Fan S L, Schroeder N J, Calverley M J, Burrin J M, Makin H L, Cunningham J
Department of Nephrology, St Bartholomew's and the Royal London School of Medicine and Dentistry, London, UK.
Nephrol Dial Transplant. 2000 Dec;15(12):1943-9. doi: 10.1093/ndt/15.12.1943.
Dihydrotachysterol(2), a licensed pharmaceutical, is hydroxylated to 25-hydroxydihydrotachysterol(2) (25(OH)DHT(2)) and 1 alpha,25-dihydroxydihydrotachysterol(2) (1 alpha,25(OH)(2)DHT(2)) in man. We have compared the biological activity of these metabolites with calcitriol and the 'non-calcaemic' analogue, 22-oxacalcitriol (OCT) in bovine parathyroid cell cultures and in rats.
The effect of each sterol on parathyroid hormone (PTH) secreted by primary bovine parathyroid cells was measured. High-performance liquid chromotography and gas chromotography-mass spectrometry were used to investigate in vitro 25(OH)DHT(2) metabolism. Rats were given a single intraperitoneal injection or five daily injections of each sterol, and changes in ionized calcium and PTH were measured.
In vitro, all sterols suppressed PTH significantly. Calcitriol and OCT were of similar potency, but 1 alpha, 25(OH)(2)DHT(2) and 25(OH)DHT(2) required higher concentrations to suppress PTH equally. We were unable to detect metabolism of 25(OH)DHT(2) to 1 alpha,25(OH)(2)DHT(2) in vitro. In rats, a single dose of 0.5 microg/rat of calcitriol increased ionized calcium at 30 and 40 h (statistically significant at 48 h). 50 microg of OCT and 1 alpha,25(OH)(2)DHT(2) did not cause significant hypercalcaemia at 48 h, although 1 alpha,25(OH)(2)DHT(2) caused hypercalcaemia at 30 h. In contrast, 50 microg of 25(OH)DHT(2) caused hypercalcaemia at 48 h but not at 30 h. Five daily doses of 0.001 microg/rat of calcitriol caused a significant rise in calcium and a 50% fall in PTH. OCT and 1 alpha,25(OH)(2)DHT(2) at 0.025 and 0.5 microg/rat respectively caused similar suppression of PTH but without hypercalcaemia.
1 alpha,25(OH)(2)DHT(2) and 25(OH)DHT(2) are potent suppressors of PTH in vitro and in vivo. 25(OH)DHT(2) may be active by virtue of its pseudo-1 alpha-hydroxyl group. Hypercalcaemia caused by a single dose of 1 alpha,25(OH)(2)DHT(2) appeared to be more transient than calcitriol. Five daily doses of 1 alpha, 25(OH)(2)DHT(2) and OCT could achieve 50% suppression of PTH without significant increments in ionized calcium. In contrast, suppression of PTH by calcitriol was associated with significant increments in ionized calcium. These data suggest that like OCT, 1 alpha, 25(OH)(2)DHT(2) can dissociate calcaemic actions from parathyroid-suppressing actions in a manner that may be therapeutically useful.
已获许可的药物二氢速甾醇（2）在人体内会羟基化为25-羟基二氢速甾醇（2）（25(OH)DHT(2)）和1α,25-二羟基二氢速甾醇（2）（1α,25(OH)(2)DHT(2)）。我们已在牛甲状旁腺细胞培养物和大鼠中比较了这些代谢物与骨化三醇以及“非血钙升高”类似物22-氧杂骨化三醇（OCT）的生物活性。
测定了每种甾醇对原代牛甲状旁腺细胞分泌的甲状旁腺激素（PTH）的影响。采用高效液相色谱法和气相色谱-质谱法研究体外25(OH)DHT(2)的代谢情况。给大鼠单次腹腔注射或每日注射五次每种甾醇，并测定离子钙和PTH的变化。
在体外，所有甾醇均能显著抑制PTH。骨化三醇和OCT的效力相似，但1α,25(OH)(2)DHT(2)和25(OH)DHT(2)需要更高浓度才能同等程度地抑制PTH。我们在体外未能检测到25(OH)DHT(2)代谢为1α,25(OH)(2)DHT(2)。在大鼠中，单次给予每只大鼠0.5微克骨化三醇会在30和40小时时使离子钙升高（在48小时时具有统计学意义）。50微克OCT和1α,25(OH)(2)DHT(2)在48小时时未引起显著的高钙血症，尽管1α,25(OH)(2)DHT(2)在30小时时引起了高钙血症。相比之下，50微克25(OH)DHT(2)在48小时时引起了高钙血症，但在30小时时未引起。每日五次给予每只大鼠0.001微克骨化三醇会使钙显著升高且PTH降低50%。分别给予每只大鼠0.025微克和0.5微克的OCT和1α,25(OH)(2)DHT(2)会引起类似的PTH抑制，但无高钙血症。
1α,25(OH)(2)DHT(2)和25(OH)DHT(2)在体外和体内均是PTH的有效抑制剂。25(OH)DHT(2)可能因其假1α-羟基而具有活性。单次给予1α,25(OH)(2)DHT(2)引起的高钙血症似乎比骨化三醇更短暂。每日五次给予1α,25(OH)(2)DHT(2)和OCT可实现PTH抑制50%，而离子钙无显著升高。相比之下，骨化三醇抑制PTH与离子钙显著升高相关。这些数据表明，与OCT一样，1α,25(OH)(2)DHT(2)可以以一种可能具有治疗用途的方式将血钙升高作用与甲状旁腺抑制作用分离。
