Effects of pentaerythritol tetranitrate on endothelial function in coronary artery disease: results of the PENTA study

Cardiovascular health of women 10 to 20 years after placenta-related pregnancy diseases considering the possible effect of pentaerythrityl tetranitrate treatment during pregnancy on long-term maternal cardiovascular health (PAVA study)

BACKGROUND

Women developing preeclampsia (PE) or fetal growth restriction (FGR) during pregnancy are at higher risk for cardiovascular diseases (CVD) later in life. We aimed to analyse cardiovascular health of women 10-20 years after affected pregnancies in comparison to women after uneventful pregnancies. In addition, we assessed a potential long-term effect of the NO-donor pentaerythrityl tetranitrate (PETN).

METHODS

Women 10-20 years after severe PE, including women receiving PETN during pregnancy and matched controls were recruited and assessed for baseline clinical data and cardiovascular function by transthoracic echocardiography, VICORDER and USCOM. SPSS was used for statistical analysis.

RESULTS

53 participants after PE/FGR (13 with former PETN intake) and 51 controls were recruited for follow-up at an average of 14 years after index pregnancies. Compared to controls, women after PE/FGR had a significantly higher incidence of arterial hypertension (13.7% vs. 41.5%, p<0.001), and were more likely to be hypertensive (41.2% vs. 67.30%, p = 0.008). There were no differences in cardiovascular function observed. Affected women with PETN intake during pregnancy showed lower mean values for right atrial area and ventricle in comparison to controls and also to affected women without former medication.

CONCLUSIONS

In conclusion, our study results confirm that the risk of CVD is increased in women after PE/FGR compared to women after uneventful pregnancies. Contrary to our expectations, no major cardiovascular changes were observed in our cohort 10-20 years post pregnancy. The observed differences found in right heart dimensions were within reference ranges, and should be interpreted with caution.

Biotransformation of organic nitrates by glutathione S-transferases and other enzymes: An appraisal of the pioneering work by William B. Jakoby

Organic nitrates (R-ONO₂; R, organic residue) such as nitroglycerin are used as drugs in part for more than a century. Their pharmacological use is associated with clinically relevant tolerance which is reportedly known since 1888. The underlying mechanisms of both, the mechanisms of action and the main pharmacological effect, which is vasodilatation and reduction of blood pressure, and the development of tolerance, which means increasing need of drug amount in sustained long-term therapy, are still incompletely understood. William B. Jakoby and associates were the first to report the biotransformation of organic nitrates, notably including nitroglycerin (i.e., glycerol trinitrate; GTN), by glutathione S-transferase (GST)-catalyzed conjugation of glutathione (GSH) to the nitrogen atom of one of the three nitrate groups of GTN to generate glutathione sulfenyl nitrite (glutathione thionitrate, S-nitroglutathione; GSNO₂). Jakoby's group was also the first to suggest that GSNO₂ reacts with a second GSH molecule to produce inorganic nitrite (ONO^-) and glutathione disulfide (GSSG) without the catalytic involvement of GST. This mechanism has been adopted by others to the biotransformation of GTN by mitochondrial aldehyde dehydrogenase (mtALDH-(CysSH)₂) which does not require GSH as a substrate. The main difference between these reactions is that mtALDH forms an internal thionitrate (mtALDH-(CysSH)-CysSNO₂) which releases inorganic nitrite upon intra-molecular reaction to form mtALDH disulfide (mtALDH-(CysS)₂). Subsequently, ONO^- and GSNO₂ are reduced by several proteins and enzymes to nitric oxide (NO) which is a very potent activator of soluble guanylyl cyclase to finally relax the smooth muscles thus dilating the vasculature. GSNO₂ is considered to rearrange to GSONO which undergoes further reactions including GSNO and GSSG formation. The present article is an appraisal of the pioneering work of William B. Jakoby in the area of the biotransformation of organic nitrates by GST. The two above mentioned enzymatic reactions are discussed in the context of tolerance development to organic nitrates, still a clinically relevant pharmacological concern.

