Familial amyloid polyneuropathy: receptor for advanced glycation end products-dependent triggering of neuronal inflammatory and apoptotic pathways

Quantitative sensation and autonomic test abnormalities in transthyretin amyloidosis polyneuropathy

This study assesses the value of standard quantitative autonomic (QAT) and sensation (QST) tests in detecting, characterizing, and quantitating the severity of transthyretin amyloid polyneuropathy (TTR-A-PN). This information is needed for prospective therapeutic trials, epidemiologic surveys, and medical practice. We reviewed 36 patients with TTR-A-PN who were evaluated between 1997 and 2007. They had neurologic, genetic, electrodiagnostic, and autonomic reflex screen evaluations and allowed their medical records and test results to be evaluated for research purposes. Of these, 22 patients had also been tested by quantitative sensation tests (QSTs). The median symptom duration was 4 years (range 1-30 years). Among quantitative nerve tests evaluated, composite scores of nerve conduction (Sigma5 NC nds), a composite score of QSTs (Sigma3 QST nds), and quantitative autonomic tests (QSART, HR(db), and CASS) gave high frequencies of abnormality. The results show that peripheral autonomic and small-fiber sensory dysfunction was prominent and characteristic of most of the patients we studied. However, this involvement was not selective for small-diameter sensory and autonomic nerve fibers; large motor and sensory fibers were also shown to be dysfunctional. Dysfunction of large fibers was approximately as frequent as that of small fibers. This study provides a rationale for the use of QAT, QST, and Sigma5 NC nds as standard, objective, and quantitative measures for assessing the severity of TTR-A-PN in epidemiologic surveys, therapeutic trials, and medical practice.

Tempering the wrath of RAGE: an emerging therapeutic strategy against diabetic complications, neurodegeneration, and inflammation

The multiligand receptor RAGE (receptor for advanced glycation end-products) is emerging as a central mediator in the immune/inflammatory response. Epidemiological evidence accruing in the human suggests upregulation of RAGE's ligands (AGEs, S100/calgranulins, high mobility group box-1 (HMGB1), and amyloid beta-peptide and beta-sheet fibrils) and the receptor itself at sites of inflammation and in chronic diseases such as diabetes and neurodegeneration. The consequences of ligand-RAGE interaction include upregulation of molecules implicated in inflammatory responses and tissue damage, such as cytokines, adhesion molecules, and matrix metalloproteinases. In this review, we discuss the localization of RAGE and its ligand families and the biological impact of this axis in multiple cell types implicated in chronic diseases. Lastly, we consider findings from animal model studies suggesting that although tissue-damaging effects ensue from recruitment of the ligand-RAGE interaction, in distinct settings, adaptive and repair/regeneration outcomes appear to override detrimental effects of RAGE. As RAGE blockade moves further into clinical development, clarifying the biology of RAGE garners ever-increasing importance.

RAGE expression is up-regulated in human cerebral ischemia and pMCAO rats

To determine whether the receptor for advanced glycation endproducts (RAGE) contributes to cerebral ischemia, we evaluated RAGE expression in human cerebral ischemia and a model of permanent middle cerebral artery occlusion (pMCAO) in rats. Biopsy specimens were obtained from 12 patients with unilateral cerebral infarction. For the pMCAO model, the middle cerebral artery (MCA) of Sprague-Dawley (SD) rats was permanently occluded. Immunohistochemistry and Western blotting were used to measure RAGE expression in the ischemic hemisphere relative to the normal hemisphere. PC12 cells subjected to oxygen and glucose deprivation (OGD) were used to evaluate the role of RAGE in cell injury. As expected, cerebral ischemia patients expressed elevated levels of RAGE in the ischemic hemisphere. In 1 and 2 days pMCAO rats, levels of RAGE were higher in the ischemic hemisphere relative to the non-ischemic hemisphere, and expression was primarily located in the penumbra of the ischemic hemisphere. In PC12 cells, levels of RAGE increased after 7h of OGD culture. Notably, blockade of RAGE with a selective RAGE antibody in vitro reduced the cytotoxicity caused by OGD. The present data suggest that RAGE is up-regulated in human cerebral ischemia and pMCAO rats, suggesting a role for RAGE in brain ischemia.

Activation of the heat shock response in familial amyloidotic polyneuropathy

The heat shock proteins (Hsps) have been implicated in a variety of neurodegenerative diseases in which the underlying pathology is protein aggregation. Here, we studied the heat shock response in familial amyloidotic polyneuropathy (FAP), a neurodegenerative disease caused by aggregation and extracellular tissue deposition of mutated transthyretin (TTR). We observed greater expression of Hsp27 and Hsp70 related to the presence of extracellular TTR aggregates in human FAP nerve, skin, and salivary gland biopsies than in normal controls. Transthyretin aggregates did not colocalize with Hsp, suggesting that extracellular TTR tissue deposits induce an intracellular stress response. Moreover, the heat shock transcription factor 1 was upregulated and localized to nuclei in affected tissues. Transgenic mice expressing the V30M mutant form of TTR similarly showed the presence of TTR deposits, induced activation of heat shock transcription factor 1, and increased synthesis of Hsp. Furthermore, the addition of toxic TTR aggregates to cultures of human and rodent neuroblastoma cell lines induced upregulation of Hsp70 and Hsp27. Taken together, these novel findings suggest new avenues for research on pathogenic mechanisms in FAP and identify the heat shock response as a potential pharmacologic treatment target for FAP.

