key: cord-0993074-jxinh4rx authors: Mahmud-Al-Rafat, Abdullah; Muzammal Haque Asim, Md.; Taylor-Robinson, Andrew W.; Majumder, Apurba; Muktadir, Abdul; Muktadir, Hasneen; Karim, Mahbubul; Khan, Imran; Mainul Ahasan, Mohammad; Morsaline Billah, Md. title: A combinational approach to restore cytokine balance and to inhibit virus growth may promote patient recovery in severe COVID-19 cases date: 2020-08-15 journal: Cytokine DOI: 10.1016/j.cyto.2020.155228 sha: ce1af0feb794f721cd9b2c99b7e293d290332eda doc_id: 993074 cord_uid: jxinh4rx The COVID-19 pandemic has led to twin public health and economic crises around the world. Not only has it cost hundreds of thousands of lives but also severely impacted livelihoods and placed enormous strain on community healthcare and welfare services. In this review, we explore the events associated with SARS-CoV-2 pathogenesis and host immunopathological reactivity due to the clinical manifestations of this coronavirus infection. We discuss that the metallopeptidase enzyme ADAM17, also known as tumor necrosis factor-α-converting enzyme, TACE, is responsible for shedding of angiotensin-converting enzyme 2 and membrane-bound interleukin (IL)-6 receptor. This leads to elevated pro-inflammatory responses that result in cytokine storm syndrome. We argue that cytokine balance may be restored by recovering an IL-6 trans-signaling neutralizing buffer system through the mediation of recombinant soluble glycoprotein 130 and recombinant ADAM17/TACE prodomain inhibitor. This cytokine restoration, possibly combined with inhibition of SARS-CoV-2 entry as well as replication and coagulopathy, could be introduced as a novel approach to treat patients with severe COVID-19. In cases of co-morbidity, therapies related to the management of associated disease conditions could ameliorate those clinical manifestations. We consider that a combined approach should be evaluated in which antiviral and immune 67 modulatory drugs or inhibitors may show better prospects for reducing cytokine storm severity. 68 Interleukin (IL)-6 is an inflammatory cytokine that has been demonstrated to play a leading role 69 in cytokine storm syndrome. Studies have shown that an imbalance in molar concentrations of IL-70 6, membrane-bound IL-6 receptor (IL-6R) and its soluble form (sIL-6R) can lead to up-regulation 71 of IL-6-mediated trans-signaling, thereby initiating formation of a cytokine storm [9] . Together 72 with sIL-6R, a soluble form of glycoprotein 130 (sgp130) constitutes an IL-6 neutralizing buffer 73 system [10] . ADAM Metallopeptidase Domain 17 (ADAM17), also known as tumor necrosis 74 factor-α converting enzyme (TACE), is a membrane-bound enzyme that cleaves IL-6R to produce 75 sIL-6R and which is responsible for disrupting fine tuning of the neutralizing buffer system [11] . 76 In order to develop an effective therapeutic strategy for COVID-19 new investigations should 77 consider approaches that can provide control over both viral replication and cytokine imbalance. 78 We have analyzed the different factors involved in these complex clinical manifestations as an 79 interactive model. In light of the insights gained we propose that if administered along with 80 antivirals a combination of ADAM17/TACE prodomain inhibitor (TPD), sgp130Fc protein (a 81 recombinant form of sgp130) and anti-coagulant may produce enhanced outcomes in COVID-19 82 patient recovery. 83 Explaining cytokine storm and associated complications in COVID-19: 84 Acute respiratory distress syndrome (ARDS) is identified as the cause of death in COVID-19 cases 85 [12]. Typical manifestations of ARDS include inflammation, barrier disruption, airspace edema, 86 cell injury and cell death [13] . In COVID-19 patients, all these events are consequences of 87 hyperinflammation induced by cytokine storm in which IL-6 plays a major role [14, 15] . 