Tetraphenyl-1,4-dioxin and Tetraphenyl-pyrane-4-one: Old Molecules, New Insights

Aggregation-induced emission (AIE) is a phenomenon where certain molecules or materials become highly luminescent when they aggregate or come together in a condensed state, such as a solid or a solution. Moreover, new molecules which show AIE properties are designed and synthesized for various applications like imaging, sensing, and optoelectronics. 2,3,5,6-Tetraphenylpyrazine (TPP) is one of the well-established examples of AIE. Herein, 2,3,5,6-tetraphenyl-1,4-dioxin (TPD) and 2,3,4,5-tetraphenyl-4H-pyran-4-one (TPPO), which are old molecules with TPP similarity, were studied, and new insights in terms of structure and aggregation-caused quenching (ACQ)/AIE properties were gained by means of theoretical calculations. Those calculations performed on TPD and TPPO aimed to provide a better understanding of their molecular structures and how they affect their luminescence properties. This information could be used to design new materials with improved AIE properties or to modify existing materials to overcome ACQ.

Activity-Based Photosensitizers with Optimized Triplet State Characteristics Toward Cancer Cell Selective and Image Guided Photodynamic Therapy

Activity-based theranostic photosensitizers are highly attractive in photodynamic therapy as they offer enhanced therapeutic outcome on cancer cells with an imaging opportunity at the same time. However, photosensitizers (PS) cores that can be easily converted to activity-based photosensitizers (aPSs) are still quite limited in the literature. In this study, we modified the dicyanomethylene-4H-chromene (DCM) core with a heavy iodine atom to get two different PSs (DCM_O-I, I-DCM_O-Cl) that can be further converted to aPS after simple modifications. The effect of iodine positioning on singlet oxygen generation capacity was also evaluated through computational studies. DCM_O-I showed better performance in solution experiments and further proved to be a promising phototheranostic scaffold via cell culture studies. Later, a cysteine (Cys) activatable PS based on the DCM_O-I core (DCM_O-I-Cys) was developed, which induced selective photocytotoxicity along with a fluorescence turn-on response in Cys rich cancer cells.

The Q41R mutation in the HCV-protease enhances the reactivity towards MAVS by suppressing non-reactive pathways

Recent experimental findings pointed out a new mutation in the HCV protease, Q41R, responsible for a significant enhancement of the enzyme's reactivity towards the mitochondrial antiviral-signaling protein (MAVS). The Q41R mutation is located rather far from the active site, and its involvement in the overall reaction mechanism is thus unclear. We used classical molecular dynamics and QM/MM to study the acylation reaction of HCV NS3/4A protease variants bound to MAVS and the NS4A/4B substrate and uncovered the indirect mechanism by which the Q41R mutation plays a critical role in the efficient cleavage of the substrate. Our simulations reveal that there are two major conformations of the MAVS H1'(p) residue for the wild type protease and only one conformation for the Q41R mutant. The conformational space of H1'(p) is restricted by the Q41R mutation due to a π-π stacking between H1'(p) and R41 as well as a strong hydrogen bond between the backbone of H57 and the side chain of R41. Further QM/MM calculations indicate that the complex with the conformation ruled out by the Q41R substitution is a non-reactive species due to its higher free energy barrier for the acylation reaction. Based on our calculations, we propose a kinetic mechanism that explains experimental data showing an increase of apparent rate constants for MAVS cleavage in Q41R mutants. Our model predicts that the non-reactive conformation of the enzyme-substrate complex modulates reaction kinetics like an uncompetitive inhibitor.

Peptide stapling by late-stage Suzuki–Miyaura cross-coupling

The development of peptide stapling techniques to stabilise α-helical secondary structure motifs of peptides led to the design of modulators of protein–protein interactions, which had been considered undruggable for a long time. We disclose a novel approach towards peptide stapling utilising macrocyclisation by late-stage Suzuki–Miyaura cross-coupling of bromotryptophan-containing peptides of the catenin-binding domain of axin. Optimisation of the linker length in order to find a compromise between both sufficient linker rigidity and flexibility resulted in a peptide with an increased α-helicity and enhanced binding affinity to its native binding partner β-catenin. An increased proteolytic stability against proteinase K has been demonstrated.

