Biomedical subjects

M Lagarde

Publications and source records attributed to M Lagarde.

At least 145 records · Page 8Linked to original sources

PubMed1993

Phospholipid molecular species from human placenta lipids.

The phospholipid molecular species from a large-scale preparation of human placenta lipids were analyzed. The major placental phospholipids were choline glycerophospholipids (CPL) (53.2 wt%), sphingomyelin (21.7 wt%) and ethanolamine glycerophospholipids (EPL) (14.6 wt%). 1,2-Diacyl-glycerophosphocholine was the most abundant subclass of CPL (91.7 mol%), while EPL contained 1,2-diacyl (54.6 mol%) and 1-alk-1'-enyl-2-acyl (43.8 mol%) subclasses. The level of polyunsaturated fatty acids (PUFA) in total phospholipids was remarkably constant (38.4-39.9 mol%) within all placental batches tested. The long-chain PUFA, mainly 20:4n-6 and 22:6n-3 of the n-6 and n-3 series, respectively, were found in high proportion in all phospholipid classes, especially in EPL (46.7 mol%) and in inositol glycerophospholipids (IPL) (39.9 mol%). CPL and serine glycerophospholipids were much richer in 18:1n-9 and 18:2n-6. High levels of molecular species with arachidonic acid in the sn-2 position were found particularly in 1-alk-1'-enyl-2-acyl-glycerophosphoethanolamine (with 24.0 mol% 16:0 and 22.0 mol% 18:0 in sn-1 position) and in 1,2-diacyl glycerophosphoinositol with 42.6 mol% 18:0 in sn-1 position. EPL subclasses were rich in 22:6n-3, which occurs mainly as 16:0/22:6n-3 (11.7 mol%) in the plasmalogen form and as 18:0/22:6n-3, 16:0/22:6n-3 and 18:1/22:6n-3 in the diacyl forms. Based on their availability and composition, placental phospholipids could be of interest, for example, for supplementing artificial milk preparations with n-3 and n-6 long-chain PUFA for newborn infants with insufficiently developed 18:2n-6 and 18:3n-3 desaturation/elongation.

Chromatography, Gas↗

PubMed1993

Platelet inhibitory functions of aortic endothelial cells. Effects of eicosapentaenoic and docosahexaenoic acids.

The endothelial cell platelet inhibitory potential was assessed directly by measuring the platelet inhibition induced by platelet interaction with the cultured aortic endothelial cell. The prostacyclin content of the platelet suspensions after interaction was also quantified. We found that prostacyclin production accounted for the overall platelet inhibitory potential of the aortic cells since: (a) endothelial cells incubated with aspirin, which did not produce prostacyclin, did not inhibit platelets; (b) the prostacyclin content of platelet suspensions after interaction with endothelial cells correlated with the extent of the platelet inhibition; (c) such a platelet inhibition was reproduced by adding synthetic prostacyclin in amount equivalent to that produced by endothelial cells during the interaction. Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids incorporated into endothelial phospholipids, decreased the ability of the cells to produce prostacyclin and to inhibit platelets, DHA being less effective than EPA.

Animals↗

PubMed1993

Behaviour of leukocyte membrane fluidity in presence of anaesthetic drugs. Comparison between allergic patients and control subjects.

1. In this study we compared the effects of two anaesthetic drugs on the leukocyte membrane fluidity in allergic patients versus control subjects. 2. Fluidity was assessed by means of the fluorescence polarization technique. 3. We report that the treatment of the whole leukocytes with thiopental or pancuronium enhanced membrane fluidity in the allergic group as well as in the control one, but the effect was more pronounced in allergics. 4. This finding suggests a different biophysical behaviour of the leukocyte membrane towards anaesthetic drugs in allergic diseases. 5. This agrees with the hypothesis of the existence of an intrinsic abnormality in allergic cells, expressed as an initial hyperreactive state.

Adult↗

PubMed1993

Interactions between arachidonic and eicosapentaenoic acids during their dioxygenase-dependent peroxidation.

