Group II innate lymphoid cells and microvascular dysfunction from pulmonary titanium dioxide nanoparticle exposure

Background

The cardiovascular effects of pulmonary exposure to engineered nanomaterials (ENM) are poorly understood, and the reproductive consequences are even less understood. Inflammation remains the most frequently explored mechanism of ENM toxicity. However, the key mediators and steps between lung exposure and uterine health remain to be fully defined. The purpose of this study was to determine the uterine inflammatory and vascular effects of pulmonary exposure to titanium dioxide nanoparticles (nano-TiO₂). We hypothesized that pulmonary nano-TiO₂ exposure initiates a Th2 inflammatory response mediated by Group II innate lymphoid cells (ILC2), which may be associated with an impairment in uterine microvascular reactivity.

Methods

Female, virgin, Sprague-Dawley rats (8–12 weeks) were exposed to 100 μg of nano-TiO₂ via intratracheal instillation 24 h prior to microvascular assessments. Serial blood samples were obtained at 0, 1, 2 and 4 h post-exposure for multiplex cytokine analysis. ILC2 numbers in the lungs were determined. ILC2s were isolated and phosphorylated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-?B) levels were measured. Pressure myography was used to assess vascular reactivity of isolated radial arterioles.

Results

Pulmonary nano-TiO₂ exposure was associated with an increase in IL-1ß, 4, 5 and 13 and TNF- α 4 h post-exposure, indicative of an innate Th2 inflammatory response. ILC2 numbers were significantly increased in lungs from exposed animals (1.66?±?0.19%) compared to controls (0.19?±?0.22%). Phosphorylation of the transactivation domain (Ser-468) of NF-κB in isolated ILC2 and IL-33 in lung epithelial cells were significantly increased (126.8?±?4.3% and 137?±?11% of controls respectively) by nano-TiO₂ exposure. Lastly, radial endothelium-dependent arteriolar reactivity was significantly impaired (27?±?12%), while endothelium-independent dilation (7?±?14%) and α-adrenergic sensitivity (8?±?2%) were not altered compared to control levels. Treatment with an anti- IL-33 antibody (1 mg/kg) 30 min prior to nano-TiO₂ exposure resulted in a significant improvement in endothelium-dependent dilation and a decreased level of IL-33 in both plasma and bronchoalveolar lavage fluid.

Conclusions

These results provide evidence that the uterine microvascular dysfunction that follows pulmonary ENM exposure may be initiated via activation of lung-resident ILC2 and subsequent systemic Th2-dependent inflammation.

     

Subchronic inhalation of carbon nanofibers: No apparent cross-talk between local pulmonary and cardiovascular/systemic responses

Pulmonary exposures to air pollution-derived particulate matter (PM) may result in both activation of lung responses and adverse cardiovascular (CV) effects. This suggests a cross-talk relationship between local and systemic responses potentially leading to CV disease in humans. To test this hypothesis in a normal animal model, rats were exposed to aerosols of carbon nanofibers (CNF) for 13 weeks. The highest CNF concentration (25 mg/m³) produced persistent respiratory tract (RT) inflammation/cytotoxicity throughout the exposure and 3-month recovery period, concomitant with translocation of inhaled CNF from airspace to extrapulmonary sites. The finding provided a basis for postulating that local RT effects could translocate to the systemic circulation, thereby producing CV alterations such as inflammation and/or coagulation changes. Therefore, assessments of cardiovascular endpoints such as cardiomyocyte cell proliferation (CP)/histopathology, C-reactive protein (CRP) levels, and 4 different diagnostic coagulation parameters, were investigated. No significant differences were measured between air or CNF-exposed rats when measuring fibrinogen levels, platelet counts, PT and aPTT bleeding times, and CRP levels. In addition, CP and histopathology evaluations were not different in CNF-exposed rats. Cardiac physiology and telemetry responses were not measured in this study. It was concluded that no apparent cross-talk was evident between local respiratory and systemic/cardiovascular compartments.