Simon D. Robinson

Diesel Exhaust Inhalation Causes Vascular Dysfunction and Impaired Endogenous Fibrinolysis

Background— Although the mechanisms are unknown, it has been suggested that transient exposure to traffic-derived air pollution may be a trigger for acute myocardial infarction. The study aim was to investigate the effects of diesel exhaust inhalation on vascular and endothelial function in humans. Methods and Results— In a double-blind, randomized, cross-over study, 30 healthy men were exposed to diluted diesel exhaust (300 &mgr;g/m3 particulate concentration) or air for 1 hour during intermittent exercise. Bilateral forearm blood flow and inflammatory factors were measured before and during unilateral intrabrachial bradykinin (100 to 1000 pmol/min), acetylcholine (5 to 20 &mgr;g/min), sodium nitroprusside (2 to 8 &mgr;g/min), and verapamil (10 to 100 &mgr;g/min) infusions 2 and 6 hours after exposure. There were no differences in resting forearm blood flow or inflammatory markers after exposure to diesel exhaust or air. Although there was a dose-dependent increase in blood flow with each vasodilator (P<0.0001 for all), this response was attenuated with bradykinin (P<0.05), acetylcholine (P<0.05), and sodium nitroprusside (P<0.001) infusions 2 hours after exposure to diesel exhaust, which persisted at 6 hours. Bradykinin caused a dose-dependent increase in plasma tissue plasminogen activator (P<0.0001) that was suppressed 6 hours after exposure to diesel (P<0.001; area under the curve decreased by 34%). Conclusions— At levels encountered in an urban environment, inhalation of dilute diesel exhaust impairs 2 important and complementary aspects of vascular function in humans: the regulation of vascular tone and endogenous fibrinolysis. These important findings provide a potential mechanism that links air pollution to the pathogenesis of atherothrombosis and acute myocardial infarction.

Noninvasive Targeted Imaging of Matrix Metalloproteinase Activation in a Murine Model of Postinfarction Remodeling

Background— Time-dependent activation of matrix metalloproteinases (MMPs) after myocardial infarction (MI) contributes to adverse left ventricular (LV) remodeling; however, noninvasive methods to monitor this process serially are needed. Methods and Results— MMP-targeted radiotracers were developed that displayed selective binding kinetics to the active MMP catalytic domain. Initial nonimaging studies were performed with a 111In-labeled MMP-targeted radiotracer (111In-RP782) and negative control compound (111In-RP788) in control mice (Ctrl) and in mice 1 week after surgically induced MI. Localization of 111In-RP782 was demonstrated within the MI by microautoradiography. A 334±44% increase (P<0.001 versus Ctrl) in relative retention of 111In-RP782 was confirmed by gamma well counting of myocardium. Subsequent high-resolution dual-isotope planar and hybrid micro–single-photon emission computed tomography/CT imaging studies with an analogous 99mTc-labeled MMP-targeted radiotracer (99mTc-RP805) and 201Tl demonstrated favorable biodistribution and clearance kinetics of 99mTc-RP805 for in vivo cardiac imaging, with robust retention 1 to 3 weeks after MI in regions of decreased 201Tl perfusion. Gamma well counting yielded a similar ≈300% increase in relative myocardial retention of 99mTc-RP805 in MI regions (Ctrl, 102±9%; 1 week, 351±77%; 2 weeks, 291±45%; 3 weeks, 292±41%; P<0.05 versus Ctrl). Myocardial uptake in the MI region was also significantly increased ≈5-fold when expressed as percentage injected dose per gram tissue. There was also a significant 2-fold increase in myocardial activity in remote regions relative to control mice, suggesting activation of MMPs in regions remote from the MI. Conclusions— This novel noninvasive targeted MMP radiotracer imaging approach holds significant diagnostic potential for in vivo localization of MMP activation and tracking of MMP-mediated post-MI remodeling.

