Quantification of human platelet inositides and the influence of ionic environment on their incorporation of orthophosphate-32P

Rapid, accurate, and sensitive fatty acid ethyl ester determination by gas chromatography-mass spectrometry

BACKGROUND

Fatty acid ethyl esters (FAEEs) are useful markers of ongoing alcohol use and may be associated with alcohol-induced damage to the liver and pancreas. In this article, we describe a novel method for rapid determination of the three major FAEEs found in human plasma.

METHODS

Internal standard, ethyl heptadecanoate, was added to plasma samples, and FAEEs were isolated by acetone precipitation, hexane lipid extraction, and amino-propyl silica solid phase extraction. FAEEs were quantitated by gas chromatography-mass spectrometry (GC-MS) using a nonpolar dimethylpolysiloxane column. The accuracy, precision, specificity, and sensitivity of the assay were defined from plasma samples from recently drinking and abstinent persons, with and without the addition of FAEEs.

RESULTS

Individual FAEE peaks demonstrated excellent resolution. Instrument time was reduced by more than 60%. The lower limit of detection was 5 to 10 nM, and the lower limit of quantitation for each FAEE was 60 nM (for 22 samples with known concentration 60 nM, x +/-SD: 61 +/- 5.7, 57 +/- 5.7, and 57 +/- 5.9 nM, for ethyl palmitate, ethyl oleate, and ethyl stearate, respectively). Instrument precision (coefficient of variance, CV) for these three FAEEs was 0.3%, 0.4%, and 0.7%, respectively. Intra-assay precision (CV) for total FAEEs was less than 7%. FAEEs were absent in 49 samples from abstinent persons. FAEEs were detected in all 76 samples with associated positive blood alcohol levels.

CONCLUSIONS

Our method of FAEE analysis is rapid and potentially useful in research and clinical studies. FAEE determination using this method is precise, accurate, sensitive, and specific and deserves broader application.

Alcoholic pancreatitis in rats: injury from nonoxidative metabolites of ethanol

The mechanism by which alcohol injures the pancreas remains unknown. Recent investigations suggest a role for fatty acid ethyl ester (FAEE), a nonoxidative metabolite of ethanol, in the pathogenesis of alcohol pancreatitis. In this study, we characterized ethanol-induced injury in rats and evaluated the contribution of oxidative and nonoxidative ethanol metabolites in this form of acute pancreatitis. Pancreatic injury in rats was assessed by edema, intrapancreatic trypsinogen activation, and microscopy after infusing ethanol with or without inhibitors of oxidative ethanol metabolism. Plasma and tissue levels of FAEE and ethanol were measured and correlated with pancreatic injury. Ethanol infusion generated plasma and tissue FAEE and, in a dose-dependent fashion, induced a pancreas-specific injury consisting of edema, trypsinogen activation, and formation of vacuoles in the pancreatic acini. Inhibition of the oxidation of ethanol significantly increased both FAEE concentration in plasma and pancreas and worsened the pancreatitis-like injury. This study provides direct evidence that ethanol, through its nonoxidative metabolic pathway, can produce pancreas-specific toxicity in vivo and suggests that FAEE are responsible for the development of early pancreatic cell damage in acute alcohol-induced pancreatitis.

Differential regulation of phosphoinositide metabolism by alphaVbeta3 and alphaVbeta5 integrins upon smooth muscle cell migration

Smooth muscle cell migration is a key step of atherosclerosis and angiogenesis. We demonstrate that alpha(V)beta(3) and alpha(V)beta(5) integrins synergistically regulate smooth muscle cell migration onto vitronectin. Using an original haptotactic cell migration assay, we measured a strong stimulation of phosphoinositide metabolism in migrating vascular smooth muscle cells. Phosphatidic acid production and phosphoinositide 3-kinase IA activation were triggered only upon alpha(V)beta(3) engagement. Blockade of alpha(V)beta(3) engagement or phospholipase C activity resulted in a strong inhibition of smooth muscle cell spreading on vitronectin. By contrast, blockade of alpha(V)beta(5) reinforced elongation and polarization of cell shape. Moreover, Pyk2-associated tyrosine kinase and phosphoinositide 4-kinase activities measured in Pyk2 immunoprecipitates were stimulated upon cell migration. Blockade of either alpha(V)beta(3) or alpha(V)beta(5) function, as well as inhibition of phospholipase C activity, decreased both Pyk2-associated activities. We demonstrated that the Pyk2-associated phosphoinositide 4-kinase corresponded to the beta isoform. Our data point to the metabolism of phosphoinositides as a regulatory pathway for the differential roles played by alpha(V)beta(3) and alpha(V)beta(5) upon cell migration and identify the Pyk2-associated phosphoinositide 4-kinase beta as a common target for both integrins.

Molecular characterization of a phosphatidylcholine-hydrolyzing phospholipase C

While searching for a phospholipase C (PLC) specific for phosphatidylcholine in mammalian tissues, we came across such an activity originating from a contamination of Pseudomonas fluorescens. This psychrophilic bacterium was found to contaminate placental extracts upon processing in the cold. The secreted phosphatidylcholine-hydrolyzing PLC was purified by a combination of chromatographic procedures. As substrates, the enzyme preferred dipalmitoyl-phosphatidylcholine and 1-palmitoyl-2-arachidonoyl-phosphatidylcholine over phosphatidylinositol. The active enzyme is a monomer of approximately 40 kDa. As for other bacterial PLCs, the enzyme requires Ca2+ and Zn2+ for activity; dithiothreitol affected the activity due to its chelation of Zn2+, but this inhibition could be compensated for by addition of ZnCl2. The compound D609, described to selectively inhibit phosphatidylcholine-specific PLCs, caused half-inhibition of the P. fluorescens enzyme at approximately 420 microM, while 50-fold lower concentrations similarly affected PLCs from Bacillus cereus and Clostridium perfringens. Partial peptide sequences obtained from the pure P. fluorescens enzyme after tryptic cleavage were used to clone a DNA fragment of 3.5 kb from a P. fluorescens gene library prepared from our laboratory isolate. It contains an ORF of 1155 nucleotides encoding the PLC. There is no significant sequence homology to other PLCs, suggesting that the P. fluorescens enzyme represents a distinct subclass of bacterial PLCs. The protein lacks cysteine residues and consequently contains no disulfide bonds. Interestingly, P. fluorescens reference strain DSMZ 50090 is devoid of the PLC activity described here as well as of the relevant coding sequence.

