Inhibitory Effects of Baicalin on the Expression and Activity of CYP3A Induce the Pharmacokinetic Changes of Midazolam in Rats

The Pharmacological Efficacy of Baicalin in Inflammatory Diseases

Baicalin is one of the most abundant flavonoids found in the dried roots of Scutellaria baicalensis Georgi (SBG) belonging to the genus Scutellaria. While baicalin is demonstrated to have anti-inflammatory, antiviral, antitumor, antibacterial, anticonvulsant, antioxidant, hepatoprotective, and neuroprotective effects, its low hydrophilicity and lipophilicity limit the bioavailability and pharmacological functions. Therefore, an in-depth study of baicalin's bioavailability and pharmacokinetics contributes to laying the theoretical foundation for applied research in disease treatment. In this view, the physicochemical properties and anti-inflammatory activity of baicalin are summarized in terms of bioavailability, drug interaction, and inflammatory conditions.

Effect of polyethylene glycol 400 on the pharmacokinetics and tissue distribution of baicalin by intravenous injection based on the enzyme activity of UGT1A8/1A9

Baicalin (BG) is a bioactive flavonoid extracted from the dried root of the medicinal plant, Scutellaria radix (SR) (dicotyledonous family, Labiatae), and has several biological activities. Polyethylene glycol 400 (PEG400) has been used as a suitable solvent for several traditional Chinese medicines (TCM) and is often used as an excipient for the compound preparation of SR. However, the drug-excipient interactions between BG and PEG400 are still unknown. Herein, we evaluated the effect of a single intravenous PEG400 administration on the BG levels of rats using pharmacokinetic and tissue distribution studies. A liver microsome and recombinant enzyme incubation system were used to further confirm the interaction mechanism between PEG400 and UDP-glucuronosyltransferases (UGTs) (UGT1A8 and UGT1A9). The pharmacokinetic study demonstrated that following the co-intravenous administration of PEG400 and BG, the total clearance (CL_z) of BG in the rat plasma decreased by 101.60% (p < 0.05), whereas the area under the plasma concentration-time curve (AUC)_0-t and AUC_0-inf increased by 144.59% (p < 0.05) and 140.05% (p < 0.05), respectively. Additionally, the tissue distribution study showed that the concentration of BG and baicalein-6-O-β-D-glucuronide (B6G) in the tissues increased, whereas baicalein (B) in the tissues decreased, and the total amount of BG and its metabolites in tissues altered following the intravenous administration of PEG400. We further found that PEG400 induced the UGT1A8 and UGT1A9 enzyme activities by affecting the maximum enzymatic velocity (V_max) and Michaelis-Menten constant (K_m) values of UGT1A8 and UGT1A9. In conclusion, our results demonstrated that PEG400 interaction with UGTs altered the pharmacokinetic behaviors and tissue distribution characteristics of BG and its metabolites in rats.

Baicalin Enhanced Oral Bioavailability of Sorafenib in Rats by Inducing Intestine Absorption

Background: Sorafenib (SOR) is an oral, potent, selective, irreversible epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) used as the first-line therapy for advanced hepatocellular carcinoma (HCC). Baicalin (BG) is used as adjuvant therapy for hepatitis, which accounts for the leading cause of the development of HCC, and is commonly coadministered with SOR in clinic. The purpose of the current study was to characterize the pharmacokinetic changes of SOR and the potential mechanism when SOR is administered concomitantly with BG in rats for single and multiple doses.

Methods: Parallel randomized pharmacokinetic studies were performed in rats which received SOR (50 mg/kg, i.g.) alone or coadministered with BG (160 mg/kg, i.g.) for single and multiple doses (7 days). Plasma SOR levels were quantified by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS). Rat liver microsomes (RLMs) which isolated from their livers were analyzed for CYP3A and SOR metabolism activities. The inhibitory effect of BG on the metabolism of SOR was also assessed in pooled human liver microsomes (HLMs). The effects of BG on the intestine absorption behaviors of SOR were assessed in the in situ single-pass rat intestinal perfusion model.

