Influence of light delivery on photodynamic synovectomy in an antigen- induced arthritis model for rheumatoid arthritis

Background and Objective: Minimally invasive synovectomy techniques have been unsuccessful due to lack of selectivity. The purpose of this study was to evaluate the potential of photodynamic therapy to destroy diseased synovium in an antigen-induced arthritis model. Study Design/Materials and Methods: Three sets of experiments evaluated the biodistribution and treatment effects of Photofrin (PF) in rabbits with bilatera, knee antigen- induced arthritis. The first set of experiments evaluated the biodistribution of PF in articular tissues of 30 rabbits from 6-72 hours after systemic injection of 2 mg/kg. In the second series of experiments, light was delivered to the knee joint via cleaved optical fibers, whereas for the third, light was delivered via a 600 μm diffusion fiber. Tissues were harvested at 2 and 4 weeks posttreatment. Results: The biodistribution experiments demonstrated maximal uptake in inflamed synovium at 48 hours and a lack of uptake in normal tissues. With bare cleaved fibers, necrosis was observed in one specimen at 2 weeks and was absent in all specimens at 4 weeks. In the third experiment, synovial necrosis was observed in 3 of 7 specimens at 2 weeks and 3 of 8 at 4 weeks. No damage to articular cartilage or periarticular tissues was seen with either mode of light delivery. Conclusion: These studies indicate that selective destruction of synovium can be achieved with PF and suggest that optimization of light delivery techniques will play an important role in development of this new technique.