Airway epithelial cell responses to ozone injury

The airway epithelial cells is an important target in ozone injury. Once activated, the airway epithelium responds in three phases. The initial, or immediate phase, involves activation of constitutive cells, often through direct covalent interactions including the formation of secondary ozonolysis products--hydroxyhydroperoxides, aldehydes, and hydrogen peroxide. Recently, we found hydroxyhydroperoxides to be potent agonists of bioactive eicosanoid formation by human airway epithelial cells in culture. Other probable immediate events include activation and inactivation of enzymes present on the epithelial surface (e.g., neutral endopeptidase). During the next 2 to 24 hr, or early phase, epithelial cells respond by synthesis and release of chemotactic factors, including chemokines--macrophage inflammatory protein-2, RANTES, and interleukin-8. Infiltrating leukocytes during this period also release elastase, an important agonist of epithelial cell mucus secretion and additional chemokine formation. The third (late) phase of ozone injury is characterized by eosinophil or monocyte infiltration. Cytokine expression leads to alteration of structural protein synthesis, with increases in fibronectin evident by in situ hybridization. Synthesis of epithelial antiproteases, e.g., secretory leukocyte protease inhibitor, may also increase locally 24 to 48 hr after elastase concentrations become excessive. Thus, the epithelium is not merely a passive barrier to ozone injury but has a dynamic role in directing the migration, activating, and then counteracting inflammatory cells. Through these complex interactions, epithelial cells can be viewed as the initiators (alpha) and the receptors (omega) of ozone-induced airway disease.

Refractory ceramic fibers activate alveolar macrophage eicosanoid and cytokine release

Refractory ceramic fiber has been developed for industrial processes requiring materials with high thermal and mechanical stability. To evaluate the biological activity of this fiber, rat alveolar macrophages were exposed for < or = 24 h to 0-1,000 micrograms/ml of refractory ceramic fiber, crocidolite asbestos, silica (fibrogenic particles), or titanium dioxide (a nonfibrogenic particle), and eicosanoid, tumor necrosis factor-alpha (TNF), and lactate dehydrogenase release were measured. Particle dimensions were determined by electron microscopy. Radioactivity coeluting with leukotriene B4 (LTB4) and immunoreactive LTB4 and TNF release increased after refractory ceramic fiber and were similar in magnitude after asbestos but less than after silica. For example, the total [3H]eicosanoid release increased 3.9-fold after refractory ceramic fiber, 4.6-fold after asbestos, and 8.7-fold after silica. Refractory ceramic fiber and asbestos also have similar particle dimensions (diameter, length, and surface area). Inasmuch as macrophage-derived LTB4 and TNF are potent mediators in inflammatory events, including migration and activation of neutrophils, these findings suggest that refractory ceramic fiber can activate macrophages in vitro to release mediators relevant to in vivo findings of inflammation and fibrotic lung disease in laboratory animals.

Tyrosine kinase inhibition prevents deformation-stimulated vascular smooth muscle growth

The goal of this study was to determine the role of tyrosine phosphorylation in transducing deformation-stimulated vascular smooth muscle growth. Rat aorta-derived vascular smooth muscle cells were cultured on flexible silicone elastomer membranes and subjected to cyclic deformation (15 cycles per minute, deformed 2 seconds, relaxed 2 seconds). Deformation significantly increased proto-oncogene expression, [3H]thymidine incorporation, [3H]leucine incorporation, and cell number. Time course studies showed an 8-hour lag between initiation of cell deformation and onset of [3H]thymidine incorporation, with peak levels achieved after 18 to 24 hours. Western analysis of protein blots from deformed cells (10 minutes) demonstrated increased levels of phosphotyrosine-containing proteins having molecular weights of 110 to 130 and 70 to 80 kD. Deformation-stimulated tyrosine phosphorylation was prevented by the tyrosine kinase inhibitor Herbimycin A. Tyrosine kinase inhibition also prevented deformation-stimulated vascular smooth muscle cell growth as measured by [3H]thymidine incorporation. Cyclic deformation stimulates vascular smooth muscle proliferation through activation of tyrosine kinases. Inhibition of tyrosine phosphorylation is an effective means of preventing deformation-induced vascular smooth muscle growth in vitro.

