Effects of leukotriene D on the airways in asthma

Aerosolized leukotriene D4 converts monkeys that are negative aerosolized ascaris responders to positive airway responders

We designed studies to determine if Leukotriene D4 (LTD4) could alter airway reactivity such that rhesus monkeys with positive skin reactivity and consistently negative airway responses would respond to ascaris airway challenge. The experiments were complicated by the observation that aerosolized LTD4 would occasionally increase airway hyperreactivity in some monkeys used as controls such that an airway response occurred to saline, the diluent for ascaris antigen. In spite of this, we were able to demonstrate induction of airway responsiveness to ascaris antigen. These results demonstrate that LTD4 will induce airway hyperreactivity to a nonspecific stimulus such as aerosolized saline or to an allergen.

Inhalation challenge with sulfidopeptide leukotrienes in human subjects

What is the meaning of these findings to the practicing chest physician? First, leukotrienes are potent airway constrictors; they are capable of reproducing the type of airway constriction observed in asthma. The role of leukotrienes in this regard has yet to be established, but experiments to test the importance of these agents in this setting are likely to be performed soon. Specifically, several leukotriene receptor antagonists or synthesis inhibitors have been identified and may provide the tools needed to test this crucial hypothesis. Second, the leukotrienes are unique bronchoactive agents in that the degree of hyperresponsiveness between normal and asthmatic subjects varies markedly with the bronchoconstrictor index used to assess response. When one compares normal subjects to asthmatic subjects, there is substantial overlap in leukotriene sensitivity among groups when V30-P is used as the bronchoconstrictor index. However, when the FEV1 is used as the bronchoconstrictor index, there is little overlap in sensitivity between normal and asthmatic subjects, and the separation between the two groups is even more clearly made than it is with histamine or methacholine challenge. Thus, LTD4 inhalation challenge may replace the histamine and methacholine challenges in the diagnosis of cryptic shortness of breath. Third, the differential sensitivity of various bronchoconstrictor indices in both normal and asthmatic subjects when leukotrienes are used may provide clues as to the locus of airway hyperresponsiveness in asthma. Thus, leukotrienes hold the promise of new ways to treat and diagnose asthma, as well as providing new insights into the pathobiology of the disease itself.

Identification and characterization of leukotriene D4 receptors in adult and fetal human lung

Leukotriene D4 (LTD4) receptors were identified and characterized in adult and fetal human lung membranes. Macroscopically normal adult lung tissue was selected from seventeen surgical biopsy specimens, and twenty-seven fetal lung samples were obtained from therapeutic abortions. Binding assays were performed using pooled adult or fetal human lung membranes at 30 degrees under conditions which prevented metabolism of [3H]LTD4. Specific binding reached equilibrium within 30 min, remained constant for 60 min, was enhanced by Mg2+, and was inhibited by Na+ and guanyl-5'-yl-imidodiphosphate. Computer-assisted analyses of saturation binding data showed a single class of binding sites with similar apparent Kd (0.15 +/- 0.09 and 0.12 +/- 0.003 nM) and Bmax (68 +/- 29 and 62 +/- 14 fmoles/mg protein) values for adult and fetal samples respectively. Competition binding studies with [3H]LTD4 showed the same rank order potency for adult and fetal lung receptors (5S, 6R-LTD4 greater than 5S, 6R-LTD1 greater than 5R, 6S-LTD4 greater than 5S,6R-LTE4 greater than FPL 55712). A comparison of the receptor binding affinities of these compounds with their smooth muscle contractile agonist (pD2) and antagonist (-log[KB]) activities in guinea pig lung and trachea showed a good correlation (r = 0.88), suggesting that the saturable, high-affinity, stereoselective [3H]LTD4 specific binding sites identified in human lung may be physiologically relevant receptor moieties.

Studies on the release of leukotrienes and histamine by human lung parenchymal and bronchial fragments upon immunologic and nonimmunologic stimulation. Effects of nordihydroguaiaretic acid, aspirin, and sodium cromoglycate

Fragments of human lung parenchyma or bronchi were studied by high performance liquid chromatography, gas chromatography-mass spectrometry, and bioassay for the biosynthesis of 5-lipoxygenase metabolites of arachidonic acid, and by radioenzymatic assay for the release of histamine, upon immunologic and nonimmunologic stimulation. Human lung parenchyma were passively sensitized with serum from timothy-positive allergic patients (radioallergosorbent test, 30-40%) and challenged with 0.5 microgram/ml of timothy allergen. Analysis of the incubation media showed the presence of LTB4, LTC4, LTD4, LTE4, and histamine. Maximum release of LTB4 and LTD4 was observed after 15 min of challenge (92.8 +/- 21, and 67.8 +/- 14 pmol/g tissue wet weight, respectively; mean +/- SEM) whereas maximum release of LTC4 was observed after 5 min of challenge (25 +/- 7.1 pmol). In parallel to leukotriene formation, histamine was released rapidly and reached a maximum after approximately 15 min of challenge (2.85 +/- 0.76 nmol/g tissue). When fragments of human lung parenchyma were stimulated with ionophore A23187 (4 microM), we observed a profile of leukotriene and histamine release similar to that seen in response to the allergen. Ionophore A23187 stimulated the release of two- to fivefold greater amounts of leukotrienes and histamine than did the allergen. Release of LTC4 and histamine was maximal after 5 min of stimulation (83 +/- 22.2 and 5.2 +/- 0.95 nmol/g tissue, respectively), whereas LTB4 and LTD4 release reached a maximum after 15 min (438 +/- 66.6 and 205 +/- 68 nmol/g tissue, respectively). In addition, human lung parenchyma metabolized LTB4 into omega-OH-LTB4 and omega-COOH-LTB4. This tissue also released 5-hydroxy-eicosatetraenoic acid (5-Hete), 12-Hete, and 15-Hete. Fragments of human lung bronchi also released a similar profile of leukotrienes (except LTC4) and histamine when challenged with the allergen or ionophore A23187. Maximum release of LTB4 and LTD4 by allergen or ionophore stimulation was observed after approximately 15 min (40 +/- 7.5 and 21 +/- 8 pmol/g tissue, respectively, upon allergen challenge; 100 +/- 13 and 47 +/- 10.6 pmol/g tissue, respectively, upon ionophore stimulation). The maximum release of histamine by bronchi was observed after approximately 15 min of allergen challenge and 5 min of ionophore stimulation (2.25 +/- 0.65 and 3.15 +/- 0.9 nmol/g tissue, respectively). The release of leukotrienes but not of histamine by human lung parenchyma upon both allergen and ionophore challenge was inhibited by nordihydroguaiaretic acid (NDGA) (ID50, 2 X 10(-6)M).(ABSTRACT TRUNCATED AT 400 WORDS)

