In vitro investigations with selective adsorbents for IgE and IgM

Dieter Falkenhagen (1942–2015): A Multifaceted Scientist

Dieter Falkenhagen was born in 1942 in Dresden, Germany and died in 2015. He specialized in internal medicine and nephrology. Focusing on artificial organ research, he investigated various aspects of the efficacy and safety of hemodialysis and adsorption technologies, including biocompatibility issues related to blood versus surface interactions and the adverse effects of endotoxin contamination. He studied various mathematical models to analyze efficacy and safety, and animal models to help clarify uncertainty issues. Through his studies, adsorbents were developed, resulting in Prometheus, an artificial liver support device. Anticoagulation models, including citrate perfusion, were improved and made safer by his work. He also stepped into bioreactor research to increase efficacy of liver support devices.

Selective adsorbent for the removal of immunoglobulin E in bronchial asthma

Agar-gel resin with tryptophan as ligand was synthesized as an adsorbent for the removal of Immunoglobulin E (IgE) in bronchial asthma. Factors affecting the adsorption properties of the adsorbent, such as the different kind of amino acid linked to the carrier, NaOH concentration and amount of epichlorohydrin used in activation, were studied in detail. The effect of spacer on the adsorption capacity was also investigated. Results showed that the agar-tryptophan adsorbent with a spacer could enhance the adsorption capacity to 70.73% (1309.403IU/g agar-gel), which was higher than that without spacers (53%). The selectivity and hemocompatibility of the adsorbent were also examined, which showed good selectivity for IgE and satisfactory blood compatibility.

Immunoaffinity beads for selective removal of cholesterol from human plasma

Anti-low density lipoprotein antibody (anti-LDL antibody) attached poly(2-hydroxyethyl methacrylate-methacryloylamidophenylalanine) (poly(HEMA-MAPA)) beads were prepared for selective removal of cholesterol from hypercholesterolemic human plasma. Poly(HEMA-MAPA) beads were produced by a modified suspension polymerization and then characterized by swelling tests and SEM. Blood-compatibility tests were also investigated. The water swelling ratio of the poly(HEMA-MAPA) beads increased significantly (68%) compared with pHEMA (55%). All the clotting times increased when compared with poly(HEMA) beads. Loss of platelets and leukocytes was very low. The maximum anti-LDL antibody attachment was achieved at pH 7.0. Attachment of anti-LDL antibody was 29.6 mg/g. There was a very low non-specific cholesterol binding onto the poly(HEMA-MAPA) beads, about 0.74 mg/g. Anti-LDL antibody attached beads adsorbed in the range of 13.3-16.0 mg cholesterol/g from hypercholesterolemic human plasma. Up to 92% of the adsorbed LDL was desorbed. The binding-elution cycle was repeated 10 times using the same beads. There was no significant loss of binding capacity.

Preparation of immuno-affinity membranes for cholesterol removal from human plasma

Anti-low density lipoprotein antibody (anti-LDL) immobilized polyhydroxyethylmethacrylate (pHEMA) based membrane was prepared for selective removal of cholesterol from hypercholesterolemic human plasma. In order to further increase blood-compatibility, a newly synthesized comonomer, methacryloylamidophenylalanine (MAPA) was included in the membrane formulation. p(HEMA-MAPA) membranes were produced by a photopolymerization and then characterized by swelling tests, SEM and contact angle studies. Blood-compatibility tests were also investigated. The water swelling ratio of the p(HEMA-MAPA) membrane increases significantly (133.2.9%) compared with pHEMA (58%). p(HEMA-MAPA) membranes have large pores around in the range of 5-10 microm. All the clotting times increased when compared with pHEMA membranes. Loss of platelets and leukocytes was very low. The maximum anti-LDL antibody immobilization was achieved around pH 7.0. Immobilization of anti-LDL antibody was 12.6 mg/ml. There was a very low non-specific cholesterol adsorption onto the plain p(HEMA-MAPA) membranes, about 0.36 mg/ml. Anti-LDL antibody immobilized membranes adsorbed in the range of 4.5-7.2 mg cholesterol/ml from hypercholesterolemic human plasma. Up to 95% of the adsorbed LDL antibody was desorbed. The adsorption-desorption cycle was repeated 10 times using the same membrane. There was no significant loss in the adsorption capacity.

