Fluorescent reconstitution on deposition of PM2.5 in lung and extrapulmonary organs

Abstract

The deposition of PM_2.5 (fine particulate matter in air with diameter smaller than 2.5 μm) in lungs is harmful to human health. However, real-time observation on the deposition of particles in the acinar area of the lung is still a challenge in experiments. Here, a fluorescent imaging method is developed to visualize the deposition process with a high temporal and spatial resolution. The observations reveal that the deposition pattern is nonuniform, and the maximum deposition rate in the acinar area differs significantly from the prediction of the widely used average deposition model. The method is also used to find single particles in the kidney and liver, though such particles are commonly believed to be too large to enter the extrapulmonary organs.

Keywords: PM2.5; air pollution; extrapulmonary organs; lung; particle deposition.

Fig. 1.

The fluorescent deposition patterns of PM_2.0 and PM_0.2 particles in lungs. A and B are the deposition patterns of PM_2.0 and PM_0.2 in a mouse lung by the fluorescent intensity, respectively. A1 and A2 show the high and low concentrations of PM_2.0 particles in two local areas at the left and right edges, respectively, of a mouse lung. (B) A more uniform deposition pattern of PM_0.2 in the lung with equivalent fluorescent intensity on the left and right edges of the lung. (B1) There are still a lot of PM_0.2 particles in a local acinar area at the right edge of the right lung. (B2) More PM_0.2 particles deposit in the bronchiole region. The red and the orange dots in A1, A2, B1, and B2 are fluorescent PM_2.0 particles. (The scale bars in A and B are 1 mm, while in the other four images are 20 μm.)

Fig. 2.

The real-time observation on the deposition of PM_2.0. The tissue has a green color, while the red and yellow dots are the particles. (A) The acinar region before the ventilation of particles, and no particles are seen. (B) The deposition of PM_2.0 in the area at 5 min under the PM_2.0 level of 1,750 μg/m³. (C) The deposition of PM_2.0 in the area at 16 min. At this moment, the PM_2.0 level is 0 μg/m³, and the clean air has already been ventilated for 1 min. The scale bars in the images are 20 μm. The video of the deposition process is provided in Movie S1. The deposition process of PM_0.2 is also measured, and the images are provided in SI Appendix, Fig. S3.

Fig. 3.

The deposition rates of PM_2.0 in the selected local areas. (A) The 3D image of the PM_2.0 in a local area. (B) The statistic particle number in the local areas in the high-concentration region (max.) and in the medium concentration region (avg.) in 15 min. (C) The maximum and average deposition rates of PM_2.0 in the two local areas. The dash lines are the best fitting of the deposition rate in the polluted air condition with PM_2.0 level of 1,750 μg/m³. (D) The maximum (max.) and average (avg.) mass deposition rates of PM_2.0 compared with the calculated (cal.) mass deposition rate from the average deposition model. (E) The maximum deposition rates of PM_2.0 in the local area under three PM_2.0 levels. (F) The maximum deposition rates of PM_2.0 under three PM_2.0 levels.

Fig. 4.

Deposition of PM_0.2 and PM_2.0 particles in extrapulmonary organs. A and B are the cross-section of a kidney and liver, respectively, with the deposition of PM_0.2 particles. A1 is the amplified image of the region marked in A. Red dots are fluorescent particles, and the back ground pattern is the structure of the medullary renal tubule of kidney. B1 is the amplified image of the region in B. Fluorescent particles are found on the wall of the lobular sinus of the liver. C and D are the deposition of PM_2.0 on the cross-section of kidney and liver, respectively. C1 is the amplified image of the region marked in C. A fluorescent particle is found on the background pattern of the medullary of the kidney. D1 is the amplified image of the region marked in D. A red fluorescent particle is found on the wall of a lobular sinus of the liver. (The scale bars in A–D are 0.5 mm, in A1 and B1 are 10 μm, and in C1 and D1 are 20 μm.)

Fig. 5.

Schematics of the inhalation experiment in vivo. This inhalation experiment system consists of PMs generator, PMs monitor, mini ventilation, and a two-photon imaging microscope. A small incision was made in the trachea 3–4 mm below the throat, and a tracheal cannula was inserted and well sealed by the suture.