Tissue distribution and hormonal regulation of the breast cancer resistance protein (Bcrp/Abcg2) in rats and mice.

Breast cancer resistance protein (Bcrp/Abcg2) is a member of the ABC transporter family. The purpose of this study was to quantify Bcrp mRNA in rat and mouse tissues, and to determine whether there are gender differences in Bcrp mRNA expression. Rat Bcrp mRNA levels were high in intestine and male kidney, and intermediate in testes. Mouse Bcrp expression was highest in kidney, followed by liver, ileum, and testes. Male-predominant expression of Bcrp was observed in rat kidney and mouse liver. Furthermore, gonadectomy and hypophysectomy experiments were conducted to determine whether sex steroids and/or growth hormone are responsible for Bcrp gender-divergent expression patterns. Male-predominant expression of Bcrp in rat kidney appears to be due to the suppressive effect of estradiol, and male-predominant expression of Bcrp in mouse liver appears to be due to the inductive effect of testosterone.

The embryolethality of lipopolysaccharide in CD-1 and metallothionein I-II null mice: lack of a role for induced zinc deficiency or metallothionein induction.

Lipopolysaccharide (LPS) is embryolethal in CD-1 mice. LPS induces metallothionein (MT) via cytokines, including TNF-alpha, IL-1, and IL-6, which initiate and maintain the acute phase response. Maternal hepatic MT induction in pregnant rats, by diverse toxicants, can result in maternal hypozincemia and subsequent embryonal zinc (Zn) deficiency. We examined the hypothesis that LPS causes embryo toxicity in CD-1 mice via MT induction and subsequent embryo Zn deficiency by (1) determining whether LPS induces maternal hepatic MT and causes Zn redistribution, (2) assessing the effects of maternal Zn supplementation on LPS developmental toxicity, and (3) assessing the role of MT with MT I-II null mice (MTKO). Timed pregnant CD-1 mice were dosed i.p. with LPS (S. typhimurium) (0.05 mg/kg) on gestation day (gd) 9. Zn supplementation was administered on gd 8 (10 mg/kg, pretreatment) or on gd 9 as a cotreatment (5 or 10 mg/kg). MTKO and wild type (WT) mice were dosed with LPS (0.05 or 0.1 mg/kg) on gd 9, and maternal liver MT and Zn and plasma Zn were measured. In CD-1 mice, maternal hepatic MT was elevated 24 h after LPS treatment, and cotreatment with Zn caused further elevation of MT. Maternal hepatic Zn concentrations paralleled hepatic MT concentrations. Maternal plasma Zn on gd 10 showed no consistent effect of LPS treatment or Zn cotreatment on gd 9. Zn pretreatment (10 mg/kg) on gd 8 did not ameliorate LPS embryolethality, while Zn cotreatment (5 or 10 mg/kg) on gd 9 exacerbated the toxicity of LPS. LPS produced a similar incidence of embryolethality in MTKO and WT strains on gd10. Plasma Zn concentrations were similar in both strains, while hepatic Zn concentrations were significantly higher in WT than in the MTKO strain. In conclusion, while LPS can induce maternal hepatic MT and Zn redistribution in CD-1 mice, this does not appear to be a key mechanism leading to LPS embryotoxicity.

The presence of xenobiotic transporters in rat placenta.

