Oxidised Apolipoprotein Peptidome Characterises Metabolic Dysfunction-Associated Steatotic Liver Disease.

Background: Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) encompasses a spectrum of histological conditions ranging from simple steatosis to fibrosing steatohepatitis, and is a risk factor for cardiovascular diseases (CVD). While oxidised apolipoproteins A and B have been linked to obesity and CVD, the association between other oxidised apolipoproteins and MASLD is yet to be established. To fill this gap, we characterised the circulating serum peptidome of patients with MASLD.

Methods: We studied the serum of 87 biopsy-confirmed MASLD patients and 20 age- and sex-matched control (CTRL) subjects. We first employed an untargeted LC-MS/MS peptidomics approach (9 CTRL, 32 MASLD) to identify key hits differentially modulated, and subsequently validated the most relevant findings through targeted peptidomics in an enlarged study population (87 MASLD and 20 CTRL).

Results: Untargeted serum peptidomics identified several oxidised apolipoprotein peptide fragments, including ApoE and ApoC-III, significantly upregulated in MASLD compared to CTRL. Specifically focusing on the oxidative status of intact ApoC-III, studied through its major glycoforms (ApoC-III, ApoC-III and ApoC-III), we observed a marked reduction in non-oxidised forms of these circulating peptides alongside substantially increased levels of their oxidised proteoforms in MASLD versus controls (but not within the disease stages). Oxidised ApoE and ApoC-III peptide fragments were also significantly correlated with obesity, insulin resistance, dyslipidaemia and transaminases, suggesting a potential link between circulating apolipoprotein oxidation and systemic/hepatic metabolic dysfunction.

Conclusion: Our data reveals a previously unreported oxidised apolipoprotein profile associated with MASLD. The functional and clinical implications of these findings warrant further mechanistic investigation.