Bridget Fox

The complex effects of the slow-releasing hydrogen sulfide donor GYY4137 in a model of acute joint inflammation and in human cartilage cells

The role of hydrogen sulfide (H2S) in inflammation remains unclear with both pro‐ and anti‐inflammatory actions of this gas described. We have now assessed the effect of GYY4137 (a slow‐releasing H2S donor) on lipopolysaccharide (LPS)‐evoked release of inflammatory mediators from human synoviocytes (HFLS) and articular chondrocytes (HAC) in vitro. We have also examined the effect of GYY4137 in a complete Freunds adjuvant (CFA) model of acute joint inflammation in the mouse. GYY4137 (0.1–0.5 mM) decreased LPS‐induced production of nitrite (NO2−), PGE2, TNF‐α and IL‐6 from HFLS and HAC, reduced the levels and catalytic activity of inducible nitric oxide synthase (iNOS) and cyclooxygenase‐2 (COX‐2) and reduced LPS‐induced NF‐κB activation in vitro. Using recombinant human enzymes, GYY4137 inhibited the activity of COX‐2, iNOS and TNF‐α converting enzyme (TACE). In the CFA‐treated mouse, GYY4137 (50 mg/kg, i.p.) injected 1 hr prior to CFA increased knee joint swelling while an anti‐inflammatory effect, as demonstrated by reduced synovial fluid myeloperoxidase (MPO) and N‐acetyl‐β‐D‐glucosaminidase (NAG) activity and decreased TNF‐α, IL‐1β, IL‐6 and IL‐8 concentration, was apparent when GYY4137 was injected 6 hrs after CFA. GYY4137 was also anti‐inflammatory when given 18 hrs after CFA. Thus, although GYY4137 consistently reduced the generation of pro‐inflammatory mediators from human joint cells in vitro, its effect on acute joint inflammation in vivo depended on the timing of administration.

Inducible hydrogen sulfide synthesis in chondrocytes and mesenchymal progenitor cells: is H2S a novel cytoprotective mediator in the inflamed joint?

Hydrogen sulfide (H2S) has recently been proposed as an endogenous mediator of inflammation and is present in human synovial fluid. This study determined whether primary human articular chondrocytes (HACs) and mesenchymal progenitor cells (MPCs) could synthesize H2S in response to pro‐inflammatory cytokines relevant to human arthropathies, and to determine the cellular responses to endogenous and pharmacological H2S. HACs and MPCs were exposed to IL‐1β, IL‐6, TNF‐α and lipopolysaccharide (LPS). The expression and enzymatic activity of the H2S synthesizing enzymes cystathionine‐β‐synthase (CBS) and cystathionine‐γ‐lyase (CSE) were determined by Western blot and zinc‐trap spectrophotometry, respectively. Cellular oxidative stress was induced by H2O2, the peroxynitrite donor SIN‐1 and 4‐hydroxynonenal (4‐HNE). Cell death was assessed by 3‐(4,5‐dimethyl‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays. Mitochondrial membrane potential (DCm) was determined in situ by flow cytometry. Endogenous H2S synthesis was inhibited by siRNA‐mediated knockdown of CSE and CBS and pharmacological inhibitors D,L‐propargylglycine and aminoxyacetate, respectively. Exogenous H2S was generated using GYY4137. Under basal conditions HACs and MPCs expressed CBS and CSE and synthesized H2S in a CBS‐dependent manner, whereas CSE expression and activity was induced by treatment of cells with IL‐1β, TNF‐α, IL‐6 or LPS. Oxidative stress‐induced cell death was significantly inhibited by GYY4137 treatment but increased by pharmacological inhibition of H2S synthesis or by CBS/CSE‐siRNA treatment. These data suggest CSE is an inducible source of H2S in cultured HACs and MPCs. H2S may represent a novel endogenous mechanism of cytoprotection in the inflamed joint, suggesting a potential opportunity for therapeutic intervention.

Measurement and meaning of markers of reactive species of oxygen, nitrogen and sulfur in healthy human subjects and patients with inflammatory joint disease

Reactive species of oxygen, nitrogen and sulfur play cell signalling roles in human health, e.g. recent studies have shown that increased dietary nitrate, which is a source of RNS (reactive nitrogen species), lowers resting blood pressure and the oxygen cost of exercise. In such studies, plasma nitrite and nitrate are readily determined by chemiluminescence. At sites of inflammation, such as the joints of RA (rheumatoid arthritis) patients, the generation of ROS (reactive oxygen species) and RNS overwhelms antioxidant defences and one consequence is oxidative/nitrative damage to proteins. For example, in the inflamed joint, increased RNS-mediated protein damage has been detected in the form of a biomarker, 3-nitrotyrosine, by immunohistochemistry, Western blotting, ELISAs and MS. In addition to NO•, another cell-signalling gas produced in the inflamed joint is H2S (hydrogen sulfide), an RSS (reactive sulfur species). This gas is generated by inflammatory induction of H2S-synthesizing enzymes. Using zinc-trap spectrophotometry, we detected high (micromolar) concentrations of H2S in RA synovial fluid and levels correlated with clinical scores of inflammation and disease activity. What might be the consequences of the inflammatory generation of reactive species? Effects on inflammatory cell-signalling pathways certainly appear to be crucial, but in the current review we highlight the concept that ROS/RNS-mediated protein damage creates neoepitopes, resulting in autoantibody formation against proteins, e.g. type-II collagen and the complement component, C1q. These autoantibodies have been detected in inflammatory autoimmune diseases.

Investigating the generation of hydrogen sulfide from the phosphonamidodithioate slow-release donor GYY4137

A combination of NMR spectroscopy, mass spectrometry and chemical synthesis was used to elucidate the two-step hydrolytic decomposition pathway of the slow-release hydrogen sulfide (H2S) donor GYY4137 and the key decomposition product was also prepared by an independent synthetic route. The (dichloromethane-free) sodium salt of the phosphonamidodithioate GYY4137 was also produced as a pharmaceutically more acceptable salt. In contrast with GYY4137 and its sodium salt, the decomposition product did not generate H2S or exert cytoprotective or anti-inflammatory effects in oxidatively stressed human Jurkat T-cells and LPS-treated murine RAW264.7 macrophages. The decomposition product represents a useful control compound for determining the biological and pharmacological effects of H2S generated from GYY4137.