A new form of amyloid protein associated with chronic hemodialysis was identified as beta 2-microglobulin

Citrate stabilized gold nanoparticles interfere with amyloid fibril formation: D76N and ΔN6 β2-microglobulin variants

Protein aggregation including the formation of dimers and multimers in solution, underlies an array of human diseases such as systemic amyloidosis which is a fatal disease caused by misfolding of native globular proteins damaging the structure and function of affected organs. Different kind of interactors can interfere with the formation of protein dimers and multimers in solution. A very special class of interactors are nanoparticles thanks to the extremely efficient extension of their interaction surface. In particular citrate-coated gold nanoparticles (cit-AuNPs) were recently investigated with amyloidogenic protein β2-microglobulin (β₂m). Here we present the computational studies on two challenging models known for their enhanced amyloidogenic propensity, namely ΔN6 and D76N β₂m naturally occurring variants, and disclose the role of cit-AuNPs on their fibrillogenesis. The proposed interaction mechanism lies in the interference of the cit-AuNPs with the protein dimers at the early stages of aggregation, that induces dimer disassembling. As a consequence, natural fibril formation can be inhibited. Relying on the comparison between atomistic simulations at multiple levels (enhanced sampling molecular dynamics and Brownian dynamics) and protein structural characterisation by NMR, we demonstrate that the cit-AuNPs interactors are able to inhibit protein dimer assembling. As a consequence, the natural fibril formation is also inhibited, as found in experiment.

Do Different Dialysis-Membranes Affect Beta 2-Microglobulin Kinetics during Chronic Hemodialysis?

Hemodialysis is not an absolute prerequisite for the formation of β2-microglobulin amyloidosis, but it enhances the progression of this complication related to long-standing renal failure. Thus the clearance and turnover of β2-microglobulin seems to play a major role in this disease. In a prospective multicenter study the β2-microglobulin clearance was studied in 87 patients starting hemodialysis. Serum samples were taken prior to and after the first dialysis session and also before and after dialysis at 4, 6, 12, 16, 26 and 52 weeks. Patients were either treated by cuprophane or a polyacrylonitril membrane. At the start, the mean serum β2-microglobulin level was about 18 mg/L in patients treated with a cuprophane membrane, but the levels increased after hemodialysis and reached a plateau, which was always higher than in those treated with polyacrylonitril, which cleared β2-microglobulin from the serum. However, after 12 months the difference was no longer significant. Thus β2-microglobulin excretion during dialysis differs between the two membranes, but seems to lose its significance for the β2-microglobulin serum level in chronic hemodialysis treatment.

Nanoscale Modulation of the Pore Dimensions, Size Distribution and Structure of a new Polysulfone-Based High-Flux Dialysis Membrane

Current haemodialysis therapy modalities such as haemodiafiltration enhance the removal of larger uraemic solutes from the blood of patients on end-stage renal disease. A number of clinical investigations have demonstrated the clinical benefits of such therapies in contributing towards better patient survival rates and an improved quality of life.

A fundamental prerequisite to the application of convective treatment modalities is the availability of appropriate, technologically-advanced high-flux dialysis membranes that are able to eliminate larger uraemic substances with high efficiency but without causing an excessive leakage of useful proteins. A new membrane, Helixone®, has been developed specifically to meet the present-day requirements of high-flux dialysis and haemodiafiltration therapies involving large substitution rates. The application of nanotechnology fabrication principles and procedures has enabled the development of a membrane having highly-defined inner, separating layer surface structures that offer minimal resistance to the removal of large molecular weight substances across the membrane; for the first time, pore size dimensions, pore size distribution and pore geometry have been modulated and controlled at the nanoscale level for Helixone®.

This paper describes the characterisation of the essential structure- and permeation-related parameters of the new membrane using a number of physical analytical techniques.

Amyloid Bone Disease and Highly Permeable Synthetic Membranes

The effect of different highly permeable membranes on amyloid bone disease (ABD) was retrospectively evaluated in patients on renal replacement therapy (RRT) in our Unit with a dialytic age of more than 4 years. A group of 36 patients (age 60 ± 12 years) after a variable period (28 ± 29 months) on hemodialysis with cuprophane membrane (CU-HD), were moved to HDF with a reinfusate volume of 22 ± 1 1/session, for a period of 65 ± 26 months using the following membranes: AN69 1.6 m2, PAN 1.8, PMMA 2.1, PS 1.3, polyamide (PA) 1.3 and 1.6. Bone x-rays of wrists, hips and shoulders were taken annually and the presence of ABD was evaluated according to generally accepted criteria. ABD occurred in 4 patients after a period of 73 ± 30 months on CU-HD only; it developed in 4/7 patients an AN69, in 4/6 on PAN, in 3/5 on PMMA, in 3/5 on PS; no patient of the 13 on PA developed ABD. Comparing patients on PA with those on other synthetic membranes, no significant difference was found in dialysis time (73 ± 19 vs 83 ± 28 months) as well as in age (59 ± 13 vs 61 ± 11 years) at ABD on set, when present. These data strongly encourage prospective studies enrolling more patients for a longer period of observation in order to evaluate possible differences on ABD development among various synthetic membranes.

Long-Term Comparative Evaluation of Synthetic and Cellulosic Membranes in Dialysis

A long-term retrospective evaluation (5 years) compares two groups of RDT patients (group 1 on continuous treatment with cellulosic membranes and group 2 with synthetic membranes) regarding survival, general clinical morbidity, and β2M-related morbidity. The results showed no significant long-term differences between the groups either for survival or general morbidity despite some differences in biocompatibility. The higher intradialytic removal of β2M by synthetic membranes did not lead to a reduction in either pre-dialysis β2M values or β2M related morbidity. The higher cost of synthetic over cellulosic membranes and the disappointing of many clinical expectations suggest that the use of such membranes, in association with alternative techniques, should take place only according to certain “elective” indications such as old age, diabetes, vascular instability or intradialytic disequilibrium syndrome.

