Molecular mechanisms of nitric oxide regulation. Potential relevance to cardiovascular disease

Dynamics of photodissociation of nitric oxide from S-nitrosylated cysteine and N-acetylated cysteine derivatives in water

Cysteine and N-acetylated cysteine derivatives are ubiquitous in biological systems; they have thiol groups that bind NO to form S-nitrosothiols (RSNOs) such as S-nitrosocysteine (CySNO), S-nitroso-N-acetylcysteine (NacSNO), and S-nitroso-N-acetylpenicillamine (NapSNO). Although they have been utilised as thermally or catalytically decomposing NO donors, their photochemical applications are yet to be fully explored owing to the lack of photodissociation dynamics. To this end, the photoexcitation dynamics of these RSNOs in water at 330 nm were investigated using femtosecond time-resolved infrared (TRIR) spectroscopy over a broad time range encompassing the entire reaction, which includes the primary reaction, secondary reactions of the reaction intermediates, and product formation. We discovered that the acetate and amide groups in these RSNOs have strong vibrational bands sensitive to the bondage of NO and the electronic state of the compound, which facilitates the identification of reaction intermediates involved in photoexcitation. The simplest thiol available with the acetate group-thioglycolic acid-was nitrosylated; it produced S-nitrosothioglycolic acid (TgSNO) and was comparatively investigated. Transient absorption bands in the TRIR spectra of the RSNOs were assigned using quantum chemical calculations. Photoexcited cysteine-related RSNOs either decompose into RS and NO within 0.3 ps after excitation at 330 nm with a primary quantum yield (Φ1) of 0.46-1 or relax into an electronically excited intermediate state lying at 42 ± 3 kcal mol-1 above the ground state, which relaxes into the ground state with a time constant of 460-520 ps. A majority (62-80%) of the RS radical geminately rebinds with NO at a time constant of 3-7 ps. The remaining RS reacts with the neighbouring RSNO, which produces additional NO and RSSR with a (nearly) diffusion-limited rate constant that doubles the amount of NO produced; further, it remarkably extends the time window for the dissociated NO to react with the target compound. The final fraction of NO produced from these RSNOs at 330 nm was 0.32-0.58, and it depends on the geminate rebinding yield and Φ1. The detailed dynamics of the photoexcited RSNO can be utilised in the quantitative application of these RSNOs in practical use and in the synthesis of more efficient photoactivated NO precursors.

Hydrogen Sulfide Attenuates Aortic Remodeling in Aortic Dissection Associating with Moderated Inflammation and Oxidative Stress through a NO-Dependent Pathway

Aortic dissection (AD) is a highly lethal vascular disease characterized by separation of the constituent layers of the aortic wall. An increasing body of research indicates that inflammatory response and oxidative stress are implicated in vascular remodeling, which plays a key role in the development of AD. Hydrogen sulfide (H₂S) has been found to protect against various types of cardiovascular disease, including myocardial infarction, arthrosclerosis, and hypertension. However, research on the effect of H₂S on AD is insufficient. This study therefore elucidated the effect of H₂S on the development and progression of AD, and the potential mechanism involved. Using β-aminopropionitrile fumarate (BAPN) and angiotensin II (Ang-II)-induced AD animal models, the administration of NaHS (as H₂S donor, 56 μmol/kg body weight/day) was found to retard the development of AD. Murine VSMCs (Movas) exposed to interleukin-6 (IL-6) (20 ng/mL) to induce phenotypic switch. Histological analyses indicated that H₂S administration inhibited the accumulation of inflammatory cells in the aortic wall and the related expression of inflammatory genes. Additionally, H₂S treatment elevated aortic superoxide dismutase (SOD) activity and ablated malonaldehyde (MDA) and nitric oxide (NO) levels. In mechanistic terms, H₂S attenuated IL-6 induced a pathological VSMC phenotypical switch through NO modulation by N(G)-monomethyl-L-arginine acetate salt (L-NMMA) stimulation. H₂S inhibits AD formation by decreasing the inflammatory response, and oxidative stress, and by positively participating in vascular remodeling. These findings suggest a role for H₂S as a novel and promising therapeutic strategy to prevent AD development.

DDCI-01, a novel long acting phospdiesterase-5 inhibitor, attenuated monocrotaline-induced pulmonary hypertension in rats

Pulmonary arterial hypertension is a progressive, malignant heart disease, characterized by pulmonary arteriole remodeling and increased pulmonary vascular resistance, which eventually leads to right heart failure. This study sought to evaluate the effects of a novel long-acting phospdiesterase-5 inhibitor, namely DDCI-01, as an early intervention for monocrotaline-induced pulmonary hypertensive rats. To establish this model, 50 mg/kg of monocrotaline was intraperitoneally injected into rats. At Day 7 after monocrotaline injection, two doses of DDCI-01 (3 or 9 mg/kg/day) or tadalafil (at 3 or 9 mg/kg/day) were intragastrically administered. The rats were anesthetized with pentobarbital for hemodynamic and echocardiographic measurements, at Day 21 after monocrotaline injection. Compared to the monocrotaline group, DDCI-01 at 3 and 9 mg/kg/day (P) reduced the mean pulmonary arterial pressure (mPAP), right ventricular systolic pressure, right ventricular transverse diameter, pulmonary arterial medial wall thickness (WT%), and right ventricle hypertrophy. However, no significant difference in the indices mentioned as above was found between DDCI-01 (3 mg/kg/day) and tadalafil (3 mg/kg/day). In addition, DDCI-01 at 9 mg/kg/day resulted in lower mPAP and WT%, as well as higher cyclic guanosine monophosphate levels in the lung and plasma compared with the same dose of tadalafil (9 mg/kg/day) (all P < 0.05). These findings suggested that DDCI-01 improved monocrotaline-induced pulmonary hypertension in rats, and a dose of DDCI-01 of 9 mg/kg/day might be more effective than the same dose of tadalafil in monocrotaline-induced pulmonary hypertension in rats.

New predictors of aneurysm sac behavior after endovascular aortic aneurysm repair

OBJECTIVES

This study aimed to identify new predictors of sac behavior after endovascular aortic aneurysm repair (EVAR) and to investigate whether sac behavior is associated with long-term clinical outcomes.

METHODS

A total of 168 patients undergoing successful EVAR for abdominal aortic aneurysms with CTA follow-up of at least 1 year were included. Predictors of aneurysm sac behavior and its impact on long-term clinical outcomes were retrospectively analyzed.

RESULTS

According to sac behavior, eligible patients were stratified into the sac regression group (n = 79, 47.0%) and the sac non-regression group (n = 89, 53.0%). Patients in the regression group were younger (p = 0.036) and more likely to take sarpogrelate hydrochloride postoperatively (p = 0.011) than those in the non-regression group. The incidence of postimplantation syndrome (PIS) was significantly higher in the regression group (p = 0.005). On multivariate analysis, sac regression was more likely to occur in those with PIS (hazard ratio [HR], 1.68; 95% confidence interval [CI], 1.07-2.64; p = 0.023) and less likely to occur in those with transient type II endoleaks (HR, 0.43; 95% CI, 0.20-0.95; p = 0.037) and higher thrombus density within the sac on follow-up CTA (HR, 0.97; 95% CI, 0.95-0.99; p = 0.013). Non-regression of the sac was associated with significantly higher rates of re-intervention during the follow-up period (p = 0.001).

CONCLUSIONS

In addition to type II endoleaks, PIS and thrombus density are new predictors of aneurysm sac behavior, and sac regression is significantly associated with lower rates of re-intervention.

KEY POINTS

• After endovascular aortic aneurysm repair (EVAR), patients with sac regression were younger and more likely to take sarpogrelate hydrochloride postoperatively than those with sac non-regression. • The incidence of postimplantation syndrome (PIS) was significantly higher in patients with sac regression. • In our analysis, PIS and thrombus density within the sac were newly identified predictors of aneurysm sac behavior after EVAR.

