Inhalation of Fine Particulate Matter Impairs Endothelial Progenitor Cell Function Via Pulmonary Oxidative Stress

Air Pollution in Cardio-Oncology and Unraveling the Environmental Nexus: JACC: CardioOncology State-of-the-Art Review

Although recent advancements in cancer therapies have extended the lifespan of patients with cancer, they have also introduced new challenges, including chronic health issues such as cardiovascular disease arising from pre-existing risk factors or cancer therapies. Consequently, cardiovascular disease has become a leading cause of non-cancer-related death among cancer patients, driving the rapid evolution of the cardio-oncology field. Environmental factors, particularly air pollution, significantly contribute to deaths associated with cardiovascular disease and specific cancers, such as lung cancer. Despite these statistics, the health impact of air pollution in the context of cardio-oncology has been largely overlooked in patient care and research. Notably, the impact of air pollution varies widely across geographic areas and among individuals, leading to diverse exposure consequences. This review aims to consolidate epidemiologic and preclinical evidence linking air pollution to cardio-oncology while also exploring associated health disparities and environmental justice issues.

Epithelial MAPK signaling directs endothelial NRF2 signaling and IL-8 secretion in a tri-culture model of the alveolar-microvascular interface following diesel exhaust particulate (DEP) exposure

BACKGROUND

Particulate matter 2.5 (PM2.5) deposition in the lung's alveolar capillary region (ACR) is significantly associated with respiratory disease development, yet the molecular mechanisms are not completely understood. Adverse responses that promote respiratory disease development involve orchestrated, intercellular signaling between multiple cell types within the ACR. We investigated the molecular mechanisms elicited in response to PM2.5 deposition in the ACR, in an in vitro model that enables intercellular communication between multiple resident cell types of the ACR.

METHODS

An in vitro, tri-culture model of the ACR, incorporating alveolar-like epithelial cells (NCI-H441), pulmonary fibroblasts (IMR90), and pulmonary microvascular endothelial cells (HULEC) was developed to investigate cell type-specific molecular responses to a PM2.5 exposure in an in-vivo-like model. This tri-culture in vitro model was termed the alveolar capillary region exposure (ACRE) model. Alveolar epithelial cells in the ACRE model were exposed to a suspension of diesel exhaust particulates (DEP) (20 µg/cm2) with an average diameter of 2.5 µm. Alveolar epithelial barrier formation, and transcriptional and protein expression alterations in the directly exposed alveolar epithelial and the underlying endothelial cells were investigated over a 24 h DEP exposure.

RESULTS

Alveolar epithelial barrier formation was not perturbed by the 24 h DEP exposure. Despite no alteration in barrier formation, we demonstrate that alveolar epithelial DEP exposure induces transcriptional and protein changes in both the alveolar epithelial cells and the underlying microvascular endothelial cells. Specifically, we show that the underlying microvascular endothelial cells develop redox dysfunction and increase proinflammatory cytokine secretion. Furthermore, we demonstrate that alveolar epithelial MAPK signaling modulates the activation of NRF2 and IL-8 secretion in the underlying microvascular endothelial cells.

CONCLUSIONS

Endothelial redox dysfunction and increased proinflammatory cytokine secretion are two common events in respiratory disease development. These findings highlight new, cell-type specific roles of the alveolar epithelium and microvascular endothelium in the ACR in respiratory disease development following PM2.5 exposure. Ultimately, these data expand our current understanding of respiratory disease development following particle exposures and illustrate the utility of multicellular in vitro systems for investigating respiratory tract health.

Effects of short-term exercise and endurance training on skeletal muscle mitochondria damage induced by particular matter, atmospherically relevant artificial PM2.5

Introduction

This study aimed to investigate the potential of short-term aerobic exercise to mitigate skeletal muscle mitochondrial damage following ambient PM2.5 exposure, and how 12 weeks of endurance training can enhance aerobic fitness to protect against such damage.

Methods

Twenty-four male C57BL/6 J mice were split into sedentary (SED, n = 12) and endurance training (ETR, n = 12) groups. The ETR group underwent 12 weeks of training (10-15 m/min, 60 min/day, 4 times/week), confirmed by an Endurance Exercise Capacity (EEC) test. Post-initial training, the SED group was further divided into SSED (SED and sedentary, n = 6) and SPE (SED and PM2.5 + Exercise, n = 6). Similarly, the ETR group was divided into EEX (ETR and Exercise, n = 6) and EPE (ETR and PM2.5 + Exercise, n = 6). These groups underwent 1 week of atmospherically relevant artificial PM2.5 exposure and treadmill running (3 times/week). Following treatments, an EEC test was conducted, and mice were sacrificed for blood and skeletal muscle extraction. Blood samples were analyzed for oxidative stress indicators, while skeletal muscles were assessed for mitochondrial oxidative metabolism, antioxidant capacity, and mitochondrial damage using western blot and transmission electron microscopy (TEM).

Results

After 12 weeks of endurance training, the EEC significantly increased (p < 0.000) in the ETR group compared to the SED group. Following a one-week comparison among the four groups with atmospherically relevant artificial PM2.5 exposure and exercise treatment post-endurance training, the EEX group showed improvements in EEC, oxidative metabolism, mitochondrial dynamics, and antioxidant functions. Conversely, these factors decreased in the EPE group compared to the EEX. Additionally, within the SPE group, exercise effects were evident in HK2, LDH, SOD2, and GPX4, while no impact of short-term exercise was observed in all other factors. TEM images revealed no evidence of mitochondrial damage in both the SED and EEX groups, while the majority of mitochondria were damaged in the SPE group. The EPE group also exhibited damaged mitochondria, although significantly less than the SPE group.

Conclusion

Atmospherically relevant artificial PM2.5 exposure can elevate oxidative stress, potentially disrupting the benefits of short-term endurance exercise and leading to mitochondrial damage. Nonetheless, increased aerobic fitness through endurance training can mitigate PM2.5-induced mitochondrial damage.

Indoor particulate matter concentrations and air cleaner intervention association with biomarkers in former smokers with COPD

BACKGROUND

Indoor pollutants have been associated with worse clinical outcomes in chronic obstructive pulmonary disease (COPD). Elevated biomarkers are associated with ambient pollution exposure, however the association with indoor pollution remains unclear.

METHODS

Former smokers with spirometry-confirmed COPD were randomized to portable air cleaner or placebo. Indoor particulate matter (PM2.5, PM10, and ultrafine particles [UFP; PM<0.1]) and biomarkers were measured longitudinally at pre-specified intervals and course PM fraction (PM10-2.5) was calculated. Biomarkers were categorized based on associations with biologic mechanisms: inflammation (white blood cell count, interleukin [IL]-6, IL-8, IL-1β, tumor necrosis factor-α, interferon-γ, serum amyloid A), platelet activation (P-selectin, CD40 ligand [CD40L], 11-dehdydro-thromboxane-B2 [11dTxB2]), endothelial dysfunction (Vascular Cell Adhesion Molecule [VCAM]-1, Intercellular Adhesion Molecule [ICAM]-1), and oxidative stress (thiobarbituric acid reactive substances [TBARS], 8-hydroxydeoxyguanosine, 8-isoprostane). Associations between PM concentrations and each biomarker were analyzed using multivariable linear mixed models. An intention-to-treat analysis was performed to evaluate the air cleaner intervention on the biomarker levels longitudinally.

RESULTS

Fifty-eight participants were randomized to each group. Finer PM was more strongly associated with higher IL-8 (mean difference per doubling: UFP 13.9% [p = 0.02], PM2.5 6.8% [p = 0.002], PM10-2.5 5.0% [p = 0.02]) while interferon-γ was associated with UFP and IL-1β with PM10-2.5. UFP and PM2.5 were associated with elevated levels of the oxidative stress biomarkers TBARS and 8-isoprostane respectively. For platelet activation markers, UFP was associated with higher 11dTxB2 while PM2.5 was associated with higher P-selectin and CD40L. Pollutants were not associated with biomarkers of endothelial dysfunction. In intention-to-treat analysis there was no association of the air cleaner intervention with any of the biomarkers.

DISCUSSION

Among former smokers with COPD, elevated levels of indoor air pollutants, particularly ultrafine particles (PM<0.1), were associated with elevated biomarkers of inflammation, platelet activation, and oxidative stress. However, an air cleaner intervention that reduced PM did not significantly reduce biomarker levels.

Oxidative stress is the pivot for PM2.5-induced lung injury

Fine particulate matter (PM2.5) is a primary air pollutant recognized worldwide as a serious threat to public health. PM2.5, which has a diameter of less than 2.5 μm, is known to cause various diseases, including cardiovascular, respiratory, metabolic, and neurological diseases. Studies have shown that the respiratory system is particularly susceptible to PM2.5 as it is the first line of defense against external pollutants. PM2.5 can cause oxidative stress, which is triggered by the catalyzation of biochemical reactions, the activation of oxidases and metabolic enzymes, and mitochondrial dysfunction, all of which can lead to lung injury and aggravate various respiratory diseases including chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis, and cancer. Oxidative stress plays a crucial role in the harmful effects and mechanisms of PM2.5 on the respiratory system by activating several detrimental pathways related to inflammation and cellular damage. However, experimental studies have shown that antioxidative therapy methods can effectively cure PM2.5-induced lung injury. This review aims to clarify how PM2.5 induces oxidative stress and the mechanisms by which it is involved in the aggravation of various lung diseases. Additionally, we have listed antioxidant treatments to protect against PM2.5-induced lung injury.

