Selective Removal of Albumin From Blood Fluid and Compositions Therefore

Selective fractionation of proteins in blood fluids.

It is well known that blood fluids such as plasma and serum contain many proteins which it is desirable to isolate in a pure state. Isolation procedures for such proteins are known, however, they all suffer from a common problem, namely, the presence of albumin. Albumin is the major protein constituent in plasma. Besides being a contaminant in the aforementioned procedures, it is often desirable to isolate pure albumin uncontaminated by other proteins. Thus, it would be most desirable to develop a procedure whereby albumin can be selectively removed from blood fluids without simultaneous removal of other proteins which may be present in very small quantities.

It is well known that certain proteins will bind very tightly to certain reactive dyes. It has been reported that Blue Dextran will bind tightly with lysozyme, ovalbumin, and hemoglobin when they carry net positive charge, and bovine serum albumin independent of charge. Blue Dextran is a dye generally known as Procion Blue HBS wherein the chlorine atom on the triazine moiety of the dye is replaced by the polymer Dextran being bonded to said triazine group via --O-- grouping. (White and Jencks Binding of Proteins to Blue Dextran, No. 43, Biol., Abstracts, 160th National Meeting, American Chemical Society, September 14, -18, 1970). It should be noted however that Blue Dextran is water soluble. Thus, an operative procedure would involve coupling Blue Dextran to a solid substrate from which the albumin can be removed. It would be particularly desirable if, in addition to removal of the albumin in such a manner that the absorptive capacity of the substrate was not damaged, the albumin was regenerated in such way that it was not denatured.

Cuatrecasas has disclosed a method of protein purification by affinity chromatography. In the Cuatrecasas procedure insoluble materials are prepared by coupling certain large molecules containing amino groups to agarose by activating the agarose with cyanogen bromide prior to treating the activated agarose with the amino containing moiety. (J.Biol.Chem. 245,3059,(1970).

Bohme et al (J. Chromatogr., 69, 209, (1972)) found that the condensation product of Cibacron Blue F3G-A, otherwise known as Procion Blue HBS with Dextran 2000, otherwise known as Blue Dextran 2000 (a trademarked product of Pharmacia, Uppsala, Sweden) had a high affinity for the enzyme phosphofructokinase. On the other hand, the condensation product of Dextran 2000 with Cibacron Brilliant Blue FBR-P, a dye of extremely similar structure, showed no affinity for phosphofructokinase. Neither was such activity shown when Blue Dextran was coupled with cyanogen bromide activated sepharose.

The specificity of dyes for certain polypeptides is therefore not predictable.

It has been found that certain reactive dyes when coupled to certain solid support phases provide a composition upon which albumin may be selectively adsorbed out from the presence of other proteins from substantially cell free aqueous fluids such as plasma or serum. The adsorbed albumin may be removed, in high yield, without denaturization, from said compositions and compositions may be re-utilized without loss of adsorbative capacity. The support phases which may be utilized for this purpose include agarose, more particularly sepharose, polyacrylamides, more particularly cross-linked polyacrylamide gel, and acrylic resins, more particularly anion exchange resins such as Amerlite IRC 45, containing an amino group.

These support phases are bonded to Color Index reactive dyes (hereinafter CRD) wherein the CRD has the general formula ##STR1## wherein R.sub.1 is hydrogen, an alkali metal, or an alkaline earth metal, R.sub.2 is halo or --O-- dextran R.sub.3 is hydrogen, alkyl, phenyl, alkoxy phenyl, alkyl phenyl and ##STR2## Z.sub.1 is [-H].sub.2 or --CH=CH--CH=CH-- Z.sub.2 is a nitrogen-nitrogen bond or a hydrogen attached to the nitrogen shown only, m is 1 or 0, n is 1 or 2, Q is substituted or unsubstituted aryl where Z.sub.2 is hydrogen or substituted or unsubstituted aryl-N= where Z.sub.2 is a double bond, provided that the substituent groups aforesaid are other than halo or heavy metal wherein heavy metal is defined as a metal falling in periodic groups other than 2A, 3A and 4A.

The adsorptions of the albumin onto the support phase/CRD from the fluid containing it, is suitably carried out in a buffer of at least 0.05M molarity at a pH of between 6.5 and 8.5. While the process of the invention is not limited thereto and method of contacting is considered the scope of the invention, it is considered convenient to charge the suspension of the support phase/CRD composition to a chromatographic column and to pass through said column, the substantially cell free albumin containing fluid. The eluate is substantially albumin free and may be further processed as desired.

