Once daily therapy with isosorbide-5-mononitrate causes endothelial dysfunction in humans: evidence of a free-radical-mediated mechanism

The effect of vitamin C on nitroglycerin-mediated vasodilation in individuals with and without the aldehyde dehydrogenase 2 polymorphism

AIMS

To mediate its pharmacodynamic effects, glyceryl trinitrate (GTN) requires bioactivation, by which it releases nitric oxide or a nitric oxide moiety. The exact mechanism of GTN bioactivation remains uncertain. Mitochondrial aldehyde dehydrogenase (ALDH-2) has been proposed as the primary enzyme responsible for this bioactivation process. Evidence for the importance of ALDH-2 in GTN bioactivation has been inconsistent, particularly in human models. An alternative hypothesis suggests that decreased ALDH-2 activity leads to accumulation of reactive cytotoxic aldehydes, which either inhibit the vasoactive product(s) of GTN or impair other enzymatic pathways involved in the bioactivation of GTN. We investigated the effect of supplemental vitamin C on vascular responses to GTN in healthy volunteers of East Asian descent, of whom 12 with and 12 without the ALDH-2 polymorphism participated.

METHODS

Subjects underwent 2 sequential brachial artery infusions of GTN at rates of 5, 11 and 22 nmol/min, separated by a 30-min washout period. The GTN infusions were carried out in the presence and absence of vitamin C using a randomized, crossover design. Venous occlusion plethysmography was used to measure forearm blood flow responses to GTN.

RESULTS

Compared to subjects with functional ALDH-2, the variant group exhibited blunted hemodynamic responses to intra-arterial GTN infusions, although this reduction in response was not statically significant. Contrary to our hypothesis, vitamin C had an inhibitory effect on GTN mediated vasodilation as compared to GTN during saline in both groups.

CONCLUSION

We conclude that vitamin C did not augment the acute vascular response to GTN in those with the ALDH-2 polymorphism.

Efficacy of Continuous Transdermal Nitroglycerin for Treating Hot Flashes by Inducing Nitrate Cross-tolerance in Perimenopausal and Postmenopausal Women: A Randomized Clinical Trial

Importance

Due to the potential risks of long-term systemic estrogen therapy, many menopausal women are interested in nonhormonal treatments for vasomotor symptoms. Physiologic studies indicate that nitric oxide plays a key role in mediating hot flash-related vasodilation, suggesting that nonhormonal medications that induce nitrate tolerance in the vasculature may offer therapeutic benefit for vasomotor symptoms.

Objective

To determine whether uninterrupted administration of transdermal nitroglycerin (NTG) to induce nitrate cross-tolerance decreased the frequency or severity of menopause-related hot flashes.

Design, Setting, and Participants

This randomized, double-blinded, placebo-controlled clinical trial included perimenopausal or postmenopausal women reporting 7 or more hot flashes per day who were recruited from northern California by study personnel at a single academic center. Patients were randomized between July 2017 and December 2021, and the trial ended in April 2022 when the last randomized participant completed follow-up.

Interventions

Uninterrupted daily use of transdermal NTG (participant-directed dose titration from 0.2-0.6 mg/h) or identical placebo patches.

Main Outcome Measures

Validated symptom diaries assessing changes in any hot flash frequency (primary outcome) and moderate-to-severe hot flash frequency over 5 and 12 weeks.

Results

Among the 141 randomized participants (70 NTG [49.6%], 71 placebo [50.4%]; 12 [85.8%] Asian, 16 [11.3%] Black or African American, 15 [10.6%] Hispanic or Latina, 3 [2.1%] multiracial, 1 [0.7%] Native Hawaiian or Pacific Islander, and 100 [70.9%] White or Caucasian individuals), a mean (SD) of 10.8 (3.5) hot flashes and 8.4 (3.6) moderate-to-severe hot flashes daily was reported at baseline. Sixty-five participants assigned to NTG (92.9%) and 69 assigned to placebo (97.2%) completed 12-week follow-up (P = .27). Over 5 weeks, the estimated change in any hot flash frequency associated with NTG vs placebo was -0.9 (95% CI, -2.1 to 0.3) episodes per day (P = .10), and change in moderate-to-severe hot flash frequency with NTG vs placebo was -1.1 (95% CI, -2.2 to 0) episodes per day (P = .05). At 12 weeks, treatment with NTG did not significantly decrease the frequency of any hot flashes (-0.1 episodes per day; 95% CI, -1.2 to 0.4) or moderate-to-severe hot flashes (-0.5 episodes per day; 95% CI, -1.6 to 0.7) relative to placebo. In analyses combining 5-week and 12-week data, no significant differences in change in the frequency of any hot flashes (-0.5 episodes per day; 95% CI, -1.6 to 0.6; P = .25) or moderate-to-severe hot flashes (-0.8 episodes per day; 95% CI, -1.9 to 0.2; P = .12) were detected with NTG vs placebo. At 1 week, 47 NTG (67.1%) and 4 placebo participants (5.6%) reported headache (P < .001), but only 1 participant in each group reported headache at 12 weeks.

Conclusions and Relevance

This randomized clinical trial found that continuous use of NTG did not result in sustained improvements in hot flash frequency or severity relative to placebo and was associated with more early but not persistent headache.

Trial Registration

Clinicaltrials.gov Identifier: NCT02714205.

A medication-wide association study to identify medications associated with incident clinically significant diabetic retinopathy

Background

Diabetic retinopathy, a common microvascular complication of diabetes mellitus, is one of the leading causes of vision loss worldwide. Although some oral drugs have been suggested to affect the risk of diabetic retinopathy, systematic evaluation about the associations between medications and diabetic retinopathy is still absent.