Understanding the role of transporters in placental handling of xenobiotics across the maternal-fetal interface is essential to evaluate the pharmacological and toxicological potential of therapeutic agents, drugs of abuse, and other xenobiotics to which the mother is exposed during pregnancy. Therefore, the purpose of this study was to assess mRNA levels of various transporters in placenta and to compare these to levels in maternal liver and kidney, predominant organs of excretion, to determine which transporters are likely to have a role in xenobiotic transfer within the placenta. During late stage pregnancy, relative amounts of mRNA levels of 40 genes representing 11 families/group of transporters were assessed in placenta with respect to relative maternal liver and kidney mRNA levels. Members of the following transporter families were assessed: three multidrug resistance (Mdr), six multidrug resistance-associated protein (Mrp), eight organic anion-transporting polypeptide (Oatp), three organic anion transporters (Oat), five organic cation transporters (Oct), two bile acid transporters (Na(+)/taurocholate-cotransporting polypeptide and bile salt export protein), four metal (ZnT1, divalent metal transporter 1, Menkes and Wilsons), a prostaglandin, two peptide, two sterolin, and four nucleoside transporters. Of the 40 genes evaluated, 16 [Mdr1a and 1b, Mrp1 and 5, Oct3 and Octn1, Oatp3 and 12, four metal, a prostaglandin, AbcG8, equilibrative nucleoside transporter 1 (ENT1), and ENT2] were expressed in placenta at concentrations similar to or higher than in maternal liver and kidney. The abundance of these mRNA transcripts in placenta suggests a role for these transporters in placental transport of xenobiotics and supports their role in the transport of endogenous substances.

Cadmium absorption and its relationship to divalent metal transporter-1 in the pregnant rat.

Increased intestinal absorption of essential nutrients is characteristic of pregnancy as the maternal gastrointestinal tract undergoes physiological and biochemical changes to accommodate the increased demand for essential nutrients by the fetus. Divalent metal transporter-1 (DMT-1) is primarily responsible for dietary iron uptake in the duodenum but also recognizes nonessential metals such as cadmium (Cd). Increased absorption of Cd has been reported in pregnant compared with nonpregnant mice; however, the mechanism is not understood. The purpose of this work was to determine whether Cd absorption is increased in pregnant compared with nonpregnant rats and whether this correlates with a time-dependent up-regulation of DMT-1 expression. Timed pregnant and nonpregnant female Sprague-Dawley rats were administered (109)Cd-labeled CdCl(2) by oral gavage on gestation day (gd) 19. Tissues were collected on gd 20 for (109)Cd assessment (values expressed as pmol Cd). Greater accumulation of (109)Cd was observed in duodenum than in jejunum and ileum in both pregnant and nonpregnant rats. However, the amount of Cd in small intestine was higher in pregnant than nonpregnant rats. Additionally, more Cd accumulated in the liver and kidney of pregnant than nonpregnant rats. DMT-1 mRNA levels were determined in duodenum, placenta, liver, and kidney with branched DNA signal amplification. DMT-1 mRNA levels were about sixfold higher in duodenum of (gd 21) pregnant than nonpregnant rats and the levels in pregnant rats increased from gd 15 through gd 21. The correlation between Cd absorption and DMT-1 expression observed in pregnant rats suggests a role for DMT-1 in the increased absorption of Cd during pregnancy.

Role of the maternal acute phase response and tumor necrosis factor alpha in the developmental toxicity of lipopolysaccharide in the CD-1 mouse.

The acute phase response (APR) functions to reset metabolic homeostasis following infectious, toxic, or traumatic insult. TNF-alpha, a putative mediator of the APR, has been associated with fetal death in rodents and preterm labor and delivery in humans. We hypothesized that physiologic changes associated with the maternal APR may play a role in adverse embryo/fetal outcome. Pregnant CD-1 mice injected i.p. with lipopolysaccharide (LPS), a model inducer of the APR, on gestation day (gd) 9 showed a dose-related increase in embryo death on gd 10. Histology indicated placental infarct and necrosis. Maternal serum TNF-alpha levels, measured by ELISA following administration of 0.05 mg/kg LPS on gd 9, were found to increase significantly and peak within 1 to 1.5 h. Pretreatment with 0.01 mg/kg LPS on gd 8 ameliorated embryotoxicity of the 0.05 mg/kg LPS treatment on gd 9 and also eliminated the increase in serum TNF-alpha. Direct LPS exposure in whole embryo culture was nontoxic. These data support a maternally mediated mechanism of LPS embryolethality, and suggest that TNF-alpha may be an important mediator of this developmental toxicity.