Endogenous nitric oxide in cardiovascular disease and transplantation

Influence of exercise on oxidative stress in patients with heart failure

Reactive oxygen species play an important role in the pathophysiology of heart failure (HF). In contrast, regular physical exercise can promote adaptations to reactive oxygen species that are beneficial for patients with HF. We completed a systematic review of randomized controlled trials that evaluate the influence of exercise on oxidative stress in patients with HF. Articles were searched in the PubMed, Cochrane, SciELO, and LILACS databases. The search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The quality of the included studies was assessed using the Physiotherapy Evidence Database scale. We selected 12 studies with a total of 353 participants. The included patients had a left ventricle ejection fraction of < 52% and New York Heart Association functional class II or III disease. A significant increase was observed in peak oxygen consumption (between 10 and 46%) in the group that underwent training (TG). There was an improvement in the oxidative capacity of skeletal muscles in the TG, related to the positive activity of mitochondrial cytochrome c oxidase (between 27 and 41%). An increase in the expression of the enzymes glutathione peroxidase (41%), catalase (between 14 and 42%), and superoxide dismutase (74.5%), and a decrease in lipid peroxidation (between 28.8 and 58.5%) were observed in the TG. Physical training positively influenced the cardiorespiratory capacity and enhanced the benefits of oxidant and antioxidant biomarkers in patients with HF. High-intensity training promoted a 15% increase in the plasma total antioxidant capacity, whereas moderate training had no effect.

The Lipid Mediator Resolvin D1 Reduces the Skin Inflammation and Oxidative Stress Induced by UV Irradiation in Hairless Mice

UV irradiation-induced oxidative stress and inflammation contribute to the development of skin diseases. Therefore, targeting oxidative stress and inflammation might contribute to reduce skin diseases. Resolvin D1 (RvD1) is a bioactive metabolite generated during inflammation to actively orchestrate the resolution of inflammation. However, the therapeutic potential of RvD1 in UVB skin inflammation remains undetermined, which was, therefore, the aim of the present study. The intraperitoneal treatment with RvD1 (3-100 ng/mouse) reduced UVB irradiation-induced skin edema, myeloperoxidase activity, matrix metalloproteinase 9 activity, and reduced glutathione depletion with consistent effects observed with the dose of 30 ng/mouse, which was selected to the following experiments. RvD1 inhibited UVB reduction of catalase activity, and hydroperoxide formation, superoxide anion production, and gp91phox mRNA expression. RvD1 also increased the Nrf2 and its downstream targets NQO1 and HO-1 mRNA expression. Regarding cytokines, RvD1 inhibited UVB-induced production of IL-1β, IL-6, IL-33, TNF-α, TGF-β, and IL-10. These immuno-biochemical alterations by RvD1 treatment had as consequence the reduction of UVB-induced epidermal thickness, sunburn and mast cell counts, and collagen degradation. Therefore, RvD1 inhibited UVB-induced skin oxidative stress and inflammation, rendering this resolving lipid mediator as a promising therapeutic agent.

Unsweetened Natural Cocoa Powder Has the Potential to Attenuate High Dose Artemether-Lumefantrine-Induced Hepatotoxicity in Non-Malarious Guinea Pigs

Objective. This study investigated the elemental composition of unsweetened natural cocoa powder (UNCP), its effect on nitric oxide, and its hepatoprotective potential during simultaneous administration with high-dose artemether/lumefantrine (A/L). Method. Macro- and microelements in UNCP were analyzed with EDXRF spectroscopy. Thirty (30) male guinea-pigs were then divided into five groups. For groups 3 (low-dose), 4 (medium-dose), and 5 (high-dose), the animals received oral UNCP prophylactically for 14 days. Group 1 received distilled water (14 days) and group 2 A/L for the last 3 days (days 12 to 14). After euthanisation, biochemical and histopathological examinations were carried out in all groups. Results. Phytochemical analysis of UNCP showed the presence of saponins, flavonoids, tannins, and cardiac glycosides. Thirty-eight (38) macro- and microelements were found. UNCP produced significant decreases in ALT, ALP, GGT, and AST levels. A significant increase in total protein levels was observed during A/L+UNCP administration in comparison to 75 mg/kg A/L group. Histopathological examinations buttressed the protective effects of cocoa administration. UNCP administration increased nitric oxide levels 149.71% (P < 0.05) compared to controls. Conclusion. UNCP increases nitric oxide levels and has hepatoprotective potential during A/L administration. A high level of copper was observed which may be detrimental during high daily consumptions of UNCP.

