Metabolomic Applications in Stem Cell Research: a Review.

This review describes the use of metabolomics to study stem cell (SC) characteristics and function, excluding SCs in cancer research, suited to a fully dedicated text. The interest in employing metabolomics in SC research has consistently grown and emphasis is, here, given to developments reported in the past five years. This text informs on the existing methodologies and their complementarity regarding the information provided, comprising untargeted/targeted approaches, which couple mass spectrometry or nuclear magnetic resonance spectroscopy with multivariate analysis (and, in some cases, pathway analysis and integration with other omics), and more specific analytical approaches, namely isotope tracing to highlight particular metabolic pathways, or in tandem microscopic strategies to pinpoint characteristics within a single cell. The bulk of this review covers the existing applications in various aspects of mesenchymal SC behavior, followed by pluripotent and neural SCs, with a few reports addressing other SC types. Some of the central ideas investigated comprise the metabolic/biological impacts of different tissue/donor sources and differentiation conditions, including the importance of considering 3D culture environments, mechanical cues and/or media enrichment to guide differentiation into specific lineages. Metabolomic analysis has considered cell endometabolomes and exometabolomes (fingerprinting and footprinting, respectively), having measured both lipid species and polar metabolites involved in a variety of metabolic pathways. This review clearly demonstrates the current enticing promise of metabolomics in significantly contributing towards a deeper knowledge on SC behavior, and the discovery of new biomarkers of SC function with potential translation to in vivo clinical practice.

Difficulties in Differentiating Natural from Synthetic Alkaloids by Isotope Ratio Monitoring using 13C Nuclear Magnetic Resonance Spectrometry.

Within the food and pharmaceutical industries, there is an increasing legislative requirement for the accurate labeling of the product's origin. A key feature of this is to indicate whether the product is of natural or synthetic origin. With reference to this context, we have investigated three alkaloids commonly exploited for human use: nicotine, atropine, and caffeine. We have measured by 13C nuclear magnetic resonance spectrometry the position-specific distribution of 13C at natural abundance within several samples of each of these target molecules. This technique is well suited to distinguishing between origins, as the distribution of the 13C isotope reflects the primary source of the carbon atoms and the process by which the molecule was (bio)synthesized. Our findings indicate that labeling can be misleading, especially in relation to a supplied compound being labeled as "synthetic" even though its 13C profile indicates a natural origin.

Non-statistical 13C Fractionation Distinguishes Co-incident and Divergent Steps in the Biosynthesis of the Alkaloids Nicotine and Tropine.

During the biosynthesis of natural products, isotopic fractionation occurs due to the selectivity of enzymes for the heavier or lighter isotopomers. As only some of the positions in the molecule are implicated in a given reaction mechanism, position-specific fractionation occurs, leading to a non-statistical distribution of isotopes. This can be accessed by isotope ratio monitoring (13)C NMR spectrometry. The solanaceous alkaloids S-(-)-nicotine and hyoscyamine (atropine) are related in having a common intermediate, but downstream enzymatic steps diverge, providing a relevant test case to: (a) elucidate the isotopic affiliation between carbon atoms in the alkaloids and those in the precursors; (b) obtain information about the kinetic isotope effects of as yet undescribed enzymes, thus to make predictions as to their possible mechanism(s). We show that the position-specific (13)C/(12)C ratios in the different moieties of these compounds can satisfactorily be related to their known precursors and to the known kinetic isotope effects of enzymes involved in their biosynthesis, or to similar reaction mechanisms. Thus, the pathway to the common intermediate, N-methyl-Δ(1)-pyrrolinium, is seen to introduce similar isotope distribution patterns in the two alkaloids independent of plant species, whereas the remaining atoms of each target compound, which are of different origins, reflect their specific metabolic ancestry. We further demonstrate that the measured (13)C distribution pattern can be used to deduce aspects of the reaction mechanism of enzymes still to be identified.