Background: Immunoglobulin light-chain (AL) amyloidosis results from misfolded monoclonal light chains forming amyloid fibrils. Cardiac involvement, affecting ~70 % of patients, is the major determinant of mortality. Pathogenesis involves both amyloid infiltration disrupting myocardial structure and light chain–induced proteotoxicity with oxidative stress. Current biomarkers such as NT-proBNP and troponins lack disease specificity and fail to distinguish cardiac AL amyloidosis from other entities. While cardiac tissue proteomics revealed extracellular matrix (ECM) remodeling and protease dysregulation, serum-based proteomic profiling for disease-specific markers remains limited. This study aimed to identify protein signatures associated with cardiac involvement in AL amyloidosis and differentiate them from monoclonal gammopathy and transthyretin amyloidosis (ATTR). Methods: Serum samples from 155 individuals across three German university hospitals (Freiburg, Regensburg, Berlin) included 88 AL amyloidosis (MG-AL), 48 monoclonal gammopathy controls without AL amyloidosis (MG-0), and 19 transthyretin amyloidosis with cardiac involvement (ATTRcard). Proteomic profiling by LC–MS/MS in data-independent acquisition (DIA) mode yielded 99 high-quality datasets: 36 MG-AL (16 with histologically confirmed cardiac AL amyloidosis [MG-ALcard], 20 with non-cardiac AL [MG-ALnocard]), 45 MG-0, and 18 ATTRcard. Differential protein abundance was evaluated using linear models (limma framework), followed by Gene Ontology–based enrichment analysis. Results: Proteome-wide analysis revealed distinct molecular profiles. Cardiac AL amyloidosis showed enrichment of pathways related to ECM organization, metalloproteinase regulation, and peptidase inhibition. Comparison of MG-AL versus MG-0 indicated additional enrichment in basement membrane organization, integrin signaling, and wound healing. Seven proteins—AOC3, ECM1, FBLN1, LRP1, PLXDC2, TIMP1, and TNXB—were shared across MG-ALcard vs ATTRcard, MG-ALcard vs MG-ALnocard, and MG-AL vs MG-0, consistently distinguishing cardiac AL amyloidosis. Moreover, 20 proteins were upregulated in MG-ALcard vs MG-ALnocard, including immunoglobulin variable region peptides (notably IGKV1-39 and IGHV3-family members) and metabolic or structural proteins such as ALDOC, CKM, SOD2, CORO1A, and RECK. An 18-protein subset characterized AL amyloidosis overall, comprising vascular (THBS4, VASN, GP1BA), basement membrane (LAMB1, PCOLCE), adhesion (ALCAM, CDH1), and coagulation-related proteins, differentiating AL amyloidosis from ATTR and MG-0. Conclusion: This study provides a comprehensive molecular characterization of AL amyloidosis subgroups, revealing distinct proteomic signatures associated with cardiac involvement. Alterations in ECM organization, metalloproteinase regulation, and protease inhibition emerged as key biological features. The consistently enriched proteins AOC3, ECM1, FBLN1, LRP1, PLXDC2, TIMP1, and TNXB may serve as candidate biomarkers for cardiac AL amyloidosis and support mechanistic understanding of disease progression.
