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PubMed1999

Lowered omega3 polyunsaturated fatty acids in serum phospholipids and cholesteryl esters of depressed patients.

Depression is associated with a lowered degree of esterification of serum cholesterol, an increased C20:4omega6/C20:5omega3 ratio and decreases in omega3 fractions in fatty acids (FAs) or in the red blood cell membrane. The aims of the present study were to examine: (i) serum phospholipid and cholesteryl ester compositions of individual saturated fatty acids (SFAs), monounsaturated FAs (MUFAs) and polyunsaturated FAs (PUFAs) in major depressed patients vs. healthy volunteers; (ii) the relationships between the above FAs and lowered serum zinc (Zn), a marker of the inflammatory response in depression; and (iii) the effects of subchronic treatment with antidepressants on FAs in depression. The composition of the FAs was determined by means of thin layer chromatography in conjunction with gas chromatography. Lipid concentrations were assayed by enzymatic colorimetric methods. The oxidative potential index (OPI) of FAs was computed in 34 major depressed inpatients and 14 normal volunteers. Major depression was associated with: increased MUFA and C22:5omega3 proportions and increased C20:4omega6/C20:5omega3 and C22:5omega6/C22:6omega3 ratios; lower C22:4omega6, C20:5omega3 and C22:5omega3 fractions in phospholipids; lower C18:3omega3, C20:5omega3 and total (sigma)omega3 FAs, and higher C20:4omega6/C20:5omega3 and sigmaomega6/sigmaomega3 ratios in cholesteryl esters; lower serum concentrations of phospholipids and cholesteryl esters; and a decreased OPI. In depression, there were significant and positive correlations between serum Zn and C20:5omega3 and C22:6omega3 fractions in phospholipids; and significant inverse correlations between serum Zn and the sigmaomega6/sigmaomega3, C20:4omega6/C20:5omega3, and C22:5omega6/C22:6omega3 ratios in phospholipids. There was no significant effect of antidepressive treatment on any of the FAs. The results show that, in major depression, there is a deficiency of omega3 PUFAs and a compensatory increase in MUFAs and C22:5omega6 in phospholipids. The results suggest that: (i) there is an abnormal metabolism of omega3 PUFAs in depression; (ii) the FA alterations in depression are related to the inflammatory response in that illness; and (iii) the disorders may persist despite successful antidepressant treatment.

Adult↗
PubMed1991

Modification of membrane phospholipid fatty acyl composition in a leukemic T cell line: effects on receptor mediated intracellular Ca2+ increase.

The effect of modifying fatty acyl composition of cellular membrane phospholipids on receptor-mediated intracellular free Ca2+ concentration ([Ca2+]i) increase was investigated in a leukemic T cell line (JURKAT). After growing for 72 h in medium supplemented with unsaturated fatty acids (UFAs) and alpha-tocopherol, the fatty acyl composition of membrane phospholipids in JURKAT cells was extensively modified. Each respective fatty acid supplemented in the culture medium was readily incorporated into phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine in the JURKAT cells. The total n-6 fatty acyl content was markedly reduced in phosphatidylinositol and phosphatidylcholine of cells grown in the presence of n-3 fatty acids (alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid). Conversely, in the presence of n-6 fatty acids (linoleic acid and arachidonic acid), the total n-3 fatty acyl content was reduced in all the phospholipids examined. In n-3 and n-6 polyunsaturated fatty acid (PUFA) modified JURKAT cells, the total n-9 monounsaturated fatty acyl content in the phospholipids were markedly reduced. Changing the fatty acyl composition of membrane phospholipids in the JURKAT cells appears to have no affect on the presentation of the T cell receptor/CD3 complex or the binding of anti-CD3 antibodies (OKT3) to the CD3 complex. However, the peak increase in [Ca2+]i and the prolonged sustained phase elicited by OKT3 activation were suppressed in n-3 and n-6 PUFA but not in n-9 monounsaturated fatty acid modified cells. In Ca2+ free medium, OKT3-induced transient increase in [Ca2+]i representing Ca2+ release from the inositol 1,4,5-trisphosphate-sensitive Ca2+ stores, were similar in control and UFA modified cells. Using Mn2+ entry as an index of plasma membrane Ca2+ permeability, the rate of fura-2 fluorescence quenching as a result of Mn2+ influx stimulated by OKT3 in n-9 monounsaturated fatty acid modified cells was similar to control cells, but the rates in n-3 and n-6 PUFA modified cells were significantly lower. These results suggest that receptor-mediated Ca2+ influx in JURKAT cells is sensitive to changes in the fatty acyl composition of membrane phospholipids and monounsaturated fatty acids appears to be important for the maintenance of a functional Ca2+ influx mechanism.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1999

