Air-pollutant Particulate Matter 2.5 (PM2.5)-induced Inflammation and Oxidative Stress in Diseases: Possible Therapeutic Approaches

Abstract

Today, air pollution is the greatest threat to organismal healthspan. The environment of our planet earth, the habitat of over eight billion humans and estimated twenty billion billions other animals, is contaminated with a wide variety of pollutants. Unfortunately, humans, out of billions and billions of living organisms on earth, are solely responsible for polluting the environment through emitting pollutants like particulate matter from industry, fuel engine vehicles, biomass combustion, toxic fumes from blasting, and wildfire. In the modern world, human-caused air pollutants induce massive oxidative stress and inflammation, the major contributors in initiation and progression of many diseases including pulmonary, cardiovascular, renal, hepatic, reproductive, neurological, mental, and accelerated biological aging. The provocative question is the following: how can we solve this human-created problem? As it is not realistic to clean the environment at once from human-caused pollution, initiatives have been undertaken to develop novel therapeutic approaches to control air-pollutant-induced oxidative stress and inflammation to protect humans from pollution-induced devastating diseases. In this article, I discuss the key findings of numerous recent preclinical studies documenting first, the role of air pollutant PM2.5 in augmentation of inflammation, oxidative stress, and associated diseases; and second, the efficacies of different natural and synthetic compounds in amelioration of PM2.5-induced oxidative stress, inflammation, pyroptosis, and associated pathologies.

Full text

Review Not peer-reviewed version
Air-pollutant Particulate Matter 2.5
(PM2.5)-induced Inflammation and
Oxidative Stress in Diseases: Possible
Therapeutic Approaches
Asish K Ghosh *
Posted Date: 20 December 2023
doi: 10.20944/preprints202312.1575.v1
Keywords: Air pollution; Particulate Matter2.5; Inflammation; Nlrp3; Oxidative Stress; Nrf2; PAI-1; Aging;
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Article
Air-Pollutant Particulate Maer 2.5 (PM2.5)-induced
Inammation and Oxidative Stress in Diseases:
Possible Therapeutic Approaches
Asish K Ghosh
Feinberg Cardiovascular and Renal Research Institute, Feinberg School of Medicine, Northwestern University, Chicago,
Illinois, USA
Address for Correspondence: Asish K Ghosh, MSc, PhD, FAHA, Feinberg Cardiovascular and Renal Research Institute,
Feinberg School of Medicine, Northwestern University, Tarry 12-733, 303 East Chicago Avenue, Chicago, Illinois 60611,
USA. E-mail: a-ghosh2@northwestern.edu
Abstract: Today, air pollution is the greatest threat to organismal healthspan. The environment of our planet
earth, the habitat of over eight billion humans and estimated twenty billion billions other animals, is
contaminated with a wide variety of pollutants. Unfortunately, humans, out of billions and billions of living
organisms on earth, are solely responsible for polluting the environment through emiing pollutants like
particulate maer from industry, fuel engine vehicles, biomass combustion, toxic fumes from blasting, and
wildre. In the modern world, human-caused air pollutants induce massive oxidative stress and inammation,
the major contributors in initiation and progression of many diseases including pulmonary, cardiovascular,
renal, hepatic, reproductive, neurological, mental, and accelerated biological aging. The provocative question
is the following: how can we solve this human-created problem? As it is not realistic to clean the environment
at once from human-caused pollution, initiatives have been undertaken to develop novel therapeutic
approaches to control air-pollutant-induced oxidative stress and inammation to protect humans from
pollution-induced devastating diseases. In this article, I discuss the key ndings of numerous recent preclinical
studies documenting rst, the role of air pollutant PM2.5 in augmentation of inammation, oxidative stress, and
associated diseases; and second, the ecacies of dierent natural and synthetic compounds in amelioration of
PM2.5-induced oxidative stress, inammation, pyroptosis, and associated pathologies.
Keywords: Air pollution; Particulate Maer2.5; Inammation; Nlrp3; Oxidative Stress; Nrf2; PAI-1; Aging
1. Introduction
As the fauna and ora in every corner of the earth are interdependent for survival, it is pivotal
to keep the air and water quality safe for food and shelter of all living organisms and maintenance of
healthy ecosystem. While good air quality of our habitat has immense impact on our healthy life, air
pollution is the greatest risk factor for development of numerous diseases resulting in accelerated
aging and shortened healthspan [1]. It is noteworthy that initiation of every disease stems from
impaired inammation and oxidative stress responses. The key events of inammation in response
to stress, injury, and infection are vascular dysfunction, inltration of mononuclear immune cells
including monocytes and macrophages, inammatory cytokine storm, and activation of downstream
inammatory signaling. Importantly, inammation is an essential response for healing in the early
stage of injury or infection, and thus preserves tissue homeostasis. Furthermore, inammatory cells
also contribute to oxidative stress and impaired antioxidant system, another key early cellular
response required to protect organisms from further vascular, cellular and tissue damage. However,
persistent uncontrolled inammation and oxidative stress in response to external or internal stressors
lead to initiation and progression of numerous diseases due to impaired cellular physiology and
tissue homeostasis [2]. It is noteworthy that one of the major igniters of massive inammation and
oxidative stress in the body is inhaled air pollutant. Unfortunately, human-caused air pollution is
rapidly increasing in the modern world in diverse ways as follows: emiing fuel combustion from
excessively growing number of vehicles, toxic fumes from blasting, wildre smokes, smokes from
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© 2023 by the author(s). Distributed under a Creative Commons CC BY license.

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biomass burning, coal burning, crop residue burning, and factory released smokes. These are the key
sources of elevated levels of particulate maer (PM), the major hazardous air pollutants in the
environment. Recent survey showed that the levels of air pollutants are extremely high in the
industrial belts and urban areas worldwide where billions of humans and other animals are exposing
themselves to hazardous air pollutants, particulate maer daily for several hours. In recent years, the
real time world's air pollution index exhibit that the air pollutant PM2.5 levels of many highly
populated cities in industrial belts exceeds >300-500 µg/cubic meter (m^3) compared to standard <50
µg/m^3 [World's Air Pollution: Real-time Air Quality Index @ hps://waqi.info; Current Air Quality
@ hps://www.airnow.gov]. It is well documented that both short-term and long-term exposure to
PM2.5 cause massive inammation and oxidative stress in lungs and other organs. Both impaired
inammatory and oxidative stress pathways ignite the onset of numerous human diseases including
chronic obstructive pulmonary disease, allergic rhinitis, vascular thrombosis, hypertension,
arrhythmia, stroke, dementia, hepatic and renal diseases, abnormal childbirth, autism spectrum
disorder, anxiety, infertility, cancer, and accelerated biological aging [3-10].