Redox and inflammatory mechanisms linking air pollution particulate matter with cardiometabolic derangements

Air pollution is the largest environmental risk factor for disease and premature death. Among the different components that are present in polluted air, fine particulate matter below 2.5 μm in diameter (PM2.5) has been identified as the main hazardous constituent. PM2.5 mainly arises from fossil fuel combustion during power generation, industrial processes, and transportation. Exposure to PM2.5 correlates with enhanced mortality risk from cardiovascular diseases (CVD), such as myocardial infarction and stroke. Over the last decade, it has been increasingly suggested that PM2.5 affects CVD already at the stage of risk factor development. Among the multiple biological mechanisms that have been described, the interplay between oxidative stress and inflammation has been consistently highlighted as one of the main drivers of pulmonary, systemic, and cardiovascular effects of PM2.5 exposure. In this context, PM2.5 uptake by tissue-resident immune cells in the lung promotes oxidative and inflammatory mediators release that alter tissue homeostasis at remote locations. This pathway is central for PM2.5 pathogenesis and might account for the accelerated development of risk factors for CVD, including obesity and diabetes. However, transmission and end-organ mechanisms that explain PM2.5-induced impaired function in metabolic active organs are not completely understood. In this review, the main features of PM2.5 physicochemical characteristics related to PM2.5 ability to induce oxidative stress and inflammation will be presented. Hallmark and recent epidemiological and interventional studies will be summarized and discussed in the context of current air quality guidelines and legislation, knowledge gaps, and inequities. Lastly, mechanistic studies at the intersection between redox metabolism, inflammation, and function will be discussed, with focus on heart and adipose tissue alterations. By offering an integrated analysis of PM2.5-induced effects on cardiometabolic derangements, this review aims to contribute to a better understanding of the pathogenesis and potential interventions of air pollution-related CVD.

Cigarette smoking and air pollution exposure and their effects on cardiovascular diseases

Cardiovascular disease (CVD) has no socioeconomic, topographical, or sex limitations as reported by the World Health Organization (WHO). The significant drivers of CVD are cardio-metabolic, behavioral, environmental, and social risk factors. However, some significant risk factors for CVD (e.g., a pitiable diet, tobacco smoking, and a lack of physical activities), have also been linked to an elevated risk of cardiovascular disease. Lifestyles and environmental factors are known key variables in cardiovascular disease. The familiarity with smoke goes along with the contact with the environment: air pollution is considered a source of toxins that contribute to the CVD burden. The incidence of myocardial infarction increases in males and females and may lead to fatal coronary artery disease, as confirmed by epidemiological studies. Lipid modification, inflammation, and vasomotor dysfunction are integral components of atherosclerosis development and advancement. These aspects are essential for the identification of atherosclerosis in clinical investigations. This article aims to show the findings on the influence of CVD on the health of individuals and human populations, as well as possible pathology and their involvement in smoking-related cardiovascular diseases. This review also explains lifestyle and environmental factors that are known to contribute to CVD, with indications suggesting an affiliation between cigarette smoking, air pollution, and CVD.

Sex Associations Between Air Pollution and Estimated Atherosclerotic Cardiovascular Disease Risk Determination

Objective: The purpose of this study was to investigate the sex correlations of particulate matters (PM2.5, PM10, PM2.5-10), NO2 and NOx with ASCVD risk in the UK Biobank population. Methods: Among 285,045 participants, pollutants were assessed and correlations between ASCVD risk were stratified by sex and estimated using multiple linear and logistic regressions adjusted for length of time at residence, education, income, physical activity, Townsend deprivation, alcohol, smocking pack years, BMI and rural/urban zone. Results: Males presented higher ASCVD risk than females (8.63% vs. 2.65%, p < 0.001). In males PM2.5, PM10, NO2, and NOx each were associated with an increased ASCVD risk >7.5% in the adjusted logistic models, with ORs [95% CI] for a 10 μg/m3 increase were 2.17 [1.87-2.52], 1.15 [1.06-1.24], 1.06 [1.04-1.08] and 1.05 [1.04-1.06], respectively. In females, the ORs for a 10 μg/m3 increase were 1.55 [1.19-2.05], 1.22 [1.06-1.42], 1.07 [1.03-1.10], and 1.04 [1.02-1.05], respectively. No association was observed in both sexes between ASCVD risk and PM2.5-10. Conclusion: Our findings may suggest the possible actions of air pollutants on ASCVD risk.

Long-term effects of particulate matter on incident cardiovascular diseases in middle-aged and elder adults: The CHARLS cohort study

BACKGROUND

Although there is evidence of long-term effects of particulate matter (PM) on cardiovascular diseases (CVD), researches about long-term effects of PM₁ on CVD are limited. We aimed to examine the long-term effects and magnitude of PM, especially PM₁, on incident CVD in China.

METHODS

We included 6016 participants aged ≥ 45 years without CVD at baseline in 2011 from the China Health and Retirement Longitudinal Study. Personal PM (PM₁, PM_2.5, and PM₁₀) concentrations were estimated using geocoded residential address. Generalized linear mixed models and SHapley Additive exPlanation were utilized to calculate the impacts and contributions of PM on CVD. Sensitivity analyses were used to check the robustness.

RESULTS

After a follow up of 4-year, 481 (7.99 %) participants developed CVD. Per 10 μg/m³ uptick in 1-year average concentrations of PM₁, PM_2.5 and PM₁₀ was associated with a 1.20 [95 % confidence interval (CI): 1.05-1.37], 1.13 (95 % CI: 1.11-1.15), and 1.10 (95 % CI: 1.06-1.13) fold risk of incident CVD, respectively. The 2-year average concentrations of PM₁, PM_2.5 and PM₁₀ were associated with incident CVD, corresponding to a 1.03 (95 % CI: 0.96-1.10), 1.11 (95 % CI: 1.02-1.21), and 1.09 (95 % CI: 1.03-1.15) fold risk, respectively. The SHapley Additive exPlanation values of PM₁, PM_2.5, and PM₁₀ were 0.170, 0.153, and 0.053, respectively, corresponding to the first, second, and fifth among all air pollutants. Effects of PM₁, PM_2.5 and PM₁₀ on CVD remained statistically significant in two-pollutant models. The elderly, males, smokers and alcohol drinkers tended to have slightly higher effects, while the differences were not statistically significant (all P-values > 0.05) between subgroups.

CONCLUSION

Long-term exposure to PM₁, PM_2.5, and PM₁₀ was associated with an increased incidence of CVD. The smaller the particle size, the more important it was for incident CVD indicating that emphasis should be placed on small size of PM.

Fine particulate matter (PM2.5)-induced pulmonary oxidative stress contributes to increases in glucose intolerance and insulin resistance in a mouse model of circadian dyssynchrony

Results of human and animal studies independently suggest that either ambient fine particulate matter (PM2.5) air pollution exposure or a disturbed circadian rhythm (circadian dyssynchrony) are important contributing factors to the rapidly evolving type-2-diabetes (T2D) epidemic. The objective of this study is to investigate whether circadian dyssynchrony increases the susceptibility to PM2.5 and how PM2.5 affects metabolic health in circadian dyssynchrony. We examined systemic and organ-specific changes in glucose homeostasis and insulin sensitivity in mice maintained on a regular (12/12 h light/dark) or disrupted (18/6 h light/dark, light-induced circadian dyssynchrony, LICD) light cycle exposed to air or concentrated PM2.5 (CAP, 6 h/day, 30 days). Exposures during Zeitgeber ZT3-9 or ZT11-17 (Zeitgeber in circadian time, ZT0 = begin of light cycle) tested for time-of-day PM2.5 sensitivity (chronotoxicity). Mice transgenic for lung-specific overexpression of extracellular superoxide dismutase (ecSOD-Tg) were used to assess the contribution of CAP-induced pulmonary oxidative stress. Both, CAP exposure from ZT3-9 or ZT11-17, decreased glucose tolerance and insulin sensitivity in male mice with LICD, but not in female mice or in mice kept on a regular light cycle. Although changes in glucose homeostasis in CAP-exposed male mice with LICD were not associated with obesity, they were accompanied by white adipose tissue (WAT) inflammation, impaired insulin signaling in skeletal muscle and liver, and systemic and pulmonary oxidative stress. Preventing CAP-induced oxidative stress in the lungs mitigated the CAP-induced decrease in glucose tolerance and insulin sensitivity in LICD. Our results demonstrate that circadian dyssynchrony is a novel susceptibility state for PM2.5 and suggest that PM2.5 by inducing pulmonary oxidative stress increases glucose intolerance and insulin resistance in circadian dyssynchrony.

Circadian variation in stroke onset: Differences between ischemic and hemorrhagic stroke and weekdays versus weekends

OBJECTIVES

To delineate diurnal variation onset distinguishing ischemic from hemorrhagic stroke, wake from sleep onset, and weekdays from weekends/holidays.

MATERIALS AND METHODS

We analyzed patients enrolled in the FAST-MAG trial of field-initiated neuroprotective agent in patients with hyperacute stroke within 2h of symptoms onset. Stroke onset times were analyzed in 1h, 4h, and 12h time blocks throughout the 24h day-night cycle. Patient demographic, clinical features, stroke severity, and prehospital workflow were evaluated for association with onset times.

