Stephen J. Duffy

Iron Chelation Improves Endothelial Function in Patients With Coronary Artery Disease

Background—Some epidemiological studies have shown that increased iron stores are associated with increased cardiovascular events. Redox-active iron may contribute to lipid peroxidation, endothelial cell activation, and generation of reactive oxygen species (especially hydroxyl radical, via Fenton chemistry). Increased oxidative stress is associated with impaired action of endothelium-derived nitric oxide in patients with atherosclerosis. Methods and Results—To test the hypothesis that reducing vascular iron stores would reverse endothelial dysfunction, we examined the effects of the iron chelator deferoxamine (500 mg intra-arterially over 1 hour) on vasomotor function in forearm resistance vessels of patients with coronary artery disease by venous occlusion plethysmography. Patients with coronary artery disease had impaired endothelium-dependent vasodilation in response to methacholine compared with healthy control subjects (P <0.001). Deferoxamine infusion decreased serum iron levels (P <0.001). Deferoxamine improved the blood flow response to methacholine in patients with coronary artery disease (P <0.01 by 2-way repeated-measures ANOVA) but had no effect on the response to sodium nitroprusside. In normal volunteers, deferoxamine had no effect on the response to methacholine. The nitric oxide synthase inhibitor NG-monomethyl-l-arginine abolished augmentation of the methacholine response associated with deferoxamine. The hydroxyl radical scavenger mannitol had no effect on the methacholine response. Conclusions—Deferoxamine improved nitric oxide–mediated, endothelium-dependent vasodilation in patients with coronary artery disease. These results suggest that iron availability contributes to impaired nitric oxide action in atherosclerosis.

Short- and Long-Term COX-2 Inhibition Reverses Endothelial Dysfunction in Patients With Hypertension

Abstract—Hypertension is associated with endothelial dysfunction that is attributable to oxidative stress and a proinflammatory state. Under these conditions, enhanced expression of cyclooxygenase-2 might lead to increased production of vasoconstrictor prostanoids and reactive oxygen species that reduce the bioavailability of endothelium-derived nitric oxide. To investigate the contribution of cyclooxygenase-2 activity to endothelial dysfunction in human hypertension, we evaluated brachial artery vasodilator function by ultrasound in 29 hypertensive patients before and after treatment with the selective cyclooxygenase-2 inhibitor celecoxib or placebo in a randomized, double-blind study. Brachial artery flow–mediated dilation improved from a baseline of 7.9±4.5% to 9.9±5.1% (P =0.005) 3 hours after the first dose and to 10.1±6.1% (P =0.006) after 1 week of treatment with celecoxib. In contrast, placebo treatment had no significant effect on flow-mediated dilation (8.1±4.4%, 8.3±3.5%, and 8.0±3.2%, respectively). Neither treatment altered nitroglycerin-mediated dilation, extent of reactive hyperemia, or baseline arterial diameter. Celecoxib treatment had no significant effect on the urinary concentrations of F2 isoprostane or thromboxane metabolites. However, urinary concentrations of the prostacyclin metabolite 2,3-dinor-6-ketoprostglandin F1&agr; were significantly lower after 1 week of celecoxib treatment. Thus, cyclooxygenase-2 products contribute to endothelial dysfunction in hypertension, and treatment with a cyclooxygenase-2 inhibitor could have a beneficial effect in this setting. However, cyclooxygenase-2 inhibition also has an adverse effect on prostacyclin production that could promote thrombosis, and the net clinical consequences of improved endothelial function versus loss of prostacyclin merits further investigation.

Pharmacological concentrations of ascorbic acid are required for the beneficial effect on endothelial vasomotor function in hypertension.

