Combined effects of ozone and cigarette smoke on airway responsiveness and vascular permeability in guinea pigs

The association between outdoor air pollution and body mass index, central obesity, and visceral adiposity index among middle-aged and elderly adults: a nationwide study in China

Background

Previous animal studies have suggested that air pollution (AP) exposure may be a potential risk factor for obesity; however, there is limited epidemiological evidence available to describe the association of obesity with AP exposure.

Methods

A retrospective cross-sectional study was conducted on 11,766 participants across mainland China in 2015. Obesity was assessed using body mass index (BMI), waist circumference (WC), and visceral adiposity index (VAI). The space-time extremely randomized tree (STET) model was used to estimate the concentration of air pollutants, including SO2, NO2, O3, PM1, PM2.5, and PM10, matched to participants' residential addresses. Logistic regression models were employed to estimate the associations of obesity with outdoor AP exposure. Further stratified analysis was conducted to evaluate whether sociodemographics or lifestyles modified the effects.

Results

Increased AP exposure was statistically associated with increased odds of obesity. The odds ratio (ORs) and 95% confidence interval (CI) of BMI-defined obesity were 1.21 (1.17, 1.26) for SO2, 1.33 (1.26, 1.40) for NO2, 1.15 (1.10, 1.21) for O3, 1.38 (1.29, 1.48) for PM1, 1.19 (1.15, 1.22) for PM2.5, and 1.11 (1.09, 1.13) for PM10 per 10 μg/m3 increase in concentration. Similar results were found for central obesity. Stratified analyses suggested that elderly participants experienced more adverse effects from all 6 air pollutants than middle-aged participants. Furthermore, notable multiplicative interactions were found between O3 exposure and females as well as second-hand smokers in BMI-defined obesity.

Conclusions

This study suggested that outdoor AP exposure had a significant association with the risk of obesity in the middle-aged and elderly Chinese population. Elderly individuals and women may be more vulnerable to AP exposure.

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.

Airway reactivity following repeated milk aspiration in rabbits

Asthma and gastroesophageal reflux (GER) are commonly associated disorders. Microaspiration is one possible link between these processes. The purpose of this study was to assess methacholine reactivity following repeated small-volume aspiration such as may occur with GER. This was also correlated with airway cytology. Five weekly intratracheal instillations of either milk (N = 8) or saline sham controls (N = 7) in volumes of 0.25 mL/kg were performed in anesthetized rabbits. Transpulmonary pressure, flow, tidal volume, central airways resistance, and dynamic lung compliance were measured in anesthetized and paralyzed animals at baseline, after 2 and 5 weeks of instillation, and 3 weeks after the last instillation. Doubling concentrations of methacholine were given until a 50% or greater increase in resistance occurred (PC50R). Bronchial washings for cytological evaluation were performed after the physiologic measurements and before each instillation. There were no significant differences in airway reactivity between baseline and all subsequent observation points within each of the two groups. However, methacholine responsiveness was significantly higher in the milk group before the final instillation (PC50R = 5.84 vs. 12.97 mg/mL, P = 0.03) and at recovery (PC50R = 6.40 vs. 10.56 mg/mL, P = 0.047) when compared to saline controls. This was associated with a higher neutrophil percentage (P = 0.01) at 5 weeks, and eosinophil percentage (P = 0.05) at recovery in the bronchial wash specimens from the milk group. These results show that repeated small-volume aspiration of milk in rabbits causes persistent inflammation and is associated with greater airway reactivity when compared to sham controls. This inflammation was accompanied by either increased neutrophils or eosinophils in bronchial lavage specimens. These findings lend support to a possible role of microaspiration in association with increased airway reactivity in patients with GER.