Eicosapentaenoic acid (EPA), a major polyunsaturated fatty acid of fish has been widely proposed as a potential nutrient for decreasing platelet-endothelial cell interactions and the subsequent atherogenesis and thrombogenesis. This is mainly based upon the decrease of arachidonic acid (AA) oxygenation into bioactive molecules like thromboxane A2. In addition, EPA may be oxygenated into its own active derivatives via cell dioxygenases. We report evidence for the requirement of specific peroxides, adequately provided by AA, to allow EPA to be oxygenated into its bioactive products like prostaglandin I3, a prostacyclin mimetic. On the other hand, we present some data that argue for a decreased basal AA dioxygenation (specific peroxidation) by small concentrations of EPA. The interactions between AA and EPA are then dual, EPA being able to counteract AA oxygenation whereas EPA requires AA to be efficiently oxygenated.

Aged↗

PubMed1993

Glutathione peroxidase activity and metabolism of arachidonic acid in peripheral blood mononuclear cells from elderly subjects.

1. Since ageing has been associated with a decrease in both immune responses and antioxidant defences, this study was undertaken to compare the glutathione peroxidase activity in peripheral blood mononuclear cells of healthy elderly and young donors. The mean value of glutathione peroxidase activity was significantly lower in the aged group (-36%) than that observed in the young control group (n = 10). 2. This defect was accompanied by a marked increase (+106%) in the oxygenated metabolism of endogenous arachidonic acid by lipoxygenases as judged by the radiolabel associated with hydroxyeicosatetraenoic acids in [3H]arachidonic acid-prelabelled peripheral blood mononuclear cells, whereas the cyclo-oxygenase activity, estimated by the radiolabel associated with thromboxane B2, was not significantly altered. 3. Upon stimulation by the mitogenic lectin concanavalin A, the radioactivity associated with total eicosanoids (free arachidonic acid plus hydroxyeicosatetraenoic acids plus thromboxane B2) was significantly increased over basal levels in the peripheral blood mononuclear cells of both the elderly and the control groups. However, the mitogen-induced increase was lower in the elderly group (+48%) than in the control group (+131%). Upon concanavalin A stimulation, the radioactivity of hydroxyeicosatetraenoic acids was increased by only 96% in peripheral blood mononuclear cells from the elderly group compared with 350% in control cells. Similarly, the radioactivity associated with thromboxane B2 was increased by only 82% in peripheral blood mononuclear cells from the elderly group compared with 218% in control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Inhibition of the different phosphodiesterase isoforms of rat heart cytosol by free fatty acids.

The sensitivity of the various phosphodiesterase (PDE) isoforms present in the cytosolic compartment of rat heart to the main fatty acids of the saturated, n-3 and n-6 families was assessed. High-performance liquid chromatography (HPLC) on a Mono Q ion-exchange column resolved four separate cyclic nucleotide phosphodiesterase activities: a calmodulin-activated fraction, a cyclic GMP-stimulated fraction, a cyclic AMP-specific rolipram-sensitive fraction, and a cyclic GMP-inhibited fraction. Polyunsaturated fatty acids (PUFA) were more potent inhibitors than saturated fatty acids whatever the considered PDE isoform. Although all PDE isoforms were affected, the cyclic GMP-stimulated isoform was the most sensitive to the inhibitory effect of PUFAs. The possible influences of free fatty acids (FFA) on cardiac contractility through PDE inhibition are discussed.

Animals↗

PubMed1993

Impaired G-proteins and cyclic nucleotide phosphodiesterase activity in T-lymphocytes from patients with sarcoidosis.

