Effects of selective prostaglandin EP4 receptor antagonist on osteoclast formation and bone resorption in vitro

• Published in: Bone (New York, N.Y.) Vol. 30; no. 1; pp. 159 - 163
• Main Authors: TOMITA, M, LI, X, OKADA, Y, WOODIEL, F. N, YOUNG, R. N, PILBEAM, C. C, RAISZ, L. G
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Science 2002
• Subjects: Acid Phosphatase - metabolism; Animals; Biological and medical sciences; Bone Marrow Cells - cytology; Bone Marrow Cells - drug effects; Bone Marrow Cells - metabolism; Bone Resorption - chemically induced; Bone Resorption - metabolism; Bone Resorption - pathology; Carrier Proteins - genetics; Cyclic AMP - biosynthesis; Dinoprostone - pharmacology; Fundamental and applied biological sciences. Psychology; Gene Expression - drug effects; In Vitro Techniques; Isoenzymes - metabolism; Membrane Glycoproteins - genetics; Mice; Mice, Inbred C57BL; Osteoclasts - cytology; Osteoclasts - drug effects; Osteoclasts - metabolism; Parathyroid Hormone - pharmacology; RANK Ligand; Rats; Rats, Sprague-Dawley; Receptor Activator of Nuclear Factor-kappa B; Receptors, Prostaglandin E - antagonists & inhibitors; Receptors, Prostaglandin E, EP4 Subtype; RNA, Messenger - genetics; RNA, Messenger - metabolism; Skeleton and joints; Tartrate-Resistant Acid Phosphatase; Vertebrates: osteoarticular system, musculoskeletal system; Cell culture; Rodentia; Cyclic AMP; Prostaglandin E2; Resorption; Osteoclast; Experimental study; In vitro; Osteoarticular system; Vertebrata; Mammalia; Mouse; Animal; Antagonist; Biological effect; Bone; EP4 prostanoid receptor; Biological receptor
• ISSN: 8756-3282; 1873-2763
• 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.