Interaction between circulating amyloid fibril protein precursors and extracellular tissue matrix components in the pathogenesis of systemic amyloidosis

Historical and Current Concepts of Fibrillogenesis and In vivo Amyloidogenesis: Implications of Amyloid Tissue Targeting

Historical and current concepts of in vitro fibrillogenesis are considered in the light of disorders in which amyloid is deposited at anatomic sites remote from the site of synthesis of the corresponding precursor protein. These clinical conditions set constraints on the interpretation of information derived from in vitro fibrillogenesis studies. They suggest that in addition to kinetic and thermodynamic factors identified in vitro, fibrillogenesis in vivo is determined by site specific factors most of which have yet to be identified.

Prion and prion-like diseases in animals

Transmissible spongiform encephalopaties (TSEs) are fatal neurodegenerative diseases characterized by the aggregation and accumulation of the misfolded prion protein in the brain. Other proteins such as β-amyloid, tau or Serum Amyloid-A (SAA) seem to share with prions some aspects of their pathogenic mechanism; causing a variety of so called prion-like diseases in humans and/or animals such as Alzheimer's, Parkinson's, Huntington's, Type II diabetes mellitus or amyloidosis. The question remains whether these misfolding proteins have the ability to self-propagate and transmit in a similar manner to prions. In this review, we describe the prion and prion-like diseases affecting animals as well as the recent findings suggesting the prion-like transmissibility of certain non-prion proteins.

In vitro binding of [³H]PIB to human amyloid deposits of different types

Systemic amyloidosis is caused by extracellular deposition of insoluble fibrillar proteins arranged in β-pleated sheets. [(11)C]PIB has been used in PET studies to assess Aβ deposition in brain of patients with Alzheimer's disease (AD). The possibility to visualize other types of amyloid deposits with [(11)C]PIB would be of potential clinical importance in early diagnosis and for following therapeutic effects. In the present study, we evaluated in vitro binding of [(3)H]PIB to tissues containing transthyretin (ATTR), immunoglobulin light-chain (AL), amyloid protein A (AA) and Aβ amyloid. We found significantly higher binding of [(3)H]PIB in tissue from systemic amyloidoses than in control tissue, i.e. 4.7 times higher (p < 0.05). [(3)H]PIB showed the highest affinity to cortex of AD brain (IC50 = 3.84 nM), while IC50 values were much higher for ATTR, AA and AL type of amyloidosis and large variations in affinity were observed even within tissues having the same type of amyloidosis. Extraction with guanidine-HCl, which disrupts the β-sheet structure, decreased the protein levels and, concomitantly, the binding of [(3)H]PIB in all four types of amyloidoses.

Currents concepts on the immunopathology of amyloidosis

Amyloidosis is defined as the extracellular accumulation at systemic or organ-specific level of insoluble low molecular weight protein fibrils manifesting a beta pleated sheet configuration and a characteristic staining pattern. Several different types of proteins may lead to this phenomenon, and amyloidosis is defined by the biochemical nature of the protein in the deposits and further classified according to whether the deposits are localized or systemic, acquired or inherited, and by the resulting clinical phenotype. Amyloidosis includes subtypes such as light chain, associated with serum amyloid A protein, heritable and familial forms, dialysis-related disease, and organ-specific conditions. The pathogenesis and clinical features of these clinical and pathological entities will be critically discussed in this review article.

