The in vitro skin irritation of chemicals: optimisation of the EPISKIN prediction model within the framework of the ECVAM validation process

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.

Toxic External Exposure Leading to Ocular Surface Injury

The surface of the eye is directly exposed to the external environment, protected only by a thin tear film, and may therefore be damaged by contact with ambient particulate matter, liquids, aerosols, or vapors. In the workplace or home, the eye is subject to accidental or incidental exposure to cleaning products and pesticides. Organic matter may enter the eye and cause infection. Ocular surface damage can trigger a range of symptoms such as itch, discharge, hyperemia, photophobia, blurred vision, and foreign body sensation. Toxin exposure can be assessed clinically in multiple ways, including via measurement of tear production, slit-lamp examination, corneal staining, and conjunctival staining. At the cellular level, environmental toxins can cause oxidative damage, apoptosis of corneal and conjunctival cells, cell senescence, and impaired motility. Outcomes range from transient and reversible with complete healing to severe and sight-compromising structural changes. Classically, evaluation of tolerance and safety was carried out using live animal testing; however, new in vitro and computer-based, in silico modes are superseding the gold standard Draize test. This review examines how environmental features such as pollutants, temperature, and seasonality affect the ocular surface. Chemical burns to the eye are considered, and approaches to protect the ocular surface are detailed.

Reduced specificity for the local lymph node assay for lipophilic chemicals: Implications for the validation of new approach methods for skin sensitization

Meaningful and accurate reference data are crucial for the validation of New Approach Methodologies (NAMs) in toxicology. For skin sensitization, multiple reference datasets are available including human patch test data, guinea pig data and data from the mouse local lymph node assay (LLNA). When assessed against the LLNA, a reduced sensitivity has been reported for in vitro and in chemico assays for lipophilic chemicals with a LogP ≥3.5, resulting in reliability restrictions within the h-CLAT OECD test guideline. Here we address the question of whether LLNA data are an appropriate reference for chemicals in this physicochemical range. Analysis of LLNA vs human reference data indicates that the false-discovery rate of the LLNA is significantly higher for chemicals with LogP ≥3.5. We present a mechanistic hypothesis whereby irritation caused by testing lipophilic chemicals at high test doses leads to unspecific cell proliferation. The accompanying analysis indicates that for lipophilic chemicals with negative calls in in vitro and in chemico assays, resorting to the LLNA is not necessarily a better option. These results indicate that the validation of NAMs in this particular LogP range should be based on a more holistic evaluation of the reference data and not solely upon LLNA data.

Improved Tool for Predicting Skin Irritation on Reconstructed Human Epidermis Models Based on Electrochemical Impedance Spectroscopy

The rabbit skin irritation test has been the standard for evaluating the irritation potential of chemicals; however, alternative methods that do not use animal testing are actively encouraged. Reconstructed human epidermis (RhE) models mimic the biochemical and physiological properties of the human epidermis and can be used as an alternative method. On RhE methods, the metabolic activity of RhE models is used to predict skin irritation, with a reduction in metabolic activity indicating a reduced number of viable cells and linking cell death to skin irritation processes. However, new challenges have emerged as the use of RhE models increases, including the need for non-invasive and marker-free methodologies to assess cellular states. Electrochemical impedance spectroscopy (EIS) is one such methodology that can meet these requirements. In this study, our results showed that EIS can differentiate between irritant and non-irritant chemicals, with a significant increase in the capacitance values observed in the irritant samples. A ROC curve analysis showed that the prediction method based on EIS met OECD TG 439 requirements at all time points and had 95% within-laboratory reproducibility. Comparison with the MTT viability assay showed that prediction using EIS achieved higher sensitivity, specificity, and accuracy. These results suggest that EIS could potentially replace animal testing in the evaluation of irritation potential and could be a valuable addition to in vitro testing strategies.

