Synergistic effects of pranlukast and leukotriene B4 receptor antagonist on antigen-induced pulmonary reaction

We now attempted to differentiate effects of cysteinyl-leukotrienes and leukotriene B4 on antigen-induced pulmonary reaction by using a selective leukotriene D4/E4 (CysLT1) receptor antagonist and a selective LTB4 (BLT) receptor antagonist in rats. An intratracheal challenge with ovalbumin to Brown-Norway rats actively sensitized with ovalbumin produced two phases of airway responses which were estimated based on airway resistance, the immediate-type airway response within 30 min, and the delayed-type airway response beginning from 4 to 6 h after the challenge. Pretreatment of the rats with a CysLT1 receptor antagonist (pranlukast) failed to reduce the elevation of airway resistance, and pretreatment with a BLT receptor antagonist (ONO-4057; 5-[2-(2-carboxyethyl)-3-[6-(4-methoxyphenyl)-5E-hexenyl]- oxyphenoxy] valeric acid) also produced no decrease. In contrast, combined pretreatment of the rats with pranlukast and ONO-4057 did not reduce the amplitude of the immediate-type airway response, but did allow the elevated airway resistance to return to its baseline level and also significantly inhibited the delayed-type airway response. Histological examination at 6 h after ovalbumin challenge showed infiltration of inflammatory cells with a predominance of neutrophils and scattered eosinophils in the bronchial submucosa. While pretreatment with neither pranlukast nor with ONO-4057 inhibited the infiltration of inflammatory cells in the bronchial submucosa, pretreatment with the two antagonists combined significantly inhibited the infiltration of granulocytes into the bronchial submucosa. On the contrary, intratracheal administration of either leukotriene D4 or leukotriene B4 up to 10 microg resulted in the infiltration of granulocytes into the bronchial submucosa, but no synergism for the infiltration of granulocytes was observed after combined administration. These results suggest that leukotriene B4 appears to play a significant role in the antigen-induced pulmonary reaction in association with cysteinyl-leukotrienes. Accordingly, the combined antagonism at the CysLT1 receptor and BLT receptor may be a useful intervention for the treatment of bronchial asthma.

Comparative effects of a glucocorticosteroid, theophylline and the peptido-leukotriene-antagonist CGP 45715A on antigen-induced early and late phase airway response and inflammatory cell influx in sensitised guinea pigs

A novel model of allergic early and late-phase reaction in the airways of conscious guinea pigs was developed and the effect of established and novel antiasthmatic drugs on peak of immediate response, late phase response and associated inflammatory cell influx investigated. Guinea pigs were sensitised twice in adjuvant (50 mg/kg silica + 0.1 ml/kg Bordetella pertussis). Under cover of 10 mg/kg i.p. mepyramine guinea pigs exhibited still a pronounced immediate reaction. During a screening phase about 75% of guinea pigs demonstrated a late phase reaction of decrease of tidal volume between 4-10 h after ovalbumin inhalation. In a cross over study theophylline at 50 mg/kg p.o. (-1 h before ovalbumin) tended to attenuate not only the peak of the immediate reaction by about 69% (P>0.05, n = 12), but inhibited the airway late phase response significantly (P<0.05, 5-10 h, n = 12). Methylprednisolone (40 mg/kg p.o. 1 h before ovalbumin) did not inhibit the immediate response, but the late phase response. In contrast the cysteinyl-leukotriene antagonist CGP 45715A (Iralukast; 30 mg/kg p.o. 2 h before ovalbumin) neither interfered with the peak of the immediate, nor with the late phase response. When bronchoalveolar lavage by orotracheal route was performed 24 h after ovalbumin inhalation, total cell count, eosinophils, neutrophils, macrophages and lymphocytes were significantly increased in ovalbumin-controls compared to sham (n = 5; P<0.05). Methylprednisolone reduced significantly the antigen-induced increase of total cell count and eosinophil number. Neither theophylline nor the cysteinyl-leukotriene receptor antagonist attenuated the antigen-associated cell influx. The results do not provide evidence for a major role of cysteinyl-leukotrienes in the late phase response and inflammatory cell influx in this model.