The albumin is then removed from the support phase/CRD suitably by eluting, preferably eluating a column, with a suitable eluent. The eluents may be selected from the group consisting of aqueous urea, ethanol-aqueous alkali metal phosphate, basic buffered alkanoic acids containing 2 to 10 carbon atoms and aqueous solutions of cations of Group 2A metals and potassium with pharmaceutically acceptable anions. The use of any of these eluents will provide a support phase/CRD composition of renewed activity which may be used to remove further amounts of albumin from additional charges of albumin containing fluids. However, where it is desired to isolate pure, nondenatured albumin the latter two groups of solvents should be employed. The albumin can then be isolated therefrom by, say, lyophilization in the usual manner.

In one embodiment of the present invention there may be employed as support agarose, preferably in the form of Sepharose which may be in the form of packed Sepharose (for example, grades 2B, 4B, or 6B) or cross-linked Sepharose (for example, grades 2B, 4B, or 6B).

Especially preferred are the CRD's of the formula given above wherein R.sub.1 is hydrogen, an alkali or alkaline earth metal of periodic groups 2A and 3A such as lithium, sodium, potassium, magnesium or calcium, R.sub.2 is chloro or O-dextran; and the alkyl moieties of R.sub.3 are lower alkyl moieties of 1-5 carbon atoms.

Preferably, Q is substituted phenyl, substituted naphthyl, substituted phenyl azo phenyl and anthraquinonyl.

Most preferably the aromatic nuclei of the foregoing aryl moieties are substituted by at least one sulphonic acid group, suitably in the form of the alkali metal salt thereof, additional substituent groups include hydroxyl, amino or amido groups where the amido group may be lower alkanoyl amido of 1-5, carbon atoms in the alkanoyl moiety such as formamido, acetamido, valeramido and the like, or aralkanoylamido of 1-5 carbon atoms or the alkanoyl moiety such as benzoylamido, phenylacetamido, naphthoylamido and the like. As stated heretofore, the reactive dyes which may be utilized in the present invention possess certain common structural characteristics. Certain of these dyes may be more particularly identified by means of their Color Index generic name, Color Index constitution number, or commercial name. Among these dyes thus identified may be included the following: CI Reactive Orange 2 (CI Constitution No. 17865, also known as Cibacron Orange G-E, or Procion Brilliant Orange HGRS), CI Reactive Red 4 (CICN 18105, also known as Cibacron Brilliant Red 3B-A, or Procion Brilliant Red H7BS), CI Reactive Brown 1 (CICN 26440, also known as Cibacron Brown 3GR-A, or Procion Orange Brown HGS, CI Reactive Red 9 (CICN 17910, also known as Cibacron Scarlet 2G or Procion Scarlet H3GS). Of similar structure is CI Reactive Red 16, also known as Cibacron Scarlet 4G-B. Also included in this group are the anthraquinone dyes CI Reactive Blue 2 (CICN 61211, also known as Cibacron Blue F3G-A or Procion Blue HBS, and CI Reactive Blue 5 (CICN 61210, also known as Cibacron Brilliant Blue FBR-P).

Methods of making all of these dyes will be found in Pancharteck, et al., Col.Czeck.Chem.Commune., 25, 2783 (1960).

Also within the scope of the present invention should be considered compounds wherein the terminal benzene sulfonic acid group is replaced by another substituent such as alkyl, phenyl, alkyl phenyl, alkoxy phenyl, hydrogen or the like. Typical of this group is CI Reactive Red (CICN 18159) (C. Calin, et al, Coloristica Buletin Informativ, 4, (No. 11, 1968) 179-200.

All of the foregoing dyes may be coupled with the support phase substrates by heating in water at moderately elevated temperatures, suitably above pH 6.0. In the preferred modification the mixtures are heated with stirring between 75.degree. and 95.degree. , the mixture cooled, and washed to remove the unbound dye.

The ratio of the weight of dye to the weight of support phase is not critical. Where too little dye is utilized the efficiency of the extractive process will be reduced in view of the presence of too few adsorption sites. If too much dye is used the product obtained is not only economically wasteful but problems of steric interference will arise which will actually serve to reduce the number of available adsorption sites for the albumin.

There may be utilized between 0.1 to 5 grams of dye per 4 grams of support phase. It is preferred however to utilize between 0.2 and 1 gram of dye per 4 grams of support phase. It should be noted however that from a practical point of view the support phase is not usually measured by weight but rather by volume of settled support phase in aqeous suspension. Thus, where the support phase is sepharose, 4 grams of sepharose would correspond substantially to 100 ml. of settled sepharose.

