Aloin isoforms (A and B) selectively inhibits proteolytic and deubiquitinating activity of papain like protease (PLpro) of SARS-CoV-2 in vitro

Abstract

The most common host entry point of human adapted coronaviruses (CoV) including SARS-CoV-2 is through the initial colonization in the nostril and mouth region which is responsible for spread of the infection. Most recent studies suggest that the 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 not been 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 of SARS-CoV-2 PLpro and 3CLpro. Our results indicate only aloin A and B effectively inhibited proteolytic activity of PLpro with an IC50 of 13.16 and 16.08 μM. Interestingly, neither of the aloin isoforms inhibited 3CLpro enzymatic activity. Computational structural modelling of aloin A and B interaction with PLpro revealed that, both aloin isoforms form hydrogen bond with Tyr268 of PLpro, which is critical for their proteolytic activity. Furthermore, 100 ns molecular dynamics (MD) simulation studies predicted that both aloin isoforms have strong interaction with Glu167, which is required for PLpro deubiquitination activity. Our results from the in vitro deubiquitinase inhibition assay show that aloin A and B isomers exhibit deubiquitination inhibitory activity with an IC50 value of 15.68 and 17.51 µM, respectively. In conclusion, the isoforms of aloin inhibit both proteolytic and the deubiquitinating activity of SARS-CoV-2 PLpro, suggesting potential in inhibiting the replication of SARS-CoV-2 virus.

Progress and Challenges in Targeting the SARS-CoV-2 Papain-like Protease

“…Lewis et al tested the active ingredients of mouth rinses against the SARS-CoV-2 M pro and PL pro . 86 Although none of the compounds were active against M pro , two compounds, aloin A ( 42 ) and aloin B ( 43 ), inhibited PL pro , with IC 50 values of 13.16 and 16.08 μM, respectively, in the enzymatic assay. Aloin A ( 42 ) and B ( 43 ) also inhibited the deubiquitinating activity of PL pro , with IC 50 values of 15.68 and 17.51 μM.…”

“…Commercial mouth rinses are known to inactivate SARS-CoV-2, , but the detailed mechanism remains elusive. Lewis et al tested the active ingredients of mouth rinses against the SARS-CoV-2 M pro and PL pro . Although none of the compounds were active against M pro , two compounds, aloin A ( 42 ) and aloin B ( 43 ), inhibited PL pro , with IC 50 values of 13.16 and 16.08 μM, respectively, in the enzymatic assay.…”

Antiviral Potential of Plants against COVID-19 during Outbreaks—An Update

“…Aloin A and B isomers also showed deubiquitination inhibitory activities with IC 50 values of 15.68 and 17.51 M, respectively. The isoforms of aloin limited SARS-CoV-2 PLpro proteolytic and deubiquitinating activities, indicating their possible use in preventing viral reproduction [ 108 ].…”

Utilization of Aloe Compounds in Combatting Viral Diseases

“…Further, hepatic and renal toxicity tests did not show any safety signal for aloin treatment (2.5 mg/kg body weight) in mice. Moreover, both isoforms of aloin have been demonstrated to inhibit the proteolytic and deubiquitinating activities of the papain-like protease of SARS-CoV-2 [ 35 ].…”