Early Response of the Canine Respiratory Tract Following Long-Term Exposure to a Sulfur(IV) Aerosol at Low Concentration. IV. Respiratory Lung Function

Air pollution enhance the progression of restrictive lung function impairment and diffusion capacity reduction: an elderly cohort study

BACKGROUND

Some evidences have shown the association between air pollution exposure and the development of interstitial lung diseases. However, the effect of air pollution on the progression of restrictive ventilatory impairment and diffusion capacity reduction is unknown. This study aimed to evaluate the effects of long-term exposure to ambient air pollution on the change rates of total lung capacity, residual volume, and diffusion capacity among the elderly.

METHODS

From 2016 to 2018, single-breath helium dilution with the diffusion capacity of carbon monoxide was performed once per year on 543 elderly individuals. Monthly concentrations of ambient fine particulate matters (PM_2.5) and nitric dioxide (NO₂) at the individual residential address were estimated using a hybrid Kriging/Land-use regression model. Linear mixed models were used to evaluate the association between long-term (12 months) exposure to air pollution and lung function with adjustment for potential covariates, including basic characteristics, indoor air pollution (second-hand smoke, cooking fume, and incense burning), physician diagnosed diseases (asthma and chronic airway diseases), dusty job history, and short-term (lag one month) air pollution exposure.

RESULTS

An interquartile range (5.37 ppb) increase in long-term exposure to NO₂ was associated with an additional rate of decline in total lung volume (- 1.8% per year, 95% CI: - 2.8 to - 0.9%), residual volume (- 3.3% per year, 95% CI: - 5.0 to - 1.6%), ratio of residual volume to total lung volume (- 1.6% per year, 95% CI: - 2.6 to - 0.5%), and diffusion capacity (- 1.1% per year, 95% CI: - 2.0 to - 0.2%). There is no effect on the transfer factor (ratio of diffusion capacity to alveolar volume). The effect of NO₂ remained robust after adjustment for PM_2.5 exposure.

CONCLUSIONS

Long-term exposure to ambient NO₂ is associated with an accelerated decline in static lung volume and diffusion capacity in the elderly. NO₂ related air pollution may be a risk factor for restrictive lung disorders.

Sulfur-related air pollutants induce the generation of platelet-activating factor, 5-lipoxygenase- and cyclooxygenase-products in canine alveolar macrophages via activation of phospholipases A2

Recent studies have shown that long-term in vivo exposure of dogs to neutral sulfur(IV)/sulfite aerosols induces mild inflammatory reactions, whereas the combination of neutral sulfite with acidic sulfur(VI)/sulfate aerosols evokes less pronounced effects. To understand underlying mechanisms, we studied in vitro the role of lipid mediators in the responses of alveolar macrophages (AMs) to sulfur-related compounds under neutral (pH 7) or moderate acidic (pH 6) conditions. Canine AMs incubated with sulfite at pH 7 released threefold higher amounts of platelet-activating factor than control (P < 0.005). Generation of arachidonic acid, leukotriene B4, 5-hydroxy-eicosatetraenoic acid, prostaglandin E2, thromboxane B2 and 12-hydroxyheptadecatrienoic acid increased twofold (P < 0.0005). However, these metabolites remained unchanged following incubation of AMs with sulfite at pH 6 or with sulfate at pH 7 or pH 6. Mediator release by sulfite-treated AMs at pH 7 stimulated respiratory burst activity of neutrophils. Inhibition of MAPK pathway by PD 98059, of cytosolic (cPLA2) and secretory phospholipases A2 by AACOCF3 and thioetheramide-PC, respectively, reduced sulfite-induced eicosanoid formation in AMs. Sulfite activated cPLA2 activity twofold at pH 7. This mechanism of sulfite-stimulated responses in phospholipid metabolism predicts that chronic exposure to sulfur(IV)/sulfite is associated with a considerable health risk.

