Impaired Endothelium-dependent Dilation Research Articles

Low dietary sodium intake is associated with enhanced vascular endothelial function in older adults with elevated baseline systolic blood pressure

Aging and elevated systolic blood pressure (SBP) are associated with impaired endothelium‐dependent dilation (EDD) and increased salt sensitivity. High dietary sodium impairs EDD in young rodents. We hypothesized that otherwise healthy middle‐aged and older adults (MA/O) with elevated systolic blood pressure (SBP; 130‐159 mmHg) consuming lower dietary sodium (DS) would demonstrate enhanced EDD compared with peers consuming higher DS. EDD was measured using flow‐mediated dilation (FMD) in MA/O (65±1 yr, mean±S.E.) who self‐reported lower (n=12; 73±6 mmol/d) or higher (n=13, 144±6 mmol/d) DS intake. Subjects were matched for potentially confounding characteristics including age, body mass, body mass index, SBP, diastolic BP, plasma lipids, fasting glucose, daily activity, peak oxygen uptake, and non‐DS related dietary profile. Brachial artery FMD was 34% higher (5.0±0.5 vs. 3.3±0.5 %, p<0.05) in subjects consuming low sodium, whereas endothelium‐independent dilation (brachial dilation to sublingual nitroglycerine) did not differ between groups (p=0.24). In the overall sample, FMD was inversely related to DS intake (r=‐0.53; p<0.01). These results suggest that DS intake may modulate EDD in M/O adults with elevated SBP. DS restriction may be an effective intervention to preserve vascular endothelial function with aging.NIH AG013038, AG022241, AG006537, AG000279

Pulmonary Nanoparticle Exposure Disrupts Systemic Microvascular Nitric Oxide Signaling

We have shown that pulmonary nanoparticle exposure impairs endothelium dependent dilation in systemic arterioles. However, the mechanism(s) through which this effect occurs is/are unclear. The purpose of this study was to identify alterations in the production of reactive species and endogenous nitric oxide (NO) after nanoparticle exposure, and determine the relative contribution of hemoproteins and oxidative enzymes in this process. Sprague-Dawley rats were exposed to fine TiO2 (primary particle diameter approximately 1 microm) and TiO2 nanoparticles (primary particle diameter approximately 21 nm) via aerosol inhalation at depositions of 4-90 microg per rat. As in previous intravital experiments in the spinotrapezius muscle, dose-dependent arteriolar dilations were produced by intraluminal infusions of the calcium ionophore A23187. Nanoparticle exposure robustly attenuated these endothelium-dependent responses. However, this attenuation was not due to altered microvascular smooth muscle NO sensitivity because nanoparticle exposure did not alter arteriolar dilations in response to local sodium nitroprusside iontophoresis. Nanoparticle exposure significantly increased microvascular oxidative stress by approximately 60%, and also elevated nitrosative stress fourfold. These reactive stresses coincided with a decreased NO production in a particle deposition dose-dependent manner. Radical scavenging, or inhibition of either myeloperoxidase or nicotinamide adenine dinucleotide phosphate oxidase (reduced) oxidase partially restored NO production as well as normal microvascular function. These results indicate that in conjunction with microvascular dysfunction, nanoparticle exposure also decreases NO bioavailability through at least two functionally distinct mechanisms that may mutually increase local reactive species.

B6D2F1 Mice Are a Suitable Model of Oxidative Stress-Mediated Impaired Endothelium-Dependent Dilation With Aging

To determine if B6D2F1 mice represent a suitable model of oxidative stress-mediated impaired endothelium-dependent dilation (EDD) with aging, mice were studied at 6.9 +/- 0.3 and 31.9 +/- 0.6 months. EDD to acetylcholine (ACh) was 26% (p < .001) and 12% (p < .001) lower, respectively, in isolated carotid (n = 10-11) and femoral (n = 10) arteries from older mice, and reductions in arterial pressure to systemic ACh infusion were smaller in older mice (n = 6-10; p < .01). Nitrotyrosine was marked in aorta of older mice (p < .05, n = 4). Superoxide production in carotid arteries was greater (p < .05), and TEMPOL restored dilation in carotid arteries and systemically in older mice. N(G)-nitro-l-arginine methyl ester (l-NAME) reduced carotid artery dilation in young more than older mice, whereas TEMPOL restored the effects of l-NAME in older mice. Carotid artery stiffness was increased in older compared with young mice (p = .04). Our results provide the first comprehensive evidence that B6D2F1 mice are a useful model for investigating mechanisms of reduced nitric oxide-dependent, oxidative stress-associated EDD and increased arterial stiffness with aging.

