Assessment of tryptophan and kynurenine as prognostic markers in patients with SARS-CoV-2

Correlation between immune-related Tryptophan-Kynurenine pathway and severity of severe pneumonia and inflammation-related polyunsaturated fatty acids

BACKGROUND

Immune dysfunction and oxidative stress caused by severe pneumonia can lead to multiple organ dysfunction and even death, causing a significant impact on health and the economy. Currently, great progress has been made in the diagnosis and treatment of this disease, but the mortality rate remains high (approximately 50%). Therefore, there is still potential for further exploration of the immune response mechanisms against severe pneumonia.

OBJECTIVE

This study analyzed the difference in serum metabolic profiles between patients with severe pneumonia and health individuals through metabolomics, aiming to uncover the correlation between the Tryptophan-Kynurenine pathway and the severity of severe pneumonia, as well as N-3/N-6 polyunsaturated fatty acids (PUFAs).

METHODS

In this study, 44 patients with severe pneumonia and 37 health controls were selected. According to the changes in the disease symptoms within the 7 days of admission, the patients were divided into aggravation (n = 22) and remission (n = 22) groups. Targeted metabolomics techniques were performed to quantify serum metabolites and analyze changes between groups.

RESULTS

Metabolomics analysis showed that serum kynurenine and kynurenine/tryptophan (K/T) were significantly increased and tryptophan was significantly decreased in patients with severe pneumonia; HETE and HEPE in lipids increased significantly, while eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), α-linolenic acid (linolenic acid, α-LNA), arachidonic acid (ARA), Dihomo-γ-linolenic acid (DGLA), and 13(s)-hydroperoxylinoleic acid (HPODE) decreased significantly. Additionally, the longitudinal comparison revealed that Linolenic acid, DPA, and Tryptophan increased significantly in the remission group, while and kynurenine and K/T decreased significantly. In the aggravation group, Kynurenine and K/T increased significantly, while ARA, 8(S)-hydroxyeicosatetraenoic acid (HETE), 11(S)-HETE, and Tryptophan decreased significantly. The correlation analysis matrix demonstrated that Tryptophan was positively correlated with DGLA, 12(S)-hydroxyeicosapentaenoic acid (HEPE), ARA, EPA, α-LNA, DHA, and DPA. Kynurenine was positively correlated with 8(S)-HETE and negatively correlated with DHA. Additionally, K/T was negatively correlated with DGLA, ARA, EPA, α-LNA, DHA, and DPA.

CONCLUSION

This study revealed that during severe pneumonia, the Tryptophan-Kynurenine pathway was activated and was positively correlated with the disease progression. On the other hand, the activation of the Tryptophan-Kynurenine pathway was negatively correlated with N-3/N-6 PUFAs.

The possible role of quinolinic acid as a predictive marker in patients with SARS-CoV-2

BACKGROUND AND AIMS

Quinolinic acid (QA) is a metabolite of the kynurenine pathway, which is activated by inflammatory stimuli during viral infection. We investigated the role of QA in patients infected with SARS-CoV-2, particularly its prognostic value for survival.

METHODS

Overall, 104 unvaccinated inpatients were included, divided into a survival (N = 80) and a deceased group (N = 24). Plasma levels of tryptophan, kynurenine, QA, C-reactive protein (CRP) and procalcitonin (PCT) were measured on admission and after seven days. The QA/TRP ratio and the relative differences between the measurements for QA (QA-Diff) and QA/TRP (Diff-QA/TRP) were calculated.

RESULTS

Among the kynurenine pathway markers, QA-Diff showed the highest discriminatory power for the survival prognosis (Youden index 0.467, cut-off -1.3 %, AUC 0.733, p < 0.001, sensitivity 0.79, specificity 0.675). Among the inflammatory markers, CRP showed the highest discriminatory power (Youden index 0.533, cut-off 25.0 mg/L, AUC 0.794, p < 0.001, sensitivity 0.958, specificity 0.575). A significant correlation between QA and PCT was found on admission and after one week (Spearman's rho 0.455 and 0.539, all p-values < 0.001).

CONCLUSIONS

QA may serve as prognostic marker for survival in patients with SARS-CoV-2. The repeated measurements during the first week of the disease may enhance the prognostic power.

