Immunologic studies of the major nonimmunoglobulin protein of amyloid. I. Identification and partial characterization of a related serum component

A preliminary study on effects of storage time and repeated freezing-thawing on the stability of avian serum amyloid A

Within the field of clinical research, reports on the stability of avian serum amyloid A (SAA) under varying storage conditions are currently scarce. In this study, avian plasma samples were evaluated for SAA, a major acute-phase protein in birds, to assess how varying storage periods and repeated freeze-thaw cycles impact the stability of SAA in the frozen samples. Seven plasma samples from two species and six plasma samples from three species stored at ‒20 °C were used to evaluate the time and temperature effects accordingly. A chicken-specific SAA ELISA kit was used for the measurements. Statistical analysis was performed using SPSS, and the Kruskal-Wallis test and Spearman's correlation coefficient were applied, with statistical significance set at P < 0.05. The SAA concentrations measured daily for 30 days showed no statistically significant differences over time. Freezing-thawing was repeated five times, and a significant negative relationship was confirmed over the cycles (r=‒0.8857, P < 0.05). Although no significance was observed between a decreased concentration and the number of cycles, a decrease in the concentration of > 10% was observed after the fourth cycle in four out of six samples. However, one to three freeze-thaw cycles did not result in a significant decline. Taken together, the results indicate that a negative correlation existed between the mean concentration and multiple freeze-thaw cycles, indicating that these should be avoided where possible.

[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.

Serum Amyloid A Proteins and Their Impact on Metastasis and Immune Biology in Cancer

Simple Summary

The liver responds to systemic inflammation and injury in a coordinated manner, called the acute phase response. While this normal physiological response aims to restore homeostasis, malignant transformation coopts this biology to increase the risk for metastasis, immune evasion, and therapeutic resistance. In this Review, we discuss the importance of acute phase response proteins in regulating cancer biology and treatment efficacy. We also consider potential strategies to intervene on acute phase biology as an approach to improve outcomes in cancer.

Abstract

Cancer triggers the systemic release of inflammatory molecules that support cancer cell metastasis and immune evasion. Notably, this biology shows striking similarity to an acute phase response that is coordinated by the liver. Consistent with this, a role for the liver in defining cancer biology is becoming increasingly appreciated. Understanding the mechanisms that link acute phase biology to metastasis and immune evasion in cancer may reveal vulnerable pathways and novel therapeutic targets. Herein, we discuss a link between acute phase biology and cancer with a focus on serum amyloid A proteins and their involvement in regulating the metastatic cascade and cancer immunobiology.

Causes of AA amyloidosis: a systematic review

From a clinical perspective, there is a need for a reliable and comprehensive list of diseases causing AA amyloidosis. This list could guide clinicians in the evaluation of patients with AA amyloidosis in whom an obvious cause is lacking. In this systematic review, a PubMed, Embase and Web of Science literature search were performed on causes of AA amyloidosis published in the last four decades. Initially, 4066 unique titles were identified, but only 795 full-text articles and letters were finally selected for analysis. Titles were excluded because of non-AA type of amyloidosis, language, no full-text publication or irrelevance. Hundred and fifty diseases were initially reported to be associated with the development of AA amyloidosis. The presence of AA amyloid was proven in 208 articles (26% of all) of which 140 (67%) showed a strong association with an underlying disease process. Disease associations were categorized and 48 were listed as strong, 19 as weak, 23 as unclear, and 60 as unlikely. Most newly described diseases are not really unexpected because they often cause longstanding inflammation. Based on the spectrum of identified causes, a pragmatic diagnostic approach is proposed for the AA amyloidosis patient in whom an obvious underlying disease is lacking.

Serum amyloid A3 confers protection against acute lung injury in Pseudomonas aeruginosa-infected mice

Pseudomonas aeruginosa is a gram-negative bacterium associated with serious illnesses, including ventilator-associated pneumonia and various sepsis syndromes in humans. Understanding the host immune mechanisms against P. aeruginosa is, therefore, of clinical importance. The present study identified serum amyloid A3 (SAA3) as being highly inducible in mouse bronchial epithelium following P. aeruginosa infection. Genetic deletion of Saa3 rendered mice more susceptible to P. aeruginosa infection with decreased neutrophil superoxide anion production, and ex vivo treatment of mouse neutrophils with recombinant SAA3 restored the ability of neutrophils to produce superoxide anions. The SAA3-deficient mice showed exacerbated inflammatory responses, which was characterized by pronounced neutrophil infiltration, elevated expression of TNF-α, KC/CXCL1, and MIP-2/CXCL2 in bronchoalveolar lavage fluid (BALF), and increased lung microvascular permeability compared with their wild-type littermates. BALF neutrophils from Saa3 knockout mice exhibited reduced superoxide anion production compared with neutrophils from wild-type mice. Adoptive transfer of SAA3-treated neutrophils to Saa3 knockout mice ameliorated P. aeruginosa-induced acute lung injury. These findings demonstrate that SAA3 not only serves as a biomarker for infection and inflammation, but also plays a protective role against P. aeruginosa infection-induced lung injury in part through augmentation of neutrophil bactericidal functions.

Serum Amyloid A3 is required for normal lung development and survival following influenza infection

Serum amyloid A (SAA) proteins are a family of acute phase apolipoproteins implicated to directly modulate innate and adaptive immune responses. However, new studies comparing endogenous SAAs and recombinant forms of these proteins have questioned the function of SAA in inflammation and immunity. We generated SAA3 knockout mice to evaluate the contribution of SAA3 to lung development and immune-mediated lung disease. While SAA3 deficiency does not affect the generation of house dust mite-induced allergic asthma, mice lacking SAA3 develop adult-onset obesity, intrinsic airway hyperresponsiveness, increased inflammatory and fibrotic gene expression in the lung, and elevated levels of lung citrullinated proteins. Polyclonally stimulated CD4+ T cells from SAA3-/- mice exhibit impaired glycolytic activity, decreased TH2 and TH1 cytokine secretion, and elevated IL-17A production compared to wild type cells. Polyclonally stimulated CD8+ T cells from SAA3-/- mice also exhibit impaired glycolytic activity as well as a diminished capacity to produce IL-2 and IFNγ. Finally, SAA3-/- mice demonstrate increased mortality in response to H1N1 influenza infection, along with higher copy number of viral RNAs in the lung, a lack of CD8+ T cell IFNγ secretion, and decreased flu-specific antibodies. Our findings indicate that endogenous SAA3 regulates lung development and homeostasis, and is required for protection against H1N1 influenza infection.

