Improved detection of amyloid in fat pad aspiration: An evaluation of Congo red stain by fluorescent microscopy

Congo Red Staining in Digital Pathology: The Streamlined Pipeline for Amyloid Detection Through Congo Red Fluorescence Digital Analysis

Renal amyloidosis is a rare condition caused by the progressive accumulation of misfolded proteins within glomeruli, vessels, and interstitium, causing functional decline and requiring prompt treatment due to its significant morbidity and mortality. Congo red (CR) stain on renal biopsy samples is the gold standard for diagnosis, but the need for polarized light is limiting the digitization of this nephropathology field. This study explores the feasibility and reliability of CR fluorescence on virtual slides (CRFvs) in evaluating the diagnostic accuracy and proposing an automated digital pipeline for its assessment. Whole-slide images from 154 renal biopsies with CR were scanned through a Texas red fluorescence filter (NanoZoomer S60, Hamamatsu) at the digital Nephropathology Center of the Istituto di Ricovero e Cura a Carattere Scientifico San Gerardo, Monza, Italy, and evaluated double-blinded for the detection and quantification through the amyloid score and a custom ImageJ pipeline was built to automatically detect amyloid-containing regions. Interobserver agreement for CRFvs was optimal (k = 0.90; 95% CI, 0.81-0.98), with even better concordance when consensus-based CRFvs evaluation was compared to the standard CR birefringence (BR) (k = 0.98; 95% CI, 0.93-1). Excellent performance was achieved in the assessment of amyloid score overall by CRFvs (weighted k = 0.70; 95% CI, 0.08-1), especially within the interstitium (weighted k = 0.60; 95% CI, 0.35-0.84), overcoming the misinterpretation of interstitial and capsular collagen BR. The application of an automated digital pathology pipeline (Streamlined Pipeline for Amyloid detection through CR fluorescence Digital Analysis, SPADA) further increased the performance of pathologists, leading to a complete concordance with the standard BR. This study represents an initial step in the validation of CRFvs, demonstrating its general reliability in a digital nephropathology center. The computational method used in this study has the potential to facilitate the integration of spatial omics and artificial intelligence tools for the diagnosis of amyloidosis, streamlining its detection process.

Increased Diagnostic Specificity of Congo Red Stain for Amyloid: The Potential Role of Texas Red-Filtered Fluorescence Microscopy

CONTEXT.—

The tissue diagnosis of amyloidosis is traditionally suggested by hematoxylin-eosin stain and confirmed by Congo red stain, both examined by routine light microscopy. Both false-positive and false-negative congophilia are well documented, limiting the sensitivity and specificity of the Congo red stain for the diagnosis of amyloidosis. Examination of Congo red-stained tissue by Texas Red-filtered fluorescence microscopy (TRFM) is known to enhance the amyloid-specific congophilia, thus increasing the diagnostic sensitivity.

OBJECTIVE.—

To determine whether TRFM can mitigate the false positivity and thus improve the diagnostic specificity of the Congo red stain.

DESIGN.—

Ninety-two tissue samples were categorized into 3 groups. Group I included 15 samples with tissue deposition of amyloid. Group II consisted of 63 samples in which amorphous eosinophilic structures reminiscent of amyloid were seen on hematoxylin-eosin-stained tissue sections. Group III included 14 samples in which amyloid and amyloid-like tissue were seen side by side. The final diagnosis of presence or absence of amyloidosis in each case was established by clinicopathologic correlation. The congophilic areas in each case were identified by light microscopy. The same areas were then examined by TRFM.

RESULTS.—

TRFM enhanced congophilia, confirming the diagnosis of amyloidosis in all group I cases. Enhancement was not seen in 52 of the 63 group II cases. For group III cases, TRFM enhanced the amyloid-specific congophilia, but not the nonspecific congophilia, in all cases.

CONCLUSIONS.—

TRFM increases the diagnostic yield and specificity of Congo red-stained tissue sections for detection of amyloid.

Amyloid deposition with a granulomatous reaction in a resection specimen: A clue for a preexisting Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive, highly metastatic, cutaneous neuroendocrine malignancy with poor prognosis. Here we describe a MCC excision specimen with a rare case of tumor-associated amyloid deposition in the absence of residual tumor cells. A 72-year-old man presented with a lesion of five- to six- months' duration on his left elbow, clinically thought to be a ganglion cyst. The biopsy specimen revealed a stage IIA MCC with classic histomorphologic and immunophenotypic findings, with tumor extending to the tissue edges. The patient underwent wide local excision with negative margins and a negative sentinel lymph node biopsy. Although the patient did not receive any presurgical chemotherapy, immunotherapy, or targeted therapy, the re-excision specimen showed only amphophilic, feathery deposits that were salmon-pink with Congo red stain and further confirmed as amyloid by electron microscopy; there were no residual carcinoma cells. Amyloid deposition in MCC has been described in rare case reports. Our case was extraordinary in that there was only amyloid deposition and an associated granulomatous reaction, without identifiable MCC cells. This case demonstrates that amyloid deposition may be evidence of a prior MCC at the site of a prior procedure and may warrant careful evaluation for residual MCC. This article is protected by copyright. All rights reserved.

