Serum amyloid A: evidence for its origin in polymorphonuclear leukocytes.

In this study the presence of an amyloid A, antigenically related material was determined in four subpopulations of human leukocytes. Monocytes, granulocytes, thymus-derived lymphocytes, and bone marrow-derived and null lymphocytes were isolated from the peripheral blood of five apparently normal subjects, two patients with secondary amyloidosis, three patients with acute infections, and seven patients with metastatic cancer. Mononuclear leukocytes, isolated from the interface of a Ficoll-Hypaque gradient, were separated into monocytes, thymus-derived lymphocytes, and bone marrow-derived plus null lymphocytes by glass adherence and depletion of sheep erythrocyte rosette-forming lymphocytes. Granulocytes were isolated by sedimentation in 2% methyl cellulose from the erythrocyte-rich pellet formed at the bottom of the Ficoll-Hypaque gradient. The four isolated leukocyte subpopulations were cultured and, at varying intervals, the amyloid A content of the culture medium and of sonicated, 2 x 10(6) cells was determined by radioimmunoassay. Our results indicated a 2-14 times greater amount of amyloid A-related material in the sonicated granulocytes compared with the individuals' serum amyloid A levels. The mononuclear subpopulations showed a low or negligible amyloid A content. The amount of amyloid A antigenic material was further found to increase in cultured granulocytes, reaching a peak value between the 16th and 30th h of culture. The granulocytes of only two out of eight individuals tested released amyloid A antigenically related material into the culture medium. This release was found to be blocked by the presence of colchicine, vincristine, puromycin, or cycloheximide in the culture medium. In contrast, only the presence of puromycin or cycloheximide was shown to significantly inhibit the intracellular increase of amyloid A in the cultured granulocytes. Thus, it appears that among the circulating blood cells, the granulocytes produce amyloid A antigenically related material and could release it under conditions that remain to be further defined.

Identification of elastases associated with purified plasma membranes isolated from human monocytes and lymphocytes.

Studies were carried out to understand the pathogenesis of amyloid formation and to localize the elastase-like enzymes postulated to be associated with the surface of human peripheral blood monocytes and lymphocytes. These enzymes are known to degrade serum amyloid A and amyloid A proteins. Pure plasma membrane preparations were obtained by allowing cells to attach to polyacrylamide beads, followed by their disruption. The purity of the membranes was monitored by electron microscopy and enzyme determinations. The extracted membrane enzymes which have molecular weights of 56000 and 30000, respectively, were inhibited by DFP, MeO-Suc-Ala-Ala-Pro-Val-CH2Cl, Ac-Pro-Phe-Arg-CH2Cl . HCl, and elastinal but were not inhibited by EDTA or epsilon-amino caproic acid, thus exhibiting the properties of elastases. These enzymes cleave serum amyloid A to amyloid protein A. In some individuals, cleavage stops at this point, while in others a second step occurs, resulting in complete protein degradation. This activity was comparable whether monocyte or lymphocyte plasma membranes were employed. Since lymphocyte dependent cytotoxicity has also been attributed to surface proteases, it is likely that a spectrum of membrane associated enzymes mediate important physiologic function of these mononuclear leukocytes.

Quantitative radial immunodiffusion assay for serum amyloid A protein.

A radial immunodiffusion assay for serum amyloid A protein (SAA) using a commercially available antiserum is described. Serum is applied untreated to 1% agarose gels prepared in 0.02 M barbitone buffer, pH 8.6, containing 40 g/l polyethylene glycol 6000. Incubation is carried out overnight at 37 degrees C. The assay combines the advantages of simplicity, rapidity, specificity and stability, and avoids the hazards associated with the previously described radioimmunoassays. The method has sufficient sensitivity to measure SAA in the majority (99%) of normal subjects, and confirms the behaviour of SAA as a very sensitive acute phase reactant in inflammatory disease. The method is ideally suited to the rapid processing of a large number of samples.

Amyloidosis in systemic lupus erythematosus.

Amyloidosis occurs in a significant proportion of patients with rheumatologic diseases. The fibrillar amyloid proteins in such patients are composed predominantly of amyloid A protein, which is characteristic of the amyloid deposits associated with chronic inflammatory diseases. Only four patients with amyloidosis associated with systemic lupus erythematosus (SLE) have been described previously; analyses of their fibrillar amyloid proteins were not reported. We present herein, a patient with SLE and amyloidosis. Histochemical staining of our patient's renal tissue with Congo red demonstrated that the amyloid deposits contained amyloid A protein, as defined by permanganate sensitivity. In addition, the patient's serum contained increased concentrations of serum amyloid A proteins. In review, each of the previously described patients with amyloidosis associated with SLE had renal amyloid deposits, with diagnosis in three during evaluation of proteinuria. Thus, although rare, amyloidosis should be considered in the differential diagnosis of proteinuria in patients with SLE.

