The genetics of the amyloidoses

Pathophysiology of Cardiac Amyloidosis

Amyloidosis refers to a heterogeneous group of disorders sharing common pathophysiological mechanisms characterized by the extracellular accumulation of fibrillar deposits consisting of the aggregation of misfolded proteins. Cardiac amyloidosis (CA), usually caused by deposition of misfolded transthyretin or immunoglobulin light chains, is an increasingly recognized cause of heart failure burdened by a poor prognosis. CA manifests with a restrictive cardiomyopathy which progressively leads to biventricular thickening, diastolic and then systolic dysfunction, arrhythmias, and valvular disease. The pathophysiology of CA is multifactorial and includes increased oxidative stress, mitochondrial damage, apoptosis, impaired metabolism, and modifications of intracellular calcium balance.

Effect of alanine versus serine at position 88 of human transthyretin mutants on the protein stability

Human transthyretin (TTR) is a homo-tetrameric plasma protein associated with a high percentage of β-sheet forming amyloid fibrils. It accumulates in tissues or extracellular matrices to cause amyloid diseases. Free energy simulations with thermodynamic integration based on all-atom molecular dynamics simulations have been carried out to analyze the effects of the His88 → Ala and Ser mutations on the stability of human TTR. The calculated free energy change differences (ΔΔG) caused by the His88 → Ala and His88 → Ser mutations are -1.84 ± 0.86 and 7.56 ± 0.55 kcal/mol, respectively, which are in excellent agreement with prior reported experimental values. The simulation results show that the H88A mutant is more stable than the wild type, whereas the H88S mutant is less stable than the wild type. The free energy component analysis shows that the contribution to the free energy change difference (ΔΔG) for the His88 → Ala and His88 → Ser mutations mainly arise from electrostatic and van der Waals interactions, respectively. The electrostatic term stabilizes the H88A mutant more than the wild type, but the van der Waals interaction destabilizes the H88S mutant relative to the wild type. Individual residue contributions to the free energy change show neighboring residues exert stabilizing and destabilizing influence on the mutants. The implications of the simulation results for understanding the stabilizing and destabilizing effect and its contribution to protein stability are discussed.

Alzheimer’s disease – the journey of a healthy brain into organ failure

As the most common dementia, Alzheimer’s disease (AD) exacts an immense personal, societal, and economic toll. AD was first described at the neuropathological level in the early 1900s. Today, we have mechanistic insight into select aspects of AD pathogenesis and have the ability to clinically detect and diagnose AD and underlying AD pathologies in living patients. These insights demonstrate that AD is a complex, insidious, degenerative proteinopathy triggered by Aβ aggregate formation. Over time Aβ pathology drives neurofibrillary tangle (NFT) pathology, dysfunction of virtually all cell types in the brain, and ultimately, overt neurodegeneration. Yet, large gaps in our knowledge of AD pathophysiology and huge unmet medical need remain. Though we largely conceptualize AD as a disease of aging, heritable and non-heritable factors impact brain physiology, either continuously or at specific time points during the lifespan, and thereby alter risk for devolvement of AD. Herein, I describe the lifelong journey of a healthy brain from birth to death with AD, while acknowledging the many knowledge gaps that remain regarding our understanding of AD pathogenesis. To ensure the current lexicon surrounding AD changes from inevitable, incurable, and poorly manageable to a lexicon of preventable, curable, and manageable we must address these knowledge gaps, develop therapies that have a bigger impact on clinical symptoms or progression of disease and use these interventions at the appropriate stage of disease.

Transthyretin cardiac amyloidosis in continental Western Europe: an insight through the Transthyretin Amyloidosis Outcomes Survey (THAOS)

AIMS

Transthyretin amyloidosis (ATTR amyloidosis) is a heterogeneous disorder with cardiac, neurologic, and mixed phenotypes. We describe the phenotypic and genotypic profiles of this disease in continental Western Europe as it appears from the Transthyretin Amyloidosis Survey (THAOS).

METHODS AND RESULTS

THAOS is an ongoing, worldwide, longitudinal, observational survey established to study differences in presentation, diagnosis, and natural history in ATTR amyloidosis subjects. At data cut-off, 1411 symptomatic subjects from nine continental Western European countries were enrolled in THAOS [1286 hereditary (ATTRm) amyloidosis; 125 wild-type ATTR (ATTRwt) amyloidosis]. Genotypes and phenotypes varied notably by country. Four mutations (Val122Ile, Leu111Met, Thr60Ala, and Ile68Leu), and ATTRwt, were associated with a mainly cardiac phenotype showing symmetric left ventricular (LV) hypertrophy, normal diastolic LV dimensions and volume, and mildly depressed LV ejection fraction (LVEF). Morphologic and functional abnormalities on echocardiogram were significantly more severe in subjects with cardiac (n'= 210), compared with a mixed (n = 298), phenotype: higher median (Q1-Q3) interventricular septal thickness [18 (16-21) vs. 16 (13-20) mm; P = 0.0006]; and more frequent incidence of LVEF <50% (38.1 vs. 17.5%; P = 0.0008). Subjects with cardiac mutations or ATTRwt (or cardiac or mixed phenotype) had a lower survival rate than subjects in other genotype (or the neurologic phenotype) categories (P < 0.0001, for both).

CONCLUSION

ATTR amyloidosis genotypes and phenotypes are highly heterogeneous in continental Western Europe. A geographic map of the different disease profiles and awareness that a subset of subjects have a dominant cardiac phenotype, mimicking hypertrophic cardiomyopathy, at presentation can facilitate the clinical recognition of this underdiagnosed disease.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00628745.

Synthesis and biological evaluation of quinolone derivatives as transthyretin amyloidogenesis inhibitors and fluorescence sensors

Under certain conditions, numerous soluble proteins possess an inherent tendency to convert into insoluble amyloid aggregates, which are associated with several sporadic and genetic human diseases. Transthyretin (TTR) is one of the more than 30 human amyloidogenic proteins involved in conditions such as senile systemic amyloidosis, familial amyloid polyneuropathy, and familial amyloid cardiomyopathy. Considerable effort has been focused on identifying the native tetrameric TTR stabilizers to inhibit rate-limiting tetramer dissociation and, consequently, ameliorate TTR amyloidogenesis. Here, we describe the design and synthesis of quinolin-2(1H)-one derivatives that could be structurally complementary to the thyroxine-binding site within tetrameric TTR. Among these quinolin-2(1H)-one derivatives, compound 7a allowed 16.7% of V30M-TTR (3.6 μM) fibril formation at the same concentration and 49.6% at a concentration of 1.8 μM. Compound 7a exhibited much greater potency in complex biological samples like human plasma than that observed with tafamidis, the drug approved for the treatment of TTR amyloid cardiomyopathy for wild-type or hereditary TTR-mediated amyloidosis. Furthermore, the unique spectral properties of compound 7a demonstrated its high potential for TTR quantification, imaging sensors, and fluorescent tools to study the mechanism of TTR amyloidogenesis.

