Ozone inhibition of tissue cholinesterase in guinea pigs

Air Pollution Role as Risk Factor of Cardioinhibitory Carotid Hypersensitivity

Little is known about the impact of air pollution on neuroautonomic system. The authors have investigated possible influence of air pollution and outdoor temperature on the carotid sinus hypersensitivity (CSH), as main cause of neurally mediated syncope in forty-years-old subjects and older. Pollutants’ concentrations and outdoor temperature of days in which 179 subjects with recurrent syncope underwent carotid sinus massage (CSM) were analyzed. Before this manoeuvre, cardiovascular control by short period heart and blood pressure spectral duration of segment between the end of P and R ECG-waves (PeR) were registred; RR variability on the same short period ECG recordings and their spectral coherence were also analyzed. CSH was found in 57 patients (28 with cardioinhibitory response and 29 subjects showed vasodepressor reaction), while 122 subjects had a normal response. CSM performed during high ozone concentrations was associated with slightly higher risk of cardioinhibitory response (odd ratio 1.012, 95% CI 1.001–1.023, p < 0.05), but neither this or other polluting agent nor outdoor temperature seemed to influence autonomic control in basal resting condition. Thus, ozone seemed to influence response to the CSM in CSH patients and it is probably able to facilitate a cardioinhibitory response, perhaps through an increase of nerve acetylcholine release. P→PR coherence could be useful in predicting a sinus cardioinhibitory hypersensitivity in those cases when CSM is contraindicated.

Lung macrophages: current understanding of their roles in Ozone-induced lung diseases

Through the National Ambient Air Quality Standards (NAAQS), the Clean Air Act of the United States outlines acceptable levels of six different air pollutants considered harmful to humans and the environment. Included in this list is ozone (O₃), a highly reactive oxidant gas, respiratory health hazard, and common environmental air pollutant at ground level. The respiratory health effects due to O₃ exposure are often associated with molecular and cellular perturbations in the respiratory tract. Periodic review of NAAQS requires comprehensive scientific evaluation of the public health effects of these pollutants, which is formulated through integrated science assessment (ISA) of the most policy-relevant scientific literature. This review focuses on the protective and pathogenic effects of macrophages in the O₃-exposed respiratory tract, with emphasis on mouse model-based toxicological studies. Critical findings from 39 studies containing the words O₃, macrophage, mice, and lung within the full text were assessed. While some of these studies highlight the presence of disease-relevant pathogenic macrophages in the airspaces, others emphasize a protective role for macrophages in O₃-induced lung diseases. Moreover, a comprehensive list of currently known macrophage-specific roles in O₃-induced lung diseases is included in this review and the significant knowledge gaps that still exist in the field are outlined. In conclusion, there is a vital need in this field for additional policy-relevant scientific information, including mechanistic studies to further define the role of macrophages in response to O₃.

The effects of pycnogenol on antioxidant enzymes in a mouse model of ozone exposure

BACKGROUND/AIMS

Ozone is an environmentally reactive oxidant, and pycnogenol is a mixture of flavonoid compounds extracted from pine tree bark that have antioxidant activity. We investigated the effects of pycnogenol on reactive nitrogen species, antioxidant responses, and airway responsiveness in BALB/c mice exposed to ozone.

METHODS

Antioxidant levels were determined using high performance liquid chromatography with electrochemical detection. Nitric oxide (NO) metabolites in bronchoalveolar lavage (BAL) fluid from BALB/c mice in filtered air and 2 ppm ozone with pycnogenol pretreatment before ozone exposure (n = 6) were quantified colorimetrically using the Griess reaction.

RESULTS

Uric acid and ascorbic acid concentrations were significantly higher in BAL fluid following pretreatment with pycnogenol, whereas γ-tocopherol concentrations were higher in the ozone exposed group but were similar in the ozone and pycnogenol pretreatment groups. Retinol and γ-tocopherol concentrations tended to increase in the ozone exposure group but were similar in the ozone and pycnogenol pretreatment groups following ozone exposure. Malonylaldehyde concentrations increased in the ozone exposure group but were similar in the ozone and pycnogenol plus ozone groups. The nitrite and total NO metabolite concentrations in BAL fluid, which parallel the in vivo generation of NO in the airways, were significantly greater in the ozone exposed group than the group exposed to filtered air, but decreased with pycnogenol pretreatment.

