A simple and rapid ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed for the simultaneous determination of cinnamaldehyde, cinnamic acid, and 2-methoxy cinnamic acid in rat whole blood. It was the first time to study the pharmacokinetics of 2-methoxy cinnamic acid in rat whole blood. Samples were processed by a one-step protein precipitation with acetonitrile-37% formaldehyde (90:10, v:v). Chromatographic separation was performed on a Thermo Scientific C18 column (2.1mm×50mm, 1.9μm) at room temperature. The total run time was 4min. The detection was accomplished by using positive and negative ion electrospray ionization in multiple reaction monitoring mode. The method was linear for all of the analytes over 1000 times concentration range with correlation coefficients greater than 0.99. The lower limits of quantification (LLOQ) were 0.1ng/mL for cinnamaldehyde, 5.8ng/mL for cinnamic acid, and 10ng/mL for 2-methoxy cinnamic acid, respectively. To our knowledge, this was the first time that the LLOQ for cinnamaldehyde in validated methods for biological samples was as low as 0.1ng/mL. Intra- and inter-day precision and accuracy were within ±9% for all of the analytes during the assay validation. Assay recoveries were higher than 80% and the matrix effects were minimal. The half-life were 8.7±0.7h for cinnamaldehyde, 1.0±0.5h for cinnamic acid, and 1.4±0.4h for 2-methoxy cinnamic acid, respectively. The validated assay was firstly applied to the simultaneous quantification of cinnamaldehyde, cinnamic acid, and 2-methoxy cinnamic acid, especially for 2-methoxy cinnamic acid in rat whole blood after oral administration of 15mg/kg essential oil of Cinnamoni Ramulus. It was observed that the Cmax and AUC of 2-methoxy cinnamic acid (0.01% in essential oil of Cinnamoni Ramulus) were greater than those of cinnamaldehyde (83.49% in essential oil of Cinnamoni Ramulus), which implied that 2-methoxy cinnamic acid might be the major bioactive constitutes in essential oil of Cinnamoni Ramulus.
Keywords: 2-Methoxy cinnamic acid; Cinnamaldehyde; Cinnamic acid; Cinnamomi Ramulus; Pharmacokinetics; UHPLC-MS/MS.
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