Assessing Cardiac Amyloidosis Subtypes by Unsupervised Phenotype Clustering Analysis

BACKGROUND

Cardiac amyloidosis (CA) is a set of amyloid diseases with usually predominant cardiac symptoms, including light-chain amyloidosis (AL), hereditary variant transthyretin amyloidosis (ATTRv), and wild-type transthyretin amyloidosis (ATTRwt). CA are characterized by high heterogeneity in phenotypes leading to diagnosis delay and worsened outcomes.

OBJECTIVES

The authors used clustering analysis to identify typical clinical profiles in a large population of patients with suspected CA.

METHODS

Data were collected from the French Referral Center for Cardiac Amyloidosis database (Hôpital Henri Mondor, Créteil), including 1,394 patients with suspected CA between 2010 and 2018: 345 (25%) had a diagnosis of AL, 263 (19%) ATTRv, 402 (29%) ATTRwt, and 384 (28%) no amyloidosis. Based on comprehensive clinicobiological phenotyping, unsupervised clustering analyses were performed by artificial neural network-based self-organizing maps to identify patient profiles (clusters) with similar characteristics, independent of the final diagnosis and prognosis.

RESULTS

Mean age and left ventricular ejection fraction were 72 ± 13 years and 52% ± 13%, respectively. The authors identified 7 clusters of patients with contrasting profiles and prognosis. AL patients were distinctively located within a typical cluster; ATTRv patients were distributed across 4 clusters with varying clinical presentations, 1 of which overlapped with patients without amyloidosis; interestingly, ATTRwt patients spread across 3 distinct clusters with contrasting risk factors, biological profiles, and prognosis.

CONCLUSIONS

Clustering analysis identified 7 clinical profiles with varying characteristics, prognosis, and associations with diagnosis. Especially in patients with ATTRwt, these results suggest key areas to improve amyloidosis diagnosis and stratify prognosis depending on associated risk factors.

Cardiovascular Involvement in Transthyretin Cardiac Amyloidosis

Transthyretin cardiac amyloidosis (ATTR-CA) is a systemic disorder resulting from the extracellular deposition of amyloid fibrils of misfolded transthyretin protein in the heart. ATTR-CA is a life-threatening disease, which can be caused by progressive deposition of wild type transthyretin (wtATTR) or by aggregation of an inherited mutated variant of transthyretin (mATTR). mATTR Is a rare condition transmitted in an autosomal dominant manner with incomplete penetrance, causing heterogenous phenotypes which can range from predominant neuropathic involvement, predominant cardiomyopathy, or mixed. Diagnosis of ATTR-CA is complex and requires integration of different imaging tools (echocardiography, bone scintigraphy, magnetic resonance) with genetics, clinical signs, laboratory tests, and histology. In recent years, new therapeutic agents have shown good efficacy and impact on survival and quality of life in this subset of patients, nevertheless patients affected by ATTR-CA may still carry an unfavorable prognosis, thus highlighting the need for new therapies. This review aims to assess cardiovascular involvement, diagnosis, and management of patients affected by ATTR-CA.

Common Factors of Alzheimer's Disease and Rheumatoid Arthritis-Pathomechanism and Treatment

The accumulation of amyloid plaques, or misfolded fragments of proteins, leads to the development of a condition known as amyloidosis, which is clinically recognized as a systemic disease. Amyloidosis plays a special role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease, and rheumatoid arthritis (RA). The occurrence of amyloidosis correlates with the aging process of the organism, and since nowadays, old age is determined by the comfort of functioning and the elimination of unpleasant disease symptoms in the elderly, exposure to this subject is justified. In Alzheimer's disease, amyloid plaques negatively affect glutaminergic and cholinergic transmission and loss of sympathetic protein, while in RA, amyloids stimulated by the activity of the immune system affect the degradation of the osteoarticular bond. The following monograph draws attention to the over-reactivity of the immune system in AD and RA, describes the functionality of the blood-brain barrier as an intermediary medium between RA and AD, and indicates the direction of research to date, focusing on determining the relationship and the cause-effect link between these disorders. The paper presents possible directions for the treatment of amyloidosis, with particular emphasis on innovative therapies.

Systemic Amyloidosis: a Contemporary Overview

Amyloidosis constitutes a large spectrum of diseases characterized by an extracellular deposition of a fibrillar aggregate, generating insoluble and toxic amasses that may be deposited in tissues in bundles with an abnormal cross-β-sheet conformation, known as amyloid. Amyloid may lead to a cell damage and an impairment of organ function. Several different proteins are recognized as able to produce amyloid fibrils with a different tissue tropism related to the molecular structure. The deposition of amyloid may occur as a consequence of the presence of an abnormal protein, caused by high plasma levels of a normal protein, or as a result of the aging process along with some environmental factors. Although amyloidosis is rare, amyloid deposits play a role in several conditions as degenerative diseases. Thus, the development of antiamyloid curative treatments may be a rational approach to treat neurodegenerative conditions like Alzheimer's disease in the future. Nowadays, novel treatment options are currently refined through controlled trials, as new drug targets and different therapeutic approaches have been identified and validated through modern advances in basic research. Fibril formation stabilizers, proteasome inhibitors, and immunotherapy revealed promising results in improving the outcomes of patients with systemic amyloidosis, and these novel algorithms will be effectively combined with current treatments based on chemotherapeutic regimens. The aim of this review is to provide an update on diagnosis and treatment for systemic amyloidosis.

Testicular Involvement is a Hallmark of Apo A-I Leu75Pro Mutation Amyloidosis

CONTEXT

Apo A-I Leu75Pro is a rare hereditary form of amyloidosis that mainly involves the kidney, the liver, and the testis.

