Kinetics of serum amyloid protein A in casein-induced murine amyloidosis

Serum amyloid protein (SAA) as a healthy marker for immune function in Tridacna crocea

Serum amyloid protein (SAA) is known as an acute reactive protein of innate immunity in mammals. However, in invertebrates, the role of SAA in innate immunity is still unclear. In this study, a full-length cDNA of the SAA gene (named TcSAA) was cloned from Tridacna crocea, mollusca. The gene includes a 193 bp 5' untranslated region (UTR) and a 129 bp 3' UTR sequence, and the open reading frame (ORF) with 393 bp nucleotides encodes a polypeptide of 130 amino acids. TcSAA contains a typical signal peptide and an SAA functional domain. The mRNA expression of TcSAA was detected in all 12 selected tissues and 7 different developmental stages. Furthermore, the expression of TcSAA was increased quickly in hemocytes after challenge with V. coralliilyticus or LPS. Furthermore, rTcSAA could bind V. coralliilyticus and V. alginolyticus, and the protein could reduce the lethality rate of the clams from 80% to 55% which caused by V. coralliilyticus about 48 h after injection. In summary, these results indicate that TcSAA may act as a marker for monitoring health and protecting T. crocea.

Molecular Interaction of Protein-Pigment C-Phycocyanin with Bovine Serum Albumin in a Gomphosis Structure Inhibiting Amyloid Formation

Accumulation of amyloid fibrils in organisms accompanies many diseases. Natural extracts offer an alternative strategy to control the process with potentially fewer side effects. In this study, the inhibition of C-phycocyanin from Spirulina sp. on amyloid formation of bovine serum albumin (BSA) during a 21-day incubation was investigated using fluorescence and circular dichroism (CD), and mechanisms were explored via kinetic fitting and molecular docking. C-phycocyanin (0-50 µg/mL) hindered the amyloid formation process of BSA with increased half-lives (12.43-17.73 days) based on fluorescence intensity. A kinetic model was built and showed that the k₁ decreased from 1.820 × 10^-2 d^-1 to 2.62 × 10^-3 d^-1 with the increase of C-phycocyanin, while k₂ showed no changes, indicating that the inhibition of BSA fibrillation by C-phycocyanin occurred in a spontaneous process instead of self-catalyzed one. CD results show that C-phycocyanin inhibited conformational conversion (α-helices and β-sheets) of BSA from day 6 to day 18. Molecular docking suggested that C-phycocyanin may hinder BSA fibrillation by hydrogen-bonding > 6 of 27 α-helices of BSA in a gomphosis-like structure, but the unblocked BSA α-helices might follow the self-catalytic process subsequently.

Proteomic patterns for early cancer detection

The advent of proteomics has brought with it the hope of discovering novel biomarkers that can be used to diagnose diseases, predict susceptibility, and monitor progression. Much of this effort has focused on the mass spectral identification of the thousands of proteins that populate complex biosystems such as serum and tissues. A revolutionary approach in proteomic pattern analysis has emerged as an effective method for the early diagnosis of diseases such as ovarian, breast, and prostate cancer. This technology is capable of analyzing hundreds of clinical samples per day and has the potential to be a novel, highly sensitive diagnostic tool for the early detection of diseases, or as a predictor of response to therapy.

Persistent Expression of Serum Amyloid A During Experimentally Induced Chronic Inflammatory Condition in Rabbit Involves Differential Activation of SAF, NF-κB, and C/EBP Transcription Factors

The serum amyloid A (SAA) protein has been implicated in the pathogenesis of several chronic inflammatory diseases. Its induction mechanism in response to a chronic inflammatory condition was investigated in rabbits following multiple s.c. injections of AgNO3 over a period of 35 days. During unremitting exposure to inflammatory stimulus, a persistently higher than normal level of SAA2 expression was seen in multiple tissues. Induction of SAA was correlated with higher levels of several transcription factor activities. Increased SAA-activating factor (SAF) activity was detected in the liver, lung, and brain tissues under both acute and chronic inflammatory conditions. In the heart, kidney, and skeletal muscle tissues, this activity remained virtually constant. In contrast, CCAAT enhancer binding protein (C/EBP) DNA-binding activity was transiently induced in selective tissues. Higher than normal NF-κB DNA-binding activity was detected in the lung and to a lesser extent in the liver and kidney tissues under both acute and chronic conditions. This result suggested that C/EBP, SAF, and NF-κB are required for transient acute phase induction of SAA whereas SAF and NF-κB activities are necessary for persistent SAA expression during chronic inflammatory conditions.

Amyloid deposition is delayed in mice with targeted deletion of the serum amyloid P component gene

The tissue amyloid deposits that characterize systemic amyloidosis, Alzheimer's disease and the transmissible spongiform encephalopathies always contain serum amyloid P component (SAP) bound to the amyloid fibrils. We have previously proposed that this normal plasma protein may contribute to amyloidogenesis by stabilizing the deposits. Here we show that the induction of reactive amyloidosis is retarded in mice with targeted deletion of the SAP gene. This first demonstration of the participation of SAP in pathogenesis of amyloidosis in vivo confirms that inhibition of SAP binding to amyloid fibrils is an attractive therapeutic target in a range of serious human diseases.