CONCLUSIONS

Pycnogenol may increase levels of antioxidant enzymes and decrease levels of nitrogen species, suggesting that antioxidants minimize the effects of acute ozone exposure via a protective mechanism.

Overt and latent cardiac effects of ozone inhalation in rats: evidence for autonomic modulation and increased myocardial vulnerability

BACKGROUND

Ozone (O₃) is a well-documented respiratory oxidant, but increasing epidemiological evidence points to extrapulmonary effects, including positive associations between ambient O₃ concentrations and cardiovascular morbidity and mortality.

OBJECTIVE

With preliminary reports linking O₃ exposure with changes in heart rate (HR), we investigated the hypothesis that a single inhalation exposure to O₃ will cause concentration-dependent autonomic modulation of cardiac function in rats.

METHODS

Rats implanted with telemeters to monitor HR and cardiac electrophysiology [electrocardiography (ECG)] were exposed once by whole-body inhalation for 4 hr to 0.2 or 0.8 ppm O₃ or filtered air. A separate cohort was tested for vulnerability to aconitine-induced arrhythmia 24 hr after exposure.

RESULTS

Exposure to 0.8 ppm O₃ caused bradycardia, PR prolongation, ST depression, and substantial increases in atrial premature beats, sinoatrial block, and atrioventricular block, accompanied by concurrent increases in several HR variability parameters that were suggestive of increased parasympathetic tone. Low-O₃ exposure failed to elicit any overt changes in autonomic tone, heart rhythm, or ECG. However, both 0.2 and 0.8 ppm O₃ increased sensitivity to aconitine-induced arrhythmia formation, suggesting a latent O₃-induced alteration in myocardial excitability.

CONCLUSIONS

O₃ exposure causes several alterations in cardiac electrophysiology that are likely mediated by modulation of autonomic input to the heart. Moreover, exposure to low O₃ concentrations may cause subclinical effects that manifest only when triggered by a stressor, suggesting that the adverse health effects of ambient levels of air pollutants may be insidious and potentially underestimated.

Three days after a single exposure to ozone, the mechanism of airway hyperreactivity is dependent on substance P and nerve growth factor

Ozone causes persistent airway hyperreactivity in humans and animals. One day after ozone exposure, airway hyperreactivity is mediated by release of eosinophil major basic protein that inhibits neuronal M(2) muscarinic receptors, resulting in increased acetylcholine release and increased smooth muscle contraction in guinea pigs. Three days after ozone, IL-1β, not eosinophils, mediates ozone-induced airway hyperreactivity, but the mechanism at this time point is largely unknown. IL-1β increases NGF and the tachykinin substance P, both of which are involved in neural plasticity. These experiments were designed to test whether there is a role for NGF and tachykinins in sustained airway hyperreactivity following a single ozone exposure. Guinea pigs were exposed to filtered air or ozone (2 parts per million, 4 h). In anesthetized and vagotomized animals, ozone potentiated vagally mediated airway hyperreactivity 24 h later, an effect that was sustained over 3 days. Pretreatment with antibody to NGF completely prevented ozone-induced airway hyperreactivity 3 days, but not 1 day, after ozone and significantly reduced the number of substance P-positive airway nerve bundles. Three days after ozone, NK(1) and NK(2) receptor antagonists also blocked this sustained hyperreactivity. Although the effect of inhibiting NK(2) receptors was independent of ozone, the NK(1) receptor antagonist selectively blocked vagal hyperreactivity 3 days after ozone. These data confirm mechanisms of ozone-induced airway hyperreactivity change over time and demonstrate 3 days after ozone that there is an NGF-mediated role for substance P, or another NK(1) receptor agonist, that enhances acetylcholine release and was not present 1 day after ozone.