OBJECTIVE

To define the characteristics of organ damage and testis impairment in the largest cohort collected to date of men with Apo A-I Leu75Pro amyloidosis.

DESIGN, SETTING, AND PATIENTS

Retrospective study from a prospectively collected database of 129 male subjects >18 years with Apo A-I Leu75Pro amyloidosis from a reference center at the University Hospital of Brescia, Italy.

MAIN OUTCOME MEASURES

We evaluated liver and renal function, scrotal ultrasound, reproductive hormone levels, testis biopsy, hypogonadal symptoms, and fertility.

RESULTS

Progressive involvement of testis, kidney, and liver was observed in 96/129 (74.4%) cases. Testis impairment was found in 88/129 patients (68.2%), liver in 59 (45.7%) and renal in 50 (38.8%). Testis damage was often the first manifestation of the disease and the only dysfunction in 30% of younger patients (<38 years). Testicular involvement was characterized mainly by primary (73/88 patients, 83.0%) and subclinical (8/88, 9.1%) hypogonadism. Almost all (85/88, 96.6%) also had high follicle-stimulating hormone, suggesting a primary global damage of endocrine and spermatogenic functions, and 30% of them did not conceive. Macroorchidism was found in 53/88 (60.2%) patients, especially in men <54 years (30/33, 90.9%). Apo A-I amyloid deposits were found in Sertoli cells, germinal epithelium, and vessel walls.

CONCLUSION

In men with Apo A-I Leu75Pro amyloidosis, testicular involvement is the hallmark of the disease, characterized by global primary testicular dysfunction and macroorchidism due to amyloid deposits.

Electrophysiological parameters that contribute to the pathogenesis of familial amyloid polyneuropathy caused by transthyretin mutations

Familial amyloid polyneuropathy (FAP) is a rare, hereditary peripheral neuropathy commonly caused by mutations in human transthyretin (TTR) gene. Clinically, FAP caused by TTR mutations (TTR-FAP) involves both large and small nerve fibers. Details of early electrophysiological features in TTR-FAP remain unclear. To address this issue, we evaluated nerve excitability (NET) results in motor axons of control mice and two transgenic mouse models carrying V30M (TTR^V30M) or A97S (TTR^A97S) mutations that simulate clinical features of TTR-FAP. Transgenic TTR^V30M and TTR^A97S mice demonstrated significant increases in latency in hindlimb withdraw tests, as well as, poor rotarod test performance, compared to TTR^ORF mice. NET evaluation showed reduced S2 accommodation, and increased TEd_undershoot during threshold electrotonus (TE) in motor axons of both TTR^V30M and TTR^A97S mice, indicating that axonal membranes were in a depolarized state. Decreased rheobase combined with increased refractoriness in the transgenic mice suggested that there were reduced sodium currents. Further immunohistochemical study of the sciatic nerves revealed the significantly decrease of voltage-gated sodium channel expression in the transgenic mice. Moreover, superexcitability during the recovery cycle is significantly increased in transgenic mice compared with control mice, which is attributed to increased internodal capacitance. Finally, the electron microscopy demonstrated the reduced g-ratio in TTR^A97S mice may correlate with an atrophic change of axons and/or increase of myelin thickness. In summary, we evaluated NET results in transgenic mice which modeled the clinical features presented in TTR-FAP patients. Reduced sodium channel expression and increased internodal capacitance are factors contributing to the electrophysiological changes in TTR-FAP.

New sequence variants in patients affected by amyloidosis show transthyretin instability by isoelectric focusing

The plasma protein transthyretin (TTR) can aggregate into insoluble amyloid fibrils causing systemic amyloidosis (ATTR amyloidosis) in patients carrying a variant TTR protein. If new variants arise, it is crucial to clarify whether they are disease-associated or benign. In this study, we further functionally characterize three new and unclassified TTR variants (Thr40Asn, Phe64Val and the described but not functionally assessed variant Leu12Val), using a simplified, fast isoelectric focusing (IEF) approach. After validating the system with known TTR variants, we assessed the sera of five patients carrying these new TTR variants in a heterozygous state. All three variants showed aberrant banding patterns that were similar to those of other well-characterized TTR variants, including the common Val30Met variant that causes ATTR amyloidosis. In addition to a clear band corresponding to monomeric wild-type TTR, we observed an additional variant band at the cathodal side of the IEF gel. These results indicate conformational instability of the new Thr40Asn, Phe64Val and Leu12Val variants. Together with the clinical and immunohistological data of these patients and affected family members, as well as the absence of these variants in human genetic mutation databases, our results strongly hint that these variants are amyloidogenic and therefore probably disease-associated. These findings have implications for patient therapy and for genetic counselling of family members.

Development and validation of a TTR-specific copy number screening tool, and application to potentially relevant patient cohorts

TTR amyloidosis (ATTR) is a fatal condition caused by extracellular deposits of misfolded transthyretin. Patients often present with cardiac disease, but manifestations may also involve other organs including the peripheral nervous system. ATTR is considered familial when heterozygous mutations in the TTR gene are present (ATTRmutant or ATTRm), or acquired when no TTR aberrations are detected (ATTRwildtype or ATTRwt). We hypothesized that TTR copy number variants (CNVs), which would escape the standard diagnostic approaches, contribute to ATTR-related phenotypes, and developed a multiplex ligation-dependent probe amplification-based (MLPA-based), TTR-specific copy number screening tool. High inter-sample and intra-sample homogeneity of MLPA signals and the expected drop in signal intensity for restriction digest-based positive controls validated this tool. Subsequent application to 13 patients diagnosed with ATTRwt, and to 93 patients presenting with late onset and presumably inherited polyneuropathy did not identify TTR CNVs. We discuss insufficient sensitivity of the assay as well as non-existence and non-pathogenicity of TTR CNVs as potentially underlying our negative finding, but suggest size and composition of our cohorts as more likely explanations. Our CNV-screening tool will be made available to initiatives interested in screening additional and potentially more appropriate patient samples.

Genotype and Phenotype of Transthyretin Cardiac Amyloidosis: THAOS (Transthyretin Amyloid Outcome Survey)

BACKGROUND

Transthyretin amyloidosis (ATTR) is a heterogeneous disorder with multiorgan involvement and a genetic or nongenetic basis.

