Uptake and depuration of gold nanoparticles in Daphnia magna

This study presents a series of short-term studies (total duration 48 h) of uptake and depuration of engineered nanoparticles (ENP) in neonate Daphnia magna. Gold nanoparticles (Au NP) were used to study the influence of size, stabilizing agent and feeding on uptake and depuration kinetics and animal body burdens. 10 and 30 nm Au NP with different stabilizing agents [citrate (CIT) and mercaptoundecanoic acid (MUDA)] were tested in concentrations around 0.5 mg Au/L. Fast initial uptake was observed for all studied Au NP, with CIT stabilized Au NP showing similar rates independent of size and MUDA showing increased uptake for the smaller Au NP (MUDA 10 nm > CIT 10 nm, 30 nm > MUDA 30 nm). However, upon transfer to clean media no clear trend on depuration rates was found in terms of stabilizing agent or size. Independent of stabilizing agent, 10 nm Au NP resulted in higher residual whole-animal body burdens after 24 h depuration than 30 nm Au NP with residual body burdens about one order of magnitude higher of animals exposed to 10 nm Au NP. The presence of food (P. subcapitata) did not significantly affect the body burden after 24 h of exposure, but depuration was increased. While food addition is not necessary to ensure D. magna survival in the presented short-term test design, the influence of food on uptake and depuration kinetics is essential to consider in long term studies of ENP where food addition is necessary. This study demonstrates the feasibility of a short-term test design to assess the uptake and depuration of ENP in D. magna. The findings underlines that the assumptions behind the traditional way of quantifying bioconcentration are not fulfilled when ENPs are studied.

Rapidly progressive Whipple's disease of the central nervous system

We describe a patient with rapidly progressive Whipple's disease confined to the central nervous system (CNS). The diagnosis was made pre-mortem following stereotactic and open brain biopsis and confirmed at autopsy. Despite appropriate antibiotic treatment, the disease ran a fulminant course to death after nine weeks.

Use of dimensionless residence time to study variations in breakthrough behaviour in expanded beds formed from varied particle size distributions

This work demonstrates an experimental method for studying breakthrough behaviour in expanded beds. The behaviour of beds made with differently sized particles were studied at varying flowrates. The use of a dimensionless residence time measurement allowed a more valid comparison of breakthrough characteristics in expanded bed operation by compensating for the changes in bed volume that occur during expansion. We demonstrate that bed breakthrough behaviour can be compared directly even when the beds contain different-sized particles and hence have different expanded volumes. By utilising this concept we demonstrate that, in the case of the Alcohol Dehydrogenase (ADH) / STREAMLINE Phenyl system used here, there was little or no variation in ADH breakthrough behaviour between beds of differently sized particles operating at flowrates above 100 cm/h. This suggests that the higher specific surface area and hence binding capacity of smaller particles is negated in this case due to mass transfer limitations and the increase in system void volume even at normal operating flowrates of 200-300 cm/h.

Hydrophobic interaction ligand selection and scale-up of an expanded bed separation of an intracellular enzyme from Saccharomyces cerevisiae

A prototype Streamline-Phenyl matrix was evaluated in a hydrophobic interaction mode for the direct recovery of alcohol dehydrogenase (ADH) from yeast cell homogenate. At 5% breakthrough of ADH, a yield of 100% was obtained for a dynamic expanded bed capacity of 240 U(ADH)/ml matrix with a purification factor of 9.2. This compared with a dynamic capacity of 3013 U(ADH)/ml matrix for the packed bed equivalent and a purification factor of 18. In both systems the purification factor was found to increase simultaneously with a decrease in yield as the load of homogenate or breakthrough of ADH was increased. The expanded bed mode of operation conferred considerable robustness with respect to process fouling. No loss in yield was seen over five cycles of repeat loading with an unclarified homogenate. By contrast the packed bed media showed a decrease in yield from 86 to 56% over the same period. Successful scale up of the expanded bed protocol for a 20% breakthrough was demonstrated over a fourfold increase in column diameter. The application of hydrophobic interaction chromatography mediated expanded bed adsorption and its scale-up is discussed in the context of large-scale operations.