Fullerene-Based Mimics of Biocatalysts Show Remarkable Activity and Modularity

The design of catalysts with greater control over catalytic activity and stability is a major challenge with substantial impact on fundamental chemistry and industrial applications. Due to their unparalleled diversity, selectivity, and efficiency, enzymes are promising models for next-generation catalysts, and considerable efforts have been devoted to incorporating the principles of their mechanisms of action into artificial systems. We report a heretofore undocumented catalyst design that introduces fullerenes to the field of biocatalysis, which we refer to as fullerene nanocatalysts, and that emulates enzymatic active sites through multifunctional self-assembled nanostructures. As a proof-of-concept, we mimicked the reactivity of hydrolases using fullerene nanocatalysts functionalized with the basic components of the parent enzyme with remarkable activity. Owing to the versatile amino acid-based functionalization repertoire of fullerene nanocatalysts, these next-generation carbon/biomolecule hybrids have potential to mimic the activity of other families of enzymes and, therefore, offer new perspectives for the design of biocompatible, high-efficiency artificial nanocatalysts.

Evaluating the presence of SARS-CoV-2 RNA in the particulate matters during the peak of COVID-19 in Padua, northern Italy

The airborne transmission of SARS-CoV-2, the etiologic agent of the current COVID-19 pandemic, has been hypothesized as one of the primary routes of transmission. Current data suggest a low probability of airborne transmission of the virus in open environments and a higher probability in closed ones, particularly in hospitals or quarantine facilities. However, the potential diffusion of the virus in open environments, especially using particulate matter (PM) as a transport carrier, generated concern in the exposed populations. Several authors found a correlation between the exceeding of the PM10 concentration limits in some Italian cities and the prevalence of Covid-19 cases detected in those areas. This study investigated the potential presence of SARS-COV-2 RNA on a representative series of PM samples collected in the province of Padua in Northeastern Italy during the first wave of COVID pandemic. Forty-four samples of PM2.5 and PM10 were collected between February 24 and March 9, 2020 and analyzed with RT-qPCR for SARS-CoV-2 RNA. The experimental results did not indicate the presence of SARS-CoV-2 RNA in the outdoor PMs, thus confirming the low probability of virus airborne transmission through PM.

Peptidotriazolamers Inhibit Aβ(1-42) Oligomerization and Cross a Blood-Brain-Barrier Model

In peptidotriazolamers every second peptide bond is replaced by a 1H-1,2,3-triazole. Such foldamers are expected to bridge the gap in molecular weight between small-molecule drugs and protein-based drugs. Amyloid β (Aβ) aggregates play an important role in Alzheimer's disease. We studied the impact of amide bond replacements by 1,4-disubstituted 1H-1,2,3-triazoles on the inhibitory activity of the aggregation "hot spots" K¹⁶ LVFF²⁰ and G³⁹ VVIA⁴² in Aβ(1-42). We found that peptidotriazolamers act as modulators of the Aβ(1-42) oligomerization. Some peptidotriazolamers are able to interfere with the formation of toxic early Aβ oligomers, depending on the position of the triazoles, which is also supported by computational studies. Preliminary in vitro results demonstrate that a highly active peptidotriazolamer is also able to cross the blood-brain-barrier.

Tuning the Biological Activity of RGD Peptides with Halotryptophans†

An array of l- and d-halotryptophans with different substituents at the indole moiety was synthesized employing either enzymatic halogenation by halogenases or incorporation of haloindoles using tryptophan synthase. Introduction of these Trp derivatives into RGD peptides as a benchmark system was performed to investigate their influence on bioactivity. Halotryptophan-containing RGD peptides display increased affinity toward integrin α_vβ₃ and enhanced selectivity over integrin α₅β₁. In addition, bromotryptophan was exploited as a platform for late-stage diversification by Suzuki-Miyaura cross-coupling (SMC), resulting in new-to-nature biaryl motifs. These peptides show enhanced affinity toward α_vβ₃, good affinity to α_vβ₈, and remarkable selectivity over α₅β₁ and α_IIbβ₃ while featuring fluorogenic properties. Their feasibility as a probe was demonstrated in vitro. Extensive molecular dynamics simulations were undertaken to elucidate NMR and high-performance liquid chromatography (HPLC) data for these late-stage diversified cyclic RGD peptides and to further characterize their conformational preferences.