An in vitro cellular system for generation of AA-amyloid

Different conditions for establishing a cell culture system for generation of AA-amyloid were investigated. The most effective system was based on peritoneal macrophages from CBA/J mice that had received repeated injections of Hammersten casein, with subsequent cultivation of the cells at high density, high levels of acute phase serum, and neutral pH. Staining with Congo red, thioflavin T, and anti-AA revealed amyloid-like structures associated with macrophage clusters. The structures increased in number and size from day 2 to 6 of cell cultivation. The concentration of apoSAA in the culture medium fell markedly in the amyloid-producing cell cultures, while the SAP concentration was not reduced. The described cell culture system can be useful in studies of the influence of chaperone molecules and other factors or the formation and degradation of amyloid fibrils.

Expression of rabbit C-reactive protein in transgenic mice

C-reactive protein (CRP) is a prototypic acute phase reactant in humans and rabbits whose serum concentration can increase up to 1000-fold following an acute inflammatory stimulus. CRP binds to many phosphate ester-containing compounds including phosphorylcholine, nucleotides, chromatin and snRNP. To examine the in vivo function of this protein, we produced transgenic mice capable of significant CRP synthesis. In contrast to most other vertebrates, mice synthesize CRP in only trace amounts. The transgenic animals express rabbit CRP from either the phosphoenolpyruvate carboxykinase promoter (PEPCK-CRP) or the mouse metallothionein I promoter (MT-CRP). Manipulating the diet in one of the PEPCK-CRP lines led to a rise in serum CRP levels from < 5 mu g/mL to 100-200 mu g/mL over a period of 2 days. The two MT-CRP lines examined expressed CRP constitutively which could be further elevated 2-4-fold following an inflammatory stimulus. Transgenic CRP bound phosphorylcholine was pentameric, had a circulating half-life of 30-60 min and was capable of activating mouse complement when bound to a ligand. We conclude that these transgenic lines express CRP with many of the properties of authentic rabbit CRP, and that the expression of CRP can be controlled to be dependent or independent of the acute phase response.

Transformation from SAA2-fibrils to AA-fibrils in amyloid fibrillogenesis: in vivo observations in murine spleen using anti-SAA and anti-AA antibodies

Early amyloid fibrillogenesis from serum amyloid A protein (SAA) has been observed in the murine spleen after an injection of casein-Freund's complete adjuvant in the presence of amyloid enhancing factor, using anti-SAA C-terminal (anti-SAA) and anti-amyloid A (AA) antibodies. In Western immunoblotting of sera, both SAA1 and SAA2 reached a maximum after 24 h and began to decrease after 48 h. In spleen extracts, SAA2, but not SAA1 or AA, was found from 48 h, when amyloid was first deposited in the marginal zone. Electron microscopic immunohistochemistry of this stage showed reaction products from SAA in the marginal zone as fine granules along the cell membrane of mononuclear cells and focal intercellular aggregates, which contained fine fibrils originating from the cell membrane. Amyloid nodules, surrounded by mononuclear cells, developed from this stage. In the nodules, fibrils were positive for anti-SAA only in the vicinity of the cell membrane, while anti-AA stained fibrils throughout. Our hypothesis for fibrillogenesis is thus as follows: Serum SAA2 is specifically deposited on mononuclear cells in the marginal zone and polymerized extracellularly into fibrils, retaining its antigenicity (SAA2 amyloid fibrils); these fibrils are then processed to AA amyloid fibrils in situ by cleavage of the C-terminal portion of SAA2.

Immune-complex-mediated vasculitis increases coronary artery lipid accumulation in autoimmune-prone MRL mice

MRL/lpr mice develop severe autoimmune disease and vasculitis by 5 months of age, whereas congenic strain MRL/n mice exhibit much milder vasculitis with a later age of onset. When maintained on a high-fat, high-cholesterol (atherogenic) diet, strain MRL/lpr mice exhibited a striking deposition of lipid in both the large and small coronary arteries, whereas strain MRL/n mice exhibited very little lipid accumulation. Neither strain exhibited lipid accumulation on a low-fat chow diet. The atherogenic diet induced hyperlipidemia in both strains, but surprisingly the levels of atherogenic apolipoprotein B-containing lipoproteins were much lower in MRL/lpr mice. Immunohistochemical studies revealed that immune complexes (immunoglobulins G and M), T and B lymphocytes, macrophages, granulocytes, apolipoprotein B, and serum amyloid A proteins were present in the walls of the coronary arteries that had vasculitis and lipid accumulation. By 6-7 months of age, MRL/lpr mice had a higher incidence of myocardial infarction in the atherogenic diet group (53%) compared with the chow group (14%), whereas MRL/n mice exhibited no myocardial infarction on either diet. These results suggest important interactions between vasculitis, hyperlipidemia, and arterial lipid accumulation. They support the concept that injury to the vessel wall in immune-complex-mediated vasculitis increases lipid deposition in the presence of hyperlipidemia.

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.