Use of a modified zirconia support in the separation of immunoproteins

Zirconia beads (25-38 microm in diameter) were modified with N,N,N',N'-ethylenediaminetetramethylenephosphonic acid to generate a zirconia based pseudoaffinity support, further referred to as r_PEZ. The influence of pH, salt concentration and temperature on the binding of human immunoglobulin G (hIgG) to r_PEZ was studied. Temperature had no significant impact on the maximum binding capacity (Qmax), and the equilibrium-binding constant (Kd), whereas pH and the salt concentration had a noticeable impact on both Qmax and Kd. The Qmax value of 55 mg hIgG/ml of bead was obtained at a pH of 5.5 and found to decrease with an increase of pH. The modified zirconia support allowed the separation of immunoglobulins (IgG, IgA and IgM) from untreated human serum. Elution was possible under mild conditions with a step salt gradient. Overall protein recoveries in the range of 109-125% were obtained with human serum. Human IgG, human IgA, and human IgM yields of 29.50+/-6.3, 3.22+/-0.7, and 6.84+/-0.7%, respectively, were obtained at a linear velocity of 4.32 cm/min. Purity of products, obtained from a single chromatographic step was estimated to be greater than 89.0+/-2.6%. The utility of r_PEZ in the selective removal of immunoglobulins, as in immunoadsorption was discussed.

Activated charcoal microcapsules and their applications

Activated charcoal, long known to the ancients as a substance of therapeutic value in a variety of maladies, has recently been "rediscovered" to be of great value in medical applications. Activated charcoal hemoperfusion is effective in blood purification for removal of various circulating toxic materials and waste metabolites, directly. However, particulate release and platelet adhesion prevent its continued clinical use. Polymeric coatings or microencapsulation of charcoal within polymers have improved their blood compatibility. Chitosan encapsulated activated charcoal (ACCB) beads have been extensively investigated in our group for the removal of various toxins such as urea, creatinine, uric acid, bilirubin, etc. This article highlights various methods of microencapsulation procedures of activated charcoal and the importance of this novel material for a variety of biomedical applications. Further, this review provides an insight to the future perspectives for using them in clinical practice.

Modified polyacrylamide microspheres as immunosorbent

Extracorporeal immunoadsorption system has been used for the specific removal of immunologically active substances from the blood. In this study, an attempt is made to utilise polyacrylamide microspheres as a matrix for immunoadsorption. Phenyl alanine is coupled onto the polymer beads using glutaraldehyde. These modified beads exhibit a high binding affinity for gamma-globulin compared to bare beads. The surface modified ones showed selective adsorption of immunoglobulins of IgG class. The C3 adsorption pattern is not altered significantly upon modification. Modified beads are found to be less hemolytic after modification. However, more studies are to be conducted for the development of a hemoperfusion column based on this modified matrix.

Phenyl alanine, tryptophan immobilized chitosan beads as adsorbents for selective removal of immunoproteins

The use of adsorbents for the treatment of patients suffering from various immune diseases is still in its infancy. Therefore, the development of selective absorbents for the removal or decrease of immunoproteins from plasma is of great importance. In this study, chitosan, a natural polysaccharide having structural characteristics similar to glycosamino glycans, which is non-toxic and biocompatible, has been used for protein adsorption studies. Amino acids like phenyl alanine and tryptophan in different ratios are bonded to these polymers to observe immunoadsorption. Several layers of phenyl alanine or tryptophan have been coated covalently on chitosan beads using N2-plasma, carbodiimide or glutaraldehyde treatments. Scanning electron micrographs have revealed the surface morphological changes after such modifications. The surface modified chitosan beads have exhibited high binding affinity for gamma-globulin compared to bare beads. It is also observed that the amount of fibrinogen adsorption is reduced on modified substrate. A selective removal of IgG and IgM has also been observed with these modified matrix when tested with human plasma, using immuno diffusion methods. The modified chitosan membranes have demonstrated a reduction in platelet attachment, showing that these substrates have become more blood compatible. Hence, it appears that modified chitosan surfaces may be an excellent sorbent system for haemoperfusion due to their high binding affinity for immunoproteins and blood compatibility. Further studies are needed to determine the behaviour under clinical conditions.

