Cooperative interactions between <i>Veillonella ratti</i> and <i>Lactobacillus acidophilus</i> ameliorate DSS-induced ulcerative colitis in mice

Abstract

<i>Veillonella</i> and <i>Lactobacillus</i> species are key regulators of a healthy gut environment through metabolic cross-feeding, influencing lactic acid and short-chain fatty acid (SCFA) levels, which are crucial for gut health. This study aims to investigate how <i>Veillonella ratti</i> (<i>V. ratti</i>) and <i>Lactobacillus acidophilus</i> (LA) interact with each other and alleviate dextran sulfate sodium (DSS)-induced ulcerative colitis (UC) in a mouse model. We assess their metabolic interactions regarding carbon sources through co-culturing in a modified medium. In the <i>in vitro</i> experiments, <i>V. ratti</i> and LA were inoculated in mono-cultures and co-culture, and viable cell counts, OD₆₀₀, pH, lactic acid, glucose and SCFAs were measured. For the <i>in vivo</i> experiment, 60 C57BL/6 mice were randomly divided into five groups and administered <i>V. ratti</i> and LA alone or in combination <i>via</i> oral gavage (1 × 10⁹ CFU mL^-1 per day per mouse) for 14 days. On the seventh day, 2.5% DSS was added to the drinking water to induce colitis. The effects of these probiotics on UC were evaluated by assessing intestinal barrier integrity and intestinal inflammation in the gut microenvironment. <i>In vitro</i> results demonstrated that co-culturing <i>V. ratti</i> with LA significantly increased viable cell numbers, lactic acid production, and SCFA production, while reducing pH and glucose levels in the medium. <i>In vivo</i> findings revealed that intervention with <i>V. ratti</i>, particularly in combination with LA, alleviated symptoms, including weight loss, colon shortening, and tissue damage. These probiotics mitigated intestinal inflammation by down-regulating pro-inflammatory molecules, such as IL-6, IL-1β, IL-γ, iNOS, and IFN-γ, as well as oxidative stress markers, including MDA and MPO. Concurrently, they upregulated the activity of anti-inflammatory enzymes, namely, SOD and GSH, and promoted the production of SCFAs. The combined intervention of <i>V. ratti</i> and LA significantly increased acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, and total SCFAs in cecal contents. Furthermore, the intervention of <i>V. ratti</i> and LA increased the abundance of beneficial bacteria, such as <i>Akkermansia</i>, while reducing the abundance of harmful bacteria, such as <i>Escherichia</i>-<i>Shigella</i> and <i>Desulfovibrio</i>, thereby mitigating excessive inflammation. These findings highlight the enhanced therapeutic effects resulting from the interactions between <i>V. ratti</i> and LA, demonstrating the potential of this combined probiotic approach.