ISO 10993-23 In vitro irritation testing for medical devices: Substantiating applicability to mild irritants and non-extractables

Irritation testing is an integral part of the biocompatibility assessment of medical devices and has historically been conducted on animals, either by direct contact or with polar and non-polar solvent extracts. In 2018 an ISO-sponsored interlaboratory validation study demonstrated that two reconstituted human epidermis (RhE) based assays, which were adapted from validated methods used for industrial chemicals, produced results essentially equivalent to those obtained with in vivo tests. This led to the publication of the ISO 10993-23:2021 standard on irritation testing, which states that RhE-based assays are now the preferred method. The 2018 validation study evaluated strong irritants, so we tested nine mild irritants (GHS Category 3), neat and spiked at different concentrations into medical device extracts, per ISO 10993-23:2021. The results substantiated the applicability of RhE-based assays for evaluating mild irritants in medical device extracts. Moreover, the 2018 validation study tested solid extractable medical device materials but did not consider non-extractable medical device materials (e.g., creams, gels, or sprays). By testing nine marketed non-extractable materials, either neat or spiked with irritants, we also confirmed that RhE-based assays are readily applicable to such medical device materials.

The Ex Vivo Skin Model as an Alternative Tool for the Efficacy and Safety Evaluation of Topical Products

The development of alternative approaches for safety and efficacy testing that avoid the use of animals is a worldwide trend, which relies on the improvement of current models and tools so that they better reproduce human biology. Human skin from elective plastic surgery is a promising experimental model to test the effects of topically applied products. As the structure of native skin is maintained, including cell population (keratinocytes, melanocytes, Langerhans cells and fibroblasts) and dermal matrix (containing collagen, elastin, glycosaminoglycans, etc.), it most closely matches the effects of substances on in vivo human skin. In this review, we present a collection of results that our group has generated over the last years, involving the use of human skin and scalp explants, demonstrating the feasibility of this model. The development of a test system with ex vivo skin explants, of standard size and thickness, and cultured at the air–liquid interface, can provide an important tool for understanding the mechanisms involved in several cutaneous disorders.

Skin Toxicity Assessment of Silver Nanoparticles in a 3D Epidermal Model Compared to 2D Keratinocytes

Introduction

Increased use of silver nanoparticles (AgNPs) has raised concerns that AgNPs may induce toxic effects. In vitro studies of cell monolayers and in vivo studies have produced conflicting results. The inconsistency of these results has been mainly due to limitations of two-dimensional (2D) monolayer cell systems.

Methods

A three-dimensional (3D) epidermal model called EpiKutis^®, which exhibits good tissue viability and barrier function was developed. The cytotoxicity of AgNPs against EpiKutis was compared to that against 2D keratinocytes at equivalent AgNPs doses (0.035, 0.07, 0.14, 0.28, and 0.56 ng per cell). The amount and distribution of AgNPs in the 3D EpiKutis and 2D keratinocytes after exposure were determined. The toxic mechanisms of AgNPs, such as oxidative stress and production of pro-inflammatory cytokines, were investigated.

Results

The results demonstrated that cell viability was greater than 80% and lactate dehydrogenase (LDH) release did not increase even at the highest dose of AgNPs in EpiKutis. In contrast, treatment of 2D keratinocytes with AgNPs resulted in dose-dependent decrease in cell viability from 63% to 11%, and a dose-dependent increase in LDH release from 8% to 16%. Cytotoxicity of AgNPs in 2D keratinocytes was related to oxidative damage and inflammation, as evidenced by increased levels of reactive oxygen species (ROS), malondialdehyde (MDA), IL-1α, IL-6, and IL-8. In addition, levels of superoxide dismutase (SOD) were decreased. EpiKutis treated with AgNPs did not exhibit increased oxidative damage or inflammation, which may have been due to the barrier properties of the 3D structure, resulting in reduced penetration of AgNPs. At equivalent per cell doses, total silver penetration into EpiKutis was 0.9 ± 0.1%, and total silver penetration into 2D keratinocytes was 8.8 ± 0.6% detected by ICP-MS. The penetration and distribution of AgNPs in 2D keratinocytes were confirmed by the TEM-EDS analysis, which was not found in the 3D EpiKutis. These results showed that AgNPs penetrated EpiKutis to a lesser degree than they penetrated 2D keratinocytes, which suggested that EpiKutis exhibited significant barrier function.

Discussion

The results of this study showed that AgNP toxicity should be evaluated using 3D epidermal models, which may provide better estimates of in vivo conditions than 2D models. The EpiKutis model may be an ideal model for assessment of nanotoxicity.