Among the various immune abnormalities which characterize active sarcoidosis, a low proliferative response of peripheral blood lymphocytes to mitogenic lectins has long been observed. Since membrane-associated G-proteins are very likely to be crucial elements in lectin signal transduction, we investigated the binding of 5'-guanylylimidodiphosphate (GppNHp), a non hydrolyzable GTP analogue, to blood total lymphocyte membranes and to blood T-lymphocyte membranes from patients with active sarcoidosis, and from healthy control subjects. GppNHp binding was markedly decreased in peripheral cells from patients with sarcoidosis as compared to controls, suggesting the occurrence of a defect at the level of G-protein(s). A further characterization of G-proteins in these cells by means of ADP-ribose-labelling in the presence of bacterial toxins brought forward a significant decrease in the labelling of a 40 kDa protein, the major pertussis toxin substrate, in membranes from sarcoid patients, while the labelling of the major 44 kDa cholera toxin substrate proved to be unchanged with respect to control membranes. It is hypothesized that, in sarcoid lymphocytes, a defect in the negative control of adenylate cyclase mediated by the inhibitory G-protein Gi, prevents the lowering of cAMP necessary to normal mitogenic response of blood lymphocytes to stimulation. cAMP degradation by the specialized enzyme phosphodiesterase constitutes another critical step in the control of cAMP levels. Both cAMP and cGMP phosphodiesterase activities were found decreased in blood total lymphocyte preparations from sarcoid patients. With purified T-cells, although the mean cAMP and cGMP phosphodiesterase activities from sarcoid patients were found more markedly decreased with respect to healthy donors, only the decrease in cGMP phosphodiesterase was found statistically significant. The role these defects in cyclic nucleotide degradation potentially play in the disturbance of blood lymphocytes response associated with sarcoidosis is discussed.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed1993

Effect of an n-3 fatty acid-deficient diet on the adenosine-dependent melatonin release in cultured rat pineal.

We studied the effect of a diet deficient in n-3 fatty acids on the adenosine-dependent melatonin release from cultured rat pineal gland after stimulation by 5'-N-ethylcarboxamidoadenosine (NECA), an A2 adenosine agonist. Experiments were conducted with 2-month-old rats raised on semipurified diets containing either peanut oil (n-3 deficients) or peanut plus rapeseed oil (controls). The proportion of docosahexaenoic acid (22:6 n-3) in the pineal total lipid fraction and in phosphatidylcholine and phosphatidylethanolamine was significantly decreased in n-3-deficient rats. This was compensated for partially by an increase in 22:4 n-6 and 22:5 n-6 levels. The activity of the cultured rat pineal, in terms of cyclic AMP content and N-acetylserotonin and melatonin release in the medium, was lower after stimulation by 10(-5) mol/L NECA in the group fed peanut oil than in the group fed peanut plus rapeseed oil. The increased ratio of n-6/n-3 fatty acids in pineal total lipids and the major glycerophospholipids (phosphatidylcholine and phosphatidylethanolamine) may have an important influence on the rat pineal responses. The results are discussed in the context of changes in membrane-bound proteins, including enzymes and/or receptors involved in the rat pineal gland function.

Adenosine↗

PubMed1993

Increased plasma levels of atrial natriuretic factor, renin activity, and leukotriene C4 in chronic obstructive pulmonary disease.

We studied atrial natriuretic factor (ANF), plasma renin activity (PRA), and plasma levels of leukotrienes (LTs) B4 and C4 in 23 patients with COPD undergoing right cardiac catheterization for suspected pulmonary hypertension. Hemodynamic measurements together with concomitant ANF levels (both in venous and pulmonary artery blood and right atrial and pulmonary artery plasma levels of LTC4 and LTB4, were determined at rest (T0), after 30 min of breathing oxygen (3 L/min) (T1), and after 30 min recovering and breathing air (T2). Patients with effective exacerbation or definitive evidence of left ventricular disease, hypertension, arrhythmias, or vasodilator or diuretic therapy were excluded. Increased levels of ANF, both in peripheral venous blood (117 +/- 65 pg/ml) and the pulmonary artery (153 +/- 75 pg/ml), were found in patients with COPD, with or without pulmonary hypertension. Levels of LTC4 were also significantly increased (366 +/- 406 pg/ml) when compared with our control values. No correlations among ANF, LTC4 values, functional tests, and hemodynamic measurements were found. Brief increased levels of oxygen did not modify ANF or LTC4 plasma levels, either in patients with or without pulmonary hypertension.

Atrial Natriuretic Factor↗

PubMed1993

Modulation of rat thymocyte proliferative response through the inhibition of different cyclic nucleotide phosphodiesterase isoforms by means of selective inhibitors and cGMP-elevating agents.

