Effects of a high n-3 fatty acid diet on membrane lipid composition of heart and skeletal muscle in normal swine and in swine with the genetic mutation for malignant hyperthermia

Knowledge concerning the genetic defects underlying malignant hyperthermia (MH) has expanded rapidly in recent years. In contrast, our understanding of the accompanying physiological changes is less clear. In this regard, the aim of this study was to determine whether normal swine and swine susceptible to MH (both heterozygous and homozygous animals) differ in their abilities to incorporate n-3 (omega 3) fatty acids into their skeletal and heart muscles. Swine of each genotype were fed either a diet rich in n-3 fatty acids (i.e., 5% fish oil) or an equal caloric diet low in n-3 fatty acids (i.e., 5% coconut oil). All dietary supplementations were given over a 13-week period. Subsequently, for each muscle type the following was determined: 1) the relative fatty acid profiles of eight different phospholipid classes and of neutral lipids, and 2) the total phospholipid and the total lipid content. The incorporation of n-3 fatty acids (i.e., eicosapentaenoic acid and docosahexaenoic acid) occurred within the various phospholipids and neutral lipids without influencing their total lipid content. The increased content of n-3 fatty acids in neutral lipids of skeletal muscle was related to a decreased content of medium-chain saturated fatty acids, whereas an increased incorporation of n-3 fatty acids into the membrane phospholipids was often related to a decreased content of linoleic acid and/or arachidonic acid. In general, the pattern of n-3 fatty acid incorporation was considerably different between the normal animals and the MH homozygous and heterozygous animals. The significant interaction between diet-induced n-3 fatty acid profiles and the stress-susceptible MH genotype may indicate an altered mechanism for fatty acid turnover and a repair mechanism to maintain cellular functions and structure.

Improved separation and determination of phospholipids in animal tissues employing solid phase extraction

Separation of five glycerophospholipids having different polar groups, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylglycerol (PG) and cardiolipin (CL), was investigated by means of solid-phase extraction (SPE) cartridges. First, the phospholipids were retained in an aminopropyl-bonded phase (NH2) cartridge and subsequently eluted as neutral (PC and PE) and acidic (PS, PG and CL) glycerophospholipid fractions. Secondly, a combination of silica gel (SI) cartridge and NH2 cartridge was employed to separate five glycerophospholipids. The polarity of the eluent was responsible for neutral glycerophospholipid separation. Concerning acidic glycerophospholipids, the separation of PG and CL from PS depended mainly on the pH of the eluents, and the separation of PG and CL was affected by the solvent, depending on eluent polarities. Favorable recovery (not less than 95%, for five authentic phospholipids, 10-100 micrograms each) and repeatability (sigma = 2.3 for 10 micrograms ranges) were attained by the present method. This method of separation was applicable to the analysis of phospholipids in biological samples.

Quantitative analysis of biological membrane lipids at the low picomole level by nano-electrospray ionization tandem mass spectrometry

Nano-electrospray tandem mass spectrometry allows qualitative and quantitative analysis of complex membrane lipid mixtures at the subpicomole level. We have exploited this technique to selectively detect individual classes of phospholipids from unprocessed total cellular lipid extracts by either precursor ion or neutral loss scanning. This way phosphatidylcholine, sphingomyelin, phosphatidylinositol and -phosphates, phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, phosphatidic acid, and their plasmalogen analogues can be detected. The optimized ionization and fragmentation conditions described together with the principle of internal standardization by nonnatural analogues allow the rapid and quantitative determination of membrane lipid compositions down to sample amounts of 1000 cells.

ADP-ribosylation factor 1-regulated phospholipase D activity is localized at the plasma membrane and intracellular organelles in HL60 cells

ADP-ribosylation factor (ARF), a small GTPase required for vesicle formation, has been identified as an activator of phospholipase D (PLD), thus implying that PLD is localized at intracellular organelles. HL60 cells were prelabelled with [14C]acetate for 72 h and, after disruption, fractionated on a linear sucrose gradient. ARF1-regulated PLD activity in each fraction was assessed by measurement of phosphatidylethanol production. Two peaks of activity were identified, coincident with markers for Golgi/endoplasmic reticulum/granules (endomembranes) and plasma membrane respectively. Analysis of the fractions using exogenous phosphatidylcholine as substrate confirmed the presence of ARF1-dependent PLD activity in endomembranes and plasma membrane, and also identified an additional activity in the cytosol. In formyl-Met-Leu-Phe-stimulated cells, PLD activity as assessed by phosphatidylethanol formation was also associated with both the plasma membrane and endomembranes. Since ARF1-regulated PLD activity requires phosphatidylinositol 4,5-bisphosphate (PIP2), the distributions of inositol lipids and the kinases responsible for lipid phosphorylation were examined. PIP2 was highly enriched at the plasma membrane, whereas phosphatidylinositol (PI) and phosphatidylinositol 4-phosphate (PI4P), the precursors for PIP2 synthesis, were found predominantly at endomembranes. The distribution of PI 4-kinase and PI4P 5-kinase activities confirmed the plasma membrane as the major site of PIP2 production. However, endomembranes possessed substantial PI 4-kinase activity and some PI4P 5-kinase activity, illustrating the potential for PIP2 synthesis. It is concluded that:(1) ARF1-regulated PLD activity is localized at endomembranes and the plasma membrane, (2) PIP2 is available at both membrane compartments to function as a cofactor for ARF-regulated PLD, and (3) in intact cells, formyl-Met-Leu-Phe stimulates PLD activity at endomembranes as well as plasma membrane.