Amyloid A fibril degrading activity in serum in liver disease--relation to serum acute phase and other protein levels.

Human serum contains amyloid A degrading activity. This activity is decreased in patients with reactive systemic amyloidosis. To study the specificity of this finding, we evaluated the effect of liver disease per se on the amyloid degrading activity in serum as well as its relation to serum amyloid A (SAA), the putative precursor of amyloid A fibrils, and other serum protein levels in alcoholic and non-alcoholic non-malignant liver diseases without signs of amyloidosis. The amyloid A-degrading activity was significantly decreased in liver cirrhosis. The lowest activity was seen in patients with advanced cirrhosis. There was a positive correlation between the degradative activity and indices of hepato-cellular synthetic function (serum albumin, r = 0.77; serum prealbumin, r = 0.65). Most of the patients with liver disease had a detectable SAA level; 77% had a level higher than 5 mg/l (compared to 12% among blood donors). However, the SAA increase was generally only slight, e.g. in alcoholic liver cirrhosis the median SAA level was 15 mg/l. The results show that liver dysfunction per se decreases amyloid A-degrading activity in serum. A reduced activity cannot therefore be regarded as specific for reactive amyloidosis. Since reactive amyloidosis is extremely rare in liver cirrhosis, it seems obvious that a reduced amyloid degrading activity alone, in the absence of a markedly elevated SAA level, does not predispose, at least in patients with liver disease, to amyloidosis.

Trauma, high density lipoproteins, and serum amyloid protein A.

Several apoproteins not readily detectable in normal serum lipoproteins were found in markedly increased amounts in the lipoprotein density interval 1.125-1.21 g/ml (HDL3) of serum obtained from victims of severe trauma. Following electrophoretic separations, they were shown to be isotypes of the acute-phase protein serum amyloid A (SAA) by immunoreaction with antiserum to the structurally related tissue amyloid protein A (AA). The two principal apoSAA isotypes in the HDL3 of trauma patients appear to be identical to the two principal isotypes (apoSAA1 and apoSAA2) previously isolated from the HDL3 of pooled serum representing an unselected patient population. Concentrations of apolipoproteins A-I and A-II in the HDL3 of the trauma patients were significantly lower than in the HDL3 of normal serum. Evidence is presented that several recently described 'new' families of HDL apoproteins, all of an acute-phase nature, are SAA apoproteins, which are emerging as sensitive indicators of tissue damage.

Serum amyloid A protein and C-reactive protein in systemic amyloidosis.

In 106 patients with systemic amyloidosis (56 primary, 27 secondary, and 23 familial), serum amyloid A protein (SAA) was measured by solid-phase radioimmunoassay and C-reactive protein (CRP) was measured by rate nephelometry. SAA and CRP concentrations were highly correlated (r = 0.75, P less than 0.001) throughout the normal and abnormal concentration ranges. In systemic amyloidosis, SAA was more sensitive than CRP as an indicator of the acute-phase response, particularly in secondary amyloidosis. Acute-phase proteins are only occasionally increased during the course of familial amyloidosis. The overlap of acute-phase protein levels does not permit reliable separation of primary amyloidosis from secondary amyloidosis solely on the basis of such studies despite the significantly higher SAA and CRP levels in the latter.

The effect of gold salts on casein-induced macrophage activation and serum amyloid protein SAA levels.

Previous work from our laboratory has demonstrated a marked inhibitory activity of Auranofin (Au) and Gold Sodium Aurothiomalate (GST) on monocyte-macrophage function and an important role for macrophages in the pathogenesis of casein-induced experimental amyloidosis. In the present study we have looked at the in vivo effect of Au and GST on the inhibition of casein-induced macrophage activation and serum SAA levels. Au and GST markedly inhibited casein-induced macrophage activation while only Au reduced serum SAA levels to a significant degree. The present data raises the possibility that Au may be helpful in the treatment of secondary amyloid disease.

Lowered prealbumin levels in patients with familial amyloid polyneuropathy (FAP) and their non-affected but at risk relatives.

