Activity of metabolites

Historically, the selection of the large toxicological species using the in vitro interspecies comparison study performed with liver microsomes or hepatocytes was the major link between metabolism studies and safety (see 5.39 Computational Models to Predict Toxicity). Today, with the early identification of human metabolites, the question of their potential positive (pharmacological) or negative (toxicological) activity can be asked (see 5.08 Mechanisms of Toxification and Detoxification which Challenge Drug Candidates and Drugs).

Even though toxicity of a metabolite is difficult to identify in research programs, it can be defined as either an extension of target pharmacology or mediated via other receptors. In this case the on-line combination of mass spectrometric characterization and biological screening based on ligand-receptor or antigen-antibody interactions can be attractive for some applications. An example of such an approach is on-line affinity capillary electrophoresis-MS. The receptor is present in the electrophoresis buffer and the metabolite mixture is injected as the sample. Metabolites showing strong binding to the receptor are retained and thus separated from compounds that do not interact. On-line MS detection allows direct characterization of the interesting ligands.42

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