DNA-immobilized polyhydroxyethylmethacrylate microbeads for affinity sorption of human immunoglobulin G and anti-DNA antibodies

Aptamer-Based Affinity Chromatography for Protein Extraction and Purification

Aptamers are oligonucleotide molecules able to recognize very specifically proteins. Among the possible applications, aptamers have been used for affinity chromatography with effective results and advantages over most advanced protein separation technologies. This chapter first discusses the context of the affinity chromatography with aptamer ligands. With the adaptation of SELEX, the chemical modifications of aptamers to comply with the covalent coupling and the separation process are then extensively presented. A focus is then made about the most important applications for protein separation with real-life examples and the comparison with immunoaffinity chromatography. In spite of well-advanced demonstrations and the extraordinary potential developments, a significant optimization work is still due to deserve large-scale applications with all necessary validations. Graphical Abstract Aptamer-protein complexes by X-ray crystallography.

Attachment of 3T3 and MDBK Cells onto PHEMA-Based Microbeads and their Biologically Modified Forms

Polyhydroxyethylmethacrylate (PHEMA) microbeads in a size range of 150-250 μm were prepared by suspension polymerization in an aqueous phase containing magnesium oxide. Hydroxyl groups were oxidized with NaIO4 and cell adhesive proteins, namely collagen and fibronectin, were immobilized using glutaraldehyde. A spacer-arm, hexamethylene diamine, was used in some cases. Higher amounts of collagen were immobilized, than in fibronectin. The attachment of two cell lines (i.e., 3T3 and MDBK cell lines) on these microbeads with a wide variety of surface properties was studied in vitro culture media. The attachments of both cells, even onto plain microbeads, were significant. Introducing both fibronectin and collagen onto the microbeads caused significant increases in the cell attachment. More cells attached to the microbeads carrying fibronectin covalently attached onto the microbeads through the spacer-arm molecules. Fibronectin was better than collagen for high attachment values. The mathematical model proposed successfully simulated attachment kinetics.

Collagen and Fibronectin Carrying PHEMA Microbeads as Cell Affinity Sorbents

PHEMA microbeads, produced by suspension polymerization, were modified by the immobilization of a spacer (hexamethylene diamine, HMDA), and two proteins, collagen or fibronectin. Adsorption of collagen and fibronectin onto the plain and periodate oxidized PHEMA microbeads were similar; 0.05-0.1 mg of collagen and 0.04-0.05 mg of fibronectin per g of polymer, respectively. Collagen and fibronectin immobilization on PHEMA microbeads were studied at different temperatures, time and pH. The optimal values for immobilization were 0.1 mg/mL for fibronectin; and 0.25 mg/mL for collagen at 25°C for fibronectin and 4°C for collagen; pH 7 in 120 min. Both fibroblastic 3T3 and epithelial MDBK cells were attached to unmodified and modified microbeads. The attachments of both 3T3 and MDBK cells, to the fibronectin and collagen immobilized microbeads were more than 2000 cells per mg of polymer.

Surfaces for tuning of oligonucleotide biosensing selectivity based on surface-initiated atom transfer radical polymerization on glass and silicon substrates

Covalently immobilized mixed films of oligonucleotide and oligomer components on glass and silicon surfaces are reported. This work has investigated how such films can improve selectivity for the detection of multiple base-pair mismatches. The intention was to introduce a "matrix isolation" effect on oligonucleotide probe molecules by surrounding the probes with oligomers, thereby reducing oligonucleotide-to-oligonucleotide and/or oligonucleotide-to-surface interactions. Thiol-functionalized oligonucleotide was coupled onto (3-aminopropyl)trimethoxysilane (APTMS) via a heterobifunctional linker, succinimidyl 4-[N-maleimidomethyl]cyclohexane-1-carboxylate (sulfo-SMCC). Using a variety of monomers such as 2-hydroxyethyl methacrylate (HEMA), oligomers were grown by surface-initiated atom transfer radical polymerization (ATRP) from a bromoisobutyryl NHS ester initiator which was immobilized onto APTMS sites that coated glass and oxidized silicon substrates. Various surface modification steps on silicon substrates were characterized by ellipsometry, wettability, atomic force microscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Polymerized HEMA (PHEMA) in mixture with oligonucleotide probes was evaluated for fluorescence transduction of hybridization. The presence of PHEMA was found to provide a sharper melt curve for hybrids containing both fully complementary and three base-pair mismatched targets, and this surface derivatization also minimized non-selective adsorption. The maximum increase in slope was improvement by a factor of 3-fold. An increase of up to 30% in difference of melting temperatures between fully complementary and 3 base-pair mismatched targets was achieved using PHEMA. The results suggest that the presence of oligomers dispersed among DNA hybrids can improve selectivity through what is believed to be a reduction of dispersity of interactions of probes with targets, and probes within their local environment at a surface.

