Use of subcutaneous abdominal fat biopsy specimen for detailed typing of amyloid fibril protein-AL by amino acid sequence analysis

Tissue-based diagnosis of systemic amyloidosis: Experience of the informal diagnostic center at Uppsala University Hospital

Diagnosis of systemic amyloidosis is a clinical challenge and usually relies on a tissue biopsy. We have developed diagnostic methods based on the presence of amyloid deposits in abdominal subcutaneous fat tissue. This tissue is also used to determine the biochemical type of amyloidosis, performed by western blot and immunohistochemical analyses with the aid of in-house developed rabbit antisera and mouse monoclonal antibodies. Mass spectrometric methods are under development for selected cases. The diagnostic outcome for 2018-2020 was studied. During this period, we obtained 1,562 biopsies, of which 1,397 were unfixed subcutaneous fat tissue with varying degrees of suspicion of systemic amyloidosis. Of these, 440 contained amyloid deposits. The biochemical nature of the amyloid was determined by western blot analysis in 319 specimens and by immunohistochemistry in further 51 cases.

Proteomic analysis shows that the main constituent of subepidermal localised cutaneous amyloidosis is not galectin-7

Lichen or macular localised cutaneous amyloidoses have long been described as keratinic amyloidoses and believed to be due to the deposition of cytokeratin peptides originating from epidermis in the dermal papillae. However, recently it was suggested that galectin-7 is the causative protein for this type of amyloidosis. This was based on the detection of galectin-7 in a biopsy from a patient diagnosed with Bowen's disease and localised cutaneous amyloidosis. In this study we report mass spectrometry-based proteomic analysis of the protein composition of localised cutaneous amyloid deposits from seven patients using laser microdissection and show that basal keratins are the main constituents of the amyloid deposits. Galectin-7 was not present in the dermal amyloid deposits and was only present in the overlying Congo red negative epidermis.

Imaging mass spectrometry analysis of renal amyloidosis biopsies reveals protein co-localization with amyloid deposits

Amyloidosis is a heterogeneous group of protein misfolding diseases characterized by deposition of amyloid proteins. The kidney is frequently affected, especially by immunoglobulin light chain (AL) and serum amyloid A (SAA) amyloidosis as the most common subgroups. Current diagnosis relies on histopathological examination, Congo red staining, or electron microscopy. Subtyping is done by immunohistochemistry; however, commercially available antibodies lack specificity. The purpose of this study was to identify and map amyloid proteins in formalin-fixed paraffin-embedded tissue sections using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis in an integrated workflow. Renal amyloidosis and non-amyloidosis biopsies were processed for histological and MS analysis. Mass spectra corresponding to the congophilic areas were directly linked to the histological and MS images for correlation studies. Peptides for SAA and AL were detected by MALDI IMS associated to Congo red-positive areas. Sequence determination of amyloid peptides by LC-MS/MS analysis provided protein distribution and identification. Serum amyloid P component, apolipoprotein E, and vitronectin proteins were identified in both AA and AL amyloidosis, showing a strong correlation with Congo red-positive regions. Our findings highlight the utility of MALDI IMS as a new method to type amyloidosis in histopathological routine material and characterize amyloid-associated proteins that may provide insights into the pathogenetic process of amyloid formation.

Clinical diagnosis and typing of systemic amyloidosis in subcutaneous fat aspirates by mass spectrometry-based proteomics

Examination of abdominal subcutaneous fat aspirates is a practical, sensitive and specific method for the diagnosis of systemic amyloidosis. Here we describe the development and implementation of a clinical assay using mass spectrometry-based proteomics to type amyloidosis in subcutaneous fat aspirates. First, we validated the assay comparing amyloid-positive (n=43) and -negative (n=26) subcutaneous fat aspirates. The assay classified amyloidosis with 88% sensitivity and 96% specificity. We then implemented the assay as a clinical test, and analyzed 366 amyloid-positive subcutaneous fat aspirates in a 4-year period as part of routine clinical care. The assay had a sensitivity of 90%, and diverse amyloid types, including immunoglobulin light chain (74%), transthyretin (13%), serum amyloid A (%1), gelsolin (1%), and lysozyme (1%), were identified. Using bioinformatics, we identified a universal amyloid proteome signature, which has high sensitivity and specificity for amyloidosis similar to that of Congo red staining. We curated proteome databases which included variant proteins associated with systemic amyloidosis, and identified clonotypic immunoglobulin variable gene usage in immunoglobulin light chain amyloidosis, and the variant peptides in hereditary transthyretin amyloidosis. In conclusion, mass spectrometry-based proteomic analysis of subcutaneous fat aspirates offers a powerful tool for the diagnosis and typing of systemic amyloidosis. The assay reveals the underlying pathogenesis by identifying variable gene usage in immunoglobulin light chains and the variant peptides in hereditary amyloidosis.