Acute exposure to nocturnal train noise induces endothelial dysfunction and pro-thromboinflammatory changes of the plasma proteome in healthy subjects

Nocturnal train noise exposure has been associated with hypertension and myocardial infarction. It remains unclear whether acute nighttime train exposure may induce subclinical atherosclerosis, such as endothelial dysfunction and other functional and/or biochemical changes. Thus, we aimed to expose healthy subjects to nocturnal train noise and to assess endothelial function, changes in plasma protein levels and clinical parameters. In a randomized crossover study, we exposed 70 healthy volunteers to either background or two different simulated train noise scenarios in their homes during three nights. After each night, participants visited the study center for measurement of vascular function and assessment of other biomedical and biochemical parameters. The three nighttime noise scenarios were exposure to either background noise (control), 30 or 60 train noise events (Noise30 or Noise60), with average sound pressure levels of 33, 52 and 54 dB(A), respectively. Flow-mediated dilation (FMD) of the brachial artery was 11.23 ± 4.68% for control, compared to 8.71 ± 3.83% for Noise30 and 8.47 ± 3.73% for Noise60 (p < 0.001 vs. control). Sleep quality was impaired after both Noise30 and Noise60 nights (p < 0.001 vs. control). Targeted proteomic analysis showed substantial changes of plasma proteins after the Noise60 night, mainly centered on redox, pro-thrombotic and proinflammatory pathways. Exposure to simulated nocturnal train noise impaired endothelial function. The proteomic changes point toward a proinflammatory and pro-thrombotic phenotype in response to nocturnal train noise and provide a molecular basis to explain the increased cardiovascular risk observed in epidemiological noise studies.

Pentaerythritol Tetranitrate In Vivo Treatment Improves Oxidative Stress and Vascular Dysfunction by Suppression of Endothelin-1 Signaling in Monocrotaline-Induced Pulmonary Hypertension

Objective. Oxidative stress and endothelial dysfunction contribute to pulmonary arterial hypertension (PAH). The role of the nitrovasodilator pentaerythritol tetranitrate (PETN) on endothelial function and oxidative stress in PAH has not yet been defined. Methods and Results. PAH was induced by monocrotaline (MCT, i.v.) in Wistar rats. Low (30 mg/kg; MCT30), middle (40 mg/kg; MCT40), or high (60 mg/kg; MCT60) dose of MCT for 14, 28, and 42 d was used. MCT induced endothelial dysfunction, pulmonary vascular wall thickening, and fibrosis, as well as protein tyrosine nitration. Pulmonary arterial pressure and heart/body and lung/body weight ratio were increased in MCT40 rats (28 d) and reduced by oral PETN (10 mg/kg, 24 d) therapy. Oxidative stress in the vascular wall, in the heart, and in whole blood as well as vascular endothelin-1 signaling was increased in MCT40-treated rats and normalized by PETN therapy, likely by upregulation of heme oxygenase-1 (HO-1). PETN therapy improved endothelium-dependent relaxation in pulmonary arteries and inhibited endothelin-1-induced oxidative burst in whole blood and the expression of adhesion molecule (ICAM-1) in endothelial cells. Conclusion. MCT-induced PAH impairs endothelial function (aorta and pulmonary arteries) and increases oxidative stress whereas PETN markedly attenuates these adverse effects. Thus, PETN therapy improves pulmonary hypertension beyond its known cardiac preload reducing ability.

Organic Nitrate Therapy, Nitrate Tolerance, and Nitrate-Induced Endothelial Dysfunction: Emphasis on Redox Biology and Oxidative Stress

Organic nitrates, such as nitroglycerin (GTN), isosorbide-5-mononitrate and isosorbide dinitrate, and pentaerithrityl tetranitrate (PETN), when given acutely, have potent vasodilator effects improving symptoms in patients with acute and chronic congestive heart failure, stable coronary artery disease, acute coronary syndromes, or arterial hypertension. The mechanisms underlying vasodilation include the release of •NO or a related compound in response to intracellular bioactivation (for GTN, the mitochondrial aldehyde dehydrogenase [ALDH-2]) and activation of the enzyme, soluble guanylyl cyclase. Increasing cyclic guanosine-3',-5'-monophosphate (cGMP) levels lead to an activation of the cGMP-dependent kinase I, thereby causing the relaxation of the vascular smooth muscle by decreasing intracellular calcium concentrations. The hemodynamic and anti-ischemic effects of organic nitrates are rapidly lost upon long-term (low-dose) administration due to the rapid development of tolerance and endothelial dysfunction, which is in most cases linked to increased intracellular oxidative stress. Enzymatic sources of reactive oxygen species under nitrate therapy include mitochondria, NADPH oxidases, and an uncoupled •NO synthase. Acute high-dose challenges with organic nitrates cause a similar loss of potency (tachyphylaxis), but with distinct pathomechanism. The differences among organic nitrates are highlighted regarding their potency to induce oxidative stress and subsequent tolerance and endothelial dysfunction. We also address pleiotropic effects of organic nitrates, for example, their capacity to stimulate antioxidant pathways like those demonstrated for PETN, all of which may prevent adverse effects in response to long-term therapy. Based on these considerations, we will discuss and present some preclinical data on how the nitrate of the future should be designed.

