Interlaboratory validation of the in vitro eye irritation tests for cosmetic ingredients (9). Evaluation of cytotoxicity test on HeLa cells

Statistics of Interlaboratory In Vitro Toxicological Studies

Interlaboratory studies are common in toxicology, particularly for the introduction of alternative assays. Numerous papers are available on the statistical analysis of interlaboratory studies, but these deal primarily with the case of a replicated single sample studied in several laboratories. This approach can be used for some assays, but for the majority, the results will be unsatisfactory, i.e. involving great variability between both the dose groups and the laboratories. However, the primary objective of toxicological assays is to achieve similarity between the sizes of effects, rather than to determine absolute values. In the parametric model, the sizes of effects are the studentised differences from the negative control or, for the commonly used dose-response designs, the similarity of the slopes of the dose-response curves. Standard approaches for the estimation of intralaboratory and interlaboratory variability, including Mandel plots, are introduced, and new approaches are presented for demonstrating similarity of effect sizes, with or without assuming a dose-response model. One approach is based on a modification of the parallel-line assay, the other is based on a modification of the interaction contrasts of the analysis of variance. SAS programs are given for all approaches, and real data from an interlaboratory immunotoxicological study are analysed as a demonstration.

Assessment of the Eye Irritating Properties of Chemicals by Applying Alternatives to the Draize Rabbit Eye Test: The Use of QSARs and In Vitro Tests for the Classification of Eye Irritation

Huggins has reported on the current situation relating to the development of alternatives to the Draize eye irritation test with rabbits, and an ECVAM Working Group have reviewed the efforts needed in order to replace this animal test within the next 10 years by using the results of non-animal assessment methods. Our report reviews regulatory experience gained over the last 20 years with the EU chemicals notification procedure with respect to the assessment of eye lesions observed in Draize tests. The nature of eye lesions and their importance for classification and labelling of possible hazards to human eyes are evaluated and discussed, with a view to promoting the development of specific in vitro assays which are able to discriminate between eye damage, moderate eye irritation, and minor irritation effects which are completely reversible within a few days. Structural alerts for the prediction of eye irritation/corrosion hazards to be classified and labelled according to international classification criteria, are presented, which should be validated in accordance with internationally agreed (OECD) principles for (Q)SAR system validation. Physicochemical limit values for prediction of the absence of any eye irritation potential relevant for human health can make available a definition of the applicability domains of alternative methods developed for the replacement of the Draize eye irritation test.

Effect of choline carboxylate ionic liquids on biological membranes

Choline carboxylates, ChCm, with m=2-10 and choline oleate are known as biocompatible substances, yet their influence on biological membranes is not well-known, and the effect on human skin has not previously been investigated. The short chain choline carboxylates ChCm with m=2, 4, 6 act as hydrotropes, solubilizing hydrophobic compounds in aqueous solution, while the longer chain choline carboxylates ChCm with m=8, 10 and oleate are able to form micelles. In the present study, the cytotoxicity of choline carboxylates was tested using HeLa and SK-MEL-28 cells. The influence of these substances on liposomes prepared from dipalmitoylphosphatidylcholine (DPPC) was also evaluated to provide insights on membrane interactions. It was observed that the choline carboxylates with a chain length of m>8 distinctly influence the bilayer, while the shorter ones had minimal interaction with the liposomes.

