Protective role of casuarinin from Melastoma malabathricum against a mouse model of 5-fluorouracil–induced intestinal mucositis: Impact on inflammation and gut microbiota dysbiosis

•Casuarinin isolated from the root of M. malabathricum, which could be a neutrophil elastase inhibitor.•Casuarinin improved FUIIM-associated symptoms and tissue damage in mice.•Casuarinin attenuated abnormal inflammatory responses by suppressing oxidative stress and neutrophil overexpressed.•Casuarinin alleviated intestinal barrier dysfunction and gut microbiota dysbiosis in FUIIM. 5-FU-induced intestinal mucositis (FUIIM) is a common gastrointestinal side effect of chemotherapy, leading to gastric pain in clinical cancer patients. In a previous study, we demonstrated that neutrophil elastase (NE) inhibitors could alleviate FUIIM and manipulate the homeostasis of the gut microbiota. The root of Melastoma malabathricum, also called Ye-Mu-Dan, has been used as a traditional Chinese medicine for gastrointestinal disease. Water extract of the roots of M. malabathricum exhibits an inhibitory effect on NE, with an IC50 value of 9.13 μg/ml. In this study, we aimed to isolate an anti-NE compound from the root of M. malabathricum and to determine the protective effect of the bioactive component on a mouse model of FUIIM with respect to tissue damage, inflammation, intestinal barrier dysfunction, and gut microbiota dysbiosis. A water extract of the roots of M. malabathricum was prepared and its major bioactive compound, was identified using bioactivity-guided fractionation. The effects of samples on the inhibition of NE activity were evaluated using enzymatic assays. To evaluate the effects of the bioactive compound in an FUIIM animal model, male C57BL/6 mice treated with or without casuarinin (50 and 100 mg/kg/day, p.o.), and then received of 5-fluorouracil (50 mg/kg/day) intraperitoneally for 5 days to induce FUIIM. Histopathological staining was used to monitor the tissue damage, proliferation of intestinal crypts, and expression of tight junction proteins. The inflammation score was estimated by determining the levels of oxidative stress, neutrophil-related proteases, and proinflammatory cytokines in tissue and serum. The ecology of the gut microbiota was evaluated using 16S rRNA gene sequencing. Casuarinin had the most potent and selective effect against NE, with an IC50 value of 2.79 ± 0.07 μM. Casuarinin (100 mg/kg/day, p.o.) significantly improved 5-FU-induced body weight loss together with food intake reduction, and it also significantly reversed villus atrophy, restored the proliferative activity of the intestinal crypts, and suppressed inflammation and in