Abstract
Objective: Major depressive disorder (MDD) is a common psychiatric disorder. Irisin, produced by proteolysis of FNDC5, is thought to be an exercise-induced hormone that may play a critical role in inducing antidepressant-like effects. Our study aimed to investigate the relationship between irisin and newly diagnosed MDD patients.

Methods: This cross-sectional study included 85 first-time diagnosed MDD patients and 81 healthy controls. Patients were diagnosed with MDD using the Structured Clinical Interview Questionnaire for DSM-IV Axis I and II Disorders (SCID-I, II) and the Hamilton Depression Scale (HAM-D). After an overnight fast, 5 ml of peripheral blood was drawn and serum irisin levels were measured.

Results: When the effects of age and gender variables were controlled, no statistically significant difference in irisin levels was found between the groups. (F=1.832, p=0.178). When the effects of age, gender and body mass index variables were controlled and a partial correlation was made between irisin and HAMD scores, a significant negative correlation was found between irisin and HAMD scores (p<0.001, r=-0.523). The correlation analysis showed a statistically significant negative relationship between age and irisin levels (p=0.008, r=-0.205). However, when the effects of other variables were controlled and a partial correlation was made, no statistically significant relationship was found (p=0.610, r=-0.207).

Conclusion: Our results indicate that irisin levels are associated with the severity of depression. Further studies are needed on the use of irisin as a potential biomarker for predicting clinical course and treatment response in patients with severe MDD.

Key words: Major Depressive Disorder, Irisin, Etiopathogenesis