Andrija Kornhauser

Human skin responses to UV radiation: pigment in the upper epidermis protects against DNA damage in the lower epidermis and facilitates apoptosis

Melanin plays an important role in protecting the skin against UV radiation, and melanomas and basal/squamous cell carcinomas occur more frequently in individuals with fair/light skin. We previously reported that levels of melanin correlate inversely with amounts of DNA damage induced by UV in normal human skin of different racial/ethnic groups. We have now separately examined DNA damage in the upper and lower epidermal layers in various types of skin before and after exposure to UV and have measured subsequent apoptosis and phosphorylation of p53. The results show that two major mechanisms underlie the increased photocarcinogenesis in fair/light skin. First, UV‐induced DNA damage in the lower epidermis (including keratinocyte stem cells and melanocytes) is more effectively prevented in darker skin, suggesting that the pigmented epidermis is an efficient UV filter. Second, UV‐induced apoptosis is significantly greater in darker skin, which suggests that UV‐damaged cells may be removed more efficiently in pigmented epidermis. The combination of decreased DNA damage and more efficient removal of UV‐damaged cells may play a critical role in the decreased photocarcinogenesis seen in individuals with darker skin.—Yamaguchi, Y., Takahashi, K., Zmudzka, B. Z., Kornhauser, A., Miller, S. A., Tadokoro, T., Berens, W., Beer, J. Z., Hearing, V. J. Human skin responses to UV radiation: pigment in the upper epidermis protects against DNA damage in the lower epidermis and facilitates apoptosis. FASEB J. 20, E630–E639 (2006)

β‐carotene uptake and effects on intracellular levels of retinol in vitro

The purpose of the present study was to determine beta-carotene uptake and resultant effects on intracellular levels of retinol in cell lines of varied origin. Human skin fibroblasts, mouse embryonic fibroblasts, rabbit corneal epithelial cells, and rat liver cells were studied. Cells were cultured in medium supplemented with beta-carotene in a water-dispersible beadlet formulation. At selected intervals, cells and media were sampled and analyzed by high-performance liquid chromatography for beta-carotene and retinol content. beta-Carotene was taken up by all four cell lines. An increase in the intracellular levels of retinol was concomitant with beta-carotene uptake in all cell lines. The uptake of beta-carotene and the increase in intracellular retinol were highest in the two fibroblast cell lines. Incubation with media supplemented with crystalline beta-carotene, dissolved in tetrahydrofuran, resulted in significantly lower beta-carotene uptake and intracellular retinol levels. We view these results as a demonstration that a wide variety of cells, cultured in vitro, are able to convert beta-carotene to retinol. Therefore, beta-carotenes provitamin A activity should be carefully considered when the protective effects of beta-carotene in vitro are interpreted.

Antitumor activity in skin of Skh and Sencar mice by two dietary β‐carotene formulations

There is currently a great interest in the protective potential of beta-carotene and other micronutrients against carcinogenesis. We investigated the role of beta-carotene in modifying 7,12-dimethylbenz[a]anthracene (DMBA)-initiated, 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted, two-stage skin carcinogenesis. We were interested in comparing the protective effects of two types of dietary beta-carotene, a beadlet formulation and crystalline beta-carotene, in two strains of mice (Skh:HR-1 and CR:ORL Sencar). Mice were maintained throughout the study on one of these 3% beta-carotene-fortified diets or on control diets. In Week 11 after the start of the diets, the DMBA/TPA treatment regimen was begun. The resulting skin tumors were counted weekly. In addition, serum and skin levels were monitored for beta-carotene at the time of chemical initiation and at the termination of the study. A decrease in the number of cumulative tumors in the beta-carotene-fed animals compared with the appropriate control groups was observed in both strains of mice. However, statistical evaluation of the data revealed that the decrease was significant only in Skh mice. This phenomenon might be explained by the inherent sensitivity of Sencar mice to the two-stage carcinogenesis treatment regimen. The mechanism of the protective effect found in this study is still not clear. Recent data suggest that a vitamin A pathway is not probable but that a direct 1O2 and/or radical-quenching property of the parent beta-carotene molecule may be involved. This study also demonstrates that two-stage-induced skin tumorigenesis can be modified by both types of beta-carotene-fortified diets.

Topical glycolic acid enhances photodamage by ultraviolet light

Background: Alpha‐hydroxy acids (AHAs) are widely used as ingredients in cosmetics. Several studies suggest that AHAs can increase the sensitivity of skin to ultraviolet (UV) light.

The effects of topically applied glycolic acid and salicylic acid on ultraviolet radiation-induced erythema, DNA damage and sunburn cell formation in human skin.

BACKGROUND alpha-Hydroxy acids (alphaHAs) are reported to reduce signs of aging in the skin and are widely used cosmetic ingredients. Several studies suggest that alphaHA can increase the sensitivity of skin to ultraviolet radiation. More recently, beta-hydroxy acids (betaHAs), or combinations of alphaHA and betaHA have also been incorporated into antiaging skin care products. Concerns have also arisen about increased sensitivity to ultraviolet radiation following use of skin care products containing beta-HA. OBJECTIVE To determine whether topical treatment with glycolic acid, a representative alphaHA, or with salicylic acid, a betaHA, modifies the short-term effects of solar simulated radiation (SSR) in human skin. METHODS Fourteen subjects participated in this study. Three of the four test sites on the mid-back of each subject were treated daily Monday-Friday, for a total of 3.5 weeks, with glycolic acid (10%), salicylic acid (2%), or vehicle (control). The fourth site received no treatment. After the last treatment, each site was exposed to SSR, and shave biopsies from all four sites were obtained. The endpoints evaluated in this study were erythema (assessed visually and instrumentally), DNA damage and sunburn cell formation. RESULTS Treatment with glycolic acid resulted in increased sensitivity of human skin to SSR, measured as an increase in erythema, DNA damage and sunburn cell formation. Salicylic acid did not produce significant changes in any of these biomarkers. CONCLUSIONS Short-term topical application of glycolic acid in a cosmetic formulation increased the sensitivity of human skin to SSR, while a comparable treatment with salicylic acid did not.

