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A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine selectively activates chloride efflux from human epithelial and mouse fibroblast cell lines expressing the cystic fibrosis transmembrane regulator delta F508 mutation.

Cystic fibrosis is an autosomal recessive disorder affecting chloride transport in pancreas, lung, and other tissues, which is caused by mutations in the cystic fibrosis transmembrane regulator (CFTR). The A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) stimulates 36Cl- efflux from pancreatic CFPAC-1 cells which bear the delta F508 genotype common to most cases of cystic fibrosis [Eidelman et al. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 5562-5566]. By contrast, correction of the cystic fibrosis defect by retrovirus-mediated gene transfer renders the resulting CFPAC-PLJ-CFTR cells insensitive to CPX. We now report that CPX also activates chloride efflux from the CF tracheal epithelial cell line IB3-1 bearing a delta F508 allele, but not if the IB3-1 cells have been repaired by transfection of the wild-type CFTR gene. Similar results were obtained with recombinant NIH 3T3 cells, in which CPX activates 36Cl- efflux from cells expressing the CFTR (delta F508) gene product but not from 3T3 cells expressing the wild-type CFTR. In all three cell types expressing CFTR (delta F508), CPX was found to activate 36Cl- efflux in a dose-dependent manner over the concentration range of 1-30 nM and then gradually lose potency at higher CPX concentrations. Six CPX analogues, A1 receptor antagonists of affinity similar to that of CPX, were found to be much less effective than CPX at activating 36Cl- efflux from CFPAC-1 cells. These included 2-thio-CPX. CPT (8-cyclopentyl-1,3-dimethylxanthine),3,4-dehydro-CPX,3-F-CPX,3-1-CPX, and KW-3902 (8-noradamantyl-1,3-dipropylxanthine).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

8-cyclopentyl-1,3-dipropylxanthine and other xanthines differentially bind to the wild-type and delta F508 first nucleotide binding fold (NBF-1) domains of the cystic fibrosis transmembrane conductance regulator.

Cystic fibrosis is an autosomal recessive disorder affecting chloride transport in pancreas, lung, and other tissues, which is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). Certain alkyl xanthines such as CPX (8-cyclopentyl-1,3-dipropylxanthine) stimulate Cl- efflux from cells bearing the delta F508 genotype common to most cases of cystic fibrosis. We have hypothesized that the CFTR molecule itself might be the site for CPX action, perhaps in the region of the first nucleotide binding fold (NBF-1) domain. Therefore, to test this hypothesis directly we have used a rapid membrane filtration assay to measure the kinetics of association and dissociation of [3H]CPX to both recombinant NBF-1 and recombinant NBF-1 bearing the delta F508 mutation. We report that [3H]CPX binds with higher affinity to the delta F508-NBF-1 of CFTR (Kd = 1.0 nM) than to the wild-type NBF-1 of CFTR (Kd = 17.0 nM). These Kd values were calculated from direct measurements of the association and dissociation rate constants. The rate constants for the dissociation reaction of the wild-type NBF-1 and delta F508-NBF-1 of CFTR were not different from each other. However, the corresponding rate constants for the association reaction were k(+1) (NBF-1) = 4.7 +/- 0.9 x 10(4) M(-1) s(-1) and k(+1) (delta F508-NBF-1) = 1.6 +/- 0.3 x 10(5) M(-1) s(-1), respectively. These Kd values were corroborated by equilibrium-binding experiments, which gave very similar values. We have also measured the relative displacement of various xanthines from both wild-type NBF-1 and delta F508-NBF-1, in anticipation that the order of potencies for binding might parallel the action of the different xanthines on CF cells. For wild-type NBF-1, the rank order was DA-CPX > DAX > CPX > caffeine > adenosine >> IBMX > 2-thioCPX. For delta F508-NBF-1, the rank order was DAX > CPX > caffeine > DA-CPX > adenosine >> IBMX > 2-thioCPX. These relative potencies show close parallels with previously observed relative potencies of these drugs on CF cells, and thus lend strong support to the hypothesis that the mechanism of action on CF cells may involve direct interaction with the CFTR molecule itself.

