Metabolipidomic changes induced by dermal nickel penetration determined in an ex vivo porcine ear skin model.

Rational: Nickel is one of humans' most prevalent triggers of allergic contact dermatitis. However, the underlying mechanisms of this allergy still need to be fully understood. One aspect that has yet to be explored is the direct impact of common metal allergens on the skin's metabolites and lipids composition.

Method: Our study employed matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) to analyze spatially resolved metabolic alterations induced by nickel exposure. Cross-sections of ex vivo porcine ear skin exposed to increasing nickel (II) ion concentrations (17-167 μg/cm) were measured with an AP-SMALDI AF ion source coupled to Q Exactive HF Orbitrap mass spectrometer. Additionally, the penetration of nickel ions into the skin was observed through its pink complexation with dimethylglyoxime under light microscopy.

Results: For nickel ion concentrations up to 84 μg/cm, most nickel ions were stopped within the stratum corneum, while only a very small proportion of nickel ions penetrated the viable epidermis and dermis. Stratum corneum locations with high nickel ion concentrations showed a decrease in arginine and ceramides. Furthermore, several phosphatidylcholine and sphingomyelin species were found to be downregulated in the viable epidermis and dermis due to the nickel exposure.

Conclusion: Nickel penetrates at a trace level into the viable skin and induces severe metabolomic and lipidomic changes in the stratum corneum, epidermis, and dermis, indicating a change in the skin (barrier) function. These findings contribute to a deeper understanding of nickel-induced skin allergies and provide a solid foundation for further research.