Department of Pharmaceutical Sciences, University of Ferrara, via Fossato di Mortara 17-19, 44100 Ferrara, Italy.
J Pharm Biomed Anal. 2011 Dec 5;56(4):692-7. doi: 10.1016/j.jpba.2011.07.007. Epub 2011 Jul 14.
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 1h 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 (290-320nm) filter, ethylhexyl methoxycinnamate in the cream produced a small but significant reduction of EGCG photodegradation to 61.0±2.9%, while the UVA (320-400nm) 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.
本研究旨在考察绿茶中主要儿茶素 (-)-表没食子儿茶素没食子酸酯 (EGCG) 的光稳定性，EGCG 具有重要的抗氧化和皮肤光保护特性。为了模拟局部制剂实际使用条件，在含有 1%（w/w）EGCG 的模型乳膏（油包水乳液）中进行光解研究，并在模拟日光的辐照度下暴露于太阳模拟器。通过 HPLC-UV 和 HPLC-ESI-MS 测定光降解程度。结果发现，EGCG 在照射 1 小时后分解了 68.9±2.3%。在乳液配方中添加共抗氧化剂维生素 E 或丁羟甲苯，可显著提高儿茶素的光稳定性，EGCG 的损失分别达到 85.7±1.3%和 80.5±1.4%。另一方面，在乳膏中加入 UVB（290-320nm）滤光片，甲氧基肉桂酸辛酯，可使 EGCG 的光降解率降低至 61.0±2.9%，而 UVA（320-400nm）滤光片，丁基甲氧基二苯甲酰基甲烷则无效（EGCG 降解率为 67.8±1.5%）。在相同条件下，使用水溶性 UVB 滤光片二苯甲酮-4（BP-4），可使 EGCG 光诱导分解更显著降低至 51.6±2.7%。这种效果与浓度有关，在 2.1%（w/w）BP-4 的存在下，EGCG 的光稳定性达到最大（儿茶素损失 29.4±2.2%）。因此，BP-4 是提高 EGCG 在皮肤光保护局部制剂中光稳定性的有用添加剂。
