Purification, potency and immunogenicity analysis of Vero cell culture-derived rabies vaccine: a comparative study of single-step column chromatography and zonal centrifuge purification

Continuous Vero cell lines are more suitable for large-scale production of rabies vaccine. The purification of Vero cell-derived rabies vaccine is critical because of the residual cellular DNA and serum proteins. The perfection of techniques using column chromatography with different matrix material, gel filtration and zonal centrifugation is of paramount importance for the optimal purification of rabies vaccine, leaving minimal residual cellular DNA, below the permissible level of 100 pg per dose and serum protein content of 1 ppm. In this study the potency, immunogenicity and safety of Vero cell-derived rabies vaccines were compared following purification by densely or loosely packed DEAE-sepharose CL-6B columns with different bed heights or by zonal centrifugation. The optimal virus recovery and maximum removal of substrate DNA and serum proteins were achieved only when the sepharose CL-6B column bed height was maintained at a thickness of 2-2.5 cm. The rabies virus material was purified by layering over the matrix without applying pressure. DEAE-sepharose CL-6B column purification using a simplified, cost effective technique as described in this study enhances the antigen yield by 50% in comparison with zonal purification.

Separation of membrane vesicles and cytosol from yeast, cultured cells, and bacteria in a small volume self-generated gradient in a fixed-angle rotor

There are many situations when it is necessary to separate rapidly and efficiently a cytosolic and a membrane vesicle fraction from yeast, cultured cells, or from bacteria. This Protocol Article describes the flotation of the vesicles through a self-generated gradient from a dense sample zone using the low-viscosity medium iodixanol. As the sample is exposed to the gmax the tendency of the proteins to sediment overcomes any diffusion in the opposite direction and are therefore completely separated from the vesicles.

Separation of dorsal and ventral dopaminergic neurons from embryonic rat mesencephalon by buoyant density fractionation: disassembling pattern in the ventral midbrain

The dopaminergic neurons of the ventral mesencephalon, though physically mixed with non-dopamine neurons, are organized into dorsal and ventral 'tiers' with regard to their ontogeny, efferent projections and their relative position in the various mesencephalic sub-nuclei. We have employed buoyant density fractionation to separate the dopaminergic neurons of the two compartments and compare their subsequent phenotype development with respect to their expression of the gene encoding tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine biosynthetic pathway. Using immunocytochemistry, separately and combined with in situ hybridization, we demonstrate here that sedimentation of cell suspensions from E19 rat ventral mesencephalon on 5-step Percoll gradients produces cell fractions enriched in ventral and dorsal tier DA neurons, respectively.

Biochemical characterization of the Golgi-complex proteins of Tritrichomonas foetus

Using cell-fractionation techniques (differential and discontinuous gradient centrifugation), we obtained a highly enriched fraction containing the Golgi complex of Tritrichomonas foetus. This fraction was further subfractionated by sodium carbonate (150 mM) treatment at pH 11.5, leading to the isolation of the Golgi content and membrane subfractions. Both fractions were characterized by electron microscopy. The protein content of membrane and luminal subfractions was about 40% and 60% of the total Golgi protein, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed an enrichment of 15 protein bands in the Golgi fraction, with molecular masses varying between 15 and 116 kDa. Alkaline treatment released some proteins into the medium, but most of them were associated with the Golgi membrane.

The rate zonal separation of organelles from dilute suspensions: the problem of a large sample volume

Transport vesicles that deliver proteins to the cell surface can be isolated by incubating cells that have been permeabilized by mechanical or chemical techniques in a high-K medium containing an ATP regenerating system. The vesicles released from permeabilized cells are, however, obtained as a very dilute suspension in the incubation solution. This presents a problem for the preparative separation of specific populations of vesicles by velocity sedimentation, because the small sample volume capacity of traditional glycerol or sucrose velocity gradients requires that the vesicles first be concentrated by sedimentation or that very small amounts of vesicles be loaded onto a gradient. We have addressed the problem of the loss of zonal resolution produced by the loading of large sample volumes, and we propose that high-viscosity Ficoll gradients can be used effectively to restore the resolution of zones when substantially larger sample volumes of dilute suspensions must be loaded onto velocity gradients.

