Enzymatic recycling of thermoplastic polyurethanes: Synergistic effect of an esterase and an amidase and recovery of building blocks

Biological recycling of polyurethanes (PU) is a huge challenge to take up in order to reduce a large part of the environmental pollution from these materials. However, enzymatic depolymerization of PU still needs to be improved to propose valuable and green solutions. The present study aims to identify efficient PU degrading enzymes among a collection of 50 hydrolases. Screenings based on model molecules were performed leading to the selection of an efficient amidase (E4143) able to hydrolyze the urethane bond of a low molar mass molecule and an esterase (E3576) able to hydrolyze a waterborne polyester polyurethane dispersion. Degradation activities of the amidase, the esterase and a mix of these enzymes were then evaluated on four thermoplastic polyurethanes (TPU) specifically designed for this assay. The highest degradation was obtained on a polycaprolactone polyol-based polyurethane with weight loss of 33% after 51 days measured for the esterase. Deep cracks on the polymer surface observed by scanning electron microscopy and the presence of oligomers on the remaining TPU detected by size exclusion chromatography evidenced the polymer degradation. Mixing both enzymes led to an increased amount of urethane bonds hydrolysis of the polymer. 6-hydroxycaproic acid and 4,4'-methylene dianiline were recovered after depolymerization as hydrolysis products. Such building blocks could get a second life with the synthesis of new macromolecular architectures.

Investigation of ion beam space charge compensation with a 4-grid analyzer

Experiments to investigate the space charge compensation of pulsed high-current heavy ion beams are performed at the GSI ion source text benches with a 4-grid analyzer provided by CEA/Saclay. The technical design of the 4-grid analyzer is revised to verify its functionality for measurements at pulsed high-current heavy ion beams. The experimental investigation of space charge compensation processes is needed to increase the performance and quality of current and future accelerator facilities. Measurements are performed directly downstream a triode extraction system mounted to a multi-cusp ion source at a high-current test bench as well as downstream the post-acceleration system of the high-current test injector (HOSTI) with ion energies up to 120 keV/u for helium and argon. At HOSTI, a cold or hot reflex discharge ion source is used to change the conditions for the measurements. The measurements were performed with helium, argon, and xenon and are presented. Results from measurements with single aperture extraction systems are shown.

High intensity proton injector for facility of antiproton and ion research

The high current ion source with the low energy beam transport (LEBT) will serve as injector into the proton LINAC to provide primary proton beam for the production of antiprotons. The pulsed ion source developed and built in CEA/Saclay operates with a frequency of 2.45 GHz based on ECR plasma production with two coils with 87.5 mT magnetic field necessary for the electron cyclotron resonance. The compact LEBT consists of two solenoids with a maximum magnetic field of 500 mT including two integrated magnetic steerers to adjust the horizontal and vertical beam positions. The total length of the compact LEBT is 2.3 m and was made as short as possible to reduced emittance growth along the beam line. To measure ion beam intensity behind the pentode extraction system, between solenoids and at the end of the beam line, two current transformers and a Faraday cup are installed. To get information about the beam quality and position, the diagnostic chamber with different equipment will be installed between the two solenoids. This article reports the current status of the proton injector for the facility of antiproton and ion research.

The proton injector for the accelerator facility of antiproton and ion research (FAIR)

The new international accelerator facility for antiproton and ion research (FAIR) at GSI in Darmstadt, Germany, is one of the largest research projects worldwide and will provide an antiproton production rate of 7 × 10(10) cooled pbars per hour. This is equivalent to a primary proton beam current of 2 × 10(16) protons per hour. For this request a high intensity proton linac (p-linac) will be built with an operating rf-frequency of 325 MHz to accelerate a 35 mA proton beam at 70 MeV, using conducting crossed-bar H-cavities. The repetition rate is 4 Hz with beam pulse length of 36 μs. The microwave ion source and low energy beam transport developed within a joint French-German collaboration GSI/CEA-SACLAY will serve as an injector of the compact proton linac. The 2.45 GHz ion source allows high brightness ion beams at an energy of 95 keV and will deliver a proton beam current of 100 mA at the entrance of the radio frequency quadrupole (RFQ) within an acceptance of 0.3π mm mrad (norm., rms).

