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 depression, scientists have long studied several metabolic processes or "pathways" related to inflammation. One of these pathways, called the kynurenine pathway, is the principal pathway involved in metabolizing the amino acid tryptophan. Now, a new study by a team of scientists, led by Professor Kuniaki Saito and Associate Professor Yasuko Yamamoto of Japan's Fujita Health University, shows that elevated levels of anthranilic acid--an important metabolite (product/intermediate) 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. This interesting new study is published in Scientific Reports .
Various lines of scientific evidence suggest that tryptophan metabolism is involved in the symptoms of major depressive disorder." Dr. Yasuko Yamamoto, Associate Professor of Japan's Fujita Health University
For example, past studies have reported that patients with depression and other conditions involving depression-like symptoms show increased blood levels of various tryptophan metabolites produced by the kynurenine pathway. These findings led Dr Saito's team 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, Dr 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. For 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. Compared to the healthy "controls," the patients at risk of depression had increased serum levels of anthranilic acid. Furthermore, the 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 major depressive disorder. Related Stories
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