Panax ginseng Polysaccharide Protected H9c2 Cardiomyocyte From Hypoxia/Reoxygenation Injury Through Regulating Mitochondrial Metabolism and RISK Pathway

Background and Objective: Ischemic heart disease (IHD) has been the major issue of public health. Panax ginseng (ginseng) has been verified as an effective traditional Chinese medicines and exerted cardioprotective effect. This study aimed to investigate the polysaccharide fraction of ginseng on hypoxia/reoxygenation (H/R) injury in cardiomyocytes and the underlying mechanisms.

Methods: Ginseng was extracted by ethanol and fractionated by high-speed counter current chromatography (HSCCC) and column separation. The cardioprotective effect was evaluated in H9c2 cardiomyocytes underwent H/R treatment. The cell viability, apoptosis and mitochondrial respiration were examined.

Results: An acid polysaccharides fraction of ginseng (AP1) was identified the most effective fraction in protecting cardiomyocytes from H/R injury. AP1 restored the mitochondrial function by maintaining mitochondrial membrane potential (MMP), blocking the release of cytochrome C, and increasing the ATP generation and oxygen consumption rate (OCR) of cardiomyocytes. Meanwhile, AP1 induced the expression of glucocorticoid receptor (GR) and estrogen receptor (ER) which further activated reperfusion injury salvage kinase (RISK) pathway. Finally, AP1 increased nitric oxide (NO) production and regulated endothelial function by increasing endothelial NO synthase (eNOS) expression and decreasing inducible NOS (iNOS) expression in H/R injury.

Conclusion: The results suggested that AP1 exerted a protective effect in myocardial H/R injury mainly through maintaining myocardial mitochondrial function, thereby inhibiting myocardial H/R caused apoptosis and increasing the expressions of GR and ER, which in turn mediated the activation of RISK pathway and eNOS-dependent mechanism to resist the reperfusion injury.

Reduction of Endothelial Nitric Oxide Increases the Adhesiveness of Constitutive Endothelial Membrane ICAM-1 through Src-Mediated Phosphorylation

Nitric oxide (NO) is a known anti-adhesive molecule that prevents platelet aggregation and leukocyte adhesion to endothelial cells (ECs). The mechanism has been attributed to its role in the regulation of adhesion molecules on leukocytes and the adhesive properties of platelets. Our previous study conducted in rat venules found that reduction of EC basal NO synthesis caused EC ICAM-1-mediated firm adhesion of leukocytes within 10-30 min. This quick response occurred in the absence of alterations of adhesion molecules on leukocytes and also opposes the classical pattern of ICAM-1-mediated leukocyte adhesion that requires protein synthesis and occurs hours after stimulation. The objective of this study is to investigate the underlying mechanisms of reduced basal NO-induced EC-mediated rapid leukocyte adhesion observed in intact microvessels. The relative levels of ICAM-1 at different cell regions and their activation status were determined with cellular fractionation and western blot using cultured human umbilical vein ECs. ICAM-1 adhesiveness was determined by immunoprecipitation in non-denatured proteins to assess the changes in ICAM-1 binding to its inhibitory antibody, mAb1A29, and antibody against total ICAM-1 with and without NO reduction. The adhesion strength of EC ICAM-1 was assessed by atomic force microscopy (AFM) on live cells. Results showed that reduction of EC basal NO caused by the application of caveolin-1 scaffolding domain (AP-CAV) or NOS inhibitor, L-NMMA, for 30 min significantly increased phosphorylated ICAM-1 and its binding to mAb1A29 in the absence of altered ICAM-1 expression and its distribution at subcellular regions. The Src inhibitor, PP1, inhibited NO reduction-induced increases in ICAM-1 phosphorylation and adhesive binding. AFM detected significant increases in the binding force between AP-CAV-treated ECs and mAb1A29-coated probes. These results demonstrated that reduced EC basal NO lead to a rapid increase in ICAM-1 adhesive binding via Src-mediated phosphorylation without de novo protein synthesis and translocation. This study suggests that a NO-dependent conformational change of constitutive EC membrane ICAM-1 might be the mechanism of rapid ICAM-1 dependent leukocyte adhesion observed in vivo. This new mechanistic insight provides a better understanding of EC/leukocyte interaction-mediated vascular inflammation under many disease conditions that encounter reduced basal NO in the circulation system.

THE EFFECT OF DIABETES ON CARDIOVASCULAR SYSTEM

Diabetes mellitus (DM) is a critical and long-term disorder due to the insufficient production of insulin by the pancreas or ineffective use of insulin by the body. Importantly, cardiovascular disease (CVD) has long been thought to be linked with diabetes. Despite more diabetic individuals surviving from better medications and treatments, there has been significant rise in the morbidity and mortality from CVD. Indeed, the classification of DM based on the electrocardiogram signals of the heart will be an advantageous system. Further, computer-aided classification of DM with integrated algorithms may enhance the execution of the system. In this paper, we have reviewed various studies using heart rate variability signals for automated classification of diabetes. Furthermore, the different techniques used to extract the features and the efficiency of the classification systems are discussed.

Nitric Oxide-Induced Conformational Changes Govern H-NOX and Histidine Kinase Interaction and Regulation in Shewanella oneidensis

Nitric oxide (NO) is implicated in biofilm regulation in several bacterial families via heme-nitric oxide/oxygen binding (H-NOX) protein signaling. Shewanella oneidensis H-NOX (So H-NOX) is associated with a histidine kinase (So HnoK) encoded on the same operon, and together they form a multicomponent signaling network whereby the NO-bound state of So H-NOX inhibits So HnoK autophosphorylation activity, affecting the phosphorylation state of three response regulators. Although the conformational changes of So H-NOX upon NO binding have been structurally characterized, the mechanism of HnoK inhibition by NO-bound So H-NOX remains unclear. In the present study, the molecular details of So H-NOX and So HnoK interaction and regulation are characterized. The N-terminal domain in So HnoK was determined to be the site of H-NOX interaction, and the binding interface on So H-NOX was identified using a combination of hydrogen-deuterium exchange mass spectrometry and surface-scanning mutagenesis. Binding kinetics measurements and analytical gel filtration revealed that NO-bound So H-NOX has a tighter affinity for So HnoK compared that of H-NOX in the unliganded state, correlating binding affinity with kinase inhibition. Kinase activity assays with binding-deficient H-NOX mutants further indicate that while formation of the H-NOX-HnoK complex is required for HnoK to be catalytically active, H-NOX conformational changes upon NO-binding are necessary for HnoK inhibition.

Electrochemically Modulated Nitric Oxide Release From Flexible Silicone Rubber Patch: Antimicrobial Activity For Potential Wound Healing Applications

Herein, we report a novel design and the antimicrobial efficacy of a flexible nitric oxide (NO) releasing patch for potential wound healing applications. The compact sized polydimethylsiloxane (PDMS) planar patch generates NO via electrochemical reduction of nitrite ions mediated by a copper(II)-ligand catalyst using a portable power system and an internal gold coated stainless steel mesh working electrode. Patches are fabricated via soft lithography and 3-D printing. The devices can continuously release NO over 4 days and exhibit potent bactericidal effects on both Escherichia coli and Staphylococcus aureus. The device may provide an effective, safe, and less costly alternative for treating chronic wounds.

