Kynurenine pathway changes in late-life depression.

Area of Science:

• Neuroscience
• Biochemistry
• Psychiatry

Background:

• The kynurenine pathway (KP) is implicated in neuropsychiatric disorders.
• Major depression disorder (MDD) research has overlooked KP alterations in late-life depression (LLD).

Purpose of the Study:

• To investigate tryptophan (TRP) and kynurenine (KYN) metabolism imbalances in LLD patients.
• To differentiate KP characteristics between early-onset depression (EOD) and late-onset depression (LOD).

Main Methods:

• Studied 170 LLD patients (90 EOD, 80 LOD) and 135 controls.
• Measured serum TRP, KYN, and kynurenic acid (KYNA) using liquid chromatography-tandem mass spectrometry.
• Assessed depressive symptoms with the Hamilton Depression Scale (HAMD-17).

Main Results:

• LLD patients had lower TRP, KYN, KYNA, and KYNA/KYN ratio, and a higher KYN/TRP ratio than controls.
• LOD patients exhibited decreased TRP and increased KYN/TRP ratio.
• EOD patients showed low TRP without increased KYN/TRP ratio; depression factors correlated with TRP and KYNA/KYN in EOD, but not LOD.

Conclusions:

• LLD patients exhibit significant kynurenine pathway alterations.
• Late-onset depression is characterized by profound tryptophan metabolism shifts.
• Early-onset depression involves low tryptophan and altered kynurenine metabolism, with correlations to depressive symptoms.