The advanced glycation end product pentosidine correlates to IL-6 and other relevant inflammatory markers in rheumatoid arthritis

Abstract

Oxidative stress and inflammatory processes accelerate the formation of advanced glycation end products (AGE), e.g. of pentosidine. The aim of this study was to investigate the relationships between levels of pentosidine in serum and synovial fluid, proinflammatory cytokines, other markers of inflammatory activity, and the state of radiologically visible bone destruction in patients with rheumatoid arthritis (RA). One hundred thirty-three nondiabetic RA patients and 56 age-matched, healthy subjects were included. Serum and synovial fluid pentosidine, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and rheumatoid factor levels were determined. In 30 patients, the proinflammatory cytokines interleukin (IL)-1beta, IL-6, and TNF-alpha and the soluble receptors sIL-2R, sIL-6R, sTNF-alpha, and RI/RII were also measured. Serum levels of pentosidine were on average significantly higher in RA patients than in healthy subjects and correlated significantly to ESR, CRP, and serum levels of IL-6. Serum and synovial fluid pentosidine did not show any differences. Rheumatoid factor-positive RA patients had higher pentosidine levels in the synovial fluid than rheumatoid factor-negative patients. Correlations could not be found between pentosidine and the other cytokines or cytokine receptors measured. The binding of AGE on cell receptors induces activation of nuclear factor kappa B, resulting in enhanced synthesis of proinflammatory cytokines. Moreover, AGE generation may also lead to the formation of new, immunologically relevant epitopes at synovial proteins. Both mechanisms could contribute to initiation and perpetuation of the inflammatory and destructive processes in RA.