Patent Application
20110097746
The present disclosure relates to biological fluids and methods of purifying same. More specifically, this disclosure relates to methods for the orthogonal removal of transmissible spongiform encephalopathy agents from biological fluids.
Transmissible spongiform encephalopathies (TSEs), also known as prion diseases, are a group of rare degenerative brain disorders characterized by tiny holes that give the brain a “spongy” appearance. Creutzfeldt-Jakob disease (CJD) is the most well-known of the human TSEs. It is a rare type of dementia that affects about one in every one million people each year. Other human TSEs include kuru, fatal familial insomnia (FFI), and Gerstmann-Straussler-Scheinker disease (GSS). Kuru was identified in people of an isolated tribe in Papua, New Guinea and has now almost disappeared. FFI and GSS are extremely rare hereditary diseases, found in just a few families around the world. A new type of CJD, called variant CJD (vCJD), was described in 1996 and has been found in Great Britain and several other European countries. The initial symptoms of vCJD are different from those of classic CJD and the disorder typically occurs in younger patients. Symptoms of TSEs vary, but they commonly include personality changes, psychiatric problems such as depression, lack of coordination, and/or an unsteady gait. Patients also may experience involuntary jerking movements called myoclonus, unusual sensations, insomnia, confusion, or memory problems. In the later stages of the disease, patients have severe mental impairment and lose the ability to move or speak. TSEs tend to progress rapidly and usually culminate in death over the course of a few months to a few years. Research suggests that vCJD may have resulted from human consumption of beef from cattle with a TSE disease called bovine spongiform encephalopathy (BSE), also known as “mad cow disease.” Other TSEs found in animals include scrapie, which affects sheep and goats; chronic wasting disease, which affects elk and deer; and transmissible mink encephalopathy. In a few rare cases, TSEs have occurred in other mammals such as zoo animals. There is also evidence to suggest that TSE can be transfusion transmitted however, the time between infection and the appearance of symptoms may be lengthy. For example, humans may be infected for five to twenty years before symptoms appear. Many countries have implemented different measures to prevent TSE outbreaks. The U.S. Food and Drug Administration (FDA) prohibited feeding of ruminants with proteins of animal and implemented a ban on donation from people who have spent more than ten years in France, Portugal and/or Ireland since 1980. People who spent more than six months in Great Britain from 1980-1996 already are forbidden from giving blood in the U.S., Canada, New Zealand, and Australia.
In the United States, the FDA created the TSE Advisory Committee that deals with this subject. Moreover, the FDA has already issued many documents that regulate the presence TSE agent in medicinal products.
Prion diseases such as the TSEs are accompanied by the conversion of normal cellular PrPC into its isoform which are pathogenic prion proteins that are protease-resistant (PrPSc). PrPSc are the agents believed responsible for TSE. The risk of contracting a TSE is based on effective exposure of a subject to a TSE agent. Effective exposure is a function of three main variables: the amount of the infectious agent in the contaminated material; the route of exposure; and the specific barrier effect. For example, the parenteral routes of exposure are more efficient in establishing infection than exposure via the alimentary tract. Therefore, current processes for PrPSc removal, also known as TSE agent removal, are more rigorous for parenteral pharmaceuticals originating in animals and used in humans. Similar measures are also being proposed for pharmaceuticals derived from human tissues.
One challenge to TSE agent removal from blood products comprising hemoglobin is the susceptibility of hemoglobin to degradation. Hemoglobin is a unique and highly unstable molecule that is susceptible to damage during the purification process. This tetrameric heme protein can easily dissociate into unstable dimers and oxidize; therefore losing its ability to transport oxygen, the main purpose of blood substitutes. Spontaneous autoxidation of acellular hemoglobin generates superoxide anion. The rate of this oxidation is augmented by hydrogen ions (low pH). Superoxide anion acts as catalyst and promotes further hemoglobin autoxidation and spontaneously or enzymatically dismutates to form hydrogen peroxide. Hydrogen peroxide reacts with ferrous- or ferric-hemoglobin to produce ferryl-hemoglobin. Ferryl-hemoglobin acts as a radical and initiates lipid peroxidation to the same extent as hydroxyl radicals. The control of hemoglobin oxidative reactions outside of red blood cells is difficult, since this environment does not contain the enzymatic and non-enzymatic antioxidant system that is needed to maintain heme in its functional reduced ferrous form. Thus, irreversible heme oxidation is a problem for hemoglobin-based blood substitute developers.
