Probiotic in Yogurt May Improve Depressive Symptoms

Lactobacillus, a probiotic bacteria found in live-culture yogurt, appears to reverse symptoms of depression in mice, new research shows. In addition, investigators have discovered a specific mechanism suggesting a direct link between the health of the gut microbiome and mental health.

In a recognized preclinical model of depression, investigators examined the gut microbiome of mice before and after they were exposed to chronic stress. The major change they found was a loss of Lactobacillus and an increase in circulating levels of kynurenine metabolites, which are known to drive depression. With the loss of Lactobacillus came the onset of depressive symptoms. But after supplementation with L reuteri to restore Lactobacillus, kynurenine metabolism normalized, and so did the animals’ behavior.

“A single strain of Lactobacillus is able to influence mood,” lead investigator Alban Gaultier, PhD, of the University of Virginia School of Medicine, Charlottesville, said in a release.

“This is the most consistent change we’ve seen across different experiments and different settings we call microbiome profiles. This is a consistent change. We see Lactobacillus levels correlate directly with the behavior of these mice,” said study researcher Ioana Marin, a PhD student.

The study was published online March 7 in Scientific Reports.

Gateway to New Depression Treatments?

The role of the kynurenine pathway in the relationship is especially notable, he said.

“In many ways, the neurobiological features of depression, such as stress and inflammation, create the perfect storm for increased kynurenine pathway metabolism,” said Dr Clarke.

“Although earlier studies implicated the gut microbiome as an important regulator of this metabolic cascade, we weren’t sure which particular members of the consortium of bacteria in the gut were most important for these host-microbe interactions.

“This study is important, as it demonstrates that Lactobacillus might be critical for restraining excessive production of kynurenine, and they also show that supplementation with L reuteri can help apply the brakes to this runaway metabolic train under pathological conditions.”

The broader possible implication of dietary probiotic supplementation with Lactobacillus obtained through live-culture yogurt as a means of improving depression is feasible, Dr Clarke added, noting the findings from his study on B longum.

A Note of Caution

“A note of caution is advisable, as another candidate psychobiotic we tested (L rhamnosus [JB-1]) with quite a strong preclinical signal did not translate well,” Dr Clarke said.

“Interestingly, this was also a Lactobacillus strain but with a mechanism of action based on communication via the vagus nerve rather than regulation of kynurenine production,” Dr Clarke said.

Dr Clarke noted that many aspects of microbiome-gut-brain axis are intriguing, but more research on humans is needed.

“We still need more clinical studies to confirm that the important preclinical observations, like the one made here, will translate to humans,” he said.

“The field also needs more mechanistically oriented studies, and that is one of the reasons the study reported here is an important addition to the literature.”

The study received funding from the National Multiple Sclerosis Society and the National Institute of Mental Health. Dr Clarke is currently funded by the Irish Health Research Board, the Health Service Executive, and the Air Force Office of Scientific Research. He is also on the editorial board of Scientific Reports.

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