The use of rapid on-line monitoring of products and contaminants from within an expanded bed to control separations exhibiting fast breakthrough characteristics and to maximize productivity

Conventional control of expanded-bed adsorption (EBA), like that of packed-bed chromatography, is based upon off-line measurements of the column eluant. The relatively high-void volumes in EBA systems means that this approach can lead to significant performance losses caused by the inability to achieve tight control of breakthrough. This problem is made worse if the product has a fast breakthrough characteristic or if it is necessary to operate to low levels of product loss. In this article we examine the utility of constant on-line monitoring from within the expanded bed using stopped-flow analysis (SFA) to provide data for the control of the expanded-bed operation. A modified Streamline 50 column with side ports that enable sampling along the expanded axis of the bed was used. Comparisons between off-line and on-line measurements are presented, showing how the advanced monitoring method can lead to better control and to an analysis of breakthrough development within the bed. The expanded bed was used to purify alcohol dehydrogenase from homogenized suspensions of bakers' yeast. Accurate control of breakthrough to 10% of the target enzyme was achieved using a SFA control system with a response time of 40 seconds. On-line data compared well to assays carried out off-line on the outlet stream for both the product enzyme (ADH), total protein, RNA, and cell debris levels (via UV 650 nm). This information was used to generate a series of graphs with which to track the EBA process in real-time. Results showed that bed utilization was not linear along the bed axis so that, for example, 60% of ADH is bound in the bottom 33% of the column during loading.

Experimental measurement of particle size distribution and voidage in an expanded bed adsorption system

This paper presents an experimental analysis of matrix bead size distribution and voidage variations with axial height in an expanded bed adsorption system. Use of a specially constructed expanded bed with side ports has enabled sampling from within the expanded bed along the vertical axis. Particles removed from within the bed were measured for their size distributions. Residence time distribution studies were used to estimate bed voidage. Measurements of axial and radial particle size distributions and axial voidage distribution have been made at different flow rates. Particle size was found to be radially constant, indicating constant stratification in the column. The particle size was found to decrease with increasing axial height. Voidage increased with axial height from a settled bed value of 0.39 to approaching unity for high liquid velocities and increased at a constant axial position with increased flowrate. This information provides key insight into bed stability and data for the improved modeling of this important unit operation.

Direct visualisation of plasmid DNA in individual chromatography adsorbent particles by confocal scanning laser microscopy

Confocal microscopy was used for the measurement of plasmid DNA adsorbed to individual adsorbent particles intended for anion-exchange and triple helix affinity chromatography. Plasmid DNA was visualized with the fluorescent dye YOYO-1, that forms a highly fluorescent complex with double stranded DNA. Confocal images were translated into fluorescence intensity profiles and the distribution of plasmid DNA in the particles was measured. The results that adsorption of plasmid DNA mainly takes place in an outer layer of the particles. The described procedure can also be advantageously used to demonstrate triple helix formation between plasmid DNA and immobilized oligonucleotides.

Immobilised metal ion affinity chromatography purification of alcohol dehydrogenase from baker's yeast using an expanded bed adsorption system

Alcohol dehydrogenase (ADH) from solutions of homogenised packed bakers' yeast has been successfully purified using immobilised metal-ion affinity chromatography in an expanded bed. Method scouting carried out using pure ADH solutions loaded onto 5-ml HiTrap columns charged with Zn2+, Ni2+ and Cu2+ and eluted using 0-50 mM EDTA gradient found that charging with Zn2+ gave the highest recovery and the lowest EDTA concentration required for elution. These results were used to develop a protocol for the expanded bed system and further tested using clarified yeast homogenate loaded onto XK16/20 packed beds (approximately 30 ml) packed with Chelating Sepharose FastFlow matrix in order to determine the optimum elution conditions using EDTA. The ADH was found to elute at 5 mM EDTA and the dynamic and total binding capacities of Streamline chelating for ADH were found to be 235 U/ml and 1075 U/ml matrix, respectively. Expanded bed work based on a step EDTA elution protocol demonstrated that ADH could be successfully eluted from unclarified homogenised bakers' yeast diluted to 10 mg/ml total protein content with a recovery of 80-100% that was maintained over five consecutive runs with a vigorous clean-in-place procedure between each run.

Expanded-bed adsorption in industrial bioprocessing: recent developments

Expanded-bed adsorption allows the capture of proteins from particle-containing feedstocks without prior removal of particulates, thus enabling clarification of a cell suspension or cell homogenate and the concentration of the desired product in a single operation. This usually results in higher product recovery in a shorter time period. Process development and scale-up of an expanded-bed operation is convenient because both the adsorbent and the equipment are similar to those in conventional packed-bed chromatography. This article reviews the recent developments in expanded-bed adsorption technology and the range of applications that are now being achieved.

