key: cord-296232-6zj99nuw authors: Talukdar, Jayanta; Bhadra, Bhaskar; Dattaroy, Tomal; Nagle, Vinod; Dasgupta, Santanu title: Potential of natural astaxanthin in alleviating the risk of cytokine storm in COVID-19 date: 2020-10-16 journal: Biomed Pharmacother DOI: 10.1016/j.biopha.2020.110886 sha: doc_id: 296232 cord_uid: 6zj99nuw Host excessive inflammatory immune response to SARS-CoV-2 infection is thought to underpin the pathogenesis of COVID-19 associated severe pneumonitis and acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Once an immunological complication like cytokine storm occurs, anti-viral based monotherapy alone is not enough. Additional anti-inflammatory treatment is recommended. It must be noted that anti-inflammatory drugs such as JAK inhibitors, IL-6 inhibitors, TNF-α inhibitors, colchicine, etc., have been either suggested or are under trials for managing cytokine storm in COVID-19 infections. Natural astaxanthin (ASX) has a clinically proven safety profile and has antioxidant, anti-inflammatory, and immunomodulatory properties. There is evidence from preclinical studies that supports its preventive actions against ALI/ARDS. Moreover, ASX has a potent PPARs activity. Therefore, it is plausible to speculate that ASX could be considered as a potential adjunctive supplement. Here, we summarize the mounting evidence where ASX is shown to exert protective effect by regulating the expression of pro-inflammatory factors IL-1β, IL-6, IL-8 and TNF-α. We present reports where ASX is shown to prevent against oxidative damage and attenuate exacerbation of the inflammatory responses by regulating signaling pathways like NF-ĸB, NLRP3 and JAK/STAT. These evidences provide a rationale for considering natural astaxanthin as a therapeutic agent against inflammatory cytokine storm and associated risks in COVID-19 infection and this suggestion requires further validation with clinical studies. The recent emergence of Coronavirus Disease-2019 (COVID-19) pandemic caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is highly contagious and has resulted in a global public health emergency. According to the World Health Organization (WHO), the pandemic has more than 27 million confirmed cases worldwide with over 8,97,000 deaths, as of the first week of September 2020. These numbers are changing rapidly and regularly updated in the WHO website at cause for induction of an immune pathology that results in the development of ALI, ARDS, acute cardiac injury, sepsis and multiorgan failure in COVID-19 (Table 1) [3, 7, [18] [19] [20] [21] [22] [23] . The relevant changes that occur in both innate and adaptive immune systems during SARS-CoV-2 infection have been highlighted by several authors [2] [3] [4] [5] [6] 18, [20] [21] [22] [23] . Lymphocytopenia and a modulation in total neutrophils have been reported as common hallmarks and are likely to be directly correlated with disease severity and death [3, 4, 7, 18 ]. Significant decrease in serum levels of absolute number of CD4+ cells, CD8+ have been reported in patients with severe COVID-19 [3, [18] [19] [20] [21] 23 ]. In addition, most of patients with severe COVID-19 have been reported to display significantly high serum levels of pro-inflammatory cytokines (e.g. IL-1β, IL-2, IL-6, IL-8, IL-17 and TNF-α) and chemokines (e.g., MCP-1, IP-10, MIP1-α, G-CSF, GM-CSF and CCL-3) [3, [18] [19] [20] [21] 23] . Additionally, the presumed ability of SARS-CoV-2 to evade the host's antiviral immune response also has raised a critical aspect concerning the disease severity [4, 18] . For example, SARS-CoV and MERS-CoV escape and suppress the signaling pathways mediated by type I Interferon (IFN) to heighten their anti-viral defenses [4] . Based on the genomic identity of SARS-CoV-2 with SARS-CoV, it is speculative that SARS-CoV-2 can also adopt similar strategies to modulate the host innate immune response, thus suppressing immune detection and dampening anti-viral immune defenses [4] . reported higher than non-ICU patients, thus indicating that the CS might be correlated with disease severity [3] . Plasma levels of 15 cytokines, namely IFN-α2, IFN-γ, IL-1ra, IL-1α, IL-2, IL-4, IL-7, IL-10, IL-12, IL-17, IP-10, G-CSF, M-CSF, HGF and PDGF-BB have been reported to linearly associated with lung injury based on Murray score and this could be used to predict the severity of COVID-19 [23] . In another study, Chen et al. [21] found that macrophage-related pro-inflammatory cytokines, particularly IL-6, IL-10 and TNF-α, were significantly higher in majority of severe COVID-19 cases. The immunological features, such as significant increase in serum levels of IL-6, TNF-a, IL-2R, IL-10, CD14+ J o u r n a l P r e -p r o o f and CD16+ along with the significant decrease of lymphocytes are clearly distinguishable in severe COVID-19 patients (Table 2) [3, 18, 20, 