N-acetylcysteine inhibits Na+ absorption across human nasal epithelial cells

Mucus-targeting therapies of defective mucus clearance for cystic fibrosis: A short review

In the lungs, defective CFTR associated with cystic fibrosis (CF) represents the nidus for abnormal mucus clearance in the airways and consequently a progressive lung disease. Defective CFTR-mediated Cl^- secretion results in altered mucus properties, including concentration, viscoelasticity, and the ratio of the two mucins, MUC5B and MUC5AC. In the past decades, therapies targeting the CF mucus defect, directly or indirectly, have been developed; nevertheless, better treatments to prevent the disease progression are still needed. This review summarizes the existing knowledge on the defective mucus in CF disease and highlights it as a barrier to the development of future inhaled genetic therapies. The use of new mucus-targeting treatments is also discussed, focusing on their potential role to halt the progress of CF lung disease.

The short-term rinsing of airways by N-acetylcysteine helps expectoration: The mechanism of sodium and chloride transport

N-acetyl-L-cysteine (NAC) mucolytic and antioxidant role is well known, but the effect on epithelial ion transport has not been yet described. The aim of the study was to evaluate the short-term and prolonged influence of NAC on ion transport in the epithelium. The experiment was performed on 108 fragments of rabbit tracheae. Fragments were divided into four groups: inhibited sodium (I) and chloride (II) transport, NAC with inhibited sodium (III) and NAC with inhibited chloride (IV) transport. The changes in electrophysiological parameters were measured in stationary conditions and during mechanical-chemical stimulation after immediate (15 s) and prolonged (60 min) N-acetylcysteine administration on the tissue. Each 15-second stimulation caused repeatable changes in the electric potential of the tissue. In trachea fragments with blocked chloride ion transport, significantly lower (P <0.0001) values of electric potential following prolonged NAC effect were observed when compared to short-term NAC-stimulation. The values of resistance were constant during experiments, which reflects the vitality of the tissue. Short-term NAC administration influences sodium ion transport, which is not observed in a prolonged stimulation. The use of the NAC solution to rinse the airways is of great clinical importance due to the short and intense contact with the epithelium.

How to characterize a nasal product. The state of the art of in vitro and ex vivo specific methods

Nasal delivery offers many benefits over other conventional routes of delivery (e.g. oral or intravenous administration). Benefits include, among others, a fast onset of action, non-invasiveness and direct access to the central nervous system. The nasal cavity is not only limited to local application (e.g. rhinosinusitis) but can also provide direct access to other sites in the body (e.g. the central nervous system or systemic circulation). However, both the anatomy and the physiology of the nose impose their own limitations, such as a small volume for delivery or rapid mucociliary clearance. To meet nasal-specific criteria, the formulator has to complete a plethora of tests, in vitro and ex vivo, to assess the efficacy and tolerance of a new drug-delivery system. Moreover, depending on the desired therapeutic effect, the delivery of the drug should target a specific pathway that could potentially be achieved through a modified release of this drug. Therefore, this review focuses on specific techniques that should be performed when a nasal formulation is developed. The review covers both the tests recommended by regulatory agencies (e.g. the Food and Drug Administration) and other complementary experiments frequently performed in the field.

DUOX1-mediated hydrogen peroxide release regulates sodium transport in H441 bronchiolar epithelial cells

AIM

Dexamethasone has been shown to induce the formation of epithelial domes by bronchiolar H441 cells. It stimulates the expression of both amiloride inhibitable epithelial sodium channels (ENaC) and dual oxidase-1 (DUOX1). We therefore ask the question whether DUOX1 expression and production of submillimolar amounts of H₂ O₂ is instrumental for the sodium channel upregulation observed in H441 cells.

METHODS

In vitro cell culture, nystatin-perforated whole-cell patch-clamp technique, immunocytochemistry and RT-PCR methods have been used.

