The emergence of the B.1.1.529 lineage of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in South Africa in November 2021, later designated as the Omicron variant by the World Health Organization (WHO), marked a critical development in the ongoing COVID-19 pandemic.
This variant, known as Omicron BA.1, was distinguished by an unprecedented number of mutations, including 30 amino acid substitutions, six deletions, and three insertions in the spike protein, which plays a crucial role in viral attachment and entry into host cells.
These extensive mutations raised concerns about the variant’s transmissibility and its ability to cause breakthrough infections in vaccinated individuals, leading to its classification as a Variant of Concern (VOC).
Omicron rapidly spread globally in 2022, supplanting earlier SARS-CoV-2 variants, and gave rise to several sublineages, including BA.2, BA.5, BA.2.75, and XBB.1, each with additional mutations (Supplementary Fig. S1).
Understanding the transmission dynamics of SARS-CoV-2 is paramount in managing the pandemic. The virus primarily spreads through saliva, from both COVID-19 patients and asymptomatic carriers, as it infects and replicates in salivary glands and oral mucosa.
Respiratory actions such as speaking, sneezing, and coughing can disperse virus-laden saliva in the form of droplets and aerosols, potentially infecting individuals in close proximity.
Recognizing the importance of inactivating the virus in saliva, researchers have explored various foods and food ingredients with potential antiviral properties. Previous studies demonstrated the effectiveness of green tea, roasted green tea, oolong tea, and black tea in reducing SARS-CoV-2 infectivity in vitro.
In particular, (-)-epigallocatechin gallate (EGCG), a tea catechin compound, showed potent and rapid inactivation of the virus, findings corroborated by other research groups.
Other tea components, such as galloylated theaflavins (TF3G, TF3’G, and TFDG) and theasinensin A (TSA), also exhibited similar effects by interfering with the interaction between the viral spike protein and ACE2, primarily by binding to the spike protein’s receptor binding domain (RBD).
In this comprehensive study, we aimed to assess the effectiveness of various teas, tea catechins, and catechin derivatives in inactivating Omicron subvariant strains of SARS-CoV-2. Additionally, we investigated whether saliva from healthy individuals who consumed tea-infused candy could inactivate Omicron BA.1 in vitro.
Methods
To examine the susceptibility of Omicron subvariants to tea ingredients, we conducted in vitro experiments involving green tea, Matcha green tea, black tea, and a bottled green tea beverage. We treated the virus with these substances and assessed their effectiveness in inactivating Omicron strains, comparing it with the conventional strain of SARS-CoV-2.
We also evaluated the binding affinity of tea ingredients, particularly TFDG, to the Omicron RBD of the spike protein using in silico molecular docking analysis. This analysis allowed us to understand the molecular interactions between tea components and specific amino acid substitutions within the RBD of different Omicron subvariants.
Furthermore, a clinical study was conducted to determine the inactivation potential of saliva from healthy volunteers who consumed tea-infused candy. Saliva samples were collected at various time intervals after candy consumption to assess the persistence of the inactivating effect.
Results
Our findings revealed that all Omicron subvariants tested in our study were efficiently inactivated when exposed to green tea, Matcha green tea, and black tea for just 10 seconds. This aligns with our previous research on the conventional SARS-CoV-2 strain, suggesting that tea ingredients maintain their antiviral properties against the Omicron variants.
However, the bottled green tea beverage exhibited varying levels of effectiveness against different Omicron subvariants, possibly due to differing concentrations of catechins and their derivatives compared to freshly brewed tea.
Each Omicron subvariant displayed distinct sensitivity to tea catechins and theaflavins, likely attributable to the diverse amino acid substitutions in the RBD of the spike protein in each subvariant. Notably, the N460K substitution appeared to influence the binding of EGCG to the Omicron spike protein RBD.
Discussion
Our study sheds light on the efficacy of tea catechins and their derivatives in inactivating Omicron subvariants of SARS-CoV-2. The specific amino acid substitutions within the Omicron RBDs were found to critically influence the binding of EGCG and TFDG, affecting the susceptibility of each subvariant to these compounds.
Our clinical study demonstrated that saliva from individuals who consumed tea-infused candy effectively inactivated Omicron BA.1 in vitro, consistent with previous findings showing the potential of tea components to combat SARS-CoV-2 in the presence of saliva.
The results highlight the molecular basis for the utility of tea catechins and their derivatives in suppressing the transmission of mutant viruses, which could pose future pandemic threats. These findings underscore the importance of continued research into natural antiviral agents and their potential applications in public health strategies to mitigate the spread of emerging viral variants.
reference link:https://www.nature.com/articles/s41598-023-43563-3#Sec10