Objective

To comprehensively investigate associations of systemic medications with incident clinically significant diabetic retinopathy (CSDR).

Design

Population-based cohort study.

Methods

From 2006 to 2009, more than 26 000 participants residing in New South Wales were enrolled in the 45 and Up study. Diabetic participants with self-reported physician diagnosis or records of anti-diabetic medication prescriptions were finally included in the current analysis. CSDR was defined as diabetic retinopathy cases requiring retinal photocoagulation recorded in the Medicare Benefits Schedule database from 2006 to 2016. Prescriptions of systemic medication from 5 years to 30 days prior to CSDR were retrieved from the Pharmaceutical Benefits Scheme. The study participants were equally split into training and testing datasets. Logistic regression analyses were performed for the association between each of systemic medication and CSDR in the training dataset. After controlling the false discovery rate (FDR), significant associations were further validated in the testing dataset.

Results

The 10-year incidence of CSDR was 3.9% (n = 404). A total of 26 systemic medications were found to be positively associated with CSDR, among which 15 were validated by the testing dataset. Additional adjustments for pertinent comorbidities suggested that isosorbide mononitrate (ISMN) (OR: 1.87, 95%CI: 1.00-3.48), calcitriol (OR: 4.08, 95% CI: 2.02-8.24), three insulins and analogues (e.g., intermediate-acting human insulin, OR: 4.28, 95% CI: 1.69-10.8), five anti-hypertensive medications (e.g., furosemide, OR: 2.53, 95% CI: 1.77-3.61), fenofibrate (OR: 1.96, 95% CI: 1.36-2.82) and clopidogrel (OR: 1.72, 95% CI: 1.15-2.58) were independently associated with CSDR.

Conclusion

This study investigated the association of a full spectrum of systemic medications with incident CSDR. ISMN, calcitriol, clopidogrel, a few subtypes of insulin, anti-hypertensive and cholesterol-lowering medications were found to be associated with incident CSDR.

Updates on Pharmacologic Management of Microvascular Angina

Microvascular angina (MVA), historically called cardiac syndrome X, refers to angina with nonobstructive coronary artery disease. This female-predominant cardiovascular disorder adds considerable health-related costs due to repeated diagnostic angiography and frequent hospital admissions. Despite the high prevalence of this diagnosis in patients undergoing coronary angiography, it is still a therapeutic challenge for cardiologists. Unlike obstructive coronary artery disease, with multiple evidence-based therapies and management guidelines, little is known regarding the management of MVA. During the last decade, many therapeutic interventions have been suggested for the treatment of MVA. However, there is a lack of summarization tab and update of current knowledge about pharmacologic management of MVA, mostly due to unclear pathophysiology. In this article, we have reviewed the underlying mechanisms of MVA and the outcomes of various medications in patients with this disease. Contrary to vasospastic angina in which normal angiogram is observed as well, nitrates are not effective in the treatment of MVA. Beta-blockers and calcium channel blockers have the strongest evidence of improving the symptoms. Moreover, the use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, statins, estrogen, and novel antianginal drugs has had promising outcomes. Investigations are still ongoing for vitamin D, omega-3, incretins, and n-acetyl cysteine, which have resulted in beneficial initial outcomes. We believe that the employment of the available results and results of the future large-scale trials into cardiac care guidelines would help reduce the global cost of cardiac care tremendously.

Effectiveness and Tolerability of Trimetazidine 80 Mg Once Daily in Patients with Stable Angina Uncontrolled with Bisoprolol-Based Therapy: The Modus Vivendi Observational Study

Introduction

Modus Vivendi was conducted in routine clinical practice to evaluate the effect of adding trimetazidine 80 mg once daily (TMZ 80 OD) to treat patients with persistent symptoms despite treatment with background antianginal therapies including maximally tolerated bisoprolol.

Methods

This multicenter, prospective, observational, open-label, uncontrolled study recruited adult outpatients with a confirmed diagnosis of stable angina to whom physicians had decided to prescribe TMZ 80 OD. All patients were symptomatic despite treatment, including maximally tolerated doses of bisoprolol. Data on number of angina attacks, use of short-acting nitrates, and quality of life (QoL) were collected at baseline (V1) and at 1-month (V2) and 3-month (V2) follow-up visits. Two sub-analyses assessed efficacy in patients who remained on a stable bisoprolol dose throughout the study, and in patients in whom background antianginal therapy was known.

Results

A total of 1939 patients were recruited (57.2% women). The mean age was 65.6 ± 8.8 years; 73.8% had class II and 26.2% class III angina. At V1, the mean number of angina attacks per week was 6.2 ± 6.5 despite antianginal therapy including maximally tolerated bisoprolol dosage. Following the addition of TMZ 80 OD, this decreased to 3.4 ± 4.2 attacks per week at V2, and 1.6 ± 2.6 at V3 (P < 0.05 at V2 and V3), with concomitant reductions in short-acting nitrate use (P < 0.05). Significant improvements in QoL were observed throughout the study. Subgroup analyses showed that the addition of TMZ 80 OD to guideline-recommended antianginal therapy was associated with significant reductions in the mean number of weekly angina attacks and consumption of short-acting nitrates and improvements in QoL whether patients were treated with maximally tolerated bisoprolol and TMZ 80 OD alone, or maximally tolerated bisoprolol and TMZ 80 OD on top of other antianginal therapies. Treatment was well tolerated.

Conclusion

The study findings support the addition of TMZ 80 OD to bisoprolol with or without other antianginal therapies for patients with persistent angina.

