Large scale isolation and partial primary structure of human plasma amyloid P-component

Inhibition of TTR aggregation-induced cell death--a new role for serum amyloid P component

Background

Serum amyloid P component (SAP) is a glycoprotein that is universally found associated with different types of amyloid deposits. It has been suggested that it stabilizes amyloid fibrils and therefore protects them from proteolytic degradation.

Methodology/Principal Findings

In this paper, we show that SAP binds not only to mature amyloid fibrils but also to early aggregates of amyloidogenic mutants of the plasma protein transthyretin (TTR). It does not inhibit fibril formation of TTR mutants, which spontaneously form amyloid in vitro at physiological pH. We found that SAP prevents cell death induced by mutant TTR, while several other molecules that are also known to decorate amyloid fibrils do not have such effect. Using a Drosophila model for TTR-associated amyloidosis, we found a new role for SAP as a protective factor in inhibition of TTR-induced toxicity. Overexpression of mutated TTR leads to a neurological phenotype with changes in wing posture. SAP-transgenic flies were crossed with mutated TTR-expressing flies and the results clearly confirmed a protective effect of SAP on TTR-induced phenotype, with an almost complete reduction in abnormal wing posture. Furthermore, we found in vivo that binding of SAP to mutated TTR counteracts the otherwise detrimental effects of aggregation of amyloidogenic TTR on retinal structure.

Conclusions/Significance

Together, these two approaches firmly establish the protective effect of SAP on TTR-induced cell death and degenerative phenotypes, and suggest a novel role for SAP through which the toxicity of early amyloidogenic aggregates is attenuated.

Effects of anaesthesia based on high versus low doses of opioids on the cytokine and acute-phase protein responses in patients undergoing cardiac surgery

BACKGROUND

Cardiac surgery with cardiopulmonary bypass (CPB) evokes a systemic inflammatory response involving the proinflammatory cytokines tumor necrosis factor-alpha (TNFalpha), interleukin (IL)-1, IL-6, IL-8 and anti-inflammatory cytokines such as IL-10. Like IL-10, opioids downregulate the immune responses in vivo and in vitro, including the activity of the cytokine-producing monocytes and granulocytes. The proinflammatory cytokines are potent inducers of the hepatic acute-phase protein synthesis. The aim of the present study was to investigate if choice of anaesthesia, based on high-dose opioids (fentanyl) versus low-dose opioids influenced the release of IL-6, IL-8, and IL-10. Secondly, it was investigated whether serum amyloid P-component (SAP) is an acute-phase protein in man such as C-reactive protein (CRP), with which it is physically and structurally related.

METHODS

Sixteen patients submitted to elective coronary artery bypass grafting (CABG) surgery were randomized to either low-dose opioid anaesthesia consisting of thoracic epidural analgesia combined with inhalational anaesthesia (group I) or high-dose fentanyl anaesthesia (group II). From each patient 18 blood samples were taken perioperatively. Cytokine analyses were performed with ELISA, CRP and SAP mere measured with rocket immunoelectrophoresis (RIE).

RESULTS

Surgery and CPB elicited a marked, transient and almost simultaneous proinflammatory and anti-inflammatory cytokine response with no differences between the groups. The cytokine levels returned to preoperative levels 1-3 d after operation. Anaesthesia and surgery did not affect SAP plasma levels while patients showed a major increase in CRP concentrations preceding the cytokine responses.

CONCLUSION

CABG performed during two different anaesthetic techniques, high-dose fentanyl versus low-dose opioid anaesthesia, elicited a well-defined cytokine response with minor variation in the time course of each cytokine. The cytokine production was not modified by type of anaesthesia. Finally, SAP is not an acute-phase protein in men.

Amyloidosis

Amyloidosis is a heterogenous group of diseases characterized by deposition of a fibrillar, proteinaceous material, amyloid, in various tissues and organs. Increasing knowledge about the different proteins that constitute the amyloid fibrils has made it possible to classify amyloidosis by the fibril protein, which appears more rational than the traditional classification by its clinical expression. A serum protein is the precursor of the amyloid fibril protein in the various systemic forms of amyloidosis. Although the chemical composition of amyloid is presently well known, the pathogenetic processes that convert such proteins into a fibrillar form and lay them down in the tissues are far from clarified. This review describes the amyloid deposits, some putative pathogenetic mechanisms, and the clinical, therapeutic, and prognostic aspects of the most important forms of amyloid disease.

