Identification of Puerarin and Its Metabolites in Rats by Liquid Chromatography−Tandem Mass Spectrometry
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3708 J. Agric. Food Chem. 2004, 52, 3708−3712 Identification of Puerarin and Its Metabolites in Rats by Liquid Chromatography−Tandem Mass Spectrometry JEEVAN K. PRASAIN,*,†,‡ KENNETH JONES,† NANCY BRISSIE,# RAY MOORE,§ ⊥ J. MICHAEL WYSS,# AND STEPHEN BARNES†,‡,§, Department of Pharmacology and Toxicology, Department of Cell Biology, Comprehensive Cancer Center Mass Spectrometry Shared Facility, and Purdue-UAB Botanicals Center for Age-Related Diseases, University of Alabama at Birmingham, Birmingham, Alabama 35294 Puerarin (daidzein-8-C-glucoside) is the major bioactive isoflavone of kudzu root (the root of Pueraria lobata). Its metabolic fate, however, is not well-known. In this study, a sensitive and specific LC- ESI-MS/MS method for the determination of puerarin and its metabolites daidzein, dihydrodaidzein, and equol was developed for their analysis in biological samples. Two new metabolites of puerarin, mono- and dihydroxylated derivatives, were detected in the urine and feces of rats after oral administration. The persistence of puerarin in blood and urine as the principal metabolic form for the period of 4-72 h after oral administration suggested that puerarin is rapidly absorbed from the intestine without metabolism. Its presence in organs such as the brain suggests that this glucoside may enter tissues by specific transport pathways. Study of these metabolites may provide further understanding of the health beneficial effects of puerarin in kudzu dietary supplements. KEYWORDS: Puerarin; metabolites; C-glucoside; kudzu; LC-MS/MS; rats INTRODUCTION prompted us to develop an LC-MS method for the analysis of the isoflavone-C-glycosides such as puerarin (daidzein-8-C- Glucoside conjugates of isoflavonoids (O- and C-glucosides) glucoside) and their in vivo metabolites. are the major naturally occurring isoflavones in leguminous plants, including kudzu (Pueraria lobata). Flavonoid O-glyco- Puerarin, the most abundant isoflavone-C-glucoside, isolated sides such as phlorizin are inhibitors of sodium-dependent from Pueraria Radix (the root of kudzu, P. lobata), has been glucose transporters (1, 2). This has led to the suggestion that shown to have beneficial effects on cardiovascular, neurological, - bioflavonoid glycosides could be absorbed from the small and hyperglycemic disorders (10 12). Because Pueraria Radix intestine via these transporters (3). However, currently it is has been prepared in the form of commercially available dietary generally considered that the glycosidic forms of the isoflavones supplements that are consumed by the public, it is critical to and other flavonoids must first be hydrolyzed in the intestine understand the metabolic fate of its major isoflavones. However, to release the respective aglycons by intestinal glucosidases/ little is known about the metabolism of puerarin. Understanding hydrolases (4, 5). In the case of O-glycosides, these are of its metabolism and bioavailability is very important in hydrolyzed by â-glucosidases in the small intestinal wall and defining the pharmacological and toxicological profile of this appear in plasma mostly as metabolites within a short period compound and other similar C-glycosides. In the present work of time (6, 7). Because the aglycons and their metabolites are we have applied LC-MS and MS/MS methods to the measure- more hydrophobic, they may be more efficiently transported ment of puerarin in biofluids (serum and urine), feces, and across the wall of the gastrointestinal tract than their respective tissues (heart and brain) of rats. glucosides. However, there appears to be a complex interplay between the chemical structure of glycosides and their rate of MATERIALS AND METHODS transport (8, 9). The C-glycosides of isoflavones, which are Chemicals. Puerarin was purchased from Sigma Chemical Co. (St. resistant to hydrolysis by glucosidases, represent an important Louis, MO). Apigenin and other standards, daidzein and equol, were tool to evaluate whether bioflavonoid glycosides are capable purchased from Indofine (Somerville, NJ). Dihydrodaidzein was of intestinal transport via the glucose transporter systems. This obtained from Dr. Kristiina Wa¨ha¨la (University of Helsinki), Finland. All other HPLC solvents and reagents were purchased from Fisher * Corresponding author [telephone (205) 996-2612; fax (205) 934-6944; (Norcross, GA) and were of HPLC grade. e-mail [email protected]]. Standard Solutions and Calibration Curve. Stock solutions of † Department of Pharmacology and Toxicology. standards (100 µM) and the internal standard, apigenin, were separately ‡ Purdue-UAB Botanicals Center for Age-Related Disease. # Department of Cell Biology. prepared by dissolving accurately weighed amounts in 80% aqueous § Comprehensive Cancer Center Mass Spectrometry Shared Facility. methanol. These solutions were serially diluted with the same solvent ⊥ UAB Center for Nutrient-Gene Interaction in Cancer Prevention. to obtain calibration standards. The