Cumulative labeling indices in epithelial cell populations of the respiratory tract after exposure to ozone at low concentrations

Ozone effect on the inflammatory and proteomic profile of human macrophages and airway epithelial cells

Ozone (O₃) is one of the most harmful urban pollutants, but its biological mechanisms have not been fully elucidated yet. Human bronchial epithelial cells (HBEpC) and human macrophage cells (differentiated human monocytic cell line) were exposed to O₃ at the concentration of 240 μg/m³ (120 ppb), corresponding to the European Union alert threshold. Cell viability, reactive oxygen species (ROS) production, and pro-inflammatory cytokines release (IL-8 and TNF-α) were evaluated. Results indicated that O₃ exposure increases ROS production in both cell types and enhances cytokines release in macrophages. O₃ stimulated IL-8 and TNF-α in HBEpC when the cells were pretreated with Lipopolysaccharide, used to mimic a pre-existing inflammatory condition. Proteomics analysis revealed that, in HBEpC, O₃ caused the up-regulation of aldo-keto reductase family 1 member B10, a recognized critical protein in lung carcinogenesis. In conclusion, our results show that 120 ppb O₃ can lead to potential damage to human health suggesting the need for a revision of the actual alert levels.

Effects of ozone exposure on human epithelial adenocarcinoma and normal fibroblasts cells

Previous studies show variable ozone cytotoxicity and genotoxicity in cell cultures, laboratory animals and humans directly exposed to tropospheric ozone. The aim of this study was therefore to investigate and compare the cyto and genotoxic effects of ozone using adenocarcinoma human alveolar basal epithelial cells A549 and normal human fibroblasts Hs27. A cell culture chamber with controlled atmosphere (a simulation reactor) was built to inject a flow of 120 ppb of ozone, which is two times the threshold value for the protection of human health, fixed by the EU legislation. Cell proliferation was evaluated by a luminescent cell viability assay while we assessed the genotoxic potential of ozone by the induction of micronuclei as well as evaluating DNA strand breaks by the induction of micronuclei evaluated by means of the cytokinesis-block micronucleus (CBMN) assay as well as evaluating DNA strand breaks by Alkaline Comet Assay (CA) or Comet Assay. A549 cells viability decreases significantly at 24 hours treatment with 120 ppb of O₃ while at 48 hours and 72 hours O₃ treated cells viability doesn’t differ in respect to the control. However a significative decrease of A549 viability is shown at 72 hours vs. 48 hours in both treated and not-treated cells. The viability trend in the Hs27 cells did not show any significant changes in treated samples compared to the control in all conditions. The two genotoxicity biomarkers, the micronucleus and the comet tests, showed in both the cell types exposed to ozone, a significant increase in the number of micronuclei and in the tail DNA % in respect to the control even if at different times/cell type. Moreover, we found that O₃ provokes genotoxic effects more evident in A549 cancer cells than in normal fibroblasts Hs27 ones. We applied a cell growth simulation model referred to ozone treated or not cell lines to confirm that the ozone exposure causes a slackening in the cells replication.

Alveolar epithelial cells secrete chemokines in response to IL-1beta and lipopolysaccharide but not to ozone

Ozone exposure produces acute inflammation and neutrophil influx in the distal lung. Alveolar epithelial cells cover a large surface area, secrete chemokines, and may initiate or modify the inflammatory response. The effect of ozone on chemokine production by these cells has not been defined. Isolated rat type II cells were cultured in different conditions to express the morphologic appearance and biochemical markers for the type I and the type II cell phenotypes. These cells were exposed to ozone at an air/liquid interface. The type I-like cells were more susceptible to injury than the type II cells and showed signs of injury at exposure levels of 100 ppb ozone for 60 min. Both phenotypes showed evidence of lipid peroxidation after ozone exposure as measured by 8-isoprostane production, but neither phenotype secreted increased amounts of MIP-2 (CXCL3), CINC-1 (CXCL1), or MCP-1 (CCL2) in response to ozone. Both cell phenotypes secreted MIP-2 and MCP-1 in response to IL-1beta or lipopolysaccharide, but there was no priming or synergy with ozone. It is likely that the inflammatory response to ozone in the alveolar compartment is not due to the direct effect of ozone on epithelial cells.