A protease-sensitive site in the proposed Ca(2+)-binding region of human serum amyloid P component and other pentraxins

Serum amyloid P component (SAP) is a decamer of 10 identical 25.5-kDa subunits. Limited proteolysis of SAP with alpha-chymotrypsin cleaves the subunit into two fragments of 18 and 7.5 kDa, although the fragments stay together in the decamer under nondenaturing conditions. Proteolysis does not occur in the presence of Ca2+ (10 mM). Cleavage with alpha-chymotrypsin prevents the Ca(2+)-dependent binding of SAP to zymosan extract, nucleosomes, and DNA. The alpha-chymotrypsin cleavage site identified is in a region of SAP that is highly conserved in members of the human C-reactive protein (CRP) family of proteins (pentraxins) to which SAP belongs and is similar to the Ca(2+)-binding site in calmodulin and related Ca(2+)-binding proteins (Nguyen, N.Y., Suzuki, A., Boykins, R.A., & Liu, T.-Y., 1986, J. Biol. Chem. 261, 10456-10465). Treatment of SAP with other proteases (trypsin, Pronase, and Nagarse protease) yields fragmentation patterns upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) that are similar to those obtained with alpha-chymotrypsin. Two other members of the pentraxin family of proteins, hamster female protein and rabbit CRP, also exhibit similar fragmentation patterns on SDS-PAGE when treated with the various proteases. Recently, it has been shown that the homologous protein, human CRP, is cleaved in the same homologous position as cleavage of SAP by alpha-chymotrypsin, resulting in the loss of Ca(2+)-binding (as shown by equilibrium dialysis) and Ca(2+)-dependent binding reactivities (Kinoshita, C.M., Ying, S.-C., Hugli, T.E., Siegel, J.N., Potempa, L.A., Jiang, H.J., Houghten, R.A., & Gewurz, H., 1989, Biochemistry 28, 9840-9848).(ABSTRACT TRUNCATED AT 250 WORDS)

Studies in vivo and in vitro of serum amyloid P component in normals and in a patient with AA amyloidosis

Pure serum amyloid P component (SAP) was isolated from a normal donor pool, from individuals with the different genotypes of an MspI restriction fragment length polymorphism (RFLP) linked to the SAP gene, and from a patient with AA amyloidosis. The SAP preparations were all identical and all behaved as a single homogeneous species in polyacrylamide gel electrophoresis, isoelectric focussing, reverse-phase chromatography, binding in vitro to phosphoethanolamine-Sepharose (binding constant 2.4 x 10(7) l/mol) and AL amyloid fibrils (1.6 x 10(8) l/mol), and binding to amyloid deposits in vivo in mice with casein-induced amyloidosis. The in vivo metabolism of 125I-SAP from a single donor was normal and identical in three healthy individuals representing the three different MspI RFLP genotypes. There is thus no frequent polymorphism of SAP in normal subjects, and SAP altered with respect to the characteristics studied here is not a necessary condition for pathogenesis of systemic AA amyloidosis.

Binding characteristics of human serum amyloid P component

Serum amyloid P component (SAP), a normal human plasma glycoprotein, was found in a solid phase ELISA to have Ca2+-dependent binding for keyhole limpet haemocyanin (KLH), pectic acid, trinitrophenylated (TNP) macromolecules, and plastic surfaces. The binding to TNP-KLH was used to develop a sensitive ELISA. The binding of SAP to the ligands mentioned was inhibited by EDTA, KLH, pectic acid, TNP-conjugated macromolecules (bovine serum albumin, polyacrylhydrazide), and p-nitrophenylarsonic acid. Underivatized and DNP-conjugated macromolecules did not inhibit the SAP binding; arsenilic acid, picric acid, and dinitrophenyl were weak inhibitors. SAP bound to TNP-agarose was eluated by either EDTA or p-nitrophenylarsonic acid. Thus, a unique region of SAP is responsible for the polyspecific binding. We suggest that the polyspecific binding of SAP takes place through a Ca2+ bridge: half of the metal coordination sphere is occupied by SAP, with the other half available to interact with metal ligand.

