Maternal Nanomaterial Inhalation Exposure: Critical Gestational Period in the Uterine Microcirculation is Angiotensin II Dependent

Abstract

Maternal inhalation exposure to engineered nanomaterials (ENM) has been associated with microvascular dysfunction and adverse cardiovascular responses. Pregnancy requires coordinated vascular adaptation and growth that are imperative for survival. Key events in pregnancy hallmark distinct periods of gestation such as implantation, spiral artery remodeling, placentation, and trophoblast invasion. Angiotensin II (Ang II) is a critical vasoactive mediator responsible for adaptations and is implicated in the pathology of preeclampsia. If perturbations occur during gestation, such as those caused by ENM inhalation exposure, then maternal-fetal health consequences may occur. Our study aimed to identify the period of gestation in which maternal microvascular functional and fetal health are most vulnerable. Additionally, we wanted to determine if Ang II sensitivity and receptor density is altered due to exposure. Dams were exposed to ENM aerosols (nano-titanium dioxide) during three gestational windows: early (EE, gestational day (GD) 2-6), mid (ME, GD 8-12) or late (LE, GD 15-19). Within the EE group dry pup mass decreased by 16.3% and uterine radial artery wall to lumen ratio (WLR) increased by 25.9%. Uterine radial artery response to Ang II sensitivity increased by 40.5% in the EE group. Ang II receptor density was altered in the EE and LE group with decreased levels of AT₂R. We conclude that early gestational maternal inhalation exposures resulted in altered vascular anatomy and physiology. Exposure during this time-period results in altered vascular reactivity and changes to uterine radial artery WLR, leading to decreased perfusion to the fetus and resulting in lower pup mass.

Keywords: Angiotensin II; Gestational inhalation exposure; Microcirculation; Titanium dioxide; Toxicology.

Fig. 1

Gestational exposure paradigm. Experimental design depicting the three exposure groups and the representation of the gestational periods

Fig. 2

Nano-TiO₂ aerosol real-time characterizations. Aerosol characterizations were monitored and verified during exposure. Red lines on the size distribution curves represent a log normal fit of the size data. a Software controlled aerosol mass concentration over the 6 h exposure paradigm. A feedback system held the mass concentration near the desired 12 mg/m³ target (red line). b Aerosol aerodynamic diameter was assessed using the high-resolution Electrical Low-Pressure Impactor (ELPI) showing a CMD of 157 nm with a geometric standard deviation of 1.73. c The diameter was also evaluated using a Scanning Mobility Particle Sizer (SMPS, light gray) and an Aerodynamic Particle Sizer (APS, dark gray) revealing a CMD of 118 nm with a geometric standard deviation of 2.11. d A Nano Micro-Orifice Uniform Deposit Impactor (MOUDI) indicated a MMAD of 1.03 μm with a geometric standard deviation of 2.57

Fig. 3

Pup and placental mass and placental efficiency. Combined control weights and placental efficiency versus exposure groups on GD 20 pups. a Wet pup mass. b Wet placental mass. c Wet placental efficiency. d Dry pup mass. e Dry placental mass. f Dry placental efficiency. EE early exposed, ME mid exposed, LE late exposed. *P ≤ 0.05 vs control

Fig. 4

Vascular reactivity of naïve and sham-control uterine radial arteries. Dose response curves were generated to assess if vascular reactivity of uterine radial arteries was altered between naïve and control groups. a Vascular reactivity following increasing doses of ACh. b Maximum response to ACh across the dose response curve. c Vascular reactivity following increasing doses of SNAP. d Maximum response to SNAP across the dose response curve. e Vascular response following increasing doses of PE. f Maximum response to PE across the dose response curve. g Vascular response following increasing doses of Ang II. h Maximum response to Ang II across the dose response curve. EC early control, MC mid control, LC late control

Fig. 5

Alteration of vascular reactivity following various time-periods of exposure. Dose response curves were generated to assess if vascular reactivity of uterine radial arteries was altered. a Vascular reactivity following increasing doses of ACh. b Maximum response to ACh across the dose response curve. c Vascular reactivity following increasing doses of SNAP. d Maximum response to SNAP across the dose response curve. e Vascular response following increasing doses of PE. f Maximum response to PE across the dose response curve. g Vascular response following increasing doses of Ang II. h Maximum response to Ang II across the dose response curve. EE early exposed, ME mid exposed, LE late exposed. a P ≤ 0.05 EE vs control; b P ≤ 0.05 ME vs control; c P ≤ 0.05 LE vs control; *P ≤ 0.05 vs control

Fig. 6

AT₁R and AT₂R protein concentration in uterine vasculature following nano-TiO₂ inhalation exposure. a Representative image of Western blot for protein concentration of AT₁R in control, early exposed (EE), mid exposed (ME), late exposed (LE) uterine vascular tissue, and the average relative protein density of AT₁R protein among exposed groups. b Representative image of Western blot protein concentration of AT₂R in control, EE, ME, LE uterine vascular tissue, and the average relative protein density of AT₂R protein among exposed groups

Fig. 7

Circulating estradiol (E₂) plasma concentration. Circulating levels of E₂ in pg/ml. a E₂ concentration in control groups. b E₂ concentration in combined control group and exposure groups. EC early control, MC mid control, LC late control. EE early exposed, ME mid exposed, LE late exposed