The urinary glycoprotein GP51 as a clinical marker for interstitial cystitis

GP51 is a urinary glycoprotein with a molecular weight of 51 kDa. This glycoprotein is produced and secreted by the transitional epithelium of the genitourinary tract, and has been isolated from human urine. Studies have demonstrated that GP51 levels are decreased in bladder biopsies of patients with interstitial cystitis. We evaluated urinary GP51 in a noninvasive manner as a clinical marker of interstitial cystitis.

Urinary GP51 levels were measured using antigen inhibition enzyme-linked immunosorbent assay. In blinded fashion we analyzed for quantitative differences 24-hour urine samples of 36 patients with interstitial cystitis and 23 normal controls who were age matched within 5 years (mean age 47.3). We also evaluated GP51 in random urine specimens of 17 normal controls, 14 patients with interstitial cystitis and 11 subjects who had undergone cystectomy to determine whether urinary GP51 is mainly produced by the bladder, which is the site of interstitial cystitis. To ascertain the specificity of urinary GP51 to interstitial cystitis urine samples of 34 patients with other urological diseases were measured and compared with findings in the samples of 15 with interstitial cystitis.

Low GP51 levels appeared to be unique to the interstitial cystitis state compared to normal (p = 0.008). GP51 in patients with interstitial cystitis and in those who underwent cystectomy was lower (p < 0.001) than in normal controls. These findings suggest that the major source of urinary GP51 is the bladder. Also, we observed lower GP51 levels in interstitial cystitis than in other urinary tract diseases (p < 0.0001).

Our study substantiates the possibility of using GP51 as a clinical marker for diagnosing interstitial cystitis by a noninvasive urinary assay.