Increased production of superoxide anion may contribute to impaired bioactivity of endothelium-derived nitric oxide in hypertension. Ascorbic acid is capable of scavenging superoxide anion; however, experimental studies have shown that high physiological concentrations (>1 mmol/L) of ascorbic acid are required to prevent superoxide-mediated vascular dysfunction. To seek kinetic evidence that superoxide anion contributes to endothelial vasomotor dysfunction in human hypertension, we examined the effects of 2.4 or 24 mg/min ascorbic acid intra-arterial infusions on forearm blood flow responses to methacholine or sodium nitroprusside in 30 patients with hypertension and 22 age-matched controls. Endothelium-dependent vasodilation to methacholine was significantly impaired in the hypertensive patients, with a response to the highest dose of methacholine (10 microg/min) of 12.3+/-6.7 compared with 16.1+/-5.8 mL. min(-1). dL tissue(-1) in the controls (P<0.001). The response to sodium nitroprusside was equivalent in the 2 groups. Ascorbic acid at 24 mg/min significantly improved the forearm blood flow response to methacholine in hypertensive patients with a peak response of 16.1+/-7.1 mL. min(-1). dL tissue(-1) (P=0.001). This dose produced a cephalic vein ascorbic acid concentration of 3.2+/-1. 4 mmol/L. In contrast, ascorbic acid at 2.4 mg/min had no effect on the methacholine response. Ascorbic acid at both doses had no effect on the vasodilator response to sodium nitroprusside in hypertensive patients or the methacholine response in the controls. These results agree with the predicted kinetics for superoxide anion-mediated impairment of endothelium-derived nitric oxide action. Thus, superoxide anion may contribute to impaired endothelium-dependent vasodilation in patients with hypertension.

Effects of Black Race on Forearm Resistance Vessel Function

Presentation, response to therapy, and clinical outcome in hypertension differ according to race, and these observations could relate to differences in microvascular function. We examined forearm microvascular function in age-matched black (n=56) and white subjects (n=62) using intra-arterial agonist infusion and venous occlusion plethysmography. In normotensive subjects (n=70; 34 black and 36 white normotensives), methacholine-, sodium nitroprusside-, and verapamil-induced vasodilation was equivalent in black and white subjects. In hypertensive subjects (n=48; 22 black and 26 white hypertensives), the vasodilator response to methacholine was markedly lower in black subjects compared with white subjects (P <0.001). The vasodilator responses to sodium nitroprusside and verapamil, however, were equivalent in black and white hypertensive subjects. Acute ascorbic acid infusion improved the methacholine response equally in black and white hypertensive patients, suggesting that a difference in a rapidly reversible form of oxidative stress does not explain these findings. Thus, the present study demonstrates important racial differences in vascular function and a marked impairment in endothelial vasomotor function in black patients with hypertension. Further studies will be required to elucidate the mechanisms and determine whether these insights will lead to more appropriately tailored management of hypertension and its complications.

Effect of Acute and Chronic Tea Consumption on Platelet Aggregation in Patients With Coronary Artery Disease

Abstract—Epidemiological studies suggest that tea consumption is associated with a decreased risk of cardiovascular events, but the mechanisms of benefit remain undefined. Platelet aggregation is a precipitating event in cardiovascular disease, and tea contains antioxidant flavonoids that are known to decrease platelet aggregation in vitro. To test the effect of tea consumption on platelet aggregation, we randomized 49 patients with coronary artery disease to either 450 mL of black tea or water consumed initially, followed by 900 mL of tea or water daily for 4 weeks in a crossover design. Ex vivo platelet aggregation in platelet-rich plasma was assessed in response to ADP and thrombin receptor-activating peptide at baseline and 2 hours and 4 weeks after beverage consumption. We observed dose-dependent platelet aggregation in response to each agonist, and neither relation was altered by acute or chronic tea consumption. Plasma flavonoids increased with acute and chronic tea consumption, indicating adequate absorption of tea flavonoids. In conclusion, these results demonstrate that acute and chronic black tea consumption does not affect ex vivo platelet aggregation in patients with coronary artery disease. These findings suggest that an effect of tea flavonoids on platelet aggregation is unlikely to be the explanation for the reduction in risk of cardiovascular events noted in epidemiological studies.

