Stable isotopes are a type of isotope whose radioactivity cannot be detected by naturally occurring techniques. In nature, the chemical and biological properties of stable isotopes compounds and the corresponding elements compounds are identical except for the mass number. Examples of stable isotopes mainly encompass deuterium, nitrogen-15, oxygen-18, and carbon-13. And stable isotope-labeled compounds are applicable in quantitative proteomics, metabolism research, and so forth.

With the progress of science, novel stable isotope-labeled compounds such as labeled amino acids, labeled peptides, and labeled nucleic acids have been synthesized and utilized by scientists in fields such as medicine, agriculture, environmental sciences, and life sciences during the last decade. The isotope ratio changes can be measured by many analytical instruments like mass spectrometry, nuclear magnetism, and gas chromatography, thereby revealing the reaction pathway and action mechanism.

Stable isotope-labeled substrates have wide-ranging applications. For example, amino acids labeled with stable isotopes can serve as safe, effective, and convenient tools for scientific research in medicine, biology, pharmacy, chemistry, etc. To be more specific, isotope-labeled amino acids can be utilized for the clinical diagnosis of various diseases and used to determine the transfer, transformation, efficacy, mechanism of action, toxicity, and side effects of drugs in vivo in the development of new drugs. Besides, stable isotopes labeling peptides have been developed as useful tools for quantitative peptide analysis or protein structure analysis, and kinetic determination by mass spectrometry (MS) or nuclear magnetic resonance (NMR) spectroscopy. And stable isotope-labeled lipids are routinely applied in lipidomic laboratories and they are considered ideal internal standards and the gold standard for absolute quantitation.

In addition, stable isotope labeling has become a staple technique in the analysis of small molecule metabolism and dynamics, as it is the only experimental setup by which biosynthesis, remodeling, and degradation of biomolecules can be directly measured. Using state-of-the-art analytical technologies such as chromatography-coupled high-resolution tandem mass spectrometry, the stable isotope label can be precisely localized and quantified within the biomolecules. Drug metabolism scientists and toxicologists can better understand drugs’ disposition and their potential role in target organ toxicities through the use of stable isotope-labeled compounds. And the combination of stable isotope labeling techniques with mass spectrometry and nuclear magnetic resonance spectroscopy, which allows rapid acquisition and interpretation of data, has promoted greater use of these stable isotope-labeled compounds in absorption, distribution, metabolism, and excretion (ADME) studies.

Stable isotope labeling is a powerful technique with promising applications. Depending upon this powerful technology, labeled tracers can sensitively and accurately track changes according to the location and quantity of peptides, amino acids, or carbohydrates containing isotope-labeled in vivo or in vitro. What’s more, it enables direct analysis of nutrient distribution, metabolism, conversion into metabolites, and the fate of the resulting metabolites. In contrast to radioactive labeling, there are no dangers or safety concerns, making this technique particularly well suited for metabolism studies in humans. As a result, isotope labeling technology has received progressively more recognition in the fields of medicine and biochemistry.