Relationships between inflammatory markers and suicide risk status in major depression

Pro-inflammatory status has been implicated in depression and suicidal behaviors. Polyunsaturated fatty acids (PUFAs) and cytokines, two types of inflammatory biomarkers, have been associated with suicide, independent of depression severity. How these biomarkers relate to each other is less clear. We measured plasma phospholipid levels of arachidonic acid (AA%), docosahexaenoic acid (DHA%), and eicosapentaenoic acid (EPA%) as a percentage of total phospholipids, as well as serum interleukin-6 (IL-6), interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF-alpha), in 80 patients with major depressive disorder (MDD) and 24 healthy controls (HC). Individual PUFA and cytokine species were compared using ANOVA across four suicide risk-stratified groups: 1) highest risk, recent (within 5 years) suicide attempters (n = 20); 2) high-risk, severe current suicidal ideators (having intent or plan) with no recent attempt history (n = 22); 3) low-risk, current non-ideators who were also lifetime non-attempters (n = 38); and 4) HC (n = 24). None of the participants were enrolled following an acute suicide attempt. Of biomarkers studied, only DHA% (p = 0.012) and IL-1 beta (p = 0.002) differed between groups. In post hoc testing, DHA% was lower in attempters than ideators (p = 0.018) or MDD non-ideators (trend level, p = 0.073). IL-1 beta was lowest in attempters, differentiating them from ideators (p = 0.009) and HC (p = 0.004). Recent suicide attempt, one of the most powerful predictors of suicide risk, was also most closely tied to inflammatory indices in this study. Low DHA% as an indicator of suicide risk is consistent with previous reports; however, lower IL-1 beta was unexpected and may relate to acuity/chronicity of inflammation. There is a need for prospective studies of immune status with respect to suicidal behaviors.

Automated summary

This study found that DHA% and IL-1 beta are important indicators of suicide risk, with lower DHA% in suicide attempters and lowest IL-1 beta in attempters, suggesting a close relationship between inflammation and suicidal behaviors.