Local Modulation and Measurement of Macrophage-Derived Bioactive Proteins from Implanted Biomaterials in Rat

Fibrosis around the implanted medical devices is a severe problem that can plague long-term device reliability. Activation of macrophage phenotype (macrophage polarization) has emerged as a new and possible means for reducing fibrosis in the fields of biomaterials and regenerative medicine. Macrophages are phagocytic cells that respond to microenvironmental cues that direct their phenotype. Macrophage activation has been widely studied in mouse and human in the context of tumor biology, yet little information is available regarding how macrophage activation could be used in a biomaterials context. Further, rats rather than mice are the common subjects in biomaterials experiments. A significant need is to determine if directed macrophage activation can be achieved in a biomaterials context. Cultured rat-derived macrophages (NR8383, peritoneal and spleen) were tested with modulators (dexamethasone, LPS, IL-4 and IL10) to ensure activation towards the expected phenotype. Phenotypic characterization involved gene expression assays (ARG2, CD163, CD206, NOS2, IL-12), protein analysis (IL-6, IL-10, TNF), and flow cytometry (for receptors CD86, CD163, CD206, MHC II). The successful in vitro immunomodulation suggested the feasibility of modulation in vivo. Microdialysis has been used for cytokine sampling (from various tissues including rat mammary tissue for Leptin, CCL2 and IL-6; procedures developed in this work), but can also be employed for modulator delivery. To achieve in vivo immunomodulation, microdialysis experiments were performed to locally deliver either IL-4 or IL-10. No significant differences in dialysate cytokine levels (CCL2, IL-1& and IL-6) or histological sections (H&E and Masson\u27s trichrome) of tissue surrounding the probe were observed between control and treatment groups. However, gene expression analysis of tissue to which IL-4 was delivered suggests down-regulation in CCL2 and IL-6. To enhance modulator amount and surface area, a polyvinyl alcohol (PVA) sponge model was employed. The IL-4 impregnated sponges had reduced IL-1 concentrations compared to controls. However, no significant differences in gene expression were observed. For IL-10, down regulation of CCL2 (also at protein level), IL-1, IL-12 and NOS2 genes was observed. This initial work in macrophage activation for biomaterials in rats provides a fundamental framework for future work in this fiel