A Study on Regression of Hypercholesterolemic Atherosclerosis in Rabbits by Flax Lignan Complex

Flax lignan complex (FLC) isolated from flaxseed suppresses the development of hypercholesterolemic atherosclerosis. The objectives of this study were to investigate if FLC produces regression of atherosclerosis and if regression is associated with reductions in serum lipids and oxidative stress. The studies were conducted in 4 groups of rabbits: group I, control diet (2 months); group II, 0.25% cholesterol diet (2 months); group III, 0.25% cholesterol diet (2 months) followed by regular diet (4 months); and group IV, 0.25% cholesterol diet (2 months) followed by regular diet and FLC (4 months). Serum lipids and oxidative stress parameters were measured before and at various intervals thereafter on their respective diets. The aortas were removed at the end of the protocol for assessment of atherosclerotic plaques and oxidative parameters. Atherosclerosis in group II was associated with hyperlipidemia and increased oxidative stress. Atherosclerotic changes were accelerated in group III, and this was associated with reductions in serum lipids and oxidative stress. Atherosclerotic lesions in group IV were similar to group II, but significantly smaller than those in group III, and were associated with reductions in serum lipids and oxidative stress similar to that in group III. These results indicate that FLC does not produce regression but prevents the acceleration of atherosclerosis due to the removal of cholesterol in the diet. These effects of FLC are not associated with reductions in serum lipids and oxidative stress.

Upregulation of inducible NO synthase by exogenous adenosine in vascular smooth muscle cells activated by inflammatory stimuli in experimental diabetes

Background

Adenosine has been shown to induce nitric oxide (NO) production via inducible NO synthase (iNOS) activation in vascular smooth muscle cells (VSMCs). Although this is interpreted as a beneficial vasodilating pathway in vaso-occlusive disorders, iNOS is also involved in diabetic vascular dysfunction. Because the turnover of and the potential to modulate iNOS by adenosine in experimental diabetes have not been explored, we hypothesized that both the adenosine system and control of iNOS function are impaired in VSMCs from streptozotocin-diabetic rats.

Methods

Male Sprague–Dawley rats were injected with streptozotocin once to induce diabetes. Aortic VSMCs from diabetic and nondiabetic rats were isolated, cultured and exposed to lipopolysaccharide (LPS) plus a cytokine mix for 24 h in the presence or absence of (1) exogenous adenosine and related compounds, and/or (2) pharmacological agents affecting adenosine turnover. iNOS functional expression was determined by immunoblotting and NO metabolite assays. Concentrations of adenosine, related compounds and metabolites thereof were assayed by HPLC. Vasomotor responses to adenosine were determined in endothelium-deprived aortic rings.

Results

Treatment with adenosine-degrading enzymes or receptor antagonists increased iNOS formation in activated VSMCs from nondiabetic and diabetic rats. Following treatment with the adenosine transport inhibitor NBTI, iNOS levels increased in nondiabetic but decreased in diabetic VSMCs. The amount of secreted NO metabolites was uncoupled from iNOS levels in diabetic VSMCs. Addition of high concentrations of adenosine and its precursors or analogues enhanced iNOS formation solely in diabetic VSMCs. Exogenous adenosine and AMP were completely removed from the culture medium and converted into metabolites. A tendency towards elevated inosine generation was observed in diabetic VSMCs, which were also less sensitive to CD73 inhibition, but inosine supplementation did not affect iNOS levels. Pharmacological inhibition of NOS abolished adenosine-induced vasorelaxation in aortic tissues from diabetic but not nondiabetic animals.

Conclusions

Endogenous adenosine prevented cytokine- and LPS-induced iNOS activation in VSMCs. By contrast, supplementation with adenosine and its precursors or analogues enhanced iNOS levels in diabetic VSMCs. This effect was associated with alterations in exogenous adenosine turnover. Thus, overactivation of the adenosine system may foster iNOS-mediated diabetic vascular dysfunction.

Impaired expression of neuronal nitric oxide synthase in the gracile nucleus is involved in neuropathic changes in Zucker Diabetic Fatty rats with and without 2,5-hexanedione intoxication

These studies examined the influence of 2,5-hexanedione (2,5-HD) intoxication on expression of neuronal nitric oxide synthase (nNOS) in the brainstem nuclei in Zucker Diabetic Fatty (ZDF) vs. lean control (LC) rats. Functional neuropathic changes were also investigated following axonal damage and impaired axonal transport induced by the treatment. Animals were intoxicated by i.p. injection of 2,5-HD plus unilateral administration of 2,5-HD over the sciatic nerve. The mechanical thresholds and withdrawal latencies to heat and cold stimuli on the foot were measured at baseline and after intoxication. The medulla sections were examined by nNOS immunohistochemistry and NADPH-diaphorase histochemistry at the end of the treatments. The mechanical thresholds and withdrawal latencies were significantly decreased while nNOS immunostained neurons and NADPH-diaphorase positive cells were selectively reduced in the gracile nucleus at baseline in ZDF vs. LC rats. NADPH-diaphorase reactivity and nNOS positive neurons were increased in the ipsilateral gracile nucleus in LC rats following 2,5-HD intoxication, but its up-regulation was attenuated in ZDF rats. These results suggest that diabetic and chemical intoxication-induced nNOS expression is selectively reduced in the gracile nucleus in ZDF rats. Impaired axonal damage-induced nNOS expression in the gracile nucleus is involved in neuropathic pathophysiology in type II diabetic rats.

Nitric Oxide Mediates Biofilm Formation and Symbiosis in Silicibacter sp. Strain TrichCH4B

Nitric oxide (NO) plays an important signaling role in all domains of life. Many bacteria contain a heme-nitric oxide/oxygen binding (H-NOX) protein that selectively binds NO. These H-NOX proteins often act as sensors that regulate histidine kinase (HK) activity, forming part of a bacterial two-component signaling system that also involves one or more response regulators. In several organisms, NO binding to the H-NOX protein governs bacterial biofilm formation; however, the source of NO exposure for these bacteria is unknown. In mammals, NO is generated by the enzyme nitric oxide synthase (NOS) and signals through binding the H-NOX domain of soluble guanylate cyclase. Recently, several bacterial NOS proteins have also been reported, but the corresponding bacteria do not also encode an H-NOX protein. Here, we report the first characterization of a bacterium that encodes both a NOS and H-NOX, thus resembling the mammalian system capable of both synthesizing and sensing NO. We characterized the NO signaling pathway of the marine alphaproteobacterium Silicibacter sp. strain TrichCH4B, determining that the NOS is activated by an algal symbiont, Trichodesmium erythraeum. NO signaling through a histidine kinase-response regulator two-component signaling pathway results in increased concentrations of cyclic diguanosine monophosphate, a key bacterial second messenger molecule that controls cellular adhesion and biofilm formation. Silicibacter sp. TrichCH4B biofilm formation, activated by T. erythraeum, may be an important mechanism for symbiosis between the two organisms, revealing that NO plays a previously unknown key role in bacterial communication and symbiosis.

IMPORTANCE

Bacterial nitric oxide (NO) signaling via heme-nitric oxide/oxygen binding (H-NOX) proteins regulates biofilm formation, playing an important role in protecting bacteria from oxidative stress and other environmental stresses. Biofilms are also an important part of symbiosis, allowing the organism to remain in a nutrient-rich environment. In this study, we show that in Silicibacter sp. strain TrichCH4B, NO mediates symbiosis with the alga Trichodesmium erythraeum, a major marine diazotroph. In addition, Silicibacter sp. TrichCH4B is the first characterized bacteria to harbor both the NOS and H-NOX proteins, making it uniquely capable of both synthesizing and sensing NO, analogous to mammalian NO signaling. Our study expands current understanding of the role of NO in bacterial signaling, providing a novel role for NO in bacterial communication and symbiosis.

Thrombospondin-1 and CD47 regulation of cardiac, pulmonary and vascular responses in health and disease

Cardiovascular homeostasis and health is maintained through the balanced interactions of cardiac generated blood flow and cross-talk between the cellular components that comprise blood vessels. Central to this cross-talk is endothelial generated nitric oxide (NO) that stimulates relaxation of the contractile vascular smooth muscle (VSMC) layer of blood vessels. In cardiovascular disease this balanced interaction is disrupted and NO signaling is lost. Work over the last several years indicates that regulation of NO is much more complex than previously believed. It is now apparent that the secreted protein thrombospondin-1 (TSP1), that is upregulated in cardiovascular disease and animal models of the same, on activating cell surface receptor CD47, redundantly inhibits NO production and NO signaling. This inhibitory event has implications for baseline and disease-related responses mediated by NO. Further work has identified that TSP1-CD47 signaling stimulates enzymatic reactive oxygen species (ROS) production to further limit blood flow and promote vascular disease. Herein consideration is given to the most recent discoveries in this regard which identify the TSP1-CD47 axis as a major proximate governor of cardiovascular health.

