Significance: Hydrogen sulfide is emerging as an important mediator of many aspects of inflammation, and perhaps most importantly as a factor promoting the resolution of inflammation and repair of injury. Recent Advances: In the gastrointestinal tract, H 2 S has been shown to promote healing of ulcers and the resolution of mucosal inflammation. On the other hand, suppression of endogenous H 2 S synthesis impairs mucosal defense and leads to increased granulocyte infiltration. H 2 S has been exploited in the design of more effective and safe anti-inflammatory drugs. Critical Issues: Enteric bacteria can be a significant source of H 2 S, which could affect mucosal integrity; indeed, luminal H 2 S can serve as an alternative to oxygen as a metabolic substrate for mitochondrial respiration in epithelial cells. Enterocytes and colonocytes thereby represent a ''metabolic barrier'' to the diffusion of bacteria-derived H 2 S into the subepithelial space. A compromise of this barrier could result in modulation of mucosal function and integrity by bacterial H 2 S. Future Directions: Improvements in methods for measurement of H 2 S and development of more selective inhibitors are crucial for gaining a better understanding of the pathophysiological importance of this mediator. Results from animal studies suggest that H 2 S-releasing agents are promising therapeutic agents for many indications, but these compounds need to be assessed in a clinical setting. Antioxid. Redox Signal. 17, 58-67.

Background and purpose: The inflammation-resolving lipid mediator resolvin E1 (RvE1) effectively stops inflammationinduced bone loss in vivo in experimental periodontitis. It was of interest to determine whether RvE1 has direct actions on osteoclast (OC) development and bone resorption. Experimental approach: Primary OC cultures derived from mouse bone marrow were treated with RvE1 and analysed for OC differentiation, cell survival and bone substrate resorption. Receptor binding was measured using radiolabelled RvE1. Nuclear factor (NF)-kB activation and Akt phosphorylation were determined with western blotting. Lipid mediator production was assessed with liquid chromatography tandem mass spectrometry. Key results: OC growth and resorption pit formation were markedly decreased in the presence of RvE1. OC differentiation was inhibited by RvE1 as demonstrated by decreased number of multinuclear OC, a delay in the time course of OC development and attenuation of receptor activator of NF-kB ligand-induced nuclear translocation of the p50 subunit of NF-kB. OC survival and apoptosis were not altered by RvE1. Messenger RNA for both receptors of RvE1, ChemR23 and BLT 1 is expressed in OC cultures. Leukotriene B 4 (LTB 4 ) competed with [ 3 H]RvE1 binding on OC cell membrane preparations, and the LTB 4 antagonist U75302 prevented RvE1 inhibition of OC growth, indicating that BLT 1 mediates RvE1 actions on OC. Primary OC synthesized the RvE1 precursor 18R-hydroxy-eicosapentaenoic acid and LTB 4 . Co-incubation of OC with peripheral blood neutrophils resulted in transcellular RvE1 biosynthesis. Conclusions and implications: These results indicate that RvE1 inhibits OC growth and bone resorption by interfering with OC differentiation. The bone-sparing actions of RvE1 are in addition to inflammation resolution, a direct action in bone remodelling.