Effects of simulated heat waves on cardiovascular functions in senile mice

The mechanism of the effects of simulated heat waves on cardiovascular disease in senile mice was investigated. Heat waves were simulated in a TEM1880 meteorological environment simulation chamber, according to a heat wave that occurred in July 2001 in Nanjing, China. Eighteen senile mice were divided into control, heat wave, and heat wave BH4 groups, respectively. Mice in the heat wave and heat wave BH4 groups were exposed to simulated heat waves in the simulation chamber. The levels of ET-1, NO, HSP60, SOD, TNF, sICAM-1, and HIF-1α in each group of mice were measured after heat wave simulation. Results show that heat waves decreased SOD activity in the myocardial tissue of senile mice, increased NO, HSP60, TNF, sICAM-1, and HIF-1α levels, and slightly decreased ET-1 levels, BH4 can relieve the effects of heat waves on various biological indicators. After a comprehensive analysis of the experiments above, we draw the followings conclusions regarding the influence of heat waves on senile mice: excess HSP60 activated immune cells, and induced endothelial cells and macrophages to secrete large amounts of ICAM-1, TNF-α, and other inflammatory cytokines, it also activated the inflammation response in the body and damaged the coronary endothelial cell structure, which increased the permeability of blood vessel intima and decreased SOD activity in cardiac tissues. The oxidation of lipoproteins in the blood increased, and large amounts of cholesterol were generated. Cholesterol penetrated the intima and deposited on the blood vessel wall, forming atherosclerosis and leading to the occurrence of cardiovascular disease in senile mice. These results maybe are useful for studying the effects of heat waves on elderly humans, which we discussed in the discussion chapter.

Increased oxidative stress in foam cells obtained from hemodialysis patients

Premature atherosclerosis represents the main cause of mortality among end-stage renal disease patients (ESRD). Increased inflammation and oxidative stress are involved in initiation and progression of the atherosclerotic plaque. As foam cells are capable of producing significant amounts of inflammatory mediators and free radicals, we hypothesized that foam cells from uremic patients could produce more inflammation and oxidative stress than foam cells from normal people and be, somehow, involved in the accelerated atherosclerosis of uremia. To test this hypothesis, the levels of a few markers of inflammation and oxidative stress: Tumor necrosis factor-α, inducible nitric oxide synthase, malondialdehyde, nitric oxide by-products were measured in the supernatants of macrophage-derived foam cells cultures from 18 hemodialysis patients and 18 apparently healthy individuals controls. Malondialdehyde levels in the supernatant of cell cultures (macrophages stimulated or not with native and oxidized lipoprotein) were significantly increased in uremic patients; no statistically significant difference was found between the supernatant concentrations of nitric oxide by-products, inducible nitric oxide synthase activity, and tumor necrosis factor-α between patients and controls. Our results, obtained with human macrophages and macrophage-derived foam cells, are compatible with the theory that increased cellular oxidative stress and inflammatory activity in ESRD patients could accelerate the atherosclerotic process. The present culture protocol showed it is possible to use human mononuclear cells to evaluate the oxidative metabolism of foam cells, which are considered to be the initial step of atherosclerotic lesions.

Nitric oxide regulates vascular calcification by interfering with TGF- signalling

AIMS

Vascular calcification often occurs with advancing age, atherosclerosis, and metabolic disorders such as diabetes mellitus and end-stage renal disease. Vascular calcification is associated with cardiovascular events and increased mortality. Nitric oxide (NO) is crucial for maintaining vascular function, but little is known about how NO affects vascular calcification. The aim of this study was to examine the effect of NO on vascular calcification.

METHODS AND RESULTS

In this study, we examined the inhibitory effects of NO on calcification of murine vascular smooth muscle cells (VSMCs) in vitro. We measured calcium concentration, alizarin red staining, and alkaline phosphatase activity to examine the effect of NO on calcification of VSMCs and differentiation of VSMCs into osteoblastic cells. We also determined gene expression and levels of phosphorylation of Smad2/3 by RT-PCR and western blotting. NO inhibited calcification of VSMCs and differentiation of VSMCs into osteoblastic cells. An inhibitor of cyclic guanosine monophosphate (cGMP)-dependent protein kinase restored the inhibition by NO of osteoblastic differentiation and calcification of VSMCs. NO inhibited transforming growth factor-beta (TGF-beta)-induced phosphorylation of Smad2/3 and expression of TGF-beta-induced genes such as plasminogen activator inhibitor-1. In addition, NO inhibited expression of the TGF-beta receptor ALK5.

CONCLUSION

Our data show that NO prevents differentiation of VSMCs into osteoblastic cells by inhibiting TGF-beta signalling through a cGMP-dependent pathway. Our findings suggest that NO may play a beneficial role in atherogenesis in part by limiting vascular calcification.

Tissue factor and nitric oxide: a controversial relationship!

