Sanjay Rajagopalan

Insights Into the Mechanisms and Mediators of the Effects of Air Pollution Exposure on Blood Pressure and Vascular Function in Healthy Humans

Fine particulate matter air pollution plus ozone impairs vascular function and raises diastolic blood pressure. We aimed to determine the mechanism and air pollutant responsible. The effects of pollution on heart rate variability, blood pressure, biomarkers, and brachial flow-mediated dilatation were determined in 2 randomized, double-blind, crossover studies. In Ann Arbor, 50 subjects were exposed to fine particles (150 &mgr;g/m3) plus ozone (120 parts per billion) for 2 hours on 3 occasions with pretreatments of an endothelin antagonist (Bosentan, 250 mg), antioxidant (Vitamin C, 2 g), or placebo. In Toronto, 31 subjects were exposed to 4 different conditions (particles plus ozone, particles, ozone, and filtered air). In Toronto, diastolic blood pressure significantly increased (2.9 and 3.6 mm Hg) only during particle-containing exposures in association with particulate matter concentration and reductions in heart rate variability. Flow-mediated dilatation significantly decreased (2.0% and 2.9%) only 24 hours after particle-containing exposures in association with particulate matter concentration and increases in blood tumor necrosis factor &agr;. In Ann Arbor, diastolic blood pressure significantly similarly increased during all of the exposures (2.5 to 4.0 mm Hg), a response not mitigated by pretreatments. Flow-mediated dilatation remained unaltered. Particulate matter, not ozone, was responsible for increasing diastolic blood pressure during air pollution inhalation, most plausibly by instigating acute autonomic imbalance. Only particles from urban Toronto additionally impaired endothelial function, likely via slower proinflammatory pathways. Our findings demonstrate credible mechanisms whereby fine particulate matter could trigger acute cardiovascular events and that aspects of exposure location may be an important determinant of the health consequences.

Usefulness of Visceral Obesity (Waist/ Hip Ratio) in Predicting Vascular Endothelial Function in Healthy Overweight Adults

Vascular endothelial dysfunction (VED) is associated with obesity; however, its etiology remains controversial. By determining the predictors of fasting and postprandial endothelial function in overweight adults without other cardiovascular risk factors, we were able to investigate novel mechanisms directly linking obesity to VED. Thirty-two healthy adults (body mass index [BMI] > or =27 kg/m(2)) underwent determination of fasting low-density lipoprotein (LDL) particle size, high sensitivity C-reactive protein levels, anthropometric measurements, and endothelial function by flow-mediated dilation (FMD) of the brachial artery. Postprandial lipemia and FMD were measured 4 hours after ingestion of a high-fat meal. Blood pressures and fasting levels of lipoproteins, glucose, insulin, and fatty acids were within normal limits in all subjects. An abdominal fat pattern, as determined by an increased waist/hip ratio (WHR), was the sole significant predictor of FMD (r = -0.58, p = 0.001), despite no significant correlation between whole body obesity (BMI) and FMD. At comparable levels of BMI, obese subjects with a WHR > or =0.85 had a significantly blunted FMD compared with those with a WHR <0.85 (3.93 +/- 2.85% vs 8.34 +/- 5.47%, p = 0.016). Traditional coronary risk factors, C-reactive protein, postprandial lipemia, and LDL particle size did not predict FMD. We found no appreciable alteration in the postprandial state from fasting FMD (6.31 +/- 4.62% vs 6.25 +/- 5.47%, p = 0.95). The same results were found when women were analyzed alone. Increased abdominal adiposity determined by a simple WHR is a strong independent predictor of VED even in healthy overweight adults; this is a finding unexplained by alterations in conventional risk factors, systemic inflammation, or the atherogenic lipoprotein pattern.

Mineralocorticoid Receptor Antagonism in Experimental Atherosclerosis

Background—Aldosterone has been implicated in the effects of angiotensin II in the vasculature. We hypothesized that there is local expression of the mineralocorticoid receptor (MR) in the vasculature and that the use of a selective aldosterone receptor antagonist (SARA) improves endothelial function in early atherosclerosis. Methods and Results—New Zealand rabbits were placed on normal chow or 1% cholesterol diets, randomized to placebo or SARA (eplerenone, 50 mg/kg twice daily), and killed at the end of 6 weeks for various studies. In the hyperlipidemic (HL) chow group, there was a 2.3-fold increase in superoxide (O2·−) generation. SARA normalized O2· − generation in intact aortas and reduced NADH and NADPH oxidase activity to basal levels (0.31±0.04 and 0.27±0.02 in HL versus 0.16±0.05 and 0.07±0.02 in HL-SARA, respectively;P <0.01 by ANOVA). This was associated with improvements in peak relaxations to the endothelial-dependent agonist acetylcholine (82±6% in HL-SARA versus 61±4 in HL;P <0.01 by ANOVA; ED50 6.8×10−8 mol/L in HL-SARA and 1.2×10−7 mol/L in HL;P =NS) to near-normal levels. Vessels from the HL group demonstrated hyperreactivity to angiotensin II that could not be corrected with SARA. Plasma aldosterone levels by radioimmunoassay demonstrated a 4- to 5-fold increase in response to SARA but no differences with lipid feeding. Real-time reverse transcriptase–polymerase chain reaction studies revealed expression of MR in the aorta of HL rabbits and those of controls. Conclusions—MR antagonism improves endothelial function and reduces O2·− generation in diet-induced atherosclerosis. Targeting aldosterone by blocking its receptor has potential antiatherosclerotic effects.

