Comparison of effects of ascorbic acid on endothelium-dependent vasodilation in patients with chronic congestive heart failure secondary to idiopathic dilated cardiomyopathy versus patients with effort angina pectoris secondary to coronary artery disease

Dohongsamul-tang inhibits cardiac remodeling and fibrosis through calcineurin/NFAT and TGF-β/Smad2 signaling in cardiac hypertrophy

ETHNOPHARMACOLOGICAL RELEVANCE

Dohongsammul-tang (DH) is a Korean traditional herbal medicine used to alleviate symptoms caused by extravasated blood. It is known to protect against cardiovascular diseases and promote blood circulation by activating blood circulation to dispel blood stasis. The DH based on the characteristics of its medicinal properties has discovered the potential of alleviating cardiac hypertrophy. Therefore, this study was performed to verify the pharmacological effect of DH on improving cardiovascular disorders and to demonstrate its mutual improvement effect on renal function. Furthermore, aim of this study is founding the new potential beyond the traditional medicinal efficacy of DH, a traditional medicine.

AIM OF THE STUDY

In cardiovascular disease, cardiac hypertrophy refers to a change in the shape of the heart's structure due to pressure overload. It is known that an increase in myofibrils causes thickening of the heart, resulting in high blood pressure. Therefore, suppressing cardiac hypertrophy may be a major factor in lowering the morbidity, mortality, and heart failure associated with cardiovascular disease. Therefore, the study was performed to investigate whether DH, traditionally used, has effects on improving and alleviating cardiac injury and fibrosis caused by cardiac hypertrophy.

MATERIALS AND METHODS

Dohongsamul-tang was composed of 6 herbal medicine and each material were boiled with 4 L distilled water for 2 h. The mixture for dohongsamul-tang centrifuged at 3000 rpm for 10 min and concentrated. The concentrated dohongsamul-tang extraction freeze-dried and sotred at 70 °C. The powder of dohongsamul-tang was diluted with distilled water and administered orally. In this study, pressure overload was induced by tying the transverse aortic arch, which is connected to the left ventricle, to the thickness of a 27G needle by performing a surgical operation. The resulting cardiac hypertrophy and heart remodeling was induced and maintained for 8 weeks.

RESULTS

The study administered propranolol and dohongsamul-tang orally for 10 weeks to investigate their effects on cardiac hypertrophy induced by transverse aortic contraction (TAC) surgery. Results showed that TAC group increased the left ventricle weight and decreased cardiac function, but dohongsamul-tang treatment attenuated these effects. The pressure-volume curve experiment revealed that dohongsamul-tang improved cardiovascular function, which was worsened by TAC group. Dohongsamul-tang treatment also downregulated collagen I and III through the TGF-β/Smad2 signaling pathway and improved hematological biomarkers of cardiac hypertrophy. In addition, dohongsamul-tang treatment improved renal function-related biomarkers, such as blood creatinine, blood urea nitrogen, and neutrophil gelatinase-associated lipocalin, which were increased by TAC-induced cardiac hypertrophy.

CONCLUSIONS

Taken together, dohongsamul-tang treatment inhibited cardiac remodeling due to pressure overload in the TAC-induced cardiac hypertrophy model, and this effect is thought to be manifested by improving the functional and morphological changes through the calcineurin/NFATc4 and reducing the cardiac fibrosis by suppressing TGF-β/Smad2 signaling pathways.

Endothelial dysfunction in the microcirculation of patients with obstructive sleep apnea

RATIONALE

Obstructive sleep apnea (OSA) is a risk factor for cardiovascular disease. We hypothesized that patients with OSA and no cardiovascular disease have oxidant-related microcirculatory endothelial dysfunction.

OBJECTIVES

To evaluate the microcirculation in OSA.

METHODS

This study included seven patients with OSA and seven age- and weight-matched control subjects (mean age, 38 yr; mean body mass index, 32.5 kg/m²). All participants were free of cardiovascular risk factors. Participants received measurement of brachial artery flow-mediated dilation and forearm subcutaneous biopsy. Patients underwent repeated tests 12 weeks after treatment. Microcirculatory endothelial cells were isolated, and immunohistochemistry staining for peroxynitrite in the microcirculation was performed.

MEASUREMENTS AND MAIN RESULTS

Flow-mediated dilation was lower in patients than in control subjects at baseline (mean ± SEM: 5.7 ± 0.5 vs. 9.5 ± 0.6; P = 0.02) and increased after treatment (5.7-7.3; change, 1.7 ± 0.6; P = 0.04). Microcirculatory peroxynitrite deposit was higher in patients compared with control subjects (44.0 ± 1.6 vs. 21.8 ± 1.9 stain density units; P < 0.001) and decreased after treatment from 44.0 to 30.5 stain density units (change, -13.5 ± 2.9; P = 0.009). In patients, transcription of endothelial nitric oxide synthase decreased from 5.2 to -1.3 after treatment (change, 6.5 ± 2.5; P = 0.05), and transcription of superoxide dismutase1 decreased from -4.0 to -12.3 after treatment (change, -8.3 ± 2.1; P = 0.01). These changes persisted after adjustment for weight and underlying severity of OSA.

