The cyclic nucleotide second messenger guanosine 3’5’-cyclic monophosphate (cGMP) is an important mediator of signal transduction and hence a wide range of cellular processes. It can be generated by soluble guanylyl cyclase in response to binding of nitric oxide and degraded via members of the phosphodiesterase (PDE) protein family. Zaprinast, the compound from which sildenafil (Viagra™) was developed, is a cGMP-specific phosphodiesterase inhibitor. It moderately inhibits PDE5 and PDE6 with IC₅₀ values of 0.5-0.76 and 0.15 µM, respectively, and weakly inhibits PDE9, PDE10, and PDE11 with IC₅₀ values of 35, 22, and 11-33 µM, respectively.^1,2 Zaprinast therefore enhances the vasodilatory effects of nitric oxide in a range of vascular tissues by prolonging the cGMP-mediated activation of cGMP-dependent protein kinase.² Zaprinast also activates both the rat and human G protein-coupled receptor, GPR35 with EC₅₀ values of 16 nM and 0.84 µM, respectively.³

1 Nakamizo, T., Kawamata, J., Yoshida, K., et al. Phosphodiesterase inhibitors are neuroprotective to cultured spinal motor neurons. J Neurosci Res 71 485-495 (2003).

2 Gibson, A. Phosphodiesterase 5 inhibitors and nitrergic transmission-from zaprinast to sildenafil. Eur J Pharmacol 411 1-10 (2001).

3 Taniguchi, Y., Tonai-Kachi, H., Shinjo, K. Zaprinast, a well-known cyclic guanosine monophosphate-specific phosphodiesterase inhibitor, is an agonist for GPR35. FEBS Lett 580 5003-5008 (2006).

Nakamizo, T., Kawamata, J., Yoshida, K., et al. Phosphodiesterase inhibitors are neuroprotective to cultured spinal motor neurons. J Neurosci Res 71 485-495 (2003).

Gibson, A. Phosphodiesterase 5 inhibitors and nitrergic transmission-from zaprinast to sildenafil. Eur J Pharmacol 411 1-10 (2001).

Taniguchi, Y., Tonai-Kachi, H., Shinjo, K. Zaprinast, a well-known cyclic guanosine monophosphate-specific phosphodiesterase inhibitor, is an agonist for GPR35. FEBS Lett 580 5003-5008 (2006).