Heterogeneity of human serum amyloid A proteins

Inflammation and Oxidative Stress Induced by Obesity, Gestational Diabetes, and Preeclampsia in Pregnancy: Role of High-Density Lipoproteins as Vectors for Bioactive Compounds

Inflammation and oxidative stress are essential components in a myriad of pathogenic entities that lead to metabolic and chronic diseases. Moreover, inflammation in its different phases is necessary for the initiation and maintenance of a healthy pregnancy. Therefore, an equilibrium between a necessary/pathologic level of inflammation and oxidative stress during pregnancy is needed to avoid disease development. High-density lipoproteins (HDL) are important for a healthy pregnancy and a good neonatal outcome. Their role in fetal development during challenging situations is vital for maintaining the equilibrium. However, in certain conditions, such as obesity, diabetes, and other cardiovascular diseases, it has been observed that HDL loses its protective properties, becoming dysfunctional. Bioactive compounds have been widely studied as mediators of inflammation and oxidative stress in different diseases, but their mechanisms of action are still unknown. Nonetheless, these agents, which are obtained from functional foods, increase the concentration of HDL, TRC, and antioxidant activity. Therefore, this review first summarizes several mechanisms of HDL participation in the equilibrium between inflammation and oxidative stress. Second, it gives an insight into how HDL may act as a vector for bioactive compounds. Third, it describes the relationships between the inflammation process in pregnancy and HDL activity. Consequently, different databases were used, including MEDLINE, PubMed, and Scopus, where scientific articles published in the English language up to 2023 were identified.

Proteomic diversity of high density lipoproteins: our emerging understanding of its importance in lipid transport and beyond

Recent applications of mass spectrometry technology have dramatically increased our understanding of the proteomic diversity of high density lipoproteins (HDL). Depending on the method of HDL isolation, upwards of 85 proteins have been identified, and the list continues to grow. In addition to proteins consistent with traditionally accepted roles in lipid transport, HDL carries surprising constituents, such as members of the complement pathway, protease inhibitors involved in hemostasis, acute-phase response proteins, immune function mediators, and even metal-binding proteins. This compositional diversity fits well with hundreds of studies demonstrating a wide functional pleiotrophy, including roles in lipid transport, oxidation, inflammation, hemostasis, and immunity. This review summarizes the progression of our understanding of HDL proteomic complexity and points out key experimental observations that reinforce the functional diversity of HDL. The possibility of specific HDL subspecies with distinct functions, the evidence supporting this concept, and some of the best examples of experimentally defined HDL subspecies are also discussed. Finally, key challenges facing the field are highlighted, particularly the need to identify and define the function of HDL subspecies to better inform attempts to pharmacologically manipulate HDL for the benefit of cardiovascular disease and possibly other maladies.

Purification, identification and profiling of serum amyloid A proteins from sera of advanced-stage cancer patients

Surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF-MS) is a powerful tool for screening potential biomarkers of various pathological conditions. However, low resolution and mass accuracy of SELDI-TOF-MS remain a major obstacle for determination of biological identities of potential protein biomarkers. We report here a refined workflow that combines ZipTip desalting, acetonitrile precipitation, high-performance liquid chromatography (HPLC) separation and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) analysis for the profiling, purification and identification of the targeted serum proteins found by SELDI-TOF-MS. By using this workflow, we purified ten targeted proteins from the sera of patients with various types of advanced stage (stage III–IV) cancers. These proteins were identified as isoforms of the human serum amyloid protein A (SAA) family with or without truncations at their N-terminals. This was confirmed by Western blot analysis. Different SAA expression patterns were observed by MALDI-TOF-MS profiling. SAA has long been reported as a biomarker for various cancer types such as lung cancer, ovarian cancer, and breast cancer. However, in this study we found increased SAA expression in the sera of advanced-stage cancer patients with different cancer types. Our results suggest that maybe SAA should not be used alone as a biomarker for any specific cancer type.

Plasma proteomic alterations in non-human primates and humans after chronic alcohol self-administration

Objective diagnostics of excessive alcohol use are valuable tools in the identification and monitoring of subjects with alcohol use disorders. A number of potential biomarkers of alcohol intake have been proposed, but none have reached widespread clinical usage, often due to limited diagnostic sensitivity and specificity. In order to identify novel potential biomarkers, we performed proteomic biomarker target discovery in plasma samples from non-human primates that chronically self-administer high levels of ethanol. Two-dimensional difference in-gel electrophoresis (2D-DIGE) was used to quantify plasma proteins from within-subject samples collected before exposure to ethanol and after 3 months of excessive ethanol self-administration. Highly abundant plasma proteins were depleted from plasma samples to increase proteomic coverage. Altered plasma levels of serum amyloid A4 (SAA4), retinol-binding protein, inter-alpha inhibitor H4, clusterin, and fibronectin, identified by 2D-DIGE analysis, were confirmed in unmanipulated, whole plasma from these animals by immunoblotting. Examination of these target plasma proteins in human subjects with excessive alcohol consumption (and control subjects) revealed increased levels of SAA4 and clusterin and decreased levels of fibronectin compared to controls. These proteins not only serve as targets for further development as biomarker candidates or components of biomarker panels, but also add to the growing understanding of dysregulated immune function and lipoprotein metabolism with chronic, excessive alcohol consumption.

