The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has significantly impacted the world and has driven many researchers into the pathophysiology of COVID-19. In the findings, there is a close association between purinergic signaling and the immune response. Then, this study aimed to evaluate alterations in the purinergic signaling in COVID-19 patients according to range severity. We divided the COVID-19 patients into moderate and severe cases following the guideless of NIH and WHO, together with clinical characteristics. The blood samples were collected to obtain PBMCs and platelets. We analyzed the ectonucleotidase activities through ATP, ADP, AMP, Ado hydrolysis, E-NTPDase1 (CD39), and 5'-NT (CD73) expression by flow cytometry in total leukocytes. The extracellular ATP was measured by bioluminescence, and cytokines were analyzed by flow cytometry. We observed a decrease in ATP hydrolysis and increased AMP hydrolysis in PBMCs for both groups. In severe cases, ATP hydrolysis was raised for the platelets, while ADP and AMP hydrolysis have risen significantly in both groups. Additionally, there was a significant increase in ADP hydrolysis in severe cases compared to moderate cases. In addition, we observed an increase in the ADA activity in platelets of moderate patients. Moderate and severe cases showed increased expression of CD39 and CD73 in total leukocytes. To finalize the purinergic signaling, extracellular ATP was increased in both groups. Furthermore, there was an increase in IL-2, IL-6, IL-10, and IL-17 in moderate and severe groups. Thus, for the first time, our findings confirm the changes in purinergic signaling and immune response in COVID-19, in addition to making it more evident that the severity range directly impacts these changes. Therefore, the therapeutic potential of the purinergic system must be highlighted and studied as a possible target for the treatment of SARS-CoV-2 disease. KEY MESSAGES: COVID-19 patients exhibit alterations in purinergic system and immune response. High levels of extracellular ATP lead to different inflammatory responses. CD39 and CD73 expression were increased in COVID-19 patients. Cytokines IL-2, IL-6, IL-10, and IL-17 also were altered in these patients. The purinergic system may be a possibility target to SARS-CoV-2 treatments. 

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High levels of extracellular ATP lead to different inflammatory responses in COVID-19 patients according to the severity

Purinergic signaling modulates immune function and is involved in the immunopathogenesis of several viral infections. This study aimed to investigate alterations in purinergic pathways in coronavirus disease 2019 (COVID-19) patients. Mild and severe COVID-19 patients had lower extracellular adenosine triphosphate and adenosine levels, and higher cytokines than healthy controls. Mild COVID-19 patients presented lower frequencies of CD4+ CD25+ CD39+ (activated/memory regulatory T cell [mTreg]) and increased frequencies of high-differentiated (CD27- CD28- ) CD8+ T cells compared with healthy controls. Severe COVID-19 patients also showed higher frequencies of CD4+ CD39+ , CD4+ CD25- CD39+ (memory T effector cell), and high-differentiated CD8+ T cells (CD27- CD28- ), and diminished frequencies of CD4+ CD73+ , CD4+ CD25+ CD39+ mTreg cell, CD8+ CD73+ , and low-differentiated CD8+ T cells (CD27+ CD28+ ) in the blood in relation to mild COVID-19 patients and controls. Moreover, severe COVID-19 patients presented higher expression of PD-1 on low-differentiated CD8+ T cells. Both severe and mild COVID-19 patients presented higher frequencies of CD4+ Annexin-V+ and CD8+ Annexin-V+ T cells, indicating increased T-cell apoptosis. Plasma samples collected from severe COVID-19 patients were able to decrease the expression of CD73 on CD4+ and CD8+ T cells of a healthy donor. Interestingly, the in vitro incubation of peripheral blood mononuclear cell from severe COVID-19 patients with adenosine reduced the nuclear factor-κB activation in T cells and monocytes. Together, these data add new knowledge to the COVID-19 immunopathology through purinergic regulation. 

Alterations in CD39/CD73 axis of T cells associated with COVID‐19 severity

People with cystic fibrosis should be considered at increased risk of developing severe symptoms of COVID-19. Strikingly, a broad array of evidence shows reduced spread of SARS-CoV-2 in these subjects, suggesting a potential role for CFTR in the regulation of SARS-CoV-2 infection/replication. Here, we analyzed SARS-CoV-2 replication in wild-type and CFTR-modified human bronchial epithelial cell lines and primary cells to investigate SARS-CoV-2 infection in people with cystic fibrosis. Both immortalized and primary human bronchial epithelial cells expressing wt or F508del-CFTR along with CRISPR/Cas9 CFTR-ablated clones were infected with SARS-CoV-2 and samples were harvested before and from 24 to 72 h post-infection. CFTR function was also inhibited in wt-CFTR cells with the CFTR-specific inhibitor IOWH-032 and partially restored in F508del-CFTR cells with a combination of CFTR modulators (VX-661+VX-445). Viral load was evaluated by real-time RT-PCR in both supernatant and cell extracts, and ACE-2 expression was analyzed by both western blotting and flow cytometry. SARS-CoV-2 replication was reduced in CFTR-modified bronchial cells compared with wild-type cell lines. No major difference in ACE-2 expression was detected before infection between wild-type and CFTR-modified cells, while a higher expression in wild-type compared to CFTR-modified cells was detectable at 72 h post-infection. Furthermore, inhibition of CFTR channel function elicited significant inhibition of viral replication in cells with wt-CFTR, and correction of CFTR function in F508del-CFTR cells increased the release of SARS-CoV-2 viral particles. Our study provides evidence that CFTR expression/function is involved in the regulation of SARS-CoV-2 replication, thus providing novel insights into the role of CFTR in SARS-CoV-2 infection and the development of therapeutic strategies for COVID-19.

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CFTR Modulation Reduces SARS-CoV-2 Infection in Human Bronchial Epithelial Cells

The Impact of COVID-19 in Cystic Fibrosis

This case report demonstrates a small repetition of the case series carried out in Italy wherein inhaled adenosine was administered to patients experiencing severe and worsening coronavirus disease-2019 (COVID-19). The two cases are important not only because they were the first of their type in the United States, but also because both patients were DNR/DNI and were therefore expected to die. Study repetition is vitally important in medicine. New work in pharmacology hypothesizes that adenosine-regulator proteins may play a role in the pathogenesis of COVID-19 infection. Furthermore, adenosine, by interacting with cell receptor sites, has pluripotent effects upon inflammatory cells, is anti-inflammatory, and is important in tissue hypoxia signaling. Inhaled adenosine is potentially safe; thousands have received it for asthmatic challenge testing. The effects of adenosine in these two cases were rapid, positive, and fit the pharmacologic hypotheses (as seen in prior work in this journal) and support its role as a therapeutic nucleoside.

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Case Report: Can Inhaled Adenosine Attenuate COVID-19?

Systemic pools of ATP are elevated in individuals homozygous for cystic fibrosis (CF) as evidenced by elevated blood and plasma ATP levels. This elevated ATP level seems to provide benefit in the presence of advanced solid tumors (Abraham et al., Nature Medicine 2(5):593-596, 1996). We published in this journal a paper showing that IV ATP can elevate the depleted ATP pools of advanced cancer patients up to levels found in CF patients with subsequent clinical, biochemical, and quality of life (QOL) improvements (Rapaport et al., Purinergic Signalling 11(2): 251-262, 2015). We hypothesize that the elevated ATP levels seen in CF patients may be benefiting CF patients in another way: by improving their survival after contracting COVID-19. We discuss here the reasoning behind this hypothesis and suggest how these findings might be applied clinically in the general population.

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Kent Robinson

Papers

Cystic fibrosis improves COVID-19 survival and provides clues for treatment of SARS-CoV-2.