Pharmacologic receptors for the leukotrienes

Montelukast inhibits neutrophil pro-inflammatory activity by a cyclic AMP-dependent mechanism

BACKGROUND AND PURPOSE

The objective of this study was to characterize the effects of the cysteinyl leukotriene receptor antagonist, montelukast (0.1-2 micromol x L(-1)), on Ca(2+)-dependent pro-inflammatory activities, cytosolic Ca(2+) fluxes and intracellular cAMP in isolated human neutrophils activated with the chemoattractants, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (1 micromol x L(-1)) and platelet-activating factor (200 nmol x L(-1)).

EXPERIMENTAL APPROACH

Generation of reactive oxygen species was measured by lucigenin- and luminol-enhanced chemiluminescence, elastase release by a colourimetric assay, leukotriene B(4) and cAMP by competitive binding ELISA procedures, and Ca(2+) fluxes by fura-2/AM-based spectrofluorimetric and radiometric ((45)Ca(2+)) procedures.

KEY RESULTS

Pre-incubation of neutrophils with montelukast resulted in dose-related inhibition of the generation of reactive oxygen species and leukotriene B(4) by chemoattractant-activated neutrophils, as well as release of elastase, all of which were maximal at 2 micromol x L(-1) (mean percentages of the control values of 30 +/- 1, 12 +/- 3 and 21 +/- 3 respectively; P < 0.05). From a mechanistic perspective, treatment of chemoattractant-activated neutrophils with montelukast resulted in significant reductions in both post-peak cytosolic Ca(2+) concentrations and store-operated Ca(2+) influx. These montelukast-mediated alterations in Ca(2+) handling by the cells were associated with a significant elevation in basal cAMP levels, which resulted from inhibition of cyclic nucleotide phosphodiesterases.

CONCLUSIONS AND IMPLICATIONS

Montelukast, primarily a cysteinyl leukotriene (CysLT(1)) receptor antagonist, exhibited previously undocumented, secondary, neutrophil-directed anti-inflammatory properties, which appeared to be cAMP-dependent.

Leukotriene receptor blockade in experimental heart failure

The pathophysiological role of endogenous leukotrienes in cardiovascular control and the regulation of renal function in congestive heart failure is not known. Therefore, in six conscious dogs with or without heart failure induced by right ventricular pacing (270/min, 10 days) we studied the effects of the leukotriene receptor antagonist FPL55712 on hemodynamics, plasma hormones and renal function. In healthy dogs, FPL55712 (1 mg kg-1 + 0.01 mg kg-1 min-1 i.v.) had little effect on hemodynamics, only reducing heart rate by 11% and insignificantly increasing systemic vascular resistance. Plasma levels of norepinephrine (-57%), renin (-30%) and aldosterone (-24%) were significantly decreased. Renal function parameters were not changed. In dogs with heart failure, FPL55712 significantly increased systemic vascular resistance (+16%) and decreased cardiac output (-15%). Plasma hormone levels were not changed, but renal plasma flow was decreased (-13%) and glomerular filtration rate (+12%), renal vascular resistance (+13%) and filtration fraction (+23%) were increased. It is concluded that there is no evidence for a contribution of endogenous leukotrienes to the systemic vasoconstriction in experimental heart failure. Whether the increase in systemic and renal vascular resistance induced by the leukotriene antagonist in dogs with heart failure reflects a role for endogenous leukotrienes with vasodilator action is still unclear and deserves further investigation.

Pharmacologic and pharmacokinetic profile of SK&F S-106203, a potent, orally active peptidoleukotriene receptor antagonist, in guinea-pig