5-oxo-ETE induces pulmonary eosinophilia in an integrin-dependent manner in Brown Norway rats

We have shown previously that the 5-lipoxygenase product 5-oxo-6,8, 11,14-eicosatetraenoic acid (5-oxo-ETE) is a highly potent eosinophil chemoattractant in vitro. To determine whether this substance can induce pulmonary eosinophil infiltration in vivo, it was administered to Brown Norway rats by tracheal insufflation. Eosinophils were then counted in lung sections that had been immunostained with an antibody to eosinophil major basic protein. 5-Oxo-ETE induced a dramatic increase in the numbers of eosinophils (ED50, 2.5 microg) around the walls of the airways, which reached maximal levels (five times control levels) between 15 and 24 h after administration, and then declined. LTB4 also induced pulmonary eosinophil infiltration with a similar ED50 but appeared to be somewhat less effective. In contrast, LTD4 and LTE4 were inactive. 5-Oxo-ETE-induced eosinophilia was unaffected by the LTB4 and PAF antagonists LY255283 and WEB 2170, respectively. However, it was inhibited by approximately 75% by monoclonal antibodies to CD49d (VLA-4) or CD11a (LFA-1) but was not significantly affected by an antibody to CD11b (Mac-1). In conclusion, 5-oxo-ETE induces pulmonary eosinophilia in Brown Norway rats, raising the possibility that it may be a physiological mediator of inflammation in asthma.

Activation of human polymorphonuclear leukocytes by products derived from the peroxidation of human red blood cell membranes

Oxidation of red blood cell (RBC) ghost preparations initiated by tert-butyl hydroperoxide (tBuOOH) was employed to explore the formation of lipid products derived from endogenous phospholipids that specifically expressed biological activity toward the human polymorphonuclear leukocyte (PMN). Common measure of lipid peroxidation, thiobarbituric acid-reactive substances (TBARS) and the increased absorbance at 235 nm consistent with the formation of conjugated dienes, was observed following a 90-min incubation of RBC ghosts with tBuOOH. Saponification of phospholipids and separation of the resultant fatty acids by RP-HPLC permitted direct mass spectrometric analysis of oxidized fatty acids. Individual HPLC fractions were assayed for their ability to increase intracellular free calcium ion concentrations in human PMN to guide structural investigations. Two fractions were found to contain biologically active components, and tandem mass spectrometric analysis of the abundant ions observed in these fractions resulted in the characterization of several oxidized polyunsaturated fatty acids derived from arachidonic and linoleic acids. The major components in these fractions included 5-hydroxyeicosatetraenoic acid (5-HETE) and 5-hydroperoxyeicosatetraenoic acid (5-HpETE). The dose-dependent increases in intracellular calcium in the neutrophil using synthetic 5(rac)-HETE, 5(rac)-HpETE, and 5-oxo-ETE were found to have EC50's of 250, 6, and 3 nM, respectively. The quantity of 5-oxygenated arachidonate components present in oxidized RBC was consistent with the observed biological response elicited by fractions A and B. This study suggests that 5-HETE and 5-HpETE are abundant products of lipid peroxidation of cellular membranes and that these racemic products possess significant biological activity. Such compounds could play important roles as mediators of the cellular response to toxicologic stimuli that generate free radical species.

[Leukotrienes and airway smooth muscle]

The understanding of cellular and molecular mechanisms involved in the contraction of airway smooth muscle has tremendously advanced in the recent years. Among extracellular messengers that control airway smooth muscle contraction attention has focused on leukotrienes since several strategies for pharmacological interventions in either the production or the effect of these substances have been developed. Two types of receptor, CysLT and BLT, coupled to G proteins, have been identified and airway smooth muscle contraction mostly depends on CysLT1 receptor activation. This activation induces intracellular calcium release leading to an increase in cytoplasmic calcium concentration responsible for airway smooth muscle contraction. Leukotriene antagonists are now available and their role in asthma treatment is being defined.

