Genetic and dietary regulation of the human placental BCRP transporter

Glyburide is frequently used to treat gestational diabetes due to its low fetal accumulation resulting from placental efflux by the breast cancer resistance protein (BCRP/ABCG2) transporter. However, there is little understanding of the potential consequences of reduced placental BCRP function in pregnant women prescribed glyburide. Babies born to this population of women may be at an elevated risk of neonatal hypoglycemia potentially leading to low birth weight, increased morbidity, and impaired neurological development. The purpose of this dissertation research was to determine the influence of genetic and dietary factors on the placental expression of BCRP and its ability to transport glyburide. In 10 human term placentas, there were no differences in expression of BCRP mRNA or protein across the disc, supporting the use of a single sampling site to examine the interindividual expression of this transporter. In term placentas from 108 donors, ethnicity, transcription factor expression, and single nucleotide polymorphisms (SNPs) were associated with BCRP expression including the frequent C421A SNP, which correlated with lower BCRP protein expression. Further in vitro studies revealed that C421A-BCRP overexpressing cells had low BCRP protein expression at the cell surface and impaired transport of the BCRP substrate glyburide. Additionally, the dietary soy isoflavone genistein competitively inhibited the BCRP-mediated transport of glyburide in overexpressing cells (wild-type, WT-BCRP and C421A-BCRP) and human choriocarcinoma placental BeWo cells that endogenously express BCRP. Importantly, genistein inhibited glyburide transport in placental BeWo cells at concentrations that are physiologically relevant (IC50=0.18 +/- 0.11 muM). Finally, estrogen receptor-mediated signaling stimulated by prolonged genistein treatment (48 h) down-regulated BCRP mRNA and protein expression in BeWo cells leading to reduced efflux of glyburide out of cells. Conversely, genistein (48 h) did not alter BCRP protein expression in term placental explants, suggesting that the regulation of placental BCRP expression by genistein may be limited to choriocarcinoma BeWo cells. Together, this research provides population and mechanistic data that demonstrate how a genetic variant (C421A) and diet (genistein) may alter the maternal-fetal disposition of glyburide as well as other chemicals that are BCRP substrates.