A new method to measure iron absorption from the enrichment of 57Fe and 58Fe in young erythroid cells

Iron absorption can be measured by the incorporation of stable iron isotopes into erythrocytes, 14 days after isotope administration. The disadvantage of this method is the high dose of isotopes needed to obtain a sufficient enrichment. Therefore, in this study cell fractions rich in young erythroid cells were prepared by using a density separation method. From 10 women blood was taken 4, 5, and 7 days after oral and intravenous administration of 57Fe and 58Fe. In these cell fractions and in whole blood taken 14 days after isotope administration, isotope enrichment was measured and absorption calculated. Absorption calculated from the isotope enrichment in the reticulocyte-rich cell fractions (12.2 +/- SEM 3.7%) was not significantly different from absorption based on whole-blood values (13.0 +/- 3.3%). Because a threefold higher isotope enrichment was found in the cell fractions, the required dose of stable isotopes can be reduced to one-third of the dose used in the traditional method without loss of sensitivity.

Rate zonal sedimentation of proteins in one hour or less

Rate zonal sedimentation gives information about the shape and size of proteins, and is useful for investigating protein-protein interactions. However, rate zonal sedimentation experiments typically last approximately 1 day. In contrast, this report describes a rate zonal sedimentation method requiring 1 h or less. This was accomplished by centrifuging small density gradients (200 microliters) prepared with sucrose or OptiPrep in a fixed-angle rotor at high relative centrifugal force. By using small gradient volumes, the sample dilution that occurs with larger gradients and with many chromatographic techniques was also avoided. For a variety of proteins, plots of S20,w versus distance sedimented during centrifugation in a TLA 120.2 rotor were linear. As a practical application, sedimentation of the heterotrimeric stimulatory G protein and its dissociated alpha-subunit were determined. The results were similar to those obtained with 17- to 22-h centrifugations in an SW 50.1 rotor and agreed with previously published values. Long periods of centrifugation might preclude the study of some unstable proteins or the investigation of protein-protein interactions whose affinities are to low to survive the lengthy centrifugations required to carry out traditional rate zonal sedimentation experiments. A rate zonal sedimentation technique that rivals many chromatographic methods in celerity will help to circumvent these problems.

Use of zonal centrifugation method for the preparation of mu-opioid receptor enriched membranes from bovine corpus striatum

Earlier attempts to purify the opioid receptors met with limited success because of the use of brain crude membranes. Subcellular fractionation procedures adopted now to get enriched membranes resulted in 2-3 fold enrichment. However, a procedure has been developed in our laboratory in which a crude membrane fraction obtained at 17,500 x g was lysed with 1 mM sodium bicarbonate and later subjected to zonal fractionation, employing a density gradient of 0.6-1.2 M sucrose. This could yield a membrane fraction highly enriched with mu-opioid receptors which is 9.3 fold higher than the crude membranes.

Application of the hypo-osmotic swelling test to spermatozoa prepared by swim-up and discontinuous Percoll separation

The quality of spermatozoa prepared by washing and swim-up or by discontinuous Percoll centrifugation, was compared by applying the hypo-osmotic swelling (HOS) test to semen samples from 116 men of infertile couples. The HOS test performed on 95 normal semen samples showed that the percentage of swollen spermatozoa separated by both techniques was significantly higher than in the initial ejaculate (p < 0.001). The percentage of HOS-positive spermatozoa separated by the Percoll gradient technique was significantly higher than that separated by the swim-up technique (p < 0.001). On the contrary, in 21 abnormal semen samples, there was no significant difference in the percentage of spermatozoa which were positive in the HOS test between the Percoll gradient and the swim-up technique (p = 0.44). It is suggested that the Percoll gradient technique appears to be preferable to the swim-up technique when semen parameters are normal, but there is no significant difference between these two technique in abnormal semen.

The preparation of subcellular organelles from mouse liver in self-generated gradients of iodixanol

This paper reports the use of a new density gradient compound, Iodixanol, for the resolution of the major organelles from mouse liver. A major advantage of Iodixanol over other iodinated density gradient media is its ready ability to form self-generated gradients. Gradient-forming conditions have been modulated to provide optimal recoveries of Golgi membranes, lysosomes, mitochondria, and peroxisomes. The organelles were isolated in high yield (80-90% of gradient input) and high purity. Nycodenz and Iodixanol were compared using preformed gradients. Iodixanol provided resolution superior to that of Nycodenz, notably of peroxisomes and mitochondria and the separation of lysosomes from endoplasmic reticulum. Because Iodixanol does not interfere significantly with marker enzyme activities, gradient fractions can be analyzed without removal of the gradient medium.

