Biochemical characteristics of variant transthyretins causing hereditary leptomeningeal amyloidosis

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Distribution and progression of cerebral amyloid angiopathy in early-onset V30M (p.V50M) hereditary ATTR amyloidosis

BACKGROUND

Cerebral amyloid angiopathy (CAA) is becoming the most common and serious complications in long-lived hereditary ATTR amyloidosis patients. It is therefore imperative to elucidate the characteristics of ATTR-type CAA and develop useful biomarkers.

METHODS

We enrolled 34 ATTRv amyloidosis patients with the V30M (p.V50M) variant for analysis with three-dimensional stereotactic surface projection z score imaging of Pittsburgh compound B (PiB)-PET.

RESULTS

Eight patients exhibited central nervous system (CNS) symptoms. Seven patients suffered transient focal neurologic episodes, and 2 patients each experienced cerebellar haemorrhages or cognitive decline. The amount of ¹¹C-PiB accumulation increased as a function of disease duration. ¹¹C-PiB-PET abnormalities were seen at 8 years from onset and were associated with CNS manifestations from 12 years. The annual increase rate of the standardised uptake value ratio (SUVR) in female patients was significantly higher than in male patients. CNS amyloid deposition started in the upper middle surface of the cerebellar cortex, and then spread out over the entire surface of the cerebellum, Sylvian fissure, and anterior part of the longitudinal fissure of the cerebrum.

CONCLUSIONS

PiB-PET is a useful biomarker for the early detection and treatment evaluation of ATTR-type CAA. Female gender is associated with more rapid progression of ATTR-type CAA.

The Regulatory Mechanism of Transthyretin Irreversible Aggregation through Liquid-to-Solid Phase Transition

Transthyretin (TTR) aggregation and amyloid formation are associated with several ATTR diseases, such as senile systemic amyloidosis (SSA) and familial amyloid polyneuropathy (FAP). However, the mechanism that triggers the initial pathologic aggregation process of TTR remains largely elusive. Lately, increasing evidence has suggested that many proteins associated with neurodegenerative diseases undergo liquid-liquid phase separation (LLPS) and subsequent liquid-to-solid phase transition before the formation of amyloid fibrils. Here, we demonstrate that electrostatic interactions mediate LLPS of TTR, followed by a liquid-solid phase transition, and eventually the formation of amyloid fibrils under a mildly acidic pH in vitro. Furthermore, pathogenic mutations (V30M, R34T, and K35T) of TTR and heparin promote the process of phase transition and facilitate the formation of fibrillar aggregates. In addition, S-cysteinylation, which is a kind of post-translational modification of TTR, reduces the kinetic stability of TTR and increases the propensity for aggregation, while another modification, S-sulfonation, stabilizes the TTR tetramer and reduces the aggregation rate. Once TTR was S-cysteinylated or S-sulfonated, they dramatically underwent the process of phase transition, providing a foundation for post-translational modifications that could modulate TTR LLPS in the context of pathological interactions. These novel findings reveal molecular insights into the mechanism of TTR from initial LLPS and subsequent liquid-to-solid phase transition to amyloid fibrils, providing a new dimension for ATTR therapy.

CSF/plasma levels, transthyretin stabilisation and safety of multiple doses of tolcapone in subjects with hereditary ATTR amyloidosis

PURPOSE

To investigate the effect of tolcapone on cerebrospinal fluid (CSF) transthyretin (TTR) tetramer stability in patients with hereditary transthyretin (ATTRv) amyloidosis.

METHODS

A total of 9 patients were enrolled in the study (3 men, 50.3 ± 14.4 years old). Three patients had central nervous system (CNS) involvement. Patients were assigned to receive tolcapone 300 mg/day or 600 mg/day for 7 days. Plasma and CSF were collected at baseline and 2 h after the final tolcapone dose.

