Interspecies comparisons of skin irritancy

Human relevance of in vivo and in vitro skin irritation tests for hazard classification of pesticides

Background: Test methods to inform hazard characterization and labeling of pesticides to protect human health are typically conducted using laboratory animals, and for skin irritation/corrosion the rabbit Draize test is currently required by many regulatory agencies. Although the Draize test is generally regarded to provide protective classifications for human health, new approach methodologies (NAMs) have been developed that offer more human relevant models that circumvent the uncertainty associated with species differences that exist between rabbits and humans. Despite wide applicability and use of these test methods across a broad range of chemicals, they have not been widely adopted for testing pesticides and pesticidal formulations. One of the barriers to adoption of these methods in this sector is low concordance with results from the Draize rabbit test, particularly for chemicals within the mild to moderate irritation spectrum.

Methods: This review compares and contrasts the extent to which available models used in skin irritation testing mimic the anatomy and physiology of human skin, and how each aligns with the known key events leading to chemically-induced adverse skin irritation and corrosion. Doing so fully characterizes the human relevance of each method.

Results: As alternatives to the rabbit Draize test, several protocols using ex vivo, in chemico, and in vitro skin models are available as internationally harmonized test guidelines. These methods rely on a variety of models of human skin, including excised rodent skin, synthetic biochemical models of barrier function, cell culture systems, and reconstructed human tissue models. We find these models exhibit biological and mechanistic relevance aligned with human skin irritation responses. Further, recent retrospective analyses have shown that the reproducibility of the Draize test is less than 50% for mild and moderate responses, with many of the replicate predictions spanning more than one category (e.g., a moderate response reported in one study followed by a non-irritant response reported in another study).

Conclusions: Based on this comparative evaluation, we recommend top-down and bottom-up testing strategies that use the most human relevant in vitro test methods for skin irritation and corrosion classification of pesticides and pesticide formulations. To further discriminate among mild and non-irritant formulations, optimization of a cytokine release protocol and subsequent analyses of reference formulation test results is recommended.

Safety Assessment of Inorganic Hydroxides as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) reviewed the safety of inorganic hydroxides, which function in cosmetics primarily as pH adjusters. Representatives from the cosmetic industry have indicated these ingredients are used in depilating and hair waving/straightening formulations to raise pH values. The Panel considered relevant data related to these ingredients. The Panel concluded that these inorganic hydroxides are safe in hair straighteners and depilatories under conditions of recommended use; users should minimize skin contact. These ingredients are safe for all other present practices of use and concentration described in this safety assessment when formulated to be nonirritating.

Comparative assessment of local tolerance of alcohols commonly used in alcohol-based hand rubs for hand hygiene

Hand hygiene plays a key role in nosocomial infection prevention. To achieve users' adherence, products' dermal tolerance is essential. We aimed at making a comparative assessment of skin irritation and phototoxicity of the 3 alcohols commonly used in alcohol-based hand rubs (Ethanol, Propan-2-ol, Propan-1-ol) at 60, 70, 80 or 85% w/w in water or with co-formulates (hydrating, emollient and skin protective agents). In vitro validated OECD methods 439 and 432 were used. For irritation, EpiSkin™ Small Model was the chosen Reconstructed Human Epidermis (RhE). For phototoxicity, co-formulates alone or in mixture with and without alcohol were tested using BALB/c 3T3 cell cultures. Whilst Ethanol and Propan-2-ol could not be differentiated and displayed good skin tolerance profiles, Propan-1-ol based products lead to significant viability impairments of RhE at 60, 70 or 80% and at 60% in the presence of co-formulates. However, these results could not be reproduced in another RhE model. Taking also into account bibliographic data on Propan-1-ol, this suggests that our results are probably related to a lack of specificity of the used RhE. Therefore, it can be relevant in case of significant results to use two different RhE models before performing any classification and/or performing any complementary tests.

Bioprinting technologies for disease modeling

There is a great need for the development of biomimetic human tissue models that allow elucidation of the pathophysiological conditions involved in disease initiation and progression. Conventional two-dimensional (2D) in vitro assays and animal models have been unable to fully recapitulate the critical characteristics of human physiology. Alternatively, three-dimensional (3D) tissue models are often developed in a low-throughput manner and lack crucial native-like architecture. The recent emergence of bioprinting technologies has enabled creating 3D tissue models that address the critical challenges of conventional in vitro assays through the development of custom bioinks and patient derived cells coupled with well-defined arrangements of biomaterials. Here, we provide an overview on the technological aspects of 3D bioprinting technique and discuss how the development of bioprinted tissue models have propelled our understanding of diseases' characteristics (i.e. initiation and progression). The future perspectives on the use of bioprinted 3D tissue models for drug discovery application are also highlighted.

Exposures to traditional automatic dishwashing tablets and a comparison with exposures to soluble film tablets reported to the United Kingdom National Poisons Information Service 2008-2015

INTRODUCTION

Traditional automatic dishwashing tablets are contained within an external wrapper that requires removal prior to use.

OBJECTIVE

To determine the toxicity of traditional tablets and to compare this with our previously reported experience of soluble film dishwashing tablets.

METHODS

Telephone enquiries regarding traditional tablets were analysed retrospectively for the period January 2008 to December 2015.

RESULTS

Traditional tablets: There were 503 enquiries relating to 492 patients who had been exposed to a traditional tablet. Most involved children aged 5 years or less (87.4%). The majority (78.6%) of patients did not develop symptoms after exposure; 21.1% developed minor (PSS 1) symptoms while one patient developed moderate features. Exposure occurred predominantly as a result of ingestion (n = 476, 96.7%); the most common feature in symptomatic patients (n = 99, 20.8%) was vomiting (70 [14.7%] cases). Significantly (p < 0.0001) more adults (44.9% of 49 adults; 95% CI = 31.9-58.7) were reported with features than children (18.2% of 434; 95% CI = 14.9-22.1). There were five cases of eye contact which resulted in eye pain in two patients and eye irritation in another. Only one of 11 patients exposed dermally developed features (a rash around the mouth). Comparison with soluble film exposures: The percentage of patients that were reported with clinical symptoms following ingestion of a soluble film dishwashing tablet (31.7% of 473 patients; 95% CI = 27.7-36.0) was significantly greater (p < 0.0001) than that for a traditional tablet (20.9% of 483 patients; 95% CI = 17.5-24.8). Vomiting was the most commonly reported feature and occurred significantly (p < 0.0001) more frequently amongst patients who had ingested a soluble film tablet (25.5%; 95% CI = 21.8-29.6) than a traditional tablet (14.7%; 95% CI = 11.8-18.1).

