Inhibition of cyclo-oxigenase-2 activity does not abolish the anabolic effect of prostaglandin E2 in vivo or in vitro

Abstract

It was previously reported that the expression of cyclooxigenase-2 (COX-2) is induced by prostaglandin E 2 (PGE 2 ) in vitro in an osteogenic cell line and organ culture, suggesting an autoamplification mechanism. In this study, we first tested whether this phenomenon also occurs in bone tissue in vivo and found that a single anabolic dose of PGE 2 (5 mg/kg) induced (between 30 and 120 min) in rat tibiae, an increase in the mRNA level of COX-2 (2·5-to 9-fold) but not that of COX-1. Secondly, to test whether COX-2 activity in generating endogenous prostaglandins (PGs) is required for the in vivo anabolic properties of PGE 2 , young male rats were injected daily with either vehicle (8% ethanol) or 5 mg/kg PGE 2 for 21 days. PGE 2 -injected rats received, 45 min prior to PGE 2 , either dimethyl sulphoxide (as vehicle) or one of two doses of NS-398, a selective COX-2 inhibitor: a low dose (3 mg/kg) or a high dose (10 mg/kg). PGE 2 increased bone formation (measured as cancellous mineralizing surface, mineral apposition rate and bone formation rate) and bone mass (measured as cancellous bone area and surface and cortical width). None of these increases was suppressed by pre-administration of NS-398. In contrast, the high dose of NS-398 effectively suppressed an increase in rat hind-paw volume induced by a local carrageenan injection. Furthermore, since COX-2 inactivation may affect PG receptor expression, we found that preadministration of NS-398 did not abolish the induction in EP 4 receptor mRNA levels, caused by PGE 2 in rat bone tissue. For in vitro testing, rat femoral bone marrow stromal cell cultures were initiated and were incubated in the absence or presence of PGE 2 at 100 nM (as an inducer) and with increasing concentrations of NS-398 (10 8 M to 10 5 M) for 21 days, after which time mineralized (Von-Kossa positive) nodules were counted. PGE 2 increased nodule formation as previously reported; however, NS-398 reduced nodule formation in both control and PGE 2 -treated cultures to the same extent. We conclude that while the level of COX-2 mRNA is increased in vivo by administration of PGE 2 , inhibition of its activity (i.e. generation of endogenous PGs) does not abolish the anabolic effect of PGE 2 .

Localization of cyclooxygenase-2 in mice vas deferens and its effects on fertility upon suppression using nimesulide—A preferential cyclooxygenase-2 inhibitor

“…Interestingly there is a rise in PG levels in 15 and 45 days treatment groups this might be due to compensation by COX-1 for the loss of COX-2 or another isoform COX-3 that might have been involved (Chandrasekaran et al, 2002). It has also been reported that synthesis of PGs are independent of COX (Weinreb et al, 2002).…”

AGEs induce caspase-mediated apoptosis of rat BMSCs via TNFα production and oxidative stress

“…Since diabetes in vivo increases the apoptosis of mature osteoblasts (Motyl et al 2012), we hypothesized that the differentiation of cells due to DEX treatment might render them more sensitive to the apoptosis induced by AGE-BSA. BMSCs were treated with 10 nM DEX for 6 days (a regimen that we have repeatedly used to induce osteoblastic differentiation in rat BMSCs (Weinreb et al 2002(Weinreb et al , 2004) and then exposed to 400 mg/ml AGE-BSA for 16 h. Exposure to DEX, by itself, slightly increased the apoptosis of control cells (9 vs 6%); however, whereas AGE-BSA increased the apoptosis of BMSCs not treated with DEX about twofold, it increased apoptosis of DEXtreated BMSCs threefold (Fig. 4).…”

“…One explanation is that DEX treatment induces osteoblastic differentiation in BMSCs (evidenced by the acquirement of alkaline phosphatase activity and the production of mineralized extracellular matrix (Rickard et al 1994, Weinreb et al 2002) and by doing so renders them more sensitive to AGEs-induced apoptosis (Roszer 2011). This notion stems from the observations that diabetes increases the apoptosis of mature osteoblasts in vivo , Motyl et al 2012.…”

Shear-induced Cyclooxygenase-2 via a JNK2/c-Jun-dependent Pathway Regulates Prostaglandin Receptor Expression in Chondrocytic Cells

“…COX-1, but not COX-2, has been implicated in the regulation of the expression of the prostaglandin receptors in cervical carcinomas (18). On the other hand, inactivation of COX-2 has been reported to increase EP3 and EP4 receptor expression in a murine kidney cell line (19), although it failed to interfere with it in an osteogenic cell line (20). Nevertheless, the effects of mechanical stimuli and COX activity on the regulation of prostaglandin receptors in chondrocytic cells have yet to be examined.…”