A minimally invasive clinical model to test sunscreen toxicity based on oxidative stress levels using microbiopsy and confocal microscopy – a proof of concept study

Abstract

Objective This proof‐of‐concept study demonstrated that using minimally invasive skin microsampling could enable significantly higher throughput of cosmetic testing in volunteers than conventional biopsy. Nanoparticle sunscreen was used as a model to test toxicity based on oxidative stress using microbiopsy and confocal imaging. Methods Six volunteers were recruited for this study (3 males and 3 females). Zinc oxide nanoparticle containing topical formulation was prepared at 10% w/v. Each volunteer had 3 areas of 4 cm2 each mapped on each inner forearm for a total of 6 treatment areas (intact/ tape‐stripped and with/without treatment). The topical zinc‐nanoparticle formulation was applied directly to volunteer skin (2mg/cm2) for 2 hrs. Microbiopsied tissue from each treatment group was stained for reactive oxygen and nitrogen species in addition to mitochondrial superoxide. The stained samples were then imaged using confocal microscopy prior to image analysis. Results Skin exposed to zinc oxide nanoparticles did not show any significant increases in oxidative stress. Zinc oxide nanoparticle tape‐stripped skin resulted in signal significantly lower (P < 0.001) oxidative stress levels than t‐butylated hydroxytoluene treated tape‐stripped skin for oxidative stress markers. Topically applied zinc oxide nanoparticles had no detectable effect on the oxidative status in volunteer skin. No adverse reactions or effects were observed after all treatments including microbiopsy. Conclusion The data support the hypothesis that microbiopsy is a viable approach to study cosmeceutical‐ skin interactions in volunteers with capacity for molecular assays and high throughput with very low risk to the volunteer.