Linkage of oxidative and nonoxidative ethanol metabolism in the pancreas and toxicity of nonoxidative ethanol metabolites for pancreatic acinar cells

BACKGROUND

Alcohol abuse is a major cause of pancreatic damage. Recent experimental evidence suggests that fatty acid ethyl esters (FAEE), nonoxidative ethanol metabolites, injure pancreatic acinar cells. Linkage between oxidative and nonoxidative metabolism of ethanol in the pancreas may contribute to increased FAEE levels.

METHODS

To study the association between oxidative and nonoxidative ethanol metabolism, FAEE concentration and FAEE synthase activity in rat pancreatic and liver homogenates incubated with ethanol were evaluated with and without inhibitors of oxidative ethanol metabolism. For toxicity studies, trypsinogen activation peptide synthesis as a measure of pancreatic cell injury was quantitated in unstimulated and cerulein-stimulated isolated pancreatic acinar cells incubated with ethanol or FAEE.

RESULTS

Inhibition of oxidative ethanol metabolism results in a 2- to 3-fold increase in nonoxidative ethanol metabolism to FAEE in pancreas and in liver. Both ethanol and FAEE induce increased intracellular trypsinogen activation by more than 50% in the presence of physiologic concentrations of cerulein in vitro.

CONCLUSIONS

These findings demonstrate that the inhibition of oxidative ethanol metabolism results in an increase in flux through the nonoxidative pathway and support the proposition that alcohol-induced pancreatic injury is mediated at least in part by FAEE, which are important products of pancreatic ethanol metabolism.

FcγRIIA requires a Gi-dependent pathway for an efficient stimulation of phosphoinositide 3-kinase, calcium mobilization, and platelet aggregation

FcγRIIA, the only Fcγ receptor present in platelets, is involved in heparin-associated thrombocytopenia (HIT). Recently, adenosine diphosphate (ADP) has been shown to play a major role in platelet activation and aggregation induced by FcγRIIA cross-linking or by sera from HIT patients. Herein, we investigated the mechanism of action of ADP as a cofactor in FcγRIIA-dependent platelet activation, which is classically known to involve tyrosine kinases. We first got pharmacologic evidence that the ADP receptor coupled to Gi was required for HIT sera or FcγRIIA clustering-induced platelet secretion and aggregation. Interestingly, the signaling from this ADP receptor could be replaced by triggering another Gi-coupled receptor, the α2A-adrenergic receptor. ADP scavengers did not significantly affect the tyrosine phosphorylation cascade initiated by FcγRIIA cross-linking. Conversely, the Gi-dependent signaling pathway, initiated either by ADP or epinephrine, was required for FcγRIIA-mediated phospholipase C activation and calcium mobilization. Indeed, concomitant signaling from Gi and FcγRIIA itself was necessary for an efficient synthesis of phosphatidylinositol 3,4,5-trisphosphate, a second messenger playing a critical role in the process of phospholipase Cγ2 activation. Altogether, our data demonstrate that converging signaling pathways from Gi and tyrosine kinases are required for platelet secretion and aggregation induced by FcγRIIA.

FcγRIIA requires a Gi-dependent pathway for an efficient stimulation of phosphoinositide 3-kinase, calcium mobilization, and platelet aggregation

FcγRIIA, the only Fcγ receptor present in platelets, is involved in heparin-associated thrombocytopenia (HIT). Recently, adenosine diphosphate (ADP) has been shown to play a major role in platelet activation and aggregation induced by FcγRIIA cross-linking or by sera from HIT patients. Herein, we investigated the mechanism of action of ADP as a cofactor in FcγRIIA-dependent platelet activation, which is classically known to involve tyrosine kinases. We first got pharmacologic evidence that the ADP receptor coupled to Gi was required for HIT sera or FcγRIIA clustering-induced platelet secretion and aggregation. Interestingly, the signaling from this ADP receptor could be replaced by triggering another Gi-coupled receptor, the α2A-adrenergic receptor. ADP scavengers did not significantly affect the tyrosine phosphorylation cascade initiated by FcγRIIA cross-linking. Conversely, the Gi-dependent signaling pathway, initiated either by ADP or epinephrine, was required for FcγRIIA-mediated phospholipase C activation and calcium mobilization. Indeed, concomitant signaling from Gi and FcγRIIA itself was necessary for an efficient synthesis of phosphatidylinositol 3,4,5-trisphosphate, a second messenger playing a critical role in the process of phospholipase Cγ2 activation. Altogether, our data demonstrate that converging signaling pathways from Gi and tyrosine kinases are required for platelet secretion and aggregation induced by FcγRIIA.

The hydrolysis of fatty acid ethyl esters in low-density lipoproteins by red blood cells, white blood cells and platelets

Fatty acid ethyl esters (FAEE), esterification products of fatty acids and ethanol, have been implicated as toxic mediators of ethanol ingestion. In this study, we investigated the in vitro hydrolysis of FAEE reconstituted in low-density lipoproteins (LDL) when incubated with human blood, cell free plasma, red blood cells, white blood cells, and platelets. We also determined the metabolic fate of the fatty acid originally incorporated in the FAEE following FAEE hydrolysis. When FAEE were incubated with human red blood cells. white blood cells, or platelets, at physiologic cell counts, 80% of the FAEE were hydrolyzed at 2 h. The FAEE-derived fatty acid was predominantly found in phospholipid and free fatty acid fractions. Cell free plasma contained minimal FAEE hydrolytic activity. These studies demonstrate that FAEE are degraded to free fatty acids and ethanol by the cellular elements in the blood. The generation of free fatty acids from extensive hydrolysis of FAEE adds support to the growing concept that at least some of the toxic effects of FAEE are mediated by the free fatty acids generated upon hydrolysis of the ethyl esters.

