HA oligosaccharides stimulate inflammatory response in arthritis while adenosine A2 receptor stimulation mediates anti-inflammatory action: in vitro and in vivo studies

Hyaluronan (HA) fragments produced by degradation of native highly polymerized HA during inflammation may exacerbate pro-inflammatory responses in different pathologies. In contrast, the nucleoside adenosine (ADO) interacting with cell surface ADO receptors A2AR, A2BR, A1 and A3, acts as endogenous modulator of the inflammation. In a first study the effect of ADO treatment in normal murine chondrocytes stimulated with interleukin-1beta (IL-1beta) was investigated: the study suggests that HA is partially responsible for the up-regulation of pro-inflammatory cytokines and that endogenous/exogenous ADO may reduce inflammation via PKA. A further study in mouse articular chondrocytes using 6-mer HA suggests that endogenous ADO, by exerting anti-inflammatory response via A2AR, could be a modulatory mechanism to attenuate the inflammation process enhanced by 6-mer HA. We also investigated the effects of the HA-blocking peptide Pep-1, that inhibits the pro-inflammatory action of HA oligosaccharides produced during inflammation, together with the specific A2A receptor agonist CGS-21680 in normal mouse articular chondrocytes stimulated with IL-1beta. Such stimulation produced significant mRNA expression and related protein production of TLR4, TLR2, CD44 and A2AR; a high level of NF-kB activation and increased levels of inflammatory cytokines and mediators. Treatment of chondrocytes with Pep-1 and/or CGS-21680 significantly reduced all the inflammatory parameters up-regulated by IL-1. In an in vivo study we investigated the effect of combined treatment of Pep-1 and CV-1808 in collagen-induced arthritis (CIA) in mice. CIA increased TLR4, TLR2, CD44 and A2AR mRNA expression and the related proteins in the joint cartilage, and concentrations of pro-inflammatory cytokines and mediators. Pep-1 with CV-1808 treatment significantly reduced CIA damage and all the up-regulated biochemical parameters, and results were supported by microscopic analysis and synovial fluid HA levels.