Ubiquitin: its potential significance in murine AA amyloidogenesis

Amyloid enhancing factor (AEF), which has recently been shown to have identity with ubiquitin (Ub), is believed to play a causative role in experimentally induced AA amyloidosis in mice. We have examined the profile of Ub in activated leukocytes and splenic reticulo-endothelial (RE) cells and its relationship with serum amyloid A protein (SAA) and AA amyloid deposits in an alveolar hydatid cyst (AHC)-infected mouse model of AA amyloidosis. Two monospecific antibodies, anti-ubiquitin (RABU) and anti-mouse AA amyloid, were used as immunological probes to localize Ub, SAA, and AA amyloid. In response to AHC infection, the dull and diffuse Ub immunoreactivity in normal mouse leukocytes and RE cells promptly changed to a discrete granular pattern suggesting an increase in the intracellular concentration of Ub and the formation of Ub-protein conjugates. This corresponded to an elevation in SAA levels, SAA uptake by RABU-positive phagocytic cells, co-localization of Ub-SAA immunoreactive splenocytes in the perifollicular areas, and deposition of Ub-bound AA amyloid in the splenic and hepatic tissues. These results suggest that Ub-loaded monocytoid cells may play an important role in the physiological processing of the sequestered SAA into AA amyloid. Aspects of AA amyloidogenesis are discussed in relation to other experimental models in which stress-induced Ub-protein conjugate formation and its transport to lysosomal vesicles have been studied.

Serum amyloid P component: a predictor of clinical beta 2-microglobulin amyloidosis

Beta 2-microglobulin (beta 2M) amyloidosis is common in patients on long-term hemodialysis, but the clinical conditions associated with disease activity are poorly understood. This study was designed to determine if the serum amyloid P (AP) component concentration is predictive of beta 2M amyloid disease activity. Serum AP component concentrations were determined by rocket immunoelectrophoresis and beta 2M concentrations by a commercially available kit. Radiographic evidence of beta 2M amyloidosis was determined from bone films of the hips, shoulders, and hands. Serum AP component concentrations were not different in dialysis and control patients. However, AP component concentrations in long-term (greater than or equal to 5 years) dialysis patients were significantly lower than in short-term (less than 5 years) dialysis patients (43.0 +/- 16.9 micrograms/mL [n = 28] v 56.0 +/- 18.3 micrograms/mL [n = 31], P less than 0.05). The patients on hemodialysis for 5 or more years who had radiographic evidence of severe beta 2 M amyloidosis were significantly older (57.9 +/- 9.5 v 38.3 +/- 11.3 years, P less than 0.001) and their serum AP concentrations were significantly lower (34.3 +/- 15.0 v 50.1 +/- 15.6 micrograms/mL, P less than 0.05) than long-term dialysis patients without radiographic evidence of disease. Stepwise regression analysis showed that the patient's age and serum AP component concentration were predictors of radiographic evidence of beta 2 M amyloidosis. Thus, serum AP component concentrations are decreased in long-term dialysis patients, suggesting accelerated deposition into amyloid deposits.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid enhancing factor (AEF). Isolation and biochemical and pathological characteristics

Neutrophils and spleens were prepared from mice after treatment to induce amyloid deposition. The deposition of amyloid was accelerated in normal recipients by intravenous injection of more than 2 x 10(4) neutrophils, and intraperitoneal injection of supernatants obtained by homogenization and centrifugation of the neutrophils and spleens. The supernatants were subjected individually to DEAE ion-exchange chromatography. Amyloid enhancing factor (AEF) activity was present in peaks eluted at an NaCl concentration of 0.17 M. The fractions containing AEF were subjected to high-performance liquid chromatography (HPLC), and AEF was eluted at a position corresponding to about 15 KDa. Purified AEF was analyzed by amino acid sequencing and gas chromatography. The N-terminal amino acid was blocked, and AEF contained some saccharides including glucose, mannose, galactosamine and sialic acid, and an undefined substance (probably derived from certain proteins). Immunoelectron microscopy by the pre-embedding method using an anti-AEF antiserum demonstrated that the cytosol, but not primary and specific granules in neutrophils from the spleen of amyloid-laden mice, reacted with the antiserum. These findings suggest that AEF is a glycoprotein associated with neutrophils.

Two adjacent C/EBP-binding sequences that participate in the cell-specific expression of the mouse serum amyloid A3 gene

Serum amyloid A (SAA) is a major acute-phase protein synthesized primarily in the liver. Its expression, very low in normal animals, is increased several hundredfold following acute inflammation. To examine DNA sequences involved in liver-specific expression, 5'-flanking regions of the mouse SAA3 gene were analyzed by transient transfection, band shift, and DNase I protection assays. We found that a 56-bp fragment immediately 5' to the TATA box spanning the region -93 to -38 relative to the transcription start site was sufficient to confer liver cell-specific transcriptional activation onto a heterologous promoter in a dose-dependent and orientation-independent manner. This DNA fragment could form DNA-protein complexes with heat-stable nuclear proteins, and the complexes formed could be specifically competed for by excess oligomers corresponding to the C/EBP- or DBP-binding sites but not by binding sites for three other liver-specific factors, HNF1, HNF3, and HNF4. Footprint analysis using Hep3B nuclear extracts revealed two adjacent footprint regions within this 56-bp fragment, the distal region having at least fivefold-greater affinity than the proximal region. Identical footprint patterns were observed when purified recombinant C/EBP protein was used. These results indicated that binding of C/EBP to this 56-bp fragment plays an important role in vivo in enhancing expression of the mouse SAA3 gene in hepatocytes.

