Quantitative LC-MS study of compounds found predictive of COVID-19 severity and outcome

Longitudinal kinetics of the viral infection biomarker 3'-deoxy-3',4'-didehydro-cytidine in SARS-CoV-2, influenza A virus and RSV human challenge models

3'-deoxy-3',4'-didehydro-cytidine (ddhC) is a recently discovered host biomarker for viral infections, though its temporal kinetics remain unclear. This study tests the hypothesis that ddhC is an acute phase reactant, rising shortly after viral infection and subsequently falling to baseline. We leveraged the precise monitoring facilitated by human challenge studies to investigate healthy participants inoculated with SARS-CoV-2, influenza A virus (H3N2), or respiratory syncytial virus (RSV). Using targeted liquid chromatography-tandem mass spectrometry, we quantified ddhC concentrations in serial plasma samples collected pre- and post-inoculation. In SARS-CoV-2 and H3N2 influenza A virus infection, but not RSV, ddhC levels peaked at 3-7 days post inoculation and declined to baseline by days 10-14. This pattern was also observed in asymptomatic or paucisymptomatic participants. A comparison of ddhC concentrations with matched timepoint whole blood gene expression revealed a correlation with interferon-related genes, including viperin and CMPK2-enzymes implicated in its upstream biosynthesis. Our results suggest that ddhC is a biomarker of the acute phase of viral infection, with potential to guide early interventions that reduce antimicrobial resistance and strengthen pandemic preparedness. Future work should explore ddhC dynamics in natural and experimental infections across varying severities and assess its utility in diverse populations and healthcare settings.

A Fast Immunosensor Based on Biohybrid Self-Assembled Nanostructures for the Detection of KYNA as a Cerebrospinal Fluid Biomarker for Alzehimer's Disease

Although the role of kynurenic acid (KYNA) is not yet fully understood, recent research has implicated this tryptophan (Trp) metabolite as a significant biomarker in neurodegenerative diseases. In this study, we developed an immunosensor platform based on self-assembled polyelectrolyte multilayers (PEMs), employing an enzyme-labeled immunoreagent in a competitive displacement format that requires only a single wash step. This immunosensor enables the detection of KYNA and Trp with detection limits (LOD) of 9 pg/mL and 1.2 ng/mL, respectively. Results validated by traditional ELISA methods indicated elevated levels of KYNA and an increased KYNA/Trp ratio in the cerebrospinal fluid (CSF) of Alzheimer's patients compared to controls, consistent with previous findings. Additionally, this immunosensor platform can be readily adapted to detect other neuroactive Trp metabolites by substituting specific immunoreagents, supporting a flexible profile-based approach. This platform could serve as a rapid, cost-effective clinical tool for monitoring neurological and psychiatric disorders, potentially advancing therapeutic strategy development.

Kynurenic Acid and Promotion of Activity-Dependent Synapse Elimination in Schizophrenia

OBJECTIVE

Schizophrenia is a neurodevelopmental disorder characterized by an excessive loss of synapses. Kynurenic acid (KYNA), a neuroactive metabolite of tryptophan along the kynurenine pathway, can induce schizophrenia-related phenotypes in rodents, and clinical studies have revealed elevated KYNA levels in the CNS of individuals with schizophrenia. However, the factors that cause elevated KYNA levels in schizophrenia, and the mechanisms by which KYNA contributes to pathophysiology, remain largely elusive. The authors used patient-derived cellular modeling to test the hypothesis that KYNA can induce microglia-mediated synapse engulfment by reducing neuronal activity.

METHODS

Patient-derived induced pluripotent stem cells were used to generate 2D cultures of neurons and microglia-like cells, as well as forebrain organoids with innately developing microglia, to study how KYNA influences synaptic activity and microglial uptake of synaptic structures. To verify the experimental data in a clinical context, large-scale developmental postmortem brain tissue and genetic datasets were used to study coexpression networks for the KYNA-producing kynurenine aminotransferases (KATs) regarding enrichment for common schizophrenia genetic risk variants and functional annotations.

RESULTS

In these patient-derived experimental models, KYNA induced uptake of synaptic structures in microglia, and inhibition of the endogenous KYNA production led to a decrease in the internalization of synapses in microglia. The integrated large-scale transcriptomic and genetic datasets showed that KYNA-producing KATs enriched for genes governing synaptic activity and genetic risk variants for schizophrenia.

CONCLUSIONS

Together, these results link genetic risk variants for schizophrenia to elevated production of KYNA and excessive and activity-dependent internalization of synaptic material in microglia, while implicating pharmacological inhibition of KATs as a strategy to avoid synapse loss in schizophrenia.

Ethyl Acetate Fraction of Chestnut Honey Attenuates Scopolamine-Induced Cognitive Impairment in Mice and Glutamate-Induced Neurotoxicity in HT22 Cells

