Exploration of biological markers of suicidal behavior in major depressive disorder

Objective: Most suicides occur in the context of depressive disorders. In this study, new candidate biological markers for suicide were explored. Methods: The suicidal subjects consisted of 48 depressed patients (18 males and 30 females) admitted to emergency rooms following suicide attempts. The levels of nitric oxide, brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), beta-nerve growth factor (β-NGF), and transforming growth factor-beta 1 (TGF-β1) were measured in the plasma of these 48 patients and 50 normal controls. The levels of tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin-2 (IL-2), interleukin-4 (IL-4), and interleukin-6 (IL-6) were measured in the culture supernatant after mitogen stimulation of whole blood from both groups. The lethality of the suicide attempt was measured using the Lethality Suicide Attempt Rating Scale (LSARS), and the Risk-Rescue Rating (RRR). Results: The suicidal depressed patients had significantly higher IL-6, TGF-β1, and nitric oxide (NO) levels compared with the normal controls after controlling for body mass. On the other hand, the BDNF, IL-2, IL-4 and IFN-γ levels were lower in the suicidal depressed patients than in the normal controls. The NO levels in the suicidal depressed patients were negatively significantly correlated with the LSARS and RRR scores. The IFN-γ levels in the suicidal depressed patients were positively correlated with the LSARS scores, but their TGF-β1 levels were negatively correlated with the LSARS scores. When the suicidal behaviors were divided into violent or nonviolent, the IL-6 and IFN-γ levels of the violent suicidal patients were significantly higher than those of the nonviolent suicidal patients. Conclusions: These results suggest that BDNF, NO, and cytokines could be useful as biological markers of suicidal behavior in major depression.