Exposure to concentrated ambient particulate matter induces reversible increase of heart weight in spontaneously hypertensive rats

Diesel exhaust particle extract elicits an oxPAPC-like transcriptomic profile in macrophages across multiple mouse strains

Air pollution is a prominent cause of cardiopulmonary illness, but uncertainties remain regarding the mechanisms mediating those effects as well as individual susceptibility. Macrophages are highly responsive to particles, and we hypothesized that their responses would be dependent on their genetic backgrounds. We conducted a genome-wide analysis of peritoneal macrophages harvested from 24 inbred strains of mice from the Hybrid Mouse Diversity Panel (HMDP). Cells were treated with a DEP methanol extract (DEPe) to elucidate potential pathways that mediate acute responses to air pollution exposures. This analysis showed that 1247 genes were upregulated and 1383 genes were downregulated with DEPe treatment across strains. Pathway analysis identified oxidative stress responses among the most prominent upregulated pathways; indeed, many of the upregulated genes included antioxidants such as Hmox1, Txnrd1, Srxn1, and Gclm, with NRF2 (official gene symbol: Nfe2l2) being the most significant driver. DEPe induced a Mox-like transcriptomic profile, a macrophage subtype typically induced by oxidized phospholipids and likely dependent on NRF2 expression. Analysis of individual strains revealed consistency of overall responses to DEPe and yet differences in the degree of Mox-like polarization across the various strains, indicating DEPe × genetic interactions. These results suggest a role for macrophage polarization in the cardiopulmonary toxicity induced by air pollution.

Depleted Housing Elicits Cardiopulmonary Dysfunction After a Single Flaming Eucalyptus Wildfire Smoke Exposure in a Sex-Specific Manner in ApoE Knockout Mice

Although it is well established that wildfire smoke exposure can increase cardiovascular morbidity and mortality, the combined effects of non-chemical stressors and wildfire smoke remains understudied. Housing is a non-chemical stressor that is a major determinant of cardiovascular health, however, disparities in neighborhood and social status have exacerbated the cardiovascular health gaps within the United States. Further, pre-existing cardiovascular morbidities, such as atherosclerosis, can worsen the response to wildfire smoke exposures. This represents a potentially hazardous interaction between inadequate housing and stress, cardiovascular morbidities, and worsened responses to wildfire smoke exposures. The purpose of this study was to examine the effects of enriched (EH) versus depleted (DH) housing on pulmonary and cardiovascular responses to a single flaming eucalyptus wildfire smoke (WS) exposure in male and female apolipoprotein E (ApoE) knockout mice, which develop an atherosclerosis-like phenotype. The results of this study show that cardiopulmonary responses to WS exposure occur in a sex-specific manner. EH blunts adverse WS-induced ventilatory responses, specifically an increase in tidal volume (TV), expiratory time (Te), and relaxation time (RT) after a WS exposure, but only in females. EH also blunted an increase in isovolumic relaxation time (IVRT) and the myocardial performance index (MPI) 1-week after exposures, also only in females. Our results suggest that housing alters the cardiovascular response to a single WS exposure, and that DH might cause increased susceptibility to environmental exposures that manifest in altered ventilation patterns and diastolic dysfunction in a sex-specific manner.

Particulate matter, polycyclic aromatic hydrocarbons and metals, platelet parameters and blood pressure alteration: Multi-pollutants study among population

Epidemiological findings have determined the linkage of fine particulate matter (PM2.5) and the morbidity of hypertension. However, the mode of action and specific contribution of PM2.5 component in the blood pressure elevation remain unclear. Platelets are critical for vascular homeostasis and thrombosis, which may be involved in the increase of blood pressure. Among 240 high-PM2.5 exposed, 318 low-PM2.5 exposed workers in a coking plant and 210 workers in the oxygen plant and cold-rolling mill enrolled in present study, both internal and external exposure characteristics were obtained, and we performed linear regression, adaptive elastic net regression, quantile g-computation and mediation analyses to analyze the relationship between urine metabolites of polycyclic aromatic hydrocarbons (PAHs) and metals fractions with platelets indices and blood pressure indicators. We found that PM2.5 exposure leads to increased systolic blood pressure (SBP) and pulse pressure (PP). Specifically, for every 10 μg/m3 increase in PM2.5, there was a 0.09 mmHg rise in PP. Additionally, one IQR increase in urinary 1-hydroxypyrene (1.06 μmol/mol creatinine) was associated with a 3.43 % elevation in PP. Similarly, an IQR increment of urine cobalt (2.31 μmol/mol creatinine) was associated with a separate 1.77 % and 4.71 % elevation of SBP and PP. Notably, platelet-to-lymphocyte ratio (PLR) played a mediating role in the elevation of SBP and PP induced by cobalt. Our multi-pollutants results showed that PAHs and cobalt were deleterious contributors to the elevated blood pressure. These findings deepen our understanding of the cardiovascular effects associated with PM2.5 constituents, highlighting the importance of increased vigilance in monitoring and controlling the harmful components in PM2.5.

PM2.5 exposure-induced senescence-associated secretory phenotype in airway smooth muscle cells contributes to airway remodeling

Fine particulate matter (PM2.5) has been linked to increased severity and incidence of airway diseases, especially chronic obstructive pulmonary disease (COPD) and asthma. Airway remodeling is an important event in both COPD and asthma, and airway smooth muscle cells (ASMCs) are key cells which directly involved in airway remodeling. However, it was unclear how PM2.5 affected ASMCs. This study investigates the effects of PM2.5 on airway smooth muscle and its mechanism. We first showed that inhaled particulate matter was distributed in the airway smooth muscle bundle, combined with increased airway smooth muscle bundle and collagen deposition in vivo. Then, we demonstrated that PM2.5 induced up-regulation of collagen-I and alpha-smooth muscle actin (α-SMA) expression in rat and human ASMCs in vitro. Next, we found PM2.5 led to rat and human ASMCs senescence and exhibited senescence-associated secretory phenotype (SASP) by autophagy-induced GATA4/TRAF6/NF-κB signaling, which contributed to collagen-I and α-SMA synthesis as well as airway smooth muscle remodeling. Together, our results provided evidence that SASP induced by PM2.5 in airway smooth muscle cells prompted airway remodeling.

