Simultaneous Determination of 10 Bioactive Components of Lophatherum gracile Brongn by HPLC-DAD

Journal of Chromatographic Science 2015;53:963 967 doi:10.1093/chromsci/bmu160 Advance Access publication December 19, 2014 Article Simultaneous Determination of 10 Bioactive Components of Lophatherum gracile Brongn by HPLC-DAD Qingfa Tang 1, Meng Shao 1, Ying Wang 2,3, Huinan Zhao 2,3, Chunlin Fan 2,3, Xiaojun Huang 2,3, Yaolan Li 2,3 and Wencai Ye 2,3 * 1 School of Chinese Medical Sciences, Southern Medical University, Guangzhou, PR China, 2 Institute of Traditional Chinese Medicine & Natural Products, College of Pharmacy, Jinan University, Guangzhou 510632, PR China, and 3 Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research, Jinan University, Guangzhou, PR China *Author to whom correspondence should be addressed. Email: chyewc@gmail.com These authors contributed equally to this work. Received 17 March 2014; revised 14 October 2014 A high-performance liquid chromatography method coupled with diode array detection (HPLC-DAD) was developed for simultaneous determination of two coumarins and eight flavonoids in Lophatherum gracile Brongn (Gramineae), namely 5-O-coumaroylquinic acid (i), 4-O-coumaroylquinic acid (ii), luteolin 6-C-b-D-galactopyranosiduronic acid (1!2)- b-d-glucopyranoside (iii), 7-O-b-D-glucopyranosyl-6-C-a-L-arabinopy ranoside (iv), isoorientin (v), swertiajaponin (vi), luteolin 6-C-b-D-galactopyranosiduronic acid (1!2)-a-L-arabinopyranoside (vii), Saponaretin (viii), swertisin (ix) and apigenin 6-C-b-D-galactopyranosiduronic acid (1!2)-a-L-arabinopyranoside (x). The analysis was performed on Cosmosil MS-II C 18 column (250 3 4.6 mm, 5 mm) with gradient elution of 0.1% aqueous acetic acid and acetonitrile. The detection wavelength was 330 nm. The developed method was able to determine the bioactive compounds with excellent resolution, precision and recovery. The validated method was successfully applied for the analysis of the 10 bioactive compounds in n samples from different cultivated regions. The results indicated that the developed method can be used as a suitable quality control method for L. gracile. Introduction The leaf of Lophatherum gracile, Danzhuye in Chinese, is a widely used traditional Chinese medicine to the treatment of pyreticosis, hydrodipsia, ardor urinae and urinary tract inflammation (1). In addition, the herb is an important ingredient of some herbal teas, such as Wong Lo Kat herbal tea, which are commonly used in southern China to ease common cold (2). Modern pharmacological researches demonstrated that the extracts of L. gracile had antipyretic, diuretic, antibacterial, antitumor and hypoglycemic effects (3). Coumaric acids possessed antiviral activities (4), luteolin and its glycoside possessed antibacterial and anti-inflammatory activities (5), apigenin and its glycoside possessed antioxidant and anti-tumor (6), isoorientin and swertisin possessed hypoglycemic activities (7), flavone C-glycosides have antiviral activities (8). Coumaric acids and flavonoids are the major constituents of this herb, these two kinds of compounds could be considered as the active components of L. gracile, and therefore were used as the chemical makers to control the quality of the herb in the present determination. The leaf of L. gracile has been officially recorded in the Chinese Pharmacopoeia (State Pharmacopoeia Committee, 2010) as a crude drug (9), but no quality control is listed except the character identification of the herb. Recently, there are some investigations related to the high-performance liquid chromatography (HPLC) quantitative determination of the bioactive components in L. gracile, including flavonoids, such as swertiajaponin (10), orientin, isorientin, vitexin, isovitexin (11) and tricin 7-O-glucoside (12) and coumaric acids, such as vanillic acid and trans-p-coumaric acid (13). However, these methods suffered from lower resolution, lower sensitivity as well as fewer analytes (,4 analytes). Because the therapeutic effect of TCM is usually attributed to the synergy of multiple bioactive compounds, single or fewer active compounds could not be responsible for the overall pharmacological activities of the medicines. On the other hand, as this herb is widely cultivated in different parts of China, the