Hemoglobin solutions, of bovine and human origin, to be effective oxygen carrying plasma expanders, must fulfill a number of requirements. In addition to being non-toxic, non-immunogenic, and non-pyrogenic, having an extended shelf-life, a satisfactory oxygen carrying capacity and colloid osmotic pressure and viscosity similar to plasma; these products should be free of pathogens such as TSE. While the removal of other pathogens from hemoglobin solutions (e.g., microbial) may be effectively achieved using techniques such as sterilization/ultrafiltration followed by a differential culture, the TSE clearance capacity of the manufacturing process must be validated.
Prion proteins (e.g., PrPSc) are very resistant to common deactivation methods. They can survive cooking and even autoclaving, as well as exposure to a high concentration of acid or base; conditions too aggressive for the purification of fluids comprising hemoglobin. For example, the only pharmaceutical industry method for TSE agent removal in hemoglobin containing solutions is based on a column chromatographic technique.
According to the FDA, a process that is able remove 5 logs of the TSE agent from blood products, particularly hemoglobin solutions, appears acceptable. However, in such a process, log removal by different steps is considered additive only if the clearance steps are orthogonal (i.e., remove the agent by an independent mechanism). Thus, a need exists for an orthogonal method of reducing pathogenic prion proteins from hemoglobin containing solutions.
Disclosed herein is a method comprising contacting a biological fluid comprising hemoglobin and at least one pathogenic agent with a first filter and generating a first filtrate; contacting the first filtrate with a nanofiltration device and generating a second filtrate; contacting the second filtrate with a chromatographic material and isolating an eluted fraction; contacting the eluted fraction with a hydrophobic solvent and generating a hydrophobic and a hydrophilic phase; and isolating the hydrophilic phase wherein the biological fluids comprise components of interest of equal to or less than about 65 KDa. Also disclosed herein is a method comprising contacting a biological fluid comprising high molecular weight components and at least one pathogenic agent with a first filter and generating a first filtrate; contacting the first filtrate with a hydrophilic membrane and generating a second filtrate; contacting the second filtrate with a chromatographic material and isolating an eluted fraction; contacting the eluted fraction with a hydrophobic solvent and generating a hydrophobic and a hydrophilic phase; and isolating the hydrophilic phase, wherein the high molecular weight components have molecular weights greater than about 65 kDa. Also disclosed herein is a method comprising subjecting a biological fluid comprising hemoglobin and at least one pathogenic agent to at least two filtration steps and thereby reducing the amount of pathogenic agent associated with the biological fluid. Further disclosed herein is a method comprising removing transmissible spongiform encephalopathy agents in a hemoglobin solution of human and/or animal origin by subjecting the hemoglobin solution to an orthogonal separation methodology comprising a plurality of filtration steps.
For a detailed description of the embodiments of the disclosure, reference will now be made to the accompanying drawings in which:
Disclosed herein are methods for the orthogonal removal of pathogenic agents from biological fluids, such as the removal of agents thought responsible for transmissible spongiform encephalaphaties (TSE), hereafter referred to as TSE agents. Herein a biological fluid refers to any fluid having components derived from natural sources, synthetically prepared components, or combinations thereof that may be administered to an organism to treat a disorder. In an embodiment, the biological fluid is a hemoglobin containing solution which may also be referred to as a composition or solution comprising hemoglobin. In an embodiment, the TSE agent is a prion, alternatively a pathogenic prion (PrPSc). Prion is short for proteinaceous infectious particle and can occur in both a normal form, which is a harmless protein found in the body's cells, and in an infectious form, which causes disease. In an embodiment, the TSE agents may be removed from a hemoglobin containing solution using the orthogonal methodologies disclosed herein, and as used herein the term orthogonal refers to methodologies comprising more than two steps wherein each step results in the removal and/or deactivation of a component (e.g., TSE agent) by independent mechanisms. For example, the orthogonal methodologies described herein may comprise steps that utilize different physiochemical properties of a component (e.g., TSE agent) to effect the removal or elimination of said component.