RESULTS

Among 1615 acute cerebrovascular disease patients, final diagnoses were acute cerebral ischemia in 76.5% and Intracerebral hemorrhage in 23.5%. Considering all acute cerebrovascular disease patients, frequency of wake onset times showed a bimodal pattern, with peaks on onsets at 09:00-13:59 and 17:00-18:59 and early morning (00:00-05:59) onset in only 3.8%. Circadian rhythmicity differed among stroke subtypes: in acute cerebral ischemia, a single broad plateau of elevated incidences was seen from 10:00-21:59; in Intracerebral hemorrhage, bimodal peaks occurred at 09:00 and 19:00. The ratio of Intracerebral hemorrhage to acute cerebral ischemia occurrence was highest in early morning, 02:00-06:59. Marked weekday vs weekends pattern variation was noted for acute cerebral ischemia, with a broad plateau between 09:00 and 21:59 on weekdays but a unimodal peak at 14:00-15:59 on weekends.

CONCLUSIONS

Wake onset of acute cerebrovascular disease showed a marked circadian variation, with distinctive patterns of a broad elevated plateau among acute cerebral ischemia patients; a bimodal peak among intracerebral hemorrhage patients; and a weekend change in acute cerebral ischemia pattern to a unimodal peak.

Effect of carbonaceous ultrafine particles on the structure and oligomerization of Aβ42 peptide

The impact of pervasive air pollutants on human health is a growing concern in scientific communities. Among different air pollutants, ultrafine particles (UFPs; with aerodynamic diameter <100 nm) might pass through biological barriers and have a severe impact on human health, including early progression of neurodegenerative diseases such as Alzheimer's disease (AD). A significant fraction of UFPs consists of carbonaceous compounds, composed of elemental and organic carbon (EC and OC). While in-vivo experimental studies showed the neurotoxicity of typical OC and polycyclic aromatic hydrocarbons (PAHs), the molecular interactions involved in the progression of AD remain unclear. In this study, molecular dynamics simulations were performed to investigate the impact of carbonaceous UFPs on the structure of the Aβ₄₂ monomer and the oligomerization of four Aβ₄₂ peptides, associated with the development of AD. For the simulations, a fullerene (C₆₀) was used for the modeling of EC, while benzo [a]pyrene (B[a]P) was used for the modeling of OC. The results revealed that the presence of C₆₀ accelerated the tetramerization of Aβ₄₂ peptides by 2.5 times, while C₆₀/B[a]P promoted the unfolding of the peptide monomer showing the strongest interactions with the Aβ₄₂ monomer. Similarly, C₆₀/4B[a]P decreased the number of helices in the secondary structure of the peptide monomer by 60%. The simplified UFP models in this study, promoted the early aggregation of peptides to dimers, suggesting the progression of AD.

Association between long-term exposure to ambient particulate matter and blood pressure, hypertension: an updated systematic review and meta-analysis

Evidence of more recent studies should be updated to evaluate the effect of long-term exposure to particulate matter (PM) on blood pressure and hypertension.        Studies of long-term effects of PM₁, PM_2.5 and PM₁₀ on blood pressure (SBP, DBP, MAP), hypertension were searched in Pubmed, Web of Science and Embase before May, 2021. Meta-analysis of 41 studies showed that exposure to PM₁, PM_2.5 was associated with SBP (1.76 mmHg (95%CI:0.71, 2.80) and 0.63 mmHg (95%CI:0.40, 0.85), per 10 μg/m³ increase in PM), all three air pollutants (PM₁, PM_2.5, PM₁₀) was associated with DBP (1.16 mmHg (95%CI:0.34, 1.99), 0.31 mmHg (95%CI:0.16, 0.47), 1.17 mmHg (95%CI:0.24, 2.09), respectively. As for hypertension, PM₁, PM_2.5 and PM₁₀ were all significantly associated with higher risk of hypertension (OR=1.27 (95%CI:1.06, 1.52), 1.15 (95%CI:1.10, 1.20) and 1.11 (95%CI:1.07, 1.16). In conclusion, our study indicated a positive association between long-term exposure to particulate matter and increased blood pressure, hypertension.

Fine Particulate Matter (PM2.5)-Induced Pulmonary Oxidative Stress Contributes to Changes in the Plasma Lipidome and Liver Transcriptome in Mice

Fine particulate matter (PM2.5) air pollution exposure increases the cardiovascular disease risk. Although the specific mechanisms remain elusive, it is thought that PM2.5-induced oxidative stress and endothelial dysfunction contribute to this pathogenesis. Our previous findings indicate that PM2.5 impairs vascular health via a circulating factor and that plasma lipid changes contribute to the observed vascular effects. In the current study, we extend on these findings by further characterizing PM2.5-induced changes in circulating lipids and examining whether the observed changes were accompanied by related alterations in the liver transcriptome. To address the role of pulmonary oxidative stress, we exposed wild-type (WT) mice and mice that overexpress extracellular superoxide dismutase (ecSOD-Tg) in the lungs to concentrated ambient PM2.5 (CAP, 9 days). We found that CAP decreased circulating complex lipids and increased free fatty acids and acylcarnitines in WT, but not ecSOD-Tg mice. These plasma lipid changes were accompanied by transcriptional changes in genes that regulate lipid metabolism (e.g., upregulation of lipid biosynthesis, downregulation of mitochondrial/peroxisomal FA metabolism) in the liver. The CAP-induced changes in lipid homeostasis and liver transcriptome were accompanied by pulmonary but not hepatic oxidative stress and were largely absent in ecSOD-Tg mice. Our results suggest that PM2.5 impacts hepatic lipid metabolism; however, it remains unclear whether the transcriptional changes in the liver contribute to PM2.5-induced changes in plasma lipids. Regardless, PM2.5-induced changes in the plasma lipidome and hepatic transcriptome are, at least in part, mediated by pulmonary oxidative stress.

CARD9 deficiency improves the recovery of limb ischemia in mice with ambient fine particulate matter exposure

Background

Exposure to fine particulate matter (PM) is a significant risk for cardiovascular diseases largely due to increased reactive oxygen species (ROS) production and inflammation. Caspase recruitment domain (CARD)9 is critically involved in innate immunity and inflammation. The present study was designed to test the hypothesis that CARD9 signaling is critically involved in PM exposure-induced oxidative stress and impaired recovery of limb ischemia.

Methods and results

Critical limb ischemia (CLI) was created in male wildtype C57BL/6 and age matched CARD9 deficient mice with or without PM (average diameter 2.8 μm) exposure. Mice received intranasal PM exposure for 1 month prior to creation of CLI and continued for the duration of the experiment. Blood flow and mechanical function were evaluated in vivo at baseline and days 3, 7, 14, and 21 post CLI. PM exposure significantly increased ROS production, macrophage infiltration, and CARD9 protein expression in ischemic limbs of C57BL/6 mice in association with decreased recovery of blood flow and mechanical function. CARD9 deficiency effectively prevented PM exposure-induced ROS production and macrophage infiltration and preserved the recovery of ischemic limb with increased capillary density. CARD9 deficiency also significantly attenuated PM exposure-induced increase of circulating CD11b⁺/F4/80⁺ macrophages.

Conclusion

The data indicate that CARD9 signaling plays an important role in PM exposure-induced ROS production and impaired limb recovery following ischemia in mice.

Transplantation of Endothelial Progenitor Cells: Summary and prospect

Endothelial Progenitor Cells (EPCs) are precursor cells of endothelial cells (ECs), which can differentiate into vascular ECs, protect from endothelial dysfunction and tissue ischemia, and reduce vascular hyperplasia. Due to these functions, EPCs are used as a candidate cell source for transplantation strategies. In recent years, a great progress was achieved in EPCs biology research, and EPCs transplantation has become a research hotspot. At present, transplanted EPCs have been used to treat ischemic diseases due to their powerful vasculogenesis and beneficial paracrine effects. Although EPCs transplantation has been proved to play an important role, the clinical application of EPCs still faces many challenges. This review briefly summarized the basic characteristics of EPCs, the process of EPCs transplantation promoting the healing of ischemic tissue, and the ways to improve the efficiency of EPCs transplantation. In addition, the application of EPCs in neurological improvement, cardiovascular and respiratory diseases and the challenges and problems in clinical application of EPCs were also discussed. In the end, the application of EPCs transplantation in regenerative medicine and tissue engineering was discussed.

Different components of air pollutants and neurological disorders

The harmful effects of air pollution can cause various diseases. Most research on the hazards of air pollution focuses on lung and cardiovascular diseases. In contrast, the impact of air pollution on neurological disorders is not widely recognized. Air pollution can cause various neurological conditions and diseases, such as neural inflammation, neurodegeneration, and cerebrovascular barrier disorder; however, the mechanisms underlying the neurological diseases induced by various components of air pollutants remain unclear. The present paper summarizes the effects of different components of air pollutants, including particulate matter, ozone, sulfur oxides, carbon oxides, nitrogen oxides, and heavy metals, on the nervous system and describes the impact of various air pollutants on neurological disorders, providing ideas for follow-up research.

