Effects of Sulforaphane on SARS-CoV-2 infection and NF-κB dependent expression of genes involved in the COVID-19 'cytokine storm'

Since its spread at the beginning of 2020, the coronavirus disease 2019 (COVID-19) pandemic represents one of the major health problems. Despite the approval, testing, and worldwide distribution of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines, the development of specific antiviral agents targeting the SARS-CoV-2 life cycle with high efficiency, and/or interfering with the associated 'cytokine storm', is highly required. A recent study, conducted by the authors' group indicated that sulforaphane (SFN) inhibits the expression of IL-6 and IL-8 genes induced by the treatment of IB3-1 bronchial cells with a recombinant spike protein of SARS-CoV-2. In the present study, the ability of SFN to inhibit SARS-CoV-2 replication and the expression of pro-inflammatory genes encoding proteins of the COVID-19 'cytokine storm' was evaluated. SARS-CoV-2 replication was assessed in bronchial epithelial Calu-3 cells. Moreover, SARS-CoV-2 replication and expression of pro-inflammatory genes was evaluated by reverse transcription quantitative droplet digital PCR. The effects on the expression levels of NF-& kappa;B were assessed by western blotting. Molecular dynamics simulations of NF-kB/SFN interactions were conducted with Gromacs 2021.1 software under the Martini 2 CG force field. Computational studies indicated that i) SFN was stably bound with the NF-& kappa;B monomer; ii) a ternary NF-kB/SFN/DNA complex was formed; iii) the SFN interacted with both the protein and the nucleic acid molecules modifying the binding mode of the latter, and impairing the full interaction between the NF-& kappa;B protein and the DNA molecule. This finally stabilized the inactive complex. Molecular studies demonstrated that SFN i) inhibits the SARS-CoV-2 replication in infected Calu-3 cells, decreasing the production of the N-protein coding RNA sequences, ii) decreased NF-& kappa;B content in SARS-CoV-2 infected cells and inhibited the expression of NF-kB-dependent IL-1 & beta; and IL-8 gene expression. The data obtained in the present study demonstrated inhibitory effects of SFN on the SARS-CoV-2 life cycle and on the expression levels of the pro-inflammatory genes, sustaining the possible use of SFN in the management of patients with COVID-19.