Heparan sulfate proteoglycans in amyloidosis

Amyloidosis is a generic term for a group of diseases characterized by deposits in different organ systems of insoluble materials composed mainly of distinct fibrillar proteins named amyloid. Besides amyloid, heparan sulfate proteoglycan (HSPG), is commonly found in most amyloid deposits, suggesting that HS/HSPG may be functionally involved in the pathogenesis of amyloidosis. HS or HSPG is found to interact with a number of amyloid proteins, displaying a promoting effect on amyloid fibrilization in vitro. In addition, HS is reported to be involved in processing amyloid precursor proteins and mediate amyloid toxicity. Although little is known about the in vivo mechanisms regarding the codeposition of HS with amyloid proteins in different amyloid diseases, experiments carried out in animal models, especially in transgenic mouse model where HS molecular structure is modified, support an active role for HS in amyloidogenesis. Further experimental evidence is required to strengthen these in vivo findings at a molecular level. Animal models that express mutant forms of HS due to knockout of the enzymes involved in glycosaminoglycan (GAG) biosynthesis are expected to provide valuable tools for studying the implications of HS, as well as other GAGs, in amyloid disorders.

Diffusible amyloid oligomers trigger systemic amyloidosis in mice

AA (amyloid protein A) amyloidosis in mice is markedly accelerated when the animals are given, in addition to an inflammatory stimulus, an intravenous injection of protein extracted from AA-laden mouse tissue. Previous findings affirm that AA fibrils can enhance the in vivo amyloidogenic process by a nucleation seeding mechanism. Accumulating evidence suggests that globular aggregates rather than fibrils are the toxic entities responsible for cell death. In the present study we report on structural and morphological features of AEF (amyloid-enhancing factor), a compound extracted and partially purified from amyloid-laden spleen. Surprisingly, the chief amyloidogenic material identified in the active AEF was diffusible globular oligomers. This partially purified active extract triggered amyloid deposition in vital organs when injected intravenously into mice. This implies that such a phenomenon could have been inflicted through the nucleation seeding potential of toxic oligomers in association with altered cytokine induction. In the present study we report an apparent relationship between altered cytokine expression and AA accumulation in systemically inflamed tissues. The prevalence of serum AA monomers and proteolytic oligomers in spleen AEF is consistent to suggest that extrahepatic serum AA processing might lead to local accumulation of amyloidogenic proteins at the serum AA production site.

Transthyretin and familial amyloidotic polyneuropathy

Familial amyloidotic polyneuropathy (FAP) is an inherited autosomal dominant disease that is commonly caused by accumulation of deposits of transthyretin (TTR) amyloid around peripheral nerves. The only effective treatment for FAP is liver transplantation. However, recent studies on TTR aggregation provide clues to the mechanism of the molecular pathogenesis of FAP and suggest new avenues for therapeutic intervention. It is increasingly recognized that there are common features of a number of protein-misfolding diseases that can lead to neurodegeneration. As for other amyloidogenic proteins, the most toxic forms of aggregated TTR are likely to be the low-molecular-mass diffusible species, and there is increasing evidence that this toxicity is mediated by disturbances in calcium homeostasis. This article reviews what is already known about the mechanism of TTR aggregation in FAP and describes how recent discoveries in other areas of amyloid research, particularly Alzheimer's disease, provide clues to the molecular pathogenesis of FAP.

Structures for amyloid fibrils

Alzheimer's disease and Creutzfeldt-Jakob disease are the best-known examples of a group of diseases known as the amyloidoses. They are characterized by the extracellular deposition of toxic, insoluble amyloid fibrils. Knowledge of the structure of these fibrils is essential for understanding the process of pathology of the amyloidoses and for the rational design of drugs to inhibit or reverse amyloid formation. Structural models have been built using information from a wide variety of techniques, including X-ray diffraction, electron microscopy, solid state NMR and EPR. Recent advances have been made in understanding the architecture of the amyloid fibril. Here, we describe and compare postulated structural models for the mature amyloid fibril and discuss how the ordered structure of amyloid contributes to its stability.

Amyloid in the cardiovascular system: a review

The cardiovascular system is a common target of amyloidosis. This review presents the current clinical and diagnostic approach to amyloidosis, with the emphasis on cardiovascular involvement. It summarises recent nomenclature, classification, and pathogenesis of amyloidosis. In addition, non-invasive possibilities are discussed, together with endomyocardial biopsies in the diagnosis of cardiac amyloidosis. Finally, recent advances in treatment and prognostic implications are presented.

