Effects of arachidonic acid, monohydroxyeicosatetraenoic acid and prostaglandins on the release of mucous glycoproteins from human airways in vitro

Pig bronchial mucous membrane: a model system for assessing respiratory mucus release in vitro

A convenient organ culture system is described in which fragments of mucous membrane isolated from bronchi of the pig were maintained in either screw-cap tubes or multiwell tissue culture plates. The mucous membrane of the pig bronchus, like that of the human, is rich in mucus-secreting submucosal glands and can respond to cholinergic stimulation in vitro by releasing either L-[3H]fucose- or L-[3H]serine-labeled acid-precipitable macromolecules. Reproducible cholinergic-mediated release of labeled macromolecules was attained by first washing the mucous membrane fragments in serum-free modified Earles medium (Dulbecco's) for 120 min at 4 degrees C. Maximum stimulation was obtained when the incubation medium was supplemented with 0.5-2.0% horse serum. Approximately 50% of L-[3H]fucose-labeled macromolecules were eluted in the void volume from a column of Sepharose CL-6B in 6 M urea. Cochromatography of L-[3H]- and L-[14C]fucose-labeled glycoproteins released by mucous membranes of control and methacholine-treated tissue fragments failed to reveal any significant difference in any specific population of fucose-labeled glycoproteins. It is concluded that, as a whole, many different labeled molecules are released in response to cholinergic stimulation. Taken together, these results suggest that the mucous membrane of the porcine bronchus is a useful in vitro model for studying respiratory mucus secretion.

Arachidonic acid metabolism by rabbit synovial cells in culture. Studies of non-cyclooxygenase pathways

We have investigated arachidonic acid (20:4) metabolism by rabbit synovial cells in culture. The lipoxygenase products 5-HETE, 12-HETE and 15-HETE were not detected, despite the presence of a cyclooxygenase inhibitor sodium meclofenamate (20 microM), nor after incubation with ionophore A23187 (1 microM), 20:4 (10 microM), prostaglandin E2, (1 microM), N-formylmethionylleucylphenylalanine (0.01 microM), or murine spleen cell-conditioned medium. [3H]20:4 (10 microM) was incorporated into phospholipids, triacylglycerols and diacylglycerols. A majority of the 3H content of phosphatidylinositol/phosphatidylserine and of diacylglycerols was already present at 1 min, in contrast to the slower accumulation of 3H in triacylglycerols, phosphatidylcholine and phosphatidylethanolamine. The diacylglycerol fraction contained sn-glycerol-1-acyl-2-20:4. These observations are consistent with phospholipase C activity in synovial cells under those culture conditions. The products generated by these enzymes may play important roles in the physiological processes of synovium.

Human airway monohydroxyeicosatetraenoic acid generation and mucus release

The effects of 5-, 8-, 9-, 11-, 12-, and 15-monohydroxyeicosatetraenoic acid (HETE) (0.1-100 nM) on mucous glycoprotein release from cultured human airways were determined. Each of the HETE was an active secretagogue of mucus at concentrations greater than 1-10 nM with 12- and 15-HETE, the most active. Both 5- and 9-hydroperoxyeicosatetraenoic acid (HPETE) were also active as secretagogues at 100 nM, although of somewhat lower potency. As cultured airways were capable of responding to HETE with mucous glycoprotein release, it was of interest to identify and quantitate airway HETE formation. Accordingly, airways were incubated with tracer quantities of [14C]arachidonate for 16-48 h, and the spontaneous formation of 5-, 12- and 11- and/or 15-HETE was measured by high-pressure liquid chromatography. Indeed, sizeable quantities of 11- and/or 15- greater than 5- greater than 12-HETE were generated. This HETE generation was increased by the addition of 25 micrograms/ml of arachidonate and was reduced somewhat after 18-21 d in continuous tissue culture. Reversed anaphylaxis of human airways using anti-human IgE markedly increased the HETE formation, resulting in the production of micromolar concentrations of 5- and 11- and/or 15-HETE. Thus, human airways not only are capable of responding to the presence of HETE with mucous glycoprotein release, but also generate (both spontaneously and in response to anaphylaxis) at least three species of HETE, and do so in quantities capable of acting as mucus secretagogues.

