carboxypeptidase-b and Arthritis--Rheumatoid

We evaluated the synovial effects of 2 potent biologic rheumatoid arthritis (RA) therapies, focusing on their effect on the expression level of carboxypeptidase B (CPB) and its substrates.. Patients with RA receiving infliximab (IFX; n = 9) or rituximab (RTX; n = 5) had an arthroscopic synovial biopsy at baseline and 16 weeks posttherapy. Expression of CPB, C5a, osteopontin (OPN), CD3, CD20, CD55, and CD68 was assessed by immunohistochemistry and image analysis, and compared with OA synovium. RA disease activity score was assessed at multiple timepoints. Serial serum samples were analyzed for soluble CPB and C5a levels.. The baseline clinical characteristics of patients receiving IFX and RTX were similar. At the time of the second biopsy, 50% of patients had achieved a European League Against Rheumatism good or moderate response. At baseline, expression of CPB, C5a, and OPN was markedly higher in RA compared with OA synovium and correlated with mononuclear cell infiltration. There was an overall reduction in synovial expression of CPB, C5a, and OPN paralleling a reduction in mononuclear cell infiltration, but these changes were not associated with clinical response. After an early reduction in serum C5a levels, these returned to baseline levels at later timepoints.. In response to IFX and RTX treatment, RA synovial expression of CPB, C5a, and OPN decrease independently of the clinical response, reflecting the complex proinflammatory and antiinflammatory effects of this pathway.

Topics: Adult; Aged; Antirheumatic Agents; Arthritis, Rheumatoid; Carboxypeptidase B; Female; Humans; Immunohistochemistry; Infliximab; Male; Middle Aged; Rituximab; Synovial Membrane

The immune and coagulation systems are both implicated in the pathogenesis of rheumatoid arthritis (RA). Plasma carboxypeptidase B (CPB), which is activated by the thrombin/thrombomodulin complex, plays a procoagulant role during fibrin clot formation. However, an antiinflammatory role for CPB is suggested by the recent observation that CPB can cleave proinflammatory mediators, such as C5a, bradykinin, and osteopontin. Here, we show that CPB plays a central role in downregulating C5a-mediated inflammatory responses in autoimmune arthritis. CPB deficiency exacerbated inflammatory arthritis in a mouse model of RA, and cleavage of C5a by CPB suppressed the ability of C5a to recruit immune cells in vivo. In human patients with RA, genotyping of nonsynonymous SNPs in the CPB-encoding gene revealed that the allele encoding a CPB variant with longer half-life was associated with a lower risk of developing radiographically severe RA. Functionally, this CPB variant was more effective at abrogating the proinflammatory properties of C5a. Additionally, expression of both CPB and C5a in synovial fluid was higher in patients with RA than in those with osteoarthritis. These findings suggest that CPB plays a critical role in dampening local, C5a-mediated inflammation and represents a molecular link between inflammation and coagulation in autoimmune arthritis.

Topics: Animals; Arthritis, Experimental; Arthritis, Rheumatoid; Blood Coagulation; Carboxypeptidase B; Complement C5a; Down-Regulation; Genotype; Humans; Inflammation; Isoenzymes; Mice; Mice, Inbred C57BL; Mice, Knockout; Osteopontin; Polymorphism, Single Nucleotide; Receptor, Bradykinin B2; Synovial Fluid; Synovial Membrane

Osteopontin (OPN) is a proinflammatory cytokine that plays an important role in the pathogenesis of rheumatoid arthritis (RA). OPN can be cleaved by thrombin, resulting in OPN-R and exposing the cryptic C-terminal alpha4beta1 and alpha9beta1 integrin-binding motif (SVVYGLR). Thrombin-activatable carboxypeptidase B (CPB), also called thrombin-activatable fibrinolysis inhibitor, removes the C-terminal arginine from OPN-R, generating OPN-L and abrogating its enhanced cell binding. We undertook this study to investigate the roles of OPN-R and OPN-L in synoviocyte adhesion, which contributes to the formation of invasive pannus, and in neutrophil survival, which affects inflammatory infiltrates in RA.. Using specifically developed enzyme-linked immunosorbent assays, we tested the synovial fluid of patients with RA, osteoarthritis (OA), and psoriatic arthritis (PsA) to determine OPN-R, OPN-L, and full-length OPN (OPN-FL) levels.. Elevated levels of OPN-R and OPN-L were found in synovial fluid samples from RA patients, but not in samples from OA or PsA patients. Increased levels of OPN-R and OPN-L correlated with increased levels of multiple inflammatory cytokines, including tumor necrosis factor alpha and interleukin-6. Immunohistochemical analyses revealed robust expression of OPN-FL, but only minimal expression of OPN-R, in RA synovium, suggesting that cleaved OPN is released into synovial fluid. In cellular assays, OPN-FL, and to a lesser extent OPN-R and OPN-L, had an antiapoptotic effect on neutrophils. OPN-R augmented RA fibroblast-like synoviocyte binding mediated by SVVYGLR binding to alpha4beta1, whereas OPN-L did not.. Thrombin activation of OPN (resulting in OPN-R) and its subsequent inactivation by thrombin-activatable CPB (generating OPN-L) occurs locally within inflamed joints in RA. Our data suggest that thrombin-activatable CPB plays a central homeostatic role in RA by regulating neutrophil viability and reducing synoviocyte adhesion.

Topics: Antibodies, Anti-Idiotypic; Apoptosis; Arthritis, Psoriatic; Arthritis, Rheumatoid; Carboxypeptidase B; Cell Adhesion; Cell Survival; Humans; Interleukin-6; Neutrophils; Osteoarthritis; Osteopontin; Synovial Membrane; Thrombin; Tumor Necrosis Factor-alpha