3.1 Triterpenoid saponins from Codonopsis lanceolatainhibit the infection of SARS-CoV-2
We first tested whether CL has an inhibitory activity against SARS-CoV-2
infection using a pseudovirus that expresses S protein on HIV-based
lentiviral particles (pSARS-CoV-2), which has been used as a model
system for analyzing SARS-CoV-2
infection(Crawford et al., 2020;
Kim et al., 2021). pSARS-CoV-2 entry
assay showed that the 70% EtOH extracts of the roots and aerial parts
of CL prevented pSARS-CoV-2 from entering the ACE2-overexpressing H1299
human lung carcinoma cells (ACE2+ H1299) in a
dose-dependent manner with half-maximal inhibitory concentrations
(IC50) of 251 μg/ml and 540 μg/ml, respectively, without
obvious cell toxicity (Figure. 1a and 1b). These results indicate that
CL extracts contain substances with inhibitory activity against
SARS-CoV-2 infection, which are higher in the roots than the aerial
parts. In order to identify bioactive compounds in the CL, eight main
compounds we previously isolated from the roots of CL
(Du et al., 2018) were subjected to the
examinations for their inhibitory effects against two SARS-CoV-2 entry
pathways, that is, endosomal pathway in ACE2+ H1299
cells and TMPRSS2-mediated membrane fusion in ACE2 and TMPRSS2
double-positive cells (ACE2/TMPRSS2+ H1299) (Figure
1c). Our results revealed that both SARS-CoV-2 entry pathways were
effectively blocked by pentacyclic triterpenoid saponins such as
lancemaside A (LA) and lancemaside B (LB), but not others including
lancemaside D (LD) (Figure 1d), indicating that LA and LB are
biologically active compounds responsible for the blockade of SARS-CoV-2
infection in CL extracts.