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A7.01 Abrogation of collagen-induced arthritis by a second generation peptidyl arginine deiminase inhibitor is associated with a shift from TH1/TH17 to TH2-mediated immune responses
  1. J Kawalkowska1,*,
  2. AM Quirke1,*,
  3. F Ghari2,
  4. V Subramanian3,
  5. R Li1,
  6. PR Thompson3,
  7. RO Williams1,
  8. R Fischer4,
  9. NB La Thangue2,
  10. PJ Venables1
  1. 1Kennedy Institute, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
  2. 2Laboratory of Cancer Biology, Department of Oncology, University of Oxford, Oxford, UK
  3. 3Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, USA
  4. 4Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Oxford, UK
  5. *Co-shared Authorship

Abstract

Citrullination is catalysed by peptidylarginine deiminases (PADs) and may play a role in joint inflammation by generating proteins recognised by autoantibodies and/or by targeting histones and thereby modulating gene transcription. The PAD inhibitor Cl-amidine was shown to have a modest anti-inflammatory effect in collagen-induced arthritis (CIA), when given prophylactically at high doses. While much of this benefit was thought to be due to PAD4 inhibition, recent studies have highlighted the pro-inflammatory effects of PAD2. The objective of this study was to assess the therapeutic potential BB-Cl-amidine, which is 10 fold more active than Cl-amidine against PAD2. We chose CIA as a reproducible model of immune-mediated arthritis and used a clinically-relevant therapeutic protocol, in which mice were treated after disease onset.

CIA was induced in DBA/1 mice by immunisation with bovine type II collagen. After disease onset, mice were treated daily with vehicle or BB-Cl-amidine (10 mg/kg, n = 12). On day 10, mice were culled, and paws, blood and lymph nodes collected for further analysis. In serum, cytokines were measured using a multiplex platform and anti-citrullinated peptide antibodies (ACPA) by ELISA. The phenotypes of T cells were determined by FACS. Citrullinated proteins were identified by mass spectrometry.

Treatment of arthritic mice with BB-Cl-amidine, resulted in a significant reduction in clinical scores and paw swelling. Histological changes in joints were almost completely normalised by BB-Cl-amidine. Unexpectedly, while pro-inflammatory cytokine (TNF-α, IL-1β, IL-6) levels in serum remained unaffected by BB-Cl-amidine, IL-4, IL-5 and IL-10 levels were significantly elevated. In line with this, IL-4-expressing Th2 cells were increased in the lymph nodes of BB-Cl-amidine treated mice. Further analysis revealed a decrease in Th1 and Th17 numbers with BB-Cl-amidine. In addition BB-Cl-amidine reduced histone H3.2 citrullination, with little affect on the ACPA response which suggests that BB-CL-amidine may inhibit gene expression in disease via an epigenetic mechanism.

In conclusion, BB-Cl-amidine is therapeutic in CIA due to immunomodulation rather than immunosuppression and supports anti-inflammatory Th2-type, while inhibiting pro-inflammatory Th1/Th17-type responses. We propose that these effects are mediated by transcriptional regulation and that targeting PADs is a realistic strategy for the treatment of chronic inflammatory diseases.

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