Trial Registration

This study was retrospectively registered under the number ISRCTN29992579.

Ranolazine: a better understanding of pathophysiology and patient profile to guide treatment of chronic stable angina

Chronic stable angina pectoris, the most prevalent symptomatic manifestation of coronary artery disease, greatly impairs quality of life and is associated with an increased risk for adverse cardiovascular outcomes. Better understanding of the pathophysiologic mechanisms of myocardial ischemia permitted new therapeutic strategies to optimize the management of angina patients. Ideally, antianginal drug treatment should be tailored to individual patient's profile and chosen according to the pathophysiology, hemodynamic profile, adverse effects, potential drug interactions and comorbidities. In this respect, and because of its peculiar mechanism of action, ranolazine represents an alternative therapeutic approach in patients with chronic stable angina and may be considered the first choice in presence of comorbidities that difficult the use of traditional therapies.

State of the art approach to managing angina and ischemia: tailoring treatment to the evidence

Stable angina represents a chronic and often debilitating condition that affects daily activities and quality of life in patients with chronic coronary syndromes (CCS). Current European Society of Cardiology guidelines recommend a four-step approach for the medical treatment of patients taking into consideration hemodynamic variables (heart rate and blood pressure) and the presence or absence of left ventricular dysfunction. However, CCS patients often have several comorbidities and risk factors. Thus, a tailored approach that takes into consideration patient risk factors and comorbidities may have additional benefits beyond angina relief. This is a state of the art review of stable angina treatment based on the currently available evidence.

Managing Ischemic Heart Disease in Women: Role of a Women's Heart Center

PURPOSE OF REVIEW

Heart centers for women (HCW) were developed due to the rising cardiovascular morbidity and mortality in women in the United States in the early 1990s. Our review encompasses the epidemiology, risk factors, diagnostic strategies, treatments, and the role of HCW in managing women with ischemic heart disease (IHD).

RECENT FINDINGS

HCW use a multidisciplinary team to manage women with IHD. Due to the paucity of randomized controlled trials investigating various manifestations of IHD, some treatments are not evidence-based such as those for coronary microvascular dysfunction and spontaneous coronary artery dissection. Sex-specific risk factors have been identified and multimodality cardiac imaging is improving in diagnosing IHD in women. Treatments are being studied to help improve symptoms and outcomes in women with IHD. There has been progress in the care of women with IHD. HCW can be instrumental in treating women with IHD, doing research, and being a source of research study participants.

The Role of Nicorandil in the Management of Chronic Coronary Syndromes in the Gulf Region

Chronic coronary syndromes (CCS) and stable angina are a growing clinical burden worldwide. This is of particular concern in the Gulf region given its high prevalence of cardiovascular risk factors, especially diabetes mellitus and smoking. Despite recommendations on the use of first- and second-line anti-anginal medication, management challenges remain. Current guidelines for pharmacologic treatment are not determined by the range of pathophysiological mechanisms of ischaemia and consequent angina, which may occur either in isolation or co-exist. In this article, we highlight the need to improve knowledge of the epidemiology of chronic coronary syndromes in the Middle East and Gulf region, and the need for studies of stratified pharmacologic approaches to improve symptomatic angina and quality of life in the large and growing number of patients with coronary artery disease from this region. We discuss the role of nicorandil, currently recommended as a second-line anti-anginal drug in CCS patients, and suggest that this may be a particularly useful add-on therapy for patients in the Gulf region.

The Endothelin Receptor Antagonist Macitentan Improves Isosorbide-5-Mononitrate (ISMN) and Isosorbide Dinitrate (ISDN) Induced Endothelial Dysfunction, Oxidative Stress, and Vascular Inflammation

Objective

Organic nitrates such as isosorbide-5-mononitrate (ISMN) and isosorbide dinitrate (ISDN) are used for the treatment of patients with chronic symptomatic stable coronary artery disease and chronic congestive heart failure. Limiting side effects of these nitrovasodilators include nitrate tolerance and/or endothelial dysfunction mediated by oxidative stress. Here, we tested the therapeutic effects of the dual endothelin (ET) receptor antagonist macitentan in ISMN- and ISDN-treated animals.

Methods and Results

Organic nitrates (ISMN, ISDN, and nitroglycerin (GTN)) augmented the oxidative burst and interleukin-6 release in cultured macrophages, whereas macitentan decreased the oxidative burst in isolated human leukocytes. Male C57BL/6j mice were treated with ISMN (75 mg/kg/d) or ISDN (25 mg/kg/d) via s.c. infusion for 7 days and some mice in addition with 30 mg/kg/d of macitentan (gavage, once daily). ISMN and ISDN in vivo therapy caused endothelial dysfunction but no nitrate (or cross-)tolerance to the organic nitrates, respectively. ISMN/ISDN increased blood nitrosative stress, vascular/cardiac oxidative stress via NOX-2 (fluorescence and chemiluminescence methods), ET1 expression, ET receptor signaling, and markers of inflammation (protein and mRNA level). ET receptor signaling blockade by macitentan normalized endothelial function, vascular/cardiac oxidative stress, and inflammatory phenotype in both nitrate therapy groups.

Conclusion

ISMN/ISDN treatment caused activation of the NOX-2/ET receptor signaling axis leading to increased vascular oxidative stress and inflammation as well as endothelial dysfunction. Our study demonstrates for the first time that blockade of ET receptor signaling by the dual endothelin receptor blocker macitentan improves adverse side effects of the organic nitrates ISMN and ISDN.

