Effects Of Hyperbaric Oxygen On The Expression Of Osteoprotegerin And Integrinβ1in Rabbit’s Mandibular Distraction Area

Background: Distraction Osteogenesis（DO）is technique that bone can be lengthened andwidened by gradual distraction after osteotomy through its self coalescencemechanism.Ilizalov fist reported using DO to treat lower limbs cripetura and presented thefamous Law of Tension Stress (LTS).In1992,McCarthy et al reported that they successfullytreated four cases of mandible deformity with distraction osteogenesis.More than twenty yearshas passed,DO has become a important therapy for correcting complex craniomaxillofacialdeformities and defects,which are difficult to treat with conventional surgery. During the DOprocess,the rate of new bone formation could be three to five times faster than that inchildhood.At the same time,soft tissue can also be extened,this realy reduce the recurerncerate,and is superior to conventional surgery.Unfortunately,the distraction rate is limited duringthat process.On the other hand,it’s long treatment course requires distraction devices stay inthe body for quite a long period of time to make sure the new bone maturation and avoidfracture or nonunion,this may lead to several complications, bring mental and physiologicalload.and.Therefore, seeking effective methods to promote new bone formation, shortentreatment course and reduce the complications has become a hot issue.Under thesecircumstances，some assistant methods could enhance new bone formation，improve curativeeffect.Our previous study showed that HBOT could promote the expression of certain growthfactors，increase bone mineral density and bone strength in the distraction gap at differentdistraction rate.Thus we suppose HBOT may affect the expression of Osteoprotegerin andintegrinβ1so as to promote osteoblasts proliferation and differentiation,promote new boneformation.Objective: We observed the effect of Hyperbaric-oxygen therapy(HBOT) on OPG and Itgβ1 expression during mandibular distraction osteogenesis,investigated the probable mechanismthat how Hyperbaric-oxygen therapy promote new bone formation during DO. We expectedto provide certain experimental and theory basis for clinical use of HBOT.Methods:Forty New-Zealand rabbits were used. The animals were divided into two groups of20animals each, and bilateral mandibular distraction osteogenesis was performed. After the3-day latency period,distraction started at the rate of4mm/12h for10continuousdays.Animals from experimental group were exposed to2ATA Hyperbaric oxygen for90minutes once a day since the start of distraction,and last for four weeks,in contrast,controlgroup recieved no other treatment。Five animals of each group were sacrificed at the four timepoints in consolidation period(1st day,1st week2nd week,4th week).Right mandibles wereharvested.HE stain was performed to obverse the histological change in the distraction gapwhile IHC stain was performed to detect OPG and Itgβ1expression.Semi-quantitativeanalysis was carried out by image analysis software.Results: All rabbits’ mandible were successfully lengthened.HE stain showed that on the fistday of consolidation,a large number of capillaries and inflammatory cells were observed,andcollagen fibers were parallel to the distraction direction.Both osteogenic precursor cells andosteoblasts of HBOT group were more active than that of control group.A little osteoid matrixcould be observed too. At the1st week of consolidation period,bone trabecula that wereparallel to the distraction direction could be seen in each group.Around the trabeculae were alarge mount of osteoblasts.Trabeculae in HBOT group were wider than control group.Aftertwo weeks’ consolidation,trabeculae increased and regularly distributed. Cartilaginous tissuewas observed in control group.At the4th week of consolidation period,the distraction gap wastotally synostosis,no fibrous union was found.IHC stain showed that OPG located mostly onthe cell membrane and in cytoplasm of osteoprogenitor cells and osteoblasts.The expressionof OPG increased after distraction ceased and reached a peak at the1st week ofconsolidation,then decreased gradually.OPG expression in HBOT group was significantlyhigher than that of control group at all time points(p<0.01).OPG decreased obviously in both group after four weeks’ consolidation.Itg β1mainly located in actively proliferatingosteoblasts, fibroblasts and mesenchymal cells.Its expression decreased significantly since thefist day of consolidation period.Animals underwent HBOT had significantly higher Itgβ1atthe fist two time points than control group(p<0.01).The difference was still of statisticalsignificance after two weeks’ consolidation(0.01<p<0.05).At last,the expression of Itgβ1dropped to a very low level.The comparison between the two groups had no statisticalsignificance (p>0.05).Conclusion:1. Hyperbaric-oxygen therapy can up-regulate the expression of OPG and Itgβ1in the distraction area,promote osteoblast differentiation,proliferation,enhance osteoblastfunction,so as to promote bone formation.2.The expression of OPG was positive correlatedwith Itgβ1.We suppose these two substances may cooperate with each other in the process ofbone repair.