As clinical evidence mounts that the leading cause of death in COVID-19 patients is the dangerous condition known as a cytokine storm, University of Alberta researchers have identified a protein in the blood that could be responsible.
The team found that COVID-19 patients have significantly elevated levels of a protein called galectin-9 in their blood plasma. Perhaps more importantly, they also found a positive correlation between the levels of galectin-9 and pro-inflammatory cytokines released in the blood, which can lead to a cytokine storm.
The research was led by Shokrollah Elahi, associate professor in the School of Dentistry’s Division of Foundational Sciences.
Expanding on his prior work with HIV, AIDS and cancer patients, Elahi and his team analyzed the blood plasma of 120 patients with COVID-19. They found that levels of galectin-9 were substantially higher in those patients than in individuals with HIV and cancer.
“We have reported in the past that galectin-9 levels go up in HIV infection and with some cancers,” said Elahi, who is also a member of the Women and Children’s Health Research Institute and Cancer Research Institute of Northern Alberta.
“However, when we compared the levels of galectin-9 in the COVID-19 patients to HIV and cancer patients, we could easily distinguish the COVID patients based on the galectin-9 levels.”
The findings suggest that galectin-9 levels in the body could be used as a biomarker to diagnose COVID-19 using a patient’s blood, potentially providing another non-invasive tool for COVID-19 testing. The levels could also be used to indicate the severity of the disease, though further study on that aspect is required, Elahi said.
Eye of the storm
The discovery of elevated galectin-9 levels in COVID-19 patients is important because of the positive correlation between the protein and a wide range of pro-inflammatory cytokines.
“Cytokines as small cell-signaling proteins are involved in checks and balances in the immune system; they can turn on or turn off some cells to regulate the immune system,” said Elahi.
“In the context of COVID, the problem is that there is a dysregulation of cytokine production—they are released very quickly in elevated levels. That’s what we call a ‘cytokine storm.'”
Elahi found that galectin-9 is responsible for instructing immune cells to release the pro-inflammatory cytokines quickly in response to COVID-19 infection by binding to immune cells and forcing them to produce the cytokines. Further, as tissues are damaged as a result of inflammation, more galectin-9 is released from the cells—which activates more immune cells and releases more cytokines in a vicious cycle.
The resulting cytokine storm damages tissue and organs, causes severe inflammation and can lead to death, Elahi said. Even if patients survive the storm, the dysregulation of the immune system can have ongoing consequences and could be associated with the condition known as post-COVID-19 syndrome or long COVID.
The next step is to develop treatments that block or inhibit the protein, Elahi said. While there are compounds available that could potentially be used, such as lactose or anti-galectin-9 antibodies, currently there are no treatments on the market specifically for blocking galectin-9 in humans.
“We are now looking at expanding our study to a larger cohort of patients, and then working on a proof of concept in animal models,” Elahi said. “What is killing COVID patients is not the virus; it’s the cytokine storm. Therefore, if we can reduce the cytokine storm damage by inhibiting galectin-9, then we can reduce complications, reduce hospitalizations and prevent mortality.”
The work was shared in a study published in the American Society for Microbiology journal, mBio.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1] caused a pandemic of coronavirus disease 2019 (COVID-19) with more than 125 million cases and more than 2.75 million deaths as of the end of March 2021. Severity is highly variable, ranging from asymptomatic infections, mild cold symptoms, severe pneumonia to respiratory failure requiring mechanical ventilation and death from multiple organ failure [2].
Risk factors for aggravation have been clarified including older age, smoking, obesity, and pre-existing conditions such as hypertension, diabetes mellitus, cardiovascular diseases, chronic lung diseases, cancer, and chronic kidney disease [3].
However, even if the patients have mild symptoms at their initial visit to the clinic, they may suddenly develop fatal acute respiratory syndrome and/or multiple organ failure over the course of the illness [4]. Biomarkers are strongly desired that can predict the final severity of COVID-19 in the early stages of SARS-CoV-2 infection.
Acute respiratory syndrome is caused or accompanied by cytokine storm [5], where high levels of cytokines and proinflammatory molecules are present in the plasma. These molecules are thought to cause tissue injury, especially in the lungs [6].
The monitoring of cytokines including interleukin-6 (IL-6), IL-10, and tumor necrosis factor-α was recommended for the early detection of severe disease in patients [7]. Levels of IL-6 correlated with COVID-19 severity and IL-6 has a key role in cytokine storm and the inflammatory cascade [6,8].
