Assessment of type 1 and type 3 deiodinase expression levels in depressive disorders

A depressive disorder is a disease characterized by a heterogenous background. The important processes observed and diagnosed in depressed patients indicate that the etiology of depression may include disturbances in thyroid hormone (TH) levels and the occurrence of immune-inflammatory activation. Type 1 (DIO1) and type 3 (DIO3) iodothyronine deiodinases are the enzymes which determine the peripheral and tissue levels of TH, but also interfere with immunological cells and inflammatory processes. We aimed to investigate the levels of DIO1 and DIO3 in the patients suffering from recurrent depressive disorders (rDD). Data collected from 91 rDD patients and 105 healthy controls were analyzed. The diagnoses were made based on the ICD-10 criteria (F33.0-F33.8). The expression levels of DIO1 and DIO3 were estimated using the polymerase chain reaction method and the enzyme-linked immunosorbent assay (ELISA). The expression of DIO1 on mRNA/protein levels in the rDD patients was reduced in comparison to the control subjects, while the expression of DIO3 was higher in the patients suffering from depression. No significant relationship was found between the investigated DIOs and other clinical parameters. Our results indicate and suggest a role of DIO1 and DIO3-related pathways in the pathophysiology of depression. The results represent a promising way to investigate the biological markers of depression.