Phospholipid metabolism and resistance to glucocorticoid-induced apoptosis in a human leukemic cell line: a 31P-NMR study using a phosphonium analog of choline.

In order to evaluate any connection between phospholipid metabolism and the dexamethasone resistance in CEM-C1-15 leukemic cells, a phosphonium analog of choline was used to study the phospholipid metabolism in dexamethasone-sensitive and dexamethasone-resistant leukemic cells using 31P-NMR spectroscopy. Measurements were done on the two cell lines in the presence and absence of dexamethasone, a synthetic glucocorticoid steroid. Dexamethasone was found to cause a significant reduction in the phospholipid metabolism of the dexamethasone-sensitive CEM-C7-14 cells. In contrast, dexamethasone caused a significant enhancement of the phospholipid metabolism in the dexamethasone-resistant CEM-C1-15 cells, indicating a significant difference between the two cell lines in phospholipid metabolism during apoptosis. The results of this study suggest the involvement of phospholipid metabolism in the mechanism of dexamethasone resistance in the CEM-C1-15 cells.

Apoptosis↗
PubMed1997

Ethanol alters brain phospholipid levels which correlate with altered brain morphology.

The effects of embryonic exposure on brain phospholipid levels were studied by injecting various concentrations of ethanol into fertile chicken eggs at 0 days of development. At 18 days of development, the levels of total phospholipids and various phospholipid classes were assayed in brain tissue and correlated to neuron densities within the cerebral hemispheres and the optic lobes. Although ethanol concentrations ranging from 0 to 3700 microns/Kg egg wt. failed to influence either total brain weight or total brain phospholipid levels, ethanol-induced changes in the levels of individual phospholipid classes were observed. When injected with 7 microns of ethanol/Kg egg wt., a 2- to 3-fold increase in brain phosphatidylethanolamine (PE) levels were observed with reduced levels of brain phosphatidylcholine (PC) and brain sphingomyelin (SP). When injected with 74 microns of ethanol/Kg egg wt., ethanol-induced increases in brain phosphatidylserine (PS) and PE were observed with ethanol-induced decreases in brain PC and SP. Cell fractionation studies demonstrated ethanol-induced increases in brain PE and PS and ethanol-induced decreases in brain PC and SP in nuclear, mitochondrial, and microsomal membranes. These ethanol-induced alterations in brain phospholipid profiles correlated with ethanol-induced reductions in neuron densities within the cerebral hemispheres and optic lobes.

Animals↗
PubMed1998

Low activity of key phospholipid catabolic and anabolic enzymes in human substantia nigra: possible implications for Parkinson's disease.

To determine whether increased oxidative stress in substantia nigra of patients with idiopathic Parkinson's disease might be related to decreased ability of nigral cells to detoxify oxidized membrane phospholipids, we compared levels of the major phospholipid metabolizing enzymes in autopsied substantia nigra with those in non-nigral (n = 11) brain areas of the normal human brain. Whereas most enzymes possessed a relatively homogeneous distribution, the activity of the major phospholipid catabolizing enzyme phospholipase A2, assayed in the presence of calcium ions, varied amongst different regions, with substantia nigra possessing the lowest activity. Similarly, calcium-independent phospholipase A2 activity, although possessing a relatively homogeneous regional distribution, was also low in the substantia nigra. This, coupled with low activity of phosphoethanolamine- and phosphocholine-cytidylyltransferases, major regulatory enzymes of phospholipid synthesis, in this brain region, suggest that the rate of phospholipid turnover is low in the substantia nigra. Low activity of key phospholipid catabolic and anabolic enzymes in human substantia nigra might result in reduced ability to repair oxidative membrane damage, as may occur in Parkinson's disease.

