Blom AB, van Lent PL, Libregts S, Holthuysen AE, van der Kraan PM, van Rooijen N, van den Berg W. Crucial role of macrophages in matrix metalloproteinase–mediated cartilage destruction during experimental osteoarthritis : Involvement of matrix metalloproteinase 3. Arthritis & Rheumatism. 2007;56(1):147–57.


Objective: To explore the involvement of synovial macrophages in early cartilage damage in osteoarthritis (OA), and to identify the role of matrix metalloproteinase 3 (MMP-3) in the pathology of early and late OA.

Methods: The role of synovial macrophages in MMP-mediated damage in OA was studied by depleting synovial macrophages prior to elicitation of a collagenase-induced instability model of OA. The expression of MMP in synovium and cartilage was monitored using TaqMan analysis. In spontaneous and induced OA, cartilage pathology was scored in MMP-3–knockout mice and control mice, by histologic assessment and VDIPEN staining.

Results: On day 14 following induction of OA, MMP-mediated neoepitopes were detected in cartilage from mice with mild experimental OA (mean  SD positively stained surface area 20  3.2%). Remarkably, by depleting synovial macrophages prior to induction of OA, the generation of MMP-induced neoepitopes was largely prevented (mean  SD positively stained surface area 5  1%; P< 0.001), indicating an important role for synovial macrophages in the occurrence of MMPmediated cartilage damage. We observed a strong decrease in MMP-3 and MMP-9 expression in synovial but not cartilage tissue in macrophage-depleted joints. Among 2-year-old mice, spontaneous OA–like changes in the lining layer were significantly decreased in MMP- 3–knockout mice compared with control mice. Even more striking was the 67% reduction in the occurrence of severe cartilage damage in MMP-3–knockout mice. In addition, MMP-mediated VDIPEN expression was significantly decreased, indicating reduced MMPmediated cartilage breakdown.

Conclusion: The results of this study prove that MMP-3 is involved in the generation of severe cartilage damage in murine OA. Synovial macrophages are crucial in early MMP activity and appear to mediate MMP production in synovium rather than cartilage. [custom_table]

Clodronate Concentration Total Lipid Concentration Lipid Composition Lipid Mole % Liposome Type Control Liposomes
not specified not specified EPC/Chol not specified MLV none
[/custom_table] [custom_table]
Animal Description Clodronate Dose Dosing Method/Site Target Phagocytes Systemic Dosing? Systemic Results
C57BL/6 mice2 not specified intra-articular/knee F4/80+ synovial lining no N/A

2Base strain. Other genetically altered or knockout strains were also used.



  1. Liposome prep method referenced—van Rooijen N, Sanders A, van den Berg TK. Apoptosis of macrophages induced by liposome-mediated intracellular delivery of clodronate and propamidine. Journal of Immunological Methods. 1996 Jun;193(1):93–9.
  2. Animals were injected 1 week prior to induction of arthritis with collagenase.
  3. No details of injection method or clodronate liposome dose were published, however referenced paper states that 6 µl (75 µg clodronate) were injected into the joint.


  1. F4/80+ were reduced from about 45% to 15% by day 14 and 50% to 15% by day 21 post-injection of clodronate liposomes (7 and 14 days post-induction of OA) by immunohistological analysis.
  2. Depletion was not detected in the sublining.
  3. Although the authors state that F4/80+ had begun to repopulate at 3 w post-injection of clodronate liposomes in a cited article, the depletion level had not changed in the current experiment.
  4. F4/80+ depletion correlated with a significant down-regulation in MMP-3.
  5. The authors further pursue in the possible roles of MMP’s in MMP knockout mice without the use of clodronate liposomes.