In an embodiment, the methodology comprises chromatographic techniques, chemical treatment, and nanofiltration in order to effect TSE agent removal from the biological fluid. For example, an orthogonal multi-step procedure may include a high affinity prion reduction filter, a nanofiltration device, a hydrophilic membrane, ion-exchange membrane chromatography and a hydrophobic solvent. In an embodiment, the methodologies for TSE agent removal may be carried out in any order desired by the user, alternatively the methodologies for TSE agent removal may be carried out in the sequence disclosed herein. The resultant biological fluid having been subjected to TSE agent removal (i.e., PrPsc removal) may be suitable for use in the treatment of mammalian disorders requiring the administration of a biological fluid such as a hemglobin containing solution.
An embodiment of a method for TSE agent removal from a sample, 200, is set forth in
Referring to
Without wishing to be limited by theory, the high flow affinity prion reduction filter may function to selectively remove PrPSc-containing leukocytes. Accordingly, block 10 provides a reduction in TSE agents associated with leukocytes, and the filter may be sized accordingly to trap such infected leukocytes. Such filtration may be referred to as leukofiltration.
Extraction of hemoglobin from red blood cells to obtain the starting material which is acellular hemoglobin is typically performed using techniques that damage cellular components. For example, the extraction of hemoglobin from a red blood cell suspension may be carried out by hypo-osmotic lysis. Hypo-osmotic lysis may rupture leukocytes containing PrPSc and thus releasing TSE agents (i.e., PrPSc) into the hemoglobin containing solution. Leukofiltration, or the process of removing leukocytes by filtration (e.g., using a high flow prion affinity filter) will decrease the possibility of transferring PrPSc from leukocytes to free hemoglobin solutions.
Contacting of the sample with the high flow affinity prion reduction filter may result in the removal of equal to or greater than about 1 log of TSE agent from the sample, (e.g., hemoglobin containing solution), alternatively from about 40 to about 60% (0.4-0.6 logs reduction), alternatively from about 0.7 to about 1.9 logs, alternatively from about 2 to about 3.7 logs as determined by a bioassay and a Western blot assay. A sample (e.g., hemoglobin containing solution) after having been subjected to a high flow prion affinity reduction filter is hereinafter termed a filtered sample. The filtered sample comprises the filtrate or the portion of the sample that was not retained by the high flow prion affinity reduction filter.
Referring again to
In an embodiment, samples such as those described herein which have been subjected to filtration devices may be diluted with respect to the original biological fluid. Dilute samples may be inconvenient to handle as they may comprise a large volume of liquid. Further many biological components (e.g. hemoglobin, proteins, etc . . . ) may display a reduced stability when maintained at low concentrations in a dilute solution. In an embodiment, the solutions generated by the methodologies disclosed herein may be concentrated following a particular technique to generate a more concentrated sample. Suitable techniques for concentrating these samples are known. For example, the sample may be concentrated following contacting with a nanofiltration device by introducing the sample to a dialyzer having a molecular cutoff of about 10 kDa, alternatively about 40 kDa, alternatively about 50 kDa, to concentrate the filtered sample. Alternatively, the biological fluid may be concentrated following each step in the disclosed methodology. The starting concentration and final concentration of the sample will depend on the type of device utilized. Consequently, the final concentration of the sample may be adjusted to a user-desired value by one of ordinary skill in the art.
Referring again to
Referring again to
In an embodiment, the method may then allow for further processing of the processed sample to place the sample in a condition suitable for introduction to an organism such as for example, administration to a patient. Alternatively, the sample, (e.g., hemoglobin of human or animal origin) may be used with further processing in the manufacturing of free hemoglobin based blood substitutes.
In an alternative embodiment, the biological fluid comprises plasma or serum. Plasma samples may comprise its fractions such as albumin, clotting factors, immunoglobulins or combinations thereof. Such samples may be subjected to a methodology as described in blocks 10, 30, 40 and 50. In an embodiment, the final composition to be obtained after subjecting the plasma or serum to the disclosed methodologies have components of interest (i.e. user-desired components) having a molecular weight of greater than about 65 kDa and equal to or less than about 150 kDa.