Designing stem cell niches for differentiation and self-renewal

Mesenchymal stem cells, characterized by their ability to differentiate into skeletal tissues and self-renew, hold great promise for both regenerative medicine and novel therapeutic discovery. However, their regenerative capacity is retained only when in contact with their specialized microenvironment, termed the stem cell niche Niches provide structural and functional cues that are both biochemical and biophysical, stem cells integrate this complex array of signals with intrinsic regulatory networks to meet physiological demands. Although, some of these regulatory mechanisms remain poorly understood or difficult to harness with traditional culture systems. Biomaterial strategies are being developed that aim to recapitulate stem cell niches, by engineering microenvironments with physiological-like niche properties that aim to elucidate stem cell-regulatory mechanisms, and to harness their regenerative capacity in vitro In the future, engineered niches will prove important tools for both regenerative medicine and therapeutic discoveries.

Protective barrier properties of Rhinosectan® spray (containing xyloglucan) on an organotypic 3D airway tissue model (MucilAir): results of an in vitro study

BACKGROUND

To evaluate barrier protective properties of Rhinosectan^® spray, a medical device containing xyloglucan, on nasal epithelial cells (MucilAir).

METHODS

MucilAir-Nasal, a three-dimensional organotypic (with different cell types) airway tissue model, was treated with the medical device Rhinosectan^® (30 µL) or with controls (Rhinocort-budesonide-or saline solution). The protective barrier effects of Rhinosectan^® were evaluated by: TEER (trans-epithelial electrical resistance) (preservation of tight junctions), Lucifer Yellow assay (preservation of paracellular flux) and confocal immunofluorescence microscopy (localization of tight junction proteins).

RESULTS

Exposure of MucilAir with Rhinosectan^® protected cell tight junctions (increases in TEER of 13.1% vs -6.3% with saline solution after 1 h of exposure), and preserved the paracellular flux, even after exposure with pro-inflammatory compounds (TNF-α and LPS from Pseudomonas aeruginosa 10). Results of confocal immunofluorescence microscopy demonstrated that, after treatment with the pro-inflammatory mixture, Rhinosectan^® produced a slight relocation of zona occludens-1 in the cytosol compartment (while Rhinocort induced expression of zona-occludens-1), maintaining the localization of occludin (similarly to negative control).

CONCLUSIONS

Results of our study indicates that Rhinosectan^® creates a protective physical barrier on nasal epithelial cells in vitro, allowing the avoidance of allergens and triggering factors, thus confirming the utility of this medical device in the management of nasal respiratory diseases, as rhinitis or rhinosinusitis.

Catch-up validation study of an in vitro skin irritation test method based on an open source reconstructed epidermis (phase II)

To replace the Draize skin irritation assay (OECD guideline 404) several test methods based on reconstructed human epidermis (RHE) have been developed and were adopted in the OECD test guideline 439. However, all validated test methods in the guideline are linked to RHE provided by only three companies. Thus, the availability of these test models is dependent on the commercial interest of the producer. To overcome this limitation and thus to increase the accessibility of in vitro skin irritation testing, an open source reconstructed epidermis (OS-REp) was introduced. To demonstrate the capacity of the OS-REp in regulatory risk assessment, a catch-up validation study was performed. The participating laboratories used in-house generated OS-REp to assess the set of 20 reference substances according to the performance standards amending the OECD test guideline 439. Testing was performed under blinded conditions. The within-laboratory reproducibility of 87% and the inter-laboratory reproducibility of 85% prove a high reliability of irritancy testing using the OS-REp protocol. In addition, the prediction capacity was with an accuracy of 80% comparable to previous published RHE based test protocols. Taken together the results indicate that the OS-REp test method can be used as a standalone alternative skin irritation test replacing the OECD test guideline 404.

Genes specifically modulated in sensitized skins allow the detection of sensitizers in a reconstructed human skin model. Development of the SENS-IS assay

Analysis of genes modulated during the sensitization process either on mice (LLNA) or human (blisters) combined with data mining has allowed the definition of a comprehensive panel of sensitization biomarkers. This set of genes includes already identified markers such as the ARE family and others not yet associated with the sensitization process (the so-called SENS-IS gene subset). The expression of this set of genes has been measured on reconstituted human epidermis models (Episkin) exposed to various sensitizers and non-sensitizers. Fine analysis of their expression pattern indicates that it is the number of modulated genes rather than the intensity of up-regulation that correlates best with the sensitization potential of a chemical. Moreover, sensitizers that are weak inductors of ARE genes tend to be relevant modulators of the SENS-IS subset. By combining the expression data obtained with both gene subsets, it is now possible to identify a wide variety of sensitizers on a test system (in vitro reconstructed human epidermis) that is very similar to the in vivo situation and compatible with a large variety of test substance characteristics.

