Acceleratory effects of ambient fine particulate matter on the development and progression of atherosclerosis in apolipoprotein E knockout mice by down-regulating CD4+CD25+Foxp3+ regulatory T cells

Aqueous PM2.5 promotes lipid accumulation, classical macrophage polarisation and heat shock response

Fine particulate matter (PM2.5) is an air pollutant that enhances susceptibility to cardiovascular diseases. Macrophages are the first immune cells to encounter the inhaled particles and orchestrate an inflammatory response. Given their role in atherosclerosis development, we investigated whether aqueous PM2.5 could elicit atherogenic effects by polarising macrophages to a pro-oxidative and pro-inflammatory phenotype and enhancing foam cell formation. The RAW264.7 macrophage cell line was exposed to PM2.5 for 48 h, with PBS as the control. Aqueous PM2.5 induced apoptosis and reduced cell proliferation. In surviving cells, we observed morphological, phagocytic, oxidative, and inflammatory features (i.e. enhanced iNOS, Integrin-1β, IL-6 expression), indicative of classical macrophage activation. We also detected an increase in total and surface HSP70 levels, suggesting macrophage activation. Further, exposure of high-cholesterol diet-fed mice to PM2.5 resulted in aortic wall enlargement, indicating vascular lesions. Macrophages exposed to PM2.5 and non-modified low-density lipoprotein (LDL) showed exacerbated lipid accumulation. Given the non-oxidised LDL used and the evidence linking inflammation to disrupted cholesterol negative feedback, we hypothesise that PM2.5-induced inflammation in macrophages enhances their susceptibility to transforming into foam cells. Finally, our results indicate that exposure to aqueous PM2.5 promotes classical macrophage activation, marked by increased HSP70 expression and that it potentially contributes to atherosclerosis.

Sex differences in particulate air pollution-related cardiovascular diseases: A review of human and animal evidence

Cardiovascular disease (CVD) is the leading cause of mortality globally. In the past several decades, researchers have raised significant awareness about the sex differences in CVD and the importance of heart disease in women. Besides physiological disparities, many lifestyles and environmental factors such as smoking and diet may affect CVD in a sex-dependent manner. Air pollution is a well-recognized environmental risk factor for CVD. However, the sex differences in air pollution-related CVD have been largely neglected. A majority of the previously completed studies have either evaluated only one sex (generally male) as study subjects or did not compare the sex differences. Some epidemiological and animal studies have shown that there are sex differences in the sensitivity to particulate air pollution as evidenced by the different morbidity and mortality rates of CVD induced by particulate air pollution, although this was not conclusive. In this review, we attempt to evaluate the sex differences in air pollution-related CVD and the underlying mechanisms by reviewing both epidemiological and animal studies. This review may provide a better understanding of the sex differences in environmental health research, enabling improved prevention and therapeutic strategies for human health in the future.

Toxicological Effects of Fine Particulate Matter (PM2.5): Health Risks and Associated Systemic Injuries-Systematic Review

Previous studies focused on investigating particulate matter with aerodynamic diameter ≤ 2.5 µm (PM2.5) have shown the risk of disease development, and association with increased morbidity and mortality rates. The current review investigate epidemiological and experimental findings from 2016 to 2021, which enabled the systemic overview of PM2.5's toxic impacts on human health. The Web of Science database search used descriptive terms to investigate the interaction among PM2.5 exposure, systemic effects, and COVID-19 disease. Analyzed studies have indicated that cardiovascular and respiratory systems have been extensively investigated and indicated as the main air pollution targets. Nevertheless, PM2.5 reaches other organic systems and harms the renal, neurological, gastrointestinal, and reproductive systems. Pathologies onset and/or get worse due to toxicological effects associated with the exposure to this particle type, since it can trigger several reactions, such as inflammatory responses, oxidative stress generation and genotoxicity. These cellular dysfunctions lead to organ malfunctions, as shown in the current review. In addition, the correlation between COVID-19/Sars-CoV-2 and PM2.5 exposure was also assessed to help better understand the role of atmospheric pollution in the pathophysiology of this disease. Despite the significant number of studies about PM2.5's effects on organic functions, available in the literature, there are still gaps in knowledge about how this particulate matter can hinder human health. The current review aimed to approach the main findings about the effect of PM2.5 exposure on different systems, and demonstrate the likely interaction of COVID-19/Sars-CoV-2 and PM2.5.