Directed evolution of a 13-hydroperoxide lyase (CYP74B) for improved process performance

The performance of a 13-hydroperoxide lyase from guava, an enzyme of the CYP74 family, which is of interest for the industrial production of saturated and unsaturated C6-aldehydes and their derivatives, was improved by directed evolution. Four rounds of gene shuffling and random mutagenesis improved the functional expression in E. coli by offering a 15-fold higher product yield factor. The increased product yield factor relates to an improved total turnover number of the variant enzyme, which also showed higher solubility and increased heme content. Thermal stability was also dramatically improved even though there was no direct selection pressure applied for evolving this trait. A structure based sequence alignment with the recently solved allene oxide synthase of Arabidopsis thaliana showed that most amino acid alterations occurred on the surface of the protein, distant of the active site and often outside of secondary structures. These results demonstrate the power of directed evolution for improving a complex trait such as the total turnover number of a cytochrome P450, a critical parameter for process performance that is difficult to predict even with good structural information at hand.

Ultrastructural Findings in Porcine Hearts After Extracorporeal Long-term Preservation with a Modified Langendorff Perfusion System

Preserved ultrastructure is an important precondition for functional regeneration after heart transplantation. We investigated the effectiveness of a newly developed modified Langendorff system in extracorporeal heart perfusion. (Experiment I) Cardioplegia and cold ischaemia were performed in six pigs. Hearts were connected to a modified Langendorff system, and perfused with leucocyte depleted autologous blood. (Experiment II) The untreated hearts of three healthy pigs served as controls. Forty-seven myocardial biopsies at different timepoints (I: n = 29, II: n = 18) were investigated by transmission electronmicroscopy. Cardioplegia/hypothermia (I) induced mild-to-moderate mitochondrial swelling, mild myofibrillar degeneration in cardiomyocytes and moderate endothelial oedema. After 4 h reperfusion cardiomyocytes showed moderate myofibrillar and mild sarcolemmal damage. Moderate endothelial degeneration, mild interstitial oedema and haemorrhages appeared. Untreated hearts (II) showed severely damaged mitochondria and nuclei after 30 min while the myofibrillar structure remained unaffected until 4 h later. This is a promising model for extracorporeal heart perfusion. However, ultrastructural findings indicated that some necessary modifications to prevent cellular damages during reperfusion were needed.

Experimentelle Untersuchungen zur chirurgischen Therapie des Vorhofflimmerns am Tiermodell Schaf

Gegenstand und Ziel: Vorhofflimmern ist die häufigste Ursache für kardiale Arrhythmien beim Menschen. Die Erzeugung zirkulärer transmuraler Läsionen mittels verschiedener Energieformen dient der elektrischen Isolation der autonomen Foci. Ziel der Studie war daher, am Tiermodell Schaf die Effektivität und die Risiken verschiedener Ablationstechniken systematisch zu vergleichen. Material und Methoden: Bei 39 Merinoschafen wurden zirkuläre Läsionen im Bereich des linken Atriums und der Pulmonalvenen erzeugt. Kryotechnik (n = 12), Mikrowellen (n = 9), Laser (n = 6) sowie unipolare (n = 6) und bipolare (n = 6) Hochfrequenz (HF) wurden von endokardial bzw. von epikardial eingesetzt und die Temperatur im Lumen des Ösophagus gemessen. Elektrophysiologische Untersuchungen unmittelbar sowie zwei Stunden nach der Ablation dienten dem Nachweis der erfolgreichen Reizleitungsblockade. Repräsentative Proben von linkem Atrium, Pulmonalvenen und Ösophagus wurden histopathologisch untersucht. Ergebnisse: Alle endokardialen Ablationstechniken führten zu elektrophysiologisch effektiven transmuralen Nekrosen. Im Gegensatz zu Kryoablation und unipolarer HF erzeugten Mikrowellen- und Laserenergie starke Thromben. Die epikardiale Ablation mit Kryotechnik und Mikrowellen war in acht von neun Fällen nicht effektiv, während die bipolare HF zu effektiven transmuralen Läsionen, jedoch mit deutlichen Thromben führte. In 24 von 39 Fällen wurden histologisch auch Alterationen des Ösophagus nachgewiesen. Insbesondere von endokardial applizierte unipolare HF und Kryotechnik führten zu Nekrosen der Ösophaguswand. Schlussfolgerung: Epikardial applizierte bipolare HF war das Verfahren zur Vorhofablation, das von den getesteten Methoden die geringsten Risiken der Ösophagusperforation bei bester Effektivität der Ablation aufwies. Diese Ergebnisse aus den Akutversuchen sollten jedoch noch in Langzeitversuchen überprüft werden.

