An eco-friendly system for stabilization of retinol: A step towards attending performance with improved environmental respect.

OBJECTIVE: Retinol (Vitamin A) is one of the most effective molecules for the treatment of skin aging. However, it degrades rapidly under the influence of light, oxygen, metal ions, and oxidizing agents. To prevent this, stabilizing systems are used commonly. Notably, butylated hydroxytoluene (2,6-di-tert-butyl-p-cresol) (BHT) and ethylenediaminetetraacetic acid (EDTA) salts exhibit excellent antioxidant and metal-chelating properties but are not eco-friendly. In this study, our goal was to develop a new eco-friendly stabilization system for retinol-based formulations such that the system does not interfere with retinol skin absorption, nor its clinical efficacy. METHODS: An evaluation tool called the Sustainable Product Optimization Tool (SPOT) was used to assess the environmental performance of formulations containing retinol and the various stabilizers investigated. Accelerated stability tests were performed on formulations stored for 2 months at 4 and 45°C (ISO/TR Standard 18811 2018 directives). Long-term stability evaluation was done on formulations stored for 24-months at room temperature. Retinol skin absorption was assessed by the Franz cell method using human skin explants (OECD guideline 428). Finally, a clinical study was performed to evaluate the cosmetic performance of a 0.3% stabilized retinol formulation. RESULTS: N,N'-ethylenediamine disuccinic acid ([S,S]-EDDS isomer) and pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) (PBHC) showed higher biodegradability and a reduced water footprint compared with those of BHT and EDTA. The SPOT simulation gave [S,S]-EDDS + PBHC a score of 10 versus 8.84 for EDTA + BHT. Moreover, [S,S]-EDDS + PBHC better controlled the chemical degradation of retinol compared with EDTA + BHT. Retinol skin absorption was also achieved in the case of a formulation containing [S,S]-EDDS + PBHC, and several skin attributes improved significantly after 12 weeks of product use, with over 75% of the panel perceiving benefits. CONCLUSION: Regarding retinol stabilization, the PBHC + [S,S]-EDDS combination is an eco-friendlier and more effective alternative to BHT + EDTA.

OBJECTIF: Le rétinol est l'une des molécules les plus efficaces sur les signes du vieillissement. Cependant, il se dégrade rapidement, notamment sous l'influence de la lumière, de l'oxygène, des ions métalliques et des oxydants. Il existe des systèmes de stabilisation notamment à base d'hydroxytoluène butylé (2,6-di-tert-butyl-p-crésol) (BHT) et de sels d'acide éthylènediamine tétra acétique (EDTA) qui possèdent respectivement d'excellentes propriétés antioxydantes et chélatrices des métaux bien que certaines études aient montré que les deux présentaient un profil environnemental moins que parfait. Notre objectif était de développer un nouveau système de stabilisation ayant un meilleur respect environnemental. Ce nouveau système plus durable ne doit pas impacter l'absorption cutanée du rétinol, ni son efficacité clinique. MÉTHODES: Un outil d'évaluation appelé SPOT (Sustainable Product Optimization Tool) a été utilisé pour évaluer la performance environnementale des formules contenant du rétinol et des stabilisants. Des tests de stabilité accélérés ont été réalisés 2 mois après la formulation avec des produits gardés à 4°C et 45°C (norme ISO/TR 18811 directives 2018). Les stabilités de longue durée ont été évalués sur des produits gardés 24 mois à la température ambiante. L'absorption cutanée du rétinol a été réalisée par la méthode des cellules de Franz avec des explants de peau humaine (directive OCDE 428). Enfin, une étude clinique a prouvé la performance cosmétique d'une formule de rétinol stabilisé à 0,3%. RÉSULTATS: L'association de l'acide N,N'-éthylènediamine disuccinique (isomère [S,S]-EDDS) et du pentaérythritol tétrakis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate) (PBHC) présente une biodégradabilité plus élevée et une empreinte eau réduite par rapport à BHT et EDTA. La simulation SPOT a donné au [S,S]-EDDS et au PBHC un score de 10 contre 8,84 pour l'EDTA et le BHT. De plus, le [S,S]-EDDS et le PBHC contrôlent mieux la dégradation chimique du rétinol par rapport à l'association BHT plus EDTA. L'absorption cutanée du rétinol a également été obtenue dans une formule contenant du [S,S]-EDDS et du PBHC et plusieurs attributs cutanés ont été significativement améliorés après 12 semaines d'utilisation du produit. Les bénéfices ont été perçus par plus de 75% du panel testé CONCLUSION: Concernant la stabilisation du rétinol, l'association PBHC et [S,S]-EDDS est une alternative plus écologique et plus performante que le BHT et l'EDTA.

Comparison of cutaneous bioavailability of cosmetic preparations containing caffeine or alpha-tocopherol applied on human skin models or human skin ex vivo at finite doses.

The use of human skin models for performing cutaneous bioavailability studies has been little investigated. For instance, only few studies have been reported on human skin models dealing with vehicle effects on percutaneous penetration. The present study aimed at evaluating the influence on caffeine's and alpha-tocopherol's cutaneous bioavailability of cosmetic vehicles such as a water-in-oil emulsion, an oil-in-water emulsion, a liposome dispersion and a hydrogel applied at finite dose using the reconstructed human skin models EpiDerm and Episkin. The results were compared with those obtained in human skin ex vivo using similar experimental conditions. It was demonstrated that the rank order of solute permeability could be correctly predicted when the preparation was applied at a finite dose in human skin models, at least when solutes with far different physicochemical properties such as caffeine and alpha-tocopherol were used. If only slight effects of cosmetic vehicle on skin bioavailability were observed in human skin ex vivo, they were less predictable using skin models. Especially, alcohol-containing vehicles seemed to behave differently in EpiDerm as well as in Episkin than on human skin ex vivo. Stratum corneum intercellular lipid composition and organization of human skin models differ to some extent from that of human stratum corneum ex vivo, which contributes to less pronounced barrier properties, together with the increased hydration of the outermost stratum corneum layers of the models. These features, as well as still unknown factors, may explain the differences observed in vehicle effects in human skin ex vivo versus human skin models.