In vitro inhibition of cytochrome P450 activities by active constituents of Chinese herbal drugs

Abstract

Aim: To evaluate the inhibitory effects of 10 herbal active constituents on 5 CYP isoforms in vitro in human liver microsomes (HLM). Methods: The metabolic activities of CYP1A2, 2C9, 2C19, 2D6 and 3A4 were measured in HLM by the cocktail substrate assay using phenacetin-O-deethylation, tolbutamide methyl hydroxylation, omeprazole 5-hydroxylation, dextromethorphan-O-demethylation and midazolam 1′-hydroxylation as marked reactions. A panel of known specific CYP inhibitors was applied to validate the HLM incubation system. The metabolite formation of the probe substrates in incubates were quantified by a LC-MS method. The inhibitory curves were obtained for each herbal constituent and the corresponding IC50 values were calculated. Results: Among the 10 active constituents tested, naringenin was found to be a strong inhibitor on CYP2C19 with IC50 of 0.43 μmol·L-1 and a moderate inhibitor of CYP1A2 (IC50 4.79 μmol ·L -1). Isorhamnetin was a moderate inhibitor for CYP1A2, 2C9 and 2C19 with IC50 of 5.36, 1.40 and 3.28 μmol·L-1, respectively. The IC50 values of rhein on CYP1A2 and 3A4 were 8.32 and 2.50 μmol ·L-1, suggesting that it was a moderate inhibitor for these two isoforms. Camptothecin was also a moderate inhibitor for CYP2C9 and 2C19 (IC50 2.01 and 2.48 μmol·L-1). Other three active constituents, cytosine, berberine and oleanolic acid inhibited CYP2C9, 2D6 and 2C19 with IC50 of 8.13, 4.69 and 3.56 μmol ·L-1, respectively. While no significant inhibitory effects were observed for chlorogenic acid, ferulic acid and puerarin. Conclusions: Naringenin, isorhamnetin, camptothecin, cytosine, berberine, rhein and oleanolic acid have inhibitory effects on the metabolic activities of different CYP isoforms in HLM. There may be potential drug interactions clinically when these active constituents are used concomitantly with drugs that are metabolized primarily by the CYP isoforms.