Methods for staining amyloid in tissues: a review

Lysozyme: a model protein for amyloid research

Ever since lysozyme was discovered by Fleming in 1922, this protein has emerged as a model for investigations on protein structure and function. Over the years, several high-resolution structures have yielded a wealth of structural data on this protein. Extensive studies on folding of lysozyme have shown how different regions of this protein dynamically interact with one another. Data is also available from numerous biotechnological studies wherein lysozyme has been employed as a model protein for recovering active recombinant protein from inclusion bodies using small molecules like l-arginine. A variety of conditions have been developed in vitro to induce fibrillation in hen lysozyme. They include (a) acidic pH at elevated temperature, (b) concentrated solutions of ethanol, (c) moderate concentrations of guanidinium hydrochloride at moderate temperature, and (d) alkaline pH at room temperature. This review aims to bring together similarities and differences in aggregation mechanisms, morphology of aggregates, and related issues that arise using the different conditions mentioned above to improve our understanding. The alkaline pH condition (pH 12.2), discovered and studied extensively in our lab, shall receive special attention. More than a decade ago, it was revealed that mutations in human lysozyme can cause accumulation of large quantities of amyloid in liver, kidney, and other regions of gastrointestinal tract. Understanding the mechanism of lysozyme aggregation will probably have therapeutic implications for the treatment of systemic nonneuropathic amyloidosis. Numerous studies have begun to focus attention on inhibition of lysozyme aggregation using antibody or small molecules. The enzymatic activity of lysozyme presents a convenient handle to quantify the native population of lysozyme in a sample where aggregation has been inhibited. The rich information available on lysozyme coupled with the multiple conditions that have been successful in inducing/inhibiting its aggregation in vitro makes lysozyme an ideal model protein to investigate amyloidogenesis.

Molecular mechanism of Thioflavin-T binding to amyloid fibrils

Intense efforts to detect, diagnose, and analyze the kinetic and structural properties of amyloid fibrils have generated a powerful toolkit of amyloid-specific molecular probes. Since its first description in 1959, the fluorescent dye Thioflavin-T (ThT) has become among the most widely used "gold standards" for selectively staining and identifying amyloid fibrils both in vivo and in vitro. The large enhancement of its fluorescence emission upon binding to fibrils makes ThT a particularly powerful and convenient tool. Despite its widespread use in clinical and basic science applications, the molecular mechanism for the ability of ThT to recognize diverse types of amyloid fibrils and for the dye's characteristic fluorescence has only begun to be elucidated. Here, we review recent progress in the understanding of ThT-fibril interactions at an atomic resolution. These studies have yielded important insights into amyloid structures and the processes of fibril formation, and they also offer guidance for designing the next generation of amyloid assembly diagnostics, inhibitors, and therapeutics.

A proposed histopathologic classification, scoring, and grading system for renal amyloidosis: standardization of renal amyloid biopsy report

CONTEXT

A disease associated with amyloid deposits, called amyloidosis, is associated with characteristic electron microscopic appearance, typical x-ray pattern, and specific staining. Renal involvement mainly occurs in AA amyloidosis and AL amyloidosis and usually progresses to renal failure.

OBJECTIVE

The renal histopathologic changes with amyloidosis comprise a spectrum. Clear relationships between the extent of amyloid deposition and the severity of clinical manifestations have not been demonstrated. Whether there is a lack of clinicopathologic correlation is not clear, but studies have revealed the need for standardization of the renal amyloid biopsy report. With these objectives in mind, we proposed a histopathologic classification, scoring, and grading system. Renal amyloidosis was divided into 6 classes, similar to the classification of systemic lupus erythematosus. Amyloid depositions and other histopathologic lesions were scored. The sum of these scores was termed the renal amyloid prognostic score and was divided into 3 grades.

DATA SOURCES

AA amyloidosis was detected in 90% of cases, mostly related to familial Mediterranean fever. Positive correlations between class I and grade I, class VI and grade III, and class III and grade II were observed. Also, a positive correlation was identified between severity of glomerular amyloid depositions, interstitial fibrosis, and inflammation. Because of the inadequacy of the patients' records and outcomes, different therapy regimes, and etiologies, clinical validation of this study has not been completed.

CONCLUSIONS

Standardization of the renal amyloid pathology report might be critical for patients' medication and comparison of outcome and therapeutic trials between different clinics. Because of our AA to AL amyloidosis ratio and the predisposition of familial Mediterranean fever-related AA amyloidosis, there is a need for further international collaborative studies.

Multiphoton in vivo imaging of amyloid in animal models of Alzheimer's disease

Amyloid-beta (Abeta) deposition is a defining feature of Alzheimer's disease (AD). The toxicity of Abeta aggregation is thought to contribute to clinical deficits including progressive memory loss and cognitive dysfunction. Therefore, Abeta peptide has become the focus of many therapeutic approaches for the treatment of AD due to its central role in the development of neuropathology of AD. In the past decade, taking the advantage of multiphoton microscopy and molecular probes for amyloid peptide labeling, the dynamic progression of Abeta aggregation in amyloid plaques and cerebral amyloid angiopathy has been monitored in real time in transgenic mouse models of AD. Moreover, amyloid plaque-associated alterations in the brain including dendritic and synaptic abnormalities, changes of neuronal and astrocytic calcium homeostasis, microglial activation and recruitment in the plaque location have been extensively studied. These studies provide remarkable insight to understand the pathogenesis and pathogenicity of amyloid plaques in the context of AD. The ability to longitudinally image plaques and related structures facilitates the evaluation of therapeutic approaches targeting toward the clearance of plaques.

