New adsorption column (Lixelle) to eliminate beta2-microglobulin for direct hemoperfusion

An Evolutionary Review of Hemoperfusion Adsorbents: Materials, Preparation, Functionalization, and Outlook

Accumulation of pathogenic factors in the blood may cause irreversible damage and may even be life-threatening. Hemoperfusion is an effective technique for eliminating pathogenic factors, which is widely used in the treatment of various diseases including liver failure, renal failure, sepsis, and others. Hemoperfusion adsorbents are crucial in this process as they specifically bind and remove the target pathogenic factors. This review describes the development of hemoperfusion adsorbents, detailing the different properties exhibited by inorganic materials, organic polymers, and new materials. Advances in natural and synthetic polymers and novel materials manufacturing techniques have driven the expansion of hemoperfusion adsorbents in clinical applications. Stimuli-responsive (smart responsive) adsorbents with controllable molecular binding properties have many promising and environmentally friendly biomedical applications. Knowledge gaps, future research directions, and prospects for hemoperfusion adsorbents are discussed.

Middle Molecular Uremic Toxin and Blood Purification Therapy

The purpose of blood purification therapy is to remove uremic toxins, and middle molecules (MMs) are a specific target. An MM is defined as a solute that passes through the glomerulus with a molecular weight in the range of 0.5-58 kDa, and new classifications of "small-middle 0.5-15 kDa," "medium-middle 15-25 kDa," and "large-middle 25-58 kDa" were proposed. In Japan, the removal of α1-microglobulin (αMG) in the large-middle range has been the focus, but a new theory of removal has been developed, emphasizing the antioxidant effect of αMG as a physiological function. Clinical proof of this mechanism will lead to further development of blood purification therapies.

Effects of Extracorporeal Blood Flow Rates on Patient Tolerance for LIXELLE® Treatment during Outpatient Hemodialysis

INTRODUCTION

Accumulation of β2-microglobulin (B2M) in dialysis patients contributes to several comorbidities of end-stage kidney disease (ESKD). The LIXELLE® device adsorbs B2M from blood using sorbent bead technology. Studies in Japan showed that LIXELLE treatment during hemodialysis (HD) at blood flow rates up to 250 mL/min removes B2M above HD alone and is well tolerated. We investigated tolerance for LIXELLE treatment during HD at higher HD blood flow rates standard in the USA.

METHODS

A prospective, open-label, non-randomized, single-arm, early-feasibility study (EFS) assessed tolerance and safety of LIXELLE treatment during HD at blood flow rates up to 450 mL/min. ESKD patients (40-75 years old) on thrice weekly outpatient HD were eligible. After a 1-week HD run-in, patients received LIXELLE plus HD at a blood flow rate of 250 mL/min (1 week), followed by LIXELLE plus HD at a blood flow rate up to 450 mL/min (1 week). These blood flow rates were tested with three LIXELLE column sizes in sequence (treatment = 6 weeks). B2M removal was assessed for each combination.

RESULTS

Ten patients with a historic intradialytic hypotension (IDH) rate of 0.42 events/HD session/patient were enrolled. Nine patients completed all combinations without IDH events (treatment IDH rate: 0.56 events/HD session/patient). No treatment-emergent serious adverse events or significant changes in red blood cell, platelet, or complement indices except haptoglobin were reported. B2M reduction ratios and removal of select proteins (<40 kDa) increased with escalating column size and blood flow rate.

CONCLUSION

LIXELLE plus HD across all column sizes was safe and well tolerated at blood flow rates up to 450 mL/min. Extent of B2M removal corresponded to column size-blood flow rate combinations. This EFS provides a risk profile to guide further studies of LIXELLE in ESKD patients at US-standard blood flow rates.

Design of Beta-2 Microglobulin Adsorbent Protein Nanoparticles

Beta-2 microglobulin (B2M) is an immune system protein that is found on the surface of all nucleated human cells. B2M is naturally shed from cell surfaces into the plasma, followed by renal excretion. In patients with impaired renal function, B2M will accumulate in organs and tissues leading to significantly reduced life expectancy and quality of life. While current hemodialysis methods have been successful in managing electrolyte as well as small and large molecule disturbances arising in chronic renal failure, they have shown only modest success in managing plasma levels of B2M and similar sized proteins, while sparing important proteins such as albumin. We describe a systematic protein design effort aimed at adding the ability to selectively remove specific, undesired waste proteins such as B2M from the plasma of chronic renal failure patients. A novel nanoparticle built using a tetrahedral protein assembly as a scaffold that presents 12 copies of a B2M-binding nanobody is described. The designed nanoparticle binds specifically to B2M through protein-protein interactions with nanomolar binding affinity (~4.2 nM). Notably, binding to the nanoparticle increases the effective size of B2M by over 50-fold, offering a potential selective avenue for separation based on size. We present data to support the potential utility of such a nanoparticle for removing B2M from plasma by either size-based filtration or by polyvalent binding to a stationary matrix under blood flow conditions. Such applications could address current shortcomings in the management of problematic mid-sized proteins in chronic renal failure patients.

Hemodialysis-Related Amyloidosis in the Tongue

Dialysis-related amyloidosis (DRA) represents a group of relatively rare disorders characterized by the systemic extracellular deposition of insoluble fibrils of amyloid protein in long-term dialysis patients. We describe herein a case of relatively early DRA on the tongue of a long-term dialysis patient. A 67-year-old man with a 39-year history of dialysis was referred for diagnosis of a tongue mass. On examination, a collection of whitish-yellow papules was identified on the ventral surface of the tongue tip. The pathological diagnosis was DRA. Clinicians should be aware that long-term dialysis can cause oral amyloidosis of the tongue.