Multi-elemental analysis of serum and amyloid fibrils in familial amyloid polyneuropathy patients

There is accumulating evidence of the involvement of biological metal imbalance in the progression of amyloid diseases such as Alzheimer's, Parkinson's and prion diseases. However, the mineral status in patients affected with familial amyloidotic polyneuropathy (FAP) has not been investigated. It is the aim of this study to determine the metal concentrations in the serum and in the transthyretin (TTR) amyloid fibrils of FAP amyloidogenic TTR (ATTR) V30M patients. Multi-elemental analysis of 17 metals by high-resolution inductively coupled plasma mass spectrometry (ICP-MS) revealed a significant decrease of the metals Fe, Cu, Zn, Cs and Ba in the serum of FAP patients (mean age 38.5 +/- 8.3 years; duration of disease 4 +/- 2.6 years) in comparison with that of healthy individuals (mean age 36.2 +/- 9.2 years). On the other hand, these metals, except Cs, were found at high levels in the amyloid fibrils of FAP patients (mean age 55.8 +/- 9.2; duration of disease 6.5 +/- 1.3 years) compared with other metals. These findings firstly suggest that the mineral status could be a candidate factor, which participates in the wide spectrum of clinical pictures of FAP patients.

Biomarkers in the assessment of therapies for familial amyloidotic polyneuropathy

The identification of specific biomarkers provides opportunities to develop early diagnostic parameters, monitor disease progression, and test drug efficiency in clinical trials. We previously demonstrated that in familial amyloidotic polyneuropathy (FAP) related to the abnormal extracellular tissue deposition of mutant transthyretin (TTR), inflammatory and apoptotic pathways are triggered in the presymptomatic stages of the disease, when nonfibrillar TTR deposits are present. In the present work, to better define biomarkers for future assessment of prophylactic and therapeutic drugs in the treatment of FAP, we extended the search for oxidative stress and apoptotic biomarkers to clinical samples and animal models presenting nonfibrillar and fibrillar TTR. We found that lipid peroxidation measured by hydroxynonenal, oxidative DNA damage measured by 8-hydroxy-2'-deoxyguanosine, and cellular redox homeostasis measured by glutaredoxin 1 were consistently increased in biopsy specimens from FAP patients and in tissues from transgenic mouse models presenting nonfibrillar TTR deposition. Death-receptor Fas, caspase-8, and Bax were also found to be increased, indicative of the involvement of death receptors in the observed apoptosis process. Removal of TTR deposition by an immunization protocol resulted in significant decreases of the selected markers we describe, corroborating the relationship between TTR deposition, oxidative stress, and apoptosis. Taken together, our results provide a robust biomarker profile for initial experimental animal studies and clinical trials to assess the application of the selected markers in therapies aimed at removal and/or inhibition of TTR polymerization.

Impairment of the ubiquitin-proteasome system associated with extracellular transthyretin aggregates in familial amyloidotic polyneuropathy

The ubiquitin-proteasome system (UPS) has been associated with neurodegenerative disorders of intracellular protein aggregation. We have studied the UPS in familial amyloidotic polyneuropathy (FAP), a neurodegenerative disorder caused by extracellular deposition of mutant transthyretin (TTR). The studies were conducted in TTR-synthesizing and non-synthesizing tissues from affected individuals, in transgenic mouse models for FAP, and in neuronal or Schwannoma cell lines cultured with TTR aggregates. In human FAP tissues presenting extracellular TTR aggregates, ubiquitin-protein conjugates were up-regulated, the proteasome levels were decreased and parkin and alpha-synuclein expression were both decreased. A similar response was detected in mouse models for TTR V30M or L55P. On the other hand, the liver, which normally synthesizes variant TTR V30M, did not show this response. Furthermore, transgenic mice immunized to decrease TTR deposition showed a significant reduction in ubiquitin levels and an increase in parkin and alpha-synuclein levels in comparison to control mice. Studies performed in cell lines with aggregates in the medium resulted in increased ubiquitin and decreased parkin levels. The overall results are indicative of TTR deposition as an external stimulus to an intracellular UPS response in FAP.

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

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

Cholesterol and anionic phospholipids increase the binding of amyloidogenic transthyretin to lipid membranes

Deposition of transthyretin (TTR) amyloid is a pathological hallmark of familial amyloidotic polyneuropathy (FAP). Recently we showed that TTR binds to membrane lipids via electrostatic interactions and that membrane binding is correlated with the cytotoxicity induced by amyloidogenic TTR. In the present study, we examined the role of lipid composition in membrane binding of TTR by a surface plasmon resonance (SPR) approach. TTR bound to lipid bilayers through both high- and low-affinity interactions. Increasing the mole fraction of cholesterol in the bilayer led to an increase in the amount of high-affinity binding of an amyloidogenic mutant (L55P) TTR. In addition, a greater amount of L55P TTR bound with high affinity to membranes made from anionic phospholipids, phosphatidylglycerol (PG) and phosphatidylserine (PS), than to membranes made from zwitterionic phospholipid phosphatidylcholine (PC). The anionic phospholipids (PS and PG) promoted the aggregation of L55P TTR by accelerating the nucleation phase of aggregation, whereas the zwitterionic phospholipid PC had little effect. These results suggest that cholesterol and anionic phospholipids may be important for TTR aggregation and TTR-induced cytotoxicity.

PPAR alpha-activation results in enhanced carnitine biosynthesis and OCTN2-mediated hepatic carnitine accumulation

In fasted rodents hepatic carnitine concentration increases considerably which is not observed in PPAR alpha-/- mice, indicating that PPAR alpha is involved in carnitine homeostasis. To investigate the mechanisms underlying the PPAR alpha-dependent hepatic carnitine accumulation we measured carnitine biosynthesis enzyme activities, levels of carnitine biosynthesis intermediates, acyl-carnitines and OCTN2 mRNA levels in tissues of untreated, fasted or Wy-14643-treated wild type and PPAR alpha-/- mice. Here we show that both enhancement of carnitine biosynthesis (due to increased gamma-butyrobetaine dioxygenase activity), extra-hepatic gamma-butyrobetaine synthesis and increased hepatic carnitine import (OCTN2 expression) contributes to the increased hepatic carnitine levels after fasting and that these processes are PPAR alpha-dependent.

