Detection of TTR Amyloid in the Conjunctiva Using a Novel Fluorescent Ocular Tracer.

Background: Transthyretin amyloidosis (ATTR) is a significant cause of cardiomyopathy and other morbidities in the elderly and Black Americans. ATTR can be treated with new disease-modifying therapies, but large shortfalls exist in its diagnosis. The objective of this study was to test whether TTR amyloid can be detected and imaged in the conjunctiva using a novel small-molecule fluorescent ocular tracer, with the implication that ATTR might be diagnosable by a simple eye examination. Methods: Three approaches were used in this study. First, AMDX-9101 was incubated with in vitro aggregated TTR protein, and changes in its excitation and emission spectra were quantified. Second, a cadaver eye from a patient with familial amyloid polyneuropathy type II TTR mutation and a vitrectomy sample from an hATTR patient were incubated with AMDX-9101 and counterstained with Congo Red and antibodies to TTR to determine whether AMDX-9101 labels disease-related TTR amyloid deposits in human conjunctiva and eye. Last, imaging of in vitro aggregated TTR amyloid labeled with AMDX-9101 was tested in a porcine ex vivo model, using a widely available clinical ophthalmic imaging device. Results: AMDX-9101 hyper-fluoresced in the presence of TTR amyloid in vitro, labeled TTR amyloid deposits in postmortem human conjunctiva and other ocular tissues and could be detected under the conjunctiva of a porcine eye using commercially available ophthalmic imaging equipment. Conclusions: AMDX-9101 enabled detection of TTR amyloid in the conjunctiva, and the fluorescent binding signal can be visualized using commercially available ophthalmic imaging equipment. Translational Relevance: AMDX-9101 detection of TTR amyloid may provide a potential new and noninvasive test for ATTR that could lead to earlier ATTR diagnosis, as well as facilitate development of new therapeutics.

Systemic AL amyloidosis: current approach and future direction.

Systemic Light chain (AL) amyloidosis is a monoclonal plasma cell proliferative disorder characterized by deposition of amyloidogenic monoclonal light chain fragments causing organ dysfunction. It is a fatal disease and if not diagnosed and treated early can lead to organ failure and potentially death. The renal system along with the cardiovascular system are the most common organs involved but other organs such as gut and liver can be involved as well. The initial evaluation of patients requires confirming the diagnosis with tissue biopsy and staining with Congo red followed by confirmatory typing with mass spectrometry of the Congo red positive tissue. Then establishing the extent of the organs involvement by various staging and biomarkers testing. The treatment options and the tolerability of therapy depend on the disease staging, frailty, and co-morbidities. The autologous hematopoietic cell transplantation (HCT) after high dose melphalan therapy is an effective strategy which is usually done after initial bortezomib induction therapy. Unfortunately, most systemic AL amyloidosis patients are not candidate for HCT due to frailty, old age, multi-organ involvement, renal and heart failure at the time of diagnosis. While it is widely accepted that the patients need to be treated until they achieve complete hematologic response, the maintenance therapy after HCT is not well established in AL amyloidosis. In this review, we report the literature on the latest treatment updates of AL amyloidosis and the ongoing clinical trials highlighting the future treatments.

Renal amyloidosis: a new time for a complete diagnosis.

Amyloidoses are a group of disorders in which soluble proteins aggregate and deposit extracellularly in tissues as insoluble fibrils, causing organ dysfunction. Clinical management depends on the subtype of the protein deposited and the affected organs. Systemic amyloidosis may stem from anomalous proteins, such as immunoglobulin light chains or serum amyloid proteins in chronic inflammation or may arise from hereditary disorders. Hereditary amyloidosis consists of a group of rare conditions that do not respond to chemotherapy, hence the identification of the amyloid subtype is essential for diagnosis, prognosis, and treatment. The kidney is the organ most frequently involved in systemic amyloidosis. Renal amyloidosis is characterized by acellular pathologic Congo red-positive deposition of amyloid fibrils in glomeruli, vessels, and/or interstitium. This disease manifests with heavy proteinuria, nephrotic syndrome, and progression to end-stage kidney failure. In some situations, it is not possible to identify the amyloid subtype using immunodetection methods, so the diagnosis remains indeterminate. In cases where hereditary amyloidosis is suspected or cannot be excluded, genetic testing should be considered. Of note, laser microdissection/mass spectrometry is currently the gold standard for accurate diagnosis of amyloidosis, especially in inconclusive cases. This article reviews the clinical manifestations and the current diagnostic landscape of renal amyloidosis.

Binding of proteases to fibrillar amyloid-beta protein and its inhibition by Congo red.

