Adsorbent and process for preparing the same

Abstract: Adsorbent for removing low and/or very low density lipoprotein from body fluid such as blood or plasma composed of water-insoluble porous hard gel with an exclusion limit of 10⁶ to 10⁹ daltons on which a polyanion compound and/or a sulfated compound is immobilized. The adsorbent is suitable for selective removal of VLDL and/or LDL, from blood or plasma in extracorporeal circulation treatment.

Description: The present invention relates to a novel adsorbent and a process for preparing the same, more particularly, to an adsorbent for removing low and/or very low density Lipoprotein from body fluid such as blood or plasma in extracorporeal circulation treatment. The present application is a divisional application, from EP-A-83 112 042.3 covering an adsorbent consisting of a porous cellulose gel for removing a substance to be removed from body fluid in extracorporeal circulation treatment and a process for preparing the same. There has been required a means for selectively removing harmful substances which appear in body fluid and closely relate to a cause or a progress of a disease. For example, it is known that plasma lipoprotein, especially very low density lipoprotein (hereinafter referred to as "VLDL") and/or low density lipoprotein (hereinafter referred to as "LDL") contain a large amount of cholesterol and cause arteriosclerosis. In hyperlipemia such as familial hyperlipemia or familial hypercholesterolemia, VLDL and/or LDL show several times higher values than those in normal condition, and often cause arteriosclerosis such as coronary arteriosclerosis. Although various types of treatments such as regimen and medications have been adopted, they have limitations in effect and a fear of unfavorable side effects. Particularly in familial hypercholesterolemia, a plasma exchange therapy which is composed of plasma removal and compensatory supplement of exogeneous human plasma protein solutions is probably the only treatment method being effective nowadays. The plasma exchange therapy, however, has various defects such as (1) a need for using expensive fresh plasma or plasma fractions, (2) a fear of infection by hepatitis viruses and the like, and (3) loss of all plasma components containing not only harmful components but also useful ones, i.e. in case of lipoprotein, not only VLDL and/or LDL but also high density lipoprotein (hereinafter referred to as "HDL") are lost. For the purpose of solving the above defects, a selective removal of harmful components by a membrane and the like has been adopted. These methods, however, are insufficient in selectivity and cause a large loss of useful components from body fluid. There has been also tried a selective removal of harmful components by means of adsorption. For example, a synthetic adsorbent such as active carbon or Amberlite XAD (a registered trademark, commercially available from Rohm & Hass Co.) has been utilized for liver disease. Such an adsorbent however, has many defects such as poor selectivity and disability for removing high molecular compounds. Furthermore, for the purpose of increasing selectivity, there has been adopted an adsorbent based on the principle of affinity chromatography composed of a carrier on which a material having an affinity for a substance to be specifically removed (such material is hereinafter referred to as "ligand") is immobilized. In that case, however, it is difficult to obtain a sufficient flow rate for an extracorporeal treatment because a carrier is a soft gel such as agarose. Accordingly, a particular modification in column shape is required in order to obtain a large flow rate and the risk of an occasional clogging still remains. Therefore, a stable extracorporeal circulation cannot be achieved by the above method. An adsorbent of the present invention may be used for selectively removing not only the above-mentioned VLDL and/or LDL but also other harmful substances to be removed from body fluid. It is an object of the present invention to provide an adsorbent for selectively removing harmful substances such as VLDL, LDL, virus and harmful cells from body fluid such as blood or plasma in extracorporeal circulation treatment of immune disease, metabolic disease, inflammatory disease such as hepatitis or nephritis, virus infection, and the like. A further object of the present invention is to provide a process for preparing the adsorbent. These and other objects of the present invention will become apparent from the description hereinafter. In accordance with the present invention, there is provided an adsorbent for