88 Uncontrolled production of pro-inflammatory cytokines (principally IFN-α, IFN-γ, TNF-α, IL-1β, 89 IL-6, IL-2, IL-12 and TGF-β) is a commonly reported feature of cytokine storm syndromes in 90 severe COVID-19 patients [16, 17] . Of these cytokines, IL-6 is distinguishably notable because of 91 its function in initiating pro-inflammatory responses via the IL-6 trans-signaling pathway. IL-6 92 presents a dual face in inflammatory responses [18] . Depending on its signaling cascade it can be 93 either pro-inflammatory or anti-inflammatory. Complete IL-6 signaling requires binding of IL-6 94 to IL-6R and subsequent association of IL-6/IL-6R complex with gp130 receptor. IL-6R is 95 expressed on hepatocytes and leukocytes while gp130 is expressed ubiquitously by all cells in the 96 body. IL-6R is distributed in two distinct forms, sIL-6R and IL-6R. When IL-6 binds to sIL-6R 97 and IL-6/sIL-6R complex associates with gp130, this initiates trans-signaling, which is pro-98 inflammatory in function. In contrast, in the event of IL-6 interacting with IL-6R, IL-6/IL-6R 99 complex associates with gp130 to trigger classical (cis)-signaling, which is anti-inflammatory [19] . . During infection, IL-6 trans-signaling is first to appear, classical-signaling activating later to 105 regulate the inflammation caused by trans-signaling-induced pro-inflammatory responses [19, 22] . 106 Found in the peripheral circulation, sgp130, a naturally soluble form of gp130, is generated by 107 alternatively spliced mRNA rather than by proteolytic cleavage [9] . There are three different forms 108 of sgp130. Although the individual function of different forms is not yet known but they have been 109 shown to bind to IL-6R with varying efficacy [23] . The sgp130 is the natural inhibitor of IL-6 110 trans-signaling [19, 24] . sgp130 shows high specific affinity for IL-6/sIL-6R complex but not for 6/26 111 either IL-6 or sIL-6R alone. It also confers protection from trans-signaling-mediated inflammation 112 by forming a neutralizing buffer with IL-6/sIL-6R complex. The polarization from trans-to cis-113 signaling is fully dependent on the relative concentrations of IL-6, sIL-6R and sgp130. In healthy 114 individuals, IL-6 is barely detectable in plasma, ranging between 2-6 pg/ml. Yet, during 115 inflammation IL-6 concentrations increase massively and can reach µg/ml levels. At steady state, available IL-6/sIL-6R complex, then the circulating free IL-6 binds to IL-6R and thereby initiates 128 cis-signaling to maintain cytokine homeostasis [19, 26] . In the event of ADAM17 activation, IL-6 fails to switch from trans-to cis-signaling, uncontrolled 130 release of pro-inflammatory cytokines occurs which precipitates a cytokine storm [11, 27] . disease models [37, 38] . Patients with these variants show greater shedding of IL-6R than is normal, 156 resulting in significantly higher levels of sIL-6R than detected in healthy individuals. Interestingly, 8/26 157 these patients appear to have a lower risk of acquiring multiple metabolic diseases like congestive 158 heart disease, abdominal aneurism, rheumatoid arthritis and Crohn's disease [39, 40] . This 159 protection may be explained by increased action of a neutralizing buffer system in response to 160 elevated sIL-6R [41]. Lungs are 'ground zero' for SARS-CoV-2 pathogenesis. The virus gains entry by binding to the 162 angiotensin-converting enzyme 2 (ACE2) receptor that is expressed on the membrane of 163 respiratory tract epithelial cells [42, 43] . In response to this event APC rapidly activate a pro- Since patients with comorbidity are likely to experience cytokine imbalance, we consider the first 251 priority to be rescue from cytokine storm. In order to restore the cytokine balance efforts should 252 be taken to switch IL-6 trans-signaling to classical-signaling and to curtail ADAM17-mediated 253 shedding events. In this regard, we propose the use of sgp130 and ADAM17 inhibitor with high 254 specificity, which may show considerably more therapeutic potential than either a global cytokine . Therapeutic targeting of ADAM17 inhibitor has necessarily to be highly specific 286 and non-toxic. Several ADAM17-based