RESULTS

Cells forming epithelial domes induced by dexamethasone (0.1 μmol L^-1 , 24 hours) and by 5-aza-2'-deoxytidine (1 μmol L^-1 , 48 hours) expressed more DUOX1 protein compared with other cells in the monolayer. Dome formation could be inhibited by exogenous catalase in a concentration-dependent manner and by the NADPH oxidase inhibitor diphenyliodonium, which suggested the involvement of H₂ O₂ . While single application of 0.2 mmol L^-1 H₂ O₂ induced transient dome formation, lower doses were ineffective and higher doses disrupted the cell monolayer. Hydrogen peroxide (0.1 mmol L^-1 ) activated acutely amiloride-sensitive whole-cell currents from 3.91 ± 0.79 pA pF^-1 to 4.76 ± 0.98 pA pF^-1 in dome-forming cells and had no effect in cells outside of domes. ENaC but not DUOX1 transcription was potentiated by catalase in the presence of dexamethasone, which suggested negative feedback of H₂ O₂ on ENaC gene expression.

CONCLUSION

Our observations suggest that tonic production of H₂ O₂ by DUOX1 participates in maintaining the level of vectorial sodium transport by lung epithelial cells. Moreover, the system appears to be well tuned as it would allow H₂ O₂ -dependent innate immunity without inducing airway/alveolar sodium and fluid hyperabsorption.

Evidence of a Redox-Dependent Regulation of Immune Responses to Exercise-Induced Inflammation

We used thiol-based antioxidant supplementation (n-acetylcysteine, NAC) to determine whether immune mobilisation following skeletal muscle microtrauma induced by exercise is redox-sensitive in healthy humans. According to a two-trial, double-blind, crossover, repeated measures design, 10 young men received either placebo or NAC (20 mg/kg/day) immediately after a muscle-damaging exercise protocol (300 eccentric contractions) and for eight consecutive days. Blood sampling and performance assessments were performed before exercise, after exercise, and daily throughout recovery. NAC reduced the decline of reduced glutathione in erythrocytes and the increase of plasma protein carbonyls, serum TAC and erythrocyte oxidized glutathione, and TBARS and catalase activity during recovery thereby altering postexercise redox status. The rise of muscle damage and inflammatory markers (muscle strength, creatine kinase activity, CRP, proinflammatory cytokines, and adhesion molecules) was less pronounced in NAC during the first phase of recovery. The rise of leukocyte and neutrophil count was decreased by NAC after exercise. Results on immune cell subpopulations obtained by flow cytometry indicated that NAC ingestion reduced the exercise-induced rise of total macrophages, HLA⁺ macrophages, and 11B⁺ macrophages and abolished the exercise-induced upregulation of B lymphocytes. Natural killer cells declined only in PLA immediately after exercise. These results indicate that thiol-based antioxidant supplementation blunts immune cell mobilisation in response to exercise-induced inflammation suggesting that leukocyte mobilization may be under redox-dependent regulation.

Strategic approaches for enhancement of in vivo transbuccal peptide drug delivery in rabbits using iontophoresis and chemical enhancers

PURPOSE

To evaluate the feasibility of iontophoresis and the combination effects with chemical enhancers on in vivo hypocalcemic effect of transbuccally delivered salmon calcitonin (sCT).

METHODS

N-acetyl-L-cysteine (NAC), sodium deoxyglycocholate (SDGC), and ethanol were used as chemical enhancers; and 0.5 mA/cm(2) fixed electric current was employed as a physical enhancer. sCT hydrogel was applied to rabbit buccal mucosa, and blood samples were obtained via the central auricular artery. Blood calcium level was measured by calcium kit and the conformational changes of buccal mucosa were investigated with FT-IR spectroscopy. Hematoxylin/eosin staining was used for the histological evaluation of buccal mucosa.