Results: Coadministration with BG (160 mg/kg, i.g.) for single or multiple doses significantly increased the C_max, AUC_0–t, and AUC_0–∞ of orally administered SOR by 1.68-, 1.73-, 1.70-fold and 2.02-, 1.65-, 1.66- fold in male rats and by 1.85-, 1.68-, 1.68-fold and 1.57-, 1.25-, 1.24- fold in female rats, respectively (p < 0.01 or p < 0.05). In vitro incubation assays demonstrated that there were no significant differences of K_m, V_max, and CL_int of 1-OH MDZ and SOR N-oxide in RLMs between control and multiple doses of BG-treated groups. BG has no obvious inhibitory effects on the metabolism of SOR in HLMs. In comparison with SOR alone, combining with BG significantly increased the permeability coefficient (P_eff) and absorption rate constant (K_a) of the SOR in situ single-pass rat intestinal perfusion model.

Conclusion: Notably enhanced oral bioavailability of SOR by combination with BG in rats may mainly account for BG-induced SOR absorption. A greater understanding of potential DDIs between BG and SOR in rats makes major contributions to clinical rational multidrug therapy in HCC patients. Clinical trials in humans and HCC patients need to be further confirmed in the subsequent study.

Drug-herb interactions between Scutellaria baicalensis and pharmaceutical drugs: Insights from experimental studies, mechanistic actions to clinical applications

Whilst the popular use of herbal medicine globally, it poses challenges in managing potential drug-herb interaction. There are two folds of the drug-herb interaction, a beneficial interaction that may improve therapeutic outcome and minimise the toxicity of drug desirably; by contrast, negative interaction may evoke unwanted clinical consequences, especially with drugs of narrow therapeutic index. Scutellaria baicalensis Georgi is one of the most popular medicinal plants used in Asian countries. It has been widely used for treating various diseases and conditions such as cancer, diabetes, inflammation, and oxidative stress. Studies on its extract and bioactive compounds have shown pharmacodynamic and pharmacokinetic interactions with a wide range of pharmaceutical drugs as evidenced by plenty of in vitro, in vivo and clinical studies. Notably, S. baicalensis and its bioactives including baicalein, baicalin and wogonin exhibited synergistic interactions with many pharmaceutical drugs to enhance their efficacy, reduce toxicity or overcome drug resistance to combat complex diseases such as cancer, diabetes and infectious diseases. On the other hand, S. baicalensis and its bioactives also affected the pharmacokinetic profile of many drugs in absorption, distribution, metabolism and elimination via the regulatory actions of the efflux pumps and cytochrome P450 enzymes. This review provides comprehensive references of the observed pharmacodynamic and pharmacokinetic drug interactions of Scutellaria baicalensis and its bioactives. We have elucidated the interaction with detailed mechanistic actions, identified the knowledge gaps for future research and potential clinical implications. Such knowledge is important for the practice of both conventional and complementary medicines, and it is essential to ensure the safe use of related herbal medicines. The review may be of great interest to practitioners, consumers, clinicians who require comprehensive information on the possible drug interactions with S. baicalensis and its bioactives.

Unraveling the Molecular Mechanism of Traditional Chinese Medicine: Formulas Against Acute Airway Viral Infections as Examples

Herbal medicine, including traditional Chinese medicine (TCM), is widely used worldwide. Herbs and TCM formulas contain numerous active molecules. Basically, they are a kind of cocktail therapy. Herb-drug, herb-food, herb-herb, herb-microbiome, and herb-disease interactions are complex. There is potential for both benefit and harm, so only after understanding more of their mechanisms and clinical effects can herbal medicine and TCM be helpful to users. Many pharmacologic studies have been performed to unravel the molecular mechanisms; however, basic and clinical studies of good validity are still not enough to translate experimental results into clinical understanding and to provide tough evidence for better use of herbal medicines. There are still issues regarding the conflicting pharmacologic effects, pharmacokinetics, drug interactions, adverse and clinical effects of herbal medicine and TCM. Understanding study validation, pharmacologic effects, drug interactions, indications and clinical effects, adverse effects and limitations, can all help clinicians in providing adequate suggestions to patients. At present, it would be better to use herbs and TCM formulas according to their traditional indications matching the disease pathophysiology and their molecular mechanisms. To unravel the molecular mechanisms and understand the benefits and harms of herbal medicine and TCM, there is still much work to be done.

