Chronic pain, or inflammation, is believed to be one of the major factors in the onset of major depressive disorder.
Therefore, to better understand what happens physiologically during the depression, scientists have long studied several metabolic processes or “pathways” related to inflammation.
In a new study, researchers found that elevated levels of anthranilic acid in the blood may serve as a marker for identifying people who are experiencing depression-like symptoms and are at risk of developing a major depressive disorder.
The finding shows that metabolites of the kynurenine pathway may serve as “biomarkers” that could allow early detection of patients at risk of developing depression.
The research was conducted by a team at Fujita Health University.
In the study, the team analyzed serum samples from 61 patients who had clinical test scores that indicated a high risk of developing a major depressive disorder.
For a scientifically accurate comparison, they also used a “control” group, wherein they analyzed serum samples from 51 healthy individuals.
The scientists measured the serum levels of various kynurenine pathway metabolites with a technique called high-performance liquid chromatography, which allows precise measurement of concentrations.
They found compared to the healthy “controls,” the patients at risk of depression had increased serum levels of anthranilic acid. Furthermore, women at risk of depression had reduced serum levels of tryptophan.
Given that the kynurenine pathway consumes tryptophan and produces anthranilic acid, these findings are aligned with the previous findings of increased kynurenine pathway activity in patients at risk of developing a major depressive disorder.
The scientists did further analyses on samples and data from 33 patients at risk of depression whose scores on a clinical depression scale at different time points indicated regression from a healthy state to a depressed state.
The analyses showed that increases in serum anthranilic acid levels over time correlated with the worsening of the clinical test scores.
This finding confirms that there is indeed a strong, direct correlation between anthranilic acid levels in the blood and the severity of depression on the clinical depression scale.
Because chronic pain can cause depression and related symptoms, the scientists also scrutinized tryptophan metabolite profiles in patients with chronic pain disorders affecting the mouth, jaw, and face.
By testing serum samples from 48 patients with chronic pain disorders and 42 healthy individuals, the research team found that the patients with chronic pain had elevated serum levels of anthranilic acid and lower serum levels of tryptophan, just like those who were at risk of major depressive disorder.
The team says clinicians can monitor serum levels of anthranilic acid to find out if patients are at risk of developing a major depressive disorder.
One author of the study is Professor Kuniaki Saito.
The study is published in Scientific Reports.
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