A cell culture system for the study of amyloid pathogenesis. Amyloid formation by peritoneal macrophages cultured with recombinant serum amyloid A

[History of the study of amyloidosis: from the Rokitansky's theory to the present day]

In the history of amyloidosis studying the concept of liquids dyscrasia has been predominated and finally it is resulted in accepting a serum protein-precursor as a leading amyloidogenic factor in the disease pathogenesis. Consequently basic diagnostic and treatment strategy was aimed to find and eliminate this protein from the blood and this approach evidenced high effectiveness in most frequent AA and AL-amyloidosis characterized with anomaly high levels of precursors in the blood. At the same time there are less frequent and slower progressing inheritant forms of systemic amyloidosis including transthyretin induced, which are less depending on amyloidogenecity of amyloid precursor and because of that, in example, the effectiveness of transthyretin stabilizers or blockers of its synthesis is limited comparing with the precursor elimination in AA or AL. Developed in the middle of XX century a theory of local synthesis by macrophages is more preferable to describe the pathogenesis of these forms. And modern proteome analysis using give rise to confirm the key meaning of macrophage in the amyloidogenesis and proves necessity to know deeply mechanisms of macrophagial autophagia - basic tool of maintaining intracellular protein homeostasis. That is why it is difficult to hope on high effectiveness of chemical amyloid solvents in vivo, which being under macrophages regulation never could realize its chemical activities.

Human lysozyme inhibits the fibrillation of serum amyloid a protein from systemic AA amyloidosis

BACKGROUND

Systemic AA amyloidosis is a world-wide occurring protein misfolding disease in humans and animals that arises from the formation of amyloid fibrils from serum amyloid A (SAA) protein and their deposition in multiple organs.

OBJECTIVE

To identify new agents that prevent fibril formation from SAA protein and to determine their mode of action.

MATERIALS AND METHODS

We used a cell model for the formation of amyloid deposits from SAA protein to screen a library of peptides and small proteins, which were purified from human hemofiltrate. To clarify the inhibitory mechanism the obtained inhibitors were characterised in cell-free fibril formation assays and other biochemical methods.

RESULTS

We identified lysozyme as an inhibitor of SAA fibril formation. Lysozyme antagonised fibril formation both in the cell model as well as in cell-free fibril formation assays. The protein binds SAA with a dissociation constant of 16.5 ± 0.6 µM, while the binding site on SAA is formed by segments of positively charged amino acids.

CONCLUSION

Our data imply that lysozyme acts in a chaperone-like fashion and prevents the aggregation of SAA protein through direct, physical interactions.

Amyloid deposition in granuloma of tuberculosis patients: A single-center pilot study

The formation of granuloma is one of the characteristic features of tuberculosis. Besides, elevated serum amyloid A (SAA) protein level is the indicator for chronic inflammation associated with tuberculosis. The linkage between tuberculosis and SAA-driven secondary amyloidosis is well documented. However, SAA-derived amyloid onset and deposition start sites are not well understood in tuberculosis. We hypothesized that granuloma could be a potential site for amyloid deposition because of the presence of SAA protein and proteases, cleaving SAA into aggregation-prone fragments. 150 tuberculosis patients were identified and biopsies were collected from the affected organs. Patients showing eosinophilic hyaline-rich deposits within granuloma and its periphery were further screened for the presence of amyloid deposits. Upon Congo red staining, these hyaline deposits exhibited characteristic apple-green birefringence under polarized light, confirming their amyloid nature in 20 patients. Further upon Immuno-histochemical staining with anti-SAA antibody, the amyloid enriched areas showed positive immunoreactivity. In this pilot study, we have shown granuloma as a potential site for serum amyloid A derived amyloid deposition in tuberculosis patients. This study would expand the clinical and fundamental research for understanding the mechanism of amyloid formation in granuloma underlying tuberculosis and other chronic inflammatory conditions.

Serum Amyloid A1 Induces Classically Activated Macrophages: A Role for Enhanced Fibril Formation

AA amyloidosis belongs to the group of amyloid diseases which can follow chronic inflammatory conditions of various origin. The disease is characterized by the deposition of insoluble amyloid fibrils formed by serum amyloid A1 (SAA1) leading eventually to organ failure. Macrophages are intimately involved in the fibrillogenesis as well as in the clearance of amyloid fibrils. In vivo, macrophages may occur as classically (M1) or alternatively activated (M2) macrophages. We investigate here how SAA1 might affect the macrophage phenotype and function. Gene microarray analysis revealed upregulation of 64 M1-associated genes by SAA1. M1-like polarization was further confirmed by the expression of the M1-marker MARCO, activation of the NF-κB transcription factor, and secretion of the M1-cytokines TNF-α, IL-6, and MCP-1. Additionally, we demonstrate here that M1-polarized macrophages exhibit enhanced fibrillogenic activity towards SAA1. Based on our data, we propose reconsideration of the currently used cellular amyloidosis models towards an in vitro model employing M1-polarized macrophages. Furthermore, the data suggest macrophage repolarization as potential intervention strategy in AA amyloidosis.

Ameliorative effects of apple cider vinegar on neurological complications via regulation of oxidative stress markers

Dementia linked with cognitive impairments is the most prominent indication of Alzheimer's disease (AD). In the current investigation, we have examined the streptozotocin- (STZ) induced cellular toxicity in mouse neuroblastoma (N2A) cells, and Zn with the high-fat diet- (HFD) induced neurotoxicity in mouse brain. These cells and animals were pretreated with apple cider vinegar (ACV), Chrysin, and Rivastigmine to examine their protection against cellular toxicity and neurotoxicity. Experiments have affirmed that pretreatment of ACV, Chrysin, and Rivastigmine has displayed protective outcomes in MTT reduction, tau phosphorylation, amyloid aggregation, attenuated memory impairment as well as oxidative stress, and protected cholinergic hippocampal neurons from degeneration. ACV showed better antioxidant and neuroprotection potential as compared with Chrysin and Rivastigmine. So the existence of excitatory/inhibitory enzymatic activity and higher antioxidant potential indicate that ACV, as a food beverage in a regular diet, could be promising and effective against neurological complications such as AD. PRACTICAL APPLICATIONS: In the Urban lifestyle, HFD and stress are the critical factors of various chronic and prevalent diseases, including diabetes, obesity, cardiovascular, and neurodegenerative disorders like AD. We are already familiar with the multiple benefits of ACV, such as weight loss, antimicrobial activity, diabetes, skin disorders. So in the current research work, we have gauged the effectiveness of ACV against neurological complications in comparison with a synthetic flavonoid (Chrysin) and an anti-Alzheimer's drug (Rivastigmine). To enhance the pragmatic orientation of our results, we have used the ACV in our study, which is readily available in the market for domestic consumption. All the cellular, biochemical, behavioral, and histopathological data revealed that ACV had high antioxidant potential. Our findings suggest that the addition of ACV as a food additive in the daily diet may reduce the threat of multiple neurodegenerative diseases. Therefore, our study could be the precursor of a new pharmacological therapeutic approach via ACV toward cognitive impairments associated with Alzheimer's disease.

