Guoping Zhong

Hypoxanthine guanine phosphoribosyltransferase activity is related to 6-thioguanine nucleotide concentrations and thiopurine-induced leukopenia in the treatment of inflammatory bowel disease.

Background: Thiopurine drugs are widely used in the treatment of inflammatory bowel disease (IBD). The polymorphic enzyme thiopurine S‐methyltransferase (TPMT) is of importance for thiopurine metabolism and adverse events occurrence. The role of other thiopurine‐metabolizing enzymes is less well known. This study investigated the effects of TPMT and hypoxanthine guanine phosphoribosyltransferase (HPRT) activities on 6‐thioguanine nucleotides (6‐TGNs) concentrations and thiopurine‐induced leukopenia in patients with IBD. Methods: Clinical data and blood samples were collected from 120 IBD patients who were receiving azathioprine (AZA)/6‐mercaptopurine (6‐MP) therapy. Erythrocyte TPMT, HPRT activities and 6‐TGNs concentrations were determined. HPRT activity and its correlation with TPMT activity, 6‐TGNs level, and leukopenia were evaluated. Results: The HPRT activity of all patients ranged from 1.63–3.33 (2.31 ± 0.36) &mgr;mol/min per g Hb. HPRT activity was significantly higher in patients with leukopenia (27, 22.5%) than without (P < 0.001). A positive correlation between HPRT activity and 6‐TGNs concentration was found in patients with leukopenia (r = 0.526, P = 0.005). Patients with HPRT activity > 2.70 &mgr;mol/min per g Hb could have an increased risk of developing leukopenia (odds ratio = 7.47, P < 0.001). No correlation was observed between TPMT activity and HPRT activity, 6‐TGNs concentration, or leukopenia. Conclusions: High levels of HPRT activity could be a predictor of leukopenia and unsafe 6‐TGN concentrations in patients undergoing AZA/6‐MP therapy. This could partly explain the therapeutic response or toxicity that could not be adequately explained by the polymorphisms of TPMT. (Inflamm Bowel Dis 2011;)

Effect of Wuzhi tablet (Schisandra sphenanthera extract) on the pharmacokinetics of paclitaxel in rats.

Wuzhi tablet (WZ, registration no. in China: Z20025766) is a preparation of an ethanol herb extract of Wuweizi (Schisandra sphenanthera) containing 7.5 mg Schisantherin A per tablet. It was reported recently that WZ could significantly increase the blood concentrations of tacrolimus, which might be due to the inhibitory effect of WZ and its ingredients on P‐gp and/or CYP450 activity. Paclitaxel is a substrate of the efflux transporter P‐gp, and is mainly metabolized by CYP450 enzymes in the liver. Therefore, the purpose of this study was to investigate whether and how WZ affects the pharmacokinetics of paclitaxel in rats. After pretreatment with WZ, there were significant increases in the AUC0‐24h of oral paclitaxel (from 280.8 ± 97.3 to 543.5 ± 115.2 h ng/mL; p < 0.05) and Cmax (from 44.6 ± 16.4 to 86.8 ± 16.1 ng/mL; p < 0.05). The pharmacokinetic data for i.v. paclitaxel with WZ showed a relatively small (when compared against oral paclitaxel) but still significant increase in AUC0‐24h (from 163.6 ± 22.1 to 212.7 ± 17.7 h ng/mL; p < 0.05) and a decrease in clearance (from 3.2 ± 0.6 to 2.2 ± 0.3 L/h/kg; p < 0.05). Thus, the presence of WZ improved the systemic exposure of paclitaxel in rats. The herb–drug interaction between WZ and paclitaxel should be taken into consideration in clinical use. Copyright

Enhancement of oral bioavailability of paclitaxel after oral administration of Schisandrol B in rats

