Follow-up to the ECVAM prevalidation study on in vitro tests for acute skin irritation. The European Centre for the Validation of Alternative Methods Skin Irritation Task Force report 2

Reference chemical database for the development and validation of in vitro alternatives to skin irritation and comparison of the performance of RhE models

After EU ban on animal testing for cosmetics in 2013, there has been an increasing global interest in alternatives test methods. To development for alternatives test method, we need to get the toxic data about in vitro and in vivo of chemicals. However, database sometimes provide limited in vivo and in vitro data on chemicals. Further, the data generated using the OECD TG439 (in vitro skin irritation) are scattered in difference databases, and it is not easy to navigate through them. Therefore, we complied 'Reference Chemical Database System for Skin Irritation Alternative Test (RCDS-Skin Irritation)' to allow easy, one-stop access to test chemical information. We established the systematic RCDS-Skin Irritation by collecting physiochemical properties, CAS number, human data, and in vivo (OECD TG404) data from overseas chemicals database including European Chemicals Agency (ECHA) etc., and in vitro data using Reconstructed human Epidermis (RhE) (OECD TG439). As a result, we developed the RCDS-Skin Irritation that contains information on 149 chemicals including the data we generated by performing tests using EpiDerm™ SIT, SkinEthic™ RHE and KeraSkin™ SIT. Therefore, the RCDS-Skin Irritation established based on our study will provide insight for safety assessment of chemicals and for development of alternative test methods.

Safety Evaluation of a Prototypical Diazirine-Based Covalent Crosslinker and Molecular Adhesive

bis-Diazirine reagents are increasingly being used as polymer crosslinkers, adhesives, and photopatterning agents in the materials sciences literature, but little effort has been made thus far to document their chemical safety profile. Here, we describe the results of a detailed toxicity assessment of a representative bis-diazirine. Safety was evaluated by a series of in vitro assays, which found the product to be non-mutagenic in bacterial tester strains TA98 and TA100, non-corrosive and non-irritating to skin, and requiring no classification for eye irritation or serious damage. While in vitro tests do not capture the integrated whole animal system, and thus cannot completely rule out the possibility of adverse responses, the results of this study suggest a desirable safety profile for bis-diazirine reagents and provide a solid foundation upon which to add in vivo assessment of safety risk and dose-response studies.

Assessment of the utility of the novel Phenion® full thickness human skin model for detecting the skin irritation potential of antimicrobial cleaning products

The skin is a potential route of exposure to antimicrobial cleaning products (ACP). Skin irritation, reversible damage to the skin, is an endpoint for protecting consumers and operators accidently exposed to these complex mixtures. To assess skin irritation of 24 ACP formulations, a new protocol was developed and adapted from OECD Test Guideline No. 439 with EpiDerm™ (epidermis model) replaced by Phenion® FT (full thickness tissue, including epidermis and dermis) as the test system. A full thickness tissue was utilized to provide a more human in vivo-like model. Formulations were applied to Phenion® FT and cell viability measured by MTT reduction after a 15-min exposure and 42 h post exposure period. A prediction model was applied, and results compared with in vivo rabbit skin irritation data. Concordance between in vivo and in vitro was demonstrated to be suitable (i.e., sensitivity 78%, specificity 83%, and accuracy 79%) using this modified OECD Test Guideline No. 439 method with a 70% cell viability selected as the most reasonable cut off for discriminating non-irritants (EPA Class IV). These results were considered suitable to develop a draft IATA i.e., with any ACP formulation identified as EPA Category IV in this test. The method will be further refined to distinguish irritant categories.

Microemulsion system for topical delivery of thai mango seed kernel extract: development, physicochemical characterisation and ex vivo skin permeation studies

A microemulsion system containing Thai mango seed kernel extract (MSKE, cultivar “Fahlun”) was developed and characterised for the purpose of topical skin delivery. The MSKE-loaded microemulsions were prepared by using the spontaneous emulsification method. Isopropyl myristate (IPM) was selected as the oil phase. A polyoxyethylene sorbitan monooleate and sorbitan monododecanoate (1:1, w/w) system was used as the surfactant phase; an aqueous mixture of different cosurfactants (absolute ethanol, 96.3% v/v ethanol, 1-propanol, 2-propanol or 1,2-propanediol) at a weight ratio of 1:1 was used as the aqueous phase. Among the cosurfactants studied, the 1-propanol aqueous mixture had the largest microemulsion region (48.93%) in the pseudo-ternary phase diagram. Microemulsions containing 1% MSKE demonstrated good physicochemical stability during a six-month study period at 25 ± 2 °C/60% ± 5% RH. The ex vivo skin permeation study demonstrated that the microemulsions exhibited a potent skin enhancement effect allowing MSKE to penetrate skin layers up to 60-fold higher compared with the control. Neither skin irritation nor skin corrosion was observed in ex vivo studies. The present study revealed that IPM-based microemulsion systems may be promising carriers to enhance skin penetration and delivering MSKE for topical treatment.