Accumulation of amyloid beta (Aβ) and amyloid precursor protein (APP) in tumors formed by a mouse xenograft model of inflammatory breast cancer

Accumulation of amyloid in breast cancer is a well-known phenomenon, but only immunoglobulin light-chain amyloidosis (AL) or transthyretin (TTR) amyloid had been detected in human breast tumor samples previously. We recently reported that another amyloidogenic peptide, amyloid beta (Aβ), is present in an aggregated form in animal and human high-grade gliomas and suggested that it originates systemically from the blood, possibly generated by platelets. To study whether breast cancers are also associated with these Aβ peptides and in what form, we used a nude mouse model inoculated with triple-negative inflammatory breast cancer cell (SUM-149) xenografts, which develop noticeable tumors. Immunostaining with two types of specific antibodies for Aβ identified the clear presence of Aβ peptides associated with (a) carcinoma cells and (b) extracellular aggregated amyloid (also revealed by Congo red and thioflavin S staining). Aβ peptides, in both cells and in aggregated amyloid, were distributed in clear gradients, with maximum levels near blood vessels. We detected significant presence of amyloid precursor protein (APP) in the walls of blood vessels of tumor samples, as well as in carcinoma cells. Finally, we used ELISA to confirm the presence of elevated levels of mouse-generated Aβ40 in tumors. We conclude that Aβ in inflammatory breast cancer tumors, at least in a mouse model, is always present and is concentrated near blood vessels. We also discuss here the possible pathways of Aβ accumulation in tumors and whether this phenomenon could represent the specific signature of high-grade cancers.

Diagnosis of wild-type transthyretin amyloid cardiomyopathy in Japan: red-flag symptom clusters and diagnostic algorithm

Wild‐type transthyretin amyloid cardiomyopathy (ATTRwt‐CM) is caused by the deposition of wild‐type transthyretin (TTR) amyloid fibrils in the heart. The age at diagnosis of ATTRwt‐CM is reported to be approximately 70–80 years, and patients commonly present with non‐disease‐specific cardiac abnormalities, such as heart failure with preserved ejection fraction and diastolic dysfunction. The disease can be fatal if left untreated, with an approximate survival of 3–5 years from diagnosis. An oral TTR stabilizer, tafamidis, has enabled early intervention for the treatment of ATTRwt‐CM. However, awareness of ATTRwt‐CM remains low, and misdiagnosis and a delay in diagnosis are common. This review discusses the epidemiology, characteristics, treatment strategy, and red‐flag symptoms and signs of ATTRwt‐CM based on the published literature, as well as recent advances in diagnostic modalities that enable early and accurate diagnosis of the disease. We also discuss an algorithm for early and accurate diagnosis of ATTRwt‐CM in daily clinical practice. In our diagnostic algorithm, a suspected diagnosis of ATTRwt‐CM should be triggered by unexplained left ventricular hypertrophy (LVH), which is LVH that cannot be explained by an increased afterload due to hypertension or valvular disease. In addition, heart failure symptoms, laboratory test results (N‐terminal pro‐B‐type natriuretic peptide, high‐sensitivity troponin T, or high‐sensitivity troponin I), electrocardiogram and imaging (echocardiogram or cardiac magnetic resonance) data, age (≥60 years), and medical history suggestive of ATTRwt‐CM (e.g. carpal tunnel syndrome) should be examined. Detailed examinations using bone scintigraphy and monoclonal protein detection tests followed by tissue biopsy, amyloid typing, and TTR genetic testing are warranted for a definite diagnosis of ATTRwt‐CM.

Updates in processing of anterior fat pad aspirate for amyloid (with video and sketches)

Fat pad aspiration is a commonly used method for detecting amyloid in tissue. Amyloid is detected in the small blood vessels of the aspirated adipose tissue. Optimum evaluation of amyloid with electron microscopy requires at least 15 blood vessels in the fat pad aspirate. The presence of a significant proportion of adipocytes in the aspirate dilutes the fibrovascular portion. This may compromise the evaluation for amyloid with electron microscopy and in FFPE with proteomic studies by mass spectroscopy for confirmation of the amyloid subtype. This video article describes the updated protocol for processing the anterior fat pad aspirate. It demonstrates how to remove the interference of blood and fatty component in the fat pad aspirate performed by the previously reported procedure.

