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

AA amyloidosis in vertebrates: epidemiology, pathology and molecular aspects

AA amyloidosis is a prototypic example of systemic amyloidosis: it results from the prolonged overproduction of SAA protein produced in response to chronic inflammation. AA amyloidosis primarily affects the kidneys, liver, spleen, gastrointestinal tract, leading to a variety of symptoms. First, this review examines AA amyloidosis in humans, focusing on pathogenesis, clinical presentation, and diagnosis and then in animals. In fact AA amyloidosis is the only systemic amyloidosis that has been largely documented in a remarkable number of vertebrate species: mammals, birds, and fishes, especially in individuals with comorbidities, chronic stress, or held in captivity. Secondly, here, we summarise independent sets of evidence obtained on different animal species, exploring the possible transmissibility of AA amyloidosis especially in crowded or confined populations. Finally, biochemical and structural data on native SAA and on AA amyloid fibrils from human, murine, and cat ex vivo samples are discussed. The available structural data depict a complex scenario, where SAA can misfold forming highly different amyloid assemblies. This review highlights the complexity of AA amyloidosis, emphasising the need for further research into its spread in the animal kingdom, its structural aspects, and pathogenetic mechanisms to evaluate its impact on human and animal health.

Renal amyloidosis: Pathogenesis

For many years amyloidosis was considered an extremely rare, somewhat mysterious disease. However, in the last 2-3 decades its pathogenesis, particularly that of renal amyloidosis has been carefully dissected in the research laboratory using in-vitro and, to a lesser extent, in-vivo models. These have provided a molecular understanding of sequential events that take place in the renal mesangium leading to the formation of amyloid fibrils and eventual extrusion into the mesangial matrix, which itself becomes seriously damaged and, in due time, replaced by the fibrillary material. Amyloid, once considered to be an "inert" substance, has been proven to be involved in crucial biological processes that result in the destruction and eventual replacement of normal renal constituents. This review centers on mechanisms involved in the renal glomerular amyloidosis to understand its pathogenesis.

Methods to study the structure of misfolded protein states in systemic amyloidosis

Systemic amyloidosis is defined as a protein misfolding disease in which the amyloid is not necessarily deposited within the same organ that produces the fibril precursor protein. There are different types of systemic amyloidosis, depending on the protein constructing the fibrils. This review will focus on recent advances made in the understanding of the structural basis of three major forms of systemic amyloidosis: systemic AA, AL and ATTR amyloidosis. The three diseases arise from the misfolding of serum amyloid A protein, immunoglobulin light chains or transthyretin. The presented advances in understanding were enabled by recent progress in the methodology available to study amyloid structures and protein misfolding, in particular concerning cryo-electron microscopy (cryo-EM) and nuclear magnetic resonance (NMR) spectroscopy. An important observation made with these techniques is that the structures of previously described in vitro formed amyloid fibrils did not correlate with the structures of amyloid fibrils extracted from diseased tissue, and that in vitro fibrils were typically more protease sensitive. It is thus possible that ex vivo fibrils were selected in vivo by their proteolytic stability.

Cryo-EM fibril structures from systemic AA amyloidosis reveal the species complementarity of pathological amyloids

Systemic AA amyloidosis is a worldwide occurring protein misfolding disease of humans and animals. It arises from the formation of amyloid fibrils from the acute phase protein serum amyloid A. Here, we report the purification and electron cryo-microscopy analysis of amyloid fibrils from a mouse and a human patient with systemic AA amyloidosis. The obtained resolutions are 3.0 Å and 2.7 Å for the murine and human fibril, respectively. The two fibrils differ in fundamental properties, such as presence of right-hand or left-hand twisted cross-β sheets and overall fold of the fibril proteins. Yet, both proteins adopt highly similar β-arch conformations within the N-terminal ~21 residues. Our data demonstrate the importance of the fibril protein N-terminus for the stability of the analyzed amyloid fibril morphologies and suggest strategies of combating this disease by interfering with specific fibril polymorphs.

Systemic AA amyloidosis is caused by misfolding of the acute phase protein serum amyloid A1. Here the authors present the cryo-EM structures of murine and human AA amyloid fibrils that were isolated from tissue samples and describe how the fibrils differ in their fundamental structural properties.

Generation and characterization of anti-AA amyloid-specific monoclonal antibodies

AA amyloidosis results from the pathologic deposition in the kidneys and other organs of fibrils composed of N-terminal fragments of serum amyloid A protein (SAA). Given that there are only limited means to visualize these deposits, we have developed a series of mAbs, 2A4, 7D8, and 8G9, that bind specifically with nanomolar affinity to a carboxy-terminal epitope generated following proteolysis of SAA that yields the predominant component of AA amyloid deposits. Notably, these antibodies do not recognize native SAA, they retain their immunoreactivity when radiolabeled with I-125 and, after injection into AA amyloidotic mice, localize, as evidenced by autoradiography and micro-single photon emission computed tomography imaging, to histologically confirmed areas of amyloid deposition; namely, spleen, liver, and pancreas. The results of our in vitro and in vivo studies demonstrate the AA fibril-selectivity of mAbs 2A4, 7D8, and 8G9 and warrant further investigation into their role as novel diagnostic agents for patients with AA amyloidosis.

