key: cord-0723095-fv5oykjx
authors: Soria‐Castro, Rodolfo; Meneses‐Preza, Yatsiri G.; Rodríguez‐López, Gloria M.; Romero‐Ramírez, Sandra; Sosa‐Hernández, Víctor A.; Cervantes‐Díaz, Rodrigo; Pérez‐Fragoso, Alfredo; Torres‐Ruíz, José J.; Gómez‐Martín, Diana; Campillo‐Navarro, Marcia; Álvarez‐Jiménez, Violeta D.; Pérez‐Tapia, Sonia M.; Chávez‐Blanco, Alma D.; Estrada‐Parra, Sergio; Maravillas‐Montero, José L.; Chacón‐Salinas, Rommel
title: Severe COVID‐19 is marked by dysregulated serum levels of carboxypeptidase A3 and serotonin
date: 2021-05-31
journal: J Leukoc Biol
DOI: 10.1002/jlb.4hi0221-087r
sha: ccaedbbc375dcded43bb0740029b0bfe424e54b0
doc_id: 723095
cord_uid: fv5oykjx

The immune response plays a critical role in the pathophysiology of SARS‐CoV‐2 infection ranging from protection to tissue damage and all occur in the development of acute respiratory distress syndrome (ARDS). ARDS patients display elevated levels of inflammatory cytokines and innate immune cells, and T and B cell lymphocytes have been implicated in this dysregulated immune response. Mast cells are abundant resident cells of the respiratory tract and are able to release different inflammatory mediators rapidly following stimulation. Recently, mast cells have been associated with tissue damage during viral infections, but their role in SARS‐CoV‐2 infection remains unclear. In this study, we examined the profile of mast cell activation markers in the serum of COVID‐19 patients. We noticed that SARS‐CoV‐2‐infected patients showed increased carboxypeptidase A3 (CPA3) and decreased serotonin levels in their serum when compared with symptomatic SARS‐CoV‐2‐negative patients. CPA3 levels correlated with C‐reactive protein, the number of circulating neutrophils, and quick SOFA. CPA3 in serum was a good biomarker for identifying severe COVID‐19 patients, whereas serotonin was a good predictor of SARS‐CoV‐2 infection. In summary, our results show that serum CPA3 and serotonin levels are relevant biomarkers during SARS‐CoV‐2 infection. This suggests that mast cells and basophils are relevant players in the inflammatory response in COVID‐19 and may represent targets for therapeutic intervention.

serum was a good biomarker for identifying severe COVID-19 patients, whereas serotonin was a good predictor of SARS-CoV-2 infection. In summary, our results show that serum CPA3 and serotonin levels are relevant biomarkers during SARS-CoV-2 infection. This suggests that mast cells and basophils are relevant players in the inflammatory response in COVID-19 and may represent targets for therapeutic intervention. 

Patients with COVID-19 and a control group were enrolled at Insti- 

To identify potential organ or tissue sources of CPA3, protein and mRNA expression were analyzed in Human Protein Atlas (www.

proteinatlas.org/ENSG00000163751-CPA3/tissue) and mRNA expression was obtained from HPA RNA-sEquation (www.ncbi.nlm.

nih.gov/gene/1359#gene-expression). (Fig. 1A) . Interestingly, serotonin showed decreased levels in sera from SARS-CoV-2-infected patients compared with those not infected (Fig. 1B) . Serum levels of histamine, heparin, and nitric oxide were not affected in COVID-19

patients (Supplemental Fig. 1 ).

Previous reports indicate that different immune markers are differentially expressed during severe COVID-19. 15 Therefore, we investigated whether MC-derived biomarkers were altered depending on COVID-19 severity. We observed that patients with severe disease showed increased levels of CPA3 when compared with those with mild/moderate disease, or individuals in the control group (Fig. 1C) .

