Evaluation of the modulatory effects of glucosamine, chondroitin and diacerein on human hepatic cytochrome P450 (CYP) enzymes

The widespread use of natural products in health maintenance, disease prevention and even disease treatment has raised increasing concerns on their potential in causing drug interactions. Glucosamine, chondroitin and diacerein are three popular naturally derived compounds used in treating osteoarthritis. There is however limited research on the modulatory effects of these compounds on the enzymatic activity of cytochrome P450 (CYP), the major drug metabolizing enzyme in human. Therefore, the aims of this study were to investigate the modulatory effects of these antiarthritic compounds on three major CYP isoforms (CYP2C9, CYP2D6 and CYP3A4), and to explore the drug-natural products interactions, if any. Heterologous co-expression of recombinant CYP2C9, CYP2D6 and CYP3A4 and OxR in E. coli were carried out successfully, producing ample amount of enzymatically active CYP proteins. Three HPLC-based in vitro assays (valsartan 4-hydroxylase assay for CYP2C9, dextromethorphan O-demethylase assay for CYP2D6 and testosterone 6β-hydroxylase assay for CYP3A4) were established and validated to detect CYP inhibitions. All the forms of glucosamine and chondroitin were found to be weak inhibitors of the tested CYPs in vitro (IC50 values > 300 µM) and were not expected to cause in vivo inhibition. On the other hand, diacerein exhibited moderately weak inhibition (Ki values from 30.80 to 106.89 µM) for all the tested CYP isoforms. Its major metabolite, rhein displayed stronger inhibition potencies (Ki values from 1.16 to 32.27 µM) on the catalytic functions of all three CYP isoforms, with CYP2C9 being the most susceptible form towards its inhibition. Both compounds exhibited mixed-mode of inhibition on the tested CYP isoforms. Because of the low Ki value (1.16 µM) of rhein in CYP2C9 inhibition, it is predicted to cause inhibition in vivo with drug substrates of this CYP. Preincubation study ruled out mechanism-based inactivation (MBI) of the CYP isoform by glucosamine, chondroitin and rhein, except for diacerein, but minor MBI effect was expected due to the limited amount of diacerein in human blood circulation after oral intake. Combination of diacerein and rhein indicated synergistic or additive inhibition in vitro on all the tested CYPs, but this is unlikely to occur in vivo due to the extensive first-pass effect of diacerein. In silico molecular dockings of these antiarthritic compounds on each CYP isoform supported their inhibition potencies from in vitro study. Overall, the rank order of inhibition potency of the tested antiarthritic compounds was: rhein > diacerein > glucosamine > chondroitin. In conclusions, glucosamine and chondroitin are less likely to cause clinical interaction with the drug substrates of the three tested CYP isoforms, either alone or in combination, but diacerein should be taken with caution by osteoarthritic patients, because rhein was a proven CYP inhibitor from this study. This is especially true if patients are on medications with narrow therapeutic indices. Besides, the multi-pronged approaches used in this study have allowed detailed examination of the modulatory effects of the tested antiarthritic compounds in term of inhibition potency, ligand specificity and binding mechanism on different CYP isoforms, which may serve as useful evaluation tools in other similar studies.