Cerium Dioxide Nanoparticle Exposure Improves Microvascular Dysfunction and Reduces Oxidative Stress in Spontaneously Hypertensive Rats

The elevated production of reactive oxygen species (ROS) in the vascular wall is associated with cardiovascular diseases such as hypertension. This increase in oxidative stress contributes to various mechanisms of vascular dysfunction, such as decreased nitric oxide bioavailability. Therefore, anti-oxidants are being researched to decrease the high levels of ROS, which could improve the microvascular dysfunction associated with various cardiovascular diseases. From a therapeutic perspective, cerium dioxide nanoparticles (CeO2 NP) hold great anti-oxidant potential, but their in vivo activity is unclear. Due to this potential anti-oxidant action, we hypothesize that injected CeO2 NP would decrease microvascular dysfunction and oxidative stress associated with hypertension. In order to simulate a therapeutic application, spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats were intravenously injected with either saline or CeO2NP (100 μg suspended in saline). Twenty-four hours post-exposure mesenteric arteriolar reactivity was assessed via intravital microscopy. Endothelium-dependent and –independent function was assessed via acetylcholine and sodium nitroprusside. Microvascular oxidative stress was analyzed using fluorescent staining in isolated mesenteric arterioles. Finally, systemic inflammation was examined using a multiplex analysis and venular leukocyte flux was counted. Endothelium-dependent dilation was significantly decreased in the SH rats (29.68 ± 3.28%, maximal response) and this microvascular dysfunction was significantly improved following CeO2 NP exposure (43.76 ± 4.33%, maximal response). There was also an increase in oxidative stress in the SH rats, which was abolished following CeO2 NP treatment. These results provided evidence that CeO2 NP act as an anti-oxidant in vivo. There were also changes in the inflammatory profile in the WKY and SH rats. In WKY rats, IL-10 and TNF-α were increased following CeO2 NP treatment. Finally, leukocyte flux was increased in the SH rats (34 ± 4 vs. 17 ± 3 cells/min in the normotensive controls), but this activation was decreased following exposure (15 ± 2 vs. 34 ± 4 cells/min). These results indicated that CeO2 NP may alter the inflammatory response in both SH and WKY rats. Taken together, these results provide evidence that CeO2 NP act as an anti-oxidant in vivo and may improve microvascular reactivity in a model of hypertension

Acute Inflammatory Responses of Nanoparticles in an Intra-Tracheal Instillation Rat Model

Exposure to hard metal tungsten carbide cobalt (WC-Co) “dusts” in enclosed industrial environments is known to contribute to the development of hard metal lung disease and an increased risk for lung cancer. Currently, the influence of local and systemic inflammation on disease progression following WC-Co exposure remains unclear. To better understand the relationship between WC-Co nanoparticle (NP) exposure and its resultant effects, the acute local pulmonary and systemic inflammatory responses caused by WC-Co NPs were explored using an intra-tracheal instillation (IT) model and compared to those of CeO2 (another occupational hazard) NP exposure. Sprague-Dawley rats were given an IT dose (0-500 μg per rat) of WC-Co or CeO2 NPs. Following 24-hr exposure, broncho-alveolar lavage fluid and whole blood were collected and analyzed. A consistent lack of acute local pulmonary inflammation was observed in terms of the broncho-alveolar lavage fluid parameters examined (i.e. LDH, albumin, and macrophage activation) in animals exposed to WC-Co NP; however, significant acute pulmonary inflammation was observed in the CeO2 NP group. The lack of acute inflammation following WC-Co NP exposure contrasts with earlier in vivo reports regarding WC-Co toxicity in rats, illuminating the critical role of NP dose and exposure time and bringing into question the potential role of impurities in particle samples. Further, we demonstrated that WC-Co NP exposure does not induce acute systemic effects since no significant increase in circulating inflammatory cytokines were observed. Taken together, the results of this in vivostudy illustrate the distinct differences in acute local pulmonary and systemic inflammatory responses to NPs composed of WC-Co and CeO2; therefore, it is important that the outcomes of pulmonary exposure to one type of NPs may not be implicitly extrapolated to other types of NPs

