Combined and independent effects of OCT1 and CYP2D6 on the cellular disposition of drugs

Sex-Dependent Effects of CYP2D6 on the Pharmacokinetics of Berberine in Humans

An over-the-counter product berberine (a major alkaloid in goldenseal) is a substrate of the uptake transporter OCT1 and the metabolizing enzyme CYP2D6. The two genes exhibit common functional polymorphisms. Approximately 9% of Europeans and white Americans are either poor CYP2D6 metabolizers or poor OCT1 transporters. In this study, we investigated the effects of OCT1 and CYP2D6 polymorphisms on berberine pharmacokinetics in humans. We confirmed in vitro that berberine is an OCT1 substrate (KM of 7.0 μM, CLint of 306 ± 29 μL/min/mg). Common OCT1 alleles *3 to *6 showed uptake reduced by at least 65% and Oct1/2 knockout mice showed 3.2-fold higher AUCs in liver perfusion experiments. However, in humans, poor OCT1 transporters did not show any differences in berberine pharmacokinetics compared with reference participants. In contrast, CYP2D6 polymorphisms significantly affected berberine metabolism, but exclusively in females. Females who were poor CYP2D6 metabolizers had an 80% lower M1-to-berberine ratio. General linear model analyses suggest strong synergistic, rather than additive, effects between female sex and CYP2D6 genotype. Overall, berberine displayed low oral bioavailability, yet females had a 2.8-fold higher AUC and a 3.6-fold higher Cmax than males (P < 0.001). These effects were only partially attributable to the sex-CYP2D6 genotype interaction. In conclusion, despite berberine being an OCT1 substrate, OCT1 deficiency did not affect berberine pharmacokinetics in humans. In contrast, CYP2D6 emerges as a critical enzyme for berberine metabolism in females, but not in males, highlighting sex-specific differences. We suggest that factors beyond CYP2D6 metabolism are determining berberine's systemic exposure, especially in males (NCT05463003).

Stereoselectivity in Cell Uptake by SLC22 Organic Cation Transporters 1, 2, and 3

Stereoselectivity can be most relevant in drug metabolism and receptor binding. Although drug membrane transport might be equally important for small-molecule pharmacokinetics, the extent of stereoselectivity in membrane transport is largely unknown. Here, we characterized the stereoselective transport of 18 substrates of SLC22 organic cation transporters (OCTs) 1, 2, and 3. OCT2 and OCT3 showed highly stereoselective cell uptake with several substrates and, interestingly, often with opposite stereoselectivity. In contrast, transport by OCT1 was less stereoselective, although (R)-tamsulosin was transported by OCT1 with higher apparent affinity than the (S)-enantiomer. Using OCT1 and CYP2D6 co-overexpressing cells, an additive effect of the stereoselectivities was demonstrated. This indicates that pharmacokinetic stereoselectivity may be the result of combined effects in transport and metabolism. This study highlights that the pronounced polyspecificity of OCTs not contradicts stereoselectivity in the transport. Nevertheless, stereoselectivity is highly substrate-specific and for most substrates and OCTs, there was no major selectivity.