The Effect of High-Salt Diet on Oxidative Stress Production and Vascular Function in Tff3-/-/C57BL/6N Knockout and Wild Type (C57BL/6N) Mice.

INTRODUCTION: It is well documented that high-salt (HS) diet increases systemic and vascular oxidative stress in various animal models and in humans, leading to impairment of vascular reactivity. The present study examined the interaction of genotype and HS diet intake and the potential effects of oxidative stress - antioxidative system balance on the flow-induced dilation (FID) in pressurized carotid arteries of normotensive Tff3-/-/C57BL/6N knockout mice and their wild-type (WT) controls. METHODS: Male, ten-week-old transgenic Tff3-/-/C57BL/6N (Tff3-/-) knockout mice and WT/C57BL/6N (WT) (parental strain) healthy mice were divided in LS (0.4% NaCl in rodent chow) and HS (4% NaCl in rodent chow fed for 1 week) groups. Additionally, LS and HS groups were treated with 1 mmol/L 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) dissolved in the drinking water. After anesthesia with ketamine chloride (100 mg/kg) and midazolam (5 mg/kg), blood pressure was measured, carotid arteries and aortas were isolated, and blood samples were collected. RESULTS: FID was decreased in WT_HS mice and restored by superoxide scavenger TEMPOL in vivo. On the other hand, attenuated FID of Tff3-/- mice was not further affected by HS diet or TEMPOL in vivo treatment. Vascular superoxide/reactive oxygen species levels were increased with HS diet in both strains and restored by TEMPOL. HS upregulated glutathione peroxidase 1 (GPx1) gene expression in WT_HS and Tff3-/-_HS mice, while GPx activity was significantly decreased only in WT_HS group. Systemic (serum) markers of oxidative stress (oxLDL and AOPP) and arterial blood pressure were similar among groups. CONCLUSION: HS diet increases vascular oxidative stress and impairs vasodilation in WT mice. Tff3 gene deficiency attenuates vasodilation per se, without further effects of HS intake. This can be attributed to vascular upregulation of antioxidative enzyme GPx1 in Tff3-/-/C57BL/6N mice conferring protection from oxidative stress.

Adiposomes from Obese-Diabetic Individuals Promote Endothelial Dysfunction and Loss of Surface Caveolae.

Glycosphingolipids (GSLs) are products of lipid glycosylation that have been implicated in the development of cardiovascular diseases. In diabetes, the adipocyte microenvironment is characterized by hyperglycemia and inflammation, resulting in high levels of GSLs. Therefore, we sought to assess the GSL content in extracellular vesicles derived from the adipose tissues (adiposomes) of obese-diabetic (OB-T2D) subjects and their impact on endothelial cell function. To this end, endothelial cells were exposed to adiposomes isolated from OB-T2D versus healthy subjects. Cells were assessed for caveolar integrity and related signaling, such as Src-kinase and caveolin-1 (cav-1) phosphorylation, and functional pathways, such as endothelial nitric oxide synthase (eNOS) activity. Compared with adiposomes from healthy subjects, OB-T2D adiposomes had higher levels of GSLs, especially LacCer and GM3; they promoted cav-1 phosphorylation coupled to an obvious loss of endothelial surface caveolae and induced eNOS-uncoupling, peroxynitrite generation, and cav-1 nitrosylation. These effects were abolished by Src kinase inhibition and were not observed in GSL-depleted adiposomes. At the functional levels, OB-T2D adiposomes reduced nitric oxide production, shear response, and albumin intake in endothelial cells and impaired flow-induced dilation in healthy arterioles. In conclusion, OB-T2D adiposomes carried a detrimental GSL cargo that disturbed endothelial caveolae and the associated signaling.

17ß-Estradiol promotes sex-specific dysfunction in isolated human arterioles.

