Proton Observation of ¹³C-Labelled Metabolites

Abstract

The wide chemical shift range (&gtl 200 p.p.m.) of the ¹³C nucleus often allows metabolites to be identified directly and unambiguously from their ¹³C MR spectra. The low natural abundance (1.1%) of this stable carbon isotope means that only metabolites such as triglycerides or glycogen, which are highly concentrated in certain tissues, can be directly observed at natural abundance in vivo (Alger et al., 1981), and most applications of ¹³C MR spectroscopy involve the administration of highly enriched substrates. The great advantage of this approach is that the metabolic time course of substrate use can be followed and used to determine fluxes through pathways, as well as to elucidate the pathways themselves. In recent years, these techniques, which were originally applied to studies of cell suspensions (e.g. yeast) (den Hollander et al., 1979), or hepatocytes (Cohen et al., 1979), have been extended to the study of brain metabolism in isolated tissue (Morris et al., 1986; Badar-Goffer et al., 1990), in experimental animals (Behar et al., 1986) and in humans (Gruetter et al., 1992a,b).