Phospholipid methylation and biological signal transmission

Beta-adrenergic regulation of the somatostatinergic system in rat hippocampus

Interaction of beta-adrenergic and somatostatinergic systems in the hippocampus has not been investigated fully. We studied the influence of DL-isoproterenol (ISO), a beta-adrenergic agonist and DL-propranolol (PRO), a beta-adrenergic blocking agent, on the somatostatinergic system in the rat hippocampus. The short-(5h) and long-term (14 days) administration of ISO (5 mg/kg i.p.) or of PRO (10 mg/kg i.p.) did not affect somatostatin-like immunoreactivity (SSLI) content in the hippocampus of male Wistar rats. Both short- and long-term ISO administration decreased the number of specific [125I]Tyr11-somatostatin ([125I]Tyr11-SS) receptors in synaptosomes from hippocampus (29%, P < 0.05 and 34%, P < 0.05, after short- and long-term administration, respectively) without changing the affinity constant. This decrease in the number of [125I]Tyr11-SS receptors was not due to a direct effect of ISO on these receptors since no decrease in binding was produced by high concentrations of ISO (10(-5) M) when added in vitro. In addition, this decrease could be blocked by pretreatment with PRO. Short- and long-term administration of PRO alone increased the [125I]Tyr11-SS binding in hippocampus (42%, P < 0.05 and 33%, P < 0.05, after short- or long-term administration, respectively) without changing the affinity constant. Although there is no direct evidence that the regulation of SS receptors by the beta-adrenergic system has a physiological significance, this mechanism may provide a means by which the brain environment could modulate SS receptor number and, therefore, sensitivity to SS in a subset of SS-sensitive neurons.

S-adenosyl-L-methionine-mediated enzymatic methylations in the rat retinal membranes

Enzymatic step-wise methylation of membrane phosphatidylethanolamine (PE) to phosphatidyl-N-methylethanolamine (PME) and then phosphatidyl-choline (PC) has been known to alter membrane properties and responsiveness of cells for activation of receptors by chemical transmitters. Conversion of PE to PME and PME to PC in the presence of S-adenosyl-L-methionine (SAM) are catalyzed by two phospholipid N-methyltransferases, PMT I and PMT II, of which PMT I is the rate limiting enzyme. Retina is a good neuronal model for chemical transmission. However, retina was not studied for PMT activity. Therefore, we studied the rat retina for PMT I activity. Methylation of PE in the rat retinal sonicates was assayed using 3H-SAM (2 microM) at 37 degrees C in Tris-glycylglycine buffer (50 mM, pH 8.0) and methylated phospholipids were extracted with chloroform/methanol/HCl (2/1/0.02, v/v) and separated by thin layer chromatography on Silica Gel G plates. Chromatograms were developed in a solvent system of propionic acid/n-propyl alcohol/chloroform/water (2/2/1/1, v/v). This study gave the following results: (a) the total methylated phospholipids were (M +/- SE, N = 5) 19.90 +/- 4.03 fmol/mg protein/min; (b) the major methylated phospholipid was PME (4.21 +/- 0.68 fmol/mg protein/min; (c) the fatty acid methylesters formed by fatty acid carboxymethylase (FACM) which accumulated in the solvent front amounted to 18.82 +/- 2.84 fmol/mg protein/min. Both PMT I and FACM were inhibited by S-adenosyl-L-homocysteine (I50, 1.2-5 microM). These observations indicate that rat retina contains both PMTs and FACM.

Nicotinamide methylation in patients with cirrhosis

Methylation reactions play an important role in the transformation of endogenous and exogenous substances. Up to 85% of all transmethylation reactions occur in the liver. Several studies have shown that these metabolic processes are greatly influenced by the presence of hepatic diseases. We investigated the methylation of nicotinamide in 16 control subjects and in 29 patients with cirrhosis (19 Child A, 10 Child B). The basal serum value of N-methyl-nicotinamide was measured in all subjects. In seven controls and in nine patients with cirrhosis (5 Child A and 4 Child B), the serum levels and urinary excretion (5 and 24 h) of N-methyl-nicotinamide were also evaluated after oral administration of nicotinamide (1.5 mg/kg body weight). The basal serum levels of N-methyl-nicotinamide were significantly (p < 0.05) higher in patients with cirrhosis (Child A: median 34 ng/ml, 16th percentile 24, 84th percentile 61; Child B median 45, 16th percentile 34, 84th percentile 81) than in controls (median 22, 16th percentile 13, 85th percentile 28). After the nicotinamide load the urinary excretion and the time course of serum N-methyl-nicotinamide in cirrhosis were also higher (p < 0.05) than in controls (24 h urinary excretion = 66.2 mg +/- 5 S.D. in cirrhosis; 47.2 +/- 10.3 in controls) (area under the serum concentration versus time curve = 68 micrograms.ml-1.min-1 +/- 22 S.D. in cirrhosis; 32 +/- 15 in controls). In conclusion, our results show that cirrhosis does not impair the efficiency of nicotinamide methylation.