Suppression of Lipopolysaccharide-Induced Inflammatory Response by Fragments from Serum Amyloid A

Serum amyloid A (SAA) is known as an acute-phase protein and a biomarker for inflammatory diseases. Published studies have shown that SAA possesses proinflammatory cytokine-like activity and is chemotactic for phagocytes, but the structural basis for these activities remains unidentified. In this article, we report that truncated SAA1 proteins lacking N- and C-terminal sequences exhibit reduced proinflammatory activity and strongly suppress LPS-induced expression of IL-1β, IL-6, and TNF-α in macrophages. A truncated SAA1 containing aa 11-58 was examined further and found to facilitate p38 MAPK phosphorylation while reducing LPS-stimulated phosphorylation of ERK and JNK. In LPS-challenged mice, aa 11-58 reduced the severity of acute lung injury, with significantly less neutrophil infiltration in the lungs and attenuated pulmonary expression of IL-1β, IL-6, and TNF-α. Coadministration of aa 11-58 markedly improved mouse survival in response to a lethal dose of LPS. A potent induction of IL-10 was observed in a TLR2-dependent, but TLR4-independent, manner in macrophages stimulated with aa 11-58. However, the aa 11-58 fragment of SAA1 was unable to induce chemotaxis or calcium flux through formyl peptide receptor 2. These results indicate that the N- and C-terminal sequences contain structural determinants for the proinflammatory and chemotactic activities of SAA1, and their removal switches SAA1 to an anti-inflammatory role. Given that proteolytic processing of SAA is associated with the pathological changes in several diseases, including secondary amyloidosis, our findings may shed light on the structure-function relationship of SAA1 with respect to its role in inflammation.

Structure and Expression of Different Serum Amyloid A (SAA) Variants and their Concentration-Dependent Functions During Host Insults

Serum amyloid A (SAA) is, like C-reactive protein (CRP), an acute phase protein and can be used as a diagnostic, prognostic or therapy follow-up marker for many diseases. Increases in serum levels of SAA are triggered by physical insults to the host, including infection, trauma, inflammatory reactions and cancer. The order of magnitude of increase in SAA levels varies considerably, from a 10- to 100-fold during limited inflammatory events to a 1000-fold increase during severe bacterial infections and acute exacerbations of chronic inflammatory diseases. This broad response range is reflected by SAA gene duplications resulting in a cluster encoding several SAA variants and by multiple biological functions of SAA. SAA variants are single-domain proteins with simple structures and few post-translational modifications. SAA1 and SAA2 are inducible by inflammatory cytokines, whereas SAA4 is constitutively produced. We review here the regulated expression of SAA in normal and transformed cells and compare its serum levels in various disease states. At low concentrations (10-100 ng/ml), early in an inflammatory response, SAA induces chemokines or matrix degrading enzymes via Toll-like receptors and functions as an activator and chemoattractant through a G protein-coupled receptor. When an infectious or inflammatory stimulus persists, the liver continues to produce more SAA (> 1000 ng/ml) to become an antimicrobial agent by functioning as a direct opsonin of bacteria or by interference with virus infection of host cells. Thus, SAA regulates innate and adaptive immunity and this information may help to design better drugs to treat specific diseases.

Serum amyloid A1: Structure, function and gene polymorphism

Inducible expression of serum amyloid A (SAA) is a hallmark of the acute-phase response, which is a conserved reaction of vertebrates to environmental challenges such as tissue injury, infection and surgery. Human SAA1 is encoded by one of the four SAA genes and is the best-characterized SAA protein. Initially known as a major precursor of amyloid A (AA), SAA1 has been found to play an important role in lipid metabolism and contributes to bacterial clearance, the regulation of inflammation and tumor pathogenesis. SAA1 has five polymorphic coding alleles (SAA1.1-SAA1.5) that encode distinct proteins with minor amino acid substitutions. Single nucleotide polymorphism (SNP) has been identified in both the coding and non-coding regions of human SAA1. Despite high levels of sequence homology among these variants, SAA1 polymorphisms have been reported as risk factors of cardiovascular diseases and several types of cancer. A recently solved crystal structure of SAA1.1 reveals a hexameric bundle with each of the SAA1 subunits assuming a 4-helix structure stabilized by the C-terminal tail. Analysis of the native SAA1.1 structure has led to the identification of a competing site for high-density lipoprotein (HDL) and heparin, thus providing the structural basis for a role of heparin and heparan sulfate in the conversion of SAA1 to AA. In this brief review, we compares human SAA1 with other forms of human and mouse SAAs, and discuss how structural and genetic studies of SAA1 have advanced our understanding of the physiological functions of the SAA proteins.

Identification and characterization of different amyloid fibril proteins in tissue sections

Antisera specific for 4 different classes of amyloid fibril proteins, amyloid protein AA and the immunoglobulin light-chain amyloid proteins AlambdaI, AlambdaIV, and AlambdaV, were used to identify these proteins directly in tissue sections from 25 patients with amyloidosis. The specificity of these reactions was established by blocking experiments with purified amyloid fibril proteins and Bence Jones proteins of known variable subgroups. Protein AA was detected in 17 patients, including all 13 with secondary amyloidosis, 2 with primary amyloidosis and 2 with Waldenström's macroglobulinemia. Immunoglobulin light-chain proteins AlambdaI, AlambdaIV, and AlambdaV were in 3, 1, and 2 patients, respectively, all of whom had primary or myeloma/macroglobulinemia-associated amyloidosis. Antiserum specific for the amyloid-related serum protein SAA reacted with the same tissues as anti-AA and had the same pattern of staining in tissue sections.

Serum amyloid A generates high density lipoprotein with cellular lipid in an ABCA1- or ABCA7-dependent manner

Serum amyloid A (SAA) is an amphiphilic helical protein that is found associated with plasma HDL in various pathological conditions, such as acute or chronic inflammation. Cellular lipid release and generation of HDL by this protein were investigated, in comparison with the reactions by apolipoprotein A-I (apoA-I) and several types of cells that appear with various specific profiles of cholesterol and phospholipid release. SAA mediated cellular lipid release from these cells with the same profile as apoA-I. Upregulation of cellular ABCA1 protein by liver X receptor/retinoid X receptor agonists resulted in an increase of cellular lipid release by apoA-I and SAA. SAA reacted with the HEK293-derived clones that stably express human ABCA1 (293/2c) or ABCA7 (293/6c) to generate cholesterol-containing HDL in a similar manner to apoA-I. Dibutyryl cyclic AMP and phorbol 12-myristate 13-acetate, which differentiate apoA-I-mediated cellular lipid release between 293/2c and 293/6c, also exhibited the same differential effects on the SAA-mediated reactions. No evidence was found for the ABCA1/ABCA7-independent lipid release by SAA. Characterization of physicochemical properties of the HDL revealed that SAA-generated HDL particles had higher density, larger diameter, and slower electrophoretic mobility than those generated by apoA-I. These results demonstrate that SAA generates cholesterol-containing HDL directly with cellular lipid and that the reaction is mediated by ABCA1 and ABCA7.