contents of the active components vary greatly depend on the geographical locations, climate and other factors (14 15). It is necessary to develop a satisfactory method which can analyze more bioactive compounds for controlling the quality of L. gracile. In the present study, a high-performance liquid chromatography method coupled with diode array detection (HPLC-DAD) was developed to simultaneously determine 10 different bioactive compounds in L. gracile including 5-O-coumaroylquinic acid (1), 4-O-coumaroylquinic acid (2), luteolin 6-C-b-Dgalactopyranosiduronic acid (1!2)-b-D-glucopyranoside (3), 7-O-b-D-glucopyranosyl-6-C-a-L-arabinopyranoside (4), isoorientin (5), swertiajaponin (6), luteolin 6-C-b-D-galactopyranosiduronic acid (1!2)-a-L-arabinopyranoside (7), saponaretin (8), swertisin (9) and apigenin 6-C-b-D-galactopyranosiduronic acid (1!2)- a-l-arabinopyranoside (10). Their structures are shown in Figure 1. Experimental Chemicals, reagents and materials Acetonitrile (Merk, Darmstadt, Germany) was of HPLC grade. Water for HPLC analysis was purified by a Milli-Q water purification system (Millipore, Boston, Massachusetts, USA). Other reagent solutions were of analytical grade from Guangzhuo Chemical Reagent Corporation (Guangzhuo, PR China). Standard compounds were isolated from the leaves of L. gracile. Their structures were confirmed based on spectroscopic analysis ( 1 H NMR, 13 C NMR and ESI-MS). The purity of each compound was.98% detected by HPLC-DAD. Ten raw material samples of # The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com

Figure 1. The structures of 10 bioactive components in L. gracile. L. gracile were collected from different provinces in China. All the voucher specimens, which were authenticated by Prof. Guangxiong Zhou, were kept at our department for reference. The air-dried samples were smashed into powder and passed through a 40-mesh sieve before analysis and stored in desiccators. Chromatographic conditions Chromatographic analysis was performed on an Agilent 1100 series HPLC-DAD (190 400 nm), a quaternary solvent delivery system, a column temperature controller and an autosampler. The chromatographic data were processed with Agilent Chromatographic Work Station software. The analysis was carried out at 358C on an Cosmosil MS-II C 18 column (250 4.6 mm, 5 mm). The injection volume was set to 10 ml with detection set to 330 nm. The eluents A (water acetic acid, 100 : 0.1, v/v) and B (acetonitrile) were used for separation at a flow rate of 1.0 ml min 21. The following gradient was employed: 0 20 min, 8 10.5% (B); 20 30 min, 10.5 10.5% (B); 30 40 min, 10.5 12.5% (B); 40 55 min, 12.5 12.5% (B); 55 56 min, 12.5 15.0% (B); 56 75 min, 15.00 16.0% (B); 75 77 min, 15.0 8.0% (B). Preparation of standard solutions In a clean and dry 10 ml volumetric flask, the following analytes of reference standards were dissolved in 10 ml of 70% methanol to make stock resolution: the 5-O-coumaroylquinic acid (2.567 mg), 4-O-coumaroylquinic acid (2.849 mg), luteolin 6-C-b- D-galactopyranosiduronic acid (1!2)-b-D-glucopyranoside (5.021 mg), 7-O-b-D-glucopyranosyl-6-C-a-L-arabinopyranoside (4.220 mg), isoorientin (5.884 mg), wertiajaponin (6.021 mg), luteolin 6-C-b-D-galactopyranosiduronic acid (1!2)-a- L-arabinopyranoside (4.967 mg), saponaretin (2.576 mg), swertisin (1.825 mg) and apigenin 6-C-b-D-galactopyranosiduronic acid (1!2)-a-L-arabinopyranoside (3.064 mg). Calibration working standard solutions were prepared by diluting the stock solution with 70% methanol in the appropriate quantities. All working solutions were stored at 2208C and brought to room temperature before use. The solutions were filtered through a 0.45-mm membrane prior to injection. Sample preparation All the samples were oven-dried at 508C until the weight remained constant. The dried sample (4.0 g powder) was extracted with 100 ml ethanol aqueous solution (70%, v/v) in an ultrasonic water bath for 45 min. The solution was filtered through filter paper, and evaporated to dryness in a rotary evaporator. The extract was dissolved in 10 ml of 70% methanol in a volumetric flask. Therefore, each solute was at a concentration of 0.4 mg ml 21. An aliquot of 10 ml resulting solution was filtered through a 0.45-mm membrane prior to HPLC analysis. 964 Tang et al.

