The xenoestrogens, bisphenol A and para-nonylphenol, decrease the expression of the ABCG2 transporter protein in human term placental explant cultures.

Many endogenous and xenobiotic compounds are substrates and regulators of human placental ABC transporters. ABCG2 is protecting fetus against foreign chemicals. Environmental xenoestrogens, like bisphenol A (BPA) and p-nonylphenol (p-NP), mimic natural estrogens and can affect hormonal systems. Effects of BPA, p-NP, DES (diethylstilbestrol) and estradiol (E2), on ABCG2 expression were studied using human first trimester and term placental explants. Role of estrogen receptors (ER) in the effects of chemicals was studied by ER antagonist. Term placenta expressed less ABCG2 protein. In term placentas BPA (p < 0.05), p-NP (p < 0.01) and E2 (p < 0.05) decreased the ABCG2 protein expression after 48 h exposure while after 24 h exposure, only E2 decreased the expression (p < 0.05). The chemicals did not affect ABCG2 in first trimester placentas. The ER antagonist affected differently the responses of chemicals. In conclusion, environmental xenoestrogens downregulate placental ABCG2 protein expression depending on gestational age.

Organic anion transporter 4 (OAT 4) modifies placental transfer of perfluorinated alkyl acids PFOS and PFOA in human placental ex vivo perfusion system.

INTRODUCTION: Perfluorinated alkyl acids (PFAAs) are widely used in industry and consumer products. Pregnant women are exposed to PFAAs and their presence in umbilical cord blood represents fetal exposure. Interestingly, PFAAs are substrates for organic anion transporters (OAT) of which OAT4 is expressed in human placenta. METHODS: To evaluate the contribution of OAT4 and ATP-binding cassette transporter G2 (ABCG2) proteins in the transplacental transfer of perfluoro octane sulfonate (PFOS) and perfluoro octanoate (PFOA) an ex vivo dual recirculating human placental perfusion was used. Altogether 8 placentas from healthy mothers with uncomplicated pregnancies were successfully perfused. RESULTS: Both PFOS and PFOA crossed the placenta as suggested by in vivo data in the literature. The expression of OAT4 and ABCG2 proteins were studied by immunoblotting and correlation with the transfer index %(TI %) of PFOS and PFOA at 120 and 240 min (n = 4) was studied. The expression of OAT4 was in negative correlation with TI % of PFOA (R(2) = 0.92, p = 0.043) and PFOS (R(2) = 0.99, p = 0.007) at 120 min while at 240 min the correlation was statistically significant only with PFOA. The expression of ABCG2 did not correlate with TI% of PFOS or PFOA. DISCUSSION: Data obtained in this study suggest the involvement of OAT4 in placental passage of PFAAs. Placental passage of PFOS and PFOA is modified by the transporter protein OAT4 but not by ABCG2. This is the first study indicating that OAT4 may decrease the fetal exposure to PFAAs and protect the fetus after maternal exposure to PFAAs but further studies are needed to confirm our findings.

Cadmium inhibits ABCG2 transporter function in BeWo choriocarcinoma cells and MCF-7 cells overexpressing ABCG2.

Heavy metals such as cadmium, lead and methylmercury are known to be neurotoxic to developing fetus. ABCG2 which is an efflux transporter located in the maternal facing membranes of human placenta protects fetus from xenobiotics by transferring compounds from syncytiotrophoblast to maternal circulation. The aim of this study was to clarify whether heavy metal compounds (CdCl(2), PbCl(2) and MeHgCl) affect the expression and function of ABCG2 transporter in human placental BeWo choriocarcinoma cells. The expression of ABCG2 was determined by immunoblotting and RT-PCR. The functional activity of ABCG2 was evaluated by measuring the efflux of two known ABCG2 substrates: fluorescent mitoxantrone and (14)C-labeled food carcinogen PhIP. According to MTT assay all compounds were cytotoxic as expected (MeHgCl > CdCl(2) > PbCl(2)). CdCl(2) inhibited the efflux of mitoxantrone and (14)C-PhIP suggesting inhibition of ABCG2 transporter function. PbCl(2) had no effect on mitoxantrone efflux. Because of high toxicity, the inhibitory potency of MeHgCl was not tested. According to protein data these heavy metals did not affect ABCG2 transporter protein expression. Also, the expression of ABCC1, ABCC2 or ABCG2 mRNA were not affected by heavy metals. In conclusion, although the studied metal salts did not affect mRNA or protein expression of ABCG2, CdCl(2) inhibited its function. Further studies to evaluate whether this leads to elevated placental transfer of ABCG2 substrates are needed.

Meta-analysis of data from human ex vivo placental perfusion studies on genotoxic and immunotoxic agents within the integrated European project NewGeneris.

In the E.U. integrated project NewGeneris, we studied placental transport of thirteen immunotoxic and genotoxic agents in three ex vivo placental perfusion laboratories. In the present publication, all placental perfusion data have been re-analyzed and normalized to make them directly comparable and rankable. Antipyrine transfer data differed significantly between the studies and laboratories, and therefore normalization of data was necessary. An antipyrine normalization factor was introduced making the variance significantly smaller within and between the studies using the same compound but performed in different laboratories. Non-normalized (regular) and normalized data showed a good correlation. The compounds were ranked according to their transplacental transfer rate using either antipyrine normalized AUC120 or transfer index (TI120(%)). Normalization generated a division of compounds in slow, medium and high transfer rate groups. The transfer rate differed slightly depending on the parameter used. However, compounds with passage similar to antipyrine which goes through the placenta by passive diffusion, and good recovery in media (no accumulation in the tissue or adherence to equipment) were highly ranked no matter which parameter was used. Antipyrine normalization resulted in the following ranking order of compounds according to AUC(120NORM) values: NDMA ≥ EtOH ≥ BPA ≥ IQ ≥AA ≥ GA ≥ PCB180 ≥ PhIP ≥ AFB1 > DON ≥ BP ≥ PCB52 ≥ TCDD. As the variance in all parameters within a study decreased after antipyrine normalization, we conclude that this normalization approach at least partially corrects the bias caused by the small methodological differences between studies.