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Research Article | Open Access
Effects of Borneol on Pharmacokinetics and Tissue Distribution of Notoginsenoside R1 and Ginsenosides Rg1 and Re in Panax notoginseng in Rabbits
The purpose of this study is to investigate the effects of Borneol on the pharmacokinetics of notoginsenoside R1 (NGR1) and the ginsenosides Rg1 (GRg1) and Re (GRe) in Panax notoginseng. Reversed phase high-performance liquid chromatography coupled with electrospray ion trap mass spectrometry was employed to determine the concentrations of the three compounds in rabbit plasma. In comparison with rabbits administrated Panax notoginseng extract alone, animals simultaneously taking Panax notoginseng extract and Borneol exhibited significant differences in pharmacokinetic parameters of NGR1, GRg1, and GRe, such as increasing their bioavailability. Quantities of NGR1, GRg1, and GRe in rabbit tissues were also increased after combining administration of Borneol. In addition, the apparent permeability coefficients () of NGR1, GRg1, and GRe were raised by Borneol significantly in Caco-2 cells. However, no significant changes were observed in the efflux ratio (Er) of NGR1, GRg1 and GRe. These data indicate that Borneol has the properties of enhancing the intestinal absorption, increasing the distribution, and inhibiting the metabolism of NGR1, GRg1, and GRe. The underlying mechanism might be attributed to the loosening of the intercellular tight junction.
Panax notoginseng, also known as sanchi ginseng, is famous in China and other countries for its obvious therapeutic effects on the cardiovascular system [1, 2]. Previous studies have shown that Panax notoginseng mainly contained dammarane-type saponins (ginsenosides) including sanchinoside or notoginsenoside which is unique to Panax notoginseng [3–6]. Recent researches have revealed various pharmacological effects of notoginsenosides such as blocking Ca2+ influx through the receptor, enhancing astrocyte differentiation, and inhibiting vessel restenosis and antifibrotic effects [7–10].
Various methods for the quality control of Panax notoginseng and its complex prescription have been reported previously in the literature [11–15]. Among these analytical assays, high-performance liquid chromatography coupled with an ultraviolet visible (UV-Vis) detector or a diode array detector was a common choice for the detection of saponins in Panax notoginseng. Setting the detecting wavelength at 190~205 nm due to low absorbance of these compounds in the regular UV region, however, greatly increased the baseline noise and decreased the sensitivity of detection. To address this issue, an evaporative light-scattering detector has been employed for the detection of saponins, resulting in a stable baseline even with a gradient elution [16, 17]. In addition, recent researches have shown that high-performance liquid chromatography coupled with mass spectrometry is a favorable and useful alternative for the detection of saponins in Panax notoginseng [18–20].
Borneol, a monoterpenoid component of the medicinal plant such as Blumea martiniana and Clausena dentata [21–23], is usually used as “Guide drug” in the prescription to guide the bioactive components of herbs to the proper organs to exert a harmonizing effect. A better therapeutic effect has been observed for the combined administration of other herbs, Panax notoginseng and Radix Salvia miltiorrhiza, and Borneol than the single use of other herbs for the patients with cardiovascular diseases in practice [24, 25]. However, the mechanism underlying the synergistic effect of Panax notoginseng and Borneol is still an enigma. In most of the previous studies, pharmacokinetics of saponins in Panax notoginseng and its prescriptions were investigated [25–29]. However, little attention has been paid to pharmacokinetics of notoginsenoside R1 (NGR1), ginsenosides Rg1 (GRg1), and Re (GRe), the main active components of Panax notoginseng, especially the interactive effects of Panax notoginseng and Borneol.
The current study is to investigate the effect of Borneol on the pharmacokinetics of NGR1, GRg1, and GRe in Panax notoginseng in rabbits. A sensitive and accurate SPE-HPLC-MS method was established and applied to the pharmacokinetic study of NGR1, GRg1, and GRe via determining their concentrations in rabbit plasma after oral administration of Panax notoginseng or Panax notoginseng combined with Borneol. In addition, the mechanism underlying the effect of borneol on NGR1, GRg1, and GRe was investigated by vinblastine-selected Caco-2 cells in vitro.
2. Materials and Methods
2.1. Materials and Reagents
NGR1, GRg1, and GRe (purity > 95%) were purchased from the National Institute for the Control of Pharmaceutical and Biological Products of China (Lots nos. 110754-200322; 110703-200322; and 110745-200414, resp.). Borneol (purity > 98%) was supplied by Tianjin Tasly Pharm. Co., Ltd. Caco-2 cells were acquired from Institute of Biochemistry and Cell Biology, Shanghai institute for Biological Sciences, CAS. Transwell plates (pore size 0.4 μm, 24 mm diameter) were purchased from Corning Costar Co. Foetal bovine serum and nonessential amino acids were bought from Gibco-BRL Life Technologies (Paisley, Scotland). Penicillin, streptomycin, trypsin, dimethylsulfoxide (DMSO), and ammonium formate were bought from Sigma Chemical Co. HPLC grade solvents and reagents were obtained from Fisher Scientific Company (Pittsburgh, PA, USA). Ultrapure water (18.2 MΩ) was obtained through a Milli-Q water purification system.