Binding specificity of mouse serum amyloid P-component for fibronectin

Binding between purified mouse serum amyloid P-component (SAP) and plasma fibronectin (Fn) occurred when either one of the proteins was immobilized by specific antibody and the second protein was offered in a soluble form. Binding of Fn to immobilized SAP was cooperative and saturable at a molar ratio of SAP/Fn = 7.1. The molar ratio at saturation was 3.7 for SAP/Fn when SAP was allowed to bind to immobilized Fn. The binding required 2 to 3mM amounts of Ca++. The binding of SAP to Fn was selectively inhibited by a monoclonal antibody specific for the mid-molecule region of Fn, by soluble gelatin, and by heparin in the presence of 3mM Ca++. We conclude that the SAP binding site was localized at the mid-molecule region of Fn that includes the adjacent gelatin-binding domain and the heparin-I binding domain.

Evidence for the binding of human serum amyloid P component to Clq and Fab gamma

In order to clarify the mechanism of interaction of serum amyloid P component (SAP) with complement, the interaction of SAP with C1q and with IgG was studied. It is known that SAP binds Sepharose in the presence of calcium. When purified 125I-C1q was incubated with SAP prior to Sepharose affinity chromatography, 125I-C1q was retained. However, in the absence of SAP, the 125I-C1q was not retained. To further examine the interaction of SAP with C1q, isolated SAP was incubated at varying ratios with C1q in the presence of 1.5 mM Ca2+. These mixtures were subsequently examined via crossed immunoelectrophoresis against goat anti-SAP. A change in the electrophoretic behavior of SAP was observed in the presence of C1q. In other studies, it was observed that SAP might interact with the collagen-like stem of C1q. In these latter studies, 125I-SAP was incubated with pepsin digests of C1q in a microtitre solid-phase binding assay. In addition, a microtitre solid-phase binding assay was utilized in order to investigate the possible binding of isolated 125I-SAP with IgG. Interestingly in the presence of Ca2+, human IgG and Fab gamma, but not Fc gamma, were found to bind 125I-SAP.

Isolation of the amyloid P component from the Engelbreth-Holm-Swarm (EHS) tumor of the mouse

The amyloid P component was isolated from the mouse EHS tumor, a producer of basement membrane-like material. Following collagenase treatment of the tissue homogenate and centrifugation, the supernatant was purified by calcium-dependent binding to agarose, and elution with ethylenediaminetetraacetic acid. Identification of the purified material as the amyloid P component was established by immunodiffusion and electron microscopic appearance as 8.5 nm pentagonal units, frequently assembled into columns. SDS-PAGE gel electrophoresis yielded 25,000 D bands, suggesting that the amyloid P is of the mouse type. It is proposed that the mouse amyloid P component extracted from the tumor is located within the basotubules present in the pericellular matrix.

Syrian hamster female protein: analysis of female protein primary structure and gene expression

The concentration in plasma of the female protein (FP) of the golden Syrian hamster is regulated by sex steroids and by mediators of the acute-phase response to tissue injury or inflammation. A complementary DNA (cDNA) clone corresponding to FP was isolated from a hamster liver cDNA library and used to determine the nucleotide sequence and derived amino acid sequence of native FP. The primary sequence of FP is 69 percent identical to human serum amyloid P component and 50 percent identical to human C-reactive protein. Evidence showed that sex-limited and acute-phase control of the FP gene is pretranslational. The FP protein is thus a useful model for investigating dual regulation of expression of a single gene.

