Reversible Events Research Articles

Reversible plastic events during oscillatory deformation of amorphous solids.

The effect of oscillatory shear strain on nonaffine rearrangements of individual particles in a three-dimensional binary glass is investigated using molecular dynamics simulations. The amorphous material is represented by the Kob-Andersen mixture at the temperature well below the glass transition. We find that during periodic shear deformation of the material, some particles undergo reversible nonaffine displacements with amplitudes that are approximately power-law distributed. Our simulations show that particles with large amplitudes of nonaffine displacement exhibit a collective behavior; namely, they tend to aggregate into relatively compact clusters that become comparable with the system size near the yield strain. Along with reversible displacements there exist a number of irreversible ones. With increasing strain amplitude, the probability of irreversible displacements during one cycle increases, which leads to permanent structural relaxation of the material.

Estimating the in-vivo HIV template switching and recombination rate

HIV recombination has been estimated in vitro using a variety of approaches, and shows a high rate of template switching per reverse transcription event. In-vivo studies of recombination generally measure the accumulation of recombinant strains over time, and thus do not directly estimate a comparable template switching rate. To examine whether the estimated in-vitro template switching rate is representative of the rate that occurs during HIV infection in vivo, we adopted a novel approach, analysing single genome sequences from early founder viruses to study the in-vivo template switching rate in the env region of HIV. We estimated the in-vivo per cycle template switching rate to be between 0.5 and 1.5/1000 nt, or approximately 5-14 recombination events over the length of the HIV genome. The in-vivo estimated template switching rate is close to the in-vitro estimated rate found in primary T lymphocytes but not macrophages, which is consistent with the majority of HIV infection occurring in T lymphocytes.

Delayed dynamic triggering: Local seismicity leading up to three remote M ≥ 6 aftershocks of the 11 April 2012 M8.6 Indian Ocean earthquake

AbstractThe 11 April 2012 M8.6 strike‐slip Indian Ocean earthquake (IOE) was followed by an increase in global seismic activity, with three remote M ≥ 6.0 earthquakes within 24 h. We investigate delayed dynamic triggering by systematically examining three offshore regions hosting these events for changes in microseismic activity preceding the IOE, and during the hours between the IOE surface‐wave arrival and the triggered‐event candidate. The Blanco Fault Zone, USA, and the Tiburón Fault Zone, Mexico, each host a strike‐slip event, and the Michoacán Subduction Zone, Mexico, hosts a reverse event. At these locations we estimate transient Coulomb stresses of ±1–10 kPa during the IOE. Each study area contains a regional seismic network allowing us to examine continuous waveforms at one or more nearby stations. We implement a short‐/long‐term‐average algorithm and template matching to detect events and assess the seismicity with the β‐statistic. Our results indicate low‐magnitude seismicity in the days prior to the IOE and the occurrence of earthquakes during the surface‐wave passage after more than 2 h of transient loading. We find both transtensional tectonic environments respond to the transient stresses with a substantial increase observed in the seismicity rates during the hours after the passage of surface waves. In contrast, seismicity rates remain constant in the subduction zone we investigate during the 14 h delay between the IOE and the large‐magnitude earthquake. The seismicity rate increases we observe occur after many hours of dynamic stresses and suggest the long duration of transient loading initiated failure processes leading up to these M ≥ 6.0 events.

Electronic interactions in gold(I) complexes of 2,5-diferrocenyl-1-phenyl-1H-phosphole

The synthesis of gold(I) complexes of 2,5-diferrocenyl-1-phenyl-1H-phosphole (1) is presented. Chloro(2,5-diferrocenyl-1-phenyl-1H-phosphole)gold (3) has successfully been prepared by the reaction of 1 with AuCl(SMe2) (2). Treatment of 2 with arylethyne (aryl = ferrocenyl, phenyl) using catalytical amounts of [CuI] and 1 equiv. of 1 gave arylethynyl-(2,5-diferrocenyl-1-phenyl-1H-phosphole)gold 4a and 4b (aryl: a = ferrocenyl; b = phenyl). Compound [μ-(1,4-phenylenedi-2,1-ethynediyl)]bis(2,5-diferrocenyl-1-phenyl-1H-phosphole)digold (5) could be synthesized by a similar procedure using 0.5 equiv. of 1,4-diethynylbenzene. The electrochemical properties of 3, 4a,b and 5 were investigated by cyclic and square wave voltammetry. In 3, 4a and 4b each ferrocenyl unit shows one reversible redox event with redox separations of the ferrocenyl moieties in 2,5 position of approximately 260 mV. In 5 two redox events for the four ferrocenyl groups were observed. Spectroelectrochemical measurements of 3, 4a and 4b reveal IVCT absorptions with intensities of 1100–1300 L mol−1 cm−1 and a full-width-at-half-height of ≈3650 cm−1. In 5 two mixed-valent units are present per molecule and therefore, the intensity of the IVCT band is increased to 2700 L mol−1 cm−1. Compounds 3, 4a,b and 5 can be classified as moderately coupled class II systems according to Robin and Day. The complexation of the gold(I) fragment by the phosphorus atom leads to a decreased metal–metal interaction when compared to 1.