Pharmacokinetics and Bioavailability Enhancement of Baicalin: A Review

Baicalin is one of the major bioactive components of Scutellaria radix, a Chinese herb that has been used since ancient times. Baicalin has various pharmacological activities, including antitumor, antimicrobial, and antioxidant, and has wide clinical applications. Baicalin displays a distinct pharmacokinetic profile including gastrointestinal hydrolysis, enterohepatic recycling, carrier-mediated transport, and complicated metabolism. The in vivo disposition of baicalin is affected by combinations of other herbs and baicalin can interact with other co-administered drugs due to competition between metabolic enzymes and protein binding. Furthermore, baicalin exhibits altered pharmacokinetic properties under different pathological conditions. Due to its low bioavailability, emerging novel baicalin preparations including nano/micro-scale baicalin delivery systems show better absorption and higher bioavailability in preclinical studies, and show promise for future clinical applications. Thus, this current review offers a comprehensive report on the pharmacokinetic behavior of baicalin and strategies to improve its bioavailability.

A Single Dose of Baicalin Has No Clinically Significant Effect on the Pharmacokinetics of Cyclosporine A in Healthy Chinese Volunteers

Despite its narrow therapeutic window and large interindividual variability, cyclosporine A (CsA) is the first-line therapy following organ transplantation. Metabolized mainly by CYP3A and being a substrate of P-glycoprotein (P-gp), CsA is susceptible to drug–drug interactions. Baicalin (BG) is a drug used for adjuvant therapy of hepatitis in traditional Chinese medicine. Since its aglycone baicalein (B) inhibits CYP3A and P-gP, co-administration might affect CsA pharmacokinetics. This study investigated the effect of BG on CsA pharmacokinetics. In a two-period study, 16 healthy volunteers received a single 200 mg oral CsA dose alone (reference period) or in combination with 500 mg BG (test period). Pharmacokinetic evaluation of CsA was carried out using non-compartmental analysis (NCA) and population pharmacokinetics (popPK). Treatments were compared using the standard bioequivalence method. Based on NCA, 90% CIs of AUC and C_max test-to-reference ratios were within bioequivalence boundaries. In the popPK analysis, a two-compartment model (clearance/F 62.8 L/h, central and peripheral volume of distribution/F 254 L and 388 L) with transit compartments for absorption appropriately described CsA concentrations. No clinically relevant effect of 500 mg BG co-administration on CsA pharmacokinetics was identified and both treatments were well tolerated.

Conflicting alterations in hepatic expression of CYP3A and enzyme kinetics in rats exposed to 5-fluorouracil: relevance to pharmacokinetics of midazolam

1. 5-Fluorouracil (5-FU) is a pyrimidine derivative widely used for the treatment of cancer. In this study, we investigated the effects of 5-FU on the protein expression of hepatic CYP3A and their enzyme activity for metabolizing midazolam (MDZ), a typical substrate of CYP3A, in rat liver microsomes. We also examined the pharmacokinetic behavior of intravenously administered MDZ in rats treated with 5-FU (120 mg/kg, ip). 2. 5-FU was shown to induce hepatic CYP3A2 protein 2 days after administration without changing the expression of CYP3A1/3A23. However, affinity of 5-FU-inducible CYP3A protein to MDZ for its 4- and 1'-hydroxylation was decreased. Furthermore, the susceptibility of MDZ hydroxylation activity to a CYP3A inhibitor differed between the control and 5-FU groups. 3. Pharmacokinetic analysis of the MDZ disposition demonstrated no significant differences in the total clearance (CL_tot) and elimination rate constant (k_e) between the control and 5-FU-treated rats. Lack of alteration in the metabolic clearance of MDZ may be attributable to the induction of CYP3A protein with reduced affinity for the substrate of CYP3A enzymes. 4. Our findings provide novel information regarding the manifestation of inductive and interfering actions of 5-FU toward hepatic CYP3A to help in assessing the pharmacokinetics of CYP3A substrate drugs.

Baicalin reduces ciclosporin bioavailability by inducing intestinal p-glycoprotein in rats

Objectives

To investigate the effects of multiple doses of baicalin (BG) on the pharmacokinetics of ciclosporin (CsA) in rats and the potential mechanisms.

