Frequency and distribution of senile cardiovascular amyloid. A clinicopathologic correlation

Amyloidosis

The term amyloid describes the deposition in the extracellular space of certain proteins in a highly characteristic, insoluble fibrillar form. Amyloidosis describes the various clinical syndromes that occur as a result of damage by amyloid deposits in tissues and organs throughout the body. The clinical significance of amyloid varies enormously, ranging from incidental asymptomatic deposits to localized disease through to rapidly fatal systemic forms that can affect multiple vital organs. Currently available therapy is focused on reducing the supply of the respective amyloid fibril precursor protein and supportive medical care, which together have greatly improved survival. Chemotherapy and anti-inflammatory treatment for the disorders that underlie AL and AA amyloidosis are guided by serial measurements of the respective circulating amyloid precursor proteins, i.e. serial serum free light chains in AL and serum amyloid A protein in AA type. Quality of life and prognosis of some forms of hereditary systemic amyloidosis can be improved by liver and other organ transplants. Various new therapies, ranging from silencing RNA, protein stabilizers to monoclonal antibodies, aimed at inhibiting fibril precursor supply, fibril formation or the persistence of amyloid deposits, are in development; some are already in clinical phase.

Familial amyloidotic polyneuropathy and transthyretin

There has been much progress in our understanding of transthyretin (TTR)-related amyloidosis including familial amyloidotic polyneuropathy (FAP), senile systemic amyloidosis and its related disorders from many clinical and experimental aspects. FAP is an inherited severe systemic amyloidosis caused by mutated TTR, and characterized by amyloid deposition mainly in the peripheral nervous system and the heart. Liver transplantation is the only available treatment for the disease. FAP is now recognized not to be a rare disease, and to have many variations based on genetical and biochemical variations of TTR. This chapter covers the recent advances in the clinical and pathological aspects of, and therapeutic approaches to FAP, and the trend as to the molecular pathogenesis of TTR.

High prevalence of wild-type transthyretin deposition in patients with idiopathic carpal tunnel syndrome: a common cause of carpal tunnel syndrome in the elderly

Carpal tunnel syndrome is the most common type of entrapment neuropathy. However, the cause of carpal tunnel syndrome remains unclear in most cases. Senile systemic amyloidosis, induced by wild-type transthyretin deposition, is a prevalent aging-related disorder and often accompanied by carpal tunnel syndrome. In this study, we measured the frequency of unrecognized wild-type transthyretin deposition in patients with idiopathic carpal tunnel syndrome. One hundred twenty-three patients with carpal tunnel syndrome, including 100 idiopathic patients, treated by carpal tunnel release surgery were analyzed. Tenosynovial tissues obtained at surgery were analyzed by Congo red and immunohistochemical staining. If staining for transthyretin was positive, the entire transthyretin gene was analyzed by direct DNA sequencing. We also analyzed tenosynovial tissues from 32 autopsy cases as controls. Thirty-four patients (34.0%) with idiopathic carpal tunnel syndrome showed amyloid deposition in the tenosynovial tissue, and all amyloid showed specific immunolabeling with antitransthyretin antibody. Direct DNA sequencing of the entire transthyretin gene did not reveal any mutations, indicating that all amyloid deposits were derived form wild-type transthyretin. Statistical analysis using logistic regression showed that the prevalence of transthyretin deposition in the idiopathic carpal tunnel syndrome group was significantly higher than that in controls (odds ratio, 15.8; 95% confidence interval, 3.3-5.7), and age and male sex were independent risk factors for transthyretin amyloid deposition. Our results demonstrate that wild-type transthyretin deposition is a common cause of carpal tunnel syndrome in elderly men. It is likely that many patients develop carpal tunnel syndrome as an initial symptom of senile systemic amyloidosis.

Clinicopathological features of senile systemic amyloidosis: an ante- and post-mortem study

Senile systemic amyloidosis is a common age-related amyloidosis that involves accumulation of wild-type transthyretin, with cardiac dysfunction being a predominant result. The importance of obtaining an accurate diagnosis of senile systemic amyloidosis has been increasingly recognized, so that novel treatments are being developed. However, the clinicopathological features of senile systemic amyloidosis remain to be completely understood. Here, we evaluated cardiac specimens from 181 consecutive post-mortem cases older than 40 years, including 6 cases of senile systemic amyloidosis, and 5 cases of familial amyloidotic polyneuropathy, which is a hereditary systemic amyloidosis caused by mutant forms of transthyretin. Furthermore, we studied ante-mortem clinicopathological findings of 11 senile systemic amyloidosis cases, in which 9 cases underwent gastrointestinal tract biopsy and/or subcutaneous tissue biopsy, at Kumamoto University Hospital. Of the autopsied cases of elderly Japanese (older than 80 years), 12% had senile systemic amyloidosis, with the percentage increasing with age. The occurrence of senile systemic amyloidosis in elderly Japanese patients was lower than that in previous reports, which suggests that a genetic background and/or environmental factor(s) may have important roles in the occurrence of senile systemic amyloidosis. Transthyretin amyloid deposits in familial amyloidotic polyneuropathy cases developed mainly in the pericardium and the surrounding muscle fascicles, whereas in cases with senile systemic amyloidosis the transthyretin amyloid deposits had a patchy plaque-like shape and developed mainly inside the ventricular wall. Biopsies from senile systemic amyloidosis patients evidenced amyloid deposits in 44% (4/9) of gastrointestinal tract and subcutaneous tissue samples combined. As myocardial biopsy may be dangerous for elderly people, the use of a combination of gastrointestinal tract and subcutaneous tissue biopsies may make diagnosis of senile systemic amyloidosis easier.

