Protective effect of L-pipecolic acid on constipation in C57BL/6 mice based on gut microbiome and serum metabolomic.

BACKGROUND: Functional constipation (FC) in children affects their growth, development and quality of life. L-pipecolic acid (L-PA) was decreased in FC children based on gut microbiome and serum metabolomic. In this study, loperamide-induced constipation in mice was used to evaluate the effects of L-PA on constipated mice. METHOD: 26 FC and 28 healthy children were recruited. Stool samples and serum samples were subjected to 16S rDNA sequencing and ultra-performance liquid chromatography/quadrupole time of flight (UPLC-Q/TOF-MS) approach, respectively. A loperamide-induced mouse constipation model was developed, and all mice were randomly divided into control (Con), loperamide (Lop) and L-PA (Lop + L-PA) treatment groups (6 mice per group). The mice in the Lop + L-PA group were given L-PA (250 mg/kg, once a day) and loperamide; the Lop group was given loperamide for 1 week, and the Con group was given saline. The fecal parameters and intestinal motility of mice in each group were detected. serum 5-HT levels and colon 5-HT expression were detected by ELISA and immunohistochemistry, respectively; qRT-PCR was used to detect the expression of AQP3 and 5-HT4R mRNA in each group. RESULTS: 45 differential metabolites and 18 significantly different microbiota were found in FC children. The α and ß diversity of gut microbiota in FC children was significantly reduced. Importantly, serum L-PA was significantly reduced in FC children. The KEGG pathway enrichment were mainly enriched in fatty acid biosynthesis, lysine degradation, and choline metabolism. L-PA was negatively associated with Ochrobactrum, and N6, N6, N6-trimethyl-l-lysine was positively associated with Phascolarcrobacterium. In addition, L-PA improved the fecal water content, intestinal transit rate, and increased the serum 5-HT levels in constipated mice. Moreover, L-PA increased the expression of 5-HT4R, reduced AQP3, and regulated constipation-associated genes. CONCLUSIONS: Gut microbiota and serum metabolites were significantly altered in children with FC. The abundance of Phascolarctobacterium and Ochrobactrum and serum L-PA content were decreased in FC children. L-PA was found to alleviate the fecal water content, increase intestinal transit rate and the first black stool defecation time. L-PA improved constipation by increasing 5-HT and 5-HT4R expression while down-regulating AQP3 expression.

APETx2 regulates intestinal motility and visceral sensitivity in post-infectious irritable bowel syndrome mice through 5-HT signalling pathway.

OBJECTIVES: To investigate whether APETx2, a potent and selective inhibitor of ASIC3, regulates intestinal motility and visceral sensitivity in post-infectious irritable bowel syndrome (PI-IBS) mice through the 5-HT signalling pathway. METHODS: The PI-IBS model was established by Trichinella spiralis infection of NIH mice. APETx2(120 µg/kg) was administrated to PI-IBS mice by intraperitoneal injection once a day, lasting for 7 days. The gastrointestinal function of mice was assessed by the time of the first dark stool and the number of pellets defecated within 2 h. The visceral sensitivity was tested via abdominal withdrawal reflex. The protein levels of 5-HT and CRF in colon tissues were detected by immunohistochemistry. The changes in serum 5-HT and colon CRF contents were detected by ELISA. The mRNA levels of colon 5-HT4R and CRF were detected by RT-qPCR. The protein levels of colon 5-HT4R and dorsal root ganglion (DRG) ASIC3 were detected by Western blotting. KEY FINDINGS: The results indicated that APETx2 could markedly improve gastrointestinal function and visceral sensitivity in mice. Moreover, APETx2 could reduce the expression level of ASIC3 protein in the DRG of PI-IBS mice. APETx2 could increase the expression levels of 5-HT in serum and colon, CRF and 5-HT4R in the colon, and 5-HT4R in brain tissue in PI-IBS mice. CONCLUSIONS: APETx2 can improve visceral sensitivity and intestinal motility in PI-IBS through 5-HT signalling pathway.