Gout: Epitome of painful arthritis

St. Luke's-Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons, New York, NY 10025, USA.
Metabolism: clinical and experimental (Impact Factor: 3.89). 10/2010; 59 Suppl 1(10):S32-6. DOI: 10.1016/j.metabol.2010.07.009
Source: PubMed


Arthritic pain and disability are at or near the top of the list of reasons adult patients seek medical attention. At least 47.8 million US residents have arthritis. In Europe, the magnitude of the problem is similar, affecting 8 million in the United Kingdom and 108 million across the continent. Osteoarthritis is by far the most common form of arthritis. In a regional UK study, nearly half of adults 50 years or older reported some form of osteoarthritic knee pain over a 1-year period. Among the arthritides, gout is notable for the agonizing nature and unique pathogenesis of the pain it generates. Gout is the most common cause of inflammatory arthritis among men and postmenopausal women. Because of the atypical nature of some of its clinical manifestations, gout can present serious diagnostic challenges for practicing physicians. In recent years, knowledge about gout's pathogenesis, pathophysiology, and differential diagnosis has advanced on a broad front. Genetic variants within a newly identified transport gene, SLC2A9, have been associated with a low fractional excretion of uric acid and the presence of gout in several population samples. The SLC2A9 gene encodes glucose transporter 9-a unique hexose and high-capacity urate transporter. In addition, human ATP-binding cassette, subfamily G2 (ABCG2), encoded by the ABCG2 gene, has been found to mediate renal urate secretion. Introduction of a mutation encoded in a model system by a common single nucleotide polymorphism, rs2231142, resulted in a 53% reduction in urate transport rates compared with wild-type ABCG2. Based on a large population study, it has been estimated that at least 10% of all gout cases in white persons may be attributable to this single nucleotide polymorphism causal genetic variant. Of the various categories of arthritis, the crystal-induced arthropathies, gout and pseudogout, are manifested by acute inflammation and tissue damage arising from deposition in joints and periarticular tissues of monosodium urate (MSU), calcium pyrophosphate dehydrate, or basic calcium phosphate crystals. The innate immune system rapidly detects invading pathogenic microbes and nonmicrobial "danger signals" such as MSU crystals. When these crystals are deposited in synovial tissues, NLR proteins (NOD-like receptors) form multiprotein complexes known as inflammasomes that trigger secretion of inflammation-producing cytokines like interleukin-1β and interleukin-18. Usually, gout can be diagnosed by medical history, physical examination, and presence of hyperuricemia (urate >416 μmol/L). However, a urate concentration less than 416 does not by itself rule out gout. Confirmation of the diagnosis by identification of typical MSU crystals in aspirated synovial fluid is definitive. Analysis of joint fluid is mandatory to rule out septic arthritis, which can rapidly become lethal. Because of its special ability to identify and quantitate urate deposits in peripheral tissues, dual-energy computed tomography should prove valuable in the differential diagnosis of gout. Gout mimics a variety of illnesses; for example, spinal gout may masquerade as metastatic cancer, epidural abscess, and nerve compression syndrome.

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    • "As such, it may be speculated that the over-inflammatory state produced in gout is systemic and not limited to joints. This speculation is consistent with the wide variation of co-morbidities recognized in these patients [1]. "
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    ABSTRACT: Introduction Monosodium urate monohydrate (MSU) crystals synergize with various toll-like receptor (TLR) ligands to induce cytokine production via activation of the NOD-like receptor (NLR) family, pyrin domain-containing 3 (NLPR3) inflammasome. This has been demonstrated in vitro using human cell lines or monocytes of healthy volunteers. In the present study, we have investigated the effect of MSU crystals and of their combination with TLR ligands in peripheral blood mononuclear cells (PBMC) of patients with gout. Methods PBMCs from 18 patients with primary gout and 12 healthy donors were exposed to MSU crystals in the presence or absence of saturated fatty acid C18:0 (free fatty acid, TLR2 ligand), palmitoyl-3-cystein (Pam3Cys, TLR1/2 ligand) and fibroblast stimulating factor-1 (FSL-1, TLR 2/6 ligand). Production of IL-1β, IL-6, IL-8, IL-17 and tumor necrosis factor alpha (TNFα) was determined by ELISA. mRNA transcripts of IL-1β were measured by real-time PCR. Results MSU crystals alone failed to induce IL-1β, IL-6 or TNFα in both patients and control groups, but a stronger synergy between MSU/Pam3Cys and MSU/C18:0 for the induction of IL-1β was found in patients with gout compared to healthy controls. IL-6, but not IL-8, followed the kinetics of IL-1β. No production of the neutrophil-recruiting IL-17 was detectable after stimulation of the patients' PBMCs with MSU in both the presence or absence of TLR ligands. No change of gene transcripts of IL-1β after stimulation with MSU and Pam3Cys or with MSU and C18:0 was found. A positive correlation was found between synergy in IL-1β production from PBMCs of patients between C18:0 and MSU crystals, as well as the annual number of attacks of acute gouty arthritis (rs: +0.649, P: 0.022). Conclusions The synergy between MSU crystals and TLR-2 ligands is more prominent in patients with gout than in controls. This is likely mediated by the enhanced maturation of pro-IL-1β into IL-1β.
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