The effect of prenatal dexamethasone on fetal rat lung prostaglandin synthesis

[14C]Arachidonic acid conversions were studied in homogenates of lungs from 20, 21, and 22 day fetuses with or without prenatal dexamethasone treatment. The major metabolites were in all cases 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), prostaglandin E2 (PGE2), and 12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT). Prostaglandin F2 alpha (PGF2 alpha), prostaglandin D2 (PGD2), and thromboxane B2 (TxB2) were present in small amounts. Dexamethasone treatment significantly stimulated the conversion of [14C]-arachidonic acid in fetal lung homogenates to 6-keto-PGF1 alpha, PGE2, 12-HETE, and HHT, at 20 days gestational age. This effect was dependent on the dose of dexamethasone. These results suggest that dexamethasone accelerates the maturation of the enzymes involved in prostaglandin synthesis. Because dexamethasone is also known to inhibit phospholipase A2, further studies are required to determine the overall in vivo effect of prenatal dexamethasone therapy on fetal lung prostaglandin synthesis.

Release of leukotriene C4 from guinea pig trachea

Immunological (ovalbumin) and non-immunological (calcium ionophore A23187) stimulation of guinea pig trachea induces a prolonged contraction that is enhanced by indomethacin (8.5 microM) and inhibited by nordihydroguaiaretic acid (50 microM) pretreatment of the tissue. The mediator released by the above stimuli was identified as leukotriene C4 by reverse-phase high performance liquid chromatography, and quantitated by bioassay. Indomethacin, and/or arachidonic acid (32.8 microM) did not enhance the release, whereas nordihydroguaiaretic acid reduced the contraction and release of LTC4. The results demonstrate the hitherto unproved capability of the large airways to synthesize leukotrienes and emphasize the importance of examining their role in asthma.

Bradykinin-stimulated electrolyte secretion in rabbit and guinea pig intestine. Involvement of arachidonic acid metabolites

Bradykinin (BK) increases short-circuit current (Isc) when added to the serosal side of rabbit or guinea pig ileum or rabbit colon. Significant effects on Isc are seen at concentrations as low as 10(-10) M. Anion substitution experiments and unidirectional 36Cl flux measurements indicate that this effect of BK on Isc is due to Cl secretion. The effect of BK on Isc can be partially blocked (60-70% inhibition) by cyclooxygenase inhibitors (indomethacin and/or naproxen) and completely blocked by the phospholipase inhibitor, mepacrine. The combined cyclooxygenase/lipoxygenase inhibitors BW 755 and eicosa-5,8,11,14-tetraynoic acid (ETYA) also completely block the effect of BK on Isc but the slow-reacting substance of anaphylaxis (SRS-A) antagonist FPL 55712 has no effect. None of the above inhibitors diminish the effect on Isc of other exogenously added secretory stimuli such as vasoactive intestinal peptide (VIP), theophylline, or prostaglandin E2 (PGE2). Prior desensitization of rabbit ileum to PGE2 blocks the effect on Isc of BK but not those of VIP or theophylline. Conversely, prior desensitization of rabbit ileum to BK greatly reduces the effect of PGE2 on Isc. BK also stimulates the synthesis of PGE2 in rabbit ileal and colonic mucosa and this effect can be blocked by prior addition of either indomethacin or mepacrine. These effects of BK are similar to those of exogenously added arachidonic acid (AA). AA also stimulates Cl secretion and increases PGE2 synthesis and its effect on Isc can be inhibited by prior desensitization to PGE2 or by prior addition of indomethacin. The above results indicate that BK stimulates active Cl secretion in both small and large intestine and suggest that this effect is due to the intracellular release of AA. Although the prostaglandins appear to be the major products of AA metabolism contributing to the secretory response, lipoxygenase products may also play a role.

Effects of leukotrienes C4 and D4 on glycoprotein and lysozyme secretion by human bronchial mucosa