Despite data showing that estrogen is vasculoprotective in large conduit arteries, hormone therapy (HT) during menopause has not proven to mitigate cardiovascular disease (CVD) risk. Estrogen exposure through prolonged oral contraceptive use and gender-affirming therapy can also increase cis- and trans-females' risk for future CVD, respectively. The microvasculature is a unique vascular bed that when dysfunctional can independently predict future adverse cardiac events; however, studies on the influence of estrogen on human microvessels are limited. Here, we show that isolated human arterioles from females across the life span maintain nitric oxide (NO)-mediated dilation to flow, whereas chronic (16-20 h) exposure to exogenous (100 nM) 17ß-estradiol promotes microvascular endothelial dysfunction in vessels from adult females of <40 and ≥40 yr of age. The damaging effect of estrogen was more dramatic in arterioles from biological males, as they exhibited both endothelial and smooth muscle dysfunction. Furthermore, females of <40 yr have greater endothelial expression of estrogen receptor-ß (ER-ß) and G protein-coupled estrogen receptor (GPER) compared with females of ≥40 yr and males. Estrogen receptor-α (ER-α), the prominent receptor associated with protective effects of estrogen, was identified within the adventitia as opposed to the endothelium across all groups. To our knowledge, this is the first study to report the detrimental effects of estrogen on the human microvasculature and highlights differences in estrogen receptor expression.NEW & NOTEWORTHY Microvascular dysfunction is an independent predictor of adverse cardiac events; however, the effect of estrogen on the human microcirculation represents a critical knowledge gap. To our knowledge, this is the first study to report sex-specific detrimental effects of chronic estrogen on human microvascular reactivity. These findings may offer insight into the increased CVD risk associated with estrogen use in both cis- and trans-females.

DNA methylation profile of genes involved in inflammation and autoimmunity correlates with vascular function in morbidly obese adults.

Obesity is a major risk factor for cardiovascular disease. Blood-detected epigenetic profiles may serve as non-invasive clinically relevant biomarkers. Therefore, we investigated DNA methylation of genes involved in inflammation in peripheral blood of obese subjects and lean controls and their correlation with cardiometabolic measurements. We obtained blood and adipose tissue (AT) samples from bariatric patients (n = 24) and control adults (n = 24). AT-isolated arterioles were tested for flow-induced dilation (FID) and production of nitric oxide (NO) and reactive oxygen species (ROS). Brachial artery flow-mediated dilation (FMD) was measured via doppler ultrasound. Promoter methylation of 94 genes involved in inflammation and autoimmunity were analysed in whole-blood DNA in relation to vascular function and cardiometabolic risk factors. 77 genes had ahigher methylated fraction in the controls compare obese subjects and 28 proinflammatory genes were significantly hypomethylated in the obese individuals; on top of these genes are CXCL1, CXCL12, CXCL6, IGF2BP2, HDAC4, IL12A, and IL17RA. Fifteen of these genes had significantly higher mRNA in obese subjects compared to controls; on top of these genes are CXCL6, TLR5, IL6ST, EGR1, IL15RA, and HDAC4. Methylation % inversely correlated with BMI, total fat %, visceral fat%, blood pressure, fasting plasma insulin, serum IL6 and C-reactive protein, arteriolar ROS, and alcohol consumption and positive correlations with lean %, HDL, plasma folate and vitamin B12, arteriolar FID and NO production, and brachial FMD. Our results suggest that vascular dysfunction in obese adults may be attributed to asystemic hypomethylation and over expression of the immune-related genes.

Adipose Tissue Hypoxia Correlates with Adipokine Hypomethylation and Vascular Dysfunction.

Obesity is characterized by the accumulation of dysfunctional adipose tissues, which predisposes to cardiometabolic diseases. Our previous in vitro studies demonstrated a role of hypoxia in inducing adipokine hypomethylation in adipocytes. We sought to examine this mechanism in visceral adipose tissues (VATs) from obese individuals and its correlation with cardiometabolic risk factors. We propose an involvement of the hypoxia-inducible factor, HIF1α, and the DNA hydroxymethylase, TET1. Blood samples and VAT biopsies were obtained from obese and non-obese subjects (n = 60 each) having bariatric and elective surgeries, respectively. The analyses of VAT showed lower vascularity, and higher levels of HIF1α and TET1 proteins in the obese subjects than controls. Global hypomethylation and hydroxymethylation were observed in VAT from obese subjects along with promoter hypomethylation of several pro-inflammatory adipokines. TET1 protein was enriched near the promotor of the hypomethylated adipokines. The average levels of adipokine methylation correlated positively with vascularity and arteriolar vasoreactivity and negatively with protein levels of HIF1α and TET1 in corresponding VAT samples, serum and tissue inflammatory markers, and other cardiometabolic risk factors. These findings suggest a role for adipose tissue hypoxia in causing epigenetic alterations, which could explain the increased production of adipocytokines and ultimately, vascular dysfunction in obesity.

