Involvement of the kinin-forming system in the physiopathology of rheumatoid inflammation

Kinins are potent mediators of rheumatoid inflammation. The components of the kinin-forming system are hyperactive in RA. Excessive release of kinins in the synovial fluid can produce oedema, pain and loss of functions due to activation of B1 and B2 receptors. These receptors could be stimulated via injury, trauma, coagulation pathways (Hageman factor and thrombin) and immune complexes. The activated B1 and B2 receptors might cause release of other powerful non-cytokines and cytokines mediators of inflammation, for example, PGE2, PGI2, LTs, histamine, PAF, IL-1 and TNF derived mainly from polymorphonuclear leukocytes, macrophages, endothelial cells and synovial tissue. These mediators are capable of inducing bone and cartilage damage, hypertrophic synovitis, vessels proliferation, inflammatory cells migration, and possibly angiogenesis in pannus formation. These pathological changes, however, are not yet defined in human model of chronic inflammation (RA). Hence, the role of kinin and its interacting inflammatory mediators would soon start to clarify the detailed questions they revealed in clinical and experimental models of chronic inflammatory joint diseases. Several B1 and B2 receptor antagonists are being synthesized in an attempt to study the molecular functions of kinins in inflammatory processes (RA, periodontitis and osteomyelitis), and they represent and important area for continued research in rheumatology. Future development of specific, potent and stable B1 and B2 receptor antagonists or combined B1 and B2 antagonists with y-IFN might serve as pharmacological basis of more effective rationally-based therapies for RA. This may lead to significant advances in our knowledge of the mechanisms and therapeutics of rheumatic diseases.