Ubiquinone, idebenone, and kinetin provide ineffective photoprotection to skin when compared to a topical antioxidant combination of vitamins C and E with ferulic acid.

TO THE EDITOR Ubiquinone (Coenzyme Q10) is an important lipophilic antioxidant synthesized by the body and critical for protection of mitochondrial membranes (Crane, 2001; Dallner and Sindelar, 2000). Idebenone is a synthetic derivative of ubiquinone with a shorter carbon side chain and subsequent increased solubility (Wieland et al., 1995). Both have been suggested as topical antioxidant ingredients for the protection of skin from oxidative damage caused by UV irradiation and pollution. Kinetin (N6-furfuryladenine) is a member of the cytokinin plant growth hormone family. Cytokinins are growth promoters, which positively affect cell number and division rate in both plants and animals (Vesely et al., 1985). In vitro studies have shown that kinetin has antioxidant effects, preventing oxidative damage to DNA (Olsen et al., 1999). Topical kinetin has been shown to improve skin texture and reduce the appearance of fine rhytides in humans (McCullough and Weinstein, 2002) and in animals (Kimura and Doi, 2004). We have previously reported effective photoprotection properties of an antioxidant solution containing 15% L-ascorbic acid, 1% a-tocopherol, and 0.5% ferulic acid (Cþ Eþ ferulic acid) (Lin et al., 2005). In this study, we use the same model to evaluate the antioxidant potential of ubiquinone, idebenone, and kinetin by measuring their photoprotective value. The treatment protocol and experimental design has been published in detail elsewhere (Lin et al., 2003), but will be summarized here in brief. Of each of the following, 250ml (solution) or 250 mg (cream) were applied to 7.5 10 cm patches of pig skin daily for 4 days: a solution containing 15% L-ascorbic acid, 1% a-tocopherol, and 0.5% ferulic acid (Cþ Eþ ferulic acid), solutions containing 1.0% ubiquinone, 1.0% idebenone, and 0.5% kinetin as well as commercial creams containing 0.1% kinetin (Kinerase, Valeant Pharmaceuticals, Costa Mesa, CA), 1.0% idebenone (Prevage, Allergan Inc., Irvine, CA), 0.5% idebenone (TRUE Youth Revealing Complex, TRUE Cosmetics, San Francisco, CA). A 1000 W solar simulator (Lightning Cure 200, Hamamatsu, Hamamatsu City, Japan) was used to deliver the UV radiation at an intensity of 5 mW/cm of UVB and approximately 40 mW/cm of UVA, as measured by a research radiometer (IL1700, International Light, Newburyport, MA). Patches were irradiated with solar-simulated UV as described above in triplicate from 1 to 5 minimal erythema dose (MED) in 1 MED multiples. Evaluation was conducted 24 hours later. All experimental methods were conducted within the guidelines of and with approval by the North Carolina State University Institutional Animal Care and Use Committee. A computerized colorimetry algorithm using digital photographs (Tournas JA and Pinnell SR (2005) A computerized method for skin erythema measurement. J Investig Dermatol 124(S4): A136 (abstract)) and a Microsoft Excel (Microsoft Inc., Redmond, WA) spreadsheet were used to measure and calculate the a* (redness) values of the experimental spots, as well as to compile the statistics and graph the results. After photography, 8 mm punch biopsy sections were taken of each experimental spot and fixed in formalin. Sections were embedded and sectioned for hematoxylin and eosin (Hþ E) staining. The Hþ E-stained sections were then examined for the presence of apoptotic ‘‘sunburn cells’’ (SBCs). The full 8 mm width of each section was counted and the result expressed as SBC density/mm of skin. Microsoft Excel was used to determine the mean and standard deviation of the SBC densities at each UV dosage and to graph the results. Thymine dimer analysis was carried out as in the work of Mitchell et al. (2001). An Olympus BX41 fluorescence microscope with a Q-Fire camera (Olympus America Inc., Melville, NY) was employed to obtain the immunofluorescence images. The results for erythema (a*) and SBC density are expressed as mean7SD (n1⁄4 6). The P-values were calculated by two-tailed Student’s t-test. Figure 1a shows the erythema response of skin treated with Cþ Eþ ferulic acid, 1.0% ubiquinone, 1.0% idebenone, and the 1.0 and 0.5% idebenone creams (Commercial Creams 1 and 2, respectively), and Figure 1b shows the erythema response of skin treated with Cþ Eþ ferulic acid, 0.5% kinetin solution, and the 0.1% kinetin cream. It can be seen that while Cþ Eþ ferulic acid is protective at 5 MED, ubiquinone, idebenone, and kinetin do not provide protection. The computerized colorimetric measurements show that at all UV dosage levels from 1 to 5 MED, erythema is significantly reduced (Po0.05) when skin is treated with Cþ Eþ ferulic acid compared to control, or skin treated with any of the antioxidant solutions or the commercial creams. Additionally, none of the preparations other than Cþ Eþ ferulic acid were significantly different Abbreviations: MED, minimal erythema dose; SBC, sunburn cell