21] . Evidence from literature indicates that the CS observed in COVID-19 resembles that occurring in CRS, a form of Systemic Inflammatory Response Syndrome (SIRS) and in sHLH, a hyperinflammatory syndrome characterized by fulminant and fatal hypercytokinemia with multiorgan failure [2, 4, 6, 23] . Blocking of pro-pathogenic cytokines has been used clinically for the treatment of autoimmune or autoinflammatory diseases [23] . Therefore, existing modulators of inflammatory cytokines have been repurposed as a therapeutic strategy to alleviate the risk of hypercytokinemia or CS in COVID-19 patients. The structural similarities of SARS-CoV-2 as well as the analogies in the infection mechanisms with SARS-CoV [24] give reason to speculate that SARS-CoV-2 infection may induce the activation of shared intracellular pathways, such as IRF3 (IFN regulatory factor-3), NF-ĸB and JAK/STAT signaling pathways [4] . However, it is yet to be demonstrated that such similarities between SARS-CoV and SARS-CoV-2 can be directly translated into pathological outcomes [4] . The innate immunity, which acts as the first defense barrier against any pathogen and determines the activation of immune response, could play an important role in the J o u r n a l P r e -p r o o f development of CS and be responsible for boosting more severe forms [25, 26] . Toll like receptors (TLRs) that recognize pathogen-associated molecular patterns (PAMPs) are involved in the activation of innate immunity [25, 26] . Upon entry of SARS-CoVs into the host cell by entry receptor angiotensin-converting enzyme-2 (ACE2), the viral RNAs, as PAMPs, are detected by the pattern recognition receptors (PRRs), such as TLRs and consequently results in immune cell activation [4, 26, 27] . The viral genomic RNA or the intermediates during viral replication, including dsRNA, are recognized by TLR3 and TRL7/8, and cytoplasmic RNA sensors, namely retinoic acid-inducible gene-I (RIG-I)/melanoma differentiation-associated protein 5 (MDA5) [25] . Consistently, TLRs have been reported to activate different signaling pathways in human CD14+ monocytes, correlating with differential type I IFN and cytokine secretion involved in CD4+ T cell polarization [4, 25] . As a result, downstream transduction pathways in antiviral response, such as IRF3, NF-ĸB and JAK/STAT, are activated [4, 25] . TLR3 is highly expressed on dendritic cells, placenta and pancreas, and its activation through TRIF (TIR-domain-containing adaptor-inducing interferon-β) pathway, determines the activation of NF-ĸB [25, 26] . TLR7 is expressed in human plasmacytoid treatments for severe cases [27] [28] . The lack of any effective drug for the treatment of COVID-19 leads to a sense of urgency to develop new therapeutic strategies based on pathophysiological assumptions [27] [28] [29] [30] . Besides antiviral agents, the treatment of immunological complications, such as CS using appropriate host-directed therapies that include immunosuppressive and immunomodulatory drugs has been suggested to be essential [2, 4, 6, 22, 23, [26] [27] [28] [29] [30] . A range of marketed drugs, such as DMARDs, metformin, pioglitazone, fibrates and atorvastatin, including nutrient supplements and biologics have been proposed to reduce immunopathology, boost immune responses and prevent or curb ARDS [2, 6, 28, 30] . These could be used as adjuncts to monotherapy or as combinatorial therapies with repurposed antivirals targeting SARS-CoV-2 induced COVID-19 [28, 30, 31] . As CS is a relatively common manifestation of COVID-19 infection and often leads to exacerbation with progression to ARDS, ALI and other serious organ damages, intervention with appropriate anti-inflammatory treatment should be considered in addition to antiviral treatment to prevent further injury [6, 18, [21] [22] [23] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] . Table 3 provides a representative list of potential targeted processes and examples of candidate agents which are currently entering clinical trials or have been proposed [28, 30, [32] [33] [34] ]. In addition, alternative drugs and interventions have been proposed for potential [8, 10] . ASX is not a known viricide. However, it has been shown to suppress features of viral infection owing to its potent antioxidant, antiinflammatory and immunomodulatory actions [11] [12] [13] [14] [15] [16] [17] . Studies including human trials have shown that ASX effectively regulates immunity and disease etiology, suggesting its wide array of potential therapeutic and nutritional support in prevention and treatment of various pathogenic diseases and metabolic disorders, all of which have elements of oxidative stress and/or inflammation in the pathogenesis [8, 10, 17] . The potential pharmacological effects of ASX include antioxidant [12] [13] [14] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] , anti-inflammatory [9, 12, 14, [54] [55] [56] [57] [58] [59] [60] and immune-modulating [11, 14, 15, [61] [62] [63] as well as cardiovascular, neuro-, ocular-and skin-protective effects [8, 17, 37, 64] . ASX has been suggested as a potential therapeutic agent against atherosclerotic cardiovascular disease [8, 37] , oral lichen planus (OLP) [9] , gouty arthritis [55] , ALI [12, 43] , sepsis [44] , cancers [47] [48] [49] [50] , diabetes mellitus [51] [52] [53] , etc. The biological activities of ASX is reported to originate from its potent singlet oxygen quenching and lipid peroxidation suppressing activities [65] . Recent human trials elaborating on the safety perspectives have found no negative effects of ASX consumption as a dietary supplement [66] . Results from clinical studies have shown that treatment with ASX improves blood flow in humans [67] and enhances blood rheology by increasing the flexibility of erythrocyte membranes [68] . With its unique molecular structure [10] , ASX stretches through the bilayer cell membrane providing resilient protection against oxidative stress [38] . As a potent and efficient antioxidant, ASX can prevent genotoxicity and cytotoxicity mediated by ROS, stimulate hepatic xenotoxic-metabolizing enzymes and enhance tumor immunity [14, 15] . Unlike most antioxidants, which works either in the inner side of the membrane (e.g., vitamin E and β-carotene) or on the outer side (e.g., vitamin C), ASX can scavenge and quench reactive oxygen species (ROS) and free radicals (superoxide anion, hydrogen peroxide, singlet oxygen, etc.) in both the inner and outer layers of the cell membrane [10] . The ROS scavenging effect of ASX is approximately 6000 times higher than that of vitamin C, 800 times than that of coenzyme Q10 and 550 times than that of vitamin E [65] . These pleiotropic protective effects of ASX owing to its potent antioxidant, antiinflammatory and immunomodulatory actions may support its potential adjunctive use in alleviating and management of CS and associated risks in COVID-19 patients. A representative list of potential targeted clinical characteristics of COVID-19 and possible functional role of ASX is provided in Table 4 . As there is no direct evidence of applying ASX against COVID-19, we propose in Table 5 Inflammation and oxidative stress are implicated in the pathogenesis of many chronic diseases, including diabetes, atherosclerosis, hypertension [8, 16] , gouty arthritis [55] and oral lichen planus (OLP) [9] . Hyperinflammation due to an uncontrolled inflammatory response is also considered to be a major cause of COVID-19 pathogenesis [6, 22, 27] . Inhibiting the production of intracellular ROS is a general way to suppress the pro- inflammatory reactions by producing anti-inflammatory cytokines, such as IL-10 [45] . The balance between M1/M2 phenotype is, therefore, important for regulating immune and inflammatory processes [45] . The NF-ĸB signaling pathway promotes inflammation by increasing the release of ROS and pro-inflammatory cytokines in macrophages [45] . Inversely, the nuclear factor Miyachi et al. [9] found that the administration of ASX provides both preventive and curative anti-inflammatory effects against LPS-induced inflammation in the human gingival keratinocyte line NDUSD-1 by suppressing the production of IL-6 via inhibiting activation of the NF-ĸB signaling pathway. Translocation of NF-ĸB/p65 and the levels of IL-6 and TNF-α were reported to decrease markedly following ASX treatment [9] . Similarly, ASX was demonstrated to inhibit the production of NO and prostaglandin . Moreover, ASX treatment was also found to reduce serum levels of LDH, blood urea nitrogen, creatinine, IL-1β, IL-6 and TNF-α, and also attenuated multi organ damage in CLP-induced septic rats [44] . Similarly, Farruggia et al. [45] have demonstrated that ASX significantly decreases LPS-induced mRNA expression of IL-6 and IL-1β by inhibiting the NF-ĸB/p65 signaling pathway in RAW 264.7 macrophages. Besides its role in inhibiting the nuclear translocation of NF-ĸB, ASX also exerts its antiinflammatory effect by altering the splenic macrophages to be less inflammatory and by modulating macrophage phenotype to be less inflammatory [45] . Furthermore, the antiinflammatory effect of ASX was reported to be mediated by both Nrf2-dependent andindependent mechanisms [45] . The cytokine IL-6 is one of the major pro-inflammatory cytokines produced by activating macrophages and monocytes. IL-6 mediates the innate-adaptive immunity J o u r n a l P r e -p r o o f interface and is involved in autoimmune disorders and chronic inflammation [56] . An elevated serum level of IL-6 has been discussed in COVID-19 disease progression [3, 6, 20, 21, 23] , suggesting the use of IL-6 inhibitors as potential therapeutics in the management of CS in COVD-19 [6, 28] . Numerous