, and stereochemistry of double bonds, hydroxyl groups, and other functionalities. Some have especially intriguing features, such as the tail-to-tail combination of two sphingoid bases in the α,ω-sphingoids produced by sponges. Most of these compounds participate in cell structure and regulation, and some (such as the fumonisins) disrupt normal sphingolipid metabolism and cause plant and animal disease. Many of the naturally occurring and synthetic sphingoid bases are cytotoxic for cancer cells and pathogenic microorganisms or have other potentially useful bioactivities; hence, they offer promise as pharmaceutical leads. This thematic review gives an overview of the biodiversity of the backbones of sphingolipids and the broader field of naturally occurring and synthetic sphingoid base-like compounds.

The relationship between the metabolism of sphingomyelin species and the hemolysis of sheep erythrocytes induced by Clostridium perfringens α-toxin

Clostridium perfringens alpha-toxin induces the hemolysis of sheep erythrocytes by activating the metabolism of sphingomyelin (SM) via a GTP binding protein in membranes. alpha-Toxin stimulated the formation of 15-N-nervonoyl sphingosine (C24:1-ceramide), which was identified by positive ion fast atom bombardment-MS and 1H-NMR spectroscopy. C24:1-ceramide stimulated the toxin-induced hemolysis of saponin-pretreated sheep erythrocytes and increased the production of sphingosine 1-phosphate (S1P) in the cells, but N-lignoceroyl sphingosine did not. These events elicited by the toxin in the presence of C24:1-ceramide were significantly attenuated by treatment with dihydrosphingosine, a sphingosine kinase inhibitor. TLC showed that the level of C24:1-ceramide was highest among the ceramides with an unsaturated bond in the fatty acyl chain in the detergent-resistant membranes (DRMs). The toxin specifically bound to DRMs rich in cholesterol, resulting in the hydrolysis of N-nervonoic sphingomyelin (C24:1-SM) in DRMs. Treatment of the cells with pertussis toxin (PT) inhibited the alpha-toxin-induced formation of C24:1-ceramide from C24:1-SM in DRMs and hemolysis, indicating that endogenous sphingomyelinase, which hydrolyzes C24:1-SM to C24:1-ceramide, is controlled by PT-sensitive GTP binding protein in membranes. These results show that the toxin-induced metabolism of C24:1-SM to S1P in DRMs plays an important role in the toxin-induced hemolysis of sheep erythrocytes.

Brain lipid composition in postnatal iron‐induced motor behavior alterations following chronic neuroleptic administration in mice

Several studies have shown that deficient uptake or excessive break down of membrane phospholipids may be associated with neurodegenerative and psychiatric disorders. The purpose of the present study was to examine the effects of postnatal iron administration in lipid composition and behavior and whether or not the established effects may be altered by subchronic administration of the neuroleptic compounds, clozapine and haloperidol. In addition to motor activities such as locomotion, rearing and activity, a targeted lipidomics approach has been used to investigated the brains of eight groups of mice (four vehicle groups and four iron groups) containing six individuals in each group treated with vehicle, low dose clozapine, high dose clozapine and haloperidol. Lipids were extracted by the Folch method and analyzed using reversed-phase capillary liquid chromatography coupled on-line to electrospray ionization mass spectrometry (LC/ESI/MS). Identification of phosphatidylcholine (PC) and sphingomyelin (SM) molecular species was based on their retention time, m/z ratio, head group specific up-front fragmentation and analysis of the product ions produced upon fragmentation. A comparison between the Ve-groups and Fe-groups showed that levels of PC and SM molecular species and motor activities were significantly lower in Fe-Ve compared to Ve-Ve. The effects of neuroleptic treatment with and without iron supplementation were studied. In conclusion our results support the hypothesis that an association between psychiatric disorders and lipid and behavior abnormalities in the brain exists.

ESI-MS quantitation of increased sphingomyelin in Niemann-Pick disease type B HDL

HDLs have been proposed to have antiatherogenic properties because of their role in reverse cholesterol transport as lipid acceptors. To elucidate the phospholipid profile of these particles, we used electrospray ionization mass spectrometry to examine the phosphatidylcholine (PC) and sphingomyelin (SM) composition of HDLs purified from plasma and nascently generated in vitro from fibroblasts. We also quantitatively compared the phospholipids present in these lipoproteins between normal and Niemann-Pick disease type B (NPD-B) subjects characterized by sphingomyelinase (SMase) deficiency. We demonstrated that plasma HDLs from NPD-B were significantly enriched in SM by an average of 28%, particularly the palmitoyl SM (with an increase of 95%), which accounted for approximately 25-44% of total SM molecular species. Similarly, we observed an increase of approximately 63% in total SM levels in nascent HDLs prepared from NPD-B fibroblasts. Although PC levels in nascent HDLs were comparable between control and NPD-B cells, there was a 95% increase in total PC levels similar to that of SM in plasma HDLs extracted from NPD-B subjects. These data provide insight into the structure of HDLs and identify potential new roles for SMase in lipoprotein metabolism.

Isolation of very low density lipoprotein phospholipids enriched in ethanolamine phospholipids from rats injected with Triton WR 1339

Phospholipids carried by very low density lipoprotein (VLDL) are hydrolysed in circulation by lipoprotein and hepatic lipases and lecithin-cholesterol acyltransferase. We have previously demonstrated [6] [J.J. Ågren, A. Ravandi, A. Kuksis, G. Steiner, Structural and compositional changes in very low density lipoprotein triacylglycerols during basal lipolysis, Eur. J. Biochem. 269 (2002) 6223–6232] that the infusion of Triton WR 1339 (TWR), which inhibits these lipases, leads in 2 h to five-fold increase in VLDL triacylglycerol concentration along with major differences in the composition of their molecular species. The present study demonstrates that the accumulation of triacylglycerols is accompanied by major changes in the content of the VLDL phospholipids, of which the most significant is the enrichment of phosphatidylethanolamine (PtdEtn). This finding coincides with the enrichment in PtdEtn demonstrated in the VLDL of a hepatocytic Golgi fraction but it had not been demonstrated that the Golgi VLDL, along with its unusual phospholipid composition, can be directly transferred to plasma. Aside from providing an easy access to nascent plasma VLDL, the TWR infusion demonstrates that lipoprotein and hepatic lipases are also responsible for the degradation of plasma VLDL PtdEtn, as independently demonstrated for plasma phosphatidylcholine. Our results indicate also, with the exception of lysophosphatidylcholine, that preferential basal hydrolysis no dot lead to major differences in molecular species composition between circulating and newly secreted VLDL phospholipids. The comparison of the molecular species composition of VLDL and liver phospholipids suggests a selective secretion of PtdEtn and sphingomyelin molecular species during VLDL secretion.