Skin Absorption of Anions: Part Two. Skin Absorption of Halide Ions.

Abstract

The purpose of the study was to sort skin penetration of anions with respect to their properties and to assess their mechanisms of penetration. Aqueous solutions of halides at two concentrations were prepared and quantitative penetration studies were carried out for 24h using Franz diffusion cells. The iodide permeation was also measured after blocking of anion channels and transporters to investigate the role of this specific transport. Absorption of halide ions into skin revealed large differences of transport between these anions according to the Hofmeister series. Increasing steady-state fluxes and lag times in the order F(-) < Cl(-) < Br(-) < I(-) were observed in permeation experiments. The steady-state fluxes were proportional to the concentration for each halide ion. Longer lag times for iodide or bromide ions were explained by the ability of such sticky chaotropic anions to interact with apolar lipids especially in the stratum corneum. Inhibiting ion exchangers and channels decreased the flux of iodide ions by 75%, showing the high contribution of the facilitated transport over the passive pathway. Ions transport had contributions coming from passive diffusion through the skin layers and transport mediated by ion channels and binding to ion transporters.