In this report the pharmacologic and pharmacokinetic profile of the leukotriene receptor antagonist 3(S)-[(2-carboxyethyl)thio]-3-[2-(8-phenyloctyl)phenyl] propanoic acid (SK&F S-106203) in guinea-pigs is described. In isolated guinea-pig tracheae SK&F S-106203 was a potent, competitive antagonist of leukotriene (LT) D4-induced contractions (pA2 = 7.6). SK&F S-106203 was also a potent antagonist of LTE4-induced contractions (pKB = 7.3), but had little effect on those elicited by LTC4 (pKB = 5.5). SK&F S-106203 (10 microM) had no effect on contractions produced by histamine, carbachol, KCl, U-44069, PGF2 alpha or PGD2. In addition, SK&F S-106203 (10 microM) did not inhibit cyclic nucleotide phosphodiesterase (PDE) activity of several PDE isozymes. In guinea-pig lung membrane preparations, SK&F S-106203 was a potent antagonist of 3H-LTD4 binding with a Ki = 19.4 +/- 2.1 nM (n = 5). The pharmacokinetic profile of SK&F S-106203 was determined in unanesthetized guinea-pigs. Following an i.v. (bolus) dose (25 mg/kg), SK&F S-106203 disappeared from plasma in a biphasic fashion with half-lives of 0.1 h (50% of the area under the plasma concentration-time curve, AUC) and 11 h. The AUC obtained for SK&F S-106203 following i.v. administration was 87.3 +/- 7.5 micrograms-h/ml. Following an oral dose of SK&F S-106203 (100 mg/kg), the maximal plasma concentration (Cmax) and the time Cmax was achieved (Tmax) were 21.62 +/- 2.26 micrograms/ml and 4 +/- 1 h, respectively; the AUC was 279.9 +/- 41.8 micrograms-h/ml. Studies examining the effects of i.v. infusion of SK&F S-106203 revealed that marked inhibition of LTD4-induced bronchospasm was produced with steady-state plasma levels of SK&F S-106203 less than 1 microgram/ml (less than 2 microM). Oral (p.o.) pretreatment with 100 mumol/kg SK&F S-106203 for up to 24 h essentially abolished LTD4-induced bronchospasm; this correlated with sustained plasma concentrations of greater than 2 micrograms/ml. The results indicate that in guinea-pig airways, SK&F S-106203 is a potent and selective LT receptor antagonist that is active via aerosol, oral and i.v. routes of administration. When given orally, SK&F S-106203 is highly bioavailable and has a very long duration of action which correlates with the pharmacokinetic profile of the compound. SK&F S-106203 may be useful therapy in asthma and other disorders in which the LTs are thought to play a prominent pathophysiological role.

Interaction of leukotriene C4 and Chinese hamster lung fibroblasts (V79A03 cells). 1. Characterization of binding

A novel, specific, and potent biological action of leukotriene C4 (LTC4) was demonstrated in the Chinese hamster lung fibroblast cell line V79A03 (V79 cells), namely the confirment of protection against subsequent gamma-irradiation. Consequently, studies were conducted to determine whether LTC4-conferred radioprotection could be attributed to a receptor-mediated phenomenon. Specific binding sites for leukotriene C4 (LTC4) were identified and characterized using intact V79 cells incubated at 4 degrees C in the presence of serine-borate, during which time conversion of LTC4 to LTD4 or LTE4 was undetectable. Binding was maximal in a broad region between pH 6.2 and 8.8. Ca2+, Mg2+, and Na+ were not required for binding, and binding was not altered by GTP, ATP, or cAMP, by leukotrienes B4, D4, or E4, or by the leukotriene end point antagonists LY 171883, FPL 55712, or Revlon 5901-5. Scatchard analyses and kinetic experiments indicated the presence of high-affinity [Kd = 2.5 +/- 0.63 nM, approximately 9.9 x 10(5) sites/cell] and low-affinity [Kd = 350 +/- 211 nM, approximately 2.7 x 10(6) sites/cell] binding sites. The observed binding characteristics of LTC4 to V79 cells are consistent with a receptor-mediated phenomenon. In a companion communication which follows this report, we report the subcellular distribution of LTC4 binding to V79 cells and demonstrate that this binding is unlikely to be attributed principally to interaction with glutathione-S-transferase.

Interaction of leukotriene C4 and Chinese hamster lung fibroblasts (V79A03 cells). 2. Subcellular distribution of binding and unlikely role of glutathione-S-transferase

