13C NMR isotopomeric analysis and its application in the study of endocrine cell metabolism and function

Division of Endocrinology, Department of Medicine, The University of Florida, FL, USA.
Acta bio-medica: Atenei Parmensis 02/2007; 78 Suppl 1:99-112.
Source: PubMed


Defining mechanisms and enzymatic paths critical to cellular function (e.g., secretion) of endocrine cells is a key research goal that can lead toward novel avenues of therapeutic intervention for a variety of disorders. 13C NMR spectroscopy and isotopomer analysis of cell extracts are excellent tools to quantitatively assess metabolism through intermediate labeling and estimate carbon entry to the TCA cycle. Discussed are: cell lines and in vitro culturing; extraction of intracellular material; NMR spectroscopy of the extract; isotopomeric analysis and modeling to obtain relative metabolic fluxes to the TCA cycle. This paper describes issues related to the application of NMR spectroscopic techniques on cell line extracts. Included are results of two studies that illustrate considerations that must be taken when performing analogous studies on neuroendocrine tissue: one involving the effect of media composition on cell behavior and isotopomer labeling; the second looking at effects of applying different metabolic models to 13C data and inferences that may be drawn. NMR isotopomeric analysis is a powerful technique that may be applied to better understand endocrine cell function.

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    ABSTRACT: Cryopreservation is important for clinical translation of tissue-engineered constructs. With respect to a pancreatic substitute, encapsulated islets or beta cells have been widely studied for the treatment of insulin-dependent diabetes mellitus. Besides cell viability loss, cryopreservation may affect the function of the remaining viable cells in a pancreatic substitute by altering fundamental processes in glucose-stimulated insulin secretion, such as pathways associated with intermediary metabolism, potentially leading to insulin-secretion defects. In this study, we used (13)C nuclear magnetic resonance (NMR) spectroscopy and isotopomer analysis to determine the effects of conventional freezing and ice-free cryopreservation (vitrification) on carbon flow through tricarboxylic acid (TCA) cycle-associated pathways in encapsulated murine insulinoma βTC-tet cells; the secretory function of the encapsulated cells postpreservation was also evaluated. Specifically, calcium alginate-encapsulated βTC-tet cells were frozen or vitrified with a cryoprotectant cocktail. Beads were warmed and (13)C labeling and extraction were performed. Insulin secretion rates were determined during basal and labeling periods and during small-scale glucose stimulation and K(+)-induced depolarization. Relative metabolic fluxes were determined from (13)C NMR spectra using a modified single pyruvate pool model with the tcaCALC modeling program. Treatments were compared with nonpreserved controls. Results showed that relative carbon flow through TCA-cycle-associated pathways was not affected by conventional freezing or vitrification. However, vitrification, but not freezing, led to impaired insulin secretion on a per viable cell basis. The reduced secretion from the Vitrified group occurred irrespective of scale and was present whether secretion was stimulated by glucose or K(+)-induced depolarization, indicating that it might be due to a defect in late-stage secretion events.
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