Results and Discussion Optimization of extraction procedure To obtain satisfactory extraction efficiency, ultrasonic, refluxing and soxhlet extraction were compared. It was found that the ultrasonic extraction was simpler and more effective for extraction, and therefore used in further experiments. Pure and aqueous methanol solutions were tested as the extraction solvents. In the present study, different concentrations (40, 60, 70, 90 and 100%) of methanol solutions were used for extraction procedure of L. gracile (batch no. 20080325). It was found that the extraction values of all targets increased gradually with the methanol concentration increasing when the concentration of methanol was,90%. A high methanol concentration (100%) did not Figure 2. Typical HPLC chromatograms of (A) mixed standards and (B) Lophatherum gracile. 5-O-Coumaroylquinic acid (1), 4-O-coumaroylquinic acid (2), luteolin 6-C-b-D-galactopyranosiduronic acid (1!2)-b-D-glucopyranoside (3), 7-O-b-D-glucopyranosyl-6-C-a-L-arabinopyranoside (4), isoorientin (5), swertiajaponin (6), luteolin 6-C-b-D-galactopyranosiduronic acid (1!2)-a-L-arabinopyranoside (7), Saponaretin (8), swertisin (9) and apigenin 6-C-b-D-galactopyranosiduronic acid (1!2)-a-L-arabinopyranoside (10). Simultaneous Determination of 10 Bioactive Components 965

benefit efficient extraction. Thus, 70% aqueous methanol was selected as the extraction solvent. Four sample-solvent ratios (1 : 20, 1 : 40, 1 : 60 and 1 : 80, w/v) were tested and compared, and it was found that the ratio of 1 : 40 was the best. Different extraction times (15, 30, 45 and 60 min) were also tested and 45 min was selected. The suitable extraction condition was established as follows: samples were extracted by ultrasonic extraction using 40-times of 70% aqueous methanol as the extraction solvent, and the process lasted for 45 min. Optimization of chromatographic conditions To obtain accurate, valid and optimal chromatographic conditions, different HPLC parameters were examined and compared, including various columns (Cosmosil C 18 250 4.6 mm, 5 mm; Phenomenex Luna PFP 250 4.6 mm, 5 mm; Agilent Extend C 18 250 4.6 mm, 5 mm; Phenomenex Luna C 18 250 4.6 mm, 5 mm), mobile phases (methanol water and acetonitrile water with different modifiers, including acetic acid, formic acid and phosphoric acid), column temperatures (20, 25, 30, 35 or 408C), and mobile phase flow rates (0.8, 1.0, 1.2 or 1.5 ml min 21 ). Based on the maximum absorption of the marker compounds in the UV spectra of the three-dimensional chromatograms obtained by DAD detection, the detection wavelength was set at 330 nm, where all the marker compounds could be detected and had adequate absorption. Finally, The chromatographic conditions for the method utilizing the Cosmosil MS-II C18 column on the Agilent HPLC 1100 series with gradient elution of 0.1% aqueous acetic acid and acetonitrile. The column oven heater was set to 358C. The peaks were recorded using DAD absorbance at 330 nm and the solvent flow rate was kept at 1.0 ml min 21.Figure2 shows chromatograms A and B corresponding to the mixture of the standards and sample. Method validation of quantitative analysis The method was validated in terms of linearity, LOD and LOQ, precision, reproducibility and recovery test. Calibration curves, limits of detection and quantification Methanol stock solutions containing the 10 analytes were prepared and diluted to appropriate concentrations for construction of the calibration curves. The 10 analytes solutions at six different concentrations were injected in triplicate, and the calibration curves were constructed by plotting the peak areas versus the concentrations of each analyte. Satisfactory calibration curves of the 10 bioactive components were obtained. LOD and LOQ, which were expressed by 3- and 10-fold of the ratio of the signal-to-noise (S/N), were also acquired. Detailed information regarding the calibration curves, linear ranges, LOD, and LOQ is listed in Table I. Precision, repeatability and stability Intra- and interday variations were chosen to determine the precision of the developed assay. Intraday precision was validated with three concentrations of mixed standard solutions under the optimized conditions for five times within 1 day. Interday precision was validated with the mixed standard solutions used above once a day for 3 consecutive days. To test the reproducibility of our assay, six independently prepared samples of L. gracile Table I The Regression Data, LOD and LOQ of 10 Compounds in L. gracile Compound Regression equation (Y ¼ ax þ b) R 2 Linear range LOD a LOQ b a Y ¼ 