Disorder-to-order conformational transitions in protein structure and its relationship to disease

Function in proteins largely depends on the acquisition of specific structures through folding at physiological time scales. Under both equilibrium and non-equilibrium states, proteins develop partially structured molecules that being intermediates in the process, usually resemble the structure of the fully folded protein. These intermediates, known as molten globules, present the faculty of adopting a large variety of conformations mainly supported by changes in their side chains. Taking into account that the mechanism to obtain a fully packed structure is considered more difficult energetically than forming partially "disordered" folding intermediates, evolution might have conferred upon an important number of proteins the capability to first partially fold and-depending on the presence of specific partner ligands-switch on disorder-to-order transitions to adopt a highly ordered well-folded state and reach the lowest energy conformation possible. Disorder in this context can represent segments of proteins or complete proteins that might exist in the native state. Moreover, because this type of disorder-to-order transition in proteins has been found to be reversible, it has been frequently associated with important signaling events in the cell. Due to the central role of this phenomenon in cell biology, protein misfolding and aberrant disorder-to-order transitions have been at present associated with an important number of diseases.

Experimental induction of amyloidosis by bovine amyloid fibrils in Sore Hock rabbits

We report the experimental amyloidosis associated with administration of bovine amyloid fibrils in rabbits afflicted by Sore Hock (SH), which is ulcerative pododermatitis. Two groups of SH-afflicted rabbits were subjected to five inflammatory stimulations at intervals of 4 days by intraepithelial injection of a mixture consisting of Freund's complete adjuvant and lipopolysaccharide. One group of rabbits was administered amyloid in conjunction with the last inflammatory stimulation and the other group was not. For additional control, two groups were designed. A third group consisted of rabbits without SH, which were subjected to five stimulations and were administered amyloid. A fourth group consisted of SH-afflicted rabbits, subjected to 0-4 stimulations and administered amyloid. Amyloid depositions were observed in SH-afflicted rabbits, which had been stimulated five times and given amyloid (18/18). In the 4th group, only one rabbit, which had been subjected to four stimulations, showed amyloid depositions. No amyloid depositions were observed in the other rabbits. These results suggest that bovine AA amyloid fibrils have an amyloid-enhancing factor-like effect on SH-afflicted rabbits.

Acceleration of murine AA amyloid deposition by bovine amyloid fibrils and tissue homogenates

Acceleration of amyloid deposition by administration of amyloid fibrils and transmissibility of disease have been reported for several types of amyloidosis. Reactive amyloidosis (AA) occurs in a wide variety of domestic animal species and is characterized by amyloid deposition mainly in spleen, liver, and kidneys. Because the visceral organs of domestic animals have traditionally been used in Asian cuisines, it is important to examine whether dietary ingestion of the organs themselves (rather than purified amyloid fibrils) accelerates AA amyloid deposition. Herein, we show that murine AA amyloidosis develops rapidly after intraperitoneal or oral administration of purified amyloid fibrils or homogenates of amyloid-laden bovine liver. The amyloidosis development in mice was dependent on the concentration of amyloid fibrils or amyloidotic liver homogenates. We found that experimental murine AA amyloidosis was accelerated by dietary ingestion of both purified amyloid fibrils and tissue homogenates that contain amyloid fibrils. We also investigated livers of beef cattle and food chickens to examine whether they contain amyloid-enhancing factor activity. By microscopic examination of hematoxylin and eosin- and Congo red-stained sections, no amyloid deposition was detected in these livers, and no effective activity for experimental induction of AA amyloidosis in mice was detected in homogenates of these livers.

Mutagenic exploration of the cross-seeding and fibrillation propensity of Alzheimer's beta-amyloid peptide variants

Amyloid formation is a nucleation-dependent process that is accelerated dramatically in vivo and in vitro upon addition of appropriate fibril seeds. A potent species barrier can be effective in this reaction if donor and recipient come from different biological species. This species barrier is thought to reflect differences in the amino acid sequence between seed and target polypeptide. Here we present an in vitro mutagenic cross-seeding analysis of Alzheimer's Abeta(1-40) peptide in which we mapped out the effect of systematically varied amino acid replacements on the propensity of seed-dependent amyloid fibril formation. We find that the susceptibility of different peptides toward cross-seeding relates to the intrinsic aggregation propensity of the respective polypeptide chain and, therefore, to properties such as beta-sheet propensity and hydrophobicity. These data imply that the seed-dependent formation of amyloid-like fibrils is affected by the intrinsic properties of the polypeptide chain in a manner that is similar to what has been described previously for aggregation reactions in general. Hence, the nucleus acts in this case as a catalyst that promotes the fibrillation of different polypeptide chains according to their intrinsic structural predilection.

Animal model for the pathogenesis of reactive amyloidosis

The pathogenesis of amyloidosis is not well understood. Here, Zafer Ali-Khan, Weihua Li and Sic L. Chan present a metazoan parasite mouse model of reactive amyloidosis, review the relationship between chronic inflammation and multiorgan AA amyloidosis and postulate how ubiquitin might function in the processing of serum amyloid A and in AA amyloid formation in the endosomes-lysosomes of activated murine reticuloendothetial cells.