studies as discussed above have demonstrated that ASX could effectively modulate IL-6 levels in vitro and in vivo. Kim et al. [56] demonstrated that ASX significantly suppressed the production of IL-6 in both ASX also provides neuroprotection against secondary brain injury through suppression of cerebral inflammation [54] . In a prechiasmatic cistern subarachnoid (SAH) model, activation of TLR4 increases downstream molecules MyD88 and NF-ĸB and induces pro-inflammatory markers along with ICAM-1, causing direct damage to the surrounding neural cells and neutrophil migration [54] . Reportedly, post-treatment with ASX after SAH significantly inhibited the TLR4 activation, increased sirtuin 1 expression, reduced neutrophil infiltration, suppressed the activity of NF-ĸB and inhibited subsequent J o u r n a l P r e -p r o o f inflammatory response by downregulating IL-1β, TNF-α and ICAM-1 both in vivo as well as in vitro [54] . Furthermore, administration of ASX after SAH had reportedly ameliorated secondary brain injury cascades, brain edema, neuronal death and improved neurologic function [54] . The mechanism underlying ASX regulation of pro-inflammatory cytokines has been extensively investigated and engages diverse signaling pathways, among which the NF-ĸB pathway plays an essential role [9, 12, 16, 40, 43, 45] . Besides, ASX modulations of Nrf2 and sirtuin1 signaling pathways play significant roles in its anti-inflammatory mechanism [45, 54] . The NF-ĸB signaling pathway plays a seminal role in immunity by activating pro- Oxidative stress is not only due to ROS released, but also due to pro-oxidant cytokines, such as tumor necrosis factor (TNF) and IL-1 released by activating phagocytes [69] . Recent evidence suggests that much of the ALI caused by SARS-CoV and H5N1 can be attributed to excessive ROS generation initiated by an overactive innate immune response [70] . In SARS-CoV, H5N1 avian flu and chemical agent induced ALI/ARDS models, oxidized phospholipids activate the innate immune response by the overproduction of IL-6 in alveolar macrophages via the TLR4-TRIF-TRAF6-NF-kB signaling pathway, thereby leading to ALI [70] . Stimulation of TLR4 can trigger the activation of two downstream signaling pathways: MyD88-dependent or TRIF-dependent J o u r n a l P r e -p r o o f pathways [70] . TLR4 belongs to the TLR receptor family for the innate immune system and it is also a therapeutic target for ASX. Recently, numerous studies have highlighted the possible role of oxidative stress in the progression and severity of COVID-19 [71] [72] [73] . Free radicals, such as O2 -, ClO -, NO and ONOOcould be the cause of virus induced pneumonia death [71] . Oxidative stress reportedly plays a crucial role in the pathogenesis of COVID-19, perpetuates the CS and DIC as well as exacerbates hypoxia, including mitochondrial dysfunction [72] . The interplay between ROS and CS generates a self-sustaining cycle between the CS and oxidative stress produced, leading to multiorgan failure in severe COVID-19 patients who progress to sepsis and shock [71, 72] . It has been speculated that SARS-CoV-2 infection interferes with the equilibrium between the expression of NF-ĸB (involved in expression of cytokine) and Nrf2 activation (responsible for expression of antioxidant enzyme) [73] . Studies have also implicated Nrf2 as a regulator of susceptibility to respiratory and non- (HO-1) and superoxide dismutase (SOD)-1 expression [74] . In addition, ASX has been reported to increase the activity of SOD, decrease MDA levels in the serum and alleviate fibronectin as well as collagen IV accumulation in the kidneys of diabetic rats, thereby exerting a reno-protective effect [74] . Moreover, ASX has been shown to protect against lung injury due to oxidative damage and inflammation induced by ochratoxin (OTA) in mice via the modulation of Nrf2/NFĸB pathway [75] . Exposure to OTA has been reported to induce immunotoxicity of the TLR4/MyD88 pathway by inducing ROS overproduction followed by activation of NF-ĸB, resulting in elevated levels of inflammatory markers IL-1β, IL-6 and TNF-α. Pretreatment with ASX has been reported to significantly reduce the inflammation [75] . In OTA exposed mice, ASX significantly upregulated the expression of stimulates upregulation of pro-inflammatory cytokines and chemokines synthesis [55, 59] . Interestingly, numerous studies have shown that ASX effectively attenuates NLRP3 activation [55, 59] . In a recent study, Peng et al. [55] have reported ASX as a potential treatment for gouty arthritis. Treatment with ASX has been found to inhibit the MAPK pathway, which in turn suppresses the expression levels of IL-1β, COX-2 and NLRP3 in monosodium urate crystal (MSU)-induced murine macrophage J774A.1 cell [55] . In addition, ASX has also been shown to attenuate ROS-induced acute kidney injury