Application of Ozone in Medicine

This review deals with the application of ozone in medicine, its effects on the human organism and its use as a therapeutic approach and sterilizing agent. A particular attention is paid to the therapeutic properties, therapeutic dosage and scope of application. Some mechanisms of the ozone effect at exposure on different organs and systems in human body are also considered. Ozone toxicity is reviewed. The ozone use as a sterilizing agent in the pharmaceutical industry and cosmetics, as well as in the food processing industry is discussed.

Additive effect of diesel exhaust particulates and ozone on airway hyperresponsiveness and inflammation in a mouse model of asthma

Allergic airway diseases are related to exposure to atmospheric pollutants, which have been suggested to be one factor in the increasing prevalence of asthma. Little is known about the effect of ozone and diesel exhaust particulates (DEP) on the development or aggravation of asthma. We have used a mouse asthma model to determine the effect of ozone and DEP on airway hyperresponsiveness and inflammation. Methacholine enhanced pause (P(enh)) was measured. Levels of IL-4 and IFN-gamma were quantified in bronchoalveolar lavage fluids by enzyme immunoassays. The OVA-sensitized-challenged and ozone and DEP exposure group had higher P(enh) than the OVA-sensitized-challenged group and the OVA-sensitized-challenged and DEP exposure group, and the OVA-sensitized-challenged and ozone exposure group. Levels of IFN-gamma were decreased in the OVA-sensitized-challenged and DEP exposure group and the OVA-sensitized-challenged and ozone and DEP exposure group compared to the OVA-sensitized-challenged and ozone exposure group. Levels of IL-4 were increased in the OVA-sensitized-challenged and ozone exposure group and the OVA-sensitized-challenged and DEP exposure group, and the OVA-sensitized-challenged and ozone and DEP exposure group compared to OVA-sensitized-challenged group. Co-exposure of ozone and DEP has additive effect on airway hyperresponsiveness by modulation of IL-4 and IFN-gamma suggesting that DEP amplify Th2 immune response.

Hyperresponsive airways correlate with lung tissue inflammatory cell changes in ozone-exposed rats

The role of inflammatory cell infiltration in the development of hyperresponsiveness of the airways to muscarinic challenge remains poorly understood. Unlike previous investigations that only examined conducting airway inflammation, the present study utilized both bronchoalveolar lavage (BAL) and lung tissue digestion to determine rat lung inflammatory cell contents following a 4-h exposure to 2 ppm ozone. Immediately following ozone exposure, neutrophil content of the lung tissue was significantly increased and reached a value that was fourfold higher than air-exposed controls by 3 h postexposure. Although lavage-recovered neutrophils were elevated at 24 h, tissue neutrophil numbers had returned to control values. This transient elevation of tissue neutrophils directly correlated with an elevation and subsequent decline of airway hyperresponsiveness, measured as a decrease in the intravenous dose of methacholine provoking a 200% increase in airway resistance (PD(200)R). Animals rendered neutropenic with a rabbit anti-rat neutrophil serum prior to exposure were protected from ozone-induced hyperresponsive airways, further demonstrating an association between neutrophil infiltration into the lung and altered airway physiology. Although BAL-recovered neutrophils demonstrated no adverse effects as a result of ozone exposure, macrophages were not only found to be necrotic but also displayed altered oxidative metabolism when challenged with phorbol myristate acetate. Thus, changes in the microenvironment of the airways smooth muscle were shown to be associated with transient accumulation of neutrophils within the lung tissue and abnormalities of bronchoalveolar lavage-recovered macrophages.

Airway function, oedema, cell infiltration and nitric oxide generation in conscious ozone-exposed guinea-pigs: effects of dexamethasone and rolipram

