Hyperosmolar solution effects in guinea pig airways. I. Mechanical responses to relative changes in osmolarity

Nerve growth factor reduces amiloride-sensitive Na+ transport in human airway epithelial cells

Nerve growth factor (NGF) is overexpressed in patients with inflammatory lung diseases, including virus infections. Airway surface liquid (ASL), which is regulated by epithelial cell ion transport, is essential for normal lung function. No information is available regarding the effect of NGF on ion transport of airway epithelium. To investigate whether NGF can affect ion transport, human primary air‐interface cultured epithelial cells were placed in Ussing chambers to obtain transepithelial voltage (−7.1 ± 3.4 mV), short‐circuit current (I_sc, 5.9 ± 1.0 μA), and transepithelial resistance (750 Ω·cm²), and to measure responses to ion transport inhibitors. Amiloride (apical, 3.5 × 10⁻⁵ mol/L) decreased I_sc by 55.3%. Apically applied NGF (1 ng/mL) reduced I_sc by 5.3% in 5 min; basolaterally applied NGF had no effect. The response to amiloride was reduced (41.6%) in the presence of NGF. K‐252a (10 nmol/L, apical) did not itself affect Na⁺ transport, but it attenuated the NGF‐induced reduction in Na⁺ transport, indicating the participation of the trkA receptor in the NGF‐induced reduction in Na⁺ transport. PD‐98059 (30 μmol/L, apical and basolateral) did not itself affect Na⁺ transport, but attenuated the NGF‐induced reduction in Na⁺ transport, indicating that trkA activated the Erk 1/2 signaling cascade. NGF stimulated phosphorylation of Erk 1/2 and the β‐subunit of ENaC. K‐252a and PD‐98059 inhibited these responses. NGF had no effect on I_sc in the presence of apical nystatin (50 μmol/L). These results indicate that NGF inhibits Na⁺ transport through a trkA‐Erk 1/2‐activated signaling pathway linked to ENaC phosphorylation.

Nerve growth factor (apical, 1 ng/mL) reduced amiloride‐sensitive Na⁺ transport in human cultured bronchial epithelial cells. We determined that this reduction in Na⁺ transport occurred through NGF‐mediated activation of the trkA receptor and Erk 1/2 signaling cascade to cause phosphorylation of ENaC.

Nephropathy after administration of iso-osmolar and low-osmolar contrast media: evidence from a network meta-analysis

BACKGROUND/OBJECTIVES

Contrast-induced nephropathy (CIN) may be a severe complication to the administration of iodine-based contrast media for diagnostic or interventional procedure using radiation exposure. Whether there is a difference in nephrotoxic potential between the various agents is uncertain. We aimed to perform a systematic review and network meta-analysis of randomized trials on iodine-based contrast agents.

METHODS

Randomized trials of low-osmolar or iso-osmolar contrast media were searched in CENTRAL, Google Scholar, MEDLINE/PubMed, and Scopus. Risk of CIN was appraised within a hierarchical Bayesian model computing absolute rates (AR) and odds ratios (OR) with 95% credibility intervals, and probability of being best (Pbest) for each agent.

RESULTS

A total of 42 trials (10048 patients) were included focusing on 7 different iodine-based contrast media. Risk of CIN was similarly low with iodixanol (AR=5.7% [2.2%-13.9%], Pbest=18.8%), iomeprol (AR=6.0% [2.2%-15.4%], Pbest=24.8%), iopamidol (AR=6.1% [2.2%-15.5%], Pbest=21.5%), and ioversol (AR=6.0% [2.1%-16.4%], Pbest=31.3%). Conversely, CIN was twice as common with iohexol (AR=11.2% [4.1%-29.5%], Pbest=0.1%) and ioxaglate (AR=11.0% [4.0%-26.9%], Pbest<0.1%), with both proving less safe than iodixanol (respectively OR=2.18 [1.22-3.92] and 2.05 [1.26-3.29]), iomeprol (OR=2.08 [1.04-4.17] and 1.96 [1.06-3.48]) and iopamidol (OR=2.04 [1.15-3.85] and 1.92 [1.06-3.45]). Data on iopromide were less conclusive (AR=6.9% [2.6%-17.1%], Pbest=3.6%).

