Limonin attenuates hyperlipidemia by regulating the gut microbiota-bile acid-farnesoid X receptor axis

Hyperlipidemia is an established risk factor for cardiovascular disease. Limonin, a natural tetracyclic triterpenoid compound found in the traditional Chinese herb Tangerine peel and citrus fruits, has been shown to ameliorate hyperlipidemia, although the underlying mechanisms of action are unknown. The present study employed a comprehensive approach integrating to assess the efficacy of Limonin in the treatment of hyperlipidemia and to explore its molecular mechanisms. Hyperlipidemia model was induced by high-fat diet (HFD). The effects of Limonin on hyperlipidemia were evaluated through serum, liver lipid, and Hematoxylin & eosin (H&E). Then, the mechanism of Limonin alleviates hyperlipidemia was explored by network pharmacology. Targeted metabolism was used to measure bile acids (BAs)’ changes in serum and fecal, and 16 S rDNA sequencing of gut microbiota. Finally, the expression of genes and proteins about FXR/FGF15, ASBT, and FGF15/FGFR4 signaling pathways in the distal ileum or liver was detected by qPCR, immunohistochemistry, and Western blotting. The results confirmed the significant anti-hyperlipidemia effect of Limonin. Network pharmacology analysis revealed that Limonine alleviates hyperlipidemia is possibly closely pertaining to BAs metabolism. In a mouse model of hyperlipidemia, Limonin altered the colonic BAs profile, especially in terms of elevated levels of conjugated BAs. Limonin reshaped the structure of the gut microbiome by decreasing bile salt hydrolase (BSH)-producing genera, including Lactobacillus, Bacteroides, Clostridium, Streptococcus, and Adlercreutzia. Decreased BSH activity increased levels of conjugated BAs, which inhibited activation of ileum FXR, facilitated BAs synthesis and fecal BAs excretion. The decreased FXR activity resulted in lower expression of FGF15 and ASBT in the distal ileum, lower expression of FGF15 and its receptor in the liver, and increased expression of CYP7A1 in the liver. Limonin remodels the gut microbiota to reduce BSH activity and to activate BAs synthesis pathways, thereby ameliorating dyslipidemia. These results provide a theoretical basis for clinical investigations into the use of Limonin in anti-hyperlipidemia therapies.