A New Polymethylmethacrylate Membrane for Hemodialysis

High molecular weight (MW) solutes are not removed during conventional hemodialysis (HD), and their accumulation is thought to play a role in some long-term HD complications (anemia, bone and joint pain, neuropathy, itching). The present trial was conducted to evaluate the removal capacity during in vivo HD of a new polymethylmethacrylate (PMMA) membrane (Filtryzer BK-F, 1.3 m2) compared to conventional PMMA (BK-P, 1.6 m2) and to cellulose acetate (CA, 1.3 m2). BK-F dialyzers, with a pore size of 100 A° and 62% porosity, are designed to remove high MW substances. Ten stable anuric RDT patients (53 ± 13 years) were treated for one week with each membrane in a randomized sequence. Plasma concentrations of creatinine, BUN and beta2-microglobulin (beta2-M) were measured before (b) and after (a) HD to determine the reduction rate for these substances (%). Beta2-M concentration after HD was corrected for changes in distribution volume. Samples of spent dialysate were collected after 3 minutes, 120 minutes and at the end of HD sessions, and appropriately treated and concentrated for HPLC analysis. The reduction rate for BUN and creatinine was similar for the 3 membranes. BK-F showed a higher beta2-M reduction rate than BK-P (p<0.005) or CA (p<0.0001). HPLC analysis of dialysate showed prevalent peaks < 4 kilodaltons (kDa) throughout HD for BK-P and CA. Solutes > 10 kDa were infrequently detected. Peak profile during HD with BK-F was quite different, showing a predominant peak > 50 kDa which also included albumin. However, albumin loss significantly decreased after 120 minutes and at the end of dialysis compared with the 3-minute values, and was lower than that reported in CAPD patients. With BK-F a peak of MW > 500 kDa was also detected which previous studies indicated as a range characterized by the presence of erythropoiesis inhibitors. Use of the BK-F membrane in HD could afford satisfactory removal of high MW substances, thereby preventing or controlling some long-term HD complications such as anemia or beta2-M amyloid formation.

Uremic Toxicity: Present State of the Art

The uremic syndrome is a complex mixture of organ dysfunctions, which is attributed to the retention of a myriad of compounds that under normal condition are excreted by the healthy kidneys (uremic toxins). In the area of identification and characterization of uremic toxins and in the knowledge of their pathophysiologic importance, major steps forward have been made during recent years. The present article is a review of several of these steps, especially in the area of information about the compounds that could play a role in the development of cardiovascular complications. It is written by those members of the Uremic Toxins Group, which has been created by the European Society for Artificial Organs (ESAO). Each of the 16 authors has written a state of the art in his/her major area of interest.

A Median Nerve Anterior Transposition Procedure for Multi-Recurrent Hemodialysis-Related Carpal Tunnel Syndrome

BACKGROUND

Some long-term hemodialysis patients suffer from multi-recurrent carpal tunnel syndrome because amyloid originating from β₂-microglobulin continues to be deposited mainly in the flexor tendons, tendon sheaths and flexor retinaculum during maintenance hemodialysis. These amyloid deposits inside carpal canal (tunnel) tissues increase carpal canal pressure and this leads to compression of the median nerve. When multi-recurrent carpal tunnel syndrome occurs, previous operative scarring of soft tissue may prohibit further enlargement of the carpal canal even if any carpal canal decompression procedure is used. For this reason, we developed a median nerve anterior transposition procedure, as a new approach in the treatment of multi-recurrent hemodialysis-related carpal tunnel syndrome.

METHODS

Median nerve anterior transposition procedures were performed on seven hands in six patients with multi-recurrent carpal tunnel syndrome. The mean age of the patients was 68.3 years and the mean hemodialysis duration was 35.3 years. Mean follow-up period was 9.9 months. The median nerve is transposed from inside to outside of the carpal canal under local and infiltration anesthesia without a pneumatic tourniquet on an outpatient basis. This procedure is based on the same principles applied in ulnar nerve anterior transposition procedures for cubital tunnel syndrome.

RESULTS

Main preoperative patient complaints were intolerable tingling and/or pain in the diseased hands throughout the day. Following the surgeries, preoperative clinical symptoms began to subside and eventually improved in all hands. Postoperative abductor pollicis brevis muscle power using manual muscle testing improved except in one hand. Abnormal preoperative distal motor and sensory latency were improved except in two hands following the surgeries.

CONCLUSIONS

The median nerve anterior transposition procedure is a beneficial treatment for patients suffering from hemodialysis-related multi-recurrent carpal tunnel syndrome.

Is β2-Microglobulin-Related Amyloidosis of Hemodialysis Patients a Multifactorial Disease? a New Pathogenetic Approach

Purpose

β2-microglobulin amyloidosis (Aβ2M) is one of the main long-term complications of dialysis treatment. The incidence and the onset of Aβ2M has been related to membrane composition and/or dialysis technique, with non-homogeneous results. This study was carried out to detect: i) the incidence of bone cysts and CTS from Aβ2M; ii) the difference in Aβ2M onset between cellulosic and synthetic membranes; iii) other risk factors besides the membrane.

Methods

480 HD patients were selected between 1986 to 2005 and grouped according to the 4 types of membranes used (cellulose, synthetically modified cellulose, synthetic low-flux, synthetic high-flux). The patients were analyzed before and after 1995, when the reverse osmosis treatment for dialysis water was started at our center, and the incidence of Aβ2M was compared between the two periods. Routine plain radiography, computer tomography (CT) and nuclear magnetic resonance imaging (MRI) as well as electromyography were used to investigate the clinical symptoms.

Results

Bone cysts occurred in 29.2% of patients before 1995 vs. 12.2% after 1995 (p<0.0001). CTS occurred in 24% of patients before 1995 vs. 7.1% after 1995 (p<0.0001). Bone cysts and CTS occurred in older patients, who began dialysis at a late age, with high CRP, low albumin, low residual GFR, and low Hb. Cox regression analysis showed that the risk factor for bone cysts was high CRP (RR 1.3, p<0.01), while albumin (RR 0.14, p<0.0001) and residual GFR (RR 0.81, p<0.0001) were revealed to be protective factors. Cox analysis for CTS confirmed CRP as a risk factor (RR 1.2, p<0.01), and albumin (RR 0.59, p<0.0001) and residual GFR (RR 0.75, p<0.0001) as protective factors. The comparison obtained between membranes did not suggest any protective effect on Aβ2M.

