Journal of Ethnopharmacology 156 (2014) 125–129
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Pharmacokinetics of escin Ia in rats after intravenous administration Xiu-Jun Wu a,b, Xiang-Yong Cui b, Lian-tian Tian c, Feng Gao b, Xin Guan b, Jing-Kai Gu b,n a b c
Afﬁliated Hospital of Liaoning University of Traditional Chinese Medicine, Shenyang 110032, China Research Center for Drug Metabolism, Jilin University, 2699 Qianjin Road, Changchun 130012, China No.4 west china hospital, Sichuan University, Chengdu, Sichua 610041, China
art ic l e i nf o
a b s t r a c t
Article history: Received 12 May 2014 Received in revised form 4 August 2014 Accepted 24 August 2014 Available online 3 September 2014
Ethnopharmacological relevance: Escin, a natural mixture of triterpene saponins, is commonly utilized for the treatment of chronic venous insufﬁciency, hemorrhoids, inﬂammation and edema. Escin Ia is the chief active ingredient in escin and plays key role in mediating its pharmacological effects. Adequate pharmacokinetic data are essential for proper application of escin agent in clinical practice. However, pharmacokinetic properties of escin Ia are still poorly understood and this conﬂicts with the growing use of escin agent over the years. The goal of this study is to investigate the pharmacokinetic behavior of escin Ia in rats after low, medium and high-dose intravenous administration. Materials and methods: Wistar rats were divided into 3 groups (n ¼ 6 per group) and escin Ia was administered via the caudal vein at doses of 0.5, 1.0 and 2.0 mg/kg, respectively. Subsequently, the concentrations of escin Ia and its metabolite isoescin Ia, a positional isomer of escin Ia, in rats' plasma were measured by an established liquid chromatography tandem mass spectrometry (LC–MS/MS) method at various time points following the administration of the drug. Main pharmacokinetic parameters were calculated by non-compartmental analysis using the TopFit 2.0 software package (Thomae GmbH, Germany). Results: After intravenous administration, the Cmax and AUC of escin Ia increased in a dose-proportional manner at the dose of 0.5 mg/kg and 1.0 mg/kg, while increased in a more than dose-proportional manner at the doses of 1.0 mg/kg and 2.0 mg/kg. The t1/2 was signiﬁcantly longer with increased intravenous doses, while other parameters such as CL and Vd also exhibit disagreement among three doses. Taken together, our data showed dose-dependent pharmacokinetic proﬁle of escin Ia in rats after intravenous administration at the doses of 0.5–2.0 mg/kg. After intravenous administration, escin Ia was rapidly and extensively converted to isoescin Ia. Conclusions: The results suggested dose-dependent pharmacokinetics of escin Ia at the doses of 0.5–2.0 mg/kg after intravenous administration. Escin Ia is isomerized to isoescin Ia rapidly and extensively regardless of the doses. & 2014 Elsevier Ireland Ltd. All rights reserved.
Keywords: Escin Ia Pharmacokinetics Isomerization Isoescin Ia Rats LC–MS/MS
1. Introduction Escin is a mixture of triterpenic saponins accumulated in the seeds of the horse chestnut tree (Aesculus Hippocastanum) (Yoshikawa et al., 1994, 1998). A number of reports have shown that escin exhibits remarkable antiinﬂammatory, antiedematous and vasoprotective properties and have been traditionally used to treat conditions such as chronic venous insufﬁciency (Greeske and Pohlmann, 1996; Ottillinger and Greeske, 2001; Pittler and Ernst, 2006), hemorrhoids (Guillaume and Padioleau, 1994), inﬂammation (Matsuda et al., 1997; Wei et al., 2004) and cerebral ischemic damage (Wetzel et al., 2002). In recent years, the pharmacological n
Corresponding author. Tel./fax: þ 86 431 88181611. E-mail address: [email protected]
http://dx.doi.org/10.1016/j.jep.2014.08.032 0378-8741/& 2014 Elsevier Ireland Ltd. All rights reserved.
properties of escin have been studied extensively from different aspects, including sperm quality improvement, cerebral edema attenuation, liver protection, antitumor activity, and anti-allergic and anti-nociceptive effects (Fang et al., 2010; Jiang et al., 2011; Wang et al., 2011; Li et al., 2012; Sipos et al., 2012; Wang et al., 2012). To date, about 20 individual compounds have been identiﬁed in escin (Yoshikawa et al., 1994, 1998; Sirtori, 2001; Wei et al., 2005). Amongst these, escin Ia (Fig. 1) is the main bioactive component of escin that, according to previous studies, exerted a high potency in anti-diabetic and anti-ischemic effects, anti-inﬂammation and gastroprotection (Matsuda et al., 1997, 1999), and thus has been frequently referred as a representative of escin. In China, escin Ia has been assigned as the marker compound for horse chestnut seeds in the 2005 Chinese Pharmacopoeia.