On the optimal conditions of LTC4 formation by human eosinophils in vitro

The optimal conditions for the -in vitro- LTC4 formation by the human eosinophil, isolated from peripheral blood, have been investigated in detail. LTC4 formation was found strongly Ca2+ and ionophore dependent and was complete after 20 min. Maximal LTC4 production was observed in the presence of 2 mM Ca2+, 10 microM ionophore A23187 and 5 mM glutathione. Addition of arachidonic acid resulted in a significant inhibition of the LTC4-synthesis by human eosinophils. In contrast, the formation of 15-HETE was strongly stimulated by the addition of arachidonic acid. As the LTC4 synthesis was found to be strongly inhibited by the addition of 15(S)-HETE to the incubation medium, this monohydroxy acid may be responsible for the inhibitory activity of arachidonic acid.

Identification of specific binding sites for leukotriene C4 in membranes from human lung

Leukotriene C4 (LTC4), one of the major components of the slow-reacting substance of anaphylaxis (SRS-A), is a potent constrictor of bronchial smooth muscle in many species including humans. Here we report the identification and characterization of specific binding sites for LTC4 in membranes from human lung parenchyma. At 4 degrees, 3H-LTC4 binding is specific, saturable (Bmax = 32-41 pmoles/mg prot.), rapid (equilibrium being attained within 15 min), reversible and of high affinity (Kd = 3.6-7 X 10(-8) M). The binding sites are sensitive to heat and probably possess a protein moiety, being inactivated upon trypsinization. CaCl2 affects both the association and the dissociation rate and dose-dependently enhances the binding of 3H-LTC4 at equilibrium; maximal enhancement (4-fold) occurred at 10(-2)M CaCl2. Unlabelled LTC4 is able to complete with 3H-LTC4 for its binding sites with an IC50 of 7.8 X 10(-8) M. The addition of 10(-2) M CaCl2 increases the potency of LTC4 in inhibiting the binding (2.2-fold); both the competition curves are monophasic, indicating the existence of a homogeneous class of binding sites. In the presence of CaCl2, LTD4, LTE4 and the SRS-A antagonist FPL 55712 can inhibit 3H-LTC4 specific binding, being, however, less potent than LTC4 (IC50 S = 2.2 X 10(-6), 2.4 X 10(-5) M, for LTD4, LTE4 and FPL 55712, respectively). FPL 55712 displayed a competitive mechanism; its affinity, however, was lower if absorption to glass was not prevented. The present studies indicate that specific binding sites for 3H-LTC4 exist in human lung parenchyma, and that a receptor-mediated process might be involved in the bronchoconstriction induced by LTC4.

Pulmonary synthesis, release, and metabolism of prostaglandins

Immunologic or calcium-dependent activation of proteolytically dispersed human lung cells containing 5% mast cells causes the release of large amounts of PGD2 and TxB2. In cell purification experiments, only those fractions containing mast cells had the capacity to generate PGD2 and release histamine with IgE-dependent activation. The cells of origin of T X B2 are likely to be cells of the monocyte-macrophage series, although additional eicosanoid release may occur from immunologically activated lymphocytes and eosinophils. In men who have asthma, inhalation of low concentrations of PGD2 results in bronchoconstriction, whereas higher concentrations of PGD2 are needed to produce bronchoconstriction in normal subjects. Subjects with asthma exhibited 3.5-fold greater responsiveness to inhaled PGD2 than to PGF2 alpha. These observations demonstrate that PGD2 is the most potent bronchoconstrictor prostanoid tested in man. In both normal subjects and subjects with asthma, a single inhalation of PGF2 alpha resulted in a doubling in plasma levels of 13,14-dihydro-15-keto-PGF2 alpha. Plasma levels of this metabolite did not change after PGD2 inhalation. These results indicate that the 11-keto reduction of PGD2 to PGF2 alpha with subsequent inactivation is not important in the initial metabolism of PGD2.

A presumptive role for leukotrienes in obstructive airways diseases

The likelihood that the leukotriene products derived from the 5-lipoxygenase pathway mediate aspects of obstructive airways diseases is strongly suggested by their documented capacities to effect airway spasmogenicity, airway hyperreactivity, tissue edema formation, mucus secretion, and tissue infiltration by leukocytes. That the various leukotriene components of SRS-A have unique receptors on responding tissues and are recoverable from airway surfaces in several inflammatory lung diseases and that several resident and infiltrating cell types have significant potential for leukotriene biosynthesis lend further support to their postulated pathobiologic roles. To fulfill Koch's postulates for proof of leukotrienes' etiologic role, it remains to be shown that inhibition of their biosynthesis or specific antagonism at their end-organ receptors can greatly ameliorate these disease states.

