Tryptophan metabolite concentrations in depressed patients before and after electroconvulsive therapy

Tryptophan and kynurenine pathway (KP) metabolites are implicated in the pathophysiology of depression. We aimed to investigate their plasma concentrations in medicated patients with depression (n = 94) compared to age- and sex-matched healthy controls (n = 57), and in patients with depression after electroconvulsive therapy (ECT) in a real-world clinical setting, taking account of co-variables including ECT modality and heterogenous psychopathology. Depression severity was assessed using the Hamilton Depression Rating Scale (HAM-D24). Tryptophan (TRP) and kynurenine (KYN) metabolite concentrations [anthranilic acid (AA), 3-hydroxyanthranilic acid (3HAA), picolinic acid (PA), kynurenic acid (KYNA), and xanthurenic acid (XA)] and KYNA/KYN and KYNA/quinolinic acid (QUIN) ratios were lower in patients compared to controls. For the total group there was no significant change in KP metabolites post-ECT or correlations with mood ratings. However, improvements in mood score were correlated with increased KYN, 3-hydroxykynurenine (3HK), 3HAA, QUIN, and KYN/TRP in a subgroup of unipolar depressed patients. Additionally, in remitters baseline KYN, 3HK, and QUIN were associated with baseline HAM-D24 scores, and changes in 3HK and 3HAA concentrations post-ECT correlated with improvement in mood. KYN, KYNA, AA, 3HK, XA, PA, and QUIN were increased in a smaller 3-month follow-up group (n = 19) compared to pre-ECT concentrations. Overall, the results indicate that ECT mobilizes the KP, where a moderate association between selected metabolites and treatment response in unipolar depressed patients is evident.