title: Crystalline phase modulates the potency of nanometric TiO₂ to adhere to and perturb the stratum corneum of porcine skin under indoor light.
abstract: Nanometric TiO₂ is largely employed in cosmetics, but in vitro toxic effects have been reported when nano-TiO₂ is exposed to UV light. The photoreactivity of TiO₂ largely depends on its crystal phase, namely, anatase and rutile. Surface acidity, which is also dependent on crystal structure, may impart a positive or negative charge to the nanomaterial surface and ultimately modulate particle adhesion to tissues. Three nanometric TiO₂ powders with a different crystal lattice and surface charge (anatase, rutile, and anatase/rutile) have been employed here to investigate their interaction with the skin and to examine the molecular mechanisms of the TiO₂-induced oxidative damage. The strength of the interaction of nano-TiO₂ with skin has been revealed by chemiometric mapping (μ-XRF and SEM-EDS) after tissue washing. Positively charged anatase and anatase/rutile, but not negatively charged rutile, were strongly held on the skin surface and were able to promote a structural rearrangement of the lipid bilayer in the stratum corneum (DSC and Raman) under controlled indoor illumination (UVA < 1 mW/m²). Under the same conditions, cell-free reactivity tests (ROS-mediated free-radical release and lipoperoxidation) indicated that anatase and anatase/rutile are more reactive than rutile, suggesting a ROS-mediated oxidative mechanism that may alter the structure of the stratum corneum. Both the higher oxidative potential and the stronger adhesion to skin of anatase and anatase/rutile TiO₂ may explain the stronger disorganization induced by these two samples and suggests the use of rutile to produce safer TiO₂-based cosmetic and pharmaceutical products.
authors.affiliation: Dip. Chimica, "G. Scansetti" Interdepartmental Center and NIS Excellence Center, University of Torino , via P. Giuria 7, 10125, Torino, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Turci
authors.forename: Elena
authors.initials: E
authors.lastname: Peira
authors.forename: Ingrid
authors.initials: I
authors.lastname: Corazzari
authors.forename: Ivana
authors.initials: I
authors.lastname: Fenoglio
authors.forename: Michele
authors.initials: M
authors.lastname: Trotta
authors.forename: Bice
authors.initials: B
authors.lastname: Fubini
mesh_terms: D000818:Animals; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D004817:Epidermis / Q000187:drug effects* / Q000528:radiation effects; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D010316:Particle Size; D017382:Reactive Oxygen Species / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D013552:Swine; D014025:Titanium / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D008051:Lipid Bilayers; D017382:Reactive Oxygen Species; C009495:titanium dioxide; D014025:Titanium