Hydrogen sulfide (H2S) has been shown to have powerful antioxidative and anti-inflammatory properties that can regulate multiple cardiovascular functions. However, its precise role in diabetes-accelerated atherosclerosis remains unclear. We report here that H2S reduced aortic atherosclerotic plaque formation with reduction in superoxide (O2−) generation and the adhesion molecules in streptozotocin (STZ)-induced LDLr−/− mice but not in LDLr−/−Nrf2−/− mice. In vitro, H2S inhibited foam cell formation, decreased O2− generation, and increased nuclear factor erythroid 2–related factor 2 (Nrf2) nuclear translocation and consequently heme oxygenase 1 (HO-1) expression upregulation in high glucose (HG) plus oxidized LDL (ox-LDL)–treated primary peritoneal macrophages from wild-type but not Nrf2−/− mice. H2S also decreased O2− and adhesion molecule levels and increased Nrf2 nuclear translocation and HO-1 expression, which were suppressed by Nrf2 knockdown in HG/ox-LDL–treated endothelial cells. H2S increased S-sulfhydration of Keap1, induced Nrf2 dissociation from Keap1, enhanced Nrf2 nuclear translocation, and inhibited O2− generation, which were abrogated after Keap1 mutated at Cys151, but not Cys273, in endothelial cells. Collectively, H2S attenuates diabetes-accelerated atherosclerosis, which may be related to inhibition of oxidative stress via Keap1 sulfhydrylation at Cys151 to activate Nrf2 signaling. This may provide a novel therapeutic target to prevent atherosclerosis in the context of diabetes.

BackgroundActivated platelets exert a pro-inflammatory action that can be largely ascribed to their ability to interact with leukocytes and modulate their activity. We hypothesized that platelet activation and consequent formation of monocyte-platelet aggregates (MPA) induces a pro-inflammatory phenotype in circulating monocytes.Methodology/Principal FindingsCD62P+ platelets and MPA were measured, and monocytes characterized, by whole blood flow cytometry in healthy subjects, before and two days after receiving influenza immunization. Three monocytic subsets were identified: CD14+CD16−, CD14highCD16+and CD14lowCD16+. The increase in high sensitivity C-reactive protein post-immunization was accompanied by increased platelet activation and MPA formation (25.02±12.57 vs 41.48±16.81; p = 0.01), along with enhancement of circulating CD14highCD16+ cells (4.7±3.6 vs 10.4±4.8; p = 0.003), their percentage being linearly related to levels of CD62P+-platelets (r2 = 0.4347; p = 0.0008). In separate in vitro experiments, co-incubation of CD14+CD16− cells, isolated from healthy donor subjects, with autologous platelets gave rise to up-regulation of CD16 on monocytes as compared with those maintained in medium alone (% change in CD14+CD16+ cells following 48 h co-incubation of monocytes with platelets was +106±51% vs monocytes in medium alone; p<0.001). This effect correlated directly with degree of MPA formation (r2 = 0.7731; p<0.0001) and was associated with increased monocyte adhesion to endothelial cells. P-selectin glycoprotein ligand-1 (PSGL-1) blocking antibody, which abrogates MPA formation, abolished these effects, as did the cyclooxygenase (COX)-2 selective inhibitor NS-398, aspirin and the EP1/EP2-selective antagonist AH6809.Conclusions/SignificanceThese data suggest that MPA formation, as occurs in the blood under pro-inflammatory conditions, expands the pool of circulating CD14highCD16+ monocytes in a COX-2 dependent manner, and these monocytes exhibit increased adhesion to endothelium. Our findings delineate a novel mechanism underlying the pro-inflammatory effect of platelet activation.

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1 Some animal studies suggest that b-adrenoceptor-mediated vasorelaxation is in part mediated through nitric oxide (NO) release. Furthermore, in humans, we have recently shown that forearm blood¯ow is increased by infusion of b 2 -adrenergic agonists into the brachial artery, and the nitric oxide synthase (NOS) inhibitor N G -monomethyl-L-arginine (L-NMMA) inhibits this response. 2 The purpose of the present study was to determine whether stimulation of human umbilical vein endothelial b-adrenoceptors causes vasorelaxation and nitric oxide generation, and whether this might be mediated by cyclic adenosine-3',5'-monophosphate (cyclic AMP). 5 Isoprenaline relaxed umbilical vein rings, and this vasorelaxation was abolished by b 2 -(but not b 1 -) adrenergic blockage, and by endothelium removal or 1 mM L-NMMA. In addition, vasorelaxant responses to dibutyryl cyclic AMP were inhibited by 1 mM L-NMMA, with a reduction in E max from 90.0+9.3% to 50.5+9.9% (P50.05). 6 Isoprenaline 1 mM increased NOS activity in HUVEC (34.0+5.9% above basal, P50.001). Furthermore, isoprenaline increased adenylyl cyclase activity in a concentration-dependent manner; this response was inhibited by b 2 (but not b 1 -) adrenergic blockade. Forskolin 1 mM and dibutyryl cyclic AMP 1 mM each increased NOS activity in HUVEC, to a degree similar to isoprenaline 1 mM. The increase in L-arginine to L-citrulline conversion observed with each agent was abolished by coincubation with NOS inhibitors. 7 These results indicate that endothelial b 2 -adrenergic stimulation and cyclic AMP elevation activate the L-arginine/NO system, and give rise to vasorelaxation, in human umbilical vein.