While the weight/volume ratio will of course vary with the chemical nature of the support phase and the size of the granules, within the scope of generally available support phases of the size represented by sepharose of grades 2B, 4B, and 6B, the foregoing ratios are sufficiently close to provide a satisfactory range of operability.

In the preferred modification of the coupling procedure, the dye, that is to say, between about 0.1 and 2 grams of dye, preferably between 0.2 and 1 grams of dye, is dissolved or suspended in a small amount of water, between 10 and 50 ml. is generally suitable, and added to 100 ml. (measured as settled support phase of support phase, in water. The amount of water to suspend the support phase is not critical; between 100 ml. and 1000 ml. have been found suitable. The mixture is gently agitated and warmed to below the boiling point of water. A temperature range of 75.degree. thru 95.degree. C has been found satisfactory. The pH of the solution is maintained slightly above pH 6, suitably between pH 6 and pH 8 by the addition of either aqueous alkali or a buffer. The actual reaction time will depend upon the dilution of the dye, the temperature, and the agitation of the support phase. Nevertheless, the reaction can generally be considered to be complete in between from about 5 to about 60 minutes. The coupled product (designated herein SP/CRD) is then separate from the aqueous phase, suitably by decantation and washed to remove any unreacted dye. It has been found suitably to wash thoroughly with water at ambient temperature followed by a suitable salt, such as quanidine hydrochloride (5M) which will remove any unbound dye. The use of guanidine hydrochloride solution is not critical and other washes may also be used.

The thus purified SP/CRD is then suspended in a buffer, suitably a buffer of between a pH of 6.5 and 8.5. The albumin adsorptive capacity of the product thus produced will of course depend upon the dye/support phase ratio. However, products produced in accordance with the foregoing procedures will have an absorptive capacity of the order of 30 milligrams of albumin per ml. of settled SP/CRD.

It should be borne in mind that different dyes will react at different rates with different support phases. Furthermore care must be taken that the support phase does not become physically changed, i.e. by partial or complete melting, during the coupling process. For example, it should be noted that while Cibacron Blue F-3GA reacts very rapidly with sepharose at 80.degree. C, other dyes will couple slowly with ordinary sepharose at this temperature. While at 90.degree. coupling occurs rapidly, the product produced is, although operative, not of optimum physical characteristics. Thus, where higher reaction temperatures are required, it is desirable to utilize cross-linked support phases such as cross-linked sepharose.

As examples of other support phases which may be utilized in the process of the present invention, there may be mentioned polyacrylamide gels, and acrylic resins containing amino groups, such as, for example, Amberlite IRC 45.

Also included within the scope of the present invention are the Dextran derivatives of Cibacron Blue F3GA and Cibacron Brilliant Blue FBR-P. In these dyes the chloro group of the triazine moiety is replaced by an -O- linkage to a Dextran molecule. The former when coupled with Dextran 2000 yields Blue Dextran 2000.

The foregoing coupling procedures for the formation of SP/CRD depend upon the reaction of a halo group on the triazine moiety with a labile group on the support phase. Such reaction is not feasible where this group has been replaced by a -O-Dextran linkage. Nevertheless, where the CRD possesses a labile amino group such as, for example, the primary amino group on the anthraquinone moiety of Cibacron Blue F3GA and Cibacron Brilliant Blue FBR-P, coupling may be carried out by the cyanogen bromide method of Cuatracasas. In this procedure, the support phase is activated by treatment with aqueous alkaline cyanogen bromide and the suitably buffered support phase reacted with the dye. In this procedure the Dextran/CRD in a similar buffer is then added to the activated support phase and coupling allowed to proceed. The coupling reaction may take place at temperatures between 0.degree. C and ambient temperature, however, it is preferred to carry out the reaction at approximately 4.degree. C for approximately 24 hours. After elapse of this time, the conjugate is successively washed with aqueous sodium bicarbonate (pH approximately 9.5), concentrated aqueous urea (approximately 6M), water, and a high ionic strength buffer of pH between 6.5 and 8.5. It is preferred to utilize a tris-HCl/aqueous sodium chloride buffer. Th sepharose/Dextran/CRD conjugate is then suspended in fresh buffer and may be stored at approximately 4.degree. C until used.

