Effect of early particulate air pollution exposure on obesity in mice: role of p47phox

Abstract

Objective: To evaluate the role of early-life exposure to airborne fine particulate matter (diameter, <2.5 μm [PM(2.5)]) pollution on metabolic parameters, inflammation, and adiposity; and to investigate the involvement of oxidative stress pathways in the development of metabolic abnormalities.

Methods and results: PM(2.5) inhalation exposure (6 h/d, 5 d/wk) was performed in C57BL/6 mice (wild type) and mice deficient in the cytosolic subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase p47(phox) (p47(phox-/-)) beginning at the age of 3 weeks for a duration of 10 weeks. Both groups were simultaneously fed a normal diet or a high-fat diet for 10 weeks. PM(2.5)-exposed C57BL/6 mice fed a normal diet exhibited metabolic abnormalities after exposure to PM(2.5) or FA for 10 weeks. Consistent with insulin resistance, these abnormalities included enlarged subcutaneous and visceral fat contents, increased macrophage infiltration in visceral adipose tissue, and vascular dysfunction. Ex vivo-labeled and infused monocytes demonstrated increased adherence in the microcirculation of normal diet- or high-fat diet-fed PM(2.5)-exposed mice. p47(phox-/-) mice exhibited an improvement in parameters of insulin resistance, vascular function, and visceral inflammation in response to PM(2.5).

Conclusions: Early-life exposure to high levels of PM(2.5) is a risk factor for subsequent development of insulin resistance, adiposity, and inflammation. Reactive oxygen species generation by NADPH oxidase appears to mediate this risk.

Figure 1

Glucose homeostasis and systemic inflammation in wild-type C57BL/6 mice and p47^phox−/− mice by ambient PM_2.5 exposure compared with FA-exposed mice fed an ND (n = 16) or an HFD (n = 16). A and E, Effect of PM_2.5 exposure on glucose tolerance by intra-peritoneal glucose tolerance test (IPGTT) in C57BL/6 mice and in p47^phox−/− mice, respectively. B and F, The glucose area under the curve calculated from the glucose tolerance test from parts A and E, respectively. C and G, The homeostasis model assessment IR index in C57BL/6 mice and in p47^phox−/− mice, respectively. D and H, Plasma cytokine measurement by ELISA in C57BL/6 mice and in p47^phox−/− mice, respectively. n = 8 in each group. *P<0.05 and **P<0.001. IFN indicates interferon; MCP-1, monocyte chemoattractant protein-1; RANTES, regulated on activation, normal T cell expressed and secreted (or chemokine C-C motif ligand 5).

Figure 2

Effect of PM_2.5 exposure on abdominal fat and distribution, chemotactic migration, and superoxide production in wild-type C57BL/6 mice and p47^phox−/− mice. A and E, Abdominal fat measured by MRI in C57BL/6 mice and p47^phox−/− mice, respectively. B and F, Visceral and subcutaneuous fat (fat distribution) in the abdomen, measured by MRI, in C57BL/6 mice and p47^phox−/− mice, respectively. C and G, Chemotactic migration of monocytes in C57BL/6 mice and p47^phox−/− mice, respectively. D and H, Superoxide anion measurement by chemiluminescence in visceral and subcutaneous fat tissues in wild-type C57BL/6 and p47^phox−/− mice, respectively. *P<0.05 and **P<0.001. 5HPF indicates 5 high-power fields.

Figure 3

Effect of PM_2.5 exposure on macrophage inflammation and gene expression in visceral adipose tissue in wild-type C57BL/6 and p47^phox−/− mice. A, Representative images of immunohistochemical staining for macrophages (F4/80⁺) in visceral fat tissue. B, Statistical analysis of F4/80⁺ macrophage infiltration in visceral fat tissue in C57BL/6 and p47^phox−/− mice. C and D, Real-time polymerase chain reaction analysis for macrophage M₁/M₂ phenotypic changes in C57BL/6 and p47^phox−/− mice, respectively. Itgax indicates integrin αX (or CD11c); Mgl-1, macrophage galactose N-acetyl-galactosamine specific lectin-1; Nos2, NO synthase-2; Pparγ, peroxisome proliferator–activated receptor γ. *P<0.05 and **P<0.001.

Figure 4

Effect of PM_2.5 exposure on microvascular dysfunction in wild-type C57BL/6 and p47^phox−/− mice. A and C, Monocyte rolling flux in cremasteric microcirculation via intravital microscopy in C57BL/6 and p47^phox−/− mice, respectively. B and D, Monocyte adhesion in cremasteric microcirculation via intravital microscopy in C57BL/6 and p47^phox−/− mice, respectively. *P<0.05 and **P<0.001.

Figure 5

Effect of PM_2.5 exposure on macrovascular dysfunction in wild-type C57BL/6 and p47^phox−/− mice. A through F, Vasomotor tone change in aortic rings via myograph in response to phenylephrine (A and D), acetylcholine (B and E), or insulin (C and F) in C57BL/6 and p47^phox−/− mice, respectively. *P<0.05 vs FA-ND, and ^#P<0.05 vs FA-HFD.