Male:female sex ratio in births resulting from IVF according to swim-up versus Percoll preparation of inseminated sperm

Two centers have independently reported a higher rate of male to female births following insemination of sperm prepared by a modified swim-up technique. The principle of the modified swim-up is that a small percentage of the x-bearing sperm are the fastest and travel to the top of the supernatant, followed by the y-bearing sperm; the bulk of the x-bearing sperm remain in the pellet. In this technique, the very top layer is discarded and the resulting supernatant is collected, leaving only the pellet. In contrast, with the conventional swim-up technique, the entire supernatant is collected. The study presented herein retrospectively evaluated the male to female sex ratio of births from in vitro fertilization using standard swim-up technique and compared these results to the ratio obtained from separating with Percoll. There were 53% male births with swim-up vs. 54% with Percoll in singleton pregnancies and 51% males with swim-up vs. 40% with Percoll with multiple births. Thus, conventional swim-up alone does not increase percentage of male births.

Preparation of antibody free spermatozoa by in vitro immunodepletion using immunobeads

In the present study ejaculates from six infertile men with antisperm antibodies were processed on a six step discontinuous percoll gradient. This treatment yielded a sperm fraction with a different percentage of sperm with antisperm antibodies. The resultant sperm preparation was incubated with immunobeads. Sperm were recovered following incubation by swim-up. Sperm recovered at the end of processing showed reduced populations of antisperm antibodies. Even though sufficient numbers of sperm were obtained to consider assisted reproduction, reduced motility was recorded in four of the ejaculates when compared with routine processing. Following trial preparations of semen samples this technique may play a role in sperm selection for assisted conception.

Isolation and characterization of the outer membrane proteins of Serratia marcescens W225

The study addressed the general problem of fractionating cell envelopes in order to isolate the outer membranes of gram-negative bacteria. Whereas the cells are normally transformed into spheroplasts prior to disintegration and membrane separation, Serratia marcescens was found to be resistant to spheroplast formation using the procedures available, which were originally developed for Escherichia coli. An efficient technique for spheroplasting S. marcescens was therefore developed; this comprised combining osmotic shock and lysozyme-EDTA treatment of sucrose-conditioned cells. Spheroplasting efficiency and the amount of outer membrane protein recovered were highly dependent on the spheroplasting technique used. Separation of the outer and inner membranes was performed by two methods, isopyenic centrifugation and selective detergent solubilization with Sarkosyl. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the analysis of specific inner membrane marker enzymes revealed that the protein obtained by detergent solubilization was much purer than that obtained by isopycnic centrifugation. The outer membrane isolated accounted for 60% of the envelope proteins and had a buoyant density of 1.2502 g/cm3. The protein profile of the outer membrane determined by SDS-PAGE resolved into 12 distinct protein bands, 3 of which represented major proteins.

Periportal- and perivenous-enriched hepatocyte couplets: differences in canalicular activity and in response to oxidative stress

Unlike isolated single hepatocytes, hepatocyte couplets retain their apical polarity, and, during short-term culture form an enclosed canalicular space or vacuole between the two adjacent cells into which biliary secretion is initiated. Hepatocyte couplets were prepared after partial collagenase perfusion of rat liver. Centrifugal elutriation was used to fractionate the preparation into six couplet-containing suspensions. Image analysis was used to determine the size of cultured couplets. The size of the couplets ranged from 34.1 +/- 0.76 microns and 684 +/- 24.1 microns 2 (mean length and area respectively +/- S.E.M.) in Fraction 2, to 43.7 +/- 0.57 microns and 1033 +/- 33.8 microns 2 length and area respectively in Fraction 7. Glutamine synthetase activity was assessed in each freshly eluted fraction and was shown to be predominant in Fractions 6 and 7. Pretreatment of rats with CCl4, which selectively destroys perivenous hepatocytes, decreased the proportion of couplets in these fractions by over 67%, and their glutamine synthetase activity by over 97%. It was concluded that Fractions 2 and 3 contained predominantly couplets of Zone 1 (periportal) origin, Fractions 4 and 5 those from Zone 2, and Fractions 6 and 7 predominantly couplets of Zone 3 (perivenous) origin. The development of canalicular secretory activity was assessed in the couplets after a 15 min incubation with a fluorescent bile acid, cholyl-lysyl-fluorescein (CLF). This was sigmoidal in all fractions, but slower in the periportal couplets, taking 5.1 h for 50% to show secretory activity in Fraction 2, compared with 2.7 h for Fraction 7. Incubation of hepatocyte couplets with 1 or 10 microM taurodehydrocholate, a non-toxic bile acid analogue, did not influence the rate of development of accumulation of CLF by the couplets or the area of the canalicular vacuole in any fraction. However, it did decrease the CLF content of couplets incubated with CLF for 15 min to a greater extent in those of perivenous origin. After subjecting the couplets to oxidative stress by incubation with 20 microM menadione (2-methyl-1,4-naphthoquinone), it was evident that periportal couplets were less able to maintain canalicular secretory activity than perivenous couplets.

