Phagocyte oxidants and nitric oxide in cystic fibrosis: new therapeutic targets?

Oxidation increases mucin polymer cross-links to stiffen airway mucus gels

Airway mucus in cystic fibrosis (CF) is highly elastic, but the mechanism behind this pathology is unclear. We hypothesized that the biophysical properties of CF mucus are altered because of neutrophilic oxidative stress. Using confocal imaging, rheology, and biochemical measures of inflammation and oxidation, we found that CF airway mucus gels have a molecular architecture characterized by a core of mucin covered by a web of DNA and a rheological profile characterized by high elasticity that can be normalized by chemical reduction. We also found that high levels of reactive oxygen species in CF mucus correlated positively and significantly with high concentrations of the oxidized products of cysteine (disulfide cross-links). To directly determine whether oxidation can cross-link mucins to increase mucus elasticity, we exposed induced sputum from healthy subjects to oxidizing stimuli and found a marked and thiol-dependent increase in sputum elasticity. Targeting mucin disulfide cross-links using current thiol-amino structures such as N-acetylcysteine (NAC) requires high drug concentrations to have mucolytic effects. We therefore synthesized a thiol-carbohydrate structure (methyl 6-thio-6-deoxy-α-D-galactopyranoside) and found that it had stronger reducing activity than NAC and more potent and fast-acting mucolytic activity in CF sputum. Thus, oxidation arising from airway inflammation or environmental exposure contributes to pathologic mucus gel formation in the lung, which suggests that it can be targeted by thiol-modified carbohydrates.

Inflammation, oxidative stress, and cardiovascular disease risk factors in adults with cystic fibrosis

Cystic fibrosis (CF) represents one of a number of localized lung and non-lung diseases with an intense chronic inflammatory component associated with evidence of systemic oxidative stress. Many of these chronic inflammatory diseases are accompanied by an array of atherosclerotic processes and cardiovascular disease (CVD), another condition strongly related to inflammation and oxidative stress. As a consequence of a dramatic increase in long-lived patients with CF in recent decades, the specter of CVD must be considered in these patients who are now reaching middle age and beyond. Buttressed by recent data documenting that CF patients exhibit evidence of endothelial dysfunction, a recognized precursor of atherosclerosis and CVD, the spectrum of risk factors for CVD in CF is reviewed here. Epidemiological data further characterizing the presence and extent of atherogenic processes in CF patients would seem important to obtain. Such studies should further inform and offer mechanistic insights into how other chronic inflammatory diseases potentiate the processes leading to CVDs.

Innate immunity in cystic fibrosis lung disease

Chronic lung disease determines the morbidity and mortality of cystic fibrosis (CF) patients. The pulmonary immune response in CF is characterized by an early and non-resolving activation of the innate immune system, which is dysregulated at several levels. Here we provide a comprehensive overview of innate immunity in CF lung disease, involving (i) epithelial dysfunction, (ii) pathogen sensing, (iii) leukocyte recruitment, (iv) phagocyte impairment, (v) mechanisms linking innate and adaptive immunity and (iv) the potential clinical relevance. Dissecting the complex network of innate immune regulation and associated pro-inflammatory cascades in CF lung disease may pave the way for novel immune-targeted therapies in CF and other chronic infective lung diseases.

PPARγ as a therapeutic target in cystic fibrosis

Cystic fibrosis (CF) is characterized by a proinflammatory pulmonary condition that may result from increased infections and altered intracellular metabolism in CFTR-deficient cells. The lipid-activated transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) has well-established roles in immune cell function and inflammatory modulation and has been demonstrated to play an important role in the heightened inflammatory response in CF cells. Here, we summarize current literature describing PPARγ-dependent alterations of CF cells and discuss the potential of PPARγ ligands for treating CF.

Mechanisms of the noxious inflammatory cycle in cystic fibrosis

Multiple evidences indicate that inflammation is an event occurring prior to infection in patients with cystic fibrosis. The self-perpetuating inflammatory cycle may play a pathogenic part in this disease. The role of the NF-κB pathway in enhanced production of inflammatory mediators is well documented. The pathophysiologic mechanisms through which the intrinsic inflammatory response develops remain unclear. The unfolded mutated protein cystic fibrosis transmembrane conductance regulator (CFTRΔF508), accounting for this pathology, is retained in the endoplasmic reticulum (ER), induces a stress, and modifies calcium homeostasis. Furthermore, CFTR is implicated in the transport of glutathione, the major antioxidant element in cells. CFTR mutations can alter redox homeostasis and induce an oxidative stress. The disturbance of the redox balance may evoke NF-κB activation and, in addition, promote apoptosis. In this review, we examine the hypotheses of the integrated pathogenic processes leading to the intrinsic inflammatory response in cystic fibrosis.