Conclusions

The findings that the inflammatory status as well as low albumin and the residual GFR of the uremic patient are predictive of Aβ2M lesions suggests that Aβ2M has a multifactorial origin rather than being solely a membrane- or technique-related side effect.

The interaction of β2-microglobulin with gold nanoparticles: impact of coating, charge and size

Gold nanoparticles (AuNPs) have been proved to be ideal scaffolds to build nanodevices whose performance can be tuned by changing their coating.

Interference of citrate-stabilized gold nanoparticles with β2-microglobulin oligomeric association

Citrate-coated gold nanoparticles interfere with the association equilibria of β2-microglobulin and thus inhibit the early events of fibrillogenesis.

Persistent fever and destructive arthritis caused by dialysis-related amyloidosis: A case report

RATIONALE

Dialysis-related amyloidosis (DRA) can present rheumatic manifestations in patients on long-term hemodialysis. Typical articular symptoms with DRA involve carpal-tunnel syndrome, effusion in large joints, spondyloarthropathy, or cystic bone lesions, which are usually with non-inflammatory processes.

PATIENT CONCERNS

A 64-year-old man on hemodialysis for >30 years was admitted because of intermittent fever, polyarthritis, and elevated serum C-reactive protein (CRP) level, which was continuous for 2 years. Several antibiotics were ineffective for 3 months before his admission. On physical examination, joint swelling was observed at bilateral wrists, knees, ankles, and hip joints. Laboratory tests revealed elevation of serum inflammatory markers and β2-microglobulin (β2-MG). Synovial fluid showed predominant infiltration of polymorphonuclear leukocytes and the increase of β2-MG level.

DIAGNOSIS

Significant deposition of β2-MG with inflammatory cell infiltration was found in biopsied samples from synovium, skin, and ileum.

INTERVENTIONS

We decided to switch to the hemodialysis column with membrane that can effectively absorb β2-MG in circulation.

OUTCOMES

The relief of symptoms and a decrease of CRP level by changing the membrane lead to the final diagnosis of DRA.

LESSONS

Our case demonstrates that DRA arthropathy can be inflammatory and destructive, and also develop systemic inflammatory signs and symptoms. In such cases, aggressive absorption of β2-MG in circulation might help the amelioration of symptoms.

Selection of DNA Aptamer That Blocks the Fibrillogenesis of a Proteolytic Amyloidogenic Fragment of β2 m

Dialysis-related amyloidosis (DRA) is a severe complication of hemodialysis that results in progressive destruction of bones and joints. Elevated concentrations of the β₂ -microglobulin (β₂ m) level in the serum of subjects on hemodialysis promote the formation of amyloid fibrils in osteoarticular tissues. β₂ m lacking the N-terminal six residues of the mature protein (ΔN6β₂ m) constitutes 25-30% of β₂ m in ex vivo DRA amyloid. Unlike full-length wild-type β₂ m, ΔN6β₂ m forms amyloid fibrils at neutral pH in vitro. However, the role of ΔN6β₂ m in DRA is, at present, poorly understood. In the present study, we screened novel phosphorothioate-modified aptamers directed against ΔN6β₂ m using combinatorial chemistry in vitro. We identified 11 ΔN6β₂ m aptamers; among the identified aptamers, clone #2, #8, and #10 aptamers had higher binding affinity to ΔN6β₂ m than the others. Biolayer interferometry analysis revealed that K_D values of clone #2, #8, and #10 aptamers were 56, 23, and 44 nM, respectively. Furthermore, the clone #8 aptamer inhibited fibril formation in a dose-dependent manner, as assessed by Thioflavin T fluorescence assay. Fibrils formed from ΔN6β₂ m bind to Congo red, displaying changes in the absorbance spectrum of the dye characteristic of binding to amyloid fibrils, which was completely blocked by treatment with clone #8 aptamer. These results suggest the potential of ΔN6β₂ m aptamers as tools for elucidating co-assembly mechanisms in amyloid formation.

Effect of dialyzer membrane materials on survival in chronic hemodialysis patients: Results from the annual survey of the Japanese Nationwide Dialysis Registry

BACKGROUND

Little information is available regarding which type of dialyzer membrane results in good prognosis in patients on chronic hemodialysis. Therefore, we conducted a cohort study from a nationwide registry of hemodialysis patients in Japan to establish the association between different dialyzer membranes and mortality rates.

METHODS

We followed 142,412 patients on maintenance hemodialysis (female, 39.1%; mean age, 64.8 ± 12.3 years; median dialysis duration, 7 [4-12] years) for a year from 2008 to 2009. We included patients treated with seven types of high-flux dialyzer membranes at baseline, including cellulose triacetate (CTA), ethylene vinyl alcohol (EVAL), polyacrylonitrile (PAN), polyester polymer alloy (PEPA), polyethersulfone (PES), polymethylmethacrylate (PMMA), and polysulfone (PS). Cox regression was used to estimate the association between baseline dialyzers and all-cause mortality as hazard ratios (HRs) and 95% confidence intervals for 1-year mortality adjusting for potential confounders, and propensity score matching analysis was performed.

RESULTS

The distribution of patients treated with each membrane was as follows: PS (56.0%), CTA (17.3%), PES (12.0%), PEPA (7.5%), PMMA (4.9%), PAN (1.2%), and EVAL (1.1%). When data were adjusted using basic factors, with PS as a reference group, the mortality rate was significantly higher in all groups except for the PES group. When data were further adjusted for dialysis-related factors, HRs were significantly higher for the CTA, EVAL, and PEPA groups. When the data were further adjusted for nutrition-and inflammation-related factors, HRs were significantly lower for the PMMA and PES groups compared with the PS group. After propensity score matching, HRs were significantly lower for the PMMA group than for the PS group.

CONCLUSION

The results suggest that the use of different membrane types may affect mortality in hemodialysis patients. However, further long-term prospective studies are needed to clarify these findings, including whether the use of the PMMA membrane can improve prognosis.