Involvement of lipids in ferriprotoporphyrin IX polymerization in malaria

Approximately 70% of the initial ferriprotoporphyrin IX polymerizing activity in cell-free preparations of erythrocytes infected with Plasmodium berghei was recovered in a chloroform extract. No polymerizing activity remained in the residue. In studies to identify substances that promote FP polymerization, arachidonic, linoleic, oleic, and palmitoleic acids, 1-mono- and di-oleoylglycerol, and the detergents, SDS, Tween 80, and n-octyl-glucopyranoside, were active. Tri-oleoylglycerol, cholesterol, di-oleoylphosphatidylethanolamine, and stearic and palmitic acids were inactive. The model lipid, mono-oleoylglycerol (250 nmol), co-precipitated with FP from a 0.09 M acetate medium at pH 5 and promoted the polymerization of 215 nmol (61%) of the ferriprotoporphyrin IX in the precipitate during a 24-h incubation at 37 degrees C. Polymerization was maximal at pH 5, it was approximately linear for 2 h, and it continued at a decreasing rate for 24 h. The polymer contained exclusively ferriprotoporphyrin IX (97+/-1.3%, mean+/-S.E., n=4) and exhibited the solubility and the electronic absorption and infrared spectral characteristics of the sequestered ferriprotoporphyrin IX of hemozoin. Detergents presumably promote polymerization in an acid medium by helping to dissolve monomeric FP. We suggest that unsaturated lipids co-precipitate with FP in the parasite's acidic food vacuole and also dissolve sufficient monomeric FP to allow polymerization.

Phosphatidylinositol 3,4,5-trisphosphate-dependent stimulation of phospholipase C-gamma2 is an early key event in FcgammaRIIA-mediated activation of human platelets

Platelets express a single class of Fcgamma receptor (FcgammaRIIA), which is involved in heparin-associated thrombocytopenia and possibly in inflammation. FcgammaRIIA cross-linking induces platelet secretion and aggregation, together with a number of cellular events such as tyrosine phosphorylation, activation of phospholipase C-gamma2 (PLC-gamma2), and calcium signaling. Here, we show that in response to FcgammaRIIA cross-linking, phosphatidylinositol (3,4, 5)-trisphosphate (PtdIns(3,4,5)P3) is rapidly produced, whereas phosphatidylinositol (3,4)-bisphosphate accumulates more slowly, demonstrating a marked activation of phosphoinositide 3-kinase (PI 3-kinase). Inhibition of PI 3-kinase by wortmannin or LY294002 abolished platelet secretion and aggregation, as well as phospholipase C (PLC) activation, indicating a role of this lipid kinase in the early phase of platelet activation. Inhibition of PLCgamma2 was not related to its tyrosine phosphorylation state, since wortmannin actually suppressed its dephosphorylation, which requires platelet aggregation and integrin alphaIIb/beta3 engagement. In contrast, the stable association of PLCgamma2 to the membrane/cytoskeleton interface observed at early stage of platelet activation was fully abolished upon inhibition of PI 3-kinase. In addition, PLCgamma2 was able to preferentially interact in vitro with PtdIns(3,4,5)P3. Finally, exogenous PtdIns(3,4,5)P3 restored PLC activation in permeabilized platelets treated with wortmannin. We propose that PI 3-kinase and its product PtdIns(3,4,5)P3 play a key role in the activation and adequate location of PLCgamma2 induced by FcgammaRIIA cross-linking.

Transacylase-mediated alkylacyl-GPC synthesis and its hydrolysis by phospholipase D occur in separate cell compartments in the human neutrophil

Subcellular localizations of CoA-independent transacylase and phospholipase D enzymes have been investigated in human neutrophils performing a two-step gradient system to separate plasma membranes from internal membranes and from the bulk of granules. The internal membranes were constituted by endoplasmic reticulum and by a subpopulation of specific and tertiary granules. The enzymes activities were assayed in vitro on gradient fractions using exogenous substrates. Following cell prelabelling with [3H]alkyllyso-GPC, we also analyzed the in situ localization of labelled products involving the action of both enzymes. The CoA-independent transacylase activity, together with the CoA-dependent transacylase and acyltransferase activities were only located in the internal membranes. Following 15 min cell labelling, part of the [3H]alkylacyl-GPC was recovered in plasma membranes indicating a rapid redistribution of the acylated compound. Very high contents in arachidonate containing [3H]alkylacyl-GPC were recovered both in plasma membranes and internal membranes. Phospholipase D activity being assayed in the presence of cytosol, GTP gamma S and gradient fractions, only the plasma membrane fractions from resting or stimulated cells allowed the enzyme to be active. The [3H]alkylacyl-GP and [3H]alkylacyl-GPethanol, phospholipase D breakdown products from [3H]alkylacyl-GPC, obtained after neutrophil prelabelling and activation by phorbol myristate acetate, were exclusively present in the plasma membranes. In contrast, the secondary generated [3H]alkylacylglycerols were equally distributed between plasma and internal membranes. No labelled product was recovered on azurophil granules. These data demonstrate that internal membranes are the site of action of the CoA-independent transacylase and plasma membranes are the site of action of the phospholipase D. This topographical separation between CoA-independent transacylase which generated substrate and phospholipase D which degraded it, suggested that subcellular localisation and traffic of substrates within the cell can be important to regulate the enzymes.

Low-density lipoprotein reconstituted with fatty acid ethyl esters as a physiological vehicle for ethyl ester delivery to intact cells

Fatty acid ethyl esters (FAEEs), esterification products of ethanol and fatty acids, have been found selectively in the organs damaged by ethanol abuse, and on that basis have been implicated as contributors to ethanol-induced organ damage. To directly assess the cytotoxic potential of FAEEs with intact cells in a physiological system, solubility must be achieved for these highly nonpolar lipids in aqueous medium. After ethanol ingestion, FAEEs can be found within low-density lipoproteins (LDLs). Therefore, to achieve solubility with FAEEs bound to a naturally occurring lipid carrier, we developed a method for FAEE solubilization and delivery to cells in culture. We synthesized radiolabeled FAEEs and incorporated them into human LDL particles that bind to LDL receptors and deliver FAEEs to intact cells. Ethyl palmitate and ethyl oleate were incorporated into LDLs yielding molar ratios of FAEEs to LDLs of 2,153 +/- 249 and 4,208 +/- 403, respectively. LDL reconstituted with FAEE had the same electrophoretic mobility on agarose gel electrophoresis as native LDL, indicating that the reconstituted LDL (rLDL) was not oxidatively modified. Quantitative analysis of the solubilization of FAEEs in aqueous medium was investigated by adding FAEEs to tissue culture medium either directly or reconstituted in LDL at a concentration of 27 microM. The percentage of FAEE quantitated was 40.0 +/- 2.5% and 89.3 +/- 0.6% for FAEEs added directly and in rLDLs, respectively. After sterile filtration of these two media, the percentage of FAEE that remained was 11.8 +/- 1.3% (direct addition) and 74.9 +/- 1.3% (addition within rLDL), further demonstrating that the LDL particle did solubilize the FAEE.(ABSTRACT TRUNCATED AT 250 WORDS)