Exploiting the Pleiotropic Antioxidant Effects of Established Drugs in Cardiovascular Disease

Cardiovascular disease is a leading cause of death and reduced quality of life worldwide. Arterial vessels are a primary target for endothelial dysfunction and atherosclerosis, which is accompanied or even driven by increased oxidative stress. Recent research in this field identified different sources of reactive oxygen and nitrogen species contributing to the pathogenesis of endothelial dysfunction. According to lessons from the past, improvement of endothelial function and prevention of cardiovascular disease by systemic, unspecific, oral antioxidant therapy are obviously too simplistic an approach. Source- and cell organelle-specific antioxidants as well as activators of intrinsic antioxidant defense systems might be more promising. Since basic research demonstrated the contribution of different inflammatory cells to vascular oxidative stress and clinical trials identified chronic inflammatory disorders as risk factors for cardiovascular events, atherosclerosis and cardiovascular disease are closely associated with inflammation. Therefore, modulation of the inflammatory response is a new and promising approach in the therapy of cardiovascular disease. Classical anti-inflammatory therapeutic compounds, but also established drugs with pleiotropic immunomodulatory abilities, demonstrated protective effects in various models of cardiovascular disease. However, results from ongoing clinical trials are needed to further evaluate the value of immunomodulation for the treatment of cardiovascular disease.

The nitric oxide donor pentaerythritol tetranitrate reduces platelet activation in congestive heart failure

Background

Platelet activation associated with endothelial dysfunction and impaired endogenous platelet inhibition is part of the cardiovascular phenotype of congestive heart failure (CHF) and contributes to the increased risk for thromboembolic complications. Pentaerythritol tetranitrate (PETN) has been shown to release nitric oxide without development of nitrate tolerance. We investigated the effect of chronic PETN treatment on platelet activation and aggregation in an experimental CHF model.

Methods and Results

Chronic ischemic heart failure was induced in male Wistar rats by coronary artery ligation. Starting 7 days thereafter, rats were randomised to placebo or PETN (80 mg/kg twice daily). After 9 weeks, activation of circulating platelets was determined measuring platelet bound fibrinogen, which requires activated glycoprotein IIb/IIIa on the platelet surface. Binding was quantified by flow-cytometry using a FITC-labelled anti-fibrinogen antibody. Platelet-bound fibrinogen was significantly increased in CHF-Placebo (mean fluorescence intensity: Sham 88±4, CHF-Placebo 104±6, p<0.05) and reduced following treatment with PETN (89±7, p<0.05 vs. CHF-Placebo). Maximal and final ADP-induced aggregation was significantly enhanced in CHF-Placebo vs. Sham-operated animals and normalized / decreased following chronic PETN treatment. Moreover, platelet adhesion was significantly reduced (number of adherent platelets: control: 85.6±5.5, PETN: 40±3.3; p<0.001) and VASP phosphorylation significantly enhanced following in vitro PETN treatment.

Conclusion

Chronic NO supplementation using PETN reduces platelet activation in CHF rats. Thus, PETN may constitute a useful approach to prevent thromboembolic complications in CHF.