[Effects of leukotrienes on production of interleukin 6 from mouse peritoneal macrophages]

In the present study, effects of leukotrienes on IL-6 production by mouse resident peritoneal macrophages were explored with a bioassay method involving IL-6 dependent murine hybridoma B9 cell line. The results showed that LTB4, LTC4 and LTD4 can enhance the production of IL-6 from cultured peritoneal macrophages of mice. The optimal concentractions for LTB4, LTC4 and LTD4 were found to be 1.45 x 10(-6), 6.9 x 10(-8) and 8.05 x 10(-8) mol.L-1, respectively. The results suggest that peptide leukotrienes might play important role on IL-6 production in the local milieu of inflammation.

Influence of leukotrienes on in vitro growth of human mammary carcinoma cell line MCF-7

OBJECTIVES

The aim of this work was to study the action of leukotrienes on the growth of human mammary cancer cells MCF-7.

STUDY DESIGN

The growth of the cells was measured by incorporation of 3H-thymidine. The action of leukotriene (LT)B4, LTD4, LTC4, LTE4 or arachidonate (AA) was tested in human mammary cancer cells MCF-7 in vitro.

RESULTS

LTB4 or LTD4 but not LTC4 or LTE4 reduced significant incorporation of 3H-thymidine in MCF-7 cells up to 52% or 56% respectively, when administered in concentrations 0.1-1000 pM. Agents in concentrations of 0.01 pM or 10000 pM did not effect 3H-thymidine incorporation. We have shown, that MCF-7 cells synthesise LTB4 when treated with calcium ionophor A23187 (10 microM). Leukotriene-antagonist LY171883 (10 microM) lifts inhibitory effects of LTB4 or LTD4. Arachidonic acid (10 microM) inhibits 3H-thymidine incorporation up to 72%. 5-lipoxygenase inhibitor MK-886 (100 nM) lifts the inhibitory effect of arachidonate.

CONCLUSIONS

LTB4 or LTD4 inhibits MCF-7 breast cancer cell growth. LT-receptors mediate the growth-inhibitory effect of LTB4 or LTD4.

Effects of a selective phosphodiesterase IV inhibitor (CDP-840) in a leukotriene-dependent non-human primate model of allergic asthma

The activity of CDP-840, a novel, selective phosphodiesterase IV inhibitor was determined in a leukotriene-dependent non-human primate model of allergic asthma. Measurements of specific airway resistance (sRaw) were recorded in a dual chamber plethysmograph for 1 h and 3-5 h after challenge of allergic conscious squirrel monkeys with an aerosol of ascaris antigen. Orally administered CDP-840 (10 mg/kg; 1 h before challenge) produced partial inhibition (41 and 45%, respectively) of both the acute (1 h post antigen) response and the late (3-5 h post antigen) response to antigen but failed to alter the response to an aerosol of leukotriene D4. In a second series of experiments, intravenous CDP-840 (5 mg/kg; 30 min before challenge) showed improved potency, producing 82% inhibition of the early and 51% inhibition of the late phase response. CDP-840 was inactive when tested intravenously at 1 mg/kg and was inactive against the 3-5 h response when administered after the early phase response (5 mg/kg; i.v. 60 min post antigen challenge). The novel phosphodiesterase IV inhibitor CDP-840 selectively inhibited antigen-induced bronchoconstriction in conscious squirrel monkeys. This effect appears to be independent of any direct bronchodilator action. It is concluded that the activity of CDP-840 in this model may be due to an inhibitory effect on mediator (e.g., leukotriene) release.

Modulation of migration of Oesophagostomum dentatum larvae by inhibitors and products of eicosanoid metabolism

The effects of eicosanoids and of inhibitors of eicosanoid synthesis on the migration of third-stage larvae (L3) of Oesophagostomum dentatum were studied in an in vitro migration assay procedure. The L3 were incubated with diethylcarbamazine (DEC), indomethacin (INDO) or acetylsalicylic acid (ASA). Incubation with these inhibitors of eicosanoid metabolism resulted in a dose-dependent reversible inhibition of migration. The antimigratory effect of DEC could be completely reversed by treatment of the L3 with the lipoxygenase (LOX)-products leukotriene (LT) B4 or LTC4. LTD4 had a less distinct but similar effect, while LTE4 failed to reverse migration inhibition. Treatment with combinations of cyclooxygenase (COX)-products (prostaglandin, PG) partially restored the migration ability of ASA-treated L3, while PGD2, PGE2, PGF2 alpha or PGI2 exerted no distinct effect on ASA-treated L3 when given separately. The suppression of L3 migration by compounds that are known as antagonists of eicosanoid synthesis and the stimulation of migration of inhibitor-treated L3 by simultaneous application of eicosanoids indicate that these lipid mediators may play a significant role in physiological processes that interact with worm motility.

