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Transfer Efficiency (transfer + efficiency)
Kinds of Transfer Efficiency Selected AbstractsSynthesis and Energy Transfer Efficiency of FRET Terminators Derived from Different LinkersCHEMINFORM, Issue 9 2004Shiv Kumar Abstract For Abstract see ChemInform Abstract in Full Text. [source] Transfer and efflux of cadmium and silver in marine snails and fish fed pre-exposed mussel preyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2007Ma-Shan Cheung Abstract Subcellular metal distribution may play an important role in the bioaccumulation and trophic transfer of metals in marine food chains. In the present study, we preexposed the green mussel Perna viridis to Ag and Cd and quantified their trophic transfer efficiencies to two predators (whelks [Thais clavigera] and fish [Terapon jarbua]). For the mussels, more Ag was distributed in the metal-rich granule (MRG) fraction following Ag exposure, and more Cd was distributed in the metallothionein-like protein following Cd exposure. In addition, Cd was mainly bound with the proteins having a molecular size of approximately 20 kDa. After being fed with metal-exposed mussels, the assimilation efficiencies of Ag decreased significantly (from 77 to 29,60% in whelks and from 9 to 2% in fish) with an increasing percentage of Ag deposited in the MRG fraction of the prey. In contrast, the assimilation efficiencies of Cd remained comparable (81,85% in whelks and 6,8% in fish), because its partitioning in the soluble fraction of different treatments of the prey was similar. The efflux of Ag and Cd in the two predators was comparable after feeding on preexposed mussel prey. Our results imply that the subcellular distribution of metals in prey may affect the dietary assimilation of metals in predators, but such influence is clearly metal-specific. The present study may lead to a better understanding of metal trophic transfer in different marine food chains. [source] Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2010Wentian Lin Abstract This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl-B-9-borabicyclononane (Me-B-9-BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]-catalyzed ethylene (Cp2ZrCl2 and rac -Me2Si(2-Me-4-Ph)2ZrCl2 as a catalyst) and styrene (Cp*Ti(OMe)3 as catalyst) polymerizations. The two trialkylboranes were found,in most cases,able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)-terminated PE and s -PS polymers after an oxidative workup process, suggesting the formation of the B-polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp2ZrCl2/MAO, whereas it became less effective when the catalyst changed to rac -Me2Si(2-Me-4-Ph)2ZrCl2. Both TEB and Me-B-9-BBN caused an efficient chain transfer in the Cp2ZrCl2/MAO-catalyzed ethylene polymerization; nevertheless, Me-B-9-BBN failed in vain with rac -Me2Si(2-Me-4-Ph)2ZrCl2/MAO. In the case of styrene polymerization with Cp*Ti(OMe)3/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as BH-bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane-terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534,3541, 2010 [source] Energy Transfer from Chemically Attached Rhodamine 101 to Adsorbed Methylene Blue on Microcrystalline Cellulose Particles,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2007Hernán B. Rodríguez Rhodamine 101 (R101) was chemically attached onto microcrystalline cellulose and methylene blue (MB) was adsorbed to a sample bearing nearby 6 × 10,7 mol R101 (g cellulose),1. The system was studied by reflectance and emission spectroscopy in the solid state. R101 shows no aggregation in these conditions and, while pure MB builds up dimers on cellulose even at 2 × 10,8 mol g,1, in the presence of R101 no evidence on selfaggregation or heteroaggregation is found up to around 10,6 mol g,1. No exciplex formation is found as well. The overall fluorescence quantum yield measured on thick layers, once re-absorption effects are accounted for, amounts to 0.80 ± 0.07 for pure R101 and decreases steadily on increasing the concentration of MB. Results demonstrate the occurrence of radiative and nonradiative singlet energy transfer from R101 to MB. For thick layers of particles, the combined effect of both kinds of energy transfer amounts to nearly 80% at the highest acceptor concentration, while nonradiative transfer reaches 60% both for thin and optically thick layers. The dependence of nonradiative energy transfer efficiencies on the acceptor concentration is analyzed and the origin of departures from Förster behavior at low acceptor concentration is discussed. [source] Thermodynamic Analysis of Energy Transfer in Acidogenic CulturesENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2008J.-R. Bastidas-Oyanedel Abstract A global thermodynamic analysis, normally used for pure cultures, has been performed for steady-state data sets from acidogenic mixed cultures. This analysis is a combination of two different thermodynamic approaches, based on tabulated standard Gibbs energy of formation, global stoichiometry and medium compositions. It takes into account the energy transfer efficiency, ,, together with the Gibbs free energy dissipation, ,Go, analysis of the different data. The objective is to describe these systems thermodynamically without any heat measurement. The results show that , is influenced by environmental conditions, where increasing hydraulic retention time increases its value all cases. The pH effect on , is related to metabolic shifts and osmoregulation. Within the environmental conditions analyzed, , ranges from 0.23 for a hydraulic retention time of 20,h and pH,4, to 0.42 for a hydraulic retention time of 8,h and a pH ranging from 7,8.5. The estimated values of ,Go are comparable to standard Gibbs energy of dissipation reported in the literature. For the data sets analyzed, ,Go ranges from ,1210,kJ/molx, corresponding to a stirring velocity of 300,rpm, pH,6 and a hydraulic retention time of 6,h, to ,20744,kJ/molx for pH,4 and a hydraulic retention time of 20,h. For average conclusions, the