Diagnostic value of abdominal wall fat pad biopsy in senile systemic amyloidosis

Senile systemic amyloidosis (SSA) is a main cause of intractable heart failure in elderly individuals. To demonstrate transthyretin (TTR)-derived amyloid deposition endomyocardial biopsy has been commonly carried out in the patients with SSA, but this invasive biopsy technique cannot always be performed in aged patients with severe cardiac dysfunction. During the past 3 years, 11 patients with SSA (6 males and 5 females; ages from 70 to 97 years) were examined. All underwent skin biopsy from the abdominal wall and 8 showed TTR-immunoreactive amyloid deposition (sensitivity: 73%): amyloid deposits were seen mainly in the deep layer of subcutaneous fat tissue and showed a patchy distribution. They were weakly Congophilic, but were strongly immunolabeled by an anti-TTR antibody. The severity and pattern of amyloid deposition in this biopsy of SSA patients were considerably different from those obtained from age-matched patients with TTR-related familial amyloid polyneuropathy. Surgical skin biopsy including the deep subcutaneous fat pad can be performed safely at the bedside and is useful for the histopathological diagnosis of SSA.

[Epidemiological and clinical aspects of non-hereditary systemic amyloidosis]

The amyloidoses are a large group of postsecretory protein misfolding and deposition diseases. There are over 20 secreted human proteins whose misfolding and misassembly outside the cell is linked to amyloidosis. In this paper, we described epidemiological and clinical aspects of non-hereditary systemic amyloidosis, including senile systemic amyloidosis (SSA) and systemic AL amyloidosis. SSA, induced by wild-type transthyretin (TTR) deposition, is a prevalent aging-related disorder, as about 25% of people over age 80 have TTR deposition in the heart, but it is usually detected by microscopic examination at autopsy. Although SSA is usually associated with cardiac disease, TTR deposition is not limited to the heart and is found in systemic organs. Carpal tunnel syndrome is one of the most common clinical manifestations of SSA and often precedes cardiac symptoms. Systemic AL amyloidosis is the most common non-hereditary systemic amyloidosis induced by immunoglobulin light chain deposition. Involvement of visceral organs usually dominates the clinical picture of systemic AL amyloidosis, but some patients suffer from serious peripheral neuropathy, including polyneuropathy, carpal tunnel syndrome, and autonomic dysfunction. High-dose melphalan with stem cell transplantation improves prognosis of systemic AL amyloidosis including neurological symptoms.

Clinical features and survival in senile systemic amyloidosis: comparison to familial transthyretin cardiomyopathy

Senile systemic amyloidosis (SSA) features cardiomyopathy resulting from amyloid deposits of wild-type transthyretin (TTR). From 1994 to 2009, 82 patients with SSA were diagnosed at our center; 79 were men (96%) and median age at diagnosis was 73.8 years (range, 59.1–86.0). Most patients (77/78) presented with abnormal echocardiography; median values for interventricular septal thickness and left ventricular ejection fraction were 16 mm (range, 9–24) and 50% (range, 20–70), respectively. Fat aspirates were positive for amyloid in 27% of patients. Mean levels of brain natriuretic peptide (n = 41) and troponin I (n = 19) were 422 ± 279 pg/ml and 0.151 ± 0.107 pg/ml. Median survival was 4.3 years (95% CI, 3.7–5.0). SSA and familial TTR cardiomyopathy were compared; survival distribution was significantly different across groups (log-rank test = 11.97, p-value = 0.0075). We conclude that patients with SSA are primarily men who present with dominant cardiac involvement at an older age than patients with familial TTR cardiomyopathy.

Telocytes in human isolated atrial amyloidosis: ultrastructural remodelling

The human heart can be frequently affected by an organ-limited amyloidosis called isolated atrial amyloidosis (IAA). IAA is a frequent histopathological finding in patients with long-standing atrial fibrillation (AF). The aim of this paper was to investigate the ultrastructure of cardiomyocytes and telocytes in patients with AF and IAA. Human atrial biopsies were obtained from 37 patients undergoing cardiac surgery, 23 having AF (62%). Small fragments were harvested from the left and right atrial appendages and from the atrial sleeves of pulmonary veins and processed for electron microscopy (EM). Additional fragments were paraffin embedded for Congo-red staining. The EM examination certified that 17 patients had IAA and 82% of them had AF. EM showed that amyloid deposits, composed of characteristic 10-nm-thick filaments were strictly extra-cellular. Although, under light microscope some amyloid deposits seemed to be located within the cardiomyocyte cytoplasm, EM showed that these deposits are actually located in interstitial recesses. Moreover, EM revealed that telopodes, the long and slender processes of telocytes, usually surround the amyloid deposits limiting their spreading into the interstitium. Our results come to endorse the presumptive association of AF and IAA, and show the exclusive, extracellular localization of amyloid fibrils. The particular connection of telopodes with amyloid deposits suggests their involvement in isolated atrial amyloidosis and AF pathogenesis.