Angiotensin II type 1 receptor is involved in flow-induced vasomotor responses of isolated middle cerebral arteries: role of oxidative stress.

This study aimed to determine the mechanosensing role of angiotensin II type 1 receptor (AT1R) in flow-induced dilation (FID) and oxidative stress production in middle cerebral arteries (MCA) of Sprague-Dawley rats. Eleven-week old, healthy male Sprague-Dawley rats on a standard diet were given the AT1R blocker losartan (1 mg/mL) in drinking water (losartan group) or tap water (control group) ad libitum for 7 days. Blockade of AT1R attenuated FID and acetylcholine-induced dilation was compared with control group. Nitric oxide (NO) synthase inhibitor Nω-nitro-l-arginine methyl ester (l-NAME) and cyclooxygenase inhibitor indomethacin (Indo) significantly reduced FID in control group. The attenuated FID in losartan group was further reduced by Indo only at Δ100 mmHg, whereas l-NAME had no effect. In losartan group, Tempol (a superoxide scavenger) restored dilatation, whereas Tempol + l-NAME together significantly reduced FID compared with restored dilatation with Tempol alone. Direct fluorescence measurements of NO and reactive oxygen species (ROS) production in MCA, in no-flow conditions revealed significantly reduced vascular NO levels with AT1R blockade compared with control group, whereas in flow condition increased the NO and ROS production in losartan group and had no effect in the control group. In losartan group, Tempol decreased ROS production in both no-flow and flow conditions. AT1R blockade elicited increased serum concentrations of ANG II, 8-iso-PGF2α, and TBARS, and decreased antioxidant enzyme activity (SOD and CAT). These results suggest that in small isolated cerebral arteries: 1) AT1 receptor maintains dilations in physiological conditions; 2) AT1R blockade leads to increased vascular and systemic oxidative stress, which underlies impaired FID.NEW & NOTEWORTHY The AT1R blockade impaired the endothelium-dependent, both flow- and acetylcholine-induced dilations of MCA by decreasing vascular NO production and increasing the level of vascular and systemic oxidative stress, whereas it mildly influenced the vascular wall inflammatory phenotype, but had no effect on the systemic inflammatory response. Our data provide functional and molecular evidence for an important role of AT1 receptor activation in physiological conditions, suggesting that AT1 receptors have multiple biological functions.

Sweat the small stuff: The human microvasculature and heart disease.

Traditionally thought of primarily as the predominant regulator of myocardial perfusion, it is becoming more accepted that the human coronary microvasculature also exerts a more direct influence on the surrounding myocardium. Coronary microvascular dysfunction (CMD) not only precedes large artery atherosclerosis, but is associated with other cardiovascular diseases such as heart failure with preserved ejection fraction and hypertrophic cardiomyopathy. It is also highly predictive of cardiovascular events in patients with or without atherosclerotic cardiovascular disease. This review focuses on this recent paradigm shift and delves into the clinical consequences of CMD. Concepts of how resistance arterioles contribute to disease will be discussed, highlighting how the microvasculature may serve as a potential target for novel therapies and interventions. Finally, both invasive and non-invasive methods with which to assess the coronary microvasculature both for diagnostic and risk stratification purposes will be reviewed.

An in silico simulation of flow-mediated dilation reveals that blood pressure and other factors may influence the response independent of endothelial function.

