Use of human skin cell cultures for the estimation of potential skin irritants

Interleukin-1α and Interleukin-8 Release by Human Keratinocyte Cell Culture Treated with Surfactants

The effects of four cosmetic surfactants on interleukin (IL)-1α and IL-8 release from human keratinocytes were studied to investigate the feasibility of using these effects for the prediction of the irritation potential of chemicals. After exposure of cells to surfactants, the amounts of IL-1α and IL-8 released into culture medium were measured by ELISA. Cytotoxicity was evaluated by using the neutral red uptake (NRU) cytotoxicity assay. Cytokine release was increased 7–15 times by sodium lauryl sulphate (SLS), laurtrimonium chloride, cocamidopropyl betaine (CPB) and Oleth-5 at cytotoxic concentrations. IL-8 release was increased 3–4 times by SLS, CPB and Oleth-5 at subcytotoxic concentrations. After exposure to SLS, IL-1α was released within 1 hour, suggesting that IL-1α release is associated with membrane damage, whereas IL-8 release continued for 24 hours, suggesting that IL-8 was produced within the cells. Cytotoxicity tests and IL-8 release assays were also performed on seven other surfactants. The results show that moderate irritants CPB and PEG-4 dioleate, which have weak cytotoxic effects, significantly increased IL-8 release from human keratinocytes. It is suggested that measurement of IL-8 release is useful for predicting the irritation potential of chemicals which cannot be detected by using the NRU cytotoxicity assay.

Diabetic and sympathetic influences on the water permeability barrier function of human skin as measured using transepidermal water loss: A case-control study

The presence of long-standing hyperglycemic conditions has been suggested to lead to many skin problems associated with an impaired skin barrier function. However, the relationship between impaired skin barrier status and altered peripheral nervous system function has not yet been determined. The purpose of this study was to investigate the water evaporation rate as a measure of the permeability barrier function of diabetic skin and its relationship to diabetic sensorimotor polyneuropathy (DSPN) and peripheral autonomic neuropathy (PAN) using well-controlled confounding variables.This case-control study included 42 participants with chronic diabetes and 43 matched healthy controls. The diabetic group underwent a nerve conduction study and sympathetic skin response (SSR) test to confirm the presence of DSPN and PAN, respectively. Different skin regions were analyzed using the noninvasive Tewameter instrument (Courage + Khazaka Electronic GmbH, Cologne, Germany). The impacts of PAN, DSPN, age, and diabetes duration on the values of transepidermal water loss (TEWL) were each analyzed and compared between the groups.Regardless of the presence of DSPN or PAN, the TEWL values as measured on the distal extremities were significantly lower in the diabetic group than in the control group. In the diabetic group, participants with abnormal SSR test results showed decreased TEWL values in the finger, sole, and first toe, as compared with participants with normal SSR test results. In the control group, age showed a negative correlation with the TEWL values with respect to some measured regions. However, in the diabetic group, there was no significant correlation between either patient age or diabetes duration and TEWL values.The presence of a long-term hyperglycemic state can reduce the permeability barrier function of the skin, a phenomenon that might be related to the presence of an impaired peripheral sympathetic nervous system, rather than peripheral sensorimotor denervation.

Alternatives to In Vivo Draize Rabbit Eye and Skin Irritation Tests with a Focus on 3D Reconstructed Human Cornea-Like Epithelium and Epidermis Models

Human eyes and skin are frequently exposed to chemicals accidentally or on purpose due to their external location. Therefore, chemicals are required to undergo the evaluation of the ocular and dermal irritancy for their safe handling and use before release into the market. Draize rabbit eye and skin irritation test developed in 1944, has been a gold standard test which was enlisted as OECD TG 404 and OECD TG 405 but it has been criticized with respect to animal welfare due to invasive and cruel procedure. To replace it, diverse alternatives have been developed: (i) For Draize eye irritation test, organotypic assay, in vitro cytotoxicity-based method, in chemico tests, in silico prediction model, and 3D reconstructed human cornea-like epithelium (RhCE); (ii) For Draize skin irritation test, in vitro cytotoxicity-based cell model, and 3D reconstructed human epidermis models (RhE). Of these, RhCE and RhE models are getting spotlight as a promising alternative with a wide applicability domain covering cosmetics and personal care products. In this review, we overviewed the current alternatives to Draize test with a focus on 3D human epithelium models to provide an insight into advancing and widening their utility.