Purification of viruses by centrifugation in gradients of inert substances

By using a reorienting gradient centrifuge rotor cut from a block of Nylon and fitted with eight septae, it was possible to separate the components of the haemolymph of the mollusc Turbo sarmaticus into three fractions in a sucrose gradient held in the bowl of the rotor. The fractions were (108 and 98)S, 44S and 16-22S. The success of the experiment was due to the large differences in the sedimentation coefficients of the components. When the rotor was applied to the natural mixture of the five viruses of the caterpillars of Nudaurelia cytheria only the main component could be isolated in a pure state. The viruses were separated by isopycnic centrifugation in "self formed" caesium chloride gradients, using a Beckman Model E analytical centrifuge in which a separation cell fitted with a centerpiece with two perforated partitions was used.

The optimization of large-scale density gradient isolation of human islets

The use of the COBE 2991 cell processor (COBE Laboratories, Colorado) for large-scale islet purification using discontinuous density gradients has been widely adopted. It minimizes many of the problems such as wall effects, normally encountered during centrifugation, and avoids the vortexing at interfaces that occurs during acceleration and deceleration by allowing the gradient to be formed and the islet-containing interface to be collected while continuing to spin. We have produced cross-sectional profiles of the 2991 bag during spinning which allow the area of interfaces in such step gradients to be calculated. This allows the volumes of the gradient media layers loaded on the machine to be adjusted in order to maximize the area of the gradient interfaces. However, even using the maximal areas possible (144.5 cm2), clogging of tissue at such interfaces limits the volume of digest which can be separated on one gradient to 15 ml. We have shown that a linear continuous density gradient can be produced within the 2991 bag, that allows as much as 40 ml of digest to be successfully purified. Such a system combines the intrinsic advantages of the 2991 with those of continuous density gradients and provides the optimal method for density-dependent islet purification.

Myelin isolation: comparison of sedimentation and flotation techniques

Brains from young (20 day old) and adult rats were used to compare myelin yields obtained by sedimentation and flotation techniques. The flotation method consistently gave approx 70% higher yields of myelin than the sedimentation method. Both myelin preparations have virtually identical protein composition as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Electrophoretic analysis revealed substantial concentrations of myelin proteins in the non-myelin particulate fraction obtained by the sedimentation but not by the flotation method. The study indicates that the paradigm of the sedimentation method results in a significant loss of myelin during isolation, and that this loss can be avoided or minimized by employing the flotation method.

Comparison of top and bottom loading of a dextran gradient for rat pancreatic islet purification

Rat pancreatic islet yields obtained with dextran gradient purification were compared after suspending the digest into either the top or the bottom layer of the gradient. A 5-layer discontinuous gradient was used, which consisted of 16 ml 31% dextran as bottom layer, overlayered with 25%, 23%, 20% and 11% dextran (4 ml each). When the digest of 1 rat pancreas was suspended into the top layer of the gradient, the total number of islets obtained from the 11-20, 20-23 and 23-25% interfaces was 862 +/- 38, 240 +/- 39 and 54 +/- 5, respectively. From this gradient, also 1409 +/- 81 islets were retrieved from the bottom layer (i.e., exocrine pellet). In contrast, when the pancreas digest was suspended into the bottom layer of the gradient, 1964 +/- 63, 435 +/- 42, and 177 +/- 34 islets were obtained from the successive interfaces, and only 50 +/- 20 islets from the exocrine pellet. The total islet volume obtained from the two uppermost interfaces was 3.46 +/- 0.31 microliters after top-loading, and 4.93 +/- 0.16 microliters after bottom-loading (n = 7, p < 0.01). When the islets retrieved from one bottom loaded gradient were transplanted into either 1 (n = 6) or 2 (n = 9) diabetic recipients, glucose levels normalized in all instances. We therefore conclude that a bottom-loaded dextran gradient separates islets from exocrine tissue effectively, resulting in significantly higher islet yields than obtained with a top-loaded dextran gradient.