C-reactive protein mediates the solubilization of nuclear DNA by complement in vitro

We have studied the interaction of C-reactive protein (CRP)-chromatin complexes with serum. The amount of chromatin solubilized by serum is directly proportional to the amount of CRP present. Serum minus C3 did not appreciably solubilize chromatin within the time allowed in these experiments regardless of the amount of CRP present. This indicates that, in addition to CRP, complement is critical to the solubilization process. Studies using genetically C2-deficient serum and purified C2 indicate that the classical complement pathway is primarily involved in the solubilization, however, there may be minor involvement by the alternative pathway. We used an enzyme-linked immunosorbent assay to determine the amounts of CRP in plasma from eight patients with systemic lupus erythematosus; two of the eight had levels of CRP far lower than previously reported for normal individuals, and an additional sample had antibodies reactive with CRP. Together, these results suggest that one of the functions of CRP is to mediate the removal of exposed nuclear DNA by complement-dependent solubilization of chromatin. A defect in this mechanism could (a) facilitate the production of antibodies against chromatin components exposed due to tissue damage or (b) contribute to immune complexes containing the chromatin components released from damaged tissue because they are not rapidly cleared.

Human amyloid P component: an elastase inhibitor

Amyloid deposits almost invariably contain a pentagonal-shaped protein (a so-called pentraxin), termed amyloid P component (AP), in close apposition to the amyloid fibrils. AP is also detected alongside normal elastin fibres in skin and basement membrane. In the present studies, purified human AP was shown to inhibit the activity of porcine pancreatic elastase. The inhibition of elastolytic activity was not abolished by heating AP to 70 degrees C. Furthermore, two other human serum proteins used as controls did not inhibit elastase activity: albumin, which has a similarly acidic pI, and C-reactive protein, which is a pentraxin, sharing 50% sequence homology with AP. Enzyme kinetic studies showed that elastase treated with AP had a slower elastolytic rate than untreated elastase. The inhibitory effect of AP was reversed by high substrate (fivefold) concentration. These observations suggest that AP may function in vivo to protect elastin and amyloid fibrils from proteolytic cleavage. Indeed, this may in part account for the relative resistance of amyloid deposits to resorption and proteolysis.

Amino acid sequence homology between rat and human C-reactive protein

The rat serum protein that undergoes Ca2+-dependent binding to pneumococcal C-polysaccharide and to phosphocholine residues, and that is evidently a member of the pentraxin family of proteins by virtue of its appearance under the electron microscope, has been variously designated as rat C-reactive protein (CRP) [de Beer, Baltz, Munn, Feinstein, Taylor, Bruton, Clamp & Pepys (1982) Immunology 45, 55-70], 'phosphoryl choline-binding protein' [Nagpurkar & Mookerjea (1981) J. Biol. Chem. 256, 7440-7448] and rat serum amyloid P component (SAP) [Pontet, D'Asnieres, Gache, Escaig & Engler (1981) Biochim. Biophys. Acta 671, 202-210]. The partial amino acid sequence (45 residues) towards the C-terminus of this protein was determined, and it showed 71.7% identity with the known sequence of human CRP but only 54.3% identity with human SAP. Since human CRP and SAP are themselves approximately 50% homologous, the level of identity between the rat protein and human SAP is evidence only of membership of the pentraxin family. In contrast, the much greater resemblance to human CRP confirms that the rat C-polysaccharide-binding/phosphocholine-binding protein is in fact rat CRP.

Binding specificity of serum amyloid P component for the pyruvate acetal of galactose

Serum amyloid P component (SAP) is a normal plasma protein that is of interest because of its presence in amyloid deposits, its presence in normal human glomerular basement membrane, and its stable evolutionary conservation. It has calcium-dependent ligand-binding specificity for amyloid fibrils, fibronectin (Fn), C4-binding protein (C4bp), and agarose. Although the binding to agarose, a linear galactan hydrocolloid derived from some marine algae, is unlikely per se to be related to the physiological function of SAP, it does provide a model system in which to explore the precise ligand requirements of SAP. We report here that the amount of SAP from human, mouse, and plaice (Pleuronectes platessa L.) serum able to bind to agarose from different sources reflect precisely their pyruvate content. Methylation with diazomethane of the carboxyl groups in the pyruvate moiety of agarose completely abolishes SAP binding to agarose. The pyruvate in agarose exists as the 4,6-pyruvate acetal of beta-D-galactopyranose. We have therefore synthesized this galactoside, using a novel procedure, established its structure by analysis of its nuclear magnetic resonance spectra, and shown that it completely inhibits all known calcium-dependent binding reactions of SAP. The R isomer of the cyclic acetal, methyl 4,6-O-(1-carboxyethylidene)-beta-D-galactopyranoside (MO beta DG) was effective at millimolar concentration and was more potent than its noncyclic analogue, while pyruvate, D-galactose, and methyl beta-D-galactopyranoside were without effect. The autologous protein ligands of SAP presumably, therefore express a structural determinant(s) that stereochemically resembles MO beta DG. Availability of this specific, well-characterized, low molecular weight ligand for SAP should facilitate further investigation of the function of SAP and its role in physiological and pathophysiological processes.