RESULTS

Iontophoresis groups except iontophoresis-NAC group showed significant hypocalcemic effect compared to negative control, in particular iontophoresis-SDGC combination group showed fast onset of action as well as sustained hypocalcemic effect (p < 0.05). FT-IR result demonstrated the reduction of buccal barrier function, and the histological study showed a decrease in buccal thickness as well as minor damage to the dermal-epidermal junctions in the enhancing method groups; however, the damaged tissues virtually recovered within 24 h after the removal of electrodes.

CONCLUSIONS

Iontophoresis and combination with SDGC were found to be safe and potential strategies for transbuccal peptide delivery in vivo.

Proinflammatory cytokine secretion is suppressed by TMEM16A or CFTR channel activity in human cystic fibrosis bronchial epithelia

Functional expression of either CFTR or the calcium-activated chloride channel TMEM16A attenuates expression and secretion of the proinflammatory cytokines IL-6, IL-8, and CXCL1/2 in respiratory epithelia. Thus augmented proinflammatory cytokine secretion caused by defective anion transport may contribute to lung inflammation in cystic fibrosis.

Cystic fibrosis (CF) is caused by the functional expression defect of the CF transmembrane conductance regulator (CFTR) chloride channel at the apical plasma membrane. Impaired bacterial clearance and hyperactive innate immune response are hallmarks of the CF lung disease, yet the existence of and mechanism accounting for the innate immune defect that occurs before infection remain controversial. Inducible expression of either CFTR or the calcium-activated chloride channel TMEM16A attenuated the proinflammatory cytokines interleukin-6 (IL-6), IL-8, and CXCL1/2 in two human respiratory epithelial models under air–liquid but not liquid–liquid interface culture. Expression of wild-type but not the inactive G551D-CFTR indicates that secretion of the chemoattractant IL-8 is inversely proportional to CFTR channel activity in cftr^{∆F508/∆F508} immortalized and primary human bronchial epithelia. Similarly, direct but not P2Y receptor–mediated activation of TMEM16A attenuates IL-8 secretion in respiratory epithelia. Thus augmented proinflammatory cytokine secretion caused by defective anion transport at the apical membrane may contribute to the excessive and persistent lung inflammation in CF and perhaps in other respiratory diseases associated with documented down-regulation of CFTR (e.g., chronic obstructive pulmonary disease). Direct pharmacological activation of TMEM16A offers a potential therapeutic strategy to reduce the inflammation of CF airway epithelia.

New therapeutic option with N-acetylcysteine for primary sclerosing cholangitis: two case reports

Primary sclerosing cholangitis is a progressive, cholestatic hepatic disease of unknown etiology. It is characterized by progressive inflammation, destruction, and fibrosis of the intrahepatic and extrahepatic bile ducts. Several medical therapies have been tried such as penicilamin, colchicine, methatraxate, cyclosporine, tacrolimus, and ursodeoxycholic acid. Treatment with mucolytic agents in excessively high viscosity conditions appears to have an important role. N-acetylcysteine (NAC), as a mucolytic agent, may fascilitate the drainage in partial obstructions by decreasing the mucous viscosity. We suggest that NAC and ursodeoxycholic acid have markedly positive effects on the clinical course of cholangitis and cholestasis when used together by affecting bile viscosity. Here, we present two cases treated with NAC. NAC capsul therapies at 800 mg/day were administered to two patients with primary sclerosing cholangitis. Clinical and laboratory parameters of patients saw significant improvement.

Defective CFTR induces aggresome formation and lung inflammation in cystic fibrosis through ROS-mediated autophagy inhibition