Effect of propylthiouracil-induced hypothyroidism on membranes of adult rat brain

The effect of hypothyroidism on the lipid composition of myelin and synaptosomes isolated from adult rat brain was investigated. The animals were made hypothyroid by adding 0.05% propyl-2-thiouracil to their drinking water for four weeks. This pathological state resulted in a significant increase in the relative percentage of choline glycerophospholipids in synaptosomes with a concomitant decrease in ethanolamine glycerophospholipids as compared to controls. In myelin, hypothyroidism significantly influenced only the relative percentage of sulfatides. The effect of the hypothyroid state on mature brain was also reflected in changes in the membrane fatty acid composition. Myelin and synaptosomes showed an increase in arachidonic (20:4) and eicosatrienoic (20:3) acids and an increase in the fatty acid unsaturation index. Furthermore, the 20:4/20:3 and 20:3/18:2 ratios were lower and higher, respectively, in treated animals. The data indicate that hypothyroidism affects the lipid composition of synaptosomes and myelin even though the effects were less pronounced in myelin. The lipid changes observed in hypothyroidism may be of physiological significance, as it is well known that lipid composition modulates various membrane-bound enzymes, transporters and receptors.

[Mechanism of action of antidepressants]

Modifications in noradrenergic and serotonergic systems are involved in the central mechanism of action of antidepressants. Most antidepressants (electroconvulsive therapy included) induce a desensitization of the beta-noradrenergic receptor, as shown by a decrease in noradrenaline-stimulated cAMP production. Down-regulation of the beta receptor is often associated with desensitization, as well as modifications in the activity of the serotonergic system, among which alternations in 5-HT2 receptors are frequent. Finally, complex interactions between noradrenergic and serotonergic receptors may also contribute to the pharmacological effect of long term antidepressive treatment.

Studies of lysophospholipids related to the hamster sperm acrosome reaction in vitro

Phospholipase A2 and lysophospholipids have been implicated in the mammalian sperm acrosome reaction. In this study we further investigated the role of this enzyme and lysophospholipids on the acrosome reaction of hamster spermatozoa. Hamster epididymal spermatozoa were incubated under capacitation and acrosome reaction-inducing conditions. After 3.0 and 3.5 h, the spermatozoa were treated with different doses of lysophosphatidylcholine for 12 min. Then the percentage of motility, hyperactivation, and acrosome reaction was evaluated by light microscopy. Lysophosphatidylcholine, 10 micrograms/ml, was the highest acrosome reaction-inducing dose without an effect on sperm motility. Lysophosphatidylcholine induced the acrosome reaction only when added to spermatozoa capacitated for a minimum of 2 h. This effect was apparent after 1 min of its addition and reached a plateau after 5 min. Lysophosphatidylethanolamine and lysophosphatidylinositol were also effective in inducing the acrosome reaction. Lysophosphatidylserine did not have any effect on the reaction, but caused an increase in sperm hyperactivation. Sperm treated with the phospholipase A2 inhibitors quinacrine dihydrochloride and p-bromophenacyl-bromide showed an inhibition of the spontaneous occurrence of the acrosome reaction. These inhibitors, however, did not block the acrosome reaction induced by lysophosphatidylcholine. The time course of the lysophosphatidylcholine-induced acrosome reaction was the same whether control or inhibitor treated spermatozoa were used. These results suggest that the membrane events of the acrosome reaction initiate with the activation of the phospholipase A2, thus producing the fusogen agents necessary for this exocytotic event.

In vivo effect of chronic ethanol consumption on the fatty acid composition of phosphatidylinositols in resting and anti-CD3-activated lymphocytes

Fatty acid composition of phosphatidylinositols was analyzed in peripheral blood lymphocytes from nine alcoholic patients who were well nourished and without severe acute and chronic liver disease, before and after stimulation with anti-CD3 antibody. Six comparable nondrinkers were studied as controls. A reduction in unsaturated fatty acid (mainly arachidonic) and an increase in palmitic and stearic acid molar content were observed in phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2) in unstimulated samples from alcoholic patients in comparison with normal subjects, leading to a significant decrease in the saturated/unsaturated ratio. In controls, anti-CD3 stimulation caused a marked decrease in arachidonic acid relative molar content counterbalanced by an increase in other polyunsaturated fatty acid relative molar content in PI, PIP, and PIP2 fractions. Interestingly, after anti-CD3 stimulation, alcoholic patients show the same trend of modification in the fatty acid composition resulting in a sharp reduction of arachidonic acid relative molar content. These results support the hypothesis of an alteration in nutrients being responsible for immune derangement in alcoholics.