stock solutions were kept refriger- 10.1021/jf040037t CCC: $27.50 © 2004 American Chemical Society Published on Web 05/20/2004 Analysis of Puerarin and Its Metabolites in Rats by LC-MS/MS J. Agric. Food Chem., Vol. 52, No. 12, 2004 3709 ated (4 °C). The calibration curves covered a wide range of concentra- tions (0.05, 0.1, 0.5, 1, 5, 10, 25, and 50 µM) of the standards. Animal Experiments and Sample Preparation. Sprague-Dawley male rats (n ) 9) were obtained from Harlan Sprague-Dawley Inc., Indianapolis, IN. They were kept in a controlled environment at 23 °C and 55% relative humidity under a 12 h dark-light cycle, with free access to soy-free custom diet TD86369 (Harlan TekLAD, Madison, WI) and tap water for 2 weeks. The rats were then placed in metabolic cages with access to water and food. Puerarin (50 mg/kg of body weight) was orally administered in suspension by gavage to the rats four times at intervals of 72 h. Urine samples were collected at intervals of 0-4, 4-20, 20-27, 27-43, and 43-72 h. Blood was collected at 4 h after the first puerarin administration by inserting a cannula into the femoral artery, and serum was isolated by centrifugation of the blood at 3000g for 10 min at 4 °C. The rats were anesthetized by intraperitoneal injection of sodium pentobarbital (50 mg/kg). The heart, brain, and blood were collected 24 h after the final administration, and the organs were taken at sacrifice after perfusion with ice-cold normal saline. Feces were collected and combined at the end of the experiment. All samples were kept at -20 °C until analysis. Heart and brain samples (wet weight ) 1-2.2 g) were minced and added to 1.5 mL of double-distilled water. The tissue was homogenized with a Tissue Tearor homogenizer (Biospace Product Inc., Racine, WI), and 3.5 mL of MeOH and 10 µLof50µM apigenin (internal standard) were added for extraction of puerarin and its metabolites. The samples were vortex mixed and tumbled for2hatroom temperature. The homogenate was centrifuged at 3000g for 10 min and the supernatant Figure 1. Structures of standards. removed. The tissue was re-extracted by adding an additional 5 mL of 80% aqueous MeOH. The aqueous MeOH extracts were dried under air and reconstituted in the same solvent (100 µL). Thawed urine and serum samples (200 µL) were placed in Eppendorf tubes, and 100 µL of apigenin (50 µM) was added. A further 200 µL of acetonitrile was added to precipitate proteins. Samples were vortex mixed and then centrifuged (3000g for 10 min) in Eppendorf tubes. When needed, the extract of the urine samples was filtered through a syringe filter. The supernatant was transferred to an autosampler vial, anda20µL aliquot was injected onto the LC-MS/MS system for analysis. Frozen fecal material (200 g) was extracted with 80% aqueous MeOH (250 mL × 2) and centrifuged at 3000g for 10 min, and a 100 µL aliquot was directly analyzed by ESI-MS. LC-MS/MS Analysis of Puerarin and its Metabolites. LC-MS/ MS analyses were performed using a system consisting of a model SIL-HT refrigerated Shimadzu autosampler (Shimadzu Scientific Instru- ments, Inc., Columbia, MD) and an API-III triple-quadrupole mass spectrometer (PE Sciex, Concord, Canada). Chromatography was carried out on a 100 × 4.4 mm i.d. Aquapore RP-300 reversed-phase column (Perkin-Elmer, Shelton, CT) pre-equilibrated with 10 mM ammonium acetate (NH4OAc). The mobile phase consisted of a gradient of 10-40% acetonitrile in 10 mM NH4OAc with a flow rate of 1.0 Figure 2. Product ion spectra of standards: puerarin [A], daidzein [B], mL/min. Multiple reaction monitoring (MRM) was used to perform dihydrodaidzein [C], and equol [D]. mass spectrometric quantification of puerarin and its metabolites. The MRM delivers a unique product ion that can be monitored and a range from 0.05 to 50 µM. Puerarin, daidzein, dihydrodaidzein, and quantified in the midst of a very complicated biological matrix. For equol had linear response curves with correlation coefficients >0.99. MRM-MS, the gradient was over 15 min, whereas for LC-MS, it was The detection limit of injected puerarin was 50 fmol/µL. over 30 min. The column effluent was introduced into the mass spectrometer using electrospray ionization in negative mode. The RESULTS voltage on the ionspray interface was -4900 V, and the orifice potential was set at -50 V. Selected [M - H]- (deprotonated molecular ions) LC-MS/MS Method Development. Puerarin and its me- were analyzed by collision-induced dissociation with 90% argon-10% tabolites in biological samples were investigated using LC-MS/ nitrogen gas, and product ion spectra were recorded. The MRM analysis MS methods. The first step of this work involved the charac- was conducted by monitoring the precursor ion to product ion transitions terization of the mass spectral properties of the parent compound from m/z 415/267 (puerarin), 415/295 (puerarin), 253/223 (daidzein), and other standards. 255/149 (dihydrodaidzein), 241/119 (equol), and 269/149 (apigenin). The chemical structures and molecular weights of standards MACQUAN software provided by PE SCIEX was used to process the are shown in Figure 1.