Potential Biological Mediators of Myocardial and Vascular Complications of Air Pollution-A State-of-the-Art Review

Ambient air pollution is recognised globally as a significant contributor to the burden of cardiovascular diseases. The evidence from both human and animal studies supporting the cardiovascular impact of exposure to air pollution has grown substantially, implicating numerous pathophysiological pathways and related signalling mediators. In this review, we summarise the list of activated mediators for each pathway that lead to myocardial and vascular injury in response to air pollutants. We performed a systematic search of multiple databases, including articles between 1990 and Jan 2022, summarising the evidence for activated pathways in response to each significant air pollutant. Particulate matter <2.5 μm (PM_2.5) was the most studied pollutant, followed by particulate matter between 2.5 μm-10 μm (PM₁₀), nitrogen dioxide (NO₂) and ozone (O₃). Key pathogenic pathways that emerged included activation of systemic and local inflammation, oxidative stress, endothelial dysfunction, and autonomic dysfunction. We looked at how potential mediators of each of these pathways were linked to both cardiovascular disease and air pollution and included the overlapping mediators. This review illustrates the complex relationship between air pollution and cardiovascular diseases, and discusses challenges in moving beyond associations, towards understanding causal contributions of specific pathways and markers that may inform us regarding an individual's exposure, response, and likely risk.

The pathophysiological and molecular mechanisms of atmospheric PM2.5 affecting cardiovascular health: A review

BACKGROUND

Exposure to ambient fine particulate matter (PM2.5, with aerodynamic diameter less than 2.5 µm) is a leading environmental risk factor for global cardiovascular health concern.

OBJECTIVE

To provide a roadmap for those new to this field, we reviewed the new insights into the pathophysiological and cellular/molecular mechanisms of PM2.5 responsible for cardiovascular health.

MAIN FINDINGS

PM2.5 is able to disrupt multiple physiological barriers integrity and translocate into the systemic circulation and get access to a range of secondary target organs. An ever-growing body of epidemiological and controlled exposure studies has evidenced a causal relationship between PM2.5 exposure and cardiovascular morbidity and mortality. A variety of cellular and molecular biology mechanisms responsible for the detrimental cardiovascular outcomes attributable to PM2.5 exposure have been described, including metabolic activation, oxidative stress, genotoxicity, inflammation, dysregulation of Ca2+ signaling, disturbance of autophagy, and induction of apoptosis, by which PM2.5 exposure impacts the functions and fates of multiple target cells in cardiovascular system or related organs and further alters a series of pathophysiological processes, such as cardiac autonomic nervous system imbalance, increasing blood pressure, metabolic disorder, accelerated atherosclerosis and plaque vulnerability, platelet aggregation and thrombosis, and disruption in cardiac structure and function, ultimately leading to cardiovascular events and death. Therein, oxidative stress and inflammation were suggested to play pivotal roles in those pathophysiological processes.

CONCLUSION

Those biology mechanisms have deepen insights into the etiology, course, prevention and treatment of this public health concern, although the underlying mechanisms have not yet been entirely clarified.

The macrophage senescence hypothesis: the role of poor heat shock response in pulmonary inflammation and endothelial dysfunction following chronic exposure to air pollution

INTRODUCTION

Cardiovascular diseases (CVD) have been associated with high exposure to fine particulate air pollutants (PM_2.5). Alveolar macrophages are the first defense against inhaled particles. As soon as they phagocytize the particles, they reach an inflammatory phenotype, which affects the surrounding cells and associates with CVD. Not coincidentally, CVD are marked by a depleted heat shock response (HSR), defined by a deficit in inducing 70-kDa heat shock protein (HSP70) expression during stressful conditions. HSP70 is a powerful anti-inflammatory chaperone, whose reduced levels trigger a pro-inflammatory milieu, cellular senescence, and a senescence-associated secretory phenotype (SASP). However, whether macrophage senescence is the main mechanism by which PM_2.5 propagates low-grade inflammation remains unclear.

OBJECTIVE AND DESIGN

In this article, we review evidence supporting that chronic exposure to PM_2.5 depletes HSR and determines the ability to solve the initial stress.

