Dysfunction In Conduit Arteries Research Articles

Examining sex differences in sitting-induced microvascular dysfunction: Insight from acute vitamin C supplementation

PurposeLower limb microvascular dysfunction resulting from prolonged sitting (PS) bouts has been revealed to occur independent of sex. Although acute antioxidant supplementation has been reported to blunt conduit artery dysfunction following PS in young males, it is unknown if this protective effect extends to the microvasculature or is relevant in young females, who possess intrinsic vascular protective mechanisms specific to antioxidant defense. Therefore, this study employed an acute antioxidant supplementation to further examine sex differences during PS with a specific focus on microvascular function. MethodsOn two separate visits, 14 females (23 ± 3 years) and 12 males (25 ± 4 years) had leg microvascular function (LMVF) assessed (via the passive leg movement technique) before and after 1.5 h of sitting. Prior to each visit, one gram of vitamin C (VC) or placebo (PL) was consumed. ResultsPS significantly reduced LMVF [PL: (M: −34 ± 20; F: −23 ± 18%; p < 0.01) independent of sex (p = 0.7)], but the VC condition only blunted this reduction in males (VC: −3 ± 20%; p < 0.01), but not females (VC: −18 ± 25%; p = 0.5). ConclusionYoung males and females reported similar reductions LMVF following PS, but only the young males reported a preservation of LMVF following the VC supplementation. This finding in young females was highlighted by substantial variability in LMVF measures in response to the VC condition that was unrelated to changes in the potential contributors to sitting-induced reductions in LMVF (e.g. lower limb venous pooling, reduced arterial shear rate). New and noteworthyIn this study, we employed an acute Vitamin C (VC) supplementation to examine sex differences in leg microvascular function (LMVF) following a bout of prolonged sitting. This study revealed that prolonged sitting reduced LMVF independent of sex, but only young males reported an attenuation to this lowered LMVF following VC supplementation. The young females revealed substantial variability in sitting-induced changes to LMVF that could not be explained by the potential contributors to sitting-induced reductions in LMVF (e.g. lower limb venous pooling, reduced arterial shear rate).

Impaired Endothelial Function in Patients With Postural Tachycardia Syndrome.

The purpose of this study is to evaluate endothelial function in postural tachycardia syndrome (PoTS), a poorly understood chronic condition characterized by a state of consistent orthostatic tachycardia (delta heart rate ≥30 beats per minute) upon standing without orthostatic hypotension. Nineteen patients with PoTS and 9 healthy controls were studied after 3 days of a fixed, caffeine-free, normal sodium (150 milliequivalents/day) diet. All participants underwent autonomic function testing, including sinus arrhythmia, valsalva maneuver, hyperventilation, cold pressor, handgrip, and a standing test with catecholamine measurements, followed by endothelial function testing. We analyzed 3 measures of endothelial function: percent brachial flow-mediated dilation, digital pulsatile arterial tonometry, and postischemic percent leg blood flow. Flow-mediated dilation was significantly lower in patients with PoTS (6.23±3.54% for PoTS) than in healthy controls (10.6±4.37% for controls versus, P=0.014). PoTS and controls had similar digital pulsatile arterial tonometry (1.93±0.40 arbitrary units for controls versus 2.13±0.63 arbitrary units for PoTS). PoTS had similar but suggestive percent leg blood flow to controls (313±158% for PoTS versus 468±236% for controls, P=0.098). Patients with PoTS have significantly reduced flow-mediated dilation compared with healthy controls, suggesting that PoTS is characterized by endothelial dysfunction in conduit arteries. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01308099.

Doxorubicin-Induced Oxidative Stress and Endothelial Dysfunction in Conduit Arteries Is Prevented by Mitochondrial-Specific Antioxidant Treatment