Expression analysis of metabotropic glutamate receptors I and III in mouse strains with different susceptibility to experimental temporal lobe epilepsy

Increased hippocampal excitability constitutes a pathogenetic hallmark of pharmacoresistant human temporal lobe epilepsy (TLE). Metabotropic glutamate receptors (mGluRs) can be subdivided into three classes based on sequence homologies, mechanisms of signal transduction as well as pharmacological characteristics. Generally, class I mGluRs mediate neuronal excitation whereas activation of class II and III mGluRs decreases synaptic transmission. Changes in expression of class I and III mGluR subunits have been described in human TLE. It remains to be determined whether altered mGluR expression relates to differences in seizure susceptibility or hippocampal damage. Here, we examine the transcription levels of mGluRs class I (mGluR1 and 5) and III (mGluR4 and 7) in experimental TLE and correlate differential mGluR subunit expression with mouse-strain-dependent susceptibility to TLE induced by pilocarpine. Expression of mGluRs 1, 4, 5 and 7 was determined in epileptic dentate gyrus granule cells (DG) in CD1, C57BL/6 and FVB/N mice by real time RT-PCR. FVB/N mice appear significantly more vulnerable to pilocarpine-induced seizures than C57BL/6 and CD1 strains. RT-PCR analysis demonstrates an increased expression of inhibitory mGluR 4 and downregulation of excitatory mGluR 1 in epileptic CD1 mice and a decrease of the excitatory mGluRs 1 and 5 in C57BL/6 (p<0.05, n=6 each) but not in the FVB/N strain. These results correlate differential expression of excitatory class mGluR I and inhibitory class mGluR III to seizure susceptibility and hippocampal damage. Our data suggest mGluRs class I and III as interesting potential therapeutic targets to interfere with hippocampal epileptogenesis and hyperexcitability.

Epicardial Treatment of Atrial Fibrillation Using Cryoablation in an Acute Off-pump Sheep Model

BACKGROUND

The purpose of this study was to test the feasibility and effectiveness of cryoablation therapy (SurgiFrost trade mark CryoCath, Endocare Inc., Irvine, California, USA) for linear epicardial treatment of atrial fibrillation in an acute off-pump sheep model.

METHODS

After thoracotomy, we performed epicardial cryoablation (2 min intervals at -160 degrees C) with pacing electrodes positioned at the left atrial appendage (LAA), the pulmonary veins (PVs), the right atrial appendage (RAA), and the vena cava cranialis (VCC) in 8 sheep. Circular epicardial ablations were performed with online temperature measurement in the ascending aorta and in the esophagus. The sheep were sacrificed two hours after ablation procedure, and heart, lungs, and esophagus were retrieved for histological examination. Out of all 8 sheep, histo-pathological analysis was performed on the RAA and VCC in 6 sheep and on the CAA and PV in all 8 sheep.

RESULTS

Thin-walled structures such as PVs and VCC showed electrical isolation. No significant changes in temperature in the descending aorta and the esophagus were observed. There was evidence of extensive transmural alteration including vascular lesions, myocardial degeneration and necrosis as well as epi- and endocardial necrosis in the left atria in three of 8 cases, in the right atria in 5 of 6 cases, in the VCC in 6 of 6 cases, and in the PV in 5 of 8 cases. Mild lesions of the muscular layer of the esophagus were found in 7 of 8 cases.

