Central and peripheral kynurenine pathway metabolites in COVID-19: Implications for neurological and immunological responses.
Level 4 - case-series / case-control
Case-control observational biomarker study comparing acute COVID-19 patients to non-inflammatory controls.
PubMed 39615604 · doi:10.1016/j.bbi.2024.11.031
What was done
Researchers measured kynurenine pathway metabolites in paired cerebrospinal fluid (CSF) and plasma samples from 53 patients with acute COVID-19 and 12 non-inflammatory neurological disease controls in Sweden using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Metabolite concentrations were correlated with immunological and neurodegenerative markers. Additionally, single-cell transcriptomic data from a separate cohort of 130 COVID-19 patients was analyzed to assess expression of key kynurenine pathway genes, including indoleamine 2,3-dioxygenase 1 (IDO1).
What was found
No exact numeric values, effect sizes, or correlation coefficients were reported in the abstract. Directionally, CSF levels of quinolinic acid (QUIN) and kynurenic acid (KYNA) were increased in patients with acute COVID-19. CSF levels of kynurenine, the kynurenine/tryptophan ratio, and QUIN positively correlated with markers of neurodegeneration. In plasma, tryptophan was significantly decreased (with no significant change in CSF tryptophan), and peripheral pathway activation correlated with neopterin. Single-cell transcriptomics demonstrated upregulated IDO1 expression in CD14+ and CD16+ monocytes that correlated with type II interferon responses.
Why it matters
This study provides initial evidence of elevated neuroactive and neurotoxic kynurenine metabolites in the central nervous system during acute COVID-19. It links peripheral monocyte inflammation to central quinolinic acid elevation and neurodegenerative marker release, suggesting a potential mechanistic pathway for COVID-19-related neurological dysfunction.
Limits
The study is limited by a small sample size (53 cases and 12 controls) from a single geographic setting. The abstract does not provide exact numeric data, effect sizes, or p-values. The cross-sectional and correlational design cannot prove causality. Additionally, single-cell transcriptomics were derived from a separate historical cohort rather than the primary CSF/plasma cohort, and long-term cognitive or neurological clinical outcomes were not directly evaluated.
Cited by
- supports COVID-19 infection is associated with viral brain entry, blood-brain barrier disruption, increased inflammatory cytokines (including IL-1 beta, IL-6, IL-10, and TNF-alpha), NMDA receptor stimulation, and kynurenine pathway activation producing quinolinic acid.