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

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Secretory phospholipases A2 are secreted from ciliated cells and increase mucin and eicosanoid secretion from goblet cells

BACKGROUND

Secretory phospholipases A2 (sPLA2) initiate the biosynthesis of eicosanoids, are increased in the airways of people with severe asthma, and induce mucin hypersecretion. We used IL-13-transformed, highly enriched goblet cells and differentiated (ciliary cell-enriched) human bronchial epithelial cell culture to evaluate the relative contribution of ciliated and goblet cells to airway sPLA2 generation and response. We wished to determine the primary source(s) of sPLA2 and leukotrienes in human airway epithelial cells.

METHODS

Human bronchial epithelial cells from subjects without lung disease were differentiated to a ciliated-enriched or goblet-enriched cell phenotype. Synthesis of sPLA2, cysteinyl leukotrienes (cysLTs), and airway mucin messenger RNA and protein was measured by real-time-polymerase chain reaction and an enzyme-linked immunosorbent assay, and the localization of mucin and sPLA2 to specific cells types was confirmed by confocal microscopy.

RESULTS

sPLA2 group IIa, V, and X messenger RNA expression was increased in ciliated-enriched cells (P < .001) but not in goblet-enriched cells. sPLA2 were secreted from the apical (air) side of ciliated-enriched cells but not goblet-enriched cells (P < .001). Immunostaining of sPLA2 V was strongly positive in ciliated-enriched cells but not in goblet-enriched cells. sPLA2 released cysLTs from goblet-enriched cells but not from ciliated-enriched cells, and this result was greatest with sPLA2 V (P < .05). sPLA2 V increased goblet-enriched cell mucin secretion, which was inhibited by inhibitors of lipoxygenase or cyclooxygenase (P < .02).

CONCLUSIONS

sPLA2 are secreted from ciliated cells and appear to induce mucin and cysLT secretion from goblet cells, strongly suggesting that airway goblet cells are proinflammatory effector cells.

Sulfasalazine and 5-aminosalicylic acid inhibit contractile leukotriene formation

Sulfasalazine, used therapeutically in the treatment of ulcerative colitis, is cleaved in vivo to form 5-aminosalicylic acid (5-ASA) and sulfapyridine. In an isolated preparation of rat peritoneal cells both sulfasalazine (IC50 = 0.15 mM) and 5-ASA (IC50 = 2.3 mM), but not sulfapyridine, inhibited calcium ionophore-stimulated formation of contractile leukotriene activity. This activity, although not identified directly, is attributable to a mixture of leukotriene C4 and leukotriene D4 (commonly referred to as SRS-A, or slow-reacting substance of anaphylaxis). Reference compounds evinced expected activities (IC50 = 0.024 mM for phenidone, IC50 = 0.3 microM for nordihydroguaiaretic acid, IC50 = 0.033 mM for BW 755C), whereas para-aminosalicylic acid and thiosalicylic acid were inactive. These properties of sulfasalazine may contribute to its therapeutic efficacy in vivo.

Inhibition of the 5-lipoxygenase pathway with piriprost (U-60,257) protects normal primates from ozone-induced methacholine hyperresponsive small airways

Weekly exposure to ozone in seven normal Rhesus monkeys led to induction of methacholine hypersensitive airways (RL increases 242 +/- 60% and Cdyn decreases 68 +/- 13% of baseline methacholine responses). It took 19 weeks to establish this hyperresponse that persisted for greater than 15 weeks once ozone was stopped. A second exposure led to similar response peaks in 6 weeks. At the peak of the second response, weekly 1% piriprost exposure before ozone led to a return to baseline that was not different between placebo and piriprost treated animals (9.4 +/- 1.0 and 4.3 +/- 2.9 weeks, placebo and treated, respectively P = 0.09 NS). A statistical difference in the mecholyl response in placebo and piriprost treated groups while on ozone was shown only in the Cdyn measurement (Cdyn% change 68 +/- 13 vs 24 +/- 14, placebo and piriprost, respectively P = 0.03). Off ozone (or return to baseline), a statistical difference could be detected both in RL and Cdyn (RL% changed 151 +/- 41 vs 31.1 +/- 49, P = 0.03, and for Cdyn 62.7 +/- 8 vs 9 +/- 10, P = 0.0006, placebo and piriprost, respectively). We conclude tha the primate provides a chronic model of airways reactivity in which the role of lipoxygenase is implicated because of the beneficial role of piriprost, and further that the ozone lesion is primarily in the smaller airways (possibly and alveolitis).

Airway responses to aerosolized leukotriene D4 (LTD4) in normal and Ascaris reactor primates

Normal and Ascaris reactor primates were compared for their bronchial pulmonary response to aerosolized leukotriene D4 (LTD4). When 10 micrograms/ml LTD4 was aerosolized (total amount delivered to endotracheal tube was 1.0 micrograms) into the lungs of 6 normal primates, a small increase in total lung resistance (RL) was noted (4.4 +/- 4.5% increase, in 19 separate challenges). However, a larger effect was seen in compliance (27.6 +/- 15.8% decrease, n = 19). Ascaris reactors (n=4) demonstrated a larger RL effect than normals with almost an identical Cdyn change (RL 36.1 +/- 27.7% increase, Cdyn 32.8 +/- 18.8% decrease n = 12). When the pharmacological blockers diphenhydramine, 0.5 mg/kg and atropine, 0.5 mg/kg were administered iv separately before LTD4 challenge, significant antagonist activity was seen. Diphenhydramine inhibited the LTD4 response in normal primates (RL 64.2 +/- 44.3% and Cdyn 50.5 +/- 40.9% n = 6) and in reactors (RL 47.8 +/- 43.1% and Cdyn 19.2 +/- 20.8% n = 4). Atropine inhibited normals (RL 100% and Cdyn 73.1 +/- 32.7% n = 2) and reactors (RL 96.3 +/- 7.7 and Cdyn 47.4 +/- 35.1% n = 3). These results indicate that the LTD agonist action is partially mediated through histamine, primarily acting on lung resistance (large airways) and, in addition, may have a reflex atropine-sensitive component. The difference between the response of normal and reactor primates to LTD4 is primarily a histamine-mediated large airway response.

Effects of prostaglandins E1, E2, and F2 alpha on mucin secretion from human bronchi in vitro

The effects of three prostaglandins on the output of 35S labelled mucus glycoproteins (mucins), from explants of human bronchial tissue suspended in Ussing chambers, have been investigated. Prostaglandin F2 alpha, added to the Krebs-Henseleit solution bathing both luminal and submucosal sides of the tissue, significantly increased mucin output at concentrations of 0.1 and 1.0 micrograms/ml (0.28 and 2.8 microM), 11 preparations being used for each dose. Since prostaglandin F2 alpha has been shown to be released from human airways challenged by antigen, it may be important in the regulation of mucus secretion in these circumstances. Prostaglandins E1 and E2 had no significant effects on mucin output even at the highest concentration (1.0 micrograms/ml), though in half the tissues tested PGE2 stimulated secretion consistently. These results contrast with the findings in a previous study, which showed an inhibition of mucin output by PGE2.