CONCLUSIONS

Epicardial cryoablation is not effective on thicker tissues like LAA and RAA due to the rewarming of the current blood flow. However, thin tissues like VCC and PV can be isolated. Further chronic studies are necessary to evaluate the potential for regeneration of adjacent structures.

Influence of propiverine on hepatic microsomal cytochrome p450 enzymes in male rats

The bladder spasmolytics propiverine was shown to induce hepatic cytochrome P450 (P450) and aminopyrine and aniline oxidation in rats. To characterize the type of enzyme induction and its dose dependence, activities of seven hepatic microsomal P450-dependent monooxygenases were measured in 72 male LEW1A albino rats (body weight 236-295 g) after oral treatment with 0.5, 2, 6, and 60 mg/kg of propiverine hydrochloride for 5 days and compared with the effects of 40 mg/kg beta-naphthoflavone, 10 mg/kg phenobarbital, and 20 mg/kg dexamethasone (each group, n = 8). CYP2B expression was measured by Western blotting. Furthermore, the inhibitory potency of propiverine on P450 enzymes was evaluated in competition assays with three most specific monooxygenases. Results show that Propiverine induced several monooxygenases and CYP2B expression dose dependently. The effects were well comparable with a phenobarbital-type inducer with 60 mg/kg being equipotent to 10 mg/kg phenobarbital. Furthermore, propiverine in low concentrations inhibited pentylresorufin O-dealkylase (for CYP2B) in vitro. In conclusion, propiverine is a phenobarbital-type inducer on hepatic P450 enzymes in rats in doses about 100-times above the therapeutic doses in man.

A new intracardiac microaxial pump: first results of a multicenter study

As coronary artery bypass grafting (CABG) surgery in the beating heart technique is progressing, new devices have been developed to overcome hemodynamic instabilities while tilting the heart for exposure of back wall vessels. A new device for in heart biventricular intracorporeal circulation was applied in 42 patients undergoing CABG surgery (Group 1). The control group consisted of 38 patients operated on using a conventional cardiopulmonary bypass setup (Group 2). The study protocol of the prospective, randomized multicenter study was approved by the local ethics committees. Patients were included following inclusion criteria and patient informed consent. Mean age, procedure time, mean arterial pressure (MAP), and hemolysis by means of plasma free hemoglobin (fHb) were assessed preoperatively, perioperatively, on postoperative Days 1 to 3, at discharge, and at a 3 month follow-up. The mean age was 62.1 (range 59-74) years (Group 1), 62.7 (range 48-72) years (Group 2); procedure time was 112 min +/- 31.9 min (Group 1), 137.4 min +/- 36.2 min (Group 2); and 2.3 +/- 0.6 (Group 1), 2.2 +/- 0.7 (Group 2), vessels were revascularized. The flow on pump was 3.7 (2.5/4.4) L/min (Group 1), 4.9 (3.6/6.2) L/min (Group 2) which resulted in a MAP of 69.8 (4.0/143) mm Hg (Group 1), 58.3 (5.3/94) mm Hg while assessing the vessels of the back wall. Hemolysis defined by fHB was lower than 20 mg/dl at all times pre- and postoperatively. Intraoperative maximum values were up to 100 mg/dl in 4 patients (2 in Group 1 and 2 in Group 2). Body mass index was 26.4 +/- 2.6 (Group 1), 27.9 +/- 3.2. New York Heart Association Class was II to III in both groups. There were no pump related life threatening or severe adverse events. Beating heart procedures with ICC can be reliably and safely achieved. As the device is easy to use, it may deserve a more widespread use in the future.

Three-dimensional visualization of coronary arteries in excised hearts

OBJECTIVE

We sought to image coronary arteries in excised hearts.

METHODS

Twelve excised pigs' hearts were imaged in a water bath. The aortic valve was closed surgically. A contrast agent (Echovist) was injected into the aortic root and selectively into single coronary arteries. Three-dimensional (3D) imaging was performed with TomTec Echoscan equipment. Mechanical rotations were performed at 1 degrees intervals. The hearts were visualized by InVivo software. Selective coloring of coronary arteries in 3D data sets was obtained by using color superpositioning, which differentiates information before and after injection of contrast. Distance measurements were performed in conventional 3D echocardiograms of coronary arteries and color-superimposed echocardiograms and compared with those from angiograms and casts.

