Gloria Zalos

Nitrite reduction to nitric oxide by deoxyhemoglobin vasodilates the human circulation.

Nitrite anions comprise the largest vascular storage pool of nitric oxide (NO), provided that physiological mechanisms exist to reduce nitrite to NO. We evaluated the vasodilator properties and mechanisms for bioactivation of nitrite in the human forearm. Nitrite infusions of 36 and 0.36 μmol/min into the forearm brachial artery resulted in supra- and near-physiologic intravascular nitrite concentrations, respectively, and increased forearm blood flow before and during exercise, with or without NO synthase inhibition. Nitrite infusions were associated with rapid formation of erythrocyte iron-nitrosylated hemoglobin and, to a lesser extent, S-nitroso-hemoglobin. NO-modified hemoglobin formation was inversely proportional to oxyhemoglobin saturation. Vasodilation of rat aortic rings and formation of both NO gas and NO-modified hemoglobin resulted from the nitrite reductase activity of deoxyhemoglobin and deoxygenated erythrocytes. This finding links tissue hypoxia, hemoglobin allostery and nitrite bioactivation. These results suggest that nitrite represents a major bioavailable pool of NO, and describe a new physiological function for hemoglobin as a nitrite reductase, potentially contributing to hypoxic vasodilation.

Prognostic Value of Coronary Vascular Endothelial Dysfunction

Background—Whether patients at increased risk can be identified from a relatively low-risk population by coronary vascular function testing remains unknown. We investigated the relationship between coronary endothelial function and the occurrence of acute unpredictable cardiovascular events (cardiovascular death, myocardial infarction, stroke, and unstable angina) in patients with and without coronary atherosclerosis (CAD). Methods and Results—We measured the change in coronary vascular resistance (&Dgr;CVR) and epicardial diameter with intracoronary acetylcholine (ACh, 15 &mgr;g/min) to test endothelium-dependent function and sodium nitroprusside (20 &mgr;g/min) and adenosine (2.2 mg/min) to test endothelium-independent vascular function in 308 patients undergoing cardiac catheterization (132 with and 176 without CAD). Patients underwent clinical follow-up for a mean of 46±3 months. Acute vascular events occurred in 35 patients. After multivariate analysis that included CAD and conventional risk factors for atherosclerosis, &Dgr;CVR with ACh (P =0.02) and epicardial constriction with ACh (P =0.003), together with increasing age, CAD, and body mass index, were independent predictors of adverse events. Thus, patients in the tertile with the best microvascular responses with ACh and those with epicardial dilation with ACh had improved survival by Kaplan-Meier analyses in the total population, as did those in the subset without CAD. Similar improvement in survival was also observed when all adverse events, including revascularization, were considered. Endothelium-independent responses were not predictive of outcome. Conclusions—Epicardial and microvascular coronary endothelial dysfunction independently predict acute cardiovascular events in patients with and without CAD, providing both functional and prognostic information that complements angiographic and risk factor assessment.

Endothelial progenitor cell mobilization and increased intravascular nitric oxide in patients undergoing cardiac rehabilitation.

PURPOSE: We investigated whether cardiac rehabilitation participation increases circulating endothelial progenitor cells (EPCs) and benefits vasculature in patients already on stable therapy previously shown to augment EPCs and improve endothelial function. METHODS: Forty-six of 50 patients with coronary artery disease completed a 36-session cardiac rehabilitation program: 45 were treated with HMG-CoA reductase inhibitor (statin) therapy ≥1 month (average baseline low-density lipoprotein cholesterol = 81 mg/dL). Mononuclear cells isolated from blood were quantified for EPCs by flow cytometry (CD133+/VEGFR-2+ cells) and assayed in culture for EPC colony-forming units (CFUs). In 23 patients, EPCs were stained for annexin-V as a marker of apoptosis, and nitrite was measured in blood as an indicator of intravascular nitric oxide. RESULTS: Endothelial progenitor cells increased from 35 ± 5 to 63 ± 10 cells/mL, and EPC-CFUs increased from 0.9 ± 0.2 to 3.1 ± 0.6 per well (both P < .01), but 11 patients had no increase in either measure. Those patients whose EPCs increased from baseline showed significant increases in nitrite and reduction in annexin-V staining (both P < .01) versus no change in patients without increase in EPCs. Over the course of the program, EPCs increased prior to increase in nitrite in the blood. CONCLUSIONS: Cardiac rehabilitation in patients receiving stable statin therapy and with low-density lipoprotein cholesterol at goal increases EPC number, EPC survival, and endothelial differentiation potential, associated with increased nitric oxide in the blood. Although this response was observed in most patients, a significant minority showed neither EPC mobilization nor increased nitric oxide in the blood.

