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The molecular basis for disease variability in cystic fibrosis.

Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The disease is characterized by a wide variability of clinical expression. The cloning of the CFTR gene and the identification of its mutations has promoted extensive research into the association between genotype and phenotype. Several studies showed that there are mutations, like the delta F508 (the most common mutation worldwide), which are associated with a severe phenotype and there are mutations associated with a milder phenotype. However, there is a substantial variability in disease expression among patients carrying the same mutation. This variability involves also the severity of lung disease. Furthermore, increased frequencies of mutations are found among patients with incomplete CF expression which includes male infertility due to congenital bilateral absence of the vas deferens. In vitro studies of the CFTR function suggested that different mutations cause different defects in protein production and function. The mechanisms by which mutations disrupt CFTR function are defective protein production, processing, channel regulation, and conductance. In addition, reduced levels of the normal CFTR mRNA are associated with the CF disease. These mutations are associated with a highly variable phenotype from healthy individuals or infertile males to a typical CF disease. This variability in disease expression is associated with different levels of normally spliced transcripts. Further understanding the mechanisms of CFTR dysfunction may suggest different therapeutic strategies for each class of mutations.

Cystic Fibrosis↗

Platelet activation in cystic fibrosis.

Cystic fibrosis (CF) is caused by a mutation of the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). We examined platelet function in CF patients because lung inflammation is part of this disease and platelets contribute to inflammation. CF patients had increased circulating leukocyte-platelet aggregates and increased platelet responsiveness to agonists compared with healthy controls. CF plasma caused activation of normal and CF platelets; however, activation was greater in CF platelets. Furthermore, washed CF platelets also showed increased reactivity to agonists. CF platelet hyperreactivity was incompletely inhibited by prostaglandin E(1) (PGE(1)). As demonstrated by Western blotting and reverse-transcriptase-polymerase chain reaction (RT-PCR), there was neither CFTR nor CFTR-specific mRNA in normal platelets. There were abnormalities in the fatty acid composition of membrane fractions of CF platelets. In summary, CF patients have an increase in circulating activated platelets and platelet reactivity, as determined by monocyte-platelet aggregation, neutrophil-platelet aggregation, and platelet surface P-selectin. This increased platelet activation in CF is the result of both a plasma factor(s) and an intrinsic platelet mechanism via cyclic adenosine monophosphate (cAMP)/adenylate cyclase, but not via platelet CFTR. Our findings may account, at least in part, for the beneficial effects of ibuprofen in CF.

Adenylyl Cyclases↗

A murine tracheal culture system to investigate parameters affecting gene therapy for cystic fibrosis.

Cystic fibrosis (CF) is a life-threatening condition caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Delivery of the CFTR gene to the airways offers a potential treatment for CF but requires improvement in efficiency to obtain clinical benefit. We have developed a murine tracheal culture system that maintains tissue integrity as judged by normal histological appearance, high transepithelial resistance and electrophysiological responses similar to fresh tissue. This ex vivo system allows precise control of gene delivery parameters to a structure that retains the in vivo cellular architecture. We have demonstrated correction of CFTR-dependent Cl- secretion following ex vivo delivery of the CFTR gene to tracheas from CF null mice. We have used this system to examine parameters affecting liposome-mediated gene delivery to the upper airway such as plasmid dose. We have also found that a contact time of 1 min for the transfection mixture is sufficient to achieve significant DNA binding and maximal reporter gene expression.

Animals↗

Emerging drug treatments for cystic fibrosis.

Cystic fibrosis (CF) is one of the most common life-shortening inherited disorders. Mutations in the cystic fibrosis transmembrane regulator (CFTR) gene disrupt the localisation and function of the cAMP-mediated chloride channel. Most of the morbidity and mortality arise from the lung disease which is characterised by excessive inflammation and chronic infection. Research into the mechanisms of wild-type and mutant CFTR biogenesis suggest that multiple drug targets can be identified. This review explores the current understanding of the nature of the different mutant CFTR forms and the potential for repair of the chloride channel defect. High-throughput screening, pharmacogenomics and proteomics bring recent technological advances to the field.

Anti-Infective Agents↗

Pharmacological approaches to correcting the ion transport defect in cystic fibrosis.