CONCLUSIONS

Iodixanol, iomeprol, iopamidol and ioversol are iodine-based contrast media with a similar renal safety profile. Iohexol and ioxaglate have a poorer renal safety profile, whereas further data may be required on iopromide.

Tracheal epithelium cell volume responses to hyperosmolar, isosmolar and hypoosmolar solutions: relation to epithelium-derived relaxing factor (EpDRF) effects

In asthmatic patients, inhalation of hyperosmolar saline or D-mannitol (D-M) elicits bronchoconstriction, but in healthy subjects exercise causes bronchodilation. Hyperventilation causes drying of airway surface liquid (ASL) and increases its osmolarity. Hyperosmolar challenge of airway epithelium releases epithelium-derived relaxing factor (EpDRF), which relaxes the airway smooth muscle. This pathway could be involved in exercise-induced bronchodilation. Little is known of ASL hyperosmolarity effects on epithelial function. We investigated the effects of osmolar challenge maneuvers on dispersed and adherent guinea-pig tracheal epithelial cells to examine the hypothesis that EpDRF-mediated relaxation is associated with epithelial cell shrinkage. Enzymatically-dispersed cells shrank when challenged with ≥10 mOsM added D-M, urea or NaCl with a concentration-dependence that mimics relaxation of the of isolated perfused tracheas (IPT). Cells shrank when incubated in isosmolar N-methyl-D-glucamine (NMDG) chloride, Na gluconate (Glu), NMDG-Glu, K-Glu and K2SO4, and swelled in isosmolar KBr and KCl. However, isosmolar challenge is not a strong stimulus of relaxation in IPTs. In previous studies amiloride and 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) inhibited relaxation of IPT to hyperosmolar challenge, but had little effect on shrinkage of dispersed cells. Confocal microscopy in tracheal segments showed that adherent epithelium is refractory to low hyperosmolar concentrations that induce dispersed cell shrinkage and relaxation of IPT. Except for gadolinium and erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), actin and microtubule inhibitors and membrane permeabilizing agents did not affect on ion transport by adherent epithelium or shrinkage responses of dispersed cells. Our studies dissociate relaxation of IPT from cell shrinkage after hyperosmolar challenge of airway epithelium.

Airway epithelium-derived relaxing factor: myth, reality, or naivety?

The presence of a healthy epithelium can moderate the contraction of the underlying airway smooth muscle. This is, in part, because epithelial cells generate inhibitory messages, whether diffusible substances, electrophysiological signals, or both. The epithelium-dependent inhibitory effect can be tonic (basal), synergistic, or evoked. Rather than a unique epithelium-derived relaxing factor (EpDRF), several known endogenous bronchoactive mediators, including nitric oxide and prostaglandin E2, contribute. The early concept that EpDRF diffuses all the way through the subepithelial layers to directly relax the airway smooth muscle appears unlikely. It is more plausible that the epithelial cells release true messenger molecules, which alter the production of endogenous substances (nitric oxide and/or metabolites of arachidonic acid) by the subepithelial layers. These substances then diffuse to the airway smooth muscle cells, conveying epithelium dependency.

