Cells surrounding haemodialysis-associated amyloid deposits are mainly macrophages

Myocardial inflammatory cells in cardiac amyloidosis

BACKGROUND

Immunoglobulin derived AL amyloidosis and transthyretin derived ATTR amyloidosis are the most common forms of cardiac amyloidosis. Both may present with cardiac arrhythmias, heart failure, and extracardiac symptoms. Disease outcome is often fatal. Recently, it was proposed that amyloid may cause cardiac inflammation. Here we tested the hypothesis that immune cell infiltration in cardiac tissue correlates with clinicopathological patient characteristics.

PATIENTS AND METHODS

Myocardial biopsies from 157 patients with cardiac amyloidosis (46.5% AL, 53.3% ATTR) were immunohistochemically assessed for the presence and amount of T lymphocytes (CD3), macrophages (CD68) and neutrophils (MPO). Amyloid load, cardiomyocyte diameter, apoptosis (Caspase 3), necrosis (complement 9), and various clinical parameters were assessed and correlated with immune cell density.

RESULTS

Myocardial tissue was infiltrated with T lymphocytes (CD3), macrophages (CD68) and neutrophils (MPO) with variable amounts. Significant correlations were found between the number of macrophages and NYHA class. No correlations were found between the presence and amount of T lymphocytes, neutrophils and clinicopathological patient characteristics.

CONCLUSION

The significant correlation between cardiac macrophage density and heart failure points towards a significant role of macrophages in disease pathology.

Nanotechnology for microglial targeting and inhibition of neuroinflammation underlying Alzheimer's pathology

BACKGROUND

Alzheimer's disease (AD) is considered to have a multifactorial etiology. The hallmark of AD is progressive neurodegeneration, which is characterized by the deepening loss of memory and a high mortality rate in the elderly. The neurodegeneration in AD is believed to be exacerbated following the intercoupled cascades of extracellular amyloid beta (Aβ) plaques, uncontrolled microglial activation, and neuroinflammation. Current therapies for AD are mostly designed to target the symptoms, with limited ability to address the mechanistic triggers for the disease. In this study, we report a novel nanotechnology based on microglial scavenger receptor (SR)-targeting amphiphilic nanoparticles (NPs) for the convergent alleviation of fibril Aβ (fAβ) burden, microglial modulation, and neuroprotection.

METHODS

We designed a nanotechnology approach to regulate the SR-mediated intracellular fAβ trafficking within microglia. We synthesized SR-targeting sugar-based amphiphilic macromolecules (AM) and used them as a bioactive shell to fabricate serum-stable AM-NPs via flash nanoprecipitation. Using electron microscopy, in vitro approaches, ELISA, and confocal microscopy, we investigated the effect of AM-NPs on Aβ fibrilization, fAβ-mediated microglial inflammation, and neurotoxicity in BV2 microglia and SH-SY5Y neuroblastoma cell lines.

RESULTS

AM-NPs interrupted Aβ fibrilization, attenuated fAβ microglial internalization via targeting the fAβ-specific SRs, arrested the fAβ-mediated microglial activation and pro-inflammatory response, and accelerated lysosomal degradation of intracellular fAβ. Moreover, AM-NPs counteracted the microglial-mediated neurotoxicity after exposure to fAβ.

CONCLUSIONS

The AM-NP nanotechnology presents a multifactorial strategy to target pathological Aβ aggregation and arrest the fAβ-mediated pathological progression in microglia and neurons.

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.

Evaluation of the effects of anti-psychotic drugs on the expression of CD68 on the peripheral blood monocytes of Alzheimer patients with psychotic symptoms

INTRODUCTION

Previous studies approved the important roles of CD68, as scavenger receptors, in Alzheimer's disease (AD). The aim of this study was to evaluate the effect of treatment with anti-psychotic drugs and vitamin B12 on the expression levels of CD68 in monocytes of psychotic AD patients.

MATERIAL AND METHODS

Expression of CD68 on the monocytes was evaluated in the following groups: 1. age and sex matched healthy controls (Group 1), 2. non-psychotic AD patients (Group 2), 3. psychotic AD patients (Group 3), 4. psychotic AD patients treated with Risperidone (Group 4), 5. psychotic AD patients treated with Risperidone plus vitamin B12 (Group 5), 6. psychotic AD patients treated with Quetiapine (Group 6), psychotic AD patients treated with Quetiapine plus vitamin B12 (Group 7). The expression of CD68 has been performed using flow cytometry technique.

RESULTS

The results showed that CD68 levels were significantly increased in AD patients in comparison to healthy controls and in psychotic AD patients in comparison to non-psychotic AD patients. Treatment with anti-psychotic drugs decreased the expression of CD68. Expression of CD68 has a positive correlation with pain, dementia and mental disorders symptoms in psychotic AD patients.

DISCUSSION

CD68 may play key roles in the pathogenesis of AD and its complications may be via induction of inflammation. Therefore, it may be concluded that CD68 may be considered as a risk factor for development of AD and also psychotic symptoms in the patients.

