Fig. 5: Peripheral and central kynurenic acid (KYNA) levels in bipolar disorder (BD) and healthy controls (HCs)—lifetime history of suicide attempt or self-harm.

a Plasma KYNA levels in HCs (median = 37.7, IQR = 18.6) and BD subjects (median = 37.0, IQR = 23.2) stratified on a history of suicide attempt/self-harm (median for BD no suicide attempt/self-harm = 37,2; IQR = 21.2, median for BD suicide attempt/self-harm = 32.6; IQR = 24.5). Given the high number of females among BD subjects with a history of suicide attempt/self harm (70.5 vs. 55% in BD subjects with no such history) there was no significant differences in KYNA plasma concentrations for this group compared to HCs or BD without a history of suicide attempt/self-harm when adjusting for age and sex (BD suicide attempt/self-harm vs. BD no suicide attempt/self-harm: P = 0.57). b Cerebrospinal fluid (CSF) KYNA levels in HC (median = 1.56 nM, IQR = 1.03) and BD I/II subject (median = 1.66 nM, IQR = 1.16). BD subjects with a history of suicidal behavior (median = 1.63 nM, IQR = 1.67) displayed significantly increased CSF KYNA concentrations compared to HCs although not reaching significance compared to the smaller BD without a history of suicidal behavior group (median = 1.76 nM, IQR = 1.00; P = 0.33). All reported P-values are two-sided and derived from logistic regression models with sex and age as covariates