Ayaz Rahman

Role of the T cell in the genesis of angiotensin II induced hypertension and vascular dysfunction.

Hypertension promotes atherosclerosis and is a major source of morbidity and mortality. We show that mice lacking T and B cells (RAG-1−/− mice) have blunted hypertension and do not develop abnormalities of vascular function during angiotensin II infusion or desoxycorticosterone acetate (DOCA)–salt. Adoptive transfer of T, but not B, cells restored these abnormalities. Angiotensin II is known to stimulate reactive oxygen species production via the nicotinamide adenosine dinucleotide phosphate (NADPH) oxidase in several cells, including some immune cells. Accordingly, adoptive transfer of T cells lacking the angiotensin type I receptor or a functional NADPH oxidase resulted in blunted angiotensin II–dependent hypertension and decreased aortic superoxide production. Angiotensin II increased T cell markers of activation and tissue homing in wild-type, but not NADPH oxidase–deficient, mice. Angiotensin II markedly increased T cells in the perivascular adipose tissue (periadventitial fat) and, to a lesser extent the adventitia. These cells expressed high levels of CC chemokine receptor 5 and were commonly double negative (CD3+CD4−CD8−). This infiltration was associated with an increase in intercellular adhesion molecule-1 and RANTES in the aorta. Hypertension also increased T lymphocyte production of tumor necrosis factor (TNF) α, and treatment with the TNFα antagonist etanercept prevented the hypertension and increase in vascular superoxide caused by angiotensin II. These studies identify a previously undefined role for T cells in the genesis of hypertension and support a role of inflammation in the basis of this prevalent disease. T cells might represent a novel therapeutic target for the treatment of high blood pressure.

Vitamin D Status Is Associated With Arterial Stiffness and Vascular Dysfunction in Healthy Humans

OBJECTIVES The primary objective of this study was to elucidate mechanisms underlying the link between vitamin D status and cardiovascular disease by exploring the relationship between 25-hydroxyvitamin D (25-OH D), an established marker of vitamin D status, and vascular function in healthy adults. BACKGROUND Mechanisms underlying vitamin D deficiency-mediated increased risk of cardiovascular disease remain unknown. Vitamin D influences endothelial and smooth muscle cell function, mediates inflammation, and modulates the renin-angiotensin-aldosterone axis. We investigated the relationship between vitamin D status and vascular function in humans, with the hypothesis that vitamin D insufficiency will be associated with increased arterial stiffness and abnormal vascular function. METHODS We measured serum 25-OH D in 554 subjects. Endothelial function was assessed as brachial artery flow-mediated dilation, and microvascular function was assessed as digital reactive hyperemia index. Carotid-femoral pulse wave velocity and radial tonometry-derived central augmentation index and subendocardial viability ratio were measured to assess arterial stiffness. RESULTS Mean 25-OH D was 31.8 ± 14 ng/ml. After adjustment for age, sex, race, body mass index, total cholesterol, low-density lipoprotein, triglycerides, C-reactive protein, and medication use, 25-OH D remained independently associated with flow-mediated vasodilation (β = 0.1, p = 0.03), reactive hyperemia index (β = 0.23, p < 0.001), pulse wave velocity (β = -0.09, p = 0.04), augmentation index (β = -0.11, p = 0.03), and subendocardial viability ratio (β = 0.18, p = 0.001). In 42 subjects with vitamin D insufficiency, normalization of 25-OH D at 6 months was associated with increases in reactive hyperemia index (0.38 ± 0.14, p = 0.009) and subendocardial viability ratio (7.7 ± 3.1, p = 0.04), and a decrease in mean arterial pressure (4.6 ± 2.3 mm Hg, p = 0.02). CONCLUSIONS Vitamin D insufficiency is associated with increased arterial stiffness and endothelial dysfunction in the conductance and resistance blood vessels in humans, irrespective of traditional risk burden. Our findings provide impetus for larger trials to assess the effects of vitamin D therapy in cardiovascular disease.