combined approach based on standard Gibbs energy of formation and global stoichiometry, used in this thermodynamic analysis, allows for the estimation of Gibbs energy dissipation values from the extracellular medium compositions in acidogenic mixed cultures. Such estimated values are comparable to the standard Gibbs energy dissipation values reported in the literature. It is demonstrated that , is affected by the environmental conditions, i.e., stirring velocity, hydraulic retention time and pH. However, a relationship that relates this parameter to environmental conditions was not found and will be the focus of further research. [source] Bioavailability of decabromodiphenyl ether to the marine polychaete Nereis virensENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2010Susan L. Klosterhaus Abstract The flame retardant decabromodiphenyl ether (BDE 209) accumulates in humans and terrestrial food webs, but few studies have reported the accumulation of BDE 209 in aquatic biota. To investigate the mechanisms controlling the bioavailability of BDE 209, a 28-d bioaccumulation experiment was conducted in which the marine polychaete worm Nereis virens was exposed to a decabromodiphenyl ether (deca-BDE) commercial mixture (>85% BDE 209) in spiked sediments, in spiked food, or in field sediments. Bioaccumulation from spiked substrate with maximum bioavailability demonstrated that BDE 209 accumulates in this species. Bioavailability depends on the exposure conditions, however, because BDE 209 in field sediments did not accumulate (<0.3 ng/g wet weight; 28-d biota-sediment accumulation factors [BSAFs] <0.001). When exposed to deca-BDE in spiked sediments also containing lower brominated congeners (a penta-BDE mixture), bioaccumulation of BDE 209 was 30 times lower than when exposed to deca-BDE alone. Selective accumulation of the lower brominated congeners supports their prevalence in higher trophic level species. The mechanisms responsible for limited accumulation of BDE 209 may involve characteristics of the sediment matrix and low transfer efficiency in the digestive fluid. Environ. Toxicol. Chem. 2010;29:860,868. © 2009 SETAC [source] A New Way to Improve Glass-Forming Ability by Controlling the Preparation Conditions of Bulk Metallic GlassADVANCED ENGINEERING MATERIALS, Issue 3 2010Jie Mao Abstract The effects of mold preheating temperature on the glass-forming ability of Zr64.9Al7.9Ni10.7Cu16.5 and Zr47Cu37.5Ag7.5Al8 alloys are investigated using traditional copper mold casting. It is found that there exists an optimum mold temperature for glass-forming alloy systems. For the two Zr-based alloy systems studied the optimum mold temperature is 353,K. This is explained from the perspectives of heat transfer efficiency and the wettability between liquid alloy and copper mold. [source] The skin as a biofactory for systemic secretion of erythropoietin: potential of genetically modified keratinocytes and fibroblastsEXPERIMENTAL DERMATOLOGY, Issue 6 2008Frank Scheidemann Abstract Background:, The skin is an interesting target tissue for gene therapy applications because of its ready accessibility. One possibility would be to utilize the genetically modified skin as a biofactory secreting a systemically needed product, such as erythropoietin (EPO). Methods:, Keratinocytes (KC) and fibroblasts (FB) were transduced with a retroviral vector encoding human EPO. Gene transfer efficiency was assessed by real-time PCR analysis and flow cytometry of transduced cells. In addition, EPO synthesis and secretion were analysed by quantifying the amount of RNA and secreted protein in both monolayer cultures and skin equivalents (SE). Results:, When cultured as a monolayer, EPO-KC synthesized significantly more EPO than EPO-FB, as shown by quantitatively measuring the amount of secreted protein and RNA. This correlated with an increased EPO-vector incorporation in KC compared with FB, demonstrated by determining both the percentage of transduced cells and the average transgene copy number per cell. In addition, in transduced cell cultures enriched to equally high percentages of EPO+ cells, KC showed a higher activity of EPO secretion than FB. Finally, when assembled in a SE, EPO-KC secreted significantly higher amounts of EPO than EPO-FB, although reduced secretory activity of EPO-KC monolayers grown in high calcium concentrations suggested that in stratified epidermis differentiated KC secrete less EPO than non-differentiated KC. Conclusion:, In summary, while both transduced KC and FB are able to synthesize and secrete human EPO, KC show higher potential in serving as possible target cells for therapeutic substitution with EPO, probably because of improved transduction rates and increased secretory activity. [source] Stoichiometric impacts of increased carbon dioxide on a planktonic herbivoreGLOBAL CHANGE BIOLOGY, Issue 6 2003JOTARO URABE Abstract The partial pressure of carbon dioxide (pCO2) in lake ecosystems varies over four orders of magnitude and is affected by local and global environmental perturbations associated with both natural and anthropogenic processes. Little is known, however, about how changes in pCO2 extend into the function and structure of food webs in freshwater ecosystems. To fill this gap, we performed laboratory experiments using the ecologically important planktonic herbivore Daphnia and its algal prey under a natural range of pCO2 with low light and phosphorus supplies. The experiment showed that increased pCO2 stimulated algal growth but reduced algal P : C ratio. When feeding on algae grown under high pCO2, herbivore growth decreased regardless of algal abundance. Thus, high CO2 -raised algae were poor food for Daphnia. Short-term experimental supplementation of PO4 raised the P content of the high CO2 -raised algae and improved Daphnia growth, indicating that low Daphnia growth rates under high pCO2 conditions were due to lowered P content in the algal food. These results suggest that, in freshwater ecosystems with low nutrient supplies, natural processes as well as anthropogenic