Cytotoxicity of 12 chemicals of known human and animal skin irritation potential in human keratinocyte cultures

Alternative Methods for Skin Irritation Testing: The Current Status

The ECVAM Skin Irritation Task Force was established in November 1996, primarily to prepare a report on the current status of the development and validation of alternative tests for skin irritation and corrosion and, in particular, to identify any appropriate non-animal tests for predicting human skin irritation which were sufficiently well-developed to warrant ECVAM supporting their prevalidation/validation. The task force based its discussions around the proposed testing strategy for skin irritation/corrosion emanating from an OECD workshop held in January 1996. The following have been reviewed: a) structure-activity and structure-property relationships for skin corrosion and irritation; b) the use of pH and acid/alkaline reserve measurements in predicting skin corrosivity; c) in vitro tests for skin corrosion; d) in vitro tests for skin irritation (keratinocyte cultures, organ cultures, and reconstituted human skin models); and e) human patch tests for skin irritation. It was apparent that, although several promising candidate in vitro tests for skin irritation (for example, reconstituted human skin methods, and human and animal skin organ culture methods) were under development and evaluation, a test protocol, a preliminary prediction model and supporting data on different types of chemicals were only available for a method employing EpiDerm™. Thus, it is proposed that this EpiDerm test undergoes prevalidation during 1998. In addition, since it was felt preferable to be able to include other in vitro tests in such a prevalidation study, it is recommended that a “challenge” be set to anyone interested in taking part. This involves submitting data on ten test chemicals selected by the task force, obtained according to a standard protocol with a preliminary prediction model, for review by the task force by 31 May 1998.

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.

Characterization and applications of human epidermis reconstructed in vitro on de-epidermized derma

In recent years in vitro models have been developed to avoid the use of animals in cutaneous toxicological studies. Submerged human keratinocyte cultures in vitro could be so far employed as an alternative to animal testing and a good correlation between skin irritation and cytotoxicity has been demonstrated. Nevertheless, these submerged cultures are lacking in the stratum corneum which acts as a barrier to chemical toxicity, so that this type of culture is far from the in vivo situation. A better alternative method seems to be the use of in vitro reconstructed skin at the air-liquid interface that closely resembles the in vivo situation. In this work, in a first step we have characterized human epidermis reconstructed in vitro on de-epidermized derma (DED) after a two-week air exposure. Human skin reconstituted in vitro on DED was histologically similar to the in vivo skin. A stratified epidermis including the stratum corneum was obtained. The presence of basal lamina as well as of various important markers for epidermal differentiation (involucrin, K10 keratin, and filaggrin) were revealed. In a second step we have tested the cytotoxic and morphological effects of four surfactants on our model. A good rank correlation has been shown to exist between the irritation potency of surfactants on our model and reported ocular irritancy in vivo. From our results, in vitro reconstituted human skin could represent an attractive model for irritancy testing and could be an in vitro replacement for animal testing.