Neuroprotective properties of the non-peptidyl radical scavenger IAC in rats following transient focal cerebral ischemia.

Experimental evidence suggests that reactive free radicals are generated during brain ischemia. We investigated the effect of a novel brain penetrant, low molecular weight, non-peptidyl carbon, oxygen- and nitrogen-centered radical scavenger, IAC, on infarct volume and sensory-motor performance in a rat transient middle cerebral artery occlusion model (tMCAO). Rats received 90 min tMCAO and treated with i.p. or i.v. injections of vehicle or IAC following tMCAO. Sensory-motor performance was evaluated by neuroscore tests (NS). Cerebral infarct volume was evaluated at 72 h after tMCAO. Rats treated with IAC i.p. (1 or 6 h after the onset of tMCAO) or i.v. (1 h after the onset of tMCAO) showed significant improvement in NS during the 3 or 21 day follow-up period when compared to vehicle treated rats. Cerebral infarct volumes were significantly decreased compared to vehicle in rats receiving IAC i.p. 1 h or 6 h after occlusion, approximately 30.5% decrease compared to vehicle, or i.v. 1 h after the onset of tMCAO, 48.6% decrease compared to vehicle. These results demonstrate that IAC has neuroprotective properties with a wide therapeutic window following tMCAO in rats. IAC could therefore be a candidate for the treatment of stroke.

Ambient particulate matter affects cardiac recovery in a Langendorff ischemia model.

Exposure to ambient particulate matter (PM) is associated with increased mortality and morbidity among subjects with cardiovascular impairment. We hypothesized that exposure of spontaneously hypertensive (SH) rats to PM impairs the recovery of cardiovascular performance after coronary occlusion and reperfusion-ischemia. SH rats were exposed by intratracheal instillation to saline, standard urban PM (Ottawa dust EHC-93, 10 mg/kg body weight) or endotoxin (lipopolysaccharides LPS, 350 EU/animal) to induce a similar pulmonary inflammation. At 4 h postexposure, hearts were isolated and retrograde perfused in a Langendorff model. The experimental protocol included 35 min of coronary occlusion followed by 120 min of reperfusion, during which left ventricular developing pressure (LDVP), coronary flow (CF), and heart rate (HR) were measured. Baseline LVDP in particle-instilled SH rats was significantly decreased compared to saline-instilled animals. In addition, after ischemia the recovery of LDVP was much slower in rats pretreated with PM or LPS compared to saline instilled rats. The direct effects of the soluble PM fraction and the role of Zn2+ were also tested cardiomyocytes (H9C2 cells). Both particle-free filtrate and Zn2+ inhibited ATP or ionophore-stimulated calcium influx in cardiomyocytes. This inhibitory effect was related to an effect on calcium channels, as shown with Nifedipine. This study provides evidence that exposure to instillation of PM has reversible acute effects on the recovery of cardiac physiological parameters after ischemia. The effect may be caused by a direct action of soluble metals on calcium homeostasis in heart, but pulmonary inflammation may also play a significant role.

The influence of hydrogen peroxide and histamine on lung permeability and translocation of iridium nanoparticles in the isolated perfused rat lung.

BACKGROUND: Translocation of ultrafine particles (UFP) into the blood that returns from the lungs to the heart has been forwarded as a mechanism for particle-induced cardiovascular effects. The objective of this study was to evaluate the role of the endothelial barrier in the translocation of inhaled UFP from the lung into circulation. METHODS: The isolated perfused rat lung (IPRL) was used under negative pressure ventilation, and radioactive iridium particles (18 nm, CMD, 192Ir-UFP) were inhaled during 60 minutes to achieve a lung burden of 100-200 microg. Particle inhalation was done under following treatments: i) control perfusion, ii) histamine (1 microM) in perfusate, iii) luminal histamine instillation (1 mM), and iv) luminal instillation of H2O2. Particle translocation to the perfusate was assessed by the radioactivity of 192Ir isotope. Lung permeability by the use of Tc99m-labeled diethylene triamine pentaacetic acid (DTPA). In addition to light microscopic morphological evaluation of fixed lungs, alkaline phosphatase (AKP) and angiotensin converting enzyme (ACE) in perfusate were measured to assess epithelial and endothelial integrity. RESULTS: Particle distribution in the lung was homogenous and similar to in vivo conditions. No translocation of Ir particles at negative pressure inhalation was detected in control IPL, but lungs pretreated with histamine (1 microM) in the perfusate or with luminal H2O2 (0.5 mM) showed small amounts of radioactivity (2-3 % dose) in the single pass perfusate starting at 60 min of perfusion. Although the kinetics of particle translocation were different from permeability for 99mTc-DTPA, the pretreatments (H2O2, vascular histamine) caused similar changes in the translocation of particles and soluble mediator. Increased translocation through epithelium and endothelium with a lag time of one hour occurred in the absence of epithelial and endothelial damage. CONCLUSION: Permeability of the lung barrier to UFP or nanoparticles is controlled both at the epithelial and endothelial level. Conditions that affect this barrier function such as inflammation may affect translocation of NP.