Accumulation of unwanted/misfolded proteins in aggregates has been observed in airways of patients with cystic fibrosis (CF), a life-threatening genetic disorder caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). Here we show how the defective CFTR results in defective autophagy and decreases the clearance of aggresomes. Defective CFTR-induced upregulation of reactive oxygen species (ROS) and tissue transglutaminase (TG2) drive the crosslinking of beclin 1, leading to sequestration of phosphatidylinositol-3-kinase (PI(3)K) complex III and accumulation of p62, which regulates aggresome formation. Both CFTR knockdown and the overexpression of green fluorescent protein (GFP)-tagged-CFTR(F508del) induce beclin 1 downregulation and defective autophagy in non-CF airway epithelia through the ROS-TG2 pathway. Restoration of beclin 1 and autophagy by either beclin 1 overexpression, cystamine or antioxidants rescues the localization of the beclin 1 interactome to the endoplasmic reticulum and reverts the CF airway phenotype in vitro, in vivo in Scnn1b-transgenic and Cftr(F508del) homozygous mice, and in human CF nasal biopsies. Restoring beclin 1 or knocking down p62 rescued the trafficking of CFTR(F508del) to the cell surface. These data link the CFTR defect to autophagy deficiency, leading to the accumulation of protein aggregates and to lung inflammation.

Modulation of epithelial sodium channel trafficking and function by sodium 4-phenylbutyrate in human nasal epithelial cells

Sodium 4-phenylbutyrate (4-PBA) has been shown to correct the cellular trafficking of several mutant or nonmutant plasma membrane proteins such as cystic fibrosis transmembrane conductance regulator through the expression of 70-kDa heat shock proteins. The objective of the study was to determine whether 4-PBA may influence the functional expression of epithelial sodium channels (ENaC) in human nasal epithelial cells (HNEC). Using primary cultures of HNEC, we demonstrate that 4-PBA (5 mm for 6 h) markedly stimulated amiloride-sensitive sodium channel activity and that this was related to an increased abundance of alpha-, beta-, and gamma-ENaC subunits in the apical membrane. The increase in ENaC cell surface expression (i) was due to insertion of newly ENaC subunits as determined by brefeldin A experiments and (ii) was not associated with cell surface retention of ENaC subunits because endocytosis of ENaC subunits was unchanged. In addition, we find that ENaC co-immunoprecipitated with the heat shock protein constitutively expressed Hsc70, that has been reported to modulate ENaC trafficking, and that 4-PBA decreased Hsc70 protein level. Finally, we report that in cystic fibrosis HNEC obtained from two cystic fibrosis patients, 4-PBA increased functional expression of ENaC as demonstrated by the increase in amiloride-sensitive sodium transport and in alpha-, beta-, and gamma-ENaC subunit expression in the apical membrane. Our results suggest that in HNEC, 4-PBA increases the functional expression of ENaC through the insertion of new alpha-, beta-, and gamma-ENaC subunits into the apical membrane and also suggest that 4-PBA could modify ENaC trafficking by reducing Hsc70 protein expression.

Effects of laxative and N-acetylcysteine on mucus accumulation, bacterial load, transit, and inflammation in the cystic fibrosis mouse small intestine

The accumulation of mucus in affected organs is characteristic of cystic fibrosis (CF). The CF mouse small intestine has dramatic mucus accumulation and exhibits slower interdigestive intestinal transit. These factors are proposed to play cooperative roles that foster small intestinal bacterial overgrowth (SIBO) and contribute to the innate immune response of the CF intestine. It was hypothesized that decreasing the mucus accumulation would reduce SIBO and might improve other aspects of the CF intestinal phenotype. To test this, solid chow-fed CF mice were treated with an osmotic laxative to improve gut hydration or liquid-fed mice were treated orally with N-acetylcysteine (NAC) to break mucin disulfide bonds. Treatment with laxative or NAC reduced mucus accumulation by 43% and 50%, respectively, as measured histologically as dilation of the intestinal crypts. Laxative and NAC also reduced bacterial overgrowth in the CF intestine by 92% and 63%, respectively. Treatment with laxative normalized small intestinal transit in CF mice, whereas NAC did not. The expression of innate immune response-related genes was significantly reduced in laxative-treated CF mice, whereas there was no significant effect in NAC-treated CF mice. In summary, laxative and NAC treatments of CF mice reduced mucus accumulation to a similar extent, but laxative was more effective than NAC at reducing bacterial load. Eradication of bacterial overgrowth by laxative treatment was associated with normalized intestinal transit and a reduction in the innate immune response. These results suggest that both mucus accumulation and slowed interdigestive small intestinal transit contribute to SIBO in the CF intestine.