Treatment strategy for amyloid hip arthropathy in long-term hemodialysis patients

BACKGROUND

The number of hemodialysis patients has been progressively increasing in our country. On the other hand, chronic hip arthropathy associated with long-term hemodialysis is a devastating problems affecting patients' quality of life. In our previous study, we proposed a classification system for radiological abnormalities seen in hemodialysis-related hip lesions. The purpose of the study was to propose the surgical strategy for hip disorders caused by long-term hemodialysis.

METHODS

Patients with a history of hemodialysis for more than 10 years, 191 hip lesions in 165 consecutive patients who visited our institute due to hip symptoms. Various abnormalities were identified in 116 out of 191 hips. A retrospective assessment of the patient record and radiographs was performed for the included subjects examining the natural course of the disease process as well as the results of surgical treatment.

RESULTS

Seventy-six hip lesions (69.0%) were conservatively managed at the time of the initial visit. Surgeries were performed for 75 hips (64.7%) during the study period. Among those, surgical treatment was indicated for 40 hips at the time of the initial visit. On the other hand, surgeries were performed for 35 hips during the subsequent follow-up period due to progression of the disease process.

CONCLUSIONS

Based on the analysis of our surgical experiences by the retrospective chart review, we have established a flowchart of the treatment strategy for chronic hip arthropathy in long-term hemodialysis patients.

STUDY DESIGN

This study is retrospective clinical study.

High-Performance Membrane Dialyzers and Mortality in Hemodialysis Patients: A 2-Year Cohort Study from the Annual Survey of the Japanese Renal Data Registry

BACKGROUND

Little information is available regarding the type of dialyzer which results in good prognosis. This study is aimed at investigating the association between 7 types of dialyzers and 2-year mortality.

METHODS

We conducted a cohort study using data from a nationwide registry of the Japanese Society for Dialysis Therapy. Subjects were 136,676 patients on maintenance hemodialysis (HD) between 2009 and 2011 who underwent maintenance HD for at least 2 years and were treated with one of the following 7 types of high-performance membrane dialyzers: cellulose triacetate (CTA), ethylene vinyl alcohol (EVAL), polyacrylonitrile (PAN), polyester polymer alloy (PEPA), polyethersulfone (PES), polymethylmethacrylate (PMMA), and polysulfone (PS). Cox regression was used to estimate the association between baseline dialyzers and all-cause 2-year mortality, adjusting for potential confounders.

RESULTS

Data were adjusted using basic factors, with PS as a reference group, and the hazard ratio (HR) was significantly higher in CTA, PMMA, PAN, and EVAL groups. Further data adjustment for Kt/V yielded the same results as were obtained from data adjusted for basic factors. After further adjustment for nutrition- and inflammation-related factors, HR was significantly lowered for the PES and PMMA groups compared with the PS group (HR 0.88; 95% CI 0.82-0.94 and HR 0.84 95% CI 0.76-0.93, respectively). After propensity score matching, HR for the PES and PMMA groups was significantly lowered compared with the PS group.

CONCLUSIONS

The use of different membrane types may affect mortality. Further long-term prospective studies are needed to clarify whether the PES and PMMA membranes can improve prognosis.

Multicentre cross-sectional study for bone-articular lesions associated with dialysis related amyloidosis in Japan

AIM

Dialysis-related amyloidosis (DRA) exhibits multiple bone-articular lesions, such as carpal tunnel syndrome (CTS), trigger finger (TF), spinal canal stenosis (SCS), destructive spondyloarthropathy (DSA), bone cysts, and joint pains. DRA leads to a decrease in activities of daily living (ADL). We investigated the initiation of CTS and TF, and evaluated the relationship between walking disturbances and bone-articular lesions or joint pains.

METHODS

A multicentre cross-sectional study was performed. Eighty-two patients with clinical DRA from 20 hospitals in Japan were evaluated.

RESULTS

Of the 82 patients, the first symptom of DRA was CTS in 39 patients (47.6%) and TF in 21 (25.6%). The mean new-onset vintages of 21 earlier cases in the CTS and TF groups were 86.1 ± 36.3 and 133.2 ± 56.4 (mean ± SD) months, respectively (P = 0.0091). The development of SCS and DSA appeared to be later than CTS and TF. Multiple regression analysis revealed that knee joint pain was a significant contributor to walking disturbances.

CONCLUSION

Carpal tunnel syndrome appeared significantly earlier than TF since the initiation of dialysis. In the advanced phase, knee joint pain was a major cause of decreased ADL in patients with clinical DRA.

A specific nanobody prevents amyloidogenesis of D76N β2-microglobulin in vitro and modifies its tissue distribution in vivo

Systemic amyloidosis is caused by misfolding and aggregation of globular proteins in vivo for which effective treatments are urgently needed. Inhibition of protein self-aggregation represents an attractive therapeutic strategy. Studies on the amyloidogenic variant of β₂-microglobulin, D76N, causing hereditary systemic amyloidosis, have become particularly relevant since fibrils are formed in vitro in physiologically relevant conditions. Here we compare the potency of two previously described inhibitors of wild type β₂-microglobulin fibrillogenesis, doxycycline and single domain antibodies (nanobodies). The β₂-microglobulin -binding nanobody, Nb24, more potently inhibits D76N β₂-microglobulin fibrillogenesis than doxycycline with complete abrogation of fibril formation. In β₂-microglobulin knock out mice, the D76N β₂-microglobulin/ Nb24 pre-formed complex, is cleared from the circulation at the same rate as the uncomplexed protein; however, the analysis of tissue distribution reveals that the interaction with the antibody reduces the concentration of the variant protein in the heart but does not modify the tissue distribution of wild type β₂-microglobulin. These findings strongly support the potential therapeutic use of this antibody in the treatment of systemic amyloidosis.