M. Brito R. Structure and Aggregation Mechanisms in Amyloids

The aggregation of a polypeptide chain into amyloid fibrils and their accumulation and deposition into insoluble plaques and intracellular inclusions is the hallmark of several misfolding diseases known as amyloidoses. Alzheimer′s, Parkinson′s and Huntington’s diseases are some of the approximately 50 amyloid diseases described to date. The identification and characterization of the molecular species critical for amyloid formation and disease development have been the focus of intense scrutiny. Methods such as X-ray and electron diffraction, solid-state nuclear magnetic resonance spectroscopy (ssNMR) and cryo-electron microscopy (cryo-EM) have been extensively used and they have contributed to shed a new light onto the structure of amyloid, revealing a multiplicity of polymorphic structures that generally fit the cross-β amyloid motif. The development of rational therapeutic approaches against these debilitating and increasingly frequent misfolding diseases requires a thorough understanding of the molecular mechanisms underlying the amyloid cascade. Here, we review the current knowledge on amyloid fibril formation for several proteins and peptides from a kinetic and thermodynamic point of view, the structure of the molecular species involved in the amyloidogenic process, and the origin of their cytotoxicity.

Both lipopolysaccharide and lipoteichoic acids potently induce anomalous fibrin amyloid formation: assessment with novel Amytracker™ stains

In recent work, we discovered that the presence of highly substoichiometric amounts (10⁻⁸ molar ratio) of lipopolysaccharide (LPS) from Gram-negative bacteria caused fibrinogen clotting to lead to the formation of an amyloid form of fibrin. We here show that the broadly equivalent lipoteichoic acids (LTAs) from two species of Gram-positive bacteria have similarly (if not more) potent effects. Using thioflavin T fluorescence to detect amyloid as before, the addition of low concentrations of free ferric ion is found to have similar effects. Luminescent conjugated oligothiophene dyes (LCOs), marketed under the trade name Amytracker™, also stain classical amyloid structures. We here show that they too give very large fluorescence enhancements when clotting is initiated in the presence of the four amyloidogens (LPS, ferric ions and two LTA types). The staining patterns differ significantly as a function of both the amyloidogens and the dyes used to assess them, indicating clearly that the nature of the clots formed is different. This is also the case when clotting is measured viscometrically using thromboelastography. Overall, the data provide further evidence for an important role of bacterial cell wall products in the various coagulopathies that are observable in chronic, inflammatory diseases. The assays may have potential in both diagnostics and therapeutics.

Amyloid from a histochemical perspective. A review of the structure, properties and types of amyloid, and a proposed staining mechanism for Congo red staining

Amyloid is a diverse group of unrelated peptides or proteins that have positive functionality or are associated with various pathologies. Despite vast differences, all amyloids share several features that together uniquely define the group. 1) All amyloids possess a characteristic cross-ß pattern with X-ray diffraction typical of ß-sheet secondary protein structures. 2) All amyloids are birefringent and dichroic under polarizing microscopy after staining with Congo red, which indicates a crystalline-like (ordered) structure. 3) All amyloids cause a spectral shift in the peak wavelength of Congo red with conventional light microscopy due to perturbation of π electrons of the dye. 4) All amyloids show heightened intensity of fluorescence with Congo red, which suggests an unusual degree of packing of the dye onto the substrate. The ß portion of amyloid molecules, the only logical substrate for specific Congo red staining under histochemical conditions, consists of a stack of ß-sheets laminated by hydrophilic and hydrophobic interactions between adjacent pairs. Only the first and last ß-sheets are accessible to dyes. Each sheet is composed of numerous identical peptides running across the width of the sheet and arranged in parallel with side chains in register over the length of the fibril. Two sets of grooves are bordered by side chains. X grooves run perpendicular to the long axis of the fibril; these grooves are short (the width of the sheet) and number in the hundreds or thousands. Y grooves are parallel with the long axis. Each groove runs the entire length of the fibril, but there are very few of them. While Congo red is capable of ionic bonding with proteins via two sulfonic acid groups, physical constraints on the staining solution preclude ionic interactions. Hydrogen bonding between dye amine groups and peptide carbonyls is the most likely primary bonding mechanism, because all ß-sheets possess backbone carbonyls. Various amino acid residues may form secondary bonds to the dye via any of three van der Waals forces. It is possible that Congo red binds within the Y grooves, but that would not produce the characteristic staining features that are the diagnostic hallmarks of amyloid. Binding in the X grooves would produce a tightly packed series of dye molecules over the entire length of the fibril. This would account for the signature staining of amyloid by Congo red: dichroic birefringence, enhanced intensity of fluorescence and a shift in visible absorption wavelength.