Abstract-Development and progression of end-organ damage in hypertension have been associated with increased oxidative stress. Superoxide anion accumulation has been reported in deoxycorticosterone acetate (DOCA)-salt hypertension, in which endothelin-1 plays an important role in cardiovascular damage. We hypothesized that blockade of ET A receptors in DOCA-salt rats would decrease oxidative stress. Key Words: endothelin Ⅲ receptors, endothelin Ⅲ deoxycorticosterone Ⅲ hypertension, arterial Ⅲ oxidative stress R eactive oxygen species (ROS), such as superoxide anion (⅐O 2 Ϫ ), hydrogen peroxide, and peroxynitrite (ONOO Ϫ ), are generated as intermediates in reduction-oxidation reactions. The major source of ROS in the vasculature is the nonmitochondrial NADPH oxidase. Under physiological conditions, ROS production is inactivated by an elaborate cellular and extracellular antioxidant defense system, of which glutathione peroxidase is a major component. In pathological conditions, increased generation of ROS and/or depletion of the antioxidant capacity results in increased bioavailability of ROS, referred to as oxidative stress. 1 There is increasing evidence that oxidative stress plays a pathological role in hypertension. 2 Several recent studies have provided compelling evidence for increased ROS generation in the vascular tissues of hypertensive rats. Enhanced ⅐O 2 Ϫ production has been demonstrated in mesenteric arterioles of SHR in vivo. 3 Likewise, increased ⅐O 2 Ϫ generation has been reported in cultured aortic endothelial cells from SHR compared with WKY. 4 Oxidative stress has been implicated in a variety of other hypertensive models including Angiotensin II (Ang II)-induced hypertension, 5,6 Dahl salt-sensitive hypertension, 7 and in human essential hypertension. 8 By promoting NO inactivation, lipid peroxidation, DNA damage, and protein modification, oxidative stress plays a key role in endothelial dysfunction and end-organ damage. Furthermore, ROS activate many redox-sensitive, growth-related intracellular signaling pathways in vascular smooth muscle and endothelial cells, which is particularly important in altered proliferation and hypertrophy, contributing to vascular remodeling, a characteristic feature of hypertensive disease. 9,10 Cytokines, growth factors, and vasoactive agents such as Ang II regulate the activity and expression of enzymes involved in ROS production. 1 In Ang II-dependent models of hypertension, vascular production of ⅐O 2 Ϫ is increased through activation of vascular NADPH oxidase. 5,6 Indeed,

Inflammatory diseases associated with pain are often difficult to treat in the clinic due to insufficient understanding of the nociceptive pathways involved. Recently, there has been considerable interest in the role of reactive oxygen species (ROS) in inflammatory disease, but little is known of the role of hydrogen peroxide (H(2)O(2)) in hyperalgesia. In the present study, intraplantar injection of H(2)O(2)-induced a significant dose- and time-dependent mechanical and thermal hyperalgesia in the mouse hind paw, with increased c-fos activity observed in the dorsal horn of the spinal cord. H(2)O(2) also induced significant nociceptive behavior such as increased paw licking and decreased body liftings. H(2)O(2) levels were significantly raised in the carrageenan-induced hind paw inflammation model, showing that this ROS is produced endogenously in a model of inflammation. Moreover, superoxide dismutase and catalase significantly reduced carrageenan-induced mechanical and thermal hyperalgesia, providing evidence of a functionally significant endogenous role. Thermal, but not mechanical, hyperalgesia in response to H(2)O(2) (i.pl.) was longer lasting in TRPV1 wild type mice compared to TRPV1 knockouts. It is unlikely that downstream lipid peroxidation was increased by H(2)O(2). In conclusion, we demonstrate a notable effect of H(2)O(2) in mediating inflammatory hyperalgesia, thus highlighting H(2)O(2) removal as a novel therapeutic target for anti-hyperalgesic drugs in the clinic.

Inflammation contributes to the pathogenesis of chronic kidney disease (CKD). Molecules released by the inflamed injured tissue can activate toll-like receptors (TLRs), thereby modulating macrophage and CD4(+) T-cell activity. We propose that in renal fibrogenesis, M2 macrophages are recruited and activated in a T helper subset 2 cell (T(H)2)-prone inflammatory milieu in a MyD88-dependent manner. Mice submitted to unilateral ureteral ligation (UUO) demonstrated an increase in macrophage infiltration with collagen deposition after 7 d. Conversely, TLR2, TLR4 and MyD88 knockout (KO) mice had an improved renal function together with diminished T(H)2 cytokine production and decreased fibrosis formation. Moreover, TLR2, TLR4 and MyD88 KO animals exhibited less M2 macrophage infiltration, namely interleukin (IL)-10(+) and CD206(+) CD11b(high) cells, at 7 d after surgery. We evaluated the role of a T(H)2 cytokine in this context, and observed that the absence of IL-4 was associated with better renal function, decreased IL-13 and TGF-β levels, reduced arginase activity and a decrease in fibrosis formation when compared with IL-12 KO and wild-type (WT) animals. Indeed, the better renal outcomes and the decreased fibrosis formation were restricted to the deficiency of IL-4 in the hematopoietic compartment. Finally, macrophage depletion, rather than the absence of T cells, led to reduced lesions of the glomerular filtration barrier and decreased collagen deposition. These results provide evidence that future therapeutic strategies against renal fibrosis should be accompanied by the modulation of the M1:M2 and T(H)1:T(H)2 balance, as T(H)2 and M2 cells are predictive of fibrosis toward mechanisms that are sensed by innate immune response and triggered in a MyD88-dependent pathway.

