Table 1.

The common additives and pollutants in vaping liquid, their mechanisms of pulmonary damage, or related toxicities.

Compounds	Experimental Model of the Study	Dose Range	Protein/Gene Level Regulation, Signaling Pathway Activation	Final Outcome	Reference
Nicotine derivatives (Nitrosamine compounds)	E-cigarette smoke-exposed Mice. Cultured human bronchial epithelial and urothelial cells. In vitro DNA damage-dependent repair synthesis assay.	Mice: (10 mg/mL, 3 h/d, 5 d/wk) for 12 wk	↓ DNA-repair activity and repair proteins XPC/OGG1/2 in the lung. ↑ mutational susceptibility and tumorigenic transformation of cultured human bronchial epithelial cells	DNA damage, DNA methylation changes, and adduct formation. Increased the lung cancer risk.	[85]
E-cigarette JUUL pod flavors “(Fruit Medley, Virginia Tobacco, Cool Mint, Crème Brulee, Cool Cucumber, Mango, and Classic Menthol)” and similar pod flavors (Just Mango-Strawberry Coconut and Caffé Latte)”.	Lung epithelial cells (16-HBE, BEAS-2B) and monocytes (U937) exposed to various pod aerosols	In-vitro aerosol exposure system: “66 puffs during 22 min with a three-second puff duration at 1.6 L/min flow rate and an inter-puff interval of approximately 17 s.”	↑ acellular ROS ↑ mitochondrial superoxide production in bronchial epithelial cells (16-HBE). ↑ inflammatory mediators, such as IL-8/PGE2 in lung epithelial cells (16-HBE, BEAS-2B) and monocytes (U937)	JUUL pod flavors, “Crème Brulee and Cool Cucumber”, caused epithelial barrier dysfunction in 16-HBE cells. DNA damage upon exposure in monocytes Increase oxidative stress, inflammation, epithelial barrier dysfunction, and DNA damage in lung cells.	[88]
Vaping E-cigarette components	Total RNA from nasal scrape biopsies was analyzed using the nCounter Human Immunology v2 Expression panel.	Active E-cigarette users/vapers who have been using E-cigarettes regularly for at least six months	The top five genes with changed expression in E-cigarette users were Zinc Finger and BTB Domain Containing 16 (ZBTB16), EGR1, Polymeric Immunoglobulin Receptor (PIGR), Prostaglandin-Endoperoxide Synthase 2 (PTGS2), and FK506 Binding Protein 5 (FKBP5).	↓ Expression of immune-related Genes at the level of nasal mucosa.	[118]
Menthol or tobacco-flavored EC liquids or aerosols	Human adenocarcinoma alveolar basal epithelial cells (A549). Live cell imaging, Epithelial-to mesenchymal transition (EMT) biomarker analysis, and machine learning/image processing algorithms.	exposure to EC liquids and aerosols from a popular product for 3-8 days.	EMT is accompanied by the acquisition of a fibroblast-like morphology, loss of cell-to-cell junctions, internalization of E-cadherin, and increased motility. Upregulation of EMT markers. Plasma membrane to nuclear translocation of â-catenin	An EMT of lung cancer cells during exposure to EC products	[120]
Aerosolization of commercial Cannabidiol (CBD) vaping products	Click chemistry and a novel in vitro vaping product exposure system (VaPES).	A human bronchial epithelial cell line (16HBEs) was exposed to synthetic a-CBD or a-CBDQ (Quinone) for 4 h at a range of concent. (2−35 μM).	A reactive CBD quinone (CBDQ) forms adducts with cysteine residues in human bronchial epithelial cell proteins, including “Keap1” and activates “KEAP1-Nrf2” stress response pathway genes.	Vaping CBD alters protein function and induces cellular stress pathways in the lung.	[128]
