Maternal exposure to diluted diesel engine exhaust alters placental function and induces intergenerational effects in rabbits

Abstract

Background: Airborne pollution is a rising concern in urban areas. Epidemiological studies in humans and animal experiments using rodent models indicate that gestational exposure to airborne pollution, in particular diesel engine exhaust (DE), reduces birth weight, but effects depend on exposure duration, gestational window and nanoparticle (NP) concentration. Our aim was to evaluate the effects of gestational exposure to diluted DE on feto-placental development in a rabbit model. Pregnant females were exposed to diluted (1 mg/m(3)), filtered DE (NP diameter ≈ 69 nm) or clean air (controls) for 2 h/day, 5 days/week by nose-only exposure (total exposure: 20 days in a 31-day gestation).

Results: DE exposure induced early signs of growth retardation at mid gestation with decreased head length (p = 0.04) and umbilical pulse (p = 0.018). Near term, fetal head length (p = 0.029) and plasma insulin and IGF1 concentrations (p = 0.05 and p = 0.019) were reduced. Placental function was also affected, with reduced placental efficiency (fetal/placental weight) (p = 0.049), decreased placental blood flow (p = 0.009) and fetal vessel volume (p = 0.002). Non-aggregated and "fingerprint" NP were observed at various locations, in maternal blood space, in trophoblastic cells and in the fetal blood, demonstrating transplacental transfer. Adult female offspring were bred with control males. Although fetoplacental biometry was not affected near term, second generation fetal metabolism was modified by grand-dam exposure with decreased plasma cholesterol (p = 0.008) and increased triglyceride concentrations (p = 0.015).

Conclusions: Repeated daily gestational exposure to DE at levels close to urban pollution can affect feto-placental development in the first and second generation.

Fig. 1

Experimental protocol over the 2 generations

Fig. 2

Ultrasound monitoring of placenta at 28 dpc. Drawing showing the rabbit placental structure and blood flow (a). 3D power Doppler was performed on dams to determine the Vascularization Index (b), the Flow Index (c) and the Vascularization Flow Index (d) at 28 dpc. All data are expressed as median [Q1; Q3] (*p < 0.05, **p < 0.01, compared with control group)

Fig. 3

Stereological examination of placenta at 28 dpc. At 28 dpc, immunodetection of vimentin to label fetal capillaries was performed on labyrinthine area sections from the control group (a) and the exposed group (b). Black immunostaining represents fetal vessels (FV), blue cells are trophoblasts cells (T) and the white head arrows show circulating cells in maternal space (MS). Volume fraction of trophoblast (c), fetal capillaries (d) and maternal blood space (e) and surface density of fetal capillaries (f) were quantified. All data are expressed as median [Q1; Q3] (*p < 0.05, **p < 0.01, ***p < 0.001, compared with control group)

Fig. 4

Localization of nanoparticles in the placenta at 28 dpc. Ultrathin sections were performed on labyrinthine area in placentas from control (a, e, i, m) and exposed (b-d, f-h, j-l, n-p) dams and analyzed by TEM. Arrows indicate nanoparticles and arrowheads “finger-print” like particles. Several observations were made with various magnifications allowing the observations of different cellular compartments. Scale bars: a: 2 μm; b: 800 nm; c: 2 μm; d: 100 nm; e: 1.6 μm; f: 700 nm; g: 1.25 μm; h: 1 μm; i: 1.6 μm; j: 1 μm; k: 1 μm; l: 700 nm; m: 2.5 μm; n: 1 μm; o: 400 nm; p: 20 nm. Abbreviations: E: Erythrocyte; EC: Endothelial Cell; FV: Fetal Vessel; G: Golgi apparatus; Ly: Lysosome; m: mitochondria; MBS: Maternal Blood Space; mvb: multivesicular body; N: Nucleus; rer: rough endoplasmic reticulum; T: Trophoblast