Pharmacological treatment of the biochemical defect in cystic fibrosis airways

Applications of shun shell column and nanocomposite sorbent for analysis of eleven anti-hypertensive in human plasma

High-performance liquid chromatography (HPLC) and solid phase micro membrane tip extraction (SPMMTE) methods are developed for the simultaneous analysis of eleven cardiovascular drugs in human plasma. Iron nanoparticles were obtained by the green method, characterized by XRD, FT-IR, TEM, and EDS and utilized in SPMMTE for sample preparation. The mobile phase used was ammonium acetate buffer-methanol-acetonitrile (65:18:17) with a 1.0 mL/min flow rate at 260 nm detection. Column used was Sunshell C₁₈ 150 × 4.6 mm, 2.6 µm. The values of k, α, and Rs were ranged from 040 to109.22, 1.20 to 2.67 and 1.0 to 26.18. SPMMTE and HPLC methods were fast, reproducible, precise, robust, economic and rugged for analysis of methyldopa, hydrochlorothiazide, prazosin hydrochloride, furosemide, labetalol, propranolol, valsartan, losartan potassium, diltiazem, irbesartan and spironolactone in human plasma. The recoveries (%) of methyldopa, hydrochlorothiazide, prazosin hydrochloride, furosemide, labetalol, propranolol, valsartan, losartan potassium, diltiazem, irbesartan, and spironolactone were 91.0, 85.2, 92.3, 90.4, 90.1, 85.6, 86.6, 86.2, 85.1, 86.6, and 85.7, respectively. These results showed that SPMMTE and HPLC methods can be applied to test the described drugs in several matrices.

Vibrational spectra of 3,5-diamino-6-chloro-N-(diaminomethylene) pyrazine-2-carboxamide: combined experimental and theoretical studies

In this work, the vibrational spectral analysis of 3,5-diamino-6-chloro-N-(diaminomethylene)pyrazine-2-carboxamide(3DCNDPC) was carried out using FT-Raman and FT-IR spectroscopy in the range 4000-50cm(-1) and 4000-500cm(-1) respectively. The experimental spectra were recorded in the solid phase. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) B3LYP with the standard basis set 6-311++G(d,p). The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values. Normal co-ordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. Simulation of infrared and Raman spectra utilizing the results of these calculations led to excellent overall agreement with the observed spectral patterns. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The stability of the molecule arising from hyper conjugative interactions and the charge delocalization has been analyzed by using Natural Bond Orbital (NBO) analysis. UV-Vis spectrum of the compound was recorded. The calculated HOMO and LUMO energies show that chemical activity of the molecule.

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.

Mutations in CNGA3 impair trafficking or function of cone cyclic nucleotide-gated channels, resulting in achromatopsia

CNGA3 encodes the A-subunit of the cone photoreceptor cyclic nucleotide-gated (CNG) channel, which is a crucial component of the phototransduction cascade in cone outer segments. Mutations in the CNGA3 gene have been associated with complete and incomplete forms of achromatopsia (ACHR), a congenital, autosomal recessively inherited retinal disorder characterized by lack of color discrimination, reduced visual acuity, nystagmus, and photophobia. Here we report the identification of three novel CNGA3 missense mutations in ACHR patients: c.682G>A (p.E228 K), c.1315C>T (p.R439W), and c.1405G>A (p.A469 T), and the detailed functional analyses of these new as well as five previously reported mutations (R283Q, T291R, F547L, G557R, and E590 K), in conjunction with clinical data of patients carrying these mutations, to establish genotype-phenotype correlations. The functional characterization of mutant CNGA3 channels was performed with calcium imaging and patch clamp recordings in a heterologous HEK293 cell expression system. Results were corroborated by immunostaining and colocalization experiments of the channel protein with the plasma membrane. Several mutations evoked pronounced alterations of the apparent cGMP sensitivity of mutant channels. These functional defects were fully or partially compensated by coexpressing the mutant CNGA3 subunit with the wild-type CNGB3 subunit for channels with the mutations R439W, A469 T, F547L, and E590 K. We could show that several mutant channels with agonist dose-response relationships similar to the wild-type exhibited severely impaired membrane targeting. In addition, this study presents the positive effect of reduced cell culture temperature on surface expression and functional performance of mutant CNG channels with protein folding or trafficking defects.