Aetiology and pathogenesis of alcoholic liver disease

Until the 1960s, liver disease of the alcoholic patient was attributed exclusively to dietary deficiencies. Since then, however, our understanding of the impact of alcoholism on nutritional status has undergone a progressive evolution. Alcohol, because of its high energy content, was at first perceived to act exclusively as 'empty calories' displacing other nutrients in the diet, and causing primary malnutrition through decreased intake of essential nutrients. With improvement in the overall nutrition of the population, the role of primary malnutrition waned and secondary malnutrition was emphasized as a result of a better understanding of maldigestion and malabsorption caused by chronic alcohol consumption and various diseases associated with chronic alcoholism. At the same time, the concept of the direct toxicity of alcohol came to the forefront as an explanation for the widespread cellular injury. Some of the hepatotoxicity was found to result from the metabolic disturbances associated with the oxidation of ethanol via the liver alcohol dehydrogenase (ADH) pathway and the redox changes produced by the generated NADH, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Exaggeration of the redox change by the relative hypoxia which prevails physiologically in the perivenular zone contributes to the exacerbation of the ethanol-induced lesions in zone 3. In addition to ADH, ethanol can be oxidized by liver microsomes: studies over the last twenty years have culminated in the molecular elucidation of the ethanol-inducible cytochrome P450IIE1 (CYP2E1) which contributes not only to ethanol metabolism and tolerance, but also to the selective hepatic perivenular toxicity of various xenobiotics. Their activation by CYP2E1 now provides an understanding for the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, 'over the counter' analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Ethanol causes not only vitamin A depletion but it also enhances its hepatotoxicity. Furthermore, induction of the microsomal pathway contributes to increased acetaldehyde generation, with formation of protein adducts, resulting in antibody production, enzyme inactivation and decreased DNA repair; it is also associated with a striking impairment of the capacity of the liver to utilize oxygen. Moreover, acetaldehyde promotes glutathione depletion, free-radical mediated toxicity and lipid peroxidation. In addition, acetaldehyde affects hepatic collagen synthesis: both in vivo and in vitro (in cultured myofibroblasts and lipocytes), ethanol and its metabolite acetaldehyde were found to increase collagen accumulation and mRNA levels for collagen. This new understanding of the pathogenesis of alcoholic liver disease may eventually improve therapy with drugs and nutrients.

The effects of imipramine on the methylation of phosphatidylethanolamine (PE) in the cortical membranes of Wistar rats

This study investigates the effect of imipramine (IMI) on the methylation of phosphatidylethanolamine (PE) in crude cortical membranes of rat brain in vitro and ex vivo. It was found that IMI enhanced the formation of phosphatidyl-N-monomethylethanolamine (PME) and phosphatidyl-N,N-dimethylethanolamine (PDE) and inhibited the formation of phosphatidylcholine (PC) in the cortical membranes of rats in vitro. The same effect i.e. increased incorporation of methyl groups in PE and PME and decreased formation of PC was found in the cortical membrane of rats killed 1 hr after intraperitoneal administration of IMI at a single dose of 10 mg/kg. Chronic treatment of rats with IMI for 14 days with a daily dose of 10 mg/kg i.p. led to further inhibition of PC formation but did not affect the formation of PME and PDE and abolished the stimulating effect of IMI on the formation of PME and PDE in vitro.

S-adenosyl-l-methionine inhibits phosphoinositide metabolism in the rat brain synaptosomal suspensions

S-adenosyl-l-methionine (AdoMet) has been reported to affect events linked to noradrenergic neurotransmission. In the present work, we studied the effect of AdoMet on norepinephrine (NE)-stimulated inositol phosphate production in 3H-inositol-labelled crude synaptosomal suspensions of rat brain. AdoMet (50-1000 microM) decreased both the synthesis of labelled polyphosphoinositide (30-50%) and the release of inositol mono- and bisphosphate (40-50%). The AdoMet effect was not dependent on NE concentration (10-1000 microM), suggesting that the inhibition of inositol phosphate release was not the result of a modification of the norepinephrine binding to its receptor sites. S-adenosyl-L-homocysteine (AdoHcy) (1 mM) an inhibitor of methyltransferase activities, partially inhibited (70%) the AdoMet (0.1 mM) effect, indicating that the methylation processes cannot explain all the effects observed. We conclude that, in addition to previously reported effects of AdoMet on NE transport, AdoMet may reduce NE-linked intracellular signalling.