It was reported previously that radiation-induced cytotoxicity in V79A03 (V79) cells was attenuated by pretreatment of cells with leukotriene C4 (LTC4), leading us to determine that V79 cells possessed specific binding sites, with characteristics of receptors, for LTC4 (see the preceding, companion communication). Additional studies were conducted to determine the subcellular distribution and the chemical nature of the LTC4 binding site in V79 cells. Trypsin treatment of cells before LTC4 binding assays resulted in a 74% reduction in high-affinity binding. In tests to examine the subcellular location of LTC4 binding, plasma membrane and nuclear fractions were obtained from V79 cells. In contrast to Scatchard analyses of LTC4 binding to intact cells which were curvilinear, Scatchard analyses of nuclear and plasma membrane fractions were linear, indicative of the presence in these cellular substituents of low and high-affinity binding, respectively. To examine the nature of the high-affinity LTC4 binding sites, intact V79 cells were photolyzed with [3H]-LTC4 rendered photoactive by preincubation with N-hydroxysuccinimidyl-4-azidobenzoate. The cell-bound radioactivity migrated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with an apparent molecular weight of approximately 40 kdal. Five different commercial preparations of glutathione-S-transferase (GST), which has been implicated as a source of LTC4 "specific binding" in other cells, migrated in the same SDS-PAGE system with an apparent molecular weight of 20-24 kdal. Furthermore, preincubations of V79 cells with three antisera generated against GST had minimal effects upon subsequent LTC4 binding to intact cells. These data, taken together with the data from the preceding companion communication, suggest that the radioprotective effect of LTC4 upon V79 cells may be attributable to a receptor-mediated phenomenon which appears distinct from leukotriene binding to GST.

SK&F S-106203 inhibits leukotriene C4, leukotriene D4 and leukotriene E4 vasopressor responses in the conscious rat

1. The purpose of these experiments was to investigate the effects of the selective peptidoleukotriene receptor antagonist, SK&F S-106203, on leukotriene C4 (LTC4), LTD4 and LTE4 vasopressor responses in the conscious, normotensive rat. SK&F S-106203 was administered as a bolus followed by a continuous infusion in order to provide information on the relationship between antagonism of leukotriene responses and steady-state plasma concentrations. 2. Infusion of SK&F S-106203 at doses of 0.2 mgkg-1 + 1 mgkg-1 h-1, 1 mgkg-1 + 3 mgkg- h-1 or 2 mgkg-1 + 10 mgkg-1 h-1 produced dose-dependent steady-state plasma drug concentrations of 1.0, 3.2 and 23.8 micrograms ml-1, respectively. Plasma SK&F S-106203 concentrations appeared to increase in a linear fashion at doses of 1 and 3 mgkg-1 h-1; at the highest dose the increment in plasma drug concentrations (i.e., 7-8 fold) was greater than the increment in dose (i.e., 3 fold), suggesting saturation of the primary clearance mechanism(s) at this dose. 3. SK&F S-106203 (2 mgkg-1 + 10 mgkg-1 h-1) had no effect on noradrenaline-, vasopressin-, isoprenaline-, or U 46619-induced responses. 4. SK&F S-106203 produced dose-dependent rightward shifts in the LTC4 and LTE4 dose-response curves. Administration of SK&F S-106203 at doses of 0.2mg kg1 + 1 mg kg1 h-, mg kg' + 3mgkg-'h-1, or 2mgkg-' + lOmgkg-1h'- produced dose-ratios of 1.0, 3.1 and 19.9, respectively, against LTC4 responses, and dose-ratios of 1.6, 3.8 and 9.1, respectively, against LTE4 responses. 5. Against LTD4 responses, SK&F S-106203 at doses of 0.2mgkg- + mgkg-1 h-, mg kg' + 3 mg kg- 1h - ', or 2 mg kg- + 10 mg kg- h- produced dose-ratios of 2.5, 2.8, and 11.4, respectively. Administration of D-penicillamine, a non-competitive LTD4 dipeptidase inhibitor, had no effect on LTD4 responses. 6. The similarity in the LTD4 dose-ratios at the two lower infusion rates, despite increases in the plasma drug concentrations, suggests the existence of pharmacologically heterogeneous LTD4 receptors. These results indicate that SK&F S-106203 is a potent, selective and apparently competitive antagonist of LTC4, LTD4 and LTE4 vascular responses in the intact rat.