Heparan sulfate/heparin promotes transthyretin fibrillization through selective binding to a basic motif in the protein

Transthyretin (TTR) is a homotetrameric protein that transports thyroxine and retinol. Tetramer destabilization and misfolding of the released monomers result in TTR aggregation, leading to its deposition as amyloid primarily in the heart and peripheral nervous system. Over 100 mutations of TTR have been linked to familial forms of TTR amyloidosis. Considerable effort has been devoted to the study of TTR aggregation of these mutants, although the majority of TTR-related amyloidosis is represented by sporadic cases due to the aggregation and deposition of the otherwise stable wild-type (WT) protein. Heparan sulfate (HS) has been found as a pertinent component in a number of amyloid deposits, suggesting its participation in amyloidogenesis. This study aimed to investigate possible roles of HS in TTR aggregation. Examination of heart tissue from an elderly cardiomyopathic patient revealed substantial accumulation of HS associated with the TTR amyloid deposits. Studies demonstrated that heparin/HS promoted TTR fibrillization through selective interaction with a basic motif of TTR. The importance of HS for TTR fibrillization was illustrated in a cell model; TTR incubated with WT Chinese hamster ovary cells resulted in fibrillization of the protein, but not with HS-deficient cells (pgsD-677). The effect of heparin on TTR fibril formation was further demonstrated in a Drosophila model that overexpresses TTR. Heparin was colocalized with TTR deposits in the head of the flies reared on heparin-supplemented medium, whereas no heparin was detected in the nontreated flies. Heparin of low molecular weight (Klexane) did not demonstrate this effect.

Wild-type transthyretin-derived amyloidosis in various ligaments and tendons

Transthyretin-derived amyloid deposition is commonly found in intercarpal ligaments of patients with senile systemic amyloidosis. However, the frequency of transthyretin-derived amyloid deposits in ligaments of other tissues remains to be elucidated. This study aimed to determine the frequency of amyloid deposition and the precursor proteins of amyloid found in orthopedic disorders. We studied 111 specimens from patients with carpal tunnel syndrome (flexor tenosynovium specimens), rotator cuff tears (rotator cuff tendon specimens), and lumbar canal stenosis (yellow ligament specimens). To identify amyloid precursor proteins, we used immunohistochemical staining with antibodies that react with transthyretin, immunoglobulin light chain, amyloid A protein, and β(2)-microglobulin. By means of Congo red staining, we identified 47 (42.3%) amyloid-positive samples, 39 of which contained transthyretin-derived amyloid (18 flexor tenosynovium specimens, 5 rotator cuff tendon specimens, and 16 yellow ligament specimens). Genetic testing and/or clinical findings suggested that all patients with transthyretin amyloid deposits did not have familial amyloidotic polyneuropathy. The occurrence of amyloid deposition in those tissues depended on age. These results suggest that transthyretin-derived amyloid deposits may occur more frequently in various ligaments and tendons than originally expected. In the future, such amyloid deposits may aid determination of the pathogenesis of ligament and tendon disorders in older patients.

Trapping of palindromic ligands within native transthyretin prevents amyloid formation

Transthyretin (TTR) amyloidosis is a fatal disease for which new therapeutic approaches are urgently needed. We have designed two palindromic ligands, 2,2'-(4,4'-(heptane-1,7-diylbis(oxy))bis(3,5-dichloro-4,1-phenylene)) bis(azanediyl)dibenzoic acid (mds84) and 2,2'-(4,4'-(undecane-1,11-diylbis(oxy))bis(3,5-dichloro-4,1-phenylene)) bis(azanediyl)dibenzoic acid (4ajm15), that are rapidly bound by native wild-type TTR in whole serum and even more avidly by amyloidogenic TTR variants. One to one stoichiometry, demonstrable in solution and by MS, was confirmed by X-ray crystallographic analysis showing simultaneous occupation of both T4 binding sites in each tetrameric TTR molecule by the pair of ligand head groups. Ligand binding by native TTR was irreversible under physiological conditions, and it stabilized the tetrameric assembly and inhibited amyloidogenic aggregation more potently than other known ligands. These superstabilizers are orally bioavailable and exhibit low inhibitory activity against cyclooxygenase (COX). They offer a promising platform for development of drugs to treat and prevent TTR amyloidosis.

Wild-type transthyretin significantly contributes to the formation of amyloid fibrils in familial amyloid polyneuropathy patients with amyloidogenic transthyretin Val30Met

Wild-type transthyretin is inherently an amyloidogenic protein, but its contribution to the formation of amyloid fibrils remains unclear in familial amyloid polyneuropathy patients. Our aim in this study was to elucidate the ratio of wild-type transthyretin in amyloid deposits in familial amyloid polyneuropathy patients. Abdominal fat amyloid fibrils in 44 familial amyloid polyneuropathy patients with amyloidogenic transthyretin Val30Met who had not undergone liver transplantation were examined. The amyloid fibrils were extracted from abdominal fat tissues and the composition ratios of wild-type and variant transthyretin were analyzed with liquid chromatography tandem mass spectrometry. The amyloid fibrils in abdominal fat tissues were composed of not only variant but also wild-type transthyretin in most patients (mean ratio, 40.7% ± 27.5%). The composition ratios of wild-type transthyretin in patients older than 50 years were significantly higher than those in patients younger than 50 (50.7% ± 26.9% versus 30.7 ± 24.8%). Our results indicate that wild-type transthyretin significantly contributes to the formation of amyloid fibrils in familial amyloid polyneuropathy patients with amyloidogenic transthyretin Val30Met, and its contribution tends to increase in older patients, suggesting that aging may play an important role in wild-type transthyretin-derived amyloid fibril formation in familial amyloid polyneuropathy patients. This is the first report showing the relationship between wild-type transthyretin deposition and aging in familial amyloid polyneuropathy patients. In addition, wild-type transthyretin may be more strongly amyloidogenic than previously considered because it is detectable even in amyloid fibrils isolated from young familial amyloid polyneuropathy patients.