Human chorionic gonadotropin and free beta subunits stimulate phospholipid methylation in intact rat Leydig cells

The effect of human chorionic gonadotropin (hCG) on intact Leydig cell phospholipid methylation was studied. Hormonal stimulation of rat Leydig cells increased the incorporation of [methyl-3H]methionine into phospholipids threefold. This effect was observed after 10 minutes of incubation time and was time and dose dependent with a maximal stimulation at 67 ng/ml of hCG. In the presence of hCG, 3H-labeled methyl groups were preferentially incorporated into phosphatidyl-N-monomethylethanolamine. This effect of hCG was not reproduced by dibutyryl cyclic adenosine monophosphate (cAMP), cholera toxin, or forskolin. Purified hCG beta subunit but not hCG alpha subunit had stimulatory activity on Leydig cell phospholipid methylation. We conclude that luteinizing hormone (LH)/hCG stimulates specifically Leydig cell phospholipid methylation, because LH-releasing hormone or [Arg8]-vasopressin did not modify these reactions. We postulate that these reactions are occurring at a cellular level that involves hormone-receptor interaction. It is also suggested that this biological response involves hCG beta subunit receptor interaction and does not require cAMP synthesis.

Modulation by isoproterenol and propranolol of somatostatin receptors in synaptosomes from rat frontoparietal cortex

DL-Propranolol (PRO), a beta-adrenergic blocking agent, and the neuropeptide somatostatin (SS) have central nervous system depressant and anticonvulsive properties. To investigate a possible relationship between these two components, we studied the influence of PRO and DL-isoproterenol (ISO), a beta-adrenergic agonist, on the somatostatinergic system in the rat frontoparietal cortex. The short- (5 h) and long-term (14 days) administration of ISO (5 mg/kg, intraperitoneally (i.p.)), or of PRO (10 mg/kg, i.p.) did not affect somatostatin-like immunoreactivity (SLI) content in the frontoparietal cortex of male Wistar rats. Both short- and long-term ISO administration decreased the number of specific [125I]Tyr11-SS receptors in synaptosomes from frontoparietal cortex (31%, P < 0.05, and 26%, P < 0.02, after short- and long-term administration, respectively) without changing the affinity constant. This decrease in the number of [125I]Tyr11-SS receptors was not due to a direct effect of ISO on these receptors since no decrease in binding was produced by high concentrations of ISO (10(-5) M) when added in vitro. This decrease could be blocked by pretreatment with PRO. Short- and long-term administration of PRO alone produced an increase in the [125I]Tyr11-SS binding in frontoparietal cortex (26%, P < 0.02, and 40%, P < 0.001, after short- or long-term administration, respectively) without changing the affinity constant.

Effects of dietary proteins on linoleic acid desaturation and membrane fluidity in rat liver microsomes

The effect of dietary protein, casein (CAS) and soybean protein (SOY), on linoleic acid desaturation in liver microsomes was studied in rats. The activity of delta 6 desaturase in total and rough endoplasmic reticula (ER and RER) was significantly higher in the CAS group than in the SOY group. In ER and smooth endoplasmic reticulum, the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, when incorporated into the membrane, was decreased in the SOY group and accompanied by a reduction in the cholesterol/phospholipid (CHOL/PL) ratio, consistent with an increase in membrane fluidity. In a separate study, the effect of varying dietary proteins, CAS, milk whey protein, egg albumin, SOY, potato protein and wheat gluten, on the relationship between the delta 6 desaturase activity and microsomal membrane fluidity was also examined. The results indicated that the dietary protein-dependent change in the liver microsomal CHOL/PL ratio affected membrane fluidity, and subsequently the activity of delta 6 desaturase in liver microsomes. However, since dietary protein influenced the delta 6 desaturase activity in RER without influencing membrane fluidity, it is possible that some regulation might have taken place at the level of enzyme synthesis.