Ultrastructure of the cells forming amyloid fibers in Alzheimer disease and scrapie

Ultrastructural, three-dimensional reconstruction of cells surrounding the amyloid star in classical plaques in Alzheimer disease (AD) and histochemical studies of the cells associated with the deposits of amyloid fibers in scrapie were carried out. These studies showed that in both diseases, the fibers appear within the smooth endoplasmic reticulum (ER) and infoldings of cytoplasmic membranes of microglia/macrophages. Additional information about the site of formation of the amyloid fibers derives from histochemical studies of the localization of nucleoside diphosphatase (NDPase) activity. In normal microglia, this enzyme is associated with smooth ER and cell membranes. In the cells that form amyloid fibers, the NDPase activity is associated with the newly formed amyloid fibers within the distended cisternae of ER and the finger-like cytoplasmic projections. In the center of the amyloid star, the NDPase activity disappears. The presence of NDPase-positive amyloid fibers in the same location, where the enzyme is found in non-amyloid-forming cells, further supports our conclusion that the microglia/macrophages are the source of amyloid deposits. These studies also show that in spite of the differences in the proteins that produce the amyloid fibers in AD and scrapie, in both diseases, the microglia/macrophages play a key role in amyloid formation.

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.

[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.

New insights into the biology of the acute phase response

Innate or natural immunity is a highly conserved defense mechanism against infection found in all multicellular organisms. The acute phase response is the set of immediate inflammatory responses initiated by pattern recognition molecules. These germ cell-encoded proteins recognize microbial pathogens based on shared molecular structures and induce host responses that localize the spread of infection and enhance systemic resistance to infection. Innate immunity also influences the initiation and type of adaptive immune response by regulating T cell costimulatory activity and antigen presentation by antigen presenting cells and by influencing mediator production, which affects lymphocyte function and trafficking. Acute phase protein concentrations rapidly increase after infection, and their production is controlled primarily by IL-6- and IL-1-type cytokines. The acute phase proteins provide enhanced protection against microorganisms and modify inflammatory responses by effects on cell trafficking and mediator release. For example, serum amyloid A has potent leukocyte activating functions including induction of chemotaxis, enhancement of leukocyte adhesion to endothelial cells, and increased phagocytosis. The constellation of inflammatory responses seen after endotoxin administration to humans represents an in vivo model of the acute phase response. Studies with inflammatory modifying agents, such as soluble dimeric TNF receptor and IL-10, show that these responses are not dependent on a single mediator but result from multiple overlapping inflammatory pathways. Understanding the factors that initiate and alter the magnitude and duration of the acute phase response represents an important step in the development of new therapies for infectious and inflammatory diseases.

Isolation and purification of two major serum amyloid A isotypes SAA1 and SAA2 from the acute phase plasma of mice

A new procedure was developed for isolation of two major serum amyloid A (SAA) isotypes SAA1 and SAA2 from acute-phase plasma of mice. The procedure included preparation of high-density lipoproteins (HDLs) and their separation by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The SAA proteins (Mr 12,000) were electroeluted and afterwards purified from SDS by gel permeation chromatography on a Fractogel TSK-40F column in aqueous 50% acetonitrile-0.1% TFA. Finally, the SAA proteins free from SDS were fractionated by high-performance liquid chromatography on a Vydac 214TP54 column (250 x 4.6 mm I.D., particle size 5 microm), yielding two major fractions with k=5.2 and k=5.5. The N- and C-terminal sequence analyses and mass spectrometry demonstrated the purity of these two major fractions and their identity with apo SAA1 (k=5.2) and apo SAA2 (k=5.5). The developed procedure is applicable to small amounts of pooled murine plasma (6-7 ml) and could be readily modified from small to large scale preparations.

Increased plasma concentrations of serum amyloid A: an indicator of the acute-phase response after cardiopulmonary bypass

OBJECTIVES

To assess the expression of mixed and hepatic venous serum amyloid A (SAA) concentrations and its relationship to plasma concentrations of C-reactive protein, interleukin-6 (IL-6), and endotoxin during and after cardiopulmonary bypass (CPB).

DESIGN

Prospective, consecutive sample with repeated measurements.

SETTING

Surgical intensive care unit (ICU) in a university hospital.

PATIENTS

Twenty patients who underwent elective coronary bypass grafting.

INTERVENTIONS

A radial artery catheter, pulmonary artery catheter, and right hepatic vein catheter were inserted. Blood samples were collected to determine the different mediators, lactate concentrations, and oxygen saturations.