BackgroundDoxorubicin (DOXO) chemotherapy increases risk for cardiovascular disease in part by inducing endothelial dysfunction in conduit arteries. However, the mechanisms mediating DOXO-associated endothelial dysfunction in (intact) arteries and treatment strategies are not established. ObjectivesWe tested the hypothesis that DOXO impairs endothelial function in conduit arteries via excessive mitochondrial reactive oxygen species (ROS) and that these effects could be prevented by treatment with a mitochondrial-targeted antioxidant (MitoQ). MethodsEndothelial function (endothelium-dependent dilation [EDD] to acetylcholine) and vascular mitochondrial ROS were assessed 4 weeks following administration (10 mg/kg intraperitoneal injection) of DOXO. A separate cohort of mice received chronic (4 weeks) oral supplementation with MitoQ (drinking water) for 4 weeks following DOXO. ResultsEDD in isolated pressurized carotid arteries was 55% lower 4 weeks following DOXO (peak EDD, DOXO: 42 ± 7% vs. sham: 94 ± 3%; p = 0.006). Vascular mitochondrial ROS was 52% higher and manganese (mitochondrial) superoxide dismutase was 70% lower after DOXO versus sham (p = 0.0008). Endothelial function was rescued by administration of the mitochondrial-targeted antioxidant, MitoQ, to the perfusate. Exposure to plasma from DOXO-treated mice increased mitochondrial ROS in cultured endothelial cells. Analyses of plasma showed differences in oxidative stress-related metabolites and a marked reduction in vascular endothelial growth factor A in DOXO mice, and restoring vascular endothelial growth factor A to sham levels normalized mitochondrial ROS in endothelial cells incubated with plasma from DOXO mice. Oral MitoQ supplementation following DOXO prevented the reduction in EDD (97 ± 1%; p = 0.002 vs. DOXO alone) by ameliorating mitochondrial ROS suppression of EDD. ConclusionsDOXO-induced endothelial dysfunction in conduit arteries is mediated by excessive mitochondrial ROS and ameliorated by mitochondrial-specific antioxidant treatment. Mitochondrial ROS is a viable therapeutic target for mitigating arterial dysfunction with DOXO.

Selective deficiency in endothelial PTP1B protects from diabetes and endoplasmic reticulum stress-associated endothelial dysfunction via preventing endothelial cell apoptosis

Diabetes notably increases the risk for endothelial dysfunction, a main precursor for microvascular complications. While endoplasmic reticulum stress (ERS) and protein tyrosine phosphatase 1B (PTP1B) have been associated with endothelial dysfunction in resistance vessels, whether these mechanisms also contribute to diabetes-mediated endothelial dysfunction in conduit arteries remains unknown. Herein, we tested the hypothesis that diabetes induces macrovascular endothelial dysfunction via endothelial ERS-induced, PTP1B-mediated apoptosis. We showed that diabetes concomitantly increased the expression of PTP1B and of markers of ERS, including GRP78, XBP1, splXBP1 and CHOP in human vessels. Exposure of aortic rings from wild-type mice to the ERS inducers tunicamycin and thapsigargin markedly reduced endothelium-dependent relaxation. Global and endothelial-specific deletion of PTP1B as well as pharmacological inhibition protected aortic rings from ERS-mediated endothelial dysfunction. Nitric oxide synthase inhibition with l-NAME abolished relaxation in the presence and absence of ERS, but neither reactive oxygen species scavenging with tempol or peg-catalase, nor cyclooxygenase inhibition with indomethacin prevented ERS-mediated endothelial dysfunction. However, both p38-MAPK and JNK inhibition protected aortic rings from ERS-mediated endothelial dysfunction. In HUVECs, PTP1B deletion prevented ERS-induced PARP cleavage and apoptosis. Lastly, acute ERS inhibition in aortic rings and selective deficiency of endothelial PTP1B in mice protected mice from diabetes-induced endothelial dysfunction. Altogether, these data support the contribution of the p38/JNK-apoptosis pathway in ERS-mediated endothelial dysfunction and present endothelial PTP1B as a major regulator of endothelial cell viability in conduit vessels and a potential target for the management of macrovascular diseases in diabetes.

Abstract P3011: Role of CD36 in Insulin Mediated Microvascular Vasodilation in African Americans

CD36 is a membrane protein involved in fatty acids uptake that is expressed in the endothelium, which has been associated with endothelial dysfunction in African Americans (AA). One in four AA is G-allele carriers for coding CD36 SNP rs3211938, which results in ~50% reduction in its expression. We reported that potentiating nitric oxide action (NO) with sildenafil restored endothelial dysfunction in conduit arteries in G-allele carriers. In this study, we tested the hypothesis that in G-allele carriers, sildenafil would improve insulin-induced microvascular recruitment (MBV) in response to fat infusion. We recruited 25 healthy AA (17 non-carriers [ages 34 ± 7.4] and eight G-allele carriers [42 ± 7.4 yrs]). Subjects underwent three visits: Visit 1: Saline infusion and hyperinsulinemic euglycemic clamp (HIE clamp). Visit 2: Lipid infusion and HIE clamp and Visit 3: Lipid infusion and HIE clamp after a four-week sildenafil treatment (60 mg/day). During each visit, the subjects underwent an assessment of MBV at baseline (bsl), after 3-hour insulin (Ins) infusion (40mu/m 2 /min) and after Ins and L-arginine (10mg/kg/min) for 30 min. infusion (Ins+L-arg). Ins+L-arg (saline day) increased the % change in MBV in both groups. However, this increase was less in carriers as compared to non-carriers (13.6±42.4 and 38.9±74.4), Fig. A. Intralipid (IL) infusion increased MBV but only in non-carriers, Fig. B . Treatment with sildenafil in the presence of IL infusion induced a decline in MBV in G-allele carriers Fig. C . In conclusion, healthy AAs with CD36 deficiency had a poor insulin-induced microvascular recruitment and appeared to be worsened by potentiating NO function with sildenafil.