We have investigated the role played by cyclic nucleotide phosphodiesterases (EC 3.1.4.17) in the control of T-lymphocyte response to mitogenic agents by their ability to influence the cellular level of cAMP. The importance of this messenger as a negative regulator in this cell type is well established. Multiple isoenzymes of phosphodiesterase were fractionated from the cytosol of rat thymic lymphocytes by high performance liquid chromatography on an anion exchange column. In addition to the type II, III, IV isoforms that we have already described [Valette et al., Biochem. Biophys. Res. Commun. 169:864-872 (1990)], a phosphodiesterase fraction sharing several of the characteristics of type V, cGMP-binding phosphodiesterase, was detected. Non-isoform-selective inhibitors of phosphodiesterase such as dipyridamole, papaverine, and methyl-isobutylxanthine were able to totally prevent the proliferative response of thymocytes to stimulation by the mitogenic lectin concanavalin A. In contrast, the selective inhibitor of type IV phosphodiesterases rolipram induced a rather moderate inhibition of proliferation, not exceeding 60%; and the selective inhibitors of type III and type V phosphodiesterases, milrinone and M&B 22,948, respectively, displayed only marginal inhibitory effects. The association of the type III and IV phosphodiesterase inhibitors produced synergistic inhibition of proliferation, which could then be almost totally suppressed. These inhibitory effects on cell multiplication were reflected at the level of the cell cAMP content; only rolipram was able to induce a significant (approximately 50%) increase in cAMP, and this increase was potentiated by the presence of milrinone, reaching almost 100%. The type V phosphodiesterase selective inhibitor M&B 22,948 displayed similar properties to those of milrinone, which suggests that it indirectly inhibited the type III, cGMP-inhibitable isoenzyme, by inducing a cGMP rise. This hypothesis was supported by evidence of a significant raising effect of M&B 22,948 on cGMP level, and by the ability of a cGMP-elevating agent, sodium nitroprusside, to mimic the synergistic effects of milrinone associated with rolipram. Furthermore, 8-bromo-cGMP, a potent activator of cGMP-dependent protein kinase, which showed only weak inhibitory effects on thymic type III phosphodiesterase, failed to alter the effects of rolipram on the cell proliferation. These results allow us to delineate a role for types III, IV, and V phosphodiesterase in the control of cAMP level during the proliferative response of thymic lymphocytes. They also suggest that endogenously formed cGMP might participate in the regulation of cAMP level in the cells by means of the inhibition of the type III phosphodiesterase.(ABSTRACT TRUNCATED AT 400 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1993

Pharmacokinetics of propofol and its conjugates after continuous infusion in normal and in renal failure patients: a preliminary study.

The pharmacokinetics of propofol, 2,6 diisopropylphenol, were compared in 6 end-stage renal failure patients aged 66.3 +/- 12.1 years and in 5 normal patients aged 45.5 +/- 13.5 years. Anesthesia was induced with propofol (2 and 2.5 mg.kg-1 respectively) and fentanyl (0.1 mg). Anesthesia was maintained with propofol (9 and 10 mg.kg-1 x h-1 respectively). Patients breathed spontaneously a 50 per cent oxygen in nitrous oxide mixture. Two ml blood samples were taken during anesthesia and at regular intervals until up to 24 hours after infusion. Plasma levels of propofol were determined by HPLC with electrochemical detection. Propofol conjugates were determined after hydrolysis with beta glucuronidase or HCl. Results were expressed as median [lower-upper percentiles]. Propofol clearance (1.53 [1.02-2.10] L.min-1 x kg-1 versus 1.65 [1.39-1.78] L.min-1 x kg-1 in normal patients), and half-lives elimination were not modified by renal failure. Renal failure patients exhibited a higher volume of distribution at steady state as compared to normal patients (19.28 [11.71-76.81] L.kg-1 versus 8.60 [6.58-9.81] L.kg-1, p < 0.05). Renal failure did not affect the production of conjugates but they accumulated in blood of renal failure patients. Despite this, no difference in time to eyes opening and propofol concentration were observed, confirming the absence of clinical effect of these metabolites.