Basic fibroblast growth factor-stimulated arachidonic acid release in rat pancreatic acini: sequential action of tyrosine kinase, phospholipase C, protein kinase C and diacylglycerol lipase

This study was performed to evaluate the effect of human recombinant basic fibroblast growth factor on arachidonic acid release from rat pancreatic acini and to determine the cellular mechanism involved. From enzymatic assays, basic fibroblast growth factor did not significantly stimulate phospholipase A2 activity, whereas it significantly increased diacylglycerol lipase activity. Validity of phospholipase A2 or diacylglycerol lipase inhibitors was confirmed by their ability to inhibit phospholipase A2 or diacylglycerol lipase activities. Basic fibroblast growth factor increased intracellular accumulation and extracellular release of arachidonic acid from metabolically labelled acinar cells in a concentration- and time-dependent manner. This effect was maximal with 50 pM basic fibroblast growth factor and became significant after a 5-min incubation period. The protein tyrosine kinase inhibitor, 0.5 mM genistein, inhibited arachidonic acid release in basic fibroblast growth factor-stimulated acini, whereas 100 microM vanadate, a protein tyrosine phosphatase inhibitor, enhanced arachidonic acid release. Two phospholipase A2 inhibitors, mepacrine and aristolochic acid, failed to attenuate basic fibroblast growth factor-stimulated arachidonic acid release. A diacylglycerol lipase inhibitor RHC 80267 at 150 microM and 50 microM completely inhibited 50 pM basic fibroblast growth factor-induced intracellular accumulation and extracellular release of arachidonic acid, respectively. Furthermore, basic fibroblast growth factor stimulated arachidonic acid release was also inhibited by 10 microM U73122 and by 100 nM staurosporine, phospholipase C and protein kinase C respective inhibitors. Wortmannin, an inhibitor of basic fibroblast growth factor-stimulated phospholipase D, did not affect arachidonic acid release. 100 nM 4 beta-phorbol 12-myristate 13-acetate also increased arachidonic acid release, an effect also inhibited by staurosporine. Taken together, these data demonstrate activation of diacylglycerol lipase and arachidonic acid release in pancreatic acini upon stimulation by basic fibroblast growth factor, and strongly indicate that arachidonic acid release in response to basic fibroblast growth factor depends upon the sequential action of tyrosine kinase, phospholipase C, protein kinase C and diacylglycerol lipase but not from phospholipase A2 not phospholipase D activation.

The influence of acute ethanol ingestion on phospholipase D activity in rat pancreas. An in vitro and in vivo study

CONCLUSION

Since phosphatidic acid (PA), a product of phospholipase D(PLD), is known as a second messenger probably involved in cell proliferation and differentiation, our results potentially suggest a new mechanism for pancreatic tissue injury after ethanol ingestion.

BACKGROUND

The mechanisms by which ethanol causes pancreatic injury are still not clear. In vitro studies have suggested a relationship of PLD to ethanol metabolism. This study was undertaken to establish the involvement of PLD in ethanol metabolism in isolated pancreatic acini and to determine the influence of acute ethanol ingestion on PLD activity in pancreas and pancreatic growth after cerulein (Ce) infusion.

METHODS

Dispersed pancreatic acini prelabeled with 3H myristic acid were incubated with 500 pM Ce in the presence of different concentrations of ethanol; then labeled PA and phosphatidylethanol (PEt) production were measured under the same experimental conditions. For in vivo study, male rats were infused with Ce (0.25 microgram/kg/h) or saline; 1 h before infusion, animals were treated with 40% ethanol (5 g/kg p.o.) or saline, respectively. After 1, 2, and 48 h of Ce infusion, rats were killed; dispersed pancreatic acini were then prepared and PLD activity was measured. Pancreatic weight, protein, RNA, and DNA content were also established.

