Interplay of unsaturated phospholipids and cholesterol in membranes: effect of the double-bond position.
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ABSTRACT:
SUBMITTER: Martinez-Seara H
PROVIDER: S-EPMC2547435 | biostudies-other | 2008 Oct
REPOSITORIES: biostudies-other
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Project description:The position(s) of carbon-carbon double bonds within lipids can dramatically affect their structure and reactivity and thus has a direct bearing on biological function. Commonly employed mass spectrometric approaches to the characterization of complex lipids, however, fail to localize sites of unsaturation within the molecular structure and thus cannot distinguish naturally occurring regioisomers. In a recent communication [Thomas, M. C.; Mitchell, T. W.; Blanksby, S. J. J. Am. Chem. Soc. 2006, 128, 58-59], we have presented a new technique for the elucidation of double bond position in glycerophospholipids using ozone-induced fragmentation within the source of a conventional electrospray ionization mass spectrometer. Here we report the on-line analysis, using ozone electrospray mass spectrometry (OzESI-MS), of a broad range of common unsaturated lipids including acidic and neutral glycerophospholipids, sphingomyelins, and triacylglycerols. All lipids analyzed are found to form a pair of chemically induced fragment ions diagnostic of the position of each double bond(s) regardless of the polarity, the number of charges, or the adduct ion (e.g., [M - H](-), [M - 2H](2-), [M + H](+), [M + Na](+), [M + NH(4)](+)). The ability of OzESI-MS to distinguish lipids that differ only in the position of the double bonds is demonstrated using the glycerophosphocholine standards, GPCho(9Z-18:1/9Z-18:1) and GPCho(6Z-18:1/6Z-18:1). While these regioisomers cannot be differentiated by their conventional tandem mass spectra, the OzESI-MS spectra reveal abundant fragment ions of distinctive mass-to-charge ratio (m/z). The approach is found to be sufficiently robust to be used in conjunction with the m/z 184 precursor ion scans commonly employed for the identification of phosphocholine-containing lipids in shotgun lipidomic analyses. This tandem OzESI-MS approach was used, in conjunction with conventional tandem mass spectral analysis, for the structural characterization of an unknown sphingolipid in a crude lipid extract obtained from a human lens. The OzESI-MS data confirm the presence of two regioisomers, namely, SM(d18:0/15Z-24:1) and SM(d18:0/17Z-24:1), and suggest the possible presence of a third isomer, SM(d18:0/19Z-24:1), in lower abundance. The data presented herein demonstrate that OzESI-MS is a broadly applicable, on-line approach for structure determination and, when used in conjunction with established tandem mass spectrometric methods, can provide near complete structural characterization of a range of important lipid classes. As such, OzESI-MS may provide important new insight into the molecular diversity of naturally occurring lipids.
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Project description:Cholesterol is an integral component of eukaryotic cell membranes and a key molecule in controlling membrane fluidity, organization, and other physicochemical parameters. It also plays a regulatory function in antibiotic drug resistance and the immune response of cells against viruses, by stabilizing the membrane against structural damage. While it is well understood that, structurally, cholesterol exhibits a densification effect on fluid lipid membranes, its effects on membrane bending rigidity are assumed to be nonuniversal; i.e., cholesterol stiffens saturated lipid membranes, but has no stiffening effect on membranes populated by unsaturated lipids, such as 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). This observation presents a clear challenge to structure-property relationships and to our understanding of cholesterol-mediated biological functions. Here, using a comprehensive approach-combining neutron spin-echo (NSE) spectroscopy, solid-state deuterium NMR (2H NMR) spectroscopy, and molecular dynamics (MD) simulations-we report that cholesterol locally increases the bending rigidity of DOPC membranes, similar to saturated membranes, by increasing the bilayer's packing density. All three techniques, inherently sensitive to mesoscale bending fluctuations, show up to a threefold increase in effective bending rigidity with increasing cholesterol content approaching a mole fraction of 50%. Our observations are in good agreement with the known effects of cholesterol on the area-compressibility modulus and membrane structure, reaffirming membrane structure-property relationships. The current findings point to a scale-dependent manifestation of membrane properties, highlighting the need to reassess cholesterol's role in controlling membrane bending rigidity over mesoscopic length and time scales of important biological functions, such as viral budding and lipid-protein interactions.
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Project description:Lipids are highly diverse biomolecules associated with several biological functions including structural constituent, energy storage, and signal transduction. It is essential to characterize lipid structural isomers and further understand their biological roles. Unsaturated lipids contain one or multiple carbon-carbon double bonds. Identifying double bond position presents a major challenge in unsaturated lipid characterization. Recently, several advancements have been made for double bond localization by mass spectrometry (MS) analysis. However, many of these studies require complex chemical reactions or advanced mass spectrometers with special fragmentation techniques, which limits the application in lipidomics study. Here, an innovative meta-chloroperoxybenzoic acid ( m-CPBA) epoxidation reaction coupling with collision-induced dissociation (CID)-MS/MS strategy provides a new tool for unsaturated lipidomics analysis. The rapid epoxidation reaction was carried out by m-CPBA with high specificity. Complete derivatization was achieved in minutes without overoxidized byproduct. Moreover, diagnostic ion pair with 16 Da mass difference indicated localization of carbon-carbon double bond in MS/MS spectra. Multiple lipid classes were evaluated with this strategy and generated abundant fragments for structural analysis. Unsaturated lipid analysis of yeast extract using this strategy took less than 30 min, demonstrating the potential for high-throughput lipidomics analysis by this approach. This study opens a door for high throughput unsaturated lipid analysis with minimal requirement for instrumentation, which could be widely applied in lipidomics analysis.
