Anti-inflammatory Effect of Pomelo Peel and Its Bioactive Coumarins

Citrus grandis (L.) Osbeck is a popular fruit cultivated around the world, and its peels are sometimes used for the treatment of cough, abdominal pain, and indigestion in China. However, the peel is discarded after fruit consumption in most cases, and its chemical constituents and biological activities have not been validated before. The present study focused on evaluation of the chemical and pharmacological profile of coumarins from peels of C. grandis against inflammation. The extracts and phytochemicals from peels of C. grandis were prepared, and anti-inflammatory activities were carried out in vivo and in vitro, including inhibiting xylene-induced ear edema and carrageenan-induced paw edema in mice and the production of inflammatory cytokines (interleukin 1β, prostaglandin 2, and tumor-necrosis factor α) in lipopolysaccharide (LPS)-induced RAW 264.7 cells. Results indicated that methanolic extract, ethyl acetate fraction, and four major coumarins (compounds 7, 8, 13, and 16) inhibited swelling induced by xylene and carrageenan, separately, in vivo. Furthermore, 18 coumarins inhibited inflammatory factor secretion in macrophages primed by LPS, in which compounds 4, 6, 7, 10, 17 showed the most pronounced change, which were comparable to dexamethasone. In summary, peel of C. grandis showed an anti-inflammatory effect and coumarin compounds were responsible for regulating inflammatory mediators and cytokines, which might provide a novel nutritional strategy for inflammatory diseases.