Journal of lipid mediators最新文献

The inhibitors of prostaglandin (PG) or leukotriene (LT) synthesis and antagonists of platelet-activating factor (PAF) or LTs are inhibitory in experimental keratitis and clinical symptoms of keratitis are reproduced by application of these lipid mediators. This suggests that PGE2, LTB4, LTD4, and PAF are involved in experimental immunogenic and toxic keratitis. The objective of the present study is the measurement of the concentrations of lipid mediators in the aqueous humour and their release by the cornea and iris during keratitis. In both inflammatory models the concentrations of PGE2, LTB4, LTD4, and PAF in the aqueous humour were significantly increased as compared to their controls. The release of PGE2, LTB4 and LTD4 from the cornea, and of PGE2, LTB4, and PAF from the iris was significantly increased compared to that from control tissues. The results are consistent with a role for these lipid mediators in the inflammatory models. Combined therapeutic use of synthesis inhibitors or antagonists of these mediators in eye inflammation seems possible and may serve as an alternative to topical corticosteroid therapy.

We assessed the effect of 5-lipoxygenase inhibitors on the contraction of human bronchial ring segments passively sensitized with IgE in vitro. Contraction was induced by increasing doses of anti-IgE (0.01-0.5 micrograms/ml) in the presence of the antihistamine mepyramine. Zileuton and MK-886 (10 microM) significantly inhibited the dose-related contraction to anti-IgE as compared with solvent (DMSO). At the highest dose of anti-IgE used, contraction reached 10.3 and 9.6% of the maximal carbachol contraction, respectively, as compared with 30.3% for solvent. Maximal carbachol contraction was unaffected. These results suggest a potential beneficial effect of 5-lipoxygenase inhibitors in anaphylactic reactions in man.

Basic peroxidation in brains of normal 2 month old mice was compared to that in brains of 25 month old mice by measurement of 4-hydroxy-2-nonenal and protein carbonyl contents. No significant age-related differences in 4-hydroxy-2-nonenal were observed, showing that lipid peroxidation is not a determining factor in cerebral aging. However, protein carbonyls increased with age in brains, indicating accumulation of age-related cell constituent damage. The role of excess CuZn superoxide dismutase in basal lipid peroxidation in mouse brains was studied by comparison of eight 25 month old transgenic mice and eight non-transgenic littermates. Higher 4-hydroxy-2-nonenal concentrations were found in normal mouse brains. These data suggest an increased protective role of CuZn superoxide dismutase against lipid peroxidation in transgenic mouse brains.

Reductions in shear rate are generally associated with a recruitment of rolling and adherent leukocytes within the microcirculation. In this study, we determined if platelet-activating factor (PAF) affects shear rate-dependent leukocytes adhesion in cat mesenteric venules and whether the adhesion glycoproteins CD11/CD18 and ICAM-1 contribute to this process. Shear rate was varied in postcapillary venules (25-35 microns) by graded occlusion of the superior mesenteric artery. Vessel diameter, red blood cell velocity, leukocyte rolling velocity, and the number of rolling and adherent leukocytes were measured at each shear rate either in the presence or absence of PAF superfusion. PAF superfusion resulted in an increased number of adherent, but not rolling, leukocytes at basal and reduced venular shear rates. A monoclonal antibody (MAb) directed against CD11/CD18 prevented the PAF-induced recruitment of adherent leukocytes, while an ICAM-1 specific MAb had no effect. These results indicate that PAF increases shear rate-dependent leukocyte adhesion, presumably through activation and/or increased surface expression of CD11/CD18 on granulocytes.

Human non-pancreatic PLA2 has been the object of intense scrutiny for a relatively short period of time. Its role in physiology remains enigmatic. While PLA2 may serve to remodel or remove peroxidised or senescent phospholipids, the enormous magnitude of its upregulation during infectious or inflammatory episodes is consistent with a role in host defense. However, the nature of this role remains elusive. Attempts to relegate this enzyme to the genre of acute phase reactants have not been helpful in unravelling its role. Difficulty in obtaining adequate amounts of native snp-PLA2 prior to the availability of recombinant snp-PLA2 led to the widespread use of snake venom homologs, particularly in studies of the biology of PLA2. This review has underscored the pitfalls inherent in that approach given the major differences between some venom PLA2s as compared to snp-PLA2. In addition, it bears reiterating that the complex composition of venom allows for potentiation of PLA2 activity by other constituents present in venom. Whether human host defense networks employ this interactive strategy is largely unknown. Nonetheless, in spite of these reservations, some very compelling data have emerged in recent years implicating snp-PLA2 in the initiation or potentiation of local and systemic inflammatory processes. These include sepsis and associated acute lung injury as well as inflammatory arthritides, with rheumatoid arthritis as the prototype. The mechanisms of snp-PLA2 homeostasis are considerably better understood, and it has become apparent that snp-PLA2 is an integral part of a larger network of proinflammatory cytokines, growth factors and lipid mediators. The interrelationship between the functions of secretory and cytosolic PLA2s remains to be defined. A number of selective PLA2 inhibitors have been identified which will allow for discrimination between the actions of these classes of PLA2. The availability of synthetic inhibitors in conjunction with endogenous modulators of PLA2s will shift the biology of PLA2 from the realm of the inferential to that of the mechanistic.

