Curcumin and turmeric extract inhibit SARS-CoV-2 pseudovirus cell entry and spike-mediated cell fusion

Turmeric extract (TE) with curcumin as its main active ingredient has been studied as a potential COVID-19 therapeutic. Curcumin has been studied in silico and in vitro against a naive SARS-CoV-2 virus, yet little is known about TE’s impact on SARS-CoV-2 infection. Moreover, no study reveals the potential of both curcumin and TE on the inhibition of SARS-CoV-2 cell-to-cell transmission. Here, we investigated the effects of both curcumin and TE on inhibiting SARS-CoV-2 entry and cell-to-cell transmission using pseudovirus (PSV) and syncytia models. We performed a PSV entry assay in 293T or 293 cells expressing hACE2. The cells were pretreated with curcumin or TE and then treated with PSV with or without the test samples. Next, we carried out syncytia assay by co-transfecting 293T cells with plasmids encoding spike, hACE2, and TMPRSS2 to be treated with the test samples. The results showed that in PSV entry assay on 293T/hACE/TMPRSS2 cells, both curcumin and TE inhibited PSV entry at concentrations of 1 µM and 10 µM for curcumin and 1 µg/ml and 10 µg/ml for TE. Moreover, both curcumin and TE reduced syncytia formation compared to control cells. Our study shows that TE and curcumin are potential inhibitors of SARS-CoV-2 infection at entry points, either by direct or indirect infection models. GRAPHICAL ABSTRACT