1. The effects of ozone inhalation (90 min, 2.15+/-0.05 p.p.m.) and their modification by dexamethasone (20 mg kg(-1)) or the phosphodiesterase-4 inhibitor, rolipram (1 mg kg(-1)), administered (i.p.) 24 and 0.5 h before and 24 h after ozone exposure were examined in conscious guinea-pigs. 2. Ozone caused an early-phase bronchoconstriction (EPB) as a fall in specific airways conductance (sG(aw)) measured by whole body plethysmography, followed at 5 h by a late-phase bronchoconstriction (LPB) and increased respiratory rate. Rolipram did not alter this profile but dexamethasone inhibited the EPB. 3. Airway hyperreactivity to inhaled histamine (1 mM, 20 s) occurred at 0.5, 2, 12, 24 and 48 h after ozone inhalation, the 2 h change being abolished by rolipram and dexamethasone. 4. Bronchoalveolar lavage fluid (BALF) macrophages, eosinophils and neutrophils were significantly (P<0.05) elevated at 12, 24 and 48 h after ozone exposure, the 48 h influx being significantly attenuated (P<0.05) by rolipram and dexamethasone. 5. BALF nitric oxide (NO) metabolites decreased 0.5 h after ozone exposure by 52%, recovered at 2 h and significantly increased at 12 (101%) and 24 h (127%). The elevated NO was unaffected by rolipram or dexamethasone. 6. Lung oedema, measured from wet/dry weight differences, was significant 12, 24 and 48 h after ozone exposure, the latter being significantly attenuated (P<0.05) by rolipram and dexamethasone. 7. Ozone exposure of guinea-pigs produced features common to COPD. Although rolipram and dexamethasone did not affect the airway function changes, they inhibited the inflammation, airway hyperreactivity and oedema.

Differences between inhaled and intravenous bronchial challenge to detect O(3)-induced hyperresponsiveness

Ozone (O(3))-induced airway hyperresponsiveness in laboratory animals is usually demonstrated through dose-response curves with inhaled or intravenous bronchoconstrictor agonists. However, comparability of these two routes has not been well documented. Thus guinea pig airway responsiveness to ACh and histamine was evaluated 16-18 h after O(3) (3 parts/million, 1 h) or air exposure by two plethysmographic methods (spontaneously breathing and mechanically ventilated) and by two administration routes (inhalatory or intravenous). We found that O(3) caused airway hyperresponsiveness to intravenous, but not to inhaled, agonists, independent of the plethysmographic method used. Suitability of the inhalatory route to detect airway hyperresponsiveness was corroborated with inhaled ACh after an antigen challenge or extending O(3) exposure to 3 h. Acetylcholinesterase activity was not modified after O(3) exposure in lung homogenates and blood samples. Thus inhaled agonists were less effective to reveal the airway hyperresponsiveness after an acute O(3) exposure than intravenous ones, at least for the 1-h exposure to 3 parts/million, and this difference seems not to be related to an O(3)-induced inhibition of the acetylcholinesterase activity.

Differential susceptibility to ozone-induced airways hyperreactivity in inbred strains of mice

Individuals with heightened airways reactivity, such as asthmatics, may be at risk to inflammatory effects of oxidant air pollutants. In the inbred mouse, significant interstrain variation in airways reactivity to acelycholine (ACh) and differential susceptibility to ozone (O3)-induced airways inflammation has been described previously. This study used these murine models to test hypotheses that (1) O3-induced hyperreactivity to ACh is a function of inherent baseline ACh reactivity, and (2) susceptibility to O3-induced inflammation is associated with O3-induced hyperreactivity. Strains (15-25 g, 6-8 weeks) with HYPERREACTIVE (DBA/2J, AKR/J, A/J), HYPOREACTIVE (C3H/HeJ, C57BL/6J, SJL/H), or INTERMEDIATE (129/J) phenotypes for ACh reactivity were exposed for 3 h to 2.0 ppm O3 or air (control). ACh reactivity (25 and 50 micrograms/kg, IV) was assessed 0 and 24 h after exposure. Relative to air controls, mean airways responses to 25 and 50 micrograms/kg ACh 24 h post-O3 increased significantly in the HYPERREACTIVE A/J strain (p < .05). Among HYPOREACTIVE strains, O3 significantly (p < .05) increased the response to 50 micrograms/kg ACh in C57BL/6J and SJL/J strains 24 h postexposure. A/J, C57BL/6J, and SJL/J mice are susceptible to O3-induced lung injury. O3 did not alter ACh reactivity in the other strains. O3 also did not affect airways reactivity to methacholine or carbachol, observations consistent with the hypothesis that O3-induced hyperreactivity to ACh may be due, in part, to O3 effects on cholinesterase function. Treatment of C57BL/6J and A/J mice with an immunosuppressant (cyclophosphamide) or an anti-PMN antibody significantly (p < .05) attenuated circulating and infiltrating polymorphonuclear leukocytes (PMNs), but did not affect O3-induced hyperreactivity. Therefore, O3-induced ACh hyperreactivity was not a function of baseline reactivity, but correlated with susceptibility to acute O3-induced airways injury and inflammation. Pharmacologic studies suggest that although PMNs were associated with O3-induced hyperreactivity, these cells were not the cause of the effect, and that these two events are not codependent.