Immunoadsorption of Cholesterol on Protein A Oriented Beads

Anti-low density lipoprotein antibody (anti-LDL) molecules were attached covalently and oriented through Protein A onto poly(2-hydroxyethyl methacrylate-ethylene glycol dimethacrylate) [poly(HEMA-EGDMA)] beads in order to remove cholesterol specifically from hypercholesterolemic human plasma. Poly(HEMA-EGDMA) beads were produced by suspension polymerization. Blood compatibility tests were performed. All the clotting times were increased when compared with control plasma. Loss of platelets and leukocytes was very low. The maximum anti-LDL attachment was 11.6 mg . g(-1) in the case of random immobilization and 28.3 mg . g(-1) in the case of oriented immobilization. In the latter case, Protein A loading was 8.3 mg . g(-1) at pH 7.5 (borate buffer, 0.15 M NaCl). There was low non-specific cholesterol adsorption onto the poly(HEMA-EGDMA) beads, about 0.83 mg . g(-1). Random and oriented anti-LDL attached beads adsorbed 8.2 mg and 11.7 mg cholesterol per g of bead from hypercholesterolemic human plasma, respectively. Up to 96% of the adsorbed cholesterol was desorbed. The binding-elution cycle was repeated 6 times using the same beads. There was no significant loss of binding capacity.

N-methacryloly-(L)-histidinemethylester carrying a pseudospecific affinity sorbent for immunoglobulin-G isolation from human plasma in a column system

N-methacryloly-(L)-histidinemethylester (MAH) as a pseudospecific ligand was synthesized by using methacryloyl chloride and histidine. Spherical beads with an average size of 63-75 microm were obtained by suspension polymerization of ethylene glycol dimethacrylate (EGDMA), 2-hydroxyethyl methacrylate (HEMA) and MAH conducted in an aqueous dispersion medium. The specific surface area of the beads was found to be 18.3 m2/g. Poly(EGDMA-HEMA-MAH) beads were used in the separation of immunoglobulin-G (HIgG) from aqueous solutions and/or human plasma in a packed-bed column system. HIgG adsorption capacity of the beads decreased with an increase in the flow-rate of plasma. The maximum HIgG adsorption on the poly(EGDMA-HEMA-MAH) sorbents was observed at pH 7.4. HIgG adsorption onto the poly(EGDMA-HEMA) sorbents was negligible. Higher adsorption values (up to 135 mg/g) were obtained when the poly(EGDMA-HEMA-MAH) sorbents were used from aqueous solutions. HIgG adsorption increased with decreasing temperature and the maximum adsorption achieved at 4 degrees C. MAH incorporation significantly affected HIgG adsorption capacity (135 mg/g). Higher amounts of HIgG were adsorbed from human plasma (up to 165 mg/g). Adsorption capacities of other blood proteins were obtained as 8.7 mg/g for fibrinogen and 14.6 mg/g for albumin. The total protein adsorption was determined as 191 mg/g. The pseudospecific affinity beads allowed one-step separation of HIgG from human plasma. HIgG molecules could be repeatedly adsorbed and desorbed with these sorbents without noticeable loss in their HIgG adsorption capacity.