Two adjacent C/EBP-binding sequences that participate in the cell-specific expression of the mouse serum amyloid A3 gene

Serum amyloid A (SAA) is a major acute-phase protein synthesized primarily in the liver. Its expression, very low in normal animals, is increased several hundredfold following acute inflammation. To examine DNA sequences involved in liver-specific expression, 5'-flanking regions of the mouse SAA3 gene were analyzed by transient transfection, band shift, and DNase I protection assays. We found that a 56-bp fragment immediately 5' to the TATA box spanning the region -93 to -38 relative to the transcription start site was sufficient to confer liver cell-specific transcriptional activation onto a heterologous promoter in a dose-dependent and orientation-independent manner. This DNA fragment could form DNA-protein complexes with heat-stable nuclear proteins, and the complexes formed could be specifically competed for by excess oligomers corresponding to the C/EBP- or DBP-binding sites but not by binding sites for three other liver-specific factors, HNF1, HNF3, and HNF4. Footprint analysis using Hep3B nuclear extracts revealed two adjacent footprint regions within this 56-bp fragment, the distal region having at least fivefold-greater affinity than the proximal region. Identical footprint patterns were observed when purified recombinant C/EBP protein was used. These results indicated that binding of C/EBP to this 56-bp fragment plays an important role in vivo in enhancing expression of the mouse SAA3 gene in hepatocytes.

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 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.

Regulation of amyloid A gene expression in cultured cells

Serum amyloid A (SAA) proteins are secreted by mammalian liver in response to inflammatory stimuli. Both transcriptional and posttranscriptional mechanisms have been shown to regulate the 2,000-fold increase in SAA mRNA after injection of endotoxin into mice. We report here the characterization of a cell line derived from mouse liver (BNL) in which the expression of SAA3 mRNA is regulated. In this model, SAA3 mRNA accumulated in response to conditioned medium from the mouse macrophage P388D1 cell line with kinetics similar to that seen in mouse liver (C. A. Lowell, R. S. Stearman, and J. F. Morrow, J. Biol. Chem. 261:8453-8461, 1986). In in vitro nuclear transcription assays, the SAA3 gene was transcribed equally in induced and uninduced cells. In addition, in steady-state RNA studies treatment with conditioned medium allowed the cells to rapidly accumulate SAA3 mRNA without an apparent change in half-life. These observations suggest that conditioned medium contains a factor(s) that acts directly on hepatocytes to regulate SAA3 mRNA processing.

The pathogenesis of reactive systemic amyloidosis

The diagnosis of amyloidosis is based on the presence of extracellular tissue deposits of proteinaceous material that demonstrate a characteristic green color when stained with Congo red and viewed under polarized light. Several different proteins are amyloidogenic but, in domestic animals, spontaneously occurring systemic amyloidosis is reactive in nature and characterized by the presence of amyloid protein AA. This type of systemic amyloidosis may occur secondary to chronic inflammatory or neoplastic disease, but in many instances no predisposing disease is found. A sustained increase in the serum concentration of serum amyloid A protein (SAA) is necessary but not sufficient for the development of reactive amyloidosis. Other inherited and acquired host-related factors are likely to be important in the development of reactive amyloidosis because this condition develops in few patients with chronic inflammatory disease. The tissue tropism of amyloid deposits varies with the amyloid protein itself and species affected. The consequences of amyloidosis for the host depend upon the tissues involved and the response of these tissues to the presence of the amyloid deposits. In domestic animals, reactive systemic amyloidosis is nephropathic, leading to end-stage renal disease, and the clinical presentation is that of uremia.

Echinococcus multilocularis: relationship between persistent inflammation, serum amyloid A protein response and amyloidosis in four mouse strains

LPS-hyporesponsive (C3H/HeJ) and LPS-sensitive (C57BL/6, CBA/J, C3H/HeSn) strains of mice were infected intraperitoneally with 50 alveolar hydatid cysts (AHC) to assess the effect of protracted severe inflammation on serum amyloid A protein (SAA) concentrations, splenic amyloid deposition, and pre- and postamyloidotic alterations in the splenic architecture. In general, the SAA concentrations in all the four mouse strains showed a moderate but steady increase throughout the course of infection. Splenic amyloid deposition commenced between 6 to 8 weeks postinfection (p.i.) when the SAA concentrations were relatively low and increased progressively until 12 weeks p.i. when 52 to 78% of the splenic parenchyma was obliterated. CBA mice which harbored the largest AHC throughout the 12-week course of infection showed the poorest SAA and amyloid responses; the situation was reversed in the C3H/HeSn strain. Histologically, most of the splenic follicles, during the stage of maximum amyloid deposition, appeared hypocellular. Their T-cell-dependent periarterial sinuses were either totally depleted of cells or contained plasma cells or myeloid cells. These results show that (a) there is no direct correlation between the intensity of inflammation, SAA concentrations, or amounts of amyloid deposition in either of the four mouse strains and (b) amyloidosis secondary to AHC infection differs from other experimental mouse models of amyloidosis in the magnitude of SAA elevation during the preamyloid phase.

