Free radicals and endothelial dysfunction: potential positive effects of TNF-α inhibitors

Cross-linking of IgGs bound on circulating neutrophils leads to an activation of endothelial cells: possible role of rheumatoid factors in rheumatoid arthritis-associated vascular dysfunction

BACKGROUND

Rheumatoid arthritis is characterized by the presence of circulating auto-antibodies, including rheumatoid factors, which recognize the Fc portion of IgGs. The neutrophil is the most abundant circulating leukocyte and it expresses high levels of FcγRs on its surface. The aim of the present study was to examine the capacity of circulating human neutrophils to be activated by rheumatoid factors and the consequences of these events on endothelium.

METHODS

Neutrophil-bound IgGs were cross-linked with anti-human IgGs to mimick the presence of circulating rheumatoid factors and FcγRs-dependent signalling events and functions were examined. The IgG and IgM composition of rheumatoid factors isolated from the serum of RA patients was characterized. Adhesion of neutrophils to endothelial cells was quantified in response to the addition of rheumatoid factors.

RESULTS

Cross-linking of IgGs bound on neutrophils leads to FcγRs-dependent tyrosine phosphorylation, mobilisation of intracellular calcium and the extracellular release of superoxide anions and lysozyme. Incubation of endothelial cells with the supernatant of activated neutrophils increases ICAM-1 expression and IL-8 production by endothelial cells. Finally, rheumatoid factors enhance neutrophil adhesion to endothelial cells.

CONCLUSIONS

Our results show that activation of neutrophils' FcγRs by rheumatoid factors could participate in rheumatoid arthritis-associated vascular damage.

Long-term treatment of rheumatoid arthritis with adalimumab

Rheumatoid arthritis (RA) is a chronic inflammatory disease that is associated with joint damage and progressive disability, an increased risk of morbidity related to comorbid conditions and substantial socioeconomic costs. Tumor necrosis factor-alpha (TNF-α) is a proinflammatory cytokine known to have a central role in the initial host response to infection and in the pathogenesis of various immune-mediated diseases, such as RA, ankylosing spondylitis, psoriasis and/or psoriatic arthritis, Crohn’s disease, and systemic lupus erythematosus. Five TNF-α inhibitors are available for the clinical use: infliximab; adalimumab; etanercept; golimumab; and certolizumab pegol. Infliximab is a chimeric human/murine IgG1 monoclonal antibody (mAb); adalimumab, and golimumab are human mAbs; certolizumab pegol is composed of the fragment antigen-binding anti-binding domain of a humanized anti-TNF-α mAb, combined with polyethylene glycol to increase its half-life in the body; etanercept is a fusion protein that acts as a “decoy receptor” for TNF-α. In this paper, we will briefly review the current data on efficacy and safety of adalimumab in patients with RA, its potential beneficial effects upon comorbid conditions, such as endothelial dysfunction and accelerated atherosclerosis in RA, and the immunogenicity.