The rst and foremost question is the following: how can we protect ourselves and other animals
on earth from dangerous air pollutant-induced devastating diseases and shortened healthspan?
There are two ways: obviously, the rst choice is to diminish the human-caused environmental
pollution; and the second possibility is to develop potential therapy to alleviate air pollutant-induced
pathologies. The rst choice is not realistic in this ultramodern human society within a brief period,
but it is possible only through well-planned long-term global eorts. This positive notion is at least
partially supported by the ndings that the air pollutants were signicantly reduced (40-50%) in
numerous cities in the world during COVID-19 lockdown for a short period due to less emission of
pollutant PM2.5 from fuel combustion and factories [11-13]. The second choice is quite feasible, if we
understand in-depth the air pollution exposure-induced deregulation of molecular and cellular
events those contribute to persistent inammation, oxidative stress, and development of multiple
diseases. Last two decades, many in vitro and in vivo studies have been conducted to understand the
eects of air pollutant exposure on cellular abnormality and organismal health and pathology. The
purpose of this article is to discuss the signicant ndings on the induction of massive inammation,
oxidative stress, and initiation of disease development in response to PM2.5 exposure using cellular
and animal models. The promises of dierent therapeutic approaches using synthetic and natural
compounds in amelioration of PM2.5-induced inammation, oxidative stress, and multi-organ
pathogenesis at the preclinical level are also discussed.
2. Air-Pollutant Particulate Maer (PM) and Its Mode of Action
Particulate Maer (PM) is the most hazardous air pollutant that holds a wide range of toxic
substances including radon, sulfates, nitrates, benzene, polycyclic aromatic hydrocarbons, heavy
metals like lead, cadmium, arsenic, chromium, barium, organic carbon, elemental carbon, and
airborne bacteria. Based on published data, the composition of the PM varies in dierent cities in the
world depending on the sources like generation from factory exhausts, vehicle fuel/diesel
combustion, biomass burning, fumes from blasting, and wildre, and the season of PM2.5 collection
[11-20]. The partial composition of Air pollutants collected in various parts of the world are published
[13-15,17; also see NIST Certicate of Analysis, SRM 1649a,
hps://tsapps.nist.gov/srmext/certicates/archives/]. Based on its aerodynamic diameter, PM has
been classied as coarse (10 µm or smaller in diameter PM10), ne (2.5 µm or smaller in diameter
PM2.5), and ultrane (0.1 µm or smaller in diameter PM0.1) [4,7]. Upon short-term or long-term
inhalation, these original or chemically modied forms of ne particles are associated with induction
of massive oxidative stress, inammation, and development of pathologies. The elevated level of
PM2.5 in the atmosphere is the most hazardous risk factor to human health. While the acute harmful
eects of PM2.5 may be direct, involving rapid crossover from the lung epithelium into the circulation,
the chronic eects of PM2.5 involve generation of pulmonary oxidative stress, systemic inammation,
secretion of elevated levels of inammatory cytokines and cellular dysfunction [21-24]. However,
eventually, both direct and indirect eects of PM2.5 ignite the onset of oxidative stress, inammation,
pyroptosis and progression of devastating pathologies including asthma, COPD, vascular
thrombosis, organ brosis, heart failure, and accelerated biological aging.
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3. PM2.5 in Induction of Massive Inammation and Oxidative Stress: Major Causes for the
Initiation and Progression of Pathologies
In this section, I discuss the accumulated experimental evidence supporting the negative impact
of air pollution PM2.5 in ignition of massive inammation, oxidative stress, and related pathogenesis.
3.1. PM2.5 Induces Inammation and Oxidative Stress: Evidence from Gene Expression Proling
Several unbiased global gene expression proling provide evidence that exposure to air-
pollutant PM2.5 causes activation of inammatory and oxidative stress pathways. For example, the
gene expression proling of control and PM2.5-exposed human bronchial epithelial cells (16HBE) by
RNA seq analysis reveals that exposure to PM2.5 (25 µg/cm2/for 24h) causes dierential expression of
539 genes. Gene ontology analysis illustrates that PM2.5 induces many genes involved in
inammation, oxidative stress, metabolism, xenobiotic stimuli, and cytokine-cytokine receptor
interaction pathways. Additionally, exposure of cells to PM2.5 is strongly associated with secretion of
inammatory cytokine IL-6 [25]. Histological and electron microscopy imaging data reveal that short
term-exposer (24h and 48h) of mice to PM2.5 (200 µg/mouse) causes an increased inltration of
neutrophils and macrophages in the lung tissues but not in liver compared to untreated animals [26].
Moreover, microarray analysis reveals that while, PM2.5 exposer alters gene expression proling of
dierent pathways in lungs including chemokine signaling, HIF-1 signaling, inammatory TNF- ,
IL-17 signaling and cytokine-cytokine receptor interaction; in liver, PM2.5 alters the expressions of
numerous genes involved in metabolic signaling pathways including AMPK signaling, JAK-Stat
signaling, cytokine-cytokine receptor and PPAR signaling [26]. Similarly, exposure of human and
mouse macrophages to PM2.5 (400-500 µg/ml) causes generation of oxidative stress (ROS), activation
of inammatory NF B signaling, secretion of inammatory cytokines IL-1 , TNF- and impaired
phagocytosis, and thus disrupt inammatory cell clearance by macrophages [27]. Furthermore, RNA
seq analysis of RNA extracted from control and PM2.5 (500 µg/ml for 24h) exposed PMA-primed THP-
1 human macrophages reveal that expression of 1213 genes involved in dierent cellular pathways
are deregulated by PM2.5 including upregulation of IL-17, NF B, TNF- , and PPAR- signaling
pathways and downregulation of PI3K/AKT and cytokine-receptor interaction pathways [27].
