Antioxidants add protection to a broad-spectrum sunscreen

Abstract

Exposure of human skin to ultraviolet radiation (UVR) results in erythema, pigment darkening, skin cancer and photoageing. In addition to conventional organochemical and the physical-mineral type sunscreens (SS), other non-SS protective strategies have been investigated, including antioxidants (AOx) and topical DNA repair enzymes. To investigate whether AOx could improve the protection provided by a broad-spectrum sunscreen (SS) preparation. Volunteers were exposed to repetitive solar-simulated (ss)UVR at 1.5 times minimal erythema dose for four consecutive days. Thirty minutes before each exposure and 6, 24 and 48 h after the last exposure, the test materials [vehicle, SS (sun protection factor 25) alone, AOx alone and SS plus AOx] were applied to four different sites. Another two sites received ssUVR only, or SS plus AOx only, and a third site was left untreated (neither ssUVR or product). Erythema and pigmentation were measured using a Mexameter. Biopsy specimens were taken 72 h after the last irradiation. The thickness of the stratum corneum and epidermis were measured by microscopy. Expression of cytokeratins (CKs), matrix metalloproteinases (MMPs) and CD1a-positive Langerhans cells (LCs) analysed by immunohistochemical staining, and relative expression levels were compared between all seven sites. AOx alone did not reduce erythema. There was a significant reduction in pigmentation, and the product almost completely protected against LC depletion. AOx plus SS gave better protection against pigment formation and CK5/6 induction than SS alone. AOx alone protected against ssUVR-induced hyperproliferation, as shown by epidermal thickness and CK16 biomarkers, and was better than SS alone. Interestingly, although protection against induction of MMP-9, a marker of photoageing, did not reach significance when either SS or AOx were applied separately, there was complete protection against MMP-9 induction when these were combined. Non-SS materials such as AOx can contribute significantly to sun protection when added to a broad-spectrum SS and applied topically to human skin in vivo.