removing low and/or very low density lipoprotein from body fluid in extracorporeal circulation treatment, which comprises a water-insoluble porous hard gel with exclusion limit of 10⁶ to 10⁹ daltons except a porous cellulose gel on which a dextran sulfate, a salt thereof or a mixture of the dextran sulfate and the salt thereof having a sulfur content of not less than 15 % by weight is immobilized by a covalent linkage. Figs. 1 and 2 are graphs, respectively, showing relations between flow rate and pressure-drop obtained in Reference Examples 1 and 2, It is suitable that carriers used in the present invention have the following properties: (1) relatively high mechanical strength, (2) low pressure-drop and no column clogging in case of passing body fluid through a column packed with a carrier, (3) a large number of micro pores into which a substance to be removed permeates substantially, and (4) less change caused by a sterilizing procedure such as steam sterilization by autoclaving. Therefore, the most suitable carrier used in the present invention is a water-insoluble porous polymer hard gel or a porous inorganic hard gel except a porous cellulose gel. The porous hard gel used in the present invention is less swelled with a solvent and less deformed by pressure than a soft gel such as dextran, agarose or acrylamide. The term "hard gel" and "soft gel" in the present invention is explained as follows: A hard gel is distinguished from a soft gel by the following method described in Reference Examples 1 and 2. That is, when a relation between flow rate and pressure-drop is determined by passing water through a column uniformly packed with a gel, a hard gel shows a linear relationship while a soft gel shows a non-linear relationship. In case of a soft gel, a gel is deformed and consolidated over a certain pressure so that a flow rate does not increase further. In the present invention, a gel having the above linear relationship at least by 0.3 kg/cm² is referred to as "hard gel". A pore size of the porous hard gel is selected depending on molecular weight, shape, or size of a substance to be removed, and the most suitable pore size may be selected in each case. For measuring the pore size, there are various kinds of methods such as mercury porosimetry and observation by an electron microscope as a direct measuring method. With respect to water-containing particles, however, the above methods sometimes cannot be applied. In such a case, an exclusion limit may be adopted as a measure of pore size. The term "exclusion limit" in the present invention means the minimum molecular weight of a molecular which cannot permeate into a pore in a gel permeation chromatography (cf. Hiroyuki Hatano and Toshihiko Hanai: Zikken Kosoku Ekitai Chromatography (Experimental High-Pressure Liquid Chromatography), published by Kabushiki Kaisha Kagaku Dojin). Phenomenally, a molecule having a molecular weight of more than exclusion limit is eluted near the void volume. Therefore, an exclusion limit can be determined by studying the relations between molecular weights and elution volumes using substances of various molecular weights in a gel permeation chromatography. An exclusion limit varies with a kind of substances to be excluded. In the present invention, an exclusion limit of the porous hard gel is measured by using globular proteins and/or viruses, and the suitable exclusion limit is 10⁶ to 10⁹ daltons. When the exclusion limit is more than 1 x 10⁹, the adsorbing amount of a substance to be removed decreases with a decrease of amount of immobilized ligand, and further a mechanical strength of gel is reduced. Particularly, in case of removing VLDL and/or LDL being giant molecules having a molecular weight of more than 1 x 10⁶, a porous hard gel having an exclusion limit of less than 1 x 10⁶ is not practically available. On the other hand, a porous hard gel having an exclusion limit of from 1 x 10⁶ to several million which is near a molecular weight of VLDL or LDL per se may be practically available to a certain extent. A suitable exclusion limit for removal of VLDL and/or LDL is 1 x 10⁶ to 1 x 10⁹, preferably 1 x 10⁶ to 1 x 10⁸. With respect to a porous structure of the porous hard gel used in the present invention, a structure uniformly having pores at any part of the gel (hereinafter referred to as "uniform structure") is more preferable than a structure having pores only on the surface of the gel. It is preferred that a porosity of the gel is not less than 20 %. A shape of the carrier is selected depending on a kind of a substance to be removed. The carrier may be selected from