Depleted housing elicits cardiopulmonary dysfunction after a single flaming eucalyptus wildfire smoke exposure in a sex-specific manner in ApoE knockout mice

Although it is well established that wildfire smoke exposure can increase cardiovascular morbidity and mortality, the combined effects of non-chemical stressors and wildfire smoke remains understudied. Housing is a non-chemical stressor that is a major determinant of cardiovascular health, however, disparities in neighborhood and social status have exacerbated the cardiovascular health gaps within the United States. Further, pre-existing cardiovascular morbidities, such as atherosclerosis, can worsen the response to wildfire smoke exposures. This represents a potentially hazardous interaction between inadequate housing and stress, cardiovascular morbidities, and worsened responses to wildfire smoke exposures. The purpose of this study was to examine the effects of enriched (EH) versus depleted (DH) housing on pulmonary and cardiovascular responses to a single flaming eucalyptus wildfire smoke (WS) exposure in male and female apolipoprotein E (ApoE) knockout mice, which develop an atherosclerosis-like phenotype. The results of this study show that cardiopulmonary responses to WS exposure occur in a sex-specific manner. EH blunts adverse WS-induced ventilatory responses, specifically an increase in tidal volume (TV), expiratory time (Te), and relaxation time (RT) after a WS exposure, but only in females. EH also blunted a WS-induced increase in isovolumic relaxation time (IVRT) and the myocardial performance index (MPI) 1-wk after exposures, also only in females. Our results suggest that housing alters the cardiovascular response to a single WS exposure, and that DH might cause increased susceptibility to environmental exposures that manifest in altered ventilation patterns and diastolic dysfunction in a sex-specific manner.

Impact of Intratracheal Administration of Polyethylene Glycol-Coated Silver Nanoparticles on the Heart of Normotensive and Hypertensive Mice

Silver nanoparticles are widely used in various industrial and biomedical applications; however, little is known about their potential cardiotoxicity after pulmonary exposure, particularly in hypertensive subjects. We assessed the cardiotoxicity of polyethylene glycol (PEG)-coated AgNPs in hypertensive (HT) mice. Saline (control) or PEG-AgNPs (0.5 mg/kg) were intratracheally (i.t.) instilled four times (on days 7, 14, 21, and 28 post-angiotensin II or vehicle [saline] infusion). On day 29, various cardiovascular parameters were evaluated. Systolic blood pressure and heart rate were higher in PEG-AgNPs-treated HT mice than in saline-treated HT or PEG-AgNPs-treated normotensive mice. The heart histology of PEG-AgNPs-treated HT mice had comparatively larger cardiomyocyte damage with fibrosis and inflammatory cells when compared with saline-treated HT mice. Similarly, the relative heart weight and the activities of lactate dehydrogenase and creatine kinase-MB and the concentration of brain natriuretic peptide concentration were significantly augmented in heart homogenates of HT mice treated with PEG-AgNPs compared with HT mice treated with saline or normotensive animals exposed to PEG-AgNPs. Similarly, the concentrations of endothelin-1, P-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 in heart homogenates were significantly higher than in the other two groups when HT mice were exposed to PEG-AgNPs. Markers of inflammation and oxidative and nitrosative stress were significantly elevated in heart homogenates of HT mice given PEG-AgNPs compared with HT mice treated with saline or normotensive animals exposed to PEG-AgNPs. The hearts of HT mice exposed to PEG-AgNPs had significantly increased DNA damage than those of HT mice treated with saline or normotensive mice treated with AgNPs. In conclusion, the cardiac injury caused by PEG-AgNPs was aggravated in hypertensive mice. The cardiotoxicity of PEG-AgNPs in HT mice highlights the importance of an in-depth assessment of their toxicity before using them in clinical settings, particularly in patients with pre-existing cardiovascular diseases.

Air Pollution: Another Threat to HDL Function

Epidemiological studies have consistently demonstrated a positive association between exposure to air pollutants and the incidence of cardiovascular disease, with the strongest evidence for particles with a diameter < 2.5 μm (PM2.5). Therefore, air pollution has been included among the modifiable risk factor for cardiovascular outcomes as cardiovascular mortality, acute coronary syndrome, stroke, heart failure, and arrhythmias. Interestingly, the adverse effects of air pollution are more pronounced at higher levels of exposure but were also shown in countries with low levels of air pollution, indicating no apparent safe threshold. It is generally believed that exposure to air pollution in the long-term can accelerate atherosclerosis progression by promoting dyslipidemia, hypertension, and other metabolic disorders due to systemic inflammation and oxidative stress. Regarding high density lipoproteins (HDL), the impact of air pollution on plasma HDL-cholesterol levels is still debated, but there is accumulating evidence that HDL function can be impaired. In particular, the exposure to air pollution has been variably associated with a reduction in their cholesterol efflux capacity, antioxidant and anti-inflammatory potential, and ability to promote the release of nitric oxide. Further studies are needed to fully address the impact of various air pollutants on HDL functions and to elucidate the mechanisms responsible for HDL dysfunction.

Deficiency of interleukin-6 receptor ameliorates PM2.5 exposure-induced pulmonary dysfunction and inflammation but not abnormalities in glucose homeostasis

BACKGROUND

Ambient fine particulate matter (PM_2.5) exposure increases local and systemic interleukin-6 (IL-6). However, the pathogenic role of IL-6 signalling following PM_2.5 exposure, particularly in the development of pulmonary dysfunction and abnormal glucose homeostasis, has hardly been investigated.

RESULTS

In the study, IL-6 receptor (IL-6R)-deficient (IL-6R^-/-) and wildtype littermate (IL-6R^+/+) mice were exposed to concentrated ambient PM_2.5 (CAP) or filtered air (FA), and their pulmonary and metabolic responses to these exposures were analyzed. Our results demonstrated that IL-6R deficiency markedly alleviated PM_2.5 exposure-induced increases in lung inflammatory markers including the inflammation score of histological analysis, the number of macrophages in bronchoalveolar lavage fluid (BALF), and mRNA expressions of TNFα, IL-1β and IL-6 and abnormalities in lung function test. However, IL-6R deficiency did not reduce the hepatic insulin resistance nor systemic glucose intolerance and insulin resistance induced by PM_2.5 exposure.

CONCLUSION

Our findings support the crucial role of IL-6 signalling in the development of pulmonary inflammation and dysfunction due to PM_2.5 exposure but question the putative central role of pulmonary inflammation for the extra-pulmonary dysfunctions following PM_2.5 exposure, providing a deep mechanistic insight into the pathogenesis caused by PM_2.5 exposure.

