Nanomaterial Inhalation During Pregnancy Alters Systemic Vascular Function in a Cyclooxygenase-Dependent Manner

Abstract

Pregnancy requires rapid adaptations in the uterine microcirculation to support fetal development. Nanomaterial inhalation is associated with cardiovascular dysfunction, which may impair gestation. We have shown that maternal nano-titanium dioxide (nano-TiO2) inhalation impairs microvascular endothelial function in response to arachidonic acid and thromboxane (TXA2) mimetics. However, the mechanisms underpinning this process are unknown. Therefore, we hypothesize that maternal nano-TiO2 inhalation during gestation results in uterine microvascular prostacyclin (PGI2) and TXA2 dysfunction. Pregnant Sprague-Dawley rats were exposed from gestational day 10-19 to nano-TiO2 aerosols (12.17 ± 1.67 mg/m3) or filtered air (sham-control). Dams were euthanized on gestational day 20, and serum, uterine radial arterioles, implantation sites, and lungs were collected. Serum was assessed for PGI2 and TXA2 metabolites. TXB2, the stable TXA2 metabolite, was significantly decreased in nano-TiO2 exposed dams (597.3 ± 84.4 vs 667.6 ± 45.6 pg/ml), whereas no difference was observed for 6-keto-PGF1α, the stable PGI2 metabolite. Radial arteriole pressure myography revealed that nano-TiO2 exposure caused increased vasoconstriction to the TXA2 mimetic, U46619, compared with sham-controls (-41.3% ± 4.3% vs -16.8% ± 3.4%). Nano-TiO2 exposure diminished endothelium-dependent vasodilation to carbaprostacyclin, a PGI2 receptor agonist, compared with sham-controls (30.0% ± 9.0% vs 53.7% ± 6.0%). Maternal nano-TiO2 inhalation during gestation decreased nano-TiO2 female pup weight when compared with sham-control males (3.633 ± 0.064 vs 3.995 ± 0.124 g). Augmented TXA2 vasoconstriction and decreased PGI2 vasodilation may lead to decreased placental blood flow and compromise maternofetal exchange of waste and nutrients, which could ultimately impact fetal health outcomes.

Keywords: advanced materials; microcirculation; prostacyclin; thromboxane; titanium dioxide; uterine arterioles.

Figure 1.

Nano-TiO₂ aerosol real-time characterizations. Nano-TiO₂ aerosol characteristics were monitored and verified throughout exposure. Red lines in the figures represent size distribution curves based on a log normal fit of the size data, unless otherwise specified. A, Aerosol mass concentration was controlled via software over the 6-h exposure paradigm. Target average concentration (red line) real-time nano-TiO₂ aerosol mass concentration measurements (black line) were maintained at a target of 12 mg/m³. B, Aerosol agglomerate diameter was assessed by a SMPS (light gray) and an APS (dark gray). Based on results from the SMPS and APS the particle diameter, CMD = 116 nm, and had a GSD = 2.11. C, Electrical Low-Pressure Impactor (ELPI, light gray) assessed aerosol aerodynamic diameter at a CMD of 169 nm and a geometric SD of 1.94. D, Aerosol mass size distribution was evaluated by a Nano MOUDI; particles had an MMAD of 1.03 µm and a geometric SD of 2.57. Abbreviations: Nano-TiO₂, nano-titanium dioxide; SMPS, scanning mobility particle sizer; APS, aerodynamic particle sizer; CMD, count median diameter; GSD, geometric standard deviation; MMAD, mass median aerodynamic diameter; MOUDI, Micro-Orifice Uniform Deposit Impactor. A color version of this figure appears in the online version of this article.

Figure 2.

Vascular reactivity of uterine radial arterioles. Dose-response curves were performed to assess vascular reactivity of uterine radial arterioles (n = 29 for sham-control and n = 18 for nano-TiO₂). A, Vascular reactivity following increasing doses of ACh, an endothelium-dependent vasodilator, (B) SNAP, an endothelium-independent vasodilator, and (C) PE, vasoconstrictor. *p ≤ .05 versus sham-control. Abbreviations: Nano-TiO₂, nano-titanium dioxide; Ach, acetylcholine; SNAP, s-nitroso-N-acetyl-DL-penicillamine; PE, phenylephrine.

Figure 3.

