Tea is a widely consumed beverage that has been recognized for its health benefits for centuries. One of the most interesting and promising aspects of tea is its potential antiviral activity. In recent years, numerous studies have investigated the antiviral properties of tea, particularly its polyphenols, which have been shown to inhibit various DNA polymerases and reverse transcriptases of viruses such as HIV-1, herpes simplex virus type-1, and duck hepatitis B virus replication complex. This article delves into the research on the antiviral activity of tea, specifically focusing on the inhibitory effects of tea polyphenols on various viruses and their replication processes. The article also discusses the mode of inhibition and the Ki values of tea polyphenols for different viruses, shedding light on the potential of tea as a natural antiviral agent.
Antiviral Activity of Tea Extracts
Tea extracts have been found to have antiviral effects against influenza and rotavirus. Studies have shown that black tea extract can inhibit the multiplication of influenza virus A and B by preventing their adsorption to Madin-Darby canine kidney cells. Meanwhile, extracts from black tea, blue tea, and dark tea have been found to significantly inhibit cytopathic effects caused by rotavirus in MA104 cells. However, high concentrations of tea extracts may be toxic to cells.
Antiviral Activity of Tea Polyphenols
Tea polyphenols, including (-)catechin, (-)epicatechin, (-)gallocatechin, (-)epigallocatechin, (-)catechin gallate, (-)epicatechin gallate, (-)gallocatechin gallate, and (-)epigallocatechin gallate, were tested for their ability to block influenza virus A in MDCK cells. The compounds were ranked in order of potency as follows: (-)gallocatechin gallate, (-)epigallocatechin gallate, (-)catechin gallate, (-)epicatechin gallate, (-)gallocatechin, (-)epigallocatechin, (-)catechin, and (-)epicatechin. EGCG and theaflavin digallate, purified from green and black tea, respectively, were found to effectively inhibit influenza virus A and B. Polyphenols were found to inhibit the virus’s entry and adsorption into MDCK cells, but not its multiplication inside the cells. Tea extracts containing at least 500 µM EGCG could be useful as a prophylactic against influenza virus infection. EGCG and theaflavin digallate were also found to inhibit the cytopathic effect of rota virus and enterovirus in cell cultures.
Antiviral Reverse Transcriptase and DNA Polymerase Activities of Tea Polyphenols
Tea polyphenols including (-)epigallocatechin gallate (EGCG), (-)epigallocatechin (EGC), and four theaflavins were tested for their inhibitory effects against various enzymes such as DNA polymerases (DNAP), reverse transcriptases of human immunodeficiency virus type 1 (HIV-1 RT), Moloney murine leukemia virus (MoMLV RT), terminal deoxynucleotidyltransferase (TDT), and E.coli RNA polymerase (RNAP). The results showed that EGCG and ECG inhibited HIV-1 RT the most, while theaflavins inhibited MoMLV RT the most. The mode of inhibition was analyzed kinetically and was shown to be either competitive or noncompetitive depending on the enzyme tested. EGCG and ECG were found to have low Ki values for inhibiting HIV-1 RT, DNAP α, DNAP ß, DNAP γ, and E.coli RNAP. Theaflavins were found to have Ki values for inhibiting HIV-1 RT. Bovine serum albumin (BSA) or Triton X-100 could counteract the inhibitory effects of tea polyphenols against the above enzymes. It was also reported that EGCG and ECG did not show inhibitory effects against HIV-1 in cell cultures.