Extended interaction networks with HCV protease NS3-4A substrates explain the lack of adaptive capability against protease inhibitors

Inhibitors against the NS3-4A protease of hepatitis C virus (HCV) have proven to be useful drugs in the treatment of HCV infection. Although variants have been identified with mutations that confer resistance to these inhibitors, the mutations do not restore replicative fitness and no secondary mutations that rescue fitness have been found. To gain insight into the molecular mechanisms underlying the lack of fitness compensation, we screened known resistance mutations in infectious HCV cell culture with different genomic backgrounds. We observed that the Q41R mutation of NS3-4A efficiently rescues the replicative fitness in cell culture for virus variants containing mutations at NS3-Asp168 To understand how the Q41R mutation rescues activity, we performed protease activity assays complemented by molecular dynamics simulations, which showed that protease-peptide interactions far outside the targeted peptide cleavage sites mediate substrate recognition by NS3-4A and support protease cleavage kinetics. These interactions shed new light on the mechanisms by which NS3-4A cleaves its substrates, viral polyproteins and a prime cellular antiviral adaptor protein, the mitochondrial antiviral signaling protein MAVS. Peptide binding is mediated by an extended hydrogen-bond network in NS3-4A that was effectively optimized for protease-MAVS binding in Asp168 variants with rescued replicative fitness from NS3-Q41R. In the protease harboring NS3-Q41R, the N-terminal cleavage products of MAVS retained high affinity to the active site, rendering the protease susceptible for potential product inhibition. Our findings reveal delicately balanced protease-peptide interactions in viral replication and immune escape that likely restrict the protease adaptive capability and narrow the virus evolutionary space.

Predicting the bioactive conformations of macrocycles: a molecular dynamics-based docking procedure with DynaDock

Macrocyclic compounds are of growing interest as a new class of therapeutics, especially as inhibitors binding to protein-protein interfaces. As molecular modeling is a well-established complimentary tool in modern drug design, the number of attempts to develop reliable docking strategies and algorithms to accurately predict the binding mode of macrocycles is rising continuously. Standard molecular docking approaches need to be adapted to this application, as a comprehensive yet efficient sampling of all ring conformations of the macrocycle is necessary. To overcome this issue, we designed a molecular dynamics-based docking protocol for macrocycles, in which the challenging sampling step is addressed by conventional molecular dynamics (750 ns) simulations performed at moderately high temperature (370 K). Consecutive flexible docking with the DynaDock approach based on multiple, pre-sampled ring conformations yields highly accurate poses with ligand RMSD values lower than 1.8 Å. We further investigated the value of molecular dynamics-based complex stability estimations for pose selection and discuss its applicability in combination with standard binding free energy estimations for assessing the quality of poses in future blind docking studies.

1,4-Disubstituted 1H-1,2,3-Triazole Containing Peptidotriazolamers: A New Class of Peptidomimetics With Interesting Foldamer Properties

Peptidotriazolamers are hybrid foldamers with features of peptides and triazolamers, containing alternation of amide bonds and 1,4-disubstituted 1H-1,2,3-triazoles with conservation of the amino acid side chains. We report on the synthesis of a new class of peptidomimetics, containing 1,4-disubstituted 1H-1,2,3-triazoles in alternation with amide bonds and the elucidation of their conformational properties in solution. Based on enantiomerically pure propargylamines bearing the stereogenic center in the propargylic position and α-azido esters, building blocks were obtained by copper-catalyzed azide-alkyne cycloaddition. With these building blocks the peptidotriazolamers were readily available by solution phase synthesis. A panel of homo- and heterochiral tetramers, hexamers, and heptamers was synthesized and the heptamer Boc-Ala-Val-Ψ[4Tz]Phe-LeuΨ[4Tz]Phe-LeuΨ[4Tz]Val-OAll as well as an heterochiral and a Gly-containing equivalent were structurally characterized by NMR-based molecular dynamics simulations using a specifically tailored force field to determine their conformational and solvation properties. All three variants adopt a compact folded conformation in DMSO as well as in water. In addition to the heptamers we predicted the conformational behavior of similar longer oligomers i.e., Boc-Ala-(AlaΨ[4Tz]Ala)₆-OAll as well as Boc-Ala-(d-AlaΨ[4Tz]Ala)₆-OAll and Boc-Ala-(GlyΨ[4Tz]Ala)₆-OAll. Our calculations predict a clear secondary structure of the first two molecules in DMSO that collapses in water due to the hydrophobic character of the side chains. The homochiral compound folds into a regular helical structure and the heterochiral one shows a twisted “S”-shape, while the Gly variant exhibits no clear secondary structure.

