Intra-articular hydrogel therapeutics exhibit anti-inflammatory effects on cytokine-stimulated equine cartilage and synovial membrane explants.

Overview

• This study investigated how various intra-articular (IA) hydrogel therapeutics affect inflammatory and degradative responses in equine articular cartilage (AC) and synovial membrane (SM) tissues when stimulated with inflammatory cytokines IL-1β and TNF-α.
• The research aimed to understand the anti-inflammatory potential of these therapeutics at the tissue explant level, assessing their ability to modulate key inflammatory markers and degradative molecules.

Background and Objective

• Osteoarthritis and joint inflammation involve elevated pro-inflammatory cytokines like interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), which contribute to cartilage degradation and synovial membrane inflammation.
• Intra-articular hydrogel therapeutics, including corticosteroids, hyaluronic acid, and novel hydrogel microparticles, are used clinically to reduce joint inflammation and improve joint function.
• The objective of this study was to evaluate whether these therapeutics can alter inflammatory and degradative processes induced by IL-1β or TNF-α in equine AC and SM explants.

Materials and Methods

• Tissue samples:
  • Articular cartilage (AC) from 6 horses (12 explants)
  • Synovial membrane (SM) from 3 horses (9 explants)
• Tissue stimulation:
  • Explants were stimulated with IL-1β or TNF-α to mimic inflammatory conditions.
• Treatment groups:
  • Triamcinolone acetonide (a corticosteroid)
  • Hyaluronic acid (a viscosupplement)
  • Collagen-elastin hydrogel microparticles (CEHM)
  • 2.5% polyacrylamide hydrogel (2.5% iPAAG)
  • Treatments were applied at three different doses simultaneously with cytokine stimulation.
• Incubation times:
  • Synovial membrane explants: 18 hours stimulation/treatment
  • Articular cartilage explants: 2 days stimulation/treatment followed by basal media changes every 2 days for 8 days
• Outcome measures:
  • In AC media:
    • Nitric oxide (NO) – measured by Griess reaction; a marker of inflammation
    • Glycosaminoglycans (GAGs) – measured by dimethylmethylene blue assay; indicate cartilage matrix degradation
  • In SM media:
    • Prostaglandin E2 (PGE2) – measured by ELISA; a pro-inflammatory mediator
    • C-C motif chemokine ligands (CCL2, CCL3, CCL5, CCL11), TNF-α, IL-1β – measured by multiplex immunoassay; inflammatory chemokines and cytokines

Key Findings

• All therapeutics reduced cytokine-induced nitric oxide production in articular cartilage explants, indicating a decrease in inflammatory signaling.
• Glycosaminoglycan concentrations, indicating cartilage degradation, varied widely across all groups, suggesting complex effects on matrix turnover.
• In synovial membrane explants:
  • Triamcinolone acetonide and CEHM significantly reduced IL-1β-induced prostaglandin E2 production, a key inflammatory mediator.
  • Triamcinolone acetonide, CEHM, and 2.5% iPAAG decreased CCL2 levels induced by TNF-α, indicating reduced chemokine-driven inflammation.
  • Triamcinolone acetonide and CEHM also decreased CCL5 levels in TNF-α-stimulated explants, suggesting suppression of additional inflammatory pathways.
• Overall, all tested therapeutics reduced some proinflammatory effects caused by IL-1β or TNF-α in both AC and SM explants.
• The greatest anti-inflammatory effects were observed with triamcinolone acetonide and CEHM.

Conclusions and Implications

• Beyond their known mechanical support or viscosupplementation roles, CEHM, 2.5% iPAAG, and hyaluronic acid appear to exert direct biological anti-inflammatory actions on joint tissues.
• These findings support the potential for hydrogel-based therapeutics, especially collagen-elastin hydrogel microparticles, to modulate inflammatory pathways in the joint environment.
• Such therapeutics may provide valuable alternatives or adjuncts to corticosteroids like triamcinolone acetonide for managing joint inflammation and degradation in conditions such as equine osteoarthritis.
• This study enhances understanding of the biological mechanisms by which IA hydrogels can reduce joint inflammation, potentially informing future development and optimization of injectable treatments for equine and possibly human arthritis.