A novel and potent inhibitor of dimethylarginine dimethylaminohydrolase: a modulator of cardiovascular nitric oxide

PD 404182 [6H-6-imino-(2,3,4,5-tetrahydropyrimido)[1,2-c]-[1,3]benzothiazine], a heterocyclic iminobenzothiazine derivative, is a member of the Library of Pharmacologically Active Compounds (LOPAC) that is reported to possess antimicrobial and anti-inflammatory properties. In this study, we used biochemical assays to screen LOPAC against human dimethylarginine dimethylaminohydrolase isoform 1 (DDAH1), an enzyme that physiologically metabolizes asymmetric dimethylarginine (ADMA), an endogenous and competitive inhibitor of nitric oxide (NO) synthase. We discovered that PD 404182 directly and dose-dependently inhibits DDAH. Moreover, PD 404182 significantly increased intracellular levels of ADMA in cultured primary human vascular endothelial cells (ECs) and reduced lipopolysaccharide-induced NO production in these cells, suggesting its therapeutic potential in septic shock-induced vascular collapse. In addition, PD 404182 abrogated the formation of tube-like structures by ECs in an in vitro angiogenesis assay, indicating its antiangiogenic potential in diseases characterized by pathologically excessive angiogenesis. Furthermore, we investigated the potential mechanism of inhibition of DDAH by this small molecule and found that PD 404182, which has striking structural similarity to ADMA, could be competed by a DDAH substrate, suggesting that it is a competitive inhibitor. Finally, our enzyme kinetics assay showed time-dependent inhibition, and our inhibitor dilution assay showed that the enzymatic activity of DDAH did not recover significantly after dilution, suggesting that PD 404182 might be a tightly bound, covalent, or an irreversible inhibitor of human DDAH1. This proposal is supported by mass spectrometry studies with PD 404182 and glutathione.

Effects of Polycan, a β-glucan, on experimental periodontitis and alveolar bone loss in Sprague-Dawley rats

BACKGROUND AND OBJECTIVE

Polycan is a promising candidate for the treatment of periodontal disease. This study was undertaken to examine whether Polycan, a type of β-glucan, has a protective effect on ligature-induced experimental periodontitis and related alveolar bone loss in Sprague-Dawley rats.

MATERIAL AND METHODS

 Polycan was orally administered, daily, for 10 d, at 21.25, 42.5 or 85 mg/kg, beginning 1 d after ligation. Changes in body weight and alveolar bone loss were monitored, and the anti-inflammatory effects of Polycan were determined by measuring the levels of myeloperoxidase (MPO), interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) in gingival tissue. We also evaluated inducible nitric oxide synthase (iNOS) activity and malondialdehyde (MDA) concentrations as a measure of the antioxidant effect.

RESULTS

Ligature placement led to a marked decrease in body weight, increased alveolar bone loss and increased concentrations of MPO, IL-1β, TNF-α and MDA, as well as increased iNOS activity and inflammatory cell infiltration and decreased collagen-fiber content. Histological examination revealed increases in the number and activity of osteoclast cells, decreases in alveolar bone volume and elevated percentages of osteclasts on the alveolar bone surface. Daily oral treatment with 42.5 or 85 mg/kg of Polycan for 10 d led to significant, dose-dependent inhibition of the effect of ligature placement.

CONCLUSION

Taken together, these results suggest that 10 d of oral treatment with Polycan effectively inhibits ligature placement-induced periodontitis and related alveolar bone loss via an antioxidant effect.

Importance of myocyte-nonmyocyte interactions in cardiac development and disease

Emerging data in the field of cardiac development as well as repair and regeneration indicate a complex and important interplay between endocardial, epicardial, and myofibroblast populations that is critical for cardiomyocyte differentiation and postnatal function. For example, epicardial cells have been shown to generate cardiac myofibroblasts and may be one of the primary sources for this cell lineage during development. Moreover, paracrine signaling from the epicardium and endocardium is critical for proper development of the heart and pathways such as Wnt, fibroblast growth factor, and retinoic acid signaling have been shown to be key players in this process. Despite this progress, interactions between nonmyocyte cells and cardiomyocytes in the heart are still poorly understood. We review the various nonmyocyte-myocyte interactions that occur in the heart and how these interactions, primarily through signaling networks, help direct cardiomyocyte differentiation and regulate postnatal cardiac function.

l-Tetrahydropalmatine, an active component of Corydalis yanhusuo W.T. Wang, protects against myocardial ischaemia-reperfusion injury in rats

l-Tetrahydropalmatine (l-THP) is an active ingredients of Corydalis yanhusuo W.T. Wang, which protects against acute global cerebral ischaemia-reperfusion injury. In this study, we show that l-THP is cardioprotective in myocardial ischaemia-reperfusion injury and examined the mechanism. Rats were treated with l-THP (0, 10, 20, 40 mg/kg b.w.) for 20 min before occlusion of the left anterior descending coronary artery and subjected to myocardial ischaemia-reperfusion (30 min/6 h). Compared with vehicle-treated animals, the infarct area/risk area (IA/RA) of l-THP (20, 40 mg/kg b.w.) treated rats was reduced, whilst l-THP (10 mg/kg b.w.) had no significant effect. Cardiac function was improved in l-THP-treated rats whilst plasma creatine kinase activity declined. Following treatment with l-THP (20 mg/kg b.w.), subunit of phosphatidylinositol 3-kinase p85, serine⁴⁷³ phosphorylation of Akt and serine¹¹⁷⁷ phosphorylation of endothelial NO synthase (eNOS) increased in myocardium, whilst expression of inducible NO synthase (iNOS) decreased. However, the expression of HIF-1α and VEGF were increased in I_{30 min}R_{6 h}, but decreased to normal level in I_{30 min}R_{24 h}, while treatment with l-THP (20 mg/kg b.w.) enhanced the levels of these two genes in I_{30 min}R_{24 h}. Production of NO in myocardium and plasma, activity of myeloperoxidase (MPO) in plasma and the expression of tumour necrosis factor-α (TNF-α) in myocardium were decreased by l-THP. TUNEL assay revealed that l-THP (20 mg/kg b.w.) reduced apoptosis in myocardium. Thus, we show that l-THP activates the PI3K/Akt/eNOS/NO pathway and increases expression of HIF-1α and VEGF, whilst depressing iNOS-derived NO production in myocardium. This effect may decrease the accumulation of inflammatory factors, including TNF-α and MPO, and lessen the extent of apoptosis, therefore contributing to the cardioprotective effects of l-THP in myocardial ischaemia-reperfusion injury.

Muscarinic receptor agonists and antagonists: effects on cardiovascular function

Muscarinic receptor activation plays an essential role in parasympathetic regulation of cardiovascular function. The primary effect of parasympathetic stimulation is to decrease cardiac output by inhibiting heart rate. However, pharmacologically, muscarinic agonists are actually capable of producing both inhibitory and stimulatory effects on the heart as well as vasculature. This reflects the fact that muscarinic receptors are expressed throughout the cardiovascular system, even though they are not always involved in mediating parasympathetic responses. In the heart, in addition to regulating heart rate by altering the electrical activity of the sinoatrial node, activation of M₂ receptors can affect conduction of electrical impulses through the atrioventricular node. These same receptors can also regulate the electrical and mechanical activity of the atria and ventricles. In the vasculature, activation of M₃ and M₅ receptors in epithelial cells can cause vasorelaxation, while activation of M₁ or M₃ receptors in vascular smooth muscle cells can cause vasoconstriction in the absence of endothelium. This review focuses on our current understanding of the signaling mechanisms involved in mediating these responses.