by inhibition of ROS/NLRP3 inflammasome signaling pathway [59] . In this study, Gao et al. [59] found that treatment with ASX significantly decreases the levels of ROS, NLRP3, caspase 1, IL-1β and IL-8, as well as the rate of apoptosis in iohexol-induced human proximal renal tubular epithelial cells. Furthermore, the protective action of ASX against oxidative stress mediated ischemia-reperfusion (I/R) induced injury has been studied extensively [82] [83] [84] [85] [86] . I/R is a multifactorial process that includes major oxidative stress induced by ischemia and hypoxia [83] . Excessive release of ROS plays important role in I/R injury process and scavenging ROS could be a potential target [83, 84] . Numerous studies applying different in vivo models of induced I/R injury, such as myocardial, cerebral, liver and renal injury, has been shown to have protective effects against I/R-induced renal [84] and lung injury [85] . The protective role of ASX in I/R-induced hepatorenal injury has been reconfirmed recently in rat models [86] . In acute lower extremity I/R, ASX has been reported to reduce the I/R-induced elevation of endothelial nitric oxide synthase (eNOS) and decrease the ischemic injury in liver and renal tissues by protecting the microcirculation and providing a cytoprotective effect with vasodilatation [86] . Moreover, ASX has been reported to reduce blood coagulation and platelet aggregation, and also promote fibrinolytic activity in high-fat diet-induced hyperlipidemic rats [56, 87] . These positive effects are correlated with the decrease of serum lipid and lipoprotein levels, antioxidant actions and protection of endothelial cells [87] . Oxidative/nitrative stress is an imbalance between oxidation and anti-oxidation mainly caused by excessive detrimental ROS production, MDA, MPO, iNOS and NT, and Viral lung infections leading to ALI/ARDS are the leading cause of morbidity and mortality. cytotoxic CD8+ T cells produce and release pro-inflammatory cytokines, which induce cell apoptosis [89] . Effective immune responses to these infections require precise immune regulation to preserve lung function after viral clearance [89] . Supplementation of ASX in mice has been shown to increase ex vivo splenocyte antibody response to T-dependent antigens [92] , lymphoblastogenic response and cytotoxic activity [63] . Reportedly, ASX was found to have a stimulatory effect on the production of polyclonal antibodies IgM and IgG on mouse spleen cells [93] . Dietary supplementation with ASX was found to increase IgM and IgG secreting cells in vivo in T dependent antigen (TD-Ag) primed mice but had no effect on in vitro and in vivo antibody production in response to T-independent antigen [63] . These indicate significant immunomodulating actions of ASX for humoral immune responses to TD-Ag, suggesting that ASX supplementation could be beneficial in restoring humoral immune responses in aged animals [63] . ASX has also been reported to produce immunoglobulins in human cells [15] . Moreover, in LPS-and concanavalin-activated primary cultured lymphocytes, Lin et al. [62] found that treatment with ASX modulates lymphocytic immune response in vitro and exerts ex vivo immunomodulatory effects by enhancing IFN-γ and IL-2 production without inducing cytotoxicity. T cell response to viral infections [94] . FOXO3 is known to promote apoptosis of T cells and to limit clonal expansion of CD8 T during an acute viral infection [94] . A deficiency of Numerous studies have shown that ASX efficiently activates the FOXO3 gene expression in animal models [39, 96] . Reportedly, ASX modulates the expression of FOXO3 gene significantly in heart tissue, brain, skeletal muscle and blood [39] . In a study with iohexol induced-acute kidney injury in rat model, ASX was shown to upregulate FOXO3 expression in the renal tubular epithelium in both in vitro and in vivo models [96] . Treatment with ASX was found to efficiently protect against iohexol-induced acute kidney injury [96] . Recently, in mice model, oral administration of ASX has been shown to induce rapid increase of CD8+ T cell population by upregulating CCL5 macrophages and elevate J o u r n a l P r e -p r o o f expression of IFN-γ [97] . In addition, ASX exhibits marked protection against renal fibrosis by inhibiting fibroblast activation via modulating the Smad2, Akt and STAT3 signaling pathways and suppresses epithelial to mesenchymal transition in renal tubular epithelial cells via Smad2, snail and β-catenin [97] . Moreover, ASX has been reported to prevent pulmonary fibrosis [98] and liver fibrosis [99] . [106] . Treatment with ASX also inhibits the expression of TGF-β1 and TGF-β1induced transformation of HCFs to myofibroblasts [106] . Furthermore, ASX was shown to enhance the activity of sirtuin1 without increasing the expression of sirtuin1 in TGF-β1 