Effects of hyperbaric oxygen on gene expressions of procollagen, matrix metalloproteinase and tissue inhibitor of metalloproteinase in injured medial collateral ligament and anterior cruciate ligament

Abstract Animal experiments were performed toinvestigate whether and how the administration ofhyperbaric oxygen (HBO) affects gene expressions ofprocollagens, matrix metalloproteinases (MMPs) andtissue inhibitors of metalloproteinases (TIMPs) in in jured medial collateral ligament (MCL) and anteriorcruciate ligament (ACL). In 64 Sprague-Dawley rats,the MCL of the left knee was lacerated at the mid substance, and the ACL of the left knee was laceratedadjacent to the tibial insertion in another 64 rats. Ofthese, 32 rats with lacerated MCL and 32 rats withlacerated ACL were housed in individual cages atnormal atmospheric pressure (Groups MC and AC,respectively), while the remaining 64 rats were exposedto 100% oxygen at 2.5 atmospheres absolute for 2 h for5 days a week (Groups MH and AH, respectively).Rats were sacrificed at 3, 7, 14 and 28 days postoper atively. After macroscopic examination, bilateralMCLs were harvested from Groups MC and MH, andbilateral ACLs from Groups AC and AH. Total RNAwas extracted from each specimen and gene expres sions of type I and type III procollagens, MMP-2, -9and -3, and TIMP-1 and -2 were estimated using semi quantitative reverse transcription-polymerase chainreaction (RT-PCR). Macroscopically, lacerated MCLhealed by scar tissue formation, the amount of whichappeared to be greater in Group MH than in GroupMC. In contrast, no lacerated ACLs united, and little,if any, differences were apparent in macroscopic find ings between Groups AH and AC. Gene expression oftype I procollagen was significantly greater in GroupMH than in Group MC at 7 days postoperatively andwas also significantly greater in Group AH than inGroup AC at 28 days (P < 0.05). No significant dif ferences in type III procollagen gene expression werenoted between Groups MH and MC or betweenGroups AH and AC. In addition, no significant dif ferences in gene expressions of MMPs were seen ineither ligament, except that gene expression of MMP 13 was significantly lower at 7 days in Group MH thanin Group MC (P < 0.05). Gene expressions of TIMPsdid not differ significantly between Groups MH andMC in each time interval, whereas gene expressions ofTIMPs were significantly greater in Group AH than inGroup AC at 7, 14 and 28 days for TIMP-1 and at 3, 7and 14 days for TIMP-2 (P < 0.05). RT-PCR resultssuggested that HBO enhances structural protein syn thesis and inhibits degradative processes by enhancingTIMP activities in the lacerated ACL. However, noneof the lacerated ACLs united macroscopically despiteadministration of HBO, indicating that the effect ofHBO is insufficient for healing of the injured ACL. IfHBO therapy is used as an adjunctive therapy afterprimary repair of the injured ACL, the success rate ofsurgery seems likely to be increased.