Activated human eosinophils generate SRS-A leukotrienes following IgG-dependent stimulation

Eosinophils, a class of granular leukocytes, are prominent in many inflammatory processes, particularly in asthma, certain allergic diseases and during infections with helminthic parasites. Following incubation with the Ca ionophore A23187 (refs 1-4) (a non-physiological agent which circumvents membrane calcium-gating mechanisms), eosinophils generate large amounts of sulphidopeptide leukotrienes, potent inducers of smooth muscle constriction and mucus production. These are now known to represent the activity previously termed 'slow-reacting substance of anaphylaxis' (SRS-A) but attempts to identify a physiological stimulus for SRS-A production by eosinophils have so far been unsuccessful. The cells contain recognized receptors for IgG (Fc) and it is known that they adhere to, and can be activated by, contact with the surface of large organisms such as helminthic larvae. We show here that eosinophils, particularly when activated, produce sulphidopeptide leukotrienes after contact with large particles coated with IgG.

Inhibition of leukotriene B4 formation in human neutrophils after oral nafazatrom (Bay g 6575)

Three grams of nafazatrom (Bay g 6575), given orally to healthy male volunteers in a single dose, significantly reduce the formation of leukotriene B4 in polymorphonuclear leukocytes. LTB4 synthesis fell from 57.1 +/- 17.0 ng/10(7) PMNL, mean +/- S.D., in control to 34.3 +/- 14.4 ng/10(7) PMNL 3 hr after nafazatrom (2 P less than 0.001). In vitro, nafazatrom inhibited LTB4 formation in human PMNL in a dose dependent manner. At 1 microM nafazatrom LTB4 formation was reduced to 65% of the control value. Nafazatrom had no effect on the excretion of 2,3-dinor-6-keto-PGF1 alpha and 2,3-dinor-TXB2, the major urinary metabolites of endogenously synthesized PGI2 and TXA2, respectively. Serum levels of TXB2 in clotted whole blood also remained unchanged. The inhibitory effect of nafazatrom on leukotriene biosynthesis in human PMNL suggests a therapeutic potential of this drug in processes like allergy and chronic inflammation, where leukotrienes play a pathogenetic role.

Positive interaction between leukotriene C4 and histamine and other mediators on vascular tissues

The interaction of leukotriene C4 (LTC4) with the contractile activity of histamine (H), serotonin (5HT) and norepinephrine (NE) has been investigated in isolated vascular preparations. Threshold concentration of LTC4 (5 X 10(-9) M) significantly potentiated the vasoconstricting effect of these compounds on guinea-pig pulmonary artery (GPPA). This phenomenon was long-lasting for H since it was still present 40 min after LTC4 had been washed. FPL-55712 (10(-5) M) counteracted the increased H response on GPPA induced by LTC4. Potentiation of H activity due to LTC4 was also observed on guinea-pig thoracic aorta (GPTA) indicating that LTC4-induced hyperreactivity is not a phenomenon restricted to the pulmonary vascular bed. In the experiments carried out in presence of indomethacin (3 X 10(-6) M), LTC4 still potentiated H-induced vasoconstriction on GPPA, however the time course of the phenomenon was significantly shorter than that observed in absence of the cyclooxygenase inhibitor. The contractile activity of H and NE on guinea-pig portal vein (GPPV) was not potentiated by LTC4. These results demonstrate that LTC4 induces hyperreactivity of the arterial vascular tissue to vasoactive compounds and suggest that cysteinyl-leukotrienes may have pathological significance in the hemodynamic changes occurring during anaphylactic reactions. Preliminary experiments carried out on human intralobar pulmonary artery strongly support this hypothesis.

Bronchial hyperreactivity to leucotriene D4 and histamine in exogenous asthma

Reactivity of the small and large airways to inhaled leucotriene D4, one of the leucotrienes that constitute slow reacting substance of anaphylaxis, was studied in eight patients with exogenous asthma and nine healthy subjects with no history of atopy. Non-cumulative dose response relations were constructed for leucotriene D4 in a randomised, double blind set up. Reactivity to the leucotriene was compared with reactivity to histamine in the two groups. Both groups reacted to leucotriene D4 with significant airway obstruction evident in forced expiratory volume in one second (FEV1), peak expiratory flow rate, maximal expiratory flow rate at 30% of forced vital capacity estimated from a partial flow volume curve initiated at 50% of vital capacity (V30), and an increase in volume of trapped gas. The airways of the patients were significantly (p less than 0.01) more reactive to leucotriene D4 than those of the controls. The differences were in order of magnitude, 10(2)-10(3) for FEV1 but only about 15 for V30 (p less than 0.05). The hyperreactivity of the airways of the asthmatic subjects to leucotriene D4 was comparable to that to histamine. Inhalation of leucotriene D4 caused pronounced dyspnoea only among the patients. The findings suggest a role for leucotriene D4 in human bronchial asthma.