Old men and thickened hearts

The case of a patient with confirmed amyloid, initially believed to be light chain (AL) type, whose diagnosis was clouded by an atypical gastrointestinal tract system presentation and a concomitant haematological condition, is presented. Duodenal biopsy samples subsequently stained positive for transthyretin and the diagnosis was revised to senile systemic amyloidosis. The patient was managed medically and remains alive more than 2 years after the diagnosis was formally established. Differentiating the systemic amyloidoses from one another can be challenging as the features often overlap and the most sensitive tests usually require a tertiary referral. Ultimately, cases usually require histological verification from tissue biopsies. Helpful pointers can be obtained with a careful history and examination in combination with some routinely available diagnostic tests.

Protein aggregates and novel presenilin gene variants in idiopathic dilated cardiomyopathy

BACKGROUND

Heart failure is a debilitating condition resulting in severe disability and death. In a subset of cases, clustered as idiopathic dilated cardiomyopathy (iDCM), the origin of heart failure is unknown. In the brain of patients with dementia, proteinaceous aggregates and abnormal oligomeric assemblies of beta-amyloid impair cell function and lead to cell death.

METHODS AND RESULTS

We have similarly characterized fibrillar and oligomeric assemblies in the hearts of iDCM patients, pointing to abnormal protein aggregation as a determinant of iDCM. We also showed that oligomers alter myocyte Ca(2+) homeostasis. Additionally, we have identified 2 new sequence variants in the presenilin-1 (PSEN1) gene promoter leading to reduced gene and protein expression. We also show that presenilin-1 coimmunoprecipitates with SERCA2a.

CONCLUSIONS

On the basis of these findings, we propose that 2 mechanisms may link protein aggregation and cardiac function: oligomer-induced changes on Ca(2+) handling and a direct effect of PSEN1 sequence variants on excitation-contraction coupling protein function.

Cardiac amyloidosis: approaches to diagnosis and management

Amyloidosis is a clinical disorder caused by the extracellular deposition of misfolded, insoluble aggregated protein with a characteristic ss pleated sheet configuration that produces apple-green birefringence under polarized light when stained with Congo red dye. The spectrum of organ involvement can include the kidneys, heart, blood vessels, central and peripheral nervous systems, liver, intestines, lungs, eyes, skin, and bones. Cardiovascular amyloidosis can be primary, a part of systemic amyloidosis, or the result of chronic systemic disease elsewhere in the body. The most common presentations are congestive heart failure because of restrictive cardiomyopathy and conduction abnormalities. Recent developments in imaging techniques and extracardiac tissue sampling have minimized the need for invasive endomyocardial biopsy for amyloidosis. Cardiac amyloidosis management will vary depending on the subtype but consists of supportive treatment of cardiac related symptoms and reducing the amyloid fibrils formation attacking the underlying disease. Despite advances in treatment, the prognosis for patients with amyloidosis is still poor and depends on the underlying disease type. Early diagnosis of cardiac amyloidosis may improve outcomes but requires heightened suspicion and a systematic clinical approach to evaluation. Delays in diagnosis, uncertainties about the relative merits of available therapies, and difficulties in mounting large-scale clinical trials in rare disorders combine to keep cardiac amyloidosis a challenging problem. This review outlines current approaches to diagnosis, assessment of disease severity, and treatment of cardiac amyloidosis.

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.

Distinct characteristics of amyloid deposits in early- and late-onset transthyretin Val30Met familial amyloid polyneuropathy

Late-onset transthyretin Val30Met-associated familial amyloid polyneuropathy (FAP ATTR Val30Met) cases unrelated to endemic foci in Japan show different clinicopathological features from the conventional early-onset cases in endemic foci. We compared the characteristics of amyloid deposits in early-onset FAP ATTR Val30Met cases in endemic foci and late-onset cases in non-endemic areas. Amyloid deposits in three early-onset cases from endemic foci and five late-onset cases from non-endemic areas were systematically examined post-mortem. Amyloid deposits in early-onset cases were highly congophilic and showed strong apple-green birefringence with Congo red staining and had long, parallel fibrils in most organs. On the other hand, those in late-onset cases were generally weakly congophilic and showed faint apple-green birefringence with Congo red staining and had short, haphazard fibrils. In the renal glomus and adrenal gland of early-onset cases, the characteristics of amyloid deposits were similar to those observed in late-onset cases. Analysis of cardiac amyloid using surface enhanced desorption/ionization time-of-flight mass spectrometry indicated that most transthyretin (TTR) was variant in early-onset cases, while more than half was composed of wild-type TTR in late-onset cases. Although characteristics of amyloid deposits may differ among individual organs of respective cases, especially in early-onset cases, the pattern was distinct between early- and late-onset cases. Amyloid deposition in late-onset cases may be similar to that observed in senile systemic amyloidosis with wild-type TTR deposition, suggesting that aging may play an important role in these cases.

