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Dietary Feeding of Silibinin Prevents Early Biomarkers of UVB Radiation–Induced Carcinogenesis in SKH-1 Hairless Mouse Epidermis

¹ Department of Pharmaceutical Sciences, School of Pharmacy and ² University of Colorado Cancer Center, University of Colorado Health Sciences Center, Denver, Colorado

Requests for reprints: Rajesh Agarwal, Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Health Sciences Center, 4200 East Ninth Street, Box C238, Denver, CO 80262. Phone: 303-315-1381; Fax: 303-315-6281. E-mail: Rajesh.Agarwal{at}UCHSC.edu

Solar radiation is the causal etiologic factor in the development of nonmelanoma skin cancer (NMSC). Depletion of the stratospheric ozone layer leads to an increase in ambient UV radiation loads, which are expected to further raise skin cancer incidence in many temperate parts of the world, including the United States, suggesting that skin cancer chemopreventive approaches via biomarker efficacy studies or vice versa are highly warranted. Based on our recent study reporting strong efficacy of silibinin against photocarcinogenesis, we assessed here the protective effects of its dietary feeding on UVB-induced biomarkers involved in NMSC providing a mechanistic rationale for an early-on silibinin efficacy in skin cancer prevention. Dietary feeding of silibinin at 1% dose (w/w) to SKH-1 hairless mice for 2 weeks before a single UVB irradiation at 180 mJ/cm² dose resulted in a strong and significant (P < 0.001) decrease in UVB-induced thymine dimer–positive cells and proliferating cell nuclear antigen, terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling, and apoptotic sunburn cells together with an increase (P < 0.001) in p53 and p21/cip1-positive cell population in epidermis. These findings suggest that dietary feeding of silibinin affords strong protection against UVB-induced damages in skin epidermis by (a) either preventing DNA damage or enhancing repair, (b) reducing UVB-induced hyperproliferative response, and (c) inhibiting UVB-caused apoptosis and sunburn cell formation, possibly via silibinin-caused up-regulation of p53 and p21/cip1 as major UVB-damage control sensors.

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