The usefulness of toxicogenomics for predicting acute skin irritation on in vitro reconstructed human epidermis

Discovery of Ezrin Expression as a Potential Biomarker for Chemically Induced Ocular Irritation Using Human Corneal Epithelium Cell Line and a Reconstructed Human Cornea-like Epithelium Model

Numerous studies have attempted to develop a new in vitro eye irritation test (EIT). To obtain more reliable results from EIT, potential new biomarkers that reflect eye irritation by chemicals must be identified. We investigated candidate biomarkers for eye irritation, using a proteomics approach. Sodium lauryl sulfate (SLS) or benzalkonium chloride (BAC) was applied on a reconstructed human cornea-like epithelium model, MCTT HCE, and corneal protein expression was examined by two-dimensional gel electrophoresis. We found that ezrin (EZR) was significantly upregulated by SLS or BAC. In addition, upregulation of EZR in immortalized human corneal cells treated with SLS or BAC was confirmed by quantitative reverse transcription-PCR and western blot analysis. Furthermore, other well-known eye irritants such as cetylpyridinium bromide, Triton X-100, cyclohexanol, ethanol, 2-methyl-1-pentanol, and sodium hydroxide significantly increased EZR expression in immortalized human corneal cells. Induction of EZR promoter activity in irritant-treated human corneal cells was confirmed by a luciferase gene reporter assay. In conclusion, EZR expression may be a potential biomarker for detecting eye irritation, which may substantially improve the performance of in vitro EIT.

Three-Dimensional Epidermal Model from Human Hair Follicle-Derived Keratinocytes

Three-dimensional (3D) epidermal models reconstructed from human skin-derived keratinocytes have been utilized as an alternative to animal testing and models, not only in toxicology, but also in skin biology. Although there are currently several reconstructed human epidermis (RHE) models commercially available, the donors of the keratinocytes are not identified in these models. A tailor-made system is needed to investigate the individual differences in RHE derived from each donor.It is possible to make an individual RHE using each donor's keratinocytes, which are usually obtained by invasive procedures such as skin excision or biopsy. To overcome this drawback, we established an RHE model using keratinocytes derived from plucked hair follicles as a less invasive procedure under conditions without feeder cells, serum, or matrix proteins. In this chapter, we provide a method of isolation and two-dimensional (2D) culture of keratinocytes derived from adult human plucked hair follicles including the outer root sheath (ORS). We also provide a detailed protocol for establishing an RHE model by culturing the keratinocytes under a 3D culture condition. We believe that our less invasive technique will provide a useful tool for investigating individual RHE in both normal and disease settings.

Selected Biomarkers Revealed Potential Skin Toxicity Caused by Certain Copper Compounds

Copper is an essential mineral and plays important roles in skin growth and activity. Copper delivery through skin can provide beneficial effects but its potential to induce skin irritation reactions is often overlooked. Data on dermal toxicity caused by copper compounds is scant. Some recognized in vitro skin toxicity methods are unsuitable for all metal compounds. Here, we employ a keratinocyte-based model and evaluated the skin irritation potential of copper compounds at cellular, genomic and proteomic levels. We determined cell viability and cytotoxicity by using tetrazolium reduction assay and Lactate Dehydrogenase (LDH) assay, performed real-time PCR and protein quantification to assess the expression of biomarkers after treating cells with copper peptide (GHK-Cu), copper chloride (CuCl₂) and copper acetate (Cu(OAc)₂). These copper compounds exhibited different irritancy potentials at the same treatment concentrations. GHK-Cu was not cytotoxic and did not induce any significant change in the expression levels of various skin irritation-related biomarkers. IL-1α and IL-8, HSPA1A and FOSL1 were significantly upregulated following 24-h treatment with CuCl₂ and Cu(OAc)₂ at 58 and 580 μM without concomitant inhibition in cell viability. GHK-Cu has a low potential of inducing skin irritation and therefore provides a safer alternative for the delivery of copper through skin.