RESULTS

The production of PEt in vitro after Ce stimulation was significantly elevated with 1% ethanol in the medium. In the presence of different concentrations of ethanol (0.5-2%), a significant inhibition of PA accumulation in in vitro experiments was observed. The decrease of PA accumulation with ethanol was parallel to the increase of PEt production under the same experimental conditions. PLD activity was significantly elevated after 1 and 2 h of Ce infusion (116 and 105%, respectively), reaching control value after 48 h. Acute ethanol ingestion significantly diminished PLD activity after 1 and 2 h. After 48 h of Ce infusion, a significant increase in pancreatic weight, protein, RNA, and DNA content in pancreatic tissue was found. Ethanol was not able to influence pancreatic weight, proteins and RNA content. However, it had the potency to diminish DNA content after 48 h of Ce infusion.

Hydroperoxides of erythrocyte phospholipid molecular species formed by lipoxygenase correlate with alpha-tocopherol levels

The hydroperoxides corresponding to the main molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were determined after lipoxygenase treatment of erythrocyte membranes from healthy children. This work was a preliminary study prior to applying this analytical procedure to erythrocyte membranes from children with diseases associated with vitamin E deficiency. The total molecular species corresponding to 20:4 and 22:6 associated with 16:0 and 18:0 were significantly higher in PE (26.94 +/- 4.70 nmol/mg protein) than in PC (20.14 +/- 6.70 nmol/mg protein); these concentrations represented 63% of the total molecular species in PE and 22% in PC. However, the concentrations of hydroperoxides produced from these polyunsaturated fatty acid molecular species were in the same order of magnitude in PC (3.98 +/- 1.56 nmol/mg protein) and in PE (3.61 +/- 1.63 nmol/mg protein). In contrast, the molecular species concentrations containing two double bonds, such as 16:0/18:2 and 18:0/18:2 and their corresponding hydroperoxides, were clearly more elevated in PC than in PE. There was a positive relationship between the concentrations of alpha-tocopherol and each hydroperoxide of PC and PE, and this association was particularly strong in PE (P < or = 0.0001). These results suggest that alpha-tocopherol exerts a stabilizing effect toward hydroperoxides, limiting their further degradation into peroxyl radicals. The protective effect of alpha-tocopherol could be more effective in PE because more polyunsaturated fatty acids were present.

Lipidic characterization of full-grown amphibian oocytes and their plasma membrane-enriched fractions

The content and composition of neutral lipids and phosphoglycerides from full-grown prophase-arrested Bufo arenarum Hensel oocytes and from their ghost preparations were studied. The ghosts obtained are highly enriched in plasma membrane as suggested by the activity of 5'-nucleotidase, a marker enzyme, and the level of typical membrane components such as sphingomyelin, phosphatidylserine (PS), phosphatidylinositol (PI), and phosphatidic acid. In whole oocytes, triacylglyceride (TAG) comprises about 60% of the total lipids followed by phosphatidylcholine (PC), cholesterol, and phosphatidylethanolamine (PE). TAG and diacylglycerides have a similar unsaturation index. PC and PE account for about 80% of the phosphoglycerides in the whole oocyte and in their plasma membrane-enriched fractions. Arachidonic acid (20:4n-6), 18:0, and 16:0 make up about 80 mol% of the total fatty acids in PI in whole oocytes and ghost fractions. The unsaturation index in PS is higher in intact oocytes than in ghost preparations, probably owing to the significant amount of 20:4n-6 which comprises 23 mol% of the total fatty acids in whole oocytes. The fatty acid profile in phosphatidic acid from whole oocytes is rather different from that in ghosts. Sphingomyelin contains mainly saturated and monounsaturated fatty acids, 24:1 being the principal very long chain unsaturated fatty acid in both oocytes and ghosts.

Phospholipid profiles in the oral yeast Candida

Individual molecular species of phospholipids can now be readily detected using fast atom-bombardment mass spectrometry (FAB MS). The aim was to obtain detailed information on individual molecular species of Candida phospholipids using FAB MS. Lipids were extracted from Candida isolates and prepared for FAB MS analysis in negative-ion mode. Each isolate yielded several hundred anion peaks. The major anion peaks consistent with the presence of phospholipids included those of mass/charge (m/z) 836, 743, 715, 744 and 834 tentatively identified as phosphatidylethanolamine PE(43:5), phosphatidylglycerol PG(34:3), PG(32:3), PE(36:1) and PE(43:5). Major peaks consistent with the presence of carboxylate anions were of m/z 241, 253, 255, 277, 279, 281, 283, and 307 putatively identified as C15:0, C16:1, C18:3, C18:2, C18:1, C18:0 and C20:2 which also support the putative identifications of phospholipids. Such phospholipid profiles differ from those published for other microorganisms analysed by FAB MS. Quantitative differences were observed between different candidal species. Candida albicans may be readily differentiated from C. glabrata on the basis of its carboxylate anions. Within species, there are quantitative differences in phospholipid profiles. Thus, Candida has a unique combination of phospholipid analogues with potential chemosystematic significance.

