In this section, I discuss the recent findings on the efficacies of different synthetic and natural compounds in amelioration of PM2.5-induced sustained oxidative stress, inflammation and associated pathologies using animal and cellular models.
4.1. Lessons from Studies Using Animal Models and Synthetic Compounds
The potential of different synthetic molecules to alleviate PM
2.5-induced inflammation, oxidative stress, and associated pathologies have been evaluated in preclinical settings. 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 PM
2.5 [43-49]. Recently, we evaluated the efficacy of a drug-like small molecule inhibitor
TM5614 targeting PAI-1 in amelioration of PM
2.5-induced pulmonary and cardiac pathologies. A short-term exposure (24 h) of mice to PM
2.5 (50 µg/mouse) increases the levels of circulatory PAI-1, inflammatory cytokine IL-6 and thrombin, a coagulation factor involved in vascular thrombosis. Interestingly, PM
2.5 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 specific inhibitor
TM5614 diminishes short-term (72h) PM
2.5 exposure (200 µg/mouse/once)-induced inflammatory markers Mac3, pStat3 and Vcam1, and apoptotic marker cleaved caspase 3 in lung and cardiac tissues [
28]. Analysis of RNA seq data reveals while PM
2.5 (200 µg/mouse once in 72 h) induces the inflammatory factors including Nlrp3, IL-1

, NF

B2, TNFrsf11a, TNFrsf12a, pretreatment of mice with
TM5614 (10 mg/kg/day) prevents induction of these inflammation mediators (Ghosh et al. unpublished data). After long-term exposure to PM
2.5 (100 µg/mouse/week for 4 weeks), mice develop lung and heart vascular thrombosis. Most importantly, pretreatment with
TM5614 significantly decreases PM
2.5-induced vascular thrombosis in lungs and hearts [
28]. Therefore, air pollutant PM
2.5-induced inflammation, 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 PM
2.5 (120 µg/ml for 14 days) causes massive lung inflammation and lung injury like alveolar structure disruption in mice. Importantly, PM
2.5 augments the levels of inflammatory cytokines like TNF-

, IL-6, and IL-1

, inflammasome Nlrp3 and apoptotic caspase pathway both in mouse and 16HBE cell (20 µg/ml/24h) models. Significantly, PM
2.5 exposer-induced lung inflammation and pyroptosis are blocked by the pretreatment of mice with Nlrp3-specific inhibitor
MCC950 (2.5 mg/kg) suggesting targeting Nlrp3 with small molecule inhibitor is a practical approach to control PM
2.5-induced persistent inflammation and pyroptosis-driven lung pathologies [
50]. Furthermore, exposure of 16HBE cells to PM
2.5 (10-40 µg/ml) causes elevated IL-1

expression, increased small GTPase Rac1 and increased inflammation. However, pretreatment of 16HBE for 30 min with Rac1 inhibitor
NSC23766 suppresses PM
2.5-induced IL-1

secretion. This study also showed that pharmacological inhibition of Rac1 with
NSC23766 (1mg/kg for 9 days; 30 min pretreatment before PM
2.5 exposure) blocks PM
2.5 (100 µg/every 3
rd day for 9 days)-induced increased IL-1

secretion, infiltration of neutrophils and macrophages in murine lungs [
51]. Therefore, Rac1 may be a druggable target for therapy of PM
2.5-induced increased inflammation and associated lung diseases.
4.2. Lessons from Studies Using Animal Models and Natural Compounds
Here, I discuss the efficacies of several natural compounds in alleviation of PM
2.5-induced pathologies ignited by PM
2.5-induced inflammation and oxidative stresses. As
Salvianolic acid B (SalB) is a known strong anti-oxidative and anti-inflammatory natural agent [
52], a recent study evaluated the efficacy of
SalB (0.3 mg/kg, 0.9 mg/kg and 1.8mg/kg) inhalation on PM
2.5 (10 µg daily for 5 days)-induced inflammation and oxidative stress in mice [
53]. Treatment with SalB significantly reduces PM
2.5-induced infiltration 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 inflammation in the lung tissues. Importantly, treatment of PM
2.5-exposed mice with
SalB rescued PM
2.5-induced suppression of antioxidant genes SOD, CAT, GSH and GSH-Px in mouse lungs [
53]. These results clearly suggest
SalB is highly effective in alleviation of PM
2.5-induced inflammation, oxidative stress and thus abnormal lung structure and function.
The therapeutic efficacy of steroidal alkaloid
Sipeimine, an anti-inflammatory and anti-asthmatic agent, has been evaluated in amelioration of PM
2.5-induced lung inflammation and injury [
54]. Pretreatment of mice with
Sipeimine (30 mg/kg/day/for 3 days) blocks PM
2.5 (7.5 mg/kg/day for 2days)-induced lung inflammation, pulmonary edema, and injury through suppression of inflammatory cytokines TNF-

