Preliminary metabolic characterization of hepatic lipidosis in cats using liquid chromatography–mass spectrometry and gas chromatography–mass spectrometry: pathway insights and candidate biomarkers

BACKGROUND: Feline hepatic lipidosis (FHL) lacks well-defined metabolic biomarkers and mechanistic understanding. HYPOTHESIS/OBJECTIVES: Clarify the metabolic biomarkers and mechanisms of FHL. ANIMALS: Two groups of cats were analyzed: 14 cats (7 FHL cases and 7 healthy controls) for liver metabolomics, and 60 cats (10 FHL cases and 50 healthy controls) for blood 3-hydroxybutyrate (3-HB) testing. METHODS: Hepatic lipidosis was confirmed by histopathological assessment and ultrasonography. Untargeted metabolomics was performed using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS), with pathway analysis using MetaboAnalyst 5.0. Serum 3-HB was quantified using an enzymatic assay. Statistical analysis included principal component analysis, orthogonal partial least squares discriminant analysis, cross-validation, permutation tests, and F₁ score evaluation for model validation. RESULTS: Gas chromatography-mass spectrometry identified four metabolites with variable importance in projection > 1 (bootstrap 95% stability range, 0.9-1.3) and < 0.05, whereas LC-MS identified 243 differentially abundant metabolites (101 upregulated, 142 downregulated), with 19 demonstrating diagnostic potential (area under the curve [AUC] > 0.7). Pathway analysis identified perturbations in vitamin B6 metabolism (P = .003) and fructose/mannose metabolism (P < .001). Serum 3-HB underwent analytical validation in 60 specimens (10 FHL cases, 50 healthy controls), which identified concordant hepatic and systemic increases in FHL. At the optimal cutoff (>2.43 mmol/L), it achieved an AUC of 0.86 (95% confidence interval [CI], 0.65-1.00) with 92% sensitivity (95% CI, 89%-100%) and 88% specificity (95% CI, 74%-100%) in distinguishing FHL from normal liver under controlled laboratory conditions. CONCLUSIONS AND CLINICAL IMPORTANCE: Preliminary data suggest FHL involves dysregulated fatty acid and vitamin B6 metabolism. Although serum 3-HB shows promise, future studies should include disease controls (eg, cholangitis, hepatitis) to establish specificity. These findings provide foundational insights for mechanistic research.