Tissue factor (TF) is the primary physiological initiator of blood coagulation. TF has a high-affinity for factor (F) VII resulting in the formation of (TF:FVII:FVIIa) bimolecular complex which, in the presence of Ca(2+), increases the enzymatic activity of FVIIa towards its natural substrates, FIX and FX, generating their active forms FIXa and FXa, respectively. This eventually leads to thrombin generation and a fibrin clot formation. Up-regulation of TF in injured blood vessels and atherosclerotic plaque can lead to undesirable vascular thrombosis. Nitric oxide (NO) is a free radical synthesized from L-arginine and molecular oxygen by nitric oxide synthases (NOS). NO participates in diverse physiological and pathophysiological process as an intra or extracellular messenger. A relationship between TF and NO has been proposed. Thus, models of TF regulation by NO has been studied in different cells and experimental animal models, but the results have been conflicting. The premise that NO donors can prevent TF expression in vivo has provided the foundation for a broad field of pharmacotherapeutics in vascular medicine. A new class of drugs combining a statin (inhibitors of coenzyme A reductase) with an NO-donating moiety has been described. The resulting drug, nitrostatin, has been suggested to increase the antithrombotic effects of native statin. However, it is questionable if NO release from these drugs had any significant role on TF inhibition. In summary, care must be taken in drawing conclusions about the relationship between NO and TF. Interpretation of NO studies must take several factors into consideration, including NO bioavailability, its half-life and inactivation, as well as the cell type and experimental model used.

Inhibition of inducible nitric oxide synthesis by azathioprine in a macrophage cell line

Azathioprine is used as an anti-inflammatory agent. Although there are numerous data demonstrating cytotoxic and immunosuppressive properties of azathioprine and its metabolite 6-mercaptopurine, the mechanism of the anti-inflammatory action of azathioprine has not yet been fully clarified. During our study, we investigated the effects of azathioprine on the inducible nitric oxide synthase (iNOS) in lipopolysaccharide stimulated murine macrophages (RAW 264.7) by measurement of iNOS protein (immunoblotting), iNOS mRNA (semiquantitative competitive RT-PCR), and NO production (nitrite levels). Azathioprine (0-210 muM) induces a concentration dependent inhibition of inducible nitric oxide synthesis (IC50: 33.5 muM). iNOS protein expression showed a concentration dependent reduction as revealed by immunoblotting when cells were incubated with increasing amounts of azathioprine. Azathioprine decreases iNOS mRNA levels as shown by semiquantitative competitive RT-PCR. In contrast, 6-mercaptopurine showed no inhibition of inducible nitric oxide synthesis. Azathioprine did not reduce iNOS mRNA stability after the addition of actinomycin D. Enzymatic activity assays with increasing concentrations of azathioprine (0-210 muM) showed no statistically significant inhibition of iNOS enzyme activity compared to cell lysates without azathioprine. Nuclear translocation of NF-kappaB p65 subunit and binding of NF-kappaB p50 subunit from nuclear extracts to a biotinylated-consensus sequence was unaffected by azathioprine treatment. iNOS inhibition by azathioprine was associated with a decreased expression of IRF-1 (interferon regulatory factor 1) and IFN-beta (beta-interferon) mRNA. Azathioprine induced iNOS inhibition seems to be associated with an action of the methylnitroimidazolyl substituent. This suggests a route to the rational design of nontoxic anti-inflammatory agents by replacing the 6-mercaptopurine component of azathioprine with other substituents. The inhibition of inducible nitric oxide synthesis might contribute to the anti-inflammatory activities of azathioprine.

Nitric oxide and atherosclerosis: an update

Nitric oxide (NO) is a molecule that has gained recognition as a crucial modulator of vascular disease. NO has a number of intracellular effects that lead to vasorelaxation, endothelial regeneration, inhibition of leukocyte chemotaxis, and platelet adhesion. Endothelium damage induced by atherosclerosis leads to the reduction in bioactivity of endothelial NO synthase (eNOS) with subsequent impaired release of NO together with a local enhanced degradation of NO by increased generation of reactive oxygen species with subsequent cascade of oxidation-sensitive mechanisms in the arterial wall. Many commonly used vasculoprotective agents have their therapeutic actions through the production of NO. L-Arginine, the precursor of NO, has demonstrated beneficial effects in atherosclerosis and disturbed shear stress. Finally, eNOS gene polymorphism might be an additional risk factor that may contribute to predict cardiovascular events. However, further studies are needed to understand the possible clinical implications of these correlations.

Inhibition of Hydrogen Peroxide, Nitric Oxide and TNF-.ALPHA. Production in Peritoneal Macrophages by Ethyl Acetate Fraction from Alchornea glandulosa

The effects of Alchornea glandulosa ethyl acetate fraction (AGF) on hydrogen peroxide (H2O2), nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production in peritoneal macrophages activated with lipopolysaccharide (LPS) or phorbol myristate acetate (PMA) were investigated. Analysis by thin layer chromatography (TLC) of AGF showed several constituents, including flavonoids, which may have anti-inflammatory activity. Inhibitory effects of the fraction in H2O2 and NO production ranged from 8.59+/-7.84% to 70.56+/-4.16% and from 16.06+/-3.65% to 38.73+/-3.90%, respectively. The TNF-alpha production was only partially inhibited in the tested concentrations (12.21+/-6.23% - 15.16+/-0.96%). According to these results, it is suggested that AGF has anti-inflammatory activity. This medicinal plant may have therapeutic potential in the control of inflammatory disorders.

