Session Title: Rheumamtoid Arthritis - Human Etiology and Pathogenesis
Session Type: Abstract Submissions (ACR)
Background/Purpose: To examine the role of Nicotinamide Adenine Dinucleotide Phosphate Oxidase (NADPH oxidase)-derived Reactive Oxygen Species (ROS) and NADPH oxidase-dependent redox signaling events in regulating angiogenesis and inflammation in the arthritic joint. Moreover to examine the effects of hypoxia, TNFi treatment and NADPH inhibitors on NADPH oxidase mediated angiogenesis and inflammation.
Methods: Patients with inflammatory arthritis (IA; n=48) underwent arthroscopy and synovial tissue oxygen (tpO2) measurements, synovial tissue biopsies and clinical assessment were obtained. Sixteen patients pre/post-TNFi therapy were also recruited. Macroscopic synovitis/vascularity was measured by visual analogue scale. Synovial levels of NADPH oxidase (isoform NOX2), cell-specific markers of inflammation (CD3, CD8, CD20, CD68), vascular factors (VEGF, Ang2, Factor VIII) and redox signaling factors (NF-κB, Akt, STAT3) were quantified by immunohistology/immunofluorescence. Using IA synovial explant cultures ex-vivo, the effect of the NOX2 inhibitors (DPI and APO) on IL-8 release was measured by ELISA. NOX2 protein levels were assessed in K4 cells (immortalised human synoviocytes) under normoxia and hypoxia (3%) by Western Blot.
Results: Low in vivo pO2 levels in the inflamed joint (median [range] 26.6 [3.2–63] mm Hg) were related to increased microscopic expression of NOX2 (p=0.01; r=-0.43). In biologic responders in vivo tpO2 levels increased post treatment, which was associated with a significant reduction in NOX2 level (p<0.05). In contrast in non-responders where tpO2 levels remained the same or were reduced, no significant change in NOX2 expression was observed. Furthermore in vitro hypoxia (3%) induced NOX2 protein expression in K4 cells. High synovial NOX2 expression correlated with high macroscopic vascularity (p=0.005; r=0.46), synovitis (p=0.03; r=0.37), and with increased number of cell-specific markers of T cells (CD4 p=0.0001, r=0.90; CD8 p=0.002, r=0.72), B cells (CD20 p=0.003; r=0.82) and macrophages (CD68 p=0.01; r=0.44). There was a colocalisation and strong association between synovial NOX2 and expression of VEGF (p=0.005; r=0.52), Ang2 (p=0.05; r=0.32) and a number of blood vessels (p=0.004; r=0.50). In addition, synovial NOX2 expression was linked to redox activation of NF-κB, Akt, and STAT3 signaling pathways. Functionally, stimulation of synovial explants with DPI and APO alone or in combination with TNF significantly decreased secretion levels of IL-8.
Conclusion: NADPH oxidase is strongly expressed in synovial tissue and NADPH oxidase-derived ROS may mediate angiogenic and proinflammatory processes in the inflamed joint. Furthermore these effects may in part be mediated through hypoxic activation of downstream redox sensitive signaling events.
C. T. Ng,
D. J. Veale,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/nicotinamide-adenine-dinucleotide-phosphate-oxidase-mediated-angiogenesis-and-inflammation-in-the-arthritic-joint/