Acute-phase serum amyloid A stimulation of angiogenesis, leukocyte recruitment, and matrix degradation in rheumatoid arthritis through an NF-kappaB-dependent signal transduction pathway

OBJECTIVE

To examine the role of the acute-phase protein serum amyloid A (A-SAA) in regulating cell adhesion molecule expression, leukocyte recruitment, and angiogenesis in rheumatoid arthritis (RA).

METHODS

Intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and matrix metalloproteinase 1 (MMP-1) expression was examined in RA fibroblast-like synoviocytes (FLS) and human microvascular endothelial cells (HMVECs) using flow cytometry and enzyme-linked immunosorbent assay techniques. Peripheral blood mononuclear cell (PBMC) adhesion to FLS/HMVECs was determined by flow cytometry. Angiogenesis was examined using a Boyden chemotaxis chamber and Matrigel tubule formation. NF-kappaB/IkappaBalpha mediation of the effects of A-SAA was investigated using a specific NF-kappaB inhibitor and Western blotting.

RESULTS

A-SAA significantly enhanced the time- and dose-dependent expression of ICAM-1 and VCAM-1 as effectively as interleukin-1beta/tumor necrosis factor alpha. A-SAA promoted the adhesion of PBMCs to FLS and HMVECs. In addition, A-SAA at 10 mug/ml and 50 mug/ml significantly increased endothelial cell tube formation by 69% and 207%, respectively. At 50 mug/ml and 100 mug/ml, A-SAA increased HMVEC migration by 188 +/- 54% and 296 +/- 71%, respectively (mean +/- SEM). A-SAA-induced expression of VCAM-1, ICAM-1, and MMP-1 was down-regulated by NF-kappaB inhibition. Furthermore, A-SAA induced IkappaBalpha degradation and NF-kappaB translocation, suggesting that its proinflammatory effects are mediated in part by NF-kappaB signaling.

CONCLUSION

Our findings demonstrate the ability of A-SAA to induce adhesion molecule expression, angiogenesis, and matrix degradation, mechanisms that are mediated by NF-kappaB. Targeting A-SAA and its signaling pathways may represent a new therapeutic approach in the treatment of RA.

Expression of serum amyloid A, in normal, dysplastic, and neoplastic human colonic mucosa: implication for a role in colonic tumorigenesis

Serum amyloid A (SAA) is an acute phase reactant, whose level in the blood is elevated in response to trauma, infection, inflammation, and neoplasia. Elevated levels of SAA in the serum of cancer patients were suggested to be of liver origin rather than a tumor cell product. The role of SAA in human malignancies has not been elucidated. We investigated the expression of SAA at various stages of human colon carcinoma progression. Nonradioactive in situ hybridization applied on paraffin tissue sections from 26 colon cancer patients revealed barely detected SAA mRNA expression in normal looking colonic epithelium. Expression was increased gradually as epithelial cells progressed through dysplasia to neoplasia. Deeply invading colon carcinoma cells showed the highest levels of SAA. Expression was also found in colon carcinoma metastases. Cells of lymphoid follicles of the intestinal wall, inflammatory cells, ganglion cells, and endothelial cells, also expressed SAA mRNA. Immunohistochemical staining revealed SAA protein expression that colocalized with SAA mRNA expression. RT-PCR analysis confirmed the expression of the SAA1 and SAA4 genes in colon carcinomas, expression that was barely detectable in normal colon tissues. These findings indicate local and differential expression of SAA in human colon cancer tissues and suggest its role in colonic tumorigenesis.

The hereditary amyloidoses

Hereditary amyloidosis is, in general, a systemic condition related to multiple organ system involvement by beta-structured protein deposits. As such, it often mimics the more common forms of systemic amyloidosis: immunoglobulin light chain (AL, primary) and reactive (AA, secondary). The challenge diagnostically is to recognize hereditary amyloidosis as a distinct entity and then to determine the specific type of genetic disease. There are several types of hereditary amyloidosis and precise diagnosis is essential for proper therapy and genetic counselling. This chapter strives to present the subject of hereditary amyloidosis in a way which facilitates understanding of the disease, of the means for diagnosis, of the present and possible future therapies, and of the importance of combined basic and medical research.

Enrichment of serum amyloid proteins by hydrophobic interaction chromatography combined with two-dimensional electrophoresis with immobilised pH gradients

Serum amyloid A protein was subjected to one-step octyl-Sepharose extraction in three different dimensions. Elution was performed partly without UV recording, and with urea or guanidine-based buffers. The eluent was applied directly to denaturing two-dimensional electrophoresis with immobilised pH gradient, or octyl-Sepharose extracted fractions were pooled and lyophilised before application. Proteins were characterised by N-terminal analysis or mass spectrometry. In most of the species that were studied, previously undescribed serum amyloid proteins were detected. Compared to conventional strategies, the presented techniques are more rational and yield more comprehensive information. The presented data also provide a basis for novel perspectives regarding certain inflammatory conditions.

Significance of serum amyloid A on the prognosis in patients with renal cell carcinoma

BACKGROUND

Evidence of systemic inflammation, i.e., elevation of serum C-reactive protein, interleukin-6, and/or the erythrocyte sedimentation rate, is correlated to poorer prognosis of patients with renal cell carcinoma (RCC). Serum amyloid A (SAA) has been recognized mainly as acute-phase reactant.

METHODS

Serum SAA from 72 patients with RCC were examined. Thirty-eight of 72 patients with RCC had elevated SAA compared with 17 healthy donors.

RESULTS

The disease specific survival rate was significantly lower in the elevated SAA group, and SAA level was shown to be an independent prognostic factor by univariate and multivariate analysis.

CONCLUSIONS

Evaluation of serum SM level in RCC patients may be a useful prognostic indicator.

NMR structure of human apolipoprotein C-II in the presence of sodium dodecyl sulfate

The structure and protein-detergent interactions of apolipoprotein C-II (apoC-II) in the presence of SDS micelles have been investigated using circular dichroism and heteronuclear NMR techniques applied to (15)N-labeled protein. Micellar SDS, a commonly used mimetic of the lipoprotein surface, inhibits the aggregation of apoC-II and induces a stable structure containing approximately 60% alpha-helix as determined by circular dichroism. NMR reveals the first 12 residues of apoC-II to be structurally heterogeneous and largely disordered, with the rest of the protein forming a predominantly helical structure. Three regions of helical conformation, residues 16-36, 50-56, and 63-77, are well-defined by NMR-derived constraints, with the intervening regions showing more loosely defined helical conformation. The structure of apoC-II is compared to that determined for other apolipoproteins in a similar environment. Our results shed light on the lipid interactions of apoC-II and its mechanism of lipoprotein lipase activation.

