Serum metabolic signatures and MetalnFF diagnostic score for mild and moderate metabolic dysfunction-associated steatotic liver disease.

To explore serum metabolic changes in metabolic dysfunction-associated steatotic liver disease (MASLD) with mild or moderate steatosis and develop a diagnostic index based on liver fat content to differentiate these stages. A total of 149 participants were enrolled from the Nutrition Health Atlas Project in 2019 (Stage 1, n = 92) and 2022 (Stage 2, n = 57). Serum levels of amino acids, free fatty acids (FFAs) and other organic acids were quantified using liquid or gas chromatography-mass spectrometry. The relationships between serum metabolites and magnetic resonance imaging proton density hepatic fat fraction were analyzed and a predictive model fitting fat fraction was constructed in Stage 1 and validated in Stage 2. Patients with moderate MASLD had significantly higher pyruvic acid, 2-ketoglutaric acid, malic acid, 2-hydroxyisocaproic acid and FFA(C14:0) than mild MASLD. Pathway analysis indicated that liver fat accumulation is associated with alterations in amino acid, FFA metabolism and tricarboxylic acid cycle (TCA). The MetalnFF score was developed to discriminate among three groups, achieving an area under the curve (AUC) of 0.956 (95 %CI:0.905, 1.00) for MASLD and 0.857 (95 %CI:0.745, 0.968) for moderate MASLD in Stage 1, and was further validated in Stage 2 with an AUC of 0.986 (95 %CI: 0.951, 1.00) and 0.759 (95 %CI:0.607, 0.921), respectively. In the early stages of MASLD, disrupted amino acid, FFAs metabolism and TCA cycle have occurred. As the disease progresses, metabolic disturbances in pyruvate metabolism become more severe. These findings enhance a deeper understanding of pathogenesis and propose MetalnFF score as a potential diagnostic tool.