Prevalence of germline mutations in the TTR gene in a consecutive series of surgical pathology specimens with ATTR amyloid

Transthyretin-derived amyloidosis (ATTR) amyloidosis is the third most prevalent amyloid type in surgical pathology and may occur as a hereditary disease with germline mutations in the TTR gene or as senile systemic amyloidosis (SSA) without mutations. Distinction between hereditary ATTR amyloidosis and SSA is of central importance, as the former necessitates genetic counseling and can be treated by liver transplantation. However, little is known about the prevalence of hereditary ATTR amyloidosis in surgical pathology specimens. We have examined the distribution of hereditary ATTR amyloidosis and SSA in a consecutive series of surgical pathology specimens with histologically and immunohistochemically confirmed ATTR amyloid. Thirty-three consecutive patients were retrieved from the Amyloid Registry of the Charité University Hospital. Genomic DNA was extracted from formalin-fixed and paraffin-embedded tissue or patient blood and examined by DNA sequencing. ATTR amyloid was found in the gastrointestinal tract, endomyocardium, peripheral nerve, carpal tunnel ligament, synovia, breast, and testicle. Amyloid fibrils were present as interstitial and vascular deposits, as evidenced by Congo red staining. TTR gene mutations were detected in 12 of 30 patients, with p.Val30Met being the most prevalent (5 patients). Furthermore, 2 novel mutations (p.Asp39Val and p.Glu54Asp) were found. In patients carrying a mutation, ATTR amyloid was found in the gastrointestinal tract, myocardium, nerve, and testicles. To conclude, the hereditary form of ATTR amyloid seems to be more common in elderly patients than previously thought. It is, therefore, important to genetically test every patient when diagnosing ATTR amyloidosis.

A review of the amyloidoses that infiltrate the heart

Primary amyloidosis, systemic senile amyloidosis, isolated atrial amyloidosis, and transthyretin isoleucine 122 amyloidosis frequently involve the heart. Amyloid fibrils infiltrate the myocardium, impairing ventricular contraction and relaxation. The clinical manifestations of cardiac infiltration in these disorders are protean, though congestive heart failure and arrhythmias are most common. Treatment of cardiac amyloidosis is directed at the underlying cause and at relief of symptoms. Heart transplantation is not a viable treatment option for patients with primary amyloidosis; its role in the other amyloidoses has not been established. The prognosis of patients with cardiac amyloidosis varies and is largely determined by the underlying disorder responsible for amyloid infiltration.

Significant deposition of wild type transthyretin-derived amyloid in the gastrointestinal tract of aged individuals

Two male patients aged 72 and 77 were found to have transthyretin (TTR) immunoreactive amyloid deposits in their gastrointestinal tracts when they underwent surgery for gastric and sigmoid colon cancer, respectively. They had no cardiac symptoms and there was no mutation in their TTR gene. Amyloid deposits were seen mainly on vascular walls in submucosal layers of the stomach and colon, while the muscularis mucosae, which is invariably affected in familial amyloid polyneuropathy (FAP), was completely free of amyloid deposition. The pattern of TTR-derived amyloid deposition in the gastrointestinal tract in SSA and in FAP are quite different.

Serum transthyretin levels in senile systemic amyloidosis: effects of age, gender and ethnicity

Serum transthyretin (TTR) levels are reduced in familial amyloidotic polyneuropathy (FAP). A single study of patients with senile systemic amyloidosis (SSA) in Sweden found that those individuals also had a significantly lower mean serum TTR concentration than age- and gender-matched controls. To determine if the same phenomenon prevailed in an ethnically more heterogeneous population, we compared the serum TTR levels, as determined by ELISA, in 45 documented SSA patients with congestive heart failure, 20 AL patients with congestive heart failure and population controls. Serum TTR concentrations in the controls were influenced in a statistically significant manner by age, gender and ethnicity. Although it is unlikely that such differences are clinically relevant, they must be considered when assessing the meaning of serum TTR concentrations in any clinically defined population. The serum concentrations in patients with SSA did not differ from age, gender and ethnically matched controls or from a group of AL patients with significant clinical cardiac involvement. We also compared TTR concentrations in 12 African-Americans carrying the TTR V122I allele with those in 826 African-Americans who were homozygous wild type at the TTR locus. The TTR V122I carriers had significantly lower serum TTR concentrations than appropriate controls even though the majority of such individuals had not reached the age of clinical or anatomic risk, i.e. over 60. Thus, as in carriers of other TTR mutations the serum TTR level is lower than normal, despite having a much later appearance of clinical disease.

Amyloid fibril composition is related to the phenotype of hereditary transthyretin V30M amyloidosis

Swedish familial systemic amyloidosis with polyneuropathy (FAP) depends on a mutation leading to a methionine-for-valine substitution in transthyretin. The disease appears with different clinical manifestations, including age of onset and involvement of the heart. Liver transplantation is currently the only curative treatment, but progressive cardiomyopathy may occur post-transplant. Two amyloid deposition patterns have previously been described in the heart. In one, the amyloid consists partially of transthyretin fragments and is weakly stainable by Congo red, while in the other, only full-length molecules are found and the fibrils have a strong affinity for Congo red. The present study aimed to see whether these morphological and biochemical variations have clinical implications. Subcutaneous adipose tissue biopsies were taken from 33 patients with Val30Met FAP and examined by microscopy, electrophoresis and western blot. Clinical data included age, sex, duration of disease and echocardiographic determination of the interventricular septum (IVS) thickness. It was found that fibrils composed of only full-length transthyretin were associated with early age of onset (44.8 +/- 12.9 years), no clinical cardiac involvement and a strong affinity for Congo red. In contrast, presence of transthyretin fragments in the amyloid was associated with late age of onset (67.3 +/- 7.0 years), signs of cardiac involvement and weak Congo red staining. For each individual, the same molecular type of amyloid was found in different organs. This is the first report showing that variations in clinical appearance of familial ATTR amyloidosis are associated with specific structural differences in the amyloid fibrils, and therefore may have a molecular cause. The molecular type of amyloid can be determined from a subcutaneous fat tissue biopsy.