Abnormal brachial artery flow-mediated vasodilation in young adults with major depression.

Depressive illness in patients without traditional risk factors for coronary artery disease is associated with striking abnormalities of endothelial function and elevation of circulating markers of atherosclerosis propensity. Further studies are needed to define the mechanisms that underlie these observations.

Expert position paper on air pollution and cardiovascular disease

Air pollution has wide-ranging and deleterious effects on human health and is a major issue for the global community. The Global Burden of Disease study has described the worldwide impact of air pollution with as many as 3.1 million of 52.8 million all-cause and all-age deaths being attributable to ambient air pollution in the year 2010.1 Moreover, ambient air pollution ranked ninth among the modifiable disease risk factors, being listed above other commonly recognized factors, such as low physical activity, a high-sodium diet, high cholesterol, and drug use. Finally, air pollution accounts for 3.1% of global disability-adjusted life years, an index that measures the time spent in states of reduced health.1nnAlthough it is intuitive that air pollution is an important stimulus for the development and exacerbation of respiratory diseases, such as asthma, chronic obstructive pulmonary disease, and lung cancer, there is generally less public awareness of its substantial impact on cardiovascular disease. Historically, the 1952 Great Smog of London led to an increase in cardiovascular death as well as deaths due to respiratory disease. Subsequent studies in the 1990s, such as the Harvard Six Cities2 and American Cancer Society cohort studies,2,3 established an enduring positive association between long-term exposure to air pollution and total and cardiovascular mortality, mainly due to coronary artery disease.4 In Europe, the first study that supported this association between long-term exposure and mortality was the Netherlands Cohort Study on Diet and Cancer.5 Associations with cardiovascular morbidity and mortality are also seen with short-term (e.g. day-to-day fluctuations) pollutant exposures of residents in large urban areas worldwide, including the United States of America6 …

Chronic Iron Administration Increases Vascular Oxidative Stress and Accelerates Arterial Thrombosis

Background—Iron overload has been implicated in the pathogenesis of ischemic cardiovascular events. However, the effects of iron excess on vascular function and the thrombotic response to vascular injury are not well understood. Methods and Results—We examined the effects of chronic iron dextran administration (15 mg over 6 weeks) on thrombosis, systemic and vascular oxidative stress, and endothelium-dependent vascular reactivity in mice. Thrombus generation after photochemical carotid artery injury was accelerated in iron-loaded mice (mean time to occlusive thrombosis, 20.4±8.5 minutes; n=10) compared with control mice (54.5±35.5 minutes, n=10, P =0.009). Iron loading had no effect on plasma clotting, vessel wall tissue factor activity, or ADP-induced platelet aggregation. Acute administration of dl-cysteine, a reactive oxygen species scavenger, completely abrogated the effects of iron loading on thrombus formation, suggesting that iron accelerated thrombosis through a pro-oxidant mechanism. Iron loading enhanced both systemic and vascular reactive oxygen species production. Endothelium-dependent vasorelaxation was impaired in iron-loaded mice, indicating reduced NO bioavailability. Conclusions—Moderate iron loading markedly accelerates thrombus formation after arterial injury, increases vascular oxidative stress, and impairs vasoreactivity. Iron-induced vascular dysfunction may contribute to the increased incidence of ischemic cardiovascular events that have been associated with chronic iron overload.