, IL-1

and oxidative stress through reversal of PM
2.5-induced increased MDA and decreased GSH. Importantly,
Sipeimine blocks PM
2.5-induced inhibition of Nrf2, the primary regulator of antioxidant genes, and thus diminishes oxidative stress [
54]. These results implicate the therapeutic potential of
Sipeimine for the treatment of PM
2.5-induced lung pathologies through inhibition of inflammation and oxidative stress. Additionally, pretreatment of Sprague-Dawley rats with
Sipeimine (15 mg/kg-30 mg/kg) for 3 days cause significantly decreases PM
2.5 (7.5mg/kg)-induced lung injury-related damage that is accompanied by reduced levels of inflammatory IL-1

, IL-18, TNF-

, Nlrp3 and apoptotic caspase. Thus,
Sipeimine effectively ameliorates PM
2.5-induced inflammation, pyroptosis and lung injury. This has been further supported by the observation that the beneficial effect 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-inflammatory properties, is highly effective in amelioration of PM
2.5-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 PM
2.5 (7.5 mg/kg/day)-induced lung injury as shown by the decreased inflammatory signaling molecules IL-6, TNF-α, CRP, TLR4 and NF

B pathways and oxidative stress in lungs [
56,
57]. Further,
AS-IV inhibits PM
2.5-induced PI3K/mTOR pathway and NF-kB translocation in NR8383 rat macrophages. In addition,
AS-IV blocks PM
2.5-induced suppression of antioxidant genes SOD and CAT [
57]. Importantly, pretreatment of mice with
AS-IV (50-100 mg/kg) also reduces PM
2.5 (7.5 mg/kg/twice, 0, 24h followed by harvest at 36h)-induced inflammation, oxidative stress and pyroptosis through Nlrp3 pathway because pretreatment with Nlrp3 activator nigericin diminishes beneficial effect of
AS-IV on PM
2.5-induced lung pathologies [
58]. Therefore, the bioactive herbal substance
AS-IV has therapeutic potential in amelioration of PM
2.5-induced inflammation and oxidative stress-driven lung pathologies. Thus,
AS-IV may be a future potential drug to control PM
2.5-induced lung injury and Nlrp3 is a potent druggable target for therapy.
The efficacy of
Tussilagone (TLS), a natural compound derived from flower bud, in amelioration of PM
2.5-induced lung pathologies has been evaluated [
59]. Treatment of mice with
TLS (20mg/kg/every 3 days) blunts PM
2.5 (20mg/kg/4h inhalation/day for 6 days)-induced ROS production or oxidative stress, lung inflammation as shown by reduced levels of IL-1


, IL-6, IL-12 and TNF-

and injury through downregulation of PM
2.5-induced HIF-1

and NF

B signaling. In addition, pretreatment of human lung epithelial cells (A549) with
TLS (25 µg/ml) reduces PM
2.5 (30 µg, 100 µg, 300 µg/ml for 4 days)-induced apoptosis markers like cleaved caspase 3 and LDH activity, and inflammatory cytokines IL-1

, IL-6, and TNF-α [
59]. Collectively, these results indicate the therapeutic potential of
TLS for the treatment of air pollution-induced lung inflammation and oxidative stress. The therapeutic efficacy of
Deng-Shi-Qing-Mai-Tang (DSQMT), a Chinese herbal formula, on PM
2.5-induced lung injury has been assessed [
60]. Treatment with
DSQMT (3 ml of 0.72, 1.45, 2.90 g/ml) significantly decreases the inflammatory cytokines IL-1

, IL-6, and TNF-

and pathologies like damaged lung tissues and higher lung permeability index in rats exposed to PM
2.5 (50 µg/rat/week for 8 weeks). Additionally,
DSQMT (20% of medicated serum 1.45g/ml) decreases the PM
2.5 (0.5mg/ml)-induced increased expression of many factors involved in inflammation including IL-1