Adverse effects of air pollution-derived fine particulate matter on cardiovascular homeostasis and disease

Air pollution is a rapidly growing major health concern around the world. Atmospheric particulate matter that has a diameter of less than 2.5 µm (PM2.5) refers to an air pollutant composed of particles and chemical compounds that originate from various sources. While epidemiological studies have established the association between PM2.5 exposure and cardiovascular diseases, the precise cellular and molecular mechanisms by which PM2.5 promotes cardiovascular complications are yet to be fully elucidated. In this review, we summarize the various sources of PM2.5, its components, and the concentrations of ambient PM2.5 in various settings. We discuss the experimental findings to date that evaluate the potential adverse effects of PM2.5 on cardiovascular homeostasis and function, and the possible therapeutic options that may alleviate PM2.5-driven cardiovascular damage.

Pollution and coronary risk: how much does it matter?

Air pollutants are a complex mixture of gaseous substances and particulate matter (PM). Each component potentially has specific harmful effects on human health, but several experimental and clinical studies have shown a strong impact of fine particles on major adverse cardiovascular events. Most of the available evidence concerns the effects of exposure to PM with a diameter of <2.5 µm (PM2.5) and the risk of developing coronary heart disease through inflammation and oxidative stress. While prolonged exposure to PM2.5 has been shown to be associated with the development of atherosclerosis and cardio-metabolic risk factors, short-term exposure has instead proved to be a trigger for acute coronary events, and especially in subjects with pre-existing coronary artery disease. As such, environmental PM2.5 is a major risk element for global public health. This underlines on the one hand not only the need to adopt and encourage preventive measures especially for individuals with a higher risk profile but also to practice environmental policies that are effective in promoting the reduction of exposure to pollutants.

Short-Term Exposure of PM2.5 and Epigenetic Aging: A Quasi-Experimental Study

Epigenetic age (EA) is an emerging DNA methylation-based biomarker of biological aging, but whether EA is causally associated with short-term PM_2.5 exposure remains unknown. We conducted a quasi-experimental study of 26 healthy adults to test whether short-term PM_2.5 exposure accelerates seven EAs with three health examinations performed before, during, and after multiple PM_2.5 pollution waves. Seven EAs were derived from the DNA methylation profiles of the Illumina HumanMethylationEPIC BeadChip from CD4+ T-helper cells. We found that an increase of 10 μg/m³ in the 0-24 h personal PM_2.5 exposure prior to health examinations was associated with a 0.035, 0.035, 0.050, 0.055, 0.052, and 0.037-unit increase in the changes of z-scored DNA methylation age acceleration (AA,Horvath), AA (Hannum), AA (GrimAge), DunedinPoAm, mortality risk score (MS), and epiTOC, respectively (p-values < 0.05). The same increase in the 24-48 h average personal PM_2.5 exposure yielded smaller effects but was still robustly associated with the changes in AA (GrimAge), DunedinPoAm, and MS. Such acute aging effects of PM_2.5 were mediated by the changes in several circulating biomarkers, including EC-SOD and sCD40L, with up to ∼28% mediated proportions. Our findings demonstrated that short-term PM_2.5 exposure could accelerate aging reflected by DNA methylation profiles via blood coagulation, oxidative stress, and systematic inflammation.

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.

Air pollution and cardiovascular disease: the Paul Wood Lecture, British Cardiovascular Society 2021

Air pollution is associated with up to 8.8 million excess deaths worldwide each year and is a major contributor to the global burden of disease. Cardiovascular conditions are the predominant cause for air pollution-related deaths and there is an urgent need to address the silent pandemic of air pollution on cardiovascular health. Air pollution exposure is associated with acute events like acute coronary syndrome and stroke, and with chronic conditions, such as atherosclerosis and heart failure. Several potential mechanisms have been proposed that link particle inhalation to cardiovascular disease including oxidative stress and inflammation, changes in autonomic balance and neuroendocrine regulation and the particle translocation into the circulation itself. This, in turn, can cause endothelial, vasomotor and fibrinolytic dysfunction and increased thrombogenicity and blood pressure which are implicated in the mediation of adverse cardiovascular events. Certain interventions can help mitigate these adverse effects. At an individual level, this includes the use of a facemask and indoor air purification systems. At an environmental level, interventions reducing the generation or release of combustion-derived pollutants are key and include public health policies to facilitate active transport, cleaner sources of energy and reductions in vehicular and fossil fuel emissions. In this review, we summarise the key pathways and mechanisms that draw together how air pollution can lead to adverse cardiovascular effects, as well as explore potential interventions to reduce the burden of air pollution-induced cardiovascular morbidity and mortality.

N-acetylcysteine alleviates fine particulate matter (PM2.5)-induced lung injury by attenuation of ROS-mediated recruitment of neutrophils and Ly6Chigh monocytes and lung inflammation

BACKGROUND

Exposure to particulate matter (PM) may contribute to lung inflammation and injury. The therapeutic effect of N-acetylcysteine (NAC), a well-known antioxidant, with regards to the prevention and treatment of fine PM (PM2.5)-induced lung injury is poorly understood. This study aimed to determine the effect of PM2.5 on the recruitment of neutrophils and Ly6C^high monocytes into lung alveoli and the production of proinflammatory proteins by stimulating the generation of reactive oxygen species (ROS), and to investigate the therapeutic effect of NAC on PM2.5-induced lung injury.

METHODS

C57BL/6 mice were exposed to a single administration of PM2.5 (200 μg/100 μl/mouse) or phosphate-buffered saline (control) via intratracheal instillation. The mice were injected intratracheally via a microsprayer aerosolizer with NAC (20 or 40 mg/kg) 1 h before PM2.5 instillation and 24 h after PM2.5 instillation. Total protein, VEGF, IL-6, and TNF-α in bronchoalveolar lavage fluid (BALF) were measured. Oxidative stress was evaluated by determining levels of malondialdehyde (MDA) and nitrite in BALF. Flow cytometric analysis was used to identify and quantify neutrophils and Ly6C^high and Ly6C_low monocyte subsets.

RESULTS

Neutrophil count, total protein, and VEGF content in BALF significantly increased after PM2.5 exposure and reached the highest level on day 2. Increased levels of TNF-alpha, IL-6, nitrite, and MDA in BALF were also noted. Flow cytometric analysis showed increased recruitment of neutrophils and Ly6C^high, but not Ly6C^low monocytes, into lung alveoli. Treatment with NAC via the intratracheal spray significantly attenuated the recruitment of neutrophils and Ly6C^high monocytes into lung alveoli in PM2.5-treated mice in a dose-dependent manner. Furthermore, NAC significantly attenuated the production of total protein, VEGF, nitrite, and MDA in the mice with PM2.5-induced lung injury in a dose-dependent manner.

CONCLUSION

PM2.5-induced lung injury caused by the generation of oxidative stress led to the recruitment of neutrophils and Ly6C^high monocytes, and production of inflammatory proteins. NAC treatment alleviated PM2.5-induced lung injury by attenuating the ROS-mediated recruitment of neutrophils and Ly6C^high monocytes and lung inflammation.

Air Pollution Exposure Induces Vascular Injury and Hampers Endothelial Repair by Altering Progenitor and Stem Cells Functionality

Extensive evidence indicates an association of air pollution exposure with an increased risk of cardiovascular disease (CVD) development. Fine particulate matter (PM) represents one of the main components of urban pollution, but the mechanisms by which it exerts adverse effects on cardiovascular system remain partially unknown and under investigation. The alteration of endothelial functions and inflammation are among the earliest pathophysiological impacts of environmental exposure on the cardiovascular system and represent critical mediators of PM-induced injury. In this context, endothelial stem/progenitor cells (EPCs) play an important role in vascular homeostasis, endothelial reparative capacity, and vasomotor functionality modulation. Several studies indicate the impairment of EPCs' vascular reparative capacity due to PM exposure. Since a central source of EPCs is bone marrow (BM), their number and function could be related to the population and functional status of stem cells (SCs) of this district. In this review, we provide an overview of the potential mechanisms by which PM exposure hinders vascular repair by the alteration of progenitor and stem cells' functionality.

Genetic Variations on Redox Control in Cardiometabolic Diseases: The Role of Nrf2

The transcription factor Nrf2 is a master regulator of multiple cytoprotective genes that maintain redox homeostasis and exert anti-inflammatory functions. The Nrf2-Keap1 signaling pathway is a paramount target of many cardioprotective strategies, because redox homeostasis is essential in cardiovascular health. Nrf2 gene variations, including single nucleotide polymorphisms (SNPs), are correlated with cardiometabolic diseases and drug responses. SNPs of Nrf2, KEAP1, and other related genes can impair the transcriptional activation or the activity of the resulting protein, exerting differential susceptibility to cardiometabolic disease progression and prevalence. Further understanding of the implications of Nrf2 polymorphisms on basic cellular processes involved in cardiometabolic diseases progression and prevalence will be helpful to establish more accurate protective strategies. This review provides insight into the association between the polymorphisms of Nrf2-related genes with cardiometabolic diseases. We also briefly describe that SNPs of Nrf2-related genes are potential modifiers of the pharmacokinetics that contribute to the inter-individual variability.