Modulation of Vascular Endothelial Function by Low-Density Lipoprotein Cholesterol With Aging: Influence of Habitual Exercise

Aging is associated with reduced endothelium-dependent dilation (EDD) and increased risk for cardiovascular disease (CVD), but the mechanisms are incompletely understood. Clinically elevated plasma low-density lipoprotein cholesterol (LDL-C) is associated with impaired EDD. The purpose of this study was to determine whether circulating LDL-C within the "normal" range modulates EDD in healthy older adults and whether young age or habitual aerobic exercise protects against this adverse effect. In 83 healthy men with optimal/near optimal LDL-C (<130 mg/dl) or borderline high LDL-C (130-159 mg/dl), EDD (brachial artery flow-mediated dilation, FMD), and endothelium-independent dilation (sublingual glyceryl trinitrate, GTN) were assessed. FMD was 35% lower in older nonexercising men with borderline high LDL-C vs. optimal/near optimal LDL-C (3.1 +/- 0.5 vs. 4.8 +/- 0.4%Delta, P < 0.05), whereas the GTN response did not differ (P = 0.86). In contrast, FMD was similar between groups of young nonexercising men and between groups of older exercising men differing in LDL-C (P = 0.89-0.95). FMD was inversely related to LDL-C among the older nonexercising men (r = -0.43, P < 0.001), whereas there was no relation in the other groups (P > 0.05). Borderline high plasma LDL-C is associated with impaired EDD in older sedentary men, but not in young sedentary or older exercising men. Thus, modest elevations in plasma LDL-C within the normal range may contribute to the increased risk of CVD in sedentary older men by exacerbating vascular endothelial dysfunction, whereas resistance to this adverse influence may help explain the enhanced endothelial function and reduced CVD risk associated with young age and regular aerobic exercise.

Reduced vascular tetrahydrobiopterin (BH4) and endothelial function with ageing: is it time for a chronic BH4 supplementation trial in middle‐aged and older adults?

Reduced vascular tetrahydrobiopterin (BH₄) and endothelial function with ageing: is it time for a chronic BH₄ supplementation trial in middle‐aged and older adults?

Weight Loss Alone Improves Conduit and Resistance Artery Endothelial Function in Young and Older Overweight/Obese Adults

Obesity is associated with vascular endothelial dysfunction, as indicated by impaired endothelium-dependent dilation. Presently there is no direct evidence that energy intake-restricted weight loss alone improves conduit or resistance artery endothelium-dependent dilation, the mechanisms involved, or whether improvements differ with patient age. A total of 40 overweight or obese (body mass index: >or=25<40 kg/m(2)) nondiabetic men and women aged 21 to 69 years completed 12 weeks of reduced energy intake (n=26; 15 male) or attention control (n=14; 9 male) and 4 weeks of weight maintenance (randomized trial). Energy intake restriction reduced estimated total energy intake (33%), body weight (10.5%), total and abdominal body fat, plasma leptin, oxidized low-density lipoprotein, and improved several metabolic risk factors. Brachial artery flow-mediated dilation was increased by 30% (6.0+/-0.7% versus 7.9+/-0.7%Delta; P=0.01; n=17). Peak forearm blood flow during intrabrachial artery infusion of acetylcholine was increased by 26% (16.8+/-1.4 versus 21.1+/-1.9 mL/100 mL per minute; P<0.05; n=15); this was inversely related to the reduction in the abdominal visceral:subcutaneous fat ratio (r=-0.46; P<0.05) and was abolished by inhibition of NO synthesis with N(G)-monomethyl-L-arginine. Improvements in endothelium-dependent dilation were not related to age: mean increases in subjects >50 years of age were similar to or greater than those <50 years of age. Energy intake-restricted weight loss alone is an effective intervention for improving peripheral conduit and resistance artery endothelial function in young and older overweight/obese adults. The improvements in resistance artery function are mediated by an increase in NO bioavailability and are related to reductions in abdominal visceral fat.