Amyloidogenicity at a Distance: How Distal Protein Regions Modulate Aggregation in Disease

The misfolding of proteins to form amyloid is a key pathological feature of several progressive, and currently incurable, diseases. A mechanistic understanding of the pathway from soluble, native protein to insoluble amyloid is crucial for therapeutic design, and recent efforts have helped to elucidate the key molecular events that trigger protein misfolding. Generally, either global or local structural perturbations occur early in amyloidogenesis to expose aggregation-prone regions of the protein that can then self-associate to form toxic oligomers. Surprisingly, these initiating structural changes are often caused or influenced by protein regions distal to the classically amyloidogenic sequences. Understanding the importance of these distal regions in the pathogenic process has highlighted many remaining knowledge gaps regarding the precise molecular events that occur in classic aggregation pathways. In this review, we discuss how these distal regions can influence aggregation in disease and the recent technical and conceptual advances that have allowed this insight.

Citrate-stabilized gold nanoparticles hinder fibrillogenesis of a pathological variant of β2-microglobulin

Nanoparticles have repeatedly been shown to enhance fibril formation when assayed with amyloidogenic proteins. Recently, however, evidence casting some doubt about the generality of this conclusion started to emerge. Therefore, to investigate further the influence of nanoparticles on the fibrillation process, we used a naturally occurring variant of the paradigmatic amyloidogenic protein β₂-microglobulin (β2m), namely D76N β2m where asparagine replaces aspartate at position 76. This variant is responsible for aggressive systemic amyloidosis. After characterizing the interaction of the variant with citrate-stabilized gold nanoparticles (Cit-AuNPs) by NMR and modeling, we analyzed the fibril formation by three different methods: thioflavin T fluorescence, native agarose gel electrophoresis and transmission electron microscopy. The NMR evidence indicated a fast-exchange interaction involving preferentially specific regions of the protein that proved, by subsequent modeling, to be consistent with a dimeric adduct interacting with Cit-AuNPs. The fibril detection assays showed that AuNPs are able to hamper D76N β2m fibrillogenesis through an effective interaction that competes with protofibril formation or recruitment. These findings open promising perspectives for the optimization of the nanoparticle surface to design tunable interactions with proteins.

Increased β-Sheet Dynamics and D-E Loop Repositioning Are Necessary for Cu(II)-Induced Amyloid Formation by β-2-Microglobulin

β-2-Microglobulin (β2m) forms amyloid fibrils in the joints of patients undergoing dialysis treatment as a result of kidney failure. One of the ways in which β2m can be induced to form amyloid fibrils in vitro is via incubation with stoichiometric amounts of Cu(II). To better understand the structural changes caused by Cu(II) binding that allow β2m to form amyloid fibrils, we compared the effect of Ni(II) and Zn(II) binding, which are two similarly sized divalent metal ions that do not induce β2m amyloid formation. Using hydrogen/deuterium exchange mass spectrometry (HDX/MS) and covalent labeling MS, we find that Ni(II) has little effect on β2m structure, despite binding in the same region of the protein as Cu(II). This observation indicates that subtle differences in the organization of residues around Cu(II) cause distant changes that are necessary for oligomerization and eventual amyloid formation. One key difference that we find is that only Cu(II), not Ni(II) or Zn(II), is able to cause the cis-trans isomerization of Pro32 that is an important conformational switch that initiates β2m amyloid formation. By comparing HDX/MS data from the three metal-β2m complexes, we also discover that increased dynamics in the β-sheet formed by the A, B, D, and E β strands of the protein and repositioning of residues in the D-E loop are necessary aspects of β2m forming an amyloid-competent dimer. Altogether, our results reveal new structural insights into the unique effect of Cu(II) in the metal-induced amyloid formation of β2m.

Relationship of Carpal Canal Contents Volume to Carpal Canal Pressure in Carpal Tunnel Syndrome Patients

Forty patients long-term haemodialysis with a second recurrence of carpal tunnel syndrome and concomitant loss of flexor tendon function due to flexor adhesions were treated by excision of the flexor digitorum superficialis tendons. During the procedure the carpal canal pressure was measured using a continuous infusion technique. The preoperative mean carpal canal pressure was 81 (SD, 53) mmHg. After removal of all the flexor digitorum superficialis tendons, the carpal canal pressure decreased to 10 (SD, 8) mmHg. The clinical symptoms of carpal tunnel syndrome were relieved and hand strength and finger motion were improved in all patients.

Dialysis-related amyloidosis: challenges and solutions

Amyloidosis refers to the extracellular tissue deposition of fibrils composed of low-molecular-weight subunits of a variety of proteins. These deposits may result in a wide range of clinical manifestations depending upon their type, location, and the amount of deposition. Dialysis-related amyloidosis is a serious complication of long-term dialysis therapy and is characterized by the deposition of amyloid fibrils, principally composed of β2 microglobulins (β2M), in the osteoarticular structures and viscera. Most of the β2M is eliminated through glomerular filtration and subsequent reabsorption and catabolism by the proximal tubules. As a consequence, the serum levels of β2M are inversely related to the glomerular filtration rate; therefore, in end-stage renal disease patients, β2M levels increase up to 60-fold. Serum levels of β2M are also elevated in several pathological conditions such as chronic inflammation, liver disease, and above all, in renal dysfunction. Retention of amyloidogenic protein has been attributed to several factors including type of dialysis membrane, prolonged uremic state and/or decreased diuresis, advanced glycation end products, elevated levels of cytokines and dialysate. Dialysis treatment per se has been considered to be an inflammatory stimulus, inducing cytokine production (such as interleukin-1, tumor necrosis factor-α, interleukin-6) and complement activation. The released cytokines are thought to stimulate the synthesis and release of β2M by the macrophages and/or augment the expression of human leukocyte antigens (class I), increasing β2M expression. Residual renal function is probably the best determinant of β2M levels. Therefore, it has to be maintained as long as possible. In this article, we will focus our attention on the etiology of dialysis-related amyloidosis, its prevention, therapy, and future solutions.

