Epigallocatechin gallate

Epigallocatechin gallate (EGCG), also known as epigallocatechin-3-gallate, is the most abundant catechin in tea and is found in higher concentrations in green tea compared to white and black tea. One cup of camellia sinensis green tea contains approximately 50mg of EGCG-equivalent.

EGCG's effects on CD147 & collagen degrading enzymes
There's a receptor in the body called CD147. This receptor is also called "extracellular matrix metalloproteinase inducer" (EMMPRIN) or Basigin. EMMPRIN/CD147 induces the production of matrix metalloproteinases (MMP) such as MMP-9 and MMP-2.

EGCG have been shown to inhibit the expression of EMMPRIN and MMP-9 in an in vitro study. In a mouse study intraperitoneally injected EGCG was found to decrease the expression levels of MMP-2, MMP-9, and EMMPRIN. EGCG is notorious for its low bioavailability, which could mean the studies above aren't applicable for normal oral dosages. However, this doesn't seem to be the case.

In a rat study, 20 mg EGCG per day was administered orally in the context of abdominal aortic aneurysm (rats seems to have the same low absorption of EGCG as humans ). The study found that the EGCG lowered the gene expression levels of inflammatory cytokines (TNF-a & IL-1b), promoted elastoregeneration (regeneration of elastin, an important component of connective tissue) and lowered the gelatinolytic activity of MMP-9 with 63%. The dosage was the equivalent of 0.04 mg EGCG/g body weight/day. If you convert that to a human dose (0,04/6,2 = 0,006452mg/g human dose = 6.452 mg/kg human dose) it translates to 452 mg oral EGCG/day for someone who weighs 70kg.

In a human study, breast cancer patients undergoing radiotherapy ingested 400 mg oral EGCG x3 / day for several weeks. The levels of serum active MMP-9 decreased by an average of 31% at week 2 and 55% at week 8. The levels of serum MMP-2 zymogens decreased by an average of 22% at week 2 and 51% at week 8.

SARS-CoV-2 & CD147
The SARS-CoV-2 virus can invade host cells not only via the ACE2 receptor, but also via the CD147/EMMPRIN receptor, meaning EGCG might have effects in the context COVID-19. EGCG have also been shown to have antifibrotic effects in a human study testing 600 mg oral EGCG/day in patients with pulmonary fibrosis undergoing lung biopsy. This mean that EGCG, apart from potentially having an antiviral effect against the SARS-CoV-2 virus, might reduce the risk of lung scarring from COVID-19.

Risks and safety
EGCG doses <800mg/day have not shown any hepatotoxic effects according to the European Food Safety Authority.