Prevention of transthyretin amyloid disease by changing protein misfolding energetics

Kinetic analysis of the multistep aggregation pathway of human transthyretin

Aggregation of transthyretin (TTR) is the causative agent for TTR cardiomyopathy and polyneuropathy amyloidoses. Aggregation is initiated by dissociation of the TTR tetramer into a monomeric intermediate, which self-assembles into amyloid. The coupled multiple-step equilibria and low-concentration, aggregation-prone intermediates are challenging to probe using conventional assays. We report a ¹⁹F-NMR assay that leverages a highly sensitive trifluoroacetyl probe at a strategic site that gives distinct ¹⁹F chemical shifts for the TTR tetramer and monomeric intermediate and enables direct quantification of their populations during the aggregation process. Integration of real-time ¹⁹F-NMR and turbidity measurements as a function of temperature allows kinetic and mechanistic dissection of the aggregation pathway of both wild-type and mutant TTR. At physiological temperature, the monomeric intermediate formed by wild-type TTR under mildly acidic conditions rapidly aggregates into species that are invisible to NMR, leading to loss of the NMR signal at the same rate as the turbidity increase. Lower temperature accelerates tetramer dissociation and decelerates monomer tetramerization and oligomerization via reduced hydrophobic interactions associated with packing of a phenylalanine (F87) into a neighboring protomer. As a result, the intermediate accumulates to a higher level, and formation of higher-order aggregates is delayed. Application of this assay to pathogenic (V30M, L55P, and V122I) and protective (T119M) mutants revealed significant differences in behavior. A monomeric intermediate was observed only for V122I: aggregation of V30M and L55P proceeds without an observable monomeric intermediate, whereas the protective mutant T119M remains resistant to tetramer dissociation and aggregation.

Autophagy induction by trehalose: Molecular mechanisms and therapeutic impacts

The balance between synthesis and degradation is crucial to maintain cellular homeostasis and different mechanisms are known to keep this balance. In this review, we will provide a short overview on autophagy as an intracellular homeostatic degradative machinery. We will also describe the involvement of downregulation of autophagy in numerous diseases including neurodegenerative diseases, cancer, aging, metabolic disorders, and other infectious diseases. Therefore, modulation of autophagic processes can represent a promising way of intervention in different diseases including neurodegeneration and cancer. Trehalose, also known as mycose, is a natural disaccharide found extensively but not abundantly among several organisms. It is described that trehalose can work as an important autophagy modulator and can be proficiently used in the control several diseases in which autophagy plays an important role. On these bases, we describe here the role of trehalose as an innovative drug in the treatment of neurodegenerative diseases and other illnesses opening a new scenario of intervention in conditions difficult to be treated.

Amyloid assembly and disassembly

Amyloid fibrils are protein homopolymers that adopt diverse cross-β conformations. Some amyloid fibrils are associated with the pathogenesis of devastating neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Conversely, functional amyloids play beneficial roles in melanosome biogenesis, long-term memory formation and release of peptide hormones. Here, we showcase advances in our understanding of amyloid assembly and structure, and how distinct amyloid strains formed by the same protein can cause distinct neurodegenerative diseases. We discuss how mutant steric zippers promote deleterious amyloidogenesis and aberrant liquid-to-gel phase transitions. We also highlight effective strategies to combat amyloidogenesis and related toxicity, including: (1) small-molecule drugs (e.g. tafamidis) to inhibit amyloid formation or (2) stimulate amyloid degradation by the proteasome and autophagy, and (3) protein disaggregases that disassemble toxic amyloid and soluble oligomers. We anticipate that these advances will inspire therapeutics for several fatal neurodegenerative diseases.

Summary: This Review showcases important advances in our understanding of amyloid structure, assembly and disassembly, which are inspiring novel therapeutic strategies for amyloid disorders.

Deep Learning and Its Applications in Biomedicine

Advances in biological and medical technologies have been providing us explosive volumes of biological and physiological data, such as medical images, electroencephalography, genomic and protein sequences. Learning from these data facilitates the understanding of human health and disease. Developed from artificial neural networks, deep learning-based algorithms show great promise in extracting features and learning patterns from complex data. The aim of this paper is to provide an overview of deep learning techniques and some of the state-of-the-art applications in the biomedical field. We first introduce the development of artificial neural network and deep learning. We then describe two main components of deep learning, i.e., deep learning architectures and model optimization. Subsequently, some examples are demonstrated for deep learning applications, including medical image classification, genomic sequence analysis, as well as protein structure classification and prediction. Finally, we offer our perspectives for the future directions in the field of deep learning.

Transthyretin familial amyloid polyneuropathy: an update

Transthyretin familial amyloid polyneuropathy (TTR-FAP) is a progressive, fatal, inherited disorder first identified in Portugal and now recognized in all continents. Over the past decade, thanks to the availability of the genetic test, our knowledge on the range of clinical expressions of this disorder has expanded, including different patterns and progression rates of the neuropathy, as well as aspects of the cardiomyopathy, which can be prominent. In the mean time, new tools are being developed to detect earlier TTR amyloid deposition such as cardiac scintigraphy with technetium-labelled pyrophosphate tracers or small nerve fiber alterations from skin biopsies, or using neurophysiological approaches as well as magnetic resonance neurography (MRN). Such refinements, along with an increased awareness of the disease, should reduce the diagnostic delay and facilitate early treatment. In this regard, thanks to a better understanding of the TTR amyloid formation, major advances have been made, allowing for therapeutic developments which are less invasive than liver transplantation (LT). TTR stabilizer drugs are safe and seem to delay the disease progression in some groups of patients. Indeed, positive results have just been released from 2 phase III trials on TTR gene modifiers, namely silencing RNA and antisense oligonucleotide therapies. These recent advances open a new area in the field with the hope that we can safely bring about long-term stabilization of the disease. Furthermore, immunotherapies targeting the amyloid deposits are being explored.

