Dialysis-related Amyloidosis Research Articles

Inhibition of β2-Microglobulin Amyloid Fibril Formation by α2-Macroglobulin

The relationship between various amyloidoses and chaperones is gathering attention. In patients with dialysis-related amyloidosis, α(2)-macroglobulin (α2M), an extracellular chaperone, forms a complex with β(2)-microglobulin (β2-m), a major component of amyloid fibrils, but the molecular mechanisms and biological implications of the complex formation remain unclear. Here, we found that α2M substoichiometrically inhibited the β2-m fibril formation at a neutral pH in the presence of SDS, a model for anionic lipids. Binding analysis showed that the binding affinity between α2M and β2-m in the presence of SDS was higher than that in the absence of SDS. Importantly, SDS dissociated tetrameric α2M into dimers with increased surface hydrophobicity. Western blot analysis revealed that both tetrameric and dimeric α2M interacted with SDS-denatured β2-m. At a physiologically relevant acidic pH and in the presence of heparin, α2M was also dissociated into dimers, and both tetrameric and dimeric α2M interacted with β2-m, resulting in the inhibition of fibril growth reaction. These results suggest that under conditions where native β2-m is denatured, tetrameric α2M is also converted to dimeric form with exposed hydrophobic surfaces to favor the hydrophobic interaction with denatured β2-m, thus dimeric α2M as well as tetrameric α2M may play an important role in controlling β2-m amyloid fibril formation.

Removal of intact β2‐microglobulin at neutral ph by using seed‐conjugated polymer beads prepared with β2‐microglobulin‐derived peptide (58–67)

Removal of β2-microglobulin (β2M) from the blood of patients suffering from kidney dysfunction is crucial to protect those individuals from getting the diseased state of dialysis-related amyloidosis. By harnessing the nucleation-dependent fibrillation process of amyloidogenesis, a β2M removal strategy has been proposed by preparing seed-conjugated polymer beads and assimilating soluble β2M to the fibrils on the surface at neutral pH. A novel peptide segment of β2M ranging from residue 58 to residue 67 (Lys-Asp-Trp-Ser-Phe-Tyr-Leu-Leu-Tyr-Tyr), which was capable of being fibrillated at neutral pH was isolated. Charge interaction between the positive N-terminal lysine and the negative C-terminal α-carboxylic group was demonstrated to be critical for the molecular self-assembly leading to the peptide fibril formation by favoring β-sheet conformation. Because the peptide fibrils were successful to seed intact β2M at neutral pH, the fibrils were immobilized on polymer beads of HiCore resins, and the resulting seed-conjugated beads were used to accrete intact β2M in the form of fibrils elongated on the bead surface. Its efficiency of the β2M removal was improved by placing the seed-immobilized beads in the middle of a continuous flow of the β2M-containing solution as practiced in the blood circulation during the hemodialysis. Therefore, this β2M removal system is suggested to exhibit high specificity, high binding capacity, and cost-effectiveness appropriate for eventual clinical application to remove β2M from the blood of renal failure patients.

Enhanced molecular chaperone activity of the small heat‐shock protein αB‐crystallin following covalent immobilization onto a solid‐phase support

The well-characterized small heat-shock protein, alphaB-crystallin, acts as a molecular chaperone by interacting with unfolding proteins to prevent their aggregation and precipitation. Structural perturbation (e.g., partial unfolding) enhances the in vitro chaperone activity of alphaB-crystallin. Proteins often undergo structural perturbations at the surface of a synthetic material, which may alter their biological activity. This study investigated the activity of alphaB-crystallin when covalently bound to a support surface; alphaB-crystallin was immobilized onto a range of solid material surfaces, and its characteristics and chaperone activity were assessed. Immobilization was achieved via a plasma-deposited thin polymeric interlayer containing aldehyde surface groups and reductive amination, leading to the covalent binding of alphaB-crystallin lysine residues to the surface aldehyde groups via Schiff-base linkages. Immobilized alphaB-crystallin was characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and quartz crystal microgravimetry, which showed that 300 ng cm(-2) (dry mass) of oligomeric alphaB-crystallin was bound to the surface. Immobilized alphaB-crystallin exhibited a significant enhancement (up to 5000-fold, when compared with the equivalent activity of alphaB-crystallin in solution) of its chaperone activity against various proteins undergoing both amorphous and amyloid fibril forms of aggregation. The enhanced molecular chaperone activity of immobilized alphaB-crystallin has potential applications in preventing protein misfolding, including against amyloid disease processes, such as dialysis-related amyloidosis, and for biodiagnostic detection of misfolded proteins.

