Annotation of Metabolites\nin Stable Isotope Tracing\nUntargeted Metabolomics via Khipu-web

Stable isotope tracing is a crucial technique for understanding\nthe metabolic wiring of biological systems, determining metabolic\nflux through pathways of interest, and detecting novel metabolites\nand pathways. Despite the potential insights provided by this technique,\nits application remains limited to a small number of targeted molecules\nand pathways. Because previous software tools usually require chemical\nformulas to find relevant features, and the data are highly complex,\nespecially in untargeted metabolomics and when the downstream reactions\nand metabolites are poorly characterized. We report here Khipu version\n2 and its new user-friendly web application. New functions are added\nto enhance analyzing stable isotope tracing data including metrics\nthat evaluate peak enrichment in labeled samples, scoring methods\nto facilitate robust detection of intensity patterns and integrated\nnatural abundance correction. We demonstrate that this approach can\nbe applied to untargeted metabolomics to systematically extract isotope-labeled\ncompounds and annotate the unidentified metabolites.