perturbations resulting in increased pCO2 enhance algal production but reduce energy and mass transfer efficiency to herbivores by decreasing algal nutritional quality. [source] Molecular Origin of the Temperature-Dependent Energy Migration in a Rigid-Rod Ladder-Phenylene Molecular Host,ADVANCED MATERIALS, Issue 3 2006H. Wiesenhofer Excitation diffusion is studied in a molecular host doped with a luminescent guest. An atomistic model based on the coupling of the electronic excitations to low-frequency intramolecular vibrations reproduces remarkably well the measured temperature-dependent host-to-guest energy transfer efficiency (see Figure). [source] Comparison of performance of heat regenerators: Relation between heat transfer efficiency and pressure dropINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2001Françoise Duprat Abstract Heat regenerators transfer heat from one gas to another, with an intermediate storage in solids. The heat transfer surface for gas flow application should provide at the same time high surface area and low friction factor. Three geometries of heat transfer surface, monolith, stack of woven screens and bed of spheres, have been compared. Their performance was evaluated from the pressure drop of the heat regenerator working at a given heat transfer efficiency. The comparison was performed using numerical simulation and published measurements of heat transfer and flow friction characteristics. By adjusting the length and the period of the exchanger, it is possible to obtain the same heat transfer efficiency with the three geometries. Beds of spheres give very short and compact heat regenerators, working at high pressure drop. At the opposite, monoliths form long regenerators working at low pressure drop. Stacks of woven screens cover a wide range of performance: low porosity woven screens give high heat transfer efficiency and high pressure drop, while high porosity woven screens offer performance similar to that of the monoliths. Copyright © 2001 John Wiley & Sons, Ltd. [source] Influence of maternal mass and condition on energy transfer in Weddell sealsJOURNAL OF ANIMAL ECOLOGY, Issue 3 2006KATHRYN E. WHEATLEY Summary 1Environmental variation influences food abundance and availability, which is reflected in the reproductive success of top predators. We examined maternal expenditure, offspring mass and condition for Weddell seals in 2 years when individuals exhibited marked differences in these traits. 2For females weighing 355 kg there was a positive relationship between maternal post-partum mass (MPPM) and lactation length, but below this there was no relationship, suggesting that heavier females were able to increase lactation length but lighter females were restricted to a minimum lactation period of 33 days. 3Overall, females were heavier in 2002, but in 2003 shorter females were lighter than similar-sized females in 2002 suggesting that the effects of environmental variability on foraging success and condition are more pronounced in smaller individuals. 4There was no relationship between MPPM and pup birth mass, indicating pre-partum investment did not differ between years. However, there was a positive relationship between MPPM and pup mass gain. Mass and energy transfer efficiency were 10·2 and 5·4% higher in 2002 than 2003, which suggests costs associated with a putatively poor-resource year were delayed until lactation. 5Heavier females lost a higher proportion of mass during lactation in both years, so smaller females may not have been able to provide more to their offspring to wean a pup of similar size to larger females. 6MPPM had only a small influence on total body lipid; therefore, regardless of mass, females had the same relative body composition. Females with male pups lost a higher percentage of lipid than those with female pups, but by the end of lactation female pups had 4·5% higher lipid content than males. 7It appears that for Weddell seals the consequences of environmentally induced variation in food availability are manifested in differences in maternal mass and expenditure during lactation. These differences translate to changes in pup mass and condition at weaning with potential consequences for future survival and recruitment. [source] Catalytic synthesis of styryl-capped isotactic polypropylenesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2010Huahua Huang Abstract Bis-styrenic molecules, 1,4-divinylbenzene (DVB) and 1,2-bis(4-vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H2) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac -dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, I) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl-capped isotactic polypropylenes (i -PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H2 or BVPE/H2 caused a copolymerization-like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H2 or BVPE/H2, which gave the styryl-terminated polymer chain alongside a metal-hydride active species. It was confirmed that the chain reinsertion occurred in a regio-irregular 1,2-fashion, which contrasted with a normal 2,1-insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal-hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl-terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non-conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709,3713, 2010 [source] Quantitative FRET Analysis With the E0GFP-mCherry Fluorescent Protein PairPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009Lorenzo Albertazzi Fluorescence resonance energy transfer (FRET) between fluorescent proteins (FPs) is a powerful tool to investigate protein,protein interaction and even protein modifications in living cells. Here, we analyze the E0GFP-mCherry pair and show that it can yield a reproducible quantitative determination of the energy transfer efficiency both in vivo and in vitro. The photophysics of the two proteins is reported and shows good spectral overlap (Förster radius R0 = 51 Å), low crosstalk between acceptor and donor channels, and independence of the emission spectra from pH