Metabolic target analysis and metabolic profiling are two techniques in the field of metabolomics that generate profiles of the metabolites existing within a biological sample.
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These techniques are important for the research and development of new antimicrobials, diagnostic tests, therapeutic interventions, probiotics, and vaccines. The applications of metabolic analyses continue to increase, leading both metabolic target analysis and metabolic profiling to be of growing importance.
Both types of analysis can be used as tools for identifying new biomarkers of disease, highlighting toxicologic and pathologic changes, as well as for uncovering the underlying mechanisms of biological systems, all of which are important for opening up new avenues for the development of preventions, diagnoses, and treatments for a number of diseases.
Below we discuss the differences between the two approaches.
Metabolic target analysis
In metabolic target analysis, known metabolites are profiled. The approach is based on the analyses of targeted quantitative MS and NMR, however, newer analytical methods such as CE-MS are also being incorporated into the method.
Often, targeted analysis involves multiple stable isotope-labeled standards being added into the samples to be tested before the steps of extraction and derivatization. This is to control for analyte loss that occurs during sample processing and also compensate for the effects of ionization-suppression.
Chemical solvents are used to extract aliquots of the sample which are then derivatized for the specific chemical properties of the cluster of analytes.
This process of analysis is known as processing the samples in a modular format. Amino acids, organic acids, and nucleotides, etc., that are being looked for within the sample call for an addition of cognate stable isotope standards to the sample.
An advantage of the targeted method is that it is quantitatively precise. A drawback of the method is that it is limited in its breadth of analysis as it can only analyze a certain number of metabolites at a time.
One area in which this type of analysis has seen particular success is in the survey of metabolic fuel, and profiling energy-yielding metabolic pathways.
Metabolic profiling is an untargeted approach where NMR and High-Resolution MS techniques are combined to simultaneously analyze the metabolites and proteins within a biological sample.
It can analyze as many metabolites that exist in a given sample, and the method is usually used in the identification of new biomarkers, the characterization of metabolic pathways, or the comparison between two clinical or biological states.
Commonly, the chemical identity of the NMR or MS-resolved peaks that are generated by the analyses are unknown before the testing begins, and further analysis is required to distinguish the molecules causing these peaks.
An advantage of the method is that it is an excellent tool for generating comprehensive metabolic profiles of a wide range of samples.
However, the technique is fairly low in sensitivity, and deconvolution and normalization of complex spectra provide challenges.
These limitations generally prevent the method from analyzing any more than the top 100 most abundant molecules in a sample, which means it may miss out on those low in concentration.
This is a problem because metabolites in high abundance are generally those shared between populations and situations, whereas those low in abundance often represent key differences that may have clinical significance
Summary of differences between metabolic target analysis and metabolic profiling
On the one hand, metabolic profiling is a semi-quantitative method of detecting a wide range of metabolites. It acquires data without a priori knowledge of the metabolites of interest and can be used to generate a research hypothesis. It is a middle-in strategy that can be used to find the “needle in the haystack”.
On the other hand, targeted analysis can be used for hypothesis testing or systems biology modeling. It can generate absolute quantification using isotopic internal standards and is a bottom-up strategy.
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