The hERG K+ channel: target and antitarget strategies in drug development

The human ether-à-go-go related gene (hERG) K+ channel is of great interest for both basic researchers and clinicians because its blockade by drugs can lead to QT prolongation, which is a risk factor for torsades de pointes, a potentially life-threatening arrhythmia. A growing list of agents with "QT liability" have been withdrawn from the market or restricted in their use, whereas others did not even receive regulatory approval for this reason. Thus, hERG K+ channels have become a primary antitarget (i.e. an unwanted target) in drug development because their blockade causes potentially serious side effects. On the other hand, the recent identification and functional characterization of hERG K+ channels not only in the heart, but also in several other tissues (e.g. neurons, smooth muscle and cancer cells) may have far reaching implications for drug development for a possible exploitation of hERG as a target, especially in oncology and cardiology.

Cystic fibrosis transmembrane conductance regulator (CFTR) functionality is dependent on coatomer protein I (COPI)

BACKGROUND INFORMATION

Cystic fibrosis results from mutations in the ABC transporter CFTR (cystic fibrosis transmembrane conductance regulator), which functions as a cAMP-regulated anion channel. The most prevalent mutation in CFTR, the Phe(508) deletion, results in the generation of a trafficking and functionally deficient channel. The cellular machineries involved in modulating CFTR trafficking and function have not been fully characterized. In the present study, we identified a role for the COPI (coatomer protein I) cellular trafficking machinery in the development of the CFTR polypeptide into a functional chloride channel. To examine the role of COPI in CFTR biosynthesis, we employed the cell line ldlF, which harbours a temperature-sensitive mutation in epsilon-COP, a COPI subunit, to inhibit COPI function and then determined whether the CFTR polypeptide produced from the transfected gene developed into a cAMP-regulated chloride channel.

RESULTS

When COPI was inactivated in the ldlF cells by an elevated temperature pulse (39 degrees C), the CFTR polypeptide was detected on the cell surface by immunofluorescence microscopy and cell-surface biotinylation. Therefore, CFTR proceeded upstream in the secretory pathway in the absence of COPI function, a result demonstrated previously by others. In contrast, electrophysiological measurements indicated an absence of cAMP-stimulated chloride efflux, suggesting that channel function was impaired. In comparison, expression of CFTR at the same elevated temperature (39 degrees C) in an epsilon-COP-rescued cell line [ldlF(ldlF)], which has an introduced wild-type epsilon-COP gene in addition to the mutant epsilon-COP gene, showed restoration of cAMP-stimulated channel activity, confirming the requirement of COPI for channel function.

CONCLUSIONS

These results therefore suggest that generation of the folded-functional conformation of CFTR requires COPI.

Dominant-negative effects of episodic ataxia type 2 mutations involve disruption of membrane trafficking of human P/Q-type Ca2+ channels

Episodic ataxia type 2 (EA2) is an autosomal dominant neurological disorder associated with mutations in the gene encoding pore-forming alpha(1A) subunits of human P/Q-type calcium (Ca(V)2.1) channels. The exact mechanism of how mutant channels cause such clinical EA2 features as cerebellar dysfunctions, however, remains unclear. Our previous functional studies in Xenopus oocytes support the idea that EA2 mutants may exert prominent dominant-negative effects on wild-type Ca(V)2.1 channels. To further pursue the mechanism underlying this dominant-negative effect, we examined the effects of EA2 mutants on the subcellular localization pattern of GFP-tagged wild-type Ca(V)2.1 channels in HEK293T cells. In the presence of EA2 mutants, wild-type channels displayed a significant deficiency in membrane targeting and a concurrent increase in cytoplasm retention. Moreover, the cytoplasmic fraction of wild-type channels co-localized with an endoplasmic reticulum (ER) marker, suggesting that a significant amount of wild-type Ca(V)2.1 channels was trapped in the ER. This EA2 mutant-induced ER retention pattern was reversed by lowering the cell incubation temperature from 37 to 27 degrees C. We also inspected the effects of untagged EA2 mutants on the functional expression of GFP-tagged wild-type Ca(V)2.1 channels in HEK293T cells. Whole-cell current density of wild-type channels was diminished in the presence of EA2 mutants, which was also reversed by 27 degrees C incubation. Finally, biochemical analyses indicated that EA2 mutants did not significantly affect the protein expression level of wild-type channels. Taken together, our data suggest that EA2 mutants induce significant ER retention of their wild-type counterparts, thereby suppressing the functional expression of Ca(V)2.1 channels.