Previously, we demonstrated that a short-term exposure (72h) to PM2.5 (200µg/mouse) causes
elevated levels of inammatory markers Mac3, pStat3 and Vcam1 and apoptotic marker cleaved
caspase 3 in murine lung and heart tissues [28]. Recently, we performed RNA seq analysis of RNA
extracted from controls and PM2.5 (200 µg/mouse) instilled (72h) murine lungs. The gene ontology
analysis revealed that PM2.5 signicantly upregulated inammatory pathway as shown by
deregulation of many inammatory genes including Nlrp3, IL-1 , TNFrsf8, 9, 11a, 12a, 1b, and NF-
B2. In addition, many downregulated genes in response to PM2.5 participate in metabolism (Ghosh
AK et al. unpublished data). Collectively, these results on the impacts of air pollutant PM2.5 on global
gene expression proling under dierent experimental milieus reveal that many commons signaling
pathways are deregulated by PM2.5 exposure including signicant activation of inammatory and
oxidative stress pathways.
3.2. PM2.5-Induced Inammation, Oxidative Stress, and Allergic Rhinitis
It is well known that people with allergic rhinitis (AR) are more sensitive to air-pollutants. The
impact of PM2.5 in allergic airway inammation has been studied using ovalbumin-induced AR
mouse model [29]. Exposure of ovalbumin-induced AR mice to PM2.5 (100 µg/mouse) causes
augmented inammation due to increased levels of inammatory cytokines IL-4, IL-5, and IL-13 that
eventually increases oxidative stress through malondialdehyde (MDA) synthesis. Furthermore, PM2.5
exposure inhibits the level of Nrf2, the key regulator of antioxidant genes, in AR mice showing lack
of protection of lungs from PM2.5-induced oxidative stress [29]. This is consistent with the observation
that PM2.5 (50µg/ml) reduces the levels of Nrf2 in cardiac broblasts [28]. A recent study showed that
PM2.5 (100 µg/mouse/day/for 30 days) signicantly induces the inltration of eosinophils in
bronchoalveolar lavage uid and inammatory cells in the lung tissues of ovalbumin (OVA)-induced
combined allergic rhinitis and asthma syndrome (CARAS) mouse model. While the levels of
transcription factor GATA4, and Th2 and Th17 cytokines IL-4, IL-5, IL-13, and IL-17 are signicantly
increased compared to control, the levels of Th1 cytokines like IL-12 and IFN-γ are signicantly
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4
decreased in nasal lavage uid and broncho alveolar lavage uid derived from CARAS/PM2.5 mice
compared to CARAS and control. Additionally, exposure to PM2.5 leads to activation of NF-κB
signaling in CARAS mouse model. These results conrm that PM2.5 aggravates allergic inammation
by increasing the secretion of inammatory cytokines [30]. In addition, the role of TLR2/TLR4 and
MyD88 in PM2.5-induced (100 µg/mouse/4 times in 2 weeks interval) worst inammatory
reaction in OVA-induced mouse model of asthma has been examined. While PM2.5 exposure
exacerbates OVA-induced lung inammation or eosinophilia in wildtype mice as shown by
increased levels of neutrophils, macrophages, and upregulation of IL-1 , IL-5, IL-12, IL-13,
chemokine KC in lungs, PM2.5 fails to increase inammation in TLR2 or TLR4 or MyD88
decient mice [31]. Comparable results were obtained by Wang and colleagues [32] in an
asthma mouse model exposed to PM2.5. Collectively, these results suggest that exposure to
PM2.5 aggravates allergic reaction where both inammatory and oxidative stress pathways contribute
to aggravated pulmonary symptoms in mouse model of AR and Asthma.
3.3. PM2.5-Induced Inammation, Oxidative Stress, and Fibrogenesis
PM2.5 exposure-induced inammation and oxidative stress ignite matrix remodeling in the heart
and lungs. Exposure to PM2.5 (100 µg/mouse/every 3rd day for total 9 days) induces the levels of
secreted IL-17A, IL-1 and TNF- by γδT and Th17 cells those lead to a massive inammation and
lung injury. Further, PM2.5 stimulates the levels of TGF- 1, Smad-dependent TGF- probrogenic
responses including myobroblast dierentiation, excessive collagen synthesis and brogenesis [33].
Further, the PM2.5-activated probrogenic pathway is diminished in IL-17A null murine lung tissues
compared to wildtype mice indicating IL-17A aggravates PM2.5-induced inammation and lung
brogenesis [33]. Similarly, exposure to PM2.5 increases lung injury, decreases lung functions
including lung vital capacity and airway resistance through induction of inammation and oxidative
stress in mice and mouse bronchial epithelium cells as evidenced by elevated levels of IL-1 , IL-16,
PI3K/mTOR signaling pathways [34]. Importantly, exposure to low, medium, and high doses of PM2.5
(3 mg, 8 mg, 13 mg/kg body weight/once per week for 4 weeks) induces worst inammation and lung
injury as shown by increased expression of ACP, CRP, VEGF, and IL-6 in broncho alveolar lavage
uid compared to control rats. Additionally, the protein levels of VEGF, JAK2, Stat3 and matrix
protein collagen are signicantly elevated in PM2.5-treated rat lung tissues compared to controls [35].
These results suggest that PM2.5-induced PI3K/mTOR and JAK/Stat3 signaling pathways may
contribute to massive lung inammation and brogenesis. Interestingly, exposures of mice to
printing room generated PM2.5 (5µg, 10µg or 15µg/g BW on day 1 and 3) signicantly increased
malondialdehyde (MDA) activity, increased expression of inammatory cytokines like IL-1β, TNF- ,
and IL-6 and decreased expression of antioxidant SOD on day 4 of exposure. In addition, primary
probrogenic signaling mediator TGF- -induced pERK1-MAPK activity is also increased by PM2.5
indicating exposure for a signicant amount of time to print room-generated PM2.5 is a major risk
factor for increased lung oxidative stress, inammation, pyroptosis and pulmonary brosis [36].