Organic nitrates: update on mechanisms underlying vasodilation, tolerance and endothelial dysfunction

Given acutely, organic nitrates, such as nitroglycerin (GTN), isosorbide mono- and dinitrates (ISMN, ISDN), and pentaerythrityl tetranitrate (PETN), have potent vasodilator and anti-ischemic effects in patients with acute coronary syndromes, acute and chronic congestive heart failure and arterial hypertension. During long-term treatment, however, side effects such as nitrate tolerance and endothelial dysfunction occur, and therapeutic efficacy of these drugs rapidly vanishes. Recent experimental and clinical studies have revealed that organic nitrates per se are not just nitric oxide (NO) donors, but rather a quite heterogeneous group of drugs considerably differing for mechanisms underlying vasodilation and the development of endothelial dysfunction and tolerance. Based on this, we propose that the term nitrate tolerance should be avoided and more specifically the terms of GTN, ISMN and ISDN tolerance should be used. The present review summarizes preclinical and clinical data concerning organic nitrates. Here we also emphasize the consequences of chronic nitrate therapy on the supersensitivity of the vasculature to vasoconstriction and on the increased autocrine expression of endothelin. We believe that these so far rather neglected and underestimated side effects of chronic therapy with at least GTN and ISMN are clinically important.

Nitroglycerin tolerance in caveolin-1 deficient mice

Nitrate tolerance developed after persistent nitroglycerin (GTN) exposure limits its clinical utility. Previously, we have shown that the vasodilatory action of GTN is dependent on endothelial nitric oxide synthase (eNOS/NOS3) activity. Caveolin-1 (Cav-1) is known to interact with NOS3 on the cytoplasmic side of cholesterol-enriched plasma membrane microdomains (caveolae) and to inhibit NOS3 activity. Loss of Cav-1 expression results in NOS3 hyperactivation and uncoupling, converting NOS3 into a source of superoxide radicals, peroxynitrite, and oxidative stress. Therefore, we hypothesized that nitrate tolerance induced by persistent GTN treatment results from NOS3 dysfunction and vascular toxicity. Exposure to GTN for 48-72 h resulted in nitrosation and depletion (>50%) of Cav-1, NOS3 uncoupling as measured by an increase in peroxynitrite production (>100%), and endothelial toxicity in cultured cells. In the Cav-1 deficient mice, NOS3 dysfunction was accompanied by GTN tolerance (>50% dilation inhibition at low GTN concentrations). In conclusion, GTN tolerance results from Cav-1 modification and depletion by GTN that causes persistent NOS3 activation and uncoupling, preventing it from participating in GTN-medicated vasodilation.

Nighttime aircraft noise impairs endothelial function and increases blood pressure in patients with or at high risk for coronary artery disease

Aims

Epidemiological studies suggest the existence of a relationship between aircraft noise exposure and increased risk for myocardial infarction and stroke. Patients with established coronary artery disease and endothelial dysfunction are known to have more future cardiovascular events. We therefore tested the effects of nocturnal aircraft noise on endothelial function in patients with or at high risk for coronary artery disease.

Methods

60 Patients (50p 1–3 vessels disease; 10p with a high Framingham Score of 23 %) were exposed in random and blinded order to aircraft noise and no noise conditions. Noise was simulated in the patients’ bedroom and consisted of 60 events during one night. Polygraphy was recorded during study nights, endothelial function (flow-mediated dilation of the brachial artery), questionnaires and blood sampling were performed on the morning after each study night.

Results

The mean sound pressure levels L_eq(3) measured were 46.9 ± 2.0 dB(A) in the Noise 60 nights and 39.2 ± 3.1 dB(A) in the control nights. Subjective sleep quality was markedly reduced by noise from 5.8 ± 2.0 to 3.7 ± 2.2 (p < 0.001). FMD was significantly reduced (from 9.6 ± 4.3 to 7.9 ± 3.7 %; p < 0.001) and systolic blood pressure was increased (from 129.5 ± 16.5 to 133.6 ± 17.9 mmHg; p = 0.030) by noise. The adverse vascular effects of noise were independent from sleep quality and self-reported noise sensitivity.

Conclusions

Nighttime aircraft noise markedly impairs endothelial function in patients with or at risk for cardiovascular disease. These vascular effects appear to be independent from annoyance and attitude towards noise and may explain in part the cardiovascular side effects of nighttime aircraft noise.

In vitro and in vivo characterization of a new organic nitrate hybrid drug covalently bound to pioglitazone

BACKGROUND/AIMS

Organic nitrates represent a group of nitrovasodilators that are clinically used for the treatment of ischemic heart disease. The new compound CLC-3000 is an aminoethyl nitrate (AEN) derivative of pioglitazone, a thiazolidinedione antidiabetic agent combining the peroxisome proliferator-activated receptor γ agonist activity of pioglitazone with the NO-donating activity of the nitrate moiety.