unstimulated cells, suggesting that sirtuin1 participates in the functions of ASX [106] . In another study, Gao et al. [107] found that nASX protects against acute contrast-induced renal injury via modulation of sirtuin1-p53 signaling pathway. In this study, it was also J o u r n a l P r e -p r o o f found that treatment with ASX markedly reduces the indictors of oxidative stress and significantly elevates the expression of sirtuin1 [107] . Additionally, the role of sirtuin1 in regulation of inflammatory cytokine within macrophages have been discussed [108] . In RAW264.7 macrophage/monocytic cells and primary intraperitoneal mouse macrophages, Yoshizaki and colleagues demonstrated that sirtuin1 downregulates inflammatory pathway activity, gene expression and release of TNF-α from LPS-stimulated macrophages, and that pharmacological sirtuin1 activators exert broad anti-inflammatory effects [108] . In line with this, recently Kang et al. [109] have demonstrated that ASX inhibits alcohol induced inflammation and oxidative stress in RAW 264.7 macrophages and bone marrow-derived macrophages isolated from wildtype and mice with macrophage specific-deletion of histone deacetylase 4 (HDAC4). Treatment with ASX has been shown to attenuate the ethanol-induced decrease of sirtuin1 levels and abolish the increase in acetylated histone H3 by ethanol in macrophages [109] . Reportedly, the anti-inflammatory and antioxidant actions of ASX in ethanol treated macrophages are mediated via the elevated expression of sirtuin1 and perhaps by the crosstalk between sirtuin1 and/HDAC4 [109] . Balb/cA mice infected with Helicobacter pylori [110] . Treatment with ASX was demonstrated to reduce the bacterial load and mucosal inflammation because of ASX mediated shift in cytokine release to Th2 cell response from Th1 cell response [110] . It was reported that an excessive Th1 response driven by H. pylori infection favors the development of cell mediated immune response leading to cytotoxic damage of the epithelium [110] . Treatment with ASX modulates the Th1 response with the shift in Th1/Th2 balance by downregulation of Th1-cells and up-regulation of Th2-cells, resulting in a protective and non-destructive immune response against H. pylori [110] . Evidence from these studies suggest that ASX is a potent antioxidant and a natural anti-inflammatory compound having efficient immunomodulatory action that exerts potential therapeutic benefits against oxidative and inflammation induced tissue damage. PPARs are a family of PPAR-α, PPAR-γ and PPAR-β/δ subtype transcriptions factors belonging to the ligand activated nuclear hormone receptors (NR) superfamily. These are mainly expressed in immune cells and have an emerging critical role in immune cell differentiation and regulation of inflammation [111, 112] . All three PPAR isoforms share a common structure, but manifest different tissue distribution, target genes and functions [112] . The PPARs primarily regulate lipid and glucose metabolism and have additional regulatory roles on cell proliferation and differentiation, cancer, vascular homoeostasis and atherosclerosis, the immune system and inflammation [113] . PPARs play important roles in antagonizing core inflammatory pathways, such as NF-ĸB, AP1 and STAT [114] . PPAR-α is mainly expressed in the liver, kidney, heart and skeletal muscles and is J o u r n a l P r e -p r o o f responsible for lipid metabolism and insulin sensitivity [111] . Evidence from studies also have suggested that PPAR-α might exert anti-inflammatory action by mediating a direct effect on adipocytes [112] . The probable mechanism involves sirtuin1, that suppresses the inflammatory response by inhibiting TNF-α induced CD40 expression via the sirtuin1dependent signaling pathway [115] . PPAR-β/δ is ubiquitous throughout human body and is mainly responsible for epithelial cell growth, fatty acid oxidation and wound healing [111] . PPAR-γ is, by far, the most extensively studied PPAR isoform, is primarily found in adipose tissues and is the most common therapeutic target. PPAR-γ controls the homeostasis of immune system by regulating the fate and function of various immune cells [112] . In addition to its major role in lipid and glucose homeostasis, PPAR-γ is also associated with inflammation responses, cardiovascular diseases and cancer [111] . Recently, Ciavarella et al. [116] have highlighted the possible therapeutic implications of PPAR-γ agonists in COVID-19 cytokine storm. They suggest that the activation of PPAR-γ could represent an effective therapeutic strategy to counter SARS-CoV-2 induced cytokine storm and to prevent the effects of inflammation following COVID-19 [116] . Moreover, PPAR-γ has been reported as a key regulator of the innate immune system exhibiting a shift in production from pro-inflammatory to anti-inflammatory mediators by