Impact of different nitrate therapies on long-term clinical outcomes of patients with vasospastic angina: A propensity score-matched analysis

BACKGROUND

Despite the short-term vasodilatory effects of nitrates, the prognostic effects of long-term nitrate therapy in patients with vasospastic angina (VSA) remains unclear. We investigated the prognostic impact of chronic nitrate therapy in VSA patients.

METHODS

Between January 2003 and December 2014, a total of 1154 VSA patients proven by ergonovine provocation tests were classified into nitrate (n=676) and non-nitrate (n=478) groups according to prescriptions for oral nitrates, including isosorbide mononitrate (ISMN) and nicorandil. The primary outcome was major adverse cardiovascular events (MACE), defined as a composite of cardiac death, myocardial infarction, any revascularization, or rehospitalization due to recurrent angina.

RESULTS

The nitrate group was found to have a higher risk of MACE (22.9% vs. 17.6%, hazard ratio [HR] 1.32, 95% confidence interval [CI] 1.01-1.73, p=0.043) than the non-nitrate group. After propensity score matching, the nitrate group had greater risks of MACE (HR 1.32, 95%CI 1.01-1.73, p=0.049). Patients who received the immediate-release formula of ISMN (HR 1.80, 95%CI 1.35-2.39, p<0.001) or were administered any forms of ISMN other than at bedtime (HR 1.90, 95%CI 1.41-2.57, p<0.001) had a significantly higher risk of MACE compared with the non-nitrate group. Nicorandil was shown to have a neutral effect on VSA patients (HR 1.11, 95%CI 0.73-1.69, p=0.62).

CONCLUSIONS

The long-term use of nitrate therapy was associated with increased risk of adverse cardiac events in VSA patients. The use of immediate-release ISMN or the administration of ISMN other than at bedtime was related with poor outcomes of VSA patients.

Nitric oxide and cyclic GMP functions in bone

Nitric oxide plays a central role in the regulation of skeletal homeostasis. In cells of the osteoblastic lineage, NO is generated in response to mechanical stimulation and estrogen exposure. Via activation of soluble guanylyl cyclase (sGC) and cGMP-dependent protein kinases (PKGs), NO enhances proliferation, differentiation, and survival of bone-forming cells in the osteoblastic lineage. NO also regulates the differentiation and activity of bone-resorbing osteoclasts; here the effects are largely inhibitory and partly cGMP-independent. We review the skeletal phenotypes of mice deficient in NO synthases and PKGs, and the effects of NO and cGMP on bone formation and resorption. We examine the roles of NO and cGMP in bone adaptation to mechanical stimulation. Finally, we discuss preclinical and clinical data showing that NO donors and NO-independent sGC activators may protect against estrogen deficiency-induced bone loss. sGC represents an attractive target for the treatment of osteoporosis.

Nicorandil and Long-acting Nitrates: Vasodilator Therapies for the Management of Chronic Stable Angina Pectoris

Nicorandil and long-acting nitrates are vasodilatory drugs used commonly in the management of chronic stable angina pectoris. Both nicorandil and long-acting nitrates exert anti-angina properties via activation of nitric oxide (NO) signalling pathways, triggering vascular smooth muscle cell relaxation. Nicorandil has additional actions as an arterial K⁺ _ATP channel agonist, resulting in more "balanced" arterial and venous vasodilatation than nitrates. Ultimately, these drugs prevent angina symptoms through reductions in preload and diastolic wall tension and, to a lesser extent, epicardial coronary artery dilatation and lowering of systemic blood pressure. While there is some evidence to suggest a modest reduction in cardiovascular events among patients with stable angina treated with nicorandil compared to placebo, this prognostic benefit has yet to be proven conclusively. In contrast, there is emerging evidence to suggest that chronic use of long-acting nitrates might cause endothelial dysfunction and increased cardiovascular risk in some patients.

INDIE-HFpEF (Inorganic Nitrite Delivery to Improve Exercise Capacity in Heart Failure With Preserved Ejection Fraction): Rationale and Design

Approximately half of patients with heart failure have preserved ejection fraction. There is no proven treatment that improves outcome. The pathophysiology of heart failure with preserved ejection fraction is complex and includes left ventricular systolic and diastolic dysfunction, pulmonary vascular disease, endothelial dysfunction, and peripheral abnormalities. Multiple lines of evidence point to impaired nitric oxide (NO)-cGMP bioavailability as playing a central role in each of these abnormalities. In contrast to traditional organic nitrate therapies, an alternative strategy to restore NO-cGMP signaling is via inorganic nitrite. Inorganic nitrite, previously considered to be an inert byproduct of NO metabolism, functions as an important in vivo reservoir for NO generation, particularly under hypoxic and acidosis conditions. As such, inorganic nitrite becomes most active at times of greater need for NO signaling, as during exercise when left ventricular filling pressures and pulmonary artery pressures increase. Herein, we present the rationale and design for the INDIE-HFpEF trial (Inorganic Nitrite Delivery to Improve Exercise Capacity in Heart Failure with Preserved Ejection Fraction), which is a multicenter, randomized, double-blind, placebo-controlled cross-over study assessing the effect of inhaled inorganic nitrite on peak exercise capacity, conducted in the National Heart, Lung, and Blood Institute-sponsored Heart Failure Clinical Research Network.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02742129.