Nasal epithelial and inflammatory response to ozone exposure: a review of laboratory-based studies published since 1985

This article summarizes biological events in human and animal nasal epithelium after short- and long-term exposure to ozone, the principal agent in photochemical smog. Despite anatomical and histological interspecies differences, ozone exposures resulted in common nasal qualitative alterations with an anterior-posterior gradient of phenomena occurring immediately, and with a lag time postexposure: epithelial disruption and increased permeability, inflammatory cell influx, and proliferative and secretory responses. Described mechanisms of toxicity included a direct effect of ozone on epithelial lining fluid and cellular membranes and the subsequent release of cytokines and cyclooxygenase and lipoxygenase products. An indirect effect of ozone was indicated by a decreased mucociliary clearance, free radicals production interacting with a gene promoting factor, and increased DNA synthesis. Studies highlighted the pivotal role of activated neutrophils and mast cells leading to the release of deleterious enzymes (tryptase, eosinophil cationic protein) and numerous cytokines. Experiments performed with ozone exposure/allergen challenge reported that, besides the intrinsic deleterious properties of ozone, it also had a priming effect on the late-phase response to allergen challenge, providing new insights into the pathophysiology of respiratory allergic diseases.

The relationship between alveolar epithelial proliferation and airway obstruction after ozone exposure

BACKGROUND

Proliferating cell nuclear antigen (PCNA) is a component of multiprotein complexes that are expressed during cell proliferation. Ozone induces cell necrosis and a consequent increase in cell proliferation.

METHODS

To investigate the effects of acute ozone inhalation on cell proliferation and airway obstruction in BALB/C mice, we examined enhanced pause (Penh) as an index of airway obstruction and PCNA expression by immunohistochemical staining.

RESULTS

Compared with controls that received filtered air, the ozone-exposed groups had increased PCNA expression in the alveolar epithelial cells. In rank order, the highest PCNA index was found following 2.0 p.p.m. ozone exposure. In the 2.0 p.p.m. ozone group, there was a PCNA index of 16.83 +/- 0.57% (mean +/- SEM; P< 0.01), compared with 4.25 +/- 0.5% at 0.12 p.p.m., 6.83 +/- 0.60 at 0.5 p.p.m and 12.16 +/- 0.48% at 1 p.p.m. Following ozone exposure, Penh was increased in a dose-dependent manner. There was a significant correlation between the PCNA index in alveoli and Penh (r = 0.63, P< 0.01).

CONCLUSIONS

These data suggest that ozone can induce alveolar epithelial cell proliferation in a dose-dependent manner, and that alveolar epithelial cell proliferation is correlated with airway obstruction.

Cell-specific loss of cytochrome P450 2B1 in rat lung following treatment with pneumotoxic and non-pneumotoxic trialkylphosphorothioates

This study was designed to test the hypothesis that the reduction in cytochrome P450 (CYP) 2B1 content and activity of rat lung microsomes, following dosing with pneumotoxic trimethylphosphorothioates, results from damage to specific cell types. Of the lung cells exhibiting immunolabelling for CYP2B1, only type I cells showed signs of susceptibility to the pneumotoxins O,O.S-trimethylphosphorothioate and O,S,S-trimethylphosphorodithioate. While most type I cells became necrotic, type II and Clara cells showed no signs of injury, despite their gradual loss of CYP2B1, as detected by immunogold labelling. This loss of labelling was accompanied by a 75% reduction in the immunoreactive CYP2B1 content and an 85% reduction in pentoxyresorufin O-dealkylase activity in lung microsomes. In contrast, the non-pneumotoxic analogue O,O,S-trimethylphosphorodithioate, differing from O,O,S-trimethylphosphorothioate by only the presence of a P = S rather than a P = O moiety, caused an even more rapid fall in pulmonary pentoxyresorufin O-dealkylase activity, but only a slight reduction in the microsomal content of CYP2B1. The recovery of this activity began within 12 hr of dosing. O,O,S-Trimethylphosphorodithioate, which acts as a suicidal inhibitor of pulmonary CYP2B1, did not cause any detectable lung injury or increase in cell division. These results are consistent with the initial reduction in both enzyme content and activity caused by the P = O - containing pneumotoxins resulting, almost entirely, from death of type I cells. Subsequent reductions that occur long after clearance of the toxin may be exacerbated by the onset of mitosis in Clara and type II cells.