Impedance spectroscopy for the non-destructive evaluation of in vitro epidermal models

Purpose

Reconstructed human epidermis (RHE) is standardly used for the risk assessment of chemical compounds. However, analysis is dependent on invasive methods such as histological processing or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) staining.

Methods

As an alternative, we have developed a non-destructive technology to analyze the integrity of epidermal equivalents based on impedance spectroscopy. RHEs were generated and impedance spectra were recorded. from these spectra, we extrapolated electrical characteristics such as the capacitance and the ohmic resistance. Furthermore, the measurable electrical parameters were used to quantify the effects of mechanical and chemical disruption of the epidermal integrity.

Results

A fully matured RHE exhibits typical impedance spectra in a frequency ranging between 1 Hz and 100 kHz, which is comparable to the spectra of freshly isolated human epidermal biopsies. We could show that, during RHE maturation, these characteristics change significantly. Thus, capacitance and ohmic resistance can be employed as a criterion for the quality control of skin equivalents. Additionally, our application of impedance spectroscopy reveals sufficient sensitivity to detect a transient decreased ohmic resistance caused by 2-propanol, which is classified as a non-irritant by MTT assays.

Conclusion

These results indicate that impedance spectroscopy can be employed as a non-destructive complementary method to assess mild irritative effects, which is currently not possible.

Biomimetic urothelial tissue models for the in vitro evaluation of barrier physiology and bladder drug efficacy

The bladder is an important tissue in which to evaluate xenobiotic drug interactions and toxicities due to the concentration of parent drug and hepatic/enteric-derived metabolites in the urine as a result of renal excretion. Breaching of the barrier provided by the bladder epithelial lining (the urothelium) can expose the underlying tissues to urine and cause harmful effects (e.g., cystitis or cancer). Human urothelium is most commonly represented in vitro as immortalized or established cancer-derived cell lines, but the compromised ability of such cells to undergo differentiation and barrier formation means that nonimmortalized, normal human urothelial (NHU) cells provide a more relevant cell culture system. The impressive capacity for urothelial self-renewal in vivo can be harnessed in vitro to generate experimentally-useful quantities of NHU cells, which can subsequently be differentiated to form a functional or "biomimetic" urothelium. When seeded onto permeable membranes, these barrier-forming human urothelial tissue models enable the modeling of serum and luminal (intravesical) exposure to drugs and metabolites, thus supporting efficacy/toxicity assessments. Biomimetic human urothelial constructs provide a potential step along the preclinical trail and may support the extrapolation from rodent in vivo data to determine human relevance. Early evidence is beginning to demonstrate that human urothelium in vitro can provide information that supersedes conventional rodent studies, but further validation is needed to support widespread adoption.

1,4-dihydroxy-2-naphthoic Acid Induces Apoptosis in Human Keratinocyte: Potential Application for Psoriasis Treatment

Psoriasis, which affects approximately 1–3% of the population worldwide, is a chronic inflammatory skin disorder characterized by epidermal keratinocytes hyperproliferation, abnormal differentiation, and inflammatory infiltration. Decrease in keratinocyte apoptosis is a specific pathogenic phenomenon in psoriasis. Chinese herbs have been used for the treatment of psoriasis in China showing promising effect in clinical trials. A traditional Chinese medicine has relatively fewer side effects with longer remission time and lower recurrence rate. The extract of Rubia cordifolia L. (EA) was previously found by us to induce HaCaT keratinocytes apoptosis. In this study we identified one of the components in Rubia cordifolia L., the anthraquinone precursor 1,4-dihydroxy-2-naphthoic acid (DHNA), induces HaCaT keratinocytes apoptosis through G0/G1 cell cycle arrest. We have also demonstrated that DHNA acts through both caspase-dependent and caspase-independent pathways. Besides, cytotoxicity and IL-1α release assays indicate that DHNA causes less irritation problems than dithranol, which is commonly employed to treat psoriasis in many countries. Since DHNA possesses similar apoptotic effects on keratinocytes as dithranol but causes less irritation, DHNA therefore constitutes a promising alternative agent for treating psoriasis. Our studies also provide an insight on the potential of using EA and DHNA, alternatively, as a safe and effective treatment modality for psoriasis.