RESULTS

The mean CSF tolcapone and 3-O-Methyltolcapone (3-OMT) concentration were 39.4 ± 36.3 ng/mL and 26.0 ± 4.9 ng/mL, respectively, after 7 days of tolcapone dosing. Tolcapone and 3-OMT were detected in the CSF of patients with or without CNS symptoms. The mean total study drug (tolcapone + 3-OMT) to TTR molar ratio in CSF was 1.15 ± 0.59. Orally administered tolcapone significantly increased CSF TTR concentration and decreased monomer content under semi-denaturing conditions. Eight adverse events (AEs) were reported in 6 patients. All AEs were mild in severity and resolved.

CONCLUSIONS

Tolcapone was able to cross the blood brain-barrier, highlighting its potential to decrease CNS manifestations of ATTRv amyloidosis. Tolcapone was well tolerated by patients with ATTRv amyloidosis.

Canadian Guidelines for Hereditary Transthyretin Amyloidosis Polyneuropathy Management

Hereditary transthyretin-mediated (hATTR) amyloidosis is a progressive disease caused by mutations in the TTR gene leading to multisystem organ dysfunction. Pathogenic TTR aggregation, misfolding, and fibrillization lead to deposition of amyloid in multiple body organs and frequently involve the peripheral nerve system and the heart. Common neurologic manifestations include: sensorimotor polyneuropathy (PN), autonomic neuropathy, small-fiber PN, and carpal tunnel syndrome. Many patients have significant progression due to diagnostic delays as hATTR PN is not considered within the differential diagnosis. Recently, two effective novel disease-modifying therapies, inotersen and patisiran, were approved by Health Canada for the treatment of hATTR PN. Early diagnosis is crucial for the timely introduction of these disease-modifying treatments that reduce impairments, improve quality of life, and extend survival. In this guideline, we aim to improve awareness and outcomes of hATTR PN by making recommendations directed to the diagnosis, monitoring, and treatment in Canada.

Diagnosis and Treatment of Hereditary Transthyretin Amyloidosis (hATTR) Polyneuropathy: Current Perspectives on Improving Patient Care

Hereditary transthyretin amyloidosis (hATTR) with polyneuropathy (formerly known as Familial Amyloid Polyneuropathy) is a rare disease due to mutations in the gene encoding transthyretin (TTR) and characterized by multisystem extracellular deposition of amyloid, leading to dysfunction of different organs and tissues. hATTR amyloidosis represents a diagnostic challenge for neurologists considering the great variability in clinical presentation and multiorgan involvement. Generally, patients present with polyneuropathy, but clinicians should consider the frequent cardiac, ocular and renal impairment. Especially a hypertrophic cardiomyopathy, even if usually latent, is identifiable in at least 50% of the patients. Therapeutically, current available options act at different stages of TTR production, including synthesis inhibition (liver transplantation and/or gene-silencing drugs) or tetramer TTR stabilization (TTR stabilizers), increasing survival at different disease stages.

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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.

The identification of a transthyretin variant p.D38G in a Chinese family with early-onset leptomeningeal amyloidosis

Familial amyloid polyneuropathies (FAPs) are life-threatening, autosomal dominant diseases resulting, in most instances, from transthyretin gene (TTR) variants. A small number of TTR variants lead to leptomeningeal amyloidosis (LA), which is a rare FAP subtype with late-onset central nervous system (CNS) impairment symptoms. Previous studies suggest that LA's CNS selectivity was due to complete endoplasmic reticulum-associated degradation of highly destabilized mutants in peripheral tissues. LA's later age at onset (AAO) was due to lower choroid plexus secretory efficacy. This study reports on a family with LA, including six symptomatic and three presymptomatic members. The LA diagnosis was confirmed by leptomeningeal enhancement on contrast MRI, elevated cerebrospinal fluid protein levels, and positive Congo red staining. The predominant symptoms included headaches, dizziness, vomiting, hallucinations, and cognitive impairments which associated with obstructive hydrocephalus. The TTR p.D38G variant with the lowest secretory efficacy was identified as the genetic cause by whole exome sequencing. The family had a statistically significantly earlier mean AAO of 31.3 ± 7.4 (p = 0.001). These uncommon phenotypes indicate unknown factors influencing the progress of CNS impairment via TTR mutants. Medical imaging examinations suggest the potential early diagnosis value of contrast MRI and the importance of ependyma involvement in LA. LA genetic and clinical data were reviewed and summarized. These findings expand the FAPs' phenotypic spectrum and are valuable in FAP diagnosis, treatment, and further research.

