Urine matrix metalloproteinases (MMPs) as biomarkers for the progression of fracture healing

Abstract

Whilst the majority of fractures heal normally, it is estimated that ∼10% of fractures exhibit some level of delayed or impaired healing. Although radiography is the primary diagnostic tool to assess the progression of fracture healing, radiographic features only qualitatively correlate with tissue level increases in mineral content and do not quantitatively measure underlying biological processes that are associated with the progression of healing. Specific metaloproteinases have been shown to be essential to processes of both angiogenesis and mineralised cartilage resorption and bone remodelling at different phases of fracture healing. The aim of this study was to determine the potential of using a simple urine based assay of the activity of two MMPs as a means of assessing the biological progression of fracture healing through the endochondral phase of healing. Using a standard mid-diaphyseal murine model of femoral fracture, MMP9 and MMP13 proteins and enzymatic activity levels were quantified in the urine of mice across the time-course of fracture healing and compared to the mRNA and protein expression profiles in the calluses. Both urinary MMP9 and MMP13 protein and enzymatic activity levels, assessed by Western blot, zymogram and specific MMP fluorometric substrate assays, corresponded to mRNA expression and immunohistologic assays of the proteins within callus tissues. These studies suggest that urinary levels of MMP9 and MMP13 may have potential as metabolic markers to monitor the progression of fracture healing.