Analysis of some operating parameters of novel adsorbents for recovery of proteins in expanded beds

We have analysed some operational parameters for two novel adsorbents intended for recovery of proteins from particle-containing feedstocks using expanded bed adsorption. The adsorbents tested were STREAMLINE DEAE and STREAMLINE SP, ion exchangers based on an agarose/crystalline quartz composite. Parameters analysed included bed expansion, adsorption efficiency, washing and elution. Bed expansion was considerably lower for STREAMLINE adsorbents compared to conventional agarose based media, higher flow velocities were thus possible during the expanded bed process. Breakthrough capacity was 63 mg ml-1 for lysozyme on STREAMLINE SP and 36 mg ml-1 for bovine serum albumin on STREAMLINE DEAE at a flow velocity of 300 cm h-1. To achieve high breakthrough capacity, the sedimented bed height should be at least 10 cm. Furthermore, breakthrough capacity increased to some extent when temperature was increased from room temperature to 36 degrees C, a phenomenon which can be useful in some processes. The number of living E. coli cells in the effluent was reduced by a factor of 10(5) after washing with 15 sedimented bed volumes. The optimal flow velocity for elution was 100 cm h-1 considering time for elution and volume of the eluted fraction. Flow direction during elution in packed bed mode had little impact on the elution volume, however, elution in expanded bed mode increased the volume by approx. 40%. The data presented on the performance of STREAMLINE adsorbents show that they are very useful for recovery of proteins from particle-containing feedstocks using expanded bed adsorption.

Single-step recovery of a secreted recombinant protein by expanded bed adsorption

We have used an expanded bed adsorption procedure for efficient recovery of a recombinant fusion protein, directly from a crude fermentor broth without prior cell removal. The fusion protein was designed to have a relatively low isoelectric point (pI) to allow anionic exchange adsorption at pH 5.5 where most Escherichia coli host proteins are not adsorbed. The gene product was secreted to the culture medium of the E. coli host cells in high yields (550 mg/l). The separation of cells and the concentration and recovery of the fusion protein could therefore be achieved by a single unit operation. The yield after the expanded bed adsorption exceeded 90 percent. Furthermore, the significant volume reduction by the expanded bed adsorption, enabled efficient and straight-forward polishing of the product by a subsequent affinity chromatography step, for removal of contaminating DNA and pyrogenic compounds to levels acceptable for regulatory authorities. An overall yield exceeding 90 percent was maintained after the affinity chromatography polishing step. The procedure outlined here is suitable for large-scale bioprocesses and allows efficient removal of cells, host proteins, contaminating DNA and endotoxins.

Adenovirus-human immunodeficiency virus (HIV) envelope recombinant vaccines elicit high-titered HIV-neutralizing antibodies in the dog model

Recombinant human adenoviruses (Ads) (types 4, 5, and 7) expressing the HIV-1 envelope membrane glycoprotein (gp160) were tested for immunogenicity in the dog. Administration of recombinant Ad7-env by intratracheal inoculation resulted in a low serum antibody response to gp160, which developed over several weeks. A strong neutralizing antibody response to the Ad7 vector developed within 1 week of infection. A subsequent booster inoculation 12 weeks later with the heterotypic Ad4-env recombinant virus resulted in significantly enhanced humoral responses directed at the envelope antigen, as measured by both ELISA and Western blot analysis as well as high-titer type-specific neutralizing antibodies, with some animals achieving neutralization titers approaching 1000. Recombinant HIV envelope glycoprotein derived from Ad-HIV-infected cell cultures was used as a subunit booster injection for dogs that had previously received sequential immunizations with heterotypic recombinant Ads. Significant immune responses against the envelope developed as measured by ELISA, Western blot analysis, and neutralization assays. These data indicate that live recombinant Ad-HIV vaccines are capable of inducing high-titer type-specific neutralizing antibodies to gp160 in vivo. Recombinant HIV envelope glycoprotein subunit vaccines, prepared from Ad-env-infected cells, are capable of boosting these responses.

Isolation of bacterial plasmids by density gradient centrifugation in cesium trifluoroacetate (CsTFA) without the use of ethidium bromide

Plasmids extracted from bacterial cells by alkaline extraction can easily be isolated from linear DNA by isopycnic centrifugation in CsTFA. This is a fast and simple method which circumvents the use of the intercalating dye, ethidium bromide, and consequently the problems associated with its removal. The buoyant densities for covalently closed circular DNA and linear DNA in CsTFA are 1.60 g/ml and 1.65 g/ml, respectively. The isolation is achieved regardless of plasmid size and can be accomplished at temperatures of between 4 and 30 degrees C. Plasmid DNA isolated in gradients of CsTFA are of a high purity and have been found to be intact when cleaved with restriction enzymes and ligated with T4 DNA ligase.

