title: Barrier function of intact and impaired skin: percutaneous penetration of caffeine and salicylic acid.
abstract: BACKGROUND
  Normally, percutaneous absorption tests are carried out using skin biopsies for an apparent and acceptable physiological condition. However, under different pathological conditions, the stratum corneum (SC) barrier function is impaired.
  
  
  METHODS
  The barrier function of the SC was assessed by correlation between the number of repeated applications of tape strips on the skin and its transepidermal water loss (TEWL), as well as by in vitro percutaneous absorption studies of different compounds, using Franz diffusion cells and porcine skin previously stripped.
  
  
  RESULTS
  A progressive diminution of the skin barrier function has been detected by TEWL both in vitro and in vivo as the number of skin tape strips increases. On the other hand, the percutaneous absorption of the compounds tested increases in a different way as the number of strips increases. Salicylic acid increases linearly depending on the barrier disturbance. However, percutaneous absorption of caffeine exponentially increased with barrier disturbance. Our results indicate that the barrier impairment of skin always increases the penetration behavior of a given compound; however, the hydrophilic-lipophilic balance of the compounds or formulations used could greatly modify its penetration profile, especially when a modified skin is used.
  
  
  CONCLUSIONS
  This in vitro protocol may be useful to simulate the percutaneous absorption profile of some drugs applied onto skin with an impaired SC barrier function and could be used to avoid, to some extent, the use of in vivo experimental animal models in the dermopharmaceutical field.
authors.affiliation: Department of Chemical and Surfactants Technology, IQAC-CSIC, Barcelona, Spain. laia.rubio@iqac.csic.es
authors.forename: Laia
authors.initials: L
authors.lastname: Rubio
authors.forename: Cristina
authors.initials: C
authors.lastname: Alonso
authors.forename: Olga
authors.initials: O
authors.lastname: López
authors.forename: Gelen
authors.initials: G
authors.lastname: Rodríguez
authors.forename: Luisa
authors.initials: L
authors.lastname: Coderch
authors.forename: Jaime
authors.initials: J
authors.lastname: Notario
authors.forename: Alfonso
authors.initials: A
authors.lastname: de la Maza
authors.forename: José L
authors.initials: JL
authors.lastname: Parra
mesh_terms: D000818:Animals; D002110:Caffeine / Q000493:pharmacokinetics*; D020405:Dermis / Q000378:metabolism*; D004817:Epidermis / Q000293:injuries / Q000378:metabolism*; D066298:In Vitro Techniques; D007641:Keratolytic Agents / Q000493:pharmacokinetics; D008954:Models, Biological; D010539:Permeability; D010726:Phosphodiesterase Inhibitors / Q000493:pharmacokinetics; D020156:Salicylic Acid / Q000493:pharmacokinetics*; D012869:Skin Absorption / Q000502:physiology*; D053832:Surgical Tape / Q000009:adverse effects; D034421:Sus scrofa; D014867:Water / Q000378:metabolism
chemical_list: D007641:Keratolytic Agents; D010726:Phosphodiesterase Inhibitors; D014867:Water; D002110:Caffeine; D020156:Salicylic Acid