Background/Purpose: We have recently reported that endogenously produced adenosine, interacting with A2AR, is a critical autocrine factor for maintenance of chondrocyte and cartilage homeostasis and intra-articular injections of liposomal preparations of adenosine inhibit progression of OA in a post-traumatic OA (PTOA) model in rats. We therefore determined whether intra-articular injection of a more selective A2AR agonist could also prevent progression and possibly reverse OA in this model and in the obesity related OA model in mice.

Methods:

PTOA was induced in SD rats following rupture of the anterior cruciate ligament (ACL) by application of external force to the knee. Starting 4 weeks after injury, when OA has already progressed, knees were injected with 100ul of saline, empty liposomes (LIPO) or liposomes containing CGS21680 (LIPO-CGS) every 10 days (6 injections) before sacrifice. The cartilage volume in OA and normal knees was measured by microCT after staining with hexabrix (40%). Chondrocytes were isolated from neonatal mice and cultured, only first passage chondrocytes were studied.

For the obesity-OA model, C57Bl6 mice (3/group, 12 weeks old) were fed a 60% fat diet (HFF mice). After 3 months, when OA was present, mice received intrarticular knee injection (10 µl) of LIPO, LIPO-CGS or liposomal adenosine (LIPO-Ado) every 10 days for 4 injections before sacrifice.

Results: Injection of LIPO-CGS but not saline or LIPO, significantly reduced swelling of affected rat knees (p<0.001). Surprisingly, there was an increase in tibial and femoral cartilage volume in normal knees treated with intra-articular injections of LIPO-CGS but not LIPO or saline (47% increase in tibia and 22% in femur). More importantly, intra-articular injections of LIPO-CGS, but not LIPO or saline, increased tibial and femoral cartilage volume in OA knees, as compared to normal knees and completely abrogated the histologic evidence of OA as well (OARSI score for CGS21680 0.66±0.33 vs 4.55±0.82 in the vehicle group and 3.90±0.89 in the saline group). There was marked chondrocyte proliferation in the deep cartilage of knees of rats treated with LIPO-CGS (Ki67 immunofluorescence).

Similarly, LIPO-CGS reversed the OA changes in the obesity related OA model. HFF mice had an OARSI score of 4.7±1.2. Treatments with LIPO-Ado and lipo-CGS decreased OA severity (OARSI score 1.3±0.3 and 0.7±0.6, respectively, p<0.001 vs untreated). A2AR stimulation increased TGF-β immunostaining in LIPO-CGS-injected joints and increased TGF-b production by cultured neonatal murine chondrocytes with increased SMAD2/3 phosphorylation and diminished RUNX2 expression.

Conclusion: These results demonstrate that intra-articular injection of a long-acting A2AR agonist stimulates chondrocyte and cartilage regeneration, likely by a TGF-β-dependent mechanism. More importantly, these results indicate that treatment with an A2AR agonist can reverse OA in both traumatic and obesity-related OA.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/regenerating-cartilage-and-reversing-osteoarthritis-oa-stimulation-of-adenosine-a2a-receptors-a2ar-increases-cartilage-volume-and-matrix-in-vitro-and-in-vivo/