Clonal Reversion in Genetic Syndromes: Gene Therapy at Its Best

Many genetic syndromes are characterized by a wide spectrum of clinical severity. Even within one family clinical presentations can show extreme variation. Mosaic tissue distribution caused by spontaneous correction of a germline pathogenic allele is one of multiple explanations for variety in phenotypic expression of an inherited mutation. This phenomenon, called somatic reversion, is infrequently observed and can be easily overlooked. Reversion needs to be considered if a person presents with a milder than expected clinical course or with a mixture of phenotypically normal and abnormal cells.1 Mechanisms that may explain reversion include mitotic gene conversion, back mutation, intragenic mitotic recombination and the occurrence of compensatory mutations.A mosaic pattern of somatic reversion only becomes apparent if several criteria are met. The non-mutant cells need to have a selective growth advantage over surrounding mutant cells. Furthermore, to facilitate expansion of the revertant clone the affected genes need to be expressed in regenerating organ systems like skin and blood.1 The chance of spontaneous correction of a pathogenic allele is likely increased in diseases with an underlying mechanism resulting in genomic instability or high mutation rates, like Bloom syndrome and Fanconi anemia, which are both caused by gene defects in DNA repair pathways.2,3 In skin disorders an evolving mosaic revertant pattern is easily visible. Ichthyosis with confetti, caused by mutations in KRT10, is an example of a skin disorder displaying multiple events of reversion.4 In this condition, normal skin spots appear early in life and increase in number and size over time. Each normal spot results from a separate event of loss of heterozygosity on chromosome 17q, which harbors KRT10, via mitotic recombination. Also in the genetic skin fragility disorder epidermolysis bullosa revertant mosaicism has been described repeatedly.5,6We have observed reversion, caused by mitotic recombination of mutant TE RC (telomerase RNA component) alleles in a family affected by dyskeratosis congenita (DC).7 DC is a multisystem disorder characterized amongst others by bone marrow failure and lung fibrosis. The observation of mosaic stretches of uniparental disomy (UPD) of chromosome 3q as an indication of revertant mosaicism encouraged us to develop a highly sensitive method for detecting genomic regions with low mosaic UPD in SNP array data. Indeed this tool supported us in identifying additional cases of DC and a mosaic reversion pattern in blood cells. Revertant mosaicism being a recurrent event in DC related conditions was recently confirmed by others.8Awareness of revertant mosaicism is important for improving diagnostic testing. In DC for instance it is common practice that analysis of the DC genes is performed on DNA isolated from peripheral blood cells. In case no pathogenic mutation is found, an obvious conclusion can be that the phenotype in the family is caused by an aberration in an as yet to be identified DC gene. Based on our findings, we recommend sequence analysis on DNA extracted from other cells, such as skin fibroblasts, particularly in individuals without bone marrow failure.The observation of reversion in hematological conditions is also of importance for the development of future therapies: Isolation of autologous reverted stem cells can probably circumvent more toxic and harmful therapies, like allogeneic stem cell transplantation, in a subset of individuals.1. Hirschhorn R. In vivo reversion to normal of inherited mutations in humans. J Med Genet 2003;40 (10):721-728.2 Ellis NA, Ciocci S, German J. Back mutation can produce phenotype reversion in Bloom syndrome somatic cells. Hum Genet 2001;108 (2):167-173.3 Waisfisz Q, Morgan NV, Savino M, et al. Spontaneous functional correction of homozygous fanconi anaemia alleles reveals novel mechanistic basis for reverse mosaicism. Nat Genet 1999;22 (4):379-383.4 Choate KA, Lu Y, Zhou J, et al. Mitotic recombination in patients with ichthyosis causes reversion of dominant mutations in KRT10. Science 2010;330 (6000):94-97.5 Jonkman MF, Scheffer H, Stulp R, et al. Revertant mosaicism in epidermolysis bullosa caused by mitotic gene conversion. Cell 1997;88 (4):543-51.6 Kiritsi D, Garcia M, Brander R, et al. Mechanisms of natural gene therapy in dystrophic epidermolysis bullosa. J Invest Dermatol 2014;134 (8):2097-104.7 Jongmans MC, Verwiel ET, Heijdra Y, et al. Revertant somatic mosaicism by mitotic recombination in dyskeratosis congenita. Am J Hum Genet 2012;90 (3):426-33.8 Alder JK, Stanley SE, Wagner CL, et al. Exome Sequencing Identifies Mutant TINF2 in a Family With Pulmonary Fibrosis. Chest 2015;147 (5):1361-8. DisclosuresNo relevant conflicts of interest to declare.