In the practice of the albumin removal procedure it is found desirable to place the SP/CRD conjugate in a column in a high ionic strength buffer. The tris-HCl/sodium chloride buffer mentioned hereinabove has been found especially suitable. The high ionic strength of the buffer system is important for the operation of the procedure since it prevents the SP/CRD from acting as a cationic exchange column. It has been found suitable to apply approximately 2 ml. of albumin containing plasma to approximately 10 ml. of settled SP/CRD. The plasma is then run through the column and the column washed with the aforementioned buffer. Elution was followed by uv adsorption of the eluate.

As stated heretofore the critical factor in this procedure is the ionic strength of the buffer system. In order to be operative the buffer should have an ionic strength of at least 0.05M, no upper limit being necessary, at a pH of between 6.5 and 8.5, preferably a pH of about 8.0.

The thus obtained eluate is substantially albumin free and the remaining proteins may be isolated therefrom in methods known to the art. Examination and comparison of the initial plasma and the elute shows that in addition to the albumin only small amounts of other proteins, principally, lipoproteins are removed.

The column may be regenerated by breaking the (SP/CRD)/albumin bond. Where preservation of the albumin is not required an aqueous solution of urea has been found suitable. The urea solution must be at least 1M, while solutions of 3M have been used, any strength up to saturation (ca 8M) is satisfactory. One column volume of urea solution is sufficient to break the bonds, however, 1-3 column volumes are usually employed.

Where it is desired to preserve the albumin an ethanol/aqueous alkali metal phosphate, suitable sodium phosphate solution is employed. The preferred volume ratio is 1:1 and the phosphate solution is between 0.05 and 0.1M at pH of 2.0-3, suitably 0.075M at pH 2.4, measured prior to mixing.

It has also been found that albumin may be eluted in high purity using an aqueous solution of an alkaline earth metal cation and a pharmaceutically acceptable anion. Especially suitable as cations are Ca.sup.+.sup.+ and Mg.sup.+.sup.+. K.sup.+, but not Na.sup.+ may also be employed. As anion there may be used any strong, pharmaceutically acceptable anion, suitably the chloride ion. The ionic strength of these eluents should be, preferably, at least 0.05M. Lower concentrations cause tailing. Higher concentrations, say, up to 0.1M bring a faster elution and are acceptable, these concentrations should not be considered as limiting.

It has been found desirable to buffer the eluent, suitably to a pH between pH 6.0 and 9, most preferably to a pH of about 8. This is achieved by adding a buffer such as sodium bicarbonate or trishydrochloride to the eluent. An ionic strength of about 0.05-0.1M tris hydrochloride in the eluent has been found suitable.

It has also been found that basic buffered alkanoic acids are suitable as eluents. Acids containing 2-10 carbon atoms may be employed, acids containing 8-10 carbon atoms are preferred. Octanoic acid is especially suitable as it is the stabilizing agent of choice for albumin. Utilizing alkanoic acids, especially octanoic acid as an eluent, there is made available a stabilized solution of pure albumin which may, if desired, be concentrated under reduced pressure or lyophilized to provide pure buffered albumin.

Any buffer may be employed which will raise the pH of the solution to at least pH 6.5, pH 7.5-9 being an operative range, and about pH 8.0 being preferred. Tris hydrochloride/aqueous sodiumchloride is especially suitable as a buffer.

It should be noted that the solubility of C.sub.8 -C.sub.10 alkanoic acids in water is not high. Octanoic acid has a solubility of the order of 4mM. Thus the preferred mode of preparing the eluent is to prepare a buffer such as tris hydrochloride (0.05-0.2M) suitably with 0.05-0.5M aqueous sodium chloride and add thereto as much of the alkanoic acid as will dissolve therein. Again, the solution should be buffered to at least pH 6.5, pH 7.5 - pH 9, being the operative range and a pH of about 8.0 being preferred.

Utilizing either method of column regeneration, the columns may be repeatedly utilized without loss of absorptive power.

100 ml. of settled cross linked sepharose 4B (Pharmacia Fine Chemicals, Inc) is suspended in 250 ml. of water. 1 gm. of Cibacron Brilliant Blue FBR-P is dissolved in 25 ml. of water and the solution added to the sepharose suspension. The mixture is agitated gently and heated to 80.degree. C for 45 minutes. The pH is held to at least pH 6 by addition of sodium bicarbonate or this hydrochloride. The reaction mixture is cooled to ambient temperature, the supernatant liquid decanted and the solid phase washed thoroughly, first with water (31.) then with aqueous guanidine hydrochloride solution (2 l., 5M.) and finally suspended in a mixed buffer of aqueous tris hydrochloride (0.05M) and aqueous sodium chloride (0.5M) (pH 8.0) to yield an SP/CRD conjugate of Sepharose 4B and Cibacron Brilliant Blue FBR-P.