Referring to
The hydrophilic membrane may function to further reduce the level of TSE agents (e.g., PrPSc) in the HMWS. In an embodiment, the membrane comprises polyvinylidene fluoride (PVDF), alternatively modified PVDF. The use of a membrane comprising PVDF may provide the advantages of desirable low protein-binding properties, broad chemical and temperature resistance, and high flow rate. For example, a modified PVDF membrane may reduce the level of TSE agents while allowing for transmission of a high percentage of proteins such as for example hemoglobin. An example of a hydrophilic PVDF membrane suitable for use in this disclosure includes without limitation ULTIPOR Grade DV50 membrane filter commercially available from Pall Corporation. Examples of suitable PVDF membranes are disclosed in U.S. Pat. No. 5,736,051, which is incorporated by reference herein in its entirety. A filtered HMWS sample that has been contacted with a hydrophilic membrane, hereinafter termed a processed HMWS, may have a reduction of equal to or greater than about 1 log, alternatively of from about 3.3 to about 3.7 logs, alternatively of from about 1 to about 3.2 logs, alternatively of from about 3.8 to about 4.5 logs in the amount of TSE agent when compared to the filtered HMWS. The filtrate from the hydrophilic membrane may then be employed in the subsequent steps (e.g., blocks 40 and/or 50) of the method disclosed herein.
In an embodiment, the processed HMSW is then contacted with an anion exchanger (e.g., block 40) and subsequently a hydrophobic solvent (e.g., block 50) as was described previously herein for a hemoglobin containing solution. Following contacting of the HMSW with an anion exchanger (e.g., block 40) the sample may have a reduction in the amount of TSE agent of equal to or greater than about 1 log, alternatively of from about 3.8 to about 4.3 logs, alternatively from about 1 to about 3.7 logs, alternatively from about 4.3 to about 5 logs when compared to the HMSW not subjected to the anion exchanger. Following contacting of the HMSW with a hydrophobic solvent (e.g., block 50), the sample may have a reduction in the amount of TSE agent of equal to or greater than about 1 log, alternatively of from about 0.8 to about 1.2 logs, alternatively from about 0.1 to about 0.7 logs, alternatively from about 1.3 to about 3.5 logs when compared to the HMSW not subjected to the hydrophobic solvent. As described previously, the method may then allow for further processing of the processed sample to place the sample in a condition suitable for introduction to an organism such as for example, administration to a patient. Alternatively, the sample may be used without further processing.
In an embodiment, the method further comprises determining the level of TSE agent in the samples prior to, during, or after the sample has been subjected to the disclosed methodologies. For example, at least a portion of the sample may be analyzed for the presence of TSE agents (e.g. PrPSc) prior to contacting the sample with a nanofiltration device,
The methods described herein may be carried out manually, may be automated, or may be combinations of manual and automated processes. In an embodiment, devices for the implementation of the methodologies described herein may be controlled manually, may be automated or combinations thereof. In an embodiment, the method is implemented via a computerized apparatus capable of performing the processes disclosed herein, wherein the method described herein is implemented in software on a general purpose computer or other computerized component having a processor, user interface, microprocessor, memory, and other associated hardware and operating software. The software implementing the method may be stored in tangible media and/or may be resident in memory, for example, on a computer. Likewise, input and/or output from the software, for example component amounts, comparisons, and results, may be stored in a tangible media, computer memory, hardcopy such as a paper printout, or other storage device.
The methodologies disclosed herein are a PrPSc clearance platform that comprises individual elimination steps that depend on different physical principles and address typical properties of PrPSc. The methodologies disclosed herein comprise PrPSc reduction by removal of leukocytes; PrPSc filtration with nanofilters, PrPSc absorption with anionic membrane absorbents and PrPSc inactivation with hydrophobic solvent.
This embodiments having been generally described, the following examples are given as particular embodiments and to demonstrate the practice and advantages thereof.
It is to be understood that the examples are given by way of illustration and are not intended to limit the specification of the claims in any manner.
