Depression can make a person suffer – and early diagnosis can help protect against more serious consequences / © Shot from the film “Eternal Sunshine of the Spotless Mind”

A blood test will allow you to “catch” depressive changes before they go into a severe stage.

Chronic pain and inflammation are major factors in the development of a depressive disorder. To better understand the physiological processes that occur during depression, scientists are studying specific metabolic pathways associated with inflammation. One of them is the kinurenine pathway, in which the amino acid tryptophan, which comes with food, is converted to nicotinic acid.

A group of Japanese scientists has shown that elevated blood levels of anthranilic acid, an important metabolite (intermediate) of the kinurenin pathway, can serve as a marker for identifying people who are at risk of developing major depressive disorder. Article about this study published in the journal Scientific Reports.

“Various scientific evidence suggests that tryptophan metabolism plays an important role in the development of symptoms of depressive disorder,” says Yasuko Yamamoto, one of the authors of the article. Previously, many studies have shown that patients with depression and similar conditions have an increased level of various tryptophan metabolites in the blood. This led scientists to the idea that intermediate products of the kinurenin pathway can be used as biomarkers of a depressed state.

To test his hypothesis, Yamamoto and her colleagues analyzed blood serum samples from 61 patients, the results of clinical tests of which indicated a high risk of developing a major depressive disorder. As a control group, serum samples from 51 conditionally healthy individuals were used.

The level of various kinurenin pathway metabolites was measured by high performance liquid chromatography. In patients at risk, an increased concentration of anthranilic acid was detected in the blood serum compared with the control group. In addition, serum tryptophan levels were lower in women at increased risk of developing depression.

These results are consistent with previous data on increased activity of the kinurenin pathway in patients at risk of developing major depressive disorder. Similar results were obtained for patients with chronic pain.

It was also found that tryptophan metabolite profiles predict the development of depressive symptoms. Further study of samples of 33 patients who experienced regression to a more severe condition showed that an increase in serum anthranilic acid over time correlated with worsening clinical test results.

“This finding confirms that there is indeed a strong direct correlation between the levels of anthranilic acid in the blood and the severity of depression on the clinical depression scale,” summarizes the lead author of the article, Kuniyaki Saito. “Monitoring the level of tryptophan metabolites can be useful for implementing proactive medications for depressive symptoms.”