SARS-CoV-2 Delta spike protein enhances the viral fusogenicity and inflammatory cytokine production.

The Delta variant had spread globally in 2021 and caused more serious disease than the original virus and Omicron variant. In this study, we investigated several virological features of Delta spike protein (SPDelta), including protein maturation, its impact on viral entry of pseudovirus and cell-cell fusion, and its induction of inflammatory cytokine production in human macrophages and dendritic cells. The results showed that SPΔCDelta exhibited enhanced S1/S2 cleavage in cells and pseudotyped virus-like particles (PVLPs). Further, SPΔCDelta elevated pseudovirus entry in human lung cell lines and significantly enhanced syncytia formation. Furthermore, we revealed that SPΔCDelta-PVLPs had stronger effects on stimulating NF-κB and AP-1 signaling in human monocytic THP1 cells and induced significantly higher levels of proinflammatory cytokine, such as TNF-α, IL-1ß, and IL-6, released from human macrophages and dendritic cells. Overall, these studies provide evidence to support the important role of SPΔCDelta during virus infection, transmission, and pathogenesis.

Identification and evaluation of the inhibitory effect of Prunella vulgaris extract on SARS-coronavirus 2 virus entry.

Until now, antiviral therapeutic agents are still urgently required for treatment or prevention of SARS-coronavirus 2 (SCoV-2) virus infection. In this study, we established a sensitive SCoV-2 Spike glycoprotein (SP), including an SP mutant D614G, pseudotyped HIV-1-based vector system and tested their ability to infect ACE2-expressing cells. Based on this system, we have demonstrated that an aqueous extract from the Natural herb Prunella vulgaris (NhPV) displayed potent inhibitory effects on SCoV-2 SP (including SPG614 mutant) pseudotyped virus (SCoV-2-SP-PVs) mediated infections. Moreover, we have compared NhPV with another compound, Suramin, for their anti-SARS-CoV-2 activities and the mode of their actions, and found that both NhPV and Suramin are able to directly interrupt SCoV-2-SP binding to its receptor ACE2 and block the viral entry step. Importantly, the inhibitory effects of NhPV and Suramin were confirmed by the wild type SARS-CoV-2 (hCoV-19/Canada/ON-VIDO-01/2020) virus infection in Vero cells. Furthermore, our results also demonstrated that the combination of NhPV/Suramin with an anti-SARS-CoV-2 neutralizing antibody mediated a more potent blocking effect against SCoV2-SP-PVs. Overall, by using SARS-CoV-2 SP-pseudotyped HIV-1-based entry system, we provide strong evidence that NhPV and Suramin have anti-SARS-CoV-2 activity and may be developed as a novel antiviral approach against SARS-CoV-2 infection.

Prunella vulgaris Extract Blocks SARS- Coronavirus 2 Virus Spike Protein D614 and G614 Variants Mediated Receptor Binding and Virus Entry (preprint)

Until now, there is no approved effective vaccine, and antiviral therapeutic agents available for treatment or prevention of SARS-coronavirus 2 (SCoV-2) virus infection. In this study, we established a SCoV-2 Spike glycoprotein (SP) including an SP mutant D614G pseudotyped HIV-1-based vector system and tested their ability to infect ACE2-expressing cells. This study revealed that a C-terminal 17 amino acid deletion in SCoV-2 SP significantly increases the incorporation of SP into the pseudotyped viruses and enhanced its infectivity, which is valuable information for the design of SCoV2-SP-based vaccine strategies. Also, based on this system, we have demonstrated that an aqueous extract from the Chinese herb Prunella vulgaris (CHPV) displayed potent inhibitory effects on both SCoV-2 SP (including SPG614 mutant) pseudotyped virus (SCoV-2-SP-PVs) and SARS CoV SP-pseudotyped virus-mediated infections. Moreover, we have compared CHPV with another compound, Suramin, for their anti-SARS-CoV-2 activities and the mode of their actions, and found that both CHPV and Suramin are able to directly interrupt SCoV-2–SP binding to its receptor ACE2 and block the viral entry step. Importantly, our results also revealed that CHPV and Suramin were able to efficiently inhibit the wild type SARS-CoV-2 (hCoV-19/Canada/ON-VIDO-01/2020) virus infection in Vero cells. Furthermore, our results also demonstrated that the combination of CHPV/Suramin with an anti-SARS-CoV-2 neutralizing antibody mediated a more potent blocking effect against SCoV2-SP-PVs. Overall, this study provides pieces of strong evidence that CHPV and Suramin has anti-SARS-CoV-2 activity and may be developed as a novel antiviral approach, especially as nasopharynx agents, against SARS-CoV-2 infection.Funding: This work was supported by Canadian 2019 Novel Coronavirus (COVID-19) Rapid Research Funding (OV5-170710) by Canadian Institute of Health Research (CIHR) and Research Manitoba to X-J.Y and D.K.Conflict of Interest: The authors declare no competing interests.