Adult↗

PubMed1992

Lower levels of lipid peroxidation in human platelets incubated with eicosapentaenoic acid.

The modulatory effects of eicosapentaenoic acid (EPA) on platelet arachidonic acid (AA) metabolism were applied to an in vitro model of oxidant stress. Unstimulated normal human blood platelets were first treated with a thiol-oxidizing agent, azodicarboxylic acid bis(dimethylamide) (diamide) (1 microM), and then incubated with a low concentration of EPA (100 nM). Diamide treatment led to a lower alpha-tocopherol content compared to control. Formation of MDA, a marker of the overall lipid peroxidation, as well as formation of 12-hydroxyeicosatetraenoic acid (12-HETE), the 12-lipoxygenase end-product of AA, were both higher in diamide-treated platelets. Subsequent incubation of diamide-treated platelets with EPA counteracted the effects of oxidant stress induced pharmacologically by diamide. Interestingly, EPA prevented the alpha-tocopherol level from falling and the overall lipid peroxidation from increasing as it did during diamide treatment. In particular, incubation of diamide-treated platelets with EPA led to significantly lower amounts of 12-HETE. Conversely, preincubation of platelets with 100 nM EPA protected cells from oxidizing effects induced by diamide treatment, either on the level of lipid peroxides or on the antioxidant status. These results indicate that, in this particular model, EPA permitted platelets to have control levels of tocopherol, MDA and 12-HETE despite diamide treatment. Low concentrations of EPA might have prevented the increase of lipid hydroperoxides and especially the transient accumulation of 12-hydroperoxyeicosatetraenoic acid (12-HPETE).

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed1992

In vivo inhibition of basal and estrogen-induced phospholipase A2 activities by the triphenylethylene antiestrogen, tamoxifen, in immature quail oviduct.

The effects of tamoxifen on oviductal phospholipase A2 activity were studied in immature quails. Injected alone, from 0.1 to 10 mg/kg tamoxifen significantly reduced basal phospholipase A2 activity 6 h after the injection, independently of the dose used. At 24 h, maximal inhibition (-50%) was observed with 0.1 mg/kg tamoxifen, while higher doses were less effective. Combined with estradiol benzoate, tamoxifen reduced even below the control value (1 mg/kg for 24 h) the increase in phospholipase A2 activity induced by estrogen.

Animals↗

PubMed1992

Evidence for adenosine A2b receptors in the rat pineal gland.

We describe the effects of 5'-N-ethylcarboxamidoadenosine (NECA), a mixed A2a/A2b adenosine receptor agonist and 2-[p-(carboxyethyl)-phenylethylamino]-5'-N-ethylcarboxamidoaden osin e (CGS 21680), a selective A2a agonist, on cyclic AMP and N-acetylserotonin synthesis in rat pineal gland. NECA, 1 and 10 microM, increased cyclic AMP by 5- and 25-fold and N-acetylserotonin by 40- and 60-fold respectively, whereas CGS 21680 at the same concentrations was ineffective. These results argue for the presence of adenosine A2b receptors in rat pinealocytes.

Adenosine↗

PubMed1992

Selective modulation of the human platelet thromboxane A2/prostaglandin H2 receptor by eicosapentaenoic and docosahexaenoic acids in intact platelets and solubilized platelet membranes.

