Relationship between IL17, serotonin and tryptophane metabolites and disease severity and dermatological quality of life in psoriasis patients

Aim: This study aimed to evaluate the kynurenine pathway and serotonin levels in patients with psoriasis compared to the healthy population by utilizing the relationship between IL-17A and psoriasis. It also aimed to evaluate whether there is a correlation between PASI scores and DYQI scores and tryptophan metabolites and IL-17A levels in patients with psoriasis. Materials and Methods: In our study, tryptophan kynurenine pathway metabolites, IL-17A and serotonin were studied from serum samples of 71 psoriasis patients and 71 controls, which were examined routinely in the biochemistry laboratory. PASI scores, which show the disease severity index in psoriasis patients, and DYQI scores, which are used to evaluate emotional states, were calculated in the clinic. All studies performed on serum samples were performed in the Biochemistry Department laboratory of Selcuk University Medical Faculty Hospital. Data were evaluated using IBM SPSS V 26 statistical package program. The normal distribution of data belonging to numerical variables was evaluated using the Shapiro Wilk normality test. In the comparison of two groups, independent samples t test was used if the data were normally distributed, and Mann Whitney U Test was used if the data were not normally distributed. The effects of the variables and parameters in the study were evaluated using logistic regression. The relationships between numerical variables were evaluated using the Spearman correlation coefficient. The p<0.05 value was considered statistically significant. Results: There was no difference between the patient and control groups in terms of gender and mean age. In psoriasis patients, IL-17, serotonin, tryptophan, kynurenine, TRP/KynA and KYN/TRP(IDO ACTIVITY) levels were found to be statistically significantly higher in the patient group compared to the control group. Kyna/Kyn(KAT ACTIVITY), Neuroprotection Index (Kyna/3-Hk) and TRP/3-OH KYN ratios were found to be statistically significantly higher in the patient group compared to the control group (p<0.05). No significant difference was found between the two groups in TRP/3-HAA and 3-Hk/Kyn(KMO ACTIVITY) ratios (p>0.05). A correlation was found only between disease severity and serotonin levels (Spearman's rho=0.327). No significant relationship was found between DYQI score and the parameters examined. Conclusion: In cases of systemic inflammation, there is a shift to the kynurenine pathway due to increased IDO enzyme activity. As a result of our study, increased kynurenine levels and IDO enzyme activity were found to be higher in the patient group, as expected. We think that increased IDO enzyme activities and decreased KAT enzyme activities in the patient group may be a target molecule in the treatment of psoriasis. It is also known that serotonin plays a role in processes such as vasodilation, inflammation, immunomodulation and itching in the skin. In our study, we found serotonin levels higher in the patient group, and at the same time, we detected a correlation with the PASI score in patients. We think that serotonin-directed treatments can be used to reduce disease severity in the treatment of psoriasis. However, these data should be supported by more comprehensive and broader prospective studies. Keywords: kynurenine, PASI, psoriasis, serotonin