Glucose-6-phosphate dehydrogenase activity and protein turnover in erythroblasts separated by velocity sedimentation at unit gravity and Percoll gradient centrifugation

This work was undertaken to improve a separation method for preparation of large amounts of erythroid cells of different age with homogeneous and minimal contamination of myeloid cells. Our method was suitably employed in the study of the decay mechanism of glucose-6-phosphate dehydrogenase (G6PDH) during the erythroid cell maturation. Twenty fractions of erythroid cells at different advancing stages of maturation were prepared by fractionating, at unit gravity, bone marrow cells from anaemic rabbit. The specific activity of the G6PDH was assayed and plotted vs the fraction number and the typical sigmoid curve of the activity decay was drawn. The separated cells were then grouped in three sets of fractions following the three phases of the sigmoid curve and the fractions of each set were combined. From the cytochemical analysis of the three main fractions so obtained, we found a 25-30% myeloid cell contamination in the first fraction, while in the other two fractions the myeloid contamination was 10% or less. For this reason we performed a rapid separation of the first fraction on a discontinuous percoll gradient. By this method, the myeloid cell contamination of the first fraction was levelled down to the other two. The fractions, so obtained, (I, II and III in order of increasing cell maturation) showed a four fold decrease of glucose-6-phosphate dehydrogenase activity expressed both per cell number and on protein base. On the contrary the concentration of the total soluble proteins did not change significantly in the three fractions. The three purified cellular populations were used to provide information on the protein turnover of the erythroid cells during their development. We measured, in intact cells, the rate of synthesis and degradation of total proteins and then, in cell lysates, we determined the rate of degradation of G6PDH, purified from rabbit RBC and radiolabeled by reductive methylation with C14-formaldehyde. The rates of proteolysis obtained with total proteins and methyl-G6PDH clearly indicate that the proteolytic machinery of the erythroblasts reduces its activity during the cell maturation.

Mast-cell heterogeneity: functional comparison of purified mouse cutaneous and peritoneal mast cells

To investigate the functional heterogeneity of mouse mast cells, we extracted and purified cutaneous and peritoneal mast cells from 10- to 18-week-old BALB/c mice and compared their responses to secretagogues. Cutaneous mast cells (CMC) were extracted from mouse ears after digestion with hyaluronidase and collagenase in MEM containing 25% fetal calf serum and purified on a discontinuous Percoll gradient. The histamine content of cells obtained from the 30/40% interface was 1.0 +/- 0.1 pg/cell (mean +/- SE), with a mast-cell purity of 68.6 +/- 4.4% and a viability of greater than 93%. Peritoneal mast cells (PMC) were obtained by lavage with modified Tyrode's buffer followed by purification on 22.5% and 3-9% metrizamide gradients. The histamine content of cells was 12.2 +/- 0.8 pg/cell, with a mast-cell purity of 95.9 +/- 0.6% and a viability of greater than 95%. Histamine release induced by A23187 from CMC peaked at 3.0 microM A23187 (19.1 +/- 4.2%), at 3.0 min (22.3 +/- 2.3%), and at 30 degrees C (17.6 +/- 2.6%). In contrast, histamine release from PMC peaked at 8.0 microM of A23187 (49.4 +/- 12.1%) and at 15.0 min (48.5 +/- 12.2%). Release of histamine from PMC was observed at all the temperatures tested from 22 to 45 degrees C. Histamine release from CMC and PMC induced by A23187 was calcium dependent. Histamine release induced by compound 48/80 from CMC peaked at 0.5 micrograms/ml of compound 48/80 (23.0 +/- 7.4%) and at 5.0 min incubation (16.3 +/- 2.0%), whereas release from PMC peaked at 10.0 micrograms/ml (31.9 +/- 2.6%); release from PMC was similar at all the time points examined (1-15 min). Histamine release induced by substance P (SP) from both CMC and PMC peaked at 5.0 microM (18.8 +/- 6.6% and 12.6 +/- 3.7%, respectively); however, the maximal release from CMC occurred at 3.0 min (18.2 +/- 3.2%) and from PMC at 30.0 min (11.4 +/- 2.0%). SP-induced histamine release from CMC was calcium dependent, whereas release from PMC was only partially inhibited by EDTA. This study demonstrated that functional heterogeneity exists between these two populations of mast cells.