Endothelium is required for 12-hydroperoxyeicosatetraenoic acid-induced vasoconstriction

The pharmacological effects of 12-hydroperoxyeicosatetraenoic acid (12-HPETE) were examined using isolated canine basilar artery segments and isometric tension recording. 12-HPETE produced transient contraction of the artery segment while arachidonic acid or 12-hydroxyeicosatetraenoic acid (12-HETE) had a much lower potency. 12-HPETE-induced contraction which showed a requirement of a functional endothelium and a rapid insensitivity to re-administered 12-HPETE, was completely inhibited by the potassium channel blocker, glibenclamide. Other hydroperoxides did cross-desensitize the 12-HPETE-induced contraction, however, arachidonic acid or 12-HETE did not affect markedly. Here, we present that 12-HPETE is involved in the regulation of vascular tension via its effects on the endothelium.

Leukotrienes: lipid bioeffectors of inflammatory reactions

The leukotrienes arise from oxidative metabolism of arachidonic acid through the action of the 5-lipoxygenase enzyme, leading to the unstable allylic epoxide leukotriene A4. This intermediate represents the substrate for two different specific enzymes, namely leukotriene A4-hydrolase and leukotriene C4-synthase, generating LTB4 and cysteinyl leukotrienes, respectively. The name "leukotriene" is referring to the cellular source (leukocytes are one of the major sources) as well as the conjugated triene that characterizes their structure. LTC4 and LTD4 are potent contracting agents of smooth muscle in airways and blood vessels; in addition, they induce mucus secretion and promote plasmatic exudation with direct action on endothelial cells. On the other side, LTB4 is known as a potent chemokinetic and chemotactic agent. A number of evidences reported in the literature underline the potential role of leukotrienes in the inflammatory responses that characterize asthma and other pathological conditions. These potent lipid bioeffectors are synthesized during the course of inflammatory reactions and their pharmacological modulation is able to significantly attenuate the clinical manifestations associated with different inflammatory pathologies.

Lipoxygenase products induce ultraweak light emission from human erythroleukemia cells

Several lipoxygenase products were able to enhance ultraweak light emission and membrane permeability of human erythroleukemia K562 cells. In particular, 13-hydroperoxyoctadecadienoic acid (13-HPOD) was more effective than hydrophilic hydroperoxides, like H2O2 and tert-butyl hydroperoxide. The enhancement of luminescence induced by 13-HPOD was inhibited by superoxide and hydroxyl radical scavengers. The effect of 13-HPOD was inhibited by superoxide and hydroxyl radical scavengers. The effect of 13-HPOD was potentiated by the calcium ionophore A23187 and inhibited by the calcium chelator EDTA, and was observed also in liposomes containing unsaturated lipids. Cholesterol enrichment, which decreases the membrane fluidity, did not modify the effect of 13-HPOD on K562 cells.

Prostaglandins attenuate cardiac contractile dysfunction produced by free radical generation but not by hydrogen peroxide

