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

Osteoarthritis 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 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 osteoarthritis. 33 peptide modifications of p[63–82] were custom-designed and synthesized to optimize the bioactivity. Chondrocytes and synovial fluid were collected from end-stage osteoarthritic patients at total knee arthroplasty surgery. To validate improvements in bioactivity, gene expression analysis, glycosaminoglycan content, matrix metalloproteinase-13 protein levels and alkaline phosphatase activity was measured. 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 collagen type 2 and decrease expression of collagen type 10, matrix metalloproteinase-13 and prostaglandin-endoperoxide synthase 2. The linear p[63–82] peptide and the cyclic peptide variant C2 in the same concentration were effective in suppressing the osteoartritic phenotype in SW1353 cells, despite the presence of interleukin-1β or osteoarthritic-synovial fluid. However, peptide variant C2 had a significantly more favorable bioactivity as compared to p[63–82] in reducing matrix metalloproteinase-13 protein levels in the osteoarthritic-synovial fluid 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. 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.