Membrane function and vascular reactivity

This communication examines the possibility that nitric oxide (NO) production by endothelial cells results from changes in cell membrane fluidity. Lysophosphatidylcholine (LPC) alters fluidity of the endothelial cell membranes causing vascular relaxation. Through membrane alterations LPC influences function of a number of membrane receptors and modulates enzyme activity. As a result of detergent action, lysophosphatidylcholine (LPC) causes activation of guanylate cyclase, stimulates sialyltransferase and regulates protein kinase C activity. It has already been demonstrated that ionic detergents, such as Triton X-100 also cause vascular relaxation, possibly induced by NO production from endothelial cells. It is postulated that production of nitric oxide results from changes in membrane viscosity; this may represent a mechanism for its regulation in biological systems.

Cognitive decline in the elderly: a double-blind, placebo-controlled multicenter study on efficacy of phosphatidylserine administration

This double-blind study assesses the therapeutic efficacy and the safety of oral treatment with phosphatidylserine (BC-PS) vs placebo (300 mg/day for 6 months) in a group of geriatric patients with cognitive impairment. A total of 494 elderly patients (age between 65 and 93 years), with moderate to severe cognitive decline, according to the Mini Mental State Examination and Global Deterioration Scale, were recruited in 23 Geriatric or General Medicine Units in Northeastern Italy. Sixty-nine patients dropped out within the 6-month trial period. Patients were examined just before starting therapy, and 3 and 6 months thereafter. The efficacy of treatment compared to placebo was measured on the basis of changes occurring in behavior and cognitive performance using the Plutchik Geriatric Rating Scale and the Buschke Selective Reminding Test. Statistically significant improvements in the phosphatidylserine-treated group compared to placebo were observed both in terms of behavioral and cognitive parameters. In addition, clinical evaluation and laboratory tests demonstrated that BC-PS was well tolerated. These results are clinically important since the patients were representative of the geriatric population commonly met in clinical practice.

Simplified methods for the synthesis of 2-hexadecanoylthio-1-ethylphosphorylcholine and for the determination of phospholipase A2 activity

A simple and straight forward method was developed for the synthesis of 2-hexadecanoylthio-1-ethyl phosphorylcholine (HEPC). The new procedure, which used p-toulenesulfonate instead of 2-bromoethyl phosphorylcholine, not only reduced the reaction time but also allowed the reaction to proceed under mild conditions. Using HEPC as a substrate, we have also developed a microplate assay for measuring phospholipase A2 activity which is rapid and will be useful for analyzing a large number of samples in a very short time. The applicability of this assay method for assessing phospholipases A2 from two different sources and determining their kinetic constants is also demonstrated. This method can also be extended for measuring lipases and lysophospholipases using a suitable thioester. Thus, both synthesis and assay methods will be useful in basic and applied research on phospholipases and related enzymes.

Modulation by estradiol and progesterone of the GTP effect on striatal D-2 dopamine receptors

Agonist binding properties of rat striatal D-2 dopamine (DA) receptors were investigated after in vivo or in vitro estradiol or progesterone exposures in order to elucidate the mechanism of action of steroid hormones on DA receptors. Chronic estradiol treatment of ovariectomized rats (10 micrograms, twice each day, for 2 weeks) increased lateral striatum total receptor density and left unchanged the proportion and affinity of the agonist high- and low-affinity states of this receptor in the striatum. In addition, when GTP was added in DA competition for [3H]spiperone binding experiments, D-2 receptors in the medial part of the striatum from estrogen-treated animals were more sensitive to GTP than those in the lateral part, whereas GTP had equal activity in both parts of the striatum in vehicle-treated rats. With apomorphine, but not with DA competition for [3H]spiperone binding, addition of estradiol (1 nM) to striatal homogenates of intact male rats prevented the expected shift of the high- to the low-affinity state of D-2 receptors, normally induced by GTP (100 microM) under these conditions. This effect of estradiol was not observed in the presence of 4 mM MgCl2, while in vitro progesterone (100 nM) had no effect in either the absence or presence of MgCl2. In addition, in vivo chronic progesterone treatment of ovariectomized rats left striatal [3H]spiperone density and affinity unchanged. Moreover, 1 nM estradiol increased the IC50 of GTP for inhibition of [3H]N-propylnorapomorphine binding to the high-affinity state of striatal D-2 receptors. This effect was also observed but decreased by 2-fold in the presence of MgCl2. Our data suggest that estradiol in vivo and in vitro interferes with the effect of GTP on striatal D-2 DA receptors.

