In addition to respiratory complications produced by SARS‐CoV‐2, accumulating evidence suggests that some neurological symptoms are associated with the disease caused by this coronavirus. In this study, we investigated the effects of the SARS‐CoV‐2 spike protein S1 stimulation on neuroinflammation in BV-2 microglia. Analyses of culture supernatants revealed an increase in the production of TNF-α, IL-6, IL-1β and iNOS/NO. S1 also increased protein levels of phospho-p65 and phospho-IκBα, as well as enhanced DNA binding and transcriptional activity of NF-κB. These effects of the protein were blocked in the presence of BAY11-7082 (1 µM). Exposure of S1 to BV-2 microglia also increased the protein levels of NLRP3 inflammasome and enhanced caspase-1 activity. Increased protein levels of p38 MAPK was observed in BV-2 microglia stimulated with the spike protein S1 (100 ng/ml), an action that was reduced in the presence of SKF 86,002 (1 µM). Results of immunofluorescence microscopy showed an increase in TLR4 protein expression in S1-stimulated BV-2 microglia. Furthermore, pharmacological inhibition with TAK 242 (1 µM) and transfection with TLR4 small interfering RNA resulted in significant reduction in TNF-α and IL-6 production in S1-stimulated BV-2 microglia. These results have provided the first evidence demonstrating S1-induced neuroinflammation in BV-2 microglia. We propose that induction of neuroinflammation by this protein in the microglia is mediated through activation of NF-κB and p38 MAPK, possibly as a result of TLR4 activation. These results contribute to our understanding of some of the mechanisms involved in CNS pathologies of SARS-CoV-2.

An understanding of the pathological inflammatory mechanisms involved in SARS-CoV-2 virus infection is necessary in order to discover new molecular pharmacological targets for SARS-CoV-2 cytokine storm. In this study, the effects of a recombinant SARS-CoV-2 spike glycoprotein S1 was investigated in human peripheral blood mononuclear cells (PBMCs). Stimulation of PBMCs with spike glycoprotein S1 (100 ng/mL) resulted in significant elevation in the production of TNFα, IL-6, IL-1β and IL-8. However, pre-treatment with dexamethasone (100 nM) caused significant reduction in the release of these cytokines. Further experiments revealed that S1 stimulation of PBMCs increased phosphorylation of NF-κB p65 and IκBα, and IκBα degradation. DNA binding of NF-κB p65 was also significantly increased following stimulation with spike glycoprotein S1. Treatment of PBMCs with dexamethasone (100 nM) or BAY11-7082 (1 μM) resulted in inhibition of spike glycoprotein S1-induced NF-κB activation. Activation of p38 MAPK by S1 was blocked in the presence of dexamethasone and SKF 86002. CRID3, but not dexamethasone pre-treatment, produced significant inhibition of S1-induced activation of NLRP3/caspase-1. Further experiments revealed that S1-induced increase in the production of TNFα, IL-6, IL-1β and IL-8 was reduced in the presence of BAY11-7082 and SKF 86002, while CRID3 pre-treatment resulted in the reduction of IL-1β production. These results suggest that SARS-CoV-2 spike glycoprotein S1 stimulated PBMCs to release pro-inflammatory cytokines through mechanisms involving activation of NF-κB, p38 MAPK and NLRP3 inflammasome. It is proposed that the clinical benefits of dexamethasone in COVID-19 are possibly due to its anti-inflammatory activity in reducing SARS-CoV-2 cytokine storm.