Crosstalk of mitochondria with NADPH oxidase via reactive oxygen and nitrogen species signalling and its role for vascular function

Cardiovascular diseases are associated with and/or caused by oxidative stress. This concept has been proven by using the approach of genetic deletion of reactive species producing (pro-oxidant) enzymes as well as by the overexpression of reactive species detoxifying (antioxidant) enzymes leading to a marked reduction of reactive oxygen and nitrogen species (RONS) and in parallel to an amelioration of the severity of diseases. Likewise, the development and progression of cardiovascular diseases is aggravated by overexpression of RONS producing enzymes as well as deletion of antioxidant RONS detoxifying enzymes. Thus, the consequences of the interaction (redox crosstalk) of superoxide/hydrogen peroxide produced by mitochondria with other ROS producing enzymes such as NADPH oxidases (Nox) are of outstanding importance and will be discussed including the consequences for endothelial nitric oxide synthase (eNOS) uncoupling as well as the redox regulation of the vascular function/tone in general (soluble guanylyl cyclase, endothelin-1, prostanoid synthesis). Pathways and potential mechanisms leading to this crosstalk will be analysed in detail and highlighted by selected examples from the current literature including hypoxia, angiotensin II-induced hypertension, nitrate tolerance, aging and others. The general concept of redox-based activation of RONS sources via "kindling radicals" and enzyme-specific "redox switches" will be discussed providing evidence that mitochondria represent key players and amplifiers of the burden of oxidative stress.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Heart Failure with Preserved Ejection Fraction in Older Adults

Most elderly patients, particularly women, who have heart failure, have a preserved ejection fraction. Patients with this syndrome have severe symptoms of exercise intolerance, frequent hospitalizations, and increased mortality. Despite the importance of heart failure with preserved ejection fraction (HFpEF), the understanding of its pathophysiology is incomplete, and optimal treatment remains largely undefined. Unlike the management of HFrEF, there is a paucity of large evidence-based trials demonstrating morbidity and mortality benefit for the treatment of HFpEF. An update is presented on information regarding pathophysiology, diagnosis, management, and future directions in this important and growing disorder.

Advancements in pharmacotherapy for angina

INTRODUCTION

Angina pectoris is the most prevalent symptomatic manifestation of ischemic heart disease, frequently leads to a poor quality of life, and is a major cause of medical resource consumption. Since the early descriptions of nitrite and nitrate in the 19th century, there has been considerable advancement in the pharmacologic management of angina. Areas covered: Management of chronic angina is often challenging for clinicians. Despite introduction of several pharmacological agents in last few decades, a significant proportion of patients continue to experience symptoms (i.e., refractory angina) with subsequent disability. For the purpose of this review, we searched PubMed and Cochrane databases from inception to August 2016 for the most clinically relevant publications that guide current practice in angina therapy and its development. In this article, we briefly review the pathophysiology of angina and mechanism-based classification of current therapy. This is followed by evidence-based insight into the traditional and novel pharmacotherapeutic agents, highlighting their clinical usefulness. Expert opinion: Considering the wide array of available therapies with different mechanism efficacy and limiting factors, a personalized approach is essential, particularly for patients with refractory angina. Ongoing research with novel pharmacologic modalities is likely to provide new options for management of angina.

A Novel, Direct NO Donor Regulates Osteoblast and Osteoclast Functions and Increases Bone Mass in Ovariectomized Mice

Most US Food and Drug Administration (FDA)-approved treatments for osteoporosis target osteoclastic bone resorption. Only PTH derivatives improve bone formation, but they have drawbacks, and novel bone-anabolic agents are needed. Nitrates, which generate NO, improved BMD in estrogen-deficient rats and may improve bone formation markers and BMD in postmenopausal women. However, nitrates are limited by induction of oxidative stress and development of tolerance, and may increase cardiovascular mortality after long-term use. Here we studied nitrosyl-cobinamide (NO-Cbi), a novel, direct NO-releasing agent, in a mouse model of estrogen deficiency-induced osteoporosis. In murine primary osteoblasts, NO-Cbi increased intracellular cGMP, Wnt/β-catenin signaling, proliferation, and osteoblastic gene expression, and protected cells from apoptosis. Correspondingly, in intact and ovariectomized (OVX) female C57Bl/6 mice, NO-Cbi increased serum cGMP concentrations, bone formation, and osteoblastic gene expression, and in OVX mice, it prevented osteocyte apoptosis. NO-Cbi reduced osteoclasts in intact mice and prevented the known increase in osteoclasts in OVX mice, partially through a reduction in the RANKL/osteoprotegerin gene expression ratio, which regulates osteoclast differentiation, and partially through direct inhibition of osteoclast differentiation, observed in vitro in the presence of excess RANKL. The positive NO effects in osteoblasts were mediated by cGMP/protein kinase G (PKG), but some of the osteoclast-inhibitory effects appeared to be cGMP-independent. NO-Cbi increased trabecular bone mass in both intact and OVX mice, consistent with its in vitro effects on osteoblasts and osteoclasts. NO-Cbi is a novel direct NO-releasing agent that, in contrast to nitrates, does not generate oxygen radicals, and combines anabolic and antiresorptive effects in bone, making it an excellent candidate for treating osteoporosis. © 2016 American Society for Bone and Mineral Research.