Fibrillar amyloid-beta protein (fAbeta) is the principal component of amyloid plaques in the brains of patients with Alzheimer's disease (AD). We have recently reported that activity of trypsin is inhibited by fAbeta and that trypsin can bind to fAbeta. Neprilysin and insulysin are important proteases for the clearance of soluble Abeta. Here, we report that fAbeta also binds to neprilysin and insulysin, which results in the inhibition of their proteolytic activities. These findings suggest that clearance of soluble Abeta may be defective in AD because of binding of proteases to amyloid plaques, leading to inactivation of proteases that are required for catabolism of Abeta. The identification of compounds that can inhibit binding of proteases to fAbeta may, therefore, be of significance for therapeutic intervention in AD. Congo red and Thioflavin T are widely used for histopathological examination of amyloid plaques because of their strong affinity to fibrillar amyloid proteins. We examined the effect of Congo red and Thioflavin T (potent fAbeta-binding compounds) on the binding of different proteases to fAbeta. While Congo red inhibited the binding of trypsin, neprilysin and insulysin to fAbeta, Thioflavin T did not have any effect. The effect of Congo red was concentration-dependent and the inhibitory effect was in the order of trypsin > insulysin > neprilysin. When the effect of prebound-Congo red to fAbeta was examined, trypsin was unable to bind to this complex suggesting that Congo red may have better affinity than trypsin for binding to fAbeta. Based on these results, we propose that the inhibition of binding of proteases to amyloid plaques may help in reducing the deposition of Abeta in AD.

Congo red and protein aggregation in neurodegenerative diseases.

Congo red is a commonly used histological dye for amyloid detection. The specificity of this staining results from Congo red's affinity for binding to fibril proteins enriched in beta-sheet conformation. Unexpectedly, recent investigations indicate that the dye also possesses the capacity to interfere with processes of protein misfolding and aggregation, stabilizing native protein monomers or partially folded intermediates, while reducing concentration of more toxic protein oligomers. Inhibitory effects of Congo red upon amyloid toxicity may also range from blockade of channel formation and interference with glycosaminoglycans binding or immune functions, to the modulation of gene expression. Particularly, Congo red exhibits ameliorative effect in models of neurodegenerative disorders, such as Alzheimer's, Parkinson's, Huntington's and prion diseases. Another interesting application of Congo red analogues is the development of imaging probes. Based on their small molecular size and penetrability through blood-brain barrier, Congo red congeners can be used for both antemortem and in vivo visualization and quantification of brain amyloids. Therefore, understanding mechanisms involved in dye-amyloidal fibril binding and inhibition of aggregation will provide instructive guides for the design of future compounds, potentially useful for monitoring and treating neurodegenerative diseases.

Systemic administration of Congo red does not improve motor or cognitive function in R6/2 mice.

Huntington's disease (HD) is a progressive neurodegenerative disorder for which there is no treatment. Prior to the onset of symptoms, abnormal protein aggregates (inclusions) are found in neurons in humans and R6/2 mice. It has been suggested that the progression of HD can be slowed or prevented by disruption of the aggregation process. In agreement with this, it has been reported that systemic treatment of R6/2 mice with Congo red caused a reduction in numbers of striatal inclusions and an improvement in motor symptoms and survival [Sanchez, I., Mahlke, C., Yuan, J., 2003. Pivotal role of oligomerization in expanded polyglutamine neurodegenerative disorders. Nature 421, 373-379]. Here we attempted to replicate this study. We extended the experiment to include measurement of the effects of Congo red on cognitive function in R6/2 mice. Congo red treatment failed to ameliorate either motor or cognitive deficits in R6/2 mice. We suggest that this is due to the inability of Congo red to cross the blood-brain barrier. Since it does not improve the behavioural deterioration that is a key feature of HD, Congo red is unlikely to be useful as a therapy for HD.

A systematic review of prion therapeutics in experimental models.

Prion diseases are transmissible, invariably fatal, neurodegenerative diseases which include Creutzfeldt-Jakob disease (CJD) in humans and bovine spongiform encephalopathy and scrapie in animals. A large number of putative treatments have been studied in experimental models over the past 30 years, with at best modest disease-modifying effects. The arrival of variant CJD in the UK in the 1990s has intensified the search for effective therapeutic agents, using an increasing number of animal, cellular and in vitro models with some recent promising proof of principle studies. Here, for the first time, we present a comprehensive systematic, rather than selective, review of published data on experimental approaches to prion therapeutics to provide a scientific resource for informing future therapeutics research, both in laboratory models and in clinical studies.

Evaluation of anti-prion activity of congo red and its derivatives in experimentally infected hamsters.

