A UPLC-MS/MS Method for Simultaneous Determination of Free and Total Forms of a Phenolic Acid and Two Flavonoids in Rat Plasma and Its Application to Comparative Pharmacokinetic Studies of Polygonum capitatum Extract in Rats

Abstract

The principal active constituents of Polygonum capitatum are phenolic acids and flavonoids, such as gallic acid, quercitrin, and quercetin. The aim of this study was to develop and validate a method to determine the three constituents and the corresponding conjugated metabolites of Polygonum capitatum in vivo and to conduct pharmacokinetic studies on the herb, a well-known Miao medicinal plant in China. Gallic acid, quercitrin, and quercetin were analysed by ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS). Protein precipitation in plasma samples was performed using methanol. For the determination of total forms of analytes, an additional process of hydrolysis was conducted using β-glucuronidase and sulphatase. The analytes were separated on a BEH C₁₈ column (50 mm × 2.1 mm; i.d., 1.7 μm) and quantified by multiple reaction monitoring (MRM) mode. The linear regression showed high linearity over a 729-fold dynamic range for the three analytes. The relative standard deviations of intra- and inter-day measurements were less than 9.5%, and the method was accurate to within -11.1% to 12.5%. The extraction recoveries for gallic acid, quercitrin, and quercetin were 94.3%-98.8%, 88.9%-98.8%, and 95.7%-98.5%, respectively. All samples were stable under short- and long-term storage conditions. The validated method was successfully applied to a comparative pharmacokinetic study of gallic acid, quercitrin, and quercetin in their free and total forms in rat plasma. The study revealed significantly higher exposure of the constituents in total forms for gallic acid and quercetin, while quercitrin was detected mainly in its corresponding free form in vivo. The established method was rapid and sensitive for the simultaneous quantification of free and total forms of multiple constituents of Polygonum capitatum extract in plasma.

Keywords: Polygonum capitatum extract; UPLC-ESI-MS/MS; flavonoids; hydrolysis; pharmacokinetics; phenolic acids.

Figure 1

Chemical structures of (a) gallic acid; (b) quercitrin; (c) quercetin; and (d) puerarin (I.S.).

Figure 2

Chromatograms of the analytes and puerarin (I.S.) in rat plasma. Blank plasma sample (a); a plasma sample spiked with gallic acid, quercitrin, and quercetin, or puerarin (I.S.), respectively (b); and a plasma sample obtained from a rat 60 min after oral administration of P. capitatum extract (c).

Figure 3

Mean plasma concentration-time curves of (a) gallic acid; (b) quercitrin; and (c) quercetin after oral administration of P. capitatum extract (equivalent to 21.35 mg/kg of gallic acid, 2.17 mg/kg of quercitrin, and 0.39 mg/kg of quercetin, respectively) to rats (n = 6).

Figure 4

MS/MS spectra of (a) gallic acid; (b) quercitrin; (c) quercetin; and (d) I.S.

Figure 4

MS/MS spectra of (a) gallic acid; (b) quercitrin; (c) quercetin; and (d) I.S.