Substantial fibrin amyloidogenesis in type 2 diabetes assessed using amyloid-selective fluorescent stains

BACKGROUND

We have previously shown that many chronic, inflammatory diseases are accompanied, and possibly partly caused or exacerbated, by various coagulopathies, manifested as anomalous clots in the form of 'dense matted deposits'. More recently, we have shown that these clots can be amyloid in nature, and that the plasma of healthy controls can be induced to form such clots by the addition of tiny amounts of bacterial lipopolysaccharide or lipoteichoic acid. Type 2 diabetes (T2D) is also accompanied by raised levels of LPS.

METHODS

We use superresolution and confocal microscopies to investigate the amyloid nature of clots from healthy and T2D individuals.

RESULTS

We show here, with the established stain thioflavin T and the novel stains Amytracker™ 480 and 680, that the clotting of plasma from type 2 diabetics is also amyloid in nature, and that this may be prevented by the addition of suitable concentrations of LPS-binding protein.

CONCLUSION

This implies strongly that there is indeed a microbial component to the development of type 2 diabetes, and suggests that LBP might be used as treatment for it and its sequelae.

Application of confocal laser scanning microscopy for the diagnosis of amyloidosis

We analysed specificity and sensitivity of confocal laser microscopy (CLSM) on tissue sections for a diagnosis of amyloidosis, in an attempt to reduce technical errors and better standardise pathological diagnosis. We first set up a protocol for the use of CLSM on this type of specimen, using a group of 20 amyloid negative and 20 positive samples. Of all specimens, 2, 4 and 8-μm sections were cut. Sections were stained with Congo red (CR) and thioflavin-T (ThT) and observed by cross-polarised light microscopy (CR-PL), epifluorescence microscopy (CRF-epiFM and ThT-epiFM) and CLSM (CRF-CLSM and ThT-CLSM). To validate the method in a diagnostic setting, we examined tissue samples from 116 consecutive patients with clinical suspicion of amyloidosis, selected from the period 2005 to 2014 from the database of the Pathology Unit of the University of Padua. The results were compared with those of transmission electron microscopy (TEM), which we consider as reference. We found that with CRF-CLSM, the false negative rate was reduced from 17 to 5%, while the sensitivity of detection increased to 12%. The results were in complete agreement with those of TEM ThT-CLSM; both sensitivity and specificity were 100%. Finally, ThT-CLSM results did not vary with section thickness, and small amounts of amyloid could even be detected in 2-μm sections. In conclusion, we found ThT-CLSM to be more sensitive as a screening method for amyloidosis than CR and ThT epifluorescence optical imaging. The method was easier to standardise, provided images with better resolution and resulted in more consistent pathologist diagnoses.

The human tRNA-modifying protein, TRIT1, forms amyloid fibers in vitro

TRIT1 is a highly conserved tRNA isopentenyl transferase that modifies a subset of tRNAs in human cells and is a candidate tumor suppressor in lung cancer in certain ethnic populations. The yeast homologue, Mod5, has similar tRNA-modifying functions in the cytoplasm and is required for the transcriptional silencing activity of RNA polymerase II promoters near tRNA genes in the nucleus, a phenomenon termed tRNA gene mediated (tgm) silencing. Furthermore, Mod5 can fold into amyloid fibers in vitro and in vivo, which confers resistance to certain fungicides in yeast. Since TRIT1 complements both tRNA modifying and tgm-silencing activities in yeast where the Mod5 gene has been deleted, it seemed possible that TRIT1 might also have amyloid-forming capabilities. Here we show that TRIT1, like Mod5, directly binds to tRNAs that are both substrate and non-substrates for modification with similar affinity, and to an unstructured, non-tRNA. Binding appears to involve distinct protein-RNA multimers which decrease in electrophoretic mobility as the protein to RNA ratio increases. Furthermore, we characterize TRIT1 as a novel human amyloid fiber forming protein. We discuss these data in light of TRIT1's functional roles and possible implications for disease.