Endothelial dysfunction is thought to underpin atherosclerotic cardiovascular disease. The most widely used in vivo test of endothelial function is flow-mediated dilation (FMD). However, the results of FMD may be subject to some confounding factors that are not fully understood. We investigated potential biophysical confounding factors that could cause a disassociation between FMD and true endothelial cell shear stress response (the release of endothelium-dependent relaxing factors in response to wall shear stress). Arterial hemodynamics during FMD was simulated using a novel computational modeling approach. The model included an endothelial response function relating changes in wall shear stress to changes in local vascular stiffness in the arm arteries and accounted for vascular stiffening with increasing blood pressure. The hemodynamic effects of cuff inflation and deflation were modeled by prescribing intraluminal arterial pressure changes and peripheral vasodilation. Evolution of arterial diameter and flow velocity during FMD was assessed by comparison against in vivo data. Our model revealed that vasoconstriction occurring immediately after cuff deflation is independent of endothelial response function and entirely caused by the change in transmural pressure along conduit arteries. Moreover, for the same endothelial response function model, FMD values increased exponentially with increasing peak flow velocity, decreased linearly with increasing arterial stiffness at a rate of 0.95%/MPa, and increased linearly with increasing central blood pressure at a rate of 0.22%/mmHg. Dependence of FMD on confounding factors, such as arterial stiffness and blood pressure, suggests that the current FMD test may not reflect the true endothelial cell response.NEW & NOTEWORTHY First, a novel computational model simulating arterial hemodynamics during flow-mediated dilation (FMD) was proposed. Second, the model was used to explain why FMD may be influenced by endothelium-independent factors, showing that FMD results are 1) partly masked by the vasoconstriction due to the change in transmural pressure and 2) affected by physiological factors (i.e., arterial stiffness and arterial blood pressure) that are difficult to eliminate due to their multiple interactions.

Impact of High Salt Diet on Cerebral Vascular Function and Stroke in Tff3-/-/C57BL/6N Knockout and WT (C57BL/6N) Control Mice.

High salt (HS) dietary intake leads to impaired vascular endothelium-dependent responses to various physiological stimuli, some of which are mediated by arachidonic acid (AA) metabolites. Transgenic Tff3-/- gene knockout mice (Tff3-/-/C57BL/6N) have changes in lipid metabolism which may affect vascular function and outcomes of stroke. We aimed to study the effects of one week of HS diet (4% NaCl) on vascular function and stroke induced by transient occlusion of middle cerebral artery in Tff3-/- and wild type (WT/C57BL/6N) mice. Flow-induced dilation (FID) of carotid artery was reduced in WT-HS mice, but not affected in Tff3-/--HS mice. Nitric oxide (NO) mediated FID. NO production was decreased with HS diet. On the contrary, acetylcholine-induced dilation was significantly decreased in Tff3-/- mice on both diets and WT-HS mice. HS intake and Tff3 gene depletion affected the structural components of the vessels. Proteomic analysis revealed a significant effect of Tff3 gene deficiency on HS diet-induced changes in neuronal structural proteins and acute innate immune response proteins' expression and Tff3 depletion, but HS diet did not increase the stroke volume, which is related to proteome modification and upregulation of genes involved mainly in cellular antioxidative defense. In conclusion, Tff3 depletion seems to partially impair vascular function and worsen the outcomes of stroke, which is moderately affected by HS diet.

Age-Dependent Impairment in Endothelial Function and Arterial Stiffness in Former High Class Male Athletes Is No Different to That in Men With No History of Physical Training.

Background Physical activity is generally considered to exert positive effects on the cardiovascular system in humans. However, surprisingly little is known about the delayed effect of professional physical training performed at a young age on endothelial function and arterial stiffness in aging athletes. The present study aimed to assess the impact of long-lasting professional physical training (endurance and sprint) performed at a young age on the endothelial function and arterial stiffness reported in older age in relation to glycocalyx injury, prostacyclin and nitric oxide production, inflammation, basal blood lipid profile, and glucose homeostasis. Methods and Results This study involved 94 male subjects with varied training backgrounds, including young athletes (mean age ∼25 years), older former high class athletes (mean age ∼60 years), and aged-matched untrained control groups. Aging increased arterial stiffness, as reflected by an enhancement in pulse wave velocity, augmentation index, and stiffness index (P<10-4), as well as decreased endothelial function, as judged by the attenuation of flow-mediated vasodilation (FMD) in the brachial artery (P=0.03). Surprisingly, no effect of the training performed at a young age on endothelial function and arterial stiffness was observed in the former athletes. Moreover, no effect of training performed at a young age (P>0.05) on blood lipid profile, markers of inflammation, and glycocalyx shedding were observed in the former athletes. Conclusions Our study clearly shows that aging, but not physical training history, represents the main contributing factor responsible for decline in endothelial function and increase in arterial stiffness in former athletes.