Phenotype-Specific Treatment of Heart Failure With Preserved Ejection Fraction: A Multiorgan Roadmap

Heart failure (HF) with preserved ejection fraction (EF; HFpEF) accounts for 50% of HF cases, and its prevalence relative to HF with reduced EF continues to rise. In contrast to HF with reduced EF, large trials testing neurohumoral inhibition in HFpEF failed to reach a positive outcome. This failure was recently attributed to distinct systemic and myocardial signaling in HFpEF and to diversity of HFpEF phenotypes. In this review, an HFpEF treatment strategy is proposed that addresses HFpEF-specific signaling and phenotypic diversity. In HFpEF, extracardiac comorbidities such as metabolic risk, arterial hypertension, and renal insufficiency drive left ventricular remodeling and dysfunction through systemic inflammation and coronary microvascular endothelial dysfunction. The latter affects left ventricular diastolic dysfunction through macrophage infiltration, resulting in interstitial fibrosis, and through altered paracrine signaling to cardiomyocytes, which become hypertrophied and stiff because of low nitric oxide and cyclic guanosine monophosphate. Systemic inflammation also affects other organs such as lungs, skeletal muscle, and kidneys, leading, respectively, to pulmonary hypertension, muscle weakness, and sodium retention. Individual steps of these signaling cascades can be targeted by specific interventions: metabolic risk by caloric restriction, systemic inflammation by statins, pulmonary hypertension by phosphodiesterase 5 inhibitors, muscle weakness by exercise training, sodium retention by diuretics and monitoring devices, myocardial nitric oxide bioavailability by inorganic nitrate-nitrite, myocardial cyclic guanosine monophosphate content by neprilysin or phosphodiesterase 9 inhibition, and myocardial fibrosis by spironolactone. Because of phenotypic diversity in HFpEF, personalized therapeutic strategies are proposed, which are configured in a matrix with HFpEF presentations in the abscissa and HFpEF predispositions in the ordinate.

The Nitrate-Nitrite-NO Pathway and Its Implications for Heart Failure and Preserved Ejection Fraction

The pathogenesis of exercise intolerance in patients with heart failure and preserved ejection fraction (HFpEF) is likely multifactorial. In addition to cardiac abnormalities (diastolic dysfunction, abnormal contractile reserve, chronotropic incompetence), several peripheral abnormalities are likely to be involved. These include abnormal pulsatile hemodynamics, abnormal arterial vasodilatory responses to exercise, and abnormal peripheral O2 delivery, extraction, and utilization. The nitrate-nitrite-NO pathway is emerging as a potential target to modify key physiologic abnormalities, including late systolic left ventricular (LV) load from arterial wave reflections (which has deleterious short- and long-term consequences for the LV), arterial vasodilatory reserve, muscle O2 delivery, and skeletal muscle mitochondrial function. In a recently completed randomized trial, the administration of a single dose of exogenous inorganic nitrate has been shown to exert various salutary arterial hemodynamic effects, ultimately leading to enhanced aerobic capacity in patients with HFpEF. These effects have the potential for both immediate improvements in exercise tolerance and for long-term "disease-modifying" effects. In this review, we provide an overview of key mechanistic contributors to exercise intolerance in HFpEF, and of the potential therapeutic role of drugs that target the nitrate-nitrite-NO pathway.

Vasodilator Therapy: Nitrates and Nicorandil

Nitrates have been used to treat symptoms of chronic stable angina for over 135 years. These drugs are known to activate nitric oxide (NO)-cyclic guanosine-3',-5'-monophasphate (cGMP) signaling pathways underlying vascular smooth muscle cell relaxation, albeit many questions relating to how nitrates work at the cellular level remain unanswered. Physiologically, the anti-angina effects of nitrates are mostly due to peripheral venous dilatation leading to reduction in preload and therefore left ventricular wall stress, and, to a lesser extent, epicardial coronary artery dilatation and lowering of systemic blood pressure. By counteracting ischemic mechanisms, short-acting nitrates offer rapid relief following an angina attack. Long-acting nitrates, used commonly for angina prophylaxis are recommended second-line, after beta-blockers and calcium channel antagonists. Nicorandil is a balanced vasodilator that acts as both NO donor and arterial K(+) ATP channel opener. Nicorandil might also exhibit cardioprotective properties via mitochondrial ischemic preconditioning. While nitrates and nicorandil are effective pharmacological agents for prevention of angina symptoms, when prescribing these drugs it is important to consider that unwanted and poorly tolerated hemodynamic side-effects such as headache and orthostatic hypotension can often occur owing to systemic vasodilatation. It is also necessary to ensure that a dosing regime is followed that avoids nitrate tolerance, which not only results in loss of drug efficacy, but might also cause endothelial dysfunction and increase long-term cardiovascular risk. Here we provide an update on the pharmacological management of chronic stable angina using nitrates and nicorandil.

Inhaled Sodium Nitrite Improves Rest and Exercise Hemodynamics in Heart Failure With Preserved Ejection Fraction

RATIONALE

Abnormalities in nitric oxide signaling play a pivotal role in heart failure with preserved ejection fraction (HFpEF). Intravenous sodium nitrite, which is converted to nitric oxide in vivo, improves hemodynamics in HFpEF, but its use is limited by the need for parenteral administration. Nitrite can also be administered using a novel, portable micronebulizer system suitable for chronic use.

OBJECTIVE

Determine whether inhaled nitrite improves hemodynamics in HFpEF.

METHODS AND RESULTS

In a double-blind, randomized, placebo-controlled, parallel-group trial, subjects with HFpEF (n=26) underwent cardiac catheterization with simultaneous expired gas analysis at rest and during exercise before and after treatment with inhaled sodium nitrite (90 mg) or placebo. The primary end point was the pulmonary capillary wedge pressure during exercise. Before study drug administration, HFpEF subjects displayed an increase in pulmonary capillary wedge pressure with exercise from 20±6 to 34±7 mm Hg (P<0.0001). After study drug administration, exercise pulmonary capillary wedge pressure was substantially improved by nitrite as compared with placebo (baseline-adjusted mean 25±5 versus 31±6 mm Hg; analysis of covariance P=0.022). Inhaled nitrite reduced resting pulmonary capillary wedge pressure (-4±3 versus -1±2 mm Hg; P=0.002), improved pulmonary artery compliance (+1.5±1.1 versus +0.6±0.9 mL/mm Hg), and decreased mean pulmonary artery pressures at rest (-7±4 versus -3±4 mm Hg; P=0.007) and with exercise (-10±6 versus -5±6 mm Hg; P=0.05). Nitrite reduced right atrial pressures, with no effect on cardiac output or stroke volume.