The effects of leukotrienes C4 (LTC4) and D4 (LTD4) on the secretion by human bronchial mucosa of [14C]glucosamine-labeled, trichloro-acetic acid/phosphotungstic acid-precipitable glycoprotein and lysozyme were evaluated in vitro. LTC4 and LTD4, in the concentration range of 0.16 to 1600 nM, induced a dose-related increase in the release of radiolabeled glycoprotein, but not of lysozyme. This secretagogue effect was selective for high molecular weight glycoproteins of about 2-5 x 10(6) daltons, and the median effective concentrations (EC50) of LTC4 of 9.4 x 10(-9) M and of LTD4 of 2.44 x 10(-8) M, indicate that these leukotrienes are approximately 100-fold more potent than the cholinergic agonist methacholine. Incubation of [14C]glucosamine-labeled bronchial mucosal explants with LTC4 or LTD4 for six sequential 15-min periods revealed a rapid, progressive decrement in glycoprotein release, compatible with stimulatory action on secretion rather than augmentation of the rate of glycoprotein synthesis. This interpretation is also consistent with the finding that the specific activity (ratio of bound radiolabel: protein content) of the macromolecular glycoprotein secreted by the explants is not changed with stimulation of release by the leukotrienes. Based upon the activity of synthetic leukotriene analogs, the specific C-6 chirality of the sulfidopeptide of LTD4, the presence of a hydroxyl at C-5 and the presence of eicosanoid carbons 9-20 were of no importance for secretagogue activity. These findings contrast with the stereochemical requirements for the spasmogenic response to sulfidopeptide leukotrienes and suggest that leukotriene-induced secretion is not likely to be mediated via a specific receptor.

Diphenhydramine blocks the leukotriene-C4 enhanced mucus secretion in canine trachea in vivo

Leukotrienes (C4, D4) have been shown to enhance mucus secretion in both isolated human airway tissue and intact canine trachea in vivo. They also have been implicated as putative mediators in several airways diseases. In previous canine studies the mucus enhancing effect of leukotriene-C4 was blocked by atropine, FLP 55,712, and hexamethonium but not by cutting the superior laryngeal and vagus nerves. We anesthetized mongrel dogs with chloralose (100 mg/kg) and urethane (500 mg/kg) and ventilated them on a pump. To visualize the secretions from submucosal glands, we exposed the mucosa of the upper trachea and coated its surface with powdered tantalum. Secretions from the glands formed elevation in the tantalum layer (hillocks) with time: the number of tracheal hillocks (an index of mucus secretion) was measured at one or more of the four time points on six dogs after each treatment of the treatment sequence: no LTC4, LTC4, no LTC4 + blocker, and LTC4 + blocker. The potential blocker was diphenhydramine, an H1 antagonist for histamine. LTC4 was injected into the cranial thyroid artery which directly feeds the tracheal segment. We observed hillocks through a dissecting microscope, and the number of hillocks per 1.2 cm2 were counted for a 1-4 min interval. In 6 dogs with 12 responses, LTC4 (10 micrograms) gave a positive response that was significantly different from control (p less than 0.01-0.05) at 2-4 min. Diphenhydramine (n = 6), 0.5 mg/kg, a dose which blocked a histamine challenge without blocking an acetylcholine challenge of secretion, gave a statistically significant (p less than 0.01-0.05) reduction in mucus secretion at 1-4 min. These results support the conclusion that leukotriene C4 induces mucus secretion in dogs that is blocked by prior diphenhydramine administration. This would indicate histamine has a role, but as yet an unknown mechanism in the action of leukotriene-C4 in enhancing mucus.

Control and modulation of airway epithelial cells and their secretions

Information on the control and modulation of airway epithelial cells and their secretion is obtained by three techniques: 1) in vivo studies of animal models of disease, 2) in vitro studies by organ culture of human and animal model airways, and 3) chemical analysis of human and animal bronchial secretion. The contribution of each of these techniques is described in this paper, including recent or new information. In vivo models of mucous hypersecretion can be produced by irritants, infection, and drugs more quickly than previously expected. In the rat, beta 1 and beta 2 receptors are present with evidence of different activity in various airway regions. Organ culture studies combine autoradiographic analysis of cell activity with chemical analysis of secretory product, and describe inhibitory effect of new agents such as VIP. The application of density-gradient ultracentrifugation gives total recovery of undegraded macromolecules from bronchial mucus; it is now possible to recover mucous glycoprotein of molecular weight larger than that previously isolated. The organ culture studies and density-gradient ultracentrifugation studies indicate that a proteoglycan is a significant constituent of total bronchial secretion. Differences between diseases are emerging in the macromolecular partitioning between sol and gel obtained at 160,000 X g, a higher speed than that previously applied systematically in such studies.