Manipulation of the Sphingolipid Rheostat Influences the Mediator of Flow-Induced Dilation in the Human Microvasculature.

Background Elevated levels of ceramide, a sphingolipid known to cause a transition from nitric oxide (NO)- to hydrogen peroxide-dependent flow-induced dilation (FID) in human arterioles, correlate with adverse cardiac events. However, elevations of ceramide are associated with changed concentrations of other sphingolipid metabolites. The effects of sphingolipid metabolites generated through manipulation of this lipid pathway on microvascular function are unknown. We examined the hypothesis that inhibition or activation of the ceramide pathway would determine the mediator of FID. Methods and Results Using videomicroscopy, internal diameter changes were measured in human arterioles collected from discarded adipose tissue during surgery. Inhibition of neutral ceramidase, an enzyme responsible for the hydrolysis of ceramide, favored hydrogen peroxide-dependent FID in arterioles from healthy patients. Using adenoviral technology, overexpression of neutral ceramidase in microvessels from diseased patients resulted in restoration of NO-dependent FID. Exogenous sphingosine-1-phosphate, a sphingolipid with opposing effects of ceramide, also restored NO as the mediator of FID in diseased arterioles. Likewise, exogenous adiponectin, a known activator of neutral ceramidase, or, activation of adiponectin receptors, favored NO-dependent dilation in arterioles collected from patients with coronary artery disease. Conclusions Sphingolipid metabolites play a critical role in determining the mediator of FID in human resistance arterioles. Manipulating the sphingolipid balance towards ceramide versus sphingosine-1-phosphate favors microvascular dysfunction versus restoration of NO-mediated FID, respectively. Multiple targets exist within this biolipid pathway to treat microvascular dysfunction and potentially improve patient outcomes.

Low-Fat Diet Designed for Weight Loss But Not Weight Maintenance Improves Nitric Oxide-Dependent Arteriolar Vasodilation in Obese Adults.

Obesity is associated with microvascular dysfunction. While low-fat diet improves cardiovascular risk, its contributions on microvascular function, independent of weight loss, is unknown. We tested the hypothesis that nitric oxide (NO)-dependent vasodilation in microvessels is improved by low-fat diets designed for weight loss (LFWL) compared to low-fat weight maintenance (LFWM) diet. Obese adults were randomly assigned to either a LFWL diet (n = 11) or LFWM diet (n = 10) for six weeks. Microvessels were obtained from gluteal subcutaneous fat biopsies before and after the intervention for vascular reactivity measurements to acetylcholine (Ach) and flow, with and without L-NAME or indomethacin. Vascular and serum NO and C-reactive protein (CRP) were also measured. LFWL diet increased flow-induced (FID) and ACh-induced dilation (AChID); an effect that was inhibited by L-NAME. Conversely, LFWM diet did not affect FID or AChID. Indomethacin improved FID and AChID in the baseline and this effect was minimized in response to both diets. Serum NO or CRP did not change in response to either diet. In conclusion, LFWL diet improves microvascular reactivity compared to LFWM diet and increased vascular NO contribution to the improved microvascular dilation. These data suggest that weight reduction on low fat diet is critical for microvascular health.

Acute Effects of Heat-Not-Burn, Electronic Vaping, and Traditional Tobacco Combustion Cigarettes: The Sapienza University of Rome-Vascular Assessment of Proatherosclerotic Effects of Smoking ( SUR - VAPES ) 2 Randomized Trial.

