Givaudan Schweiz AG, Ueberlandstrasse 138, CH-8600 Duebendorf, Switzerland.
Chem Res Toxicol. 2012 Oct 15;25(10):2203-15. doi: 10.1021/tx300278t. Epub 2012 Sep 20.
Skin sensitizers chemically modify skin proteins rendering them immunogenic. Sensitizing chemicals have been divided into applicability domains according to their suspected reaction mechanism. The widely accepted Schiff base applicability domain covers aldehydes and ketones, and detailed structure-activity-modeling for this chemical group was presented. While Schiff base formation is the obvious reaction pathway for these chemicals, the in silico work was followed up by limited experimental work. It remains unclear whether hydrolytically labile Schiff bases can form sufficiently stable epitopes to trigger an immune response in the living organism with an excess of water being present. Here, we performed experimental studies on benzaldehydes of highly differing skin sensitization potential. Schiff base formation toward butylamine was evaluated in acetonitrile, and a detailed SAR study is presented. o-Hydroxybenzaldehydes such as salicylaldehyde and the oakmoss allergens atranol and chloratranol have a high propensity to form Schiff bases. The reactivity is highly reduced in p-hydroxy benzaldehydes such as the nonsensitizing vanillin with an intermediate reactivity for p-alkyl and p-methoxy-benzaldehydes. The work was followed up under more physiological conditions in the peptide reactivity assay with a lysine-containing heptapeptide. Under these conditions, Schiff base formation was only observable for the strong sensitizers atranol and chloratranol and for salicylaldehyde. Trapping experiments with NaBH₃CN showed that Schiff base formation occurred under these conditions also for some less sensitizing aldehydes, but the reaction is not favored in the absence of in situ reduction. Surprisingly, the Schiff bases of some weaker sensitizers apparently may react further to form stable peptide adducts. These were identified as the amides between the lysine residues and the corresponding acids. Adduct formation was paralleled by oxidative deamination of the parent peptide at the lysine residue to form the peptide aldehyde. Our results explain the high sensitization potential of the oakmoss allergens by stable Schiff base formation and at the same time indicate a novel pathway for stable peptide-adduct formation and peptide modifications by aldehydes. The results thus may lead to a better understanding of the Schiff base applicability domain.
皮肤致敏剂通过化学修饰皮肤蛋白使其具有免疫原性。根据可疑的反应机制，致敏化学品已被分为适用性域。广泛接受的席夫碱适用性域涵盖醛和酮，并提出了针对该化学基团的详细结构-活性模型。虽然席夫碱的形成是这些化学品的明显反应途径，但在计算机上的工作之后，只有有限的实验工作。目前尚不清楚在存在大量水的情况下，水解不稳定的席夫碱是否能够形成足够稳定的表位，从而在活体中引发免疫反应。在这里，我们对具有高度不同皮肤致敏潜力的苯甲醛进行了实验研究。在乙腈中评估了与丁胺形成席夫碱的情况，并提出了详细的 SAR 研究。邻羟基苯甲醛，如水杨醛和橡木苔过敏原阿特拉醇和氯代阿特拉醇，具有形成席夫碱的高倾向。对于非致敏香草醛等对羟基苯甲醛，反应性大大降低，而对于对烷基和对甲氧基苯甲醛，反应性则处于中间水平。在含有赖氨酸的七肽肽反应性测定中，在更生理条件下进行了后续工作。在这些条件下，只有强致敏剂阿特拉醇和氯代阿特拉醇以及水杨醛才能观察到席夫碱的形成。用 NaBH₃CN 进行的捕获实验表明，在这些条件下，一些致敏性较弱的醛也发生了席夫碱的形成，但在没有原位还原的情况下，该反应不受青睐。令人惊讶的是，一些较弱的致敏剂的席夫碱显然可能进一步反应形成稳定的肽加合物。这些被鉴定为赖氨酸残基与相应酸之间的酰胺。加合物的形成伴随着亲肽在赖氨酸残基上的氧化脱氨，形成肽醛。我们的结果通过稳定的席夫碱形成解释了橡木苔过敏原的高致敏潜力，同时表明了醛形成稳定肽加合物和肽修饰的新途径。因此，这些结果可能导致对席夫碱适用性域的更好理解。
