Department of Pathology and Laboratory Medicine, University of Tennessee Health Science Center, Memphis, Tennessee, USA.
FASEB J. 2012 Sep;26(9):3901-15. doi: 10.1096/fj.12-208975. Epub 2012 Jun 8.
We define previously unrecognized in vivo pathways of vitamin D(3) (D3) metabolism generating novel D3-hydroxyderivatives different from 25-hydroxyvitamin D(3) [25(OH)D3] and 1,25(OH)(2)D3. Their novel products include 20-hydroxyvitamin D(3) [20(OH)D3], 22(OH)D3, 20,23(OH)(2)D3, 20,22(OH)(2)D3, 1,20(OH)(2)D3, 1,20,23(OH)(3)D3, and 17,20,23(OH)(3)D3 and were produced by placenta, adrenal glands, and epidermal keratinocytes. We detected the predominant metabolite [20(OH)D3] in human serum with a relative concentration ∼20 times lower than 25(OH)D3. Use of inhibitors and studies performed with isolated mitochondria and purified enzymes demonstrated involvement of the steroidogenic enzyme cytochrome P450scc (CYP11A1) as well as CYP27B1 (1α-hydroxylase). In placenta and adrenal glands with high CYP11A1 expression, the predominant pathway was D3 → 20(OH)D3 → 20,23(OH)(2)D3 → 17,20,23(OH)(3)D3 with further 1α-hydroxylation, and minor pathways were D3 → 25(OH)D3 → 1,25(OH)(2)D3 and D3 → 22(OH)D3 → 20,22(OH)(2)D3. In epidermal keratinocytes, we observed higher proportions of 22(OH)D3 and 20,22(OH)(2)D3. We also detected endogenous production of 20(OH)D3, 22(OH) D3, 20,23(OH)(2)D3, 20,22(OH)(2)D3, and 17,20,23(OH)(3)D3 by immortalized human keratinocytes. Thus, we provide in vivo evidence for novel pathways of D3 metabolism initiated by CYP11A1, with the product profile showing organ/cell type specificity and being modified by CYP27B1 activity. These findings define the pathway intermediates as natural products/endogenous bioregulators and break the current dogma that vitamin D is solely activated through the sequence D3 → 25(OH)D3 → 1,25(OH)(2)D3.
我们定义了维生素 D（3）（D3）代谢的先前未被识别的体内途径，生成了不同于 25-羟维生素 D（3）[25（OH）D3]和 1,25（OH）（2）D3 的新型 D3-羟基衍生物。它们的新型产物包括 20-羟维生素 D（3）[20（OH）D3]、22（OH）D3、20,23（OH）（2）D3、20,22（OH）（2）D3、1,20（OH）（2）D3、1,20,23（OH）（3）D3 和 17,20,23（OH）（3）D3，由胎盘、肾上腺和表皮角质形成细胞产生。我们在人血清中检测到主要代谢产物[20（OH）D3]，其相对浓度比 25（OH）D3 低约 20 倍。使用抑制剂和使用分离的线粒体和纯化的酶进行的研究表明，类固醇生成酶细胞色素 P450scc（CYP11A1）以及 CYP27B1（1α-羟化酶）参与其中。在高 CYP11A1 表达的胎盘和肾上腺中，主要途径是 D3→20（OH）D3→20,23（OH）（2）D3→17,20,23（OH）（3）D3，进一步进行 1α-羟化，次要途径是 D3→25（OH）D3→1,25（OH）（2）D3 和 D3→22（OH）D3→20,22（OH）（2）D3。在表皮角质形成细胞中，我们观察到 22（OH）D3 和 20,22（OH）（2）D3 的比例较高。我们还通过永生化人角质形成细胞检测到内源性 20（OH）D3、22（OH）D3、20,23（OH）（2）D3、20,22（OH）（2）D3 和 17,20,23（OH）（3）D3 的产生。因此，我们提供了体内证据证明 CYP11A1 启动的 D3 代谢的新途径，其产物谱显示出器官/细胞类型特异性，并受 CYP27B1 活性的修饰。这些发现将这些途径中间体定义为天然产物/内源性生物调节剂，并打破了维生素 D 仅通过序列 D3→25（OH）D3→1,25（OH）（2）D3 激活的当前教条。