Tracer kinetic evidence for abnormal methyl metabolism in schizophrenia

The original transmethylation hypothesis of schizophrenia has evolved with time and experiment to the present concept that a defect in the methyl-carbon metabolic pathway may be causative in this illness. Various researchers have proposed that specific steps in the methyl-carbon pathway may be defective, and have presented evidence to support these possibilities. We have tested the general concept of the hypothesis by administering methionine labeled with 11C or 14C in the S-methyl carbon to patients with schizophrenia and to controls and measured the expiration of 11CO2 and 14CO2. We found that the rate and total expiration of labeled CO2 were three times less in the patients than in the controls, with no overlap of data points in the two groups. Specific steps in the methylcarbon pathway that might be defective and produce the results seen here are discussed in light of this and other researchers' findings.

Effect of oxidative stress on receptors and signal transmission

Reactive oxygen metabolites affect binding of ligands to membrane receptors and also coupling of receptors to G-proteins and effector enzymes. Peroxidation of membrane lipids may lead to a lowered receptor density and also will alter the viscosity of the plasma membrane, which affects receptor coupling. Reactive oxygen species may also interact with thiol/disulfide moieties on receptor proteins or on other factors in the receptor system, which is responsible for alterations in receptor binding or coupling. Moreover, lipid peroxidation is associated with the phospholipase A2 pathway, which might indirectly affect receptor function. Moreover, oxidative stress may lead to a disturbance in cellular Ca(2+)-homeostasis. This might be related to an effect on Ca(2+)-mobilizing receptors, but there is also evidence for a decreased Ca(2+)-sequestration by ATPases. In addition, peroxidation of membrane lipids increases membrane permeability to Ca2+. Finally, reactive oxygen species interfere with actions of nitric oxide, thus affecting another pharmacological messenger system.

Effect of S-adenosyl-L-methionine on brain muscarinic receptors of aged rats

The number of muscarinic receptors in the striatum and hippocampus of aged rats is significantly lower than the number measured in young animals. The treatment of aged rats for 30 days with S-adenosyl-L-methionine (SAM) restored the number of muscarinic receptors to levels found in the striatum and hippocampus from young animals. We did not observe a clear-cut difference between the dissociation constants of untreated young and untreated or SAM-treated aged rats, whereas the binding capacity varied. Moreover, in vitro addition of SAM to hippocampal membranes from aged rats resulted in a significant increase in the number of binding sites. This in vitro effect was antagonized by S-adenosyl-L-homocysteine, a specific in vitro inhibitor of methyltransferase activity. The reduction in the muscarinic receptor density could be related to a decrease in neuronal membrane fluidity induced by aging, while its increase after SAM treatment might be ascribed to the ability of this methyl donor to increase the fluidity of cell membranes by stimulating phospholipid synthesis.

Influence of chronic ethanol consumption on the inositol phospholipid fatty acid composition of human peripheral blood lymphocytes

The breakdown of inositol phospholipids is an important event after the binding of antigens to the T-cell antigen receptor. In alcoholics, changes either in early or in late steps of lymphocyte activation have been documented, however no study on the role of phosphoinositide fatty acid composition in signal transduction has been reported. We have analyzed the fatty acid pattern of phosphatidylinositol, phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate from peripheral blood lymphocytes of alcoholic patients and healthy controls, in order to point out the possible compositional differences which could interfere with the signal transmission responsible for the early events in lymphocyte activation. In alcoholics, the arachidonic acid relative molar content in all the inositol phospholipid (PtdIns) fractions derived from lymphocytes was lower than in controls; all PtdIns classes appeared much more saturated than the corresponding fractions from control lymphocytes. The different fatty acid pattern of PtdIns in alcoholic patients could be responsible for an altered second messenger production, above all the production of a modified diacylglycerol which, in turn, could cause a different activation pattern of protein kinase C, with a consequent alteration in cell proliferation. The decrease in arachidonic acid molar content in the phosphoinositides and particularly in the phosphatidylinositol-4,5-bisphosphate fraction of PBL of alcoholic patients could lead to a reduced synthesis of prostanoids of the (n-6) series, and, as a consequence, to an alteration in the mitogenic response of the cells.

