Gut microbiota and its relation to inflammation in patients with bipolar depression: a cross-sectional study

Abstract

Background: To explore the gut microbiota characteristics in depressed patients with bipolar disorder (BD) as well as the connection between the gut microbiota and inflammatory markers.

Methods: Totally 72 depressed BD patients and 16 healthy controls (HCs) were enrolled in the study. Blood and feces samples were taken from each subject. With the help of 16S-ribosomal RNA gene sequencing, the characteristics of the gut microbiota in each participant were examined. Correlation analysis was then utilized to assess the relationship between the gut microbiota and clinical parameters.

Results: We found the taxonomic composition of the gut microbiota, but not its diversity, was significantly different in BD patients compared to HCs. We found the abundance of Bacilli, Lactobacillales and genus Veillonella were higher in BD patients than in HCs, while genus Dorea was more abundant in HCs. Additionally, correlation analysis showed that the bacterial genera' abundance in BD patients was strongly correlated with the severity of depression and inflammatory markers.

Conclusions: According to these results, the gut microbiota characteristics were changed in depressed BD patients, which may have been associated with the severity of depression and the inflammatory pathways.

Keywords: Bipolar disorder; Depression; Gene sequencing; Gut microbiota; Inflammation.

Fig. 1

Gut microbiota diversity in BD patients and HCs. (i) There was no significant difference in BD patients and HCs according to the α-diversity index (Shannon, Simpson, invsimpson, obs, chao1 and ice index). (ii) PCoA at OTU level showed that no significant difference was found in two groups

Fig. 2

Gut microbiota taxonomic composition changes in BD patients and HCs. Compared to HCs, the abundance of Bacilli, Lactobacillales and Veillonella was increased, while genus Dorea was decreased (P < 0.05, LDA score > 2)

Fig. 3

Associations between gut microbiota and clinical parameters. Heat map revealed that gut microbiota was closely associated with severity of depression and inflammatory markers in depressed BD patients (P < 0.05). Red and blue edges denoted Spearman’s rank correlation coefficient > 0.2 and <  − 0.2, respectively

Fig. 4

Association between gut microbiota and MADRS scores in BD patients. Pairwise correlation of MADRS with the abundance of Pseudomonas, Faecalibacterium, Lachnospiracea_incertae_sedis and Fusobacterium (P < 0.05)

Fig. 5

Association between gut microbiota and inflammatory markers in BD patients. (i) Serum levels of IL-6 were positively correlated with Enterobacter, Pseudomonas and Leuconostoc abundance, but negatively associated with Cloacibacillus abundance (P < 0.05). (ii) Serum CRP levels were positively correlated with Prevotella abundance, but negatively associated with Butyricicoccus, Lachnospiraceae incertae sedis and Dorea abundance (P < 0.05). (iii) TNF-α levels correlated positively with Parabacteroides, Clostridium IV and Bilophila abundance but negatively with Prevotella abundance (P < 0.05)