Methods

Pharmacokinetic parameters of CsA were determined in male rats after administration of CsA (3 mg/kg, i.g. or i.v.) to rats in the presence and absence of BG (80 mg/kg, i.g. or i.v.) for 7 days. The livers and intestines of rats were isolated and the CYP3A and p-glycoprotein (P-gp) expression were analysed. The effect of BG on the intestinal absorptive behaviour of CsA was also investigated using in-vitro everted rat gut sac model.

Key findings

Baicalin (80 mg/kg, i.v., 7 days) had no effect on the intravenously administered CsA. However, BG (80 mg/kg, i.g., 7 days) significantly decreased the Cmax, AUC0–t and AUC0–∞ of orally administered CsA by 38, 26 and 25%, respectively (P &lt; 0.01 or P &lt; 0.05). Further study revealed that the expression of P-gp in intestine increased in oral multiple doses of BG-treated rats. The in-vitro everted rat gut sac model demonstrated BG (10 μm) significantly decreased the absorption of CsA (10 μm) in intestine (P &lt; 0.05).

Conclusions

Multiple doses of BG decreased the oral bioavailability of CsA in rats significantly, which may be mainly attributable to inhibition of absorption of CsA in intestine and induction of P-gp. The interaction between BG and CsA may occur when BG and CsA were co-administered for long-term use. The dosage adjustment and blood concentration monitoring of CsA may be required in clinic.

Therapeutic Risk and Benefits of Concomitantly Using Herbal Medicines and Conventional Medicines: From the Perspectives of Evidence Based on Randomized Controlled Trials and Clinical Risk Management

Despite increased awareness of the potential of herb-drug interactions (HDIs), the lack of rigorous clinical evidence regarding the significance provides a challenge for clinicians and consumers to make rational decisions about the safe combination of herbal and conventional medicines. This review addressed HDIs based on evidence from randomized controlled trials (RCTs). Literature was identified by performing a PubMed search till January 2017. Risk description and clinical risk management were described. Among 74 finally included RCTs, 17 RCTs (22.97%) simply addressed pharmacodynamic HDIs. Fifty-seven RCTs (77.03%) investigated pharmacokinetic HDIs and twenty-eight of them showed potential or actual clinical relevance. The extent of an HDI may be associated with the factors such as pharmacogenomics, dose of active ingredients in herbs, time course of interaction, characteristics of the object drugs (e.g., administration routes and pharmacokinetic profiles), modification of herbal prescription compositions, and coexistence of inducers and inhibitors. Clinical professionals should enhance risk management on HDIs such as increasing awareness of potential changes in therapeutic risk and benefits, inquiring patients about all currently used conventional medicines and herbal medicines and supplements, automatically detecting highly substantial significant HDI by computerized reminder system, selecting the alternatives, adjusting dose, reviewing the appropriateness of physician orders, educating patients to monitor for drug-interaction symptoms, and paying attention to follow-up visit and consultation.

Role of Intestinal Microbiota in Baicalin-Induced Drug Interaction and Its Pharmacokinetics

Since many glycoside compounds in natural products are hydrolyzed by intestinal microbiota when administered orally, it is of interest to know whether their pharmacological effects are derived from the glycoside itself or from the aglycone form in vivo. An interesting example is baicalin versus baicalein, the aglycone of baicalin, which is contained in some herbs from Labiatae including Scutellaria baicalensis Georgi and Scutellaria lateriflora Linne. The herbs have been extensively used for treatment of inflammatory diseases in Asia. Although there have been numerous reports regarding the pharmacological effects of baicalin and baicalein in vivo and in vitro, some reports indicated that the glycoside form would hardly be absorbed in the intestine and that it should be hydrolyzed to baicalein in advance for absorption. Therefore, the role of metabolism by intestinal microbiota should also be considered in the metabolism of baicalin. In addition, baicalin contains a glucuronide moiety in its structure, by which baicalin and baicalein show complex pharmacokinetic behaviors, due to the interconversion between them by phase II enzymes in the body. Recently, concerns about drug interaction with baicalin and/or baicalein have been raised, because of the co-administration of Scutellaria species with certain drugs. Herein, we reviewed the role of intestinal microbiota in pharmacokinetic characteristics of baicalin and baicalein, with regards to their pharmacological and toxicological effects.