Signaling inhibitors of IL-6 are candidate drugs for cytokine storm and tocilizumab (TCZ), a humanized monoclonal antibody that recognizes membrane-bound and soluble IL-6 receptors, which might be useful to treat COVID-19 pneumonia. A previous study of TCZ administration showed a significant clinical improvement in COVID-19 patients with pneumonia requiring a ventilator [9,10].
However, clinical improvement and mortality were not improved by TCZ therapy [11], and ICU admission and mortality rates were not reduced [12,13]. It should be noted that TCZ therapy is associated with severe infections [14], and a possible correlation between TCZ therapy and medication-related osteonecrosis of the jaws was indicated [15].
Detailed immunological analyses of COVID-19 patients showed significant increases in proinflammatory or anti-inflammatory cytokines, including T helper type-1 and type-2 cytokines, chemokines, and galectins. Galectin (Gal)-1, Gal-3, and Gal-9 were increased in patients compared with controls [16,17].
In addition, high plasma levels of granulocyte macrophage colony stimulating factor, IL-18, C-C motif chemokine 2, C-X-C motif chemokine ligand 10, and osteopontin (OPN) confirmed the importance of monocytes in pneumonia associated with COVID-19 [18]. Gal-9 and OPN are matricellular proteins that interact with cellular receptors and proteases [19,20]. The full-length Gal-9 (FL-Gal9) is the active form and the cleavage by proteases degrades the activity [21,22], while the cleaved form of OPN demonstrates distinct immunological properties compared with the FL-OPN [23].
We reported that FL-Gal9 was elevated in the plasma of patients with acute HIV [24], dengue [25], or malaria [26] and that their levels reflected disease severity. Furthermore, the FL and cleaved forms of OPN were elevated in the plasma of dengue patients [27]. Gal-9 is cleaved by neutrophil elastase, matrix metalloproteinase (MMP)-3 [28], and thrombin [29], and OPN is cleaved by thrombin, MMP-3, MMP-7, and MMP-9 [30,31].
Thrombin is involved in COVID-19-associated coagulopathy and is highly expressed in inflamed lesions and sites of tissue remodeling [32,33]. These enzymes might cleave Gal-9 and/or OPN in inflamed tissues; therefore, we measured their FL and cleaved forms to provide in-depth pathophysiological information on COVID-19 patients. We previously reported that analysis by enzyme-linked immunosorbent assay (ELISA) differentiated between the levels of the cleaved form of OPN (undefined (Ud)-OPN) and FL-OPN [27].
Recently, we established the ELISA system which can differentiate the truncated form of Gal-9 (Tr-Gal9) and FL-Gal9 [34], and reported that plasma levels of Tr-Gal9 reflected inflammation and the severity of disease in acquired immunodeficiency syndrome (AIDS) and AIDS associated with tuberculosis (AIDS/TB) patients [35].
As a systemic inflammatory marker, C-reactive protein (CRP) was associated with disease development and showed good performance in predicting severity in an early stage of COVID-19 [36]. CRP is known to be synthesized by IL-6-dependent and -independent pathways [37]. Cytokine, soluble interleukin-2 receptor α (sIL-2R), also known as CD25, released mainly from lymphocytes and monocytes, appears to play a role in the biology of COVID-19 and reflects its severity [38,39].
Patients with COVID-19 with markedly elevated d-dimer levels may require hospitalization, despite the severity of clinical presentation, according to the International Society of Thrombosis and Hemostasis guideline [40]. The elevations of d-dimer and ferritin, another inflammatory coagulation marker, were also known to be associated with poor outcome of the patients [41].
It is known that kidney diseases are associated with COVID-19 infection and creatinine levels are elevated in these patients [42]. Patients with elevated urinary β2-microglobulin (B2M) and creatinine levels showed lower rates of discharge [43].
In this study, we measured the levels of FL-OPN, FL-Gal9, and their truncated forms in COVID-19 patients and investigated the correlation with the above clinically commonly used indicators of inflammation, renal function, and abnormal coagulation. We also determined whether they reflect clinical severity and the therapeutic efficacy of TCZ in COVID-19 patients.
reference link : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8125627/
More information: Najmeh Bozorgmehr et al, Galectin-9, a Player in Cytokine Release Syndrome and a Surrogate Diagnostic Biomarker in SARS-CoV-2 Infection, mBio (2021). DOI: 10.1128/mBio.00384-21
