Pharmacokinetics


A


B


Figure 3: Intrinsic clearance of MDZ was calculated from linear regression analysis of the percentage of parent remaining (log transformed) versus time profile to estimate the elimination rate. *P value ≤0.05 when compared with solvent control


in vitro findings of S. chinensis to predict potential clinically-relevant interactions.


Sandwich-cultured Transporter Certified™ hepatocytes as a model for studying clinically-relevant botanical-drug interactions Transporter Certified™ hepatocytes in sandwich culture provide a fully-integrated hepatic cell sys- tem that maintains drug clearance pathways (metabolism and transport) and key regulatory pathways necessary for quantitative assessments of BDI potential7-8. Because the system integrates bil- iary excretion, intracellular concentrations are likely more physiologically-relevant resulting in more accurate recapitulation of in vivo conditions compared to other systems. Other hepatocyte sys- tems (eg conventional monolayer) do not support biliary excretion resulting in higher intracellular concentrations likely biasing the ultimate cellular outcome (eg toxicity). When one considers the use of liver microsomes for BDI assessment, which do not account for drug transport or adaptive response (eg induction), it becomes readily clear how results from such simplistic systems could under- or over-predict clinically-relevant risk. Thus, it is not surprising that poor in vitro to in vivo correlations have been observed in the major- ity of in vitro studies conducted with botanical extracts.


Proof-of-concept study design We evaluated the effectiveness of the sandwich-cul- tured human hepatocytes model in predicting in


Drug Discovery World Fall 2018


vivo BDI outcomes using an intrinsic clearance approach. Additional mechanistic studies focused on inhibition and induction of CYP3A4 were per- formed to asses specific BDI following Schisandra spp. exposure9. When designing BDI studies, quantification of at


least the major phytochemical constituents is help- ful in setting dose concentrations for use in in vitro studies. Unfortunately, there is rarely plasma con- centration data on extract constituents so it is par- ticularly important in these studies to include a wide range of dosing concentrations. As mentioned above, the intracellular concentration of a com- pound is responsible for the ultimate cellular out- come(s).


Results Mechanistic inhibition studies in sandwich-cul- tured human hepatocytes demonstrated that S. chi- nensis and S. sphenanthera inhibited the rate of hydroxymidazolam formation (CYP3A4/5 activi- ty) from midazolam in a concentration and time- dependent manner (Figure 1 A-B). Pre-incubation with either extract increased inhibition potency (eg


IC50) ≥3-fold indicative of time-dependent inhibi- tion9. Induction assessment in sandwich-cultured


human hepatocytes demonstrated S. chinensis and S. sphenanthera induced CYP3A4 mRNA content in a dose-related manner following 72 hours of exposure (Figure 2). Induction responses stimulat- ed by SSE (30mg/ml) and SCE (32mg/ml) exposure were greater than the response produced by St John’s wort (SJW) treatment, a well-established


References 1 Smith, T et al. Herbal supplement sales in US increase 8.5% in 2017, topping $8 billion. Herbalgram 2018, 119:62-71. 2 US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics (2017). Health, United States, 2016: with chartbook on long-term trends in health. https://www.cdc.gov/nchs/data/ hus/hus16.pdf#079. 3 Sprouse, AA and van Breemen, RB (2016). Pharmacokinetic Interactions between Drugs and Botanical Dietary Supplements. DMD, 44:162-171. 4 Iwata, H et al (2004). Identification and characterization of potent CYP3A4 inhibitors in Schisandra fruit extract. DMD, 32(12):1351-1358. 5 Xin, HW et al (2007). Effects of Schisandra sphenanthera extract on the pharmacokinetics of tacrolimus in healthy volunteers. British J of Clinical Pharmacology, 64:4:469-475.


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