The scrapie agent used in this example was the hamster 263K strain that was well characterized and widely accepted as a surrogate marker for TSE infectivity. The scrapie preparation used was a 10% hamster brain homogenate that was sonicated, centrifuged at 10,000 rpm for 10 minutes and filtered through a cascade of filters with porosities of 0.45 and 0.22 μm, prior to spiking experiments performed at the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7.
Bovine blood was obtained from multiple healthy donors or from an individual animal raised under U.S. FDA guidelines. Blood was drawn by puncture of the external jugular vein under aseptic conditions. Approximately 2 liters of blood was obtained from one animal and collected into four 500 mL evacuated, sterile, pyrogen-free bottles containing 75 mL of ACD anticoagulant (The Metrix Company, Dubuque, Iowa 52002, U.S.A.). Blood from different animals was not mixed. The bottles were kept on gel ice in transit to the blood substitute manufacturing facility. The blood was then subjected to separation of red blood cells from leukocytes by LEUKOTRAP and from platelets and plasma by centrifugation. This step reduced the load of non-heme proteins and other substances from which hemoglobin must be ultimately purified. The removal of all leukocytes also removes any viruses associated with these cells such as cytomegalovirus, human immunodeficiency virus and others. Moreover, the complete removal of leukocytes eliminated TSE agents that tended to be present in these cells.
The removal of leukocytes that may carry viruses and TSE agents was performed with a PALL LEUKOTRAP AFFINITY PRION REDUCTION FILTER SYSTEM (Pall Corporation, East Hills, N.Y. 11548, U.S.A.). According to the manufacturer the prion reduction performance for PrPSc is 2.9±0.7 log. The purification was performed either on whole blood within 8 hours of donation, alternatively on blood held overnight at 4 degrees C., in a volume of 450 mL per filter, at blood temperatures ranging from 4 to 22 degrees C., in accordance with the manufacturer's instructions.
Then, the red blood cells were purified from platelets and plasma by centrifugation at about 170×g at 15 degrees C. for 20 minutes and a series of five washings and five centrifugations with isotonic saline solution (red blood cells:saline, 1:4 vol/vol; 760×g at 4 degrees in a 10 minute cycle) in sterile, pyrogen-free plastic containers (Fenwal Laboratories, Deerfield, Ill. 60015, U.S.A.) using standard blood banking procedures under aseptic conditions.
To confirm the absence of leukocytes and platelets, cell counts were carried out by use of a Coulter cell counter, and the absence of protein in the suspension was verified by routine chemical methods such as a spectrophotometric method.
The extraction of hemoglobin from red blood cells was carried out by hypo-osmotic dialysis—ultrafiltration using a high flow filtration modules with porosity of 0.45 μm. In order to minimize proteolysis during hemoglobin isolation, the procedure was done at 4 degrees C., using slightly hypotonic media (240-260 mOsm kg) and a transmembrane pressure of less than 10 p.s.i. The extracted hemoglobin was filtered through a 0.2 μm filter such as Pall SSUPOR DCF Capsule Filter (Pall Corporation), changed to a carbon-monoxy form by saturation with carbon monoxide, and stored in FENWAL transfer packs at 4 degrees C.
In this example, approximately 500 mL of bovine hemoglobin in a concentration of 60±10 grams per liter in TRIS buffer, pH 6.8±0.2, spiked with a 10% hamster brain homogenate was subjected for nanofiltration using a commercially available high performance hemoconcentrator, HEMOCOR HPH 1400 with optional tubing set (Minntech Corporation). This polysulfone-based hollow fiber dialysis membrane has an effective fiber length of 20.9 cm, a membrane filtration area of 1.31 m2, a priming volume of 86 mL and an average molecular weight cutoff of 65 kDa. The filtration was performed with a flow rate of 300 mL/min, a transmembrane pressure of 30 kPa and completed in 2 hours.
The dialysate was collected and concentrated almost to the original level of Hb of 55±8 grams per liter, using a commercially available low flux polysulfone-based dialyzer, OPTIFLUX, with optional tubing set (Fresenius Medical Care, Lexington, Mass. 02420, U.S.A.). This device had a surface area of 1.5 m2, a prime volume of 83 mL and an average molecular weight cutoff of 10 kDa.