Paclitaxel is a substrate of the efflux transporters such as P-glycoprotein, and is mainly metabolized by the liver. Schisandrol B (Sch B), one of the active components in Schisandra, has been reported to be able to inhibit the activity of P-gp and CYP3A. It might be possible that Sch B would alter the pharmacokinetic behavior of paclitaxel. Therefore, the purpose of this study was to investigate the effect of Sch B on the pharmacokinetics of paclitaxel administered orally and intravenously in rats. Paclitaxel were administered to rats orally (30 mg/kg) or intravenously (0.5 mg/kg) with or without the concomitant administration of Sch B (10 or 25 mg/kg). Oral pharmacokinetic parameters of paclitaxel were significantly altered when pretreated with Sch B. There were significant increases in AUC(0-24h) (from 297.7+/-110.3 to 838.9+/-302.1 h*ng/ml; p<0.05) and C(max) (from 51.7+/-20.1 to 136.4+/-35.5 ng/ml; p<0.05) in the presence of Sch B (25 mg/kg). The pharmacokinetic parameters for i.v. paclitaxel were not significantly affected by Sch B in contrast to that of oral administration. Since the presence of Sch B enhanced the systemic exposure of paclitaxel, their pharmacokinetic interaction should be taken into consideration. As the oral bioavailability of paclitaxel was increased about 3-fold in the presence of Sch B, the concomitant use of Sch B may provide a benefit in the oral delivery of paclitaxel.

Effect of Tacrolimus on the pharmacokinetics of bioactive lignans of Wuzhi tablet (Schisandra sphenanthera extract) and the potential roles of CYP3A and P-gp

We recently reported that Wuzhi tablet (WZ), a preparation of the ethanol extract of Wuweizi (Schisandra sphenanthera), had significant effects on blood concentrations of Tacrolimus (FK506) in renal transplant recipients and rats. The active lignans in WZ are schisandrin A, schisandrin B, schisandrin C, schisandrol A, schisandrol B, schisantherin A, and schisantherin B. Until now, whether the pharmacokinetics of these lignans in WZ would be affected by FK506 remained unknown. Therefore, this study aimed to investigate whether and how FK506 affected pharmacokinetics of lignans in WZ in rats and the potential roles of CYP3A and P-gp. After a single oral co-administration of FK506 and WZ, the blood concentration of lignans in WZ was decreased by FK506; furthermore, the AUC of schisantherin A, schisandrin A, schisandrol A and schisandrol B was only 64.5%, 47.2%, 55.1% and 57.4% of that of WZ alone group, respectively. Transport study in Caco-2 cells showed that these lignans were not substrates of P-gp, suggesting decreased blood concentration of lignans by FK506 was not via P-gp pathway. Metabolism study in the human recombinant CYP 3A showed that these lignans had higher affinity to CYP3A than that of FK506, and thus had a stronger CYP3A-mediated metabolism. It was concluded that the blood concentrations of these lignans were decreased and their CYP3A-mediated metabolisms were increased in the presence of FK506 since these lignans had higher affinity to CYP3A.

Pharmacokinetic characterization of hydroxylpropyl-β-cyclodextrin-included complex of cryptotanshinone, an investigational cardiovascular drug purified from Danshen (Salvia miltiorrhiza)

1. The study aimed to investigate the pharmacokinetics of cryptotanshinone in a hydroxylpropyl-β-cyclodextrin-included complex in dogs and rats. 2. Animals were administrated the inclusion complex of cryptotanshinone and the concentrations of cryptotanshinone and its major metabolite tanshinone IIA were determined by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. 3. Cryptotanshinone in inclusion complex was absorbed slowly after an oral dose, and the Cmax and AUC0–t were dose-proportional. The bioavailability of cryptotanshinone in rats was (6.9% ± 1.9%) at 60 mg kg−1and (11.1% ± 1.8%) in dogs at 53.4 mg kg−1. The t1/2 of the compound in rats and dogs was 5.3–7.4 and 6.0–10.0 h, respectively. Cryptotanshinone showed a high accumulation in the intestine, lung and liver after oral administration, while the lung, liver and heart had the highest level following intravenous dose. Excretion data in rats showed that cryptotanshinone and its metabolites were mainly eliminated from faeces and bile, and the dose recovery rate was 0.02, 2.2, and 14.9% in urine, bile, and faeces, respectively. 4. The disposition of cryptotanshinone in an inclusion complex was dose-independent and the bioavailability was increased compared with that without cyclodextrin used to formulate the drug. Cryptotanshinone was distributed extensively into different organs. Excretion of cryptotanshinone and its metabolites into urine was extremely low, and they were mainly excreted into faeces and bile.