Prostanoids synthesis in lymphocyte subpopulations by adrenergic and cholinergic receptor stimulation

The release of eicosanoids (PGE2 and TXB2) as a consequence of specific neurotransmitter receptor agonist stimulation is described herein. The differential expression of beta adrenergic and muscarinic cholinergic receptors on sets and subsets of lymphocytes was first identified. Saturation assays with a specific radioligand for beta adrenergic receptors (3H-DHA) showed that B-, T-, T-helper (Th) and T-suppressor/cytotoxic (Ts/c) lymphocyte enriched populations all displayed beta adrenergic receptors. In contrast, when a specific radioligand for muscarinic cholinergic receptors (3H-QNB) was used, B-lymphocytes showed a lack of high-affinity muscarinic cholinergic receptors, while T-lymphocytes expressed them. Ts/c murine lymphocytes had more muscarinic cholinergic receptors than did Th cells. Specific receptor stimulation by the agonist caused a release of different eicosanoids depending on the cell type. Isoproterenol, triggered the release of TXB2 by B and Th-cells, but had no effect on Ts/c-cells. On the other hand, the muscarinic cholinergic agonist, carbachol only induced the release of PGE2 by Ts/c-cells. These results suggest differences in the expression and function of neurotransmitter receptors in sets and subsets of murine lymphocytes regarding the release of eicosanoids.

Polyamines in neurotrauma. Ubiquitous molecules in search of a function

In spite of their abundance, the function of PAs in the adult nervous system remains enigmatic. It is postulated that after trauma, the induction of polyamine metabolism (i.e. the polyamine response), which is inherently transient, is an integral part of a protective biochemical program that is essential for neuronal survival. Several functions ascribed to PAs may assume importance in cellular defense. Thus, regulation of the ionic environment, modulation of signal pathways, control of cellular Ca2+ homeostasis, inhibition of lipid peroxidation, and interaction with nucleic acids are all putative sites for PA action. During maturation, the CNS, unlike the peripheral nervous system, undergoes changes which result in the expression of an incomplete polyamine response after trauma. This may be due to an altered pattern of gene expression, and/or restrictive compartmentalization of the PAs and their metabolizing enzymes. Induction of this partial polyamine response after injury results in a sustained accumulation of putrescine, which by itself may be harmful, without the concomitant increase in spermidine and spermine. Administration of exogenous PAs after trauma exerts a neuroprotective effect. Exogenous PAs are postulated to gain access into cells via an induced uptake system after trauma, and function similarly to newly synthesized PAs. Besides the injured neurons themselves, tissues which are connected or associated with these neurons may be potential targets where PAs could act to stimulate neurotrophic factor production. Based on the neuroprotective effects of PAs in laboratory animals and on their proposed role in mechanisms of neuronal survival, the development of PA-based compounds as therapeutic neuroprotective agents should be pursued.

Methylation effects on the microdomain structures of phosphatidylethanolamine monolayers

Increasing methylation of the headgroup in DPPE results in an increase of minimum area per molecule in highly compressed monolayers at the air-water interface. The shape of solid domains, as observed by epifluorescence microscopy, also exhibits marked changes upon increasing headgroup methylation. Branching domains are observed in DPPE and DP(Me)PE, whereas U-shaped or round domains are observed in DP(Me)2PE and DPPC under our experimental conditions. The domain shape is determined more by the headgroup methylatin than by the corresponding shift in critical temperatures, as shown by the study of PCs of different acyl chain moieties. In mixed lipid monolayers, PC (phosphatidylcholine) and PE (phosphatidylethanolamine) do not mix ideally, as indicated by the non-linear variation of the average area per molecule with composition, and by distinct domain shapes in LE/LC (liquid expanded/liquid condensed) coexisting phases representing PE-enriched or PC-enriched domains in those mixed monolayers.

Phospholipid N-methylation in diabetic erythrocytes: effects on membrane Na+, K+ ATPase activity

Phospholipid methylation was quantified in non-diabetic and streptozotocin diabetic rat erythrocytes. While the total mass of methylated lipids remained the same in both groups, the relative abundance of individual methylated lipid species differed significantly in diabetic erythrocytes. Moreover, incubation of erythrocytes membranes with S-adenosyl methionine, a substrate for methyl transferases, not only increased membrane lipid methylation but also decreased Na+, K+ ATPase activity significantly. These results suggest that phospholipid methylation may cause the observed depression of erythrocyte Na+, K+ ATPase activity in diabetes and could contribute to the altered rheology of erythrocytes in diabetes.

In utero ethanol exposure decreases the biosynthesis of phosphatidylserine in rat pup cerebrum

Phosphatidylserine is enriched in the brain and has been implicated to play a role in regulating neuronal membrane functions. In this study, three experimental protocols were used to examine the effects of in utero ethanol exposure on phosphatidylserine biosynthesis in rat pup brain, namely, (1) assay of the serine base-exchange enzyme activity in brain microsomes, (2) incubation of brain slices with [3H] serine, and (3) incorporation in vivo of [3H]serine into phosphatidylserine as well as serine-related phospholipids in brain. Results from all three protocols point to a decrease in phosphatidylserine biosynthesis in newborn rat pup cerebrum on exposure to ethanol in utero compared with the pair-fed controls. When in utero ethanol-exposed pups were nursed by mothers given a chow diet, the differences gradually returned to control levels by 17 days of age. The decrease in phosphatidylserine biosynthesis may be important in explaining some of the neuronal deficits associated with in utero ethanol exposure.

