bwa-4c and Asthma

In conclusion, an effective modulator of the AA cascade for the treatment of asthma and other inflammatory diseases may require 5-LO inhibitory activity as well as LTD4 antagonism in order to limit the effects of LTB4, LTD4, and 5-HPETE. The unknown role of LTC4 with respect to bronchoconstriction and mucus production could mask the efficacy of a pure LTD4 antagonist in man, whereas the chemotactic property of LTB4 for eosinophils can contribute to lung inflammation. Indeed, it is observed that the blood of patients with bronchial asthma has increased numbers of hypodense eosinophils. In addition, the formation of lipid-derived peroxide radicals, such as 5-HPETE, are believed to be responsible for various types of cellular injuries associated with the inflammatory disease process. Because inhibition of the CO pathway is thought to explain the therapeutic effects of nonsteroidal antiinflammatory agents in rheumatic diseases, a 5-LO inhibitor with CO inhibitory activity may also be desirable profile for an antiasthma agent. The validation of the LT hypothesis of disease had to wait for the demonstration of a clinical effect by either a LTD4 receptor antagonist or a LT synthesis inhibitor (5-LO inhibitor). Only very recently has this evidence become available and it is now apparent that compounds that antagonize LTD4 receptors or inhibit LT synthesis have shown clinical efficacy in a wide range of diseases. Due to the breakthrough nature of this approach, certain of these compounds are being considered for expedited development. The absence of side effects seen in the clinical trials of selective 5-LO inhibitors is gratifying and argues that LTs are not important in homeostasis. Only time will tell whether 5-LO inhibitors will take their place in the therapeutic armamentarium; however, the recent demonstration of clinical efficacy by a number of these compounds is a significant step in this direction.

Topics: Animals; Arachidonate 5-Lipoxygenase; Asthma; Eosinophils; Humans; Inflammation; Leukotriene Antagonists; Lipoxygenase Inhibitors; Lung Diseases; Neutrophils; Quinolines

Eosinophilia is a feature of airway inflammation associated with asthma. Leukotriene antagonists provide therapeutic benefit in asthma, but their potential antiinflammatory actions have not been fully explored. We have examined the role of eosinophil-derived cysteinyl leukotrienes in the maintenance of eosinophil survival, and the involvement of leukotrienes in the paracrine stimulation of eosinophil survival by mast cells and lymphocytes. We obtained eosinophils and autologous lymphocytes from peripheral blood of asthmatic subjects. Leukotriene (LT)-B(4), LTC(4) and LTD(4), granulocyte-macrophage colony-stimulating factor (GM-CSF), and fibronectin promoted eosinophil survival. LTD(4) (10(-)(6) M) was as effective as GM-CSF (5 ng/ml) and fibronectin (400 ng/ml) in promoting survival. Lymphocytes and conditioned medium from a human mast cell line (HMC-1) induced eosinophil survival. Blockade of cysteinyl leukotriene receptors with SKF 104353 (pobilukast, 3 nM), and inhibition of 5-lipoxygenase (5-LO) with BW A4C (1 microM) and of 5-LO activating protein with MK 886 (1 microM), all increased basal rates of eosinophil apoptosis and reversed GM-CSF-induced eosinophil survival. Fifty percent reversal of GM-CSF- induced survival was achieved with SKF 104353 at 0.3 nM. The potency of SKF 104353 was two orders of magnitude greater than that of the LTB(4) receptor antagonist SB 201146. Mast cell- and lymphocyte-induced eosinophil survival were completely reversed by SB 201146, SKF 104353, BW A4C, and MK 886. These findings provide evidence for the involvement of an autocrine cysteinyl leukotriene pathway that supports eosinophil survival in response to a range of survival stimuli. They also suggest that LTB(4) could act as a paracrine stimulus of eosinophil survival.

Topics: Acrylates; Adult; Aged; Apoptosis; Asthma; Benzeneacetamides; Bronchial Hyperreactivity; Cell Survival; Culture Media, Conditioned; Dicarboxylic Acids; Eosinophils; Female; Fibronectins; Granulocyte-Macrophage Colony-Stimulating Factor; Humans; Hydroxamic Acids; Indoles; Leukotriene Antagonists; Leukotrienes; Lymphocytes; Male; Mast Cells; Middle Aged; Pyridines; Respiratory Hypersensitivity

