Pharmacokinetic profile and metabolite identification of bornyl caffeate and caffeic acid in rats by high performance liquid chromatography coupled with mass spectrometry

Abstract

Bornyl caffeate was initially discovered as a bioactive compound in medicinal plants. Despite the promising pharmacological activities including anti-tumor and antibacterial activities, the pharmacokinetics of the compound remain open. This work developed a high performance liquid chromatography-tandem mass spectrometric method for the determination of bornyl caffeate and caffeic acid (major metabolite and a main unit of bornyl caffeate) in vivo. Successful application of the method included identification of its metabolites and investigation on the drug pharmacokinetics. A total of 30 compounds were identified as the metabolites of bornyl caffeate in rats. We attributed these metabolites to phase I metabolic routes of reduction, oxidation, hydrolysis and phase II metabolic reactions of glucuronidation, sulfation, O-methylation and glycine. Glucuronidation, sulfation, O-methylation and reduction were the main metabolic pathways of bornyl caffeate. The method presented a linear range of 1-4000 ng mL^-1. The pharmacokinetic profile of bornyl caffeate was found to be a three compartment open model, while caffeic acid fitted to a two compartment open model when it was administered alone or served as the main metabolite of bornyl caffeate. The time to peak concentration (T _max) and the maximum plasma concentration (C _max) of bornyl caffeate were 0.53 h and 409.33 ng mL^-1. Compared with original caffeic acid, the compound displayed an increased half-life of elimination (T _1/2β), area under the concentration time curve from 0 to t (AUC_0-t ) and area under the concentration time curve from 0 to ∞ (AUC_0-∞), a decreased half-life of absorption (T _1/2α) and an identical C _max. Taking together, we concluded that bornyl caffeate is able to rapidly initiate therapeutic effect and last for a relatively long time in rats; metabolic pathways of O-methylation and reduction is key to interpret the mechanism and toxicity of bornyl caffeate.

Fig. 1. The MS² spectra of bornyl caffeate (a), caffeic acid (b) and phenethyl caffeate ((c) IS).

Fig. 2. Representative extracted ion chromatograms of rat plasma samples: (a) blank plasma; (b) blank plasma spiked with bornyl caffeate (0.7 ng mL⁻¹) and caffeic acid (0.3 ng mL⁻¹) at LLOQ; (c) plasma collected at 0.53 h after a single oral administration of 30 mg kg⁻¹ bornyl caffeate; (d) plasma collected at 0.25 h after a single oral administration of 17 mg kg⁻¹ caffeic acid.

Fig. 3. Mean plasma concentration–time profile of bornyl caffeate, CA-metabolite and CA-ig (n = 6).

Fig. 4. The extracted ion chromatograms (EICs) of in vivo metabolites M1 to M19 of bornyl caffeate in rat.

Fig. 5. Proposed metabolic pathway and metabolites of bornyl caffeate.