A comparison of fine particulate matter (PM2.5) in vivo exposure studies incorporating chemical analysis

The complex, variable mixtures present in fine particulate matter (PM_2.5) have been well established, and associations between chemical constituents and human health are expanding. In the past decade, there has been an increase in PM_2.5 toxicology studies that include chemical analysis of samples. This investigation is a crucial component for identifying the causal constituents for observed adverse health effects following exposure to PM_2.5. In this review, investigations of PM_2.5 that used both in vivo models were explored and chemical analysis with a focus on respiratory, cardiovascular, central nervous system, reproductive, and developmental toxicity was examined to determine if chemical constituents were considered in the interpretation of the toxicity findings. Comparisons between model systems, PM_2.5 characteristics, endpoints, and results were made. A vast majority of studies observed adverse effects in vivo following exposure to PM_2.5. While limited, investigations that explored connections between chemical components and measured endpoints noted significant associations between biological measurements and a variety of PM_2.5 constituents including elements, ions, and organic/elemental carbon, indicating the need for such analysis. Current limitations in available data, including relatively scarce statistical comparisons between collected toxicity and chemical datasets, are provided. Future progress in this field in combination with epidemiologic research examining chemical composition may support regulatory standards of PM_2.5 to protect human health.

Redox Regulatory Changes of Circadian Rhythm by the Environmental Risk Factors Traffic Noise and Air Pollution

Significance: Risk factors in the environment such as air pollution and traffic noise contribute to the development of chronic noncommunicable diseases. Recent Advances: Epidemiological data suggest that air pollution and traffic noise are associated with a higher risk for cardiovascular, metabolic, and mental disease, including hypertension, heart failure, myocardial infarction, diabetes, arrhythmia, stroke, neurodegeneration, depression, and anxiety disorders, mainly by activation of stress hormone signaling, inflammation, and oxidative stress. Critical Issues: We here provide an in-depth review on the impact of the environmental risk factors air pollution and traffic noise exposure (components of the external exposome) on cardiovascular health, with special emphasis on the role of environmentally triggered oxidative stress and dysregulation of the circadian clock. Also, a general introduction on the contribution of circadian rhythms to cardiovascular health and disease as well as a detailed mechanistic discussion of redox regulatory pathways of the circadian clock system is provided. Future Directions: Finally, we discuss the potential of preventive strategies or "chrono" therapy for cardioprotection. Antioxid. Redox Signal. 37, 679-703.

Ambient air pollution and cardiovascular diseases: An umbrella review of systematic reviews and meta-analyses

The available evidence on the effects of ambient air pollution on cardiovascular diseases (CVDs) has increased substantially. In this umbrella review, we summarized the current epidemiological evidence from systematic reviews and meta-analyses linking ambient air pollution and CVDs, with a focus on geographical differences and vulnerable subpopulations. We performed a search strategy through multiple databases including articles between 2010 and 31 January 2021. We performed a quality assessment and evaluated the strength of evidence. Of the 56 included reviews, the most studied outcomes were stroke (22 reviews), all-cause CVD mortality, and morbidity (19). The strongest evidence was found between higher short- and long-term ambient air pollution exposure and all-cause CVD mortality and morbidity, stroke, blood pressure, and ischemic heart diseases (IHD). Short-term exposures to particulate matter <2.5 μm (PM_2.5 ), <10 μm (PM₁₀ ), and nitrogen oxides (NO_x ) were consistently associated with increased risks of hypertension and triggering of myocardial infarction (MI), and stroke (fatal and nonfatal). Long-term exposures of PM_2.5 were largely associated with increased risk of atherosclerosis, incident MI, hypertension, and incident stroke and stroke mortality. Few reviews evaluated other CVD outcomes including arrhythmias, atrial fibrillation, or heart failure but they generally reported positive statistical associations. Stronger associations were found in Asian countries and vulnerable subpopulations, especially among the elderly, cardiac patients, and people with higher weight status. Consistent with experimental data, this comprehensive umbrella review found strong evidence that higher levels of ambient air pollution increase the risk of CVDs, especially all-cause CVD mortality, stroke, and IHD. These results emphasize the importance of reducing the alarming levels of air pollution across the globe, especially in Asia, and among vulnerable subpopulations.

PM2.5 increases mouse blood pressure by activating toll-like receptor 3

BACKGROUND AND AIMS

Plenty of literature has documented that fine particulate matter (PM2.5) exposure is related to blood pressure (BP) elevation. Vascular dysfunction is the initiation of cardiovascular diseases, such as hypertension. This thesis set out to assess the role of Toll-like receptor 3 (TLR3) in the increase in BP induced by PM2.5.

METHODS

C57BL/6 and TLR3 deficient (TLR3-/-) male mice were randomly allocated to filtered air chamber or real-world inhaled concentrated PM2.5 chamber. BP was evaluated using non-invasive BP recordings. After euthanasia, the aortas and small mesenteric arteries (SMAs) were isolated, and vascular tone was measured using a wire myograph. Leucocytes were detached to assess myeloid-derived suppressor cells using flow cytometry. siRNA transfection was performed to silence TLR3 expression in the human vascular endothelial cells incubated with PM2.5. The gene expression levels of inflammation, adhesion molecules, and oxidative stress in the aortas were assessed by quantitative PCR.

RESULTS

Exposure to PM2.5 increased mouse BP, and TLR3 deficiency protected against PM2.5 exposure-induced BP increase. Additionally, the injury of vascular function in the aortas and SMAs was inhibited in TLR3-/- mice. The intercellular adhesion molecule-1 (ICAM-1) was attenuated in TLR3-/- mice, accompanied by the inhibition of inflammatory and oxidized genes of the aortas, such as F4/80, interleukin-6, interleukin-1 beta, and NADPH oxidase 4. In vitro, the enhanced mRNA expression of genes encoding inflammation, oxidative stress, and ICAM-1 by PM2.5 was inhibited by TLR3 silence as well.

CONCLUSIONS

PM2.5 exposure increased BP via TLR3 activation and impaired vascular function.

Impacts of Environmental Insults on Cardiovascular Aging

PURPOSE OF REVIEW

With cardiovascular disease (CVD) being the top cause of deaths worldwide, it is important to ensure healthy cardiovascular aging through enhanced understanding and prevention of adverse health effects exerted by external factors. This review aims to provide an updated understanding of environmental influences on cardiovascular aging, by summarizing epidemiological and mechanistic evidence for the cardiovascular health impact of major environmental stressors, including air pollution, endocrine-disrupting chemicals (EDCs), metals, and climate change.