[AA Amyloidosis: recent knowledges on pathophysiology]

PURPOSE

Amyloidosis is a rare disease associated with an underestimated frequency because of the need of a pathological diagnosis identifying extracellular deposits with affinity for Congo red. There are moreover 20 proteins that can form extracellular fibril deposits. Some amyloidosis forms are more common than others, especially AA amyloidosis and AL amyloidosis. Among genetic amyloidosis, the transthyretin related amyloidosis is the most prevalent. The amyloid frequency could also be increased if amyloidosis related to Alzheimer's disease or prion's disease is included. In the absence of specific treatment for amyloidosis, researches are focused on amyloidosis pathophysiology especially, on AA amyloid pathophysiology.

CURRENT KNOWLEDGE AND KEY POINTS

Amyloid is not only composed of fibrils but also of proteoglycanes, P component and amyloid-enhancing factor. A new research aim is focused on the cells involved in amyloid formation and on the relationship between amyloid, proteoglycanes and P component.

FUTURE PROSPECTS AND PROJECTS

It was demonstrated that, in the absence of macrophages, an extracellular amyloid formation was possible with amyloid-enhancing factor as starting point. Some inhibitors of intra or extracellular amyloid formation are still to be discovered. Anti-P component has been recently developed; it was successful in the treatment of murin AA amyloidosis and gave some hope concerning the treatment of human amyloidosis.

Pathogenesis of beta2-microglobulin amyloidosis

Hemodialysis-related amyloidosis is a relatively new form of systemic amyloidosis, with beta2-microglobulin (B2M) being identified as the major constituent protein. Most of the clinical findings are related to amyloid deposition in osseo-articular tissues. B2M amyloid deposits first appear in the cervical intervertebral discs, which are well known to be susceptible to mechanical stress. A close relationship between changes of microenvironment caused by such stress and amyloid deposition is highly suggested. In advanced cases, an inflammatory reaction composed of macrophages, multinucleated giant cells, and granulation tissue, is observed around the amyloid deposits. Purified amyloid protein is native B2M, and mutations and proteolysis are not believed to be important for its deposition. Plasma levels of B2M are elevated as much as 5-10 times because of the inability of hemodialysis equipment removal of B2M from blood plasma, the duration being very important for B2M amyloid fibrillogenesis. Heparan sulfate proteoglycans, perlecan, is increased at the same sites of amyloid deposits from the early stages. In B2M amyloidosis, an increase of heparan sulfate proteoglycans is observed in the vascular wall and synovium, but in the discs, ligaments and cartilage, there is an increase of chondroitin sulfate proteoglycans predominantly. B2M has an affinity for heparan sulfate proteoglycans, although it is weaker than that for laminin and type IV collagen. This is related to the interactions between negative charges of sulfate groups of proteoglycans and positive charges of basic amino acids in N-terminal side of B2M. Increased cytokines production in the synovium, induced by advanced glycation end products as well as elevated plasma levels, is also linked to inflammatory reactions. Increased expression of matrix metalloproteinases (MMP), especially MMP-1 and -9, is related to the destructive changes of the bone and cartilage. The decrease of plasma levels by high flux membrane and control of inflammatory reactions are very important for prevention of B2M amyloidosis.

Amyloid precursors and amyloidosis in rheumatoid arthritis

Amyloidosis refers to the extracellular accumulation of amyloid fibrils, derived from a circulating precursor, in various tissue and organs. The most common form of amyloidosis worldwide is that which occurs secondary to chronic inflammatory disease, particularly rheumatoid arthritis. The precursor molecule is serum amyloid A (SAA), an acute phase reactant, which can be used as a surrogate marker of inflammation in many diseases. SAA has a number of immunomodulatory roles, can induce chemotaxis and adhesion molecule expression, has cytokine-like properties and can promote the upregulation of metalloproteinases. It enhances the binding of high density lipoprotein to macrophages and thus helps in the delivery of lipids to sites of injury for use in tissue repair. It is thus thought to be an integral part of the disease process. Moreover, elevated levels of SAA over time predispose to secondary amyloidosis. Pathogenic factors underlying this disease are outlined along with guidelines for diagnosis and management.