Simple Tyrosine Derivatives Act as Low Molecular Weight Organogelators

The gelation of L-Tyr(tBu)-OH in tetrahydrofuran (THF) was discovered serendipitously. It was noted that this tremendously low molecular weight (LMW) compound has the ability to gel a wide variety of organic solvents (e.g., N,N-Dimetylformamide (DMF), THF, butanol, toluene), even in very low concentrations (i.e., 0.1 wt/v% in DMF). Addition of bases such as NaOH and piperidine enhanced the gel property. By changing the side-chain protecting group to tert-butyldimethylsilyl (TBDMS), a fluoride ion-responsive organogel was also acquired. This new organogelator responded fluoride ion concentration as low as 0.2 ppm. Characterization of microstructures and gel behaviours were studied by powder X-Ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), rheological measurements and molecular dynamics (MD) simulations. Experimental observations and theoretical simulations consistently show a fibre-like structure of the gel, in which the organogelator molecules are held together via a dense network of hydrogen bonds, and via van der Waals interactions between hydrophobic groups.

Semi-Empirical Born-Oppenheimer Molecular Dynamics (SEBOMD) within the Amber Biomolecular Package

Semi-empirical quantum methods from the neglect of differential diatomic overlap (NDDO) family such as MNDO, AM1, or PM3 are fast albeit approximate quantum methods. By combining them with linear scaling methods like the divide & conquer (D&C) method, it is possible to quickly evaluate the energy of systems containing hundreds to thousands of atoms. We here present our implementation in the Amber biomolecular package of a SEBOMD module that provides a way to run semi-empirical Born-Oppenheimer molecular dynamics. At each step of a SEBOMD, a fully converged self-consistent field (SCF) calculation is performed to obtain the semiempirical quantum potential energy of a molecular system encaged or not in periodic boundary conditions. We describe the implementation and the features of our SEBOMD implementation. We show the requirements to conserve the total energy in NVE simulations, and how to accelerate SCF convergence through density matrix extrapolation. Specific ways of handling periodic boundary conditions using mechanical embedding or electrostatic embedding through a tailored quantum Ewald summation is developed. The parallel performance of SEBOMD simulations using the D&C scheme are presented for liquid water systems of various sizes, and a comparison between the traditional full diagonalization scheme and the D&C approach for the reproduction of the structure of liquid water illustrates the potentiality of SEBOMD to simulate molecular systems containing several hundreds of atoms for hundreds of picoseconds with a quantum mechanical potential in a reasonable amount of CPU time.

Amber-Compatible Parametrization Procedure for Peptide-like Compounds: Application to 1,4- and 1,5-Substituted Triazole-Based Peptidomimetics

