title: Histamine derived from probiotic Lactobacillus reuteri suppresses TNF via modulation of PKA and ERK signaling.
abstract: Beneficial microbes and probiotic species, such as Lactobacillus reuteri, produce biologically active compounds that can modulate host mucosal immunity. Previously, immunomodulatory factors secreted by L. reuteri ATCC PTA 6475 were unknown. A combined metabolomics and bacterial genetics strategy was utilized to identify small compound(s) produced by L. reuteri that were TNF-inhibitory. Hydrophilic interaction liquid chromatography-high performance liquid chromatography (HILIC-HPLC) separation isolated TNF-inhibitory compounds, and HILIC-HPLC fraction composition was determined by NMR and mass spectrometry analyses. Histamine was identified and quantified in TNF-inhibitory HILIC-HPLC fractions. Histamine is produced from L-histidine via histidine decarboxylase by some fermentative bacteria including lactobacilli. Targeted mutagenesis of each gene present in the histidine decarboxylase gene cluster in L. reuteri 6475 demonstrated the involvement of histidine decarboxylase pyruvoyl type A (hdcA), histidine/histamine antiporter (hdcP), and hdcB in production of the TNF-inhibitory factor. The mechanism of TNF inhibition by L. reuteri-derived histamine was investigated using Toll-like receptor 2 (TLR2)-activated human monocytoid cells. Bacterial histamine suppressed TNF production via activation of the H(2) receptor. Histamine from L. reuteri 6475 stimulated increased levels of cAMP, which inhibited downstream MEK/ERK MAPK signaling via protein kinase A (PKA) and resulted in suppression of TNF production by transcriptional regulation. In summary, a component of the gut microbiome, L. reuteri, is able to convert a dietary component, L-histidine, into an immunoregulatory signal, histamine, which suppresses pro-inflammatory TNF production. The identification of bacterial bioactive metabolites and their corresponding mechanisms of action with respect to immunomodulation may lead to improved anti-inflammatory strategies for chronic immune-mediated diseases.
authors.affiliation: Interdepartmental Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Carissa M
authors.initials: CM
authors.lastname: Thomas
authors.forename: Teresa
authors.initials: T
authors.lastname: Hong
authors.forename: Jan Peter
authors.initials: JP
authors.lastname: van Pijkeren
authors.forename: Peera
authors.initials: P
authors.lastname: Hemarajata
authors.forename: Dan V
authors.initials: DV
authors.lastname: Trinh
authors.forename: Weidong
authors.initials: W
authors.lastname: Hu
authors.forename: Robert A
authors.initials: RA
authors.lastname: Britton
authors.forename: Markus
authors.initials: M
authors.lastname: Kalkum
authors.forename: James
authors.initials: J
authors.lastname: Versalovic
mesh_terms: D001681:Biological Assay / Q000379:methods; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005285:Fermentation; D006632:Histamine / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry; D006640:Histidine Decarboxylase / Q000737:chemistry; D006801:Humans; D007778:Lactobacillus / Q000378:metabolism; D052200:Limosilactobacillus reuteri / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D013058:Mass Spectrometry / Q000379:methods; D016296:Mutagenesis; D019936:Probiotics / Q000737:chemistry*; D011970:Receptors, Histamine H2 / Q000737:chemistry; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D011970:Receptors, Histamine H2; D014409:Tumor Necrosis Factor-alpha; D006639:Histidine; D006632:Histamine; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D006640:Histidine Decarboxylase