The changing concepts of amyloid

The first issue of the Archives of Pathology & Laboratory Medicine, published 75 years ago, contained an article by Richard Jaffé on the experimental induction of amyloidosis in mice. This publication was one of a series of milestones that have marked our ongoing and evolving concept of amyloidosis, beginning with the first description by Virchow more than a century ago. Since that time, scientific understanding of amyloidogenesis has expanded through the involvement of newly developed techniques, such as biochemical analysis, electron microscopy, and molecular genetics. As a result of these investigations, it is now known that amyloidoses comprise an entire family of sporadic, familial and/or inherited, degenerative, and infectious disease processes, linked by the common theme of abnormal protein folding and deposition. This article seeks to provide a synopsis of the present state of our knowledge with regard to these disorders, including current terminology, classification, major clinical syndromes, and diagnosis.

Human apolipoprotein C-II forms twisted amyloid ribbons and closed loops

Human apolipoprotein C-II (apoC-II) self-associates in solution to form aggregates with the characteristics of amyloid including red-green birefringence in the presence of Congo Red under cross-polarized light, increased fluorescence in the presence of thioflavin T, and a fibrous structure when examined by electron microscopy. ApoC-II was expressed and purified from Escherichia coli and rapidly exchanged from 5 M guanidine hydrochloride into 100 mM sodium phosphate, pH 7.4, to a final concentration of 0.3 mg/mL. This apoC-II was initially soluble, eluting as low molecular weight species in gel filtration experiments using Sephadex G-50. Circular dichroism (CD) spectroscopy indicated predominantly unordered structure. Upon incubation for 24 h, apoC-II self-associated into high molecular weight aggregates as indicated by elution in the void volume of a Sephadex G-50 column, by rapid sedimentation in an analytical ultracentrifuge, and by increased light scattering. CD spectroscopy indicated an increase in beta-sheet content, while fluorescence emission spectroscopy of the single tryptophan revealed a blue shift and an increase in maximum intensity, suggesting repositioning of the tryptophan into a less polar environment. Electron microscopy of apoC-II aggregates revealed a novel looped-ribbon morphology (width 12 nm) and several isolated closed loops. Like all of the conserved plasma apolipoproteins, apoC-II contains amphipathic helical regions that account for the increase in alpha-helix content on lipid binding. The increase in beta-structure accompanying apoC-II fibril formation points to an alternative folding pathway and an in vitro system to explore the general tendency of apolipoproteins to form amyloid in vivo.

Expression and function of serum amyloid A, a major acute-phase protein, in normal and disease states

Serum amyloid A (SAA), the precursor protein in inflammation-associated reactive amyloidosis (AA-type), is an acute phase reactant whose level in the blood increases in response to various insults. It is expressed in the liver, but its physiological role is not well understood. Recently, a broader view of SAA expression and function has been emerging. Expression studies show local production of SAA proteins in histologically normal, atherosclerotic, Alzheimer, inflammatory, and tumor tissues. Binding sites in the SAA protein for high density lipoproteins, calcium, laminin, and heparin/heparan-sulfate were described. Adhesion motifs were identified and new functions, affecting cell adhesion, migration, proliferation and aggregation have been described. These findings emphasize the importance of SAA in various physiological and pathological processes, including inflammation, atherosclerosis, thrombosis, AA-amyloidosis, rheumatoid arthritis, and neoplasia. In addition, recent experiments suggest that SAA may play a "housekeeping" role in normal human tissues.

[Mechanisms of amyloidosis and the proteins involved]

INTRODUCTION

Recent data in amyloid research have shed light on the amyloid substance and have broadened our knowledge on the mechanism of amyloid deposition.

CURRENT KNOWLEDGE AND KEY POINTS

Despite uniform physical properties relating to the presence of beta-pleates, amyloid deposits are chemically heterogeneous and have different origins; additional types will probably be described in the future. Immunohistochemical techniques using specific antisera for each of the major protein present in fibrils could help greatly to subclassify these disorders. In most circumstances, a circulating precursor protein may result from overproduction of either intact or aberrant molecule, a reduction in its degradation or excretion, or genetic abnormalities associated with variant proteins. The cleavage of protein precursor molecules of the protein component of amyloid fibrils characterizes amyloidogenesis, though it is not necessary for some amyloidosis forms. This review summarizes advances in the understanding of the nature of amyloid substances, the mechanism of amyloid deposition and the principal pathogenic hypothesis.

FUTURE PROSPECTS AND PROJECTS

SAP component is common in all amyloidosis and may be the target for future therapy.

The relation between familial Mediterranean fever and amyloidosis

Familial Mediterranean fever (FMF) is the most prevalent type of hereditary recurrent fever. Although the inflammatory attacks that characterize the disease may sometimes be debilitating, reactive amyloidosis remains the most serious manifestation of FMF. Daily treatment with colchicine can prevent both the attacks and amyloid deposition, but FMF-associated amyloidosis has not been eradicated and is still a cause of chronic renal failure in children and adults. The discovery of the gene responsible for FMF, Mediterranean fever gene (MEFV), and of associated mutations represents a major advance that now allows researchers to establish a strong, although nonexclusive association between one specific mutation, M694V, and the amyloid phenotype.

Serum amyloid A (SAA): a concise review of biology, assay methods and clinical usefulness

Serum amyloid A (SAA) is a family of proteins encoded in a multigene complex. Acute phase isotypes SAA1 and SAA2 are synthesized in response to inflammatory cytokines. SAA and C-reactive protein (CRP) are now the most sensitive indicators for assessing inflammatory activity. In viral infection and kidney allograft rejection, SAA proved more useful than CRP. Development of convenient assay methods for SAA will facilitate its use in clinical laboratories.

