Long-term treatment with oral N-acetylcysteine: affects lung function but not sputum inflammation in cystic fibrosis subjects. A phase II randomized placebo-controlled trial.

PURPOSE: To evaluate the effects of oral N-acetylcysteine (NAC), which replenishes systemic glutathione, on decreasing inflammation and improving lung function in CF airways. METHODS: A multicenter, randomized, double-blind proof of concept study in which 70 CF subjects received NAC or placebo orally thrice daily for 24 weeks. ENDPOINTS: primary, change in sputum human neutrophil elastase (HNE) activity; secondary, FEV(1) and other clinical lung function measures; and safety, the safety and tolerability of NAC and the potential of NAC to promote pulmonary hypertension in subjects with CF. RESULTS: Lung function (FEV(1) and FEF(25-75%)) remained stable or increased slightly in the NAC group but decreased in the placebo group (p=0.02 and 0.02). Log(10) HNE activity remained equal between cohorts (difference 0.21, 95% CI -0.07 to 0.48, p=0.14). CONCLUSIONS: NAC recipients maintained their lung function while placebo recipients declined (24 week FEV1 treatment effect=150 mL, p<0.02). However no effect on HNE activity and other selected biomarkers of neutrophilic inflammation were detected. Further studies on mechanism and clinical outcomes are warranted.

Phase II studies of nebulised Arikace in CF patients with Pseudomonas aeruginosa infection.

RATIONALE: Arikace is a liposomal amikacin preparation for aerosol delivery with potent Pseudomonas aeruginosa killing and prolonged lung deposition. OBJECTIVES: To examine the safety and efficacy of 28 days of once-daily Arikace in cystic fibrosis (CF) patients chronically infected with P aeruginosa. METHODS: 105 subjects were evaluated in double-blind, placebo-controlled studies. Subjects were randomised to once-daily Arikace (70, 140, 280 and 560 mg; n=7, 5, 21 and 36 subjects) or placebo (n=36) for 28 days. Primary outcomes included safety and tolerability. Secondary outcomes included lung function (forced expiratory volume at one second (FEV1)), P aeruginosa density in sputum, and the Cystic Fibrosis Quality of Life Questionnaire-Revised (CFQ-R). RESULTS: The adverse event profile was similar among Arikace and placebo subjects. The relative change in FEV1 was higher in the 560 mg dose group at day 28 (p=0.033) and at day 56 (28 days post-treatment, 0.093L±0.203 vs -0.032L±0.119; p=0.003) versus placebo. Sputum P aeruginosa density decreased >1 log in the 560 mg group versus placebo (days 14, 28 and 35; p=0.021). The Respiratory Domain of the CFQ-R increased by the Minimal Clinically Important Difference (MCID) in 67% of Arikace subjects (560 mg) versus 36% of placebo (p=0.006), and correlated with FEV1 improvements at days 14, 28 and 42 (p<0.05). An open-label extension (560 mg Arikace) for 28 days followed by 56 days off over six cycles confirmed durable improvements in lung function and sputum P aeruginosa density (n=49). CONCLUSIONS: Once-daily Arikace demonstrated acute tolerability, safety, biologic activity and efficacy in patients with CF with P aeruginosa infection.

Sodium 4-phenylbutyrate downregulates HSC70 expression by facilitating mRNA degradation.

Intracellular trafficking of the DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) is repaired by sodium 4-phenylbutyrate (4PBA) by an undetermined mechanism. 4PBA downregulates protein and mRNA expression of the heat shock cognate protein HSC70 (the constitutively expressed member of the 70-kDa heat shock protein family) by approximately 40-50% and decreases formation of a HSC70-DeltaF508 CFTR complex that may be important in the intracellular degradation of DeltaF508 CFTR. We examined the potential mechanisms by which 4PBA decreases HSC70 mRNA and protein expression. In IB3-1 cells, 1 mM 4PBA did not alter the activity of the Chinese hamster ovary HSC70 promoter or of a human HSC70 promoter fragment in luciferase reporter assays nor did it alter HSC70 mRNA synthesis in nuclear runoff assays. In contrast, preincubation with 4PBA increased the rate of HSC70 mRNA degradation by approximately 40%. The initial rate of 35S-HSC70 protein synthesis in 4PBA-treated IB3-1 cells was reduced by approximately 40%, consistent with the steady-state mRNA level, whereas its rate of degradation was unaltered by 4PBA. 4PBA also reduced the steady-state accumulation of (35)S-HSC70 by approximately 40%. These data suggest that 4PBA decreases the expression of HSC70 mRNA and protein by inducing cellular adaptations that result in the decreased stability of HSC70 mRNA.

A simplified cyclic adenosine monophosphate-mediated sweat rate test for quantitative measure of cystic fibrosis transmembrane regulator (CFTR) function.