METHODS

In vitro and in vivo characterization was performed by isometric tension recording, platelet function, bleeding time and detection of oxidative stress.

RESULTS

In vitro, CLC-3000 displayed more potent vasodilation than pioglitazone alone or classical nitrates. In vitro, some effects on oxidative stress parameters were observed. Authentic AEN or the AEN-containing linker CLC-1275 displayed antiaggregatory effects. In vivo treatment with CLC-3000 for 7 days did neither induce endothelial dysfunction nor nitrate tolerance nor oxidative stress. Acute or chronic administration of AEN increased the tail vein bleeding time in mice.

CONCLUSION

In summary, the results of these studies demonstrate that CLC-3000 contains a vasodilative and antithrombotic activity that is not evident with pioglitazone alone, and that 7 days of exposure in vivo showed no typical signs of nitrate tolerance, endothelial dysfunction or other safety concerns in Wistar rats.

Efficacy of the long-acting nitro vasodilator pentaerithrityl tetranitrate in patients with chronic stable angina pectoris receiving anti-anginal background therapy with beta-blockers: a 12-week, randomized, double-blind, placebo-controlled trial

Background

The organic nitrate pentaerithrityl tetranitrate (PETN) has been shown to have ancillary properties that prevent the development of tolerance and endothelial dysfunction. This randomized, double-blind, placebo-controlled, multicentre study (‘CLEOPATRA’ study) was designed to investigate the anti-ischaemic efficacy of PETN 80 mg b.i.d. (morning and mid-day) over placebo in patients with chronic stable angina pectoris.

Methods and results

A total of 655 patients were evaluated in the intention-to-treat population, randomized to PETN (80 mg b.i.d., n = 328) or placebo (n = 327) and completed the study. Patients underwent treadmill exercise tests at randomization, after 6 and 12 weeks of treatment. Treatment with PETN over 12 weeks did not modify the primary endpoint total exercise duration (TED, P = 0.423). In a pre-specified sub-analysis of patients with reduced exercise capacity (TED at baseline ≤9 min, n = 257), PETN appeared more effective than placebo treatment (P = 0.054). Superiority of PETN over placebo was evident in patients who were symptomatic at low exercise levels (n = 120; P = 0.017). Pentaerithrityl tetranitrate 80 mg b.i.d. was well tolerated, and the overall safety profile was comparable with placebo.

Conclusion

Although providing no additional benefit in unselected patients with known coronary artery disease, PETN therapy, administered in addition to modern anti-ischaemic therapy, could increase exercise tolerance in symptomatic patients with reduced exercise capacity.

More answers to the still unresolved question of nitrate tolerance

Organic nitrates are traditionally felt to be a safe adjuvant in the chronic therapy of patients with coronary artery disease. Despite their long use, progress in the understanding of the pharmacology and mechanism of action of these drugs has been achieved only in the last two decades, with the identification of the role of oxidative stress in the pathophysiology of nitrate tolerance, with, the discovery of the ancillary effects of nitrates, and with the demonstration that nitrate therapy has important chronic side effects that might modify patients' prognosis. These advances are however mostly confined to the molecular level or to studies in healthy volunteers, and the true impact of organic nitrates on clinical outcome remains unknown. Complicating this issue, evidence supports the existence of important differences among the different drugs belonging to the group, and there are reasons to believe that the nitrates should not be treated as a homogeneous class. As well, the understanding of the effects of alternative nitric oxide (NO) donors is currently being developed, and future studies will need to test whether the properties of these new medications may compensate and prevent the abnormalities imposed by chronic nitrate therapy. Intermittent therapy with nitroglycerin and isosorbide mononitrate is now established in clinical practice, but they should neither be considered a definitive solution to the problem of nitrate tolerance. Both these strategies are not deprived of complications, and should currently be seen as a compromise rather than a way fully to exploit the benefits of NO donor therapy.

