Probiotic Mixture Containing Lactobacillus helveticus, Bifidobacterium longum and Lactiplantibacillus plantarum Affects Brain Responses Toward an Emotional Task in Healthy Subjects: A Randomized Clinical Trial

Abstract

Background: Evidence from preclinical studies suggests that probiotics affect brain function via the microbiome-gut-brain axis, but evidence in humans remains limited.

Objective: The present proof-of-concept study investigated if a probiotic product containing a mixture of Bifidobacterium longum R0175, Lactobacillus helveticus R0052 and Lactiplantibacillus plantarum R1012 (in total 3 × 109 CFU/day) affected functional brain responses in healthy subjects during an emotional attention task.

Design: In this double-blinded, randomized, placebo-controlled crossover study (Clinicaltrials.gov, NCT03615651), 22 healthy subjects (24.2 ± 3.4 years, 6 males/16 females) were exposed to a probiotic intervention and a placebo for 4 weeks each, separated by a 4-week washout period. Subjects underwent functional magnetic resonance imaging while performing an emotional attention task after each intervention period. Differential brain activity and functional connectivity were assessed.

Results: Altered brain responses were observed in brain regions implicated in emotional, cognitive and face processing. Increased activation in the orbitofrontal cortex, a region that receives extensive sensory input and in turn projects to regions implicated in emotional processing, was found after probiotic intervention compared to placebo using a cluster-based analysis of functionally defined areas. Significantly reduced task-related functional connectivity was observed after the probiotic intervention compared to placebo. Fecal microbiota composition was not majorly affected by probiotic intervention.

Conclusion: The probiotic intervention resulted in subtly altered brain activity and functional connectivity in healthy subjects performing an emotional task without major effects on the fecal microbiota composition. This indicates that the probiotic effects occurred via microbe-host interactions on other levels. Further analysis of signaling molecules could give possible insights into the modes of action of the probiotic intervention on the gut-brain axis in general and brain function specifically. The presented findings further support the growing consensus that probiotic supplementation influences brain function and emotional regulation, even in healthy subjects. Future studies including patients with altered emotional processing, such as anxiety or depression symptoms are of great interest.

Clinical trial registration: [https://ichgcp.net/clinical-trials-registry/NCT03615651" title="See in ClinicalTrials.gov">NCT03615651].

Keywords: brain activity; emotional attention task (EAT); functional connectivity; functional magnetic resonance imaging (fMRI); gut microbiota; gut-brain axis; probiotics; task-related.

Conflict of interest statement

LLS was employed by Pfizer Consumer Healthcare. This study received funding from Pfizer Consumer Healthcare. LLS was involved in study design and discussion of the results, but had no involvement in collection, analysis, interpretation of data or the decision to submit this article for publication. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2022 Rode, Edebol Carlman, König, Repsilber, Hutchinson, Thunberg, Andersson, Persson, Kiselev, Lathrop Stern, Salomon, Mohammed, Labus and Brummer.

Figures

FIGURE 1

Study design. fMRI, functional magnetic resonance imaging.

FIGURE 2

Sub-clusters that were found to be associated with significant (p < 0.05) changes in brain activity between both interventions (probiotic > placebo) before multiplicity correction, during the EAT paradigm. Two of these sub-clusters covered predefined ROIs (italic). Clusters are superimposed on average anatomical scans. Clusters can be identified by the coordinates of their peak (x y z). EAT, emotional attention task; ROI, region of interest.

FIGURE 3

Cluster pairs that were found to be associated with significant (FDR-corrected p < 0.05) connectivity changes between both interventions (probiotic < placebo), during the EAT paradigm. None of these sub-clusters was among the predefined ROIs. Four of those sub-cluster belonged to the same larger cluster spanning over several BNA regions (italic). Clusters are superimposed on average anatomical scans. Clusters can be identified by the coordinates of their peak (x y z). BNA, Brainnetome atlas; EAT, emotional attention task; FDR, false discovery rate; ROI, region of interest.

FIGURE 4

Baseline-corrected salivary cortisol concentrations after EAT after placebo and probiotic intervention. No statistically significant differences were found between both interventions. Line presents median, box presents 25th and 75th percentile, whiskers present minimum to maximum; paired t-test; n = 21. EAT, emotional attention task.

FIGURE 5

Subjective stress ratings (VAS 0-100) of the fMRI examinations itself and the EAT paradigm by visit and intervention. Wilcoxon matched-pairs signed rank test; n = 22; *** p < 0.001; line presents median, box presents 25th and 75th percentile, whiskers present minimum to maximum. EAT, emotional attention task; fMRI, functional magnetic resonance imaging; VAS, visual analogous scale.