Impairment of Coronary Arteriolar Endothelium-Dependent Dilation after Multi-Walled Carbon Nanotube Inhalation: A Time-Course Study

Engineered nanomaterials have been developed for widespread applications due to many highly unique and desirable characteristics. The purpose of this study was to assess pulmonary inflammation and subepicardial arteriolar reactivity in response to multi-walled carbon nanotube (MWCNT) inhalation and evaluate the time course of vascular alterations. Rats were exposed to MWCNT aerosols producing pulmonary deposition. Pulmonary inflammation via bronchoalveolar lavage and MWCNT translocation from the lungs to systemic organs was evident 24 h post-inhalation. Coronary arterioles were evaluated 24–168 h post-exposure to determine microvascular response to changes in transmural pressure, endothelium-dependent and -independent reactivity. Myogenic responsiveness, vascular smooth muscle reactivity to nitric oxide, and α-adrenergic responses all remained intact. However, a severe impact on endothelium-dependent dilation was observed within 24 h after MWCNT inhalation, a condition which improved, but did not fully return to control after 168 h. In conclusion, results indicate that MWCNT inhalation not only leads to pulmonary inflammation and cytotoxicity at low lung burdens, but also a low level of particle translocation to systemic organs. MWCNT inhalation also leads to impairments of endothelium-dependent dilation in the coronary microcirculation within 24 h, a condition which does not fully dissipate within 168 h. The innovations within the field of nanotechnology, while exciting and novel, can only reach their full potential if toxicity is first properly assessed

Cerium dioxide nanoparticle exposure and microvascular dysfunction: Potential mechanistic links

Cerium dioxide nanoparticles (CeO2 NP), an engineered nanomaterial, have great potential from a consumer and therapeutic perspective. Currently, CeO2 NP are added to diesel fuel to decrease the soot emissions commonly associated with diesel engines. CeO2 NP also have therapeutic applications (e.g. improve outcomes following stroke and radiation treatments) due to their anti-oxidant capabilities. These applications increase CeO2 NP exposure risk not only for manufacturers, but also for the general community; however, there are currently limited studies that investigated the effects of CeO2 NP exposure via multiple exposure routes. Furthermore, there are no studies that investigate the microvascular consequences of CeO2 NP exposure despite its importance in blood pressure and flow regulation.;Therefore, the aim of the first study was to determine the microvascular impacts of pulmonary CeO2 NP exposure. Based on previous studies with other nanoparticles, we predicted that CeO2 NP exposure would cause microvascular dysfunction that was dose and microvascular bed dependent. Microvascular function was assessed in mesenteric and coronary arterioles via isolated microvessels. Following exposure, endothelium-dependent and -independent arteriolar dilation was significantly impaired. CeO2 NP exposure also resulted in pulmonary inflammation (assessed via bronchoalveolar lavage). Finally, these impairments and inflammatory changes were dose dependent and microvascular bed dependent.;The aims of the second study were 1) determine the microvascular impacts of CeO2 NP exposure via non-pulmonary exposure routes (e.g. injection and ingestion) and 2) investigate the underlying mechanisms of microvascular dysfunction. Isolated mesenteric arterioles were analyzed 24 h post-exposure. Endothelium-dependent and -independent dilation was significantly impaired following the injection and ingestion of CeO2 NP and the severity of dysfunction was dose and exposure route dependent. Finally, this study determined that these impairments might be mechanistically linked to decreased soluble guanylyl cyclase activation, cyclic guanosine monophosphate responsiveness, and nitric oxide (NO) bioavailability. Finally, this study, along with the first study, established the dose, which caused a 50% impairment in arteriolar reactivity (EC50) for each exposure route.;The final study in this dissertation aimed to determine the in vivo anti-oxidant activity of CeO2 NP in the presence of a pre-existing pathology. Based on CeO2 NP catalytic activity, we predicted that exposure would decrease the microvascular dysfunction and oxidative stress associated with hypertension. Endothelium-dependent dilation was assessed via intravital microscopy and was significantly improved in spontaneously hypertensive (SH) rats following CeO2 NP exposure. Vascular oxidative stress was also significant reduced in the SH rats post-CeO2 NP exposure. Finally, CeO2 NP altered the expression of pro-inflammatory cytokines in the Wistar-Kyoto and SH groups.;In conclusion, these studies indicated that CeO2 NP exposure results in microvascular alterations, which are microvascular bed, exposure route, dose, and pathology dependent. Furthermore, these alterations may be due to changes in inflammation, oxidative stress, NO bioavailability, and/or intracellular signaling. These studies improve our understanding of the microvascular effects of CeO2 NP, which is essential for the development of these nanoparticles in commercial and therapeutic applications