49 commercially available e-liquid flavors	Free radicals generated from the flavors were captured/analyzed by electron paramagnetic resonance (EPR). The flavorant composition of each e-liquid was analyzed by gas chromatography mass spectroscopy (GCMS).	The flow meter of the E-cigarette setup was connected to the house vacuum and adjusted to a flow rate of 500 mL/min.	Nearly half of the flavors modulated free radical generation. Ethyl vanillin inhibited the radical formation in a concentration dependent manner. Free radical production was closely linked with the capacity to oxidize biologically relevant lipids.	Flavoring agents could enhance/inhibit the free radicals’ production in flavored E-cigarette aerosols. Some flavorants ↑ lipid peroxidation products. Some flavorants ↑ formation of 8-isoprostane (the oxidation products of arachidonic acid).	[140]
Ethyl maltol (EM; sweet flavor)	The Calu-6 and A549 lung epithelial cell lines co-exposed to EM and copper (Cu)	EM at 3 mM concentration as it was not toxic.	Cell viability DNA damage response Reactive oxygen species generation Ferritin light chain and heme oxygenase 1 mRNA upregulation	Co-exposure to EM and Cu at concentrations not toxic for either chemical individually induces oxidative stress, apoptosis, and DNA damage in lung epithelial cells.	[141]
Aldehydes	Different organs of mice exposed to mainstream tobacco smoke (MTS). Immortalized human bronchial epithelial cells BEAS-2B and urothelial cells UROtsa. Buccal cells and sputum. Lung tissues of tobacco smokers obtained from the marginal non-cancerous lung tissue samples of cancer patients.	Exposure of mice to MTS (75 mg/m3) for 6 h/d, 5 d/wk for 12 wk.	DNA Damage markers DNA Repair proteins determination. PdG adducts formation in human bronchial epithelial and urothelial cells	DNA damage DNA adducts formation and impairment of DNA repair proteins and activity.	[142]
Vitamin E acetate (VEA)	Human bronchial epithelial cells (BEAS-2B).	VEA vaping emissions were generated using a 0.46 L min-1 critical orifice to restrict the flow rate. Emissions were vaped into a glass cold trap submerged in dry ice; condensed emissions were dissolved in acetonitrile (ACN) for chemical analysis and cell culture media for cell exposure analysis. HMOX-1 and NQO1 gene expression analysis after 0, 3, 6, 12, and 24 h exposure to VEA vaping emissions.	Exposure to vaping emissions resulted in significant upregulation of NQO1 and HMOX-1 genes in BEAS-2B cells.	Oxidative damage Acute lung injury Synergistic interactions between thermal decomposition products of VEA could be evident, highlighting “the multifaceted nature of vaping toxicity”.	[143]
CBD/counterfeit vape cartridges and their constituents vitamin E acetate (VEA) and medium-chain triglycerides (MCT).	Bronchial epithelial cells (BEAS-2B). In Vivo Mouse Exposures with mouse arterial oxygen saturation and bronchoalveolar lavage (BALF) collection.	For in vitro exposures, cell culture plates were exposed to two 70 mL puffs of the aerosol under air-liquid interface conditions for 10 min. For in vivo exposures, wild-type mice with C57BL/6 background were exposed to 1 h MCT, VEA, and cartridge aerosols with 70 mL puffs, two puffs/min using the Scireq inExpose system	↑ IL-6, eotaxin, and G-CSF in BALF. ↑ Eicosanoid inflammatory mediators and leukotrienes in mouse BALF. ↑ hydroxyeicosatetraenoic acid (HETEs) and various eicosanoid levels in plasma from E-cig users. ↑ Surfactant-associated protein-A (SP-A) in lung homogenates from male mice exposed to VEA.	Acute exposure to specific vape cartridges induces in vitro cytotoxicity, barrier dysfunction, and inflammation. In vivo, mouse exposure induces acute inflammation with elevated proinflammatory markers. Prolonged exposure may cause significant lung damage, which is involved in the pathogenesis of E-cigarette or vaping products-associated lung injury (EVALI).	[144]