Varying levels of small microcalcifications and macrophages in ATTR and AL cardiac amyloidosis: implications for utilizing nuclear medicine studies to subtype amyloidosis

BACKGROUND

Recently, there has been much interest in using nuclear medicine studies to noninvasively identify and subtype cardiac amyloidosis. In particular, modified bone scans using (99m)Tc-3,3-diphosphono-1,2-propanodicarboxylic acid ((99m)Tc-DPD) and (99m)Tc-pyrophosphate ((99m)Tc-PYP) are being used to selectively identify patients with ATTR amyloidosis rather than AL amyloidosis. The morphologic basis underlying the selectivity of these imaging modalities for ATTR amyloidosis has been unclear.

METHODS

To determine if variations in microcalcifications and/or macrophages within ATTR and AL amyloidosis might be responsible for the selectivity for these imaging modalities, 8 endomyocardial biopsies of ATTR amyloidosis and 7 endomyocardial biopsies of AL amyloidosis were stained with von Kossa calcium stains and with immunohistochemistry for the macrophage marker CD68.

RESULTS

Compared with AL amyloidosis, there was a greater density of small microcalcifications in cases of ATTR amyloidosis (mean=16.8 vs. 6.5 per 200× field, P=.008). In contrast, there were fewer macrophages in ATTR amyloidosis compared with AL amyloidosis (mean=2.5 vs. 11.7 per 200× field, P=.0004). The density of microcalcifications within each group was not related to patient age, echocardiographic features of cardiac function, or serum levels of calcium and creatinine.

CONCLUSIONS

These data suggest that microcalcifications but not macrophages likely underlie the selectivity of modified bone scans for ATTR amyloidosis and suggest that other pathologic entities containing microcalcifications might also result in positive scans with these imaging modalities.

Accumulation of advanced glycation end products and beta 2-microglobulin in fibrotic thickening of the peritoneum in long-term peritoneal dialysis patients

Characteristics of pathological alterations in long-term peritoneal dialysis (PD) are thickening of submesothelial compact (SMC) zone, small-vessel vasculopathy, and loss of mesothelial cells. Bioincompatible PD fluid plays crucial roles in peritoneal injury. Encapsulating peritoneal sclerosis (EPS), a rare and serious complication, occurred in patients on long-term PD or frequent peritonitis episodes, and ~50 % of EPS developed after PD cessation. We hypothesized that PD-related peritoneal injury factors induced by bioincompatible PD fluid accumulated in the peritoneum and might induce EPS. We therefore examined the accumulation of advanced glycation end products (AGE) and beta 2-microglobulin (β2M) in peritoneum and evaluated the relationship between their accumulation, clinical parameters, and outcome after PD cessation. Forty-five parietal peritoneal specimens were obtained from 28 PD patients, 14 uremic patients, and three patients with normal kidney function. The peritoneal equilibration test was used for peritoneal function. AGE- and β2M-expressing areas were found in vascular walls, perivascular areas, and the deep layer of the SMC in short-term PD patients and extended over the entire SMC in long-term patients. Peritonitis and prolonged PD treatment aggravated peritoneal thickening and the proportion of AGE-expressing areas. The proportion of β2M-expressing areas was increased in long-term PD patients. Thickening of the SMC and the proportions of AGE- and β2M-expressing areas were not related to ascites or EPS after PD withdrawal. It appears that the increased proportion of AGE and β2M deposition induced by long-term exposure of PD fluid may be a marker of peritoneal injury.

Role of scavenger receptors in glia-mediated neuroinflammatory response associated with Alzheimer's disease

It is widely accepted that cells serving immune functions in the brain, namely, microglia and astrocytes, are important mediators of pathological phenomena observed in Alzheimer's disease. However, it is unknown how these cells initiate the response that results in cognitive impairment and neuronal degeneration. Here, we review the participation of the immune response mediated by glial cells in Alzheimer's disease and the role played by scavenger receptors in the development of this pathology, focusing on the relevance of class A scavenger receptor (SR-A) for A β clearance and inflammatory activation of glial cell, and as a potential target for Alzheimer's disease therapy.

Fever associated with severe dialysis-related amyloidosis

Dialysis-related amyloidosis (DRA) is one of the most important complications in patients on long-term hemodialysis (HD). DRA often affects the osteoarticular system; however, little is known about the role of β₂-microglobulin in the induction of fever in HD patients. We report a 64-year-old woman on long-term (24 years) HD who developed polyarthralgia and intermittent fever. Infectious diseases, connective tissue diseases, and malignant neoplasm were ruled out. Computed tomography and magnetic resonance imaging showed swelling of the soft tissues around bilateral shoulder and hip joints, suggestive of amyloid deposits. Gallium scintigraphy showed abnormal uptake in the vicinity of several large joints. It was presumed that the fever was related to the amyloid joint deposits, and the patient was treated with prednisolone and β₂-microglobulin adsorption therapy. The treatment resulted in the resolution of fever, relief of arthralgia, and normalization of several inflammatory cytokines and C-reactive protein. The findings suggest that massive DRA could cause systemic inflammatory response in patients on long-term HD.