Endogenous Endothelin in Human Coronary Vascular Function. Differential Contribution of Endothelin Receptor Types A and B

Endothelin 1 mediates coronary vasoconstriction and endothelial dysfunction via endothelin receptor type A (ETA) activation. However, the effects of selective endothelin receptor type B (ETB) and combined ETA+B receptor blockade on coronary vasomotion are unknown. We measured coronary vascular tone and endothelium-dependent and -independent vasomotor function before and after selective infusion of BQ-788 (an ETB receptor antagonist) or combined infusion of BQ-788+BQ-123 (an ETA antagonist) into unobstructed coronary arteries of 39 patients with coronary atherosclerosis or risk factors undergoing cardiac catheterization. BQ-788 did not affect epicardial diameter but constricted the microcirculation (P<0.0001), increased coronary sinus endothelin, and reduced nitrogen oxide levels. In contrast, BQ-123+BQ-788 dilated epicardial (P<0.0001) and resistance (P=0.022) arteries. Responses to acetylcholine and sodium nitroprusside were unaffected by BQ-788 alone. Epicardial endothelial dysfunction improved after BQ-123+BQ-788 (P=0.007). Coronary microvascular responses to acetylcholine and sodium nitroprusside were unaffected by BQ-123+BQ-788. We conclude that selective ETB receptor antagonism causes coronary microvascular constriction, without affecting epicardial tone or endothelial function, via reduced endothelin clearance and NO availability. Combined ETA+B blockade dilates coronary conduit and resistance vessels and improves endothelial dysfunction of the epicardial coronary arteries. Thus, endogenous endothelin, predominantly via ETA receptor stimulation, contributes to basal constrictor tone and endothelial dysfunction, whereas ETB activation mediates vasodilation in human coronaries. Our data suggest that selective ETA blockade may have greater therapeutic potential than nonselective agents, particularly for treatment of endothelial dysfunction in atherosclerosis.

Microarray-Based Characterization of a Colony Assay Used to Investigate Endothelial Progenitor Cells and Relevance to Endothelial Function in Humans

Objective—An assay proposed to quantify endothelial progenitor cell (EPC) colonies in humans was investigated to determine the phenotype of recovered cells and their relevance to in vivo endothelial function. Methods and Results—Twelve sedentary subjects participating in a worksite wellness program underwent endothelial flow-mediated dilation (FMD) testing of the brachial artery and blood sampling for EPC colony assay. Microarray-based genotypic characterization of colonies showed surface markers consistent with T lymphocyte phenotype, but not with an EPC (CD34, CD133, VEGFR-2) or endothelial (CD146) phenotype. Gene expression patterns more closely matched T lymphocytes (r=0.87) than endothelial cells (r=0.66) in our microarray database. Flow cytometry of colonies confirmed large populations of CD3+CD45+ T cells (>75%) and few CD146+CD45− endothelial cells (<1%). Further, there was no correlation between colony number and the magnitude of FMD (r=−0.1512, P=0.6389). After exercise training, subjects improved FMD, from 6.7±2.0 to 8.7±1.9% (P=0.0043). Colonies also increased (P=0.0210), but without relation to FMD (r=0.1074, P=0.7396). T lymphocyte phenotype persisted after exercise (r=0.87). Conclusions—Cells in a commonly used EPC colony assay have a gene expression and cell surface marker profile consistent with a predominance of T lymphocytes and have an unclear relevance to endothelial function, either before or after exercise training.

Predictors of Endothelial Function in Employees With Sedentary Occupations in a Worksite Exercise Program