[Entrapment of antibiotics in liposomes containing phosphatidylethanol]

Antibiotic entrapment to liposomes containing phosphatidyl ethanol, a negatively charged phospholipid, as a lipid component was studied. Antibiotics of various groups such as doxorubicin, rifampicin and doxycycline were entrapped to liposomes consisting of a mixture of phosphatidyl choline and phosphatidyl ethanol at a ratio of 1:1 (v/v) or phosphatidyl choline alone. It was shown that the liposomes containing phosphatidyl ethanol were able to entrap the antibiotics in higher amounts by comparison with the liposomes containing phosphatidyl choline. Phosphatidyl ethanol in the composition of the liposomes had the highest effect on the entrapment of doxorubicin.

Mammalian phospholipase D: activation by ammonium sulfate and nucleotides

Phospholipase D (PLD) associated with the rat kidney membrane was activated by guanine 5'-[gamma-thio]triphosphate and a cytosol fraction that contained ADP-ribosylation factor. When assayed by measuring the phosphatidyl transfer reaction to ethanol with exogenously added radioactive phosphatidylcholine as substrate, the PLD required a high concentration (1.6 M) of ammonium sulfate to exhibit high enzymatic activity. Other salts examined were far less effective or practically inactive, and this dramatic action of ammonium sulfate is not simply due to such high ionic strength. Addition of ATP but not of nonhydrolyzable ATP analogue adenosine 5'-[beta, gamma-imido]diphosphate further enhanced the PLD activation approximately equal to 2- to 3-fold. This enhancement by ATP needed cytosol, implying a role of protein phosphorylation. A survey of PLD activity in rat tissues revealed that, unlike in previous observations reported thus far, PLD was most abundant in membrane fractions of kidney, spleen, and liver in this order, and the enzymatic activity in brain and lung was low.

Age-associated changes in the content and fatty acid composition of brain glycerophospholipids

The fatty acid composition of total lipids and individual phospholipids and the ratio of cholesterol-to-phospholipid content were studied in cerebral cortex, subcortical white matter, cerebellum and medulla oblongata/pons in 4-, 21.5- and 28-month-old rats. The cholesterol-to-phospholipid molar ratio in subcortical white matter, medulla oblongata/pons and cerebellum in 28-month-old rats was found to be 17, 17 and 16% higher, respectively, than in adult rats. These alterations in the molar ratio were produced as a result of a net increase in cholesterol content rather than by changes in the total phospholipid content. The content of alkenylacylglycerophosphoethanolamine (alkenylacyl GPE) increased in 28-month-old rats with respect to 4-month-old rats, following the order cerebral cortex > cerebellum > medulla oblongata/pons > subcortical white matter. The fatty acid composition of total lipids showed an increase in monounsaturated fatty acids (MUFA) and a decrease in polyunsaturated fatty acid (PUFA) content with increasing age in all regions studied, such changes being more marked in cerebellum, medulla oblongata/pons and subcortical white matter than in cerebral cortex. The proportion of 22:6(n-3) in cholineglycerophospholipids in the different brain regions of 28-month-old rats showed a slight decrease with respect to that in adult rats following the order cerebellum > medulla oblongata/pons > subcortical white matter, whereas that of 20:4(n-6) decreased only in cerebellum. Ethanolamineglycerophospholipid fatty acid composition was modified in 28-month-old rats through a marked increase in monounsaturated fatty acids (18:1(n-9) and 20:1(n-9) specifically) in all brain areas. The MUFA content of alkenylacyl GPE increased with increasing age in all the regions studied, in the order cerebral cortex > medulla oblongata/pons > subcortical white matter > cerebellum. An increase in the MUFA content of diacylglycerophosphoethanolamine was observed in medulla oblongata/pons and cerebellum of aged rats with respect to control rats. PUFA content of alkenylacyl GPE decreased mainly in medulla oblongata/pons, cerebral cortex and subcortical white matter of aged rats. The PUFA content of serineglycerophospholipids was the most affected by aging. Changes occurred mainly in the content of 22:6(n-3), 22:4(n-6) and 20:4(n-6) in cerebellum and of 22:6(n-3) and 22:4(n-6) in subcortical white matter. Changes in the inositolglycerophospholipid fatty acid content of 28-month-old rats were observed mainly in medulla oblongata/pons, which showed a decrease in PUFA (22:4(n-6) and 22:6(n-3)) content and an increase in MUFA (18:1 and 20:1).

High-performance liquid chromatography of phosphatidic acid

This paper reviews existing high-performance liquid chromatographic (HPLC) methods for the analysis of phosphatidic acid (PA) in various sample matrices. In addition to the introductory background discussion on important aspects of PA in lipid biochemistry, the review provides comprehensive coverage in the areas of derivatization techniques, detection methods, and HPLC separation techniques. Conversions of PA to suitable derivatives enhance the detection sensitivity and improve the chromatographic behavior of the analytes. Detection methods include the use of state-of-the-art detectors and are discussed in terms of sensitivity, specificity, and compatibility with analytical systems. Pertinent normal-phase and reversed-phase HPLC data for PA are compiled from published methods.

