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Background: Indoleamine 2,3-dioxygenase (IDO) activity is induced by cellular immune activation and therefore associated to inflammatory diseases, among others psychiatric disorders. This review aims to elucidate IDO activity reflected by kynurenine (KYN) to tryptophan (TRP) ratio in severe mental disorders. Methods: A systematic literature search in MEDLINE and EMBASE was conducted targeting clinical trials in English language measuring KYN/TRP in individuals with a diagnosis of depression, bipolar disorder, or schizophrenia. Results: Five out of 15 studies found higher levels of KYN/TRP in depression compared to a control group while the same amount found no difference. Moreover, three studies showed lower levels. In bipolar disorder, four out of six and in psychotic disorders three out of four trials found higher levels in patients compared to controls. There are only two studies comparing KYN/TRP in major depression and bipolar disorder, showing conflicting results. Eight studies focused on associations between KYN/TRP and clinical parameters, whereas two studies found positive correlations between KYN/TRP and severity of depressive symptoms. In contrast, four studies did not show an association. IDO activity during specific psychiatric treatment was analyzed by eight studies. Conclusion: In summary, this review demonstrates an inconsistency of findings of studies investigating KYN/TRP in severe mental disorders. Although there are hints that inflammation associated TRP catabolism towards the KYN pathway via elevated IDO activity seems likely, no conclusive statements can be drawn. Presumably, the consideration of influencing factors as inflammatory processes, metabolic activities and psychological/neuropsychiatric symptoms are pivotal for a deeper understanding of the underlying mechanisms.

BackgroundThe processes underlying believing have been labeled “creditions”, which are important brain functions between emotion and cognition. Creditions are influenced by both internal and external factors, one of which is the coronavirus disease 2019 (COVID-19) pandemic and the vaccination against the disease.MethodsTo investigate believing processes shortly before the implementation of a mandatory vaccination in Austria, both vaccinated and unvaccinated workers in the health sector (WHS) were surveyed in December 2021/January 2022. In total, 1,062 vaccinated and 97 unvaccinated WHS (920 females) completed the online survey. Beliefs were assessed using the parameters of the credition model (narrative, certainty, emotion, and mightiness) with regard to (1) the COVID-19 pandemic in general, and (2) the vaccination. Type of emotion and narrative were divided into positive, negative, and indifferent. Moreover, the congruence between emotion and narrative was calculated.ResultsThe vaccination rate of the sample was 91.6%, with a significantly higher percentage of men being in the group of vaccinated (21.1%) as compared to unvaccinated individuals (12.4%). Pertaining beliefs about the COVID-19 vaccination, unvaccinated WHS reported more negative and less positive emotions as well as content of narrative than vaccinated WHS. In addition, they showed higher levels of certainty as well as mightiness while believing and felt less sufficiently informed about governmental and workplace-related COVID-19 measures. The groups did not differ in the type of emotion or content of narrative in their beliefs about the pandemic in general.ConclusionIn conclusion, unvaccinated WHS had more negative and less positive emotions and thoughts than vaccinated WHS in their beliefs about the COVID-19 vaccination and their motivations for not having received it. They were more certain about their beliefs and felt stronger negative emotions in their beliefs compared to vaccinated individuals. Providing unvaccinated WHS with adequate information might be helpful in reducing their mental burden.