SR 27388 (N-(2-dimethylaminoethyl)-N-(3-pyridinylmethyl[4-(3,5-di(tert- butyl)-4-hydroxylphenyl)thiazol-2-yl]amine) is a potent and competitive antagonist of the binding of [3H]PAF to its receptor on rabbit platelets exhibiting an equilibrium inhibition constant for PAF binding of 10.5 +/- 1.2 nM (n = 3). SR 27388 potently inhibited PAF-induced aggregation of rabbit platelets in vitro (IC50 = 65 +/- 12 nM) (n = 4). In this respect, SR 27388 was as potent as the triazolothienodiazepine WEB-2086 against PAF-induced aggregation of rabbit platelets and had no effect on the action of other platelet aggregating agents. SR 27388 prevented in a dose-dependent manner the formation of thiobarbituric acid reactive substances during membrane peroxidation (IC50 = 0.7 microM) and inhibited reduction of the stable 1,1-diphenyl-2-picrylhydrazyl radical, indicating that the antioxidant potency of SR 27388 was due to an efficient radical scavenging activity. SR 27388 displayed marked in vitro inhibition of zymosan-induced oxidative burst in human monuclear cells (IC50 = 3 microM). In vivo, SR 27388 protected mice from 100 micrograms/kg PAF-induced death with an ED50 value of 500 micrograms/kg, when given i.v., 5 min before PAF challenge or p.o. (ED50 = 800 micrograms/kg) when given 1 h before PAF administration. Similarly, i.v. or oral doses of SR 27388 afforded in mice complete protection against endotoxin-induced lethality (ED50 values were 250 micrograms/kg and 1.3 mg/kg, respectively). Neither BHT, vitamin E nor catechin exhibited significant protection against PAF- or endotoxin-induced death. In ovalbumin-presensitized rabbits, SR 27388 premixed with the allergen inhibited in a dose-dependent manner allergen-induced oedema formation in the skin (ED50 = 0.1 mumol/site). After an i.v. administration of 10 mg/kg, SR 27388 significantly protected mice against alloxan-induced diabetes. These results show that SR 27388 is a potent and orally active dual PAF receptor antagonist and antioxidant.

The role played by platelet-activating factor (PAF) and tumor necrosis factor (TNF-alpha) in myocardial ischaemia-reperfusion injury was investigated. Pentobarbital anaesthetized rats were subjected to left main coronary artery ligation (1 h) followed by reperfusion (1 h; MI/R). Sham-operated rats were used as controls (Sham MI/R). Myocardial ischaemia-reperfusion injury produced a marked myocardial injury (necrotic area/area-at-risk = 60 +/- 5%; necrotic area/total area = 50 +/- 6%), high serum creatine phosphokinase activity (Sham MI/R = 25 +/- 10 U/ml; MI/R = 190 +/- 12 U/ml), a severe leukopenia (Sham MI/R = 10367 +/- 630 WBC x mm3; MI/R = 4123 +/- 120 WBC x mm3) and elevated myocardial myeloperoxidase activity (investigated as an index of leukocytes adhesion and accumulation) in the area-at-risk (6.2 +/- 0.5 U x 10(-3)/g tissue) and in necrotic area (6.6 +/- 0.7 U x 10(-3)/g tissue. Plasma PAF and serum TNF-alpha were significantly increased only during reperfusion. The peak of PAF plasma levels (6.5 +/- 1.2 pmol/ml) occurred earlier (15 min of reperfusion) than the peak of serum TNF-alpha (150 U/ml at 30 min of reperfusion). At the end of reperfusion, macrophage TNF-alpha was also enhanced (Sham MI/R = undetectable; MI/R = 148 +/- 12 U/ml). The administration of CV 6209, a specific PAF receptor antagonist (5 mg/kg, 5 min after occlusion), significantly reduced myocardial injury (necrotic area/area-at-risk = 27 +/- 3%, P < 0.001; necrotic area/total area = 10 +/- 2%, P < 0.001), blunted the increase in serum creatine phosphokinase (70 +/- 12 U/ml), partially restored leukopenia (8234 +/- 143 WBC x mm3) and lowered myeloperoxidase activity in area-at-risk (2.3 +/- 0.3 U x 10(-3)/g tissue; P < 0.001) and in necrotic area (2.8 +/- 0.5 U x 10(-3)/g tissue). In addition, administration of CV 6209 reduced the serum and macrophage levels of TNF-alpha. The results of this study, therefore, suggest that PAF and TNF-alpha are key mediators of myocardial ischaemia-reperfusion injury and that PAF plays a permissive role in inducing the release of other factor(s) relevant to reperfusion injury.

