Muhiddin Ozkor

Endothelium-Derived Hyperpolarizing Factor Determines Resting and Stimulated Forearm Vasodilator Tone in Health and in Disease

Background— We assessed the contribution of endothelium-derived hyperpolarizing factors to resting and agonist-stimulated vasodilator tone in health and disease. Tetraethylammonium chloride (TEA) was used to inhibit K+Ca channel activation and fluconazole was used to inhibit cytochrome P450 2C9–mediated epoxyeicosatrienoic acid synthesis. We hypothesized that endothelium-derived hyperpolarizing factors contribute to resting vascular tone by K+Ca channel activation and epoxyeicosatrienoic acid release and that endothelium-derived hyperpolarizing factors compensate for reduced nitric oxide bioavailability at rest and with endothelium-dependent vasodilators. Methods and Results— In 103 healthy subjects and 71 nonhypertensive subjects with multiple risk factors, we measured resting forearm blood flow (FBF) using venous occlusion plethysmography before and after intra-arterial infusions of NG-monomethyl-L-arginine (L-NMMA), TEA, fluconazole, and their combination. The effects of these antagonists on resting FBF and on bradykinin- and acetylcholine-mediated vasodilation were studied. Resting FBF decreased with TEA and L-NMMA in all subjects (P<0.001); however, the vasoconstrictor response to L-NMMA was greater (P=0.04) and to TEA was lower (P=0.04) in healthy subjects compared with those with risk factors. Fluconazole decreased resting FBF in all subjects, and the addition of TEA further reduced FBF after fluconazole, suggesting that cytochrome P450 metabolites and other hyperpolarizing factor(s) activate K+Ca channels. Both L-NMMA and TEA attenuated bradykinin-mediated vasodilation in healthy and hypercholesterolemic subjects (P<0.001). In contrast, acetylcholine-mediated vasodilation remained unchanged with TEA in healthy subjects but was significantly attenuated in hypercholesterolemia (P<0.04). Conclusions— First, by activating TEA-inhibitable K+Ca channels, endothelium-derived hyperpolarizing factors, together with nitric oxide, contribute to resting microvascular dilator tone. The contribution of K+Ca channel activation compared with nitric oxide is greater in those with multiple risk factors compared with healthy subjects. Second, activation of K+Ca channels is only partly through epoxyeicosatrienoic acid release, indicating the presence of other hyperpolarizing mechanisms. Third, bradykinin, but not acetylcholine, stimulates K+Ca channel–mediated vasodilation in healthy subjects, whereas in hypercholesterolemia, K+Ca channel-mediated vasodilation compensates for the reduced nitric oxide activity. Thus, enhanced endothelium-derived hyperpolarizing factor activity in conditions of nitric oxide deficiency contributes to maintenance of resting and agonist-stimulated vasodilation. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00166166.

Endothelium-Derived Hyperpolarizing Factor and Vascular Function

Endothelial function refers to a multitude of physiological processes that maintain healthy homeostasis of the vascular wall. Exposure of the endothelium to cardiac risk factors results in endothelial dysfunction and is associated with an alteration in the balance of vasoactive substances produced by endothelial cells. These include a reduction in nitric oxide (NO), an increase in generation of potential vasoconstrictor substances and a potential compensatory increase in other mediators of vasodilation. The latter has been surmised from data demonstrating persistent endothelium-dependent vasodilatation despite complete inhibition of NO and prostaglandins. This remaining non-NO, non-prostaglandin mediated endothelium-dependent vasodilator response has been attributed to endothelium-derived hyperpolarizing factor/s (EDHF). Endothelial hyperpolarization is likely due to several factors that appear to be site and species specific. Experimental studies suggest that the contribution of the EDHFs increase as the vessel size decreases, with a predominance of EDHF activity in the resistance vessels, and a compensatory up-regulation of hyperpolarization in states characterized by reduced NO availability. Since endothelial dysfunction is a precursor for atherosclerosis development and its magnitude is a reflection of future risk, then the mechanisms underlying endothelial dysfunction need to be fully understood, so that adequate therapeutic interventions can be designed.