In accordance with the above procedures, there may be utilized packed sepharose polyacrylamide gel and Amberlite IRC 45 to yield similar SP/CRD's.

In accordance with the procedures of the principle example, but using as CRD's, Procion Brilliant Orange HGRS, Procion blue HBS, Procion Brilliant Red H7B5, Procion Orange Brown HGS, Procion Scarlet H3GS, Cibacron Scarlet 4GP and Cibacron Brilliant Red BA, and as SP utilizing a cross-linked Sepharose, polyacrylamide gel or a polyacrylic amino group containing resin similar SP/CRD's are obtained provided the temperature of reaction is raised to 90.degree.-95.degree. C.

100 ml. of settled Sepharose 4B (Pharmacia Fine Chemicals Inc) is treated with an aqueous solution of cyanogen bromide (16g) at pH 11.0 and 10.degree. C for 5 hours. After completion of the reaction the supernatant liquid is removed by decantation and the sepharose agitated with sodium bicarbonate buffer (0.1M, pH 9.5). The supernatant liquid is again removed by decantation and Blue Dextran (1g) in 100 ml. of aqueous sodium bicarbonate, (0.1M, pH 9.5) is added. The reagents are allowed to stand for 24 hours at 4.degree. C. The supernatant liquid is then removed by decantation and the product washed successively with aqueous sodium bicarbonate (4 l, 0.1M, pH 9.5), aqueous urea (4 l., 6M), water (4 l.) and a mixed buffer consisting of aqueous tris-hydrochloride (0.05M) and aqueous sodium chloride (0.5M) (4 l., pH 8.0). After removal of the supernatant wash of this last buffer, the thus produced SP/CRD is suspended in a similar solution and, if desired, stored at 4.degree. C.

A chromatographic column (1.0 .times. 20 cm) is charged with circa 10 ml. of SP/CRD produced in accordance with Example II suspended in the aforementioned tris-hydrochloride/sodium chloride buffer. 2 ml. of plasma is applied to the column and eluted with buffer until no further protein was eluted. This is checked by ultra-voilet examination of the eluate wherein A.sub.280 is less than 0.020. The eluate is then reduced in volume by diaflowing (utilizing an Anion-UM[10 membrane) to a volume of 2 ml.

The procedure was controlled by running control samples through a sepharose 4B column which had not been conjugated with Blue Dextran. The diaflowed eluate is then subjected to assay by cellulose acetate membrane electrophoresis to yield the results set forth in Table I.

Fractions were quantitatively assayed after cellulose acetate membrane electrophoresis as described in text. Total protein was determined by the method of Lowry, et al, (J. Biol. Chem. 193, 265 (1951)).

A chromatographic column (1.0 .times. 20 cm) is charged with circa 10 ml. of SP/CRD produced in accordance with Example I utilizing as SP, cross linked sepharose 4B and as CRD, Procion Brilliant Red H7BS, suspended in the aforementioned tris-hydrochloride/sodium chloride buffer. 2 ml of plasma is applied to the column and eluted with buffer until no further protein was eluted. This is checked by ultra-violet examination of the eluate wherein A.sub.280 is less than 0.020. The eluate is then the aforementioned tris-sodium chloride buffer.

The column of Example IV is regenerated by washing through the column two column volumes of aqueous urea (6M) followed by the aforementioned tris-sodium chloride buffer. This method of column regeneration, although entirely satisfactory for re-use of the column, denatures the albumin.

The albumin containing column of Example III is washed with 2cv of aqueous sodium phosphate (0.075M, pH 2.4) and ethanol, the ratio of ethanol to aqueous sodium phosphate being 1:1. The eluate is then diaflowed utilizing the Amicon UM-10 membrane to yield pure, undenatured albumin 65 mg. (ca 80% recovery).

The albumin containing column of Example III is washed with two column volumes of a mixture comprising octanoic acid (4 mm), tris hydrochloride (0.05M) and aqueous sodium chloride (0.05M) at pH 8. The eluate is lyophilized to provide pure stabilized albumin.

In accordance with the aforegoing procedure there may be utilized nonanoic acid and decanoic acid in place of octanoic acid.

The albumin containing column of Example IV is washed with two column volumes of a mixture comprising calcium chloride (0.05M) and tris hydrochloride (0.05M) at pH 8.0. The eluate is then diaflowed utilizing the Amicon UM-10 membrane to yield pure undenatured albumin.

In accordance with the foregoing procedures but using magnesium chloride or potassium chloride in place of calcium chloride, the same result is obtained.