Increased membrane fluidity in blood leukocytes from allergic subjects. A possible role for leukotriene B4

Modifications of lipid metabolism and increased plasma membrane fluidity may occur during cell activation and occur in leukocytes of patients with allergic disease. Using a fluorescent probe (TMA-DPH) and a polarization technique, we studied the variations of membrane fluidity in blood leukocytes from allergic and normal subjects. The anisotropic coefficient, which is inversely related to the rotational motion of the probe in membrane phospholipids, was significantly higher in normal subjects than in allergic ones. This result implies an increased membrane fluidity in leukocytes from allergic patients. No correlation could be observed with the etiology or the severity of allergic disease, nor with cell preparation composition or serum IgE level. Such a modification of membrane fluidity has been reproduced after incubation of leukocytes from normal subjects with leukotriene B4, but not with cells from allergic patients. Establishing the mechanism of these differences requires further investigations.

The contribution of arachidonic acid to the aetiology and pathophysiology of focal brain oedema; studies using an infusion oedema model

Arachidonic acid solution (2 to 15 mg/ml) was infused into the right forebrain white matter of anaesthetised cats over three hours to evaluate its contribution to the genesis and pathophysiology of vasogenic brain oedema. The 0.6 ml infusion increased local white matter water content by a mean of 11.3 ml/100 g tissue but did not increase cortical water content. Histological studies revealed local expansion and trabeculation of the white matter with aggregations of granulocytic neutrophils in the venules and perivenular brain. The adjacent cortical cytoarchitecture was normal. The white matter around the infusion site was stained lightly and over a variable area (15-20 mm2) by intravenously administered Evans Blue dye 2%. Regional cerebral blood flow (rCBF) adjacent to the frontal infusion did not change significantly during the period of infusion and remained similar to rCBF in the contralateral hemisphere. Following the arachidonic acid infusion regional CBF CO2 reactivity was normal and three was no asymmetry of either cortical somatosensory evoked potential (SEP) or motor evoked potential (MEP) waveforms. The increase in brain water content and changes in the ICP and ICP related biodynamics (pressure-volume index, lumped craniospinal compliance and CSF outflow resistance) were similar to those seen following infusion of 0.6 ml saline. These studies suggest that free intraparenchymal arachidonic acid, at concentrations exceeding those occurring in most neuropathological conditions, can increase the normal brain parenchymal capillary permeability but does not disrupt focal cerebrovascular and electrophysiological function. The clinical implications of these findings are discussed.

Eicosanoid release and early changes in two acute non specific inflammatory reactions. Major role of prostacyclin and leukotrienes

We have compared the early development (0-4h) of two acute non-specific inflammatory reactions induced by the intrapleural injection of isologous serum or a suspension of CaPP crystals. The intensity of the reactions was assessed in terms of the exudate volume, the number and ratio of pleural cells and different cell functions and secretions. The number of exudative cells elicited by isologous serum was higher than with CaPP but the PMN/Monocytes ratio was the same. The amount of protein in the serum-induced exudate was constant from 1 h to 4 h and was similar in the CaPP-induced pleural exudate at the latter time. The amount of complement increased similarly in the two models. The chemotactic potency of the exudates and cell supernatants following incubation showed similar values in the two models. Eicosanoid levels were higher in CaPP--than in isologous serum-induced exudates. Prostacyclin and peptidoleukotrienes were released in specially large amounts at the very outset of the inflammatory reactions.

