The relationship between impulsivity, suicidal characteristics, and serum S100B and BDNF levels in patients with Schizophrenia

Objective: Schizophrenia is a chronic psychiatric disorder that causes significant impairments in thought, emotion, and behavior, and is frequently associated with high-risk clinical features such as suicidal behavior and impulsivity. The risk of suicide in this population is markedly elevated compared to the general population. In schizophrenia, impulsivity not only contributes to suicidal behavior but also leads to negative consequences such as aggression, non-adherence to treatment, engagement in risky behaviors, and deterioration in social functioning. Therefore, the ability to predict the risk of symptoms such as suicidality and impulsivity is of critical importance for both individual well-being and public mental health prevention strategies. In recent years, research has increasingly focused on identifying biological markers capable of predicting such behavioral tendencies. Among these, S100B and brain-derived neurotrophic factor (BDNF) have been proposed as potential biomarkers associated with both the pathophysiology of schizophrenia and suicidal behavior. However, studies exploring the relationship between these biomarkers and clinical features such as impulsivity and suicidality are still limited. This study aims to investigate the relationship between impulsivity, suicidal features, and serum levels of S100B and BDNF in individuals diagnosed with schizophrenia, and to determine the diagnostic discriminatory power of these biomarkers. The ultimate goal is to provide insights into biological indicators that may assist in identifying high-risk clinical features—such as impulsivity and a history of suicidal behavior—during the diagnostic process of schizophrenia. Materials and Methods: A total of 40 patients who presented to the Psychiatry Outpatient Clinic of Karadeniz Technical University (KTU) Faculty of Medicine between May 2024 and November 2024 were included in the study. Patients were first evaluated by at least one clinician and diagnosed with schizophrenia according to DSM-5 criteria. A second interview was conducted by the researcher using the Structured Clinical Interview for DSM-5 Axis I Disorders (SCID-5) to confirm the diagnosis. Patients who met inclusion criteria, had no exclusion criteria, had been in remission for at least six months, and consented to participate were enrolled. The control group consisted of 40 healthy volunteers matched with the patient group in terms of age, gender, and educational level. After being informed about the study, all participants completed a sociodemographic and clinical data form. The Positive and Negative Syndrome Scale (PANSS) was used to assess symptom severity, and the Calgary Depression Scale for Schizophrenia (CDSS) was used to assess depressive symptoms in the patient group. All participants were administered the Barratt Impulsiveness Scale-11 (BIS-11) and the UPPS Impulsive Behavior Scale to assess impulsive traits, and the Suicide Probability Scale (SPS) to assess current suicidal ideation. Blood samples were collected from all participants between 08:00 and 12:00 on the same day the psychological assessments were administered. Matched patients and controls had blood drawn simultaneously. Serum S100B and BDNF levels were measured using ELISA kits. Results: Compared to the control group, serum BDNF levels were significantly lower and serum S100B levels were significantly higher in the schizophrenia group. As a novel finding, BDNF predicted schizophrenia diagnosis with 82.5% sensitivity and 70% specificity, while S100B predicted schizophrenia with 85% sensitivity and 82.5% specificity. However, S100B and BDNF levels alone were not sufficient to directly predict impulsivity or suicidality. In the schizophrenia group, CDSS scores and SPS total scores were positively correlated with impulsivity. BIS-11 total scores and subscale scores for motor impulsivity, attentional impulsivity, and non-planning were significantly higher in patients compared to controls. SPS scores were also significantly higher in the patient group, particularly in the "suicidal ideation" and "suicide planning" subscales. Correlation analysis across all participants showed a positive correlation between S100B and SPS scores, suggesting that higher S100B levels are associated with increased suicide risk. A negative correlation was observed between BDNF and BIS-11 scores. Among patients, BDNF levels were moderately negatively correlated with the UPPS sensation seeking subscale, while S100B levels were weakly to moderately positively correlated with the SPS hopelessness subscale. No statistically significant correlations were found between S100B/BDNF and other scale scores. Conclusion: In patients with schizophrenia, serum S100B levels were found to be significantly elevated, while BDNF levels were significantly reduced. These findings suggest that increased S100B may be associated with heightened suicide risk, and reduced BDNF may be linked to increased impulsivity. Impulsivity and suicidality were markedly more pronounced in the schizophrenia group compared to healthy individuals. These results support the hypothesis that S100B and BDNF are not only involved in the pathophysiology of schizophrenia but may also be associated with risky behaviors that impact the course of the disorder. Thus, these biomarkers may serve as clinically meaningful indicators for early identification of individuals with high levels of impulsivity and suicide risk. The incorporation of such biological indicators into clinical evaluations may pave the way for more targeted and personalized psychiatric interventions. However, further large-scale and longitudinal studies are needed to generalize these findings. Such research would provide stronger evidence for the clinical utility of biomarkers such as S100B and BDNF.