Comparative pharmacokinetics of paclitaxel after oral administration of Taxus yunnanensis extract and pure paclitaxel to rats

Taxus yunnanensis (T. yunnanensis) is endemic to China and has been used in traditional medicine for the treatment of cancer, diabetic ailments and others. Paclitaxel is a representative antitumor compound in the Taxus species. The pharmacokinetic behavior of paclitaxel after oral administration of the crude extract of T. yunnanensis has not been investigated. This study attempts to compare the pharmacokinetics of paclitaxel after an oral administration of the crude extract of the twigs and leaves of T. yunnanensis and pure paclitaxel. A UPLC and a UPLC/MS/MS analysis method were developed for the determination of paclitaxel in T. yunnanensis extract and in the comparative pharmacokinetic study. Caco-2 cells were used to investigate the transport profile of paclitaxel in vitro. In the pharmacokinetic study, rats were randomly grouped and administered with T. yunnanensis extract or pure paclitaxel. The results showed that the AUC and C(max) of paclitaxel in rats receiving the T. yunnanensis extract were significantly increased than those receiving the pure paclitaxel, and the in vitro Caco-2 cell monolayer transport study found that the coexisting constituents in the extract of T. yunnanensis could inhibit the efflux of paclitaxel. These findings suggested that the oral absorption and bioavailability of paclitaxel in T. yunnanensis extract were remarkably higher when compared with the pure paclitaxel, and the coexisting constituents in the T. yunnanensis extract might play an important role for the enhancement of the oral absorption and bioavailability of paclitaxel.

Simultaneous determination of mifepristone and monodemethyl-mifepristone in human plasma by liquid chromatography-tandem mass spectrometry method using levonorgestrel as an internal standard: application to a pharmacokinetic study.

A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed and validated to simultaneously determine mifepristone and monodemethyl-mifepristone in human plasma using levonorgestrel as the internal standard (IS). After solid-phase extraction of the plasma samples, mifepristone, monodemethyl-mifepristone and the IS were subjected to LC-MS/MS analysis using electro-spray ionization (ESI) in the multiple reaction monitoring (MRM) mode. Chromatographic separation was performed on an XTERRA MS C(18) column (150 x 2.1 mm i.d., 5 microm). The method had a chromatographic run time of 4.5 min and linear calibration curves over the concentration ranges of 5-2000 ng/mL for mifepristone and monodemethyl-mifepristone. The recoveries of the method were found to be 94.5-103.7% for mifepristone and 70.7-77.3% for monodemethyl-mifepristone. The method had a lower limit of quantification (LLOQ) of 5.0 ng/mL and a lower limit of detection (LOD) of 1.0 ng/mL for both mifepristone and monodemethyl-mifepristone. The intra- and inter-batch precision was less than 15% for all quality control samples at concentrations of 10, 100 and 1000 ng/mL. These results indicate that the method was efficient with a short run time (4.5 min) and acceptable accuracy, precision and sensitivity. The validated LC-MS/MS method was successfully used in a pharmacokinetic study in healthy female volunteers after oral administration of 25 mg mifepristone tablet.

