Metabolic deuterium oxide (DO) labeling in quantitative omics studies: A tutorial review.

Mass spectrometry (MS) is an invaluable tool for sensitive detection and characterization of individual biomolecules in omics studies. MS combined with stable isotope labeling enables the accurate and precise determination of quantitative changes occurring in biological samples. Metabolic isotope labeling, wherein isotopes are introduced into biomolecules through biosynthetic metabolism, is one of the main labeling strategies. Among the precursors employed in metabolic isotope labeling, deuterium oxide (DO) is cost-effective and easy to implement in any biological systems. This tutorial review aims to explain the basic principle of DO labeling and its applications in omics research. DO labeling incorporates D into stable C-H bonds in various biomolecules, including nucleotides, proteins, lipids, and carbohydrates. Typically, DO labeling is performed at low enrichment of 1%-10% DO, which causes subtle changes in the isotopic distribution of a biomolecule, instead of the complete separation between labeled and unlabeled samples in a mass spectrum. DO labeling has been employed in various omics studies to determine the metabolic flux, turnover rate, and relative quantification. Moreover, the advantages and challenges of DO labeling and its future prospects in quantitative omics are discussed. The economy, versatility, and convenience of DO labeling will be beneficial for the long-term omics studies for higher organisms.