RECENT FINDINGS

Recent studies generally support positive associations of exposure to multiple chemical environmental stressors (air pollution, EDCs, toxic metals) and extreme temperatures with increased risks of cardiovascular mortality and morbidity in the population. Environmental stressors have also been associated with a number of cardiovascular aging-related subclinical changes including biomarkers in the population, which are supported by evidence from relevant experimental studies. The elderly and patients are the most vulnerable demographic groups to majority environmental stressors. Future studies should account for the totality of individuals' exposome in addition to single chemical pollutants or environmental factors. Specific factors most responsible for the observed health effects related to cardiovascular aging remain to be elucidated.

PM2.5 Exposure of Mice during Spermatogenesis: A Role of Inhibitor κB Kinase 2 in Pro-Opiomelanocortin Neurons

BACKGROUND

Epidemiological studies have shown that exposure to ambient fine particulate matter with aerodynamic diameter less than or equal to 2.5 μm (PM2.5) correlates with a decrease in sperm count, but the biological mechanism remains elusive.

OBJECTIVES

This study tested whether hypothalamic inflammation, an emerging pathophysiological mediator, mediates the development of lower epididymal sperm count due to PM2.5 exposure.

METHODS

Inhibitor κB kinase 2 (IKK2) was conditionally knocked out either in all neurons or subtypes of hypothalamic neurons of mice. Effects of concentrated ambient PM2.5 (CAP) exposure on hypothalamic inflammation, the hypothalamic-pituitary-gonadal (HPG) axis, and epididymal sperm count of these mouse models were then assessed. Furthermore, to test whether hypothalamic inflammation is sufficient to decrease sperm production, we overexpressed constitutively active IKK2 (IKK2ca) either in all neurons or subtypes of hypothalamic neurons and assessed hypothalamic inflammation, the HPG axis, and sperm production of these overexpression mouse models.

RESULTS

CAP-exposed wild-type control mice vs. filtered air (FA)-exposed wild-type control mice had a higher expression of hypothalamic inflammatory markers, lower functional indexes of the HPG axis, and a lower epididymal sperm count. In contrast, all these measurements for CAP- vs. FA-exposed mice deficient of IKK2 in all neurons were comparable. We also found that overexpression of IKK2ca in either all neurons or pro-opiomelanocortin (POMC) neurons only, but not in Agouti-related protein (AgRP) neurons only, resulted in lower functional indexes of the HPG axis and a lower epididymal sperm count. Moreover, we showed that CAP- vs. FA-exposed mice deficient of IKK2 in POMC neurons had a comparable expression of hypothalamic inflammatory markers, comparable functional indexes of the HPG axis, and a comparable epididymal sperm count.

DISCUSSION

This mouse model study shows a causal role of IKK2 of POMC neurons in the development of lower epididymal sperm count due to PM2.5 exposure, providing a mechanistic insight into this emerging pathogenesis. https://doi.org/10.1289/EHP8868.

Real-world particulate matters induce lung toxicity in rats fed with a high-fat diet: Evidence of histone modifications

Exposure to ambient particulate matters (PMs) has been associated with a variety of lung diseases, and high-fat diet (HFD) was reported to exacerbate PM-induced lung dysfunction. However, the underlying mechanisms for the combined effects of HFD and PM on lung functions remain poorly unraveled. By performing a comparative proteomic analysis, the current study investigated the global changes of histone post-translational modifications (PTMs) in rat lung exposed to long-term, real-world PMs. In result, after PM exposure the abundance of four individual histone PTMs (1 down-regulated and 3 up-regulated) and six combinatorial PTMs (1 down-regulated and 5 up-regulated) were significantly altered in HFD-fed rats while only one individual PTM was changed in rats with normal diet (ND) feeding. Histones H3K18ac, H4K8ac and H4K12ac were reported to be associated with DNA damage response, and we found that these PTMs were enhanced by PM in HFD-fed rats. Together with the elevated DNA damage levels in rat lungs following PM and HFD co-exposure, we demonstrate that PM exposure combined with HFD could induce lung injury through altering more histone modifications accompanied by DNA damage. Overall, these findings will augment our knowledge of the epigenetic mechanisms for pulmonary toxicity caused by ambient PM and HFD exposure.

Synergistic effects of carbon nanoparticle-Cr-Pb in PM2.5 cause cell cycle arrest via upregulating a novel lncRNA NONHSAT074301.2 in human bronchial epithelial cells

Inhalation of carcinogenic PM_2.5 particles is a severe threat to all the people in both developing and developed nations. However, which components of PM_2.5 and how they perturb human cells to cause various diseases are still not understood. Here, employing a reductionism approach, we revealed that one of the crucial toxic and pathogenic mechanisms of PM_2.5 was the blocking of human bronchial cell cycle through upregulation of a novel long non-coding RNA NONHSAT074301.2 by carbon particles with payloads of Cr(VI) and Pb²⁺. We also discovered that NONHSAT074301.2 is a key regulatory molecule controlling cell cycle arrest at G2/M phase. This work highlights cellular function and molecular signaling events investigations using a 16-membered combinational model PM_2.5 library which contain carbon particles carrying four toxic pollutants in all possible combinations at environmental relevant concentrations. This work demonstrates a very powerful methodology to elucidate mechanisms at molecular level and help unlock the "black box" of PM_2.5-induced toxicities.

Cardiac dysfunction and metabolic remodeling due to seasonally ambient fine particles exposure

Increasing epidemiological evidences have revealed the association between ambient fine particulate matter (PM_2.5) pollution and cardiovascular disease's morbidity and mortality. However, how seasonal PM_2.5 exposure influence cardiac function and the underlying mechanism converged in energy metabolic remodeling remain to be elucidated. This study focused on seasonal PM_2.5-induced cardiac dysfunction and metabolic remodeling, and the toxicity differences of PM_2.5 samples from different sampling seasons and different exposure dosages were discussed. The results showed that seasonal haze caused cardiac dysfunctions, including decreases in heart rate (HR) and heart rate variability (HRV), abnormal changes in hemodynamic and echocardiographic parameters. Concurrently, the energy production in myocardial tissues was evidently disturbed. In particular, low dose of PM_2.5 exposure notably induced the elevation of beta oxidation (β-oxidation) and tricarboxylic acid cycle (TCA cycle) as the compensation for the disturbed energy metabolism in animals, whereas high dose of PM_2.5 exposure attenuated this process and the glycolysis levels were strikingly promoted, thus causing the reduced energy production and cardiac dysfunction. Comparatively, winter PM_2.5 exposure caused more severe cardiac toxicity than did summer haze samples, possibly due to the existence of different components and pollutant levels in seasonal hazes. The findings on seasonal PM_2.5 induced cardiac dysfunction and myocardial metabolic remodeling provided new insights into cardiovascular disease risks from haze exposure.

