Photodegradation of (−)-epigallocatechin-3-gallate in topical cream formulations and its photostabilization

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The aim of the study was to examine the photostability of the major catechin of green tea, (−)-epigallocatechin-3-gallate (EGCG), which possesses important antioxidant and skin photoprotective properties. In order to simulate realistic conditions of use of topical preparations, the photolysis studies were performed in model creams (oil-in-water emulsions) containing 1% (w/w) EGCG and exposed to a solar simulator at an irradiance corresponding to natural sunlight. The extent of photodegradation was measured by HPLC–UV and HPLC–ESI-MS. EGCG was found to decompose by 68.9 ± 2.3%, after 1 h irradiation. Addition of the coantioxidants, vitamin E or butylated hydroxytoluene to the emulsion formulation, significantly enhanced the photolability of the catechin, the EGCG loss reached 85.7 ± 1.3% and 80.5 ± 1.4%, respectively. On the other hand, inclusion of the UVB (290–320 nm) filter, ethylhexyl methoxycinnamate in the cream produced a small but significant reduction of EGCG photodegradation to 61.0 ± 2.9%, while the UVA (320–400 nm) filter, butyl methoxydibenzoylmethane was ineffective (EGCG degradation, 67.8 ± 1.5%). A more marked decrease in the light-induced decomposition of EGCG to 51.6 ± 2.7% was achieved, under the same conditions, using the water-soluble UVB filter, benzophenone-4 (BP-4). This effect was concentration dependent, maximal EGCG photostabilization (catechin loss, 29.4 ± 2.2%) was attained in the presence of 2.1% (w/w) BP-4. Therefore, BP-4 represents a useful additive to improve the light stability of EGCG in topical formulations for skin photoprotection.

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