Diagnosis and management of transthyretin familial amyloid polyneuropathy in Japan: red-flag symptom clusters and treatment algorithm

Hereditary ATTR (ATTRm) amyloidosis (also called transthyretin-type familial amyloid polyneuropathy [ATTR-FAP]) is an autosomal-dominant, adult-onset, rare systemic disorder predominantly characterized by irreversible, progressive, and persistent peripheral nerve damage. TTR gene mutations (e.g. replacement of valine with methionine at position 30 [Val30Met (p.Val50Met)]) lead to destabilization and dissociation of TTR tetramers into variant TTR monomers, which form amyloid fibrils that deposit in peripheral nerves and various organs, giving rise to peripheral and autonomic neuropathy and several non-disease specific symptoms.

Phenotypic and genetic variability and non–disease-specific symptoms often delay diagnosis and lead to misdiagnosis. Red-flag symptom clusters simplify diagnosis globally. However, in Japan, types of TTR variants, age of onset, penetrance, and clinical symptoms of Val30Met are more varied than in other countries. Hence, development of a Japan-specific red-flag symptom cluster is warranted. Presence of progressive peripheral sensory-motor polyneuropathy and ≥1 red-flag sign/symptom (e.g. family history, autonomic dysfunction, cardiac involvement, carpal tunnel syndrome, gastrointestinal disturbances, unexplained weight loss, and immunotherapy resistance) suggests ATTR-FAP. Outside of Japan, pharmacotherapeutic options are first-line therapy. However, because of positive outcomes (better life expectancy and higher survival rates) with living donor transplant in Japan, liver transplantation remains first-line treatment, necessitating a Japan-specific treatment algorithm.

Herein, we present a consolidated review of the ATTR-FAP Val30Met landscape in Japan and summarize findings from a medical advisory board meeting held in Tokyo on 18th August 2016, at which a Japan-specific ATTR-FAP red-flag symptom cluster and treatment algorithm was developed. Beside liver transplantation, a TTR-stabilizing agent (e.g. tafamidis) is a treatment option. Early diagnosis and timely treatment using the Japan-specific red-flag symptom cluster and treatment algorithm might help guide clinicians regarding apt and judicious use of available treatment modalities.

Pathological, biochemical, and biophysical characteristics of the transthyretin variant Y114H (p.Y134H) explain its very mild clinical phenotype

Transthyretin (TTR) is a homotetrameric protein that must misfold in order to form amyloid fibrils. Misfolding includes rate limiting tetramer dissociation, followed by fast tertiary structural changes of the monomer that enable aggregation. Hereditary ATTR amyloidosis is an autosomal dominant genetic disorder with systemic deposition of amyloid fibrils induced by TTR gene mutation. We identified a rare Y114H (p.Y134H) TTR variant in a Japanese patient presenting with late-onset, very mild clinical course. The patient had an extremely low serum variant TTR concentration (18% of total TTR), whereas the composition of variant TTR was 55% in amyloid fibrils in tenosynovial tissues obtained at carpal tunnel release surgery. The amyloid fibril deposits in the ATTR Y114H patient had an altered structure compared with that in wild-type ATTR patients, as determined by luminescent conjugated poly/oligo-thiophene fluorescence spectroscopy. Biophysical studies using recombinant protein showed that Y114H TTR was markedly destabilized both thermodynamically and kinetically and was highly amyloidogenic in vitro. These data suggest that extremely low serum variant Y114H TTR concentration, probably due to endoplasmic reticulum-associated degradation of unstable variant TTR protein, protected this patient from severe amyloidosis, as self-assembly of the amyloidogenic intermediate is a concentration-dependent process.