and halide ion concentration. Acceptor photobleaching (APB) and one- and two-photon fluorescence lifetime imaging microscopy (FLIM) are used to quantitatively determine FRET efficiency values. A FRET standard is introduced based on a tandem construct comprising donor and acceptor together with a 20 amino acid long cleavable peptidic linker. Reference values are obtained via enzymatic cleavage of the linker and are used as benchmarks for APB and FLIM data. E0GFP-mCherry shows ideal properties for FLIM detection of FRET and yields high accuracy both in vitro and in vivo. Furthermore, the recently introduced phasor approach to FLIM is shown to yield straightforward and accurate two-photon FRET efficiency data even in suboptimal experimental conditions. The consistence of these results with the reference method (both in vitro and in vivo) reveals that this new pair can be used for very effective quantitative FRET imaging. [source] Two mechanisms of 1D2 fluorescence quenching of Pr3+ -doped Y2SiO5 crystalPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003Yu. V. Malyukin Abstract In Y2SiO5:Pr3+ crystals (0.1 at%, 0.3 at%, 0.6 at% , and 1.8 at% Pr3+) characterized by the existence of two types of Pr3+ optical centers, the energy transfer has been investigated using time-resolved site-selective spectroscopy techniques. The results obtained show that at certain conditions there are two different mechanisms of fluorescence quenching of the excited 1D2 states of Pr3+ ions. At 0.3 at% Pr3+ and under the excitation of 1D2 states as the result of 3P0 , 1D2 nonradiative relaxation, the phonon-assisted energy transfer from 1D2 states of the I-type Pr3+ ions to the II-type ones has been found. The nonexponential part of donor fluorescence decay was described by the law t0.5. and the transfer efficiency exhibits a strong temperature dependence in the range of 1.5,80 K. At the direct selective excitation of the 1D2 states of one type Pr3+ optical centers it was possible to observe only their own fluorescence which quenched at a concentration above 0.6 at% Pr3+. The donor fluorescence decay was not fit by the law t0.5 and the quenching efficiency was characterized by the square-loaw dependence on the concentration and a very poor dependency on the temperature. The analysis of some models allows us to assume, that in this case, the cooperative quenching of the 1D2 states of both type Pr3+ optical centers can take place. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dimer,monomer equilibrium of human thymidylate synthase monitored by fluorescence resonance energy transferPROTEIN SCIENCE, Issue 5 2010Filippo Genovese Abstract An ad hoc bioconjugation/fluorescence resonance energy transfer (FRET) assay has been designed to spectroscopically monitor the quaternary state of human thymidylate synthase dimeric protein. The approach enables the chemoselective engineering of allosteric residues while preserving the native protein functions through reversible masking of residues within the catalytic site, and is therefore suitable for activity/oligomerization dual assay screenings. It is applied to tag the two subunits of human thymidylate synthase at cysteines 43 and 43, with an excitation energy donor/acceptor pair. The dimer,monomer equilibrium of the enzyme is then characterized through steady-state fluorescence determination of the intersubunit resonance energy transfer efficiency. [source] Hydrodynamics and mass transfer in a pulsed packed columnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2000Yu Jie Abstract The hydrodynamics and mass transfer characteristics of a pulsed packed column (PPC) filled with a stainless steel super mini ring (SMR), ceramic and stainless steel Raschig rings have been studied using a 30% tributyl phosphate-kerosene (dispersed phase)/acetic acid/water (continuous phase) system. Experiments were performed in a 100 mm internal diameter column with 1.0 m height of packing. The mass transfer and axial mixing parameters were estimated simultaneously from the measured concentration profiles of two-phase based on the backflow model. It was found that pulsation has great influence on hydrodynamics and mass transfer characteristics of PPC with the SMR. Hoxp and Hox decrease significantly with pulsation, whereas flooding velocity decreases only slightly. Comparison among the three types of packing showed that the SMR has superior characteristics both in terms of capacity and mass transfer efficiency. The influence of mass transfer on characteristics of PPC was also studied. New empirical equations of characteristic velocity, Hoxand Hoxd were proposed and good agreement between calculated and experimental data was obtained. Les caractéristiques de l'hydrodynamique et du transfert de matiére dans une colonne pulsée garni (PPC) contenant des super mini-anneaux (SMR) d'acier inoxydable et des anneaux de Raschig de céramique et d'acier inoxydable (s.s.) ont été étudiées à l'aide du système 30% de phosphate de tributyl-kérosène (phase dispersée)/acide acétique/eau (phase continue). On a mené des expériences dans une colonne de 100 mm de diamètre intérieur avec une hauteur de garnissage de 1.0 m. Les paramètres de transfert de matière et de mélange axial ont été estimés simultanément à partir des profils de concentration mesurés de deux phases d'après le modèle de reflux. On a trouvé que la pulsation avait une grande influence sur les caractéristiques de l'hydrodynamique et de transfert de matière de la colonne PPC avec le SMR. Hoxp et Hox diminuent de maniére significative avec la pulsation, tandis que la vitesse d'engorgement ne diminue que Iégèrement. Une comparaison entre les trois types de garnissage montre que le SMR possède des caractéristiques supérieures à la fois en termes de capacité et d'efficacité du transfert de matière. L'influence du transfert de matière sur les caractéristiques de la colonne PPC a également été étudiée. De nouvelles équations empiriques de la vitesse caractéristique, Hox et Hoxd, sont proposées et un bon accord est obtenu entre les données