Since I wrote my article on tea against viruses, about ten studies on the effects of tea against COVID-19 have been published in different scientific journals. What exactly is the status of these studies? Would tea destroy the virus? Block the virus? Prevent it from entering the body? These are different questions that deserve more clarification.
For almost a year now, we have been living in a period of unprecedented health crisis. While several therapies or prevention devices against COVID-19 are being developed, it is still too early to know the real results and to prove their safety. Some scientists are interested in naturally occurring molecules, such as tea polyphenols, which may be able to limit the entry of certain viruses and even have antiviral activity.
But how does COVID-19 work?
COVID-19 belongs to the Coronaviridae family, RNA viruses surrounded by a viral envelope. The virus is transmitted by airborne and close contact. On the surface of their viral envelope, there are spines (spicules) containing proteins that bind to receptors on the surface of our cells. Among the receptors that bind viral proteins is ACE2, which is present on the surface of alveolar lung cells. When COVID-19 binds to the receptor, it enters the lung cells and all the processes of viral replication take place. To allow viral genetic material to replicate and to allow the synthesis of viral proteins of the newly formed viruses, the virus has a number of enzymes. 3CLpro or Mpro is one of the most studied proteases in COVID-19 because it is key for the replication and transcription of viral genetic material.
Could tea interfere with the virus?
Some researchers have been interested in the inhibitory power of the polyphenols contained in tea (green tea catechins, black tea theaflavins) on the enzymes of the virus, i.e. do the polyphenols bind to the active sites of the viral enzymes and prevent their activity.
For this purpose, bioinformatic docking studies have been carried out. Based on the known 3D structure and amino acid composition of viral enzymes, their active site and polyphenols, it is possible to model computer models whether a polyphenol can bind to the site of activity of the viral enzyme to prevent its activity and to predict the binding strength of the polyphenol to the viral enzyme.
Bhardwaj et al. and Ghosh et al. compared the binding strength and inhibitory potential of polyphenols of the flavonoid family (Theasinensin-D from oolong), theaflavins (Theaflavin-3-O-gallate from black tea) or catechins (EGCG from green tea, Oolonghomobisflavan-A from oolong, etc.) against known viral Mpro blockers. In these two studies, it appears that the binding strength of these polyphenols would be equivalent to the different Mpro blockers. In addition, the 3D modeling suggests that the polyphenols would bind to the active site of Mpro with a stability close to the Mpro blockers. Looking at other viral replication enzymes such as RoRp (RNA synthesis), Singh et al. obtain close projections to the other two research teams for theaflavins and catechins of green and black tea.
But that's not all! Other studies based on docking reveal that TF3, a theaflavin derivative, binds to RBD, a viral spicules protein necessary for virus binding to the ACE2 receptor of alveolar lung cells. Potentially, this would mean that the virus may not be able to enter the cell because of this molecular clutter.
This initial screening is encouraging as it allows scientists to explore new avenues. But this is not enough to demonstrate the therapeutic action of a molecule. For the moment, a publication released in mid-September has demonstrated in vitro that the activity of the viral protease Mpro could be reduced by up to 90% under the action of EGCG and theaflavine. However, this first result should be taken with a grain of salt because in this study, Mpro was artificially recreated without taking the whole virus or considering in parallel the infected cell. Moreover, the polyphenol concentrations used are not representative of the reality in the cup.
Meanwhile, what happens to the immune system in the face of COVID-19?
In order to stop viral infection, it seems that the innate immune system, comprising the immune cells circulating in the blood and present in the pulp cells, is able to recognize molecular patterns on the surface of viruses (PAMP). As a result, these immune cells will secrete pro-inflammatory cytokines, molecules capable of attracting other immune cells to the site of infection. They will also secrete molecules capable of regulating the immune response and reducing viral replication, such as interferons. This is the first setting of inflammation.
This initial immune response may not be sufficient. An adapted response is put in place, specifically directed against COVID-19 viral proteins and not PAMP motifs. The adaptive immune response will be orchestrated by Th1 lymphocytes, allowing the action of LTc cells that destroy infected cells, of LB cells secreting antibodies that bind to the virus so that it is recognized by the immune system, and of macrophages that will absorb cellular debris and viruses. This immune response requires the secretion of pro-inflammatory cytokines to attract and activate these cells. In some patients, the inflammation generated because of these cytokines is such that we speak of a "cytokine hurricane", the immune activity is too strong and ends up destroying the lungs.
Tea, a gendarme for an overly active immune system?
In my article on tea and the immune system, I explained that tea would not be able to boost the immune system but to regulate it to prevent it from getting out of control, especially in the case of autoimmune pathologies or chronic inflammation. Since the writing of my article, no scientific publication on the effect of tea on the immune system of patients with COVID-19 has been written. However, we do know that green tea catechins could lower cytokine levels in the case of over-inflammation and could protect against pulmonary fibrosis, one of the complications observed during severe pneumonia.
Today, we know that many tea polyphenols such as catechins, theaflavins and flavonoids may be able to block the viral proteins needed to infect our cells and replicate the virus. In addition, these polyphenols may help to alleviate the "cytokinic hurricane" and pulmonary fibrosis, complications observed in patients. However, all of these data remain preliminary because they are based on in silico bioinformatics studies or on an analysis of the scientific literature for other viruses. Don't throw yourself on your tea hoping to protect yourself from COVID-19, you risk squatting your toilet after 3L of tea!