JOURNAL OF COSMETIC SCIENCE 362 To test the potential usefulness of boosting MSRA levels in skin, mp was then added to the media of skin models for 48 h, exposed to 100 mJ/cm2 UVB, and then incubated for an additional 24 h post-irradiation. The skin model samples were fi xed, subjected to histological analysis, and stained with hematoxylin and eosin. In Figure 4, light micro- scopic images of these skin models show an increase in sunburn cells in UVB-exposed skin model samples. Sunburn cells are characterized by increased pyknotic nuclei and eosinophilic staining (10). In contrast, the presence of sunburn cells in skin model samples pre-treated with the mp prior to UVB exposure was signifi cantly diminished by 31.1% (±10.0% S.E.). DISCUSSION Human skin has developed many strategies to counteract the effects of environmental exposures and their consequent trauma. In this report, we describe the presence of msrA in NHEK and its induction by UVB. Our data indicate a rapid and protective Figure 2. H2O2 levels decreased in the presence of 0.35 and 0.70 mg/ml MSRA by 24.7% (±3.3% S.E.) and 36.1% (±0.5% S.E.), respectively (∗ = Student’s t-test assuming unequal variances, p 0.05, n = 3). Figure 3. Conventional RT-PCR analysis of NHEK pre-treated with mp. msrA expression increased by 18.2% (±4.0% S.E., n = 4) when treated with 0.01 mg/ml mp and normalized to β-microglobulin. Higher levels (0.1 and 0.25 mg/ml) of mp also induced increases in msrA, whereas the unoxidized form had no effect.

PROTECTION AGAINST UVB-INDUCED OXIDATIVE STRESS 363 response to UVB-induced ROS, which may be critical for normal protein function. We further show how an mp can trigger this protective response in NHEK. Additionally, when this mp was incubated with a skin model sample, we saw a reduction in UVB- induced cellular damage. Thus, in order to account for the effects observed in skin models, we postulate that proteins sensitive to the presence and repair of metSO are related to the activation of signaling and apoptotic mechanisms. We thus conclude that MSRA plays a protective role at the protein level in NHEK and could also provide protection at the cellular level in skin. Future work in this area should include the ap- plication of small interfering RNA to silence msrA or the overexpression of transfected msrA cDNA in order to further delineate the role played by MSRA in NHEK. Lastly, topical application of small molecular weight peptides containing metSO may provide protection to human skin against UV-induced photodamage leading to improved cu- taneous health. REFERENCES (1) D . R. Bickers and M. Athar, Oxidative stress in the pathogenesis of skin disease, J. Invest. Dermatol., 126, 2565–2575 (2006). (2) E . Pelle, D. Maes, G. A. Padulo, E. K. Kim, and W. P. Smith, An in vitro model to test relative anti- oxidant potential: ultraviolet-induced lipid peroxidation in liposomes, Arch. Biochem. Biophys., 283, 234–240 (1990). (3) E. Pelle, X. Huang, T. Mammone, K. Marenus, D. Maes, and K. Frenkel, Ultraviolet-B-induced oxidative DNA base damage in primary normal human epidermal keratinocytes and inhibition by a hydroxyl radical scavenger, J. Invest. Dermatol., 121, 177–183 (2003). (4) E. R. Stadtman, C. N. Oliver, R. L. Levine, L. Fucci, and A. J. Rivett, Implication of protein oxidation in protein turnover, aging, and oxygen toxicity, Basic Life Sci., 49, 331–339 (1988). (5) N. Brot and H. Weissbach, Peptide methionine sulfoxide reductase: biochemistry and physiological role, Biopolymers, 55, 288–296 (2000). (6) R. L. Levine, B. S. Berlett, J. Moskcovitz, L. Mosoni, and E. R. Stadtman, Methionine residues may protect proteins from critical oxidative damage, Mech. Ageing Dev., 107, 323–332 (1999). Figure 4. Histological cross-sections of skin models stained with hematoxylin and eosin after 100 mJ/cm2 UVB irradiation with and without 1 mg/ml mp treatment. A 31.1% (±10.0% S.E.) reduction in sunburn cells (see arrows) was calculated from fi ve contiguous light microscopic fi elds (40x) in two separate experiments. (a) Unexposed, (b) UVB-exposed, (c) mp + UVB-exposed.