A minimally invasive clinical model to test sunscreen toxicity based on oxidative stress levels using microbiopsy and confocal microscopy - A Proof of concept study.Int J Cosmet Sci. 2020 Jul 03 [Online ahead of print]IJ
Nanoparticle containing sunscreen use to protect against skin ageing and skin cancer is at an all-time high, but so is the controversy over the toxicity of sunscreen nanoparticles. There is a clear disconnect between in vitro and volunteer outcomes. One of the primary contributors to this is the lack of bridging data between models. The assays, outcomes and throughput from in vitro models cannot be realized in volunteer studies in an ethical manner. We hypothesize that the use of skin microbiopsy could enable volunteer studies to be done using in vitro assays which could help to link in vitro outcomes to clinical risk and benefit. We further hypothesize that using minimally invasive skin microsampling could enable significantly higher throughput of cosmetic testing in volunteers than conventional biopsy. We believe that this approach could be applied to any topical cosmeceutical product testing to enable high quality volunteer data without scarring or pain. Our report is the first to apply in vitro analytical methods for determining oxidative stress to sunscreen treated volunteers. Oxidative stress is most cited mechanism of nanoparticle sunscreen toxicity. We report relative oxidative stress levels in intact and tape-stripped volunteer epidermal tissue after exposure to zinc oxide nanoparticle containing sunscreens (ZnO-NP) to test our hypothesis. Skin exposed to ZnO-NP did not show any significant increase in oxidative stress. ZnO-NP treated tape-stripped skin resulted in signal significantly lower (p ≤ 0.001) oxidative stress levels than tBHP treated tape-stripped skin for both assays (2.2 and 2.0 fold decrease, respectively). Topically applied ZnO-NP had no detectable effect on the oxidative status in volunteer skin. The data support the hypothesis that this 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.