The role of NOS in heart failure: lessons from murine genetic models

Nitric Oxide Synthases (NOSs) are a group of related proteins that produce nitric oxide (NO). In mammals, there are three known members of this gene family: nNOS (NOS1), iNOS (NOS2) and eNOS (NOS3). Each has been disrupted by targeted gene ablation in mice and the corresponding phenotypes examined. These mice have allowed an examination of the contribution of each NOS in a variety of experimental models and continue to provided insights into the patho-physiological role of NOS and NO. With increasing sophistication, murine transgenic approaches continue to offer a wealth of information, and invaluable tools to further study the NOS system. The focus of this review will be an examination of the tools available, and the insights gained from studies done on murine NOS genetic models in the context of heart failure.

Nitric oxide donor drugs: current status and future trends

Nitric oxide synthesised in endothelial cells that line blood vessels has a wide range of functions that are vital for maintaining a healthy cardiovascular system. Reduced nitric oxide availability is implicated in the initiation and progression of many cardiovascular diseases and delivery of supplementary nitric oxide to help prevent disease progression is an attractive therapeutic option. Nitric oxide donor drugs represent a useful means of systemic nitric oxide delivery and organic nitrates have been used for many years as effective therapies for symptomatic relief from angina. However, nitrates have limitations and a number of alternative nitric oxide donor classes have emerged since the discovery that nitric oxide is a crucial biological mediator. This review focuses on novel advances and possible future directions in nitric oxide donor drug development.

L-arginine polymer mediated inhibition of graft coronary artery disease after cardiac transplantation

BACKGROUND

Nitric oxide (NO) limits the development of graft coronary artery disease (GCAD) in transplanted hearts. We hypothesized that l-arginine polymers administered to cardiac allografts ex vivo would translocate across vascular cellular membranes, up-regulate inducible nitric oxide synthase (iNOS) production of NO, and inhibit the development of GCAD.

METHODS

Three groups of PVG rat donor hearts were incubated with either 0.8 ml phosphate-buffered saline, (PBS, n=12) or 50 microM L-arginine polymer solutions of length five (R5, n=12) or nine (R9, n=12) prior to heterotopic transplantation into ACI recipients. Graft vessels were scored at POD 60 and 90 for percentage luminal narrowing (%LN), intima to media ratio (I/M), and percentage affected vessels (%AV). Translocation efficiency was determined by treatment with biotinylated polymers. NO production of treated aortic segments was determined in vitro by Griess reaction.

RESULTS

Translocation efficiencies were 89+/-19% (R9), 7+/-10% (R5), and 0+/-0% PBS (ANOVA, P<0.001) which corresponded to NO production in treated aortic segments of 0.175+/-0.17 (R9), 0.120+/-0.006 (R5), and 0.135+/-0.035 microM/mg (PBS), (ANOVA, P=0.002). GCAD scores at POD 60 were: %LN: 3.2+/-3.8% (R9), 12.6+/-6.7% (R5), 11.3+/-4.2% (PBS) (ANOVA, P=0.025); I/M: 0.03+/-0.04 (R9), 0.13+/-0.07 (R5), 0.12+/-0.05 (PBS) (ANOVA, P=0.037); %AV: 7+/-7% (R9), 19+/-7%(R5), 22+/-9%(PBS) (ANOVA, P=0.021). Reduction of GCAD parameters was maintained at POD 90.

CONCLUSION

R9 efficiently translocated across cytoplasmic membranes, enhanced vascular NO production, and decreased neointimal hyperplasia. This ex vivo treatment may have a therapeutic role in preventing GCAD.

L-arginine polymers inhibit the development of vein graft neointimal hyperplasia

OBJECTIVE

We sought to determine whether L -arginine polymer treatment of vein grafts enhances vascular production of nitric oxide and inhibits the development of neointimal hyperplasia.

METHODS

External jugular veins of New Zealand White rabbits (n = 42) were harvested; treated intraluminally for 15 minutes with phosphate-buffered saline solution or L -arginine polymer 5, 7, or 9 at either 10 or 100 micromol/L; and then grafted into the contralateral carotid artery. Rabbits were killed after 28 days, and 5-microm sections of vessels were stained with hematoxylin and scored for intima/media ratio by using computerized morphometric analysis. Separate veins were treated in a similar fashion with biotinylated polymers and phosphate-buffered saline solution to assess for translocation efficiencies. Finally, vein segments pretreated with either phosphate-buffered saline solution or L -arginine polymers were cultured in Dulbecco's modified Eagle's medium containing lipopolysaccharide (100 microg/mL) and interferon gamma (200 U/mL) for 48 hours before measuring nitric oxide levels by means of the Griess reaction.

