Abstract
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Objectives Osteoarthritis (OA) is a degenerative disease due in part to permanent destruction of cartilage matrix, causing patients pain and immobility. The destruction occurs by highly activated proteases in the matrix, predominantly matrix metalloproteinase (MMP). We used an optical probe, cleaved and activated by MMP enzymes in the cartilage and assessed its ability for early detection and monitoring of OA progression in animal models.
Methods Il-1β treated human chondrocytes were incubated with MMP-activatable probe for immunofluorescence microscopic evaluation. We developed 2 models of OA in 40 adult male CD1 mice. The 1st group received intra-articular (IA) injection of Monosodium Iodoacetate (MIA) in the right (Rt) knee joint and PBS in the left (Lt) joint. The 2nd group underwent destabilization of medical meniscus (DMM) in Rt knee and sham surgery in Lt (control). Multispectral near infrared fluorescent imaging was performed at multiple time points (5min-24 h) after IA injection of 5mL probe and Rt/Lt signal intensity ratio was calculated. DMM mice were imaged weekly after the surgery until 8 weeks to monitor the progression of OA. NIRF results were correlated to the histopathologic findings at each time point.
Results In-vitro studies showed high uptake of the probe in 2D and 3D scaffolds with growing human chondrocytes. NIRF imaging showed the maximum Rt/Lt signal intensity 2h after injection of the probe (85.1 ± 12). The MIA group developed moderate level of OA over 10 days. The DMM group showed OA progression more chronically with primary histopathologic changes 4 weeks after surgery and progressed to moderate degradation at 8 weeks. Rt/Lt Signal intensity ratio increased constantly over the time in DMM joints (2 ± 0.8 at 1 week vs. 93.2 ± 11 at 8 week).
Conclusions Targeting MMP is a promising non-invasive method for early detection of cartilage matrix destruction in early stages of OA and in evaluation of treatment response in osteoarthritic joints. The method is readily translatable to humans.