Increased urinary IL‐6 and mucosal COX‐2 expression in patients with idiopathic detrusor overactivity

Hypothesis / aims of study Chronic inflammation has been hypothesised to be involved in overactive bladder (OAB) syndrome, and studies have also suggest that OAB could be a subtype of neurogenic inflammation. Previously we demostated that the serum concentrations of Interleukin‐6 (IL‐6) and C‐reactive protein (CRP) in OAB patients were significantly higher than those in the controls [1]. A significant three‐fold elevation of urniary anti‐inflammation cytokine IL‐10 was found in the patients with OAB [2]. IL‐6 and cyclooxygenase‐2 (COX‐2) were reported to be triggered by inflammatory stimuli and involved in the pathogenesis of several diseases [1,3]. This study aimed to measure the expressions of muscosal COX‐2, urinary IL‐6 and IL‐10 in patients with idiopathic detrusor overactivity (IDO) and elucidate the association between these inflammatory mediators. Study design, materials and methods Urine samples were collected from 28 IDO patients and 12 control subjects. The concentration of urinary IL‐6 and IL‐10 were quantified using a bead‐based human cytokine/chemokine kit (Millipore, Billerica, MA, USA) according to the manufacturer's instructions. Suburothelial tissues of patients with urodynamically and clinically proven IDO ( n = 12) were taken before intravesical 200 U onabotulinumtoxin A (BoNT/A) injection and 5 bladder tissues were obtained from controls with asymptomatic microscopichematuria. Mucosal COX‐2 receptor expression levels were measured by western blotting. Differences in mucosal COX‐2, urinary IL‐6 and IL‐10 levels between the OAB patients and the controls were compared by the non‐parametric Mann‐Whitney U test. Furthermore, Pearson's correlation coefficients were calculated to ascertain correlations between COX‐2, IL‐6 and IL‐10. A p ‐value < 0.05 was considered to indicate statistical significance. All statistical analyses were performed using the statistical package SPSS for Windows (Version 12, SPSS, Chicago, IL, USA). Results The mucosal COX‐2, urinary IL‐6 and IL‐10 assay showed that mucosal COX‐2 ( p = 0.04) and urinary IL‐6 ( p = 0.01) expression levels both were significantly higher in IDO patients than those in the controls ( Table 1, Fig. 1). Although the OAB patients were older than the control subjects, neither mucosal COX‐2, urinary IL‐6 nor IL‐10 were correlated with age in all of the subjects. Analysis of the association between expressions of these mediators in IDO patients showed a significant correlation between IL‐6 and IL‐10 ( p = 0.00, Fig. 2A). Although the correlation between IL‐6 and COX‐2 was not significant ( p = 0.10, Fig. 2B), the R 2 value was 0.24, suggesting that it might be due to the small sample size. Interpretation of results Proinflammatory cytokines, such as IL‐1β and IL‐6, can induce COX‐2 expressions in vitro , and NF‐κB is known to play a crucial role in this signaling pathway. Our study demonstrated IDO patients have significantly higher urinary IL‐6 and mucosal COX‐2 expressions than the controls. The finding suggests that chronic inflammation is involved in pathogenesis of IDO and COX‐2 inhibitor may offer an important strategy to the treatment for patient with IDO. Interestingly, synergistic increase of the pro‐inflammatory cytokine IL‐6 and anti‐inflammatory cytokine IL‐10 was also noticed in this study. Recent report demonstrated that IL‐6 and IL‐10 significantly enhanced membrane localization of gap junction protein Cx43, and specifically modulated coupling between human bladder smooth muscle cells via gap junctions [4]. The presence of elevated urinary IL‐6 and IL‐10 levels that are related to inflammation and tissue repair suggests a role for inflammation in IDO, and may help in diagnosis and elucidate the pathogenesis of this disease. Concluding message Elevation of urinary IL‐6 and mucosal COX‐2 protein expressions in IDO patients implies chronic inflammation is involved in pathogenesis of IDO. Down‐regulation of COX‐2 by COX‐2 inhibitors may be developed to be an important component of the management strategy of IDO. Synergistic increase of the pro‐inflammatory cytokine IL‐6 and anti‐inflammatory cytokine IL‐10 suggests immune system disorder plays roles in the pathogenesis of the disease. Reducing abnormal immune system activity may be an innovative approach for the treatment of IDO. 1 Expression of mucosal COX‐2, urinary IL‐6 and IL‐10 in IDO patients and controlsControls ( n = 12) IDO ( n = 28) pGender F:8 M:4 F: 17 M: 11Age 44.69± 4.73 (20~76) 70.54±2.31 (39~87) 0.00 **Mucosal COX‐2 0.09 ± 0.06 (0.00~0.29) 0.34 ± 0.08 (0.00~0.93) 0.04 *Urinary IL‐6 (pg/ml) 0.81 ± 0.72 (0.00~8.69) 0.98 ± 0.22 (0.00~3.65) 0.01 *UrinaryIL‐10 (pg/ml) 1.81 ± 0.16 (0.93~2.84) 2.02 ± 0.12 (0.76~2.98) 0.36Mean ± standard error (Min ~ Max)