Increased arterial stiffness in patients with chronic obstructive pulmonary disease; a mechanism for increased cardiovascular risk

Rationale: Chronic obstructive pulmonary disease (COPD) is associated with a 2–3-fold increase in the risk of ischaemic heart disease, stroke and sudden death. The mechanisms responsible for this association are not clear and appear to be independent of smoking history. Objective: We test the hypothesis that patients with COPD have increased arterial stiffness and blood pressure in comparison with age and smoking matched controls. Methods: In a prospective case control study, we recruited 102 patients with COPD and 103 healthy controls matched for age and smoking status. Patients were assessed by clinical history and spirometry, with arterial stiffness and blood pressure determined using radial artery applanation tonometry and sphygmomanometry. Results: Patients with COPD had increased arterial stiffness compared with matched controls, with elevated augmentation pressure (17 (1) vs 14 (1) mm Hg; p = 0.005) and a reduced time to wave reflection (131 (1) vs 137 (2) ms; p = 0.004). These differences were associated with increases in both diastolic (82 (1) vs 78 (1) mm Hg; p = 0.005) and systolic blood pressure (147 (2) vs 132 (2) mm Hg; p<0.001). Serum C reactive protein concentrations were threefold higher in patients (6.1 (0.9) vs 2.3 (0.4) mg/l; p = 0.001). Data are presented as mean (SEM). Conclusions: Patients with COPD have increased arterial stiffness and blood pressure in comparison with controls matched for age and smoking status. We speculate that increased systemic inflammation and vascular dysfunction could potentially explain the excess cardiovascular morbidity and mortality associated with COPD.

Exposure to Concentrated Ambient Particles Does Not Affect Vascular Function in Patients with Coronary Heart Disease

Background Exposure to fine particulate air pollution is associated with increased cardiovascular morbidity and mortality. We previously demonstrated that exposure to dilute diesel exhaust causes vascular dysfunction in humans. Objectives We conducted a study to determine whether exposure to ambient particulate matter causes vascular dysfunction. Methods Twelve male patients with stable coronary heart disease and 12 age-matched volunteers were exposed to concentrated ambient fine and ultrafine particles (CAPs) or filtered air for 2 hr using a randomized, double-blind cross-over study design. We measured peripheral vascular vasomotor and fibrinolytic function, and inflammatory variables—including circulating leukocytes, serum C-reactive protein, and exhaled breath 8-isoprostane and nitrotyrosine—6–8 hr after both exposures. Results Particulate concentrations (mean ± SE) in the exposure chamber (190 ± 37 μg/m3) were higher than ambient levels (31 ± 8 μg/m3) and levels in filtered air (0.5 ± 0.4 μg/m3; p < 0.001). Chemical analysis of CAPs identified low levels of elemental carbon. Exhaled breath 8-isoprostane concentrations increased after exposure to CAPs (16.9 ± 8.5 vs. 4.9 ± 1.2 pg/mL, p < 0.05), but markers of systemic inflammation were largely unchanged. Although there was a dose-dependent increase in blood flow and plasma tissue plasminogen activator release (p < 0.001 for all), CAPs exposure had no effect on vascular function in either group. Conclusions Despite achieving marked increases in particulate matter, exposure to CAPs—low in combustion-derived particles—did not affect vasomotor or fibrinolytic function in either middle-aged healthy volunteers or patients with coronary heart disease. These findings contrast with previous exposures to dilute diesel exhaust and highlight the importance of particle composition in determining the vascular effects of particulate matter in humans.

Air Pollution and Atherothrombosis

Observational studies have consistently demonstrated an association between exposure to air pollution and increased cardiovascular morbidity and mortality. This association is strongest for particulate matter (PM), of which combustion-derived particulate is an important component. Studies assessing the effects of PM exposure in vitro and in vivo have provided insight into the biological mechanisms underlying these observations. In this review we discuss the potential for inhaled particles to impact on the development and progression of atherosclerosis. Oxidative stress and inflammation are central to both the toxicology of PM and the pathogenesis of atherosclerosis. It is possible that nanoparticulates or soluble components of PM may translocate into the bloodstream, resulting in direct effects on atherosclerotic plaque stability, the vascular endothelium, platelet function, and thrombosis. We summarize the latest experimental research and relate this to current understanding of the role of inflammation and vascular dysfunction in the pathogenesis of atherothrombosis. Ongoing research in this area will continue to provide insight into the adverse vascular effects of PM, with the possibility of therapeutic interventions to reduce the impact of environmental air pollution on cardiovascular disease a realistic goal.