Amyloid fibrils in familial amyloid polyneuropathy, the familial (AF) form of systemic amyloidosis, are composed of the monomeric unit (14,000 MW) of prealbumin molecules. By radioimmunoassay, the serum level of prealbumin was measured in 25 patients from 12 different kinships with this dominantly inherited form of amyloidosis and 56 unaffected, but at risk, relatives from two of the kinships. Results were compared to prealbumin levels in normal individuals and patients with primary (AL) and secondary (AA) forms of systemic amyloidosis. Significantly lowered prealbumin levels were found in the AF patients (149.2 micrograms/ml) and their at risk relatives (169.0 micrograms/ml) when compared to normal individuals (232.9 micrograms/ml), AL patients (221.9 micrograms/ml) and AA patients (211.7 micrograms/ml). No abnormality was found in levels of retinol binding protein (RBP), which is carried by prealbumin, in the serum of either the AF patients or their relatives. The depressed prealbumin levels may indicate a structural variant molecular form, an extra hepatic synthesis or an abnormality in catabolism of this protein that is present prior to the clinical or histopathologic onset of the AF disease.

Posttransplantation monitoring of high-density lipoprotein-associated serum amyloid A protein: a new diagnostic aid in the detection of renal allograft rejection.

The concentrations of serum amyloid A protein, a high-density lipoprotein-associated protein synthesized in the liver, were monitored in 66 recipients of cadaveric renal allografts. Acute graft rejection episodes were associated with dramatic elevations of serum amyloid A. Electrofocusing and immunoblotting of rejection sera showed a polymorphic serum amyloid A pattern similar to that obtained with control (apo) serum amyloid A isolated from the high-density lipoprotein fraction of plasma. Rejections in patients receiving cyclosporine alone as posttransplantation immunosuppressive medication were characterized by significantly higher serum amyloid A levels than in those receiving cyclosporine in combination with methylprednisolone. Due to the dramatic rejection-induced serum amyloid A elevation, limit values could be used which combined high sensitivity (87-96%) with reasonably high predictive value of a positive test (82%). The serum amyloid A test was applicable also in patients with initially nonfunctioning or poorly functioning grafts. It is concluded that monitoring of the serum amyloid A concentrations offers a valuable noninvasive aid in the early diagnosis of acute renal allograft rejection, including patients with acute tubular necrosis of the graft.

Serum amyloid A protein in acute myocardial infarction.

Tissue injury including myocardial infarction leads to a variety of changes in plasma proteins commonly referred to as "the acute phase response". In this report the concentrations of serum amyloid A protein (SAA) were measured serially in 6 patients with myocardial infarction and 4 with angina. SAA was found to be increased in all patients with infarction, but in no patients with angina. Significantly increased SAA levels were detected 12 hours after the peak level of creatine kinase, and the concentrations of SAA seemed to correlate to the amount of damaged tissue. The SAA-response was both faster and more extensive than the response of C-reactive protein (CRP), but the correlation between SAA and CRP was very good.

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.

Characterization of amyloid proteins AA and SAA as apolipoproteins of high density lipoprotein (HDL). Displacement of SAA from the HDL-SAA complex by apo AI and apo AII.

An AA-like protein with a molecular weight of 8600 complexed to high-density lipoprotein (HDL) was demonstrated in several acute-phase sera with high levels of SAA. The protein 'apo AA' (to distinguish it from tissue AA) was isolated by elution from sodium dodecyl sulphate (SDS)-polyacrylamide gel, and showed antigenic identity with purified tissue protein AA in double immunodiffusion. Normal HDL was shown to bind purified tissue AA in vitro. When the in vitro-associated HDL-AA complexes were given intravenously to mice during induction of amyloidosis, human AA was incorporated in the amyloid fibrils. Both apo AI and apo AII were shown to displace SAA from acute phase HDL when added to HDL-SAA complexes in vitro. This might be of importance in amyloidogenesis, as the liver and the small intestine, which are the main sites for AI and AII synthesis, are also sites of early amyloid deposition.

Serum amyloid-A protein concentration in inflammatory diseases and its relationship to the incidence of reactive systemic amyloidosis.

Serum amyloid-A protein (SAA) is the putative precursor of amyloid-A (AA) protein which forms the fibrils in reactive systemic or secondary amyloidosis. By means of a novel immunoradiometric assay, the concentration of SAA was found to be greatly elevated in patients with rheumatoid arthritis and juvenile chronic arthritis and correlated with activity of their primary disease. However, in patients with systemic lupus erythematosus SAA levels were only modestly raised, even in those with severe active disease, unless significant intercurrent microbial infection was also present. In Crohn's disease SAA levels showed a pattern similar to that seen in rheumatoid arthritis, whereas in ulcerative colitis it resembled that of systemic lupus erythematosus. The level of SAA response in these different disorders corresponds with the incidence of reactive systemic amyloidosis in them. These observations support the view that major increases in SAA levels are a necessary condition for the deposition of this form of amyloid and suggest that prospective monitoring of the SAA concentration in predisposing diseases may help to identify those individuals who are most at risk for amyloidosis.