calculées et les données expérhentales. [source] Characterisation of a P140K mutant O6 -methylguanine-DNA-methyltransferase (MGMT)-expressing transgenic mouse line with drug-selectable bone marrowTHE JOURNAL OF GENE MEDICINE, Issue 9 2006Belinda A. Kramer Abstract Background Gene transfer of the P140K mutant of O6 -methylguanine-DNA-methyltransferase (MGMT(P140K)) into hematopoietic stem cells (HSC) provides a mechanism for drug resistance and the selective expansion of gene-modified cells in vivo. Possible clinical applications for this strategy include chemoprotection to allow dose escalation of alkylating chemotherapy, or combining MGMT(P140K) expression with a therapeutic gene in the treatment of genetic diseases. Our aim is to use MGMT(P140K)-driven in vivo selection to develop allogeneic micro-transplantation protocols that rely on post-engraftment selection to overcome the requirement for highly toxic pre-transplant conditioning, and to establish and maintain predictable levels of donor/recipient chimerism. Methods Using stably transfected murine embryonic stem (ES) cells, we have generated a C57BL/6 transgenic mouse line with expression of MGMT(P140K) within the hematopoietic compartment for use as a standard source of donor HSC in such models. Functional characterisation of transgene expression was carried out in chemotherapy-treated transgenic mice and in allogeneic recipients of transgenic HSC. Results Expression of the transgene provided chemoprotection and allowed in vivo selection of MGMT(P140K)-expressing cells in transgenic mice after exposure to O6 -benzylguanine (BG) and N,N,-bis(2-chloroethyl)- N -nitrosourea (BCNU). In an allogeneic transplant experiment in which transgenic HSC were engrafted into 129 strain recipients following low intensity conditioning (Busulfan, anti-CD8, anti-CD40Ligand), MGMT(P140K)-expressing cells could be selected using chemotherapy. Conclusions This MGMT(P140K) transgenic mouse line provides a useful source of drug-selectable donor cells for the development of non-myeloablative allogeneic transplant models in which variation in transplant conditioning elements can be investigated independently of gene transfer efficiency. Copyright © 2006 John Wiley & Sons, Ltd. [source] Novel two-stage screening procedure leads to the identification of a new class of transfection enhancersTHE JOURNAL OF GENE MEDICINE, Issue 6 2006Birgit Neukamm Abstract Background Non-viral gene transfer efficiency is low as compared to viral vector systems. Here we describe the discovery of new drugs that are capable of enhancing non-viral gene transfer into mammalian cells using a novel two-stage screening procedure. Methods First, potential candidates are preselected from a molecular library at various concentrations by a semi-automated yeast transfection screen (YTS). The maximal transfection efficiency of every positive drug is subsequently determined in independent experiments at the optimal concentration and compared to the inhibitory effect of the drug on cell growth (IC50). In a subsequent mammalian cell transfection screen (MTS), the maximal transfection efficiency and the IC50 are determined for all preselected drugs using a human cell line and a luciferase reporter gene construct. Results Employing our novel system we have been able to identify a new class of transfection enhancers, the tricyclic antidepressants (i.e. doxepin, maprotiline, desipramine and amoxapine). All positive drugs enhanced gene transfer in both yeast and human cell lines, but lower concentrations were sufficient for mammalian cells. With a triple combination of doxepin, amoxapine and chloroquine we obtained a transfection efficiency that exceeded that of chloroquine, one of the best-known transfection enhancers of mammalian cells, by nearly one order of magnitude. Conclusions Non-viral gene transfer efficiency can be increased significantly using new transfection enhancers that are identified by a novel, semi-automated two-stage screening system employing yeast cells in the first and specific human target cells in the second round. Copyright © 2006 John Wiley & Sons, Ltd. [source] Enhancing rAAV vector expression in the lungTHE JOURNAL OF GENE MEDICINE, Issue 7 2005Isabel Virella-Lowell Abstract Despite favorable DNA transfer efficiency, gene expression from recombinant adeno-associated virus (rAAV2) vectors in the lung has been variable in the context of cystic fibrosis (CF) gene therapy. This is due, in part, to the large size of the CF transmembrane regulator (CFTR)-coding sequence which necessitates the use of compact endogenous promoter elements versus stronger exogenous promoters. We evaluated the possibility that gene expression from rAAV could be improved by using AAV capsid serotypes with greater tropism for the apical surface of airway cells (i.e. rAAV5 or rAAV1) and/or using strong promoters such as the cytomegalovirus (CMV) enhancer/chicken beta-actin hybrid (C,) promoter. The relative activity of the CMV immediate-early (CMVie) promoter, the C, promoter, and the C, promoter with a downstream woodchuck hepatitis virus post-transcriptional regulatory element (wpre) were assessed in vitro and in vivo in C57\Bl6 mice using human alpha-1 antitrypsin (hAAT) as a secreted reporter. In vivo, the C,-AAT-wpre group achieved maximum serum levels of 1.5 mg/ml of hAAT. AAV capsid serotypes were then compared in vivo utilizing the transcriptionally optimized CB-wpre cassette in rAAV serotype 1, 2 or 5 capsids (rAAV1, rAAV2, and rAAV5), utilizing luciferase as a reporter to compare expression over a wide dynamic range. The pulmonary luciferase levels at 8 weeks were similar in rAAV5 and rAAV1 groups (2.9 × 106 relative light units (RLU)/g tissue and 2.7 × 106 RLU/g tissue, respectively), both of which were much higher than rAAV2. Although the advantage of rAAV5 over rAAV2 in the lung has already been described, the availability of another serotype (rAAV1) capable of efficient gene transfer in the lung could be useful. Copyright © 2005 John Wiley & Sons, Ltd. [source] Deficiency of oncoretrovirally