Cell proliferation in nasal respiratory epithelium of people exposed to urban pollution

The nasal passages are a common portal of entry and are a prime site for toxicant-induced pathology. Sustained increases in regenerative cell proliferation can be a significant driving force in chemical carcinogenesis. The atmosphere in Mexico City contains a complex mixture of air pollutants and its residents are exposed chronically and sequentially to numerous toxicants and potential carcinogens. We were concerned that exposure to Mexico City's atmosphere might induce cytotoxicity and increase nasal respiratory epithelial cell proliferation. Nasal biopsies were obtained for DNA cell cycle analysis from 195 volunteers. The control population consisted of 16 adults and 27 children that were residents in a Caribbean island with low pollution. The exposed Mexico City population consisted of 109 adults and 43 children. Sixty-one of the adult subjects were newly arrived in Mexico City and were followed for 25 days from their arrival. Control children, control adult and exposed Mexico City children all had similar percentages of cells in the replicative DNA synthesis phase (S phase) of the cell cycle (%S). A significant increase in %S in nasal epithelial cells was seen in exposed adult residents in Mexico City biopsied at three different dates compared with control adults. Newly arrived adults exhibited a control level of cell turnover at day 2 after coming to the city. However, at days 7, 14 and 25 they exhibited significant increases in %S. These data demonstrate an increased and sustained nasal cell turnover rate in the adult population observable in as little as 1 week of residence in Mexico City. This increase in cell proliferation is in agreement with other reports of induced pathological changes in the nasal passages of Mexico City dwellers. These observations suggest an increased potential risk factor of developing nasal neoplasms for residents of large cities with heavy pollution.

Proliferation of airway epithelium after ozone exposure: effect of apocynin and dexamethasone

Ozone is an environmental pollutant with potent oxidizing properties. We investigated whether exposure to ozone-induced cell proliferation in the lungs of rats, and determined the effect of an antioxidant and of a glucocorticosteroid in Brown-Norway (BN) rats. Following single ozone exposure (0.5, 1.0, or 3.0 ppm for 6 h), proliferating cell nuclear antigen (PCNA) expression, as determined with immunohistochemistry, was significantly increased in the bronchial epithelium and alveolar epithelium as compared with controls exposed to filtered air with a maximal effect at 24 to 48 h (p < 0.001). Apocynin (5 mg/kg, orally), a reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, reduced the PCNA index in bronchial epithelium induced by ozone (3 ppm, 6 h) from 11.5 +/- 1.3% (percent of nuclear cells expressing PCNA) to 4.4 +/- 1.3% (mean +/- SEM; p < 0.05). Dexamethasone (3 mg/kg, intraperitoneally) also reduced the PCNA index in bronchial epithelium, from 19.2 +/- 2.3% to 10.9 +/- 2.6% (p < 0.05). Dexamethasone but not apocynin inhibited ozone-induced neutrophil influx. Rats exposed repeatedly to ozone (3.0 ppm, 3 h, on three occasions 48 h apart) expressed a lower PCNA index in bronchial epithelium than did rats exposed only once at 1.9 +/- 0.7% versus 6.0 +/- 0.9%, respectively (p < 0.05). The proliferative epithelial response following a single exposure to ozone is modulated through oxidative and inflammatory mechanisms probably involving neutrophils.

Comparison of acute hepatocellular proliferating cell nuclear antigen labeling indices and growth fractions, p34cdc2 kinases, and serum enzymes in carbon tetrachloride-treated rats

We evaluated various biomarkers associated with cell proliferation immediately following insult with the classic hepatotoxicant carbon tetrachloride (CCl4). Rats were administered a single necrogenic dose of CCl4 and euthanized at either t = 4, 8, 12, 16, or 24 hr postdose. Parameters evaluated included the following: immunohistochemical detection of hepatocellular proliferating cell nuclear antigen labeling indices (PCNA-LIs; percentage of cells in S phase) and growth fractions (PCNA-GFs; percentage of cells in the cell cycle); PCNA and the cyclin-dependent kinase p34cdc2 (CDK) protein in S-9 fractions by Western blot and enzyme-linked immunosorbent assay (ELISA); and liver-related serum enzymes. An increase in PCNA-GF was observed at t = 4 hr, concomitant with elevations in CDK and PCNA protein (Western blot). PCNA-LIs were increased by t = 24 hr, as were CDK and PCNA by ELISA. Sorbitol dehydrogenase was the most sensitive enzyme, with increases observed at t = 4 hr. Our results indicate that PCNA-GF, CDK, and PCNA levels reflect hepatocellular regeneration as early as 4 hr following CCl4 insult. We conclude that these assays are early and sensitive indicators of acute hepatotoxicity that may be advantageous to evaluate in the early stages of exploratory studies.