Effect of different walking break strategies on superficial femoral artery endothelial function.

Breaking up prolonged sitting with physical activity (PA) breaks prevents conduit artery dysfunction. However, the optimal break strategy to achieve this, in terms of the frequency or duration of PA, is not known. This study assessed the effect of breaking up sitting with different PA break strategies on lower limb peripheral artery endothelial function. Fifteen participants (10 male, 35.8 ± 10.2 years, BMI: 25.5 ± 3.2 kg m−2) completed, on separate days, three 4‐h conditions in a randomized order: (1) uninterrupted sitting (SIT), (2) sitting with 2‐min light‐intensity walking breaks every 30 min (2WALK), or (3) sitting with 8‐min light‐intensity walking breaks every 2 h (8WALK). At baseline and 4 h, superficial femoral artery function (flow‐mediated dilation; FMD), blood flow, and shear rate (SR) were assessed using Doppler ultrasound. For each condition, the change in outcome variables was calculated and data were statistically analyzed using a linear mixed model. There was no significant main effect for the change in FMD (P = 0.564). A significant main effect was observed for the change in blood flow (P = 0.022), with post hoc analysis revealing a greater reduction during SIT (−42.7 ± 14.2 mL·min) compared to 8WALK (0.45 ± 17.7 mL·min; P = 0.012). There were no significant main effects for mean, antegrade, or retrograde SR (P > 0.05). Superficial femoral artery blood flow, but not FMD, was reduced following uninterrupted sitting. This decline in blood flow was prevented with longer duration, less frequent walking breaks rather than shorter, more frequent breaks suggesting the dose (duration and frequency) of PA may influence the prevention of sitting‐induced decreases in blood flow.

Short and Long term Effects of Exercise Intensity on Conduit Artery Function in Cardiac Rehabilitation Patients

PURPOSE: Patients with coronary artery disease (CAD) commonly present with conduit artery dysfunction characterized by decreased brachial artery flow-mediated dilation (FMD). Reduced FMD of 1% is associated with an 8-13% increased risk of future cardiovascular events1, and thus interventions designed to improve FMD in patients with CAD are warranted. Short-term supervised exercise training may improve FMD, however whether improvements are maintained longer term following cessation of supervised cardiac rehabilitation (CR), is unclear. We compared the short- and long-term effect of High Intensity Interval Training (HIIT) and Moderate Intensity Continuous Training (MICT) on FMD in patients with CAD commencing a 4-week CR program in a real world hospital-based setting. METHODS:Patients with angiographically-proven CAD (Age: 64+7; 35 males, 3 females) completed 3 sessions per week (2 supervised, 1 home-based) for 4-weeks, randomized to either 1) HIIT (n=21): 4 x 4 minute high intensity intervals at a rating of perceived exertion (RPE) 15-18 interspersed with 3 minute active recovery periods or 2) MICT usual care (n=17): 40 minutes moderate intensity continuous exercise at an RPE 11-13. Patients then continued 3 unsupervised home-based sessions per week of their randomized training for a further 11 months. FMD was measured at baseline, 4 weeks, 3 months, 6 months, and 12 months. Data was analyzed using a linear mixed model with baseline diameter and shear rate as covariates. Data is presented as mean (95% CI). RESULTS:Baseline FMD was not different between groups [HIIT: 3.1%(2.2 to 4.0); MICT: 2.9%(1.9 to 3.9), p=0.657]. FMD increased from baseline at 4 weeks, 6 months and 12 months in the HIIT group [4 weeks: +1.8%(0.8 to 2.7), p<0.001; 6-months: +1.6%(0.7 to 2.6), p=001; 12-months: +1.4%(0.4 to 2.3), p=0.007], with negligible changes in the MICT group [4 weeks: +0.4%(-1.1 to 1.0), p=0.94; 6 months: +1.0%(-0.1 to 2.1), p=0.063; 12 months: +0.3%(-0.7 to 1.3), p=0.52]. CONCLUSIONS: A 4-week CR program of HIIT, but not MICT (usual care), improved conduit artery function in patients with CAD. Improved FMD with HIIT was maintained long-term at 6- and 12 months with home-based training. 1Ras, R et al. (2013). Int. J. Cardiology 168:344-351 Supported by Wesley Medical Research Grant 2015-17 and NHMRC Scholarship APP1133622

Vascular Dysfunction in Exfoliation Syndrome.