Enhanced β2-microglobulin binding of a "navigator" molecule bearing a single-chain variable fragment antibody for artificial switching of metabolic processing pathways

Kidney dysfunction increases the blood levels of β2-microglobulin (β2-m), triggering dialysis-related amyloidosis. Previously, we developed a navigator molecule, consisting of a fusion protein of the N-terminal domain of apolipoprotein E (ApoE NTD) and the α3 domain of the major histocompatibility complex class I (MHC α3), for switching the metabolic processing pathway of β2-m from the kidneys to the liver. However, the β2-m binding of ApoE NTD-MHC α3 was impaired in the blood. In the current study, we replaced the β2-m binding part of the navigator protein (MHC α3) with an anti-β2-m single-chain variable fragment (scFv) antibody. The resultant ApoE NTD-scFv exhibited better β2-m binding than ApoE NTD-MHC α3 in buffer, and even in serum. Similar to ApoE NTD-MHC α3, in the mice model ApoE NTD-scFv bound to the liver cells' surfaces in vitro and accumulated mainly in the liver, when complexed with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Both ApoE NTD-MHC α3 + DMPC and ApoE NTD-scFv + DMPC significantly switched the β2-m accumulation in mice from the kidneys to the liver, but only the ApoE NTD-scFv + DMPC group showed a significantly higher ratio of β2-m accumulation in the liver versus the kidneys, compared with the control group. These results suggest that the enhanced β2-m binding activity of the navigator molecule increased the efficiency of switching the metabolic processing pathway of the etiologic factor.

Beta-2 Microglobulin Amyloidosis: Past, Present, and Future

Almost half a century has elapsed since the first description of dialysis-related amyloidosis (DRA), a disorder caused by excessive accumulation of β-2 microglobulin (B2M). Within that period, substantial advances in RRT occurred. These improvements have led to a decrease in the incidence of DRA. In many countries, DRA is considered a "disappearing act" or complication. Although the prevalence of patients living with RRT increases, not all will have access to kidney transplantation. Consequently, the number of patients requiring interventions for treatment of DRA is postulated to increase. This postulate has been borne out in Japan, where the number of patients with ESKD requiring surgery for carpal tunnel continues to increase. Clinicians treating patients with ESKD have treatment options to improve B2M clearance; however, there is a need to identify ways to translate improved B2M clearance into improved quality of life for patients undergoing long-term dialysis.

Nanobody-Based high-performance immunosorbent for selective beta 2-microglobulin purification from blood

Removing β2-microglobulin (β2M) from blood circulation is considered to be the most effective method to delay the occurrence of dialysis-related amyloidosis (DRA). The ideal extracorporeal β2M removal system should be cost-effective, highly specific and having a high capacity. However, the traditional technologies based on size exclusion do not have an adequate specificity, and alternative immunosorbents have limited applications due to low capacity and their high cost. Nanobodies (Nbs), the smallest functional recombinant antibody fragments, offer several advantages to overcome these obstacles. In this study, an anti-β2M Nb with a C-terminal thiol-tag was successfully prepared from E. coli for site-directed and oriented immobilization and usage as capture ligand in a β2M-selective immunosorbent. The prepared immunosorbent showed a high binding capacity of up to 7 mg β2M per mL resin, which is 17 times higher than that of previous studies using single-chain variable antibody fragments (scFv). Furthermore, an exceptional high specificity has been demonstrated as other human serum proteins were not adsorbed during dynamic adsorption experiments. About 80% of the original binding capacity of the immunosorbent was restored after four consecutive easy regenerations, whereas 90% of the original capacity was retained after 1-month storage of the resin. Moreover, the mathematical model fitted very well the in vitro perfusion. The results with this pioneering immunosorbent confirm its possible clinical application and is expected to reach the required clinical effect of immunoadsorption therapy. STATEMENT OF SIGNIFICANCE: Dialysis-related amyloidosis (DRA), associated with the accumulation of β2-microglobulin (β2M), is a serious complication of end-stage kidney disease. Removing β2M from blood circulation by extracorporeal blood purification is considered to be the most effective method to delay the occurrence of DRA. However, the existing methods are incapable to eliminate sufficient quantities of β2M from circulation, either because of lack of specificity, high cost or for low capacity. In this manuscript, we provide a practical and economic immunosorbent based on anti-β2M nanobody for DRA. The prepared immunosorbent was reusable and storable, and demonstrated high specificity and realized a high binding capacity of up to 7 mg β2M per mL resin, which is 17 times higher than that of the previous studies.

