Effects of methacholine and uridine 5'-triphosphate on tracheal mucus rheology in mice

Enzymatic Synthesis of Nucleoside Triphosphates and Deoxynucleoside Triphosphates by Surface-Displayed Kinases

Nucleoside triphosphates and deoxynucleoside triphosphates are important biochemical molecules. In this study, recombinant Escherichia coli that could display nucleotide kinases (INP-N-NMKases) and acetate kinase (INP-N-ACKase) on the cell surface were constructed by fusing an enzyme (NMKase/ACKase) to the N-terminus of ice nucleation protein (INP-N). By using intact recombinant bacteria cells as a catalyst coupled with an ACKase-catalyzed adenosine-5'-triphosphate (ATP) regeneration system, nucleoside triphosphates (NTPs) and deoxynucleoside triphosphates (dNTPs) could be synthesized efficiently. In a reaction system with 5 mmol/l substrate, the conversion rates of cytidine-5'-triphosphate (CTP) and deoxycytidine-5'-triphosphate (dCTP) were 96% and 93%, respectively, the conversion rate of ATP and deoxyadenosine-5'-triphosphate (dATP) was 96%, the conversion rate of deoxythymidine-5'-triphosphate (dTTP) was 91%, and the conversion rate of uridine-5'-triphosphate (UTP) was 80%. There was no obvious degradation. At 37 °C, the stability of the surface-displayed fusion protein, especially in the presence of the substrate, was significantly improved. Each whole cell could be reused more than 8 times.

Pharmacotherapy of the ion transport defect in cystic fibrosis

1. More than 1300 different mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF), a disease characterized by deficient epithelial Cl- secretion and enhanced Na+ absorption. The clinical course of the disease is determined by the progressive lung disease. Thus, novel approaches in pharmacotherapy are based primarily on correction of the ion transport defect in the airways. 2. The current therapeutic strategies try to counteract the deficiency in Cl- secretion and the enhanced Na+ absorption. A number of compounds have been identified, such as genistein and xanthine derivatives, which directly activate mutant CFTR. Other compounds may activate alternative Ca2+-activated Cl- channels or basolateral K+ channels, which supply the driving force for Cl- secretion. Apart from that, Na+ channel blockers, such as phenamil and benzamil, are being explored, which counteract the hyperabsorption of NaCl in CF airways. 3. Clinical trials are under way using purinergic compounds such as the P2Y(2) receptor agonist INS365. Activation of P2Y(2) receptors has been found to both activate Cl- secretion and inhibit Na+ absorption. 4. The ultimate goal is to recover Cl- channel activity of mutant CFTR by either enhancing synthesis and expression of the protein or by activating silent CFTR Cl- channels. Strategies combining these drugs with compounds facilitating Cl- secretion and inhibiting Na+ absorption in vivo may have the best chance to counteract the ion transport defect in cystic fibrosis.

Effects of dextran sulfate on tracheal mucociliary velocity in dogs

We have shown that low molecular weight dextran, as a potential mucolytic agent, reduced the viscoelasticity and spinnability of cystic fibrosis (CF) sputum and improved its ciliary transportability in vitro; it also reduced viscoelasticity of healthy dog mucus in in vitro testing. In anesthetized dogs, dextran administered by aerosol at 65 mg/mL increased tracheal mucus velocity, but this increase was not sustained for higher concentrations. The purpose of the present study is to evaluate whether low mol. wt. dextran sulfate, a charged oligosaccharide, exhibits similar effects to previously tested neutral dextran when administered by aerosol to anesthetized dogs in terms of mucus rheology and mucociliary clearance rate. Healthy mongrel dogs were anesthetized with pentobarbital and intubated. Aerosols of Ringer's solution or dextran sulfate (m.w. 5000) dissolved in Ringer's were generated by Pari LC STAR nebulizer, and delivered during 30-min periods of spontaneous breathing. Tracheal transepithelial potential difference (PD, using agar filled electrodes) and tracheal mucociliary velocity (TMV, by charcoal marker particle transport) were measured under bronchoscopic control, and mucus for viscoelasticity analysis by magnetic rheometry was collected by the endotracheal tube method. We performed experiments in seven dogs, involving 30-min administrations of aerosol, separated by 30-min periods of no aerosol. All dogs received inhalations of 6.5 mg/mL, 20 mg/mL, and 65 mg/mL dextran sulfate. Tracheal mucus viscoelasticity (average log G* over 1-100 rad/s) decreased progressively with increasing dose of dextran sulfate; for the highest concentration (65 mg/mL), log G* decreased by a factor of 2.61 (p = 0.021). A modest increase in the TMV was observed for the first dose of dextran sulfate (128% of baseline at 6.5 mg/mL, p = 0.066); thereafter TMV was stable. PD increased significantly at each concentration of dextran sulfate compared with Ringer control; however, there was no additional change between the three groups. The solids content of collected airway fluid (%SC) was gradually increased during successive 30-min dextran sulfate aerosols, indicating a significant residence time for the dextran in the mucus, and correlating with the decrease in viscoelasticity. These results suggest that dextran sulfate may be potentially of therapeutic value as a mucolytic agent, assisting mucus clearance by cough and physiotherapy, although whether it stimulates mucociliary clearance remains to be proven.