Isopycnic centrifugation of rat-liver microsomes in isoosmotic gradients of Percoll and release of microsomal material by low concentrations of sodium deoxycholate

Rat-liver microsomes were subjected to isopycnic centrifugation under isoosmotic conditions in gradients of Percoll containing 0%, 0.05%, 0.1% and 0.2% sodium deoxycholate, respectively. The buoyant density of the microsomes was in the range 1.043 to 1.046 g/ml, independent of the detergent concentration. Absorbance measurements and polyacrylamide gel electrophoresis revealed that the detergent causes an increase in the release of material from the microsomes. Electron microscopy studies showed that membrane disassembly was avoided if the microsomes were isolated at concentrations below 0.1% sodium deoxycholate.

Purification of bovine papilloma virus by gel filtration on Sephacryl S-1000 superfine

Bovine papilloma virus was purified from crude extracts of bovine warts by gel filtration in Sephacryl S-1000 Superfine. Analysis by sodium dodecyl sulphate polyacrylamide gel electrophoresis and electron microscopy shows that the virus preparation is as pure as that obtained by alternative techniques. The yield of virus particles is in the range 55-80%. The main advantage of using the gel filtration technique is that it is much less time-consuming than currently used centrifugation procedures.

Removal of percoll from microsomal vesicles by gel filtration on sephacryl-S-1000 superfine

A microsomal vesicle fraction was prepared from rat liver homogenate by centrifugation in gradients of Percoll. The microsomes were subjected to gel filtration on Sephacryl S-1000 Superfine, which resolved the microsomes from Percoll. The elution pattern of the microsomal marker enzyme NADPH-cytochrome c reductase showed that the main part of the enzyme was present in a peak at Kav about 0.1, while Percoll eluted in a broad peak at Kav about 0.7. The total yield of eluted enzyme activity was 85%. The gel filtration had to be carried out in the presence of 10 mM tris or NaCl. At lower ionic strength or in 0.25 M sucrose alone, anomalous behaviour of the Percoll particles and microsomes on the gel was observed. Electron microscopy of samples from the void volume fraction of the Sephacryl S-1000 Superfine column showed an almost complete removal of Percoll from the microsomes. Furthermore, the vesicle preparation was essentially free of membrane fragments.

A rapid method for purification of human granulocytes using percoll. A comparison with dextran sedimentation

A simple one-step method for purification of human granulocytes, based on the use of a discontinuous gradient of Percoll, is described. The cell yield is 55% and the purity of the granulocyte fraction is 97%. The cells' ability to exclude trypan blue and phagocytic function are not altered during the purification process. We conclude that centrifugation in Percoll is superior to conventional dextran sedimentation; it is also less time-consuming.

The isolectins of Helix pomatia. Separation by isoelectric focusing and preliminary characterization

Helix pomatia lectin was fractionated into several (at least 12) components by isolectric focusing in PharmalyteTM. Eight of these were recovered from a preparative column experiment and shown to be essentially pure by analytical electrofocusing in polyacrylamide gel slabs. The lectin components had haemagglutinating activity against human group A erythrocytes and similar molecular weights of 80 000 as determined vidual components showed slight variations in composition. The components are considered to be isolectins. Isoelectric focusing of lectin samples prepared from single snails from two different biotopes showed isolectin patterns similar to that of pooled lectin. Gel filtration of the lectin and flat bed electrofocusing of isolated isolectins both in the presence of 6 M ura, indicated that the lectin molecules are formed by different combinations of a range subunits with similar molecular weight but with different isoelectric points.

The use of wheat-germ lectin-Sepharose for the purification of human haemopexin

Haemopexin was prepared in 37% yield from normal human serum by a simple procedure involving fractional poly(ethylene glycol) precipitation and subsequent chromatography on DEAE-Sepharose CL-6B. One peak from the ion exchanger consisted of only haemopexin and transferrin. These proteins were separated by chromatography on wheat-germ lectin-Sepharose 6MB. Haemopexin was selectively bound and was subsequently desorbed by N-acetyl-D-glucosamine. No impurities could be detected in the final preparation by immunoelectrophoresis or by immunodiffusion against a range of antisera. The protein gave two partially separated bands in polyacrylamide-gradient-gel electrophoresis, corresponding to apohaemopexin and haem-haemopexin complex.