Anti‐inflammatory treatment restores endothelium‐dependent dilation in older mice by increasing nitric oxide bioavailability

Chronic low‐grade inflammation may contribute to impaired endothelium‐dependent dilation (EDD) with aging, but evidence is limited. To gain further insight, we studied isolated carotid arteries from young (Y, 4–7 mo) and older (O, 29–34 mo) B6D2F1 mice (n=6–8/group). Maximal carotid artery dilation to acetylcholine (ACh), an endothelium‐dependent dilator, was 24% lower in O (76±3 vs. 99±1%, mean±SE, P=0.001). Administration of the nitric oxide (NO) synthase inhibitor NG‐nitro‐L arginine methyl ester (L‐NAME) decreased ACh dilation less (P=0.02) in O (−20% to 56±8%) vs. Y (−51% to 48±8%). Treatment with the anti‐inflammatory compound sodium salicylate (200 mg/kg/d via diet for 5 d, n=5/group) resulted in similar ACh dilation (P=0.98) in O and Y mice before (O: 97±2 vs. Y: 99±1%) and after (O: 45±15 vs. Y: 43±9%) L‐NAME. Inhibition of superoxide with TEMPOL markedly improved EDD in untreated, but not in sodium salicylate treated O mice or in Y mice. Carotid artery dilation to the endothelium‐independent dilator sodium nitroprusside was not different in Y and O and was not affected by sodium salicylate (P=0.93). These preliminary results support the hypothesis that the development of vascular inflammation plays a key role in impaired EDD with aging in B6D2F1 mice through an oxidative stress‐mediated reduction in NO bioavailability. Supported by NIH AG006537, AG013038 and AG022241

Nanoparticle inhalation augments particle-dependent systemic microvascular dysfunction

BackgroundWe have shown that pulmonary exposure to fine particulate matter (PM) impairs endothelium dependent dilation in systemic arterioles. Ultrafine PM has been suggested to be inherently more toxic by virtue of its increased surface area. The purpose of this study was to determine if ultrafine PM (or nanoparticle) inhalation produces greater microvascular dysfunction than fine PM. Rats were exposed to fine or ultrafine TiO2 aerosols (primary particle diameters of ~1 μm and ~21 nm, respectively) at concentrations which do not alter bronchoalveolar lavage markers of pulmonary inflammation or lung damage.ResultsBy histopathologic evaluation, no significant inflammatory changes were seen in the lung. However, particle-containing macrophages were frequently seen in intimate contact with the alveolar wall. The spinotrapezius muscle was prepared for in vivo microscopy 24 hours after inhalation exposures. Intraluminal infusion of the Ca2+ ionophore A23187 was used to evaluate endothelium-dependent arteriolar dilation. In control rats, A23187 infusion produced dose-dependent arteriolar dilations. In rats exposed to fine TiO2, A23187 infusion elicited vasodilations that were blunted in proportion to pulmonary particle deposition. In rats exposed to ultrafine TiO2, A23187 infusion produced arteriolar constrictions or significantly impaired vasodilator responses as compared to the responses observed in control rats or those exposed to a similar pulmonary load of fine particles.ConclusionThese observations suggest that at equivalent pulmonary loads, as compared to fine TiO2, ultrafine TiO2 inhalation produces greater remote microvascular dysfunction.

