ABSTRACT
The coronavirus disease 2019 (COVID-19) pandemic underlines a persistent threat of respiratory tract infectious diseases and warrants preparedness for a rapid response. At present, COVID-19 has had a serious social impact and imposed a heavy global burden on public health. The exact pathogenesis of COVID-19 has not been fully elucidated. Since the outbreak of COVID-19, a renewed attention has been brought to Toll-like receptors (TLRs). Available data and new findings have demonstrated that the interaction of human TLRs and SARS-CoV-2 is a vital mediator of COVID-19 immunopathogenesis. TLRs such as TLR2, 4, 7 and 8 are potentially important in viral combat and activation of immunity in patients with COVID-19. Therapeutics targeting TLRs are currently considered promising options against the pandemic. A number of TLR-targeting immunotherapeutics are now being investigated in preclinical studies and different phases of clinical trials. In addition, innovative vaccines based on TLRs under development could be a promising approach for building a new generation of vaccines to solve the current challenges. In this review, we summarize recent progress in the role of TLRs in COVID-19, focusing the new candidate drugs targeting TLRs, the current technology and potential paths forward for employing TLR agonists as vaccine adjuvants.Copyright © 2023 The Scandinavian Foundation for Immunology.
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Background: Viral infections pose some of the most serious human health concerns worldwide. The infections caused by several viruses, including coronavirus, hepatitis virus, and human immunodeficiency virus, are difficult to treat. Method(s): This review details the findings of a literature search performed on the antiviral properties of luteolin. The keywords engaged in the search are "virus" along with "luteolin." Results: Luteolin possesses antiviral properties, which is the basis for the current review. It is an important natural flavonoid with numerous important biological properties, including anti-inflammatory, immune regulatory, and antitumor effects, and is found in vegetables, fruits, and several medicinal plants. Recent studies have revealed that many traditional Chinese medicines that contain luteolin inhibit the replication of coronaviruses. Conclusion(s): Luteolin effectively inhibits the replication of coronavirus, influenza virus, enterovirus, rotavirus, herpes virus, and respiratory syncytial virus, among others. In particular, it prevents viral infection by improving the body's nonspecific immunity and antioxidation capacity and inhibiting many pathways related to virus infection and replication, such as MAPK, PI3K-AKT, TLR4/8, NF-kappaB, Nrf-2/hemeoxygenase-1, and others. It also regulates the expression of some receptors and factors, including hepatocyte nuclear factor 4alpha, p53, NLRP3, TNF-alpha, and interleukins, thereby interfering with the replication of viruses in cells. Luteolin also promotes the repair of damaged cells induced by proinflammatory factors by regulating the expression of inflammatory molecules. The overall effect of these processes is the reduction in viral replication and, consequently, the viral load. This review summarizes the antiviral effect of luteolin and the mechanism underlying this property.Copyright © The Author(s) 2023.
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Objectives: Toll-like receptors (TLRs) are an important family of receptors that recognize infectious agents and play an important role in the innate immune system. TLRs are a potential candidate to control infection in the early stages of the disease and to produce vaccines against SARS-CoV-2. In addition, studies have suggested that TLR polymorphisms are also associated with antiviral responses against SARS-CoV-2. Therefore, we aimed to investigate the relationship of TLR7 and TLR8 polymorphisms with COVID-19 disease prognosis. Materials-Methods: A total of 120 COVID-19 patients, including 40 outpatients, 40 patients with mild and moderate clinical status, hospitalized and severe pneumonia, and 40 patients followed in the intensive care unit (ICU), were included in the study. The classification of disease severity was made according to WHO criteria. TLR7 (rs179009), TLR8 -129 C/G (rs3764879) and TLR8 Met1Val (rs3764880) polymorphisms were genotyped using the PCR-RFLP method. Result(s): Since TLR7 and TLR8 are located on the X chromosome, men and women were analyzed separately. There was no significant difference between the groups in terms of 3 polymorphisms in males. On the other hand, in women, individuals carrying AG genotype and G allele for TLR8 Met1Val polymorphism were found at a higher rate in patients hospitalized in ICU than in patients followed in the service (p <0.05). In terms of the other two polymorphisms, no significant difference was found between the groups in women. Conclusion(s): We suggest that the AG genotype and G allele of TLR8 Met1Val polymorphism can be considered as an important risk factor that increases the severity of the disease in women.
