Toxicological Responses of α-Pinene-Derived Secondary Organic Aerosol and Its Molecular Tracers in Human Lung Cell Lines

Abstract

Secondary organic aerosol (SOA) is a major component of airborne fine particulate matter (PM 2.5 ) that contributes to adverse human health effects upon inhalation. Atmospheric ozonolysis of α-pinene, an abundantly emitted monoterpene from terrestrial vegetation, leads to significant global SOA formation; however, its impact on pulmonary pathophysiology remains uncertain. In this study, we quantified an increasing concentration response of three well-established α-pinene SOA tracers (pinic, pinonic, and 3-methyl-1,2,3-butanetricarboxylic acids) and a full mixture of α-pinene SOA in A549 (alveolar epithelial carcinoma) and BEAS-2B (bronchial epithelial normal) lung cell lines. The three aforementioned tracers contributed ∼57% of the α-pinene SOA mass under our experimental conditions. Cellular proliferation, cell viability, and oxidative stress were assessed as toxicological end points. The three α-pinene SOA molecular tracers had insignificant responses in both cell types when compared with the α-pinene SOA (up to 200 μg mL –1 ). BEAS-2B cells exposed to 200 μg mL –1 of α-pinene SOA decreased cellular proliferation to ∼70% and 44% at 24- and 48-h post exposure, respectively; no changes in A549 cells were observed. The inhibitory concentration-50 (IC 50 ) in BEAS-2B cells was found to be 912 and 230 μg mL –1 at 24 and 48 h, respectively. An approximate 4-fold increase in cellular oxidative stress was observed in BEAS-2B cells when compared with untreated cells, suggesting that reactive oxygen species (ROS) buildup resulted in the downstream cytotoxicity following 24 h of exposure to α-pinene SOA. Organic hydroperoxides that were identified in the α-pinene SOA samples likely contributed to the ROS and cytotoxicity. This study identifies the potential components of α-pinene SOA that likely modulate the oxidative stress response within lung cells and highlights the need to carry out chronic exposure studies on α-pinene SOA to elucidate its long-term inhalation exposure effects.

Heterogeneous Reactions of α-Pinene on Mineral Surfaces: Formation of Organonitrates and α-Pinene Oxidation Products

“…The oxidation products of α-pinene are widely seen in the atmosphere and have shown to readily form in the presence of typical atmospheric oxidants. ,,, However, their formation in the presence of gas-phase NO 2 and in the absence of other oxidizers such as O 3 and HO • was not previously observed. Therefore, it is proposed that the α-pinene oxidation by NO 2 can occur in the presence of mineral surfaces, thereby producing the observed oxidation products of α-pinene.…”

“… 24 In addition, reactions of α-pinene with atmospheric oxidizers, such as O 3 and OH radicals lead to the formation of a range of α-pinene oxidation products that are known as first generation oxidation products. 4 , 6 , 25 , 26 Several of these products have been identified as pinonaldehyde, pinonic acid, and α-pinene oxide, as well as a structurally diverse set of organic peroxides. These oxidation products can also act as a reactant in generating atmospheric ON compounds.…”

“…Aerosols are known to play a key role in climate and air quality, with high concentrations leading to adverse health effects (e.g., cardiovascular disease, lung cancers). − Aerosols also cause reduced visibility and haze conditions associated with urban air pollution . α-Pinene, C 10 H 16 , is the most abundant atmospheric monoterpene with an average estimated emission of 66 Tg yr –1 .…”

“…In another study, the photochemistry of the hydroxyl radical oxidation of α-pinene under high NO x conditions was studied and the formation of a range of ON compounds from α-pinene in the presence of nitric oxide (NO) was reported . In addition, reactions of α-pinene with atmospheric oxidizers, such as O 3 and OH radicals lead to the formation of a range of α-pinene oxidation products that are known as first generation oxidation products. ,,, Several of these products have been identified as pinonaldehyde, pinonic acid, and α-pinene oxide, as well as a structurally diverse set of organic peroxides. These oxidation products can also act as a reactant in generating atmospheric ON compounds .…”

Pathogenic Mechanisms of Secondary Organic Aerosols

“…A series of cell culture studies reported the capacity of SOA to induce cell toxicity. ,,,,,, Moreover, it has also been reported that SOA have the capacity to alter transcriptomic profiles of lungs cells (e.g., upregulation of tumor protein 53 (p53) signaling pathway). , The latter, known as the guardian of the genome, regulates various processes in response to stress detection. Indeed, p53-targeted genes can induce cell cycle arrest, apoptosis, or autophagy in a dependent manner of SOA.…”