Production of early and late pulmonary responses with inhaled leukotriene D4 in allergic sheep

Some allergic sheep respond to inhalation of Ascaris suum antigen with both immediate and late increases in airflow resistance (late response). The mechanism of the late response is unknown but recent evidence suggests that the initial generation of slow-reacting substance of anaphylaxis (SRS-A) immediately after antigen challenge is a necessary pre-requisite for the physiologic expression of this late response. Based on this evidence we hypothesized that airway challenge with leukotriene D4 (LTD4), an active component of SRS-A would produce acute and late airway responses in allergic sheep similar to those observed with antigen. In five allergic sheep with documented early and late pulmonary responses to Ascaris suum antigen, inhalation of leukotriene D4 aerosol (delivered dose (mean +/- SE) 0.55 +/- 0.08 ug) resulted in significant early and late increases in specific lung resistance (SRL). In three allergic sheep which only demonstrated acute responses to antigen, LTD4 aerosol (delivered dose 0.59 +/- 0.09 ug) only produced an acute increase in SRL. In the late responders pretreatment with aerosol cromolyn sodium (1 mg/kg) did not affect the acute response but blunted the late increase in SRL. Pretreatment with aerosol FPL-57231 (1% w/v solution) completely blocked both the acute and late responses. These data support the hypothesis that initial release of LTD4 in the airways of sensitive animals is important for the physiologic expression of the late response.

Late asthmatic responses: inquiry into mechanisms and significance

Late asthmatic responses are common, simulate a chronic phase of asthma, and are associated with an influx of inflammatory cells. The precise sequence of events leading to late inflammatory responses and increased hyperresponsiveness of the airways is uncertain, but likely begins with the triggering of mediator release from local (luminal or interstitial) mast cells or, conceivably, alveolar macrophages. Consequent influx and activation of granulocytes, including eosinophils and neutrophils, possibly T lymphocytes, basophils, and platelets, and subsequently later-arriving monocytes and macrophages, may be responsible for a continuing inflammatory reaction, airways hyperresponsiveness, and continuing active bronchial asthma. Identification of the relative importance of responsible cells and mediators will help clarify pathogenesis of bronchial asthma and should lead to a better understanding and design of therapeutic regimens and preventive measures in the management of this common and important disease.

Comparative study of the pulmonary effects of intravenous leukotrienes and other bronchoconstrictors in anaesthetized guinea pigs

Pulmonary responses to intravenous leukotrienes C4, D4 and E4 administered as a bolus injection and by continuous infusion were studied in anesthetized guinea pigs. LTD4, LTC4 and LTE4 (respective ED50 of 0.21 +/- .1, 0.64 +/- .2 and 2.0 +/- .1 microgram kg-1) produced dose-dependent increases in insufflation pressure when given as a bolus injection to anesthetized guinea pigs (Konzett-Rössler). Bronchoconstriction was antagonized by FPL-55712 (50-200 micrograms kg-1), and indomethacin (50-200 micrograms kg-1) but was not significantly altered by mepyramine (1.0 mg kg-1), methysergide (0.1 mg kg-1), intal (10 mg kg-1) mepacrine (5 mg kg-1) or dexamethasone (10 mg kg-1). The beta adrenoceptor blocker, timolol (5 micrograms kg-1) produced a significantly greater potentiation of the responses to the leukotrienes than to arachidonic acid, histamine and acetylcholine. Responses to bolus injection of LTE4 but not LTD4 or LTC4 were partially antagonized by atropine (100 micrograms kg-1) and bilateral vagotomy. In experiments of a different design, continuous infusion of LTD4 and LTE4 (2.8-3.2 micrograms kg-1 min-1) into indomethacin-treated animals produced slowly developing increases in pulmonary resistance and decreases in compliance. The increase in resistance produced by LTE4 and LTD4 was partly reversed by intravenous FPL-55712 (1.0 mg kg-1) and atropine (100 micrograms kg-1) but was almost completely reversed by FPL-55712 (3 - 10 mg kg-1). These findings indicate that leukotrienes can produce bronchoconstriction in guinea pigs through cyclooxygenase-dependent and cyclooxygenase independent mechanisms both of which are blocked by FPL-55712. Cholinergic mechanisms are involved in the mediation of part of the response to bolus injection of LTE4 as well as a small part of the initial response to continuous infusion of LTD4 and LTE4. Intrinsic beta adrenoceptor activation serves to down modulate responses to the leukotrienes to a greater extent than responses to arachidonic acid, histamine and acetylcholine.

[Eicosanoids and phospholipases]

Prostaglandins, thromboxanes, and leukotrienes have been implicated to play an important role in physiology as well as in a growing list of pathophysiologic conditions. These oxidation products of 8.11.14-eicosatrienoic-, 5.8.11.14.-eicosatetraenoic-, and 5.8.11.14.17.-pentaenoic acids have been collectively designated eicosanoids. Many clinically important diseases are associated with altered eicosanoid biosynthesis. Furthermore, a series of hormones are known to induce acutely formation of eicosanoids, suggesting a crucial role in a multitude of tissue responses including phenomena such as secretion, platelet aggregation, chemotaxis, and smooth muscle contraction. The major precursor for the eicosanoids seems to be 5.8.11.14.-eicosatetraenoic acid or arachidonic acid. Virtually all of arachidonic acid however is present in esterified form in complex glycerolipids. Since cyclooxygenase and the lipoxygenases utilize arachidonic acid in its free form, a set of acylhydrolases is required to liberate arachidonic acid from membrane lipids before eicosanoid formation can occur. It became only recently apparent that a minor acidic phospholipid, phosphatidylinositol, comprising only 5%-10% of the phospholipid mass in mammalian cells, plays an important role in arachidonic acid metabolism. Phosphatidylinositol--after phosphorylation to phosphatidylinositolphosphate and phosphatidylinositolbisphosphate--appears to be hydrolyzed by specific phospholipases C generating 1-stearoyl-2-arachidonoyl-diglyceride. Diglyceride serves as substrate for diglyceride lipase to form monoglyceride and free fatty acid. Alternatively diglyceride is phosphorylated by diglyceride kinase yielding phosphatidic acid, which is believed to be reincorporated into phosphatidylinositol. In addition to phosphatidylinositol phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid may contribute to arachidonic acid release. These phospholipids are substrates for phospholipases A2 generating free arachidonic acid and the respective lysophospholipid. Understanding of the biochemistry of arachidonic acid liberation may be critical in developing strategies of pharmacological intervention in a variety of pathological conditions.