Phosphate removal by resin hemoperfusion efficacy and biocompatibility of a new exchange resin

A new coated anionic exchange resin for blood purification specifically designed to remove phosphates was experimentally employed in animals. 3 pigs, in which uremia had been surgically induced, underwent 6 extracorporeal hemoperfusion sessions (2 per pig) with a cartridge containing 100 gr of resin. The phosphate clearance proved satisfactory, values being 120 ml/min after 10' and around 80 ml/min after 2 hours. The biocompatibility of the resin and of the coating membrane was satisfactory. The negligible variation in pH and plasma bicarbonate during all sessions confirmed the low absorption by the tested resin of other blood anions competing with phosphate.

DNA-coated carbon adsorbents experimental assessment and results of severe psoriasis treatment

Newly developed combined adsorbents, containing from 1 to 8 mg of thymic DNA per 1 g of the granulated or the fibrous carbonic matrix, demonstrated good biocompatibility and selectivity for DNA- and DNP-binding substances. In a group of 14 patients with severe psoriasis (uncontrol trial) a single hemoperfusion procedure through DNA-coated granulated synthetic carbons (perfusion volume was 2.5-3.1 L, sorbent quantity was 30 g) resulted in complete remission in 6 patients and in substantial improvement of clinical status in 6 other patients. A positive effect was observed in 4 patients during 7-11 months; in 8 patients it is being observed for more than 29-33 months. The double-blind tests in the group of patients subjected to hemoperfusion through the DNA-coated charcoal (27 people) and uncoated charcoal (9 people) showed the full-scale remission in 55.5% and 11.2% respectively. The authors believe that the DNA-coated activated carbons can be an effective therapeutic procedure for treatment of numerous immuno-dependent diseases and states associated with disorders in the kinetics of cell division.

Specific removal of IgE by therapeutic immunoadsorption system

A therapeutic immunoadsorption system was developed that can remove IgE effectively and specifically from the plasma of patients with an allergy or other hyper-IgE syndrome. The immunoadsorbent (IA) consists of immunoaffinity purified anti-IgE antibody (a-IgE ab) immobilized on controlled pore glass beads (50 nm pore size). Adsorption isotherms for IgE, which were reduced by the Freundlich adsorption equation, were obtained with IA that immobilized various amounts of a-IgE ab. An optimum amount of a-IgE ab to be immobilized was selected. IA worked sufficiently in a wide range of IgE concentrations. Clinical treatment requires an amount of 41 mg of IgE to be removed from a patient's plasma for 3 h. An IA for clinical use was designed to contain 10 g of the support binding 325 mg or more of the antibody. In fact, our study in vitro simulating a clinical case showed that serum IgE was removed by IA, as expected: the level decreased from 11,000 to 3000 U/ml after a 3 h perfusion (1 U = 2.3 ng). A very small amount of a-IgE ab (goat IgG) was found to be detached from IA by flowing plasma; the average level was 20 ng/ml, which seems to be safe. However, we installed the second column in a circuit that adsorbs a-IgE ab leaked into plasma, because the amounts of a-IgE ab infused into the patient must be minimized. The second column contained IgE immobilized on the same support, since IgE as a ligand adsorbed more a-IgE ab than did anti-goat IgG antibody. This is an effective and safe therapeutic immunoadsorption system and has been subjected to clinical tests.