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Administration of the thienopyridine P2Y12 receptor antagonist, clopidogrel, increased the erosive arthritis induced by peptidoglycan polysaccharide (PG-PS) in rats or by injection of the arthritogenic K/BxN serum in mice. To determine if the detrimental effects are caused exclusively by clopidogrel, we evaluated prasugrel, a third-generation thienopyridine pro-drug, that contrary to clopidogrel is mostly metabolized into its active metabolite in the intestine. Prasugrel effects were examined on the PG-PS-induced arthritis rat model. Erosive arthritis was induced in Lewis rats followed by treatment with prasugrel for 21 days. Prasugrel treated arthritic animals showed a significant increase in the inflammatory response, compared with untreated arthritic rats, in terms of augmented macroscopic joint diameter associated with significant signs of inflammation, histomorphometric measurements of the hind joints and elevated platelet number. Moreover, fibrosis at the pannus, assessed by immunofluorescence of connective tissue growth factor, was increased in arthritic rats treated with prasugrel. In addition to the arthritic manifestations, hepatomegaly, liver granulomas and giant cell formation were observed after PG-PS induction and even more after prasugrel exposure. Cytokine plasma levels of IL-1 beta, IL-6, MIP1 alpha, MCP1, IL-17 and RANTES were increased in arthritis-induced animals. IL-10 plasma levels were significantly decreased in animals treated with prasugrel. Overall, prasugrel enhances inflammation in joints and liver of this animal model. Since prasugrel metabolites inhibit neutrophil function ex-vivo and the effects of both clopidogrel and prasugrel metabolites on platelets are identical, we conclude that the thienopyridines metabolites might exert non-platelet effects on other immune cells to aggravate inflammation.

The P2Y12 receptor plays a crucial role in the regulation of platelet activation by several agonists, which is irreversibly antagonized by the active metabolite of clopidogrel, a widely used anti-thrombotic drug. In this study, we investigated whether reduction of platelet reactivity leads to reduced inflammatory responses using a rat model of erosive arthritis. We evaluated the effect of clopidogrel on inflammation in Lewis rats in a peptidoglycan polysaccharide (PG-PS)-induced arthritis model with four groups of rats: 1) untreated, 2) clopidogrel-treated, 3) PG-PS-induced, and 4) PG-PS-induced and clopidogrel-treated. There were significant differences between the PG-PS+clopidogrel group when compared to the PG-PS group including: increased joint diameter and clinical manifestations of inflammation, elevated plasma levels of pro-inflammatory cytokines (IL-1 beta, interferon (IFN) gamma, and IL-6), an elevated neutrophil blood count and an increased circulating platelet count. Plasma levels of IL-10 were significantly lower in the PG-PS+clopidogrel group compared to the PG-PS group. Plasma levels of platelet factor 4 (PF4) were elevated in both the PG-PS and the PG-PS+clopidogrel groups, however PF4 levels showed no difference upon clopidogrel treatment, suggesting that the pro- inflammatory effect of clopidogrel may be due to its action on cells other than platelets. Histology indicated an increase in leukocyte infiltration at the inflammatory area of the joint, increased pannus formation, blood vessel proliferation, subsynovial fibrosis and cartilage erosion upon treatment with clopidogrel in PG-PS-induced arthritis animals. In summary, animals treated with clopidogrel showed a pro-inflammatory effect in the PG-PS-induced arthritis animal model, which might not be mediated by platelets. Elucidation of the mechanism of clopidogrel-induced cell responses is important to understand the role of the P2Y12 receptor in inflammation.

Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with leukocyte adhesion to and extravasation through vascular endothelium into synovial tissue. Recent evidence indicates that the thrombospondin 1 gene is up‐regulated in patients with RA. We have identified a region within the TSP‐1 type 3 repeats that inhibits human neutrophil elastase (HNE) and binds to human neutrophils. The present study was undertaken to investigate the therapeutic benefit of this TSP‐1–derived peptide sequence and its effect on connective tissue growth factor (CTGF), a protein involved in fibrotic disorders and in neovascularization, which is a hallmark of RA.CTGF gene and protein expression, as well as protein levels of CTGF in the synovium, after treatment with the TSP‐1–derived peptide were studied in the peptidoglycan–polysaccharide animal model of erosive arthritis.Peptide treatment prevented joint infiltration and inflammation and was associated with reduced circulating antigen levels of HNE and TSP‐1. Additionally, CTGF was up‐regulated in this experimental model of RA. Treatment with the TSP‐1–derived peptide was associated with down‐regulation of the message and protein levels of CTGF. Immunofluorescence studies showed that the mean area fraction of CTGF immunoreactivity in the peptide‐treated group of animals was significantly less than that in the untreated group.These results document a role for TSP‐1 in regulating CTGF gene and protein expression in synovial tissue, suggesting a link with the disease course in this model of RA. This TSP‐1–derived synthetic peptide may represent an important template for drug development in RA and other inflammatory conditions associated with neutrophil activation. [ABSTRACT FROM AUTHOR]

To compare inflammatory peripheral arthritis in wild‐type and high molecular weight kininogen (HK)–deficient rats, both on the genetically susceptible Lewis background.By backcrossing Brown‐Norway HK‐deficient rats with Lewis rats for 6 generations, 2 new strains were produced, wild‐type F6 and HK‐deficient F6, each with a 98.5% Lewis genome. Inflammatory arthritis was induced by intraperitoneal injection of peptidoglycan–polysaccharide (PG‐PS), and the clinical, histopathologic, and biochemical responses were compared in both strains.Eighteen days after PG‐PS injection, rats with normal concentrations of HK showed weight loss and marked increase in hind ankle diameter with severe synovial inflammation and cartilage abnormalities. In contrast, HK‐deficient rats showed no weight loss (P < 0.05), no increase in hind ankle diameter (P < 0.05), and an absence of inflammatory changes (P < 0.05), as measured by the histologic and morphometric Mankin grading system for synovial and cartilage injury.Plasma HK is a key mediator of acute and chronic inflammatory arthritis in genetically susceptible Lewis rats. [ABSTRACT FROM AUTHOR]