Thiol protein groups correlate with cognitive impairment in patients with recurrent depressive disorder

Depressive disorders are multifactorial diseases in which cognitive impairments are one of typical features. Thiol protein groups (TPGs) are elements of chemical structure of compounds having antioxidative properties (glutathione peroxidase, metallothioneins) and their oxidation reflects the lost of compensatory capacity of antioxidative mechanisms. The purpose of this study was to determine the level of TPGs in patients with recurrent depressive disorder (rDD) and to define relationship between plasma levels of TPGs and the cognitive performance.

The study comprised 76 subjects: patients with rDD (n=43) and healthy subjects (comparison group, CG - n=33). Cognitive function assessment was based on the following 4 tests: the Trail Making Test (TMT), the Stroop Test, Verbal Fluency Test (VFT) and Auditory Verbal Learning Test (AVLT).

The level of TPGs was higher in patients with rDD. In rDD group, the elevated concentration of TPGs in plasma was associated with a decrease in efficiency of declarative-memory, working memory and verbal fluency. The higher was the concentration of plasma TPGs, the greater was the severity of depressive symptoms measured by 21-item Hamilton Depression Rating Scale (HDRS), before and after pharmacotherapy. In CG group, the elevated TPGs levels were associated with worse cognitive test performance (AVLT and VFT tests).

1) Our study confirms previous results showing increased TPGs level in depression. 2) Our data suggest relation between increased plasma TPGs level in depression and cognitive impairment. 3) The elevated levels of plasma TPGs are related to impairment of the short-term and delayed declarative memory, verbal fluency and working memory.