Apios americana Medikus tuber starch alleviates diphenoxylate-induced constipation by modulating neurotransmitters and gut microbiota in mice

As the modulator of gut microbiota, resistant starch (RS) demonstrates the significant therapeutic efficacy against difficult defecation. This study investigated the novel prebiotic effects of Apios americana Medikus tuber starch (AS) on diphenoxylate-induced constipation in mice. AS was characterized by a typical B-type crystalline pattern with a high RS content of 87.25 %. Treatment with the high dosage of AS (AS-H), the wet weight and number of black feces, and gastrointestinal transit ratio of constipated mice significantly enhanced by 57.5 %, 242.9 % and 33.9 %, respectively, in comparison with the model group. Moreover, AS-H supplementation significantly inhibited the levels of inflammation-related factors including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) as well as the increased protein expression levels of zonula occluden-1 (ZO-1) and occludin in the colon tissue of constipated mice. AS-H group showed marked increases in the excitatory neurotransmitters with concurrent decreases in the inhibitory neurotransmitters. Additionally, the colonic expression of vasoactive intestinal peptide receptor 1 (VIPR1) was significantly suppressed, while serotonin receptor 4 (5-HT4) was enhanced by AS-H treatment. A significant increase at gut bacterial genus level (such as Bacteroides, Lachnospiraceae_NK4A136_group and Oscillibacter) accompanied by increasing concentrations of SCFAs was observed after AS-H treatment, with these changes directly correlating to the alleviation of constipation. Importantly, fecal microbiota transplantation (FMT) intervention with a AS-derived microbiome notably ameliorated the fecal parameters in constipated mice. Collectively, supplementation with AS could promote the fecal excretion by modulating enteric neurotransmitters and gut microbiota in mice, providing the conduct of subsequent human clinical trials.