Does smoking influence tryptophan metabolism in periodontal inflammation? A cross-sectional study

OBJECTIVES

The aim of this study was to identify the effects of smoking and periodontal inflammation on tryptophan-kynurenine metabolism as well as the correlation between these findings and clinical periodontal parameters.

BACKGROUND

It has been shown that the tryptophan amino acid's primary catabolic pathway, the kynurenine pathway (KP), may serve as a key biomarker for periodontal disease. Although there are studies investigating the effect of smoking on KYN-TRP metabolism, the effect of smoking on periodontal disease through KP has not been revealed so far.

METHODS

The salivary and serum samples were gathered from 24 nonsmoker (NS-P) stage III, grade B generalized periodontitis and 22 smoker (S-P) stage III, grade C generalized periodontitis patients, in addition to 24 nonsmoker (NS-C) and 24 smoker (S-C) periodontally healthy control individuals. Saliva and serum IL-6, kynurenine (KYN), and tryptophan (TRP) values, and KYN/TRP ratio were analyzed by liquid chromatography-mass spectrometry. Clinical periodontal measurements were recorded.

RESULTS

Salivary TRP values were significantly higher in both periodontitis groups than control groups (p < .05). Salivary KYN values were highest in NS-P group (p < .05). Salivary KYN values did not differ significantly between periodontitis groups (p = .84). Salivary KYN/TRP ratio was significantly lower in NS-P group compared to other groups (p < .001). Serum TRP value is higher in S-P group than other groups; however, significant difference was found in S-C group (p < .05). Serum KYN values were significantly lower in smokers than nonsmokers. Serum KYN/TRP ratio is higher in NS-P group. NS-P group has the highest salivary IL-6 levels, NS-C group has the lowest values (p < .05).

CONCLUSIONS

Our results point out that smoking exacerbates inflammation in the periodontium and increases TRP destruction and decreases IDO activity by suppressing KP in serum. As a result, kynurenine and its metabolites may be significant biomarkers in the link between smoking and periodontal disease.

The value of prospective metabolomic susceptibility endotypes: broad applicability for infectious diseases

BACKGROUND

As new infectious diseases (ID) emerge and others continue to mutate, there remains an imminent threat, especially for vulnerable individuals. Yet no generalizable framework exists to identify the at-risk group prior to infection. Metabolomics has the advantage of capturing the existing physiologic state, unobserved via current clinical measures. Furthermore, metabolomics profiling during acute disease can be influenced by confounding factors such as indications, medical treatments, and lifestyles.

METHODS

We employed metabolomic profiling to cluster infection-free individuals and assessed their relationship with COVID severity and influenza incidence/recurrence.

FINDINGS

We identified a metabolomic susceptibility endotype that was strongly associated with both severe COVID (ORICUadmission = 6.7, p-value = 1.2 × 10-08, ORmortality = 4.7, p-value = 1.6 × 10-04) and influenza (ORincidence = 2.9; p-values = 2.2 × 10-4, βrecurrence = 1.03; p-value = 5.1 × 10-3). We observed similar severity associations when recapitulating this susceptibility endotype using metabolomics from individuals during and after acute COVID infection. We demonstrate the value of using metabolomic endotyping to identify a metabolically susceptible group for two-and potentially more-IDs that are driven by increases in specific amino acids, including microbial-related metabolites such as tryptophan, bile acids, histidine, polyamine, phenylalanine, and tyrosine metabolism, as well as carbohydrates involved in glycolysis.

INTERPRETATIONS

These metabolites may be identified prior to infection to enable protective measures for these individuals.

FUNDING

The Longitudinal EMR and Omics COVID-19 Cohort (LEOCC) and metabolomic profiling were supported by the National Heart, Lung, and Blood Institute and the Intramural Research Program of the National Center for Advancing Translational Sciences, National Institutes of Health.

Prolonged indoleamine 2,3-dioxygenase-2 activity and associated cellular stress in post-acute sequelae of SARS-CoV-2 infection

BACKGROUND

Post-acute sequela of SARS-CoV-2 infection (PASC) encompass fatigue, post-exertional malaise and cognitive problems. The abundant expression of the tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase-2 (IDO2) in fatal/severe COVID-19, led us to determine, in an exploratory observational study, whether IDO2 is expressed and active in PASC, and may correlate with pathophysiology.

