Epigallocatechin Gallate

What is epigallocatechin gallate?

Epigallocatechin gallate (EGCG) is the most plentiful and most powerful antioxidant extracted from green tea (R, R).

Is epigallocatechin gallate stable?

The stability of EGCG is dependent on the pH, temperature, ionic strength and the solvent used. Degradation increases rapidly with increases in temperature, pH and ionic strength, while glycerin-based vehicles prolong the stability of EGCG in solution (R).

EGCG is also highly photolabile, with model creams containing 1% EGCG decomposing by 69% after just 1 hour of exposure to solar-simulated sunlight (R). The reduction in the antioxidant power is much lower than the extent of degradation however, suggesting the formation of products with antioxidant properties (R).

The addition of some co-antioxidants such as α-lipoic acid and vitamin C exerts a stabilising effect, decreasing the light-induced decomposition of EGCG, but other antioxidants such as butylated hydroxytoluene and vitamin E have no effect or even enhance photolysis (R). The inclusion of UVB filters, particularly benzophenone-4 and to a lesser extent ethylhexyl methoxycinnamate, has also been shown to improve the light stability of EGCG in topical formulations (R).

Does epigallocatechin gallate get absorbed?

The gallate group of EGCG retards its skin permeation through steric hindrance (R, R, R). As a result, it passes through the skin less easily than the smaller green tea polyphenols, and is usually localised to the skin surface and stratum corneum, rather than the epidermis or the dermis (R, R).

The extent to which EGCG penetrates the skin is also affected by the vehicle used for topical delivery. A hydrophilic ointment containing 10% EGCG resulted in substantial intradermal uptake of up to 20% of the applied dose (R), but EGCG encapsulated in liposomes did not seem to reach the deeper skin layers. This may be because it has high affinity for and therefore binds to the lipid bilayer of the liposomes, hindering their release from the carrier (R).

What happens after epigallocatechin gallate is absorbed?

EGCG is hydrolysed by esterases in the stratum corneum to epigallocatechin (EGC) and epicatechin (EC) (R, R),