Regulation of amyloid A gene expression in cultured cells

Serum amyloid A (SAA) proteins are secreted by mammalian liver in response to inflammatory stimuli. Both transcriptional and posttranscriptional mechanisms have been shown to regulate the 2,000-fold increase in SAA mRNA after injection of endotoxin into mice. We report here the characterization of a cell line derived from mouse liver (BNL) in which the expression of SAA3 mRNA is regulated. In this model, SAA3 mRNA accumulated in response to conditioned medium from the mouse macrophage P388D1 cell line with kinetics similar to that seen in mouse liver (C. A. Lowell, R. S. Stearman, and J. F. Morrow, J. Biol. Chem. 261:8453-8461, 1986). In in vitro nuclear transcription assays, the SAA3 gene was transcribed equally in induced and uninduced cells. In addition, in steady-state RNA studies treatment with conditioned medium allowed the cells to rapidly accumulate SAA3 mRNA without an apparent change in half-life. These observations suggest that conditioned medium contains a factor(s) that acts directly on hepatocytes to regulate SAA3 mRNA processing.

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.

Pathological Society of Great Britain and Ireland. 154th meeting, 7-9 January 1987. Synopses of papers

The transformation of serum proteins into Congo red-sensitive fibrillar material is requisite for the onset and progression of amyloid disease. All the mechanisms which lead to the disease itself have not been elucidated, but our knowledge has increased significantly. It is apparent that in all types of amyloid fibrils, three common features are displayed by the major protein constituents. These are that the fibril protein has a serum precursor, a high degree of anti-parallel beta-sheet conformation and a distinctive ultrastructure on electron microscopy. In the AL and AA forms of amyloidosis, the putative precursors appear to undergo limited degradation to form the protein component of amyloid fibrils. It has been suggested that there may be certain primary structural characteristics inherent in precursor molecules which make them amyloidogenic, thus predisposing them to amyloid fibril formation. This would include certain subtypes of immunoglobulin light chains, possibly kappa I and lambda VI, in the AL type of amyloidosis and one of the polymorphic SAA species, SAA2, which has been identified as the predominating isotype found in AA amyloid fibrils. In AH amyloidosis, the mechanism of amyloid fibril formation appears to be simply a concentration phenomenon where elevated concentrations of B2-M are not handled normally and amyloid deposition is the result. Amyloidogenesis in the hereditary form of systemic amyloidosis may involve other factors in addition to the presence of a variant precursor prealbumin as indicated by the delayed onset of the disease. It is evident that the elucidation of the mechanism(s) which governs the onset and progression of the amyloidoses will allow future regulation and treatment of these all too often complex disorders.

The induction of accelerated murine amyloid with human splenic extract. Probable role of amyloid enhancing factor

Amyloid enhancing factor (AEF) is derived from the tissues of pre-amyloidotic and amyloidotic animals and, when transferred, greatly accelerates amyloid induction in the recipient murine models. It has also been reported that similarly accelerated amyloid induction can be achieved in mice by injection of human splenic homogenates from patients with amyloidosis. The present study has attempted to characterize further the mechanism of this "heterologous transfer of amyloid". Treatment of mice with the "tissue homogenate" or the "AEF extract" of AA-, AL- and A prealbumin-laden human spleens followed by daily subcutaneous casein injections induced amyloidosis in an accelerated fashion. The resultant amyloid deposits in mice had strongly positive immunohistochemical reactions with anti-mouse AA, and negative reaction with anti-human AA or anti-human prealbumin. The results lend support to the idea that accelerated amyloid induction in the recipient mice is unlikely to be due to transfer of human amyloid substance, but rather to formation of "native" murine amyloid under the influence of a human AEF factor similar to or identical with AEF described in mouse-to mouse transfer models.

Amyloid A gene family expression in different mouse tissues

Serum amyloid A (SAA) is a major acute-phase reactant and apoprotein of high density lipoprotein (HDL). SAA is encoded by a family of three active genes. We examined hepatic expression and searched for extrahepatic expression of the three SAA mRNAs after injection with casein or LPS. Studies using an SAA cDNA, which detects all three SAA mRNAs, revealed that after casein injection liver SAA mRNA was elevated approximately 1,000-fold. Adrenal gland expressed SAA mRNA at a low level (0.5% of hepatic level), and was the only extrahepatic tissue with elevated SAA mRNA after casein injection. The small intestine, primarily the ileum, and the large intestine of unstimulated control animals contained 5- and 15-fold higher SAA mRNA levels than control liver. LPS also elevated liver SAA mRNA approximately 1,000-fold. However, in contrast to casein injection, every extrahepatic tissue examined expressed SAA mRNA. Lung and kidney contained 2-5% and large intestine contained nearly 10% of SAA mRNA levels found in liver RNA. SAA mRNA levels were lower in the remaining tissues and ranged from 0.1% in the brain and pancreas to 1.0% in the small intestine, with the ileum containing 50-fold more than the duodenum. Analysis of liver with SAA1, SAA2, and SAA3 mRNA-specific oligonucleotide probes revealed that SAA1 and SAA2 mRNA were elevated approximately 50-fold higher than SAA3 mRNA after casein administration. LPS, however, induced all three SAA mRNAs equally. In extrahepatic tissues, SAA1, SAA2, and SAA3 mRNAs were expressed differentially and can be grouped into three general classes: tissues expressing all three genes, tissues expressing SAA1 and SAA3, and tissues expressing predominantly or only SAA3.

