Preparation of heparin-immobilized PVA and its adsorption for low-density lipoprotein from hyperlipemia plasma

In this study, heparin was covalently coupled by glutaraldehyde to Poly(vinyl alcohol) [PVA] in solid-liquid two-phase reaction system by two-step synthesis method to prepare a LDL-selective adsorbent. The parameters (the material ratio, reaction time and dosage of catalyzer) were investigated to evaluate their effect upon the immobilized amount of heparin onto the surface of PVA, IR was used to verify the covalent immobilization result and the heparin-modified PVA was also undergone the evaluation of its adsorption capability for low-density lipoprotein from hyperlipemia plasma, and its hemocompatibility was preliminarily evaluated by platelet adhesion test. Results showed: (1) under optimized reaction conditions the highest immobilization amount of heparin onto PVA surface within the experiments of this study has been obtained; (2) the optimized reaction conditions were: (i) at the refluxing temperature 78 degrees C; (ii) the material ratio of "PVA(g): 50% glutaraldehyde (ml)" was about "1:3"; (iii) the reaction time was about 5 h; and (iv) the amount of catalyzer (concentrated HCL) was about 1% of the 50% glutaraldehyde; (3) within the experiments of this study the highest immobilization amount would be up to 25 microg heparin on the surface of per g PVA granules; (4) the heparin-modified PVA granules showed significant adsorption for LDL under faintly alkaline environment (pH=7.2-9.5) ; (5) The result of platelet adhesion test showed no platelet adhered to its surface. Therefore, immobilization of heparin onto the surface of a support is one approach to prepare a kind of LDL adsorbent for blood purification.

A novel amphiphilic adsorbent for the removal of low-density lipoprotein

Dextran adsorbent with amphiphilic ligands for adsorption of low-density lipoprotein (LDL) was prepared by the following procedures. Cholesterol group was linked to Dextran G 75 by reacting with cholesterol N-(6-isocyanatohexyl) carbamate in the presence of pyridine in DMSO at 80. In order to introduce the hydrophilic moiety, it was then reacted with chlorosulfonic acid in formamide which introduced the sulfonic group. Adsorption capacity of the adsorbent was studied which showed the removal of LDL-cholesterol (LDL-C), total cholesterol (TC) and TG to be 1.916, 2.132 and 1.349 mg/ml, respectively without significantly affecting total protein levels in the plasma. Moreover, the adsorbent has a better selectivity in removing LDL-C, TC, TG compared to dextran which has only hydrophobic or hydrophilic ligand.

In vitro, in vivo studies of a new amphiphilic adsorbent for the removal of low-density lipoprotein

A new amphiphilic adsorbent for the removal of low-density lipoprotein (LDL) was prepared according to the literature (Artif. Cells Blood Subs., Immob. Biotechnol. 30 (4) (2002) 285). The effects of sulfonation and grafting time of cholesterol on the swelling property of adsorbent were studied. When sulfonation and grafting time of cholesterol was 3 and 5 h, respectively, the amphiphilic adsorbent had a high adsorption capacity for LDL without significantly adsorbing high-density lipoprotein. The adsorption capacity of the adsorbent for the removal of LDL, total cholesterol (TC) and TG was 1.916, 2.132, 1.349 mg/ml, respectively. Hyperlipidemia rabbits were developed by feeding with fodder containing high content of cholesterol or yolk, which was then perfused with an optimal amount of amphiphilic adsorbent. After 2 h hemoperfusion, the LDL levels decreased from 3.619+/-0.354 to 0.724+/-0.07 mmol/l, which showed that the adsorbent could effectively remove LDL without side effect.

Surface functionalization of polypyrrole film with glucose oxidase and viologen

A surface modification technique was developed for the functionalization of polypyrrole (PPY) film with glucose oxidase (GOD) and viologen moieties. The PPY film was first graft copolymerized with acrylic acid (AAc) and GOD was then covalently immobilized through the amide linkage formation between the amino groups of the GOD and the carboxyl groups of the grafted AAc polymer chains in the presence of a water-soluble carbodiimide. Viologen moieties could also be attached to the PPY film via graft-copolymerization of vinyl benzyl chloride with the PPY film surface followed by reaction with 4,4'-bipyridine and alpha,alpha'-dichloro-p-xylene. X-ray photoelectron spectroscopy (XPS) was used to characterize the PPY films after each surface modification step. Increasing the AAc graft concentration would allow a greater amount of GOD to be immobilized but this would decrease the electrical conductivity of the PPY film. The activity of the immobilized GOD was compared with that of free GOD and the kinetic effects were also studied. The immobilized GOD was found to be less sensitive to temperature deactivation as compared to the free GOD. The results showed that the covalent immobilization technique offers advantages over the technique involving the entrapment of GOD in PPY films during electropolymerization. The presence of viologen in the vicinity of the immobilized GOD also enabled the GOD-catalyzed oxidation of glucose to proceed under UV irradiation in the absence of O(2).

