Organic anion transporting polypeptide 2B1 and breast cancer resistance protein interact in the transepithelial transport of steroid sulfates in human placenta.

The human placenta has both protective and nurturing functions for the fetal organism. Uptake and elimination of xenobiotics and endogenous substances are facilitated by various transport proteins from the solute carrier (SLC) and ABC families, respectively. A functional interaction of uptake and elimination, which is a prerequisite for vectorial transport across cellular barriers, has not been described for placenta. In this study, we examined expression of organic anion transporter (OAT) 4 (SLC22A11), organic anion transporting polypeptide (OATP) 2B1 (SLCO2B1, OATP-B), and breast cancer resistance protein (BCRP) (ABCG2) in human placenta (n = 71) because all three proteins are involved in transmembranal transfer of estrone 3 sulfate (E3S; metabolic product) and dehydroepiandrosterone sulfate (DHEAS; precursor molecule). On the mRNA level, we found a significant correlation of OATP2B1 and BCRP (R(2) = 0.534; p < 0.01) but not between OAT4 and BCRP (R(2) = -0.104; p > 0.05). Localization studies confirmed basal expression of OATP2B1 and apical expression of BCRP. To study functional interactions between OATP2B1 and BCRP, we developed a Madin-Darby canine kidney cell model expressing both transport proteins simultaneously (OATP2B1 and BCRP in the basal and apical membrane, respectively). Using this cell model in a transwell system resulted in a significantly increased basal to apical transport of both E3S and DHEAS, when both transporters were expressed with no change of transfer in the apical to basal direction. Taken together, these data show the potential for a functional interaction of OATP2B1 and BCRP in transepithelial transport of steroid sulfates in human placenta.

Organic anion transporting polypeptide 2B1 is a high-affinity transporter for atorvastatin and is expressed in the human heart.

BACKGROUND: The cardiac effects of statins are subject to controversial discussion, and the mechanism of their uptake into the human heart is unknown. A candidate protein is the organic anion transporting polypeptide (OATP) 2B1 (SLCO2B1), because related transporters are involved in the uptake of statins into the human liver. In this study we examine OATP2B1 expression in the human heart and describe statins as inhibitors and substrates of OATP2B1. METHODS: The expression of OATP2B1 was analyzed in 46 human atrial and 15 ventricular samples, including samples from hearts with dilated cardiomyopathy and hearts with ischemic cardiomyopathy. RESULTS: Significant messenger ribonucleic acid expression was found in all samples, with no difference in the diseased hearts. However, patients who had taken atorvastatin exhibit decreased OATP2B1 messenger ribonucleic acid expression compared with patients with no statin treatment. OATP2B1 protein was detected at approximately 85 kd in atrial samples, as well as ventricular samples, and could be localized to the vascular endothelium. Furthermore, estrone-3-sulfate transport into OATP2B1-overexpressing Madin-Darby canine kidney II cells was inhibited by various drugs, including atorvastatin, simvastatin, cerivastatin, glyburide (INN, glibenclamide), and gemfibrozil, with the most pronounced effect being found for atorvastatin (inhibition constant, 0.7 +/- 0.4 micromol/L). Whereas simvastatin (lactone) itself was not transported by OATP2B1, atorvastatin was identified as a high-affinity substrate for OATP2B1 (Michaelis-Menten constant, 0.2 micromol/L) by direct transport measurement via liquid chromatography-tandem mass spectrometry. CONCLUSION: OATP2B1 is a high-affinity uptake transporter for atorvastatin and is expressed in the vascular endothelium of the human heart, suggesting its involvement in cardiac uptake of atorvastatin.

Expression, localization, and function of the carnitine transporter octn2 (slc22a5) in human placenta.

L-carnitine is assumed to play an important role in fetal development, and there is evidence that carnitine is transported across the placenta. The protein involved in this transfer, however, has not been identified on a molecular level. We therefore characterized localization and function of the carnitine transporter OCTN2 in human placenta. Significant expression of OCTN2 mRNA was detected in human placenta applying real-time polymerase chain reaction technology. Confocal immunofluorescence microscopy using an antibody directed against the carboxy terminus of OCTN2 protein revealed that it is predominantly expressed in the apical membrane of syncytiotrophoblasts. This was confirmed by the costaining of organic anion-transporting polypeptide B and MRP2, which are known to be expressed mainly in the basal and apical syncytiotrophoblasts membrane, respectively. To further support this finding, we performed transport studies using basal and apical placenta membrane vesicles. We could demonstrate that the carnitine uptake into the apical vesicles was about eight times higher compared with the basal ones. Moreover, this uptake was sodium- and pH-dependent with an apparent K(m) value of 21 muM and inhibited by verapamil, which is in line with published data for recombinant OCTN2. Finally, experiments using trophoblasts in cell culture revealed that expression of OCTN2 paralleled human choriogonadotropin production and thus is modulated by cellular differentiation. In summary, we show expression and function of OCTN2 in human placenta. Moreover, several lines of evidence indicate that OCTN2 is localized in the apical membrane of syncytiotrophoblasts, thereby suggesting a major role in the uptake of carnitine during fetal development.