Cyclooxygenase metabolites vascular radial reactivity. Subpopulations of nano-TiO₂ exposed uterine radial arterioles displayed hyperreactive responses to both COX metabolites. This subpopulation of vessels is shown herein as a separate group, and dose-response curves were assessed for vascular reactivity. A, Vascular responses following increasing doses of U46619, a TXA₂ mimetic (n = 29 for sham-control, n = 8 for nonaugmented nano-TiO₂, and n = 9 for augmented nano-TiO₂). B, Maximum response to U46619 across the dose-response curve. C, Vascular reactivity following increasing doses of carbaprostacyclin, a stable PGI₂ agonist (n = 29 for sham-control, n = 5 for nonaugmented nano-TiO₂, and n = 11 for augmented nano-TiO₂). D, Maximum response to carbaprostacyclin across the dose-response curve. *p ≤ .05 versus sham-control. ^p ≤ .05 versus nano-TiO₂. Abbreviations: nano-TiO₂, nano-titanium dioxide; COX, cyclooxygenase; TXA₂, thromboxane A₂; PGI₂, prostacyclin I₂.

Figure 4.

TXA₂ vascular reactivity of uterine radial arterioles in the presence of antagonists. Uterine radial arterioles were exposed to a single dose of the thromboxane receptor antagonist, SQ29,548, and then a dose-response curve to U46619, a stable TXA₂ mimetic, was performed. A, Sham-control (n = 12) versus nano-TiO₂ (n = 11) vascular response following antagonist addition and increasing doses of U46619. B, Maximum response to U46619, in the presence of the receptor antagonist, across the dose-response curve. C, Nonaugmented nano-TiO₂ (n = 11) versus augmented nano-TiO₂ (n = 8) vascular response following antagonist addition and increasing doses of U46619. D, Maximum response to U46619 in the presence of the antagonist across the dose-response curve. *p ≤ .05 versus sham-control. ^p ≤ .05 versus nano-TiO₂. ^Φp ≤ .05 versus nano-TiO₂ with SQ29,548. Abbreviations: nano-TiO₂, nano-titanium dioxide; TXA₂, thromboxane A₂.

Figure 5.

PGI₂ vascular reactivity of uterine radial arterioles in the presence of antagonists. Prostacyclin receptor antagonist, R01138452, was added to the bath as a single dose, and then a dose-response curve of carbaprostacyclin, a stable PGI₂ agonist, followed. A, Sham-control (n = 12) versus nonaugmented nano-TiO₂ (n = 8) vascular response following antagonist addition and then increasing doses of carbaprostacyclin. B, Maximum response to pretreated vessels with the prostacyclin receptor antagonist is represented in the bar graph. C, Nonaugmented nano-TiO₂ (n = 8) versus augmented nano-TiO₂ (n = 8) vascular response after R01138452 pretreatment to dose-response curve. D, Maximum response to carbaprostacyclin in the presence of the antagonist across the dose-response curve. *p ≤ .05 versus sham-control. ^p ≤ .05 versus nano-TiO₂. ^Φp ≤ .05 vs nano-TiO₂ with R01138,452. ^†p ≤ .05 versus augmented nano-TiO₂ with R01138. Abbreviations: PGI₂, prostacyclin I₂; nano-TiO₂, nano-titanium dioxide.

Figure 6.

Circulating 6-keto-PGF_1α and TXB₂ serum concentration. Maternal sham-control (N = 9) versus nano-TiO₂ (N = 9) circulating levels of 6-keto-PGF_1α (A) and TXB₂ (B) in pg/ml. *p ≤ .05 versus sham-control. Abbreviations: 6-keto-PGF_1α, 6-keto-prostaglandin F_1α; nano-TiO₂, nano-titanium dioxide; TXB₂, thromboxane B₂.

Figure 7.

Cytosolic PLA₂ enzymatic activity. Cytosolic PLA₂ enzymatic activity (N = 5–8) in (A) uterine artery and (B) implantation sites in U/mg. *p ≤ .05 versus sham-control. Abbreviations: PLA₂, phospholipase A₂.

Figure 8.

COX enzymatic activity. COX-2 enzymatic activity (N = 4–6) in (A) lung, (B) uterine artery, and (C) implantation sites in µU/mg. Abbreviations: COX, cyclooxygenase.