Adenosine↗

[Relation between gene mutations and pancreatic exocrine function in patients with cystic fibrosis].

Cystic fibrosis (CF), is the most common autosomal-recessive disease in Caucasians, with an incidence of approximately 1:2500 live births and a carrier frequency of approximately 4-5%. Causes of the disease are mutations in the CF gene which is located on chromosome 7 (region 7q31). Although a single mutation, a deletion of phenylalanine at position 508 (DF508) in exon 10, accounts for almost 70% of all CF chromosomes, over 900 other mutations have been identified in this large gene. CF gene encodes a membrane protein, which functions as aion channel- CFTR (cystic fibrosis transmembrane regulator protein). The exocrine pancreas is a gland that secretes water, enzymes and electrolytes into the intestinal lumen. These enzymes are needed for the normal digestion of food, and their reduced secretion in cystic fibrosis will cause malabsortion and malnutrition in CF patients. Pancreatic dysfunction in CF begins in uteri. Most patients with CF typically present insufficient pancreatic exocrine function (PI phenotype) and 10-15% of CF patients are pancreatic sufficient (PS phenotype). It has been shown elsewhere that the pancreatic function status in CF could be correlated to mutations in the CFTR gene. To determine the relation between genotype and pancreatic status, we analyzed 32 CF patients in whom both CF gene mutant alleles were identified (Table 1). Patients included in this study attended the Paediatric Department of Mother and Child Health Institute in Belgrade. The diagnosis was based on typical clinical manifestations and high levels of sweat chloride concentration (higher than 60 mmol/L). Of the 32 patients studied, only one (3.12%) was PS and the rest (96.88%) had PI phenotype. For each CF genotype the number of patients who were PI or PS is given in Table 1. The most striking observation was that all given genotypes correlated with either PI or PS, but not with both. On the basis of both preceding hypotheses and our present data (Table 2 and Table 3), it was possible to classify mutations as "severe" or "mild" with respect to pancreatic function (Table 4). This study strengthens the hypothesis that pancreatic function status in CF is genetically determined by specific mutations at the CF locus. Our data also strongly support the hypothesis that, with respect to pancreatic function, "mild" mutant alleles confer a higher residual CFTR activity than do "severe" mutant alleles. Although PS occurs in patients who have one or two "mild" mutations, PI occurs in patients who are homozygous or who are genetic compounds of two "severe" mutant alleles.

Adult↗

Hepatic manifestations of pulmonary diseases.

Pulmonary complications from chronic liver disease are well known and include hepatopulmonary syndrome, hepatic hydrothorax, and pulmonary hypertension. This article reviews the hepatic complications of diseases that are primarily pulmonary diseases. The authors focus on alpha 1 antitrypsin deficiency, an autosomal recessive metabolic disorder that can affect the lungs, liver, kidneys, and pancreas; sarcoidosis, a systemic disease of unknown origin that can affect multiple organs; and cystic fibrosis, an autosomal recessive disease that affects the lungs, exocrine pancreas, liver, and intestines.

Animals↗

Immunoreactive serum trypsin in diseases of the pancreas.

Immunoreactive serum trypsin was measured with a double antibody radioimmunoassay in normal subjects and patients with various diseases of the pancreas. The normal range is 115-350 ng/ml with a geometric mean of 212 ng/ml. No trypsin was found in serum after total duodenopancreatectomy, in about 75% of patients with cystic fibrosis and in a few patients with pancreas carcinoma or chronic pancreatitis. Reduced serum trypsin levels between 10 and 100 ng/ml were measured in the remaining 25% of cystic fibrosis and in one third of the patients with chronic pancreatitis. Serum trypsin was increased to 700-17,000 ng/ml in all patients with acute pancreatitis or during the acute phase of chronic pancreatitis. Absent or reduced serum trypsin is a reliable indicator of total or partial exocrine pancreatic insufficiency whereas considerably increased serum trypsin concentration do indicate acute pancreatitis.

Acute Disease↗