Saraev Dmitry D, Wu Zijun, Kim Hye-Young H, Porter Ned A, Pratt Derek A
Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie Pvt., Ottawa, ON K1N 6N5, Canada.
Department of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37235, United States.
ACS Chem Biol. 2023 Sep 15;18(9):2073-2081. doi: 10.1021/acschembio.3c00412. Epub 2023 Aug 28.
The one-electron reduction of lipid hydroperoxides by low-valent iron species is believed to be a driver of cellular lipid peroxidation and associated ferroptotic cell death. We investigated reactions of cholesterol 7α-OOH, the primary cholesterol autoxidation product, with Fe to find that 7-ketocholesterol (7-KC, an oxidation product) is the major product under these (reducing) conditions. Mechanistic studies reveal the intervention of a 1,2-H-atom shift upon formation of the 7-alkoxyl radical to yield a ketyl radical that can be oxidized by either Fe or O to give 7-KC, the most abundant oxysterol . We also investigated the corresponding reduction of the isomeric cholesterol 5α-OOH and again found that an oxidation product (5-hydroxycholesten-3-one) predominates under reducing conditions. An intramolecular H-atom shift (this time 1,4-) in the initially formed 5-alkoxyl radical is suggested to yield a ketyl radical that is oxidized to give the observed product. It would appear that a 1,2-H shift also accounts for the predominance of ketones over alcohols when unsaturated fatty acid hydroperoxides are exposed to iron-based reductants, which had previously been reported with hematin and demonstrated here with Fe. The predominance of 7-KC over the corresponding alcohol is maintained when cholesterol 7α-OOH embedded in phospholipid liposomes is treated with Fe or when ferroptosis is induced in mouse embryonic fibroblasts. Our observation that 7-KC accumulates in ferroptotic cells suggests that it may be a good biomarker for ferroptosis.
低价铁物种对脂质氢过氧化物的单电子还原被认为是细胞脂质过氧化及相关铁死亡细胞死亡的驱动因素。我们研究了胆固醇自氧化的主要产物胆固醇7α-OOH与铁的反应，发现在这些（还原）条件下，7-酮胆固醇（7-KC，一种氧化产物）是主要产物。机理研究表明，在7-烷氧基自由基形成时会发生1,2-氢原子转移，生成一个酮基自由基，该自由基可被铁或氧氧化生成7-KC，即最丰富的氧化甾醇。我们还研究了异构体胆固醇5α-OOH的相应还原反应，同样发现在还原条件下一种氧化产物（5-羟基胆甾-3-酮）占主导。最初形成的5-烷氧基自由基中发生的分子内氢原子转移（这次是1,4-转移）被认为会生成一个酮基自由基，该自由基被氧化生成观察到的产物。当不饱和脂肪酸氢过氧化物暴露于铁基还原剂时，酮类相对于醇类的优势似乎也由1,2-氢转移所导致，此前用血红素报道过这一现象，本文用铁进行了验证。当用铁处理嵌入磷脂脂质体中的胆固醇7α-OOH或在小鼠胚胎成纤维细胞中诱导铁死亡时，7-KC相对于相应醇类的优势得以保持。我们观察到7-KC在铁死亡细胞中积累，这表明它可能是铁死亡的一个良好生物标志物。
