Metabolism And Drug Interaction Of Ginkgo Flavones In Vitro

Ginkgo flavones are a group of flavonioids widely occurring in plants and foods in nature. These compounds exhibit a multitude of biological activities such as anioxidative,antiproliferative and so on. Ginkgo flavones are used to treat or prevent disease in clinical.As a drug,it needs to be eaten for a long time.During this periods, man may be suffering from other disease and need to use lots of other drugs.This will improve the posibility of drug interaction.A majority of drugs are cleared via P450-mediated metabolism,therefore the inhibition of P450 enzymes can lead to serious clinical drug interaction.The CYP3A4 isoenzyme is responsible for the metabolism of the widest rang of drugs and endogenous compounds in humans.It accounts for 50% of cytochrome enzymes in the liver. Quercetin and Kaempferol are inhibitors of CYP3A and 1A.They could greatly affect the metabolism of coadministrered drugs and lead to severe side effects. So to obtain the mechanisms and drug interactions is importance. Several authors have reported that quercetin is found in plasma and urine as conjugates of glucuronic acid and sulfate groups.We select the method of glucuronic acid reaction to study in vitro drug interaction of ginkgo flavones. To develop a method for assaying ginkgo flavones in rat hepticalmicrosome.Fixed the concentration of subatrate, ginkgo flavones were co-incubated with a series of inhibitors in rat hepatic microsome at 25.We obtain IC50 to estimate whether inhibitors have strong inhibitions on ginkgo flavones or not.Then we calculate IC50, Kj to make sure the principle of inhibition.According to [I]/Kj,we can predict the risk degree of drug interaction in vivo.1. To develop a method for assaying ginkgo flavones which reacted byUDPGA in rat heptical microsomeAIM To develop a method for assaying ginkgo flavones in rat heptical microsome. To obtain Km , Vm values of ginkgo flavones by glucuronic acid reaction. METHOD A 1ml reaction mixture containing 0.5mg/ml of microsomal protein,1mg/ml UDPGA in Tris buffer pH7.5 (containing 1mol/L MgCl2), 0.2~8mg/L quercetin, isorhamnetin and keampferol were incubated together at 25 for 3 min.The reaction was stopped by adding 6%HC1O4 0.5ml.After incubation the samples were centrifuged at 2000 rpm for 10 min then extracted with ether-acetone.The supernatant was transferred into avial and 20l injected into the HPLC. Results The assay was linear over the rang of0.2-8 mg-L for ginkgo flavones. LOQ for method was 0.1mg/L (RSD<15%, n=3) .The recoveries of three components of ginkgo flavones were 99.9%~113.8% for quercetin (RSD<0.9%), 100.8%~117.3% for isorhamnetin (RSD<2%) and 100.7%~116.5% for keampferol (RSD<2%, N=5). The metabolic rate were 42.9% for quercetin, 64.2% for isorhamnetin , 71.1% for keampferol with vacuity microsome; and 80.9% for quercetin, 85.8% for isorhamnetin,77.1% for keampferol with microsome induced by BNF.This results indicated that the activity of the enzyme induced by BNF is higher in comparison with vacuity microsome. With the enzyme induced by BNF ,Vmax of ginkgo flavones was 20.4 3.4, 13.4 2.3,9.7 1.6mol/g/min and Km of ginkgo flavones was 8.2 1.3, 31.1 5.0,30.5 4.9umol/L . With vacuity microsome, Vmax of ginkgo flavones was 1.8 1.0, 3.91.0, 3.8?.9umol/g/min and Km of ginkgo flavones was 6.6?.3, 12.1 ?.7,14.3 11.5umol/L. This results indicated that the activity of the enzyme towards ginkgo flavones is microsome induced by BNF > vacuity microsome; the protein binding ability towards ginkgo flavones is vacuity microsome>microsome induced by BNF. Meanwhile, Vmax and Km of quercetin different from ginkgo flavones indicated that there maybe interactions in compounds of ginkgo flavones. CONCLUSION The method can be used for investigation of metabolism of ginkgo flavones. Microsome induced by BNF shows more activity in glucuronic acid reaction.2. Interaction of ginkgo flavonoids with other drugs in vitroAIM To obtain the information on the glucuronidation of Ginkgo flavonoid and theinteraction profile of ginkgo flavones with other drugs in vi...