Differences of Plasma Levels of Tryptophan, Serotonin, 5-Hydroxyindole Acetic Acid, and Kynurenine between Healthy People and Patients of Major Monopolar Depression at Various Age and Gender

Background: It is not well analyzed whether there are\r\ndifferences in plasma levels of tryptophan (TRP) metabolites between healthy\r\ncontrol people (HC) and patients of major monopolar depression (MMD). Methods: Ultra high-speed liquid chromatography/mass spectrometry has been\r\nused for the simultaneous determination of plasma levels of tryptophan metabolites\r\nin depressive patients. Results: There are no significant differences between plasma levels of TRP between HC\r\nand MMD. Plasma levels of TRP of HC are higher in young men, young women, old\r\nmen, and old women in this order. Serotonin (5-HT) levels are higher in MMD\r\nthan HC. Plasma levels of 5-HIAA of HC are also higher than those of patients\r\nof MMD. Plasma levels of kynurenine (KYN) of healthy old men and old women are\r\nhigher than those of young men and old women. Plasma levels of KYN are higher\r\nin old women and young men of MMD than those of HC. Conclusion: Plasma\r\nlevels of 5-HT are higher in patients of MMD than those of HC, which may\r\nsuggest that use of drugs inhibiting the 5-HT transportation may increase\r\nplasma levels of 5-HT in MMD.