| S-EPMC6408215 | biostudies-other
Project description:The position and configuration of carbon-carbon double bonds in unsaturated fatty acids is crucial for their biological functions and influences health and disease. However, double bond isomers are not routinely distinguished by classical mass spectrometry workflows. Instead, they require sophisticated analytical approaches usually based on chemical derivatization and/or instrument modification. In this work, a novel strategy to investigate fatty acid double bond isomers (18:1) without prior chemical treatment or modification of the ion source was implemented by non-covalent adduct formation in the gas phase. Fatty acid adducts with sodium, pyridinium, trimethylammonium, dimethylammonium, and ammonium cations were characterized by a combination of cryogenic gas-phase infrared spectroscopy, ion mobility-mass spectrometry, and computational modeling. The results reveal subtle differences between double bond isomers and confirm three-dimensional geometries constrained by non-covalent ion-molecule interactions. Overall, this study on fatty acid adducts in the gas phase explores new avenues for the distinction of lipid double bond isomers and paves the way for further investigations of coordinating cations to increase resolution.
| S-EPMC8141490 | biostudies-literature
Project description:Using differential scanning calorimetry and lifetime analysis of trans-parinaric acid fluorescence, we have examined how cholesterol and cholesteryl phosphocholine (CholPC) affect gel-phase properties of palmitoyl ceramide (PCer) in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dioleyol-sn-glycero-3-phosphocholine (DOPC) bilayers. By 2H NMR, we also measured fluid-phase interactions among these lipids using deuterated analogs of POPC, PCer, and cholesterol. The PCer-rich gel phase in POPC bilayers (9:1 molar ratio of POPC to PCer) was partially and similarly dissolved (and thermostability decreased) by both cholesterol and CholPC (sterol was present equimolar to PCer, or in fourfold excess). In DOPC bilayers (4:1 DOPC/PCer molar ratio), CholPC was much more efficient in dissolving the PCer-rich gel phase when compared to cholesterol. This can be interpreted as indicating that PCer interaction with POPC was stronger than PCer interaction with DOPC. PCer-CholPC interactions were also more favored in DOPC bilayers compared to POPC bilayers. In the fluid POPC-rich phase, cholesterol increased the order of the acyl chain of d2-PCer much more than did CholPC. In DOPC-rich fluid bilayers, both cholesterol and CholPC increased d2-PCer acyl chain order, and the ordering induced by CholPC was more efficient in DOPC than in POPC bilayers. In fluid POPC bilayers, the ordering of 3-d1-cholesterol by PCer was weak. In summary, we found that in the gel phase, sterol effects on the PCer-rich gel phase were markedly influenced by the acyl chain composition of the fluid PC. The same was true for fluid-phase interactions involving the sterols. Our results further suggest that PCer did not display high affinity toward either of the sterols used. We conclude that the nature of unsaturated phospholipids (POPC versus DOPC) in bilayers has major effects on the properties of ceramide gel phases and on sterol-ceramide-phospholipid interactions in such complex bilayers.
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Project description:Background/objectivesConsumption of cholesterol-rich foods, such as eggs, has a minimal effect on circulating cholesterol levels in healthy humans. To gain insight, we investigated whether phospholipids rich in eggs (EPL) interfere with intestinal cholesterol absorption in vivo.Materials/methodsTo investigate the acute effect of EPL on intestinal cholesterol absorption, male C57BL/6J mice were orally administered with 6, 11, or 19 mg of EPL for three days. We also tested the effect of chronic EPL consumption on cholesterol metabolism in the small intestine and the liver in mice with diet-induced hypercholesterolemia. Male C57BL/6J mice were fed a high fat/high cholesterol (HF/HC; 35% fat, 0.25% cholesterol, w/w) diet for 4 weeks to induce hypercholesterolemia, and subsequently the mice were either fed 0, 0.4 or 0.8% (w/w) of EPL for 6 weeks.ResultsIntestinal cholesterol absorption was significantly decreased by the highest dose of acute EPL administration compared to control. Chronic EPL supplementation did not significantly alter intestinal cholesterol absorption nor plasma levels of total cholesterol and low-density lipoprotein cholesterol. In the small intestine and the liver, EPL supplementation minimally altered the expression of genes which regulate cellular cholesterol levels.ConclusionAlthough chronic EPL consumption was not able to counteract hypercholesterolemia in HF/HC-fed mice, acute EPL administration decreased intestinal cholesterol absorption. This study provides in vivo evidence that acute administration of PLs in eggs prevent cholesterol absorption in the intestine, suggesting a mechanism for a minimal effect of egg consumption on circulating cholesterol levels.