Secretogogue responses of leukotriene C4, D4: comparison of potency in canine trachea in vivo

By the use of close arterial injection of leukotrienes into the circulation supplying the upper cervical canine trachea, it has been possible to assess the secretogogue effects of leukotriene C4, and D4 on mucus secretion. Both LTC4 and LTD4 increased mucus secretion over baseline levels by a statistically significant level (p = less than 0.05). LTD4 was more potent than C4 with relative potencies of 2500, 320, 630, and 500 based on hillock formation (a measure of secretion) at 1, 2, 3, and 4 minutes after injection. The overall difference in potency in this animal model of mucus production was LTD4 greater than C4 by 1000-fold.

Possible mechanisms underlying mucus secretion in aspirin-sensitive asthma

To study the hypersecretion of mucus in human airways, an in vitro model was developed. The effect of prostaglandins, nonsteroidal anti-inflammatory drugs, lipoxygenase products of arachidonic acid, and other mucus-stimulating and mucus-inhibiting agents was studied. The data suggest that arachidonic acid metabolized through its lipoxygenase pathway leads to the formation of potent stimulators of mucus release. Among them are the monohydroxyeicosatetraenoic acids, which are produced in large quantities by human airways, and the leukotrienes, which are generated during allergic reactions of the lung. As the lipoxygenase pathway is the only operant metabolic system available for arachidonic acid in the presence of aspirin and non-steroidal anti-inflammatory drugs--and as the nonsteroidal anti-inflammatory drugs themselves stimulate mucus production--it is possible that the mechanism responsible for mucus release in aspirin-sensitive asthmatics is the formation of these lipoxygenase products.

Concepts regarding formation, action, and pharmacologic inhibition of arachidonic acid metabolites in asthma

Lipid products derived from the metabolism of arachidonic acid have a central role in inflammatory reactions and probably contribute to the pathophysiology of bronchial asthma as well as other obstructive diseases of the lung. Metabolites of arachidonic acid also modulate numerous physiologic responses. The goal of pharmacologic intervention is to enhance the beneficial effects of certain arachidonate metabolites and to inhibit those which are undesirable. Development of new pharmacologic agents which selectively inhibit synthesis or action of certain arachidonic acid metabolites, particularly the bronchospastic leukotrienes, may provide more effective treatment of asthma in the future.

Leukotriene-C4 enhances mucus production from submucosal glands in canine trachea in vivo

Because leukotrienes have been implicated as putative mediators in upper airways disease, we studied whether leukotriene C4 (LTC4) might also have a mucus enhancing effect on submucosal glands. We anesthetized mongrel dogs with chloralose (100 mg/kg) and urethane (500 mg/kg) and ventilated them on a pump. To help visualize the secretions from submucosal glands, we exposed the mucosa of the upper trachea and coated its surface with powdered tantalum. Secretions from the glands (hillocks) were measured with time: The number of hillocks was measured at four time points on 19 dogs after each treatment in the sequence: no LTC4, LTC4, no LTC4 and LTC4 + blocker. The potential blockers were nerve cutting, atropine, FPL-55,712, and hexamethonium. Each potential blocker was used on 3-5 dogs. LTC4 was injected into the cranial thyroid artery. In 19 dogs with 27 responses, LTC4(8.6-11.0 micrograms) gave a positive response that was significantly different from control (P less than 0.01) at 1-4 min. These effects were not abolished in 5 dogs by cutting the superior laryngeal (SLN) and the vagus nerves (P less than 0.01). Pretreatment of the dogs (n = 5) with atropine, hexamethonium and the specific SRS-A (LTC4) antagonist FPL 55,712 (n = 3) gave a statistically significant (P less than 0.01-0.05) reduction in mucus secretion at all times for atropine, hexamethonium, and at all times except 4 min for (FPL 55,712). These results indicate that leukotriene C4 induces mucus secretion in dogs. This secretion does not depend on an intact reflex pathway but is altered at the individual gland by agents which block ganglionic motor pathways.

The effect of leukotriene C4 on mucin release into the cat trachea in vivo and in vitro

We have tested the effect of leukotriene C4 (LTC4, 6 X 10(-8) to 6 X 10(-5) M) on the output of radiolabelled mucins from the trachea of the anaesthetized cat. Doses between 6 X 10(-7) M and 6 X 10(-5) M stimulated mucin release. FPL 55712 (9.5 X 10(-6) M) partially antagonized the effect of the highest dose of LTC4. Tests of LTC4 (6 X 10(-8) to 6 X 10(-6) M) on cat trachea in vitro failed to show any effect on mucin secretion. We conclude that leukotrienes may be one of the mediators of mucus secretion into the inflamed airway.