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Many of the complications of severe coronavirus disease-2019 (COVID-19) are caused by blood hyperviscosity driven by marked hyperfibrinogenemia. This results in a distinctive hyperviscosity syndrome which affects areas of high and low shear. A change in blood viscosity causes a threefold inverse change in blood flow, which increases the risk of thrombosis in both arteries and veins despite prophylactic anticoagulation. Increased blood viscosity decreases perfusion of all tissues, including the lungs, heart, and brain. Decreased perfusion of the lungs causes global ventilation-perfusion mismatch which results in silent hypoxemia and decreased efficacy of positive pressure ventilation in treating pulmonary failure in COVID-19. Increased blood viscosity causes a mismatch in oxygen supply and demand in the heart, resulting in myocarditis and ventricular diastolic dysfunction. Decreased perfusion of the brain causes demyelination because of a sublethal cell injury to oligodendrocytes. Hyperviscosity can cause stasis in capillaries, which can cause endothelial necrosis. This can lead to the rarefaction of capillary beds, which is noted in "long-COVID." The genome of the virus which causes COVID-19, severe acute respiratory syndrome coronavirus 2, contains an extraordinarily high number of the oligonucleotide virulence factor 5'-purine-uridine-uridine-purine-uridine-3', which binds to toll-like receptor 8, hyperactivating innate immunity. This can lead to a marked elevation in fibrinogen levels and an increased prevalence of neutrophil extracellular traps in pulmonary failure, as seen in COVID-19 patients.
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Background: Dysregulation of antiviral immunity has been implicated in the progression of acute respiratory syndrome coronavirus 2 infection into severe cases of coronavirus disease of 2019 (COVID-19). Imbalances in the inflammatory response drive the overabundant production of pro-inflammatory cytokines and chemokines. The low molecular weight fraction of 5% human serum albumin commercial preparation (AMP5A) is a novel biologic drug currently under clinical investigation for the treatment of osteoarthritis and the hyperinflammatory response associated with COVID-19. This study aims to elucidate AMP5A effects following the activation of immune cells with agonists of Toll-like receptor (TLR) 7 and/or 8, which detect ssRNA viral sequences. Methods: CXCL10 ELISAs were used to evaluate the dynamics of myeloid cells activated with CL075 and CL307, agonists of TLR7/8 and TLR7, respectively. In addition, enrichment analysis of gene sets generated by ELISA arrays was utilized to gain insight into the biologic processes underlying the identified differentially expressed cytokine profiles. Finally, relative potency (REP) was employed to confirm the involvement of mechanisms of action paramount to AMP5A activity. Results: AMP5A inhibits the release of CXCL10 from both CL075- and CL307-activated PMA-differentiated THP-1 and peripheral blood mononuclear cells. Furthermore, AMP5A suppresses a distinct set of pro-inflammatory cytokines (including IL-1ß, IL-6, IL-12, and CXCL10) associated with COVID-19 and pro-inflammatory NF-κB activation. REP experiments using antagonists specific for the immunomodulatory transcription factors, peroxisome proliferator-activated receptor γ, and aryl hydrocarbon receptor, also indicate that these pathways are involved in the ability of AMP5A to inhibit CXCL10 release. Conclusion: Due to the biphasic course of COVID-19, therapeutic approaches that augment antiviral immunity may be more beneficial early in infection, whereas later interventions should focus on inflammation suppression. In this study, we show that AMP5A inhibits TLR 7/8 signaling in myeloid cells, resulting in a decrease in inflammatory mediators associated with hyperinflammation and autoimmunity. Furthermore, data demonstrating that AMP5A activates immunomodulatory transcription factors found to be protective in lung disease is provided. These findings suggest that the modes and mechanisms of action of AMP5A are well suited to treat conditions involving dysregulated TLR 7/8 activation.
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The clinical spectrum of COVID-19 is extremely variable. Thus, it is likely that the heterogeneity in the genetic make-up of the host may contribute to disease severity. Toll-like receptor (TLR)8 plays a vital role in the innate immune response to SARS-CoV-2 infection. We genotyped 60 adult COVID-19 samples taken from 20 patients, 20 recovery persons and 20 healthy people for TLR8 (rs3764880 A/G) polymorphisms usingTetra-ARMS Technique. The frequency of alleles of TLR8 gene polymorphism of A allele is 57.5% in patients and 60.0% in control group, while frequency of G allele is 42.5% in patients and 40.0% in control group. While, the frequency of alleles of TLR8 gene polymorphism of A allele is 55.0% in recovery and 60.0% in control group, while frequency of G allele is 45.0% in recovery and 40.0% in control group.