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Project description:Two 2-phenyl-benzofurans, moracin C {2-[3',5'-dihydroxy-4'-(3-methlbut-2-enyl)phenyl]-6-hydroxybenzofuran} and its isomer iso-moracin C{2-[3',5'-dihydroxy-4'-(3-methlbut-1-enyl)phenyl]-6-hydroxybenzofuran}, were comparatively studied using redox-related antioxidant assays and non-redox antioxidant assays. Moracin C always resulted in higher IC50 values than iso-moracin C in the redox-related antioxidant assays, including •O₂--inhibition, Cu2+-reducing power, DPPH•-inhibition, and ABTS⁺•-inhibition assays. In the non-redox antioxidant assay, moracin C and iso-moracin C underwent similar radical-adduct-formation (RAF), evidenced by the peaks at m/z 704 and m/z 618 in HPLC-MS spectra. In conclusion, both moracin C and iso-moracin C can act as 2-phenyl-benzofuran antioxidants; their antioxidant mechanisms may include redox-related ET and H⁺-transfer, and non-redox RAF. A double bond at the conjugation position can enhance the redox-related antioxidant potential, but hardly affects the RAF potential.
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Project description:It was shown that 100mug quantities of 4,4'-dimethyl[2-(3)H(2)]cholesta-8,14-dien-3beta-ol (IIIa), tritiated cholesta-8,14-dien-3beta-ol, 4,4'-dimethyl[2-(3)H(2)]cholesta-7,14-dien-3beta-ol, dihydro[2-(3)H(2)]lanosterol and [24-(3)H]lanosterol were converted by a 10000g supernatant of rat liver homogenate into cholesterol in 17%, 54%, 6%, 9.5% and 24% yields respectively. From an incubation of dihydro[3alpha-(3)H]lanosterol with a rat liver homogenate in the presence of a trap up to 38% of the radioactivity was found to be associated with a fraction that was unambiguously shown to be 4,4'-dimethylcholesta-8,14-dien-3beta-ol. Another related compound, 4,4'-dimethylcholesta-7,14-dien-3beta-ol was also shown to be equally effective in its ability to trap compound (IIIa) from an incubation of dihydro[3alpha-(3)H]lanosterol. The mechanism of the further conversion of the compound (IIIa) into cholesterol occurred by the reduction of the 14,15-double bond and involved the addition of a hydrogen atom from the medium to C-15 and another from the 4-position of NADPH to C-14. Two possible mechanisms for the removal of the 14alpha-methyl group in sterol biosynthesis are discussed.
| S-EPMC1176495 | biostudies-other
Project description:Amyloid-? peptides interact with cell membranes in the human brain and are associated with neurodegenerative diseases, such as Alzheimer's disease. An emerging explanation of the molecular mechanism, which results in neurodegeneration, places the cause of neurotoxicity of the amyloid- peptides on their potentially negative interaction with neuronal membranes. It is known that amyloid-? peptides interact with the membrane, modifying the membrane's structural and dynamic properties. We present a series of X-ray diffraction experiments on anionic model lipid membranes containing various amounts of cholesterol. These experiments provide experimental evidence for an interaction of both the full length amyloid-?1-42 peptide, and the peptide fragment amyloid-?22-40 with anionic bilayer containing cholesterol. The location of the amyloid-? peptides was determined from these experiments, with the full length peptide embedding into the membrane, and the peptide fragment occupying 2 positions-on the membrane surface and embedded into the membrane core.
| S-EPMC4704014 | biostudies-literature
Project description:The effect of lipid composition on the rate of cholesterol movement between cellular membranes is investigated using lipid vesicles. The separation of donor and acceptor vesicles required for rate measurement is achieved by differential centrifugation so that the lipid effect can be quantified in the absence of a charged lipid generally used for ion-exchange-based separation. The rate of cholesterol transfer from small unilamellar vesicles (SUVs) containing 50 mol% cholesterol to a common large unilamellar vesicle (LUV) acceptor containing 20 mol% cholesterol decreases with increasing mol% of sphingomyelin in the SUVs, while phosphatidylethanolamine and phosphatidylserine have no appreciable effect at physiologically relevant levels. There is a large decrease in rate when phosphatidylethanolamine constitutes 50 mol% of donor phospholipids. Interestingly, gangliosides which have the same hydrocarbon moiety as sphingomyelin exert an opposite effect. The effect of spingomyelin seems to be mediated by its ability to decrease the fluidity of the lipid matrix, while that of gangliosides may arise from a weakening of phosphatidylcholine-cholesterol interactions or from a more favourable (less polar) microenvironment for the desorption of cholesterol provided by the head-group interactions involving sugar residues. If the effect of asymmetric transbilayer distribution of lipids is taken into consideration, the observed composition-dependent rate changes could partly account for the large difference in the rates of cholesterol desorption from the inner and outer layers of plasma membrane. Such rate differences may be responsible for an unequal steady-state distribution of cholesterol among various cellular membranes and lipoproteins.
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