Chronic exposure to polluted urban air aggravates myocardial infarction by impaired cardiac mitochondrial function and dynamics

Air pollution exposure positively correlates with increased cardiovascular morbidity and mortality rates, mainly due to myocardial infarction (MI). Herein, we aimed to study the metabolic mechanisms underlying this association, focusing on the evaluation of cardiac mitochondrial function and dynamics, together with its impact over MI progression. An initial time course study was performed in BALB/c mice breathing filtered air (FA) or urban air (UA) in whole-body exposure chambers located in Buenos Aires City downtown for up to 16 weeks (n = 8 per group and time point). After 12 weeks, lung inflammatory cell recruitment was evident in UA-exposed mice. Interestingly, impaired redox metabolism, characterized by decreased lung SOD activity and increased GSSG levels and NOX activity, precede local inflammation in this group. At this selected time point, additional mice were exposed to FA or UA (n = 12 per group) and alveolar macrophage PM uptake and nitric oxide (NO) production was observed in UA-exposed mice, together with increased pro-inflammatory cytokine levels (TNF-α and IL-6) in BAL and plasma. Consequently, impaired heart tissue oxygen metabolism and altered mitochondrial ultrastructure and function were observed in UA-exposed mice after 12 weeks, characterized by decreased active state respiration and ATP production rates, and enhanced mitochondrial H₂O₂ production. Moreover, disturbed cardiac mitochondrial dynamics was detected in this group. This scenario led to a significant increase in the area of infarcted tissue following myocardial ischemia reperfusion injury in vivo, from 43 ± 3% of the area at risk in mice breathing FA to 66 ± 4% in UA-exposed mice (n = 6 per group, p < 0.01), together with a sustained increase in LVEDP during myocardial reperfusion. Taken together, our data unravel cardiac mitochondrial mechanisms that contribute to the understanding of the adverse health effects of urban air pollution exposure, and ultimately highlight the importance of considering environmental factors in the development of cardiovascular diseases.

Tempol Preserves Endothelial Progenitor Cells in Male Mice with Ambient Fine Particulate Matter Exposure

Ambient fine particulate matter (PM) exposure associates with an increased risk of cardiovascular diseases (CVDs). Major sex differences between males and females exist in epidemiology, pathophysiology, and outcome of CVDs. Endothelial progenitor cells (EPCs) play a vital role in the development and progression of CVDs. PM exposure-induced reduction of EPCs is observed in male, not female, mice with increased reactive oxygen species (ROS) production and oxidative stress. The lung is considered an important source of ROS in mice with PM exposure. The aim of the present study was to investigate the sex differences in pulmonary superoxide dismutase (SOD) expression and ROS production, and to test the effect of SOD mimic Tempol on the populations of EPCs in mice with PM exposure. Both male and female C57BL/6 mice (8–10 weeks) were exposed to intranasal PM or vehicle for 6 weeks. Flow cytometry analysis demonstrated that PM exposure significantly decreased the levels of EPCs (CD34⁺/CD133⁺) in both blood and bone marrow with increased ROS production in males, but not in females. ELISA analysis showed higher levels of serum IL-6 and IL-1βin males than in females. Pulmonary expression of the antioxidant enzyme SOD1 was significantly decreased in males after PM exposure, but not in females. Administration of the SOD mimic Tempol in male mice with PM exposure attenuated the production of ROS and inflammatory cytokines, and preserved EPC levels. These data indicated that PM exposure-induced reduction of EPC population in male mice may be due to decreased expression of pulmonary SOD1 in male mice.

Paternal long-term PM2.5 exposure causes hypertension via increased renal AT1R expression and function in male offspring

Maternal exposure to fine particulate matter (PM2.5) causes hypertension in offspring. However, paternal contribution of PM2.5 exposure to hypertension in offspring remains unknown. In the present study, male Sprague-Dawley rats were treated with PM2.5 suspension (10 mg/ml) for 12 weeks and/or fed with tap water containing an antioxidant tempol (1 mM/L) for 16 weeks. The blood pressure, 24 h-urine volume and sodium excretion were determined in male offspring. The offspring were also administrated with losartan (20 mg/kg/d) for 4 weeks. The expressions of angiotensin II type 1 receptor (AT1R) and G-protein-coupled receptor kinase type 4 (GRK4) were determined by qRT-PCR and immunoblotting. We found that long-term PM2.5 exposure to paternal rats caused hypertension and impaired urine volume and sodium excretion in male offspring. Both the mRNA and protein expression of GRK4 and its downstream target AT1R were increased in offspring of PM2.5-exposed paternal rats, which was reflected in its function because treatment with losartan, an AT1R antagonist, decreased the blood pressure and increased urine volume and sodium excretion. In addition, the oxidative stress level was increased in PM2.5-treated paternal rats. Administration with tempol in paternal rats restored the increased blood pressure and decreased urine volume and sodium excretion in the offspring of PM2.5-exposed paternal rats. Treatment with tempol in paternal rats also reversed the increased expressions of AT1R and GRK4 in the kidney of their offspring. We suggest that paternal PM2.5 exposure causes hypertension in offspring. The mechanism may be involved that paternal PM2.5 exposure-associated oxidative stress induces the elevated renal GRK4 level, leading to the enhanced AT1R expression and its-mediated sodium retention, consequently causes hypertension in male offspring.

The involvement of DRP1-mediated caspase-1 activation in inflammatory response by urban particulate matter in EA.hy926 human vascular endothelial cells

Atmospheric particulate matter (PM) has been reported to be closely related to cardiovascular adverse events. However, the underlying mode of action remains to be elucidated. Previous studies have documented that PM induces mitochondrial damage and inflammation, the relation between these two biological outcomes is still unclear though. In this study, we used EA.hy926 human vascular endothelial cells and a standard PM, PM SRM1648a to study the potential effects of mitochondrial dysfunction on endothelial inflammatory responses. As a result, PM SRM1648a changes mitochondrial morphology and interrupts mitochondrial dynamics with a persistent tendency of fission in a dose-dependent manner. Additionally, the caspase-1/IL-1β axis is involved in inflammatory responses but not cell pyroptosis in EA.hy926 cells following the exposure to PM SRM1648a. The activation of caspase-1 has implications in inflammation but not pyroptosis, because caspase-1-dependent pyroptosis is not the main modality of cell death in PM SRM1648a-treated EA.hy926 cells. With regard to the association between mitochondrial damage and inflammation in the case of particle stimulation, DRP1-mediated mitochondrial fission is responsible for inflammatory responses as a result of caspase-1 activation. The current study showed that PM SRM1648a has the ability to disturb mitochondrial dynamics, and trigger endothelial inflammation via DRP1/caspase-1/IL-1β regulatory pathway. In a conclusion, mitochondrial fission enables EA.hy926 cells to facilitate caspase-1 activation in response to PM SRM1648a, which is a crucial step for inflammatory reaction in vascular endothelial cells.

Cardiovascular Effects of Particulate Air Pollution

Inhalation of fine particulate matter (PM_2.5), produced by the combustion of fossil fuels, is an important risk factor for cardiovascular disease. Exposure to PM_2.5 has been linked to increases in blood pressure, thrombosis, and insulin resistance. It also induces vascular injury and accelerates atherogenesis. Results from animal models corroborate epidemiological evidence and suggest that the cardiovascular effects of PM_2.5 may be attributable, in part, to oxidative stress, inflammation, and the activation of the autonomic nervous system. Although the underlying mechanisms remain unclear, there is robust evidence that long-term exposure to PM_2.5 is associated with premature mortality due to heart failure, stoke, and ischemic heart disease. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Combination of Antioxidant Enzyme Overexpression and N-Acetylcysteine Treatment Enhances the Survival of Bone Marrow Mesenchymal Stromal Cells in Ischemic Limb in Mice With Type 2 Diabetes

Background

Therapy with mesenchymal stem cells remains a promising but challenging approach to critical limb ischemia in diabetes because of the dismal cell survival.

Methods and Results

Critical limb ischemia in type 2 diabetes mouse model was used to explore the impact of diabetic limb ischemia on the survival of bone marrow mesenchymal stromal cells (bMSCs). Inhibition of intracellular reactive oxygen species was achieved with concomitant overexpression of superoxide dismutase (SOD)‐1 and glutathione peroxidase‐1 in the transplanted bMSCs, and extracellular reactive oxygen species was attenuated using SOD‐3 overexpression and N‐acetylcysteine treatment. In vivo optical fluorescence imaging and laser Doppler perfusion imaging were used to track cell retention and determine blood flow in diabetic ischemic limb, respectively. Survival of the transplanted bMSCs was significantly decreased in diabetic ischemic limb compared with the control. In vitro study indicated that advanced glycation end products, not high glucose, significantly decreased the proliferation of bMSCs and increased their apoptosis associated with increased reactive oxygen species production and selective reduction of SOD‐1 and SOD‐3. In vivo study demonstrated that concomitant overexpression of SOD‐1, SOD‐3, and glutathione peroxidase‐1, or host treatment with N‐acetylcysteine, significantly enhanced in vivo survival of transplanted bMSCs, and improved critical limb ischemia in diabetic mice. Combination of triple antioxidant enzyme overexpression in bMSCs with host N‐acetylcysteine treatment further improved bMSC survival with enhanced circulatory and functional recovery from diabetic critical limb ischemia.

Conclusions

Simultaneous suppression of reactive oxygen species from transplanted bMSCs and host tissue could additively enhance bMSC survival in diabetic ischemic limb with increased therapeutic efficacy in diabetes.

