The composition of bacterial species in the human gut is associated with depressive symptoms in at least 6 ethnic groups, according to the results of two cohort studies published at the same time, in which the faecal microbiome was compared with clinical diagnoses in the Netherlands. A possible causal relationship is supported by the fact that among the 13 implied taxa there are several that synthesize messenger substances that play a role in depression – such as glutamate and serotonin.
Background
Although depression is a leading cause of death and economic inequalities, the disease is poorly understood and treatment options are limited, the authors of the two recent studies write in a joint press release.”The gut microbiome is thought to play a role in depressive disorders, making it an attractive target for interventions,” says one publication, and similarly the second publication points out: “It is urgent to identify the molecular and biological mechanisms behind depression, and the gut microbiome has recently become of interest.”
Design
In the HELIUS cohort, the researchers recorded 3211 Dutch people of different ethnicities, but all living in the same metropolitan area (Amsterdam). The 2nd publication was initially based on 1054 participants of the Rotterdam study, after which the results were verified with 1539 individuals from the HELIUS cohort.
Results
- Both alpha diversity (a measure of site-specific biodiversity) and beta diversity (which measures differences in species diversity between individuals) were predictive of depressive symptoms in the HELIUS cohort as assessed with the PHQ-9 questionnaire.Since the demographics and behavior of the participants were also included in the regression analyses, the predictive power of the microbial signature with regard to depressive symptoms was largely independent of ethnicity.
- The strongest associations with depressive symptoms were found for the presence of the bacterial genera Christensenellaceae, Lachnospiraceae and Ruminococcaceae (1).
- In the second study (2), Lachnospiraceae and Ruminococcaceae were also associated with depressive symptoms, as well as 8 other taxa, including Eggerthella, which was already conspicuous in earlier studies. “These bacteria are involved in the synthesis of glutamate, butyrate, serotonin and gamma-aminobutyric acid (GABA), which play a key role as neurotransmitters in depression,” the authors note.
- Representatives of all other taxa were less frequently found in the stool samples of patients with depressive symptoms.
Clinical significance
The two studies confirm that the composition of the gut microbiome may play a key role in depression.Similar findings have been reported several times recently for specific bacterial genera. For example, Coprococcus was decreased in patients with anxiety disorders and depression. A causal role is suggested by an animal study in which rats showed a loss of Coprococcus in their intestines after fecal transplantation of depressed patients, and subsequently developed depressive behavior. It is to be expected that as detailed knowledge of the biochemical relationships progresses, the chances of success for biological interventions using probiotics and faecal transplants will increase.
Funding: Amsterdam University Medical Centers, Public Health Service of Amsterdam.
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Source – https://www.univadis.de/viewarticle/bakterien-zusammensetzung-im-darm-mit-depressiver-2022a100297p