Fluorotryptophan Incorporation Modulates the Structure and Stability of Transthyretin in a Site-Specific Manner

Abnormal deposition of aggregated wild-type (WT) human transthyretin (TTR) and its pathogenic variants is responsible for cardiomyopathy and neuropathy related to TTR amyloidosis. The tryptophan (Trp) fluorescence measurements typically used to study structural changes of TTR do not yield site-specific information on the two Trp residues per TTR protomer. To obtain such information, tryptophan labeled with fluorine at the 5 and 6 positions (5FW and 6FW) was incorporated into TTR. Fluorescence of 5FW and 6FW-labeled WT-TTR (WT-5FW and WT-6FW) and a single-Trp mutant W41Y showed that the photophysics of incorporated fluoro-Trp is consistent with site-specific solvation of the indole ring of W41 and W79. ¹⁹F-NMR showed that solvent accessibility depends on both the location of the Trp and the position of the fluorine substituent in the indole ring. Unexpectedly, differences were observed in the rates of aggregation, with WT-6FW aggregating more rapidly than WT-5FW or WT-TTR. Real-time ¹⁹F-NMR urea unfolding experiments revealed that WT-5FW is kinetically more stable than WT-6FW, consistent with the aggregation assay. In addition, structural perturbations of residues distant from either Trp site are more extensive in WT-6FW. Notably, residues in the dimer interfaces are perturbed by 6FW at residue 79; pathogenic mutations in these regions are associated with reduced tetramer stability and amyloidogenesis. The differences in behavior that arise from the replacement of a fluorine at the 5-position of a tryptophan with one at the adjacent 6-position emphasize the delicate balance of stability in the TTR tetramer.

Biology and Pathobiology of TDP-43 and Emergent Therapeutic Strategies

Cytoplasmic TDP-43 mislocalization and aggregation is a pathological hallmark of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. TDP-43 is an RNA-binding protein (RBP) with a prion-like domain (PrLD) that promotes TDP-43 misfolding. PrLDs possess compositional similarity to canonical prion domains of various yeast proteins, including Sup35. Strikingly, disease-causing TDP-43 mutations reside almost exclusively in the PrLD and can enhance TDP-43 misfolding and toxicity. Another ∼70 human RBPs harbor PrLDs, including FUS, TAF15, EWSR1, hnRNPA1, and hnRNPA2, which have surfaced in the etiology of neurodegenerative diseases. Importantly, PrLDs enable RBP function and mediate phase transitions that partition functional ribonucleoprotein compartments. This PrLD activity, however, renders RBPs prone to populating deleterious oligomers or self-templating fibrils that might spread disease, and disease-linked PrLD mutations can exacerbate this risk. Several strategies have emerged to counter TDP-43 proteinopathies, including engineering enhanced protein disaggregases based on Hsp104.

Natural Conformational Sampling of Human TNFα Visualized by Double Electron-Electron Resonance

Double electron-electron resonance in conjunction with site-directed spin labeling has been used to probe natural conformational sampling of the human tumor necrosis factor α trimer. We suggest a previously unreported, predeoligomerization conformation of the trimer that has been shown to be sampled at low frequency. A model of this trimeric state has been constructed based on crystal structures using the double-electron-electron-resonance distances. The model shows one of the protomers to be rotated and tilted outward at the tip end, leading to a breaking of the trimerous symmetry and distortion at a receptor-binding interface. The new structure offers opportunities to modulate the biological activity of tumor necrosis factor α through stabilization of the distorted trimer with small molecules.

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).

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.

Impact of genotype and phenotype on cardiac biomarkers in patients with transthyretin amyloidosis - Report from the Transthyretin Amyloidosis Outcome Survey (THAOS)

Aim

Cardiac troponins and natriuretic peptides are established for risk stratification in light-chain amyloidosis. Data on cardiac biomarkers in transthyretin amyloidosis (ATTR) are lacking.

Methods and results

Patients (n = 1617) with any of the following cardiac biomarkers, BNP (n = 1079), NT-proBNP (n = 550), troponin T (n = 274), and troponin I (n = 108), available at baseline in the Transthyretin Amyloidosis Outcomes Survey (THAOS) were analyzed for differences between genotypes and phenotypes and their association with survival. Median level of BNP was 68.0 pg/mL (IQR 30.5–194.9), NT-proBNP 337.9 pg/mL (IQR 73.0–2584.0), troponin T 0.03 μg/L (IQR 0.01–0.05), and troponin I 0.08 μg/L (IQR 0.04–0.13). NT-proBNP and BNP were higher in wild-type than mutant-type ATTR, troponin T and I did not differ, respectively. Non-Val30Met patients had higher BNP, NT-proBNP and troponin T levels than Val30Met patients, but not troponin I. Late-onset Val30Met was associated with higher levels of troponin I and troponin T compared with early-onset. 115 patients died during a median follow-up of 1.2 years. Mortality increased with increasing quartiles (BNP/NT-proBNP Q1 = 1.7%, Q2 = 5.2%, Q3 = 21.7%, Q4 = 71.3%; troponin T/I Q1 = 6.5%, Q2 = 14.5%, Q3 = 33.9%, Q4 = 45.2%). Three-year overall-survival estimates for BNP/NT-proBNP and troponin T/I quartiles differed significantly (p<0.001). Stepwise risk stratification was achieved by combining NT-proBNP/BNP and troponin T/I. From Cox proportional hazards model, age, modified body mass index, mutation (Val30Met vs. Non-Val30Met) and BNP/NT-proBNP (Q1–Q3 pooled vs. Q4) were identified as independent predictors of survival in patients with mutant-type ATTR.

Conclusions

In this ATTR patient cohort, cardiac biomarkers were abnormal in a substantial percentage of patients irrespective of genotype. Along with age, mBMI, and mutation (Val30Met vs. Non-Val30Met), cardiac biomarkers were associated with surrogates of disease severity with BNP/NT-proBNP identified as an independent predictor of survival in ATTR.