Fibronectin purification from human plasma in a packed-bed column system with gelatin immobilized PHEMA microspheres

Bioaffinity chromatography has a unique and powerful role that is used as a purification tool in the production of therapeutic plasma protein derivatives. In this study, a bioaffinity-ligand, i.e. gelatin, was covalently immobilized with PHEMA microspheres (150-200 microm in diameter). The affinity sorbent carrying 7.5 mg gelatin g(-1) polymer was then used to separate fibronectin from human plasma in a packed-bed column system. Fibronectin separation from human plasma on unmodified PHEMA microspheres was 0.45 mg g(-1), while much higher adsorption values, up to 21.8 mg g(-1), were obtained with gelatin-immobilized microspheres. The fibronectin adsorption capacity of the microspheres decreased with an increase in the recirculation rate of plasma. Fibronectin adsorption increased with decreasing temperature, and the maximum adsorption achieved at 4 degrees C (26.3 mg fibronectin g(-1)). Up to 94.7% of the adsorbed fibronectin was desorbed by using 2 M urea in the presence of 1 M sodium chloride as elution agent. The adsorption-desorption cycle was repeated ten times using the same affinity column. There was no remarkable reduction in the adsorption capacity of the gelatin-immobilized PHEMA microspheres.

Dye-ligand affinity systems

Dye-ligands have been considered as one of the important alternatives to natural counterparts for specific affinity chromatography. Dye-ligands are able to bind most types of proteins, in some cases in a remarkably specific manner. They are commercially available, inexpensive, and can easily be immobilized, especially on matrices bearing hydroxyl groups. Although dyes are all synthetic in nature, they are still classified as affinity ligands because they interact with the active sites of many proteins mimicking the structure of the substrates, cofactors, or binding agents for those proteins. A number of textile dyes, known as reactive dyes, have been used for protein purification. Most of these reactive dyes consist of a chromophore (either azo dyes, anthraquinone, or phathalocyanine), linked to a reactive group (often a mono- or dichlorotriazine ring). The interaction between the dye ligand and proteins can be by complex combination of electrostatic, hydrophobic, hydrogen bonding. Selection of the supporting matrix is the first important consideration in dye-affinity systems. There are several methods for immobilization of dye molecules onto the support matrix, in which usually several intermediate steps are followed. Both the adsorption and elution steps should carefully be optimized/designed for a successful separation. Dye-affinity systems in the form of spherical sorbents or as affinity membranes have been used in protein separation.

Mannosylerythritol lipid, a yeast extracellular glycolipid, shows high binding affinity towards human immunoglobulin G

BACKGROUND

There have been many attempts to develop new materials with stability and high affinity towards immunoglobulins. Some of glycolipids such as gangliosides exhibit a high affinity toward immunoglobulins. However, it is considerably difficult to develop these glycolipids into the practical separation ligand due to their limited amounts. We thus focused our attention on the feasible use of "mannosylerythritol lipid A", a yeast glycolipid biosurfactant, as an alternative ligand for immunoglobulins, and undertook the investigation on the binding between mannosylerythritol lipid A (MEL-A) and human immunoglobulin G (HIgG).

RESULTS

In ELISA assay, MEL-A showed nearly the same binding affinity towards HIgG as that of bovine ganglioside GM1. Fab of human IgG was considered to play a more important role than Fc in the binding of HIgG by MEL-A. The bound amount of HIgG increased depending on the attached amount of MEL-A onto poly (2-hydroxyethyl methacrylate) (polyHEMA) beads, whereas the amount of human serum albumin slightly decreased. Binding-amount and -selectivity of HIgG towards MEL-A were influenced by salt species, salt concentration and pH in the buffer solution. The composite of MEL-A and polyHEMA, exhibited a significant binding constant of 1.43 x 10(6) (M(-1)) for HIgG, which is approximately 4-fold greater than that of protein A reported.

CONCLUSIONS

MEL-A shows high binding-affinity towards HIgG, and this is considered to be due to "multivalent effect" based on the binding molar ratio. This is the first report on the binding of a natural human antibody towards a yeast glycolipid.

Polyhydroxyethylmethacrylate-based magnetic DNA-affinity beads for anti-DNA antibody removal from systemic lupus erythematosus patient plasma

