Natsch Andreas, Emter Roger
Biosciences, Givaudan Schweiz AG , Ueberlandstrasse 138, CH-8600 Duebendorf, Switzerland.
Chem Res Toxicol. 2017 Jan 17;30(1):315-331. doi: 10.1021/acs.chemrestox.6b00365. Epub 2016 Nov 30.
The publication by the OECD of the adverse outcome pathway (AOP) for skin sensitization has accelerated the development and validation of mechanistic tests and testing strategies to assess the potential of new molecules to trigger skin allergies. The molecular initiating event (MIE) in the AOP is reaction with skin peptides/proteins. It is followed by a number of cellular events. Currently, only one in chemico test to characterize the MIE was proposed to and underwent adoption by the OECD, while two cell-based assays have completed the process. A multitude of further cellular assays is currently in the validation pipeline, but no further reactivity test has gone through full standardization. Here, we review data on in chemico methods, identify gaps, and discuss how these methods can be improved to better characterize the MIE and to become even more informative. We focus on the importance of kinetics, the information gained from studying adduct formation, and the difficulties posed by side reactions such as peptide oxidation. We then highlight mechanistic insights from reaction chemistry: the relative contribution of different target nucleophiles, the migration of amino acid modifications, and the potential of peptide-cross-linking. We illustrate in a case study how kinetic in chemico methods might have been used to better predict the risk of three preservatives, which have led to serious epidemics of contact dermatitis. In a case study on Michael acceptors, we show the impact of additional substituents around the electrophilic olefin moiety on reactivity, and we highlight the shortcomings which current in silico methods to predict reaction chemistry still have, illustrating the need for experimental in chemico data to improve such models. Finally, based on the information reviewed and the presented case studies, a strong argument is made to continue the journey of developing nonredundant, informative in chemico methods, and not to solely focus on new cell-based methods to further populate the AOP for skin sensitization.
经济合作与发展组织（OECD）发布的皮肤致敏不良结局途径（AOP）加速了用于评估新分子引发皮肤过敏潜力的机制性试验及测试策略的开发与验证。AOP中的分子起始事件（MIE）是与皮肤肽/蛋白质发生反应，随后是一系列细胞事件。目前，OECD仅提议并采用了一项用于表征MIE的体外试验，而两项基于细胞的试验已完成该流程。目前有大量其他细胞试验正在验证流程中，但尚无其他反应性试验经过全面标准化。在此，我们回顾体外方法的数据，找出差距，并讨论如何改进这些方法以更好地表征MIE并提供更多信息。我们重点关注动力学的重要性、研究加合物形成所获得的信息，以及肽氧化等副反应带来的困难。然后，我们强调反应化学的机制性见解：不同目标亲核试剂的相对贡献、氨基酸修饰的迁移以及肽交联的可能性。我们通过一个案例研究说明体外动力学方法如何可能被用于更好地预测三种导致严重接触性皮炎流行的防腐剂的风险。在一个关于迈克尔受体的案例研究中，我们展示了亲电烯烃部分周围额外取代基对反应性的影响，并强调了当前预测反应化学的计算机模拟方法仍然存在的缺点，说明了需要实验性体外数据来改进此类模型。最后，基于所回顾的信息和所呈现的案例研究，我们有力地论证了应继续开发非冗余、信息丰富的体外方法，而不是仅仅专注于新的基于细胞的方法，以进一步完善皮肤致敏的AOP。
