Stable isotope studies at Profil
Profil Germany has extensive experience in the use of tracer dilution methods to quantify fluxes in glucose and lipid metabolism. Long-standing co-operations with specialist GLP-approved laboratories and renowned academic institutions ensure high-quality mass spectrometric analyses, state-of-the-art modeling and valid evaluation of results.
The science of stable isotope studies
In metabolic and nutritional science, stable isotopes of metabolic compounds are widely applied as tracers. In vivo, a stable isotope of a substrate will be absorbed and metabolized in the same way as the natural compound, enabling a quantitative measurement of the absorption, synthesis and degradation of a specific metabolite. Numerous labeled nutritional and metabolic products are available, including labeled isotopes of glucose and other monosaccharides, amino acids, and substrates of lipid metabolism such as glycerol or fatty acids.
Tracer dilution models aim to quantify substrate fluxes. They were developed to study processes of physiological regulation and the pathophysiology of metabolic diseases, and they have greatly contributed to our understanding of the effects of novel treatments in humans. In particular, labeled glucose products have been widely used as orally or parenterally administered tracers to enable measurement of endogenous glucose production, intestinal glucose absorption and other parameters of glucose metabolism.
When an infusion of a stable glucose isotope (e.g., 6,6-2H2-glucose) is administered, the assessment of glucose production and glucose disposal is in principle based on the measurement of the tracer-to-tracee ratio as measured in blood samples via mass spectrometry. The degree of dilution of the tracer by the abundant natural tracee enables an estimation of its rate of appearance and disappearance, and a calculation of parameters of glucose turnover, such as endogenous glucose production and peripheral glucose uptake. While this principle can be easily applied in subjects in a fasted steady state, numerous complex models were developed over the past 60 years to account for non-steady state conditions (e.g., after exercise, food intake or an injection of insulin), where the rate of appearance and rate of disappearance are no longer in balance, and multiple pools of distribution with varying pool sizes and fluxes between pools must be taken into consideration.
Moreover, double or triple tracer models were introduced which combine oral and intravenous application of different glucose isotopes to quantify intestinal absorption and to allow the observation of effects on glucose turnover after food intake.
It is an exciting aspect that the assessment of glucose turnover can easily be combined with other experimental setups, such as those involving methods for the assessment of energy expenditure and the glucose clamp technique
. The isotope dilution technique allows the assessment of additional metabolic parameters in a routine phase 1 glucose clamp study and can provide a deeper insight into a compound’s mechanism of action.