Probiotics effectively regulated lipid metabolism and improved hyperlipidemia. The purpose of this study was to further evaluate the functions of lipid-lowering strains in vivo and elucidate the mechanism. The hyperlipidemia model was constructed using a high fat diet, and four lipid-lowering strains were selected for intervention. In the four strains, the strains Lactobacillus vaginalis FN3 (FN3) and Bifidobacterium animalis subsp. Lactis F1-7 (F1-7) reduced TG, TC and LDL and increased HDL. These two strains decreased TC and TC in the liver of high fat diet fed mice, and they increased total bile acids (TBA) in feces. F1-7 and FN3 reduced the mRNA levels of Farnesoid X Receptor (FXR), recombinant Fibroblast Growth Factor 15 (FGF 15) and Niemann-Pick C1-Like 1 (NPC1L1), and up-regulated the Liver X Receptor (LXR) mRNA level. They decreased the protein expressions of FXR and NPC1L1. In addition, F1-7 up-regulated the protein expression of cholesterol 7-alpha hydroxylase (CYP7A1). In summary, Bifidobacterium animalis subsp. Lactis F1-7 and Lactobacillus vaginalis FN3 could regulate bile acid metabolism by downregulating the FXR gene and reduce the absorption of exogenous cholesterol by regulating NPC1L1. F1-7 could also participate in the FXR/FGF15 pathway to improve hyperlipidemia, which showed better effects than FN3.

Probiotics and natural products can promote humoral transport and effectively relieve intestinal motility. This study investigated the effects of probiotics in combination with konjac glucomannan (KGM) and an aqueous extract of Prunus persica on constipation. The growth promotion effect of these natural products on probiotics was investigated using co-culture in vitro. The combined effect of probiotics and natural products on constipation was observed in mice. The tryptophan, tryptamine and short-chain fatty acid levels were determined using enzyme-linked immunosorbent assay, reverse-phase high-performance liquid chromatography, and gas chromatography. The key genes and proteins involved in humoral transport were identified using real-time polymerase chain reaction, western blotting and fluorescence immunoassay. KGM promoted the growth of Bifidobacterium animalis F1-7 in vitro, and a mixture of KGM and B. animalis F1-7 effectively promoted defaecation in mice, increased the faecal water content, shortened the defaecation time and improved the gastrointestinal transit rate. In mice, the KGM + F1-7 mixture reduced the tryptophan level and increased the levels of tryptamine, acetic acid, propionic acid, butyric acid and valeric acid. In addition, the KGM + F1-7 mixture effectively increased the mRNA level of 5-HT₄-G-protein-coupled receptors (5-HT₄GPCR)/mucins-2 (MUC-2) and reduced the level of aquaporins (AQP₃); furthermore, it upregulated the protein level of 5-HT₄GPCR/MUC-2 and downregulated the protein level of AQP₃. These findings indicated that the KGM + F1-7 mixture effectively improved intestinal motility and alleviated constipation through humoral transport-related pathways.

The relationship between bacterial strains and serotonin regulation was studied via the in vitro screening of the strains. Using the transparent visibility of zebrafish, the strains for intestinal peristalsis were quickly screened. The methods and results were as follows: (1) 18 strains with outstanding gastrointestinal viability via their surface hydrophobicity, self-aggregation ability, acid tolerance, bile tolerance, simulated gastric digestion and intestinal fluid tolerance were determined from 54 unpublished strains. (2) 5dpf zebrafish were randomly selected and divided into 22 groups with 12 tails in each group. The intestinal peristalsis frequency of each group within 1 min was calculated after immersing the model zebrafish in a 10⁸ CFU mL⁻¹ strain solution, with 5 effective strains obtained. (3) The serotonin in zebrafish was measured by Elisa and fluorescence immunization. The regulation mechanism of serotonin by Bifidobacterium animalis F1-7 was revealed by RT-PCR and the results show that this most effective strain promotes intestinal peristalsis in zebrafish via the modulation of serotonin release and key genes for serotonin synthesis in zebrafish.