Both exfoliation syndrome (XFS) and exfoliation glaucoma (XFG) are associated with systemic vascular diseases and abnormalities. Although no uniform relationship between XFS/XFG and clinical systemic vascular diseases has been established across various populations, vascular dysfunction with or without clinically significant consequences has been repeatedly detected with both epidemiological and pathophysiological methods. Elevated plasma homocysteine, reduced cutaneous capillary flow reactions, damaged conduit artery dysfunction, impaired baroreflex sensitivity, parasympathetic cardiovascular neuropathy, and pathologic heart rate variability indices have all been shown in XFS and XFG. These pathophysiological alterations exceed the normal age-dependent decline and are considered strongly related to systemic elastosis and increased oxidative stress, but are not direct consequences of the presence of the risk alleles of the lysyl oxydase-like 1 gene. The mechanisms of the development of the clinically significant consequences (eg, increased frequency of myocardial dysfunction, stroke, aorta aneurism, and white matter lesions) are only partially understood. The current knowledge on vascular dysfunction in XFS/XFG is summarized in this article.

Alteration in the availability of epoxyeicosatrienoic acids contributes with NO to the development of endothelial dysfunction in conduit arteries during aging

Background and aimsThe mechanisms involved in endothelial dysfunction in humans during aging are largely unknown at the level of conduit arteries. We aimed to asses the role of NO and CYP450 epoxygenases-derived epoxyeicosatrienoic acids (EETs) in the regulation of endothelium-dependent flow-mediated dilatation of conduit arteries during aging. MethodsRadial artery diameter and mean wall shear stress were determined by echotracking coupled with Doppler in 83 subjects (19–71 years old) during a sustained flow increase induced by hand skin heating, with the brachial infusion of saline or NO-synthase and cytochrome P450 epoxygenase inhibitors (L-NNMA and fluconazole respectively). Local blood sampling was performed for the quantification of NO metabolite nitrite and EETs. ResultsThe magnitude of flow-mediated dilatation was independently and negatively correlated with age, baseline artery diameter and systolic blood pressure, and positively correlated with the increase in shear stress induced by heating. There was an increase in nitrite level during heating until the age of 35–40 years, which declined thereafter. However, the inhibitory effect of L-NMMA on flow-mediated dilatation progressively decreased during aging, demonstrating a decrease in functional NO availability. Moreover, aging progressively reduced the increase in EET level during heating as well as the inhibitory effect of fluconazole on flow-mediated dilatation. ConclusionsThese results show that aging impairs the availability of EETs and NO and epoxyeicosatrienoic acids in peripheral conduit arteries, contributing to the development of endothelial dysfunction.

Mechanisms of I/R-Induced Endothelium-Dependent Vasodilator Dysfunction.

Ischemia/reperfusion (I/R) induces leukocyte/endothelial cell adhesive interactions (LECA) in postcapillary venules and impaired endothelium-dependent, NO-mediated dilatory responses (EDD) in upstream arterioles. A large body of evidence has implicated reactive oxygen species, adherent leukocytes, and proteases in postischemic EDD dysfunction in conduit arteries. However, arterioles represent the major site for the regulation of vascular resistance but have received less attention with regard to the mechanisms underlying their reduced responsiveness to EDD stimuli in I/R. Even though leukocytes do not roll along, adhere to, or emigrate across arteriolar endothelium in postischemic intestine, recent work indicates that I/R-induced venular LECA is causally linked to EDD in arterioles. An emerging body of evidence suggests that I/R-induced EDD in arterioles occurs by a mechanism that is triggered by LECA in postcapillary venules and involves the formation of signals in the interstitium elicited by the proteolytic activity of emigrated leukocytes. This activity releases matricryptins from or exposes matricryptic sites in the extracellular matrix that interact with the integrin αvβ3 to induce mast cell chymase-dependent formation of angiotensin II (Ang II). Subsequent activation of NAD(P)H oxidase by Ang II leads to the formation of oxidants which inactivate NO and leads to eNOS uncoupling, resulting in arteriolar EDD dysfunction. This work establishes new links between LECA in postcapillary venules, signals generated in the interstitium by emigrated leukocytes, mast cell degranulation, and impaired EDD in upstream arterioles. These fundamentally important findings have enormous implications for our understanding of blood flow dysregulation in conditions characterized by I/R.