OBJECTIVE: Sweat production is stimulated by both cholinergic and beta-adrenergic pathways in the sweat gland secretory coil. beta-Adrenergic pathway-mediated sweating is absent in cystic fibrosis (CF) because cyclic adenosine monophosphate (cAMP)-mediated chloride transport through the cystic fibrosis transmembrane regulator (CFTR) is disrupted. We report the development of a rapid, reproducible, macroscopic, and quantitative methodology to test the hypothesis that beta-adrenergic sweat rate discriminates among 3 different CFTR phenotypes-CF, heterozygote CF carriers, and non-CF. STUDY DESIGN: Intradermal injection of a mixture of 50 micromol/L isoproterenol, 5 mmol/L aminophylline (to potentiate the beta-adrenergic stimulation), and 140 micromol/L atropine (to block potential cholinergic stimulation) in lactated Ringer's solution was performed in duplicate on one forearm. A single injection of 0.5 mmol/L methacholine to stimulate sweat production by the cholinergic pathway was performed on the other forearm. Sweat rate was determined as the amount of sweat collected on filter paper over 20 minutes. RESULTS AND CONCLUSIONS: Median cAMP-mediated sweat rates were 1.45 mg/20 min (CF, n = 29), 2.55 mg/20 min (CF heterozygote carriers, n = 30), and 3.65 mg/20 min (non-CF, n = 30) and were significantly different in all 3 groups (P =.0001, Kruskal-Wallis test). Methacholine-stimulated sweat rates were similar for all 3 groups. The cAMP-mediated sweat rate test may be a useful endpoint for studies of new agents to increase the function of CFTR.

Mutation in the gene responsible for cystic fibrosis and predisposition to chronic rhinosinusitis in the general population.

CONTEXT: Chronic rhinosinusitis (CRS) is a common condition in the US general population, yet little is known about its underlying molecular cause. Chronic rhinosinusitis is a consistent feature of the autosomal recessive disorder cystic fibrosis (CF). OBJECTIVE: To determine whether mutations in the cystic fibrosis transmembrane regulator (CFTR) gene, which is responsible for CF, predispose to CRS. DESIGN: Case-control study conducted from 1996 to 1999 in which the DNA of CRS patients and controls was typed for 16 mutations that account for 85% of CF alleles in the general population. Chronic rhinosinusitis patients with 1 CF mutation were evaluated for a CF diagnosis by sweat chloride testing, nasal potential difference measurement, and DNA analysis for additional mutations. SETTING: Otolaryngology-head and neck clinic of a US teaching hospital. PARTICIPANTS: One hundred forty-seven consecutive adult white patients who met stringent diagnostic criteria for CRS and 123 CRS-free white control volunteers of similar age range, geographic region, and socioeconomic status. MAIN OUTCOME MEASURES: Presence of CF mutations by DNA analysis among CRS patients vs controls. RESULTS: Eleven CRS patients were found to have a CF mutation (DeltaF508, n = 9; G542X, n = 1; and N1303K, n = 1). Diagnostic testing excluded CF in 10 of these patients and led to CF diagnosis in 1. Excluding this patient from the analyses, the proportion of CRS patients who were found to have a CF mutation (7%) was significantly higher than in the control group (n = 2 [2%]; P =.04, both having DeltaF508 mutations). Furthermore, 9 of the 10 CF carriers had the polymorphism M470V, and M470V homozygotes were overrepresented in the remaining 136 CRS patients (P =.03). CONCLUSION: These data indicate that mutations in the gene responsible for CF may be associated with the development of CRS in the general population. JAMA. 2000;284:1814-1819.

Sodium 4-phenylbutyrate downregulates Hsc70: implications for intracellular trafficking of DeltaF508-CFTR.

The most common mutation of the cystic fibrosis transmembrane conductance regulator (CFTR), DeltaF508, is a trafficking mutant that has prolonged associations with molecular chaperones and is rapidly degraded, at least in part by the ubiquitin-proteasome system. Sodium 4-phenylbutyrate (4PBA) improves DeltaF508-CFTR trafficking and function in vitro in cystic fibrosis epithelial cells and in vivo. To further understand the mechanism of action of 4PBA, we tested the hypothesis that 4PBA modulates the targeting of DeltaF508-CFTR for ubiquitination and degradation by reducing the expression of Hsc70 in cystic fibrosis epithelial cells. IB3-1 cells (genotype DeltaF508/W1282X) that were treated with 0.05-5 mM 4PBA for 2 days in culture demonstrated a dose-dependent reduction in Hsc70 protein immunoreactivity and mRNA levels. Immunoprecipitation with Hsc70-specific antiserum demonstrated that Hsc70 and CFTR associated under control conditions and that treatment with 4PBA reduced these complexes. Levels of immunoreactive Hsp40, Hdj2, Hsp70, Hsp90, and calnexin were unaffected by 4PBA treatment. These data suggest that 4PBA may improve DeltaF508-CFTR trafficking by allowing a greater proportion of mutant CFTR to escape association with Hsc70.