The heparin/heparan sulfate-binding site on apo-serum amyloid A. Implications for the therapeutic intervention of amyloidosis

Serum amyloid A isoforms, apoSAA1 and apoSAA2, are apolipoproteins of unknown function that become major components of high density lipoprotein (HDL) during the acute phase of an inflammatory response. ApoSAA is also the precursor of inflammation-associated amyloid, and there is strong evidence that the formation of inflammation-associated and other types of amyloid is promoted by heparan sulfate (HS). Data presented herein demonstrate that both mouse and human apoSAA contain binding sites that are specific for heparin and HS, with no binding for the other major glycosaminoglycans detected. Cyanogen bromide-generated peptides of mouse apoSAA1 and apoSAA2 were screened for heparin binding activity. Two peptides, an apoSAA1-derived 80-mer (residues 24-103) and a smaller carboxyl-terminal 27-mer peptide of apoSAA2 (residues 77-103), were retained by a heparin column. A synthetic peptide corresponding to the CNBr-generated 27-mer also bound heparin, and by substituting or deleting one or more of its six basic residues (Arg-83, His-84, Arg-86, Lys-89, Arg-95, and Lys-102), their relative importance for heparin and HS binding was determined. The Lys-102 residue appeared to be required only for HS binding. The residues Arg-86, Lys-89, Arg-95, and Lys-102 are phylogenetically conserved suggesting that the heparin/HS binding activity may be an important aspect of the function of apoSAA. HS linked by its carboxyl groups to an Affi-Gel column or treated with carbodiimide to block its carboxyl groups lost the ability to bind apoSAA. HDL-apoSAA did not bind to heparin; however, it did bind to HS, an interaction to which apoA-I contributed. Results from binding experiments with Congo Red-Sepharose 4B columns support the conclusions of a recent structural study which found that heparin binding domains have a common spatial distance of about 20 A between their two outer basic residues. Our present work provides direct evidence that apoSAA can associate with HS (and heparin) and that the occupation of its binding site by HS, and HS analogs, likely caused the previously reported increase in amyloidogenic conformation (beta-sheet) of apoSAA2 (McCubbin, W. D., Kay, C. M., Narindrasorasak, S., and Kisilevsky, R. (1988) Biochem. J. 256, 775-783) and their amyloid-suppressing effects in vivo (Kisilevsky, R., Lemieux, L. J., Fraser, P. E., Kong, X., Hultin, P. G., and Szarek, W. A. (1995) Nat. Med. 1, 143-147), respectively.

In vitro peroxidase oxidation induces stable dimers of beta-amyloid (1-42) through dityrosine bridge formation

beta-amyloid (A beta) is a normal soluble peptide found in the cerebrospinal fluid (CSF) and other biological fluids. A beta fibrils are associated with Alzheimer's disease (AD) senile plaques. We have used purified soluble A beta (1-42) and A beta (12-28) peptides in order to determine the oxidative modification induced in these peptides by exposure to peroxidase and hydrogen peroxide. We have demonstrated that under these in vitro conditions, dimeric forms of A beta (1-42) can be detected by high-resolution polyacrylamide SDS-PAGE electrophoresis. Further experiments performed by reverse-phase high performance liquid chromatography (RP-HPLC), and monitored by fluorescence detection, showed that the dimeric A beta (1-42) forms induced by the peroxidase reaction are the outcomes of dityrosine bridge formation. This cross-link results from the enzyme catalyzed oxidation. During this reaction, phenolic coupling of tyrosine residues of two A beta (1-42) peptides occurs. No detectable peroxidative modifications were observed with the A beta (12-28) peptide which lacks a tyrosine residue. Since oxidative stress is thought to be associated with AD, the experimental model described here can help in understanding the early events leading to chemical, structural and conformational modifications before the conversion of sA beta to amyloid fibrils and eventually the formation of senile plaques in AD.

Aqueous two-phase partition and detergent precipitation of a drug-responsive NADH oxidase from the HeLa cell surface

The partitioning behaviour of a drug (capsaicin)-responsive NADH oxidase (tNOX) activity released from HeLa cells by low pH treatment followed by heat and proteinase K was determined. When partitioned in a standard 6.4% PEG 3350/6.4% dextran T-500 two-phase system, the bulk of the tNOX activity was in the dextran-rich lower phase. The activity was inhibited by and bound to the triazine dye, Cibacron blue. Affinity partition, where the Cibacron blue was coupled to amino PEG 5000 and added to the first two-phase separation step, resulted in the partitioning of activity to the upper PEG phase. A second partition with PEG-salts resulted in the release of the tNOX from the Cibacron blue amino PEG enriched phase into the salt-enriched lower phase. The phase-purified protein exhibited anomalous behavior and tended to multimerize in sodium dodecyl sulphate (SDS) prior to SDS-polyacrylamide gel electrophoresis (PAGE). Multimerization appeared to be enhanced by PEG. The multimerization was enhanced with the reduced protein in the presence of detergent prior to SDS-PAGE. In addition, the activity was precipitated by PEG 8000 at concentrations between 6 and 30% by weight. In the presence of or after exposure to PEG 3350 or PEG 8000, the protein could not be detected by Western blot analysis after SDS-PAGE suggesting that the protein failed to enter the gel even though other HeLa cell surface proteins were unaffected. The anomalous multimerization behavior has thus far precluded the use of phase partition as a practical purification step for the oxidase.

Characterization of high affinity binding between laminin and the acute-phase protein, serum amyloid A

Serum amyloid A isoforms, apoSAA1 and apoSAA2, are acute-phase proteins of unknown function and can be precursors of amyloid AA peptides (AA) found in animal and human amyloid deposits. These deposits are often a complication of chronic inflammatory disorders and are associated with a local disturbance in basement membrane (BM). In the course of trying to understand the pathogenesis of this disease laminin, a major BM glycoprotein, has been discovered to bind saturably, and with high affinity to murine acute-phase apoSAA. This interaction involves a single class of binding sites, which are ionic in nature, conformation-dependent, and possibly involve sulfhydryls. Binding activity was significantly enhanced by Zn2+, an effect possibly mediated through Cys-rich zinc finger-like sequences on laminin. Collagen type IV also bound apoSAA but with lower affinity. Unexpectedly, no binding was detected for perlecan, a BM proteoglycan previously implicated in AA fibrillogenesis, although a low affinity interaction cannot be excluded. Entactin, another BM protein that functions to cross-link the BM matrix and is normally complexed with laminin, could inhibit laminin-apoSAA binding suggesting apoSAA does not bind to normal BM. Since laminin binds apoSAA with high affinity and has previously been shown to codeposit with AA amyloid fibrils, we postulate that laminin interacts with apoSAA and facilitates nucleation events leading to fibrillogenesis. This work also provides further support for the hypothesis that a disturbance in BM metabolism contributes to the genesis of amyloid. The specificity and avidity of the laminin-apoSAA interaction also implies that it may be a normal event occurring during the inflammatory process, which mediates one or more of the functions recently proposed for apoSAA.

Vitreous amyloidosis in familial amyloidotic polyneuropathy. Report of a case with the Val30Met transthyretin mutation

We present a clinical pathological review of vitreous amyloidosis in a case of familial amyloidotic polyneuropathy, type I. Vitreous opacification was the first manifestation of disease in the proband, who was successfully treated with vitrectomy. The eyes were obtained at autopsy after the patient died from an unrelated cause, and the histopathology is presented here. Analysis of DNA from the pathology specimen revealed the most commonly reported transthyretin mutation, Val30Met. The classification of systemic and ocular amyloidosis as well as the genetics of familial amyloidotic polyneuropathy are briefly reviewed.