2.2. Preparation of Herb Extract
250 grams of Panax notoginseng were immersed in an 8-fold ethanol/water (V : V, 70 : 30) solution for 30 min and refluxed twice (1.5 h each time). The suspension was then filtered followed by concentrating to 50 mL to obtain the Panax notoginseng extract. The Panax notoginseng extract combined with Borneol was prepared by adding 1.42 g Borneol to 50 mL Panax notoginseng extract. The concentrations of NGR1, GRg1, and GRe in the extract were determined to be 87.5, 124.6, and 40.2 mg·mL−1, respectively, by the HPLC method.
The ethical use of animals in this study was approved by the Advisory Board on Animal Experiments of the Xi’an Jiaotong University in China. New Zealand rabbits (weight 1.7–2.3 kg) were provided by the Animal Center of Xi’an Jiaotong University. The rabbits were maintained in air-conditioned animal quarters at a temperature of 22 ± 2°C and a relative humidity of 50 ± 10%. The cannula (Terumo, 22 G × 1, i.d. 0.60 × 20 mm) was placed in the central ear artery and used for blood collection. The animals were acclimatized to the facilities for 5 days, and then fasted and had free access to water for 12 h prior to experiment.
2.4. Liquid Chromatographic and Mass Spectrometric Conditions
Liquid chromatography was carried out on an Agilent 1100 HPLC system with an auto sampler, a quaternary pump and a vacuum degasser (Waldoboro, Frankfurt, Germany). Operations were controlled by Agilent Chemstation 4.2 software (Littleforts, Philadelphia, USA). Separations were achieved on a reversed-phase HPLC column (Zorbax SB-C18 150 2.1 mm, 5.0 m particle size). A solution of acetonitrile and water (V : V, 20 : 80) with 0.1% (V : V) ammonium formate was used as the mobile phase. The flow rate was set at 0.3 mL· and the column temperature was 25°C. Under these conditions, NGR1, GRg1, and GRe in plasma samples were separated efficiently without any interferences.
MSn detection was performed on an Agilent SL trap MS system (Waldoboro, Frankfurt, Germany). The ion source-dependent (electrospray ionization) conditions were the same for all analyses with a spraying voltage of −4500 V in the negative ion mode. The pressure of the nebulizing gas (nitrogen) was set at 35 p.s.i. The flow rate of the drying gas (nitrogen) was set at 7.0 L·min−1 with the temperature of 325°C. The collision gas (He) for the MSn mode at trap was set at flow of 4 (instrument unit). The voltage of the capillary was set at 4000 V, and its end plate offset was −500 V. Scan range was from 500 to 1500 m/z.
2.5. Preparation of Calibration Standard Working Solutions
Primary stock solutions of 0.28 mg·min−1 NGR1, 0.30 mg·min−1 GRg1 and 0.72 mg·min−1 GRe were prepared in methanol. Working standard solutions of NGR1, GRg1, and GRe were prepared by diluting the aliquots of the primary solution with methanol. The solutions were stored at 4°C in glass tubes until further use.
2.6. Extraction of Sample
Frozen plasma and tissue samples were thawed in a water bath at 37°C and were then vortexed followed by centrifuging at 5000 r·min−1 for 5 min. An aliquot of 1.0 mL of the supernatant from each sample was loaded onto C18 Bond Elute Solid phase extraction (SPE) cartridges (1000 mg, 1 cc reservoir, Varian, Harbor City, CA, USA) pretreated with 2.0 mL hexane, isopropanol, methanol, and water, sequentially. The SPE cartridges were then washed with 1.0 mL water, 20% methanol/water solution, 40% methanol/water solution, and 60% methanol/water solution, sequentially. Finally, analytes were eluted twice with 1.0 mL of 70% methanol/water solution. The eluant was evaporated to dryness under nitrogen. The residues were then reconstituted in 1.0 mL mobile phase. An aliquot of 10 μL was injected into the LC-MS system.