CONCLUSIONS

This is the first direct evaluation of the microcirculation in OSA. Patients with OSA with low cardiovascular risk status had increased oxidant production in the microcirculation and endothelial dysfunction, both of which improved with treatment. Endothelial nitric oxide synthase transcription decreased with treatment.

Role of marginal vitamin C deficiency in atherogenesis: in vivo models and clinical studies

Vitamin C is a pivotal redox modulater in many biological reactions of which several remain poorly understood. Naturally, vitamin C has been the subject of many investigations over the past decades in relation to its possible beneficial effects on cardiovascular disease primarily based on its powerful yet general antioxidant properties. However, growing epidemiological, clinical and experimental evidence now suggests a more specific role of ascorbate in vasomotion and in the prevention of atherosclerosis. For example, in contrast to most other biological antioxidants, administration of vitamin C can apparently induce vasodilation. Millions of people worldwide can be diagnosed with vitamin C deficiency according to accepted definitions. In this perspective, the present review examines the evidence for a specific link between vitamin C deficiency and increased risk of atherosclerosis as well as the possible mechanisms by which vitamin C may exert its protective function.

Endothelial function and peripheral vasomotion in the brachial artery in neurally mediated syncope

BACKGROUND

Paradoxical peripheral vasodilation is one of the suspected mechanisms of neurally mediated syncope. Parasympathetic stimulation following sympathetic activation during orthostatic stress mainly contributes to this vasodilation.

HYPOTHESIS

Since endothelial function modulates peripheral vascular tone, this study aimed to determine whether endothelial function and inappropriate peripheral vasomotion has a significant role in the pathogenesis of neurally mediated syncope.

METHODS

To investigate whether endothelial function is augmented or whether abnormal peripheral vasomotion exits, flow-mediated dilation (FMD, endothelium-dependent vasodilation) and sublingual glyceryl trinitrate-induced dilation (0.3 mg, GTN-D, endothelium-independent vasodilation) were measured in the brachial artery in 16 patients with neurally mediated syncope, aged 33 +/- 10 years, by using high-resolution ultrasound. All patients underwent positive head-up tilt testing. These measures were compared with those in 16 control subjects matched with the patients by age, gender, and coronary risk factors. For FMD, percent diameter changes were obtained from baseline to hyperemic conditions (1 min after 5 min occlusion of the forearm artery). There were five smokers in both the patient and the control groups, but there was no structural heart disease in either group.

RESULTS

Baseline brachial artery diameters were comparable (3.8 +/- 0.6 vs. 3.8 +/- 0.7 mm, NS). Flow-mediated dilation in patients with neurally mediated syncope had a normal value of 9.8 +/- 5.0% despite the inclusion of five smokers. Flow-mediated dilation and GTN-D in patients with neurally mediated syncope were significantly greater than those in controls (9.0 +/- 5.0 vs. 3.0 +/- 3.5%, p<0.05; 18.4 +/- 5.5 vs. 14.1 +/- 4.4%, p<0.05).

CONCLUSIONS

Augmented endothelial function and/or abnormal peripheral vasomotion in peripheral arteries are important in patients with neurally mediated syncope in selected populations.

Aminothiol redox alterations in patients with chronic heart failure of ischaemic or non-ischaemic origin

OBJECTIVE

Oxidative stress plays a role in the progression of chronic heart failure (CHF), but whether and how ischaemic heart disease (IHD) or non-IHD aetiology may account for differential redox alterations is currently unclear. We assessed the relation between thiol redox state and lipid peroxidation, as a marker of oxidative stress, in patients with CHF of ischaemic or non-ischaemic origin.

METHODS

Blood reduced glutathione, plasma total and reduced cysteine, cysteinylglycine, homocysteine, glutathione, plasma alpha-tocopherol, ascorbic acid, and free malondialdehyde were assessed in 43 CHF heart transplant candidates (24 IHD and 19 non-IHD) and 30 controls matched for age, gender and number of atherosclerotic risk factors.

RESULTS

Reduced cysteine was increased in CHF patients compared with controls. The highest levels were found in IHD versus non-IHD patients versus controls. Malondialdehyde levels were significantly higher in IHD patients than in controls, whereas antioxidant vitamins did not differ among the three groups.