Anomalous Near-Surface Low-Salinity Pulses off the Central Oregon Coast.

From mid-May to August 2011, extreme runoff in the Columbia River ranged from 14,000 to over 17,000 m3/s, more than two standard deviations above the mean for this period. The extreme runoff was the direct result of both melting of anomalously high snowpack and rainfall associated with the 2010–2011 La Niña. The effects of this increased freshwater discharge were observed off Newport, Oregon, 180 km south of the Columbia River mouth. Salinity values as low as 22, nine standard deviations below the climatological value for this period, were registered at the mid-shelf. Using a network of ocean observing sensors and platforms, it was possible to capture the onshore advection of the Columbia River plume from the mid-shelf, 20 km offshore, to the coast and eventually into Yaquina Bay (Newport) during a sustained wind reversal event. Increased freshwater delivery can influence coastal ocean ecosystems and delivery of offshore, river-influenced water may influence estuarine biogeochemistry.

Timescales and Frequencies of Reversible and Irreversible Adhesion Events of Single Bacterial Cells.

In the environment, most bacteria form surface-attached cell communities called biofilms. The attachment of single cells to surfaces involves an initial reversible stage typically mediated by surface structures such as flagella and pili, followed by a permanent adhesion stage usually mediated by polysaccharide adhesives. Here, we determine the absolute and relative timescales and frequencies of reversible and irreversible adhesion of single cells of the bacterium Caulobacter crescentus to a glass surface in a microfluidic device. We used fluorescence microscopy of C. crescentus expressing green fluorescent protein to track the swimming behavior of individual cells prior to adhesion, monitor the cell at the surface, and determine whether the cell reversibly or irreversibly adhered to the surface. A fluorescently labeled lectin that binds specifically to polar polysaccharides, termed holdfast, discriminated irreversible adhesion events from reversible adhesion events where no holdfast formed. In wild-type cells, the holdfast production time for irreversible adhesion events initiated by surface contact (23 s) was 30-times faster than the holdfast production time that occurs through developmental regulation (13 min). Irreversible adhesion events in wild-type cells (3.3 events/min) are 15-times more frequent than in pilus-minus mutant cells (0.2 events/min), indicating the pili are critical structures in the transition from reversible to irreversible surface-stimulated adhesion. In reversible adhesion events, the dwell time of cells at the surface before departing was the same for wild-type cells (12 s) and pilus-minus mutant cells (13 s), suggesting the pili do not play a significant role in reversible adhesion. Moreover, reversible adhesion events in wild-type cells (6.8 events/min) occur twice as frequently as irreversible adhesion events (3.3 events/min), demonstrating that most cells contact the surface multiple times before transitioning from reversible to irreversible adhesion.

Synaptically Localized Mitogen-Activated Protein Kinases: Local Substrates and Regulation.