Cell assay for the identification of amyloid inhibitors in systemic AA amyloidosis

Systemic AA amyloidosis is still, up to this day, a life-threatening complication of chronic inflammatory diseases. Despite the success of anti-inflammatory treatment, the prognosis of some AA patients is still poor, which is why therapies directed at the amyloidogenic pathway in AA amyloidosis are being sought after. The cell culture model of amyloid formation from serum amyloid A1 (SAA1) protein remodels crucial features of AA amyloid deposit formation in vivo. We here demonstrate how the cell model can be utilized for the identification of compounds with amyloid inhibitory activity. Out of five compounds previously reported to inhibit self-assembly of various amyloidogenic proteins, we found that epigallocatechin gallate (EGCG) inhibited the formation of SAA1-derived fibrils in cell culture. From a series of compounds targeting the protein quality control machinery, the autophagy inhibitor wortmannin reduced amyloid formation, while the other tested compounds did not lead to a substantial reduction of the amyloid load. These data suggest that amyloid formation can be targeted not only via the protein self-assembly pathway directly, but also by treatment with compounds that impact the cellular protein machinery.

High-density lipoprotein inhibits serum amyloid A-mediated reactive oxygen species generation and NLRP3 inflammasome activation

Serum amyloid A (SAA) is a high-density apolipoprotein whose plasma levels can increase more than 1000-fold during a severe acute-phase inflammatory response and are more modestly elevated in chronic inflammation. SAA is thought to play important roles in innate immunity, but its biological activities have not been completely delineated. We previously reported that SAA deficiency protects mice from developing abdominal aortic aneurysms (AAAs) induced by chronic angiotensin II (AngII) infusion. Here, we report that SAA is required for AngII-induced increases in interleukin-1β (IL-1β), a potent proinflammatory cytokine that is tightly controlled by the Nod-like receptor protein 3 (NLRP3) inflammasome and caspase-1 and has been implicated in both human and mouse AAAs. We determined that purified SAA stimulates IL-1β secretion in murine J774 and bone marrow-derived macrophages through a mechanism that depends on NLRP3 expression and caspase-1 activity, but is independent of P2X7 nucleotide receptor (P2X7R) activation. Inhibiting reactive oxygen species (ROS) by N-acetyl-l-cysteine or mito-TEMPO and inhibiting activation of cathepsin B by CA-074 blocked SAA-mediated inflammasome activation and IL-1β secretion. Moreover, inhibiting cellular potassium efflux with glyburide or increasing extracellular potassium also significantly reduced SAA-mediated IL-1β secretion. Of note, incorporating SAA into high-density lipoprotein (HDL) prior to its use in cell treatments completely abolished its ability to stimulate ROS generation and inflammasome activation. These results provide detailed insights into SAA-mediated IL-1β production and highlight HDL's role in regulating SAA's proinflammatory effects.

Cellular mechanism of fibril formation from serum amyloid A1 protein

Serum amyloid A1 (SAA1) is an apolipoprotein that binds to the high-density lipoprotein (HDL) fraction of the serum and constitutes the fibril precursor protein in systemic AA amyloidosis. We here show that HDL binding blocks fibril formation from soluble SAA1 protein, whereas internalization into mononuclear phagocytes leads to the formation of amyloid. SAA1 aggregation in the cell model disturbs the integrity of vesicular membranes and leads to lysosomal leakage and apoptotic death. The formed amyloid becomes deposited outside the cell where it can seed the fibrillation of extracellular SAA1. Our data imply that cells are transiently required in the amyloidogenic cascade and promote the initial nucleation of the deposits. This mechanism reconciles previous evidence for the extracellular location of deposits and amyloid precursor protein with observations the cells are crucial for the formation of amyloid.

Cell-to-cell transfer of SAA1 protein in a cell culture model of systemic AA amyloidosis

Systemic AA amyloidosis arises from the misfolding of serum amyloid A1 (SAA1) protein and the deposition of AA amyloid fibrils at multiple sites within the body. Previous research already established that mononuclear phagocytes are crucial for the formation of the deposits in vivo and exposure of cultures of such cells to SAA1 protein induces the formation of amyloid deposits within the culture dish. In this study we show that both non-fibrillar and fibrillar SAA1 protein can be readily transferred between cultured J774A.1 cells, a widely used model of mononuclear phagocytes. We find that the exchange is generally faster with non-fibrillar SAA1 protein than with fibrils. Exchange is blocked if cells are separated by a membrane, while increasing the volume of cell culture medium had only small effects on the observed exchange efficiency. Taken together with scanning electron microscopy showing the presence of the respective types of physical interactions between the cultured cells, we conclude that the transfer of SAA1 protein depends on direct cell-to-cell contacts or tunneling nanotubes.

Deposition, Clearance, and Reinduction of Amyloid A Amyloid in Interleukin 1 Receptor Antagonist Knockout Mice

Amyloid A (AA) amyloidosis is characterized by the extracellular deposition of AA amyloid and results in the irreversible dysfunction of parenchymal organs. In experimental models, AA amyloid deposits are cleared following a decrease in circulating serum amyloid A (SAA) concentrations. Additional inflammatory stimuli during this recovery process may induce more severe amyloid redeposition. In the present study, we confirmed the deposition, clearance, and reinduction of AA amyloid deposits in interleukin 1 receptor antagonist knockout mice (IL-1raKO) and studied the SAA levels and amyloid-enhancing factor activity based on the time-dependent changes of amyloid deposition. Histopathologically, following initial (day 0) injection of amyloid-enhancing factor in combination with an inflammatory stimulus (silver nitrate [AgNO₃]), amyloid deposition peaked by day 20, and its deposition gradually decreased after day 35. SAA concentrations in serum were precipitously elevated on day 1 but returned to normal levels by day 10, whereas the SAA dimer was detected in serum after day 45. An additional AgNO₃ injection was administered to mice with amyloidosis on day 5, 10, 35, or 50, and all mice developed large amyloid deposits. Amyloid deposition was most severe in mice treated with AgNO₃ on day 35. The inoculation of sera from mice with AA amyloidosis, combined with AgNO₃, induced AA amyloidosis. Serum samples collected on days 35 and 50, which contained high concentrations of the SAA dimer, induced amyloidosis in a high proportion (83%) of mice. Therefore, increased SAA and/or its dimer in serum during the recovery process may markedly exacerbate the development of AA amyloidosis.

Electron tomography reveals the fibril structure and lipid interactions in amyloid deposits

Electron tomography is an increasingly powerful method to study the detailed architecture of macromolecular complexes or cellular structures. Applied to amyloid deposits formed in a cell culture model of systemic amyloid A amyloidosis, we could determine the structural morphology of the fibrils directly in the deposit. The deposited fibrils are arranged in different networks, and depending on the relative fibril orientation, we can distinguish between fibril meshworks, fibril bundles, and amyloid stars. These networks are frequently infiltrated by vesicular lipid inclusions that may originate from the death of the amyloid-forming cells. Our data support the role of nonfibril components for constructing fibril deposits and provide structural views of different types of lipid-fibril interactions.

[Pathological and clinical correlations in renal AA amyloidosis: A Moroccan series of 30 cases]

OBJECTIVE

Study of histological and clinical correlations of 30 cases of renal amyloidosis AA diagnosed between November 2010 and December 2012.

RESULTS

The main causes associated with amyloidosis AA were represented by chronic infectious diseases (60%). Nephrotic syndrome and renal failure were observed in 94% and 73% respectively. The distribution of amyloid deposits: 90% of patients had a glomerular form and 10% had a vascular form. Inflammatory reaction associated with AA renal amyloidosis was present in 50% of cases. This inflammation was observed near amyloid deposits associated with a deposition of immunoglobulin chains and/or complement factors.

CONCLUSION

Our study confirms the predominance of AA amyloidosis complicating chronic infectious diseases, especially tuberculosis. Our data point out a relationship between the morphology of renal AA amyloidosis, its clinical presentation and prognosis.