Assuring consumer safety without animals: Applications for tissue engineering

Humans are exposed to a variety of chemicals in their everyday lives through interactions with the environment and through the use of consumer products. It is a basic requirement that these products are tested to assure they are safe under normal and reasonably foreseeable conditions of use. Within the European Union, the majority of tests used for generating toxicological data rely on animals. However recent changes in legislation (e.g., 7(th) amendment of the Cosmetics Directive and REACH) are driving researchers to develop and adopt non-animal alternative methods with which to assure human safety. Great strides have been made to this effect, but what other opportunities/technologies exist that could expedite this? Tissue engineering has increasing scope to contribute to replacing animals with scientifically robust alternatives in basic research and safety testing, but is this application of the technology being fully exploited? This review highlights how the consumer products industry is applying tissue engineering to ensure chemicals are safe for human use without using animals, and identifies areas for future development and application of the technology.

Perspectives on Non-Animal Alternatives for Assessing Sensitization Potential in Allergic Contact Dermatitis

Skin sensitization remains a major environmental and occupational health hazard. Animal models have been used as the gold standard method of choice for estimating chemical sensitization potential. However, a growing international drive and consensus for minimizing animal usage have prompted the development of in vitro methods to assess chemical sensitivity. In this paper, we examine existing approaches including in silico models, cell and tissue based assays for distinguishing between sensitizers and irritants. The in silico approaches that have been discussed include Quantitative Structure Activity Relationships (QSAR) and QSAR based expert models that correlate chemical molecular structure with biological activity and mechanism based read-across models that incorporate compound electrophilicity. The cell and tissue based assays rely on an assortment of mono and co-culture cell systems in conjunction with 3D skin models. Given the complexity of allergen induced immune responses, and the limited ability of existing systems to capture the entire gamut of cellular and molecular events associated with these responses, we also introduce a microfabricated platform that can capture all the key steps involved in allergic contact sensitivity. Finally, we describe the development of an integrated testing strategy comprised of two or three tier systems for evaluating sensitization potential of chemicals.

Decontamination of tetramethylammonium hydroxide (TMAH) splashes: promising results with Diphoterine in vitro

Tetramethylammonium hydroxide (TMAH), used in microelectronic industries and research and development, has both corrosive properties and systemic toxicity. Two fatal TMAH occupational exposure cases have been published. Studies comparing initial TMAH decontamination with Diphoterine versus tap water were performed: an in vitro pH titration study and an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) in vitro cytotoxicity cell viability assay. For pH normalization, 17 times more tap water than Diphoterine was required. In the cytotoxicity test, two-thirds of the cells remained viable after Diphoterine washing, compared with only one-third after tap water washing (p < .001). Diphoterine washing is a promising TMAH decontamination method.

In vitro tools for photobiological testing: molecular responses to simulated solar UV of keratinocytes growing as monolayers or as part of reconstructed skin

Epidermal keratinocytes are critical targets for UV-induced genotoxicity as their transformation by sunlight overexposure can lead to skin cancer such as basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Therefore, assessment of photoprotection should involve early markers associated with DNA photodamage. Here, the same normal human keratinocytes either in monoculture (KC) or in full thickness reconstructed skin (RS) were compared with respect to their response to simulated solar UV (SSUV) exposure. Irradiation conditions (spectral power distribution and doses) were designed to mimic environmental zenithal UV from sunlight. At doses where survival was higher than 80%, comet assay showed more single strand breaks (SSB) and cyclobutane pyrimidine dimers (CPD) in keratinocytes in RS than in KC one hour post-exposure. The transcription factor p53 was activated in both models. While in KC p53 accumulation displayed a linear dose-dependency up to 24 h post-exposure, in RS it followed a bell-shaped profile and reverted to its basal rate. QRT-PCR demonstrated that among genes controlled by p53, P21 and MDM2 were clearly induced by SSUV in KC, whereas GADD45 expression was strongly and almost exclusively up-regulated in RS. Nrf2-dependent antioxidant genes (Ferritin light chain, NQO1) were only induced in RS, yet at low doses for NQO1. In vitro models such as KC or RS allowing the development of quantitative methodologies should be used as surrogates for in vivo tests assessing photogenotoxicity.