The procedure was completed in approximately 1 hour, and the concentrated product was subjected, along with the pre-dialysis samples for measurement of the prion protein levels by BSE-SCRAPIE ANTIGEN TEST EIA KIT (IDEXX Laboratories, Inc., Westbrook, Me. 04092, U.S.A.) that recognizes PrPSc, according to the manufacturer. Alternatively, after treatment with proteases, the sample was run using a SPI-BIO EIA kit (Cayman Chemical Co., Ann Arbor, Mich. 48108, U.S.A.) that employs two antibodies that were raised against a preparation of denatured scrapie associated fibril agents (SAFs) from infected hamster brain, according to the manufacturer's instructions.
All experiments were done in triplicate and clearance of PrPSc was expressed by calculation of the log reduction factor (RF) using the equation: RT=log 10 (sample starting volume×initial PrPSc concentration)/(sample volume after filtration×final PrPSc concentration). Results indicated that HEMOCOR HPH 1400 filtered more than 90% of hemoglobin after 2 hours, at a ratio of hemoglobin to hollow fiber surface area of 400 mL per m2 and as indicated in Table 1, the nanofiltration was able to reduce the PrPSc level by an average 3.47±0.14 logs.
The filtrates, which were also evaluated by in vivo assay were: (1) the bovine hemoglobin solution spiked with scrapie agent and not subjected to the nanofiltration processand (2) the bovine hemoglobin solution spiked with PrPSc and subjected to nanofiltration, both samples were evaluated at the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7.
The in vivo assay for scrapie infectivity involved intracerebral (i.e.) inoculation of hamsters (weanlings approximately 6-8 weeks of age) with an aliquot of a solution of interest. Five hamsters were assigned to each dilution group of spiked unpurified and spiked purified hemoglobin solutions (5 animals per dilution and seven dilutions per titration). Control hamsters were inoculated with hemoglobin alone. The animals were observed daily for 200 days and monitored for typical clinical signs of scrapie infection (ataxia, chronic wasting and neurological characteristics such as circular wandering) and survival rates. The 200 day observation period was chosen based on the indication that transmission of bovine prions to transgenic mice exhibit an incubation time of approximately 200 days. Thus, after 200 days, all surviving animals were sacrificed by an anesthesia overdose and their brains were examined by electron microscopy for characteristic tubuli of scrapie infection, scrapie associated fibril agent. The brains of dead animals and those terminated due to clinical signs of scrapie infection were also examined by electron microscopy for SAF. The survival and SAF positive rates are presented in Table 2.
The results suggest that the spiked unpurified bovine hemoglobin preparation has a scrapie infectivity titer of approximately 105/mL. After nanofiltration the reduction in scrapie infectivity of approximately 103.5 was achieved. These results are consistent with the results obtained by ELIA studies. Thus, nanofiltration alone was unable to fully eliminate the PrPSc infectivity, and at dilutions of 100 and 10−1 some animals did not survive. Further, the results suggest that nanofiltration, even through hollow fibers with pore size of about 65 kDa, cannot serve as an independent method for complete PrPSc clearance from hemoglobin solution when a scrapie infectivity titer is about 105/mL.
The scrapie agent also used in this example was the hamster 263K strain. The scrapie preparation used was a 10% hamster brain homogenate that was sonicated, centrifuged at 10,000 rpm for 10 minutes and filtered through a cascade of filters with porosities of 0.45 and 0.22 μm, prior to spiking experiments performed at the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7.
In this example, 100 mL of bovine hemoglobin solution, prepared as in Example 1, in a concentration of 60±10 grams per liter in TRIS buffer, pH 6.8±2, spiked with a 10% hamster brain homogenate, was subjected for anion exchange membrane chromatography using a commercially available Pall ACRODISC Unit with MUSTANG Q MEMBRANE (Pall Corporation, Ann Arbor, Mich. 48103-9019, U.S.A.).