CONCLUSIONS

Acute administration of inhaled sodium nitrite reduces biventricular filling pressures and pulmonary artery pressures at rest and during exercise in HFpEF. Further study is warranted to evaluate chronic effects of inhaled nitrite in HFpEF.

CLINICAL TRIAL REGISTRATION

This single center randomized clinical trial is registered at clinicaltrials.gov (NCT02262078).

Continuous transdermal nitroglycerin therapy for menopausal hot flashes: a single-arm, dose-escalation trial

OBJECTIVE

To describe the efficacy and tolerability of continuous nitroglycerin for treatment of hot flashes.

METHODS

Perimenopausal and postmenopausal women reporting at least seven hot flashes per day were recruited into a single-arm, dose-escalation trial of continuous transdermal nitroglycerin. Participants were started on a generic 0.1 mg/hour nitroglycerin patch applied daily without patch-free periods. During 4 weeks, participants escalated dosage weekly to 0.2, 0.4, or 0.6 mg/hour as tolerated, then discontinued nitroglycerin during the final week. Changes in hot flash frequency and severity were assessed using symptom diaries. Paired t tests examined change in outcomes between baseline and maximal-dose therapy and after discontinuation of nitroglycerin.

RESULTS

Of the 19 participants, mean age was 51.4 (±4.3) years. Women reported an average 10.6 (±3.0) hot flashes and 7.1 (±3.8) moderate-to-severe hot flashes per day at baseline. Eleven women escalated to 0.6 mg/hour, three to 0.4 mg/hour, two to 0.2 mg/hour, and one remained on 0.1 mg/hour nitroglycerin. Two discontinued nitroglycerin before the first outcomes assessment. Among the remaining 17 women, the average daily frequency of hot flashes decreased by 54% and the average frequency of moderate-to-severe hot flashes decreased by 69% from baseline to maximum-dose therapy (P < 0.001 for both). After discontinuing nitroglycerin, participants reported an average 23% increase in frequency of any hot flashes (P = 0.041) and 96% increase in moderate-to-severe hot flashes (P < 0.001).

CONCLUSIONS

Continuous nitroglycerin may substantially and reversibly decrease hot flash frequency and severity. If confirmed in a randomized blinded trial, it may offer a novel nonhormonal hot flash treatment.

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.

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.

Central blood pressure: current evidence and clinical importance

Pressure measured with a cuff and sphygmomanometer in the brachial artery is accepted as an important predictor of future cardiovascular risk. However, systolic pressure varies throughout the arterial tree, such that aortic (central) systolic pressure is actually lower than corresponding brachial values, although this difference is highly variable between individuals. Emerging evidence now suggests that central pressure is better related to future cardiovascular events than is brachial pressure. Moreover, anti-hypertensive drugs can exert differential effects on brachial and central pressure. Therefore, basing treatment decisions on central, rather than brachial pressure, is likely to have important implications for the future diagnosis and management of hypertension. Such a paradigm shift will, however, require further, direct evidence that selectively targeting central pressure, brings added benefit, over and above that already provided by brachial artery pressure.

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.

Enhancing vascular relaxing effects of nitric oxide-donor ruthenium complexes

Ruthenium-derived complexes have emerged as new nitric oxide (NO) donors that may help circumvent the NO deficiency that impairs vasodilation. NO in vessels can be produced by the endothelial cells and/or released by NO donors. NO interacts with soluble guanylyl-cyclase to produce cGMP to activate the kinase-G pathway. As a result, conductance arteries, veins and resistance arteries dilate, whereas the cytosolic Ca2+ levels in the smooth muscle cells decrease. NO also reacts with oxygen or the superoxide anion, to generate reactive oxygen species that modulate NO-induced vasodilation. In this article, we focus on NO production by NO synthase and discuss the vascular changes taking place during hypertension originating from endothelial dysfunction. We will describe how the NO released from ruthenium-derived complexes enhances the vascular effects arising from failed NO generation or lack of NO bioavailability. In addition, how ruthenium-derived NO donors induce the hypotensive effect by vasodilation is also discussed.

[Differential therapy in coronary heart disease]

The various contemporary therapeutic options for coronary artery disease (CAD) require differentiated, individualized treatment strategies. The foundations of CAD therapy are lifestyle modifications targeted on the individual risk profile of the patients. Pharmacological therapy of CAD should prevent secondary coronary events (e.g. platelet aggregation inhibitors and statins) and reduce angina in symptomatic patients (e.g. short-acting nitrates, beta blockers, calcium channel blockers and if necessary ivabradine and ranolazine). Revascularization therapy has to be performed promptly in patients with acute coronary syndromes; however, in patients with stable CAD the decision to perform revascularization therapy has to consider symptoms, detection of ischemia and if appropriate intracoronary assessment of hemodynamic relevance of an intermediate stenosis (fractional flow reserve). The differential indications of percutaneous coronary intervention compared to coronary artery bypass grafting depend on the severity of coronary artery disease and the morphology (SYNTAX score), comorbidities and the will of the individual patient. The international guidelines emphasize the value of an interdisciplinary treatment decision in a "heart team". In summary, differential therapy of CAD has become challenging in the current clinical practice; future developments will probably further improve individualized strategies to treat patients with CAD.