Non-steroid anti-inflammatory drugs in asthma: dangerous or useful therapy?

The therapeutic potential of non-steroid anti-inflammatory drugs in clinical asthma is offset by the real possibility of hypersensitivity and induction of severe airways obstruction. The influence of indomethacin on the antigen-induced asthmatic response was tested. Early and delayed asthmatic responses were recorded after antigen challenge in 13 subjects. Indomethacin pretreatment totally or partially inhibited the delayed asthmatic response in 10 of 11 subjects. Inhibition by indomethacin of products of the arachidonic cascade which participate in the pathogenesis of the delayed asthmatic response could explain this phenomenon. A similar therapeutic response was documented without adverse drug reactions when five subjects were restudied after several months. In the same group the early asthmatic response was suppressed in six, enhanced in two and unchanged in four of 12-subjects. This variable response indicates that spasmogenic prostaglandin breakdown products may be important for certain individuals, but are generally of less importance in the early asthmatic response. Clinical trials with indomethacin as a steroid saving agent in allergic asthma appear feasible and can be conducted safely.

Airway responses to aerosolized leukotriene D4 (LTD4) in normal and Ascaris reactor primates

Normal and Ascaris reactor primates were compared for their bronchial pulmonary response to aerosolized leukotriene D4 (LTD4). When 10 micrograms/ml LTD4 was aerosolized (total amount delivered to endotracheal tube was 1.0 micrograms) into the lungs of 6 normal primates, a small increase in total lung resistance (RL) was noted (4.4 +/- 4.5% increase, in 19 separate challenges). However, a larger effect was seen in compliance (27.6 +/- 15.8% decrease, n = 19). Ascaris reactors (n=4) demonstrated a larger RL effect than normals with almost an identical Cdyn change (RL 36.1 +/- 27.7% increase, Cdyn 32.8 +/- 18.8% decrease n = 12). When the pharmacological blockers diphenhydramine, 0.5 mg/kg and atropine, 0.5 mg/kg were administered iv separately before LTD4 challenge, significant antagonist activity was seen. Diphenhydramine inhibited the LTD4 response in normal primates (RL 64.2 +/- 44.3% and Cdyn 50.5 +/- 40.9% n = 6) and in reactors (RL 47.8 +/- 43.1% and Cdyn 19.2 +/- 20.8% n = 4). Atropine inhibited normals (RL 100% and Cdyn 73.1 +/- 32.7% n = 2) and reactors (RL 96.3 +/- 7.7 and Cdyn 47.4 +/- 35.1% n = 3). These results indicate that the LTD agonist action is partially mediated through histamine, primarily acting on lung resistance (large airways) and, in addition, may have a reflex atropine-sensitive component. The difference between the response of normal and reactor primates to LTD4 is primarily a histamine-mediated large airway response.

Allergen-induced release of sulphidopeptide leukotrienes (SRS-A) and LTB4 in allergic rhinitis

Leukotrienes are a recently discovered group of arachidonic acid-derived lipid mediators. Using radioimmunoassay and high pressure liquid chromatography (HPLC), we have identified the SRS-A sulphidopeptide leukotrienes (LTC4, LTD4 and LTE4) in nasal washings from patients with allergic rhinitis who underwent nasal challenge with specific allergen. Smaller, but significant, amounts of LTB4 were also detected. The concentrations of nasal leukotrienes were directly related to the dose of allergen, and were recovered in washings in a time-dependent fashion after challenge. When the patients were subjected to methacholine nasal challenge on a control day, we found only negligible amounts of either the sulphidopeptide leukotrienes or LTB4. These findings support the view that LTC4, LTD4 and LTE4 might contribute to the pathogenesis of allergic rhinitis as a result of their recognized effects on mucous hypersecretion and vasopermeability, and that the potent chemoattractant LTB4 might be involved in the subsequent infiltration of inflammatory cells.

Involvement of capsaicin-sensitive afferent neurones in a vagal-dependent interaction between leukotriene D4 and histamine on bronchomotor tone

Leukotriene D4 (LTD4, 0.1-0.5 micrograms/kg, i.v.), administered 20 s before histamine (H, 1-4 micrograms/kg, i.v.), enhanced the bronchoconstrictor response to H by between 105 and 168%. Bilateral vagotomy, atropine or indomethacin each attenuated, whereas hexamethonium completely prevented, this enhancement. LTD4 failed to enhance the bronchoconstrictor effects of either acetylcholine (ACh) or electrical stimulation of the vagi. Capsaicin pretreatment reduced bronchoconstrictor responses to electrical stimulation of the vagi, but did not affect depressor responses. There was no interaction between LTD4 and H on bronchomotor tone in capsaicin-pretreated guinea-pigs. It is concluded that LTD4 enhances H-induced bronchoconstriction by a mechanism which involves an increased activity of efferent cholinergic nerves innervating the airways. However, the failure of LTD4 to enhance bronchoconstriction due to ACh or vagal stimulation, together with the prevention of the interaction between LTD4 and H by capsaicin-pretreatment, suggests that the site of the interaction may be on capsaicin-sensitive afferent neurones.