OBJECTIVES

The goal of this study was to describe ATTR in the United States by using data from the THAOS (Transthyretin Amyloidosis Outcomes Survey) registry.

METHODS

Demographic, clinical, and genetic features of patients enrolled in the THAOS registry in the United States (n = 390) were compared with data from patients from other regions of the world (ROW) (n = 2,140). The focus was on the phenotypic expression and survival in the majority of U.S. subjects with valine-to-isoleucine substitution at position 122 (Val122Ile) (n = 91) and wild-type ATTR (n = 189).

RESULTS

U.S. subjects are older (70 vs. 46 years), more often male (85.4% vs. 50.6%), and more often of African descent (25.4% vs. 0.5%) than the ROW. A significantly higher percentage of U.S. patients with ATTR amyloid seen at cardiology sites had wild-type disease than the ROW (50.5% vs. 26.2%). In the United States, 34 different mutations (n = 201) have been reported, with the most common being Val122Ile (n = 91; 45.3%) and Thr60Ala (n = 41; 20.4%). Overall, 91 (85%) of 107 patients with Val122Ile were from the United States, where Val122Ile subjects were younger and more often female and black than patients with wild-type disease, and had similar cardiac phenotype but a greater burden of neurologic symptoms (pain, numbness, tingling, and walking disability) and worse quality of life. Advancing age and lower mean arterial pressure, but not the presence of a transthyretin mutation, were independently associated with higher mortality from a multivariate analysis of survival.

CONCLUSIONS

In the THAOS registry, ATTR in the United States is overwhelmingly a disorder of older adult male subjects with a cardiac-predominant phenotype. Val122Ile is the most common transthyretin mutation, and neurologic phenotypic expression differs between wild-type disease and Val122Ile, but survival from enrollment in THAOS does not. (Transthyretin-Associated Amyloidoses Outcome Survey [THAOS]; NCT00628745).

Stability and crystal structures of His88 mutant human transthyretins

Destabilization of human transthyretin (TTR) has been implicated in its misfolding and aggregation. A previous study on the neutron crystal structure of TTR suggested that a large hydrogen bond network around H88 which includes water molecules is significantly involved in the stability of wild-type TTR (WT-TTR). Here, we demonstrate that the H88R mutant associated with amyloid cardiomyopathy is substantially destabilized compared with WT-TTR. In order to clarify the role of H88 and the hydrogen bond network in the stability of TTR, we determined the thermodynamic stability and the crystal structure of H88 mutants (H88A, H88F, H88Y, and H88S). Our results suggest that in some cases TTR is destabilized due to alterations in bound water molecules as well as structural changes in TTR itself.

Semi-quantitative models for identifying potent and selective transthyretin amyloidogenesis inhibitors

Rate-limiting dissociation of the tetrameric protein transthyretin (TTR), followed by monomer misfolding and misassembly, appears to cause degenerative diseases in humans known as the transthyretin amyloidoses, based on human genetic, biochemical and pharmacologic evidence. Small molecules that bind to the generally unoccupied thyroxine binding pockets in the native TTR tetramer kinetically stabilize the tetramer, slowing subunit dissociation proportional to the extent that the molecules stabilize the native state over the dissociative transition state-thereby inhibiting amyloidogenesis. Herein, we use previously reported structure-activity relationship data to develop two semi-quantitative algorithms for identifying the structures of potent and selective transthyretin kinetic stabilizers/amyloidogenesis inhibitors. The viability of these prediction algorithms, in particular the more robust in silico docking model, is perhaps best validated by the clinical success of tafamidis, the first-in-class drug approved in Europe, Japan, South America, and elsewhere for treating transthyretin aggregation-associated familial amyloid polyneuropathy. Tafamidis is also being evaluated in a fully-enrolled placebo-controlled clinical trial for its efficacy against TTR cardiomyopathy. These prediction algorithms will be useful for identifying second generation TTR kinetic stabilizers, should these be needed to ameliorate the central nervous system or ophthalmologic pathology caused by TTR aggregation in organs not accessed by oral tafamidis administration.

Identification of Transthyretin Fibril Formation Inhibitors Using Structure-Based Virtual Screening

Transthyretin (TTR) is the primary carrier for thyroxine (T₄ ) in cerebrospinal fluid and a secondary carrier in blood. TTR is a stable homotetramer, but certain factors, genetic or environmental, could promote its degradation to form amyloid fibrils. A docking study using crystal structures of wild-type TTR was planned; our aim was to design new ligands that are able to inhibit TTR fibril formation. The computational protocol was thought to overcome the multiple binding modes of the ligands induced by the peculiarity of the TTR binding site and by the pseudosymmetry of the site pockets, which generally weaken such structure-based studies. Two docking steps, one that is very fast and a subsequent step that is more accurate, were used to screen the Aldrich Market Select database. Five compounds were selected, and their activity toward inhibiting TTR fibril formation was assessed. Three compounds were observed to be actives, two of which have the same potency as the positive control, and the other was found to be a promising lead compound. These results validate a computational protocol that is able to archive information on the key interactions between database compounds and TTR, which is valuable for supporting further studies.

Insight of brain degenerative protein modifications in the pathology of neurodegeneration and dementia by proteomic profiling

Dementia is a syndrome associated with a wide range of clinical features including progressive cognitive decline and patient inability to self-care. Due to rapidly increasing prevalence in aging society, dementia now confers a major economic, social, and healthcare burden throughout the world, and has therefore been identified as a public health priority by the World Health Organization. Previous studies have established dementia as a 'proteinopathy' caused by detrimental changes in brain protein structure and function that promote misfolding, aggregation, and deposition as insoluble amyloid plaques. Despite clear evidence that pathological cognitive decline is associated with degenerative protein modifications (DPMs) arising from spontaneous chemical modifications to amino acid side chains, the molecular mechanisms that promote brain DPMs formation remain poorly understood. However, the technical challenges associated with DPM analysis have recently become tractable due to powerful new proteomic techniques that facilitate detailed analysis of brain tissue damage over time. Recent studies have identified that neurodegenerative diseases are associated with the dysregulation of critical repair enzymes, as well as the misfolding, aggregation and accumulation of modified brain proteins. Future studies will further elucidate the mechanisms underlying dementia pathogenesis via the quantitative profiling of the human brain proteome and associated DPMs in distinct phases and subtypes of disease. This review summarizes recent developments in quantitative proteomic technologies, describes how these techniques have been applied to the study of dementia-linked changes in brain protein structure and function, and briefly outlines how these findings might be translated into novel clinical applications for dementia patients. In this review, only spontaneous protein modifications such as deamidation, oxidation, nitration glycation and carbamylation are reviewed and discussed.