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.

Organic nitrate metabolism and action: toward a unifying hypothesis and the future-a dedication to Professor Leslie Z. Benet

This review summarizes the major advances that had been reported since the outstanding contributions that Professor Benet and his group had made in the 1980s and 1990s concerning the metabolism and pharmacologic action of organic nitrates (ORNs). Several pivotal studies have now enhanced our understanding of the metabolism and the bioactivation of ORNs, resulting in the identification of a host of cysteine-containing enzymes that can carry out this function. Three isoforms of aldehyde dehydrogenase, all of which with active catalytic cysteine sites, are now known to metabolize, somewhat selectively, various members of the ORN family. The existence of a long-proposed but unstable thionitrate intermediate from ORN metabolism has now been experimentally observed. ORN-induced thiol oxidation in multiple proteins, called the "thionitrate oxidation hypothesis," can be used not only to explain the phenomenon of nitrate tolerance, but also the various consequences of chronic nitrate therapy, namely, rebound vasoconstriction, and increased morbidity and mortality. Thus, a unifying biochemical hypothesis can account for the myriad of pharmacological events resulting from nitrate therapy. Optimization of the future uses of ORN in cardiology and other diseases could benefit from further elaboration of this unifying hypothesis.

[Which future in cardiovascular therapy for nitric oxide and its derivatives?]

Nitric oxide (NO) is involved in the regulation of several physiological processes such as vascular homeostasis. Exogenous NO supply offers major therapeutic interest, especially in the treatment of coronary artery disease, ischemic syndromes and other cardiovascular pathologies. Nevertheless, the administration of NO itself is limited by its short half-life. NO prodrugs have been marketed for decades, e.g. organic nitrates for angina pectoris. These prodrugs display undeniable advantages such as angina crisis relief and preconditioning effect. Nevertheless, they suffer from several drawbacks: toxicity, tolerance, endothelial dysfunction exacerbation. These negative effects are related to massive production of reactive species derived from oxygen or nitrogen, which trigger oxidative and nitrosative stress. New NO donors are under development to overcome those disadvantages, among which the S-nitrosothiols family seems especially promising.

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.

Nitric oxide modulation as a therapeutic strategy in heart failure

Nitric oxide (NO) is recognized as one of the most important cardiovascular signaling molecules, with multiple regulatory effects on myocardial and vascular tissue as well as on other tissues and organ systems. With the growth in understanding of the range and mechanisms of NO effects on the cardiovascular system, it is now possible to consider pharmaceutical interventions that directly target NO or key steps in NO effector pathways. This article reviews aspects of the cardiovascular effects of NO, abnormalities in NO regulation in heart failure, and clinical trials of drugs that target specific aspects of NO signaling pathways.

Free radical biology of the cardiovascular system

Most cardiovascular diseases (CVDs), as well as age-related cardiovascular alterations, are accompanied by increases in oxidative stress, usually due to increased generation and/or decreased metabolism of ROS (reactive oxygen species; for example superoxide radicals) and RNS (reactive nitrogen species; for example peroxynitrite). The superoxide anion is generated by several enzymatic reactions, including a variety of NADPH oxidases and uncoupled eNOS (endothelial NO synthase). To relieve the burden caused by this generation of free radicals, which also occurs as part of normal physiological processes, such as mitochondrial respiratory chain activity, mammalian systems have developed endogenous antioxidant enzymes. There is an increased usage of exogenous antioxidants such as vitamins C and E by many patients and the general public, ostensibly in an attempt to supplement intrinsic antioxidant activity. Unfortunately, the results of large-scale trails do not generate much enthusiasm for the continued use of antioxidants to mitigate free-radical-induced changes in the cardiovascular system. In the present paper, we review the clinical use of antioxidants by providing the rationale for their use and describe the outcomes of several large-scale trails that largely display negative outcomes. We also describe the emerging understanding of the detailed regulation of superoxide generation by an uncoupled eNOS and efforts to reverse eNOS uncoupling. SIRT1 (sirtuin 1), which regulates the expression and activity of multiple pro- and anti-oxidant enzymes, could be considered a candidate molecule for a 'molecular switch'.

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.

Heme oxygenase-1 induction and organic nitrate therapy: beneficial effects on endothelial dysfunction, nitrate tolerance, and vascular oxidative stress

Organic nitrates are a group of very effective anti-ischemic drugs. They are used for the treatment of patients with stable angina, acute myocardial infarction, and chronic congestive heart failure. A major therapeutic limitation inherent to organic nitrates is the development of tolerance, which occurs during chronic treatment with these agents, and this phenomenon is largely based on induction of oxidative stress with subsequent endothelial dysfunction. We therefore speculated that induction of heme oxygenase-1 (HO-1) could be an efficient strategy to overcome nitrate tolerance and the associated side effects. Indeed, we found that hemin cotreatment prevented the development of nitrate tolerance and vascular oxidative stress in response to chronic nitroglycerin therapy. Vice versa, pentaerithrityl tetranitrate (PETN), a nitrate that was previously reported to be devoid of adverse side effects, displayed tolerance and oxidative stress when the HO-1 pathway was blocked pharmacologically or genetically by using HO-1^+/– mice. Recently, we identified activation of Nrf2 and HuR as a principle mechanism of HO-1 induction by PETN. With the present paper, we present and discuss our recent and previous findings on the role of HO-1 for the prevention of nitroglycerin-induced nitrate tolerance and for the beneficial effects of PETN therapy.