Pulmonary effects after acute inhalation of oil dispersant (COREXIT EC9500A) in rats

COREXIT EC9500A (COREXIT) was used to disperse crude oil during the 2010 Deepwater Horizon oil spill. While the environmental impact of COREXIT has been examined, the pulmonary effects are unknown. Investigations were undertaken to determine whether inhaled COREXIT elicits airway inflammation, alters pulmonary function or airway reactivity, or exerts pharmacological effects. Male rats were exposed to COREXIT (mean 27 mg/m(3), 5 h). Bronchoalveolar lavage was performed on d 1 and 7 postexposure. Lactate dehydrogenase (LDH) and albumin were measured as indices of lung injury; macrophages, neutrophils, lymphocytes, and eosinophils were quantified to evaluate inflammation; and oxidant production by macrophages and neutrophils was measured. There were no significant effects of COREXIT on LDH, albumin, inflammatory cell levels or oxidant production at either time point. In conscious animals, neither breathing frequency nor specific airway resistance were altered at 1 hr, 1 d and 7 d postexposure. Airway resistance responses to methacholine (MCh) aerosol in anesthetized animals were unaffected at 1 and 7 d postexposure, while dynamic compliance responses were decreased after 1 d but not 7 d. In tracheal strips, in the presence or absence of MCh, low concentrations of COREXIT (0.001% v/v) elicited relaxation; contraction occurred at 0.003-0.1% v/v. In isolated, perfused trachea, intraluminally applied COREXIT produced similar effects but at higher concentrations. COREXIT inhibited neurogenic contractile responses of strips to electrical field stimulation. Our findings suggest that COREXIT inhalation did not initiate lung inflammation, but may transiently increase the difficulty of breathing.

Hyperosmolarity-induced dilation and epithelial bioelectric responses of guinea pig trachea in vitro: role of kinase signaling

Exercise-induced airway obstruction is thought to involve evaporative water loss and hyperosmolarity of the airway surface liquid. Hyperosmolar challenge of the epithelium of isolated, perfused guinea pig trachea rapidly alters transepithelial potential difference (V(t)), and it elicits smooth muscle relaxation mediated by epithelium-derived relaxing factor (EpDRF). In many cell types, protein kinases mediate responses to hyperosmolarity and regulatory volume increase. In this study, inhibitors were used to investigate the involvement of kinases and phosphatases in bioelectric responses of epithelium to hyperosmolarity and their possible relationship to EpDRF-mediated relaxation. After contraction of the perfused trachea with extraluminal methacholine, D-mannitol applied intraluminally (< or = 80 mosM) increased V(t) and elicited dilation of the smooth muscle with a similar concentration-dependence; higher concentrations decreased V(t). In tracheas exposed to 30 mosM D-mannitol (approximately EC(50)), 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB 203580) and SKF 86002 [6-(4-fluorophenyl)-2,3-dihydro-5-(4-pyridyl)imidazo[2,1-b]thiazole] (p38 inhibitors) potentiated the dilation, whereas SP 600125 [anthra[1,9-cd]pyrazol-6(2H)-one-1,9-pyrazoloanthrone] and dicumarol [c-Jun NH(2)-terminal kinase (JNK) inhibitors], chelerythrine [nonselective protein kinase C (PKC) inhibitor], and NaAsO(2) (mitogen-activated protein kinase stress inducer) and Na(3)VO(4) (protein tyrosine phosphatase inhibitor) inhibited the hyperpolarization. Large increases in the phosphorylation of p38 and JNK occurred at concentrations higher than those needed to elicit functional responses. The phosphatidylinositol 3-kinase inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY 294002) and Na(3)VO(4) did not affect the V(t) responses, but they inhibited methacholine-induced constriction; SP 600125 and dicumarol potentiated, and chelerythrine inhibited, methacholine-induced epithelial hyperpolarization. These results suggest that JNK, PKC, and phosphatase(s) are involved in hyperosmolarity-induced hyperpolarization of the tracheal epithelium but that p38 is involved in EpDRF-mediated relaxation.

Altered ion transport and responsiveness to methacholine and hyperosmolarity in air interface-cultured guinea-pig tracheal epithelium

INTRODUCTION

Challenge of guinea-pig tracheal epithelium with hyperosmolar solution alters ion transport and evokes the release of epithelium-derived relaxing factor (EpDRF). Cultured tracheal epithelial cells (CE) offer the potential to examine biochemical pathways related to EpDRF release, but whether the bioelectric properties and responses of fresh, adherent epithelial cells (FE) are modeled by CE has not been established.