Microglial scavenger receptors and their roles in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is increasing in prevalence with the aging population. Deposition of amyloid-β (Aβ) in the brain of AD patients is a hallmark of the disease and is associated with increased microglial numbers and activation state. The interaction of microglia with Aβ appears to play a dichotomous role in AD pathogenesis. On one hand, microglia can phagocytose and clear Aβ, but binding of microglia to Aβ also increases their ability to produce inflammatory cytokines, chemokines, and neurotoxic reactive oxygen species (ROS). Scavenger receptors, a group of evolutionally conserved proteins expressed on the surface of microglia act as receptors for Aβ. Of particular interest are SCARA-1 (scavenger receptor A-1), CD36, and RAGE (receptor for advanced glycation end products). SCARA-1 appears to be involved in the clearance of Aβ, while CD36 and RAGE are involved in activation of microglia by Aβ. In this review, we discuss the roles of various scavenger receptors in the interaction of microglia with Aβ and propose that these receptors play complementary, nonredundant functions in the development of AD pathology. We also discuss potential therapeutic applications for these receptors in AD.

Characterization of the response of primary cells relevant to dialysis-related amyloidosis to β2-microglobulin monomer and fibrils

The formation of insoluble amyloid fibrils is associated with an array of devastating human diseases. Dialysis-related amyloidosis (DRA) is a severe complication of hemodialysis that results in the progressive destruction of the bones and joints. Elevated concentrations of β₂-microglobulin (β₂m) in the serum of subjects on hemodialysis promote the formation of amyloid fibrils in the osteoarticular tissues, but the cellular basis for the destruction of these tissues in DRA is poorly understood. In this study we performed a systematic analysis of the interaction of monomeric and fibrillar β₂m with primary human cells of the types present in the synovial joints of subjects with DRA. Building upon observations that macrophages infiltrate β₂m amyloid deposits in vivo we demonstrate that monocytes, the precursors of macrophages, cannot degrade β₂m fibrils, and that both monomeric β₂m and fibrillar β₂m are cytotoxic to these cells. β₂m fibrils also impair the formation of bone resorbing osteoclasts from monocytes and reduce the viability of osteoblasts, the cell type that produces bone. As a consequence, we predict that β₂m amyloid will disrupt the remodelling of the bone, which is critical for the maintenance of this tissue. Moreover, we show that β₂m fibrils reduce the viability of chondrocytes, rationalizing the loss of cartilage in DRA. Together, our observations demonstrate that β₂m cytotoxicity has multiple cellular targets in the osteoarticular tissues and is likely to be a key factor in the bone and joint destruction characteristic of DRA.

Review: membranes for haemodialysis

Haemodialysis, by design, uses a semipermeable membrane to separate blood from dialysate. The qualities of this membrane determine the nature of the 'traffic' between the blood and dialysate. In this sense, the qualities of the membrane determine what size molecules move from one compartment to the other, the amount and rate at which they might move and the amount and rate of water movement across the membrane. In addition, the nature of the membrane influences the biological response of the patient both in terms of what is or is not removed by the dialysis process and by way of the reaction to the biocompatibility of the membrane. This brief review will explore aspects of dialysis membrane characteristics.

Investigation into the role of macrophages in the formation and degradation of beta2-microglobulin amyloid fibrils

Dialysis related amyloidosis is a serious complication of long-term hemodialysis in which beta(2)-microglobulin (beta(2)m) forms amyloid fibrils that deposit predominantly in cartilaginous tissues. How these fibrils form in vivo, however, is poorly understood. Here we perform a systematic investigation into the role of macrophages in the formation and degradation of beta(2)m amyloid fibrils, building on observations that macrophages are found in association with beta(2)m amyloid deposits in vivo and that these cells contain intra-lysosomal beta(2)m amyloid. In live cell imaging experiments we demonstrate that macrophages internalize monomeric beta(2)m, whereupon it is sorted to lysosomes. At lysosomal pH beta(2)m self-associates in vitro to form amyloid-like fibrils with an array of morphologies as visualized by atomic force microscopy. Cleavage of the monomeric protein by both macrophages and lysosomal proteases isolated from these cells results in the rapid degradation of the monomeric protein, preventing amyloid formation. Incubation of macrophages with preformed fibrils revealed that macrophages internalize amyloid-like fibrils formed extracellularly, but in marked contrast with the monomeric protein, the fibrils were not degraded within macrophage lysosomes. Correspondingly beta(2)m fibrils were highly resistant to degradation by high concentrations of lysosomal proteases isolated from macrophages. Despite their enormous degradative capacity, therefore, macrophage lysosomes cannot ameliorate dialysis-related amyloidosis by degrading pre-existing amyloid fibrils, but lysosomal proteases may play a protective role by eliminating amyloid precursors before beta(2)m fibrils can accumulate in what may represent an otherwise fibrillogenic environment.