N-acetyl cysteine ameliorates aortic fibrosis by promoting M2 macrophage polarization in aging mice

Background: Vascular fibrosis is a universal phenomenon associated with aging, and oxidative stress plays an important role in the genesis of vascular damage in line with the aging process. However, whether antioxidants can ameliorate vascular fibrosis remains unclear.

Objectives: The present study was to determine antioxidant N-acetylcysteine (NAC) could ameliorates aortic fibrosis in aging wild-type C57BL/6 mice.

Methods: The aortas were harvested from both 12-week and 60-week wild-type mice. The 60-week mice were treated with and without the NAC for 12 weeks starting at the age of 48 weeks. Hematoxylin and eosin (H&E) staining and Masson's trichrome staining of aortic samples were performed, and the levels of reactive oxygen species (ROS), RNA expression of GAPDH, TNF-α, MCP-1, IL-6, IL-10, IL-4, SIRT-1, SIRT-3, FOXO-1, and macrophage polarization were determined.

Results: There is a positive relationship between collagen deposition and the M1/M2 macrophage ratio in the aortic wall of aged wild-type C57BL/6 mice. The higher collagen area percentage in the aortas of 60-week-old mice than in 12-week-old mice was reversed by NAC. NAC could not impact the total number of macrophages, but partly promoted M2 macrophage polarization. By performing qRT-PCR using aortic samples from these mice, we identified that SIRT-1, SIRT-3, FOXO-1 could be somehow responsible for aging-related fibrosis.

Conclusions: NAC ameliorates aortic fibrosis in aging wild type mice partly by promoting M2 macrophage polarization.

Fine particulate matter air pollution and aortic perivascular adipose tissue: Oxidative stress, leptin, and vascular dysfunction

Exposure to fine particulate matter (PM2.5 ) air pollution increases blood pressure, induces vascular inflammation and dysfunction, and augments atherosclerosis in humans and rodents; however, the understanding of early changes that foster chronic vascular disease is incomplete. Because perivascular adipose tissue (PVAT) inflammation is implicated in chronic vascular diseases, we investigated changes in aortic PVAT following short-term air pollution exposure. Mice were exposed to HEPA-filtered or concentrated ambient PM2.5 (CAP) for 9 consecutive days, and the abundance of inflammatory, adipogenic, and adipokine gene mRNAs was measured by gene array and qRT-PCR in thoracic aortic PVAT. Responses of the isolated aorta with and without PVAT to contractile (phenylephrine, PE) and relaxant agonists (acetylcholine, ACh; sodium nitroprusside, SNP) were measured. Exposure to CAP significantly increased the urinary excretion of acrolein metabolite (3HPMA) as well as the abundance of protein-acrolein adducts (a marker of oxidative stress) in PVAT and aorta, upregulated PVAT leptin mRNA expression without changing mRNA levels of several proinflammatory genes, and induced PVAT insulin resistance. In control mice, PVAT significantly depressed PE-induced contractions-an effect that was dampened by CAP exposure. Pulmonary overexpression of extracellular dismutase (ecSOD-Tg) prevented CAP-induced effects on urinary 3HPMA levels, PVAT Lep mRNA, and alterations in PVAT and aortic function, reflecting a necessary role of pulmonary oxidative stress in all of these deleterious CAP-induced changes. More research is needed to address how exactly short-term exposure to PM2.5 perturbs PVAT and aortic function, and how these specific genes and functional changes in PVAT could lead over time to chronic inflammation, endothelial dysfunction, and atherosclerosis.

Exposure to Fine Particulate Matter Air Pollution Alters mRNA and miRNA Expression in Bone Marrow-Derived Endothelial Progenitor Cells from Mice

Exposure to fine particulate matter (PM2.5) air pollution is associated with quantitative deficits of circulating endothelial progenitor cells (EPCs) in humans. Related exposures of mice to concentrated ambient PM2.5 (CAP) likewise reduces levels of circulating EPCs and induces defects in their proliferation and angiogenic potential as well. These changes in EPC number or function are predictive of larger cardiovascular dysfunction. To identify global, PM2.5-dependent mRNA and miRNA expression changes that may contribute to these defects, we performed a transcriptomic analysis of cells isolated from exposed mice. Compared with control samples, we identified 122 upregulated genes and 44 downregulated genes in EPCs derived from CAP-exposed animals. Functions most impacted by these gene expression changes included regulation of cell movement, cell and tissue development, and cellular assembly and organization. With respect to miRNA changes, we found that 55 were upregulated while 53 were downregulated in EPCs from CAP-exposed mice. The top functions impacted by these miRNA changes included cell movement, cell death and survival, cellular development, and cell growth and proliferation. A subset of these mRNA and miRNA changes were confirmed by qRT-PCR, including some reciprocal relationships. These results suggest that PM2.5-induced changes in gene expression may contribute to EPC dysfunction and that such changes may contribute to the adverse cardiovascular outcomes of air pollution exposure.

Circulating Endothelial Progenitor Cells Are Preserved in Female Mice Exposed to Ambient Fine Particulate Matter Independent of Estrogen

Males have a higher risk for cardiovascular diseases (CVDs) than females. Ambient fine particulate matter (PM) exposure increases CVD risk with increased reactive oxygen species (ROS) production and oxidative stress. Endothelial progenitor cells (EPCs) are important to vascular structure and function and can contribute to the development of CVDs. The aims of the present study were to determine if sex differences exist in the effect of PM exposure on circulating EPCs in mice and, if so, whether oxidative stress plays a role. Male and female C57BL/6 mice (8–10 weeks old) were exposed to PM or a vehicle control for six weeks. ELISA analysis showed that PM exposure substantially increased the serum levels of IL-6 and IL-1β in both males and females, but the concentrations were significantly higher in males. PM exposure only increased the serum levels of TNF-α in males. Flow cytometry analysis demonstrated that ROS production was significantly increased by PM treatment in males but not in females. Similarly, the level of circulating EPCs (CD34⁺/CD133⁺ and Sca-1⁺/Flk-1⁺) was significantly decreased by PM treatment in males but not in females. Antioxidants N-acetylcysteine (NAC) effectively prevented PM exposure-induced ROS and inflammatory cytokine production and restored circulating EPC levels in male mice. In sharp contrast, circulating EPC levels remained unchanged in female mice with PM exposure, an effect that was not altered by ovariectomy. In conclusion, PM exposure selectively decreased the circulating EPC population in male mice via increased oxidative stress without a significant impact on circulating EPCs in females independent of estrogen.

Acute effects of short-term exposure to ambient air pollution on reproductive hormones in young males of the MARHCS study in China

Air pollution, which is associated with male reproductive health. However, it is unknown the acute effects of ambient air pollutants exposure on male reproductive hormones. The current study, we measured serum levels of reproductive hormone in 2030 blood samples gathered from The Male Reproductive Health in Chongqing College Students (MARHCS) cohort study. We derived a full coverage of ambient air pollutant (PM₁₀, PM_2.5, SO₂, NO₂, CO and O₃) concentrations by employing machine learning algorithms, and used a mixed-effect model to estimate single-day and cumulative effects of air pollutants exposure on serum reproductive hormones. Our results showed that (1) PM₁₀ and PM_2.5 concentrations were positively associated with estradiol (E₂) in both single and cumulative lag days, but were negatively associated with the ratio of Testosterone/E₂ (the T/E₂ ratio). NO₂ was positively associated with estradiol at lag day 2 (95% CI: 0.290, 0.881; corrected P = 0.048) and lag 0-2 days (95% CI: 0.523, 1.337; corrected P = 0.003), with progesterone (P) at lag day 2 and lag day 3 (corrected P < 0.05). There was also a positive association between CO exposure and progesterone at lag day 2. (2) SO₂ was inversely associated with E₂ at lag day 3, 4 and lag 0-4 days, and progesterone at lag day 0, 1, 2 and lag 0-1, 0-2, 0-4 days, but positively associated with the T/E₂ ratio at lag day 3, 4 and lag 0-4 days (corrected P < 0.05). O₃ exposure was negatively associated with E₂ at lag day 3 (95% CI: -0.216, -0.074, corrected P = 0.03). (3) No significant associations were found between the cumulative daily average air pollutant exposure of CO, O₃ and hormone outcomes. This study suggests that short-term exposure to air pollutants may thus alter reproductive hormone levels, especially on serum estradiol, progesterone levels and the T/E₂ ratio.