CONCLUSIONS

Specific abnormalities in the thiol pattern are associated with heart failure aetiology in CHF patients. Our findings point to the possible role of reduced cysteine in the progression of chronic IHD to heart failure status, as an additional pro-oxidant stimulus for worsening oxidative stress.

Distinguishing between ischemic and non-ischemic dilated cardiomyopathy based on non-invasive ultrasonic evaluation of peripheral arteries

BACKGROUND: Recently, high-frequency transducers have been introduced in echocardiography laboratories to non-invasively evaluate peripheral arteries. Our aim was to assess the usefulness of these non-invasive vascular ultrasonic techniques in differentiating between ischemic and non-ischemic dilated cardiomyopathy. METHODS: Forty patients with dilated cardiomyopathy of uncertain origin who underwent echocardiographic examination were studied. In all patients, carotid, femoral, and brachial arteries were scanned using high-frequency transducers in order to detect atherosclerotic plaques and to measure intima-media wall thickness. Also, flow-mediated vasodilation was measured at the brachial artery. RESULTS: Of the 40 patients studied, 24 (60%) had significant coronary lesions. In patients with ischemic cardiomyopathy, carotid plaques were found more frequently (79% vs. 25%, p=0.001), and intima-media wall thickness was higher in carotid (1.14+/-0.23 vs. 0.84+/-0.20 mm, <0.001), femoral (1.21+/-0.15 vs. 0.90+/-0.17 mm, p<0.001), and brachial (0.85+/-0.11 vs. 0.68+/-0.12, p<0.001) arteries. Carotid intima-media thickness of 1 mm or more was 83% sensitive and 69% specific for the diagnosis of ischemic cardiomyopathy. The highest diagnostic accuracy for any isolated vascular finding was obtained for femoral intima-media thickness greater than 1.1 mm (83% sensitivity, 88% specificity) and for brachial intima-media thickness greater than 0.7 mm (88% sensitivity and 81% specificity). The highest sensitivity (92%) was obtained for the presence of 1 or more vascular findings, and the highest specificity (94%) for 3 or more vascular findings. CONCLUSION: Non-invasive assessment of peripheral arteries is of help in differentiating between ischemic and non-ischemic dilated cardiomyopathy. These ultrasonic techniques should be considered as complementary examinations in the evaluation of patients with dilated cardiomyopathy in echocardiography laboratories.

Endothelial cell activation in patients with decompensated heart failure

BACKGROUND

Vascular endothelial functions, other than nitric oxide (NO)-mediated control of vasomotor tone, are poorly characterized in patients with chronic heart failure (CHF). Veins and arteries are exposed to the same circulating proinflammatory mediators in patients with CHF. The present study tested whether endothelial cell activation occurs in veins of patients with decompensated CHF and whether activation, if present, subsides with return to a clinically compensated state.

METHODS AND RESULTS

Fifteen patients with decompensated CHF requiring transient inotropic support and 6 age-matched, healthy controls were studied. Endothelial cells and blood were collected from a forearm vein, and brachial artery flow-mediated dilation (FMD) was measured before and 24 hours after discontinuation of short-term inotropic therapy, when patients had returned to a steady compensated state. Nitrotyrosine immunoreactivity (an intracellular marker of oxidative stress), cyclooxygenase-2 (COX-2), and inducible NO synthase (iNOS) expression were significantly higher in venous endothelial cells of patients in clinical decompensation when compared with healthy subjects. Return to a compensated state resulted in a significant reduction in nitrotyrosine immunoreactivity, COX-2, and iNOS expression. Concomitantly, a significant increase in FMD and a decline in plasma total 8-isoprostane and bicycloprostaglandin E2 levels were observed. Venous endothelial NOS expression was unaffected by clinical decompensation.

CONCLUSIONS

Clinical decompensation in CHF is associated with activation of the venous endothelium. Return to a compensated state after short-term inotropic therapy results in a significant reduction in endothelial nitrotyrosine formation, COX-2, and iNOS expression.

Assessment of flow-mediated vasodilatation (FMD) of the brachial artery: effects of technical aspects of the FMD measurement on the FMD response

AIMS

The ability to assess endothelial function non-invasively with B-mode ultrasound has lead to its widespread application in a variety of studies. However, the absolute values obtained using this approach vary considerably across studies. We studied whether technical aspects of the methodology can explain the wide variety in absolute values across studies.

