John A. Wagner

Activation of intestinal CFTR Cl- channel by heat-stable enterotoxin and guanylin via cAMP-dependent protein kinase.

Heat‐stable enterotoxins (STa) produced by pathogenic bacteria induce profound salt and water secretion in the gut, leading to diarrhea. Recently, guanylin, an endogenous peptide with properties similar to STa, was identified. While STa and guanylin bind to the same receptor guanylyl cyclase and raise cell cGMP, the signaling mechanism distal to cGMP remains controversial. Here we show that STa, guanylin and cGMP each activate intestinal Cl‐ secretion, and that this is abolished by inhibitors of cAMP‐dependent protein kinase (PKA), suggesting that PKA is a major mediator of this effect. These agents induce Cl‐ secretion only in cells expressing the wild‐type CFTR, indicating that this molecule is the final common effector of the signaling pathway. The involvement of CFTR suggests a possible cystic fibrosis heterozygote advantage against STa‐induced diarrhea.

A Phase II, double-blind, randomized, placebo-controlled clinical trial of tgAAVCF using maxillary sinus delivery in patients with cystic fibrosis with antrostomies

tgAAVCF, an adeno-associated cystic fibrosis transmembrane conductance regulator (CFTR) viral vector/gene construct, was administered to 23 patients in a Phase II, double-blind, randomized, placebo-controlled clinical trial. For each patient, a dose of 100,000 replication units of tgAAVCF was administered to one maxillary sinus, while the contralateral maxillary sinus received a placebo treatment, thereby establishing an inpatient control. Neither the primary efficacy endpoint, defined as the rate of relapse of clinically defined, endoscopically diagnosed recurrent sinusitis, nor several secondary endpoints (sinus transepithelial potential difference [TEPD], histopathology, sinus fluid interleukin [IL]-8 measurements) achieved statistical significance when comparing treated to control sinuses within patients. One secondary endpoint, measurements of the anti-inflammatory cytokine IL-10 in sinus fluid, was significantly (p < 0.03) increased in the tgAAVCF-treated sinus relative to the placebo-treated sinus at day 90 after vector instillation. The tgAAVCF administration was well tolerated, without adverse respiratory events, and there was no evidence of enhanced inflammation in sinus histopathology or alterations in serum-neutralizing antibody titer to adeno-associated virus (AAV) capsid protein after vector administration. In summary, this Phase II trial confirms the safety of tgAAVCF but provides little support of its efficacy in the within-patient controlled sinus study. Various potentially confounding factors are discussed.

Safety and Biological Efficacy of an Adeno‐Associated Virus Vector–Cystic Fibrosis Transmembrane Regulator (AAV‐CFTR) in the Cystic Fibrosis Maxillary Sinus

Objective: The host immune response and low vector efficiency have been key impediments to effective cystic fibrosis transmembrane regulator (CFTR) gene transfer for cystic fibrosis (CF). An adeno‐associated virus vector (AAV‐CFTR) was used in a phase I dose‐escalation study to transfer CFTR cDNA into respiratory epithelial cells of the maxillary sinus of 10 CF patients. Study Design: A prospective, randomized, unblinded, dose‐escalation, within‐subjects, phase I clinical trial of AAV‐CFTR was conducted. Patients: Ten patients with previous bilateral maxillary antrostomies were treated. Main Outcome Measures: Safety, gene transfer as measured by semiquantitative polymerase chain reaction (PCR), and sinus transepithelial potential difference (TEPD) were measured. Results: The highest level of gene transfer was observed in the range of 0.1–1 AAV‐CFTR vector copy per cell in biopsy specimens obtained 2 weeks after treatment. When tested, persistence was observed in one patient for 41 days and in another for 10 weeks. Dose‐dependent changes in TEPD responses to pharmacologic intervention were observed following treatments. Little or no inflammatory or immune responses were observed. Conclusion: AAV‐CFTR administration to the maxillary sinus results in successful, dose‐dependent gene transfer to the maxillary sinus and alterations in sinus TEPD suggestive of a functional effect, with little or no cytopathic or host immune response. Further study is warranted for AAV vectors as they may prove useful for CFTR gene transfer and other in vivo gene transfer therapies. A prospective, randomized, double‐blind, placebo‐controlled, within‐subjects, phase II clinical trial of the effect AAV‐CFTR on clinical recurrence of sinusitis will determine the clinical efficacy of AAV gene therapy for CF.