Acyltransferases↗
PubMed2001

Cloning and expression in phospholipid containing cultures of the gene encoding the specific phosphatidylglycerol/phosphatidylinositol transfer protein from Aspergillus oryzae: evidence that the pg/pi-tp is tandemly arranged with the putative 3-ketoacyl-CoA thiolase gene.

The phosphatidylglycerol/phosphatidylinositol transfer protein (PG/PI-TP) is a new and original phospholipid transfer protein (PLTP) isolated from the Deuteromycete, Aspergillus oryzae. We have isolated a genomic clone of the A. oryzae pg/pi-tp using a probe derived from the corresponding cDNA and sequenced the complete gene. The DNA sequence analysis revealed that pg/pi-tp gene is composed of three exons encoding a 18,823 Da protein of 175 amino acids as previously described and of two introns as deduced by cDNA and genomic sequence alignment. The isolated pg/pi-tp gene do not show similarity with other PLTP genes or the deduced PG/PI-TP protein with proteins already known. Comparison of the encoded PG/PI-TP with other deduced proteins from recent genomic or cDNA sequence from databases revealed that the PG/PI-TP was close to two encoded proteins deduced from the cDNA database of Aspergillus nidulans (54% identity and 68% similarity) and the second from Neurospora crassa (53% identity and 76% similarity). Therefore, we suggested that both proteins might belong to the PLTP family. Southern blot analysis of A. oryzae genomic DNA show that the PG/PI-TP was encoded by a single gene. Expression of pg/pi-tp was performed in phospholipid containing cultures with increasing carbon source concentrations in order to study the regulation of the PLTPs in the filamentous fungus cell. This was done to know if a high density culture could yield a high amount of biomass with high phospholipid transfer activity. Results showed that phospholipids as compared to glucose in standard cultures stimulated mycelial growth and global phospholipid transfer activity, but not the pg/pi-tp transcript accumulation. However, high concentration of both carbon sources yielded an inhibition of the expression of the pg/pi-tp gene and of the global phospholipid transfer activity. In conclusion, both carbon sources are not suitable to increase the PLTP production in high density cultures for biotechnological applications. Finally, using the gene walking sequencing method it is demonstrated that the pg/pi-tp is tandemly arranged on opposite DNA strands in a tail-to-tail orientation with a putative gene encoding the 3-ketoacyl-CoA thiolase (EC 2.3.1.16). Unlike the pg/pi-tp gene, this thiolase gene show a putative 'beta-oxidation box' and encodes a putative 44,150 Da protein of 321 amino acids composed of a putative N-terminal PTS2 (Peroxisomal Targeting Signal) consensus sequence for the peroxisome targeting. Comparison of the amino acid sequence of the A. oryzae thiolase to that of the Yarrowia lipolytica showed a 50% identity and a 69% similarity.

Acetyl-CoA C-Acyltransferase↗
PubMed2000

Fatty acid composition of the milk lipids of Fulani women and the serum phospholipids of their exclusively breast-fed infants.