CNS involvement in V30M transthyretin amyloidosis: clinical, neuropathological and biochemical findings

OBJECTIVES

Since liver transplant (LT) was introduced to treat patients with familial amyloid polyneuropathy carrying the V30M mutation (ATTR-V30M), ocular and cardiac complications have developed. Long-term central nervous system (CNS) involvement was not investigated. Our goals were to: (1) identify and characterise focal neurological episodes (FNEs) due to CNS dysfunction in ATTR-V30M patients; (2) characterise neuropathological features and temporal profile of CNS transthyretin amyloidosis.

METHODS

We monitored the presence and type of FNEs in 87 consecutive ATTR-V30M and 35 non-ATTR LT patients. FNEs were investigated with CT scan, EEG and extensive neurovascular workup. MRI studies were not performed because all patients had cardiac pacemakers as part of the LT protocol. We characterised transthyretin amyloid deposition in the brains of seven ATTR-V30M patients, dead 3-13 years after polyneuropathy onset.

RESULTS

FNEs occurred in 31% (27/87) of ATTR-V30M and in 5.7% (2/35) of the non-ATTR transplanted patients (OR=7.0, 95% CI 1.5 to 33.5). FNEs occurred on average 14.6 years after disease onset (95% CI 13.3 to 16.0) in ATTR-V30M patients, which is beyond the life expectancy of non-transplanted ATTR-V30M patients (10.9, 95% CI 10.5 to 11.3). ATTR-V30M patients with FNEs had longer disease duration (OR=1.24; 95% CI 1.07 to 1.43), renal dysfunction (OR=4.65; 95% CI 1.20 to 18.05) and were men (OR=3.57; 95% CI 1.02 to 12.30). CNS transthyretin amyloidosis was already present 3 years after polyneuropathy onset and progressed from the meninges and its vessels towards meningocortical vessels and the superficial brain parenchyma, as disease duration increased.

CONCLUSIONS

Our findings indicate that CNS clinical involvement occurs in ATTR-V30M patients regardless of LT. Longer disease duration after LT can provide the necessary time for transthyretin amyloidosis to progress until it becomes clinically relevant. Highly sensitive imaging methods are needed to identify and monitor brain ATTR. Disease modifying therapies should consider brain TTR as a target.

A look into amyloid formation by transthyretin: aggregation pathway and a novel kinetic model

The kinetics of transthyretin aggregation from acid-unfolded monomers to amyloid fibrils was studied by several biophysical techniques and may be described as a two-step process with transient accumulation of oligomeric species.

Mutation and low pH effect on the stability as well as unfolding kinetics of transthyretin dimer

Transthyretin (TTR) dissociation and aggregation appear to cause several amyloid diseases. TTR dimer is an important intermediate that is hard to be observed from the biological experiments. To date, the molecular origin and the structural motifs for TTR dimer dissociation, as well as the unfolding process have not been rationalized at atomic resolution. To this end, we have investigated the effect of low pH and mutation L55P on stability as well as the unfolding pathway of TTR dimer using constant pH molecular dynamics simulations. The result shows that acidic environment results in loose TTR dimer structure. Mutation L55P causes the disruption of strand D and makes the CE-loop very flexible. In acidic conditions, dimeric L55P mutant exhibits notable conformation changes and an evident trend to separate. Our work shows that the movements of strand C and the loops nearby are the beginning of the unfolding process. In addition, hydrogen bond network at the interface of the two monomers plays a part in stabilizing TTR dimer. The dynamic investigation on TTR dimer provides important insights into the structure-function relationships of TTR, and rationalizes the structural origin for the tendency of unfolding and changes of structure that occur upon introduction of mutation and pH along the TTR dimer dissociation and unfolding process.

Activated microglia mediate synapse loss and short-term memory deficits in a mouse model of transthyretin-related oculoleptomeningeal amyloidosis

Oculoleptomeningeal amyloidosis (OA) is a fatal and untreatable hereditary disease characterized by the accumulation of transthyretin (TTR) amyloid within the central nervous system. The mechanisms underlying the pathogenesis of OA, and in particular how amyloid triggers neuronal damage, are still unknown. Here, we show that amyloid fibrils formed by a mutant form of TTR, A25T, activate microglia, leading to the secretion of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and nitric oxide. Further, we found that A25T amyloid fibrils induce the activation of Akt, culminating in the translocation of NFκB to the nucleus of microglia. While A25T fibrils were not directly toxic to neurons, the exposure of neuronal cultures to media conditioned by fibril-activated microglia caused synapse loss that culminated in extensive neuronal death via apoptosis. Finally, intracerebroventricular (i.c.v.) injection of A25T fibrils caused microgliosis, increased brain TNF-α and IL-6 levels and cognitive deficits in mice, which could be prevented by minocycline treatment. These results indicate that A25T fibrils act as pro-inflammatory agents in OA, activating microglia and causing neuronal damage.