Exposure to PM2.5 (50µg/mouse/every 3 days/total 6 times) causes increased inltration of
inammatory cells and lung injury including peri-bronchial brosis and airway wall thickening in
mice [27]. PM2.5 (4mg/kg daily for 5days) also signicantly increases the levels of CXCL1, IL-6 and IL-
18. The levels of Nlrp3/NF B and Akt signaling are signicantly elevated in hearts of PM2.5 exposed
mice. Therefore, Nlrp3/NF B-induced inammation may contribute to PM2.5-induced cardiac
pathologies including brogenesis [37]. As HDAC3 plays a key role in regulation of inammatory
genes and control inammation in response to external stresses, the signicance of HDAC3 in PM2.5-
induced inammation-related symptoms in mice has been examined [38]. While PM2.5 inhalation
(101.5+/- 2.3 µg/^m3, ow rate: 75L/min for 6h/day/5 time per week) induces the Smad-dependent
TGF- signaling in wildtype mice, this probrogenic signaling is further activated in lungs derived
from PM2.5-exposed HDAC3 decient mice [38]. Therefore, specic activation of HDAC3 may be a
viable approach to control the extent of PM2.5-induced lung inammation and brosis. Exposure to
concentrated PM2.5 (671.87µg/m^3 for 8 or 16 weeks, 6 h/day) also imparts its negative inuence on
the cardiac structure and function as shown by cardiac hypertrophy, brosis, and abnormal cardiac
systolic function. PM2.5 induces inammation through activation of PI3K/Akt/FOXO1 signaling
pathways that contribute to cardiac hypertrophy and brogenesis [39]. Furthermore, the ospring
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from mice exposed to PM2.5 during gestation period develop cardiac hypertrophy that is associated
with increased levels of acetyltransferase p300, acetylated H3K9 and cardiac transcriptional
regulators Gata4 and Mef2c [40]. Therefore, prenatal, or postnatal exposure to environmental
pollutant PM2.5 induces cardiac inammation, cellular apoptosis, brogenesis and abnormal cardiac
structure and function.
3.4. PM2.5-Induced Inammation, Oxidative Stress, Metabolic Syndrome, and Accelerated Aging
Exposure to PM2.5 is associated with accelerated aging and metabolic disorders [9,10,41]. Using
Drosophila as a model for longevity study, Wang and colleagues [42] showed that exposure to
concentrated PM2.5 (80 µg/m^3/) reduces Drosophila lifespan in both males and females compared to
Drosophila exposed to ltered air (PM2.5:4 µg/m^3). Interestingly, males are more sensitive to PM2.5
than females (50% survival 20-21 days vs 40 days for ltered air exposed ies). It is important to note
that PM2.5 driven Drosophila mortality is also associated with increased oxidative stress as evidenced
by increased expression of SOD1, Catalase, Thor and Duox as an adaptive responses to PM2.5-induced
stress; and inammation as shown by elevated expression of Jak, Jnk and NF- B in Drosophila whole
body. Additionally, DCFH oxidation is signicantly increased in whole body lysates from
concentrated PM2.5-exposed ies compared to ltered air exposed ies indicating PM2.5 induces
systemic oxidative stress. Exposure of Drosophila for 15 days to concentrated PM2.5 (6h/day,
5days/week, average concentration of PM2.5 (17µg and 24 µg.m^3/24h) also induces abnormal
metabolism including deregulated insulin signaling and insulin resistance as evidenced by elevated
levels of glucose and trehalose and increased expression of Ilp2 and Ilp5 transcripts in Drosophila [42].
Therefore, the results of this in vivo study conrmed the negative impact of PM2.5-induced
inammation and oxidative stress on organismal metabolism and longevity.
As shortening of telomere length is a bonade marker of chronological and accelerated aging,
the impact of air-pollution exposure on cord blood and placental telomere length in 641 newborns
has been investigated [9]. Upon measuring the telomere length in cord blood buy coat and placental
tissues, this study showed that mothers exposed to higher levels of PM2.5 (5 µg/m^3 increase during
entire pregnancy period) gave birth to newborns with signicantly shorter telomere length, an
indicator of shorter lifespan [9]. Hence, this study further indicates that prenatal exposure to
increased levels of air pollutants is associated with accelerated biological aging process. Further, a
recent study on the eects of PM2.5 on Caenorhabditis elegans lifespan dene that exposure to low dose
(94 µg/ml) and high dose (119 µg/ml) of water-soluble component of PM2.5 (WS-PM2.5) signicantly
shortened the lifespan of C. elegans. PM2.5 imparts adverse eects on healthspan as evidenced by
reduced rate of head thrashing and pharyngeal pumping and decreased body length compared to
control animal without PM2.5 exposure under heat stress environment. RNA seq analysis revealed
that the adverse eects of PM2.5 on nematode lifespan and healthspan are associated with
deregulation in insulin/IGF-1 signaling and fat metabolism [10]. Collectively, the results of these in
vivo studies clearly indicate the deleterious eects of PM2.5 exposure on organismal lifespan and
healthspan. Further research is needed to determine the molecular basis underlying the negative
eects of PM2.5 on mammalian lifespan and healthspan using suitable mammalian models.
It is evident from the above-discussed studies that for each investigation, dierent experimental
milieu in terms of sources, concentration, heterogeneity in the composition of particulate maer, time
of collection, period of exposure to PM2.5, cell lines and animal models are used. However, despite
the experimental heterogeneity, the results of all the studies provide clear and convincing evidence
that PM2.5 induces massive inammation and oxidative stresses, the root causes of all air pollutant-
induced multi-organ pathologies and accelerated biological aging process.
4. Ecacies of Natural and Synthetic Compounds in Alleviation of PM2.5-Induced Inammation,
Oxidative stress, and Diseases
In this section, I discuss the recent ndings on the ecacies of dierent synthetic and natural
compounds in amelioration of PM2.5-induced sustained oxidative stress, inammation and associated
pathologies using animal and cellular models.
4.1. Lessons from Studies Using Animal Models and Synthetic Compounds
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The potential of dierent synthetic molecules to alleviate PM2.5-induced inammation, oxidative
stress, and associated pathologies have been evaluated in preclinical seings. A wealth of research
demonstrates that an imbalance in the level of plasminogen activator inhibitor-1 (PAI-1), the most
potent inhibitor of serine proteases uPA/t-PA, is associated with a wide variety of diseases including
cardiovascular, pulmonary, metabolism and accelerated aging, and upregulated by the exposure to
PM2.5 [43-49]. Recently, we evaluated the ecacy of a drug-like small molecule inhibitor TM5614
targeting PAI-1 in amelioration of PM2.5-induced pulmonary and cardiac pathologies. A short-term
exposure (24 h) of mice to PM2.5 (50 µg/mouse) increases the levels of circulatory PAI-1, inammatory
cytokine IL-6 and thrombin, a coagulation factor involved in vascular thrombosis. Interestingly, PM2.5
did not increase the levels of circulatory PAI-1, thrombin, and IL-6 in mice pretreated with PAI-1
inhibitor TM5614 (10mg/kg/day). Importantly, PAI-1 specic inhibitor TM5614 diminishes short-term
(72h) PM2.5 exposure (200 µg/mouse/once)-induced inammatory markers Mac3, pStat3 and Vcam1,
and apoptotic marker cleaved caspase 3 in lung and cardiac tissues [28]. Analysis of RNA seq data
reveals while PM2.5 (200 µg/mouse once in 72 h) induces the inammatory factors including Nlrp3,
IL-1 , NF B2, TNFrsf11a, TNFrsf12a, pretreatment of mice with TM5614 (10 mg/kg/day) prevents
induction of these inammation mediators (Ghosh et al. unpublished data). After long-term exposure
to PM2.5 (100 µg/mouse/week for 4 weeks), mice develop lung and heart vascular thrombosis. Most
importantly, pretreatment with TM5614 signicantly decreases PM2.5-induced vascular thrombosis
in lungs and hearts [28]. Therefore, air pollutant PM2.5-induced inammation, apoptosis and vascular
thrombosis can be controlled by promising drug-like small molecule TM5614 targeting PAI-1, a pro-
thrombotic and pro-aging factor. Future preclinical study using large animal cohort is required to
proceed for clinical trials of this drug for treatment of air-pollutant-induced pathologies.