Establishing the fluorescent amyloid ligand h-FTAA for studying human tissues with systemic and localized amyloid

Rapid and accurate detection of amyloid deposits in routine surgical pathology settings are of great importance. The use of fluorescence microscopy in combination with appropriate amyloid specific dyes is very promising in this regard. Here we report that a luminescent conjugated oligothiophene, h-FTAA, rapidly and with high sensitivity and selectivity detects amyloid deposits in verified clinical samples from systemic amyloidosis patients with AA, AL and ATTR types; as well as in tissues laden with localized amyloidosis of AANF, AIAPP and ASem1 type. The probe h-FTAA emitted yellow red fluorescence on binding to amyloid deposits, whereas no apparent staining was observed in surrounding tissue. The only functional structure stained with h-FTAA showing the amyloidotypic fluorescence spectrum was Paneth cell granules in intestine. Screening of 114 amyloid containing tissues derived from 107 verified (Congo red birefringence and/or immunohistochemistry) amyloidosis patients revealed complete correlation between h-FTAA and Congo red fluorescence (107/107, 100% sensitivity). The majority of Congo red negative control cases (27 of 32, 85% specificity) were negative with h-FTAA. Small Congo red negative aggregates in kidney, liver, pancreas and duodenum were found by h-FTAA fluorescence in five control patients aged 72-83 years suffering from diverse diseases. The clinical significance of these false-positive lesions is currently not known. Because h-FTAA fluorescence is one magnitude brighter than Congo red and as the staining is performed four magnitudes lower than the concentration of dye, we believe that these inclusions are beyond detection by Congo red. We conclude that h-FTAA is a fluorescent hypersensitive, rapid and powerful tool for identifying amyloid deposits in tissue sections. Use of h-FTAA can be exploited as a rapid complementary technique for accurate detection of amyloid in routine surgical pathology settings. Our results also implicate the potential of the technique for detection of prodromal amyloidosis as well as for discovery of new amyloid-like protein aggregates in humans.

The Successful Diagnosis and Typing of Systemic Amyloidosis Using A Microwave-Assisted Filter-Aided Fast Sample Preparation Method and LC/MS/MS Analysis

Laser microdissection followed by mass spectrometry has been successfully used for amyloid typing. However, sample contamination can interfere with proteomic analysis, and overnight digestion limits the analytical throughput. Moreover, current quantitative analysis methods are based on the spectrum count, which ignores differences in protein length and may lead to misdiagnoses. Here, we developed a microwave-assisted filter-aided sample preparation (maFASP) method that can efficiently remove contaminants with a 10-kDa cutoff ultrafiltration unit and can accelerate the digestion process with the assistance of a microwave. Additionally, two parameters (P- and D-scores) based on the exponentially modified protein abundance index were developed to define the existence of amyloid deposits and those causative proteins with the greatest abundance. Using our protocol, twenty cases of systemic amyloidosis that were well-typed according to clinical diagnostic standards (training group) and another twenty-four cases without subtype diagnoses (validation group) were analyzed. Using this approach, sample preparation could be completed within four hours. We successfully subtyped 100% of the cases in the training group, and the diagnostic success rate in the validation group was 91.7%. This maFASP-aided proteomic protocol represents an efficient approach for amyloid diagnosis and subtyping, particularly for serum-contaminated samples.

Systemic AA amyloidosis: epidemiology, diagnosis, and management

The term “amyloidosis” encompasses the heterogeneous group of diseases caused by the extracellular deposition of autologous fibrillar proteins. The global incidence of amyloidosis is estimated at five to nine cases per million patient-years. While amyloid light-chain (AL) amyloidosis is more frequent in developed countries, amyloid A (AA) amyloidosis is more common in some European regions and in developing countries. The spectrum of AA amyloidosis has changed in recent decades owing to: an increase in the median age at diagnosis; a percent increase in the frequency of primary AL amyloidosis with respect to the AA type; and a substantial change in the epidemiology of the underlying diseases. Diagnosis of amyloidosis is based on clinical organ involvement and histological evidence of amyloid deposits. Among the many tinctorial characteristics of amyloid deposits, avidity for Congo red and metachromatic birefringence under unidirectional polarized light remain the gold standard. Once the initial diagnosis has been made, the amyloid subtype must be identified and systemic organ involvement evaluated. In this sense, the ¹²³I-labeled serum amyloid P component scintigraphy is a safe and noninvasive technique that has revolutionized the diagnosis and monitoring of treatment in systemic amyloidosis. It can successfully identify anatomical patterns of amyloid deposition throughout the body and enables not only an initial estimation of prognosis, but also the monitoring of the course of the disease and the response to treatment. Given the etiologic diversity of AA amyloidosis, common therapeutic strategies are scarce. All treatment options should be based upon a greater control of the underlying disease, adequate organ support, and treatment of symptoms. Nevertheless, novel therapeutic strategies targeting the formation of amyloid fibrils and amyloid deposition may generate new expectations for patients with AA amyloidosis.