We previously reported that, relative to milk of women elsewhere in the world, the lipid fraction of milk of Fulani women in northern Nigeria contained relatively low proportions of alpha-linolenic acid and docosahexaenoic acid (DHA). This led us to question the essential fatty acid status of Fulani infants and the relation between the proportion of critical n-3 and n-6 fatty acids in the serum phospholipids of the mothers, their milk, and the serum phospholipids of their exclusively breast-fed infants. We were also interested in the effect de novo intermediate chain length-fatty acids (C10-C14) had on the proportions of critical and non-essential fatty acids in milk. Capillary gas-liquid chromatography was used to analyze the fatty acid content of the total milk lipids of 34 Fulani women, as well as the fatty acid content of serum phospholipids of the women and their breast-fed infants during the first 6 months of life. The proportions of critical n-3 and n-6 fatty acids in the milk of the Fulani women were adequate, but the proportions of these same fatty acids were low in their exclusively breast-fed infants. The serum phospholipids of the infants contained 18.8% linoleic acid, 0.13% alpha-linolenic acid, 12.8% arachidonic acid, and 3.40% DHA, whereas, the mean percentages of linoleic, alpha-linolenic, arachidonic and DHA in the serum phospholipids of the Fulani mothers' were 21.4, 0.20, 9.79, and 1.97, respectively. There was a strong positive correlation between fatty acid content of serum phospholipids of Fulani women and the fatty acid content of their milk lipids. As the proportion of C10-C14 fatty acids in the milk lipids increased, the proportions of critical n-3 and n-6 fatty acids in milk remained relatively constant; however, proportions of three non-essential fatty acids decreased dramatically. C10-C14 fatty acids do not appear to displace critical n-3 and n-6 fatty acids in milk.

Adolescent↗
PubMed1999

Serial phospholipid analysis in preterm infants: comparison of Exosurf and Survanta.

The initial clinical response to synthetic or natural surfactant is different and long-term complications from meta-analysis suggest that bronchopulmonary dysplasia and retinopathy of prematurity may be increased in infants given synthetic surfactant. It is possible that this is due to differences in the phospholipid composition of lung fluid following administration of these surfactants. Infants less than 32 weeks gestation with respiratory distress syndrome (RDS) were randomly assigned to receive either Exosurf, an artificial surfactant, or Survanta, a natural surfactant. Endotracheal or hypopharyngeal aspirates were obtained from these infants and from control infants who had normal lungs. The aspirates were taken prior to and up to 28 days following surfactant administration. The different phospholipids were separated by thin layer chromatography and expressed as a percent of total phospholipid measured. Infants with normal lungs had a higher proportion of phosphatidylcholine than those with RDS prior to treatment. The infants with normal lungs had a greater proportion of phosphatidylinositol in their lung aspirates than both treatment groups at 24 h. Infants in the Survanta group had a higher proportion of phosphatidylglycerol at 48 h than the group with normal lungs. No other differences were found in phospholipid composition up to 28 days. There were no major differences in the phospholipid profile in infants with RDS treated with either Exosurf or Survanta. In conclusion, neither the clinical differences initially seen between infants treated with either Exosurf or Survanta, nor the long-term outcome could be explained by the phospholipid composition of serial samples of lung aspirates.

Analysis of Variance↗
PubMed1980

Comparative determination of plasma phospholipids by automated gas--liquid chromatographic and manual colorimetric phosphorus methods.

Plasma samples obtained during a prevalence study of hyperlipemia in a free-living urban population were analyzed for phosphatidylcholine, sphingomyelin and lysophosphatidylcholine content by automated high-temperature gas--liquid chromatographic (GLC) and manual colorimetric phosphorus (thin-layer chromatographic, TLC) methods. The GLC estimates were obtained from a quantitative analysis of the diacylglycerol, ceramide and monoacylglycerol moieties released from the parent phospholipids by digestion with phospholipase C, while the TLC estimates were derived by manual colorimetric phosphorus analyses of the individual phospholipid classes resolved by TLC. On samples analyzed over a two-year period the methods gave excellent correlation for the total phospholipids (r = 0.98), phosphatidylcholine (r = 0.98) and sphingomyelin (r = 0.90), but resulted in a poor agreement for lysophosphatidylcholine (r = 0.69). Comparable results were obtained for estimates of these phospholipids in plasma very low density, low density and high density lipoproteins. The between-method coefficient of variation ranged from 3 to 5% for phosphatidylcholine and from 5 to 10% for sphingomyelin. The relative error for the estimates of lysophosphatidylcholine ranged from 10 to 25%, and was due to the inclusion in the GLC estimates of a variable proportion of plasma free monoacylglycerols. Other differences between the two methods are due to various analytical errors and biases inherent in the two techniques. The within-day, within GLC, relative error averaged 1% for phosphatidylcholine, 3% for sphingomyelin and 5% for lysophosphatidylcholine. The apparent high precision and accuracy of the GLC method recommend it as an alternative to conventional direct methods of phospholipid analyses based on TLC isolation of lipid classes and colorimetric measurements of their phosphorus content. The GLC analyses of the plasma phospholipids are particularly convenient in conjunction with GLC measurements of plasma cholesterol and triacylglycerols, where a smaller throughput of samples is not a limitation and where both total amount and relative proportion of the lipids are of interest.

