The examination of the relationship between clinical symptoms, cognitive functions and the tryptophan kynurenine pathway in schizophrenia patients

Objective: In this study, it is aimed to examine the relationship between the increasing tryptophan destruction products kynurenic acid (KYNA) levels, schizophrenia symptom clusters and cognitive functions. As far as is known, such a study has not been recorded in literature. For this reason, it is believed that this study will contribute to the development of pharmacological agents, directing towards the negative and cognitive symptoms of schizophrenia patients and targeting specific zymases of the kynurenine pathway. Methods: Blood serotonin level, the last product, to evaluate the tryptophan synthesis pathway and blood kynurenic acid level to evaluate the destruction will be looked at. Furthermore, tryptophan destruction zymase and some inflammation biodeterminers supposed to increase İndoleamine 2,3-dioksijenaz (IDO) activity will be evaluated. High-sensitivity C-reactive protein (hsCRP) as an inflammation biodeterminer and neopterin level, which has been recently accepted as a strong determiner of cellular immunity, will be evaluated. Neopterin production begins with interferon gamma (IFN-γ) stimulation three days before T lymphocyte proliferation by monocytes and macrophages reaches its maximum level, and its level is determined approximately a week before the specific anticors become positive. Therefore, neopterin is accepted as a strong determiner of cellular immunity in early period. There are studies showing that neopterin level increases in body fluids in neuropsychiatric disorders such as schizophrenia and multiple skleroz. Results: In our study, it is detected that as a result of the comparison of cognitive functions, compared to the control group, there is a widespread deterioration in relation to cognitive functions in the patient group. The findings reached through the Wisconsin Card Sorting Test (WKET) used to evaluate mainly propulsive functions, working storage, perseverative tendency, the behaviour of changing category or setup and to determine attention and characteristics; through the Stroop Test used to evaluate the ability of changing reactions, the speed of information processing; through the Chase Test used to evaluate attention speed, mental flexibility, visual scanning, motor speed, and also propulsive functions with its Part B, and through Rey Auditory Verbal Learning Test (AVLT) Test used to evaluate verbal learning, free recall, disruptive effect towards back and forth, instantaneous and retorted free recall and recognition memory are, compared to the control group, determined as deteriorated and statistically significant in the patient group. Moreover, compared to the control group, (2,57 ± 4,49), the average of neopterin level is found low in the patient group (1,24 ± 0,89). This difference is not shown statistically significant (p=0,073). Although, compared to the control group, it is found out that IDO serum values were low in the patient group, this difference is not found statistically significant. Compared to the control group, KYNA and serotonin serum levels were found low and statistically significant in the patient group. A positive correlation in relation to the cognitive functions and clinical characteristics (Positive Syndrome Scale (SAPS) - Negative Syndrome Scale (SANS)) in schizophrenia patients was found out between SANS scale points and chase error number. A negative correlation was found between Stroop Test Part 1 error number, Part 5 entire span and between Stroop interference span and KYNA. A positive correlation was found between the total of correct answers of AVLT B1 of Auditory/Verbal Memory Processes Test measurement and serotonin values. Finally, a positive correlation was found out between WKET completed category number in the correlation of cognitive functions and neopterin and neopterin level. Conclusion: In our study, it is shown that compared to the control group, the serum serotonin and KYNA levels of the schizophrenia patients are low and there is a relationship between them and cognitive functions. In future, KYNA might be a potent candidate for a therapeutic discovery for the treatment of neurodegenerative diseases such as schizophrenia. With our study, we aimed to contribute to the related literature in which the findings are limited. Key Words: Schizophrenia, Cognitive Functions, Kynurenine Pathway.