Effects of Fine Particulate Matter (PM2.5) on Systemic Oxidative Stress and Cardiac Function in ApoE(-/-) Mice

Abstract

Aim: In this study, we aimed to explore the toxic mechanisms of cardiovascular injuries induced by ambient fine particulate matter (PM2.5) in atherosclerotic-susceptible ApoE(-/-) mice. An acute toxicological animal experiment was designed with PM2.5 exposure once a day, every other day, for three days.

Methods: ApoE(-/-) and C57BL/6 mice were randomly categorized into four groups, respectively (n = 6): one control group, three groups exposed to PM2.5 alone at low-, mid-, and high-dose (3, 10, or 30 mg/kg b.w.). Heart rate (HR) and electrocardiogram (ECG) were monitored before instillation of PM2.5 and 24 h after the last instillation, respectively. Cardiac function was monitored by echocardiography (Echo) after the last instillation. Biomarkers of systemic oxidative injuries (MDA, SOD), heart oxidative stress (MDA, SOD), and NAD(P)H oxidase subunits (p22phox, p47phox) mRNA and protein expression were analyzed in mice. The results showed that PM2.5 exposure could trigger the significant increase of MDA, and induce the decrease of heart rate variability (HRV), a marker of cardiac autonomic nervous system (ANS) function with a dose-response manner. Meanwhile, abnormal ECG types were monitored in mice after exposure to PM2.5. The expression of cytokines related with oxidative injuries, and mRNA and protein expression of NADPH, increased significantly in ApoE(-/-) mice in the high-dose group when compared with the dose-matched C57BL6 mice, but no significant difference was observed at Echo. In conclusion, PM2.5 exposure could cause oxidative and ANS injuries, and ApoE(-/-) mice displayed more severe oxidative effects induced by PM2.5.

Keywords: PM2.5; atherosclerosis; autonomic nervous system (ANS); echocardiography (Echo); oxidative stress.

Figure 1

Electrocardiogram (ECG) types before instillation and after instillation in C57BL/6 mice. (A,C,E,G) represent the ECG in the mice before PM_2.5 treatment; (B,D,F,H) represent the ECG in the mice after PM_2.5 treatment, the doses were 0, 3, 10, and 30 mg/kg b.w., respectively; (F) black arrows represent ST-segment depression; and (H) black arrows represent ventricular escape rhythm.

Figure 2

Electrocardiogram (ECG) types before instillation and after instillation in ApoE^−/− mice. (A,C,E,G) represent the ECG in the mice before PM_2.5 treatment; (B,D,F,H) represent the ECG in the mice after PM_2.5 treatment, the doses were 0, 3, 10, and 30 mg/kg b.w., respectively; (F) black arrows represent left bundle-branch block; and (H) black arrows represent right bundle-branch block (RBBB).

Figure 3

Echocardiography images of ApoE^−/− mice. (A) Represent control group, normal structure; (B) represent ApoE^−/− mice was exposed to high doses PM_2.5 (30 mg/kg b.w.). White arrows represent LVAW_d and LVPW_d increased significantly in ApoE^−/− mice exposed to high-dose PM_2.5, respectively.

Figure 4

The levels of SOD and MDA in the plasma of mice (n = 6) after exposed to PM_2.5. (A) represents SOD activity in plasma; (B) represents MDA activity in plasma. The doses were 0 (control), 3, 10, and 30 mg/kg b.w., respectively. Significant difference (^a p < 0.05) between PM_2.5 group and control group, and significant difference (^b p < 0.05) between C57BL/6 and dose-matched ApoE^−/− mice were observed.

Figure 5

The mRNA expression of p22phox and p47phox in myocardium of mice after exposed to PM_2.5. (A) represents the relative p22phox mRNA expression in mice; (B) represents the relative p47phox mRNA expression in mice. The doses were 0.0 (control), 3, 10, and 30 mg/kg b.w. Significant difference (^a p < 0.05) between PM_2.5 group and the control group, and significant difference (^b p < 0.05) between C57BL/6 and dose- matched ApoE^−/− mice were observed.

Figure 6

Protein expression of p22phox and p47phox in mice myocardium exposed to PM_2.5 by Western blot. (A) represents the relative p22phox protein expression in mice; (B) represents the relative p47phox protein expression in mice. The doses were 0 (control), 3, 10, and 30 mg/kg b.w. Significant difference (^a p < 0.05) between PM_2.5 group and control group, and significant difference (^b p < 0.05 ) between C57BL6 and dose- matched ApoE^−/− mice were observed.

Figure 7

Left ventricle histological evaluation and pathological scores in mice after exposed to PM_2.5. (A–D) represent histological lesions (×200) of left ventricle in C57BL/6 mice exposed to PM_2.5 in dose of 0 (control), 3, 10, and 30 mg/kg b.w., respectively; (E–H) represent histological lesions (×200) of left ventricle in ApoE^−/− mice exposed to PM_2.5 in dose of 0 (control), 3, 10, and 30 mg/kg b.w., respectively.

Figure 7

Left ventricle histological evaluation and pathological scores in mice after exposed to PM_2.5. (A–D) represent histological lesions (×200) of left ventricle in C57BL/6 mice exposed to PM_2.5 in dose of 0 (control), 3, 10, and 30 mg/kg b.w., respectively; (E–H) represent histological lesions (×200) of left ventricle in ApoE^−/− mice exposed to PM_2.5 in dose of 0 (control), 3, 10, and 30 mg/kg b.w., respectively.

Figure 8

Coronary artery histological evaluation and pathological scores in mice after exposed to fine particles. (A) represents normal vessel tissue in C57BL/6 mice; (B) black arrows represent plague formation in ApoE^−/− mice. Histological lesions (×200) of coronary arteries in mice.