Anti-Inflammatory and Antioxidant Effects of Quercetin, Luteolin, and Proanthocyanidins in Canine PBMCs Stimulated with Escherichia coli

Chronic gastrointestinal disorders in dogs are complex conditions often associated with oxidative stress, dysbiosis, and persistent immune activation, which can impair intestinal barrier integrity and promote bacterial translocation. Among intestinal bacteria, Escherichia coli may act as an opportunistic pathogen under inflammatory conditions and contribute to systemic inflammation. This study aimed to establish an in vitro model using primary canine peripheral blood mononuclear cells stimulated with canine-derived E. coli strains to investigate inflammatory and oxidative responses, and to evaluate the anti-inflammatory and antioxidant effects of selected flavonoids. Inflammatory activation was strongest following exposure to the enrofloxacin-inhibited E. coli 863 strain for 24 h. Treatments with quercetin, luteolin, and grape seed proanthocyanidins at concentrations of 25 and 50 µg/mL were then assessed. Minimum inhibitory and mutant prevention concentrations, intracellular reactive oxygen species, and tumor necrosis factor-α levels were determined. Although the tested flavonoids showed moderate antibacterial activity, all significantly reduced intracellular oxidative stress and inflammatory cytokine production compared to infected controls. These findings suggest that dietary flavonoids may exert beneficial immunomodulatory effects and could serve as potential adjuncts in managing canine chronic gastrointestinal inflammation. Further in vitro and in vivo validation is required to confirm their therapeutic relevance.