Trial registration

ClinicalTrials.gov NCT00628745

One mutation, two distinct disease variants: unravelling the impact of transthyretin amyloid fibril composition

Although hereditary transthyretin (h-ATTR) amyloidosis is a monogenetic disease, a large variation in its phenotype has been observed. The common hypothesis of amyloid fibril formation involves dissociation of the transthyretin (TTR) tetramer into monomers that after misfolding reassemble into amyloid fibrils. This notion is partly challenged by the finding of two distinct types of amyloid fibrils. One of these, type A, consists of C-terminal ATTR fragments and full-length TTR, whereas the other, type B, consists only of full-length TTR. All organs of an individual patient contain ATTR deposits of either type A or type B fibrils, and the composition in each individual remains unchanged over time. The finding of two distinct types of ATTR fibrils suggests that there are at least two different pathways in operation for ATTR fibril formation. For the most common European mutation, TTR Val30Met, ATTR fibril composition is related to the outcome of liver transplantation, which is the first successful treatment for the disease, and the penetrance of the trait. In addition, the presence of C-terminal ATTR fragments has an impact on the affinity for various tracers used for noninvasive imaging of amyloid depositions such as 99 m-technetium-diphosphono-propanodicarboxylic acid scintigraphy and positron emission tomography utilizing Pittsburgh component B, and even for the gold standard diagnostic procedure, tissue biopsy stained by Congo red and examined under polarized light. The importance of amyloid fibril composition needs to be taken into consideration when designing clinical trials of treatment modalities, and also in the evaluation of diagnostic methods such as imaging techniques.

Cavity filling mutations at the thyroxine-binding site dramatically increase transthyretin stability and prevent its aggregation

More than a hundred different Transthyretin (TTR) mutations are associated with fatal systemic amyloidoses. They destabilize the protein tetrameric structure and promote the extracellular deposition of TTR as pathological amyloid fibrils. So far, only mutations R104H and T119M have been shown to stabilize significantly TTR, acting as disease suppressors. We describe a novel A108V non-pathogenic mutation found in a Portuguese subject. This variant is more stable than wild type TTR both in vitro and in human plasma, a feature that prevents its aggregation. The crystal structure of A108V reveals that this stabilization comes from novel intra and inter subunit contacts involving the thyroxine (T₄) binding site. Exploiting this observation, we engineered a A108I mutation that fills the T₄ binding cavity, as evidenced in the crystal structure. This synthetic protein becomes one of the most stable TTR variants described so far, with potential application in gene and protein replacement therapies.

Screening methods for identifying pharmacological chaperones

This review highlights recent screening methods for identifying pharmacological chaperones, which are small-molecules capable of rescuing misfolded proteins.

Current and Future Treatment Approaches in Transthyretin Familial Amyloid Polyneuropathy

OPINION STATEMENT

Treatment of transthyretin familial amyloid polyneuropathy (TTR FAP) must be tailored to disease stage. Patients with early stage disease (i.e., without major impairment in walking ability), especially younger patients, should be referred as soon as possible for liver transplantation (LT) in the absence of major comorbid conditions. LT remains the most effective treatment option to date and should be offered to these patients as early as possible. Bridging therapy with an oral TTR stabilizer (tafamidis or diflunisal, according to local access to these treatments) should be started as soon as the diagnosis of TTR FAP is established. Early stage patients who do not wish to or have contraindications to LT should be treated with an oral TTR stabilizer or get access to the newly developed therapeutic options (IONIS TTR-Rx, patisiran, doxycycline/TUDCA). Late stage patients (presenting with significant walking impairment) are usually older and notoriously difficult to treat. They should be offered an oral TTR stabilizer but are not candidates for LT due to a significant rate of perioperative complications and increased risk of progressive neurological and especially cardiac disease despite LT. Access to the different therapies in development should also be considered depending on respective inclusion and exclusion criteria. The abovementioned treatment options were mostly validated in Val30Met mutation patients, but should also be offered to non-Val30Met patients, although mortality rates after LT are higher in these patients. Treatment decisions should be made on an individual basis. Screening for heart, eye, and renal involvement is mandatory for every patient at disease diagnosis and regularly thereafter, even in transplanted patients. Symptomatic treatment should be offered as needed, as well as genetic counseling to at-risk family members. Asymptomatic mutation carriers should benefit from regular screening for early symptoms of disease. Current therapeutic management of TTR FAP will hopefully be changed in the near future with data from the ongoing phase 2/3 studies testing the TTR gene silencing agents. In the longer term, it is likely that combined therapeutic approaches will be necessary to reverse the disease process.

Discovery of Age-Related Protein Folding Stability Differences in the Mouse Brain Proteome

Described here is the application of thermodynamic stability measurements to study age-related differences in the folding and stability of proteins in a rodent model of aging. Thermodynamic stability profiles were generated for 809 proteins in brain cell lysates from mice, aged 6 (n = 7) and 18 months (n = 9) using the Stability of Proteins from Rates of Oxidation (SPROX) technique. The biological variability of the protein stability measurements was low and within the experimental error of SPROX. A total of 83 protein hits were detected with age-related stability differences in the brain samples. Remarkably, the large majority of the brain protein hits were destabilized in the old mice, and the hits were enriched in proteins that have slow turnover rates (p < 0.07). Furthermore, 70% of the hits have been previously linked to aging or age-related diseases. These results help validate the use of thermodynamic stability measurements to capture relevant age-related proteomic changes and establish a new biophysical link between these proteins and aging.

Chaperonin-Based Biolayer Interferometry To Assess the Kinetic Stability of Metastable, Aggregation-Prone Proteins

Stabilizing the folded state of metastable and/or aggregation-prone proteins through exogenous ligand binding is an appealing strategy for decreasing disease pathologies caused by protein folding defects or deleterious kinetic transitions. Current methods of examining binding of a ligand to these marginally stable native states are limited because protein aggregation typically interferes with analysis. Here, we describe a rapid method for assessing the kinetic stability of folded proteins and monitoring the effects of ligand stabilization for both intrinsically stable proteins (monomers, oligomers, and multidomain proteins) and metastable proteins (e.g., low Tm) that uses a new GroEL chaperonin-based biolayer interferometry (BLI) denaturant pulse platform. A kinetically controlled denaturation isotherm is generated by exposing a target protein, immobilized on a BLI biosensor, to increasing denaturant concentrations (urea or GuHCl) in a pulsatile manner to induce partial or complete unfolding of the attached protein population. Following the rapid removal of the denaturant, the extent of hydrophobic unfolded/partially folded species that remains is detected by an increased level of GroEL binding. Because this kinetic denaturant pulse is brief, the amplitude of binding of GroEL to the immobilized protein depends on the duration of the exposure to the denaturant, the concentration of the denaturant, wash times, and the underlying protein unfolding-refolding kinetics; fixing all other parameters and plotting the GroEL binding amplitude versus denaturant pulse concentration result in a kinetically controlled denaturation isotherm. When folding osmolytes or stabilizing ligands are added to the immobilized target proteins before and during the denaturant pulse, the diminished population of unfolded/partially folded protein manifests as a decreased level of GroEL binding and/or a marked shift in these kinetically controlled denaturation profiles to higher denaturant concentrations. This particular platform approach can be used to identify small molecules and/or solution conditions that can stabilize or destabilize thermally stable proteins, multidomain proteins, oligomeric proteins, and, most importantly, aggregation-prone metastable proteins.