Effect of Tetracyclines on the Dynamics of Formation and Destructuration of β2-Microglobulin Amyloid Fibrils

The discovery of methods suitable for the conversion in vitro of native proteins into amyloid fibrils has shed light on the molecular basis of amyloidosis and has provided fundamental tools for drug discovery. We have studied the capacity of a small library of tetracycline analogues to modulate the formation or destructuration of β2-microglobulin fibrils. The inhibition of fibrillogenesis of the wild type protein was first established in the presence of 20% trifluoroethanol and confirmed under a more physiologic environment including heparin and collagen. The latter conditions were also used to study the highly amyloidogenic variant, P32G. The NMR analysis showed that doxycycline inhibits β2-microglobulin self-association and stabilizes the native-like species through fast exchange interactions involving specific regions of the protein. Cell viability assays demonstrated that the drug abolishes the natural cytotoxic activity of soluble β2-microglobulin, further strengthening a possible in vivo therapeutic exploitation of this drug. Doxycycline can disassemble preformed fibrils, but the IC(50) is 5-fold higher than that necessary for the inhibition of fibrillogenesis. Fibril destructuration is a dynamic and time-dependent process characterized by the early formation of cytotoxic protein aggregates that, in a few hours, convert into non-toxic insoluble material. The efficacy of doxycycline as a drug against dialysis-related amyloidosis would benefit from the ability of the drug to accumulate just in the skeletal system where amyloid is formed. In these tissues, the doxycycline concentration reaches values several folds higher than those resulting in inhibition of amyloidogenesis and amyloid destructuration in vitro.

A Case of Small-intestine Perforation Due to Dialysis-Related Amyloidosis

長期透析患者の透析アミロイドーシスによる小腸穿孔のまれな1例を経験した．症例は79歳の女性で，17年間の血液透析歴がある．透析導入後，右手根幹症候群手術2回，S状結腸憩室出血手術を受け，狭心症，急性心不全，肺結核の治療を受けていた．外傷歴のない右大腿骨頸部骨折にて入院し，手術を受けた．術直後より腹痛と下痢を認め，術後2日目に腹痛が増強した．CT上，腹腔内の遊離ガス像と腹水貯留を認め緊急手術を施行した．小腸に穿孔部を2か所認めたため切除吻合を行った．病理学的に穿孔部周囲の粘膜下層の小血管壁にアミロイドの沈着を認めた．術後，創感染，深在性真菌症，難治性下痢，急性心不全を発症したが保存的治療で改善し，緊急術後78日目に軽快退院した．

Carpal tunnel syndrome in hemodialysis patients as a dialysis-related amyloidosis manifestation – incidence, risk factors and results of surgical treatment