The effect of particulate matter on resistance and conductance vessels in the rat.

Epidemiological and clinical studies suggest that air pollution, in particular ambient particulate matter (PM), increases mortality in patients with cardiovascular disease (CVD). Several in vivo studies have shown an increase of blood pressure by PM, but so far the mechanism or responsible particle-component has not been elucidated. We exposed small mesenteric rat artery (SMRA) and rat aorta to ambient particles (EHC-93) to test the ability of ambient particles to modify the vascular tone of different vessel types. PM suspensions (10-100 microg/ml) and filtrates containing only the water-soluble components failed to modify the resting tension of either the aorta or SMRA. However, PM did elicit a dose-dependent vasorelaxation in phenylephrine precontracted SMRA and aorta. The effect of the PM suspensions was higher than that of PM filtrate (without particles). The relaxation was already visible at 10 microg/ml, and the difference with filtrate became significant at 100 microg/ml for aorta (maximal relaxation E(max) = 18% vs. 12% PM filtrate) and as low as 30 microg/ml for SMRA (E(max) = 13% vs. 5% PM filtrate). Although the effect of PM was biggest in aorta, the concentration to cause half of the maximal effect (EC(50)) of suspension and filtrate was the same in both capacity (aorta) and resistance vessels (SMRA). The main difference seen between SMRA and aorta was that PM did not modify the phenylephrine-induced dose-response vasoconstriction in SMRA, while it did do so in the aorta. In conclusion, the in vitro exposure of precontracted blood vessels to ambient PM results in an acute vasorelaxation, which is in contrast to the observation that PM can cause increased blood pressure. Dose calculations show that the elevation of blood pressure observed in vivo is not likely due to direct effects of particles or constituents. We therefore suggest that the in vivo effect of PM on vasoconstriction acts through other pathways, such as the central nervous system.

Vascular effects of ambient particulate matter instillation in spontaneous hypertensive rats.

Exposure to ambient particulate matter (PM) is associated with increased mortality and morbidity among those people with cardiovascular impairment. We have studied the effects of exposure to PM or lypopolysaccharide (LPS) on ex vivo vascular function of spontaneous hypertensive rats (SHR) at 4 and 24 h post-instillation. Receptor-dependent and -independent relaxation was studied by using acetylcholine (ACh) and sodium nitroprusside (SNP), respectively. We have used phenylephrine (Phe) and KCl for receptor-dependent and -independent contraction. The role of the endothelium was investigated using denuded aorta rings. Exposure to PM (EHC-93, 10 mg/kg) or LPS (350 EU/animal) caused maximal pulmonary inflammation at 24 h post-instillation. PM and LPS elicited a significant increase in receptor-dependent vasorelaxation of aorta compared to saline-instilled rats. The largest effect was seen with PM at 4 h post-instillation (EC50 ACh = 2.3 vs. 5 nM control), while at 24 h effects were much smaller (EC50 ACh = 5.6 vs. 5 nM control). SNP-induced vasorelaxation was increased only in EHC-93-treated rats (EC50 = 71.9 vs. 95.7 nM) at 4 h, and this response was higher than that observed at 24 h. Phe induced a dose-dependent vasoconstriction, but no difference was seen between treatments in the presence or absence of endothelium at 4 h. However, at 24 h after instillation of LPS, a right shift of contraction curve was seen (EC50 = 65.3 vs. 43.3 nM). No change was seen in receptor-independent vasoconstriction induced by KCl, except in the LPS group at 24 h. A direct relaxation was also observed upon in vitro exposure of aorta rings to PM, and model particles coated with metals. Blood metal analysis showed an increase of zinc and vanadium concentration at 1 and 4 h post-instillation. In conclusion, our data show that PM and LPS instillation has a transient effect on the vasorelaxation of rat aorta that is maximal at 4 h. On the other hand, pulmonary inflammation reaches a maximum at 24 h and coincides with impairment of vasorelaxation. Current data do not allow discriminating among the potential mechanisms, but suggest that both a direct effect of metals and inflammation play a role.