A comparative study of leukaemia inhibitory factor and interleukin-1alpha intracellular content in a human keratinocyte cell line after exposure to cosmetic fragrances and sodium dodecyl sulphate

According to European laws animal testing in cosmetic industry will be prohibited in a few years and it will be replaced by alternative methods based on cell and tissue culture. Many ingredients of cosmetic formulations are potentially causes of skin inflammation and sensibilization. Since cytotoxicity is known, among other factors, to trigger irritation, in an alternative model for evaluation of skin irritation, it can be considered also the precocious release of inflammatory mediators, i.e. cytokines, originating mainly from keratinocytes. In this in vitro study we have analysed some parameters directly or indirectly related to irritation/inflammation, in NCTC 2544 human keratinocytes during short-time exposure to some potential irritants cosmetic fragrances, included in the European Laws 2003/15/EEC. IIC50 was extrapolated by MTT and NRU viability indexes after exposure of cell ultures to Geraniol Limonene and Benzylic Alcohol for 1, 3 and 6h. NCTC cells were then exposed to sub-toxic doses of selected compounds and interleukin-1alpha (IL-1alpha) and leukaemia inhibitory factor (LIF) expressions were analysed as early proinflammatory cytokines. To our knowledge our findings demonstrated for the first time that NCTC cells synthesize and modulate LIF after exposure to selected irritating stimuli. Moreover, our results give evidence on LIF role as in vitro precocious endpoint for the assessment of the risk in cosmetic field, because its response under irritation stimuli is very quick and comparable to IL-1alpha.

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.

Leiden reconstructed human epidermal model as a tool for the evaluation of the skin corrosion and irritation potential according to the ECVAM guidelines

In the ECVAM validation studies two common skin protocols have been developed, the skin corrosion and skin irritation protocol. Both protocols include next to general and functional conditions that the skin model must meet, also the correct prediction of the activity of certain reference chemicals. For the skin corrosion protocol, the OECD TG 431 defined 12 reference chemicals that should be correctly predicted by the epidermal skin model. For skin irritation 20 test substances should meet the defined criteria. In this study we aimed to subject our Leiden human epidermal (LHE) model to both common protocols according to the ECVAM guidelines. The LHE model generated in this study has been fully characterized and shows very high similarities with the native skin. After minor technical changes in both protocols, corrosion classifications were obtained in concordance with those reported for the validated human skin models EpiSkin and EpiDerm. The results obtained with the common skin irritation protocol were very similar to that of earlier studies with the SkinEthic, EpiSkin and EpiDerm models. This means that the protocols and prediction models developed during the validation studies with a specific skin model can be used with other similar skin models. This study demonstrates that reconstructed human skin equivalents have been proven to be efficient and reliable alternatives to animal testing.

In vitro skin absorption and drug release – A comparison of six commercial prednicarbate preparations for topical use

Reconstructed human epidermis is a useful tool for in vitro skin absorption studies of chemical compounds. If this may hold true also for topical dermatics, we investigated the glucocorticoid prednicarbate applied by two sets (innovator and generic) of cream, ointment and fatty ointment using the commercially available EpiDerm model. Moreover, stability and local tolerability of the preparations as well as drug release were studied, to estimate an influence on prednicarbate absorption and metabolism. While release ranked in the order cream<fatty ointment<ointment for both sets of preparations, prednicarbate penetration and permeation of the EpiDerm model did not. Less PC uptake observed with the generic ointment and fatty ointment appeared to be linked to impaired enzymatic ester cleavage within the tissue. Thus with drugs subject to skin metabolism, cutaneous uptake is not to be derived from drug release studies, yet has to be studied experimentally with viable skin or reconstructed human epidermis.

Alternative Methods for Eye and Skin Irritation Tests: An Overview

The evaluation of eye and skin irritation potential is essential to ensuring the safety of individuals in contact with a wide variety of substances designed for industrial, pharmaceutical or cosmetic use. The Draize rabbit eye and skin irritancy tests have been used for 60 years to attempt to predict the human ocular and dermal irritation of such products. The Draize test has been the standard for ocular and dermal safety assessments for decades. However, several aspects of the test have been criticised. These include: the subjectivity of the method; the overestimation of human responses; and the method's cruelty. The inadequacies of the Draize test have led to several laboratories over the last 20 years making efforts to develop in vitro assays to replace it. Protocols that use different types of cell cultures and other methods have been devised to study eye and skin irritation. Different commercial kits have also been developed to study eye and skin irritation, based on the action of chemicals on these tissues. This article presents a review of the main alternatives developed to replace the use of animals in the study of chemical irritation. Particular attention is paid to the reproducibility of each method.