MUSTANG Q polyethersulfone membrane, with 0.8 μm porosity, is a strong anion exchanger that effectively binds plasmid DNA, negatively-charged proteins, and viral particles. The chromatography was performed using one disposable Pall ACRODISC unit per 20 mL of hemoglobin. Before chromatography, the ACRODISC unit was preconditioned with 4 mL 1 M NaOH followed by 4 mL of 1 M NaCl, and equilibrated with 20 mM TRIS buffer, pH 6.8+0.2. Spiked hemoglobin solution (pH 6.8±0.2) in the carbon-monoxy form, was subjected to chromatographic separation at a flow of 4 mL/min. At a pH of 6.8, hemoglobin is without charge. The elimination of the electric charge of hemoglobin is intended to prevent its binding to this strong anion exchange membrane equilibrated with 20 mM TRIS buffer with a pH of 6.80.2. This chromatography method is also intended not to affect the binding of DNA and viral particles to the membrane. After 5 chromatographic runs, using separate ACRODISC units, the collected fractions were pooled together and the final volume determined.
The pre- and post-chromatography samples in the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7, were subjected for measurement of the prion protein levels by BSE-SCRAPIE ANTIGEN TEST EIA KIT (IDEXX Laboratories, Inc., Westbrook, Me. 04092, U.S.A.) that recognizes PrPSc, according to the manufacturer's instructions. Additionally, after treatment with proteases, the samples were run by SPI-BIO EIA kit (Cayman Chemical Co., Ann Arbor, Mich. 48108, U.S.A.) that employs two antibodies that were raised against a preparation of denatured SAFs from infected hamster brain, according to the manufacturer's instructions.
All experiments were done in triplicate. Clearance of PrPSc was expressed by calculation of the log reduction factor (RF) using the equation: RT=log 10 (sample starting volume×initial PrPSc concentration)/(sample volume after filtration×final PrPSc concentration). The results indicated that the samples contacted with the MUSTANG Q MEMBRANE anion exchanger did not exhibit a decrease in the level of hemoglobin, when the ratio of hemoglobin to membrane surface area of the exchanger was approximately 5 mL per cm2. However, as indicated in Table 3, anion exchange membrane chromatography with MUSTANG Q was able to reduce the PrPSc level in the sample by 4.01±0.24 logs.
The scrapie agent also used in this example was the hamster 263K strain. The scrapie preparation used was a 10% hamster brain homogenate that was sonicated, centrifuged at 10,000 rpm for 10 minutes and filtered through a cascade of filters with porosities of 0.45 and 0.22 μm, prior to spiking experiments performed at the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7.
In this example, 200 mL of bovine hemoglobin solution in carbon-monoxy form, prepared as in the Example 1, in a concentration of 60±10 grams per liter in TRIS buffer, pH 8.0±2, spiked with a 10% hamster brain homogenate, was subjected to hydrophobic solvent treatment with chloroform (HPLC Grade, Fisher Scientific).
A series of three treatments with chloroform followed by centrifugation steps were carried out using a Sorvall centrifuge (Model RC5C with SS-34 rotor), in the following manner: (1) hemoglobin mixed with chloroform at a ratio of 15 to 1 (vol/vol) was vortexed for 15 minutes and centrifuged at 760×g and 4 degrees C., for 30 minutes; (2) the supernatants were passed into a second series of tubes, mixed with chloroform at a ratio of 16 to 1 (vol/vol), vortexed for 10 minutes and centrifuged at 1,600×g and 4 degrees C., for 15 minutes, and at 3,800×g for 15 minutes; (3) the supernatants were transferred into a third series of tubes and centrifuged without chloroform at 48,400×g and 4 degrees C., for 90 minutes. After the third centrifugation, the hemoglobin solution was subjected to removal of remaining traces of chloroform by flushing with nitrogen gas followed by carbon monoxide to assure its full conversion to carbon-monoxy form.
The pre- and post-chloroform treated samples in the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7were subjected for measurement of the prion protein levels by BSE-SCRAPIE ANTIGEN TEST EIA KIT (IDEXX Laboratories, Inc., Westbrook, Me. 04092, U.S.A.) that recognizes PrPSc, according to the manufacturer's instructions. Additionally, after treatment with proteases, the samples were run by SPI-BIO EIA kit (Cayman Chemical Co., Ann Arbor, Mich. 48108, U.S.A.) that employs two antibodies that were raised against a preparation of denatured SAFs from infected hamster brain, according to the manufacturer's instructions.