Ocular amyloidosis, with special reference to the hereditary forms with vitreous involvement

The complex of diseases referred to as amyloidosis is characterized by the deposition of amyloid substance in various tissues. The amyloid protein differs in the various forms of amyloidosis. This variation is the basis of the differences in affected tissues and subsequent clinical dissimilarities. Vitreous involvement in amyloidosis seems to be especially linked to some of the hereditary neuropathies associated with the amyloid protein transthyretin. Characterization of the amyloid proteins during recent decades has allowed a chemical and immunologic classification of amyloid fibrils. This paper presents the basis for classification of amyloidosis, reviews the literature on ocular amyloidosis, with special reference to vitreous involvement, and summarizes clinical findings and frequency of vitreous amyloid involvement in Swedish patients with familial amyloidotic polyneuropathy.

First evidence for the existence of multiple isoforms of bovine serum amyloid-A (apoSAA)

Bovine serum amyloid-A (SAA) was purified from acute-phase high density lipoprotein (HDL) by affinity chromatography and subsequent gel filtration chromatography. The identity of the isolated protein was checked by Western blotting following SDS-urea-PAGE using antisera raised against the purified protein fraction (SAA) and Amyloid A (AA). The antiserum raised against the purified SAA stained Congo red positive regions in the kidney of an AA-amyloidotic cow and reacted on Western blot with an AA-related protein of approximately 14 kDa. Moreover, it immunostained two to three bands, of approximately 14 kDa, present in serum from diseased cows, proportionally to the serum SAA concentration as measured by ELISA. Isoelectric focusing of the purified bovine SAA fraction revealed three major (pI 5.5, 6.0, 6.4) and three minor (pI 4.8, 5.0, 7.3) isoforms and two-dimensional SDS-urea-PAGE confirmed the identity of the major isoforms. Isoelectric focusing of SAA isolated from sera, obtained from cows affected with different diseases, showed a variable ratio of the isoforms. In SAA isolated from serum obtained from a cow suffering from spontaneous AA-amyloidosis only one isoform (pI 4.8) was detectable. It is concluded that the results give first evidence for the existence of multiple isoforms of bovine SAA, occurring in different plasma concentration ratios during different diseases.

The molecular basis of reactive amyloidosis

Reactive amyloidosis is a disease occurring in patients suffering from chronic infections, inflammation, and certain malignant conditions that are characterized by a considerable elevation of the acute phase reactant serum amyloid A (SAA). It is defined by the presence of extracellular deposits of fibrillar material containing amyloid A (AA) as its main component. AA is an 8.5-kd protein structurally identical to the NH2-terminal of the acute phase reactant SAA. SAA consists of a group of evolutionally conserved amphipathic proteins, encoded by a large number of genes and produced abundantly during inflammation, all suggesting an important role, probably of a neutralizing (anti-inflammatory) nature. An analysis of various aspects of SAA provides no clues to the mechanism of amyloid production, its occurrence in only selected individuals, and its preferential relationship to one isotype of SAA. Until more data is available, the present view on AA amyloidogenesis remains hypothetical.

Direct evidence for SAA deposition in tissues during murine amyloidogenesis

To study the mechanism of amyloid deposition, the nature of amyloid proteins formed in experimental murine amyloidosis, was examined. Spleen specimens, 15-60 mg, were homogenized and extracted using aqueous acidic acetonitrile, in a recently developed procedure, making it possible to obtain amyloid proteins from minute amounts of tissue. The extracted material, 1.5-4 mg, was analysed by Western blotting and ELISA using antibodies recognizing differentially proteins AA and SAA. Two immunoreactive proteins of 8 and 12 KDa were isolated and subjected to amino acid analysis and N-terminal sequence determination. The results of immunochemical and chemical examination showed that the 8 and 12 KDa proteins represented proteins AA and SAA, respectively. The data obtained provide new direct evidence for SAA in tissues during murine amyloidogenesis.

Serum amyloid A protein in mink during endotoxin induced inflammation and amyloidogenesis

Two-dimensional electrophoresis was used to study SAA and AA proteins in mink during lipopolysaccharide-induced inflammation and amyloidogenesis. Three isotypes, SAA pI 6.8 and SAA pI 6.5 (both SAA1-like), and SAA pI 6.0 (SAA1- and SAA2-like), were identified in serum after both single and multiple LPS injections. Total SAA serum levels were highest in the early phase of induction, followed by a decrease ranging from 1 to 50% of the peak value during the rest of the experiment. The variation in the total SAA levels correlated with the total SAA mRNA levels. Low total SAA levels were seen both in non-amyloidotic and amyloidotic animals, and a general decrease of all isotypes was demonstrated. In hepatic amyloid fibrils, several AA isotypes, with amino acid sequence homologous exclusively to that of SAA2, were found. In the corresponding splenic material, fragments of histones H2A and H2B constituted most of the low molecular mass proteins, and no protein AA was detected. In spite of low serum levels and a non-specific isotype removal, the results confirm that SAA2 is amyloidogenic in mink.

Serum amyloid A: an acute phase apolipoprotein and precursor of AA amyloid

Serum amyloid A is an acute phase protein complexed to HDL as an apoprotein. The molecular weight is 11.4-12.5 kDa in different species and the protein has from 104 to 112 amino acids, without or with an insertion of eight amino acids at position 72. The protein is very well conserved throughout evolution, indicating an important biological function. The N-terminal part of the molecule is hydrophobic and probably responsible for the lipid binding properties. The most conserved part is from position 38 to 52 and this part is therefore believed to be responsible for the until now unknown biological function. The protein is coded on chromosome 11p in man, and chromosome 7 in mice, and found in all mammals until now investigated, and also in the Peking duck. In the rat a truncated SAA mRNA has been demonstrated, but no equivalent serum protein has been reported. Acute phase SAA is first of all produced in hepatocytes after induction by cytokines, but extrahepatic expression of both acute phase and constitutive SAA proteins have been demonstrated. Several cytokines, first of all IL-1, IL-6 and TNF are involved in the induction of SAA synthesis, but the mutual importance of these cytokines seems to be cell-type specific and to vary in various experimental settings. The role of corticosteroids in SAA induction is somewhat confusing. In most in vitro studies corticosteroids show an enhancing or synergistic effect with cytokines on SAA production in cultured cell. However, in clinical studies and in vivo studies in animals an inhibitory effect of corticosteroids is evident, probably due to the all over anti-inflammatory effect of the drug. Until now no drug has been found that selectively inhibits SAA production by hepatocytes. Effective anti-inflammatory or antibacterial treatment is the only tool for reducing SAA concentration in serum and reducing the risk of developing secondary amyloidosis. The function of SAA is still unclear. Interesting theories, based on current knowledge of the lipid binding properties of the protein and the relation to macrophages, in the transportation of cholesterol from damaged tissues has been advanced. A putative role in cholesterol metabolism is supported by the findings of SAA as an inhibitor of LCAT. The potential that SAA is a modifying protein in inflammation influencing the function of neutrophils and platelets is interesting and more directly related to the inflammatory process itself.(ABSTRACT TRUNCATED AT 400 WORDS)