Unfolding and aggregation of transthyretin by the truncation of 50 N-terminal amino acids

Senile systemic amyloidosis (SSA) is caused by amyloid deposits of wild-type transthyretin in various organs. Amyloid deposits from SSA contain large amounts of the C-terminal fragments starting near amino acid residue 50 as well as full-length transthyretin. Although a number of previous studies suggest the importance of the C-terminal fragments in the pathogenesis of SSA, little is known about the structure and aggregation properties of the C-terminal fragments of transthyretin. To understand the role of C-terminal fragments in SSA, we examined the effects of the truncation of the N-terminal portions on the structure and aggregation properties of wild-type transthyretin. The deletion mutant lacking 50 N-terminal residues was largely unfolded in terms of secondary and tertiary structure, leading to self-assembly into spherical aggregations under nearly physiological conditions. By contrast, the deletion mutant lacking 37 N-terminal residues did not have a strong tendency to aggregate, although it also adopted a largely unfolded conformation. These results suggest that global unfolding of transthyretin by proteolysis near amino acid residue 50 is an important step of self-assembly into aggregations in SSA.

The modulation of transthyretin tetramer stability by cysteine 10 adducts and the drug diflunisal. Direct analysis by fluorescence-detected analytical ultracentrifugation

Transthyretin (TTR) is normally a stable plasma protein. However, in cases of familial TTR-related amyloidosis and senile systemic amyloidosis (SSA), TTR is deposited as amyloid fibrils, leading to organ dysfunction and possibly death. The mechanism by which TTR undergoes the transition from stable, soluble precursor to insoluble amyloid fibril and the factors that promote this process are largely undetermined. Most models involve the dissociation of the native TTR tetramer as the initial step. It is largely accepted that the TTR gene mutations associated with TTR-related amyloidosis lead to the expression of variant proteins that are intrinsically unstable and prone to aggregation. It has been suggested that amyloidogenicity may be conferred to wild-type TTR (the form deposited in SSA) by chemical modification of the lone cysteine residue (Cys(10)) through mixed disulfide bonds. S-Sulfonation and S-cysteinylation are prevalent TTR modifications physiologically, and studies have suggested their ability to modulate the structure of TTR under denaturing conditions. In the present study, we have used fluorescence-detected sedimentation velocity to determine the effect of S-sulfonate and S-cysteine on the quaternary structural stability of fluorophore-conjugated recombinant TTR under nondenaturing conditions. We determined that S-sulfonation stabilized TTR tetramer stability by a factor of 7, whereas S-cysteinylation enhanced dissociation by 2-fold with respect to the unmodified form. In addition, we report the direct observation of tetramer stabilization by the potential therapeutic compound diflunisal. Finally, as proof of concept, we report the sedimentation of TTR in serum and the qualitative assessment of the resulting data.

Early cardiac involvement in senile systemic amyloidosis: a case report

Senile systemic amyloidosis (SSA) is caused by the deposition of wild-type transthyretin (TTR)-derived amyloid fibrils. This type of amyloidosis is not rare in elderly individuals over the age of 80 and is usually detected on postmortem microscopic examination of myocardium. We report a 67-year-old male patient who was clinically diagnosed as having SSA with cardiac involvement. The initial event was cerebral infarction conceivably due to cardiac embolism. Endomyocardial biopsy was performed twice, which led to a definitive diagnosis of amyloidosis at the second biopsy. This amyloid was immunolabeled by an anti-TTR antibody and direct DNA sequencing of the TTR gene did not detect any mutation. Clinical confirmation of SSA in individuals before the age of 70 is infrequent and cardiac amyloidosis associated with this disease might have been the cause of cerebral embolism in our patient. Additionally, it is important to distinguish cardiac amyloidosis of SSA from that of primary immunoglobulin light chain (AL)-derived amyloidosis, because the treatment and prognosis differ considerably from those of primary AL amyloidosis.

Senile systemic amyloidosis affects 25% of the very aged and associates with genetic variation in alpha2-macroglobulin and tau: a population-based autopsy study

BACKGROUND

Senile systemic amyloidosis (SSA) is characterized by deposition of wild-type transthyretin (TTR)-based amyloid in parenchymal organs in elderly individuals. Previously, no population-based studies have been performed on SSA.

METHODS

Here we have studied the prevalence and risk factors for SSA in a Finnish autopsied population aged 85 or over, as part of the population-based Vantaa 85+ Autopsy Study (n = 256). The diagnosis of SSA was based on histological examination of myocardial samples stained with Congo red and anti-TTR immunohistochemistry. The genotype frequencies of 20 polymorphisms in 9 genes in subjects with and without SSA were compared.

RESULTS

The prevalence of SSA was 25%. SSA was associated with age, myocardial infarctions, the G/G (Val/Val) genotype of the exon 24 polymorphism in the alpha2-macroglobulin (alpha2M), and the H2 haplotype of the tau gene (P-values 0.002, 0.004, 0.042, and 0.016).

CONCLUSION

This population-based study shows that SSA is very common in old individuals, affecting one-quarter of people aged over 85 years. Myocardial infarctions and variation in the genes for alpha2M and tau may be associated with SSA.

