Regulation of blood–brain barrier integrity and cognition by the microbiome-associated methylamines trimethylamine-N-oxide and trimethylamine

Communication between the gut microbiota and the brain is primarily mediated via soluble microbe-derived metabolites, but the details of this pathway remain poorly defined. Methylamines produced by microbial metabolism of dietary choline and L-carnitine have received attention due to their proposed association with vascular disease, but their effects upon the cerebrovascular circulation have not hitherto been studied. Here we use an integrated in vitro/in vivo approach to show that physiologically relevant concentrations of the dietary methylamine trimethylamine N- oxide (TMAO) enhanced and protected blood-brain barrier (BBB) integrity, acting through the tight junction regulator annexin A1. In contrast, the TMAO precursor trimethylamine (TMA) impaired BBB function and disrupted tight junction integrity. Moreover, we show that long-term exposure to TMAO has beneficial effects upon cognition in mice, improving visual recognition memory. Our findings demonstrate a direct interaction of microbiome-associated metabolites with the mammalian BBB, with consequences for cerebrovascular and cognitive function.