CONCLUSIONS

Exposure to both traditional and soluble film tablets only rarely produced clinically significant symptoms (PSS ≥2). However, ingestion of a soluble film tablet was significantly more likely to result in clinical features than ingestion of a traditional tablet.

5: Final Report on the Safety Assessment of Sodium Sesquicarbonate, Sodium Bicarbonate, and Sodium Carbonate

Sodium Sesquicarbonate, Sodium Carbonate, and Sodium Bicarbonate are used in cosmetic products at concentrations ranging up to 50%. The LD50 in rats for Sodium Bicarbonate ranged from 7.6 g/kg to 8.9 g/kg. Sodium Sesquicarbonate, Sodium Carbonate, and Sodium Bicarbonate caused conjunctivitis. Sodium Bicarbonate was not an ocular irritant to laboratory animals. Neither Sodium Bicarbonate nor Sodium Carbonate was a teratogen to laboratory animals. Sodium Sesquicarbonate and Sodium Bicarbonate were not mutagenic to two different cell cultures. Dermatitis, but not sensitization, was observed in employees of a Trona (Sodium Sesquicarbonate) mining facility. Sodium Carbonate, but not Sodium Bicarbonate, is a skin and eye irritant due to the alkaline nature of its solutions, The cosmetic use of Sodium Carbonate at high concentrations is mainly limited to products designed to be diluted before use and in products where pH is buffered to near neutrality. It is concluded that Sodium Sesquicarbonate, Sodium Bicarbonate, and Sodium Carbonate are safe as presently used in cosmetics.

Toxicity of soluble film automatic dishwashing products as reported to the United Kingdom National Poisons Information Service 2008-2015

INTRODUCTION

Soluble film automatic dishwashing tablets, unlike their traditional counterparts, require no removal from an outer protective wrapper prior to use. Instead, the tablets are enclosed by a water-soluble polyvinyl alcohol film and are loaded straight into the dishwashing machine. They most commonly contain a source of hydrogen peroxide (often as sodium percarbonate) and non-ionic surfactants. Other constituents in some formulations include sodium carbonate, sodium tripolyphosphate and sodium silicate, which reduce water hardness. The pH once dissolved in water is alkaline.

OBJECTIVE

To determine the toxicity from exposure to soluble film automatic dishwashing tablets.

METHODS

Telephone enquiries to the United Kingdom National Poisons Information Service regarding soluble film automatic dishwashing products were analysed retrospectively for the period January 2008 to December 2015.

RESULTS

There were 498 enquiries relating to 488 patients. Almost all exposures occurred in the home (98.4%) and involved children aged ≤5 years (92.8%). Exposure occurred mainly as a result of ingestion alone (n = 470, 96.3%); eye contact alone (n = 9, 1.8%) and exposures involving multiple routes (ingestion with skin or eye contact; n = 9, 1.8%) made up the remaining cases. The majority of patients were asymptomatic following exposure (n = 325, 67.4%). The most common feature following ingestion was vomiting which occurred in 121 of 474 cases (25.5%) where clinical data were available. Nausea (n = 8, 1.7%) and coughing (n = 6, 1.3%) were also reported; three patients developed stomatitis and another five developed a rash where ingestion alone was considered to be the sole route of exposure. Ocular exposure to the tablet contents resulted in blurred vision, eye pain or conjunctivitis in seven of ten patients.

CONCLUSION

Ingestion of a soluble film automatic dishwashing tablet rarely resulted in clinically significant symptoms, which is surprising given the potential hazard of the ingredients. Hence, it seems probable that the amount of material actually ingested was very small or that most was spat out.

Evaluation of fibrin-based dermal-epidermal organotypic cultures for in vitro skin corrosion and irritation testing of chemicals according to OECD TG 431 and 439

Reconstructed human epidermis (RhE) models have been used for in vitro testing of the potential harmful effects of exposure to chemical compounds on health. In the past, skin irritation and corrosion were evaluated in animal models; however, in recent years, due to the bioethics implications of the method and, to minimize the use of experimental animals, alternative procedures have been proposed. The Organisation for Economic Co-operation and Development (OECD) in its test guidelines (TG) 431 and 439 indicates the requirements for validating new methods for the evaluation of skin corrosion and irritation, respectively. Here, we present an in-house human dermal-epidermal model, useful for the performance of these tests. Using the methods described in this work, it was possible to obtain human fibrin-based dermal-epidermal organotypic skin cultures (ORGs) displaying similar histological characteristics to native skin and expressing specific differentiation epithelial proteins. The end points to classify a substance as irritant or corrosive were cell viability evaluated by MTT assay, and cytokine release measured by BD CBA for human inflammatory cytokines. According to the MTT test, the ORGs correctly classified irritating and corrosive substances. Moreover, the cytokine release assay was difficult to interpret in the context of testing chemical hazard classification. Further experiments are needed to validate this new model for the evaluation of surfactants because the fibrin matrix was affected in the presence of these substances.

Large Animal Toxicology: Introduction and General Principles

Large animal toxicity studies, also called nonrodent studies, are very different from rodent (rat, mouse, guinea pig, and rabbit) studies in significant ways. The differences between the two study types, as well as the advantages and disadvantages of each, are evaluated in detail. Also examined are causes for selecting specific species, regulatory requirements for using nonrodent species, and an overview of major species characteristics for dogs, primates, pigs, and ferrets.

Dermal toxicity studies: factors impacting study interpretation and outcome

The field of dermal toxicity continues to evolve in order to accurately predict dermal (and systemic) responses in humans to topically applied chemicals. Although the testing methods have undergone extensive refinements, idiosyncrasies and unexpected issues during the conduct of these studies are not unusual due to the plethora of new vehicles available for formulating test substances, changing regulatory requirements, and introducting new strain and/or species of laboratory animals as no single species or method seems to suffice for evaluating skin toxicity. The objective of this article is to illustrate some pragmatic issues that should be considered during the conduct as well as interpretation of dermal toxicity studies. Routine procedure-related issues such as hair clipping, tape stripping, and wrapping the animal's torso to prevent oral ingestion can influence the interpretation. Excipients used in dermal toxicity studies may be nontoxic when used alone but complex dermal formulations can result in unexpected irritation and toxicity. In conclusion, interpretation and risk assessment of dermal toxicity studies should be done in a comprehensive manner, taking into account procedure-related impact on study results, unique species susceptibility, limitation of gross visual (naked eye) observation for evidence of toxicity, and normal anatomical variation.

