title: Glycerol and urea can be used to increase skin permeability in reduced hydration conditions.
abstract: The natural moisturizing factor (NMF) is a group of hygroscopic molecules that is naturally present in skin and protects from severe drying. Glycerol and urea are two examples of NMF components that are also used in skin care applications. In the present study, we investigate the influence of glycerol and urea on the permeability of a model drug (metronidazole, Mz) across excised pig skin membranes at different hydrating conditions. The degree of skin hydration is regulated by the gradient in water activity across the membrane, which in turn depends on the water activity of the formulation in contact with the skin membrane. Here, we determine the water activity of all formulations employed using an isothermal calorimetric method. Thus, the gradient in water activity is controlled by a novel experimental set-up with well-defined boundary conditions on both sides of the skin membrane. The results demonstrate that glycerol and urea can retain high steady state flux of Mz across skin membranes at dehydrating conditions, which otherwise would decrease the permeability due to dehydration. X-ray diffraction measurements are performed to give insight into the effects of glycerol and urea on SC molecular organization. The novel steady state flux results can be related to the observation that water, glycerol, and urea all affect the structural features of the SC molecular components in a similar manner.
authors: Physical Chemistry, The Center for Chemistry and Chemical Engineering, Lund University, Box 124, SE-221 00 Lund, Sweden; Biomedical Laboratory Science and Technology, Faculty of Health and Society, Malmö University, SE-205 06 Malmö, Sweden. Electronic address: Sebastian.Bjorklund@fkem1.lu.se.
authors: Sebastian
authors: S
authors: Björklund
authors: Johan
authors: J
authors: Engblom
authors: Krister
authors: K
authors: Thuresson
authors: Emma
authors: E
authors: Sparr
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D005990:Glycerol / Q000494:pharmacology*; D066298:In Vitro Techniques; D008795:Metronidazole / Q000494:pharmacology; D010539:Permeability / Q000187:drug effects; D012867:Skin / Q000187:drug effects* / Q000378:metabolism; D012869:Skin Absorption / Q000187:drug effects*; D013552:Swine; D014508:Urea / Q000494:pharmacology*; D014867:Water / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D014867:Water; D008795:Metronidazole; D014508:Urea; D005990:Glycerol
keywords: Natural moisturizing factor (NMF); Skin hydration; Stratum corneum; Transdermal drug delivery; Water activity; X-ray diffraction