Recurrent preterm birth

Recurrent preterm birth is frequently defined as two or more deliveries before 37 completed weeks of gestation. The recurrence rate varies as a function of the antecedent for preterm birth: spontaneous versus indicated. Spontaneous preterm birth is the result of either preterm labor with intact membranes or preterm prelabor rupture of the membranes. This article reviews the body of literature describing the risk of recurrence of spontaneous and indicated preterm birth. Also discussed are the factors which modify the risk for recurrent spontaneous preterm birth (a short sonographic cervical length and a positive cervicovaginal fetal fibronectin test). Patients with a history of an indicated preterm birth are at risk not only for recurrence of this subtype, but also for spontaneous preterm birth. Individuals of black origin have a higher rate of recurrent preterm birth.     

Group B streptococcus infection in pregnancy

Group B streptococcus (streptococcus agalactiae), a gram-positive coccus, is one of the major causes of maternal or neonatal severe infection and sepsis. Maternal infection associated with GBS includes acute chorioamnionitis, endometritis, and urinary tract infection.     

Cryo-EM structure of DNA-bound Smc5/6 reveals DNA clamping enabled by multi-subunit conformational changes

Structural maintenance of chromosomes (SMC) complexes are essential for chromatin organization and functions throughout the cell cycle. The cohesin and condensin SMCs fold and tether DNA, while Smc5/6 directly promotes DNA replication and repair. The functions of SMCs rely on their abilities to engage DNA, but how Smc5/6 binds and translocates on DNA remains largely unknown. Here, we present a 3.8 Å cryogenic electron microscopy (cryo-EM) structure of DNA-bound Saccharomyces cerevisiae Smc5/6 complex containing five of its core subunits, including Smc5, Smc6, and the Nse1-3-4 subcomplex. Intricate interactions among these subunits support the formation of a clamp that encircles the DNA double helix. The positively charged inner surface of the clamp contacts DNA in a nonsequence-specific manner involving numerous DNA binding residues from four subunits. The DNA duplex is held up by Smc5 and 6 head regions and positioned between their coiled-coil arm regions, reflecting an engaged-head and open-arm configuration. The Nse3 subunit secures the DNA from above, while the hook-shaped Nse4 kleisin forms a scaffold connecting DNA and all other subunits. The Smc5/6 DNA clamp shares similarities with DNA-clamps formed by other SMCs but also exhibits differences that reflect its unique functions. Mapping cross-linking mass spectrometry data derived from DNA-free Smc5/6 to the DNA-bound Smc5/6 structure identifies multi-subunit conformational changes that enable DNA capture. Finally, mutational data from cells reveal distinct DNA binding contributions from each subunit to Smc5/6 chromatin association and cell fitness. In summary, our integrative study illuminates how a unique SMC complex engages DNA in supporting genome regulation.

