Nitric Oxide-Driven Hypoxia Initiates Synovial Angiogenesis, Hyperplasia and Inflammatory Lesions in Mice

Fei Bao,Pei Wu,Frank Qiu,Qing-Ping Zeng,Na Xiao,Pierre Bobé

doi:10.1371/journal.pone.0034494

Fei Bao, Pei Wu + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0034494

Copy DOI

Abstract

BackgroundRheumatoid arthritis (RA) is an inflammatory articular disease with cartilage and bone damage due to hyperplasic synoviocyte invasion and subsequent matrix protease digestion. Although monoclonal antibodies against tumor necrosis factor alpha (TNFα) have been approved for clinical use in patients with RA, desired therapeutic regimens suitable for non-responders are still unavailable because etiological initiators leading to RA remain enigmatic and unidentified.Methodology/Principal FindingsBacteria-induced arthritis (BIA) that simulates collagen-induced arthritis (CIA) is developed in mice upon daily live bacterial feeding. The morphological lesions of paw erythema and edema together with the histological alterations of synovial hyperplasia and lymphocytic infiltration emerge as the early-phase manifestations of BIA and CIA. Bacteria- or collagen-mediated global upregulation of pro-inflammatory cytokines is accompanied by the burst of nitric oxide (NO). Elevation of the serum NO level is correlated with decline of the blood oxygen saturation percentage (SpO2), reflecting a hypoxic consequence during development towards arthritis. NO-driven hypoxia is further evident from a positive relationship between NO and lactic acid (LA), an end product from glycolysis. Upregulation of hypoxia inducible factor 1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF) validates hypoxia-induced angiogenesis in the inflamed synovium of modeling mice. Administration of the NO donor compound sodium nitroprusside (SNP) causes articular inflammation by inducing synovial hypoxia. Anti-bacteria by the antibiotic cefotaxime and/or the immunosuppressant rapamycin or artesunate that also inhibits nitric oxide synthase (NOS) can abrogate NO production, mitigate hypoxia, and considerably ameliorate or even completely abort synovitis, hence highlighting that NO may serve as an initiator of inflammatory arthritis.Conclusions/SignificanceLike collagen, bacteria also enable synovial lesions via upregulating pro-inflammatory cytokines, triggering NO production, driving hypoxic responses, and inducing synovial angiogenesis and hyperplasia, suggesting that sustained infection might be, in part, responsible for the onset of synovitis and arthritis in mice.

Highlights

Rheumatoid arthritis (RA) is a chronic articular inflammatory disease mainly affecting joints and destroying cartilage and bone, often with severe and disabling consequences [1]
While the severity was scored as eight in total or two for each in collagen-induced arthritis (CIA) mice, only half of severity scores, i.e., four in total or one for each, could be recorded for Bacteria-induced arthritis (BIA) mice. This result indicated that prolonged live bacterial feeding could mimick collagen II (CII)-complete Freund’s adjuvant (CFA) immunization to cause a typical, albeit mild, arthritic phenotype in mice
As a gaseous free radical with pleiotropic functions in biological systems, nitric oxide (NO) is produced from the oxidation of L-arginine to Lcitrulline by the catalysis of either isoform of three types of nitric oxide synthase (NOS): inducible NOS, endothelial NOS and neuronal NOS [25]

Summary

Introduction

Rheumatoid arthritis (RA) is a chronic articular inflammatory disease mainly affecting joints and destroying cartilage and bone, often with severe and disabling consequences [1]. Therapeutic regimens sensitive, effective and suitable for non-responders are unavailable because no etiological initiators leading to RA have been validated Given these facts that TNFa is produced upon exposure to bacterial components such as lipopolysaccharide (LPS) and other endotoxins, TNFa is stimulated by microbial pathogens for orchestrating anti-microbial responses, and TNFa inhibitory biologic agents render users at a raised risk of serious infection [9,10,11], it is conceivable that TNFa blockers or antagonists should ameliorate RA by abolishing infection-evoked TNFa, and logically reasonable that the onset of RA is likely attributed, in part, to microbial pathogens. Monoclonal antibodies against tumor necrosis factor alpha (TNFa) have been approved for clinical use in patients with RA, desired therapeutic regimens suitable for non-responders are still unavailable because etiological initiators leading to RA remain enigmatic and unidentified

Methods

Results

Conclusion