Yield of noncardiac biopsy for the diagnosis of transthyretin cardiac amyloidosis

Transthyretin (ATTR) cardiac amyloidosis may be because of mutant transthyretin causing familial amyloid cardiomyopathy (FAC) or wild-type transthyretin causing systemic senile amyloidosis (SSA). Histologic confirmation is often challenging and may require endomyocardial biopsy (EMB). The purpose of this study was to determine the frequency of amyloid protein deposition in positive noncardiac organ biopsy or fat aspiration in patients with ATTR cardiac amyloidosis. The medical records of 286 patients (mean age 66 ± 11, 85% men) with a diagnosis of ATTR cardiac amyloidosis at our institution who underwent noncardiac biopsy or subcutaneous fat aspiration were reviewed, including 186 patients (65%) with FAC and 100 patients (35%) with SSA. One hundred and thirty-one patients (46%) had EMB, all of which were positive. There were 210 patients (73%) with positive noncardiac tissue sampling, including 175 patients (94%) with FAC and 35 patients (35%) with SSA (p <0.001). There were 141 patients (76%) with FAC and 84 patients (84%) with SSA who underwent fat aspiration, and 67% and 14% were positive, respectively, whereas 100 (54%) and 64 (64%) underwent bone marrow biopsy, and 41% and 30% were positive, respectively. Rectal and sural nerve biopsies were performed in 52 (28%) and 54 (29%) patients with FAC and were positive in 81% and 83%, respectively. Biopsy of other noncardiac sites was performed with relatively lower frequency. In conclusion, although EMB is more commonly required to establish the diagnosis of SSA than FAC, noncardiac biopsy or fat aspiration could be considered as initial testing in patients evaluated for ATTR cardiac amyloidosis with characteristic echocardiography findings.

An evaluation of Congo red fluorescence for the diagnosis of amyloidosis

Congo red stain apple-green birefringence under polarized light is the most popular method for detecting amyloid; however, it has limitations. The goal of this study was to evaluate if examination of Congo red stain by fluorescent microscopy (FM) significantly enhances the diagnostic yield. Congo red-stained tissue sections were retrospectively and prospectively examined by light microscopy (LM) with and without polarizer and by FM using the Texas red filter and results by each method compared. Congo red-stained amyloid recognized by LM was unequivocally and easily identified by FM in each of 48 cases. In 22 of them, FM either confirmed the presence of a small amount of amyloid or lead to a definitive diagnosis, which was otherwise missed. Eight cases with Congo red-negative by LM were also negative by FM. In 8 cases with a false-positive Congo red stain, FM still detected the signal in 5, but it was absent in 3 cases. In conclusion, Congo red fluorescence improves the diagnostic yield of LM for both positive and negative cases.

SFTPC mutations cause SP-C degradation and aggregate formation without increasing ER stress

BACKGROUND

Mutations in the gene encoding surfactant protein C (SP-C) cause familial and sporadic interstitial lung disease (ILD), which is associated with considerable morbidity and mortality. Unfortunately, effective therapeutic options are still lacking due to a very limited understanding of pathomechanisms. Knowledge of mutant SP-C proprotein (proSP-C) trafficking, processing, intracellular degradation and aggregation is a crucial prerequisite for the development of specific therapies to correct aberrant trafficking and processing of proSP-C and to hinder accumulation of cytotoxic aggregates.

MATERIALS AND METHODS

To identify possible starting points for therapeutic intervention, we stably transfected A549 alveolar epithelial cells with several proSP-C mutations previously found in patients suffering from ILD. Effects of mutant proSP-C were assessed by Western blotting, immunofluorescence and Congo red staining.

RESULTS

A group of mutations (p.I73T, p.L110R, p.A116D and p.L188Q) resulted in aberrant proSP-C products, which were at least partially trafficked to lamellar bodies. Another group of mutations (p.P30L and p.P115L) was arrested in the endoplasmic reticulum (ER). Except for p.I73T, all mutations led to accumulation of intracellular Congo red-positive aggregates. Enhanced ER stress was detectable in none of these stably transfected cells.

CONCLUSIONS

Different SP-C mutations have unique consequences for alveolar epithelial cell biology. As these cannot be predicted based upon the localization of the mutation, our data emphasize the importance of studying individual mutations in detail in order to develop mutation-specific therapies.

Cross-β-sheet supersecondary structure in amyloid folds: techniques for detection and characterization

The formation of protein aggregates is linked to the onset of several human disorders of increasing prevalence, ranging from dementia to diabetes. In most of these diseases, the toxic effect is exerted by the self-assembly of initially soluble proteins into insoluble amyloid-like fibrils. Independently of the protein origin, all these macromolecular assemblies share a common supersecondary structure: the cross-β-sheet conformation, in which a core of β-strands is aligned perpendicularly to the fibril axis forming extended regular β-sheets. Due to this ubiquity, the presence of cross-β-sheet conformational signatures is usually exploited to detect, characterize, and screen for amyloid fibrils in protein samples. Here we describe in detail some of the most commonly used methods to analyze such supersecondary structure.