Altered Tetrahydrobiopterin Metabolism in Atherosclerosis. Implications for Use of Oxidized Tetrahydrobiopterin Analogues and Thiol Antioxidants

Objective—Tetrahydrobiopterin (BH4) is of fundamental importance for the normal function of endothelial NO synthase. The purpose of this study was to investigate the effects of hyperlipidemia on vascular BH4 levels and the effect of supplementation with sepiapterin in the presence and absence of N-acetylcysteine (NAC). Methods and Results—New Zealand White rabbits were fed normal chow (normocholesterolemic [NC] group) or hyperlipidemic chow (hyperlipidemic [HL] group) for 8 to 10 weeks. Mean cholesterol levels were 1465±333 and 53±17 mg/dL in the HL and NC group, respectively. Markedly diminished BH4 levels were found in the HL group compared with the NC group, but these levels could be restored after 6 hours of incubation with sepiapterin. Peak relaxations to acetylcholine and A23187 were impaired in the HL group. Supplementation with sepiapterin resulted in a further diminution of relaxation in the HL but not NC group. Incubation with NAC for 6 hours failed to raise BH4 levels, whereas NAC in conjunction with sepiapterin raised BH4 levels ≈221-fold. However, this increase did not improve relaxations to A23187 and acetylcholine. Conclusions—Prolonged exposure to sepiapterin impairs vasorelaxation in hyperlipidemia despite repletion of endogenous BH4. Antioxidant thiols do not correct this impairment. These studies have implications for the use of sepiapterin in the correction of vasomotor tone in atherosclerosis.

Sustained Vascular Endothelial Growth Factor Delivery Enhances Angiogenesis and Perfusion in Ischemic Hind Limb

PurposeWe hypothesized that sustained delivery of vascular endothelial growth factor (VEGF) using a polymer [85:15 poly(lactide-co-glycolide) (PLG)] would enhance angiogenesis and improve perfusion of ischemic tissue.MethodsC57BL/6J mice (n = 20/group) underwent unilateral hind limb ischemia surgery and were randomized to groups of no scaffold implantation (∅-Implant), unloaded scaffold implantation (Empty-PLG), or implantation of scaffolds incorporating 3xa0μg of VEGF165 (PLG-VEGF). Endpoints included laser Doppler perfusion imaging (LDPI, ischemic/nonischemic limb, %), local vessel counts, immunohistochemistry for CD31, and α-smooth muscle actin. In vitro release kinetics of VEGF from PLG was also measured.ResultsPLG-VEGF resulted in improved lower extremity perfusion vs. controls as measured by LDPI% at 7, 14, 21, and 28 days (p < 0.05). PLG-VEGF was associated with significantly greater percentage of vessels staining for CD31 and α-smooth muscle actin compared to the Empty-PLG or ∅-Implant (p < 0.05 for both).ConclusionsThe PLG-VEGF scaffolds resulted in sustained VEGF delivery, improved tissue perfusion, greater capillary density, and more mature vasculature compared to the controls. The sustained-release PLG polymer vehicle is a promising delivery system for therapeutic neovascularization applications.

Regional angiogenesis with vascular endothelial growth factor (VEGF) in peripheral arterial disease: Design of the RAVE trial

BACKGROUNDnPatients with intermittent claudication caused by infrainguinal atherosclerosis have limited pharmacologic options Therapeutic angiogenesis is a novel treatment approach that seeks to improve perfusion of ischemic limbs by the induction of collateral vessel formation. This trial is a phase 2 randomized double-blind placebo-controlled proof of concept trial that will use an intramuscular adenoviral gene transfer approach of vascular endothelial growth factor, 121 isoform (Ad(GV)VEGF(121.10)) to patients with severe IC caused by infrainguinal disease.nnnMETHODSnThis is a phase 2, double-blind, randomized, placebo-controlled, dose-finding, multicenter study. Patients with severe intermittent claudication caused by infrainguinal atherosclerosis predominantly involving the superficial femoral artery confirmed with imaging studies that meet inclusion criteria will be stratified on the basis of the presence or absence of diabetes mellitus and randomized in a 1:1:1 fashion to low dose (4 x 10(9) particle units), high dose (4 x 10(10) particle units), or placebo arms (35-36 patients per group). Subjects are required to have exercise-limiting IC in the index extremity during 2 qualifying exercise treadmill tests, with peak walking times between 1 and 10 minutes. A single dose of Ad(GV)VEGF(121.10) will be administered as 20 intramuscular injections throughout the area of the lower limb requiring collateralization.nnnRESULTSnThe primary efficacy parameter for the Regional Angiogenesis With Vascular Endothelial Growth Factor (RAVE) trial is the change in peak walking time at 12 weeks compared with baseline. The sample size is expected to provide an 80% power to detect a difference of 1.5 minutes between any of the 2 treatment groups and the placebo group. Secondary efficacy parameters include claudication onset time, hemodynamic effects of therapy assessed with ankle-brachial index, assessment of physical impairment, and health-related quality of life as measured with the Walking Impairment Questionnaire and SF-36 Health Survey. All randomized patients will also be evaluated for safety.

“Environmental Hypertensionology” The Effects of Environmental Factors on Blood Pressure in Clinical Practice and Research

J Clin Hypertens (Greenwich). 2011;13:836–842. ©2011 Wiley Periodicals, Inc.