Apolipoprotein C-II Deposition Amyloidosis: A Potential Misdiagnosis as Light Chain Amyloidosis

Hereditary amyloidoses are rare and pose a diagnostic challenge. We report a case of hereditary amyloidosis associated with apolipoprotein C-II deposition in a 61-year-old female presenting with renal failure and nephrotic syndrome misdiagnosed as light chain amyloidosis. Renal biopsy was consistent with amyloidosis on microscopy; however, immunofluorescence was inconclusive for the type of amyloid protein. Monoclonal gammopathy evaluation revealed kappa light chain. Bone marrow biopsy revealed minimal involvement with amyloidosis with kappa monotypic plasma cells on flow cytometry. She was started on chemotherapy for light chain amyloidosis. She was referred to the Mayo clinic where laser microdissection and liquid chromatography mass spectrometry detected high levels of apolipoprotein C-II, making a definitive diagnosis. Apolipoprotein C-II is a component of very low-density lipoprotein and aggregates in lipid-free conditions to form amyloid fibrils. The identification of apolipoprotein C-II as the cause of amyloidosis cannot be solely made with routine microscopy or immunofluorescence. Further evaluation of biopsy specimens with laser microdissection and mass spectrometry and DNA sequencing of exons should be done routinely in patients with amyloidoses for definitive diagnosis. Our case highlights the importance of determining the subtype of amyloidosis that is critical for avoiding unnecessary therapy such as chemotherapy.

Systemic optimization and structural evaluation of quinoline derivatives as transthyretin amyloidogenesis inhibitors

Wild type transthyretin (TTR) and mutant TTR misfold and misassemble into a variety of extracellular insoluble amyloid fibril and/or amorphous aggregate, which are associated with a variety of human amyloid diseases. To develop potent TTR amyloidogenesis inhibitors, we have designed and synthesized a focused library of quinoline derivatives by Pd-catalyzed coupling reaction and by the Horner-Wadsworth-Emmons reaction. The resulting 2-alkynylquinoline derivatives, (E)-2-alkenylquinoline derivatives, and (E)-3-alkenylquinoline derivatives were evaluated to inhibit TTR amyloidogenesis by utilizing the acid-mediated TTR fibril formation. Among these quinoline derivatives, compound 14c exhibited the most potent anti-TTR fibril formation activity in the screening studies, with IC50 values of 1.49 μM against WT-TTR and 1.63 μM against more amyloidogenic V30 M TTR mutant. That is comparable to that of approved therapeutic drug, tafamidis, to ameliorate transthyretin-related amyloidosis. Furthermore, rationalization of the increased efficacy of compound 14c bearing a hydrophobic substituent, such as chloride, was carried out by utilizing in silico docking study that could focus on the region of the thyroid hormone thyroxine (T4) binding sites. Additionally, the most potent compound 14c exhibited good pharmacokinetics properties. Taken together, the novel quinoline derivatives could potentially be explored as potential drug candidates to treat the human TTR amyloidosis.

Synthesis and structural analysis of halogen substituted fibril formation inhibitors of Human Transthyretin (TTR)

Transthyretin (TTR), a β-sheet-rich tetrameric protein, in equilibrium with an unstable amyloidogenic monomeric form is responsible for extracellular deposition of amyloid fibrils, is associated with the onset of neurodegenerative diseases, such as senile systemic amyloidosis, familial amyloid polyneuropathy and familial amyloid cardiomyopathy. One of the therapeutic strategies is to use small molecules to stabilize the TTR tetramer and thus curb amyloid fibril formation. Here, we report the synthesis, the in vitro evaluation of several halogen substituted 9-fluorenyl- and di-benzophenon-based ligands and their three-dimensional crystallographic analysis in complex with TTR. The synthesized compounds bind TTR and stabilize the tetramer with different potency. Of these compounds, 2c is the best inhibitor. The dual binding mode prevalent in the absence of substitutions on the fluorenyl ring, is disfavored by (2,7-dichloro-fluoren-9-ylideneaminooxy)-acetic acid (1b), (2,7-dibromo-fluoren-9-ylideneaminooxy)-acetic acid (1c) and (E/Z)-((3,4-dichloro-phenyl)-methyleneaminooxy)-acetic acid (2c), all with halogen substitutions.

Models for the binding channel of wild type and mutant transthyretin with glabridin

Our results indicate that additional high-occupancy hydrogen bonds were observed at the binding interface between the two dimers in V30A TTR, while stabilisation hydrophobic interactions between residues in the mutant AB loop decreased.

The Temporal Profiles of Changes in Nerve Excitability Indices in Familial Amyloid Polyneuropathy

Familial amyloid polyneuropathy (FAP) caused by a mutation in transthyretin (TTR) gene is an autosomal dominant inherited disorder. The aim of this study is to explore the pathophysiological mechanism of FAP. We prospectively recruited 12 pauci-symptomatic carriers, 18 patients who harbor a TTR mutation, p.A97S, and two-age matched control groups. Data of nerve excitability test (NET) from ulnar motor and sensory axons were collected.NET study of ulnar motor axons of patients shows increased threshold and rheobase, reduced threshold elevation during hyperpolarizing threshold electrotonus (TE), and increased refractoriness. In sensory nerve studies, there are increased threshold reduction in depolarizing TE, lower slope of recovery and delayed time to overshoot after hyperpolarizing TE, increased refractoriness and superexcitability in recovery cycle. NET profiles obtained from the ulnar nerve of carriers show the increase of threshold and rheobase, whereas no significant threshold changes in hyperpolarizing TE and superexcitability. The regression models demonstrate that the increase of refractoriness and prolonged relative refractory period are correlated to the disease progression from carriers to patients. The marked increase of refractoriness at short-width stimulus suggests a defect in sodium current which may represent an early, pre-symptomatic pathophysiological change in TTR-FAP. Focal disruption of basal lamina and myelin may further increase the internodal capacity, manifested by the lower slope of recovery and delayed time to overshoot after hyperpolarization TE as well as the increase of superexcitability. NET could therefore make a pragmatic tool for monitoring disease progress from the very early stage of TTR-FAP.

