Antiarthritic activity of an orally active C5a receptor antagonist against antigen-induced monarticular arthritis in the rat
Related Experiment Video
Updated: Sep 29, 2026
An Adoptive Transfer Model of Rheumatoid Arthritis in Mice
Published on: June 6, 2025
Trent M Woodruff1, Anna J Strachan, Nathan Dryburgh
1University of Queensland, St. Lucia, Australia.
Objective:
To determine if the new, orally active C5a receptor antagonist, the cyclic peptide AcF-[OPdChaWR], reduces the severity of pathology in a rat model of immune-mediated monarticular arthritis.
Methods:
Arthritis was induced in the right knee of previously sensitized rats by the intraarticular injection of methylated bovine serum albumin. Rats were examined for either 14 days or 28 days, or for 49 days following a second antigen challenge at 28 days. The C5a antagonist (1 or 3 mg/kg/day) and/or ibuprofen (30 mg/kg/day) were administered orally on a daily basis either before or after arthritis induction.
Results:
Rats receiving AcF-[OPdChaWR] had significant reductions in right knee swelling, gait disturbance, lavaged joint cell numbers, and right knee histopathology, as well as in serum levels of tumor necrosis factor alpha (TNFalpha) and intraarticular levels of interleukin-6 and TNFalpha on day 14. In the 14- and 28-day studies, ibuprofen resulted in a similar reduction in gait abnormalities and intraarticular inflammatory cells compared with the C5a antagonist, but was less effective in reducing knee swelling over the course of the study and had no effect on knee histopathology. Combination therapy with AcF-[OPdChaWR] and ibuprofen resulted in no greater efficacy than with the C5a antagonist alone. Rats injected twice with the antigen in the 49-day study displayed the most severe histopathology and this, as well as knee swelling and gait abnormalities, was significantly reduced by repeated treatment with the C5a antagonist.
Conclusion:
An agent that inhibits the action of C5a in this model significantly reduced joint pathology, while ibuprofen was not effective. C5a antagonists could therefore have broader therapeutic benefits than nonsteroidal antiinflammatory drugs as antiarthritic agents for rheumatoid arthritis.
Insights
A novel C5a receptor antagonist significantly reduced joint swelling and pathology in a rat arthritis model. This finding suggests C5a antagonists may offer greater therapeutic benefits for rheumatoid arthritis than traditional anti-inflammatory drugs.
Area of Science:
- Immunology
- Pharmacology
- Rheumatology
Background:
- Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by joint inflammation and destruction.
- Current treatments, including nonsteroidal anti-inflammatory drugs (NSAIDs), have limitations in efficacy and safety.
- The complement system, particularly C5a, plays a significant role in mediating inflammatory responses in RA.
Purpose of the Study:
- To evaluate the efficacy of a new orally active C5a receptor antagonist, AcF-[OPdChaWR], in reducing pathology in a rat model of immune-mediated monarticular arthritis.
- To compare the therapeutic effects of the C5a antagonist with ibuprofen, a common NSAID.
- To investigate the potential synergistic effects of combination therapy with the C5a antagonist and ibuprofen.
Main Methods:
- Immune-mediated monarticular arthritis was induced in rats via intraarticular injection of methylated bovine serum albumin.
- Rats were treated daily with oral doses of the C5a antagonist (1 or 3 mg/kg/day) and/or ibuprofen (30 mg/kg/day) before or after arthritis induction.
- Arthritis severity was assessed by measuring knee swelling, gait disturbance, joint cell counts, histopathology, and levels of inflammatory cytokines (TNF-alpha, IL-6).
Main Results:
- The C5a antagonist AcF-[OPdChaWR] significantly reduced knee swelling, gait disturbance, joint inflammation, and histopathological damage.
- AcF-[OPdChaWR] also decreased serum levels of tumor necrosis factor alpha (TNF-alpha) and intra-articular levels of interleukin-6 (IL-6).
- Ibuprofen showed moderate effects on gait and inflammation but was less effective in reducing swelling and had no impact on histopathology. Combination therapy did not enhance efficacy over the C5a antagonist alone.
Conclusions:
- The C5a receptor antagonist AcF-[OPdChaWR] effectively ameliorated joint pathology in this rat arthritis model.
- C5a antagonism demonstrated superior efficacy compared to ibuprofen in reducing key arthritis markers.
- These findings suggest that C5a antagonists hold promise as a novel therapeutic strategy for rheumatoid arthritis, potentially offering advantages over conventional NSAIDs.