Long-term outcome of live donor kidney transplantation for renal amyloidosis

BACKGROUND

The short-term outcome of kidney transplantation in patients with amyloidosis has been reported. The aim of this study is to investigate long-term results in patients with renal amyloidosis.

METHODS

We studied results of renal transplantation in 23 amyloidotic transplant recipients compared with those in a control group of 47 nonamyloidotic patients. Amyloidosis was secondary to familial Mediterranean fever (FMF) in 16 patients, whereas it was primary (idiopathic) in 7 transplant recipients. The 2 groups were homogeneous regarding age, sex, HLA matching, immunosuppression, and duration of transplantation.

RESULTS

Five- and 10-year actuarial graft survival rates were similar in both groups (79.35% versus 84.04% and 65.92% versus 56.61%, respectively ). Five- and 10-year actuarial patient survival rates also were similar (80% versus 94% and 68% versus 87%, respectively). Moreover, 72.4% of controls experienced at least 1 rejection episode, whereas only 43.5% of amyloidotic transplant recipients experienced 1 or more such events (P = 0.02). Nonetheless, mean serum creatinine concentrations did not differ between the 2 groups during the observation period. Maintenance colchicine therapy prevented the recurrence of both FMF symptoms and amyloidosis. Recurrence was documented in only 1 amyloidotic transplant recipient (4.3%) 10 years posttransplantation. Significant gastrointestinal (GI) problems were more frequent in amyloidotic patients (65% versus 38%; P = 0.03). Amyloidotic patients with GI problems, except for 2 patients, were administered cyclosporine. Eleven of these patients had FMF, which appeared to reflect the effects of both cyclosporine and colchicine. Infections were similar in the groups; whereas amyloidotic patients had significantly lower blood pressures.

CONCLUSION

In our experience, long-term (5 to 10 years) outcome of live related donor kidney transplantation in patients with amyloidosis is similar to that in the general transplant population.

Urinary glycosaminoglycans in the course of familial Mediterranean fever

Familial Mediterranean fever (FMF) is characterised by recurrent fever and serositis. The most important complication of the disease is amyloidosis. Cheap and non-invasive methods would be important in predicting or establishing the early diagnosis of amyloidosis. For this purpose, we studied the role of urinary glycosaminoglycans (GAG). The study group included 123 FMF patients without an attack and 11 patients with FMF associated amyloidosis. Ten healthy children and ten patients with primary nephrotic syndrome served as controls. In patients with amyloidosis, urinary GAG were lower than in patients with FMF, patients with nephrotic syndrome and controls (median and range: 8.54 mg hexuronic acid/g creatinine (1.87-25.5), 5.8 (1.7-17.26), 23.12 (8.74-28.06) and 19.25 (14.2-26.9) respectively, P<0.01). There was a significant negative correlation between the duration of the disease and urinary GAG ( r= -043, P=0.002). In 49 FMF patients with a low GAG, urinary GAG increased significantly after an increase in the colchicine dose (median and range: 6.64 mg hexuronic acid/g creatinine (1.77-19.39) and 9.45 mg hexuronic acid/g creatinine (2.36-28.9), P<0.01).

CONCLUSION

These results suggest that urinary glycosaminoglycan levels may be a predictor of amyloidosis in patients with familial Mediterranean fever. We also suggest that effective colchicine doses may be monitored by following urinary glycosaminoglycan excretion.

Evaluation of feline serum amyloid A (SAA) as an inflammatory marker

The concentration of feline serum amyloid A (fSAA) was determined by a direct enzyme-linked immunosorbent assay (ELISA) by using fSAA specific monoclonal antibodies, to evaluate the fSAA as an inflammatory marker in cats. The mean concentration +/- standard deviation of fSAA was found to be 0.60 +/- 1.06 microg/m l and 33.65 +/- 67.59 microg/ml in serum samples from normal cats (n=45) and cats (n=312) with various diseases and disorders, respectively. A significant difference (p<0.001) was found between the two groups. It was also found that the concentration of fSAA begins to increase rapidly at approximately 3-6 hr after spay, and increases up to significantly high levels in some disorders, like injury, renal failure, infectious diseases, etc.