ESBRA 1994 Award Lecture. Phosphatidylethanol formation: specific effects of ethanol mediated via phospholipase D

Phosphatidylethanol is a unique phospholipid which is formed in cell membranes only in the presence of ethanol. The reaction is catalysed by phospholipase D, an enzyme that normally catalyses the hydrolysis of phospholipids leading to the formation of phosphatidic acid. However, phospholipase D also utilizes short-chain alcohols as substrates resulting in the formation of the corresponding phosphatidylalcohol. This is a specific mechanism through which ethanol may interact with cell function. Phospholipase D is activated by several different receptors and has during recent years been suggested to play a role in cellular signalling. Secretory processes as well as long-term changes of cell function have been associated with the activation of phospholipase D. Since ethanol competes with water as a substrate for this enzyme, phosphatidylethanol is formed at the expense of the normal lipid product, phosphatidic acid, in an ethanol concentration-dependent manner. Therefore, the phospholipase D-mediated signal transduction diverges from production of the normal signalling lipid in the presence of ethanol. However, phosphatidic acid may also be formed by other pathways and their relative contribution to the formation of this lipid depends on the cell and receptor type. Thus, it is important to identify the signalling systems where phospholipase D dominates the lipid messenger production since these may be especially vulnerable to ethanol. In addition to a change in phospholipase D-mediated signal transduction, accumulation of phosphatidylethanol in cell membranes may also induce disturbances in cell function. Significant amounts of this abnormal phospholipid have been detected after ethanol exposure in brain and other organs from rat, in cultured cells as well as in human blood cells. The degradation of phosphatidylethanol is relatively slow and it remains in the cells after ethanol has disappeared. It is possible that an abnormal phospholipid that accumulates in cell membranes affects membrane-associated processes. Phosphatidylethanol is a lipid with a small, anionic head group and its biophysical properties are different compared with other phospholipids. Moreover, this lipid has been demonstrated to influence membrane characteristics, enzyme activities and levels of signalling molecules. Thus, both the inhibition of phospholipase D-mediated signal transduction and the accumulation of phosphatidylethanol represent possible pathways through which ethanol may disturb cell function.

Quantitation of phospholipids on thin layer chromatographic plates using a desk-top scanner

A method for quantitating phospholipids separated on thin layer chromatographic plates by computer-assisted photodensitometry is described. After development, the plates are stained with molibdic reagent and the image obtained is acquired as TIFF file in the memory of a personal computer. The color intensity of the single spots of the digitalized image is analyzed using a dedicated software. Sensitivity and reproducibility are adequate for most of the needs of lipid chemist. When compared to conventional photodensitometric procedures, the present method offers the advantage of requiring a much cheaper hardware.

Defective phospholipase D activation in Ki-ras-transformed NIH3T3 cells: evidence for downstream effector of PLC-gamma 1 in PDGF-mediated signal transduction

Platelet-derived growth factor (PDGF), a potent mitogen for fibroblasts and many other cell types, was used to examine phosphatidylcholine-specific phospholipase D (PLD), phosphoinositide-specific phospholipase C (PI-PLC) and tyrosine phosphorylation in NIH3T3 fibroblast and its Ki-ras-transformed derivative, DT. When cells prelabeled with [3H] myristic acid were stimulated by 10 and 50 ng/ml of PDGF in presence of 0.3% butanol, formation of phosphatidylbutanol (PtdBut) was increased three to six fold in NIH3T3 fibroblasts whereas it was marginal in DT cells. Myo-[3H]inositol-labeled cells showed higher inositol phosphate production in nontransformed control fibroblasts, indicating higher phospholipase C activity compared to the transformed DT cells. PDGF caused increase in tyrosine phosphorylation of a group of proteins with 110-130 kDa, PLC-gamma 1 and PDGF receptor in NIH3T3 cells. There was no significant increase in tyrosine phosphorylation in both PDGF receptor and PLC-gamma 1 in DT cells. These results suggest that PLD acts as a downstream effector molecule of PLC-gamma 1 in the PDGF-mediated signal transduction pathway.