Amyloidogenesis recapitulated in cell culture: a peptide inhibitor provides direct evidence for the role of heparan sulfate and suggests a new treatment strategy

To date 22 different polypeptides, including Abeta in Alzheimer's disease and PrP(Sc) in prion disorders, are known to re-fold and assemble into highly organized fibrils, which associate with heparan sulfate (HS) proteoglycans to form tissue deposits called amyloid. Mononuclear phagocytes have long been thought to be involved in this process, and we describe a monocytic cell culture system that can transform the acute-phase protein serum amyloid A (SAA1.1) into AA-amyloid and appears to recapitulate all the main features of amyloidogenesis observed in vivo. These features in common include nucleation-dependent kinetics, identical proteolytic processing of SAA1.1, and co-deposition of HS with the fibrils. Heparin and polyvinylsulfonate previously reported to block AA-amyloidogenesis in mice are also effective inhibitors in this cell culture model. Furthermore, a synthetic peptide (27-mer) corresponding to a HS binding site of SAA, blocks amyloid deposition at a concentration that is several-orders-of-magnitude lower than any other peptide-based inhibitor previously reported. The 27-mer's inhibitory activity may target the amyloidogenic pathway specifically as it does not interfere with the binding of SAA to monocytes. These data provide direct evidence that SAA1.1:HS interactions are a critical step in AA-amyloidogenesis and suggest a novel treatment strategy for other amyloidoses.

Circulating level of α2-macroglobulin–β2-microglobulin complex in hemodialysis patients

BACKGROUND

The presence of alpha2-macroglobulin (alpha2M) in amyloid tissue from patients with dialysis-related amyloidosis (DRA) was demonstrated by Argilés et al in 1989. Thereafter, the formation of the complex of beta2-microglobulin (beta2m) with alpha2m was confirmed directly by in vitro study. In Alzheimer's disease, complex formation of amyloid beta-peptide and alpha2M is considered to play an important role in the pathogenesis by modifying the degradation processes of amyloid protein. Thus, we hypothesized that the alpha2M-beta2m complex is an important factor in the pathogenesis of DRA as well. Here, we measured the circulating levels of alpha2M-beta2m complex in the maintenance hemodialysis patients and discussed about its clinical significance in DRA.

METHODS

One hundred and thirty-seven hemodialysis patients and 11 prehemodialysis chronic renal failure (CRF) patients were included in this study. The affinity of purified alpha2M for beta2m was confirmed by a highly sensitive 27 MHz quartz crystal microbalance (QCM). The presence of circulating alpha2M-beta2m complex was analyzed by immunoblotting analysis. Furthermore, the serum levels of alpha2M-beta2m complex were measured by sandwich enzyme immunoassay.

RESULTS

QCM analysis revealed the high affinity of alpha2M for beta2m. The presence of circulating alpha2M-beta2m complex was detected in two out of a total 11 prehemodialysis CRF patients and in 95 out of the total of 137 hemodialysis patients. None of the healthy subjects, however, were observed to present with any alpha2M-beta2m complex. Serum levels of the alpha2M-beta2m complex were correlated to the duration of hemodialysis (P= 0.043). Serum levels of the alpha2M-beta2m complex were significantly higher in patients with high DRA score than in patients with negative DRA score (P= 0.018). Moreover, serum levels of the alpha2M-beta2m complex showed significantly lower in the hemodiafiltration patients compared to the hemodialysis patients (P= 0.002) and showed a strong correlation with DRA score in hemodialysis patients excluding 11 hemodiafiltration patients (P= 0.0004).

CONCLUSION

This study is the first to demonstrate the presence of circulating alpha2M-beta2m complex in hemodialysis patients. Furthermore, we observed the correlation between serum levels of alpha2M-beta2m complex and clinical characteristics of DRA. Thus we concluded that a formation of an alpha2M-beta2m complex may be implicated in DRA.

Current clinical and pathogenetic understanding of β2 -m amyloidosis in long-term haemodialysis patients

As the number of patients undergoing long-term haemodialysis continues to grow, beta2-microglubulin (beta2-m) amyloidosis is emerging as an increasingly common complication. The frequency of beta2-m amyloid-related osteoarthropathy in haemodialysis patients rises steadily with length of survival. We confirmed that the prevalence of carpal tunnel syndrome increases with years of dialysis. Up to 50% of patients had developed this complication after 20 years were affected and the percentage was even higher after 25 years. Although retention of beta2-m is a necessary requirement for onset of amyloidosis, it is probably not sufficient. Using an in vitro model of beta2-m-related amyloid fibril (fAbeta2-m) extension, we demonstrated that various amyloid-associated molecules, such as apolipoprotein (apo) E and proteoglycans, accelerate beta2-m amyloid fibril formation. General categories of therapeutic approaches for amyloidosis include prevention of onset or progression, symptomatic therapy (conservative treatment, orthopedic procedures, and physiotherapy), and renal transplantation. In association of haemodialysis, beta2-m has been removed by high-flux membranes or a beta2-m adsorption column. However, proof is lacking that amyloid deposits are decreased by long-term use of dialysis techniques to eliminate beta2-m. More effective treatment procedures are needed.