RESULTS AND DISCUSSION

When exposed to PM_2.5, macrophages increase the production of reactive oxygen species, which activate nuclear factor-kappa B (NF-κB). NF-κB is naturally a pro-inflammatory factor that drives prostaglandin E2 (PGE2) synthesis and causes fever. PGE2 can be converted into prostaglandin A2, a powerful inducer of HSR. Therefore, when transiently activated, NF-κB can trigger the anti-inflammatory response through negative feedback, by inducing HSP70 expression. However, when chronically activated, NF-κB heads a set of pathways involved in mitochondrial dysfunction, endoplasmic reticulum stress, unfolded protein response, inflammasome activation, and apoptosis. During chronic exposure to PM_2.5, cells cannot properly express sirtuin-1 or activate heat shock factor-1 (HSF-1), which delays the resolution phase of inflammation. Since alveolar macrophages are the first immune defense against PM_2.5, we suppose that the pollutant impairs HSR and, consequently, induces cellular senescence. Accordingly, senescent macrophages change its secretory phenotype to a more inflammatory one, known as SASP. Finally, macrophages' SASP would propagate the systemic inflammation, leading to endothelial dysfunction and atherosclerosis.

The underlying mechanism of PM2.5-induced ischemic stroke

Under the background of global industrialization, PM_2.5 has become the fourth-leading risk factor for ischemic stroke worldwide, according to the 2019 GBD estimates. This highlights the hazards of PM_2.5 for ischemic stroke, but unfortunately, PM_2.5 has not received the attention that matches its harmfulness. This article is the first to systematically describe the molecular biological mechanism of PM_2.5-induced ischemic stroke, and also propose potential therapeutic and intervention strategies. We highlight the effect of PM_2.5 on traditional cerebrovascular risk factors (hypertension, hyperglycemia, dyslipidemia, atrial fibrillation), which were easily overlooked in previous studies. Additionally, the effects of PM_2.5 on platelet parameters, megakaryocytes activation, platelet methylation, and PM_2.5-induced oxidative stress, local RAS activation, and miRNA alterations in endothelial cells have also been described. Finally, PM_2.5-induced ischemic brain pathological injury and microglia-dominated neuroinflammation are discussed. Our ultimate goal is to raise the public awareness of the harm of PM_2.5 to ischemic stroke, and to provide a certain level of health guidance for stroke-susceptible populations, as well as point out some interesting ideas and directions for future clinical and basic research.

PM2.5 induce the defective efferocytosis and promote atherosclerosis via HIF-1α activation in macrophage

Epidemiological studies demonstrate that fine particulate matter (PM_2.5) promotes the development of atherosclerosis. However, the mechanism insight of PM_2.5-induced atherosclerosis is still lacking. The aim of this study was to explore the biological effects of hypoxia-inducible factor 1α (HIF-1α) on PM_2.5-triggered atherosclerosis. The vascular stiffness, carotid intima-media thickness (CIMT), lipid and atherosclerotic lesion were increased when von Hippel-Lindau (VHL)-null mice were exposed to PM_2.5. Yet, knockout of HIF-1α markedly decreased the PM_2.5-triggered atherosclerotic lesion. We firstly performed microarray analysis in PM_2.5-treated bone morrow-derived macrophages (BMDMs), which showed that PM_2.5 significantly changed the genes expression patterns and affected biological processes such as phagocytosis, apoptotic cell clearance, cellular response to hypoxia, apoptotic process and inflammatory response. Moreover, the data showed knockout of HIF-1α remarkably relieved PM_2.5-induced defective efferocytosis. Mechanistically, PM_2.5 inhibited the level of genes and proteins of efferocytosis receptor c-Mer tyrosine kinase (MerTK), especially in VHL-null BMDMs. In addition, PM_2.5 increased the genes and proteins of a disintegrin and metallopeptidase domain 17 (ADAM17), which caused the MerTK cleavage to form soluble MerTK (sMer) in plasma and cellular supernatant. The sMer was significantly up-regulated in plasma of VHL-null PM_2.5-exposed mice. Moreover, PM_2.5 could induce defective efferocytosis and activate inflammatory response through MerTK/IFNAR1/STAT1 signaling pathway in macrophages. Our results demonstrate that PM_2.5 could induce defective efferocytosis and inflammation by activating HIF-1α in macrophages, ultimately resulting in accelerating atherosclerotic lesion formation and development. Our data suggest HIF-1α in macrophages might be a potential target for PM_2.5-related atherosclerosis.