The aim of this study is to prepare magnetic poly(2-hydroxyethylmethacrylate) (mPHEMA) beads and to investigate their utility for the removal of anti-DNA antibodies from systemic lupus erythematosus (SLE) patient plasma. mPHEMA beads, in the size range of 80-120 microm, were produced by a modified suspension technique. Then, DNA was coupled onto mPHEMA beads by carbodiimide activation. The amount of ligand coupled was changed by changing the initial concentrations of carbodiimide and DNA. Human immunoglobulin G (HIgG) and anti-DNA antibody adsorption from aqueous solutions and human plasma were examined in a batch system. mPHEMA beads were characterized by swelling tests, electron spin resonance (ESR) and scanning electron microscopy. Important results obtained in this study are as follows: the swelling ratio of mPHEMA beads was 34%. The presence of magnetite particles in the polymeric structure was confirmed by ESR. The mPHEMA beads have a spherical shape and porous structure. Maximum DNA coupling of carbodiimide activated mPHEMA beads was 4.4 mg/g. Maximum HIgG adsorption from an aqueous solution was 47.5 mg/g. Anti-DNA antibody adsorption from SLE plasma was observed as 87.6 mg/g. Non-specific HIgG adsorption was 0.1 mg/g. More than 90% of the adsorbed HIgG molecules and anti-DNA antibodies were desorbed succesfully by using NaSCN solution. It was possible to reuse these DNA-affinity beads without significant losses in the antibody adsorption capacities.

Protein A-immobilized microporous polyhydroxyethylmethacrylate affinity membranes for selective sorption of human-immunoglobulin-G from human plasma

Microporous membranes made of poly(2-hydroxyethylmethacrylate) [poly(HEMA)] carrying protein A were used for selective sorption of human-IgG from human plasma. Poly(HEMA) membranes were prepared by a photo-polymerization technique, and activated by cyanogen bromide (CNBr) in an alkaline medium (pH 11.5). Bioligand protein A was then immobilized by covalent binding onto these CNBr-activated membranes. The amount of immobilized protein A was controlled by changing pH and the initial concentrations of CNBr and protein A. The non-specific adsorption of protein A on the plain poly(HEMA) membranes was 2.9 microg cm(-2). Maximum protein A immobilization was observed at pH 9.5. Up to 186 microg cm(-2) was immobilized on the CNBr-activated poly(HEMA) membranes. The maximum adsorption of human-IgG on the protein A-immobilized poly(HEMA) membranes was observed at pH 8.0. The non-specific adsorption of human-IgG onto the plain poly(HEMA) membranes was low (about 4.4 microg cm(-2)). Higher human-IgG adsorption values (up to 394 microg cm(-2)) were obtained in which the protein A-immobilized poly(HEMA) membranes were used. Much higher amounts of human-IgG (up to 489 microg cm(-2)) were adsorbed from human plasma. Up to 91% of the adsorbed human-IgG was desorbed by using 0.1 M aminoacetic acid as elution agent. The adsorption-desorption cycle was repeated ten times using the same polymeric membranes. There was no remarkable reduction in the adsorption capacity of the protein A-immobilized poly(HEMA) membranes.

DNA adsorption onto polyethylenimine-attached poly(p-chloromethylstyrene) beads

In this study, DNA adsorption properties of polyethylenimine (PEI)-attached poly(p-chloromethylstyrene) (PCMS) beads were investigated. Spherical beads with an average size of 186 microm were obtained by the suspension polymerization of p-chloromethylstyrene conducted in an aqueous dispersion medium. Owing to the reasonably rough character of the bead surface, PCMS beads had a specific surface area of 14.1 m2/g. PEI chains could be covalently attached onto the PCMS beads with equilibrium binding capacities up to 208 mg PEI/g beads, via a direct chemical reaction between the amine and chloromethyl groups. After PEI adsorption with 10% (w/w) initial PEI concentration, free amino content of PEI-attached PCMS beads was determined as 0.91 mequiv./g. PEI-attached PCMS beads were utilized as sorbents in DNA adsorption experiments conducted at +4 degrees C in a phosphate buffer medium of pH 7.4. DNA immobilization capacities up to 290 mg DNA/g beads could be achieved with the tried sorbents. This value was approximately 50-times higher relative to the adsorption capacities of previously examined sorbents.