Structural maintenance of chromosomes (SMC) complexes are essential genome regulators in both prokaryotes and eukaryotes. In eukaryotes, the cohesin and condensin SMC complexes organize DNA, while the Smc5/6 complex (referred to as Smc5/6) directly regulates DNA replication and repair (1). At the structural level, SMC complexes share similarities while possessing unique attributes (1). Each complex contains a pair of SMC subunits and a set of non-SMC subunits. The SMC subunits define the tripartite filamentous architecture of the complex: their approximal 50-nm long coiled coil arm region connects their dimerized hinge and adenosine triphosphatase (ATPase) head regions (1). A non-SMC kleisin subunit uses its N- and C-terminal domains to link the head of one SMC to the head-proximal arm region (neck) of another SMC, forming a trimeric SMC-kleisin structure. In cohesin and condensin, two large U-shaped HEAT (Huntington, elongation factor 3, PR65/A, TOR) repeat HAWK (HEAT proteins associated with kleisins) subunits attach to the middle region of the kleisin. By contrast, the Smc5/6 kleisin (Nse4) binds to smaller WH (winged helix)-containing KITE (kleisin interacting tandem WH elements) subunits (Nse1 and Nse3) (2).SMC-mediated functions depend on interactions with DNA. Recent cryogenic electron microscopy (cryo-EM) structures of DNA-bound cohesin and condensin revealed that their HAWK subunits and the SMC head-neck regions form a clamp to enclose a single DNA double helix (3–7). DNA clamping can be critical for cohesin and condensin to extrude DNA loops for chromatin folding (5, 7–9). DNA loop extrusion additionally requires arm bending at a region called the elbow, which is found in both cohesin and condensin (5, 7–9). By contrast, a lack of arm bending in Smc5/6 was suggested by negative stain EM and cross-linking mass spectrometry (CLMS) data (10–14). Since Smc5/6 does not contain HAWK proteins nor shows arm-bending, it has remained unclear how Smc5/6 engages DNA to accomplish its multiple functions.Here we address the molecular mechanisms by which this unique SMC complex binds DNA using an integrative approach, coupling a cryo-EM-based structural characterization with CLMS analyses and functional investigation. Our atomic structure of a DNA-bound Saccharomyces cerevisiae Smc5/6 complex reveals that the head-neck Smc5-6 regions and the Nse1-3-4 subcomplex together form a clamp entrapping the DNA helix. The structure further reveals protein subunit folds and association, as well as how the subunits collaborate to entrap DNA. Comparison of CLMS analyses of DNA-free Smc5/6 with the structure of the DNA-bound Smc5/6 unveils large scale, multi-subunit conformational changes that enable Smc5/6 to encircle DNA. Finally, our mutational data suggest distinct contributions from each of the DNA binding regions to Smc5/6 chromatin association and cellular fitness. Comparison of our findings with those of other SMCs reveals that diverse SMC complexes use a similar DNA clamping strategy despite structural differences, and that Smc5/6 possesses unique features distinct from cohesin, condensin, and prokaryotic SMCs. Our work lays the foundation for an in-depth understanding of how Smc5/6 fulfills unique roles in genome protection.     

Blood transfusion and increased risk for vasospasm and poor outcome after subarachnoid hemorrhage

OBJECT: Nitric oxide (NO) metabolism may influence vasospasm after subarachnoid hemorrhage (SAH). It has been demonstrated in recent studies that erythrocytes carry NO for release in vessels, whereas transfused erythrocytes may lack stored NO. Several converging lines of evidence also indicate that blood transfusion may exacerbate poor outcomes in some critically ill patients. In this study the authors hypothesized that patients with SAH who received red blood cell (RBC) transfusions were at greater risk for vasospasm and poor outcome. METHODS: The authors retrospectively reviewed a prospective observational database, including hospital records, computerized tomography (CT) scans, and pre- and postoperative four-vessel angiograms, in which the management methods used in 441 patients undergoing surgery for ruptured cerebral aneurysms were described. Two hundred seventy patients (61.2%) received an RBC transfusion during their hospital stay. After adjustment for Hunt and Hess grade, SAH grade on CT scans, delay between rupture and surgery, smoking status, and intraoperative aneurysm rupture, a worse outcome was more likely in patients who received intraoperative blood (odds ratio [OR] 2.44, confidence interval [CI] 1.32-4.52; 120 patients). Intraoperative RBC transfusion did not influence subsequent angiographically confirmed vasospasm (OR 0.92, CI 0.6-1.4). Worse outcome was observed in patients who received blood postoperatively (OR 1.81, CI 1.21-2.7), but not after adjustments were made for confounding variables (OR 1.48, CI 0.83-2.63). Angiographic vasospasm was observed in 217 patients and, after adjusting for confounding variables, was more frequent among patients who received postoperative RBC transfusion (OR 1.68, CI 1.02-2.75). Among patients in whom angiographically confirmed vasospasm developed there was a tendency to have received more blood than in those with no vasospasm; however, a clear dose-dependent response was not observed. CONCLUSIONS: Development of angiographically confirmed vasospasm after SAH is associated with postoperative RBC transfusion and worse outcome is associated with intraoperative RBC transfusion. Before blood is transfused, patients with SAH should be carefully assessed to determine if they are symptomatic because of anemia.     

