title: Influence of repetitive UVA stimulation on skin protection capacity and antioxidant efficacy.
abstract: OBJECTIVE
  Topically applied antioxidants (AOs) are widely used in cosmetic products - especially in day and sun care - to help reduce oxidative stress caused by exogenous influences such as ultraviolet (UV) radiation. Despite several advances in recent years, little is known about the duration of protective effects by application of topical AOs, AO protection capacity (APC) or the activation of an endogenous protection capacity (EPC).
  
  
  METHODS
  By measuring oxidative-stress-induced photon emission of human skin in vivo with the ICL-S method (induced chemiluminescence of human skin), the protective effect of daily AO treatment for 2 weeks was examined on 4 consecutive days after treatment. UVA-dose-independent effects were investigated by decay curve intersection point analysis. In addition, chemiluminescence signal integration was used to investigate the influence of different UVA doses for stimulation on the determined APC as well as the modulation of the EPC by repetitive UVA stimulation both forming the skin protection capacity (SPC).
  
  
  RESULTS
  The SPC showed a strong dependency on the UVA dose used for stimulation. AO pretreatment was more effective against lower UVA doses. Over the course of 4 days, the AO-induced SPC did not change significantly for a given UVA dose. Analyzing the decay curve intersection point for 2 different UVA doses, however, revealed a decrease in SPC with time. In addition, we found that a repetitive UVA irradiation of 1 J/cm(2) caused a statistically significant protective effect against UVA irradiation by stimulation of endogenous mechanisms.
  
  
  CONCLUSIONS
  Topically supplemented AOs provide a protective effect against oxidative stress for at least 3 days, supporting their widespread use in cosmetic products. Especially their interaction with cutaneous protective mechanisms should be investigated in more detail for maximal protection, as endogenous defense mechanisms are already triggered by 2 low-dose UVA irradiations within 24 h. In summary, the in vivo measurement of UVA-induced cutaneous chemiluminescence permits the UVA-dose-independent determination of the AO efficacy for better comparability of the results while also taking endogenous defense mechanisms into account.
authors.affiliation: Institut Dr. Schrader Creachem GmbH, Holzminden, Germany. mathias.rohr@schrader-institute.de
authors.forename: Mathias
authors.initials: M
authors.lastname: Rohr
authors.forename: Ingrid
authors.initials: I
authors.lastname: Rieger
authors.forename: Anil
authors.initials: A
authors.lastname: Jain
authors.forename: Andreas
authors.initials: A
authors.lastname: Schrader
mesh_terms: D000328:Adult; D000975:Antioxidants / Q000494:pharmacology*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D018384:Oxidative Stress; D012867:Skin / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D013473:Sunscreening Agents / Q000494:pharmacology*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D000975:Antioxidants; D013473:Sunscreening Agents