Recent MS applications demonstrate that progress is being made in this area, indicating that in the near future, MS and NMR will most likely be used as complementary technologies in large-scale epidemiology studies [44•• and 46••]. When not reporting absolute concentrations but relatively (to internal standards) quantified data of identified/unidentified

metabolites, as is often the case in global but also still biology-driven platforms, it is crucial to use pooled samples and/or AT13387 internal standards as quality controls and for correction of variations and possible biases in the overall analytical procedure during studies [47 and 48]. However, to accelerate biological interpretation by comparison across studies and labs, and integration with other omics or clinical data (Figure 2), availability of identities and preferably the concentrations of the metabolites is important. As the concentration is influenced by the sample preparation procedure, availability of reference samples is important. To zoom into biochemical processes and pathways, and/or to validate biochemical mechanisms and to translate findings from cell systems to animals and to humans, and vice versa, stable-isotope based metabolomics is an emerging promising strategy [38•, 39 and 40]. For the discovery of biomarkers of disease risk epidemiological studies

are typically used. Associations between metabolite profiles and clinical outcome, increasingly Ribonucleotide reductase also in combination with genetic data, suggest relevant pathways for the onset or progression of a multifactorial disease. However, these biomarkers are not able to Caspase inhibitor predict the disease onset or progression of an individual. For the discovery of metabolic fingerprints to predict disease onset and progression or outcome of interventions at an individual level, longitudinal

studies are needed based on monitoring individuals over a year or more. We are convinced that understanding the dynamics during loss of allostasis or (sudden) systemic changes will be crucial to understand the underlying biological processes. As an example the oral glucose tolerance test is the widely expected approach to test for an early onset of diabetes type 2. Whereas under unperturbed conditions no diagnostic conclusion could be obtained, studying the system response revealed differences, and studying the response from a broader system perspective yielded even more insights [49]. Drugs are an alternative to perturb biological systems to study diseases and their modulation by drugs [3]. These longitudinal studies ask for innovative analytical approaches allowing the analysis of thousands of samples at a low price per sample most likely in the order of tenths of Euro’s. Where NMR and direct-infusion mass spectrometry are slowly reaching the desired throughput, they only partially cover the biochemical networks needed for personalized health monitoring.