A possible role for leukotrienes in the regulation of glomerular haemodynamics in the dog

In anaesthetized beagles, saralasin, phentolamine, 1-penicillamine-2-O-methyl-tyrosine-8-arginine-vasopressin and SCH 23390, a DA1 antagonist, were infused into the left renal artery (i.r.a.) and indomethacin and aprotinin intravenously (Group 1). In Groups 2 and 3, i.r.a. infusion of two chemically different putative leukotriene (LT) antagonists, FPL 55712 (100 micrograms/kg/min) and LY 171883 (500 micrograms/kg/min), respectively, was superimposed in the fourth period of experiments. In comparison to Group 1, there was an increase (40% in Group 2 and 33% in Group 3) in renal blood flow and a decrease in glomerular filtration rate (16% and 17%, respectively) and filtration fraction (36% and 41%, respectively). Similar changes were observed on the single nephron level. Directly measured glomerular capillary pressure decreased by 10% and 12%, respectively. A decrease in total arteriolar resistance by 34% and 25%, respectively, was caused by a comparatively higher decrease in efferent (44% and 34%, respectively) than afferent (26% and 15%, respectively) arteriolar resistance values. No change in the ultrafiltration coefficient, Kf, was detected. Providing FPL 55712 and LY 171883 are specific LT antagonists, these experiments suggest a possible constrictory role of LT (expressed more on the efferent than afferent arteriole) in anaesthetised mildly surgically stressed dogs.

Efficacy of a combination thromboxane receptor antagonist and lipoxygenase inhibitor in traumatic shock

The effects of a thromboxane receptor antagonist having lipoxygenase inhibitory activity, L-655,240 (3-[1-(4-chlorobenzyl)-5-fluoro-3-methyl-indol-2-yl]2,2-dimethylpropa noic acid) (1 mg/kg per h) were studied in a standardized model of traumatic shock. Pentobarbital (35 mg/kg) anesthetized rats subjected to Noble-Collip drum trauma were characterized by a 82 +/- 12 min survival time, a 20-fold increase in plasma cathepsin D activity, and a 6-fold increase in plasma myocardial depressant factor (MDF) activity. L-655,240 significantly attenuated the accumulation of MDF activity in the plasma (74 +/- 3 vs. 46 +/- 4 units/ml), vehicle vs. drug, respectively, and significantly (P less than 0.01) prolonged survival time to 206 +/- 26 min. However, plasma cathepsin D was not significantly altered with L-655,240 administration during traumatic shock. L-655,240 at 20 micrograms/ml markedly attenuated minced rat lung fragments from producing LTC4 and LTD4.L-655,240 exhibited significant anti-proteolytic activity in pancreatic homogenates. Therefore, L-655,2340 does not stabilize lysosomal membranes directly, but exerts an anti-proteolytic action which appears to curtail the production of a myocardial depressant factor by the ischemic pancreas, thus protecting during traumatic shock. A combination anti-eicosanoid drug such as L-655,240 may therefore prove to be an important therapeutic agent in acute ischemic disorders including traumatic shock.

Adenosine and leukotrienes have a regulatory role in lung surfactant secretion in the newborn rabbit

Previous studies have shown that secretion of phosphatidylcholine in cultured adult rat type II pneumocytes is stimulated by purinoceptor agonists and leukotrienes. The objective of the present study was to determine if such agents have a physiological role in the regulation of surfactant secretion. We chose the newborn rabbit as the experimental model, since in this system there is a marked increase in surfactant secretion immediately after birth. We examined the effects of an inhibitor of leukotriene biosynthesis, nordihydroguaiaretic acid, two leukotriene antagonists, FPL-55712 and FPL-57231, and a P1 purinoceptor antagonist, 8-phenyltheophylline, on this increase. Newborn rabbits were delivered by Cesarean section at 30 days gestation. Some animals in each litter were killed immediately, while others were injected with test agents or solvent vehicle while still in the amniotic sacs. After breathing for 3 h in an incubator, these animals were also killed. The lungs were lavaged with saline and the phospholipid content and composition of the lung lavage liquid was measured. In control animals, there was a greater than 2-fold increase in the amounts of total phospholipid and phosphatidylcholine and in the phosphatidylcholine/sphingomyelin ratio during the 3 h period of breathing. The increases in total phospholipid and phosphatidylcholine were decreased 38-62% by the antagonists, while the increase in the phosphatidylcholine/sphingomyelin ratio was decreased 61-77%. These data show that the ventilation-induced increase in secretion of lung surfactant in the newborn rabbit is inhibited by leukotriene and P1 receptor antagonists and by an inhibitor of leukotriene biosynthesis and, when taken together with the data from the tissue culture system, support a role for leukotrienes and adenosine in the physiological regulation of surfactant secretion.