Amyloidogenesis. One serum amyloid A isotype is selectively removed from the circulation

The deposits of fibrils found in amyloidosis of the A type are derived from only one of the three serum amyloid A (SAA) gene products, namely SAA2. In order to explore the mechanism of SAA isotype-specific amyloid protein AA deposition, the molecular kinetics of the serum amyloid proteins were examined in CBA mice during casein induction of amyloidosis. The presence of SAA mRNA in spleen was searched for; hepatic SAA1 and SAA2 mRNA levels, rates of specific protein synthesis and secretion by hepatocytes, and serum levels were measured during a 20-d period of amyloid induction. We observed the following: small amounts of amyloid substance appeared in the spleen by day 5 and increased steadily over the ensuing 15 d to occupy nearly 30% of splenic volume by day 20. No SAA mRNA was detected in spleen at any time during induction of amyloid formation. Total serum SAA levels peaked 1 d after we began casein treatment, and thereafter declined. This decline was accounted for entirely by a dramatic fall in SAA2, while SAA1 levels remained nearly constant throughout. The ratios of hepatic SAA2:SAA1 mRNA, as determined by in vitro translation, remained constant during the 20-d period, as did amounts of SAA1 and SAA2 synthesized and secreted by freshly isolated hepatocytes. These data indicate that the deposition of amyloid A protein derived from SAA2 is not due to local SAA production in spleen, nor excessive SAA2 production compared with SAA1, but involves the selective and accelerated removal of SAA2 from the circulating pool of both SAA1 and SAA2.

AA-amyloidosis in dogs: partial amino acid sequence of protein AA and immunohistochemical cross-reactivity with human and cow AA-amyloid

Protein AA was purified from the kidneys of dogs with spontaneous reactive amyloidosis. The protein had a blocked N-terminal. Sequence analysis of a peptide obtained after cyanogen bromide cleavage revealed an amino acid sequence corresponding to positions 24-42 of human AA. This region showed a strong homology to protein AA of other species. Antiserum to both human and dog protein AA reacted immunohistochemically with AA amyloid of human, dog and cow origin.

Immunocytochemical study of hepatocyte synthesis of amyloid AA. Demonstration of usual site of synthesis and intracellular pathways but unusual retention on the surface membrane

For determination of the intracellular site of synthesis and the pathways followed by amyloid protein AA, immunocytochemical localization of the anti-AA reactive substance was investigated in the livers of CBA/J mice in an acute-phase response evoked by a single subcutaneous injection of 0.5 ml of 10% casein. In the cytoplasm of the hepatocytes, the positive reaction was localized on and/or in the rough endoplasmic reticulum and the single membrane-bound vesicles, vacuoles and lamellae including the Golgi apparatus, confirming that amyloid protein AA follows the common routes of synthesis and secretion established for other proteins. The anti-AA-reactive substance was also localized on the free surface of the hepatocyte membrane, including the microvilli. The latter reaction appeared as early as but lasted at least several hours longer than its cytoplasmic counterpart, suggesting that a certain retention period exists before the release of the AA-reactive substance from the cellular surface to the free blood plasma.

Age-related changes of serum apoprotein SASSAM, apoprotein A-I and low-density lipoprotein levels in senescence accelerated mouse (SAM)

Age-related changes of serum concentration of apo SASSAM, an apoprotein of high density lipoprotein (HDL) which cross-reacts with antiserum against murine senile amyloid fibril protein (ASSAM) were estimated in senescence accelerated mouse (SAM-P) and in senescence resistant series (SAM-R), as a control, using a single radial immunodiffusion technique. Serum concentrations of apo A-I, a major apoprotein of HDL, and low density lipoprotein (LDL) were also measured. In SAM-P (SAM-P/1 and SAM-P/2) with a high incidence of senile systemic amyloidosis, we observed age-associated decreases in serum apo SASSAM levels. The concentrations of apo SASSAM at 16 months of age were below 40% of the concentration at 2 months of age, regardless of the sex. In contrast with SAM-P, we observed no age-associated decrease of serum apo SASSAM levels in SAM-R (SAM-R/1 and SAM-R/2) with a low incidence of amyloidosis. Serum apo SASSAM concentration was higher in SAM-R/1 than in any other strain of mice observed. Serum apo A-I concentration was highly and significantly correlated with the serum concentration of apo SASSAM and decreased with advancing age in SAM-P but not in SAM-R. Age-related changes of LDL were not observed in any strain, but the concentration was lower in the females. In old SAM-P (16 months' old), the concentration of apo SASSAM decreased to one-third of that in the young SAM-P (4 months' old) and the serum concentrations of albumin and total protein did not decrease, compared with those in the young mice. All these findings taken together suggest that abnormality of metabolism in apo SASSAM, putative precursor of ASSAM, might occur in SAM-P.