Human SAA1-derived amyloid deposition in cell culture: a consistent model utilizing human peripheral blood mononuclear cells and serum-free medium

Amyloid A (AA) amyloidosis is a fatal disease caused by extracellular deposition of fibrils derived from serum AA (SAA). AA amyloid fibril formation has previously been modeled in macrophage cultures using highly amyloidogenic mouse SAA1.1, but attempts to do the same with human SAA invariably failed. Our objective was to define conditions that support human SAA-derived amyloid formation in peripheral blood mononuclear cell (PBMC) cultures. Two conditions were found to be critical - omission of fetal calf serum and use of StemPro34, a lipid-enriched medium formulated for hematopoietic progenitor cells. Cultures maintained in serum-free StemPro34 and provided with recombinant human SAA1 in the complete absence of amyloid-enhancing factor exhibited amyloid deposition within 7 d. Amyloid co-localized with cell clusters that characteristically included cells of fibrocytic/dendritic morphology as well as macrophages. These cells formed networks that appeared to serve as scaffolding within and upon which amyloid accumulated. Cells in amyloid-forming cultures demonstrated increased adherence, survival and expression of extracellular matrix components. Of the three human SAA1 isoforms, SAA1.3 showed the most extensive amyloid deposition, consistent with it being the most prevalent isoform in Japanese patients with AA amyloidosis. Attesting to the reproducibility and general applicability of this model, amyloid formation has been documented in cultures established from eight PBMC donors.

Efficient amyloid A clearance in the absence of immunoglobulins and complement factors

Amyloid A amyloidosis is a protein misfolding disease characterized by deposition of extracellular aggregates derived from the acute-phase reactant serum amyloid A protein. If untreated, amyloid A amyloidosis leads to irreversible damage of various organs, including the kidneys, liver, and heart. Amyloid A deposits regress upon reduction of serum amyloid A concentration, indicating that the amyloid can be efficiently cleared by natural mechanisms. Clearance was proposed to be mediated by humoral immune responses to amyloid. Here, we report that amyloid clearance in mice lacking complement factors 3 and 4 (C3C4(-/-)) was equally efficient as in wild-type mice (C57BL/6), and was only slightly delayed in agammaglobulinemic mice (J(H-/-)). Hence, antibodies or complement factors are not necessary for natural amyloid clearance, implying the existence of alternative physiological pathways for amyloid removal.

Serum amyloid A activates the NLRP3 inflammasome via P2X7 receptor and a cathepsin B-sensitive pathway

Serum amyloid A (SAA) is an acute-phase protein, the serum levels of which can increase up to 1000-fold during inflammation. SAA has a pathogenic role in amyloid A-type amyloidosis, and increased serum levels of SAA correlate with the risk for cardiovascular diseases. IL-1β is a key proinflammatory cytokine, and its secretion is strictly controlled by the inflammasomes. We studied the role of SAA in the regulation of IL-1β production and activation of the inflammasome cascade in human and mouse macrophages, as well as in THP-1 cells. SAA could provide a signal for the induction of pro-IL-1β expression and for inflammasome activation, resulting in secretion of mature IL-1β. Blocking TLR2 and TLR4 attenuated SAA-induced expression of IL1B, whereas inhibition of caspase-1 and the ATP receptor P2X(7) abrogated the release of mature IL-1β. NLRP3 inflammasome consists of the NLRP3 receptor and the adaptor protein apoptosis-associated speck-like protein containing CARD (a caspase-recruitment domain) (ASC). SAA-mediated IL-1β secretion was markedly reduced in ASC(-/-) macrophages, and silencing NLRP3 decreased IL-1β secretion, confirming NLRP3 as the SAA-responsive inflammasome. Inflammasome activation was dependent on cathepsin B activity, but it was not associated with lysosomal destabilization. SAA also induced secretion of cathepsin B and ASC. In conclusion, SAA can induce the expression of pro-IL-1β and activation of the NLRP3 inflammasome via P2X(7) receptor and a cathepsin B-sensitive pathway. Thus, during systemic inflammation, SAA may promote the production of IL-1β in tissues. Furthermore, the SAA-induced secretion of active cathepsin B may lead to extracellular processing of SAA and, thus, potentially to the development of amyloid A amyloidosis.

Differential affinity of serum amyloid A1 isotypes for high-density lipoprotein

Serum amyloid A (SAA), a precursor of reactive amyloid deposits, is a multigene product. SAA1, predominant both as an amyloid precursor and in plasma, consists of three allelic variants (SAA1.1, SAA1.3, and SAA1.5). Several investigations have shown that the SAA1.3 allele is associated with susceptibility to AA-amyloidosis in Japanese, and the SAA1.5 allele is related with higher serum concentrations of SAA. However, these results have not been interpreted functionally. This study assessed the affinity of SAA isotypes for high-density lipoprotein (HDL), to which SAA binds in plasma. Using a surface plasmon resonance-based apparatus (BIAcore), the affinity between immobilized recombinant human SAAs and HDL was determined. The SAA concentration was measured in fractions after ultracentrifugation (d = 1.23) of sera from patients with rheumatoid arthritis, whose SAA1 genotypes were determined. In the BIAcore analysis, as the dissociation reaction under the conditions used was too rapid to fit the typical kinetic model, the steady-state affinity model was used. The affinity (kd) of SAA1.1, SAA1.3, and SAA1.5 for HDL was 1.4 x 10(-5), 1.8 x 10(-5), and 3.7 x 10(-6), respectively. rSAA1.5 showed significantly (p < 0.05) stronger affinity than the other two. The fraction of lipid-free SAA in serum was significantly (p < 0.001) lower in the patients with larger numbers of the 1.5 allele at the SAA1 locus. These results suggest that the relatively high affinity of SAA1.5 may cause the high serum concentration and may be related to the low susceptibility to amyloidosis.

Cathepsin D activity protects against development of type AA amyloid fibrils

BACKGROUND

The extracellular, fibrillar deposits of reactive (secondary) amyloidosis are composed of amyloid A (AA) protein, a proteolytically derived fragment of the acute phase protein serum amyloid A (SAA). While complete degradation of SAA precludes amyloid formation, limited cleavage which generates AA protein is considered part of the pathogenic mechanism.

MATERIALS AND METHODS

In this study, we investigated SAA degradation by lysosomal enzymes cathepsins B, D, and K, and assessed the impact of cathepsin activity on AA amyloid formation in a cell culture model using peripheral blood mononuclear cells from healthy volunteers.

RESULTS

Lysates of human mononuclear cells were capable of degrading SAA. Degradation was significantly reduced by inhibition of cathepsin D with pepstatin A. Inhibition of cathepsin B or cathepsin K, however, had no effect. The SAA fragment pattern generated by mononuclear cell lysates was similar to that produced by incubating SAA with purified human cathepsin D. Consistent with in vitro findings, amyloid formation in human monocyte cultures was increased by 43% when cathepsin D was inhibited, but remained unaffected by inhibition of cathepsin B or cathepsin K.

CONCLUSION

These data provide evidence that cathepsin D but not cathepsin B or cathepsin K is physiologically important in SAA degradation and hence in preventing SAA from accumulating and serving as precursor of AA amyloid fibrils.