Background Little clinical research on new-generation heat-not-burn cigarettes ( HNBC ) in comparison with electronic vaping cigarettes ( EVC ) and traditional tobacco combustion cigarettes ( TC ) has been reported. We aimed to appraise the acute effects of single use of HNBC , EVC, and TC in healthy smokers. Methods and Results This was an independent, cross-over, randomized trial in 20 TC smokers, with allocation to different cycles of HNBC , EVC , and TC . All participants used all types of products, with an intercycle washout of 1 week. End points were oxidative stress, antioxidant reserve, platelet activation, flow-mediated dilation, blood pressure, and satisfaction scores. Single use of any product led to an adverse impact on oxidative stress, antioxidant reserve, platelet function, flow-mediated dilation, and blood pressure. HNBC had less impact than EVC and TC on soluble Nox2-derived peptide (respectively, P=0.004 and 0.001), 8-iso-prostaglandin F2α- III ( P=0.004 and <0.001), and vitamin E ( P=0.018 and 0.044). HNBC and EVC were equally less impactful than TCs on flow-mediated dilation ( P=0.872 for HNBC versus EVC ), H2O2 ( P=0.522), H2O2 breakdown activity ( P=0.091), soluble CD 40 ligand ( P=0.849), and soluble P-selectin ( P=0.821). The effect of HNBC and, to a lesser extent EVC , on blood pressure was less evident than that of TC , whereas HNBC appeared more satisfying than EVC (all P<0.05). Conclusions Acute effects of HNBC , EVC, and TC are different on several oxidative stress, antioxidant reserve, platelet function, cardiovascular, and satisfaction dimensions, with TCs showing the most detrimental changes in clinically relevant features. Clinical Trial Registration URL : http://www.clinicaltrials.gov . Unique identifier: NCT 03301129.

Endothelial Dysfunction, Increased Arterial Stiffness, and Cardiovascular Risk Prediction in Patients With Coronary Artery Disease: FMD-J (Flow-Mediated Dilation Japan) Study A.

BACKGROUND: The usefulness of vascular function tests for management of patients with a history of coronary artery disease is not fully known. METHODS AND RESULTS: We measured flow-mediated vasodilation (FMD) and brachial-ankle pulse wave velocity (baPWV) in 462 patients with coronary artery disease for assessment of the predictive value of FMD and baPWV for future cardiovascular events in a prospective multicenter observational study. The first primary outcome was coronary events, and the second primary outcome was a composite of coronary events, stroke, heart failure, and sudden death. During a median follow-up period of 49.2 months, the first primary outcome occurred in 56 patients and the second primary outcome occurred in 66 patients. FMD above the cutoff value of 7.1%, derived from receiver-operator curve analyses for the first and second primary outcomes, was significantly associated with lower risk of the first (hazard ratio, 0.27; 95% confidence interval, 0.06-0.74; P=0.008) and second (hazard ratio, 0.32; 95% confidence interval, 0.09-0.79; P=0.01) primary outcomes. baPWV above the cutoff value of 1731 cm/s was significantly associated with higher risk of the first (hazard ratio, 1.86; 95% confidence interval, 1.01-3.44; P=0.04) and second (hazard ratio, 2.19; 95% confidence interval, 1.23-3.90; P=0.008) primary outcomes. Among 4 groups stratified according to the combination of cutoff values of FMD and baPWV, stepwise increases in the calculated risk ratio for the first and second primary outcomes were observed. CONCLUSIONS: In patients with coronary artery disease, both FMD and baPWV were significant predictors of cardiovascular events. The combination of FMD and baPWV provided further cardiovascular risk stratification. CLINICAL TRIAL REGISTRATION: URL: www.umin.ac.jp. Unique identifier: UMIN000012950.

High salt intake shifts the mechanisms of flow-induced dilation in the middle cerebral arteries of Sprague-Dawley rats.

The goal of the present study was to examine the effect of 1 wk of high salt (HS) intake and the role of oxidative stress in changing the mechanisms of flow-induced dilation (FID) in isolated pressurized middle cerebral arteries of male Sprague-Dawley rats ( n = 15-16 rats/group). Reduced FID in the HS group was restored by intake of the superoxide scavenger tempol (HS + tempol in vivo group). The nitric oxide (NO) synthase inhibitor Nω-nitro-l-arginine methyl ester, cyclooxygenase inhibitor indomethacin, and selective inhibitor of microsomal cytochrome P-450 epoxidase activity N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide significantly reduced FID in the low salt diet-fed group, whereas FID in the HS group was mediated by NO only. Cyclooxygenase-2 mRNA (but not protein) expression was decreased in the HS and HS + tempol in vivo groups. Hypoxia-inducible factor-1α and VEGF protein levels were increased in the HS group but decreased in the HS + tempol in vivo group. Assessment by direct fluorescence of middle cerebral arteries under flow revealed significantly reduced vascular NO levels and increased superoxide/reactive oxygen species levels in the HS group. These results suggest that HS intake impairs FID and changes FID mechanisms to entirely NO dependent, in contrast to the low-salt diet-fed group, where FID is NO, prostanoid, and epoxyeicosatrienoic acid dependent. These changes were accompanied by increased lipid peroxidation products in the plasma of HS diet-fed rats, increased vascular superoxide/reactive oxygen species levels, and decreased NO levels, together with increased expression of hypoxia-inducible factor-1α and VEGF. NEW & NOTEWORTHY High-salt (HS) diet changes the mechanisms of flow-induced dilation in rat middle cerebral arteries from a combination of nitric oxide-, prostanoid-, and epoxyeicosatrienoic acid-dependent mechanisms to, albeit reduced, a solely nitric oxide-dependent dilation. In vivo reactive oxygen species scavenging restores flow-induced dilation in HS diet-fed rats and ameliorates HS-induced increases in the transcription factor hypoxia-inducible factor-1α and expression of its downstream target genes.

