Leukotriene antagonists and inhibitors of leukotriene biosynthesis as potential therapeutic agents

In vitro susceptibility of Helicobacter pylori to protolichesterinic acid from the lichen Cetraria islandica

With reference to the traditional use of Cetraria islandica (Iceland moss) for relief of gastric and duodenal ulcer, plant extracts were screened for in vitro activity against Helicobacter pylori. (+)-Protolichesterinic acid, an aliphatic alpha-methylene-gamma-lactone, was identified as an active component. The MIC range of protolichesterinic acid, in free as well as salt form, was 16 to 64 micrograms/ml.

Involvement of leukotrienes in allergic pleurisy in actively sensitized rats: inhibition by the lipoxygenase inhibitor T-0757 of the increase in vascular permeability and leukotriene E4 production

The relative contributions of inflammatory mediators to the increase in vascular permeability in antigen-induced pleurisy were examined in rats actively sensitized with ovalbumin. The effects of various inhibitors were assessed on the exudate volume and plasma exudation rate in the pleural cavity. Two peaks were observed in plasma exudation rate at 0.5 and 3 h after antigen challenge. At 0.5 h, there was a marked decrease in the histamine content of the pleural cells and also a sharp increase in the LTE4 level in the exudate, which was inhibited dose-dependently by the lipoxygenase inhibitor T-0757. Indomethacin and cyproheptadine both depressed exudate volume and exudation rate, whereas T-0757 only reduced the exudation rate. At 3 h, a substantial LTE4 concentration was still detected in the exudate, and the exudation rate was depressed by T-0757 and indomethacin, but not by cyproheptadine. These results suggest that histamine is involved mainly in the early phase, and leukotrienes predominantly contribute to the later phase of exudation. Prostaglandins appear to be involved in both phases. Allergic pleurisy of rats, therefore, may be a suitable model to examine the roles of these inflammatory mediators.

Effect of a 5-lipoxygenase inhibitor, ZM 230487, on cutaneous allergic inflammation in the guinea-pig

1. Leukotrienes have potent biological effects in vitro and in vivo and are found in tissue and in biological fluids in various pathological conditions including allergic diseases. Leukotriene B4 (LTB4) is a potent stimulus for eosinophil accumulation and activation and there is much interest in determining its importance in mediating the accumulation of eosinophils at sites of allergic inflammation in vivo. In this study, we investigated the effects of a potent 5-lipoxygenase inhibitor, ZM 230487, on the accumulation of eosinophils and on local oedema formation in cutaneous inflammation in the guinea-pig. 2. The i.d. injection of increasing concentrations of arachidonic acid (AA) led to a dose-dependent accumulation of 111In-eosinophils but oedema formation was only significant at the top dose of AA tested (3 x 10(-8) mol per site). Co-injection of ZM 230487 with AA inhibited 111In-eosinophil accumulation up to 99% but the small oedema response to AA was only partially inhibited. AA-induced oedema formation was only effectively inhibited when a combination of a PAF antagonist, an antihistamine and ZM 230487 was used. 3. Local administration of the cyclo-oxygenase inhibitor, ibuprofen, partially inhibited AA-induced oedema formation suggesting that vasodilator prostaglandins may be released following i.d. injection of AA. AA-induced 111In-eosinophil accumulation was also partially inhibited by ibuprofen. 4. PAF-induced 111In-eosinophil accumulation was partially suppressed by local administration of ZM 230487. In contrast, LTB4-induced 111In-eosinophil accumulation was enhanced by ZM 230487. These data suggest that locally-released leukotrienes may modulate mediator-induced eosinophil accumulation. ZM 230487 had no effect on PAF- or LTB4-induced oedema formation. 5. ZM230487 significantly inhibited the accumulation of 111 In-eosinophils, but did not affect local oedema formation, in a passive cutaneous anaphylaxis (PCA) reaction. However, the PAF antagonist WEB 2086 either alone or in combination with ZM 230487 had no effect on "'In-eosinophil accumulation or oedema formation in the PCA reaction.6. In conclusion, it appears that a product of 5-lipoxygenase, probably LTB4, is important for the accumulation of "'In-eosinophils, but not local oedema formation, in the PCA reaction in guinea-pigskin. These data support a major role for LTB4 in allergic inflammation in the guinea-pig and make this animal (and the PCA model) suitable for studying the effects of inhibitors of leukotriene synthesis or action in vivo.