METHODS AND RESULTS

A literature search was performed to identify published reports on flow-mediated vasodilatation (FMD) of the brachial artery published between 1992 and 2001. Information on type of equipment (wall track/B-mode), location of the measurement (antecubital fossa/upper arm), occlusion site (lower/upper arm), occlusion duration (min), and occlusion pressure was extracted. Patient characteristics were also extracted. For the healthy populations, mean FMD varied from 0.20 to 19.2%; for the coronary heart disease (CHD) patients FMD varied from -1.3 to 14%; for subjects with diabetes mellitus FMD varied from 0.75 to 12%. Compared with occlusion at the upper arm, lower arm occlusion was related to decreased FMD (mean difference in FMD -2.47%; 95% CI 0.55-4.39). An occlusion duration of > or =4.5 min was related to an increased FMD compared with an occlusion time of < or =4 min (mean difference 1.30%; 95% CI 0.35-2.46). These findings were adjusted for other technical aspects of the methodology and for differences in risk factors between populations.

CONCLUSION

Mean FMD differs widely between studies. There is a great overlap between populations (healthy, CHD, diabetics). Our findings suggest that the technical aspects of the measurements, the location, and the duration of the occlusion may explain some of these differences, whereas type of equipment, location of the measurement, and occlusion pressure do not.

Malfunction of vascular control in lifestyle-related diseases: endothelial nitric oxide (NO) synthase/NO system in atherosclerosis

Nitric oxide (NO) from the endothelial NO synthase (eNOS) is believed to be implicated in the development and progression of atherosclerosis. The impaired endothelium-dependent vasodilatory response (EDR) has been demonstrated in vessels exposed to hypercholesterolemia and atherosclerosis. The extent of impairment serves as a predictor of future progression of atherosclerosis. As to the mechanisms of impaired EDR, increased production of superoxide is important. Recently it was revealed that eNOS becomes dysfunctional and produces superoxide rather than NO under conditions in which vascular tissue levels of tetrahydrobiopterin (BH4), a co-factor for eNOS, are deficient or lacking. Dysfunctional eNOS is closely implicated in the endothelial dysfunction represented by impaired EDR in various vascular disorders including atherosclerosis. Regarding the role of eNOS in atherogenesis, experimental studies in vitro have revealed that NO from eNOS constitutes as an anti-atherogenic molecule. In eNOS-knockout mice, eNOS deficiency augments atherosclerotic lesion formation, although the effects may be partly due to the associated hypertension. However, in eNOS-transgenic mice (eNOS-Tg) crossbred with apolipoprotein E-deficient mice (apoE-KO/eNOS-Tg), we found the accelerated lesion formation in association with increased superoxide production from vessels compared with apoE-KO mice. The vascular tissue levels of BH4 were reduced and BH2, an oxidized form, levels were increased. Chronic administration of exogenous BH4 or overexpression of GTPCH-1, a rate limiting enzyme for BH4 synthesis, restored the lesion to the levels comparable to apoE-KO mice. Therefore, eNOS may have two faces in the pathophysiology of atherosclerosis depending on tissue BH4 levels.

Dysfunction of endothelial nitric oxide synthase and atherosclerosis

Atherosclerosis is associated with an impairment of endothelium-dependent relaxations, which represents the reduced bioavailability of nitric oxide (NO) produced from endothelial NO synthase (eNOS). Among various mechanisms implicated in the impaired EDR in atherosclerosis, superoxide generated from dysfunctional eNOS has attracted attention. Under conditions in which vascular tissue levels of tetrahydrobiopterin (BH4), a cofactor for NOS, are deficient or lacking, eNOS becomes dysfunctional and produces superoxide rather than NO. Experimental studies in vitro have revealed that NO from eNOS constitutes an anti-atherogenic molecule. A deficiency of eNOS was demonstrated to accelerate atherosclerotic lesion formation in eNOS knockout mice. In contrast, eNOS overexpression with hypercholesterolemia may promote atherogenesis via increased superoxide generation from dysfunctional eNOS. Thus, eNOS may have 2 faces in the pathophysiology of atherosclerosis depending on tissue BH4 metabolisms. An improved understanding of tissue BH4 metabolisms in atherosclerotic vessels is needed, which would help in developing new strategies for the inhibition and treatment of atherosclerosis.

Coping with endothelial superoxide: potential complementarity of arginine and high-dose folate

