Urothelial cytoprotective activity of Tamm–Horsfall protein isolated from the urine of healthy subjects and patients with interstitial cystitis

PURPOSE: Tamm-Horsfall protein (THP) is a ubiquitous urinary protein with essentially no known function. We propose that THP is a cytoprotective agent that protects the urothelium from cationic species. To test this hypothesis we isolated THP from normal and interstitial cystitis urine to see if it could protect cultured cells from damage induced by the polyamine, protamine sulfate (PS). METHODS: Tamm-Horsfall protein was extracted from the urine of interstitial cystitis (IC) patients (N=28) and normal volunteers (N=5). Urothelial target cells (T24) were radiolabeled with 51Cr and then exposed to PS (0-1.0 mg/mL) for either 1.5 or 20 h. The resulting cytotoxicity data (dose-response curves) were then compared with the data obtained when PS was preincubated with 0-0.5 mg/mL of THP (IC vs normal), the semisynthetic polysaccharide, pentosan polysulfate (Elmiron), or human serum albumin. RESULTS: Toxicity of PS was significantly reduced by incubation with THP (or Elmiron) prior to evaluation by the chromium release assay, but not reduced by incubating with another protein, albumin. Tamm-Horsfall protein from IC patients' urine was less protective than an equal quantity of THP from normal urine. CONCLUSIONS: These experiments suggest that THP has an important role in bladder mucosal defense mechanisms, protecting the bladder surface from injury. Inability of THP to prevent cytotoxic damage by urinary polyamine or other urinary toxins (cationic species) may be relevant in the etiology of interstitial cystitis, as putative urinary toxic components have been described in the urine of some patients.