Background and purpose: Recent findings suggest that the noxious gas H2S is produced endogenously, and that physiological concentrations of H2S are able to modulate pain and inflammation in rodents. This study was undertaken to evaluate the ability of endogenous and exogenous H2S to modulate carrageenan-induced synovitis in the rat knee. Experimental approach: Synovitis was induced in Wistar rats by intra-articular injection of carrageenan into the knee joint. Sixty minutes prior to carrageenan injection, the rats were pretreated with indomethacin, an inhibitor of H2S formation (DL-propargylglycine) or an H2S donor [Lawesson's reagent (LR)]. Key results: Injection of carrageenan evoked knee inflammation, pain as characterized by impaired gait, secondary tactile allodynia of the ipsilateral hindpaw, joint swelling, histological changes, inflammatory cell infiltration, increased synovial myeloperoxidase, protein nitrotyrosine residues, inducible NOS (iNOS) activity and NO production. Pretreatment with LR or indomethacin significantly attenuated the pain responses, and all the inflammatory and biochemical changes, except for the increased iNOS activity, NO production and 3-NT. Propargylglycine pretreatment potentiated synovial iNOS activity (and NO production), and enhanced macrophage infiltration, but had no effect on other inflammatory parameters. Conclusions and implications:Whereas exogenous H2S delivered to the knee joint can produce a significant antiinflammatory and anti-nociceptive effect, locally produced H2S exerts little immunomodulatory effect. These data further support the development and use of H2S donors as potential alternatives (or complementary therapies) to the available anti-inflammatory compounds used for treatment of joint inflammation or relief of its symptoms.

Background and Purpose ATB‐346 is a hydrogen sulfide (H2S)‐releasing anti‐inflammatory and analgesic drug. Animal studies demonstrated negligible gastrointestinal (GI) damage despite marked inhibition of COX activity and significant analgesic and anti‐inflammatory effects. In humans, ATB‐346 (250 mg once daily) was found to inhibit COX to the same extent as naproxen (550 mg twice daily). Experimental Approach Two hundred forty‐four healthy volunteers completed a 2‐week, double‐blind study, taking either ATB‐346 (250 mg once daily) or naproxen (550 mg twice daily), with upper GI ulceration being examined endoscopically. Key Results Forty‐two per cent of the subjects taking naproxen developed at least one ulcer (≥3‐mm diameter), while only 3% of the subjects taking ATB‐346 developed at least one ulcer. The two drugs produced comparable and substantial (>94%) suppression of COX activity. Subjects in the naproxen group developed more ulcers per subject than ATB‐346‐treated subjects and a greater incidence of larger ulcers (≥5‐mm diameter). The incidence of dyspepsia, abdominal pain, gastro‐oesophageal reflux, and nausea was lower with ATB‐346 than with naproxen. Subjects treated with ATB‐346 had significantly higher plasma levels of H2S than those treated with naproxen. Conclusions and Implications This Phase 2B study provides unequivocal evidence for a marked reduction of GI toxicity of the H2S‐releasing analgesic/anti‐inflammatory drug, ATB‐346, as compared to the conventional dose of naproxen that produced equivalent suppression of COX. Linked Articles This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc

This study shows that simvastatin therapy leads to a reversal of the cyclosporine A-induced bone loss, which may be mediated by downregulation of interleukin-1beta and prostaglandin E(2) production.