Oxidative stress pathways of air pollution mediated toxicity: Recent insights

Ambient air pollution is a leading environmental cause of morbidity and mortality globally with most of the outcomes of cardiovascular origin. While numerous mechanisms are proposed to explain the link between air pollutants and cardiovascular events, the evidence supports a role for oxidative stress as a critical intermediary pathway in the transduction of systemic responses in the cardiovascular system. Indeed, alterations in vascular function are a critical step in the development of cardiometabolic disorders such as hypertension, diabetes, and atherosclerosis. This review will provide an overview of the impact of particulate and gaseous pollutants on oxidative stress from human and animal studies published in the last five years. We discuss current gaps in knowledge and evidence to date implicating the role of oxidative stress with an emphasis on inhalational exposures. We conclude with the identification of gaps, and an exhortation for further studies to elucidate the impact of oxidative stress in air pollution mediated effects.

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Particulate matter air pollution is the leading risk factor for cardiovascular morbidity and mortality globally.

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Mechanisms of oxidative stress mediated pathways.

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How does lung inflammation crucial to inhalational exposure mediate systemic toxicity?

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Review of recent animal and human exposure studies providing insights into oxidative stress pathways.

Ambient PM2.5 caused cardiac dysfunction through FoxO1-targeted cardiac hypertrophy and macrophage-activated fibrosis in mice

Plenty of epidemiological evidences have shown that ambient particulate matter (PM2.5) exposure increased the prevalence of cardiovascular disease, but the potential mechanism has not been known clearly. We established mice models by ambient PM2.5 exposure system to explore the adverse effects of PM2.5 on cardiac function in mice. Forty-eight C57BL/6 mice were randomly divided into 3 groups and exposed to filtered air (FA), unfiltered air (UA) and concentrated PM2.5 air (CA) for 8 or 16 weeks, 6 hours per day, 7 days per week, respectively. The changes of cardiac structure and function, histological analysis and related mechanism were investigated. The main manifestations of cardiac structure were cardiac hypertrophy and fibrosis in a dose- and time-dependent manner after PM2.5 exposure, which led to the decrease of cardiac systolic function. Cardiac hypertrophy in mice might be regulated by PI3K/Akt/FoxO1 signal. Cardiac fibrosis might be attributed to inflammatory infiltration caused by macrophage activation. Consequently, our data indicated that cardiac hypertrophy and fibrosis might be important factors of PM2.5-induced cardiac dysfunction in mice.

Brain lipid profiles in the spontaneously hypertensive rat after subchronic real-world exposure to ambient fine particulate matter

Recent studies have illustrated an association between ambient fine particulate matter (PM_2.5) exposure and neuronal toxicity in epidemiological studies and animal models. However, the possible molecular effects on brains under real-world exposure to PM_2.5 remain unclear. In this pilot study, male spontaneously hypertensive rats were whole-bodily exposed to ambient air from the outdoor environment of Taipei City for 3 months, while the control rats inhaled HEPA-filtered air. The PM_2.5-induced phosphatidylcholine and sphingomyelin profiles in the hippocampus, cortex, medulla, cerebellum, and olfactory bulb were assessed by mass spectrometry (MS)-based lipidomics. Partial least squares discriminant analysis (PLS-DA) and the Wilcoxon rank sum test were used to examine the lipid changes between the exposed and control groups. The PLS-DA models showed that phosphatidylcholine and sphingomyelin profiles of the PM_2.5 exposure group were different from those of the control group in each brain region except the cortex. More lipid changes were found in the hippocampus, while fewer lipid changes were observed in the olfactory bulb. The lipid alteration in the hippocampus may strengthen membrane integrity, modulate signaling pathways, and avoid accumulation of lipofuscin to counter the PM_2.5-induced stress. The lipid changes in the cortex and medulla may respond to PM_2.5-induced injury and inflammation; while the lipid changes in the cerebellum were associated with neuron protection. This study suggests that the MS-based lipidomics is a powerful approach to discriminate the brain lipid profiles even at the environmental level of ambient PM_2.5 and has the potential to suggest possible adverse health effects in long-term PM_2.5 exposure studies.

Influence of mental stress and environmental toxins on circadian clocks: Implications for redox regulation of the heart and cardioprotection

Risk factors in the environment such as air pollution and mental stress contribute to the development of chronic non-communicable disease. Air pollution was identified as the leading health risk factor in the physical environment, followed by water pollution, soil pollution/heavy metals/chemicals and occupational exposures, however neglecting the non-chemical environmental health risk factors (e.g. mental stress and noise). Epidemiological data suggest that environmental risk factors are associated with higher risk for cardiovascular, metabolic and mental diseases, including hypertension, heart failure, myocardial infarction, diabetes, arrhythmia, stroke, depression and anxiety disorders. We provide an overview on the impact of the external exposome comprising risk factors/exposures on cardiovascular health with a focus on dysregulation of stress hormones, mitochondrial function, redox balance and inflammation with special emphasis on the circadian clock. Finally, we assess the impact of circadian clock dysregulation on cardiovascular health and the potential of environment-specific preventive strategies or "chrono" therapy for cardioprotection. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Glucose Homeostasis following Diesel Exhaust Particulate Matter Exposure in a Lung Epithelial Cell-Specific IKK2-Deficient Mouse Model

BACKGROUND

Pulmonary inflammation is believed to be central to the pathogenesis due to exposure to fine particulate matter with aerodynamic diameter [Formula: see text] ([Formula: see text]). This central role, however, has not yet been systemically examined.

OBJECTIVE

In the present study, we exploited a lung epithelial cell-specific inhibitor [Formula: see text] kinase 2 (IKK2) knockout mouse model to determine the role of pulmonary inflammation in the pathophysiology due to exposure to diesel exhaust particulate matter (DEP).