New clothes for amyloid enhancing factor (AEF): silk as AEF

Amyloid enhancing factor (AEF) is an activity that appears naturally during the course of persistent inflammation and precedes, by 24-48 h, AA amyloid deposition in appropriate murine models. AEF is defined by its biological properties, namely, when administered intravenously or intraperitoneally to a mouse, it primes the recipient for the rapid induction of AA amyloid when they are given an inflammatory stimulus. Available evidence indicates that AEF is protein in nature, but a specific molecular species (if a singular species exits) has not been identified. Past work (Ganowiak et al., Biochem. Biophys. Res. Commun. 199:306-312, 1994) has shown that AEF activity may be imparted to two different proteins (IAPP and beta-protein) provided each is organized in the form of an amyloid fibril. Since a characteristic property of proteins in amyloid fibrils is their beta-sheet organization, one possibility is that AEF activity, in part, depends on such organization, and other proteins with such properties may also have AEF activity. To investigate this possibility, silk, a protein which contains substantial beta-sheet content, was denatured in LiSCN and allowed to renature slowly under reducing conditions to form a gel. The denatured silk preparation was then sonicated thoroughly to permit intravenous injection and assessed for AEF activity. The modified silk, presented as small fibrils in a beta-sheet conformation as assessed by electron microscopy and circular dichroism, respectively. This silk at 0-50 micrograms/animal was administered intravenously as "AEF" followed immediately by subcutaneous AgNO3 as the inflammatory stimulus. Six days later the spleens were examined for the presence of AA amyloid and following Congo red staining, the amount of amyloid quantified by image analysis. Modified silk without an inflammatory stimulus, and non-sonicated modified silk, failed to induce AA amyloid. Sonicated modified silk followed by AgNO3 induced large quantities of splenic AA amyloid in a dose dependent fashion. Modified silk in quantities as small as 1-5 micrograms/animal can function as AEF. The AEF properties of the modified silk were stable at 4 degrees C for at least 4 weeks (the longest period tested). This procedure may provide a means of standardizing AEF preparations.

Amyloid enhancing factor and dietary transmission in accelerated amyloid A amyloidosis

The etiology and pathogenesis of amyloid A (AA) amyloidosis that may occur as an occasional complication of chronic inflammatory and infectious diseases are poorly understood. The preamyloid phase of experimentally induced AA amyloidosis can be greatly shortened in recipient animals by intravenous or intraperitoneal transfer of amyloid enhancing factor (AEF) when there is a concomitant inflammatory episode. AEF is an operational term applied to poorly characterized tissue extracts and increased AEF activity that precedes amyloid deposition. We now report that AA is rapidly formed in mice following oral administration of an AEF preparation that does not contain AA peptides. This finding indicates that a transmissible agent present in diet may be a contributory factor in amyloid fibril formation.

A beta amyloidogenesis: unique, or variation on a systemic theme?

For more than a century amyloid was considered to be an interesting, unique, but inconsequential pathologic entity that rarely caused significant clinical problems. We now recognize that amyloid is not one entity. In vivo it is a uniform organization of a disease, or process, specific protein co-deposited with a set of common structural components. Amyloid has been implicated in the pathogenesis of diseases affecting millions of patients. These range from Alzheimer's disease, adult-onset diabetes, consequences of prolonged renal dialysis, to the historically recognized systemic forms associated with inflammation and plasma cell disturbances. Strong evidence is emerging that even when deposited in local organ sites significant physiologic effects may ensue. With emphasis on A beta amyloid, we review the present definition, classification, and general in vivo pathogenetic events believed to be involved in the deposition of amyloids. This encompasses the need for an adequate amyloid precursor protein pool, whether precursor proteolysis is required prior to deposition, amyloidogenic amino acid sequences, fibrillogenic nucleating particles, and an in vivo microenvironment conducive to fibrillogenesis. The latter includes several components that seem to be part of all amyloids. The role these common components may play in amyloid accumulation, why amyloids tend to be associated with basement membranes, and how one may use these findings for anti-amyloid therapeutic strategies is also examined.

Interaction of the anthracycline 4'-iodo-4'-deoxydoxorubicin with amyloid fibrils: inhibition of amyloidogenesis

All types of amyloidosis are structurally characterized by the cross beta-pleated sheet conformation of the fibrils, irrespective of their biochemical composition. The clinical observation that the anthracycline 4'-iodo-4'-deoxy-doxorubicin (IDOX) can induce amyloid resorption in patients with immunoglobulin light chain amyloidosis was the starting point for this investigation of its possible mechanism of action. IDOX binds strongly to all five types of natural amyloid fibrils tested: immunoglobulin light chains, amyloid A, transthyretin (methionine-30 variant), beta-protein (Alzheimer), and beta 2-microglobulin. Quantitative binding studies showed that IDOX, but not doxorubicin, binds strongly to amyloid fibrils. This binding is saturable and involves two apparently distinct binding sites with Kd values of 5.9 x 10(-11) M and 3.4 x 10(-9) M. IDOX inhibited in vitro insulin amyloid fibrillogenesis. In vivo studies using the experimental amyloid murine model confirmed the specific targeting of IDOX to amyloid deposits. Preincubation of amyloid enhancing factor with IDOX significantly reduced the formation of amyloid deposits. It is hypothesized that IDOX exerts its beneficial effects through the inhibition of fibril growth, thus increasing the solubility of existing amyloid deposits and facilitating their clearance. IDOX may represent the progenitor of a class of amyloid-binding agents that could have both diagnostic and therapeutic potential in all types of amyloidoses.

