Chemistry: natural resins or derivatives; peptides or proteins; – Proteins – i.e. – more than 100 amino acid residues – Lipoproteins – e.g. – egg yolk proteins – cylomicrons – etc.
Reexamination Certificate
1997-09-05
2003-05-06
Low, Christopher S. F. (Department: 1653)
Chemistry: natural resins or derivatives; peptides or proteins;
Proteins, i.e., more than 100 amino acid residues
Lipoproteins, e.g., egg yolk proteins, cylomicrons, etc.
C530S412000, C530S421000, C530S422000, C530S424000
Reexamination Certificate
active
06559284
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a composition and process for purifying apolipoprotein A or apolipoprotein E, which are important components of the high density and low density lipoproteins in plasma. More particularly, this invention relates to a composition containing a first and a second polymeric material for use in a process comprising a primary aqueous two-phase separation step followed by separation of ApoA or ApoE from the second polymeric material exhibiting preference for ApoA or ApoE.
BACKGROUND OF THE INVENTION
The main function of lipoproteins in plasma is to transport lipids, such as cholesterol and triglycerides. For transport in plasma, cholesterol, normally as cholesteryl esters, and the triglycerides are included into lipoprotein particles in which they form a hydrophobic core. The core is surrounded by a surface coat containing phospholipids, unesterified cholesterol and proteins called apolipoproteins. The latter are responsible for the lipid transport, and in addition, some may interact with many of the enzymes involved in lipid metabolism. To date, at least nine apolipoproteins have been identified: A-I, A-II, A-IV, B, C-I, C-II, C-III, D and E.
There are four major classes of lipoproteins: chylomicrons (CM), very low density (VLDL), low density (LDL) and high density (HDL) lipoproteins. Of these, HDL is directly involved in the removal of cholesterol from peripheral tissues, carrying it back either to the liver or to other lipoproteins, by a mechanism known as “reverse cholesterol transport” (RCT).
The “protective” role of HDL has been confirmed in a number of studies. Recent studies directed to the protective mechanism(s) of HDL have been focused on apolipoprotein A-I (ApoA-I), the major component of HDL. High plasma levels of ApoA-I are associated with a reduced risk of CHD and presence of coronary lesions.
The apolipoprotein A-IMilano (ApoA-IM) is the first described molecular variant of human ApoA-I (Franceschini et al. (1980) J. Clin. Invest. 66: 892-900). It is characterized by the substitution of Arg 173 with Cys 173 (Weisgraber et al. (1983) J. Biol. Chem. 258: 2508-2513). The mutant apolipoprotein is transmitted as an autosomal dominant trait and 8 generations of carriers have been identified (Gualandri et al. (1984) Am. J. Hum. Genet. 37: 1083-1097). The status of a ApoA-IM carrier individual is characterized by a remarkable reduction in HDL-cholesterol level. In spite of this, the affected subjects do not apparently show any increased risk of arterial disease. Indeed, by examination of the genealogical tree it appears that these subjects may be “protected” from atherosclerosis.
To make possible production of sufficient quantities of ApoA-I in general, and more specifically ApoA-IM, use is made of recombinant DNA techniques, e.g. in
E. coli.
Thus, recombinant preparation and use of ApoA-IM, monomers as well as dimers, are disclosed in patent specifications WO-A-88/03166 assigned to Farmitalia Carlo Erba (FICE), WO-A-90/12879 assigned to Sirtori et al, as well as WO-A-93/12143 and WO-A-94/13819 both assigned to Pharmacia AB (formerly Kabi Pharmacia AB).
Apo A-IM is a protein containing at least six major &agr;-helix segments and with a very dense structure. Several of the &agr;-helices are amphiphilic, creating an amphiphilic protein where one surface is hydrophobic and the other is hydrophilic (D. Eisenberg et al, Nature, vol. 299 (1982), pp. 371-374). The amphiphilic properties of ApoA-IM and other ApoAs create a tendency to form micellar structures with other proteins and lipids in aqueous solutions.
Apolipoprotein E (ApoE) is a ligand for the LDL receptor. As a result, ApoE plays an important role in cholesterol metabolism. In addition, ApoE is involved in the hepatic clearance of chylomicron remnants.