The putative role of some conserved water molecules in the structure and function of human transthyretin

Human transthyretin (hTTR) is a multifunctional protein that is involved in several neurodegenerative diseases. Besides the transportation of thyroxin and vitamin A, it is also involved in the proteolysis of apolipoprotein A1 and Aβ peptide. Extensive analyses of 32 high-resolution X-ray and neutron diffraction structures of hTTR followed by molecular-dynamics simulation studies using a set of 15 selected structures affirmed the presence of 44 conserved water molecules in its dimeric structure. They are found to play several important roles in the structure and function of the protein. Eight water molecules stabilize the dimeric structure through an extensive hydrogen-bonding network. The absence of some of these water molecules in highly acidic conditions (pH ≤ 4.0) severely affects the interfacial hydrogen-bond network, which may destabilize the native tetrameric structure, leading to its dissociation. Three pairs of conserved water molecules contribute to maintaining the geometry of the ligand-binding cavities. Some other water molecules control the orientation and dynamics of different structural elements of hTTR. This systematic study of the location, absence, networking and interactions of the conserved water molecules may shed some light on various structural and functional aspects of the protein. The present study may also provide some rational clues about the conserved water-mediated architecture and stability of hTTR.

X-ray crystal structure and activity of fluorenyl-based compounds as transthyretin fibrillogenesis inhibitors

Transthyretin (TTR) is a 54 kDa homotetrameric protein that transports thyroxine (T4) and retinol (vitamin A), through its association with retinol binding protein (RBP). Under unknown conditions, it aggregates to form fibrils associated with TTR amyloidosis. Ligands able to inhibit fibril formation have been studied by X-ray crystallography. The use of polyethylene glycol (PEG) instead of ammonium sulphate or citrate has been evaluated as an alternative to obtain new TTR complexes with (R)-3-(9-fluoren-9-ylideneaminooxy)-2-methyl-N-(methylsulfonyl) propionamide (48R(1)) and 2-(9H-fluoren-9-ylideneaminooxy) acetic acid (ES8(2)). The previously described fluorenyl based inhibitors (S)-3-((9H-fluoren-9-ylideneamino)oxy)-2-methylpropanoic acid (6BD) and 3-((9H-fluoren-9-ylideneamino)oxy)propanoic acid (7BD) have been re-evaluated with the changed crystallization method. The new TTR complexes with compounds of the same family show that the 9-fluorenyl motif can occupy alternative hydrophobic binding sites. This augments the potential use of this scaffold to yield a large variety of differently substituted mono-aryl compounds able to inhibit TTR fibril formation.

In vivo detection of nerve injury in familial amyloid polyneuropathy by magnetic resonance neurography

See Morrow and Reilly (doi:10.1093/awu396) for a scientific commentary on this article.

Transthyretin familial amyloid polyneuropathy is a rare, autosomal-dominant multisystem disorder. Kollmer et al. show that high-resolution MR-neurography can quantify and localize lower limb nerve injury in vivo, both in symptomatic patients and in asymptomatic mutation carriers. Lesions appear at thigh-level and are predominantly proximal, although symptoms start and prevail distally.

Transthyretin familial amyloid polyneuropathy is a rare, autosomal-dominant inherited multisystem disorder usually manifesting with a rapidly progressive, axonal, distally-symmetric polyneuropathy. The detection of nerve injury by nerve conduction studies is limited, due to preferential involvement of small-fibres in early stages. We investigated whether lower limb nerve-injury can be detected, localized and quantified in vivo by high-resolution magnetic resonance neurography. We prospectively included 20 patients (12 male and eight female patients, mean age 47.9 years, range 26–66) with confirmed mutation in the transthyretin gene: 13 with symptomatic polyneuropathy and seven asymptomatic gene carriers. A large age- and sex-matched cohort of healthy volunteers served as controls (20 male and 20 female, mean age 48.1 years, range 30–73). All patients received detailed neurological and electrophysiological examinations and were scored using the Neuropathy Impairment Score–Lower Limbs, Neuropathy Deficit and Neuropathy Symptom Score. Magnetic resonance neurography (3 T) was performed with large longitudinal coverage from proximal thigh to ankle-level and separately for each leg (140 axial slices/leg) by using axial T₂-weighted (repetition time/echo time = 5970/55 ms) and dual echo (repetition time 5210 ms, echo times 12 and 73 ms) turbo spin echo 2D sequences with spectral fat saturation. A 3D T₂-weighted inversion-recovery sequence (repetition time/echo time 3000/202 ms) was acquired for imaging of the spinal nerves and lumbar plexus (50 axial slice reformations). Precise manual segmentation of the spinal/sciatic/tibial/common peroneal nerves was performed on each slice. Histogram-based normalization of nerve–voxel signal intensities was performed using the age- and sex-matched control group as normative reference. Nerve-voxels were subsequently classified as lesion-voxels if a threshold of >1.2 (normalized signal-intensity) was exceeded. At distal thigh level, where a predominant nerve–lesion–voxel burden was observed, signal quantification was performed by calculating proton spin density and T₂-relaxation time as microstructural markers of nerve tissue integrity. The total number of nerve–lesion voxels (cumulated from proximal-to-distal) was significantly higher in symptomatic patients (20 405 ± 1586) versus asymptomatic gene carriers (12 294 ± 3199; P = 0.036) and versus controls (6536 ± 467; P < 0.0001). It was also higher in asymptomatic carriers compared to controls (P = 0.043). The number of nerve–lesion voxels was significantly higher at thigh level compared to more distal levels (lower leg/ankle) of the lower extremities (f-value = 279.22, P < 0.0001). Further signal-quantification at this proximal site (thigh level) revealed a significant increase of proton-density (P < 0.0001) and T₂-relaxation-time (P = 0.0011) in symptomatic patients, whereas asymptomatic gene-carriers presented with a significant increase of proton-density only. Lower limb nerve injury could be detected and quantified in vivo on microstructural level by magnetic resonance neurography in symptomatic familial amyloid polyneuropathy, and also in yet asymptomatic gene carriers, in whom imaging detection precedes clinical and electrophysiological manifestation. Although symptoms start and prevail distally, the focus of predominant nerve injury and injury progression was found proximally at thigh level with strong and unambiguous lesion-contrast. Imaging of proximal nerve lesions, which are difficult to detect by nerve conduction studies, may have future implications also for other distally-symmetric polyneuropathies.