Lysozyme Amyloid Oligomers and Fibrils Induce Cellular Death via Different Apoptotic/Necrotic Pathways

Among the newly discovered amyloid properties, its cytotoxicity plays a key role. Lysozyme is a ubiquitous protein involved in systemic amyloidoses in vivo and forming amyloid under destabilising conditions in vitro. We characterized both oligomers and fibrils of hen lysozyme by atomic force microscopy and demonstrated their dose (5-50 microM) and time-dependent (6-48 h) effect on neuroblastoma SH-SY5Y cell viability. We revealed that fibrils induce a decrease of cell viability after 6 h due to membrane damage shown by inhibition of WST-1 reduction, early lactate dehydrogenase release, and propidium iodide intake; by contrast, oligomers activate caspases after 6 h but cause the cell viability to decline only after 48 h, as shown by fluorescent-labelled annexin V binding to externalized phosphatidylserine, propidium iodide DNA staining, lactate dehydrogenase release, and by typical apoptotic shrinking of cells. We conclude that oligomers induce apoptosis-like cell death, while the fibrils lead to necrosis-like death. As polymorphism is a common property of an amyloid, we demonstrated that it is not a single uniform species but rather a continuum of cross-beta-sheet-containing amyloids that are cytotoxic. An abundance of lysozyme highlights a universal feature of this phenomenon, indicating that amyloid toxicity should be assessed in all clinical applications involving proteinaceous materials.

Pathologies involving the S100 proteins and RAGE

The S100 proteins are exclusively expressed in vertebrates and are the largest subgroup within the superfamily of EF-hand Ca2(+)-binding proteins Generally, S100 proteins are organized as tight homodimers (some as heterodimers). Each subunit is composed of a C-terminal, 'canonical' EF-hand, common to all EF-hand proteins, and a N-terminal, 'pseudo' EF-hand, characteristic of S100 proteins. Upon Ca2(+)-binding, the C-terminal EF-hand undergoes a large conformational change resulting in the exposure of a hydrophobic surface responsible for target binding A unique feature of this protein family is that some members are secreted from cells upon stimulation, exerting cytokine- and chemokine-like extracellular activities via the Receptor for Advanced Glycation Endproducts, RAGE. Recently, larger assemblies of some S100 proteins (hexamers, tetramers, octamers) have been also observed and are suggested to be the active extracellular species required for receptor binding and activation through receptor multimerization Most S100 genes are located in a gene cluster on human chromosome 1q21, a region frequently rearranged in human cancer The functional diversification of S100 proteins is achieved by their specific cell- and tissue-expression patterns, structural variations, different metal ion binding properties (Ca2+, Zn2+ and Cu2+) as well as their ability to form homo-, hetero- and oligomeric assemblies Here, we review the most recent developments focussing on the biological functions of the S100 proteins and we discuss the presently available S100-specific mouse models and their possible use as human disease models In addition, the S100-RAGE interaction and the activation of various cellular pathways will be discussed. Finally, the close association of S100 proteins with cardiomyopathy, cancer, inflammation and brain diseases is summarized as well as their use in diagnosis and their potential as drug targets to improve therapies in the future.

Transthyretin oligomers induce calcium influx via voltage-gated calcium channels

The deposition of transthyretin (TTR) amyloid in the PNS is a major pathological feature of familial amyloidotic polyneuropathy. The aim of the present study was to examine whether TTR could disrupt cytoplasmic Ca(2+) homeostasis and to determine the role of TTR aggregation in this process. The aggregation of amyloidogenic TTR was examined by solution turbidity, dynamic light scattering and atomic force microscopy. A nucleation-dependent polymerization process was observed in which TTR formed low molecular weight aggregates (oligomers < 100 nm in diameter) before the appearance of mature fibrils. TTR rapidly induced an increase in the concentration of intracellular Ca(2+) ([Ca(2+)](i)) when applied to SH-SY5Y human neuroblastoma cells. The greatest effect on [Ca(2+)](i) was induced by a preparation that contained the highest concentration of TTR oligomers. The TTR-induced increase in [Ca(2+)](i) was due to an influx of extracellular Ca(2+), mainly via L- and N-type voltage-gated calcium channels (VGCCs). These results suggest that increasing [Ca(2+)](i) via VGCCs may be an important early event which contributes to TTR-induced cytotoxicity, and that TTR oligomers, rather than mature fibrils, may be the major cytotoxic form of TTR.

Amyloidosis-associated kidney disease

The amyloidoses are a group of disorders in which soluble proteins aggregate and deposit extracellularly in tissues as insoluble fibrils, causing progressive organ dysfunction. The kidney is one of the most frequent sites of amyloid deposition in AL, AA, and several of the hereditary amyloidoses. Amyloid fibril formation begins with the misfolding of an amyloidogenic precursor protein. The misfolded variants self-aggregate in a highly ordered manner, generating protofilaments that interact to form fibrils. The fibrils have a characteristic appearance by electron microscopy and generate birefringence under polarized light when stained with Congo red dye. Advances in elucidating the mechanisms of amyloid fibril formation, tissue deposition, and tissue injury have led to new and more aggressive treatment approaches for these disorders. This article reviews the pathogenesis, diagnosis, clinical manifestations, and treatment of the amyloidoses, focusing heavily on the renal aspects of each of these areas.

Dialysis-related amyloidosis: late finding or hidden epidemic?

Dialysis-related amyloidosis is a complication of end-stage renal disease (ESRD) that results from retention of beta2-microglobulin (beta2M) and its deposition as amyloid fibrils into osteoarticular tissue. The clinical manifestations usually develop after several years of dialysis dependence and include carpal tunnel syndrome, destructive arthropathy, and bone cysts and fractures. High-flux membranes, daily dialysis, and hemofiltration all would be expected to delay the onset of dialysis-related amyloidosis because, to varying degrees, each increases the clearance of beta2M from the plasma. Thus what is currently a late complication of ESRD might become an even later complication as dialysis practices change. The significance of histologically evident but clinically silent beta2M amyloid, detectable not only in osteoarticular tissue but also in blood vessels, is unclear. Accumulating evidence that amyloidogenic proteins have direct and specific effects on cell processes irrespective of the extent of amyloid deposition raises the possibility that early, clinically silent beta2M amyloid deposits have unrecognized importance.

