Research paperEffects of herbal drugs in Mahuang decoction and their main components on intestinal transport characteristics of Ephedra alkaloids evaluated by a Caco-2 cell monolayer model

Ethnopharmacological relevanceMahuang decoction, Ephedra combined with Cassia twig, Bitter apricot kernel and Prepared licorice, has been widely used as a multi-herb prescription in traditional Chinese medicine (TCM). Many modern pharmacological studies have shown that the compatibility application of these four herbs has promising therapeutic effects on respiratory infection, acute glomerulonephritis and chronic renal failure. However, the underlying principles for governing the formulation of Mahuang decoction remain unknown. In this study, we used a Caco-2 cell monolayer model to explicate the possible compatibility mechanism of Mahuang decoction from the perspective of intestinal absorption.Material and methodsFirstly, the apical-to-basolateral and basolarteral-to-apical transport of the main characteristic active alkaloids in Ephedra, l-ephedrine (LEP), d-pseudoephedrine (DPEP) and l-methylephedrine (LMEP), as a single compound, was investigated. Secondly, the influence of main components in Cassia twig, Bitter apricot kernel and Prepared licorice on the transport of LEP, DPEP and LMEP was investigated. Finally, the bidirectional transport of these three alkaloids in single Ephedra extract, in Mahuang decoction and in drug pair extracts, such as Ephedra-Cassia twig, Ephedra-Bitter apricot kernel, Ephedra-Prepared licorice, was assessed.ResultsThe investigated LEP, DPEP and LMEP could transport through the Caco-2 cell monolayer at a high level, with the efflux ratio (ER) of 1.41, 1.33 and 1.30, respectively, when the cells were treated with each single compound solution. In the presence of verapamil, the permeability from apical side to basolateral side (PAB) of the three alkaloids increased significantly (P<0.05), and their ERs decreased. The treatment of cells with Mahuang decoction and the drug pair extracts from Ephedra-Cassia twig, Ephedra-Bitter apricot kernel and Ephedra-Prepared licorice appreciably decreased PAB of LEP, DPEP and LMEP with increased ERs, compared to the treatment with single Ephedra extract. When concomitant administration with herbal drugs and their main ingredients (including cinnamaldehyde-cinnamyl alcohol-cinnamic acid group, volatile oil from Cassia twig, liquiritin-glycyrrhizic acid group from Prepared licorice, Cassia twig extract, Bitter apricot kernel extract and Prepared licorice extract), was adopted, PAB of LEP, DPEP and LMEP were reduced significantly and the ERs of the corresponding compounds were promoted appreciably. Only amygdalin (from Bitter apricot kernel) had little influence on the transport of Ephedra alkaloids.ConclusionThe findings indicate that LEP, DPEP and LMEP in Ephedra extract have similar absorption as in the pure solution of each compound. The intestinal absorption of LEP, DPEP and LMEP is through passive diffusion and these compounds may be P-gp substrates. The compatibility application of Cassia twig, Bitter apricot kernel and Prepared licorice, and their main components except amygdalin can suppress the absorption of the three main Ephedra alkaloids across the Caco-2 cell monolayer. On the basis of our results, Cassia twig, Bitter apricot kernel and Prepared licorice in Mahuang decoction decrease the absorption of Ephedra alkaloids, which may alleviate the drastic diaphoretic function and toxicity of Ephedra.

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