The aim of this study was to examine and compare the potential influence of cyclooxygenase or lipoxygenase derived metabolites of arachidonic acid on myocardial injury produced either by a free radical generating system consisting of purine plus xanthine oxidase or that produced by hydrogen peroxide. A free radical generating system consisting of purine (2.3 mM) and xanthine oxidase (10 U/L) as well as hydrogen peroxide (75 microM) produced significant functional changes in the absence of either significant deficits in high energy phosphates or ultrastructural damage. Prostaglandin F2 alpha (30 nM) significantly attenuated both the negative inotropic effect of purine plus xanthine oxidase as well as the ability of the free radical generator to elevate diastolic pressure. An identical concentration of prostaglandin 12 (prostacyclin) significantly reduced diastolic pressure elevation only and had no effect on contractile depression. The salutary effects of the two PGs occurred in the absence of any inhibitory influence on superoxide anion generation produced by the purine and xanthine oxidase reaction. None of prostaglandins modulated the response to hydrogen peroxide. In addition, neither prostaglandin E2 nor leukotrienes exerted any effect on changes produced by either type of oxidative stress. A 5 fold elevation in the concentrations of free radical generators or hydrogen peroxide produced extensive injury as characterized by a virtual total loss in contractility, 400% elevation in diastolic pressure, ultrastructural damage and significant depletions in high energy phosphate content. None of these effects were modulated by eicosanoid treatment. Our results therefore demonstrate a selective ability of both prostaglandin F2 alpha and to a lesser extent prostacyclin, to attenuate dysfunction produced by purine plus xanthine oxidase but not hydrogen peroxide. It is possible that these eicosanoids may represent endogenous protective factors under conditions of enhanced oxidative stress associated with superoxide anion generation.

The effects of intraventricular/periventricular blood on cerebral 3',5'-cyclic adenosine monophosphate concentration and cerebrovascular reactivity in newborn pigs

This study investigated the effects of intraventricular/periventricular blood on cerebral cAMP production and cortical cerebrovascular reactivity. Under halothane and N2O anesthesia, 3 mL of either autologous blood or artificial cerebrospinal fluid (CSF) were injected into the left caudate nucleus; volume was adequate to result in extrusion of fluid or blood into the lateral ventricles of 1-2-d-old piglets. Twenty-four hours later, a closed cranial window was implanted over the left parietal cortex. Pial arteriolar responses to vasodilator and vasoconstrictor stimuli were monitored. Before the application of vasoactive agents, cortical periarachioid CSF was collected for cAMP measurement. Pial arteriolar responses to topical application of endothelin-1 (10(-9) and 10(-8) M) and to leukotriene C4 (10(-10) and 10(-9) M) were similar between the two groups. However, pial arteriolar responses to topical application of cAMP-mediated vasodilators, prostaglandin E2 (10(-6) and 10(-5) M), and histamine (10(-6) and 10(-5) M), respectively, were markedly reduced in the blood group when compared with the artificial CSF (control) group. Mean CSF cAMP level in the blood group was significantly lower than the control group (199 +/- 31 versus 1092 +/- 238 fmol/mL, p = 0.0006). We conclude that in newborn pigs intraventricular/periventricular blood results in a marked reduction of CSF cAMP concentration and attenuation of the cerebrovascular responses to cAMP-mediated vasodilators on the cortical surface remote from the site of blood or hematoma.

The effect of 15-HPETE on airway responsiveness and pulmonary cell recruitment in rabbits

1. In the present study we have investigated the effect of 15-hydroperoxyeicosatetraenoic acid (15-HPETE) and 15-hydroxyeicosatetraenoic acid (15-HETE) on airway responsiveness to inhaled histamine in rabbits in vivo. 2. 15-HPETE increased airway responsiveness to histamine 24 h after tracheal instillation and this was associated with a cellular infiltration consisting mainly of neutrophils, as measured by bronchoalveolar lavage. The airway hyperresponsiveness induced by 15-HPETE was still present 72 h after tracheal instillation of 15-HPETE, but had returned to baseline values one week post challenge. The number of neutrophils in bronchoalveolar lavage remained significantly elevated compared to pre-challenge levels. In contrast to 15-HPETE, the major metabolite 15-HETE, failed to alter airway hyperresponsiveness to histamine despite the recruitment of neutrophils into the lung, suggesting that the effect of 15-HPETE was not secondary to the generation of this metabolite nor dependent on the influx of neutrophils. 3. Both capsaicin and atropine but not the peripherally acting mu-opioid receptor agonist, BW443C (H-Tyr-D-Arg-Gly-Phe(4-NO2)-Pro-NH4), attenuated 15-HPETE-induced hyperresponsiveness. The increased cellular infiltration induced by 15-HPETE was only attenuated by capsaicin. 4. The results of the present study suggest that the release of 15-HPETE into the airways could contribute to sensitization of afferent nerve endings analogous to the hyperalgesia induced by this mediator in skin.

