Development of a controlled-release platform for investigation of proteases following rotator cuff tear

Abstract

Surgical reattachment of torn rotator cuff tendons has a high rate of re-tear (failure) and the procedure does not reverse joint tissue degeneration present at the time of surgery. Following rotator cuff tear, three different joint tissues (tendon, muscle, and articular cartilage) develop degenerative changes. A possible cause for the extensive joint tissue degeneration observed following rotator cuff tear is the prolonged activation of proteases, which are specialized enzymes whose primary function is to degrade proteins. Systemic delivery of several protease inhibitors have been tested in human clinical trials to for a variety of diseases including osteoarthritis and osteoporosis, but all have been abandoned due to off-target effects. However, local delivery of protease inhibitors could reduce disease progression without deleterious side effects. The long-term goal of this dissertation was to understand how proteases contribute to joint tissue degeneration (tendon, muscle, and cartilage) after rotator cuff tear. Understanding the spatial and temporal distribution of upregulated proteases after rotator cuff tear can best inform therapeutic treatments to prevent degeneration, which would result in improved surgical outcomes after rotator cuff tear re-attachment surgery. First, using a rat model of rotator cuff tear that has been shown to replicate degenerative damage seen in humans, we investigated active proteases in each joint tissue over time. Second, we designed a novel microfluidic device to fabricate uniformly sized microparticles that can be loaded with protease inhibitors for subsequent use in vivo. Also, we reinvented a currently available fluorogenic substrate assay for the detection of E-64 (a broad, small molecule cathepsin inhibitor), which was our desired therapeutic. Lastly, we tested our E-64 loaded microparticles system on supraspinatus tendon tissue in our rat model of rotator cuff tear as a test bed to elucidate the effect of sustained release of a broad cathepsin inhibitor on active proteases.