RESULTS

Biotinylated L -arginine polymers demonstrated a dose- and length-dependent uptake into intimal and medial cells of treated vessels. Nitric oxide levels were significantly higher in vein segments treated with 100 micromol/L of L -arginine polymer 9 compared with control segments. Finally, the intima/media ratio also reflected both length- and concentration-dependent inhibition of neointimal hyperplasia.intima/media ratio PBS R5 R7 R9 10 micromol/L 0.909 +/- 0.072 0.920 +/- 0.073 0.861 +/- 0.138 0.710 +/- 0.122 100 micromol/L 0.924 +/- 0.061 0.581 +/- 0.089* 0.529 +/- 0.093* PBS, Phosphate-buffered saline solution; R, L -arginine polymer. *P <.001 versus phosphate-buffered saline solution and L -arginine polymer 5 controls (Bonferroni-corrected value).

CONCLUSIONS

Arginine polymers of sufficient length and concentration were effective in increasing nitric oxide levels and reducing neointimal hyperplasia in this vein graft model.

Interactions between nitric oxide and lipid oxidation pathways: implications for vascular disease

Nitric oxide ((.)NO) signaling pathways and lipid oxidation reactions are of central importance in both the maintenance of vascular homeostasis and the progression of vascular disease. Because both of these pathways involve free radical species that can also react together at extremely fast rates, convergent interactions between these pathways are expected. Biochemical and cell biology studies have defined multiple interactions of (.)NO with oxidizing lipids that could lead to either vascular protection or potentiation of inflammatory vascular injury. For example, low levels of (.)NO generated by endothelial nitric oxide synthase can terminate propagating lipid radicals and inhibit lipoxygenases, reactions that would be protective. Alternatively, if generated at elevated levels, for example, after inducible nitric oxide synthase expression in inflammation, (.)NO can be converted to prooxidant species, such as peroxynitrite (ONOO(-)) and nitrogen dioxide ((.)NO(2)), that can potentiate inflammatory injury to vascular cells. Finally, both enzymatic and nonenzymatic lipid oxidation reactions can influence (.)NO bioactivity by directly scavenging (.)NO or altering the induction and catalytic activity of nitric oxide synthase enzymes. In this review, we summarize the biochemical interactions between (.)NO and lipid oxidation reactions and discuss the recognized and potential roles of these reactions in the vasculature.

Leflunomide inhibits activation of inducible nitric oxide synthase in rat astrocytes

Highly reactive gaseous free radical nitric oxide (NO), generated by astrocytes and infiltrating macrophages is implicated in inflammatory destruction of brain tissue, including that occurring in multiple sclerosis. Therefore, the influence of immunosuppressive drug leflunomide on inducible nitric oxide synthase (iNOS)-dependent NO production in rat astrocytes and macrophages was investigated. Under the same cultivating conditions, leflunomide's active metabolite A77 1726 caused a dose-dependent decrease of NO production in IFN-gamma+LPS-stimulated primary astrocytes, but not in macrophages. While A77 1726 did not alter iNOS enzymatic activity, it markedly suppressed IFN-gamma+LPS-triggered expression of iNOS mRNA in astrocytes. In the presence of transcription inhibitor actinomycin D, A77 1726 failed to inhibit astrocyte NO production, suggesting transcriptional regulation of iNOS by leflunomide. This assumption was further supported by the ability of A77 1726 to inhibit IFN-gamma+LPS-induced expression of mRNA for an important iNOS transcription factor IRF-1. PD98059, a specific inhibitor of mitogen-activated protein kinase kinase (MAPKK/MEK), but not genistein, an unselective protein tyrosine kinase inhibitor, completely mimicked cell type-specific inhibition of NO synthesis by A77 1726. Therefore, previously described inhibition of MEK/MAP pathway by leflunomide could present a possible mechanism for A77 1726-mediated suppression of iNOS activation in astrocytes. Accordingly to results obtained with primary astrocytes, both A77 1726 and PD98059 significantly reduced IFN-gamma+LPS-induced NO synthesis in the cultures of rat astrocytoma cell line C6. The ability to suppress iNOS induction in astrocytes supports potential use of leflunomide in the treatment of multiple sclerosis and other NO-dependent inflammatory brain disorders.

Inducible nitric oxide synthase in the myocard

Recognition of significance of nitric oxide synthases (NOS) in cardiovascular regulations has led to intensive research and development of therapies focused on NOS as potential therapeutic targets. However, the NOS isoform profile of cardiac tissue and subcellular localization of NOS isoforms remain a matter of debate. The aim of this study was to investigate the localization of an inducible NOS isoform (NOS2) in cardiomyocytes. Employing a novel immunocytochemical technique of a catalyzed reporter deposition system with tyramide and electron microscopical immunocytochemistry complemented with Western blotting and RT-PCR, we detected NOS2 both in rat neonatal and adult cultured cardiomyocytes and in the normal myocard of adult rats as well as in the human myocard of patients with dilative cardiomyopathy. NOS2 was targeted predominantly to a particulate component of the cardiomyocyte--along contractile fibers, in the plasma membrane including T-tubules, as well as in the nuclear envelope, mitochondria and Golgi complex. Our results point to an involvement of NOS2 in maintaining cardiac homeostasis and contradict to the notion that NOS2 is expressed in cardiac tissue only in response to various physiological and pathogenic factors. NOS2 targeting to mitochondria and contractile fibers suggests a relationship of NO with contractile function and energy production in the cardiac muscle.