Shengmai Yin alleviated plaque vulnerability and ischemic myocardial damage in diesel exhaust particle-aggravated atherosclerosis with myocardial ischemia

Exposure to diesel exhaust particles (DEP) increases the risk of ischemic heart disease, especially heart attacks and ischemic/thrombotic strokes. Shengmai Yin (SMY) is a traditional Chinese medicine used to treat coronary heart disease. The aim of this study was to determine the protective role of SMY and the mechanism by which SMY affects DEP-induced cardiovascular injury. This study is expected to provide the basis for the development of an adaptive signature of SMY in the prevention of atherosclerotic cardiovascular disease and premature death from global air pollution exposure. We developed animal models of myocardial ischemia and atherosclerosis (AS) in response to DEP exposure. After SMY treatment, serum lipids returned to normal. Aortic plaque area and MMP9 expression were significantly reduced and collagen fiber expression increased after SMY treatment compared to DEP exposure alone. Thus, the risk of plaque formation and vulnerability is reduced. In addition, SMY improved left ventricular structure, morphology, function, blood flow, infarct area, myocardial damage, and ROS accumulation to varying degrees in ApoE-/- mice. These results indicate that the use of SMY is effective, to varying degrees, for the treatment of dyslipidemia, atherosclerosis, myocardial ischemia, and oxidative stress in ApoE-/- mice. SMY has a potential protective effect in DEP-aggravated AS in people with myocardial ischemia.

Influence of air pollutants on circulating inflammatory cells and microRNA expression in acute myocardial infarction

Air pollutants increase the risk and mortality of myocardial infarction (MI). The aim of this study was to assess the inflammatory changes in circulating immune cells and microRNAs in MIs related to short-term exposure to air pollutants. We studied 192 patients with acute coronary syndromes and 57 controls with stable angina. For each patient, air pollution exposure in the 24-h before admission, was collected. All patients underwent systematic circulating inflammatory cell analyses. According to PM_2.5 exposure, 31 patients were selected for microRNA analyses. STEMI patients exposed to PM_2.5 showed a reduction of CD4⁺ regulatory T cells. Furthermore, in STEMI patients the exposure to PM_2.5 was associated with an increase of miR-146a-5p and miR-423-3p. In STEMI and NSTEMI patients PM_2.5 exposure was associated with an increase of miR-let-7f-5p. STEMI related to PM_2.5 short-term exposure is associated with changes involving regulatory T cells, miR-146a-5p and miR-423-3p.

Melatonin alleviates PM2.5-triggered macrophage M1 polarization and atherosclerosis via regulating NOX2-mediated oxidative stress homeostasis

It is reported that oxidative stress homeostasis was involved in PM_2.5-induced foam cell formation and progression of atherosclerosis, but the exact molecular mechanism is still unclear. Melatonin is an effective antioxidant that could reverse the cardiopulmonary injury. The main purpose of this study is to investigate the latent mechanism of PM_2.5-triggered atherosclerosis development and the protective role of melatonin administration. Vascular Doppler ultrasound showed that PM_2.5 exposure reduced aortic elasticity in ApoE^-/- mice. Meanwhile, blood biochemical and pathological analysis demonstrated that PM_2.5 exposure caused dyslipidemia, elicited oxidative damage of aorta and was accompanied by an increase in atherosclerotic plaque area; while the melatonin administration could effectively alleviate PM_2.5-induced macrophage M1 polarization and atherosclerosis in mice. Further investigation verified that NADPH oxidase 2 (NOX2) and mitochondria are two prominent sources of PM_2.5-induced ROS production in vascular macrophages. Whereas, the combined use of two ROS-specific inhibitors and adopted with melatonin markedly rescued PM_2.5-triggered macrophage M1 polarization and foam cell formation by inhibiting NOX2-mediated crosstalk of Keap1/Nrf2/NF-κB and TLR4/TRAF6/NF-κB signaling pathways. Our results demonstrated that NOX2-mediated oxidative stress homeostasis is critical for PM_2.5-induced atherosclerosis and melatonin might be a potential treatment for air pollution-related cardiovascular diseases.

Exposure to ambient fine particulate matter impedes the function of spleen in the mouse metabolism of high-fat diet

Epidemiological and experimental evidence has been associating the exposure with ambient fine particulate matter (PM_2.5) with metabolic malfunctions such as obesity and cardiovascular disease. As the blood-filter and the important lymphatic organ, spleen participates in the regulation of metabolic balance. In this work, liquid chromatography-mass spectrometry (LC-MS)-based lipidomics, metabolomics and proteomics were performed to study the effects of PM_2.5 exposure and high-fat diet (HFD) induced obesity on mice spleen. By comparing the differences in lipids, metabolites, and proteins in the spleens from PM_2.5 and HFD treated mice, we discovered the individual and combined effects of the two risk factors. The results showed the PM_2.5 exposure altered energy metabolism of the mice, as evidenced by the upregulation of TCA cycle. In addition, the metabolism of branched-chain amino acids was also significantly changed, which might be related to the preventive function of spleen in lipid metabolism. The PM_2.5-induced metabolic changes in spleen could further aggravate the adverse impacts of HFD on mice, resulting in impeded splenic metabolism of lipids. This study revealed the effects of PM_2.5 and obesity mice spleen, which might be of great significance to public health.

