Abstract
Assessing skin irritation potential is critical for the safety evaluation of topical drugs and other consumer products such as cosmetics. The use of advanced cellular models, as an alternative to replace animal testing in the safety evaluation for both consumer products and ingredients, is already mandated by law in the European Union (EU) and other countries. However, there has not yet been a large-scale comparison of the effects of topical-use compounds in different cellular skin models. This study assesses the irritation potential of topical-use compounds in different cellular models of the skin that are compatible with high throughput screening (HTS) platforms. A set of 451 topical-use compounds were first tested for cytotoxic effects using two-dimensional (2D) monolayer models of primary neonatal keratinocytes and immortalized human keratinocytes. Forty-six toxic compounds identified from the initial screen with the monolayer culture systems were further tested for skin irritation potential on reconstructed human epidermis (RhE) and full thickness skin (FTS) three-dimensional (3D) tissue model constructs. Skin irritation potential of the compounds was assessed by measuring tissue viability, trans-epithelial electrical resistance (TEER), and secretion of cytokines interleukin 1 alpha (IL-1α) and interleukin 18 (IL-18). Among known irritants, high concentrations of methyl violet and methylrosaniline decreased viability, lowered TEER, and increased IL-1α secretion in both RhE and FTS models, consistent with irritant properties. However, at low concentrations, these two compounds increased IL-18 secretion without affecting levels of secreted IL-1α, and did not reduce tissue viability and TEER, in either RhE or FTS models. This result suggests that at low concentrations, methyl violet and methylrosaniline have an allergic potential without causing irritation. Using both HTS-compatible 2D cellular and 3D tissue skin models, together with irritation relevant activity endpoints, we obtained data to help assess the irritation effects of topical-use compounds and identify potential dermal hazards.
Highlights
Skin provides a physical barrier to protect the body from environmental insults, including chemical agents (Liu et al, 2016)
A total of 396 topical chemicals from the Toxicology in the 21st Century (Tox21) 10K library and 55 Organization for Economic Co-operation and Development (OECD) reference chemicals were tested in neonatal primary keratinocytes (NKTC) and immortalized human keratinocytes (NHEK) for cytotoxic activity
Keratinocytes growing as a monolayer were treated with chemicals at 11 concentrations ranging from 100 nM to 92 μM in 1536-well plates for 24 h
Summary
Skin provides a physical barrier to protect the body from environmental insults, including chemical agents (Liu et al, 2016). Most RhE skin equivalents are tissues made with keratinocytes that model a stratified epidermis, but have the following drawbacks: (1) these models do not have the sample throughput needed for large scale profiling of compounds at different doses; and (2) they do not reproduce the physiological complexity found in human skin tissue, including the lack of cell-cell interactions between keratinocytes and fibroblasts in the dermis layer These cell-cell interactions are important for the normal function of skin as a physical barrier for the body, including formation of epidermaldermal junction, epidermal differentiation, and stratification (El Ghalbzouri et al, 2005; Wojtowicz et al, 2014). There is a need for a platform of cellular assays that enables the large-scale screening of compounds while producing data that are relevant to and predictive of irritation responses in humans
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