title: Dermal contributions to UVA-induced oxidative stress in skin.
abstract: BACKGROUND
  When the skin is exposed to solar irradiation, UVA photons interact with skin tissues and induce excessive reactive oxygen species, resulting in oxidative stress. We have shown in a previous study that in vivo chemiluminescence's measurement can be used to evaluate the overall level of UVA-induced oxidative stress in human skin. However, the origin of the observed chemiluminescence signals remains unclear.
  
  
  METHODS
  UVA-induced chemiluminescence measurements were conducted: (a) in vitro on collagen solutions and solid collagen sheet preparations, (b) ex vivo on human and mouse skin biopsies, and (c) in vivo on human skin of various constitutive pigmentation levels. Fluorescence was measured on collagen in vitro as well as on skin for the in vivo experiments.
  
  
  RESULTS
  We found in the in vitro experiments that UVA-induced chemiluminescence increases with the presence of collagen cross-links. When dermal sides were exposed to UVA irradiation, both mouse and human skin biopsies demonstrated significantly higher chemiluminescence levels than when epidermal sides were exposed to UVA. The amount of collagen cross-links decreases slightly following UVA exposure, as shown both by in vivo fluorescence and by UVA-induced chemiluminescence. Finally, there was less measurable UVA-induced chemiluminescence in dark skin compared with light pigmented skin in vivo.
  
  
  CONCLUSIONS
  The dermis is very sensitive to UVA photons. Dermal cross-links are potential UVA sensitizers. The oxidative stress induced by UVA and measured by chemiluminescence may largely be attributed to the breakdown of dermal collagen cross-links.
authors.affiliation: Scientific Affairs, Neutrogena Corporation, Los Angeles, CA 90045, USA. houyan4@neuus.jnj.com
authors.forename: Hao
authors.initials: H
authors.lastname: Ou-Yang
authors.forename: Georgios
authors.initials: G
authors.lastname: Stamatas
authors.forename: Nikiforos
authors.initials: N
authors.lastname: Kollias
mesh_terms: D000818:Animals; D001706:Biopsy; D003094:Collagen / Q000378:metabolism; D062109:Dermatologic Surgical Procedures; D006801:Humans; D008163:Luminescent Measurements; D051379:Mice; D018384:Oxidative Stress / Q000528:radiation effects*; D012867:Skin / Q000378:metabolism* / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D003094:Collagen