Metabolomics analysis reveals that benzo[a]pyrene, a component of PM2.5, promotes pulmonary injury by modifying lipid metabolism in a phospholipase A2-dependent manner in vivo and in vitro

Abstract

Particulate matter with an aerodynamic diameter less than 2.5 μM (PM2.5) is one of the major environmental pollutants in China. In this study, we carried out a metabolomics profile study on PM2.5-induced inflammation. PM2.5 from Beijing, China, was collected and given to rats through intra-tracheal instillation in vivo. Acute pulmonary injury were observed by pulmonary function assessment and H.E. staining. The lipid metabolic profile was also altered with increased phospholipid and sphingolipid metabolites in broncho-alveolar lavage fluid (BALF) after PM2.5 instillation. Organic component analysis revealed that benzo[a]pyrene (BaP) is one of the most abundant and toxic components in the PM2.5 collected on the fiber filter. In vitro, BaP was used to treat A549 cells, an alveolar type II cell line. BaP (4 μM, 24 h) induced inflammation in the cells. Metabolomics analysis revealed that BaP (4 μM, 6 h) treatment altered the cellular lipid metabolic profile with increased phospholipid metabolites and reduced sphingolipid metabolites and free fatty acids (FFAs). The proportion of ω–3 polyunsaturated fatty acid (PUFA) was also decreased. Mechanically, BaP (4 μM) increased the phospholipase A2 (PLA2) activity at 4 h as well as the mRNA level of Pla2g2a at 12 h. The pro-inflammatory effect of BaP was reversed by the cytosolic PLA2 (cPLA2) inhibitor and chelator of intracellular Ca2+. This study revealed that BaP, as a component of PM2.5, induces pulmonary injury by activating PLA2 and elevating lysophosphatidylcholine (LPC) in a Ca2+-dependent manner in the alveolar type II cells.

Quantitative evaluation of lung injury caused by PM2.5 using hyperpolarized gas magnetic resonance

“…After treatment with PM 2.5 , total septal thickness was approximately 1.1‐fold larger than that in NS rats. The increase in the pulmonary septum and exchange time constant in PM 2.5 rats was most possibly caused by the exudation and infiltration of polymorphonuclear neutrophils, as reported in previous studies . Thickening of the septal wall in PM 2.5 rats could also be observed in histology, as shown in Figure .…”

“…After collection, the quartz fiber filters were cut into small pieces (5 × 5 mm 2 ), sonicated in ultrapure water for 180 minutes (30 min/time, 6 times), and then the solution was filtered using 8‐layer sterile gauze. Thereafter, the PM 2.5 powder was extracted using a vacuum freeze dryer and then was suspended in normal saline (NS) . PM 2.5 size was measured using dynamic light scattering (ZEN3690; Malvern Instruments Ltd, Malvern, UK), and the average diameter was ~300 nm.…”

“…Twelve male Sprague–Dawley rats (weight, 200 ± 20 g) were randomly divided into 2 groups ( n = 6) after acclimatization. Six rats were treated with the PM 2.5 solution (16.2 mg/kg body weight, twice a week) for 4 weeks, and the other rats treated with an equivalent volume (0.6 mL) of NS served as the control group . The PM 2.5 solution or NS was instilled into rat lungs by inserting a vein‐detained needle (14 G) into the trachea carefully through its rima glottidis after anesthetization, as shown in Figure C.…”

“…Lung physiological section analysis, bronchoalveolar lavage fluid (BALF) analysis, and enzyme‐linked immunosorbent assay are the most widely used methods to analyze the physiological changes in the lung caused by PM 2.5 . Thickening of alveolar wall and infiltration of neutrophils were observed in the lung injury model of PM 2.5 by hemotoxylin and eosin (H&E)‐stained lung physiological sections . Using the BALF method, total cell number, tumor necrosis factor alpha level, interleukin‐6 level, lactate dehydrogenase level, and total protein level in BALF were also found to be higher in the model animals instilled with PM 2.5 solution than in control animals .…”

“…Thickening of alveolar wall and infiltration of neutrophils were observed in the lung injury model of PM 2.5 by hemotoxylin and eosin (H&E)‐stained lung physiological sections . Using the BALF method, total cell number, tumor necrosis factor alpha level, interleukin‐6 level, lactate dehydrogenase level, and total protein level in BALF were also found to be higher in the model animals instilled with PM 2.5 solution than in control animals . Additionally, synchrotron‐based X‐ray fluorescence has also been reported to study the mechanism of PM 2.5 toxicity to the lungs .…”