ETHNOPHARMACOLOGICAL RELEVANCE:Aurantii Fructus Immaturus is a traditional qi-regulating herb with a bitter, slightly sour taste and refreshing aroma. It breaks stagnant qi, promotes digestion, resolves phlegm, and treats constipation. Clinically, its bran-fried form moderates its potent properties. However, the material basis of its bitterness and its link to energy metabolism modulation remain unclear.
AIM OF THE STUDY:To screen bitter constituents of Aurantii Fructus Immaturus using molecular docking and high-performance liquid chromatography (HPLC), and to examine the changes in key bitter compound contents before and after bran-frying of different sources. Further, to investigate the impact of these bitter constituents on mitochondrial energy metabolism in rats with slow transit constipation (STC) through pharmacodynamic experiments.
MATERIALS AND METHODS:Using molecular docking technology and molecular dynamics simulations, the chemical components of Aurantii Fructus Immaturus were docked with bitter taste receptors to screen for potential bitter compounds. HPLC was used to quantitatively analyze the key bitter constituents of Aurantii Fructus Immaturus from various sources before and after bran-frying. STC was induced in rats with loperamide hydrochloride, followed by interventions with Aurantii Fructus Immaturus and bran-fried products, as well as their bitter constituents. Therapeutic effects were evaluated through assessments of mental state, body weight, and fecal morphology. Histopathological changes in colonic tissues were observed using hematoxylin and eosin (HE) staining. Mitochondrial respiratory chain complex activities and ATP levels in colonic and gastric tissues were measured via ELISA to assess mitochondrial energy status. Real-time quantitative PCR (qPCR) and Western blot analyses determined the mRNA and protein expression levels of Drp1, Mfn1, Mfn2, Opa1, and Fis1 in colonic mitochondria.
RESULTS:Molecular docking identified 36 bitter chemical constituents, mainly flavonoids and limonoids, including naringin, hesperidin, and others. Twelve major bitter components-naringin, neohesperidin, hesperidin, eriocitrin, narirutin, didymin, poncirin, nobiletin, tangeretin, limonin, nomilin, and obacunone-were used as indicators in this study. HPLC content analysis and statistical evaluation revealed that the main sources of bitter taste differences among Aurantii Fructus Immaturus were hesperidin, didymin, neohesperidin, and naringin. Naringin and neohesperidin levels were lower in sweet orange but higher in sour orange. Conversely, hesperidin and didymin levels were higher in sweet orange and lower in sour orange. The bitter component content was significantly higher in sour orange than in sweet orange. After bran-frying, the content of bitter components decreased across sources. Specifically, neohesperidin, naringin, hesperidin, and narirutin significantly declined in sour orange bran-frying, while neohesperidin, naringin, and nobiletin significantly decreased in sweet orange. Pharmacological experiments showed that the high-dose group of bran-fried Aurantii Fructus Immaturus significantly alleviated STC symptoms in rats compared to other groups. All treatment groups upregulated ATP, MRCC Ⅰ, MRCC Ⅳ, and MRCC V expression in gastric and colonic tissues, indicating improved mitochondrial function. They also increased Mfn1, Mfn2, and Opa1 mRNA and protein levels and decreased Drp1 and Fis1 expression, thereby improving mitochondrial energy metabolism and alleviating constipation symptoms. The therapeutic efficacy followed the order: bran-fried Aurantii Fructus Immaturus > raw Aurantii Fructus Immaturus > Aurantii Fructus Immaturus bitter ingredient group.
CONCLUSION:Molecular docking validated that the bitter components of Aurantii Fructus Immaturus are mainly flavonoids and limonoids, consistent with existing literature, confirming the approach's accuracy. The content of bitter components varied significantly among sources, decreasing after bran-frying in both sour and sweet oranges. All forms-raw and bran-fried-demonstrated potential in treating STC by improving mitochondrial energy metabolism, with bran-fried products showing superior effects. The bitter components of Aurantii Fructus Immaturus also effectively relieved constipation symptoms, supporting the role of bitter constituents in promoting excretion effects.