The role of leukotriene B4 in neutrophil infiltration in experimentally-induced inflammation of rat tooth pulp

Inflammation was induced in rat dental pulp by applying bacterial lipopolysaccharide (LPS). Extirpated tissue samples from inflamed pulps were incubated in vitro in a Krebs buffer containing Ca2+ ionophore A23187, and leukotriene (LT) B4 released into the medium was determined by radio-immunoassay. Production of LTB4 could be detected three to 24 h after the application of LPS and showed a maximum at 12 h. Histologically, marked infiltration of neutrophils, but not other leukocytes, was characteristically observed in the LPS-applied pulps, and the temporal change in neutrophil infiltration was almost parallel, but somewhat more delayed than LTB4 production. When BW755C, a dual inhibitor of cyclo-oxygenase and lipoxygenase, was given to the animals before the application of LPS, both the production of LTB4 and the number of infiltrated neutrophils were significantly decreased, whereas administration of indomethacin had no effect. These results suggest that LTB4 may be involved in neutrophil infiltration in pulpal inflammation. It was also suggested that a major early source of LTB4 in experimental pulpitis was leukocytes, primary neutrophils, because the synthesis of LTB4 in the inflammed pulp was diminished by depletion of circulating leukocytes with cyclophosphamide prior to the application of LPS.

Neutrophil chemotactic factors

Polymorphonuclear leukocytes (neutrophils) are recruited to inflammatory sites by a variety of soluble mediators (chemoattractants) that stimulate neutrophil directed migration (chemotaxis). Many neutrophil chemoattractants such as neutrophil activating proteins, leukotriene B4 (LTB4), platelet activating factor, and complement-derived C5a, are generated endogenously by host cells or enzymatic cleavage of host proteins. Other chemoattractants such as N-formyl peptides are generated exogenously by bacteria that invade the host. Oxidative modification of methionine residues or changes in the amino acid sequence of peptide chemoattractants dramatically alter their chemoattractive properties. Many of the well-defined neutrophil chemotactic factors and studies of their structure-function relationships will be reviewed.

Platelet-activating factor- and leukotriene B4-induced release of lactoferrin from blood neutrophils of atopic and nonatopic individuals

We found increased accumulation of neutrophils and their components, lactoferrin (Lf) and elastase, as well as platelet-activating factor (PAF) and leukotriene B4 (LTB4) at sites of ongoing human allergic reactions. To determine whether PAF or LTB4, could be the stimulus for in vivo Lf release, blood neutrophils of 17 subjects were incubated with PAF, LTB4, or the phorbol ester, phorbol myristate acetate (PMA), and the released Lf (ELISA assay) was compared with spontaneous release. Significantly increased Lf release was induced by PAF, 10(-5) to 10(-8) mol/L (p less than 0.002); LTB4, 10(-7) to 10(-8) mol/L (p less than 0.004); and PMA (0.05 micrograms/ml) in a dose-dependent reaction. Cytochalasin was not required for Lf secretion but did enhance such responses. PAF-induced Lf secretion was inhibited by the specific PAF antagonist, BN 52063. More Lf was released from neutrophils of atopic than from nonatopic subjects in response to PAF, 10(-6) mol/L (4.2 micrograms/ml +/- 0.2 versus 2.6 micrograms/ml +/- 0.2; p less than 0.001) but not to LTB4, PMA, or buffer (p, not significant). We conclude that (1) PAF and LTB4 released in vivo could stimulate local neutrophils to release Lf with possible pathogenic effects and (2) neutrophils of atopic subjects are more responsive to PAF than neutrophils of nonatopic subjects in this regard.

Mechanism of acute gastrointestinal mucosal damage in endotoxic shock and the effect of Fragmin

1. PAF and LTs may be mediators of the acute gastrointestinal mucosal damage due to endotoxic shock. 2. LTs may be mediators of the acute gastrointestinal mucosal damage due to PAF administration. 3. LMW heparin and unfractionated heparin prevented the increase of LTs due to endotoxin and PAF administration.

Biosynthesis and biological activity of leukotriene B4

The leukotrienes are a family of biologically active molecules derived from arachidonic acid. While prostaglandins and thromboxanes are products of the cyclooxygenase pathway of arachidonic acid metabolism, the leukotrienes are formed by arachidonate 5-lipoxygenase, an enzyme present in phagocytes, mast cells, and basophils. Inflammatory stimuli, such as chemotactic peptides, platelet-activating factor, phagocytic particles, and immunological stimuli, which activate phagocytes and mast cells, stimulate leukotriene synthesis. Leukotriene B4, a dihydroxy derivative of arachidonic acid, has a unique stimulatory activity on important functional responses of phagocytes; leukotriene B4 exerts chemotactic and chemokinetic activity towards phagocytes in vitro and in vivo, and it is a putative mediator of inflammation.