N-Acetyl-D-glucosamine oligosaccharides induce mucin secretion from colonic tissue and induce differentiation of human keratinocytes

Chitin oligosaccharides (DP2, DP3, DP4, DP5 and DP7) were investigated for their effects on epithelial cells and tissue (skin keratinocytes in-vitro and ex-vivo, and gastrointestinal epithelial membranes ex-vivo). Oligomers DP2, DP3 and DP5 at 10 μg mL−1 significantly stimulated the mitochondrial activity of cultured keratinocytes in-vitro (primary cells and HaCaT cell line), with highest activity observed for the pentamer (150% of untreated control). The effects were dose dependent. This higher energy status of primary cells was triggered into a higher differentiation status, as determined by the early and late differentiation markers keratins K1/K10 and involucrin, respectively. In contrast, increased mitogenic cell proliferation was not induced by the oligosaccharides. Toxic effects on keratinocytes were absent. Additionally for the first time a mucin-stimulating effect of chitin oligosaccharides DP3 and DP5 was observed in an ex-vivo model based on intestinal epithelial mucosa tissue. Mucin secretion was time dependent, leading to the secretion of polymers comparable to those normally secreted under physiological conditions. Mucin induction was observed from colonic tissue isolated from humans and pigs. Also, porcine stomach mucosa was stimulated by DP5, while ileum tissue reacted to only a minor extent. Potential developments towards products with wound-healing capacity and activity against chronic bowel disease are discussed.

Assessment of human epidermal model LabCyte EPI-MODEL for in vitro skin irritation testing according to European Centre for the Validation of Alternative Methods (ECVAM)-validated protocol

A validation study of an in vitro skin irritation testing method using a reconstructed human skin model has been conducted by the European Centre for the Validation of Alternative Methods (ECVAM), and a protocol using EpiSkin (SkinEthic, France) has been approved. The structural and performance criteria of skin models for testing are defined in the ECVAM Performance Standards announced along with the approval. We have performed several evaluations of the new reconstructed human epidermal model LabCyte EPI-MODEL, and confirmed that it is applicable to skin irritation testing as defined in the ECVAM Performance Standards. We selected 19 materials (nine irritants and ten non-irritants) available in Japan as test chemicals among the 20 reference chemicals described in the ECVAM Performance Standard. A test chemical was applied to the surface of the LabCyte EPI-MODEL for 15 min, after which it was completely removed and the model then post-incubated for 42 hr. Cell v iability was measured by MTT assay and skin irritancy of the test chemical evaluated. In addition, interleukin-1 alpha (IL-1alpha) concentration in the culture supernatant after post-incubation was measured to provide a complementary evaluation of skin irritation. Evaluation of the 19 test chemicals resulted in 79% accuracy, 78% sensitivity and 80% specificity, confirming that the in vitro skin irritancy of the LabCyte EPI-MODEL correlates highly with in vivo skin irritation. These results suggest that LabCyte EPI-MODEL is applicable to the skin irritation testing protocol set out in the ECVAM Performance Standards.

Toward an evidence-based toxicology

The increasing demands on toxicology of large-scale risk assessment programmes for chemicals and emerging or expanding areas of chemical use suggest it is timely to review the toxicological toolbox. Like in clinical medicine, where an evidence-based medicine (EBM) is critically reviewing traditional approaches, toxicology has the opportunity to reshape and enlarge its methodology and approaches on the basis of compounded scientific knowledge. Such revision would have to be based on structured reviews of current practice, ie, assessment of test performance characteristics, mechanistic understanding, extended quality assurance, formal validation and the use of integrated testing strategies. This form of revision could optimize the balance between safety, costs and animal welfare, explicitly stating and, where possible, quantifying uncertainties. After a self-critical reassessment of current practices and evaluation of the thus generated information, such an evidence-based toxicology (EBT) promises to make better use of resources and to increase the quality of results, facilitating their interpretation. It shall open up hazard and also risk assessments to new technologies, flexibly accommodating current and future mechanistic understanding. An EBT will be better prepared to answer the continuously growing safety demands of modern societies.

