Mechanistic Investigations On Enalaprilat Transmembrane Transport And Its Interaction Potential

Enalaprilat is the active metabolite of enalapril,a widely used antihypertension and anti-heart failure drug.In aging populations where chronic ailments(hypertension,hyperlipidemia,hyperuricemia,etc.)are prevalent,prescribed medicines and natural remedies such as flavonoid products are often used concomitantly.Consequently,herb/drug-drug interactions have attracted a much heightened attention.In present study,herb/drug-drug interaction potentials between enalaprilat and selected drugs/flavonoids were investigated in vitro and in vivo.In the present study,transport kinetics of enalaprilat in stably transfected cell lines were first characterized,and judging from Vmax/Km ratios(indicators for the intrinsic uptake clearance),the order of uptake transporters was OAT3>>OAT1>OATP2B1>OATP1B1.OAT3 was identified as a major uptake transporter for enalaprilat,suggesting a role in the renal clearance of enalaprilat.The inhibition of OAT3 transport activity was examined for a number of flavonoid and drug molecules and species difference was also investigated between rat and human in vitro.A number of drugs including URAT1 inhibitors exhibited potent inhibition potency against human OAT3(hOAT3)and it appeared that species differences in inhibition potency were compound-dependent.A varying degree of inhibition potency was demonstrated for selected flavonoids,with IC50 values ranging from 0.03 to 22.6μM.Pharmacophore and 3D-QSAR analyses revealed the presence of a polar center and hydrophobic center.In the polar center,hydroxyl groups present in flavonoids could act as either hydrogen bond donors or acceptors,and the number and position of hydroxyl groups were critical drivers for inhibition potency.In vivo relevance of OAT3-mediated enalaprilat uptake was evaluated in rats.The potent in vitro inhibition of rOat3 by febuxostat(an anti-hyperuricemia drug)was recapitulated in vivo,with a 2-fold increase in AUC0-t(plasma exposure of enalaprilat)and a delay in MRT.In contrast,a lack of interaction between enalaprilat and luteolin(a flavonoid)was noted in rats.This in vitro-in vivo disconnect could be explained by the structural features of luteolin,where rapid metabolism via hydroxyl group conjugation and/or high plasma protein binding might led to low effective free concentrations.Taken together,the inhibition of enalaprilat uptake by selected flavonoids and drugs led to the identification of unique structural features for OAT3 inhibitors,and renal clearance via OAT3-mediated transport is an important mechanism for underlying herb/drug-drug interactions.Furthermore,in vivo herb-drug interaction potential of flavonoids as OAT3 inhibitors should be evaluated more thoroughly and individually with respect to structural features,disposition mechanism,pharmacokinetic behaviors and clinical significance.