Schroeder Neil J, Burrin Jacky M, Noonan Kate, Makin Hugh L J, Cunningham John
Department of Endocrinology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, London, UK.
Nephron Physiol. 2003;94(4):p62-73. doi: 10.1159/000072519.
New 'non-calcaemic' analogues of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are entering the clinical arena and some of them have been shown to have differential effects in bone. This may have a bearing on the evolution of bone lesions in uraemic patients receiving vitamin D therapies. A potential mechanism for differential effects of analogues lies in their target cell inactivation.
Using a human osteoblastic cell line, MG-63, three analogues, 22-oxacalcitriol (OCT), 19-nor-1,25-dihydroxyvitamin D2 (paricalcitol) and 1alpha,25-dihydroxydihydrotachysterol2(1,25(OH)2DHT2), were compared with 1,25(OH)2D3 for (1) their affinity for the vitamin D receptor (VDR) by competitive displacement of tritiated 1,25(OH)2D3 from calf thymus VDR; (2) effects on 24-hydroxylase mRNA expression using comparative RT-PCR, and (3) rates of metabolism, using high performance liquid chromatography, over a 24-hour time course.
Relative VDR-binding affinities (IC50) were 1,25(OH)2D3 (100%), OCT (25%), paricalcitol (14%) and 1,25(OH)2DHT2 (0.3%). A > or =3-fold increase in 24-hydroxylase mRNA expression was observed for all compounds at 2 h peaking at 7- to 8-fold above control levels by 12 h, with no significant difference between the analogues and 1,25(OH)2D3. Differences in their rates of metabolism were observed [calculated t(1/2) values = OCT (1.2 h) > paricalcitol (2.3 h) > 1,25(OH)2D3 (2.6 h) > 1,25(OH)2DHT2 (3.4 h)], with OCT having a significantly shorter half-life.
In MG-63 cells these analogues up-regulate 24-hydroxylase mRNA expression with similar potency, in each case accelerating ligand inactivation, despite significant differences in VDR affinity. VDR affinity did not correspond to either 24-hydroxylase mRNA expression or the rates of ligand disappearance, suggesting cellular metabolism is one of several factors that determine the analogue specificity of these agents in bone.
1,25 - 二羟基维生素D3（1,25(OH)2D3）的新型“非钙血症”类似物正在进入临床领域，其中一些已显示出对骨骼有不同的作用。这可能与接受维生素D治疗的尿毒症患者骨病变的演变有关。类似物产生不同作用的一个潜在机制在于其靶细胞失活。
使用人成骨细胞系MG - 63，将三种类似物，即22 - 氧代骨化三醇（OCT）、19 - 去甲 - 1,25 - 二羟基维生素D2（帕立骨化醇）和1α,25 - 二羟基二氢速甾醇2（1,25(OH)2DHT2）与1,25(OH)2D3进行比较，以研究：（1）通过从小牛胸腺维生素D受体（VDR）竞争性置换氚标记的1,25(OH)2D3来测定它们对VDR的亲和力；（2）使用比较逆转录 - 聚合酶链反应（RT - PCR）检测对24 - 羟化酶mRNA表达的影响；（3）使用高效液相色谱法在24小时时间进程中测定代谢速率。
相对VDR结合亲和力（IC50）分别为1,25(OH)2D3（100%）、OCT（25%）、帕立骨化醇（14%）和1,25(OH)2DHT2（0.3%）。所有化合物在2小时时24 - 羟化酶mRNA表达均增加≥3倍，在12小时时达到比对照水平高7至8倍的峰值，类似物与1,25(OH)2D3之间无显著差异。观察到它们代谢速率的差异[计算的t(1/2)值 = OCT（1.2小时）>帕立骨化醇（2.3小时）> 1,25(OH)2D3（2.6小时）> 1,25(OH)2DHT2（3.4小时）]，OCT的半衰期明显更短。
在MG - 63细胞中，尽管这些类似物的VDR亲和力存在显著差异，但它们以相似的效力上调24 - 羟化酶mRNA表达，每种情况均加速配体失活。VDR亲和力与24 - 羟化酶mRNA表达或配体消失速率均不对应，表明细胞代谢是决定这些药物在骨骼中类似物特异性的几个因素之一。