Cystic fibrosis (CF) is a lethal genetic disease caused by a mutation in a membrane protein, the cystic fibrosis transmembrane conductance regulator (CFTR), which mainly (but not exclusively) functions as a chloride channel. The main clinical symptoms are chronic obstructive lung disease, which is responsible for most of the morbidity and mortality associated with CF, and pancreatic insufficiency. About 1000 mutations of the gene coding for CFTR are currently known; the most common of these, present in the great majority of the patients (Delta508) results in the deletion of a phenylalanine at position 508. In this mutation, the aberrant CFTR is not transported to the membrane but degraded in the ubiquitin-proteasome pathway. The aim of this review is to give an overview of the pharmacologic strategies currently used in attempts to overcome the ion transport defect in CF. One strategy to develop pharmacologic treatment for CF is to inhibit the breakdown of DeltaF508-CFTR by interfering with the chaperones involved in the folding of CFTR. At least in in vitro systems, this can be accomplished by sodium phenylbutyrate, or S-nitrosoglutathione (GSNO), and also by genistein or benzo[c]quinolizinium compounds. It is also possible to stimulate CFTR or its mutated forms, when present in the plasma membrane, using xanthines, genistein, and various other compounds, such as benzamidizoles and benzoxazoles, benzo[c]quinolizinium compounds or phenantrolines. Experimental results are not always unambiguous, and adverse effects have been incompletely tested. Some clinical tests have been done on sodium phenyl butyrate, GSNO and genistein, mostly in respect to other diseases, and the results demonstrate that these drugs are reasonably well tolerated. Their efficiency in the treatment of CF has not yet been demonstrated, however. An alternative strategy is to compensate for the defective chloride transport by CFTR by stimulation of other chloride channels. This can be done via purinergic receptors. A phase I study using a stable uridine triphosphate analog has recently been completed. A second alternative strategy is to attempt to maintain hydration of the airway mucus by inhibiting Na(+) uptake by the epithelial Na(+) channel using amiloride or stable analogs of amiloride. Clinical tests so far have been inconclusive. A number of other suggestions are currently being explored. The minority of patients with CF who have a stop mutation may benefit from treatment with gentamicin. The difficulties in finding a pharmacologic treatment for CF may be due to the fact that CFTR has additional functions besides chloride transport, and interfering with CFTR biosynthesis or activation implies interference with central cellular processes, which may have undesirable adverse effects.

Cystic Fibrosis↗

Tear mucus crystallization in children with cystic fibrosis.

Cystic fibrosis is characterized by an abnormally high electrolyte concentration in exocrine secretions. The authors performed the tear mucus ferning test in 26 eyes of children with cystic fibrosis and compared the results to those in an equal number of age-matched normals. The results suggest that the increased electrolyte concentration could be responsible for the increased hyperviscosity of mucus. The tear mucus ferning test appears to be a suitable diagnostic test for the assessment of cystic fibrosis.

Adolescent↗

[An appendiceal-vesical fistula in a patient with cystic fibrosis].

Cystic fibrosis is an hereditary disease in which abnormally viscous secretion of exocrine glands causes chronic pulmonary infections and gastrointestinal disorders. The authors report the case of a patient with cystic fibrosis and appendicitis complicated by appendico-vesical fistula. The appendico-vesical fistula has been described during appendicitis; its association with the cystic fibrosis however has never been reported in the literature.

Adult↗

Gastrointestinal manifestations of cystic fibrosis.

Cystic fibrosis is clearly a multisystem disease, which the potential for prominent gastrointestinal and hepatobiliary involvement. While the routine patient with pancreatic insufficiency may be easily managed with pancreatic enzyme and nutritional therapy, a large number of individuals with cystic fibrosis will present the clinician with gastrointestinal problems requiring additional thoughtful evaluation and treatment. Familiarity with the common gastrointestinal manifestations of cystic fibrosis and emerging therapies is necessary to provide the comprehensive care these patients deserve.

Child↗

Microscopic epididymal sperm aspiration (MESA): a new option for treatment of the obstructive azoospermia associated with cystic fibrosis.

Cystic fibrosis is a life-threatening disease. Only recently has the prognosis improved. In the male patient there is an almost invariable absence or maldevelopment of the vas deferens, creating a situation of obstructive azoospermia. Consequently, their fertility potential has been considered nonexistent. Having gained experience in microscopic epididymal sperm aspiration coupled with the advanced reproductive technologies for the treatment of congenital absence of the vasa, we sought to extend this treatment option to the male cystic fibrosis population. An Indian male with clinically evident and genetically confirmed cystic fibrosis underwent microscopic retrieval of epididymal sperm. The anatomy of the epididymis and the quality of sperm obtained were similar to those patients with congenital absence of the vas deferens. After appropriate spousal genetic testing, superovulation, and transvaginal oocyte retrieval, in vitro insemination of sperm was performed. Fifty percent of the oocytes were subjected to partial zona dissection and a single embryo resulted. Subsequent to transfer, no conception was realized but the effort expanded the clinical usefulness of microscopic epididymal sperm aspiration. This should open up an avenue of treatment for couples in whom only the most dire predictions for fertility have been made to date.