Role of Interleukin 17 in Inflammation, Atherosclerosis, and Vascular Function in Apolipoprotein E–Deficient Mice

Objective—Interleukin 17A (IL17A) is involved in many inflammatory processes, but its role in atherosclerosis remains controversial. We examined the role of IL17A in mouse and human atherosclerosis. Methods and Results—Atherosclerosis was induced in apolipoprotein E (ApoE)−/− and IL17A/ApoE−/− mice using high-fat feeding, angiotensin II infusion, or partial carotid ligation. In ApoE−/− mice, 3 months of high-fat diet induced interferon-&ggr; production by splenic lymphocytes, and this was abrogated in IL17A/ApoE−/− mice. IL17A/ApoE−/− mice had reduced aortic superoxide production, increased aortic nitric oxide levels, decreased aortic leukocyte and dendritic cell infiltration, and reduced weight gain after a high-fat diet compared with ApoE−/− mice. Despite these favorable effects, IL17A deficiency did not affect aortic plaque burden after a high-fat diet or angiotensin II infusion. In a partial carotid ligation model, IL17A deficiency did not affect percentage of stenosis but reduced outward remodeling. In this model, neutralization of the related isoform, IL17F, in IL17A/ApoE−/− mice did not alter atherosclerosis. Finally, there was no correlation between IL17A levels and carotid intima-media thickness in humans. Conclusion—IL17 contributes to vascular and systemic inflammation in experimental atherosclerosis but does not alter plaque burden. The changes in plaque composition caused by IL17 might modulate plaque stability.

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.

Association of a Genetic Risk Score With Prevalent and Incident Myocardial Infarction in Subjects Undergoing Coronary Angiography

Background—Genome-wide association studies have identified multiple variants associating with coronary artery disease (CAD) and myocardial infarction (MI). Whether a combined genetic risk score (GRS) is associated with prevalent and incident MI in high-risk subjects remains to be established. Methods and Results—In subjects undergoing cardiac catheterization (n=2597), we identified cases with a history of MI onset at age <70 years and controls ≥70 years without prior MI and followed them for incident MI and death. Genotyping was performed for 11 established CAD/MI variants, and a GRS was calculated based on average number of risk alleles carried at each locus weighted by effect size. Replication of association findings was sought in an independent angiographic cohort (n=2702). The GRS was significantly associated with prevalent MI, occurring before age 70, compared with older controls (≥70 years of age) with no history of MI (P<0.001). This association was successfully replicated in a second cohort, yielding a pooled P value of <0.001. The GRS modestly improved the area-under–the–curve statistic in models of prevalent MI with traditional risk factors; however, the association was not statistically significant when elderly controls without MI but with s\ angiographic CAD were examined (pooled P=0.11). Finally, during a median 2.5-year follow-up, only a nonsignificant trend was noted between the GRS and incident events, which was also not significant in the replication cohort. Conclusions—A GRS of 11 CAD/MI variants is associated with prevalent MI but not near-term incident adverse events in 2 independent angiographic cohorts. These findings have implications for understanding the clinical use of genetic risk scores for secondary as opposed to primary risk prediction.

Effects of storage-aged red blood cell transfusions on endothelial function in hospitalized patients.

Clinical and animal studies indicate that transfusions of older stored red blood cells (RBCs) impair clinical outcomes as compared to fresh RBC transfusions. It has been suggested that this effect is due to inhibition of nitric oxide (NO)‐mediated vasodilation after transfusion of older RBC units. However, to date this effect has not been identified in human transfusion recipients.

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.

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

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.

Nitric Oxide Contributes to Vasomotor Tone in Hypertensive African Americans Treated With Nebivolol and Metoprolol.

Endothelial dysfunction is more prevalent in African Americans (AAs) compared with whites. The authors hypothesized that nebivolol, a selective β1‐antagonist that stimulates nitric oxide (NO), will improve endothelial function in AAs with hypertension when compared with metoprolol. In a double‐blind, randomized, crossover study, 19 AA hypertensive patients were randomized to a 12‐week treatment period with either nebivolol 10 mg or metoprolol succinate 100 mg daily. Forearm blood flow (FBF) was measured using plethysmography at rest and after intra‐arterial infusion of acetylcholine and sodium nitroprusside to estimate endothelium‐dependent and independent vasodilation, respectively. Physiologic vasodilation was assessed during hand‐grip exercise. Measurements were repeated after NO blockade with L‐NG‐monomethylarginine (L‐NMMA) and after inhibition of endothelium‐derived hyperpolarizing factor (EDHF) with tetraethylammonium chloride (TEA). NO blockade with L‐NMMA produced a trend toward greater vasoconstriction during nebivolol compared with metoprolol treatment (21% vs 12% reduction in FBF, P=.06, respectively). This difference was more significant after combined administration of L‐NMMA and TEA (P<.001). Similarly, there was a contribution of NO to exercise‐induced vasodilation during nebivolol but not during metoprolol treatment. There were significantly greater contributions of NO and EDHF to resting vasodilator tone and of NO to exercise‐induced vasodilation with nebivolol compared with metoprolol in AAs with hypertension.