In vitro human skin irritation test for evaluation of medical device extracts

The aim of this study was to determine if the EpiDerm™ reconstructed human skin model (MatTek Corp.) could be an acceptable alternative to the ISO 10993-required rabbit skin irritation test for assessing medical device biocompatibility. Eleven medical device polymers were tested. Four extracts were prepared per polymer, two each with saline and sesame oil; half were spiked with two R-38 irritants, lactic acid for saline extracts and heptanoic acid for the sesame oil extracts. Tissue viability was assessed by MTT reduction and the proinflammatory response was assessed by IL-1α release. LOAELs of 2% for lactic acid in saline and 0.7% for heptanoic acid in sesame oil were determined. A cell viability reduction of >50% was indicative of skin irritation. Cells exposed to saline extracts spiked with 3.25% lactic acid had significantly reduced mean cell viabilities (12.6-17.2%). Cells exposed to sesame oil extracts spiked with 1.25% heptanoic acid also exhibited reduced mean cell viabilities (25.5%-41.7%). All spiked cells released substantial amounts of IL-1α (253.5-387.4pg/ml) signifying a proinflammatory response. These results indicate that the EpiDerm™ model may be a suitable in vitro replacement for the assessment of the irritation potential of medical device extracts.

Dermal irritation of petrolatum in rabbits but not in mice, rats or minipigs

Petrolatum is widely used in cosmetics, topical pharmaceuticals and also as a vehicle in dermal toxicity studies. New Zealand white rabbits treated with white petrolatum (vehicle control) in a 2-week dermal irritation study exhibited moderate to severe erythema starting on Day 7 that subsided towards the end of the study. Histological examination of abraded and non-abraded petrolatum-treated skin obtained at termination (Day 15) revealed mild acanthosis, hyperkeratosis, dermal edema with mixed inflammatory cells in the dermis. Macroscopic and microscopic features noted in rabbits were consistent with dermal irritation to petrolatum. Wistar-Han rats, CD1 mice, C57/Bl/6J mice and Göttingen minipigs treated topically with white petrolatum did not exhibit clinical or histologic evidence of dermal irritation. Therapeutic agents developed for topical application are generally tested in rabbits during some point in development. Interpretation of skin irritation data from a single species can impact risk assessment for humans and on product labeling.

Review of skin irritation/corrosion Hazards on the basis of human data: A regulatory perspective

Regulatory classification of skin irritation has historically been based on rabbit data, however current toxicology processes are transitioning to in vitro alternatives. The in vitro assays have to provide sufficient level of sensitivity as well as specificity to be accepted as replacement methods for the existing in vivo assays. This is usually achieved by comparing the in vitro results to classifications obtained in animals. Significant drawback of this approach is that neither in vivo nor in vitro methods are calibrated against human hazard data and results obtained in these assays may not correspond to situation in human.The main objective of this review was to establish an extended database of substances classified according to their human hazard to serve for further development of alternative methods relevant to human health as well as resource for improved regulatory classification. The literature has been reviewed to assemble all the available information on the testing of substances in the human 4 h human patch test, which is the only standardized protocol in humans matching the exposure conditions of the regulatory accepted in vivo rabbit skin irritation test.A total of 81 substances tested according to the defined 4 h human patch test protocol were found and collated into a dataset together with their existing in vivo classifications published in the literature. While about 50% of the substances in the database are classified as irritating based on the rabbit skin test, on using the 4 h HPT test, less than 20% were identified as acutely irritant to human skin. Based on the presented data, it can be concluded that the rabbit skin irritation test largely over-predicts human responses for the evaluated chemicals. Correct classification of the acute skin irritation hazard will only be possible if newly developed in vitro toxicology methods will be calibrated to produce results relevant to man.

Emergency do not consume/do not use concentrations for blended phosphates in drinking water

The U.S. Congress [PL 107–188] amended the Safe Drinking Water Act and required each community water system serving more than 3,000 people to conduct vulnerability assessments. These assessments address potential circumstances that could compromise the safety and reliability of municipal water. The present evaluation concerns the concentrations of the blended phosphates (also known as polyphosphates, condensed complex phosphates, polyphosphate glassy balls, and pyrophosphates) intended to aid regulatory agencies in decisions to avoid contact with affected water. Polyphosphates are direct food additives and they are used to treat municipal drinking water, but depending upon the concentration and duration of exposure these substances can induce chemical burns. Ingested polyphosphates are degraded by phosphatase enzymes to monophosphates, substances that are over-the-counter bowel purgatives. High oral doses of the monophosphates can induce transient hyperphosphatemia in older and susceptible young people, which can lead to acute phosphate nephropathy. In some patients, the condition is fatal. Based on the acute diarrhea after the ingestion of a single oral dose of monobasic (NaH2PO4) and dibasic (Na2HPO4) monophosphates in adults, a do not consume concentration of 600 mg PO4/L can be derived. Based on mild local irritation after topical application of 1.0% sodium metaphosphate [(NaPO3)6 • H2O] to intact skin of sensitive volunteers, a do not use concentration of 8,000 mg PO4/L can be assigned. Given the lack of eye irritation in rabbits after direct instillation of 0.2% (NaPO3)6 • H2O, an acute ocular contact limit of 50 mg PO4/L serves as the overall do not use level.

Evaluation of five decontamination methods for filtering facepiece respirators

Concerns have been raised regarding the availability of National Institute for Occupational Safety and Health (NIOSH)-certified N95 filtering facepiece respirators (FFRs) during an influenza pandemic. One possible strategy to mitigate a respirator shortage is to reuse FFRs following a biological decontamination process to render infectious material on the FFR inactive. However, little data exist on the effects of decontamination methods on respirator integrity and performance. This study evaluated five decontamination methods [ultraviolet germicidal irradiation (UVGI), ethylene oxide, vaporized hydrogen peroxide (VHP), microwave oven irradiation, and bleach] using nine models of NIOSH-certified respirators (three models each of N95 FFRs, surgical N95 respirators, and P100 FFRs) to determine which methods should be considered for future research studies. Following treatment by each decontamination method, the FFRs were evaluated for changes in physical appearance, odor, and laboratory performance (filter aerosol penetration and filter airflow resistance). Additional experiments (dry heat laboratory oven exposures, off-gassing, and FFR hydrophobicity) were subsequently conducted to better understand material properties and possible health risks to the respirator user following decontamination. However, this study did not assess the efficiency of the decontamination methods to inactivate viable microorganisms. Microwave oven irradiation melted samples from two FFR models. The remainder of the FFR samples that had been decontaminated had expected levels of filter aerosol penetration and filter airflow resistance. The scent of bleach remained noticeable following overnight drying and low levels of chlorine gas were found to off-gas from bleach-decontaminated FFRs when rehydrated with deionized water. UVGI, ethylene oxide (EtO), and VHP were found to be the most promising decontamination methods; however, concerns remain about the throughput capabilities for EtO and VHP. Further research is needed before any specific decontamination methods can be recommended.