Amyloids: from Pathogenesis to Function

The term "amyloids" refers to fibrillar protein aggregates with cross-β structure. They have been a subject of intense scrutiny since the middle of the previous century. First, this interest is due to association of amyloids with dozens of incurable human diseases called amyloidoses, which affect hundreds of millions of people. However, during the last decade the paradigm of amyloids as pathogens has changed due to an increase in understanding of their role as a specific variant of quaternary protein structure essential for the living cell. Thus, functional amyloids are found in all domains of the living world, and they fulfill a variety of roles ranging from biofilm formation in bacteria to long-term memory regulation in higher eukaryotes. Prions, which are proteins capable of existing under the same conditions in two or more conformations at least one of which having infective properties, also typically have amyloid features. There are weighty reasons to believe that the currently known amyloids are only a minority of their real number. This review provides a retrospective analysis of stages in the development of amyloid biology that during the last decade resulted, on one hand, in reinterpretation of the biological role of amyloids, and on the other hand, in the development of systems biology of amyloids, or amyloidomics.

Characterization of Salt-Induced Oligomerization of Human β2-Microglobulin at Low pH

Misfolding and amyloid aggregation of human β2-microglobulin (β2m) have been linked to dialysis-related amyloidosis. Previous studies have shown that in the presence of different salt concentrations and at pH 2.5, β2m assembles into aggregates with distinct morphologies. However, the structural and mechanistic details of the aggregation of β2m, giving rise to different morphologies, are poorly understood. In this work, we have extensively characterized the salt-induced oligomers of the acid-unfolded state of β2m using an array of biophysical tools including steady-state and time-resolved fluorescence, circular dichroism, dynamic light scattering, and atomic force microscopy imaging. Fluorescence studies using the oligomer-sensitive molecular rotor, 4-(dicyanovinyl)-julolidine, in conjunction with the light scattering and cross-linking assay indicated that at low salt (NaCl) concentrations β2m exists as a disordered monomer, capable of transforming into ordered amyloid. In the presence of higher concentrations of salt, β2m aggregates into a larger oligomeric species that does not appear to transform into amyloid fibrils. Site-specific fluorescence experiments using single Trp variants of β2m revealed that the middle region of the protein is incorporated into these oligomers, whereas the C-terminal segment is highly exposed to bulk water. Additionally, stopped-flow kinetic experiments indicated that the formation of hydrophobic core and oligomerization occur concomitantly. Our results revealed the distinct pathways by which β2m assembles into oligomers and fibrils.

Rational design of mutations that change the aggregation rate of a protein while maintaining its native structure and stability

A wide range of human diseases is associated with mutations that, destabilizing proteins native state, promote their aggregation. However, the mechanisms leading from folded to aggregated states are still incompletely understood. To investigate these mechanisms, we used a combination of NMR spectroscopy and molecular dynamics simulations to compare the native state dynamics of Beta-2 microglobulin (β2m), whose aggregation is associated with dialysis-related amyloidosis, and its aggregation-resistant mutant W60G. Our results indicate that W60G low aggregation propensity can be explained, beyond its higher stability, by an increased average protection of the aggregation-prone residues at its surface. To validate these findings, we designed β2m variants that alter the aggregation-prone exposed surface of wild-type and W60G β2m modifying their aggregation propensity. These results allowed us to pinpoint the role of dynamics in β2m aggregation and to provide a new strategy to tune protein aggregation by modulating the exposure of aggregation-prone residues.

A Population Shift between Sparsely Populated Folding Intermediates Determines Amyloidogenicity

The balance between protein folding and misfolding is a crucial determinant of amyloid assembly. Transient intermediates that are sparsely populated during protein folding have been identified as key players in amyloid aggregation. However, due to their ephemeral nature, structural characterization of these species remains challenging. Here, using the power of nonuniformly sampled NMR methods we investigate the folding pathway of amyloidogenic and nonamyloidogenic variants of β2-microglobulin (β2m) in atomic detail. Despite folding via common intermediate states, we show that the decreased population of the aggregation-prone ITrans state and population of a less stable, more dynamic species ablate amyloid formation by increasing the energy barrier for amyloid assembly. The results show that subtle changes in conformational dynamics can have a dramatic effect in determining whether a protein is amyloidogenic, without perturbation of the mechanism of protein folding.

Utility of Ultrasonography of the Median Nerve With a High-Frequency Probe for the Diagnosis of Dialysis-Related Carpal Tunnel Syndrome

This cross-sectional study aimed to determine the utility of ultrasonography with improved resolution using a high-frequency probe for dialysis-related carpal tunnel syndrome (CTS). This study targeted 125 hemodialysis patients at our hospital. A 12 MHz probe was placed on the carpal tunnel area to identify the median nerve. The compression rate of the nerve was calculated by measuring the smallest diameter of the compressed nerve and largest diameter of the unaffected part. To quantify CTS symptoms, we determined the presence of Tinel's sign, measured pinch strength, and used questionnaires to assess numbness and pain. The association of these clinical data with the compression rate was examined. Mean compression rate was 12.1 ± 1.1%. The compression rate cutoff value for those positive with Tinel's sign was 25%, (sensitivity and specificity were 0.80 and 0.91, respectively), and that for those with a history of CTS surgery was 25% (sensitivity and specificity were 0.67 and 0.89, respectively). Multiple regression analysis identified duration of dialysis, β2-microglobulin(β2-Mg) concentration, positivity for Tinel's sign, history of CTS surgery, and pinch strength as independent compression rate determinants. Notably, compression rates were significantly higher in patients with a ≥4-year duration of dialysis and a β2-Mg level of 20 mg/L or more. The compression rate of the median nerve measured by an improved ultrasound device significantly correlated with clinical symptoms, medical history, and serological features associated with dialysis-related CTS. Because ultrasonography is non-invasive, the examination might be a simple method especially for early diagnosis of dialysis-related CTS.

The Implication and Significance of Beta 2 Microglobulin: A Conservative Multifunctional Regulator

OBJECTIVE

This review focuses on the current knowledge on the implication and significance of beta 2 microglobulin (β2M), a conservative immune molecule in vertebrate.

DATA SOURCES

The data used in this review were obtained from PubMed up to October 2015. Terms of β2M, immune response, and infection were used in the search.

STUDY SELECTIONS

Articles related to β2M were retrieved and reviewed. Articles focusing on the characteristic and function of β2M were selected. The exclusion criteria of articles were that the studies on β2M-related molecules.