Nitrate therapy and nitrate tolerance in patients with coronary artery disease

Despite the continuous development of newer drugs, the therapy of coronary artery disease remains challenging. Organic nitrates are among the oldest drugs, but they still remain a widely used adjuvant in the treatment of symptomatic coronary artery disease. While their efficacy in relieving angina pectoris symptoms in acute settings and in preventing angina before physical or emotional stress is undisputed, the chronic use of nitrates has been associated with potentially important side effects such as tolerance and endothelial dysfunction. The identification of the mitochondrial aldehyde dehydrogenase as the enzyme responsible for the bioactivation of nitroglycerin has allowed the formulation of a complex but plausible hypothesis regarding the mechanism of action and the development of the side effects associated with nitrate therapy. Further, the discovery of important differences among nitrates suggests that these drugs should not be considered as a homogeneous class. Finally, the identification of nonhemodynamic properties of nitrates, and newer insight on the mechanism of nitrate tolerance, have led us to question the prognostic impact of these drugs.

Chronic protection against ischemia and reperfusion-induced endothelial dysfunction during therapy with different organic nitrates

INTRODUCTION

Ischemic and pharmacologic preconditioning have great clinical potential, but it remains unclear whether their effects can be maintained over time during repeated exposure.We have previously demonstrated that the acute protective effect of nitroglycerin (GTN) is attenuated during repeated daily administration. Pentaerythrityl tetranitrate (PETN) is an organic nitrate with different hemodynamic and biochemical properties. The purpose of the current experiment was to study the preconditioning-like effects of PETN and GTN during repeated daily exposure.

METHODS AND RESULTS

In a randomized, investigator-blind parallel trial, 30 healthy (age 25-32) volunteers were randomized to receive (1) transdermal GTN (0.6 mg/h) administered for 2 h a day for 6 days; (2) oral PETN (80 mg) once a day for 6 days; or (3) no therapy. One week later, endothelium-dependent flow-mediated dilation was assessed before and after exposure to ischemia and reperfusion (IR). IR caused a significant blunting of the endothelium-dependent relaxation in the control group (FMD before IR: 5.8 ± 2.1%; after IR 1.0 ± 2.1%; P < 0.01). Daily, 2-h exposure to GTN partially prevented IR-induced endothelial dysfunction (FMD before IR: 7.7 ± 2.4%; after IR 4.3 ± 3.0%; P < 0.01 compared to before IR). In contrast, daily PETN administration afforded greater protection from IR-induced endothelial injury (FMD before IR: 7.9 ± 1.7%; after IR 6.4 ± 5.3%, P = ns; P < 0.05 ANOVA across groups). In vitro, incubation of human endothelial cells with GTN (but not PETN) was associated with inhibition (P < 0.01) of aldehyde dehydrogenase, an enzyme that is important for both nitrate biotransformation and ischemic preconditioning.

DISCUSSION

We previously showed that upon repeated administration, the preconditioning-like effects of GTN are attenuated. The present data demonstrate a gradient in the extent of protection afforded by the two nitrates, suggesting that PETN-induced preconditioning is maintained after prolonged administration in a human in vivo model of endothelial dysfunction induced by ischemia. Using isolated human endothelial cells, we propose a mechanistic explanation for this observation based on differential effects of GTN versus PETN on the activity of mitochondrial aldehyde dehydrogenase.

Chronic therapy with isosorbide-5-mononitrate causes endothelial dysfunction, oxidative stress, and a marked increase in vascular endothelin-1 expression

AIMS

Isosorbide-5-mononitrate (ISMN) is one of the most frequently used compounds in the treatment of coronary artery disease predominantly in the USA. However, ISMN was reported to induce endothelial dysfunction, which was corrected by vitamin C pointing to a crucial role of reactive oxygen species (ROS) in causing this phenomenon. We sought to elucidate the mechanism how ISMN causes endothelial dysfunction and oxidative stress in vascular tissue.

METHODS AND RESULTS

Male Wistar rats (n= 69 in total) were treated with ISMN (75 mg/kg/day) or placebo for 7 days. Endothelin (ET) expression was determined by immunohistochemistry in aortic sections. Isosorbide-5-mononitrate infusion caused significant endothelial dysfunction but no tolerance to ISMN itself, whereas ROS formation and nicotinamide adenine dinucleotidephosphate (NADPH) oxidase activity in the aorta, heart, and whole blood were increased. Isosorbide-5-mononitrate up-regulated the expression of NADPH subunits and caused uncoupling of the endothelial nitric oxide synthase (eNOS) likely due to a down-regulation of the tetrahydrobiopterin-synthesizing enzyme GTP-cyclohydrolase-1 and to S-glutathionylation of eNOS. The adverse effects of ISMN were improved in gp91phox knockout mice and normalized by bosentan in vivo/ex vivo treatment and suppressed by apocynin. In addition, a strong increase in the expression of ET within the endothelial cell layer and the adventitia was observed.

