Application of the adverse outcome pathway framework for investigating skin sensitization potential of nanomaterials using new approach methods

Abstract

Background Currently, considerable efforts to standardize methods for accurate assessment of properties and safety aspects of nanomaterials are being made. However, immunomodulation effects upon skin exposure to nanomaterial have not been explored. Objectives To investigate the immunotoxicity of single‐wall carbon nanotubes, titanium dioxide, and fullerene using the current mechanistic understanding of skin sensitization by applying the concept of adverse outcome pathway (AOP). Methods Investigation of the ability of nanomaterials to interact with skin proteins using the micro‐direct peptide reactivity assay; the expression of CD86 cell surface marker using the U937 cell activation test (OECD No. 442E/2018); and the effects of nanomaterials on modulating inflammatory response through inflammatory cytokine release by U937 cells. Results The nanomaterials easily internalized into keratinocytes cells, interacted with skin proteins, and triggered activation of U937 cells by increasing CD86 expression and modulating inflammatory cytokine production. Consequently, these nanomaterials were classified as skin sensitizers in vitro. Conclusions Our study suggests the potential immunotoxicity of nanomaterials and highlights the importance of studying the immunotoxicity and skin sensitization potential of nanomaterials to anticipate possible human health risks using standardized mechanistic nonanimal methods with high predictive accuracy. Therefore, it contributes toward the applicability of existing OECD (Organisation for Economic Co‐operation and Development) testing guidelines for accurate assessment of nanomaterial skin sensitization potential.

Skin Sensitization Evaluation of Carbon-Based Graphene Nanoplatelets

“…In summary, the skin sensitization results for GNPs using the two alternative tests were negative. In our study, it was shown that the well-known sensitizer-induced inflammation indicator IL-1alpha was not induced [ 30 , 31 ]. Moreover, when judged considering all the results such as IL-1beta, IL-8 and TNF-alpha, which are cytokines related to acute inflammatory reactions, graphene does not appear to have an inflammatory effect on keratinocytes.…”

In silico Prediction of Skin Sensitization: Quo vadis?

“…It is of interest to note that this method has been submitted to OECD and the drafted proposal has been publicized on the OCED website ( OECD, 2016b ; OECD, 2018c ). This method recently has been used to evaluate the role of nanomaterials in skin sensitization ( Bezerra et al, 2021 ).…”

Adverse outcome pathways – development and potential regulatory application

“…To comply with the 3Rs policy, non-animal methods have been proposed to assess potential chemical sensitizers 54,55 . In 2016, the Brazilian National Council for the The recent report by Bezerra et al 60 exemplifies a practical contribution toward the applicability of the existing OECD guidance 59 for skin AOPs and the IATA. These authors evaluated the immunotoxicity of carbon nanotubes containing titanium dioxide and of fullerene.…”

“…These authors evaluated the immunotoxicity of carbon nanotubes containing titanium dioxide and of fullerene. By using in vitro assays for accurate assessment of skin sensitization, these authors indicated that the nanomaterials were internalized into keratinocytes (KE1), interacted with skin protein-like molecules (KE2), and stimulated inflammatory cytokine production by monocytic cells (KE3) 60 . Accordingly, the nanomaterials were deemed to be skin sensitizers in vitro, indicating that they should be considered for further higher tier studies to support risk assessment, including exposure and dose-response evaluations.…”