Kinetics of cytochrome P450 enzymes for metabolism of sodium tanshinone IIA sulfonate in vitro

BACKGROUND: Sodium tanshinone IIA sulfonate (STS) is a water-soluble derivative of tanshinone IIA for treating cardiovascular disorders. The roles of cytochrome P450 enzymes (CYPs) in the metabolism of STS have remained unclear. This study aims to screen the main CYPs for metabolism of STS and study their interactions in vitro. METHODS: Seven major CYPs were screened for metabolism of STS by human liver microsomes (HLMs) or recombinant CYP isoforms. Phenacetin (CYP1A2), coumarin (CYP2A6), tolbutamide (CYP2C9), metoprolol (CYP2D6), chlorzoxazone (CYP2E1), S-mephenytoin (CYP2C19), and midazolam (CYP3A4) were used as probe substrates to determine the potential of STS in affecting CYP-mediated phase I metabolism in humans. Enzyme kinetic studies were performed to investigate the modes of inhibition of the enzyme–substrate interactions by GraphPad Prism Enzyme Kinetic 5 Demo software. RESULTS: Sodium tanshinone IIA sulfonate inhibited the activity of CYP3A4 in a dose–dependent manner by the HLMs and CYP3A4 isoform. The K(m) and V(max) values of STS were 54.8 ± 14.6 µM and 0.9 ± 0.1 nmol/mg protein/min, respectively, for the HLMs and 7.5 ± 1.4 µM and 6.8 ± 0.3 nmol/nmol P450/min, respectively, for CYP3A4. CYP1A2, CYP2A6, CYP2C9, CYP2D6, CYP2E1, and CYP2C19 showed minimal or no effects on the metabolism of STS. CONCLUSION: This in vitro study showed that STS mainly inhibited the activities of CYP3A4. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13020-016-0083-z) contains supplementary material, which is available to authorized users.