Molecular Network-Based Identification of Tramadol Metabolites in a Fatal Tramadol Poisoning

Identification of xenobiotics and their phase I/II metabolites in poisoned patients remains challenging. Systematic approaches using bioinformatic tools are needed to detect all compounds as exhaustively as possible. Here, we aimed to assess an analytical workflow using liquid chromatography coupled to high-resolution mass spectrometry with data processing based on a molecular network to identify tramadol metabolites in urine and plasma in poisoned patients. The generated molecular network from liquid chromatography coupled to high-resolution tandem mass spectrometry data acquired in both positive and negative ion modes allowed for the identification of 25 tramadol metabolites in urine and plasma, including four methylated metabolites that have not been previously reported in humans or in vitro models. While positive ion mode is reliable for generating a network of tramadol metabolites displaying a dimethylamino radical in their structure, negative ion mode was useful to cluster phase II metabolites. In conclusion, the combined use of molecular networks in positive and negative ion modes is a suitable and robust tool to identify a broad range of metabolites in poisoned patients, as shown in a fatal tramadol-poisoned patient.

Automated summary

Identification of xenobiotics and their metabolites in poisoned patients is challenging. This study used a liquid chromatography approach coupled with high-resolution mass spectrometry and molecular network analysis to successfully identify tramadol metabolites in urine and plasma. The use of both positive and negative ion modes allowed for the identification of previously unreported metabolites and clustering of phase II metabolites. The combined use of positive and negative ion modes in molecular network analysis is a suitable and robust tool for identifying a broad range of metabolites in poisoned patients.