Endoplasmic Reticulum Stress Associated with Extracellular Aggregates

The hallmark of familial amyloid polyneuropathy (FAP) is the presence of extracellular deposits of transthyretin (TTR) aggregates and amyloid fibers in several tissues, particularly in the peripheral nervous system. The molecular pathways to neurodegeneration in FAP still remain elusive; activation of nuclear factor kappaB, pro-inflammatory cytokines, oxidative stress, and pro-apoptotic caspase-3 has been demonstrated "in vivo" in clinical samples and in cell culture systems. In this study, we investigated the involvement of endoplasmic reticulum (ER) stress response in FAP by showing activation of the classical unfolded protein response pathways in tissues not specialized in TTR synthesis but presenting extracellular TTR aggregate and fibril deposition. We also proved cytotoxicity by Ca2+ efflux from the ER in cell cultures incubated with TTR oligomers. Taken together, these studies evidence ER stress associated with a extracellular signal in a misfolding disorder.

In vitro inhibition of transthyretin aggregate-induced cytotoxicity by full and peptide derived forms of the soluble receptor for advanced glycation end products (RAGE)

Familial amyloidotic polyneuropathy is a neurodegenerative disorder characterized by systemic extracellular deposition of transthyretin (TTR) amyloid fibrils. The latter have been proposed to trigger neurodegeneration through engagement of the receptor for advanced glycation end products (RAGE). Here we show that TTR interaction with RAGE is conserved across mouse and human species and is not dependent on RAGE glycosylation. Moreover, strand D of TTR structure seems important for the TTR-RAGE interaction as well as a motif in RAGE (residues 102-118) located within the V-domain; this motif suppressed TTR aggregate-induced cytotoxicity in cell culture.

Activation of ERK1/2 MAP kinases in Familial Amyloidotic Polyneuropathy

Familial amyloidotic polyneuropathy (FAP) is a neurodegenerative disorder characterized by the extracellular deposition of transthyretin (TTR), especially in the PNS. Given the invasiveness of nerve biopsy, salivary glands (SG) from FAP patients were used previously in microarray analysis; mitogen-activated protein (MAP) kinase phosphatase 1 (MKP-1) was down-regulated in FAP. Results were validated by RT-PCR and immunohistochemistry both in SG and in nerve biopsies of different stages of disease progression. MKP-3 was also down-regulated in FAP SG biopsies. Given the relationship between MKPs and MAPKs, the latter were investigated. Only extracellular signal-regulated kinases 1/2 (ERK1/2) displayed increased activation in FAP SG and nerves. ERK1/2 kinase (MEK1/2) activation was also up-regulated in FAP nerves. In addition, an FAP transgenic mouse model revealed increased ERK1/2 activation in peripheral nerve affected with TTR deposition when compared to control animals. Cultured rat Schwannoma cell line treatment with TTR aggregates stimulated ERK1/2 activation, which was partially mediated by the receptor for advanced glycation end-products (RAGE). Moreover, caspase-3 activation triggered by TTR aggregates was abrogated by U0126, a MEK1/2 inhibitor, indicating that ERK1/2 activation is essential for TTR aggregates-induced cytotoxicity. Taken together, these data suggest that abnormally sustained activation of ERK in FAP may represent an early signaling cascade leading to neurodegeneration.

Doxycycline disrupts transthyretin amyloid: evidence from studies in a FAP transgenic mice model

Familial amyloidotic polyneuropathy is an autosomal dominant disorder mainly characterized by the extracellular deposition of transthyretin, with special involvement of the peripheral nerve. Several animal models have been generated, including transgenic mice carrying the most prevalent TTR mutation (TTR Val30Met). TTR-Val30Met mice without endogenous TTR (TTR-Val30Met X TTR-KO) were previously analyzed in our laboratory and approximately 60% of the animals over 1 year of age were found to have deposition as amyloid, i.e., with Congo red (CR) -positive material, constituting a good tool to investigate the effect of drugs on TTR deposition and fibrillogenesis. We recently showed that the drug doxycycline acts in vitro as a TTR fibril disrupter. In the present work we assessed the activity of this drug in vivo in the TTR-Met30Val X TTR-KO mice. Doxycycline was administrated in the drinking water to 23- to 28-month-old mice over a period of 3 months. Immunohistochemistry analyses revealed no differences in nonfibrillar TTR deposition between treated (n=11) and untreated mice (n=11). However, CR-positive material was observed only in the control group (untreated) whereas none of the animals treated with doxycycline was CR-positive. Immunohistochemistry for several markers associated with amyloid, such as matrix metalloproteinase-9 (MMP-9) and serum amyloid P component (SAP), was performed. MMP-9 was altered with significantly lower levels in treated animals compared with the control group. Mouse SAP was absent in treated animals, being observed only in untreated animals presenting TTR congophilic deposits. These results indicate that doxycycline is capable of disrupting TTR CR-positive amyloid deposits and decreases standard markers associated with fibrillar deposition, being a potential drug in the treatment of amyloidosis.

Argpyrimidine, a methylglyoxal-derived advanced glycation end-product in familial amyloidotic polyneuropathy

FAP (familial amyloidotic polyneuropathy) is a systemic amyloid disease characterized by the formation of extracellular deposits of transthyretin. More than 80 single point mutations are associated with amyloidogenic behaviour and the onset of this fatal disease. It is believed that mutant forms of transthyretin lead to a decreased stability of the tetramer, which dissociates into monomers that are prone to unfolding and aggregation, later forming beta-fibrils in amyloid deposits. This theory does not explain the formation of beta-fibrils nor why they are toxic to nearby cells. Age at disease onset may vary by decades for patients with the same mutation. Moreover, non-mutated transthyretin also forms the same deposits in SSA (senile systemic amyloidosis), suggesting that mutations may only accelerate this process, but are not the determinant factor in amyloid fibril formation and cell toxicity. We propose that glycation is involved in amyloidogenesis, since amyloid fibrils present several properties common to glycated proteins. It was shown recently that glycation causes the structural transition from the folded soluble form to beta-fibrils in serum albumin. We identified for the first time a methylglyoxal-derived advanced glycation end-product, argpyrimidine [N(delta)-(5-hydroxy-4,6-dimethylpyrimidin-2-yl)-L-ornithine] in amyloid fibrils from FAP patients. Unequivocal argpyrimidine identification was achieved chromatographically by amino acid analysis using dabsyl (4-dimethylaminoazobenzene-4'-sulphonyl) chloride. Argpyrimidine was found at a concentration of 162.40+/-9.05 pmol/mg of protein in FAP patients, and it was not detected in control subjects. The presence of argpyrimidine in amyloid deposits from FAP patients supports the view that protein glycation is an important factor in amyloid diseases.

