CUHK electronic theses & dissertations collection

Danshen, the dried root of Salvia miltiorrhiza Bunge, is a herb listed in the Chinese Pharmacopoeia for the treatment of cardiovascular and cerebrovascular diseases. Danshen has been reported to have antiplatelet, cardioprotective, anti-inflammatory, hepatoprotective, and anti-HIV effects in preclinical studies. However, exaggerated anticoagulation and bleeding complications have also been observed during concurrent use of Danshen and warfarin in patients, although the mechanism(s) of the herb-drug interaction, pharmacodynamic and/or pharmacokinetic interactions, remained uncertain. Characterization of the cytochrome P450 isoforms responsible for the metabolism(s) of drugs and herbal constituents is important for the identification of potential drug-drug or drug-herb interactions. The present study investigated the effects of Danshen on the metabolism of probe substrates of specific CYP isoforms including CYP1A2, CYP3A and CYP2C9, the isoforms that are responsible for the metabolism of warfarin to assess the potential interactions of Danshen with drugs that utilize these isoforms for their biotransformation.Firstly, the effects of Danshen and its tanshinone components on CYP1A2 activity were investigated in vitro and in vivo in the rat. Formulated Danshen extract, the ethanolic extract and the aqueous extract from Danshen root, and individual tanshinones inhibited phenacetin O-deethylation (CYP1A2) activity in vitro. Enzyme kinetic studies showed that tanshinone I, tanshinone IIA, cryptotanshinone, and dihydrotanshinone were competitive CYP1A2 inhibitors. Acute, sub-chronic and chronic pretreatments of formulated Danshen extract decreased the clearance (CL) of caffeine, with a concomitant increase in the area under concentration-time curve (AUC), and prolongation of the plasma half-life (T 1/2). These results suggested that Danshen inhibited rat CYP1A2 activity and altered the pharmacokinetics of the CYP1A2 probe substrates in vivo.In conclusion, these results confirmed that Danshen-inhibited CYP activity, especially CYP1A2, then CYP2C9/11 (CYP2C9 in human, CYP2C11 in rats) in vitro. In vivo studies confirmed the clearance of the probe substrates was also decreased when co-administered with Danshen. Given that CYP1A2, CYP2C9 and CYP3A4 are responsible for the metabolism and disposition of a large number of drugs currently used in man, the concomitant use of Danshen with drugs which are substrates of CYP1A2, 2C9 and 3A4, especially CYP1A2, must be met with great caution.Secondly, the effects of Danshen and its tanshinone components on CYP3A activity were investigated in vitro and in vivo in the rat. Formulated Danshen extract, the ethanolic extract from Danshen root, and tanshinones inhibited testosterone 6beta-hydroxylation (CYP3A) activity in vitro. Enzyme kinetic studies showed that tanshinone I, tanshinone IIA, and cryptotanshinone were competitive CYP3A inhibitors, whereas dihydrotanshinone was a noncompetitive CYP3A inhibitor. In vivo studies showed the pretreatments of formulated Danshen extract did not significantly change the pharmacokinetics of midazolam.The effects of Danshen and its tanshinones on human CYP1A2 (phenacetin O-deethylation), CYP3A4 (testosterone 6beta-hydroxylation), and CYP2C9 (tolbutamide 4-hydroxylation) activities were also investigated in vitro using pooled human liver microsomes and human CYP isoforms. The ethanolic fraction of Danshen root was more effective than water-soluble fraction in inhibiting human CYP1A2, CYP3A4 and CYP2C9 activities. Enzyme kinetic studies showed that tanshinone I, tanshinone IIA, and cryptotanshinone were competitive inhibitors of CYP1A2, CYP3A4 and CYP2C9 with varying effectiveness. Dihydrotanshinone was not a competitive inhibitor of CYP1A2 and CYP2C9, but a noncompetitive CYP3A4 inhibitor. CYP1A2 was most affected and CYP3A4 was least affected by Danshen and tanshinones. Compared with the results obtained from rat and human, rat is a good animal model for predicting Danshen-drug interactions in humans, especially drugs which are substrates of CYP1A2.Thirdly, the effects of Danshen and its tanshinone components on CYP2C11 activity were investigated in vitro and in vivo in the rat. Formulated Danshen extract, the ethanolic extract from Danshen root, and tanshinones inhibited testosterone 2alpha-hydroxylation (CYP2C11) activity in vitro. Enzyme kinetic studies showed that tanshinone I, tanshinone IIA, cryptotanshinone, and dihydrotanshinone were competitive CYP2C11 inhibitors. Sub-chronic pretreatment of formulated Danshen extract increased the AUC, T1/2 but decreased CL of tolbutamide. These results suggested that Danshen inhibited the CYP2C activity in the rat. In conclusion, these results confirmed the possible mechanism is enzyme inhibition, involved in the interaction of Danshen and warfarin previously observed in rats.Wang, Xin."September 2007."Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4699.Thesis (Ph.D.)--Chinese University of Hong Kong, 2007.Includes bibliographical references (p. 284-302).Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Abstract in English and Chinese.School code: 1307