Fluorescence microscopy is superior to polarized microscopy for detecting amyloid deposits in Congo red-stained trephine bone marrow biopsy specimens

The classic gold standard for detecting amyloid deposits is Congo red-stained bright field and polarized microscopy (CRPM). A prior study showed that Congo red fluorescence (CRF) microscopy had increased sensitivity compared with traditional CRPM when analyzing fat pad specimens. The purpose of the current study was to determine the sensitivity of CRF for evaluating Congo red-stained bone marrow biopsy specimens, and to compare these results with those of CRPM. We compared the CRPM and the CRF analyses of 33 trephine bone marrow biopsy specimens with clinical or morphologic suspicion of amyloid deposits. These results were verified against immunohistochemical staining with anti-amyloid P antibody. CRF achieved 100% sensitivity, and CRPM achieved 75% sensitivity. Both groups showed 100% specificity compared with amyloid P immunohistochemical staining. The results show that CRF is a sensitive method to analyze trephine bone marrow biopsy specimens for amyloid deposits.

Detection of amyloid in abdominal fat pad aspirates in early amyloidosis: Role of electron microscopy and Congo red stained cell block sections

Background:

Fine-needle aspiration biopsy (FNA) of the abdominal fat pad is a minimally invasive procedure to demonstrate tissue deposits of amyloid. However, protocols to evaluate amyloid in fat pad aspirates are not standardized, especially for detecting scant amyloid in early disease.

Materials and Methods:

We studied abdominal fat pad aspirates from 33 randomly selected patients in whom subsequent tissue biopsy, autopsy, and/or medical history for confirmation of amyloidosis (AL) were also available. All these cases were suspected to have early AL, but had negative results on abdominal fat pad aspirates evaluated by polarizing microscopy of Congo Red stained sections (CRPM). The results with CRPM between four reviewers were compared in 12 cases for studying inter observer reproducibility. 24 cases were also evaluated by ultrastructural study with electron microscopy (EM).

Results:

Nine of thirty-three (27%) cases reported negative by polarizing microscopy had amyloidosis. Reanalysis of 12 mixed positive-negative cases, showed considerable inter-observer variability with frequent lack of agreement between four observers by CRPM alone (Cohen's Kappa index of 0.1, 95% CI -0.1 to 0.36). EM showed amyloid in the walls of small blood vessels in fibroadipose tissue in four out of nine cases (44%) with amyloidosis.

Conclusion:

In addition to poor inter-observer reproducibility, CRPM alone in cases with scant amyloid led to frequent false negative results (9 out of 9, 100%). For improved detection of AL, routine ultrastructural evaluation with EM of fat pad aspirates by evaluating at least 15 small blood vessels in the aspirated fibroadipose tissue is recommended. Given the high false negative rate for CRPM alone in early disease, routine reflex evaluation with EM is highly recommended to avert the invasive option of biopsying various organs in cases with high clinical suspicion for AL.

PTAA and B10: new approaches to amyloid detection in tissue-evaluation of amyloid detection in tissue with a conjugated polyelectrolyte and a fibril-specific antibody fragment

AIMS

We analysed the suitability of two little known substances for the detection of amyloid in surgical pathology specimens, that is the conjugated polyelectrolyte polythiophene acetic acid (PTAA) and the camelid antibody domain B10.

METHODS

We compared the amyloid detection of PTAA and B10 to Congo red in 106 amyloid-containing tissue biopsies of diverse anatomical and precursor origin by evaluating the accordance in four grades (grade 0: no staining, grade 1: staining of <33% of the amyloid deposits, grade 2: 33-66% and grade 3:>66%).

RESULTS

PTAA showed grade 2-3 staining in 57 (54%) cases, while B10 presented this accordance in only 25 (24%) tissue biopsies. Grade 1 staining was found in 11 (10%) samples with PTAA and in 62 (58%) cases with B10. No staining at all (grade 0) occurred in 38 (36%) biopsies when using PTAA and in 19 (18%) cases when using B10.

CONCLUSION

Although conformation-sensitive detection seemed promising, PTAA and B10 stain only a fraction of the examined amyloid samples when using routine surgical pathology settings. This study emphasises the necessity of having optimised pre-analytical protocols for recovery, storage and handling of samples if these novel amyloid ligands are to be used in routine diagnosis of amyloid.

