Exploration of cytochrome P450 inhibition mediated drug-drug interaction potential of kratom alkaloids

In vitro cytochrome P450 inhibition of major kratom alkaloids: mitragynine (MTG), speciogynine (SPG), speciocilliatine (SPC), corynantheidine (COR), 7-hydroxymitragynine (7HMG) and paynantheine (PAY) was evaluated using human liver microsomes (HLMs) to understand their drug-drug interaction potential. CYP450 isoform-specific substrates of CYP1A2, 2C8, 2C9, 2C19, 2D6, and 3A4/5 were incubated in HLMs with or without alkaloids. Preliminary CYP450 inhibition (IC50) data were generated for each of these isoforms. In addition, the type of inhibition and estimation of the inhibition constants (Ki) of MTG and COR were determined. Among the tested alkaloids, MTG and COR were potent inhibitors of CYP2D6 (IC50, 2.2 and 4.2 μM, respectively). Both MTG and COR exhibited competitive inhibition of CYP2D6 activity and the Ki were found to be 1.1 and 2.8 μM, respectively. SPG and PAY showed moderate inhibition of CYP2D6 activity. Additionally, moderate inhibitory effects by SPC, MTG, and SPG were observed on CYP2C19 activity. Interestingly, inhibition of only midazolam hydroxylase CYP3A4/5 activity by COR, PAY, and MTG was observed while no inhibitory effect was observed when testosterone was used as a probe substrate. In conclusion, MTG and COR may lead to clinically significant adverse drug interactions upon coadministration of drugs that are substantially metabolized by CYP2D6.

Bioanalytical method development and validation of corynantheidine, a kratom alkaloid, using UPLC-MS/MS, and its application to preclinical pharmacokinetic studies

Corynantheidine, a minor alkaloid found in Mitragyna speciosa (Korth.) Havil, has been shown to bind to opioid receptors and act as a functional opioid antagonist, but its unique contribution to the overall properties of kratom remains relatively unexplored. The first validated bioanalytical method for the quantification of corynantheidine in rat plasma is described. The method was linear in the dynamic range from 1-500 ng/mL, requires a small plasma sample volume (25 μL), and a simple protein precipitation method for extraction of the analyte. The separation was achieved with Waters BEH C18 2.1 × 50 mm column and the 3-minute gradient of 10 mM ammonium acetate buffer (pH = 3.5) and acetonitrile as mobile phase. The method was validated in terms of accuracy, precision, selectivity, sensitivity, recovery, stability, and dilution integrity. It was applied to the analysis of the male Sprague Dawley rat plasma samples obtained during pharmacokinetic studies of corynantheidine administered both intravenously (I.V.) and orally (P.O.) (2.5 mg/kg and 20 mg/kg, respectively). The non-compartmental analysis performed in Certara Phoenix® yielded the following parameters: clearance 884.1 ± 32.3 mL/h, apparent volume of distribution 8.0 ± 1.2 L, exposure up to the last measured time point 640.3 ± 24.0 h*ng/mL, and a mean residence time of 3.0 ± 0.2 h with I.V. dose. The maximum observed concentration after a P.O. dose of 213.4 ± 40.4 ng/mL was detected at 4.1 ± 1.3 h with a mean residence time of 8.8 ± 1.8 h. Absolute oral bioavailability was 49.9 ± 16.4 %. Corynantheidine demonstrated adequate oral bioavailability, prolonged absorption and exposure, and an extensive extravascular distribution. In addition, imaging mass spectrometry analysis of the brain tissue was performed to evaluate the distribution of the compound in the brain. Corynantheidine was detected in the corpus callosum and some regions of the hippocampus.