Inhibition of SARS-CoV-2 spike S1-ACE2 binding interaction and downregulation of ACE2 gene expression by Malaysian stingless bee honey and its bioactive compound, stilbamidine (SDC).

BACKGROUND: The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus infects host cells by binding to angiotensin-converting enzyme 2 (ACE2). Stilbamidine (SDC), a compound identified in Malaysian Kelulut honey (KH), has been reported to exhibit favourable binding affinity towards ACE2. This study aims to determine the effects of KH and SDC on the binding of spike protein to the ACE2 receptor, as well as to assess their modulatory potential on ACE2 gene and protein expression in lung and kidney cells.

METHODS AND RESULTS: KH, SDC, and MLN 4760 (ACE2 inhibitor) were tested using an in vitro spike S1:ACE2 inhibition assay. Their modulatory effects on the ACE2 gene and protein expression were further examined through real-time PCR and western blot analysis. KH inhibited the binding of Spike S1 to ACE2, surpassing MLN4760, with maximum effects (Emax) of 82.66 ± 0.24% and 59.81 ± 8.00%, respectively, while the Emax for SDC was 19.93 ± 0.4%. KH caused a significant, dose-dependent downregulation of ACE2 gene expression in kidney-derived Vero E6 cells after 24 h of treatment, whereas SDC reduced ACE2 gene expression in lung-derived A549-ACE2-TMPRSS2 cells after 72 h. Nevertheless, ACE2 protein expression remained unchanged following both treatments.

CONCLUSIONS: KH and SDC inhibit the binding of the SARS-CoV-2 spike S1 protein to the ACE2 receptor and reduce ACE2 gene expression. The efficacy of ACE2-targeted interventions may be limited by ACE2 polymorphisms and inter-individual expression differences. Further in vivo studies are needed to confirm their prophylactic and therapeutic potential against SARS-CoV-2 infection.