Other improvements emerging are better and innovative fractionation schemes, use of nanoLC approaches, new microfluidic enrichment or separation devices [23] and improvements in mass spectrometry. The majority of peaks observed in a biological sample by global but sensitive mass spectrometry-based analytical platforms are often still unknown as it is a highly challenging and time-consuming procedure to identify them [18•• and 24]. We expect that recent improvements in Navitoclax manufacturer metabolite

identification/assignment software tools for a more efficient annotation and structure elucidation of the thousands of peaks typically obtained for a complex biological sample will yield many new metabolites [25, 26, 27, 28 and 29]. Although the general tendency is to analyze as many metabolites as possible in a given biological sample with the aim to obtain maximal biochemical information, this is not necessarily required in order to obtain insights into biological problems. Actually, Christians et al. recently suggested that screening for changes in selected metabolic pathways AZD2281 using a set of validated and quantitative analytical platforms would be more suited than a global metabolic profiling approaches, in which many computational and chemometric steps are needed to relate changes

in metabolic profiles to biochemical pathways [ 30]. The available biochemical information for a certain disease is used efficiently in such a biology-driven

approach. The global metabolomics strategy and the biology-driven approach are nicely exemplified in the recent work of Hazen and co-workers [ 31 and 32]. A global metabolomics Adenosine triphosphate analysis of plasma revealed a pathway in both humans and mice linking microbiota metabolism of dietary choline and phosphatidylcholine to cardiovascular disease (CVD) pathogenesis [ 31]. It was found that plasma levels of three metabolites of dietary phosphatidylcholine — choline, betaine and trimethylamine N-oxide (TMAO) — are associated with increased risk of CVD. In a follow-up study, the gut microbiota-dependent metabolism of l-carnitine to produce TMAO in both rodents and humans was examined using a biology-driven approach [ 32]. Using stable isotope tracer studies in humans and animal models, the authors demonstrated a role for gut microbiota metabolism of l-carnitine in atherosclerosis pathogenesis. From the previous section it is clear that the total number of detectable yet identifiable compounds is extensive, indicating that efficient sample pretreatment techniques combined with complementary analytical platforms are minimally required in order to cover a significant fraction of the human metabolome [18••].