Preparation of anti-canine serum amyloid A (SAA) serum and purification of SAA from canine high-density lipoprotein

Antiserum to canine serum amyloid A (SAA) was prepared in rabbits by immunization with crude SAA which was prepared from high-density lipoprotein 3 (HDL3) obtained from canine acute-phase serum. The antiserum was absorbed for contaminating antibodies by affinity chromatography using Sepharose 4B coupled with normal canine serum proteins. The rabbit anti-canine SAA serum reacted with a protein and formed a single precipitin line at the position of the alpha 1-region of the immunoelectrophoresis of canine acute-phase serum but did not react with the normal canine serum on immunoelectrophoresis. The antibody to canine SAA was also confirmed by Western blotting analysis. Canine SAA was purified as a low molecular weight protein component from crude SAA by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) after gel filtration chromatography. Purified canine SAA had a molecular weight of 15,000 as estimated by SDS-PAGE. This SAA level was found by enzyme-linked immunosorbent assay (ELISA) to increase 1 day after inoculation with Bordetella bronchiseptica to 9.0-20.1 times the preinoculation value.

Expression of serum amyloid A genes in mink during induction of inflammation and amyloidosis

Serum amyloid A (SAA) is an acute phase protein and the precursor of amyloid protein A (AA) in deposits of secondary amyloidosis. Several isotypes exist in mink, but previous studies suggest that mink AA is derived from only one. To assess the effect of repeated episodes of inflammation and induction of amyloidosis, qualitative and quantitative changes in hepatic and extrahepatic SAA mRNA were studied. Young female mink received subcutaneous lipopolysaccharide injections for amyloid induction. Studies were performed using RNA probes and oligonucleotide probes specific for each of two SAA mRNA species. Northern blot hybridization showed that hepatic SAA1 and SAA2 mRNA levels increased dramatically after inflammatory stimulation, and were subsequently maintained at elevated levels, showing considerable interindividual variation, but only a slight decrease during repeated inflammatory stimuli and the early stages of amyloid deposition. No preferential accumulation of mRNA specifying a particular isotype was found during the experiment. Differential expression of mink SAA mRNA during repeated inflammatory stimulation does not seem to explain why only SAA2-derived AA is found in amyloid deposits. Extrahepatic SAA mRNA seemed to be independently regulated and may thus represent another, yet not characterized, SAA isotype.

Recombinant murine serum amyloid A from baculovirus-infected insect cells: purification and characterization

Serum amyloid A (SAA) is an extremely sensitive acute-phase reactant and precursor to the subunit protein in reactive amyloid deposits. Although the mouse has long served as an informative experimental model, both the function of SAA and the pathogenic mechanism of amyloid formation remain unknown. The production of SAA by a heterologous system was pursued as means of generating readily-renewable amounts of SAA of defined sequence. Murine SAA2 has been expressed in and purified from baculovirus-infected insect cells. Using the transfer vector pBlueBac, SAA2 cDNA was cloned into baculovirus DNA such that expression was under the control of the polyhedrin promoter. Lysates prepared from infected cells contained three amyloid A-immunoreactive forms which accumulated intracellularly over a three day periods. The form having the lowest relative molecular mass, 12.5 kDa, co-migrated in SDS-polyacrylamide gels with the SAA2 present in murine acute-phase serum. Recombinant SAA2 was purified by Sepharose CL-6B chromatography followed by chromatofocusing between pH 8 and pH 5. Amino-terminal sequencing of the purified 12.5 kDa sample confirmed the first 20 residues of mature murine SAA2. After incubation with normal mouse serum, purified recombinant SAA2 fractionated exclusively with lipoprotein complexes, suggesting that it was bound to HDL. Based on this observation, we believe that recombinant SAA can serve as a suitable substitute for the native protein in physiologically relevant studies.

Serum amyloid A (SAA): an acute phase protein and apolipoprotein

Serum amyloid A (SAA) proteins comprise a family of apolipoproteins coded for by at least three genes with allelic variation and a high degree of homology between species. The synthesis of certain members of the family is greatly increased in inflammation. However, SAA is not often used as an acute-phase marker despite being at least as sensitive as C-reactive protein. SAA proteins can be considered as apolipoproteins since they associate with plasma lipoproteins mainly within the high density range, perhaps through amphipathic alpha-helical structure. It is not known why certain subjects expressing SAA develop secondary systemic amyloidosis. There is still no specific function attributed to SAA; however, a popular hypothesis suggests that SAA may modulate metabolism of high density lipoproteins (HDL). This may impede the protective function of HDL against the development of atherosclerosis. The potential significance of the association between SAA and lipoproteins needs further evaluation.

Nomenclature of amyloid and amyloidosis. WHO-IUIS Nomenclature Sub-Committee

This classification of amyloid and amyloidosis is based on the amyloid fibril proteins, followed by a designation of the fibril protein precursor. Additional information includes the protein type or variant (where applicable) and the clinical diagnosis.

A functional characterization of macrophage alterations in casein-treated B6C3F1 mice

We have previously reported that subcutaneous injection of casein, a potent inducer of the immunomodulatory acute phases reactant, serum amyloid A (SAA) protein, produces a marked suppression of humoral responses that require macrophage accessory cell cooperativity in the B6C3F1 mouse. The objective of these studies was to further characterize the immunological changes produced by casein treatment. It was observed that the inhibition of the sRBC IgM AFC response which accompanies casein treatment is dose related to the amount of casein introduced subcutaneously to the mouse. These studies, as well as those previously reported by several laboratories including our own have demonstrated that spleen cells isolated from casein-treated mice also exhibit markedly suppressed humoral responses in vitro. However, casein added directly to naive spleen cell cultures at concentrations significantly higher than those which would be found in the lymphoid tissues of the intact animal have no direct inhibitory effect on the sRBC IgM AFC response, suggesting that casein alone does not exert a direct immunosuppressive effect. Kinetics of recovery studies indicate that the casein-induced immunosuppression is readily reversible. Humoral responses are fully recovered within 3 days, once subcutaneous injections of casein are terminated. In vitro measurements of IL-1 secretion following stimulation of splenic macrophages, isolated from casein treated mice, with lipopolysaccharide indicate no significant effect on the capacity of these cells to produce this cytokine. Direct addition of recombinant IL-1 or interferon-gamma to spleen cell cultures isolated from casein-treated mice also was found to be incapable of reversing the inhibited IgM AFC response. Taken together, these studies strongly suggest that the accessory cell dysfunction associated with macrophages from casein-treated mice is not due to the inability of these cells to secrete IL-1 and indicate that the dysfunction cannot be reversed by IL-1 or interferon-gamma. Casein treatment was also found to markedly inhibit DTH, a cell-mediated immune response requiring macrophage accessory cell function. interestingly, the DTH responses were only affected by casein when it was administered post-sensitization with antigen (sRBC) but prior to antigen challenge. When casein was administered prior to sensitization with antigen, which is analogous to the treatment schedule that was found to suppress the sRBC antibody response, no effect was observed on DTH.

