Fuchs J, Freisleben H J, Podda M, Zimmer G, Milbradt R, Packer L
Zentrum der Dermatologie und Venerologie, Abteilung II, Universitätsklinikum, Frankfurt, Germany.
Free Radic Biol Med. 1993 Oct;15(4):415-23. doi: 10.1016/0891-5849(93)90041-r.
Nitroxide radicals are important chemical tools in dermatologic research (e.g., for studying biophysical properties of skin lipids and epidermal membranes with the method of electron paramagnetic resonance, EPR, spectroscopy). However, nitroxides may loose their paramagnetic properties in biological tissues, which could limit their usefulness in biomedical applications. We analyzed the biostability of various chemical types of nitroxide radicals in keratinocytes, epidermis homogenate, and intact skin. EPR signal loss of imidazoline, pyrrolidine, piperidine, and oxazolidine nitroxides is attributed to their reduction to the corresponding hydroxylamine. The rate of nitroxide reduction in skin varies considerably with nitroxide ring structure and substitution. The order of nitroxide stability in isolated human keratinocytes, mouse epidermis homogenate, and intact mouse and human skin is imidazoline > pyrrolidine > di-t-butylnitroxide (DTBN) > piperidine > oxazolidine. Cationic nitroxides are reduced much faster than neutral or anionic probes, presumably due to transmembrane electron shuttle or internalization. The results indicate that imidazoline- and pyrrolidine-type nitroxides should be used when high biostability of nitroxides is needed. Piperidine-type nitroxides are versatile probes for studying one-electron transfer reactions in skin.
氮氧自由基是皮肤病学研究中的重要化学工具（例如，用于通过电子顺磁共振光谱法研究皮肤脂质和表皮膜的生物物理性质）。然而，氮氧化物在生物组织中可能会失去其顺磁性质，这可能会限制它们在生物医学应用中的实用性。我们分析了各种化学类型的氮氧自由基在角质形成细胞、表皮匀浆和完整皮肤中的生物稳定性。咪唑啉、吡咯烷、哌啶和恶唑烷氮氧自由基的电子顺磁共振信号损失归因于它们被还原为相应的羟胺。皮肤中氮氧自由基的还原速率因氮氧自由基环结构和取代基的不同而有很大差异。在分离的人角质形成细胞、小鼠表皮匀浆以及完整的小鼠和人皮肤中，氮氧自由基稳定性的顺序为咪唑啉＞吡咯烷＞二叔丁基氮氧自由基（DTBN）＞哌啶＞恶唑烷。阳离子氮氧自由基的还原速度比中性或阴离子探针快得多，这可能是由于跨膜电子穿梭或内化作用。结果表明，当需要氮氧自由基具有高生物稳定性时，应使用咪唑啉型和吡咯烷型氮氧自由基。哌啶型氮氧自由基是研究皮肤中单电子转移反应的通用探针。