One-step Preparation of a VHH-based Immunoadsorbent for the Extracorporeal Removal of β2-microglobulin

Dialysis-related amyloidosis (DRA), which has been widely recognized to be associated with the accumulation of β2-microglobulin (β2-m) in blood, is one of the most common complications in patients receiving long-term dialysis treatment. The most significant side-effect of existing hemodialysis sorbents for the removal of β2-m from blood is the loss of vital proteins due to non-specific adsorptions. Although the traditional antibodies have the capability to specifically remove β2-m from blood, high cost limits their applications in clinics. Single domain antibodies derived from the Camelidae species serve as a superior choice in the preparation of immunoadsorbents due to their small size, high stability, amenability, simplicity of expression in microbes, and high affinity to recognize and interact with β2-m. In this study, we modified the anti-β2-m VHH by the formylglycine-generating enzyme (FGE), and then directly immobilized the aldehyde-modified VHH to the amino-activated beads. Notably, the fabrication is cost- and time-effective, since all the preparation steps were performed in the crude cell extract without rigorous purification. The accordingly prepared immunoadsorbent with VHHs as ligands exhibited the high capacity of β2-m (0.75 mg/mL). In conclusion, the VHH antibodies were successfully used as affinity ligands in the preparation of novel immunoadsorbents by the site-specific immobilization, and effectively adsorbed β2-m from blood, therefore opening a new avenue for efficient hemodialysis.

Depletion of amyloid-β peptides from solution by sequestration within fibril-seeded hydrogels

Aggregation of amyloid-β (Aβ) peptides in brain tissue leads to neurodegeneration in Alzheimer's disease (AD). Regardless of the kinetics or detailed mechanisms of Aβ aggregation, aggregation can only occur if Aβ concentrations exceed their local equilibrium solubility values. We propose that excess Aβ peptides can be removed from supersaturated solutions, including solutions in biological fluids, by the addition of hydrogels that are seeded with Aβ fibril fragments. Fibril growth within the hydrogels then sequesters excess peptides until equilibrium concentrations are reached. Experiments with 40- and 42-residue Aβ peptides (Aβ40 and Aβ42) in phosphate buffer at 24°C and in filtered fetal bovine serum at 37°C, using crosslinked polyacrylamide hydrogels, demonstrate the validity of this concept. Aβ sequestration in fibril-seeded hydrogels (or other porous media) may prove to be a useful technique in experiments with animal models of AD and may represent a possible approach to preventing or slowing the progression of AD in humans.

Transplantation of Nonvascularized Kidney Tissue Fragments into the Rat Liver with the Aim of Preserving Renal Function

For research in regenerative medicine, not only the study of cellular pluripotency but also knowledge of the reorganization of tissue structure is crucial. However, the latter will probably be more difficult to acquire. When small fragments of kidney (approx. 1 × 1 mm) were implanted in the liver of syngeneic LEW rats, the tissue survived at least 2 weeks with retention of normal structure including glomeruli and tubules. In contrast, no kidney structure survived when transplanted to subcutaneous sites, omentum, or spleen. Molecules involved in renal tubular function, such as megalin and glut2 transporter protein, were detectable in the implanted tissue by immunohistochemistry, suggesting that the cells were biologically active. Survival of cortex, medulla, and calyx tissues was then compared. All three components were still detectable 8 weeks after transplantation but cortex and medulla were replaced by granuloma at 6 months. Only calyx tissue survived for up to 12 months after transplantation. There was no marked difference in tissue survival, either when the recipient liver was partially resected or when infantile donor kidney was implanted instead of adult kidney. The present method opens new avenues in the development of regenerative medicine (i.e., tissue transplantation) as an intermediate modus between organ transplantation and cell transplantation.

Pharmacokinetic analysis of antibiotic adsorption (vancomycin and teicoplanin) by the Lixelle extracorporeal unit

PURPOSE

The pharmacokinetic properties of vancomycin (VAN) and teicoplanin (TEC) may be affected by adsorption during hemofiltration as well as hemoperfusion therapies. The aim of this in vitro study was to investigate VAN and TEC removal adsorption kinetics with mass balance analysis by direct hemoperfusion (DHP) with the Lixelle S-35 cartridge (Lixelle, Kaneka Corporation, Tokyo).

METHODS

Mock DHP was performed for 120 min using VAN and TEC solutions (46.08 ± 0.81 and 74.79 ± 1.24 mg/l per N = 6). Clinical plasma antibiotic concentrations were circulated in a closed circuit simulating DHP using an adsorption column (Lixelle S-35) at flow rate of 250 ml/min. Samples were collected at 10, 60, and 120 min through both arterial and venous ports; drug levels were measured with particle enhanced turbidimetric inhibition immunoassay and fluorescence polarization immunoassay. All tests were performed in triplicate.

RESULTS

Results subsequent to DHP at the primary assessment interval for VAN mass was 49.06 ± 1.47 mg, indicating a significant reduction of the starting mass (94.74 ± 1.63 mg). The observed reduction of TEC levels greatly exceeded that of VAN at the first interval (10 min). At 120 min of DHP, the estimated mass adsorption of VAN was 45.68 ± 2.26 mg, while the mesured total TEC mass adsorbed was 126.86 ± 0.91 mg.

CONCLUSIONS

A VAN adsorption plateau indicating the VAN loading dose may be required in patients receiving DHP with the Lixelle S-35. The total TEC mass was adsorbed subsequent to 60 min of circulation, so the loading dose should be closely considered. In addition, the Lixelle S-35 may represent an option as a rescue therapy in accidental overdose of TEC.

New option for the treatment of hyperbilirubinemia: in vitro direct hemoperfusion with the Lixelle S-35

PURPOSE

Limited options are available to treat critically ill patients with acute liver failure (ALF) and acute-on-chronic liver failure (AoCLF), therefore we set up an in vitro study in order to test the bilirubin adsorption capacity of the Lixelle S-35 cartridge by direct hemoperfusion (DHP).

