Expression of metalloproteinase 2 in the cell response to porous demineralized bovine bone matrix

The purpose of the study was to analyze the involvement of metalloproteinase 2 (MMP-2) and macrophages in the tissue and cell response to the organic graft material produced from bovine cancellous bone. Thirty adult male white Wistar rats (Rattus norvegicus) received implants of blocks of demineralized bovine bone matrix between the fasciae of the quadriceps muscle. The specimens collected at 3, 7, 14, 21 and 28 days after implantation (n = 6/period). Sections of 6 mu m thick were stained with hematoxylin and eosin and immunolabeled with anti-MMP-2 and anti-CD68 using standard avidin-biotin-peroxidase method. The tissue response to the material was initially mediated by polymorphonuclear neutrophils, evolving to a mononuclear inflammatory infiltrate with macrophages and few lymphocytes and plasma cells and presence of inflammatory multinucleated giant cells (GC) in contact with the material that exhibited signs of resorption. The number of cells immunolabeled to MMP-2 was highest at day 7 (103.2 +/- 39.1), but significantly decreased (F = 3.67; p = 0.044) until day 28 (45.9 +/- 13.1). CD68 immunostaining also significantly decreased (F = 6.75; p = 0.007) from day 7 (49.5 +/- 10.4) to day 28 (19.5 +/- 8.9). A positive and statistically significant correlation was observed between the evolutions of these two variables. The material had been almost completely resorbed at day 28. Among cells present at the granuloma, anti-MMP-2 immunostaining was predominant and more intense in macrophages, yet lightly immunolabeled multinucleated giant cells were found in close contact with the material. Thus, considering the experimental limitations of this study, we concluded that MMP-2 produced by macrophages participates in the resorption of demineralized bovine bone.