Association of the MCP-1 gene polymorphism A-2518G with carpal-tunnel syndrome in hemodialysis patients

Carpal-tunnel syndrome (CTS) in long-term hemodialysis patients is caused by the deposition of amyloid as well as by the local inflammatory process. The recruitment of monocytes/macrophages in the tenosynovium, promoted by chemokines such as monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1alpha (MIP-1alpha), is thought to play an important role in CTS development. The genetic polymorphism of these chemokines has been identified and their clinical function has been partly revealed We attempted to analyze the relationship between these polymorphisms and their susceptibility to CTS. The subjects of this study were 366 patients who underwent hemodialysis. Ninety-five patients received surgery for CTS. No significant difference was observed in the genotype distributions of MCP-1 or MIP-1alpha between patients who received CTS surgery and those that did not. However, with the use of a logistic regression model, the MCP-1 GG genotype was identified as a risk factor for the development of CTS, in addition to the duration and the age of initiation of dialysis, as confirmed by a Cox proportional hazards model. In conclusion, homozygosity for G at -2518 in the MCP-1 gene might be a candidate for the genetic marker of CTS development in Japanese hemodialysis patients.

Beta 2-microglobulin amyloidosis: role of monocytes/macrophages

PURPOSE OF REVIEW

Macrophage infiltration is a distinctive histological characteristic of beta2-microglobulin amyloidosis. Studies reported during the past years have helped to clarify the role of monocytes/macrophages in the fibrillar precipitation of beta2-microglobulin and in the pathogenesis of osteoarticular pathology.

RECENT FINDINGS

Contrary to the original view, macrophage infiltration is more likely a secondary phenomenon of amyloidosis rather than an initiating event. The observation that macrophages are associated with a later stage of beta2-microglobulin amyloidosis suggests a possible role of these cells in transformation of clinical silent deposits into symptomatic osteoarticular destruction. Accumulating evidence suggests that beta2-microglobulin modified with advanced glycation end products plays a key role in recruitment and activation of macrophages through an advanced glycation end products receptor-mediated pathway, and thus may contribute to the development of local cellular inflammation in beta2-microglobulin amyloidosis.

SUMMARY

Beta 2-microglobulin amyloidosis arthropathies may result from progressive accumulation of advanced glycation end products in long-lived amyloid linked to a heightened cellular response. Antagonism of the interaction between advanced glycation end products and their receptor may be a relevant strategy for cellular inflammation in beta2-microglobulin amyloidosis.

Receptor for advanced glycation end products on human synovial fibroblasts: role in the pathogenesis of dialysis-related amyloidosis

An important component of amyloid fibrils in dialysis-related amyloidosis (DRA) is beta(2)-microglobulin (beta(2)m) modified with advanced glycation end products (AGE). The amyloid deposits are located principally in joint structures, with adjacent chronic inflammatory reaction characterized by monocyte infiltration. This study examined the interaction of AGE-beta(2)m with human synovial fibroblasts and investigated the proinflammatory effects of that interaction. It was demonstrated that human synovial fibroblasts constitutively expressed the receptor for AGE (RAGE). RAGE expression was detected mainly in synovial intima and was upregulated in DRA synovium. (125)I-AGE-beta(2)m bound to immobilized human synovial fibroblasts in a specific, dose-dependent manner (K(d) of approximately 138.0 nM), and binding was inhibited by anti-RAGE IgG. Incubation of human synovial fibroblasts with AGE-beta(2)m induced degradation of this AGE-modified protein, as well as increased monocyte chemoattractant protein-1 (MCP-1) mRNA and protein expression. The amount of MCP-1 produced by AGE-beta(2)m-stimulated human synovial fibroblasts was sufficient to induce the chemotaxis of monocytes. MCP-1 synthesis resulted from engagement of RAGE, because the increase in MCP-1 synthesis was attenuated by preincubation of human synovial fibroblasts with anti-RAGE IgG. These data provide evidence of RAGE-mediated perturbation of human synoviocytes, which may be involved in the pathogenesis of inflammatory processes associated with DRA.

Signal transduction of beta2m-induced expression of VCAM-1 and COX-2 in synovial fibroblasts

BACKGROUND

beta2 microglobulin (beta2m) amyloidosis is a destructive articular disease affecting dialysis patients. We have demonstrated that beta2m increases the expression of vascular cell adhesion molecule (VCAM-1) and cyclooxygenase-2 (COX-2) in human osteoarthritic synovial fibroblasts (SFLs).

METHODS

To determine the cell signaling pathways, SFLs were incubated with beta2m in the presence or absence of various inhibitors for 24 hours. Intracellular calcium ([Ca2+]i) was measured by fluorometric techniques and vascular cell adhesion molecule-1 (VCAM-1) and cyclooxygenase-2 (COX-2) expression was determined by immunohistochemistry and Western blotting.

RESULTS

beta2m increased [Ca2+]i levels in a dose dependent manner (P < 0.05) in SFLs. BAPTA-AM, a [Ca2+]i chelator, completely inhibited beta2m-induced expression of VCAM-1 and COX-2. U73122 [phospholipase C (PLC) inhibitor] or 2-APB [specific inhibitor of inositol 1,4,5-trisphosphate (IP3)-induced [Ca2+]i release] completely blocked the beta2m-induced increase in [Ca2+]i and the up-regulation of VCAM-1 and COX-2. However, pretreatment with staurosporin, a protein kinase C inhibitor, had no effect. Disruption of the actin cytoskeleton by treatment with cytochalasin D or latrunculin A blocked beta2m up-regulation of VCAM-1 and COX-2. Finally, cells treated with phosphatidylinositol-3 kinase (PI-3 kinase) inhibitors wortmannin or LY294002 also failed to express VCAM-1 and COX-2.