Identification of cornifelin and early growth response-1 gene as novel biomarkers for in vitro eye irritation using a 3D reconstructed human cornea model MCTT HCE™

Evaluation of the eye irritation is essential in the development of new cosmetic products. Draize rabbit eye irritation test has been widely used in which chemicals are directly applied to rabbit eye, and the symptoms and signs of eyes are scored. However, due to the invasive procedure, it causes substantial pain and discomfort to animals. Recently, we reported in vitro eye irritation test method using a 3D human corneal epithelial model (MCTT HCE™) which is reconstructed from remaining human tissues after a corneal transplantation. This model exhibited an excellent predictive capacity for 25 reference chemicals (sensitivity 100%, specificity 77% and accuracy 88% vs. GHS). To improve the test performance, we explored new biomarkers for the eye irritation through transcriptomic approach. Three surfactants were selected as model eye irritants that include sodium lauryl sulfate, benzalkonium chloride and triton X-100. After test chemicals were treated, we investigated differentially expressed genes through a whole-gene microarray (Affymetrix GeneChip(®) Human Gene 2.0 ST Array, 48,000 probes). As a result, we identified that mRNAs of cornifelin (CNFN), a constituent of the insoluble cornified cell envelope of stratified squamous epithelia, and early growth response-1 (EGR1), a nuclear transcriptional regulator, were significantly up-regulated by all three irritants. Up-regulation of CNFN and EGR1 was further confirmed by Q-RT-PCR, and immunohistochemistry revealed increased level of CNFN in irritant-treated tissues, supporting the relevance of CNFN and EGR1 as new biomarkers for eye irritation.

Retinoic acid and hydroquinone induce inverse expression patterns on cornified envelope-associated proteins: implication in skin irritation

BACKGROUND

Hydroquinone (HQ) with or without retinoic acid (RA) is routinely used for the treatment of hyperpigmented conditions. Skin irritation is a major problem with popular depigmenting agents, resulting in postinflammatory hyperpigmentation.

OBJECTIVE

To examine the molecular mechanism associated with skin irritation by RA or HQ.

METHODS

A genome-wide transcriptional profiling analysis was performed using monolayer cultures of human keratinocytes treated with or without irritant doses of RA, HQ, or sodium lauryl sulfate (SLS), a representative irritant. Differentially expressed genes (DEGs) were mapped on human chromosomes using a Manhattan plot. For the validation of candidate DEGs, the chemicals with different concentrations of varying irritation intensities were applied in vitro and in vivo and analyzed using real time-PCR and Western blotting.

RESULTS

DEGs mapped to the 1q21 locus, which is composed of a cluster of genes encoding the cornified envelope precursors, showed an inverse expression pattern in response to HQ and RA. Concentrations of RA and HQ that induced a broad range of irritant responses in cultured cells or mice skin also induced inverse effects on the expression of cornified envelope-associated proteins.

CONCLUSIONS

Genetic modulation on cornified envelope-associated proteins by RA-induced irritation, which may be involved in physiological skin barrier disturbance, could be inverse to that by HQ- or SLS-induced irritation.

HSP27 as a biomarker for predicting skin irritation in human skin and reconstructed organotypic skin model

In vitro alternative tests aiming at replacing the traditional animal test for predicting the irritant potential of chemicals have been developed, but the assessing parameters or endpoints are still not sufficient. To discover novel endpoints for skin irritation responses, 2DE-based proteomics was used to analyze the protein expression in human skin exposed to sodium lauryl sulfate (SLS) following the test protocol of the European Centre for the Validation of Alternative Methods (ECVAM) in the present study. HSP27 was up-regulated most significantly among the eight identified proteins, consistent with our previous reports. Acid and basic chemicals were applied on human skin for further validation and results showed that the up-regulated expression of HSP27 was induced in 24h after the exposure. Skin-equivalent constructed with fibroblasts, basement membrane and keratinocytes was used to investigate the potential of HSP27 as a biomarker or additional endpoint for the hazard assessment of skin irritation. Our skin-equivalent (Reconstructed Organotypic Skin Model, ROSM) had excellent epidermal differentiation and was suitable for the skin irritation test. HSP27 also displayed an up-regulated expression in the ROSM in 24h after the irritants exposure for 15min. All these results suggest that HSP27 may represent a potential marker or additional endpoint for the hazard assessment of skin irritation caused by chemical products.