Acute hypertriglyceridemia is associated with peripheral vasodilation and increased basal flow in healthy young adults

Prior studies suggest that acute elevations in plasma triglycerides alter vascular tone and impair endothelial function. To investigate the relation between acute hypertriglyceridemia and vascular function, we examined the effects of high- and low-fat meals on brachial artery reactivity in 14 healthy volunteers. Flow-mediated dilation declined from 14.7 +/- 8.3% to 10.6 +/- 6.2% after the high-fat meal only (p <0.001), and this decline was associated with a 6% increase in baseline brachial artery diameter (3.50 +/- 0.74 mm to 3.70 +/- 0.81 mm, p <0.001), but not a decrease in the arterial diameter during hyperemia. The high-fat meal increased serum triglycerides and insulin by 94% and 438%, respectively. To investigate the effects of triglyceride elevation in isolation from hyperinsulinemia, we examined vascular responses to an intravenous infusion of a triglyceride emulsion in 28 subjects. Triglyceride emulsion increased serum triglycerides 197% but had no effect on serum insulin. Brachial artery diameter increased 4%, from 3.68 +/- 0.51 mm to 3.81 +/- 0.56 mm (p <0.05), and forearm flow increased 36%, reflecting vasodilation of forearm resistance vessels. Flow-mediated dilation and nitroglycerin-mediated dilation were unaffected. The triglyceride emulsion had no direct dilator effect on rabbit aortic tissue in vitro. In conclusion, acute hypertriglyceridemia is associated with vasodilation of conduit and resistance vessels in the arm and does not impair endothelial vasodilator function per se. The dilator effect is not insulin-dependent and does not appear to be a direct effect of triglycerides on vascular tissue.

Low-Renin Hypertension With Relative Aldosterone Excess Is Associated With Impaired NO-Mediated Vasodilation

Recent studies suggest that hypertension associated with low renin status and hyperaldosteronism is associated with increased risk for end-organ damage and cardiovascular events compared with other forms of hypertension. Additionally, experimental studies have demonstrated impaired nitric oxide-mediated bioactivity in these states. To investigate the relation between renin/aldosterone status and resistance vessel function, we examined plasma renin activity, serum aldosterone level, and forearm blood flow responses to the endothelium-dependent vasodilator methacholine and the endothelium-independent vasodilators sodium nitroprusside and verapamil using venous occlusion plethysmography in 130 volunteers (43 hypertensive, 87 normotensive). Low renin status was associated with impaired responses to methacholine and nitroprusside in patients with hypertension. Peak methacholine response was 8.7±5.6 mL/min per dL in the lowest renin quartile (0.1 to 0.3 ng/mL per hour) versus 14.3±7.3 mL/min per dL in the highest 3 renin quartiles combined (0.4 to 4.6 ng/mL per hour; P<0.001). Peak nitroprusside response was 5.6±2.3 mL/min per dL in the lowest renin quartile versus 13.3±4.1 mL/min per dL in the highest 3 renin quartiles combined (P<0.001). Blood pressure and other clinical characteristics were similar in all 4 quartiles. Vasodilator responses to verapamil did not relate to renin activity. Methacholine and nitroprusside responses did not relate to renin status in normotensive controls (P=0.34). Importantly, hypertensive patients with a high aldosterone/renin ratio also had impaired responses to methacholine. This study demonstrates that low-renin hypertension is associated with marked impairment of nitric oxide-mediated vasodilation of resistance vessels in the forearm vasculature of humans. This impairment could contribute to adverse outcomes in patients with low-renin hypertension and relative aldosterone excess.

Effect of atorvastatin on endothelium-dependent vasodilation in patients with coronary artery disease

response to sublingual nitroglycerin (0.4 mg) was assessed. In a double-blind fashion, patients were random- ized to take oral placebo or atorvastatin 80 mg the evening after the baseline ultrasound study and also the next evening. Forty-eight hours after the baseline study (approximately 36 hours after the first dose of atorvastatin), vascular function was reassessed. Care was taken to image the identical portion of the bra- chial artery by using the same probe position and anatomic landmarks. The 2 studies were performed at the same time of day, by the same sonographer, and using the same ultrasound system. Arterial diameter was measured using customized software. Ten sec- onds of consecutive images were analyzed at baseline and beginning 55 seconds after cuff release. The flow-velocity integral and arterial diameter were used to calculate the extent of reactive hyperemia. Fasting serum glucose, total cholesterol, triglycerides, and high-density lipoprotein (HDL) cholesterol were de- termined using a Hitachi model 917 automated ana- lyzer (Hitachi Instruments, Indianapolis, Indiana). Low-density lipoprotein (LDL) cholesterol was calcu- lated using Friedewalds formula. Clinical characteristics of the atorvastatin and pla-