title: Identification of α2-macroglobulin as a master inhibitor of cartilage-degrading factors that attenuates the progression of posttraumatic osteoarthritis.
abstract: OBJECTIVE
  To determine if supplemental intraarticular α2-macroglobulin (α2 M) has a chondroprotective effect in a rat model of osteoarthritis (OA).
  
  
  METHODS
  Using Western blotting, mass spectrometry, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry, α2 M was identified as a potential therapeutic agent through a comparison of α2 M concentrations in serum, synovial fluid (SF), and cartilage from normal subjects and patients with OA. In cultured chondrocytes, the effects of α2 M on interleukin-1 (IL-1)-induced cartilage catabolic enzymes were evaluated by Luminex assay and ELISA. In vivo effects on cartilage degeneration and matrix metalloproteinase 13 (MMP-13) concentration were evaluated in male rats (n = 120) randomized to 1 of 4 treatments: 1) anterior cruciate ligament transection (ACLT) and saline injections, 2) ACLT and 1 IU/kg injections of α2 M, 3) ACLT and 2 IU/kg injections of α2 M, or 4) sham operation and saline injections. Rats were administered intraarticular injections for 6 weeks. The concentration of MMP-13 in SF lavage fluid was measured using ELISA. OA-related gene expression was quantified by real-time quantitative polymerase chain reaction. The extent of OA progression was graded by histologic examination.
  
  
  RESULTS
  In both normal subjects and OA patients, α2 M levels were lower in SF as compared to serum, and in OA patients, MMP-13 levels were higher in SF than in serum. In vitro, α2 M inhibited the induction of MMP-13 by IL-1 in a dose-dependent manner in human chondrocytes. In the rat model of ACLT OA, supplemental intraarticular injection of α2 M reduced the concentration of MMP-13 in SF, had a favorable effect on OA-related gene expression, and attenuated OA progression.
  
  
  CONCLUSIONS
  The plasma protease inhibitor α2 M is not present in sufficient concentrations to inactivate the high concentrations of catabolic factors found in OA SF. Our findings suggest that supplemental intraarticular α2 M provides chondral protection in posttraumatic OA.
authors.affiliation: Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, Rhode Island; The Second Hospital of Shanxi Medical University, Taiyuan, Shanxi, China, and Zhejiang University School of Medicine, Hangzhou, Zhejiang, China.
authors.forename: Shaowei
authors.initials: S
authors.lastname: Wang
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Wei
authors.forename: Jingming
authors.initials: J
authors.lastname: Zhou
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Kai
authors.initials: K
authors.lastname: Li
authors.forename: Qian
authors.initials: Q
authors.lastname: Chen
authors.forename: Richard
authors.initials: R
authors.lastname: Terek
authors.forename: Braden C
authors.initials: BC
authors.lastname: Fleming
authors.forename: Mary B
authors.initials: MB
authors.lastname: Goldring
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ehrlich
authors.forename: Ge
authors.initials: G
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Wei
mesh_terms: D000368:Aged; D000818:Animals; D016118:Anterior Cruciate Ligament / Q000378:metabolism; D000070598:Anterior Cruciate Ligament Injuries; D002356:Cartilage / Q000378:metabolism; D019902:Chondrocytes / Q000166:cytology / Q000187:drug effects*; D004195:Disease Models, Animal; D018450:Disease Progression; D005260:Female; D006801:Humans; D007270:Injections, Intra-Articular; D007718:Knee Injuries / Q000150:complications / Q000188:drug therapy* / Q000473:pathology; D008297:Male; D053509:Matrix Metalloproteinase 13 / Q000097:blood / Q000378:metabolism; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000188:drug therapy* / Q000209:etiology / Q000473:pathology; D061251:Primary Cell Culture; D011897:Random Allocation; D051381:Rats; D013582:Synovial Fluid / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000511:alpha-Macroglobulins; C507079:MMP13 protein, human; D053509:Matrix Metalloproteinase 13; C507083:Mmp13 protein, rat