Scientists from Wuhan University have found a molecule secreted by a gut bacteria that may be behind symptoms of depression in some people. Research published in the journal Cell Metabolism.
The researchers analyzed blood samples from 91 women aged 18 to 45 with depression and 98 women without depression. Serum levels of the hormone estradiol (a form of estrogen) were almost half as high in depressed patients.
Estradiol is formed in the ovaries and, after doing its job, is processed in the liver and then enters the intestines. Here, the hormone is partially reabsorbed into the bloodstream. The researchers hypothesized that the decreased estradiol levels were due to gut bacteria. They added stool microbiome samples from depressed women to a laboratory dish containing estradiol. Within two hours, the hormone level dropped by 78%. At the same time, in a test tube of microbiome samples from women without depression, the level decreased by only 20%.
The authors found that gut bacteria are responsible for the elimination of estradiol. Klebsiella aerogens TS2020. This was confirmed in experiments on mice: when the stool microbiota of depressed women was transplanted into them, they began to show signs of depression. The introduction of the antibiotic cefotaxime put them at ease.
Bacteria needed the 3β-HSD enzyme to destroy the enzyme. Incorporating the gene for this enzyme into the genome of common E. coli was capable of destroying estradiol and causing depression in mice. At the same time, estradiol levels were decreased in the mice’s brains, including the hippocampus, an area of the brain involved in the development of depression.
The results of the study mean that the enzyme produced by microbes can lead to brain disorders and the development of depression.
In a previous study, researchers found high levels of the same enzyme in male patients with depression: the enzyme can also break down testosterone. The scientists noted that there may be other bacteria that destroy the hormones.
Previously, some scientists suggested treating depression with estrogens. The discovery could mean that administering the hormones would be useless, as the bacteria would break them down in the gut.