Effects of lactitol and Bifidobacterium infantis on AQP3 and ICC in a rat model of constipation

Abstract

Objective To analyze the roles and mechanisms of lactitol and Bifidobacterium infantis in the treatment of rat constipation and to investigate their effects on aquaporin3 (AQP3) and interstitial cells of Cajal (ICC) in colon tissues. Methods Thirty SD male rats were recruited in this study, 6 of which were randomly selected as the control and the rest were given 4 mg/kg.d of loperamide for 5 consecutive days to construct the rat model of constipation. The rats with constipation were randomly divided into four groups including model group, lactitol treatment group, Bifidobacterium infantis treatment group and lactitol in combination with Bifidobacterium infantis treatment group. General indexes including food intake, water intake, body weight, fecal water content and intestinal transit rate of each rat were measured after receiving corresponding treatments for 7 consecutive days. The levels of substance P (SP) and vasoactive intestinal peptide (VIP) in serums samples were detected by ELISA. The expression of protein kinase A (PKA) and neurokinin-1 receptor (NK-1) at mRNA level in colon tissues were detected by real-time polymerase chain reaction (real-time PCR). Western blot assay and real-time PCR analysis were used to detect the expression of AQP3 and c-kit at protein and mRNA levels, respectively. Results Compared with the rats in model group, the levels of fecal water content and intestinal transit rate, the concentrations of SP and VIP in serums samples, the expression of PKA and NK-1 at mRNA level and the expression of AQP3 and c-kit at mRNA and protein levels were significantly increased in rats from the three treatment groups (P<0.05). The most effective treatment was lactitol in combination with Bifidobacterium infantis, followed by the lactitol treatment and then the Bifidobacterium infantis treatment. Conclusion The combination therapy with lactitol and Bifidobacterium infantis increased the serum levels of SP and VIP in rats with constipation. SP could enhance the contraction of gastrointestinal smooth muscles and improve the intestinal motility by binding to the NK-1 receptor on the membrane of ICC. VIP could promote the absorption of water in intestinal tracts, soften stools and alleviate constipation by upregulating the expression of AQP3 at both protein and mRNA levels via the cyclic adenosine monophosphate-PKA (cAMP-PKA) signaling pathway. Key words: Constipation; Lactitol; Bifidobacterium infantis; Aquaporin3; Interstitial cells of Cajal