ON THE MECHANISMS FOR THE SELECTIVE ACTION OF VITAMIN-D ANALOGS
ON THE MECHANISMS FOR THE SELECTIVE ACTION OF VITAMIN-D ANALOGS
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DOI：
10.1210/endo-128-4-1687
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发表时间：
1991-04-01
期刊：
影响因子：
4.8
通讯作者：
BROWN, AJ
中科院分区：
文献类型：
--
作者：
DUSSO, AS;NEGREA, L;BROWN, AJ
已经开发了多种具有比1，25-（OH）2D 3更低的钙离子活性和更低的受体结合亲和力的1，25-（OH）2D 3类似物。 然而，这些化合物具有相同或更大的分化白血病细胞和银屑病成纤维细胞的能力，并抑制PTH合成和分泌。 这种选择性的机制尚未阐明。 由于麦角钙化醇与胆钙化醇相比在预防或治疗雏鸡佝偻病方面的较低效力与禽类维生素D结合蛋白（DBP）对维生素D2的较低亲和力相关，我们测试了具有低钙活性的五种类似物，包括22-氧杂-1，25-（OH）2D 3（OCT）、MC 903、1，25-（OH）2-16烯-23-炔D3，1，25-（OH）2D 3（OCT）、MC 903、1，25-（OH）2-16烯-23-炔D3、1，25-（OH）2- 26，27二高-22-烯-D3和1，25-（OH）2-24-三高-22-烯-D3对大鼠血清DBP的亲和力。 所有类似物对DBP的亲和力都很低，比1，25-（OH）2D 3的亲和力低50-3000倍。 OCT也以低亲和力与犬和人血清DBP结合。 我们用OCT测试了其对血清DBP的低亲和力的可能后果。 DBP的功能之一是延长循环中1，25-（OH）2D 3的寿命。 使用单次推注技术在8只正常犬中定量OCT的代谢清除率（MCR），结果显示OCT的清除率为48.2 +/- 7.5 ml/min，比1，25-（OH）2D 3（6.8 +/- 0.4 ml/min）快约6-7倍。 OCT在循环中的估计半衰期为2.5 +/- 0.3 h，而1，25-（OH）2D 3为7.0 +/- 0.6 h; n = 7。 由于我们的主要兴趣是OCT在治疗CRF继发性甲状旁腺功能亢进中的潜力，我们还在5/6只肾切除犬中测量了OCT的MCR。 尿毒症不影响OCT从循环中的清除率（MCR：56.8 ± 4.5; t1/2 = 2.1 ± 0.2 n = 4）。 尽管OCT的半衰期较短，但在尿毒症犬体内可抑制PTH分泌。 使用超滤程序测定与DBP的低结合对游离甾醇百分比的影响。 我们比较了0. 1% BSA-PBS中游离（未结合）OCT和1，25-（OH）2D 3的比例，人血清浓度范围为0- 25%。 对于每个检测的血清浓度，游离形式的OCT比例均显著高于1，25-（OH）2D 3。 在正常人巨噬细胞中测试了较高百分比的游离OCT的生理相关性。 1，25-（OH）2D 3和OCT（100 pg/ml）均显著刺激维生素D catalysts。 孵育培养基中血清的存在以剂量依赖性方式降低了这两种化合物的刺激，表明游离形式的甾醇是造成这种效应的原因。 由于游离OCT的比例较高，对于每个测试的血清浓度，该类似物在刺激维生素D catalysts方面比1，25-（OH）2D 3更有效。 未结合活性形式中较高比例的OCT可能抵消其较低的受体结合亲和力和更快的清除率。 这些实验表明，非钙甾醇类似物对DBP的低亲和力导致血清中游离、活性形式的比例更高，从循环中清除更快，因此，维生素D类似物选择性作用的替代机制可能是：1）需要特异性载体蛋白将甾醇递送到各种靶组织; 2）类似物和母体激素之间的药代动力学差异; 3）不同靶细胞优先摄取游离或结合形式;和4）不同靶组织中不同的细胞内信号传导。
A variety of analogs of 1,25-(OH)2D3 with less calcemic activity and lower receptor binding affinity than 1,25-(OH)2D3 have been developed. However, these compounds have equal or greater ability to differentiate leukemia cells and psoriatic fibroblasts and to suppress PTH synthesis and secretion. The mechanism for this selectivity has not been elucidated. Because the lower potency of ergocalciferol compared to cholecalciferol in preventing or curing rickets in chicks was associated with a lower affinity of the avian vitamin D binding protein (DBP) for vitamin D2, we tested five analogs with low calcemic activity including 22-oxa-1,25-(OH)2D3 (OCT), MC903, 1,25-(OH)2-16 ene-23-yne D3, 1,25-(OH)2D3 (OCT), MC903, 1,25-(OH)2-16 ene-23-yne D3, 1,25-(OH)2-26,27 dihomo-22-ene-D3, and 1,25-(OH)2-24-trihomo-22-ene-D3 for their affinity for rat serum DBP. All analogs had a low affinity for DBP, ranging from 50-3000 times less than that of 1,25-(OH)2D3. OCT also bound with low affinity to dog and human serum DBP. We tested with OCT the possible consequences of its low affinity for serum DBP. One of the functions of DBP is to prolong the lifetime of 1,25-(OH)2D3 in circulation. Quantification of the metabolic clearance rate (MCR) of OCT in 8 normal dogs using a single bolus injection technique showed that OCT was cleared at a rate of 48.2 +/- 7.5 ml/min, approximately 6-7 times more rapidly than 1,25-(OH)2D3 (6.8 +/- 0.4 ml/min). The estimated half-life of OCT in the circulation was 2.5 +/- 0.3 h compared to 7.0 +/- 0.6; n = 7 for 1,25-(OH)2D3. As our primary interest is the potential of OCT in treating the secondary hyperparathyroidism of CRF, we also measured the MCR of OCT in 5/6 nephrectomized dogs. Uremia does not affect the rate of clearance of OCT from the circulation (MCR: 56.8 +/- 4.5; t1/2 = 2.1 +/- 0.2 n = 4). Despite its shorter half-life, OCT suppressed PTH secretion in vivo in uremic dogs. The effects of low binding to DBP on the percentage of free sterol were determined using an ultrafiltration procedure. We compared the proportion of free (unbound) OCT and 1,25-(OH)2D3 in 0.1% BSA-PBS with concentrations of human serum ranging from 0-25%. The proportion of OCT in the free form was significantly higher than that of 1,25-(OH)2D3 for every serum concentration tested. The physiological relevance of a higher percentage of free OCT was tested in normal human macrophages. Both 1,25-(OH)2D3 and OCT (100 pg/ml) significantly stimulated vitamin D catabolism. The presence of serum in the incubation media decreased this stimulation in a dose-dependent manner for both compounds, suggesting that the free form of the sterol was responsible for this effect. Due to a higher proportion of free OCT, the analog was more effective than 1,25-(OH)2D3 in stimulating vitamin D catabolism for every serum concentration tested. A higher proportion of OCT in the unbound active form may offset its lower receptor binding affinity and its more rapid clearance. These experiments demonstrate that the low affinity of the noncalcemic analogs for DBP results in a higher proportion of the free, active form in serum and more rapid clearance from the circulation.Therefore, alternative mechanisms for the selective action of vitamin D analogs may be: 1) the requirement of specific carrier proteins for the delivery of the sterol to various target tissues; 2) pharmacokinetic differences between the analog and the parent hormone; 3) preferential uptake of either the free or bound form by different target cells; and 4) different intracellular signaling in different target tissues.