METHODS

Mock DHP was performed for 120 min using hyperbilirubinic human plasma and blood obtained from a plasmapheresis and exchange transfusion, respectively. The total bilirubin (TBIL) and direct bilirubin (DBIL) baseline concentrations were 17.57 ± 0.53, 12.57 ± 0.23 mg/dl for plasma and 23.10 ± 0.47, 15.37 ± 0.24 mg/dl for blood. Plasma and blood were separately circulated in a closed circuit simulating DHP using an adsorption column (Lixelle S-35) at flow rate of 100 ml/min. TBIL and DBIL levels were measured at 10, 30, 60, and 120 min from arterial and venous ports and assessed with the Jendrassik-Grof method. All tests were performed in triplicate.

RESULTS

The total removal subsequent to DHP (120 min) was seen as TBIL in plasma 55.60%, TBIL in blood 62.16%, DBIL plasma 58.87%, DBIL in blood 64.41%, respectively. The estimated mass adsorption of TBIL in plasma 958.20 ± 5.72 mg, TBIL in blood 1233.60 ± 10.22 mg, DBIL in plasma 680.70 ± 10.68, DBIL in blood 818.10 ± 4.68, respectively.

CONCLUSIONS

The bilirubin adsorption rates after DHP were very promising for both hyperbilirubinic plasma and blood. Although further in vitro investigations are required, including comparisons with other techniques, these findings have shown that the Lexille S-35 should represent an option for the management of hyperbilirubinemia in ALF or AoCLF.

The blood compatibilities of blood purification membranes and other materials developed in Japan

The biocompatibilities in blood purification therapy are defined as "a concept to stipulate safety of blood purification therapy by an index based on interaction in the body arising from blood purification therapy itself." The biocompatibilities are associated with not only materials to be used but also many factors such as sterilization method and eluted substance. It is often evaluated based on impacts on cellular pathways and on humoral pathways. Since the biocompatibilities of blood purification therapy in particular hemodialysis are not just a prognostic factor for dialysis patients but a contributory factor for long-term complications, it should be considered with adequate attention. It is important that blood purification therapy should be performed by consistently evaluating not only risks associated with these biocompatibilities but also the other advantages obtained from treatments. In this paper, the biocompatibilities of membrane and adsorption material based on Japanese original which are used for blood purification therapy are described.

Long-term efficacy and safety of the small-sized β2-microglobulin adsorption column for dialysis-related amyloidosis

Dialysis-related amyloidosis (DRA) is one of the major complications often seen in long-term dialysis patients, and is one of the factors that decreases quality of life. β2-microglobulin (β2-m) is considered to be a major pathogenic factor in dialysis-related amyloidosis. The Lixelle adsorbent column, with various capacities, has been developed to adsorb β2-m from the circulating blood of patients with dialysis-related amyloidosis. Using a minimum type of β2-m-adsorbing column (Lixelle S-15), we evaluated its therapeutic efficacy and safety in dialysis patients. Seventeen hemodialysis patients with DRA were treated with the S-15 column for one year. Treatment was performed three times a week in this study. During the study period, pinch strength, visual analog scale for joint pain, and activities of daily living were evaluated every three months, and blood sampling was performed every six months. After one year's treatment with the S-15 column, the β2-m level decreased from 29.3±9.6mg/L to 24.7±5.1mg/L (P<0.05), and the high sensitive C-reactive protein level decreased from 2996±4380ng/mL to 1292±1774ng/mL. After one year of S-15 column use, pinch strength increased from 5.9±3.0pounds to 7.2±3.2pounds (P<0.05), and the visual analog scale for joint pain and activities of daily living score also improved. Long-term use of the Lixelle S-15 column is safe and effective for improvement of quality of life in chronic dialysis patients. Improvement of chronic inflammation may be one of the mechanisms through which the beneficial effects of the column is effected.

Extracorporeal strategies for the removal of middle molecules

Uremic toxins with a molecular weight of less than 500 Da are classified as small nitrogenous waste products. They are highly water soluble, relatively homogeneous, and have no protein binding. Other uremic retention toxins differ significantly from the small nitrogenous metabolite class in molecular weight, heterogeneity, protein binding, and hydrophobicity. The European Uremic Toxin Work Group subdivided molecules into two categories: protein-bound solutes and middle molecules. Middle molecules were defined as toxins in the molecular weight range of 500-60,000 Da, which exceeds the molecular weight of 2000 Da defined in the original middle molecule hypothesis. Under this new proposed definition, most of these middle molecules are low molecular weight peptides and proteins (LMWPs). This concise review focuses on LMWPs. The metabolism of LMWPs is described, including molecular weight, physical conformation, and charge. Factors influencing dialytic removal of LMWPs such as membrane characteristics, protein-membrane interactions, and solute removal mechanisms, as well as strategies to enhance clearance of these compounds are discussed.