Injury of plant cells as well as mammalian cells is connected with the activation of 'dormant' lipoxygenases. In the presence of oxygen, these enzymes are activated and enabled to catalyze the formation of hydroperoxides of linoleic and other polyunsaturated fatty acids. Reactivity of dormant lipoxygenases seems to be dependent on the carbon number between the alkyl end and the double bond situated next to this end in an unsaturated acid. In contrast to these dormant lipoxygenases there exists a second group of lipoxygenases, which are active in plant cells all the time, independent of an injury. They react mainly with acids possessing two homoconjugated double bonds within a distance of seven CH2 groups from the carboxylic end. Thus, they 'count' from the reverse end of the molecule. These lipoxygenases produce F-acids. They are converted, when plant cells are injured by hydroperoxides produced from unsaturated acids, into dioxoenoic acid intermediates which probably are used for defense. In mammalian tissues, lipoxygenases produce in the case of cell injury plasmalogen epoxides. These are analogous to dioxoenoic acids' highly reactive intermediates (in a chemical sense) which react immediately with nucleophiles. Such transformation of plasmalogens may be responsible for the development of chronic diseases, e.g., atherosclerosis, Alzheimer's disease and also for aging.

The coumarin derivative, cloricromene, an antithrombotic drug previously indicated as AD6, is known to inhibit the release of radioactive arachidonic acid from human platelets prelabelled with arachidonic acid and stimulated with thrombin. This effect might be due to the drug itself or to its catabolite, cloricromene acid. When added to platelet lysates neither compound inhibited phospholipase A2 activity assayed either with endogenous or with exogenous substrates. However, some inhibition was instead shown when intact platelets were first exposed to cloricromene and then enzyme activity was assayed in the lysate. Preincubation of platelets with the drug caused a dose-dependent inhibition of arachidonic acid mobilization in fluoroaluminate-stimulated platelets. beta-Thromboglobulin (beta-TG) release, a phenomenon previously shown to share common steps with phospholipase A2 activation, was also dose-dependently inhibited by cloricromene. Cloricromene also reduced the radioactivity associated with phosphatidic acid in fluoroaluminate-stimulated platelets but not in platelets stimulated with thrombin. These results are consistent with the hypothesis that cloricromene, or its catabolite, inhibits the production of arachidonic acid in stimulated platelets by interfering with a G-protein mediated activation of phospholipase A2 that is independent from the receptor-activated phosphoinositide phospholipase C.

In ascites tumor cells, phosphoinositide metabolism can be activated by short-term treatment with exogenously added 1-oleoyl-2-acetyl-sn-glycerol (OAG), which is the membrane-permeable analog of diacylglycerides (DAG). Quiescent cells prelabeled with D-myo-2-[3H]inositol and then stimulated with OAG (20 micrograms/ml of medium) reveal transient increases in the liberation of inositol 1,4-bis- and inositol 1,4,5-trisphosphate with peaks at 30 min, and a sustained accumulation of inositol phosphate 30 min after stimulation. The labeling patterns of the corresponding inositol lipids show transient activity profiles for phosphatidylinositol 4-phosphate (PtdIns(4)P) and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), and a sustained high activity level for PtdIns 30 min after OAG treatment. These data demonstrate a temporal relationship between synthesis and phospholipase C (PLC)-induced hydrolysis of these lipids. Simultaneous labeling of the cellular inositol phospholipids with [1-14C]arachidonic acid reveals modest accumulations after OAG stimulation. The relative 3H radioactivity distribution between the lipids and their inositol metabolites show that about 10% of the polyphosphoinositide pools are metabolically active. Long-term culturing of the cells (> 24 h) under OAG supplementation produces significant reductions in the catalytic activities of PLC and the PtdIns and PtdIns(4)P-specific kinases which is paralleled by a reduced radioactive labeling of PtdIns(4)P and PtdIns(4,5)P2 under these conditions. These data suggest that diglycerides affect the phosphoinositide metabolism by controlling PLC and phosphoinositide kinase activities probably via modification of membrane properties, and by functioning as modulator of other events.