MEASUREMENTS AND MAIN RESULTS

After induction of anesthesia, baseline values were obtained and the following parameters were determined 20 mins after onset of CPB, 20 mins after termination of CPB, at admission to the ICU, and 6, 8, 12, and 24 hrs later: hemodynamics, body core temperature, hepatic venous oxygen saturation, and mixed and hepatic venous lactate, endotoxin, interleukin (IL)-6, C-reactive protein (CRP), and SAA concentrations. Endotoxin and IL-6 plasma concentrations increased during CPB, peaked 6 hrs after admission to the ICU (endotoxin: 23.1 +/- 6.2 pg/mL; IL-6: 646 +/- 104 pg/mL), and decreased thereafter; SAA and CRP concentrations began to increase after 6 and 8 hrs, respectively, with the highest concentrations reached 24 hrs postoperatively (CRP: 14 +/- 3.6 mg/L; SAA: 668 +/- 114 micrograms/mL). Lactate concentrations began to increase 20 mins after CPB, and continued to increase until 12 hrs postoperatively. There were no significant differences between mixed and hepatic venous values of endotoxin, IL-6, CRP, SAA, and lactate (p < .05). Body core temperature, which was < 37.5 degrees C before surgery for all patients, increased 6 hrs after admission to the ICU and peaked 12 hrs postoperatively (38.3 +/- 1.1 degrees C). Hepatic venous oxygen saturation did not change. Correlations were obtained between IL-6 values and heart rate (r2 = .20; p < .005), and endotoxin concentrations and systemic vascular resistance (r2 = .18; p < .001). Body core temperature correlated significantly closer with SAA (r2 = .52; p < .0001) values than with IL-6 (r2 = .27; p < .0001) or CRP (r2 = .16; p < .001) values (p < .05).

CONCLUSIONS

SAA is an additional and sensitive marker of the acute-phase response following CPB; the increase in SAA concentrations parallels the temporary increase in body core temperature and is preceded by endotoxemia and IL-6 secretion.

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)

Serum amyloid A is a chemoattractant: induction of migration, adhesion, and tissue infiltration of monocytes and polymorphonuclear leukocytes

Serum amyloid A (SAA) is an acute phase protein that in the blood is bound to high density lipoproteins; SAA is secreted mainly by hepatocytes, and its concentration increases in the blood up to 1000 times during an inflammatory response. At present, its biological function is unclear. Since some forms of secondary amyloidosis are caused by deposition in tissues of peptides derived from the SAA and leukocytes seem to be involved in this process, we investigated the effect of human SAA on human monocytes and polymorphonuclear cells (PMN). When recombinant human SAA (rSAA) was used at concentrations corresponding to those found during the acute phase (> 0.8 microM), it induced directional migration of monocytes and polymorphonuclear leukocytes. Preincubation of rSAA with high density lipoproteins blocked this chemoattractant activity for both monocytes and PMN. rSAA also regulated the expression of the adhesion proteins CD11b and leukocyte cell adhesion molecule 1 and induced the adhesion of PMN and monocytes to umbilical cord vein endothelial cell monolayers. When subcutaneously injected into mice, rSAA recruited PMN and monocytes at the injection site. On the basis of these data, we suggest that SAA may participate in enhancing the migration of monocytes and PMN to inflamed tissues during an acute phase response.

Amyloidosis

The biochemistry of amyloidosis as it relates to clinical medicine and experimental pathology is presented. Amyloidoses are complex disorders in which normally soluble precursors undergo pathological conformational changes and polymerize as insoluble fibrils with the beta-pleated sheet conformation. Over the past 20 years, 16 biochemically diverse proteins have been identified as fibrillar constituents of amyloid deposits; in all cases the protein-protein interactions that result in amyloid fibril formation appear to be stabilized both by the structure and the microenvironment of the precursor protein. Either genetic predisposition or dysfunctions of the immune system favor amyloid fibril formation. In particular, macrophage function is a factor in the pathogenesis of many of the amyloidoses. The diagnosis of amyloidosis involves acquisition of a tissue biopsy, staining of the specimen with Congo red, and observation of classic green birefringence on polarization microscopy. The subdiagnosis of the systemic amyloidoses involves characterization of variant or monoclonal plasma amyloid precursor proteins in the context of clinical symptoms. Treatment is generally supportive, with the use of antiinflammatory therapy, dialysis, or transplantation and genetic counseling where indicated.

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.

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.

Characterization of an isoelectric focusing variant of SAA1 (ASP-72) in a family of Turkish origin

An acidic variant of serum amyloid A (SAA) identified previously by isoelectrofocusing in a family of Turkish origin has been characterized at the genomic level. DNA sequence analysis revealed that individuals expressing the variant pI6.1/pI5.7 isoforms (the mother and three of four children) were heterozygous at the SAA1 gene locus. Their SAA1 gene sequences contained an adenine, as well as the usual guanine, at the position corresponding to the second base of codon 72. The presence of both bases predicts two SAA1 protein sequences, one having aspartic acid and the other glycine at position 72. While the Gly-72 SAA1 (+/- Arg-1) sequence represents the normal pI6.5/pI6.0 isoforms, the Asp-72 SAA1 (+/- Arg-1) sequence corresponds to the variant pI6.1/pI5.7 isoforms.

Identification of a novel serum amyloid A protein in BALB/c mice

Four serum amyloid A protein (SAA) genes and two SAA gene products, SAA1 and SAA2, were identified in BALB/c mice. Using analytical isoelectric focusing we have identified a quantitatively significant new member of the SAA family and designated it 'SAA5'. This protein has characteristics never before described for any SAA molecule. In the highly conserved region between amino acids 33 and 44, identical in all SAAs from all species examined, SAA5 had four amino acid substitutions. In addition, the induction of SAA5 by lipopolysaccharide had different kinetics from that of the other mouse SAAs. Our data suggest that the mouse SAA gene family is more complex in composition and regulation than previously surmised.