Modulation of arachidonic acid metabolites as potential therapy of asthma

Bronchial asthma is a multifactorial disease characterized by reversible bronchoconstriction, airway hyperreactivity, oedema and excessive mucus production. Present therapy directed against specific mediators has not been overwhelmingly successful. Even though there exists a multiplicity of purported mediators, perhaps the key to better therapy is a vigorous understanding of the arachidonic acid cascade and investigations to modulate specific products of these pathways. Within the cyclooxygenase pathway an interesting scenario might be to effectively antagonize the potent bronchoconstrictive effects of prostaglandin (PG)D2 and its recently identified predominant metabolite, an 11-hydroxyl epimer, 9 alpha,11 beta-PGF2. PGD2 is the major cyclooxygenase product released from sensitized human lung and bronchoalveolar lavage (BAL) mast cells; it possesses a myriad of biological actions relevant to the pathogenesis of asthma. While no specific antagonists of PGD2 or 9 alpha,11 beta-PGF2 have been identified, some preliminary studies have suggested that, perhaps, PGD2 may be interacting, at least in part, with thromboxane receptors. In addition, peroxidation of arachidonic acid catalyzed by 5-lipoxygenase produces the leukotrienes, which are extremely potent bronchoconstrictors as well as oedema and mucus secretagogues. Leukotrienes are primary mast cell mediators which may be the vital link to both early (acute) and late (chronic) asthmatic attacks. Research seeking leukotriene antagonists has been intensive. Leading clinical candidates have emerged from Smith Kline and French, Lilly, Merck-Frosst, ICI-Stuart and other groups. However, we must await the outcome of ongoing clinical trials in asthmatics to determine just how important the leukotrienes really are in the pathogenesis of asthma, allergy and inflammation. Thus, modulation of the effects of products of arachidonic acid metabolism may provide a new and more specific treatment for bronchial asthma.

Vascular smooth muscle cell leukotriene C4 synthesis: requirement for transcellular leukotriene A4 metabolism

Leukotriene synthesis and metabolism were studied in cultured porcine aortic smooth muscle cells (PSM). Cultures stimulated with calcium ionophore A23187, with or without exogenous arachidonic acid, did not release detectable levels of leukotriene B4, C4, D4 or E4. Those products were assayed by high-performance liquid chromatography, ultraviolet spectrometry and, in some cases, radioimmunoassay. Smooth muscle cultures were able to convert leukotriene A4 to leukotriene C4, indicating the presence of leukotriene C4 synthetase. Although this enzymatic activity has previously been found in cultured porcine aortic endothelial cells, it was not detectable in cardiac myocytes, fibroblasts from several organs or renal epithelial cells. It is known from previous work that inflammatory cells such as polymorphonuclear leukocytes (PMNL) or mast cells release leukotriene A4 when stimulated. Further, increased numbers of these cell-types are found associated with vascular tissue during several pathologic situations. Therefore, the potential for a leukocyte-smooth muscle cell interaction involving the transcellular metabolism of leukotriene A4 was assessed. Stimulation of PMNL suspensions in the presence of PSM resulted in a significant increase in total leukotriene C4 produced in comparison to either cell-type alone (255% of PMNL alone, P less than 0.05). Furthermore, after the intracellular glutathione pool of PSM was prelabelled with 35S, a PSM-PMNL coincubation produced levels of [35S]leukotriene C4 which were significantly greater (P less than 0.05) than those found after coincubating prelabelled PMNL with unlabelled PSM. These data demonstrate a PMNL-PSM interaction in which smooth muscle cell leukotriene C4 synthesis results from the transcellular metabolism of PMNL-derived leukotriene A4. Since leukotriene C4 and its metabolites are vasoconstrictors and cause increased vascular permeability, the biochemical interaction described in this report may be relevant to the pathophysiology of arterial vasospasm, atherogenesis and to the abnormalities of tissue perfusion associated with ischemic or inflammatory disorders.

