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 β 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.