Suppression of eosinophil function by RP 73401, a potent and selective inhibitor of cyclic AMP‐specific phosphodiesterase: comparison with rolipram

1. We have investigated the inhibitory potency of RP 73401, a novel, highly selective and potent inhibitor of cyclic AMP-specific phosphodiesterase (PDE IV), against partially-purified PDE isoenzymes from smooth muscle and the particulate PDE IV from guinea-pig eosinophils. The inhibitory effects of RP 73401 on the generation of superoxide (.O2-), major basic protein (MBP) and eosinophil cationic protein (ECP) from guinea-pig eosinophils have also been studied. 2. RP 73401 potently inhibited partially-purified cyclic AMP-specific phosphodiesterase (PDE IV) from pig aortic smooth muscle (IC50 = 1.2 nM); it was similarly potent against the particulate PDE IV from guinea-pig peritoneal eosinophils (IC50 = 0.7 nM). It displayed at least a 19000 fold selectivity for PDE IV compared to its potencies against other PDE isoenzymes. Rolipram was approximately 2600 fold less potent than RP 73401 against pig aortic smooth muscle PDE IV (IC50 = 3162 nM) and about 250 times less potent against eosinophil PDE IV (IC50 = 186 nM). 3. Solubilization of the eosinophil particulate PDE IV increased the potency of rolipram 10 fold but did not markedly affect the potency of RP 73401. A similar (10 fold) increase in the PDE IV inhibitory potency of rolipram, but not RP 73401, was observed when eosinophil membranes were exposed to vanadate/glutathione complex (V/GSH). 4. Reverse transcription polymerase chain reaction (RT-PCR), using primer pairs designed against specific sequences in four distinct rat PDE IV subtype cDNA clones (PDE IVA-D), showed only mRNA for PDE IVD in guinea-pig eosinophils. PDE IVD was also the predominant subtype expressed in pig aortic smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)