suitable shapes such as particle, fiber, sheet and hollow fiber. In case of using a carrier in the shape of particle, although a particle having a smaller size generally shows an excellent adsorbing capacity, the pressure-drop increases with an extremely small size. Therefore, a particle having a size of 1 µm to 5000 µm is preferred. Furthermore, it is preferred that a carrier has functional groups to be utilized for the immobilization of ligand or groups to be easily activated. Examples of the group are, for instance, amino, carboxyl, hydroxyl, thiol, acid anhydride, succinylimide, chlorine, aldehyde, amido and epoxy group. Representative examples of the water-insoluble porous hard gel used in the present invention are, for instance, a porous hard gel of a synthetic polymer such as styrene-divinylbenzene copolymer, cross-linked polyvinyl alcohol, cross-linked polyacrylate, cross-linked vinyl ether-maleic anhydride copolymer, cross-linked styrene-maleic anhydride copolymer or cross-linked polyamide, an inorganic porous hard gel such as silica gel, porous glass, porous alumina, porous silica alumina, porous hydroxyapatite, porous calcium silicate, porous zirconia or porous zeolite. Of course it is to be understood that the porous hard gels used in the present invention are not limited to those set forth as above examples. The surface of the above-mentioned porous hard gel may be coated with polysaccharides and synthetic polymers. These porous hard gels may be employed alone or in an admixture thereof. In the above representative examples, some of the porous polymer hard gels composed of synthetic polymers have a fear of toxicity due to unreacted monomers and a less adsorbing capacity than that of a soft gel. As a substance to be removed, there may be included from a substance having a molecular weight of less than 1000 such as bilirubin to a substance having more than tens of millions of molecular weight such as viruses. The porous hard gel of the present invention is selected depending on molecular weight and molecular size of a substance to be removed, and also affected by various factors such as a kind of ligand and a shape of a substance to be removed. For example, it is suitable that the porous hard gels having from hundreds of thousands to tens of millions, and from tens of millions to hundreds of millions of exclusion limits are employed, respectively, to remove substances having millions and tens of millions of molecular weights. Dextran sulfate and/or the salt thereof are explained in more detail hereinbelow. Examples of the salt of the above compound are, for instance, a water-soluble salt such as sodium salt or potassium salt. Dextran sulfate and/or the salt thereof are sulfuric acid ester of dextran being a polysaccharide produced by Leuconostoc mesenteroides, and/or the salt thereof. It has been known that dextran sulfate and/or the salt thereof form a precipitate with lipoproteins in the presence of a divalent cation, and dextran sulfate and/or the salt thereof having a molecular weight of about 5 x 10⁵ (intrinsic viscosity of about 0.20 dl/g) are generally employed for this precipitation. However, as shown in the following Example 38 of Run Nos. (1) and (2), a porous hard gel on which the above-mentioned dextran sulfate and/or the salt thereof are immobilized is sometimes poor in affinity to VLDL and/or LDL. As a result of extensive studies to solve the above problems, it has now been found that dextran sulfate having an intrinsic viscosity of not more than 0.12 dl/g, preferably not more than 0.08 dl/g, and a sulfur content of not less than 15 % by weight has high affinity and selectivity to VLDL and/or LDL. Furthermore, the adsorbent of the present invention employing such dextran sulfate and/or the salt thereof as a ligand has high affinity and selectivity even in the absence of a divalent cation. Although a toxicity of dextran sulfate and/or the salt thereof is low, the toxicity increases with increasing of molecular weight. From this point of view, the use of dextran sulfate and/or the salt thereof having an intrinsic viscosity of not more than 0.12 dl/g, preferably not more than 0.08 dl/g can prevent a danger in case that the immobilized dextran sulfate and/or the salt thereof should be released from a carrier. In addition, dextran sulfate and/or the salt thereof are less changed by a sterilizing procedure such as steam sterilization by autoclaving, because they are linked mainly by α(1→6)-glycosidic linkage. Although there are various methods for measuring a molecular weight of dextran sulfate and/or the salt thereof, a method by measuring