Effect of BW B70C, a novel inhibitor of arachidonic acid 5-lipoxygenase, on allergen-induced bronchoconstriction and late-phase lung eosinophil accumulation in sensitised guinea-pigs

The actions of BW B70C, an orally available, biologically persistent and selective inhibitor of arachidonic acid 5-lipoxygenase, have been examined in two systems of anaphylaxis in actively sensitised guinea-pigs in vivo. In anaesthetised, artificially ventilated animals pretreated with mepyramine and indomethacin to leave only the "peptidoleukotriene-dependent" component (leukotrienes C4, D4 and E4) of the anaphylactic response, direct inhalation of nebulised allergen resulted in a slowly developing bronchoconstriction which was prevented in a dose-dependent manner by BW B70C (2-50 mg/kg p.o.) administered 1 or 6 h before challenge. In conscious animals fasted overnight and then pretreated with mepyramine to prevent death due to acute bronchial anaphylaxis, exposure to nebulised allergen produced slight respiratory symptoms. When blood and lung samples were analysed 4-48 h after allergen provocation a sustained leukocytosis and pulmonary eosinophil accumulation were observed. In contrast, in food-replete conscious animals, the early respiratory symptoms were still observed upon allergen inhalation, but no significant blood leukocytosis or accumulation of eosinophils in the lungs occurred subsequently. The eosinophil influx induced by allergen in fasted animals was assessed both by histological examination and determination of tissue peroxidase content, two measures which demonstrated reasonable agreement. Administration of a single dose of BW B70C (10 mg/kg p.o.) 1 h prior to allergen challenge did not affect the subsequent eosinophil infiltration 24 h later, but 20 mg/kg given in divided doses (-1 and +12 h) produced 67% inhibition of cell accumulation. A single dose of 50 mg/kg (-1 h) had a similar effect (78% inhibition). The potent glucocorticosteroid betamethasone was used as a reference compound, and 4 mg/kg given as a divided dose (-1 and +7) fully inhibited lung inflammation assessed 24 h after provocation with allergen. BW B70C inhibited both acute and allergic bronchoconstriction and late-phase eosinophil accumulation subsequent to allergen inhalation in guinea-pigs. In view of the apparent requirement for sustained plasma levels of BW B70C in order to prevent late-phase eosinophil recruitment to the lung after a single challenge with allergen, it is unclear whether inhibition of 5-lipoxygenase underlies the observed anti-eosinophil accumulation effects of the compound, but the anti-bronchoconstrictor effects are consistent with the known inhibitory activity of BW B70C against 5-lipoxygenase.

Pre-clinical pharmacology of ICI D2138, a potent orally-active non-redox inhibitor of 5-lipoxygenase

1. This paper describes the pre-clinical pharmacology of ICI D2138, a potent orally-active non-redox inhibitor of 5-lipoxygenase which is undergoing clinical evaluation. 2. ICI D2138 potently inhibited leukotriene synthesis in murine peritoneal macrophages (IC50 = 3 nM) and human blood (IC50 = 20 nM). In human and dog blood, ICI D2138 did not inhibit thromboxane B2 synthesis at a concentration of 500 microM, thus the selectivity ratio (cyclo-oxygenase: 5-lipoxygenase) was greater than 20,000. In contrast, zileuton (a 5-lipoxygenase inhibitor also undergoing clinical evaluation) exhibited a selectivity ratio of 15-100. 3. ICI D2138 potently and dose-dependently inhibited ex vivo leukotriene B4 (LTB4) synthesis by rat blood with ED50 values of 0.9, 4.0 and 80.0 mg kg-1 p.o. at 3, 10 and 20 h respectively after dosing. Similar activity was observed for inhibition of LTB4 production in a zymosan-inflamed rat air pouch model. Zileuton produced ED50 values of 5 and 20 mg kg-1 at 3 and 10 h respectively. 4. Oral administration of 1, 3 or 10 mg kg-1 ICI D2138 to dogs produced maximal inhibition of ex vivo LTB4 synthesis by blood for 5, 9 and 31 h respectively. A dose of 5 mg kg-1 p.o. of zileuton caused maximal inhibition of LTB4 for 24 h. 5. Oral administration of 10 mg kg-1 ICI D2138 caused total inhibition of LTB4 production in zymosan-inflamed rabbit knee joint. 6. Topical administration of ICI D2138 to rabbit skin caused a dose-related inhibition of arachidonic acid-induced plasma extravasation with an ID30 of 1.08 nmol per site. Zileuton was approximately 40 times less potent.7. Oral anti-inflammatory activity was assessed in an arachidonic acid-induced mouse ear oedema model in animals treated with indomethacin to block pro-inflammatory prostanoids. ICI D2138, given orally, caused dose-dependent inhibition of oedema with an approximate ID50 of 1.8 mg kg'. Zileuton was approximately 10 times less potent.8. ICI D2138 caused a dose-dependent inhibition of antigen-induced broncho-constriction in guineapigs with an approximate ID50 of 0.1 mg kg-', i.v. Zileuton was approximately 10 times less potent.9. In view of the pharmacological profile described here, ICI D2138 has the potential to provide improved clinical efficacy compared to existing lipoxygenase inhibitors such as zileuton.