Peptidomimetics are molecules of particular interest in the context of drug design and development. They are proteolytically and metabolically more stable than their natural peptide counterparts but still offer high specificity toward their biological targets. In recent years, 1,4- and 1,5-disubstituted 1,2,3-triazole-based peptidomimetics have emerged as promising lead compounds for the design of various inhibitory and tumor-targeting molecules as well as for the synthesis of peptide analogues. The growing popularity of triazole-based peptidomimetics and a constantly broadening range of their application generated a demand for elaborate theoretical investigations by classical molecular dynamics simulations and molecular docking. Despite this rising interest, accurate and coherent force field parameters for triazole-based peptidomimetics are still lacking. Here, we report the first complete set of parameters dedicated to this group of compounds, named TZLff. This parametrization is compatible with the latest version of the AMBER force field (ff14SB) and can be readily applied for the modeling of pure triazole-based peptidomimetics as well as natural peptide sequences containing one or more triazole-based modifications in their backbone. The parameters were optimized to reproduce HF/6-31G* electrostatic potentials as well as MP2/cc-pVTZ equilibrium Hessian matrices and conformational potential energy surfaces through the use of a genetic algorithm-based search and least-squares fitting. Following the standards of AMBER, we introduce residue building units, thus allowing the user to define any given sequence of triazole-based peptidomimetics. Validation of the parameter set against ab initio- and NMR-based reference systems shows that we obtain fairly accurate results, which properly capture the conformational features of triazole-based peptidomimetics. The successful and efficient parametrization strategy developed in this work is general enough to be applied in a straightforward manner for parametrization of other peptidomimetics and, potentially, any polymeric assemblies.

1,5-Disubstituted 1,2,3-Triazole-Containing Peptidotriazolamers: Design Principles for a Class of Versatile Peptidomimetics

Peptidotriazolamers are hybrid foldamers combining features of peptides and triazolamers-repetitive peptidomimetic structures with triazoles replacing peptide bonds. We report on the synthesis of a new class of peptidomimetics, containing 1,5-disubstituted 1,2,3-triazoles in an alternating fashion with amide bonds and the analysis of their conformation in solid state and solution. Homo- or heterochiral peptidotriazolamers were obtained from enantiomerically pure propargylamines with stereogenic centers in the propargylic position and α-azido esters by ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) under microwave conditions in high yields. With such building blocks the peptidotriazolamers are readily available by solution phase synthesis. While the conformation of the homochiral peptidotriazolamer Boc-Ala[5Tz]Phe-Val[5Tz]Ala-Leu[5Tz]Val-OBzl resembles that of a β VIa1 turn, the heterochiral peptidotriazolamer Boc-d-Ala[5Tz]Phe-d-Val[5Tz]Ala-d-Leu[5Tz]Val-OBzl adopts a polyproline-like repetitive structure.

Gliotoxin Biosynthesis: Structure, Mechanism, and Metal Promiscuity of Carboxypeptidase GliJ

The formation of glutathione (GSH) conjugates, best known from the detoxification of xenobiotics, is a widespread strategy to incorporate sulfur into biomolecules. The biosynthesis of gliotoxin, a virulence factor of the human pathogenic fungus Aspergillus fumigatus, involves attachment of two GSH molecules and their sequential decomposition to yield two reactive thiol groups. The degradation of the GSH moieties requires the activity of the Cys-Gly carboxypeptidase GliJ, for which we describe the X-ray structure here. The enzyme forms a homodimer with each monomer comprising one active site. Two metal ions are present per proteolytic center, thus assigning GliJ to the diverse family of dinuclear metallohydrolases. Depending on availability, Zn²⁺, Fe²⁺, Fe³⁺, Mn²⁺, Cu²⁺, Co²⁺, or Ni²⁺ ions are accepted as cofactors. Despite this high metal promiscuity, a preference for zinc versus iron and manganese was noted. Mutagenesis experiments revealed details of metal coordination, and molecular modeling delivered insights into substrate recognition and processing by GliJ. The latter results suggest a reaction mechanism in which the two scissile peptide bonds of one gliotoxin precursor molecule are hydrolyzed sequentially and in a given order.

DynaDom: structure-based prediction of T cell receptor inter-domain and T cell receptor-peptide-MHC (class I) association angles

Background

T cell receptor (TCR) molecules are involved in the adaptive immune response as they distinguish between self- and foreign-peptides, presented in major histocompatibility complex molecules (pMHC). Former studies showed that the association angles of the TCR variable domains (Vα/Vβ) can differ significantly and change upon binding to the pMHC complex. These changes can be described as a rotation of the domains around a general Center of Rotation, characterized by the interaction of two highly conserved glutamine residues.