X.-J. Wu et al. / Journal of Ethnopharmacology 156 (2014) 125–129
H3C C O
O OR1 CH2OR2
O OH OH OH
Fig. 1. Chemical structures of escin Ia (R1 ¼ COCH3, R2 ¼H) and isoescin Ia (R1 ¼ H, R2 ¼ COCH3).
The application of traditional medicines is greatly growing in clinical practice. Adequate pharmacokinetic data of traditional medicines are pivotal to ensure safe and proper application. To study pharmacokinetic properties, the major active components are usually chosen to characterize the pharmacokinetic proﬁles of these medicines in practice. Recently, we have performed a series of studies to elucidate the pharmacokinetics of escin. Escin Ia, together with escin Ib, isoescin Ia and isoescin Ib, has been chosen as the major active components of escin based on previous pharmacological activity and the content analysis (Liu et al., 2010; Wu et al., 2010, 2012). Escin was shown to be poorly absorbed through digestive tract with the bioavailability of less than 0.3%, which may be caused by extensive ﬁrst pass metabolism by the gut microbiota (Yang et al., 2004; Wu et al., 2012). Therefore, administration by intravenous injections may be beneﬁcial for improving its action. Furthermore, we have found that administration of herbal preparations of escin in a clinical setting resulted in a longer duration of action than administration of each isomer alone (Wu et al., 2012, 2014). However, the mechanism is unclear. As a continuation of our previous research, we carried out this work to study the pharmacokinetic behavior of escin Ia in rats after intravenous administration at different doses and to elucidate the dose-dependent response of escin Ia in rats. This work provides signiﬁcant evidences for comprehensive understanding of the pharmacokinetic properties of escin in vivo.
2. Materials and methods 2.1. Chemicals Escin Ia and isoescin Ia (498.0% HPLC purity) were isolated from the seeds of the horse chestnut tree. Their structural identities were conﬁrmed using 1H NMR, and the results were consistent with the 1H NMR data reported by Yoshikawa et al. (1996, 1998). Roxithromycin (I.S., 499.5% purity) was purchased from the National Institute for the Control of Pharmaceutical and Biological Products (Beijing, China). Methanol and acetonitrile were of HPLC grade and purchased from Fisher Scientiﬁc (Fair
Lawn, NJ, USA). All other materials were obtained from standard vendors, and were of the highest quality available. 2.2. Dosing preparations The dosing solution was prepared by dissolving escin Ia in 5% glucose injection containing 5% ethanol. All preparations were reconstituted immediately before administration. 2.3. Animals Wister rats (male and female, 180–220 g) were purchased from the experimental animal center (Jilin University). All the animals were maintained according to the Chinese government guidelines for care and use of laboratory animals under a constant temperature between 20 and 23 1C with 12 h light and dark cycles and a relative humidity of 50%. Filtered tap water and a standard animal diet were available ad libitum. All experiments were conducted under the ethics permission obtained from the Institutional Animal Care and Use Committee at the Jilin University. 2.4. Drug administration and sample collection Escin Ia at doses of 0.5 (n ¼6), 1.0 (n ¼6) and 2.0 (n¼ 6) mg/kg was administered via the caudal vein (infusion volume of approximately 1.0 mL). Approximately 200 μL of blood sample was collected from each animal at each time point using a heparinized test tube. The designated time points were 0 (serve as control), 5 min, 15 min, 30 min, 1, 1.5, 2, 4, 6, 8, 12, 24, 36 and 48 h after the start of the intravenous administration. Blood samples were immediately centrifuged at 15,000 rpm for 10 min at 4 1C and aliquots of plasma (100 μl) were mixed with 20 μl 1% formic acid and stored at 80 1C until further analysis. 2.5. Liquid chromatography–tandem mass spectrometry analysis 60 μl acidic sample was supplemented with 50 μl I.S. solution (5.0 ng/ml), 50 μl methanol–water (4:3, v/v) or a standard or quality control (QC) solution of escin Ia and isoescin Ia and 250 μl methanol. The mixture was vortexed for 30 s and
X.-J. Wu et al. / Journal of Ethnopharmacology 156 (2014) 125–129
