Methods to Study Metabolomics

Metabolic diseases, namely obesity, nonalcoholic fatty liver disease (NAFLD), and type 2 diabetes (T2D), are important risk factors for co-morbidities and mortality. However, not all subjects with metabolic diseases progress toward more severe forms. Thus, it is becoming urgent the discovery of biomarkers that can differentiate phenotypes with different associated risks as well as pathophysiological markers of disease that can be targeted. The use of new omics techniques (i.e., genomics, transcriptomics, metabolomics, lipidomics, and metagenomics) is now becoming a common way to discover biomarkers of metabolic alteration and progression toward more severe morbidity and mortality. Metabolomics has the advantage that it can be investigated directly in plasma samples taken during fasting or postprandial conditions, or in other biological samples, such as urine or feces. Metabolite concentrations are a mirror of alterations in metabolic fluxes. Moreover, also the gut microbiome is involved in the worsening of metabolic diseases since gut bacteria produce metabolites that can either stimulate hormone secretion or act as signaling molecules. Thus, the study of most relevant metabolites is necessary for the elucidation of pathophysiological pathways. This chapter focuses on the metabolites considered relevant for human metabolism and describes the approaches currently used to study the metabolomic profile in biological samples by discussing the targeted versus untargeted approaches and the analytical workflow required to study different classes of metabolites.