Exposure to PM2.5 (120 µg/ml for 14 days) causes massive lung inammation and lung injury
like alveolar structure disruption in mice. Importantly, PM2.5 augments the levels of inammatory
cytokines like TNF- , IL-6, and IL-1 , inammasome Nlrp3 and apoptotic caspase pathway both in
mouse and 16HBE cell (20 µg/ml/24h) models. Signicantly, PM2.5 exposer-induced lung
inammation and pyroptosis are blocked by the pretreatment of mice with Nlrp3-specic inhibitor
MCC950 (2.5 mg/kg) suggesting targeting Nlrp3 with small molecule inhibitor is a practical approach
to control PM2.5-induced persistent inammation and pyroptosis-driven lung pathologies [50].
Furthermore, exposure of 16HBE cells to PM2.5 (10-40 µg/ml) causes elevated IL-1 expression,
increased small GTPase Rac1 and increased inammation. However, pretreatment of 16HBE for 30
min with Rac1 inhibitor NSC23766 suppresses PM2.5-induced IL-1 secretion. This study also showed
that pharmacological inhibition of Rac1 with NSC23766 (1mg/kg for 9 days; 30 min pretreatment
before PM2.5 exposure) blocks PM2.5 (100 µg/every 3rd day for 9 days)-induced increased IL-1
secretion, inltration of neutrophils and macrophages in murine lungs [51]. Therefore, Rac1 may be
a druggable target for therapy of PM2.5-induced increased inammation and associated lung diseases.
4.2. Lessons from Studies Using Animal Models and Natural Compounds
Here, I discuss the ecacies of several natural compounds in alleviation of PM2.5-induced
pathologies ignited by PM2.5-induced inammation and oxidative stresses. As Salvianolic acid B (SalB)
is a known strong anti-oxidative and anti-inammatory natural agent [52], a recent study evaluated
the ecacy of SalB (0.3 mg/kg, 0.9 mg/kg and 1.8mg/kg) inhalation on PM2.5 (10 µg daily for 5 days)-
induced inammation and oxidative stress in mice [53]. Treatment with SalB signicantly reduces
PM2.5-induced inltration of neutrophil and macrophage, expression levels of IL-1 , TNF- , KC, TGF-
, TLR4, MyD88, TRAP6 and Nlrp3 in a dose-dependent manner and thus alleviates inammation
in the lung tissues. Importantly, treatment of PM2.5-exposed mice with SalB rescued PM2.5-induced
suppression of antioxidant genes SOD, CAT, GSH and GSH-Px in mouse lungs [53]. These results
clearly suggest SalB is highly eective in alleviation of PM2.5-induced inammation, oxidative stress
and thus abnormal lung structure and function.
The therapeutic ecacy of steroidal alkaloid Sipeimine, an anti-inammatory and anti-asthmatic
agent, has been evaluated in amelioration of PM2.5-induced lung inammation and injury [54].
Pretreatment of mice with Sipeimine (30 mg/kg/day/for 3 days) blocks PM2.5 (7.5 mg/kg/day for 2days)-
induced lung inammation, pulmonary edema, and injury through suppression of inammatory
cytokines TNF- , IL-1 and oxidative stress through reversal of PM2.5-induced increased MDA and
decreased GSH. Importantly, Sipeimine blocks PM2.5-induced inhibition of Nrf2, the primary regulator
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of antioxidant genes, and thus diminishes oxidative stress [54]. These results implicate the therapeutic
potential of Sipeimine for the treatment of PM2.5-induced lung pathologies through inhibition of
inammation and oxidative stress. Additionally, pretreatment of Sprague-Dawley rats with Sipeimine
(15 mg/kg-30 mg/kg) for 3 days cause signicantly decreases PM2.5 (7.5mg/kg)-induced lung injury-
related damage that is accompanied by reduced levels of inammatory IL-1 , IL-18, TNF- , Nlrp3
and apoptotic caspase. Thus, Sipeimine eectively ameliorates PM2.5-induced inammation,
pyroptosis and lung injury. This has been further supported by the observation that the benecial
eect of Sipeimine is blocked by pretreatment with Nlrp3 activator nigericin [55]. Similarly,
Astragaloside IV (AS-IV), a plant product from Astragalus Membranaceous with anti-oxidative and
anti-inammatory properties, is highly eective in amelioration of PM2.5-induced massive lung
pathologies in a rat model [56,57]. Pretreatment of rats with AS-IV (50-100 mg/kg/day/for 3 days)
improved PM2.5 (7.5 mg/kg/day)-induced lung injury as shown by the decreased inammatory
signaling molecules IL-6, TNF-, CRP, TLR4 and NF B pathways and oxidative stress in lungs
[56,57]. Further, AS-IV inhibits PM2.5-induced PI3K/mTOR pathway and NF-kB translocation in
NR8383 rat macrophages. In addition, AS-IV blocks PM2.5-induced suppression of antioxidant genes
SOD and CAT [57]. Importantly, pretreatment of mice with AS-IV (50-100 mg/kg) also reduces PM2.5
(7.5 mg/kg/twice, 0, 24h followed by harvest at 36h)-induced inammation, oxidative stress and
pyroptosis through Nlrp3 pathway because pretreatment with Nlrp3 activator nigericin diminishes
benecial eect of AS-IV on PM2.5-induced lung pathologies [58]. Therefore, the bioactive herbal
substance AS-IV has therapeutic potential in amelioration of PM2.5-induced inammation and
oxidative stress-driven lung pathologies. Thus, AS-IV may be a future potential drug to control PM2.5-
induced lung injury and Nlrp3 is a potent druggable target for therapy.