First evaluation of real-time nitric oxide changes in the coronary circulation in patients with non-ischaemic dilated cardiomyopathy using a catheter-type sensor

AIMS

No direct method has yet been developed to measure real-time plasma nitric oxide (NO) concentration in humans. In this study, we evaluated a new method for measuring plasma NO concentration in patients with dilated cardiomyopathy (DCM) and in normal controls using a catheter-type sensor.

METHODS AND RESULTS

We simultaneously measured average peak velocity (APV) of the coronary artery flow and change in plasma NO concentration using the NO sensor placed in the great cardiac vein of 10 DCM patients and 10 control subjects. These evaluations were performed in response to sequential intracoronary infusions of acetylcholine (ACh, 10⁻⁸-10⁻⁶ M), N(G)-monomethyl-l-arginine (l-NMMA, 200 µmol) and co-infusion of ACh and l-NMMA. The change in plasma NO concentration in DCM patients was significantly impaired compared with the control group (P < 0.01). Pretreatment with l-NMMA completely suppressed the ACh-induced NO concentration, whereas APV in the left anterior descending coronary artery was partially suppressed in both groups. Plasma NO concentration reached its peak value later than the maximum APV following the injection of ACh (10⁻⁶ M) in both groups.

CONCLUSION

The catheter-type NO sensor could be applied to clinically evaluate the endothelial function (i.e. reduced endothelium-derived NO bioavailability) in patients with cardiovascular diseases.

Regulation of endothelial permeability via paracellular and transcellular transport pathways

The endothelium functions as a semipermeable barrier regulating tissue fluid homeostasis and transmigration of leukocytes and providing essential nutrients across the vessel wall. Transport of plasma proteins and solutes across the endothelium involves two different routes: one transcellular, via caveolae-mediated vesicular transport, and the other paracellular, through interendothelial junctions. The permeability of the endothelial barrier is an exquisitely regulated process in the resting state and in response to extracellular stimuli and mediators. The focus of this review is to provide a comprehensive overview of molecular and signaling mechanisms regulating endothelial barrier permeability with emphasis on the cross-talk between paracellular and transcellular transport pathways.

NO formation by a catalytically self-sufficient bacterial nitric oxide synthase from Sorangium cellulosum

The role of nitric oxide (NO) in the host response to infection and in cellular signaling is well established. Enzymatic synthesis of NO is catalyzed by the nitric oxide synthases (NOSs), which convert Arg into NO and citrulline using co-substrates O2 and NADPH. Mammalian NOS contains a flavin reductase domain (FAD and FMN) and a catalytic heme oxygenase domain (P450-type heme and tetrahydrobiopterin). Bacterial NOSs, while much less studied, were previously identified as only containing the heme oxygenase domain of the more complex mammalian NOSs. We report here on the characterization of a NOS from Sorangium cellulosum (both full-length, scNOS, and oxygenase domain, scNOSox). scNOS contains a catalytic, oxygenase domain similar to those found in the mammalian NOS and in other bacteria. Unlike the other bacterial NOSs reported to date, however, this protein contains a fused reductase domain. The scNOS reductase domain is unique for the entire NOS family because it utilizes a 2Fe2S cluster for electron transfer. scNOS catalytically produces NO and citrulline in the presence of either tetrahydrobiopterin or tetrahydrofolate. These results establish a bacterial electron transfer pathway used for biological NO synthesis as well as a unique flexibility in using different tetrahydropterin cofactors for this reaction.

Effects of angiotensin converting enzyme inhibitor and angiotensin II receptor antagonist combination on nitric oxide bioavailability and atherosclerotic change in Watanabe heritable hyperlipidemic rabbits

We investigated the effects of co-administration of an angiotensin-converting enzyme inhibitor (ACEI) and angiotensin type 1 receptor blocker (ARB) on nitric oxide (NO) bioavailability in genetically hyperlipidemic rabbits with our newly developed NO sensor. Plasma NO was measured using the new NO sensor in the abdominal aorta of anesthetized Watanabe heritable hyperlipidemic (WHHL) rabbits. Acetylcholine (ACh)-stimulated (20 microg in 5 min into the aortic arch) NO production was recorded after an 8 week per os pretreatment with 1) vehicle (control), 2) the ACEI enalapril (E: 3 mg/kg/day), 3) the ARB losartan (L: 30 mg/kg/day) and 4) enalapril (1.5 mg/kg/day)+losartan (15 mg/kg/day) (E+L). Intra-aortic infusion of ACh produced an increase in plasma NO concentration, which was significantly greater with all the drug treatments than with the control. E increased ACh-induced NO significantly more than L (by 6.9 nmol/L, and 4.7 nmol/L, respectively). E+L increased ACh-induced NO by 9.5 nmol/L, significantly more than either E or L. Plasma peroxynitrite concentration was 1.2 pmol/mg protein in the control group and significantly less than in the E- and L-group. The lowest peroxynitrite concentration was observed in the E+L group (0.5 pmol/mg protein), which was significantly lower than in the E-group and the L-group. Optical coherence tomography and histology of the thoracic aorta revealed that the plaque area decreased significantly more with the combination than with the monotherapy (p<0.01). In conclusion, the combined treatment with an ACEI and an ARB may have additive protective effects on endothelial function as well as atherosclerotic change.

Effects of pioglitazone on nitric oxide bioavailability measured using a catheter-type nitric oxide sensor in angiotensin II-infusion rabbit

Recently, peroxisome proliferator-activated receptor gamma (PPARgamma) ligands have been reported to increase nitric oxide (NO) bioavailability in vitro but not in vivo because of the difficulty of measuring plasma NO. Here, we investigated the effects of PPARgamma on plasma NO concentrations using the newly developed NO sensor in angiotensin II (Ang II)-infused rabbits. Male New Zealand rabbits were randomized for infusion with Ang II, either alone or in combination with pioglitazone (a PPARgamma agonist). Plasma NO concentration was measured using the catheter-type NO sensor placed in the aorta. We then infused N(G)-methyl-L-arginine (L-NMMA) and acetylcholine (ACh) into the aortic arch to measure the basal and ACh-induced plasma NO concentration. Vascular nitrotyrosine levels were examined by enzyme-linked immunoassay (ELISA). Both an immunohistochemical study and Western blotting were performed to examine the PPARgamma and gp91phox expression. The cotreatment with pioglitazone significantly suppressed the negative effects of Ang II, that is, the decreases in basal and ACh-induced NO production and the increase in vascular nitrotyrosine levels. Both the immunohistochemical study and Western blotting demonstrated that pioglitazone treatment enhaced PPARgamma expression and greatly inhibited Ang II-induced up-regulation of gp91phox. In conclusion, the PPARgamma agonist pioglitazone significantly improved NO bioavailability in Ang II-infused rabbits, most likely by attenuating nitrosative stresses.

Reduced NO synthesis and eNOS mRNA expression in endothelial cells from newborns with a strong family history of type 2 diabetes

BACKGROUND

A deficient synthesis of nitric oxide (NO) may play a role in the early endothelial dysfunction of healthy humans with a strong family history of type 2 diabetes (DM2). In this study, we evaluate the intracellular synthesis of NO and the expression of eNOS transcripts in human umbilical vein endothelial cells (HUVECs), exposed to high glucose concentrations, of healthy newborns with (experimental) and without (control) a strong family history of DM2.

METHODS

HUVECs were incubated in M-199 culture media (containing a 5 mmol/L physiological glucose concentration) or supraphysiological glucose concentrations (15 or 30 mmol/L), for 48 h. Flow cytometry, reactive of Griess and RT-PCR were used to determine intracellular NO synthesis, presence of NO metabolites, and expression of eNOS, GLUT1 or p53 transcripts.