Platelet-associated NAD(P)H oxidase contributes to the thrombogenic phenotype induced by hypercholesterolemia

Elevated cholesterol levels promote proinflammatory and prothrombogenic responses in venules and impaired endothelium-dependent arteriolar dilation. Although NAD(P)H oxidase-derived superoxide has been implicated in the altered vascular responses to hypercholesterolemia, it remains unclear whether this oxidative pathway mediates the associated arteriolar dysfunction and platelet adhesion in venules. Platelet and leukocyte adhesion in cremasteric postcapillary venules and arteriolar dilation responses to acetylcholine were monitored in wild-type (WT), Cu,Zn-superoxide dismutase transgenic (SOD-TgN), and NAD(P)H oxidase-knockout (gp91 phox−/−) mice placed on a normal (ND) or high-cholesterol (HC) diet for 2 weeks. HC elicited increased platelet and leukocyte adhesion in WT mice versus ND. Cytosolic subunits of NAD(P)H oxidase (p47phox and p67phox) were expressed in platelets. This was not altered by hypercholesterolemia; however, platelets and leukocytes from HC mice exhibited elevated generation of reactive oxygen species compared to ND mice. Hypercholesterolemia-induced leukocyte recruitment was attenuated in SOD-TgN–HC and gp91 phox−/−–HC mice. Recruitment of platelets derived from WT–HC mice in venules of SOD-TgN–HC or gp91 phox−/−–HC recipients was comparable to ND levels. Adhesion of SOD-TgN–HC platelets paralleled the leukocyte response and was attenuated in SOD-TgN–HC recipients, but not in WT–HC recipients. However, gp91 phox−/−–HC platelets exhibited low levels of adhesion comparable to those of WT–ND in both hypercholesterolemic gp91 phox−/− and WT recipients. Arteriolar dysfunction was evident in WT–HC mice, compared to WT–ND. Overexpression of SOD or, to a lesser extent, gp91 phox deficiency restored arteriolar vasorelaxation responses toward WT–ND levels. These findings reveal a novel role for platelet-associated NAD(P)H oxidase in producing the thrombogenic phenotype in hypercholesterolemia and demonstrate that NAD(P)H oxidase-derived superoxide mediates the HC-induced arteriolar dysfunction.

Inhalation of Ultrafine Titanium Dioxide Augments Particle‐Dependent Microvascular Dysfunction

We have shown that pulmonary exposure to fine particulate matter (PM) impairs endothelium dependent dilation in systemic arterioles. Ultrafine PM has been suggested to be more toxic by virtue of its increased surface area. The purpose of this study was to determine if ultrafine PM inhalation produces greater microvascular dysfunction than fine PM. Rats were exposed to fine or ultrafine TiO2 via inhalation (mean particle diameters of ~1 μm, and ~123 nm, respectively) at concentrations relevant to ambient air pollution. The spinotrapezius muscle was prepared for in vivo microscopy 24 hours after pulmonary exposures. Intraluminal infusion of the Ca2+ ionophore A23187 was used to evaluate endothelium dependent arteriolar dilation. In control rats, A23187 infusion produced dose-dependent arteriolar dilations. In rats exposed to fine TiO2, A23187 infusion elicited vasodilations that were blunted in proportion to pulmonary particle deposition. In rats exposed to ultrafine TiO2, A23187 infusion produced arteriolar constrictions or significantly impaired vasodilator responses as compared to the responses observed in control rats or those exposed to an identical pulmonary load of fine particles. Various tissues were harvested for pathological analysis and measurements of pulmonary load and peripheral particle deposition. These observations suggest that at equivalent pulmonary loads, as compared to fine TiO2, ultrafine TiO2 inhalation produces greater remote microvascular dysfunction.

P-selectin-mediated adhesion impairs endothelium-dependent arteriolar dilation in hypercholesterolemic mice

Hypercholesterolemia is associated with an attenuation of endothelium-dependent dilation in arterioles and an increase in leukocyte and platelet adhesion in venules. The proximity of closely paired arterioles and venules is thought to facilitate heat and mass transport between the two and could be involved in transport of inflammatory and/or vasoactive mediators from venule to arteriole. In the current study, we tested the hypothesis that the impaired arteriolar dilation associated with hypercholesterolemia might be dependent on P-selectin-dependent blood cell adhesion in the closely paired venules. Leukocyte and platelet recruitment in venules and the endothelium-dependent response to bradykinin in second-order arterioles were observed in the mouse intestinal submucosa using intravital microscopy. Four weeks of a high-cholesterol diet decreased bradykinin-induced arteriolar dilation more dramatically in closely paired arterioles than in distantly paired arterioles. The dysfunctional arteriolar dilation of closely paired arterioles in hypercholesterolemic mice was significantly improved when the experiments were repeated in P-selectin-deficient mice (given the high-cholesterol diet) or in hypercholesterolemic mice injected with a P-selectin monoclonal antibody. A similar improvement in dilation of closely paired arterioles was attained in hypercholesterolemic mice given the superoxide dismutase mimetic Tempol. These findings indicate that hypercholesterolemia-induced increases in venular leukocyte and platelet adhesion might contribute to the impaired endothelium-dependent dilation of closely paired arterioles via a mechanism that is distance limited and dependent on P-selectin and superoxide.