transduced hematopoietic stem cells and correction through ex vivo expansionTHE JOURNAL OF GENE MEDICINE, Issue 2 2005David Bryder Abstract Background Extensive efforts to develop hematopoietic stem cell (HSC) based gene therapy have been hampered by low gene marking. Major emphasis has so far been directed at improving gene transfer efficiency, but low gene marking in transplanted recipients might equally well reflect compromised repopulating activity of transduced cells, competing for reconstitution with endogenous and unmanipulated stem cells. Methods The autologous settings of clinical gene therapy protocols preclude evaluation of changes in repopulating ability following transduction; however, using a congenic mouse model, allowing for direct evaluation of gene marking of lympho-myeloid progeny, we show here that these issues can be accurately addressed. Results We demonstrate that conditions supporting in vitro stem cell self-renewal efficiently promote oncoretroviral-mediated gene transfer to multipotent adult bone marrow stem cells, without prior in vivo conditioning. Despite using optimized culture conditions, transduction resulted in striking losses of repopulating activity, translating into low numbers of gene marked cells in competitively repopulated mice. Subjecting transduced HSCs to an ex vivo expansion protocol following the transduction procedure could partially reverse this loss. Conclusions These studies suggest that loss of repopulating ability of transduced HSCs rather than low gene transfer efficiency might be the main problem in clinical gene therapy protocols, and that a clinically feasible ex vivo expansion approach post-transduction can markedly improve reconstitution with gene marked stem cells. Copyright © 2004 John Wiley & Sons, Ltd. [source] Improved gene transfer and normalized enzyme levels in primitive hematopoietic progenitors from patients with mucopolysaccharidosis type I using a bioreactorTHE JOURNAL OF GENE MEDICINE, Issue 12 2004Dao Pan Abstract Background One of the major barriers to the clinical application of hematopoietic stem cell (HSC) gene therapy has been relatively low gene transfer efficiency. Other inadequacies of current transduction protocols are related to their multi-step procedures, e.g., using tissue-culture flasks, roller bottles or gas-permeable bags for clinical application. Methods In comparison with a conventional bag transduction protocol, a ,closed' hollow-fiber bioreactor system (HBS) was exploited to culture and transduce human peripheral blood CD34+ progenitor cells (PBPCMPS) from patients with mucopolysaccharidosis type I (MPS I) using an amphotropic retroviral vector based on a murine Moloney leukemia virus LN prototype. Both short-term colony-forming cell (CFC) and long-term culture initiating cell (LTCIC) assays were employed to determine transduction frequency and transgene expression in committed progenitor cells and primitive progenitors with multi-lineage potentials. Results A novel ultrafiltration-transduction method was established to culture and transduce enzyme-deficient PBPCMPS over a 5-day period without loss in viability and CD34 identity (n = 5). Significantly higher transduction efficiencies were achieved in primary CFC that derived from the HBS (5.8,14.2%) in comparison with those from gas-permeable bags (undetectable to 1.7%; p < 0.01). Up to 15-fold higher-than-normal enzyme activity was found in selected PBPCMPS -LP1CD transductants. Moreover, higher gene transfer (4.4-fold) and expression in very primitive progenitors were observed in products from the HBS compared with bag experiments as indicated by CFC derived from primitive LTCIC. Remarkably, with relatively modest gene transfer levels in LTCIC from HBS experiments, the expression of the IDUA transgene corrected the enzyme-deficiency in 5-week long-term cultures (LTC). Conclusions MPS I progenitor cells achieved normalized enzyme levels in LTC after transduction in a HBS system. These studies demonstrate the advantages of a bioreactor-transduction system for viral-mediated stem cell gene transfer. Copyright © 2004 John Wiley & Sons, Ltd. [source] An efficient targeted radiotherapy/gene therapy strategy utilising human telomerase promoters and radioastatine and harnessing radiation-mediated bystander effectsTHE JOURNAL OF GENE MEDICINE, Issue 8 2004Marie Boyd Abstract Background Targeted radiotherapy achieves malignant cell-specific concentration of radiation dosage by tumour-affinic molecules conjugated to radioactive atoms. Combining gene therapy with targeted radiotherapy is attractive because the associated cross-fire irradiation of the latter induces biological bystander effects upon neighbouring cells overcoming low gene transfer efficiency. Methods We sought to maximise the tumour specificity and efficacy of noradrenaline transporter (NAT) gene transfer combined with treatment using the radiopharmaceutical meta-[131I]iodobenzylguanidine ([131I]MIBG). Cell-kill was achieved by treatment with the ,-decay particle emitter [131I]MIBG or the ,-particle emitter [211At]MABG. We utilised our novel transfected mosaic spheroid model (TMS) to determine whether this treatment strategy could result in sterilisation of spheroids containing only a small proportion of NAT-expressing cells. Results The concentrations of [131I]MIBG and [211At]MABG required to reduce to 0.1% the survival of clonogens derived from the TMS composed of 100% of NAT gene-transfected cells were 1.5 and 0.004 MBq/ml (RSV promoter), 8.5 and 0.0075 MBq/ml (hTR promoter), and 9.0 and 0.008 MBq/ml (hTERT promoter), respectively. The concentrations of radiopharmaceutical required to reduce to 0.1% the survival of clonogens derived from 5% RSV/NAT and 5% hTERT/NAT TMS were 14 and 23 MBq/ml, respectively, for treatment with [131I]MIBG and 0.018 and 0.028 MBq/ml, respectively, for treatment with [211At]MABG. Conclusions These results indicate that the telomerase promoters have the capacity to drive the expression of the NAT. The potency of [211At]MABG is approximately three orders