Triantafyllou GA et al. Vaping-Associated Acute Lung Injury: A Case Series. AJRCCM 2019

Vaping may cause damage to the lung through a variety of pathways. For example, vaping alters the expression of approximately 200 proteins in bronchial epithelial cells with
significant implications for gene expression, protein secretion and apoptosis (5). Further, vaping substrates may influence distinct biochemical pathways. For example, propylene
glycol and vegetable glycerin, which are vehicles for nicotine delivery, have been shown to induce airway remodeling (5). Nicotine vapor and, to a lesser extent, nicotine free
electronic-cigarette vapor may be harmful through alveolar macrophage activation by free radicals, particulates, formaldehyde, nitrosamines, volatile organic compounds, and
polycyclic aromatic hydrocarbons (6). Flavoring agents may also be noxious. For example, cinnamaldehyde, a cinnamon flavoring agent, inhibits mitochondrial function, disrupts
bioenergetic processes, and reduces adenosine triphosphate levels in the respiratory epithelium (7). Moreover, marijuana vaping may cause lung injury by increasing the
permeability of the alveolar epithelium (8). Finally, butane hash oil, a dried cannabis extraction used in many vaping solutions, is rich in terpene products. These are
metabolized to methacrolein which can also cause acute lung injury (9).

5. Ghosh A et al. Chronic E-Cigarette Exposure Alters the Human Bronchial Epithelial Proteome. Am J Respir Crit Care Med 2018; 198: 67-76.
6. Scott A et al. Pro-inflammatory effects of e cigarette vapour condensate on human alveolar macrophages. Thorax 2018; 73: 1161-9.
7. Clapp PW et al. Cinnamaldehyde in flavored e-cigarette liquids temporarily suppresses bronchial epithelial cell ciliary motility by dysregulation of mitochondrial function. Am J Physiol Lung Cell Mol Physiol 2019; 316: L470-l486.
8. He T et al. "Tree-in-Bloom": Severe Acute Lung Injury Induced by Vaping Cannabis Oil. Ann Am Thorac Soc 2017; 14: 468-70.
9. Anderson RP, Zechar K. Lung injury from inhaling butane hash oil mimics pneumonia. Respir Med Case Rep 2019; 26: 171-3.