In vitro assessment of some traditional medications used in South Africa for pharmacokinetics drug interaction potential

[摘要] ENGLISH ABSTRACT: IntroductionEarlier studies have shown the popularity of herbal products among people as traditional,complementary or alternative medication. One of the major clinical risks in the concomitantadministration of herbal products and prescription medicine is pharmacokinetic herb-drug interaction(HDI). This is brought about by the ability of phytochemicals to inhibit or induce the activity ofmetabolic enzymes and transport proteins. The aim of this study was to investigate the potential of thecrude extracts of popular medicinal herbs used in South Africa to inhibit major cytochrome P450(CYP) enzymes and transport proteins through in vitro assessment.MethodsMedicinal herbs were obtained from traditional medical practitioners and 15 were selected for thisstudy. The selected herbal products were extracted and incubated with human liver microsomes tomonitor the following reactions as markers for the metabolic activities of the respective CYP:phenacetin O-deethylation (CYP1A2), diclofenac 4‟-hydroxylation (CYP2C9), S-mephenytoin 4‟-hydroxylation (CYP2C19) and testosterone 6β-hydroxylation (CYP3A4). In addition, the influence ofLessertia frutescens (formerly Sutherlandia frutescens) and Hypoxis hemerocallidea was investigatedon more isozymes: coumarin 7-hydroxylation (CYP2A6), bupropion hydroxylation (CYP2B6),paclitaxel 6α-hydroxylation (CYP2C8), bufuralol 1‟-hydroxylation (CYP2D6), chlorzoxazone 6-hydroxylation (CYP2E1) and midazolam 1‟-hydroxylation (CYP3A4/5). The generation of the CYPspecificsubstrates/metabolites were monitored and quantified with the aid of LC-MS/MS. Themetabolic clearance of midazolam using cryopreserved hepatocytes was monitored in the presence ofLessertia frutescens and Hypoxis hemerocallidea. The potential of both to inhibit human ATP-bindingcassette (ABC) transporter activity was assessed using recombinant MDCKII and LLC-PK1 cells overexpressinghuman breast cancer resistant protein (BCRP) and human P-glycoprotein (P-gp),respectively. Similarly, the potential for interactions with human organic anion transporting polypeptide(OATP1B1 and OATP1B3) was assessed using recombinant HEK293 cells over-expressingOATP1B1 and OATP1B3, respectively.ResultsBowiea volubilis, Kedrostis Africana, Chenopodium album, Lessertia frutescens (methanolic extract),Hypoxis hemerocallidea, Spirostachys africana and Lessertia frutescens (aqueous extract), inascending order of potency demonstrated strong inhibition of CYP1A2 activity (IC50 = 1-100 g/mL).Similarly, Emex australis, Alepidea amatymbica, Pachycarpus concolor, Lessertia frutescens,Capparis sepiaria, Kedrostis africana and Pentanisia prunelloides inhibited CYP2C9 with IC50 lessthan 100 g/mL. The following demonstrated strong inhibition of CYP2C19 with IC50 values less than100 g/mL: Acacia karroo, Capparis sepiaria, Chenopodium album, Pachycarpus concolor,Ranunculus multifidus, Lessertia frutescens and Zantedeschia aethiopica. CYP3A4 was inhibited byLessertia frutescens, Hypoxis hemerocallidea, Spirostachys Africana, Bowiea volubilis, Zantedeschiaaethiopica, Chenopodium album, Kedrostis Africana, Acacia karroo, Emex australis, Pachycarpusconcolor, Ranunculus multifidus, Capparis sepiaria and Pentanisia prunelloides. Time-dependent(irreversible) inhibition of CYP3A4/5 (KI = 296 μg/mL, kinact = 0.063 min-1) and delay in theproduction of midazolam metabolites in the human hepatocytes, leading to a 40% decreasedmidazolam upscaled in vivo clearance, was observed with Lessertia frutescens. Further, Lessertiafrutescence inhibited the activity of P-gp (IC50 = 324.8 μg/mL), OATP1B1 (IC50 = 10.4 μg/mL) andOATP1B3 (IC50 = 6.6 μg/mL). Hypoxis hemerocallidea inhibited the activity of OATP1B1 (IC50 = 118.7μg/mL) and OATP1B3 (IC50 = 290.1 μg/mL) with no potent inhibitory effects on P-gp. None of the twoinhibited the activity of BCRP within the tested concentrations.ConclusionThe result indicates the potential for HDI between the selected medicinal herbs and the substrates ofthe enzymes investigated in this study, if sufficient in vivo concentrations are achieved.

[发布机构] Stellenbosch University