Diabetic Risk Factors Promote Islet Amyloid Polypeptide Misfolding by a Common, Membrane-mediated Mechanism

The current diabetes epidemic is associated with a diverse set of risk factors including obesity and exposure to plastics. Notably, significant elevations of negatively charged amphiphilic molecules are observed in obesity (e.g. free fatty acids and phosphatidic acid) and plastics exposure (monophthalate esters). It remains unclear whether these factors share pathogenic mechanisms and whether links exist with islet amyloid polypeptide (IAPP) misfolding, a process central to β-cell dysfunction and death. Using a combination of fluorescence, circular dichroism and electron microscopy, we show that phosphatidic acid, oleic acid, and the phthalate metabolite MBzP partition into neutral membranes and enhance IAPP misfolding. The elevation of negative charge density caused by the presence of the risk factor molecules stabilizes a common membrane-bound α-helical intermediate that, in turn, facilitates IAPP misfolding. This shared mechanism points to a critical role for the membrane-bound intermediate in disease pathogenesis, making it a potential target for therapeutic intervention.

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.

Current and future treatment of amyloid diseases

There are more than 30 human proteins whose aggregation appears to cause degenerative maladies referred to as amyloid diseases or amyloidoses. These disorders are named after the characteristic cross-β-sheet amyloid fibrils that accumulate systemically or are localized to specific organs. In most cases, current treatment is limited to symptomatic approaches and thus disease-modifying therapies are needed. Alzheimer's disease is a neurodegenerative disorder with extracellular amyloid β-peptide (Aβ) fibrils and intracellular tau neurofibrillary tangles as pathological hallmarks. Numerous clinical trials have been conducted with passive and active immunotherapy, and small molecules to inhibit Aβ formation and aggregation or to enhance Aβ clearance; so far such clinical trials have been unsuccessful. Novel strategies are therefore required and here we will discuss the possibility of utilizing the chaperone BRICHOS to prevent Aβ aggregation and toxicity. Type 2 diabetes mellitus is symptomatically treated with insulin. However, the underlying pathology is linked to the aggregation and progressive accumulation of islet amyloid polypeptide as fibrils and oligomers, which are cytotoxic. Several compounds have been shown to inhibit islet amyloid aggregation and cytotoxicity in vitro. Future animal studies and clinical trials have to be conducted to determine their efficacy in vivo. The transthyretin (TTR) amyloidoses are a group of systemic degenerative diseases compromising multiple organ systems, caused by TTR aggregation. Liver transplantation decreases the generation of misfolded TTR and improves the quality of life for a subgroup of this patient population. Compounds that stabilize the natively folded, nonamyloidogenic, tetrameric conformation of TTR have been developed and the drug tafamidis is available as a promising treatment.

Novel trans-Stilbene-based Fluorophores as Probes for Spectral Discrimination of Native and Protofibrillar Transthyretin

Accumulation of misfolded transthyretin (TTR) as amyloid fibrils causes various human disorders. Native transthyretin is a neurotrophic protein and is a putative extracellular molecular chaperone. Several fluorophores have been shown in vitro to bind selectively to native TTR. Other compounds, such as thioflavin T, bind TTR amyloid fibrils. The probe 1-anilinonaphthalene-8-sulfonate (ANS) binds to both native and fibrillar TTR, becoming highly fluorescent, but with indistinguishable emission spectra for native and fibrillar TTR. Herein we report our efforts to develop a fluorescent small molecule capable of binding both native and misfolded protofibrillar TTR, providing distinguishable emission spectra. We used microwave synthesis for efficient production of a small library of trans-stilbenes and fluorescence spectral screening of their binding properties. We synthesized and tested 22 trans-stilbenes displaying a variety of functional groups. We successfully developed two naphthyl-based trans-stilbenes probes that detect both TTR states at physiological concentrations. The compounds bound with nanomolar to micromolar affinities and displayed distinct emission maxima upon binding native or misfolded protofibrillar TTR (>100 nm difference). The probes were mainly responsive to environment polarity providing evidence for the divergent hydrophobic structure of the binding sites of these protein conformational states. Furthermore, we were able to successfully use one of these probes to quantify the relative amounts of native and protofibrillar TTR in a dynamic equilibrium. In conclusion, we identified two trans-stilbene-based fluorescent probes, (E)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (11) and (E)-4-(2-(naphthalen-2-yl)vinyl)benzene-1,2-diol (14), that bind native and protofibrillar TTR, providing a wide difference in emission maxima allowing conformational discrimination by fluorescence spectroscopy. We expect these novel molecules to serve as important chemical biology research tools in studies of TTR folding and misfolding.

Peripheral Blood Cell Gene Expression Diagnostic for Identifying Symptomatic Transthyretin Amyloidosis Patients: Male and Female Specific Signatures

Background: Early diagnosis of familial transthyretin (TTR) amyloid diseases remains challenging because of variable disease penetrance. Currently, patients must have an amyloid positive tissue biopsy to be eligible for disease-modifying therapies. Endomyocardial biopsies are typically amyloid positive when cardiomyopathy is suspected, but this disease manifestation is generally diagnosed late. Early diagnosis is often difficult because patients exhibit apparent symptoms of polyneuropathy, but have a negative amyloid biopsy. Thus, there is a pressing need for an additional early diagnostic strategy for TTR-aggregation-associated polyneuropathy and cardiomyopathy.

