Korean Circ J.  2021 Feb;51(2):157-170. 10.4070/kcj.2020.0255.

High Level of Real Urban Air Pollution Promotes Cardiac Arrhythmia in Healthy Mice

• Park H
• Lim S
• Lee S
• Mun D
• Kang J
• Kim H
• Park H
• Kim C
• Park S
• Lim YM
• Joung B

• KMID: 2512454
• DOI: http://doi.org/10.4070/kcj.2020.0255

Abstract

Background and Objectives
Ambient particulate matter (PM) in real urban air pollution (RUA) is an environmental health risk factor associated with increased cardiac events. This study investigated the threshold level to induce arrhythmia, as well as arrhythmogenic mechanism of RUA that mainly consisted of PM <2.5 μm in aerodynamic diameter close to ultrafine particles.
Methods
RUA was artificially produced by a lately developed pyrolysis based RUA generator.C57BL/6 mice were divided into 4 groups: a control group (control, n=12) and three groups with exposure to RUA with the concentration of 200 µg/㎥ (n=12), 400 µg/㎥ (n=12), and 800 µg/㎥ (n=12). Mice were exposed to RUA at each concentration for 8 hr/day and 5 day/week to mimic ordinary human activity during 3 weeks.
Results
The QRS and QTc intervals, as well as intracellular Ca²⁺ duration, apicobasal action potential duration (APD) gradient, fibrosis, and inflammation of left ventricle of mouse hearts were increased dose-dependently with the increase of RUA concentration, and significantly increased at RUA concentration of 400 µg/㎥ compared to control (all p<0.001). In mice exposed to RUA concentration of 800 µg/㎥ , spontaneous ventricular arrhythmia was observed in 42%, with significant increase of inflammatory markers, phosphorylated Ca²⁺ /calmodulindependent protein kinase II (CaMKII), and phospholamban (PLB) compared to control.
Conclusions
RUA could induce electrophysiological changes such as APD and QT prolongation, fibrosis, and inflammation dose-dependently, with significant increase of ventricular arrhythmia at the concentration of 400 µg/㎥ . RUA concentration of 800 µg/㎥ increased phosphorylation of CaMKII and PLB.

Keyword

Air pollution; Arrhythmia; Inflammation; Fibrosis

Figure

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  Figure 1 RUA generator and study protocol. (A) Schematic image of RUA generating system, (B) Picture of gas (upper panel) and electron microscope image of particles (lower panel) from RUA generator, (C) Particle number concentration, (D) Study protocol.RUA = real urban air pollution.

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  Figure 2 RUA dose-dependent increase of QT intervals and ventricular arrhythmia. (A) Typical examples of electrocardiogram lead I. (B) Heart rate, QRS, QT, QTc, RR and PR intervals. Data are expressed as mean±standard error of the mean. (C) Spontaneous premature ventricular contractions (upper panel), non-sustained (middle panel), and sustained ventricular tachycardia (lower panel) during RUA exposure. (D) Dose-dependent increase of mouse with spontaneous VT or VF in RUA group (n=12 per group).RUA = real urban air pollution; VF = ventricular fibrillation; VT = ventricular tachycardia.

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  Figure 3 RUA dose-dependent increase of APD and CaD in RUA group. (A) Typical action potential traces of voltage (black) and calcium (red) at the pacing cycle length of 200 ms. (B) Comparison of APD and CaD among various groups. Note a RUA dose-dependent increase of APD and CaD (n=10 for each group tested). Data are expressed as mean±standard error of the mean.APD = action potential duration; CaD = calcium duration; RUA = real urban air pollution.

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  Figure 4 RUA dose-dependent increase of apicobasal APD90 difference and ventricular arrhythmia inducibility. (A) Activation, action potential duration, and conduction vector maps in control and in mouse exposed to RUA of 800 μg/m3. Dotted line marks interventricular septum. Base (①) and apex (②) of left ventricle are action potential recording sites. (B) Action potential tracings recorded from base (①) and apex (②) of left ventricle at the pacing cycle length of 200 ms in Langendorff-perfused mouse heart. (C) RUA dose-dependent increase of apicobasal APD difference. (D) RUA dose-dependent increase of VT or VF inducibility (n=10 for each group tested). Data are expressed as mean±standard error of the mean.ACT = activation; APD = action potential duration; CV = conduction velocity; LV = left ventricle; RUA = real urban air pollution; RV = right ventricle; VF = ventricular fibrillation; VT = ventricular tachycardia.

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  Figure 5 RUA dose-dependent increase of inflammation. (A) Typical CD68 DAB stain images of hearts at each dosage of RUA. (B) TNF-α, IL-6 and HMGB1 in serum (n=10 for each group tested). Data are expressed as mean±standard error of the mean.HMGB1 = high-mobility group protein B1; IL = interleukin; RUA = real urban air pollution; TNF = tumor necrosis factor.

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  Figure 6 RUA dose-dependent increase of fibrosis. (A) Images of Masson trichrome staining patterns of heart at each dosage of RUA. (B) Scatterplots show quantification of the percentage of fibrotic areas in the histological sections. (C, D) Protein expression levels of TGF-β, MMP-2, MMP-9, Col-Iand Col-III were detected by western blotting and were quantified using GAPDH as an internal reference.RUA = real urban air pollution; TGF-β = transforming growth factor-beta.

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  Figure 7 Exposure to RUA of 800 μg/m3 increases inflammation, oxidative stress, and phosphorylation of Ca2+-handling proteins. (A) Western blot-based expression analysis of IL-6, COX-2, TNF-α, iNOS, and HMGB1 proteins (upper panels), and quantification in left ventricular tissues from each group (lower panels). (B) Level of autophosphorylated CaMKII at Thr287, PLB, CSQ2, and NCX in left ventricular tissue from each group. Data are expressed as mean±standard error of the mean.CaMKII = calmodulin-dependent protein kinase II; CSQ2 = calsequestrin 2; HMGB1 = high-mobility group protein B1; IL = interleukin; PLB = phospholamban; RUA = real urban air pollution; TNF = tumor necrosis factor.

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