Publicly-accessible QSAR software tools developed by the Joint Research Centre

To promote the availability of reliable computer-based estimation methods for use in the regulatory assessment of chemicals, the European Chemicals Bureau (ECB) within the European Commission's Joint Research Centre (JRC) has developed a range of user-friendly and freely available software tools. The article gives an overview of four of these tools, explaining their main functionalities and applicability: Toxtree, Toxmatch, DART and the JRC QSAR Model Database. Toxtree predicts different types of toxicological hazard and modes of action by applying decision tree approaches; it can be used for initial hazard assessments. Toxmatch is a tool for chemical similarity assessment; it can be used to compare model training and test sets, to facilitate the formation of chemical categories and to support the application of read-across between analogues. DART (Decision Analysis by Ranking Techniques) provides a variety of Multi-criteria Decision Making (ranking) methods, and can be used to support the ranking of chemicals according to their environmental and toxicological concern. Finally, the JRC QSAR Model Database is a web-based inventory of (Q)SAR models to help industry and government authorities to identify suitable (Q)SARs for chemicals undergoing regulatory review.

Real-time detection of stress in 3D tissue-engineered constructs using NF-kappaB activation in transiently transfected human dermal fibroblast cells

The main objective of this study was to develop a nondestructive reporter system for assessing the response of human cells contained within a three-dimensional (3D) tissue-engineered construct to exogenous stress. Dermal fibroblasts were transiently transfected with a reporter construct linked to nuclear factor kappaB (NF-kappaB) activation which led to expression of a nonstable form of enhanced green fluorescent protein (d2EGFP) after stimulation. This led to a temporary production of fluorescence, which could be readily detected but was not intrinsically toxic, as cells were able to metabolize the initial cycle of d2EGFP produced. This permitted the model to be used for restimulation post recovery. To investigate the performance and predictive ability of this method for assessing cellular response to stress in 3D, we used a range of compounds known to have pro-inflammatory or oxidative properties. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1-beta (IL-1beta) were selected for having a direct cytokine action; lipopolysaccharide (LPS) was selected for modeling bacterial-mediated inflammation; and hydrogen peroxide was selected as a crude method for delivering an oxidative stress. Transfected cells were stimulated with the above compounds in 3D and the synthesis of d2EGFP was detected as a measure of NF-kappaB activation. The resultant fluorescence was scored using a series of photomicrographs taken by epifluorescence microscopy. All agents activated NF-kappaB when cells were grown in 3D scaffolds but did not cause any significant reduction in cell viability as measured by a standard MTT-ESTA viability test. Parallel NF-kappaB activation and MTT measurements was also conducted in two-dimension (2D) and confirmed findings in 3D. The 3D model described using a fluorescent reporter gene is a highly sensitive and reliable method for detecting cellular stress and represents a key step in developing tissue engineering models with the potential for screening pharmaceutical and cosmetic compounds, as an alternative to existing in vitro and in vivo methods.

In vitro phototoxicity test using artificial skin with melanocytes

BACKGROUND

Exposure to ultraviolet radiation (UVR) has been shown to induce cutaneous biological changes and phototoxic reactions.

OBJECTIVE

This study was designed to evaluate the usefulness of artificial skin (AS) composed of keratinocytes and melanocytes as an in vitro phototoxicity model for topical agents.

MATERIALS AND METHODS

AS was manufactured with three-dimensionally cultured keratinocytes and melanocytes on a de-epidermized dermis (DED). The photobiological responses in AS with and without melanocytes were comparatively examined after ultraviolet A (UVA) exposure. Three test chemicals (8-methoxypsoralen, 6-methylcoumarin and tetracycline) were topically applied onto the AS with melanocytes and after UVA irradiation, the released inflammatory cytokines (IL-1alpha, IL-beta and IL-6) were analyzed.

RESULTS

AS with melanocytes showed better epidermal structures, stronger resistance to UVA exposure and photobiological responses closer to in vivo human skin. Releases of inflammatory cytokines were well correlated with the increased phototoxicities of test chemicals. Among the measured cytokines, IL-6 could be the most reliable in vitro marker indicative of phototoxic potential, because it showed statistically significant increase only in case of concurrent exposure to chemicals and UVA.

CONCLUSION

The AS with melanocytes may be a useful tool especially for examining UV-induced cutaneous changes and a promising in vitro phototoxicity test model for topical agents.

