Selective modulation of placental and fetal MDR transporters by chronic in utero exposure to NRTIs in Sprague-Dawley rats: Importance for fetoprotection.

Multidrug resistance (MDR) transporters present in placenta and fetal tissues reduce intracellular accumulation of their substrates. Consequently, induction of protein expression may further reduce toxic effects of specific xenobiotics. This work aimed to study whether sustained drug treatments in utero could modulate MDR transporters P-gp, BCRP, and MRP2 and thus impact their fetoprotective action. Pregnant Sprague-Dawley rats were daily treated by gavage with zidovudine (AZT, 60 mg/kg) or lamivudine (3TC, 30 mg/kg) from gestation day (GD) 11 to 20. On GD 21, DNA damage and MDR protein abundance were assessed by comet assay and western blotting, respectively. Moreover, a single IV dose of AZT or 3TC was administered on GD 21 and drug concentrations were measured in maternal blood and fetal liver by HPLC-UV. Chronic exposure to 3TC caused significantly higher DNA damage than AZT in fetal liver cells, whereas no differences were observed in maternal blood cells. Increased levels of BCRP protein were found in the placenta and fetal liver after AZT, but not 3TC, chronic in utero exposure. Contrarily, no modifications in the protein abundance of P-gp or MRP2 were found after sustained exposure to these drugs. The area under the curve of AZT in fetal liver was significantly lower in the AZT-pretreated rats than in the VEH or 3TC groups. Moreover, pre-administration of the BCRP inhibitor gefitinib (20 mg/kg, IP) increased AZT levels to the values observed in the VEH-treated group in this tissue. On the other hand, the disposition of 3TC in maternal blood or fetal liver was not modified after chronic treatment in either group. In conclusion, chronic exposure to AZT selectively induces BCRP expression in the placenta and fetal liver decreasing its own accumulation which may account for the lower DNA damage observed for AZT compared to 3TC in fetal liver cells.

Induction of ABCG2/BCRP restricts the distribution of zidovudine to the fetal brain in rats.

Safety concerns for fetus development of zidovudine (AZT) administration as prophylaxis of vertical transmission of HIV persist. We evaluated the participation of the ATP-binding cassette efflux transporter ABCG2 in the penetration of AZT into the fetal brain and the relevance for drug safety. Oral daily doses of AZT (60mg/kg body weight) or its vehicle were administered between post gestational days 11 (E11) and 20 (E20) to Sprague-Dawley pregnant rats. At E21, animals received an intravenous bolus of 60mg AZT/kg body weight in the presence or absence of the ABCG2 inhibitor gefitinib (20mg/kg body weight, ip) and AZT in maternal plasma and fetal brain were measured by HPLC-UV. ABCG2 protein expression in placenta and fetal brain, as well as mitochondrial function and ultrastructure in fetal brain were also analyzed. In utero chronic exposure to AZT markedly induced ABCG2 expression in placenta and fetal brain whereas did not significantly alter mitochondrial functionality in the fetal brain. The area-under-the-concentration-time-curve of AZT significantly decreased in fetal brains isolated from AZT-exposed fetuses compared to control group, but this effect was abolished by ABCG2 inhibition. Our results suggest that the absence of mitochondrial toxicity in the fetal brain after chronic in utero administration of AZT could be attributed to its low accumulation in the tissue caused, at least in part, by ABCG2 overexpression. We propose that any interference with ABCG2 activity due to genetic, pathological or iatrogenic factors would increase the amount of AZT reaching the fetal brain, which could increase the risk of toxicity of this drug on the tissue.