Microvascular Dysfunction as Opposed to Conduit Artery Disease Explains Sex-specific Chest Pain in Emergency Department Patients With Low to Moderate Cardiac Risk

PurposeChest pain is a common emergency department (ED) presentation that is often unexplained. Recent evidence suggests that disease of the microvessels (arterioles) as opposed to the coronary artery (conduit artery) could explain one third of these cases, particularly in women. Brachial artery reactivity (BAR) is a validated surrogate measure of coronary artery vasomotion. ObjectivesThe goal of this study was to compare brachial artery conduit vessel function (BAR) and microvascular function (postischemic peak reactive hyperemia [RH]) in subjects with and without chest pain and grouped according to sex. MethodsThis prospective cohort study was conducted from January through March 2010. Cases were patients admitted to an ED chest pain center with low to moderate risk of acute coronary syndrome; they were eligible for study if their creatinine level was <2.0 mg/dL and systolic blood pressure was >100 mm Hg or <180 mm Hg. Asymptomatic healthy volunteers on no medications were recruited as control subjects. BAR as a change in brachial artery diameter in response to transient forearm ischemia (endothelium-dependent vasodilation) and RH as a change in flow velocities were measured with a high-resolution ultrasound. Telephone follow-up visits were made at 1 month for recurrence of chest pain and recidivism. FindingsA total of 57 patients and 21 control subjects were enrolled; there was 100% follow-up at 1 month. Most patients (86%) had at least 1 cardiac risk factor. Neither BAR nor RH varied significantly between patients and control subjects (P > 0.05). Symptomatic men had lower mean BAR than women (2.67% vs 6.22%; P < 0.01), even when normalized for shear stress (P = 0.01). Conversely, women with chest pain had lower RH compared with men (2.85 vs 4.61; P = 0.01). The sex-specific differences adjusted for age and Framingham risk scores persisted for BAR (P = 0.003) and RH (P = 0.002). Of 57 patients, 53% had recurrent pain, and 4 returned to the hospital within 1 month. ImplicationsDifferences in BAR and RH in patients ruled out for myocardial infarction suggest that the pathophysiology of acute chest pain might be sex-specific. Men with chest pain exhibited lower BAR, indicating peripheral conduit artery dysfunction. Conversely, women with chest pain exhibited lower postischemic peak hyperemia, indicative of peripheral microvascular dysfunction. Sex differences in pathophysiology of chest pain and vascular dysfunction could inform development of effective therapeutics for patients with recurrent or persistent chest pain in the absence of obstructive coronary artery disease.

Endothelial dysfunction in conduit arteries and in microcirculation. Novel therapeutic approaches.

The vascular endothelium not only is a single monolayer of cells between the vessel lumen and the intimal wall, but also plays an important role by controlling vascular function and structure mainly via the production of nitric oxide (NO). The so called "cardiovascular risk factors" are associated with endothelial dysfunction, that reduces NO bioavailability, increases oxidative stress, and promotes inflammation contributing therefore to the development of atherosclerosis. The significant role of endothelial dysfunction in the development of atherosclerosis emphasizes the need for efficient therapeutic interventions. During the last years statins, angiotensin-converting enzyme inhibitors, angiotensin-receptor antagonists, antioxidants, beta-blockers and insulin sensitizers have been evaluated for their ability to restore endothelial function (Briasoulis et al., 2012). As there is not a straightforward relationship between therapeutic interventions and improvement of endothelial function but rather a complicated interrelationship between multiple cellular and sub-cellular targets, research has been focused on the understanding of the underlying mechanisms. Moreover, the development of novel diagnostic invasive and non-invasive methods has allowed the early detection of endothelial dysfunction expanding the role of therapeutic interventions and our knowledge. In the current review we present the available data concerning the contribution of endothelial dysfunction to atherogenesis and review the methods that assess endothelial function with a view to understand the multiple targets of therapeutic interventions. Finally we focus on the classic and novel therapeutic approaches aiming to improve endothelial dysfunction and the underlying mechanisms.