Advanced glycation end products induce death of retinal neurons via activation of nitric oxide synthase

The purpose of this study was to determine whether advanced glycation end products (AGEs) are neurotoxic for cultured retinal neurons consisting mainly of amacrine cells, and to determine whether endogenous nitric oxide (NO) is involved in the toxicity. Cultured retinal neurons obtained from fetal Wistar rats (gestational age 19 days) were maintained in culture for 10 days, and then exposed to different concentrations of AGEs (0.02, 0.1, and 0.5 mg ml(-1)) in cultured media for different lengths of time. Both trypan blue exclusion and TUNEL assay were used to determine whether AGEs were neurotoxic, and NG-nitro-L-arginine methyl ester (L-NAME, 500 microM), a nitric oxide synthase (NOS) inhibitor, was used to determine whether NO was involved. Immunohistochemical analyses were performed to determine whether specific receptors of AGEs (RAGE) are present on cultured retinal neurons; caspase-3 was activated, and 3-nitrotyrosine was expressed on neurons treated with AGEs. Nitrite levels were measured in the supernatants of the media where neurons were incubated with AGEs. AGEs induced cell death in a time- and dose-dependent manner. TUNEL-positive cells and immunoreactivity to cleaved caspase-3 were enhanced on neurons following exposure to AGEs. L-NAME significantly suppressed the AGEs-induced neurotoxicity as assessed by both trypan blue exclusion and TUNEL assays. Activation of NOS was suggested by enhanced immunoreactivity to 3-nitrotyrosine on neurons and increased nitrite levels in the media incubated with AGEs. These results indicate that AGEs are neurotoxic to retinal neurons in culture through the activation of NOS. Apoptotic pathways may be in part involved in the death of the neurons.

A phytol-enriched diet induces changes in fatty acid metabolism in mice both via PPARalpha-dependent and -independent pathways

Branched-chain fatty acids (such as phytanic and pristanic acid) are ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARalpha) in vitro. To investigate the effects of these physiological compounds in vivo, wild-type and PPARalpha-deficient (PPARalpha-/-) mice were fed a phytol-enriched diet. This resulted in increased plasma and liver levels of the phytol metabolites phytanic and pristanic acid. In wild-type mice, plasma fatty acid levels decreased after phytol feeding, whereas in PPARalpha-/- mice, the already elevated fatty acid levels increased. In addition, PPARalpha-/- mice were found to be carnitine deficient in both plasma and liver. Dietary phytol increased liver free carnitine in wild-type animals but not in PPARalpha-/- mice. Investigation of carnitine biosynthesis revealed that PPARalpha is likely involved in the regulation of carnitine homeostasis. Furthermore, phytol feeding resulted in a PPARalpha-dependent induction of various peroxisomal and mitochondrial beta-oxidation enzymes. In addition, a PPARalpha-independent induction of catalase, phytanoyl-CoA hydroxylase, carnitine octanoyltransferase, peroxisomal 3-ketoacyl-CoA thiolase, and straight-chain acyl-CoA oxidase was observed. In conclusion, branched-chain fatty acids are physiologically relevant ligands of PPARalpha in mice. These findings are especially relevant for disorders in which branched-chain fatty acids accumulate, such as Refsum disease and peroxisome biogenesis disorders.

Up-regulation of the extracellular matrix remodeling genes, biglycan, neutrophil gelatinase-associated lipocalin, and matrix metalloproteinase-9 in familial amyloid polyneuropathy

Familial amyloid polyneuropathy (FAP) is characterized by extracellular deposition of transthyretin (TTR) aggregates and amyloid fibrils, particularly in the peripheral nervous system (PNS) and is accompanied with changes in connective tissue. Given the invasiveness of nerve biopsy, FAP salivary glands (SGs) were used in microarray analysis; biglycan and neutrophil gelatinase-associated lipocalin (NGAL), two genes related to extracellular matrix (ECM) remodeling were overexpressed in FAP. Results were validated by RT-PCR and immunohistochemistry both in SG and in nerve biopsies of different stages of disease progression. Matrix metalloproteinase-9 (MMP-9), which exists as a complex with NGAL, was also increased in FAP and in vitro degraded TTR aggregates and fibrils; however in the presence of serum amyloid P, a universal amyloid component, TTR fibrils became resistant to MMP-9 proteolysis. Biglycan, NGAL, and MMP-9 are transcriptionally up-regulated by NF-kappaB, a transcription factor that is activated in FAP nerves and SG. Given the relationship between inflammation and ECM remodeling, and the increase of proinflammatory cytokines in FAP, IL-10 expression in FAP nerves was investigated; IL-10 increased after fibril deposition, suggesting a balance between proinflammatory and anti-inflammatory mechanisms. Changes in ECM-related proteins and inflammatory events may be relevant for therapy in FAP and other neurodegenerative disorders.

Anaemia of chronic disease in AA amyloidosis is associated with allele 2 of the interleukin-1beta-511 promoter gene and raised levels of interleukin-1beta and interleukin-18

OBJECTIVE

In amyloid A (AA) amyloidosis the receptor for advanced glycation end products is a target for the circulating amyloid precursor protein (SAA) resulting in upregulation of the proinflammatory cytokine pathway. Besides inducing hepatic SAA synthesis the interleukin-1 cytokine family is involved in the regulation of haematopoiesis. We therefore studied the relationship between the circulating levels of interleukin-1beta (IL-1beta) and interleukin-18 (IL-18), a new member of the IL-1 complex, as well as polymorphisms within the IL-1 cluster with the occurrence of anaemia in patients with AA amyloidosis.

