Antioxidants in Sunscreens for Improved ROS Protection

Oct 1, 2011 | Contact Author | By: Kerry Hanson and Christoper Bardeen, University of California; Donathan Beasley and Thomas Meyer, PhD, Merck
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Title: Antioxidants in Sunscreens for Improved ROS Protection
UV filterx reactive oxygen speciesx antioxidantsx sunscreenx
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Keywords: UV filter | reactive oxygen species | antioxidants | sunscreen

Abstract: In the present article, sunscreens containing the antioxidants vitamin E and diethylhexyl syringylidene malonate were tested for their efficacy in preventing UV-induced reactive oxygen species in the lower stratum corneum. The addition of the antioxidants was found to significantly improve the ability of low to high SPF sunscreens to attenuate ROS formation in UV-exposed skin.

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K Hanson, C Bardeen, D Beasley and T Meyer, Antioxidants in Sunscreens for Improved ROS Protection, Cosm & Toil 126(11) 710 (2011)

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Sunscreens are designed to provide broad-spectrum protection to skin against the damaging effects of ultraviolet (UV) radiation. In doing so, they prevent sunburn and help to reduce the risk of skin cancer.1 Today’s consumers are increasingly concerned about the side effects of photoaging, e.g., fine lines, wrinkles, sagging, age spots, etc., which compromise skin’s youthful appearance.

Photoaging is believed to be triggered primarily by reactive oxygen species (ROS).2 ROS form within the epidermis and dermis when endogenous chromophores such as urocanic acid, nicotinamide adenine dinucleotide (NADH), melanin and collagen absorb UV radiation then dissipate the absorbed energy through pathways that sensitize the formation of ROS. Just a few of the ROS found in the skin include singlet oxygen (1O2), hydrogen peroxide (H2O2) and superoxide radical anions (O2-•). These ROS can react with lipid membranes, proteins, DNA and most other molecules in their paths. While intrinsic antioxidant mechanisms within the extracellular and intracellular spaces of the epidermis and dermis counteract some UV-induced ROS, these mechanisms can become overloaded easily, resulting in ROS-mediated cell damage.3, 4

To minimize ROS levels while concurrently preventing sunburn, sunscreens are being formulated with both UV filters and efficacious antioxidants. However, there is a lack of understanding regarding how well antioxidants reduce ROS levels for different degrees of UV attenuation. For example, do higher SPF formulations need the same level of antioxidants as lower SPF formulations to minimize ROS levels? In this report, two-photon fluorescence microscopy is used to evaluate the extra-protective benefits afforded by an antioxidant combination of 0.5% vitamin E and 0.9% diethylhexyl syringylidene malonate (DESM) in sunscreens of low to high SPF by assessing its ability to reduce UV-induced ROS levels within the stratum corneum (SC).

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Table 1. Generalized comparison of formula compositions tested

Table 1.  Generalized comparison of formula compositions tested

A generalized comparison of the formula compositions appears in Table 1.

Table 2. Sunscreen actives and antioxidant combinations in the five formulations tested

Table 2. Sunscreen actives and antioxidant combinations in the five formulations tested

The specific types and levels of sunscreen actives and antioxidants contained in the formulas appear in Table 2.

Figure 1. TPM images a) before and b) after UV irradiation of skin with the placebo applied

Figure 1. TPM images a) before and b) after UV irradiation of skin with the placebo applied

As Figure 1 illustrates, the ability of TPM to visualize the generation of ROS at different skin depths is one of its greatest advantages.

Figure 2. TPM images after UV-irradiation of skin applied with four test formulations

Figure 2. TPM images after UV-irradiation of skin applied with four test formulations

Formulations contained either UV filters only (Figures 2a–d) or UV filters and antioxidants (Figures 2e–h).

Figure 3. TPM images after UV-irradiation of skin with three difference test formulations applied on a different intensity scale to demonstrate the difference in fluorescence intensity between the + and – antioxidant SPF 15, 50 and 70 formulations

Figure 3. TPM images after UV-irradiation of skin with three difference test formulations applied on a different intensity scale to demonstrate the difference in fluorescence intensity between the + and – antioxidant SPF 15, 50 and 70 formulations

Figure 3 redisplays the Figure 2 image data for SPF 15, 50 and 70 at a lower intensity scale to show the difference in fluorescence intensity between the +/- antioxidant samples.

Figure 4. fROS (Eq. 2) in the lower SC following 1 MED UVB-UVA irradiation for sunscreens with or without antioxidants

Figure 4. f<sub>ROS</sub> (Eq. 2) in the lower SC following 1 MED UVB-UVA irradiation for sunscreens with or without antioxidants

Interestingly, Figure 4 also illustrates that even a formula with an SPF of 4, using UVB filters, and with or without antioxidants, provided significant protection against ROS formation.

Footnotes (CT1110 Hanson)

a Oxynex ST Liquid (INCI: Diethylhexyl Syringylidene Malonate (and) Caprylic/Capric Triglyeride) is a product of the Rona Cosmetic Business Unit of EMD Chemicals, Gibbstown, N.J.. USA.
b The Dihyrorhodamine-123 ROS fluorescence probe is manufactured by InVitrogen, Carlsbad, Calif., USA.
c The Epiderm skin equivalent is manufactured by MatTek Corp., Ashland, Ma., USA.
d MatTek cell culture media is manufactured by MatTek Corp.
e Photophate Buffered Saline is manufactured by MatTek Corp.
f The Solar Simulator Model 16s-150 with the dose delivery module PMA 2100 is manufactured by Solar Light Co.

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