different doses on the pharmacokinetic behavior of escin using escin Ia, a major active component of escin, as the study object. The mean plasma concentration–time proﬁles of escin Ia after intravenous administration are shown in Fig. 2, and results of the non-compartmental pharmacokinetic analysis are summarized in Table 1. The Cmax and AUC of escin Ia increased with dose in a dose-proportional manner at the doses of 0.5 mg/kg and 1.0 mg/kg, while increased with dose in a more than dose-proportional manner
15000 0.5 mg/kg
centrifuged at 12,000 rpm for 10 min, and 10 μl of the supernatant was injected into the LC–MS/MS system. The LC–MS/MS system consisted of an Agilent 1100 series (Agilent Technologies, Palo Alto, CA, USA) binary pump, an autosampler connected to an HC–C18 column (5 μm, 150 4.6 mm i.d. from Agilent Technologies) maintained at 25 1C, and an Applied Biosystems Sciex API 4000 Mass Spectrometer (Applied Biosystems Sciex, Ontario, Canada) with an ESI source. The mobile phase of 45% solvent A (10 mM ammonium acetate and 0.05% formic acid in puriﬁed water) and 55% solvent B (methanol:acetonitrile 50:50, v/v) was delivered at 1.0 ml/min as a linear gradient as follows: 0.0–0.5 min 55% B, 0.5–7.0 min 55–70% B, 7.0–7.5 min 70–55% B, 7.5–8.0 min 55% B. An approximately 1:1 split of the column eluent was included before the mass spectrometer. The detector was operated at low resolution using multiple-reaction monitoring (MRM) of the [Mþ H] þ ions of escin Ia and isoescin Ia at m/z 1131.8-807.6 and of roxithromycin at m/z 838.2-158.1. Optimum MS operating conditions were as follows: curtain gas, gas 1 and gas 2 (nitrogen) 15, 55 and 45 units, respectively; dwell time 200 ms; source temperature 400 1C; ion spray voltage 5500 V. The method was fully validated according to the US Food and Drug Administration (FDA) Bioanalytical Method Validation Guide (FDA, 2001). The calibration curve of escin Ia or isoescin Ia was linear in the range 5.00 15,000 ng/ml. Intra- and inter-day precisions (as coefﬁcient of variation) of escin Ia and isoescin Ia at QC concentrations were r8.2% with accuracies (as relative error) in the range 7.9% to 6.1%. The mean recoveries of escin Ia and isoescin Ia were Z 90.0%. The study of matrix effects showed that concentrations of escin Ia and isoescin Ia were 715% of nominal values.
1.0 mg/kg 9000
24.0 32.0 Time (h)
Fig. 2. Mean plasma concentration–time proﬁles of escin Ia after intravenous administration of escin Ia at doses of 0.5, 1.0 and 2.0 mg/kg to rats. Bars represent standard deviations.
2.6. Pharmacokinetic analysis The pharmacokinetic parameters were analyzed by noncompartmental analysis using the Topﬁt 2.0 software package (Thomae GmbH, Germany). The area under the plasma concentration–time curves (AUC0 t) was calculated by the trapezoidal method; the area from the last datum point to time inﬁnity (for the calculation of AUCt 1) was estimated by dividing the last measured plasma concentration by the terminal rate constant. The maximum plasma concentration (Cmax) and the time to reach the maximum plasma concentration (tmax) were obtained by visual inspection of the experimental data; the terminal half-life (t1/2) was calculated as 0.693/k, and k was the slope of the terminal regression line, the systemic clearance (CL) as dose/AUC0 t and the apparent volume of distribution (Vd) as dose/(λz AUC0 t).
Table 1 Pharmacokinetic parameters of escin Ia in rats after intravenous administration of the drug at doses of 0.5, 1.0 and 2.0 mg/kg (Mean 7S.D., n¼ 6). Parameters
Cmax (ng/mL) t1/2 (h) AUC0–48 h (ng h/mL) AUC0 1 (ng h/mL) CL (mL/min/kg) Vd (L/kg) MRT (h)
2280 7 485 7.5 7 2.1 10,036 7 4203 10,1457 4270 4.82 7 2.13 2.86 7 1.39 5.46 7 1.54
4362 7 1298 9.6 7 1.9 12,989 7 3101 13,1857 3302 6.05 7 1.95 5.02 7 3.85 5.39 7 0.880
11,220 7 2330 12.2 7 1.7 29,1567 6495 29,9417 6753 5.81 7 1.30 6.167 3.53 6.29 7 1.16
A P-value of less than 0.05 was considered to be statistically signiﬁcant using a t-test between the two means for the unpaired data, or a Duncan's multiple range test of Statistical Package for the Social Sciences (SPSS) posteriori analysis of variance (ANOVA) among the three means for the unpaired data. All results are expressed as means 7standard deviation.
