Complementary antioxidants deliver sustained sunscreen protection: Study

“Acquiring immediate and longer-term antioxidant effects is difficult to manage due to several strict requirements: quick delivery of antioxidant to have immediate effect and stability of the antioxidant in order to have long-term effect over 24h,” ​the study states.

The investigation, published this month in the International Journal of Cosmetic Science​, measured the dermal bioavailability and antioxidative properties of a formulation sunscreen containing oxothiazolidine (OTZ) and δ​-tocopheryl glucoside (DTG).

What it found was complementary sunlight protective action with “an immediate delivery of OTZ just after topical application of the formulation and a prolonged skin delivery of δ-tocopherol from the slower penetration and metabolism of DTG.”​ ​

Complementary antioxidants​

OTZ on its own is specifically designed to reduce damage caused by ultraviolet wavelengths and is a common ingredient in sunscreen. It penetrates the skin to scavenge free radicals and combat the degenerative effect of solar radiation. In the process, it forms taurine – a naturally occurring amino sulfonic acid with a number of important functions in the body, including regulation of oxidative stress.

Meanwhile, DTG is metabolized in δ​-tocopherol - a biologically active form of vitamin E - to achieve antioxidative activities. The study shows that its considerable reservoir effect, useful in reinforcing antioxidants in the skin, increases when used alone or in combination with OTZ, as compared to a formulation with OTZ alone.

Reconstructed human epidermis and solar-simulated radiation​

To test their hypothesis, researchers applied the formulation topically to a hair follicle-derived reconstructed human epidermis (RHE) model, followed by solar-simulated radiation. The lab then measured the kinetics of bioavailability and antioxidative responses over 24 hours using malondialdehyde (MDA), superoxide dismutase (SOD) and catalase activities as markers for oxidative stress.

“DTG slowly penetrated into the skin and was present in the skin at all post-irradiation timepoints, thus allowing a slow but constant supply of δ-tocopherol over at least 24h. By contrast, the oxidative protection by OTZ was immediate but short-lived due to its rapid penetration through the RHE and into the receptor fluid,” ​the study concluded.

These findings, researchers say, correlate with the physicochemical properties of the two antioxidants and the structure of the thin stratum corneum ​layer of the RHE model. OTZ, a hydrophilic with a low molecular weight, is more likely to enter the epidermal keratinocyte layer, whereas DTG is lipophilic and more likely to remain on the surface of the skin and in the stratum corneum.

As for what’s next for this technology, Cosmetics Design contacted the researchers for comment but did not receive a response prior to publication.

Source: https://doi.org/10.1111/ics.12705​

Sustained effect of two antioxidants (oxothiazolidine and δ-tocopheryl glucoside) for immediate and long-term sun protection in a sunscreen emulsion based on their different penetrating properties​

Authors: Jacques C, Bacqueville, D, Jeanjean-Miquel C, et. al