Purine nucleoside phosphorylase inhibition- an effective approach for the treatment of chemical hemorrhagic cystitis.

Hemorrhagic cystitis may be induced by infection, radiation therapy, medications, or may be idiopathic. Along with hemorrhagic features, symptoms include urinary urgency and frequency, dysuria (painful urination) and visceral pain. Cystitis-induced visceral pain is one of the most challenging types of pain to treat and an effective treatment would address a major unmet medical need. We assessed the efficacy of a purine nucleoside phosphorylase (PNPase) inhibitor, 8-aminoguanine (8-AG) for the treatment of hemorrhagic/ulcerative cystitis. Lower urinary tract (LUT) function and structure were assessed in adult Sprague Dawley rats, treated chronically with cyclophosphamide (CYP; sacrificed day 8) and randomized to daily oral treatment with 8-AG (begun 14 days prior to CYP induction) or its vehicle. CYP-treated rats exhibited multiple abnormalities including increased urinary frequency and neural mechanosensitivity, reduced bladder levels of inosine, urothelial inflammation/damage, and activation of spinal cord microglia, associated with pain hypersensitivity. 8-AG treatment of CYP-treated rats normalized all observed histological, structural, biochemical, and physiological abnormalities. In cystitis 8-AG improved function and reduced both pain and inflammation likely by increasing inosine, a tissue-protective purine metabolite. These findings demonstrate that 8-AG has translational potential for reducing pain and preventing bladder damage in cystitis-associated LUT dysfunctions.