Department of Chemistry and Centre for Biotechnology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada.
Division of Nutritional Sciences, Savage Hall, Cornell University, Ithaca, NY 14853, USA.
Bioorg Med Chem. 2018 Nov 1;26(20):5555-5565. doi: 10.1016/j.bmc.2018.10.002. Epub 2018 Oct 5.
α-Tocopherol (α-TOH) is the primary lipophilic radical trapping antioxidant in human tissues. Oxidative catabolism of α-tocopherol (αTOH) is initiated by ω-hydroxylation of the terminal carbon (C-13) of the isoprenoid sidechain followed by oxidative transformations that sequentially truncate the chain to yield the 2,5,7,8-tetramethyl(3'carboxyethyl)-6-hydroxychroman (α-CEHC). After conjugation to glucuronic acid, 3'-carboxyethyl-6-hydroxychroman glucuronide is excreted in urine. We report here that the same enzyme that accomplishes this task, the cytochrome P450 monooxygenase CYP-4F2, can also ω-hydroxylate the terminal carbon of α-tocopheryl quinone. A standard sample of ω-OH-α-tocopheryl quinone (ω-OH-α-TQ) was synthesized as a mixture of stereoisomers by allylic oxidation of α-tocotrienol using SeO followed by double-bond reduction and oxidation to the quinone. After incubating human liver microsomes or insect cell microsomes expressing only recombinant human CYP-4F2, cytochrome b5, and NADPH P450 reductase with d-α-tocopheryl quinone (d-αTQ), we showed that the ω-hydroxylated (13-OH) d-α-TQ was produced. We further identified the production of the terminal carboxylic acid d-13-COOH-αTQ. The ramifications of this discovery to the understanding of tocopherol utilization and metabolism, including the quantitative importance of the αTQ-ω-hydroxylase pathway in humans, are discussed.
α-生育酚（α-TOH）是人体组织中主要的亲脂性自由基捕获抗氧化剂。α-生育酚（αTOH）的氧化分解代谢首先由末端碳原子（C-13）的ω-羟化作用启动，随后是氧化转化，这些转化依次缩短链以生成 2,5,7,8-四甲基（3'羧乙基）-6-羟基色满（α-CEHC）。与葡萄糖醛酸共轭后，3'-羧乙基-6-羟基色满葡萄糖醛酸苷从尿液中排出。我们在这里报告，完成这项任务的相同酶，细胞色素 P450 单加氧酶 CYP-4F2，也可以ω-羟化α-生育酚醌的末端碳。ω-OH-α-生育酚醌（ω-OH-α-TQ）的标准样品作为立体异构体的混合物通过使用 SeO 对α-生育三烯酚进行烯丙基氧化来合成，然后进行双键还原和氧化为醌。在孵育仅表达重组人 CYP-4F2、细胞色素 b5 和 NADPH P450 还原酶的人肝微粒体或昆虫细胞微粒体与 d-α-生育酚醌（d-αTQ）后，我们表明生成了ω-羟基化的（13-OH）d-α-TQ。我们进一步鉴定了末端羧酸 d-13-COOH-αTQ 的产生。讨论了这一发现对了解生育酚利用和代谢的意义，包括αTQ-ω-羟化酶途径在人体中的定量重要性。