Melanoma patient derived xenografts acquire distinct Vemurafenib resistance mechanisms

Variable clinical responses, tumor heterogeneity, and drug resistance reduce long-term survival outcomes for metastatic melanoma patients. To guide and accelerate drug development, we characterized tumor responses for five melanoma patient derived xenograft models treated with Vemurafenib. Three BRAF^V600E models showed acquired drug resistance, one BRAF^V600E model had a complete and durable response, and a BRAF^V600V model was expectedly unresponsive. In progressing tumors, a variety of resistance mechanisms to BRAF inhibition were uncovered, including mutant BRAF alternative splicing, NRAS mutation, COT (MAP3K8) overexpression, and increased mutant BRAF gene amplification and copy number. The resistance mechanisms among the patient derived xenograft models were similar to the resistance pathways identified in clinical specimens from patients progressing on BRAF inhibitor therapy. In addition, there was both inter- and intra-patient heterogeneity in resistance mechanisms, accompanied by heterogeneous pERK expression immunostaining profiles. MEK monotherapy of Vemurafenib-resistant tumors caused toxicity and acquired drug resistance. However, tumors were eradicated when Vemurafenib was combined the MEK inhibitor. The diversity of drug responses among the xenograft models; the distinct mechanisms of resistance; and the ability to overcome resistance by the addition of a MEK inhibitor provide a scheduling rationale for clinical trials of next-generation drug combinations.     

Aggressive Angiomyxoma of Inguinoscrotal Region Mimicking Inguinal Hernia: a Case Report

Aggressive angiomyxoma (AAM) is a rare mesenchymal tumour of pelvis and perineum, almost exclusively occurring in females. We are reporting a case of a 53-year-old gentleman who presented with a long standing inguinoscrotal swelling misdiagnosed as inguinal hernia, for which he underwent incomplete excision at local hospital and then was referred to our centre for completion surgery.     

Opposite malaria and pregnancy effect on oral bioavailability of artesunate – a population pharmacokinetic evaluation

Aim

The aim was to compare the pharmacokinetic properties of artesunate and dihydroartemisinin in the same women: i) pregnant with acute uncomplicated malaria on day 1 and 2, ii) pregnant with convalescent malaria on day 7 and iii) in a healthy state 3 months post-partum on day 1, 2 and 7.

Methods

Non-linear mixed-effects modelling was used to compare plasma concentration–time profiles of artesunate and dihydroartemisinin over 7 days of treatment following oral and intravenous artesunate administration to pregnant women with uncomplicated Plasmodium falciparum malaria during their second or third trimesters of pregnancy. The same women were restudied 3 months after delivery when fully recovered. Non-compartmental results of the same study have been published previously.

Results

Twenty pregnant patients on the Thailand-Myanmar border were studied and 15 volunteered to be restudied 3 months post-partum. Malaria and pregnancy had no effect on the pharmacokinetic properties of artesunate or dihydroartemisinin after intravenous artesunate administration. However, malaria and pregnancy had opposite effects on the absorption of orally administered artesunate. Malaria increased the absolute oral bioavailability of artesunate by 87%, presumably by inhibiting first pass effect, whereas pregnancy decreased oral bioavailability by 23%.

Conclusions

The population pharmacokinetic analysis demonstrated opposite effects of malaria and pregnancy on the bioavailability of orally administered artesunate. Lower drug exposures during the second and third trimesters of pregnancy may contribute to lower cure rates and thus the development of drug resistance. Dose optimization studies are required for artesunate containing artemisinin-based combination therapies (ACTs) in later pregnancy.     

Plasmodium vivax resistance to chloroquine in Dawei, southern Myanmar

Objective  To assess the efficacy of chloroquine in the treatment of Plasmodium vivax malaria in in Dawei District, southern Myanmar.
Methods  Enrolled patients at Sonsinphya clinic >6 months of age were assessed clinically and parasitologically every week for 28 days. To differentiate new infections from recrudescence, we genotyped pre- and post-treatment parasitaemia. Blood chloroquine was measured to confirm resistant strains.
Results  Between December 2002 and April 2003, 2661 patients were screened, of whom 252 were included and 235 analysed. Thirty-four per cent (95% CI: 28.1–40.6) of patients had recurrent parasitaemia and were considered treatment failures. 59.4% of these recurrences were with a different parasite strain. Two (0.8%) patients with recurrences on day 14 had chloroquine concentrations above the threshold of 100 ng/ml and were considered infected with chloroquine resistant parasites. 21% of failures occurred during the first 3 weeks of follow-up: early recurrence and median levels of blood chloroquine comparable to those of controls suggested P. vivax resistance.
Conclusions  Plasmodium vivax resistance to chloroquine seems to be emerging in Dawei, near the Thai-Burmese border. While chloroquine remains the first-line drug for P. vivax infections in this area of Myanmar, regular monitoring is needed to detect further development of parasite resistance.