RESULTS

NO synthesis in experimental HUVECs showed a progressive reduction in the presence of increasing glucose concentration (11% for 5 mmol to 8% for 30 mmol; p < 0.01), whereas control HUVECs showed an increase in NO synthesis (3% for 5 mmol to 31% for 30 mmol; p < 0.001). In experimental HUVECs, we found a diminished expression of eNOS and p53, and also an enhanced expression of GLUT1 mRNA transcripts. Control HUVECs showed an increase in eNOS, and no modifications in p53 or GLUT1 mRNA transcripts.

CONCLUSIONS

Our results show how HUVECs, isolated from healthy newborns with a strong family history of DM2, have an abnormal intracellular synthesis of NO and an impaired expression of eNOS, GLUT1 and p53 genes, all associated with NO synthesis.

Regression of hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed

Secoisolariciresinol diglucoside (SDG) isolated from flaxseed is a lipid-lowering and antioxidant agent. It suppresses the development of hypercholesterolemic atherosclerosis in rabbits. It is however not known if SDG would produce regression of atherosclerosis. The objectives of this study were to determine (i) if SDG produces regression of atherosclerosis; (ii) if regression is associated with reduction in serum lipids, oxidative stress or both; and (iii) if the duration of treatment has an effect on regression. Rabbits were assigned to five groups: Group I, regular diet (control); Group II, 0.5% cholesterol diet for 2 months (mo); Group III, same as Group II but followed by regular diet for 2 mo; Group IV, same as Group II and followed by regular diet with SDG (20mg x kg body wt(-1) x day(-1) PO) for 2 mo; and Group V, same as Group IV but SDG treatment for an additional 2 mo. Blood samples were collected from rabbits before and at monthly intervals thereafter on their respective diet regimen for measurement of triglycerides (TG), total cholesterol (TC), LDL-C, HDL-C and malondialdehyde (MDA), a lipid peroxidation product. At the end of the protocol, the aorta was removed for assessment of atherosclerotic lesions, aortic MDA and aortic chemiluminescence (Aortic-CL), a measure of antioxidant reserve. MDA and Aortic-CL provide an index of oxidative stress. Increases in serum TG, TC, LDL-C, HDL-C and the risk ratio TC/HDL-C in Group II were associated with an increase in oxidative stress and development of atherosclerosis (57% of aortic intimal surface covered with lesions). Serum lipids decreased to a similar extent in Groups III-V, however atherosclerotic lesions were 84%, 63% and 44%, respectively in Groups III-V. There were more atherosclerotic lesions in Group III (+48.9%) as compared to Group II. The atherosclerotic lesions decreased by 24% and 45%, respectively in Groups IV and V compared to Group III. The reduction in atherosclerotic lesions was associated with a reduction in oxidative stress. These results suggest that (i) regular diet following a high cholesterol diet accelerates atherosclerosis in spite of a decrease in serum lipids; (ii) SDG treatment prevents the progression of atherosclerosis on a regular diet following a high cholesterol diet; (iii) prevention of progression is associated with a reduction of aortic oxidative stress and not with reductions in serum lipids; (iv) a longer duration of treatment reduces the progression of atherosclerosis to a greater extent, and tends to regress the atherosclerosis.

Role of nitric oxide pathway in placental dysfunction following fetal bypass

BACKGROUND

The etiology of placental dysfunction after fetal cardiopulmonary bypass remains unknown. The placental nitric oxide (NO) pathway has been implicated in this pathophysiology. We set out to examine possible perturbations in this pathway in an ovine model of fetal bypass.

METHODS

Ovine fetuses (n = 14) between 100 and 114 days of gestation, instrumented to measure hemodynamics and umbilical blood flow, were placed on bypass for 30 minutes and followed after bypass for 2 hours. Sham controls (n = 6) were instrumented but did not undergo bypass. Real-time, in-vivo NO concentrations were measured in the placental circulation. To examine other components of the NO pathway, fetal plasma samples were analyzed by immunoassays for total NO metabolite and cyclic guanosine 3',5'-cyclic monophosphate (cGMP) levels. In addition, the expression of phosphodiesterase-5 was examined in placenta by immunohistochemistry. Statistical analysis was performed using analysis of variance with least significant difference post hoc tests (p < or = 0.05).

RESULTS

With the onset of bypass, an immediate increase occurs in umbilical NO concentrations. These return to baseline with cessation of bypass, and decline thereafter. In contrast, there was a linear increase in fetal plasma cGMP levels and a decline in NO metabolite concentrations through the post-bypass period. There was a dramatic increase in placental phosphodiesterase-5 expression with 30 minutes of bypass. The changes occur simultaneously with decreasing umbilical flows, increased placental vascular resistance, and worsening placental gas exchange.

CONCLUSIONS

Fetal bypass leads to significant reductions in placental NO concentrations despite increases in fetal plasma cGMP and placental phosphodiesterase-5 levels, indicative of perturbations in the fetal-placental NO pathway.

Flipping the switch: How a sperm activates the egg at fertilization

Sperm interaction with an egg in animals was first documented 160 years ago in sea urchins by Alphonse Derbès (1847) when he noted the formation of an "envelope" following the sperm's "approach" to the egg. The "envelope" in sea urchins is an obvious phenotype of fertilization in this animal and over the past 35 years has served to indicate a presence of calcium released from cytoplasmic stores essential to activate the egg. The mechanism of calcium release has been intensely studied because it is a universal regulator of cellular activity, and recently several intersecting pathways of calcium release have been defined. Here we examine these various mechanisms with special emphasis on recent work in eggs of both sea urchins and mice.

Nitric oxide donors alter cardiomyocyte cytokine secretion and cardiac function

OBJECTS

The mechanisms by which nitric oxide produces beneficial/detrimental effects on physiologic function are unclear. In this study, we hypothesized that nitric oxide promotes cyclic guanosine monophosphate (cGMP) formation, which, in turn, promotes cardiomyocyte secretion of inflammatory cytokines as well as accumulation of intracellular Na+/Ca2+; these factors contribute to altered cardiac contractile function.

DESIGN

Laboratory study.

SETTING

Medical Center.

SUBJECTS

Adult Sprague Dawley rats weighing 325-350 g.

INTERVENTIONS

Cardiomyocytes were prepared by collagenase perfusion of rat hearts; cells were plated (5 x 10(4) cells/microtiter well) and challenged with either vehicle or nitric oxide donor (S-nitroso-N-acetyl-penicillamine [SNAP] or PAPA NONOATE, 3-[2-Hydroxy-2-nitroso-1-propythdrazinol]-1-propanamine], NOC-15 [PAPA-NO], 0.3 or 1.0 mM of each nitric oxide donor) in the presence/absence of methylene blue (10 microM/L to inhibit cGMP). After 3 hrs, supernatants were collected to measure nitrite/nitrate (nitric oxide), cytokines (tumor necrosis factor-alpha, interleukin-1beta, interleukin-6), and cGMP levels; cells were then loaded with a fluorescent indicator (Fura-2AM or sodium-binding benzofurzan isophthalate) to measure myocyte Ca2+ or Na+, respectively. Parallel experiments included the addition of nitric oxide donor (0.3 or 1.0 mM SNAP or PAPA-NO) to perfused hearts in presence or absence of the methylene blue to examine cGMP-mediated effects on myocardial contraction-relaxation, while other experiments determined a) potential lipopolysaccharide contamination of myocyte preparations; and b) whether a cGMP analogue recapitulated the effects of nitric oxide donors on cytokine secretion.

MEASUREMENTS AND MAIN RESULTS

Nitric oxide donors produced a dose-dependent increase in cGMP levels in myocyte supernatants as well as an increase in myocyte cytokine secretion, increased myocyte loading of Na+/Ca2+, and produced myocardial contractile dysfunction. Addition of the cGMP analog, 8-bromo-cGMP, recapitulated the effects of nitric oxide donors on myocyte cytokine secretion. Nitric oxide donor-related effects were ablated by pretreatment of myocytes or isolated hearts with methylene blue. Treatment of myocytes with recombinant bactericidal/permeability-increasing protein to scavenge lipopolysaccharide confirmed that cytokine responses to nitric oxide donors were not related to lipopolysaccharide contamination of myocyte preparations.

