Direct inhibition of Re Du Ning Injection and its active compounds on human liver cytochrome P450 enzymes by a cocktail method.

The aim of this study was to investigate the direct inhibitory effects of Re Du Ning Injection (RDN) and its active compounds on the major cytochrome P450 enzyme (CYP) isoforms (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A4) of human liver microsomes by 'a cocktail method'. The activity of each CYP isform was represented as the formation rate of the specific metabolite from relevant substrate. Then a sensitive and specific ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to simultaneously analyze the seven metabolites. RDN (0.035-2.26 mg/mL) showed a strong inhibitiory effect on CYP2C8, followed by CYP2C9, CYP2B6, CYP2C19, CYP1A2 and CYP3A4. The IC50 value for each enzyme was 0.19, 0.66, 0.72, 1.27, 1.66 and 2.13 mg/mL, respectively. RDN competitively inhibited the activities of CYP1A2 (Ki  = 1.22 mg/mL), CYP2B6 (Ki  = 0.65 mg/mL) and CYP3A4 (Ki  = 0.88 mg/mL); it also exhibited mixed inhibition of CYP2C8, CYP2C9 and CYP2C19 with a Ki value of 0.26, 0.64 and 0.82 mg/mL, respectively. However, the activity of CYP2D6 was not significantly inhibited even by 2.26 mg/mL RDN. Moreover, the data of nine active compounds on the CYPs showed that cryptochlorogenin acid, sochlorogenic acid B and sochlorogenic acid C were the major contributors to the inhibitory effect of RDN on CYP2C8, while the inhibitory effect of RDN on CYP2C9 might be caused by sochlorogenic acid A and sochlorogenic acid C. Moreover, neochlorogenic acid might be the major contributor to the inhibitory effect on CYP2B6. All of the findings suggested that drug-drug interactions may occur and great caution should be taken when RDN is combined with drugs metabolized by these CYPs.