Adult↗

Chloride impermeability in cystic fibrosis.

Cystic fibrosis is the most common fatal genetic disease affecting caucasians and is perhaps best characterized as an exocrinopathy involving a disturbance in fluid and electrolyte transport. A high NaCl concentration in the sweat is characteristic of patients with this disease; the basic physiological reason for this abnormality is unknown. We have microperfused isolated sweat ducts from control subjects and cystic fibrosis patients, and report here results which suggest that abnormally low Cl- permeability in cystic fibrosis leads to poor reabsorption of NaCl in the sweat duct, and hence to a high concentration of NaCl in the sweat.

Adult↗

Pulmonary infections in patients with cystic fibrosis.

Cystic fibrosis (CF) is an autosomal-recessive disorder and affects about 60,000 people worldwide. The CF gene, the cystic fibrosis transmembrane conductance regulator (CFTR), was found in 1989 and over 800 mutations have been sequenced. Although our understanding of the pathophysiology of CF has increased, pulmonary infections remain the major cause of morbidity and mortality. During the first decade of life, Staphylococcus aureus and nontypable Haemophilus influenza are most common, but Pseudomonas aeruginosa may be the first pathogen isolated in infants. By 18 years of age, 80% of patients harbor P. aeruginosa and 3.5% harbor Burkholderia cepacia. Stenotrophomonas maltophilia, Achromobacter xylosoxidans, and nontuberculous mycobacteria may be newly emerging CF pathogens. The traditional approach to managing patients with CF is to treat acute pulmonary exacerbations with intravenous antimicrobial agents. However, prophylactic strategies to prevent initial infection or to delay chronic infection with P. aeruginosa or chronic maintenance therapy to slow deterioration of lung function may also improve clinical status. Recognition of the role of inflammation, even early in life, in the absence of clinical symptoms, has led to treatment with anti-inflammatory agents. Novel strategies to disrupt biofilm formation, stimulate chloride conductance, and replace abnormal CFTR are currently being studied.

Burkholderia cepacia↗

Management and care of the newly diagnosed patient with cystic fibrosis.

Cystic fibrosis is the most common autosomal recessive fatal disease among whites. Life expectancy is now at 31 years of age. The major cause of morbidity and mortality is chronic progressive lung disease. Lung disease occurs early in cystic fibrosis, suggesting the need for early and aggressive treatment of any pulmonary symptoms and malnutrition. This treatment is ideally performed within a cystic fibrosis center, and new therapies are being sought for management of the early stages of disease.

Adolescent↗

Application of a new test for vitamin E deficiency to cystic fibrosis.

Cystic fibrosis patients with pancreatic insufficiency are at risk for the development of vitamin E deficiency. We report here the outcome of screening 13 cystic fibrosis patients with conventional descriptive measures of vitamin E status and a new functional test. The results were compared with those from age appropriate controls. Nine patients were found to be vitamin E sufficient based upon normal plasma vitamin E levels, the ratio of plasma vitamin E to total plasma lipids, and normal levels of in vitro erythrocyte malondialdehyde formation, the new functional measure of vitamin E status. Four patients considered vitamin E deficient, based upon low plasma vitamin E levels and plasma vitamin E to total plasma lipid ratios, demonstrated increased erythrocyte malondialdehyde formation in vitro when compared to age-matched controls. Since limited reference data in children are available to define normal plasma vitamin E levels and plasma vitamin E to total plasma lipid ratios, we suggest that for cystic fibrosis patients the functional in vitro malondialdehyde formation test may be a better measure of vitamin E status than static plasma levels.

Adolescent↗

Nutrition and cystic fibrosis.

Cystic fibrosis is commonly associated with energy deficiency in children and adults. Chronic undernutrition will lead to failure to thrive, wasting, and stunting of linear growth; nutrition and survival are intimately related in cystic fibrosis. These problems can simply be considered as energy imbalance, and management centers on restoration of energy balance. Specific nutrient deficiencies, such as fat soluble vitamins, are common in cystic fibrosis. Recent work has highlighted problems with bone density and also the prevalence of vitamin K deficiency. Management of nutritional problems can be complex, and injudicious treatment can further worsen the situation, as the relationship between high daily doses of pancreatic enzymes and the development of fibrosing colonopathy illustrates.

