Bile acid metabolomics reveals distinct immunometabolic niches and enables accurate diagnosis of AQP4-IgG–seronegative NMOSD

Background and ObjectiveDifferentiating neuromyelitis optica spectrum disorder (NMOSD) from multiple sclerosis (MS) is clinically difficult, especially when patients are seronegative for anti–aquaporin-4 immunoglobulin G (AQP4-IgG). Bile acids (BAs) function as important immunoregulatory metabolites, yet their metabolic signatures have not been profiled across NMOSD subtypes or compared with MS.

We therefore profiled BA metabolism in NMOSD and MS to determine diagnostic utility.MethodsWe enrolled 112 NMOSD patients (32 AQP4-IgG seronegative, 80 AQP4-IgG seropositive), 50 MS patients, and 66 healthy controls. Targeted liquid chromatography–mass spectrometry quantified 15 bile acids, from which 71 derived metabolic indices were computed.

Candidate biomarkers were identified using nested cross-validation combined with stability selection and integrated into diagnostic models evaluated under a pre-specified internal multi-level validation framework. Associations between BA profiles and neurological disability were assessed using Spearman correlation.ResultsSerum BA signatures differed markedly between NMOSD and MS.

NMOSD showed a pronounced increase in primary conjugated BAs, whereas MS displayed enhanced secondary BA metabolism. Notably, AQP4-IgG seronegative NMOSD had significantly lower secondary BA concentrations than all other groups.