Flux of a Nickel(II) Salt versus a Nickel(II) Soap across Human Skin in vitro

Abstract

Background: Contrary to in vitro data on skin diffusivity of nickel salts indicating slow rates of diffusion, contact allergy to nickel among the general population is frequent, indicating facile skin penetration. Objective: To demonstrate that the preferred diffusion of a lipophilic oxidation product of nickel formed in contact with the skin follows the multilamellar lipid region which envelops the corneocytes. Method: Diffusion of nickel chloride was compared with that of the lipophilic nickel soap, the dioctanoate. Results: The dioctanoate soap showed a significantly lower rate of diffusion (K_p = 1.4 × 10^–3 ± 5.7 × 10^–4 cm/h) than the chloride salt (K_p = 9.8 × 10^–3 ± 4.8 × 10^–4 cm/h), with a relatively high level of nickel retained in the tissue. Conclusions: (a) The molecular volume of the nickel dioctanoate overrides the effect of compound polarity; (b) the rates of diffusion measured through dermatomed skin are higher than those heretofore measured through full-thickness skin, epidermal tissue or stratum corneum; (c) both the nickel salt and soap appear to diffuse primarily via appendages; (d) the cause for the pronounced immune response to nickel in contact with the skin appears to lie in amounts retained in the viable skin strata; (e) skin from a young donor appears more permeable to nickel compounds than skin from an older source stemming from the same anatomical site.