DESIGN, SETTING AND SUBJECTS

The study included 54 adult patients with biopsy-proven reactive amyloidosis allocated into three groups on the basis of haemoglobin (Hb) level: group I included all patients with Hb < 110 g L(-1) (n = 16); group II patients (Hb > 110 g L(-1), n = 16) were selected to match group I patients with respect to sex, age, underlying disease (seropositive, erosive rheumatoid arthritis) and renal function; and group III patients (n = 38) represented all patients (unselected) with Hb > or = 110 g L(-1). Gene polymorphisms were studied by polymerase chain reaction restriction length assay and included the base exchange at position-889 of the IL-1alpha gene, the polymorphic region at position-511 and the polymorphic locus at exon 5, position +3954 of the IL-1beta gene, as well as the IL-1 receptor antagonist (IL-1Ra) exon 2 polymorphism caused by the 86-bp tandem repeats. Plasma IL-1beta, IL-1alpha, IL-18, IL-1 Ra, SAA, ferritin, soluble transferrin receptor and erythropoietin levels were studied by enzyme immunoassays.

RESULTS

Circulating IL-beta and IL-18 were significantly raised in the anaemic patients with AA amyloidosis when compared with group II patients (matched, Hb > 110 g L(-1)) as well as group III patients (nonmatched, Hb > or = 110 g L(-1)). A significant inverse relationship was found between IL-1beta and haemoglobin levels, as well as between IL-18 and haemoglobin levels. The frequency of allele 2 (T) of the IL-1beta-511 promoter gene was significantly increased and that of allele 1 (C) decreased in anaemic amyloid patients (group I) when compared with group II and III patients. Circulating IL-1beta levels tended to be higher amongst the IL-1beta-511 allele 2 carriers than amongst the noncarriers, as well as amongst the anaemic amyloid patients filling all criteria of anaemia of chronic disease.

CONCLUSION

The occurrence of anaemia in patients with AA amyloidosis is associated with allele 2 (T) of the IL-1beta-511 promoter gene and elevated levels of circulating IL-1beta and IL-18. In AA amyloidosis the raised cytokine levels may generate a vicious cycle leading to accelerated amyloidogenesis, suppression of erythropoiesis and aggravation of the underlying inflammatory disorder.

Deposition and passage of transthyretin through the blood-nerve barrier in recipients of familial amyloid polyneuropathy livers

Familial amyloid polyneuropathy (FAP) is characterized by deposition of mutated transthyretin (TTR) in the peripheral nervous system. Prior to amyloid fibrils, nonfibrillar TTR aggregates are deposited inducing oxidative stress with increased nitration (3-NT). As the major source of TTR is the liver, liver transplantation (LT) is used to halt FAP. Given the shortage of liver donors, domino LT (DLT) using FAP livers is performed. The correlation between TTR deposition in the skin and nerve was tested in biopsies from normal individuals, asymptomatic carriers (FAP 0) and FAP patients; in FAP 0, nonfibrillar TTR was observed both in the skin and nerve in the same individuals; in patients, amyloid was detected in both tissues. The occurrence of amyloidosis in recipients of FAP livers was evaluated 1-7 years after DLT: TTR deposition occurred in the skin 3 years after transplantation either as amyloid or aggregates; in one of the recipients, fibrillar TTR was present in the epineurium 6 years after DLT. Deposits were scarce and 3-NT immunostaining was irrelevant. Nerve biopsies from DLT recipients had no FAP-related neuropathy. Our findings suggest that TTR amyloid formation occurs faster than predicted and that TTR of liver origin can cross the blood-nerve barrier. Recipients of FAP livers should be under surveillance for TTR deposition and tissue damage.

Glycation, inflammation, and RAGE: a scaffold for the macrovascular complications of diabetes and beyond

The cardiovascular complications of diabetes represent the leading cause of morbidity and mortality in affected subjects. The impact of hyperglycemia may be both direct and indirect: indirect consequences of elevated blood glucose lead to generation of advanced glycation endproducts, the products of nonenzymatic glycation/oxidation of proteins/lipids that accumulate in the vessel wall, and are signal transduction ligands for Receptor for AGE (RAGE). Although enhanced in diabetes, AGE accumulation also occurs in euglycemia and aging, albeit to lower degrees, driven by oxidant stress and inflammation. In hyperglycemia, production of 3-deoxyglucosone, at least in part via the polyol pathway, provides an amplification loop to sustain AGE generation, oxidant stress, and vascular activation. Furthermore, recruitment of inflammatory cells bearing S100/calgranulins, also ligands for RAGE, augments vascular dysfunction. We hypothesize that activation of RAGE is a final common pathway that transduces signals from these diverse biochemical and molecular species, leading to cardiovascular perturbation. Ultimately, these pathways synergize to construct a scaffold on which the complications of diabetes in the vasculature and heart may be built. We propose that antagonism of RAGE will provide a unique means to dismantle this scaffold and, thereby, suppress initiation/progression of vascular disease and cardiac dysfunction that accompany diabetes and aging.

Neurodegeneration in familial amyloid polyneuropathy: from pathology to molecular signaling

Familial amyloid polyneuropathy (FAP) is an autosomal dominant neurodegenerative disorder related to the systemic deposition of mutated transthyretin (TTR) amyloid fibrils, particularly in peripheral nervous system (PNS). TTR fibrils are diffusely distributed in the PNS of FAP patients, involving nerve trunks, plexuses and ganglia. In peripheral nerves, amyloid deposits are prominent in the endoneurium, near blood vessels, Schwann cells and collagen fibrils. Fiber degeneration is axonal, beginning in the unmyelinated and low diameter myelinated fibers. Several hypotheses have been raised to explain axonal and neuronal loss: (i) compression of the nervous tissue by amyloid; however, a cause-effect relationship between amyloid deposition, structural nerve changes and degeneration was never clearly made; (ii) role of nerve ischemia secondary to lesions caused by perivascular amyloid, which is also doubtful as compromised blood flow was never demonstrated; (iii) lesions in the dorsal root ganglia neurons or Schwann cells. Recently, evidence for the presence of toxic non-fibrillar TTR aggregates early in FAP nerves constituted a first step to unravel molecular signaling related to neurodegeneration in FAP. The toxic nature of TTR non-fibrillar aggregates, and not mature TTR fibrils, was evidenced by their ability to induce the expression of oxidative stress and inflammation-related molecules in neuronal cells, driving them into apoptotic pathways. How these TTR aggregates exert their effects is debatable; interaction with cellular receptors, namely, the receptor for advanced glycation endproducts (RAGE), is a probable candidate mechanism. The pathology and the yet unknown molecular signaling mechanisms responsible for neurodegeneration in FAP are discussed.