Nonexpression of the human serum amyloid A three (SAA3) gene

Serum amyloid A (SAA) is a major acute-phase plasma protein synthesized by the liver. In addition to the two major plasma isoforms described in humans (SAA1 and SAA2), a third form (SAA3) has been demonstrated in several other species and is distinguished by predominant extrahepatic expression. Two clones, Ch11g5-1-1 and HDg1-1, containing the human SAA3 gene are described in this report. The human SAA3 gene is comparable in organization to the SAA1 and SAA2 genes and shares with them 87% nucleotide identity in the region spanning exon 3 through exon 4. Sequences 5' to exon 3, however, are strikingly different from those in the SAA1 and SAA2 genes. For instance, the sequence deduced for amino acids 1-12 (exon 2) has only 25% identity with human SAA1 and SAA2; it most closely resembles that of rabbit SAA3 isolated from synovial fibroblast cultures (75% identity). Although rabbit SAA3 induces collagenase production in an autocrine fashion the human SAA3 gene is not expressed. This is shown by: (i) a single base insertion in the sequence corresponding to codon 31, (ii) the inability of a 918-bp fragment immediately upstream from SAA3 exon sequences to direct transcription of a chloramphenicol acetyltransferase reporter gene, and (iii) the absence of detectable human SAA3 in mRNA.

Acute phase protein, serum amyloid A, inhibits IL-1- and TNF-induced fever and hypothalamic PGE2 in mice

The effect of serum amyloid A (SAA) on fever induced by recombinant interleukin-1 beta (rIL-1 beta) or recombinant tumour necrosis factor alpha (rTNF alpha) was studied in mice. Serum amyloid A is an acute phase protein whose rise in pathological events is induced by the cytokines IL-1, IL-6 and TNF. Administration of human serum amyloid A to mice inhibited fever induced by rIL-1 beta or rTNF alpha in vivo, while the addition of human serum amyloid A to mice hypothalamic slices inhibited IL-1 beta- or TNF alpha-induced prostaglandin E2 (PGE2) production in vitro. Since serum amyloid A did not affect body temperature or hypothalamic PGE2 levels when administered alone, it may represent a specific servo-mechanism for fever regulation in acute events, and it suggests, for the first time, a possible feedback relationship between serum amyloid A and the immunoregulatory cytokines.

Characterization of high molecular weight amyloid A proteins

Human amyloid A protein (AA) is usually composed of the NH2-terminal 76 amino acid residue of serum amyloid A protein (SAA), although lower and higher molecular weight fragments have been reported. We studied the primary structure of six AA proteins with molecular weights of 11 kDA-15kDA, as determined by SDS-PAGE. Automated Edman degradation of the intact purified proteins and sequence analysis of enzymatic peptides revealed that the AA proteins were composed of only 74 to 87 residues. Moreover, fragments of apolipoprotein E or histones 2a, 3 and 4 were associated with these AA molecules. Thus, AA heterogeneity may reflect diverse processing of the SAA precursor and a very close association with other proteins.

Serum amyloid A isoforms in inflammation

Serum amyloid A protein (SAA) was extracted from serum using hydrophobic interaction chromatography and four or six isoforms were separated by isoelectric-focusing. These represented three pairs of isoforms, each with and without an N-terminal arginine. SAA1 (pI 6.1), SAA1 des-arg (pI 5.9), SAA2 alpha (pI 6.9) and SAA2 alpha des-arg (pI 6.6) were found to be present in all individuals from Europe and the USA. A minority of these individuals (11 of 56) expressed SAA2 beta (pI 7.1) and SAA2 beta des-arg (pI 6.8). Serum from patients in Papua New Guinea and Malawi both showed a much higher frequency of SAA2 beta. There was no indication of altered isoforms in regions with high incidence of reactive AA amyloidosis. In sequential serum samples, concentrations of des-arg isoforms were found to reach a maximum 0-24 h later than isoforms with an arginine. Concentrations of the isoform SAA1 decreased faster in five of six patients (16 +/- 7.5 h to decrease 50%) than SAA1 des-arg (22 +/- 11 h to decrease 50%). Variations in the handling of N-terminal arginine may be important for the formation-susceptibility of amyloid deposits.

Use of ethanol-eluted hydrophobic interaction chromatography in the purification of serum amyloid A

A two-step procedure for the purification of the acute-phase reactant serum amyloid A from serum is described. A hydrophobic interaction chromatography medium, octyl-Sepharose CL4B, eluted with increasing concentrations of EtOH was used as the first step in the purification. The concentrate from this step was applied to a gel filtration column of Sephacryl S-200 and eluted with 10% formic acid. The overall recovery of purified serum amyloid A from serum was 56%. This represents the first time that serum amyloid A has been purified without the use of high concentrations of guanidine or urea. The method presented could easily be scaled up to allow the purification of large quantities of serum amyloid A or readily adapted to the purification of other serum apolipoproteins.

Heterogeneity of serum amyloid A with respect to molecular mass

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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.