Performing and processing FNA of anterior fat pad for amyloid

Historically, heart, liver, and kidney biopsies were performed to demonstrate amyloid deposits in amyloidosis. Since the clinical presentation of this disease is so variable and non-specific, the associated risks of these biopsies are too great for the diagnostic yield. Other sites that have a lower biopsy risk, such as skin or gingival, are also relatively invasive and expensive. In addition, these biopsies may not always have sufficient amyloid deposits to establish a diagnosis. Fat pad aspiration has demonstrated good clinical correlation with low cost and minimal morbidity. However, there are no standardized protocols for performing this procedure or processing the aspirated specimen, which leads to variable and nonreproducible results. The most frequently utilized modality for detecting amyloid in tissue is an apple-green birefringence on Congo red stained sections using a polarizing microscope. This technique requires cell block preparation of aspirated material. Unfortunately, patients presenting in early stage of amyloidosis have minimal amounts of amyloid which greatly reduces the sensitivity of Congo red stained cell block sections of fat pad aspirates. Therefore, ultrastructural evaluation of fat pad aspirates by electron microscopy should be utilized, given its increased sensitivity for amyloid detection. This article demonstrates a simple and reproducible procedure for performing anterior fat pad aspiration for the detection of amyloid utilizing both Congo red staining of cell block sections and electron microscopy for ultrastructural identification.

Binding mode of Thioflavin T and other molecular probes in the context of amyloid fibrils-current status

Because understanding amyloid fibrillation in molecular detail is essential for development of strategies to control amyloid formation and overcome neurodegenerative disorders, increased understanding of present molecular probes as well as development of new probes are of utmost importance. To date, the binding modes of these molecular probes to amyloid fibrils are by no means adequately described or understood, and the large number of studies on Thioflavin T (ThT) and Congo Red (CR) binding have resulted in models that are incomplete and conflicting. Different types of binding sites are likely to be present in amyloid fibrils with differences in binding modes. ThT may bind in channels running parallel to the long axis of the fibril. In the channels, ThT may bind in either a monomeric or dimeric form of which the molecular conformation is likely to be planar. CR may bind in grooves formed along the β-sheets as a planar molecule in either a monomeric or supramolecular form.

Diagnosis and typing of systemic amyloidosis: The role of abdominal fat pad fine needle aspiration biopsy

Introduction:

Systemic amyloidosis (SA) has a broad nonspecific clinical presentation. Its diagnosis depends on identifying amyloid in tissues. Abdominal fat pad fine needle aspiration (FPFNA) has been suggested as a sensitive and specific test for diagnosing SA.

Materials and Methods:

Thirty-nine FPFNA from 38 patients (16 women and 20 men, age range 40–88 years) during a 15-year period were reviewed. Smears and cell blocks were stained with Congo red (CR). A panel of antibodies (serum amyloid protein, serum amyloid A, albumin, transthyretin, kappa light chain and lambda light chain) was used on six cell blocks from five patients. The FNA findings were correlated with clinical and histological follow-up.

Results:

FPFNAs were positive, confirmed by CR in 5/39 (13%), suspicious in 1/39 (3%), negative in 28/39 (72%), and insufficient for diagnosis in 5/39 (13%) of cases. In all the positive cases, SA was confirmed within 2–16 weeks. Among the 28 negative cases, SA was diagnosed in 21, the rest were lost to follow-up. Among the insufficient cases, SA was diagnosed in four and one was lost to follow-up. Specificity was 100%, whereas sensitivity was 19%. SA typing using cell block sections was successful in three, un-interpretable in one, and negative in two cases.

Conclusion:

FPFNA for SA is not as good as previously reported. This may be due to different practice setting, level of experience, diagnostic technique, or absence of abdominal soft tissue involvement. A negative result of FPFNA does not exclude SA. Immune phenotyping of amyloid is possible on cell block.

Sensitive and colorimetric detection of the structural evolution of superoxide dismutase with gold nanoparticles

The detection and characterization of protein aggregates are critical in terms of advanced diagnostic applications and investigations of protein stability. A variety of analytical methods (e.g., circular dichroism, size exclusion chromatography, and fluorescence microscopy) have been used in this regard, but they are limited in the trace detection of the structural evolution of protein aggregation. Here we report the gold nanoparticle (AuNP)-based highly sensitive and colorimetric detection of the temporal evolution of superoxide dismutase (SOD1) aggregates implicated in the pathology of amyotrophic lateral sclerosis (ALS). For the temporal discrimination of SOD1 aggregation, AuNPs were conjugated with SOD1 monomers (SOD1-AuNPs). Upon exposure of the probes (SOD1-AuNPs) with SOD1 aggregates, significant changes in both surface plasmon resonance spectra and concomitant colors were observed which are attributed to the formation of probe aggregates of variable sizes onto the SOD1 aggregates.