Amyotrophic lateral sclerosis is a non-amyloid disease in which extensive misfolding of SOD1 is unique to the familial form

Amyotrophic lateral sclerosis (ALS) is a conformational disease in which misfolding and aggregation of proteins such as SOD1 (familial ALS) and TDP-43 (sporadic ALS) are central features. The conformations adopted by such proteins within motor neurons in affected patients are not well known. We have developed a novel conformation-specific antibody (USOD) targeted against SOD1 residues 42-48 that specifically recognizes SOD1 in which the beta barrel is unfolded. Use of this antibody, in conjunction with the previously described SEDI antibody that recognizes the SOD1 dimer interface, allows a detailed investigation of the in vivo conformation of SOD1 at the residue-specific level. USOD and SEDI immunohistochemistry of spinal cord sections from ALS cases resulting from SOD1 mutations (A4V and DeltaG27/P28) shows that inclusions within remaining motor neurons contain SOD1 with both an unfolded beta barrel and a disrupted dimer interface. Misfolded SOD1 can also be immunoprecipitated from spinal cord extracts of these cases using USOD. However, in ten cases of sporadic ALS, misfolded SOD1 is not detected by either immunohistochemistry or immunoprecipitation. Using the amyloid-specific dyes, Congo Red and Thioflavin S, we find that SOD1-positive inclusions in familial ALS, as well as TDP-43- and ubiquitin-positive inclusions in sporadic ALS, contain non-amyloid protein deposits. We conclude that SOD1 misfolding is not a feature of sporadic ALS, and that both SOD1-ALS and sporadic ALS, rather than being amyloid diseases, are conformational diseases that involve amorphous aggregation of misfolded protein. This knowledge will provide new insights into subcellular events that cause misfolding, aggregation and toxicity.

Revealing molecular-level surface structure of amyloid fibrils in liquid by means of frequency modulation atomic force microscopy

We have investigated the surface structure of islet amyloid polypeptide (IAPP) fibrils and α-synuclein protofibrils in liquid by means of frequency modulation atomic force microscopy (FM-AFM). Ångström-resolution FM-AFM imaging of isolated macromolecules in liquid is demonstrated for the first time. Individual β-strands aligned perpendicular to the fibril axis with a spacing of 0.5 nm are resolved in FM-AFM images, which confirms cross-β structure of IAPP fibrils in real space. FM-AFM images also reveal the existence of 4 nm periodic domains along the axis of IAPP fibrils. Stripe features with 0.5 nm spacing are also found in images of α-synuclein protofibrils. However, in contrast to the case for IAPP fibrils, the stripes are oriented 30° from the axis, suggesting the possibility of β-strand alignment in protofibrils different from that in mature fibrils or the regular arrangement of thioflavin T molecules present during the fibril preparation aligned at the surface of the protofibrils.

Non-coding RNA as a trigger of neuropathologic disorder phenotypes in transgenic Drosophila

At most, many protein-misfolding diseases develop as environmentally induced sporadic disorders. Recent studies indicate that the dynamic interplay between a wide repertoire of noncoding RNAs and the environment play an important role in brain development and pathogenesis of brain disorders. To elucidate this new issue, novel animal models which reproduce the most prominent disease manifestations are required. For this, transgenic Drosophila strains were constructed to express small highly structured, non-coding RNA under control of a heat shock promoter. Expression of the RNA induced formation of intracellular aggregates revealed by Thioflafin T in embryonic cell culture and Congo Red in the brain of transgenic flies. Also, this strongly perturbed the brain control of locomotion monitored by the parameters of sound production and memory retention of young 5-day-old males. This novel model demonstrates that expression of non-coding RNA alone is sufficient to trigger neuropathology.

Hyalinizing Pancreatic Adenocarcinoma in Six Dogs

Exocrine pancreatic carcinoma is a particularly malignant neoplasm of the dog. Clinical and pathologic findings of an unusual variant of exocrine pancreatic neoplasia termed hyalinizing pancreatic adenocarcinoma were evaluated in 6 dogs. On microscopic examination, neoplasms were composed of tubules and acini of epithelial cells, with bright eosinophilic granular apical cytoplasm. Tubular lumina and tumor stroma contained abundant hyaline material that resembled amyloid. The hyaline material was not congophilic, and tumor cells and hyaline material were immunohistochemically negative for amyloid A, immunoglobulin light chains (κ and λ), amylin (islet amyloid polypeptide), laminin, and α1-antitrypsin. Two patients survived longer than 15 months after diagnosis; one of these dogs was untreated and had grossly evident metastasis at the time of diagnosis. The deaths of the other 4 dogs occurred as a result of poor recovery after partial pancreatectomy or in association with other concurrent life-threatening conditions. Two dogs were diagnosed with panniculitis, a condition rarely associated with pancreatic disease. Further evaluation is needed to determine the composition and biologic significance of intratumor hyaline material. Studies that associate exocrine pancreatic carcinoma grade and histologic subtype with prognostic outcomes in the dog are warranted such that appropriate therapy can be elected.

Prions

Prions were originally defined as infectious agents of protein nature, which caused neurodegenerative diseases in animals and humans. The prion concept implies that the infectious agent is a protein in special conformation that can be transmitted to the normal molecules of the same protein through protein-protein interactions. Until the 1990s, the prion phenomenon was associated with the single protein named PrP. Discovery of prions in lower eukaryotes, the yeast Saccharomyces cerevisiae and fungus Podospora anserina, suggests that prions have wider significance. Prions of lower eukaryotes are not related to diseases; their propagation caused by aggregation of prion-like proteins underlies the inheritance of phenotypic traits and most likely has adaptive significance. This review covers prions of mammals and lower eukaryotes, mechanisms of their appearance de novo and maintenance, structure of prion particles, and prospects for the treatment of prion diseases. Recent data concerning the search for new prion-like proteins is included. The paper focuses on the [PSI+] prion of S. cerevisiae, since at present it is the most investigated one. The biological significance of prions is discussed.

Polymerizing the fibre between bacteria and host cells: the biogenesis of functional amyloid fibres

Amyloid fibres are proteinaceous aggregates associated with several human diseases, including Alzheimer's, Huntington's and Creutzfeldt Jakob's. Disease-associated amyloid formation is the result of proteins that misfold and aggregate into beta sheet-rich fibre polymers. Cellular toxicity is readily associated with amyloidogenesis, although the molecular mechanism of toxicity remains unknown. Recently, a new class of 'functional' amyloid fibres was discovered that demonstrates that amyloids can be utilized as a productive part of cellular biology. These functional amyloids will provide unique insights into how amyloid formation can be controlled and made less cytotoxic. Bacteria produce some of the best-characterized functional amyloids, including a surface amyloid fibre called curli. Assembled by enteric bacteria, curli fibres mediate attachment to surfaces and host tissues. Some bacterial amyloids, like harpins and microcinE492, have exploited amyloid toxicity in a directed and functional manner. Here, we review and discuss the functional amyloids assembled by bacteria. Special emphasis will be paid to the biology of functional amyloid synthesis and the connections between bacterial physiology and pathology.

