Assessment of neopterin and indoleamine 2,3-dioxygenase activity in patients with seasonal influenza: A pilot study

Biological variation of serum neopterin concentrations in apparently healthy individuals

OBJECTIVES

The aims of this study were to determine the biological variation (BV), reference change value (RCV), index of individuality (II), and quality specifications for serum neopterin concentrations; a measurand provided by clinical laboratories as an indicator of cellular immunity.

METHODS

The study delivered serum samples collected for 10 consecutive weeks from 12 apparently healthy individuals (3 male, 9 female). Serum neopterin concentrations were measured using high-performance liquid chromatography with fluorometric detection. The data analysis was performed using an online statistical tool and addressed published criteria for estimation of biological variation.

RESULTS

The mean neopterin concentration was 5.26 nmol/L. The within-subject biological variation (CVI) with 95 % confidence interval (CI) of neopterin serum concentrations was 11.54 % (9.98-13.59), and the between-subject biological variation (CVG) with 95 % CI was 43.27 % (30.52-73.67). The neopterin asymmetrical RCV was -24.9 %/+33.1 %, and the II was 0.27. The desirable quality specifications for neopterin were <5.77 % for precision, <11.20 % for bias, and <20.72 % for total allowable error (TEa). When analytical variation was used instead of CVI to calculate TEa, the desirable TEa was <18.39.

CONCLUSIONS

This study determined BV data for neopterin, an indicator of cell-mediated immune response. Asymmetric RCV values, of 24.9 % decrease or a 33.1 % increase between consecutive measurements indicate significant change. The II of 0.27 indicates a high degree of individuality, therefore that it is appropriate to consider the use of personal reference data and significance of change rather than the reference interval as points of reference for the evaluation of neopterin serum concentrations.

Neopterin and kynurenine in serum and urine as prognostic biomarkers in hospitalized patients with delta and omicron variant SARS-CoV-2 infection

OBJECTIVES

Currently, no biomarker or scoring system could clearly identify patients at risk of progression to a severe coronavirus disease (COVID)-19. Even in patients with known risk factors, the fulminant course cannot be predicted with certainty. Analysis of commonly determined clinical parameters (frailty score, age, or body mass index) together with routine biomarkers of host response (C-reactive protein and viral nucleocapsid protein) in combination with new biomarkers neopterin, kynurenine, and tryptophan, could aid in predicting the patient outcome.

METHODS

In 2021 and 2022, urine and serum samples were prospectively collected on 1st to 4th day after hospital admission in 108 consecutive COVID-19 patients hospitalized at the University Hospital Hradec Králové, Czech Republic. Delta and omicron virus variants were studied. Neopterin, kynurenine and tryptophan were determined by liquid chromatography.

RESULTS

A significant correlation was observed between urinary and serum biomarker concentrations. Urinary and serum neopterin, kynurenine and kynurenine/tryptophan ratio were significantly (p≤0.05) higher in patients who subsequently needed oxygen therapy vs. patients without oxygen therapy. These parameters were also significantly increased in patients who died during the hospitalization compared to survivors. Complex equations have been derived using the investigated biomarkers and other clinical or laboratory parameters to predict the risk of subsequent oxygen therapy or death during hospitalization.

CONCLUSIONS

Present data demonstrate that neopterin, kynurenine and kynurenine/tryptophan ratio in the serum or in the urine represent promising biomarkers in the management of COVID-19 that may help to guide important therapeutic decisions.

The usability of neopterin in determining disease course in COVID-19

OBJECTIVES

To investigate the usability of neopterin in demonstrating the progression of COVID-19. As a result of uncontrolled activation of COVID-19 monocytes and macrophages, IFN gamma increases and the resulting inflammatory response causes organ damage. IFN released from T cells causes an increase in gamma neopterin levels. Therefore, measurement of neopterin levels can be used to indicate immune system activation and disease progression.

METHODS

The study was carried out prospectively in two different centers. The patients were divided into two groups (mild-moderate and severe) and clinical, laboratory, imaging findings and neopterin levels at hospitalization were compared.

RESULTS

100 patients were included in our study, 41 of these patients were male. Forty-six patients were identified as severe COVID-19. C-reactive protein, lymphocyte count, fibrinogen, D dimers, lactate dehydrogenase, procalcitonin, troponin and neopterin levels were significant in indicating disease severity. (p<0.05). In ROC analysis, 0.642 for neopterin, 0.698 C-reactive protein, 0.331 lymphocyte count, 0.679 procalcitonin, 0.633 fibrinogen, 0.667 D dimers, 0.655 troponin and 0.706 lactate dehydrogenase were detected and these values were significant.

