Comparative effects of inhaled diesel exhaust and ambient fine particles on inflammation, atherosclerosis, and vascular dysfunction

Abstract

Ambient air PM(2.5) (particulate matter less than 2.5 mum in diameter) has been associated with cardiovascular diseases (CVDs), but the underlying mechanisms affecting CVDs are unknown. The authors investigated whether subchronic inhalation of concentrated ambient PM(2.5) (CAPs), whole diesel exhaust (WDE), or diesel exhaust gases (DEGs) led to exacerbation of atherosclerosis, pulmonary and systemic inflammation, and vascular dysfunction; and whether DEG interactions with CAPs alter cardiovascular effects. ApoE(-/-) mice were simultaneously exposed via inhalation for 5 hours/day, 4 days/week, for up to 5 months to one of five different exposure atmospheres: (1) filtered air (FA); (2) CAPs (105 microg/m(3)); (3) WDE (DEP = 436 microg/m(3)); (4) DEG (equivalent to gas levels in WDE group); and (5) CAPs+DEG (PM(2.5): 113 microg/m(3); with DEG equivalent to WDE group). After 3 and 5 months, lung lavage fluid and blood sera were analyzed, and atherosclerotic plaques were quantified by ultrasound imaging, hematoxylin and eosin (H&E stain), and en face Sudan IV stain. Vascular functions were assessed after 5 months of exposure. The authors showed that (1) subchronic CAPs, WDE, and DEG inhalations increased serum vascular cell adhesion molecule (VCAM)-1 levels and enhanced phenylephrine (PE)-induced vasoconstriction; (2) for plaque exacerbation, CAPs > WDE > DEG = FA, thus PM components (not present in WDE) were responsible for plaque development; (3) atherosclerosis can exacerbated through mechanistic pathways other than inflammation and vascular dysfunction; and (4) although there were no significant interactions between CAPs and DEG on plaque exacerbation, it is less clear whether the effects of CAPs on vasomotor dysfunction and pulmonary/systemic inflammation were enhanced by the DEG coexposure.

Figure 1

A schematic diagram of the exposure system. Diagram includes the VACES CAPs exposure system, the diesel engine exhaust exposure system, and the design to allow for the mixture of the CAPs and diesel exhaust gases.

Figure 2

(A) Representatives of the en face Sudan IV staining for plaque in whole aortic segments. Areas in red indicate plaque. (B) Plaque quantification by en face Sudan IV staining in whole aortic segments. Mean (SEM); n = 3/group. (C) Representatives of the H&E staining in brachiocephalic artery cross-sections. Left: Clear artery with no plaque. Right: Artery with large area of plaque in a cross-sectional view. (D) Plaque quantification by H&E staining in brachiocephalic artery cross-sections. Mean (SEM); n = 5–6/group. (E) Representatives of b-mode image of brachiocephalic artery by ultrasound biomicroscopy. Left: A representative ultrasound image of brachiocephalic artery cross-section. Right: Plaque identification and measurement for the left image. (F) Plaque quantification by ultrasound imaging in the brachiocephalic artery. Mean (SEM); n = 6–8/group.

Figure 2

(A) Representatives of the en face Sudan IV staining for plaque in whole aortic segments. Areas in red indicate plaque. (B) Plaque quantification by en face Sudan IV staining in whole aortic segments. Mean (SEM); n = 3/group. (C) Representatives of the H&E staining in brachiocephalic artery cross-sections. Left: Clear artery with no plaque. Right: Artery with large area of plaque in a cross-sectional view. (D) Plaque quantification by H&E staining in brachiocephalic artery cross-sections. Mean (SEM); n = 5–6/group. (E) Representatives of b-mode image of brachiocephalic artery by ultrasound biomicroscopy. Left: A representative ultrasound image of brachiocephalic artery cross-section. Right: Plaque identification and measurement for the left image. (F) Plaque quantification by ultrasound imaging in the brachiocephalic artery. Mean (SEM); n = 6–8/group.

Figure 3

Vascular responses to graded dose of (A) vasoconstrictor PE; (B) vasoconstrictor serotonin; (C) relaxation agonist acetylcholine; (D) relaxation agonist sodium nitroprusside. Five mice per group, two (for PE and 5-HT) or four (for ACH and SNP) aortic rings per mouse, were tested. Error bar represents SEM.

Figure 4

(A) Vascular responses to 1 μM PE after NOS inhibition. (B) Vascular responses to 1 μM PE after superoxide inhibition.