A new long-acting β2-agonist, formoterol, has been reported to have a greater efficacy and duration of action in asthmatic patients as compared to conventional β2-agonists. We recently demonstrated that formoterol inhibited antigen-induced late asthmatic response (LAR) and accompanying airway eosinophilia in guinea pigs. In this study, we investigated the direct effect of formoterol in vitro on human eosinophil function, focusing on platelet-activating factor (PAF)-induced eosinophil chemotaxis and eosinophil cationic protein (ECP) release. Purified normodense eosinophils were separated by discontinuous gradient from 12 mild asthmatic patients. Formoterol in concentrations of 1-100 μM significantly inhibited PAF-induced eosinophil chemotaxis in a dose-dependent manner with a concentration of drug required to produce 50 inhibition (IC50) of 10.16 μM; inhibition: 22.9 ± 13.0 (1 μM), 51.6 ± 12.7 (10 μM), 75.0 ± 11.3 (100 μM). When formyl-methionyl-leucyl-phenylamine (FMLP) was used as a chemoattractant, a similar inhibition of eosinophil chemotaxis by formoterol was observed; inhibition: 13.1 ± 5.0 (1 μM). 47.7 ± 7.6 (10 μM), 65.5 ± 16.5 (100 μM). A conventional β2-agonist, salbutamol, at doses to 100 μM did not show any inhibitory effects on PAF-induced eosinophil chemotaxis. Formoterol in concentrations of 1–100 μM also significantly inhibited PAF-induced ECP release from eosinophils; inhibition: 21.7 ± 9.0 (1 μM), 39.3 ± 7.4 (10 μM), 39.6 ± 8.4 (100 μM). In the presence of phosphodiesterase inhibitors, theophylline or isobutylmethyl xanthine (IBMX), the inhibition by formoterol on PAF-induced ECP release was enhanced. The combination of formoterol (10 μM) and IBMX (10 μM) achieved 70.3 ± 7.6 inhibition. Salbutamol in concentrations of 0.1–100 μM failed to inhibit PAF-induced ECP release. The inhibition of PAF-induced eosinophil chemotaxis and ECP release by formoterol were not abolished by propranolol. This comparison between formoterol and salbutamol suggestes that formoterol is not only a longer-acting β2-agonist but may have more beneficial properties to prevent eosinophil-mediated inflammatory processes of LAR than co
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