Serologic evaluation of clinical and subclinical secondary hepatic amyloidosis in rhesus macaques (Macaca mulatta)

Secondary hepatic amyloidosis in nonhuman primates carries a grave prognosis once animals become clinically ill. The purpose of this study was to establish serologic parameters that potentially could be used to identify rhesus macaques undergoing subclinical development of secondary hepatic amyloidosis. A retrospective analysis was completed by using serum biochemical profiles from 26 histologically diagnosed amyloidotic macaques evaluated at 2 stages of disease, clinical and subclinical (3 to 32 mo prior to clinical signs of disease). Standard serum biochemistry values for cases were compared with institutional age- and gender-specific references ranges by construction of 95% confidence intervals for the difference between means. In addition, 19 histologically diagnosed amyloidotic macaques and 19 age-matched controls were assayed for changes in various parameters by using routinely banked, frozen (-80 degrees C) sera available from clinical and subclinical time points. Clinically amyloidotic animals displayed increased levels of alkaline phosphatase, aspartate aminotransferase, lactate dehydrogenase, gamma glutamyltranspeptidase, and macrophage colony-stimulating factor and significantly decreased quantities of albumin and total cholesterol. Subclinical amyloidotic animals displayed increased levels of alkaline phosphatase, aspartate aminotransferase, lactate dehydrogenase, and serum amyloid A and decreased concentrations of albumin and total cholesterol. The serologic parameters studied indicate a temporal relationship of these factors not previously described, show a clear pattern of disease progression, and could be useful in subclinical disease detection.

Acute-phase response protein serum amyloid A stimulates renal tubule formation: studies in vitro and in vivo

Serum amyloid A protein (SAA) surges 1,000-fold in the blood of acute-phase animals, and yet its function during these acute events remains unknown. We report herein that SAA stimulates a developmental program in cultured NRK-52E cells that culminates in differentiated and functional tubules that feature a proximal tubule phenotype. We also found strong SAA expression in states of tubule formation (in utero stage) and regeneration (recovery from ischemia-reperfusion injury). These data lend support to a novel view of a more localized renal acute-phase reaction, where renal SAA may act as a paracrine or autocrine molecule that promotes tubule formation during development and repair.

Diffusible amyloid oligomers trigger systemic amyloidosis in mice

AA (amyloid protein A) amyloidosis in mice is markedly accelerated when the animals are given, in addition to an inflammatory stimulus, an intravenous injection of protein extracted from AA-laden mouse tissue. Previous findings affirm that AA fibrils can enhance the in vivo amyloidogenic process by a nucleation seeding mechanism. Accumulating evidence suggests that globular aggregates rather than fibrils are the toxic entities responsible for cell death. In the present study we report on structural and morphological features of AEF (amyloid-enhancing factor), a compound extracted and partially purified from amyloid-laden spleen. Surprisingly, the chief amyloidogenic material identified in the active AEF was diffusible globular oligomers. This partially purified active extract triggered amyloid deposition in vital organs when injected intravenously into mice. This implies that such a phenomenon could have been inflicted through the nucleation seeding potential of toxic oligomers in association with altered cytokine induction. In the present study we report an apparent relationship between altered cytokine expression and AA accumulation in systemically inflamed tissues. The prevalence of serum AA monomers and proteolytic oligomers in spleen AEF is consistent to suggest that extrahepatic serum AA processing might lead to local accumulation of amyloidogenic proteins at the serum AA production site.

AA-amyloidosis can be transferred by peripheral blood monocytes

Spongiform encephalopathies have been reported to be transmitted by blood transfusion even prior to the clinical onset. Experimental AA-amyloidosis shows similarities with prion disease and amyloid-containing organ-extracts can prime a recipient for the disease. In this systemic form of amyloidosis N-terminal fragments of the acute-phase reactant apolipoprotein serum amyloid A are the main amyloid protein. Initial amyloid deposits appear in the perifollicular region of the spleen, followed by deposits in the liver. We used the established murine model and induced AA-amyloidosis in NMRI mice by intravenous injections of purified amyloid fibrils ('amyloid enhancing factor') combined with inflammatory challenge (silver nitrate subcutaneously). Blood plasma and peripheral blood monocytes were isolated, sonicated and re-injected into new recipients followed by an inflammatory challenge during a three week period. When the animals were sacrificed presence of amyloid was analyzed in spleen sections after Congo red staining. Our result shows that some of the peripheral blood monocytes, isolated from animals with detectable amyloid, contained amyloid-seed that primed for AA-amyloid. The seeding material seems to have been phagocytosed by the cells since the AA-precursor (SAA1) was found not be expressed by the monocytes. Plasma recovered from mice with AA amyloidosis lacked seeding capacity. Amyloid enhancing activity can reside in monocytes recovered from mice with AA-amyloidosis and in a prion-like way trigger amyloid formation in conjunction with an inflammatory disorder. Human AA-amyloidosis resembles the murine form and every individual is expected to be exposed to conditions that initiate production of the acute-phase reactant. The monocyte-transfer mechanism should be eligible for the human disease and we point out blood transfusion as a putative route for transfer of amyloidosis.

Rapid induction of experimental AA amyloidosis in mink by intravenous injection of amyloid enhancing factor

Studies of amyloid enhancing factor (AEF)-induced amyloidosis are commonly performed in mice. In mink, earlier studies of amyloid A (AA) amyloidosis showed that the predeposition phase was highly variable. Thus, the aim of the study was to establish an AEF-induced AA amyloidosis model in mink to facilitate studies of early amyloid deposition in a species with prominent ellipsoids, anatomical structures lacking in mice but present in most other mammals. AEF was extracted from mink spleens containing AA. Mink received one intravenous injection of AEF and repeated subcutaneous injections of lipopolysaccharide (LPS) as an inflammatory stimulus. On day 4, small amounts of amyloid were detected in the marginal zone in the spleen. On day 7, considerable amyloid deposition was detected in the ellipsoids and marginal zones in the spleen and in the space of Disse in the liver. By immunohistochemistry, the deposits were identified as AA amyloid. Immunolabeling was also detected in lymphoid follicles and the red pulp of some animals. Control animals receiving only AEF were negative. Control animals receiving only LPS were negative except for one of three animals which had small amounts of amyloid in the spleen. The mink AEF model is a suitable tool to study the development of AA amyloidosis in a species with a spleen containing both well-developed ellipsoids and marginal zone.

Lovastatin inhibits formation of AA amyloid

Amyloid A (AA) amyloidosis is a severe complication of many chronic inflammatory disorders, including the hereditary periodic fever syndromes. However, in one of these periodic fever syndromes, the hyper IgD and periodic fever syndrome, amyloidosis is rare despite vigorous, recurring inflammation. This hereditary syndrome is caused by mutations in the gene coding for mevalonate kinase, an enzyme of the isoprenoid pathway. In this study, we used a cell culture system with human monocytes to show that inhibition of the isoprenoid pathway inhibits amyloidogenesis. Inhibition of the isoprenoid pathway by lovastatin resulted in a dose-dependent reduction of amyloid formed [53% at 10 microM (P=0.01)] compared with mononuclear cells that are exposed only to serum AA. The inhibitory effects of lovastatin are reversible by addition of farnesol but not geranylgeraniol. Farnesyl transferase inhibition also inhibited amyloidogenesis. These results implicate that the isoprenoid metabolism could be a potential target for prevention and treatment of AA amyloidosis.