Interrelationship between brachial artery function and renal small artery sclerosis in chronic kidney disease

Chronic kidney disease (CKD), characterized by senile inflammation, is a risk factor for cardiovascular disease. Conduit artery function and small artery structure relate to cardiovascular disease. We examined the correlations, determinants and interrelationships of arterial indices in association with CKD in a cross-sectional study of 139 patients (60% male; mean age 44 years) with CKD (stages 3-5, 39%) who underwent a renal biopsy. Conduit artery function and small artery sclerosis were assessed by brachial artery flow-mediated dilatation (FMD) and semiquantitative evaluation of small artery intimal thickening (SA-IT), respectively. The estimated glomerular filtration rate correlated with FMD (r=0.31, P=0.0002) and inversely correlated with SA-IT (r=-0.54, P<0.0001). Multiple regression analysis showed that FMD was inversely correlated with SA-IT and vice versa. In addition, high-sensitivity C-reactive protein (hs-CRP) was significantly correlated with SA-IT, but not FMD. Multiple logistic analysis revealed that higher hs-CRP concomitant with decreased FMD was further associated with the risk of severe SA-IT compared with their individual effects. These findings suggest that both conduit artery and small artery disease develop with mutual interaction in parallel with decreased kidney function. Coexistence of inflammation and conduit artery dysfunction may be closely related to renal small artery sclerosis in patients with CKD.

Homocysteine levels are inversely associated with capillary density in men, not in premenopausal women

Homocysteine is an independent predictor of cardiovascular risk. The mechanisms underlying this link are not fully elucidated. Whereas the role of vascular dysfunction in conduit arteries is extensively studied, the role of the microcirculation in this relationship is largely unexplored. We assessed the relationship between homocysteine levels and microvascular structure and function in a healthy, population-based cohort. We cross-sectionally studied 260 participants (aged 42 years, 47% men) of the Amsterdam Growth and Health Longitudinal Study. Nailfold videocapillaroscopy was used to assess capillary density at baseline, during venous occlusion and during peak reactive hyperaemia. The relationship between tertiles of homocysteine and microvascular outcomes was evaluated using linear regression analyses, with adjustment for BMI and blood pressure. Stratified analyses were performed for men and women. In men, we observed a negative, nonlinear relationship between homocysteine and baseline capillary density, showing a lower capillary density in the highest tertile of homocysteine [adjusted B -8.65 capillaries/mm(2) (95%-CI: -16.05 to -1.25); P = 0.02]. In women, no significant associations were found between homocysteine and microvascular outcomes. In men, higher homocysteine levels are associated with a reduction in basal perfusion of skin capillaries. This finding provides a novel potential explanation for how homocysteine influences cardiovascular disease risk.

Abstract 184: Sirt3 is a Critical Mediator of Diet-induced Vasomotor Dysfunction

Increases in mitochondrial reactive oxygen species (ROS) can contribute to endothelial dysfunction in conduit arteries by reducing nitric oxide bioavailability. SIRT3 is a protein deacetylase localized to mitochondria and regulates activity of numerous electron transport chain enzymes, and can be inactivated by increases in mitochondrial ROS. Whether reductions in SIRT3 are an independent contributor to endothelial dysfunction, however, are unknown. Therefore, we hypothesized that SIRT3 null mice (SIRT3 -/- ) will have impaired relaxation to acetylcholine (MR Ach ) compared to wild-type littermates (SIRT3 +/+ ), and that this difference will be exacerbated by Western diet feeding for 3 months (TD88137, 42% of kcal from fat, 0.2% cholesterol). Endothelial function was measured using isolated organ bath chambers, and endothelium-dependent (MR Ach ) and endothelium-independent (sodium nitroprusside, MR SNP ) relaxation were measured. In contrast to our hypothesis, MR ACH was virtually identical between SIRT3 +/+ and SIRT3 -/- fed a standard chow diet (MR ACH = 68±2% and 69±3%; respectively), and MR SNP also remained unchanged between the two genotypes. In groups fed a Western diet, however, endothelium-dependent relaxation was significantly impaired in SIRT3 -/- mice compared to SIRT3 +/+ littermates (MR ACH = 49±4% and 58±3%, respectively; p&lt;0.05). MR SNP was not altered by either Western diet feeding or SIRT3 deficiency. Interestingly, impairments in MR Ach in SIRT3 -/- mice fed a Western diet were not rescued with acute incubation of apocynin (an NAD(P)H oxidase inhibitor) or mito-tempol (a mitochondria-targeted antioxidant), suggesting that chronic antioxidant and/or acetyltransferase inhibition may be required to improve vasomotor function in this model. Collectively, our data suggest that SIRT3 plays a major role in regulating endothelial function with dietary stress, and may be a useful therapeutic target to reduce cardiovascular risk.