Guideline of transthyretin-related hereditary amyloidosis for clinicians

Transthyretin amyloidosis is a progressive and eventually fatal disease primarily characterized by sensory, motor, and autonomic neuropathy and/or cardiomyopathy. Given its phenotypic unpredictability and variability, transthyretin amyloidosis can be difficult to recognize and manage. Misdiagnosis is common, and patients may wait several years before accurate diagnosis, risking additional significant irreversible deterioration. This article aims to help physicians better understand transthyretin amyloidosis—and, specifically, familial amyloidotic polyneuropathy—so they can recognize and manage the disease more easily and discuss it with their patients. We provide guidance on making a definitive diagnosis, explain methods for disease staging and evaluation of disease progression, and discuss symptom mitigation and treatment strategies, including liver transplant and several pharmacotherapies that have shown promise in clinical trials.

Sulfated glycosaminoglycans accelerate transthyretin amyloidogenesis by quaternary structural conversion

Glycosaminoglycans (GAGs), which are found in association with all extracellular amyloid deposits in humans, are known to accelerate the aggregation of various amyloidogenic proteins in vitro. However, the precise molecular mechanism(s) by which GAGs accelerate amyloidogenesis remains elusive. Herein, we show that sulfated GAGs, especially heparin, accelerate transthyretin (TTR) amyloidogenesis by quaternary structural conversion. The clustering of sulfate groups on heparin and its polymeric nature are essential features for accelerating TTR amyloidogenesis. Heparin does not influence TTR tetramer stability or TTR dissociation kinetics, nor does it alter the folded monomer-misfolded monomer equilibrium directly. Instead, heparin accelerates the conversion of preformed TTR oligomers into larger aggregates. The more rapid disappearance of monomeric TTR in the presence of heparin likely reflects the fact that the monomer-misfolded amyloidogenic monomer-oligomer-TTR fibril equilibria are all linked, a hypothesis that is strongly supported by the light scattering data. TTR aggregates prepared in the presence of heparin exhibit a higher resistance to trypsin and proteinase K proteolysis and a lower exposure of hydrophobic side chains comprising hydrophobic clusters, suggesting an active role for heparin in amyloidogenesis. Our data suggest that heparin accelerates TTR aggregation by a scaffold-based mechanism, in which the sulfate groups comprising GAGs interact primarily with TTR oligomers through electrostatic interactions, concentrating and orienting the oligomers, facilitating the formation of higher molecular weight aggregates. This model raises the possibility that GAGs may play a protective role in human amyloid diseases by interacting with proteotoxic oligomers and promoting their association into less toxic amyloid fibrils.

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.

Suppression of choroid plexus transthyretin levels by antisense oligonucleotide treatment

Leptomeningeal amyloidosis associated with mutations in transthyretin (TTR) is a rare but fatal form of amyloidosis. Dementia and intracerebral haemorrhage are prominent features of this disease for which no specific therapy is known. In previous studies, we have shown that antisense oligonucleotides (ASOs) specific for human TTR could inhibit hepatic synthesis of TTR in mice transgenic for a human amyloid-associated TTR and may offer a medical means of treating systemic TTR amyloidosis. Parenteral administration of TTR-specific ASO, however, had no effect on the expression of TTR by the choroid plexus, which is believed to be the source of the amyloid protein in patients who have leptomeningeal amyloidosis. In the present study, mice transgenic for the human TTR amyloid-associated mutation Ile84Ser were treated by administration of TTR-specific ASO (50 microg or 75 microg per day) via an osmotic pump into the cerebral ventricular system over a 4-week period. Intraventricular administration of TTR-specific ASO significantly reduced choroid human TTR mRNA levels, and these findings correlated with decreased TTR in choroid plexus epithelial cells as demonstrated by immunohistochemistry. Suppression of choroid TTR expression by intraventricular administered ASO may offer a medical means of treating leptomeningeal amyloidosis.