Ambient air pollution and stillbirth: An updated systematic review and meta-analysis of epidemiological studies

Stillbirth has a great impact on contemporary and future generations. Increasing evidence show that ambient air pollution exposure is associated with stillbirth. However, previous studies showed inconsistent findings. To clarify the effect of maternal air pollution exposure on stillbirth, we searched for studies examining the associations between air pollutants, including particulate matter (diameter ≤ 2.5 μm [PM_2.5] and ≤10 μm [PM₁₀]) and gaseous pollutants (sulfur dioxide [SO₂], nitrogen dioxide [NO₂], carbon monoxide [CO] and ozone [O₃]), and stillbirth published in PubMed, Web of Science, Embase and Cochrane Library until December 11, 2020. The pooled effect estimates and 95% confidence intervals (CI) were calculated, and the heterogeneity was evaluated using Cochran's Q test and I² statistic. Publication bias was assessed using funnel plots and Egger's tests. Of 7546 records, 15 eligible studies were included in this review. Results of long-term exposure showed that maternal third trimester PM_2.5 and CO exposure (per 10 μg/m³ increment) increased the odds of stillbirth, with estimated odds ratios (ORs) of 1.094 (95% CI: 1.008-1.180) and 1.0009 (95% CI: 1.0001-1.0017), respectively. Entire pregnancy exposure to PM_2.5 was also associated with stillbirth (OR: 1.103, 95% CI: 1.074-1.131). A 10 μg/m³ increment in O₃ in the first trimester was associated with stillbirth, and the estimated OR was 1.028 (95% CI: 1.001-1.055). Short-term exposure (on lag day 4) to O₃ was also associated with stillbirth (OR: 1.002, 95% CI: 1.001-1.004). PM₁₀, SO₂ and NO₂ exposure had no significant effects on the incidence of stillbirth. Additional well-designed cohort studies and investigations regarding potential biological mechanisms are warranted to elaborate the suggestive association that may help improve intergenerational inequality.

Fine particulate matter (PM2.5) inhalation-induced alterations in the plasma lipidome as promoters of vascular inflammation and insulin resistance

Fine particulate matter (PM2.5) air pollution exposure increases the risk of developing cardiovascular disease (CVD). Although the precise mechanisms by which air pollution exposure increases CVD risk remain uncertain, research indicates that PM2.5-induced endothelial dysfunction contributes to CVD risk. Previous studies demonstrate that concentrated ambient PM2.5 (CAP) exposure induces vascular inflammation and impairs insulin and vascular endothelial growth factor (VEGF) signaling dependent on pulmonary oxidative stress. To assess whether CAP exposure induces these vascular effects via plasmatic factors, we incubated aortas from naïve mice with plasma isolated from mice exposed to HEPA-filtered air or CAP (9 days) and examined vascular inflammation and insulin and VEGF signaling. We found that treatment of naïve aortas with plasma from CAP-exposed mice activates NF-κBα and induces insulin and VEGF resistance, indicating transmission by plasmatic factor(s). To identify putative factors, we exposed lung-specific ecSOD-transgenic (ecSOD-Tg) mice and wild-type (WT) littermates to CAP at concentrations of either ∼60 µg/m3 (CAP60) or ∼100 µg/m3 (CAP100) and measured the abundance of plasma metabolites by mass spectrometry. In WT mice, both CAP concentrations increased levels of fatty acids such as palmitate, myristate, and palmitoleate and decreased numerous phospholipid species; however, these CAP-induced changes in the plasma lipidome were prevented in ecSOD-Tg mice. Consistent with the literature, we found that fatty acids such as palmitate are sufficient to promote endothelial inflammation. Collectively, our findings suggest that PM2.5 exposure, by inducing pulmonary oxidative stress, promotes unique lipidomic changes characterized by high levels of circulating fatty acids, which are sufficient to trigger vascular pathology.NEW & NOTEWORTHY We found that circulating plasma constituents are responsible for air pollution-induced vascular pathologies. Inhalation of fine particulate matter (≤PM2.5) promotes a unique form of dyslipidemia that manifests in a manner dependent upon pulmonary oxidative stress. The air pollution-engendered dyslipidemic phenotype is characterized by elevated free fatty acid species and diminished phospholipid species, which could contribute to vascular inflammation and loss of insulin sensitivity.

Ruscogenin attenuates particulate matter-induced acute lung injury in mice via protecting pulmonary endothelial barrier and inhibiting TLR4 signaling pathway

The inhalation of particulate matter (PM) is closely related to respiratory damage, including acute lung injury (ALI), characterized by inflammatory fluid edema and disturbed alveolar-capillary permeability. Ruscogenin (RUS), the main active ingredient in the traditional Chinese medicine Ophiopogonis japonicus, has been found to exhibit anti-inflammatory activity and rescue LPS-induced ALI. In this study, we investigated whether and how RUS exerted therapeutic effects on PM-induced ALI. RUS (0.1, 0.3, 1 mg·kg-1·d-1) was orally administered to mice prior to or after intratracheal instillation of PM suspension (50 mg/kg). We showed that RUS administration either prior to or after PM challenge significantly attenuated PM-induced pathological injury, lung edema, vascular leakage and VE-cadherin expression in lung tissue. RUS administration significantly decreased the levels of cytokines IL-6 and IL-1β, as well as the levels of NO and MPO in both bronchoalveolar lavage fluid (BALF) and serum. RUS administration dose-dependently suppressed the phosphorylation of NF-κB p65 and the expression of TLR4 and MyD88 in lung tissue. Furthermore, TLR4 knockout partly diminished PM-induced lung injury, and abolished the protective effects of RUS in PM-instilled mice. In conclusion, RUS effectively alleviates PM-induced ALI probably by inhibition of vascular leakage and TLR4/MyD88 signaling. TLR4 might be crucial for PM to initiate pulmonary lesion and for RUS to exert efficacy against PM-induced lung injury.

Endothelial progenitor cells as critical mediators of environmental air pollution-induced cardiovascular toxicity

Environmental air pollution exposure is a leading cause of death worldwide, and with increasing industrialization and urbanization, its disease burden is expected to rise even further. The majority of air pollution exposure-associated deaths are linked to cardiovascular disease (CVD). Although ample research demonstrates a strong correlation between air pollution exposure and CVD risk, the mechanisms by which inhalation of polluted air affects cardiovascular health are not completely understood. Inhalation of environmental air pollution has been associated with endothelial dysfunction, which suggests that air pollution exposure impacts CVD health by inducing endothelial injury. Interestingly, recent studies demonstrate that air pollution exposure affects the number and function of endothelial progenitor cells (EPCs), subpopulations of bone marrow-derived proangiogenic cells that have been shown to play an essential role in maintaining cardiovascular health. In line with their beneficial function, chronically low levels of circulating EPCs and EPC dysfunction (e.g., in diabetic patients) have been associated with vascular dysfunction, poor cardiovascular health, and increases in the severity of cardiovascular outcomes. In contrast, treatments that improve EPC number and function (e.g., exercise) have been found to attenuate cardiovascular dysfunction. Considering the critical, nonredundant role of EPCs in maintaining vascular health, air pollution exposure-induced impairments in EPC number and function could lead to endothelial dysfunction, consequently increasing the risk for CVD. This review article covers novel aspects and new mechanistic insights of the adverse effects of air pollution exposure on cardiovascular health associated with changes in EPC number and function.

Long-Term PM2.5 Exposure and Risks of Ischemic Heart Disease and Stroke Events: Review and Meta-Analysis

Background

Fine particulate matter <2.5 µm in diameter (PM_2.5) has known effects on cardiovascular morbidity and mortality. However, no study has quantified and compared the risks of incident myocardial infarction, incident stroke, ischemic heart disease (IHD) mortality, and cerebrovascular mortality in relation to long‐term PM_2.5 exposure.

Methods and Results

We sought to quantitatively summarize studies of long‐term PM_2.5 exposure and risk of IHD and stroke events by conducting a review and meta‐analysis of studies published by December 31, 2019. The main outcomes were myocardial infarction, stroke, IHD mortality, and cerebrovascular mortality. Random effects meta‐analyses were used to estimate the combined risk of each outcome among studies. We reviewed 69 studies and included 42 studies in the meta‐analyses. In meta‐analyses, we found that a 10‐µg/m³ increase in long‐term PM_2.5 exposure was associated with an increased risk of 23% for IHD mortality (95% CI, 15%–31%), 24% for cerebrovascular mortality (95% CI, 13%–36%), 13% for incident stroke (95% CI, 11%–15%), and 8% for incident myocardial infarction (95% CI, −1% to 18%). There were an insufficient number of studies of recurrent stroke and recurrent myocardial infarction to conduct meta‐analyses.

Conclusions

Long‐term PM_2.5 exposure is associated with increased risks of IHD mortality, cerebrovascular mortality, and incident stroke. The relationship with incident myocardial infarction is suggestive of increased risk but not conclusive. More research is needed to understand the relationship with recurrent events.

Protocol to assess the efficacy of carnosine supplementation in mitigating the adverse cardiovascular responses to particulate matter (PM) exposure: the Nucleophilic Defense Against PM Toxicity (NEAT) trial

INTRODUCTION

Exposure to airborne particulate matter (PM) is associated with cardiovascular disease. These outcomes are believed to originate from pulmonary oxidative stress and the systemic delivery of oxidised biomolecules (eg, aldehydes) generated in the lungs. Carnosine is an endogenous di-peptide (β-alanine-L-histidine) which promotes physiological homeostasis in part by conjugating to and neutralising toxic aldehydes. We hypothesise that an increase of endogenous carnosine by dietary supplementation would mitigate the adverse cardiovascular outcomes associated with PM exposure in humans.

METHODS AND ANALYSIS

To test this, we designed the Nucleophilic Defense Against PM Toxicity trial. This trial will enroll 240 participants over 2 years and determine if carnosine supplementation mitigates the adverse effects of PM inhalation. The participants will have low levels of endogenous carnosine to facilitate identification of supplementation-specific outcomes. At enrollment, we will measure several indices of inflammation, preclinical cardiovascular disease and physical function. Participants will be randomly allocated to carnosine or placebo groups and instructed to take their oral supplement for 12 weeks with two return clinical visits and repeated assessments during times of peak PM exposure (June-September) in Louisville, Kentucky, USA. Statistical modelling approaches will be used to assess the efficacy of carnosine supplementation in mitigating adverse outcomes.