drug candidates have been tested in the past, of which a 287 number were discontinued due to their lesser efficacy and higher toxicity [83] . Recently, a 288 recombinant ADAM17/TACE prodomain (TPD) was developed, which is reported to be stable, Recently, an open-label, randomized, phase 2 trial of a triple drug combination was announced. This reported a better outcome by using two antiviral drugs, lopinavir-ritonavir and ribavirin, in 312 combination with immunomodulatory cytokine IFN-β-1b [94] . The findings of this study support 15/26 313 our notion to develop a combinatorial therapeutic approach with emphasis on IL-6 signaling 314 modulation. However, we prefer to consider immune-modulation by inhibiting IL-6 trans-315 signaling specifically rather than by a global means. A complex and interconnected picture of the 316 immunopathogenesis observed in COVID-19 is described herein. Following consideration of these 317 networked events we propose a combinatorial drug-based approach to therapy that includes TPD 318 in order to inhibit shedding of ACE2 and IL-6 that ultimately cascades to cytokine storm, sgp130Fc 319 in order to restore cytokine balance, an antiviral in order to reduce viral load, and an anticoagulant 320 in order to avoid inflammation-associated coagulopathy. Theoretically at least, we consider that 321 this drug combination may well promote enhanced recovery from COVID-19, yet its safety and 322 efficacy first needs to be explored fully by pre-clinical testing and in clinical trials. 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Lower left: When infection is activated ADAM17 triggers IL-744 6R shedding. Once the concentration of sIL-6R is higher than that of IL-6, sgp130 cannot 745 neutralize increased levels of IL-6/sIL-6R complexes. IL-6 trans-signaling is triggered and Figure 2: Proposed therapeutic model Administration of sgp130Fc suppresses IL-6 trans-signaling by trapping available IL-6/sIL-6R 750 complexes (upper section). TPD inhibits ADAM17 activation and stops shedding of ACE2 IL-6 receptors. As a consequence, the concentration of sIL-6R becomes lower than that of IL-6 whereupon IL-6 switches from trans-to classical-signaling. By this means, regulation of cytokine 753 storm may be achieved, while antiviral therapy will restrict viral host cell entry ☒ The authors declare that they have no known competing financial interests or personal relationships 757 that could have appeared to influence the work ☐The authors declare the following financial interests/personal relationships which may be considered 760 as potential competing interests Figure 1: Establishment of cytokine storm in COVID-19 From upper left to right: SARS-CoV-2 binds with ACE2, thereby facilitating entry of viral RNA 770 into the host cell Centre: IL-6/sIL-6R complexes are neutralized by sgp130 until the concentration of 772 sIL-6R is lower than that of IL-6. Lower left: When infection is activated ADAM17 triggers IL-773 6R shedding. Once the concentration of sIL-6R is higher than that of IL-6, sgp130 cannot 774 neutralize increased levels of IL-6/sIL-6R complexes. IL-6 trans-signaling is triggered and Figure 2: Proposed therapeutic model Administration of sgp130Fc suppresses IL-6 trans-signaling by trapping available IL-6/sIL-6R 779 complexes (upper section). TPD inhibits ADAM17 activation and stops shedding of ACE2 IL-6 receptors. As a consequence, the concentration of sIL-6R becomes lower than that of IL-6 By this means, regulation of cytokine 782 storm may be achieved, while antiviral therapy will restrict viral host cell entry. 783 784 Highlights: 785  Inhibition of IL-6 trans-signaling is crucial to rescue from cytokine storm  sgp130Fc selectively inhibit IL-6 trans-signaling TACE prodomain inhibitor (TPD) effectively stop ADAM17 shedding activity  Combination of sgp130Fc and TPD have potentiality to reduce cytokine storm in COVID-19  A combination of these inhibitors along with antivirals and anti-coagulants may show better efficacy 790 in severe COVID-19 cases