Proteomics in molecular diagnosis: typing of amyloidosis

Amyloidosis is a group of disorders caused by deposition of misfolded proteins as aggregates in the extracellular tissues of the body, leading to impairment of organ function. Correct identification of the causal amyloid protein is absolutely crucial for clinical management in order to avoid misdiagnosis and inappropriate, potentially harmful treatment, to assess prognosis and to offer genetic counselling if relevant. Current diagnostic methods, including antibody-based amyloid typing, have limited ability to detect the full range of amyloid forming proteins. Recent investigations into proteomic identification of amyloid protein have shown promise. This paper will review the current state of the art in proteomic analysis of amyloidosis, discuss the suitability of techniques based on the properties of amyloidosis, and further suggest potential areas of development. Establishment of mass spectrometry aided amyloid typing procedures in the pathology laboratory will allow accurate amyloidosis diagnosis in a timely manner and greatly facilitate clinical management of the disease.

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.

Amyloidogenic and associated proteins in systemic amyloidosis proteome of adipose tissue

In systemic amyloidoses, widespread deposition of protein as amyloid causes severe organ dysfunction. It is necessary to discriminate among the different forms of amyloid to design an appropriate therapeutic strategy. We developed a proteomics methodology utilizing two-dimensional polyacrylamide gel electrophoresis followed by matrix-assisted laser desorption/ionization mass spectrometry and peptide mass fingerprinting to directly characterize amyloid deposits in abdominal subcutaneous fat obtained by fine needle aspiration from patients diagnosed as having amyloidoses typed as immunoglobulin light chain or transthyretin. Striking differences in the two-dimensional gel proteomes of adipose tissue were observed between controls and patients and between the two types of patients with distinct, additional spots present in the patient specimens that could be assigned as the amyloidogenic proteins in full-length and truncated forms. In patients heterozygotic for transthyretin mutations, wild-type peptides and peptides containing amyloidogenic transthyretin variants were isolated in roughly equal amounts from the same protein spots, indicative of incorporation of both species into the deposits. Furthermore novel spots unrelated to the amyloidogenic proteins appeared in patient samples; some of these were identified as isoforms of serum amyloid P and apolipoprotein E, proteins that have been described previously to be associated with amyloid deposits. Finally changes in the normal expression pattern of resident adipose proteins, such as down-regulation of alphaB-crystallin, peroxiredoxin 6, and aldo-keto reductase I, were observed in apparent association with the presence of amyloid, although their levels did not strictly correlate with the grade of amyloid deposition. This proteomics approach not only provides a way to detect and unambiguously type the deposits in abdominal subcutaneous fat aspirates from patients with amyloidoses but it may also have the capability to generate new insights into the mechanism of the diseases by identifying novel proteins or protein post-translational modifications associated with amyloid infiltration.

Classification of amyloidosis: misdiagnosing by way of incomplete immunohistochemistry and how to prevent it

Classification of every individual case of amyloid disease is necessary in order to recognize its origin and its possible pathogenesis for therapeutic consideration. Classification of the amyloids can be performed in different ways. One method primarily exploits serum proteins-but these are risk factors only, and therefore render only ancillary information. In principle, one cannot establish the diagnosis alone through their use. Another approach analyzes the origin of the deposited amyloids, either by extracting the amyloid proteins followed by immunochemical or chemical analysis, or by using immunohistochemistry. Based on chemical analysis of prototypes of amyloid fibril proteins, we have developed a profile of antibodies over the years that specifically identify amyloid in tissue sections. These antibodies have been used for years as a routine service for clinicians and pathologists in immunohistochemically classifying amyloid found in formalin-fixed tissue sections. The typing is always controlled by established amyloid classes. In several cases, we have been asked for a second opinion on a diagnosed amyloid class. Our own immunohistochemical data were then compared with those submitted. These submitted immunohistochemical results represented misdiagnoses of amyloid classes in most patients, since the technique performed was usually incomplete. It is the purpose of this report to analyze such cases and to document some of the typical mistakes. Here, we show how to avoid common pitfalls and how one can arrive at a correct diagnosis using immunohistochemistry appropriately.