Changes in natural killer activities in experimental secondary amyloidosis

Natural killer (NK) cell activity in experimental murine amyloidosis was studied. In CBA/J mice, which show a high incidence of amyloidosis, NK activity was significantly decreased after 1 week of casein treatment. In C3H mice, which show a low incidence of amyloidosis, NK activity was not changed by casein treatment. Pretreatment with lipopolysaccharide in vivo enhanced the NK activities in CBA/J and C3H mice. These increases were not observed after casein treatment. The lowered NK activity of cells from CBA/J mice after casein treatment was restored to the normal range by indomethacine in vitro. Depletion of adherent cells from the spleen cells treated with casein had no effect on NK activity. Single-cell assay showed that casein treatment impaired the killing but not the binding of NK cells to target cells. After casein treatment, the splenic serum amyloid A (SAA) level gradually increased in CBA/J mice but remained low in C3H mice. NK activity was suppressed by the addition of serum obtained from CBA/J mice treated with casein but not by normal control serum. And partially purified AA protein obtained from the spleen of CBA/J mice treated with casein also suppressed NK activity in vitro.

Murine tissue amyloid protein AA. NH2-terminal sequence identity with only one of two serum amyloid protein (ApoSAA) gene products

Amyloid protein AA is the presumptive fragment of an acute phase serum apolipoprotein, apoSAA. Two major murine apoSAA isotypes (apoSAA1 and apoSAA2) have been identified. The NH2-terminal amino acid sequences of purified murine apoSAA1 and apoSAA2 have been examined and compared with that of murine amyloid protein AA. Our results indicate that apoSAA1 and apoSAA2 are separate gene products and that amyloid protein AA has NH2-terminal amino acid sequence identity with only one of these isotypes, namely apoSAA2.

The degradation of serum amyloid A protein by activated polymorphonuclear leucocytes: participation of granulocytic elastase

To determine the role of inflammation in amyloidogenesis, we have studied the degradation of human serum amyloid A (SAA) protein by purified preparations of human blood polymorphonuclear leucocytes (PMN) and monocytes. When both PMN and monocytes were incubated in SAA-containing medium, the concentration of SAA as measured by a competitive anti-AA radioimmunoassay decreased over time. The rate of decrease of SAA was similar for both monocytes and PMN and there were no differences between four patients with amyloidosis and three normal controls. Resting PMN from normal volunteers were able to degrade SAA to smaller acid-soluble peptides within 16 hr while zymosan-activated PMN produced significant degradation within 1 hr (31%–50%). The supernatants from zymosan-treated PMN also caused marked SAA degradation within 1 hr.

The following enzyme inhibitors were able to prevent degradation of SAA by PMN supernatants; phenylmethylsulphonyl fluoride, a serine esterase inhibitor; α₁ anti-trypsin and soybean trypsin inhibitor; and acetyl-ala-ala-pro-val-chloromethyl ketone, an elastase inhibitor. The ability of a neutral lysosomal enzyme to degrade SAA was further confirmed by showing that purified PMN elastase significantly degraded ¹²⁵I-SAA.

We conclude that PMN contain one or more lysosomal enzymes capable of degrading SAA, an apoprotein of HDL₃ serum lipoproteins. Alteration in SAA proteolysis by activated PMN may contribute to the deposition of amyloid fibrils in the tissues of patients with chronic inflammatory disease.

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.

The role of interleukin 1 in acute phase serum amyloid A (SAA) and serum amyloid P (SAP) biosynthesis

The acute phase SAA and SAP profiles have been compared for localized and endotoxin induced inflammation in LPS responder and nonresponder strains of mice. The SAP profile can reflect a delay with respect to the start of the increase. Its maximum is on the order of ten times the nonacute phase concentration and elevated concentrations are sustained 24 to 48 hours after SAA concentration is rapidly decreasing to normal. The role of Interleukin 1, known to have an essential role in SAA production, was investigated for SAP production. Purified mouse IL 1 and rabbit IL 1 produced a minimal elevation of SAP concentration above normal values, especially when compared with their effects on SAA concentration. BCG infection was shown to synergistically augment SAA induction by LPS and was shown to enhance IL 1 production by macrophages in response to LPS. Unlike SAA synthesis, BCG-preinfection fails to synergistically augment the LPS-induced SAP response. BCG infection alone produced highly elevated and sustained increases in SAP concentration, whereas, the effect on SAA concentration was minimal. Macrophages appear to play an important role in SAP acute phase elevation, but the mechanism in different from that of SAA elevation.