Malarial haemozoin/beta-haematin supports haem polymerization in the absence of protein

Malarial parasites growing inside erythrocytes digest up to 80% of the host cell's haemoglobin within a lysosomal organelle, the digestive vacuole. They sequester the potentially toxic haem (Fe (II) protohaematoporphyrin) that is released during this process into an insoluble pigment called haemozoin, which consists of polymerized Fe (III) protohaematoporphyrin subunits. We have studied this process of haem polymerization, which was previously reported to be enzyme-mediated and the target of the quinoline antimalarial drugs chloroquine and quinine. Here we show that, rather than being enzyme-mediated, haem polymerization is actually a chemical process, dependent only on the presence of haem-derived material associated with haemozoin and not on protein. This discovery does not invalidate haem polymerization as a target for drug intervention and the mechanism by which haemozoin formation is initiated is still not understood, but our view of this process and of the action of choroquine must be reconsidered.

Use of acetyl chloride/methanol for assumed selective methylation of plasma nonesterified fatty acids results in significant methylation of esterified fatty acids

The albumin-bound nonesterified fatty acid pool in plasma, which represents a very small percentage of total plasma fatty acids, has previously been quantitated by a variety of methods. In the present study we determined that the nonesterified fatty acid concentrations in the plasma, quantitated by a popular method using acetyl chloride and methanol which is reported to be specific for methylation of nonesterified fatty acids in the presence of esterified fatty acids (i.e., without prior isolation of the plasma nonesterified fatty acids), were significantly overestimated due to cleavage and methylation of esterified fatty acids. Quantitation of the contaminating fatty acid from the esterified pool demonstrated that the amount of fatty acid cleaved from the esterified pool was enough to exceed the entire mass of nonesterified fatty acids. As an established method for comparison, we isolated nonesterified fatty acids from the plasma by thin-layer chromatography prior to methylation, using a number of simple precautions to limit oxidation. By performing all thin-layer chromatography steps in an atmosphere of nitrogen and by including fatty acid standards in the plasma with 0, 1, 2 or 4 double bonds, we were able to accurately and reproducibly determine the concentration of nonesterified fatty acids in the plasma, including arachidonate. We demonstrated that no oxidation occurred in the thin-layer chromatographic isolation of nonesterified fatty acids and that the coefficients of variation for repeat measurements of the same sample were < 11% using our reference method. Our data indicate that the use of acetyl chloride and methanol for assumed selective methylation of plasma nonesterified fatty acids results in significant methylation of esterified fatty acids.

Human neutrophil phospholipase D activation by N-formylmethionyl-leucylphenylalanine reveals a two-step process for the control of phosphatidylcholine breakdown and oxidative burst

A comparative study of real-time kinetics of respiratory burst, monitored by H2O2-dependent chemiluminescence, and phospholipase D (PLD)-mediated phosphatidylcholine breakdown has been undertaken on human neutrophils stimulated by N-formylmethionyl-leucylphenylalanine in the absence of cytochalasin B. The fungal metabolite 17-hydroxywortmannin (HWT), an inhibitor of NADPH oxidase activation, decreases phosphatidic acid (PA) production by 30% at a concentration of 1 nM. Higher concentrations (10 nM-1 microM) inhibit PA formation maximally by 50% as compared with control. In all cases, the inhibition is delayed by 20-30 s after addition of the agonist. Thus the full PA generation is actually the result of an early (HWT-insensitive) and a late (HWT-sensitive) phosphatidylcholine breakdown. However, under all conditions, alkylacylglycerol remains at the basal level. PLD activity is dependent on Ca2+ influx, but is fully inhibited in cells depleted of Ca2+ with EGTA and Quin 2. The effect of HWT on the respiratory burst was investigated by measuring the kinetics of H2O2-induced chemiluminescence. This method allows to distinguish various phases of superoxide ion production: a lag, an increase in H2O2 formation (early phase), the duration of H2O2 production (late phase) and the termination of the oxidative burst. The lag remains constant for all HWT concentrations. A concentration of 10 nM-HWT, which fully inhibits the HWT-sensitive part of PA production, decreases superoxide ion production with a delay of about 20 s after addition of the agonist. Higher HWT concentrations, which have no additional effect on PLD inhibition, equally affect an early and a late phase of the burst. Thus high doses of HWT have a site of action which decreases the whole burst but does not affect the PLD any more. Therefore HWT and Ca2+ provide evidence for a two-step process for PLD activation. Only the delayed PA generation is functionally linked to a late phase of the oxidative burst.

Regulation of the concentration of free arachidonic acid in homogenates of human platelets

With the intention to study the regulation of the availability of free arachidonic acid through the enzymes of the Lands cycle, we established a model system in homogenates of human platelets. Phospholipase A2, arachidonoyl-CoA synthetase and lysophosphatidyl acyltransferase proved to be simultaneously active and a steady turnover of arachidonic acid was the consequence. EGTA suppressed the deacylating activity that acted on endogenous membrane phospholipids and prevented eicosanoid formation from previously esterified exogenous arachidonoyl-CoA. The reacylating enzymes took part in the control of eicosanoid biosynthesis by re-esterification of liberated arachidonic acid. Blockade of the reacylation by apyrase made arachidonic acid completely available for further metabolization into 12-HETE and thereby induced an increase in the eicosanoid release.