Deficiency in inducible nitric oxide synthase results in reduced atherosclerosis in apolipoprotein E-deficient mice

Inducible NO synthase (iNOS) present in human atherosclerotic plaques could contribute to the inflammatory process of plaque development. The role of iNOS in atherosclerosis was tested directly by evaluating the development of lesions in atherosclerosis-susceptible apolipoprotein E (apoE)-/- mice that were also deficient in iNOS. ApoE-/- and iNOS-/- mice were cross-bred to produce apoE-/-/iNOS-/- mice and apoE-/-/iNOS+/+ controls. Males and females were placed on a high fat diet at the time of weaning, and atherosclerosis was evaluated at two time points by different methods. The deficiency in iNOS had no effect on plasma cholesterol, triglyceride, or nitrate levels. Morphometric measurement of lesion area in the aortic root at 16 wk showed a 30-50% reduction in apoE-/-/iNOS-/- mice compared with apoE-/-/iNOS+/+ mice. Although the size of the lesions in apoE-/-/iNOS-/- mice was reduced, the lesions maintained a ratio of fibrotic:foam cell-rich:necrotic areas that was similar to controls. Biochemical measurements of aortic cholesterol in additional groups of mice at 22 wk revealed significant 45-70% reductions in both male and female apoE-/-/iNOS-/- mice compared with control mice. The results indicate that iNOS contributes to the size of atherosclerotic lesions in apoE-deficient mice, perhaps through a direct effect at the site of the lesion.

FK409, a spontaneous nitric oxide releaser, attenuates allograft vasculopathy in a rat aortic transplant model

Although systemic administration of NO donors has been shown to attenuate the development of neointimal hyperplasia in the balloon injury model, this strategy has not been tested in a model of allograft vasculopathy. In this study, we investigated the effect of FK409, a spontaneous NO releaser, on the development of allograft vasculopathy, using a rat aortic transplant model. Thoracic aortas from ACI rats were transplanted heterotopically into the abdominal aorta of Wistar-Furth rats. Postoperatively, recipients received FK409 orally every 8 hours from the day of transplantation to the time of euthanization. Morphometric and immunohistochemical analyses were performed on the aortic grafts 8 weeks after transplantation. Control allografts showed severe neointimal hyperplasia, which consists mainly of alpha-actin-containing vascular smooth muscle cells. The FK409-treated allografts showed a dose-dependent reduction (statistically significant compared with the control) in the neointimal thickness as the dose increased from 1 to 10 mg/kg (thrice per day). However, there was no significant difference in the neointimal thickness between groups treated with 10 and with 20 mg/kg. FK409 treatment (10 mg/kg) caused a significant decrease in DNA synthesis (5-bromo-2-deoxyuridine [BrdU] uptake), an increase in DNA fragmentation (terminal deoxynucleotidyltransferase-mediated uridine nick-end labeling [TUNEL]), and upregulation of Fas expression, in the neointimal vascular smooth muscle cells. These data suggest that FK409 attenuates the allograft vasculopathy in a rat aortic transplant model.

Role of inducible nitric oxide synthase in transplant arteriosclerosis

1. Transplant arteriosclerosis is a major obstacle to long-term allograft survival. Nitric oxide (NO) has been implicated as a mediator in the development of this disease. 2. We and others have shown that inducible nitric oxide synthase (iNOS) is up-regulated in allografts with transplant arteriosclerosis. Despite the acute cytotoxic effects produced by high levels of NO, a chronic increase in NO availability is protective against neointimal hyperplasia, mainly by suppressing the inflammatory cell recruitment and neointimal smooth muscle cell accumulation. 3. Currently, we have the technology to directly transfer the iNOS gene to allografts. We have demonstrated that this exciting strategy is feasible and therapeutic and may improve the long-term survival and function of allografts. Future challenges include optimizing the methods and the vectors of gene delivery.

Pharmacological modulation of nitric oxide synthesis by mechanism-based inactivators and related inhibitors