Endothelial Fibrinolytic Capacity Predicts Future Adverse Cardiovascular Events in Patients With Coronary Heart Disease

Objective—The endothelium-derived fibrinolytic factor tissue plasminogen activator (t-PA) is a major determinant of vessel patency after coronary plaque rupture and thrombosis. We assessed whether endothelial fibrinolytic capacity predicts atherothrombotic events in patients with coronary heart disease. Methods and Results—Plasma t-PA and plasminogen activator inhibitor (PAI)-1 concentrations were measured during intrabrachial substance P infusion in 98 patients with angiographically proven stable coronary heart disease. Forearm blood flow was measured during infusion of substance P and sodium nitroprusside. Cardiovascular events (cardiovascular death, myocardial infarction [MI], ischemic stroke [CVA], and emergency hospitalization for unstable angina) were determined during 42 months of follow-up. Patients experiencing a cardiovascular event (n=19) had similar baseline characteristics to those free of events. Substance P caused a dose-dependent increase in plasma t-PA concentrations (P<0.001). However, net t-PA release was 72% lower in the patients who experienced death, MI, or CVA, and 48% lower in those who suffered death, MI, CVA or hospitalization for unstable angina (P<0.05). Major adverse cardiovascular events were most frequent in those with the lowest fibrinolytic capacity (P=0.03 for trend); patients with the lowest quartile of t-PA release had the highest rate of adverse events (P=0.01). Conclusion—Endothelial fibrinolytic capacity, as measured by stimulated t-PA release, predicts the future risk of adverse cardiovascular events in patients with coronary heart disease. We suggest that endothelial fibrinolytic capacity is a powerful novel determinant of cardiovascular risk.

Atherosclerosis Plaque Heterogeneity and Response to Therapy Detected by In Vivo Molecular Imaging of Matrix Metalloproteinase Activation

Matrix metalloproteinases (MMPs) play a key role in the development of atherosclerosis and its complications. In vivo detection and quantification of MMP activation can help track the propensity to complications and response to therapy. We sought to establish an in vivo imaging approach for monitoring MMP activation in atherosclerotic mouse aorta and use it to assess the response to dietary modification. Method: Apolipoprotein-deficient mice were fed normal chow or a high-fat diet (HFD) for up to 3 mo or a HFD for 2 mo, followed by 1 mo on normal chow. Then they underwent micro-SPECT/CT, along with autoradiography and oil red O staining of tissues. Results: After 3 mo of HFD, there was considerable atherosclerosis in the aorta. In vivo micro-SPECT/CT using RP782 (an 111In-labeled tracer targeting activated MMPs) showed a heterogeneous pattern of tracer uptake along the aorta. Heterogeneity of RP782 uptake was confirmed by autoradiography, and specificity was demonstrated using excess unlabeled precursor. Tracer uptake quantified by micro-SPECT significantly correlated with uptake quantified by autoradiography. Comparison of oil red O staining with autoradiography demonstrated areas of discordance between plaque presence and tracer uptake. HFD withdrawal led to significant reduction in RP782 uptake beyond the effect on plaque area. MMP expression and macrophage infiltration were similarly heterogeneous along the aorta and significantly reduced after withdrawal from the HFD. Finally, RP782 uptake significantly correlated with aortic macrophage content. Conclusion: Molecular imaging of MMP activation reveals the heterogeneity of atherosclerotic plaques and is a useful tool for tracking plaque biology and response to therapy.

Cardiovascular effects of tumour necrosis factor α antagonism in patients with acute myocardial infarction: a first in human study

