Disposition and biotransformation of C-Benzo(a)pyrene in a pig ear skin model: Ex vivo and in vitro approaches

Biotransformation of chemicals by the skin is a critical determinant of systemic exposure in humans following dermal absorption. Pig ear skin potentially represents a valuable alternative model since it closely resembles to human skin. We developed an ex vivo pig ear skin system which absorption, diffusion and metabolic capabilities were investigated using benzo(a)pyrene [B(a)P] as a model molecule. The potential of the ex vivo pig ear skin model to biotransform xenobiotics was compared with metabolic data obtained using dermal and hepatic microsomes from human and pig. ¹⁴C-B(a)P [50–800 nmol] was applied on the surface of skin models. The diffusion and the production of B(a)P metabolites were quantified by radio-HPLC, LC–MS/MS and NMR. B(a)P was extensively metabolized by pig ear skin explants, the major metabolites being B(a)P-glucuronide and sulfate conjugates. B(a)P-OHs, B(a)P-diols, B(a)P-catechols and B(a)P-diones were also identified. In the pig ear skin model developed, skin diffusion was maintained over 72 h and both phase I and phase II activities were expressed, with the formation of similar metabolites as produced in incubations with liver and skin microsomal fractions. This ex vivo model, which combines a functional skin barrier and active biotransformation capabilities, appears to represent a valuable alternative tool in transdermal exposure studies.     

Classification and labeling of industrial products with extreme pH by making use of in vitro methods for the assessment of skin and eye irritation and corrosion in a weight of evidence approach

Classification and labeling of products with extreme pH values (?2 or ?11.5) is addressed in chemicals legislation. Following determination of pH and alkaline/acid reserve, additional in vitro tests are needed, especially to substantiate results less than corrosive. However, only limited experience with the practical application of in vitro methods to determine appropriate classifications for pH extreme products is available so far. Expert judgment and weight of evidence are given major roles under the globally harmonized system of classification and labeling of chemicals (GHS) and should be performed on a sound data basis. We have used a tiered testing strategy to assess 20 industrial products (cleaning and metal pretreatment) regarding their corrosive and irritating properties towards human skin models in vitro in the EpiDerm™ skin corrosion and/or skin irritation test. Nine dilutions of individual compounds were additionally tested. Non-corrosive samples were tested in the Hen’s egg test chorioallantoic membrane (HET-CAM). We demonstrate how data is combined in a weight of evidence expert judgment, and give examples of classification decisions. To our knowledge this is the first comprehensive analysis of industrial products with extreme pH values to determine irritating and corrosive properties by making use of in vitro methods in a weight of evidence approach.