What samples can be detected by metabolomics?
A: Metabolomics focuses on small molecule metabolites (MW<1000) as substrates and products of various metabolic pathways. The samples that can be assayed are mainly urine, plasma or serum, saliva, and cell and tissue extracts. We have also done plant, fungal, and microbial extracts, cerebrospinal fluid, lymphatic fluid, insect hemolymph, amniotic fluid, follicular fluid, knee synovial fluid, tears, semen, fecal and intestinal contents extracts, etc.
Do I need to set up biological replicates for metabolomics? How many biological replicates should be set up?
A: Compared with genes and proteins, metabolites are in the downstream of life activities and have high dynamic fluctuations. Therefore, it is necessary to set up many biological replicates to increase the reliability and persuasiveness of the data in order to reduce individual differences.
For example, 6-8 replicates can be used for plants and microorganisms, and 10 or more replicates for animals. However, the clinical requirements are much higher, as individual differences in humans are so great that 30 or more biological replicates are generally recommended.
What is the lowest level of metabolites that can be detected by metabolomics?
A: Different detection platforms have different sensitivities. LC-MS has the highest sensitivity, which can reach fM level. The ionization efficiency and signal response intensity of mass spectrometry can vary greatly for different substances with the same content due to their own chemical properties. The detection sensitivity of a substance is related to its own chemical properties. The influence of chemical properties is mainly expressed in the ionization efficiency and mass spectrometry fragmentation behavior. Therefore, different substances with the same content may be detected by one and not the other.
If the final number of samples collected from the two groups is not the same, is it okay to compare the two groups in this way?
A: Yes. It is more important that the number of biological replicates in each group is sufficiently high than the comparative analysis of the two groups.
Can the same batch of untargeted metabolomics samples be tested in batches across a longer period of time?
A: Yes, but batches spanning more than two weeks are not recommended. This is because the response of the instrument will vary somewhat from time to time, and the peak area of the same amount of substance tested at different times is different. Untargeted metabolomics analysis calculates the content change multiplication based on the peak area. Detection in two or more batches can lead to large errors in the calculation results.