Pulmonary vascular amyloidosis in aged dogs. A new form of spontaneously occurring amyloidosis derived from apolipoprotein AI

The N-terminus of a mutant form of apolipoprotein AI [apoAI] has previously been shown to be the subunit protein of amyloid fibrils in a human kindred with a form of familial amyloid polyneuropathy (FAP, type III) and in a recently reported kindred with a form of non-neuropathic hereditary amyloidosis. In this study, we demonstrate by amino-acid sequence analysis, that a form of vascular amyloidosis occurring in the lungs of aged dogs is derived from a N-terminal fragment of apoAI and that no amino acid substitution is present in this confirmed sequence. This represents the first documentation of apoAI as a precursor for a form of amyloidosis in animals, and provides the first documentation of apoAI as a precursor for amyloid fibrils in a form of age-associated ("senile") amyloidosis. Secondary structure prediction analysis of the N-terminal regions of normal human and dog apoAI indicated a propensity for beta-pleated sheet conformation, and thus amyloidogenesis, in 40 and 45% of the respective sequences. These results suggest that apoAI (like transthyretin) may serve as an amyloid precursor protein for both familial and senile forms of amyloidosis. ApoAI should, therefore, be considered as a potential amyloid precursor when forms of human senile amyloidosis of unknown origin are evaluated.

Purification of serum amyloid A and its isoforms from human plasma by hydrophobic interaction chromatography and preparative isoelectric focusing

The present work was aimed at isolating human serum amyloid A, (SAA), an acute-phase protein mainly complexed to high density lipoproteins, directly from human plasma without sequential ultracentrifugation of lipoproteins and subsequent delipidation of the apolipoprotein moiety. Hydrophobic-interaction fast-protein liquid chromatography on Octylsepharose, using stepwise gradient elution profiles under dissociating conditions, followed by fast-protein liquid-gel permeation chromatography on a Superdex TM75 column revealed a higher than 95% purity of isolated SAA. Further purification of SAA from coeluting apolipoproteins C and A-II was achieved by preparative isoelectric focusing between pH5-7 using a Rotofor apparatus. Separation of the main SAA isoforms, SAA1 (pI 6.5) and SAA1 des-Arg (pI 6.0, lacking the N-terminal arginine), was achieved by anion-exchange fast-protein liquid chromatography on a Fractogel EMD DEAE 650-S column. The purity of the SAA1 and SAA1 des-Arg isoforms, thus isolated, was checked by immunochemical techniques and amino acid analysis. With the described method various SAA isoforms can be isolated, purified and separated directly from human plasma/serum without prior ultracentrifugation.

A sensitive immunochemiluminescence assay for human serum amyloid A protein

We describe an immunochemiluminescence assay for human plasma serum amyloid A protein (SAA) in which specific rabbit polyclonal antibodies against synthetic peptides are used. The detection of the antigen-antibody reaction at 425 nm is based on a brief emission of light by a luminophor component (signal) in response to chemical energy. The working range of the assay covers plasma SAA concentrations from 5 to 100 micrograms/L. The lower detection limit is 5 micrograms/L, the within- and between-assay CVs are less than 12%. Bilirubin, cholesterol and triglyceride in final concentrations of up to 220 mumol/L, 8.1 mmol/L and 2.68 mmol/L, respectively, do not interfere with the assay. Results were correlated with those obtained by the enzyme-linked immunosorbent assay using the same antibodies (r = 0.95; p less than 0.001; n = 50). This method is inexpensive, simple and easily automated.

Analysis and quantitation of the beta-amyloid precursor protein in the cerebrospinal fluid of Alzheimer's disease patients with a monoclonal antibody-based immunoassay

One of the major clinical findings in Alzheimer's disease (AD) is the formation of deposits of beta-amyloid protein in amyloid plaques, derived from the beta-amyloid precursor protein (beta-APP). To determine the possible use of beta-APP as a diagnostic marker for AD in CSF, a monoclonal antibody-based immunoassay specific for this protein was developed. The assay does not differentiate between beta-APP695 and beta-APP751 forms but does preferentially recognize beta-APP751 complexed with a protease. Of the two sets of CSF samples tested, one set, obtained from living patients, gave a slightly lower level of beta-APP in AD and Parkinson's disease patients relative to controls, whereas the other set, composed of postmortem samples, showed no significant differences between the AD and control groups.

Properties of four acute phase proteins: C-reactive protein, serum amyloid A protein, alpha 1-acid glycoprotein, and fibrinogen

Four plasma proteins, referred to as positive acute phase proteins because of increases in concentration following inflammatory stimuli, are reviewed: C-reactive protein (CRP), serum amyloid A protein (SAA), alpha 1-acid glycoprotein (AAG), and fibrinogen. The CRP and SAA may increase in concentration as much as 1000-fold, the AAG and fibrinogen approximately twofold to fourfold. All are synthesized mainly in the liver, but each may be produced in a number of extrahepatic sites. The role of cytokines in induction of the acute phase proteins is discussed, particularly the multiple functional capabilities of interleukin-6 (IL-6). Other cytokines that regulate acute phase gene expression and protein synthesis include IL-1, tumor necrosis factor alpha, interferon gamma, as well as other stimulatory factors and cofactors. The physicochemical characteristics of each protein are reviewed together with the molecular biology. For each protein, the known biological effects are detailed. The following functions for CRP have been described: reaction with cell surface receptors resulting in opsonization, enhanced phagocytosis, and passive protection; activation of the classical complement pathway; scavenger for chromatin fragments; inhibition of growth and/or metastases of tumor cells; modulation of polymorphonuclear function; and a few additional diverse activities. The role of plasma SAA is described as a precursor of protein AA in secondary amyloidosis; other functions are speculative. AAG may play an immunoregulatory role as well as a role in binding a number of diverse drugs. In addition to clot formation, new data are described for binding of fibrinogen and fibrin to complement receptor type 3. Finally, the concentration of each protein is discussed in a wide variety of noninfectious and infectious disease states, particularly in connective tissue diseases. The quantification of the proteins during the course of various acute and chronic inflammatory disorders is useful in diagnosis, therapy, and in some cases, prognosis.