Methods and Findings: Global peripheral blood cell mRNA expression profiles from 263 tafamidis-treated and untreated V30M Familiar Amyloid Neuropathy patients, asymptomatic V30M carriers, and healthy, age- and sex-matched controls without TTR mutations were used to differentiate symptomatic from asymptomatic patients. We demonstrate that blood cell gene expression patterns reveal sex-independent, as well as male- and female-specific inflammatory signatures in symptomatic FAP patients, but not in asymptomatic carriers. These signatures differentiated symptomatic patients from asymptomatic V30M carriers with >80% accuracy. There was a global downregulation of the eIF2 pathway and its associated genes in all symptomatic FAP patients. We also demonstrated that the molecular scores based on these signatures significantly trended toward normalized values in an independent cohort of 46 FAP patients after only 3 months of tafamidis treatment.

Conclusions: This study identifies novel molecular signatures that differentiate symptomatic FAP patients from asymptomatic V30M carriers as well as affected males and females. We envision using this approach, initially in parallel with amyloid biopsies, to identify individuals who are asymptomatic gene carriers that may convert to FAP patients. Upon further validation, peripheral blood cell mRNA expression profiling could become an independent early diagnostic. This quantitative gene expression signature for symptomatic FAP could also become a biomarker to demonstrate significant disease-modifying effects of drugs and drug candidates. For example, when new disease modifiers are being evaluated in a FAP clinical trial, such surrogate biomarkers have the potential to provide an objective, quantitative and mechanistic molecular diagnostic of disease response to therapy.

A novel mechano-enzymatic cleavage mechanism underlies transthyretin amyloidogenesis

The mechanisms underlying transthyretin-related amyloidosis in vivo remain unclear. The abundance of the 49–127 transthyretin fragment in ex vivo deposits suggests that a proteolytic cleavage has a crucial role in destabilizing the tetramer and releasing the highly amyloidogenic 49–127 truncated protomer. Here, we investigate the mechanism of cleavage and release of the 49–127 fragment from the prototypic S52P variant, and we show that the proteolysis/fibrillogenesis pathway is common to several amyloidogenic variants of transthyretin and requires the action of biomechanical forces provided by the shear stress of physiological fluid flow. Crucially, the non-amyloidogenic and protective T119M variant is neither cleaved nor generates fibrils under these conditions. We propose that a mechano-enzymatic mechanism mediates transthyretin amyloid fibrillogenesis in vivo. This may be particularly important in the heart where shear stress is greatest; indeed, the 49–127 transthyretin fragment is particularly abundant in cardiac amyloid. Finally, we show that existing transthyretin stabilizers, including tafamidis, inhibit proteolysis-mediated transthyretin fibrillogenesis with different efficiency in different variants; however, inhibition is complete only when both binding sites are occupied.

The Val30Met familial amyloid polyneuropathy specific Rasch-built overall disability scale (FAP-RODS(©) )

Familial amyloid polyneuropathy (FAP) is a chronic debilitating multi-organic disorder, mainly assessed using ordinal-based impairment measures. To date, no outcome measure at the activity and participation level has been constructed in FAP. The current study aimed to design an interval activity/participation scale for FAP through Rasch methodology. A preliminary FAP Rasch-built overall disability scale (pre-FAP-RODS) containing 146 activity/participation items was assessed twice (interval: 2-4 week; test-retest reliability) in 248 patients with Val30Met FAP examined in Porto, Portugal, of which 65.7% have received liver transplantation. An ordinal-based 24-item FAP-symptoms inventory questionnaire (FAP-SIQ) was also assessed (validity purposes). The pre-FAP-RODS and FAP-SIQ data were subjected to Rasch analyses. The pre-FAP-RODS did not meet model's expectations. On the basis of requirements such as misfit statistics, differential item functioning, and local dependency, items were systematically removed until a final 34-item FAP-RODS(©) was constructed fulfilling all Rasch requirements. Acceptable reliability/validity scores were demonstrated. In conclusion, the 34-item FAP-RODS(©) is a disease-specific interval measure suitable for detecting activity and participation restrictions in patients with FAP. The use of the FAP-RODS(©) is recommended for future international clinical trials in patients with Val30Met FAP determining its responsiveness and its cross-cultural validation. Its expansion to other forms of FAP should also be focus of future clinical studies.

Survival After Transplantation in Patients With Mutations Other Than Val30Met: Extracts From the FAP World Transplant Registry

Background

Liver transplantation (LTx) has been performed for hereditary transthyretin amyloidosis (ATTR) since 1990. Outcomes for a relatively large series of LTx ATTR patients with the Val30Met (mutation are available, but for non-Val30Met patients, only a few reports with a small number of patients exist. Here, we present outcomes for non-Val30Met ATTR patients after LTx, as reported to the Familial Amyloid Polyneuropathy World Transplant Registry (FAPWTR).

Methods

Data regarding outcome were extracted for all non-Val30Met patients reported to the registry. Survival rates were analyzed by the Kaplan-Meier method and log-rank test.

Results

The total number of patients with a non-Val30Met mutation in the registry was 264 (174 men and 90 women), representing 57 mutations. The 10-year survival varied markedly for the 9 most common mutations, ranging from 21% for Ser50Arg to 85% for Val71Ala. Poor survival was noted for all mutations with leptomeningeal complications except for those with the Tyr114Cys mutation.

Conclusions

Large differences in survival were observed relative to different mutations and between mutations with similar phenotypes. Excellent survival was noted for mutations, such as Leu111Met, Val71Ala, and Leu58His. Patients with mutations other than Val30Met are not a homogeneous group, and the term non-Val30Met should be used with caution or avoided. Moreover, for several mutations, data are too limited to allow evaluation of the efficacy of LTx, and continuous international collaboration is important for obtaining treatment guidance.

Pharmacological Chaperones: Design and Development of New Therapeutic Strategies for the Treatment of Conformational Diseases

Errors in protein folding may result in premature clearance of structurally aberrant proteins, or in the accumulation of toxic misfolded species or protein aggregates. These pathological events lead to a large range of conditions known as conformational diseases. Several research groups have presented possible therapeutic solutions for their treatment by developing novel compounds, known as pharmacological chaperones. These cell-permeable molecules selectively provide a molecular scaffold around which misfolded proteins can recover their native folding and, thus, their biological activities. Here, we review therapeutic strategies, clinical potentials, and cost-benefit impacts of several classes of pharmacological chaperones for the treatment of a series of conformational diseases.