Improved nasal absorption of salmon calcitonin by powdery formulation with N-acetyl-L-cysteine as a mucolytic agent

To establish a new formulation technology for the nasal delivery of peptide and protein drugs, we examined whether a mucolytic agent, N-acetyl-L-cysteine (NAC), could enhance the nasal absorption of a powder form of salmon calcitonin, a model peptide drug. We used ethylcellulose as an inert water-insoluble excipient. Various test formulations were prepared, and the effects on nasal absorbability were evaluated in rats and dogs. The powder formulation with NAC gave significant nasal absorption of SCT in both animal models, with absolute bioavailabilities of 30.0% in rats and 24.9% in dogs. Also, nasal administration of this formulation gave a quicker absorption rate than subcutaneous administration of SCT. NAC may reduce nasal fluid viscocity and improve accessibility of the drug to the epithelial membrane. The powder SCT/NAC/ethylcellulose formulation did not induce irritation or histological damage to the nasal membrane in rabbits. These results suggest that this formulation technology may be widely applicable for the nasal delivery of peptide or protein drugs.

Is It Go or NO Go for S-Nitrosylation Modification-Based Therapies of Cystic Fibrosis Transmembrane Regulator Trafficking?: Fig. 1

Nitric-oxide synthases (NOS) are abundant in the respiratory epithelium and generate the NO radical, which can activate guanylate cyclase, react with superoxide, or modify proteins by S-nitrosylation (SNO) of Cys thiols. There is increasing appreciation that SNO modification is analogous to phosphorylation, because both signaling mechanisms modulate a wide range of cellular functions. Zaman et al. (p. 1435) in this issue report on the capability of S-nitrosoglutathione (GSNO) to increase the expression, trafficking, and function of mutant and wild-type cystic fibrosis transmembrane regulator (CFTR). The CFTR is a cAMP-regulated chloride channel that functions to regulate salt and water content in glands and ducts of secretory epithelia. GSNO is a low molecular weight SNO (S-nitrosothiol) formed during oxidation of NO. The authors use GSNO as a lead compound to restore mutant CFTR function. Earlier contradictory reports that GSNO decreased CFTR function by oxidative modification (glutathionylation) may now be explained by high concentrations of GSNO associated with decreased CFTR transcription and disruption of CFTR function. Zaman et al. show that at physiologic concentrations, GSNO and the constitutively active S-nitroso-glutathione diethyl ester stimulate CFTR transcription through SP1 and SP3 and promote normal trafficking. The mechanism behind rescue from the degradative pathway relies on increasing the expression of cysteine string proteins and SNO modification of chaperones involved in mediating CFTR transit through the endoplasmic reticulum and Golgi apparatus.

A viscoelastic traction layer model of muco-ciliary transport

A new mathematical model of the transport of mucus and periciliary liquid (PCL) in the airways by cilia is presented. Mucus is represented by a linearly viscoelastic fluid, the mat of cilia is modelled as an 'active porous medium.' The propulsive effect of the cilia is modelled by a time-dependent force acting in a shear-thinned 'traction layer' between the mucus and the PCL. The effects of surface and interface tension are modelled by constraining the mucus free surface and mucus-PCL interface to be flat. It is assumed that the epithelium is impermeable to fluid. Using Fourier series, the system is converted into ODEs and solved numerically. We calculate values for mean mucus speed close to those observed by Matsui et al. [J. Clin. Invest., 102(6):1125-1131, 1998], (approximately 40 microm s(-1)). We obtain more detail regarding the dynamics of the flow and the nonlinear relationships between physical parameters in healthy and diseased states than in previously published models. Pressure gradients in the PCL caused by interface and surface tension are vital to ensuring efficient transport of mucus, and the role of the mucus-PCL interface appears to be to support such pressure gradients, ensuring efficient transport. Mean transport of PCL is found to be very small, consistent with previous analyses, providing insight into theories regarding the normal tonicity of PCL.