Low concentrations of lipid hydroperoxides prime human platelet aggregation specifically via cyclo-oxygenase activation

There is mounting evidence that lipid peroxides contribute to pathophysiological processes and can modulate cellular functions. The aim of the present study was to investigate the effects of lipid hydroperoxides on platelet aggregation and arachidonic acid (AA) metabolism. Human platelets, isolated from plasma, were incubated with subthreshold (i.e. non-aggregating) concentrations of AA in the absence or presence of hydroperoxyeicosatetraenoic acids (HPETEs). Although HPETEs alone had no effect on platelet function, HPETEs induced the aggregation of platelets co-incubated with non-aggregating concentrations of AA, HPETEs being more potent than non-eicosanoid peroxides. The priming effect of HPETEs on platelet aggregation was associated with an increased formation of cyclo-oxygenase metabolites, in particular thromboxane A2, and was abolished by aspirin, suggesting an activation of cyclo-oxygenase by HPETEs. It was not receptor-mediated because the 12-HPETE-induced enhancement of AA metabolism was sustained in the presence of SQ29, 548 or RGDS, which blocked the aggregation. These results indicate that physiologically relevant concentrations of HPETEs potentiate platelet aggregation, which appears to be mediated via a stimulation of cyclo-oxygenase activity.

Ca2+-dependent K+ channels in bovine adrenal chromaffin cells are modulated by lipoxygenase metabolites of arachidonic acid

Fatty acids play an important role in a variety of physiological processes including ion channel modulation and catecholamine release. Using patch-clamp techniques we show that arachidonic acid (AA) is converted to lipoxygenase metabolites (LOMs) to potentiate activity of the Ca2+ and voltage-dependent, large-conductance K+ channel (BK) in bovine adrenal medullary chromaffin cells (BAMCCs). AA and LOM potentiation of BK current and recovery from potentiation were unaffected by the nonhydrolyzable ATP analogue AMP-PNP, or by exclusion of nucleotides in excised patch recordings. Also, AA and LOM potentiation of BK channel activity in outside-out patches exposed to strong Ca2+ buffering ruled out cytoplasmic messengers or changes in intracellular Ca2+ levels as causative factors. Lipoxygenase inhibitor attenuated AA, but not LOM potentiation of BK activity in outside-out patches, indicating that lipoxygenase processing of AA is possible in excised membrane patches, possibly via a membrane associated lipoxygenase. AA and LOM release have been implicated in the mechanics of catecholamine secretion from BAMCCs. By limiting action potential duration and thus voltage-gated Ca2+ influx, fatty acid potentiation of BK current may serve an inhibitory feedback function in regulating secretion from BAMCCs.

5-HPETE is a potent inhibitor of neuronal Na+, K(+)-ATPase activity

The effects of 1 microM concentrations of arachidonic acid hydroperoxide (HPETES) products of 5-, 12- and 15-lipoxygenase on Na+, K(+)-ATPase activity were investigated in synaptosomal membrane preparations from rat cerebral cortex. 5-HPETE inhibited Na+, K(+)-ATPase activity by up to 67 %. In contrast, 12-HPETE and 15-HPETE did not inhibit Na+, K(+)-ATPase activity. In addition, neither 5-HETE or LTA4 inhibited Na+, K(+)-ATPase activity. Dose-response studies indicated that 5-HPETE was a potent (IC25 = 10(-8) M) inhibitor of Na+, K(+)-ATPase activity. These findings indicate that 5-HPETE inhibits Na+, K(+)-ATPase activity by a mechanism that is dependent on the hydroperoxide position and independent of further metabolism by 5-lipoxygenase. It is proposed that 5-HPETE production by 5-lipoxygenase and subsequent inhibition of neuronal Na+, K(+)-ATPase activity may be a mechansim for modulating synaptic transmission.