SummaryBackgroundCarpal tunnel syndrome (CTS) is the most common complication of dialysis-related amyloidosis (DRA) developing in patients on long-term dialysis therapy. The aim of this study was to evaluate the incidence of CTS and identify factors influencing the development of CTS in patients on maintenance hemodialysis, as well as results of its surgical treatment.Material/MethodsThe study included 386 patients, among whom CTS was diagnosed in 40 patients (10.4%) on the basis of signs and physical symptoms, as well as by nerve conduction. The group of patients with CTS and the group of patients without CTS were compared according to age (mean 54.50 vs. 56.48 years) and duration of dialysis treatment. Initial analysis of CTS incidence by sex, presence of anti-HCV antibodies, and location of arterio-venous fistula (AV fistula) was undertaken.ResultsDuration of dialysis treatment was the statistically significant risk factor for the development of CTS (16.05 vs. 4.51 years; p<0.0001). Among patients treated for a long period on hemodialysis (20–30 years), 100% required surgical release procedures, while 66.66% of those treated for 15–19 years, 42.1% of those treated for 10–14 years, and 1.6% of those treated for less than 10 years. CTS was diagnosed more often in anti-HCV-positive patients as compared with anti-HCV-negative patients (47.5 vs. 6.9%; p<0.0001). No significant differences were found when comparing CTS incidence by sex or between the development of CTS requiring surgical release intervention and location of the AV fistula.ConclusionsSurgical release procedure of the carpal tunnel gave good treatment results in patients with CTS.

Treatment of Dialysis-related Amyloidosis of the Shoulder

Treatment of Dialysis-related Amyloidosis of the Shoulder

β₂-microglobulin forms three-dimensional domain-swapped amyloid fibrils with disulfide linkages.

Summaryβ2-microglobulin (β2m) is the light chain of type I major histocompatibility complex. It deposits as amyloid fibrils within joints during long-term hemodialysis treatment. Despite the devastating effects of dialysis-related amyloidosis, full understanding of how fibrils form from soluble β2m remains elusive. Here we show that β2m can oligomerize and fibrillize via 3D domain swapping. Isolating a covalently bound, domain-swapped dimer from β2m oligomers on the pathway to fibrils, we were able to determine its crystal structure. The hinge loop which connects the swapped domain to the core domain includes the fibrillizing segment LSFSKD, whose atomic structure we also determined. The LSFSKD structure reveals a Class 5 steric zipper, akin to other amyloid spines. The structures of the dimer and the zipper spine fit well into an atomic model for this fibrillar form of β2m, which assembles slowly under physiological conditions.

Intermolecular alignment in β2-microglobulin amyloid fibrils.

The deposition of amyloid-like fibrils, composed primarily of the 99-residue protein β2-microglobulin (β2m), is one of the characteristic symptoms of dialysis-related amyloidosis. Fibrils formed in vitro at low pH and low salt concentration share many properties with the disease related fibrils and have been extensively studied by a number of biochemical and biophysical methods. These fibrils contain a significant β-sheet core and have a complex cryoEM electron density profile. Here, we investigate the intrasheet arrangement of the fibrils by means of 15N−13C MAS NMR correlation spectroscopy. We utilize a fibril sample grown from a 50:50 mixture of 15N,12C- and 14N,13C-labeled β2m monomers, the latter prepared using 2-13C glycerol as the carbon source. Together with the use of ZF-TEDOR mixing, this sample allowed us to observe intermolecular 15N−13C backbone-to-backbone contacts with excellent resolution and good sensitivity. The results are consistent with a parallel, in-register arrangement of the protein subunits in the fibrils and suggest that a significant structural reorganization occurs from the native to the fibril state.

Nanoporous protein matrix made of amyloid fibrils of β2‐microglobulin

Amyloid fibrils are considered as novel nanomaterials because of their nanoscale width, a regular constituting structure of cross β-sheet conformation, and considerable mechanical strength. By using an amyloidogenic protein of β(2)-microglobulin (β(2)M) related to dialysis-related amyloidosis, nanoporous protein matrix has been prepared. The β(2) M granules made of around 15 monomers showed an average size of 23.1 nm. They formed worm-like fibrils at pH 7.4 in 20 mM sodium phosphate containing 0.15 M NaCl following vigorous nondirectional shaking incubation, in which they became laterally associated and interwound to generate the porous amyloid fibrillar matrix with an average pore size of 30-50 nm. This nanoporous protein matrix was demonstrated to be selectively disintegrated by reducing agents, such as tris-(2-carboxyethyl) phosphine. High surface area with nanopores on the surface has been suggested to make the matrix of β(2) M amyloid fibrils particularly suitable for applications in the area of nanobiotechnology including drug delivery and tissue engineering.