Leukotriene D4 potentiates histamine-induced bronchoconstriction in guinea-pigs

Histamine concentration-response curves performed on isolated airways smooth muscle preparations were unaffected by threshold constrictor concentrations of LTD4 (194 +/- 34 pM for parenchymal strips and 1940 +/- 480 pM for isolated trachea, respectively). In contrast, LTD4, when administered between 2 and 60 s beforehand, potentiated bronchoconstrictor responses to histamine in anaesthetized, artificially ventilated guinea-pigs. Doses of LTD4, which did not produce direct effects on airways resistance, potentiated histamine-induced bronchoconstriction to a lesser degree than those having small direct effects. This potentiation was prevented by bilateral vagotomy. In addition, the antagonists atropine (100 micrograms/kg), FPL55712 (5 mg/kg) and indomethacin (1 mg/kg) effectively prevented the interaction. It is suggested that the interaction between LTD4 and histamine involves a specific leukotriene receptor, possibly linked to the generation of a cyclo-oxygenase metabolite and requires intact cholinergic innervation of airways smooth muscle. Furthermore, these results are consistent with the hypothesis that LTD4 may be a mediator of bronchial hyperreactivity.

The evolution and future horizons of research on the metabolism of arachidonic acid by 5-lipoxygenase

Leukotrienes have potent biologic actions in various biologic systems. Leukotriene (LT) B4 has inflammatory properties and has been detected in exudates from human inflammatory disease including psoriasis. LTC4, LTD4, and LTE4 have potent bronchoconstrictor actions in vitro and in normal human subjects. LTE4 causes very long-lasting bronchoconstriction. LTC4 and LTD4 are potent vasoconstrictors in coronary and other vascular beds of anesthetized animals. Sulfidopeptide LTs may therefore have a role in asthma and vasospastic disease.

Leukotriene E4-induced airway hyperresponsiveness of guinea pig tracheal smooth muscle to histamine and evidence for three separate sulfidopeptide leukotriene receptors

Bronchial hyperresponsiveness to contractile agonists and nonspecific irritants is a characteristic feature of bronchial asthma. The mechanisms causing this hyperirritability are unknown. The existence of separate receptors for leukotrienes C4 and D4 (LTC4 and LTD4) has been demonstrated previously by physiologic and radioligand binding studies. The rank order of potency of the sulfidopeptide leukotrienes for contracting tracheal spirals [leukotriene E4 (LTE4) greater than LTD4 = LTC4] is different from that for contracting parenchymal strips (LTD4 greater than LTE4 greater than LTC4), thereby suggesting the existence of a separate receptor for LTE4. We now report that LTE4, the most stable of the leukotrienes comprising slow reacting substance of anaphylaxis, enhances the contractile response of guinea pig tracheal spirals but not of parenchymal strips to histamine in a time- and dose-dependent fashion. The ability of LTE4 to increase histamine responsiveness occurred after removal of the free agonist and recovery of the tissues to baseline tensions and was not produced by leukotrienes C4 and D4, which elicited the same magnitude of contraction of tracheal smooth muscle as LTE4. These findings suggest that LTE4-induced airway hyperirritability is not mediated by the contractile response per se and may be mediated through a receptor distinct from those for leukotrienes C4 and D4.

Leukotrienes and prostaglandins in asthma

Leukotrienes and prostaglandins possess properties which are central in the asthmatic reaction. They are bronchoconstrictors, they inhibit the mucociliary clearance, increase blood flow and permeability and thereby induce edema formation, and they attract and activate leukocytes. They are formed partly by allergic reactions and partly by a large number of other more non-specific reactions. Finally, the concentration of prostanoids has been found increased in the asthmatic reaction in vivo. The leukotrienes have not been traced in vivo in asthmatic attacks so far, but have been found in vivo in man in a specific type I allergic conjunctival reaction. Much evidence suggests that these mediators are relevant in asthmatic diseases, even though prostaglandin inhibitors have no effect in asthma. There still remains the need to investigate the influence on asthmatic diseases by as yet unavailable leukotriene blocking agents. Even though leukotrienes are judged today to be important mediators in asthma, it does not seem reasonable to expect that a single mediator is responsible for asthmatic diseases. Rather, it seems quite likely that asthma is caused by a complex interplay of a large number of mediators, circulating hormones, nervous mechanisms, receptor abnormalities, intracellular metabolic defects, etc. Despite this complexity, investigations in recent years have increased the knowledge of the biochemistry and human physiological effects of leukotrienes and prostaglandins which has created an improved understanding of the asthmatic reaction's pathophysiology, contributed a pharmacological rationale for previously used therapy, and stimulated new perspectives for specific pharmacological research.

Characterization of specific receptors for leukotriene D4 on human alveolar macrophages

Using 3H-leukotriene D4, a specific receptor assay has been developed for human alveolar macrophages, obtained by broncho-alveolar lavage of patients undergoing fiberoptic bronchoscopy because of suspected bronchial carcinoma. Lavage was performed in a carcinoma-free lobe of the lung and alveolar macrophages were subsequently isolated and incubated for binding studies. 3H-Leukotriene D4 was found to bind specifically with high affinity (Kd = 3.8 nM), in a saturable manner (Bmax = 90 fmol/10(6) cells), reversible and selective. Specific binding was linear with protein concentration and equilibrium binding at 4 degrees C was reached at 50 min. Scatchard and Hill analysis revealed a single class of binding sites with no cooperativity among the sites. Displacement studies with LTD4, the selective SRS-A antagonist FPL 55712 and with leukotriene C4 revealed respective Ki values of 3.4; 16; and 110 nM. The data suggest that human alveolar macrophages may contain a specific receptor type for LTD4, which has a relatively low affinity for LTC4, and are discussed in relation to modulatory processes in the lung, apart from direct actions of LTD4 on smooth muscle receptors. From the data here acquired, it may be apparent that the study of characteristics of receptors specific for a broncho-active substance like LTD4 on human alveolar macrophages, which play an important role in immuno-inflammatory processes seen in many chronic lung diseases, may yield major insights into the pathogenesis and therapy decisions involved in these diseases.