Characterization of monoclonal antibodies specific for feline serum amyloid (SAA) protein

Serum amyloid A (SAA) has been characterized as an inflammatory marker in many species. In this study, we have developed and characterized monoclonal antibodies (MAbs) against feline SAA (fSAA) derived from culture hybridomas. These hybridomas were produced from the fusion of Balb/c-derived myeloma s/p20-Ag14 and splenocytes from mice immunized with purified recombinant feline SAA (rfSAA). Six hybridomas secreting MAbs, M2, M5, M7, M8, M13, and M15, were selected and subcloned on the basis of their specificity to rfSAA by enzyme-linked immunoabsorbent assay (ELISA), and confirmed based on their specificity to rf-SAA by immunoblot analysis. Out of six clones, two clones (M5 and M7) showed higher reactivity with rf-SAA, and were selected for further analysis of ELISA additivity and Western blot cross-reactivity tests. As a result, M5 and M7 clones recognized the same or excessively near epitopes on rfSAA and reacted with rfSAA, fSAA and equine recombinant SAA, but showed no reaction with human recombinant SAA. Because of their specificity, these MAbs may be usefully applied in studying the measurement of SAA concentration in cat serum.

Molecular cloning and sequencing of equine cDNA encoding serum amyloid A (SAA)

The serum amyloid A (SAA) protein is a characteristic and sensitive acute phase reactant in all vertebrates investigated. We molecularly cloned the equine cDNA encoding SAA from the liver of a healthy horse by polymerase chain reaction (PCR). The cloned cDNA is 480 bases in length, and contains an open reading frame (ORF) of 387 nucleotides encoding a precursor SAA protein of 128 amino acids. The precursor of horse SAA seems to have an 18-residue signal peptide and differs from the reported amino acid sequences of the horse SAA by substitution of valine at residue 81. It shows high homology with SAA amino acid sequence of other species such as dog (80.6%), mink (77.5%), human (76.9%) and duck (71.9%). An insertion of eight amino acids at residues between 85 and 92, as compared to human SAA, has also been found in horse SAA. The availability of the equine SAA cDNA will provide a useful reagent for studying its role in diseased horses.

Abnormalities in thrombin-antithrombin pathway in AL amyloidosis

Various pathogenic factors have been proposed to explain the abnormal hemostasis observed in AL amyloidosis. Since imbalance between clotting factors and inhibitors could play a pathogenic role in both hemorrhagic and thrombotic manifestations, we investigated the thrombin-antithrombin pathway in 35 patients with AL amyloidosis. Ten patients suffered from bleeding while 3 patients experienced deep venous thrombosis. Thrombin time was prolonged in 29 subjects, the mean values of antithrombin III activity (ATIII Act) were significantly lower than those of antithrombin III antigen (ATIII Ag) with loss of relationship between these two different techniques of ATIII detection, normally observed in healthy controls. In 19 patients increased levels of thrombin-antithrombin (TAT) complexes were present. Crossed immunoelectrophoresis of ATIII, performed in presence of heparin, evidenced ATIII forms with reduced binding capacity to heparin and TAT complexes of various electrophoretic mobilities. In conclusion, the impairment of the thrombin-antithrombin pathway, in association with the low ATIII biological activity, might play a pathogenic role in the hypercoagulable state reported in AL amyloidosis, despite the higher frequency of bleeding manifestations.

