In a recent study published in Scientific Reports, researchers assessed the efficacy of tea and its catechins in inactivating the Omicron subvariant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Study: Effects of tea, catechins and catechin derivatives on Omicron subvariants of SARS-CoV-2. Image Credit: grafvision/Shutterstock.com
SARS-CoV-2 Omicron subvariants are highly contagious due to multiple spike (S) glycoprotein mutations.
Previous research by the authors revealed that tea catechins, particularly (-)-epigallocatechin gallate (EGCG) and its derivative theaflavin-3,3'-di-O-digallate (TFDG), effectively deactivated SARS-CoV-2 by interacting with the receptor-binding domain (RBD) of the S glycoprotein.
In this study, the researchers aimed to determine if tea and its catechins could neutralize Omicron subvariants. They also investigated whether saliva from individuals who consumed candies containing black or green tea could deactivate the Omicron BA.1 subvariant in vitro.
To assess the impact of tea on Omicron subvariants, they exposed Omicron suspensions to freshly brewed black or green tea, prepared by mixing powdered green Matcha tea or immersing tea leaves in heated water at 90% concentration.
The infectivity of Omicron subvariants was evaluated by treating them with various tea catechins for 10 seconds, followed by 50% tissue culture infectious dose (TCID50) experiments.
The researchers also examined the influence of different quantities of EGCG and TFDG on Omicron subvariants and provided theaflavins (TF, TF3'G, TF3G, and TFDG) in quantities similar to those found in black tea. Additionally, they investigated the impact of varying TFDG concentrations on Omicron subvariant inactivation.
To assess EGCG's antiviral effects on cells or the virus, cells were pretreated with EGCG before infection with Omicron BA.1 treated with distilled water (DW). Neutralization experiments were conducted to determine if EGCG, GCG, and TFDG hindered interaction with the BA.1 RBD and angiotensin-converting enzyme 2 (ACE2).
Molecular docking simulations were also performed to explore how EGCG and TFDG inhibited the physical connection between Omicron S RBD and ACE2. Finally, the researchers investigated whether consuming candies containing green or black tea could generate saliva capable of inactivating SARS-CoV-2.
Green tea, Matcha, and black tea effectively inactivated Omicron subvariants. EGCG and TFDG significantly reduced infectivity of Omicron BA.1 and XE subvariants but had a smaller impact on the BA.2.75 subvariant. EGCG and TFDG also reduced the interaction between BA.1 RBD and ACE2.
RBD mutations N460K, G446S, and F490S affected EGCG/TFDG binding to the RBDs. Treatment with any tea sample reduced the titer of BA.1 to less than 1/100 of that of the DW-treated control virus, with similar results for other subvariants.
Green tea notably reduced infectivity of BA.1, BA.5, and BQ.1.1 variants but had less effect on BA.2.75. GCG and EGCG reduced BA.1 and XE subvariant titers to less than one percent and BA.2.75 subvariant to 1/10, with EGCG extracts showing similar antiviral effects to green tea.
EGCG effectively inactivated nearly all BA.1 and BA.5 subvariants but had limited success against BA.2 subvariant, BA.2.75 subvariant, XBB.1 subvariant, and BQ.1.1 subvariant strains. GCG reduced BA.1, XE, and XBB.1 subvariant titers to less than one percent but was less effective against BA.5, BA.2.75, and BQ.1.1 subvariants.
TFDG significantly reduced the titers of BA.1, XE, BA.5, XBB.1, and BQ.1.1 subvariants but had less statistically significant effects on BA.2 and BA.2.75 subvariants. TF3G lowered BA.1 infectivity to less than one percent without similar effects on other Omicron subvariants. Non-galloylated forms of TF and TF3'G did not reduce viral titers to less than one percent.
TFDG, at concentrations of 50 M or 100 M, reduced the infectivity of most Omicron subvariants to one percent or less, except for BA.2.75, which remained infectious at 100 M. EGCG inactivated the virus but did not exhibit antiviral actions in the cells. EGCG reduced RBD-ACE2 interaction by binding to RBD rather than ACE2.
The study suggested that the N460K mutation is linked to EGCG's viral inactivation, and the G446S substitution was present in BA.1, BA.2.75, and Omicron XBB.1 but not in BA.1. TFDG's interaction with Y449, Y453, F486, Q493R, Q498R, and N501Y in BA.2 and BA.2.75 intercepted hydrogen bonds with ACE2's H34, E35, D38, Y41, Q42, L79, M82, Y83, and K357.
The same interaction with BA.2.75's Y449, Q493R, and Q498R disrupted hydrogen bonds with ACE2's H34, E35, D38, Y41, and Q42. Saliva from individuals who consumed candies containing green or black tea significantly reduced BA.1 infectivity in vitro.
This study demonstrated that green tea, Matcha, and black tea effectively inactivate Omicron subvariants.
Specific amino acid changes in RBDs play a substantial role in the binding of EGCG/TFDG to the RBDs and the sensitivity of each Omicron subvariant to EGCG/TFDG.
These findings provide insights into the potential use of these compounds to combat mutant viruses that may arise in the future and lead to pandemics.