title: Combined chemical and electrical enhancement modulates stratum corneum structure.
abstract: In a previous in vitro study it has been shown that pretreatment with a water-based surfactant formulation results in a two-fold increase in transdermal iontophoretic transport of R-apomorphine compared to iontophoresis only. The aim of the study presented in this paper was to unravel the mechanisms involved in the increased iontophoretic delivery. Freeze fracture electron microscopy and cryo-scanning electron microscopy were used to visualise the ultrastucture of human stratum corneum after (i) application of the surfactant formulation, (ii) iontophoresis and (iii) application of the surfactant formulation followed by iontophoresis. Non-occlusive application of the surfactant formulation did not exert any detectable changes in the ultrastructure of the stratum corneum, except for swelling of the outermost corneocyte layers. Application of a current density of 0.5 mA/cm(2) for 9 h induced a swelling of the corneocytes and the formation of water pools that were occasionally present in the intercellular regions. Application of the surfactant formulation followed by iontophoresis resulted in a further swelling of the corneocytes and a frequent presence of water pools in the intercellular regions throughout the whole stratum corneum. The observed changes in the ultrastructure of the stratum corneum can explain the increased R-apomorphine transport during iontophoresis.
authors.affiliation: Department of Pharmaceutical Technology, Leiden Amsterdam Center for Drug Research, Gorlaeus Laboratories, University of Leiden, P.O. Box 9502, 2300 RA, Leiden, The Netherlands.
authors.forename: A M
authors.initials: AM
authors.lastname: de Graaff
authors.forename: G L
authors.initials: GL
authors.lastname: Li
authors.forename: A C
authors.initials: AC
authors.lastname: van Aelst
authors.forename: J A
authors.initials: JA
authors.lastname: Bouwstra
mesh_terms: D000279:Administration, Cutaneous; D001058:Apomorphine / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics*; D015194:Diffusion Chambers, Culture; D018491:Dopamine Agonists / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics*; D004817:Epidermis / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007478:Iontophoresis; D008854:Microscopy, Electron; D012869:Skin Absorption; D013237:Stereoisomerism; D013268:Stimulation, Chemical; D013329:Structure-Activity Relationship; D013501:Surface-Active Agents / Q000737:chemistry / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D018491:Dopamine Agonists; D013501:Surface-Active Agents; D001058:Apomorphine