Nanoparticle inhalation impairs coronary microvascular reactivity via a local reactive oxygen species-dependent mechanism

Abstract

We have shown that nanoparticle inhalation impairs endothelium-dependent vasodilation in coronary arterioles. It is unknown whether local reactive oxygen species (ROS) contribute to this effect. Rats were exposed to TiO(2) nanoparticles via inhalation to produce a pulmonary deposition of 10 microg. Coronary arterioles were isolated from the left anterior descending artery distribution, and responses to acetylcholine, arachidonic acid, and U46619 were assessed. Contributions of nitric oxide synthase and prostaglandin were assessed via competitive inhibition with N(G)-Monomethyl-L-Arginine (L-NMMA) and indomethacin. Microvascular wall ROS were quantified via dihydroethidium (DHE) fluorescence. Coronary arterioles from rats exposed to nano-TiO(2) exhibited an attenuated vasodilator response to ACh, and this coincided with a 45% increase in DHE fluorescence. Coincubation with 2,2,6,6-tetramethylpiperidine-N-oxyl and catalase ameliorated impairments in ACh-induced vasodilation from nanoparticle exposed rats. Incubation with either L-NMMA or indomethacin significantly attenuated ACh-induced vasodilation in sham-control rats, but had no effect in rats exposed to nano-TiO(2). Arachidonic acid induced vasoconstriction in coronary arterioles from rats exposed to nano-TiO(2), but dilated arterioles from sham-control rats. These results suggest that nanoparticle exposure significantly impairs endothelium-dependent vasoreactivity in coronary arterioles, and this may be due in large part to increases in microvascular ROS. Furthermore, altered prostanoid formation may also contribute to this dysfunction. Such disturbances in coronary microvascular function may contribute to the cardiac events associated with exposure to particles in this size range.

Fig. 1

a Representative images of coronary arterioles loaded with DHE from sham-control and nano-TiO₂ exposed rats. b Mean fluorescence calculated from ROI was significantly greater in coronary arterioles from rats exposed to nano-TiO₂ compared to sham-controls, indicating greater basal ROS generation. Values are means ± S.E. *, P ≤ 0.05 sham-control versus nano-TiO₂

Fig. 2

ACh-induced vasodilation was impaired in coronary arterioles from rats exposed to nano-TiO₂ compared to sham-controls. After a 30-min preincubation with TEMPOL (1 × 10⁻⁴ M) and catalase (50 units/mL), vasodilation in response to ACh was restored in coronary arterioles from rats exposed to nano-TiO₂. Values are means ± S.E. * P ≤ 0.05 sham-control vs. nano-TiO₂. ^†P ≤ 0.05 significant treatment effect within group

Fig. 3

Maximal dilation in response to ACh in the presence of normal superfusate, TEMPOL (1 × 10⁻⁴ M) and catalase (50 units/mL), L-NMMA (1 × 10⁻⁴ M), or indomethacin (1 × 10⁻⁵ M) in coronary arterioles from sham-control and nano-TiO₂ exposed rats. Incubation with L-NMMA or indomethacin decreased the Ach-induced vasodilation in arterioles from sham-control rats, but did not alter maximal dilation from nano-TiO₂ rats. Values are means ± S.E. * P ≤ 0.05 sham-control vs. nano-TiO₂. ^†P ≤ 0.05 significant treatment effect within group

Fig. 4

a Nano-TiO₂ inhalation caused a slight, but significant vasoconstriction in coronary arterioles in response to arachidonic acid compared to vasodilation observed in sham-control rats. b There were no group differences in the vasoconstriction of coronary arterioles in response to the T×A₂ analog U46619. Values are means ± S.E. * P ≤ 0.05 sham-control versus nano-TiO₂