Modulation of phorbol ester-induced contraction by endogenously released cyclooxygenase products in rat aorta

This study tests the hypothesis that prostaglandins (PGs) released in response to phorbol esters act as modulators of the phorbol ester-induced smooth muscle contraction. The rate and magnitude of the phorbol 12-myristate 13-acetate (PMA)-induced contraction of deendothelialized rat aorta were decreased by the cyclooxygenase inhibitor, indomethacin. The thromboxane (Tx) A2/PGH2 receptor antagonist, SQ-29548, also inhibited PMA-induced contraction, and the magnitude of inhibition was greater than that due to indomethacin. PMA induced the release of PGI2, PGE2, PGF2 alpha, and arachidonic acid, but not TxA2. The amount of PGI2 released was greater than that of PGE2 and PGF2 alpha. Indomethacin blocked the PMA-induced release of PG, but not of arachidonic acid. In PMA-contracted tissues, PGF2 alpha, PGE2, and the stable PGI2 and PGH2 analogues, carbacyclin and U-46619, respectively, induced further contraction. Pretreatment of PMA-contracted tissues with SQ-29548 partially inhibited the PGF2 alpha- and PGE2-induced contractions, completely inhibited contraction to U-46619, and reversed the carbacyclin-induced contraction to relaxation. These results demonstrate that, in rat aorta, PMA induces the release of PGs that exert both contractile and relaxant effects but whose net effect is to accelerate and augment the contraction induced by PMA. The PG-induced increase in PMA contraction is mediated, in large part, through TxA2/PGH2 receptor activation. The ability of various PGs, including carbacyclin, to activate the TxA2/PGH2 receptor suggests that one or more of these PGs, in addition to, presumably, PGH2, may be responsible for the increase in PMA contraction. PGI2 is the only endogenously released PG that can account for the relaxant effect.

Ozonolysis products of membrane fatty acids activate eicosanoid metabolism in human airway epithelial cells

When inhaled, ozone reacts at the airway luminal surface with unsaturated fatty acids contained in the extracellular fluid and plasma membrane to form an aldehyde and hydroxyhydroperoxide. The resulting hydroxyhydroperoxide degrades in aqueous systems to yield a second aldehyde and hydrogen peroxide (H2O2). Previously, we demonstrated that ozone can augment eicosanoid metabolism in bovine airway epithelial cells. To examine structure-activity relationships of ozone-fatty acid degradation products on eicosanoid metabolism in human airway epithelial cells, 3-, 6-, and 9-carbon saturated aldehydes and hydroxyhydroperoxides were synthesized and purified. Eicosanoid metabolism was evaluated by determination of total 3H-activity release from confluent cells previously incubated with [3H]arachidonic acid and by identification of specific metabolites with high performance liquid chromatography and radioimmunoassay. The major metabolites detected were prostaglandin E2, prostaglandin F2 alpha, and 15-hydroxyeicosatetraenoic acid. The 9-carbon aldehyde, nonanal, in contrast to 3- or 6-carbon aldehydes, stimulated release at concentrations > or = 100 microM, suggesting that the stimulatory effect increases with increasing chain length. When tested under identical conditions, the 3-, 6-, and 9-carbon hydroxyhydroperoxides were more potent than the corresponding aldehydes. Again, a greater effect was noted when the chain length was increased. One possible explanation for the increased potency of the hydroxyhydroperoxides over the aldehydes could be due to degradation of the hydroxyhydroperoxide into H2O2 and aldehyde. We consider this an unlikely explanation because responses varied with chain length (although each hydroxyhydroperoxide would produce an equivalent amount of H2O2) and because exposure to H2O2 alone or H2O2 plus hexanal produced a response dissimilar to 1-hydroxy-1-hexanehydroperoxide.(ABSTRACT TRUNCATED AT 250 WORDS)

Viral infection of bovine bronchial epithelial cells induces increased neutrophil chemotactic activity and neutrophil adhesion

1. Acute bronchitis secondary to viral infection is associated with an influx of neutrophils. We hypothesized that bronchial epithelial cells are capable of releasing neutrophil chemotactic activity in response to viral infection. 2. To test this hypothesis, primary cultures of bovine bronchial epithelial cells were inoculated with a bovine respiratory pathogen, bovine herpes virus-1. 3. Supernatants collected from inoculated cells, before signs of toxicity, demonstrated significant neutrophil chemotactic activity using a blind well chamber neutrophil chemotaxis assay. Lipoxygenase inhibitors markedly reduced the amount of neutrophil chemotactic activity released after bovine herpes virus-1 inoculation. Analysis of arachidonic acid metabolites in cell supernatants by reverse-phase h.p.l.c. confirmed that leukotriene B4, a potent neutrophil chemoattractant, was released. 4. We also confirmed that adhesion of neutrophils to bovine herpes virus-1-inoculated bronchial epithelial cells was increased and mediated in part by the neutrophil integrin, LFA-1. 5. Thus, virally infected airway epithelial cells release leucocyte chemoattractants and hence adhesive interactions, functions that are likely to be important in the inflammatory acute response to viral infection.