The ecacy of Tussilagone (TLS), a natural compound derived from ower bud, in amelioration
of PM2.5-induced lung pathologies has been evaluated [59]. Treatment of mice with TLS
(20mg/kg/every 3 days) blunts PM2.5 (20mg/kg/4h inhalation/day for 6 days)-induced ROS production
or oxidative stress, lung inammation as shown by reduced levels of IL-1 , IL-6, IL-12 and TNF-
and injury through downregulation of PM2.5-induced HIF-1 and NF B signaling. In addition,
pretreatment of human lung epithelial cells (A549) with TLS (25 µg/ml) reduces PM2.5 (30 µg, 100 µg,
300 µg/ml for 4 days)-induced apoptosis markers like cleaved caspase 3 and LDH activity, and
inammatory cytokines IL-1 , IL-6, and TNF- [59]. Collectively, these results indicate the
therapeutic potential of TLS for the treatment of air pollution-induced lung inammation and
oxidative stress. The therapeutic ecacy of Deng-Shi-Qing-Mai-Tang (DSQMT), a Chinese herbal
formula, on PM2.5-induced lung injury has been assessed [60]. Treatment with DSQMT (3 ml of 0.72,
1.45, 2.90 g/ml) signicantly decreases the inammatory cytokines IL-1 , IL-6, and TNF- and
pathologies like damaged lung tissues and higher lung permeability index in rats exposed to PM2.5
(50 µg/rat/week for 8 weeks). Additionally, DSQMT (20% of medicated serum 1.45g/ml) decreases
the PM2.5 (0.5mg/ml)-induced increased expression of many factors involved in inammation
including IL-1 , IL-6 and TNF- in rat alveolar macrophages, NR8383 [60]. Thus, this study
implicated DSQMT as a potential natural compound to control air pollution-induced lung injury
through modulation of PM2.5-induced inammatory responses. As Schisandrae Fructus fruit is known
to possesses the anti-inammatory and antioxidant activities, the therapeutic ecacy of Schisandrae
Fructus ethanol extract (SF) (200 µg and 400 µg/ml pretreated for 1h) on PM2.5 (50 µg/ml for 24h)-
induced inammatory and oxidative stress developed in RAW264.7 macrophages and post fertilized
(day3) zebrash larvae has been evaluated [61]. Signicantly, SF reduces the expression of PM2.5-
induced inammatory cytokines IL-6 and IL-1 , NO and COX2 through disruption of nuclear
translocation of NF B from cytoplasm to nucleus and impaired NF B signaling. Pretreatment with
SF also blocks PM2.5-induced ROS activity in macrophages and zebrash larvae as shown by ROS
uorescence intensity [61]. Therefore, SF with anti-inammatory as well as antioxidative properties
is an excellent choice for the treatment of oxidative stress- and inammation-induced tissue damages.
Future in vivo studies are needed to explore the therapeutic ecacy of SF in amelioration of PM2.5-
induced massive inammation and oxidative stress in mammalian models.
Bergapten (5-methoxysporalen), a bergamont essential oil, possesses antioxidant and anti-
inammatory properties. While exposure to PM2.5 (100 µg/mouse for 30 days) aggravates OVA-
induced combined allergic rhinitis and asthma syndrome (CARAS) with massive lung inammation
and lung injury in mice, treatment of mice with Bergapten (3,10,30 mg/kg) induces OVA-specic
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IgG2A and decreases the level of IgE and IgG1 in serum. Most importantly, Bergapten reduces the
inammation in nasal mucosa and lungs through induction of Th1 cytokine IL-12, IFN- and
reduction of Th2 cytokines IL-4, IL-5, and IL-13 [62]. These results indicate that Bergapten is a potential
natural therapeutic agent to treat CARAS and PM2.5-induced worst lung pathologies. Similarly, the
ecacy of Rosavidin, a phenylpropanoid compound having multiple biological activities extracted
from the Rhodiola crenulata plant, in amelioration of PM2.5-induced lung pathology has been
examined in a rat model. Pretreatment of rats with Rosavidin (50-100 mg/kg/day for 3 days)
diminishes PM2.5 (7.5mg/kg twice in 36h at 0h and 24h)-induced inammation and ameliorates lung
pathologies in rats through inhibition of inammatory and apoptotic regulators including IL-1 ,
Nlrp3 inammasome, and caspase. This study further demonstrated that Nlrp3 specic activator
nigerin blunts Rosavidin-mediated amelioration of PM2.5-induced lung pathologies [63].Therefore,
Rosavidin has potential to be a remedy to controlling PM2.5-induced inammation and pyroptosis-
driven lung pathologies. It is well documented that exposure to PM2.5 causes worst lung pathologies
in COPD patients [64,65]. Bufei Yishen formula (ECC-BYF), a Chinese herbal medicinal formula,
eciently improves COPD in a rat model that was developed by repeated cigaree smoke inhalation
(2 times daily, 30 min each time for 8 weeks and intranasal instillation of pneumonia bacteria once
for every 5 days). Whole body exposure of COPD rats to PM2.5 for another 8 weeks (average daily
conc. of PM2.5 739.97µg/m^3; 4h/day for 8 weeks) leads to excessive lung inammation, lung tissue
remodeling and decreased lung function in this rat model of COPD. However, PM2.5 failed to induce
inammation, oxidative stress, pyroptosis and excessive collagen deposition in the lungs of ECC-
BYF-treated COPD rat model [66]. These results clearly indicate the therapeutic ecacy of ECC-BYF
for the treatment of PM2.5-induced worst lung inammation, pyroptosis and lung injury in COPD in
a preclinical seing.