Blood purification for critical illness: cytokines adsorption therapy

Blood purification therapies have been clinically applied to treat cytokine-induced pathological effects. The effects of broad-spectrum adsorption using Lixelle (beta2-microglobulin adsorption column; Kaneka Corporation, Osaka, Japan) for the condition of hypercytokinemia in vitro, in an animal model and in humans with sepsis were investigated. We found that Lixelle could selectively adsorb not only beta2-microglobulin but also cytokines composed of glycoproteins in vitro. In addition, Lixelle beads could adsorb not only endotoxin (ET) but also microbial fragments such as peptidoglycan (PG) which is a component of Gram-positive bacteria. Hypercytokinemic rats were connected to a direct hemoperfusion (DHP) system using a mini Lixelle column and time-course changes in plasma levels of inflammatory cytokines were examined. In addition, a Lixelle column was used in direct hemoperfusion in patients with systemic inflammatory response syndrome (SIRS), and the relationship between a decrease in cytokines and clinical course was examined. The increases in plasma levels of IL-6 and tumor necrosis factor-alpha (TNF-alpha) were significantly inhibited in the group treated with the Lixelle column in an animal model. In humans with sepsis, for IL-1beta, IL-1Ra, IL-6, IL-8, and TNF-alpha, the adsorbing rates in vivo before and after the use of the Lixelle column tended to decrease with time. However, the reduction rates at 5 min after the start were 31.4, 39.3, 36.4, 76.2 and 71.6%, respectively, and at 3 h after the start, the rates were 18.0, 17.7, 12.9, 31.8, and 32.9%, respectively. Clinically, their blood pressure increased and they recovered from shock status. These results suggest that SIRS and sepsis with hypercytokinemia can be treated with the DHP using the Lixelle column.

Adsorption of the uremic toxin p-cresol onto hemodialysis membranes and microporous adsorbent zeolite silicalite

Para-cresol CH3C6H4OH is a protein-bound solute which is not eliminated efficiently by hemodialysis systems. In this study, we present adsorption of p-cresol as a complementary process to hemodialysis. The kinetics and isotherms of adsorption onto cellulose-based membranes (cellulose diacetate and triacetate), synthetic membranes (polyamide, polysulfone, polyacrylonitrile and polymethylmethacrylate) and microporous zeolite silicalite (MFI), have been evaluated in static conditions. The results indicate that p-cresol has a low affinity to all membranes but polysulfone and polyamide and that the times to reach equilibrium conditions are slow. In contrast, equilibration time on silicalite is fast (2 min to eliminate 90%) while adsorption levels are high (maximum adsorption about 106 mg g(-1)). Adsorption onto microporous adsorbents could be a novel way to eliminate uremic toxins from blood.

β2-Microglobulin-selective direct hemoperfusion column for the treatment of dialysis-related amyloidosis

Lixelle is a direct hemoperfusion-type adsorption column that was developed to selectively eliminate beta2-microglobulin (beta2-m) from the circulating blood of patients with dialysis-related amyloidosis (DRA). The adsorbent in Lixelle comprises porous cellulose beads to which hydrophobic hexadecyl alkyl chain is covalently bound. One milliliter of wet Lixelle beads eliminates more than 1 mg of beta2-m in vitro. In hemodialysis patients who were treated with Lixelle, Lixelle improved joint pain, nocturnal awakening, pinch strength, motor terminal latency, and their activity of daily living. The adsorbent adsorbs beta2-m selectively but not specifically, as well as inflammatory cytokines such as interleukin-1beta and IL-6 which are considered to be involved in the development of DRA. Lixelle treatments reduce the circulating levels of beta2-m and inflammatory cytokines, thereby improving the symptoms of patients with DRA.

Assessment of the Stability of an Immunoadsorbent for the Extracorporeal Removal of Beta-2-Microglobulin from Blood

BACKGROUND

Dialysis-related amyloidosis (DRA) is a devastating and costly condition that affects patients with end stage kidney disease. A key feature of DRA is the formation of amyloid fibrils, consisting primarily of beta2-microglobulin. Except for kidney transplantation, conventional kidney replacement therapies, which are based on nonspecific mechanisms, do not adequately address beta2-microglobulin removal. An antihuman beta2-microglobulin single-chain variable region antibody fragment (scFv) was developed to confer specificity to beta2-microglobulin removal during hemodialysis.

METHODS

The scFv was immobilized onto agarose and characterized for beta2m binding capacity, thermal stability at 37 degrees C, regeneration capacity, storage conditions, and sterility.

RESULTS

The beta2-microglobulin binding capacity was 1.3 mg/ml scFv gel. The immunoadsorbent is thermally stable, can be regenerated, stored short-term in 20% ethanol, lyophilized for long-term storage, and withstand process conditions similar to that of a patient's hemodialysis therapy.

CONCLUSIONS

The results support further investigation of immobilized scFvs as a novel tool to remove beta2-microglobulin from blood.

Dialysis-related amyloidosis of the temporomandibular joint

Dialysis-related amyloidosis (DRA) is a serious complication occurring most commonly in patients undergoing long-term hemodialysis. We describe a case of amyloidosis of the bilateral temporomandibular joint (TMJ) that developed after long-term hemodialysis therapy.

Arresting Dialysis-Related Amyloidosis: A Prospective Multicenter Controlled Trial of Direct Hemoperfusion with a beta2-Microglobulin Adsorption Column

We investigated the clinical efficacy of direct hemoperfusion with a beta2-microglobulin (beta2-m) adsorption column for the treatment of patients with dialysis-related amyloidosis. A 2-year prospective controlled study was performed to compare the effects of passaging blood through a (beta2-m) adsorption column (Lixelle) before it is passaged through the dialysis polysulfone membrane on the severity of amyloidosis in these individuals. Patients (n = 22) whose blood went through the Lixelle column prior to dialysis had a higher beta2-m removal rate compared to an equal number of controls, and they showed earlier improvement in their symptoms which included impaired daily activities, joint stiffness, and pain. The appearance of additional bone cysts was prevented in pre-adsorbed patients but not in the controls. Thus, the Lixelle column is useful in preventing the progression of dialysis-related amyloidosis and in ameliorating or arresting the progression of the symptoms of this disorder.

