Tomita M, Li X, Okada Y, Woodiel F N, Young R N, Pilbeam C C, Raisz L G
Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030, USA.
Bone. 2002 Jan;30(1):159-63. doi: 10.1016/s8756-3282(01)00688-3.
Prostaglandin estradiol (PGE(2)) stimulates bone resorption by a cyclic AMP (cAMP)-dependent mechanism that involves prostaglandin E receptors of the EP2 and EP4 subtypes. We tested a potent selective EP4 antagonist (EP4RA), which blocks PGE(2) binding to EP4 receptors. We examined the effects of EP4RA on osteoclastogenesis in murine marrow cultures, on cAMP production in primary osteoblastic (POb) cell cultures, and on bone resorption in organ cultures. EP4RA (1 micromol/L) decreased the number of tartrate-resistant acid phosphatase-positive multinucleated cells (TRAP(+) MNC) by 46%-48% in cultures treated with 0.1-1.0 micromol/L PGE(2) and by 96% in cultures treated with 0.01 micromol/L PGE(2). EP4RA also decreased TRAP(+) MNC formation by 60% in 1,25-dihydroxyvitamin D (1,25D)-treated cultures and by 62% in parathyroid hormone (PTH)-treated cultures. A chemically related analog of EP4RA that lacks antagonist activity did not inhibit TRAP(+) MNC formation. EP4RA decreased cAMP production in PGE(2)-treated POb by 44% but did not block cAMP response to PTH. EP4RA inhibited the increase in receptor activator of NF-kappaB ligand (RANKL) mRNA levels produced by PGE(2). In fetal rat long bone cultures, EP4RA decreased 45Ca release from control, unstimulated cultures by 12%-25% and from PGE(2)-stimulated cultures by 22%-37%. Because EP4RA partially inhibited osteoclastogenesis not only in response to PGE(2) but also in response to 1,25D and PTH, these results suggest that activation of the EP4 receptor may play a general role in osteoclastic bone resorption. EP4RA showed partial inhibition of PGE(2)-stimulated osteoclastogenesis at 1 micromol/L, but almost complete inhibition at 0.01 micromol/L PGE(2). This could be due to the limited efficacy of the antagonist at high concentrations of PGE(2), or an alternative pathway, such as activation of the EP2 receptor.
前列腺素雌二醇(PGE(2))通过一种依赖环磷酸腺苷(cAMP)的机制刺激骨吸收,该机制涉及EP2和EP4亚型的前列腺素E受体。我们测试了一种有效的选择性EP4拮抗剂(EP4RA),它可阻断PGE(2)与EP4受体的结合。我们研究了EP4RA对小鼠骨髓培养物中破骨细胞生成、原代成骨细胞(POb)培养物中cAMP产生以及器官培养物中骨吸收的影响。在经0.1 - 1.0微摩尔/升PGE(2)处理的培养物中,EP4RA(1微摩尔/升)使抗酒石酸酸性磷酸酶阳性多核细胞(TRAP(+) MNC)的数量减少了46% - 48%,在经0.01微摩尔/升PGE(2)处理的培养物中减少了96%。EP4RA还使经1,25 - 二羟基维生素D(1,25D)处理的培养物中TRAP(+) MNC的形成减少了60%,在经甲状旁腺激素(PTH)处理的培养物中减少了62%。一种缺乏拮抗剂活性但化学结构相关的EP4RA类似物并未抑制TRAP(+) MNC的形成。EP4RA使经PGE(2)处理的POb中cAMP的产生减少了44%,但并未阻断对PTH的cAMP反应。EP4RA抑制了PGE(2)诱导的核因子κB受体活化因子配体(RANKL)mRNA水平的升高。在胎鼠长骨培养物中,EP4RA使对照未刺激培养物中的45Ca释放减少了12% - 25%,使经PGE(2)刺激的培养物中的45Ca释放减少了22% - 37%。由于EP4RA不仅部分抑制了对PGE(2)的破骨细胞生成反应,还抑制了对1,25D和PTH的反应,这些结果表明EP4受体的激活可能在破骨细胞性骨吸收中起普遍作用。EP4RA在1微摩尔/升时对PGE(2)刺激的破骨细胞生成表现出部分抑制作用,但在0.01微摩尔/升PGE(2)时几乎完全抑制。这可能是由于拮抗剂在高浓度PGE(2)时疗效有限,或者是由于存在替代途径,如EP2受体的激活。