CONCLUSION

Chronic treatment with ISMN causes endothelial dysfunction and oxidative stress, predominantly by an ET-dependent activation of the vascular and phagocytic NADPH oxidase activity and NOS uncoupling. These findings may explain at least in part results from a retrospective analysis indicating increased mortality in post-infarct patients in response to long-term treatment with mononitrates.

Direct Antioxidant Properties of Bilirubin and Biliverdin. Is there a Role for Biliverdin Reductase?

Reactive oxygen species (ROS) and signaling events are involved in the pathogenesis of endothelial dysfunction and represent a major contribution to vascular regulation. Molecular signaling is highly dependent on ROS. But depending on the amount of ROS production it might have toxic or protective effects. Despite a large number of negative outcomes in large clinical trials (e.g., HOPE, HOPE-TOO), antioxidant molecules and agents are important players to influence the critical balance between production and elimination of reactive oxygen and nitrogen species. However, chronic systemic antioxidant therapy lacks clinical efficacy, probably by interfering with important physiological redox signaling pathways. Therefore, it may be a much more promising attempt to induce intrinsic antioxidant pathways in order to increase the antioxidants not systemically but at the place of oxidative stress and complications. Among others, heme oxygenase (HO) has been shown to be important for attenuating the overall production of ROS in a broad range of disease states through its ability to degrade heme and to produce carbon monoxide and biliverdin/bilirubin. With the present review we would like to highlight the important antioxidant role of the HO system and especially discuss the contribution of the biliverdin, bilirubin, and biliverdin reductase (BVR) to these beneficial effects. The BVR was reported to confer an antioxidant redox amplification cycle by which low, physiological bilirubin concentrations confer potent antioxidant protection via recycling of biliverdin from oxidized bilirubin by the BVR, linking this sink for oxidants to the NADPH pool. To date the existence and role of this antioxidant redox cycle is still under debate and we present and discuss the pros and cons as well as our own findings on this topic.

Organic nitrates differentially modulate circulating endothelial progenitor cells and endothelial function in patients with symptomatic coronary artery disease

Symptomatic coronary artery disease (CAD) is usually treated with organic nitrates. Endothelial progenitor cells (EPCs) are a circulating cell population participating in vascular homeostasis in a nitric oxide-dependent manner. We investigated the effects of the nitric oxide donors isosorbide dinitrate (ISDN) and pentaerythritol tetranitrate (PETN) on EPC and endothelial function in patients with symptomatic CAD. We randomized 36 patients with angiographically proven CAD to treatment with either ISDN (40 mg retarded release orally two times per day; n = 18) or PETN (80 mg orally two times per day; n = 18) for 14 days (clinical trial number: NCT01030367). PETN treatment substantially increased numbers of circulating CD34(+)/KDR(+) EPCs (p = 0.02), whereas no effects were observed in patients treated with ISDN. EPC function assessed by formation of endothelial colonies was enhanced by twofold (p = 0.04) in patients treated with PETN. No changes were observed after ISDN treatment. Endothelial function, assessed by peripheral arterial tonometry, remained unchanged during PETN treatment, but was significantly impaired in patients treated with ISDN. Treatment of symptomatic CAD patients with PETN for 14 days significantly increased levels of circulating EPC and improved markers for EPC function, whereas ISDN was without effects on EPCs and worsened endothelial function.

Differential effects of organic nitrates on arterial diameter among healthy Japanese participants with different mitochondrial aldehyde dehydrogenase 2 genotypes: randomised crossover trial

OBJECTIVES

To determine whether polymorphisms at codon 487 (*1, GAA=Glu; *2, AAA=Lys) of mitochondrial aldehyde dehydrogenase 2 (ALDH2) influence nitroglycerine (glyceryl trinitrate (GTN))-induced vasodilation, and whether GTN or isosorbide dinitrate (ISDN) is a more effective antianginal agent in each ALDH2 genotype.