Superoxide overproduction is a prominent mediator of the endothelial dysfunction associated with a range of vascular disorders, acting in a number of complementary ways to inhibit effective endothelial nitric oxide (NO) activity. The ability of superoxide to quench NO is well known, but oxidants derived from superoxide also appear to inhibit dimethylarginine dimethylaminohydrolase (DDAH) and to oxidize tetrahydrobiopterin (THBP). The former effect boosts the level of methylated arginines that act as potent competitive inhibitors of NO synthase, whereas the latter effect decreases the ability of this enzyme to generate NO, while converting it to a form that readily generates superoxide. The adverse impact of DDAH deficiency on NO production can be offset with supplemental arginine. Although supplementation with THBP has the potential to compensate for the rapid oxidative destruction of this compound, and maintaining optimal vitamin C nutrition may protect or restore the endothelial THBP pool to a limited extent, the most practical way to optimize NO synthase activity in the context of THBP deficit may be administration of high-dose folic acid. The primary circulating metabolite of folate, 5-methyltetrahydrofolate (5MTHF), is structurally analogous to THBP, and appears to normalize the activity of NO synthase in THBP-depleted endothelial cells, either because it "pinch hits" for the absent THBP, or interacts allosterically with NO synthase in some other way to promote the proper function of this enzyme. This observation may rationalize recent clinical studies showing a favorable effect of oral folic acid (5-10 mg daily) on dysfunctional endothelium, independent of any concurrent modulation of homocysteine levels. A recent study reports that, whereas either arginine or THBP alone have only a modest impact on dysfunctional aortic endothelium derived from hypercholesterolemic mice, the combination of the two produces a complete normalization of endothelial function. In aggregate, these considerations suggest that joint administration of arginine and high-dose folate may represent a fruitful approach to preventing and treating vascular disorders - albeit the underlying overproduction of superoxide should also be addressed by ameliorating relevant vascular risk factors.

Myocardial perfusion reserve and peripheral endothelial function in patients with idiopathic dilated cardiomyopathy

The aim of this study was to assess the relation between peripheral endothelial function and myocardial perfusion reserve in patients with mild heart failure due to idiopathic dilated cardiomyopathy (IDC). Myocardial perfusion and brachial artery flow mediated dilation (FMD) were measured in 20 clinically stable patients with IDC (New York Heart Association classes I to III, ejection fraction 35 +/- 9%) and 13 apparently healthy subjects who were matched for age and lipid profile. Resting and hyperemic (dipyridamole; 0.56 mg/kg/min) perfusion were measured using oxygen-15-labeled water and positron emission tomography (PET). Perfusion reserve was calculated as the ratio of hyperemic to resting perfusion. FMD was assessed by measuring the change in brachial artery diameter in response to reactive hyperemia. Patients with IDC had lower hyperemic perfusion (1.73 +/- 0.83 vs 3.01 +/- 1.20 ml/min/g, p <0.001) and perfusion reserve (2.01 +/- 0.91 vs 3.08 +/- 1.35, p <0.01) compared with healthy subjects. Brachial artery FMD, however, was not different from that of the healthy subjects. Furthermore, neither hyperemic perfusion nor perfusion reserve was correlated with FMD in the patients with IDC, whereas the healthy subjects demonstrated a positive correlation between FMD and perfusion reserve (r = 0.57; p = 0.04). Thus, abnormal myocardial perfusion characterizes patients with IDC. Myocardial perfusion reserve and peripheral endothelial function do not parallel each other in patients with IDC.

Improvement of peripheral endothelial dysfunction by acute vitamin C application: different effects in patients with coronary artery disease, ischemic, and dilated cardiomyopathy

BACKGROUND

Endothelial dysfunction has been described in patients with coronary artery disease (CAD) or chronic heart failure (CHF). Vitamin C administration leads to an improvement of endothelial function by reducing elevated levels of reactive oxygen species. It remains unclear, however, whether the degree of endothelial dysfunction caused by oxidative stress differs between CAD and CHF because of ischemic (ICM) or dilated cardiomyopathy (DCM).

METHODS

In patients with CAD (n = 9; left ventricular ejection fraction [LVEF], 64% +/- 3%), ICM (n = 9; LVEF, 25% +/- 4%), DCM (n = 9; LVEF, 25% +/- 3%), and healthy subjects (HS; n = 5; LVEF, 66% +/- 5%) a change in internal radial artery diameter in response to acetylcholine (Ach; 15 and 30 microg/min) was measured with high-resolution ultrasound scanning during a co-infusion of normal saline or vitamin C (25 mg/min).

RESULTS

Ach-mediated vasodilation was blunted in patients with CHF (DCM, 90 +/- 20 microm; ICM, 86 +/- 20 microm) and patients with CAD (336 +/- 20 microm) as compared with HS (496 +/- 43 microm; P <.05 vs patients with DCM, ICM, CAD). Vitamin C co-infusion increased Ach-mediated vasodilation by 180 +/- 35 microm (to 270 +/- 30 microm) in DCM (P <.05 vs CAD, HS) and by 294 +/- 40 microm (to 380 +/- 20 microm) in ICM (P <.05 vs DCM, CAD, HS). In patients with CAD, vitamin C increased Ach-mediated vasodilation by 146 +/- 35 microm to normal values, whereas vascular diameter remained unchanged in HS (14 +/- 20 microm; P = not significant).