Inhaled budesonide fails to inhibit the PAF-induced increase in plasma leukotriene B4 in man

1. We studied the ability of inhaled budesonide to modulate PAF-induced acute effects in nine healthy nonsmoking volunteers. Responses in inflammatory cells and mediators in peripheral blood as well as in pulmonary function and circulation were monitored. 2. Inhalation of increasing doses of PAF (total cumulative dose of 500 micrograms) caused a rapid and profound decrease in circulating white blood cells, especially in granulocytes (P less than 0.01), which was turned to an increased number of these cells (P less than 0.05, P less than 0.025, respectively) in the blood samples taken 8 min after completion of the PAF challenge. No changes in the circulating platelets or their thromboxane production were found. Plasma concentrations of histamine or methylhistamine remained unchanged during PAF-inhalation, while plasma LTB4 tripled from the baseline level at 10 min (P less than 0.0005) and was returned to the pre-PAF value at 60 min. 3. PAF inhalation induced a bronchial obstruction (P less than 0.025), but no bronchial hyperresponsiveness to methacholine was found in any of our subjects when measured 24 h after the PAF challenge. Furthermore, PAF caused a decrease in systolic blood pressure (P less than 0.05). 4. Budesonide pretreatment of 400 micrograms twice daily during the preceding 5 days had no effect on any PAF-induced events measured in our study. That fact may also contradict the role of bronchial resident or alveolar cells as a source of the PAF-induced LTB4 burst in plasma. 5. We conclude that in healthy volunteers inhaled PAF induces a marked increase in plasma LTB4, which is not inhibited by inhaled budesonide.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioxidant therapy for recurrent pancreatitis: biochemical profiles in a placebo-controlled trial

The usefulness of micronutrient antioxidant therapy for recurrent (non-gallstone) pancreatitis has recently been endorsed by a 20-week double-blind double-dummy cross-over trial in 20 patients. Treatment was delivered as two types of tablets, providing daily doses of 600 micrograms organic selenium, 9000 i.u. beta-carotene, 0.54 g vitamin C, 270 i.u. vitamin E and 2 g methionine. We report antioxidant profiles in blood samples collected before entry, at the cross-over stage and upon completion of trial. Baseline serum concentrations of selenium, beta-carotene and vitamin E in the patients were significantly lower than in healthy controls, were unaltered by placebo and normalized by active treatment, but reverted to basal values in the subgroup that received placebo subsequently. The baseline serum concentration of a free radical marker--the 9-cis, 11-trans isomer of linoleic acid--was significantly higher in the patients than in controls, fell inexplicably in the placebo phase and fell further upon active treatment. Discriminant analysis eliminated the overlap in free radical marker and selenium concentrations between control sera on the one hand and baseline or post-placebo samples from the patients on the other: antioxidant treatment normalized the relationship between these biochemical parameters. Subnormal baseline serum levels of S-adenosylmethionine drifted downwards upon active treatment whereas a sharp rise was noted when a relapse of pancreatitis occurred during the placebo phase. The results confirm that adequate exposure to antioxidants in the active treatment phase was associated with amelioration of oxidative stress, and that there was no residual effect 10 weeks after switching over to placebo treatment. Furthermore, the paradoxical behaviour of S-adenosylmethionine may imply that the beneficial effect of micronutrient antioxidants in recurrent pancreatitis is linked with preservation of the methionine trans-sulfuration pathway in pancreatic acinar cells.

Blunting by chronic phosphatidylserine administration of the stress-induced activation of the hypothalamo-pituitary-adrenal axis in healthy men

The effect of chronic administration of phosphatidylserine derived from brain cortex on the neuroendocrine responses to physical stress has been examined in a placebo-controlled study in 9 healthy men. Phosphatidylserine 800 mg/d for 10 days significantly blunted the ACTH and cortisol responses to physical exercise (P = 0.003 and P = 0.03, respectively), without affecting the rise in plasma GH and PRL. Physical exercise significantly increased the plasma lactate concentration both after placebo and phosphatidylserine. The results suggest that chronic oral administration of phosphatidylserine may counteract stress-induced activation of the hypothalamo-pituitary-adrenal axis in man.