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Background: Enpatoran is a selective and potent dual toll-like receptor (TLR) 7/8 inhibitor in development for the treatment of cutaneous and systemic lupus erythematosus (CLE/SLE). Enpatoran inhibits TLR7/8 activation in vitro and suppresses disease activity in lupus mouse models.1 Enpatoran was well tolerated and had linear pharmacokinetic (PK) parameters in healthy volunteers.2 As TLR7/8 mediate immune responses to single-stranded RNA viruses, including SARS-CoV-2, it was postulated that enpatoran may prevent hyperinfammation and cytokine storm in COVID-19. Objectives: In response to the COVID-19 pandemic, we conducted an exploratory Phase II trial to assess safety and determine whether enpatoran prevents clinical deterioration in patients (pts) hospitalized with COVID-19 pneumonia. PK and pharmacodynamics (PD) of enpatoran were also evaluated. Methods: ANEMONE was a randomized, double-blind, placebo (PBO)-con-trolled study conducted in Brazil, the Philippines, and the USA (NCT04448756). Pts aged 18-75 years, hospitalized with COVID-19 pneumonia (WHO 9-point scale score =4) but not mechanically ventilated, with SpO2 <94% and PaO2/FiO2 ≥150 (FiO2 maximum 0.4) were eligible. Those with a history of uncontrolled illness, active/unstable cardiovascular disease and SARS-CoV-2 vaccination were excluded. Pts received PBO or enpatoran (50 or 100 mg twice daily [BID]) for 14 days, with monitoring to Day 28 and safety follow-up to Day 60. Primary outcomes were safety and time to recovery (WHO 9-point scale ≤3). Clinical deterioration (time to clinical status >4, WHO 9-point scale) was a secondary outcome. Exploratory endpoints were enpatoran and biomarker concentrations (cytokines, C-reactive protein [CRP], D-dimer and interferon gene signature [IFN-GS] scores) assessed over time. Results: 149 pts received either PBO (n=49), or enpatoran 50 mg (n=54) or 100 mg (n=46) BID;88% completed treatment and 86% received concomitant steroids. Median age was 50 years (77% <60 years old), 66% were male, and 50% had ≥1 comorbidity (40% hypertension, 24% diabetes). Overall, 59% pts reported a treatment-emergent adverse event (TEAE) with three non-treatment-related deaths;11% reported a treatment-related TEAE. The proportion of pts in the enpatoran group reporting serious TEAEs was low (50 mg BID 9%;100 mg BID 2%) vs PBO (18%). Gastrointestinal disorders were most common (PBO 8%;50 mg BID 28%;100 mg BID 9%). The primary outcome of time to recovery with enpatoran vs PBO was not met;medians were 3.4-3.9 days. A positive signal in time to clinical deterioration from Day 1 through Day 28 was observed;hazard ratios [95% CI] for enpatoran vs PBO were 0.39 [0.13, 1.15] (50 mg BID) and 0.30 [0.08, 1.08] (100 mg BID). Mean enpatoran exposure was dose-proportional, and PK properties were within expectations. The median (quartile [Q]1-Q3) interleukin 6 (IL-6), CRP and D-dimer baseline concentration across the groups were 5.7 (4.0-13.5) pg/mL, 30.04 (11.40-98.02) and 0.62 (0.39-1.01) mg/L, respectively. Baseline IFN-GS scores were similar across groups. Conclusion: The ANEMONE trial was the frst to evaluate the safety and efficacy of a TLR7/8 inhibitor in an infectious disease for preventing cytokine storm. Enpa-toran up to 100 mg BID for 14 days was well tolerated by patients acutely ill with COVID-19 pneumonia. Time to recovery was not improved with enpatoran, perhaps due to the younger age of patients who had fewer comorbidities compared to those in similar COVID-19 trials. However, there was less likelihood for clinical deterioration with enpatoran than placebo. This trial provides important safety, tolerability, PK and PD data supporting continued development of enpatoran in SLE and CLE (NCT04647708, NCT05162586).