Role of alveolar epithelial sodium transport in high altitude pulmonary edema (HAPE)

Alveolar edema results from an imbalance between fluid filtration into the alveolar space and removal by reabsorption. Hypoxia increases filtration by raising pulmonary capillary pressure and increasing endothelial and epithelial permeability allowing fluid and blood cells to access the alveoli. Active Na-reabsorption drives the fluid reabsorption from the alveolar space, but hypoxia inhibits reabsorption by inhibition of epithelial Na-channels (ENaC) and Na/K-ATPase. A (genetically determined) low activity of alveolar reabsorption in normoxia and further inhibition by hypoxia might cause HAPE-susceptibility, since at some point the depressed reabsorption may not keep pace with increased filtration. Na-reabsorption might even prove totally inefficient in the presence of large leaks of the alveolar barrier. Alveolar Na-reabsorption has not been measured in HAPE. Nasal epithelial Na-transport has been used as surrogate marker based on similarities in subunit expression of ENaC in nasal, airway, and alveolar epithelium. At high altitude cold, dryness, and nasal infections affect the nasal potential making any extrapolation to processes at the alveolar epithelium unreliable. The variability in nasal Na- and Cl-transport reduces the usefulness of nasal potentials to diagnose HAPE-susceptibility.

Enhancement of nasal absorption of large molecular weight compounds by combination of mucolytic agent and nonionic surfactant

For improving the nasal absorption of poorly absorbable hydrophilic compounds, the suitability of a combination of a mucolytic agent, N-acetyl-L-cysteine (NAC), and a nonionic surfactant, polyoxyethylene (C25) lauryl ether (laureth-25), was examined. Rat studies with fluorescent isothiocyanate-labeled dextran (molecular weight ca. 4.4 kDa, FD-4) as a model hydrophilic compound revealed dramatic enhancement of nasal absorption when NAC and laureth-25 were simultaneously applied. The nasal bioavailability of FD-4 in saline solution was 8.2+/-0.6% but increased to 40.0+/-5.5% when 5% NAC and 5% laureth-25 were added. This synergistic enhancement could result from the mucolytic activity of NAC in reducing mucous viscosity by which the accessibilities of FD-4 and laureth-25 to the epithelial membrane were increased. Further rat studies proved that this formulation increased nasal absorption of salmon calcitonin. Absolute bioavailability from saline solution containing 5% NAC and 1% laureth-25 was 26.8+/-2.2%, 3.5 times that of the commercial calcitonin nasal spray Miacalcin (7.7+/-2.1%). The potential of the new formulation to cause tissue damage in terms of hemolytic activity and liberation of phospholipid from the nasal membranes was nil or slight. The combination of NAC and laureth-25 appears suitable for use in development of nasal products for poorly absorbable drugs, especially peptide and protein drugs.

Therapeutic approaches to mucus hypersecretion

Mucolytic and related agents have been in use since prehistoric times. Although widely prescribed and used extensively in over-the-counter preparations, their efficacy and mechanisms of action remain in doubt. These agents belong to several distinct chemical classes. Mucolytic agents such as N-acetyl-cysteine are thiols with a free-sulfhydryl group. They are assumed to break disulfide bonds between gel-forming mucins and thus reduce mucus viscosity. Mucokinetic agents are thiols with a blocked sulfhydryl group. Expectorants such as guaifenesin increase mucus secretion. They may act as irritants to gastric vagal receptors, and recruit efferent parasympathetic reflexes that cause glandular exocytosis of a less viscous mucus mixture. Cough may be provoked. This combination may flush tenacious, congealed mucopurulent material from obstructed small airways and lead to a temporary improvement in dyspnea or the work of breathing. The roles of anticholinergic agents, DNase, and other drugs are also discussed with regard to their roles in reducing mucus production in rhinitis and other airway diseases.