Respiratory mechanics in mice: strain and sex specific differences

To assess the contribution of genetic background to respiratory mechanics, we developed a ventilator unit to measure lung function parameters in the mouse. We studied two commonly used inbred mice strains originating from Mus musculus domesticus (C57BL/6 and C3HeB/FeJ) and a third strain derived from Mus musculus molossinus [Japanese fancy mouse 1 (JF1)]. The ventilator allows for accurate performance of the different breathing manoeuvres required for measuring in- and expiratory reserve capacity, quasi-static and dynamic compliance, and airway resistance. In combination with a mass spectrometer for monitoring gas concentrations, single-breath manoeuvres were performed and He-expirograms obtained, from which dead space volume and slope of phase III were determined. From each strain and each sex, 10, 2-month old animals were studied immediately after being killed by an intraperitoneal overdose of xylazine and ketamine. C3HeB/FeJ and C57BL/6 exhibited comparable lung volumes. In male C3HeB/FeJ mice, e.g. vital capacity (VC) was 1072 +/- 79 microL, inspiratory reserve capacity 782 +/- 88 microL, and dead space volume at total lung inflation 216 +/- 18 microL. Lung volumes of JF1 were significantly lower (e.g. VC 611 +/- 53 microL, P < 0.01) even when normalized to body weight. In all three strains, specific lung volumes were significantly higher in females than in males, possibly explained by a higher oxygen demand during pregnancy and lactation, both of which fill most of their life times. Static compliance in C3HeB/FeJ was 64.3 +/- 5.4 microL cmH2O-1. It was smaller in C57BL/6 and JF1 mice, even when related to the lung volume. Analysis of the degree of genetic vs. non-genetic components of the phenotypic variation revealed that at least 80% of the total variation of lung volumes and static compliance in the mixed population is attributable to genetic differences between individuals. These differences will be verified in further studies by segregation and genetic linkage analysis.

Health effects of sulfur-related environmental air pollution. III. Nonspecific respiratory defense capacities

Recently concern has been raised about health effects related to environmental sulfur and/or acidic aerosols. To assess long-term effects on respiratory lung function, 8 beagle dogs were exposed over a period of 13 mo for 16.5 h/day to 1.0 microm neutral sulfite aerosol with a particle associated sulfur(IV) concentration of 0.32 mg m(-3) and for 6 h/day to 1.1 microm acidic sulfate aerosol providing an hydrogen ion concentration of 15.2 micromol m(-3) for inhalation. Prior to exposure the dogs were kept under clean air conditions for 16 mo to establish physiological baseline values for each dog. A second group of eight dogs (control) was kept for the entire study under clean air conditions. Nonspecific defense mechanisms in the airways and in the peripheral lung were studied during chronic exposure of the combination of neutral sulfur(IV) and acidic sulfur(VI) aerosols. No functional changes of tracheal mucus velocity were found, in agreement with unchanged morphometry of the airways. However, the exposure resulted in changes of several alveolar macrophage (AM) mediated particle clearance mechanisms: (1) Based on in vivo clearance analysis and cultured AM studies using moderately soluble cobalt oxide particles, intracellular particle dissolution was significantly reduced since phagolysosomal proton concentration was decreased. We deduce exposure-related malfunction of proton pumps bound to the phagolysosomal membrane as a result of an increase of cytosolic proton concentration. (2) Based on in vivo clearance analysis using insoluble polystyrene particles, AM-mediated particle transport from the lung periphery toward ciliated terminal bronchioli and further to the larynx was significantly reduced. Activation of epithelial type II cells at the entrance of alveoli was inferred from observed type II cell proliferation at those alveolar ridges and enhanced secretion of alkaline phosphatase in the fluid of bronchoalveolar lavages. As a result, hypersecretion of chemotactic mediators by activated type II cells at these loci led to the observed decrease of particle transport toward ciliated bronchioli. (3) Based on in vivo clearance analysis using insoluble polystyrene particles, particle transport from the alveolar epithelium into interstitial tissues was increased and (4) particle transport to the tracheobronchial lymph nodes was significantly enhanced. Particle transport into interstitial tissues is the most prominent clearance pathway from the canine alveolar epithelium. We conclude that the deteriorated particle transport toward ciliated terminal bronchioli resulted in an enhanced particle transport across the epithelial membrane into interstitial tissues and the lymphatic drainage. The observed alterations in alveolar macrophage-mediated clearance mechanisms during chronic exposure of these air pollutants indicate an increased risk of health.

Health effects of sulfur-related environmental air pollution. IV. Respiratory lung function

Recently concern has been raised about health effects related to environmental sulfur and/or acidic aerosols. To assess long-term effects on respiratory lung function, 8 beagle dogs were exposed over a period of 13 mo for 16.5 h/day to 1-microm neutral sulfite aerosol with a particle-associated sulfur(IV) concentration of 0.32 mg m(-3) and for 6 h/day to 1.1-microm acidic sulfate aerosol providing an hydrogen ion concentration of 15.2 micromol m(-3) for inhalation. Prior to exposure the dogs were kept under clean air conditions for 16 mo to establish physiological baseline values for each dog. A second group of eight dogs (control) was kept for the entire study under clean air conditions. Before and at the end of exposure, respiratory lung function was evaluated in both groups in anesthetized and mechanically ventilated animals. Lung volumes as well as static and dynamic lung compliances were measured. Series dead-space volumes and slopes of the alveolar plateau for respiratory (O2, CO2) and inert test gases (He, SF6) were determined from single-breath washout tracings. Monodisperse 0.9-microm DEHS droplets were used to assess convective mixing in the lungs and to evaluate airway dimensions in vivo. Gas exchange across the alveolar-capillary layer was characterized by membrane diffusing capacity for carbon monoxide and alveolar-arterial pressure differences for respiratory gases. A bronchial challenge with carbachol was used to assess airway responsiveness. In comparison to the control group, dogs exposed to sulfur(IV) and acidic aerosol exhibited no significant changes in any respiratory lung function parameter. Also the responsiveness of the bronchial airways to carbachol was not affected. In view of the results obtained in this and previous studies, we conclude that anticipated synergistic effects of the two air pollutants on pulmonary lung function were not observed. It is hypothesized that antagonistic effects of the air pollutants on the activity of phospholipase A2 play an important role and account for counteracting physiological compensatory mechanisms. The results emphasize the complexity of health effects on lung function in response to the complex mixtures of ambient air pollutants and witness the precariousness in the risk assessment of air pollutants for humans.