The emergence of SARS‐CoV‐2 has resulted in a global pandemic. In addition to respiratory complications as a result of SARS‐CoV‐2 illness, accumulating evidence suggests that neurological and neuropsychiatric symptoms are associated with the disease caused by the virus. In this study, we investigated the effects of the SARS‐CoV‐2 spike glycoprotein S1 stimulation on neuroinflammation in BV-2 microglia. Analyses of culture supernatants revealed an increase in the production of TNFα, IL-6, IL-1β and iNOS/NO. SARS‐CoV‐2 spike glycoprotein S1 increased protein expressions of phospho-p65 and phospho-IκB, as well as enhancing DNA binding and transcriptional activity of NF-κB. Pro-inflammatory effects of the glycoprotein effects were reduced in the presence of BAY11-7082 (1 μM). The presence of SARS‐CoV‐2 spike glycoprotein S1 in BV-2 microglia increased the protein expression of NLRP3, as well as caspase-1 activity. However, pre-treatment with CRID3 (1 μM) or BAY11-7082 (1 μM) resulted in the inhibition of NLRP3 inflammasome/caspase-1. It was also observed that CRID3 attenuated SARS‐CoV‐2 spike glycoprotein S1-induced increase in IL-1β production. Increased protein expression of p38 MAPK was observed in BV-2 microglia stimulated with the spike glycoprotein S1, and was reduced in the presence of SKF 86002. These results have provided the first evidence demonstrating SARS-CoV-2 spike S1 glycoprotein-induced neuroinflammation in BV-2 microglia. We propose that promotion of neuroinflammation by this glycoprotein is mediated through activation of NF-κB, NLRP3 inflammasome and p38 MAPK. These results are significant because of their relevance to our understanding of neurological and neuropsychiatric symptoms observed in patients infected with SARS-CoV-2.

An understanding of the pathological inflammatory mechanisms involved in SARS CoV-2 virus infection is necessary in order to discover new molecular pharmacological targets for SARS-CoV-2 spike glycoprotein. In this study, the effects of a recombinant SARS CoV-2 spike glycoprotein S1 was investigated in human peripheral blood mononuclear cells (PBMCs). Stimulation with spike glycoprotein S1 (100 ng/mL) resulted in significant elevation in the production of TNFα, IL-6, IL-1β and IL-8. However, pre-treatment with dexamethasone (100 nM) caused a significant reduction in the release of these cytokines. Further experiments revealed that S1 stimulation of PBMCs increased phosphorylation of NF-κB p65 and IκBα, while increasing IκBα degradation. DNA binding of NF-κB p65 was also significantly increased following stimulation with S1. Treatment of PBMCs with dexamethasone (100 nM) or BAY11-7082 (1 μM) resulted in inhibition of S1-induced NF-κB activation. Activation of p38 MAPK by S1 was blocked in the presence of dexamethasone and SKF 86002. CRID3, but not dexamethasone pre-treatment produced significant inhibition of S1-induced activation of NLRP3/caspase 1. Further experiments revealed that S1-induced increase in the production of TNFα, IL-6, IL-1β and IL-8 was reduced in the presence of BAY11-7082 and SKF 86002, while CRID3 pre-treatment resulted in the reduction of IL-1β production. These results suggest that SARS-CoV-2 spike glycoprotein S1 stimulate PBMCs to release pro inflammatory cytokines through mechanisms involving activation of NF-κB, p38 MAPK and NLRP3 inflammasome. It is proposed that clinical benefits of dexamethasone in COVID-19 is possibly due to its anti-inflammatory activity in reducing SARS-CoV-2 cytokine storm.

Symptoms and complications associated with severe SARS-CoV-2 infection such as acute respiratory distress syndrome (ARDS) and organ damage have been linked to SARS-CoV-2 spike glycoprotein S1-induced increased production of pro inflammatory cytokines by immune cells. In this study, the effects of an extract of Garcinia kola seeds and garcinoic acid were investigated in SARS-CoV-2 spike glycoprotein S1-stimulated human PBMCs. Results of ELISA experiments revealed that Garcinia kola extract (6.25, 12.5 and 25 μg/mL) and garcinoic acid (1.25, 2.5 and 5 μM) significantly reduced SARS-CoV-2 spike glycoprotein S1-induced increased secretion of TNFα, IL-6, IL-1β and IL-8 in PBMCs. In-cell western assays showed that pre-treatment with Garcinia kola extract and garcinoic acid reduced elevated expressions of both phospho-p65 and phospho-IκBα proteins, as well as NF-κB DNA binding capacity and NF-κB driven luciferase expression following stimulation of PBMCs with spike glycoprotein S1. Furthermore, pre-treatment of PBMCs with Garcinia kola extract prior to stimulation with SARS-CoV-2 spike glycoprotein S1 resulted in reduced damage to adjacent A549 lung epithelial cells. Gas Chromatography-Mass Spectrometry (GCMS) and HPLC-PDA confirmed the presence of garcinoic acid in the Garcinia kola extract used in this study. These results suggest that the seed of Garcinia kola and garcinoic acid are natural products which may possess pharmacological/therapeutic benefits in reducing cytokine storm during the late stage of severe SARS-CoV-2 and other coronavirus infections.