CONCLUSIONS

Acute vitamin C administration restored peripheral endothelial function in patients with CAD to normal values, whereas endothelial function remained attenuated in CHF, in particular in patients with DCM. These results suggest that in patients with CHF, factors other than oxidative stress (eg, cytokines) contribute to the pathologic endothelial function.

Role of nitric oxide in the pathophysiology of heart failure

Nitric oxide (NO) plays critical roles in the regulation of integrated cardiac and vascular function and homeostasis. An understanding of the physiologic role and relative contribution of the three NO synthase isoforms (neuronal--NOS1, inducible--NOS2, and endothelial--NOS3) is imperative to comprehend derangements of the NO signaling pathway in the failing cardiovascular system. Several theories of NO and its regulation have developed as explanations for the divergent observations from studies in health and disease states. Here we review the physiologic and pathophysiologic influence of NO on cardiac function, in a framework that considers several theories of altered NO signaling in heart failure. We discuss the notion of spatial compartmentalization of NO signaling within the myocyte in an effort to reconcile many controversies about derangements in the influences of NO in the heart and vasculature.

Acute and chronic endothelial dysfunction: implications for the development of heart failure

Heart failure has been characterized by a reduction in cardiac contractile function resulting in reduced cardiac output. The clinical symptoms including mild tachycardia, reduced arterial pressure, increased venous or filling pressure and exercise intolerance have conceptually, to a large degree, been attributed to cardiac myocyte dysfunction. More recently, a vascular component has been recognized to contribute to heart failure. Among the most studied vascular mechanisms that might contribute to the development of heart failure has been the reduced production of nitric oxide or the reduced bioactivity of NO associated with both basic models of heart failure and disease in patients. The still evolving concept that heart failure is a cytokine activated state has, in addition, focused attention on the possibility that the cytokine driven isoform of NO synthase (NOS), iNOS, may produce sufficient quantities of NO to actually suppress cardiac myocyte function contributing to the reduced inotropic state in the failing heart. Thus, our view of the role of NO in the development of heart failure has evolved from simply a reduction in production of NO in blood vessels, to altered substrate availability (i.e. L-arginine), to increased scavenging of NO by superoxide anion, to increased production of NO from iNOS. As these concepts develop, our approach to the therapeutics of heart failure has also progressed with the recognition of the need to develop treatments directed towards addressing one or more of these etiologies. This review will focus on these aspects of the involvement of NO in the development of heart failure and some of the treatments that have developed from our understanding of the basic biology of NO to address these pathohysiologic states.

The oxidative stress hypothesis of congestive heart failure: radical thoughts

There is extensive experimental evidence from in vitro and animal experiments that congestive heart failure (CHF) is a state of oxidative stress. Moreover, in animal models, the development of CHF is accompanied by changes in the antioxidant defense mechanisms of the myocardium as well as evidence of oxidative myocardial injury. This has led to the hypothesis that oxidative stress may be a mechanism of disease progression in CHF. Indeed, many patients consume antioxidant supplements making the assumption that no harm will result and, possibly, that this therapy will yield some clinical benefits. The focus of this review is to examine the oxidative stress hypothesis of CHF as it pertains to humans. To date, human studies that have sought evidence for a role of oxidative stress in patients with CHF have fallen short of providing strong support for this hypothesis. Studies that have demonstrated an association between oxidant stress and CHF are small and are hindered by methodologic limitations that diminish the impact of their conclusions. Randomized trials of antioxidant supplementation for CHF are scarce, and to our knowledge no study yet convincingly demonstrates any benefit from consuming antioxidant supplements. Therefore, the available evidence is insufficient to support or negate the oxidative stress hypothesis of CHF and the use of antioxidants cannot be recommended as a specific therapy for this condition.

Hyperglycemia-induced ascorbic acid deficiency promotes endothelial dysfunction and the development of atherosclerosis

Dehydroascorbic acid, the oxidized form of vitamin C, is transported into mammalian cells via facilitative glucose transporters and hyperglycemia inhibits this process by competitive inhibition. This inhibited transport may promote oxidative stress and contribute to the increase in atherosclerotic cardiovascular disease observed in patients with diabetes mellitus. This review explores the importance of this proposed mechanism in light of current research. For example, recent reports suggest that administration of antioxidants, such as vitamin C, may slow atherogenesis by improving endothelium-dependent vasodilation in individuals with abnormal glucose and lipid metabolism, perhaps by preventing the oxidation of nitric oxide, an important regulator of vasomotor tone. Endothelial dysfunction plays a key role in the development of atherosclerosis and endothelial cells may be particularly affected by hyperglycemia-induced ascorbic acid deficiency as they line the interior of blood vessels. In addition, we discuss evidence of several other mechanisms by which vitamin C status may affect the development of atherosclerotic cardiovascular disease, particularly its inverse relationship to multiple cardiovascular disease risk factors and indicators. Given these factors, vitamin C administration is recommended during periods of both acute and chronic hyperglycemia to help preserve endothelial function.

