Gender-based reciprocal expression of transforming growth factor-ß1 and the inducible nitric oxide synthase in a rat model of cyclophosphamide- induced cystitis

Abstract

Background. The pluripotent cytokine transforming growth factor-1 (TGF-1) is the central regulator of inducible Nitric Oxide Synthase (iNOS) that is responsible for nitric oxide (NO) production in inflammatory settings. Previous studies have implicated a role for NO, presumably derived from iNOS, in cyclophosphamide (CYP)-induced cystitis in the bladder. TGF-1 is produced in latent form and requires dissociation from the latency-associated peptide (LAP) to act as primary anti-inflammatory and pro-healing modulator following tissue injury in the upper urinary tract. Since the role of TGF-1 in lower urinary tract inflammation is currently unknown, and since gender-based differences exist in the setting of interstitial cystitis (IC), the present study examined the relationship between TGF-1 and iNOS/NO in the pathogenesis of CYP-induced cystitis in both male and female rats. Methods. Sprague-Dawley rats, 4 months of age, of either gender were given 150 mg/kg CYP intraperitoneally. Urinary and bladder tissue TGF-1 and NO reaction products (NO2-/NO3-) were quantified as a function of time following CYP. Expression of active and latent TGF-1 as well as iNOS in harvested bladder tissue was assessed by immunohistochemistry. Results. Female rats had significantly higher levels of NO2-/NO3-in urine even at baseline as compared to male rats (p < 0.001), whereas there was no gender based significant difference in urine levels of active or latent TGF-1 prior to CYP injection. Inflammatory and cytotoxic changes were induced by CYP in the bladder of both sexes that were accompanied by differences in the urine levels of NO2-/NO3 -and TGF-1. Male rats responded to CYP with significantly lower levels of NO2-/NO3-and significantly higher levels of TGF-1 in urine (p < 0.05) as compared to females at all time points after CYP. The urine levels of NO2-/NO3-after CYP were inversely correlated to latent and active TGF-1 (Pearson coefficient of -0.72 and -0.69 in females and -0.89 and -0.76 in males, respectively; p < 0.01). Bladder tissue of male rats exhibited significantly higher levels of both latent and active TGF-1 (p < 0.01) compared to female rats after CYP. TGF-1 and iNOS protein was mostly localized in the urothelium. Conclusion. The results of this study suggest that there exists an inverse relationship between the expression of TGF-1 and iNOS/NO2-/NO3-in CYP-inflamed bladder. The gender of the animal appears to magnify the differences in urine levels of TGF-1 and NO2-/NO3-in this inflammatory setting. These results support the hypothesis that TGF-1 can suppress iNOS expression associated with bladder inflammation and reduce systemic levels of NO2-/NO3 -, and further suggest that this feature of TGF-1 can be harnessed for therapy and diagnosis of interstitial cystitis. © 2009 Tyagi et al.