[Optimization study of an animal model for interstitial cystitis/bladder pain syndrome based on the dose effect of cyclophosphamide].

Objective: To evaluate the efficacy of cyclophosphamide (CYP) at different doses in replicating the symptoms of interstitial cystitis/bladder pain syndrome (IC/BPS) in an animal model, thereby providing an experimental basis for understanding the pathophysiology of IC/BPS and assessing treatment strategies.

Methods: Twenty-eight female Sprague-Dawley rats aged seven weeks were divided into four groups: Group a (25 mg/kg CYP), group b (75 mg/kg CYP), group c (125 mg/kg CYP), and group d (a control group). The rats were injected intraperitoneally with either CYP or saline solution. Evaluations included urine spot tests, von Frey filament pain threshold tests, urodynamic examinations, and histological assessments.

Results: The study found that the 25 mg/kg CYP dosage significantly outperformed higher doses in simulating bladder dysfunction and inflammatory responses while minimizing the impact on the rats' physiological functions. Specifically, urine spot area, group a showed a significant reduction in urine spot area compared with the control group (P < 0.05), while groups b and c did not show significant differences. Pain threshold: The von Frey filament test indicated increased visceral pain in group a, aligning closely with IC/BPS patient symptoms, without a significant increase in urination frequency. Urodynamic assessments: Group a exhibited decreased bladder compliance and reduced maximum bladder capacity (P < 0.05), with no significant differences in baseline bladder pressure and maximum detrusor pressure across all groups. Histological analysis: Hematoxylin-eosin (HE) staining revealed that bladder tissue in group a had moderate inflammatory reactions, whereas groups b and c showed severe inflammation and tissue damage, correlating with the higher doses of CYP. Furthermore, the urine spot tests and von frey filament tests provided quantitative data supporting the model's reliability, urine spot count, group a had an average urine spot count of (15±3) spots, significantly higher than the control group's (5±2) spots (P < 0.01). Nociceptive score: Group a nociceptive score increased to 0.5±0.1, indicating heightened pain sensitivity compared with the control group 0.10±0.05 (P < 0.01).

Conclusion: The 25 mg/kg CYP demonstrated significant advantages in simulating the key features of non-ulcerative IC/BPS, summarizing the main aspects of the human condition, including persistent visceral pain and mild inflammatory reactions in bladder tissue. These findings offer substantial experimental support for drug development and treatment research in IC/BPS and provide new insights into the complex patho-physiology of the disease.