, IL-6 and TNF-α 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 PM
2.5-induced inflammatory responses. As
Schisandrae Fructus fruit is known to possesses the anti-inflammatory and antioxidant activities, the therapeutic efficacy of
Schisandrae Fructus ethanol extract (SF) (200 µg and 400 µg/ml pretreated for 1h) on PM
2.5 (50 µg/ml for 24h)-induced inflammatory and oxidative stress developed in RAW264.7 macrophages and post fertilized (day3) zebrafish larvae has been evaluated [
61]. Significantly,
SF reduces the expression of PM
2.5-induced inflammatory 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 PM
2.5-induced ROS activity in macrophages and zebrafish larvae as shown by ROS fluorescence intensity [
61]. Therefore,
SF with anti-inflammatory as well as antioxidative properties is an excellent choice for the treatment of oxidative stress- and inflammation-induced tissue damages. Future
in vivo studies are needed to explore the therapeutic efficacy of
SF in amelioration of PM
2.5-induced massive inflammation and oxidative stress in mammalian models.
Bergapten (5-methoxysporalen), a bergamont essential oil, possesses antioxidant and anti-inflammatory properties. While exposure to PM
2.5 (100 µg/mouse for 30 days) aggravates OVA-induced combined allergic rhinitis and asthma syndrome (CARAS) with massive lung inflammation and lung injury in mice, treatment of mice with
Bergapten (3,10,30 mg/kg) induces OVA-specific IgG2A and decreases the level of IgE and IgG1 in serum. Most importantly,
Bergapten reduces the inflammation 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 PM
2.5-induced worst lung pathologies. Similarly, the efficacy of
Rosavidin, a phenylpropanoid compound having multiple biological activities extracted from the Rhodiola crenulata plant, in amelioration of PM
2.5-induced lung pathology has been examined in a rat model. Pretreatment of rats with
Rosavidin (50-100 mg/kg/day for 3 days) diminishes PM
2.5 (7.5mg/kg twice in 36h at 0h and 24h)-induced inflammation and ameliorates lung pathologies in rats through inhibition of inflammatory and apoptotic regulators including IL-1

, Nlrp3 inflammasome, and caspase. This study further demonstrated that Nlrp3 specific activator nigerin blunts
Rosavidin-mediated amelioration of PM
2.5-induced lung pathologies [
63].Therefore,
Rosavidin has potential to be a remedy to controlling PM
2.5-induced inflammation and pyroptosis-driven lung pathologies. It is well documented that exposure to PM
2.5 causes worst lung pathologies in COPD patients [
64,
65].
Bufei Yishen formula (ECC-BYF), a Chinese herbal medicinal formula, efficiently improves COPD in a rat model that was developed by repeated cigarette 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 PM
2.5 for another 8 weeks (average daily conc. of PM
2.5 739.97µg/m^3; 4h/day for 8 weeks) leads to excessive lung inflammation, lung tissue remodeling and decreased lung function in this rat model of COPD. However, PM
2.5 failed to induce inflammation, oxidative stress, pyroptosis and excessive collagen deposition in the lungs of
ECC-BYF-treated COPD rat model [
66]. These results clearly indicate the therapeutic efficacy of
ECC-BYF for the treatment of PM
2.5-induced worst lung inflammation, pyroptosis and lung injury in COPD in a preclinical setting.
As
Juglanin is a plant product with anti-inflammatory and anti-oxidative properties, the therapeutic efficacy of
Juglanin on PM
2.5-induced inflammation, oxidative stress, and liver injury has been assessed [
67]. Interestingly,
Juglanin (40mg/kg/day, via gavage 6h prior to PM
2.5 exposure) reduces PM
2.5 (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 inflammatory signaling. It is important to note that Nrf2 and SIKE KO mice are more susceptible to PM
2.5-induced oxidative stress/ROS generation as shown by higher level of MDA, lower level of SOD, and increased inflammation 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 beneficial effects of
Juglanin on PM
2.5-induced liver injury have also been replicated
in vitro using human liver cell line LO2 [
67]. Together, this study suggests the significant involvement of Nrf2 and SIKE pathways in PM
2.5-induced liver injury and most importantly,
Juglanin is a potential therapeutic agent to controlling PM
2.5-induced inflammation, oxidative stress, and liver pathologies. A recent study also showed that Nrf2 protects PM
2.5 (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 PM
2.5 are more severe in Nrf2-deficient lung tissue and cellular model [
68]. Similarly,
Tectoridin (50-100 mg/kg), a bioactive molecule, also ameliorates PM
2.5 (20mg/kg for 7 days)-induced lung injury as revealed by decreased morphological damage, necrosis, edema and inflammation 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 PM
2.5 (400µg/ml for 24h)-induced ROS generation through activation of Nrf2, GSH and inhibition of PM
2.5-induced inflammatory MDA [
68]. These results suggest that
Tectoridin has potential to controlling PM
2.5-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-inflammatory agent that diminishes metabolic syndrome [
69]. Interestingly, pretreatment of mice with recombinant
Irisin (250 µg/kg) significantly diminishes the PM
2.5 (8mg/kg for 24h)-induced increased level of inflammatory cytokines IL-1