Suppression and acceleration of experimental amyloidosis in mouse model

Leupeptins, protease inhibitors, suppress the appearance of experimental amyloidosis in CBA mice induced by the injections with complete Freund's adjuvant. This substance, however, should be administered continuously from 1 week prior to amyloid induction to the end of the experiment. On the other hand, Trypan blue, inhibitors of lysosomal enzymes, accelerates experimental amyloidosis in the mouse model above-mentioned. Trypan blue is effective when given either prior to or at the same time of the initiation of amyloid induction. Organic Germanium has not been confirmed to be a potent suppressor of experimental murine amyloidosis but the experimental group administered this substance continuously from 1 week prior to the induction shows a rather low incidence of amyloidosis, and the average number of amyloidotic organs per affected mouse is about half of that of the control group. The suppression and acceleration of experimental murine amyloidosis presented here are a useful tool for investigating the pathogenesis of amyloidosis.

Redistribution of amyloid deposits

After 21 daily subcutaneous injections of 0.5 ml 10% casein, CBA/J mice were left untreated and evaluated periodically for 6 months for the development of amyloid in spleens, livers, and kidneys. At the end of the amyloid-inducing regimen, the mice developed moderate to heavy splenic amyloid, trace to light hepatic amyloid, and virtually no renal amyloid. Renal amyloid appeared about 2 months after cessation of the casein and then increased steadily, while splenic and hepatic amyloid gradually diminished. Six months after the cessation of casein, moderate amyloid deposits were observed in the kidneys whereas no, or only traces of, amyloid remained in spleens and livers. This renal amyloid was localized predominantly in the peritubular area and differed from the renal amyloid seen in rapidly induced disease, when it localizes dominantly in glomeruli. This phenomenon is interpreted in the light of possible redistribution of amyloid deposits from organ to organ, and the clinical and investigative significances of this possibility and others are discussed.

Serum amyloid protein levels in south american children with rheumatoid arthritis: a co-operative study

Serum amyloid protein (SAA) levels were determined by radioimmunoassay in 90 children with juvenile rheumatoid arthritis (JRA). Significantly higher levels of SAA were present in children with the polyarticular and systemic forms of the disease. SAA levels correlate with disease activity, increasing during acute exacerbations, decreasing during remission and in patients having prednisone therapy. High serum SAA concentrations in children with JRA did not correlate with the presence of secondary amyloidosis and may be useful as a disease monitor.

Differences in the acute phase responses of serum amyloid P-component (SAP) and C3 to injections of casein or bovine serum albumin in amyloid-susceptible and -resistant mouse strains

In CBA/Ca and C57Bl/Cbi mice, which are susceptible to casein-induced amyloidosis, daily injections of casein caused a marked rise in the level of circulating serum amyloid P-component (SAP), which was sustained while injections continued. In contrast, mice given bovine serum albumin (BSA) injections showed only a small, transient increase in SAP levels. A/J mice, which are relatively resistant to casein-induced amyloidosis, also developed high SAP levels initially, but the increase was not maintained despite continued administration of casein. A/J mice receiving BSA had a slowly progressive rise in SAP which reached the same level as in the casein-treated animals. Administration of colchicine, which prevents casein-induced amyloidosis, suppressed the SAP response to casein in CBA mice. The serum level of the C3 component of complement, which is not an amyloid protein but is an acute phase reactant, also increased following casein injection. The rise in C3 was, however, proportionately less than that of SAP, was less sustained and was scarcely affected by colchicine. The present results therefore demonstrate different patterns in the acute phase response of different proteins in different mouse strains, and suggest that there may be a relationship between sustained high levels of SAP and the deposition of amyloid.

The effect of levamisole in experimental murine amyloidosis

In casein-induced murine amyloidosis various lines of investigation have implicated immunodeficiency as playing a role in amyloid formation. In this study, the immunopotentiating agent levamisole failed to prevent amyloidogenesis or to accelerate resolution of preformed amyloid deposits in the mouse model. The serum precursor of amyloid, serum amyloid protein A (SAA), was increased by levamisole in both normal and amyloidotic mice.

Binding of serum amyloid P-component (SAP) by amyloid fibrils

Serum amyloid P-component (protein SAP) was found to bind in vitro to isolated amyloid fibrils of both primary and secondary types. The binding was strictly calcium-dependent, optimal uptake requiring at least 0.5 mM calcium ion. Using normal human serum as the source of protein SAP different fibril preparations became saturated with between 5--20 micrograms of SAP per mg dry weight of fibril. Isolated pure protein SAP bound in greater amounts. In control experiments SAP did not bind significantly to collagen fibrils, sheep erythrocytes, plastic shavings, or the following immobilized proteins: human kappa or lambda Bence-Jones proteins; human; rabbit or mouse IgG; human serum albumin. C-reactive protein, which resembles protein SAP structurally but has calcium-dependent specificity for different ligands, bound significantly to only one of five different amyloid fibril preparations.

Characterization of amyloid of ageing obese-hyperglycaemic mice and their lean littermates

Amyloid fibrils, isolated from 18-month-old obese-hyperglycaemic mice and their lean littermates, were characterized immunologically and chemically. The main amyloid fibril subunit protein was protein AA, which cross-reacted completely with an antiserum against amyloid from mice with experimentally induced amyloidosis and had an amino acid composition and N-terminal amino acid sequence identical to that protein. These results indicate that the spontaneously occurring amyloidosis in obese-hyperglycaemic mice and their lean littermates corresponds to human, secondary amyloidosis and may serve as a model for that disease.