Pharmacokinetics And Brain Distribution Of 6-HKA And Its Structural Modified Compounds

Numerous studies have shown that the extracts of Ginkgo biloba leaves(EGb)are considered to have pharmacological effects of improving memory and increasing blood circulation,and have been used in the treatment of early Alzheimer’s dementia,vascular cognitive impairment and other diseases.6-hydroxykynurenic acid(6-HKA),a nitrogen-containing phenolic acid compound,is low in EGb,but should not be ignored.At present,the research on 6-HKA is still mainly focused on the ingredients separation,synthesis and analysis.There are few reports on its pharmacological effects.It only has been proved in vitro that 6-HKA has the peroxynitrite scavenging activity and was a low-affinity antagonist of N-methyl-d-aspartic acid(NMDA)receptor,suggesting that it may have neuroprotective effects.However,the drug metabolism and pharmacokinetics(DM/PK),pharmacological activity studies in vivo,and structural modified compounds of 6-HKA have not been studied.Therefore,in order to understand the DM/PK,improve the bioavailability and blood-brain barrier(BBB)permeability,and provide the evidences for the development and utilization of 6-HKA,the study investigated the PK,brain distribution,transport,metabolism,excretion and the effects of ischemic injury and structural modification of 6-HKA.1.Pharmacokinetics and brain distribution of 6-HKA in ratsAn UPLC-MS/MS method for the determination of 6-HKA in rat plasma and brain homogenate was established and has been applied to investigate the PK and the brain distribution of 6-HKA.The results showed that 6-HKA was absorbed rapidly(Tmax=0.39±0.09 h).However,the absorption of 6-HKA was poor(Cmax=152.0±85.5μg/L,AUC(0-t)=340.0±136.3μg/L*h),and the bioavailability was low(3.96± 1.45%).Moreover,6-HKA was difficult to entry the brain through the BBB(the contents of 6-HKA in rat brains were almost below 6 ng/g brain).2.Interaction with drug transporters,in vitro and in vivo metabolism and excretion of 6-HKA in ratsThe results of interaction between 6-HKA and drug transporters showed that 6-HKA was not only an inhibitor of OAT3,OCT2,MATE2K and OCTN2,but also a substrate for OAT3.The results of in vivo and in vivo metabolism and excretion showed that 6-HKA was directly excreted after oral administration through urine or feces.without metabolism.3.Effect of focal cerebral ischemia injury on brain distribution of 6-HKABy investigating the distribution of left and right cerebral cortexes in the middle cerebral artery occlusion(MCAO)group and the sham-operated group after oral administration of 6-HKA for 4 consecutive days,it was demonstrated that MCAO-induced focal cerebral ischemic injury can reduce the resistance of BBB to 6-HKA,increase the amount of 6-HKA into the brain,improve ratio of brain to plasma concentration.4.Effects of 6-HKA structural modified compounds on apparent permeability coefficients in cells,and pharmacokinetics and brain distribution in ratsUPLC-MS/MS methods of three 6-HKA structural modified compounds(170518-3,170518-4 and 170518-5)in rat plasma and brain homogenate were established and have been applied to investigate the effects of 6-HKA structural modified compounds on apparent permeability coefficients in cells,and the PK and brain distribution in rats.The results showed that the esteritication of 6-HKA carboxyl group can greatly improve the apparent permeability coefficient and bioavailability.Among three structural modified compounds,isopropyl esterified 6-HKA(170518-4)was the most promising one.Comparing with 6-HKA,the bioavailability after oral administration of 170518-4 was greatly improved(from 3.96±1.45%to 41.8±15.3%),and the contents of 6-HKA in rat brains(49.7±9.2 ng/g brain)were significantly higher.