Arachidonic acid (AA) liberation and metabolism via cyclo-oxygenase or lipoxygenases may be an important regulatory pathway for mitogenic signalling in human cultured airway smooth muscle (ASM) cells. In cytokine-treated cells, thrombin markedly enhances production of the anti-mitogenic arachidonic acid metabolite, PGE(2). In this study, in the absence of cytokines, we examined the role of endogenous AA metabolism in thrombin-stimulated ASM DNA synthesis. Selective inhibitors of cyclo-oxygenase of 5-lipoxygenase metabolism had no significant effect on 0.3 U/ml thrombin-stimulated DNA synthesis. However, the non-selective, redox-active lipoxygenase inhibitors NDGA and BWA4C inhibited thrombin-stimulated DNA synthesis. Under basal conditions, and following stimulation by thrombin, the levels of the AA metabolites PGE(2), TxA(2), and LTC(4), remained below assay detection limits. Exogenous addition of AA, LTD(4), or 5-, 12-, and 15-HETE and HpETE metabolites had no consistent or substantial stimulatory effect on either basal or thrombin-stimulated DNA synthesis. These data suggest that the non-selective lipoxygenase inhibitors influence DNA synthesis via effects unrelated to lipoxygenase inhibition. The lack of detection of AA metabolites, the lack of influence of selective antagonists/inhibitors of the AA pathway, and the failure of selected AA metabolites to either enhance or directly stimulate DNA synthesis suggest that in the absence of cytokines, cyclo-oxygenase and lipoxygenase metabolism has little role in signalling of human ASM DNA synthesis by thrombin.

Topics: Arachidonate 5-Lipoxygenase; Arachidonic Acid; Asthma; Benzeneacetamides; Bronchi; Cells, Cultured; Cyclooxygenase Inhibitors; DNA; Humans; Hydroxamic Acids; Lipoxygenase Inhibitors; Masoprocol; Muscle, Smooth; Prostaglandin-Endoperoxide Synthases; Radioimmunoassay; Thrombin

Inhibition of 5-lipoxygenase (5-LO) is a potential target for therapeutic intervention in asthma. Acetohydroxamic acids such as BW A4C are potent and selective 5-LO inhibitors in vitro and also inhibit 5-LO activity in vivo following oral administration. In man, BW A4C is metabolised relatively rapidly (t1/2 = approx. 2h) but nevertheless inhibits 5-LO with reasonable persistence. Chemical modification of BW A4C has resulted in compounds, including the alpha-methyl analogues BW B218C and BW A360C and the hydroxyurea BW B70C, that retain high in vitro potency as selective 5-LO inhibitors and, compared to BW A4C, have a higher potency and longer duration of action in vivo. Members of both the hydroxamic acid and hydroxyurea series of 5-LO inhibitors are presently being considered as potential anti-asthma drugs.

Topics: Anaphylaxis; Animals; Asthma; Benzeneacetamides; Bronchial Diseases; Guinea Pigs; Humans; Hydroxamic Acids; Hydroxyurea; Lipoxygenase Inhibitors

The generation and metabolism of leukotrienes (LTs) B4, C4, D4, and E4 were studied in vitro in the A23187-stimulated whole blood of normal (N) and atopic asthmatic (AA) human subjects. Using a combination of reversed-phase high performance liquid chromatography and radioimmunoassay, we have demonstrated that the blood cells of atopic asthmatic patients have an enhanced ability to release LTB4 and LTC4 when compared to those of normal subjects. The release of LTB4 and LTC4 in response to ionophore is dose- and time-dependent. Half-maximal doses of ionophore caused the generation of high, sustained levels of LTB4, which are significantly higher in the AA blood than in N blood. Incubations of 3H-LTB4 in ionophore-stimulated N and AA blood revealed a slow metabolism to 20-OH-LTB4 and 20-COOH-LTB4. LTC4 is generated in smaller amounts than LTB4, with an early peak after 10 min which is significantly higher (p less than 0.01) in the AA blood compared to the N blood. Subsequent metabolism of LTC4 elicits significantly greater amounts of LTD4, and consistently higher levels of LTE4, in the AA blood. Parallel incubations of 3H-LTC4 in ionophore-stimulated N and AA blood demonstrated rapid metabolism of LTC4 by the glutathione detoxification pathway. The elevated production of LTB4 and LTC4 in AA blood was not accounted for by differences in leukocyte sub-type counts in the two groups, nor by differences in their rates of catabolism. The novel, selective 5-lipoxygenase inhibitor BW A4C [N-(3-phenoxycinnamyl) acetohydroxamic acid] caused dose-dependent inhibition of LTB4 and LTC4 generation and was equipotent in N and AA blood.

Topics: Asthma; Benzeneacetamides; Calcimycin; Chromatography, High Pressure Liquid; Female; Humans; Hydroxamic Acids; In Vitro Techniques; Leukocyte Count; Leukotriene B4; Leukotrienes; Lipoxygenase Inhibitors; Male; Radioimmunoassay; Reference Values