38.378x 2 9.5178 0.9995 1.03 51.34 0.07 0.25 b Y ¼ 37.093x 2 2.4389 0.9996 1.14 56.98 0.06 0.24 c Y ¼ 10.102x 2 3.2583 0.9991 2.00 100.42 0.26 1.06 d Y ¼ 13.64x 2 2.3931 0.9999 1.69 84.39 0.20 0.88 e Y ¼ 14.397x 2 6.3333 0.9999 2.35 117.67 0.16 0.70 f Y ¼ 9.8525x 2 2.0958 0.9993 2.41 120.42 0.21 0.82 g Y ¼ 12.397x 2 3.1014 1.0000 1.99 99.34 0.20 1.13 h Y ¼ 28.468x 2 4.8762 0.9994 1.03 51.52 0.11 0.49 i Y ¼ 32.423x 2 5.5868 0.9998 0.73 36.50 0.08 0.28 j Y ¼ 22.978x 2 0.4875 1.0000 1.22 61.29 0.13 0.56 a LOD refers to the limits of detection, S/N ¼ 3. b LOQ refers to the limits of quantification, S/N ¼ 10. Table II Precision, Repeatability, Stability and Recovery of 10 Analytes Analyte a Precision (RSD, %) Repeatability (RSD, %, n ¼ 6) Intraday (n ¼ 6) Interday (n ¼ 3) Stability (RSD, %, n ¼ 7) Recovery (%, n ¼ 3) Mean RSD (%) a 0.89 1.34 2.06 2.60 97.3 1.57 b 0.98 2.31 0.91 0.43 98.1 0.96 c 0.78 1.98 0.89 2.04 102.2 1.97 d 0.67 2.01 2.78 1.89 101.1 3.04 e 0.55 1.23 2.44 2.23 96.9 3.15 f 0.61 2.21 1.92 1.18 99.3 2.86 g 0.71 1.44 2.01 2.71 100.5 1.61 h 0.81 1.75 1.77 2.41 103.2 1.54 i 0.52 2.10 2.13 1.71 97.8 1.67 j 0.91 2.56 2.27 2.21 98.6 2.87 a The notation for analyte refers to Figure 1. (batch no. 20080325) in parallel were prepared and analyzed. Stability was tested at room temperature and samples were analyzed at 0, 2, 4, 8, 12, 24 and 48 h within 2 days. Stability was expressed as the percentage decrease of sample solution: (content in sample solution at 0 h 2 content in sample solution at 24 h)/ content in sample solution at 0 h. Variations were expressed by relative standard deviations (RSD). All the results were shown in Table II, indicating that the intra- and interday, repeatability and stability RSD values of the 10 compounds were all,4.11%. Recovery test The recovery test was done by the standard addition method. Low, medium and large amounts of the 10 standards were added to the known sample (L. gracile, batch no. 20080325) and then extraction and analysis were done as described in Sample preparation section. The mean recovery was counted according to the following formula: recovery (%) ¼ (amount found 2 original amount)/amount spiked 100%, and RSD (%) ¼ (SD/mean) 100%. The mean recovery of the 10 compounds was 96.32 103.9% and their RSD value was,3.15% (Table II). It was found that the HPLC-DAD method was precise, accurate and sensitive enough for simultaneous quantitative evaluation of the 10 compounds in L. gracile. Sample analysis The newly established analytical method was subsequently applied to simultaneous determination of 10 active compounds in 966 Tang et al.

Table III The Contents (mg/g) of the 10 Targets in L. gracile Purchased from Different Places Batch number Sample source a b c d e f g h i j Total 20081028 Sichuan 0.149 0.157 0.496 0.122 0.233 1.112 0.228 0.066 0.081 0.109 2.75 20081216 Anhui 0.295 0.319 0.582 0.035 0.081 0.502 0.038 0.034 0.083 0.037 2.01 20080615 Hunan 0.277 0.360 0.546 0.069 0.173 0.807 0.042 0.043 0.076 0.019 2.41 20080812 Shanxi 0.356 0.347 0.690 0.070 0.153 0.629 0.046 0.036 0.103 0.044 2.47 20081108 Zhejiang 0.288 0.294 1.701 0.053 0.128 0.477 0.081 0.035 0.066 0.052 3.18 20080325 Guangdong 0.287 0.303 0.957 0.162 0.223 0.705 0.071 0.073 0.079 0.029 2.89 20080906 Shangdong 0.269 0.329 1.430 0.090 0.141 0.680 0.081 0.064 0.087 0.068 3.24 20081103 Ningxia 0.199 0.223 0.434 0.070 0.148 0.667 0.036 0.055 0.082 0.033 1.95 20080708 Anhui 0.224 0.272 1.118 0.051 0.117 0.609 0.042 0.032 0.073 0.048 2.58 20080906 Shangdong 0.276 0.332 0.299 0.076 0.148 1.019 0.051 0.069 0.081 0.034 2.37 10 commercial samples of L. gracile (10 batches) from the same manufacturer. All samples were analyzed using the optimized extraction method under optimized HPLC conditions. Each sample was analyzed in triplicate to determine the mean content (mg g 21 ). Table III shows that swertiajaponin (0.447 1.112 mgg 21 ), luteolin 6-C-b-D-galactopyranosiduronic acid (1!2)-b-D-glucopyranoside (0.434 1.701 mg g 21 )werethe main components of Dan ZhuYe commercial samples, followed by 4-O-coumaroylquinic acid (0.157 0.360 mg g 21 )and5-ocoumaroylquinic acid (0.119 0.356 mg g 21 ). The targets could be detected in all the commercial samples from different provinces, and the content of the 10 bioactive components in the 10 batches of Dan ZhuYe was similar. Conclusions A simple and accurate method was developed for simultaneous analysis of 10 active compounds in L. gracile from different sources. This was the first report on the simultaneous quantification of 10 bioactive constituents in L. gracile. 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