Antiallergic compounds

REV 2871 (CHBZ): a potent antiallergic agent with a novel mechanism of action. I. Activity profile as an inhibitor of mediator release

REV 2871 (CHBZ) and its putative metabolite REV 3579-Z (also designated in the literature as RHC 3579-Z) were shown to be potent and orally effective inhibitors of passive cutaneous anaphylaxis (PCA) in the rat (ED50 = 12 mg/kg). The activity profiles of CHBZ, REV 3579-Z and disodium cromoglycate (DSCG) were compared as inhibitors of histamine release (HR) in vitro from rat mast cells, human basophils, and guinea pig lung slices. CHBZ was a potent inhibitor of both immunologic and non-immunologic HR (I50 2-20 microM from rat mast cells). The activity profile of CHBZ as an inhibitor of HR from rat mast cells differed from that of DSCG and REV 3579-Z in the following respects: increasing inhibition of HR with increasing preincubation time; irreversibility of the inhibition; lack of tachyphylaxis and cross-tachyphylaxis to DSCG; potentiation of the inhibition of antigen-induced release of histamine (AIR) by DSCG; and inhibition of HR induced by dextran + phosphatidyl serine, compound 48/80, ionophore A23187 and platelet activating factor (PAF). In the human basophil model, CHBZ was: a potent inhibitor (I50 = 25 microM) of anti-IgE-induced release (AbIR), whereas DSCG and REV 3579-Z had no effect on AbIR; more potent as an inhibitor of AbIR than ionophore-induced release, whereas the reverse was true for proxicromil; an inhibitor of PAF-induced release, whereas proximcromil stimulated it; and potentiative with proxicromil for inhibition of AbIR. In the guinea pig lung slice model, CHBZ inhibited AIR (I50 = 800 microM) whereas DSCG and REV 3579-Z did not (I50 greater than 300 microM). We conclude that CHBZ is an orally effective antiallergic agent whose mechanism of action as an inhibitor of mediator release is different from DSCG and proxicromil.

Modification of bronchial hyperreactivity after treatment with sodium cromoglycate during pollen season

Repeated bronchial histamine challenges before, during, and after the birch pollen season were performed in 22 allergic patients with bronchial hyperreactivity (BHR) treated for 6 wk with sodium cromoglycate (SCG), 20 mg, four times a day, or placebo in a double-blind, randomized group comparison. Clinical assessments of the asthmatic symptom score and peak expiratory flow revealed less symptoms and less use of bronchodilators in the SCG group. Responsiveness to histamine was significantly increased in the placebo group after 14 days with high pollen counts. After the season there was an immediate return to preseasonal value. There was no change in responsiveness in the SCG group, demonstrating significant protection against pollen-induced increase of BHR. The results support the hypothesis that inhibition of mediator release, which is demonstrated for SCG, leads to a reduction of the nonspecific BHR.

Bronchial hyperreactivity after treatment with sodium cromoglycate in atopic asthmatic patients not exposed to relevant allergens

The bronchial hyperreactivity, measured as the responsiveness to histamine, was studied in 14 atopic patients before, during, and after 4 wk of treatment with sodium cromoglycate (SCG) and placebo in a double-blind, randomized, crossover study. The patients were not exposed to relevant allergens during the study. The variations in provocation concentrations corresponding to 20% decrease in FEV1 (PC20) were small during both placebo and active drug treatment. After SCG treatment, PC20 increased (less responsiveness) in nine of the 14 patients, especially in those with low PC20 values. The difference between placebo and active drug treatment was not statistically significant. Although SCG has a mediator-inhibiting effect, this study gave no support for the assumption that inhibition of mediator release leads to a reduction of the bronchial hyperreactivity in atopic asthmatic subjects who are not exposed to relevant allergens.

Nedocromil sodium: a new drug for the management of bronchial asthma

Nedocromil sodium (FPL 59002) is a pyranoquinoline dicarboxylic acid that has been developed for the management of bronchial asthma. We report the results of a double blind group comparative trial in which the disodium salt of nedocromil delivered by pressurised aerosol and a placebo were compared in the management of patients with a diagnosis of bronchial asthma who entered the double blind period on a minimum dose of beclomethasone dipropionate. In almost all the assessments of clinical activity nedocromil sodium was shown to be more effective than placebo. These include improvements in diary card symptom scores, reduction in concomitant use of a bronchodilator aerosol, and patients' and investigators' assessments of efficacy. Unwanted effects were few and mild. No patients were withdrawn from the trial.

Characterization of various antiallergic agents using a new method for inducing systemic anaphylaxis in the rat

Five different types of antiallergic agents were studied using a newly developed method for inducing IgE-mediated bronchial and cardiovascular anaphylaxis in the rat. With the exception of the histamine H1 antagonist mepyramine (no activity at all), each antiallergic tested showed a different and characteristic profile of antiallergic activity. Prednisolone and the SRS-A antagonist FPL 55712 protected the rats completely against mortality, whereas cromoglycate and ketotifen offered only partial protection. The cardiovascular events were favorably influenced by FPL 55712 and cromoglycate, but ketotifen was completely ineffective in this respect. However, ketotifen showed the highest activity in suppressing the antigen-induced bronchoconstriction, followed by cromoglycate and prednisolone, whereas FPL 55712 was practically inactive. It can be concluded that the antiallergic activity of various types of antiallergics can be characterized and differentiated by means of this highly reproducible method.