Although, oxidative stress is closely associated with pathological mechanisms and symptoms of urinary bladder dysfunction [1], roles of redox signaling in bladder function is still under investigation. Therefore, the aim of this study was to use in vitro muscle strip contractility studies to explore the physiological role of reactive oxygen species (ROS) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) in regulating bladder function in normal bladders from humans and dogs. Understanding such mechanisms in normal bladders is warranted for better knowledge of potential treatment strategies for patients with urinary dysfunctions resulting from increased oxidative stress, such as those caused by ischemia/reperfusion injury [2].

Mucosa-denuded bladder smooth muscle strips obtained from 7 human organ donors and 4 normal dogs were mounted in muscle baths, and trains of electrical field stimulation (EFS) applied for 20 minutes at 90-second intervals. Subsets of strips were incubated with hydrogen peroxide (H2O2), angiotensin II (Ang II; Nox activator), apocynin (inhibitor of Noxs and ROS scavenger), or ZD7155 (specific inhibitor of angiotensin type 1 (AT1) receptor) for 20 minutes in continued EFS trains. Subsets treated with inhibitors were then treated with H2O2 or Ang II.

In human and dog bladders, the exogenous ROS, H2O2 (100µM), caused muscle strip contractions and enhanced EFS-induced contractions. Apocynin (100µM) attenuated EFS-induced strip contractions in both species; subsequent treatment with H2O2 improved the EFS-induced contractions. Ang II (1µM) enhanced the EFS-induced contractions in dog, but not human bladder muscle strips, yet induced direct strip contractions in both species. In dog bladders, Ang II enhanced both EFS-induced and direct strip contractions. Ang II also partially restored EFS-induced strip contractions attenuated by prior apocynin treatment. In both species, treatment with ZD7155 (10µM) inhibited EFS-induced muscle strip activity; subsequent treatment with Ang II did not restore strip activity.

The enhancement of EFS-evoked strip contractions by H2O2 and the inhibition of these contractions by the Nox inhibitor apocynin demonstrates the functional relevance of ROS in regulating human bladder smooth muscle activity and suggests that endogenous Nox-derived ROS regulates smooth muscle function. The augmentation of strip contractions by Ang II suggests that activation of Nox via a receptor’s ligand can also enhance smooth muscle activity and that the effect of Ang II is mediated by AT1, which was further supported by the inhibitory effect of the selective antagonist ZD7155.

Collectively, these data provide evidence for the functional significance of Nox-derived ROS in human bladder and that ROS can modulate bladder function without exogenous stimuli. The excitatory effects of angiotensin II on bladder smooth muscle function may have significant pathological implications since inflammation is an important mechanism associated with oxidative damage.

Sezginer, Ecem Kaya, et al. "Effects of varying degrees of partial bladder outlet obstruction on urinary bladder function of rats: A novel link to inflammation, oxidative stress and hypoxia." LUTS: Lower Urinary Tract Symptoms 11.2 (2019): O193-O201.
Miyata, Yasuyoshi, et al. "A review of oxidative stress and urinary dysfunction caused by bladder outlet obstruction and treatments using antioxidants." Antioxidants 8.5 (2019): 132.