Identification of α2-macroglobulin as a master inhibitor of cartilage-degrading factors that attenuates the progression of posttraumatic osteoarthritis

Arthritis Rheumatol. 2014 Jul;66(7):1843-53. doi: 10.1002/art.38576.


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.

Conclusion: 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Animals
  • Anterior Cruciate Ligament / metabolism
  • Anterior Cruciate Ligament Injuries
  • Cartilage / metabolism
  • Chondrocytes / cytology
  • Chondrocytes / drug effects*
  • Disease Models, Animal
  • Disease Progression
  • Female
  • Humans
  • Injections, Intra-Articular
  • Knee Injuries / complications
  • Knee Injuries / drug therapy*
  • Knee Injuries / pathology
  • Male
  • Matrix Metalloproteinase 13 / blood
  • Matrix Metalloproteinase 13 / metabolism
  • Middle Aged
  • Osteoarthritis, Knee / drug therapy*
  • Osteoarthritis, Knee / etiology
  • Osteoarthritis, Knee / pathology
  • Primary Cell Culture
  • Random Allocation
  • Rats
  • Synovial Fluid / metabolism
  • alpha-Macroglobulins / metabolism
  • alpha-Macroglobulins / pharmacology*


  • alpha-Macroglobulins
  • MMP13 protein, human
  • Matrix Metalloproteinase 13
  • Mmp13 protein, rat