Differential effects of epithelium removal on the responsiveness of guinea-pig tracheal smooth muscle to bronchoconstrictors

1 The influence of the epithelium on contractions produced by the peptidoleukotrienes, 5-hydroxytryptamine (5-HT) and the thromboxane mimetic, U-44069, was examined in trachea from control and ovalbumin-sensitized guinea-pigs. 2 In control tissues removal of the epithelium produced an approximately 2 to 4 fold leftward shift in leukotriene C4 (LTC4) and LTD4 concentration-response curves, but no effect on LTE4-induced contractions. Similar results were obtained in preparations from ovalbumin-sensitized animals. 3 Responses produced by 5-HT or U-44069 were similar in the presence and absence of the epithelium in control guinea-pigs. 4 Indomethacin produced contrasting effects on leukotriene-induced contractions in control guinea-pigs: an increase in sensitivity to LTC4 in the presence but not absence of the epithelium, no effect on LTD4-induced contractions and a decrease in sensitivity to LTE4 in both epithelium-containing and epithelium-free preparations. 5 These results indicate that there is selectivity in the effects of epithelium removal on agonist-induced contractions of the guinea-pig trachea. This provides further evidence for the modulatory influence of the epithelium on the reactivity of mammalian airway smooth muscle and supports the postulated existence of an epithelium-derived inhibitory factor. The observation that in intact trachea indomethacin mimics the effects of epithelium removal on LTC4-induced responses, suggests the involvement of a prostanoid(s) in this phenomenon.

Inhibition of leukotriene-induced contraction of guinea pig trachea by 5-lipoxygenase inhibitors

The effects of the 5-lipoxygenase inhibitors nordihydroguiaretic acid (NDGA), 5, 8, 11, 14-eicosatetraynoic acid (ETYA), 1-phenyl-3-pyrazolidone (phenidone) and BW-755c, on the contractile response to LTC4 or LTD4 were examined on the isolated guinea pig trachea. Responses to either LTC4 or LTD4 were obtained on indomethacin treated tissues, in the presence of either L-serine-borate complex or L-cysteine, respectively, to inhibit metabolic conversion of the leukotrienes. NDGA (30 microM) and ETYA (100 microM) produced a selective competitive antagonism of LTD4-induced contractions, while phenidone antagonized both LTC4- and LTD4-induced responses in a non-competitive manner. In contrast, BW-755c (30 microM) did not significantly antagonize LTC4 or LTD4 concentration-response curves. The results suggest that leukotriene antagonism may be produced by large concentrations of some 5-lipoxygenase inhibitors.

Antagonistic effect of KC-404, a new anti-asthmatic agent, on leukotriene D4-induced contractile responses in isolated guinea pig smooth muscles

The inhibitory effects of KC-404, a novel clinically available anti-asthmatic drug, on leukotriene(LT) D4-, LTC4-, histamine- and acetylcholine(ACh)-induced contractile responses in isolated guinea pig lung parenchymal, tracheal and ileal longitudinal strips were compared using an organ bath system. In lung parenchyma, KC-404 antagonized LTD4 in a competitive fashion, whereas it antagonized histamine noncompetitively. The pA2 value against LTD4 was 7.39. KC-404 hardly antagonized LTC4 and ACh. A ranked order of potency estimated from its minimum effective concentrations (MEC) was LTD4 greater than histamine greater than LTC4 greater than ACh. In trachea, KC-404 antagonized LTC4 and LTD4 in a competitive fashion, while it antagonized histamine noncompetitively. The pA2 values against LTC4 and LTD4 were 5.99 and 6.51, respectively. KC-404 hardly antagonized ACh. A ranked order of the potency estimated from MEC was LTD4 greater than LTC4 greater than histamine greater than ACh. The pA2 values of KC-404 against LTD4 in lung parenchyma and trachea were little or not altered, while its inhibitory effect on histamine-induced contraction in trachea was markedly diminished by the pretreatment of tissues with indomethacin. In ileum, KC-404 noncompetitively antagonized all of the agonists used. A ranked order of the potency estimated from pD2 values was LTD4 divided by LTC4 greater than histamine greater than ACh. These results suggest that KC-404 is a selective antagonist of LTD4 and that it might interact with LTD4 receptor in airway smooth muscles but not in ileum. Another possibility that the drug might interact with LTD4 specific excitation-contraction coupling mechanism was also discussed.

Synthesis and vascular actions of an arachidonic acid ethylene-diamino-triethyl-ester (AA-EDTA) derivative

An ethylene-diamino-triethyl-ester derivative of arachidonic acid (AA-EDTA) was newly synthesized and tested for its coronary vasoactivity in isolated perfused cat coronary arteries. This arachidonic acid analog exerted a coronary vasodilator effect and significantly antagonized the coronary vasoconstrictor effect of LTD4. The constrictor response to the thromboxane analog carbocyclic thromboxane A2 was unaffected by AA-EDTA. These properties of AA-EDTA may be useful in counteracting the vasoconstrictor influence of leukotrienes in situations such as coronary artery vasospasm.