Neutrophil elastase increases secretory leukocyte protease inhibitor transcript levels in airway epithelial cells

Airway inflammation is often associated with the infiltration of activated neutrophils and subsequent protease release. Although aiding in the digestion and phagocytosis of foreign proteins and microorganisms, neutrophil proteases can indiscriminately damage healthy lung tissue. In the conducting airway, proteases, particularly neutrophil elastase, are counter-balanced by several antiproteases, including secretory leukocyte protease inhibitor (SLPI). SLPI can be produced locally by a number of cells including the airway epithelial cell. To examine the effects of neutrophil granule components on SLPI transcript levels, airway epithelial cells were treated (up to 96 h) with elastase, other proteases, or enzymes isolated from human sputum. We found that neutrophil elastase increased SLPI transcript levels in primary and transformed human airway epithelial cells in a time- and dose-dependent manner. Other neutrophil products, such as cathepsin G, myeloperoxidase, and lysozyme, had little or no effect on SLPI transcript levels. However, two nonneutrophil proteases, trypsin and pancreatic elastase, also increased SLPI transcript levels at higher doses than that required of neutrophil elastase. Two inflammatory cytokines, tumor necrosis factor-alpha and interleukin-8, produced little or no effect on SLPI transcript levels. This study demonstrates one way in which SLPI is regulated, via a protease that it inhibits, neutrophil elastase.

Formaldehyde-induced airway hyperreactivity in vivo and ex vivo in guinea pigs

Human exposure to formaldehyde is extensive, in both the indoor and the outdoor environment. The airways are clearly an important site of action of formaldehyde. Although many previous studies have examined the effect of formaldehyde in the upper respiratory tract, it remains controversial whether this compound can affect the lower respiratory tract. To determine whether formaldehyde induces airway hyperreactivity, guinea pigs were exposed to formaldehyde or filtered air (sham control) for 2 or 8 hr. Airway smooth muscle responsiveness was evaluated in vivo and ex vivo. Specific pulmonary resistance and airway reactivity (to infused acetylcholine) increased with formaldehyde exposure. Formaldehyde exposure caused bronchoconstriction and hyperreactivity at lower concentrations when exposure duration was extended from 2 to 8 hr. Exposure to > or = 0.3 ppm formaldehyde for 8 hr was sufficient to produce a significant increase in airway reactivity, while similar effects only occurred after > 9 ppm formaldehyde for 2 hr. Formaldehyde exposure also heightens airway smooth muscle responsiveness to acetylcholine (or carbachol) ex vivo. These effects occurred with no evidence of epithelial damage or inflammation up to 4 days after formaldehyde exposure. Thus, at concentrations relevant to environmental exposure, formaldehyde, a common indoor air pollutant, alters airway smooth muscle reactivity in guinea pigs. These findings suggest that the duration of exposure is important to the induction of airway hyperreactivity and that prolonged, low-level exposures may generate abnormal physiological responses in the airways not detectable after acute exposures.

Ozone inhalation stimulates expression of a neutrophil chemotactic protein, macrophage inflammatory protein 2

Short-term exposure of humans and animals to ozone results in increased lung neutrophils; however, the mechanisms underlying this response are not completely understood. We examined the potential involvement of the neutrophil chemotactic factor, macrophage inflammatory protein 2 (MIP-2), in ozone-induced inflammation. Exposure-response relationships for ozone and MIP-2 expression were characterized by exposing C57B1/6 mice to 0.1-2 ppm ozone for 3 hr and determining lung levels of MIP-2 mRNA 6 hr after exposure. Temporal relationships between ozone and MIP-2 were determined by exposing mice (2 ppm ozone x 3 hr) and characterizing MIP-2 mRNA expression 0, 2, 6, and 24 hr after exposure. Neutrophils in lung lavage fluid were determined in both exposure-response and time course studies. Ozone concentrations > or = 1.0 ppm increased MIP-2 mRNA and this increase corresponded with recruitment of neutrophils. MIP-2 mRNA was increased immediately after ozone exposure and decreased to control levels by 24 hr. To examine the role of direct oxidant effects in ozone-induced MIP-2 expression, alveolar macrophages were exposed in vitro for 4 hr to 10(-10)-10(-5) M hydrogen peroxide and MIP-2 expression was characterized. MIP-2 mRNA levels in lung macrophages were increased by > or = 10(-9) M hydrogen peroxide. In summary, our findings suggest the chemotactic protein MIP-2 may be responsible, at least in part, for ozone-induced increases in lung neutrophils and indicate that direct exposure of alveolar macrophages to an oxidant is sufficient to induce MIP-2 expression.

Carba-prostacyclin inhibits 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced transformation in sensitive murine epidermal JB6 cells

The ability of carba-prostacyclin (cPGI2), a stable analog of prostacyclin (PGI2), to inhibit 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced transformation of JB6 cells was investigated. JB6 cells sensitive (P+) and resistant (P-) to TPA-induced transformation to anchorage-independent growth were plated in soft agar in the presence or absence of cPGI2 for 14-21 days. Transformation frequencies were determined by recording colony numbers. cPGI2 was found to inhibit TPA-induced transformation of P+ cells in a dose-dependent fashion with 1 microM cPGI2 producing approximately 50% inhibition of colonies in soft agar. Our findings are consistent with the hypothesis that TPA-induced transformation in JB6 cell variants is mediated by PGI2 via regulation of adenylate cyclase activity and cAMP accumulation, with resultant inhibition of expression of the transformed phenotype, reflected in anchorage-independent growth.

