Epidemiological aspects and inflammatory cytokine profiles associated with Toxoplasma gondii infection in suicide attempters in Iran.

Background: This study aims to investigate the prevalence, socio-economic characteristics, risk factors, and cytokine profile (IL-6, TNF-α, and IFN-γ) of Toxoplasma gondii among individuals who have attempted suicide and referred to health centers in Lorestan province, Western Iran.

Methods: This research is a case-control study involved a sample of 250 patients diagnosed with attempting suicide (AS) and 250 healthy individuals without AS (non-AS), who were referred to healthcare centers in Lorestan province, Iran, from September 2023 to September 2024. A questionnaire was provided to collect demographic information, socio-economic factors, and potential risk factors. To evaluate the seroprevalence of T. gondii infection, ELISA kits were used to detect the anti-Toxoplasma IgG and IgM antibodies. The serum and expression levels of interleukin-6, interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α) among AS and non-AS groups were also assessed by ELISA and Real-time PCR methods.

Results: In the AS group, 98 participants (39.2%) and 8 participants (3.2%) were positive for anti-T. gondii IgG and IgM antibody, respectively. Conversely, in the non-AS group, 55 individuals (22.0%) and 5 individuals (2.0%) were positive for anti-T. gondii IgG and IgM antibody, respectively (p < 0.001). In AS patients, age (p = 0.012, OR = 0.288, CI = 0.109-0.761), educational level (p = 0.024, OR = 0.328, CI = 0.124-0.866), residence (p = 0.018, OR = 0.429, CI = 0.212-0.867), consumption of fast food (p = 0.004, OR = 3.719, CI = 1.538-8.993) and history of suicide (p = 0.020, OR = 2.716, CI = 1.170-6.306) demonstrated a significant predictive effect on seropositivity to T. gondii infection. Whereas, a negative result on the antibody test was associated with a 0.465-fold decrease in the likelihood of suicide (p = 0.038, OR = 0.465, CI = 0.225-0.960). The likelihood of suicide demonstrates a positive correlation with increased concentrations of inflammatory cytokines, specifically IL-6 (p = 0.029, OR = 1.134, CI = 1.833-2.951) and IFN-γ (p = 0.004, OR = 1.998, CI = 1.342-2.919).

Conclusion: Our study revealed that individuals who have attempted suicide exhibited a greater seroprevalence of anti-T. gondii antibodies compared to healthy control subjects. We also exhibited elevated serum and expression levels of IL-6 and IFN-γ, as the main proinflammatory cytokines linked to suicide behaviors, in the AS patients who tested positive for T. gondii antibodies. Consequently, this may aid in the identification of biomarkers that could inform the development of effective prevention strategies and ultimately reduce suicide mortality. The findings of the study indicate that while there may be a causal link between T. gondii infection and suicide attempts, the cross-sectional nature of the data may restrict the ability to draw definitive causal inferences. To substantiate this potential causal relationship, longitudinal studies that incorporate larger sample sizes, investigate additional biomarkers related to suicide, and control for various confounding variables would be beneficial.