Exploring the role of galectin-9 and artemin as biomarkers in long COVID with chronic fatigue syndrome: links to inflammation and cognitive function

Abstract

This study aimed to assess plasma galectin-9 (Gal-9) and artemin (ARTN) concentrations as potential biomarkers to differentiate individuals with Long COVID (LC) patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) from SARS-CoV-2 recovered (R) and healthy controls (HCs). Receiver operating characteristic (ROC) curve analysis determined a cut-off value of plasma Gal-9 and ARTN to differentiate LC patients from the R group and HCs in two independent cohorts. Positive correlations were observed between elevated plasma Gal-9 levels and inflammatory markers (e.g. SAA and IP-10), as well as sCD14 and I-FABP in LC patients. Gal-9 also exhibited a positive correlation with cognitive failure scores, suggesting its potential role in cognitive impairment in LC patients with ME/CFS. This study highlights plasma Gal-9 and/or ARTN as sensitive screening biomarkers for discriminating LC patients from controls. Notably, the elevation of LPS-binding protein in LC patients, as has been observed in HIV infected individuals, suggests microbial translocation. However, despite elevated Gal-9, we found a significant decline in ARTN levels in the plasma of people living with HIV (PLWH). Our study provides a novel and important role for Gal-9/ARTN in LC pathogenesis.

Keywords: HIV; artemin; chronic fatigue syndrome; galectin-9; long COVID; microbial translocation.

Figure 1

The diagnostic value of galectin-9 (Gal-9) in Long-COVID patients. (A) The receiver operating characteristic (ROC) curve for Gal-9 in LC versus healthy controls (HC) in the discovery cohort. (B) The ROC curve for Gal-9 in LC versus recovered individuals (R) in the discovery cohort. (C) The ROC curve for Gal-9 in LC versus R in the validating cohort. (D) The correlation between plasma Gal-9 and SAA, and (E) IP-10 levels in LC patients of the discovery cohort. (F) The correlation between plasma Gal-9 and SAA, and (G) IP-10 levels in LC patients of the validating cohort.

Figure 2

The correlation of Gal-9 with inflammatory and cognitive impairment in LC patients. (A) The correlation between plasma sCD14 and Gal-9 in the discovery, and (B) validating cohort. (C) The correlation between plasma I-FABP and Gal-9 in the discovery, and (D) validating cohort. (E) Detected concentrations of LPS-binding protein (LPS-BP) in the plasma of LC versus R in both cohorts. (F) The correlation between plasma Gal-9 and cognitive failure score in the discovery, and (G) validating cohort. The symbol **** shows a p value less than 0.0001 or P < 0.0001.

Figure 3

The diagnostic value of artemin (ARTN) in Long-COVID patients. (A) The ROC curve for ARTN in LC versus HCs in the discovery cohort. (B) The ROC curve for ARTN in LC versus the R group in the discovery cohort. (C) The ROC curve for ARTN in LC versus R in the validating cohort. (D) The correlation between plasma Gal-9 and ARTN in LC patients of the discovery, and (E) validating cohort. (F) Detected ARTN levels in plasma samples from HIV-infected individuals, HCs and LC patients of both cohorts. (G) TGF-β levels in plasma samples from HIV-infected individual versus HCs. The symbol **** shows a p value less than 0.0001 or P < 0.0001.

Figure 4

The proposed graphic summary. The gastrointestinal involvement during acute SARS-CoV-2 infection and the possible persistence of viral antigen/replication beyond the acute phase result in compromised gut barrier integrity. This, subsequently, leads to the translocation of microbial by-products (e.g. LPS) into the blood circulation. This leads to the activation of innate immune cells and the release of variety of pro-inflammatory cytokines and chemokines. This inflammatory cascade may result in immune/non-immune cell apoptosis and the release of damage-associated molecular patterns (e.g. Gal-9). Gal-9 may influence the activation/deactivation of different immune cells and ultimately may directly/indirectly influence the effector functions of microglia and astrocytes.