Effect of Wuzhi Tablet (Schisandra sphenanthera extract) on the Pharmacokinetics of Cyclosporin A in Rats

In our previous reports, Wuzhi tablet (an herbal preparation of ethanol extract of Wuweizi (Schisandra sphenanthera)) can significantly increase the blood concentration of tacrolimus and paclitaxel in rats by inhibiting the CYP3A‐mediated metabolism and the P‐gp‐mediated efflux. Cyclosporin A (CsA), a well‐known immunosuppressant agent, is also a substrate of CYP3A and P‐gp. Therefore, this study aimed to investigate whether and how WZ affects pharmacokinetics of CsA in rats. The AUC0–48h and Cmax of CsA were increased by 40.1% and 13.1%, respectively, with a single oral co‐administration of WZ and high dose of CsA (37.8 mg/kg). Interestingly, after a single oral co‐administration of WZ and low dose of CsA (1.89 mg/kg), the AUC0–36 h and Cmax of CsA were dramatically increased by 293.1% (from 1103.2 ± 293.0 to 4336.5 ± 1728.3 ng.h/mL; p < 0.05) and 84.1% (from 208.5 ± 67.9 to 383.1 ± 92.5 ng/mL; p < 0.05), respectively. The CL/F was decreased from 1.7 L/h/kg to 0.5 L/h/kg. Thus, the effect of WZ on high dose of CsA was not significant, but pharmacokinetic parameters of CsA at low dose were significantly influenced by co‐administration of WZ. The herb–drug interaction should be taken into consideration at this situation. Copyright

Determination of levonorgestrel in human plasma by liquid chromatography–tandem mass spectrometry method: application to a bioequivalence study of two formulations in healthy volunteers

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC/MS/MS) method to determine levonorgestrel in human plasma was developed and fully validated. After hexane-ethyl acetate (70:30, v/v) induced extraction from the plasma samples, levonorgestrel was subjected to LC/MS/MS analysis using electro-spray ionization. The MS system was operated in the selected reaction monitoring mode. Chromatographic separation was performed on a Hypersil BDS C18 column (i.d. 2.1x50 mm, particle size 3 microm). The method had a chromatographic running time of 2.0 min and linear calibration curves over the concentration ranges of 0.25-90 ng/mL for levonorgestrel. The lower limit of quantification of the method was 0.25 ng/mL for levonorgestrel. The intra- and inter-batch precision was 3.7-10.2 and 5.1-12.9%, respectively, for all quality control samples at concentrations of 0.5, 6.0 and 45.0 ng/mL. These results indicate that the method was efficient with a simple preparation procedure and a very short running time (2.0 min) for levonorgestrel compared with those methods reported in the literature and had high selectivity, acceptable accuracy, precision and sensitivity. The validated LC/MS/MS method was successfully used for a bioequivalence study of two tablet formulations of levonorgestrel in healthy volunteers.

Down-regulation of P-gp expression and function after Mulberroside A treatment: Potential role of protein kinase C and NF-kappa B

P-Glycoprotein (P-gp) plays a major role in drug-drug and herb-drug interactions. Mulberroside A (Mul A) is one of the main bioactive constituents of Sangbaipi, the dried root-bark of Morus alba L. (white mulberry), which is officially listed in the Chinese Pharmacopoeia. In the present study, we investigated the effect of Mul A treatment on mRNA expression and protein expression of P-gp in the Caco-2 cells by real-time qPCR and Western blot analysis. The effect of Mul A treatment on the function of P-gp in vitro and in vivo was assessed by Rho123 transport assay and a pharmacokinetic study. The potential roles of protein kinase C (PKC) and nuclear factor kappa B (NF-κB) in the expression regulation of P-gp after Mul A treatment were also investigated. The results revealed that Mul A treatment significantly decreased the mRNA and protein expression of P-gp in Caco-2 cells after treatment with Mul A (5-20 μM). Furthermore, Mul A treatment displayed apparently inhibitory effect on the function of P-gp both in vitro and in vivo. In addition, activation of PKC activity and NF-κB nuclear translocation were observed in the presence of Mul A, which suggested that PKC and NF-κB might play crucial roles in Mul A-induced suppression of P-gp. Our study demonstrated that Mul A treatment could down-regulate P-gp expression and function accompanied by the activation of PKC and NF-κB, and this should be taken into consideration in potential herb-drug interactions when Mul A or M. alba are co-administered with other drugs transported by P-gp.