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1.  Human Placental Adenosine Receptor Expression is Elevated in Preeclampsia and Hypoxia Increases Expression of the A2A Receptor 
Placenta  2009;30(5):434-442.
Placental hypoxia as a result of impaired trophoblast invasion is suggested to be involved in the pathophysiology of preeclampsia. Hypoxia is a potent stimulus for the release of adenosine, and the actions of adenosine are mediated through four adenosine receptors, A1, A2A, A2B and A3. We investigated the presence, distribution and expression of adenosine receptor subtypes in the human placenta, the expression of the adenosine receptors in placentas from pregnancies complicated by preeclampsia, small for gestational age (SGA) infants and uncomplicated pregnancies, and the effect of hypoxia on placental adenosine receptor expression. Immunofluorescent microscopy localized A1, A2A, A2B and A3 adenosine receptors to the syncytiotrophoblast, endothelial cells and myo-/fibroblasts within the human placenta. Adenosine receptor protein and message expression levels were significantly higher in placentas from preeclamptic pregnancies with or without SGA infants, but not different in pregnancies with SGA infants alone. In vitro exposure of placental villous explants to hypoxia (2% oxygen) increased the expression of A2A adenosine receptor 50%. These data indicate that all four known adenosine receptors are expressed in the human placenta and adenosine receptor expression is significantly higher in pregnancies complicated by preeclampsia. These data are consistent with the hypothesis that differences in placental adenosine receptors may contribute to alterations in placental function in preeclampsia.
doi:10.1016/j.placenta.2009.02.004
PMCID: PMC2674514  PMID: 19303140
2.  Uric Acid Inhibits Placental System A Amino Acid Uptake☆ 
Placenta  2008;30(2):195-200.
Hyperuricemia, a common clinical characteristic of preeclamptic pregnancies, has historically been considered a marker of reduced renal function in preeclamptic women. More recently it has been suggested that uric acid may directly contribute to pathological cell signaling events involved in disease progression as well as maternal and fetal pregnancy outcomes including fetal growth restriction. We hypothesize that the increased frequency of restricted fetal growth seen in relation to increasing uric acid concentrations in preeclamptic women is in part the result of uric acid-induced reductions in amino acid transport across the placenta. The objective of the current study was to examine the effects of uric acid on human placental System A amino acid transport using a primary placental villous explant model. Further, we examined the necessity of uric acid uptake and the role of redox signaling as a potential mechanism through which uric acid may attenuate System A activity. Placental uptake of a radiolabeled amino acid analogue, specific to the System A transporter, was reduced in a concentration-dependent fashion with increasing uric acid (0−7 mg/dL), corresponding to uric acid concentrations measured in healthy pregnant and preeclamptic women in the third trimester. Uric acid-induced reduction in System A activity was partially reversed by NADPH oxidase inhibition and completely eliminated by antioxidant treatment. This study demonstrates inhibition of placental System A amino acid transport with uric acid treatment, as a result of uric acid-induced stimulation of intracellular redox signaling cascades. These findings may be relevant to the increased frequency of fetal growth restriction observed in hyperuricemic preeclampsia. Additionally the results of this study, indicating a detrimental effect of hyperuricemia on amino acid transport in the placenta, at concentrations present in women with preeclampsia, also suggest a role for uric acid in the pathophysiology of preeclampsia.
doi:10.1016/j.placenta.2008.10.015
PMCID: PMC2677697  PMID: 19058847
Uric acid; Amino acid transport; System A; Antioxidants; Redox signaling; Placenta; Preeclampsia; Fetal growth restriction; Hyperuricemia; NADPH oxidase; Probenecid; Explants
3.  Placental System A Amino Acid Transport is Reduced in Pregnancies With Small For Gestational Age (SGA) Infants but Not in Preeclampsia with SGA Infants 
Placenta  2008;29(10):879-882.
Preeclampsia and intrauterine growth restriction (IUGR) are both associated with abnormal remodeling of maternal spiral arteries perfusing the placental site. This would be expected to be associated with reduced fetal growth, yet only one third of infants of mothers with preeclampsia are growth restricted. Infants with IUGR have decreased concentrations of amino acids in their blood and system A amino acid transporter activity is reduced in their placentas. Since infants of preeclamptic pregnancies have increased circulating amino acids, we tested system A amino acid transport activity of placental villous fragments from pregnancies with small for gestational age (SGA) infants with and without maternal preeclampsia and from uncomplicated and preeclamptic pregnancies with normal sized infants. We confirm the reduced uptake of amino acids in SGA pregnancies without preeclampsia but report that placental amino acid uptake of SGA infants with maternal preeclampsia is not reduced and is identical to uptake by normal and preeclamptic pregnancies with normal weight infants.
doi:10.1016/j.placenta.2008.07.001
PMCID: PMC2703008  PMID: 18718657
Placental transport; Amino acid; Preeclampsia; Intrauterine growth restriction

Results 1-3 (3)