Superoxide mediates cigarette smoke-induced infiltration of neutrophils into the airways through nuclear factor-kappaB activation and IL-8 mRNA expression in guinea pigs in vivo

We examined the hypothesis that superoxide mediates infiltration of neutrophils to the airways through nuclear factor (NF)-kappaB and interleukin-8 (IL-8) after acute exposure to cigarette smoke (CS) in vivo. Male Hartley strain guinea pigs were exposed to air or 20 puffs of CS and killed 5 h after the exposure. The differential cell count of bronchoalveolar lavage fluid and specific myeloperoxidase enzyme assay demonstrated that acute exposure to CS caused neutrophil accumulation to the airways and parenchyma, respectively. Acute exposure to CS increased DNA-binding activity of NF-kappaB in the lung. Acute exposure to CS also increased IL-8 messenger RNA (mRNA) expression in the lung. Pretreatment of guinea pigs with recombinant human superoxide dismutase (rhSOD) aerosols reduced the CS-induced neutrophil accumulation to the airways. Both activation of NF-kappaB and increased IL-8 mRNA expression were also inhibited by the pretreatment of rhSOD aerosols. Strong immunoreactivities for p65 and p50 were detected in the nuclei of alveolar macrophages after acute exposure to CS. The signal for IL-8 mRNA expression was demonstrated in the alveolar space after acute exposure to CS. Neither significant immunoreactivities for p65 and p50 nor IL-8 mRNA signals were observed in airway epithelium. These observations suggest that acute exposure to CS initiates superoxide-dependent mechanism that, through NF-kappaB activation and IL-8 mRNA expression, produces infiltration of neutrophils to the airways in vivo. It was also suggested that the alveolar macrophage is one potential source of NF-kappaB activation and IL-8 mRNA expression after acute exposure to CS.

Guinea pig lung resistance shows circadian rhythmicity not influenced by ozone

Increased circadian variability of airway caliber is a key feature of asthmatic patients, but it has not been addressed in animal models of asthma. Furthermore, animal studies on circadian rhythmicity of airway resistance are very scanty. We used a plethysmographic method for unrestrained guinea pigs to monitor a lung resistance index (iRL) during 24 h. We found circadian variability of iRL values, which were fitted by a sinusoidal curve. Acrophase and bathyphase, characterizing the timing of narrowest and widest airway caliber, respectively, were found at 02:03, and 15:34 h. iRL values at these time-points were statistically different (P < 10(-5)). Moreover, average resistance during the dark period was significantly higher (P < 0.0001) than during the light period. Immediately after an acute ozone exposure (3 ppm for 1 h) an increase in iRL was demonstrated (P < 0.01), which lasted for 2 h, and tended to remain high for the next hour. After guinea pigs recovered from this obstruction, the circadian rhythm and variability of airway caliber were unaffected. Our results show that a circadian rhythm of iRL takes place in guinea pigs, greatly resembling what occurs in humans, and that ozone exposure causes a transient airway obstruction, but fails to reproduce the increased variability of airway caliber observed in asthmatic patients.

Interaction of ozone exposure with airway hyperresponsiveness and inflammation induced by trimellitic anhydride in sensitized guinea pigs

The effect of prior ozone (O3) exposure on airway hyperresponsiveness and inflammation induced by trimellitic anhydride (TMA) has been investigated in TMA-sensitized guinea pigs. Airway responsiveness was measured as the concentration of acetylcholine needed to increase baseline lung resistance (RL) by 300% (PC300). Ozone (3 ppm for 3 h) caused an increase in -log PC300 at 1 h after exposure, with return of -log PC300 to control levels at 8 h. Ozone also increased baseline RL at 8 h. TMA challenge increase -log PC300 in TMA-sensitized guinea pigs at 8 h after challenge from 3.85 +/- 0.09 to 4.11 +/- 0.09. Ozone exposure prior to TMA challenge prevented the induction of airway hyperresponsiveness with a mean -log PC300 of 3.51 +/- 0.20, which was not different from that of control TMA-sensitized group. Baseline RL was significantly higher in ozone-pretreated animals after TMA challenge when compared to those of either control or challenged with TMA alone. Ozone had no effect on TMA challenge-induced BAL eosinophilia and neutrophilia. We conclude that a single exposure to ozone inhibits the increase in airway responsiveness but increases the bronchoconstrictor response induced by TMA in TMA-sensitized guinea pigs; however, the inflammatory airway response to TMA is unchanged by preexposure to ozone.

