Improvement of polyphenol properties upon glucosylation in a UV‐induced skin cell ageing model

Synopsis Objective Polyphenols are strong antioxidant molecules allowing prevention of skin photo-ageing damages, but their use is limited due to low solubility and toxicity towards skin cells. We postulated that enzymatic glucosylation could improve their solubility, stability and, consequently, their efficacy. The aim of this work was to study changes induced by addition of a glucose moiety on two polyphenols displaying very different chemical structures [caffeic acid (CA), epigallocatechin-3-gallate (EGCG) and there glucosylated form, Glc-CA and Glc-EGCG] by assessing their cytotoxic properties and their antioxidant and anti-inflammatory activities. Methods Their antioxidant effect was assessed first by the classical DPPH radical-scavenging method. Then, a panel of human skin cells (keratinocytes, melanocytes, fibroblasts and endothelial cells) was used to evaluate their effect on cell toxicity and their antioxidant activities. With this aim, a photo-ageing model based on UV irradiation of skin cells was established. Molecule activity was assessed on reactive oxygen species (ROS) production, on superoxide dismutase (SOD) and catalase activities and, finally, on inflammatory factor production IL-6, IL-8 and IL-1β. Results In an acellular model, antioxidant activity assessed by DPPH method was strongly reduced for Glc-CA compared to CA, whereas it remained the same for Glc-EGCG compared to EGCG. Glucosylated derivatives did not display more toxic effect on various skin cells. Moreover, toxicity was even strongly reduced for caffeic acid upon glucosylation. The efficacy of glucosyl-compounds against UV-induced ROS production was preserved, both with pre- and post-UV treatments. Particularly, a better antioxidant efficacy was shown by Glc-EGCG, vs. EGCG, on keratinocytes. In addition, an induction of SOD and catalase activity was clearly observed for Glc-CA. Both glucosyl-polyphenols display the same activity as their parent molecule in decreasing inflammatory factor production. Conclusion Our results demonstrated that enzymatic glucosylation of CA and EGCG led to an improved or preserved antioxidant activity in a cellular model of UV-induced skin ageing, despite the decrease in instantaneous antioxidant properties observed for Glc-CA. Glc-EGCG is specifically more active on keratinocytes, suggesting a specific targeting. Such glucosylated polyphenols displaying improved physicochemical and biological properties should be better candidates than natural ones for use in food additives and cosmetics. Resume Objectifs Les polyphenols sont des molecules ayant un fort pouvoir antioxydant permettant de prevenir les dommages dus au photovieillissement de la peau mais leur utilisation est limitee de par leur faible solubilite et leur toxicite envers les cellules de la peau. Nous avons postule que la glucosylation enzymatique pourrait ameliorer leurs solubilite, stabilite et, en consequence, leur efficacite. Le but de ce travail est d'etudier les changements induits par l'addition d'un glucose sur deux polyphenols ayant une structure chimique tres differente [acide cafeique (CA), epigallocatechin-3-gallate (EGCG) et leurs formes glucosylees, Glc-CA et Glc-EGCG] en evaluant leurs proprietes cytotoxiques et leurs activites antioxydante et anti-inflammatoire. Methodes Leur pouvoir antioxydant a d'abord ete evalue par la methode classique de reduction du radical DPPH. Puis, un ensemble de cellules de peau humaine (keratinocytes, melanocytes, fibroblastes et cellules endotheliales) a ete utilise pour evaluer leur effet sur la toxicite cellulaire et leurs activites anti-oxydantes. Pour cela, un modele de photovieillissement base sur l'irradiation UV de cellules de peau a ete etabli. L'activite des molecules a ete evaluee sur la production d'especes reactives de l'oxygene (ROS), sur les activites superoxyde dismutase (SOD) et catalase et, enfin, sur la production de facteurs anti-inflammatoires IL-6, IL-8 et IL1β. Resultats Dans un modele acellulaire, l'activite antioxydante mesuree par la methode au DPPH etait fortement reduite pour le Glc-CA compare au CA, alors qu'elle restait la meme pour le Glc-EGCG compare a l'EGCG. Les derives glucosyles ne presentaient pas plus d'effet toxique sur les differentes cellules de peau. De plus, la toxicite etait meme fortement reduite pour l'acide cafeique suite a sa glucosylation. L'efficacite des composes glucosyles contre la production de ROS induite par les UV etait preservee, a la fois lors des traitements pre et post-UV. En particulier, une meilleure efficacite antioxydante a ete demontree avec le Glc-EGCG, vs. EGCG, sur les keratinocytes. Une augmentation des activites SOD et catalase a ete nettement observee pour le Glc-CA. Les deux polyphenols glucosyles montrent la meme activite que leur molecule parente en diminuant la production de facteurs anti-inflammatoires. Conclusions Nos resultats demontrent que la glucosylation enzymatique de CA et EGCG conduit a la preservation de leur activite antioxydante dans un modele cellulaire de vieillissement de la peau par les UV, en depit de la diminution de l'activite antioxydante instantanee observe pour Glc-CA. Glc-EGCC est specifiquement plus actif que l'EGCG sur les keratinocytes, suggerant un ciblage specifique. Ces antioxydants glucosyles presentant une amelioration de leurs proprietes physicochimiques et biologiques devraient etre de meilleurs candidats que les molecules naturelles pour etre utilises comme complements alimentaires ou en cosmetique.