The levels and possible involvement of leukotriene B4 and prostaglandin F2 alpha in the control of interstitial fluid volume in the rat testis

The possible involvement of two arachidonic acid metabolites, prostaglandin F2 alpha (PGF2 alpha) and leukotriene B4 (LTB4), in the stimulatory effect of human chorionic gonadotrophin (hCG) on the volume of interstitial fluid (IF) in the rat testis has been investigated. Administration of hCG caused a time- and dose-dependent increase in the IF levels of PGF2 alpha while LTB4 showed no clear dose-dependence, but did decrease significantly at 2-8 h after injection of 100 IU hCG. Administration of ethane dimethane sulphonate (EDS), which specifically destroys Leydig cells, decreased the volume of IF but the IF levels of LTB4 and PGF2 alpha were unchanged. This indicates that although the absence of Leydig cells results in significant changes in IF volume, LTB4 and PGF2 alpha are probably not involved in these changes. Furthermore, these findings suggest that Leydig cells are not the only contributors to LTB4 and prostaglandins E2 and F2 alpha in testicular IF. In rats injected peripherally with hCG, intratesticular administration of the cycloxygenase inhibitor, indomethacin, decreased PGF2 alpha levels in IF after 2 and 4 h but not at later times. However, no inhibitory effect of indomethacin on the hCG-stimulated increase in IF volume was detected; indeed, at 2 h after injection of indomethacin + hCG there was a significant increase in IF volume in the indomethacin-injected testis. It is concluded that, although prostaglandins and LTB4 are secreted into IF in the rat testis, these arachidonic acid metabolites are apparently not the primary mediators of the increase in IF volume that follows hCG treatment.

[Possible involvement of leukotriene B4 on human luteal function: special reference to determination of leukotriene B4 produced by cultured luteal cells]

The present study was undertaken to determine the production of leukotriene B4 (LTB4) by cultured human luteal cells in the mid-luteal phase using a reverse phase column (C8). The luteal cells were cultured with or without hCG at 100 ng/ml for 8 days. In the preliminary experiment, methods for extracting culture media samples were assessed prior to radioimmunoassay. Reverse phase column C8, but not C18, made possible the determination of LTB4 produced by human luteal cells. Progesterone (P) production by cultured luteal cells reached its maximum on day 4 following exposure to hCG, and then declined gradually. The concentrations of LTB4 produced by luteal cells varied from 100 to 500 pg/10(5) cells/2 days. However, exposure to hCG did not affect LTB4 production by cultured luteal cells. The level of LTB4 in culture medium (115.0 +/- 37.8 pg/10(5) cells/2 days) was reduced on day 4, but increased thereafter. LTB4 production appeared to decrease concomitantly with increased P production of cultured luteal cells. In conclusion, cultured luteal cells produced considerable amounts of LTB4 throughout the entire culture period. These results suggest that lipoxygenase activity of luteal cells may be closely related to steroidogenic potential.

Manipulation of the acute inflammatory response by dietary polyunsaturated fatty acid modulation