Mitogen-activated protein kinases (MAPKs) are expressed in postmitotic neurons and act as important regulators in intracellular signaling. In addition to their nuclear distribution and roles in regulating gene expression, MAPKs, especially the extracellular signal-regulated kinase (ERK) subclass, reside in peripheral dendritic spines and synapses, including the postsynaptic density (PSD) microdomain. This peripheral pool of MAPKs/ERKs is either constitutively active or sensitive to changing synaptic input. Active MAPKs directly interact with and phosphorylate local substrates to alter their trafficking and subcellular/subsynaptic distributions, through which MAPKs regulate function of substrates and contribute to long-lasting synaptic plasticity. A number of physiologically relevant substrates of MAPKs have been identified at synaptic sites. Central among them are key synaptic scaffold proteins (PSD-95 and PSD-93), cadherin-associated proteins (δ-catenin), Kv4.2 K+ channels, and metabotropic glutamate receptors. Through a reversible phosphorylation event, MAPKs rapidly and efficiently modulate the function of these substrates and thus determine the strength of synaptic transmission. This review summarizes the recent progress in cell biology of synaptic MAPKs and analyzes roles of this specific pool of MAPKs in regulating local substrates and synaptic plasticity.

Nitric oxide activation by distal redox modulation in tetranuclear iron nitrosyl complexes.

A series of tetranuclear iron complexes displaying a site-differentiated metal center was synthesized. Three of the metal centers are coordinated to our previously reported ligand, based on a 1,3,5-triarylbenzene motif with nitrogen and oxygen donors. The fourth (apical) iron center is coordinatively unsaturated and appended to the trinuclear core through three bridging pyrazolates and an interstitial μ4-oxide moiety. Electrochemical studies of complex [LFe3(PhPz)3OFe][OTf]2 revealed three reversible redox events assigned to the Fe(II)4/Fe(II)3Fe(III) (-1.733 V), Fe(II)3Fe(III)/Fe(II)2Fe(III)2 (-0.727 V), and Fe(II)2Fe(III)2/Fe(II)Fe(III)3 (0.018 V) redox couples. Combined Mössbauer and crystallographic studies indicate that the change in oxidation state is exclusively localized at the triiron core, without changing the oxidation state of the apical metal center. This phenomenon is assigned to differences in the coordination environment of the two metal sites and provides a strategy for storing electron and hole equivalents without affecting the oxidation state of the coordinatively unsaturated metal. The presence of a ligand-binding site allowed the effect of redox modulation on nitric oxide activation by an Fe(II) metal center to be studied. Treatment of the clusters with nitric oxide resulted in binding of NO to the apical iron center, generating a {FeNO}(7) moiety. As with the NO-free precursors, the three reversible redox events are localized at the iron centers distal from the NO ligand. Altering the redox state of the triiron core resulted in significant change in the NO stretching frequency, by as much as 100 cm(-1). The increased activation of NO is attributed to structural changes within the clusters, in particular, those related to the interaction of the metal centers with the interstitial atom. The differences in NO activation were further shown to lead to differential reactivity, with NO disproportionation and N2O formation performed by the more electron-rich cluster.

Coercivity and morphology in Fe/NiO films deposited on nanoporous Al2O3 membranes

The occurrence of ferro-antiferromagnetic (F/AF) interfaces in Fe/NiO bilayers brings about the possibility of controlling the Fe layer hysteretic properties through the unidirectional anisotropy induced by the presence of unbalanced, antiferromagnetic phase moments at that interface. In this work, we report on the Fe thickness and temperature dependencies of the hysteretic parameters measured in Fe/NiO bilayers deposited on Al2O3 nanoporous membranes. The Fe/NiO bilayers grew in a six-fold columnar way around each one of the membrane nanopores. The in-plane hysteresis loops measured by field cooling the samples down to different temperatures below 300K, evidenced the occurrence of coercive forces larger than that associated to the Fe anisotropy field and also of significant loop shifts, both of them clearly linked to the occurrence of exchange bias at the Fe/NiO interfaces. The magnetization reversal mechanism active in the Fe/NiO bilayers essentially differs from that responsible for the reversal occurring in continuous films incorporating lithographed antidots, due to the fact that in our samples it does not involve either domain wall propagation or pinning, and the reversal events are spatially restricted to the Fe-covered, hexagonally closely packed dot-like tops of the NiO columns.

Alternative translation initiation codons for the plastid maturase MatK: unraveling the pseudogene misconception in the Orchidaceae.

