Intra-articular leflunomide-loaded poly(ε-caprolactone) implants to treat synovitis in rheumatoid arthritis

Rheumatoid arthritis is an autoimmune pathology that manifests as chronic inflammatory arthropathy and synovitis. Treatment of rheumatoid arthritis is based on the administration of different types of drugs, including leflunomide, an antirheumatic drug. However, the long-term systemic use of leflunomide may be associated with adverse effects. Local therapy could be an efficient strategy to treat synovitis triggered by rheumatoid arthritis without inducing adverse effects. In this study, leflunomide-loaded poly(ε-caprolactone) implants (leflunomide PCL implants) were evaluated as local drug delivery systems capable of attenuating inflammation and angiogenesis, which represent events of synovitis. Leflunomide PCL implants were designed by hot molding technique; and they were characterized by FTIR and DSC. These analytical techniques demonstrated the chemical integrity and dispersion of drug into the polymeric chains. Then, a spectrophometric method was developed and validated to quantify the leflunomide incorporated into the PCL implants and released from them. Linearity was obtained by ordinary least squares regression method to estimate the linear regression equation. Residues were evaluated considering normality, independence and homoscedasticity. Precision was lower than 5 %, and accuracy ranged from 98 to 104.5 %. Quantitation limit was 2.0 μg mL^-1. PCL implants provided controlled and sustained release of leflunomide for 30 consecutive days after inserting these systems in the subcutaneous tissue of mice. The main mechanisms of drug delivery were solubilization and diffusion from polymer. Then, a non-biocompatible sponge was inserted into the subcutaneous tissue of mice to function as a frame to develop the inflammatory and angiogenic processes. Leflunomide PCL implants were inserted in direct contact with the sponge. At 4, 7 and 10 days after-sponge implantation, the key components of inflammatory angiogenesis were measured to verify the regression of these events induced by drug. Leflunomide controlled released from polymeric implants downregulated the neutrophil and monocyte/macrophage infiltration due to the reduced expression of myeloperoxidase (MPO) and N-acetyl-β-d-glucosaminidase (NAG), respectively. As the influx of these pro-inflammatory cells was modulated by leflunomide, the production of nitric oxide (NO), a pro-inflammatory substance, reached low concentrations in the sponge. As a consequence of the modulation of inflammation at the pathological site, the angiogenic process was downregulated, since the hemoglobin levels in the sponge were drastically reduced. The accumulation of leflunomide in the pathological site did not induce nephrotoxicity or hepatototoxicity, as confirmed by histological analyses. Finally, intra-articular leflunomide PCL implants represent a potential therapeutic alternative to treat locally the synovitis triggered by rheumatoid arthritis without inducing systemic adverse effects.