Ni Bai

Particulate matter exposure induces persistent lung inflammation and endothelial dysfunction

Epidemiologic and animal studies have shown that exposure to particulate matter air pollution (PM) is a risk factor for the development of atherosclerosis. Whether PM-induced lung and systemic inflammation is involved in this process is not clear. We hypothesized that PM exposure causes lung and systemic inflammation, which in turn leads to vascular endothelial dysfunction, a key step in the initiation and progression of atherosclerosis. New Zealand White rabbits were exposed for 5 days (acute, total dose 8 mg) and 4 wk (chronic, total dose 16 mg) to either PM smaller than 10 mum (PM(10)) or saline intratracheally. Lung inflammation was quantified by morphometry; systemic inflammation was assessed by white blood cell and platelet counts and serum interleukin (IL)-6, nitric oxide, and endothelin levels. Endothelial dysfunction was assessed by vascular response to acetylcholine (ACh) and sodium nitroprusside (SNP). PM(10) exposure increased lung macrophages (P<0.02), macrophages containing particles (P<0.001), and activated macrophages (P<0.006). PM(10) increased serum IL-6 levels in the first 2 wk of exposure (P<0.05) but not in weeks 3 or 4. PM(10) exposure reduced ACh-related relaxation of the carotid artery with both acute and chronic exposure, with no effect on SNP-induced vasodilatation. Serum IL-6 levels correlated with macrophages containing particles (P=0.043) and ACh-induced vasodilatation (P=0.014 at week 1, P=0.021 at week 2). Exposure to PM(10) caused lung and systemic inflammation that were both associated with vascular endothelial dysfunction. This suggests that PM-induced lung and systemic inflammatory responses contribute to the adverse vascular events associated with exposure to air pollution.

Changes in atherosclerotic plaques induced by inhalation of diesel exhaust.

OBJECTIVE Exposure to particulate matter air pollution may be an independent risk factor for cardiovascular morbidity and mortality; however, the biological mechanisms are unclear. We hypothesize that exposure to diesel exhaust (DE), an important source of traffic-related particulate air pollution, promotes changes of atherosclerotic plaque component that may lead to plaque vulnerability. METHODS AND RESULTS 30-week old ApoE knockout mice fed with regular chow inhaled DE (at 200 μg/m(3) of particulate) or filtered-air (control) for 7 weeks (6 h/day, 5 days/week) (12 mice/group). Total number of alveolar macrophages (p<0.01) and alveolar macrophages positive for particles (p<0.0001) were more than 8-fold higher after DE inhalation than the control. DE inhalation caused 1.5 to 3-fold increases in plaque lipid content (p<0.02), cellularity (p<0.02), foam cell formation (p<0.04), and smooth muscle cell content (p<0.05). The expression of oxidative stress markers, iNOS, CD36, and nitrotyrosine was significantly increased by 1.5 to 2-fold in plaques, with enhanced systemic lipid and DNA oxidation (p<0.02). Increased foam cells and the expression of iNOS (R(2)=0.72, p=0.0081) and CD36 (R(2)=0.49, p=0.015) in plaques were positively correlated with the magnitude of DE exposure. CONCLUSIONS Exposure to DE promotes changes in atherosclerotic plaques characteristic of unstable vulnerable plaques. Increased systemic and plaque oxidative stress markers suggest that these changes in plaques could be due to DE-induced oxidative stress.

Particulate Matter Induces Translocation of IL-6 from the Lung to the Systemic Circulation