of magnitude greater than that of [131I]MIBG. Spheroids composed of only 5% of cells expressing NAT under the control of the RSV or hTERT promoter were sterilised by radiopharmaceutical treatment. This observation is indicative of bystander cell-kill. Copyright © 2004 John Wiley & Sons, Ltd. [source] In vivo gene marking of rhesus macaque long-term repopulating hematopoietic cells using a VSV-G pseudotyped versus amphotropic oncoretroviral vectorTHE JOURNAL OF GENE MEDICINE, Issue 4 2004Patricia A. Shi Abstract Background Gene transfer efficiency into primitive hematopoietic cells may be limited by their expression of surface receptors allowing vector entry. Vectors pseudotyped with the vesicular stomatitis virus (VSV-G) envelope do not need receptors to enter cells, and therefore may provide superior transduction efficiency. Methods Using a competitive repopulation model in the rhesus macaque, we examined in vivo gene marking levels of blood cells transduced with two vectors: (i) a VSV-G pseudotyped retrovirus and (ii) a conventional amphotropic retrovirus. The VSV-G vector, containing the human glucose-6-phosphate dehydrogenase (G6PD) gene, was constructed for treatment of severe hemolytic anemia caused by G6PD deficiency. Three myeloablated animals were transplanted with peripheral blood CD34+ cells, half of which were transduced with the VSV-G vector and the other half with the amphotropic vector. Results In all animals post-transplantation, levels of in vivo marking in circulating granulocytes and mononuclear cells were similar: 1% or less with both vectors. In one animal, the human G6PD enzyme transferred by the VSV-G vector was expressed in erythrocytes, early after transplantation, at a level of 45% of the endogenous rhesus G6PD protein. Conclusions In a clinically relevant animal model, we found similar in vivo marking with a VSV-G pseudotyped and a standard amphotropic oncoretroviral vector. Amphotropic receptor expression may not be a limiting factor in transduction efficiency, but VSV-G pseudotypes possess other practical advantages that may make them advantageous for clinical use. Copyright © 2004 John Wiley & Sons, Ltd. [source] Lactosylated polyethylenimine for gene transfer into airway epithelial cells: role of the sugar moiety in cell delivery and intracellular trafficking of the complexesTHE JOURNAL OF GENE MEDICINE, Issue 3 2004Stéphanie Grosse Abstract Background As we have previously shown that lactosylated polyethylenimine (PEI) is the most efficient glycosylated PEI for gene transfer into human airway epithelial cells in primary culture, we have studied here the role of the lactose residue in the enhancement of gene transfer efficiency observed with lactosylated PEI as compared with unsubstituted PEI in immortalized (,CFTE29o- cells) and primary human airway epithelial cells. Methods and results After three transfections of 1 h performed daily, 60% of ,CFTE29o- cells were transfected with lactosylated PEI, whereas 25% of cells were transfected with unsubstituted PEI (p < 0.05). Cell viability was 1.8-fold greater with lactosylated PEI as compared with unsubstituted PEI (p < 0.05). As assessed by flow cytometry, the cellular uptake of lactosylated complexes was greater than that of complexes made with unsubstituted PEI (p < 0.05) and involved mostly a receptor-mediated endocytosis. The study of the intracellular trafficking in airway epithelial cells of complexes showed an endosomal and lysosomal accumulation of lactosylated complexes. In the presence of a proton pump inhibitor, the level of lactosylated and unsubstituted PEI-mediated gene expression was reduced more than 20-fold, whereas the cell viability increased to almost 100%. For both complexes, a nuclear localization was observed for less than 5% of intracellular complexes. Conclusions Our results show that the greater gene transfer efficiency observed for lactosylated complexes may be attributed to a higher amount of lactosylated complexes incorporated by airway epithelial cells and a lower cytotoxicity that might be related to reduced endosomolytic properties. However, the lactose residues substituting the PEI did not promote the entry of the plasmid into the nucleus. Copyright © 2004 John Wiley & Sons, Ltd. [source] Timing of Human Insulin-Like Growth Factor-1 Gene Transfer in Reinnervating Laryngeal Muscle,THE LARYNGOSCOPE, Issue 4 2004Hideki Nakagawa MD Abstract Objectives/Hypothesis The authors have designed a rat laryngeal paralysis model to study gene transfer strategies using a muscle-specific expression system to enhance local delivery of human insulin-like growth factor-1 (hIGF-1). In preliminary studies, a nonviral vector containing the ,-actin promoter and human hIGF-1 sequence produced both neurotrophic and myotrophic effects 1 month after single injection of plasmid formulation into paralyzed rat thyroarytenoid muscle in vivo. Based on these findings, it is hypothesized that the effects of hIGF-1 will enhance the results of laryngeal muscle innervation procedures. The timing of gene delivery relative to nerve repair is likely to be important, to optimize the results. Study Design Prospective analysis. Methods The effects of nonviral gene transfer for the delivery of hIGF-1 were evaluated in rats treated immediately following recurrent laryngeal nerve transection and repair and in rats receiving a delayed treatment schedule, 30 days after nerve transection and repair. Gene transfer efficiency was determined using polymerase chain reaction and reverse transcriptase,polymerase chain reaction techniques. Muscle fiber diameter, motor endplate length, and percentage of motor endplates with nerve contact were examined to assess hIGF-1 trophic effects. Results Compared with reinnervated untreated control samples, both early and delayed hIGF-1 transfer resulted in significant increase in muscle fiber diameter. Motor endplate length was significantly decreased and nerve/motor endplate contact was significantly increased following delayed gene transfer, but not after early treatment. Conclusion We