Dietary polyunsaturated fatty acid modulation has been used as an anti-inflammatory strategy in experimental models of disease as well as in clinical trials. To elucidate the mechanisms underlying the anti-inflammatory effects of manipulating dietary polyunsaturated fatty acids, the in vivo effects of essential fatty acid (EFA) deficiency and (n-3) fatty acid supplementation were contrasted using a model of acute inflammation induced by the i.p. injection of zymosan into mice. Both diets led to a substantial decrease in tissue (n-6) fatty acid content. EFA deficiency was also characterized by the accumulation of (n-9) fatty acids, particularly 20:3 (n-9), the fatty acid that uniquely characterizes the deficiency state. Dietary (n-3) fatty acid supplementation led instead to marked increases in (n-3) fatty acids, especially 20:5 (n-3). With respect to the antiinflammatory effects of the two diets, EFA deficiency, but not (n-3) fatty acid supplementation, depleted levels of resident peritoneal macrophages. EFA deficiency was also more effective than (n-3) fatty acid supplementation in inhibiting the influx of polymorphonuclear neutrophils in response to zymosan. The effect of the two diets on the in vivo generation of leukotriene(LT)B also differed markedly. EFA deficiency completely inhibited the synthesis of LTB. Dietary (n-3) fatty acid supplementation, in contrast, reduced the production of LTB4 by only 50%. With (n-3) fatty acid supplementation LTB5 was produced. The more modest effect of (n-3) fatty acid supplementation in decreasing LTB4 generation was not due to blockade of the cyclooxygenase pathway. EFA deficiency, but not (n-3) fatty acid supplementation, was associated with the decreased synthesis of thromboxane. Although dietary fatty acid modulation has been shown to diminish platelet activating factor (PAF) synthesis, studies using the PAF receptor blocker, L659989, established that PAF was not a significant factor in the elicitation of leukocytes in this model of inflammation. In summary, the anti-inflammatory effect of EFA deficiency was more marked that that of dietary (n-3) fatty acid supplementation in acute inflammation. This difference in anti-inflammatory potential appeared to be due to either the greater effect of EFA deficiency in decreasing levels of resident peritoneal macrophages or in suppressing the in vivo generation of LTB4.

Synovitis reduced by inhibition of leukotriene B4. Carrageenan-induced gonarthritis studied in dogs

The pathophysiologic significance of leukotriene B4 (LTB4) in arthritis was studied in dogs by unilateral intraarticular deposition of 15-hydroxy-eicosatetraenoic acid (15-HETE), an endogenous inhibitor of the formation and the effects of LTB4, in bilateral carrageenan-induced gonarthritis. LTB4 in synovial fluid was selectively inhibited in 15-HETE treated joints, the formation of prostaglandin E2 (PGE2) being largely unaffected. The clinical symptoms, intraarticular pressure, and extractable synovial fluid volume were reduced in treated joints. No effect could be discerned regarding blood flow in the synovial membrane, capsule, or juxta-articular bone as measured by tracer microspheres; and no effect on bone metabolism was found as judged by 99mTc-diphosphonate uptake. Thus, inhibition of LTB4 reduces joint exudation, but does not seem to interfere with changes in juxta-articular hemodynamics or bone metabolism following synovial inflammation.

Rapid adhesive responses of endothelial cells and of neutrophils induced by leukotriene B4 are mediated by leucocytic adhesion protein CD18

Controversy has existed as to the ability of leukotriene B4 (LTB4) to enhance adhesive properties of human neutrophils (PMN) and endothelial cells. We found that LTB4 induced a rapid but transient adhesion of PMN to an albumin-coated plastic surface and to cultured human umbilical vein endothelial cells (HUVEC). Although the adhesive response of PMN to the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) was longer lasting, peak hyperadherence was of similar magnitude as to LTB4 and was less susceptible to assay conditions. Adherence induced by either LTB4 or fMLP could be abrogated by the monoclonal antibody 60.3, indicating similar dependence on the leucocyte adhesion protein CD18. Lipoxin A did not induce PMN hyperadherence. Treating HUVEC with LTB4, but not with its omega-oxidized metabolites 20-OH- and 20-COOH-LTB4, lipoxin A, or with fMLP conferred a rapid, dose-related, enhanced adhesion of PMN. This effect was dependent on CD18 and on divalent cations. It disappeared with prolonged exposure to LTB4, required a metabolically active HUVEC, and was not due to passive binding of LTB4 to HUVEC. Thus, LTB4 induces a transient expression of hyperadhesiveness in HUVEC as well as in neutrophils, and both effects are dependent on expression of CD18.