METHODS

Plasma or serum, and peripheral blood mononuclear cells (PBMC) were obtained from well-characterized PASC patients and SARS-CoV-2-infected individuals without PASC. We assessed tryptophan and its degradation products by UPLC-MS/MS. IDO2 activity, its potential consequences, and the involvement of the aryl hydrocarbon receptor (AHR) in IDO2 expression were determined in PBMC from another PASC cohort by immunohistochemistry (IHC) for IDO2, IDO1, AHR, kynurenine metabolites, autophagy, and apoptosis. These PBMC were also analyzed by metabolomics and for mitochondrial functioning by respirometry. IHC was also performed on autopsy brain material from two PASC patients.

FINDINGS

IDO2 is expressed and active in PBMC from PASC patients, as well as in brain tissue, long after SARS-CoV-2 infection. This is paralleled by autophagy, and in blood cells by reduced mitochondrial functioning, reduced intracellular levels of amino acids and Krebs cycle-related compounds. IDO2 expression and activity is triggered by SARS-CoV-2-infection, but the severity of SARS-CoV-2-induced pathology appears related to the generated specific kynurenine metabolites. Ex vivo, IDO2 expression and autophagy can be halted by an AHR antagonist.

INTERPRETATION

SARS-CoV-2 infection triggers long-lasting IDO2 expression, which can be halted by an AHR antagonist. The specific kynurenine catabolites may relate to SARS-CoV-2-induced symptoms and pathology.

FUNDING

None.

Mechanism of gastrointestinal injury in COVID-19 and potential use of ghrelin therapy

In Corona Virus Disease 2019 (COVID-19), the most obvious symptoms occur in the respiratory and digestive systems, posing a serious threat to the health of patients. Decreased appetite is the most common digestive system symptom and is an important predictor of mortality. A large number of patients have decreased appetite after infection and do not show obvious organic disease characteristics. Currently, no drugs can directly alleviate such symptom. In order to reduce the number of severe and critically ill patients and decrease the hospitalization rate, it is very important to understand the pathogenic mechanism of appetite loss caused by COVID-19 and manage such symptom. Ghrelin is a key gastric hormone that has anti-inflammatory, neuroprotective, and antidepressant effects. In this paper, we will review the progress in the understanding of the mechanism of appetite loss associated with COVID-19, and introduce a potential therapeutic drug, ghrelin.

Multiplatform analyses reveal distinct drivers of systemic pathogenesis in adult versus pediatric severe acute COVID-19

The pathogenesis of multi-organ dysfunction associated with severe acute SARS-CoV-2 infection remains poorly understood. Endothelial damage and microvascular thrombosis have been identified as drivers of COVID-19 severity, yet the mechanisms underlying these processes remain elusive. Here we show alterations in fluid shear stress-responsive pathways in critically ill COVID-19 adults as compared to non-COVID critically ill adults using a multiomics approach. Mechanistic in-vitro studies, using microvasculature-on-chip devices, reveal that plasma from critically ill COVID-19 adults induces fibrinogen-dependent red blood cell aggregation that mechanically damages the microvascular glycocalyx. This mechanism appears unique to COVID-19, as plasma from non-COVID sepsis patients demonstrates greater red blood cell membrane stiffness but induces less significant alterations in overall blood rheology. Multiomics analyses in pediatric patients with acute COVID-19 or the post-infectious multi-inflammatory syndrome in children (MIS-C) demonstrate little overlap in plasma cytokine and metabolite changes compared to adult COVID-19 patients. Instead, pediatric acute COVID-19 and MIS-C patients show alterations strongly associated with cytokine upregulation. These findings link high fibrinogen and red blood cell aggregation with endotheliopathy in adult COVID-19 patients and highlight differences in the key mediators of pathogenesis between adult and pediatric populations.

Alteration of the kynurenine pathway is inversely associated with the humoral immune response in patients with SARS-CoV-2

Background

The scale and the course of antibody production in patients with SARS-CoV-2 is highly variable. Factors involved in the immune regulation during the infection may play a major role in the antibody response. We investigated the relationship between the inflammatory markers of the kynurenine pathway and the concentration of antibodies against SARS-CoV-2 in infected patients 8 – 11 days after admission.