Abeta-globulomers are formed independently of the fibril pathway

Soluble A beta-oligomers are currently discussed as the major causative species for the development of Alzheimer's disease (AD). Consequently, the beta-amyloid cascade hypothesis was extended by A beta-oligomers and their central neuropathogenic role in AD. However, the molecular structure of A beta-oligomers and their relation to amyloid fibril formation remains elusive. Previously we demonstrated that incubation of A beta(1-42) with SDS or fatty acids induces the formation of a homogeneous globular A beta-oligomer termed A beta-globulomer. In this study we investigated the role of A beta-globulomers in the aggregation pathway of A beta-peptide. We used in vitro assays such as thioflavin-T binding and aggregation inhibitors like Congo red to reveal that A beta-peptide in its A beta-globulomer conformation is a structural entity which is independent from amyloid fibril formation. In addition, cellular Alzheimer's-like plaque forming assays show the resistance of A beta-globulomers to deposition as amyloid plaques. We hypothesize that a conformational switch of A beta is decisive for either fibril formation or alternatively and independently A beta-globulomer formation.

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.

Mast cells in the pathogenesis of rheumatic diseases and as potential targets for anti-rheumatic therapy

Increasing evidence suggests that mast cells (MCs), in addition to acute allergic reactions, are involved in the pathogenesis of chronic inflammatory diseases and in particular in rheumatoid arthritis (RA). MCs reside in connective tissues and in synovial tissue of joints. They produce an array of proinflammatory mediators, tissue destructive proteases, and cytokines, most prominently tumor necrosis factor-alpha, which is one of the key cytokines in the pathogenesis of RA. MCs may also participate in the development of secondary or amyloid A amyloidosis, as the partial degradation of the serum amyloid A (SAA) protein by MCs leads to the generation of a highly amyloidogenic N-terminal fragment of SAA. MCs may contribute to the pathogenesis of connective tissue diseases, scleroderma, vasculitic syndromes, and systemic lupus erythematosus, although the data available are limited. Inhibition of the most important growth factor receptor of human MCs, c-Kit, by the selective tyrosine kinase inhibitor imatinib mesylate, induces apoptosis of synovial tissue MCs. As MCs are long-lived cells, induction of their apoptosis could be a feasible approach to inhibit their functions. Preliminary findings suggest that a drug that inhibits c-Kit could have anti-rheumatic activity in the treatment of patients with RA and spondyloarthropathies.

Identification of molecular compounds critical to Alzheimer's-like plaque formation

Amyloid diseases are characterized by the formation of insoluble amyloid fibrils from previously soluble polypeptides. In Alzheimer's disease (AD), amyloid fibrils, formed from beta-amyloid peptides, are deposited as extracellular amyloid plaques only inside the brain. As previously shown, Alzheimer's-like plaque formation in human monocyte culture recapitulates the features of in vivo amyloid plaque formation. Here we show that this cell model can be used to screen compounds that potentially influence amyloid formation in a throughput manner. We found that cellular amyloid fibril formation can be enhanced by dextran sulfate as well as heparin and can be impaired by stabilization of a micell-like beta-amyloid conformer by using myoinositol or by inhibition of phagocytosis with cytochalasin D. Altogether, our data demonstrate the utility of this cell model for investigating pathways and molecular interactions critical to amyloidogenesis.

Serum amyloid a as a useful indicator of disease activity in patients with ankylosing spondylitis

PURPOSE

To investigate whether serum amyloid A (SAA) levels are increased in patients with ankylosing spondylitis (AS) and whether its levels correlate well with AS disease activity.

MATERIALS AND METHODS

Thirty-eight patients with AS and 38 age- and sex-matched control subjects were enrolled in this cross-sectional study. Their SAA levels were quantitatively measured by immunonephelometry. An established, self-administered instrument for evaluating disease activity (Bath Ankylosing Spondylitis Disease Activity Index, BASDAI) was used to measure and acute phase reactants, including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), in patients with AS.

RESULTS

Patients with AS had a significantly higher mean SAA level than controls (9.52 +/- 7.49mg/L versus 2.73 +/- 1.57mg/L, p < 0.05), and the mean BASDAI score of patients with elevated SAA levels was significantly higher than that of patients with normal SAA levels (5.6 +/- 1.3 versus 4.4 +/- 1.5, p < 0.05). SAA levels showed significant correlations with BASDAI scores (r=0.431, p=0.007), ESR (r=0.521, p=0.001) and CRP levels (r=0.648, p < 0.001). Additionally, the correlation between ESR and CRP levels also appeared significant (r=0.703, p < 0.001). In those with normal ESR or CRP levels, SAA levels and BASDAI scores were elevated (p < 0.05) and showed a trend of positive correlation with one another.

CONCLUSION

Our data showed that SAA levels were increased in patients with AS and correlated well with disease activity. These findings suggest that SAA can be used as a valuable indicator of disease activity in AS.

Cellular events associated with the initial phase of AA amyloidogenesis: insights from a human monocyte model

Reactive amyloidosis is a systemic protein deposition disease that develops in association with chronic inflammation. The deposits are composed of extracellular, fibrillar masses of amyloid A (AA) protein, an N-terminal fragment of the acute-phase serum protein serum amyloid A (SAA). The pathogenic conversion of SAA into amyloid has been studied in two human cell culture models, peritoneal cells and peripheral blood monocytes. Human monocyte cultures proved more robust than either mouse or human peritoneal cells at initiating amyloid formation in the absence of a preformed nidus such as amyloid-enhancing factor and particularly well suited for examination of individual cells undergoing amyloid formation. Amyloid-producing monocyte cultures were stained with Congo red and Alcian blue for detection of amyloid and glycosaminglycans, respectively; immunocytochemistry was performed to identify SAA/AA, CD68, CD14, lysosomal protein Lamp-1, and early endosomal protein EEA1. SAA interaction with monocytes was also visualized directly via fluorescence confocal microscopy. Amyloid was initially detected only in intracellular vesicles, but with time was seen extracellularly. Morphologic changes in lysosomes were noted during the early phase of amyloid formation, suggesting that exocytosis of fibrils may occur via lysosome-derived vesicles. Cultures engaged in amyloid formation remained metabolically active; no cytotoxic effects were observed. Mimicking in vivo phenomena, amyloid formation was accompanied by increased glycosaminoglycan content and C-terminal processing of SAA. The ability of human monocytes to endocytose and intracellularly transform SAA into amyloid via a mechanism that requires and maintains, rather than compromises, metabolic activity distinguishes them as a useful model for probing earliest events in the disease process.

Alzheimer-like Plaque Formation by Human Macrophages Is Reduced by Fibrillation Inhibitors and Lovastatin

The cerebral deposition of Abeta-peptide as amyloid fibrils and plaques represents a hallmark characteristic of Alzheimer's disease (AD). AD plaques are defined by their green birefringence after Congo red staining, their spherulite-like superstructure and their association with specific secondary components. Here we show that primary human macrophages promote the formation of amyloid plaques that correspond in all aforementioned characteristics to typical amyloid plaques from diseased tissues: they consist of aggregated Abeta-peptide, they reveal the typical ''Maltese cross" structure and they are associated with the secondary components glycosaminoglycanes, apolipoprotein E (apoE) and the raft lipids cholesterol and sphingomyelin. Plaque formation can be impaired in this cell system by addition of small molecules, such as Congo red, melantonine and lovastatin, suggesting potential applications for the study of cellular amyloid formation and for the identification or validation of drug candidates.