Involvement of leucocytes and leukotrienes in ischaemic dysfunction of the coronary microcirculation

Recent evidence suggests that leucocytes may exert an important influence on microvessel flow during pathophysiologic conditions. This is particularly true in the case of coronary occlusive disorders. Diminution of coronary perfusion pressure favours trapping of the large, stiff leucocytes in capillaries. Perhaps more importantly, ischaemic changes in the endothelial lining of microvessels promote early sequestration of leucocytes within capillaries of ischaemic regions during underperfusion and, to a much greater degree, during reperfusion. If these trapped leucocytes are activated by the ischaemic environment, the mechanical plugging of microvessels can be significantly complicated by leucocyte release of a variety of materials affecting the function of blood vessels and myocytes. Leukotrienes are a potent group of inflammatory mediators released by activated leucocytes. A subgroup, the peptidoleukotrienes (C4, D4, and E4), has a profound vasoconstrictor influence on coronary microvessels. Members of this group can also cause platelet aggregation. Agents that block peptidoleukotriene synthesis, such as nafazatrom, have been reported to diminish the adverse effects of myocardial ischaemia. However, these agents often have non-specific actions that blur the interpretation of their anti-ischaemic efficacy. Our laboratory has made a number of observations that cast doubt--or at least stimulate further inquiry--on the role of peptidoleukotrienes on promotion of sustained microvessel constriction in ischaemic coronary beds. Most importantly, we found that continuous intracoronary administration of leukotriene C4 or D4 led initially to marked diminution of coronary flow and myocardial contractility. However, this was soon followed by a complete, dose-independent escape from these effects even though leukotrienes continued to be infused at a constant rate. The cause of this escape is unclear, but it may involve a specific product released when leukotrienes interact with platelets. In a second series of experiments, we found that the coronary constrictor efficacy of bolus leukotrienes (and also the stable thromboxane A2 analogue, U46619) was markedly reduced by concomitant myocardial ischaemia. Constrictor responses were rapidly restored with reperfusion, suggesting a transient metabolic blockade of constrictor responsiveness during myocardial ischaemia. Nevertheless, these data indicate that leukotrienes may not act simply as agents that exaggerate underperfusion due to proximal coronary occlusion. Finally, we have measured the leukotriene immunoreactivity in coronary venous blood exiting from beds made ischaemic (and dysfunctional) by partial occlusion of epicardial arteries. Although the occlusion was sufficient to cause release of lactate and other metabolic markers of ischaemia, we were unable to find measurable rises in release of any of the leukotrienes after occlusions lasting 3 h and reperfusions lasting up to 1 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Leukotriene B4 increases pulmonary transvascular filtration by a neutrophil-independent mechanism

We examined the role of circulating granulocytes in the pulmonary microvascular response to leukotriene B4 (LTB4) by prior depletion of circulating granulocytes using hydroxyurea. LTB4 (2 micrograms/kg injection followed by infusion of 2 micrograms/kg over 15 min) produced transient increases in pulmonary arterial pressure and pulmonary vascular resistance, indicating that neutrophils were not required for the pulmonary hemodynamic effects of LTB4. Infusion of LTB4 in granulocyte-depleted sheep also resulted in transient increases in pulmonary lymph flow (QL) with no significant change in the lymph-to-plasma protein concentration ratio (L/P), findings similar to those in control animals. In vitro studies indicated that LTB4 (10(-7) or 10(-9) M) produced a transient adherence of neutrophils to cultured pulmonary artery endothelial monolayers. Maximal responses occurred at 10 min after the addition of LTB4 to the endothelial cell-neutrophil coculture system, and the adherence decreased to base line within 60 min. LTB4 infusion in sheep also produced a transient uptake of autologous 111In-oxine-labeled neutrophils. The results indicate that LTB4-mediated increase in pulmonary transvascular protein clearance (QL x L/P) is independent of circulating granulocytes.