Detection of endothelial cell-reactive immunoglobulin in patients with anti-phospholipid antibodies

Individuals with anti-phospholipid antibodies are at increased risk for the development of thrombosis and fetal loss. The pathogenesis of these syndromes is unknown, but may involve antibody-mediated alterations in endothelial cell coagulant activity. To address this possibility, we determined the incidence of endothelial cell-reactive antibodies in 76 patients whose plasma contained anti-phospholipid antibodies, but who had no clinically-evident immune disorder. Plasma from 47 patients deposited significantly more immunoglobulin on cultured endothelial cells than control plasma. Positive tests were more frequent in patients with a history of thrombosis than in those without (17/19 v 23/48; P = 0.004). However, we observed no correlation between immunoglobulin deposition on cardiolipin and endothelial cells by individual plasmas. Furthermore, endothelial cell reactivity was not diminished by adsorption of anti-cardiolipin antibodies from patient sera using liposomes. Immunoglobulin fractions prepared from 5/6 patient sera immunoprecipitated a approximately 70 kDa endothelial cell surface protein; 4/5 of these fractions also induced the release of von Willebrand factor from endothelial cells. These results demonstrate that plasma from many patients with anti-phospholipid antibodies, but no clinically-evident autoimmune disease, also contains endothelial cell-reactive antibodies. Detection of such antibodies might help identify individuals in this patient population at greatest risk for thrombosis.

Mechanism of the interaction of human platelet profilin with actin

We have reexamined the interaction of purified platelet profilin with actin and present evidence that simple sequestration of actin monomers in a 1:1 complex with profilin cannot explain many of the effects of profilin on actin assembly. Three different methods to assess binding of profilin to actin show that the complex with platelet actin has a dissociation constant in the range of 1 to 5 microM. The value for muscle actin is similar. When bound to actin, profilin increases the rate constant for dissociation of ATP from actin by 1,000-fold and also increases the rate of dissociation of Ca2+ bound to actin. Kinetic simulation showed that the profilin exchanges between actin monomers on a subsecond time scale that allows it to catalyze nucleotide exchange. On the other hand, polymerization assays give disparate results that are inconsistent with the binding assays and each other: profilin has different effects on elongation at the two ends of actin filaments; profilin inhibits the elongation of platelet actin much more strongly than muscle actin; and simple formation of 1:1 complexes of actin with profilin cannot account for the strong inhibition of spontaneous polymerization. We suggest that the in vitro effects on actin polymerization may be explained by a complex mechanism that includes weak capping of filament ends and catalytic poisoning of nucleation. Although platelets contain only 1 profilin for every 5-10 actin molecules, these complex reactions may allow substoichiometric profilin to have an important influence on actin assembly. We also confirm the observation of I. Lassing and U. Lindberg (1985. Nature [Lond.] 318:472-474) that polyphosphoinositides inhibit the effects of profilin on actin polymerization, so lipid metabolism must also be taken into account when considering the functions of profilin in a cell.

The affinities of human platelet and Acanthamoeba profilin isoforms for polyphosphoinositides account for their relative abilities to inhibit phospholipase C

In light of recent work implicating profilin from human platelets as a possible regulator of both cytoskeletal dynamics and inositol phospholipid-mediated signaling, we have further characterized the interaction of platelet profilin and the two isoforms of Acanthamoeba profilin with inositol phospholipids. Profilin from human platelets binds to phosphatidylinositol-4-monophosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2) with relatively high affinity (Kd approximately 1 microM for PIP2 by equilibrium gel filtration), but interacts only weakly (if at all) with phosphatidylinositol (PI) or inositol trisphosphate IP3) in small-zone gel-filtration assays. The two isoforms of Acanthamoeba profilin both have a lower affinity for PIP2 than does human platelet profilin, but the more basic profilin isoform from Acanthamoeba (profilin-II) has a much higher (approximately 10-microM Kd) affinity than the acidic isoform (profilin-I, 100 to 500-microM Kd). None of the profilins bind to phosphatidylserine (PS) or phosphatidylcholine (PC) in small-zone gel-filtration experiments. The differences in affinity for PIP2 parallel the ability of these three profilins to inhibit PIP2 hydrolysis by soluble phospholipase C (PLC). The results show that the interaction of profilins with PIP2 is specific with respect to both the lipid and the proteins. In Acanthamoeba, the two isoforms of profilin may have specialized functions on the basis of their identical (approximately 10 microM) affinities for actin monomers and different affinities for PIP2.

Alteration of the cellular fatty acid profile and the production of eicosanoids in human monocytes by gamma-linolenic acid

We administered borage seed oil (9 capsules/day) for 12 weeks to 7 normal controls and to 7 patients with active rheumatoid arthritis. The therapy provided 1.1 gm/day of gamma-linolenic acid (GLA). GLA administration resulted in increased proportions of its first metabolite, dihomo-gamma-linolenic acid (DGLA), in circulating mononuclear cells. The ratios of DGLA to arachidonic acid and DGLA to stearic acid increased significantly in these cells. Significant reductions in prostaglandin E2, leukotriene B4, and leukotriene C4 produced by stimulated monocytes were seen after 12 weeks of GLA supplementation. The antiinflammatory effects of GLA administration observed in animal models, and the apparent clinical improvement experienced by 6 or 7 rheumatoid arthritis patients given borage seed oil in this open, uncontrolled study may be due in part to reduced generation of arachidonic acid oxygenation products.

The actin-binding protein profilin binds to PIP2 and inhibits its hydrolysis by phospholipase C

Profilin is generally thought to regulate actin polymerization, but the observation that acidic phospholipids dissociate the complex of profilin and actin raised the possibility that profilin might also regulate lipid metabolism. Profilin isolated from platelets binds with high affinity to small clusters of phosphatidylinositol 4,5-bisphosphate (PIP2) molecules in micelles and also in bilayers with other phospholipids. The molar ratio of the complex of profilin with PIP2 is 1:7 in micelles of pure PIP2 and 1:5 in bilayers composed largely of other phospholipids. Profilin competes efficiently with platelet cytosolic phosphoinositide-specific phospholipase C for interaction with the PIP2 substrate and thereby inhibits PIP2 hydrolysis by this enzyme. The cellular concentrations and binding characteristics of these molecules are consistent with profilin being a negative regulator of the phosphoinositide signaling pathway in addition to its established function as an inhibitor of actin polymerization.