Animal models for reactive amyloidosis

For over 70 years animal experiments have been performed to elucidate the pathogenesis of reactive amyloidosis and to investigate the formation of the beta-pleated sheet-rich amyloid fibrils in general. In appropriate species, primarily rodents like mouse and hamster, amyloid is formed after stimulation with amyloid-inducing injections after a lag phase (secondary or reactive amyloid, AA amyloid). For the formation of this AA amyloid, elevated values in blood of its precursor protein, SAA, is the first prerequisite. SAA is an acute phase protein of hepatic origin, released after stimulation by cytokines, and is associated in serum with high-density lipoprotein (apoSAA). In mouse, hamster and mink amyloidogenic subtypes of SAA are found. In the rat SAA is absent, although its mRNA is transcribed. Evidence is increasing that SAA crystallizes to fibrils first, whilst loss of its C-terminal end can be a post-fibrillogenic phenomenon. Glycoproteins, proteoglycans, glycosaminoglycans and lipids are reintroduced in experimental amyloid research. Basement membrane heparan sulphate proteoglycans (perlecans) are attributed to have a primary role. The pentraxin serum amyloid P-component is a calcium-dependent secondary phenomenon. Membrane-bound, lipid-rich vesicles are found amongst the newly deposited pericellular amyloid fibrils. These vesicles probably have to be interpreted as indicators of primary membrane alteration during amyloid fibril crystallization. The vesicles will be formed after rupture of the membranes caused by the stiff intramembranously crystallized protein fibrils. Morphological evidence supporting this hypothesis has been found in immunoelectron microscopical studies. Accumulation of intramembranous SAA preceded amyloid fibril deposition. Fibril formation then might be related to conformational change of the intramembranous SAA. The lag phase for amyloid deposition is shortened after a single injection of a fraction of amyloid, the AEF. It is a low-molecular-weight glycoprotein that easily associates with other molecules. When isolated from amyloid fibrils, the (F)AEF contains a large proportion of beta-pleated sheet molecular structure. It is probable that this structure holds an explanation for its enhancing potency: forming a nidus for physical crystallization. The major substances and animal species used in animal experiments on amyloidosis, are mentioned. Overlooked by-effects of amyloidogenic stimuli are discussed. Polyarthritis after systemic endotoxin injections found in the hamster acts as a source of cytokines, further triggering the reactive amyloidosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Amyloidosis

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

Increase in plasma concentration of ubiquitin in dialysis patients: possible involvement in beta 2-microglobulin amyloidosis

beta 2-Microglobulin(beta 2-M) amyloidosis is a serious complication of dialysis therapy; however, its pathogenesis is still unclear. Recent studies have indicated that ubiquitin has amyloid enhancing factor activity, raising the possibility that ubiquitin plays a role in beta 2-M amyloidogenesis. In this study, synovial tissue from patients with long-term dialysis was examined immunohistochemically. The synovial tissue was labeled with anti-ubiquitin antibody, indicating co-deposition of ubiquitin with beta 2-M amyloid. To elucidate the involvement of plasma ubiquitin, we established a specific radioimmunoassay for ubiquitin. Using this method, we observed that the plasma concentration of ubiquitin-like immunoreactivity in dialysis patients was significantly higher than that in normal subjects. In chronic renal failure patients, the plasma concentration of ubiquitin-like immunoreactivity was also significantly higher than that in normal controls, which finding suggests that a reduction in renal clearance is, at least in part, responsible for the increased plasma concentration of ubiquitin. In dialysis patients, plasma concentrations of ubiquitin-like immunoreactivity in patients with carpal tunnel syndrome, one of the major symptoms of beta 2-M amyloidosis, were significantly higher than those in patients not exhibiting this syndrome. These results suggest a possible involvement of plasma ubiquitin in beta 2-M amyloidosis.

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.

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.

Ubiquitin profile and amyloid enhancing factor activity in Alzheimer and 'normal' human brain extracts

Tris-HCl or Laemmli sample buffer extracted frontal lobe and hippocampal samples from normal aged and Alzheimer's disease (AD) subjects were used to determine total ubiquitin (Ub), distribution of monomeric Ub and Ub-protein conjugates and amyloid enhancing factor (AEF) activity using the dot-blot, Western blot and mouse AEF bioassay techniques, respectively. The AD samples, as compared to the normals, demonstrated a 1.7-fold increase in total Ub, elevated levels of Ub-protein conjugates and an appreciably enhanced AEF activity. Many of the hippocampal Ub-protein conjugates were found to be soluble only in the Laemmli sample buffer. The possible roles of elevated Ub levels and of the association of AEF activity with Ub are discussed in regard to pathogenesis of brain amyloidosis.

Amyloid enhancing factor activity is associated with ubiquitin

Crude amyloid enhancing factor (AEF) drastically reduces the pre-amyloid phase on passive transfer and induces amyloid deposition in the recipient mice in 48-120 h. We attempted to purify AEF from murine amyloidotic liver and spleen extracts by using gel filtration, preparative sodium dodecyl sulphate-polyacrylamide gel electrophoresis and ion exchange chromatography and isolated a 5.5 kDa peptide. In the mouse bioassay, this peptide induced accelerated splenic AA deposition in a dose-dependent manner. Based on structural, electrophoretic and immunochemical criteria the peptide was identified as ubiquitin. A polyclonal rabbit anti-bovine ubiquitin IgG antibody (RABU) abolished the in vivo AEF activity of crude murine AEF in a dose-dependent manner. Monomeric ubiquitin and its large molecular weight adducts were isolated from crude AEF using cyanogen bromide-activated sepharose conjugated to RABU and size exclusion chromatography methods. These were assayed and were found to possess AEF activity. Furthermore, increased levels of ubiquitin, a phenomenon similar to that of AEF, were detected by immunocytochemistry in mouse peritoneal leucocytes prior to and during amyloid deposition. Since AEF shares a number of biological and functional properties with ubiquitin, we suggest a possible role of ubiquitin as an AEF, and that serum amyloid protein A and ubiquitin, the two reactants generated during inflammatory stress conditions, may converge to induce AA amyloid deposition.

