Introduction: Phosphodiesterase type 5 inhibitors (PDE5i), the most widely used drugs for erectile dysfunction, could also improve lower urinary tract symptoms, essentially due to overactive bladder (OAB), a condition hypothesized to be a result of an increased RhoA/Rho-kinase (ROCK) signaling. Phosphorylation/inactivation of RhoA by cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG) activity has been described in vascular smooth muscle.
Aim: The aim of this paper was to investigate whether vardenafil-induced cGMP accumulation reduces RhoA/ROCK signaling in bladder.
Methods: Spontaneously hypertensive rats (SHRs), a strain genetically prone to develop OAB, were treated with vardenafil (10 mg/kg/day) for 2 weeks. Wistar-Kyoto rats (WKY) were used as control. In vitro experiments were performed in human bladder smooth muscle cells (hBCs).
Main outcome measures: Urodynamic parameters were registered in vivo in anesthetized WKY and SHRs. RhoA/ROCK activity in bladder was evaluated by molecular and functional studies in tissues and cells.
Results: The intercontraction interval and bladder capacity, and were decreased in SHRs and restored by vardenafil. The in vitro relaxant effect of the ROCK inhibitor Y-27632 was higher in bladder strips from SHR than from WKY and reduced by vardenafil. Nomega-nitro-L-arginine-methyl-ester (a NO-synthase inhibitor, 40 mg/kg/day during the last week of the 2-week treatment with vardenafil) partially antagonized vardenafil effect on Y-27632 responsiveness. Vardenafil prevented RhoA membrane translocation/activation, decreased ROCK activity, and increased cGMP levels in vivo (rat) and in vitro (hBCs). Exposing hBCs to vardenafil increased Ser(188) RhoA phosphorylation, to the same extent as the PDE5-insensitive PKG agonist Sp-8-Br-PET-cGMP. Moreover, vardenafil inhibited several RhoA-dependent functions in hBCs, including smooth muscle gene transcription and endothelin-1-induced migration. These effects were reverted by the PKG inhibitor KT 5823, further suggesting a cGMP/PKG-dependency. In hBCs, vardenafil was active in the low nanomolar range.
Conclusions: This is the first study demonstrating that the effect of vardenafil on OAB could be partially determined by a cGMP-dependent RhoA/ROCK signaling inhibition.