METHODS

[Formula: see text] (lung epithelial cell-specific IKK2 knockout, KO) and [Formula: see text] (wild-type, tgWT) mice were intratracheally instilled with either vehicle or DEP for 4 months, and their inflammatory response and glucose homeostasis were then assessed.

RESULTS

In comparison with tgWT mice, lung epithelial cell-specific IKK2-deficient mice had fewer DEP exposure-induced bronchoalveolar lavage fluid immune cells and proinflammatory cytokines as well as fewer DEP exposure-induced circulating proinflammatory cytokines. Glucose and insulin tolerance tests revealed that lung epithelial cell-specific IKK2 deficiency resulted in markedly less DEP exposure-induced insulin resistance and greater glucose tolerance. Akt phosphorylation analyses of insulin-responsive tissues showed that DEP exposure primarily targeted hepatic insulin sensitivity. Lung epithelial cell-specific IKK2-deficient mice had significantly lower hepatic insulin resistance than tgWT mice had. Furthermore, this difference in insulin resistance was accompanied by consistent differences in hepatic insulin receptor substrate 1 serine phosphorylation and inflammatory marker expression.

DISCUSSION

Our findings suggest that in a tissue-specific knockout mouse model, an IKK2-dependent pulmonary inflammatory response was essential for the development of abnormal glucose homeostasis due to exposure to DEP. https://doi.org/10.1289/EHP4591.

PM2.5 exposure impairs sperm quality through testicular damage dependent on NALP3 inflammasome and miR-183/96/182 cluster targeting FOXO1 in mouse

Exposure to ambient fine particular matter (PM2.5) has been clearly associated with male reproductive disorders. However, very limited toxicological studies were carried out to investigate the potential mechanisms underlying the PM2.5-induced sperm quality decline. In the present study, we established a real time whole-body PM2.5 exposure mouse model to investigate the effects of PM2.5 on sperm quality and its potential mechanisms. Sixty male C57BL/6 mice were randomly subjected to three groups: filtered air group, unfiltered air group and concentrated air group. Half of the mice from each group were sacrificed for study when the exposure duration accumulated to 8 weeks and the rest of the mice were sacrificed when exposed for 16 weeks. Our results suggested that PM2.5 exposure could induce significant increases in circulating white blood cells and inflammation in lungs. PM2.5 exposure induced apparently DNA damages and histopathologic changes in testes. There were significantly decreased sperm densities of mice, which were paralleled with the down-regulated testosterone levels in testes tissue of mice after exposure to PM2.5 for 16 weeks. The numbers of motile sperms were decreased and sperms with abnormal morphology were increased after PM2.5 exposure in a time-depended and dose-depended manner. PM2.5 exposure significantly increased the expression of the major components of the NACHT, LRR and PYD domains-containing protein3 (NALP3) inflammasome, accompanied by the increased expression of miR-183/96/182 targeting FOXO1 in testes. The present data demonstrated that sperm quality decline induced by PM2.5 could be partly explained by the inflammatory reaction in testes which might be a consequence of systemic inflammation. The molecular mechanism was depended on the activation of NALP3 inflammasome accompanied by miR-183/96/182 targeting FOXO1 in testes.

Probucol protects circulating endothelial progenitor cells from ambient PM2.5 damage via inhibition of reactive oxygen species and inflammatory cytokine production in vivo

Bone marrow-derived circulating endothelial progenitor cells (EPCs) contribute to angiogenesis and vascular repair. The number and function of EPCs are significantly decreased following exposure to ambient fine particulate matter of ≤2.5 µm in diameter (PM_2.5) through reactive oxygen species (ROS) generation and inflammatory cytokine secretion. The anti-oxidant drug probucol reduces ROS and inflammatory cytokine production. The present study was designed to determine the protective effects of probucol on EPCs from PM_2.5-associated impairment in vivo and to explore the potential underlying mechanisms. Male C57BL/6 mice were exposed to ambient air containing PM_2.5 for one month with or without probucol treatment. Mice that breathed filtered air were used as a control group. Serum and blood cells were collected for analysis. The results indicated that PM_2.5 exposure induced increases in blood intracellular ROS, serum inflammatory cytokine levels and the blood cell apoptotic rate, while it decreased the number and proliferation rate of circulating EPCs in the mice with PM_2.5 exposure. These effects were significantly reduced/abrogated by probucol treatment. The present in vivo study suggested that probucol protects EPCs from damage through PM_2.5 exposure by inhibiting ROS generation and inflammatory cytokine production.

Analysis of differentially changed gene expression in EA.hy926 human endothelial cell after exposure of fine particulate matter on the basis of microarray profile

Epidemiological studies have illustrated that PM2.5 is closely related to cardiovascular disease (CVD), but underlying toxicological mechanisms are not yet clear. The main purpose of this study is to disclose the potential biological mechanisms responsible for PM2.5-dependent adverse cardiovascular outcomes through the appliance of genome-wide transcription microarray. From results, compared with the control group, there are 97 genes significantly altered in 2.5 μg/cm² PM2.5 treated group and 440 differentially expressed genes in 10 μg/cm² group. Of note, when 2.5 μg/cm² and 10 μg/cm² group were respectively compared with the control group, 46 significantly altered genes showed a consistent tendency in two treated groups, of which 31 genes were upregulated while 15 genes were meanwhile downregulated. Based on Gene Ontology (GO) annotation, altered genes are mainly gathered in functions of cellular processes and immune regulation. Pathway analysis indicated that TNF signaling pathway, NOD-like receptor (NLRs) signaling pathway, MAPK signaling pathway and gap junction are vital pathways involved in PM2.5-induced toxicity in EA.hy926. Moreover, results from RT-qPCR further corroborated that changed genes are implicated in oxidative stress, inflammation and metabolic disorder. In addition, metabolism of xenobiotics by cytochrome P450 pathway is the critical pathway which may serve as a target to prevent PM2.5-induced CVD. To sum up, our effort provides a fundamental data for further studies regarding mechanisms of PM2.5-induced cardiovascular toxicity on the basis of genome-wide screening.

