Nearly half a million people die annually due to mosquito-borne diseases. Despite aggressive mosquito population-control efforts, current strategies are limited in their ability to control these ...vectors. A better understanding of mosquito metabolism through modern approaches can contribute to the discovery of novel metabolic targets and/or regulators and lead to the development of better mosquito-control strategies. Currently, cutting-edge technologies such as gas or liquid chromatography–mass spectrometry-based metabolomics are considered 'mature technologies' in many life-science disciplines but are still an emerging area of research in medical entomology. This review primarily discusses recent developments and progress in the application of mass spectrometry-based metabolomics to answer multiple biological questions related to mosquito metabolism.
Innovations in mass spectrometry (MS)-based hardware, software, and curated databases have improved metabolomics workflows with the capability to advance our understanding of fundamental life processes.MS-based metabolomics coupled with genetic techniques has shed light on how mosquito metabolism is modulated under different experimental conditions.Variations in metabolite abundance in eggs, larvae, or adult mosquitoes have provided critical clues to understand how mosquitoes cope with temperature and humidity extremes, and exposure to toxic compounds or pathogens.The application of MS-based metabolomics combined with 15N or 13C isotope tracing has empowered scientists to perform high-precision dynamic studies, monitor multiple isotopologs simultaneously over time, and reveal metabolic pathways at the atomic level in mosquito samples.
Primary sclerosing cholangitis (PSC) is a variably progressive, fibrosis-causing autoimmune disorder of the intra- and extra-hepatic bile ducts of unclear etiology. PSC is commonly (in 60-90% of ...cases) associated with an inflammatory bowel disease (IBD) like PSC-IBD, and less commonly with an autoimmune hepatitis (AIH) like PSC-AIH or AIH-overlap disorder. Hepatologists and Gastroenterologists often consider these combined conditions as distinctly different from the classical forms in isolation. Here, we review recent epidemiologic observations and highlight that PSC-IBD and PSC-AIH overlap appear to represent aspects of a common PSC clinico-pathological pathway and manifest in an age-of-presentation dependent manner. Particularly from the pediatric experience, we hypothesize that all cases of PSC likely originate from a complex "Early PSC"-"IBD"-"AIH" overlap in which PSC defines the uniquely and variably associated "AIH" and "IBD" components along an individualized lifetime continuum. We speculate that a distinctly unique, 'diverticular autoimmunity' against the embryonic cecal- and hepatic diverticulum derived tissues may be the origin of this combined syndrome, where "AIH" and "IBD" variably commence then variably fade while PSC progresses with age. Our hypothesis provides an explanation for the age-dependent variation in the presentation and progression of PSC. This is critical for the optimal targeting of studies into PSC etiopathogenesis and emphasizes the concept of a "developmental window of opportunity for therapeutic mitigation" in what is currently recognized as an irreversible disease process. The discovery of such a window would be critically important for the targeting of interventions, both administration of current therapies and therapeutic trial planning.
Gut microbes can synthesize multiple neuro-active metabolites. We profiled neuro-active compounds produced by the gut commensal Bacteroides ovatus in vitro and in vivo by LC-MS/MS. We found that ...B. ovatus generates acetic acid, propionic acid, isobutyric acid, and isovaleric acid. In vitro, B. ovatus consumed tryptophan and glutamate and synthesized the neuro-active compounds glutamine and GABA. Consistent with our LC-MS/MS-based in vitro data, we observed elevated levels of acetic acid, propionic acid, isobutyric acid, and isovaleric acid in the intestines of B. ovatus mono-associated mice compared with germ-free controls. B. ovatus mono-association also increased the concentrations of intestinal GABA and decreased the concentrations of tryptophan and glutamine compared with germ-free controls. Computational network analysis revealed unique links between SCFAs, neuro-active compounds, and colonization status. These results highlight connections between microbial colonization and intestinal neurotransmitter concentrations, suggesting that B. ovatus selectively influences the presence of intestinal neurotransmitters.
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•Bacteroides ovatus modulates key neuro-active compounds in vivo in gnotobiotic animals
Neuroscience; Microbiology; Microbiome
Arginine‐ornithine metabolism plays a crucial role in bacterial homeostasis, as evidenced by numerous studies. However, the utilization of arginine and the downstream products of its metabolism ...remain undefined in various gut bacteria. To bridge this knowledge gap, we employed genomic screening to pinpoint relevant metabolic targets. We also devised a targeted liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) metabolomics method to measure the levels of arginine, its upstream precursors, and downstream products in cell‐free conditioned media from enteric pathobionts, including Escherichia coli, Klebsiella aerogenes, K. pneumoniae, Pseudomonas fluorescens, Acinetobacter baumannii, Streptococcus agalactiae, Staphylococcus epidermidis, S. aureus, and Enterococcus faecalis. Our findings revealed that all selected bacterial strains consumed glutamine, glutamate, and arginine, and produced citrulline, ornithine, and GABA in our chemically defined medium. Additionally, E. coli, K. pneumoniae, K. aerogenes, and P. fluorescens were found to convert arginine to agmatine and produce putrescine. Interestingly, arginine supplementation promoted biofilm formation in K. pneumoniae, while ornithine supplementation enhanced biofilm formation in S. epidermidis. These findings offer a comprehensive insight into arginine‐ornithine metabolism in enteric pathobionts.