Among transmissible spongiform encephalopathies (TSE), particularly dreadful are the bovine spongiform encephalopathy (BSE), because of its epidemic character, and the new variant of Creutzfeldt-lakob disease (vCJD) in man, possibly related to BSE prion, through the intake of infected food. To treat TSE, many potentially therapeutic agents have been tested: some of them, among which is Congo Red (CAS 573-58-0, CR), delayed the onset of symptoms in scrapie-infected rodents, and some CR derivatives proved to be effective in vitro. The capacity of a synthesized CR derivative (CR-A) and of the aromatic central benzidine rings of CR (CR-B) to abrogate scrapie-induced disease in experimentally infected hamsters was assayed. CR, used as reference substance, administered i.c. after pre-incubation with the scrapie inoculum, was strongly effective in slowing the progression of the infection, while both CR-A and CR-B, administered alone or together, were not effective. Both CR-A and CR, when administered by subcutaneous route in i.c. scrapie-infected animals. prolonged the survival time in comparison to controls; CR-B was not effective. Moreover, both CR and CR-A were very effective in prolonging the survival time of i.p. scrapie-infected hamsters. The hypothesis of possible different mechanisms of interaction between CR or CR-A and the scrapie agent related to the chemical structures of the molecules is discussed.

Opposite effects of dextran sulfate 500, the polyene antibiotic MS-8209, and Congo red on accumulation of the protease-resistant isoform of PrP in the spleens of mice inoculated intraperitoneally with the scrapie agent.

The mode and the site of action of the major antiscrapie drugs have been studied by investigating their effects on the abnormal protease-resistant isoform of PrP (PrPres) and on its accumulation in mouse spleen. Day-by-day PrPres accumulation in the spleen and in other peripheral organs was first monitored to describe the early steps of scrapie pathogenesis. Three phases were identified: the detection of scrapie inoculum on the day of scrapie infection, a clearance phase, and then the peripheral accumulation of PrPres. In a second step, the effects of the polyene antibiotic MS-8209, the polyanion dextran sulfate 500 (DS500), and Congo red were assessed on these phases, after the drugs were coincubated with scrapie inoculum. Highly different mechanisms and sites of action were apparent. MS-8209 had a weak effect on the accumulation of PrPres in spleen, suggesting another site of intervention for this drug. DS500 delayed the beginning of the clearance phase but then blocked PrPres synthesis for a long period of time, probably because of its immunological effects on the spleen. Surprisingly, Congo red suppressed the clearance phase of scrapie inoculum and then increased transiently accumulation of PrPres in spleen. We showed in vitro that this effect was related to a direct enhancement of the protease resistance of PrPres by the drug.

Screening Congo Red and its analogues for their ability to prevent the formation of PrP-res in scrapie-infected cells.

Transmissible spongiform encephalopathies (TSEs) are incurable, fatal diseases. The dye Congo Red (CR) can cure cells infected with agents of the sheep TSE, scrapie, but is not used as a therapeutic or prophylactic agent in vivo, as its effects are small, possibly due to low blood-brain barrier permeability, and complicated by its intrinsic carcinogenicity. In this paper, the development is described of a structure-activity profile for CR by testing a series of analogues of this dye for their ability to inhibit the formation of the protease-resistant prion protein, PrP-res, a molecular marker for the infectious agent, in the scrapie-infected, SMB cell line. It was found that the central benzidine unit in CR, which gives the molecule potential carcinogenicity, can be replaced by other, less toxic moieties and that the sulphonate groups on the core molecule can be replaced by carboxylic acids, which should improve the brain permeability of these compounds. However, detailed dose-response curves were generated for several derivatives and they revealed that, while some compounds showed inhibition of PrP-res accumulation at high concentrations, at low concentrations they actually stimulated levels of PrP-res above control values.

New chelate-forming polymer microspheres carrying dyes as chelators for iron overload.

Dye-incorporated [poly(EGDMA-HEMA)] microspheres were investigated as a new chelate-forming polymer for iron overload. Poly(EGDMA-HEMA) microspheres, in the size range of 150-200 microm, were produced by a modified suspension polymerization of EGDMA and HEMA. The reactive dye-ligands (i.e. Cibacron Blue F3GA, Alkali Blue 6B and Congo Red) were covalently incorporated to the microspheres. The maximum dye incorporations were 16.5 micromol Cibacron Blue F3GA g(-1), 23.7 micromol Alkali Blue 6B g(-1), and 14.5 micromol Congo Red g(-1). The maximum Fe(III) adsorptions on the dye-incorporated microspheres from aqueous solutions containing different amounts of Fe(III) ions were 51.0, 37.3, and 25.1 mg g(-1) for the Cibacron Blue F3GA, Alkali Blue 6B, and Congo Red carrying microspheres, respectively. The maximum Fe(III) adsorptions were observed at pH 4.0 in all cases. Fe(III) removal from human plasma was also investigated. The maximum adsorption capacities of Fe(III) ions from human plasma for Cibacron Blue F3GA, Alkali Blue 6B, and Congo Red, were of 12.0, 7.5, and 3.8 mg g(-1) polymer, respectively. It was observed that Fe(III) could be repeatedly adsorbed and desorbed without significant loss in adsorption capacity.