Skin safety evaluation of laundry detergent products

The conduct of a scientifically sound safety assessment of new ingredients and finished products is essential prior to their introduction into the marketplace. Such assessments are based on a risk assessment paradigm established by the National Academy of Science (NAS, 1983) that consists of a four-step process: hazard identification, dose-response assessment, exposure assessment, and risk characterization. This risk assessment paradigm has been (1) used as a framework for estimating an adverse health risk posed by environmental chemicals, and (2) applied to systemic toxicological endpoints. The general principles of risk assessment may be applied to skin safety evaluation of consumer products, considering that dermal toxicity is also a threshold phenomenon. This study describes a risk assessment-based approach for skin safety evaluation of laundry detergent products.

Establishment and characteristics of Gottingen minipig skin in organ culture and monolayer cell culture: relevance to drug safety testing

Skin from Gottingen minipigs was used as a source of tissue for organ and cell culture and compared to human skin for growth conditions and sensitivity to irritants. Optimal organ culture conditions were determined, based on the preservation of the histological structure. These included serum-free, growth factor-free conditions with a calcium concentration of 1.5mM. Formulations in which the calcium concentration were low (0.075-0.15mM) failed to support tissue viability (even in the presence of dialyzed serum). Epidermal keratinocytes were grown from tissue explants and as single cells from enzyme-disrupted tissue. Optimal keratinocyte growth was achieved using a serum-free, growth factor-supplemented culture medium with a calcium concentration of 0.15mM. Fibroblasts were optimally grown from explant cultures using a medium with 1.5mM calcium and 10% fetal bovine serum. The conditions that were optimal for maintenance of intact pig skin, as well as for the isolated cells, are the same conditions that have been shown previously to be optimal for intact human skin and skin cells. In additional studies, pig skin keratinocytes and fibroblasts were exposed to a panel of contact irritants and contact sensitizers. Using growth inhibition as the response, the median effective dose values with each agent were very similar to the values previously determined for human epidermal keratinocytes and human dermal fibroblasts. Taken together, these data suggest that the skin from the Gottingen minipig can be used as a surrogate for human skin in ex vivo skin safety studies.

Subchronic (26- and 52-week) toxicity and irritation studies of a novel microbicidal gel formulation containing sodium lauryl sulfate in animal models

The safety of an ethylene oxide/propylene oxide gel formulation containing sodium lauryl sulfate (2%, w/w), that could be a potent candidate as a topical microbicide, has been evaluated. More specifically, the subchronic (26- and 52-week) toxicity of the formulation when applied intravaginally as well as its irritating potential for the rectal, penile, eye, skin and buccal mucosa have been examined in animal models. The results showed that the vaginal administration of the gel formulation containing sodium lauryl sulfate once and twice daily (with doses 12 +/- 2 h apart) for 26 weeks to rats and for 52 weeks to rabbits induced slight to moderate histopathological alterations. When the formulation was applied intrarectally to male and female rabbits once and twice daily (with doses 12 +/- 2 h apart) for 14 days, no macroscopic or microscopic changes were reported. For both vaginal and rectal dosing, no effect was seen on the haematology, coagulation and serum chemistry parameters as well as on the body weight of animals and the relative organ weights. Other sporadic macroscopic and histopathological findings were incidental in origin and of no toxicological significance. The gel formulation containing sodium lauryl sulfate was considered as mildly irritating for the penile mucosa of rabbits, non-irritating for the eye of rabbits, mildly irritating for the skin in a rabbit model and non-irritating for the hamster cheek pouch. It is suggested that the gel formulation containing sodium lauryl sulfate is safe for most tissues that could be exposed to the product under normal use.

Human skin in organ culture and human skin cells (keratinocytes and fibroblasts) in monolayer culture for assessment of chemically induced skin damage

Human skin cells (epidermal keratinocytes and dermal fibroblasts) in monolayer culture and human skin in organ culture were exposed to agents that are known to produce irritation (redness, dryness, edema and scaly crusts) when applied topically to skin. Among the agents used were three well accepted contact irritants (i.e., all-trans retinoic acid [RA], sodium lauryl sulfate [SLS] and benzalkonium chloride) as well as the corrosive organic mercury compound, aminophenyl mercuric acetate (APMA), and 5 contact sensitizers (oxazolone, nickel sulfate, eugenol, isoeugenol and ethylene glycol dimethacrylate [EGDM]). As a group, the contact irritants (including the corrosive mercuric compound) were cytotoxic for keratinocytes and fibroblasts and suppressed growth at lower concentrations than the contact sensitizers. The contact irritants also produced histological changes (hyperplasia, incomplete keratinization, loss of the granular layer, acantholysis and necrosis) in organ-cultured skin at dose levels at which the contact sensitizers appeared to be inert. Finally, the profile of secreted molecules from organ-cultured skin was different in the presence of contact irritants versus contact sensitizers. Taken together, these data suggest that the use of organ-cultured skin in conjunction with cells derived from the skin in monolayer culture may provide an initial approach to screening agents for deleterious changes in skin.

Electrical impedance model for evaluation of skin irritation in rabbits and humans

BACKGROUND/AIM

The electrical impedance method has been used as a quantitative technique for evaluating changes in the skin during irritation within the invisible range. The purpose of this study was to apply an electrical model of skin to the interpretation of impedance data after the application of an irritant (SLS) in the skin of humans and rabbits.

METHODS

Investigations were performed on 12 humans and 15 albino rabbits. Responses were evaluated by measuring electrical impedance before irritant exposure and 24 h after its removal and also by visual inspection. Using the raw impedance parameter, a novel index was developed and its value was correlated with visual scoring.

RESULTS

The derived impedance index showed a significant correlation with visual scores and its value decreased (P<0.05) after irritant removal even without macroscopic signs of irritation.

CONCLUSION

The proposed electrical model of skin seems to be suitable for the detection and interpretation of changes in the impedance characteristics of skin induced by SLS in rabbits and humans.

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%.

The hairless guinea-pig as a model for treatment of acute irritation in humans

BACKGROUND

The effect of six skin care formulations on experimentally induced acute irritation was studied in hairless guinea-pigs (HLGP) and in human volunteers (HV). The formulations were a basic cream, a carbomer cream and four modifications of the carbomer cream, containing either 10% isopropyl palmitate (IPP cream), 10% glycerol (glycerol cream), 19.5% canola oil (canola oil cream) or 0.5% (-)-alpha-bisabolol (bisabolol cream).

