Interrogation of the mammalian gut–brain axis using LC–MS/MS-based targeted metabolomics with in vitro bacterial and organoid cultures and in vivo gnotobiotic mouse models

The metabolites of lactic acid bacteria: classification, biosynthesis and modulation of gut microbiota

“…Signals from the CNS are directly passed to the enteric nervous system (ENS), and are involved in the control of the gut microbiota through neuronal circuits [66]. Bidirectionally, the gut microbiota can communicate to the brain through several routes: bacterial metabolites (e.g., SCFAs, folate and EPS ), production of neurotransmitters (e.g., GABA and 5-hydroxytryptamine (5-HT)) , enteroendocrine cell activation (e.g., glucagon-like peptide 1), immunomodulation (e.g., IL-6 and tumor necrosis factoralpha (TNF-α)), and stimulation of the ENS and the vagal nerve [67][68][69]. Apart from the factors mentioned above, stability of the intestinal environment, invasion of pathogenic bacteria, drug treatment, emotional changes and other factors are involved in the complex regulatory network of the intestinal flora.…”

Identification of Metabolite Interference Is Necessary for Accurate LC-MS Targeted Metabolomics Analysis

“…The multiple reaction monitoring (MRM) process uses quadrupoles to select a metabolite’s precursor ion (Q1), fragment it into smaller ions (Q2), and further select a metabolite’s product ion (Q3) sequentially before sending the ions to the detector , (Figure S1). The LC and MS sections separate different metabolites by chromatographic retention times (RTs) and the mass-to-charge ratio ( m/z ) of the precursor and product ions (Q1 and Q3 m/z ). − The combination of RT, Q1 m/z, and Q3 m/z has enabled many successful metabolite-specific measurements. − …”

Innovation in identifying metabolites from complex metabolome—Highlights of recent analytical platforms and protocols

“…In 2022, five studies on high-throughput mass spectrometry metabolomics analytical platforms and softwares for identifying metabolites and delineating their contribution were published in Nature Protocols ( Fu et al, 2022 ; Horvath et al, 2022 ; Kilgour et al, 2022 ; Kirkwood et al, 2022 ; Pang et al, 2022 ). These studies have shown metabolic profiling of candidate metabolites as a dominant technology that enables rapid detection of the metabolic features in the spectral data, which may be followed by spectral and peak data preprocessing, statistical analysis and functional interpretation.…”

“…Recently, a study published in Nature Protocols by Horvath et al developed a LC/MS quantitative analytical platform for liquid chromatography-tandem mass spectrometry metabolomics method for targeting analysis and monitoring the content change of microbially derived short-chain fatty acids and neurotransmitters from the bacterial cultures, organoid cultures and in vivo samples ( Horvath et al, 2022 ). This method has been customized for the targeted metabolite measurements of different microbial subsets and growth media.…”

“…It can comprehensively specifically identify microbial signals within the host, and evaluate the relationship between microbial colonization and neurotransmitters of gut-brain axis in vivo and in vitro (media and organoids) models, reveal the contributions of microbes to host neurotransmitters, and dissect the important bidirectional connections, between commensal microbes and host. In this study, the authors demonstrated a systematic approach to reveal how the bacteria regulate the CNS and gut, provide valuable information by determining the specific pathways into the functional mechanisms that specific microbes influence host metabolism ( Horvath et al, 2022 ). In regard to cellular metabolism, Kilgour et al, focused on performing identification of general metabolic characteristics for specific cell populations by high-dimensional flow cytometry and MS-based metabolite profiling.…”