A sedentary workforce may be at increased risk for future cardiovascular disease. Exercise at the work site has been advocated, but effects on endothelium as a biomarker of risk and relation to weight loss, lipid changes, or circulating endothelial progenitor cells (EPCs) have not been reported. Seventy-two office and laboratory employees (58 women; average age 45 years, range 22 to 62; 26 with body mass index values >30 kg/m(2)) completed 3 months of participation in the National Heart, Lung, and Blood Institutes Keep the Beat program, with the determination of vital signs, laboratory data, and peak oxygen consumption (VO(2)) during treadmill exercise. Brachial artery endothelium was tested by flow-mediated dilation (FMD), which at baseline was inversely associated with Framingham risk score (r = -0.3689, p <0.0001). EPCs were quantified by colony assay. With exercise averaging 98 +/- 47 minutes each workweek, there was improvement in FMD (from 7.8 +/- 3.4% to 8.5 +/- 3.0%, p = 0.0096) and peak VO(2) (+1.2 +/- 3.1 ml O(2)/kg/min, p = 0.0028), with reductions in diastolic blood pressure (-2 +/- 8 mm Hg, p = 0.0478), total cholesterol (-8 +/- 25 mg/dl, p = 0.0131), and low-density lipoprotein cholesterol (-7 +/- 19 mg/dl, p = 0.0044) but with a marginal reduction in weight (-0.5 +/- 2.1 kg, p = 0.0565). By multiple regression modeling, lower baseline FMD, greater age, reductions in total and low-density lipoprotein cholesterol and diastolic blood pressure, and increases in EPC colonies and peak VO(2) were jointly statistically significant predictors of change in FMD and accounted for 47% of the variability in FMD improvement with program participation. Results were similar when modeling was performed for women only. In contrast, neither adiposity at baseline nor change in weight was a predictor of improved endothelial function. In conclusion, daily exercise achievable at their work sites by employees with sedentary occupations improves endothelial function, even with the absence of weight loss, which may decrease cardiovascular risk, if sustained.

Relation of Endothelial Function to Cardiovascular Risk in Women With Sedentary Occupations and Without Known Cardiovascular Disease

Our purpose was to determine predictors of endothelial function and potential association with cardiovascular risk in women with sedentary occupations, in whom obesity-associated risk factors may contribute to excess morbidity and mortality. Ninety consecutive women (age range 22 to 63 years, 22 overweight (body mass index [BMI] > or =25 to 29.9 kg/m(2)) and 42 obese (BMI > or = 30 kg/m(2)), had vital signs, lipids, insulin, glucose, high-sensitivity C-reactive protein, and sex hormones measured. Endothelial function was determined using brachial artery flow-mediated dilation after 5 minutes of forearm ischemia. Treadmill stress testing was performed with gas exchange analysis at peak exercise (peak oxygen consumption [Vo(2)]) to assess cardiorespiratory fitness. Brachial artery reactivity was negatively associated with Framingham risk score (r = -0.3542, p = 0.0007). Univariate predictors of endothelial function included peak Vo(2) (r = 0.4483, p <0.0001), age (r = -0.3420, p = 0.0010), BMI (r = -0.3065, p = 0.0035), and high-sensitivity C-reactive protein (r = -0.2220, p = 0.0400). Using multiple linear regression analysis with stepwise modeling, peak Vo(2) (p = 0.0003) was the best independent predictor of brachial artery reactivity, with age as the only other variable reaching statistical significance (p = 0.0436) in this model. In conclusion, endothelial function was significantly associated with cardiovascular risk in women with sedentary occupations, who were commonly overweight or obese. Even in the absence of routine exercise, cardiorespiratory fitness, rather than conventional risk factors or body mass, is the dominant predictor of endothelial function and suggests a modifiable approach to risk.

Blood pressure changes during transient myocardial ischemia : Insights into mechanisms

OBJECTIVES We investigated the contribution of changes in systemic blood pressure to the genesis of spontaneous myocardial ischemia. BACKGROUND Although increases in heart rate often precede the development of spontaneous myocardial ischemia, it remains a subject of controversy whether these are accompanied by simultaneous changes in blood pressure. METHODS Using an ambulatory monitoring device that triggered blood pressure recordings from the level of the ST segment, we documented systolic and diastolic blood pressure and heart rate changes related to episodes of ST segment depression in 17 patients with stable coronary artery disease. RESULTS Systolic blood pressure and heart rate, but not diastolic pressure, increased significantly before the onset of ST segment depression and persisted throughout the ischemic episode. There was a significant correlation between the changes in heart rate and systolic blood pressure during episodes of myocardial ischemia (r = 0.5, p = 0.0005) and between heart rate and systolic blood pressure changes at 1-mm ST segment depression during treadmill exercise testing and ambulatory monitoring (r = 0.73, p = 0.0005 for heart rate; r = 0.77, p = 0.0008 for systolic blood pressure), indicating that patients with a low heart rate threshold during ischemic episodes also had a lower systolic blood pressure threshold before ischemia during both tests. Circadian changes in systolic blood pressure paralleled the variations in heart rate and ischemic episodes, with the lowest values at night. CONCLUSIONS Significant increases in myocardial oxygen demand, including systolic blood pressure, occur during episodes of spontaneous myocardial ischemia. Patients with a lower heart rate threshold during ischemic episodes had a lower systolic blood pressure threshold during both ambulatory monitoring and treadmill exercise. The effects of antianginal therapy on blood pressure changes during ischemia need to be explored further.