CONCLUSION

In our study, neopterin was detected as an important indicator in determining the course of COVID-19.

Interferon-gamma Mediated Metabolic Pathways in Hospitalized Patients During Acute and Reconvalescent COVID-19

Background:

Fatigue, sleep disturbance, and neurological symptoms during and after COVID-19 are common and might be associated with inflammation-induced changes in tryptophan (Trp) and phenylalanine (Phe) metabolism.

Aim:

This pilot study investigated interferon gamma inducible biochemical pathways (namely Trp catabolism, neopterin, tyrosine [Tyr], and nitrite formation) during acute COVID-19 and reconvalescence.

Patients and methods:

Thirty one patients with moderate to severe COVID-19 admitted to the University Hospital of Innsbruck in early 2020 (March-May) were followed up. Neurotransmitter precursors Trp, Phe, Tyr as well as kynurenine (Kyn), neopterin, nitrite, and routine laboratory parameters were analyzed during acute infection and at a follow-up (FU) 60 days thereafter. Clinical symptoms of patients (neurological symptoms, fatigue, sleep disturbance) were recorded and associations with concentrations of laboratory parameters investigated.

Results and conclusion:

Almost half of the patients suffered from neurological symptoms (48.4%), the majority of patients experienced sleep difficulties (56.7%) during acute COVID-19. Fatigue was present in nearly all patients. C-reactive protein (CRP), interleukin-6 (IL-6), neopterin, Kyn, Phe concentrations were significantly increased, and Trp levels depleted during acute COVID-19. Patients with sleep impairment and neurological symptoms during acute illness presented with increased CRP and IL-6 concentrations, Trp levels were lower in patients with sleep disturbance. In general, inflammatory markers declined during reconvalescence. A high percentage of patients suffered from persistent symptoms at FU (neurological symptoms: 17.2%, fatigue: 51.7%, sleeping disturbance: 34.5%) and had higher CRP concentrations. Nitrite and Phe levels were lower in patients with sleeping difficulties at FU and Kyn/Trp ratio, as indicator of IDO activity, was significantly lower in patients with neurological symptoms compared to patients without them at FU. In summary, inflammation induced alterations of amino acid metabolism might be related to acute and persisting symptoms of COVID-19.

Single-nucleus transcriptomic profiling of multiple organs in a rhesus macaque model of SARS-CoV-2 infection

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes diverse clinical manifestations and tissue injuries in multiple organs. However, cellular and molecular understanding of SARS-CoV-2 infection-associated pathology and immune defense features in different organs remains incomplete. Here, we profiled approximately 77 000 single-nucleus transcriptomes of the lung, liver, kidney, and cerebral cortex in rhesus macaques ( Macaca mulatta) infected with SARS-CoV-2 and healthy controls. Integrated analysis of the multi-organ dataset suggested that the liver harbored the strongest global transcriptional alterations. We observed prominent impairment in lung epithelial cells, especially in AT2 and ciliated cells, and evident signs of fibrosis in fibroblasts. These lung injury characteristics are similar to those reported in patients with coronavirus disease 2019 (COVID-19). Furthermore, we found suppressed MHC class I/II molecular activity in the lung, inflammatory response in the liver, and activation of the kynurenine pathway, which induced the development of an immunosuppressive microenvironment. Analysis of the kidney dataset highlighted tropism of tubule cells to SARS-CoV-2, and we found membranous nephropathy (an autoimmune disease) caused by podocyte dysregulation. In addition, we identified the pathological states of astrocytes and oligodendrocytes in the cerebral cortex, providing molecular insights into COVID-19-related neurological implications. Overall, our multi-organ single-nucleus transcriptomic survey of SARS-CoV-2-infected rhesus macaques broadens our understanding of disease features and antiviral immune defects caused by SARS-CoV-2 infection, which may facilitate the development of therapeutic interventions for COVID-19.

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.