Ozone-induced bradycardia and arrhythmia and their relation to sleep-wakefulness in rats

Rats were chronically implanted with electrodes for EEG, EMG and ECG recordings and exposed to 0.1 ppm, 0.2 ppm ozone (O3) or clean air as control for 5 consecutive days. Amounts of wakefulness (W), slow-wave sleep (SWS) and paradoxical sleep (PS) of the O3-exposed rats were not statistically different from respective control values. Compared with control rats, heart rates of the O3-exposed rats decreased and the number of bradyarrhythmic episodes increased with an increase in O3 levels. The O3-induced bradyarrhythmias occurred more prevalently in the order of W, SWS and PS state. Parasympathetic mechanisms were suggested on those cardiac abnormalities.

Biochemical basis of ozone toxicity

Ozone (O3) is the major oxidant of photochemical smog. Its biological effect is attributed to its ability to cause oxidation or peroxidation of biomolecules directly and/or via free radical reactions. A sequence of events may include lipid peroxidation and loss of functional groups of enzymes, alteration of membrane permeability, and cell injury or death. An acute exposure to O3 causes lung injury involving the ciliated cell in the airways and the type 1 epithelial cell in the alveolar region. The effects are particularly localized at the junction of terminal bronchioles and alveolar ducts, as evident from a loss of cells and accumulation of inflammatory cells. In a typical short-term exposure the lung tissue response is biphasic: an initial injury-phase characterized by cell damage and loss of enzyme activities, followed by a repair-phase associated with increased metabolic activities, which coincide with a proliferation of metabolically active cells, for example, the alveolar type 2 cells and the bronchiolar Clara cells. A chronic exposure to O3 can cause or exacerbate lung diseases, including perhaps an increased lung tumor incidence in susceptible animal models. Ozone exposure also causes extrapulmonary effects involving the blood, spleen, central nervous system, and other organs. A combination of O3 and NO2, both of which occur in photochemical smog, can produce effects which may be additive or synergistic. A synergistic lung injury occurs possibly due to a formation of more powerful radicals and chemical intermediates. Dietary antioxidants, for example, vitamin E, vitamin C, and selenium, can offer a protection against O3 effects.

In vivo exposure to hyperoxia increases airway responsiveness in rats. Demonstration in vivo and in vitro

Studies regarding O2-induced lung injury have concentrated on damage to alveolar structures and pulmonary vasculature without consideration of alterations that may be occurring in airways. This study was undertaken to determine the effects of in vivo hyperoxic exposure on airway responses to excitatory stimuli in intact, anesthetized rats and in intrapulmonary bronchi isolated from hyperoxia-exposed rats. Using lung conductance (G1) as an index of bronchoconstriction, intravenously administered 5-hydroxytryptamine (5HT) elicited greater bronchoconstrictor responses in anesthetized, mechanically ventilated rats that had been exposed to 85% O2 for 7 days rather than to air. Further, airways of hyperoxia-exposed rats were more sensitive to the effects of intravenously administered 5HT as evidenced by the lower log dose of 5HT required to decrease G1 30%. Cylindrical segments of intrapulmonary bronchi isolated from hyperoxia-exposed rats were more responsive to the contractile effects of 5HT and electrical field stimulation. However, no differences in responsiveness to bethanechol or KCl were observed between the two groups. The log concentration of 5HT and the log frequency of electrical field stimulation that elicited half-maximal responses were smaller in bronchi isolated from hyperoxia-exposed animals, indicating an increase in sensitivity of the airways to these stimuli. These results suggest that prolonged exposure to greater than ambient levels of O2 can alter airway function; however, the mechanism responsible for these changes remains to be determined.