Barbaloin (Aloin-A) and isobarbaloin (Aloin-B) selectively inhibit activity of papain like protease (PLpro) of SARS-CoV-2 in vitro

Suwanee, GA

In human adapted corona viruses (including SARS-CoV-2), the most common host entry point is through the initial colonization in the laryngeal and pharyngeal regions which are responsible for spread of the infection. Recent studies suggest that commercially available oral and nasal rinse products are effective in inhibiting the viral replication, however, the anti-viral mechanism of the active ingredients present in the oral rinses have yet to be studied. In the present study, we have assessed in vitro enzymatic inhibitory activity of active ingredients in the oral mouth rinse products: aloin-A and B, chlorhexidine, eucalyptol, hexetidine, menthol, triclosan, methyl salicylate, sodium fluoride and povidone, against two important proteases, Plpro and 3CLpro of SARS-CoV-2. Our results indicate only aloin-A and B effectively inhibited proteolytic activity of PLpro with an IC of 13.16 and 16.08 μM. Interestingly, neither of the aloin isoforms inhibited 3CLpro enzymatic activity. Computational structural modeling of aloin-A and B interaction with PLpro revealed that, both aloin isoforms form hydrogen bonds with Tyr of PLpro, which is critical for their proteolytic activity. Furthermore, 100ns molecular dynamics (MD) simulation studies predicted that both aloin isoforms have strong interaction with Glu , which is required for PLpro deubiquitination activity. The results we have obtained via inhibition assay from the in vitro deubiquitinase show that aloin A and B isomers exhibit deubiquitination inhibitory activity with IC values of 38.03 and 38.75 μM, respectively. In conclusion, the isoforms of aloi, inhibit both proteolytic and the deubiquitinating activity of SARS-CoV-2 PLpro, suggesting potential benefits in reducing the spread of SARS-CoV-2 virus, however, these studies need to be validated in additional pre-clinical and clinical studies.