Human amyloid P component: a circulating lectin that modulates immunological responses

Amyloid P component (AP/SAP), a glycoprotein, precipitated with purified snail galactans from Helix pomatia and Arianta arbustorum in a dose-dependent manner. Radiolabelled AP binds to human peripheral blood mononuclear cells (PBMC), erythrocytes, and cells derived from human non-T, non-B acute lymphocytic leukaemia. The AP cell binding is specific in that it is dose-dependent and can be blocked both by excess cold AP and by Helix pomatia galactan, although it cannot be blocked by an equal amount of the monosaccharide galactose. In vitro studies of human PBMC immune responses demonstrated that AP inhibits PBMC proliferation responses to mycobacterial purified protein derivative and to phytohaemagglutinin and the humoral, antibody response to pokeweed mitogen. The AP-induced suppression of non-specific antibody production by human PBMC was dependent on the time at which AP was added to the culture. AP was suppressive if added in the first 48 h of the 7-day culture, and the suppression could not be reversed by washing the cells after the exposure to AP. The mechanism of AP-induced immunosuppression is still unclear, but human SAP circulates as a pair of pentameric rings, having ten identical subunits that bind to galactose polymers, and our present data suggest that AP affects the immune response through its properties as a lectin.

Fibronectin and serum amyloid P component stimulate C3b- and C3bi-mediated phagocytosis in cultured human monocytes

Fibronectin (FN) and serum amyloid P component (SAP) markedly enhance phagocytosis mediated by the C3b and C3bi receptors of cultured human monocytes but not of granulocytes. (The C3b and C3bi receptors of granulocytes can be activated by treatment of these phagocytes with PMA.) Activation of monocyte C3 receptors by FN is developmentally regulated: Freshly explanted monocytes respond to FN with a small increase in C3 receptor-mediated phagocytosis while monocytes matured in culture exhibit a much greater response. The mechanism of action of FN on C3 receptors of cultured monocytes is unique in two respects. First, while substrate-bound FN or SAP activate monocyte C3 receptors, soluble FN does not. Second, stimulation of the basal surface of monocyte plasma membranes by substrate-bound FN activates C3b and C3bi receptors on the apical surface of the plasma membrane, i.e., at sites remote from the segments of membrane in contact with the FN or SAP.

Acute phase proteins with special reference to C-reactive protein and related proteins (pentaxins) and serum amyloid A protein

