Association of peripheral and cerebral inflammatory markers with suicidal deaths in Indian population

Globally, a suicide occurs every 43 seconds. In India, approximately 465 suicides took place daily in 2022, with a suicide rate of 12.4 per 100,000 population, exceeding the global rate of 9. This study aims to investigate differences in cytokine levels, including vascular endothelial growth factor (VEGF), between individuals who died by suicide and those who did not. Additionally, it aims to explore any pattern between plasma and cerebrospinal fluid (CSF) levels of these analytes. Concentrations of inflammatory cytokines, i.e., Interleukins: IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-13, Tumor Necrosis Factor-α and VEGF in plasma and CSF were analyzed among suicide death subjects (N = 6, cases) and non-suicidal death subjects (N = 59, controls). All analytes were quantified using a customized multiplex (9-plex) kit, with 50 µl of plasma and CSF in duplicates. Significantly higher levels of IL-6 (p < 0.001) and IL-10 (p < 0.05) were observed in the plasma of the suicidal group. However, no statistically significant changes were found in the rest of the analytes between the two groups. In CSF, only VEGF levels were significantly lower in the suicidal group (p < 0.01). In cases, significant positive correlations were observed between plasma and CSF levels of IL-1β, IL-4, IL-6, and IL-10, whereas in controls, only IL-8 demonstrated a significant positive correlation, indicating a moderate relationship between these cytokines systemic and central concentrations. Dysregulation of inflammatory biomarkers appears to play a crucial role in the pathophysiology of suicide. We conclude that higher levels of IL-6 are present in the plasma of suicide completers compared to non-suicidal deceased individuals.