A critical analysis of postulated pathogenetic mechanisms in amyloidogenesis

This review has examined several of the major thrusts in amyloid research, past and present. The data concerning amyloid precursor quantity, primary protein and gene structure, and precursor proteolysis have shown that there are contradictions that must be resolved before these elements can be reamalgamated into a unified view of amyloidogenesis. One possibility is presented in Figure 2. A general hypothesis of amyloid formation that accounts for the uniformity of fibril structure, amyloid staining properties, and the specific selection of precursors and their specific anatomic localization in each form of amyloid has yet to be proposed. Some of these questions may be answered by an analysis of common structural constituents in amyloid deposits. Analyzing amyloid generation in the context of these common elements separates amyloid research into several specific areas (Figure 2). The first area concerns factors that govern the expression of amyloid precursor protein genes, thus providing adequate quantities of the precursor, if such a precursor pool does not already exist. Without such a pool, amyloid deposition clearly cannot occur. The second area concerns information as to where these precursors usually bind and/or exert their normal function. Once determined, this information will likely indicate the site or sites where the particular precursor may give rise to amyloid deposits. The last area concerns factors at these local sites that govern the interaction of the precursor with basement membrane or related extracellular matrix elements that would define both the site and the final common pathway for amyloid deposition.

Brain ubiquitin is markedly elevated in Alzheimer disease

Levels of ubiquitin, microtubule associated protein tau and tubulin were determined by immunoassays in homogenates of cerebrum and cerebellum of Alzheimer disease and aged control cases. Ubiquitin levels increased many fold in the cerebral cortex of Alzheimer disease cases and the increase correlated strongly with the degree of neurofibrillary changes in the tissue. The increase in ubiquitin was much less remarkable in the cerebral white matter. Cerebellum which is unaffected with neurofibrillary changes in Alzheimer disease had normal levels of ubiquitin both in gray matter and in white matter. There was an appreciable increase in abnormally phosphorylated tau in an Alzheimer disease brain with severe neurofibrillary degeneration, whereas the normal tau levels were increased only slightly. Tubulin was slightly decreased in the cerebral gray matter but not in the adjacent white matter. Marked increase in brain ubiquitin in Alzheimer disease suggests the role of ubiquitin in the pathobiology of Alzheimer disease.

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.

Fibril amyloid enhancing factor (FAEF)-accelerated amyloidosis in the hamster is not dependent on serine esterase activity and mononuclear phagocytosis

Cells of the mononuclear phagocytic system (MPS) were described as playing a decisive role in amyloidogenesis. A relationship between the amyloid enhancing factor (AEF) and MPS cells was suggested and recently AEF activity was attributed to a serine esterase (SE) of leucocytic origin. In the present study, no correlation was found between the SE content and AEF activity in either peritoneal cell lysates or AEF preparations of different origin. Furthermore, pretreatment of fibril AEF (FAEF) with the SE inhibitor phenylmethylsulphonyl fluoride (PMSF) did not affect its activity in the hamster. Blockade of the MPS by dextran sulphate did not inhibit deposition of amyloid after intravenous injection of FAEF but amyloid deposition was inhibited when FAEF was administered intraperitoneally. These results suggest that MPS cells could be involved in transport of AEF, but that phagocytic activity of MPS cells is not essential in AA-amyloid fibrillogenesis. It is concluded that these results are not consistent with the previously suggested nature of the AEF or with the proposed central role of the MPS in amyloidogenesis.

Binding of ubiquitin to experimentally induced murine AA amyloid

Amyloid enhancing factor (AEF) activity has recently been demonstrated in ubiquitin purified from amyloidotic murine tissues and Alzheimer brain extract. Since AEF is known to bind to amyloid fibrils and 'fibril-AEF' on passive transfer induces accelerated amyloidogenesis in the recipient animals, it was of interest to investigate whether ubiquitin binds to amyloid. Immunohistological studies were carried out on liver sections from amyloidotic mice. Biotin-strepavidin-peroxidase methods using monospecific rabbit anti-mouse AA amyloid IgG (RAAG) and rabbit anti-bovine ubiquitin IgG (RABU) antibodies were employed to immunostain the amyloid and ubiquitin deposits, respectively. RABU-treated liver sections were counterstained with thioflavine S. RAAG reacted strongly with the amyloid, indicating that it is AA type, and RABU-positive immunodeposits were found bound to the thioflavine-S-positive AA deposits. Treatment of the liver sections with 0.1 M sodium acetate containing 0.5 M NaCl, pH 4, for 2-3 h at 37 degrees C nearly completely desorbed the AA amyloid-bound ubiquitin. Since ubiquitin demonstrates AEF activity in vivo and binds non-covalently to AA amyloid, we suggest that ubiquitin may indeed be 'fibril-AEF' and may play a crucial role in the pathogenesis of amyloidosis. To our knowledge, this is the first time that ubiquitin bound to extracellularly deposited amyloid has been demonstrated.