Isoproteins and an isoelectric focusing mutant of human apoprotein serum amyloid A

On isoelectric focusing of human plasma and subsequent immunoblotting, using antii-human serum amyloid A (SAA) antibodies, a genetic variant of SAA was detected in a family of Turkish origin. All affected members of the family were apparent heterozygotes for the mutant protein, which underwent a charge shift of about one charge unit toward the anode. The variant is likely to be a mutant of the most prominent forms of SAA (SAA1 and SAA2, or SAA1 and SAA1 des Arg). The appearance of a genetic variant of two of the six reported SAA-isoforms in human plasma supports the concept of SAA proteins being products of different genes.

Variations in apolipoproteins serum amyloid A, A-I, A-II, and C-III in severely head-injured patients

In five severely head-injured patients we determined the plasma concentrations of apolipoproteins serum amyloid A, A-I, A-II, C-III, and B, prealbumin and C-reactive protein on day 1, 5, 10 and 15 after head injury where possible. A dramatic increase in apolipoprotein serum amyloid A up to a mean plasma level of 0.764 g/l was accompanied by a considerable decrease in apolipoprotein A-I, apolipoprotein A-II and apolipoprotein C-III concentrations. The variations observed by immunological methods were confirmed by two-dimensional gel electrophoresis performed on plasma and different lipoprotein fractions. In addition to its association with high density lipoproteins, apolipoprotein serum amyloid A was also found with lipoproteins of low and very low density. Two-dimensional electrophoresis also showed the presence of several different serum amyloid A-peptides not seen in plasmas from healthy subjects. We propose that apolipoprotein serum amyloid A may be responsible for the decrease of the main HDL apolipoproteins in head-injured patients.

Heterogeneity of human serum amyloid A protein. Five different variants from one individual demonstrated by cDNA sequence analysis

Serum amyloid A (SAA), a chemically polymorphic protein, is the most sensitive marker protein of the acute phase and the precursor of reactive amyloidosis, which is characterized by deposits of amyloid A protein (AA). We investigated the variability of the SAA gene family in one individual by sequencing 11 SAA-specific clones from an acute-phase-liver cDNA library. At least five different SAA variants were deduced from six different cDNAs. The 3' untranslated gene segments fall into two groups, based on nucleotide sequence and variability in length. Various nucleotide and amino acid substitutions were found predominantly in the 3' portion. Some of these substitutions are unique and increase the number of SAA variants in one individual to at least five. Moreover, genomic DNA of four individuals was examined by analysis of restriction-fragment length polymorphism. Besides two conserved strongly labelled bands, additional polymorphic bands were observed, indicating isotypic and/or allotypic SAA variations. Finally, three different mRNA species were detected by Northern-blot analysis, a finding that might be of relevance for the stability of SAA transcripts.

Direct binding enzyme-linked immunosorbent assay (ELISA) for serum amyloid A (SAA)

A solid-phase, direct binding ELISA for serum amyloid A (SAA) proteins is described, in which noncovalent interactions of SAA with other plasma constituents are disrupted to permit direct coating of the wells of flexible polyvinyl chloride microtitration plates with an amount of SAA antigen proportional to its concentration in plasma. The wells are coated overnight at 60 degrees C with plasma diluted in 3 M potassium bromide and 0.1 M sodium bicarbonate. pH 9.6. The next day, any remaining sites on the wells are blocked by incubation for 1 h at ambient temperature with a 5% solution of dry milk solids and 0.05% Tween 20 in 0.02 M phosphate buffer, pH 7.4. The wells are rinsed and incubated for 90 min at 37 degrees C with polyclonal rabbit or rat anti-human SAA antiserum. Then, the wells are rinsed and incubated with goat anti-rabbit or rat IgG antiserum to which has been conjugated horseradish peroxidase. o-phenylenediamine and hydrogen peroxide substrates are added to the wells, color is allowed to develop, and sulfuric acid is added to stop the enzyme-catalyzed reaction. The amount of SAA coated to wells is quantified by absorbance at 490 nm. Four or more serial three-fold dilutions of plasma samples are assayed simultaneously on separate plates. Each plate contains a set of wells with identical concentrations of SAA standard protein diluted in decreasing concentrations of plasma proteins corresponding to the dilution of sample. The method can detect SAA concentrations in plasma samples ranging from 1 microgram/ml to greater than 1000 micrograms/ml. The method is suited to serial monitoring of SAA concentration in patients undergoing treatment for inflammatory conditions and to the quantitative analysis of large numbers of samples.

Detection of human serum amyloid A protein in very low density--and high density lipoproteins of patients after acute myocardial infarction

Two acute-phase proteins have been identified in very low density (VLDL)- and high density lipoproteins (HDL) of patients after acute myocardial infarction. Both proteins have a relative molecular weight of 11,000 and isoelectric points pI 6.08 and 6.27, and do not contain cysteine or sugar residues. Polyclonal antibodies to these acute phase reactants did not cross-react with other serum apolipoproteins. Evidence is given that both proteins are polymorphic forms of the human serum amyloid A protein.

Human serum amyloid A protein. Behaviour in aqueous and urea-containing solutions and antibody production

Human serum amyloid A protein (apo-SAA) can be prepared by gel filtration of delipidated acute-phase high-density lipoprotein in the presence of urea. The resultant apo-SAA is soluble (greater than 90% solubility) in a wide range of buffer solutions, with all of the six major isoforms of apo-SAA being equally soluble. In urea-containing solutions the isoforms behave qualitatively differently in various urea concentrations, probably reflecting subtle primary-structure variations. The higher-pI isoforms are only completely unfolded at greater than 7 M-urea. By immunizing with apo-SAA adsorbed to acid-treated bacteria (Salmonella minnesota R595), high-titre antibodies can easily be elicited in rabbits.