Hydrogen-bond network and pH sensitivity in human transthyretin

Transthyretin (TTR) is a tetrameric protein. TTR misfolding and aggregation are associated with human amyloid diseases. Dissociation of the TTR tetramer is believed to be the rate-limiting step in the amyloid fibril formation cascade. Low pH is known to promote dissociation into monomer and the formation of amyloid fibrils. In order to reveal the molecular mechanisms underlying pH sensitivity and structural stabilities of TTR, neutron diffraction studies were conducted using the IBARAKI Biological Crystal Diffractometer with the time-of-flight method. Crystals for the neutron diffraction experiments were grown up to 2.5 mm(3) for four months. The neutron crystal structure solved at 2.0 Å revealed the protonation states of His88 and the detailed hydrogen-bond network depending on the protonation states of His88. This hydrogen-bond network is involved in monomer-monomer and dimer-dimer interactions, suggesting that the double protonation of His88 by acidification breaks the hydrogen-bond network and causes the destabilization of the TTR tetramer. Structural comparison with the X-ray crystal structure at acidic pH identified the three amino acid residues responsible for the pH sensitivity of TTR. Our neutron model provides insights into the molecular stability related to amyloidosis.

THAOS - The Transthyretin Amyloidosis Outcomes Survey: initial report on clinical manifestations in patients with hereditary and wild-type transthyretin amyloidosis

BACKGROUND

Transthyretin (TTR) amyloidosis is a rare, life-threatening, systemic, autosomal dominant condition occurring in adults, with two main forms: hereditary (associated with TTR gene mutations) and wild-type. Studies indicate considerable heterogeneity in disease presentation, with predominantly polyneuropathic, predominantly cardiac, or mixed phenotypes.

METHODS

THAOS - the Transthyretin Amyloidosis Outcomes Survey - is the first global, multicenter, longitudinal, observational survey that collects data on the natural history of TTR amyloidosis (ClinicalTrials.gov: NCT00628745). This paper presents data on signs and symptoms, neurological and cardiac assessments, biomarkers and quality of life in the patients enrolled in THAOS from its inception in December 2007 to September 2011.

RESULTS

At the time of this analysis, data were available from 611 symptomatic patients with hereditary TTR amyloidosis, 67 symptomatic patients with wild-type TTR amyloidosis, and 274 currently asymptomatic individuals with a TTR mutation. Nineteen countries were participating in the registry. The largest patient groups came from Portugal (n = 453), the USA (n = 129), Italy (n = 70), and Japan (n = 68). Predominant symptom presentation in patients with hereditary TTR amyloidosis differed according to the underlying disease-causing mutation (polyneuropathy for Val30Met, cardiomyopathy for Val122Ile and Leu111Met, and mixed for Glu89Gln). However, each mutation was associated with clear multisystem involvement. Similarly, although cardiomyopathy was predominant in patients with wild-type TTR amyloidosis, many also showed symptoms consistent with neuropathy. Quality of life in patients with hereditary TTR amyloidosis, but not asymptomatic carriers of disease-causing mutations, was severely impaired relative to that of the age-matched general US population.

CONCLUSIONS

This preliminary analysis highlights the considerable phenotypic heterogeneity for neurological and cardiac manifestations in patients with hereditary and wild-type TTR amyloidosis and the necessity of providing multidisciplinary care. THAOS registry data will help better characterize the diverse presentation and course of TTR amyloidosis worldwide and aid in improving and standardizing diagnosis and treatment.

Hydrogen-bond network and pH sensitivity in transthyretin: Neutron crystal structure of human transthyretin

Transthyretin (TTR) is a tetrameric protein associated with human amyloidosis. In vitro, the formation of amyloid fibrils by TTR is known to be promoted by low pH. Here we show the neutron structure of TTR, focusing on the hydrogen bonds, protonation states and pH sensitivities. A large crystal was prepared at pD 7.4 for neutron protein crystallography. Neutron diffraction studies were conducted using the IBARAKI Biological Crystal Diffractometer with the time-of-flight method. The neutron structure solved at 2.0Å resolution revealed the protonation states of His88 and the detailed hydrogen-bond network depending on the protonation states of His88. This hydrogen-bond network is composed of Thr75, Trp79, His88, Ser112, Pro113, Thr118-B and four water molecules, and is involved in both monomer-monomer and dimer-dimer interactions, suggesting that the double protonation of His88 by acidification breaks the hydrogen-bond network and causes the destabilization of the TTR tetramer. In addition, the comparison with X-ray structure at pH 4.0 indicated that the protonation occurred to Asp74, His88 and Glu89 at pH 4.0. Our neutron model provides insights into the molecular stability of TTR related to the hydrogen-bond network, the pH sensitivity and the CH···O weak hydrogen bond.

Misfolded protein aggregates: mechanisms, structures and potential for disease transmission

Some of the most prevalent human degenerative diseases appear as a result of the misfolding and aggregation of proteins. Compelling evidence suggest that misfolded protein aggregates play an important role in cell dysfunction and tissue damage, leading to the disease. Prion protein (Prion diseases), amyloid-beta (Alzheimer's disease), alpha-synuclein (Parkinson's disease), Huntingtin (Huntington's disease), serum amyloid A (AA amyloidosis) and islet amyloid polypeptide (type 2 diabetes) are some of the proteins that trigger disease when they get misfolded. The recent understanding of the crucial role of misfolded proteins as well as the structural requirements and mechanism of protein misfolding have raised the possibility that these diseases may be transmissible by self-propagation of the protein misfolding process in a similar way as the infamous prions transmit prion diseases. Future research in this field should aim to clarify this possibility and translate the knowledge of the basic disease mechanisms into development of novel strategies for early diagnosis and efficient treatment.

