Development of a novel targeted LC-MS/MS methods for the typing of cardiac amyloidosis.

BACKGROUND

The treatment and prognosis of cardiac amyloidosis (CA) depend heavily on the accurate identification of amyloid protein types. Histopathological methods are the most commonly used approach, but often produce inconclusive results. The application of mass spectrometry with laser microdissection mass spectrometry based on non-targeted proteomics in CA diagnosis is gradually being recognized, but it is expensive, time-consuming, and still in the early stages of scientific research applications. This study aims to establish a novel typing method based on targeted semi-quantitative proteomics to address the shortcomings of existing methods.

RESULTS

Formalin-fixed, paraffin-embedded (FFPE) myocardial tissue samples from 52 CA and 52 hypertrophic cardiomyopathy (HCM) patients were analyzed. A semi-quantitative typing method was developed using triple quadrupole mass spectrometry, with laser microdissection mass spectrometry (LMD-MS) serving as the reference standard. A total of 52 peptides were analyzed. Key amyloid-associated proteins (AAPs) -apolipoprotein A-IV (apo A-IV), apolipoprotein E (apo E), and serum amyloid P component (SAP) - showed high diagnostic accuracy, with AUC values of 0.964, 0.999, and 0.923, respectively. Transthyretin (TTR), immunoglobulin light chains- κ (IGL - κ), and IGL-λ were semi-quantified using normalized scores (NS) adjusted for microdissection and peptide peak areas. An NS cutoff of 0.066 distinguished transthyretin amyloidosis (ATTR), while NS-NS differentiated AL-κ (≤-0.04758) from AL-λ (>0.00999). The method successfully identified 15 ATTR, 10 AL-κ, 21 AL-λ, and mixed subtypes, aligning with LMD-MS results. By contrast, immunohistochemistry accurately typed only 14 cases, with most results inconclusive.

SIGNIFICANCE

This targeted semi-quantitative mass spectrometry method has high consistency with non-targeted LMD-MS typing, with an accuracy higher than IHC (100 % vs. 30.8 %), while compensating for the shortcomings of non-targeted proteomics. It provides a practical method for CA typing in routine clinical laboratories and may help identify rare subtypes of amyloidosis in the future.