Impaired flow-mediated dilation with age is not explained by l-arginine bioavailability or endothelial asymmetric dimethylarginine protein expression

Aging is associated with a decline in vascular endothelial function, manifesting in part as impaired flow-mediated arterial dilation (FMD), but the underlying mechanisms are uncertain. Impaired FMD may be mediated in part by a decrease in synthesis of nitric oxide by endothelial nitric oxide synthase, and in clinical populations this has been attributed to competitive inhibition of l-arginine binding sites by asymmetric dimethylarginine (ADMA). If this mechanism is involved in the age-associated decline in FMD, increasing l-arginine concentration may swing the competitive balance in favor of l-arginine binding, restoring nitric oxide synthesis, and enhancing FMD in older humans. To test this hypothesis, we measured FMD (brachial ultrasound) in 10 younger (21 +/- 1 yr) and 12 older healthy men and women (60 +/- 2 yr) following infusion of vehicle or vehicle + l-arginine. Baseline FMD in the older subjects was only approximately 60% of that in the younger subjects (P = 0.002). l-Arginine did not significantly increase FMD in either group despite 23-fold (older) and 19-fold (younger) increases in plasma l-arginine concentrations (P < 0.0001 vs. control). Protein expression (immunofluorescence) in vascular endothelial cells showed that ADMA and the enzyme isoform that controls its degradation, dimethylarginine dimethylaminohydrolase II, were not different in the younger and older subjects. Endothelium-independent vasodilation (sublingual nitroglycerine) was not different between age groups or conditions. We conclude that acutely increasing plasma concentrations of l-arginine do not significantly improve brachial artery FMD in healthy older subjects and thus does not restore the age-associated loss of FMD. Together with the finding that endothelial cell ADMA protein expression was not increased in older adults, these findings suggest that competitive inhibition of l-arginine binding sites on endothelial nitric oxide synthase by ADMA is not an important mechanism contributing to impaired conduit artery endothelium-dependent dilation with aging in healthy humans.

Hypertrophy of Cerebral Arterioles in Mice Deficient in Expression of the Gene for CuZn Superoxide Dismutase

Reactive oxygen species are believed to be an important determinant of vascular growth. We examined effects of genetic deficiency of copper-zinc superoxide dismutase (CuZnSOD; SOD1) on structure and function of cerebral arterioles. Systemic arterial pressure (SAP) and cross-sectional area of the vessel wall (CSA) and superoxide (O2-) levels (relative fluorescence of ethidium [ETH]) were examined in maximally dilated cerebral arterioles in mice with targeted disruption of one (+/-) or both (-/-) genes encoding CuZnSOD. Wild-type littermates served as controls. Vasodilator responses were tested in separate groups of mice. CSA and ETH were significantly increased (P<0.05) in both CuZnSOD+/- and CuZnSOD-/- mice (CSA=435+/-24 and 541+/-48 microm2; ETH=18+/-1 and 34+/-2%) compared with wild-type mice (CSA=327+/-28 microm2; ETH=6%). Furthermore, the increases in CSA and ETH relative to wild-type mice were significantly greater (P<0.05) in CuZnSOD-/- mice than in CuZnSOD+/- mice (CSA=108 versus 214 microm2; ETH=12 versus 28%). In addition, dilatation of cerebral arterioles in response to acetylcholine, but not nitroprusside, was reduced by approximately 25% in CuZnSOD+/- (P<0.075) and 50% in CuZnSOD-/- mice (P<0.05) compared with wild-type mice. Cerebral arterioles in CuZnSOD+/- and CuZnSOD-/- mice undergo marked hypertrophy. These findings provide the first direct evidence in any blood vessel that CuZnSOD normally inhibits vascular hypertrophy suggesting that CuZnSOD plays a major role in regulation of cerebral vascular growth. The findings also suggest a gene dosing effect of CuZnSOD for increases in O2-, induction of cerebral vascular hypertrophy and impaired endothelium-dependent dilatation.