Serum amyloid A (SAA) activates human mast cells which leads into degradation of SAA and generation of an amyloidogenic SAA fragment

Serum amyloid A (SAA) is a precursor for the amyloid A in AA type of amyloidosis. Distribution of mast cells in tissues is similar to the distribution of amyloid deposits in secondary AA-amyloidosis. Therefore, we studied whether mast cells could be involved in SAA metabolism. Human mast cell line (HMC-1) cells were cultured with recombinant human apoSAA (rhSAA), and the production of tumour necrosis factor (TNF)-alpha and interleukin (IL)-1 beta was determined by ELISA. RhSAA and human SAA (huSAA) were incubated with human chymase, tryptase or with intact human mast cell (huMC) in cultures, and degradation of SAA was followed by gel electrophoresis, liquid chromatography and mass spectrometry. SAA induced dose-dependent production of TNF-alpha and IL-1 beta in HMC-1 cells. Tryptase, chymase, and huMC granules degraded efficiently the SAA protein. Degradation of SAA by tryptase, but not by chymase, released a highly amyloidogenic N-terminal fragment of SAA. Finally, incubation of huMC with rhSAA alone resulted in degradation of SAA and formation of protofibrillar intermediates. These results suggest a pathogenic role for mast cells in AA-amyloidosis.

Chemical typing of porcine systemic amyloid as AA-amyloid

Systemic AA amyloidosis is frequently reported in a wide variety of domestic and wild animal species. Porcine amyloidosis is rare and the amyloid has not been typed chemically thus far. In the present study, we have extracted porcine amyloid from formalin-fixed tissue sections. By subsequent amino acid sequencing, an N-terminal fragment was obtained identifying porcine systemic amyloid as AA amyloid. The N-terminal sequence had a great homology to bovine and ovine SAA1, suggesting that pig AA amyloid is derived from the systemic isoform of SAA. It is argued that the low incidence of amyloidosis in pigs is not likely to be attributed to unique features of porcine amyloid precursor protein. Elucidation of the basis for the high apparent resistance of pigs against amyloidosis may yield important clues for treatment and prevention of amyloidosis in other species. This is the first report on chemical identification of porcine amyloid.

Raft lipids as common components of human extracellular amyloid fibrils

Amyloid fibrils are fibrillar polypeptide aggregates from several degenerative human conditions, including Alzheimer's and Creutzfeldt-Jakob diseases. Analysis of amyloid fibrils derived from various human diseases (AA, ATTR, Abeta2M, ALlambda, and ALkappa amyloidosis) shows that these are associated with a common lipid component that has a conserved chemical composition and that is specifically rich in cholesterol and sphingolipids, the major components of cellular lipid rafts. This pattern is not notably affected by the purification procedure, and no tight lipid interactions can be detected when preformed fibrils are mixed with lipids. By contrast, the early and prefibrillar aggregates formed in an AA amyloid-producing cell system interact with the raft marker ganglioside-1, and amyloid formation is impaired by addition of cholesterol-reducing agents. These data suggest the existence of common cellular mechanisms in the generation of different types of clinical amyloid deposits.

Protein folding pathology in domestic animals

Fibrillar proteins form structural elements of cells and the extracellular matrix. Pathological lesions of fibrillar microanatomical structures, or secondary fibrillar changes in globular proteins are well known. A special group concerns histologically amorphous deposits, amyloid. The major characteristics of amyloid are: apple green birefringence after Congo red staining of histological sections, and non-branching 7-10 nm thick fibrils on electron microscopy revealing a high content of cross beta pleated sheets. About 25 different types of amyloid have been characterised. In animals, AA-amyloid is the most frequent type. Other types of amyloid in animals represent: AIAPP (in cats), AApoAI, AApoAII, localised AL-amyloid, amyloid in odontogenic or mammary tumors and amyloid in the brain. In old dogs Abeta and in sheep APrPsc-amyloid can be encountered. AA-amyloidosis is a systemic disorder with a precursor in blood, acute phase serum amyloid A (SAA). In chronic inflammatory processes AA-amyloid can be deposited. A rapid crystallization of SAA to amyloid fibrils on small beta-sheeted fragments, the 'amyloid enhancing factor' (AEF), is known and the AEF has been shown to penetrate the enteric barrier. Amyloid fibrils can aggregate from various precursor proteins in vitro in particular at acidic pH and when proteolytic fragments are formed. Molecular chaperones influence this process. Tissue data point to amyloid fibrillogenesis in lysosomes and near cell surfaces. A comparison can be made of the fibrillogenesis in prion diseases and in enhanced AA-amyloidosis. In the reactive form, acute phase SAA is the supply of the precursor protein, whereas in the prion diseases, cell membrane proteins form a structural source. Abeta-amyloid in brain tissue of aged dogs showing signs of dementia forms a canine counterpart of senile dementia of the Alzheimer type (ccSDAT) in man. Misfolded proteins remain potential food hazards. Developments concerning prevention of amyloidogenesis and therapy of amyloid deposits are shortly commented.

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.

Inhibition of amyloid A amyloidogenesis in vivo and in tissue culture by 4-deoxy analogues of peracetylated 2-acetamido-2-deoxy-alpha- and beta-d-glucose: implications for the treatment of various amyloidoses

Two novel sugars, 2-acetamido-1,3,6-tri-O-acetyl-2,4-dideoxy-alpha- and beta-D-xylo-hexopyranoses, have been synthesized and their effects on heparan sulfate biosynthesis using primary mouse hepatocytes in tissue culture have been assessed. At concentrations of 0.1 and 1.0 mmol/L a mixture of both anomers significantly inhibited the biosynthesis of heparan sulfate by 60% and 99%, respectively. At 1.0 mmol/L the average molecular weight of the heparan sulfate synthesized is reduced from 77 kd to 40 kd. The biosynthetic inhibition is apparent within 1 hour (the earliest time point examined) of exposure of the hepatocytes to the analogues and appears virtually complete throughout a 24-hour incubation period. Using a radiolabeled version of the beta-anomer we demonstrate that the analogue is incorporated into growing heparan sulfate chains. The nature of the analogue, the quantity of analogue isotope incorporated, and the reduction in the size of the heparan sulfate polysaccharide are consistent with UDP activation and incorporation of the analogue and truncation of the growing heparan sulfate chain. At 0.1 mmol/L, and in the presence of a constant concentration of serum amyloid A (the precursor to AA amyloid), each analogue inhibited amyloid deposition (by 95 to 99%) in a tissue culture model of AA amyloidogenesis. At 6 mg/dose twice daily each analogue inhibited in vivo splenic AA amyloid deposition by 65 to 70% when using a rapid induction model of mouse AA amyloidogenesis. These data indicate that polysaccharides, such as heparan sulfate, play an integral part in the pathogenesis of AA amyloid deposition, and potentially other forms of amyloid. These data support our previous work that demonstrated that agents that mimic aspects of heparan sulfate structure and that interfere with heparan sulfate:amyloid protein binding inhibit AA amyloid deposition. They emphasize that heparan sulfate likely plays a critical role in amyloidogenesis, and compounds that interfere with heparan sulfate biosynthesis may provide leads for the development of anti-amyloid therapeutic agents.

Immunolocalization of lipid peroxidation/advanced glycation end products in amyloid A amyloidosis

Chronic inflammation, superimposed by amyloid fibril deposition, is believed to trigger the cascade of oxidative stress response in the affected organs and tissues. We examined immunohistochemically the distribution of 4-hydroxy-2-nonenal (HNE) and N(epsilon)-(carboxymethyl)lysine (CML), markers of lipid peroxidation and advance glycation end products (AGE), respectively, in spleen sections and peritoneal macrophages (MPhi) from mice before and during AA amyloidosis. With time, both HNE and CML immunoreactivities increased significantly in MPhi and splenic reticuloendothelial cells, known to be associated with the clearance of serum amyloid A, the precursor of AA fibrils. HNE and CML were localized to the plasma membrane and the cytoplasmic compartment of MPhi and HNE only at the nuclear membrane. These markers were also colocalized bound to AA fibrils infiltrating the splenic sinus walls. Our results reinforce the notion that oxidative stress is an integral component of amyloidotic tissues. Both lipid peroxidation and AGE have been implicated in protein modification and amyloid fibril formation. The significance of HNE and CML associated with the monocytoid cells and implicated in SAA clearance and AA fibril formation, is discussed with the pathogenesis of AA fibrils.