viscosity is general. Dextran sulfate and/or the salt thereof, however, show different viscosities depending on various conditions such as ion strength, pH value, and sulfur content (content of sulfonic acid group). The term "intrinsic viscosity" used in the present invention means a viscosity of sodium salt of dextran sulfate measured in a neutral 1 M NaCl aqueous solution, at 25°C. The dextran sulfate and/or the salt thereof used in the present invention may be in the form of straight-chain or branched-chain. For coupling a ligand with a carrier, various methods such as physical adsorption methods, ionic coupling methods and covalent coupling methods may be employed. In order to use the adsorbent of the present invention in extracorporeal circulation treatment, it is important that the ligand is not released. Therefore, a covalent coupling method having a strong bond between ligand and carrier is preferred. In case of employing other methods, a modification is necessary to prevent the release of ligand. If necessary, a spacer may be introduced between ligand and carrier. It is preferred that a gel is activated by a reagent such as a cyanogen halide, epichlorohydrin, a polyoxirane compound such as bisepoxide or triazine halide, and then reacted with a ligand to give the desired adsorbent. In that case, it is preferred that a gel having a group to be activated such as hydroxyl group is employed as a carrier. In the above reagents, epichlorohydrin or a polyoxirane compound such as bisepoxide is more preferred, because a ligand is strongly immobilized on a carrier activated by using such a reagent and a release of a ligand is reduced. Epichlorohydrin and a polyoxirane compound, however, show lower reactivity, particularly lower to dextran sulfate and/or the salt thereof, because dextran sulfate and/or the salt thereof have hydroxyl group alone as a functional group. Therefore, it is not easy to obtain a sufficient amount of immobilized ligand. As a result of extensive studies, it has now been found that the following coupling method is preferred in case of using dextran sulfate and/or the salt thereof as a ligand. That is, a porous polymer hard gel except a porous cellulose gel is reacted with epichlorohydrin and/or a polyoxirane compound to introduce epoxy groups into the gel, and then dextran sulfate and/or the salt thereof is reacted with the resulting epoxy-activated gel in a concentration of not less than 3 % based on the weight of the whole reaction system excluding the dry weight of the gel, more preferably not less than 10 %. This method gives a good immobilizing efficiency. On the other hand, when a porous inorganic hard gel is employed as a carrier, it is preferred that the gel is activated with a reagent such as an epoxysilane, e.g. γ-glycidoxypropyltrimethoxysilane or an aminosilane, e.g. γ-aminopropyltriethoxysilane, and then reacted with a ligand to give the desired adsorbent. Particularly, for removal of VLDL and/or LDL by using dextran sulfate and/or the salt thereof as a ligand, it is preferred that the amount of immobilized ligand is not less than 0.2 mg/ml of bed volume. After the coupling reaction, the unreacted polyanion compound may be recovered for reuse by purification, etc. It is preferred that the remaining unreacted active groups are blocked by e.g. ethanolamine, The adsorbent of the present invention may be employed for various kinds of use. Representative example of the use is extracorporeal circulation treatment performed by incorporating a column into extracorporeal circulation circuit and passing body fluid such as blood or plasma through the column, the column being packed with the adsorbent of the present invention. The use of the adsorbent is not necessarily limited to the above example. The adsorbent of the present invention can be subjected to steam sterilization by autoclaving so long as the ligand is not largely degenerated, and this sterilization procedure does not affect on micro pore structure, particle shape and gel volume of the adsorbent. The present invention is more specifically described and explained by means of the following Reference Examples and Examples, and it is to be understood that the present invention is not limited to the Reference Examples and Examples. Reference Example 1 Biogel A5m (a commercially available agarose gel made by Biorad Co., particle size: 50 to 100 mesh) as a soft gel and Toyopearl HW65 (a commercially available cross-linked polyacrylate gel made by Toyo Soda Manufacturing Co., Ltd., particle size: 50 to 100 µm) as a hard gel was uniformly packed, in a glass column (inner diameter: 9 