Differences in Vascular Nitric Oxide and Endothelium-Derived Hyperpolarizing Factor Bioavailability in Blacks and Whites

Objective—Abnormalities in nitric oxide (NO) bioavailability have been reported in blacks. Whether there are differences in endothelium-derived hyperpolarizing factor (EDHF) in addition to NO between blacks and whites and how these affect physiological vasodilation remain unknown. We hypothesized that the bioavailability of vascular NO and EDHF, at rest and with pharmacological and physiological vasodilation, varies between whites and blacks. Approach and Results—In 74 white and 86 black subjects without known cardiovascular disease risk factors, forearm blood flow was measured using plethysmography at rest and during inhibition of NO with NG-monomethyl-L-arginine and of K+Ca channels (EDHF) with tetraethylammonium. The reduction in resting forearm blood flow was greater with NG-monomethyl-L-arginine (P=0.019) and similar with tetraethylammonium in whites compared with blacks. Vasodilation with bradykinin, acetylcholine, and sodium nitroprusside was lower in blacks compared with whites (all P<0.0001). Inhibition with NG-monomethyl-L-arginine was greater in whites compared with blacks with bradykinin, acetylcholine, and exercise. Inhibition with tetraethylammonium was lower in blacks with bradykinin, but greater during exercise and with acetylcholine. Conclusions—The contribution to both resting and stimulus-mediated vasodilator tone of NO is greater in whites compared with blacks. EDHF partly compensates for the reduced NO release in exercise and acetylcholine-mediated vasodilation in blacks. Preserved EDHF but reduced NO bioavailability and sensitivity characterizes the vasculature in healthy blacks. Clinical Trial Registration—URL: http://clinicaltrials.gov/. Unique identifier: NCT00166166.

Vasodilation by Hyperpolarization Beyond NO

Clinical assessment of human vascular endothelial function in vivo involves use of specific antagonists such as l-N G monomethyl arginine (l-NMMA) and cyclooxygenase inhibition to establish the contribution of NO and prostaglandins, respectively, to either resting vascular tone, agonist-stimulated vasodilation, or physiological and metabolic vasodilation.1–4 Even after complete inhibition of NO and prostaglandin (PG) synthesis, endothelium-dependent vasodilation persists, revealing the existence of a substantial NO- and PG-independent component that has been attributed to endothelium-derived hyperpolarizing factor (EDHF) release. Prime candidate EDHFs that often differ by species and circulatory beds have been extensively reviewed (Figure).5,6 Mechanisms of potential endothelial cell mediated relaxation/hyperpolarization. Agonist (bradykinin) or shear stress increases the activity of endothelial nNO synthase (eNOS) and cyclooxygenase (COX), providing NO and prostacyclin-mediated dilation. There are multiple potential EDHF pathways. Agonist (bradykinin) or shear stress–mediated increases in intracellular calcium activates phospholipase A2 (PLC) to produce arachadonic acid. Its metabolism by cytochrome P450 2C (CYP4502c) generates EETs that can stimulate KCa channels in endothelial and smooth muscle cells. EETs may also directly activate gap junctions(Gap). The increase in K+ in the interstitium may activate KCa,channels, KIR, or the Na+-K+ pump on smooth muscle cells and cause hyperpolarization. The action of eNOS (with cofactor tetrahydrobiopterin [BH4]) and oxidases on oxygen (O2) produces the reactive oxygen species superoxide (O2·−). Hydrogen peroxide (H2O2) generated by dismutation of superoxide anions (O2·−) by superoxide dismutase (SOD) can also cause hyperpolarization by activating endothelial and smooth muscle KCa channels or by gap junctions. AC indicates adenylyl cyclase; cAMP, cAMP; cGMP, cyclic guanosine monophosphate; sGC, soluble guanylyl cyclase; IP, prostacyclin receptor. In the human vasculature, endothelium-dependent hyperpolarization is at least partly caused by the release …

Contribution of endothelium-derived hyperpolarizing factor to exercise-induced vasodilation in health and hypercholesterolemia.