The biological mechanisms responsible for an association between elevated concentrations of ambient particulate matter (PM) and increased cardiovascular morbidity and mortality remain unclear. Our laboratory showed that exposure to PM induces systemic inflammation that contributes to vascular dysfunction. This study was designed to determine whether the lung is a major source of systemic inflammatory mediators, using IL-6 as a surrogate marker. We also sought to determine the impact on vascular dysfunction after exposure to PM of less than 10 μm in diameter (PM(10)). C57BL/6 mice were intratracheally exposed to a single instillation of PM(10) (10 or 200 μg) or saline. Four hours or 24 hours after exposure, venous and arterial blood samples were simultaneously collected from the right atrium and descending aorta. Concentrations of IL-6 were measured in bronchoalveolar lavage fluid (BALF) and serum samples. Vascular functional responses to acetylcholine (ACh) and phenylephrine were measured in the abdominal aorta. Concentrations of IL-6 in BALF samples were increased at 4 and 24 hours after exposure to PM(10). At baseline, concentrations of IL-6 in venous blood were higher than those in arterial blood. Exposure to PM(10) reversed this arteriovenous gradient, 4 hours after exposure. The relaxation responses of the abdominal aorta to ACh decreased 4 hours after exposure to 200 μg PM(10). In IL-6 knockout mice, the instillation of recombinant IL-6 increased IL-6 concentrations in the blood, and exposure to PM(10) did not cause vascular dysfunction. These results support our hypothesis that exposure to PM(10) increases pulmonary inflammatory mediators that translocate to the circulation, contributing to systemic inflammation, with downstream effects such as vascular dysfunction.

Acute lung injury induces cardiovascular dysfunction: Effects of IL-6 and budesonide/formoterol

Acute lung injury (ALI) is associated with systemic inflammation and cardiovascular dysfunction. IL-6 is a biomarker of this systemic response and a predictor of cardiovascular events, but its possible causal role is uncertain. Inhaled corticosteroids and long-acting β2 agonists (ICS/LABA) down-regulate the systemic expression of IL-6, but whether they can ameliorate the cardiovascular dysfunction related to ALI is uncertain. We sought to determine whether IL-6 contributes to the cardiovascular dysfunction related to ALI, and whether budesonide/formoterol ameliorates this process. Wild-type mice were pretreated for 3 hours with intratracheal budesonide, formoterol, or both, before LPS was sprayed into their tracheas. IL-6-deficient mice were similarly exposed to LPS. Four hours later, bronchoalveolar lavage fluid (BALF) and serum were collected, and endothelial and cardiac functions were measured, using wire myography of the aortic tissue and echocardiography, respectively. LPS significantly impaired vasodilatory responses to acetylcholine (P < 0.001) and cardiac output (P = 0.002) in wild-type but not IL-6-deficient mice. Intratracheal instillations of exogenous IL-6 into IL-6-deficient mice restored these impairments (vasodilatory responses to acetylcholine, P = 0.005; cardiac output, P = 0.025). Pretreatment with the combination of budesonide and formoterol, but not either alone, ameliorated the vasodilatory responses to acetylcholine (P = 0.018) and cardiac output (P < 0.001). These drugs also attenuated the rise in the systemic expression of IL-6 (P < 0.05) related to LPS. IL-6 contributes to the cardiovascular dysfunction related to LPS, and pretreatment with budesonide/formoterol reduces the systemic expression of IL-6 and improves cardiovascular dysfunction. ICS/LABA may reduce acute cardiovascular events related to ALI.

Statins attenuate the development of atherosclerosis and endothelial dysfunction induced by exposure to urban particulate matter (PM10).

Exposure to ambient air particulate matter (particles less than 10μm or PM10) has been shown to be an independent risk factor for the development and progression of atherosclerosis. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have well-established anti-inflammatory properties. The aim of this study was to determine the impact of statins on the adverse functional and morphological changes in blood vessels induced by PM10. New Zealand White rabbits fed with a high fat diet were subjected to balloon injury to their abdominal aorta followed by PM10/saline exposure for 4weeks±lovastatin (5mg/kg/day) treatment. PM10 exposure accelerated balloon catheter induced plaque formation and increased intimal macrophages and lipid accumulation while lovastatin attenuated these changes and promoted smooth muscle cell recruitment into plaques. PM10 impaired vascular acetylcholine (Ach) responses and increased vasoconstriction induced by phenylephrine as assessed by wire myograph. Supplementation of nitric oxide improved the impaired Ach responses. PM10 increased the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in blood vessels and increased the plasma levels of endothelin-1 (ET-1). Incubation with specific inhibitors for iNOS, COX-2 or ET-1 in the myograph chambers significantly improved the impaired vascular function. Lovastatin decreased the expression of these mediators in atherosclerotic lesions and improved endothelial dysfunction. However, lovastatin was unable to reduce blood lipid levels to the baseline level in rabbits exposed to PM10. Taken together, statins protect against PM10-induced cardiovascular disease by reducing atherosclerosis and improving endothelial function via their anti-inflammatory properties.