Suppression of interleukin 2-dependent human T cell growth in vitro by prostaglandin E (PGE) and their precursor fatty acids. Evidence for a PGE-independent mechanism of inhibition by the fatty acids

PGE represent oxygenation products of polyunsaturated essential fatty acids and are important regulators of cell-mediated immune responses. Because oils enriched in such fatty acids reduce inflammation and tissue injury in vivo, we examined the effects of these PGE precursors on IL-2-driven growth of human T lymphocytes. Dihomogamma linoleic acid (DGLA), AA, and their metabolites (PGE1 and PGE2, respectively) strongly inhibited short- and long-term growth of IL-2-dependent T cell cultures; EPA was much less inhibitory and its product, PGE3, failed to suppress IL-2 responses. Short-term pretreatment of the cells with DGLA or AA and removal of the fatty acids before the proliferation assay resulted in a smaller reduction in [3H]TdR incorporation. PGE and fatty acids did not alter the number of high affinity IL-2 binding sites on the T cell cultures but reduced the percentage of cells expressing CD25 and HLA class II molecules. No PGE was detected in supernatants from the fatty acid-treated cultures. Moreover, indomethacin, a cyclooxygenase inhibitor, did not reverse the antiproliferative effects of the fatty acids. Together, these findings indicate that fatty acids can inhibit IL-2-driven T cell growth via a PGE-independent mechanism and might be relevant to inflammatory diseases associated with persistent T cell activation.

Suppression of human synovial cell proliferation by dihomo-gamma-linolenic acid

Prostaglandin E1 (PGE1) and oils enriched in its precursor fatty acids suppress inflammation and joint tissue injury in several animal models. Since synovial cell proliferation is a hallmark of rheumatoid arthritis, we studied the effect of dihomo-gamma-linolenic acid (DGLA), an immediate precursor of PGE1, on the growth of human adherent synovial cells (ASC) in tissue culture. When stimulated by appropriate concentrations of recombinant interleukin-1 beta (rIL-1 beta), ASC proliferate and produce PGE. DGLA-enriched medium suppressed both baseline and rIL-1 beta-stimulated ASC growth fivefold, compared with medium supplemented with arachidonic acid. Indomethacin reduced the effect of the DGLA. Synovial cells incorporated the DGLA, and rIL-1 beta-stimulated cells that were incubated with DGLA exhibited a 14-fold increase in PGE1 (to 25.2 +/- 6.0 ng/ml, mean +/- SD) and a 70% decrease in PGE2 (to 25.2 +/- 4.2 ng/ml) compared with cells in control medium. At equivalent concentrations (5 x 10(-7) M), PGE1 increased the level of cellular cAMP to a greater extent than did PGE2 (16.8 +/- 2.0 pmoles versus 4.3 +/- 1.9 pmoles, mean +/- SEM). Exogenous PGE1 was also a more effective inhibitor of cell growth. Similarly, cAMP concentrations in cells exposed to DGLA for 6 hours were greater than concentrations in arachidonic acid-enriched cultures (17.8 +/- 3.3 pmoles versus 2.1 +/- 2.0 pmoles). These observations suggest that DGLA can restrain ASC growth, an effect which may be due to its capacity to increase PGE1 production and subsequent cellular cAMP concentration.

Differential activation by fMet-Leu-Phe and phorbol ester of a plasma membrane phosphatidylcholine-specific phospholipase D in human neutrophil

Signal transduction involving phosphatidylcholine hydrolysis has been investigated in human neutrophils (PMN) after in situ generation of [3H]alkylacyl-sn-glycero-3-phosphocholine ([3H]alkylacyl-GPC) by cell incubation with [3H]alkylacetyl-GPC. When PMN were stimulated with the chemotactic peptide N-formyl-Met-Leu-Phe(fMLP) or phorbol myristate acetate (PMA) in the presence of cytochalasin B, both 1-O-alkyl-2-acyl-sn-glycero-3-phosphate (PA) and 1-O-alkyl-2-acyl-sn-glycerol (AAG) were generated. On addition of the agonists in the presence of ethanol, phosphatidylethanol (PEt) [corrected] was formed with a concomitant decrease in PA and AAG. These results indicate the presence of a phospholipase D (PLD) acting on phosphatidylcholine in human PMN. The kinetics of hydrolysis were quite different according to the stimulus. Whereas fMLP induced a maximum rise in PA and AAG at 30-45 s, these products began to appear only after 1 min upon cell incubation with PMA. Similar amounts of products were formed at 1 min with fMLP and only at 5 min with PMA. Although similar time courses of PA generation were obtained in the absence of cytochalasin B, AAG were no longer involved and therefore cannot account for intracellular second messenger under physiological conditions. Subcellular distribution studies demonstrated the exclusive location of PA and PEt [corrected] in the plasma membrane. The possible involvement of PA in respiratory burst activation is discussed.

Protein kinase C is activated in glomeruli from streptozotocin diabetic rats. Possible mediation by glucose

Glomerular inositol content and the turnover of polyphosphoinositides was reduced by 58% in 1-2 wk streptozotocin diabetic rats. Addition of inositol to the incubation medium increased polyphosphoinositide turnover in glomeruli from diabetic rats to control values. Despite the reduction in inositol content and polyphosphoinositide turnover, protein kinase C was activated in glomeruli from diabetic rats, as assessed by an increase in the percentage of enzyme activity associated with the particulate cell fraction. Total protein kinase C activity was not different between glomeruli from control and diabetic rats. Treatment of diabetic rats with insulin to achieve near euglycemia prevented the increase in particulate protein kinase C. Moreover, incubation of glomeruli from control rats with glucose (100-1,000 mg/dl) resulted in a progressive increase in labeled diacylglycerol production and in the percentage of protein kinase C activity which was associated with the particulate fraction. These results support a role for hyperglycemia per se in the enhanced state of activation of protein kinase C seen in glomeruli from diabetic rats. Glucose did not appear to increase diacylglycerol by stimulating inositol phospholipid hydrolysis in glomeruli. Other pathways for diacylglycerol production, including de novo synthesis and phospholipase C mediated hydrolysis of phosphatidylcholine or phosphatidyl-inositol-glycan are not excluded.