Mechanisms of aldehyde-induced bronchial reactivity: role of airway epithelium

To investigate the relative irritant potencies of inhaled aldehydes, guinea pigs were exposed to formaldehyde or acrolein and specific total pulmonary resistance and bronchial reactivity to intravenous acetylcholine were assessed. The mechanisms associated with these responses were investigated by analyzing morphologic and biochemical changes in airway epithelial cells after in vivo and in vitro exposures. Immediately after exposure to formaldehyde or acrolein, specific resistance increased transiently and returned to control values within 30 to 60 minutes. Bronchial hyperreactivity, assessed by the acetylcholine dose necessary to double resistance, increased and became maximal two to six hours after exposure to at least 9 parts per million2 (ppm) formaldehyde or at least 1 ppm acrolein for two hours. The effect of exposure to 3 ppm formaldehyde for two hours was less than the effect of exposure to 1 ppm formaldehyde for eight hours; thus, extended exposures produced a disproportionate heightening of bronchial reactivity. Bronchial hyperreactivity often persisted for longer than 24 hours. Increases in three bronchoconstrictive eicosanoids, prostaglandin F2 alpha, thromboxane B2, and leukotriene C4, occurred immediately after exposure, whereas an influx of neutrophils into lavage fluid occurred 24 hours later. Histological examination of the tracheal epithelium and lamina propria also demonstrated a lack of inflammatory cell infiltration. Treatment with leukotriene synthesis inhibitors and receptor antagonists inhibited acrolein-induced hyperreactivity, supporting a causal role for these compounds in this response. Acrolein also stimulated eicosanoid release from bovine epithelial cells in culture. However, the profile of metabolites formed differed from that found in lavage fluid after in vivo exposure. Similarly, human airway epithelial cells did not produce cysteinyl leukotriene or thromboxane B2. However, cysteinyl leukotrienes were mitogenic for human airway epithelial cells in a concentration-dependent manner and exhibited a structure-activity relationship; leukotriene C4 was more potent than its sequential metabolites D4 and E4. The potency of leukotriene C4 was striking, stimulating colony-forming efficiency in concentrations as low as 0.01 pM. Together, these findings suggest that environmentally relevant concentrations of aldehydes can induce bronchial hyperreactivity in guinea pigs through a mechanism involving injury to cells present in the airways during exposure (rather than from subsequently recruited migratory cells) and that this response is dependent on leukotriene biosynthesis.

JB6 murine epidermal cell lines sensitive and resistant to 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced transformation exhibit differential arachidonic acid metabolism in response to TPA and the calcium ionophore A23187

In a study of arachidonic acid metabolism in murine epidermal JB6 cells, promoter-sensitive (P+) and promoter-resistant (P-) variants, labeled with [3H]arachidonic acid, were treated successively with 12-O-tetradecanoylphorbol-13-acetate (TPA) and the calcium ionophore A23187. Released radiolabel was separated by HPLC and identified by coelution of standards. Prostacyclin release was then quantified by radioimmunoassay for 6-keto prostaglandin (PG)F1 alpha. A23187 alone resulted in a small but significant enhanced release of radiolabel from both cell variants (0.7 +/- 0.2% for P- and 0.6 +/- 0.3% for P+ cells; mean +/- SD). Treatment with TPA and subsequent treatment with A23187 resulted in a synergistically enhanced release of radiolabel from both cell variants (4.1 +/- 0.8% for P- and 3.4 +/- 0.9% for P+ cells) relative to that with either agent alone. Although the predominant product for each treatment regimen was prostaglandin E2 (PGE2), the TPA-resistant cells (P-) released significantly more 6-keto PGF1 alpha, a stable breakdown product of PGI2, than did the TPA-sensitive (P+) cells. These results indicate differential arachidonic acid metabolism between JB6 cell variants resistant and sensitive to TPA-induced transformation.

Endotoxin stimulates bronchial epithelial cells to release chemotactic factors for neutrophils. A potential mechanism for neutrophil recruitment, cytotoxicity, and inhibition of proliferation in bronchial inflammation