CONCLUSIONS

These results demonstrate that IP3-mediated [Ca2+]i release, PI-3 kinase, and actin cytoskeleton reorganization are involved in beta2m-induced expression of VCAM-1 and COX-2 in human SFLs. Understanding the potential pathways by which beta2m exerts its inflammatory-like effects may lead to the development of future therapies.

Pathogenesis of beta(2)-microglobulin amyloidosis: role of monocytes/macrophages

beta(2)-microglobulin (beta(2)M) amyloidosis (A beta(2)M) is a serious, often incapacitating complication for patients undergoing long-term hemodialysis. Amyloid deposits composed of beta(2)M fibrils as the major constituent protein are mainly localized in joints and periarticular bone and lead to chronic arthralgias, carpal tunnel syndrome, and eventually destructive arthropathy. Although recent histologic studies have shown the accumulation of monocytes/macrophages around amyloid deposits, the factor(s) causing their infiltration and pathologic involvement have yet to be fully elucidated. Immunohistochemical staining reveals that macrophages in tenosynovial tissues express CD13, CD14, CD33, HLA-DR, and CD68 antigens on their surfaces and express interleukin (IL)-1 beta, tumor necrosis factor (TNF)-alpha, and IL-6. Many of these cells also express LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), and VLA-4 (CD49d/CD29) on their surfaces. AGE-modified beta(2)M enhances chemotaxis of monocytes and stimulates macrophages to release bone-resorbing cytokines, such as IL-1 beta, TNF-alpha and IL-6. Via a RAGE-mediated pathway, AGE-modified, but not unmodified beta(2)M, significantly delays constitutive apoptosis of human peripheral blood monocytes. Monocytes survival in an advanced glycation end product (AGE) beta(2)M-containing microenvironment is associated with their phenotypic alteration into macrophage-like cells that generate more reactive oxygen species and elaborate greater quantities of IL-1 beta and TNF-alpha. Thus through regulation of their survival and differentiation, AGE beta(2)M in amyloid deposits may be able to influence the presence and quantity of infiltrated monocytes, and hence their biologic effects.

Pathological aspects of beta(2)-microglobulin amyloidosis

Histology remains the gold standard to diagnose beta(2)-microglobulin amyloidosis (A beta(2)M). Two diagnostic criteria are required: positive Congo red staining with typical birefringence under polarized light and immunostaining of amyloid deposits with a labeled anti-beta(2)M antibody. A beta(2)M is preferentially located in the joints. Small deposits are also found in various organs, mainly the heart and gastrointestinal tract. Pathologic studies have demonstrated a high prevalence of articular A beta(2)M early in the course of hemodialysis and peritoneal dialysis, antedating clinical manifestations by several years. The stages of beta(2)M amyloid formation have been delineated: beta(2)M amyloid deposits first on the surface of the cartilage, in the absence of macrophages (stage 1), and subsequently involves capsules and synovia (stage 2), with eventual recruitment of macrophages around large beta(2)M amyloid deposits (stage 3). Clinical manifestations are likely associated with the inflammation observed in stage 3. The factors triggering the fibrillar precipitation of beta(2)M remain unknown. Macrophages do not play a role: their presence is the consequence rather than the cause of beta(2)M amyloid deposits. Several substances coprecipitated with beta(2)M amyloid have been incriminated: highly sulfated glycosaminoglycans such as chondroitin or keratan sulfate, antiproteases such as alpha(2)-macroglobulin, and apolipoprotein E. As yet, no definitive conclusion has been reached.

Histological characteristics of sternoclavicular beta 2-microglobulin amyloidosis and clues for its histogenesis

BACKGROUND

The pathogenesis of beta 2-microglobulin amyloidosis (A beta 2m) has yet to be fully elucidated.

METHODS

We describe the distribution and extent of A beta 2m deposition and macrophagic infiltration in cartilage, capsule, and synovium of sternoclavicular joints obtained postmortem from 54 patients after 3 to 244 (median 46) months of dialysis. Twenty-four nonuremic patients served as a control group. The diagnosis of amyloidosis (A) rested on a positive Congo Red staining (typical birefringence) and that of A beta 2m on positive immunostaining of the A deposits with a monoclonal anti-beta 2m antibody. The size of A deposits was measured.

RESULTS

A beta 2m was detected in 32 (59%), and non-beta 2m amyloid (Anon beta 2m) was detected in an additional 8 (15%) of the 54 dialyzed patients. A beta 2m deposits were present in the cartilage of all A beta 2m (+) patients (100%). They were localized solely in the cartilage in 27% of the cases, either as a thin patchy layer or as a continuous thicker layer (identified as stage I). A beta 2m was additionally present in the capsule and/or synovium without macrophages in 27% of the cases (identified as stage II). The correlation between the size of cartilaginous deposits and dialysis duration (P = 0.02) as well as with the prevalence (P = 0.03) and size of capsular deposits (P = 0.02) suggests that stage II is a later stage of A deposition. Clusters of macrophages were detected around capsular and synovial amyloid deposits in 46% of the cases (identified as stage III). The longer duration of dialysis in those with stage III as well as the relationship between the size of the A beta 2m deposits and the prevalence of macrophagic infiltration suggests that stage III is the last stage of A beta 2m deposition. Marginal bone erosions were observed in 9 out of 12 patients with stage III deposits. Their size was correlated with that of cartilaginous deposits (P = 0.01). Among the 24 control patients, Anon beta 2m was detected in 12 patients (cartilage 100%, capsule 8%, synovium 30%).