The EpiSkin phototoxicity assay (EPA): development of an in vitro tiered strategy using 17 reference chemicals to predict phototoxic potency

The aim of the study was to investigate the ability of human reconstructed epidermis EpiSkin(LM) to identify the phototoxic potency of topically or systemically applied chemicals (EPA: EpiSkin phototoxicity assay). Three classes, according to their available human phototoxic potential, were evaluated: systemic phototoxic compounds, topical phototoxic chemicals and non-phototoxic compounds. Non-cytotoxic concentrations of chemicals were applied topically or directly added to the underlying culture medium in order to mimic a systemic-like administration. Following treatment, tissues were exposed to non-cytotoxic dose of UVA (50 J cm(-2)). Cell viability and pro-inflammatory mediators (IL-1alpha) were investigated 22 h after UVA exposure. Our results show that the phototoxic potential of chemicals can be determined using cell viability combined with inflammatory mediator measurements (cytokine IL-1alpha) in a 3-D epidermis model. Moreover, the EPA was able to discriminate efficiently between phototoxic and non-phototoxic products. Furthermore, the EPA is sensitive to the administration route in the prediction of the phototoxic potency of the tested chemical. Differences observed between the two routes of administration (topical or systemic-like) may be linked in part to chemicals bioavailability which depends on specific penetration potential, epidermis barrier function and also on keratinocytes absorption/metabolization processes. Results were very promising and showed a very good sensitivity (92.3%) and an excellent specificity (100%) with an overall accuracy of 94.1%. The performances of the EPA showed that the EpiSkin(LM) model is an interesting tool able to integrate decision-making processes to address the question of phototoxicity linked to the application site.

Proteomic analysis of the response of EpiDermTM cultures to sodium lauryl sulphate

The analysis of EpiDerm cultures treated with the known skin irritant sodium lauryl sulphate (SLS) was performed using 2D-gel electrophoresis in order to understand the mechanism of action and thereby identify novel markers of skin irritation. A range of both broad and narrow pH gradient first-dimension gels were run (pH 4-7, 6-11, 4-5, 5-6 and 6-9) consistently followed by 12% SDS-PAGE in the second-dimension. Following treatment of EpiDerm with SLS, 67 proteins of interest were identified, of which 8 were selected as interesting: calmodulin-like skin protein, involucrin, epithelial cell marker protein, HS1, peroxiredoxin 1, serine protease inhibitor, KIAA0117 and ribosomal protein L17. Involucrin was confirmed as being up-regulated by both ELISA and Western blotting. The use of proteomics has identified a number of proteins which could be used as general markers for skin irritation and which may in particular be of value for the development of in vitro predictive models.

Assessment of the human epidermis model SkinEthic RHE for in vitro skin corrosion testing of chemicals according to new OECD TG 431

Based on two successfully completed ECVAM validation studies for in vitro skin corrosion testing of chemicals, the National Co-ordinators of OECD Test Guideline Programme endorsed in 2002 two new test guidelines: TG 430 'Transcutaneous Electrical Resistance assay' and TG 431 'Human Skin Model Test'. To allow all suitable in vitro human reconstructed (dermal or epidermal) models to be used for skin corrosion testing, the OECD TG 431 defines general and functional conditions that the model must meet before it will be routinely used for skin corrosion testing. In addition, the guideline requires correct prediction of 12 reference chemicals and assessment of intra- and inter-laboratory variability. To show that the OECD TG 431 concept works, in 2003 ZEBET tested several chemicals from the ECVAM validation trials on the SkinEthic reconstituted human epidermal (RHE) model. Based on knowledge that reconstructed human skin models perform similarly in toxicological studies, it was decided to adopt the validated EpiDerm skin corrosion test protocol and prediction model to the SkinEthic model. After minor technical changes, classifications were obtained in concordance with those reported for the validated human skin models EPISKIN and EpiDerm. To allow adequate determination of inter-laboratory reproducibility, a blind trial was conducted in three laboratories -- ZEBET (D), Safepharm (UK) and BASF (D), in which the 12 endorsed reference chemicals were tested. Results obtained with the SkinEthic epidermal model were reproducible, both within and between laboratories, and over time. Concordance between the in vitro predictions of skin corrosivity potential obtained with the SkinEthic model and the predictions obtained with the accepted tests of OECD TG 430 and TG 431 was very good. The new test was able to distinguish between corrosive and non-corrosive reference chemicals with an accuracy of 93%.