Abstract
The effect of flosequinan and its sulphone metabolite BTS 53 554, on phosphodiesterase isoenzymes isolated from guinea-pig cardiac and vascular smooth using DEAE-cellulose chromatography was investigated. Zaprinast and milrinone showed peak I and peak III selectivity, and IBMX non-selective activity, against both cardiac and vascular smooth muscle isoenzymes, as expected for these reference inhibitors. Flosequinan and BTS53 554 demonstrated non-selective inhibition with similar potency against both cardiac and vascular smooth muscle isoenzymes and, overall, were the least potent compounds tested. The high inhibitory concentrations observed (IC 50 peak III 660 μM for cardiac tissue and 230 μM for vascular smooth muscle with flosequinan) relative to its clinically effective plasma concentration (10 μM) questions the relevance of phosphodiesterase inhibition to the efficacy of flosequinan in heart failure.
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