Polyphosphoinositide breakdown and subsequent exocytosis in the Ca2+/ionophore-induced acrosome reaction of mammalian spermatozoa

An investigation was made of the modifications in phospholipids that occur during the exocytotic event known as the 'sperm acrosome reaction'. Phospholipids were prelabelled with 32P, and exocytosis was induced with Ca2+ and the ionophore A23187. When incubated with [32P]Pi in various media suitable for supporting sperm survival or fertilization in vitro, spermatozoa from all five species examined (ram, boar, guinea pig, mouse and human) incorporated 32P rapidly into the components of the phosphoinositide cycle. There were differences both between species and between media with respect to the actual rate of incorporation of label, and also between species with respect to other phospholipids labelled. Treatment of spermatozoa with Ca2+ and A23187 to induce the acrosome reaction resulted in a rapid breakdown of phosphatidylinositol 4, 5-bisphosphate and phosphatidylinositol 4-phosphate, which was complete within 3 min; there was also a great increase in labelling of phosphatidate. Occurrence of acrosome reactions in the sperm population was only observed after 5-10 min and reached a maximum response of greater than 90% after more than 30 min. The phosphoinositide breakdown was related to subsequent exocytosis: after EGTA/ionophore treatment, neither inositide breakdown nor exocytosis took place; however, later addition of Ca2+ resulted in immediate inositide breakdown, and exocytosis followed, with a delay relative to Ca2+ addition exactly similar to that following standard Ca2+/ionophore treatment. Neomycin inhibited both inositide breakdown and subsequent exocytosis provided it was added together with Ca2+ and ionophore; however, if the drug was added 3 min after Ca2+ and ionophore (by which time inositide breakdown was already complete), exocytosis was not inhibited. Ca2+ seemed to have several consecutive roles in the acrosome reaction. Low (micromolar) levels of free Ca2+ were needed both for phosphoinositide breakdown and for an event downstream of this breakdown; no other bivalent cation could substitute for Ca2+ in either event, and inositide breakdown was actually inhibited by Mg2+. In addition, millimolar levels of Ca2+ were needed for later stages of exocytosis, although this requirement could be satisfied by Sr2+. We conclude that breakdown of polyphosphoinositides is an essential early process after Ca2+ entry in the chain of events that lead to exocytosis in the mammalian sperm acrosome reaction.

Bradykinin-increased phospholipid deacylation-reacylation in rat renal medulla is inhibited by dBc AMP

The effect of bradykinin on the mobilization of arachidonic acid was analyzed separately by acylation and degradation. Acylating activity was determined by the incorporation of [14C]arachidonic acid into the phospholipids at different times. Different concentrations of bradykinin had no effect on the phospholipid acylating activities. The degradation of the phospholipids was performed on renal medullary slices prelabeled with [14C]arachidonic acid. Treatment with bradykinin produced an initial degradation of phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, with a concomitant increase in lysophosphatidylcholine, lysophosphatidylethanolamine and lysophosphatidylinositol within 5 min of incubation. Phosphatidylcholine-, phosphatidylethanolamine- and phosphatidylinositol increased thereafter and reached the control values after 10 min of incubation. After 30 min, incubation of prelabeled slices with bradykinin produced a significant concentration-dependent increase in the phospholipid-labeling by reutilization of [14C]arachidonic acid. The effect of bradykinin on the phospholipid-labeling was blocked by preincubation with increasing concentrations of dBc AMP. Mepacrine also blocked the bradykinin stimulation in phosphatidylcholine and phosphatidylethanolamine, but had no effect on bradykinin-induced changes in the phosphatidylinositol arachidonic acid moiety.

Role for protein kinase C in the modulation of glomerular PGE2 production by angiotensin II

Angiotensin II increased PGE2 release from superfused glomeruli, and stimulated labeled inositol phosphate production. 12-O-Tetradecanoyl phorbol -13-acetate (TPA, 10(-7) M), which stimulates protein kinase C activity in soluble fractions of glomerular homogenates, suppressed angiotensin II actions on inositol phosphate production and PGE2. By contrast, 4a phorbol 12,13 di-decanoate and phorbol had no effect on protein kinase C activity or angiotensin II induced increases in inositol phosphate or PGE2. 1-(5-Isoquinolinyl)-2-methylpiperazine (H-7), which inhibits protein kinase C activity in soluble fractions of glomerular homogenates, prevented TPA induced suppression of angiotensin II actions on inositol phosphate production and PGE2. Moreover H-7 prolonged the time course of angiotensin II induced inositol phosphate production and enhanced angiotensin II actions on glomerular PGE2 production. The results support a role for inositol phospholipid hydrolysis through the phospholipase C pathway in the mediation of angiotensin II actions on PGE2 in glomeruli and are consistent with negative modulation of these actions by protein kinase C.

Lipid composition of miniature pig platelets

1. Analyses of platelet lipid composition were carried out on material pooled from male and female miniature pigs. 2. The cholesterol/phospholipid molar ratio was 0.6. 3. Phosphatidylcholine represents the major class of phospholipids (47%) and phosphatidylinositol the minor (2%). 4. The main fatty acids of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and sphingomyelin were: palmitic, stearic, oleic, linoleic and arachidonic acids. 5. The ratios of saturated to unsaturated fatty acids were: sphingomyelin, 1.7; phosphatidylcholine, 1.2; phosphatidylserine, 0.9; phosphatidylethanolamine and phosphatidylinositol, 0.6. 6. Our results suggests that human and miniature pig platelet lipids bear several characteristics in common. This fact would allow miniature pig to be used as a new experimental model.

