Bilirubin Reduces the Uptake of Estrogen Precursors and the Followed Synthesis of Estradiol in Human Placental Syncytiotrophoblasts via Inhibition and Downregulation of Organic Anion Transporter 4

Abstract

Estrogen biosynthesis in human placental trophoblasts requires the hOAT4-mediated uptake of fetal derived precursors such as dehydroepiandrosterone-3-sulfate (DHEAS) and 16α-hydroxy-DHEA-S (16α-OH-DHEAS). Scant information is available concerning the contribution of fetal metabolites on the impact of placental estrogen precursor transport and the followed estrogen synthesis. This study substantiated the roles of bilirubin as well as bile acids (taurochenodeoxycholic acid, TCDCA; taurocholic acid, TCA; glycochenodeoxycholic acid, GCDCA; chenodeoxycholic acid, CDCA) on the inhibition of hOAT4-mediated uptake of probe substrate 6-carboxylfluorescein (6-CF) and DHEAS in stably transfected hOAT4-CHO cells, with the IC 50 of 1.53 and 0.98 μM on 6-CF and DHEAS respectively for bilirubin, and 90.2, 129, 16.4 and 12.3 μM on 6-CF for TCDCA, GCDCA, TCA and CDCA. Bilirubin (2.5~10 μM)concentration-dependently inhibited the accumulation of estradiol precursor DHEAS in human choriocarcinoma JEG-3 cells (reduced by 60% at 10 μM) and primary human trophoblast cells (PHTCs, reduced by 80% at 10 μM). Further study confirmed that bilirubin (0.625~2.5 μM) concentration-dependently reduced the synthesis and secretion of estradiol in PHTCs, among which 2.5 μM bilirubin reduced the synthesis of estradiol by 30% and secretion by 35%. In addition, immunostaining and Western Blot results revealed a distinct down-regulation of hOAT4 protein expression in PHTCs pretreated with 2.5 μM bilirubin. In conclusion, this study demonstrated that bilirubin reduced the uptake of estrogen precursors and the followed synthesis of This article has not been copyedited and formatted. The final version may differ from this version.

A Literature Review of Changes in Phase II Drug-Metabolizing Enzyme and Drug Transporter Expression during Pregnancy

“…Observed in the liver, kidney, intestine, central nervous system, skeletal muscle, heart, lung, pancreas, and adrenal gland, OATs are anion exchangers that pair the uptake of an anionic substrate with the efflux of another anion [44]. Though OAT1-3 are predominantly expressed in excretory organs [16], OAT4 mediates the transport of anions [27] and the uptake of estrogen precursors [46] in the placenta.…”