Limonene alleviated ulcerative colitis via anti-inflammation, anti-oxidation and regulating intestinal microenvironment in vivo and in vitro

Limonene, a monoterpene naturally abundant in various Citrus fruits, is widely used as a fragrance component and dietary supplement. Ulcerative colitis (UC), a representative inflammatory bowel disease, is characterized by an arising incidence and considerable impact on human health. Although several reports have demonstrated the beneficial effects of limonene on UC, detailed mechanisms remain incompletely understood. In this study, we employed a dextran sulfate sodium (DSS)-induced UC murine model and a lipopolysaccharide (LPS)-stimulated Caco-2 cell model to explore the mechanisms of limonene on UC. The results revealed that limonene significantly decreased disease activity index (DAI) score and alleviated pathological damage in UC mice, exhibiting therapeutic potential for UC. Limonene significantly inhibited interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and malondialdehyde (MDA) while increased superoxide dismutase (SOD) in both DSS-induced UC mice and LPS-induced Caco-2 cells. Furthermore, limonene significantly increased expressions of Zonula occludens-1 (ZO-1), occludin, and claudin-1, thereby enhancing intestinal barrier integrity. Limonene mitigated UC-associated dysbiosis by shifting the gut microbial composition toward that of healthy controls. Specifically, it modulated the microbiota at the phylum, family, genus and species levels, increasing the abundance of anti-inflammatory bacteria while decreasing inflammatory related taxa. Collectively, our in vivo and in vitro results demonstrate that limonene alleviates UC involving in anti-inflammation, anti-oxidation, restoration of intestinal barrier integrity and regulation of the gut microbiota. Future studies are warranted to explore whether gut microbial metabolites contribute to the protective effects of limonene in UC.