To test the effect of endotoxin on bronchial epithelial cells (BEC), BEC were isolated from bovine lungs and cultured in the presence of bacterial endotoxin. The BEC culture supernatant fluids were harvested, and neutrophil chemotactic activity (NCA) was determined with a blindwell chamber technique; cytotoxicity determined by lactate dehydrogenase release and BEC proliferation determined by Coulter counting. Endotoxin caused a dose- and time-dependent release of NCA from BEC cultures compared with media alone (82.3 +/- 8.1 vs 12.0 +/- 3.1 cells/high power field, p less than 0.001). To further characterize this activity, reverse phase HPLC analysis of release eicosanoid metabolites after [3H]arachidonic acid incorporation was performed. Endotoxin stimulated the release of the neutrophil chemoattractants, leukotriene B4 and 12-hydroxyeicosatetraenoic acids. Endotoxin also resulted in a dose and time dependent release of lactate dehydrogenase (42.9 +/- 4.2 vs 20.2 +/- 2.2 U/liter, p less than 0.001) although higher doses were required to cause cytotoxicity than to stimulate chemotaxis. Finally, endotoxin resulted in a dose dependent inhibition of BEC proliferation (176 x 10(3) +/- 16 x 10(3) vs 1,080 x 10(3) +/- 38 x 10(3) cells/ml measured at day 14, p less than 0.001). These data suggest that bacterial release of endotoxin may contribute to the pathophysiologic changes observed in bronchial inflammation by stimulating BEC to release NCA, denuding airway epithelium by causing cytotoxicity of BEC, and inhibiting epithelial repair by inhibiting BEC proliferation.

Endotoxin stimulates bronchial epithelial cells to release chemotactic factors for neutrophils. A potential mechanism for neutrophil recruitment, cytotoxicity, and inhibition of proliferation in bronchial inflammation

To test the effect of endotoxin on bronchial epithelial cells (BEC), BEC were isolated from bovine lungs and cultured in the presence of bacterial endotoxin. The BEC culture supernatant fluids were harvested, and neutrophil chemotactic activity (NCA) was determined with a blindwell chamber technique; cytotoxicity determined by lactate dehydrogenase release and BEC proliferation determined by Coulter counting. Endotoxin caused a dose- and time-dependent release of NCA from BEC cultures compared with media alone (82.3 +/- 8.1 vs 12.0 +/- 3.1 cells/high power field, p less than 0.001). To further characterize this activity, reverse phase HPLC analysis of release eicosanoid metabolites after [3H]arachidonic acid incorporation was performed. Endotoxin stimulated the release of the neutrophil chemoattractants, leukotriene B4 and 12-hydroxyeicosatetraenoic acids. Endotoxin also resulted in a dose and time dependent release of lactate dehydrogenase (42.9 +/- 4.2 vs 20.2 +/- 2.2 U/liter, p less than 0.001) although higher doses were required to cause cytotoxicity than to stimulate chemotaxis. Finally, endotoxin resulted in a dose dependent inhibition of BEC proliferation (176 x 10(3) +/- 16 x 10(3) vs 1,080 x 10(3) +/- 38 x 10(3) cells/ml measured at day 14, p less than 0.001). These data suggest that bacterial release of endotoxin may contribute to the pathophysiologic changes observed in bronchial inflammation by stimulating BEC to release NCA, denuding airway epithelium by causing cytotoxicity of BEC, and inhibiting epithelial repair by inhibiting BEC proliferation.

Bronchial epithelial cells release monocyte chemotactic activity in response to smoke and endotoxin

An increase in mononuclear phagocytes occurs within the airways during airway inflammation. Bronchial epithelial cells could release monocyte chemotactic activity and contribute to this increase. To test this hypothesis, bovine bronchial epithelial cells were isolated and maintained in culture. Bronchial epithelial cell culture supernatant fluids were evaluated for monocyte chemotactic activity. Epithelial cell culture supernatant fluids attracted significantly greater numbers of monocytes compared to media alone and the number of monocytes attracted increased in a time dependent manner. Endotoxin and smoke extract induced a dose and time dependent release of monocyte chemotactic activity compared with cells cultured in media (52.5 +/- 2.6 (endotoxin), 30.5 +/- 2.3 (smoke) vs 20.5 +/- 2.2 cells/high power field (HPF) p less than 0.001). The released activity was chemotactic by checkerboard analysis. Stimulation of the epithelial cells by opsonized zymosan, calcium ionophore (A23187), and PMA also resulted in an increase in monocyte chemotactic activity (p less than 0.01). Because the release of activity was blocked by the lipoxygenase inhibitors, nordihydroguaiaretic acid and diethycarbamazine, epithelial cell monolayers were cultured with 3 microCi [3H]arachidonic acid for 24 h and then exposed to A23187, PMA, or both stimuli, for 4, 8, and 24 h. Analysis of the released 3H activity was performed with reverse-phase HPLC and revealed that the major lipoxygenase product was leukotriene B4. These data suggest that monocytes may be recruited into airways in response to chemotactic factors released by bronchial epithelial cells.