A case of hemodialysis-associated amyloidosis localized to the external auditory canal

Amyloidosis of the external auditory canal is extremely rare. Only 12 cases, including the present case, have been reported, and this is the second reported case attributed to dialysis. This case involved a 56-year-old man who had been on dialysis for 12 years. A tumor was visible in the right external auditory canal and caused pain. The tumor was resected at another hospital, but subsequently recurred with rapid increase in size due to infection. We therefore performed further resection at our hospital. We report our experiences herein, together with a discussion of the literature.

Glycosaminoglycans enhance the fibrillation propensity of the β 2-microglobulin cleavage variant – ΔK58-β 2m

Dialysis related amyloidosis (DRA) is a serious complication to long-term hemodialysis treatment which causes clinical symptoms such as carpal tunnel syndrome and destructive arthropathies. The disease is characterized by the assembly and deposition of β 2-microglobulin (β 2m) predominantly in the musculoskeletal system, but the initiating events leading to β 2m amyloidogenesis and the molecular mechanisms underlying amyloid fibril formation are still unclear. Glycosaminoglycans (GAGs) and metal ions have been shown to be related to the onset of protein aggregation and to promote de novo fiber formation. In this study, we show that fibrillogenesis of a cleavage variant of β 2m, ΔK58-β 2m, which can be found in the circulation of hemodialysis patients and is able to fibrillate at near-physiological pH in vitro, is affected by the presence of copper ions and heparan sulfate. It is found that the fibrils generated when heparan sulfate is present have increased length and diameter, and possess enhanced stability and seeding properties. However, when copper ions are present the fibrils are short, thin and less stable, and form at a slower rate. We suggest that heparan sulfate stabilizes the cleaved monomers in the early aggregates, hereby promoting the assembly of these into fibrils, whereas the copper ions appear to have a destabilizing effect on the monomers. This keeps them in a structure forming amorphous aggregates for a longer period of time, leading to the formation of spherical bodies followed by the assembly of fibrils. Hence, the in vivo formation of amyloid fibrils in DRA could be initiated by the generation of ΔK58-β 2m which spontaneously aggregate and form fibrils. The fibrillogenesis is enhanced by the involvement of GAGs and/or metal ions, and results in amyloid-like fibrils able to promote the de novo formation of β 2m amyloid by a scaffold mechanism.

Magic angle spinning NMR analysis of beta2-microglobulin amyloid fibrils in two distinct morphologies.

Beta(2)-microglobulin (beta(2)m) is the major structural component of amyloid fibrils deposited in a condition known as dialysis-related amyloidosis. Despite numerous studies that have elucidated important aspects of the fibril formation process in vitro, and a magic angle spinning (MAS) NMR study of the fibrils formed by a small peptide fragment, structural details of beta(2)m fibrils formed by the full-length 99-residue protein are largely unknown. Here, we present a site-specific MAS NMR analysis of fibrils formed by the full-length beta(2)m protein and compare spectra of fibrils prepared under two different conditions. Specifically, long straight (LS) fibrils are formed at pH 2.5, while a very different morphology denoted as worm-like (WL) fibrils is observed in preparations at pH 3.6. High-resolution MAS NMR spectra have allowed us to obtain (13)C and (15)N resonance assignments for 64 residues of beta(2)m in LS fibrils, including part of the highly mobile N-terminus. Approximately 25 residues did not yield observable signals. Chemical shift analysis of the sequentially assigned residues indicates that these fibrils contain an extensive beta-sheet core organized in a non-native manner, with a trans-P32 conformation. In contrast, WL fibrils exhibit more extensive dynamics and appear to have a smaller beta-sheet core than LS fibrils, although both cores seem to share some common elements. Our results suggest that the distinct macroscopic morphological features observed for the two types of fibrils result from variations in structure and dynamics at the molecular level.

