Prostatitis is one of the most common urinary tract problems for men at any age with an estimated prevalence in the community of about 9%. In addition, more than 90% of patients with prostatitis are classified into chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), which is the category IIIA and IIIB without bacterial infection in National Institutes of Health (NIH) classification of prostatitis. Although CP/CPPS often reduces quality of life, the underlying mechanism is still not fully clarified.  Also, the currently available treatments such as alpha-blockers, anti-inflammatory drugs and phytotherapeutic agents are often ineffective  to improve CP/CPPS symptoms including pain, pressure and discomfort related to the lower urinary tract as well as overactive bladder (OAB)-like storage symptoms.  Our previous studies reported that a rat model of prostatic inflammation (PI) showed bladder overactivity, afferent hyperexcitability due to prostatic-to-bladder cross-organ sensitization, and nerve growth factor (NGF) upregulation in the bladder epithelium and that intravesical instillation of liposome conjugated with NGF antisense oligonucleotide, which normalized local NGF overexpression, significantly reduced bladder overactivity [1]. Therefore, local blockade of NGF in the bladder could be a therapeutic modality for male lower urinary tract symptoms (LUTS) due to PI.  Neurotrophic factors including NGF and brain derived neurotrophic factor (BDNF) are known to bind to high-affinity tropomyosin receptor kinase (Trk) receptors such TrkA and TrkB, respectively.  Because increased expression of TrkA and TrkB receptors has been reported in inflamed urinary bladders [2], we hypothesized that blockade of Trk receptors such as TrkA and TrkB is effective for the treatment of male LUTS in patients with PI. Thus, in the present study, we examined the effects of systemic non-selective Trk receptor inhibition on bladder hypersensitivity using a rat model of PI.

Male Sprague-Dawley rats at 8 to 9 weeks of age were used and they were divided into three groups (n = 6 in each group): (1) Control group; rats without intraprostatic instillation and with oral administration of vehicle. (2) Untreated groups; PI rats with oral administration of vehicle (3) Treated group; PI rats with oral administration of non-selective Trk inhibitor (GNF 5837). PI was induced by intraprostatic 5% formalin injection (50 μl per each ventral lobe) in Untreated and Treated groups. Then, GNF 5837 at a dose of 40 mg/kg dissolved in methyl cellulose (0.5w/v %, 0.1 ml) and TWEEN 80 (0.5w/v %, 0.1 ml) [3], or vehicle was given to each group daily by oral gavage for 10 days from day 18 after inducing PI. On day 28, conscious cystometry (CMG) was performed. Tissues were then harvested for histological analysis as well as for evaluation of protein expression levels of NGF and BDNF in the bladder mucosa and the ventral lobes of prostate by ELISA, mRNA expression levels of Trk receptors (TrkA, B and C), a C-fiber afferent marker (TRPV1) in L6-S1 dorsal root ganglia (DRG), and inflammation markers (IL-1β, IL-18) in the ventral lobes of prostate by RT-PCR.

In CMG, Treated group demonstrated a significant decrease in non-voiding contractions (Fig. 1A; NVC) compared to Untreated group in association with reductions of NGF and BDNF protein expression levels in both bladder mucosa and prostate, whereas there were no significant differences between Treated and Control groups (Fig. 2A). In other CMG parameters including intercontraction intervals (ICI), there were no significant differences among three groups. In Untreated group, mRNA expression levels of all Trk receptor subtypes (Trk A, B and C) and TRPV1 in L6-S1 DRG were significantly increased, compared to Control group; however, these changes were normalized in Treated group (Fig. 2B and 2C). In Untreated group, mRNA expression levels of IL-1β and IL-18 in the prostate were significantly greater than those of Control group whereas there were no significant differences between Treated and Control groups (Fig. 2D). In addition, although there were inflammatory cells infiltration in the prostatic stroma of Untreated group compared to Control group, these changes in Treated group were lesser than in Untreated group (Fig. 1B).

Systemic blockade of Trk receptors reduced NGF and BDNF expression in both bladder and prostate, which was increased after PI. Also, oral administration of non-selective Trk inhibitor reduced PI as well as PI-induced bladder overactivity shown by increased NVC and C-fiber afferent marker (TRPV1) overexpression in L6-S1 DRG that contain bladder and prostate afferent neurons. Thus, it is assumed that Trk receptors plays a significant role in prostate-to-bladder cross-organ sensitization, which induces bladder overactivity due to enhanced bladder afferent activity after PI.

Systemic blockade of Trk receptors improved not only PI, but also bladder overactivity shown by increased NVC in a rat model of PI. Also, improvement of bladder overactivity is associated with reductions of Trk A, B and C receptors, TRPV1 in L6-S1 DRG as well as NGF and BDNF in the bladder mucosa and the prostate. Thus, the NGF/BDNF-Trk receptor mechanism would be a potential target for the treatment of irritative bladder symptoms in patients with chronic prostatitis.

Igarashi T, et al. Therapeutic effects of nerve growth factor-targeting therapy for bladder overactivity in rats with prostatic inflammation. The Prostate, 2021. 81(16): p. 1303–9
QiaoLY,, et al. Cystitis-induced upregulation of tyrosine kinase (TrkA, TrkB) receptor expression and phosphorylation in rat micturition pathways. J Comp Neurol. 2002; 9;454(2): p.  200-11
Pam A, et al. Discovery of GNF-5837, a Selective TRK Inhibitor with Efficacy in Rodent Cancer Tumor Models. ACS Medicinal Chemistry Letters, 2012. 3(2): p. 140-5

Continence 2S2 (2022) 100318
DOI: 10.1016/j.cont.2022.100318