All experiments were done in triplicate. Clearance of PrPSc was expressed by calculation of the log reduction factor (RF) using the equation: RT=log 10 (sample starting volume×initial PrPSc concentration)/(sample volume after filtration×final PrPSc concentration). As indicated in Table 4, a treatment with chloroform reduced the PrPSc level by 1.15±0.14 logs. This data suggests that chloroform treatment can be considered as an inactivation step with respect to purification of hemoglobin solutions from PrPSc.
The scrapie agent also used in this example was the hamster 263K strain. The scrapie preparation used was a 10% hamster brain homogenate that was sonicated, centrifuged at 10,000 rpm for 10 minutes and filtered through a cascade of filters with porosities of 0.45 and 0.22 μm, prior to spiking experiments performed at the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7.
The solutions evaluated by in vivo assay were: (1) the bovine hemoglobin solution spiked with scrapie agent and not subjected to the prion purification process, in the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7and (2) the bovine hemoglobin solution spiked with scrapie agent and subjected to the cascade prion purification process based on nanofiltration, anion exchange membrane chromatography and hydrophobic treatment, in the following dilutions: 100, 10−1, 10−2, 10−3, 10−4, 10−5, 10−6 and 10−7. The starting material for this example was bovine hemoglobin solution, in carbon-monoxy form, and was prepared as in Example 1, and spiked as in described previously.
The TSE purification process combined: (1) nanofiltration, (2) anion exchange membrane chromatography and (3) hydrophobic solvent treatment with chloroform, as described in Examples 1, 2 and 3, respectively. To maintain low absorption of hemoglobin to nanofiltration and anionic membrane exchange devices, hemoglobin was dissolved in a buffer system that eliminated its charge and therefore its electrostatic interaction. Such a buffer system is described in Examples 1 and 2. Additionally, in order to protect heme against oxidation, the heme oxygen was completely replaced with carbon monoxide, forming carbon-monoxy hemoglobin, which is highly resistant to oxidative challenge. Any changes in sample volume were corrected for dilution by estimating hemoglobin concentration. The average hemoglobin concentrations in pre-purified samples were approximately 60±10 grams per liter and after purification, were approximately 55±8 grams per liter.
The in vivo assay for scrapie infectivity involved intracerebral (i.c.) inoculation of hamsters (weanlings approximately 6-8 weeks of age) with an aliquot of a solution of interest. Five hamsters were assigned to each dilution group of spiked unpurified and spiked purified hemoglobin solutions (5 animals per dilution and seven dilutions per titration). Control hamsters were inoculated with hemoglobin alone. The animals were observed daily for 200 days and monitored for typical clinical signs of scrapie infection (ataxia, chronic wasting and neurological characteristics such as circular wandering) and survival rates. After 200 days, all surviving animals were sacrificed by an anesthesia overdose and their brains were examined by electron microscopy for characteristic tubuli of scrapie infection (scrapie associated fibril agent—SAF). The brains of dead animals and those terminated due to clinical signs of scrapie infection were also examined by electron microscopy for SAF. The survival and SAF positive rates are presented in Table 5.
Results suggest that the spiked unpurified bovine hemoglobin preparation has a scrapie infectivity titer of approximately 105/mL. After this multi-step purification procedure of the scrapie spiked bovine hemoglobin samples, no scrapie infectivity was detectable. Inoculation of animals with hemoglobin alone did not result in any observed clinical and morphological changes.
These data suggest that purification of bovine hemoglobin solution from TSE agent by sequential stepwise use of nanofiltration, anion exchange membrane chromatography and hydrophobic solvent treatment can effectively eliminate scrapie infectivity.
This multi-step purification procedure of bovine hemoglobin from PrPSc may be considered as orthogonal, since it contains elements of removal (nanofiltration and anion exchange membrane chromatography) and inactivation (hydrophobic solvent) of the TSE agent.
While embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications are possible and are within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, etc.
Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the embodiments of the present invention. The discussion of a reference herein is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to those set forth herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2007/088976 | 12/27/2007 | WO | 00 | 12/20/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60882612 | Dec 2006 | US |
