Assessing Transporter-Mediated Natural Product-Drug Interactions Via In vitro-In Vivo Extrapolation: Clinical Evaluation With a Probe Cocktail

Abstract

The botanical natural product goldenseal can precipitate clinical drug interactions by inhibiting cytochrome P450 (CYP) 3A and CYP2D6. Besides P-glycoprotein, effects of goldenseal on other clinically relevant transporters remain unknown. Established transporter-expressing cell systems were used to determine the inhibitory effects of a goldenseal extract, standardized to the major alkaloid berberine, on transporter activity. Using recommended basic models, the extract was predicted to inhibit the efflux transporter BCRP and uptake transporters OATP1B1/3. Using a cocktail approach, effects of the goldenseal product on BCRP, OATP1B1/3, OATs, OCTs, MATEs, and CYP3A were next evaluated in 16 healthy volunteers. As expected, goldenseal increased the area under the plasma concentration-time curve (AUC0-inf ) of midazolam (CYP3A; positive control), with a geometric mean ratio (GMR) (90% confidence interval (CI)) of 1.43 (1.35-1.53). However, goldenseal had no effects on the pharmacokinetics of rosuvastatin (BCRP and OATP1B1/3) and furosemide (OAT1/3); decreased metformin (OCT1/2, MATE1/2-K) AUC0-inf (GMR, 0.77 (0.71-0.83)); and had no effect on metformin half-life and renal clearance. Results indicated that goldenseal altered intestinal permeability, transport, and/or other processes involved in metformin absorption, which may have unfavorable effects on glucose control. Inconsistencies between model predictions and pharmacokinetic outcomes prompt further refinement of current basic models to include differential transporter expression in relevant organs and intestinal degradation/metabolism of the precipitant(s). Such refinement should improve in vitro-in vivo prediction accuracy, contributing to a standard approach for studying transporter-mediated natural product-drug interactions.

Conflict of interest statement

Conflict of Interest: The authors declared no competing interest for this work.

© 2020 The Authors. Clinical Pharmacology & Therapeutics © 2020 American Society for Clinical Pharmacology and Therapeutics.

Figures

Figure 1.

Healthy adult volunteers were enrolled in a two-arm, open-label, fixed sequence, crossover study. Arm 1 (baseline) entailed administration of a transporter probe cocktail containing 1 mg furosemide, 50 mg metformin, 10 mg rosuvastatin, and 2.5 mg midazolam (black inverted triangle). A minimum of 9 days of washout ensured no residual analytes. Arm 2 (goldenseal exposure) entailed administration of 1 g goldenseal thrice daily for 5 consecutive days to ensure berberine reached steady state (t1/2 28 h). On day 6 of Arm 2, participants were administered the oral probe cocktail with 1 g goldenseal; two additional doses of goldenseal (1 g) were administered in 4-hour increments (gold inverted triangles). During both arms, plasma was collected at designated times (shaded in red) up to 96 hours post-cocktail administration; urine was collected in 12-hour intervals (0–12 and 12–24; shaded in yellow) immediately following cocktail administration.

Figure 2.

Plasma concentration vs. time profiles for (A) midazolam, (B) furosemide, (C) metformin, and (D) rosuvastatin acid (●) and rosuvastatin lactone (■) following oral administration to 16 healthy volunteers alone (open symbols) or upon five-day exposure to oral goldenseal (solid symbols). Symbols and error bars denote geometric means and 90% confidence intervals, respectively.

Figure 3.

Goldenseal exposure-to-baseline geometric mean ratios (GMRs), with 90% confidence intervals, of the area under the plasma concentration-time curve (AUC), maximum concentration (Cmax), and renal clearance (ClR) for each probe substrate. The AUC ratios for furosemide, rosuvastatin (rsv) acid, and rsv lactone were calculated using plasma concentration-time curves up to the last quantifiable time point (AUC0-last), whereas AUC ratios for midazolam and metformin were calculated using plasma concentration-time curves to time infinity (AUC0-inf). ■ – midazolam; ■ – furosemide; ■ – metformin; ■ – rsv acid; ■ – rsv-lactone.

Figure 4.

Proposed transporter-mediated mechanism underlying the decreased metformin systemic exposure upon goldenseal exposure. The indicated transporters have been reported to facilitate intestinal absorption of metformin.– Arrows represent uptake or efflux; double-headed arrows represent bidirectional transport. Red X’s represent inhibition of indicated transporters by goldenseal; green O’s represent induction of indicated transporters by goldenseal. Solid blue circles represent metformin molecules. OCT, organic cation transporter; PMAT, plasma membrane monoamine transporter; SERT, serotonin reuptake transporter; ThTR-2, thiamine transporter 2.