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

PLOS ONE, Dec 2019

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 µM. 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.

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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)


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Na Gao, Dan Zou, Hai-Ling Qiao. 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, PLOS ONE, 2013, 1, DOI: 10.1371/journal.pone.0053038