In vivo research with stable isotopes in biochemistry, nutrition and clinical medicine: An overview

Tracers and kinetic modelling provide the opportunity to follow the movemen t and to quantify the metabolic fates of biological compounds in vivo. For studies in children and for repeated studies in adults, the use of stable i sotopically labelled substrates are preferable and safe. Measurement of iso topic enrichment in biological molecules is highly specific and can be extr emely precise. This allows the development of models of biological system d ynamics in cells and organs that are otherwise inaccessible for sampling. A pplications in biochemistry, nutrition and clinical medicine show the poten tial of stable isotopes in vivo. Methodology is of paramount importance and includes the choice of bolus studies, (primed) continuous infusions, use o f multiple tracers and use of isotopomer information and intrinsic labels. There is no limit to the number and kind of compounds that can be traced. T opics include intermediate metabolism (lipids, proteins and carbohydrates) using hydrogen, carbon and nitrogen labels. In clinical medicine, C-13-brea th tests are available for detection of Helicobacter pylori ([C-13]urea bre ath test), and for assessment of a variety of gastro-intestinal and hepatic functions (e.g. [C-13]octanoate and mixed [C-13]triglyceride breath tests for studies of gastric emptying and fat absorption, respectively). Because theoretical, methodological, physiological and practical aspects are intert wined, in vivo research with stable isotopes demands close collaboration be tween the clinical researcher and the chemist responsible for the mass spec trometry.