Human keratinocyte cultures in an in vitro approach for the assessment of surfactant-induced irritation

A specific, mechanistic, in vitro approach for the assessment of human skin irritation potential is outlined for the evaluation of surfactants and the results compared with in vivo human patch test data. The level of free available surfactant monomer and the solubilization of the corn protein zein in vitro were confirmed to be related to surfactant in vivo human skin irritation potential. In vitro cytotoxicity to monolayer keratinocyte cultures could not discriminate between the moderate human skin irritant sodium dodecyl sulfate (SDS) and the mild irritants cocamidopropylbetaine (CA) and Polysorbate 20 (P20). An in vitro stratified differentiated human epidermal equivalent (HEE) exhibited reduced cytotoxicity to the test chemicals, compared with monolayer culture responses, and was able to discriminate between the toxic potential of SDS and CA. Stimulation of interleukin-1alpha release from the A431 human keratinocyte cell line reflected in vivo erythema scores more closely than cytotoxic potential, and coincided with nitric oxide production by macrophages upon exposure to A431-conditioned medium. Combination of these mechanistic assays has allowed a profile of likely in vivo human responses to be approximated. Additional knowledge of skin penetrability and rate of recovery from toxic damage would affirm these predictions.

Cytotoxicity testing of beta-lactam antibiotics, non-steroidal anti-inflammatory drugs and sulfonamides in primary human keratinocyte cultures

We have studied the cytotoxity to human keratinocytes of three main classes of drugs known to induce cutaneous adverse reactions, namely beta-lactam antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs) and sulfonamides, using the neutral red uptake as an endpoint. IC(50) values were determined for 21 drugs, after 20 hr of exposure and compared with those obtained with rat hepatocytes. NSAIDs were found to be more cytotoxic than beta-lactum antibiotics to human keratinocytes. Large variations in IC(50) values were obtained between molecules of a same class, as well as between keratinocyte cultures from different donors, especially for beta-lactum antibiotics. All NSAIDs and beta-lactam antibiotics tested were more cytotoxic to rat hepatocytes (1.6- to 27-fold). Both cell types were only slightly sensitive to sulfonamides, if at all.

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.

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

In view of the increasing need to identify non-animal tests able to predict acute skin irritation of chemicals, the European Centre for the Validation of Alternative Methods (ECVAM) focused on the evaluation of appropriate in vitro models. In vitro tests should be capable of discriminating between irritant (I) chemicals (EU risk: R38) and non-irritant (NI) chemicals (EU risk: "no classification"). Since major in vivo skin irritation assays rely on visual scoring, it is still a challenge to correlate in vivo clinical signs with in vitro biochemical measurements. Being particularly suited to test raw materials or chemicals with a wide variety of physical properties, in vitro skin models resembling in vivo human skin were involved in prevalidation processes. Among many other factors, cytotoxicity is known to trigger irritation processes, and can therefore be a first common event for irritants. A refined protocol (protocol 15min-18hours) for the EPISKIN model had been proposed for inclusion in the ECVAM formal validation study. A further improvement on this protocol, mainly based on a post-treatment incubation period of 42 hours (protocol 15min-42hours), the optimised protocol, was applied to a set of 48 chemicals. The sensitivity, specificity and accuracy with the MTT assay-based prediction model (PM) were 85%, 78.6% and 81.3% respectively, with a low rate of false negatives (12%). The improved performance of this optimised protocol was confirmed by a higher robustness (homogeneity of individual responses) and a better discrimination between the I and NI classes. To improve the MTT viability-based PM, the release of a membrane damage marker, adenylate kinase (AK), and of cytokines IL-1alpha and IL-8 were also investigated. Combining these endpoints, a simple two-tiered strategy (TTS) was developed, with the MTT assay as the first, sort-out, stage. This resulted in a clear increase in sensitivity to 95%, and a fall in the false-positive rate (to 4.3%), thus demonstrating its usefulness as a "decision-making" tool. The optimised protocol proved, both by its higher performances and by its robustness, to be a good candidate for the validation process, as well as a potential alternative method for assessing acute skin irritation.

The use of standardized human skin models for cutaneous pharmacotoxicology studies

Reconstructed skin and epidermis models are finding increasingly numerous applications in cosmetology and dermatology. In particular, they are currently employed to assess the tolerability and efficacy of raw materials and formulations, in conditions approaching those of normal use. Importantly, the use of such models greatly reduces the need for animal testing. Various models of reconstructed skin and epidermis have been developed [1-4] and some are now produced industrially [5-8]. They are used for the prediction of cutaneous irritancy and, to a lesser extent, percutaneous absorption and cutaneous metabolism. However, before being officially recognized as valid alternative methods and entering routine use, standard protocols must be developed to assess their reproducibility and performance as compared with in situ human studies.