The systemic amyloidoses

PURPOSE OF REVIEW

Clinical management of the amyloidoses has historically been the province of rheumatologists, because of the relation to long-standing inflammation in rheumatoid arthritis, ankylosing spondylitis, and juvenile chronic arthritis. Currently, nephrologists, hematologist-oncologists, neurologists, and transplant surgeons all have a diagnostic or therapeutic interest. Current advances, using the tools of physical biochemistry, cell biology, and genetics, have begun to impact the diagnosis and clinical management of these disorders and raise questions regarding our notions of protein conformation in vivo and how nonnatively folded proteins may produce disease.

RECENT FINDINGS

It appears that all amyloidogenic precursors undergo some degree of misfolding that allows them to populate an immediate precursor pool from which they rapidly aggregate. Depending on the particular protein, a variety of mechanisms appear operative, some of which involve nonphysiologic proteolysis, defective physiologic proteolysis, mutations involving changes in thermodynamic or kinetic properties, and pathways that are yet to be defined. Whatever the particular process, the result is a tendency toward oligomeric aggregation followed by the assembly of higher order structures that become insoluble under physiologic conditions. Detailed analyses have been described for transthyretin (senile systemic amyloidosis and familial amyloid polyneuropathy), immunoglobulin light chains (light-chain amyloid), beta2 microglobulin (dialysis-related amyloid), and apolipoprotein A1, and are in process for others. SUMMARY Therapies have been proposed based on precursor stabilization (transthyretin), elimination of the synthesizing cell (light-chain amyloid), fibril disruption and immunization to induce host-mediated aggregate clearance (Alzheimer disease, light-chain amyloid, prions), and aggressive therapy of a primary inflammatory process (amyloid A). During the next decade, the value of these therapies, and others, suggested by studies on the basic properties of cells and proteins, will become clear.

Blockade of receptor for advanced glycation endproducts: a new target for therapeutic intervention in diabetic complications and inflammatory disorders

The glycation and oxidation of proteins/lipids leads to the generation of a new class of biologically active moieties, the advanced glycation endproducts (AGEs). Recent studies have elucidated that carboxymethyllysine (CML) adducts of proteins/lipids are a highly prevalent AGE in vivo. CML-modified adducts are signal transduction ligands of the receptor for AGE (RAGE), a member of the immunoglobulin superfamily. Importantly, CML-modified adducts accumulate in diverse settings. In addition to enhanced formation in settings of high glucose, these adducts form in inflammatory milieu. Studies performed both in vitro and in vivo have suggested that the proinflammatory/tissue destructive consequences of RAGE activation in the diabetic/inflamed environment may be markedly attenuated by blockade of the ligand-RAGE axis. Here, we will summarize the known consequences of RAGE activation in the tissues and highlight novel areas for therapeutic intervention in these disease states.

Glycation induces formation of amyloid cross-beta structure in albumin

Amyloid fibrils are components of proteinaceous plaques that are associated with conformational diseases such as Alzheimer's disease, transmissible spongiform encephalopathies, and familial amyloidosis. Amyloid polypeptides share a specific quarternary structure element known as cross-beta structure. Commonly, fibrillar aggregates are modified by advanced glycation end products (AGE). In addition, AGE formation itself induces protein aggregation. Both amyloid proteins and protein-AGE adducts bind multiligand receptors, such as receptor for AGE, CD36, and scavenger receptors A and B type I, and the serine protease tissue-type plasminogen activator (tPA). Based on these observations, we hypothesized that glycation induces refolding of globular proteins, accompanied by formation of cross-beta structure. Using transmission electron microscopy, we demonstrate here that glycated albumin condensates into fibrous or amorphous aggregates. These aggregates bind to amyloid-specific dyes Congo red and thioflavin T and to tPA. In contrast to globular albumin, glycated albumin contains amino acid residues in beta-sheet conformation, as measured with circular dichroism spectropolarimetry. Moreover, it displays cross-beta structure, as determined with x-ray fiber diffraction. We conclude that glycation induces refolding of initially globular albumin into amyloid fibrils comprising cross-beta structure. This would explain how glycated ligands and amyloid ligands can bind to the same multiligand "cross-beta structure" receptors and to tPA.

4'-iodo-4'-deoxydoxorubicin and tetracyclines disrupt transthyretin amyloid fibrils in vitro producing noncytotoxic species: screening for TTR fibril disrupters

Transthyretin Leu55Pro is one of the most aggressive mutations in familial amyloidotic polyneuropathy, an autosomal dominant disorder characterized by extracellular deposition of fibrillar amyloid protein. This variant has the ability to form fibrils in vitro under physiological conditions (PBS, pH 7.4). We studied by transmission electron microscopy the effect of the drug 4'-iodo-4'-deoxydoxorubicin (I-DOX) on the in vitro assembly of TTR Leu55Pro fibrils by following fibril growth over a 15 day period. Our results showed that I-DOX at a concentration of 10-5 M/100 microg fibrils does not inhibit fibril formation in up to 10 days since fibrils identical to the ones present in the untreated sample were observed. However, after 15 days of treatment, only round particles, resembling soluble native TTR, were observed. We also tested the ability of tetracyclines and nitrophenols to interfere with amyloid fibril formation for 17 days; the group of compounds tested showed fibril disruption activity to different extents: doxycycline and 2,4-dinitrophenol resulted in complete disaggregation of fibrils. The species generated upon I-DOX and tetracyclines treatments were nontoxic, as revealed by the lack of significant caspase-3 activation on a Schwannoma cell line, making them potential therapeutic drugs in TTR-related and other amyloidosis.