Protein glutathionylation and oxidative stress

Liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS) demonstrated that glutathionyl hemoglobin (Hb) levels are increased in patients with diabetes, hyperlipidemia, uremia and Friedreich's ataxia. Glutathionylation of Hb is enhanced by oxidative stress. High performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) have also been developed for the quantification of glutathionyl Hb. Glutathionyl-lens proteins were detected in uremic patients and cataractous aged subjects. Glutathionylation of numerous enzymes is induced by oxidative stress, reduces their catalytic activities and may be involved in protection from the damaging effects of oxidative agents. Thioredoxin, glutaredoxin (thioltransferase) and protein disulfide isomerase are the key enzymes in controlling cellular oxidative stress that catalyze reduction of glutathionyl protein disulfide bonds. Thus, protein glutathionylation is closely associated with oxidative stress.

Vitamin A and E deficiency and lung disease in infants with cystic fibrosis

OBJECTIVES

Vitamin A and E deficiency is common in cystic fibrosis (CF). These vitamins have immunomodulating properties and we determined whether decreased serum vitamin A and E levels in young infants are associated with early CF lung disease and lower airway inflammation.

METHODS

A post-hoc analysis was undertaken on previous data collected prospectively in 39 newly diagnosed infants identified by a newborn CF screening programme. Assessment of CF genotype, nutrition, pancreatic status, serum retinol and alpha-tocopherol levels was performed at diagnosis. Pulmonary status was determined clinically, by Brasfield chest radiographic scores and analysis of bacterial counts and inflammatory indices in bronchial lavage (BL) fluid. These assessments were repeated 12 months later.

RESULTS

At diagnosis, 20 out of 39 (51%) CF infants had low serum retinol (mean (SD) 0.7 (0.3) micromol/L) and 9/38 (24%) had low alpha-tocopherol (mean (SD) 13.4 (8.4) micromol/L) levels. Dietary energy intake was related to serum retinol concentrations at diagnosis (r(2) = 0.27; P = 0.001). At 1 year, serum retinol and alpha-tocopherol levels had normalized following vitamin A and E supplementation. Respiratory symptoms, radiographic scores and BL inflammatory indices systematically deteriorated during infancy, reaching significance for free neutrophil elastase activity (9 out of 29 vs 21 out of 33; P = 0.01) and IL-8 levels (79 vs 416; P = 0.046) in BL fluid. No association was seen between serum vitamin levels at diagnosis and airway inflammatory indices at either diagnosis or 12 months later.

CONCLUSION

We found in this CF birth cohort no evidence to implicate vitamin A or E deficiency in the development of lung disease or airway inflammation during infancy.

Lipid peroxidation of lung surfactant due to reactive oxygen species released from phagocytes stimulated by bacteria from children with cystic fibrosis

We used Pseudomonas aeruginosa, Burkholderia cepacia and Stenotrophomonas maltophilia, live or heat-killed, isolated from the airways of children with Cystic Fibrosis, to stimulate human neutrophils (PMN) and rat alveolar macrophages (AM) to produce reactive oxygen metabolites in the presence or absence of Curosurf, a natural porcine lung surfactant. We determined: (1) the amount of lipid peroxidation (LPO) as assessed by the amounts of malondialdehyde (MDA) and 4-hydroxyalkenals (4-HNE) using the LPO 586 test kit; (2) the production by AM of superoxide with the nitroblue tetrazolium test and (3) of nitric oxide (NO) with the Griess reaction. Stimulation of PMN or AM increases LPO of Curosurf and cell wall lipids. In both types of phagocytes, B. cepacia induced the highest LPO levels followed by P. aeruginosa and S. maltophilia. PMN, stimulated by live bacteria, induced higher LPO than those stimulated by heat-killed bacteria. B. cepacia stimulated AM to produce more superoxide and NO than did P. aeruginosa and S. maltophilia. The high phagocyte-stimulating ability of B. cepacia and its higher surfactant LPO than those of the other bacteria used in this in vitro study may play a role in vivo in the serious clinical condition known as the "Cepacia syndrome".

