title: Comparative evaluation of different co-antioxidants on the photochemical- and functional-stability of epigallocatechin-3-gallate in topical creams exposed to simulated sunlight.
abstract: The catechin (-)-epigallocatechin-3-gallate (EGCG) exhibits high antioxidant activity and it has been reported to provide protection of the skin against damage induced by solar UV radiation. However, EGCG is highly unstable under sunlight. The present study aimed to compare the effectiveness of the co-antioxidant agents vitamin E, butylated hydroxytoluene, vitamin C and a-lipoic acid for their potential to protect the catechin from photochemical degradation. Model creams (oil-in-water emulsions) containing EGCG (1%, w/w) alone or combined with equimolar concentrations of co-antioxidant were exposed to a solar simulator at an irradiance corresponding to natural sunlight. Photodegradation was evaluated by HPLC-UV and HPLC-ESI-MS/MS. Addition of the co-antioxidants vitamin C and a-lipoic acid to the formulation significantly reduced the light-induced decomposition of EGCG from 76.9 ± 4.6% to 20.4 ± 2.7% and 12.6 ± 1.6%, respectively. Conversely, butylated hydroxytoluene had no effect (EGCG loss, 78.1 ± 4.6%) and vitamin E enhanced the EGCG photolysis to 84.5 ± 3.4%. The functional stability of the catechin in the creams exposed to the solar simulator was also evaluated by measuring the in vitro antioxidant activity. Following irradiation, the reduction of the EGCG formulation antioxidant power was lower (21.8%) than the extent of degradation (76.9%), suggesting the formation of photoproducts with antioxidant properties. The influence of the examined co-antioxidants on the functional stability of the catechin under simulated sunlight paralleled that measured for the EGCG photodecomposition, a-lipoic acid exerting the greatest stabilising effect (antioxidant activity decrease, 1.4%). These results demonstrated that a-lipoic acid is an effective co-antioxidant agent for the stabilization of EGCG in dermatological products for skin photoprotection.
authors.affiliation: Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17, 44121 Ferrara, Italy. sls@unife.it
authors.forename: Santo
authors.initials: S
authors.lastname: Scalia
authors.forename: Nicola
authors.initials: N
authors.lastname: Marchetti
authors.forename: Anna
authors.initials: A
authors.lastname: Bianchi
mesh_terms: D000975:Antioxidants / Q000737:chemistry* / Q000528:radiation effects; D001205:Ascorbic Acid / Q000737:chemistry / Q000528:radiation effects; D001713:Biphenyl Compounds / Q000737:chemistry; D002084:Butylated Hydroxytoluene / Q000737:chemistry / Q000528:radiation effects; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects; D002626:Chemistry, Pharmaceutical; D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D004655:Emulsions / Q000737:chemistry / Q000528:radiation effects; D005609:Free Radicals / Q000737:chemistry; D008027:Light; D010084:Oxidation-Reduction; D010782:Photolysis; D010851:Picrates / Q000737:chemistry; D063465:Skin Cream / Q000737:chemistry / Q000528:radiation effects*; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D008063:Thioctic Acid / Q000737:chemistry* / Q000528:radiation effects; D014810:Vitamin E / Q000737:chemistry / Q000528:radiation effects
chemical_list: D000975:Antioxidants; D001713:Biphenyl Compounds; D004655:Emulsions; D005609:Free Radicals; D010851:Picrates; D014810:Vitamin E; D002084:Butylated Hydroxytoluene; D008063:Thioctic Acid; D002392:Catechin; C045651:epigallocatechin gallate; C004931:1,1-diphenyl-2-picrylhydrazyl; D001205:Ascorbic Acid