Serum and Tissue Light-Chains as Disease Biomarkers in AL Amyloidosis

Abstract

Amyloid light-chain (AL) amyloidosis is the most prevalent type of diagnosed systemic amyloidosis in Western countries, characterized by the deposition of misfolded immunoglobulin light chains (LCs) in various organs, most commonly the heart and kidneys. Circulating free LC (FLC) measurement, which can be performed by mass spectrometry or antibody-based techniques, is a crucial tool for AL amyloidosis diagnosis, risk assessment, and management. Additionally, diagnosing AL amyloidosis requires accurate detection of LC deposits in tissues. In addition to immunohistochemical techniques, mass spectrometry-based methods are now available.

Keywords: AL amyloidosis; amyloid fibrils; free light-chains; heart failure; immunoglobulin; plasma cell disorder.

Figure 3

Proteomic workflow for amyloid typing from formalin-fixed, paraffin-embedded endomyocardial biopsy specimens. (A) A histological section is stained with Congo Red (without a coverslip) to identify amyloid deposits; (B) Congo Red-positive areas are isolated by laser microdissection and processed for proteomic analysis; (C) Fragmentation spectra are matched against an in silico-generated database; (D) The most abundant amyloidogenic protein is identified, while co-precipitating proteins represent part of a characteristic amyloid protein signature. FFPE, formalin-fixed, paraffin-embedded; LC–MS/MS, liquid chromatography coupled with tandem mass spectrometry; PSM, peptide-spectrum match. Modified with permission from Musetti et al., 2022 [80].

Figure 1

Mechanisms of damage for free light chains. On the left, the direct cytotoxic effect of light chains on cells; on the right, the mass effect of amyloid deposition on tissue. In the myocardial cell on the left box, there is a brief representation of the molecular cascade of the direct damage [23].

Figure 2

Normal range of kappa/lambda FLC ratio Freelite^® assay. The serum quantification of free light chains (FLCs) and the kappa/lambda ratio vary according to renal function. (a) A normal kappa/lambda ratio in case of normal renal function (0.26–1.65) has a 100% negative predictive value for light-chain cardiac amyloidosis (AL-CA). If a kidney disease is present, the normal range is 0.37–3.10. (b) Comparison of two widely used serum free light chain (sFLC) assays. Freelite^® (The Binding Site, Birmingham, UK) uses polyclonal antibodies and is available on multiple clinical chemistry analyzers. N Latex FLC (Siemens Healthineers, Erlangen, Germany) employs a monoclonal antibody mixture and is available exclusively on Siemens nephelometric platforms.