2.7. Calibration Procedure
Samples calibration standards containing 0.28, 0.56, 2.8, 5.6, 14.0, 28.0, and 56.0 μg·min−1 of NGR1, 0.30, 0.60, 3.0, 6.0, 15.0, 30.0, and 60.0 μg·min−1 of GRg1, and 0.36, 0.72, 3.6, 7.2, 18.0, 36.0, and 72.0 μg·min−1 of GRe were freshly prepared daily by diluting the working standard solution with blank sample. The calibration curve was then obtained by plotting the peak areas of the extracted ion current versus the concentrations of the standards using weighted linear regression. The results showed that the linear range of NGR1, GRg1, and GRe was 0.28–56.0, 0.30–60.0, and 0.36–72.0 μg·min−1, respectively.
2.8. Method Validation
Validation of the proposed method included assessment of the calibration curve performance, as well as accuracy and precision of the method, and stability of the analytes at various test conditions.
The precision of the assay was determined for the quality control (QC) plasma and tissue samples by replicate analyses of three levels of concentration at 0.5, 5.0, and 35.0 μg·min−1 for NGR1, 0.4, 3.0, and 40.0 μg·min−1 for GRg1, and 0.8, 8.0, and 48.0 μg·min−1 for GRe. Intraday precision and accuracy were determined via repeated analysis of the QC plasma and tissue samples within one day (). Interday precision and accuracy were determined via repeated analysis on five consecutive days. The concentration of each sample was determined using the prepared calibration curve and analyzed on the same day. All stabilities were evaluated at different concentration levels. Short-term stability of NGR1, GRg1, and GRe were assessed by analyzing QC samples kept at 4°C for 4–24 h. Freeze-thaw stability was evaluated at three consecutive freeze-thaw cycles. Long-term stability was studied by analyzing samples during a period of 8 weeks of storage at −70°C.
2.9. Pharmacokinetics Study
Eighteen rabbits were randomly divided into three groups of 6 subjects and were orally given 3.0 mL·kg−1 normal saline, 3.0 mL·kg−1 Panax notoginseng extract, and 3.0 mL·kg−1Panax notoginseng extract combined with Borneol, respectively. Plasma samples were collected in heparinized tubes from the central ear artery at 0.0, 5.0, 10.0, 20.0, 30.0, 45.0, 60.0, 75.0, 90.0, 120.0, 180.0, 300.0 and 480.0 min after dose. After each sampling, the same volume of 0.9% saline solution was injected from the ear vein to compensate the loss of blood. The plasma obtained was frozen at −70°C for storage and was processed prior to analysis with the proposed method as described in Section 2.6.
2.10. Tissue Distribution Study
One group of rabbits () was orally administered a dose of 3.0 mL·kg−1Panax notoginseng extract, while another group of rabbits () was orally given 3.0 mL·kg−1Panax notoginseng extract combined with Borneol. At 0.5, 1, and 3 h after administration, blood samples were collected from the central ear artery of six rabbits from each group, and the heart, liver, lung, kidney, and brain were immediately removed after animals were sacrificed by decapitation. An accurately weighed amount of tissue (1 g) was collected to be rinsed, dried, minced, and homogenized (400 r·min−1) in normal saline (1.5 mL). All of the samples were stored at −70°C and were processed prior to analysis with the proposed method as described in Section 2.6.
2.11. Transport Studies
The Caco-2 cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 20% foetal bovine serum, 1% nonessential amino acids and penicillin-streptomycin, at 37°C in an atmosphere with a relative humidity of 95% and a CO2 flow of 5%. Medium was replaced every 2-3 days. When the cell monolayer reached 80% confluence, the cells were detached with a solution of 0.02% EDTA and 0.25% trypsin. The vinblastine-selected Caco-2 cells were cultivated in the presence of 10 nM vinblastine to induce P-glycoprotein (P-gp) expression. The culture medium was changed to a fresh medium without vinblastine 24 h before experiments, and the cells were used between passages 25 and 46. Prior to the transport study, cytotoxicity of NGR1, GRg1, GRe, and Borneol toward Caco-2 cells was determined using MTT assays. Noncytotoxic concentrations of 500 μM NGR1, GRg1, GRe, and 200 μM Borneol (dissolved in DMSO) were chosen for transport study.
In transport studies, vinblastine-selected Caco-2 cells were seeded on polycarbonate filter of transwells for 18–21 days before starting transport study, and the monolayers with the transepithelial electrical resistance (TEER) values greater than 300 cm2 were used. Caco-2 monolayers were rinsed twice with Hanks’ balanced salt solution (HBSS) and preincubated in HBSS at 37°C for 30 min before starting experiments. To start the experiments, 500 μM of NGR1, GRg1, and GRe in final concentrations were added to the donor side with or without 200 μM Borneol and then incubated at 37°C. An aliquot of 0.1 mL samples were withdrawn from receiver chambers at 0, 30, 60, 90, and 120 min after the loading. After each sampling, 0.1 mL of HBSS was added to the receiver chamber to maintain a constant volume. All the experiments were performed five times in duplicate. The collected samples were stored at −20°C until HPLC analysis. During the above transport studies, the TEER values were also monitored before and at the end of each experiment. Apparent permeability coefficients () were then calculated according to the following equation: where is the rate of the test compound appearing in the receiver chamber, is the volume of the solution in the receiver chamber, is the cell monolayer surface area, and is the initial concentration of the test compound added in the donor chamber.