Humoral Proinflammatory Cytokine and SAA Generation Profiles and Spatio-Temporal Relationship Between SAA and Lysosomal Cathepsin B and D in Murine Splenic Monocytoid Cells During AA Amyloidosis

Evidence shows that tissue macrophages (MPhis), in mice undergoing AA amyloidosis, endocytose acute-phase humoral serum amyloid A (SAA) and traffic it to lysosomes where it is degraded. Incomplete degradation of SAA leads to intracellular nascent AA fibril formation. In vitro, cathepsin (Cat) B is known to generate amyloidogenic SAA derivatives, whereas Cat D generates non-amyloidogenic SAA derivatives, and interferon (IFN-gamma)-treated MPhis show selective increase in Cat B concentration, a factor conducive to AA amyloidogenesis. To understand the cumulative effect of these factors in AA amyloidosis, humoral levels of SAA, IFN-gamma, tumour necrosis factor (TNF-alpha) and granulocyte-macrophage colony-stimulating factor were determined in azocasein (AZC)-treated CD-1 mice. We correlated these responses with the spatio-temporal distribution of SAA, Cat B- and Cat D-immunoreactive splenic reticuloendothelial (RE) cells. AZC-treated CD-1 mice similar to that of A/J mice showed partial amyloid resistance; their peak humoral IFN-gamma and SAA responses overlapped during the pre-amyloid phase. Unexpectedly, Cat D immunoreactivity (IR), instead of Cat B IR, was predominant in the splenic RE cells, indicating an apparent lack of causal relationship between IFN-gamma-mediated increase in Cat B expression. Partial amyloid resistance in CD-1 mice, probably a genetic trait, may be linked to high levels of Cat D expression, causing a delay in nascent AA fibril formation.

[AA Amyloidosis: recent knowledges on pathophysiology]

PURPOSE

Amyloidosis is a rare disease associated with an underestimated frequency because of the need of a pathological diagnosis identifying extracellular deposits with affinity for Congo red. There are moreover 20 proteins that can form extracellular fibril deposits. Some amyloidosis forms are more common than others, especially AA amyloidosis and AL amyloidosis. Among genetic amyloidosis, the transthyretin related amyloidosis is the most prevalent. The amyloid frequency could also be increased if amyloidosis related to Alzheimer's disease or prion's disease is included. In the absence of specific treatment for amyloidosis, researches are focused on amyloidosis pathophysiology especially, on AA amyloid pathophysiology.

CURRENT KNOWLEDGE AND KEY POINTS

Amyloid is not only composed of fibrils but also of proteoglycanes, P component and amyloid-enhancing factor. A new research aim is focused on the cells involved in amyloid formation and on the relationship between amyloid, proteoglycanes and P component.

FUTURE PROSPECTS AND PROJECTS

It was demonstrated that, in the absence of macrophages, an extracellular amyloid formation was possible with amyloid-enhancing factor as starting point. Some inhibitors of intra or extracellular amyloid formation are still to be discovered. Anti-P component has been recently developed; it was successful in the treatment of murin AA amyloidosis and gave some hope concerning the treatment of human amyloidosis.

Novel glycosaminoglycan precursors as anti-amyloid agents, part III

In vivo amyloids consist of two classes of constituents. The first is the disease-defining protein, e.g., amyloid beta (Abeta) in Alzheimer's disease (AD). The second is a set of common structural components that usually are the building blocks of basement membrane (BM), a tissue structure that serves as a scaffold onto which cells normally adhere. In vitro binding interactions between one of these BM components and amyloidogenic proteins rapidly change the conformation of the amyloidogenic protein into amyloid fibrils. The offending BM component is a heparan sulfate (HS) proteoglycan (HSPG), part of which is protein, and the remainder is a specific linear polysaccharide that is the portion responsible for binding and imparting the typical amyloid structure to the amyloid precursor protein/peptide. Our past work has demonstrated that agents that inhibit the binding between HS and the amyloid precursor are effective antiamyloid compounds both in vitro and in vivo. Similarly, 4-deoxy analogs of glucosamine (a precursor of HS biosynthesis) are effective antiamyloid compounds both in culture and in vivo. Our continuing work concerns (1) the testing of our 4-deoxy compounds in a mouse transgenic model of AD, and (2) the continuing design and synthesis of modified sugar precursors of HS, which when incorporated into the polysaccharide will alter its structure so that it loses its amyloid-inducing properties. Since our previous report, 14 additional compounds have been designed and synthesized based on the known steps involved in HS biosynthesis. Of these, eight have been assessed for their effect on HS biosynthesis in hepatocyte tissue cultures, and the two anomers of a 4-deoxy-D-glucosamine analog have been assessed for their inflammation-associated amyloid (AA amyloid) inhibitory properties in vivo. The promising in vivo results with these two compounds have prompted studies using a murine transgenic model of brain Abeta amyloidogenesis. A macrophage tissue-culture model of AA amyloidogenesis has been devised based on the work of Kluve-Beckerman et al. and modified so as to assess compounds in the absence of potential in vivo confounding variables. Preliminary results indicate that the anomers of interest also inhibit AA amyloid deposition in macrophage tissue culture. Finally, an in vitro technique, using liver Golgi (the site of HS synthesis) rather than whole cells, has been devised to directly assess the effect of analogs on HS biosynthesis. The majority of the novel sugars prepared to date are analogs of N-acetylglucosamine. They have been modified either at the 2-N, C-3, C-4, or C-3 and C-4 positions. Results with the majority of the 2-N analogs suggest that hepacyte N-demethylases remove the N-substituent removal. Several of these have the desired effect on HS biosynthesis using hepatocyte cultures and will be assessed in the culture and in vivo AA amyloid models. To date 3-deoxy and 3,4-dideoxy analogs have failed to affect HS synthesis significantly. Compounds incorporating the 6-deoxy structural feature are currently being designed and synthesized.

Heme-oxygenase-1 response, a marker of oxidative stress, in a mouse model of AA amyloidosis

Expression of heme-oxygenase-1 (HO-1), an important marker of oxidative stress, has been studied extensively in the context of Alzheimer's disease. Evidence of HO-1 expression during AA amyloidosis is, at best, sketchy. We present comparative data on HO-1 response in alveolar hydatid cyst (AHC) infected amyloid sensitive (C57BL/6) and amyloid resistant (CE/J) mouse strains. Histochemical and peroxidase-immunoperoxidase methods were used to monitor serum amyloid A (SAA) and AA fibril deposition and HO-1 expression in hepato-splenic reticuloendothelial (RE) cells of the AHC-infected mice prior and during AA fibril deposition. Based on the cumulative data, we conclude that HO-1 expression corresponded closely with tissue deposition of SAA, but was unrelated to AA fibril deposition. To ascertain whether SAA deposition might act as the trigger for HO-1 expression in the RE cells, macrophages were incubated for up to 72 h with SAA-containing mouse serum. The SAA-treated macrophages, although negative for HO-1 protein, demonstrated SAA in the cell extracts and immunocytochemically in the vacuolar compartments, indicating macrophage-mediated endocytosis and trafficking of SAA. In sum, these results exclude SAA and AA fibrils as the primary triggers in the induction of HO-1 expression in RE cells; the potential role of inflammatory cytokines in HO-1 response need to be investigated further.