Health effects of sulfur-related environmental air pollution. II. Cellular and molecular parameters of injury

Recently, concern has been raised about effects related to environmental sulfur and/or acidic aerosols. To assess long-term effects on nonrespiratory lung function, 8 beagle dogs were exposed over a period of 13 mo for 16.5 h/day to a neutral sulfite aerosol at a sulfur(IV) concentration of 0.32 mg m(-3) and for 6 h/day to an acidic sulfate aerosol providing a hydrogen concentration of 15.2 micromol m(-3) for inhalation. Prior to exposure the dogs were kept under clean air conditions for 16 mo to establish physiological baseline values for each animal. A second group of eight dogs (control) was kept for the entire study under clean air conditions. No clinical symptoms were identified that could be related to the combined exposure. Biochemical and cellular parameters were analyzed in sequential bronchoalveolar lavage (BAL) fluids. The permeability of the alveolo-capillary membrane and diethylenetriaminepentaacetic acid (DTPA) clearance was not affected. Similarly, oxidant burden of the epithelial lining fluid evaluated by levels of oxidation products in the BAL fluid protein fraction remained unchanged. Both the lysosomal enzyme beta-N-acetylglucosaminidase and the alpha-1-AT were increased (p <.05). In contrast, the cytoplasmic marker lactate dehydrogenase remained unchanged, indicating the absence of severe damages to epithelial cells or phagocytes. Various surfactant functions were not altered during exposure. Three animals showed elevated levels of the type II cell-associated alkaline phosphatase (AP), indicating a nonuniform response of type II cells. Significant correlations were found between AP and total BAL protein, but not between AP and lactate dehydrogenase, suggesting proliferation of alveolar type II cells. Absolute and relative cell counts in the BAL fluid were not influenced by exposure. Alveolar macrophages showed no alterations with regard to their respiratory burst upon stimulation with opsonized zymosan. The percentage of alveolar macrophages capable of phagocytozing latex particles was significantly decreased (p<.05), while the phagocytosis index was not altered. In view of the results of this and previous studies, we conclude that there is no synergism of effects of these two air pollutants on nonrespiratory lung functions. It is hypothesized that antagonistic effects of these air pollutants on phospholipase A2-dependent pathways account for compensatory physiological mechanisms. The results emphasize the complexity of health effects on lung functions in response to the complex mixture of air pollutants and disclose the precariousness in the risk assessment of air pollutants for humans.

Influence of intrinsic particle properties on the assessment of convective gas transport by aerosol bolus technique

Aerosol bolus measurements are increasingly being used in patients and healthy subjects to assess convective gas transport and mixing in the lungs. To investigate the extent to which intrinsic particle properties confound parameters derived for the assessment of intrapulmonary transport, bolus inhalation experiments were performed in six anesthetized, intubated, and mechanically ventilated beagle dogs using DEHS particles of 0.5, 1, or 2 microns diameter. Therefore, particle displacement by diffusion varied by a factor of two, settling velocity by a factor of 13, and particle inertia as inferred from the stopping distance by a factor of 16. By using a standardized breathing maneuver 6-mL boluses were inhaled into lung depths between 75 and 475 mL. Mode, half-width, and intrapulmonary particle deposition along with mean, standard deviation, and skewness of the particle concentration distributions in the expired air were determined. For all particle sizes studied particle deposition increased with increasing lung depth not exceeding 25% for 0.5-micron particles, but being 80% in deep lung regions for 2-micron particles. Whereas half-width and standard deviation exhibited only small differences between particle sizes (less than 20%), mode and mean of the exhaled bolus were clearly dependent on particle size, in particular for particles inhaled deep into the lung. No significant effects were detectable for the skewness. Hence, convective mixing assessed by half-width or standard deviation is only slightly dependent on particle size, but the estimate of convective bulk transport as inferred from the mean volume from which the bolus is exhaled is highly dependent on particle size. Yet, the intrinsic mobility of unit-density 0.5-micron particles was found to be small enough to consider these particles as ideal tracers for probing convective gas transport in the lungs.