The efflux ratio () was calculated using the following equation:
2.12. Statistical Analysis
Statistical analysis of the biological data was performed using the Student’s -test. The drug analysis system 2.0 (DAS 2.0, T.C.M., Shanghai, China) was used to calculate the pharmacokinetic parameters, such as the area under curve (AUC), the maximum plasma concentration (), the time needed to reach the maximum plasma concentration () and the half-life of absorption, and distribution and elimination ().
3. Results and Discussion
3.1. Method Validation
The base peaks of each mass spectrum for NGR1, GRg1, and GRe were observed during the infusion of the standard solution in negative mode. Three precursor ions, m/z 931.6 for NGR1, m/z 799.5 for GRg1, and m/z 945.1 were subjected to collision-induced dissociation (CID). The product ions were recorded as m/z 799.4 , 637.3 , and m/z 799.2 , respectively. Mass transition patterns, m/z 931.6 799.4, m/z 799.5 637.3, and m/z 945.1 799.2, were selected to monitor NGR1, GRg1, and GRe. Representative HPLC-MS ion chromatograms of blank plasma samples, plasma standard solutions of 5.0 μg·mL−1 NGR1, 3.0 μg·mL−1 GRg1 and 8.0 μg·mL−1 GRe as well as plasma samples after administration of Panax notoginseng extract at a dose volume of 3.0 mL·kg−1 are shown in Figure 1. No endogenous peaks were found to be coeluted with the analytes, indicating high specificity of the proposed method.
3.1.2. Calibration Curve Performance
The calibration curves were created by plotting the peak areas of NGR1, GRg1, and GRe to their various concentrations in the spiked plasma and tissue standards. A weighted (1/[nominal concentration]) least-squares linear regression of the type was used to fit the curves (Table 1). The lowest correlation coefficient of determination () among the five calibration curves of NGR1, GRg1, and GRe were between 0.9982 and 0.9996. Thus, the calibration curves exhibited good linearity within the chosen range.
3.1.3. Limit of Detection and Quantitation
The limit of detection (LOD) was estimated as the amount of NGR1, GRg1, and GRe, which caused a signal three times that of noise (). The LOD was determined to be 0.57, 0.30, and 0.24 ng·mL−1 in lung and liver, and 0.28, 0.15, and 0.12 ng·mL−1 in plasma and other tissues, respectively. The lower limit of quantitation (LLOQ) was defined as the lowest concentration with the accuracy and precision better than 20% and a signal to noise ratio of >10. The LLOQ for NGR1, GRg1, and GRe were determined to be 1.8, 1.0, and 0.8 ng·mL−1 in lung and liver and 1.0, 0.5, and 0.4 ng·mL−1 in plasma and other tissues, respectively.
3.1.4. Accuracy and Precision
Data for intraday and interday precision and accuracy assessed by analyzing QC samples at different concentrations are presented in Table 2. The results suggested that the method was adequately accurate and reproducible for the determination of NGR1, GRg1, and GRe in rabbit plasma and tissues.
3.1.5. Extraction Recovery and Stability
The extraction recovery analysis was conducted with NGR1, GRg1, and GRe spiked biosamples at three QC levels and calculated by comparing the NGR1, GRg1, and GRe peak areas in extracted biosamples with those found by direct injection of standard solutions at the same concentration. The mean recoveries of NGR1, GRg1, and GRe in plasma and tissue samples at three different concentrations were above 90.0% (Table 2).
The stability studies were performed by evaluating small variations in three different conditions. The results were expressed as the percentage of initial content of NGR1, GRg1, and GRe in the freshly treated samples, suggesting that NGR1, GRg1, and GRe showed no significant change in plasma and tissue samples (Table 3).
3.2. Pharmacokinetics Study
After oral administration of Panax notoginseng or Panax notoginseng combined with Borneol, the plasma concentrations of NGR1, GRg1, and GRe were determined by the described LC/MS/MS method. Figure 2 showed the plasma concentration-time curves of NGR1, GRg1, and GRe following ingestion of Panax notoginseng or Panax notoginseng combined with Borneol (). The statistical results through DAS 2.0 indicated that the plasma drug concentration-time course of the three compounds in rabbits confirmed the 2-compartment open models. The corresponding regression pharmacokinetic parameters were shown in Table 4.