ETHICS AND DISSEMINATION

This study protocol has been approved by the Institutional Review Board at the University of Louisville. Results from this study will be disseminated at scientific conferences and in peer-reviewed publications.Trial registration: NCT03314987; Pre-results.

Ambient Air Pollution and Atherosclerosis: Insights Into Dose, Time, and Mechanisms

Ambient air pollution due to particulate matter ≤2.5 μ is the leading environmental risk factor contributing to global mortality, with a preponderant majority of these deaths attributable to atherosclerotic cardiovascular disease (ASCVD) causes such as stroke and myocardial infarction. Epidemiological studies in humans have provided refined estimates of exposure risk, with evidence suggesting that risk association with particulate matter ≤2.5 levels and ASCVD continues at levels well below air quality guidelines in North America and Europe. Mechanistic studies in animals and humans have provided a framework of understanding of the duration and pathways by which air pollution exposure may predispose to atherosclerosis. Although acute exposure to particulate matter ≤2.5 is associated with oxidative stress and inflammation, system transmission of signals from the lungs to extrapulmonary sites may involve direct translocation of components, biologic intermediates, and autonomic nervous system activation. End-organ effector pathways such as endothelial barrier disruption/dysfunction, thrombosis, vasoconstriction/increased blood pressure, and plaque instability, may contribute to ASCVD. The strength of the association of air pollution with ASCVD offers an opportunity to mitigate its consequences. Although elimination of anthropogenic sources of air pollution with a switch to clean energy provides the ultimate solution, this may not be possible in the interim and may require personal protection efforts and an integrated approach to managing risk posed by air pollution for ASCVD.

Prevention of Fine Dust-Induced Vascular Senescence by Humulus lupulus Extract and Its Major Bioactive Compounds

Both short- and long-term exposure to fine dust (FD) from air pollution has been linked to various cardiovascular diseases (CVDs). Endothelial cell (EC) senescence is an important risk factor for CVDs, and recent evidence suggests that FD-induced premature EC senescence increases oxidative stress levels. Hop plant (Humulus lupulus) is a very rich source of polyphenols known to have nutritional and therapeutic properties, including antioxidant behavior. The aims of this study were to evaluate whether Humulus lupulus extract prevents FD-induced vascular senescence and dysfunction and, if so, to characterize the underlying mechanisms and active components. Porcine coronary arteries and endothelial cells were treated with FD in the presence or absence of hop extract (HOP), and the senescence-associated-beta galactosidase (SA-β-gal) activity, cell-cycle progression, expression of senescence markers, oxidative stress level, and vascular function were evaluated. Results indicated that HOP inhibited FD-induced SA-β-gal activity, cell-cycle arrest, and oxidative stress, suggesting that HOP prevents premature induction of senescence by FD. HOP also ameliorated FD-induced vascular dysfunction. Additionally, xanthohumol (XN) and isoxanthohumol (IX) were found to produce the protective effects of HOP. Treatment with HOP and its primary active components XN and IX downregulated the expression of p22phox, p53, and angiotensin type 1 receptor, which all are known FD-induced redox-sensitive EC senescence inducers. Taken together, HOP and its active components protect against FD-induced endothelial senescence most likely via antioxidant activity and may be a potential therapeutic agent for preventing and/or treating air-pollution-associated CVDs.

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.

Urinary levels of the acrolein conjugates of carnosine are associated with inhaled toxicants

OBJECTIVE

The inhalation of air-borne toxicants is associated with adverse health outcomes which can be somewhat mitigated by enhancing endogenous anti-oxidant capacity. Carnosine is a naturally occurring dipeptide (β-alanine-L-histidine), present in high abundance in skeletal and cardiac muscle. This multi-functional dipeptide has anti-oxidant properties, can buffer intracellular pH, chelate metals, and sequester aldehydes such as acrolein. Due to these chemical properties, carnosine may be protective against inhaled pollutants which can contain metals and aldehydes and can stimulate the generation of electrophiles in exposed tissues. Thus, assessment of carnosine levels, or levels of its acrolein conjugates (carnosine-propanal and carnosine-propanol) may inform on level of exposure and risk assessment.

METHODS

We used established mass spectroscopy methods to measure levels of urinary carnosine (n = 605) and its conjugates with acrolein (n = 561) in a subset of participants in the Louisville Healthy Heart Study (mean age = 51 ± 10; 52% male). We then determined associations between these measures and air pollution exposure and smoking behavior using statistical modeling approaches.

RESULTS

We found that higher levels of non-conjugated carnosine, carnosine-propanal, and carnosine-propanol were significantly associated with males (p < 0.02) and those of Caucasian ethnicity (p < 0.02). Levels of carnosine-propanol were significantly higher in never-smokers (p = 0.001) but lower in current smokers (p = 0.037). This conjugate also demonstrated a negative association with mean-daily particulate air pollution (PM2.5) levels (p = 0.01).

CONCLUSIONS

These findings suggest that urinary levels of carnosine-propanol may inform as to risk from inhaled pollutants.

Cellular and Molecular Mechanisms of Environmental Pollutants on Hematopoiesis

Hematopoiesis is a complex and intricate process that aims to replenish blood components in a constant fashion. It is orchestrated mostly by hematopoietic progenitor cells (hematopoietic stem cells (HSCs)) that are capable of self-renewal and differentiation. These cells can originate other cell subtypes that are responsible for maintaining vital functions, mediate innate and adaptive immune responses, provide tissues with oxygen, and control coagulation. Hematopoiesis in adults takes place in the bone marrow, which is endowed with an extensive vasculature conferring an intense flow of cells. A myriad of cell subtypes can be found in the bone marrow at different levels of activation, being also under constant action of an extensive amount of diverse chemical mediators and enzymatic systems. Bone marrow platelets, mature erythrocytes and leukocytes are delivered into the bloodstream readily available to meet body demands. Leukocytes circulate and reach different tissues, returning or not returning to the bloodstream. Senescent leukocytes, specially granulocytes, return to the bone marrow to be phagocytized by macrophages, restarting granulopoiesis. The constant high production and delivery of cells into the bloodstream, alongside the fact that blood cells can also circulate between tissues, makes the hematopoietic system a prime target for toxic agents to act upon, making the understanding of the bone marrow microenvironment vital for both toxicological sciences and risk assessment. Environmental and occupational pollutants, therapeutic molecules, drugs of abuse, and even nutritional status can directly affect progenitor cells at their differentiation and maturation stages, altering behavior and function of blood compounds and resulting in impaired immune responses, anemias, leukemias, and blood coagulation disturbances. This review aims to describe the most recently investigated molecular and cellular toxicity mechanisms of current major environmental pollutants on hematopoiesis in the bone marrow.

Environmental Factors Such as Noise and Air Pollution and Vascular Disease

Significance: According to the World Health Organization, noncommunicable diseases are the globally leading cause of mortality. Recent Advances: About 71% of 56 million deaths that occurred worldwide are due to noncommunicable cardiovascular risk factors, including tobacco smoking, unhealthy diets, lack of physical activity, overweight, arterial hypertension, diabetes, and hypercholesterolemia, which can be either avoided or substantially reduced. Critical Issues: Thus, it is estimated that 80% of premature heart disease, stroke, and diabetes can be prevented. More recent evidence indicates that environmental stressors such as noise and air pollution contribute significantly to the global burden of cardiovascular disease. In the present review, we focus primarily on important environmental stressors such as transportation noise and air pollution. We discuss the pathophysiology of vascular damage caused by these environmental stressors, with emphasis on early subclinical damage of the vasculature such as endothelial dysfunction and the role of oxidative stress. Future Directions: Lower legal thresholds and mitigation measures should be implemented and may help to prevent vascular damage.

Significant Unresolved Questions and Opportunities for Bioengineering in Understanding and Treating COVID-19 Disease Progression

COVID-19 is a disease that manifests itself in a multitude of ways across a wide range of tissues. Many factors are involved, and though impressive strides have been made in studying this novel disease in a very short time, there is still a great deal that is unknown about how the virus functions. Clinical data has been crucial for providing information on COVID-19 progression and determining risk factors. However, the mechanisms leading to the multi-tissue pathology are yet to be fully established. Although insights from SARS-CoV-1 and MERS-CoV have been valuable, it is clear that SARS-CoV-2 is different and merits its own extensive studies. In this review, we highlight unresolved questions surrounding this virus including the temporal immune dynamics, infection of non-pulmonary tissue, early life exposure, and the role of circadian rhythms. Risk factors such as sex and exposure to pollutants are also explored followed by a discussion of ways in which bioengineering approaches can be employed to help understand COVID-19. The use of sophisticated in vitro models can be employed to interrogate intercellular interactions and also to tease apart effects of the virus itself from the resulting immune response. Additionally, spatiotemporal information can be gleaned from these models to learn more about the dynamics of the virus and COVID-19 progression. Application of advanced tissue and organ system models into COVID-19 research can result in more nuanced insight into the mechanisms underlying this condition and elucidate strategies to combat its effects.