neutrophils, platelets and macrophages [117] . PPAR-γ modulates platelet and neutrophil function, prevents platelet-leucocyte interactions, promotes neutrophil apoptosis, alters macrophage trafficking, increases phagocytosis and promotes J o u r n a l P r e -p r o o f alternative M2 macrophages activation, suggesting its roles in adaptive immune response [117] . Considering such implications of PPAR-γ activation on inflammatory process, modulators of PPARs and specifically, agonists of PPAR-γ have been proposed among the possible therapeutic compounds that may be able to attenuate CS that typically occurs during severe respiratory viral infection such as influenza A virus (IAV), respiratory syncytial virus (RSV), etc. [116, 118, 119] . In this regard, Aldridge and colleagues [118] demonstrated that pioglitazone administration in mice reduces the amount of dendritic ASX has a potent PPAR activity. The modulation of PPARs by ASX and its therapeutic implications in various pathophysiological conditions have been reviewed recently [111, 120] . Treatment with ASX shows a differential regulatory action on PPARs. Primarily, ASX acts as an agonist of PPAR-α [121] [122] [123] and antagonist of PPAR-β/δ [123] . However, ASX exerts both PPAR-γ agonist and antagonist actions depending on the cell context [124, 125] . Under normal physiological conditions, ASX acts as a PPAR-α agonist and PPAR-γ antagonist [121, 122] . Inoue et al. [124] reported that ASX acts as a PPAR-γ agonist in oxidative-stress related conditions in macrophages. ASX has been shown to induce the liver X receptor (LXR) and CD36 mRNA expression via PPAR-γ activation in macrophages in a dose-dependent manner [124] . In addition to their involvement in the metabolism of cholesterol and lipid, LXRs also suppress the expression of proinflammatory TNF-α, COX-2, iNOS and MMP9 [111] . From this study, it is evident that anti-inflammatory effects of ASX are mediated by PPAR-γ activation [111] . As reported, ASX exerts protective actions against H. pylori infection [110] , which may be by stress, etc. [128] [129] . IL-6 binds to IL-6 receptor-subunit-α (IL-6R) and triggers a heterohexameric complex with IL6 receptor-subunit-B (gp130, IL-6ST) and activates the IL-6/JAK/STAT3 pathway, that includes activation of inflammation-related downstream targets [129] . In addition to its role in activation of JAK/STAT3 signaling pathway, IL-6 is one of the pivotal inflammatory cytokines highly expressed in COVID-19 cytokine storm J o u r n a l P r e -p r o o f [129] . Elevated serum levels of IL-6 has been considered as one of the main indicators of poor prognosis in COVID-19 [3, 20] . Activation of the IL6/JAK/STAT3 signaling pathway results in a systemic cytokine storm involving secretion of VEGF, which contributes to vascular permeability and the extravasation of immune cells from blood vessels [6] . Attenuation of the JAK/STAT3 pathway would play a pivotal role in preventing the inflammation that occurs in COVID-19 [127] [128] [129] . Mehta et al. [127] have suggested that the inhibition of JAK/STAT pathway can affect both inflammation and cellular viral entry in COVID-19, which possibly can reduce the case fatality rate of severe COVID-19 due to sHLH or CRS. In this context, it would be pertinent to mention that the ASX modulation of the JAK/STAT3 signaling pathway has been revealed [48, 50, 130] . Supplementation of ASX abrogates constitutive activation of STAT3 by preventing its phosphorylation and subsequent nuclear translocation, thereby inhibition of the JAK/STAT3 signaling pathway [50] . Kowshik et al. [50] demonstrated that administration of dietary ASX inhibits JAK/STAT signaling by suppressing the levels of IL-6 and restraining the phosphorylation of STAT3. In addition, ASX administration markedly decreases the expression of MMP2, MMP9 [50] . Moreover, ASX significantly modulates the major downstream events triggered by the JAK/STAT signaling pathway. Abrogation of STAT3 by ASX was reported to be associated with the downregulation of the key mediators of angiogenesis, the VEGF and VEGF receptor 2 (VEGFR2) [50] . In addition, ASX also inhibits nuclear translocation of hypoxia inducible J o u r n a l P r e -p r o o f factor 1α (HIF-1α), a master regulator of angiogenesis responsible for transactivation of several hypoxia responsive genes including VEGF and VEGFR2 [50] . The study supports that ASX is a potent inhibitor of the JAK/STAT signaling pathway, revealing it as a promising anti-angiogenic candidate, and thus could be a potential therapeutic agent against COVID-19 as well. Evidence suggests that ASX is a potent antioxidant and anti-inflammatory compound with immunomodulatory actions showing pleiotropic therapeutic benefits against oxidative damage, inflammation and immune dysregulation. Its modulatory actions on innate immune system