, IL-18, TNF-

and mediators of inflammation including NF

B, and Nlrp3 inflammasome [
70]. Therefore,
Irisin is an effective myokine in amelioration of PM
2.5-induced lung pathologies through suppression of inflammatory 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 efficacious in diminishing PM2.5-induced pathologies through suppression of massive inflammation 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 inflammation and oxidative stress.
4.3. Lessons from Studies Using Cellular Models and Synthetic Compounds
In this section, I discuss the major findings on the efficacies of several synthetic and natural compounds in amelioration of PM2.5-induced cellular abnormalities including activation of oxidative stress and inflammatory pathways using cellular models.
Fine particulate matter (PM
2.5)-induced detrimental effects on endothelial cells, the first cellular barrier of the cardiovascular system, have been well studied. To investigate the contribution of oxidative stress and inflammation on PM
2.5-induced endothelial injury, the effect of PM
2.5 on EA.hy926 endothelial cells was examined [
71]. PM
2.5 exposure (50 µg/ml for 24h) induces NOX1/4, superoxide, H
2O
2, ET1 and decreases NO pathway. Furthermore, PM
2.5 causes an imbalance in the ratio of t-PA to PAI-1 due to significantly increased expression of PAI-1 and decreased expression of t-PA. Exposure to PM
2.5 also augments the expression levels of inflammatory cytokines including IL-1

and IL-18 in this cell line, indicating PM
2.5 exposure contributes to endothelial dysfunction. Importantly, pretreatment of EAhy.926 cells with NOX1/4 inhibitor (
GSK 13783) (5uM) diminishes PM
2.5-induced oxidative stress and inflammation and thus ameliorates PM
2.5-induced endothelial dysfunction [
71]. Hence, NOX1/4 may be a druggable target to reduce air pollutant PM
2.5-induced endothelial dysfunction and associated cardiovascular diseases. The pharmacological effect of
Ropivacaine, a widely used local anesthetic, on PM
2.5-induced acute lung injury has been explored in cultured lung cells [
72]. Exposure to PM
2.5 (100µg/ml) induces the inflammatory and oxidative stress in lung cells BEAS-2B as shown by increased expression of inflammatory 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 PM
2.5-induced inflammatory pathway, oxidative stress, and cell death through downregulation of inflammasome Nlrp3 and apoptotic caspase pathways [
72], indicating
Ropivacaine has potential to reduce PM
2.5-induced inflammation, oxidative stress, and thus may be effective 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 PM
2.5 (5, 10. 20 µg/ml)-induced inflammation and pyroptosis of 16HBE cells as evidenced by decreased levels of LDH activity, caspase, inflammatory cytokines IL-1

and IL-18, the downstream targets of Nlrp3 [
19]. These results show the potential of caspase inhibitors to block wildfire/wood smoke-induced massive inflammation and pyroptosis.
As
Vitamin D3 possesses anti-inflammatory activity, the therapeutic potential of
VitD3 in PM
2.5-induced inflammation has been assessed in human bronchial epithelial cells (16HBE) [
73]. PM
2.5 (200µg/ml for 48h)-treated 16HBE cells produce elevated levels of ROS and MDA, and the secretion of inflammatory mediators IL-6, IL-18, NF

B and Nlrp3 inflammasome. However, pretreatment of 16HBE with
VitD3 (1nM) for 24h decreases the PM
2.5-induced ROS generation, and expression of MDA, IL-6, IL-8, NF