Use of protein repair therapy in the treatment of cystic fibrosis.

Disruption in the biosynthesis or function the cystic fibrosis transmembrane conductance regulator (CFTR) results from over 700 different mutations in the CFTR gene. It is useful to classify these mutations by the nature of the resulting defect. Understanding the molecular mechanism that leads to CFTR dysfunction stimulates the design of therapeutic strategies based on restoration of CFTR function to the mutant protein, or "protein repair therapy." This review links the classification of CFTR mutations to a number of new pharmacologic strategies that lead to enhancement of CFTR function by manipulation of mutant CFTR.

A pilot clinical trial of oral sodium 4-phenylbutyrate (Buphenyl) in deltaF508-homozygous cystic fibrosis patients: partial restoration of nasal epithelial CFTR function.

Sodium 4-phenylbutyrate (Buphenyl, 4PBA) is a new FDA approved drug for management of urea cycle disorders. We have previously presented data suggesting that 4PBA, at clinically achievable concentrations, induces CFTR channel function on the plasma membrane of deltaF508-expressing cystic fibrosis (CF) airway epithelial cells in vitro (Rubenstein, R. C., and P. L. Zeitlin, 1997. J. Clin. Invest. 100:2457-2463). We hypothesized that 4PBA would induce epithelial CFTR function in vivo in individuals homozygous for deltaF508-CFTR. A randomized, double-blind, placebo-controlled trial in 18 deltaF508-homozygous patients with CF was performed with the maximum approved adult dose of 4PBA, 19 grams p.o. divided t.i.d., given for 1 wk. Nasal potential difference (NPD) response patterns and sweat chloride concentrations were determined before and after study drug treatment, and 4PBA and metabolites were assayed in plasma and urine at the end of study drug treatment. Subjects in the 4PBA group demonstrated small, but statistically significant improvements of the NPD response to perfusion of an isoproterenol/amiloride/chloride-free solution; this measure reflects epithelial CFTR function and is highly discriminatory between patients with and without CF. Subjects who had received 4PBA did not demonstrate significantly reduced sweat chloride concentrations or alterations in the amiloride-sensitive NPD. Side effects due to drug therapy were minimal and comparable in the two groups. These data are consistent with 4PBA therapy inducing CFTR function in the nasal epithelia of deltaF508-homozygous CF patients.

In vitro pharmacologic restoration of CFTR-mediated chloride transport with sodium 4-phenylbutyrate in cystic fibrosis epithelial cells containing delta F508-CFTR.

The most common cystic fibrosis transmembrane conductance regulator mutation, delta F508-CFTR, is a partially functional chloride channel that is retained in the endoplasmic reticulum and degraded. We hypothesize that a known transcriptional regulator, sodium 4-phenylbutyrate (4PBA), will enable a greater fraction of delta F508-CFTR to escape degradation and appear at the cell surface. Primary cultures of nasal polyp epithelia from CF patients (delta F508 homozygous or heterozygous), or the CF bronchial epithelial cell line IB3-1 (delta F508/W1282X) were exposed to 4PBA for up to 7 d in culture. 4PBA treatment at concentrations of 0.1 and 2 mM resulted in the restoration of forskolin-activated chloride secretion. Protein kinase A-activated, linear, 10 pS chloride channels appeared at the plasma membrane of IB3-1 cells at the tested concentration of 2.5 mM. Treatment of IB3-1 cells with 0.1-1 mM 4PBA and primary nasal epithelia with 5 mM 4PBA also resulted in the appearance of higher molecular mass forms of CFTR consistent with addition and modification of oligosaccharides in the Golgi apparatus, as detected by immunoblotting of whole cell lysates with anti-CFTR antisera. Immunocytochemistry in CF epithelial cells treated with 4PBA was consistent with increasing amounts of delta F508-CFTR. These data indicate that 4PBA is a promising pharmacologic agent for inducing correction of the CF phenotype in CF patients carrying the delta F508 mutation.

CFTR gene transduction in neonatal rabbits using an adeno-associated virus (AAV) vector.