Alzheimer's disease brain-derived ubiquitin has amyloid-enhancing factor activity: behavior of ubiquitin during accelerated amyloidogenesis

Amyloid-enhancing factor (AEF) is believed to be a crucial common pathogenetic link in diverse forms of human amyloidosis. Passive transfer of crude AEF is known to trigger accelerated splenic amyloid deposition in mice. We have recently identified AEF activity in ubiquitin isolated from murine amyloidotic tissues. Using similar techniques we have purified ubiquitin, from crude Alzheimer's disease (AD) brain extracts, to apparent homogeneity. Based on the partial amino acid sequence homology, immunochemical and pathophysiological criteria, the approximately 5.5-kDa AD-derived protein was identified as ubiquitin (AD-ubiquitin) with AEF activity. Ten to twenty micrograms of this protein per mouse, with or without CaCl2, in conjunction with four subcutaneous injections of 0.5 ml of 1% aqueous AgNO3, induced accelerated splenic amyloid deposition. By immunohistochemistry, using anti-mouse AA amyloid antibody, the AD-ubiquitin-induced amyloid was identified as AA type. With anti-bovine ubiquitin antibody, using similar spleen sections as above, ubiquitin was found to co-deposit with AA amyloid in the splenic perifollicular areas. These results strongly suggest that ubiquitin may be involved in the pathogenesis of amyloidosis.

Crush and smear technique for rapid detection and semiquantitation of amyloid deposition

A method using Congo red to rapidly identify and semiquantitate amyloid deposits in tissues for experimental research and clinical medicine is described. Examination by polarization microscopy revealed amyloid deposits as bright green birefringent clumps on a dark red background. On semiquantitative evaluation, good correlation was found between this technique and the conventional histological one, the present technique being more sensitive. The method described saves time and expense.

apo-SAA1/apo-SAA2 isotype ratios during casein- and amyloid-enhancing-factor-induced secondary amyloidosis in A/J and C57BL/6J mice mice

A/J mice are resistant while C57BL/6J are susceptible to casein-induced secondary amyloidosis. One mechanism responsible for this phenotypic expression of resistance/susceptibility was shown to operate at the level of production of the 'amyloid-enhancing factor' (AEF). AEF and processing of the apo-SAA protein appear almost concomitantly during amyloidogenesis. In order to determine if AEF played a role in the processing of the apo-SAA protein, three major parameters (apo-SAA1/apo-SAA2 ratios, level of AEF, and fibril formation) were determined during casein-induced secondary amyloidosis. Kinetics of AEF production and serum levels of the two major apo-SAA isotypes were compared in A/J and C57BL/6J animals. Both strains showed equal relative amounts of the two isotypes after seven, 15 and 21 casein injections, irrespective of the fact that the A/J strain had no detectable level of AEF and no amyloid deposition; while C57BL/6J mice had a high AEF level and were amyloidotic after 15 and 21 injections. An increased apo-SAA1/apo-SAA2 ratio due to a decrease in apo-SAA2 was noted after 38 days of casein injections when both strains had extensive deposits of amyloid fibrils. Involvement of AEF as an effector molecule was determined by following the ratio of the two major serum apo-SAA isotypes and fibril formation during an accelerated protocol of amyloid induction in C57BL/6J animals. AEF had no direct effect on apo-SAA isotype ratios in the serum.

Murine tissue macrophages synthesize and secrete amyloid proteins different to amyloid A (AA)

We recently demonstrated that serum amyloid A (SAA) gene expression can be induced in extrahepatic sites with exception of the brain. Furthermore we demonstrated that tissue macrophages express SAA-gene constitutively and that SAA-gene expression can be increased by endotoxin. Until now the protein corresponding to the SAA-specific mRNA contained in macrophages has not been identified. We compared proteins precipitated from endogenously labelled samples by three antisera against amyloid A (AA) raised in different laboratories. Radiolabelled samples were derived from murine hepatocyte cultures, from cell-free translation of acute phase liver RNA or hepatocytes RNA and from peritoneal macrophages as well as Kupffer cells. All three antisera recognize a protein of 12.5 kDa Mr produced by hepatocytes (SAA), and a major protein of 14.3 kDa Mr contained in the cell-free translation products; this is the precursor of the mature SAA as demonstrated by cleavage experiments with canine pancreas microsomal enzymes. The antisera also recognize two proteins--a major one of 14.5 kDa Mr and a second of 12.5 kDa Mr contained in the supernatants and cell lysates of liver and peritoneal macrophages. New antisera raised against the two proteins do not recognize any protein, either of hepatocyte or of cell-free translation samples; they specifically precipitate two proteins from macrophage samples with the same molecular mass as that of the proteins precipitated by the anti SAA antisera. Murine acute phase sera do not react with the new antisera. However, amyloid deposits of amyloidotic mice specifically react with the new antisera. We describe two new components of murine amyloid produced by tissue macrophages.

