Probiotic Treatment in Improving Major Depressive Disorder

The Rising Epidemic of Depression and Current Treatment

Depression has become the second largest cause of human morbidity, according to data from the World Health Organization in 2020. Over 350 million people worldwide are believed to be suffering from depression, with less than half receiving effective treatment. Depression is conventionally characterized by emotional disturbances, sleep disorders, and gastrointestinal dysfunction, which in turn lead to social impairments. One theory suggests the lack of 5-HT, a suppressive neurotransmitter prevalent in mammalian tissues, especially in the cortical matter and synapses in the brain, contributes to depression. Consequently, first-line anti-depressants, such as Fluoxetine, Paroxetine, and Citalopram which are 5-HT reuptake inhibitors, are being extensively used to treat depression.

An Innovative Approach: Probiotic Treatment for Depression Disorder

In recent years, researchers have studied the potential mental impact of administering three types of probiotics - Bifidobacterium breve, Bifidobacterium longum, and Pediococcus acidilactici - to patients with major depression. Forty patients with major depression were randomly assigned to a placebo group or probiotics group and the patients in the probiotics group received a 4-week oral probiotic treatment. The psychological and gastrointestinal status of patients were evaluated using clinical rating scales before and after the treatment, and their gut microflora were analyzed using 16S rRNA gene amplicon sequencing. Remarkably, patients in the probiotic group exhibited a significant decrease in their self-rated depression scores and displayed distinct improvements in their gastrointestinal function compared to the placebo group.

The Potential Mechanisms Behind the Beneficial Effects of Probiotics

Two processes, researchers speculate, are likely responsible for the beneficial changes. Firstly, probiotics increase the level of short-chain fatty acids (SCFA) in the gut, which increases the osmotic pressure of feces and water absorption, thereby promoting bowel movement. Secondly, probiotics boost the levels of 5-HT in the gut, a neurotransmitter crucial for promoting intestinal motility. Plenty of research has indicated the biosynthesis of gut 5-HT is dependent on gut microbiota, and SCFA likely plays a key role in this process. However, even when the levels of SCFA changed, no change was seen in the biosynthesis levels of 5-HT. Researchers observed an overexpression of the colonic 5-HT transport protein gene (Slc6a4) in depressive mice. However, by reducing the expression of colonic Slc6a4, over-uptake of synaptic 5-HT was restored to normal levels in mice treated with probiotics.

Fig.1 Probiotic treatment for depression disorder.²

In conclusion, this research offers evidence that a combination of three probiotics can improve both the mental symptoms and co-morbid gastrointestinal symptoms of patients with major depression. The modulation of the 5-HT system is a key mechanism that drives the beneficial impact of probiotics on both the brain and the gut. These findings open a promising new avenue for the treatment of depression and other gut-brain axis-related disorders. However, further research involving a larger population is still required to confirm the specific clinical directions for probiotic therapy.

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Reference

1. Tian, Peijun, et al. "Multi-Probiotics ameliorate Major depressive disorder and accompanying gastrointestinal syndromes via serotonergic system regulation." Journal of Advanced Research 45 (2023): 117-125.

For Research Use Only. Not intended for use in food manufacturing or medical procedures (diagnostics or therapeutics). Do Not Use in Humans.