Cellular Immunity In Subacute Thyroiditis: A New Perspective Through Neopterin

Subacute thyroiditis (SAT) is an inflammatory disorder of the thyroid gland. Although its etiology is not fully understood, it is believed to occur shortly after viral infections and is mostly associated with human leukocyte antigen (HLA)-B*35. Cellular immunity is prominent in SAT. Neopterin is produced by activated monocytes/macrophages and is a marker of cellular immunity. Its production is stimulated by interferon gamma (IFN-γ), provided mainly by activated helper T lymphocytes type 1 (Th1) in the adaptive immune system. Therefore, with these cells' activation, an increase in serum neopterin levels is expected. We aimed to evaluate neopterin levels in demonstrating cellular immunity in SAT and compared 15 SAT patients with 16 healthy controls. Since all SAT patients were in the active thyrotoxic phase, we found a significant difference in thyroid functions, classical inflammatory markers, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), were markedly elevated in the patient group. Although we expected to find an increase considering that cellular immunity is at the forefront in the pathogenesis of SAT, we found serum neopterin levels significantly lower in the patient group than in the control group. There is an increase in CD8+ T cells in the thyroid tissue in SAT. The possible relationship with HLA-B*35- MHC class I in SAT, and the antigen presentation to CD8+ T cells may be the reason why we observed low serum neopterin levels in patients due to the cytokine imbalance. Neopterin provides unique and independent data from classical acute phase response indicators.

Kynurenine pathway in Coronavirus disease (COVID‐19): Potential role in prognosis

Background

It is known that inflammatory responses play an important role in the pathophysiology of COVID‐19.

Aims

In this study, we aimed to examine the role of kynurenine (KYN) metabolism on the severity of COVID‐19 disease AQ5.

Materials & Methods

Seventy COVID‐19 patients of varying severity and 30 controls were included in the study. In addition to the classical laboratory parameters, KYN, tryptophan (TRP), kynurenic acid (KYNA), 3 hydroxykynurenine (3OHKYN), quinolinic acid (QA), and picolinic acid (PA) were measured with mass spectrometry.

Results

TRP, KYN, KYN:TRP ratio, KYNA, 3OHKYN, PA, and QA results were found to be significantly different in COVID‐19 patients (p < 0.001 for all). The KYN:TRP ratio and PA of severe COVID‐19 patients was statistically higher than that of mild‐moderate COVID‐19 patients (p < 0.001 for all). When results were examined, statistically significant correlations with KYN:TRP ratio, IL‐6, ferritin, and procalcitonin were only found in COVID‐19 patients. ROC analysis indicated that highest AUC values were obtained by KYN:TRP ratio and PA (0.751 vs 0.742). In determining the severity of COVID‐19 disease, the odd ratios (and confidence intervals) of KYN:TRP ratio and PA levels that were adjusted according to age, gender, and comorbidity were determined to be 1.44 (1.1–1.87, p = 0.008) and 1.06 (1.02–1.11, p = 0.006), respectively.

Discussion & Conclusion

According to the results of this study, KYN metabolites play a role in the pathophysiology of COVID‐19, especially KYN:TRP ratio and PA could be markers for identification of severe COVID‐19 cases.

Neopterin: A Promising Candidate Biomarker for Severe COVID-19

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection has rapidly spread across the world since its first emergence in China in late 2019. It is a major public health concern with no effective treatct 3ments. The immunopathology of SARS-CoV-2 is associated with an excessive inflammatory response. Macrophage activation syndrome (MAS) is also associated with the severity of the disease in SARS-CoV-2-infected patients. Neopterin is a macrophage activation marker produced by monocytes and macrophages upon activation by interferon-gamma (IFN-γ). Neopterin is a well-established marker in a variety of diseases, and recent evidence indicates that it could be helpful in early prediction of the severity of COVID-19 disease and serve as a prognostic marker. Here, we outline the role of macrophage activation syndrome in the pathogenesis of SARS-CoV-2 and suggest that neopterin could be used as a biomarker for progression of COVID-19.

The potential role of neopterin in Covid-19: a new perspective

Neopterin (NPT) is a member of pteridines group, synthesized by macrophages when stimulated by interferon gamma (INF-γ). NPT is regarded as a macrophage stimulation indicator, marker of cellular immune activation and T helper 1 (Th1) type 1 immune response. Here, we aimed to provide a view point on the NPT features and role in Covid-19. Serum NPT level is regarded as an independent prognostic factor for Covid-19 severity, with levels starting to increase from the 3rd day of SARS-CoV-2 infection, being associated with severe dyspnea, longer hospitalization period and complications. Also, early raise of NPT reflects monocytes/macrophages activation before antibody immune response, despite the NPT level may also remain high in Covid-19 patients or at the end of incubation period before the onset of clinical symptoms. On the other hand, NPT attenuates the activity of macrophage foam cells and is linked to endothelial inflammation through inhibition of adhesion molecules and monocytes migration. However, NPT also exerts anti-inflammatory and antioxidant effects by suppressing NF-κB signaling and NLRP3 inflammasomes. NPT can be viewed as a protective compensatory mechanism to counterpoise hyper-inflammation, oxidative stress, and associated organ damage.