infer from results of the study that delayed hIGF-1 gene transfer delivered by a single intramuscular injection will enhance the process of muscle reinnervation. The clinical relevance of these findings supports the future application of gene therapy using nonviral vectors for management of laryngeal paralysis and other peripheral nerve injuries. [source] Exploration of target molecules for prostate cancer gene therapyTHE PROSTATE, Issue 11 2007Kazuhiro Suzuki Abstract BACKGROUND Focusing on Adv-FZ33, a modified adenovirus in which a synthetic 33-amino-acid immunoglobulin G-binding domain was inserted into the adenoviral fiber protein, we tried to identify suitable target molecules for prostate cancer-specific gene therapy. METHODS Hybridomas were established from mice immunized with prostate cancer cell lines. The hybridomas were screened using Adv-FZ33 to create monoclonal antibodies (mAbs) that induced high gene transfer efficiency for PC-3 cells. Furthermore, we identified target antigens of the mAbs by immunoprecipitation and mass spectrometry, and investigated the expression of target molecules by flow cytometry and immunocytochemistry. RESULTS Using Adv-FZ33, we established four different mouse mAbs that increased transduction efficiency for PC-3. The target antigens identified were Ep-CAM, CD155, HAI-1, and Na,K-ATPase ,1. These antigens were expressed in several cancer cell lines, including prostate cancer. Human prostatic myofibroblast cells lacked expression of Ep-CAM and HAI-1. CONCLUSIONS We established anti-Ep-CAM mAb and anti- HAI-1 mAbs. Gene transduction via Ep-CAM and HAI-1 may be a novel strategy for treatment of prostate cancer. Prostate 67: 1163,1173, 2007. © 2007 Wiley-Liss, Inc. [source] Hemocompatibility Assessment of Carbonic Anhydrase Modified Hollow Fiber Membranes for Artificial LungsARTIFICIAL ORGANS, Issue 5 2010Heung-Il Oh Abstract Hollow fiber membrane (HFM)-based artificial lungs can require a large blood-contacting membrane surface area to provide adequate gas exchange. However, such a large surface area presents significant challenges to hemocompatibility. One method to improve carbon dioxide (CO2) transfer efficiency might be to immobilize carbonic anhydrase (CA) onto the surface of conventional HFMs. By catalyzing the dehydration of bicarbonate in blood, CA has been shown to facilitate diffusion of CO2 toward the fiber membranes. This study evaluated the impact of surface modifying a commercially available microporous HFM-based artificial lung on fiber blood biocompatibility. A commercial poly(propylene) Celgard HFM surface was coated with a siloxane, grafted with amine groups, and then attached with CA which has been shown to facilitate diffusion of CO2 toward the fiber membranes. Results following acute ovine blood contact indicated no significant reduction in platelet deposition or activation with the siloxane coating or the siloxane coating with grafted amines relative to base HFMs. However, HFMs with attached CA showed a significant reduction in both platelet deposition and activation compared with all other fiber types. These findings, along with the improved CO2 transfer observed in CA modified fibers, suggest that its incorporation into HFM design may potentiate the design of a smaller, more biocompatible HFM-based artificial lung. [source] Carrier effects on oxygen mass transfer behavior in a moving-bed biofilm reactorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Jie Ying Jing Abstract This study investigates the carrier effects on the oxygen mass transfer behavior of a gas,liquid biofilm surface, and aims to provide evidence for parameter optimization in the practical operation of a moving-bed biofilm reactor (MBBR) during the coking-plant wastewater process. By using the dynamic oxygen dissolution method, the volumetric oxygen mass transfer coefficient KLa was measured by varying the suspended carrier stuffing rate and the intensity of aeration. Within the range of fluidizable flow rate, the efficiency of oxygen mass transfer increased with suspended carrier stuffing rate, and KLa reached its peak value when the stuffing rate was 40%. KLa has an increasing trend with an increase of the aeration intensity, but high aeration intensity was not favorable for reactor operation. Better oxygen mass transfer effect and higher oxygen transfer efficiency could be achieved when the aeration intensity was 0.3 m3 h,1 and the suspended carrier stuffing rate was 30,50%. The possible mechanisms that can account for carrier effects on oxygen mass transfer are the changes in the gas,liquid interfacial area. The ammonia nitrogen removal performance of the coking-plant wastewater in MBBR was satisfied by using the above-suggested conditions. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Efficiency of non-reactive isothermal bubble column based on mass transferASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008Subrata Kumar Majumder Assistant Professor Abstract Bubble column reactor as a gas,liquid contactor is extensively used in the chemical and biochemical industries. Mass transfer coefficients governing the transport processes in bubble contactors are a growing concern in chemical and biotechnological processes whose rates are often limited by the mass transfer rate. The influences of different physical, dynamic and geometric variables affect the efficiency characterization of the equipment which are involved in gas/liquid mass transfer processes. This characterization has great importance to optimize the process plant design. In this article, efficiency of two-phase mass transfer in bubble column reactors has been analyzed based on dynamic, geometric and physical variables of the system. An empirical correlation for mass transfer efficiency has also been developed in terms of those variables. The present analysis on the gas,liquid mass transfer efficiency of bubble column may give insight into a further understanding and modeling of multiphase reactors in industrial applications. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||