Isoprenoid-mediated changes in the glycerophospholipid molecular species of the sterol auxotrophic fungus Lagenidium giganteum

The mosquito pathogenic fungus Lagenidium giganteum (Oomycetes: Lagenidiales) is a sterol auxotroph that can grow vegetatively in the absence of these compounds, but requires an exogenous source of sterols to enter its sexual and asexual reproductive cycles. Electrospray mass spectrometry (MS) and electrospray MS/MS were used to examine three major glycerophospholipid molecular species--glycerophosphocholine (GPC), glycerophosphoethanolamine (GPE) and glycerophosphoinositol (GPI)--from fungal mycelium and nuclei grown in defined medium with and without isoprenoids which induce (cholesterol and ergosterol) or do not induce (squalene, cholestane) reproduction. Testosterone supplementation of defined media inhibited growth of L. giganteum, so the effect of this steroid on phospholipid metabolism could not be assessed. Mycelium grown in defined media supplemented with these isoprenoids produced significantly different quantities of total phospholipid relative to unsupplemented media and to each other, ranging from a mean of 292 micrograms phosphate per g wet weight for cholesterol-supplemented media to 56 micrograms phosphate per g wet weight for mycelium grown in the presence of squalene. A very large percentage of the GPC (69-80 mol%) and GPI (74-79 mol%) molecular species from mycelia and nuclei contained ether linkages. GPE molecular species had 13-20 mol% ether-containing moieties. The elevated levels of ether lipids may be related to the sterol auxotrophic nature of the fungus. Isoprenoid supplementation of defined growth media resulted in many significant changes in molecular species for all three lipid classes. Significant differences (P < 0.05) in the percentage of total cell ether lipids in GPC and GPE were generated by isoprenoid supplements to culture media. Mycelium grown in the presence of the two sterols which induce asexual and sexual reproduction in L. giganteum, cholesterol and ergosterol, had a significantly greater percentage of ether-containing GPE moieties. The glycerolipid species from nuclei isolated from cultures grown with cholesterol and ergosterol were similar to the composition of nuclei isolated from fungus cultured in defined medium without any supplement or supplemented with squalene. The nuclear membrane from mycelia grown in cholestane-supplemented media, however, had a very different glycerophospholipid composition relative to either whole cells or nuclei from cells grown on other media. It appears that one of the reasons that cyclic isoprenoids such as cholestane do not induce fungal reproduction is that they drastically alter the nuclear membrane glycerophospholipid composition.

Antibody ligation of CD7 leads to association with phosphoinositide 3-kinase and phosphatidylinositol 3,4,5-trisphosphate formation in T lymphocytes

The CD7 40-kDa glycoprotein is present on a major subset of human T cells and in the presence of phorbol esters mediates an accessory pathway of T cell activation. Hitherto, the intracellular events elicited by CD7 have been ill-defined. This report demonstrates that cross-linking of CD7 results in the formation of phosphatidic acid in the absence of phosphatidylinositol-4,5-bisphosphate metabolism and also the formation of D-3 phosphoinositides lipids which have been postulated to act as intracellular regulatory molecules. The magnitude of D-3 phosphoinositide formation was similar to that induced by CD3. Both the CD7- and CD3-induced elevation of phosphatidylinositol 3,4,5-trisphosphate approximately 5-10 fold less than that elicited by ligation of the costimulatory molecule CD28 by its counter receptor CD80. The formation of D-3 phosphoinositides following ligation of CD7 coincided with the co-association of CD7 with phosphoinositide 3-kinase, the enzyme which mediates the formation of D-3 phosphoinositide lipids. In contrast, ligation of another reported T cell accessory molecule CD5, failed to elicit formation of D-3 phosphoinositides, implying that phosphoinositide 3-kinase is not coupled to all T cell molecules with accessory functions. Since D-3 phosphoinositides have been suggested to play a pivotal role in T cell costimulatory signals induced by CD28, the results presented in this study suggest that CD7 may also influence T cell activation via this pathway.

Origin of triacylglycerol moiety of plasma very low density lipoproteins in the rat: structural studies

We have compared the molecular species composition of the glycerolipids of rat liver and rat plasma very low density lipoproteins (VLDL). There were differences in the stereospecific distribution of the fatty acids in the triacylglycerols (TG) of the liver and of VLDL. While chiral and reversed phase chromatography with mass spectrometry (LC/MS) revealed great similarities in positional distribution and molecular association of the fatty acids between the sn-1,2-diacylglycerol (DG) moieties of the VLDL and liver TG, the corresponding sn-2,3-DG were distinctly different. The free hepatic sn-1,2-DG and the sn-1,2-DG moiety contained within hepatic phosphatidic acid showed a maximum 60% homology to the sn-1,2-DG contained within the TG of the liver and of VLDL. By contrast, the smaller pool of hepatic free sn-2,3-DG was nearly identical to the sn-2,3-DG moiety contained in the TG of the liver. These differences between hepatic and VLDL TG indicate that direct transfer of hepatic triacylglycerols is not a major mechanism of VLDL TG formation. On the other hand, the results suggest that stored hepatic TG are largely hydrolyzed to sn-1,2-DG and then reesterified to TG before being secreted as VLDL TG. Although an involvement of 2-monoacylglycerol pathway could not be excluded, it probably plays a minor role in VLDL TG formation. Our data suggest that a minimum of 60% of the VLDL TG could have been derived via hydrolysis to DG and reesterification, and a maximum of 40% could have originated via the conventional phosphatidic acid pathway.