Role of aggregated medin in the pathogenesis of thoracic aortic aneurysm and dissection

The pathogenesis of sporadic thoracic aortic aneurysm and dissection, which may lead to rupture of the aorta, remains largely unknown. Amyloid deposits, formed from the medin peptide, are very prevalent in the media of the thoracic aorta. We have studied the occurrence of medin-derived amyloid in specimens from patients with thoracic aortic aneurysm, aortic dissection type A and normal dimensioned aorta. Surprisingly, the amount of amyloid was significantly lower in the aneurysm and dissection groups (0.63+/-0.13 and 0.36+/-0.24 amyloid particles per mm2, respectively) compared to the control material (2.37+/-0.58). However, focal medin immunoreactivity not associated with amyloid was found more conspicuously in the media of the two diseased groups. Recent amyloid research indicates that prefibrillar oligomeric aggregates, rather than mature amyloid fibrils, are toxic to the surrounding cells. The non-amyloid medin immunoreactivity observed may represent such toxic oligomers. This is supported by the fact that aggregated medin induced death of aortic smooth muscle cells in vitro. In addition, cells incubated together with medin increased the production of matrix metalloproteinase-2, a protease that degrades elastin and collagen and subsequently weakens the vessel wall. We therefore propose that medin oligomers are involved in the degeneration process of sporadic thoracic aortic aneurysm and dissection.

Human-murine transthyretin heterotetramers are kinetically stable and non-amyloidogenic. A lesson in the generation of transgenic models of diseases involving oligomeric proteins

The transthyretin amyloidoses appear to be caused by rate-limiting tetramer dissociation and partial monomer unfolding of the human serum protein transthyretin, resulting in aggregation and extracellular deposition of amorphous aggregates and amyloid fibrils. Mice transgenic for few copies of amyloid-prone human transthyretin variants, including the aggressive L55P mutant, failed to develop deposits. Silencing the murine transthyretin gene in the presence of the L55P human gene resulted in enhanced tissue deposition. To test the hypothesis that the murine protein interacted with human transthyretin, preventing the dissociation and partial unfolding required for amyloidogenesis, we produced recombinant murine transthyretin and human/murine transthyretin heterotetramers and compared their structures and biophysical properties to recombinant human transthyretin. We found no significant differences between the crystal structures of murine and human homotetramers. Murine transthyretin is not amyloidogenic because the native homotetramer is kinetically stable under physiologic conditions and cannot dissociate into partially unfolded monomers, the misfolding and aggregation precursor. Heterotetramers composed of murine and human subunits are also kinetically stable. These observations explain the lack of transthyretin deposition in transgenics carrying a low copy number of human transthyretin genes. The incorporation of mouse subunits into tetramers otherwise composed of human amyloid-prone transthyretin subunits imposes kinetic stability, preventing dissociation and subsequent amyloidogenesis.

Evaluation and management of the cardiac amyloidosis

Cardiac amyloidosis describes clinically significant involvement of the heart by amyloid deposition, which may or may not be associated with involvement of other organs. The purpose of this review is to summarize the current state of evidence for the effective evaluation and management of cardiac amyloidosis. Acquired systemic amyloidosis occurs in more than 10 per million person-years in the U.S. population. Although no single noninvasive test or abnormality is pathognomonic of cardiac amyloid, case-control studies indicate that echocardiographic evidence of left ventricular wall thickening, biatrial enlargement, and increased echogenicity in conjunction with reduced electrocardiographic voltages is strongly suggestive of cardiac amyloidosis. Furthermore, newer echocardiographic techniques such as strain and strain rate imaging can demonstrate impairment in longitudinal function before ejection fraction becomes abnormal. Recent observational studies also suggest that cardiovascular magnetic resonance imaging yields characteristic findings in amyloidosis, offering promise for the early detection of cardiac involvement, and the presence of detectable cardiac troponin and elevated B-type natriuretic peptide in serum of affected patients portends an adverse prognosis. Management strategies for cardiac amyloid are largely based on nonrandomized single-center studies. One of the few published randomized studies shows the superiority of oral prednisolone and melphalan compared with colchicine in systemic AL amyloidosis. Intermediate-dose infusional chemotherapy regimes (such as vincristine, adriamycin, and dexamethasone) and high-dose chemotherapy with peripheral stem cell rescue have been used widely, but treatment-related mortality remains substantial with chemotherapy. Recent studies also indicate promising strategies to stabilize the native structures of amyloidogenic proteins; inhibit fibril formation; and disrupt established deposits using antibodies, synthetic peptides, and small-molecule drugs.

Molecular targeting of proteins by L-homocysteine: mechanistic implications for vascular disease

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease, complications of pregnancy, cognitive impairment, and osteoporosis. That elevated homocysteine leads to vascular dysfunction may be the linking factor between these apparently unrelated pathologies. Although a growing body of evidence suggests that homocysteine plays a causal role in atherogenesis, specific mechanisms to explain the underlying pathogenesis have remained elusive. This review focuses on chemistry unique to the homocysteine molecule to explain its inherent cytotoxicity. Thus, the high pKa of the sulfhydryl group (pKa, 10.0) of homocysteine underlies its ability to form stable disulfide bonds with protein cysteine residues, and in the process, alters or impairs the function of the protein. Studies in this laboratory have identified albumin, fibronectin, transthyretin, and metallothionein as targets for homocysteinylation. In the case of albumin, the mechanism of targeting has been elucidated. Homocysteinylation of the cysteine residues of fibronectin impairs its ability to bind to fibrin. Homocysteinylation of the cysteine residues of metallothionein disrupts zinc binding by the protein and abrogates inherent superoxide dismutase activity. Thus, S-homocysteinylation of protein cysteine residues may explain mechanistically the cytotoxicity of elevated L-homocysteine.

