Determination of depression biomarkers in rat plasma by liquid chromatography-mass spectrometry for the study of the antidepressant effect of Zhi-Zi-Hou-Po decoction on rat model of chronic unpredictable mild stress

• A LC-MS method was developed for determination of depression biomarkers.
• The method assisted in objective clinical diagnosis of depression.
• The method was applied to the antidepressant effect of Zhi-Zi-Hou-Po decoction.
• The method was based on the holistic view of biosystem.
• The method provided insight into therapeutic effect and mechanism of prescriptions.

Zhi-Zi-Hou-Po decoction (ZZHPD), a traditional Chinese medicine (TCM) formula, has been used for treatment of depressive-like symptoms for centuries. However, studies of its antidepressant effect and mechanism are challenging, owing to the complex pathophysiology of depression and complexity of ZZHPD with multiple constituents acting on different metabolic pathways. The present study was designed to develop a liquid chromatography-mass spectrometry (LC-MS) method for simultaneous determination of depression biomarkers: tryptophan (Trp), phenylalanine (Phe), tyrosine (Tyr), indole-3-acetic acid (IAA), hippuric acid (HA), phenaceturic acid (PA), creatinine (Cr), glutamic acid (Glu), succinic acid (SA) and γ-aminobutyric acid (GABA), as well as to study the antidepressant effect and potential mechanism of ZZHPD based on holistic view of an organism. The analysis was performed on a CAPCELL PAK C18 column with methanol and 0.01% formic acid in water using gradient elution. The method showed a good linearity (r2 > 0.99) with the other validation parameters were within acceptance range. The results demonstrated Trp, Phe, Tyr, IAA, HA, Cr, Glu and SA levels were significant lower in model group, while PA and GABA were significant higher than those in control group. The rats with ZZHPD treatment showed a tendency of bringing the levels of all these biomarkers to normal except Cr and Glu. It could be a powerful manner to provide mechanistic insights into the therapeutic effects of complex prescriptions and further understand pathophysiology of depression to assist in clinical diagnosis.