Quantum-Chemical Design of Cryptand-like Ditopic Salt Binders

Hartree-Fock, density functional, and MP2 methods are applied to the problem of designing neutral, bicyclic C3-symmetric cages incorporating interacting anion- and cation-binding sites which strongly bind NaCl as an ion contact pair. A large number of trial ligands L and their complexes L:NaCl are tested, with the focus on maximizing binding by (i) optimizing the cavity size and shape and (ii) varying the nature of the anion- and cation-binding functionalities. The corresponding complexes L:Cl(-) and L:Na(+) are also studied in some detail. An analysis of their structures and charge distributions helps to build a consistent picture of the requirements for a successful NaCl binding. The 'best' candidate ligand utilizes a tripodal triether-substituted amine N(CH2CH2OR-)3 to bind the sodium cation; three thiourea groups in a tripodal arrangement with a 1,3,5-trisubstituted benzyl spacer group {C6H3(CH2NHC [Formula: see text] XNH-)3 X=O,S} to bind chloride; and a -CH2CH2- spacer linking the two binding sites. A simple Quantitative Structure-Property analysis suggests that the binding cavity shape and size is near to the optimal one for this system.

Unusually common cystic fibrosis mutation in Portugal encodes a misprocessed protein

A561E, a novel cystic fibrosis (CF) associated mutation in the first nucleotide binding domain of CFTR, is the second most common CF mutation in Portugal. Properties of the A561E-CFTR protein were studied by immunoblotting, pulse-chase, immunocytochemistry, and MQAE halide-efflux assay in stably transfected BHK cells. Altogether, results presented here suggest that A561E causes protein mislocalization in the endoplasmic reticulum where the mutant protein must be trapped by the quality control mechanism. We conclude that A561E originates a protein trafficking defect, thus belonging to class II of CFTR mutations. As it is the case for F508del-CFTR (the most common CF mutant), low temperature treatment partially rescues a functional A561E-CFTR channel, suggesting that substitution of glutamic acid for alanine at position 561 does not completely abolish CFTR function. Pharmacological strategies previously reported for treatment of CF patients with the F508del mutation could thus be also effective in CF patients bearing the A561E mutation.

Cystic fibrosis: cost of illness and considerations for the economic evaluation of potential therapies

Cystic fibrosis (CF) is the most common life-shortening inherited disease of the Caucasian race, with a prevalence of around 1 in 2500 live births. Advances in the treatment and management of respiratory and pancreatic disorders have dramatically increased the life expectancy of patients with CF. This article presents an overview of cost-of-illness studies of CF, identifies deficits in the available health economic analyses of CF and discusses which specific factors are essential for the economic evaluation of potential therapies, based on a critical review of the health economic literature on two main therapeutic strategies. Cost-of-illness studies of CF have predominantly been restricted to direct costs. According to the literature, direct costs amount to between 6200- 16300 US dollars (1996 values) per patient per year. As most studies likely underestimated the actual costs (e.g. by disregarding provision of certain healthcare services), real healthcare costs tend to be at the upper end of the cost range. Healthcare costs depend on the patient's age (for adults, costs are approximately twice as high as for children), the grade of severity (the cost relationship of severe to mild CF is between 4.5 and 7.1) and other factors. Lifetime direct costs of CF are estimated at 200 000-300000 US dollars (at 1996 values and a discount rate of 5%). Home intravenous (IV) antibacterial therapy and recombinant human DNase (rhDNase; dornase alfa) treatment are the two main therapeutic strategies most often evaluated in health economic studies of CF. While home IV antibacterial therapy (compared with inpatient IV antibacterial therapy) is assumed to be cost saving, rhDNase treatment is a very cost-intensive therapy intended to efficiently achieve health improvements. Health economic analyses of future CF therapeutic technologies should present explicit data regarding healthcare services provision, resource consumption and unit costs. Indirect costs and patient costs should be considered more often than they have to date, particularly when they are significantly influenced by novel CF technologies. The perspective of health economic studies should be stated explicitly and always include the societal perspective. More economic studies should be based on a controlled, and preferably randomised, design. The observation period must be long enough to identify long-term effects of interventions. A greater number of effectiveness studies should be performed to determine costs and outcomes of therapies applied under everyday life conditions for patients with CF. Finally, international comparison studies should identify the influence of different healthcare systems on the costs and outcomes of interventions.