via PPARs and potent anti-angiogenic activity further suggest that ASX could be a potential therapeutic agent against COVID-19. Taken together, we anticipate that ASX modulation of inflammatory pathways could exert potential therapeutic benefits against COVID-19 cytokine storm and its associated risks ( Figure 1 ). Although there is no study related to the use of ASX in COVID-19 patients, there have been clinical studies that investigated the effects of ASX in human health benefits and disease involving oxidative stress and inflammation ( Table 6 ). The most clinically demonstrated effects of ASX include antioxidation, anti-inflammation, immune modulation, lipid-metabolism-modulating and glucose lowering. In a double-blind randomized controlled trial, Choi et al. [131] reported that obese adult had higher serum levels of oxidative biomarkers (MDA and isoprostanes) and lower anti-oxidant capacity (SOD and total antioxidant capacity); however, three weeks of ASX supplementation (5 mg/d or 20 mg/d) lowered oxidative biomarkers and increased antioxidant capacity. Oxidation of low-density LDL and cell membrane lipids contributed to atherosclerosis and thrombus formation [8] . Iwamoto et al. [46] reported that ASX could protect human LDL against oxidation. The antioxidant effect of ASX against human LDL oxidation was further confirmed in an ex vivo study with 24 healthy adults supplemented with ASX (3.6 mg/day) for 14 days [8] . Nakagawa et al. [132] reported the effectiveness of ASX supplementation (6 and 12 mg/day) on phospholipid hydroperoxides (PLOOH) levels in erythrocytes in 30 healthy subjects. After 12 weeks of ASX administration, decreased PLOOH levels and increased ASX in erythrocytes were reported [132] . In another study involving human subjects, Karppi et al. [133] reported that supplementation of ASX for 12 weeks reduced the levels of plasma 12-and 15-hydroxy fatty acids in healthy males. These studies suggest that ASX exerts an antioxidant effect in human subjects that may potentially alleviate lipid peroxidation in vivo. Reportedly, in diet-induced obesity in mice, ASX significantly lowered the concentration of plasma triglyceride, alanine transaminase (ALT) and aspartate aminotransferase (AST), and increased the mRNA expression of antioxidant genes regulated by Nrf2 in the liver [134] . In addition, ASX has been reported to decrease macrophage infiltration and apoptosis on vascular cells in atherosclerosis plaques [135] . In a placebo-controlled study, Yoshida et al. [136] investigated the lipid-metabolismmodulating effect of ASX in 61 non-obese humans using ASX administration at doses of 0, 6, 12 and 18 mg/day for 12 weeks. The study showed that administration of 12-and 18 mg/day of ASX significantly reduced serum triglyceride and adiponectin levels and 6-and 12 mg/day doses significantly increased HDL-cholesterol [136] . Furthermore, in a randomized double-blind placebo-controlled study, Katagiri et al. [137] demonstrated that administration of ASX-rich H. pluvialis extract (6 or 12 mg/day) for 12 weeks improved cognitive function in healthy aged humans. J o u r n a l P r e -p r o o f widely used in the fields of health food applications and biomedical research [142] . The U.S Food and Drug Administration (FDA) approved ASX as a dietary supplement [143] and notified the "generally recognized as safe" (GRAS) status to H. pluvialis derived ASX product [66] . Multiple preclinical and human clinical studies involving orally administered ASX in doses ranging from 4 mg to 100 mg/day have shown no adverse or toxic effects [8, 138] . Human clinical studies have found ASX to be safe for human consumption and orally bioavailable [139] . H. pluvialis derived ASX has been reported to be more bioavailable, probably due to the presence of astaxanthin esters [17] . Maximal blood concentration of ASX has been reported to occur between 8 and 10 h after ingestion of 40 mg in healthy adults [139, 140] . Following consumption of 40 mg ASX, the plasma elimination half-life period was estimated as 15.9 ± 5.3h [139] and the same for 100 mg ASX ingestion was estimated as 52 ± 40h [141] . This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. All authors declare no competing interests. No ethical approval was obtained as all relevant information were retrieved from publicly available literature through multiple databases and no primary data was collected or generated during the review process. [13] Z.X. Zhang ↓CD4+ T, ↓CD8+ T, ↑↑ IL-2R, ↑↑ IL-6, ↑↑ IL-10, ↑↑ TNF-α Chen et al. [21] → normal values, ↓ decreased, ↓↓ severe decreased, ↑ increased, ↑↑ severe increased. 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cytokine production Imbalance RAS signaling pathway induce ROS, inflammation Inverse correlation We thank our employer for providing all necessary resources to write this article.