From the Cover: Lung-Specific Overexpression of Constitutively Active IKK2 Induces Pulmonary and Systemic Inflammations but Not Hypothalamic Inflammation and Glucose Intolerance

The lung is constantly exposed to ambient pollutants such as ambient fine particulate matter (PM2.5), making it one of the most frequent locations of inflammation in the body. Given the establishment of crucial role of inflammation in the pathogenesis of cardiometabolic diseases, pulmonary inflammation is thus widely believed to be an important risk factor for cardiometabolic diseases. However, the causality between them has not yet been well established. To determine if pulmonary inflammation is sufficient to cause adverse cardiometabolic effects, SFTPC-rtTA+/-tetO-cre+/-pROSA-inhibitor κB kinase 2(IKK2)ca+/- (LungIKK2ca) and littermate SFTPC-rtTA+/-tetO-cre-/-pROSA-IKK2ca+/- wildtype (WT) mice were fed with doxycycline diet to induce constitutively active Ikk2 (Ikk2ca) overexpression in the lung and their pulmonary, systemic, adipose, and hypothalamic inflammations, vascular function, and glucose homeostasis were assessed. Feeding with doxycycline diet resulted in IKK2ca overexpression in the lungs of LungIKK2ca but not WT mice. This induction of IKK2ca was accompanied by marked pulmonary inflammation as evidenced by significant increases in bronchoalveolar lavage fluid leukocytes, pulmonary macrophage infiltration, and pulmonary mRNA expression of tumor necrosis factor α (Tnfα) and interleukin-6 (Il-6). This pulmonary inflammation due to lung-specific overexpression of IKK2ca was sufficient to increase circulating TNFα and IL-6 levels, adipose expression of Tnfα and Il-6 mRNA, aortic endothelial dysfunction, and systemic insulin resistance. Unexpectedly, no significant alteration in hypothalamic expression of Tnfα and Il-6 mRNA and glucose intolerance were observed in these mice. Pulmonary inflammation is sufficient to induce systemic inflammation, endothelial dysfunction, and insulin resistance, but not hypothalamic inflammation and glucose intolerance.

Ambient fine particulate matter exposure induces reversible cardiac dysfunction and fibrosis in juvenile and older female mice

BACKGROUND

Cardiovascular disease is the leading cause of mortality in the advanced world, and age is an important determinant of cardiac function. The purpose of the study is to determine whether the PM2.5-induced cardiac dysfunction is age-dependent and whether the adverse effects can be restored after PM2.5 exposure withdrawal.

METHODS

Female C57BL/6 mice at different ages (4-week-old, 4-month-old, and 10-month-old) received oropharyngeal aspiration of 3 mg/kg b.w. PM2.5 every other day for 4 weeks. Then, 10-month-old and 4-week-old mice were exposed to PM2.5 for 4 weeks and withdrawal PM2.5 1 or 2 weeks. Heart rate and systolic blood pressure were measured using a tail-cuff system. Cardiac function was assessed by echocardiography. Left ventricles were processed for histology to assess myocardial fibrosis. ROS generation was detected by photocatalysis using 2',7'-dichlorodihydrofluorescein diacetate (DCFHDA). The expression of cardiac fibrosis markers (Col1a1, Col3a1) and possible signaling molecules, including NADPH oxidase 4 (NOX-4), transforming growth factor β1 (TGFβ1), and Smad3, were detected by qPCR and/ or Western blot.

RESULTS

PM2.5 exposure induced cardiac diastolic dysfunction of mice, elevated the heart rate and blood pressure, developed cardiac systolic dysfunction of 10-month-old mice, and caused fibrosis in both 4-week-old and 10-month-old mice. PM2.5 exposure increased the expression of Col1a1, Col3a1, NOX-4, and TGFβ1, activated Smad3, and generated more reactive oxygen species in the myocardium of 4-week-old and 10-month-old mice. The withdrawal from PM2.5 exposure restored blood pressure, heart rate, cardiac function, expression of collagens, and malonaldehyde (MDA) levels in hearts of both 10-month-old and 4-week-old mice.

CONCLUSION

Juvenile and older mice are more sensitive to PM2.5 than adults and suffer from cardiac dysfunction. PM2.5 exposure reversibly elevated heart rate and blood pressure, induced cardiac systolic dysfunction of older mice, and reversibly induced fibrosis in juvenile and older mice. The mechanism by which PM2.5 exposure resulted in cardiac lesions might involve oxidative stress, NADPH oxidase, TGFβ1, and Smad-dependent pathways.

The Adverse Effects of Environmental Noise Exposure on Oxidative Stress and Cardiovascular Risk

Epidemiological studies have provided evidence that traffic noise exposure is linked to cardiovascular diseases such as arterial hypertension, myocardial infarction, and stroke. Noise is a nonspecific stressor that activates the autonomous nervous system and endocrine signaling. According to the noise reaction model introduced by Babisch and colleagues, chronic low levels of noise can cause so-called nonauditory effects, such as disturbances of activity, sleep, and communication, which can trigger a number of emotional responses, including annoyance and subsequent stress. Chronic stress in turn is associated with cardiovascular risk factors, comprising increased blood pressure and dyslipidemia, increased blood viscosity and blood glucose, and activation of blood clotting factors, in animal models and humans. Persistent chronic noise exposure increases the risk of cardiometabolic diseases, including arterial hypertension, coronary artery disease, diabetes mellitus type 2, and stroke. Recently, we demonstrated that aircraft noise exposure during nighttime can induce endothelial dysfunction in healthy subjects and is even more pronounced in coronary artery disease patients. Importantly, impaired endothelial function was ameliorated by acute oral treatment with the antioxidant vitamin C, suggesting that excessive production of reactive oxygen species contributes to this phenomenon. More recently, we introduced a novel animal model of aircraft noise exposure characterizing the underlying molecular mechanisms leading to noise-dependent adverse oxidative stress-related effects on the vasculature. With the present review, we want to provide an overview of epidemiological, translational clinical, and preclinical noise research addressing the nonauditory, adverse effects of noise exposure with focus on oxidative stress. Antioxid. Redox Signal. 28, 873-908.

Inactivation of TNF/LT locus alters mouse metabolic response to concentrated ambient PM2.5

BACKGROUND

Exposure to ambient fine particulate matter (PM_2.5) is associated with increased cardiometabolic morbidity and mortality. This is widely believed to be attributable to PM_2.5 exposure-induced pulmonary and subsequent systemic inflammation. Tumor necrosis factor alpha (TNFα), lymphotoxin α (LTα), and lymphotoxin β (LTβ) are three homologous pro-inflammatory cytokines, each with both unique and redundant activities in inflammation. Their role in PM_2.5 exposure-induced inflammation and adverse cardiometabolic effects has to be determined.