The amino acid L‐arginine is converted by bacteria into a variety of downstream metabolites, including citrulline, agmatine, ornithine, putrescine, and gamma‐aminobutyric acid (GABA). Our study shows that both Gram‐negative bacteria (Escherichia coli, Klebsiella pneumoniae, Klebsiella aerogenes, Pseudomonas fluorescens, and Acinetobacter baumannii) and Gram‐positive bacteria (Streptococcus agalactiae, Staphylococcus epidermidis, Staphylococcus aureus, and Enterococcus faecalis) consume arginine, glutamine, and glutamate, and generate citrulline, ornithine, and GABA. This suggests that these pathways are conserved and essential within gut bacteria. We also found that Escherichia coli, Klebsiella pneumoniae, Klebsiella aerogenes, and Pseudomonas fluorescens generate the arginine intermediate agmatine and produce the polyamine putrescine. These findings indicate that arginine is a crucial amino acid for gut bacteria.
Endoplasmic reticulum (ER) stress compromises the secretion of MUC2 from goblet cells and has been linked with inflammatory bowel disease (IBD). Although Bifidobacterium can beneficially modulate ...mucin production, little work has been done investigating the effects of Bifidobacterium on goblet cell ER stress. We hypothesized that secreted factors from Bifidobacterium dentium downregulate ER stress genes and modulates the unfolded protein response (UPR) to promote MUC2 secretion. We identified by mass spectrometry that B. dentium secretes the antioxidant γ-glutamylcysteine, which we speculate dampens ER stress-mediated ROS and minimizes ER stress phenotypes. B. dentium cell-free supernatant and γ-glutamylcysteine were taken up by human colonic T84 cells, increased glutathione levels, and reduced ROS generated by the ER-stressors thapsigargin and tunicamycin. Moreover, B. dentium supernatant and γ-glutamylcysteine were able to suppress NF-kB activation and IL-8 secretion. We found that B. dentium supernatant, γ-glutamylcysteine, and the positive control IL-10 attenuated the induction of UPR genes GRP78, CHOP, and sXBP1. To examine ER stress in vivo, we first examined mono-association of B. dentium in germ-free mice which increased MUC2 and IL-10 levels compared to germ-free controls. However, no changes were observed in ER stress-related genes, indicating that B. dentium can promote mucus secretion without inducing ER stress. In a TNBS-mediated ER stress model, we observed increased levels of UPR genes and pro-inflammatory cytokines in TNBS treated mice, which were reduced with addition of live B. dentium or γ-glutamylcysteine. We also observed increased colonic and serum levels of IL-10 in B. dentium- and γ-glutamylcysteine-treated mice compared to vehicle control. Immunostaining revealed retention of goblet cells and mucus secretion in both B. dentium- and γ-glutamylcysteine-treated animals. Collectively, these data demonstrate positive modulation of the UPR and MUC2 production by B. dentium-secreted compounds.
The intestinal microbiota influences the development and function of the mucosal immune system. However, the exact mechanisms by which commensal microbes modulate immunity is not clear. We previously ...demonstrated that commensal Bacteroides ovatus ATCC 8384 reduces mucosal inflammation. Herein, we aimed to identify immunomodulatory pathways employed by B. ovatus. In germ-free mice, mono-association with B. ovatus shifted the CD11b+/CD11c+ and CD103+/CD11c+ dendritic cell populations. Because indole compounds are known to modulate dendritic cells, B. ovatus cell-free supernatant was screened for tryptophan metabolites by liquid chromatography–tandem mass spectrometry and larger quantities of indole-3-acetic acid were detected. Analysis of cecal and fecal samples from germ-free and B. ovatus mono-associated mice confirmed that B. ovatus could elevate indole-3-acetic acid concentrations in vivo. Indole metabolites have previously been shown to stimulate immune cells to secrete the reparative cytokine IL-22. Addition of B. ovatus cell-free supernatant to immature bone marrow–derived dendritic cells stimulated IL-22 secretion. The ability of IL-22 to drive repair in the intestinal epithelium was confirmed using a physiologically relevant human intestinal enteroid model. Finally, B. ovatus shifted the immune cell populations in trinitrobenzene sulfonic acid–treated mice and up-regulated colonic IL-22 expression, effects that correlated with decreased inflammation. Our data suggest that B. ovatus–produced indole-3-acetic acid promotes IL-22 production by immune cells, yielding beneficial effects on colitis.
Dried blood spot (DBS) analysis has existed for >50 years, but application of this technique to fecal analysis remains limited. To address whether dried fecal spots (DFS) could be used to measure ...fecal bile acids, we collected feces from five subjects for each of the following cohorts:
) healthy individuals,
) individuals with diarrhea, and
)
infected patients. Homogenized fecal extracts were loaded onto quantitative DBS (qDBS) devices, dried overnight, and shipped to the bioanalytical lab at ambient temperature. For comparison, source fecal extracts were shipped on dry ice and stored frozen. After 4 mo, frozen fecal extracts and ambient DFS samples were processed and subjected to targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based metabolomics with stable isotope-labeled standards. We observed no differences in the bile acid levels measured between the traditional extraction and the qDBS-based DFS methods. This pilot data demonstrates that DFS-based analysis is feasible and warrants further development for fecal compounds and microbiome applications.
Stool analysis in remote settings can be challenging, as the samples must be stored at -80°C and transported on dry ice for downstream processing. Our work indicates that dried fecal spots (DFS) on Capitainer quantitative DBS (qDBS) devices can be stored and shipped at ambient temperature and yields the same bile acid profiles as traditional samples. This approach has broad applications for patient home testing and sample collection in rural communities or resource-limited countries.
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