Effects and mechanism of Bifidobacterium on intestinal inflammation resulting from deoxycholic acid-induced M1 polarization of macrophages.

High-fat diet (HFD) or deoxycholic acid (DCA) promotes infiltration of colon macrophages and their polarization toward the M1 phenotype.

• HFD and DCA both induced macrophage recruitment and pro-inflammatory (M1) polarization in the colon
• Polarization was assessed through real-time polymerase chain reaction and immunofluorescence staining
• This M1 polarization was associated with intestinal inflammation in the HFD animal model

Both vancomycin and Bifidobacterium inhibited HFD- or DCA-induced M1 polarization of macrophages.

• Vancomycin was administered to significantly reduce the population of intestinal gram-positive bacteria, thereby reducing fecal DCA levels
• Bifidobacterium supplementation similarly inhibited M1 macrophage polarization
• Both interventions reduced recruitment of pro-inflammatory macrophages in the HFD animal model

Bifidobacterium enhanced species richness and uniformity of intestinal microbiota in HFD mice, but this effect was not observed in the presence of vancomycin.

• Bifidobacterium improved alpha diversity metrics (species richness and uniformity) in HFD-fed mice
• Co-administration of vancomycin abolished Bifidobacterium's ability to improve these diversity parameters
• Bifidobacterium did not increase the absolute abundance of microbiota in either HFD-fed or HFD-and-vancomycin-treated mice
• Intestinal microbiota composition was assessed using 16S rRNA high-throughput sequencing

HFD altered the relative abundance of intestinal microbiota at both the phylum and genus levels, and these changes were partially mitigated by Bifidobacterium or vancomycin.

• HFD induced shifts in microbiota composition at multiple taxonomic levels
• Both Bifidobacterium supplementation and vancomycin treatment partially reversed HFD-induced changes in microbiota relative abundance
• Changes were characterized using 16S rRNA high-throughput sequencing

Bifidobacterium may regulate bile acid levels and target cholesterol metabolism pathways as mechanisms underlying its anti-inflammatory effects.

• Fecal DCA levels were measured using liquid chromatography-mass spectrometry
• Vancomycin reduced gram-positive bacteria populations, which contributed to reduced fecal DCA levels, suggesting a microbiota-bile acid axis
• Bifidobacterium's regulation of bile acid levels and cholesterol metabolism pathways were identified as potential therapeutic strategies for HFD-associated colitis