Several methods have been proposed for purifying ApoA and ApoE, either from plasma or produced by recombinant DNA techniques. On a laboratory scale use is commonly made of centrifugation, ion-exchange chromatography, affinity chromatography, isoelectric focusing, gel filtration and high-performance liquid chromatography (HPLC) (see Methods in Enzymology, vol. 128, Academic Press, San Diego, Calif., USA (1986)). There is, however, a need for additional methods suitable for purification of ApoA and ApoE, especially on an industrial or pilot-plant scale. Such methods would increase the number of process techniques available to optimize the overall purification of ApoA and ApoE.
Aqueous two-phase systems have widespread use in biochemistry and biotechnology for purifying biological materials such as cells, proteins, nucleic acids and steroids (see e.g. P.-Å Albertsson, Partition of cell particles and macromolecules, 3rd ed., Wiley, New York City, N.Y., USA (1986) and H. Walter et al, Partitioning in Aqueous Two-Phase Systems, Academic Press, Orlando, Fla., USA (1985)). The systems are suitable for biological materials because each phase contains about 70 to 90% by weight of water, thereby substantially reducing the risk of denaturation of biomolecules such as proteins (H. Walter et al, Aqueous two-phase systems, Methods in Enzymology, vol. 228, Academic Press, San Diego, Calif., USA (1994)).
The aqueous two-phase systems are composed of two immiscible polymeric materials or one polymeric material in combination with a high salt concentration. Elevating the concentrations above a certain critical value produces two immiscible aqueous phases in which the polymeric materials or polymeric material and salt are partitioned.
The partitioning of proteins in aqueous two-phase systems mainly depends upon protein hydrophobicity, charge and size. The partitioning can be influenced by changing polymeric materials, the molecular weight of the polymeric materials, the pH and by adding salts to the system (G. Johansson, Acta Chem. Scand., B 28 (1974), pp. 873-882).
Aqueous two-phase systems can be scaled up readily, since the partitioning of biological materials such as proteins is essentially independent of the size of the system. The time for phase separation can, however, be prolonged in large-scale systems depending e.g. on the geometry of the separation vessel.
On a laboratory scale, use is commonly made of dextran and polyethylene glycol (PEG) as the immiscible polymeric materials. Dextran is, however, a relatively expensive polymeric material and for large-scale purification, e.g. industrial scale enzyme extraction, various combinations of PEG and salts are more frequent (K. Köhler et al, Methods in Enzymology, vol. 228, Academic Press, Orlando, Fla., USA, (1994), pp. 627-640).
U.S. Pat. No. 4,740,304 to Perstorp AB relates to compositions containing hydroxyalkyl starch for use in systems with two or more phases for extraction, purification, concentration and/or separation of biological substances. In one preferred embodiment, the hydroxyalkyl starch is hydroxypropyl starch (LIPS). In another preferred embodiment the hydroxyalkyl starch is combined with another polymer, e.g. polyethylene glycol (PEG) or polypropylene glycol. In the examples of U.S. Pat. No. 4,740,304, use is made of various enzymes.
The use of aqueous two-phase systems for purifying biomolecules has been limited, however, since the target products have been contaminated with a phase-system polymer, thus necessitating additional and complicated purification steps. Thus, hitherto the target products to be purified have been partitioned to a salt solution or remained dissolved together with a phase-system polymer. To alleviate this problem, the use of thermo-separating polymeric materials in aqueous two-phase systems has been introduced. This makes it possible to perform temperature-induced phase separation whereby the target biomolecule can be separated from the polymeric material in a very efficient way. This technique has been utilized on a laboratory scale for purifying various enzymes. Thus, temperature-induced phase separation has been used to purify 3-phosphoglycerate kinase and hexokinase from baker's yeast homogenate (P. A. Harris et al, Biosepa
Ageland Hans
Nyström Lena
Persson Josefine
Tjerneld Folke
Esperion Therapeutics, Inc.
Gupta Anish
Holland & Knight LLP
Low Christopher S. F.
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