Cyclooxygenase-2 inhibition selectively attenuates bone morphogenetic protein-6 synthesis and bone formation during guided tissue regeneration in a rat model.
OBJECTIVE
Bone formation during guided tissue regeneration is a tightly regulated process involving cells, extracellular matrix and growth factors. The aims of this study were (i) to examine the expression of cyclooxygenase-2 (COX-2) during bone regeneration and (ii) the effects of selective COX-2 inhibition on osseous regeneration and growth factor expression in the rodent femur model.


METHODS
A standardized transcortical defect of 5 x 1.5 mm was prepared in the femur of 12 male rats and a closed half-cylindrical titanium chamber was placed over the defect. The expression of COX-2 and of platelet-derived growth factor-B (PDGF-B), bone morphogenetic protein-6 (BMP-6) and insulin-like growth factor-I/II (IGF-I/II) was analyzed at Days 3, 7, 21 and 28 semiquantitatively by reverse transcriptase-polymerase chain reaction and immunohistochemistry. The effects of COX-2 inhibition by intraperitoneal injection of NS-398 (3 mg/kg/day) were analyzed in five additional animals sacrificed at Day 14.


RESULTS
Histomorphometry revealed that new bone formation occurred in the cortical defect area as well as in the supracortical region, i.e. region within the chamber by Day 7 and increased through Day 28. Immunohistochemical evidence of COX-2 and PDGF-B levels were observed early (i.e. Day 3) and decreased rapidly by Day 7. BMP-6 expression was maximal at Day 3 and slowly declined by Day 28. In contrast, IGF-I/II expression gradually increased during the 28-day period. Systemic administration NS-398 caused a statistically significant reduction (P<0.05) in new bone formation (25-30%) and was associated with a statistically significant reduction in BMP-6 protein and mRNA expression (50% and 65% at P<0.05 and P<0.01, respectively). PDGF-B mRNA or protein expression was not affected by NS-398 treatment.


CONCLUSIONS
COX-2 inhibition resulted in reduced BMP-6 expression and impaired osseous regeneration suggesting an important role for COX-2-induced signaling in BMP synthesis and new bone formation.
Damrongsri
Damrong
D
Department of Anatomy, School of Dentistry, Chulalongkorn University, Bangkok, Thailand.
Geva
Sarah
S
Salvi
Giovanni E
GE
Williams
Ray C
RC
Limwongse
Visaka
V
Offenbacher
Steven
S
D000818:Animals; D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis*; D001861:Bone Regeneration / Q000187:drug effects* / Q000502:physiology; D051546:Cyclooxygenase 2 / Q000096:biosynthesis*; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology*; D005269:Femur / Q000601:surgery; D006133:Growth Substances / Q000096:biosynthesis; D048091:Guided Tissue Regeneration / Q000379:methods; D007150:Immunohistochemistry; D008297:Male; D009578:Nitrobenzenes / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013449:Sulfonamides / Q000494:pharmacology*
C525818:Bmp6 protein, rat; D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins; D052246:Cyclooxygenase 2 Inhibitors; D006133:Growth Substances; D009578:Nitrobenzenes; D012333:RNA, Messenger; D013449:Sulfonamides; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D051546:Cyclooxygenase 2