PURPOSE: Sodium pentosan polysulfate has been promoted as a urothelial cytoprotective agent for treating interstitial cystitis. The nuclear transcription factor nuclear factor kappaB is thought to have a role in mediating the urothelial inflammatory response of interstitial cystitis. We further defined a possible cytoprotective effect of sodium pentosan polysulfate by characterizing the effect of the drug on the expression of nuclear factor kappaB. MATERIALS AND METHODS: For cell culture human urothelial cells were incubated in various concentrations of sodium pentosan polysulfate for 16 hours in keratinocyte serum-free medium. They were subsequently treated with the known nuclear factor kappaB stimulants tumor necrosis factor-alpha, lipopolysaccaride (LPS) and double-stranded RNA (dsRNA). Each stimulant was then incubated with sodium pentosan polysulfate separately and the mixture was used to treat cultured urothelial cells. For electrophoretic mobility shift assay total cell extracts were prepared and run in electrophoretic mobility shift assays using a radiolabeled nuclear factor kappaB consensus sequence as a probe. Western blot analysis was done to assess nuclear factor kappaB activation by measuring degradation of the inhibitory subunit of the nuclear factor kappaB complex. RESULTS: Nuclear factor kappaB activation by tumor necrosis factor-alpha, LPS and dsRNA was unaltered when cultured cells were incubated in sodium pentosan polysulfate before treatment. In contrast, nuclear factor kappaB activation by LPS and dsRNA was suppressed when the stimulants were incubated with sodium pentosan polysulfate before cell treatment. This suppressive effect was confirmed by Western blot analysis. CONCLUSION: Sodium pentosan polysulfate may have a nonspecific effect against the viral (dsRNA) and bacterial (LPS) activation of nuclear factor kappaB. The observed clinical effect of sodium pentosan polysulfate may be mediated by nonspecific binding of sodium pentosan polysulfate molecules and the inflammatory stimulants of urothelial activation. These findings suggest a mechanism of action for sodium pentosan polysulfate that occurs in the urine rather than at the mucosal membrane by direct interaction of the drug with potential interstitial cystitis inducing inflammatory agents.