METHODS AND RESULTS

LTα/TNFα/LTβ triple-knockout (TNF/LT KO) and wildtype (WT) mice were exposed to concentrated ambient PM_2.5 (CAP) for 5 months. Lung pathological analysis revealed that TNF/LT deficiency reduced CAP exposure-induced pulmonary inflammation. However, glucose homeostasis assessments showed that TNF/LT deficiency significantly aggravated CAP exposure-induced glucose intolerance and insulin resistance. Consistent with glucose homeostasis assessments, CAP exposure significantly increased the body weight and adiposity of TNF/LT KO but not WT mice. In contrast to its body weight effects, CAP exposure reduced food intake of WT but not TNF/LT KO mice. On the other hand, CAP exposure induced marked fat droplet accumulation in brown adipose tissues of WT mice and significantly decreased their uncoupling protein 1 (UCP1) expression, and these effects were markedly exacerbated in TNF/LT KO mice.

CONCLUSION

The present study suggests that TNF/LT deficiency influences PM_2.5 exposure-induced response of energy metabolism through alterations in both food intake and energy expenditure.

Pulmonary endothelial cell DNA methylation signature in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a severe and incurable pulmonary vascular disease. One of the primary origins of PAH is pulmonary endothelial dysfunction leading to vasoconstriction, aberrant angiogenesis and smooth muscle cell proliferation, endothelial-to-mesenchymal transition, thrombosis and inflammation. Our objective was to study the epigenetic variations in pulmonary endothelial cells (PEC) through a specific pattern of DNA methylation. DNA was extracted from cultured PEC from idiopathic PAH (n = 11), heritable PAH (n = 10) and controls (n = 18). DNA methylation was assessed using the Illumina HumanMethylation450 Assay. After normalization, samples and probes were clustered according to their methylation profile. Differential clusters were functionally analyzed using bioinformatics tools. Unsupervised hierarchical clustering allowed the identification of two clusters of probes that discriminates controls and PAH patients. Among 147 differential methylated promoters, 46 promoters coding for proteins or miRNAs were related to lipid metabolism. Top 10 up and down-regulated genes were involved in lipid transport including ABCA1, ABCB4, ADIPOQ, miR-26A, BCL2L11. NextBio meta-analysis suggested a contribution of ABCA1 in PAH. We confirmed ABCA1 mRNA and protein downregulation specifically in PAH PEC by qPCR and immunohistochemistry and made the proof-of-concept in an experimental model of the disease that its targeting may offer novel therapeutic options. In conclusion, DNA methylation analysis identifies a set of genes mainly involved in lipid transport pathway which could be relevant to PAH pathophysiology.

Chronic PM2.5 exposure and risk of infant bronchiolitis and otitis media clinical encounters

Chronic particulate matter less than 2.5μm in diameter (PM_2.5) exposure can leave infants more susceptible to illness. Our objective is to estimate associations of the chronic PM_2.5 exposure with infant bronchiolitis and otitis media (OM) clinical encounters. We obtained all first time bronchiolitis (n=18,029) and OM (n=40,042) clinical encounters among children less than 12 and 36 months of age, respectively, diagnosed from 2001 to 2009 and two controls per case matched on birthdate and gestational age from the Pregnancy to Early Life Longitudinal data linkage system in Massachusetts. We applied conditional logistic regression to estimate odds ratios (OR) and confidence intervals (CI) per 2-μg/m³ increase in lifetime average satellite based PM_2.5 exposure_. Effect modification was assessed by age, gestational age, frequency of clinical encounter, and income. We examined associations between residential distance to roadways, traffic density, and infant bronchiolitis and OM risk. PM_2.5 was not associated with infant bronchiolitis (OR=1.02, 95% CI=1.00, 1.04) and inversely associated with OM (OR=0.97, 95% CI=0.95, 0.99). There was no evidence of effect modification. Compared to infants living near low traffic density, infants residing in high traffic density had elevated risk of bronchiolitis (OR=1.23, 95% CI=1.14, 1.31) but not OM (OR=0.98, 95% CI=0.93, 1.02) clinical encounter. We did not find strong evidence to support an association between early-life long-term PM_2.5 exposure and infant bronchiolitis or OM. Bronchiolitis risk was increased among infants living near high traffic density.

Targeting vascular (endothelial) dysfunction

Cardiovascular diseases are major contributors to global deaths and disability-adjusted life years, with hypertension a significant risk factor for all causes of death. The endothelium that lines the inner wall of the vasculature regulates essential haemostatic functions, such as vascular tone, circulation of blood cells, inflammation and platelet activity. Endothelial dysfunction is an early predictor of atherosclerosis and future cardiovascular events. We review the prognostic value of obtaining measurements of endothelial function, the clinical techniques for its determination, the mechanisms leading to endothelial dysfunction and the therapeutic treatment of endothelial dysfunction. Since vascular oxidative stress and inflammation are major determinants of endothelial function, we have also addressed current antioxidant and anti-inflammatory therapies. In the light of recent data that dispute the prognostic value of endothelial function in healthy human cohorts, we also discuss alternative diagnostic parameters such as vascular stiffness index and intima/media thickness ratio. We also suggest that assessing vascular function, including that of smooth muscle and even perivascular adipose tissue, may be an appropriate parameter for clinical investigations.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Combined toxicity of silica nanoparticles and methylmercury on cardiovascular system in zebrafish (Danio rerio) embryos

This study was to investigate the combined toxicity of silica nanoparticles (SiNPs) and methylmercury (MeHg) on cardiovascular system in zebrafish (Danio rerio) embryos. Ultraviolet absorption analysis showed that the co-exposure system had high absorption and stability. The dosages used in this study were based on the NOAEL level. Zebrafish embryos exposed to the co-exposure of SiNPs and MeHg did not show any cardiovascular malformation or atrioventricular block, but had an inhibition effect on bradycardia. Using o-Dianisidine for erythrocyte staining, the cardiac output of zebrafish embryos was decreased gradually in SiNPs, MeHg, co-exposure groups, respectively. Co-exposure of SiNPs and MeHg enhanced the vascular endothelial damage in Tg(fli-1:EGFP) transgenic zebrafish line. Moreover, the co-exposure significantly activated the oxidative stress and inflammatory response in neutrophils-specific Tg(mpo:GFP) transgenic zebrafish line. This study suggested that the combined toxic effects of SiNPs and MeHg on cardiovascular system had more severe toxicity than the single exposure alone.