While global metabolic profiling (untargeted metabolomics) has been the center of much interest and research activity in the past few decades, more recently targeted metabolomics approaches have begun to gain ground. These analyses are, to an extent, more hypothesis-driven, as they focus on a set of predefined metabolites and aim towards their determination, often to the point of absolute quantification. The continuous development of the technological platforms used in these studies facilitates the analysis of large numbers (up to hundreds) of well-characterized metabolites present in complex matrices.
Targeted metabolomics methods focus on the detection of specific metabolites or groups of metabolites and can take a number of different forms. At their simplest, they are performed on a limited list of metabolites (numbering from a few to several hundreds) likely to have some relevance to the conditions under study. In practice, a targeted method can either focus on:
- A biosynthetic pathway (e.g. arginine biosynthesis and catabolism or the TCA cycle) where the whole pathway, or the majority of the molecules that comprise it, are determined
- A defined group of related metabolites (e.g. saccharides or lipids) which may be involved in different pathways
- A broad collection of known metabolites covering a range of structural classes designed to reflect changes in multiple pathways (sometimes referred to as “widely targeted” metabolomics).
In addition, in “pseudotargeted” metabolomics potential biomarkers are detected in untargeted mode and are specifically targeted during reanalysis by targeted methods. The following Figure shows a schematic description of these approaches.
Targeted methods often provide only qualitative (or semiquantitative) “fold change” information on the compounds being determined. Overall targeted approaches provide the advantage that the detection/quantification and validation of the predefined analytes is better controlled in comparison with untargeted data which may be difficult to control and validate.
Currently, LC-MS is the most widely applied platform for the targeted profiling of both polar and non-polar compounds. An increasing number of targeted methods are appearing in the international literature
The Biomics group has developed targeted metabolomics application in HILIC-MS/MS that provide coverage of more than 120 metabolites and has applied these methods in the analysis in several thousands of samples of various types (blood, urine, amniotic fluid, tissue, feces, grape, honey, royal jelly, wine and others). Metabolites covered include aminoacids, sugars, nucleotides, vitamins, cofactors and others.
We provide results that can range from semi-quantitative approach (fold change) to absolute quantification.
Virgiliou, C., et al., Development and validation of a HILIC- MS/MS multi-targeted method for metabolomics applications. Electrophoresis, 2015