慢性血液透析患者における肩関節超音波検査の検討― 透析アミロイドーシス診断の指標としてのshoulder-capsular distance (SCD)―

Dialysis-related amyloidosis (DRA) is a serious complication in patients receiving long-term hemodialysis. Intrigued by the fact that the shoulder joint is primarily favored by DRA, we measured the shoulder-capsular distance (SCD) by ultrasonography to investigate the relationship between SCD and the duration of hemodialysis, patient age and biochemistry findings. The SCD of patients receiving hemodialysis was significantly increased, and there was a positive correlation between SCD and the duration of hemodialysis. The SCD tended to show a significant increase in patients receiving long-term hemodialysis over 10 years. Although the SCD was not significantly correlated with serum levels of beta 2-microglobulin and C-PTH, there was a significant positive correlation between the SCD and the serum levels of AI. In patients receiving long-term hemodialysis for 10 years or more, the SCD was increased significantly in the groups patients with the complications of carpal tunnel syndrome (CTS), cystic radiolucencies (CRL) or destructive spondyl arthropathy (DSA) compared with the value in complication-free patients. The results of this study suggest that the majority of patients with SCD > 8mm had the complication of DRA. Since ultrasonography is a non-invasive, east-to-perform procedure, ultrasonographic measurement of the SCD seems to be useful in the diagnosis of DRA.

A Combined High‐Resolution Mass Spectrometric and in silico Approach for the Characterisation of Small Ligands of β2‐Microglobulin

Beta(2)-microglobulin (beta(2)-m) is a protein responsible for a severe complication of long-term hemodialysis, known as dialysis-related amyloidosis, in which initial beta(2)-m misfolding leads to amyloid fibril deposition, mainly in the skeletal tissue. Whereas much attention is paid to understanding the complex mechanism of amyloid formation, the evaluation of small molecules that may bind beta(2)-m and possibly inhibit the aggregation process is still largely unexplored mainly because the protein lacks a specific active site. Based on our previous findings, we selected a pilot set of sulfonated molecules that are known to either bind or not to the protein, including binders that are anti-amyloidogenic. We show how a complementary approach, using high-resolution mass spectrometry and in silico studies, can offer rapid and precise information on affinity, as well as insight into the structural requisites that favour or disfavour the inhibitory activity. Overall, this approach can be used for predictive purposes and for a rapid screening of fibrillogenesis inhibitors.

DE‐loop mutations affect β2 microglobulin stability, oligomerization, and the low‐pH unfolded form

Beta2 microglobulin (beta2m) is the light chain of class-I major histocompatibility complex (MHC-I). Its accumulation in the blood of patients affected by kidney failure leads to amyloid deposition around skeletal joints and bones, a severe condition known as Dialysis Related Amyloidosis (DRA). In an effort to dissect the structural determinants of beta2m aggregation, several beta2m mutants have been previously studied. Among these, three single-residue mutations in the loop connecting strands D and E (W60G, W60V, D59P) have been shown to affect beta2m amyloidogenic properties, and are here considered. To investigate the biochemical and biophysical properties of wild-type (w.t.) beta2m and the three mutants, we explored thermal unfolding by Trp fluorescence and circular dichroism (CD). The W60G mutant reveals a pronounced increase in conformational stability. Protein oligomerization and reduction kinetics were investigated by electrospray-ionization mass spectrometry (ESI-MS). All the mutations analyzed here reduce the protein propensity to form soluble oligomers, suggesting a role for the DE-loop in intermolecular interactions. A partially folded intermediate, which may be involved in protein aggregation induced by acids, accumulates for all the tested proteins at pH 2.5 under oxidizing conditions. Moreover, the kinetics of disulfide reduction reveals specific differences among the tested mutants. Thus, beta2m DE-loop mutations display long-range effects, affecting stability and structural properties of the native protein and its low-pH intermediate. The evidence presented here hints to a crucial role played by the DE-loop in determining the overall properties of native and partially folded beta2m.