Inhaled silica nanoparticles exacerbate atherosclerosis through skewing macrophage polarization towards M1 phenotype

BACKGROUND AND AIMS

Exposure to environmental nanoparticles is related to the adverse impact on health, including cardiovascular system. Various forms of nanoparticles have been reported to interact with endothelium and induce inflammation. However, the potential role of nanoparticles in the pathogenesis of atherosclerosis and their mechanisms of action are still unclear. The aim of this study was to investigate the effect of two broadly used nanomaterials, which also occur in natural environment - silicon oxide (SiO2) and ferric oxide (Fe2O3) in the form of nanoparticles (NPs) - on the development of atherosclerosis.

METHODS

We used apolipoprotein E-knockout mice exposed to silica and ferric oxide nanoparticles in a whole body inhalation chamber.

RESULTS

Inhaled silica nanoparticles augmented the atherosclerotic lesions and increased the percentage of pro-inflammatory M1 macrophages in both the plaque and the peritoneum in apoE-/- mice. Exposure to ferric oxide nanoparticles did not enhance atherogenesis process, however, it caused significant changes in the atherosclerotic plaque composition (elevated content of CD68-positive macrophages and enlarged necrotic core accompanied by the decreased level of M1 macrophages). Both silica and ferric oxide NPs altered the phenotype of T lymphocytes in the spleen by promoting polarization towards Th17 cells.

CONCLUSIONS

Exposure to silica and ferric oxide nanoparticles exerts impact on atherosclerosis development and plaque composition. Pro-atherogenic abilities of silica nanoparticles are associated with activation of pro-inflammatory macrophages.

Urban fine particulate air pollution exposure promotes atherosclerosis in apolipoprotein E-deficient mice by activating perivascular adipose tissue inflammation via the Wnt5a/Ror2 signaling pathway

Urban fine particulate matter (PM_2.5) is a deleterious risk factor in the ambient air and is recognized to exacerbate atherosclerosis. Perivascular adipose tissue (PVAT) secretes a large number of inflammatory cytokines and plays a crucial role in the pathogenic microenvironment of atherogenesis. However, there is a lack of knowledge about the role of PVAT inflammation in the genesis of PM_2.5-related atherosclerosis. The aim of this research was to probe the latent links between PM_2.5 exposure and PVAT inflammation and further discovered the underlying mechanisms of PM_2.5-triggered atherosclerosis pathogenesis. Apolipoprotein E-deficient (ApoE^-/-) mice were exposed to real-world atmospheric PM_2.5 or filtered clean air for three months, the Wnt5a inhibitor Box5 and the Ror2 inhibitor β-Arrestin2 were applied to verify the possible mechanisms. We noticed that the average daily PM_2.5 mass concentration was 84.27 ± 28.84 μg/m³. PM_2.5 inhalation might significantly expedite the deterioration of atherosclerosis, increase the protein and mRNA expressions of MCP-1, IL-6, TNF-α, Wnt5a, and Ror2 in PVAT tissues, upregulate the distributions of IL-6, TNF-α, MCP-1, and leptin in the histological sections of PVAT, promote lipid deposition in the aorta, elevate the plasma levels of leptin, MCP-1, IL-6, TNF-α, LDL-C, TC, and TG, however, decrease the plasma levels of adiponectin and HDL-C, downregulate the distribution of adiponectin. Nevertheless, these effects caused by PM_2.5 exposure were dramatically diminished after the administration of Box5 or β-Arrestin2. This research illuminated that PVAT inflammation was involved in the PM_2.5-induced atherosclerosis process, as well as lipid deposition, which was closely associated with the activation of the Wnt5a/Ror2 signaling pathway.