Autoanalysis↗
PubMed1997

Solid-phase extraction of phospholipids from hemoglobin solutions using Empore styrene-divinylbenzene disks.

Styrene-divinylbenzene Empore disks were investigated for the extraction of phospholipids from red blood cells or aqueous solutions of hemoglobin as a means to reduce the time and solvent use required in sample preparation. Red blood cells are the source for hemoglobin used in the preparation of a hemoglobin-based oxygen carrier which is being developed to replace blood in transfusion therapy. Phospholipids are a major component of the membrane of red blood cells, and are toxic when administered directly into the vasculature. Sensitive analytical methods are required to detect phospholipids to ensure that concentrations in purified hemoglobin are well below toxic levels. This requires isolation from large volumes of purified hemoglobin solutions. The method described utilizes Empore disks to extract phospholipids from 30 ml of stroma free Hb preparations. Phosphatidylethanolamine, phosphatidylinositol, phosphatidylcholine and sphingomyelin were recovered with an average of 92% yield. The recovery of phosphatidylserine was 65%. The use of solvent and time required for sample preparation were reduced by an average of 80% relative to liquid-liquid extraction. The capacity of the 47-mm disk for the total of five phospholipids exceeds 0.3 mg. The method has been used for quantitation of phospholipids in red blood cells and stroma free hemoglobin solutions.

Chromatography, High Pressure Liquid↗
PubMed1998

A developmental profile of the effects of ethanol on the levels of chick brain phospholipids.

The effects of embryonic exposure to ethanol on brain phospholipid levels were studied by injecting various concentrations of ethanol, ranging from 0 to 149 microns kg-1 egg, into fertile chicken eggs at 0 days of incubation. At 7, 9, 11, 15 and 18 days of incubation, brains were collected and the levels of total phospholipids and various phospholipid classes were measured. Although embryonic exposure to ethanol failed to influence total phospholipid levels, ethanol-induced changes in the levels of individual phospholipid classes were observed. Ethanol-induced increases in the levels of phosphatidylethanolamine (PE) and phosphatidylserine (PS) and ethanol-induced decreases in the levels of phosphatidylcholine (PC) were observed at 9, 11, 15 and 18 days of incubation. Ethanol-induced decreases in brain sphingomyelin (SP) levels were observed at 7 and 18 days of development. These ethanol-induced changes in brain phospholipid levels preceded detectable alcohol dehydrogenase (ADH) activities in both brain and liver.

Acetaldehyde↗
PubMed2002

The acyl composition of mammalian phospholipids: an allometric analysis.

Data concerning the acyl composition of tissue phospholipids from mammal species, ranging in size from the shrew (7 g) to cattle (370 kg), has been collated from the literature and analysed allometrically. Phospholipids from heart, skeletal muscle, liver and kidney exhibited similar allometric trends whereby phospholipids had a significant decrease in unsaturation index (number of double bonds per 100 acyl chains) as species body size increased whilst there was no change in the percent of unsaturated acyl chains. Whilst total polyunsaturate content did not change with body mass, both heart and skeletal muscle phospholipids showed a significant allometric decrease in the omega-3 polyunsaturate content. The content of the highly polyunsaturated docosahexaenoic acid (22:6 n-3) in phospholipids showed significant and substantial allometric decline with increasing body mass in all four tissues (exponents ranged from -0.19 in liver to -0.40 in skeletal muscle). Brain phospholipids showed no allometric trends in acyl composition and were highly polyunsaturated in all species. These trends are discussed in light of the hypothesis that the relative content of polyunsaturated acyl chains in membranes, and especially docosahexaenoate (22:6 n-3), can act as a membrane pacemaker for metabolic activity.

