Flat spectrum sun screen protects against ultraviolet radiation induced damage to key extracellular matrix components in vitro

Ultraviolet radiation has profound effects on the structure and function of extracellular matrix components. We have previously demonstrated that molecules rich in amino acid UV-chromophores (fibrillin and fibronectin), are susceptible to physiological doses of solar simulated radiation (SSR). In the current study we have investigated whether a flat-spectrum sunscreen (similar absorbance at all wavelengths) is capable of protecting fibrillin and fibronectin from degradation by SSR. Suspensions of fibronectin and fibrillin microfibrils derived from photoprotected human dermis were exposed to a single dose of SSR (290-400nm; 23.7J/cm2): i) in the absence of any protection (SSR); ii) covered by a quartz plate coated with vehicle (1mg/cm2; SSR+V); iii) covered by a quartz plate coated with a flat-spectrum sunscreen (1mg/cm2; SSR+SS) (n=3). The effect of SSR on molecular structure was determined by atomic force microscopy (fibrillin) and native PAGE (fibronectin). Following irradiation, fibrillin microfibril structure underwent profound remodelling in SSR and SSR+V samples which was partially prevented by the flat-spectrum sunscreen. Microfibril periodicity in the unexposed sample was unimodally distributed (centred at 55.4nm). However, irradiation (in the absence of sunscreen) abolished this single population (bimodal with peaks centred at 45.3 and 66.1nm). In SSR+SS samples, this molecular remodelling was partially prevented (bimodal with peaks at 51.9 and 65nm). SSR exposure induced significant aggregation of fibronectin (p=0.005), which was abrogated by the flat-spectrum sunscreen (p=0.033) but not the vehicle control (p=0.754). We conclude that a flat spectrum sunscreen can reduce direct UV-mediated damage of key dermal molecules and thereby in part prevent UV-induced skin damage.