Blocking the action of NLRP3 inflammasome by inhaled ibuprofenate on pulmonary macrophages infected by SARS‐CoV‐2

Abstract

We present a Graphical Abstract that would represent the potential therapeutic effects of inhaled ibuprofenate on lung macrophages infected by SARS-CoV-2 and its link with the NLRP3 inflammasome. Furthermore, in the manuscript we will provide data on observational studies in pneumonias and Cards. In this manuscript, we will describe the possible mechanisms of action of the non-steroidal anti-inflammatory drug (NSAID) inhaled sodium ibuprofenate in hypertonic saline formulation (NaIHS), through its anti-inflammatory and immunomodulatory therapeutic effects, focusing primarily on the potential blockade of NOD-like receptor protein 3 (NLRP3) inflammasome action in Severe Acute Respiratory Syndrome-Coronavirus 2 (SARS-CoV-2)-infected lung macrophages. Currently, there are available three observational studies in the compassionate use modality in moderate and severe Coronavirus Disease 2019 (COVID-19) pneumonia, carried out in Argentina,1-3 with all three studies concluding that there was a significant reduction in mortality.1-3 The most recent of these was conducted with the approval of the Institutional Review Board of the National Bureau of Economic Research (NBER) of Harvard and Columbia Universities, which analysed data from 5146 patients and concluded that NaIHS reduced mortality by 48.7%,3 although randomized clinical trials are steel needed to confirm these data. NLRP3 inflammasome is a cytosolic multiprotein complex that plays a key role in the regulation of the innate immune system and inflammatory signalling, mostly against viral infections and cell damage.4 Their activation and assembly occurs mainly through different insults: activation of pattern recognition receptors (PRRs) through the pathogen-associated molecular patterns (PAMPs) and the danger-associated molecular patterns (DAMPs), both at the plasma membrane by toll-like receptor 4 (TLR4), as well as at the cytosolic level by nod-like receptor 2 (NLR2), hypoxaemia, renin-angiotensin system (RAS) imbalance, mitochondrial dysfunction and oxidative stress, lysosomal leakage with cathepsin-B release, ion fluxes and others.4 In the face of infection of lung macrophages by SARS-CoV-2, hyperactivation and assembly of the NLRP3 inflammasome is triggered, resulting in a cascade of positive caspase-1 signalling (first step), pro-inflammatory cytokines and inflammatory signalling pathways.4 This way, the activated NLRP3 inflammasome leads to the maturation and release by proteolytic cleavage of immature precursors of: caspase-1, interleukin-1 beta (IL-1β), IL-18 and gasdermin-D (GSDMD).4 The NLRP3 inflammasome promotes, on one arm, the release and activation of IL-1β and IL-18 and these cytokines, in turn, lead to the activation of the nuclear factor kappa light chain enhancer of activated B cells (NF-κB), the stimulation of natural killer (NK) cells, the release of interferon-γ (IFN-γ) and the inhibition of IL-33 activity.4 In addition, on the other arm, the NLRP3 inflammasome promotes GSDMD-mediated release and activation of IL-1β and IL-18 through membrane pores and it also leads to the release and activation of GSDMD-NT, which together with caspase-4 and caspase-5 would lead to T-cell pyroptosis.4 This cascade of events triggers the activation and recruitment of pulmonary macrophages, generating the cytokine storm, activation of inflammatory signalling pathways and also provoking a positive immune-inflammatory amplifying feed-back loop between all the above-mentioned components.4 It might block NLRP3 inflammasome action through the following effects: In vitro and in vivo, ibuprofen inhibits the activation of NLRP3 inflammasome6 and thus significantly reduces the levels of caspase-1,6 IL-1β6 and IL-18.6 It might inhibit NLRP3 inflammasome due to its peroxisome proliferator-activated receptor-gamma (PPAR-γ) agonist effect,4, 7 and it also might inhibit NLRP3 inflammasome via inhibition of membrane volume anion chloride channel and thus chloride efflux.4, 8 It might prevent pyroptosis through negative modulation of the inflammatory signalling pathway phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR),4, 7 caspase-14, 6, caspase-44, 9 and caspase-54, 9. It might negatively modulate the activation and recruitment of pulmonary macrophages.6 It would negatively modulate the main inflammatory signalling pathways: COX25, NF-κB,5 signal transducer and activator of transcription 3 (STAT3),5 TLR45 and PI3K/AKT/mTOR7. It would negatively modulate the main pro-inflammatory cytokines: IL-1β,5 tumor necrosis factor-alpha (TNF-α),5 IL-65, IFN-γ,5 transforming growth factor-beta 1 (TGF-β1),5 intercellular adhesion molecule-1 (ICAM-1)5 and IL-186. It may revert hypoxaemia, exclusively of the vasoplegic type10 and thus, it might prevent NLRP3 inflammasome activation. It would restore the RAS imbalance5 and thus, it also might prevent NLRP3 inflammasome activation. We have herein postulated the potential therapeutic effects of adjuvant treatment with NaIHS that might block NLRP3 inflammasome action in SARS-CoV-2-infected lung macrophages, and it might negatively modulate activation with monocyte recruitment, cytokine storm and activation of inflammatory signalling pathways. And above all, NaIHS has demonstrated in the aforementioned observational studies: a significant reduction in mortality, improvement of clinical outcomes, rapid reversal of hypoxaemia and decrease in hospitalization stay in pneumonia and Coronavirus Disease 2019-associated Acute Respiratory Distress Syndrome (CARDS). Yet, randomised clinical trials are still needed to confirm these emerging data. The authors declare that they have no conflicts of interest to this manuscript. The authors received no funding for this article.