Evaluation of fine particulate matter on vascular endothelial function in vivo and in vitro

Ambient fine particulate matter (PM_2.5) and high-fat diet (HFD) are linked to the development of atherosclerosis. However, there is still unknown about the PM_2.5-induced atherosclerosis formation on vascular endothelial injury after co-exposed to PM_2.5 and HFD. Thus, the aim of this study was to evaluate the effects of PM_2.5 on atherogenesis in C57BL/6 mice and endothelial cells, as well as the co-exposure effect of PM_2.5 and HFD. In vivo study, C57BL/6 mice exposed to PM_2.5 and fed with standard chow diet (STD) or HFD for 1 month. PM_2.5 could increase vascular stiffness accessed by Doppler ultrasound, and more serious in co-exposure group. PM_2.5 impaired vascular endothelial layer integrity, exfoliated endothelial cells, and inflammatory cells infiltration through H&E staining. PM_2.5 reduced the expression of platelet/endothelial cell adhesion molecule-1 (PECAM-1) in vessel. Moreover, PM_2.5 could induce systemic inflammation detected by Mouse Inflammation Array. In vitro study, PM_2.5 triggered markedly mitochondrial damage by transmission electron microscope (TEM) and flow cytometer. Inflammatory cytokines were significantly increased in PM_2.5-exposed group. The cell viability and migration of endothelial cells were significantly suppressed. In addition, PM_2.5 remarkably declined the expression of vascular endothelial growth factor receptor 2 (VEGFR2) and increased the expression of somatostatin (SST) and its receptor. In conclusion, co-exposure of PM_2.5 and HFD might induce systemic inflammation and endothelial dysfunction in normal mice. Moreover, PM_2.5 could reduce vascular endothelial repair capacity through inhibiting the proliferation and migration of endothelial cells.

Atmospheric fine particulate matter exposure exacerbates atherosclerosis in apolipoprotein E knockout mice by inhibiting autophagy in macrophages via the PI3K/Akt/mTOR signaling pathway

Fine particulate matter (PM_2.5) exposure is intimately linked to atherosclerosis. Defective macrophages autophagy plays an accelerated role in advanced atherosclerosis, however, whether macrophages autophagy has been implicated in the development of PM_2.5-induced atherosclerosis has not been analyzed in full detail. Here we aimed to investigate the association between macrophages autophagy and PM_2.5-induced atherosclerosis, as well as the underlying mechanisms. ApoE^-/- mice were randomly exposed to PM_2.5 or filtered air for 3 months, macrophage RAW264.7 cells were isolated and were stimulated with PM_2.5 sample, selective inhibitors of PI3K/Akt/mTOR pathway LY294002, triciribine, and rapamycin were used in vitro and in vivo to detect the potential mechanisms. We found that PM_2.5 could significantly accelerate atherosclerotic plaque formation in ApoE^-/- mice, increase serum levels of TC and LDL-C, accelerate lipid accumulation in RAW264.7 cells, elevate serum and supernatant levels of IL-6, TNF-α and hs-CRP, decrease the number of autophagosomes in aortic plaque and RAW264.7 cells, reduce the expressions of autophagy-related genes LC3-I, LC3-II and Beclin1 in aortic tissues and RAW264.7 cells but increase the expression of autophagy regulator p62, elevate PI3K, Akt and mTOR distributions in aorta, and increase p-PI3K, p-Akt and p-mTOR protein expressions in aorta and RAW264.7 cells. However, these effects of PM_2.5 were aggravated with the administration of LY294002, triciribine, or rapamycin. This study indicated that the PI3K/Akt/mTOR pathway is involved in the suppression of autophagy induced by PM_2.5 in macrophages, the accelerated effect of PM_2.5 on atherosclerosis was mediated by down-regulation of macrophages autophagy via activating the PI3K/Akt/mTOR signaling pathway.

Ambient fine particulate matter aggravates atherosclerosis in apolipoprotein E knockout mice by iron overload via the hepcidin-ferroportin axis

AIMS

Exposure to fine particulate matter (PM2.5) is correlated to atherosclerosis, but the mechanism remains largely undefined. Iron overload is a significant contributor to atherosclerosis, and iron homeostasis is highly regulated by the hepcidin-ferroportin (FPN) axis. Here we aimed to investigate the association between iron overload and PM2.5-induced atherosclerotic mice.

MAIN METHODS

Apolipoprotein E knockout (ApoE-/-) mice were randomly assigned to filtered air (FA group) or PM2.5 (PM2.5 group) for 3-month inhalation. Daily PM2.5 mass concentrations, serum levels of ferritin, iron, pro-atherosclerotic cytokines and lipid profiles, atherosclerotic lesion areas, hepcidin, FPN and iron depositions in atherosclerotic lesions, hepcidin, FPN mRNA and protein expressions in the aorta were detected, respectively.