Inhibitory effect of leukotrienes on luteinizing hormone release

The aim of this work was to study the effect of high concentrations of leukotrienes on luteinizing hormone (LH) secretion in rat anterior pituitary cells. We also investigated the effect of leukotrienes in parallel with gonadotropin-releasing hormone (GnRH) action. Experiments were on cells gained from trypsinized pituitaries of female rats. Tests were performed by superfusion of the cells attached to cytodex-1 carrier beads. The LH content in samples of perfusate was estimated by radioimmunoassay. This work reports 48% inhibition of basic LH release by action of leukotriene C4 in superfused cells when applied continuously at a concentration of 100 nmol/l. Moreover, we have shown that leukotrienes suppressed GnRH-induced LH secretion in rat pituitary cells when applied in parallel to GnRH (1 nmol/l) as a 4-min pulse at a concentration of 0.1 nmol/l. GnRH-induced LH release was reduced to 66% of its value by leukotriene (LT) B4 (0.1 nmol/l) action; also to 54% by LTC4, 66% by LTD4 and 74% by LTE4 action. In contrast, arachidonic acid (50 pmol/l) and its other 5-lipoxygenase metabolites: 5-hydroperoxyeicosatetraenoic acid (5-HPETE) (50 pmol/l), or 5-hydroxyeicosatetraenoic acid (5-HETE) (50 pmol/l), had no inhibitory effect on GnRH-induced LH release. Arachidonic acid and 5-HETE potentiated GnRH-induced LH release up to 249% and 429%, respectively, when applied in parallel with GnRH (1 nmol/l) as a 4-min pulse at a concentration of 10 pmol/l. In our earlier work we have shown that several leukotrienes are potent stimulants of LH release. The present report documents the finding that the 5-lipoxygenase pathway is also involved in the inhibitory regulation of hormone release in anterior pituitary cells.

Altered responses of human macrophages to lipopolysaccharide by hydroperoxy eicosatetraenoic acid, hydroxy eicosatetraenoic acid, and arachidonic acid. Inhibition of tumor necrosis factor production

The regulation of allergic and autoimmune inflammatory reactions by polyunsaturated fatty acids and their metabolic products (eicosanoids) continues to be of major interest. Our data demonstrate that arachidonic acid 5,8,11,14-eicosatetraenoic acid (20:4n-6) and its hydroxylated derivatives 15(s)-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE) and 15(s)-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) regulate agonist-induced tumor necrosis factor alpha (TNF) production, a cytokine that plays a role in inflammatory diseases. Although 20:4n-6 and 15-HETE caused a reduction in production of TNF in mononuclear leukocytes stimulated with phytohaemagglutinin, pokeweed mitogen, concanavalin A, and Staphylococcus aureus, 15-HPETE was far more active. 15-HPETE was also found to dramatically depress the ability of bacterial lipopolysaccharide to induce TNF production in monocytes and the monocytic cell line Mono Mac 6. These fatty acids depressed the expression of TNF mRNA in Mono Mac 6 cells stimulated with LPS; 15-HPETE was fivefold more active than 20:4n-6 and 15-HETE. While 15-HPETE treatment neither affected LPS binding to Mono Mac 6 cells nor caused a decrease in CD14 expression, the fatty acid significantly reduced the LPS-induced translocation of PKC (translocation of alpha, betaI, betaII, and epsilon isozymes), suggesting that 15-HPETE acts by abrogating the early signal transduction events. The findings identify another molecule that could form the basis for development of antiinflammatory pharmaceuticals.

Role of platelet activating factor, leukotrienes and polymorphs in the FMLP induced increase in microvascular leakage in rabbit trachea