Cerium dioxide nanoparticle exposure improves microvascular dysfunction and reduces oxidative stress in spontaneously hypertensive rats

The elevated production of reactive oxygen species (ROS) in the vascular wall is associated with cardiovascular diseases such as hypertension. This increase in oxidative stress contributes to various mechanisms of vascular dysfunction, such as decreased nitric oxide bioavailability. Therefore, anti-oxidants are being researched to decrease the high levels of ROS, which could improve the microvascular dysfunction associated with various cardiovascular diseases. From a therapeutic perspective, cerium dioxide nanoparticles (CeO2 NP) hold great anti-oxidant potential, but their in vivo activity is unclear. Due to this potential anti-oxidant action, we hypothesize that injected CeO2 NP would decrease microvascular dysfunction and oxidative stress associated with hypertension. In order to simulate a therapeutic application, spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats were intravenously injected with either saline or CeO2 NP (100 µg suspended in saline). Twenty-four hours post-exposure mesenteric arteriolar reactivity was assessed via intravital microscopy. Endothelium-dependent and –independent function was assessed via acetylcholine and sodium nitroprusside. Microvascular oxidative stress was analyzed using fluorescent staining in isolated mesenteric arterioles. Finally, systemic inflammation was examined using a multiplex analysis and venular leukocyte flux was counted. Endothelium-dependent dilation was significantly decreased in the SH rats (29.68 ± 3.28%, maximal response) and this microvascular dysfunction was significantly improved following CeO2 NP exposure (43.76 ± 4.33%, maximal response). There was also an increase in oxidative stress in the SH rats, which was abolished following CeO2 NP treatment. These results provided evidence that CeO2 NP act as an anti-oxidant in vivo. There were also changes in the inflammatory profile in the WKY and SH rats. In WKY rats, IL-10 and TNF-α were increased following CeO2 NP treatment. Finally, leukocyte flux was increased in the SH rats (34 ± 4 vs. 17 ± 3 cells/min in the normotensive controls), but this activation was decreased following exposure (15 ± 2 vs. 34 ± 4 cells/min). These results indicated that CeO2 NP may alter the inflammatory response in both SH and WKY rats. Taken together, these results provide evidence that CeO2 NP act as an anti-oxidant in vivo and may improve microvascular reactivity in a model of hypertension

Histology of isolated BAL fluid cells from a representative A) control (vehicle only) rat and B) 500 μg WC-Co NP exposed rat.

<p>Scale bars = 20 μm. (black arrow = alveolar macrophage, AM; arrow head = erythrocyte; dotted arrow = polymorphonuclear leukocyte, PMN; wide arrow = AM with WC-Co NPs)</p

Pulmonary inflammation parameters assessed in the BAL fluid following 24-hr exposure to WC-Co and CeO₂ NPs: A) LDH activity, B) albumin, and C) AM chemiluminescence.

<p>Values presented as mean ± SD. (*P < 0.05, ‡P < 0.001 compared to the vehicle control, and †P < 0.01 compared to WC-Co NP exposed groups)</p

Inflammatory cytokine concentrations in A) BAL fluid and B) blood plasma.

<p>(†P < 0.05 compared to the vehicle control and WC-Co NP exposed groups)</p

Summary of the characteristics of WC-Co NP, including size and elemental composition.

<p>Summary of the characteristics of WC-Co NP, including size and elemental composition.</p