Endothelin stimulates chloride secretion across canine tracheal epithelium

The endothelins (ET) are a group of isopeptides produced by a number of cells, including canine tracheal epithelial cells. Because these compounds are endogenous peptides that may activate eicosanoid metabolism, we investigated the effects of ET on Cl secretion in canine tracheal epithelium. Endothelin 1 (ET-1) was found to produce a dose-dependent change in short-circuit current (Isc) that increased slowly and reached a maximal value within 10-15 min. When isopeptides of ET were compared, 300 nM ET-1 and ET-2 produced comparable maximal increases in Isc, whereas ET-3 produced smaller changes in Isc (half-maximal concentrations of 2.2, 7.2, and 10.4 nM, respectively). Ionic substitution of Cl with nontransported anions, iodide and gluconate, reduced ET-1-induced changes in Isc. Furthermore, the response was inhibited by the NaCl cotransport inhibitor, furosemide. In paired tissues, ET-1 significantly increased mucosal net 36Cl flux without significant effect on 22Na flux. The increase in Isc induced by ET was diminished by pretreatment with indomethacin. The second messengers mediating the increase in Isc were investigated in cultured canine tracheal epithelial cells. ET-1 stimulated the release of [3H]arachidonate from membrane phospholipids, increased intracellular Ca2+ (occasionally producing oscillations), and increased adenosine 3',5'-cyclic monophosphate accumulation. The latter was diminished by indomethacin. Thus ET is a potent agonist of Cl secretion (with the isopeptides having the following potency: ET-1 greater than or equal to ET-2 greater than ET-3) and acts, in part, through a cyclooxygenase-dependent mechanism.

Bronchial epithelial cells release monocyte chemotactic activity in response to smoke and endotoxin

An increase in mononuclear phagocytes occurs within the airways during airway inflammation. Bronchial epithelial cells could release monocyte chemotactic activity and contribute to this increase. To test this hypothesis, bovine bronchial epithelial cells were isolated and maintained in culture. Bronchial epithelial cell culture supernatant fluids were evaluated for monocyte chemotactic activity. Epithelial cell culture supernatant fluids attracted significantly greater numbers of monocytes compared to media alone and the number of monocytes attracted increased in a time dependent manner. Endotoxin and smoke extract induced a dose and time dependent release of monocyte chemotactic activity compared with cells cultured in media (52.5 +/- 2.6 (endotoxin), 30.5 +/- 2.3 (smoke) vs 20.5 +/- 2.2 cells/high power field (HPF) p less than 0.001). The released activity was chemotactic by checkerboard analysis. Stimulation of the epithelial cells by opsonized zymosan, calcium ionophore (A23187), and PMA also resulted in an increase in monocyte chemotactic activity (p less than 0.01). Because the release of activity was blocked by the lipoxygenase inhibitors, nordihydroguaiaretic acid and diethycarbamazine, epithelial cell monolayers were cultured with 3 microCi [3H]arachidonic acid for 24 h and then exposed to A23187, PMA, or both stimuli, for 4, 8, and 24 h. Analysis of the released 3H activity was performed with reverse-phase HPLC and revealed that the major lipoxygenase product was leukotriene B4. These data suggest that monocytes may be recruited into airways in response to chemotactic factors released by bronchial epithelial cells.

Acrolein stimulates eicosanoid release from bovine airway epithelial cells

Injury to the airway mucosa after exposure to environmental irritants is associated with pulmonary inflammation and bronchial hyperresponsiveness. To better understand the relationships between mediator release and airway epithelial cell injury during irritant exposures, we studied the effects of acrolein, a low-molecular-weight aldehyde found in cigarette smoke, on arachidonic acid metabolism in cultured bovine tracheal epithelial cells. Confluent airway epithelial cell monolayers, prelabeled with [3H]arachidonic acid, released significant levels of 3H activity when exposed (20 min) to 100 microM acrolein. [3H]arachidonic acid products were resolved using reverse-phase high-performance liquid chromatography. Under control conditions the released 3H activity coeluted predominantly with the cyclooxygenase product, prostaglandin (PG) E2. After exposure to acrolein, significant "peaks" in 3H activity coeluted with the lipoxygenase products 12-hydroxyeicosatetraenoic acid (HETE) and 15-HETE, as well as with PGE2, PGF2 alpha, and 6-keto-PGF1 alpha. Dose-response relationships for acrolein-induced release of immunoreactive PGF2 alpha and PGE2 from unlabeled epithelial monolayers demonstrated 30 microM acrolein as the threshold dose, with 100 microM acrolein inducing nearly a fivefold increase in both PGF2 alpha and PGE2. Cellular viability after exposure to 100 microM acrolein, determined by released lactate dehydrogenase activity, was not affected until exposure periods were greater than or equal to 2 h. These results implicate the airway epithelial cell as a possible source of eicosanoids after exposure to acrolein.