beta-Carotene uptake, metabolism, and distribution in BALB/c 3T3 cells

Although a growing number of epidemiological studies indicate that dietary beta-carotene has anticarcinogenic activity, the mechanism(s) of beta-carotene protection remains to be definitively established. In this context, in vitro studies of beta-carotene have been, and continue to be, valuable. We examined the following critical features in designing an in vitro system for studying the protection action of beta-carotene: 1) form of beta-carotene used for cellular uptake, 2) cellular metabolism of beta-carotene, and 3) subcellular distribution of beta-carotene. It was determined that beta-carotene added to medium in a water-dispersible formulation is readily taken up by BALB/c 3T3 cells and is located predominantly in cellular membranes. Cellular uptake of beta-carotene added to medium in an organic solvent is greatly reduced. It was also found that intracellular retinol increased significantly after a three-day exposure of BALB/c 3T3 cells to media containing beta-carotene. This result suggests that the ability to metabolize beta-carotene to retinoids is not limited to cells of intestinal origin. The results and methodology described here will be useful in the rational design of in vitro assays for elucidating the mechanism(s) of beta-carotene protective effects at the cellular level.

Applications of hydroxy acids: classification, mechanisms, and photoactivity

Hydroxy acids (HAs) represent a class of compounds which have been widely used in a number of cosmetic and therapeutic formulations in order to achieve a variety of beneficial effects for the skin. We review and discuss the most frequently used classes of these compounds, such as α-hydroxy acids, β-hydroxy acids, polyhydroxy acids, and bionic acids, and describe their applications as cosmetic and therapeutic agents. Special emphasis is devoted to the safety evaluation of these formulations, in particular on the effects of their prolonged use on sun-exposed skin. Furthermore, we summarize the very limited number of studies dealing with the modifications evoked by topical application of products containing HAs on photocarcinogenesis. In spite of the large number of reports on the cosmetic and clinical effects of HAs, their biological mechanism(s) of action still require more clarification. Some of these mechanisms are discussed in this article along with important findings on the effect of HAs on melanogenesis and on tanning. We also emphasize the important contribution of cosmetic vehicles in these types of studies. Thus, HAs play an important role in cosmetic formulations, as well as in many dermatologic applications, such as in treating photoaging, acne, ichthyosis, rosacea, pigmentation disorders, and psoriasis.

Animal Models for Phototoxicity Testing

An increasing number of industrial, household, drug, and cosmetic chemicals are developed and marketed each year. Most new compounds to which workers and consumers may be exposed, especially topically, are screened for safety by standardized skin-irritation toxicity testing protocols. However, the testing of these materials for their phototoxic potential is not routine, and thus the development of phototoxicity test procedures has been slow. Today there exists a need for meaningful, reliable, and standardized tests for determining the phototoxic potential of the many chemicals and products that we may come in contact with in our daily lives.Phototoxicity (photoirritation) is a light-induced skin response, similar to an exaggerated sunburn, that can be elicited after a single exposure to a photoactive chemical. This chemical may reach the target tissues directly by topical application, or indirectly by ingestion, or by other means that allow the chemical to enter the bloodstream. Phototoxicity differs from...

β-carotene inhibition of chemically induced toxicity in vivo and in vitro

In the past several years there has been a great deal of interest in the antioxidant beta-carotene and other micronutrients for their protective potential against various toxic insults. Two studies concerning the protective effects of beta-carotene, which were conducted in our laboratory, are reported here. The first involved the role of beta-carotene in modifying two-stage skin tumorigenesis initiated by 7,12-dimethylbenz[a]anthracene (DMBA) and promoted by phorbol 12-myristate 13-acetate (PMA, TPA). In this study, the protective effects of two types of dietary beta-carotene, a beadlet formulation and crystalline beta-carotene, were compared in two strains of mice (Skh:HR-1 and CR:ORL Sencar). Mice were maintained on food fortified with 3% beta-carotene or on control diets. Mice receiving the beta-carotene-supplemented diets had fewer tumours than mice in the control groups. However, only in the Skh strain of mice was this difference statistically significant. In the second study, an in vitro experiment, BALBc 3T3 mouse fibroblasts were used to determine beta-carotenes accumulation in cells and the ability of these cells to metabolize beta-carotene to vitamin A. This in vitro model was also used to show a beta-carotene protective effect towards 8-MOP phototoxicity. These studies contributed to the increasing evidence of in vivo and in vitro protection by beta-carotene against chemically induced toxicity.

Effects of Cosmetic Formulations Containing Hydroxyacids on Sun-Exposed Skin: Current Applications and Future Developments

This paper describes recent data on the effects of various skin formulations containing hydroxyacids (HAs) and related products on sun-exposed skin. The most frequently used classes of these products, such as α- and β-hydroxyacids, polyhydroxy acids, and bionic acids, are reviewed, and their application in cosmetic formulations is described. Special emphasis is devoted to the safety evaluation of these formulations, particularly on the effects of their prolonged use on sun-exposed skin. We also discuss the important contribution of cosmetic vehicles in these types of studies. Data on the effects of HAs on melanogenesis and tanning are also included. Up-to-date methods and techniques used in those explorations, as well as selected future developments in the cosmetic area, are presented.