Mechanism of Action and Clinical Application of Tafamidis in Hereditary Transthyretin Amyloidosis

Transthyretin (TTR) transports the retinol-binding protein-vitamin A complex and is a minor transporter of thyroxine in blood. Its tetrameric structure undergoes rate-limiting dissociation and monomer misfolding, enabling TTR to aggregate or to become amyloidogenic. Mutations in the TTR gene generally destabilize the tetramer and/or accelerate tetramer dissociation, promoting amyloidogenesis. TTR-related amyloidoses are rare, fatal, protein-misfolding disorders, characterized by formation of soluble aggregates of variable structure and tissue deposition of amyloid. The TTR amyloidoses present with a spectrum of manifestations, encompassing progressive neuropathy and/or cardiomyopathy. Until recently, the only accepted treatment to halt progression of hereditary TTR amyloidosis was liver transplantation, which replaces the hepatic source of mutant TTR with the less amyloidogenic wild-type TTR. Tafamidis meglumine is a rationally designed, non-NSAID benzoxazole derivative that binds with high affinity and selectivity to TTR and kinetically stabilizes the tetramer, slowing monomer formation, misfolding, and amyloidogenesis. Tafamidis is the first pharmacotherapy approved to slow the progression of peripheral neurologic impairment in TTR familial amyloid polyneuropathy. Here we describe the mechanism of action of tafamidis and review the clinical data, demonstrating that tafamidis treatment slows neurologic deterioration and preserves nutritional status, as well as quality of life in patients with early-stage Val30Met amyloidosis.

Rational design of mutations that change the aggregation rate of a protein while maintaining its native structure and stability

A wide range of human diseases is associated with mutations that, destabilizing proteins native state, promote their aggregation. However, the mechanisms leading from folded to aggregated states are still incompletely understood. To investigate these mechanisms, we used a combination of NMR spectroscopy and molecular dynamics simulations to compare the native state dynamics of Beta-2 microglobulin (β2m), whose aggregation is associated with dialysis-related amyloidosis, and its aggregation-resistant mutant W60G. Our results indicate that W60G low aggregation propensity can be explained, beyond its higher stability, by an increased average protection of the aggregation-prone residues at its surface. To validate these findings, we designed β2m variants that alter the aggregation-prone exposed surface of wild-type and W60G β2m modifying their aggregation propensity. These results allowed us to pinpoint the role of dynamics in β2m aggregation and to provide a new strategy to tune protein aggregation by modulating the exposure of aggregation-prone residues.

Modifications of the 7-Hydroxyl Group of the Transthyretin Ligand Luteolin Provide Mechanistic Insights into Its Binding Properties and High Plasma Specificity

Amyloid formation of the plasma protein transthyretin (TTR) has been linked to familial amyloid polyneuropathy and senile systemic amyloidosis. Binding of ligands within its natural hormone binding site can stabilize the tetrameric structure and impair amyloid formation. We have recently shown that the flavonoid luteolin stabilizes TTR in human plasma with a very high selectivity. Luteolin, however, is inactivated in vivo via glucuronidation for which the preferred site is the hydroxy group at position 7 on its aromatic A-ring. We have evaluated the properties of two luteolin variants in which the 7-hydroxy group has been exchanged for a chlorine (7-Cl-Lut) or a methoxy group (7-MeO-Lut). Using an in vitro model, based on human liver microsomes, we verified that these modifications increase the persistence of the drug. Crystal structure determinations show that 7-Cl-Lut binds similarly to luteolin. The larger MeO substituent cannot be accommodated within the same space as the chlorine or hydroxy group and as a result 7-MeO-Lut binds in the opposite direction with the methoxy group in position 7 facing the solvent. Both 7-Cl-Lut and 7-MeO-Lut qualify as high-affinity binders, but in contrast to luteolin, they display a highly non-specific binding to other plasma components. The binding of the two conformations and the key-interactions to TTR are discussed in detail. Taken together, these results show a proof-of-concept that the persistence of luteolin towards enzymatic modification can be increased. We reveal two alternative high-affinity binding modes of luteolin to TTR and that modification in position 7 is restricted only to small substituents if the original orientation of luteolin should be preserved. In addition, the present work provides a general and convenient method to evaluate the efficacy of TTR-stabilizing drugs under conditions similar to an in vivo environment.

Autoimmune response to transthyretin in juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common pediatric rheumatological condition. Although it has been proposed that JIA has an autoimmune component, the autoantigens are still unknown. Using biochemical and proteomic approaches, we identified the molecular chaperone transthyretin (TTR) as an antigenic target for B and T cell immune responses. TTR was eluted from IgG complexes and affinity purified from 3 JIA patients, and a statistically significant increase in TTR autoantibodies was observed in a group of 43 JIA patients. Three cryptic, HLA-DR1-restricted TTR peptides, which induced CD4⁺ T cell expansion and IFN-γ and TNF-α production in 3 out of 17 analyzed patients, were also identified. Misfolding, aggregation and oxidation of TTR, as observed in the synovial fluid of all JIA patients, enhanced its immunogenicity in HLA-DR1 transgenic mice. Our data point to TTR as an autoantigen potentially involved in the pathogenesis of JIA and to oxidation and aggregation as a mechanism facilitating TTR autoimmunity.

A current pharmacologic agent versus the promise of next generation therapeutics to ameliorate protein misfolding and/or aggregation diseases

The list of protein aggregation-associated degenerative diseases is long and growing, while the portfolio of disease-modifying strategies is very small. In this review and perspective, we assess what has worked to slow the progression of an aggregation-associated degenerative disease, covering the underlying mechanism of pharmacologic action and what we have learned about the etiology of the transthyretin amyloid diseases and likely amyloidoses in general. Next, we introduce emerging therapies that should apply more generally to protein misfolding and/or aggregation diseases, approaches that rely on adapting the protein homeostasis or proteostasis network for disease amelioration.

