Ioannis Papageorgiou

The nucleobase–ascorbate transporter (NAT) family: genomics, evolution, structure–function relationships and physiological role

This review summarizes knowledge concerning a ubiquitous plasma transmembrane protein family that mediates nucleobase or ascorbate secondary active transport (NAT). We show that prototype bacterial and mostly fungal members have become unique model systems to unravel structure-function relationships and regulation of expression, using classical and reverse genetics, as well as biochemical approaches. We discuss the importance of NAT-mediated ascorbate transport in mammals and how changes in substrate specificity, from different nucleobases to ascorbate, might have evolved at the molecular level. Finally, we also discuss how modelling NAT-purine interactions might constitute a step towards the use of NAT proteins as specific gateways for targeting pathogenic microbes.

Specific Interdomain Synergy in the UapA Transporter Determines Its Unique Specificity for Uric Acid among NAT Carriers

UapA, a uric acid-xanthine permease of Aspergillus nidulans, has been used as a prototype to study structure-function relationships in the ubiquitous nucleobase-ascorbate transporter (NAT) family. Using novel genetic screens, rational mutational design, chimeric NAT molecules, and extensive transport kinetic analyses, we show that dynamic synergy between three distinct domains, transmembrane segment (TMS)1, the TMS8-9 loop, and TMS12, defines the function and specificity of UapA. The TMS8-9 loop includes four residues absolutely essential for substrate binding and transport (Glu356, Asp388, Gln408, and Asn409), whereas TMS1 and TMS12 seem to control, through steric hindrance or electrostatic repulsion, the differential access of purines to the TMS8-9 domain. Thus, UapA specificity is determined directly by the specific interactions of a given substrate with the TMS8-9 loop and indirectly by interactions of this loop with TMS1 and TMS12. We finally show that intramolecular synergy among UapA domains is highly specific and propose that it forms the basis for the evolution of the unique specificity of UapA for uric acid, a property not present in other NAT members.

Absence of Transplacental Passage of the Low Molecular Weight Heparin Enoxaparin

Background: Venous thromboembolism (VTE) during pregnancy and puerperium remains a major cause of maternal morbidity and mortality. The use of low molecular weight heparin (LMWH) constitutes a promising alternative for the prevention of VTE instead of unfractionated heparin as it can be administered subcutaneously once daily and without coagulation measurement. Unfortunately, the safety of LMWHs administration for the mother and fetus has not been well established. Study Design: In order to examine the safety of enoxaparin to the fetus, 24 women were recruited and 40 mg of enoxaparin was administered in 14 of them. All 24 women were going to have an early termination of pregnancy due to major fetal malformations. Maternal blood samples were drawn before and after the injection of enoxaparin, while fetal blood samples were taken only after the drug administration. Anti-IIa and anti-Xa activities were measured. Results: A statistically significant increase of anti-Xa activity in the mothers studied was pointed out, while there was no detection of anti-IIa and anti-Xa activities in the fetuses. Conclusions: Since no anti-IIa and anti-Xa activities were detected in the fetuses’ blood samples, it is concluded that enoxaparin does not cross the placenta and therefore appears safe for the fetus.

Dynamic Elements at Both Cytoplasmically and Extracellularly Facing Sides of the UapA Transporter Selectively Control the Accessibility of Substrates to Their Translocation Pathway

In the UapA uric acid-xanthine permease of Aspergillus nidulans, subtle interactions between key residues of the putative substrate binding pocket, located in the TMS8-TMS9 loop (where TMS is transmembrane segment), and a specificity filter, implicating residues in TMS12 and the TMS1-TMS2 loop, are critical for function and specificity. By using a strain lacking all transporters involved in adenine uptake (DeltaazgA DeltafcyB DeltauapC) and carrying a mutation that partially inactivates the UapA specificity filter (F528S), we obtained 28 mutants capable of UapA-mediated growth on adenine. Seventy-two percent of mutants concern replacements of a single residue, R481, in the putative cytoplasmic loop TMS10-TMS11. Five missense mutations are located in TMS9, in TMS10 or in loops TMS1-TMS2 and TMS8-TMS9. Mutations in the latter loops concern residues previously shown to enlarge UapA specificity (Q113L) or to be part of a motif involved in substrate binding (F406Y). In all mutants, the ability of UapA to transport its physiological substrates remains intact, whereas the increased capacity for transport of adenine and other purines seems to be due to the elimination of elements that hinder the translocation of non-physiological substrates through UapA, rather than to an increase in relevant binding affinities. The additive effects of most novel mutations with F528S and allele-specific interactions of mutation R481G (TMS10-TMS11 loop) with Q113L (TMS1-TMS2 loop) or T526M (TMS12) establish specific interdomain synergy as a critical determinant for substrate selection. Our results strongly suggest that distinct domains at both sides of UapA act as selective dynamic gates controlling substrate access to their translocation pathway.