Acylation↗
PubMed2006

[Fractionation and high performance capillary electrophoretic analysis of phospholipids].

Phosphatidylcholine of high purity (PC, content 92.80%) was prepared from market soybean power phospholipids (PC content 14.05%) by using solvent extraction and column chromatography. As the main objective, micellar electrokinetic capillary chromatography (MECC) was established for the separation and analysis of phospholipids. MECC conditions such as surfactant and its concentration, pH of running buffer solution, organic modifier and its volume content, concentration of buffer solution, temperature etc were optimized to provide good separation and larger peak area of phospholipids. The optimum MECC conditions were as follows: running buffer system of 35 mmol/L sodium deoxycholate (SDC)-1 mmol/L borax buffer solution/n-propanol (57 : 43, v/v) with pH 8.30, column temperature of 44 degrees C, applied voltage of 25 kV and ultraviolet (UV) detection at 200 nm. Addition of standards was used to identify the components of phospholipids. External standard method was used to determine PC content. As the results shown, five components of phospholipids could be effectively separated under the optimum MECC conditions. Correlation coefficient within 0.1 - 1 g/L PC concentration reached 0.999 0. The average recovery of PC was 98.0%. The intra-day relative standard deviation (RSD) and inter-day RSD of peak area of PC were 1.36% and 3.27%, respectively. The qualitative result of PC obtained by MECC was consistent with that determined by thin layer chromatography and infrared analysis, respectively. So MECC can be used as an effective tool for the separation, analysis and quality control of phospholipids.

Buffers↗
PubMed2006

Characterizing the phospholipid profiles in mammalian tissues by MALDI FTMS.

Discussed here is an analytical method for profiling lipids and phospholipids directly from mammalian tissues excised from Mus musculus (house mouse). Biochemical analysis was accomplished through the use of matrix-assisted laser desorption/ionization (MALDI) Fourier transform mass spectrometry, where whole tissue sections of mouse brain, heart, and liver were investigated. Lipid and phospholipid ions create complex MALDI mass spectra containing multiple ions with different m/z values corresponding to the same fundamental chemical species. When a computational sorting approach is used to group these ions, the standard deviation for observed relative chemical abundance can be reduced to 6.02%. Relative standard deviations of 10% are commonly accepted for standard chromatographic phospholipid analyses. Average mass measurement accuracy for 232 spectra representing three tissue types from 12 specimens was calculated to be 0.0053 Da. Further it is observed, that the data and the analysis between all the animals have near-identical phospholipid contents in their brain, heart, and liver tissues, respectively. In addition to the need to accurately measure relative abundances of phospholipid species, it is essential to have adequate mass resolution for complete and accurate overall analysis. It is reasonable to make mass composition assignments with spectral resolving power greater than 8000. However, results from the present study reveal 14 instances (C12 carbon isotope) of multiple m/z ions having the same nominal value that require greater resolution in order that overlap will not occur. Spectra measured here have an average resolving power of 12 000. It is established that high mass resolution and mass accuracy coupled with MALDI ionization provide for rapid and accurate phospholipid analysis of mammalian tissue sections.

Animals↗
PubMed1993

Thermotropic phase behavior of mixtures of long chain fatty acid species of cerebroside sulfate with different fatty acid chain length species of phospholipid.