Subcutaneous fat tissue for diagnosis and studies of systemic amyloidosis

The systemic amyloidoses comprise a biochemically heterogeneous group of potentially lethal disorders. An early and precise diagnosis is crucial for the treatment and prognosis. Subcutaneous fat biopsy is a simple and safe method to obtain a diagnosis of systemic amyloidosis and the material can be used for exact determination of amyloid type. A method is described for immunochemical typing of the amyloid based on Western blot analysis combined with specific amyloid fibril protein antibodies.

Characterization of Systemic Amyloid Deposits by Mass Spectrometry

The human systemic (noncerebral) amyloidoses represent a heterogeneous group of disorders characterized by the widespread deposition of proteins as fibrils in organs or tissues throughout the body. The unequivocal identification of the type of amyloid deposited is critical to the correct diagnosis and treatment of patients with these illnesses. Heretofore, this information was inferred from clinical data, ancillary laboratory tests, and results of immunohistochemical, as well as genetic, analyses. However, to establish definitively the type of amyloid present, the chemical composition of the fibrillar components must be determined. For this purpose, we have developed micro-methods, whereby this information can be obtained by tandem mass spectrometry (MS/MS) using material extracted from formalin-fixed, amyloid-containing tissue biopsy specimens or subcutaneous fat aspirates. The ability to identify precisely the protein nature of the pathologic deposits has diagnostic, therapeutic, and prognostic implications for patients with amyloid-associated disease.

Chemical characterization of a lambda I amyloid protein isolated from formalin-fixed and paraffin-embedded tissue sections

Amyloid protein was isolated from formalin-fixed paraffin-embedded heart tissue sections from a patient with primary (AL) amyloidosis by extraction with 6 M guanidine HCl. SDS-PAGE analysis of extracted material showed a major band at 16 kDa and a minor band at 18 kDa. Edman degradation analysis before and after pyroglutamate aminopeptidase treatment showed that the amyloid protein contained N-terminal pyroglutamic acid and was derived from an immunoglobulin lambda light chain. Analysis of tryptic peptides from the extract identified the amyloid protein as a lambda I. Of particular interest is that almost the entire amyloid protein amino acid sequence could be obtained from the cardiac sections. These results demonstrate that formalin-fixed paraffin-embedded tissue sections can be used for extensive biochemical characterization of amyloid proteins and will become a valuable source for isolation and extensive biochemical characterization of amyloid proteins as they are now a valuable source for isolation of DNA for genetic analysis.

Role of VLDL/chylomicron in amyloid formation in familial amyloidotic polyneuropathy

We examined the affinity of transthyretin (TTR) for lipoproteins and the effect of lipoproteins on TTR-related amyloidogenesis using serum samples from healthy volunteers and patients with familial amyloidotic polyneuropathy (FAP) ATTRVal30Met. In both volunteers and patients, TTR levels were highest in the VLDL fraction containing chylomicrons (VLDL/CM) and next highest in the HDL fraction. Levels were lowest in the LDL fraction. Mass spectrometric analyses of TTR spectra revealed significant TTR association with VLDL/CM and the levels of variant TTR were decreased in the FAP patients. Examination of the affinity of wild-type and variant TTRs for lipoprotein via a quartz crystal microbalance (QCM) revealed the highest affinity of both proteins for VLDL/CM. In in vitro amyloid formation test measured with thioflavin T and electron microscopy, in the presence of VLDL/CM, amyloid formation of TTR was enhanced more than in the presence LDL or in the absence of lipoprotein species. These results suggest that TTR should be highly associated especially with VLDL/CM and amyloidogenicity of TTR should be enhanced around the adipocytes.