Pharmacological inhibition ofS-nitrosoglutathione reductase improves endothelial vasodilatory function in rats in vivo

Nitric oxide (NO) exerts a wide range of cellular effects in the cardiovascular system. NO is short lived, but S-nitrosoglutathione (GSNO) functions as a stable intracellular bioavailable NO pool. Accordingly, increased levels can facilitate NO-mediated processes, and conversely, catabolism of GSNO by the regulatory enzyme GSNO reductase (GSNOR) can impair these processes. Because dysregulated GSNOR can interfere with processes relevant to cardiovascular health, it follows that inhibition of GSNOR may be beneficial. However, the effect of GSNOR inhibition on vascular activity is unknown. To study the effects of GSNOR inhibition on endothelial function, we treated rats with a small-molecule inhibitor of GSNOR (N6338) that has vasodilatory effects on isolated aortic rings and assessed effects on arterial flow-mediated dilation (FMD), an NO-dependent process. GSNOR inhibition with a single intravenous dose of N6338 preserved FMD (15.3 ± 5.4 vs. 14.2 ± 6.3%, P = nonsignificant) under partial NO synthase inhibition that normally reduces FMD by roughly 50% (14.1 ± 2.9 vs. 7.6 ± 4.4%, P < 0.05). In hypertensive rats, daily oral administration of N6338 for 14 days reduced blood pressure (170.0 ± 5.3/122.7 ± 6.4 vs. 203.8 ± 1.9/143.7 ± 7.5 mmHg for vehicle, P < 0.001) and vascular resistance index (1.5 ± 0.4 vs. 3.2 ± 1.0 mmHg · min · l(-1) for vehicle, P < 0.001), and restored FMD from an initially impaired state (7.4 ± 1.7%, day 0) to a level (13.0 ± 3.1%, day 14, P < 0.001) similar to that observed in normotensive rats. N6338 also reversed the pathological kidney changes exhibited by the hypertensive rats. GSNOR inhibition preserves FMD under conditions of impaired NO production and protects against both microvascular and conduit artery dysfunction in a model of hypertension.

Commentaries on Viewpoint: The human cutaneous circulation as a model of generalized microvascular function

Commentaries on Viewpoint: The human cutaneous circulation as a model of generalized microvascular function

Improved Vascular Function upon Pioglitazone Treatment in Type 2 Diabetes is not Associated with Changes in Mononuclear NF-κB Binding Activity

Thiazolidinediones such as pioglitazone have been shown to exert anti-inflammatory effects independent of their insulin sensitizing effects by reducing activation of the proinflammatory transcription factor NF-kappaB in animal models of experimental diabetes. Furthermore, short-term pioglitazone treatment ameliorates endothelial dysfunction in conduit arteries of patients with type 2 diabetes. Since inflammation is supposed to impair flow-mediated vasodilatation, we studied the effects of an 8-week pioglitazone intervention on endothelial function and mononuclear NF-kappaB activation in patients with type 2 diabetes. Twenty patients were included in a randomized, double-blind, placebo-controlled study receiving 30 mg pioglitazone or placebo, respectively. Flow-mediated endothelium dependent vasodilatation (FMD) of the brachial artery, NF-kappaB binding activity in peripheral blood mononuclear cells [pBMC, determined by electrophoretic mobility shift assay (EMSA)] and interleukin-6 (IL-6)-transcription rates (determined by real-time PCR) were measured at study entry and after eight weeks of intervention. Pioglitazone treatment resulted in a significant improvement of FMD (4.3%+/-3.3; p=0.003), while no effect was seen under placebo medication (2.0%+/-2.7; p=0.71). The correction of FMD was neither paralleled by a pioglitazone-dependent reduction in mononuclear NF-kappaB binding activity (DeltaNF-kappaB activity: pioglitazone: 9.2%+/-6.7, p=0.24; placebo: 5.7%+/-19.6; p=0.82) nor in NF-kappaB dependent gene transcription as determined for IL-6 (DeltaIL-6 pioglitazone: +1.8%+/-12.0, p=0.93; placebo: -0.2%+/-9.7; p=0.92). These data demonstrate for the first time that pioglitazone treatment improves endothelial dysfunction in patients with type 2 diabetes without affecting NF-kappaB binding activity and NF-kappaB dependent proinflammatory gene expression in pBMC.

