Skin Sensitization
Intro to Skin Sensitization
Determination of skin sensitization potential is a critical toxicological endpoint in the safety assessment of new chemicals. Although the Guinea Pig Maximization Test (GPMT) and in vivo Local Lymph Node assay (LLNA) have traditionally been used to assess skin sensitization, recent activity has focused on the development of novel non-animal assays for this endpoint. (more…)
Direct Peptide Reactivity Assay (DPRA, OECD 442C)
The DPRA (OECD 442C) is an in chemico assay that models the first key event in the skin sensitization Adverse Outcome Pathway (AOP) – skin, protein reactivity.
Compounds implicated in causing Allergic Contact Dermatitis (ACD) are generally electrophilic in nature. This assay identifies dermal sensitizers based on their reactivity with synthetic peptides containing the nucleophilic amino acid residues lysine and cysteine. Using LC/UV, conjugation of the test material with the peptides can be analyzed.
ARE-Nrf2 Luciferase Keratinocyte Activation Test Method (OECD 442D)
KeratinoSensTM is a cell-based reporter gene assay that models the second key event in the Adverse Outcome Pathway for Dermal Sensitization (keratinocyte activation). The assay measures the induction of a stably transfected luciferase gene under the control of the antioxidant response element (ARE) derived from the human AKR1C2 gene.
Human Cell Line Activation Test (h-CLAT, OECD 442E)
The human Cell Line Activation Test (h-CLAT) is a cell-based assay that identifies skin sensitizers by examining changes in the expression of cell surface markers (CD54 and CD86) implicated in dendritic cell activation, the third key event of the skin sensitization AOP. Following exposure of the THP-1 human monocyte cell line to the test substance, expression levels of CD54 and CD86 are quantified by flow cytometry and compared to controls.
Kinetic Direct Peptide Reactivity Assay (kDPRA, OECD 442C)
Building on the original DPRA (OECD TG 442C), this test assesses multiple substance concentrations and time points to provide quantitative reaction data. This information can assist in determining skin sensitization potency and is being proposed to discriminate UN GHS sub-category 1A substances from those falling into category 1B and/or non-categorized.
Similar to the DPRA assay, kDPRA examines the reactivity of test materials with nucleophilic peptides. High levels of conjugation are indicative of a potential sensitizer.
Predicted EC3 Evaluation/Potency Assessment
The ability to ascertain the maximum limit of a compound that can be applied to the skin without inducing skin sensitization is a critical safety criterion to virtually any risk assessment. Using regression models developed by Givaudan, IIVS is able to perform a computational approach to determine predicted EC3 values (Effective Concentration required to induce a 3-fold upregulation of lymph node cell proliferation) using a combination of OECD approved NAMs (KeratinoSens, hCLAT, and kDPRA). This value can be used to assess risk for compounds to be included in formulations.
Defined Approaches for Skin Sensitization (Based on OECD TG 497)
Determination of skin sensitization potential is a critical endpoint in the safety assessment of raw materials, chemicals, mixtures and formulations. Although the Guinea Pig Maximization Test (GPMT) and Local Lymph node assay (LLNA) have historically been used to address this adverse effect, in silico and in vitro assays have been developed and validated in order to replace these resource-intensive animal tests. (more…)