Microwave CO2 plasma-initiated vapour phase graft polymerization of acrylic acid onto polytetrafluoroethylene for immobilization of human thrombomodulin

The functionalization of polytetrafluoroethylene (PTFE) for human thrombomodulin (hTM) binding has been achieved by CO2 plasma activation and subsequent vapour phase graft polymerization of acrylic acid (AA). The PTFE surfaces after CO2 plasma treatment, AA grafting and hTM immobilization were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) spectroscopy, as well as by zeta potential and wetting measurements to quantitatively control each step of modification. The activity of immobilized hTM was estimated by the protein C activation test.

Immunoadsorption procedure as a potential method for the specific beta 2-microglobulin removal from plasma of patients with chronic renal failure

beta 2-Microglobulin (beta 2-M), which accumulates in the plasma of patients undergoing long-term dialysis, has been identified as the principal precursor protein of amyloid fibrils in dialysis-related amyloidosis. As no specific treatment for this affection has been yet established, an extracorporeal immunoadsorption procedure appears to be an attractive therapeutic approach to remove beta 2-M. Several murine monoclonal antibodies to human beta 2-M were developed and compared as affinity ligands. One of them was selected on the basis of its specificity and adsorption capacity. In order to achieve maximum efficiency in protein removal, different parameters of the procedure were studied and optimized: effect of antibody coupling density, determination of maximum adsorption capacity of the immunoadsorbents and influence of antigen concentration and of flow-rate on antigen capture efficiency. The conditions of regeneration of immunoaffinity sorbents were also investigated to allow their multiple use without loss of adsorption capacity. The results show the validity of the proposed technique in removing beta-M from plasma of patients with chronic renal failure.

A new pectin-based material for selective LDL-cholesterol removal

A new material, natural polysaccharide-pectin, was tested for removal of human blood lipoproteins. Pectin was prepared in a granular form with the help of the specifically designed gelification device and tested in batch sorption experiments in vitro for removal of total cholesterol (TC), LDL-cholesterol (LDL-C), and HDL-cholesterol (HDL-C) from human plasma. Pectin granules removed 40% of TC, 45% of LDL-C, and 36% of HDL-C on average with respect to the initial amounts whereas corresponding values for LA-40 Kanegafuchi adsorbent were 69%, 81%, and 33% in the same experimental conditions (shaking 1 g of sorbent sample with 2 ml of plasma).

Trypsin immobilization on to polymer surface through grafted layer and its reaction with inhibitors

Trypsin was covalently immobilized and physically adsorbed on to the surface of poly(ethylene terephthalate) fibres using poly(acrylic acid) (PAAc) chains grafted on to the ozonized fibres. The covalent immobilization was accomplished through amide formation between amino groups of trypsin and carboxyl groups of grafted PAAc chains, with the use of water-soluble carbodiimide. A set of samples with surface concentrations of grafted polymer ranging from 0.03 to 2.5 micrograms/cm2 was used to study the effects of grafted layer on the enzymatic activity of immobilized trypsin and its inhibition by trypsin inhibitors of different molecular sizes. The amount of immobilized trypsin increased linearly with an increase in graft yield of fibres, but the activity of immobilized enzyme reached saturation at a certain graft yield, probably because of diffusion limitation for the transport of enzyme substrate molecules into the grafted PAAc layer. The reduction of inhibition with an increase in graft yield and in molecular weight of inhibitors was attributed to enhancement of steric hindrance and enzyme inactivation in the dense grafted layer. We also found that the adsorbed trypsin was inhibited more easily than the covalently immobilized at any concentration of the grafted PAAc and for any type of inhibitor used.

Flow Rate Dependence of in vitro Removal of Anti-A and Anti-B Antibodies by Immunoadsorbents with Synthetic Oligosaccharides Representing Blood Group Substances

In vitro removal of anti-A and anti-B antibodies by immunoadsorbents with synthetic oligosaccharide structures representing blood group substances have been studied under controlled and simulated extracorporeal perfusion conditions at different flow rates ranging from 20 to 160 mL/min. There is a gradual decline in antibody titers in the plasma, as it relates to the antibody binding capacity and efficiency of the immunoadsorbents, both as a function of time and plasma volume at any of the flow rates employed. Approximately the same maximal binding capacity is achieved in about 4 hours of perfusion regardless of the flow rate, whereas increased number of plasma volumes are required at higher flow rates to compensate for the appropriate residence times needed in the column to utilize the same capacity. The perfusion time alone appears to be a critical factor which via the flow rate determines the residence time between the plasma and the immobilized hapten in the column. Also, the optimal flow rate at which maximum binding capacity of the immunoadsorbent may be utilized efficiently appears to fall within a range of the flow rate. The factors determining this range and the efficiency of the immunoadsorbents under dynamic conditions are discussed. The results obtained under the controlled conditions and the discussions that follow are expected to be generally useful, at least, as approximate clinical guidelines, for selective removal of specific substances by extracorporeal perfusion techniques utilizing therapeutic intervention with immunoadsorbents in this important area of medical therapy