2D-Spatially-Selective Real-Time Magnetic Resonance Imaging for the Assessment of Microvascular Function and Its Relation to the Cardiovascular Risk Profile

While local endothelial dysfunction of conduit arteries is well recognized as an early step in atherogenesis, contradictory observations are reported with regard to alterations in the microcirculation and their association with cardiovascular risk factors (RFs). A real-time MR approach was developed to investigate the relationship between the RFs profile and microcirculatory alterations assessed as impairment of reactive hyperemic flow in the leg circulation. The MR technique was applied to patients (n = 17, Pats1) with 1.8 +/- 0.8 RFs but without peripheral arterial occlusive disease (PAD), to age-matched healthy controls (n = 13, Con1), to young controls (n = 12, 23 +/- 4 y), and to patients with RFs and PAD (n = 8, Pats2). Superficial femoral artery (SFA) peak hyperemic flow in Pats1 was reduced vs Con1 (24.6 +/- 4.2 vs 30.4 +/- 7.3 mL min-1 100 mL-1 calf tissue, p < 0.02), and minimal vascular resistance increased incrementally with the number of RFs and with Framingham and Procam risk scores. Flow-mediated vasodilation (FMD) of the SFA was blunted in both Pats1 and Con1 (-0.5 +/- 3.4% and +0.6 +/- 3.2%, respectively, both ns vs 0). In young controls, peak hyperemic flow (30.1 +/- 3.3 mL min-1. 100 mL-1) and endothelium-independent vasodilation (9.2 +/- 10.0%) were preserved, while FMD was minimal (2.0 +/- 5.9%,p < 0.02 vs endothelium-independent vasodilation). In Pats2, peak hyperemic flow was severely reduced (12.2 +/- 3.6 mL min-1 100 mL-1, p < 0.0003 vs Con1 and Pats1), and both FMD and endothelium-independent vasodilation were absent. Reactive hyperemic flow in the SFA, reflecting microcirculatory function of the lower limb, gradually decreases with increasing cardiovascular risk suggesting a role for microvascular dysfunction in atherogenesis. The presented MR approach might become a valuable tool to study (micro)-vascular pathophysiology.

Short-Term Pioglitazone Treatment Improves Vascular Function Irrespective of Metabolic Changes in Patients With Type 2 Diabetes

To determine whether pioglitazone influences endothelial function directly, we examined in a randomized, crossover, placebo-controlled, double-blind trial the effects of 4 weeks of pioglitazone treatment in 20 male type 2 diabetic patients. We conclude that short-term pioglitazone treatment ameliorates endothelial dysfunction in conduit arteries irrespective of significant beneficial changes in plasma levels of insulin, FFA, adiponectin, or CRP in type 2 patients with diabetes. Pioglitazone, a PPARgamma agonist, not only improves insulin resistance and glycemic control but may also have additional beneficial vascular effects in patients with type 2 diabetes. Low-grade inflammation, free fatty acids, and adiponectin may play a role in modulation of vascular function. We studied the effect of 4 weeks of pioglitazone treatment on endothelial function, metabolic changes, and C-reactive protein in patients with type 2 diabetes. A randomized, crossover, placebo-controlled, double-blind trial was performed in which pioglitazone 30 mg once daily was administered to 20 patients with type 2 diabetes on oral antihyperglycemic agents for 4 weeks. Shear stress-induced flow-mediated dilation (FMD) of the brachial artery was used as outcome parameter for vascular function. Brachial artery endothelial function was significantly increased by pioglitazone treatment compared with placebo (FMD 5.4 +/- 0.5% versus 3.1 +/- 0.5%, P = 0.001). Endothelium-independent vasodilation was not different between the 2 study periods. Pioglitazone treatment reduced insulin, FFA, and C-reactive protein concentrations compared with placebo (18.3 +/- 2.4 versus 14.8 +/- 2.1 mU/L, P = 0.03; 641 +/- 46 versus 542 +/- 33 mumol/L, P = 0.04; and 3.5 +/- 0.6 mg/L versus 2.6 +/- 0.5 mg/L, P = 0.01; respectively). A significant increase in plasma adiponectin concentration (3.95 +/- 0.57 microg/mL versus 7.59 +/- 0.95 microg/mL, P = 0.002) was also observed. No correlations were found between these metabolic changes and the improvement of conduit artery endothelial function. Short-term pioglitazone treatment ameliorates endothelial dysfunction in conduit arteries irrespective of changes in insulin, FFA, adiponectin, or CRP in type 2 patients with diabetes.