Co-occurring words and retrieval efficiency: finding information about alternatives to animal testing in relation to skin irritation testing

Words appearing in abstracts of scientific articles are often useful as search terms, particularly those words and word patterns that are unique to the relevant field of endeavour. In view of the heightened interest in obtaining information about alternatives to animal testing, efforts directed toward enhancing retrieval of pertinent references from the biomedical literature are warranted. Words and phrases, and word-phrase co-occurrences describing methods of experimentation in abstracts about alternatives to skin-irritation testing in animals, were evaluated with regard to retrieval efficiency in the National Library of Medicine database, Toxline(. Precision of retrieval was defined as the number of pertinent references found in the total number of citations retrieved. Retrieval precision values ranged from 0.25% to 100%.

Gene expression analysis of EpiDerm following exposure to SLS using cDNA microarrays

There is a need to investigate the mechanistic basis of the human skin irritation response if relevant in vitro test systems for the predictive identification of skin irritation hazards are to be developed. Recent progress in genomics technologies mean that tools for the identification and investigation of important biochemical events in the processes of skin irritation are now available. The aim of this work was to identify genes (for further mechanistic investigation) which may be regulated in response to skin irritation, following exposure of the EpiDerm skin model to the known skin irritant sodium lauryl sulphate (SLS). EpiDerm cultures were treated in triplicate with a non-cytotoxic dose of SLS (0.1 mg/ml, as determined by the MTT assay and histological examination) for 15 min, 30 min, 1 h, 2 h, 3 h, 4 h and 24 h. Total RNA was extracted from the pooled EpiDerm cultures and used to probe Atlas human arrays (Clontech) covering approximately 3600 genes. Preliminary data indicated an up-regulation at early time points (15-30 min) of a number of genes involved in transportation (e.g. the sodium and chloride dependent taurine transporter) and receptors (e.g. ZAP70 and protocadherin 42 precursor). The gene encoding the UV excision repair protein and other DNA repair genes (e.g. DNA-directed RNA polymerase II) were up-regulated after 1-3 h, along with TGF beta 3 and other tumour suppressors, which play a role in cellular development and wound healing. At the later time points of 4-24 h, genes involved in protein translation (e.g. Cathepsin D receptor) and metabolism (e.g. CYP27A) were up-regulated. In addition, a number of genes were down-regulated in response to treatment with SLS, although these followed less of a time dependent pattern. These results indicate the differential regulation of a number of genes in response to treatment with SLS, some of which may provide additional clues to the molecular events underpinning the irritation response to this particular surfactant and possibly to other chemical irritants.

In vitro cytotoxicity tests on cultured human skin fibroblasts to predict skin irritation potential of surfactants

Cultured human skin cells are a potentially useful model for skin irritancy testing. We have investigated the use of human skin fibroblasts for in vitro screening for skin toxicity. To assess the cytotoxic effects of surfactants, cell viability was measured by the NRU (neutral red uptake) assay and AB (Alamar blue) assay as in vitro methods. The skin irritation potential of surfactants by human skin patch test was assessed as in vivo methods. The close relationship was found between AB assay with human skin fibroblasts and human patch test (r=0.867). There was a relatively good agreement between the NRU and in vivo patch test (r=0.648). These results suggest that AB and NRU assay using cultured human fibroblast could be predictable methods for the irritancy of various surfactants in human.

In vitro testing of tensides employing monolayer cultures: a comparison with results of patch tests on human volunteers

Evaluation of the irritant potential of new products or ingredients prior to human testing is generally performed in vivo on animals. However, according to the 6th amendment and following updates of the European Community directive on cosmetic products (93/35/EEC), animal testing will be banned when suitable substitutes will be available. To know whether in vitro tests for assessment of skin irritancy provide results approaching human conditions, comparisons have to be made between data deriving from in vitro tests and skin response in humans. The aim of our study was to assess the validity of the monolayer culture system of normal human keratinocytes as a model for the evaluation of the irritant effects of detergents, by comparing in vitro cell culture data to in vivo acute skin irritancy effects of cocamidopropyl betaine (CAPB), an amphoteric compound, Tween 20 (TW20) (polysorbate 20) and Tween 80 (TW80) (polysorbate 80), representing nonionic compounds, applied to the skin of 24 healthy volunteers at a concentration similar to that employed in commercial products. As parameters for cytotoxicity, cell proliferation, cell membrane integrity and cell metabolism were assessed by cell counts, thymidine incorporation, MTT conversion, and Neutral Red uptake. In order to increase the sensitivity of the in vivo evaluation, bioengineering methods for assessment of the effects of test products on the skin were employed. Whereas all 4 in vitro methods ranked the tensides according to their toxicity in the following order: CAPB>SLS>TW20>TW80, both in vivo methods agreed in identifying SLS as the most irritating substance. Moreover, as compared with the irritation potential on human skin, all 4 in vitro tests overestimated the toxicity of CAPB. This suggests that the keratinocyte monolayer cell culture technique cannot directly replace in vivo methods, and that data obtained by this method should be interpreted cautiously.