Regulation of CI− channels by multifunctional CaM kinase

cAMP kinase has been shown to mediate the cAMP pathway for regulation of Cl- channels in lymphocytes, but the mediator of an alternative, Ca2+ pathway has not been identified. We show here that Ca2+ ionophore activates Cl- currents in cell-attached and whole-cell patch-clamp recordings of Jurkat T lymphocytes, but this activation is not direct. The effect of Ca2+ ionophore on whole-cell Cl- currents is inhibited by a specific peptide inhibitor of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase). Furthermore, Cl- channels are activated in excised patches by purified CaM kinase in a fashion that mimics the effect of Ca2+ ionophore in cell-attached recordings. These results suggest that CaM kinase mediates the Ca2+ pathway of Cl- channel activation.

Nerve terminal proteins of the rabbit visual relay nuclei identified by axonal transport and two-dimensional gel electrophoresis.

The proteins in nerve terminals can be uniquely identified by two-dimensional gel electrophoresis of proteins labeled during synthesis in the cell body and then transported intra-axonally to the terminals. We have explored the potential of the identification procedure by comparing the proteins which are transported from the retina to the lateral geniculate nucleus (LGN) and the superior colliculus (SC) of the rabbit. We have been able to identify between 150 and 200 proteins which ate common to both LGN and SC nerve terminals, very few of which are present at significantly different concentrations in one nucleus relative to the other. The similarity between proteins sent from the retina along two neural pathways subserving different functions illustrates the subtlety of biochemical changes that must underlie physiological differences. Only a small fraction of the labeled proteins are major proteins of the relay nuclei as judged by Coomassie-staining, and some of these arise from in situ nonspecific labeling with blood-borne radioactivity, rather than by transport to the terminals. We have shown that about 5 times more proteins are transported at fast than at intermediate transport rates. More than 50% of the fast proteins turn over rapidly and are gone in 24 h. Few intermediate proteins turn over rapidly. Since only 6% of the proteins in the relay nuclei (at 36 h) could not be detected in the optic tract at that time, transsynaptic labeling by breakdown and resynthesis must be small, if it occurs at all.

Maxillary sinusitis as a surrogate model for CF gene therapy clinical trials in patients with antrostomies

Assessing the biological activity and clinical efficacy of gene therapy is critically important in cystic fibrosis (CF). It is widely accepted that clinical testing using surrogate markers including pulmonary function will be useful in assessing clinical efficacy. One problem with pulmonary surrogate markers of CF disease is the large number of patients and length of time required to demonstrate clinical efficacy. An alternative to pulmonary testing of new CF treatments is use of the maxillary sinuses as a surrogate model of CF lung disease. Using CF sinusitis as a surrogate model for testing clinical efficacy of new treatments is attractive because CF upper respiratory disease is similar to the lower respiratory disease with respect to electrophysiology and microbiology.

Two novel mutations in a cystic fibrosis patient of Chinese origin

Abstract Cystic fibrosis is rare in non-Caucasian populations, and in such populations little is known about the spectrum of mutations and polymorphisms in the CFTR gene. We studied a 23-year-old patient of Chinese ethnicity with sweat chloride values of 104 mM/l, pancreatic sufficiency, an FEV1 60% of normal, sputum cultures positive for Staphylococcus aureus and Burkholderia cepacia, and a history of allergic bronchopulmonary aspergillosis. Genetic screening for 31 common CFTR mutations was negative, leading us to search for unknown mutations using single-strand conformation polymorphism and heteroduplex analysis (SSCP/HA). Two novel mutations were detected. In exon 4, a deletion of 8 bp (451–458, ΔGCTTCCTA) causes a frameshift and immediately creates a stop codon. In exon 16, mutation 3041G→A causes the missense change G970D. Functional analysis using an isotopic flux assay indicated that the G970D mutation retains partial function; western blotting indicated that the protein is glycosylated. The patient is heterozygous for the common polymorphisms (2694T/G) in exon 14a and (GATT)6/7 in intron 6a, indicating that these variants arose in ancestors common to Caucasians and Chinese.