[Carpal tunnel syndrome as a predictor of isolated systemic primary AL amyloidosis]

The diagnosis of common carpal tunnel syndrome, usually relies only on clinical grounds and electromyographic study. We present a 60-year-old woman who was diagnosed with systemic primary AL amyloidosis many years after the carpal tunnel syndrome had begun.

Pathogenic chaperone-like RNA induces congophilic aggregates and facilitates neurodegeneration in Drosophila

Protein aggregation is a hallmark of many neurodegenerative diseases. RNA chaperones have been suggested to play a role in protein misfolding and aggregation. Noncoding, highly structured RNA recently has been demonstrated to facilitate transformation of recombinant and cellular prion protein into proteinase K-resistant, congophilic, insoluble aggregates and to generate cytotoxic oligomers in vitro. Transgenic Drosophila melanogaster strains were developed to express highly structured RNA under control of a heat shock promoter. Expression of a specific construct strongly perturbed fly behavior, caused significant decline in learning and memory retention of adult males, and was coincident with the formation of intracellular congophilic aggregates in the brain and other tissues of adult and larval stages. Additionally, neuronal cell pathology of adult flies was similar to that observed in human Parkinson's and Alzheimer's disease. This novel model demonstrates that expression of a specific highly structured RNA alone is sufficient to trigger neurodegeneration, possibly through chaperone-like facilitation of protein misfolding and aggregation.

Vocal Fold Deposits in Macrophagic Myofasciitis

Macrophagic myofasciitis was first reported in 1998. This disease manifests as diffuse myalgia and chronic fatigue. Its pathophysiology has been traced to the presence of an aluminum adjuvant used in vaccines against hepatitis A and B virus and tetanus toxoid; the adjuvant aggregates at the site of injection. One-third of patients with macrophagic myofasciitis develop autoimmune disease. Vocal fold deposits have been described in autoimmune diseases such as sarcoidosis, systemic lupus erythematosus, multiple sclerosis, rheumatoid arthritis, Sjögren's syndrome, and Hashimoto's thyroiditis. We report what to the best of our knowledge is the first published case of vocal fold deposits in macrophagic myofasciitis.

Hyperforin prevents beta-amyloid neurotoxicity and spatial memory impairments by disaggregation of Alzheimer's amyloid-beta-deposits

The major protein constituent of amyloid deposits in Alzheimer's disease (AD) is the amyloid beta-peptide (Abeta). In the present work, we have determined the effect of hyperforin an acylphloroglucinol compound isolated from Hypericum perforatum (St John's Wort), on Abeta-induced spatial memory impairments and on Abeta neurotoxicity. We report here that hyperforin: (1) decreases amyloid deposit formation in rats injected with amyloid fibrils in the hippocampus; (2) decreases the neuropathological changes and behavioral impairments in a rat model of amyloidosis; (3) prevents Abeta-induced neurotoxicity in hippocampal neurons both from amyloid fibrils and Abeta oligomers, avoiding the increase in reactive oxidative species associated with amyloid toxicity. Both effects could be explained by the capacity of hyperforin to disaggregate amyloid deposits in a dose and time-dependent manner and to decrease Abeta aggregation and amyloid formation. Altogether these evidences suggest that hyperforin may be useful to decrease amyloid burden and toxicity in AD patients, and may be a putative therapeutic agent to fight the disease.

Diagnostic accuracy of subcutaneous abdominal fat tissue aspiration for detecting systemic amyloidosis and its utility in clinical practice

OBJECTIVE

Aspiration of subcutaneous abdominal fat is a simple and fast method for detecting systemic amyloidosis; however, the sensitivity of this approach remains undetermined. The aim of this study was to assess the accuracy of fat tissue aspiration for detecting systemic amyloidosis and the utility of this method in clinical practice.

METHODS

All consecutive patients with established and suspected systemic amyloidosis who attended our tertiary referral hospital between 1994 and 2004 underwent aspiration of subcutaneous abdominal fat. Congo red-stained tissue was assessed quickly in a single smear in a routine manner by a single observer, and was also assessed thoroughly in 3 smears by 2 independent observers.

RESULTS

One hundred twenty patients with established systemic amyloidosis were studied (38 with AA amyloidosis, 70 with AL amyloidosis, and 12 with ATTR amyloidosis). Routine (quick) assessment was associated with a sensitivity of 80% (95% confidence interval [95% CI] 72-87%). Sensitivity increased to 93% (95% CI 87-97%) when 3 smears were thoroughly examined. The specificity of fat aspiration in 45 control subjects was 100% (95% CI 92-100%). One hundred sixty-two patients for whom there was a clinical suspicion of systemic amyloidosis were screened for amyloidosis by fat tissue aspiration and biopsy of at least 1 other tissue. In 69 (43%) of these 162 patients, a diagnosis of amyloidosis was established, and in 66 (96%) of these patients, the results of fat tissue aspiration were positive. The clinical utility of fat tissue aspiration was greater than that of biopsy of the rectum.

CONCLUSION

Subcutaneous abdominal fat aspiration is the preferred method for detecting systemic amyloidosis, with sensitivity of 80% associated with use of a routine approach. The use of a thorough assessment (3 fat smears, 2 observers) increased sensitivity to >90%. If the results of fat tissue aspiration are negative, the additional value of a subsequent biopsy of the rectum is negligible.

Polarimetric imaging of amyloid

New developments in optical microscopy are discussed with relevance to the imaging of amyloid plaques that are pathognomonic of a variety of degenerative disorders. We present the results of linear birefringence, linear dichroism, and circular dichroism imaging of Congo red stained plaques ex vivo and in vitro. A new technique for measuring rapid changes in linear anisotropies is introduced. The application of polarimetric imaging as demonstrated here can be extended to broader pathological practice since polarimetric measurements are sensitive to transformations in tissues that are specific disease signatures.