Myasthenia gravis and pregnancy

Three pregnancies in two women with myasthenia gravis (MG), are presented. The first woman expressed no antenatal complications and delivered a full-term 3350 g baby by caesarean section, because of a previous caesarean. The second woman had two preterm births in subsequent pregnancies, which were complicated by hydramnios. Her first pregnancy ended in neonatal death of a 860 g female with multiple congenital anomalies. In her second pregnancy there was an exacerbation of MG and the baby, an 880 g male died soon after birth, due to respiratory failure.

Takayasu Arteritis in Pregnancy: Safe Management Options in Antenatal Care

Takayasu arteritis is a nonspecific chronic inflammatory vascular disease of unknown etiology with a higher incidence during the child-bearing years. It usually involves the branches of the aortic arch. Most of the patients enter the pregnancy being already diagnosed as having the disease and being on medication. The state of the disease in early pregnancy is a definitive factor for determining its management. Although it seems that pregnancy is a state favorable to this disease, nevertheless, complications should be anticipated, and close multidisciplinary maternal and fetal surveillance is mandatory. Early-onset hypertension is the commonest complication, and its magnitude during the late gestational period is the second definitive factor for the management of these pregnancies. A vaginal delivery should be aimed at term with continuous electronic fetal monitoring. The immediate postpartum period is usually uncomplicated despite the circulatory alterations that take place.

Placental Pathology and Blood Pressure’s Level in Women with Hypertensive Disorders in Pregnancy

Objective. The aim of this study was to investigate the extent of placental lesions associated with blood pressure (BP) levels in pregnancies complicated by hypertension. Methods. 55 singleton pregnancies complicated by mild hypertension were recruited and compared to 55 pregnancies complicated by severe hypertension. The histological assessment was carried out with regard to the following aspects: vessels number/field of vision, infarction, villous fibrinoid necrosis, villous hypermaturity, avascular villi, calcifications, lymphohistiocytic villitis, and thickened vessels. Statistical analysis was performed by SPSS. Results. All placental lesions were observed more often in the severe hypertension group. Vessels number was significantly decreased, and infarction and villous fibrinoid necrosis were significantly increased in the placentas of the severe hypertension group compared to the mild hypertension group (P < 0.001). Conclusion. This study supports that the extent of placental lesions in hypertensive pregnancies is correlated with hypertension level and so highlights blood pressure level as a mirror of placental function.

Non-Hodgkin's lymphoma during pregnancy--case report.

Occurrence of Non Hodgkins lymphoma (NHL) in pregnancy is very rare. A 24-year-old woman with NHL stage IVB complicating pregnancy is presented. The diagnosis was made by biopsy at 27 weeks. The patient received combination chemotherapy which led to remission of the disease. The baby was delivered by an emergency caesarean section, due to fetal distress at 31 weeks. Unfortunately after a short period of remission a relapse occurred and magnetic resonance imaging (MRI) showed cerebral involvement, indicating a poor prognosis. She died seven months later from disseminated disease.

Intracervical Prostaglandin E2 Gel for Cervical Ripening and Labor Induction: What Is the Appropriate Dose?

In order to evaluate a dose-related response of cervical ripening and labor induction to a prostaglandin E2 (PGE2) gel, 110 women with uncomplicated postdate pregnancies and unripe cervices received intracervically 0.5 mg PGE2 (n = 40), 1.5 mg PGE2 (n = 35) or 2.5 mg PGE2 (n = 35). The failure rate in terms of cervical ripening was similar in all groups. Labor characteristics such as the duration of the latent phase as well as the total length of labor, the cesarean-section rate, instrumental deliveries and neonatal outcome were similar in all groups. The number of women who required oxytocin for labor augmentation was negatively correlated to the dose of PGE2 (p < 0.05). In addition, 3 out of 35 women in the 2.5-mg group presented hypertonic uterine activity. The increase in the dose of PGE2 gel did not increase the possibility for a vaginal delivery, but reduced the requirement for oxytocin while increasing hypertonic uterine action.

Systemic Lupus Erythematosus – Associated Acute Severe Thrombocytopenia and Leukopenia First Presented in Pregnancy

We report a rare case of acute severe thrombocytopenia and leukopenia, which first presented at 37 weeks’ gestation. Based on clinical as well as on laboratory findings the diagnosis of systemic lupus erythematosus was made. The patient was successfully managed with an emergency transfusion of 6 units of platelets and intravenous immunoglobulin infusion followed by methylprednisolone administration. A caesarean section was performed at 39 weeks. The neonate was not thrombocytopenic at birth, nor at the age of 1 month.