CONCLUSIONS

We suggest that nitric oxide synthesis in injury and disease promotes cGMP formation, which, in turn, modulates cardiac contraction/relaxation by a) altering cardiomyocyte secretion of inflammatory cytokines and b) altering myocyte handling of Na+/Ca2+.

An anti-ulcer drug, geranylgeranylacetone, suppresses inducible nitric oxide synthase in cultured vascular smooth muscle cells

OBJECTIVE

Geranylgeranylacetone (GGA) is commonly used as an anti-ulcer drug. If GGA affects inducible nitric oxide synthase (iNOS) in the vascular tissue, it could influence disease progression in coronary arteries. We investigated the effects of the anti-ulcer drug GGA on iNOS activity in vascular smooth muscle cells.

METHODS

We measured the production of nitrite, a stable metabolite of nitric oxide, in cultured rat vascular smooth muscle cells with the Griess reagent. iNOS protein and mRNA expressions were assayed by western blotting and northern blotting, respectively. The levels of nuclear factor (NF)-kappaB proteins in nuclear extracts were analyzed by gel retardation assay. Heat shock protein 70, a cytoprotective molecule, was evaluated by western blotting.

RESULTS

Incubation of cultures with interleukin-1beta for 24 h caused a significant increase in nitrite generation. Interleukin-1beta-induced nitrite production by vascular smooth muscle cells was significantly suppressed by GGA in a dose-dependent manner. GGA-suppressed nitrite production was accompanied by decreased iNOS mRNA and protein accumulations. GGA by itself did not modulate the basal level of nitrite production. Interleukin-1beta induced NF-kappaB activation in vascular smooth muscle cells, and the addition of GGA further inhibited this NF-kappaB activation. GGA itself induced heat shock protein 70 expression in a dose-dependent manner.

CONCLUSION

These findings demonstrated that GGA suppresses iNOS expression in cytokine-stimulated cultured vascular smooth muscle cells partially through the suppression of NF-kappaB activation, suggesting that GGA may modulate the pathophysiology of cardiovascular diseases including atherosclerosis. In addition, this effect may be associated with heat shock protein 70 production by GGA.

Basal endothelial nitric oxide release is preserved in overweight and obese adults

OBJECTIVE

Impaired basal nitric oxide release is associated with a number of cardiovascular disorders including hypertension, arterial spasm, and myocardial infarction. We determined whether basal endothelial nitric oxide release is reduced in otherwise healthy overweight and obese adult humans.

RESEARCH METHODS AND PROCEDURES

Seventy sedentary adults were studied: 32 normal weight (BMI <25 kg/m(2)), 24 overweight (BMI > or = 25 < 30 kg/m(2)), and 14 obese (BMI > or = 30 kg/m(2)). Forearm blood flow (FBF) responses to intra-arterial infusions of N(g)-monomethyl-L-arginine (5 mg/min), a nitric oxide synthase inhibitor, were used as an index of basal nitric oxide release.

RESULTS

N(g)-monomethyl-L-arginine elicited significant reductions in FBF in the normal weight (from 4.1 +/- 0.2 to 2.7 +/- 0.2 mL/100 mL tissue/min), overweight (4.1 +/- 0.1 to 2.8 +/- 0.2 mL/100 mL tissue/min), and obese (3.9 +/- 0.3 to 2.7 +/- 0.2 mL/100 mL tissue/min) subjects. Importantly, the magnitude of reduction in FBF (approximately 30%) was similar among the groups.

DISCUSSION

These results indicate that the capacity of the endothelium to release nitric oxide under basal conditions is not compromised in overweight and obese adults.

What sense lies in antisense inhibition of inducible nitric oxide synthase expression?

The impact of nitric oxide (NO) synthesized after activation by proinflammatory cytokines and/or bacterial products by an inducible NO synthase (iNOS) is still contradictory. Expression of iNOS in inflammatory reactions is often found predominantly in cells of epithelial origin, and in these cases NO may serve as a protective agent limiting pathogen spreading, downregulating local inflammatory reactions by inducing production of Th2-like responses in a classical feedback circle, or limiting tissue damage during stress conditions. However, an abundant amount of data on chronic human disorders with predominant proinflammatory Th1-like reactions points to a destructive role of iNOS activity calling for a specific inhibition. Various methods to inhibit iNOS have been established to elucidate a protective versus a destructive role of NO during various stresses. In this review, we focus on antisense (AS)-mediated gene knock-down as a relatively new method to inhibit NO production and summarize the techniques applied and their successes. At least in theory, it provides a specific, rapid, and potentially high-throughput method for inhibiting gene expression and function. We here discuss the opportunities of iNOS-directed AS-ODN, and extensively deal with limitations and experimental problems.

Interflavin one-electron transfer in the inducible nitric oxide synthase reductase domain and NADPH-cytochrome P450 reductase

In this study, we have analyzed interflavin electron transfer reactions from FAD to FMN in both the full-length inducible nitric oxide synthase (iNOS) and its reductase domain. Comparison is made with the interflavin electron transfer in NADPH-cytochrome P450 reductase (CPR). For the analysis of interflavin electron transfer and the flavin intermediates observed during catalysis we have used menadione (MD), which can accept an electron from both the FAD and FMN sites of the enzyme. A characteristic absorption peak at 630 and 520 nm can identify each FAD and FMN semiquinone species, which is derived from CPR and iNOS, respectively. The charge transfer complexes of FAD with NADP+ or NADPH were monitored at 750 nm. In the presence of MD, the air-stable neutral (blue) semiquinone form (FAD-FMNH*) was observed as a major intermediate during the catalytic cycle in both the iNOS reductase domain and full-length enzyme, and its formation occurred without any lag phase indicating rapid interflavin electron transfer following the reduction of FAD by NADPH. These data also strongly suggest that the low level reactivity of a neutral (blue) FMN semiquinone radical with electron acceptors enables one-electron transfer in the catalytic cycle of both the FAD-FMN pairs in CPR and iNOS. On the basis of these data, we propose a common model for the catalytic cycle of both CaM-bound iNOS reductase domain and CPR.

Role of endothelial nitric oxide in microvascular oxygen delivery and consumption

Nitric oxide (NO) is an important signaling molecule modulating diverse processes such as vasodilation, neurotransmission, long-term potentiation, and immune responses. The endothelium contributes a significant fraction of NO from endothelial NO synthase (eNOS). The objective of this work was to analyze the role of eNOS in the modulation of oxygen supply to the tissues and in adaptation to maintain oxygenation uncompromised. Oxygen delivery and consumption were measured in the microcirculation of homozygous mutant endothelial nitric oxide synthase-deficient (eNOS(-/-)) and wild-type mice. Animals were implanted with a dorsal window chamber, allowing us to assess the intact microvascular system. Hemodynamics and oxygen tension were assessed in the microcirculation of conscious animals. The eNOS(-/-) mice had significantly higher blood pressure and lower heart rate (146 +/- 8 mm Hg, 401 +/- 17 bpm) than wild type (127 +/- 6 mm Hg, 428 +/- 20 bpm). Microvascular hemodynamic parameters were not significantly different between groups. The eNOS(-/-) animals delivered less oxygen to the microcirculation and released more oxygen to the tissue; both differences were statistically significant compared to wild type. The arteriolar vessel wall oxygen gradient, a measure of vascular smooth muscle cells and endothelial cell wall oxygen consumption, was significantly lower for eNOS(-/-) than for wild type, suggesting that the inhibition of eNOS is an antianoxia (oxygen sparing) mechanism. Finally, the findings of the study support the argument that NO availability limits oxygen consumption by the tissue.

