Introduction to Metabolomics

Metabolomics is a discipline that studies the types and quantities of endogenous metabolites in organisms and their changing laws under internal and external factors. It is an important part of systems biology. In the late 1990s, Nicholson first proposed the concept of "metabonomics", which means "quantitative determination of the dynamic response of biological systems to pathophysiological stimuli and multi-parameter metabolism caused by genetic changes." Subsequently, Fiehn put forward the concept of "metabolomics" for the first time, defining metabolomics as the qualitative and quantitative determination of the overall metabolic profile in biological samples under specific restricted conditions. With the development of this subject research, scientists now believe that metabonomics/metabolomics is a scientific study of qualitative and quantitative analysis of all low-molecular-weight (MW <1,000) metabolites in a certain organism or cell. Analyze the relationship between the dynamic changes of metabolites produced by internal and external factors and the pathophysiology.rnMetabolomics is the metabolome of the sum of small molecular metabolites in the organism, which is the intermediate or final product produced by gene expression and metabolism. Metabolomics is at the end of the transmission of life information. It can represent the final result of the overall function or state of a biological system. Metabolomics and genomics, transcriptomics and proteomics together constitute the overall systems biology. With the continuous development of analysis technology and the continuous optimization of data processing methods, the research scope of metabolomics covers many research fields such as microbiology, botany, food and nutrition science, toxicology research, clinical disease diagnosis, drug development, etc.rnMetabolomics is divided into targeted metabolomics and untargeted metabolomics. Targeted metabolomics analysis is mainly to quantify specific metabolites. The typical focus is on one or several related metabolic pathways. It is often used to study the pharmacokinetics of drug metabolism and to measure the effect of a certain therapy or genetic modification. Untargeted metabolomics has a wide range and is often used to analyze as many metabolites as possible simultaneously from biological samples.rnThe metabolomics research process generally includes biological sample collection, sample pretreatment, data collection, analysis and interpretation, etc. Metabolites need to be determined by appropriate methods. The main analytical techniques such as separation and analysis techniques such as nuclear magnetic resonance (NMR), chromatography, mass spectrometry (MS) and the combination of multiple analytical platforms have been widely used in metabolomics research.rnNMR technologyrnThe advantages of NMR technology are simple pretreatment, less sample usage, non-invasiveness, large amount of measurable information, and the same sensitivity for all compounds. Especially the hydrogen spectrum of NMR responds to hydrogen-containing compounds. Therefore, most compounds can be detected and a wealth of sample information can be obtained. However, due to the small molecules of metabolites and many endogenous substances, the peaks of many compounds in the NMR spectrum overlap and interfere with each other, so that biomarkers are often interfered by irrelevant substances. In addition, the narrow dynamic range of NMR measurement and the broadening of spectral lines result in relatively low sensitivity.rnChromatography-mass spectrometry technologyrnCompared with NMR, chromatography-mass spectrometry technology has the advantages of diverse detection and separation modes and direct correlation of variables with metabolites. It has gradually become one of the most important analytical tools in metabolomics research.rnThe most common are liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Liquid chromatography is divided into ultra-high-performance liquid chromatography (UPLC) and high-performance liquid chromatography (HPLC).rnIn the analysis of untargeted metabolomics, chromatography can be used in combination with mass spectrometry such as TOF, Orbitrap, IT-TOF, Q-TOF, etc. In the analysis of targeted metabolomics, chromatography can be connected in tandem with mass spectrometry such as triple quadrupole (QQQ) or Q-Trap for detection by multiple reaction monitoring (MRM) instruments.