Nitric oxide synthase (NOS) (EC 1.14.13.39) is a homodimeric cytochrome P450 monooxygenase analog that generates nitric oxide (NO) from the amino acid L-arginine. Enzymatically produced NO acts as an intracellular messenger in neuronal networks, blood pressure regulatory mechanisms, and immune responses. Isoform-selective pharmacological modulation of NO synthesis has emerged as a new therapeutic strategy for the treatment of diverse clinical conditions associated with NO overproduction. Mechanism-based inactivators (MBIs) represent a class of NOS mechanistic inhibitors that require catalytic turnover to produce irreversible inactivation of the ability of NOS to generate NO. Diverse isoform-selective NOS MBIs have been characterized with respect to their kinetic parameters and chemical mechanisms of inactivation. In studies with isolated and purified NOS isoforms, MBIs produce irreversible inactivation of NOS enzymatic activities. The inactivation process is associated with covalent modification of the NOS active site and proceeds either through heme destruction, its structural alteration, or covalent modification of the NOS protein chain. The behavior of NOS MBIs in intact cells is different from their behavior observed with the isolated NOS isoforms. In cytokine-induced RAW 264.7 macrophages, treatment with MBIs produces a complete loss of cellular NOS synthetic competence and inducible NOS activity. However, following drug removal, cells can recover at least partially in the absence of protein synthesis. In GH3 cells containing the neuronal NOS isoform, calcium transients are too low and abbreviated to allow significant NOS inactivation; hence, the cellular effects of MBIs on the neuronal isoform are almost completely and immediately reversible.

Nitric oxide in atherosclerosis: vascular protector or villain?

1. Nitric oxide (NO) has important roles in physiological vasodilatation, cytotoxicity and vascular disease. Nitric oxide and prostacyclin (PGI2), both released from the endothelium, act synergistically to inhibit platelet aggregation and adhesion. These autacoids also inhibit the adhesion and migration of leucocytes and, in some arteries, they synergize in terms of vasodilation. 2. The development of atherosclerosis and hyperlipaemia per se is accompanied by impairment of endothelium-dependent vasodilation. 3. Atherosclerosis is associated with marked changes in the activity of isoforms of NO synthase (NOS) in the artery wall, including increased expression of the NOS2 (inducible) isoform in complex human lesions as well as in the neointima of experimental animal models. 4. Failure of NO release from the endothelium with normal physiological stimuli, which has been attributed to a defect in the operation of the endothelial NOS (NOS3), provides conditions propitious for leucocyte adhesion, vasospasm, thrombosis and, in addition, may promote increased proliferation of intimal cells. 5. Nitric oxide and superoxide anions generated by inflammatory cells in atherosclerosis react to form cytodestructive peroxynitrite radicals, potentially causing injury to the endothelium and myocytes, and this may be a factor in apoptosis of cells leading to plaque rupture. 6. We have been able to reverse these NO defects with therapeutic agents, including angiotensin-converting enzyme inhibitors, antagonists of platelet-activating factor and NO donor compounds, all offering promise in protecting against some manifestations of vascular disease.

Electron spin resonance analysis of heme-nitrosyl and reduced iron-sulfur centered complexes in allogeneic, heterotopic cardiac transplants: effects of treatment with pyrrolidine dithiocarbamate

Inhibition of inducible nitric oxide synthase (iNOS) prolongs allograft survival suggesting a role for nitric oxide (.NO) in allograft rejection. Induction of iNOS is regulated by the oxidant-sensitive, nuclear factor kappa B (NF-kappaB) in many cell types. In the present study using electron spin resonance (ESR) spectroscopy, we evaluated whether pyrrolidine dithiocarbamate (PDTC), a metal chelator and antioxidant, might limit .NO production during the development of rejection in cardiac allografts. We performed either isogeneic (Lewis to Lewis) or allogeneic (Wistar-Furth to Lewis) heterotopic abdominal cardiac transplantation. Allograft recipients received daily injections of PDTC or aminoguanidine (a known inhibitor of iNOS). At postoperative days 4 or 6, grafted and native hearts of transplant recipients were flushed with cardioplegic solution to remove blood contamination. ESR data of allografts revealed a triplet nitrogen signal (aN=17.5 G) and centered at g=2.012 and an additional broad signal at g=2.08. This signal was not seen in either isografts or native hearts of either isograft or allograft recipients. Based upon these parameters, these signals are attributed to nitrosomyoglobin. This signal was inhibited by treatment with aminoguanidine or PDTC. Under these conditions, PDTC also prolonged graft survival from 6.6+/-0.2 to 11.7+/-0.3 days. Thus, it is conceivable that nitrosylmyoglobin formation precedes rejection in cardiac allografts and inhibition of nitrosomyoglobin with agents such as PDTC contribute to improved graft survival.

Role of angiotensin-converting enzyme inhibition in reversal of endothelial dysfunction in coronary artery disease

Angiotensin-converting enzyme (ACE) inhibitors have shown unexpected benefits in the prevention of ischemic events in patients with hypertension and congestive heart failure. In addition to these clinical observations, there is a growing body of knowledge about the molecular and cellular effects of ACE inhibitors. For example, ACE inhibition prevents stimulation of smooth muscle cell angiotensin II receptors, thereby blocking both contractile and proliferative actions. Angiotensin II blockade also diminishes the production of superoxide anion, which inactivates ambient nitric oxide. ACE inhibition of kininase II inhibits the breakdown of bradykinin, a direct stimulant of nitric oxide release from the intact endothelial cell. Thus, at the cellular level within the vasculature, ACE inhibition shifts the balance of ongoing mechanisms in favor of those promoting vasodilatory, antiaggregatory, antithrombotic, and antiproliferative effects. These effects underlie the potential benefits of ACE inhibition in the therapy of ischemia and atherosclerosis. Some data is available in humans to show that these effects can be sustained for months, thereby maintaining improved endothelial function and, presumably, allowing the initiation of steps that might alter the progression of atherosclerosis. Definitive information is not yet available in humans to show that ACE inhibition clearly alters the progression of atherosclerosis or diminishes coronary events in uncomplicated coronary disease. This promising area of investigation is, however, the subject of multiple clinical trials, which should provide clarification of this important question in coming years.