Antipeptide antibodies discriminate between different SAA proteins in human plasma

Antipeptide antibodies raised against two distinct sequences of human serum amyloid A (SAA) discriminate between different plasma isoforms of this acute phase reactant. As different SAA gene products have meanwhile been identified in human plasma, the discrimination between these different isoforms may help to clarify further the time of appearance of these different forms in plasma and their potential amyloidogenicity.

Serum amyloid A in the mouse. Sites of uptake and mRNA expression

Murine serum amyloid A1 (SAA1) and serum amyloid A2 (SAA2) are circulating, acute phase, high density apolipoproteins of unknown function. To pursue issues relating to their possible function their uptake and formation were studied. Kinetics of SAA protein distribution and gene expression after acute phase stimulation by casein or lipopolysaccharide were examined using immunocytochemistry for protein and RNA blot and in situ hybridization with probes for SAA1 and SAA2 mRNA. After casein injection, interstitial cells of testes, cells of adrenal cortex, kidney proximal convoluted tubule epithelia, and some parafollicular cells of spleen took up SAA in a time pattern related to plasma SAA levels. Extrahepatic SAA1 and SAA2 mRNA were induced by lipopolysaccharide in kidney proximal and distal convoluted tubule epithelia, and SAA1 mRNA was induced in epithelial lining the mucosa of the ileum and large intestine, indicating that there may be more than one function for the apoSAA gene family related to site of and stimulus for expression.

Expression and sequence analyses of serum amyloid A in the Syrian hamster

Reactive amyloidosis occurs during chronic inflammation and involves deposition of amyloid A (AA) fibrils in many organs. Amyloid A is derived by proteolysis from serum amyloid A component (SAA), a major acute-phase reactant in many species. Since spontaneous amyloidosis occurs commonly in Syrian hamsters, we have studied the structure and expression of SAA genes during inflammation in these animals. Two cDNA clones and one genomic clone were sequenced, suggesting that Syrian hamster SAA is encoded by at least two genes. Hepatic mRNA analyses showed that SAA was inducible in many hamster organs during acute inflammation. These studies also demonstrated that SAA mRNA for one isotype is maximally expressed at a site of local tissue damage.

Expression of the third member of the serum amyloid A gene family in mouse adipocytes

Three homologous genes that code for three related proteins comprise the serum amyloid A (SAA) family in the mouse. Endotoxin induces equally vigorous expression of mRNAs for the three SAA genes in liver. In extrahepatic tissues SAA1 and/or SAA2 mRNAs have been found only in kidney and intestine, however, SAA3 is expressed in all extrahepatic tissues thus far examined. This observation raised the question: is SAA3 mRNA expressed by a single cell system dispersed throughout all tissues, or by differentiated cells of each tissue? This question was explored in various tissues by in situ hybridization with a single-stranded cRNA probe specific for SAA3 mRNA. We found expression in the liver of SAA3 mRNA by other cells as well as by hepatocytes. A common feature among extrahepatic tissues was SAA3 mRNA expression in adipocytes. SAA3 mRNA was also found in two nonadipose cells, Leydig cells of the testis, and some of the cells located in parafollicular zones of the spleen.

Rat tissues express serum amyloid A protein-related mRNAs

Serum amyloid A (SAA) is a small (12 kDa) acute-phase apoprotein of high density lipoprotein found in mammals. It is also the precursor to amyloid protein A, the main protein constituent of fibrils found in amyloidosis secondary to chronic or recurrent inflammation--e.g., rheumatoid arthritis. However, rats do not develop amyloidosis and SAA is not an apoprotein of rat high density lipoprotein; thus rats appear to be an exception in regard to expression of SAA genes. We report here that rats do have representatives of the SAA gene family and express two distinct SAA mRNAs. Moreover, the pattern of genes expressed among tissues, and their induction by inflammatory agents, is similar to that of related mouse genes. RNA from various tissues of normal and injured rats was examined by RNA blot hybridization with SAA cDNA and complementary RNA probes for the three murine SAA genes. A SAA mRNA of approximately 400 nucleotides related to mouse SAA1 and SAA2 mRNAs reached a high level in liver 24 hr after injection of bacterial lipopolysaccharide. No extra-hepatic tissues were found to express the SAA1/SAA2-related mRNA. Turpentine induced two hepatic SAA1/SAA2-related mRNAs of approximately 400 and approximately 500 nucleotides in length. Liver SAA1/SAA2-related mRNA hybrid selected and translated in a wheat germ protein-synthesizing system, from lipopolysaccharide- and turpentine-injected rats, produced a single protein with an estimated molecular mass of 8 kDa. This rat liver SAA-related mRNA appears to lack a highly conserved coding region for portions of two amphipathic helical domains and the joining sequence. An mRNA related to mouse SAA3 was found expressed at a high level in lung after lipopolysaccharide but not following turpentine injection. This mRNA was also expressed at high levels in ileum and large intestine of control rats and was not found in the liver of control or challenged rats. These observations show that the SAA gene family is present and expressed in rats and that its expression is found under situations similar to those found in mice. This lends support for the importance of the SAA gene family in the response to injury by vertebrates.