Methods

The study included 72 SARS-CoV-2 - positive inpatients hospitalized between August 2020 and April 2021. The plasma concentrations of tryptophan, kynurenine, anti-SARS-CoV-2 antibodies and the leucocyte count were measured 8 – 11 days after admission. The kynurenine/tryptophan ratio (KYN/TRP ratio) was calculated. Tertiles based on the values for tryptophan, kynurenine, KYN/TRP ratio and the leucocytes were generated.

Results

Statistically significant correlations were observed between anti-SARS-CoV-2 antibodies and tryptophan, kynurenine, KYN/TRP ratio and the leucocytes (p-values < 0.001–0.007). The high kynurenine and KYN/TRP ratio tertiles showed significantly lower antibody titers compared to the low tertiles (p-values 0.017 and < 0.001). The low tryptophan and leucocytes tertiles showed significantly lower antibody titers compared to the high tertiles (p-values 0.001 and 0.008).

Conclusion

Patients with higher activation levels of the kynurenine pathway tended to develop lower anti-SARS-CoV-2 antibody titers.

Decreased Gut Microbiome Tryptophan Metabolism and Serotonergic Signaling in Patients With Persistent Mental Health and Gastrointestinal Symptoms After COVID-19

INTRODUCTION

An estimated 15%-29% of patients report new gastrointestinal (GI) symptoms after coronavirus-19 disease (COVID-19) while 4%-31% report new depressive symptoms. These symptoms may be secondary to gut microbiome tryptophan metabolism and 5-hydroxytryptamine (5-HT)-based signaling.

METHODS

This study used specimens from 2 patient cohorts: (i) fecal samples from patients with acute COVID-19 who participated in a randomized controlled trial testing prebiotic fiber and (ii) blood samples from patients with acute COVID-19. Six months after recovering from COVID-19, both cohorts answered questions related to GI symptoms and anxiety or depression. Microbiome composition and function, focusing on tryptophan metabolism-associated pathways, and plasma 5-HT were assessed.

RESULTS

In the first cohort (n = 13), gut microbiome L-tryptophan biosynthesis during acute COVID-19 was decreased among those who developed more severe GI symptoms (2.0-fold lower log activity comparing those with the most severe GI symptoms vs those with no symptoms, P = 0.06). All tryptophan pathways showed decreased activity among those with more GI symptoms. The same pathways were also decreased in those with the most severe mental health symptoms after COVID-19. In an untargeted analysis, 5 additional metabolic pathways significantly differed based on subsequent development of GI symptoms. In the second cohort (n = 39), plasma 5-HT concentration at the time of COVID-19 was increased 5.1-fold in those with GI symptoms alone compared with those with mental health symptoms alone ( P = 0.02).

DISCUSSION

Acute gut microbiome-mediated reduction in 5-HT signaling may contribute to long-term GI and mental health symptoms after COVID-19. Future studies should explore modification of 5-HT signaling to reduce post-COVID symptoms.

Distinct post-sepsis induced neurochemical alterations in two mouse strains

Sepsis associated encephalopathy, occurs in 70% of severe septic cases, following which survivors exhibit long-term cognitive impairment or global loss of cognitive function. Currently there is no clearly defined neurochemical basis of septic encephalopathy. Moreover, the lingering neurological complications associated with the severe acute respiratory syndrome CoV 2 (SARS-CoV-2) and the significant worsening in outcomes for those individuals with SARS-Cov-2 following sepsis underscore the need to define factors underlying the susceptibility to acute toxic encephalitis. In this study, differential neurochemical sequelae in response to sepsis (lipopolysaccharide (LPS)-induced endotoxemia and caecal ligation and puncture (CLP)), were evaluated in two inbred mouse strains, known to differ in behaviour, immune profile, and neurotransmitter levels, namely BALB/c and C57BL/6J. It was hypothesized that these strains would differ in sepsis severity, cytokine profile, peripheral tryptophan metabolism and central monoamine turnover. BALB/c mice exhibited more pronounced sickness behavioural scores, hypothermia, and significant upregulation of cytokines in the LPS model relative to C57BL/6J mice. Increased plasma kynurenine/tryptophan ratio, hippocampal serotonin and brainstem dopamine turnover were evident in both strains, but the magnitude was greater in BALB/c mice. In addition, CLP significantly enhanced kynurenine levels and hippocampal serotonergic and dopaminergic neurotransmission in C57BL/6J mice. Overall, these studies depict consistent changes in kynurenine, serotonin, and dopamine post sepsis. Further evaluation of these monoamines in the context of septic encephalopathy and cognitive decline is warranted. Moreover, these data suggest the continued evaluation of altered peripheral kynurenine metabolism as a potential blood-based biomarker of sepsis.