METHODS

Acute irritation was induced by occlusive tests with 1% sodium lauryl sulfate aq. in both HLGP and HV, and in HV also by using nonanoic acid in n-propanol (NON) 20%. The irritant reactions were treated twice daily with the formulations from the time of removal of the patches. Evaluation of skin irritation and efficacy of treatments was performed daily for 4 days using clinical scoring, evaporimetry (transepidermal water loss), hydration measurement and colorimetry.

RESULTS

The glycerol cream was the only product showing effects potentially better than no treatment in HV.

CONCLUSION

The HLGP was too sensitive an animal model as a predictor for effect in humans. There was no difference in efficacy of the formulations against the two different irritants in HV.

In vitro skin irritation testing on reconstituted human epidermis: Reproducibility for 50 chemicals tested with two protocols

Since it is of high importance to establish the skin irritation potential of industrial chemicals, toxicologists developed tests on various skin models. Most test data come from the rabbit Draize test, but its reproducibility is questionable. Some human in vivo test data exist, but they concern only few compounds. The emergence of new tools such as reconstituted human skin tissues offers a promising future to alternative methods. We describe here two in vitro skin irritation test protocols performed on reconstituted human epidermis. One is a direct topical application test and the other an in vitro patch test. Both protocols were performed using multiple endpoint analysis including cell viability (MTT reduction), histology, and IL-1alpha release. Fifty chemicals were tested: 20 compounds were used in the ECVAM pre-validation study and 30 products were previously tested in a human in vivo patch test. These in vitro skin irritation tests have not only the advantages of enhanced convenience and of reduced costs, but a good reproducibility is observed by endpoint, and by compound. A prediction model is proposed to classify the chemicals as irritant or non-irritant, and the results are compared to available rabbit and human data. We do not wish to overgeneralize from these 50 compounds; but, instead suggest that this data set be extensively extended to include chemicals of varying physico-chemical properties.

Comparative assessment of the acute skin irritation potential of detergent formulations using a novel human 4-h patch test method

Predictive skin irritation test methods, which do not require use of animals, are needed for the pre-market assessment of detergent formulations. The utility of a novel and ethical human acute skin irritation patch test method, originally developed for chemical skin irritation assessment, was evaluated. In this IRB-approved method, subjects were patched under occlusion for increasing periods of time up to 4h in duration. The total incidence of positive skin reactions for test products was compared to a positive control (20% aqueous sodium dodecyl sulfate [SDS]). Acutely irritating formulas were defined as those showing a significantly increased or equal incidence of positive responders compared with that of SDS. The time of exposure required for 50% of subjects to show a positive skin reaction (TR50 value) was calculated for each product and enabled test product comparisons within and between studies. Using this approach, 24 detergent formulations of various types were tested in seven individual studies. The skin irritation profiles were generally consistent within product types, which could be categorized as follows (by decreasing irritancy): mold/mildew removers (average TR50 = 0.37 h) > disinfectants/sanitizers (0.64 h) > fabric softener concentrate (1.09 h) = aluminum wash (1.20 h) > 20% SDS (1.81 h) > liquid laundry detergents (3.48 h) > liquid dish detergents (4.16 h) = liquid fabric softeners (4.56 h) = liquid hand soaps (4.58 h) = shampoos (5.40 h) = hard surface cleaners (6.34 h) > powder automatic dish detergents (>16 h) = powder laundry detergents (>16 h). In addition to formulation effects, some seasonal effects were noted; particularly greater winter-time reactivity to 20% SDS and the hard surface cleaner and liquid laundry formulations. These results demonstrate the utility of this patch test method for the comparative skin irritation assessment of these different product types.

Final report on the safety assessment of potassium silicate, sodium metasilicate, and sodium silicate

Potassium Silicate, Sodium Metasilicate, and Sodium Silicate combine metal cations with silica to form inorganic salts used as corrosion inhibitors in cosmetics. Sodium Metasilicate also functions as a chelating agent and Sodium Silicate as a buffering and pH adjuster. Sodium Metasilicate is currently used in 168 formulations at concentrations ranging from 13% to 18%. Sodium Silicate is currently used in 24 formulations at concentrations ranging from 0.3% to 55%. Potassium Silicate and Sodium Silicate have been reported as being used in industrial cleaners and detergents. Sodium Metasilicate is a GRAS (generally regarded as safe) food ingredient. Aqueous solutions of Sodium Silicate species are a part of a chemical continuum of silicates based on an equilibrium of alkali, water, and silica. pH determines the solubility of silica and, together with concentration, determines the degree of polymerization. Sodium Silicate administered orally is readily absorbed from the alimentary canal and excreted in the urine. The toxicity of these silicates has been related to the molar ratio of SiO2/Na2O and the concentration being used. The Sodium Metasilicate acute oral LD50 ranged from 847 mg/kg in male rats to 1349.3 mg/kg in female rats and from 770 mg/kg in female mice to 820 mg/kg in male mice. Gross lesions of variable severity were found in the oral cavity, pharynx, esophagus, stomach, larynx, lungs, and kidneys of dogs receiving 0.25 g/kg or more of a commercial detergent containing Sodium Metasilicate; similar lesions were also seen in pigs administered the same detergent and dose. Male rats orally administered 464 mg/kg of a 20% solution containing either 2.0 or 2.4 to 1.0 ratio of sodium oxide showed no signs of toxicity, whereas doses of 1000 and 2150 mg/kg produced gasping, dypsnea, and acute depression. Dogs fed 2.4 g/kg/day of Sodium Silicate for 4 weeks had gross renal lesions but no impairment of renal function. Dermal irritation of Potassium Silicate, Sodium Metasilicate, and Sodium Silicate ranged from negligible to severe, depending on the species tested and the molar ratio and concentration tested. Sodium Metasilicate was negative in the local lymph node assay (LLNA), but a delayed-type hypersensitivity response was observed in mice. Potassium Silicate was nonirritating in two acute eye irritation studies in rabbits. Sodium Metasilicate (42.4% H2O) was corrosive to the rabbit eye. Sodium Silicate was a severe eye irritant in some eye irritation studies, but was irritating or nonirritating in others. A skin freshener containing Sodium Silicate was nonirritating. Sodium Metasilicate was nonmutagenic in bacterial cells. Rats given Sodium Silicate (600 and 1200 ppm of added silica) in the drinking water in reproductive studies produced a reduced number of offspring: to 67% of controls at 600 ppm and to 80% of controls at 1200 ppm. Three adult rats injected intratesticularly and subcutaneously with 0.8 mM/kg of Sodium Silicate showed no morphological changes in the testes and no effect on the residual spermatozoa in the ductus deferens. Sodium Metasilicate (37% in a detergent) mixed with water was a severe skin irritant when tested on intact and abraded human skin, but 6%, 7%, and 13% Sodium Silicate were negligible skin irritants to intact and abraded human skin. Sodium Silicate (10% of a 40% aqueous solution) was negative in a repeat-insult predictive patch test in humans. The same aqueous solution of Sodium Silicate was considered a mild irritant under normal use conditions in a study of cumulative irritant properties. The Cosmetic Ingredient Review (CIR) Expert Panel recognized the irritation potential of these ingredients, especially in leave-on products. However, because these ingredients have limited dermal absorption and Sodium Metasilicate is a GRAS direct food substance, the Panel deemed the ingredients safe for use in cosmetic products in the practices of use and concentration described in this safety assessment, when formulated to avoid irritation.