Oral nutritional supplements and heart disease: a review

The use of nutritional supplements in the treatment of cardiovascular disease is rapidly growing in the United States. Many substances are marketed with anecdotal claims of efficacy. Most have not been scientifically studied. Excitement exists in the lay press about the homocysteine hypothesis of coronary artery disease and vitamin cures. A MEDLINE search and review of papers covering the study of popular nutritional supplements were undertaken. The papers were limited to peer-review journals using patient series reports, double-blinded prospective studies, and population studies. A compendium of the available data was obtained and an analysis of each paper's methodology was done. A review of the most popular and most studied oral nutritional supplements for the treatment of heart disease demonstrated relatively few well-founded indications for the widespread application of substances with the exception of the bioflavonoids. Some modest effects for endothelial dysfunction were noted for vitamins C and E. Red wines and beers were also noted to be beneficial. The majority of substances either had no effect or were deleterious.

Carvedilol improves endothelium-dependent dilatation in patients with coronary artery disease

OBJECTIVE

Flow-mediated, endothelium-dependent dilatation (FMD) of the coronary and peripheral circulation is impaired by increased oxidative stress in patients with coronary artery disease (CAD). Carvedilol is a novel beta-blocker that also shows an antioxidant effect in vitro. However, the effect of carvedilol on endothelial dysfunction associated with established coronary atherosclerosis has not been examined in the clinical setting.

METHODS

We studied 29 patients with CAD, including 17 with recent myocardial infarction and 12 with stable effort angina pectoris. Nineteen patients received carvedilol (10 with infarction and 9 with angina), and 10 were treated with placebo (7 with infarction and 3 with angina). We also studied 13 age- and sex-matched control subjects. Brachial FMD during reactive hyperemia and nitroglycerin-induced, endothelium-independent dilatation were assessed by high-resolution ultrasound.

RESULTS

FMD was smaller in patients with CAD compared with controls, although nitroglycerin-induced dilatation was similar. Carvedilol significantly improved FMD after long-term treatment (5. 1% +/- 0.4% at baseline to 7.8% +/- 0.3% after 4 months; P <.01) but not after short-term treatment (5.1% +/- 0.4% at baseline to 5.0% +/- 0.7% after 2 hours). Placebo therapy had no effect on endothelial dysfunction. Neither carvedilol nor placebo had an effect on nitroglycerin-induced dilatation after short- and long-term treatment. Long-term carvedilol therapy also significantly decreased the plasma level of thiobarbituric acid-reactive substances compared with placebo (carvedilol, 5.8 +/- 0.4 nmol/mL to 4.6 +/- 0.3 nmol/mL, P <.01; placebo, 5.9 +/- 0.4 nmol/mL to 5.8 +/- 0.4 nmol/mL, P = not significant).

CONCLUSION

These findings suggest that the improvement of endothelial function by carvedilol may be caused by its antioxidant activity.

Nitrotyrosine causes selective vascular endothelial dysfunction and DNA damage

Vascular endothelial dysfunction is recognized as a contributor to a wide array of cardiovascular disease states, but the initiating events involved are incompletely defined. Elevated plasma levels of free 3-nitro-L-tyrosine (3NT, biomarker of peroxynitrite formation) have been measured in settings of endothelial dysfunction, but its pathologic significance is unknown. We tested the hypothesis that clinically demonstrated concentrations of 3NT can induce vascular and endothelial dysfunction in vitro. Further studies evaluated involvement of DNA fragmentation and/or apoptosis as a potential mechanism. Preincubation of rat thoracic aorta segments with 3NT (100, 250 microM) resulted in selective, concentration-dependent impairment of acetylcholine (ACH) maximal response, with no change in KCL, phenylephrine, nitroprusside, or ACH EC50 effects (ACH Emax, 53+/-2, 42+/-5, 31+/-2%; Control, 100 microM, 250 microM 3NT). Vascular segments treated with 3NT also demonstrated concentration-dependent DNA damage, assessed using DNA nick-end labeling techniques (TUNEL staining), compared with control (TUNEL-positive nuclei/linear mm: 5.4+/-1.2, 13.7+/-1.2, 16.9+/-3.2; Control, 100 microM, 250 microM 3NT), which was confined to the endothelial layer. Equimolar tyrosine had no significant effects. Frequency of positively stained nuclei was statistically correlated to extent of endothelial dysfunction (p < 0.01). Free 3NT is apparently more than a benign biomarker in vivo, and may contribute to vascular endothelial dysfunction through promotion of DNA damage and/or apoptosis.