Immunohistochemical identification of amyloid, using an anti-human serum amyloid P component (SAP) antibody, is possible in ruminants but not in dogs and cats

Amyloidosis represents a heterogenous group of diseases that have in common the deposition of fibrils composed of proteins of beta-pleated sheet structure, a structure which can be specifically identified by histochemistry using the Congo red or similar stains. Amyloid consists primarily of the amyloid fibrils but also of the amyloid P component (AP). This component, which is identical with the serum counterpart (SAP), is found in all types of human amyloid, and immunohistochemical identification of AP has been proposed as an adjunct to the universal, type-independent diagnosis of human amyloidosis. In the present study of animal amyloidosis, we compared the amyloid-specific Congo red stain with an immunohistochemical protocol using an anti-human SAP antibody for the identification of amyloid in formalin fixed tissue samples. The species and types of amyloidoses investigated were: (i) seven cows, one yak (Bos grunniens), and one sheep affected with amyloidosis of presumed AA type, (ii) one dog with a pancreatic endocrine tumour producing amyloid of presumed AIAPP type, (iii) two cats with presumed AIAPP-amyloidosis of the islets of Langerhans, one cat with presumed AA-amyloidosis, and one cat with an amyloid-producing odontogenic tumour. Intense immunostaining co-localized with amyloid, identified by its congophilia and green birefringence, using a protocol without any antigen retrieval in each of the seven cows, the yak and the sheep. The method seemed more sensitive in the ruminants than the Congo red stain, but was unable to detect amyloid in the dog and the cats regardless of the application of various antigen retrieval protocols. However, specific identification of amyloid still rests on the Congo red method or similar histochemical techniques.

Semiautomated cell-free conversion of prion protein: applications for high-throughput screening of potential antiprion drugs

Transmissible spongiform encephalitis (TSE) is a lethal illness with no known treatment. Conversion of the cellular prion protein (PrP(C)) into the infectious isoform (PrP(Sc)) is believed to be the central event in the development of this disease. Recombinant PrP (rPrP) protein folded into the amyloid conformation was shown to cause the transmissible form of prion disease in transgenic mice and can be used as a surrogate model for PrP(Sc). Here, we introduced a semiautomated assay of in vitro conversion of rPrP protein to the amyloid conformation. We have examined the effect of known inhibitors of prion propagation on this conversion and found good correlation between their activity in this assay and that in other in vitro assays. We thus propose that the conversion of rPrP to the amyloid isoform can serve as a high-throughput screen for possible inhibitors of PrP(Sc) formation and potential anti-TSE drugs.

Risk-adjusted manipulation of melphalan dose before stem cell transplantation in patients with amyloidosis is associated with a lower response rate

High-dose chemotherapy and autologous stem cell transplantation are used increasingly to treat patients with light-chain-related amyloidosis (AL). Treatment-related mortality is approximately 15%. To enable more patients to undergo stem cell transplantation, a risk-adapted strategy has been developed to treat with lower chemotherapy doses those patients who are at excessive risk. It is unclear whether reducing the chemotherapy dose in patients at excessive risk of treatment toxicity reduces the overall response. We retrospectively reviewed 171 AL patients who underwent conditioning chemotherapy with stem cell transplantation. The patients comprised two groups: those receiving standard high-dose melphalan and those receiving intermediate-dose melphalan. Responses were categorized as hematologic response, which used criteria for myeloma response. The two groups showed statistically significant differences; the overall response rates were 75% in the high-dose group and 53% in the intermediate-dose group although treatment-related mortality was the same in both groups. Reducing the melphalan dose appeared to render more AL patients eligible for stem cell transplantation but sacrificed an element of response. Methods are needed to reduce treatment-related toxicity so that more patients can receive full-dose conditioning chemotherapy.

Human-like rodent amyloid-beta-peptide determines Alzheimer pathology in aged wild-type Octodon degu

It is generally accepted that human Alzheimer's disease (AD) neuropathology markers are completely absent in rodent brains. We report here that an aged wild-type South American rodent, Octodon degu, expresses neuronal beta-amyloid precursor protein (beta-APP695) displaying both intracellular and extracellular deposits of amyloid-beta-peptide (Abeta), intracellular accumulations of tau-protein and ubiquitin, a strong astrocytic response and acetylcholinesterase (AChE)-rich pyramidal neurons. The high amino acid homology (97.5%) between deguAbeta and humanAbeta sequences is probably a major factor in the appearance of AD markers in this aged rodent. Our results indicate that aged O. degu constitutes the first wild-type rodent model for neurodegenerative processes associated to AD.

Beta-sheet breaker peptide prevents Abeta-induced spatial memory impairments with partial reduction of amyloid deposits

Current evidence supports the notion that beta-amyloid deposits or Abeta intermediates may be responsible for the pathogenesis in Alzheimer's disease (AD) patients. In the present work, we have assessed the neuroprotective effect of the chronic intraperitoneal administration of a five-amino-acid beta-sheet breaker peptide (iAbeta5p) on the rat behavioral deficit induced by the intrahippocampal Abeta-fibrils injection. At 1 month after the injection, animals showed a partial reduction of the amyloid deposits formed and a decreased astrocytic response around the injection site. More importantly, we report that following the iAbeta5p treatment, hippocampal-dependent spatial learning paradigms, including the standard Morris water maze and a working memory analysis, showed a significant prevention from impairments induced by Abeta deposits in the dorsal hippocampus. Thus, it is possible that a noninvasive treatment such as the one presented here with beta-sheet breaker peptides may be used as a potential therapy for AD patients.

Acetylcholinesterase-Abeta complexes are more toxic than Abeta fibrils in rat hippocampus: effect on rat beta-amyloid aggregation, laminin expression, reactive astrocytosis, and neuronal cell loss

Neuropathological changes generated by human amyloid-beta peptide (Abeta) fibrils and Abeta-acetylcholinesterase (Abeta-AChE) complexes were compared in rat hippocampus in vivo. Results showed that Abeta-AChE complexes trigger a more dramatic response in situ than Abeta fibrils alone as characterized by the following features observed 8 weeks after treatment: 1). amyloid deposits were larger than those produced in the absence of AChE. In fact, AChE strongly stimulates rat Abeta aggregation in vitro as shown by turbidity measurements, Congo Red binding, as well as electron microscopy, suggesting that Abeta-AChE deposits observed in vivo probably recruited endogenous Abeta peptide; 2). the appearance of laminin expressing neurons surrounding Abeta-AChE deposits (such deposits are resistant to disaggregation by laminin in vitro); 3). an extensive astrocytosis revealed by both glial fibrillary acidic protein immunoreactivity and number counting of reactive hypertrophic astrocytes; and 4). a stronger neuronal cell loss in comparison with Abeta-injected animals. We conclude that the hippocampal injection of Abeta-AChE complexes results in the appearance of some features reminiscent of Alzheimer-like lesions in rat brain. Our studies are consistent with the notion that Abeta-AChE complexes are more toxic than Abeta fibrils and that AChE triggered some of the neurodegenerative changes observed in Alzheimer's disease brains.