mm, height: 150 mm) having filters (pore size: 15 µm) at both top and bottom of the column. Water was passed through the thus obtained column, and a relation between flow rate and pressure-drop was determined. The results are shown in Fig. 1. As shown in Fig. 1, flow rate increased approximately in proportion to increase of pressure-drop in the porous polymer hard gel. On the other hand, the agarose gel was consolidated. As a result, increasing pressure did not make flow rate increase. Reference Example 2 The procedures of Reference Example 1 were repeated except that FPG 2000 (a commercially available porous glass made by Wako Pure Chemical Industry Ltd., particle size: 80 to 120 mesh) instead of porous polymer hard gel was employed as a porous inorganic hard gel. The results are shown in Fig. 2. As shown in Fig. 2, flow rate increased approximately in proportion to increase of pressure-drop in the porous glass, while not in the agarose gel. Preparation Example 1 Toyopearl HW55 (a commercially available cross-linked polyacrylate gel made by Toyo Soda Manufacturing Co., Ltd., exclusion limit: 7 x 10⁵, particle size: 50 to 100 µm) having a uniform structure was employed as a carrier. To 10 ml of the gel were added 6 ml of saturated NaOH aqueous solution and 15 ml of epichlorohydrin, and the reaction mixture was subjected to reaction with stirring at 50°C for 2 hours. The gel was washed successively with alcohol and water to introduce epoxy groups into the gel. To the resulting epoxy-activated gel was added 20 ml of concentrated aqueous ammonia, and the reaction mixture was stirred at 50°C for 2 hours to introduce amino groups into the gel. Three ml portion of the thus obtained activated-gel containing amino groups was added to 10 ml of aqueous solution (pH 4.5) containing 200 mg of heparin. To the resulting reaction mixture was added 200 mg of 1-ethyl-3-(dimethylaminopropyl)-carbodiimide while maintaining the reaction mixture at pH 4.5, and then the reaction mixture was shaken at 4°C for 24 hours. After completion of the reaction, the resulting reaction mixture was washed successively with 2 M NaCl aqueous solution, 0.5 M NaCl aqueous solution and water to give the desired gel on which heparin was immobilized (hereinafter referred to as "heparin-gel"). The amount of immobilized heparin was 2.2 mg/ml of bed volume. Preparation Example 2 Cellulofine A-3 was treated in the same manner as in Example 5 to introduce epoxy groups into the gel. Two ml of the thus obtained epoxy-activated gel was added to 2 ml of aqueous solution containing 0.5 g of sodium salt of dextran sulfate (intrinsic viscosity 0.055 dl/g, average polymerization degree: 40, sulfur content: 19 % by weight), and the reaction mixture was adjusted to pH 12. The concentration of sodium salt of dextran sulfate was about 10 % by weight. The resulting reaction mixture was filtered and washed successively with 2 M NaCl aqueous solution, 0.5 M NaCl aqueous solution and water to give the desired sodium salt of dextran sulfate-Cellulofine A-3. The remaining unreacted epoxy groups were blocked with monoethanolamine. The amount of immobilized sodium salt of dextran sulfate was 1.5 mg/ml of bed volume. Example 1 Toyopearl HW65 was treated in the same manner as in Preparation Example 1 to introduce epoxy groups into the gel. Two ml of the thus obtained epoxy-activated gel was treated in the same manner as in Preparation Example 2 to give the desired sodium salt of dextran sulfate-Toyopearl HW65. The amount of immobilized sodium salt of dextran sulfate was 0.4 mg/ml of bed volume. Preparation Example 3 FPG 2000 (exclusion limit: 1 x 10⁹, particle size: 80 to 120 mesh, average pore size: 1950 Å) was heated in diluted nitric acid for 3 hours. After washing and drying, the gel was heated at 500°C for 3 hours and then refluxed in 10 % γ-aminopropyltriethoxysilane solution in toluene for 3 hours. After washing with methanol, a γ-aminopropyl-activated glass was obtained. Two g of the thus obtained activated glass was added to 10 ml of aqueous solution (pH 4.5) containing 200 mg of heparin. The reaction mixture was treated in the same manner as in Example 1 to give the desired heparin-FPG 2000. The amount of immobilized heparin was 1.2 mg/ml of bed volume. Example 2 FPG 2000 was treated in the same manner as in Preparation Example 3 to introduce γ-aminopropyl groups into the gel. The thus obtained activated gel was reacted with sodium salt of dextran sulfate in the same manner as in Example 10 to give the desired sodium salt of dextran sulfate-FPG 2000. The amount of immobilized sodium salt of dextran sulfate was 0.5 mg/ml