Methods

We developed a computational method, DynaDom, for the prediction of TCR Vα/Vβ inter-domain and TCR/pMHC orientations in TCRpMHC complexes, which allows predicting the orientation of multiple protein-domains. In addition, we implemented a new approach to predict the correct orientation of the carboxamide endgroups in glutamine and asparagine residues, which can also be used as an external, independent tool.

Results

The approach was evaluated for the remodeling of 75 and 53 experimental structures of TCR and TCRpMHC (class I) complexes, respectively. We show that the DynaDom method predicts the correct orientation of the TCR Vα/Vβ angles in 96 and 89% of the cases, for the poses with the best RMSD and best interaction energy, respectively. For the concurrent prediction of the TCR Vα/Vβ and pMHC orientations, the respective rates reached 74 and 72%. Through an exhaustive analysis, we could show that the pMHC placement can be further improved by a straightforward, yet very time intensive extension of the current approach.

Conclusions

The results obtained in the present remodeling study prove the suitability of our approach for interdomain-angle optimization. In addition, the high prediction rate obtained specifically for the energetically highest ranked poses further demonstrates that our method is a powerful candidate for blind prediction. Therefore it should be well suited as part of any accurate atomistic modeling pipeline for TCRpMHC complexes and potentially other large molecular assemblies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12900-016-0071-7) contains supplementary material, which is available to authorized users.

Water interactions with hydrophobic groups: assessment and recalibration of semiempirical molecular orbital methods

In this work, we present a study of the ability of different semiempirical methods to describe intermolecular interactions in water solution. In particular, we focus on methods based on the Neglect of Diatomic Differential Overlap approximation. Significant improvements of these methods have been reported in the literature in the past years regarding the description of non-covalent interactions. In particular, a broad range of methodologies has been developed to deal with the properties of hydrogen-bonded systems, with varying degrees of success. In contrast, the interactions between water and a molecule containing hydrophobic groups have been little analyzed. Indeed, by considering the potential energy surfaces obtained using different semiempirical Hamiltonians for the intermolecular interactions of model systems, we found that none of the available methods provides an entirely satisfactory description of both hydrophobic and hydrophilic interactions in water. In addition, a vibrational analysis carried out in a model system for these interactions, a methane clathrate cluster, showed that some recent methods cannot be used to carry out studies of vibrational properties. Following a procedure established in our group [M. I. Bernal-Uruchurtu, M. T. C. Martins-Costa, C. Millot, and M. F. Ruiz-López, J. Comput. Chem. 21, 572 (2000); W. Harb, M. I. Bernal-Uruchurtu, and M. F. Ruiz-López, Theor. Chem. Acc. 112, 204 (2004)], we developed new parameters for the core-core interaction terms based on fitting potential energy curves obtained at the MP2 level for our model system. We investigated the transferability of the new parameters to describe a system, having both hydrophilic and hydrophobic groups, interacting with water. We found that only by introducing two different sets of parameters for hydrophilic and hydrophobic hydrogen atom types we are able to match the features of the ab initio calculated properties. Once this assumption is made, a good agreement with the MP2 reference is achieved. The results reported in this work provide therefore a direction for future developments of semiempirical approaches that are still required to investigate chemical processes in biomolecules and in large disordered systems.

Effect of environmental conditions on the erosional resistance of cohesive sediment deposits in sewers

The potential to adjust sewer network operation in order to control the level of transported sediment in sewage so as to enhance the performance of end-of-pipe treatment works is now being investigated. However for this to become a practical management option there is a need to be able to understand the processes which control the movement of sediments that are found in many combined sewers. Crucial to this understanding is an ability to predict how sediments from in-sewer deposits, are released by the action of vigorous flows. This paper reports on a laboratory investigation that aimed to investigate the effect that the environmental conditions during deposit formation can have on the ability of fine-grained organic sediment within in-sewer deposits to resist erosion and subsequent release into transport.