Skin capacitance imaging and corneosurfametry. A comparative assessment of the impact of surfactants on stratum corneum

Silicon image sensor (SIS) technology was recently introduced as an innovative tool (SkinChip, L'Oréal) providing sensitive imaging of the skin capacitance. This method can detect discrete focal variations in skin surface hydration, and thus early discrete manifestations of skin irritation induced by surfactants. In the present in vivo study, 2 neat and diluted shampoos, and 5% and 10% sodium laurylsulfate solutions were tested on human skin. Each surfactant solution was gently rubbed on the skin using wet hair wicks mimicking the casual use of a shampoo on the scalp. Clinical and SIS evaluations were carried out. In addition, the same products were tested using the ex vivo corneosurfametry bioassay performed on human stratum corneum (SC) harvested by cyanoacrylate skin surface strippings. The colourimetric index of mildness (CIM) was measured on these samples. The product reactivity with the SC was recognized by darker skin capacitance images, and by both lowered SkinChip-generated values and lowered CIM values. The extent in changes varied according to the nature of the test products and their concentrations. The SkinChip image changes likely corresponded to the acute surfactant-induced water swelling of the corneocytes. Skin capacitance imaging and corneosurfametry allow to disclose discrete surfactant-induced alterations of corneocytes.

Silicon Image Sensor Technology for in vivo Detection of Surfactant-Induced Corneocyte Swelling and Drying

BACKGROUND

Several instrumental methods can indirectly assess some specific aspects of cutaneous irritation at the level of the stratum corneum (SC).

OBJECTIVE

There is a need for developing more sensitive approaches in this field.

METHODS

We assessed a recently introduced innovative tool (SkinChip) based on capacitive pixel-sensing technology in its potential to detect early discrete manifestations of skin irritation. The sensor generates a detailed non-optical picture corresponding to a capacitance map of the skin surface reaching 50 microm pixel resolution. Some topographical details can be easily disclosed and the SC hydration as well. Two surfactant solutions were tested on volunteers. These solutions were applied under test patches for 2 days on the volar forearms. Clinical and SkinChip assessments were performed 3 h after removing the patch.

RESULTS

The generated images allowed a precise observation of skin irritation which appeared as a two-step process. Early changes consisted of darker pixels corresponding to overhydrated swollen corneocytes at the irritated sites. Two days later, the same area appeared as white pixels, indicating the loss of corneocyte hydration.

CONCLUSION

The SkinChip device appears to be a very sensitive tool for detecting the early steps of surfactant-induced skin irritation affecting the SC.

Skin irritation: prevalence, variability, and regulatory classification of existing in vivo data from industrial chemicals

In vivo rabbit data for skin irritation registered in the European New Chemicals Database (NCD) and an ECETOC Database were evaluated to characterise the distribution of irritation potential among chemicals and to assess the variability of the animal test. These databases could be used to determine experimental and rudimentarily within-laboratory variability, but not between-laboratory variability. Our evaluation suggests that experimental variability is small. Using two classification systems--the system currently used in Europe and the Globally Harmonised System (GHS)--the prevalence of skin irritation data obtained from NCD was analysed. This analysis revealed that out of 3121 chemicals tested, less than 10% showed an irritation potential in rabbits which would require an appropriate hazard label and 64% did not cause any irritation. Furthermore, it appears that in practical use the European classification system introduces bias towards overclassification. Based on these findings, we conclude, that the classification systems should be refined taking prevalence into account. Additionally, prevalence should be incorporated into the design and analysis of validation studies for in vitro test methods and in the definition of testing strategies.

Assessment of the potential irritation and photoirritation of novel amino acid-based surfactants by in vitro methods as alternative to the animal tests

The ultraviolet-A radiation damage effects on skin and eyes will be increased by phototoxic compounds which could be present in pharmaceutical or cosmetic formulations. Great efforts have been made in the last years to find surfactants to replace those with phototoxic potential in commercial use. Series of different in vitro models for phototoxicity, included to validated neutral red uptake (NRU) 3T3 phototoxicity assay are useful screening tools. The phototoxic effects of a novel family of glycerol amino acid-based surfactant compounds were examined via these assays. Human red blood cells and two immortalised cell lines, murine fibroblast cell line 3T3, and one human keratinocyte cell line, HaCaT, were the in vitro models employed to predict potential photoirritation. The phototoxic end-points assessed were hemolysis (human red blood cell test) and resazurin transformation to resorufin and NRU in cell culture methods. The results suggest that no phototoxic effects by any new amino acid derived-surfactants, could be identified.