In vitro skin irritation: facts and future. State of the art review of mechanisms and models

The skin is the main target tissue for exogenous noxes, protecting us from harmful environmental hazards, UV-irradiation and endogenous water loss. It is composed of three layers, whereas the outermost epidermis is a squamous epithelium that mainly consists of keratinocytes. These cells execute a terminal differentiation, which finally results in the assembly of the stratum corneum. This layer, consisting of cornified keratinocytes, is an effective barrier against a vast number of substances. Apart of this, keratinocytes play crucial roles in the immune surveillance and the initiation, modulation and regulation of inflammation in the epidermis. Regarding cutaneous inflammatory reactions, skin irritation is one of the most common adverse effect in humans. For reasons of human safety assessment new chemicals are still evaluated for irritant potentials by application to animals followed by visible changes such as erythema and oedema. Testing for skin irritation in animals potentially cause them pain and discomfort. Furthermore, the results are not always predictive for those found in humans. In order to replace animal testing and to improve the prediction of irritants, the cosmetic and toiletry industry, in Europe represented by Colipa, develops and uses several alternative in vitro test systems. In this respect, the use of in vitro reconstructed organotypic skin equivalents are mostly favored, because of their increasingly close resemblance to human skin. Due to ethical and scientific questions and on account of the 7th amendment of the European Council Directive 76/768/EEC, the authors see the requirement to drive the development of alternative tests for irritants. Therefore, this article centres on cosmetic ingredients and provides the readership an overview of the state of art of cellular mechanisms of skin irritation and summarizes the results of the commonly used skin equivalents to evaluate irritation in vitro.

Tiered testing strategies--acute local toxicity

More work has been done to develop alternatives to animal use in the areas of eye and skin irritation than in any area other than carcinogenicity. There has long been a belief both in the scientific community and among the public that the development of nonanimal tests in these areas should be simple and straightforward. After more than 20 yr of research, we can identify materials corrosive to the skin without using animals, but the assessment of irritation using in vitro methods alone is still an illusive goal. This review of current recommendations and industry practices that reduce the number of animals needed for these two tests concludes that animal use for skin irritation testing is not necessary today, with currently available and accepted methodology, except for regulatory reasons. Scientifically sound improvements in current eye irritation methods are also available. Advances in the understanding of the mechanisms of eye irritation that have been made in the last 5 yr should lead to improved in vitro methods for this endpoint. In the meantime, changes should be made in the current animal protocol to reduce pain and distress. This paper provides an overview of the progress that has been made toward discontinuing the use of animals in tests to determine the potential of materials to cause skin or eye damage after a single acute exposure. It also discusses some additional changes that could be made now to reduce animal use further or to reduce pain and distress in the testing that must still be done until such time as we can meet the ultimate goal--validated and accepted nonanimal methods for these endpoints.

Effect of skin barrier competence on SLS and water-induced IL-1alpha expression

For screening of a potential irritant it is essential that an early marker for irritation should be chosen which could be detected before the physiological signs of irritation occur. Interleukin 1 alpha (IL-1alpha) is widely accepted as such a marker in both in vivo and in vitro test systems. In this study, we have determined the mRNA levels of IL-1alpha in the epidermis after topical application of sodium dodecyl sulphate (SLS) in both a commercially available epidermal kit (EpiDerm) and in excised skin. Furthermore, we have determined the effect of water, the vehicle for SLS, on IL-1alpha mRNA levels. Topical application of water to excised skin increases IL-1alpha mRNA levels sixfold in the epidermis whereas topical application of water to EpiDerm cultures did not alter IL-1alpha mRNA levels. This is explained by the finding that EpiDerm cultures have a sub-optimal barrier function when compared with excised skin - topical application of SLS was clearly toxic at much lower concentrations in EpiDerm cultures (0.2% SLS) than in excised skin (5% SLS). Also caffeine penetration was 10-fold higher through EpiDerm cultures than through the excised skin. Therefore, incubation of control EpiDerm cultures at 100% humidity effectively mimics topical exposure to water. An additional increase in IL-1alpha mRNA levels observed between topical application of water and SLS is similar (about threefold) in both experimental systems. In conclusion, in vitro reconstructed epidermis models, such as EpiDerm, can be used as a predictive model for irritancy screening. However, great care should be taken when interpreting the results due to the fact that EpiDerm cultures do not have a competent barrier function and therefore lower irritant concentrations are required than in in vivo or ex vivo studies in order to induce cytotoxic effects. Furthermore, the irritant effects of the vehicle should not be neglected. Our results show clearly that the topical application of water to excised skin results in increased levels of IL-1alpha mRNA in the epidermis. This is a cytokine that is widely used as an early marker for skin irritation.

Non-animal testing strategies for assessment of the skin corrosion and skin irritation potential of ingredients and finished products

The dermatotoxicologist today is faced with a dilemma. Protection of workers and consumers from skin toxicities (irritation and allergy) associated with exposure to products, and the ingredients they contain, requires toxicological skin testing prior to manufacture, transport, or marketing. Testing for skin corrosion or irritation has traditionally been conducted in animals, particularly in rabbits via the long established Draize test method. However, this procedure, among others, has been subject to criticism, both for its limited predictive capacity for human toxicity, as well as for its use of animals. In fact, legislation is pending in the European Union which would ban the sale of cosmetic products, the ingredients of which have been tested in animals. These considerations, and advancements in both in vitro skin biology and clinical testing, have helped drive an intensive effort among skin scientists to develop alternative test methods based either on in vitro test systems (e.g. using rat, pig or human skin ex vivo, or reconstructed human skin models) or ethical clinical approaches (human volunteer studies). Tools are now in place today to enable a thorough skin corrosion and irritation assessment of new ingredients and products without the need to test in animals. Herein, we describe general testing strategies and new test methods for the assessment of skin corrosion and irritation. The methods described, and utilized within industry today, provide a framework for the practicing toxicologist to support new product development initiatives through the use of reliable skin safety testing and risk assessment tools and strategies.