Ultrafine particulate matter inhalation induces remote microvascular dysfunction

We have shown that pulmonary exposure to fine particulate matter (PM) impairs endothelium dependent dilation in systemic arterioles. The purpose of this study was to determine if ultrafine PM inhalation produces greater microvascular dysfunction than fine PM. Our inhalation chamber creates stable TiO2 aerosols at concentrations up to 20 mg/m3. TiO2 is a well characterized particle devoid of soluble metals. Rats were exposed to fine or ultrafine TiO2 (mean particle diameters of ~1 μm, and ~160 nm, respectively) at concentrations to produce equivalent pulmonary loads of 0.25 mg/rat. The spinotrapezius muscle was prepared for in vivo microscopy 24 hours after pulmonary exposure. Intraluminal infusion of the Ca2+ ionophore A23187 was used to evaluate endothelium dependent arteriolar dilation (micropipette ejection pressures of 5, 10, 20 and 40 psi). In control rats, A23187 infusion produced dose dependent arteriolar dilations that were near maximal at 40 psi. In rats exposed to fine TiO2, A23187 infusion failed to elicit a significant arteriolar response. In rats exposed to ultrafine TiO2, A23187 infusion produced dose dependent arteriolar constrictions that were significantly different from the responses observed in rats exposed to fine TiO2. These observations suggest that at equivalent pulmonary loads, compared to fine TiO2, ultrafine TiO2 inhalation produces greater remote microvascular dysfunction. This effect may be due to alterations in endothelial integrity and/or signaling. Support: Health Effects Institute #4730

Age‐related impaired endothelium‐dependent dilation is associated with increased vascular endothelial cell protein expression of NF‐kB in humans

Chronic vascular inflammation is involved in all stages atherosclerosis including endothelial dysfunction. Age, a major atherogenic risk factor, is considered a state of systemic chronic inflammation and associated with impaired endothelium dependent-dilation (EDD), the central feature of endothelial dysfunction. The main aims of this study were to determine if: 1) vascular (venous) endothelial cell protein expression (ECPE) of NF-κB (quantitative immunofluorescence), a major redox-sensitive transcription factor that mediates expression of inflammatory mediators, is increased with aging; and 2) the age-related decline in EDD is associated with increased endothelial NF-κB. Endothelial cell protein expression of NF-κB was 52 % greater in older (n=11, 64±2 years, MEAN±SE) compared with young (n=8, 24±1 years) subjects (0.21±0.02 vs. 0.44±0.07 ECPE/HUVEC; P<0.001). Brachial artery flow-mediated dilation (FMD), a measure of EDD, was 60 % lower in older than young subjects (3.1±0.6 vs. 7.6±0.8 %, P<0.001), whereas endothelium independent dilation (EID) was similar in both groups. Brachial artery FMD was inversely related to NF-κB in the pool sample (r=−0.70, P=0.008), but not to EID. These preliminary results indicate that endothelial NF-κB protein expression in increased with age and related to impaired EDD in healthy humans. Supported by NIH AG006537, AG013038, and AG022241.

Systemic Microvascular Dysfunction and Inflammation after Pulmonary Particulate Matter Exposure