We previously demonstrated that nonesterified as well as esterified eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) inhibit U46619-induced platelet aggregation and [3H]U46619 specific binding to washed human platelets. It was also demonstrated that esterification of these fatty acids resulted in a decrease in the affinity of [3H]U46619 for the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor. In order to investigate the specificity of this inhibition, the effects of 20:5n-3 and 22:6n-3 on the function and binding of the platelet alpha 2-adrenergic receptor were studied. It was found that neither 20:5n-3 nor 22:6n-3 (nonesterified or esterified) altered epinephrine-induced aggregation or [3H]yohimbine specific binding. Moreover, Scatchard analysis revealed that esterification with either 20:5n-3 or 22:6n-3 did not alter the dissociation constant for [3H]yohimbine binding. Modulation of the TXA2/PGH2 receptor by 20:5n-3 and 22:6n-3 was next evaluated using CHAPS- and digitonin-solubilized platelet membranes. [3H]SQ29,548 dissociation constants of 26.5 nM and 20.8 nM were measured for CHAPS and digitonin-solubilized membranes, respectively. Competitive binding experiments in these solubilized preparations revealed that 20:5n-3 or 22:6n-3 blocked [3H] SQ29,548 binding with IC50 values in the range of 6-15 microM, while concentrations of these fatty acids of up to 100 microM showed no effect on [3H]yohimbine binding. On the other hand, the IC50 values for inhibition of [3H] SQ29,548 binding by linoleic acid (18:2n-6) and gamma-linolenic acid (18:3n-6) were in the range of 150 microM. Furthermore, 18:2n-6 and 18:3n-6 showed similar inhibitory effects on [3H]yohimbine binding. Finally, competition binding studies performed in a partially purified TXA2/PGH2 receptor preparation also demonstrated inhibition of [3H]SQ29,548 binding by 20:5n-3 and 22:6n-3. Collectively, these findings support the notion that 20:5n-3 and 22:6n-3 can selectively and directly modulate TXA2/PGH2 receptor function, and that this mechanism of action may contribute to the antiplatelet activity associated with diets rich in these fatty acids.

Blood Platelets↗

PubMed1992

Diethyldithiocarbamate (ditiocarb sodium) effect on arachidonic acid metabolism in human mononuclear cells. Glutathione peroxidase-like activity.

Diethyldithiocarbamate (DTC), a thiol delivery agent, has been shown to significantly reduce the frequency of primary opportunistic infections in HIV-infected patients. This therapeutic effect has been related to the capacity of DTC to reverse the deleterious effects of the oxidative stress occurring in HIV infection. The influence of DTC on the oxygenated metabolism of arachidonic acid (AA) was investigated in mitogen-stimulated human peripheral blood mononuclear cells (PBMC). Upon incubation with PBMC previously labelled with [3H]AA, Concanavalin A (Con A) markedly increased cyclooxygenase and lipoxygenase activities, within 30 min, as judged by thromboxane B2 (TxB2) and hydroxyeicosatetraenoic acid (HETE) production. Con A activation of [3H]AA platelets also increased 12-HETE production but did not induce any TxB2 synthesis. Micromolar concentrations of DTC, added simultaneously with the mitogen, significantly enhanced the synthesis of HETEs above the Con A-induced level while TxB2-induced synthesis was inhibited but only at DTC concentrations higher than 50 microM. In the presence of nordihydroguaiaretic acid, a lipoxygenase inhibitor, which inhibited the Con A-induced synthesis of HETEs by 78%, DTC no longer stimulated HETE production above the Con A-induced level. Reverse phase HPLC analysis showed that Con A increased the PBMC production of 5-, 12- and 15-HETEs. In the presence of 5 microM DTC, 5-HETE production was entirely suppressed whereas the 15-HETE level was markedly enhanced, 12-HETE production by the contaminating platelets remained unchanged. In vitro experiments indicated that DTC alone did not significantly influence 15-hydroperoxyeicosatetraenoic (15-HPETE) production by the soybean 15-lipoxygenase but, in the presence of added reduced glutathione, DTC markedly reduced 15-HPETE into 15-HETE. In addition, DTC was able to substitute for cellular extract in the glutathione peroxidase (GPx) assay system. Taken together, these results indicate that DTC, through its "GPx-like" activity is able to modify the lipoxygenase cascade. Its ability to selectively reduce 15-HPETE known to stimulate immunosuppressive T-cells might help to explain its positive regulatory effect upon the immune system.

Arachidonic Acid↗

PubMed1992

Incorporation and turnover of eicosapentaenoic and docosahexaenoic acids in human blood platelets in vitro.

