Concentration-Dependent Inhibitory Effect of Baicalin on the Plasma Protein Binding and Metabolism of Chlorzoxazone, a CYP2E1 Probe Substrate, in Rats In Vitro and In Vivo
in Rats In Vitro and In Vivo. PLoS ONE 8(1): e53038. doi:10.1371/journal.pone.0053038
Concentration-Dependent Inhibitory Effect of Baicalin on the Plasma Protein Binding and Metabolism of Chlorzoxazone, a CYP2E1 Probe Substrate, in Rats In Vitro and In Vivo
Na Gao 0
Dan Zou 0
Hai-Ling Qiao 0
Daniel S. Sem, Concordia University Wisconsin, United States of America
0 1 Department of Clinical Pharmacology, School of Medicine, Zhengzhou University , Zhengzhou , P. R. China , 2 Department of Histology and Embryology, Henan Medical College for Staff and Workers , Zhengzhou , P. R. China
Some of the components found in herbs may be inhibitors or inducers of cytochrome P450 enzymes, which may therefore result in undesired herb-drug interactions. As a component extracted from Radix Scutellariae, the direct effect of baicalin on cytochrome P450 has not been investigated sufficiently. In this study, we investigated concentration-dependent inhibitory effect of baicalin on the plasma protein binding and metabolism of chlorzoxazone (CZN), a model CYP2E1 probe substrate, in rats in vitro and in vivo. Animal experiment was a randomized, three-period crossover design. Significant changes in pharmacokinetic parameters of CZN such as Cmax, t1/2 and Vd were observed after treatment with baicalin in vivo (P,0.05). Cmax decreased by 25% and 33%, whereas t1/2 increased by 34% and 53%, Vd increased by 37% and 50% in 225 mg/kg and 450 mg/kg baicalin-treated rats, respectively. The AUC and CL of CZN were not affected (P.0.05). Correlation analysis showed that the changes in CZN concentrations and baicalin concentrations were in good correlation (r.0.99). In vitro experiments, baicalin decreased the formation of 6-OH-chlorzoxazone in a concentration-dependent manner and exhibited a competitive inhibition in rat liver microsomes, with a Ki value of 145.8 mM. The values of Cmax/Ki were 20 and 39 after treatment with baicalin (225 and 450 mg/kg), respectively. Protein binding experiments in vivo showed that the plasma free-fraction (fu) of CZN increased 2.6-fold immediately after baicalin treatment (450 mg/kg) and in vitro showed that baicalin (125-2500 mg/L) increased the unbound CZN from 1.63% to 3.58%. The results indicate that pharmacokinetic changes in CZN are induced by inhibitory effect of baicalin on the plasma protein binding of CZN and CYP2E1 activity.
-
Funding: This work was supported by the National Natural Science Foundation of China (No. 81041113). The funder had no role in study design, data collection
and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Baicalin is a major flavone extracted from Radix Scutellariae, a
plant which was widely used in traditional Chinese herbal
medicine [1,2]. Baicalin has been reported to possess a wide
variety of pharmacological properties including anti-inflammatory,
anti-oxidant, anti-viral, anti-cancer properties,and scavenging
potential [3]. As a main component, baicalin has been used in a
variety of preparations such as Huang-Lian-Jie-Du-Tang,
SanHuang-Xie-Xin-Tang, Da-Chai-Hu-Tang, and
Xiao-Chai-HuTang et al [4]. These herbal medicines have been used in Asia
since ancient times and have also been taken by European and
American as remedy supplements and herbal teas in recent years
[5,6].
Some of the components found in herbs may be inhibitors,
inducers, or substrates of cytochrome P450 (CYP) enzymes, and
may cause undesired herb-drug interactions, and potentially limit
its clinic application. CYP enzymes are heme-thiolate proteins that
are responsible for the oxidative metabolism of numerous
xenobiotics as well as endogenous substrates. The activities of
CYP enzymes can be increased or decreased by many drugs,
which is the main reason for drug-induced toxicity via drugdrug
interactions [7]. It had demonstrated that Radix Scutellariae and its
extracts, including baicalin, influenced the pharmacokinetics of
coadministered cyclosporine [8]. Previous studies have found that
baicalin enhanced the levels of liver microsomal CYP and
selectively induced CYP1A1, 2B1, and 2C11 in mice [9]. Jang
et al reported that oral treatment to mice with baicalin resulted in
a significant decrease in acetaminophen-induced CYP2E1 activity
together with its inhibition of acetaminophen-induced CYP2E1
expression [10]. Recent studies had found that baicalin could
significantly induce CYP2B6-catalyzed bupropion hydroxylation
and had no effect on gene expression of CYP3A4 and MDR1
[4,11]. In summary, the effect of baicalin to different kinds of
cytochrome P450 has not been completely understood and the
direct relationship between baicalin and CYP2E1 is still unclear.
CYP2E1 is a natural ethanol-inducible enzyme and responsible
for six percent drug metabolism involving a diversity of drugs,
including alcohols, monocyclic compounds (e.g., benzene,
pnitrophenol), bicyclic heterocycles (e.g., coumarin,) and even (...truncated)