Single-chain antibody fragment-based adsorbent for the extracorporeal removal of β2-microglobulin

BACKGROUND

Dialysis-related amyloidosis (DRA) is a frequent complication of end-stage renal disease (ESRD) that has been associated with the accumulation of beta2-microglobulin (beta2-m). Removal of beta2-m results in the loss of important proteins due to the nonspecific nature of current therapies. Although whole antibodies can potentially be used to confer specificity to beta2-m removal from blood, single-chain variable region (scFv) antibody fragments could potentially offer several advantages as immunoadsorption ligands due to their size, genetic definition, ability to be expressed by microbes, and amenability for in vitro evolution.

METHODS

An antihuman beta2-m scFv was constructed from the BBM.1 hybridoma and expressed by a yeast display vector. The binding affinity of the wild-type scFv fragment was quantified by flow cytometry analysis. Soluble scFv was expressed by a yeast secretion vector, purified, and immobilized onto agarose beads. The binding capacity of the immunoadsorbent was measured by equilibrating samples with saturating quantities of fluorescent beta2-m in serum.

RESULTS

The displayed scFv possessed a nanomolar affinity (KD= 0.008 +/- 0.004 mg-beta2-m/L). The immunoadsorbent exhibited an adsorption site density of 0.41 +/- 0.01 mg beta2-m/mL settled gel. Under saturating conditions, the mass ratio of adsorbed beta2-m to immobilized antibody is 70% greater than any previous literature report for whole antibodies. Preliminary specificity experiments suggest that the scFv-based immunoadsorbent is specific toward human beta2-m.

CONCLUSION

Recombinant DNA technology was successfully used to engineer an scFv-based immunoadsorbent. Use of immobilized scFvs during hemodialysis may minimize loss of valuable proteins and facilitate the removal of macromolecules that are significantly larger than the molecular weight cut-off of the membrane.

Beta-2 microglobulin in ESRD: an in-depth review

Beta-2 microglobulin is the most widely studied low-molecular-weight protein in end-stage renal disease. It is known to cause dialysis-related amyloidosis (DRA), by virtue of its retention when renal function fails, its deposition in tissues, its aggregation into fibrils, and its ability to become glycosylated. The onset of DRA may be protracted by the use of noncellulosic membranes, especially when high-volume hemodiafiltration is used in the treatment of renal failure. Adsorptive methods have been developed to improve the removal of beta-2 microglobulin. There seems to be a relative risk reduction in mortality when patients are treated with dialysis membranes that have a higher clearance of beta-2 microglobulin.

Effect of beta(2)-microglobulin adsorption column on dialysis-related amyloidosis

BACKGROUND

beta2-microglobulin (beta2-m) is considered a major pathogenic factor in dialysis-related amyloidosis (DRA), often seen in long-term dialysis patients. No effective therapy for this severely debilitating disease is currently available. Lixelle, an adsorption column, has been developed for the elimination of beta2-m; the efficacy of this column has been evaluated in this study.

METHODS

Seventeen hemodialysis patients with DRA were first treated with high-flux dialysis for a minimum of 1 year. This was followed by 1-year treatment with Lixelle column connected in series to the high-flux dialyzer. Treatments were used three times a week for both phases of this study. During the study period, beta2-m, pinch strength, motor terminal latency, and activities of daily living were evaluated.

RESULTS

After 1-year treatment with high-flux dialysis the beta2-m level remained unchanged; however, after 1-year treatment with the addition of the Lixelle column, beta2-m level decreased significantly from 34.5 +/- 8.4 mg/L to 28.8 +/- 7.3 mg/L (P < 0.05). After 1 year of Lixelle column use, the pinch strength increased from 6.8 +/- 4.7 pounds to 9.1 +/- 5.5 pounds (P < 0.01), and the median motor terminal latency was significantly reduced from 5.1 +/- 1.0 mseconds to 4.5 +/- 1.1 mseconds. A significant improvement was also observed in the activities of daily living score of the upper extremities.

CONCLUSION

These results suggest that the addition of Lixelle to the high-flux dialyzer is associated with a significant clinical improvement in DRA patients.

Middle molecules and small-molecular-weight proteins in ESRD: properties and strategies for their removal

Molecular weight has traditionally been the parameter most commonly used to classify uremic toxins, with a value of approximately 500 Da frequently used as a demarcation point below which the molecular weights of small nitrogenous waste products fall. This toxin group, the most extensively studied from a clinical perspective, is characterized by a high degree of water solubility and the absence of protein binding. However, uremia is mediated by the retention of a plethora of other compounds having characteristics that differ significantly from those of the previously mentioned group. As opposed to the relative homogeneity of the nitrogenous metabolite class, other uremic toxins collectively are a very heterogeneous group, not only with respect to molecular weight but also other characteristics, such as protein binding and hydrophobicity. A recently proposed classification scheme by the European Uraemic Toxin Work Group subdivides the remainder of molecules into 2 categories: protein-bound solutes and middle molecules. For the latter group, the Work Group proposes a molecular weight range (500-60,000 Da) that incorporates many toxins identified since the original middle molecule hypothesis, for which the upper molecular weight limit was approximately 2,000 Da. In fact, low-molecular-weight peptides and proteins (LMWPs) comprise nearly the entire middle molecule category in the new scheme. The purpose of this article is to provide an overview of the middle molecule class of uremic toxins, with the focus on LMWPs. A brief review of LMWP metabolism under conditions of normal (and in a few cases, abnormal) renal function will be presented. The physical characteristics of several LMWPs will also be presented, including molecular weight, conformation, and charge. Specific LMWPs to be covered will include beta 2-microglobulin, complement proteins (C3a and Factor D), leptin, and proinflammatory cytokines. The article will also include a discussion of the treatment-related factors influencing dialytic removal of middle molecules. Once these factors, which include membrane characteristics, protein-membrane interactions, and solute removal mechanisms, are discussed, an overview of the different therapeutic strategies used to enhance clearance of these compounds is provided.