BackgroundThe plastid maturase MatK has been implicated as a possible model for the evolutionary “missing link” between prokaryotic and eukaryotic splicing machinery. This evolutionary implication has sparked investigations concerning the function of this unusual maturase. Intron targets of MatK activity suggest that this is an essential enzyme for plastid function. The matK gene, however, is described as a pseudogene in many photosynthetic orchid species due to presence of premature stop codons in translations, and its high rate of nucleotide and amino acid substitution.ResultsSequence analysis of the matK gene from orchids identified an out-of-frame alternative AUG initiation codon upstream from the consensus initiation codon used for translation in other angiosperms. We demonstrate translation from the alternative initiation codon generates a conserved MatK reading frame. We confirm that MatK protein is expressed and functions in sample orchids currently described as having a matK pseudogene using immunodetection and reverse-transcription methods. We demonstrate using phylogenetic analysis that this alternative initiation codon emerged de novo within the Orchidaceae, with several reversal events at the basal lineage and deep in orchid history.ConclusionThese findings suggest a novel evolutionary shift for expression of matK in the Orchidaceae and support the function of MatK as a group II intron maturase in the plastid genome of land plants including the orchids.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0491-1) contains supplementary material, which is available to authorized users.

Amphiphilic Elastin-Like Block Co-Recombinamers Containing Leucine Zippers: Cooperative Interplay between Both Domains Results in Injectable and Stable Hydrogels.

Many biological processes are regulated by reversible binding events, with these interactions between macromolecules representing the core of dynamic chemistry. As such, any attempt to gain a better understanding of such interactions, which would pave the way to the extrapolation of natural designs to create new advanced systems, is clearly of interest. This work focuses on the development of a leucine zipper-elastin-like recombinamer (ZELR) in order to elucidate the behavior of such domains when coexisting along the same molecule and to engineer reversible, injectable and stable hydrogels. The unique propensity of the Z-moiety selected to dimerize, together with the thermosensitive behavior of the ELR, which has been constructed as a thermosensitive amphiphilic tetrablock, has been engineered into a single recombinant molecule. In this molecular design, the Z-moieties are unable to form a network, while the ELR is below its Tt, thus, guaranteeing the liquid-like state of the system. However, this situation changes rapidly as the temperature increases above Tt, where a stable hydrogel is formed, as demostrated by rheological tests. The inability of the ELR molecule (without Z-domains) to form such a stable hydrogel above Tt clearly points to a positive cooperative effect between these two domains (Z and EL), and no conformational changes in the former are involved, as demonstrated by circular dichroism analysis. AFM shows that Z-motifs seem to induce the aggregation of micelles, which supports the enhanced stability displayed by ZELRs when compared to ELR at the macroscale level. To the best of our knowledge, this is the first time that such an interplay between these two domains has been reported. Furthermore, the cytocompatibility of the resulting hydrogels opens the door to their use in biomedical applications.

Ichthyosis with confetti: clinics, molecular genetics and management.

Ichthyosis with confetti (IWC) is an autosomal dominant congenital ichthyosis also known as ichthyosis variegata or congenital reticular ichthyosiform erythroderma. It manifests at birth with generalized ichthyosiform erythroderma or with a collodion baby picture. The erythrodermic and ichthyotic phenotype persists during life and its severity may modify. However, the hallmark of the disease is the appearance, in childhood or later in life, of healthy skin confetti-like spots, which increase in number and size with time. IWC is a very rare genodermatosis, with a prevalence <1/1,000,000 and only 40 cases reported worldwide. The most important associated clinical features include ear deformities, mammillae hypoplasia, palmoplantar keratoderma, hypertrichosis and ectropion. IWC is due to dominant negative mutations in the KRT10 and KRT1 genes, encoding for keratins 10 and keratin 1, respectively. In this context, healthy skin confetti-like spots represent “repaired” skin due to independent events of reversion of keratin gene mutations via mitotic recombination. In most cases, IWC clinical suspicion is delayed until the detection of white skin spots. Clinical features, which may represent hint to the diagnosis of IWC even before appearance of confetti-like spots, include ear and mammillae hypoplasia, the progressive development of hypertrichosis and, in some patients, of adherent verrucous plaques of hyperkeratosis. Altogether the histopathological finding of keratinocyte vacuolization and the nuclear staining for keratin 10 and keratin 1 by immunofluorescence are pathognomonic. Nevertheless, mutational analysis of KRT10 or KRT1 genes is at present the gold standard to confirm the diagnosis. IWC has to be differentiated mainly from congenital ichthyosiform erythroderma. Differential diagnosis also includes syndromic ichthyoses, in particular Netherton syndrome, and the keratinopathic ichthyoses. Most of reported IWC cases are sporadic, but familial cases with autosomal dominant mode of inheritance have been also described. Therefore, knowledge of the mutation is the only way to properly counsel the couples. No specific and satisfactory therapy is currently available for IWC. Like for other congenital ichthyoses, topical treatments (mainly emollients and keratolytics) are symptomatic and offer only temporary relief. Among systemic treatments, retinoids, in particular acitretin, improve disease symptoms in most patients. Although at present there is no curative therapy for ichthyoses, treatments have improved considerably over the years and the best therapy for each patient is always the result of both physician and patient efforts.Electronic supplementary materialThe online version of this article (doi:10.1186/s13023-015-0336-4) contains supplementary material, which is available to authorized users.