The thermotropic phase behavior of asymmetric, long fatty acid chain species of cerebroside sulfate, C24-CBS and C26-CBS, with symmetric species of phosphatidylcholine (PC) containing fatty acid chains of 14-18 carbons in length (diC14-PC, diC16-PC, diC18-PC) and dimyristoylphosphatidylethanolamine (diC14-PE) in 0.1 M KCl was studied by differential scanning calorimetry. Novel cerebroside sulfate (CBS) spin labels containing long chain C24 and C26 fatty acid spin labels with the nitroxide group on the twenty-second carbon were used to study the lipid organization of the gel phases of these mixtures. The phase diagrams of all the mixtures indicated the presence of two immiscible gel phases at low CBS concentrations. All except the C26-CBS/diC14-PC mixture had eutectic phase behavior at low CBS concentrations suggesting that the long fatty acid chain of the CBS species had a destabilizing effect on the gel phase of most of the phospholipids. The C26-CBS/diC14-PC mixture had peritectic phase behavior at low CBS concentrations indicating a stabilizing effect of the CBS C26 acyl chain on diC14-PC. These results are consistent with the relative compatibility of the CBS acyl chain length with the bilayer thickness of the PC; only in the case of the C26-CBS/diC14-PC mixture is the acyl chain of CBS long enough to span the PC bilayer. At intermediate to high CBS concentrations, the CBS and phospholipid (PL) were miscible with the exception of the C24-CBS/diC18-PC combination, which had eutectic phase behavior over a wide concentration range. Thus when the PL acyl chain length was similar to the sphingosine chain length of CBS, CBS bilayers could accommodate symmetric phospholipid molecules better than phospholipid bilayers could accommodate asymmetric molecules of CBS. Use of the spin labels indicated that, at low temperatures and at intermediate to high CBS concentrations, all of the mixtures were in a triple chain mixed interdigitated gel phase which immobilized the spin label. This gel phase slowly transformed over a wide temperature range to a double chain partially interdigitated gel phase in which the spin labels had much more motion. This transformation could be detected as a broad low enthalpy transition by differential scanning calorimetry. In all cases the presence of phospholipid destabilized the mixed interdigitated phase. Stabilization of the partially interdigitated bilayer by intermolecular hydrogen bonding interactions must outweigh the destabilizing forces caused by disruptions in packing and van der Waals interactions between CBS molecules resulting from insertion of molecules of phospholipid into this type of bilayer.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry, Differential Scanning↗
PubMed1992

Role of apolipoprotein E in hepatic lipase catalyzed hydrolysis of phospholipid in high-density lipoproteins.

We reported earlier that hepatic lipase (HL)-catalyzed hydrolysis of phospholipid monolayers is activated by apolipoprotein (apo) E [Thuren et al. (1991b) J. Biol. Chem. 266, 4853-4861]. On the basis of these studies, it was postulated that apoE-rich high-density lipoproteins (HDL) were preferred substrates for HL. In the present study, we tested this hypothesis, as well as further characterizing the activation of HL hydrolysis of phospholipid by apoE. The apoE-rich HDL, referred to as HDL-I, were isolated by heparin-Sepharose chromatography, and the phospholipid hydrolysis by HL was compared to an apoE-poor HDL, designated HDL-II. The hydrolysis of HDL-I phosphatidylcholine was approximately 3-fold higher than HDL-II, supporting the hypothesis that HL preferably hydrolyzes the phospholipids in apoE-rich HDL. In order to gain additional insight into the nature of the activation, we used phospholipid monolayers as model systems. Comparison of the ability of the two thrombolytic fragments of apoE (22 kDa, residues 1-191; 12 kDa, residues 192-299) revealed that only the 12-kDa fragment was capable of activating the hydrolysis of phospholipid by HL (1.75-fold). However, activation was less than with the intact protein (2.8-fold for apoE3), suggesting that the intact protein was required for full activation. The fact that the 12-kDa fragment, which represents a major lipid region of the protein, did activate HL suggests that activation occurs at the lipid-water interface.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1992

Enzyme-catalyzed oxidation of cholesterol in mixed phospholipid monolayers reveals the stoichiometry at which free cholesterol clusters disappear.