Adolescent↗

CFTR-mediated inhibition of epithelial Na+ conductance in human colon is defective in cystic fibrosis.

Cystic fibrosis (CF) patients show characteristic defects in epithelial ion transport, such as failure in cAMP-dependent Cl- secretion. Because the cystic fibrosis transmembrane conductance regulator (CFTR) also functions as a downregulator of epithelial Na+ channels (ENaC), enhanced Na+ conductance was found in the airways of CF patients. Here, we examined whether enhanced epithelial Na+ conductance is also present in the colonic epithelium of CF patients and examined the underlying mechanisms. Thus transepithelial voltages were measured, and equivalent short-circuit currents (I(sc-eq)) were determined by means of a novel type of Ussing chamber. Non-CF tissues demonstrated cAMP-dependent Cl- secretion that was absent in biopsies of CF patients. Correspondingly, Isc-eq was inhibited in non-CF but not in CF epithelia when synthesis of endogenous prostaglandins was blocked by indomethacin. In the presence of indomethacin, a larger portion of amiloride-sensitive Isc-eq was detected in CF tissues, suggesting enhanced ENaC conductance in colonic mucosa of CF patients. Increase of intracellular cAMP by forskolin and IBMX inhibited amiloride-sensitive ENaC currents in non-CF tissues but not in CF biopsies. Therefore, enhanced epithelial Na+ conductance is present in the CF colon and is probably due to missing downregulation by CFTR.

Adolescent↗

Organ-specific over-sulfation of glycosaminoglycans and altered extracellular matrix in a mouse model of cystic fibrosis.

Cystic fibrosis (CF) is a fatal inherited disease caused by the loss of function of a plasma membrane chloride channel-the cystic fibrosis transmembrane conductance regulator (CFTR). It is characterized by viscous mucous secretions which have abnormal glycosylation and sulfation. The development of a CFTR knockout mouse has allowed in vivo experiments aimed at investigating the over-sulfation phenomenon reported for CF glycoconjugates. Four CF and five control mice injected with [35S]sulfate were examined for differences in the sulfation of glycosaminoglycans (GAGs) synthesized by 12 tissues after 48 h. The liver and pancreas of CF mice incorporated significantly higher amounts of [35S]sulfate into GAGs (dpm/microg) than the controls, while the ileum, jejunum, colon, cecum, spleen, trachea, and gall bladder of CF mice exhibited higher incorporation levels that were not significant. The lung and nasal septum were not different, and the nasal mucosa of CF mice was significantly lower (P < 0.05). Structural analysis of the chondroitin/dermatan sulfate component by strong anion-exchange HPLC revealed that the liver and ileum of CF mice incorporated significantly more total sulfate than controls. However, for other organs, the explanation for higher isotope incorporation was a 40-50% higher specific activity of [35S]sulfate within GAGs. This finding implied different uptake kinetics of sulfate from the circulation or that CF mice have altered sulfate pools. CF mice also had altered proportions of chondroitin/dermatan sulfate to heparan sulfate in the ileum and gall bladder (P < 0.05). We conclude that extracellular matrix architecture in some CF organs may be abnormal and that sulfation of glycoconjugates by some organs and sulfate utilization in others have been affected by the loss of CFTR. This study provides the first in vivo evidence for an influence of CFTR on glycoconjugate sulfation and suggests other secondary manifestations of CFTR dysfunction associated with abnormalities of the extracellular matrix.

Animals↗

Questionnaire survey of urinary incontinence in women with cystic fibrosis.

Cystic fibrosis is an inherited disease characterised by the production of infected secretions, and it requires lifelong daily treatment by airway clearance. We knew that some women attending our clinic for adults with cystic fibrosis leaked urine when performing airway clearance or spirometry, but they were dismissive during discussion and were rarely forthcoming about the problem. This study was designed to determine the prevalence of urinary incontinence in women with cystic fibrosis, to establish the importance of the problem as perceived by the patients, and to identify those women who wanted help.

Adolescent↗

Gene therapy for cystic fibrosis.

Cystic fibrosis (CF) is associated with significant morbidity and mortality, despite significant advances in conventional treatment. The field of gene therapy has progressed rapidly since the cystic fibrosis transmembrane conductance regulator (CFTR) gene was cloned. In this review we discuss current knowledge on the underlying molecular defect in CF, and the progress in gene transfer studies from the early in vitro work through to clinical trials, including the development of endpoints to assess efficacy. We highlight the problems encountered, and likely future directions of the field.

Adenoviridae↗