of bed volume. Example 3 FPG 2000 was refluxed in 10 % solution of γ-glycidoxypropyltrimethoxysilane for 3 hours and then washed with methanol. The thus obtained activated gel was reacted with sodium salt of dextran sulfate in the same manner as in Preparation Example 2 except that the reaction was carried out at pH 8.5 to 9 and at 45°C to give the desired sodium salt of dextran sulfate-FPG 2000. Test Example 1 Each adsorbent obtained in Examples 1 to 3 was uniformly packed in a column (internal volume: about 3 ml, inner diameter: 9 mm, height: 47 mm) and 18 ml of plasma containing 200 U of heparin was passed through the column at a flow rate of 0.3 ml/minute with varying the plasma origins depending on the kind of the desired substance to be removed. That is, human plasma derived from familial hypercholesterolemia, normal human plasma, normal human plasma containing about 100 µg/ml of a commercially available endotoxin, human plasma derived from rheumatism, human plasma derived from systemic lupus erythematosus and human plasma derived from myasthenia gravis were used, respectively, for the tests of removing VLDL and/or LDL; IgG, C 1q or haptoglobin; endotoxin; rheumatoid factor; anti-DNA antibody or DNA; and anti-acetylcholine receptor antibody. The pressure-drop in the column was 0,02 bar (15 mmHg)or less throughout the test period and no crogging was observed. In each adsorbent, a substance to be removed in plasma which was passed through the column was determined to obtain a removal efficiency. The results are summarized in Table 1. Example 4 The adsorbent obtained in Example 1 was sterilized in an autoclave at 120°C for 15 minutes. The resulting sterilized adsorbent was subjected to the determination of removal efficiency for LDL in the same manner as in Test Example 1. As a result, the removal efficiencies was not inferior to such obtained without sterilizing by autoclaving. In addition, pressure-drop was not changed.

Claims: An adsorbent for removing low and/or very low density lipoprotein from body fluid in extracorporal circulation treatment, which comprises a water-insoluble porous hard gel except with a porous cellulose gel with exclusion limit of 10⁶ to 10⁹ daltons on which a dextran sulfate, a salt thereof or a mixture of the dextran sulfate and the salt thereof having a sulfur content of not less than 15 % by weight is immobilized by a covalent linkage. The adsorbent of Claim 1, wherein said water-insoluble porous hard gel is a water-insoluble porous polymer hard gel. The adsorbent of Claim 1, wherein said water-insoluble porous hard gel is a porous inorganic hard gel. The adsorbent of Claim 3, wherein said water-insoluble inorganic hard gel is a member selected from the group consisting of porous glass, porous silica gel and porous alumina. The adsorbent of Claim 1, wherein the dextran sulfate, a salt thereof or a mixture of the dextran sulfate and the salt has intrinsic viscosity of not more than 0.12 dl/g. The adsorbent of Claim 1, wherein the dextran sulfate, a salt thereof or a mixture of the dextran sulfate and the salt thereof is immobilized in an amount of not less than 0.2 mg/ml of bed volume. A process of preparing an adsorbent for removing low and/or very low density lipoprotein from body fluid in extracorporeal circulation treatment comprising a water-insoluble porous hard gel with exclusion limit of 10⁶ to 10⁹ daltons, except a porous cellulose gel, on which a dextran sulfate, a salt thereof or a mixture of the dextran sulfate and the salt thereof having a sulfur content of not less than 15 % by weight is immobilized by a covalent linkage, wherein said water-insoluble porous hard gel is reacted with epichlorhydrin or a polyoxyrane compound to introduce epoxy groups on the gel and then the resulting epoxy-activated gel is reacted with the dextran sulfate, a salt thereof or a mixture of the dextran sulfate and the salt thereof having a sulfur content of not less than 15 % by weight. The process of Claim 7, wherein said water-insoluble hard gel is a water-insoluble porous polymer hard gel. The process of Claim 7, wherein said dextran sulfate, the salt thereof or the mixture of the dextran sulfate and the salt is reacted with the epoxy-activated gel in a concentration of not less than 3 % by weight based on the weight of the whole reaction system excluding the dry weight of the porous hard gel.

Inventors: HAYASHI TSUNEO, TANI NOBUTAKA, HAYASHI, TSUNEO, TANI, NOBUTAKA
Applicants: KANEGAFUCHI CHEMICAL IND, KANEGAFUCHI KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1983
Main classification: B01J20
IPC codes: B01J20, A61M1, A61K35