Ex vivo biocompatibility of a new beta2-microglobulin hemoperfusion polymer

Beta2-microglobulin (beta2-m) is an 11.8 kD protein that is excreted by the kidneys. In renal insufficiency, it accumulates in the body and can result in AB amyloidosis with bone and joint destruction. Four modifications of a new beta2-m adsorbent material were tested for biocompatibility with human whole blood. 500 ml of heparinized blood from healthy human donors was perfused ex vivo through minicolumns (adsorber beads: divinylbenzene with different biocompatible coatings) in the single-pass mode. Blood samples were taken from the antecubital vein before and at the column outlet during the 50 min test runs. Red and white cell counts remained virtually constant. No signs of hemolysis could be detected. Thrombogenicity of the columns was low as shown by the insignificant platelet loss, only slight platelet activation and moderate thrombin-antithrombin formation. There was no activation of leukocytes nor monocytes. Complement and bradykinin activation was minimal. Electrolyte concentrations and pH remained essentially constant. In conclusion, this new beta2-m adsorbent material exhibited favorable biocompatibility features in our ex vivo model and is thus a promising candidate for future clinical beta2-m hemoperfusion studies in patients.

Sorbent hemoperfusion in end-stage renal disease: an in-depth review

The excessive mortality in dialysis patients has rekindled interest in research of adsorbent removal of nontraditional uremic toxins. Middle-molecular-weight substances, predominantly small proteins, have been correlated with specific uremic syndromes and implicated in the uremic state. New developments in polymer technology and carbon pyrrolization techniques have produced sorbents possessing mesopores of sufficient size to trap middle-molecular-weight substances. Clinical application of hemoperfusion devices containing these sorbents is early in its development. Studies related to hemoperfusion in uremia are discussed in detail.

Outcomes of hemodiafiltration based on Japanese dialysis patient registry

Effectiveness of various therapeutic modalities was analyzed among 1,196 patients entered in the registry of the Japanese Society for Dialysis Therapy who were on hemopurification therapy as of the end of 1998 and developed dialysis-related amyloidosis during 1999. In the investigation, the effectiveness of various hemopurification modalities on the dialysis-related amyloidosis was ranked as exacerbation, unchanged, or alleviation, so as to analyze the possible relationship between the hemopurification modality and its effectiveness. The analysis was performed using a logistic regression approach, and the results were shown as "the risk of a worse therapeutic ranking" among the hemopurification modalities. The smaller "the risk of a worse therapeutic effect" was, the more effective the treatment modality. When the risk of a worse therapeutic effect for the hemodialysis patients treated by a regular membrane was put at 1.0, the risk for hemodialysis patients using high-flux membrane was 0.489, the off-line hemodiafiltration risk was 0.117, the on-line hemodiafiltration risk was 0.013, and the risk of push/pull hemodiafiltration was 0.017. For hemodialysis with a beta(2)-microglobulin adsorption column, a low risk of 0.054 was found. The results indicated that hemodiafiltration therapy and simultaneous hemodialysis with beta(2)-microglobulin adsorption therapy were more effective treatment for dialysis-related amyloidosis.

A novel immunoadsorption device for removing beta2-microglobulin from whole blood

BACKGROUND

High plasma levels of beta2-microglobulin (beta2m) have been implicated in the formation of the severely destructive and potentially fatal amyloid deposits that are characteristic of dialysis-related amyloidosis (DRA). Conventional renal replacement technologies remove insufficient quantities of beta2m to normalize plasma levels. This limitation arises because of nonspecific adsorptive qualities and reliance on size exclusion, which can also remove other middle molecular weight proteins. These nonspecific approaches also make it difficult to evaluate the role and contribution of middle molecular weight molecules to the pathology of DRA and other morbidities of end-stage renal disease. A high-affinity and biologically specific approach could target a protein, prevent a significant loss of other important molecules, and improve the apparent adsorption rate within an extracorporeal device.

METHODS

Agarose-immobilized murine anti-human beta2m monoclonal antibodies were used in a Vortex Flow Plasmapheretic Reactor (VFPR) to remove donor baseline and controlled amounts of recombinant beta2m from human blood in vitro. The extracorporeal circuit was hemoperfused at 200 mL/min for two hours.

RESULTS

The immunoadsorptive media had a binding site density of 30 microg beta2m per mL of settled gel. The VFPR cleared baseline quantities of donor beta2m below detectable limits of the assay. The experiments with higher initial beta2m concentrations reached an equilibrium concentration within 20 minutes, corresponding to a 92% clearance. No deleterious hemocompatibility issues were observed (complete blood count, total protein, and plasma free hemoglobin).

CONCLUSIONS

The adsorptive kinetics of the VFPR are optimal for the conditions used and support the use of immunoadsorption for the removal of beta2m.

