The neutral red release assay: a review.

The neutral red release (NRR) assay is a cytotoxicity test that can be used to measure the immediate toxic effects of test substances on the cell membrane, resulting in the leaking of intracellular contents. The assay has already been used for several years to evaluate the cytotoxicities of various kinds of products, such as cosmetics, pharmaceuticals, industrial chemicals and household products. It has undergone in-house validation by many companies, and has been found to be particularly useful for identifying substances that are potentially capable of causing adverse reactions on coming into brief contact with the eye or the skin at relatively high concentrations, such as might occur in an adventitious splash into the eye or onto the skin, followed by a quick rinse. Because of the relatively long existence of the NRR assay, its practicality and its proven usefulness for particular purposes, ECVAM decided to review the status of the method, in order to decide whether prevalidation and formal validation studies on the test might be profitable. The review of the status of the test was carried out by performing a comprehensive review of the literature, and by conducting a survey involving companies and institutes with experience in using the test. Both the review and the survey revealed that the assay could provide extremely valuable information when it was used for particular purposes, such as for the evaluation and comparison of immediate toxic effects on the eye or the skin caused by certain products or chemicals such as surfactants. Most of those who responded in the survey favoured a prevalidation/validation study.

Detection of skin irritation potential of cosmetics by non-invasive measurements.

This study analyses the ability of four non-invasive techniques (laser Doppler velocimetry, evaporimetry, chromametry and corneometry) to discriminate between irritant and non-irritant products, when compared to appropriate controls, and to detect subliminal changes in barrier function and erythema. These changes, which remain undetectable in the traditional visual and palpable clinical assessment, can be used as early reactions that are followed by the development of overt skin irritation. Laser Doppler velocimetry and evaporimetry were good discriminators between irritant and non-irritant substances, whereas corneometry and chromametry did not clearly distinguish between them. Laser Doppler velocimetry and evaporimetry detected early stages in the development of an irritant reaction before it became visible, but chromametry was not able to detect an early irritant response. It was concluded that non-invasive measurements could improve the quality and relevance of data obtained from human irritation testing, since the data they provide are objective, quantitative and sometimes subclinical, which also allows the concentration of a positive control to be reduced, resulting in the induction of less skin damage in human volunteers and reducing the ethical concerns related to the deliberate induction of an irritant response in a 'healthy' volunteer.

Predicting visual assessment of allergic patch test reactions by non-invasive measurements.

The quantification of allergic patch test reactions to several compounds was evaluated on patients using laser Doppler velocimetry (LDV), transepidermal water loss and colorimetry. The correlation between visual scores and instrumental measurements was investigated by the implementation of a modern statistical method: a classification tree. The LDV showed the highest correlation with the severity of the reaction. The best prediction model was obtained when the data of the three instruments were considered together. Using the classification tree methodology, a model of classification, independent of human observation, was developed. The technique can not only predict an allergic reaction for a new patient, but can also give a measure of how reliable its predictions are. This new method, when entirely standardised and approved, could help in the harmonisation of patch test reactions in different laboratories, thus allowing a more homogenous interpretation of these reactions.