key: cord-289574-engwi8h3
authors: An, Peng-jiao; Yi, Zhun Zhu; Yang, Li-ping
title: Biochemical indicators of coronavirus disease 2019 exacerbation and the clinical implications
date: 2020-05-23
journal: Pharmacol Res
DOI: 10.1016/j.phrs.2020.104946
sha: 
doc_id: 289574
cord_uid: engwi8h3

Coronavirus Disease 2019 (COVID-19) has sparked a global pandemic, affecting more than 4 million people worldwide. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause acute lung injury (ALI) and even acute respiratory distress syndrome (ARDS); with a fatality of 7.0 %. Accumulating evidence suggested that the progression of COVID-19 is associated with lymphopenia and excessive inflammation, and a subset of severe cases might exhibit cytokine storm triggered by secondary hemophagocytic lymphohistiocytosis (sHLH). Furthermore, secondary bacterial infection may contribute to the exacerbation of COVID-19. We recommend using both IL-10 and IL-6 as the indicators of cytokine storm, and monitoring the elevation of procalcitonin (PCT) as an alert for initiating antibacterial agents. Understanding the dynamic progression of SARS-CoV-2 infection is crucial to determine an effective treatment strategy to reduce the rising mortality of this global pandemic.

(GF) and chemokines. Cytokines participate in immune responses through the activation of multiple signaling pathways, such as JAK-STAT, TRAF-NF-κB, TRAF-AP-1, and IRAK-NF-κB [32] . The term "cytokine storm" appeared for the first time in an article relating to graft-versus-host disease in 1993 [52] as an interpretation for mechanisms of immune diseases or chronic inflammation.

Gradually, scientists found that viruses, including cytomegalovirus, streptococci, influenza virus, and SARS-CoV, can also evoke cytokine storms [53] [54] [55] [56] . During viral infection, PRRs activate IRF and NF-κB pathways by recognizing PAMP, then promote the release of pro-inflammatory cytokines and chemokines from infected local epithelial cells or macrophages. These cytokineactivated macrophages and virus-infected dendritic cells (DC) lead to a broader immune response, attracting more inflammatory cells to inflammatory sites, releasing a large number of cytokines, which eventually, results in a cytokine storm. Excessive cytokines may spill into the circulatory system and cause systemic cytokine storms, resulting in multiple organ dysfunction [7, 57] .

Previously, it has been found that the serum levels of pro-inflammatory cytokines [IFN-γ, IL-1, IL-6, IL-12, and transforming growth factor-β (TGF-β)], and chemokines (CCL2, CXCL9, CXCL10, and IL-8) in SARS-CoV infected patients were higher than those in healthy individuals.

While the level of anti-inflammatory cytokine IL-10 in severe patients was significantly lower than that in healthy controls [58] [59] [60] . At the beginning of the epidemic, Huang et al reported that the plasma levels of IL2, IL7, GSCF, CXCL10, MCP1, MIP1A, and TNF-α were higher in COVID-19 patients in the intensive care unit (ICU) than those of COVID-19 patients outside the ICU [61] . Furthermore, the relatively higher level of serum ferritin was also seen in deceased patients comparing with discharged patients, and in severe patients comparing with mild patients [62, 63] .

Thus, the pattern of cytokine storm in COVID-19 patients was thought to be similar to secondary hemophagocytic lymphohistiocytosis (sHLH) [64] [65] [66] . Unlike the cytokines profile of SARS patients, COVID-19 patients have a remarkable increase of anti-inflammatory cytokines IL-10 (Table 1) , which has been often seen in HLH patients in previous studies [61, 67, 68] . Compared with other increased cytokines, increased IL-10 was frequently associated with IL-6 in patients with severe disease (Table 1) , and subsets of activated T cells, as well as by non-immune cells like fibroblasts, epithelial cells, and keratinocytes [74] [75] [76] [77] . It can activate JAK/STAT, Ras/ERK/C/EBP, and PⅠ3K/Akt pathways through IL-6R and signal-transducing coreceptor gp130 [78, 79] . IL-6 also regulates B cell proliferation and differentiation and induces T cell differentiation [80] [81] [82] . Although IL-6 has been proposed to be involved in the repair of lung injury in the mouse model of influenza A H1N1 virus [83] , it contributes to the pathogenesis of inflammatory or autoimmunity diseases [84, 85] , and excessive production of IL-6 leads to serious disease progression in viral infection [86, 87] .

IL-10 is also a pleiotropic cytokine that limits and terminates inflammatory responses through inhibiting antigen-presenting cells (APC), pro-inflammatory cytokines production, and T cell response [88] . Various subpopulations of CD4 + helper T (Th) cells, including Th1, Th2, and Th17, produce IL-10, as an important self-regulatory function of Th cells during infections [89] [90] [91] [92] .

