Highly Sensitive Biological Assay for Determining the Photoprotective Efficacy of Sunscreen

The results revealed significant protection against the effects elicited by UVB radiation; there was no efficient protection from DNA lesions and cell death induced by UVA radiation or natural sunlight

André P. Schuch; Maria Carolina S. Moraes; Teiti Yagura; Carlos F. M. Menck

2014

Scholarcy highlights

  • The protective effect of sunscreens has been extensively evaluated in vivo as a measure of erythema induced in human skin and is expressed as Sun Protection Factor
  • The results revealed significant protection against the effects elicited by UVB radiation; there was no efficient protection from DNA lesions and cell death induced by UVA radiation or natural sunlight
  • In addition to SPF, other UVA protection parameters, such as in vivo Persistent Pigment Darkening and in vitro UVA-PF, have recently been described. An important issue concerning biological relevance is that these parameters do not reflect the deleterious effects of UV radiation, including immunosuppression, photoaging, and carcinogenesis. it is evident that SPF labeling directly influences personal exposure time; people use sunscreens to intentionally prolong sun exposure.
  • The severe depletion that the stratospheric ozone layer suffered over the last decades resulted in an increase of the incidence of UV radiation on the Earth’s surface, which has been predicted to continue to increase throughout most of this century. In addition, the synergistic interaction between ozone depletion and global warming will possibly enhance the incidence of skin cancer by about 20% in the UK alone, an increase estimated in 5,000 to 6,000 cases per year by 2050. a similar but proportionally higher impact can be expected in tropical countries, such as Brazil, where increasing exposure to very high UV doses should deal a heavy blow in terms of public healthcare
  • It is important to emphasize that the choice of a single UVB/UVA dose higher than the median lethal dose was made as this leads to less than 1% viability, allowing quantification of almost 100% of photoprotection against lethal damage
  • Using a combination of enzymic digestion assays coupled with gel electrophoresis, immunodot blot assays, and DNA footprinting assays, we demonstrated a unique wavelength-dependent formation of photodimeric lesions, i.e., cyclobutane pyrimidine dimers and photoproducts, based on direct UV absorption of DNA, in irradiated mouse genomic DNA, which could partially explain the induction of mutations in mouse cells irradiated with simulated sunlight
  • Solar UV radiation is widely known as an environmental genotoxic agent that affects ecosystems and the human population, generating concerns and motivating worldwide scientific efforts to better understand the role of sunlight in the induction of DNA damage, cell death, mutagenesis, and carcinogenesis

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