Histomorphological variations in systemic AA amyloidosis: clues of AA protein polymorphism

The histological location of amyloid within various organs in 25 cases of systemic AA amyloidosis was studied with a view to determine whether different morphological patterns exist in this category of amyloidosis. Although morphological variations due to progressive severity of disease were observed, there were appreciable variations in the patterns of amyloid deposition in the kidney and spleen that could not be simply explained on those grounds. Eleven (61%) of 18 kidneys examined showed severe glomerular involvement with mild degrees of vascular deposition while the remaining seven showed predominantly vascular involvement. The glomerular pattern appeared to be more ominous, being significantly associated with severe proteinuria or chronic renal failure. In nine (69%) of 13 spleens examined, amyloid was confined to the walls of small and medium-sized arteries while in the remaining four, vascular involvement was less severe and amyloid was deposited mainly along the reticulin of the white pulp. Possible explanations for these different patterns included resorption and redistribution of amyloid within the body during the course of the disease, and variation in tissue deposition as a manifestation of polymorphism of amyloid proteins. The latter appeared more feasible in view of the recent demonstration of SAA polymorphism and AA heterogeneity in man.

Molecular analysis of the human serum amyloid A (SAA) gene family

We have assigned the human serum amyloid A (SAA) gene family to a 90 kb region on the short arm of human chromosome 11 (11p) by hybridization of defined genomic fragments of human SAA genes to DNA from rodent-human somatic cell hybrids and to large DNA fragments separated by transverse alternating field gel electrophoresis. We have also characterized SAA probe hybridization patterns in human DNA cleaved with restriction endonucleases Hind III, Pst I, BglII, TaqI, and XbaI and found invariant patterns except for a two-allele restriction fragment length polymorphism (RFLP) with Hind III. These studies show that the SAA gene family comprises at least three members in the haploid human genome and will be useful in identifying variant patterns and establishing linkage between members of the SAA gene family and other markers on chromosome 11.

Serum amyloid A and high density lipoproteins during the acute phase response

Serum amyloid A and high density lipoprotein (HDL) interrelationships were evaluated in 11 normal men during an acute phase response induced by the inflammatory steroid etiocholanolone. Compared with baseline, HDL-cholesterol levels were significantly elevated at 30 h but not at 50 h (P less than 0.05) after etiocholanolone. A-apoprotein concentrations were unchanged at 30 h but were reduced at 54 h (P less than 0.01). Four subjects were sampled every 6-8 h for 5 days. Two men had peak SAA concentrations of 30 and 33 mg dl-1. Their A-apoprotein levels declined as SAA rose and remained low even after SAA levels had returned to baseline. High density lipoprotein cholesterol levels did not fall, however, when SAA was increasing, and fell only after SAA levels declined. No changes in HDL-cholesterol or protein were observed in two subjects whose peak SAA concentrations were 10 and 12 mg dl-1. These observations suggest that a threshold level of acute phase response is required before HDL reductions occur. Column chromatography of SAA-rich plasma did not demonstrate the presence of either SAA or A-apoproteins that were unassociated with lipoproteins. Serum amyloid A, moreover, demonstrated little capacity to displace A-proteins from HDL at SAA concentrations typically observed during the acute phase response. We infer from these studies that SAA may substitute for the A-apoproteins and temporarily maintain HDL-cholesterol levels; but that low HDL levels during the acute phase response are likely due to reduced A-protein synthesis rather than displacement by SAA.

Amyloidosis

The clinical amyloidosis syndromes are a heterogeneous group of disorders characterised by abnormal extracellular accumulation of autologous protein material. Amyloid deposits are largely composed of insoluble protein fibrils which are intimately associated with sulphated glycosaminoglycan residues. Amyloid P component (AP) is a minor but almost universal constituent of the deposits and is derived from the normal circulating glycoprotein serum amyloid P component (SAP), a member of the pentraxin family of plasma proteins. The current classification of amyloidosis is based on the chemical nature of the fibril protein subunits. Systemic amyloidosis is well known as a relatively rare but important cause of serious morbidity, and vital organ involvement is usually fatal. In recent years it has become increasingly recognised that amyloid deposition in a variety of sites is a universal feature of ageing, and in particular that amyloid in the cerebral blood vessels and within the brain itself is an integral part of the pathology of Alzheimer's disease. Also recently, a new form of amyloid has emerged, confined to patients who have received long term haemodialysis for end stage renal failure, in whom beta 2-microglobulin (beta 2M) is laid down as amyloid fibrils predominantly in periarticular and bony tissues. Considerable progress in knowledge of the composition, molecular structure and properties of many different constituents of amyloid has been made in the past 30 years. However, the precise mechanisms of amyloid fibril formation, deposition and persistence are not known and no generally effective therapy yet exists which can arrest amyloid deposition or promote its resolution. A major reason for our ignorance of the natural history of amyloidosis is that it is an exclusively histological diagnosis, at the time of which most patients with systemic disease have extensive amyloid deposits throughout many organs and a very poor prognosis. Some optimism has been generated from recent work suggesting that amyloid fibrils are not inherently non-biodegradable and that the use of radiolabelled SAP may permit non-invasive sensitive, scintigraphic imaging of amyloid deposits in vivo.