Serotonin levels were decreased in severe COVID-19 (Fig. 1D ) Remarkably, CPA3 also associated with the disease severity score quick Sepsis-related Organ Failure Assesment (qSOFA), (r = 0.335, P = 0.00862) (Fig. 2C) .

Finally, to evaluate the potential clinical utility of serotonin and CPA3, ROC curves were performed to distinguish SARS-CoV-2 infection. Serotonin showed an acceptable AUC (area under the curve) values that allow to distinguish between SARS-CoV-2 infected from noninfected individuals (AUC 0.77) (Fig. 2E) . When ROC curves were analyzed to differentiate between mild/moderate and severe COVID-19

patients, CPA3 (AUC 0.77) was more reliable than serotonin (AUC 0.58) or IL-6 (AUC 0.56) to detect patients with severe disease. This was close to the predictive values seen for C-reactive protein (AUC 0.93) (Fig. 2F) . As a whole, these results suggest a relationship between MC activation, as reflected by CPA3 levels in serum, and severe COVID-19.

To the best of our knowledge, this is the first evidence of alteration in serum CPA3 levels during COVID-19. The source of this CPA3 in serum is unknown; however, CPA3 is abundantly expressed in different Fig. 3) .

Remarkably, MC granules contain other abundant proteases, such as chymase and tryptase, which are relevant in clinical pathologies such as hemorrhagic dengue 18 and mastocytosis. 19 Further work is needed to ascertain whether other MC proteases are modified during COVID-19.

Interestingly, a second potential cellular source of CPA3 are basophils, which are found in blood and migrate to inflamed tissues. 20 CPA3

is an enzyme that cleaves C-terminal amino acid residues from proteins and is an abundant protein in MC granules (16 μg CPA3 per 10 6 MC). This enzyme is released after cell degranulation and is associated with allergic pathologies of the respiratory tract. 21 Identified substrates for CPA3 include neurotensin, kinetensin, neuromedin N, angiotensin I, and endothelin-1, which is associated with pulmonary fibrosis, 22 a sequela observed in COVID-19 patients. 23 Interestingly, we noticed that CPA3 correlated with clinical parameters associated with systemic inflammation during COVID-19. Remarkably, CPA3 correlated with circulating neutrophils and CPR, which are associated with an exacerbated inflammatory response during COVID-19 15 ; however, CPA3 potential as a disease severity biomarker needs to be further analyzed in larger prospective cohorts. Previous studies have noticed the importance of MC activation for the recruitment of neutrophils to sites of infection. 24 Furthermore, this increase in tissue neutrophil is proposed to be one mechanism of tissue damage and organ failure during COVID-19. 25 Our results are in agreement with a recent histologic study, where an increased number of MC in the lungs of COVID-19 patients was observed. 26 These results suggest an important role of MC and basophils in SARS-CoV-2 infection, but further work is needed to understand the mechanisms involved.

The second marker that was modified during SARS-CoV-2 infection was serotonin. Traditionally serotonin is considered as an important neurotransmitter regulating several neuronal activities in the central nervous system. However, recent evidence indicates that systemic serotonin distributed by the blood plays a more complex function in the organism. Blood serotonin is produced by different cell lineages, including MC, but is mainly produced by enterochromaffin cells of the intestine. Once in the blood, serotonin levels are primarily regulated by platelets that capture and store in dense granules that are secreted after cell activation. 27 Previous studies have shown that infections can decrease, increase, or maintain serotonin levels in blood. 28 showed that SERT is not modified in platelets from COVID-19 patients. adaptive immune response. 27 Activation of serotonin receptor 5-H2TA diminishes inflammation induced by TNF-α. 34 Furthermore, serotonin decreases IL-6 and TNF-α production by macrophages and lymphocytes, 35 

The authors declare no conflicts of interest. The data supporting the conclusions of this article will be made available by the authors upon reasonable request.

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Severe COVID-19 is marked by dysregulated serum levels of carboxypeptidase A3 and serotonin