Although reducing IL-10 levels could improve the resistance to infection in some animal models, the weakening control of inflammatory responses may cause significant damage to the hosts at the same time [93] . Thus, IL-10 plays a central role in maintaining a balance between damage and protection.

and Th17 cells produce IL-10 that regulates the immune response [94] [95] [96] [97] [98] . (Figure 1 ). The similarity in the signaling network between IL-10 receptors and IL-6R suggests the common biological process among IL-10 and IL-6 [99] . It has been reported that IL-6 cooperated with IL-10 to eliminate pathogens and modulate the cellular immune response in the patient infected with the H1N1 influenza virus, but the produced immunosuppressive environment delayed virus clearance or increase secondary infection [86, 100] . Pathological findings of a deceased COVID-19 patient showed elevated IL-6 and IL-10 with increased highly proinflammatory CCR4 + CCR6 + Th17 in peripheral CD4 + T cells [101] . Rapid accumulation of proinflammatory cytokines stimulates the over-reaction of anti-inflammatory response, resulting in severe immune injury in patients. Chinese

suggests the increase of IL-6 as an indicator for critical patients [16] . We recommend measuring both IL-10 and IL-6 as the signs of the cytokine storm intensification in COVID-19 patients.

Great attention has been paid to the cytokine storm in COVID-19 infection to address the J o u r n a l P r e -p r o o f immediate need for reducing the rising mortality. Anti-inflammatory medications are commonly used for the management of cytokine storm, which includes GCs, intravenous immune globulin (IVIG), and inflammatory cytokines antagonists (such as IL-1R antagonists, IL-6R antagonists, and JAK inhibitors). However, GCs may slow down the clearance of the coronavirus [102] . High-dose IVIG at the early stage of clinical deterioration was reported to be successful in three cases [103] , and an ongoing randomized controlled trial (RCT) of IVIG in severe COVID-19 patients (NCT04261426) may provide more authoritative evidence of this treatment.

Since IL-1β and IL-6 are the major cytokines involved in the pathogenesis of sHLH [65] , the IL-6R antagonist (tocilizumab and sarilumab) and IL-1R antagonists (anakinra) may be effective choices. A retrospective study of continuous intravenous infusion of anakinra in five patients established a rapid serologic and subsequent clinical improvement in adult patients with sHLH [104] and a randomized, placebo-controlled phase III trial indicated that anakinra reduced mortality in sepsis patients with features of sHLH [105] . Tocilizumab, which attracts more attention compared with anakinra, was found to improve fever, hypoxemia, lung lesions, and CRP levels in most of the severe COVID-19 patients with no obvious adverse reactions in retrospective studies, but several patients still aggravated [106, 107] . Serum level of IL-6 after tocilizumab therapy tended to further spike initially, and then decrease, while the patients who failed treatment exhibited a persistent and dramatic increase of IL-6 [107, 108] . Nevertheless, we cannot draw any firm conclusions on the efficacy and safety of anakinra or tocilizumab due to the limited sample size and retrospective method of the present evidence. Further studies are required to determine the probability of potential secondary infection, and to find an appropriate biochemical indicator for monitoring the therapeutic effect. Clinical trials evaluating anakinra (NCT04341584, NCT04324021, NCT04339712, and NCT04330638) and tocilizumab (ChiCTR2000029765, ChiCTR2000030796, ChiCTR2000030894, NCT04317092, NCT04335071, and NCT04320615 et al) in the treatment of COVID-19 are ongoing across the world.

Secondary bacterial infection has been found to further exacerbate viral pneumonia, which is also related to the imbalance of T cells and plasma cytokines [109] . Bacterial coinfection is known to be associated with approximately 40% of viral respiratory tract infections requiring J o u r n a l P r e -p r o o f hospitalization [110] . Early detection of bacterial infection and timely intervention will help to alleviate the deterioration of COVID-19. Procalcitonin (PCT), released by bacterial infectious tissues under the irritation of pro-inflammatory cytokines, is a more specific marker of serious bacterial infection compared to C-reactive protein (CRP) and IL-6 [111] PCT-based strategy has been applied to guide antibiotic use in ICU or emergency wards, since the serum PCT levels in patients with severe bacterial infections are much higher than those with simple viral infections or non-specific inflammatory diseases [111] [112] [113] . Antimicrobial interventions are encouraged in patients with lower respiratory tract infection who has the value of PCT > 0.25ng/ml or > 0.5ng/ml, for they are likely or highly-likely respectively, to undergo a bacterial infection [113, 114] .

Multiple studies have shown that PCT levels increased in critical or deceased COVID-19

patients. ( Table 2 ) Li et al [115] reported that 90.5% of deceased patients had elevated PCT levels (0.11-75ng/ml), including PCT > 0.25 ng/ml in 12 patients and PCT > 0.5ng/ml in 9 patients, and the PCT value increased from the admission to death. In another retrospective study of 1,099 COVID-19 patients, higher proportions of PCT > 0.5ng/ml were found in severe cases than mild cases (13.7% vs 3.7%) [8] . Patients who reached primary composite endpoint (including admission to an ICU, the use of mechanical ventilation, or death) had a higher proportion of PCT > 0.5ng/ml than patients without end-point events (24.0% vs 3.9%) [8] . The correlation between increased PCT and severe COVID-19 was also observed in pediatric patients [116] . These findings, although might be a better option. Previous studies have shown that in addition to antibacterial effects, these drugs can also alleviate inflammatory reactions by reducing the accumulation of pro-inflammatory cytokines and regulating neutrophil function and apoptosis [117] [118] [119] [120] . including mean ± SD, median (IQR), and median (mix-max). c PCT value≥0.05. d P-value of the comparison between the PCT value of two groups. e P-value of the comparison between the proportion of the patients with increased PCT value in two groups. The tests with a P-value of <0.05 are considered statistically significant.

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