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Effects of gut-derived trimethylamines on the blood–brain barrier

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Title: Effects of gut-derived trimethylamines on the blood–brain barrier
Authors: McArthur, S
Carvalho, A
Fonseca, S
Snelling, T
Nicholson, J
Glen, R
Carding, S
Hoyles, L
Item Type: Poster
Abstract: Introduction: The gut microbiota and its metabolites exert significant effects on host health, with disturbances to composition and function associated with conditions including obesity, type II diabetes and, more recently, Alzheimer’s disease (AD). Communication between microbes and the host can take a number of forms, but central to all of them is a role for gut-derived microbial metabolites, with trimethylamine N-oxide (TMAO) and its precursor trimethylamine (TMA) being important examples. TMA produced by gut bacteria is converted to TMAO in the liver by flavin monooxygenases whereupon it enters the circulation. TMAO was recently identified as potentially important in genetic pathways associated with AD, and has been shown to influence peripheral vascular function. Given these links, the key position of the cerebral vasculature as the major interface between circulating molecules and the brain, and evidence that deficits in blood–brain barrier (BBB) function occur early in AD, we investigated the effects of TMAO and TMA on key BBB properties in vitro and in vivo. Materials and Methods: Male C57Bl/6 mice (n=4-5) were used to examine the effect of TMAO treatment (1.8 mg/kg, 2 h, dose equivalent to circulating human concentrations) upon BBB permeability in vivo, assessed by Evans’ blue dye extravasation. TMA was not investigated as the average mouse plasma concentration of this methylamine is substantially greater than that seen in humans (TMAO-to-TMA ratio 1:10 in mice, 10:1 in humans). Human hCMEC/D3 cerebromicrovascular cells were used as an in vitro model of the BBB to investigate the effects of 24 h treatment with human physiologically relevant doses of TMAO (40 μM) and TMA (0.4 μM), studying (i) functional barrier properties of cell monolayers and (ii) gene expression. Results: Administration of TMAO to mice enhanced BBB integrity above baseline after 2 h treatment (p<0.05). Similarly, in vitro exposure of hCMEC/D3 cells to TMAO enhanced transendothelial electrical resistance (p<0.001) and reduced paracellular permeability to a 70 kDa dextran tracer (p<0.001). In contrast, whilst TMA (0.4 μM) enhanced electrical resistance (p<0.001), it significantly increased tracer paracellular permeability (p<0.05), consistent with compromised barrier function. Analysis of human-genome transcriptomic data suggested that TMAO acts by increasing expression of annexin A1, a protein we have previously shown to enhance tight junction function through promotion of cortical actin. Similar analysis for TMA indicated that this metabolite may induce actin stress fibre formation, a feature known to impair BBB integrity. Validation of these results is ongoing. Conclusions: TMAO and TMA affect BBB function in a metabolite-specific manner, likely through modulation of the actin cytoskeleton and tight junctions. Variation in circulating levels of these metabolites with aging may play a role in the BBB changes seen in AD.
Issue Date: 20-Mar-2018
URI: http://hdl.handle.net/10044/1/62968
Copyright Statement: © 2018 The Author(s).
Sponsor/Funder: Medical Research Council (MRC)
Medical Research Council (MRC)
Alzheimer's Research UK
Funder's Grant Number: MR/L01632X/1
Conference Name: Alzheimer's Research UK Research Conference 2018
Appears in Collections:Department of Surgery and Cancer