Generation of glycerophospholipid molecular species in the yeast Saccharomyces cerevisiae. Fatty acid pattern of phospholipid classes and selective acyl turnover at sn-1 and sn-2 positions

Acyl chains linked to phospholipids of the yeast, Saccharomyces cerevisiae, are mainly C16:1 and C18:1 accompanied by minor amounts of C14:0, C16:0 and C18:0. In view of this rather simple fatty acid composition, the question arose whether in yeast, as in higher eukaryotes, fatty acyl groups were characteristically distributed among the sn-1 and sn-2 positions of distinct phospholipid classes. Analysis of fatty acids linked to the sn-1 and sn-2 positions of the major phospholipids showed that indeed saturated fatty acyl groups predominated in the sn-1 positions. While the percentage of saturated fatty acids was low (10%) in phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) from cells grown on rich medium, it was higher in phosphatidylserine (PtdSer) (25%) and highest in phosphatidylinositol (PtdIns) (41%). Oleate was mainly linked to position sn-2, while palmitoleate predominated in position sn-1. Striking differences in the fatty acid distribution of phospholipids that are metabolically closely related (e.g. PtdSer and PtdEtn, PtdEtn and PtdCho, and PtdIns and PtdSer) suggest that pathways must exist for the generation of distinct phospholipid molecular species within the different phospholipid classes. The highly selective incorporation of exogenous [14C]palmitic acid (90%) and [3H]oleic acid (99%) into the sn-2 position of PtdCho, and the preferential incorporation of these fatty acids into the sn-2 position of PtdEtn (70 and 90%, respectively, for palmitic and oleic acid) are compatible with the postulate that phospholipase A2-mediated deacylation followed by reacylation of the lysophospholipids is involved in the generation of phospholipid species in yeast.

Activation of phospholipase D induced by platelet-derived growth factor is dependent upon the level of phospholipase C-gamma 1

The mechanism of phospholipase D (PLD) activation by platelet-derived growth factor (PDGF) was examined using a NIH 3T3 fibroblast cell line (3T3-gamma 1) that stably overexpresses PLC-gamma 1 isozyme. Immunoblot analysis revealed that 3T3-gamma 1 cells contained about 10-fold more PLC-gamma 1 than a control cell line (3T3-C) transfected with expression vector lacking PLC-gamma 1 cDNA. PDGF-stimulated PLD activation was 10-fold greater in 3T3-gamma 1 cells than in 3T3-C cells, indicating that PLD activation is dependent upon the level of PLC-gamma 1. Phorbol 12-myristate 13-acetate (PMA) treatment increased PLD activity to a similar extent in both 3T3-gamma 1 cells and control cells. Pretreatment with tyrosine kinase inhibitors including staurosporine and genistein decreased PLD activity by 82.6% and 87.2%, respectively, and completely blocked tyrosine phosphorylation of PDGF receptor and PLC-gamma 1 in 3T3-gamma 1 cells stimulated with PDGF. Moreover, down-regulation of protein kinase C by pretreatment of PMA caused complete inhibition of PDGF- and PMA-stimulated PLD activation. Therefore, these results suggest that PDGF-induced PLD activation may be a consequence of primary stimulation of PLC-gamma 1 and that PLD may play a role downstream from PLC-gamma 1 in PDGF-triggered mitogenesis.

Microwave frequency dependence of ESR spectra from spin labels undergoing two-site exchange in myelin proteolipid membranes

Measurement at two microwave frequencies allows the unambiguous assignment of two-component spin-label ESR spectra such as are observed frequently from biological membranes and reconstituted protein-lipid complexes. Consistent spectral subtractions were obtained with 9 and 34 GHz ESR spectra of spin-labeled lipids from lipid-protein complexes for two related myelin proteins, and the 34 GHz difference spectra further showed restriction of axial lipid rotation at the hydrophobic protein surface. Extension of lineshape simulations with the exchange-coupled Bloch equations to 34 GHz, by allowing for nonaxial g tensors and including linear dispersion distortions, yielded consistent rates of lipid exchange at the protein interface and reflected the different lipid selectivities for the two proteins. The present data at two microwave frequencies leave little doubt that the spin-label ESR spectra from these myelin protein-lipid complexes consist of two components in slow exchange.

