Occupational exposure assessment with solid substances: choosing a vehicle for in vitro percutaneous absorption experiments

An update of skin permeability data based on a systematic review of recent research

“…Hopf et al ., even recommended a pH close to 7.35 15 . Donor type The influence of the formulation or vehicle on skin penetration is evident and well documented, as certain vehicles or vehicle components help test substances to cross the SC barrier 84 , 85 , modify the flux and the t lag 13 , 55 , 86 . This is why GN156 recommends that the test preparations are similar to what humans are exposed to 11 .…”

“…A vehicle of interest in this perspective could be water but we must keep in mind that water modifies some skin properties (hydration, swelling, etc.) 13 . Moreover, this raises the question of substances that are not very soluble in water, such as lipophilic substances.…”

Less efficient skin penetration of the metal allergen Pd2+ compared to Ni2+ and Co2+ from patch test preparations

“…During sensitization, the innate immune system becomes activated, resulting in the maturation of dendritic cells such as epidermal Langerhans cells. The dendrites of Langerhans cells can extend outwards into the lower layers of the s.c. 53 In this study, concentrations of about 450-750 μM of Ni 2+ , Co 2+ and Pd 2+ were determined in the lower layers of the s.c. (strips [17][18][19][20]. Such concentrations were shown to activate a plethora of pathways in dendritic cells in vitro, for example, due to reactive oxygen species formation.…”

“…Most of these experiments were carried out with incubation times of 24 h, making it difficult to predict metal permeation rates after 48 h, which is the typical duration of the patch test 19 . Since most studies are designed to mimic real‐life human exposure, mainly undissolved metal salts or metal nanoparticles in artificial sweat formulations have been investigated 19–21 . The analysis of skin penetration from artificial sweat is not representative of the metal ion release from PTPs into the skin because of the different physicochemical properties of the formulations.…”

“…19 Since most studies are designed to mimic real-life human exposure, mainly undissolved metal salts or metal nanoparticles in artificial sweat formulations have been investigated. [19][20][21] The analysis of skin penetration from artificial sweat is not representative of the metal ion release from PTPs into the skin because of the different physicochemical properties of the formulations. For instance, when investigating the penetration properties of 5% NiSO 4 PTPs, no Ni 2+ was found in the receptor phase after 48 h. 22 In the present study, the metal ion penetration of the patch test salts NiSO 4 , CoCl 2 , PdCl 2 and Na 2 PdCl 4 into pigskin was determined using FDC assays combined with inductively coupled plasma mass spectrometry (ICP-MS) analysis.…”