Increased Expression of MDR1 mRNAs and P-glycoprotein in Placentas from HIV-1 Infected Women
Introduction
The placenta assumes different functions during pregnancy allowing respiratory exchanges, transfer of micronutrients between maternal and fetal circulations, and providing hormones which are essential for the development of the fetus. Although placenta was viewed as a protective barrier, its weakness towards the materno-fetal passage of medical drugs and other xenobiotics is now widely demonstrated [1].
Different mechanisms are evoked to describe the translocation of endogenous molecules or pharmaceuticals across membranes of the syncytiotrophoblasts and endothelium of fetal capillaries. Passive diffusion represents the major phenomenon implicated in both materno-fetal and feto-maternal transfer. Recent studies have found that placenta also contains numerous transporters more or less dedicated to the removal of compounds, particularly involved in the passage of drugs from the fetal to the maternal side [2], [3]. Among them, P-glycoprotein (P-gp), which is encoded by the MDR1 gene in humans or by the two MDR1a and MDR1b genes in rodents, is one of the best characterized ATP-dependent drug efflux transporters in placenta [4], [5]. This protein is expressed on the border of the syncytiotrophoblast microvillus plasma membrane and participates in export process of drugs into the maternal blood supply, thereby reducing chemical exposure of the fetal compartment [6], [7]. These results have been confirmed on animals and with in vitro models showing on one hand that MDR1a gene knockout mice lacking placental P-gp have an increased fetal susceptibility to ivermectin-induced teratogenicity, and on the other hand that P-gp extrudes cyclosporin backwards into the maternal compartment [8], [9].
Where possible, the use of drugs is avoided during pregnancy, but in conditions where the benefits of treatment outweigh the fetal or maternal risks, they should be used. The use of antiretroviral drugs to treat HIV infection falls into this category. The goals of antiretroviral regimens are to simultaneously treat the mother's infection and prevent vertical transmission [10], [11]. Various combinations of different antiretroviral drugs, which are more effective than the use of only one class of drugs, are increasingly administered to HIV-seropositive pregnant women with the aim of treating the mother's infection as well as preventing mother-to-child transmission. Treatment usually consists of a combination of HIV nucleoside analogues and at least one protease inhibitor (PI). Among the advised drugs, PIs are substrates of P-gp and several reports have evaluated fetal exposure to these compounds in humans [12], [13], [14], [15]. Thus, concentration of Ritonavir studied in an ex vivo placental perfusion model was shown to be extremely low in fetal compared to maternal compartment [16]. This finding was confirmed and extended to other PIs by the measure of their in vivo concentration in cord blood [17]. Therefore, understanding the importance of P-gp in the trophoblast layer is a crucial element in devising new drug delivery strategies in pregnant women. P-gp expression can be modulated by several inhibitors and inducers [18]. It is now well established that consequent levels of P-gp are expressed in the placenta depending on the stage of pregnancy but no information was documented regarding P-gp or MDR1 expression in placentas from HIV-infected mothers [19], [20].
The purpose of this study was to assess the extent of expression of MDR1 transcripts and P-gp in full-term placentas from HIV-1 infected women compared to non-infected women, in order to understand how variable expression of this transporter may change with the disease state, thus affecting clinical outcome.
Section snippets
Patients and placenta samples
Fifty-nine (i.e., 35 non-infected and 24 HIV-infected) women were included in this study with their consent and following local ethical committee's guidelines. Clinical information including the age of the patient, the number of weeks of pregnancy at delivery and the mode of delivery (vaginal or caesarean section) was collected. Non-infected women were devoid of pathology and medical treatment during their pregnancy. Regarding HIV-infected women, data such as the plasmatic viral load, the CD4+
Patients and treatment during pregnancy
In this study, 59 full-term placentas were collected from uncomplicated deliveries, including 35 from non-infected and 24 from HIV-infected women. Both groups were comparable according to the mean age of the mother at delivery, 34 ± 5 (extremes: 24–44) and 32 ± 5 (extremes: 25–39) years old, respectively, and according to the mean gestational week of delivery, 39.4 ± 1.3 (extremes: 38–42) and 38.5 ± 0.8 (extremes: 35–39) weeks, in non-infected and HIV-infected groups, respectively. The mode of delivery
Discussion
We studied MDR1 expression in chorionic villi since they are the only components of the placenta supplied by both maternal and fetal circulations and they represent the area where primarily maternal–fetal exchanges occur [30]. We successfully developed an accurate and reproducible method to enable the quantification of MDR1 transcripts in this tissue [31]. To our knowledge, this is the first study measuring MDR1 gene expression by real-time PCR using a SYBR Green I detection, in placenta from
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