Functional Changes of Mouse Placental Multidrug Resistance Phosphoglycoprotein (ABCB1) With Advancing Gestation and Regulation by Progesterone

Multidrug resistance phosphoglycoprotein (ABCB1) has been shown to limit maternal-fetal transfer by actively excluding ABCB1 substrates. The authors have previously demonstrated a marked decrease in placental ABCB1 expression in the human and mouse with advancing gestation. In the present study, it is hypothesized that the decrease in ABCB1 expression will result in increased transplacental transfer of ABCB1 substrates over the second half of gestation and that progesterone exhibits a regulatory role on placental ABCB1 expression and function. The authors demonstrate a significant increase in transplacental transfer of [(3)H]digoxin (an ABCB1 substrate) in late gestation (E18.5; P < .001) when compared to earlier embryonic days. Furthermore, maternal plasma progesterone levels did not influence expression or function of ABCB1. The authors conclude that the fetus is increasingly exposed to both endogenous and exogenous substrates of ABCB1 present in the maternal circulation with advancing gestation and that progesterone does not elicit a regulatory role on placental ABCB1 expression or function in vivo.

Multidrug resistance phosphoglycoprotein (ABCB1) expression in the guinea pig placenta: developmental changes and regulation by betamethasone

Placental ABCB1 plays an important role in fetal protection against xenobiotics in the maternal circulation. Limited evidence indicates that glucocorticoids regulate ABCB1 expression in other tissues. Since approximately 10% of pregnant women are treated with synthetic glucocorticoids for threatened preterm labour, the effects of synthetic glucocorticoids on placental ABCB1 are important. We hypothesized that placental levels of ABCB1 are reduced in late gestation in the guinea pig and that synthetic glucocorticoids downregulate ABCB1 production. There was a significant decrease in placental Abcb1 mRNA expression in late gestation. Treatment of guinea pigs with betamethasone (1 mg/kg) on gestational days 40/41 and 50/51 resulted in a significant decrease in placental Abcb1 mRNA and protein expression. No sex differences were observed. Understanding the regulation of ABCB1 function will facilitate the development of treatment strategies for human fetal protection against maternally derived endobiotics and xenobiotics.

Expression and localisation of breast cancer resistance protein (BCRP) in human fetal membranes and decidua and the influence of labour at term

Breast cancer resistance protein (BCRP) is a multidrug resistant ABC transport protein (ABCG-2). It extrudes a wide range of substrates, including many chemotherapy drugs, steroids and folate. It is present in many cancers, as well as normal tissues, in particular barrier tissues such as the blood-brain barrier, the intestine, blood vessels and the human placenta. Human fetal membranes (amnion and chorion laeve) provide the barrier between the maternal uterine environment and the fetus. In the present study, we defined the expression and localisation of BCRP mRNA and protein in human fetal membranes (amnion and chorion) and attached decidua obtained before and following labour at term. BCRP protein and mRNA was expressed in all tissues examined and the levels of expression were not altered by labour. BCRP was localised to the amnion epithelial cells, chorion trophoblast cells and decidua stromal cells, as well as the endothelial cells of maternal blood vessels in the decidua, but was absent from mesenchymal cells. In the amnion epithelium, BCRP protein was localised to the apical surface, cytoplasm and membrane between cells. In the chorion trophoblast and decidua stromal cells, BCRP protein was localised to the plasma membrane. However, in the chorion trophoblast, BCRP protein was also highly expressed in the nucleus. The level of BCRP protein in the membranes was comparable to that in the placenta. These high levels raise the possibility that this transporter plays an important role in the physiological function of the tissues.

Breast Cancer Resistance Protein (Bcrp1/Abcg2) in Mouse Placenta and Yolk Sac: Ontogeny and its Regulation by Progesterone

Breast Cancer Resistance Protein (BCRP), a recently-discovered transporter belonging to ABC superfamily, is highly expressed within the labyrinth of the placenta, the primary site of exchange between the maternal and fetal circulation. It has been proposed to function as an efflux pump protecting the fetus from a wide range of xenobiotics. It has also been recently shown that the yolk sac, in addition to the placenta, may be involved in transport of certain substances to and from the fetus. We hypothesised that there are changes in placental Bcrp1 (the mouse orthologue of human BCRP) expression during pregnancy and that these correlate with changes in progesterone production that occur in late gestation. We also hypothesised that Bcrp1 is expressed in the yolk sac, and that levels change with advancing gestation. Either whole concepti, or placenta and yolk sac, were collected from pregnant mice and analysed at embryonic (E) day 9.5, 12.5, 15.5 and 18.5 (term approximately E19.5). Peak expression of Bcrp1 mRNA was detected using in situ hybridisation within the placenta at E9.5 and the yolk sac at E12.5. There was a significant decrease thereafter in both tissues (p<0.001). In contrast, expression of Bcrp1 protein as assessed by immunohistochemistry and Western immunoblots did not change significantly during gestation either in the placenta nor the yolk sac, and no sex difference in Bcrp1 protein expression in either tissue was observed at E12.5. Daily progesterone treatment starting at E14.5 and continuing until E18.5 significantly increased maternal progesterone levels, but did not elicit any changes in the Bcrp1 mRNA or Bcrp1 protein expression either in the placenta or the yolk sac. Significant expression of Bcrp1 protein in fetal tissue was evident at the end of gestation, while expression in the fetal brain endothelium was evident as early as E12.5. We suggest that the placenta and the yolk sac, both of which express Bcrp1, may limit fetal exposure to the potentially adverse effects of xenobiotics including therapeutic drugs which the mother may be exposed to during pregnancy. The significant decrease in Bcrp1 mRNA expression in both the yolk sac and the placenta from mid to late gestation may be counter-balanced by an increase in Bcrp1 expression in fetal organs involved in absorption, excretion and protection.