Synthesis and characterization of the gold dithiolene monoanion, (Bu4N)[Au(pdt = 2,3-pyrazinedithiol)2

We report the first synthesis and isolation of the gold dithiolene complex (Bu4N)[Au(pdt=2,3-pyrazinedithiol)2]. We characterize this complex using X-ray crystallography, infrared spectroscopy, cyclic voltammetry, and UV–Vis spectroscopy. The title complex is structurally similar to other gold dithiolene complexes. We find that the monoanion and dianion are linked by a reversible electrochemical event, but electrochemical generation of other redox states are irreversible processes. Generation of the dianion and protonation of the monoanion lead to reversible changes in the UV–Vis spectroscopy – primarily for the HOMO−1→LUMO transition.

Angiographic findings of in-stent intimal hyperplasia after stent-assisted coil embolization: are they permanent findings?

Stent-assisted coil embolization for the treatment of intracranial aneurysms has been used widely. This study aimed to investigate the effect of stent implantation in the nonatherosclerotic parent artery with cerebral aneurysms. The authors evaluated luminal changes and the related factors following stent-assisted coil embolization. This study included 97 patients harboring a total of 99 unruptured aneurysms of the distal internal carotid artery (ICA) who underwent single-stent implantation and more than 1 session of conventional angiography during follow-up (midterm follow-up only, n = 70; midterm and long-term follow-up, n = 29) between January 2009 and April 2014. The luminal narrowing point was measured using a local thickness map (ImageJ plug-in). Stent-assisted coil embolization caused dynamic luminal narrowing of approximately 82% of the parent artery diameter on average after 8 months, which was reversed to 91% after 25 months. In addition, luminal narrowing greater than 40% was noticed in 2 (7%) of the 29 patients who experienced spontaneous reversion without additional management during follow-up. Most luminal narrowing changes seen were diffuse. Luminal narrowing after aneurysm stent-assisted coil embolization is a dynamic process and appears to be a spontaneously reversible event. Routine management of luminal narrowing may not cause adverse events that require additional treatment.

Redox-Switchable Chiral Anions and Cations Based on Heteroatom-Fused Biferrocenes

A new class of planar chiral heteroatom-bridged biferrocene species was prepared using (pR,pR,SS,SS)-2,2″-bis(p-tolylsulfinyl)-1,1″-biferrocene (pR,pR,SS,SS)-2 as a readily accessible precursor. Initially, one of the sulfinate groups in compound 2 is replaced with a trimethylstannyl or dimesitylboryl group. Replacement of the second sulfinate group with t-BuLi then results in cyclization to give the Me2Sn-bridged species (pS,pS)-4Sn and the Mes2B-bridged borate anion [(pS,pS)-4B]−. The products are redox active, as cyclic and square wave voltammetry data of (pS,pS)-4Sn and [Li(12-c-4)2][(pS,pS)-4B] reveal two separate reversible oxidation events. The mixed-valent species [(pS,pS)-4Sn]+ and (pS,pS)-4B can also be obtained by chemical oxidation with AgPF6 or by simple exposure to air, respectively. A comparison of X-ray crystal structures reveals that the oxidized (mixed-valent) species contain distinct Fe(II) and Fe(III) sites, but UV–visible–NIR spectra display IVCT bands at ca. 4000 and 5000 cm–1, indica...

A phase II dose-escalation trial of perioperative desmopressin (1-desamino-8-d-arginine vasopressin) in breast cancer patients.