CONCLUSIONS

The earliest stage of A beta 2m deposition occurs in the cartilage. A beta 2m subsequently extends to capsule and synovium. These two first stages do not require macrophage infiltration. Macrophages are eventually recruited around larger synovial or capsular deposits in the final stage. Marginal bone erosions develop in this late stage.

Impaired lysosomal processing of beta2-microglobulin by infiltrating macrophages in dialysis amyloidosis

BACKGROUND

Macrophages may participate in amyloid fibril formation by processing the protein precursor. Although this theory seems to apply for amyloidosis, in which proteolytic cleavage is a prerequisite for amyloid fibril formation, it has not been demonstrated for beta2-microglobulin (beta2m) amyloidosis. We aimed to establish the role played by macrophages in beta2m amyloidosis.

METHODS

We used a double immunogold electron microscopy technique, including mouse antihuman CD68, rabbit antihuman beta2m, amyloid P component, and lysosome-associated membrane protein (LAMP-1) antibodies. Differential density labeling studies of beta2m and amyloid P component were performed extra- and intracellularly to assess protein processing by macrophages.

RESULTS

The cells surrounding amyloid fibrils were found to be mostly CD68 positive, suggesting that they were of monocyte-macrophage lineage. Intracellular accumulation of amyloid fibrils was also observed; these fibrils were constantly surrounded by LAMP-1-linked gold particles, demonstrating that intracellular beta2m was almost exclusively lysosomal. The rough-surface endoplasmic reticulum was not labeled by beta2m antibody, suggesting that there was no active synthesis of beta2m by the cells. As a marker of endocytosis, protruded cytoplasmic processes in close relation with the intracellular accumulations of beta2m amyloid fibrils were observed. No difference in density labeling (extracellular vs. intracellular) was observed for beta2m, whereas intracellular P component labeling was significantly decreased.

CONCLUSIONS

All of these data are strongly suggestive of phagocytosis and not synthesis of amyloid fibrils by macrophages. Further, they demonstrate an impaired lysosomal processing specific for beta2m, as other compounds of the amyloid fibrils (P component) are significantly cleared.

Alterations in nonenzymatic biochemistry in uremia: origin and significance of "carbonyl stress" in long-term uremic complications

Advanced glycation end products (AGEs), formed during Maillard or browning reactions by nonenzymatic glycation and oxidation (glycoxidation) of proteins, have been implicated in the pathogenesis of several diseases, including diabetes and uremia. AGEs, such as pentosidine and carboxymethyllysine, are markedly elevated in both plasma proteins and skin collagen of uremic patients, irrespective of the presence of diabetes. The increased chemical modification of proteins is not limited to AGEs, because increased levels of advanced lipoxidation end products (ALEs), such as malondialdehydelysine, are also detected in plasma proteins in uremia. The accumulation of AGEs and ALEs in uremic plasma proteins is not correlated with increased blood glucose or triglycerides, nor is it determined by a decreased removal of chemically modified proteins by glomerular filtration. It more likely results from increased plasma concentrations of small, reactive carbonyl precursors of AGEs and ALEs, such as glyoxal, methylglyoxal, 3-deoxyglucosone, dehydroascorbate, and malondialdehyde. Thus, uremia may be described as a state of carbonyl overload or "carbonyl stress" resulting from either increased oxidation of carbohydrates and lipids (oxidative stress) or inadequate detoxification or inactivation of reactive carbonyl compounds derived from both carbohydrates and lipids by oxidative and nonoxidative chemistry. Carbonyl stress in uremia may contribute to the long-term complications associated with chronic renal failure and dialysis, such as dialysis-related amyloidosis and accelerated atherosclerosis. The increased levels of AGEs and ALEs in uremic blood and tissue proteins suggest a broad derangement in the nonenzymatic biochemistry of both carbohydrates and lipids.

Beta 2-microglobulin modified with advanced glycation end products modulates collagen synthesis by human fibroblasts

Beta 2-microglobulin amyloidosis (A beta 2m) is a serious complication for patients undergoing long-term dialysis. beta 2-microglobulin modified with advanced glycation end products (beta 2m-AGE) is a major component of the amyloid in A beta 2m. It is not completely understood whether beta 2m-AGE plays an active role in the pathogenesis of A beta 2m, or if its presence is a secondary event of the disease. beta 2-microglobulin amyloid is mainly located in tendon and osteo-articular structures that are rich in collagen, and local fibroblasts constitute the principal cell population in the synthesis and metabolism of collagen. Recent identification of AGE binding proteins on human fibroblasts lead to the hypothesis that the fibroblast may be a target for the biological action of beta 2m-AGE. The present study demonstrated that two human fibroblast cell lines exhibited a decrease in procollagen type I mRNA and type I collagen synthesis after exposure to beta 2m-AGE for 72 hours. Similar results were observed using AGE-modified albumin. Antibody against the RAGE, the receptor for AGE, attenuated this decrease in synthesis, indicating that the response was partially mediated by RAGE. In addition, antibody against epidermal growth factor (EGF) attenuated the decrease in type I procollagen mRNA and type I collagen induced by beta 2m-AGE, suggesting that EGF acts as an intermediate factor. These findings support the hypothesis that beta 2m-AGE actively participates in connective tissue and bone remodeling via a pathway involving fibroblast RAGE, and at least one interposed mediator, the growth factor EGF.