Synthetic membrane transporters

An increasing number of synthetic compounds have been shown to facilitate ion and polar molecule transport across bilayer membranes. Most notably, recent advances in anion transport have yielded synthetic chloride channels and phospholipid translocases. Attention has also turned to the ability of short amino acid sequences to transport peptides and proteins across cellular membranes.

Disease genes: flattery and deception

Completion of the human genome project raises the possibility of genetically based treatments for a multitude of human diseases. As yet only a handful of patients have benefited clinically from this approach. Why gene transfer is such a complex issue is discussed in this article. Theoretically, the easiest diseases to treat are single gene recessive diseases, where, presumably, gene delivery to somatic cells is all that is required. Two prime candidates for gene therapy are severe combined immunodeficiency disease (SCID) and cystic fibrosis (CF). Attempts to treat both of these diseases by gene therapy commenced in the late 1980s. Some clinical benefit has been recorded with SCID, but none, as yet, has been recorded with CF.

Urogenital abnormalities in male children with cystic fibrosis

BACKGROUND

Congenital bilateral absence of the vas deferens (CBAVD) is presumed to occur prenatally and is present in over 99% of adult males with cystic fibrosis (CF).

AIMS

To describe ultrasonic features in male children with CF. We aimed to describe urogenital anomalies, comparing pancreatic sufficient and insufficient CF patients.

METHODS

Pelvic and scrotal ultrasonography were performed in 12 boys with CF aged 2-12 years and 16 age matched healthy controls.

RESULTS

Nine patients had pancreatic insufficiency (PI): seven had two severe mutations and two had unknown mutations. Three boys were pancreatic sufficient (PS), two with splicing mutations (5T and 3849+10kb C-T respectively) and borderline sweat tests. Seminal vesicles were visualised in 5/12 patients and 8/16 controls, compared to non-visualisation reported in all adults with CBAVD. Testicular microlithiasis was found in 4/18 PI, 0/6 PS, and 0/32 control testes, compared to 0.6-1.4% in healthy males and 15% in CF adults; 7/18 PI, 4/6 PS, and 0/32 control testes were smaller than predicted for age. The epididymal head was non-homogeneous with cysts, hypo-, or hyper-echogenicity in 5/18 PI, 1/6 PS, and 0/32 control testes.

CONCLUSIONS

Genital abnormalities may occur early in CF, but are less common than described in adults. They are found more often in pancreatic insufficient than in pancreatic sufficient CF patients. However, a positive finding, if present, may aid in the diagnosis of the latter. A larger longitudinal study is recommended to better define the onset and progression of urogenital abnormalities.

Pharmacological rescue of human K(+) channel long-QT2 mutations: human ether-a-go-go-related gene rescue without block

BACKGROUND

Defective protein trafficking is a consequence of gene mutations. Human long-QT (LQT) syndrome results from mutations in several genes, including the human ether-a-go-go-related gene (HERG), which encodes a delayed rectifier K(+) current. Trafficking-defective mutant HERG protein is a mechanism for reduced delayed rectifier K(+) current in LQT2, and high-affinity HERG channel-blocking drugs can result in pharmacological rescue. Methods and Results- We postulated that drug molecules modified to remove high-affinity HERG block may still stabilize mutant proteins in a conformation required for rescue. We tested terfenadine carboxylate (fexofenadine) and terfenadine, structurally similar drugs with markedly different affinities for HERG block, for rescue of trafficking-defective LQT2 mutations. Terfenadine rescued the N470D mutation but blocked the channels. In contrast, fexofenadine rescued N470D with a half-maximal rescue concentration of 177 nmol/L, which is approximately 350-fold lower than the half-maximal channel block concentration. The G601S mutation was also rescued without channel block.

CONCLUSIONS

Pharmacological rescue can occur without channel block. This could represent a new antiarrhythmic paradigm in the treatment of some trafficking-defective LQT2 mutations.