Specific intracellular signature of SARS-CoV-2 infection using confocal Raman microscopy

SARS-CoV-2 infection remains spread worldwide and requires a better understanding of virus-host interactions. Here, we analyzed biochemical modifications due to SARS-CoV-2 infection in cells by confocal Raman microscopy. Obtained results were compared with the infection with another RNA virus, the measles virus. Our results have demonstrated a virus-specific Raman molecular signature, reflecting intracellular modification during each infection. Advanced data analysis has been used to distinguish non-infected versus infected cells for two RNA viruses. Further, classification between non-infected and SARS-CoV-2 and measles virus-infected cells yielded an accuracy of 98.9 and 97.2 respectively, with a significant increase of the essential amino-acid tryptophan in SARS-CoV-2-infected cells. These results present proof of concept for the application of Raman spectroscopy to study virus-host interaction and to identify factors that contribute to the efficient SARS-CoV-2 infection and may thus provide novel insights on viral pathogenesis, targets of therapeutic intervention and development of new COVID-19 biomarkers.

The tryptophan catabolite or kynurenine pathway in COVID-19 and critical COVID-19: a systematic review and meta-analysis

Background

Coronavirus disease 2019 (COVID-19) is accompanied by activated immune-inflammatory pathways and oxidative stress, which both induce indoleamine-2,3-dioxygenase (IDO), a key enzyme of the tryptophan (TRP) catabolite (TRYCAT) pathway. The aim of this study was to systematically review and meta-analyze the status of the TRYCAT pathway, including the levels of TRP and kynurenine (KYN) and the activity of IDO, as measured by the ratio of KYN/TRP.

Methods

This systematic review searched PubMed, Google Scholar, and Web of Sciences and included 14 articles that compared TRP and tryptophan catabolites (TRYCATs) in COVID-19 patients versus non-COVID-19 controls, as well as severe/critical versus mild/moderate COVID-19. The analysis was done on a total of 1269 people, including 794 COVID-19 patients and 475 controls.

Results

The results show a significant (p < 0.0001) increase in the KYN/TRP ratio (standardized mean difference, SMD = 1.099, 95% confidence interval, CI: 0.714; 1.484) and KYN (SMD = 1.123, 95% CI: 0.730; 1.516) and significantly lower TRP (SMD = − 1.002, 95%CI: − 1.738; − 0.266) in COVID-19 versus controls. The KYN/TRP ratio (SMD = 0.945, 95%CI: 0.629; 1.262) and KYN (SMD = 0.806, 95%CI: 0.462; 1.149) were also significantly (p < 0.0001) higher and TRP lower (SMD = − 0.909, 95% CI: − 1.569; − 0.249) in severe/critical versus mild/moderate COVID-19. No significant difference was detected in kynurenic acid (KA) and the KA/KYN ratio between COVID-19 patients and controls.

Conclusions

Our results indicate increased activity of the IDO enzyme in COVID-19 and severe/critical patients. The TRYCAT pathway is implicated in the pathophysiology and progression of COVID-19 and may signal a worsening outcome of the disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07582-1.