As Juglanin is a plant product with anti-inammatory and anti-oxidative properties, the
therapeutic ecacy of Juglanin on PM2.5-induced inammation, oxidative stress, and liver injury has
been assessed [67]. Interestingly, Juglanin (40mg/kg/day, via gavage 6h prior to PM2.5 exposure)
reduces PM2.5 (151.1 +/- 2.5 µg/m^3, 6 h /day, 5 times/week for 24 weeks)-induced liver injury through
activation of antioxidant gene regulator Nrf2, and suppressor of IKKe (SIKE), a known negative
regulator of inammatory signaling. It is important to note that Nrf2 and SIKE KO mice are more
susceptible to PM2.5-induced oxidative stress/ROS generation as shown by higher level of MDA,
lower level of SOD, and increased inammation as shown by higher IL-1 , IL-6, TNF- , and liver
injury as shown by higher ALT and AST compared to wildtype mice. These in vivo observations on
the benecial eects of Juglanin on PM2.5-induced liver injury have also been replicated in vitro using
human liver cell line LO2 [67]. Together, this study suggests the signicant involvement of Nrf2 and
SIKE pathways in PM2.5-induced liver injury and most importantly, Juglanin is a potential therapeutic
agent to controlling PM2.5-induced inammation, oxidative stress, and liver pathologies. A recent
study also showed that Nrf2 protects PM2.5 (20mg/kg)-induced lung injury through its regulation of
iron-dependent cellular death or ferroptosis. This is supported by the observation that ferroptosis
and lung injury in response to PM2.5 are more severe in Nrf2-decient lung tissue and cellular model
[68]. Similarly, Tectoridin (50-100 mg/kg), a bioactive molecule, also ameliorates PM2.5 (20mg/kg for 7
days)-induced lung injury as revealed by decreased morphological damage, necrosis, edema and
inammation with decreased IL-6 and TNF- through stimulation of antioxidant gene regulator Nrf2
and antioxidant genes like GSH and GPX4. Similarly, pretreatment of BEAS-2B cells with Tectoridin
(25, 50 and 100 uM for 1 h) reduces PM2.5 (400µg/ml for 24h)-induced ROS generation through
activation of Nrf2, GSH and inhibition of PM2.5-induced inammatory MDA [68]. These results
suggest that Tectoridin has potential to controlling PM2.5-induced oxidative stress, ferroptosis, and
lung pathologies. It is known that exercise-induced myokine, Irisin, a polypeptide derived from
muscle and adipose tissues, is a potent anti-inammatory agent that diminishes metabolic syndrome
[69]. Interestingly, pretreatment of mice with recombinant Irisin (250 µg/kg) signicantly diminishes
the PM2.5 (8mg/kg for 24h)-induced increased level of inammatory cytokines IL-1 , IL-18, TNF- and
mediators of inammation including NF B, and Nlrp3 inammasome [70]. Therefore, Irisin is an
eective myokine in amelioration of PM2.5-induced lung pathologies through suppression of
inammatory pathways.
Collectively, the results from all these studies in this section strongly suggest that irrespective of
the unique characteristics of each natural compound and doses used, all the tested compounds are
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9
ecacious in diminishing PM2.5-induced pathologies through suppression of massive inammation
and oxidative stress. However, further long-term in vivo, and in vitro studies are essential to
understand in-depth the underlying molecular mechanisms by which these natural compounds
govern the factors/mediators involved in inammation and oxidative stress.
4.3. Lessons from Studies Using Cellular Models and Synthetic Compounds
In this section, I discuss the major ndings on the ecacies of several synthetic and natural
compounds in amelioration of PM2.5-induced cellular abnormalities including activation of oxidative
stress and inammatory pathways using cellular models.
Fine particulate maer (PM2.5)-induced detrimental eects on endothelial cells, the rst cellular
barrier of the cardiovascular system, have been well studied. To investigate the contribution of
oxidative stress and inammation on PM2.5-induced endothelial injury, the eect of PM2.5 on
EA.hy926 endothelial cells was examined [71]. PM2.5 exposure (50 µg/ml for 24h) induces NOX1/4,
superoxide, H2O2, ET1 and decreases NO pathway. Furthermore, PM2.5 causes an imbalance in the
ratio of t-PA to PAI-1 due to signicantly increased expression of PAI-1 and decreased expression of
t-PA. Exposure to PM2.5 also augments the expression levels of inammatory cytokines including IL-
1 and IL-18 in this cell line, indicating PM2.5 exposure contributes to endothelial dysfunction.
Importantly, pretreatment of EAhy.926 cells with NOX1/4 inhibitor (GSK 13783) (5uM) diminishes
PM2.5-induced oxidative stress and inammation and thus ameliorates PM2.5-induced endothelial
dysfunction [71]. Hence, NOX1/4 may be a druggable target to reduce air pollutant PM2.5-induced
endothelial dysfunction and associated cardiovascular diseases. The pharmacological eect of
Ropivacaine, a widely used local anesthetic, on PM2.5-induced acute lung injury has been explored in
cultured lung cells [72]. Exposure to PM2.5 (100µg/ml) induces the inammatory and oxidative stress
in lung cells BEAS-2B as shown by increased expression of inammatory cytokines IL-6, IL-8, IL-1 ,
TNF- and oxidative stress-related MDA, and decreased expression of GSH. However, pretreatment
of BEAS-2B cells with Ropivacaine (1 µM, 10 µM, 100 µM) reduces PM2.5-induced inammatory
pathway, oxidative stress, and cell death through downregulation of inammasome Nlrp3 and
apoptotic caspase pathways [72], indicating Ropivacaine has potential to reduce PM2.5-induced
inammation, oxidative stress, and thus may be eective in diminishing lung injury-associated
pathologies. Similarly, pretreatment of human bronchial epithelial cells (16HBE) with Caspase
inhibitors Z-VAD-FMK and VX-765 block wood smoke-derived PM2.5 (5, 10. 20 µg/ml)-induced
inammation and pyroptosis of 16HBE cells as evidenced by decreased levels of LDH activity,
caspase, inammatory cytokines IL-1 and IL-18, the downstream targets of Nlrp3 [19]. These results
show the potential of caspase inhibitors to block wildre/wood smoke-induced massive
inammation and pyroptosis.
As Vitamin D3 possesses anti-inammatory activity, the therapeutic potential of VitD3 in PM2.5-
induced inammation has been assessed in human bronchial epithelial cells (16HBE) [73]. PM2.5
(200µg/ml for 48h)-treated 16HBE cells produce elevated levels of ROS and MDA, and the secretion
of inammatory mediators IL-6, IL-18, NF B and Nlrp3 inammasome. However, pretreatment of
16HBE with VitD3 (1nM) for 24h decreases the PM2.5-induced ROS generation, and expression of
MDA, IL-6, IL-8, NF B and Nlrp3. indicating VitD3 is eective in inhibition of PM2.5-induced
inammatory and oxidative stress responses [73]. Similarly, pretreatment of rat neonatal
cardiomyocytes with VitD3 (10^-8 mol/L) signicantly reduce the cooking oil fumes-derived PM2.5 (50
µg/ml)-induced ROS production, inammation and pyroptosis through suppression of inammatory
signaling pathways JAK/Stat1 and NF B. Further, VitD3 also prevents PM2.5-induced inhibition of
antioxidant SOD and GSH in cardiomyocytes [74]. Collectively, these results indicate that VitD3 is
cardioprotective from PM2.5-induced inammation, oxidative stress, and associated pathologies.
