Chondroprotective and anti‐inflammatory role of melanocortin peptides in TNF‐α activated human C‐20/A4 chondrocytes

BACKGROUND AND PURPOSE Melanocortin MC1 and MC3 receptors, mediate the anti‐inflammatory effects of melanocortin peptides. Targeting these receptors could therefore lead to development of novel anti‐inflammatory therapeutic agents. We investigated the expression of MC1 and MC3 receptors on chondrocytes and the role of α‐melanocyte‐stimulating hormone (α‐MSH) and the selective MC3 receptor agonist, [DTRP8]‐γ‐MSH, in modulating production of inflammatory cytokines, tissue‐destructive proteins and induction of apoptotic pathway(s) in the human chondrocytic C‐20/A4 cells. EXPERIMENTAL APPROACH Effects of α‐MSH, [DTRP8]‐γ‐MSH alone or in the presence of the MC3/4 receptor antagonist, SHU9119, on TNF‐α induced release of pro‐inflammatory cytokines, MMPs, apoptotic pathway(s) and cell death in C‐20/A4 chondrocytes were investigated, along with their effect on the release of the anti‐inflammatory cytokine IL‐10. KEY RESULTS C‐20/A4 chondrocytes expressed functionally active MC1,3 receptors. α‐MSH and [DTRP8]‐γ‐MSH treatment, for 30 min before TNF‐α stimulation, provided a time‐and‐bell‐shaped concentration‐dependent decrease in pro‐inflammatory cytokines (IL‐1β, IL‐6 and IL‐8) release and increased release of the chondroprotective and anti‐inflammatory cytokine, IL‐10, whilst decreasing expression of MMP1, MMP3, MMP13 genes.α‐MSH and [DTRP8]‐γ‐MSH treatment also inhibited TNF‐α‐induced caspase‐3/7 activation and chondrocyte death. The effects of [DTRP8]‐γ‐MSH, but not α‐MSH, were abolished by the MC3/4 receptor antagonist, SHU9119. CONCLUSION AND IMPLICATIONS Activation of MC1/MC3 receptors in C‐20/A4 chondrocytes down‐regulated production of pro‐inflammatory cytokines and cartilage‐destroying proteinases, inhibited initiation of apoptotic pathways and promoted release of chondroprotective and anti‐inflammatory cytokines. Developing small molecule agonists to MC1/MC3 receptors could be a viable approach for developing chondroprotective and anti‐inflammatory therapies in rheumatoid and osteoarthritis.