Application of Stable Isotope-Labeled Compounds in Metabolism and in Metabolism-Mediated Toxicity Studies

Abstract

Stable isotope-labeled compounds have been synthesized and utilized by scientists from various areas of biomedical research during the last several decades. Compounds labeled with stable isotopes, such as deuterium and carbon-13, have been used effectively by drug metabolism scientists and toxicologists to gain better understanding of drugs' disposition and their potential role in target organ toxicities. The combination of stable isotope-labeling techniques with mass spectrometry and nuclear magnetic resonance (NMR) 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. Examples of the use of stable isotope-labeled compounds in elucidating structures of metabolites and delineating complex metabolic pathways are presented in this review. The application of labeled compounds in mechanistic toxicity studies will be discussed by providing an example of how strategic placement of a deuterium atom in a drug molecule mitigated specific-specific renal toxicity. Other examples from the literature demonstrating the application of stable isotope-labeled compounds in understanding metabolism-mediated toxicities are presented. Furthermore, an example of how a stable isotope-labeled compound was utilized to better understand some of the gene changes in toxicogenomic studies is discussed. The interpretation of large sets of data produced from toxicogenomics studies can be a challenge. One approach that could be used to simplify interpretation of the data, especially from studies designed to link gene changes with the formation of reactive metabolites thought to be responsible for toxicities, is through the use of stable isotope-labeled compounds. This is a relatively unexplored territory and needs to be further investigated. The employment of analytical techniques, especially mass spectrometry and NMR, used in conjunction with stable isotope-labeled compounds to establish and understand mechanistic link between reactive metabolite formation, genomic, and proteomic changes and onset of toxicity is proposed. The use of stable isotope-labeled compounds in early human ADME studies as a way of identifying and possibly quantifying all drug-related components present in systemic circulation is suggested.

Non-targeted Tracer Fate Detection

“…Such studies often use radiolabeled compounds or analyze stable isotope labeling in a targeted manner [39]. NTFD can provide insights into metabolism of xenobiotics without the need of radiolabeled compounds.…”

Applications of stable isotopes in clinical pharmacology

“…However, knowledge about the mechanism of toxicity and advrse effects on a molecular level is limited [36]. For example, while troglitazone was withdrawn from the market in 2000 because of serious hepatotoxicity and replaced by chemical analogues, the mechanism of toxicity has to date not been elucidated [37].…”

“…Further detailed insight may be generated by selective deceleration of certain metabolic pathways by selective replacement of hydrogen with deuterium. The relative amounts of different metabolites generated may be changed and related to different toxicity profiles [36].…”

Synthesis and analysis of stable isotope-labelled N-acyl homoserine lactones

“…34 Besides the application as standard, isotope-labelled molecules are often used in absorption, distribution, metabolism and excretion (ADME) studies and to study reaction mechanisms. 35 Hereby, mostly a 1:1 mixture of non-labelled and isotope-labelled compounds is used, to create a recognizable mass spectral ion pattern to study the in vitro and in vivo metabolic dispersion. [35][36][37][38] However, no methodology is available to synthesize AHLs belonging to the major different classes with an isotope label in the acyl chain, starting from one, easily available deuterated building block.…”