2.7. Statistical analysis
1.0 mg/kg 2.0 mg/kg
1500 1000 500
3. Results and discussion As a widely used natural product in clinical practice, the pharmacokinetics of escin has been extensively studied. However, the pharmacokinetic parameters from these studies varied greatly. For example, the t1/2 value ranged from 6 to 19 h, with variations such as doses, objects and formulations being the possible causes of the difference. In this study, we have investigated the effect of
24.0 32.0 Time (h)
Fig. 3. Mean plasma concentration–time proﬁles of isoescin Ia after intravenous administration of escin Ia at doses of 0.5, 1.0 and 2.0 mg/kg to rats. Bars represent standard deviations.
X.-J. Wu et al. / Journal of Ethnopharmacology 156 (2014) 125–129
Table 2 Pharmacokinetic parameters of isoescin Ia in rats after intravenous administration of escin Ia at doses of 0.5, 1.0 and 2.0 mg/kg (Mean 7 S.D., n¼ 6). Parameters
Cmax (ng/mL) tmax (h) t1/2 (h) AUC0–48 h (ng h/mL) AUC0 1 (ng h/mL) AUC0–48 h ratio of isoescin Ia/escin Ia
584 7 172 5.7 7 2.0 8.1 7 0.8 9879 7 4446 10,519 7 4787 0.99 7 0.25
875 7 196 4.5 7 1.2 7.9 7 1.5 14,094 7 4580 14,4317 4969 1.127 0.06
2058 7 385 3.5 7 0.4 10.4 7 1.8 32,4017 8791 33,8327 9336 1.117 0.10
at the doses of 1.0 mg/kg and 2.0 mg/kg. The t1/2 values were 7.5, 9.6 and 12.2 h at the doses of 0.5, 1.0 and 2.0 mg/kg, respectively, which prolonged signiﬁcantly with increasing intravenous doses with correlation coefﬁcient Z0.99. Other parameters, such as CL, MRT and Vd also exhibited disagreement among three doses, indicating nonlinear elimination of escin Ia in rats after intravenous administration at the doses range of 0.5–2.0 mg/kg. Isoescin Ia, the isomer of escin, exhibits difference from the position of acetyl group in the structure (Fig. 1), which results in lower activity and toxicity compared to escin Ia. The trans-esteriﬁcation reaction between escin Ia and isoescin Ia has been demonstrated both in vitro and in vivo. The molecular mechanism of isomer conﬁguration transformation of escin Ia and isoescin Ia has been studied by the molecular simulation method, which surmised that the intrinsic mechanism underlying the translation from escin to isoescin was the intramolecular reversible reaction of ester group hydrolysis and esteriﬁcation in an acidic or a basic environment, but not enzymatically mediated. In this study, we found that escin Ia converted to isoescin Ia rapidly and extensively after administration. Isoescin Ia was detected from the blood sample collected as early as 5 min, and its concentration reached the peak level approximately at 7 h (Fig. 3 and Table 2). Subsequently, the plasma concentrations of isoescin Ia declined slowly for up to 48 h. Furthermore, the AUC0–48 ratios of isoescin Ia/escin Ia were calculated for 0.5, 1.0 and 2.0 mg/kg. No remarkable difference was found among them, suggesting that the dose has no effect on the isomerzation of escin Ia to isoesin Ia, which supported the hypothesis proposed in previous studies. In conclusion, pharmacokinetic proﬁles of escin Ia given intravenously at the doses of 0.5, 1.0 and 2.0 mg/kg were determined using a sensitive LC–MS/MS method. The results showed that the t1/2 increased signiﬁcantly with increasing intravenous doses. Other parameters such as CL and Vd varied with dose change, suggesting the dose-dependent pharmacokinetic properties of escin Ia in rats after intravenous administration at the doses of 0.5–2.0 mg/kg. However, escin Ia was found to isomerize to isoescin Ia rapidly and extensively regardless of the doses.
Acknowledgments This project was supported by grants from the National Natural Science Foundation of China (30772613), Key Projects in the National Science & Technology Pillar Program during the Eleventh Five-year Plan (Technical Platform for Preclinical Pharmacokinetic Studies, No. 2009ZX09304-003) and National Key Technology R&D Program (No. 2008BAI51B03), P.R. China.
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