Peter J. Walter, Ph.D.
The Mass Spectrometry Clinical Core collaborates with investigators from across NIDDK’s Intramural Research Program to conduct stable isotope tracer studies in both human and mammalian subjects. Clinical studies using stable isotopes involve administering a subject with substances labeled with rare, non-radioactive, stable isotopes; collecting samples; and monitoring production or decay in the isotopic ratio of the labeled product. Stable isotopes are advantageous for clinical studies because they are chemically and physically indistinguishable from the predominant natural isotope of the same element but they are readily distinguished and quantitated by isotope-ratio mass spectrometers. The most commonly used stable isotopes are hydrogen (2H), oxygen(18O) and carbon (13C), and, to a lesser extent, nitrogen (15N) and sulfur (34S).
The doubly labeled water (DLW) method was developed to measure total energy expenditure. A person or animal is administered a dose of water enriched in deuterium (D) and 18oxygen. Labeled hydrogen can only be lost through water, whereas oxygen can be lost as water or carbon dioxide. Calculating the rate of carbon dioxide production then yields a measure of total energy expenditure.
Metabolic studies with stable isotopes cover a vast range of investigations. Currently, we are developing the use of D- or 13C-labeled glucose as a measure of glucose metabolism and labeled free fatty acids.
Across all of these efforts, the core advises, develops, and validates novel research assays in support of ongoing clinical research projects and actively seeks new areas for collaboration with staff members from across the NIH.