Application of the reconstructed rabbit corneal epithelium model to assess the in-vitro eye irritant test of chemicals

The rabbit corneal epithelium model (RCE model) was developed as a three-dimensional in vitro model to replace animal testing for the assessment of eye irritation. In the model, a stratified culture of rabbit corneal epithelial cells is grown at the air-liquid interface on collagen gel that acts as a parabasal membrane. Histological cross-sections show that the structure of the RCE model closely parallels that of the rabbit corneal epithelium. The eye irritation potency of test samples is estimated from the measurement of viability using the MTT assay in conjunction with the RCE model. A set of 30 chemicals belonging to different families with known in vivo Draize score was investigated with the in vitro eye irritation test using the RCE model in order to internally validate the protocol. Use of the RCE model at concentrations of 0.05%, 0.50%, and 1.00% and the calculation of the IC(50) and percentage of viability allowed the irritants to be divided into four classes. The performance of the in vitro eye irritation test at a concentration of 0.50% using the RCE model was characterized by good sensitivity (92.3%), good specificity (100%), and good accuracy (93.3%) compared with the irritation classification predicted by in vivo Draize score at concentrations of 10% and 100%. These results indicate that the RCE model may provide a useful and sensitive in vitro eye irritation test as an alternative method to the Draize test.

Determining the cytotoxicity of catanionic surfactant mixtures on HeLa cells

The cytotoxicity of commonly used synthetic surfactants and catanionic mixtures of those was evaluated using MTT on HeLa cells. The 50% inhibition concentration (IC(50)) for MTT reduction was calculated. The effect on chain length increase and inclusion of polyoxyethylene groups on the toxicity was tested on single surfactant systems. A general trend of increasing toxicity with increasing chain length and the presence of polyoxyethylene groups was observed. The measured IC(50) values of catanionic systems lie between those of participating surfactants. The increase in toxicity as the cationic surfactant is added to the anionic one is however not linear. A steep decrease of the IC(50) values (and therefore increase in the toxic properties) is observed immediately already at low concentrations of the cationic surfactants. This behavior is analogous to the enzyme activity in catanionic microemulsions.

An In Vitro Tier Evaluation for the Identification of Cosmetic Ingredients Which are Not Ocular Irritants

A tier evaluation system was assessed as an alternative method for the identification of cosmetic ingredients which are not ocular irritants. The system employed monolayer cultures of SIRC cells, an established cell line originally derived from the rabbit cornea, and a three-dimensional living dermal model (LDM), MATREX™, which consists of human dermal fibroblasts in a contracted collagen lattice. Effects on the cell monolayer cultures were determined by using SIRC cell-Crystal Violet staining (SIRC-CVS), and effects on the LDM were assessed by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. A non-irritating ingredient was defined as a compound having a maximal average total score (MAS) of 5 or less in the Draize eye test, as this is the criterion used in the Japanese draft guidance for evaluating cosmetic ingredients. Among 34 test substances with known characteristics, 30 were classified accurately. Based on these encouraging results, the possibility of simplifying the MTT assay on the LDM for more-practical use, by selecting only three concentration levels to discriminate non-irritants from irritants, was assessed. The simplified method, involving a three-dose set (the three-dose method), was confirmed as being suitable for the identification of non-irritating ingredients, with triethanolamine used as a negative reference standard. Finally, the LDM was used to evaluate compounds at similar concentrations to those tested in vivo, aiming to predict the concentration at which an ingredient can be formulated into products without causing eye irritation. On the basis of previous validation data and our additional results, it was found that test samples that resulted in a cell viability of 50% or more in this model, could be classified as non-irritating ingredients. In all, these results indicate that the tier evaluation system may be suitable for the evaluation of ingredients intended to be used in cosmetics and medicated cosmetics in Japan.

Spontaneous formation of bilayers and vesicles in mixtures of single-chain alkyl carboxylates: effect of pH and aging and cytotoxicity studies

We report the observation of bilayer fragments, some of which close to form vesicles, over a large range of pH at room temperature from mixtures of single-chain biocompatible commercially available nontoxic alkyl carboxylic surfactants after neutralization with HCl. The pH at which the morphological transitions occur is varied only by changing the ratio between two surfactants: the alkyloligoethyleneoxide carboxylate and sodium laurate. The effect of aging of the mixed surfactant systems in the pH region desired for dermatologic application (4.5 < pH < 7) is also studied. Finally, we show results of cytotoxicity studies on the surfactant mixtures.