Patterns and behavior of transient myocardial ischemia in stable coronary disease are the same in both men and women: A comparative study

OBJECTIVES This study sought to compare the circadian variations in transient ischemic activity, mean heart rate and ischemic threshold between women and men with coronary artery disease. BACKGROUND There is a circadian variation in ischemic activity, onset of myocardial infarction and sudden cardiac death in patients with coronary artery disease, but studies assessing ischemia have incorporated predominantly male subjects. METHODS Thirty-one women and 45 men underwent at least 48 h of ambulatory ST segment monitoring. RESULTS There was a similar and significant circadian variation in ischemic activity in both women and men (p < 0.0001 and p < 0.0001, respectively), with a trough at night, a surge in the morning and a peak between 1 and 2 PM, corresponding to a similar circadian variation in mean hourly heart rate (p < 0.0001) that was not different between men and women (p = 0.28, power to detect a shift 99.9%). Mean heart rate at onset of ischemia (ischemic threshold) had similar variability in women and men (p = 0.96), and harmonic regression analysis confirmed a significant circadian variation (p < 0.0001), with a trough at night and a peak during activity hours. Heart rate increased significantly in the 5 min before ischemia throughout the 24 h (p < 0.0001), with no gender differences in the pattern of preonset to onset heart rate changes over time (p = 0.52); the smallest differences were recorded in the middle of the night. The majority of ischemic episodes (80%) had a heart rate increase > 5 beats/min in the 5 min before ischemia, but there were no gender differences. CONCLUSIONS Women with coronary artery disease have a pattern of ischemic activity and underlying pathophysiologic mechanisms very similar to men. The importance of increase in myocardial oxygen demand in the genesis of ischemia in both men and women is reflected by similar magnitude of heart rate increases before ischemia. The lower ischemic threshold during the nocturnal hours, when blood pressure is also lower, is consistent with a circadian variation in underlying coronary vascular tone.

High-Density Lipoprotein Cholesterol Efflux, Nitration of Apolipoprotein A-I, and Endothelial Function in Obese Women

Subjects at risk of atherosclerosis might have dysfunctional high-density lipoprotein (HDL) despite normal cholesterol content in the plasma. We considered whether the efflux of excess cellular cholesterol to HDL from obese subjects is associated with impaired arterial endothelial function, a biomarker of cardiovascular risk. A total of 54 overweight (body mass index [BMI] 25 to 29.9 kg/m(2)) or obese (BMI ≥30 kg/m(2)) women, aged 46 ± 11 years, were enrolled in a worksite wellness program. The HDL cholesterol averaged 57 ± 17 mg/dl and was inversely associated with the BMI (r = -0.419, p = 0.002). Endothelial function was assessed using brachial artery flow-mediated dilation. Cholesterol efflux from (3)H-cholesterol-labeled baby hamster kidney cells transfected with the adenosine triphosphate-binding cassette transporter 1 showed 8.2% to 22.5% cholesterol efflux within 18 hours when incubated with 1% serum and was positively correlated with brachial artery flow-mediated dilation (p <0.05), especially in the 34 subjects with BMI ≥30 kg/m(2) (r = 0.482, p = 0.004). This relation was independent of age, HDL or low-density lipoprotein cholesterol concentrations in plasma, blood pressure, or insulin resistance on stepwise multiple regression analysis (β = 0.31, R(2) = 0.21, p = 0.007). Nitration of apolipoprotein A-I tyrosine residues (using sandwich enzyme-linked immunosorbent assay) was significantly greater in women with a BMI ≥30 kg/m(2) and the lowest cholesterol efflux than in women with a BMI of 25 to 29.9 kg/m(2) and the greatest cholesterol efflux (p = 0.01). In conclusion, we have shown that decreased cholesterol efflux by way of the adenosine triphosphate-binding cassette transporter 1 is associated with increased nitration of apolipoprotein A-I in HDL and is an independent predictor of impaired endothelial function in women with a BMI of ≥30 kg/m(2). This finding suggests that the functional measures of HDL might be better markers for cardiovascular risk than the HDL cholesterol levels in this population.