Cysteinyl leukotrienes enhance growth of human airway epithelial cells

Epithelial inflammation may play an obligatory role in the pathogenesis of a number of chronic pulmonary diseases such as asthma or bronchitis and has been implicated during the promotion phase of multistage carcinogenesis. At sites of inflammation, bioactive lipid mediators are released and activate a wide range of pathophysiological responses including bronchospasm. Previous studies suggest that one class of inflammatory mediators, the eicosanoids, can also influence cell growth. Epithelial cell proliferation and hyperplasia are common sequelae to irritation and inflammation, and because the lung has a high capacity to produce eicosanoids, we investigated the effects of a group of these compounds, the cysteinyl leukotrienes, on growth of human airway epithelial cells. Leukotrienes were found to be mitogenic in a concentration-dependent manner and exhibit a structure-activity relationship, with leukotriene C4 being more potent than its sequential metabolites leukotriene D4 and E4. The potency of leukotriene C4 is striking, stimulating colony-forming efficiency in concentrations as low as 10 fM. These findings suggest a new physiological role for leukotrienes in the lung that links inflammation with epithelial cell proliferation.

Electromechanical effects of endothelin on ferret bronchial and tracheal smooth muscle

The effects of endothelin (ET) on transmembrane potential and isometric force were studied in ferret bronchial and tracheal smooth muscles. At rest, the muscle cells were electrically and mechanically quiescent. The mean resting potential for the bronchial cells was -70 +/- 1 mV (n = 25 cells/8 ferrets), and that of the tracheal cells was -60 +/- 1 mV (n = 7 cells/2 ferrets). ET depolarized and contracted both types of muscle cells in a concentration-dependent manner. At 1 nM ET, the bronchial muscle cells were significantly depolarized with concomitant force generation. In contrast, greater than 30 nM ET was required for the tracheal muscle cells to respond. The bronchial cells were further depolarized by 10 and 100 nM ET with electrical slow-wave activity present. The calcium channel antagonist verapamil substantially inhibited the contractions produced by 100 nM ET and abolished the slow-wave activity without affecting the base-line depolarization. Pretreatment of the bronchial muscle with 30 microM indomethacin did not affect the ET-induced contraction. These results suggest that ET modulates airway smooth muscle tone by direct activation and/or depolarization-induced activation of sarcolemmal calcium channels.

Sulfidopeptide leukotrienes mediate acrolein-induced bronchial hyperresponsiveness

The sulfidopeptide leukotrienes are bronchoconstrictive lipid mediators thought to have an important role in the pathophysiology of asthma. The objective of this study was to determine if treatment with a leukotriene receptor antagonist and 5-lipoxygenase inhibitors could diminish acrolein-induced bronchial hyperresponsiveness and to determine whether leukotriene (LT) C4 generation is augmented by acrolein exposure. Guinea pigs (groups of 6-7) were exposed to 1.3 ppm acrolein for 2 h and bronchial responsiveness to intravenous acetylcholine determined twice before, and once 1, 2, 6, and 24 h after exposure. Immediately after acrolein exposure (5 min) specific total airway resistance (sRt) increased from 0.86 +/- 0.01 to 1.29 +/- 0.07 ml.cmH2O.ml-1.s. Within 1 h after exposure, the effective dose of acetylcholine sufficient to double sRt (ED200) decreased from 114.0 +/- 6.6 to 58.5 +/- 6.5 micrograms.kg-1.min-1. Bronchial hyperresponsiveness became maximal at 2 h with ED200 = 44.7 +/- 4.2 and persisted for up to 24 h after exposure (24 h ED200 = 60.2 +/- 11.6 micrograms.kg-1.min). A LTC4/LTD4 receptor antagonist, L-649,923 (10 mg/kg iv), and two putative inhibitors of 5-lipoxygenase, L-651,392 (10 mg/kg po) and U-60,257 (5 mg/kg i.v.), diminished the immediate bronchoconstriction and markedly inhibited bronchial hyperresponsiveness. Analysis of bronchoalveolar lavage fluid obtained from guinea pigs after acrolein exposure revealed a significant increase in immunoreactive LTC4 concentrations (control LTC4 = 8.8 +/- 0.3, n = 7; exposed LTC4 = 15.9 +/- 2.4 pg/ml, n = 6). Treatment with L-651,392 inhibited this response (acrolein exposed = 9.4 +/- 2.4 pg/ml, n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchial responsiveness and inflammation in guinea pigs exposed to acrolein