Inhibitory effects of dronedarone on muscarinic K+ current in guinea pig atrial cells

Dronedarone (SR33589), an amiodarone-like noniodinated antiarrhythmic agent, is undergoing clinical trials in atrial fibrillation. Because vagal activation plays a role in the pathophysiology of supraventricular arrhythmias, we have assessed the ability of dronedarone (0.01, 0.1, and 1 microM), compared with amiodarone (0.1, 1, and 10 microM) to inhibit the muscarinic acetylcholine receptor-operated K+ current (I(K(ACh))) in single cells isolated from guinea pig atria (patch-clamp technique). I(K(ACh)) was activated by extracellular application of carbachol (10 microM) or by intracellular loading with GTP-gamma-S (100 microM). Dronedarone and amiodarone reduced the carbachol-induced I(K(ACh)) with an IC50 (concentration required for 50% inhibition) slightly above 10 nM and 1 microM, respectively. Dronedarone also inhibited the GTP-gamma-S induced K+ current by 28% and 58% at 0.01 and 0.1 microM, respectively. These data suggest that dronedarone inhibits I(K(ACh)) by depressing the function of K(ACh) channel itself or associated GTP-binding proteins. Compared with amiodarone, dronedarone is approximately 100 times more potent on I(K(ACh)) and seems more selective in inhibiting I(K(ACh)) with respect to its antagonism of other inward and outward currents reported in the literature. This relative high potency of dronedarone to reduce I(K(ACh)) may be involved, at least in part, in the antiarrhythmic action of dronedarone against atrial fibrillation.

[Distal traumatic avulsion of the triceps brachii. Apropos of a treated cases]

Traumatic distal avulsion of triceps brachii is a rare injury, usually due to a fall on the outstre ched elbow, with sudden contraction of the triceps muscle. Examination reveals pain, swelling, and a palpable depression just proximal to the olecranon. Lateral X rays show avulsed osseous material. Surgical therapy was advisable for complete avulsion. In this case, the authors used absorbable sutures for this reinsertion. Immediate surgical repair always achieves good results.

A comparative analysis of physiological responses at submaximal workloads during different laboratory simulations of field cycling

The purpose of this study was to evaluate the relationships between heart rate (fc), oxygen consumption (VO2), peak force and average force developed at the crank in response to submaximal exercise employing a racing bicycle which was attached to an ergometer (RE), ridden on a treadmill (TC) and ridden on a 400-m track (FC). Eight male trained competitive cyclists rode at three pre-determined work intensities set at a proportion of their maximal oxygen consumption (VO2max): (1) below lactate threshold [work load that produces a VO2 which is 10% less than the lactate threshold VO2 (sub-LT)], (2) lactate threshold VO2 (LT), and (3) above lactate threshold [workload that produces a VO2 which is 10% greater than lactate threshold VO2 (supra-LT)], and equated across exercise modes on the basis of fc. Voltage signals from the crank arm were recorded as FM signals for subsequent representation of peak and average force. Open circuit VO2 measurements were done in the field by Douglas bag gas collection and in the laboratory by automated gas collection and analysis. fc was recorded with a telemeter (Polar Electro Sport Tester, PE3000). Significant differences (P < 0.05) were observed: (1) in VO2 between FC and both laboratory conditions at sub-LT intensity and LT intensities, (2) in peak force between FC and TC at sub-LT intensity, (3) in average force between FC and RE at sub-LT. No significant differences were demonstrated at supra-LT intensity for VO2. Similarly no significant differences were observed in peak and average force for either LT or supra-LT intensities. These data indicate that equating work intensities on the basis of fc measured in laboratory conditions would overestimate the VO2 which would be generated in the field and conversely, that using fc measured in the laboratory to establish field work intensity would underestimate mechanical workload experienced in the field.

SR47063, a potent channel opener, activates KATP and a time-dependent current likely due to potassium accumulation

(i) We studied the effects of a new cromakalim analogue, SR47063, in guinea-pig ventricular cells. The experiments were carried out in whole-cell patch clamp with internal and external solutions supposedly similar to the physiological ones. (ii) SR47063 reversibly activated a time-independent current reversing near the potassium equilibrium potential, and a time-dependent current reversing at a more positive potential. Both currents were blocked by application of glibenclamide. (iii) The time-independent and the time-dependent currents were activating for the same concentration of agonist in every cell, this concentration being very different from cell to cell. (iv) The amplitude of the time-dependent current was shown to depend directly neither on agonist concentration nor on potential, but rather on the amplitude of the current flowing during the prepulse before the test pulse. (v) We conclude that SR47063 is a potent KATP channel opener acting at concentrations lower than one micromolar, and that the time-dependent current is likely due to accumulation and depletion of potassium in restricted areas of the cells.