Interrelationships Among Flow-Mediated Vasodilation, Nitroglycerine-Induced Vasodilation, Baseline Brachial Artery Diameter, Hyperemic Shear Stress, and Cardiovascular Risk Factors.

BACKGROUND: Flow-mediated vasodilation (FMD) of the brachial artery has been used for the assessment of endothelial function. Considering the mechanism underlying the vasodilatory response of the brachial artery to reactive hyperemia, hyperemic shear stress (HSS), a stimulus for FMD; nitroglycerine-induced vasodilation (NID), an index of endothelium-independent vasodilation; and baseline brachial artery diameter (BAD) are also involved in vasodilatory response. The purpose of this study was to investigate the interrelationships among FMD, HSS, NID, baseline BAD, and cardiovascular risk factors. METHODS AND RESULTS: We measured FMD, HSS, NID, and baseline BAD simultaneously in 1033 participants (633 men and 400 women; mean age: 58.6±17.0 years). Framingham risk score was negatively correlated with FMD, HSS, and NID and was positively correlated with baseline BAD. HSS and NID were positively correlated with FMD, and baseline BAD was negatively correlated with FMD. In participants with normal NID, FMD was correlated with HSS, NID, and baseline BAD, all of which were independent variables of FMD in multivariate analysis. In participants with impaired NID, FMD was correlated with NID and baseline BAD, both of which were independent variables of FMD in multivariate analysis, but there was no association between FMD and HSS. CONCLUSIONS: NID and baseline BAD were independent variables of FMD regardless of the status of endothelium-independent vasodilation, whereas there was a significant association between FMD and HSS in participants with normal NID but not in those with impaired NID. The influence of HSS on FMD seems to be dependent on the status of endothelium-independent vasodilation.

The percentage flow-mediated dilation index: a large-sample investigation of its appropriateness, potential for bias and causal nexus in vascular medicine.

The percentage flow-mediated dilation index (FMD%) scales the increase in arterial diameter (Ddiff) as a constant proportion of baseline artery diameter (Dbase). We have demonstrated, albeit with small samples, that the scaling properties of FMD% can lead to biased inferences on endothelial dysfunction. Therefore, we aimed to investigate the underlying rationale and potential bias of FMD% using a selection of new examples from the large (n = 3499) and diverse Multi-Ethnic Study of Atherosclerosis (MESA). In this dataset, we found that smaller values of Ddiff are associated with larger values of Dbase, which contradicts the scaling properties of FMD%. Consequently, FMD% 'over-scales' and naturally generates an even stronger negative correlation between itself and Dbase. Using a data simulation, we show that this FMD%-Dbase correlation can be a statistical artefact due to inappropriate scaling. The new examples we present from MESA indicate that FMD% biases the differences in flow-mediated response between men and women, Framingham risk score categories, and diseased and healthy people. We demonstrate how FMD%, as an exposure for predicting cardiovascular disease, is confounded by its dependency on Dbase, which itself could be clinically important. This critical review, incorporating an allometric analysis of a large dataset, suggests that the FMD% index has a less-than-clear rationale, can itself generate the Dbase-dependency problem, provides biased estimates of differences in the flow-mediated response, complicates the interpretation of the flow-mediated protocol and clouds the causal pathway to vascular disease. These interpretative problems can be resolved by applying accepted allometric principles to the flow-mediated response.