Objective The inflammatory cytokine, tumour necrosis factor α (TNF-α), exerts deleterious cardiovascular effects. We wished to determine the effects of TNF-α antagonism on endothelial function and platelet activation in patients with acute myocardial infarction. Design and setting and patients A double-blind, parallel group, randomised controlled trial performed in a tertiary referral cardiac centre. 26 patients presenting with acute myocardial infarction randomised to receive an intravenous infusion of etanercept (10 mg) or saline placebo. Main outcome measures Leucocyte count, plasma cytokine concentrations, flow cytometric measures of platelet activation and peripheral vasomotor and fibrinolytic function were determined before and 24 h after study intervention. Results Consistent with effective conjugation of circulating TNF-α, plasma TNF-α concentrations increased in all patients following etanercept (254±15 vs 0.12±0.02 pg/ml; p<0.0001), but not saline infusion. Etanercept treatment reduced neutrophil (7.4±0.6 vs 8.8±0.6×109 cells/l; p=0.03) and plasma interleukin-6 concentrations (5.8±2.0 vs 10.6±4.0 pg/ml; p=0.012) at 24 h but increased platelet–monocyte aggregation (30±5 vs 20±3%; p=0.02). Vasodilatation in response to substance P, acetylcholine and sodium nitroprusside, and acute tissue plasminogen activator release were unaffected by either treatment (p>0.1 for all). Conclusions Following acute myocardial infarction, etanercept reduces systemic inflammation but increases platelet activation without affecting peripheral vasomotor or fibrinolytic function. We conclude that TNF-α antagonism is unlikely to be a beneficial therapeutic strategy in patients with acute myocardial infarction.

Cardiovascular effects of tumour necrosis factor α antagonism in patients with acute myocardial infarction

Objective The inflammatory cytokine, tumour necrosis factor α (TNF-α), exerts deleterious cardiovascular effects. We wished to determine the effects of TNF-α antagonism on endothelial function and platelet activation in patients with acute myocardial infarction. Design and setting and patients A double-blind, parallel group, randomised controlled trial performed in a tertiary referral cardiac centre. 26 patients presenting with acute myocardial infarction randomised to receive an intravenous infusion of etanercept (10 mg) or saline placebo. Main outcome measures Leucocyte count, plasma cytokine concentrations, flow cytometric measures of platelet activation and peripheral vasomotor and fibrinolytic function were determined before and 24 h after study intervention. Results Consistent with effective conjugation of circulating TNF-α, plasma TNF-α concentrations increased in all patients following etanercept (254±15 vs 0.12±0.02 pg/ml; p<0.0001), but not saline infusion. Etanercept treatment reduced neutrophil (7.4±0.6 vs 8.8±0.6×109 cells/l; p=0.03) and plasma interleukin-6 concentrations (5.8±2.0 vs 10.6±4.0 pg/ml; p=0.012) at 24 h but increased platelet–monocyte aggregation (30±5 vs 20±3%; p=0.02). Vasodilatation in response to substance P, acetylcholine and sodium nitroprusside, and acute tissue plasminogen activator release were unaffected by either treatment (p>0.1 for all). Conclusions Following acute myocardial infarction, etanercept reduces systemic inflammation but increases platelet activation without affecting peripheral vasomotor or fibrinolytic function. We conclude that TNF-α antagonism is unlikely to be a beneficial therapeutic strategy in patients with acute myocardial infarction.

Phosphodiesterase type 5 inhibition does not reverse endothelial dysfunction in patients with coronary heart disease

Objectives: To investigate whether sildenafil citrate, a selective phosphodiesterase type 5 inhibitor, may improve endothelial vasomotor and fibrinolytic function in patients with coronary heart disease. Design: Randomised double blind placebo controlled crossover study. Patients and methods: 16 male patients with coronary heart disease and eight matched healthy men received intravenous sildenafil or placebo. Bilateral forearm blood flow and fibrinolytic parameters were measured by venous occlusion plethysmography and blood sampling in response to intrabrachial infusions of acetylcholine, substance P, sodium nitroprusside, and verapamil. Main outcome measures: Forearm blood flow and acute release of tissue plasminogen activator. Results: Mean arterial blood pressure fell during sildenafil infusion from a mean (SEM) of 92 (1) to 82 (1) mm Hg in patients and from 94 (1) to 82 (1) mm Hg in controls (p < 0.001 for both). Sildenafil increased endothelium independent vasodilatation with sodium nitroprusside (p < 0.05) but did not alter the blood flow response to acetylcholine or verapamil in patients or controls. Substance P caused a dose dependent increase in plasma tissue plasminogen activator antigen concentrations (p < 0.01) that was unaffected by sildenafil in either group. Conclusions: Sildenafil does not improve peripheral endothelium dependent vasomotor or fibrinolytic function in patients with coronary heart disease. Phosphodiesterase type 5 inhibitors are unlikely to reverse the generalised vascular dysfunction seen in patients with coronary heart disease.