Psychological outcomes of COVID-19 survivors at sixth months after diagnose: the role of kynurenine pathway metabolites in depression, anxiety, and stress

Coronavirus disease 2019 (COVID-19) has resulted in long-term psychiatric symptoms because of the immunologic response to the virus itself as well as fundamental life changes related to the pandemic. This immune response leads to altered tryptophan (TRP)-kynurenine (KYN) pathway (TKP) metabolism, which plays an essential role in the pathophysiology of mental illnesses. We aimed to define TKP changes as a potential underlying mechanism of psychiatric disorders in post-COVID-19 patients. We measured plasma levels of several TKP markers, including KYN, TRP, kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), and quinolinic acid (QUIN), as well as the TRP/KYN, KYNA/3-HK, and KYNA/QUIN ratios, in 90 post-COVID-19 patients (on the first day of hospitalization) and 59 healthy controls (on the first admission to the Check-Up Center). An online questionnaire that included the Depression, Anxiety and Stress Scale-21 (DASS-21) was used 6 months after the initial assessment in both groups. A total of 32.2% of participants with COVID-19 showed depressive symptoms, 21.1% exhibited anxiety, and 33.3% had signs of stress at follow-up, while 6.6% of healthy controls exhibited depressive and anxiety symptoms and 18.6% had signs of stress. TRP and 3-HK were negative predictors of anxiety and stress, but KYN positively predicted anxiety and stress. Moreover, TRP negatively predicted depression, while KYNA/3-HK was a negative predictor of anxiety. The correlation between depression, anxiety, and stress and TKP activation in COVID-19 could provide prospective biomarkers, especially the reduction in TRP and 3HK levels and the increase in KYN. Our results suggest that the alteration of TKP is not only a potential biomarker of viral infection-related long-term psychiatric disorders but also that the therapy targets future viral infections related to depression and anxiety.

Metabolic Profiling at COVID-19 Onset Shows Disease Severity and Sex-Specific Dysregulation

Background

metabolic changes through SARS-CoV-2 infection has been reported but not fully comprehended. This metabolic dysregulation affects multiple organs during COVID-19 and its early detection can be used as a prognosis marker of severity. Therefore, we aimed to characterize metabolic and cytokine profile at COVID-19 onset and its relationship with disease severity to identify metabolic profiles predicting disease progression.

Material and Methods

we performed a retrospective cross-sectional study in 123 COVID-19 patients which were stratified as asymptomatic/mild, moderate and severe according to the highest COVID-19 severity status, and a group of healthy controls. We performed an untargeted plasma metabolic profiling (gas chromatography and capillary electrophoresis-mass spectrometry (GC and CE-MS)) and cytokine evaluation.

Results

After data filtering and identification we observed 105 metabolites dysregulated (66 GC-MS and 40 CE-MS) which shown different expression patterns for each COVID-19 severity status. These metabolites belonged to different metabolic pathways including amino acid, energy, and nitrogen metabolism among others. Severity-specific metabolic dysregulation was observed, as an increased transformation of L-tryptophan into L-kynurenine. Thus, metabolic profiling at hospital admission differentiate between severe and moderate patients in the later phase of worse evolution. Several plasma pro-inflammatory biomarkers showed significant correlation with deregulated metabolites, specially with L-kynurenine and L-tryptophan. Finally, we describe a strong sex-related dysregulation of metabolites, cytokines and chemokines between severe and moderate patients. In conclusion, metabolic profiling of COVID-19 patients at disease onset is a powerful tool to unravel the SARS-CoV-2 molecular pathogenesis.

Conclusions

This technique makes it possible to identify metabolic phenoconversion that predicts disease progression and explains the pronounced pathogenesis differences between sexes.

Unbalanced IDO1/IDO2 Endothelial Expression and Skewed Keynurenine Pathway in the Pathogenesis of COVID-19 and Post-COVID-19 Pneumonia

Despite intense investigation, the pathogenesis of COVID-19 and the newly defined long COVID-19 syndrome are not fully understood. Increasing evidence has been provided of metabolic alterations characterizing this group of disorders, with particular relevance of an activated tryptophan/kynurenine pathway as described in this review. Recent histological studies have documented that, in COVID-19 patients, indoleamine 2,3-dioxygenase (IDO) enzymes are differentially expressed in the pulmonary blood vessels, i.e., IDO1 prevails in early/mild pneumonia and in lung tissues from patients suffering from long COVID-19, whereas IDO2 is predominant in severe/fatal cases. We hypothesize that IDO1 is necessary for a correct control of the vascular tone of pulmonary vessels, and its deficiency in COVID-19 might be related to the syndrome’s evolution toward vascular dysfunction. The complexity of this scenario is discussed in light of possible therapeutic manipulations of the tryptophan/kynurenine pathway in COVID-19 and post-acute COVID-19 syndromes.