Exposure to diesel exhaust up-regulates iNOS expression in ApoE knockout mice

UNLABELLED Traffic related particulate matter air pollution is a risk factor for cardiovascular events; however, the biological mechanisms are unclear. We hypothesize that diesel exhaust (DE) inhalation induces up-regulation of inducible nitric oxide synthase (iNOS), which is known to contribute to vascular dysfunction, progression of atherosclerosis and ultimately cardiovascular morbidity and mortality. METHODS ApoE knockout mice (30-week) were exposed to DE (at 200 μg/m³ of particulate matter) or filtered-air (control) for 7 weeks (6 h/day, 5 days/week). iNOS expression in the blood vessels and heart was evaluated by immunohistochemistry and western blotting analysis. To examine iNOS activity, thoracic aortae were mounted in a wire myograph, and vasoconstriction stimulated by phenylephrine (PE) was measured with and without the presence of the specific inhibitor for iNOS (1400 W). NF-κB (p65) activity was examined by ELISA. The mRNA expression of iNOS and NF-κB (p65) was determined by real-time PCR. RESULTS DE exposure significantly enhanced iNOS expression in the thoracic aorta (4-fold) and heart (1.5 fold). DE exposure significantly attenuated PE-stimulated vasoconstriction by ~20%, which was partly reversed by 1400 W. The mRNA expression of iNOS and NF-κB was significantly augmented after DE exposure. NF-κB activity was enhanced 2-fold after DE inhalation, and the augmented NF-κB activity was positively correlated with iNOS expression (R²=0.5998). CONCLUSIONS We show that exposure to DE increases iNOS expression and activity possibly via NF-κB-mediated pathway. We suspect that DE exposure-caused up-regulation of iNOS contributes to vascular dysfunction and atherogenesis, which could ultimately lead to urban air pollution-associated cardiovascular morbidity and mortality.

Statins Reduce Ambient Particulate Matter-Induced Lung Inflammation by Promoting the Clearance of Particulate Matter < 10 μm From Lung Tissues

BACKGROUND The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) suppress ambient particulate matter, 10 μm (PM(10) )-induced inflammatory response in vitro. The aim of this study was to determine the effect of statins on PM(10) -induced lung inflammation in vivo. METHODS New Zealand white rabbits were exposed to either PM(10) (1.0 mg/kg) or saline by direct intratracheal instillation three times a week for 4 weeks lovastatin 5.0 mg/kg/d. BAL fluid was assessed for cell counts and proinflammatory cytokine levels. Lung inflammation was quantified using immunohistochemical techniques and morphometric methods. Ex vivo phagocytosis assay of alveolar macrophages using PM 10 particles was performed. Distribution of PM(10) particles in lung tissues and draining lymph nodes was quantified morphometrically to evaluate the clearance of PM(10) particles. RESULTS PM(10) exposure increased the production of IL-6 and IL-8, promoted the recruitment of macrophages and polymorphonuclear leukocytes into the lung, and activated these recruited leukocytes. Lovastatin significantly suppressed all these effects. Lovastatin increased the phagocytic activity of macrophages and promoted the migration of PM 10 -laden macrophages to the regional lymph nodes. CONCLUSIONS Lovastatin attenuates the PM(10) -induced recruitment and activation of alveolar macrophages and polymorphonuclear leukocytes, reduces local proinflammatory cytokine production, and promotes the clearance of PM(10) particles from lung tissues to regional lymph nodes. These novel pleiotropic properties of statins are most likely to contribute to the downregulation of PM(10) -induced lung inflammation.

