Liquid chromatography-mass spectrometric multiple reaction monitoring-based strategies for expanding targeted profiling towards quantitative metabolomics.

Recent advances in analytical methodologies have made it possible to bring metabolomic profiling into quantitative metabolomics that permits precise measurements of comprehensive small-molecule profiles. Modern liquid chromatography-tandem mass spectrometry (LC-MS/MS) with multiple reaction monitoring (MRM) mode serves as the foundation for accurate simultaneous multi-analyte quantitation across large sample sets to provide high-quality information on target molecular profiles in complex systems. Despite the intrinsic multiplexing potential of the LC-MRM-MS technique, the key bottleneck in current LC-MRM-based assays is generally the limited analyte coverage and throughput capacity. Nowadays, the MRM-based approach has emerged as an attractive strategy for quantitative proteomic analysis and high-throughput biomarker discovery. So far, the full potential of the contemporary LCMRM methodology unleashed for quantitative metabolite profiling and metabolomic measurements of non-peptidic small molecules is rarely discussed. In this review we attempt to provide an overview on the major recent developments in LC-MRM-based strategies for quantitative profiling of multi- and non-target small molecules in biological samples. This article highlights the utility and power of the LC-MRM-based targeted approaches as valuable bioanalytical tools for low-cost, multiplexed quantitation on a large scale, with special emphasis on the promise of combining various strategies for expanding coverage and throughput of the LC-MRM-based assays to cover the gap between a widely targeted profiling and large-scale unknown screening towards comparative or quantitative metabolomics. General issues raised in metabolite profiling, such as basic aspects of bioanalysis, methodological dilemmas and challenges in quantitative metabolomics are addressed, and different strategies to circumvent the existing bottleneck and potential pitfalls of the current LC-MRM-MS techniques are outlined. In addition, the rudiments of LC-MRM-MS and its recent applications in combination with such strategies for biomarker quantitation and verification is also described.