Inhibition of Magnolol and Honokiol on Cytochrome P450 Enzymes in Rat and Human Liver Microsomes

Objective The purpose of this work is to evaluate the in vitro inhibitory effect of magnolol（MN） and honokiol（HN） on rat / human cytochrome P450（CYP） enzymes（1A2/1A2, 2D/2D6, 3A/3A4, 2E1/2E1, and 2C/2C9）. Methods Rat liver microsomes（RLM） and human liver microsomes（HLM） were used as the enzyme sources. After the probe substrate of each CYP isoforms was co-incubated individually with MN or HN in RLM or HLM, the metabolite production of each probe substrate in RLM and HLM incubation medium was determined and used to evaluate the activity of corresponding CYP isoforms. Results MN inhibited rat CYP1A2 and human CYP3A4 with the IC50 values of 10.0 and 56.2 μmol/L, respectively. HN inhibited rat CYP1A2 and CYP2E1, human CYP1A2 and CYP3A4 with the IC50 values of 12.1, 12.6, 17.8, and 43.9 μmol/L, respectively. Conclusion HN is a moderate or weak inhibitor of human CYP1A2. Both MN and HN are weak or non inhibitors of the other tested human CYP isoforms. The results suggest that no significant metabolic interaction seems likely to occur when the substrate drugs of CYP isoforms tested in the present work are co-administered with MN and HN.

Inhibition of Cytochrome P450 by Nomilin and Obacunone and Potential Mechanism in Human Liver Microsomes

Objective Nomilin and obacunone are two important limonoids that are well known for their anticancer effect. Previous studies showed that limonoids had inhibitory effect on cytochrome P450 3A4（CYP3A4）. However these effects are inconclusive with regards to prediction of potential drug interactions. Methods Nomilin or obacunone was pre-incubated with HLMs for 30 min. Following 10-fold dilution from the pre-incubation concentration, a second incubation was performed in the presence of NADPH and cytochrome P450 substrates for 15 min. The reaction was quenched and the supernatants were analyzed by chromatography/mass spectrometry. Results In this study, nomilin and obacunone showed potent inhibitory effect on CYP3A4 with the IC_（50） values of 3.50 and 6.08 μmol/L, respectively. The inhibition of CYP3A4 was in a time-, concentration-and NADPH-dependent manner with Ki values of 2.92 and 1.25 μmol/L and Kinact values of 0.033 and 0.078 min^（-1） for nomilin and obacunone respectively. These results elucidated that they were time-dependent inhibitors for CYP3A4. Conclusion Concomitant use of limonoids and other drugs may call for extra caution for purposes of clinical safety.

Inhibition of Re Du Ning Injection on Enzyme Activities of Rat Liver Microsomes Using Cocktail Method

Objective Re Du Ning Injection （RDN）, a Chinese materia medica injection, is made from the extracts of LoniceraeJaponicae Flos, Gardeniae Fructus, and Artemisiae Annuae Herba. Since last decade, RDN has been widely used in China for the treatment of viral infection, fever, and inflammation. To assess the potential interacting of RDN with co-administered drugs, the inhibitory effects of RDN on the enzyme activities （CYP1A1, CYP1A2, CYP2C11, CYP2D1, and CYP3A1/2） of rat liver microsomes were investigated by a cocktail method. Methods A sensitive and specific LC-MS method capable of simultaneous quantification of five metabolites in rat liver microsomes was developed and validated. Then RDN （0.625%-1.0%） was incubated with rat liver microsomes and specific substrates. The enzyme activities were expressed as the formation rate of the specific metabolites of the substrates （pmol- mg. protein-1 . min-1）. Results RDN competitively inhibited the activities of CYP1A2 and CYP2C11, with inhibition constant （/~） values determined to be 0.18% and 0.63%, respectively. RDN exhibited the mixed inhibition on the activity of CYP2D1, with a K1 value of 0.15%. The activities of CYP1A1 and CYP3A1/2 were not markedly inhibited even by 1.0% RDN. Conclusion RDN could inhibit the rat enzyme activities of CYP1A2, 2Cll, and 2D1 in vitro with different inhibition modes, which is worthy of promoting safety and efficacy of RDN.