Molten Globule Precursor States Are Conformationally Correlated to Amyloid Fibrils of Human β-2-Microglobulin

Misfolding intermediates play a key role in defining aberrant protein aggregation and amyloid formation in more than 15 different human diseases. However, their experimental characterization is challenging due to the transient nature and conformational heterogeneity of the involved states. Here, we demonstrate that direct carbon-detected NMR experiments allow observation, assignment, and structural analysis of molten globule amyloid intermediates that are severely broadened by conformational exchange. The method is used to characterize the structure and dynamics of partially unfolded intermediates of the 99-residue protein beta-2-microglobulin, which is the major component of insoluble aggregates occurring in dialysis-related amyloidosis. Comparison of the conformational properties of the molten globule-like intermediates with levels of deuterium incorporation into amyloid fibrils of beta-2-microglobulin revealed a close relationship between the conformational properties of the metastable intermediates and the beta-sheet-rich insoluble aggregates of beta-2-microglobulin.

The amyloid fibrils of the constant domain of immunoglobulin light chain

Light chain-associated (AL) amyloidosis is characterized by dominant fibril deposition of the variable domain (VL) of an immunoglobulin light chain, and thus its constant domain (CL) has been considered not to be amyloidogenic. We examined the in vitro fibril formation of the isolated CL in comparison with β 2-microglobulin (β2-m), an immunoglobulin domain-like amyloidogenic protein responsible for dialysis-related amyloidosis. Two methods useful for β2-m at neutral pH also induced amyloid fibrils of CL, which were monitored by thioflavin-T binding and electron microscopy (EM). These results suggest that CL plays an important role, more than previously assumed, in the development of AL-amyloidosis.

Pre-Steady-State Kinetic Analysis of the Elongation of Amyloid Fibrils of β 2-Microglobulin with Tryptophan Mutagenesis

Amyloid fibrils elongate seed dependently, with preformed fibrils providing a template for propagation of amyloidogenic conformation. Most seeding experiments use relatively few seed fibrils in comparison with monomers, resembling steady-state enzyme kinetics. Pre-steady-state kinetics should also be useful for characterizing the elongation process. With β 2-microglobulin (β 2-m), a protein responsible for dialysis-related amyloidosis, we measured the pre-steady-state kinetics of fibril elongation at pH 2.5, conditions under which the monomer is largely unfolded. β 2-m has Trp residues at positions 60 and 95. We used three single Trp mutants and fluorescence spectroscopy to study structural change upon fibril elongation. To focus on conformational change in monomers, we prepared seeds with a mutant without a Trp residue. At a fixed concentration of monomeric β 2-m, the apparent rate of fibril elongation increased with an increase in the concentration of seeds and then saturated, suggesting the accumulation of a rate-limiting intermediate. Importantly, saturation occurred at a seed/monomer ratio of around 10, as expressed by the concentration of the monomer. Because the number of monomers constituting the seed fibrils is much larger than 10, the results suggest that the elongation process is limited by “non-active-site binding.” Spectral analysis indicated that, upon this non-active-site binding, both Trp60 and Trp95 are exposed to the solvent, and then only Trp60 is buried upon transition to the fibrils. We propose a new model of fibril elongation in which non-active-site binding plays a major role.

Laser-induced Propagation and Destruction of Amyloid β Fibrils

The amyloid deposition of amyloid beta (Abeta) peptides is a critical pathological event in Alzheimer disease (AD). Preventing the formation of amyloid deposits and removing preformed fibrils in tissues are important therapeutic strategies against AD. Previously, we reported the destruction of amyloid fibrils of beta(2)-microglobulin K3 fragments by laser irradiation coupled with the binding of amyloid-specific thioflavin T. Here, we studied the effects of a laser beam on Abeta fibrils. As was the case for K3 fibrils, extensive irradiation destroyed the preformed Abeta fibrils. However, irradiation during spontaneous fibril formation resulted in only the partial destruction of growing fibrils and a subsequent explosive propagation of fibrils. The explosive propagation was caused by an increase in the number of active ends due to breakage. The results not only reveal a case of fragmentation-induced propagation of fibrils but also provide insights into therapeutic strategies for AD.