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.

Validity and ethics of the human 4-h patch test as an alternative method to assess acute skin irritation potential

For more than 50 years, the Draize rabbit skin irritation test has reigned supreme as the regulatory method of choice for the identification of skin irritant chemicals. To date no in vitro alternative test has been validated as an adequate replacement. However, one potential option, to test the endpoint of concern (skin irritation) in the species of concern (man) has been overlooked. The advent of predictive in vitro tools for the identification of substances corrosive to the skin has opened up the practical possibility of carrying out safe and ethical studies on small panels of humans. The human 4-h patch test has been developed to meet the needs of identifying chemical skin irritation potential, providing data which is inherently superior to that given by a surrogate model, such as the rabbit. This paper reviews in detail the present state of the human 4-h patch test, highlighting its advantages and noting its utility as the 'gold standard' on which to build future in vitro models.

Human in vivo studies of non-pharmaceutical products

Two principal types of human in vivo studies with non-pharmaceuticals can be distinguished: (1) human metabolism studies are used for identification of target metabolites which can subsequently be used in biological monitoring studies. Furthermore, they allow extrapolation from excretion of metabolite(s) to exposure to the parent compound on the basis of an understanding of human pharmacokinetics. (2) Pharmacodynamic or effect studies are restricted to the study of acute and inherently reversible changes and are most likely to improve risk assessment in the following areas: neurobehavioural effects (e.g. alcohol, organic solvents), alterations in biochemical markers (e.g. cholinesterase inhibition following organophosphate exposure) and topical effects (e.g. skin irritancy). Ethical considerations are of prime importance and, as a minimum, any human study must comply with the principles of the Declaration of Helsinki. The protocol should include scientifically sound objectives, a justification of subject numbers, a formal risk-benefit analysis and provisions for appropriate ethical review. The welfare of the individual participating in the study must be paramount. Informed consent has to be obtained and subjects must be free to withdraw from the study at any time. Compensation should be given for the inconvenience of participating in the study, but never for undergoing risk. Provided these conditions are met, human volunteer studies can be a powerful tool in risk assessment and risk management of exposure to non-pharmaceutical products.

In vitro and human testing strategies for skin irritation

Prior to the manufacture, transport, and marketing of chemicals or products, it is critical to assess their potential for skin toxicity (corrosion or irritation), thereby protecting the worker and consumer from adverse skin effects due to intended or accidental skin exposure. Traditionally, animal testing procedures have provided the data needed to assess the more severe forms of skin toxicity, and current regulations may require animal test data before permission can be obtained to manufacture, transport, or market chemicals or the products that contain them. In recent years, the use of animals to assess skin safety has been opposed by some as inhumane and unnecessary. The conflicting needs of the industrial toxicologist to (1) protect human safety, (2) comply with regulations, and (3) reduce animal testing have led to major efforts to develop alternative, yet predictive, test methods. A variety of in vitro skin corrosion test methods have been developed and several have successfully passed initial international validation. These have included skin or epidermal equivalent assays that have been shown to distinguish corrosive from noncorrosive chemicals. These skin/epidermal equivalent assays have also been modified and used to assess skin irritation potential relative to existing human exposure test data. The data show a good correlation between in vitro assay data and different types of human skin irritation data for both chemicals and consumer products. The effort to eliminate animal tests has also led to the development of a novel human patch test for assessment of acute skin irritation potential. A case study shows the benefits of in vitro and human skin irritation tests compared to the animal tests they seek to replace, and strategies now exist to adequately assess human skin irritation potential without the need to rely on animal test methods.

Arachidonic acid metabolism in primary irritant dermatitis produced by patch testing of human skin with surfactants

A clinical study was performed to determine the effects of patch testing human skin with four industrially used surfactants on erythema formation, transepidermal water loss, and the contents in suction blister fluids of primary proinflammatory mediators including arachidonic acid, eicosanoids, and IL-1 alpha, which were analyzed by quantitative gas chromatography/negative ion chemical ionization mass spectrometry and by an enzyme-immunoassay, respectively. Benzalkonium chloride (BKCI) and sodium lauryl sulfate (SLS) elicited erythema and caused increased transepidermal water loss, indicating a disturbance of the epidermal barrier. Triethanolamine (TEA) and Tween 80 did not evoke these gross symptoms of inflammation. Suction blister fluids collected after a 24-h application of BKCl, SLS, and Tween 80 contained significantly increased amounts of individual eicosanoids whereas TEA induced no response. The induced eicosanoid profile was characteristic for each compound, pointing to different cell types of skin to be involved in their production. The elevation of prostaglandin and LTB4 contents correlated with the induction of erythema and the impairment of the epidermal barrier as shown for BKCl and SLS and preceded the maximum of erythema formation. IL-1 alpha contents did not correlate with these gross symptoms of inflammation. The results of this in vivo study support those of a previous study using human keratinocytes in culture indicating the release of arachidonic acid and prostaglandins to be an early event involved in the interaction of keratinocytes with surfactants. Moreover, the in vivo data with human skin underscore the mechanistic relationship to the in vitro model and support the concept that arachidonic acid and eicosanoid release from keratinocytes can be used as a marker of primary skin irritation.

A hairless mouse model for assessing the chronic toxicity of topically applied chemicals

An enormous number of synthetic chemicals are incorporated in topical drugs, cosmetics and toiletries. These have the potential to cause irritant reactions when chronically applied to human skin. In predictive tests for assessing the irritancy potential of these chemicals, haired species, especially rabbits, guinea pigs and mice, have figured prominently. Customarily these tests, including the renowned Draize rabbit test, have entailed a single acute exposure or at most daily exposures over a few weeks. Estimation of inflammation and tissue injury in these models have relied on visual assessment. We submit that this approach is no longer acceptable. Visual assessments are unreliable. Reactions which are scored equivalently by the naked eye may differ strikingly when examined histologically. Moreover, tissue injury may be present in clinically normal skin. Short-term results. even when abetted by routine histological evaluations, cannot predict the degree of injury from long-term exposures. Cosmetics and toiletries, for example, are used daily for decades, often over most of the lifespan of persons who are well groomed. We present the hairless mouse as a convenient, reliable model for assessing the chronic toxicity of diverse chemicals. Histological examination enables a detailed description of the different tissue components which participate in the complex cascade of changes that comprise the inflammatory response.