Multidrug Resistance Phosphoglycoprotein (ABCB1) in the Mouse Placenta: Fetal Protection1

The multidrug resistance phosphoglycoprotein ATP-binding cassette subfamily B (ABCB1) actively extrudes a range of structurally and functionally diverse xenobiotics as well as glucocorticoids. ABCB1 is present in many cancer cell types as well as in normal tissues. Although it has been localized within the mouse placenta, virtually nothing is known about its regulation. In the mouse, two genes, Abcb1a and Abcb1b, encode ABCB1. We hypothesized that there are changes in placental Abcb1a and Abcb1b gene expression and ABCB1 protein levels during pregnancy. Using in situ hybridization, we demonstrated that Abcb1b mRNA is the predominant placental isoform and that there are profound gestational changes in the expression of both Abcb1a and Abcb1b mRNA. Placentas from pregnant mice were analyzed between Embryonic Days (E) 9.5 and 19 (term approximately 19.5d). Abcb1b mRNA was detected in invading trophoblast cells by E9.5, peaked within the placental labyrinth at E12.5, and then progressively decreased toward term (P < 0.0001). Abcb1a mRNA, although lower than that of Abcb1b at midgestation, paralleled changes in Abcb1b mRNA. Changes in Abcb1 mRNA were reflected by a significant decrease in ABCB1 protein (P < 0.05). A strong correlation existed between placental Abcb1b mRNA and maternal progesterone concentrations, indicating a potential role of progesterone in regulation of placental Abcb1b mRNA. In conclusion, there are dramatic decreases in Abcb1a and Abcb1b mRNA and in ABCB1 at the maternal-fetal interface over the second half of gestation, suggesting that the fetus may become increasingly susceptible to the influences of xenobiotics and natural steroids in the maternal circulation.

Biphasic modulation of acetaminophen bioactivation and hepatotoxicity by pretreatment with the interferon inducer polyinosinic-polycytidylic acid

Interferons and interferon induction can inhibit cytochromes P-450 and reduce the bioactivation and hepatotoxicity of acetaminophen. However, since P-450 inhibition often is followed by P-450 induction, which would enhance acetaminophen hepatotoxicity, the possibility of a biphasic modulation of acetaminophen hepatotoxicity by interferons was investigated. Outbred male CD-1 mice of various ages, and young inbred male C57BL/6 mice were given the interferon inducer, polyinosinic-polycytidylic acid (Poly I-C), 10 mg/kg intraperitoneally, followed 1 to 48 days later by a single dose of acetaminophen, 300 to 450 mg/kg intraperitoneally. Hepatotoxicity was assessed by the peak plasma concentration of alanine aminotransferase (ALT) occurring between 0 and 48 hr after acetaminophen treatment. Poly I-C inhibited the hepatotoxicity of acetaminophen given within 8 days, with maximal inhibition between 1 and 4 days. Conversely, a maximal 7-fold enhancement of ALT concentration was observed in CD-1 mice when 300 mg/kg of acetaminophen was given 32 days after Poly I-C (P less than 0.05). In the C57BL/6 strain, Poly I-C inhibited the hepatotoxicity of acetaminophen when given within 16 days, whereas a maximal 20-fold enhancement of ALT concentration was observed when 300 mg/kg of acetaminophen was given 24 days after Poly I-C (P less than 0.05). The mechanism of toxicologic enhancement was examined in male C57BL/6 mice using the same treatment regimen. Biochemical assessment of hepatotoxicity was confirmed by detailed histologic evaluation. Plasma concentrations of acetaminophen and metabolites were determined by high-performance liquid chromatography. Acetaminophen bioactivation was quantified by production of the glutathione-derived cysteine and mercapturic acid conjugates of acetaminophen. Poly I-C pretreatment produced a 5-fold increase in acetaminophen-induced ALT release (P less than 0.05), which correlated with histologic evidence of centrilobular necrosis. Poly I-C pretreatment produced respective 3-fold and 1.3-fold increases in the production of cysteine and mercapturic acid conjugates (P less than 0.05), which correlated with peak ALT concentrations (cysteine, r = 0.92, P less than 0.001; mercapturic acid, r = 0.75, P = 0.006). Thus, the hepatotoxicity of acetaminophen can be inhibited when given within days after interferon induction, and conversely enhanced when given after several weeks. The toxicologic enhancement appears to be due to increased P-450-catalyzed bioactivation of acetaminophen.