Comparative MD analysis of the stability of transthyretin providing insight into the fibrillation mechanism

Proteins can misfold and aggregate, which is believed to be the cause of a variety of diseases, affecting very diverse organs in the body. Many questions about the nature of aggregation and the proteins that are involved in these events are still left unanswered. One of the proteins that is known to form amyloids is transthyretin (TTR), the secondary transporter of thyroxine, and transporter of retinol-binding protein. Several experimental results have helped to explain this aberrant behavior of TTR; however, structural insights of the amyloidgenic process are still lacking. Therefore, we have used all-atom MD simulation and free energy calculations to study the initial phase of this process. We have calculated the free energy changes of the initial tetramer dissociation under different conditions and in the presence of thyroxine. We show that tetramer formation is indeed only thermodynamically favorable in neutral pH conditions. We find that binding of two thyroxine molecules stabilizes the complex, and that this occurs with negative cooperativity. In addition to the energetic calculations, we have also investigated the dominant motions of the TTR and found that only the dimeric form of the protein could undergo the initial fibril formation.

A novel type of familial transthyretin amyloidosis, ATTR Asn124Ser, with co-localization of kappa light chains

A 68-year-old Italian woman who had a clinical history of thyroidectomy in 2002 presented with slowly progressing renal insufficiency and non-nephrotic proteinurea in 2004. A renal biopsy showed the occurrence of amyloid; the thyroid biopsy previously taken also revealed amyloid infiltration. Other amyloid-containing tissues included bone marrow and heart. The plasma cell level in the bone marrow was found to be less than 5% and both serum and urine samples were positive for a monoclonal kappa light chain band. DNA analysis unexpectedly revealed the presence of a novel transthyretin (TTR) mutation, ATTR Asn124Ser. Histologically, amyloid deposits in the thyroid had a homogeneous appearance with moderate Congophilia. In immunohistochemistry, a kappa light chain antiserum showed positive immunoreactivity with amyloid deposits in the thyroid. Furthermore, a TTR antiserum, anti-TTR50-127, also recognized a number of amyloid deposits stained positive with the kappa light chain antiserum. Overall, the kappa light chain antiserum reacted with most of the amyloid deposits in the thyroid, whereas TTR immunoreactivity was scarcer, with a scattered appearance. In contrast, only the anti-TTR50-127 antiserum labeled amyloid in the kidney, albeit not all deposits. In this study, we report a patient having a novel TTR variant, ATTR Asn124Ser, with co-localization of kappa light chains in the amyloid deposits in the thyroid tissue.

Les amyloses à transthyrétine

PURPOSE

Transthyretin amyloidoses are the most common form of amyloidosis. Two different types of transthyretin amyloidoses are described, one is rare, familial, its precursor is the mutated transthyretin, this type is called transthyretin amyloid, the other is more common, its precursor is wild transthyretin, this second type is called senile amyloid. The review describes the molecular, clinical and evolutives features of both types.

CURRENT KNOWLEDGE AND KEY POINTS

Transthyretin is a naturally beta-pleated protein. Reported mutations increase its proteolysis resistance and its ability to form amyloid deposits. While transthyretin amyloid is clinically aggressive (neuropathy, cardiomyopathy, nephropathy, and vitreous deposits), senile amyloid is slightly symptomatic (rarely congestive heart failure). The differential diagnosis is essentially based on molecular biology.

FUTURE PROSPECTS AND PROJECTS

Liver transplantation is an effective treatment of transthyretin amyloid because it switches the mutated protein synthesis to the wild protein synthesis. Liver transplantation is sometimes associated with cardiac or kidney transplantation depending of the clinical presentation. Concerning a specific treatment, P component analogous are developed for inhibiting amyloid deposits formation. Tetrameric transthyretin structure stabilisators are in development.

Detailed structural analysis of amyloidogenic wild-type transthyretin using a novel purification strategy and mass spectrometry

Wild-type transthyretin (TTR), normally a soluble plasma-circulating protein, can be amyloidogenic, i.e., form tissue-deposited fibrillar material in the extracellular matrix of various organs throughout the body. Senile systemic amyloidosis (SSA) is one such pathology and features TTR-containing amyloid deposits that are found primarily in the heart. The cause for this transition from soluble to insoluble protein in SSA is yet to be determined as specific structural features that might favor TTR fibrillogenesis have not yet been identified. The precise characterization of ex vivo fibril deposits might provide insight, but structural analyses of TTR from amyloid deposits have been hindered thus far by the lack of purification strategies that overcome the insolubility of the tissue-derived protein without degrading it. Consequently, the true biochemical nature of deposited TTR remains in question. In this study, we provide detailed analyses of both the soluble (serum) and deposited (tissue) forms of TTR from cases of SSA. In the serum, a distribution of mixed disulfides, specifically S-sulfonated and S-cysteinylated forms of TTR, as well as the unmodified protein were identified. The relative levels of the three TTR species in the SSA group were comparable to amounts present in sera from age-matched control groups. For characterization of the amyloid deposited TTR, we investigated cardiac tissue samples obtained from three separate cases of SSA. We report a novel chromatographic purification strategy performed under nonreducing conditions (to maintain cysteine disulfide status) and the use of this procedure in conjunction with detailed mass spectrometric analysis of TTR from the amyloid deposits. A series of C-terminal TTR fragments with N-termini ranging from amino acids 46 to 55 were identified. We also determined that the deposits in all samples contained Cys10 disulfide-linkedhomodimers composed of full-length TTR monomers. This last finding suggests an important role for Cys10 conjugation in the transition from soluble TTR to the pathological amyloid fibril.