Biological actions of leukotrienes. State of the art lecture

Leukotrienes are novel mediators derived from arachidonic acid through the 5-lipoxygenase enzyme system. Leukotriene B4 has potent effects on leukocyte function and in vivo induces leukocyte accumulation and changes in vascular permeability and modulates pain responses. Peptido-lipid leukotrienes are potent smooth muscle--contracting agents. They may have important cardiovascular actions through mechanisms involving either vasoconstriction or indirect vasodilatation. Evidence for leukotriene production has been found in subjects with allergic conditions and psoriasis, indicating a putative role for these substances in human disease.

Leukotriene-associated toxic oxygen metabolites induce airway hyperreactivity

The effect of toxic oxygen metabolite scavengers was examined in a guinea pig trachealis model of leukotriene (LTD4)-induced synergism upon histamine contractures. Under both physiologic (2.5 mM) and low (OmM) extracellular calcium conditions, LTD4 (10(-7) to 10(-9) M) potentiated histamine isometric tension responses. This LTD4-induced histamine hyperresponse was inhibited by pretreatment with superoxide dismutase. Inhibition of LTD4 receptor binding by FPL 55712 (10(-5) M) also aborted this interaction. Actual trachealis superoxide anion (O2-) generation by LTD4 was observed with a maximal release of 15 nM O2-/CPK unit X 10(-2) over 60 min. Phorbol myristate acetate (PMA) also generated O2- in this preparation. Trachealis muscle hyperreactivity to histamine induced by 10(-8) M LTD4 assayed in OmM (Ca++)E was not induced by PMA. It is concluded that exogenous LTD4 activates toxic oxygen metabolites which interact to induce an acquired hyperreactivity to agonist histamine in trachealis smooth muscle.

Leukotrienes as mediators of ischemia and shock

Leukotrienes have been implicated as mediators of ischemia and shock. Recent evidence has been obtained supporting the four major criteria of acceptance of leukotrienes as mediators of shock, namely (a) increased concentration in body fluids during shock states, (b) ability to exert significant pathophysiologic effects which aggravate ischemia and shock, (c) amelioration of the shock state by leukotriene synthesis inhibitors and leukotriene receptor antagonists, and (d) production of a shock-like state by exogenous administration of leukotrienes. In conclusion, both LTB4 and the peptide leukotrienes (e.g. LTC4, LTD4 and LTE4) also known as the slow reacting substance of anaphylaxis (SRS-A) can be considered as mediators of ischemia and shock. Although difficulties exist with measuring leukotrienes in circulating blood and in obtaining long lasting selective blockers of leukotriene synthesis, innovative experiments measuring leukotrienes in bile and other body fluids and in employing specific leukotriene receptor antagonists have helped in assessing the significance of the leukotrienes in shock states. Additional studies are necessary to evaluate these findings in perspective, and to compare and contrast the role of leukotrienes to that of other vascular mediators including prostaglandins and thromboxanes, as well as non-eicosanoids including serotonin, histamine, angiotensin II and vasopressin, all of which can play a mediator role in ischemia and shock states. Further clarification of these issues promises to open exciting new chapters in shock research.

Functional characteristics of leukotriene C4- and D4-metabolizing enzymes (gamma-glutamyl transpeptidase, dipeptidase) within human plasma

Several properties of the leukotriene C4- and leukotriene D4-metabolizing enzymes within human plasma were studied after fractionation of the plasma proteins using ammonium sulfate precipitation. Leukotriene D4-metabolizing enzymes were widely distributed among the fractions obtained. They showed different pH optima (pH 6.5, pH 7.0 and pH greater than or equal to 8.5) and revealed a different degree of thermal stability. The results indicate the presence of more than one enzyme in plasma which interacts with leukotriene D4. EDTA and L-cysteine inhibited the metabolism of leukotriene D4. Two leukotriene C4-metabolizing activities (gamma-glutamyl transpeptidases) differing in their molecular weights were detected after gel filtration. Their molecular weights were estimated to be Mr greater than or equal to 150 000 and Mr between 55 000 and 100 000.