Role of Sialic Acid in Urinary Cytoprotective Activity of Tamm-Horsfall Protein

Abstract

Tamm-Horsfall protein (THP) from normal urine has been shown to protect against the cytotoxic effects of toxic urinary cations (TFs) in vivo and in vitro. This study investigated the effect of desialylation on the cytoprotective activity of THP. From pooled 24-hour urine specimens from healthy individuals, both TFs and THP were obtained. Sprague-Dawley rats received intravesical NaCl or KCl, and the baseline urodynamic percentage of nonvoiding contractions (NVCs) was recorded. Then, rehydrated TF, TF plus THP, or TF plus THP-desialylated (THP-d) were instilled, followed by KCl, and the urodynamic measurements were repeated. In vitro, human HTB4 bladder cells were incubated overnight with the rehydrated TF, TF plus THP, TF plus THP-d, or assay media alone, and the cytotoxicity levels were determined. Acid hydrolysis resulted in an 88% loss of sialic acid. TFs consistently demonstrated a greater than 50% toxicity for human HTB4 cells compared with cells incubated in media (P <0.01). TF cytotoxic activity was blocked by preincubation with THP but not by preincubation with THP-d. Similarly, rat bladder NVCs increased significantly over baseline when KCl was infused after TF infusion (1.68 NVCs/min; P <0.0001). NVCs were significantly reduced by preincubating TFs with THP (0.42 NVCs/min) but not by preincubating with THP-d (1.55 NVCs/min, P <0.0001). The cytoprotective function of urinary THP in the bladder can be compromised when a decrease is present in the sialic acid residues on THP. Such a decrease in THP cytoprotective activity may play a critical role in the pathophysiology of interstitial cystitis.