DESIGN

A randomised, open-label, crossover trial with 117 healthy Japanese (20-39 years) whose genotypes were determined (*1/*1, n=47; *1/*2, n=48; *2/*2, n=22) was performed at Kyushu University Hospital, Fukuoka, Japan. Participants were randomly assigned to treatment: sublingual spray of GTN (0.3 mg) or ISDN (1.25 mg). After ≥ 1 week, measurements were repeated using the other drug. The main outcome measures were the maximal rate of increase in the brachial artery diameter determined by ultrasonography, the time required to attain maximal dilation (T(max)) and the time required to attain 90% maximal dilation (T(0.9)).

RESULTS

The maximal artery diameter increase in response to GTN or ISDN did not differ among genotypes. However, GTN T(max) was significantly longer for *2/*2 (299.7 s, 269.0-330.4) than *1/*1 (254.7 s, 238.6-273.4; p=0.0190). GTN T(0.9) was significantly longer in the *1/*2 (206.1 s, 191.7-219.3) and *2/*2 (231.4 s, 211.8-251.0) genotypes than *1/*1 (174.9 s, 161.5-188.3; p=0.0068, p<0.0001, respectively). In contrast, the time-course of ISDN-induced vasodilation did not differ among genotypes. GTN T(max) and T(0.9) among *1 allele carriers (*1/*1 and *1/*2) were significantly shorter than those of ISDN, whereas the time course of GTN and ISDN vasodilation did not differ among participants carrying *2/*2.

CONCLUSIONS

The amplitude of GTN-induced vasodilation was not influenced by the ALDH2 genotype, but the response was significantly delayed in *2 allele carriers, especially *2/*2. GTN dilated the artery more quickly than ISDN in *1/*1 and *1/*2, but not in *2/*2. Trial registration number UMIN000001492 (UMIN-CTR database).

Organic nitrates and nitrate resistance in diabetes: the role of vascular dysfunction and oxidative stress with emphasis on antioxidant properties of pentaerithrityl tetranitrate

Organic nitrates represent a class of drugs which are clinically used for treatment of ischemic symptoms of angina as well as for congestive heart failure based on the idea to overcome the impaired NO bioavailability by “NO” replacement therapy. The present paper is focused on parallels between diabetes mellitus and nitrate tolerance, and aims to discuss the mechanisms underlying nitrate resistance in the setting of diabetes. Since oxidative stress was identified as an important factor in the development of tolerance to organic nitrates, but also represents a hallmark of diabetic complications, this may represent a common principle for both disorders where therapeutic intervention should start. This paper examines the evidence supporting the hypothesis that pentaerithrityl tetranitrate may represent a nitrate for treatment of ischemia in diabetic patients. This evidence is based on the considerations of parallels between diabetes mellitus and nitrate tolerance as well as on preliminary data from experimental diabetes studies.

Organic nitrates and nitrate tolerance--state of the art and future developments

The hemodynamic and antiischemic effects of nitroglycerin (GTN) are lost upon chronic administration due to the rapid development of nitrate tolerance. The mechanism of this phenomenon has puzzled several generations of scientists, but recent findings have led to novel hypotheses. The formation of reactive oxygen and nitrogen species in the mitochondria and the subsequent inhibition of the nitrate-bioactivating enzyme mitochondrial aldehyde dehydrogenase (ALDH-2) appear to play a central role, at least for GTN, that is, bioactivated by ALDH-2. Importantly, these findings provide the opportunity to reconcile the two "traditional" hypotheses of nitrate tolerance, that is, the one postulating a decreased bioactivation and the concurrent one suggesting a role of oxidative stress. Furthermore, recent animal and human experimental studies suggest that the organic nitrates are not a homogeneous group but demonstrate a broad diversity with regard to induction of vascular dysfunction, oxidative stress, and other side effects. In the past, attempts to avoid nitrate-induced side effects have focused on administration schedules that would allow a "nitrate-free interval"; in the future, the role of co-therapies with antioxidant compounds and of activation of endogeneous protective pathways such as the heme oxygenase 1 (HO-1) will need to be explored. However, the development of new nitrates, for example, tolerance-free aminoalkyl nitrates or combination of nitrate groups with established cardiovascular drugs like ACE inhibitors or AT(1)-receptor blockers (hybrid molecules) may be of great clinical interest.