Patients with cystic fibrosis develop lung disease after birth, therefore CFTR gene replacement therapy should be most efficacious in the neonatal period prior to the onset of pulmonary damage. An adeno-associated virus (AAV) vector, SA306 (Flotte TR et al Proc Natl Acad Sci USA 1993; 90: 10613-10617), which contains the AAV inverted terminal repeats flanking the human CFTR cDNA linked to an amino-terminal epitope tag, was used to transduce a human CFTR fusion protein into neonatal New Zealand white rabbits. Vector inocula of 1 x 10(5) to 5 x 10(10) particles were given by intratracheal instillation on day 3 of life and the rabbit lungs were studied at 3 or 4 days, 2-6 weeks, or 6 months after infection; the 2-6 week time-point corresponds to the completion of the alveolar phase of lagomorph lung development. Vector DNA was detected by an in situ polymerase chain reaction (PCR) using vector-specific primers at up to 6 weeks after inoculation. Human CFTR mRNA was detected by Northern analysis at up to 2 weeks after vector inoculation, and by a reverse transcriptase PCR assay at up to 3 weeks after infection. Epithelial expression of the human CFTR fusion protein was detected using antisera to both the human CFTR R domain and the amino-terminal epitope at up to 6 weeks after vector inoculation. Vector DNA, mRNA, or human CFTR immunoreactivity were not observed at the 6 month time-point. Rabbits infected with SA306 were clinically indistinguishable from their uninfected litter mates. These data indicate that CFTR gene transduction using an AAV vector is feasible in the neonatal rabbit, and that expression of vector-derived CFTR persists throughout the alveolar phase of lung development. The apparent lack of vector persistence after the alveolar phase may reflect dilution of transduced cells by further lung growth or a lack of transduction of pulmonary epithelial stem cells.

Selectivity of the beta-adrenergic receptor among Gs, Gi's, and Go: assay using recombinant alpha subunits in reconstituted phospholipid vesicles.

The selective regulation of Gs (long and short forms), Gi's (1, 2, and 3), and Go by the beta-adrenergic receptor was assessed quantitatively after coreconstitution of purified receptor, purified G-protein beta gamma subunits, and individual recombinant G-protein alpha subunits that were expressed in and purified from Escherichia coli. Receptor and beta gamma subunits were incorporated into phospholipid vesicles, and the alpha subunits bound to the vesicles stoichiometrically with respect to beta gamma. Efficient regulation of alpha subunit by receptor required the presence of beta gamma. Regulation of G proteins was measured according to the stimulation of the initial rate of GTP gamma S binding, steady-state GTPase activity, and equilibrium GDP/GDP exchange. The assays yielded qualitatively similar results. GDP/GDP exchange was a first-order reaction for each subunit. The rate constant increased linearly with the concentration of agonist-liganded receptor, and the dependence of the rate constant on receptor concentration was a reproducible measurement of the efficiency with which receptor regulated each G protein. Reconstituted alpha s (long or short form) was stimulated by receptor to approximately the extent described previously for natural Gs. Both alpha i,1 and alpha i,3 were regulated with 25-33% of that efficiency. Stimulation of alpha o and alpha i,2 was weak, and stimulation of alpha o was barely detectable over its high basal exchange rate. Reduction of the receptor with dithiothreitol increased the exchange rates for all G proteins but did not alter the relative selectivity of the receptor.

The hydrophobic tryptic core of the beta-adrenergic receptor retains Gs regulatory activity in response to agonists and thiols.

The function of structural domains of the beta-adrenergic receptor were probed by studying the ability of tryptic fragments of the receptor to catalyze the binding of guanosine-5'-O-(3-thiotriphosphate (GTP gamma S) to the GTP-binding regulatory protein, Gs. beta-Adrenergic receptor purified from turkey erythrocytes was treated with trypsin under nondenaturing conditions. Such treatment decreased beta-adrenergic ligand binding activity by only 15-25%. Active components of the limit digest were repurified by affinity chromatography on alprenolol-agarose and then reconstituted with purified Gs into unilamellar phospholipid vesicles. After reconstitution, the proteolyzed receptor was able to catalyze agonist-stimulated binding of GTP gamma S to Gs at a rate and extent equivalent to that of the nonproteolyzed receptor. The proteolyzed receptor was also partially activated upon reduction by dithiothreitol, as previously reported for the intact receptor (Pedersen, S.E., and Ross, E.M. (1985) J. Biol. Chem. 260, 14150-14157). The repurified, active tryptic digest contained two detectable peptides. One, of approximately 2 X 10(4) Da, contained either four or five of the amino-terminal membrane-spanning domains plus the intervening hydrophilic loops but not the amino-terminal extracellular, glycosylated peptide. The second, of 9,000-10,000 Da, was composed essentially of the two carboxyl-terminal membrane-spanning domains and the intervening extracellular, hydrophilic loop. These data indicate that most of the large intracellular hydrophilic loop and the hydrophilic, carboxyl-terminal region of the receptor are not necessary for the agonist-stimulated regulation of Gs.