The effects of indomethacin and prostaglandins E2 and F2 alpha on canine tracheal mucus generation

The effects of prostaglandins on respiratory smooth muscle are well known; however, their role in mucus generation has received little attention. This investigation was undertaken to study the actions of prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) on secretion and synthesis of respiratory mucus glycoproteins. The method employed canine tracheal explants; radiochemical precursors were used in the culture media for labelling and quantitation of the secreted glycoproteins. Glycoprotein secretion was not significantly influenced by PGE2 (1 x 10(-10) to 1 x 10(-3) M) or PGF2 alpha (1 x 10(-8) to 1 x 10(-4) M). However, PGF2 alpha (1 x 10(-3) M and 1 x 10(-2) M), significantly stimulated glycoprotein secretion. The mechanism may have involved a contractile effect on myoepithelial cells of the submucosal glands. Synthesis of glycoproteins was significantly inhibited by PGF2 alpha (1 x 10(-5) M), indomethacin (1 x 10(-6) M), and the combination PGF2 alpha (1 x 10(-5) M)/indomethacin (1 x 10(-6) M). PGE2 (1 x 10(-5) M) and arachidonic acid (1 x 10(-5) M) were without effect. These data suggested that indomethacin inhibited glycoprotein synthesis by a mechanism other than an action on prostaglandin synthetase. In addition, because these agents inhibited synthesis of glycoproteins which were labeled with 3H-glucosamine, 35S-sulfate, and 14C-serine, it appears that their action was primarily upon synthesis of the protein core.

Nonphagocytic clearance of Staphylococcus aureus from murine lungs

Several investigations of host and bacterial factors critical to staphylococcal clearance from lungs suggest that alveolar macrophages may not provide the principal defense against inhaled staphylococci. We evaluated possible contributions of extracellular bactericidal activities in lungs with a standard aerosol challenge model by using methods which allowed recovery of macrophages for in vitro bactericidal assays and recovery of intrapulmonary staphylococci for clearance studies. Macrophages recovered by a gentle lavage technique immediately after aerosol exposure contained 6.0 +/- 2.3 colony-forming units of viable staphylococci per 100 glass-adherent macrophages. These intracellular staphylococci were killed in vitro with a half-life of 10.8 +/- 2.1 h, which is identical to our results with a completely in vitro system for ingestion and killing. However, 99.4 +/- 0.2% and 94.9 +/- 1.5% of the viable cocci recovered in bronchoalveolar lavage at 0.5 and 6.0 h after aerosol exposure were sensitive to lysostaphin, a rapidly bactericidal enzyme with no demonstrable activity against intracellular organisms and therefore, presumably extracellular. Photomicrographs from lavage pellets obtained 0.5, 1.5, 3.0, and 5.5 h after aerosol exposure confirmed the presence of numerous extracellular cocci. These extracellular cocci were eliminated at the same rate as whole lung cocci (half-life = 3.07 and 3.14 h, respectively) and at a much faster rate than intracellular cocci. In summary, we found large numbers of extracellular staphylococci in bronchoalveolar spaces during the first 6 h after aerosol exposure that are inactivated at the same rate as the whole lung bacterial population. Since only a small number of staphylococci are ingested by macrophages and intracellular bactericidal activity appears too slow to explain intrapulmonary killing, we conclude that an as yet unidentified extracellular killing process contributed to staphylococcal clearance.

Effects of arachidonic acid hydroperoxides on vascular and non-vascular smooth muscle

The omega-6 and omega-9 hydroperoxides of arachidonic acid (AA) caused dose-dependent contraction of rabbit aortic strip (RAS) and guinea pig ileum (GPI) at concentrations between 5 and 200 microM. At these concentrations, arachidonic acid had no effect in these preparations. The contractions could not be blocked by indomethacin, methysergide, phenoxybenzamine, propranolol, diphenhydramine, scopolamine, or the SRS-A antagonist FPL-55712, but were abolished by the calcium channel blocker nimodipine. In both tissues, the hydroperoxides initiated a sustained contraction. The onset of GPI contraction however, was much faster than the response of RAS to these hydroperoxides. 15-HPETE produced a more sustained contraction than 12-HPETE in both RAS and GPI. These results suggest that hydroperoxides generated from AA by the action of lipoxygenase can directly induce smooth muscle contraction and this effect is probably mediated through altering calcium fluxes in these smooth muscle preparations.