The cytotoxicity of volatile JP-8 jet fuel components in keratinocytes

In vitro models are being used to evaluate the toxic and irritating effects of JP-8, a kerosene-based jet fuel. JP-8 components are volatile, which makes in vitro studies difficult to evaluate dose-response relationships due to changes in chemical dosimetry caused by evaporation from the exposure medium. An in vitro approach testing volatile chemical toxicity that we have recently developed was used to evaluate the toxicity of the JP-8 components m-xylene, 1-methylnaphthalene (1-MN), and n-nonane in keratinocytes. Partition coefficients were measured and used to estimate the chemical concentration in the keratinocytes. The EC50 for m-xylene and 1-MN decreased significantly (P < or = 0.05) at 1, 2, and 4h. For n-nonane, no significant decreases in the EC50 values were observed over time; marginal cytotoxicity of n-nonane in keratinocytes was observed at 1h. Within 4h, about 75-90% of each volatile chemical was observed to be lost from the exposure medium when tissues were exposed in unsealed 24-well plates. This decrease resulted in significantly higher medium chemical concentrations needed to obtain EC50 values when compared to tissues exposed in sealed vials. This study demonstrates that chemical evaporation during in vitro exposures can significantly affect toxicological endpoint measurements. Ultimately, relating target cell chemical concentration to cellular responses in vitro could be used in determining an equivalent external dose using a biologically-based mathematical model.

Dermal toxicity and microscopic alterations by JP-8 jet fuel components in vivo in rabbit

In this study, we investigated the skin irritation, macroscopic and microscopic barrier alteration in vivo in rabbits from aliphatic and aromatic components of jet propellant-8 (JP-8) jet fuel. Macroscopic barrier properties were evaluated by measuring transepidermal water loss (TEWL), skin capacitance, and skin temperature; microscopic changes were observed by light microscopy. Draize visual scoring system was used to measure skin irritation. We found significant (P<0.05) increase in temperature at the site of all chemically saturated patches immediately after patch removal in comparison to the control site. Tridecane (TRI) produced a greater increase in temperature and capacitance at all time points than all the other components of JP-8. Both the aliphatic and aromatic components increased the TEWL at all time points. Tridecane produced greater increase in TEWL followed by naphthalene (NAP), 1-methylnaphthalene (1-MN), 2-metylnaphthalene (2-MN), tetradecane (TET), and dodecane (DOD). All of the above components of JP-8 caused moderate to severe erythema and edema, which were not resolved to the baseline even after 24h of patch removal. Light microscopy revealed an increase in epidermal thickness (ET), and decrease in length and thickness of collagen fibers' bundle by the above components of JP-8. These results suggest potential dermatotoxicity from the JP-8 components.

The effect of m-xylene on cytotoxicity and cellular antioxidant status in rat dermal equivalents

Exposure of the skin to volatile organic chemicals (VOCs) can lead to irritation, inflammation and cytotoxicity. Since VOCs are used in industrial, commercial and military applications, concern is mounting with respect to VOC safe exposure limits. Although traditional toxicological assessment of VOCs has utilized animal models, the use of alternative in vitro models is becoming more widespread. We have previously developed a sealed exposure system that prevents chemical loss through evaporation and enables calculation of target cell chemical dose. The present study utilized this in vitro exposure method to assess m-xylene-induced cytotoxicity and antioxidant status in dermal equivalents (dermal fibroblasts in a collagen matrix). At the end of a 1- or 4-h exposure, cytotoxicity was measured using the MTT assay and the EC50 values determined were 1481 +/- 88 and 930 +/- 33, respectively. Decreases in cellular thiols and catalase activity were observed, which occurred in a time and dose-dependent manner. Treatment of dermal equivalents with the antioxidants N-acetylcysteine (NAC) and catalase provided some protection against m-xylene-induced cytotoxicity. When compared to m-xylene exposures, treatment with either 1.0 or 5.0 mM NAC led to increases in the EC50 values at 1 and 4 h. Increases in these EC50 values ranged from 1.22- to 1.32-fold at 1 h and 1.27- to 1.54-fold at 4 h. Although treatment with catalase (1000 U/ml) led to a 1.35-fold increase in cell viability at 1 h, no significant differences were observed at either 1 or 4 h when compared to dermal equivalents exposed to m-xylene alone. These results suggest that exposure to m-xylene leads to a time- and dose-dependent decrease in cellular antioxidants and that cellular thiols may provide protection against the cytotoxic properties of m-xylene.