PAF-induced conjunctivitis in the rabbit is mediated by peptido-leukotrienes

Platelet activating factor (PAF) released by many cell types is involved in several steps of inflammatory reactions in various organs including the eye. It has been reported that some effects of PAF could be mediated by arachidonic acid metabolites generated after PAF-receptor interaction. In the study we investigated the protective effect of CBS-113A, a dual inhibitor of 5-lipoxygenase/cyclooxygenase in PAF-induced conjunctivitis in the rabbit. Moreover, the characterization of the icosanoid potentially mediating the PAF activity has been performed by using specific pharmacological agents. Subconjunctival injection of PAF (10-1000 ng) provoked Evans' blue extravasation measured in tissues within 30 min. Simultaneous injection of a PAF antagonist (BN 50730) inhibited the dye leakage, showing specific PAF receptor-mediated vascular reaction. CBS-113A applied in eye drops also inhibited Evans' blue extravasation. By contrast, indometacin administered either topically or by subconjunctival injection was not effective in reducing the effect of PAF. These results suggesting the involvement of a 5-lipoxygenase metabolite were confirmed by the effectiveness of local injection of SKF 104353, a specific leukotriene D4 antagonist. The present study shows that PAF-induced plasma leakage in conjunctivitis is mediated by peptido-leukotrienes.

Human glomerular mesangial cells inactivate leukotriene B4 by reduction into dihydro-leukotriene B4 metabolites

Due to its potent chemotactic properties leukotriene B4 is an important mediator of inflammatory reactions. Cultured human kidney mesangial cells converted exogenously added leukotriene B4 efficiently into three different more lipophilic metabolites, two of them probably representing dihydro-leukotriene B4 isomers. This represents an alternative metabolic pathway, in contrast to leukotriene B4 omega-oxidation found in human polymorphonuclear leukocytes. Both dihydro-leukotriene B4 isomers had nearly completely lost their ability to induce leukocyte chemotaxis as compared to leukotriene B4.

Possible role of leukotrienes in gastritis associated with Campylobacter pylori

This study was done to evaluate the role of leukotrienes (LTs) in gastritis associated with Campylobacter pylori. Biopsy specimens of gastric mucosa were obtained endoscopically from 18 patients with nonulcer dyspepsia for bacteriological and histological examination and extraction of LTs. There was correlation between the LTB4 level in the mucosa and the degree of gastritis evaluated histologically. The level was higher when infiltration of neutrophils in the gastric mucosa was more extensive. The LTB4 level in mucosa infected with C. pylori was higher than that in noninfected mucosa. These findings suggest that endogenous LTs may be related to the pathogenesis of gastritis associated with C. pylori.

Hyperalgesic pain: a review

Pain induced by a stimulus that is normally not painful is referred to as hyperalgesic pain. Inhibition of arachidonic acid metabolism and/or sympathectomy have been found to be effective treatment for this type of pain. We propose that the lowered pain threshold is induced by arachidonic acid metabolites produced in inflamed tissue or by sympathetic postganglionic neurons after nerve injury. The most extensively studied hyperalgesic mediators are prostaglandin E(2) (PGE(2)) and prostacyclin (PGI(2)), products of the cyclooxygenase pathway of arachidonic acid metabolism, whose production is inhibited by nonsteroidal antiinflammatory analgesics (NSAIAs). Recent studies, however, have demonstrated that products of the NSAIA-resistant lipoxygenase pathway of arachidonic acid metabolism are also hyperalgesic. Their production is inhibited by corticosteroids and current experimental agents.

External ocular inflammatory effects of lipoxygenase enzyme products

We systematically observed the effects of lipoxygenase enzyme products (5-, 8-, 9-, 12-, and 15-HETE and leukotrienes (LT) C4, D4, and B4) on the external ocular inflammatory process in rabbits. Our results, using 1 and 10 micrograms enzymatic preparations topically applied to the conjunctiva, were consistent with the potent chemotactic activity of 12-HETE and LTB4. Modulation of the inflammatory process can be accomplished better, as a result of our findings, by inhibition of both the lipoxygenase and cyclooxygenase pathways.