Feasibility of Using Serum, Plasma, and Platelet 5-hydroxytryptamine as Peripheral Biomarker for the Depression Diagnosis and Response Evaluation to Antidepressants: Animal Experimental Study

Abstract

Objective: Whether peripheral blood 5-hydroxytrptamine (5-HT) levels serve as biomarker for depression diagnosis/response evaluation has not been well determined. This work was explored to address this inconclusive issue.

Methods: Animals were randomized into normal control group (NC, n = 10) and chronic unpredictable mild stress model group (CUMS-model, n = 20), respectively. Animals in CUMS-model group were subjected to chronic stress, then they were randomly subdivided into CUMS subgroup and CUMS + fluoxetine subgroup (CUMS + FLX). After FLX treatment, blood and tissues were collected. 5-HT and relevant protein expression were measured.

Results: In mice model, there was a significant increase in serum and a significant reduction in plasma 5-HT levels in CUMS-model group versus NC group, while platelet 5-HT levels change little. After FLX treatment, serum and platelet 5-HT levels were significantly decreased in CUMS + FLX subgroup, while plasma 5-HT levels had not much change versus CUMS subgroup. Chronic stress enhanced colon and platelet serotonin transporter (SERT) expression and FLX treatment mitigated SERT expression. In rats' model, there was a significant increase in serum 5-HT levels while plasma and platelet 5-HT levels showed little change in CUMS group versus NC group. After FLX treatment, serum, plasma and platelet 5-HT levels were significantly decreased in CUMS + FLX subgroup versus CUMS subgroup. The profile of relevant proteins expression changed by FLX were like those in mice.

Conclusion: Serum 5-HT levels might serve as a potential biomarker for depression diagnosis, meanwhile serum and platelet 5-HT levels might respond to antidepressant treatment.

Keywords: Biomarkers; Chronic unpredictable mild stress; Depression; Fluoxetine; Serotonin.

Fig. 1

Schematic representation of experimental procedure. NC, normal control; CUMS, chronic unpredictable mild stress; w, week; FLX, fluoxetine.

Fig. 2

Chronic stress models were established successfully and fluoxetine intervention improved depression-like behavior stress–induced in mice and rats. (A) Sucrose preference in SPT of mice at the end of CUMS. (B) Central area distance in OFT of mice at the end of CUMS. (C) Immobility time in TST of mice at the end of CUMS. (D) Immobility time in FST of mice at the end of CUMS (n = 10 in NC group, n = 20 in CUMS group). (E) Sucrose preference in SPT of mice at the end of treatment. (F) Central area distance in OFT of mice at the end of treatment. (G) Immobility time in TST of mice at the end of treatment. (H) Immobility time in FST of mice at the end of treatment (n = 10/group). (I) Sucrose preference in SPT of rats at the end of CUMS. (J) Central area distance in OFT of rats at the end of CUMS. (K) Immobility time in FST of rats at the end of CUMS (n = 10 in NC group, n = 20 in CUMS group). (L) Sucrose preference in SPT of rats at the end of treatment. (M) Central area distance in OFT of rats at the end of treatment. (N) Immobility time in FST of rats at the end of treatment (n = 10/group). Data were shown as the mean ± standard error of mean. The statistical analyses involved the two independent samples t test for comparisons between two groups and one-way analyses of variance alongside the Tukey test for comparisons across multiple groups. NC, normal control; CUMS, chronic unpredictable mild stress; FLX, fluoxetine; SPT, sucrose preference test; OFT, open field test; TST, tail suspension test; FST, forced swimming test. *p < 0.05, **p < 0.01.

Fig. 3

Gavaged with fluoxetine reversed the weight loss caused by CUMS. (A) Body weight in the process of CUMS of mice. (B) Body weight gain at the end of CUMS of mice (n = 10 in NC group, n = 20 in CUMS group). (C) Body weight in the process of treatment of mice. (D) Body weight gain at the end of treatment of mice (n = 10/group; *p < 0.05, **p < 0.01, CUMS group vs. NC group; ^##p < 0.01, CUMS + FLX group vs. NC group). (E) Body weight in the process of CUMS of rats. (F) Body weight gain at the end of CUMS of rats (n = 10 in NC group, n = 20 in CUMS group). (G) Body weight in the process of treatment of rats. (H) Body weight gain at the end of treatment of rats (n = 10/group, ^#p < 0.05, ^##p < 0.01, CUMS group vs. NC group; *p < 0.05, **p < 0.01, CUMS + FLX group vs. NC group). The statistical analyses in-volved the two independent samples t test for comparisons between two groups and one-way analyses of variance alongside the Tukey test for comparisons across multiple groups. NC, normal control; CUMS, chronic unpredictable mild stress; FLX, fluoxetine.

Fig. 4

Peripheral blood and tissue 5-HT of mice and rats. (A) Serum 5-HT of mice at the end of CUMS. (B) Plasma 5-HT of mice at the end of CUMS. (C) Platelet 5-HT of mice at the end of CUMS (n = 10 in NC group, n = 20 in CUMS group). (D) Serum 5-HT of mice after treatment. (E) Plasma 5-HT of mice after treatment. (F) Platelet 5-HT of mice after treatment (n = 10/group). (G) Cerebral cortex 5-HT of mice. (H) Hippocampus 5-HT of mice. (I) Colon 5-HT of mice. (J) Serum 5-HT of rats at the end of CUMS. (K) Plasma 5-HT of rats at the end of CUMS. (L) Platelet 5-HT of rats at the end of CUMS (n = 10 in NC group, n = 20 in CUMS group). (M) Serum 5-HT of rats after treatment. (N) Plasma 5-HT of rats after treatment. (O) Platelet 5-HT of rats after treatment (n = 10/group). (P) Cerebral cortex 5-HT of rats. (Q) Hippocampus 5-HT of rats. (R) Colon 5-HT of rats. Data were shown as the mean ± standard error of mean. Statistical com-parisons between the two groups were performed using the two independent samples t test. Com-parisons between multiple groups were performed using one-way analyses of variance and Tukey test. 5-HT, 5-hydroxytryptamine; NC, nor-mal control; CUMS, chronic unpredictable mild stress; FLX, fluoxetine. *p < 0.05, **p < 0.01.

Fig. 5

Tissue and platelet 5-HT-related protein expression in mice and rats (n = 3/group). (A) TPH₂ and 5-HT_1A expression in the cerebral cortex of mice. (B) SERT, TPH₂, and 5-HT_1A expression in the hippocampus of mice. (C) TPH₁ and 5-HT_1A expression in the colon of mice. (D) platelet SERT and 5-HT_1A expression of mice. (E) SERT, TPH₂, and 5-HT_1A expression in the cerebral cortex of rats. (F) SERT, TPH₂, and 5-HT_1A expression in the hippocampus of rats. (G) SERT, TPH₁, and 5-HT_1A expression in the colon of rats. (H) SERT and 5-HT_1A expression in the platelets of rats. Data were shown as the mean ± standard error of mean. Statistical comparisons between the two groups were performed using the two independent samples t test. Comparisons between multiple groups were performed using one-way analyses of variance and Tukey test. NC, normal control; CUMS, chronic unpredictable mild stress; FLX, fluoxetine; TPH, tryptophan hydroxylase; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; 5-HT, 5-hydroxytryptamine; SERT, 5-HT transporter. *p < 0.05, **p < 0.01.