Experimental Studies on Guanosine 3’,5’-Cyclic Monophosphate Levels and Airway Responsiveness of the Novel Phosphodiesterase Type 5 Inhibitor

Abstract

The effect of 1-cyclopentyl-3-ethyl-6-(3-ethoxypyrid-4-yl)-1H-pyrazolo [3,4-d]pyrimidin-4-one (SR 265579), a potent inhibitor of guanosine 3',5'-cyclic monophosphate (cyclic GMP) phosphodiesterase (PDE5), was examined regarding its specificity toward the other cyclic nucleotide phosphodiesterases, the effect on cyclic nucleotide levels and the bronchodilatory activity, both in vitro and in vivo in guinea-pigs. The effects were compared to those obtained with zaprinast (CAS 37762-06-4), a known PDE5 inhibitor. Anion-exchange chromatography of the soluble fraction of guinea-pig homogenates revealed 5 peaks which corresponded to PDE1, PDE2, PDE3, PDE4 and PDE5. SR 265579 produced a potent and competitive inhibition, with respect to cyclic GMP, of PDE5 with a Ki of 6.4 nmol/l. The compound was 25 fold more potent than zaprinast and demonstrated selectivity toward PDE5. The selectivity index was 14 and 33 with respect to PDE4 and 3, respectively. PDE1 and 2 were only inhibited at considerably higher concentrations. SR 265579 specifically increased the intracellular cyclic GMP levels in guinea-pig tracheal epithelial cells (EC 50 = 117 nmol/l). Moreover, in the guinea pig, plasma cyclic GMP levels were significantly increased after the intravenous or oral administration of doses as low as 1 mg/kg. Isolated guinea-pig trachea were relaxed by the addition of SR 265579 as evaluated by measuring either spontaneous tone or relaxation of histamine and acetylcholine-precontracted preparations. PD 2 values were of 7.64, 6.52 and 5.25, respectively. In vivo, after i.v. administration, bronchodilatory activity was demonstrated in an artificially-ventilated guinea-pig histamine-induced bronchospasm model with an ED 50 of 0.63 mg/ kg. In all experiments, SR-265579 was proved to be more active than zaprinast. These results demonstrate that SR 265579 is an orally active, potent and specific inhibitor of PDE5.

Biochanin A, a Phytoestrogenic Isoflavone with Selective Inhibition of Phosphodiesterase 4, Suppresses Ovalbumin‐Induced Airway Hyperresponsiveness

“…It is now known that PDEs comprise at least 11 distinct enzyme families hydrolyzing cAMP and/or cGMP [ 7 ]. PDE1~5 isozymes, which are calcium/calmodulin-dependent (PDE1), cGMP-stimulated (PDE2), cGMP-inhibited (PDE3), cAMP-specific (PDE4), and cGMP-specific (PDE5) were found to be present in the canine trachea [ 8 ], guinea pig lung [ 9 ], and human bronchi [ 10 ]. PDE3 and PDE4 were identified in the guinea pig airway [ 11 ], but other isozymes might also be present.…”

New Avenues for Phosphodiesterase Inhibitors in Asthma

“…[8][9][10] Roflumilast was found unable to exert any effect on the acute phase response (bronchoconstriction), but it reduced the late phase asthmatic response and prevented the subsequent increase in bronchial reactivity following an allergen challenge. 33 Furthermore, it consistently improved lung function of asthmatic patients when combined with ICS or montelukast. 42 A series of PDE4 inhibitors, such as cilomilast, revamilast, MEM 1414 and BLX-028914, reached the clinical stage in asthma, but their development was abandoned.…”

Hesperidin-3′-O-Methylether Is More Potent than Hesperidin in Phosphodiesterase Inhibition and Suppression of Ovalbumin-Induced Airway Hyperresponsiveness

“…It is now known that phosphodiesterases (PDEs) comprise at least 11 distinct enzyme families that hydrolyze adenosine 3′,5′ cyclic monophosphate (cAMP) and/or guanosine 3′,5′ cyclic monophosphate (cGMP) [ 1 ]. PDE1 ∼ 5 isozymes, which are calcium/calmodulin dependent (PDE1), cGMP stimulated (PDE2), cGMP inhibited (PDE3), cAMP specific (PDE4), and cGMP specific (PDE5), were found to be present in the canine trachea [ 2 ], guinea pig lungs [ 3 ], and human bronchi [ 4 ]. PDE3 and PDE4 were identified in the guinea pig airway [ 5 ], but other isozymes might also be present.…”