An ex vivo approach to botanical–drug interactions: A proof of concept study

Abstract

Ethnopharmacological relevance Botanical medicines are frequently used in combination with therapeutic drugs, imposing a risk for harmful botanical-drug interactions (BDIs). Among the existing BDI evaluation methods, clinical studies are the most desirable, but due to their expense and protracted time-line for completion, conventional in vitro methodologies remain the most frequently used BDI assessment tools. However, many predictions generated from in vitro studies are inconsistent with clinical findings. Accordingly, the present study aimed to develop a novel ex vivo approach for BDI assessment and expand the safety evaluation methodoloy in applied ethnopharmacological research. Materials and Methods This approach differs from conventional in vitro methods in that rather than botanical extracts or individual phytochemicals being prepared in artificial buffers, human plasma/serum collected from a limited number of subjects administered botanical supplements was utilized to assess BDIs. To validate the methodology, human plasma/serum samples collected from healthy subjects administered either milk thistle or goldenseal extracts were utilized in incubation studies to determine their potential inhibitory effects on CYP2C9 and CYP3A4/5, respectively. Silybin A and B, two principal milk thistle phytochemicals, and hydrastine and berberine, the purported active constituents in goldenseal, were evaluated in both phosphate buffer and human plasma based in vitro incubation systems. Results Ex vivo study results were consistent with formal clinical study findings for the effect of milk thistle on the disposition of tolbutamide, a CYP2C9 substrate, and for goldenseal’s influence on the pharmacokinetics of midazolam, a widely accepted CYP3A4/5 substrate. Compared to conventional in vitro BDI methodologies of assessment, the introduction of human plasma into the in vitro study model changed the observed inhibitory effect of silybinA, silybin B and hydrastine and berberine on CYP2C9 and CYP3A4/5, respectively, results which more closely mirrored those generated in clinical study. Conclusions Data from conventional buffer-based in vitro studies were less predictive than the ex vivo assessments. Thus, this novel ex vivo approach may be more effective at predicting clinically relevant BDIs than conventional in vitro methods.

“…Not Intended to Diagnose, Treat, Cure or Prevent Any Disease.” 25 Years of Botanical Dietary Supplement Research and the Lessons Learned

“…Recently, two novel tactics have demonstrated that in vitro methods can be useful predictors of in vivo HDI. An ex vivo approach devised by Markowitz et al and Wang et al revealed that circulating plasma concentrations of goldenseal isoquinoline alkaloids and their metabolites could inhibit CYP isoforms to a degree similar to that observed in a clinical HDI study, lending credence to the physiological relevance of this procedure. This method has the advantage of exposing hepatocytes, isolated CYPs, or other in vitro enzyme/transporter systems to phytochemical species generated during gastrointestinal absorption that are physiologically germane (i.e., parent compounds and metabolites), an aspect frequently neglected in conventional in vitro HDI studies.…”

Pharmacokinetic Interactions between Herbal Medicines and Drugs: Their Mechanisms and Clinical Relevance

“…More recently, Wang and colleagues [ 126 ], using an ex vivo approach by plasma/serum samples collected from healthy subjects administered with goldenseal extracts, have confirmed the inhibitory effects towards CYP3A-catalyzed midazolam 1′-hydroxylation. Particularly, the authors have calculated an IC 50 value of 33.03 μM for hydrastine and 473.0 μM for berberine, indicating that hydrastine is more potent in terms of inhibiting CYP3A [ 126 ]. Moreover, concurrent, albeit moderate, inhibition of P-gp in humans [ 127 ] might contribute increasing drug exposure in subjects assuming also goldenseal.…”

Systematic review of pharmacokinetics and potential pharmacokinetic interactions of flavonolignans from silymarin

“…A plethora of articles tested the in vitro interaction of silymarin, or its constituents, mainly racemic silybin, with cytochrome P450 isoforms, 142,168,188–208 UDP‐glucuronosyl transferases, 199,200,202,209 and/or transporters 179,192,198,205,207,210–221 . The data from these articles are summarized graphically in Figures 5 and 6.…”

“…I, intestine; L, liver; M, mouse; P, poor metabolizer or the level of the enzyme was low; R, recombinant enzyme; rP, recombinant enzyme with lower (“poor”) metabolic activity. Source : Data are from References [142,168,188–191,196,198,199,201,202,204–209,211]…”