Evidence for qualitative abnormalities in high-density lipoproteins from myeloma patients: the presence of amyloid A protein could explain HDL modifications

HDL apolipoproteins (apo) from normal subjects and patients with multiple myeloma were studied by isoelectric focusing (IEF) and by two-dimensional gel electrophoresis. Qualitative abnormalities were detected in myeloma HDL apolipoproteins. We observed two new bands not previously described in this disease. As determined by IEF and two-dimensional gel electrophoresis, the relative molecular weight of these two proteins was 12,600, with pI = 6.04 and 6.36, respectively. They correspond to two isoforms of serum amyloid A protein (SAA), as confirmed by western blot assay against specific antiserum to SAA. The high sensitivity of this assay revealed also other SAA isoforms. Our data are consistent with the hypothesis that major apolipoproteins of normal HDL, apo A-I and apo A-II, could be displaced by SAA isoproteins in myeloma HDL. This could lead structural changes in HDL.

Phosphorylation of human serum amyloid A protein by protein kinase C

Monokine-induced hepatic secretion of serum amyloid A protein (apo-SAA), an acute-phase reactant, is followed by rapid association with high-density lipoprotein (HDL) in plasma. Plasma clearance of apo-SAA is more rapid than any of the other HDL apolipoproteins. It has been shown that, of the acute-phase HDL3 apolipoproteins, apo-SAA preferentially associates with neutrophil membranes. HDL apolipoproteins have been shown to activate protein kinase C in endothelial cells. We therefore investigated potential phosphorylation of HDL3 apolipoproteins by protein kinase C. Apo-SAA was the only apolipoprotein phosphorylated (Km = 12 mM). Phosphorylation of the apo-SAA-containing HDL3 particle was selective for the more basic isoforms of apo-SAA (pI 7.0, 7.4, 7.5 and 8.0), with more acidic isoforms being phosphorylated when delipidated acute-phase apolipoproteins were used as substrate. However, phosphorylation was not in itself responsible for the establishment of the apo-SAA isoforms.

Purification of serum amyloid A and other high density apolipoproteins by hydrophobic interaction chromatography

A chromatographic procedure is described for the purification of apolipoprotein components of high density lipoprotein from serum. Hydrophobic interaction chromatography (HIC) using phenyl- or octyl-Sepharose was used to purify the high density lipoprotein (HDL)-associated acute phase reactant serum amyloid A (SAA). The purification of SAA is described in detail and it is shown how the main components of normal HDL, apolipoproteins AI and AII (Apo-AI, Apo-AII), can also be purified. Serum was applied at a low salt concentration and apolipoproteins were eluted with a gradient into 4 M guanidine hydrochloride, 30% ethanediol, and 10 mM NaOH. This method was also used to partially purify the low density lipoprotein component apolipoprotein B. Apolipoproteins are purified free from lipid in one rapid chromatographic procedure rather than several ultracentrifugation steps and delipidation with organic solvents. The apolipoproteins from HIC chromatography are already partially separated and can be purified to homogeneity using conventional chromatographic methods under dissociating conditions.

Identification of three isoform patterns of human serum amyloid A protein

Three patterns of human apo-SAA (serum amyloid A protein) isoforms have been identified by electrofocusing. In pattern 1, six major apo-SAA isoforms of pI 6.0, 6.4, 7.0, 7.4, 7.5 and 8.0 were found. In pattern 2, the apo-SAA isoforms of pI 7.4 and 8.0 were not detected, whereas in pattern 3 the pI-7.0 and -7.5 isoforms were lacking. Six patients displayed apo-SAA isoform pattern 1, 11 displayed pattern 2 and one displayed pattern 3.

Amyloidosis

Recent studies have provided new insight into the pathogenesis of amyloidosis and have broadened our knowledge of the mechanisms of deposition and resolution of amyloid. In particular, the structure, synthesis and plasma clearance of the inflammation-associated amyloid precursor, SAA, have been extensively studied and the precursor-product relationship between circulating SAA, protein AA and fibrillar amyloid A clarified. Information has been accumulating about the enzymatic processes involved in the cleavage of SAA and the degradation of protein AA and a new view has been presented on the possible role of amyloid P component in AA amyloidogenesis. The current model of AA pathogenesis emphasizes the dynamic character of amyloid.

Degradation and deposition of amyloid AA fibrils are tissue specific

The complete amino acid sequences of two related AA proteins (Mr 9700 and 5300) derived from thyroid tissue from a patient, NOR, with the autosomal recessive disease familial Mediterranean fever were determined. Heterogeneity found at position 52 indicates these proteins are fragments of two allelic or isotypic SAA precursor molecules similarly degraded at unusual sites and deposited in the thyroid. Degradation appears to be tissue and/or enzyme(s) specific since the carboxy terminus of both fragments is Ala-Ala and is different from other AA amyloid fibrils extracted from various tissues in different patients. Electron micrographic studies reveal these fragments retain the characteristics of native amyloid fibrils under physiological conditions even after exposure to dissociating agents.