Long-term inflammation of the urinary bladder is associated with tissue damage and afferent nerve sensitization. In some cases, inflammation can progress to chronic pelvic pain, believed to result from sensitization of sensory nerves that co-innervate multiple tissues. An effective treatment for pelvic pain has been elusive as treating the inflammation does not always mitigate the pain responses. Previous studies have suggested nitric oxide (NO) mediated cGMP signalling can reduce sensitization of bladder sensory nerves [1], however, whether the pathway also affects referred pelvic pain responses is unclear. Therefore, we investigate the effect of a small molecule soluble guanylate cyclase (sGC) activator, on nociceptive responses in a cyclophosphamide (CYP) induced chronic bladder inflammation model.

Animal. Adult (8 to 12 weeks old) male and female C57Bl/6J mice were purchased from Jackson Labs. Chemical cystitis was induced by four intraperitoneal administrations of CYP (50 mg/kg in sterile saline) over a 7-day period based on a previously reported protocol [2]. After completion of CYP treatment, mice were implanted with a subcutaneous osmotic pump to deliver cinaciguat (10 mg/kg/day) or vehicle (50% DMSO/50% PEG-400) for 14 days (figure 1A). 

Pelvic tactile sensitivity evaluation. Tactile sensitization of the pelvic region was evaluated using the MouseMet electronic Von Frey device (Topcat Metrology). Mice were placed into specialized testing cages and allowed to acclimate for a minimum of 30 minutes. The lower abdomen was probed at least five times during the session to determine the tactile threshold.

Data and statistical analysis. Data are expressed as mean ± standard error of mean. Statistical analyses were performed in GraphPad Prism 10 software. Comparison of data sets were performed using a two-way ANOVA followed by Tukey’s multiple comparison post-hoc test where the null hypothesis was rejected at p<0.05.

The tactile threshold of the pelvic region was significantly decreased at day 7 following CYP administration. Subsequent treatment with cinaciguat increased the mechanosensitive threshold at 14 days following cinaciguat treatment versus vehicle treated mice (figure 1B).

Cinaciguat treatment ameliorated pelvic nociception caused by chronic CYP induced bladder inflammation in both male and female mice. Based on the known actions of cinaciguat, it is hypothesized that the mode of action involves cinaciguat mediated increases in cGMP/protein kinas G signalling in sensitized afferent nerves.

Treatments for bladder centric pelvic pain has been limited both in number and efficacy. The NO-cGMP signalling pathway may be a new target for painful bladder syndrome/interstitial cystitis treatments.

Aizawa et al. Effects of nitric oxide on primary bladder afferent activities of the rat with and without intravesical acrolein treatment, European Urology, 59(2)264-71, 2011.
Golubeva et al. The mouse cyclophosphamide model of bladder pain syndrome: tissue characterization, immune profiling, and relationship to metabotropic glutamate receptors, Physiological Reports, 2(3):e00260, 2014