[Digestive arterial obstructive diseases in three young women]

The authors report three cases of severe intestinal ischaemia occurring in young women (age 29-44), all of them being smokers. In all cases, intestinal ischaemia was recognized lately and lead to death within two years. The occlusive arterial lesions concerned nearly exclusively the intestinal arteries. Microscopic lesions were heterogeneous and non-specific. In a case, an occlusive intimal fibrosis was noted; in another case, fibrosis of the media and the adventitia was observed; and in the last case, the lesions were suggestive of thromboangiitis obliterans. The authors advocate for the systematic recording of cases of intestinal ischaemia in young women, in order to identify the risk factors and pathogenic features of this rare condition.

[Aging and procedural memory. Study of a series of tests on microcomputers]

The authors have assessed perceptual motor tasks involving the learning of the mouse control by locking at a Macinthosh computer screen during three consecutive sessions. Tests were performed by 102 control subjects aged between 16 and 85 years. Concerning age, there was a significant time difference (ANOVA) but improvement was the same for all subjects. Educational level and IQP results didn't influence procedural performance. Men were faster in three tasks. We can argue that implicit learning abilities appear before explicit memory and within the adult life span there appears to be little significant deterioration in implicit memory abilitie.

Efficacy and tolerability of imipenem-cilastatin versus ceftazidime plus tobramycin as empiric therapy of presumed bacterial infection in neutropenic cancer patients

The efficacy and tolerability of monotherapy with imipenem-cilastatin (I-C) were compared with that of ceftazidime plus full-course therapy with an aminoglycoside (tobramycin) (C&T) in the treatment of presumed bacterial infection in neutropenic cancer patients. A total of 106 adult patients diagnosed with presumed bacterial infection and an underlying malignancy with an absolute neutrophil count (ANC) < 500/mm3 were enrolled in this open-label study. A total of 131 febrile episodes occurred. Forty-five patients in the I-C group and 41 in the C&T group, who were well matched on demographic and baseline characteristics, were evaluable for efficacy and safety. Seventy-two hours after the start of therapy, no significant between-group differences in treatment outcomes, including withdrawals or deaths, were seen. Thirty-five (78%) of 45 patients in the I-C group and 29 (71%) of the 41 in the C&T group had successful outcomes at the final evaluation. Superinfection occurred in 8 (18%) I-C patients and 3 (7%) C&T patients. Within the subgroup of patients with an initial ANC < 100/mm3, the final evaluation showed no significant differences in treatment outcome between groups. Of the 131 in the safety population 30 (46%) I-C patients and 28 (42%) C&T patients had one or more adverse experiences; drug-related adverse events occurred in 25 (38%) patients in the I-C group and 11 (17%) patients in the C&T group. The data suggest that imipenem-cilastatin should be considered for initial empiric therapy of presumed bacterial infection in neutropenic cancer patients.

Evidence that large granular lymphocytes of donor origin mediate acute graft-versus-host disease

We have studied the phenotype of mononuclear cells infiltrating target organs of mice with acute graft-versus-host disease after bone marrow transplantation from H-2-identical donors. Infiltrating mononuclear cells with characteristics of large granular lymphocytes (LGL) were frequently found in close association with dead or dying epithelial cells in the skin, liver, and colon. The phenotype of these putative effector cells was Thy-1+, ASGM1+, Mac-1+, Lyt-1-, Lyt-2-, Ia-, which is characteristic of LGL. Differences in the Thy-1 allele between donor and host were used to demonstrate that these cells were of donor origin. Analysis of cytolytic function in GVHD splenocytes indicated high natural killer activity and low cytolytic T lymphocyte (CTL) activity. These findings suggest that an important effector cell in systemic acute graft-versus-host disease is a large granular lymphocyte of donor origin.