Inoshita M, et al. - This systematic review and meta-analysis investigated the possibility of variation in the blood glutamate levels between major depressive disorder (MDD) subjects and control participants. Compared to the control group, blood glutamate levels appeared to be substanially higher in MDD patients. Findings demonstrated that altered glutamate levels could be implicated in MDD. This, in turn, yielded evidence of glutamatergic dysfunction in MDD.

Methods

• The design of this research was a systematic review and meta-analysis.
• Twelve association studies between blood glutamate levels and MDD were analyzed in a total of 529 MDD patients and 590 controls.
• Through subgroup analyses and a meta-regression analysis, the sources of potential heterogeneity were assessed.

Results

• As per the random effects model, blood glutamate levels appeared to be considerably higher in MDD patients than in controls (standardized mean difference=0.54, 95% CI=0.27-0.82, p=8.5×10-5) with high heterogeneity (I²=75.0%, p < 0.05).
• Elevated glutamate levels in MDD patients compared with controls in plasma were disclosed in the subgroup analyses.
• This was not found in the serum studies.
• It was revealed in studies using high-performance liquid chromatography but not with mass spectrometry for glutamate assay.
• The meta-regression analysis did not exhibit any effects of age, gender, medication use, sample size, and published year on blood glutamate levels.