Imaging linear birefringence and dichroism in cerebral amyloid pathologies

New advances in polarized light microscopy were used to image Congo red-stained cerebral amyloidosis in sharp relief. The rotating-polarizer method was used to separate the optical effects of transmission, linear birefringence, extinction, linear dichroism, and orientation of the electric dipole transition moments and to display them as false-color maps. These effects are typically convolved in an ordinary polarized light microscope. In this way, we show that the amyloid deposits in Alzheimer's disease plaques contain structurally disordered centers, providing clues to mechanisms of crystallization of amyloid in vivo. Comparisons are made with plaques from tissues of subjects having Down's syndrome and a prion disease. In plaques characteristic of each disease, the Congo red molecules are oriented radially. The optical orientation in amyloid deposited in blood vessels from subjects having cerebral amyloid angiopathy was 90 degrees out of phase from that in the plaques, suggesting that the fibrils run tangentially with respect to the circumference of the blood vessels. Our result supports an early model in which Congo red molecules are aligned along the long fiber axis and is in contrast to the most recent binding models that are based on computation. This investigation illustrates that the latest methods for the optical analysis of heterogeneous substances are useful for in situ study of amyloid.

Vocal fold deposits in autoimmune disease--an unusual cause of hoarseness

The objective of this study was to evaluate the symptoms and clinical characteristics in patients with autoimmune vocal fold deposits. Fourteen patients underwent videolaryngostroboscopic examination and voice recording. Eleven of the 14 patients underwent rheumatological examination. In all cases, endoscopic examination showed transverse white-yellow band lesions in the middle of the membranous portion of the vocal folds. In most cases, the lesions were bilateral but not exactly opposing each other. The most common voice characteristics were instability and intermittent aphonia. Inflammatory disease was present in 10 patients; five of these had rheumatoid arthritis (RA). No immunological signs common for all patients could be found. The histological examination was consistent with rheumatoid nodules. Vocal fold deposits, occurring most often in patients with RA, is an uncommon cause of hoarseness. Because the patients may have hoarseness as their primary symptom, it is important for otolaryngologists to be familiar with this disorder.

Amyloidosis of medium-sized arteries presenting as perioral mass: a case report

We report a case of amyloidosis localized to the medium-sized arteries of the face and presenting as prominent perioral swelling. The condition was identified as primary AL-type amyloidosis on the basis of immunohistochemical reactivity, predominantly for anti-lambda light chain antibody within amyloid deposits. Subsequent radiographic and laboratory evaluation of the patient disclosed multiple myeloma. Although amyloid deposits were subsequently detected in the temporal arteries, evidence of widespread amyloidosis has not been observed after 1 year of follow-up. To the best of our knowledge, this is the first report of myeloma-associated amyloidosis mainly localized to the medium-sized arteries of the face.

Recombinant endostatin forms amyloid fibrils that bind and are cytotoxic to murine neuroblastoma cells in vitro

Endostatin is a fragment of collagen XVIII that acts as an endogenous inhibitor of tumor angiogenesis and tumor growth. Anti-tumor effects have been described using both soluble and insoluble recombinant endostatin. However, differences in endostatin structure are likely to cause differences in bioactivity. In the present study we have investigated the structure and cellular effects of insoluble endostatin. We found that insoluble endostatin shows all the hallmarks of amyloid aggregates. Firstly, it binds Congo red and shows the characteristic apple-green birefringe when examined under polarized light. Secondly, electron microscopy shows that endostatin forms short unbranched fibrils. Thirdly, X-ray analysis shows the abundant presence of cross-beta sheets, the tertiary structure that underlies fibrillogenesis. None of these properties was observed when examining soluble endostatin. Soluble endostatin can be triggered to form cross-beta sheets following denaturation, indicating that endostatin is a protein fragment with an inherent propensity to form amyloid deposits. Like beta-amyloid, found in the brains of patients with Alzheimer's disease, amyloid endostatin binds to and is toxic to neuronal cells, whereas soluble endostatin has no effect on cell viability. Our results demonstrate a previously unrecognized functional difference between soluble and insoluble endostatin, only the latter acting as a cytotoxic amyloid substance.

In vivo conversion of racemized beta-amyloid ([D-Ser 26]A beta 1-40) to truncated and toxic fragments ([D-Ser 26]A beta 25-35/40) and fragment presence in the brains of Alzheimer's patients

The lag between beta-amyloid (A beta) deposition and neurodegeneration in Alzheimer's disease (AD) suggests that age-dependent factors are involved in the pathogenesis. Racemization of Ser and Asp in A beta is a typical age-dependent modification in AD. We have shown recently that A beta1-40 racemized at Ser(26) ([D-Ser(26)]A beta 1-40) is soluble and non-toxic to neuronal cells, but is easily converted by brain proteases to truncated toxic fragments, [D-Ser(26)]A beta 25-35/40. Furthermore, [D-Ser(26)]A beta1-40 in vivo, produced a drastic and synergistic neuronal loss by enhancing the excitotoxicity when co-injected into rat hippocampus with ibotenic acid, an excitatory amino acid, suggesting an in vivo conversion of non-toxic [D-Ser(26)]A beta1-40 to toxic fragments including [D-Ser(26)]A beta 25-35/40. In this study, we further investigated the mechanism behind the in vivo neuronal loss by [D-Ser(26)]A beta1-40 and ibotenic acid in rats, and also searched for the presence of [D-Ser(26)]A beta 25-35/40 antigens in AD brains. Quantitative analyses of the damaged area indicate clearly that non-toxic [D-Ser(26)]A beta 1-40 caused as much neurodegeneration as toxic [D-Ser(26)]A beta 25-35/40. MK-801, an NMDA receptor antagonist, completely inhibited the neurodegeneration. The immunohistochemical analyses using anti-[D-Ser(26)]A beta 25-35/40-specific antibodies demonstrated the presence of [D-Ser(26)]A beta 25-35/40 antigens in senile plaques and in degenerating hippocampal CA1 neurons in AD brains, but not in age-matched control brains. These results strengthen our hypothesis that soluble [D-Ser(26)]A beta1-40, possibly produced during aging, is released from plaques and converted by proteolysis to toxic [D-Ser(26)]A beta 25-35/40, which damage hippocampal CA1 neurons by enhancing excitotoxicity in AD. This may account for the lag between A beta deposition and neurodegeneration in AD.