Suppression of experimental autoimmune encephalomyelitis by selective blockade of encephalitogenic T-cell infiltration of the central nervous system

Multiple sclerosis (MS) is a devastating neuroinflammatory disorder of the central nervous system (CNS) in which T cells that are reactive with major components of myelin sheaths have a central role. The receptor for advanced glycation end products (RAGE) is present on T cells, mononuclear phagocytes and endothelium. Its pro-inflammatory ligands, S100-calgranulins, are upregulated in MS and in the related rodent model, experimental autoimmune encephalomyelitis (EAE). Blockade of RAGE suppressed EAE when disease was induced by myelin basic protein (MBP) peptide or encephalitogenic T cells, or when EAE occurred spontaneously in T-cell receptor (TCR)-transgenic mice devoid of endogenous TCR-alpha and TCR-beta chains. Inhibition of RAGE markedly decreased infiltration of the CNS by immune and inflammatory cells. Transgenic mice with targeted overexpression of dominant-negative RAGE in CD4+ T cells were resistant to MBP-induced EAE. These data reinforce the importance of RAGE-ligand interactions in modulating properties of CD4+ T cells that infiltrate the CNS.

Receptor for advanced glycation endproducts: a multiligand receptor magnifying cell stress in diverse pathologic settings

Receptor for Advanced Glycation Endproducts (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules capable of interacting with a broad spectrum of ligands, including advanced glycation endproducts (AGEs), amyloid fibrils, S100/calgranulins and amphoterin. The biology of RAGE is dictated by the accumulation of these ligands at pathologic sites, leading to upregulation of the receptor and sustained RAGE-dependent cell activation eventuating in cellular dysfunction. Although RAGE is not central to the initial pathogenesis of disorders in which it ultimately appears to be involved, such as diabetes, amyloidoses, inflammatory conditions and tumors (each of these conditions leading to accumulation of RAGE ligands), the receptor functions as a progression factor driving cellular dysfunction and exaggerating the host response towards tissue destruction, rather than restitution of homeostasis. These observations suggest that RAGE might represent a therapeutic target in a diverse group of seemingly unrelated disorders linked only by a multiligand receptor with an unusually wide and diverse repertoire of ligands, namely, RAGE.

Amyloid: morphology and toxicity

We have expressed transthyretin (TTR) mutants which have significantly destabilised tetramers that aggregate into amyloid fibrils via a series of intermediates. We used atomic force microscopy to follow the morphology of aggregates during fibril formation. Initially, amorphous aggregates are formed that subsequently mature into fibrillar structures. This observation is interpreted as an optimisation of beta-strand registers. The rate of aggregation and maturation is highly temperature-dependent suggesting that entropic forces significantly contribute to stability. In addition, we identified a correlation between the presence of early formed aggregates of TTR and cytotoxicity. The toxic response was mediated via an apoptotic mechanism. The fact that early formed amorphous aggregates, but not more mature fibrils, exert a toxic response suggests that the rate of fibril formation may be a critical parameter. We propose that a slow rate of aggregation facilitates an increased concentration of a toxic intermediate.

Presence of variant transthyretin in aqueous humor of a patient with familial amyloidotic polyneuropathy after liver transplantation

To determine the origin of transthyretin (TTR) in the aqueous humor of patients with familial amyloidotic polyneuropathy (FAP), we measured TTR levels and analyzed the TTR forms in the aqueous humor of three FAP patients (one patient; liver transplanted, and two patients; non-transplanted). The total TTR levels were almost the same as reported previously in non-transplanted patients and slightly increased in a transplanted patient. Analyses with mass spectrometry in the two non-transplanted FAP ATTR V30M patients revealed that both wild type and variant TTR forms were detected in their aqueous humor samples. Moreover, variant TTR forms could be detected in the aqueous humor of the transplanted patient while the liver produced no variant TTR. These results suggest that variant TTR in aqueous humor may be derived from retina where TTR was produced. In conclusion, TTR metabolism may occur in its own ocular cycle and variant TTR produced by the retina may play an important role in amyloid formation in the ocular tissues of FAP patients.

Evidence for early cytotoxic aggregates in transgenic mice for human transthyretin Leu55Pro

Familial amyloidotic polyneuropathy (FAP) is a lethal autosomal dominant disorder characterized by systemic extracellular deposition of transthyretin (TTR) amyloid fibrils. Several groups have generated transgenic mice carrying human TTR Val30Met, the most common mutation in FAP. To study amyloidogenicity and cytotoxicity of different TTRs, we produced transgenic mice expressing human TTR Leu55Pro, one of the most aggressive FAP-related mutations. TTR deposition and presence of amyloid fibrils was investigated and compared to animals carrying the human TTR Val30Met gene kept under the same conditions. Deposition in a C57BL/6J background (TTR-Leu55Pro mice) and in a TTR-null background [TTR-Leu55Pro X TTR-knockout (KO) mice] was compared. Animals in a C57BL/6J background presented early (1 to 3 months) nonfibrillar TTR deposition but amyloid was absent. In a TTR-null background, presence of amyloid fibrils was detected starting at 4 to 8 months with a particular involvement of the gastrointestinal tract and skin. This data suggested that TTR homotetramers are more prone to fibril formation than TTR murine wild-type/human mutant heterotetramers. The nature of the deposited material was further investigated by immunocytochemistry. Both amorphous aggregates and small TTR fibrils were present in TTR-Leu55Pro X TTR-KO transgenics. We observed that these TTR deposits mimic the toxic effect of TTR deposits in FAP: animals with TTR deposition, present approximately twofold increased levels of nitrotyrosine in sites related to deposition. The TTR-Leu55Pro X TTR-KO mice here described are an important tool for the dual purpose of investigating factors involved in amyloidogenesis and in cytotoxicity of deposited TTR.