An Intracellular Metabolic Signature as a Potential Donor-Independent Marker of the Osteogenic Differentiation of Adipose Tissue Mesenchymal Stem Cells

This paper describes an untargeted NMR metabolomics study to identify potential intracellular donor-dependent and donor-independent metabolic markers of proliferation and osteogenic differentiation of human adipose mesenchymal stem cells (hAMSCs). The hAMSCs of two donors with distinct proliferating/osteogenic characteristics were fully characterized regarding their polar endometabolome during proliferation and osteogenesis. An 18-metabolites signature (including changes in alanine, aspartate, proline, tyrosine, ATP, and ADP, among others) was suggested to be potentially descriptive of cell proliferation, independently of the donor. In addition, a set of 11 metabolites was proposed to compose a possible donor-independent signature of osteogenesis, mostly involving changes in taurine, glutathione, methylguanidine, adenosine, inosine, uridine, and creatine/phosphocreatine, choline/phosphocholine and ethanolamine/phosphocholine ratios. The proposed signatures were validated for a third donor, although they require further validation in a larger donor cohort. We believe that this proof of concept paves the way to exploit metabolic markers to monitor (and potentially predict) cell proliferation and the osteogenic ability of different donors.

Simultaneous determination of natural-abundance δ15N values and quantities of individual amino acids in proteins from milk of lactating women and from infant hair using gas chromatography/isotope ratio mass spectrometry

RATIONALE

In isotope tracer experiments used in nutritional studies, it is frequently desirable both to determine the (15)N/(14)N ratios of target compounds and to quantify these compounds. This report shows how this can be achieved in a single chromatographic run for protein amino acids using an isotope ratio mass spectrometer.

METHODS

Protein hydrolysis by acidic digestion was used to release amino acids, which were then derivatized as their N-pivaloyl-O-isopropyl esters. Suitable conditions for sample preparation were established for both hair and milk proteins. The N-pivaloyl-O-isopropyl esters of amino acids were separated by gas chromatography (GC) on a 60 m ZB-WAX column linked via a combustion interface to an isotope ratio mass spectrometer. The (15)N/(14)N ratios were obtained from the m/z 28, 29 and 30 peak intensities and the quantities from the Area All (Vs) integrated peak areas.

RESULTS

It is shown from a five-point calibration curve that both parameters can be measured reliably within the range of 1.0 to 2.0 mg/mL for the major amino acids derived from the hydrolysis of human maternal milk or hair samples. The method was validated in terms of inter-day and inter-user repeatability for both parameters for 14 amino acids. The amino acid percentage composition showed a good correlation with literature values. The method was applied to determine the variability in a population of lactating mothers and their infants.

CONCLUSIONS

It has been established that δ(15)N values can be simultaneously determined for a complex mixture of amino acids at variable concentrations. It is shown that the percentage composition obtained correlates well with that obtained by calculation from the protein composition or from literature values. This procedure should provide a significant saving in analysis time, especially in those cases where the GC run-time is necessarily long. It allows the satisfactory determination of the variation within a sample population.