Multi-Probiotics ameliorate Major depressive disorder and accompanying gastrointestinal syndromes via serotonergic system regulation

Abstract

Introduction: Major depressive disorder (MDD) is a leading global psychiatric disease. MDD is highly comorbid with gastrointestinal abnormalities, such as gut motility dysfunction. An effective strategy to manage depression and its accompanying gastrointestinal symptoms is warranted.

Objectives: Three probiotic strains (Bifidobacterium breve CCFM1025, Bifidobacterium longum CCFM687, and Pediococcus acidilactici CCFM6432) had previously been validated in mice to possess antidepressant-like potential. This study investigated the potential psychotropic effects of a combined three-strain probiotic intervention for human MDD patients. The mechanism of action was further investigated in the stress-induced depression mice model.

Methods: MDD patients were given a freeze-dried, mixed probiotic formula for four weeks. The patients' psychometric and gastrointestinal conditions were evaluated using clinical rating scales before and after treatment. Their gut microbiome was also analysed using 16S rRNA gene amplicon sequencing. The mechanisms underlying the beneficial probiotic effects were determined using a chronic stress-induced depressive mouse model.

Results: Multi-probiotics significantly reduced depression scores, and to a greater extent than the placebo (based on the Hamilton Depression Rating, Montgomery-Asberg Depression Rating, and Brief Psychiatric Rating Scales). Multi-probiotics also significantly improved the patients' gastrointestinal functions (based on self-evaluation using the Gastrointestinal Symptom Rating Scale). Serotonergic system modification was demonstrated as the key mechanism behind the probiotics' benefits for the brain and the gut.

Conclusion: Our findings suggest a novel and promising treatment to manage MDD and accompanying gut motility problems, and provide options for treating other gut-brain axis-related disorders.

Keywords: Depression; Gut motility; Probiotics; Serotonin; Stress.

Graphical abstract

Fig. 1

Psychometric and gastrointestinal changes after multi-probiotics treatment. (A) Clinical experimental design. (B) Score changes of the Hamilton Depression Rating Scale (HAMDS) in the placebo and probiotic groups. (C) Score reduction of the HAMDS from the baseline. (D) Score changes of the Montgomery-Asberg Depression Rating Scale (MADRS) in the placebo and probiotic groups. (E) Score reduction of the MADRS from the baseline. (F) Score changes of the Brief Psychiatric Rating Scale (BPRS) in the placebo and probiotic groups. (G) Score reduction of the BPRS from the baseline. (H) Score changes of the Gastrointestinal Symptom Rating Scale (GSRS) in the placebo and probiotic groups. (G) Score reduction of the GSRS from the baseline. (J) GSRS factor analysis. ^#P <.05, ^##P <.01, ^####P <.0001 in Sidak’s multiple comparisons test after two-way ANOVA. *P <.05, **P <.01, ****P <.0001 in the unpaired t-tests.

Fig. 2

Gut microbial alterations. (A) Shannon diversity. (B) Observed operational taxonomic units (OTUs). ^#P <.05, ^##P <.01, ^###P <.001 in Sidak’s multiple comparisons test after two-way ANOVA. (C) Principal component analysis (PCA) showing the microbial compositions of patients before and after the treatment. Lines link the same subject and show the distance travelled over time. (D) Differential microbial taxa before and after the treatment between placebo and probiotic groups, identified by linear discriminant analysis (LDA) effect size (LEfSe) analyses. Data were computed with an LDA score above 2.00 and a P-value below 0.05 for the factorial Kruskal-Wallis test.

Fig. 3

Antidepressant-like effects and possible mechanisms of the probiotics. (A) Animal experimental schedule. (B) Forced swim test (n = 8 in each group). (C) Tail suspension test (n = 8 in each group). (D) Basal serum corticosterone levels (n = 8 in each group). (E) Hypothalamus corticotropin-releasing factor (CRF) levels (n = 6 in each group). (F) 5-HT turnover in the prefrontal cortex (n = 5–7 in each group). (G) 5-HT turnover in the brainstem (n = 6–7 in each group). (H) Immunohistochemistry examination of hippocampal proBDNF levels. The left panel shows representative staining of the target protein. Histogram bars indicate the relative expression of proBDNF to the Non-stressed group (n = 3 in each group). (I) Immunofluorescence staining of mature BDNF levels in the hippocampus. The nucleus was stained with 4′,6-diamidino-2-phenylindole (DAPI, blue), and BDNF was labelled with fluorescein (FITC, green). Histogram bars indicate the relative expression of BDNF to the Non-stressed group (n = 3 in each group).

Fig. 4

Gastrointestinal effects and possible probiotic mechanisms. (A) Gastrointestinal (GI) transit test. Bars indicate the food transiting distance (percentage of the whole intestine) within 30 min after gavage (n = 5–7 in each group). (B) Time of the first coloured defecation after gavage (n = 8 in each group). (C) 5-HT levels in colon tissue (n = 8 in each group). (D) Transcriptional levels of the colonic serotonin transporter gene (Slc6a4; n = 7–8 in each group). (E) Transcriptional levels of the colonic tryptophan hydroxylase 1 gene (Tph1; n = 8 each group). (F) Stool moisture. (G) Caecal short-chain fatty acid levels (n = 8 each group; *P <.05, **P <.01, ***P <.001, ****P <.0001 in the unpaired t-tests).