SELDI-TOF Mass Spectrometry Evaluation of Variant Transthyretins for Diagnosis and Pathogenesis of Familial Amyloidotic Polyneuropathy

Background: Mass spectrometric analyses are valuable for detection of transthyretin (TTR) variants, which cause familial amyloidotic polyneuropathy (FAP). However, those methods require an immunoprecipitation step with an anti-TTR antibody and are not suitable for quantitative detection. We investigated the usefulness of SELDI-TOF mass spectrometry (MS) without an immunoprecipitation step.

Methods: We used ProteinChips with chromatographic capture formats to detect TTRs. We attempted to correlate the intensity of mixed samples of amyloidogenic TTR (ATTR) V30M to wild-type (WT) TTR. We analyzed the proportion of ATTR V30M in amyloid-laden cardiac tissues from FAP patients, and also evaluated samples from FAP patients with 16 other TTR mutations.

Results: Detection of ATTR required only 3 h of SELDI-TOF MS analysis. We determined that SELDI-TOF MS was suitable for quantitative detection of ATTR V30M and demonstrated that the proportion of ATTR V30M to WT TTR was 46.6% in amyloid-laden cardiac tissue from an FAP patient who died 10 years after liver transplantation. With this method, we identified 12 of 17 TTR variants. Small mass shifts and low concentrations of variants prevented ATTR detection. By changing the analytical conditions, we achieved detection of low concentrations of ATTR Y114C in serum.

Conclusions: SELDI-TOF MS is a reliable tool for quantitative evaluation of TTR variants, in both tissue amyloid deposits and body fluids. This method is useful for the diagnosis and investigation of the pathogenesis of FAP.

The molecular biology and clinical features of amyloid neuropathy

Neuropathy is often a major manifestation of systemic amyloidosis. It is most frequently seen in patients with hereditary transthyretin (TTR) amyloidosis, but is also present in 20% of patients with systemic immunoglobulin light chain (primary) amyloidosis. Familial amyloid polyneuropathy (FAP) is the most common form of inherited amyloidotic polyneuropathy, with clinical and electrophysiologic findings similar to neuropathies with differing etiologies (e.g., diabetes mellitus). Hereditary amyloidosis is an adult-onset autosomal-dominant disease with varying degrees of penetrance. It is caused by specific gene mutations, but demonstration that a patient has one such mutation does not confirm the diagnosis of amyloidosis. Diagnosis requires tissue biopsy with demonstration of amyloid deposits either by special histochemical stains or electron microscopy. Transthyretin amyloidosis is treated by liver transplantation, which eliminates the mutated transthyretin from the blood, but for some patients continued amyloid deposition can occur from wild-type (normal) transthyretin. Presently, a study is ongoing to determine whether amyloid deposition can be inhibited by small organic molecules that are hypothesized to affect the fibril-forming ability of transthyretin. Proposed gene therapy with antisense oligonucleotides (ASOs) to suppress hepatic transthyretin synthesis is effective in a transgenic mouse model but has not yet been tested in humans.

Identification of human hepatocellular carcinoma-related proteins by proteomic approaches

Hepatocellular carcinoma (HCC) is the most common malignant liver tumor. Analysis of human serum from HCC patients using two-dimensional gel electrophoresis (2DE) combined with nano-high-performance liquid chromatography electrospray ionization tandem mass spectrometry (nano-HPLC-ESI-MS/MS) identified fourteen different proteins differentially expressed between HCC patients and the control group. Twelve proteins were up-regulated and two down-regulated. By using nano-HPLC-MS/MS system to analyze proteome in human serum, 317 proteins were identified, twenty-nine of which to high confidence levels (protein matched at last two unique peptide sequences). Of these twenty-nine proteins, six were present only in HCC patients and may serve as biomarkers for HCC.