The gut and brain communicate with each other through a bidirectional signaling pathway called the gut-brain axis, which may be dysregulated in depression. Key elements of this pathway are the tens of trillions of bacteria, viruses, and fungi that comprise the intestinal microbiota. Diagnosis of depression relies heavily on clinical evaluation instead of measurement of biomarkers, often leading to misdiagnosis. Authors of a new report aimed to identify which specific microbial and metabolic biomarkers are altered in patients with depression.
Changes to the microbes that live in the gut or the metabolites that these microbes consume and produce may be responsible for the development and severity of depression. Previous research has demonstrated that transplanting the microbiota of patients with depression into germ-free mice can induce depressive symptoms in these animals.
The study involved 311 participants between the ages of 18 and 65 years, roughly half of whom had been diagnosed with major depressive disorder. The participants completed testing that included submission of a fecal sample to characterize the gut metagenome (sum of all DNA and RNA) and metabolome (sum of all proteins). They also completed surveys to assess depression severity, diet quality, and lifestyle habits.
The authors reported large and consistent disturbances in amino acid metabolic metabolism in participants with depression. These disturbances may disrupt the balance of neurotransmitters, such as dopamine, glutamate, and GABA. Most of the bacterial species that were increased in patients with depression belong to the genera Bacteroides, which the authors believe is responsible for the increase in inflammatory markers found in the depression group. The authors also reported an association between select viruses in the gut and metabolites associated with depression.
Utilizing both metagenomic and metabolic data enabled the authors to identify strong associations between altered amino acid metabolism in the gut and depression. The authors noted that these findings are preliminary and require further investigation in a larger, more diverse sample.
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