The bronchoconstrictor effect of inhaled prostaglandin D2 in normal and asthmatic men

Although prostaglandin D2 is the most abundant prostanoid generated by human lung mast cells and causes bronchoconstriction in animals, its effects have not been studied in human beings. We have compared the effects of inhaled prostaglandin D2 and prostaglandin F2 alpha on specific airway conductance in seven normal subjects and seven patients with mild allergic asthma. In dose-response studies in normal subjects, prostaglandin D2 caused a significant (20 +/- 6 per cent) fall in specific airway conductance after the two highest concentrations (250 and 500 micrograms per milliliter), whereas prostaglandin F2 alpha had no effect. In the asthmatic subjects, both prostaglandin D2 and prostaglandin F2 alpha caused a dose-related fall in specific airway conductance, starting at the lowest concentration of 4 micrograms per milliliter. Prostaglandin D2 was 3.5 times more potent than prostaglandin F2 alpha. In a single-dose study of both drugs (250 micrograms per milliliter), a minor fall in specific airway conductance occurred with prostaglandin D2 in the normal subjects, and a larger fall occurred with both drugs in the asthmatic subjects. Maximum effects were seen at three minutes: there was a 75 +/- 5 per cent fall with prostaglandin D2 and a 33 +/- 8 per cent fall with prostaglandin F2 alpha. These results suggest that prostaglandin D2 may be involved in the pathogenesis of bronchoconstriction in allergic asthma.

Comparative effects of inhaled leukotriene C4, leukotriene D4, and histamine in normal human subjects

The comparative actions of inhaled leukotriene C4 (LTC4), leukotriene D4 (LTD4), and histamine were studied in six normal subjects. LTC4 and LTD4 were shown to be more potent bronchoconstrictors than histamine, with a more sustained action. LTC4 and LTD4 caused wheezing without cough or throat irritation and were shown to act on large and small airways.

Sustained inhibition of antigen-induced histamine release from human lung by the beta 2-adrenoceptor agonist terbutaline

Antigen-induced histamine release from passively sensitized human lung tissue was inhibited in the presence of the beta 2-adrenoceptor agonist, terbutaline. A sustained and statistically significant suppression was detected in the concentration interval 3 X 10(-8)-1 X 10(-6) M. Fifty per cent inhibition IC50, was obtained at an interpolated concentration of 5.3 X 10(-8) +/- 0.4 X 10(-8) M (n = 13), when the histamine secretion was elicited with optimum concentration of antigen. Histamine release induced with a suboptimum concentration of antigen was inhibited to a greater extent than release initiated with optimum concentration. The data in the present investigation support the concept that terbutaline-induced inhibition of mediator release from human lung tissue can contribute to the clinical effectiveness of the drug during treatment of allergic asthma.

Leukotriene D4 elicits a non-sustained contraction of the guinea pig trachea in calcium-free buffer

The contraction of the isolated guinea pig trachea elicited by leukotriene D4 (LTD4) in Ca2+-free buffer (containing 10(-4) M EGTA) achieved a maximum at 6-8 min and relaxed back to baseline approximately 25 min after challenge with LTD4. In contrast, LTD4 elicited a sustained contraction in the presence of 1.8 mM calcium. This sustained contraction in the presence of calcium was reproduced upon repeated LTD4 challenge, whereas in Ca2+-free buffer, only one LTD4-induced contraction could be obtained. The amplitude of the LTD4-induced contraction in Ca2+-free buffer decreased in a time-dependent manner which was also dependent upon the concentration of LTD4. At 10(-7) and 10(-6) M LTD4, small contractions (11% and 20% of control, respectively) were measured after 30 min in Ca2+-free buffer, whereas 10(-8) M LTD4 elicited a contraction at 15 min but not after 30 min in Ca2+-free buffer. Whereas washing the trachea for 5 min with LaCl3 (1.8 mM) only partially suppressed the LTD4-induced contraction in the presence of calcium, the contraction elicited by LTD4 in Ca2+-free buffer was not affected by LaCl3. The LTD4-induced contraction in Ca2+-free buffer was not affected by verapamil (10(-6) M); in contrast, the putative intracellular calcium antagonist, TMB-8 (10(-4) M), blocked the LTD4-induced contraction. These results provide evidence that the release of an intracellular calcium store plays an important role in the initiation of the LTD4-induced contraction of the guinea pig trachea. In addition, these results suggest that an extracellular calcium source may account for a small part of the LTD4-induced contraction.

Identification of specific binding sites for leukotriene C4 in human fetal lung

Specific leukotriene C4 (LTC4)1 binding sites were identified in membrane preparations from human fetal lung. Specific binding of [3H]-LTC4 represented 95 percent of total binding, reached steady-state within 10 minutes and was rapidly reversible upon addition of excess unlabeled LTC4. Binding assays were performed at 4 degrees C under conditions which prevented metabolism of [3H]-LTC4 (80 mM serine-borate, 10 mM cysteine, 10 mM glycine). Under these conditions, greater than 95 percent of the membrane bound radioactivity, as analyzed by high performance liquid chromatography, co-eluted with the LTC4 standard. Computer-assisted analyses of saturation binding data showed a single class of binding sites with a dissociation constant (Kd) of 26 + 6 nM and a density (Bmax) of 84 + 18 pmol/mg protein. Pharmacological specificity was demonstrated by competition studies in which specific binding of [3H]-LTC4 was displaced by LTC4 and its structural analogs with inhibition constants (Ki) of 10 to 30 nM, whereas LTD4, diastereoisomers of LTD1, LTE4 and the end organ antagonist FPL 55712 were 150 to 700 fold less potent competitors than LTC4. These results provide evidence for specific, reversible, saturable, high affinity binding sites for [3H]-LTC4 in human fetal lung membranes.