Desmopressin (dDAVP) is a well-known peptide analog of the antidiuretic hormone vasopressin, used to prevent excessive bleeding during surgical procedures. dDAVP increases hemostatic mediators, such as the von Willebrand factor (vWF), recently considered a key element in resistance to metastasis. Studies in mouse models and veterinary trials in dogs with locally-advanced mammary tumors demonstrated that high doses of perioperative dDAVP inhibited lymph node and early blood-borne metastasis and significantly prolonged survival. We conducted a phase II dose-escalation trial in patients with breast cancer, administering a lyophilized formulation of dDAVP by intravenous infusion in saline, 30–60 min before and 24 h after surgical resection. Primary endpoints were safety and tolerability, as well as selection of the best dose for cancer surgery. Secondary endpoints included surgical bleeding, plasma levels of vWF, and circulating tumor cells (CTCs) as measured by quantitative PCR of cytokeratin-19 transcripts. Only 2 of a total of 20 patients experienced reversible adverse events, including hyponatremia (grade 4) and hypersensitivity reaction (grade 2). Reactions were adequately managed by slowing the infusion rate. A reduced intraoperative bleeding was noted with increasing doses of dDAVP. Treatment was associated with higher vWF plasma levels and a postoperative drop in CTC counts. At the highest dose level evaluated (2 μg/kg) dDAVP appeared safe when administered in two slow infusions of 1 μg/kg, before and after surgery. Clinical trials to establish the effectiveness of adjunctive perioperative dDAVP therapy are warranted. This trial is registered on www.clinicaltrials.gov (NCT01606072).

Abstract 2984: Heterogeneous mechanisms of acquired resistance in high grade serous ovarian cancer

Abstract In contrast to other solid cancers, overall survival for patients with high-grade serous ovarian cancer (HGSC) is little changed over the last 30 years and it has been difficult to advance beyond platinum-based combination chemotherapy. As HGSC are driven by genomic copy number change rather than recurrent point mutation, we undertook whole genome sequence (WGS) analysis of a large HGSC cohort in order to survey structural variation at high resolution. Utilizing 114 tumours from 92 patients, we performed transcriptome, methylation, and miRNA expression analyses to support the WGS data, and compared resistant, refractory, and sensitive primary disease. We evaluated tumour and normal DNA samples from patients with primary refractory, primary resistant or primary sensitive disease to better understand the drivers of these clinical phenotypes. We also characterized paired pre-treatment chemosensitive and post-resistance samples, and end-stage HGSC obtained from patients who underwent a research autopsy. We found that gene breakage involving tumour suppressors such as NF1 and RB1 is a common form of inactivation in HGSC and in other circumstances contributes to acquired chemotherapy resistance in some patients. We found evidence of a chemotherapy footprint in the genome of recurrent tumour samples. We observed a striking degree of diversity of other mechanisms of acquired resistance, including multiple independent germline BRCA1 or BRCA2 reversion events in individual patients, loss of BRCA1 promoter methylation, a shift in molecular subtype to a desmoplastic phenotype, and a recurrent promoter fusion associated with overexpression of a driver of drug resistance, validated in an independent dataset. Collectively our findings underscore the plasticity of the HGSC genome and indicate that pre-empting resistance by modifying current first line therapy or countering it when it emerges will require a diversity of approaches. Citation Format: David D L Bowtell. Heterogeneous mechanisms of acquired resistance in high grade serous ovarian cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2984. doi:10.1158/1538-7445.AM2015-2984

3D Imaging of Fuel Cell Electrode Structure Degraded under Cell Voltage Reversal Conditions Using Nanoscale X-Ray Computed Tomography