Chestnut honey has various benefits, such as antioxidative, anti-inflammatory, immunomodulatory, antibacterial, and antiviral effects. However, the effects of chestnut honey or the ethyl acetate fraction of chestnut honey (EACH) on neurodegenerative diseases and their related cognitive impairment and neurotoxicity have not yet been established. Therefore, in this study, we investigated the mitigating effect of the EACH on scopolamine (SCO)-injected cognitive decline in mice and glutamate-exposed neurotoxicity in HT22 cells. EACH administration significantly reversed SCO-induced cognitive decline in mice, as demonstrated through the Morris water maze and passive avoidance tests. The EACH treatment showed a significant alleviation effect by recovering more than 80% of the cell viability decrease induced by glutamate exposure in the HT22 neuronal cell model. Furthermore, the EACH significantly reduced reactive oxygen species accumulation, lactate dehydrogenase release, mitochondrial depolarization, and neuronal apoptosis. The EACH regulated the level of apoptosis-related proteins, induced the nuclear translocation of nuclear factor-E2-related factor 2 (Nrf-2) and the expression of related antioxidant proteins, and induced the phosphorylation of tropomyosin-related kinase receptor B (TrkB)/cAMP-calcium response element-binding protein (CREB) and the expression of brain-derived neurotrophic factor. These data indicate that the EACH can prevent neurons from oxidative damage and improve cognitive dysfunction by activating Nrf-2 and TrkB/CREB signaling pathways. Therefore, the EACH demonstrates potential therapeutic value in mitigating oxidative stress-induced neurotoxicity, cognitive decline, and related neurodegenerative diseases.

The Biology and Biochemistry of Kynurenic Acid, a Potential Nutraceutical with Multiple Biological Effects

Kynurenic acid (KYNA) is an antioxidant degradation product of tryptophan that has been shown to have a variety of cytoprotective, neuroprotective and neuronal signalling properties. However, mammalian transporters and receptors display micromolar binding constants; these are consistent with its typically micromolar tissue concentrations but far above its serum/plasma concentration (normally tens of nanomolar), suggesting large gaps in our knowledge of its transport and mechanisms of action, in that the main influx transporters characterized to date are equilibrative, not concentrative. In addition, it is a substrate of a known anion efflux pump (ABCC4), whose in vivo activity is largely unknown. Exogeneous addition of L-tryptophan or L-kynurenine leads to the production of KYNA but also to that of many other co-metabolites (including some such as 3-hydroxy-L-kynurenine and quinolinic acid that may be toxic). With the exception of chestnut honey, KYNA exists at relatively low levels in natural foodstuffs. However, its bioavailability is reasonable, and as the terminal element of an irreversible reaction of most tryptophan degradation pathways, it might be added exogenously without disturbing upstream metabolism significantly. Many examples, which we review, show that it has valuable bioactivity. Given the above, we review its potential utility as a nutraceutical, finding it significantly worthy of further study and development.

Laboratory parameters related to disease severity and physical performance after reconvalescence of acute COVID-19 infection

Research into the molecular basis of disease trajectory and Long-COVID is important to get insights toward underlying pathophysiological processes. The objective of this study was to investigate inflammation-mediated changes of metabolism in patients with acute COVID-19 infection and throughout a one-year follow up period. The study enrolled 34 patients with moderate to severe COVID-19 infection admitted to the University Clinic of Innsbruck in early 2020. The dynamics of multiple laboratory parameters (including inflammatory markers [C-reactive protein (CRP), interleukin-6 (IL-6), neopterin] as well as amino acids [tryptophan (Trp), phenylalanine (Phe) and tyrosine (Tyr)], and parameters of iron and vitamin B metabolism) was related to disease severity and patients' physical performance. Also, symptom load during acute illness and at approximately 60 days (FU1), and one year after symptom onset (FU2) were monitored and related with changes of the investigated laboratory parameters: During acute infection many investigated laboratory parameters were elevated (e.g., inflammatory markers, ferritin, kynurenine, phenylalanine) and enhanced tryptophan catabolism and phenylalanine accumulation were found. At FU2 nearly all laboratory markers had declined back to reference ranges. However, kynurenine/tryptophan ratio (Kyn/Trp) and the phenylalanine/tyrosine ratio (Phe/Tyr) were still exceeding the 95th percentile of healthy controls in about two thirds of our cohort at FU2. Lower tryptophan concentrations were associated with B vitamin availability (during acute infection and at FU1), patients with lower vitamin B12 levels at FU1 had a prolonged and more severe impairment of their physical functioning ability. Patients who had fully recovered (ECOG 0) presented with higher concentrations of iron parameters (ferritin, hepcidin, transferrin) and amino acids (phenylalanine, tyrosine) at FU2 compared to patients with restricted ability to work. Persistent symptoms at FU2 were tendentially associated with IFN-γ related parameters. Women were affected by long-term symptoms more frequently. Conclusively, inflammation-mediated biochemical changes appear to be related to symptoms of patients with acute and Long Covid.

Integrative Molecular Structure Elucidation and Construction of an Extended Metabolic Pathway Associated with an Ancient Innate Immune Response in COVID-19 Patients

We present compelling evidence for the existence of an extended innate viperin-dependent pathway, which provides crucial evidence for an adaptive response to viral agents, such as SARS-CoV-2. We show the in vivo biosynthesis of a family of novel endogenous cytosine metabolites with potential antiviral activities. Two-dimensional nuclear magnetic resonance (NMR) spectroscopy revealed a characteristic spin-system motif, indicating the presence of an extended panel of urinary metabolites during the acute viral replication phase. Mass spectrometry additionally enabled the characterization and quantification of the most abundant serum metabolites, showing the potential diagnostic value of the compounds for viral infections. In total, we unveiled ten nucleoside (cytosine- and uracil-based) analogue structures, eight of which were previously unknown in humans allowing us to propose a new extended viperin pathway for the innate production of antiviral compounds. The molecular structures of the nucleoside analogues and their correlation with an array of serum cytokines, including IFN-α2, IFN-γ, and IL-10, suggest an association with the viperin enzyme contributing to an ancient endogenous innate immune defense mechanism against viral infection.