Tissue-type plasminogen activator is a multiligand cross-beta structure receptor

Tissue-type plasminogen activator (tPA) regulates fibrin clot lysis by stimulating the conversion of plasminogen into the active protease plasmin. Fibrin is required for efficient tPA-mediated plasmin generation and thereby stimulates its own proteolysis. Several fibrin regions can bind to tPA, but the structural basis for this interaction is unknown. Amyloid beta (Abeta) is a peptide aggregate that is associated with neurotoxicity in brains afflicted with Alzheimer's disease. Like fibrin, it stimulates tPA-mediated plasmin formation. Intermolecular stacking of peptide backbones in beta sheet conformation underlies cross-beta structure in amyloid peptides. We show here that fibrin-derived peptides adopt cross-beta structure and form amyloid fibers. This correlates with tPA binding and stimulation of tPA-mediated plasminogen activation. Prototype amyloid peptides, including Abeta and islet amyloid polypeptide (IAPP) (associated with pancreatic beta cell toxicity in type II diabetes), have no sequence similarity to the fibrin peptides but also bind to tPA and can substitute for fibrin in plasminogen activation by tPA. Moreover, the induction of cross-beta structure in an otherwise globular protein (endostatin) endows it with tPA-activating potential. Our results classify tPA as a multiligand receptor and show that cross-beta structure is the common denominator in tPA binding ligands.

BetaAPP and furin mRNA concentrates in immature senile plaques in the brain of Alzheimer patients

This study examined the possibility that in Alzheimer disease (AD) beta-amyloid precursor protein (betaAPP) mRNA is delivered to senile plaques (SPs) via dendritic processes. BetaAPP mRNA was detected in SPs by in situ hybridization, using a 1.4-kb cRNA in which both [35S]-UTP and [35S]-CTP were incorporated together. The betaAPP mRNA was compared with that of furin, a proteolytic enzyme putatively involved in betaAPP processing, and its orthologue proprotein convertase PCI served as a control. Human presenile AD cases with mostly immature SPs and AD cases generally with mature SPs were analyzed. To decrypt SPs after hybridization, brain sections were stained with thioflavin S. To establish relationships between the density of dystrophic fibers, the degree of plaque maturation, and the concentration of mRNA in SPs, the plaque maturity markers Abeta(1-42) and Abeta(1-40) peptides were co-localized with neurofilament protein 200 and compared with microtubule-associated protein 2 (MAP 2). The results suggest that immature, Abeta(1-42)- and dystrophic dendrite-containing SPs (but not mature SPs containing Abeta(1-40) and missing dystrophic dendrites) are capable of concentrating specific mRNAs. Dystrophic dendrites may thus serve as a route for the transport of specific mRNAs from the cell bodies to SPs.

Subepithelial amyloid deposits in congenital hereditary endothelial dystrophy: a histopathologic study of five cases

PURPOSE

To report the clinical, histologic, ultrastructural, and immunohistochemical features of congenital hereditary endothelial dystrophy (CHED) associated with subepithelial amyloid deposits.

METHODS

The clinical features of seven patients and histologic characteristics of eight corneal buttons were evaluated. The corneal specimens included five cases with histologic features of CHED associated with subepithelial amyloid. The remaining three corneal buttons of CHED without amyloid were obtained from the fellow eye of an affected patient and from siblings of two affected patients. Light microscopic studies were performed on sections stained with hematoxylin and eosin, periodic acid Schiff stain, and Congo red stain with and without permanganate bleach. Immunohistochemistry with an antibody to the amyloid AA protein and lambda and kappa light chains was done on all specimens. Electron microscopy was performed on three corneal specimens. The cases were followed for 1-9 years.

RESULTS

The notable clinical findings included decreased vision, history of parental consanguinity (4/7 cases), and affected siblings (5/7 cases). Examination revealed nystagmus (5/7 cases) and bilateral ground-glass corneas in all patients. In addition, central subepithelial whitish opacities were noted in patients with CHED and amyloid. Three patients had associated congenital glaucoma. The patients underwent penetrating keratoplasty at a mean age of 10 years. Histologically, five corneal buttons of CHED revealed varying degrees of subepithelial amyloid deposits associated with a subepithelial fibrous pannus. Immunohistochemically, the deposits were nonreactive to anti-amyloid A antibody but were immunoreactive with an antibody to lambda light chains in two cases. Electron microscopy confirmed the presence of subepithelial amyloid. Thickening of Descemet's membrane and attenuation of corneal endothelial cells, noted in all cases, was consistent with features of CHED. The corneal buttons from the fellow eye and the siblings showed histologic features of CHED, with a subepithelial fibrous pannus without amyloid deposits. Spheroidal degeneration was noted in two corneal specimens. To date, no recurrence of the amyloid deposits has been seen in the grafts.

CONCLUSIONS

This study demonstrates that subepithelial amyloidosis may be rarely associated with a recessive form of congenital hereditary endothelial dystrophy. The clinical, histologic, and immunohistochemical features suggest a secondary form of amyloidosis.

Non-fibrillar oligomeric species of the amyloid ABri peptide, implicated in familial British dementia, are more potent at inducing apoptotic cell death than protofibrils or mature fibrils

Familial British dementia (FBD) is an autosomal dominant neurodegenerative disorder, with biochemical and pathological similarities to Alzheimer's disease. FBD is associated with a point mutation in the stop codon of the BRI gene. The mutation extends the length of the wild-type protein by 11 amino acids, and following proteolytic cleavage, results in the production of a cyclic peptide (ABri) 11 amino acids longer than the wild-type (WT) peptide produced from the normal gene BRI. ABri was found to be the main component of amyloid deposits in FBD brains. However, pathological examination of FBD brains has shown the presence of ABri as non-fibrillar deposits as well as amyloid fibrils. Taken together, the genetic, pathological and biochemical data support the hypothesis that ABri deposits play a central role in the pathogenesis of FBD. Here we report that ABri, but not WT peptide, can oligomerise and form amyloid-like fibrils. We show for the first time that ABri induces apoptotic cell death, whereas WT is not toxic to cells. Moreover, we report the novel findings that non-fibrillar oligomeric species of ABri are more toxic than protofibrils and mature fibrils. These findings provide evidence that non-fibrillar oligomeric species are likely to play a critical role in the pathogenesis of FBD and suggest that a similar process may also operate in other neurodegenerative diseases.