The role of natural antioxidants in preserving the biological activity of endothelium-derived nitric oxide

Endothelium-derived nitric oxide (EDNO) is a pivotal molecule in the regulation of vascular tone via the stimulation of vascular smooth muscle cell relaxation and concomitant vasodilation. In addition, EDNO exerts a number of other potent antiatherogenic effects, including inhibition of leukocyte-endothelial interactions, smooth muscle cell proliferation, and platelet aggregation. Endothelial vasodilator dysfunction has been observed in patients with CAD or coronary risk factors such as hypercholesterolemia, hyperhomocysteinemia, essential hypertension, diabetes mellitus, smoking, and aging. Most of these conditions are associated with increased oxidative stress, particularly increased production of superoxide radicals and elevated levels of oxidized LDL, both of which can attenuate the biological activity of EDNO. The levels of superoxide and oxidized LDL can be decreased by administering the small molecule antioxidants vitamins E and C. Vitamin C also spares intracellular thiols, which in turn can stabilize EDNO through the formation of biologically active S-nitrosothiols. Here we review the role that vitamins E and C and thiol compounds play in endothelium-dependent vasodilation. Understanding the mechanisms of the reversal of endothelial dysfunction by natural antioxidants will lead to successful therapeutic interventions of CAD and its clinical sequelae.

Redox control of vascular nitric oxide bioavailability

NO is an important component of vascular homeostasis and abnormal NO bioactivity has been implicated in number of disease states with important public health implications. One clear mechanism of impaired NO bioactivity and vascular disease is excess vascular oxidative stress. There is now a wealth of developing data that manipulation of vascular antioxidant stress is the considerable influence of the biologic activity of endothelium-derived NO. It remains to be seen if this influence can be exploited in a manner that truly alters the course of human disease.

Systemic endothelial function is preserved in men with both active and inactive variant angina pectoris

To test the hypothesis that coronary spasm could be a coronary manifestation of systemic endothelial dysfunction and that the activity of coronary spasm could influence systemic endothelial function, we examined brachial flow-mediated, endothelium-dependent vasodilation and nitroglycerin-induced endothelium-independent vasodilation with high-resolution ultrasound in 11 men with variant angina pectoris (6 active and 5 inactive) without established coronary atherosclerosis. Endothelium-dependent vasodilation in peripheral circulation was preserved in men with active and inactive variant angina pectoris, suggesting that systemic endothelial dysfunction is not involved in either the pathogenesis or the activity of coronary spasm.

Antiatherosclerotic activity of drugs in relation to nitric oxide function

Many studies have shown that loss of endothelium-derived nitric oxide is a major factor of ischemic episodes in patients with coronary artery disease and there is increasing evidence to suggest that nitric oxide might exert antiatherosclerotic actions. Based on these concepts, the results of animal studies on the effects of lipid lowering drugs, antioxidants, angiotensin converting enzyme inhibitors, Ca2+ channel blockers, estrogens and agents which modulate nitric oxide bioavailability are presented and compared to the results of patient studies and clinical trials. In spite of encouraging results obtained with antioxidants in animals, clinical trials could only show a clear positive effect of vitamin E treatment on the outcome of cardiovascular disease. Angiotensin converting enzyme inhibitors can ameliorate endothelial dysfunction in coronary heart disease, but their impact on disease progression remains unclear. There is evidence that estrogen replacement therapy in post-menopausal women may increase the bioavailability of nitric oxide. Finally, improved endothelial function and plaque stability clearly contribute to the clinical benefits of lipid lowering interventions, statins in particular. Taken together, these studies lend support to the concept that improving endothelial function and nitric oxide release might serve as valuable elements in the prevention or therapy of cardiovascular disease.

Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans

The current recommended dietary allowance (RDA) for vitamin C for adult nonsmoking men and women is 60 mg/d, which is based on a mean requirement of 46 mg/d to prevent the deficiency disease scurvy. However, recent scientific evidence indicates that an increased intake of vitamin C is associated with a reduced risk of chronic diseases such as cancer, cardiovascular disease, and cataract, probably through antioxidant mechanisms. It is likely that the amount of vitamin C required to prevent scurvy is not sufficient to optimally protect against these diseases. Because the RDA is defined as "the average daily dietary intake level that is sufficient to meet the nutrient requirement of nearly all healthy individuals in a group," it is appropriate to reevaluate the RDA for vitamin C. Therefore, we reviewed the biochemical, clinical, and epidemiologic evidence to date for a role of vitamin C in chronic disease prevention. The totality of the reviewed data suggests that an intake of 90-100 mg vitamin C/d is required for optimum reduction of chronic disease risk in nonsmoking men and women. This amount is about twice the amount on which the current RDA for vitamin C is based, suggesting a new RDA of 120 mg vitamin C/d.