Immunocytochemical evidence of amyloid-enhancing factor (AEF) in polymorphonuclear leukocytes

Amyloid-enhancing factor (AEF) was extracted from spleens of mice that had received amyloidogenic stimulation. Sephacryl S-300 gel filtration of the crude AEF yielded five fractions, among which strong AEF activity was present in the first peak (F1), and confirmed by an amyloid induction experiment. An anti-AEF antiserum was obtained from a rabbit by immunization with F1. This antibody reacted strongly with splenic polymorphonuclear leukocytes (PML) from mice given amyloidogenic stimulation, and weakly with those from normal untreated mice. Isoelectric focusing (IEF) analysis of both F1 and sera from mice given amyloidogenic stimulation was performed. A single band was observed on IEF analysis of F1, whereas many bands were seen on IEF analysis of the sera. After the substances in the gel had been transferred to nitrocellulose membranes by capillary blotting, the membranes were made to react with the anti-AEF antiserum. The results suggested that AEF is a high-molecular-weight substance derived from PML and increases in the serum at the time of, or shortly prior to, amyloid deposition in the spleen.

Presence of glycosaminoglycans in purified AA type amyloid fibrils associated with juvenile rheumatoid arthritis

Previous studies have strongly suggested an association between glycosaminoglycans and tissue deposits of amyloid. The present study was aimed at studying this association in purified preparations of hepatic amyloid fibrils obtained from human AA type secondary amyloidosis. Glycosaminoglycans were isolated by gradient ion exchange chromatography of purified amyloid fibrils treated with pronase. Degradation with specific enzymes identified the glycosaminoglycans as chondroitin sulphate, dermatan sulphate, and heparin/heparan sulphate. The total amount of glycosaminoglycans specifically coisolated with the amyloid fibrils was 15 micrograms/mg fibril weight. The presence of glycosaminoglycans in amyloid may play a part in the incorporation of structurally diverse protein precursors into amyloid fibrils of identical ultrastructure.

Amyloid enhancing factor (AEF) in the aging mouse

Amyloid enhancing factor (AEF) activity was tested in spleen homogenates from 52, 28, and 9-week-old untreated mice. Strong AEF activity was present in the supernatant of spleen homogenate from the 52-week-old mice. Only weak activity was observed in the supernatant from the 28-week-old mice, and none was seen in that from the 9-week-old mice. Crude spleen homogenates from the 52-week-old mice were subjected to Sephacryl S-300 gel filtration. AEF activity existed in the first gel filtration peak. These findings suggest that AEF increases in the spleens of aged mice and that AEF may be a substance of high molecular weight.

Effects of culture substrates and normal hepatic sinusoidal cells on in vitro hepatocyte synthesis of Apo-SAA

Primary hepatocyte cultures synthesize apo-SAA upon stimulation with supernatant from lipopolysaccharide (LPS)-treated macrophages. The matrices on which the hepatocytes were grown influence their basal apo-SAA synthetic capability. Fibronectin was superior. Coculturing hepatocytes with hepatic sinusoidal cells did not adversely affect the ability of hepatocytes to synthesize and secrete apo-SAA into the culture medium. In 72 h, clear islands of endothelial cells nestled in layers of hepatocytes. Both apo-SAA and apo-SAA were made in considerable quantities but no evidence could be obtained that the apo-SAA were free of apo-A-1. The coculturing of hepatocytes with liver sinusoidal cells, the site of ultimate AA deposition, is a first step in establishing an in vitro system for AA amyloidogenesis.

Evidence for increased amyloid enhancing factor activity in Alzheimer brain extract

Soluble brain extracts containing 0.1 to 16 mg of protein from 3 normal human brain and 11 patients with Alzheimer's disease, Down's syndrome and other neurological disorders were assayed for amyloid enhancing factor (AEF) activity in the mouse bioassay. At the 0.1 mg dosage, five of seven brain extracts from amyloid-positive samples and only one of four amyloid-negative samples demonstrated AEF activity. Marginal AEF activity was detected in the normal brain extracts at 8 or 16 mg protein dosage. Alzheimer-AEF was aggregated by exhaustive dialysis against 0.01 M phosphate buffer, pH 6 or distilled water and the solubilized aggregate was fractionated on a BioGel P-60 column. Of the two protein peaks, AEF activity was present only in the low mol.wt second fraction, which on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining showed two discrete and three minor peptide bands between 60 and 66 kDa and one of these was periodic acid-Schiff positive, and three fuzzy bands near 14 kDa. Pretreatment of the crude and second fraction with 10 mM phenylmethylsulfonyl fluoride (PMSF) nearly completely abolished the in vivo AEF bioactivity. It is suggested that (a) a higher AEF concentration is present in amyloid-positive brain samples than those negative for amyloid or normal brain tissues, (b) AEF-positive fraction contains at least five dominant peptides ranging between 14 to 66 kDa, and (c) abolition of PMSF-treated Alzheimer-AEF activity, similar to that of murine AEF, might be due to its serine/thiol proteinase nature. To our knowledge, this is the first time that AEF activity has been demonstrated in Alzheimer brain samples.