Effect of fantofarone, a new Ca2+ channel antagonist, on angioplasty-induced vasospasm in an atherosclerotic rabbit model

In order to prevent and treat angioplasty-induced vasospasm, we investigated the effects of a new Ca2+ channel antagonist, fantofarone, a nondihydropyridine compound with a novel site of action on the L-type Ca2+ channel, in an animal model of angioplasty in rabbits with femoral atherosclerotic lesions. Vasospasm which occurred in saline-treated animals following angioplasty was markedly reduced by fantofarone (50 microg/kg, i.v.) at both the distal and proximal sites. Although it totally inhibited distal vasospasm, isosorbide dinitrate (0.3 mg/kg, i.v.) did not significantly affect proximal diameter decrease. Verapamil (0.2 mg/kg, i.v.) was much less potent than fantofarone in reducing angioplasty-induced vasospasm. Our results confirm the preventive effects of Ca2+ blockers on this phenomenon and extend this observation to a potent compound: fantofarone.

Inducible nitric oxide synthase suppresses the development of allograft arteriosclerosis

In cardiac transplantation, chronic rejection takes the form of an occlusive vasculopathy. The mechanism underlying this disorder remains unclear. The purpose of this study was to investigate the role nitric oxide (NO) may play in the development of allograft arteriosclerosis. Rat aortic allografts from ACI donors to Wistar Furth recipients with a strong genetic disparity in both major and minor histocompatibility antigens were used for transplantation. Allografts collected at 28 d were found to have significant increases in both inducible NO synthase (iNOS) mRNA and protein as well as in intimal thickness when compared with isografts. Inhibiting NO production with an iNOS inhibitor increased the intimal thickening by 57.2%, indicating that NO suppresses the development of allograft arteriosclerosis. Next, we evaluated the effect of cyclosporine (CsA) on iNOS expression and allograft arteriosclerosis. CsA (10 mg/kg/d) suppressed the expression of iNOS in response to balloon-induced aortic injury. Similarly, CsA inhibited iNOS expression in the aortic allografts, associated with a 65% increase in intimal thickening. Finally, we investigated the effect of adenoviral-mediated iNOS gene transfer on allograft arteriosclerosis. Transduction with iNOS using an adenoviral vector suppressed completely the development of allograft arteriosclerosis in both untreated recipients and recipients treated with CsA. These results suggest that the early immune-mediated upregulation in iNOS expression partially protects aortic allografts from the development of allograft arteriosclerosis, and that iNOS gene transfer strategies may prove useful in preventing the development of this otherwise untreatable disease process.

Nitric oxide reverses aspirin antagonism of t-PA thrombolysis in a rabbit model of thromboembolic stroke

Randomized trials of thrombolytic therapy in stroke have reported an improvement in neurologic outcome; however, the addition of aspirin has resulted in a significant increase in mortality and antagonism of clot lysis in clinical and animal studies, respectively. This finding is in contradistinction to the known synergy in mortality reduction for aspirin and thrombolytics in myocardial infarction. It is hypothesized that aspirin antagonism of clot lysis is related to inhibition of nitric oxide (NO) and may be reversed by providing a source of NO. Twenty rabbits were treated with aspirin (20 mg/kg, i.v.) prior to internal carotid clot embolization. One-half hour following embolization, rabbits were randomized to receive vehicle (n = 5), the NO precursor L-arginine (300 mg/kg, i.v. bolus at 0.5 and 2.5 h postembolus; n = 5), or a nitric oxide donor (nitroprusside, 1 mg/kg/h, i.a., or nitroglycerin, 10 microg/kg/min, i.v., n = 5 each agent). Tissue plasminogen activator (t-PA) (6.3 mg/kg) was administered from 1 to 3 h after embolization. Lysis of the tin-tagged clot was followed with serial X rays and gross examination. No rabbit in the control group experienced complete clot lysis. However, 2 of 5 rabbits in the L-arginine group and 6 of 10 rabbits in the nitric oxide donor (nitroprusside and nitroglycerin) groups noted complete clot lysis (P < 0.05, Fisher exact test). Thus, administration of an NO donor (nitroglycerin or nitroprusside) and, to a lesser extent L-arginine, reversed aspirin's antagonism of t-PA thrombolysis. This study may help explain the discrepant results seen with aspirin and thrombolytics.