Bronchial hyperresponsiveness can be produced experimentally after inhalation of numerous nonimmunospecific stimuli; our objective was to determine whether acrolein, a component of cigarette smoke, could increase bronchial reactivity to intravenously administered acetylcholine in guinea pigs. Bronchial responsiveness was assessed twice before and 1, 2, 6, and 24 h after exposures to less than or equal to 0.01 (sham), 0.31, 0.67, 0.94, or 1.26 parts per million for 2 h (5-7 guinea pigs/group). To examine the possible relationships of responsiveness to inflammatory mediator release and cellular infiltration, bronchoalveolar lavage was performed in another 30 guinea pigs before (control) and 0, 1, 2, 6, or 24 h after exposures. Pulmonary resistance was increased immediately after exposure (5 min) and returned to control values within 30-60 min. Increased bronchial responsiveness was evident within 1 h and became maximal 2-4 h after exposure. The acetylcholine dose necessary to double resistance decreased from 104.2 +/- 7.3 to 79.6 +/- 15.9 at 1 h and was 32.5 +/- 7.9 at 2 h and 32.8 +/- 7.6 micrograms.kg-1 at 6 h. Increases in two eicosanoids, thromboxane B2 (from 167 +/- 21 to 314 +/- 77 pg/ml) and prostaglandin F2 alpha (from 98 +/- 20 to 285 +/- 62 pg/ml) occurred immediately after exposure, whereas an influx of neutrophils occurred 24 h later (from 2.2 +/- 1.2 to 11.3 +/- 3.6%). These temporal relationships suggest that neutrophil infiltration may be a sufficient but not a necessary condition for the onset of bronchial hyperresponsiveness and that injury to cells normally present in the lung are responsible for the mediators thought to influence bronchial responsiveness.

Isolation, characterization, and long-term culture of fetal bovine tracheal epithelial cells

Epithelial cells were isolated from fetal bovine trachea by exposing and stripping the mucosal epithelium from the adjacent connective tissue. The tissue was minced and enzymically dissociated in Ca-Mg-free medium containing dispase and dithiothreitol. The stripping procedure and selective trypsinization produced epithelial cell cultures free of fibroblasts. Seeded on plastic, the plating efficiency was 21.5% with a doubling time of 24 h. Dome formation, evidence of occluding junctions and active ion transport characteristic of epithelial cells, was common. Growth of the cells on glass, collagen, and Engelbreth-Holm-Swarm (EHS) substrate demonstrated a striking difference in morphology. Cells grown on EHS presented a more distinctly three-dimensional growth pattern and many more microvilli when compared to cells grown on glass or collagen. The cells retained their epithelioid characteristics through more than 30 passages as shown by the presence of distinct apical and basolateral membranes, tight junctions, and positive keratin staining.

Ozone-induced augmentation of eicosanoid metabolism in epithelial cells from bovine trachea

Epithelial injury and inflammation have been implicated in ozone-induced airway hyperresponsiveness. Because ozone is relatively insoluble and highly reactive, toxicologic effects of this compound may be limited to the plasma membranes of airway epithelium. We hypothesize that oxidant damage to epithelium may result in elaboration of various eicosanoids, which are known to alter airway smooth muscle responsiveness and epithelial cell functions (including ion transport). To examine eicosanoid metabolism after exposure to 0.1 to 10.0 ppm ozone, epithelial cells derived from bovine trachea were isolated and grown to confluency. Bovine tracheal cells in culture expressed differentiated features characteristic of epithelial cells, including a plasma membrane with a specialized polar morphology, an extensive network of filaments that were connected through intercellular junctional complexes, and keratin-containing monofilaments as determined by indirect immunofluorescent localization. Monolayers were alternately exposed to ozone and culture medium for 2 h in a specially designed in vitro chamber using a rotating inclined platform. Eicosanoid products were measured by the release of [3H]-labeled products from cells incubated with [3H]-arachidonic acid for 24 h before exposure and by the release of immunoreactive products into the cell supernatant. Both methods revealed ozone-induced increases in cyclooxygenase and lipoxygenase product formation with significant increases in prostaglandins E2, F2 alpha, 6-keto F1 alpha, and leukotriene B4. Release rates of immunoreactive products were dose-dependent, and ozone concentrations as low as 0.1 ppm produced an increase in prostaglandin F2 alpha. These findings are consistent with the hypothesis that ozone can augment eicosanoid metabolism in airway epithelial cells.

Ion transport across cat and ferret tracheal epithelia

Sheets of trachea from ferret and cat were mounted in Ussing chambers and continuously short circuited. Under resting conditions, in both the cat and ferret there was little or no Cl secretion, and Na absorption accounted for most of the short-circuit current (Isc). Ouabain (10(-4) M, serosal bath) reduced Isc to zero in 30-60 min. This decline was matched by a decrease in net Na absorption. Amiloride (10(-4) M, luminal bath) caused a significant decrease in Isc and conductance (G) in both species. Bumetanide (10(-4) M, serosal bath) had negligible effects on Isc and G. In both species, isoproterenol increased Isc by stimulating Cl secretion. Methacholine induced equal amounts of Na and Cl secretion, with little change in Isc. In the cat, prostaglandins E2 and F2 alpha and bradykinin increased Isc, responses which were abolished in Cl-free medium. In open-circuited cat tissues, Na flux from the serosal to mucosal side was measured simultaneously with the secretion of nondialyzable 35S. Prostaglandins E1, E2, and F2 alpha, histamine, bradykinin, methacholine and isoproterenol all increased both Na and 35S-mucin secretion.