The polyphenol Oleuropein aglycone hinders the growth of toxic transthyretin amyloid assemblies

Transthyretin (TTR) is involved in a subset of familial or sporadic amyloid diseases including senile systemic amyloidosis (SSA), familial amyloid polyneuropathy and cardiomyopathy (FAP/FAC) for which no effective therapy has been found yet. These conditions are characterized by extracellular deposits primarily found in the heart parenchyma and in peripheral nerves whose main component are amyloid fibrils, presently considered the main culprits of cell sufferance. The latter are polymeric assemblies grown from misfolded TTR, either wt or carrying one out of many identified mutations. The recent introduction in the clinical practice of synthetic TTR-stabilizing molecules that reduce protein aggregation provides the rationale to search natural effective molecules able to interfere with TTR amyloid aggregation by hindering the appearance of toxic species or by favoring the growth of harmless aggregates. Here we carried out an in depth biophysical and morphological study on the molecular features of the aggregation of wt- and L55P-TTR involved in SSA or FAP/FAC, respectively, and on the interference with fibril aggregation, stability and toxicity to cardiac HL-1 cells to demonstrate the ability of Oleuropein aglycone (OleA), the main phenolic component of the extra virgin olive oil. We describe the molecular basis of such interference and the resulting reduction of TTR amyloid aggregate cytotoxicity. Our data offer the possibility to validate and optimize the use of OleA or its molecular scaffold to rationally design promising drugs against TTR-related pathologies that could enter a clinical experimental phase.

Mutant Proteogenomics

Identification of mutant proteins in biological samples is one of the emerging areas of proteogenomics. Despite the fact that only a limited number of studies have been published up to now, it has the potential to recognize novel disease biomarkers that have unique structure and desirably high specificity. Such properties would identify mutant proteoforms related to diseases as optimal drug targets useful for future therapeutic strategies. While mass spectrometry has demonstrated its outstanding analytical power in proteomics, the most frequently applied bottom-up strategy is not suitable for the detection of mutant proteins if only databases with consensus sequences are searched. It is likely that many unassigned tandem mass spectra of tryptic peptides originate from single amino acid variants (SAAVs). To address this problem, a couple of protein databases have been constructed that include canonical and SAAV sequences, allowing for the observation of mutant proteoforms in mass spectral data for the first time. Since the resulting large search space may compromise the probability of identifications, a novel concept was proposed that included identification as well as verification strategies. Together with transcriptome based approaches, targeted proteomics appears to be a suitable method for the verification of initial identifications in databases and can also provide quantitative insights to expression profiles, which often reflect disease progression. Important applications in the field of mutant proteoform identification have already highlighted novel biomarkers in large-scale investigations.

Evolution of magnetization due to asymmetric dimerization: theoretical considerations and application to aberrant oligomers formed by apoSOD12SH

A set of coupled differential equations is presented describing the evolution of magnetization due to an exchange reaction whereby a pair of identical monomers form an asymmetric dimer.

Pharmacological chaperone for α-crystallin partially restores transparency in cataract models

Cataracts reduce vision in 50% of individuals over 70 years of age and are a common form of blindness worldwide. Cataracts are caused when damage to the major lens crystallin proteins causes their misfolding and aggregation into insoluble amyloids. Using a thermal stability assay, we identified a class of molecules that bind α-crystallins (cryAA and cryAB) and reversed their aggregation in vitro. The most promising compound improved lens transparency in the R49C cryAA and R120G cryAB mouse models of hereditary cataract. It also partially restored protein solubility in the lenses of aged mice in vivo and in human lenses ex vivo. These findings suggest an approach to treating cataracts by stabilizing α-crystallins.

Liver Transplantation for Hereditary Transthyretin Amyloidosis: After 20 Years Still the Best Therapeutic Alternative?

BACKGROUND

Until recently, liver transplantation (Ltx) was the only available treatment for hereditary transthyretin (TTR) amyloidosis; today, however, several pharmacotherapies are tested. Herein, we present survival data from the largest available database on transplanted hereditary TTR patients to serve as a base for comparison.

METHODS

Liver transplantation was evaluated in a 20-year retrospective analysis of the Familial Amyloidosis Polyneuropathy World Transplant Registry.

RESULTS

From April 1990 until December 2010, data were accumulated from 77 liver transplant centers. The Registry contains 1940 patients, and 1379 are alive. Eighty-eight Ltx were performed in combination with a heart and/or kidney transplantation. Overall, 20-year survival after Ltx was 55.3%. Multivariate analysis revealed modified body mass index, early onset of disease (<50 years of age), disease duration before Ltx, and TTR Val30Met versus non-TTR Val30Met mutations as independent significant survival factors. Early-onset patients had an expected mortality rate of 38% that of the late-onset group (P < 0.001). Furthermore, Val30Met patients had an expected mortality rate of 61% that of non-TTR Val30Met patients (P < 0.001). With each year of duration of disease before Ltx, expected mortality increased by 11% (P < 0.001). With each 100-unit increase in modified body mass index at Ltx, the expected mortality decreased to 89% of the expected mortality (P < 0.001). Cardiovascular death was markedly more common than that observed in patients undergoing Ltx for end-stage liver disease.

CONCLUSIONS

Long-term survival after Ltx, especially for early-onset TTR Val30Met patients, is excellent. The risk of delaying Ltx by testing alternative treatments, especially in early-onset TTR Val30Met patients, requires consideration.

Targeting protein aggregation for the treatment of degenerative diseases

The aggregation of specific proteins is hypothesized to underlie several degenerative diseases, which are collectively known as amyloid disorders. However, the mechanistic connection between the process of protein aggregation and tissue degeneration is not yet fully understood. Here, we review current and emerging strategies to ameliorate aggregation-associated degenerative disorders, with a focus on disease-modifying strategies that prevent the formation of and/or eliminate protein aggregates. Persuasive pharmacological and genetic evidence now supports protein aggregation as the cause of postmitotic tissue dysfunction or loss. However, a more detailed understanding of the factors that trigger and sustain aggregate formation and of the structure-activity relationships underlying proteotoxicity is needed to develop future disease-modifying therapies.

Novel strategies for the diagnosis and treatment of cardiac amyloidosis

Systemic amyloidoses are rare, complex diseases caused by misfolding of autologous protein. The presence of heart involvement is the most important prognostic determinant. The diagnosis of amyloid cardiac involvement relies on echocardiography and magnetic resonance imaging, while scintigraphy with bone tracers is helpful in differentiating light chain amyloidosis from other types of amyloidosis involving the heart. Although these diseases are fatal, effective treatments exist that can alter their natural history, provided that they are started before irreversible cardiac damage has occurred. Refined diagnostic techniques, accurate patients' stratification based on biomarkers of cardiac dysfunction, the availability of novel, more powerful drugs, and ultimately, the unveiling of the cellular mechanisms of cardiac damage created a favorable environment for a dramatic improvement in the treatment of this disease that we expect in the next few years.