Is Congo red an amyloid-specific dye?

Congo red (CR) binding, monitored by characteristic yellow-green birefringence under crossed polarization has been used as a diagnostic test for the presence of amyloid in tissue sections for several decades. This assay is also widely used for the characterization of in vitro amyloid fibrils. In order to probe the structural specificity of Congo red binding to amyloid fibrils we have used an induced circular dichroism (CD) assay. Amyloid fibrils from insulin and the variable domain of Ig light chain demonstrate induced CD spectra upon binding to Congo red. Surprisingly, the native conformations of insulin and Ig light chain also induced Congo red circular dichroism, but with different spectral shapes than those from fibrils. In fact, a wide variety of native proteins exhibited induced CR circular dichroism indicating that CR bound to representative proteins from different classes of secondary structure such as alpha (citrate synthase), alpha + beta (lysozyme), beta (concavalin A), and parallel beta-helical proteins (pectate lyase). Partially folded intermediates of apomyoglobin induced different Congo red CD bands than the corresponding native conformation, however, no induced CD bands were observed with unfolded protein. Congo red was also found to induce oligomerization of native proteins, as demonstrated by covalent cross-linking and small angle x-ray scattering. Our data suggest that Congo red is sandwiched between two protein molecules causing protein oligomerization. The fact that Congo red binds to native, partially folded conformations and amyloid fibrils of several proteins shows that it must be used with caution as a diagnostic test for the presence of amyloid fibrils in vitro.

Neuroanatomical abnormalities in behaviorally characterized APP(V717F) transgenic mice

Histological analyses were performed on the brains of APP(V717F) transgenic (Tg)mice previously studied in a battery of behavioral tests. We describe here the regional and age-dependent deposition of amyloid in both heterozygous and homozygous Tg mice. We also report that Tg mice show significant and age-dependent changes in synaptic density measured by synaptophysin immunoreactivity. Surprisingly, a rather marked hippocampal atrophy is observed as early as 3 months of age in Tg mice (20-40%). Statistical analyses revealed that the deficits in object recognition memory are related to the number of amyloid deposits in specific brain regions, whereas deficits in spatial reference and working memory are related to the changes in synaptic density and hippocampal atrophy. Our study suggests that the behavioral deficits observed in Tg mice are only in part related to amyloid deposition, but are also related to neuroanatomical alterations secondary to overexpression of the APP(V717F) transgene and independent of amyloid deposition.

Distribution of beta-amyloid and amyloid precursor protein in the brain of spawning (senescent) salmon: a natural, brain-aging model

Brain amyloid precursor protein (APP), a normal constituent of neurons, glial cells and cerebrospinal fluid, has several proposed functions (e.g., in neuronal growth and survival). It appears, however, that altered processing of APP is an initial or downstream step in the neuropathology of brain aging, Alzheimer's disease (AD), and Down's syndrome (DS). Some studies suggest that proteolytic cleavage of APP, producing beta-amyloid (Abeta(1-42)), could have neurotoxic or neuroprotective effects. In this study, we utilized antibodies to human APP(695) and Abeta(1-42,) and Congo red staining, to search for amyloid deposition in the brain of semelparous spawning kokanee salmon (Oncorhynchus nerka kennerlyi). Intracellular APP(695) immunoreactivity (APP-ir) was observed in brain regions involved in gustation (glomerulosus complex), olfaction (putative hippocampus, olfactory bulb), vision (optic tectum), the stress response (nucleus preopticus and nucleus lateralis tuberis), reproductive behavior (nucleus preopticus magnocellularis, nucleus preopticus periventricularis, ventral telencephalon), and coordination (cerebellum). Intra- and extra-neuronal Abeta(1-42) immunoreactivity (Abeta-ir) were present in all APP-ir regions except the nucleus lateralis tuberis and Purkinje cells of the cerebellum (coordination). Thus, the relationship between APP and Abeta deposition during brain aging could shed light on the processing of APP into Abeta, neurodegeneration, and possible protection of neurons that are functioning in spawning but senescent salmon. Pacific salmon, with their predictable and synchronized life history, could provide research options not available with the existing models for studies of brain aging and amyloidosis.

In vitro immunoglobulin light chain fibrillogenesis

These techniques permit the production of bulk quantities of fibrils and provide methods for monitoring the kinetics of fibrillogenesis. Experiments performed in the fluorimeter require low protein concentrations, sampling is not necessary (with ThT in situ), and the measured fluorescence signal is indicative of fibril content and is not complicated by the presence of amorphous aggregates. However, ASF using the orbital shaker is a simple, rapid, initial procedure, adequate for screening for fibrillogenic potential, in which multiple experiments can be performed simultaneously and over long periods of incubation. These methods may be used to investigate the fibrillogenesis of VL proteins and BJps as a means of predicting pathogenicity, as well as providing information on the basic biophysical principles underlying light chain aggregation.

Predicting the in vitro toxicity of synthetic beta-amyloid (1-40)

The in vitro toxicity of synthetic beta-amyloid (betaA4) is variable and unpredictable, limiting its use as a research tool. This study describes a method using Congo red (CR) to predict the in vitro toxicity of betaA4 solutions. Histopathologically, CR is used to stain the neuritic, betaA4-containing plaques, one of the hallmarks of Alzheimer's disease. In this study, synthetic betaA4 solutions were incubated with CR at a molar ratio of 1.0:2.5. The solutions were centrifuged and the absorbance of the supernatants were measured. Predictions of nontoxicity correlated with absorbance readings near zero. Toxicity was evaluated relative to control cells (vehicle only), using a hemocytometer to count PC-12 cells that excluded trypan blue. The positive predictive value of the test was 78% and the negative predictive value was 100%. To use this test, the toxic concentration(s) of betaA4 must first be established empirically. Then, the CR test can be used to evaluate the potential toxicity of betaA4 solutions at similar concentrations. Thus, this test can be used under a variety of laboratory circumstances.

An in vitro cellular system for generation of AA-amyloid

Different conditions for establishing a cell culture system for generation of AA-amyloid were investigated. The most effective system was based on peritoneal macrophages from CBA/J mice that had received repeated injections of Hammersten casein, with subsequent cultivation of the cells at high density, high levels of acute phase serum, and neutral pH. Staining with Congo red, thioflavin T, and anti-AA revealed amyloid-like structures associated with macrophage clusters. The structures increased in number and size from day 2 to 6 of cell cultivation. The concentration of apoSAA in the culture medium fell markedly in the amyloid-producing cell cultures, while the SAP concentration was not reduced. The described cell culture system can be useful in studies of the influence of chaperone molecules and other factors or the formation and degradation of amyloid fibrils.

