Several enzymes and metabolites of the kynurenine pathway (KP) have immunomodulatory effects. Modulation of the activities and levels of these molecules might be of particular importance under disease conditions when the amelioration of overreacting immune responses is desired. Results obtained by the use of animal and tissue culture models indicate that by eliminating or decreasing activities of key enzymes of the KP, a beneficial shift in disease outcome can be attained. This review summarizes experimental data of models in which IDO, TDO, or KMO activity modulation was achieved by interventions affecting enzyme production at a genomic level. Elimination of IDO activity was found to improve the outcome of sepsis, certain viral infections, chronic inflammation linked to diabetes, obesity, aorta aneurysm formation, and in anti-tumoral processes. Similarly, lack of TDO activity was advantageous in the case of anti-tumoral immunity, while KMO inhibition was found to be beneficial against microorganisms and in the combat against tumors, as well. On the other hand, the complex interplay among KP metabolites and immune function in some cases requires an increase in a particular enzyme activity for the desired immune response modulation, as was shown by the exacerbation of liver fibrosis due to the elimination of IDO activity and the detrimental effects of TDO inhibition in a mouse model of autoimmune gastritis. The relevance of these studies concerning possible human applications are discussed and highlighted. Finally, a brief overview is presented on naturally occurring genetic variants affecting immune functions via modulation of KP enzyme activity.

Tryptophan is metabolized primarily via the kynurenine pathway (KP), which involves several enzymes, including indoleamine 2,3-dioxygenase, tryptophan 2,3 dioxygenase (TDO), kynurenine aminotransferases (KATs), kynurenine monooxygenase (KMO) etc. The majority of metabolites are neuroactive: some of them, such as kynurenic acid, show neuroprotective effects, while others contribute to free radical production, leading to neurodegeneration. Imbalance of the pathway is assumed to contribute to the development of several neurodegenerative diseases, psychiatric disorders, migraine and multiple sclerosis. Our aim was to summarize published data on genetic alterations of enzymes involved in the KP leading to disturbances of the pathway that can be related to different diseases. To achieve this, a PubMed literature search was performed for publications on genetic alterations of the KP enzymes upto April 2017. Several genetic alterations of the KP have been identified and have been proposed to be associated with diseases. Here we must emphasize that despite the large number of recognized genetic alterations, the number of firmly established causal relations with specific diseases is still small. The realization of this by those interested in the field is very important and finding such connections should be a major focus of related research. Polymorphisms of the genes encoding the enzymes of the KP have been associated with autism, multiple sclerosis and schizophrenia, and were shown to affect the immune response of patients with bacterial meningitis, just to mention a few. To our knowledge, this is the first comprehensive review of the genetic alterations of the KP enzymes. We believe that the identification of genetic alterations underlying diseases has great value regarding both treatment and diagnostics in precision medicine, as this work can promote the understanding of pathological mechanisms, and might facilitate medicinal chemistry approaches to substitute missing components or correct the disturbed metabolite balance of KP.

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Background Clinical complexity is increasingly prevalent among patients with atrial fibrillation (AF). The ‘Atrial fibrillation Better Care’ (ABC) pathway approach has been proposed to streamline a more holistic and integrated approach to AF care; however, there are limited data on its usefulness among clinically complex patients. We aim to determine the impact of ABC pathway in a contemporary cohort of clinically complex AF patients. Methods From the ESC-EHRA EORP-AF General Long-Term Registry, we analysed clinically complex AF patients, defined as the presence of frailty, multimorbidity and/or polypharmacy. A K-medoids cluster analysis was performed to identify different groups of clinical complexity. The impact of an ABC-adherent approach on major outcomes was analysed through Cox-regression analyses and delay of event (DoE) analyses. Results Among 9966 AF patients included, 8289 (83.1%) were clinically complex. Adherence to the ABC pathway in the clinically complex group reduced the risk of all-cause death (adjusted HR [aHR]: 0.72, 95%CI 0.58–0.91), major adverse cardiovascular events (MACEs; aHR: 0.68, 95%CI 0.52–0.87) and composite outcome (aHR: 0.70, 95%CI: 0.58–0.85). Adherence to the ABC pathway was associated with a significant reduction in the risk of death (aHR: 0.74, 95%CI 0.56–0.98) and composite outcome (aHR: 0.76, 95%CI 0.60–0.96) also in the high-complexity cluster; similar trends were observed for MACEs. In DoE analyses, an ABC-adherent approach resulted in significant gains in event-free survival for all the outcomes investigated in clinically complex patients. Based on absolute risk reduction at 1 year of follow-up, the number needed to treat for ABC pathway adherence was 24 for all-cause death, 31 for MACEs and 20 for the composite outcome. Conclusions An ABC-adherent approach reduces the risk of major outcomes in clinically complex AF patients. Ensuring adherence to the ABC pathway is essential to improve clinical outcomes among clinically complex AF patients.

Aims The 4S-AF classification scheme comprises of four domains: stroke risk (St), symptoms (Sy), severity of atrial fibrillation (AF) burden (Sb), and substrate (Su). We sought to examine the implementation of the 4S-AF scheme in the EORP-AF General Long-Term Registry and compare outcomes in AF patients according to the 4S-AF-led decision-making process. Methods and results  Atrial fibrillation patients from 250 centres across 27 European countries were included. A 4S-AF score was calculated as the sum of each domain with a maximum score of 9. Of 6321 patients, 8.4% had low (St), 47.5% EHRA I (Sy), 40.5% newly diagnosed or paroxysmal AF (Sb), and 5.1% no cardiovascular risk factors or left atrial enlargement (Su). Median follow-up was 24 months. Using multivariable Cox regression analysis, independent predictors of all-cause mortality were (St) [adjusted hazard ratio (aHR) 8.21, 95% confidence interval (CI): 2.60–25.9], (Sb) (aHR 1.21, 95% CI: 1.08–1.35), and (Su) (aHR 1.27, 95% CI: 1.14–1.41). For CV mortality and any thromboembolic event, only (Su) (aHR 1.73, 95% CI: 1.45–2.06) and (Sy) (aHR 1.29, 95% CI: 1.00–1.66) were statistically significant, respectively. None of the domains were independently linked to ischaemic stroke or major bleeding. Higher 4S-AF score was related to a significant increase in all-cause mortality, CV mortality, any thromboembolic event, and ischaemic stroke but not major bleeding. Treatment of all 4S-AF domains was associated with an independent decrease in all-cause mortality (aHR 0.71, 95% CI: 0.55–0.92). For each 4S-AF domain left untreated, the risk of all-cause mortality increased substantially (aHR 1.35, 95% CI: 1.16–1.56). Conclusion  Implementation of the novel 4S-AF scheme is feasible, and treatment decisions based on this scheme improve mortality rates in AF.