Antibodies to amyloid A protein in rheumatic diseases.

Circulating autoantibodies against amyloid A protein (AA) were demonstrated by enzyme immunoassay in 18/62 patients with rheumatoid arthritis (RA) and in 9/27 patients with systemic lupus erythematosus (SLE). In the subset of RA patients who had developed amyloid, the frequency of antibodies to AA was lower than in those without amyloid (P less than 0.05). The antibody levels showed some variation in serial serum samples during follow-up (1-4 years) of patients with amyloidosis or SLE, but did not correlate with disease activity. In contrast to the patients with rheumatic diseases, patients with inflammatory bowel disease and acute bacterial peritonitis had antibody levels within the range of the healthy control subjects. The results show that autoantibodies to protein AA may occur in rheumatic diseases; their occurrence does not, however, identify subjects with tissue amyloid deposits. Absorption experiments suggest that the antibodies may be directed to circulating amyloid A protein.

Dexamethasone modulation of LPS, IL-1, and TNF stimulated serum amyloid A synthesis in mice.

Three secretory products of the macrophage, interleukin 1 (IL-1), tumor necrosis factor/cachectin (TNF) and hepatocyte stimulating factor/interleukin 6 (IL-6) modulate liver protein synthesis during the acute phase response. Induction of serum amyloid A (SAA) synthesis is one of the most notable acute phase changes in liver proteins, with maximal SAA concentrations varying over a thousand-fold range in proportion to the amount of tissue injury and cell necrosis. Exogenous IL-1 and TNF induce SAA synthesis in vivo and in vitro, while exogenous IL-6 is a far less potent stimulus of in vivo SAA gene expression. Dexamethasone (DEX), a potent inhibitor of macrophage IL-1, TNF and IL-6 synthesis, was utilized to analyze the endogenous mediators of SAA synthesis in mice injected with lipopolysaccharide (LPS). DEX, although itself exhibiting the capacity to stimulate SAA synthesis to a limited extent, significantly reduced LPS induced SAA production. However, DEX did not reduce, but rather potentiated, IL-1 and TNF stimulated SAA production, indicating that these monokines do not require macrophage products to mediate their in vivo SAA inducer activity. SAA synthesis was observed in adrenalectomized mice, following administration of LPS, IL-1 and TNF, indicating that SAA induction by monokines is not secondary to corticosteroid release.

Serum amyloid A-containing human high density lipoprotein 3. Density, size, and apolipoprotein composition.

Serum amyloid A protein (apo-SAA), an acute phase reactant, is an apolipoprotein of high density lipoproteins (HDL), in particular the denser subpopulation HDL3. The structure of HDL3 isolated from humans affected by a variety of severe disease states was investigated with respect to density, size, and apolipoprotein composition, using density gradient ultracentrifugation, gradient gel electrophoresis, gel filtration, and solid phase immunoadsorption. Apo-SAA was present in HDL particles in increasing amounts as particle density increased. Apo-SAA-containing HDL3 had bigger radii than normal HDL3 of comparable density. Purified apo-SAA associated readily with normal HDL3 in vitro, giving rise to particles containing up to 80% of their apoproteins as apo-SAA. The addition of apo-SAA resulted in a displacement of apo-A-I and an increase in particle size. Acute phase HDL3 represented a mixture of particles, polydisperse with respect to apolipoprotein content; for example, some particles were isolated that contained apo-A-I, apo-A-II, and apo-SAA, whereas others contained apo-A-I and apo-SAA but no apo-A-II. We conclude that apo-SAA probably associates in the circulation of acute phase patients with existing HDL particles, causing the remodeling of the HDL shell to yield particles of bigger size and higher density that are relatively depleted of apo-A-I.

Three assays for the characterization and quantitation of human serum amyloid A.

Two different radioimmunoassays (RIA) and an enzyme-linked immunosorbent assay (ELISA) were developed for the quantitation and antigenic characterization of amyloid A (AA) and serum amyloid A (SAA) proteins, and the three assays were evaluated and compared with each other. Sensitivity, reproducibility, effect of denaturation and storage of serum and range of determination were considered. All three assays were found useful, but for different purposes. The most suitable method for the determination of SAA in whole serum was a second antibody precipitation RIA with purified SAA as labelled tracer and standard, and polyclonal rabbit anti-SAA as first antibody. This assay provided SAA concentrations in absolute amounts (mg/l) and acceptable reproducibility without need for prior denaturation of serum. Both advantages and disadvantages of ELISA using monoclonal antibodies to SAA and a solid-phase RIA using AA, SAA, anti-AA and anti-SAA were observed. The three assays were found suitable for antigenic studies of AA and SAA.