The role of endothelium-derived hyperpolarizing factor (EDHF) in either the healthy circulation or in those with hypercholesterolemia is unknown. In healthy and hypercholesterolemic subjects, we measured forearm blood flow (FBF) using strain-gauge plethysmography at rest, during graded handgrip exercise, and after sodium nitroprusside infusion. Measurements were repeated after l-NMMA, tetraethylammonium (TEA), and combined infusions. At rest, l-NMMA infusion reduced FBF in healthy but not hypercholesterolemic subjects. At peak exercise, vasodilation was lower in hypercholesterolemic compared to healthy subjects (274% vs 438% increase in FBF, p=0.017). TEA infusion reduced exercise-induced vasodilation in both healthy and hypercholesterolemic subjects (27%, p<0.0001 and −20%, p<0.0001, respectively). The addition of l-NMMA to TEA further reduced FBF in healthy (–14%, p=0.012) but not in hypercholesterolemic subjects, indicating a reduced nitric oxide and greater EDHF-mediated contribution to exercise-induced vasodilation in hypercholesterolemia. In conclusion, exercise-induced vasodilation is impaired and predominantly mediated by EDHF in hypercholesterolemic subjects. Clinical Trial Registration Identifier: NCT00166166

Coronary Endothelial Dysfunction, Obesity and Metabolic Syndrome

Objective To define the impact of metabolic syndrome (MetS) and obesity on coronary vascular function, with the hypothesis that subjects with MetS will have endothelial dysfunction. Background: Obesity or the metabolic syndrome (MetS) is associated with a higher risk of diabetes and coronary artery disease (CAD). Endothelial dysfunction is a common causal pathway in the initiation and progression of CAD. Methods: A total of 418 patients (165 obese, 239 MetS) with and without angiographic evidence of CAD underwent coronary vascular function testing by measuring coronary blood flow (CBF) velocity in response to intracoronary infusion of acetylcholine (ACH) and sodium nitroprusside (SNP) and coronary flow reserve with adenosine. Results: Endothelium-dependent microvascular vasodilation correlated with BMI (r=-0.12, p=0.02), with ACH responses significantly lower in overweight, obese and MetS subjects (p=0.003). The number of MetS components correlated with the response to ACH in both the coronary microcirculation and the epicardial coronary arteries, and with impaired coronary microcirculatory responses to adenosine. No significant correlation was observed with SNP. In multivariable analysis, beyond age, only the total number of MetS components, and not BMI, emerged as an independent predictor of impaired microvascular response to ACH (CBF: β=−0.18, P<0.001). Low-grade inflammation (C-reactive protein) was higher in patients with MetS, but was not associated with coronary vascular function. Conclusions: We demonstrate that the clustering of MetS components is an important and independent determinant of coronary endothelial dysfunction in subjects with and without CAD.

Endothelium-derived hyperpolarizing factor mediates bradykinin-stimulated tissue plasminogen activator release in humans

Aims: Bradykinin (BK) stimulates tissue plasminogen activator (t-PA) release from human endothelium. Although BK stimulates both nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) release, the role of EDHF in t-PA release remains unexplored. This study sought to determine the mechanisms of BK-stimulated t-PA release in the forearm vasculature of healthy human subjects. Methods: In 33 healthy subjects (age 40.3 ± 1.9 years), forearm blood flow (FBF) and t-PA release were measured at rest and after intra-arterial infusions of BK (400 ng/min) and sodium nitroprusside (3.2 mg/min). Measurements were repeated after intra-arterial infusion of tetraethylammonium chloride (TEA; 1 µmol/min), fluconazole (0.4 µmol·min-1·l-1), and NG-monomethyl-L-arginine (L-NMMA, 8 µmol/min) to block nitric oxide, and their combination in separate studies. Results: BK significantly increased net t-PA release across the forearm (p < 0.0001). Fluconazole attenuated both BK-mediated vasodilation (-23.3 ± 2.7% FBF, p < 0.0001) and t-PA release (from 50.9 ± 9.0 to 21.3 ± 8.9 ng/min/100 ml, p = 0.02). TEA attenuated FBF (-14.7 ± 3.2%, p = 0.002) and abolished BK-stimulated t-PA release (from 22.9 ± 5.7 to -0.8 ± 3.6 ng/min/100 ml, p = 0.0002). L-NMMA attenuated FBF (p < 0.0001), but did not inhibit BK-induced t-PA release (nonsignificant). Conclusion: BK-stimulated t-PA release is partly due to cytochrome P450-derived epoxides and is inhibited by K+Ca channel blockade. Thus, BK stimulates both EDHF-dependent vasodilation and t-PA release.