METHODS

Tracheal epithelial cells grown in air-interface culture and fresh tracheal segments were mounted in Ussing chambers to determine short circuit current (I(sc)) and transepithelial resistance (R(t)) and to compare responses to transport inhibitors, methacholine and hyperosmolarity.

RESULTS

Significant differences in basal I(sc) and R(t) between FE and CE were observed (I(sc), 41.3+/-3.5 and 8.5+/-0.8 microA/cm(2), P<0.05; R(t), 106+/-7 and 422+/-4 Omega cm(2), P<0.05; respectively); basal spontaneous potential difference values were not different (4.2+/-0.3 and 3.4+/-0.3 mV, respectively). Amiloride (mucosal, 3 x 10(-5) M), bumetanide (basolateral, 10(-5) M) and ouabain (basolateral, 10(-5) M) reduced I(sc) equally in FE and CE. In contrast, NPPB (10(-5) M) in the presence of amiloride had a differential effect, decreasing I(sc) by 11% in FE and 71% in CE (P<0.05). Iberiotoxin (basolateral, 10(-7) M) was without effect in either preparation. In FE, serosal methacholine (3x10(-5) M) elicited an NPPB-insensitive monotonic increase in I(sc), but in CE caused a large, transient, NPPB-inhibitable increase which was followed by an NPPB-resistant plateau. Addition of apical D-mannitol (0.3-267 mosM) to increase osmolarity decreased I(sc) in FE, whereas in CE d-mannitol initially increased (0.3-84.3 mosM) and then decreased (84.3-267 mosM) I(sc).

DISCUSSION

Cell culture causes substantial changes in the bioelectric and pharmacological properties of respiratory epithelium. Caution should be exercised when using CE as a substitute for FE in studies of ion transport- and cell volume-dependent processes.

Hyperosmolar solution effects in guinea pig airways. III. Studies on the identity of epithelium-derived relaxing factor in isolated perfused trachea using pharmacological agents

Hyperosmolar challenge of airway epithelium stimulates the release of epithelium-derived relaxing factor (EpDRF), but the identity of EpDRF is not known. We examined the effects of pharmacological agents on relaxant responses of methacholine (3 x 10(-7) M)-contracted guinea pig perfused trachea to mucosal hyperosmolar challenge using D-mannitol. Responses were inhibited by gossypol (5 x 10(-6) M), an agent with diverse actions, by the carbon monoxide (CO) scavenger hemoglobin (10(-6) M), and by the heme oxygenase (HO) inhibitor zinc (II) protoporphyrin IX (10(-4) M). The HO inhibitor chromium (III) mesoporphyrin IX (10(-4) M) was not inhibitory, and the HO activator heme-L-lysinate (3 x 10(-4) M) did not evoke relaxant responses. The CO donor tricarbonyldichlororuthenium (II) dimer (2.2 x 10(-4) M) elicited small relaxation responses. Other agents without an effect on responses included: apyrase, adenosine, 6-anilino-5,8-quinolinequinone (LY83583), proadifen, (E)-3-[[[3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid (MK 571), diphenhydramine, glibenclamide, HgCl2, tetrodotoxin, nystatin, alpha-hemolysin, 8-bromoguanosine 3',5'-cyclic monophosphothioate, Rp-isomer, 12-O-tetradecanoylphorbol-13-acetate, cholera toxin, pertussis toxin, thapsigargin, nifedipine, Ca(2+)-free mucosal solution, hydrocortisone, and epidermal growth factor. Cytoskeleton inhibitors, includingerythro-9-(2-hydroxyl-3-nonyl)adenine, colchicine, nocodazole, latrunculin B, and cytochalasins B and D, had no effect on relaxation responses. The results suggest provisionally that a portion of EpDRF activity may be due to CO and that the release of EpDRF does not involve cytoskeletal reorganization.