Expression and its significance of aquaporin 8 in patients with functional constipation or constipated irritable bowel syndrome

Abstract

Objective To detect the expression level of aquaporin 8 (AQP8) in patients with functional constipation(FC) or constipated irritable bowel syndrome (IBS-C), and the correlation between the expression of AQP8 and clinical features. Methods From March to December 2014, a total of 16 patients with IBS-C and 19 patients with FC met Rome Ⅲ criteria were collected, and nine healthy individuals were assigned to control group at the same period. The ascending and decending colonic tissues mucosa of FC, IBS-C and control group were taken under endoscope. The expression of AQP8 at mRNA and protein level was detected by real-time polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC). The differences in AQP8 mRNA expression and AQP8 relative area were analyzed by Kruskal-Wallis test among groups, and Pearson correlation coefficient was performed for correlation analysis between the expression and clinical features. Results The relative expressions of AQP8 mRNA of ascending colon and descending colon of FC patients (1.38, 0.61 to 4.09; 2.65, 0.82 to 7.52) and IBS-C patients (2.23, 0.82 to 4.67; 1.35, 0.51 to 2.03) were higher than those of control group (0.56, 0.19 to 0.97; 0.38, 0.21 to 1.19), and the differences were statistically significant (ZFC=-2.435, -3.149, ZIBS-C=-2.690, -2.152; all P 0.05). Most of AQP8 of FC group was expressed in cytoplasm of colonic mucosa epithelial cells, while that of IBS-C group and control group was mostly expressed at apical membrane and basal membrane of epithelial cells. The results of semi-quantification demonstrated that AQP8 relative area of descending colon of FC and IBS-C group increased compared with that of control group (3.42%(1.24% to 5.61%), 2.45%(1.72% to 4.27%) vs 1.18%(0.35% to 2.81%); Z=-2.534, -2.151, both P<0.05). Meanwhile, AQP8 relative area of ascending colon of FC group increased compared with that of control group (2.46%(1.48% to 4.18%) vs 1.14%(1.29% to 2.15%) Z=-2.041, P<0.05). Conclusion There are differences in AQP8 expression quantity and location in cells of descending colon between patients with FC and patients with IBS-C, which is a way for differentiation these two diseases. Key words: Functional constipation; Irritable bowel syndrome; Aquaporin 8; Colonic mucosa; Clinical features