B and Nlrp3. indicating
VitD3 is effective in inhibition of PM
2.5-induced inflammatory and oxidative stress responses [
73]. Similarly, pretreatment of rat neonatal cardiomyocytes with
VitD3 (10^-8 mol/L) significantly reduce the cooking oil fumes-derived PM
2.5 (50 µg/ml)-induced ROS production, inflammation and pyroptosis through suppression of inflammatory signaling pathways JAK/Stat1 and NF

B. Further,
VitD3 also prevents PM
2.5-induced inhibition of antioxidant SOD and GSH in cardiomyocytes [
74]. Collectively, these results indicate that
VitD3 is cardioprotective from PM
2.5-induced inflammation, oxidative stress, and associated pathologies. Another study [
75] showed that while the expression levels of inflammatory TLR4, NF

B and COX2 are significantly increased in PM
2.5 (250 µg/ml for 24-72 h)-treated RAW254.7 macrophages, pretreatment with TLR4-inhibitor
TAK242 (5-20 µM) significantly inhibits PM
2.5-induced pro-inflammatory signaling molecules IL-6, MCP1 and TNF-

[
75]. Therefore, TLR4-specific inhibitor has potential to controlling PM
2.5-induced inflammation. Similarly, the levels of inflammatory markers IL-1

, COX2 and oxidative stress marker Hmox1 are also significantly elevated in PM
2.5-exposed (30 µg/ml for 3h) mouse macrophages. While PM
2.5-induced inflammatory responses are decreased in macrophages either by pretreatment with endotoxin neutralizer
polymyxin B (0.5mg/ml) or NF-kB 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 PM
2.5-induced inflammation and oxidative stress pathways can be effectively blocked by different synthetic compounds.
4.4. Lessons from Studies Using Cellular Models and Natural Compounds
It is known that exposure to PM
2.5 not only affects lungs and cardiovascular system but also affects brain and cognitive functions. Air pollutant PM
2.5 can reach to the brain and contributes to accelerated neurological syndromes including Alzheimer’s disease [
77,
78]. As carotenoid,
Astaxanthin is a known anti-inflammatory and neuroprotective agent, the efficacy of Astaxanthin on PM
2.5-induced inflammation and neurotoxicity has been evaluated and demonstrated that PM
2.5 stimulates the levels of ROS/oxidative stress, inflammatory mediators IL-1

, IL-6, TNF-

, TLR2/4, and COX2 and stress-induced protein HO-1 in BV-2 microglial cells. Most importantly, PM
2.5 (50 µg/ml/24h) failed to induce the inflammatory markers in rat glial cells pretreated with
Astaxanthin (1, 10 µg/ml) for 4 h.
Astaxanthin also prevents PM
2.5-induced inhibition of IL-10 and Arg-1. Hence,
Astaxanthin is effective in prevention of PM
2.5-induced inflammation, oxidative stress and associated neurological disorders [
79]. The plant product
Ophiopogonin D is also an anti-inflammatory agent. Pretreatment of mouse lung epithelial cells MLE-12 with
Ophiopogonin D (10-80 µM) for 1h inhibits PM
2.5 (15 µg/cm^2 for 24h)-induced inflammation as shown by the decreased levels of IL-1

, IL-6, IL-8, and TNF-

. The
Ophiopogonin D exerts its anti-inflammatory effect through downregulation of NF

B signaling and activation of AMPK activity as pretreatment of cells with AMPK inhibitor (Compound C, 10 µM) blocks anti-inflammatory activity of
Ophiopogonin D [
80]. As the dihydrophenanthrene
Coelonin, derived from the flowering plant
Bletilla striata, is a known anti-inflammatory agent [
81,
82], its therapeutic efficacy in amelioration of PM
2.5-induced inflammation has been evaluated [
83]. Pretreatment with
Coelonin (1.25, 2.5 or 5 µg/ml for 2h) ameliorates PM
2.5 (200µ/ml for 18h)-induced inflammation, oxidative stress and pyroptosis of RAW264 and 1774A.1 macrophages through suppression of Nlrp3 inflammasome, IL-6, TNF-

, TLR4, COX2, and NFkB signaling [
83]. These results suggest that different natural compounds are effective in diminishing PM
2.5-induced massive inflammation, oxidative stress, and pyroptosis.
Therefore, the results of all these cell biology studies suggest that pharmacological modulation of inflammatory 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 efficacies of these natural and synthetic compounds before proceeding for clinical trials.