The antidiabetic medication metformin reduces anxiety-like behaviours in male mice by increasing serotonin availability in the brain, according to a study published in the Journal of Neuroscience. These findings could have major implications for the treatment of patients with both metabolic and mental disorders.
People with diabetes have an increased risk for mood disorders such as depression. Although the mechanisms underlying the relationship between insulin resistance, a symptom of diabetes, and depression are unknown, previous research has highlighted the neurotransmitter serotonin as the culprit.
In mice raised on a high fat diet, researchers demonstrated that the insulin-sensitising drug metformin reduces levels of amino acids that impair the entry of tryptophan in the brain and thereby limit its conversion into serotonin. The drug's antidepressant-like effects were accompanied by improved neurotransmission in the hippocampus. The team achieved similar effects by reducing the amount of branched chained amino acids (BCAAs) in the diet.
Results suggest that metformim may act by decreasing circulating levels of BCAAs and promote antidepressant-like effects in mice fed a high fat diet. These findings also indicate that a diet low in BCAAs, provided either alone or as an adjunct to conventional antidepressant drugs, could help to relieve depressive symptoms in patients with metabolic comorbidities.