Involvement of phospholipase D in the activation of transcription factor AP-1 in human T lymphoid Jurkat cells

The induction of the AP-1 transcription factor has been ascribed to the early events leading to T lymphocyte activation. We have examined the possibility that stimulation of phospholipase D (PLD) may regulate activation of transcription factor AP-1 in human T cells by transfecting human T lymphocyte Jurkat cells with a plasmid containing an AP-1 enhancer element and a chloramphenicol acetyltransferase reporter gene. We have detected activatable PLD in Jurkat cells, and we have found that addition of phosphatidic acid (PA), the physiologic product of PLD action on phospholipids, is rapidly incorporated into Jurkat cells and leads to activation of transcription factor AP-1. Treatment of Jurkat cells with anti-CD3 mAb activated both PLD and transcription factor AP-1. Wortmannin, an inhibitor of receptor-coupled PLD activation, blocked the anti-CD3-induced increases in both PLD activity and AP-1 enhancer activity. We found a good correlation in the transfected cells between PLD activation and induction of AP-1 enhancer activity under different experimental conditions. Furthermore, ethanol, an inhibitor of the PLD pathway, blocked the anti-CD3-stimulated AP-1 enhancer activity. However, this anti-CD3-mediated response was not inhibited by neomycin, an inhibitor of phosphoinositide hydrolysis. The increases in AP-1 enhancer activity induced by PA or anti-CD3 mAb were efficiently abrogated by the presence of propranolol, an inhibitor of PA phosphohydrolase and protein kinase C (PKC). Furthermore, the PA- and the anti-CD3-induced increases in AP-1 enhancer activity were blocked by the presence of PKC inhibitors or by PKC down-regulation. These data indicate that PLD stimulation can activate the transcription factor AP-1 in T lymphocytes, and suggest that the induction of AP-1 enhancer factor activity by PA is mediated via PKC stimulation, either through a direct activating effect of PA or through PA-derived diacylglycerol formation. These data also provide evidence for a role of PLD-derived lipids in the induction of AP-1 enhancer activity resulting from stimulation of the TCR/CD3 complex, suggesting that increased PLD activity can play an important role in T lymphocyte activation.

Quantitation of the fatty acid composition of phosphatidic acid by capillary gas chromatography electron-capture detection with picomole sensitivity

We describe a relatively simple and sensitive method to measure femtomole amounts of phosphatidic acid in cells. Phosphatidic acid was extracted from cells in the presence of 1-heptadecanoyl-2-heptadecanoyl-sn-glycero-3-phosphate as an internal standard, purified by two-dimensional thin-layer chromatography, and hydrolyzed to its constituent free fatty acids which were then derivatized to the corresponding pentafluorobenzyl esters. Pentafluorobenzyl esters of fatty acids were analyzed by gas chromatography with electron-capture detection. Long-chain fatty acids were resolved with excellent signal-to-noise ratios. Using heptadecanoic acid as an internal standard for quantitation, as little as 1 fmol of pentafluorobenzyl ester of stearic acid was detected with a linear response up to 10 pmol. Linear detector responses were obtained for all major classes of fatty acids. For phosphatidic acid measurement, the detection limit was at least 50 fmol thus achieving a 1000-fold increase in sensitivity compared to the most sensitive of the previously described methods. An example is provided of quantitating phosphatidic acid from minute amounts of biological samples such as islets of Langerhans.

Comparative study of high-glucose effect on phosphatidylcholine hydrolysis of cultured retinal capillary pericytes and endothelial cells

Recent studies have suggested the importance of phosphatidylcholine (PC) hydrolysis in the control of cell growth. Because of the different replicative behavior between retinal pericytes and endothelial cells in early diabetic retinopathy, we have compared PC metabolism of these two types of cells under high-glucose conditions. Both types of cells growing in controlled glucose conditions were prelabeled with [32P]P(i) for testing phosphatidylethanol (PEt), a unique product of PC-specific phospholipase D, with [14C]glycerol for determining 1,2-diacylglycerol (DAG) de novo synthesis and labeled with selective fatty acids for PC-derived and phosphoinositide (PI)-derived DAG. The prelabeled cells were stimulated with ATP, a purinergic agonist. Analyses of products of PI and PC hydrolysis were carried out by TLC and/or HPLC. In both types of cells, ATP activated PI and PC hydrolysis. The dose and time dependencies of IP3 and PI-derived DAG formation with respect to ATP were essentially identical. When the level of IP3 and PI-derived DAG returned toward the baseline, a second increase in DAG mainly derived from PC occurred, lasting at least 1 h. High glucose altered DAG kinetics: in pericytes it suppressed both PI- and PC-derived DAG formation; in endothelial cells it stimulated the PC-derived DAG increase, but kept the PI-derived DAG unchanged. DAG de novo synthesis was stimulated in endothelial cells growing in high glucose, but was left unchanged in pericytes. Contrast to endothelial cells, in pericytes, subsequent mitogenic process may be negatively regulated by the inhibitory effects of high glucose on PI and PC hydrolysis, resulting in reduced levels of PC-derived DAG.