Increased kynurenine-to-tryptophan ratio in the serum of patients infected with SARS-CoV2: An observational cohort study

Immune dysregulation is a hallmark of patients infected by SARS-CoV2 and the balance between immune reactivity and tolerance is a key determinant of all stages of infection, including the excessive inflammatory state causing the acute respiratory distress syndrome. The kynurenine pathway (KP) of tryptophan (Trp) metabolism is activated by pro-inflammatory cytokines and drives mechanisms of immune tolerance. We examined the state of activation of the KP by measuring the Kyn:Trp ratio in the serum of healthy subjects (n = 239), and SARS-CoV2-negative (n = 305) and -positive patients (n = 89). Patients were recruited at the Emergency Room of St. Andrea Hospital (Rome, Italy). Kyn and Trp serum levels were assessed by HPLC/MS-MS. Compared to healthy controls, both SARS-CoV2-negative and -positive patients showed an increase in the Kyn:Trp ratio. The increase was larger in SARS-CoV2-positive patients, with a significant difference between SARS-CoV2-positive and -negative patients. In addition, the increase was more prominent in males, and positively correlated with age and severity of SARS-CoV2 infection, categorized as follows: 1 = no need for intensive care unit (ICU); 2 ≤ 3 weeks spent in ICU; 3 ≥ 3 weeks spent in ICU; and 4 = death. The highest Kyn:Trp values were found in SARS-CoV2-positive patients with severe lymphopenia. These findings suggest that the Kyn:Trp ratio reflects the level of inflammation associated with SARS-CoV2 infection, and, therefore, might represent a valuable biomarker for therapeutic intervention.

The prognostic role of neopterin in COVID-19 patients

In Coronavirus disease-2019 (COVID-19) cases, hyper inflammation is associated with the severity of the disease. High levels of circulating cytokines were reported in severe COVID-19 patients. Neopterin produced by macrophages on stimulation with interferon-gamma, which is an important cytokine in the antiviral immune response, hence it can be used to predict the severity of disease in COVID-19 cases. In this study, it was aimed to determine the prognostic value of the neopterin for the prediction of severe disease in patients with COVID-19. This single-center, prospective study was conducted in hospitalized COVID-19 patients and healthy volunteers. Severe and mild COVID-19 cases were compared in terms of clinical and laboratory findings as well as serum neopterin levels on hospital admission. To assess the prognostic utility of neopterin between the severe and mild COVID-19 groups, a receiver-operating characteristic (ROC) curve was generated, and the area under the curve (AUC) was calculated. The median serum neopterin level was four times higher in COVID-19 patients than the healthy controls (46 vs. 12 nmol/L; p < .001). The AUC value of serum neopterin was 0.914 (95% confidence interval, 0.85-0.97). The sensitivity and specificity of serum neopterin for the cut-off value of 90 nmol/L to identify severe COVID-19 cases were 100% and 76%, respectively. Serum neopterin levels on hospitalization were significantly higher in severe COVID-19 disease than mild COVID-19 patients. Neopterin levels can be used as an early prognostic biomarker for COVID-19 on admission.

Assessment of neopterin and indoleamine 2,3-dioxygenase activity in patients with seasonal influenza: A pilot study

BACKGROUND

Seasonal influenza is an important cause of morbidity and mortality worldwide. Immune activation after stimulation with interferon-gamma leads to increased production of neopterin but also results in increased tryptophan catabolism through indoleamine 2,3-dioxygenase (IDO). Our pilot study determined neopterin serum levels and IDO activity in patients with influenza infection and investigated whether neopterin is linked to clinical outcome parameters (mortality ≤30 days, acute cardiac events (ACE) length of hospitalization, ICU admission).

METHODS

Neopterin concentrations were analyzed in serum samples of 40 patients with a confirmed diagnosis of influenza infection and in-hospital treatment for >24 hours. Data were compared to values of 100 healthy blood donors and 48 age-matched pneumonia patients. In a subgroup of 14 patients, tryptophan and kynurenine concentrations, as well as kynurenine-to-tryptophan ratio, were analyzed.

RESULTS

In all influenza patients, neopterin concentrations were increased and significantly higher compared to those determined in patients with pneumonia and healthy controls. Positive correlations between the duration of hospitalization and neopterin were found. Significantly higher levels of kynurenine, kynurenine-to-tryptophan ratio, and lower levels of tryptophan were seen in influenza patients compared to healthy controls.

CONCLUSIONS

Neopterin seems to be related to the course of the disease and could be a valuable biomarker to identify patients at an elevated risk of a worsened outcome; however, further prospective validation studies are needed to support the here presented preliminary results.