The acute phase response among plasma proteins is a normal response to tissue injury and is therefore a fundamental aspect of many diverse disease processes. It probably usually has a beneficial net function in limiting damage and promoting repair but in some circumstances it may have pathological consequences. Sustained high levels of acute phase proteins and especially SAA are associated with the development of amyloidosis in some individuals. Increased concentrations of CRP may, by activating the complement system, contribute to inflammation and enhance tissue damage. Failure of the normal or appropriate CRP response may also possibly have deleterious effects. SAA is a polymorphic protein which is normally present only in trace amounts but which, during the acute phase response, becomes one of the major apolipoproteins associated with high-density lipoprotein particles. The function of apoSAA is not known but it must have considerable physiological significance apart from its role as the putative precursor of amyloid A protein fibrils. CRP and SAP have been very stably conserved throughout vertebrate evolution and homologous proteins are apparently present even in vertebrates. This strongly suggests that they have important functions although these have not yet been precisely delineated. The main role of CRP may be to provide for enhanced clearance of inappropriate materials from the plasma whether these are of extrinsic origin, such as microorganisms and their products, or the autologous products of cell damage and death. The interaction between aggregated CRP and plasma low-density lipoprotein may play a significant part in the normal function of CRP and may also have a role in lipoprotein metabolism, clearance, and deposition. SAP is a normal tissue protein as well as being a plasma protein. Aggregated SAP selectively binds fibronectin and this may represent an aspect of the normal function of SAP. The deposition of SAP in amyloid is evidently not a normal function but it is not known whether this deposition is involved in the pathogenesis of amyloid or whether it is merely an epiphenomenon. In any case immunohistochemical staining for SAP is useful in the diagnosis of amyloid, in investigation of glomerulonephritis, and in studying disorders of elastic tissue. Regardless of its physiological or pathophysiological functions, the assay of serum CRP is a valuable aid to clinical management in a number of different situations and in different diseases provided results are interpreted in the light of full clinical information.(ABSTRACT TRUNCATED AT 400 WORDS)

Low density lipoprotein and very low density lipoprotein are selectively bound by aggregated C-reactive protein

C-reactive protein (CRP), the classical acute-phase protein, can bind phospholipids by virtue of its specific, calcium-dependent reactivity with phosphorylcholine residues. However, analysis of acute-phase serum by gel filtration and by density gradient ultracentrifugation showed that the CRP was in a free, uncomplexed form, despite the coexistent presence of the various classes of serum lipoproteins, all of which contain phospholipids. In contrast, when isolated CRP was aggregated by immobilization at a sufficient density on a solid phase and then exposed to normal human serum, it selectively bound low density lipoprotein (LDL) and traces of very low density lipoprotein. The reaction was calcium dependent and reversible by free phosphorylcholine but not by heparin. LDL isolated from normal plasma was also bound by aggregated CRP. CRP reacts in vitro with a wide variety of different ligands both of extrinsic and of autogenous origin, e.g., microbial products and damaged cell membranes, respectively. If CRP aggregated in vivo by complexing with these ligands than acquires the capacity to selectively bind LDL, the phenomenon may have significant implications for the function of CRP and for the metabolism, clearance, and deposition of LDL.

C-reactive protein in human lattice corneal dystrophy

Lattice corneal dystrophy (LCD), an autosomal dominantly inherited disease, is characterized by a branching network of subepithelial and stromal amyloid deposits (1). Due to their small size and close association with stromal components and epithelial cells, their chemical composition is as yet undetermined. Amyloid deposits in other types of diseases have been found to contain amyloid P protein (AP). Serum amyloid P component (SAP) and C-reactive protein (CRP) resemble each other in molecular structure and amino acid sequence, but appear to be antigenically distinct (2-6). A humoral mediator most likely stimulates CRP release by hepatocytes and could be related to Interleukin-I synthesis from macrophages (4-6). Rabbit corneal epithelial cells also produced an Interleukin-I-like activity and contain a thymocyte activating cytokine (7). In this study, corneas from normal controls, primary LCD and recurrent LCD were fixed in formalin with lmM CaCl2 and tested with antibodies to CRP, AP and AA (non-immunoamyloid), using the immunoperoxidase technique. The stroma of LCD and normal corneas did not stain with antibodies to AP, AA or CRP. However, we now report that antibodies to CRP show immunospecific binding to the corneal epithelium in primary and recurrent LCD.

The human C-reactive protein gene (CRP) and serum amyloid P component gene (APCS) are located on the proximal long arm of chromosome 1

The genes encoding two pentraxins, C-reactive protein (CRP) and serum amyloid P component (SAP), are located on the proximal long arm of human chromosome 1. Mapping of the CRP and SAP genes between the centromere and band q32 was achieved by Southern blot analysis of DNA from a panel of human X Chinese hamster somatic cell hybrids carrying defined fragments of human chromosome 1. Both genes were localized more precisely between bands q12 and q23 by in situ hybridization to human metaphase chromosomes.