Role of calcium in arachidonic acid-induced contractions of guinea pig airways

We have previously shown that arachidonic acid (AA)-induced contractions of indomethacin-pretreated guinea pig trachea and parenchyma are due to the synthesis of leukotrienes C4 and D4. The present experiments were designed to investigate the role of calcium (Ca2+) in the above. AA (66 microM)-induced contractions of trachea, but not parenchyma, were reduced in Ca2+-free Krebs-Henseleit solution ( KHS ). However the contractions of both trachea and parenchyma were abolished in Ca2+-free KHS with either lanthanum chloride (1 mM) or EDTA (300 microM). The Ca2+ antagonists, verapamil (100 microM), nitrendipine (100 microM), and TMB-8 (100 microM), reduced AA-induced contractions of both trachea and parenchyma. Re-addition of Ca2+ (2.2 mM) to trachea and parenchyma in Ca2+-free KHS in the presence of lanthanum restored the AA-induced contractions. This effect of Ca2+ was reduced by verapamil (100 microM) or nitrendipine (100 microM). LTC4-induced contractions of trachea and parenchyma were unaffected by nitrendipine (100 microM), whereas tracheal contractions were reduced in Ca2+-free KHS . Both tracheal and parenchymal contractions to LTC4 were reduced in Ca2+-free KHS in the presence of lanthanum chloride (1 mM). We conclude that superficially bound pools of Ca2+ are important in AA-induced contractions of the airways. Furthermore, nitrendipine reduces AA-induced contractions by inhibiting AA metabolism and not by inhibiting airway smooth muscle contraction induced by released leukotrienes.

Aspirin tolerance induced in aspirin-sensitive asthmatics

Twenty-nine patients with asthma and aspirin-sensitivity were studied in an attempt to induce tolerance to aspirin (ASA). Starting with the smallest ASA doses eliciting bronchial obstruction (threshold doses) we doubled the doses on subsequent days and finally achieved good tolerance of 600 mg ASA per day in 27 patients. It was more difficult to achieve tolerance in patients with low ASA-thresholds than in patients with high ones. Daily ASA administration led to prolongation of the refractory state but when the intervals between consecutive doses were increased, aspirin hypersensitivity recurred. The pause sufficient for a recurrence of sensitivity to ASA was measured in 16 patients and ranged from 24 h to 9 days. Twelve patients challenged with indomethacin after ASA-desensitisation showed good drug tolerance.

Pharmacological profile of AA-861, a 5-lipoxygenase inhibitor

AA-861, a selective 5-lipoxygenase inhibitor, suppressed A23187-induced formations of 5-HETE and LTB4 in rat peritoneal macrophages. Immunologically-stimulated generation of SRS-A was also inhibited in guinea pig lung and rat peritoneal cavity. AA-861 had no effects on histamine release from rat mast cells or passive cutaneous anaphylaxis in rats. Essentially no antagonistic activity to LTD4 or histamine was observed. This compound exerted an obvious inhibition of allergic bronchoconstriction in guinea pigs and a moderate reduction of carrageenin-induced paw edema and pleurisy in rats. These findings suggest that SRS-A plays an important role in asthmatic and inflammatory reactions.

The extraction of leukotrienes (LTC4, LTD4, and LTE4) from tissue fluids: the metabolism of these mediators during IgE-dependent hypersensitivity reactions in lung

The metabolites of arachidonic acid known as the leukotrienes are a class of lipid mediators which have potent and diverse biological effects in pulmonary tissue. Leukotrienes C, D, and E (LTC4, LTD4, and LTE4) are known to be principal mediators of immunoglobulin E (IgE)-mediated hypersensitivity reactions in lung tissue. It is therefore important to develop reliable and quantitative isolation techniques for estimating levels of these mediators in tissue. In this study, LTC4, LTD4, and LTE4 were separated from other arachidonate metabolites by organic extraction procedures. 5-Hydroxyeicosatetraeonic acid and leukotriene B4 extract efficiently into the organic layer of aqueous:ether or aqueous:chloroform extractions, whereas arachidonate metabolites containing conjugated peptides (e.g., LTC4, LTD4, and LTE4) failed to extract into these organic solvents. An extraction step was therefore developed that affords quantitative extraction of LTC4, LTD4, and LTE4 into the organic phase of an isopropanol:ether:H2O mixture. This step is the key for a two-step extraction method that isolates histamine, LTC4, LTD4, and LTE4 with a recovery of 100, 85, 75, and 57%, respectively. One advantage of this separation procedure for obtaining these mediators by organic extraction is an ability to expediently process many samples. Furthermore, the leukotriene content of extracted samples can be analyzed using the guinea pig ileum bioassay without interference from vasoamines or platelet-activating factor. These later substances are eliminated from leukotriene-enriched fractions by this extraction process. When histamine and LTC4 were added to supernatant fluids recovered from isolated lung tissue, they were quantitatively recovered using this extraction method.(ABSTRACT TRUNCATED AT 250 WORDS)