Another study [75] showed that while the expression levels of inammatory TLR4, NF B and COX2
are signicantly increased in PM2.5 (250 µg/ml for 24-72 h)-treated RAW254.7 macrophages,
pretreatment with TLR4-inhibitor TAK242 (5-20 µM) signicantly inhibits PM2.5-induced pro-
inammatory signaling molecules IL-6, MCP1 and TNF- [75]. Therefore, TLR4-specic inhibitor has
potential to controlling PM2.5-induced inammation. Similarly, the levels of inammatory markers
IL-1 , COX2 and oxidative stress marker Hmox1 are also signicantly elevated in PM2.5-exposed (30
µg/ml for 3h) mouse macrophages. While PM2.5-induced inammatory responses are decreased in
macrophages either by pretreatment with endotoxin neutralizer polymyxin B (0.5mg/ml) or NF-kB
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inhibitor Bay 11-7085 (10 µM), the oxidative stress responses are decreased by antioxidant n-acetyl
cysteine (NAC) (10mM) [76]. Collectively, the results of these in vitro studies provide clear evidence
that PM2.5-induced inammation and oxidative stress pathways can be eectively blocked by
dierent synthetic compounds.
4.4. Lessons from Studies Using Cellular Models and Natural Compounds
It is known that exposure to PM2.5 not only aects lungs and cardiovascular system but also
aects brain and cognitive functions. Air pollutant PM2.5 can reach to the brain and contributes to
accelerated neurological syndromes including Alzheimer’s disease [77,78]. As carotenoid, Astaxanthin
is a known anti-inammatory and neuroprotective agent, the ecacy of Astaxanthin on PM2.5-
induced inammation and neurotoxicity has been evaluated and demonstrated that PM2.5 stimulates
the levels of ROS/oxidative stress, inammatory mediators IL-1 , IL-6, TNF- , TLR2/4, and COX2
and stress-induced protein HO-1 in BV-2 microglial cells. Most importantly, PM2.5 (50 µg/ml/24h)
failed to induce the inammatory markers in rat glial cells pretreated with Astaxanthin (1, 10 µg/ml)
for 4 h. Astaxanthin also prevents PM2.5-induced inhibition of IL-10 and Arg-1. Hence, Astaxanthin is
eective in prevention of PM2.5-induced inammation, oxidative stress and associated neurological
disorders [79]. The plant product Ophiopogonin D is also an anti-inammatory agent. Pretreatment of
mouse lung epithelial cells MLE-12 with Ophiopogonin D (10-80 µM) for 1h inhibits PM2.5 (15 µg/cm^2
for 24h)-induced inammation as shown by the decreased levels of IL-1 , IL-6, IL-8, and TNF- . The
Ophiopogonin D exerts its anti-inammatory eect through downregulation of NF B signaling and
activation of AMPK activity as pretreatment of cells with AMPK inhibitor (Compound C, 10 µM)
blocks anti-inammatory activity of Ophiopogonin D [80]. As the dihydrophenanthrene Coelonin,
derived from the owering plant Bletilla striata, is a known anti-inammatory agent [81,82], its
therapeutic ecacy in amelioration of PM2.5-induced inammation has been evaluated [83].
Pretreatment with Coelonin (1.25, 2.5 or 5 µg/ml for 2h) ameliorates PM2.5 (200µ/ml for 18h)-induced
inammation, oxidative stress and pyroptosis of RAW264 and 1774A.1 macrophages through
suppression of Nlrp3 inammasome, IL-6, TNF- , TLR4, COX2, and NFkB signaling [83]. These
results suggest that dierent natural compounds are eective in diminishing PM2.5-induced massive
inammation, oxidative stress, and pyroptosis.
Therefore, the results of all these cell biology studies suggest that pharmacological modulation
of inammatory mediators or oxidative stress regulators are ideal therapeutic approaches to
controlling air-pollutant PM2.5-induced disease development. However, more in-depth preclinical
studies using proper models are necessary to reproduce the ecacies of these natural and synthetic
compounds before proceeding for clinical trials.
5. Concluding Remarks
Air pollution is one of the major risk factors to human health and shortening of healthspan
worldwide. In search of remedies for the air pollution driven stress-induced health risk, many
investigations have been undertaken worldwide as discussed in this article. A careful analysis of all
these preclinical studies on air pollutant PM2.5 and its impact on organismal health unequivocally
proved the pivotal contribution of PM2.5-induced inammation and oxidative stress in initiation and
progression of a wide variety of pathologies and accelerated aging process. Hence, the development
of drug-like small molecules targeting PM2.5-deregulated pathogenic factors will be a promising
approach for amelioration of PM2.5-induced oxidative stress, inammation, and associated
pathologies. Meta-analysis of related published data set on air-pollution deregulated molecules,
cellular and biological processes may be helpful to identify unique and common pathogenic factor(s).
Based on the observations made by dierent independent investigations under dierent
experimental milieus as has been discussed earlier in this article, it is noticeable that while the
expression level of antioxidant gene regulator Nrf2 is decreased, the levels of inammasome Nlrp3
and pro-aging factor PAI-1 are signicantly elevated in response to air pollutant PM2.5 exposures.
Therefore, development of natural or synthetic drugs either, as an activator targeting Nrf2 or
repressor/inhibitor targeting Nlrp3 or PAI-1 will be a feasible approach to abate air pollution-induced
initiation of multiorgan pathologies [see Graphical Abstract]. Further, it is crucial to evaluate the
ecacies of the above-discussed natural and synthetic compounds in diminishing PM2.5-induced
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11
oxidative stress, inammation, and cell death by large cohort studies in an unbiased preclinical
seing. To rule out the possible harmful eects, it is also crucial to determine the toxicity of each
synthetic as well as natural compound after long-term use in control and PM2.5-exposed animal
models. An identication of the most ecacious and non-toxic safe compound for the clinical trial
and its success will save billions of people worldwide from air pollution-induced devastating
diseases, and thus will increase the healthspan.
Conicts of Interest: The author declares no conict of interest.
Acknowledgments: The American Heart Association-Innovative Project Award (18IPA34170365 to AKG)
supported author's work.
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