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Absorption and metabolism of three monoester-diterpenoid alkaloids in Aconitum carmichaeli after oral administration to rats by HPLC–MS

Zhang, Hai, Wu, Qiong, Li, Wuhong, Sun, Sen, Zhang, Wen, Zhu, Zhenyu, Zhang, Guoqing, Chai, Yifeng
Journal of ethnopharmacology 2014 v.154 no.3 pp. 645-652
Aconitum, P-glycoproteins, absorption, alkaloids, bacterial artificial chromosomes, bioavailability, chemical constituents of plants, herbal medicines, high performance liquid chromatography, liver microsomes, males, mass spectrometry, oral administration, pharmacokinetics, quality control, rats, toxicity, traditional medicine
Ethnopharmacological relevance:Aconitum carmichaelii (AC) is a well-known herbal medicine for its excellent pharmacological effects and toxicity. The monoester-diterpenoid alkaloids (MDAs), including benzoylmesaconine (BMC), benzoylaconine (BAC) and benzoylhyaconine (BHC), are the main active components in AC. It was found that the diester alkaloids could be transformed into monoester-diterpenoid alkaloids after being decocted. In Chinese pharmacopoeia, the MDAs are also used as phytochemical markers for the quality control of AC. Benzoylmesaconine, benzoylaconine and benzoylhyaconine are representatives of monoester-diterpenoid alkaloids. It was reported that the absolute bioavailability of MDAs was very low but there was toxicity often occurred in AC. Because most of DDAs are transformed into MDAs after decoction, we speculate that some other components may promote the bioavailability of MDAs but result in toxicity by enhancing their absorption. To demonstrate the dynamic changes of MDAs in vivo and reveal the causes of low bioavailability and toxicity, this study will explore the mechanisms of absorption and metabolism of 3 MDAs.Materials and methods: A sensitive, accurate and specific LC-MS method was developed to determine the three MDAs in rat plasma. The pharmacokinetic parameters were estimated after orally administered 3 MDAs to the Male Sprague-Dawley rats, and the metabolism stability was calculated after incubating with rat liver microsomes, finally, the absorption characteristics of the 3 MDAs were investigated using Caco-2 transwell model.Results: It was found that the pharmacokinetic parameters of 3 MDAs were similar, Cmax and Tmax were very small, and t1/2 was large, which indicated 3 MDAs can be absorbed rapidly and is difficult to be metabolized or excreted. However, the low Cmax indicated that the bioavailability of 3 MDAs will be very low and their absorption may be inhibited by some transport proteins. By incubating three MDAs in rat liver microsomes, it was proved that they almost can’t be metabolized in vivo. The Caco-2 transwell experiments reveal that the P-gp inhibits the absorption of MDAs.Conclusions: LC-MS combined with a direct precipitation method for the simultaneous quantification of 3 MDAs in rat plasma has been developed and validated and successfully used in pharmacokinetic study of 3 MDAs. It was proved that the three components almost can’t be metabolized in vivo, and P-gp inhibits the absorption of MDAs.