Benign prostatic hyperplasia (BPH), a non-malignant enlargement due to proliferation of stromal and epithelial cells, is one of the most common conditions in aging men often leading to benign prostatic obstruction (BPO) with concomitant lower urinary tract symptoms (LUTS). Currently available pharmacological agents including α1-adrenoceptor antagonists (e.g., tamsulosin) and 5α reductase inhibitors (e.g., finasteride), treat the consequences rather than the cause and are often ineffective. The phosphodiesterase 5 (PDE5) inhibitor, tadalafil, was also approved for BPH-associated LUTS, however, refractoriness can occur in aging. Thus, there is a critical need to characterize the pathways involved in BPH development and test new therapies. Since BPO/LUTS are the main BPH consequence affecting men’s quality of life, most BPH associated studies are focused on these aspects of the disease. However, rodents lack the fibrous capsule that circumscribes the human prostate, so enlargement in mice or rats is not believed to lead to BPO. Thus, BPO is often modelled by ligating the urethra [1] or altering the testosterone to estradiol (T1:E2) ratios [2] in adult animals. Our extensive histological assessments of aged rats and mice have allowed us to describe a native BPH/BPO model without the need for ligatures or exogenous steroids. The rodent prostatic urethra, unlike humans, is surrounded by the EUS which constrains tissue expansion within this region resulting in naturally occurring BPO; in humans the EUS is below the prostate. Since PDE5 inhibitors are beneficial, we hypothesized that decreased tissue cGMP levels are involved in BPH development and have shown that the soluble guanylate cyclase (sGC) activator, cinaciguat, reversed BPH (determined histologically) and BPO (determined urodynamically) in aged mice and rats.

The study utilized aged (>24 mo) and adult (9 mo) male C57Bl/6 mice and Fisher F344 rats obtained from the NIA Office of Biological Resources. Their LUTS were assessed using urine spot tests after which animals were divided in groups treated orally with cinaciguat (10 mg/kg/day/14 days, n ≥ 4) or vehicle (100-200 µl of 0.5% methylcellulose and 10% DMSO, n ≥ 6). Following 2 weeks treatment, animals were assessed by decerebrated cystometry and length-tension recordings of the bladder strips. Prostates with prostatic urethras were isolated, saved in 10% buffered formalin, embedded in paraffin and sectioned 4 µm sick for histological evaluation using modified Verhoeff Van Gieson or Trichrome stains for cell hyperplasia and collagen deposition or Toluidine Blue for mast cell calculation. Slides were imaged using brightfield montage microscopy (Olympus Fluoview microscope) and analyzed using NDP and HCImage software (Hamamatsu Photonics). Unpaired Student’s t-test determined differences between aged versus adult groups or parameters with and without treatment.

In ~75% of aged rodents, prostates were significantly heavier than in adults. The ventral lobes had nodules, while the dorsolateral lobes exhibited glandular atrophy, cellular hyperplasia, basal layer thickening, inflammation, increased stromal collagen content and mast cell infiltration and activation. Furthermore, prostatic urethras of aged rodents also exhibited increased collagen content, hyperplasia, granular atrophy, urethral epithelium hyperplasia and significantly decreased urethral openings (Fig. 1). Summary of these results from rats is shown in Fig. 2. Decerebrated cystometry recordings demonstrated shorten intercontraction intervals and non-voiding contractions in aged animals in comparison to adults (not shown). Length-tension curves from bladders of aged rodents were shifted left demonstrating stiffness. Alternatively, aged animals treated with cinaciguat had prostate weighs similar to adults with a return to near normal prostatic and urethral tissue architecture. Bladder function in these animals was similar to adults. Moreover, cinaciguat administered to adult rodents exhibited no significant effects.

The majority of prostates from untreated aged animals exhibited benign nodules, increased collagen:tissue ratios, increased numbers of both prostate epithelial and stromal/smooth muscle cells, as well as prostatic urethral epithelial, smooth muscle and lamina propria cells and mast cell infiltration. The prostate weights as well as prostate/body weight ratios were significantly greater in aged versus adult animals. Urethral lumen size was dramatically decreased in ~75% of aged animals with BPH suggestive of BPO. Bladders of the aged animals also exhibited overactivity, fibrosis and low compliance; symptoms often seen in men with BPH/BPO. These changes were reversed by cinaciguat treatment which did not exhibit noticeable effects in adult animals.

Clinically, BPH is a histological diagnosis referring to proliferation of smooth muscle, connective and glandular epithelial tissues in the prostatic transition zone. It is ubiquitous in the aging males reaching 60% by age 60 and 80% by age 80. We have demonstrated that aged rodent prostates often undergo similar changes. Especially important is that these processes also occur within rodent prostatic urethra surrounded by EUS where tissue expansion leads to urethral obstruction and can serve as a naturally occurring model for studying BPH/BPO. Oral cinaciguat reverses BPH, BPO and LUTS in aged animals suggesting that sGC mediated increases in cGMP production in the prostate are a contributing factor.

Su et al. Am J Physiol Renal Physiol, 284(4):F644-652. 2003
Nicholson et al. Endocrinology, 153(11):5556-5565. 2012