RESULTS

β2M is critical for the immune surveillance and modulation in vertebrate animals. The dysregulation of β2M is associated with multiple diseases, including endogenous and infectious diseases. β2M could directly participate in the development of cancer cells, and the level of β2M is deemed as a prognostic marker for several malignancies. It also involves in forming major histocompatibility complex (MHC class I or MHC I) or like heterodimers, covering from antigen presentation to immune homeostasis.

CONCLUSIONS

Based on the characteristic of β2M, it or its signaling pathway has been targeted as biomedical or therapeutic tools. Moreover, β2M is highly conserved among different species, and overall structures are virtually identical, implying the versatility of β2M on applications.

A systematic molecular dynamics approach to the structural characterization of amyloid aggregation propensity of β2-microglobulin mutant D76N

Beta-2 microglobulin (β2m) is an amyloidogenic protein belonging to the immunoglobulin superfamily, responsible for the dialysis-related amyloidosis (DRA).

Decoding the Structural Bases of D76N ß2-Microglobulin High Amyloidogenicity through Crystallography and Asn-Scan Mutagenesis

D76N is the first natural variant of human β-2 microglobulin (β2m) so far identified. Contrary to the wt protein, this mutant readily forms amyloid fibres in physiological conditions, leading to a systemic and severe amyloidosis. Although the Asp76Asn mutant has been extensively characterized, the molecular bases of its instability and aggregation propensity remain elusive. In this work all Asp residues of human β2m were individually substituted to Asn; D-to-N mutants (D34N, D38N, D53N, D59N, D96N and D98N) were characterised in terms of thermodynamic stability and aggregation propensity. Moreover, crystal structures of the D38N, D53N, D59N and D98N variants were solved at high-resolution (1.24–1.70 Å). Despite showing some significant variations in their thermal stabilities, none showed the dramatic drop in melting temperature (relative to the wt protein) as observed for the pathogenic mutant. Consistently, none of the variants here described displayed any increase in aggregation propensity under the experimental conditions tested. The crystal structures confirmed that D-to-N mutations are generally well tolerated, and lead only to minor reorganization of the side chains in close proximity of the mutated residue. D38N is the only exception, where backbone readjustments and a redistribution of the surface electrostatic charges are observed. Overall, our results suggest that neither removing negative charges at sites 34, 38, 53, 59, 96 and 98, nor the difference in β2m pI, are the cause of the aggressive phenotype observed in D76N. We propose that the dramatic effects of the D76N natural mutation must be linked to effects related to the crucial location of this residue within the β2m fold.

Endocytosed 2-Microglobulin Amyloid Fibrils Induce Necrosis and Apoptosis of Rabbit Synovial Fibroblasts by Disrupting Endosomal/Lysosomal Membranes: A Novel Mechanism on the Cytotoxicity of Amyloid Fibrils

Dialysis-related amyloidosis is a major complication in long-term hemodialysis patients. In dialysis-related amyloidosis, β2-microglobulin (β2-m) amyloid fibrils deposit in the osteoarticular tissue, leading to carpal tunnel syndrome and destructive arthropathy with cystic bone lesions, but the mechanism by which these amyloid fibrils destruct bone and joint tissue is not fully understood. In this study, we assessed the cytotoxic effect of β2-m amyloid fibrils on the cultured rabbit synovial fibroblasts. Under light microscopy, the cells treated with amyloid fibrils exhibited both necrotic and apoptotic changes, while the cells treated with β2-m monomers and vehicle buffer exhibited no morphological changes. As compared to β2-m monomers and vehicle buffer, β2-m amyloid fibrils significantly reduced cellular viability as measured by the lactate dehydrogenase release assay and the 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay and significantly increased the percentage of apoptotic cells as measured by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method. β2-m amyloid fibrils added to the medium adhered to cell surfaces, but did not disrupt artificial plasma membranes as measured by the liposome dye release assay. Interestingly, when the cells were incubated with amyloid fibrils for several hours, many endosomes/lysosomes filled with amyloid fibrils were observed under confocal laser microscopy and electron microscopy, Moreover, some endosomal/lysosomal membranes were disrupted by intravesicular fibrils, leading to the leakage of the fibrils into the cytosol and adjacent to mitochondria. Inhibition of actin-dependent endocytosis by cytochalasin D attenuated the toxicity of amyloid fibrils. These results suggest that endocytosed β2-m amyloid fibrils induce necrosis and apoptosis by disrupting endosomal/lysosomal membranes, and this novel mechanism on the cytotoxicity of amyloid fibrils is described.

A covalent homodimer probing early oligomers along amyloid aggregation

Early oligomers are crucial in amyloid aggregation; however, due to their transient nature they are among the least structurally characterized species. We focused on the amyloidogenic protein beta2-microglobulin (β2m) whose early oligomers are still a matter of debate. An intermolecular interaction between D strands of facing β2m molecules was repeatedly observed, suggesting that such interface may be relevant for β2m dimerization. In this study, by mutating Ser33 to Cys, and assembling the disulphide-stabilized β2m homodimer (DimC33), such DD strand interface was locked. Although the isolated DimC33 display a stability similar to wt β2m under native conditions, it shows enhanced amyloid aggregation propensity. Three distinct crystal structures of DimC33 suggest that dimerization through the DD interface is instrumental for enhancing DimC33 aggregation propensity. Furthermore, the crystal structure of DimC33 in complex with the amyloid-specific dye Thioflavin-T pinpoints a second interface, which likely participates in the first steps of β2m aggregation. The present data provide new insight into β2m early steps of amyloid aggregation.

Optimization of dilution refolding conditions for a camelid single domain antibody against human beta-2-microglobulin

Single domain antibody (sdAb) is often expressed as inclusion bodies in Escherichia coli cytoplasm. Establishing an effective in vitro refolding method for sdAb obtained from inclusion bodies would be important for sdAb research. In this study, dilution refolding condition for a camelid sdAb specific against human beta-2-microglobulin was optimized for the sdAb purified from the inclusion bodies of E. coli BL21 (DE3). Single factor methods based on protein concentration, velocity of dilution, incubation time and refolding buffer composition were first investigated. Then the key refolding buffer compositions were selected for further optimization by means of the Box-Behnken design of response surface methodology (RSM). The activity of the refolded sdAb was determined by measuring its specific antigen-binding ability using indirect ELISA. The optimized refolding condition of sdAb consisted of a 10-fold dilution in 10 mM Tris-HCl (pH 8.0) containing 1.24 mM GSH, 1mM GSSG, 352 mM L-Arg, 0.65% PEG-2000, and a 16 h incubation at 4 °C. Further comparison of the activities between the refolded sdAb and purified soluble sdAb expressed in E. coli Rosetta-gami (DE3) pLysS indicated that the sdAb was correctly refolded, as assayed by isothermal titration calorimetry. This work could provide an important strategy for the recombinant production and application of sdAb.