RESULTS

After a learning curve, during which optimal conditions for the visualization of coronary arteries were determined, a quick display of all major parts of the coronary tree was obtained. Distance measurements (n >400) revealed that fundamental contrast echocardiography overestimated angiography by 25% +/- 5% and casts by 28% +/- 6%. However, distances in color-superimposed echocardiograms (flow mode 4) were not significantly different from those obtained from angiograms and casts. In harmonic contrast echocardiograms, color super-positioning gave smaller distances compared with those from fundamental contrast echocardiograms, though they were still significantly larger than the reference diameters.

CONCLUSIONS

The 3D imaging of epicardial coronary arteries under ideal conditions in a water bath seems feasible and provides insight into coronary visualization with the use of ultrasonography.

Apoptosis is initiated by myocardial ischemia and executed during reperfusion

Ischemia/reperfusion leading to myocyte cell death has been reported as either necrotic or apoptotic or a combination of both. The importance of necrosis is well established but the role of apoptosis and the time of initiation are still unknown. Normothermic global ischemia of either 45 or 90 min duration followed by 6 h of reperfusion were induced in isolated canine hearts. After 45 min of ischemia, left ventricular function and adenine nucleotide (AN) content had recovered during reperfusion indicating reversible injury. DNA fragmentation determined by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) was absent as was the 85 kDa fragment of poly-(ADP-ribose) polymerase (PARP). After 90 min of ischemia, electron microscopy indicated necrotic cell death in 90% of myocytes. Recovery of function and AN content during reperfusion was minimal. At the end of ischemia, caspase-3 was activated in 30% of all myocytes and PARP 85 kDa fragments were present by Western blot, indicating initiation of the apoptotic cascade. Lamin-B(1)labeling was significantly reduced from 90% in myocytes in control and ischemia to 30% in early reperfusion. Completion of apoptosis seen by TUNEL was evident in late reperfusion (7.6% of myocytes and 8.3% of non-myocytes). Experiments with 6 h ischemia without reperfusion showed absence of DNA fragmentation. We conclude that apoptotic cell death is initiated by ischemia but that reperfusion is needed for completion of the apoptotic cascade. Furthermore, it is concluded that cell death in acute global ischemia followed by reperfusion occurs predominantly by necrosis and that apoptosis is of minor importance in this pathophysiological situation.

Time course of mitosis and collateral growth following coronary microembolization in the porcine heart

In ischaemic porcine myocardium, the growth of collateral vessels by angiogenesis is observed in clusters in the vicinity of focal necroses. Because mitosis of endothelial cells is a prerequisite for angiogenesis, the purpose of this study has been to evaluate the time course of mitosis as an indicator of vascular growth in a porcine model of coronary microembolization. Ischaemia was induced by injection of 25-microm microspheres in the left circumflex artery, followed by tissue collection from non-ischaemic and ischaemic areas of the same heart after 24, 72 or 168 h microembolization. Tissue was studied by histone H3 in-situ hybridization, PCNA/cyclin immunohistochemistry and electron microscopy. The number of blood vessels in ischaemic myocardium was compared with that in normal control tissue. Capillary growth started as early as 24 h after microembolization, as indicated by increasing numbers of proliferating, histone H3- and PCNA/cyclin-positive cells in the necrotic inflammatory foci of the ischaemic area. At 72 h and 168 h, the number of blood vessels was significantly higher in ischaemic than in normal myocardium, whereas at 168 h, mitosis of cells was, as in normal myocardium, a rare event. Coronary microembolization of porcine myocardium thus leads to an increased cellular proliferation rate between 24 h and less than 7 days after the onset of microembolization, followed by enhanced capillary growth. In-situ hybridization with histone H3 and PCNA/cyclin immunohistochemistry seem to be reliable markers for proliferation and vascular growth in non-cancerogenic tissue.