Inhibition of human organic anion transporter 4 (OAT4) activity by bisphenol analogues

Organic anion transporter (OAT) 4 is a kidney and placental membrane protein implicated in the transport of xenobiotics, including pollutants. The present study was designed to determine whether environmental bisphenol (BP) analogues, including emerging bisphenol A substitutes, can interact with OAT4. 6-carboxyfluorescein-related OAT4 activity displayed by OAT4-overexpressing HEK-293 cells was inhibited by 7/23 BP analogues used at 10 μM, especially by the thermal paper-contained color developer Pergafast® 201 (PF201) and the flame retardants tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA), acting in a concentration-dependent manner (with IC₅₀ values in the 0.95-1.48 μM range). Most of these BP analogues moreover decreased membrane transport of estrone-3-sulfate, a hormonal endogenous substrate for OAT4. Some of them, especially PF201, additionally blocked activity of the renal transporters OAT1 and OAT3. Interaction of BP analogues with OAT4 was further supported by docking simulation studies, indicating that PF201 binds to the Arg473-containing electropositive pocket of OAT4, presumed to play a key role in inhibition of OAT4-mediated transport. BP analogues however failed to trans-stimulate OAT4 activity and OAT4-overexpressing cells exhibited no or marginally increased sensitivity to PF201, TBBPA and TCBPA, thus suggesting that these BP analogues are not or poorly transported by OAT4. In vitro to in vivo extrapolation finally demonstrated that occupational exposure to PF201 is predicted to result in human OAT4 inhibition. Overall, OAT4 was demonstrated to be a target for BP analogues, including BPA substitutes, with possible deleterious consequences in terms of OAT4-mediated transport of endogenous compounds or drugs, notably for workers exposed to PF201.