Polymer electrolyte fuel cells (PEFCs) have gained significant attention as highly efficient and clean power sources for fuel cell electric vehicles (FCEVs). One challenge faced by PEFCs is hydrogen starvation at the anode that can arise from either malfunction of the hydrogen supply system or hydrogen passage blockage by water flooding, ice formation in wintertime, or foreign impurities [1,2]. In particular, hydrogen starvation could be exacerbated when FCEVs are operated under transient conditions such as start-up and rapid load change. When the anode is starved of hydrogen, the anode requires an additional source of protons and its potential increases until the cell potential reverses and water electrolysis occurs, typically followed by carbon corrosion at higher potentials. These cell voltage reversal events eventually lead to catastrophic cell failure [2]. In order to develop highly robust FCEVs, it is important to understand the detailed morphological change in fuel cell electrodes under cell voltage reversal conditions. Over the last few years, nano-scale X-ray computed tomography (nano-CT) with the ability to image within samples in a non-invasive and non-destructive nature has been adopted to investigate the three-dimensional (3D) structure of fuel cell electrodes [3,4]. However, visualization of the 3D structure of degraded electrodes using nano-CT has been lacking, with a key challenge being the extraction of undisturbed samples from end-of-life (EOL) cells. Here we present the morphological analysis of fuel cell electrodes degraded under cell voltage reversal conditions by nano-CT using high precision laser micro-milling for sample preparation. The value in nano-CT imaging is the ability to image internal 3D structure without surface sample preparation artifacts. A standard membrane-electrode assembly (MEA) consisting of typical membrane (Nafion® NRE211CS (H+), DuPont) and electrodes (Pt/C catalyst (HISPEC4000®, Johnson Matthey) and ionomer binder (Nafion® D2021, DuPont)) was used throughout the study. An in-house 4 cm2 MEA was produced through a decal transfer process using a polyimide (Kapton® HN, DuPont) film. Under hydrogen (anode) and air (cathode) conditions, a single fuel cell was fully activated and then the beginning-of-life (BOL) polarizations were measured at 65oC and 100 % relative humidity. Cell voltage reversal tests were performed by operating the fuel cell at 0.2 A cm-2 under nitrogen (anode) and air (cathode) conditions until the cell voltage reached -2 V using a potentiostat. Cell polarization curves were measured after each reversal test. When the cell voltage at 1.2 A cm-2 was reduced to 34% of its BOL value, the cell status was considered to be at EOL. The EOL MEA sample was taken out of the cell for post-mortem analysis. A nano-scale resolution X-ray computed tomography microscope (UltraXRM-L200, Carl Zeiss X-ray Microscopy) was used for resolving the electrode structures as described in literature [3,4]. For sample preparation, a razor blade was used to cut out a small area of MEA (ca. 1.0 x 0.7 mm). The anode side of the MEA was ablated using a high-precision (~ 1 μm) laser mill (QuickLaze 50ST2, ESI®), leaving only the pillar-shaped anode specimen of approximately 65 μm in diameter on the membrane surface. Figure 1(a) shows the polarization curves of the MEA measured after cell voltage reversal tests. The cell performance decreases significantly as the voltage reversal tests were repeated, which may be attributed to combined degradation due to carbon corrosion at anode and an increased Ohmic resistance as characterized by electrochemical impedance spectroscopy and in-situ cyclic voltammetry. Figure 1(b) represents the nano-CT image of the EOL anode in the MEA. It is found that the thickness of the EOL anode is reduced by approximately 50%, from about 4 μm to 2 μm (EOL), implying a severe carbon corrosion at anode during the cell voltage reversal tests. The interface between the membrane and electrode appears mostly intact over the interface area, a feature difficult to observe from 2D SEM cross-sections, indicating that the increased Ohmic resistance could be mainly related with the structural collapse of anode, but not with a significant delamination at the interface. A variety of post-mortem analysis data will be presented to further elucidate the fundamental aspects of the cell voltage reversal degradation.

The Réunion Subchron vegetation and climate history of the northeastern Russian Arctic inferred from the Lake El'gygytgyn pollen record

Abstract The 318-m-thick sediment record from Lake El'gygytgyn provides unique opportunities for a detailed examination of environmental changes during the Reunion Subchron polarity reversal event (2.1384–2.1216 Myr BP) in the northeastern Russian Arctic. The paper describes vegetation and climate fluctuations between ~ 2.15 and 2.10 Myr BP as inferred from palynological data. Biome reconstructions indicate that throughout this interval the tundra (TUND) biome generally has higher affinity scores as compared to cold steppe (STEP) or cold deciduous forest (CLDE). An exception is the climatic optimum between ~ 2.139 and 2.131 Myr BP, coinciding with Marine Isotope Stage 81 (approximately the Reunion Subchron), when the CLDE biome has the highest scores. Landscape-openness indices suggest that more closed vegetation characterized most of the interval between 2.146 and 2.127 Myr BP, when deciduous forest and shrubs expanded in the regional vegetation and climate was relatively warm and wet. Peaks in green algal colonies (Botryococcus) and Zygnema-type spores ~ 2.150–2.146, ~ 2.131–2.123, and ~ 2.112–2.102 Myr BP indicate expansions of shallow-water habitats and lowered lake levels. Comparisons with biome reconstructions from other interglacial intervals at Lake El'gygytgyn suggest that precession-related summer insolation intensity and obliquity-related duration of summer daylight are major controls on the onset of interglaciations, whereas obliquity probably plays a more significant role on vegetation succession at northern high latitudes during the Pleistocene.