Plasma-Targeted Proteomic and Lipidomic Profiling of MASLD, MASH, and Hepatitis C Virus Infection

Background Metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) are chronic liver diseases characterized by lipid accumulation and persistent inflammation, often progressing to fibrosis or hepatocellular carcinoma (HCC). Hepatitis C virus (HCV) infection shares overlapping pathological features, including chronic inflammation and fibrogenesis. Despite their prevalence, reproducible molecular markers to distinguish disease stages or inform treatment monitoring remain limited. Methods We conducted targeted proteomic and lipidomic profiling of several hundred plasma samples from Japanese patients diagnosed with MASLD, MASH, or HCV infection. Targeted proteomics quantified 184 plasma proteins using the Olink Proximity Extension Assay, and targeted lipidomics quantified approximately 500 phospholipid and triglyceride species using LC-MS-based selected reaction monitoring. Reproducibility was assessed across three independent cohorts. Results Seven proteins consistently exhibited differential abundance: CASP-8, CCL20, and CTSD were elevated in MASH, while SCF, MMP-3, TRAIL, and TWEAK were downregulated. Similar alterations were observed in HCV, indicating shared immune dysregulation. Lipidomic analysis revealed decreased ether-linked phosphatidylethanolamine (PE), increased ester-linked PE, and elevated saturated sphingomyelin in MASH, reflecting oxidative stress and impaired lipid metabolism. Triglycerides containing linoleic acid (18:2) were consistently reduced in MASH and correlated with CTSD, implicating lysosomal pathways. Correlation analyses indicated coordinated relationships between protein and lipid alterations, suggesting immune–lipid cross-talk during disease progression. Conclusions This study provides the first large-scale dual-omics plasma analysis in Japanese cohorts with MASLD, MASH, and HCV. Rather than establishing definitive diagnostic biomarkers, our results should be interpreted as reproducible, hypothesis-generating reference data. These findings provide a framework and resource for future studies aiming at risk stratification, therapeutic monitoring, and mechanistic validation in chronic liver disease.