Mass changes in the incorporation of linoleic (C18:2), eicosapentaenoic (C20:5) and docosahexaenoic (C22:6) acids in human blood platelet phospholipids were induced by incubating the cells and these fatty acids complexed to albumin. The remodelling of [14C]C18:2, [14C]C20:5 and [14C]C22:6 in classes, subclasses and molecular species of platelet phospholipids was studied in resting and thrombin-stimulated cells. More than 85% of the incorporation was located in phospholipids, representing 5-fold and 2.5-fold increases in the phospholipid C20:5 and C22:6 endogenous content respectively. Thrombin stimulation induced a 30% degradation of 1-acyl-2-C20:5-glycerophosphocholine (GPC) and 1-acyl-2-C22:6-GPC, but did not induce significant release of C18:2 from 1-acyl-2-C18:2-GPC. There was no change in the [14C]fatty acid composition of 1-alkyl-2-acyl-GPC. Thrombin-dependent increases in 1-alkenyl-2-C20:5-glycerophosphoethanolamine (GPE) and 1-alkenyl-2-C22:6-GPE of 2.1-fold and 2.5-fold respectively accounted for the rise in GPE radioactivity and partly compensated for the loss of these fatty acids from 1,2-diacyl-GPC: transfer to 1-alkenyl-2-acyl-GPE was 0.4 and 1.5 nmol/10(9) platelets for C20:5 and C22:6 respectively. [14C]C20:5 and [14C]C22:6 were incorporated into six different species of 1,2-diacyl-GPC, with acylation in the major endogenous forms (C18:1 +C16:0 and C18:0 species) representing 76% and 66% respectively of the total radioactivity present in 1,2-diacyl-GPC. Stimulation by thrombin induced significant release of these fatty acids from the main molecular species of 1,2-diacyl-GPC, but significantly stimulated the synthesis of alkenyl forms of GPE containing C18:1/C22:6 +C16:0/C22:6, C18:0/C22:6 and C18:0/C20:5. C18:0/C18:2, the major endogenous C18:2 molecular species, represented only 10.5% of the incorporation; none of the [14C]C18:2 molecular species was a substrate for transfer towards 1-alkenyl-2-acyl-GPE. It is concluded that when C20:5 and C22:6, but not C18:2, are acylated in 1,2-diacyl-GPC, they participate in thrombin-dependent phospholipid remodelling, and might compete with the turnover and release of arachidonic acid from platelet phospholipids and the subsequent activation of the cells.

Blood Platelets↗

PubMed1992

Early increase in lymphocyte cyclic nucleotide phosphodiesterase activity upon mitogenic activation of human peripheral blood mononuclear cells.

Cyclic nucleotide phosphodiesterase activity of human peripheral blood mononuclear cells was significantly increased following a short (30 min) incubation with the mitogenic lectin Concanavalin A. Con A stimulated phosphodiesterase activity to the same extent whatever the subcellular compartment (homogenate, cytosol or pellet). Further separation of the Con A-activated mononuclear cells into lymphocyte-enriched and monocyte-enriched populations showed that the Con A-induced increase of phosphodiesterase activity exclusively affected the lymphocyte-enriched population. In lymphocytes, cyclic GMP phosphodiesterase activity was more importantly enhanced by Con A (+275%) than cyclic AMP phosphodiesterase activity (+75%). The increase of both activities occurred as early as from 10 min of Con A incubation and proved to be maximal with Con A doses of 2.5 and 5 micrograms per 10(6) cells, lower and higher doses being less effective. Inhibition experiments with reference inhibitors suggested that, among the high affinity phosphodiesterase isoforms, the cyclic GMP-inhibited enzyme might be more selectively enhanced by Con A than the cyclic AMP-specific, Rolipram-sensitive one. The non-mitogenic lectin Helix pomatia hemagglutinin, was not able to enhance cyclic nucleotide phosphodiesterase activity of human mononuclear cells whereas anti-CD3 monoclonal antibody, although being less effective than Con A, exhibited a significant stimulatory effect. Putting together these results suggest that the early increase in phosphodiesterase activity might be a normal step involved in the mitogenic activation of human lymphocyte.

3',5'-Cyclic-AMP Phosphodiesterases↗