This study was designed to determine the time course of N-formyl-methionyl-leucyl-phenylalanine (FMLP) induced microvascular leakage in the airways of anaesthetized, tracheostomized New Zealand white rabbits. We have previously shown that FMLP increases microvascular leakage in the rabbit trachea at 30 min post challenge. A further aim was to determine the mechanisms underlying this response. Microvascular leakage was assessed using the albumin binding dye, Evans blue which was injected intravenously (50 mg/kg) immediately prior to FMLP challenge (10 mg nebulised for 2 min) or the control (dimethylsulphoxide/saline). Microvascular leakage was assessed in the trachea and bronchi at 15 min, 22.5 min, 45 min and 120 minutes with n = 6 for each group. The only significant difference between control and FMLP challenged groups was at 45 min in the bronchi (FMLP 77.6 +/- 12.2, control 33.4 +/- 5.7, P < 0.05). To determine the mechanism underlying FMLP-induced increases in microvascular leakage rabbits were treated with one of the following: (i) nitrogen mustard (1.75 mg/kg intravenously), which depletes circulating polymorphs (n = 6); (ii) the platelet activating factor (PAF) receptor antagonist WEB 2086 (10 mg/kg; n = 5); (iii) the Cys-LTR1 receptor antagonist ICI198615 (nebulised 10(-4) mol/L), or challenged with the thromboxane agonist U46619. Tracheal Evans blue concentration was assessed at 30 min after FMLP challenge and compared with the appropriate control. Treatment with WEB 2086 significantly (P < 0.05) reduced tracheal microvascular leakage (FMLP 76.3 +/- 13.1 WEB 2086/FMLP 31.4 +/- 3.7 micrograms/g trachea) as did ICI198615 (FMLP 69.8 +/- 11.5 ICI198615/FMLP 30.0 +/- 5.7). In conclusion FMLP induced an increase in tracheal microvascular leakage which was significant in the bronchi at 45 min and this increase was mediated by platelet activating factor and the sulphidopeptide leukotrienes C4 and D4.

Effect of leukotriene inhibitor on salicylate induced morphologic changes of isolated cochlear outer hair cells

Our previous studies have shown that salicylate ototoxicity is associated with decreased levels of prostaglandins (PGs) and increased levels of leukotrienes (LTs) in the perilymph. Other studies have demonstrated that salicylate ototoxicity is associated with decreased cochlear blood flow, reversible changes in isolated cochlear outer hair cells (OHCs), and decreased otoacoustic emission. We have shown that pretreatment with an LT inhibitor prevents salicylate induced hearing loss, a decrease in cochlear blood flow and changes in otoacoustic emissions. The objectives of the current study were to determine the effect of exposure of salicylate and LTs on the morphology of isolated OHSc and to determine the effect of LT inhibitors on salicylate induced morphologic changes of isolated OHCs. Isolated OHCs from chinchilla cochlea were exposed to different test solutions. The groups included sodium salicylate (10 mM) with or without pretreatment with an LT inhibitor (L-663, 536, 30 microM), 0.1 or 1.0 microM solution of LTC4, LTD4, LTE4, and two control solutions, standard bathing solution (SBS) or leukotriene inhibitor alone. Osomolality of all solutions were kept at 305 +/- 5 mmolkg-1. The OHCs were observed under an inverted microscope. Images were stored onto a computer and analyzed later. OHCs exposed to the salicyalate developed a decrease in mean cell length. The exposure of OHCs to LTC4, LTD4, and LTE4 also demonstrated a similar decrease in mean cell length. Cells in the control SBS or LT inhibitor alone groups did not show any change. OHCs exposed to salicylate in the presence of the LT inhibitor did not exhibit morphologic changes. This study suggest that arachidonic acid metabolites, especially an increase in the concentration of LTs, seem to play an important role in the pathogenesis of salicylate ototoxicity.

Effect of 15-hydroperoxyeicosatetraenoic acid on the fibrinolytic factor release and the antithrombin binding of vascular endothelial cells

15-Hydroperoxyeicosatetraenoic acid (15-HPETE), an arachidonate lipoxygenase product, is reported to induce severe endothelial injury. In this study, we examined the effect of 15-HPETE on the release of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) from cultured human umbilical vein endothelial cells (HUVEC). The addition of 15-HPETE to the serum-free medium reduced the release of t-PA antigen from HUVEC, while the release of PAI-1 antigen was significantly enhanced. However, treatment of the cultured HUVEC with alpha-tocopherol or nordihydroguaiaretic acid completely suppressed the 15-HPETE-induced change in t-PA and PAI-1 antigen release. 15-Hydroxyeicosatetraenoic acid (15-HETE) had no effect on the release of either antigen from cultured HUVEC. The HUVEC surfaces exposed to 15-HPETE decreased the potency for binding antithrombin III. In a reconstituted system with heparin and phosphatidylcholine, 15-HPETE decreased the ability of heparin to inactivate thrombin activity. These results suggest that the fibrinolytic factor release and the antithrombin binding of vascular endothelial cells are impaired by the attack of 15-HPETE, and that the presence of antioxidants prevents the injurious action of lipid hydroperoxide.