Calceolarioside B inhibits SARS-CoV-2 Omicron BA.2 variant cell entry and modulates immune response.

Abstract

This study evaluated the inhibitory effects of calceolarioside B, extracted from the traditional Chinese herb Mutong (Akebia quinata Thumb), on the SARS-CoV-2 Omicron BA.2 variant. Molecular docking and molecular dynamics simulations predicted the binding sites and interactions between calceolarioside B and the Omicron BA.2 spike (S) protein. Biolayer interferometry (BLI) and immunofluorescence assays validated its high-affinity binding. Pseudovirus entry assays assessed the inhibitory effects of calceolarioside B on viral entry into host cells, while enzyme-linked immunosorbent assay (ELISA) measured inflammatory cytokine levels. Flow cytometry was used to analyze its effects on macrophage phenotype switching. Results demonstrated that calceolarioside B could bind to the Omicron BA.2 S protein with high affinity, and significantly inhibited viral entry into host cells by interfering with the binding of angiotensin-converting enzyme 2 (ACE2) receptor and S protein. Additionally, calceolarioside B reduced IL(interleukin)-6 expression levels and promoted the switch of macrophages from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype. These findings suggest that calceolarioside B possesses antiviral and immunomodulatory effects, making it a potential dual-function inhibitor for the treatment of COVID-19.