Exploration of bioactive variants of the BMP7-derived p[63-82] peptide for ameliorating the OA-associated chondrocyte phenotype

Introduction: Osteoarthritis (OA) is a highly prevalent, age-associated joint disease characterized by cartilage degeneration, joint dysfunction, and chronic pain. We previously developed a bone morphogenetic protein 7 (BMP7) derived peptide p[63-82], which may be a novel disease-modifying treatment option for OA. In this study we aimed to optimize the bioactivity and biostability of this peptide in the intra-articular environment to evaluate the therapeutic potential of these peptides to treat OA. Methods: 33 peptide modifications of p[63-82] were custom-designed and synthesized to optimize the bioactivity and biostability. Chondrocytes and synovial fluid were collected from end-stage OA patients at TKA surgery. To validate improvements in bioactivity, gene expression analysis, sGAG content, MMP13 protein levels and ALP activity was measured. Results: Several biochemical approaches were used to explore optimization of the original p[63-82] peptide. One cyclized peptide (C2) was able to significantly increase the expression of COL2A1 and decrease expression of COL10A1, MMP13 and PTGS2. The linear p[63-82] peptide and the cyclic peptide variant C2 in the same concentration were effective in suppressing the OA phenotype in SW1353 cells, despite the presence of IL1β or OA-synovial fluid However, peptide variant C2 had a significantly more favorable bioactivity as compared to p[63-82] in reducing MMP13 protein levels in the OA-SF exposed condition. At lower concentrations, the cyclic peptide C2 showed a higher bioactivity as compared to the linear p[63-82] peptide. When the activity of both peptides on primary human articular chondrocytes was evaluated, we found that the linear p[63-82] peptide as well as peptide C2 counteract the hypertrophic and inflammatory state of primary OA chondrocytes. Conclusion: This study demonstrates that among various tested modifications of p[63-82], one cyclic variant (C2) showed similar results in bioactivity as compared to the linear peptide p[63-82], whilst the other modified peptide variants had inactive bioactive properties as compared to the original p[63-82] peptide. This highlights the challenge in enhancing peptide properties without compromising their biological activity and emphasises the need for a cautious approach in peptide modification for therapeutic use. This research underscores that while cyclization and other structural changes may offer benefits, they should be carefully evaluated on a case-by-case basis.