ECVAM and new technologies for toxicity testing

The development of alternative empirical (testing) and non-empirical (non-testing) methods to traditional toxicological tests for complex human health effects is a tremendous task. Toxicants may potentially interfere with a vast number of physiological mechanisms thereby causing disturbances on various levels of complexity of human physiology. Only a limited number of mechanisms relevant for toxicity ('pathways' of toxicity) have been identified with certainty so far and, presumably, many more mechanisms by which toxicants cause adverse effects remain to be identified. Recapitulating in empirical model systems (i.e., in vitro test systems) all those relevant physiological mechanisms prone to be disturbed by toxicants and relevant for causing the toxicity effect in question poses an enormous challenge. First, the mechanism(s) of action of toxicants in relation to the most relevant adverse effects of a specific human health endpoint need to be identified. Subsequently, these mechanisms need to be modeled in reductionist test systems that allow assessing whether an unknown substance may operate via a specific (array of) mechanism(s). Ideally, such test systems should be relevant for the species of interest, i.e., based on human cells or modeling mechanisms present in humans. Since much of our understanding about toxicity mechanisms is based on studies using animal model systems (i.e., experimental animals or animal-derived cells), designing test systems that model mechanisms relevant for the human situation may be limited by the lack of relevant information from basic research. New technologies from molecular biology and cell biology, as well as progress in tissue engineering, imaging techniques and automated testing platforms hold the promise to alleviate some of the traditional difficulties associated with improving toxicity testing for complex endpoints. Such new technologies are expected (1) to accelerate the identification of toxicity pathways with human relevance that need to be modeled in test methods for toxicity testing (2) to enable the reconstruction of reductionist test systems modeling at a reduced level of complexity the target system/organ of interest (e.g., through tissue engineering, use of human-derived cell lines and stem cells etc.), (3) to allow the measurement of specific mechanisms relevant for a given health endpoint in such test methods (e.g., through gene and protein expression, changes in metabolites, receptor activation, changes in neural activity etc.), (4) to allow to measure toxicity mechanisms at higher throughput rates through the use of automated testing. In this chapter, we discuss the potential impact of new technologies on the development, optimization and use of empirical testing methods, grouped according to important toxicological endpoints. We highlight, from an ECVAM perspective, the areas of topical toxicity, skin absorption, reproductive and developmental toxicity, carcinogenicity/genotoxicity, sensitization, hematopoeisis and toxicokinetics and discuss strategic developments including ECVAM's database service on alternative methods. Neither the areas of toxicity discussed nor the highlighted new technologies represent comprehensive listings which would be an impossible endeavor in the context of a book chapter. However, we feel that these areas are of utmost importance and we predict that new technologies are likely to contribute significantly to test development in these fields. We summarize which new technologies are expected to contribute to the development of new alternative testing methods over the next few years and point out current and planned ECVAM projects for each of these areas.

Evaluation of the skin irritation using a DNA microarray on a reconstructed human epidermal model

To avoid the need to use animals to test the skin irritancy potential of chemicals and cosmetics, it is important to establish an in vitro method based on the reconstructed human epidermal model. To evaluate skin irritancy efficiently and sensitively, we determined the gene expression induced by a topically-applied mild irritant sodium dodecyl sulfate (SDS) in a reconstructed human epidermal model LabCyte EPI-MODEL (LabCyte) using a DNA microarray carrying genes that were related to inflammation, immunity, stress and housekeeping. The expression and secretion of IL-1alpha in reconstructed human epidermal culture is known to be induced by irritation. We detected the induction of IL-1alpha expression and its secretion into the cell culture medium by treatment with 0.075% SDS for 18 h in LabCyte culture using DNA microarray, quantitative reverse-transcription polymerase chain reaction (RT-PCR) and ELISA. DNA microarray analysis indicated that the expression of 10 of the 205 genes carried on the DNA microarray was significantly induced in a LabCyte culture by 0.05% or 0.075% SDS irritation for 18 h. RT-PCR analysis confirmed that SDS treatment significantly induced the expressions of interleukin-1 receptor antagonist (IL-1RN), FOS-like antigen 1 (FOSL1), heat shock 70 kDa protein 1A (HSPA1) and myeloid differentiation primary response gene (88) (MYD88), as well as the known marker genes for irritation IL-1beta and IL-8 in a LabCyte culture. Our results showed that a DNA microarray is a useful tool for efficiently evaluating mild skin irritation using a reconstructed human epidermal model.

Expression profiling of senescent-associated genes in human dermis from young and old donors. Proof-of-concept study

It is often described that it is difficult to really discriminate the cause of intrinsic skin aging. The aim of this study was to compare the profiles of expression of senescence-associated genes in biopsies of dermis from young and old human donors. TGF-beta1 was up-regulated in the dermis of old donors as well as the TGF-beta1-regulated genes. The anti-oxidant enzymes Selenium-dependent Glutathione peroxidase and Glutatione S-Transferase Theta 1 were also up-regulated in old dermis as well as Tumor Necrosis Factor Receptor Superfamily 1A. None of these genes had altered expression level in skin fibroblasts embedded in a collagen matrix and exposed to sublethal doses of UVB, suggesting their involvement in intrinsic aging. This study represents a proof-of-concept of larger whole transcriptome studies where all avenues should be used to subtract changes in gene expression due to extrinsic aging from changes potentially due to intrinsic aging.