Dialysis-related amyloidosis: pathogenesis focusing on AGE modification

Dialysis-related amyloidosis (DRA) is a serious complication in long-term dialysis patients, and presents with carpal tunnel syndrome, cystic bone lesions, destructive spondylarthropathy, diffuse arthritis and periarthritis, systemic organ involvement, and dialysis-related spinal canal stenosis (DSCS). Recently a new concept of DSCS has been proposed that includes both destructive spondylarthropathy and myeloradiculopathy induced by extradural thickness. beta(2)-microglobulin (beta(2)M) amyloid was demonstrated to be modified with advanced glycation end products (AGEs) such as imidazolone, N(epsilon)-(carboxymethyl)lysine (CML), and pentosidine. Imidazolone is a reaction product of arginine residue in proteins with 3-deoxyglucosone (3-DG), which is markedly accumulated in uremic serum. Imidazolone is generated under nonoxidative conditions, while CML and pentosidine are formed by oxidative processes. Immunoelectron microscopy demonstrated that AGEs were localized not only in dialysis amyloid but also in nonamyloid collagenous structures, supporting the hypothesis that AGE modification of collagen might have pathogenic relevance in the deposition of beta(2)M on collagen. Serum levels of AGEs are increased in uremic patients. The dimeric form of beta(2)M in the dialysate and urine of uremic patients is more susceptible to imidazolone modification as observed in dialysis amyloid. However, the major component of dialysis amyloid is a native form of beta(2)M, while AGE-modified beta(2)M and truncated beta(2)M are the minor components. Thus I propose that 3-DG and the other dicarbonyl compounds accumulating in uremic serum promote the modification of beta(2)M with AGEs mainly after deposition of beta(2)M as amyloid. For the prevention and treatment of DRA, beta(2)M should be efficiently eliminated from circulating blood by kidney transplantation, hemodialysis, or hemodiafiltration using high-flux membranes and an adsorbent (Lixelle) column.

Nontransplant therapy for dialysis-related amyloidosis

There is no specific treatment for dialysis-related amyloidosis (DRA). Available therapy is directed at removal of large quantities of beta(2)-microglobulin (beta(2)M) and palliation of symptoms. Plasma concentrations of beta(2)M in end-stage renal disease (ESRD) depend on the degree of residual renal function, the type of blood purification therapy, and properties of the dialysis filtration membrane. Retention of beta(2)M appears to be a necessary, although not sufficient, condition for DRA. While preserving residual renal function is important, dialysis modality largely determines beta(2)M removal. Convective dialysis treatments (hemofiltration and hemodiafiltration) remove beta(2)M more efficiently than diffusive treatments (conventional dialysis). In addition, column adsorption of beta(2)M can extensively remove the molecule, as can nocturnal hemodialysis. Hemodialysis membrane properties that are particularly important with regard to beta(2)M removal include permeability, adsorptive capacity, and biocompatibility. As such, beta(2)M removal with highly permeable biocompatible membranes such as polysulfone and polyacrylonitrile is relatively large. Several studies have suggested that use of such membranes can significantly delay DRA development and may be useful in ameliorating DRA-associated symptoms. Non-dialysis-related therapy for DRA is palliative and includes both medical and surgical therapies. Medical therapy includes low-dose corticosteroids and nonsteroidal anti-inflammatory drugs (NSAIDs). Surgical therapy consists of relief of carpal tunnel syndrome, or palliation of shoulder pain, destroyed weight-bearing joints, or spinal cord compression. DRA is a serious complication of long-term dialysis. It is important for nephrologists to recognize the condition and attempt to slow its progression.

Modalities for the removal of beta 2-microglobulin from blood

The long-term accumulation of beta(2)-microglobulin (beta(2)M) in patients with kidney failure results in a debilitating condition referred to as dialysis-related amyloidosis (DRA). There have been few methods specifically designed to remove the large quantities of beta(2)M that are produced by the body. This article briefly reviews current modalities and concepts for the removal of beta(2)M from blood. The various approaches are classified according to the mechanism of beta(2)M clearance. The potential application of immunoadsorption, a biologically specific approach to remove macromolecules, in the treatment and understanding of DRA is discussed.

Effect of hemodialysis membranes on beta 2-microglobulin amyloidosis

Early after the identification of beta(2)-microglobulin amyloidosis (A beta(2)M) as the cause of carpal tunnel syndrome, it was thought that hemodialysis was a major cause in the development of the disease. It was subsequently shown that hemodialysis was not necessary for the development of dialysis-related amyloidosis; however, it was believed that the different dialysis membranes did modulate the progression of the disease. Current data demonstrate that hemodialysis fails to prevent or reverse the disease, but there is substantial evidence that high-flux, high-efficiency dialyzers slow its progression. Many factors related to hemodialysis have been evaluated in relation to A beta(2)M, including the effect of the bioincompatibility of the membrane, the capacity of the different membranes to remove beta(2)M, and the effect of reuse on beta(2)M levels. Moreover, there have been intensive efforts to evaluate, explore, and improve the different mechanisms in beta(2)M removal, with adsorption as a promising prospect. With the available evidence, it seems that the removal of beta(2)M by the membrane plays the most important role in modulating the disease outcome and rate of progression, although a large, long-term, multicentered and randomized study is still lacking to prove this relationship. However, it is possible that with the continuing advances in optimizing the beta(2)M removal efficiency of the different membranes, the frequency and severity of the disease can be substantially decreased.