Immunohistochemical characterization of amyloid fibril precursors in renal tissue

Amyloidosis is a heterogeneous group of disorders characterised by extracellular deposition of abnormal protein fibrils which are derived from different proteins in different forms of the disease. Almost all patients with amyloidosis have renal disorders. Distinguishing type of amyloidosis is important for therapeutic and investigative purposes. The different types of amyloid fibril proteins can be evaluated by immunohistochemistry, but not by routine histochemical techniques. On the basis of immunohistochemical studies two groups of amyloidosis were distinguished. In all cases, whatever the type, P component was detected, while none of the biopsies revealed transthyretin. The immunoperoxidase technique has the advantage of being able to detect amyloid in formalin-fixed paraffin embedded tissues and remains the simplest and very specific method for identifying amyloid fibril proteins.

Vitreous amyloidosis in familial amyloidotic polyneuropathy. Report of a case with the Val30Met transthyretin mutation

We present a clinical pathological review of vitreous amyloidosis in a case of familial amyloidotic polyneuropathy, type I. Vitreous opacification was the first manifestation of disease in the proband, who was successfully treated with vitrectomy. The eyes were obtained at autopsy after the patient died from an unrelated cause, and the histopathology is presented here. Analysis of DNA from the pathology specimen revealed the most commonly reported transthyretin mutation, Val30Met. The classification of systemic and ocular amyloidosis as well as the genetics of familial amyloidotic polyneuropathy are briefly reviewed.

Amyloidosis

Amyloidosis is a heterogeneous group of disorders characterized by extracellular deposition of abnormal protein fibrils which are derived from different proteins in different forms of the disease. Asymptomatic amyloid deposition in a variety of tissues is a universal accompaniment of ageing, and clinical amyloidosis is not rare. Intracerebral and cerebrovascular beta-protein amyloid deposits are a hallmark of the pathology of both sporadic and familial Alzheimer's disease, beta 2-microglobulin-derived amyloid is a common complication of long term haemodialysis, and islet amyloid polypeptide is the fibril protein in the universal islet amyloidosis of type II diabetes mellitus. New fibril proteins have lately been identified in hereditary amyloidosis, including variants of gelsolin, apolipoprotein AI, lysozyme and fibrinogen. The development of radiolabelled serum amyloid P component (SAP) scintigraphy has allowed amyloid to be diagnosed non-invasively in vivo for the first time, provided unique insight into the distribution and size of amyloid deposits, and yielded novel information on the natural history and the effects of treatment. Amyloid deposits are in a state of dynamic turnover and can regress if new fibril formation is halted. The recent elucidation of the three dimensional structure of human SAP may enable the design of specific therapeutic agents.

Diagnosis and monitoring of amyloidosis

The diagnosis of systemic amyloidosis is only occasionally suspected on clinical grounds alone and is more often considered when an associated condition, such as a chronic inflammatory disease or monoclonal gammopathy, is present. No blood test is diagnostic of amyloid although routine haematological and biochemical investigations have important roles in defining the underlying disease process in amyloidosis, and evaluating organ function. A number of non-invasive investigations including echocardiography, electrocardiography and soft tissue scintigraphy with bone-seeking tracers give characteristic results in some patients with amyloidosis, but are non-specific. The diagnosis can only be confirmed by demonstrating the presence of amyloid deposits in the tissues. Histology is the traditional method in routine clinical practice and is sensitive for revealing microscopic deposits and permits immunotyping of fibril proteins. Disadvantages are that biopsies are invasive, open to sampling error and can only give limited information on the distribution and extent of amyloid deposits in an individual. Scintigraphic and turnover studies with radioiodinated SAP are new specific methods for confirming the presence of amyloid in tissues, based on the affinity of SAP for all types of amyloid fibril. Labelled SAP scans survey the whole body macroscopically for the presence and anatomical distribution of amyloid in a quantitative manner, and SAP turnover studies provide information on the whole body amyloid load. Although the availability of SAP scintigraphy presently remains restricted, the technique has been used in over 400 patients with amyloid in prospective studies, and has already provided a number of new insights into the natural history of amyloidosis. These include the observation that there is a consistently poor correlation between the quantity of amyloid in an organ and the resulting degree of functional impairment. Amyloid deposits accumulate at rates which vary substantially between different organs in a single subject and between individuals with similar types of amyloidosis, even when the rates of amyloid fibril precursor protein supply are apparently similar. In some patients amyloid accumulation may plateau without any measurable alteration in the precursor supply. In patients with amyloidosis in whom the supply of fibril precursors is reduced, either as a result of therapy directed towards the underlying process or through a natural remission, substantial regression of amyloid frequently occurs. This has been observed in patients with AA, AL and variant TTR-associated amyloidosis, and is usually associated with clinical benefits. In some such cases, however, the function of affected organs may continue to deteriorate despite halting the accumulation of amyloid, presumably because irreversible structural damage has already occurred.(ABSTRACT TRUNCATED AT 400 WORDS)

Amyloidosis

The biochemistry of amyloidosis as it relates to clinical medicine and experimental pathology is presented. Amyloidoses are complex disorders in which normally soluble precursors undergo pathological conformational changes and polymerize as insoluble fibrils with the beta-pleated sheet conformation. Over the past 20 years, 16 biochemically diverse proteins have been identified as fibrillar constituents of amyloid deposits; in all cases the protein-protein interactions that result in amyloid fibril formation appear to be stabilized both by the structure and the microenvironment of the precursor protein. Either genetic predisposition or dysfunctions of the immune system favor amyloid fibril formation. In particular, macrophage function is a factor in the pathogenesis of many of the amyloidoses. The diagnosis of amyloidosis involves acquisition of a tissue biopsy, staining of the specimen with Congo red, and observation of classic green birefringence on polarization microscopy. The subdiagnosis of the systemic amyloidoses involves characterization of variant or monoclonal plasma amyloid precursor proteins in the context of clinical symptoms. Treatment is generally supportive, with the use of antiinflammatory therapy, dialysis, or transplantation and genetic counseling where indicated.