KEY FINDINGS

The daily average concentration of atmospheric PM2.5 was 68.2 ± 21.8 μg/m3. Serum levels of ferritin, iron, VEGF, MCP-1, IL-6, TNF-α, TC and LDL-C, atherosclerotic lesion areas, hepcidin and iron depositions in atherosclerotic lesions, hepcidin mRNA and protein expressions in the PM2.5 group were observably higher than those in the FA group. Nevertheless, FPN deposition in atherosclerotic lesions, FPN mRNA and protein expressions in the aorta of the PM2.5 group were markedly lower than those of the FA group.

SIGNIFICANCE

PM2.5 inhalation could exacerbate the formation and development of atherosclerosis in ApoE-/- mice, the potential mechanisms may be partly associated with iron overload via the hepcidin-FPN axis, as well as iron-triggered systemic inflammation and hyperlipidemia.

Low-dose combined exposure of carboxylated black carbon and heavy metal lead induced potentiation of oxidative stress, DNA damage, inflammation, and apoptosis in BEAS-2B cells

Black carbon (BC) and heavy metal lead (Pb), as typical components of atmospheric PM_2.5, have been shown to cause a variety of adverse health effects. However, co-exposure to BC and Pb may induce pulmonary damage by aggravating toxicity via an unknown mechanism. This study aimed to investigate the combined toxicity of carboxylated black carbon (c-BC) and lead acetate (Pb) on human bronchial epithelial cells (BEAS-2B) at the no-observed-adverse-effect level (NOAEL). Cells were exposed to c-BC (6.25 μg/mL) and Pb (4 μg/mL) alone or their combination, and their combined toxicity was investigated by focusing on cell viability, oxidative stress, DNA damage, mitochondrial membrane potential (MMP), apoptosis, and cellular inflammation. Factorial analyses were also used to determine the potential interactions between c-BC and Pb. The results suggested that the combination of c-BC and Pb could significantly increase the production of reactive oxygen species (ROS), malondialdehyde (MDA), and lactate dehydrogenase leakage (LDH) and decrease the activities of glutathione (GSH) and superoxide dismutase (SOD). The excessive oxidative stress could increase the levels of inflammatory cytokine IL-6 and TNF-α, and induce oxidative DNA damage and dissipation of MMP. Moreover, the results also suggested that the combined group could enhance the cellular apoptotic rate and the activation of apoptotic markers like caspase-3, caspase-8, and caspase-9. The factorial analysis further demonstrated that synergistic interaction was responsible for the combined toxicity of c-BC and Pb co-exposure. Most noticeably, the co-exposure of c-BC and Pb could induce some unexpected toxicity, even beyond the known toxicities of the individual compounds in BEAS-2B cells at the NOAEL.

The critical role of endothelial function in fine particulate matter-induced atherosclerosis

Ambient and indoor air pollution contributes annually to approximately seven million premature deaths. Air pollution is a complex mixture of gaseous and particulate materials. In particular, fine particulate matter (PM2.5) plays a major mortality risk factor particularly on cardiovascular diseases through mechanisms of atherosclerosis, thrombosis and inflammation. A review on the PM2.5-induced atherosclerosis is needed to better understand the involved mechanisms. In this review, we summarized epidemiology and animal studies of PM2.5-induced atherosclerosis. Vascular endothelial injury is a critical early predictor of atherosclerosis. The evidence of mechanisms of PM2.5-induced atherosclerosis supports effects on vascular function. Thus, we summarized the main mechanisms of PM2.5-triggered vascular endothelial injury, which mainly involved three aspects, including vascular endothelial permeability, vasomotor function and vascular reparative capacity. Then we reviewed the relationship between PM2.5-induced endothelial injury and atherosclerosis. PM2.5-induced endothelial injury associated with inflammation, pro-coagulation and lipid deposition. Although the evidence of PM2.5-induced atherosclerosis is undergoing continual refinement, the mechanisms of PM2.5-triggered atherosclerosis are still limited, especially indoor PM2.5. Subsequent efforts of researchers are needed to improve the understanding of PM2.5 and atherosclerosis. Preventing or avoiding PM2.5-induced endothelial damage may greatly reduce the occurrence and development of atherosclerosis.