Constant region of a kappa III immunoglobulin light chain as a major AL-amyloid protein

AL-amyloidoses are generally described as a group of disorders in which N-terminal fragments of monoclonal immunoglobulin light chains are transferred into amyloid fibrils. We have, by amino acid sequence analyses and immunological methods, characterized the Bence-Jones protein and the corresponding AL protein as a kappa III immunoglobulin light chain from material of a patient with systemic AL-amyloidosis presenting as a local inguinal tumour. The two proteins showed some unique features. The major part of the AL amyloid fibril protein consisted of C-terminal fragments of the Bence-Jones protein. Furthermore, both the Bence-Jones protein and the AL protein were glycosylated, with possibly a glycosylation in the constant part of the light chain.

Interaction between glycosaminoglycans and immunoglobulin light chains

Amyloidosis is a pathological process in which normally soluble proteins polymerize to form insoluble fibrils (amyloid). Amyloid formation is found in a number of diseases, including Alzheimer's disease, adult-onset diabetes, and light-chain-associated amyloidosis. No pharmaceutical methods currently exist to prevent this process or to remove the fibrils from tissue. The search for treatment and prevention methods is hampered by a limited understanding of the biophysical basis of amyloid formation. Glycosaminoglycans (GAGs) are long, unbranched heteropolysaccharides composed of repeating disaccharide subunits and are known to associate with amyloid fibrils. The interaction of amyloid-associated free light chains with GAGs was tested by both size-exclusion high-performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis experiments. The results indicated that heparin 16 000 and chondroitin sulfate B and C precipitated both human intact light chains and recombinant light chain variable domains. Although all light chains interacted with heparin, the strongest interactions were obtained with proteins that had formed amyloid. Molecular modeling indicated the possibility of interaction between heparin and the conserved saddlelike surface of the light chain dimer opposite the complementarity-determining segments that form part of the antigen-binding site of a functional antibody. This suggestion might offer a new path to block the aggregation of amyloid-associated light chain proteins, by design of antagonists based on properties of GAG binding. A hexasaccharide was modeled as the basis for a possible antagonist.

The putative role of alpha-1-antitrypsin in the disaggregation of amyloid lambda fibrils

BACKGROUND AND OBJECTIVES

Interactions between hydrophobic compounds like cholesterol and lithocholic acid and alpha-1-antitrypsin (alpha-1-AT) have previously been described. We studied the putative interaction between alpha-1-AT and the insoluble, hydrophobic, beta-pleated sheet, light-chain-derived fibrils that predominate the tissue deposits in primary immunocytic (AL) related amyloidosis.

SUBJECTS AND METHODS

Amyloid fibrils were isolated from two cases with lambda and two cases with kappa AL amyloidosis.

RESULTS

The lambda fibrils could be completely disaggregated (as shown by light and electron microscopy and Congo red uptake) by alpha-1-AT added in the molar ratio 1:5, whereas fibrils with predominantly kappa chains remained unaffected. The lambda-chain interaction was accompanied by characteristic changes of the physicochemical and biological properties of alpha-1-AT apparent in an increased thermal stability and loss of elastase-inhibitory activity. These findings are compatible with a transition of alpha-1-AT from a native, stressed conformation to a relaxed form.

CONCLUSIONS

Disaggregation of lambda AL amyloid fibrils can be achieved by addition of alpha-1-AT. The findings may have therapeutic implications in primary amyloidosis.

Bovine glomerular amyloidosis: morphological studies

Bovine kidney material with advanced glomerular deposits of amyloid was studied immunohistochemically using the avidin biotin complex immunoperoxidase method, with rabbit anti-horse AA serum as primary antibody. Severely affected glomeruli consisted of strongly reacting positive material, obscuring all cellular structures. Transmission electron microscopy revealed that the amyloidotic areas, with evident amyloid fibrils, also contained a considerable admixture of cellular remnants. In this investigation it was found that such material was more abundant in the bovine glomerular amyloid masses than in amyloid laden organs from other animal species, and it is discussed to what extent this observation may explain the varying tinctorial properties of amyloid deposits in bovine tissues, and the relative high content of histones in bovine amyloid proteins.