Nitric oxide synthase 1 as a potential modifier gene of decline in lung function in patients with cystic fibrosis

BACKGROUND

The severity of lung disease varies widely in patients with cystic fibrosis (CF) who have the same type of mutations of the cystic fibrosis transmembrane regulator (CFTR) gene, suggesting involvement of "modifier" genes. The nitric oxide synthase 1 (NOS1) gene is a candidate for this role because exhaled nitric oxide (NO) is reduced in patients with CF and NOS1 activity contributes to transepithelial ionic transport, immune defence, and non-specific inflammation of the airways.

METHODS

Dinucleotide GT repeat polymorphism was studied in the 5' untranslated region of the NOS1 gene, immediately upstream from the transcription initiation site, in 59 patients with CF and 59 healthy controls.

RESULTS

Nineteen alleles of the NOS1 gene were identified according to the number of GT repeats (from 18 to 36) in the 5 untranslated region. Exhaled NO levels were significantly correlated with the number of GT repeats. Patients with CF who had the NOS1 genotype associated with high NO production had a slower decline in lung function during the 5 year follow up period. There was no confounding effect of age, chronic bacterial colonisation of the airway, or CFTR genotype.

CONCLUSIONS

These data suggest a possible link between the NOS1 gene locus and the rate of decline in lung function in patients with CF.

Organic solutes rescue the functional defect in delta F508 cystic fibrosis transmembrane conductance regulator

The most common defect in cystic fibrosis, deletion of phenylalanine from position 508 of the cystic fibrosis transmembrane conductance regulator (Delta F508 CFTR), decreases the trafficking of this protein to the cell surface membrane. Previous studies have shown that low temperature and high concentrations of glycerol or trimethylamine N-oxide can partially counteract the processing defect of Delta F508 CFTR. The present study investigates whether physiologically relevant concentrations of organic solutes, accumulated by cotransporter proteins, can rescue the misprocessing of Delta F508 CFTR. Myoinositol alone or myoinositol, betaine, and taurine given sequentially increased the processing of core-glycosylated, endoplasmic reticulum-arrested Delta F508 CFTR into the fully glycosylated form of CFTR in IB3 cells or NIH 3T3 cells stably expressing Delta F508 CFTR. Pulse-chase experiments using transiently transfected COS7 cells demonstrated that organic solutes also increased the processing of the core-glycosylated form of green fluorescent protein-Delta F508 CFTR. Moreover, the prolonged half-life of the complex-glycosylated form of GFP-Delta F508 CFTR suggests that this treatment stabilized the mature form of the protein. In vitro studies of purified NBD1 stability and aggregation showed that myoinositol stabilized both the Delta F508 and wild type CFTR and inhibited Delta F508 misfolding. Most significantly, treatment of CF bronchial airway cells with these transportable organic solutes restores cAMP-stimulated single channel activity of both CFTR and outwardly rectifying chloride channel in the cell surface membrane and also restores a forskolin-stimulated macroscopic 36Cl- efflux. We conclude that organic solutes can repair CFTR functions by enhancing the processing of Delta F508 CFTR to the plasma membrane by stabilizing the complex-glycosylated form of Delta F508 CFTR.

Mechanisms of diaphragm fatigue

The importance of respiratory muscle fatigue, particularly of the diaphragm, has become well recognized in the last decade. If the diaphragm muscle fails, so does effective ventilation and tissue respiration. Balance between energy supply and demand determines diaphragmatic endurance. An imbalance between energy supply and demand leads to the development of diaphragmatic fatigue. It has become clear that the process of fatigue is a complex phenomenon with multiple mechanisms accounting for changes in muscle performance. The various mechanisms involved are probably interdependent, synergistic, and integrative in nature. This article focuses on the concept of diaphragm fatigue and explores the mechanisms occurring with diaphragm fatigue including sodium-potassium derangements, which cause a decrease in velocity of propagation of muscle action; inhibition of calcium release from the sacroplasmic reticulum; and increased oxygen free radical formation related to cellular energetics. Additionally, review of therapeutic approaches to the treatment of diaphragm fatigue are presented.