Anti-inflammatory drugs for modulation of host response to biomaterials and application in diabetes therapy

Abstract

Host response to implanted biomaterials and medical devices poses tremendous challenges to their clinical applications. Today, the quest to mitigate this immunological attack for improved longevity of these devices remains daunting. This thesis aims to explore the use of anti-inflammatory drugs in minimizing the host response and improve the efficacy of implantable and transplantable therapeutics. Firstly, we developed a new non-invasive in vivo imaging technique to study the activity of early immune cells in the host response to implanted biomaterials. A fluorescent imaging probe (Prosense680*, Perkin Elmer) activatable by cathepsins, a class of inflammatory proteases secreted from immune cells, was used for simultaneous biocompatibility screening of up to 8 different materials per animal in immunocompetent hairless SKH1E mice. In this assay, the different biocompatibility properties of polystyrene beads, alginate and saline were correlated with varying levels of cathepsin activities as acquired by imaging. Comparison of the imaging results with traditional histological analysis validated that this new fluorescent imaging technique can be used to assess material biocompatibility efficiently and rapidly. We applied this new fluorescent imaging technique to investigate the in vivo spatial and temporal host response to a subcutaneously-injected, controlled-release anti-inflammatory drug formulation. Poly-lactic-coglycolic (PLGA) microparticles with low loading (1.3wt%) of dexamethasone locally inhibited the activity of cathepsin enzymes from immune cells, while high drug loading formulation (26wt%) resulted in systemic immunosuppression. We also showed that incorporation of dexamethasone at a low loading (1.3wt%) attenuated the coverage of polymeric microparticles by immune cell layers. Temporal monitoring of the drug effect confirmed that incorporation of dexamethasone decreased early enzymatic activity and long-term cellular infiltration to implanted materials. Next, we performed in vivo subcutaneous screening of 16 small molecule anti-inflammatory drugs (NSAIDs, polyphenols, glucocorticoids and other non-steroidal immunosuppressants) encapsulated in PLGA microparticles in immunocompetent hairless SKH-1E mice. Using non-invasive fluorescent imaging coupled with parallel bioluminescent imaging, we identified dexamethasone and curcumin as the most effective drugs in inhibiting the activities of inflammatory proteases and reactive oxygen species respectively. Histological analysis also showed that dexamethasone and curcumin encapsulated in PLGA microparticles decreased subsequent cellular infiltration and fibrosis formation surrounding the subcutaneously injected PLGA microparticles for up to 4 weeks and 2 weeks respectively. Lastly, we designed hybrid alginate hydrogel microcapsules co-encapsulating pancreatic rat islets and dexamethasone or curcumin. Uniform spherical microcapsules containing homogeneously distributed dexamethasone (2mg/ml) or curcumin (1mg/ml) were transplanted into streptozotocin-induced C57B6/J diabetic mice. Using a marginal islet mass of 250 islet equivalents, curcumin-loaded capsules effectively improved glycemic control by increasing the graft survival time to 30 days compared to 15 and 21 days by control and dexamethasone-containing capsules respectively. Curcumin also significantly reduced fibrotic overgrowth on the encapsulated islets explanted on day 60 as evidenced by DNA fluorescent staining of the fibrotic cell layers on the surface of the retrieved capsules. Taken together, the results of this thesis demonstrate that anti-inflammatory drugs have the potential to minimize the attack by host immune system and improve the efficacy or functional longevity of cell-based therapeutics and possibly other implantable medical devices.