Synovial inflammatory cells captured 131I-beta 2-microglobulin in patients with dialysis related amyloidosis

Dialysis related amyloidosis (DRA) is a major complication of long term hemodialysis therapy. It is well recognized that scintigraphic study using radioisotope-labeled beta 2-microglobulin (beta 2M) as a tracer is a sensitive and specific technique to diagnose DRA non-invasively. The aim of this study is to clarify the mechanism of 131I-beta 2M accumulation around the amyloid tissue. Three dialysis patients with carpal tunnel syndromes were examined for consecutive 131I-beta 2M scintigraphies every 24 hours for 3 days till the carpal tunnel synovectomy. Removed synovial tissues were processed for histological study. The scintigraphic study demonstrated tracer accumulations in the joints involved with DRA and the intensity increased in a time dependent fashion. Microscopic observations revealed many inflammatory cells presenting CD68-monocytes/macrophages antigen infiltrated into the synovial tissues. 131I-beta 2M was evident in the cytoplasm of the infiltrating cells, while no radioactivity was detected above background in the amyloid tissues. In conclusion, the tracer accumulations observed in the 131I-beta 2M scintigraphic studies were the consequence of circulating beta 2M assimilated by the infiltrating monocytes/macrophages. Thus, the undetermined elimination pathway of circulating beta 2M in the dialysis patients was identified as the storage pool in those inflammatory cells. The inflammatory change may play a crucial role in the local progression of DRA through the accumulation of circulating beta 2M around the established amyloid tissues.

Human choroid plexus is an uniquely involved area of the brain in amyloidosis: a histochemical, immunohistochemical and ultrastructural study

To better understand the characteristics of amyloid deposition in the choroid plexus, we examined autopsied brain by routine histology, immunohistochemistry, and electron microscopy in three group of patients: primary systemic amyloidosis (n = 7), cerebral amyloid angiopathy (CAA, n = 6), and controls (n = 3). Three of the CAA patients had Alzheimer's disease. Congophilic, birefringent amyloid deposits of the choroid plexus were seen in six of the seven cases of systemic light chain amyloidosis. Immunohistochemistry revealed that the deposited amyloids had reactivity for immunoglobulin light chain and amyloid P component. Accumulation of macrophages labeled with monoclonal antibodies against CD 68 and major histocompatibility complex class II antigens were observed around the massive amyloid deposits. The presence of approximately 10 nm amyloid fibrils along the epithelial basement membrane as well as in the vascular walls was ascertained by electron microscopy. In CAA, Congo red-positive amyloid deposits were consistently present in meningeal blood vessels and were often found in senile plaques of the cerebral parenchyma; congophilic amyloid deposits were absent in the choroid plexus. Choroid plexus epithelial cells exhibited immunostaining for beta amyloid precursor protein (APP) with N-terminal- and C-terminal-specific antibodies; in particular, consistent staining was obtained for the latter antibody. Immunoreactivity for amyloid beta protein (A beta) with monoclonal antibodies (6E10, 4G8) was often found in choroid plexus epithelial cells. These findings suggest that amyloid deposition of the choroid plexus depends on the major component protein in amyloidosis, and that the choroid plexus may produce APP and A beta protein although A beta amyloidosis is not evident in the choroid plexus.

Alpha 2-macroglobulin protects some of the protein constituents of dialysis-associated amyloidosis from protease degradation

A crucial point to know in the prevention and treatment of beta 2-microglobulin (beta 2-m) amyloidosis is the putative resorption of amyloid fibrils in vivo. Although still controversial, long term clinical studies suggest that there is no resorption of amyloid fibrils in vivo, even after the suppression of the primary cause of amyloidosis. Two in vitro studies on murine and human AA amyloidosis as well as Alzheimer's disease suggest that protein constituents of amyloid fibrils may be resorbed. Protein resorption can be inhibited by the antiprotease amyloid P component. We extended these in vitro studies on beta 2-m amyloidosis, and assessed the effect of alpha 2-macroglobulin (alpha 2-M), a serum antiprotease previously found in this type of amyloidosis, on the putative protease induced protein resorption. Here, we show that amyloid proteins, beta 2-m and light chains of immunoglobulins, were degraded by trypsin. Preincubation of the amyloid proteins with alpha 2-M significantly inhibited the trypsin induced protein degradation of lambda chains. These data add further support to the hypothesis proposing a role for alpha 2-M and other antiproteases in the formation and/or persistence of beta 2-m amyloidosis.