The epidemiologic association between pulmonary exposure to ambient particulate matter (PM) and cardiovascular dysfunction is well known, but the systemic mechanisms that drive this effect remain unclear. We have previously shown that acute pulmonary exposure to PM impairs or abolishes endothelium-dependent arteriolar dilation in the rat spinotrapezius muscle. The purpose of this study was to further characterize the effect of pulmonary PM exposure on systemic microvascular function and to identify local inflammatory events that may contribute to these effects. Rats were intratracheally instilled with residual oil fly ash (ROFA) or titanium dioxide at 0.1 or 0.25 mg/rat 24 hr before measurement of pulmonary and systemic microvascular responses. In vivo microscopy of the spinotrapezius muscle was used to study systemic arteriolar responses to intraluminal infusion of the Ca2+ ionophore A23187 or iontophoretic abluminal application of the adrenergic agonist phenylephrine (PHE). Leukocyte rolling and adhesion were quantified in venules paired with the studied arterioles. Histologic techniques were used to assess pulmonary inflammation, characterize the adherence of leukocytes to systemic venules, verify the presence of myeloperoxidase (MPO) in the systemic microvascular wall, and quantify systemic microvascular oxidative stress. In the lungs of rats exposed to ROFA or TiO2, changes in some bronchoalveolar lavage markers of inflammation were noted, but an indication of cellular damage was not found. In rats exposed to 0.1 mg ROFA, focal alveolitis was evident, particularly at sites of particle deposition. Exposure to either ROFA or TiO2 caused a dose-dependent impairment of endothelium-dependent arteriolar dilation. However, exposure to these particles did not affect microvascular constriction in response to PHE. ROFA and TiO2 exposure significantly increased leukocyte rolling and adhesion in paired venules, and these cells were positively identified as polymorphonuclear leukocytes (PMNLs). In ROFA- and TiO2-exposed rats, MPO was found in PMNLs adhering to the systemic microvascular wall. Evidence suggests that some of this MPO had been deposited in the microvascular wall. There was also evidence for oxidative stress in the microvascular wall. These results indicate that after PM exposure, the impairment of endothelium-dependent dilation in the systemic microcirculation coincides with PMNL adhesion, MPO deposition, and local oxidative stress. Collectively, these microvascular observations are consistent with events that contribute to the disruption of the control of peripheral resistance and/or cardiac dysfunction associated with PM exposure.

Endothelial dysfunction occurs in peripheral circulation patients with acute and stable coronary artery disease

Atherosclerosis is a diffuse, systemic process. In addition, acute coronary syndromes (ACS) are associated with inflammatory marker elevations that are hypothesized to affect the function of nonculprit coronary as well as peripheral vessels. We investigated whether femoral vascular reactivity and/or fibrinolytic capacity are impaired in ACS patients over and above any dysfunction associated with stable coronary artery disease. Patients undergoing diagnostic coronary angiography (n = 42 total, 14 patients/group) were recruited into three groups as follows: 1) stable coronary syndromes (SAP group), 2) ACS as defined by rest angina with ECG changes and troponin rise (ACS group), and 3) angiographically normal coronary arteries (control group). After diagnostic coronary angiography, femoral artery endothelial and smooth muscle function were assessed by infusing acetylcholine (ACh) and nitroglycerin (GTN), and tissue-type plasminogen activator (t-PA) release across the femoral circulation was measured as the difference between arterial and venous concentrations before and after ACh and GTN stimulation. There were no significant differences between groups in relevant baseline characteristics apart from significantly higher C-reactive protein levels and reduced net t-PA release in the ACS group at baseline (P < 0.05). The ACS and SAP groups had equivalent angiographic severity of coronary artery disease. Endothelium-dependent dilatation was significantly higher in control individuals (14.9 +/- 9.1%; P < 0.001) compared with either stable patients (2.3 +/- 8.1%) or those with unstable syndromes (2.6 +/- 8.9%, who were similar to each other; P = not significant). Although baseline t-PA release was impaired in the ACS patients (0.09 +/- 0.06 compared with 0.39 +/- 0.33 and 0.49 +/- 0.56 ng/ml; P = 0.03), stimulation of t-PA release by ACh and GTN occurred only in the control subjects and not in the ACS or SAP patients. Coronary artery disease is associated with impaired endothelium-dependent dilatation and impaired stimulation of t-PA release in the systemic circulation. These aspects of endothelial dysfunction, however, were equally severe in acute and chronic coronary syndrome patients.