Supersaturation-Limited and Unlimited Phase Spaces Compete to Produce Maximal Amyloid Fibrillation near the Critical Micelle Concentration of Sodium Dodecyl Sulfate

Although various natural and synthetic compounds have been shown to accelerate or inhibit the formation of amyloid fibrils, the mechanisms by which they achieve these adverse effects in a concentration-dependent manner currently remain unclear. Sodium dodecyl sulfate (SDS), one of the compounds that has adverse effects on fibrillation, is the most intensively studied. Here we examined the effects of a series of detergents including SDS on the amyloid fibrillation of β2-microglobulin at pH 7.0, a protein responsible for dialysis-related amyloidosis. In all the detergents examined (i.e., SDS, sodium decyl sulfate, sodium octyl sulfate, and sodium deoxycholate), amyloid fibrillation was accelerated and inhibited at concentrations near the critical micelle concentration (CMC) and higher than CMC, respectively. The most stable conformation changed from monomers with a β-structure to amyloid fibrils with a β-structure and then to α-helical complexes with micelles with an increase in detergent concentrations. These results suggest that competition between supersaturation-limited fibrillation and unlimited mixed micelle formation between proteins and micelles underlies the detergent concentration-dependent complexity of amyloid fibrillation.

Destructive Spondyloarthropathy in Patients on Long-Term Peritoneal Dialysis or Hemodialysis

Destructive spondyloarthropathy (DSA) is the most serious spinal complication of dialysis-related amyloidosis in patients on long-term hemodialysis (HD), but we could not find any information about DSA in patients on peritoneal dialysis (PD) for over 10 years. We retrospectively evaluated factors contributing to DSA in HD and PD patients. Sixty-seven patients on dialysis for 10 to 19 years were compared between a PD group (n = 23) or a HD group (n = 44). In the PD group, nine patients (39%) developed DSA. The mean age of DSA patients was significantly higher than that of non-DSA patients (66.2 ± 10.0 vs. 51.0 ± 12.8 years, P = 0.03). The frequency of cervical spine DSA did not show any difference between the PD and HD groups, but the frequency of lumbar spine DSA showed a significant difference (22% vs. 5%, P = 0.04). The serum beta-2 microglobulin (B2MG) level was significantly higher in PD patients than in HD patients (38.4 mg/L vs. 27.4 mg/L, P = 0.0025). Mechanical stress such as elevation of the intra-abdominal pressure due to infusion of PD fluid (1500 mL to 2000 mL) for over 10 years might contribute to lumbar DSA in patients on long-term PD.

Probing the influence of citrate-capped gold nanoparticles on an amyloidogenic protein

Nanoparticles (NPs) are known to exhibit distinct physical and chemical properties compared with the same materials in bulk form. NPs have been repeatedly reported to interact with proteins, and this interaction can be exploited to affect processes undergone by proteins, such as fibrillogenesis. Fibrillation is common to many proteins, and in living organisms, it causes tissue-specific or systemic amyloid diseases. The nature of NPs and their surface chemistry is crucial in assessing their affinity for proteins and their effects on them. Here we present the first detailed structural characterization and molecular mechanics model of the interaction between a fibrillogenic protein, β2-microglobulin, and a NP, 5 nm hydrophilic citrate-capped gold nanoparticles. NMR measurements and simulations at multiple levels (enhanced sampling molecular dynamics, Brownian dynamics, and Poisson-Boltzmann electrostatics) explain the origin of the observed protein perturbations mostly localized at the amino-terminal region. Experiments show that the protein-NP interaction is weak in the physiological-like, conditions and do not induce protein fibrillation. Simulations reproduce these findings and reveal instead the role of the citrate in destabilizing the lower pH protonated form of β2-microglobulin. The results offer possible strategies for controlling the desired effect of NPs on the conformational changes of the proteins, which have significant roles in the fibrillation process.

Wild type beta-2 microglobulin and DE loop mutants display a common fibrillar architecture

Beta-2 microglobulin (β2m) is the protein responsible for a pathologic condition known as dialysis related amyloidosis. In recent years an important role has been assigned to the peptide loop linking strands D and E (DE loop) in determining β2m stability and amyloid propensity. Several mutants of the DE loop have been studied, showing a good correlation between DE loop geometrical strain, protein stability and aggregation propensity. However, it remains unclear whether the aggregates formed by wild type (wt) β2m and by the DE loop variants are of the same kind, or whether the mutations open new aggregation pathways. In order to address this question, fibrillar samples of wt and mutated β2m variants have been analysed by means of atomic force microscopy and infrared spectroscopy. The data here reported indicate that the DE loop mutants form aggregates with morphology and structural organisation very similar to the wt protein. Therefore, the main effect of β2m DE loop mutations is proposed to stem from the different stabilities of the native fold. Considerations on the structural role of the DE loop in the free monomeric β2m and as part of the Major Histocompatibility Complex are also presented.

Systemic amyloidosis: lessons from β2-microglobulin

β₂-Microglobulin is responsible for systemic amyloidosis affecting patients undergoing long-term hemodialysis. Its genetic variant D76N causes a very rare form of familial systemic amyloidosis. These two types of amyloidoses differ significantly in terms of the tissue localization of deposits and for major pathological features. Considering how the amyloidogenesis of the β₂-microglobulin mechanism has been scrutinized in depth for the last three decades, the comparative analysis of molecular and pathological properties of wild type β₂-microglobulin and of the D76N variant offers a unique opportunity to critically reconsider the current understanding of the relation between the protein's structural properties and its pathologic behavior.