Assessment of the Kinetics of the Antioxidative Capacity of Topical Antioxidants

March 2011 | Volume 10 | Issue 3 | Original Article | 262 | Copyright © March 2011

Marko Lens MD PhD,a Marie-Helen Podesta Marty PharmDb

aKing's College, Genetic Epidemiology Unit, St. Thomas Hospital, United Kingdom bPMIC, Dermo-Cosmetic Research Center, Antony, France

Abstract
While there is at least one standardized test available for evaluating the antioxidant capacity of cosmetic formulations, the authors proposed a new in vivo method to determine kinetics of squalene (SQ) photo-oxidation products (squalene monohydroperoxide, SQ mOOH) as a reliable method with which to evaluate antioxidant capacity of a cosmetic formulation. Topical antioxidant formulation was applied on the foreheads of 30 volunteers. Sebum samples were collected before application of topical antioxidant and after one hour, three hours and five hours from the application of topical antioxidant. One half of the sebutape was irradiated and SQmOOH/SQ ratios in the skin lipid were analyzed using HPLC method. These results showed protective action of the topical antioxidant formulation against skin lipid peroxidation with a significant reduction of the quantity of SQmOOH (P<0.0001). Determination of the kinetics of squalene peroxidation is a reliable in vivo method in the evaluation of antioxidant capacity of cosmetic formulations.

J Drugs Dermatol. 2011;10(3):262-267.

INTRODUCTION

Ultraviolet (UV) light represents the major factor in skin photoaging and skin cancerogenesis.1,2 UV exposure causes acute inflammatory changes (such as erythema, edema, and subsequently pigmentation or tanning) and chronic changes (such as immunosupression, photoaging and photocarcinogenesis). Exposure to UV light generates reactive oxygen species (ROS), which are central players in oxidative damage to lipids, proteins and cellular DNA.3,4
The skin possesses a range of enzymatic and non-enzymatic antioxidants charged with protecting the skin against oxidative stress caused by damaging free radicals.5 While these natural antioxidants provide protection of the skin at the intracellular and extracellular level, they are not able to effectively offset excessive production of free radicals induced by UV light and other environmental aggressors.6 Thus, it has been suggested that topical application of antioxidants may be useful in providing protection of the skin against oxidative damage, particularly in the areas where the skin needs additional protection.7
Several in vitro and in vivo studies have clearly demonstrated antiradical potential of different topical antioxidant formulations and their photoprotective efficacy in preventing ROS-induced skin damage.7–12
In vitro testing of cosmetic formulations with antioxidants is complex and very often the results achieved in these studies cannot be confirmed in vivo studies. Furthermore, many clinical studies evaluating the efficacy of topical antioxidants are based on the assessment of the prevention of UV-induced erythema and sunburn cell formation.13 However, currently there is no standardized method to evaluate the complex effects of topical formulations combining different antioxidant ingredients.
It has been demonstrated that UV exposure induces the photooxidation of skin surface lipids (SSL) derived from epidermal lipids and from the sebum.14 Thus, evaluation of the major sebum lipid, squalene, may be used for determination of antiradical capacity of topical antioxidants.
The aim of this study was: (1) to assess efficacy of topical antioxidant formulation in prevention of the skin lipid peroxidation in the upper parts of the epidermis of the face and (2) to propose a new in vivo method to determine kinetics of squalene photo-oxidation products (squalene monohydroperoxide, SQmOOH) as a reliable method to evaluate antioxidant capacity of a cosmetic formulation.