Photodynamic treatment as a novel approach in the therapy of arthritic joints

Background and Objective: Minimal invasive local treatment of joints is a desirable option in the therapy of rheumatoid arthritis (RA). Aim of this study was to evaluate the effects of photodynamic treatment (PDT) with different doses of the photosensitizer meta-tetra(hydroxyphenyl)chlorin (m-THPC; or temoporfin) in a murine model of RA (antigen-induced arthritis, AIA). Methods In vivo distribution: The distribution of native and liposomal m-THPC (including a formulation with polyethylene glycol [PEG] coating) was assessed by fluorescence spectrometry in arthritic joints, normal joints, and skin. Treatment: ATA mice received different concentrations of pegylated liposomal m-THPC (0.1, 0.05, 0.01, or 0.005 mg/kg body weight; n = 5 per group) and subjected to PDT with a laser system 12 hours post-injection of the photosensitizer. Treatment effects were evaluated histologically in comparison to untreated AIA (n = 5). Results: Pegylated liposomal m-THPC showed the most favorable accumulation in arthritic joints compared to native m-THPC and to non-peg-liposomal m-THPC, therefore it was selected as photosensitizer for PDT treatment. In comparison to untreated AIA, PDT reduced the arthritic score with all doses of pegylated liposomal m-THPC; statistical significant effects were obtained with doses of 0.05 and 0.01 mg/kg. Conclusion: Our study demonstrated that local PDT of arthritic joints is feasible. Application of pegylated liposomal m-THPC for PDT resulted in significant reduction of arthritis scores.