Pal and colleagues applied zinc oxide nanoparticles (under 50 nm and under 100 nm) and bulk zinc oxide (under 5 µm) at 5% and 10% w/v to hairless mouse skin, with or without UVB at 50 mJ/cm2. Skin zinc rose in a dose-dependent way. For the 10% nanoparticle groups, UVB increased zinc further, along with reactive oxygen species, myeloperoxidase activity, hyperplasia, COX-2 and MAPK/NF-κB signalling. The authors conclude that UVB-damaged skin allows more nanoparticle penetration and dissolution into zinc ions.
Key numbers
100 µl of formulation was applied over 4 cm2, which equals 1.25 mg zinc oxide per cm2 at 5% and 2.5 mg/cm2 at 10%. UVB was given 30 minutes after application. The text reports direction and significance only. At 6 h, 10% nanoparticles plus UVB raised skin zinc above 5% nanoparticles. At 24 h, the largest increase was with the under-100 nm particles at 5% plus UVB. Between 24 and 48 h skin zinc fell in every group except bulk zinc oxide. The concentrations are shown in supplementary Fig. S1, which is not in this collection, so no numeric skin-zinc value is recorded here.
Methods (brief)
Skin was digested in nitric and perchloric acid and total zinc measured by atomic absorption spectroscopy. The study also used SEM/EDX, TEM, a reactive-oxygen-species assay, myeloperoxidase activity, histology, immunohistochemistry and western blot.
Evidence fitness
The paper is animal evidence that one form of acute barrier damage (UVB) can increase zinc uptake from zinc oxide. Its result differs from the pig-skin in vitro finding reported by SCCS. It gives no human, infant or diaper data.
Limitations
The numeric data are in the supplement. Mouse skin is more permeable than human skin. UVB injury is a different kind of damage from diaper dermatitis.
Related evidence
Update history
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