The effect of glucose and mental stress on cutaneous microvascular endothelial function

Glucose and mental stress, independently, have been found to impair arterial endothelial function (an indicator of vascular health). The present study sought to determine whether the combination of glucose and stress would have a greater effect on microvascular endothelial function than each on its own. To assess endothelial function, surges in skin blood flow (reactive hyperemia), following the release of cuff pressure to the upper arm at 200 mmHg for 5 min, were measured with laser Doppler flowmetry in 40 young, healthy females. Endothelial function did not change significantly following a 5-min mathematics stressor or the consumption of 75 g of glucose. However, the combination of glucose and stress impaired endothelium-dependent dilatation 30 min after glucose consumption. These findings suggest that combinations of vascular risk factors may be more threatening to cardiovascular health than singularly occurring factors.

Impaired Progenitor Cell Activity in Age-Related Endothelial Dysfunction

We investigated whether human age-related endothelial dysfunction is accompanied by quantitative and qualitative alterations of the endothelial progenitor cell (EPC) pool. Circulating progenitor cells with an endothelial phenotype contribute to the regeneration and repair of the vessel wall. An association between the loss of endothelial integrity and EPC modification may provide a background to study the mechanistic nature of such age-related vascular changes. In 20 old and young healthy individuals (61 +/- 2 years and 25 +/- 1 year, respectively) without major cardiovascular risk factors, endothelial function, defined by flow-mediated dilation of the brachial artery via ultrasound, as well as the number and function of EPCs isolated from peripheral blood, were determined. Older subjects had significantly impaired endothelium-dependent dilation of brachial artery (flow-mediated dilation [FMD] 5.2 +/- 0.5% vs. 7.1 +/- 0.6%; p < 0.05). Endothelium-independent dilation after glycerol trinitrate (GTN) was not different, but the FMD/GTN ratio was significantly lower in old subjects (49 +/- 4% vs. 37 +/- 3%; p < 0.05), suggesting endothelial dysfunction. There were no differences in the numbers of circulating EPCs, defined as CD34/KDR or CD133/KDR double-positive cells in peripheral blood. In contrast, lower survival (39 +/- 6 cells/mm(2) vs. 65 +/- 11 cells/mm(2); p < 0.05), migration (80 +/- 12 vs. 157 +/- 16 cells/mm(2); p < 0.01), and proliferation (0.20 +/- 0.04 cpm vs. 0.44 +/- 0.07 cpm; p < 0.05) implicate functional impairment of EPCs from old subjects. The FMD correlated univariately with EPC migration (r = 0.52, p < 0.05) and EPC proliferation (r = 0.49, p < 0.05). Multivariate analysis showed that both functional features represent independent predictors of endothelial function. Maintenance of vascular homeostasis by EPCs may be attenuated with age based on functional deficits rather than depletion of CD34/KDR or CD133/KDR cells.

Ascorbic acid improves impaired venous and arterial endothelium-dependent dilation in smokers1

To compare the acute effects of ascorbic acid on vasodilation of veins and arteries in vivo. Twenty-six healthy non-smokers and 23 healthy moderate smokers were recruited in this study. The dorsal hand vein compliance technique and flow-mediated dilation were used. Dose-response curves to bradykinin and sodium nitroprusside were constructed to test the endothelium-dependent and -independent relaxation before and after acute infusion of ascorbic acid. Smokers had an impaired venodilation with bradykinin compared with non-smokers (68.3%+/-13.2% vs 93.7%+/-20.1%, respectively; P<0.05). Ascorbic acid administration in the dorsal hand vein significantly increased the venodilation with bradykinin in smokers (68.3%+/-13.2% vs 89.5%+/-6.3% before and after infusion, respectively; P<0.05) but not in non-smokers (93.7%+/-20.1% vs 86.4%+/-12.4% before and after infusion, respectively). Similarly, the arterial response in smokers had an impaired endothelium-dependent dilation compared with that in non-smokers (8.8%+/-2.7% vs 15.2%+/-2.3%, respectively; P<0.05) and ascorbic acid restored this response in smokers (8.8%+/-2.7% vs 18.7%+/-6.5% before and after infusion, respectively; P<0.05), but no difference was seen in non-smokers (15.2%+/-2.3% vs 14.0%+/-4.4% before and after infusion, respectively). The endothelium-independent dilation did not differ in both the groups studied. No important hemodynamic change was detected using the Portapress device. Smokers had impaired endothelium-dependent vasodilation responsiveness in both arterial and venous systems. Ascorbic acid restores this responsiveness in smokers.