Pharmacogenomics and herb-drug interactions: merge of future and tradition

The worldwide using of herb products and the increasing potential herb-drug interaction issue has raised enthusiasm on discovering the underlying mechanisms. Previous review indicated that the interactions may be mediated by metabolism enzymes and transporters in pharmacokinetic pathways. On the other hand, an increasing number of studies found that genetic variations showed some influence on herb-drug interaction effects whereas these genetic factors did not draw much attention in history. We highlight that pharmacogenomics may involve the pharmacokinetic or pharmacodynamic pathways to affect herb-drug interaction. We are here to make an updated review focused on some common herb-drug interactions in association with genetic variations, with the aim to help safe use of herbal medicines in different individuals in the clinic.

Change in pharmacokinetic behavior of intravenously administered midazolam due to increased CYP3A2 expression in rats treated with menthol

Menthol is used widely as a constituent of functional foods and chemical drugs. The present study investigated changes in the pharmacokinetic behavior of intravenously administered midazolam (MDZ), a probe for CYP3A, when rats were treated with menthol. The study also examined which isoforms of CYP3A1 and 3A2 were menthol-inducible and contributed to the altered disposition of midazolam. Menthol was administered intraperitoneally to rats once daily for 3 days at a dose of 10 mg/kg, while the control rats received vehicle alone. The pharmacokinetic examination of i.v. administered midazolam revealed that serum midazolam concentrations at each sampling point were lower in the menthol-treated rats than in the control rats. Regarding the pharmacokinetic parameters of the menthol-treated group, the area under the curve (AUC) was decreased significantly and, correspondingly, the elimination rate constant at terminal phase (ke) was increased significantly without significant changes in the volume of distribution at steady state (Vdss). The metabolic production of the 1'-hydroxylated and 4'-hydroxylated forms of MDZ by hepatic microsomes was significantly greater in the menthol-treated rats than in the control rats. The expression levels of mRNA and protein for hepatic CYP3A2 were more than 2.5-fold higher than the control levels when the rats were treated with menthol, whereas no changes were observed in the expression levels of CYP3A1. These results indicate that menthol enhanced the elimination clearance of midazolam by inducing hepatic CYP3A2 and that careful attention should be paid when menthol is ingested in combination with drugs that act as substrates for CYP3A.

In vitro inhibitory effects of scutellarin on six human/rat cytochrome P450 enzymes and P-glycoprotein

Inhibition of cytochrome P450 (CYP) and P-glycoprotein (P-gp) are regarded as the most frequent and clinically important pharmacokinetic causes among the various possible factors for drug-drug interactions. Scutellarin is a flavonoid which is widely used for the treatment of cardiovascular diseases. In this study, the in vitro inhibitory effects of scutellarin on six major human CYPs (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4) and six rat CYPs (CYP1A2, CYP2C7, CYP2C11, CYP2C79, CYP2D4, and CYP3A2) activities were examined by using liquid chromatography-tandem mass spectrometry. Meanwhile, the inhibitory effects of scutellarin on P-gp activity were examined on a human metastatic malignant melanoma cell line WM-266-4 by calcein-AM fluorometry screening assay. Results demonstrated that scutellarin showed negligible inhibitory effects on the six major CYP isoenzymes in human/rat liver microsomes with almost all of the IC50 values exceeding 100 μM, whereas it showed values of 63.8 μM for CYP2C19 in human liver microsomes, and 63.1 and 85.6 μM for CYP2C7 and CYP2C79 in rat liver microsomes, respectively. Scutellarin also showed weak inhibitory effect on P-gp. In conclusion, this study demonstrates that scutellarin is unlikely to cause any clinically significant herb-drug interactions in humans when co-administered with substrates of the six CYPs (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4) and P-gp.

Comparison of the Inhibitory Potential of Bavachalcone and Corylin against UDP-Glucuronosyltransferases