In this study, we have used cholesterol oxidase as a probe to study cholesterol/phospholipid interactions in mixed monolayers at the air/water interface. Mixed monolayers, containing a single phospholipid class and cholesterol at differing cholesterol/phospholipid molar ratios, were exposed to cholesterol oxidase at a lateral surface pressure of 20 mN/m (at 22 degrees C). At equimolar ratios of cholesterol to phospholipid, the average rate of cholesterol oxidation was fastest in unsaturated phosphatidylcholine mixed monolayers (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and egg yolk phosphatidylcholine), intermediate in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, and slowest in sphingomyelin monolayers (egg yolk or bovine brain sphingomyelin). The average oxidation rate in mixed monolayers was not exclusively a function of monolayer packing density, since egg yolk and bovine brain sphingomyelin mixed monolayers occupied similar mean molecular areas even though the measured average oxidation rate was different with these two phospholipids. This suggests that the phospholipid acyl chain composition influenced the oxidation rate. The importance of the phospholipid acyl chain length on influencing the average oxidation rate was further examined in defined phosphatidylcholine mixed monolayers. The average oxidation rate decreased linearly with increasing acyl chain lengths (from di-8:0 to di-18:0). When the average oxidation rate was examined as a function of the cholesterol to phospholipid (C/PL) molar ratio in the monolayer, the otherwise linear function displayed a clear break at a 1:1 stoichiometry with phosphatidylcholine mixed monolayers, and at a 2:1 C/PL stoichiometry with sphingomyelin mixed monolayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol↗
PubMed1983

Amphipathic helix and its relationship to the interaction of calcitonin with phospholipids.

Salmon, porcine, and human calcitonins interact with phosphatidylglycerol to form water-soluble complexes, but these peptides do not interact with the zwitterionic lipids phosphatidylcholine or sphingomyelin. The calcitonins are more helical in the presence of dimyristoylphosphatidylglycerol than in its absence, but human calcitonin is considerably less helical than the other two, particularly in the presence of the lipid. This may explain the previously reported faster rate of degradation of human compared with salmon calcitonin in vivo. The ability of human calcitonin to solubilize dimyristoylphosphatidylglycerol and to alter the phase transition properties of this phospholipid while maintaining a low content of helix indicates that the presence of an amphipathic helix is not a requirement for these effects. The binding of salmon calcitonin to dimyristoylphosphatidylglycerol has been studied by determining the dependence of the circular dichroism properties of the peptide on the concentration of lipid. At 25 degrees C, salmon calcitonin binds to five molecules of dimyristoylphosphatidylglycerol with an affinity constant of 1 X 10(5) M-1. Little change in these parameters is observed at 38 degrees C, and the complex is stable over a wide range of temperatures both above and below the phase transition temperature. The rate of reaction of salmon calcitonin with dimyristoylphosphatidylglycerol is rapid at or above the phase transition temperature of the lipid but not at low temperatures. Salmon calcitonin also interacts with egg phosphatidylglycerol. These results demonstrate that salmon calcitonin can react with phosphatidylglycerol at or above its phase transition temperature to form complexes which are at least kinetically stable both above and below the phase transition temperature. Salmon calcitonin can solubilize mixtures of dimyristoylphosphatidylglycerol and dimyristoylphosphatidylcholine containing 25% or more of the former phospholipid. The helical content of the peptide in the presence of these lipid mixtures is dependent on the fraction of the lipid which is phosphatidylglycerol, with larger fractions of this lipid leading to the formation of a higher helical content. At 25% phosphatidylglycerol, salmon calcitonin can solubilize the lipid mixture without much increase in the helix content of the peptide, again demonstrating that an amphipathic helical structure is not required for the solubilization of phospholipids. Ionic bonding appears to be an important component in the binding of the cationic calcitonins to phospholipids. Salmon calcitonin binds to the acidic phospholipids phosphatidylinositol and phosphatidic acid, but not to zwitterionic phospholipids. In addition, high concentrations of NaCl cause the dissociation of the complex between salmon calcitonin and dimyristoylphosphatidylglycerol.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