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BACKGROUND: Cytokine storm in COVID-19 patients has contributed to many morbidities and mortalities in patients. Studies have found that toll-like receptors (TLRs) and some Fc receptors play essential roles in the hyperactivation of the immune system. Up to date, researchers are still in progress to discover effective and safe drugs to alleviate the hyperinflammatory state in COVID-19. The previous studies had shown that Carthamus tinctorius and its bioactive compounds might have anti-inflammatory activities in animal models. AIM: We aimed to investigate the possible interactions of several flavonoids from C. tinctorius with several immune system components using a biocomputational approach. METHODS: Molecular docking was done using the AutoDock program based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) COVID-19 pathway. The most suitable receptors found were studied to study the interactions with several flavonoids from C. tinctorius. RESULTS: TLR4, TLR8, and FcγRIIa were found to bind with SARS CoV2 inflammatory pathway and further selected as macromolecules for potential interactions study with 22 flavonoids from C. tinctorius. Of the 22 flavonoids studied, daphnoretin showed the best binding affinity with TLR4 and Rutin was shown to attach best with FcγRIIa. Unlike its excellent binding to TLR4, daphnoretin showed weak binding to TLR8. CONCLUSION: Daphnoretin showed an excellent affinity with TLR4 and might be a good candidate as an inhibitor in hyperinflammatory reactions in COVID-19 DTLR8.
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Background. Enpatoran, formerly known as M5049, is a potential first-in-class small molecule antagonist of toll-like receptors (TLR) 7 and 8, which may prevent viral-associated hyperinflammatory response and progression to 'cytokine storm' in coronavirus disease 2019 (COVID-19) patients. The objective of this study was to leverage existing population pharmacokinetic/pharmacodynamic (popPK/PD) models for enpatoran to inform dose selection for an accelerated Phase II study in COVID-19 patients with pneumonia. Methods. The popPK/PD models were based on plasma PK and PD biomarker (ex vivo-stimulated interleukin [IL]6 and interferon α [IFNα] secretion) data from the enpatoran first-in-human Phase I study in healthy participants (Port A, et al. Lupus Sci Med 2020;7(Suppl. 1): P135). A two-compartment model describing PK used a sigmoidal Emax model with proportional decrease from baseline characterizing the PD response across the investigated single and multiple daily dose range of 1-200 mg (N=72). Concentrations that inhibited 50% and 90% (IC50/IC90) of cytokine secretion were estimated and stochastic simulations were performed to assess target coverage under different dosing regimens. Results. Simulations suggested that, to achieve maximal inhibition of IL-6 over time, enpatoran PK concentrations would be maintained above the IC90 throughout the dosing interval with doses of 100 mg and 50 mg twice daily in 90% and 30% of participants, respectively. In comparison, IFNα inhibition was predicted to be lower, with IC90 coverage in 60% and 8% of participants with twice daily doses of 100 mg and 50 mg enpatoran, respectively. Conclusion. Utilization of existing popPK/PD models allowed for the accelerated development of enpatoran in COVID-19 to address an unprecedented global pandemic. Rational model-informed dose selection was supported by data from a Phase I study in which there were no safety concerns.
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Regulation of proinflammatory cytokine expression is critical in the face of single-stranded RNA (ssRNA) virus infections. Many viruses, including coronavirus and influenza virus, wreak havoc on the control of cytokine expression, leading to the formation of detrimental cytokine storms. Understanding the regulation and interplay between inflammatory cytokines is critical to the identification of targets involved in controlling the induction of cytokine expression. In this study, we focused on how the antiviral cytokine interleukin-27 (IL-27) regulates signal transduction downstream of Toll-like receptor 7 (TLR7) and TLR8 ligation, which recognize endosomal single-stranded RNA. Given that IL-27 alters bacterial-sensing TLR expression on myeloid cells and can inhibit replication of single-stranded RNA viruses, we investigated whether IL-27 affects expression and function of TLR7 and TLR8. Analysis of IL-27-treated THP-1 monocytic cells and THP-1-derived macrophages revealed changes in mRNA and protein expression of TLR7 and TLR8. Although treatment with IL-27 enhanced TLR7 expression, only TLR8-mediated cytokine secretion was amplified. Furthermore, we demonstrated that imiquimod, a TLR7 agonist, inhibited cytokine and chemokine production induced by a TLR8 agonist, TL8-506. Delineating the immunomodulatory role of IL-27 on TLR7 and TLR8 responses provides insight into how myeloid cell TLR-mediated responses are regulated during virus infection.