Differential effects of the phosphodiesterase type 5 inhibitors sildenafil, vardenafil, and tadalafil in rat aorta

Presumably, the vasorelaxant properties of phosphodiesterase type 5 (PDE5) inhibitors are similar in isolated blood vessels. We aimed to explore the mechanisms underlying the vasorelaxation induced by the selective PDE5 inhibitors sildenafil, vardenafil, and tadalafil in the rat aorta. Aortic rings were mounted in 5-ml organ baths, and concentration-response curves for PDE5 inhibitors (0.0001-10 microM) were constructed in phenylephrine (PE)-precontracted endothelium-intact and -denuded rings. Cyclic nucleotides were measured using enzyme immunoassay kits. Sildenafil, vardenafil, and tadalafil concentration dependently relaxed aortic rings and increased cGMP, but not cAMP, concentrations. Endothelium denudation caused marked rightward shifts in the curves to sildenafil (45-fold), tadalafil (21-fold), and vardenafil (251-fold). Maximal responses to sildenafil and tadalafil were substantially reduced (38 +/- 1% and 53 +/- 2%, respectively), whereas that evoked by vardenafil was not affected. Likewise, inhibition of NO synthase (N(omega)-nitro-L-arginine methyl ester, 100 microM), guanylyl cyclase (1H-[1,2,4]oxadiazolo [4,3,-a]quinoxalin-1-one, 10 microM), or scavenging of NO ([carboxy-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), 100 microM]) caused similar attenuation of the vasorelaxations evoked by PDE5 inhibitors. Sildenafil, tadalafil, and vardenafil significantly potentiated relaxations mediated by glyceryl trinitrate (0.0001-3 microM; 8-13-fold) and atrial natriuretic peptide (0.1-100 nM; 2-3-fold). Contractions evoked by CaCl(2) (0.01-5 mM) in PE-treated rings were significantly reduced (26 +/- 4%) by vardenafil, but not sildenafil or tadalafil, whereas phorbol 12,13-dibutyrate-induced contractions were not affected. Ouabain, cyclopiazonic acid, and calyculin A failed to affect vasorelaxations induced by the PDE5 inhibitors. These results suggest that vardenafil, but not sildenafil or tadalafil, affects Ca(2+) handling in the rat aorta in addition to increasing cGMP levels through inhibition of PDE5 to cause relaxation.

Modulation of prostaglandin biosynthesis by nitric oxide and nitric oxide donors

The biosynthesis and release of nitric oxide (NO) and prostaglandins (PGs) share a number of similarities. Two major forms of nitric-oxide synthase (NOS) and cyclooxygenase (COX) enzymes have been identified to date. Under normal circumstances, the constitutive isoforms of these enzymes (constitutive NOS and COX-1) are found in virtually all organs. Their presence accounts for the regulation of several important physiological effects (e.g. antiplatelet activity, vasodilation, and cytoprotection). On the other hand, in inflammatory setting, the inducible isoforms of these enzymes (inducible NOS and COX-2) are detected in a variety of cells, resulting in the production of large amounts of proinflammatory and cytotoxic NO and PGs. The release of NO and PGs by the inducible isoforms of NOS and COX has been associated with the pathological roles of these mediators in disease states as evidenced by the use of selective inhibitors. An important link between the NOS and COX pathways was made in 1993 by Salvemini and coworkers when they demonstrated that the enhanced release of PGs, which follows inflammatory mechanisms, was nearly entirely driven by NO. Such studies raised the possibility that COX enzymes represent important endogenous "receptor" targets for modulating the multifaceted roles of NO. Since then, numerous papers have been published extending the observation across various cellular systems and animal models of disease. Furthermore, other studies have highlighted the importance of such interaction in physiology as well as in the mechanism of action of drugs such as organic nitrates. More importantly, mechanistic studies of how NO switches on/off the PG/COX pathway have been undertaken and additional pathways through which NO modulates prostaglandin production unraveled. On the other hand, NO donors conjugated with COX inhibitors have recently found new interest in the understanding of NO/COX reciprocal interaction and potential clinical use. The purpose of this article is to cover the advances which have occurred over the years, and in particular, to summarize experimental data that outline how the discovery that NO modulates prostaglandin production has impacted and extended our understanding of these two systems in physiopathological events.

Evaluation of bioavailability of nitric oxide in coronary circulation by direct measurement of plasma nitric oxide concentration

Although bioavailability of NO in the coronary circulation is commonly evaluated by acetylcholine (ACh)-induced vasodilation, a change in plasma NO concentration and its relation to the flow response after injection of ACh are still unknown. Thus, we directly measured the concentration of NO in the coronary sinus by using a catheter-type NO sensor for coronary sinus. An NO-sensitive sensor was located and fixed in a 4-Fr catheter with a soft tip for protection of vascular wall. After calibration with an NO-saturated pure water, the catheter-type NO sensor was located in the coronary sinus in anesthetized dogs. The coronary flow velocity (CFV) was measured with a Doppler guide wire. Intracoronary injection of ACh (0.4 and 1.0 microg/kg) increased plasma NO concentration in a dose-dependent manner (3-10 nM). Although ACh increased CFV by 95%, there was no significant difference between the two ACh doses. After ACh, the peak value of plasma NO concentration was observed significantly later than CFV. N(G)-methyl-L-arginine (NO synthase inhibitor) decreased basal NO concentration by 3 nM and suppressed the ACh-induced NO synthesis with no significant change in average peak velocity. We conclude that production of NO in the coronary circulation can be evaluated in the coronary sinus. Although ACh increases both CFV and NO concentration, CFV dose not reflect NO concentration in terms of magnitude and time course. Direct measurement of plasma NO concentration by the catheter-type NO sensor is useful to evaluate bioavailability of NO in the coronary circulation.

Visualizing inducible nitric-oxide synthase in living cells with a heme-binding fluorescent inhibitor

The study of nitric-oxide synthase (NOS) physiology is constrained by the lack of suitable probes to detect NOS in living cells or animals. Here, we characterized a fluorescent inducible NOS (iNOS) inhibitor called PIF (pyrimidine imidazole FITC) and examined its utility for microscopic imaging of iNOS in living cells. PIF binding to iNOS displayed high affinity, isoform selectivity, and heme specificity, and was essentially irreversible. PIF was used to successfully image iNOS expressed in RAW264.7 cells, HEK293T cells, human A549 epithelial cells, and freshly obtained human lung epithelium. PIF was used to estimate a half-life for iNOS of 1.8 h in HEK293T cells. Our work reveals that fluorescent probes like PIF will be valuable for studying iNOS cell biology and in understanding the pathophysiology of diseases that involve dysfunctional iNOS expression.

Inhibition or knock out of inducible nitric oxide synthase result in resistance to bleomycin-induced lung injury

BACKGROUND

In the present study, by comparing the responses in wild-type mice (WT) and mice lacking (KO) the inducible (or type 2) nitric oxide synthase (iNOS), we investigated the role played by iNOS in the development of on the lung injury caused by bleomycin administration. When compared to bleomycin-treated iNOSWT mice, iNOSKO mice, which had received bleomycin, exhibited a reduced degree of the (i) lost of body weight, (ii) mortality rate, (iii) infiltration of the lung with polymorphonuclear neutrophils (MPO activity), (iv) edema formation, (v) histological evidence of lung injury, (vi) lung collagen deposition and (vii) lung Transforming Growth Factor beta1 (TGF-beta1) expression.

METHODS

Mice subjected to intratracheal administration of bleomycin developed a significant lung injury. Immunohistochemical analysis for nitrotyrosine revealed a positive staining in lungs from bleomycin-treated iNOSWT mice.

RESULTS

The intensity and degree of nitrotyrosine staining was markedly reduced in tissue section from bleomycin-iNOSKO mice. Treatment of iNOSWT mice with of GW274150, a novel, potent and selective inhibitor of iNOS activity (5 mg/kg i.p.) also significantly attenuated all of the above indicators of lung damage and inflammation.

CONCLUSION

Taken together, our results clearly demonstrate that iNOS plays an important role in the lung injury induced by bleomycin in the mice.