The association of subchronic exposure to low concentration of PM2.5 and high-fat diet potentiates glucose intolerance development, by impairing adipose tissue antioxidant defense and eHSP72 levels

The subchronic exposure to fine particulate matter (PM2.5) and high-fat diet (HFD) consumption lead to glucose intolerance by different mechanisms involving oxidative stress and inflammation. Under stressful conditions, the cells exert a heat shock response (HSR), by releasing the 72-kDa heat shock proteins (eHSP72), fundamental chaperones. The depletion of the HSR can exacerbate the chronic inflammation. However, there are few studies about the early effects of the association of HFD consumption and exposure to low concentrations of PM2.5 in the oxidative stress and HSR, in the genesis of glucose intolerance. Thus, we divided 23 male B6129SF2/J mice into control (n = 6), polluted (n = 6), HFD (n = 6), and high-fat diet + polluted (HFD + polluted) (n = 5) groups. Control and polluted received a standard diet (11.4% of fats), while HFD and HFD + polluted received HFD (58.3% of fats). Simultaneously, polluted and HFD + polluted received 5 μg/10 μL of PM2.5, daily, 7×/week, while control and HFD were exposed to 10 μL of saline solution 0.9% for 12 weeks. At the 12th week, animals were euthanized. We collected the metabolic tissues to analyze oxidative parameters, total blood to the hematological parameters, and plasma to eHSP72 measurement. The association of HFD and PM2.5 impaired glucose tolerance in the 12th week. Besides, it triggered an antioxidant defense by the adipose tissue, which was negatively correlated with eHSP72 levels. In conclusion, a low concentration of PM2.5 exposure associated with HFD consumption leads to glucose intolerance, by impairing adipose tissue antioxidant defense and systemic eHSP72 levels.

Pathogenic Role of Air Pollution Particulate Matter in Cardiometabolic Disease: Evidence from Mice and Humans

Significance: Air pollution is a considerable global threat to human health that dramatically increases the risk for cardiovascular pathologies, such as atherosclerosis, myocardial infarction, and stroke. An estimated 4.2 million cases of premature deaths worldwide are attributable to outdoor air pollution. Among multiple other components, airborne particulate matter (PM) has been identified as the major bioactive constituent in polluted air. While PM-related illness was historically thought to be confined to diseases of the respiratory system, overwhelming clinical and experimental data have now established that acute and chronic exposure to PM causes a systemic inflammatory and oxidative stress response that promotes cardiovascular disease. Recent Advances: A large body of evidence has identified an impairment of redox metabolism and the generation of oxidatively modified lipids and proteins in the lung as initial tissue response to PM. In addition, the pathogenicity of PM is mediated by an inflammatory response that involves PM uptake by tissue-resident immune cells, the activation of proinflammatory pathways in various cell types and organs, and the release of proinflammatory cytokines as locally produced tissue response signals that have the ability to affect organ function in a remote manner. Critical Issues: In the present review, we summarize and discuss the functional participation of PM in cardiovascular pathologies and its risk factors with an emphasis on how oxidative stress, inflammation, and immunity interact and synergize as a response to PM. Future Directions: The impact of PM constituents, doses, and novel anti-inflammatory therapies against PM-related illness is also discussed.

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.

Validation of PM2.5 model particle through physicochemical evaluation and atherosclerotic plaque formation in ApoE-/- mice

PM_2.5 particles are regarded as prominent risk factors that contribute to the development of atherosclerosis. However, the composition of PM_2.5 is rather complicated. This study aimed to provide a model particle that simulates the behavior of actual PM_2.5, for subsequent use in exploring mechanisms and major complications arising from PM_2.5. To establish model particles of PM_2.5, a series of monodisperse SiO₂ microspheres with different average grain diameters were mixed according to the size distribution of actual PM_2.5. The organic carbon (OC) was removed from PM_2.5 and coated onto the SiO₂ model particle, to formulate simulant PM_2.5. Results showed that the size distribution of the model particle was highly approximate to that of the PM_2.5 core. The polycyclic aromatic hydrocarbon (PAHs) composition profile of the simulated PM_2.5 were approximate to PM_2.5, and loading efficiency was approximately 80%-120%. Furthermore, compared to the control, SiO₂-only model particle had negligible cytotoxicity on cell viability and oxidative stress of HUVECs, and marginal effect on the lipid metabolism and atherosclerotic plaque formation in ApoE^-/- mice. In contrast, simulated PM_2.5 exhibited similar cytotoxic and detrimental effects on lipid metabolism and atherosclerotic plaque formation with actual PM_2.5. Traffic-related PM_2.5 had negative effects on endothelial function and led to the formation of atherosclerosis via oxidative stress. The simulated PM_2.5 simulated the outcomes of actual PM_2.5 exposure. Here, we show that SiO₂ particle model cores coated with OC could significantly assist in the evaluation of the effects of specific organic compositions bound on PM_2.5, specifically in the context of environmental health and safety.