Stimulation of chloride secretion by P1 purinoceptor agonists in cystic fibrosis phenotype airway epithelial cell line CFPEo

1 P1 purinoceptor agonists like adenosine have been shown to stimulate Cl−1 transport in secretory epithelia. In the present study, we investigated whether P1 agonist‐induced Cl−1 secretion is preserved in cystic fibrosis airway epithelium and which signalling mechanism is involved. The effects of purinoceptor agonists on Cl−1 secretion were examined in a transformed cystic fibrosis airway phenotype epithelial cell line, CFPEo‐. 2 Addition of adenosine (ADO; 0.1 – 1 mm) markedly increased 125I efflux rate. The rank order of potency of purinoceptor agonists in stimulating 125I efflux was ADO > AMP > ADP ≃ ATP. A similar order of potency was seen in transformed cystic fibrosis nasal polyp cells, CFNPEo‐ (ADO > ATP > AMP > ADP). These results are consistent with the activation of Cl−1 secretion via a P1 purinoceptor. 3 The P1 agonists tested (at 0.01 and 0.1 mm) revealed a rank order of potency of 5′‐N‐ethylcarboxamine adenosine (NECA) > 2‐chloro‐adenosine (2‐Cl‐ADO) > R‐phenylisopropyl adenosine (R‐PIA). 4 The known potent A2 adenosine receptor (A2AR) agonist, 5′‐(N‐cyclopropyl) carboxamidoadenosine (CPCA, 2 μm) but not the A1 adenosine receptor agonist, N6‐phenyl adenosine (N6‐phenyl ADO, 10 μm) markedly increased 125I efflux rate (baseline, 5.9 ± 2.0% min−1, + CPCA, 10.9 ± 0.6% min−1; P < 0.01). The stimulant effect of CPCA (10 μm) was abolished by addition of the A2AR antagonist 3,7‐dimethyl‐1‐propargylxanthine (DMPX) (100 μm; reported K1 = 11 ± 3 μm). These results favour the involvement of A2AR. 5 ADO (0.1 – 1 mm) and CPCA (2 μm) both induced a marked increase in intracellular [Ca2+] ([Ca2+]i); the effect of the latter was again abolished by pretreatment of the cells with DMPX. By contrast, N6‐phenyl ADO did not affect [Ca2+]i. 6 In patch‐clamp experiments, ADO (1 mm) induced an outwardly‐rectified whole‐cell Cl−1 current (baseline, 2.5 ± 0.8 pA pF−1, + ADO, 78.4 ± 23.8 pA pF−1; P < 0.02), which was largely inhibited in cells internally perfused with a selective inhibitory peptide of the multifunctional Ca2+/calmodulin‐dependent protein kinase, CaMK [273–302] (20 μm), as compared to a control peptide, CaMK [284–302]. Addition of BAPTA (10 mm), a Ca2+ chelator, to the perfusion pipette also abolished the ADO‐elicited Cl−1 current. 7 In conclusion, our results suggest that A2AR participates in regulation of airway Cl−1 secretion via a Ca2+‐dependent signalling pathway, which involves CaMK and appears to be at least partially conserved in cystic fibrosis airway epithelial cells.

Regulation of Lymphocyte Chloride Channels

The chloride permeability defect which characterizes the apical membrane of secretory epithelial cells in cystic fibrosis has been difficult to study in part because of lack of accessibility of tissue for study. This problem has fostered attempts by investigators both to immortalize epithelial cell lines and to search for other cells which may serve as a model to study chloride conductances. As we describe here, transformed lympho-blasts have whole cell chloride currents under conditions of stimulation by cAMP agonists, calcium ionophore, or hypotonicity which are quite similar to the aggregate chloride currents measured under similar conditions in epithelial cells. In addition, transformed B and malignant T cells have an outwardly rectifying, 40pS, chloride selective channel that is activated during patch clamp recording by one of at least three ways: 1) patch excision and depolarization; 2) phosphorylation by cAMP-dependent protein kinase (PKA); 3) by exposure of the lympho-blast to Ca2+ ionophore during cell-attached recording. This channel is closely similar or identical to the outwardly rectifying chloride channel identified by patch clamp recording from the apical membrane in secretory epithelial cells (Frizzell et al., 1986; Welsh, 1986; Welsh and Liedtke, 1986; Schoumacher et al., 1987; Li et al., 1988).