Bavachalcone and corylin are two major bioactive compounds isolated from Psoralea corylifolia L., which has been widely used as traditional Chinese medicine for many years. As two antibiotic or anticancer drugs, bavachalcone and corylin are used in combination with other drugs; thus it is necessary to evaluate potential pharmacokinetic herb-drug interactions (HDI) of the two bioactive compounds. The aim of the present study was to compare the effects of liver UDP-glucuronosyltransferase (UGT) 1A1, UGT1A3, UGT1A7, UGT1A8, UGT 1A10, and UGT2B4 inhibited by bavachalcone and corylin. 4-Methylumbelliferone (4-MU) was used as a nonspecific “probe” substrate. Bavachalcone had stronger inhibition on UGT1A1 and UGT1A7 than corylin which did not inhibit UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A10, and UGT2B4. Data fitting using Dixon and Lineweaver-Burk plots demonstrated the noncompetitive inhibition of bavachalcone against UGT1A1 and UGT1A7-mediated 4-MU glucuronidation reaction. The values of inhibition kinetic parameters (Ki) were 5.41 μM and 4.51 μM for UGT1A1 and UGT1A7, respectively. The results of present study suggested that there was a possibility of UGT1A1 and UGT1A7 inhibition-based herb-drug interaction associated with bavachalcone and provided the basis for further in vivo studies to investigate the HDI potential between bavachalcone and UGT substrates.

Inhibition of baicalin on metabolism of phenacetin, a probe of CYP1A2, in human liver microsomes and in rats

Baicalin has been used as mainly bioactive constituent of about 100 kinds of traditional Chinese medicines in Chinese pharmacopoeia. The effect of baicalin on cytochrome P450 should be paid more attention because baicalin was used widely. The aim of this study was to investigate whether baicalin could inhibit CYP1A2 in pooled human liver microsomes (HLMs) and in rats in vivo and the gene polymorphisms could affect inter-individual variation in IC50 in 28 human livers. Phenacetin was used as probe of CYP1A2. Kinetic parameter of CYP1A2 and IC50 of baicalin on CYP1A2 to each sample were measured and the common CYP1A2 polymorphisms (-3860G>A and -163C>A) were genotyped. The results showed that baicalin exhibited a mixed-type inhibition in pooled HLMs, with a Ki value of 25.4 µM. There was substantial variation in Km, Vmax, CLint of CYP1A2 and IC50 of baicalin on CYP1A2 (3∼10-fold). The range was from 26.6 to 114.8 µM for Km, from 333 to 1330 pmol·min(-1)·mg(-1)protein for Vmax and from 3.8 to 45.3 µL·min(-1)·mg(-1) protein for CLint in HLMs (n = 28). The Mean (range) value of IC50 in 28 HLMs was 36.3 (18.9 to 56.1) µM. The genotypes of -3860G>A and -163C>A had no significant effect on the inhibition of baicalin on CYP1A2. The animal experiment results showed that baicalin (450 mg/kg, i.v.) significantly decreased the Cmax and CL of phenacetin, and increased C(60 min), t1/2, Vd and AUC (P<0.05). There were significant correlations between percentage of control in C(60 min), t1/2, CL, AUC of phenacetin and Cmax of baicalin in 11 rats (P<0.05). Protein binding experiments in vitro showed that baicalin (0-2000 mg/L) increased the unbound phenacetin from 14.5% to 28.3%. In conclusion, baicalin can inhibit the activity of CYP1A2 in HLMs and exhibit large inter-individual variation that has no relationship with gene polymorphism. Baicalin can change the pharmacokinetics of phenacetin in rats.

Contribution of baicalin on the plasma protein binding displacement and CYP3A activity inhibition to the pharmacokinetic changes of nifedipine in rats in vivo and in vitro

Baicalin purified from the root of Radix scutellariae is widely used in clinical practices. This study aimed to evaluate the effect of baicalin on the pharmacokinetics of nifedipine, a CYP3A probe substrate, in rats in vivo and in vitro. In a randomised, three-period crossover study, significant changes in the pharmacokinetics of nifedipine (2 mg/kg) were observed after treatment with a low (0.225 g/kg) or high (0.45 g/kg) dose of baicalin in rats. In the low- and high-dose groups of baicalin-treated rats, C max of total nifedipine decreased by 40%±14% (P<0.01) and 65%±14% (P<0.01), AUC0-∞ decreased by 41%±8% (P<0.01) and 63%±7% (P<0.01), Vd increased by 85%±43% (P<0.01) and 224%±231% (P<0.01), and CL increased by 97%±78% (P<0.01) and 242%±135% (P<0.01), respectively. Plasma protein binding experiments in vivo showed that C max of unbound nifedipine significantly increased by 25%±19% (P<0.01) and 44%±29% (P<0.01), respectively, and there was a good correlation between the unbound nifedipine (%) and baicalin concentrations (P<0.01). Furthermore, in vitro results revealed that baicalin was a competitive displacer of nifedipine from plasma proteins. In vitro incubation experiments demonstrated that baicalin could also competitively inhibit CYP3A activity in rat liver microsomes in a concentration-dependent manner. In conclusion, the pharmacokinetic changes of nifedipine may be modulated by the inhibitory effects of baicalin on plasma protein binding and CYP3A-mediated metabolism.