Endotoxin-induced cardiovascular dysfunction in mice: effect of simvastatin

Lung infections are associated with acute lung injury (ALI), systemic inflammation, and vascular events. Clinical studies suggest that statins improve health outcomes of patients with pneumonia and ALI. The mechanisms by which this occurs are unknown. The aim of this study was to determine whether statins attenuate systemic inflammation and cardiovascular dysfunction related to ALI in mice. Simvastatin (SS; 20 mg/kg) or vehicle solution was instilled intraperitoneally into mice 24 h before and again just prior to intratracheal LPS instillation (1 μg/g). These mice were then anesthetized with 2.0% isoflurane and underwent a short surgical procedure to instill LPS. Four hours later, IL-6 levels in bronchoalveolar lavage fluid and in arterial and venous serum were measured. Cardiac function was evaluated using 2-D echocardiography, and endothelial function was determined using wire myography on aortic sections. LPS induced a significant increase in serum IL-6 levels. SS reduced venous (P = 0.040) but not arterial concentrations of IL-6 (P = 0.112). SS improved the maximal vasodilatory response of the aorta to ACh (P = 0.004) but not to sodium nitroprusside (P = 1.000). SS also improved cardiac output (P = 0.023). Vasodilatory response to ACh was impaired when aorta from untreated mice was incubated with ex vivo IL-6 (P = 0.004), whereas in the aorta from mice pretreated with SS, the vasodilatory response did not change with IL-6 incubation (P = 0.387). SS significantly improved LPS-induced cardiovascular dysfunction possibly by reducing systemic expression of IL-6 and its downstream signaling pathways. These findings may explain how statins improve health outcomes in patients with ALI.

Diesel exhaust inhalation induces heat shock protein 70 expression in vivo

Exposure to urban air pollution is an independent risk factor for increased cardiovascular diseases. Heat shock protein 70 (HSP70) has been implicated in the pathogenesis of vascular dysfunction and cardiovascular diseases. This study has been designed to determine whether inhalation of urban air induces HSP70 expression in the lung and blood as well as the association of HSP70 and air pollution-induced vascular dysfunction. Apolipoprotein E (Apo-E) deficient mice were exposed to diesel exhaust (DE) either acutely (3 days, 200 or 400 µg/m3 for 6 h/day) or chronically (7 weeks, 200 or 400 µg/m3 for 6 h/day). HSP70 was measured in the lung using immunohistochemistry, and in the plasma by ELISA. Abdominal aorta rings were used to determine vascular functional responses. Chronic DE-exposure increased the fraction of HSP70 positive alveolar macrophages (AM) that was related to the fraction of particle-laden AM in the lung (r2 = 0.48, p < 0.01). Chronic DE-exposure increased plasma HSP70 levels and reduced blood vessel responses to phenylephrine (PE). The fraction of particle-laden HSP70 positive AM was associated with abnormal vasoconstriction responses to PE induced by DE-exposure (r2 = 0.12, p = 0.02). Our results show that chronic inhalation of DE increases HSP70 expression in the lung and systemic circulation, and we postulate that HSP70 possibly contributes to air pollution induced vascular dysfunction and cardiovascular diseases.

Systemic and vascular effects of circulating diesel exhaust particulate matter

Abstract Objective: Numerous studies have found an association between transiently increased particulate matter air pollution and acute adverse cardiovascular health effects; however, the mechanisms underlying these effects are not clear. Translocation of ultra-fine ambient particulate matter has been proposed to play a key role in these acute side effects. This study was designed to determine the contribution of circulating (translocated) diesel exhaust particles (DEPs) to the systemic and vascular effects. Methods: C57 mice (10-week) received intravenous DEPs via tail vein injection. Following 1-h post-injection, inflammatory cytokines (IL-1β, IL-6 and TNF-α), peripheral blood cell counts, band cell counts, aortic endothelial function and vascular constriction were assessed. Thoracic aortae were isolated, and endothelial function was examined by measuring acetylcholine (ACh) and sodium nitroprusside (SNP)-stimulated vascular relaxation using a wire myograph. In addition, phenylephrine (PE)-stimulated vasoconstriction was also measured. The amount of DEPs deposited and trapped in tissues (the spleen, liver, lungs and heart) were quantified. Results: Acute systemic DEP exposure caused a significant increase in TNF-α, peripheral neutrophil and band cell counts. ACh and SNP-induced relaxation were not affected by acute systemic DEP exposure, neither was PE-stimulated constriction. There was a significantly increased DEP deposition in the spleen as well as in the liver. No significantly increased DEPs were detected in the lung and heart. Conclusion: Here we show that circulating DEPs induce a systemic response characterized by increased TNF-α, peripheral granulocytes, but does not impact endothelial function. Our study also suggests that circulating particles are rapidly removed from the circulation and predominantly sequestered in the spleen and liver.