Endothelium: Dysfunction and Repair

Endothelial function refers to a multitude of physiological processes of the vascular endothelium that maintain healthy homeostasis of the vascular wall and may be used as a barometer of the injury/repair inflicted by multiple environmental and genetic factors.1-3

TCT-259 Coronary artery perforation during percutaneous coronary intervention: incidence and outcomes

nos: 260 272 TCT-260 Outcomes of Chronic Total Occlusion PCI in Patients with Diabetes – Insights from the OPEN CTO Registry Adam Salisbury, James Sapontis, J. Aaron Grantham, Mohammed Qintar, Kensey Gosch, William Lombardi, Dimitrios Karmpaliotis, Jeffrey Moses, John Spertus, David Cohen, Mikhail Kosiborod Saint Lukes Mid America Heart Institute, Parkville, Missouri, United States; MonashHeart, Victoria, Victoria, Australia; University of Missouri Kansas City and Mid America Heart Institute, Kansas City, Missouri, United States; Saint Lukes Mid America Heart Institute, Overland Park, Kansas, United States; Imperial College London; University of Washington Medical Center, Seattle, Washington, United States; Interventional Cardiologist, Atlanta, Georgia, United States; NewYork-Presbyterian Hospital/Columbia University Medical Center, New York, New York, United States; Mid America Heart Institute, Kansas City, Missouri, United States; Saint Luke’s Mid America Heart Institute, Kansas City, Missouri, United States; St. Luke’s Mid America Heart Institute, Kansas City, Missouri, United States BACKGROUND Chronic total occlusions (CTOs) are more common among diabetic than non-diabetic patients, and are associated with high symptom burden, yet CTO PCI is less often attempted in this group. This may reflect greater disease complexity (small vessels, diffuse disease), higher perceived complication risk, or lack of data

Differences in Vascular Nitric Oxide and Endothelium-Derived Hyperpolarizing Factor Bioavailability in Blacks and WhitesSignificance

Objective—Abnormalities in nitric oxide (NO) bioavailability have been reported in blacks. Whether there are differences in endothelium-derived hyperpolarizing factor (EDHF) in addition to NO between blacks and whites and how these affect physiological vasodilation remain unknown. We hypothesized that the bioavailability of vascular NO and EDHF, at rest and with pharmacological and physiological vasodilation, varies between whites and blacks. Approach and Results—In 74 white and 86 black subjects without known cardiovascular disease risk factors, forearm blood flow was measured using plethysmography at rest and during inhibition of NO with NG-monomethyl-L-arginine and of K+Ca channels (EDHF) with tetraethylammonium. The reduction in resting forearm blood flow was greater with NG-monomethyl-L-arginine (P=0.019) and similar with tetraethylammonium in whites compared with blacks. Vasodilation with bradykinin, acetylcholine, and sodium nitroprusside was lower in blacks compared with whites (all P<0.0001). Inhibition with NG-monomethyl-L-arginine was greater in whites compared with blacks with bradykinin, acetylcholine, and exercise. Inhibition with tetraethylammonium was lower in blacks with bradykinin, but greater during exercise and with acetylcholine. Conclusions—The contribution to both resting and stimulus-mediated vasodilator tone of NO is greater in whites compared with blacks. EDHF partly compensates for the reduced NO release in exercise and acetylcholine-mediated vasodilation in blacks. Preserved EDHF but reduced NO bioavailability and sensitivity characterizes the vasculature in healthy blacks. Clinical Trial Registration—URL: http://clinicaltrials.gov/. Unique identifier: NCT00166166.