Quantification of apigenin trimethyl ether in rat plasma by liquid chromatography-tandem mass spectrometry: Application to a pre-clinical pharmacokinetic study

Apigenin trimethyl ether (5,7,4'-trimethoxyflavone, ATE) is a naturally occurring polymethoxyflavone with a wide range of health-promoting activities. In this study, a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of ATE in rat plasma. Protein precipitation was applied as plasma clean-up procedure; the electrospray ionization was operated in its positive ion mode while ATE and formononetin (internal standard) were measured by multiple reactions monitoring (ATE: m/z 313.1 -> 298.1; formononetin: 269.2 -> 213.3). This LC-MS/MS method displayed good selectivity, sensitivity (lower limit of quantification = 2.5 ng/ml), accuracy (both intra- and inter-day analytical recovery within 100 +/- 10%) and precision (both intra- and inter-day RSD < 10%). The matrix effect was found to be insignificant. The pharmacokinetic profiles of ATE were subsequently examined in Sprague-Dawley rats after single oral administration (10 mg/kg). When given in an aqueous suspension, ATE was slowly absorbed with quite low plasma exposure (AUC). Fasting further attenuated its oral absorption and led to similar to 70% drops in average maximal plasma concentration (C-max) and AUC. When dosed in a solution formulated with 2-hydroxypropyl-beta-cyclodextrin, the oral absorption of ATE was substantially improved with similar to 500% increases in average Cmax and AUC. Clearly, aqueous solubility has been identified as a barrier to the oral absorption of ATE. The information obtained from this study will facilitate further medicinal exploration on ATE. (C) 2017 Elsevier B.V. All rights reserved.