Functional Effects of Bacillus velezensis Metabolites on Barrier Formation, Cytokine Responses, and Phagocytic Activity in Canine Epithelial and Immune Cells.

Bacillus velezensis-based probiotics are increasingly recognized for their potential to enhance intestinal health in companion animals, yet their mechanisms of action in canine epithelial systems remain incompletely defined. This study aimed to evaluate whether a live Bacillus velezensis probiotic consortia (BC) modulates epithelial barrier integrity, immune signaling, apoptosis-renewal pathways, and metabolic activity in canine-relevant intestinal and macrophage cell models. MCA-B1 proximal gastrointestinal epithelial cells and DH82 macrophage-like cells were exposed to BC cultures, followed by quantification of tight-junction expression, permeability (FITC-Dextran), cytokine responses, phagocytic activity, apoptosis-related markers, and metabolomic profiles. BC treatment significantly strengthened the epithelial barrier, inducing a marked upregulation of Claudin 1 (CLDN1) (11.3 fold), CLDN4 (2.4 fold), Occludin (OCLN, 1.7 fold), and increasing key proteins including ZO-2 and cingulin while reducing LPS-induced FITC-Dextran permeability to 94.5%. BC concurrently modulated innate immune signaling, increasing MyD88 (33.2%), IL-8 (14.6 fold), IL-18 (2.6 fold), and IFNB1 protein levels, while enhancing anti-inflammatory regulation, including a robust rise in DH82-derived IL-10. Apoptosis-renewal markers shifted toward physiological turnover, with increased BCL2 (1.9 fold) and reduced BAK1. Metabolomic profiling of BC activity revealed elevated AMP, abundant Peptide Transporter 1 (PEPT1)-transportable peptides, increased γ-glutamyl metabolites, and lower Glutathione disulfide (GSSG), consistent with AMPK-linked tight-junction assembly and glutathione-supported redox buffering. Together, these data indicate that Bacillus velezensis-derived metabolites positively influence barrier-related, immunological, and metabolic responses in a canine proximal intestinal epithelial system and modulate functional responses in macrophage-like cells. These in vitro findings contribute to the mechanistic understanding of host cellular responses to Bacillus-associated metabolites.