Micropurification techniques in the analysis of amyloid proteins

This review describes the different microtechniques developed for the extraction and purification of amyloid proteins from small specimens of fresh and formalin fixed tissues. These procedures differ with respect to solvent type, extraction conditions, and protein purification strategy. The advantages and disadvantages of the different microtechniques are discussed by taking into consideration tissue type (fresh of fixed) and size, amyloid type, and its content in the tissue. The review demonstrates the applicability of these techniques for the immunochemical and chemical characterisation of amyloid in different clinical forms of amyloidosis and in experimental small animal models. The clinical value of the applied microtechniques and their importance in the study of the pathogenesis of amyloid related diseases are outlined.

Chemical typing of amyloid protein contained in formalin-fixed paraffin-embedded biopsy specimens

The human amyloidoses represent a heterogeneous group of disorders characterized by the deposition of fibrillar protein in vital organs. Given the fact that at least 20 different molecules can form fibrils, the unambiguous identification of the type of amyloid deposited is critical to the correct diagnosis and treatment of patients with these disorders. Heretofore, this information has been inferred from particular clinical features of the disease, ancillary laboratory tests, and results of immunohistochemical analyses. However, to establish unequivocally the kind of protein that is deposited as amyloid, it is necessary to determine its chemical composition through amino acid sequencing or mass spectroscopy of material extracted from fibrillar deposits. We have developed a micromethod whereby such studies can be performed readily using sections of formalin-fixed, paraffin-embedded biopsy specimens. The ability to identify precisely the nature of the tissue deposits has diagnostic, therapeutic, and prognostic implications for patients with amyloid-associated disorders.

Microextraction and purification techniques applicable to chemical characterization of amyloid proteins in minute amounts of tissue

This article described micromethods useful for the extraction, purification, and amino acid sequencing of amyloid proteins contained in minute specimens obtained from patients with systemic forms of amyloidosis. We posit that these procedures can also be applied to the biochemical characterization of cerebral amyloid deposits. The selection of the techniques is dependent on the type of sample to be extracted (fresh or formalin fixed) as well as the amount of congophilic material present. Although amyloid proteins are isolated and purified more easily from fresh tissue, it must be noted that formalin-fixed specimens are available more readily for analysis due to the common diagnostic use of fine needle tissue biopsies and are therefore, important for both current and retrospective studies. Remarkably, despite the expected difficulties associated with formalin treatment we were able to extract and sequence amyloid proteins from fixed tissues presumably due to the resistance of amyloid to formalin cross-linking. Through the continued development of techniques for small-scale protein separation and application of highly sensitive microsequencing and mass spectral methods, exact identification of the protein contained in fibrillar amyloid deposits can be determined. Such information has therapeutic and prognostic relevance and can increase our understanding of the pathogenesis of amyloidosis.

Fragments of the constant region of immunoglobulin light chains are constituents of AL-amyloid proteins

Immunoglobulin light chains are the precursor proteins of AL-amyloidosis. In the fibril formation process properties of the variable part of the immunoglobulin light chains are believed to be of major importance. In this work it is shown that fragments of the constant part of the immunoglobulin light chain are a constituent of the AL-amyloid proteins of kappa type. A specific antiserum has identified these fragments in gel filtration fractions where the absorbance approached the base line after the main retarded peak. The fragments are small and have been overlooked previously in the purification process. The significance of the constant part in AL-proteins is unclear, but adds new aspects to the discussion of pre- or post-fibrillogenic cleavage of the immunoglobulin light chains.

Diagnosing amyloidosis

Diagnosis of amyloidosis still relies on tissue biopsy for microscopic examination. Biopsy from a symptom-giving organ may be used but more often an easily available tissue which is affected in most forms of systemic amyloidosis is utilized. Rectal biopsy has its place but a fine needle aspiration biopsy of subcutaneous adipose tissue offers a safe and more convenient alternative. With increasing knowledge about the chemical nature, prognosis and treatment of the different systemic amyloidoses there is an increasing demand of exact chemical typing of amyloid deposits. This typing can be performed immunologically on tissue biopsies, e.g. from subcutaneous adipose tissue, by several different methods. The distribution of amyloid in the body and the therapeutic effects can be monitored by scintigraphy after administration of radiolabelled amyloid P-component.