Thrombin-induced abnormal platelet activation in spontaneously hypertensive rats is linked with phosphoinositides turnover and phosphorylation of 47,000 and 20,000 dalton proteins

We have shown earlier that abnormal platelet aggregation in spontaneously hypertensive rats (SHR) is not caused by prostaglandins. In this study platelets from SHR and normotensive (Wistar Kyoto, WKY) rats were used to examine the role of phosphoinositides and phosphorylation of 47,000 and 20,000 Dalton proteins in abnormal platelet activation in hypertension. Thrombin (0.05 U/ml) induced a rapid decrease in (32P)-P04 labelled phosphatidylinositol-4, 5-bisphosphate (PIP2), phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol (PI) in washed rat platelets. However, significantly greater loss of PIP2 and PI was seen in SHR platelets than in WKY platelets. For example the level of PIP2 declined by 32% in SHR platelets and only by 13% in WKY platelets at five seconds of incubation with thrombin. The loss of PI was similar in SHR and WKY platelets for the first five seconds of incubation with thrombin. However, by 15 seconds SHR platelets showed a significantly greater loss (24%) in PI than in WKY platelets (8%). Thrombin induced a 14% and 18% decrease in PIP at three seconds in WKY and SHR platelets respectively. In SHR platelets PIP level returned to the baseline in five seconds and then rose to 20% above the baseline by 30 seconds. In contrast PIP level in WKY platelets slowly reached the basal value by 30 seconds. Thrombin also produced a two- to three-fold greater accumulation of (32P)-phosphatidic acid (PA) in SHR platelets than in WKY platelets. Thrombin (0.05 U/ml) induced rapid phosphorylation of 47,000 Dalton (P47) and 20,000 Dalton (P20) proteins in both WKY and SHR platelets. Thrombin induced a four-fold greater increase in phosphorylation of P47 in SHR platelets than in WKY platelets in the first five seconds. Thrombin produced significantly greater increase in phosphorylation of P20 in SHR platelets (34% and 41%) than in WKY platelets (18% and 28%) at 5 and 15 seconds. Phosphorylation of P20 was followed by dephosphorylation in both WKY and SHR platelets. Aspirin (500 microM) did not affect phosphorylation of either P47 or P20 in SHR or WKY platelets. In other experiments prostaglandin E1 (0.5 microM), which stimulates adenylate cyclase via a guanine nucleotide regulatory protein termed Gs, caused an eighteen-fold increase in cyclic AMP level in SHR platelets as compared to a six-fold increase in WKY platelets. These data lead us to suggest that increased turnover of phosphoinositides and increased phosphorylation of P47 and P20 are involved in abnormal platelet activation in SHR platelets.

Isolation of 1-monomethylphosphoinositol 4,5-bisphosphate [a product of methanolysis of inositol 1,2-(cyclic)-4,5-trisphosphate] from Swiss mouse 3T3 cells

We have noted two previously undescribed inositol polyphosphates in neutral methanol extracts from Swiss mouse 3T3 cells that were grown in [3H]inositol and stimulated with platelet-derived growth factor. They have been identified as 1-monomethylphosphoinositol 4,5-bisphosphate and 1-monomethylphosphoinositol 4-phosphate by comparison to a synthesized standard using HPLC chromatography, paper electrophoresis, and enzymatic dephosphorylation with inositol polyphosphate 5-phosphomonoesterase and intestinal alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1]. We propose that these compounds are formed by methanolysis of inositol 1,2-(cyclic)-4,5-trisphosphate and inositol 1,2-(cyclic)-4-bisphosphate present in the cells. Inositol cyclic phosphates did not react with neutral methanol in the absence of the cells, which are required for the methanolysis reaction. These findings suggest a role for inositol cyclic phosphates as reactive compounds that are added to as yet unidentified cellular acceptors.

Lipid composition of Bacillus megaterium spores and spore membranes

Bacillus megaterium QM B1551 spore lipids were extracted by an improved technique, and the phospholipid and fatty acid compositions were determined. Phospholipids accounted for 65% of the total fatty acids; the neutral lipid fraction contained 15% and the remaining fatty acids were in the interphase, aqueous phase and pellet from the lipid extraction. Each phospholipid had similar fatty acid compositions as did the delipidated pellet. However, the aqueous phase and, to some extent, the interphase had unique fatty acid compositions. Also, fatty acids were found acylated to proteins, which was observed by electrophoresis of delipidated proteins from spores grown in [1-14C]palmitate. Therefore, spores contain unique non-phosphatide fatty acid components that can now be analyzed.

The phosphoinositides exist in multiple metabolic pools in rabbit platelets

The labelling of the phosphoinositides and phosphatidic acid in washed rabbit platelets incubated with [32P]phosphate or [3H]glycerol was studied in the presence of isotope and after unincorporated isotope had been removed. With both isotopes the increase in the specific radioactivity of phosphatidylinositol 4,5-bisphosphate (PIP2) lagged behind that of phosphatidylinositol 4-phosphate (PIP) but the specific radioactivity remained higher after unincorporated isotope had been removed. This result was consistent with the presence of a second pool of PIP2, which interconverted slowly with the pool of PIP2 which was in direct equilibrium with PIP, proposed to explain the increase in specific radioactivity of PIP2 which accompanies the decrease in amount of PIP2 at 10 s in ADP-stimulated platelets. In platelets labelled with [3H]glycerol, the specific radioactivity of PIP2 became higher than that of PIP and the specific radioactivity of PIP became higher than that of phosphatidylinositol (PI). These results were interpreted to indicate that there were two pools of PIP; of these the pool with the higher specific radioactivity was the precursor of PIP2. Similarly, two pools of PI were proposed. The presence of pools of the phosphoinositides with different specific radioactivities necessitates the measurement of chemical amount of these compounds when studying the effect of stimulation of the platelets, since changes in labelling may not accurately reflect changes in the amount of the phosphoinositides.

Lipid composition of the membrane released after an in vitro acrosome reaction of epididymal boar sperm

Prior to fertilization, mammalian sperm must undergo the acrosome reaction, which involves modifications of the plasma and outer acrosomal membranes followed by vesiculation and release of the membranes. The membrane fraction that was released from caudal boar sperm undergoing an in vitro acrosome-like reaction was isolated and characterized with respect to density, marker enzymes and lipid composition. This membrane had a lower phospholipid/protein ratio (mg/mg) than the sperm plasma membrane, whereas both membranes had similar molar sterol/phospholipid ratios. The major phospholipid was sphingomyelin, followed by phosphatidylethanolamine and phosphatidylcholine, whereas in the plasma membrane the order was reversed; the two major phosphoglycerides contained alkylacyl and alkenylacyl species in addition to the diacyl species. The released membrane also contained lower amounts of cholesterol sulfate and unsaturated fatty acids than the plasma membranes. These results, in combination with our studies on the changes of the sperm membranes during maturation and acrosome reaction, will allow a better understanding of the mechanism of the sperm acrosome reaction.