Comparison of the chemical constituents of raw Fructus Aurantii and Fructus Aurantii stir-baked with bran, and the biological effects of auraptene

Fructus Aurantii (FA) is a Chinese herbal medicine commonly used in clinical practice to improve gastrointestinal motility, treat dyspepsia, and relieve constipation. More than 20 processing methods of FA have been recorded, among which FA stir-baked with bran is the earliest, most time consuming, and the most popular one. Raw FA has a strong ability to promote qi-moving and has middle-energizer-soothing effects; therefore, it is often used to relieve hypochondrium distension and pain, and to relax the stagnation of the liver Qi. FA stir-baked with bran is more effective in nourishing the stomach and curing indigestion. In this study, the chemical composition and differences between raw FA and FA stir-baked with bran were systematically compared. The chemical components that increased after stir-baking FA and bran were separated and their pharmacodynamic characteristics were determined. Lastly, the processing mechanism of FA was further explained. Twelve main chemicals in raw FA and FA stir-baked with bran were compared using high-performance liquid chromatography (HPLC). The main differential components were identified, separated, purified, and then analyzed using pharmacodynamic tests. The intestine-pushing test, in vitro smooth muscle test, and in vitro acetylcholinesterase (AchE) activity test in mice were performed to explain the mechanism of auraptene in improving gastrointestinal motility. Using HPLC, the primary chemical that differed between raw FA and FA stir-baked with bran was identified as auraptene. The processed FA was extracted, separated, and purified to obtain pure auraptene. The intestine-pushing test in mice showed that low (0.6 mg·kg−1) and medium doses (1.2 mg·kg−1) of auraptene could promote peristalsis of the small intestine, whereas a high dose (2.4 mg·kg−1) inhibited peristalsis. In vitro studies on the smooth muscle of mice showed that a low dose of auraptene (0.2 mmol·L−1, 10–800 μL) could promote contraction, whereas a high dose (0.2 mmol·L−1, >1000 μL) had the opposite effect. Auraptene has a mechanism of action similar to that of the acetylcholinesterase inhibitor, neostigmine. Additionally, auraptene could inhibit AchE activity in vitro. Auraptene is the main chemical constituent that differs between raw FA and FA stir-baked with bran. Pharmacodynamic tests showed that auraptene has a cholinergic effect, by virtue of its role as an acetylcholinesterase inhibitor. Moreover, auraptene could dually regulate the gastrointestinal smooth muscle. Auraptene was present in low levels and its content varied in FA stir-baked with bran, depending on the origin and source of FA, and the treatment procedures it was subjected to. In the Chinese Pharmacopoeia, the recommended dose of FA stir-baked with bran is a low dose of 3–10 g, which effectively promotes small-intestinal peristalsis. The mechanism of action is attributed to an increase in the relative content of acetylcholine by the inhibition of AchE activity to promote gastrointestinal motility. The increased levels of auraptene in FA stir-baked with bran are the main reason and the primary purpose for the change in its medicinal properties. This technique, therefore, has potential to be used as one of the main processing mechanisms of raw FA.