Pharmacokinetic changes of unbound theophylline are due to plasma protein binding displacement and CYP1A2 activity inhibition by baicalin in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Baicalin is one of the major bioactive constituents of Scutellariae Radix, the root of Scutellariae baicalensis Georgi and possesses a wide variety of pharmacological properties.

AIM OF THE STUDY

To elucidate the effect of baicalin on the pharmacokinetics of theophylline in rats, focusing on plasma protein binding displacement and inhibition effect on CYP1A2 in vivo and in vitro.

MATERIALS AND METHODS

The study was a randomized, three-period crossover design. Nine rats were given saline (control) or 450 mg/kg baicalin (dosage regimen A or B). Dosage regimen A was administered once at 0 h. Dosage regimen B was divided into three dosages (225,112.5, 112.5 mg/kg) and was given at 0, 2 and 4 h, respectively. Then theophylline (5 mg/kg, i.v.) was administered immediately. The effect of baicalin on CYP1A2 activity was determined by metabolism of phenacetin in vitro and plasma protein binding of theophylline was determined by ultrafiltration.

RESULTS

C(max) decreased from (12.4 ± 1.6) to (8.7 ± 0.9) and (8.6 ± 2.0) mg/L, T(1/2) increased by 116 and 96%, V(d) increased by 51 and 49% for total theophylline in rats treated with dosage regimen A and B of baicalin, respectively. Cmax was significantly increased, V(d) decreased by 43 and 29% for unbound theophylline in rats treated with dosage regimen A and B of baicalin, respectively (P < 0.01). T(1/2) of unbound theophylline increased by 104% only in rats treated with dosage regimen B. No significant effects on the CL and AUC of both total and unbound theophylline were observed in the rats treated with dosage regimen A, but the CL decreased and AUC increased for total theophylline and CL decreased for unbound theophylline in the group treated with dosage regimen B (P < 0.05). Correlation analysis showed that the mean unbound theophylline (%) and mean baicalin concentration was in good correlation (P < 0.01). Baicalin decreased metabolism of phenacetin and exhibited a mixed-type inhibition in rat liver microsomes, with a K(i) value of 88.1 μM in vitro. Moreover baicalin was a competitive displacer of theophylline from plasma protein in vitro.

CONCLUSIONS

The changes in Cmax, T(1/2), CL and AUC of theophylline due to baicalin may be attributed to two mechanisms, plasma protein binding displacement and CYP1A2 activity inhibition.

Baicalin pharmacokinetic profile of absorption process using novel in-vitro model: cytochrome P450 3A4-induced Caco-2 cell monolayers combined with rat intestinal rinse fluids

Objectives

This study was designed to investigate baicalin (BG) pharmacokinetic profile in absorption process using a new model and evaluate the potentiality as a new model.

Methods

The effects of BG on intestinal cytochrome P450 3A4 (CYP3A) protein/mRNA expression, activity and permeability glycoprotein (P-gp) were evaluated in CYP3A4-induced Caco-2 cell monolayers or rats. Intestinal rinse fluids (IF) were obtained from rat were added to modified Caco-2 monolayers.

Key findings

Orally administered BG (7 days pretreatment) inhibited intestinal CYP3A activity and protein expression. Baicalein (B) converted from BG by IF was detected in the upper jejunum in a portion-dependent manner. Subsequently, most BG were converted to B in the caecum. In modified Caco-2 monolayers, BG exhibited no effect on CYP3A4 activity or mRNA, whereas B and BG treated with IF inhibited CYP3A4 transcription and activity.

Conclusions

Intestinal CYP3A was inhibited following oral administration of BG to rat. Correspondingly, BG-mediated CYP3A inhibition was shown in vitro using modified Caco-2 monolayers treated with IF. Hence, in-vivo intestinal absorption pharmacokinetic was reproduced in vitro. IF is a key determinant of intestinal absorption, and it facilitated inhibition of CYP3A by B, not BG.