A competition assay to identify amyloidogenesis inhibitors by monitoring the fluorescence emitted by the covalent attachment of a stilbene derivative to transthyretin

Herein we demonstrate that competition between candidate kinetic stabilizer binding to transthyretin (TTR) and stilbene binding to and reaction with the same thyroxine sites within TTR can be utilized to discover potent and highly selective non-covalent TTR amyloidogenesis inhibitors. We report two stilbenes, S1 and S2, for use in distinct competition assays. Each bind selectively to TTR and then chemoselectively react to form an amide bond with the Lys-15 residue of TTR, creating a fluorescent conjugate. We used 28 TTR kinetic stabilizers exhibiting a known spectrum of plasma TTR binding selectivities and TTR amyloid fibril inhibition efficacies to validate the 'TTR fluorescence conjugate competition assay'. The kinetic stabilizers competed with S1 for binding to recombinant TTR in buffer and with S2 for binding to endogenous levels of TTR in human blood serum. In both assay scenarios, we demonstrate that the lower the TTR-stilbene conjugate fluorescence after a 3 h competition, the greater the binding selectivity and potency of the candidate TTR kinetic stabilizer. These assays, particularly the assay utilizing S2 in human serum, replace two assays previously utilized to gather the same information. While not the focus of this manuscript, it is clear that the 'TTR fluorescence conjugate competition assay' could be adapted for high throughput screening applications.

A substructure combination strategy to create potent and selective transthyretin kinetic stabilizers that prevent amyloidogenesis and cytotoxicity

Transthyretin aggregation-associated proteotoxicity appears to cause several human amyloid diseases. Rate-limiting tetramer dissociation and monomer misfolding of transthyretin (TTR) occur before its aggregation into cross-beta-sheet amyloid fibrils. Small molecule binding to and preferential stabilization of the tetrameric state of TTR over the dissociative transition state raises the kinetic barrier for dissociation, imposing kinetic stabilization on TTR and preventing aggregation. This is an effective strategy to halt neurodegeneration associated with polyneuropathy, according to recent placebo-controlled clinical trial results. In three recent papers, we systematically ranked possibilities for the three substructures composing a typical TTR kinetic stabilizer, using fibril inhibition potency and plasma TTR binding selectivity data. Herein, we have successfully employed a substructure combination strategy to use these data to develop potent and selective TTR kinetic stabilizers that rescue cells from the cytotoxic effects of TTR amyloidogenesis. Of the 92 stilbene and dihydrostilbene analogues synthesized, nearly all potently inhibit TTR fibril formation. Seventeen of these exhibit a binding stoichiometry of >1.5 of a maximum of 2 to plasma TTR, while displaying minimal binding to the thyroid hormone receptor (<20%). Six analogues were definitively categorized as kinetic stabilizers by evaluating dissociation time-courses. High-resolution TTR.(kinetic stabilizer)(2) crystal structures (1.31-1.70 A) confirmed the anticipated binding orientation of the 3,5-dibromo-4-hydroxyphenyl substructure and revealed a strong preference of the isosteric 3,5-dibromo-4-aminophenyl substructure to bind to the inner thyroxine binding pocket of TTR.

Abeta aggregation and possible implications in Alzheimer's disease pathogenesis

Amyloid β protein (Aβ) has been associated with Alzheimer's disease (AD) because it is a major component of the extracellular plaque found in AD brains. Increased Aβ levels correlate with the cognitive decline observed in AD. Sporadic AD cases are thought to be chiefly associated with lack of Aβ clearance from the brain, unlike familial AD which shows increased Aβ production. Aβ aggregation leading to deposition is an essential event in AD. However, the factors involved in Aβ aggregation and accumulation in sporadic AD have not been completely characterized. This review summarizes studies that have examined the factors that affect Aβ aggregation and toxicity. By necessity these are studies that are performed with recombinant-derived or chemically synthesized Aβ. The studies therefore are not done in animals but in cell culture, which includes neuronal cells, other mammalian cells and, in some cases, non-mammalian cells that also appear susceptible to Aβ toxicity. An understanding of Aβ oligomerization may lead to better strategies to prevent AD.

Novel transthyretin amyloid fibril formation inhibitors: synthesis, biological evaluation, and X-ray structural analysis

Transthyretin (TTR) is one of thirty non-homologous proteins whose misfolding, dissociation, aggregation, and deposition is linked to human amyloid diseases. Previous studies have identified that TTR amyloidogenesis can be inhibited through stabilization of the native tetramer state by small molecule binding to the thyroid hormone sites of TTR. We have evaluated a new series of β-aminoxypropionic acids (compounds 5–21), with a single aromatic moiety (aryl or fluorenyl) linked through a flexible oxime tether to a carboxylic acid. These compounds are structurally distinct from the native ligand thyroxine and typical halogenated biaryl NSAID-like inhibitors to avoid off-target hormonal or anti-inflammatory activity. Based on an in vitro fibril formation assay, five of these compounds showed significant inhibition of TTR amyloidogenesis, with two fluorenyl compounds displaying inhibitor efficacy comparable to the well-known TTR inhibitor diflunisal. Fluorenyl 15 is the most potent compound in this series and importantly does not show off-target anti-inflammatory activity. Crystal structures of the TTR∶inhibitor complexes, in agreement with molecular docking studies, revealed that the aromatic moiety, linked to the sp²-hybridized oxime carbon, specifically directed the ligand in either a forward or reverse binding mode. Compared to the aryl family members, the bulkier fluorenyl analogs achieved more extensive interactions with the binding pockets of TTR and demonstrated better inhibitory activity in the fibril formation assay. Preliminary optimization efforts are described that focused on replacement of the C-terminal acid in both the aryl and fluorenyl series (compounds 22–32). The compounds presented here constitute a new class of TTR inhibitors that may hold promise in treating amyloid diseases associated with TTR misfolding.

Toward optimization of the second aryl substructure common to transthyretin amyloidogenesis inhibitors using biochemical and structural studies

Transthyretin (TTR) amyloidogenesis inhibitors are typically composed of two aromatic rings and a linker. We have previously established optimal structures for one aromatic ring and the linker. Herein, we employ a suboptimal linker and an optimal aryl-X substructure to rank order the desirability of aryl-Z substructures--using a library of 56 N-(3,5-dibromo-4-hydroxyphenyl)benzamides. Coconsideration of amyloid inhibition potency and ex vivo plasma TTR binding selectivity data reveal that 2,6, 2,5, 2, 3,4,5, and 3,5 substituted aryls bearing small substituents generate the most potent and selective inhibitors, in descending order. These benzamides generally lack undesirable thyroid hormone receptor binding and COX-1 inhibition activity. Three high-resolution TTR.inhibitor crystal structures (1.31-1.35 A) provide insight into why these inhibitors are potent and selective, enabling future structure-based design of TTR kinetic stabilizers.