Individual, ethnic and seasonal variability in irritant susceptibility of skin: the implications for a predictive human patch test

Since irritants are the major cause of contact dermatitis, it is important to identify those chemicals that possess significant ability to cause skin irritation. This process must then be followed by risk assessment and risk management. Historically, animal tests have played a major rôle in this process, but human volunteer studies are of increasing importance in this field. Where the appropriate safety and ethical controls are in place, human testing can give data that identifies skin irritation hazard. To be of widest value, these human studies must not be flawed due to inter-individual, inter-ethnic or seasonal variation. We conducted a large dose-response study and studied the impact of summer and winter weather on a predictive human assay. Sodium dodecyl sulphate (SDS) was tested at 0.1%-20% in 3 national groups of approximately 100 volunteers, using 25 mm Hill Top chambers loaded with 0.2 ml, solution and applied to the upper outer arm for 4 h. Reactions were scored at 24, 48 and/or 72 h after patch application. The German and Chinese studies were completed in a few weeks under similar winter conditions, whereas the UK work was spread fairly evenly over about a 15-month period. Some relatively minor differences were observed in the dose-response curves obtained, probably due to weather conditions. The effect of the weather on the intensity, but not the pattern, of irritant reactivity was also evident in the smaller specific study that assessed reactions to SDS in summer and in winter. Whereas 45% of the panel reacted to 20% SDS in summer, 91% reacted in the winter. However, in both studies, substantial inter-individual variations in response to SDS dominated the pattern of response. When designing a human patch test to discriminate skin irritant substances from those that are of minimal effect, it is this inter-individual variability, rather than any small inter-ethnic or seasonal variation, which must be taken into account. This can be achieved by the routine inclusion of a suitable positive irritant control, which then calibrates each human volunteer panel.

The impact of atopic status on a predictive human test of skin irritation potential

There has been much interest in recent years in the replacement of the Draize rabbit skin test for the identification of chemical skin irritants. A considerable effort has gone into the development of cell culture based assays. However, where ethical and safety considerations permit, the most obvious alternative is to use man himself. Data obtained using a suitable assay based on the endpoint of concern in the species of concern should be accurate and will represent a vital data base on which to develop sound in vitro assays. Thus, it is important to ensure the data produced in human assays is representative for man generally. To this end we have chosen to examine a number of variables and in this work report the effect of atopic status on the results obtained in a recently described human 4-h patch test. 30 atopic (defined by specific IgE to common allergens and by elevated total IgE) and 28 non-atopic volunteers were tested in this human 4-h patch test using 20% sodium dodecyl sulfate (SDS), 10% hydrochloric acid (HCl) and undiluted cocotrimethyl ammonium chloride (coco TAC). The level of irritant reaction was higher for SDS in the atopic panel, but was similar for HCl and coco TAC. The rank order of irritancy was the same in both panels. The results indicate that, whilst the intensity of reactions may be higher in atopics, their pattern of responses is similar to non-atopics. There is no evidence to indicate that they should either be deliberately included or excluded from the test panels recruited on a routine basis.

Ocular and dermal irritation studies of some quaternary ammonium compounds

The primary ocular and dermal irritations of four quaternary ammonium compounds, namely cetylpyridinium chloride (CPC), stearylphenylethyldimethylammonium tosylate (SPDAT), dimethyldistearylammonium bisulfate (DDABS) and tri(N-butyl)benzylammonium 4-hydroxynapththalene-1-sulfonate (TBAHNS), were studied. Both CPC and SPDAT were extremely or severely irritating to the eyes of the test animals, whereas DDABS and TBAHNS were mildly or minimally irritating. Both CPC and SPDAT were also severely or extremely irritating to the skin of the test animals, while DDABS and TBAHNS were non-irritating. These quaternary ammonium compounds have little similarity in chemical structure and possess different solubilities. CPC is very soluble in both lipid and water; SPDAT is very soluble in lipid but only slightly soluble in water; and DDABS and TBAHNS are poorly soluble in either lipid or water. The irritancy of these compounds is likely to be related to their solubility, in addition to the cationic characteristics. It appears that not all quaternary ammonium compounds in this study are irritants. Those that are not soluble are not expected to be absorbed in eye/skin tissues and thus irritation reactions will not take place. The use of in vitro alternatives should be considered when assessing the ocular and dermal irritancy potential of water- and lipid-soluble quaternary ammonium compounds.

Arachidonic acid release: an in vitro alternative for dermal irritancy testing

Validated in vitro alternatives are being utilized extensively for mutagenicity and ocular irritancy testing. However, validation of alternative assays for dermal irritancy is progressing more slowly. As the irritant response in human skin is mediated, at least in part, by eicosanoids derived from arachidonic acid, the effect of relatively pure anionic surfactants (AS, n=8) and surfactant-containing finished products (FP, n=25) on the release of [3H]arachidonic acid from a prelabelled murine fibroblast cell line (C3H-10T1/2 cells) in vitro was examined. Test substances were administered at various non-lethal concentrations, in triplicate, to 12- and 24-well plates containing preconfluent monolayers (80-90% confluence) of C3H-10T1/2 cells. Because it is impossible to test all concentrations of each test substance in a single assay, statistical techniques were developed to 'standardize' in vitro assay results. In each assay, radiolabel release due to a positive control was also measured, using 0.04, 0.05 and 0.06 mM concentrations of sodium dodecyl sulfate (SDS). Test substance releases were then transformed into 'SDS equivalent' responses, significantly reducing both inter- and intra-assay variability. A straight line was fitted to the test substance responses and compared with that for SDS to calculate the relative potency in vitro for individual AS and FP. Relative potencies correlated with in vivo responses, that is primary dermal irritation indices obtained in rabbits, with Spearman p=0.408 (P<0.03) for 32 tested agents, and p=0.976 (P<0.001) for the eight AS. Exclusion of extremely alkaline or acidic FP (pH>11 or <2, n=4) and those which were insoluble in the aqueous cell culture media at the 1% stock dilution (n=5), improved the overall in vivo-in vitro correlation significantly (p=0.683, P<0.001, n=23) and produced a significant correlation for FP alone (p=0.539, P<0.05, n=15). These results suggest that release of [3H]arachidonic acid from cultured skin cells represents a novel, mechanistically based in vitro screen for dermal irritancy testing.

Variation in response of human skin to irritant challenge

A major obstacle to the establishment of a protocol for in vivo irritant skin testing in humans is the apparent variability of responses between individuals. This study of the threshold response of normal human skin to a standard irritant (sodium lauryl sulfate 0.3-10%), in a group of 22 subjects, revealed a marked interindividual variation in their threshold reaction. The results demonstrate that this phenomenon does exist and that it will have to be allowed for in future human irritant test systems or assays.