(232h) Nanomagnetic Illuminators for In Vivo Optical Imaging of Osteoarthritic Knee Joints

Nanoparticle formulations of various sizes and charges are being developed to diagnose and treat osteoarthritis (OA), a maladaptive disease of the joint. However, the transport and in vivo bio-distribution of nanocarriers in the joint space remain poorly understood. Developing a biocompatible platform for visualizing and quantifying the distribution of nanoparticles in the joint space could help engineer better nanoparticles for drug delivery and disease diagnosis. Here, we focus on block copolymer stabilized nanomagnetic illuminators obtained by encapsulating near-IR lipophilic dyes. We apply both in-vivo imaging system (IVIS) and electron paramagnetic resonance spectroscopy (EPR) to visualize and quantify the distribution of these multifunctional magnetic carriers in the healthy and osteoarthritic joints of Lewis rats.

Magnetic nanoparticles synthesized by a high temperature synthesis method under aerobic conditions, block copolymer PEG_5kDa_PDLLA_6kDa, and lipophilic tracer 1,1'-Dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide (DiR) were dissolved in the water miscible solvent THF. Rapid mixing of the solutes against water (anti-solvent) using a confined impingement jet mixer under high local supersaturation condition resulted in kinetically frozen structures of about 200 nm. The magnetic composite nanocarriers were purified via magnetic separation and dye encapsulation was confirmed using absorbance measurements and an in vivo imaging system.

Toxicity of the DiR loaded magnetic nanocarrier on fibroblast-like synoviocytes was tested using an MTS assay, a colorimetric assay used to analyse cell metabolism. Greater than 80% of the synoviocytes were found viable after 24 hours of particle exposure in the concentration range of 0.1 to 0.8 mg iron oxide/mL, suggesting negligible toxic effects of the nanocarrier under these conditions.

Biodistribution and particle retention studies were performed on 15-month old Lewis rats with healthy and OA induced knees. 60 ug of DiR loaded magnetic composite nanocarrier was injected and distribution of the nanomagnetic illuminator was tracked for 14 days. Further, the retention of the particles in organs of euthanized rats was visualized by IVIS imaging and quantified via EPR. IVIS images of the organs analyzed for radiant efficiency suggested that particles were predominantly retained in the knee joint and cleared faster in a healthy joint as compared to an osteoarthrtic knee. Based on the EPR measurements on the lyophilized organs, we found that ~60 % of the injected iron oxide nanoparticles remained in the joint space. Our studies involving both visualization and quantification of DiR loaded magnetic particle indicate that this carrier can be explored as a safe option to better understand transport of nanoparticles in tissues of joint space and also to deliver hydrophobic drugs for treatment.