Pathology of the temporomandibular joint of patients with rheumatoid arthritis--case reports of secondary amyloidosis and macrophage populations

INTRODUCTION

The pathogenetic features of rheumatoid arthritis of the temporomandibular joint (TMJ) are not well defined. In this paper the histological features of TMJs affected by rheumatoid arthritis, and the detection of secondary amyloidosis and macrophage populations in the TMJs of two patients with progressive rheumatoid arthritis are described.

METHODS

In two patients (64-year-old man and 61-year-old woman) with rheumatoid arthritis total TMJ replacement were performed. The surgical specimens were studied histologically.

RESULTS

It was found that the articular cartilage had been completely replaced by proliferating fibrous tissue. Congo red staining and polarizing microscopy revealed amyloid deposition in the connective tissue of the joint space. Immunohistochemical staining showed CD 68 positive macrophages around the amyloid deposition in the proliferating soft tissue.

CONCLUSION

TMJ involvement in rheumatoid arthritis followed the same destructive pathway as in other joints. Amyloid deposition and macrophage populations were detected in two TMJs affected by rheumatoid arthritis.

Amyloid-enhancing factor mediates amyloid formation on fibroblasts via a nidus/template mechanism

OBJECTIVE

To determine the mechanism by which amyloid-enhancing factor (AEF) promotes amyloid deposition, and to test whether AEF seeds deposition of serum amyloid A (SAA) and facilitates conversion to beta-sheet structure.

METHODS

Fibroblasts were cultured with mouse recombinant SAA1.1 and AEF, SAA1.1, or AEF. AEF was prepared as a glycerol extract of spleen from amyloidotic mice. Amyloid was identified by staining with Congo red and examining for green birefringence under polarized light. SAA was localized immunohistochemically. Texas Red-labeled SAA was visualized in living cultures by fluorescence confocal microscopy. AEF was characterized by Western blot analysis using anti-SAA antiserum and N-terminal sequence analysis. Subunits comprising amyloid in fibroblast cultures were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

RESULTS

Amyloid was produced in fibroblast cultures by an AEF-dependent mechanism. AEF, added to culture medium as insoluble protein precipitates, adhered to fibroblast monolayers. SAA bound preferentially to the adherent precipitates. Coincident with SAA binding, precipitates developed an affinity for Congo red. Over time, as more SAA was added, networks of Congo red-positive material producing bright green birefringence also developed outward from AEF precipitates. Amyloid built upon AEF in this manner was composed of full-length SAA. No amyloid was produced in cultures treated with either SAA or AEF alone. SAA and SAA peptides processed in the C-terminal region were the most prominent proteins in the glycerol-extracted AEF preparation.

CONCLUSION

AEF binds to fibroblast monolayers and acts as a sink for SAA. SAA that collects on AEF assembles into an amyloid structure. Thus, it is concluded that AEF serves as both a nidus and a template for amyloid formation.

A pulse-chase study tracking the conversion of macrophage-endocytosed serum amyloid A into extracellular amyloid

OBJECTIVE

To determine whether serum amyloid A (SAA) is internalized by and processed in macrophages en route to deposition as extracellular amyloid.

METHODS

SAA was tracked in cultures of peritoneal macrophages, using a pulse-chase protocol. Macrophages were pulsed with either fluorescently (with Texas Red) tagged SAA (TxR-SAA) or iodinated SAA ((125)I-SAA). Cells were then rinsed and shifted to chase medium containing unlabeled SAA and amyloid-enhancing factor (AEF) to induce amyloid formation. At selected times, TxR-SAA in living cells was observed by confocal scanning microscopy. (125)I-SAA was visualized and quantified in cell lysates and medium by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and phosphorimaging. The presence of amyloid was confirmed by Congo red staining.

RESULTS

Confocal microscopy immediately after the pulse revealed TxR-SAA in endosomal vesicles, with no extracellular or cell surface accumulation. After 24 hours and 72 hours of chase, virtually all TxR-SAA remained intracellular. By 10 days, extracellular fluorescence was very strong, indicating that SAA had moved out of cells. Congo red staining revealed amyloid colocalized with areas of extracellular fluorescence. Experiments using (125)I-SAA showed that while 90-95% of internalized (125)I-SAA was degraded within 24 hours, 5-10% persisted as intact SAA or SAA peptides. Immediately after the pulse, SAA was full-length, but within 24 hours, discrete (125)I-SAA peptides were seen. Each peptide had an intact SAA amino-terminus, as expected for AA protein. Amyloid was detected in cultures as early as 24 hours after initiation of treatment with SAA and AEF and appeared to be intracellular.

CONCLUSION

The results of this study provide direct evidence that SAA internalized by and processed in macrophages forms extracellular amyloid. Based on the presence of (125)I-AA protein in macrophage lysates prior to the appearance of extracellular TxR-labeled amyloid, it was concluded that cleavage of SAA to AA occurs intracellularly.

Binding, trafficking and accumulation of serum amyloid A in peritoneal macrophages

Murine serum amyloid A1.1 (SAA1.1) has been conjugated with the fluorophore Texas Red (TxR), and its interaction with peritoneal macrophages has been visualized by scanning confocal microscopy. Binding of TxR-SAA to cell surfaces was inhibited by an excess of unlabelled SAA indicating the involvement of saturable receptors. Internalized TxR-SAA was seen initially as small punctate signals which in some cells evolved into a fine fluorescent network, a pattern typical of tubular endosomes. Colocalization of TxR-SAA with Cy5-labelled low density lipoprotein (LDL) but not with Oregon Green-labelled transferrin suggested that SAA trafficked through endosomes and lysosomes for degradation rather than through recycling compartments. Consistent with this catabolic pathway, macrophages loaded with TxR-SAA lost fluorescence within several days after being shifted to a fluorophore-free medium. In sharp contrast to this, cells maintained under amyloid-forming conditions, i.e. in the presence of unlabelled SAA and amyloid-enhancing factor (AEF) before and after treatment with TxR-SAA, remained brightly fluorescent over the course of 5 days. Immunocytochemistry verified the accumulation of SAA within macrophages. These findings support the hypothesis that a decreased catabolism of internalized SAA plays a role in AA amyloid pathogenesis.

Amyloid precursors and amyloidosis in inflammatory arthritis

Recent data demonstrating the multifunctional role of serum amyloid A (SAA) in the pathogenesis of amyloidosis have yielded important insights into this potentially fatal consequence of chronic inflammation. SAA has been shown to participate in chemotaxis, cellular adhesion, cytokine production, and metalloproteinase secretion and is thus integrally involved in the disease process. In addition to its production by the liver as part of the acute phase response, SAA is also expressed by several pathologic tissues such atherosclerotic plaques, rheumatoid synovitis and in the brains of patients with Alzheimer disease. Its constitutive production in normal tissue suggests a role for SAA in host defense and tissue turnover. Many pathways are involved in the regulation of SAA, and as more becomes known about these, potential therapeutic targets may be identified. However, the prevention of secondary amyloidosis is best achieved by early and adequate treatment of patients with chronic inflammatory disorders. Suppression of the acute phase response and normalization of SAA levels are likely to significantly impact on the incidence of amyloidosis in inflammatory arthritis.