Microbiome–host systems interactions: protective effects of propionate upon the blood–brain barrier, 2018, Hoyles et al

Abstract

Background
Gut microbiota composition and function are symbiotically linked with host health and altered in metabolic, inflammatory and neurodegenerative disorders. Three recognised mechanisms exist by which the microbiome influences the gut–brain axis: modification of autonomic/sensorimotor connections, immune activation, and neuroendocrine pathway regulation. We hypothesised interactions between circulating gut-derived microbial metabolites, and the blood–brain barrier (BBB) also contribute to the gut–brain axis. Propionate, produced from dietary substrates by colonic bacteria, stimulates intestinal gluconeogenesis and is associated with reduced stress behaviours, but its potential endocrine role has not been addressed.

Results
After demonstrating expression of the propionate receptor FFAR3 on human brain endothelium, we examined the impact of a physiologically relevant propionate concentration (1 μM) on BBB properties in vitro. Propionate inhibited pathways associated with non-specific microbial infections via a CD14-dependent mechanism, suppressed expression of LRP-1 and protected the BBB from oxidative stress via NRF2 (NFE2L2) signalling.

Conclusions
Together, these results suggest gut-derived microbial metabolites interact with the BBB, representing a fourth facet of the gut–brain axis that warrants further attention.

Open access, https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-018-0439-y

 

I don't understand the weird obsession with the "gut-brain axis". Every organ in the body is directly connected to the brain, literally everything has to. Never hear about the liver-brain axis. Or any other combination. The interaction between the brain/nervous system and the immune system? Somehow not interesting. Even though they are fully integrated. Probably because it's too complex, and that just takes it off the list of "simple answers to complex questions that are just vague enough to sound substantial".

Ex nihilo ideas about medicine are super weird.

 

Suspect it's the vagus nerve effect..