Transthyretin (ATTR) amyloidosis: clinical spectrum, molecular pathogenesis and disease-modifying treatments

Transthyretin (ATTR) amyloidosis is a life-threatening, gain-of-toxic-function disease characterised by extracellular deposition of amyloid fibrils composed of transthyretin (TTR). TTR protein destabilised by TTR gene mutation is prone to dissociate from its native tetramer to monomer, and to then misfold and aggregate into amyloid fibrils, resulting in autosomal dominant hereditary amyloidosis, including familial amyloid polyneuropathy, familial amyloid cardiomyopathy and familial leptomeningeal amyloidosis. Analogous misfolding of wild-type TTR results in senile systemic amyloidosis, now termed wild-type ATTR amyloidosis, characterised by acquired amyloid disease in the elderly. With the availability of genetic, biochemical and immunohistochemical diagnostic tests, patients with ATTR amyloidosis have been found in many nations; however, misdiagnosis is still common and considerable time is required before correct diagnosis in many cases. The current standard first-line treatment for hereditary ATTR amyloidosis is liver transplantation, which allows suppression of the main source of variant TTR. However, large numbers of patients are not suitable transplant candidates. Recently, the clinical effects of TTR tetramer stabilisers, diflunisal and tafamidis, were demonstrated in randomised clinical trials, and tafamidis has been approved for treatment of hereditary ATTR amyloidosis in European countries and in Japan. Moreover, antisense oligonucleotides and small interfering RNAs for suppression of variant and wild-type TTR synthesis are promising therapeutic approaches to ameliorate ATTR amyloidosis and are currently in phase III clinical trials. These newly developed therapies are expected to be effective for not only hereditary ATTR amyloidosis but also wild-type ATTR amyloidosis.

Discovery of γ-Mangostin as an Amyloidogenesis Inhibitor

Transthyretin (TTR) is a homotetrameric protein involved in human hereditary amyloidoses. The discovery and development of small molecules that inhibit the amyloid fibril formation of TTR is one of the therapeutic strategies for these diseases. Herein, we discovered that γ-mangostin (γ-M) is an effective inhibitor against the amyloid fibril formation of V30M amyloidogenic TTR. In-vitro binding assays revealed that γ-M was the most potent of the selected xanthone derivatives, and it bound to the thyroxine (T4)-binding sites and stabilized the TTR tetramer. X-ray crystallographic analysis revealed the diagonal binding mode of γ-M and the two binding sites of chloride ions at the T4-binding site. One of the chloride ions was replaced with a water molecule in the α-mangostin complex, which is a methylated derivative of γ-M. The stronger inhibitory potency of γ-M could be explained by the additional hydrogen bonds with the chloride ion. The present study establishes γ-M as a novel inhibitor of TTR fibrillization.

Protein fibrillation lag times during kinetic inhibition

Protein aggregation is linked to more than 30 human pathologies, including Alzheimer's and Parkinson's diseases. Since small oligomers that form at the beginning of the fibrillation process probably are the most toxic elements, therapeutic strategies involving fibril fragmentation could be detrimental. An alternative approach, named kinetic inhibition, aims to prevent fibril formation by using small ligands that stabilize the parent protein. The factors that govern fibrillation lag times during kinetic inhibition are largely unknown, notwithstanding their importance for designing effective long-term therapies. Inhibitor-bound species are not likely to be incorporated into the core of mature fibrils, although their presence could alter the kinetics of the fibrillation process. For instance, inhibitor-bound species may act as capping elements that impair the nucleation process and/or fibril growth. Here, we address this issue by studying the effect of two natural inhibitors on the fibrillation behavior of lysozyme at neutral pH. We analyzed a set of 79 fibrillation curves obtained in lysozyme alone and a set of 37 obtained in the presence of inhibitors. We calculated the concentrations of the relevant species at the beginning of the curves using the inhibitor-binding constants measured under the same experimental conditions. We found that inhibitor-bound protein species do not affect fibrillation onset times, which are mainly determined by the concentration of unbound protein species present in equilibrium. In this system, knowledge of the fibrillation kinetics and inhibitor affinities suffices to predict the effect of kinetic inhibitors on fibrillation lag times. In addition, we developed a new methodology to better estimate fibrillation lag times from experimental curves.

Left ventricular deformation and torsion assessed by speckle-tracking echocardiography in patients with mutated transthyretin-associated cardiac amyloidosis and the effect of diflunisal on myocardial function

Background

Mutated transthyretin-associated (ATTRm) amyloidosis with heart failure is associated with decreased longitudinal left ventricular (LV) myocardial contraction, as measured by strain Doppler echocardiography. We sought to clarify whether speckle-tracking echocardiography (STE) would provide useful information in patients with ATTRm cardiac amyloidosis.

Methods

One hundred twenty-three consecutive patients with ATTRm amyloidosis were divided into 3 groups. Group 1 had no evidence of cardiac involvement (n = 47), group 2 had heart involvement but no congestive heart failure (CHF) and/or serum brain natriuretic peptide (BNP) levels < 100 pg/mL (n = 35), and group 3 had heart involvement and CHF and/or serum BNP levels ≥ 100 pg/mL (n = 41). All patients underwent standard 2-dimensional (2D), Doppler echo, and STE.

Results

By standard 2D and Doppler echo, differences in parameters were only apparent between group 3 and groups 1 and 2. Global circumferential strains by STE at each LV level and LV torsion were different between group 1 and groups 2 and 3, but not between group 2 and group 3. In contrast, global longitudinal LV strain showed significant intergroup differences (− 17.3 ± 2.3%, − 13.3 ± 2.3%, − 9.9 ± 3.3% for groups 1 to 3, respectively, P < 0.0001). Radial strain also showed significant intergroup differences for each basal LV segment. Among 41 patients who could have been followed up after 1 year, 34 patients with diflunisal treatment had shown improvement in apical rotation and torsion without deterioration in multidirectional strains.

Conclusion

ATTRm cardiac amyloidosis is characterized by progressive impairment in longitudinal and basal LV radial function when global circumferential shortening and torsion remain unchanged.

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.