Study IDs Blood Biomarker of Early-Stage Depression
A new Japanese study may have identified a blood biomarker for people at risk for major depressive disorder (MDD). The findings are published in the journal Scientific Reports.
Inflammation has been linked to the onset of MDD. Therefore, to better understand what happens in the body during depression, scientists have long studied several metabolic processes or “pathways” related to inflammation.
One of these pathways, called the kynurenine pathway, is significantly involved in metabolizing the amino acid tryptophan.
Now, the new study at Fujita Health University shows that elevated levels of anthranilic acid — an important metabolite of the kynurenine pathway — in the blood may serve as a marker for identifying individuals who are experiencing depression-like symptoms and are at risk of developing major depressive disorder.
“Various lines of scientific evidence suggest that tryptophan metabolism is involved in the symptoms of major depressive disorder,” said Associate Professor Yasuko Yamamoto of Japan’s Fujita Health University.
For example, past research has shown that patients with depression and other conditions involving depression-like symptoms exhibit increased blood levels of various tryptophan metabolites produced by the kynurenine pathway.
These studies prompted study leader Professor Kuniaki Saito to speculate that metabolites of the kynurenine pathway may serve as “biomarkers” that could allow early detection of patients at risk of developing depression.
To test this idea, Saito’s team analyzed serum (fractionated, clear part of blood) samples from 61 patients who had clinical test scores that indicated a high risk of developing major depressive disorder. They also analyzed serum samples from 51 healthy individuals.
Compared to the healthy “controls,” the patients at risk of depression showed increased serum levels of anthranilic acid. In addition, at-risk women had reduced serum levels of tryptophan.
Given that the kynurenine pathway consumes tryptophan and produces anthranilic acid, these findings are aligned with the previous studies of increased kynurenine pathway activity in patients at risk of developing major depressive disorder.
The scientists also wanted to see if tryptophan metabolite profiles can predict the progression of depression-related symptoms. For that, they conducted further analyses on samples and data from 33 patients at risk of depression whose scores on a clinical depression scale at different timepoints indicated regression from a healthy state to a depressed state.
The analyses showed that increases in serum anthranilic acid levels over time correlated with worsening of the clinical test scores. Saito said, “this finding confirms that there is indeed a strong, direct correlation between anthranilic acid levels in blood and the severity of depression on the clinical depression scale.”
Since chronic pain can lead to depression and related symptoms, the researchers also studied 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, they found that the chronic pain patients had elevated serum levels of anthranilic acid and lower serum levels of tryptophan, just like those who were at risk of major depressive disorder.
Overall, the findings suggest that clinicians may be able to monitor serum levels of anthranilic acid to see if patients are at risk of developing major depressive disorder.
Source: Fujita Health University
Pedersen, T. (2020). Study IDs Blood Biomarker of Early-Stage Depression. Psych Central. Retrieved on February 28, 2020, from https://psychcentral.com/news/2020/02/13/study-ids-blood-biomarker-of-early-stage-depression/154062.html