Human serum albumin chromatography by Cibacron Blue F3GA-derived microporous polyamide hollow-fiber affinity membranes

An affinity dye ligand, Cibacron Blue F3GA was covalently attached onto commercially available microporous polyamide hollow-fibre membranes for human serum albumin (HSA) adsorption from both aqueous solutions and human plasma. Different amounts of Cibacron Blue F3GA were incorporated on the polyamide hollow-fibres by changing the dye attachment conditions, i.e. initial dye concentration, addition of sodium carbonate and sodium chloride. The maximum amount of Cibacron Blue F3GA attachment was obtained at 42.5 micromol g(-1) when the hollow-fibres were treated with 3 M HCI for 30 min before performing the dye attachment. HSA adsorption onto unmodified and Cibacron Blue F3GA-derived polyamide hollow-fibre membranes was investigated batchwise. The non-specific adsorption of HSA was very low (6.0 mg g(-1) hollow-fibre). Cibacron Blue F3GA attachment onto the hollow-fibres significantly increased the HSA adsorption (147 mg g(-1) hollow-fibre). The maximum HSA adsorption was observed at pH 5.0. Higher HSA adsorption was observed from human plasma (230 mg HSA g(-1) hollow-fibre). Desorption of HSA from Cibacron Blue F3GA derived hollow-fibres was obtained using 0. 1 M Tris-HCl buffer containing 0.5 M NaSCN or 1.0 M NaCl. High desorption ratios (up to 98% of the adsorbed HSA) were observed. It was possible to reuse Cibacron Blue F3GA derived polyamide hollow-fibre without significant decreases in the adsorption capacities.

Diamine-plasma treated and Cu(II)-incorporated poly(hydroxyethylmethacrylate) microbeads for albumin adsorption

Poly(2-hydroxyethylmethacrylate) (PHEMA) microbeads prepared by suspension polymerization were treated with diamine-plasmas (i.e. ethylene-diamine (EDA) and hexamethylene diamine (HMDA)) in a glow-discharge reactor in which the exposure time and glow-discharge power were changed between 5 and 30 min and 5 and 20 W, respectively. The amount of nitrogen deposition increased both with increase in exposure time and glow-discharge power. The maximum amounts of nitrogen deposition on the microbeads were 22.3 and 23.4 micromol g(-1) with the EDA- and HMDA-plasmas. Then, Cu(II) ions were incorporated onto the PHEMA microbeads by chelating with the nitrogen-carrying functional groups. Different amounts of Cu(II) ions (2.4-6.8 mg g(-1)) were incorporated on the PHEMA microbeads by changing the initial concentration of Cu(II) ions. Bovine serum albumin (BSA) adsorption onto the unmodified PHEMA, diamine-plasma treated PHEMA, and diamine-plasma treated Cu(II)-incorporated PHEMA microbeads was investigated. The non-specific adsorption of BSA on the unmodified microbeads was very low (0.22 mg BSA g(-1)). Deposition of nitrogen increased the BSA adsorption (9.3 mg g(-1) for EDA-plasma and 12.7 mg g(-1) for HMDA-plasma). Cu(II)-incorporation significantly increased the BSA adsorption (154 mg g(-1) for EDA-plasma and 178 mg g(-1) for HMDA-plasma). Further increases in the albumin adsorption capacities of the polymer microbeads (185 mg g(-1) for EDA-plasma and 208 mg g(-1) for HMDA-plasma) were observed when human plasma was used. More than 92% of the adsorbed albumin molecules was desorbed in 1 h in the desorption medium containing 0.5 M NaSCN at pH 8.0. Repeated adsorption-desorption cycles showed the feasibility of these plasma-modified polymer microbeads.

Preparation of DNA-immobilized immunoadsorbent for treatment of systemic lupus erythematosus

A new DNA-immobilized immunoadsorbent was prepared to remove the pathogenic anti-DNA antibody from the serum of systemic lupus erythematosus (SLE) patients. A non-woven poly(ethylene terephthalate) (PET) fabric made of 3.5-microm diameter fibers was used as the support of the immunoadsorbent. A cationic monomer, N,N-dimethylaminoethyl methacrylate (DAM), was graft polymerized onto the PET fiber surface by UV irradiation or with a chemical initiator. Polyion complexation between the cationic groups of the graft chains and DNA molecules was employed to immobilize DNA onto the fiber surface. No DNA leaching was observed when the DNA-immobilized fabrics were placed in 0.9 and 2.0 wt% NaCl solution at 37 degrees C overnight. In vitro evaluation of this DNA-immobilized immunoadsorbent demonstrated that this adsorbent could selectively adsorb anti-DNA antibody from the serum of SLE patients.