The Organization for Economic Cooperation and Development (OECD) has approved the first comprehensive test strategy for predicting allergic skin reactions without animal testing. The strategy was developed over decades of collaboration between the German chemical company BASF and the Swiss flavor and fragrance specialist Givaudan. According to Givaudan’s Head of In Vitromolecular screening, Andreas Natch, it is better to predict allergy risks in humans than conventional animal experiments.

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Skin sensitization is one of the possible effects that must be assessed on a cosmetic product. As Robert Landsiedel, Vice President Special Toxicology at BASF, explains, the team analyzed the sensitization process from the first contact of a substance with human skin to the onset of allergic contact dermatitis (ACD) with repeated exposure and identified several key events that lead to ACD. For certain key events, various in vitro methods had been approved by the OECD in the past decade, but no overall strategy that could make animal testing superfluous.

The team found that combining methods would be enough to assess three of the key events. The first, the direct peptide reactivity assay, examines whether the test substance binds to skin proteins (the first step in the sensitization process) using synthetic heptapeptides as surrogates.

This binding event causes dendritic cells in the skin to migrate to the lymph nodes. The second test, an activation test for human cell lines, measures changes in the dendritic cells upon incubation with the test substance.

The immune system usually only reacts to the changed proteins if they also cause stress or injury. A third method uses a cellular stress response pathway linked to a bioluminescent reporter gene and two luminometer-based methods are available to detect the response.

While the combination of these three methods can determine whether a test substance is a skin sensitizer, its effectiveness was not quantified. To fix this, the first test was expanded to measure how fast the binding occurs. This new kinetic test has now also been adopted by the OECD.

“In contrast to almost all other toxicological effects, good human data are available for skin sensitization,” says Landsiedel. “We can therefore compare the results of the standard animal experiments and the new animal-free approach with the actual skin-sensitizing potential of test substances in humans.”

The approval of the strategy by the OECD was welcomed by Fiona Sewell, Head of Toxicology at the UK’s National Center for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs). “This is an important step towards achieving the goal of reducing dependence on test animals in assessing the safety of chemicals and drugs,” she says, adding that the new kinetic assay is also an important step forward.

Landsiedel says BASF and Givaudon are continuing to work on other alternative methods, including reproductive toxicity and respiratory poisoning. “Methods and test strategies for endocrine effects are currently a priority of ours

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