Airway inflammation despite loss of bronchial hyper-responsiveness after multiple ozone exposures

The effect of single and multiple exposures to ozone (O3) on airway responsiveness and inflammation was examined in guinea pigs. Airway responsiveness, measured as acetylcholine concentration needed to increase baseline airway resistance (RL) by 250% (PC250), increased 1 h after exposure to ozone at 3 ppm for 3 h (-log PC250 from 3.88 +/- 0.17 to 4.78 +/- 0.18; P < 0.05), but returned to baseline at 8 h. An increase in neutrophil numbers was found at 8 h in bronchoalveolar lavage fluid (BALF). After O3 exposure on 4 successive days, baseline RL increased and airway responsiveness decreased at 1, 8 and 72 h (-log PC250 = 2.88 +/- 0.17, 2.83 +/- 0.10 and 3.12 +/- 0.08, respectively, compared to control value of 3.48 +/- 0.05). Repeated exposures to O3 also increased neutrophil numbers in bronchoalveolar lavage fluid and in bronchial submucosa. Thus, single exposure to O3 caused a rapid and transient increase in airway responsiveness, while multiple exposures induced a rapid but prolonged decrease in airway responsiveness associated with persistent bronchoconstriction. Both single and multiple exposures induced airway inflammation as evidenced by an increase in neutrophil influx. These studies demonstrated a dissociation between ozone-induced changes in airway responsiveness and neutrophil influx, and indicate that multiple exposures to O3 induce persistent bronchoconstriction with airway hyporesponsiveness.

Involvement of superoxide anions in ozone-induced airway hyperresponsiveness in unanesthetized guinea pigs

To evaluate the involvement of superoxide in ozone (O(3))-induced airway hyperresponsiveness, we studied the effects of superoxide dismutase (SOD), a scavenger of superoxide anion, and apocynin, an inhibitor of superoxide anion-generating NADPH oxidase in phagocytes, on the airway responses induced by O(3) in unanesthetized guinea pigs. Airway responsiveness was measured by PC(200)Mch, the concentration required to produce a doubling in the baseline specific airway resistance to an inhaled methacholine aerosol, in spontaneously breathing animals. Before exposure to 3 ppm O(3) for 30 min, animals inhaled either SOD (5000 U/ml) or vehicle for 5 min. Although SOD did not affect PC(200)Mch in the air control group, this agent reduced the O(3)-induced airway hyperresponsiveness. Repeated administration of apocynin (12 mg/kg for 4 days) also attenuated the O(3)-induced airway hyperresponsiveness. These data suggest that superoxide may be involved in the pathogenesis of O(3)-induced airway hyperresponsiveness, possibly through the stimulation of superoxide anions release from bronchoalveolar phagocytes. The data also suggest a potential therapeutic role for antioxidants in oxidant injury by air pollutants.

Effect of ozone exposure on antigen-induced airway hyperresponsiveness in guinea pigs

Airway hyperresponsiveness can be induced by several stimuli including antigen and ozone, both of which may be present in the air of polluted cities. Though the effect of ozone on the bronchoconstrictor response to antigen has been well described, the combined effect of these stimuli on airway hyperresponsiveness has not yet been studied. Sensitized guinea pigs with or without ozone exposure for 1 h at 3 ppm, 18 h prior to study, were challenged with a dose-response curve to histamine (0.01-1.8 micrograms/kg, iv) followed by an antigen challenge (ovalbumin, 50 micrograms/kg, iv), and then by a second histamine dose-response curve 1 h later. Airway responses were measured as the increase in pulmonary insufflation pressure. In sensitized guinea pigs, the histamine ED50 significantly decreased after antigen challenge, demonstrating the development of airway hyperresponsiveness. Sensitized guinea pigs exposed to ozone showed airway hyperresponsiveness to histamine when compared with nonexposed animals, and such hyperresponsiveness was further enhanced after antigen challenge. We conclude that in this guinea pig model of acute allergic bronchoconstriction both antigen challenge and ozone induce airway hyperresponsiveness, while ozone exposure does not modify the development of antigen-induced hyperresponsiveness.