Safety of chronic hypertonic bicarbonate inhalation in a cigarette smoke-induced airway irritation guinea pig model.

BACKGROUND: Cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) are often associated with airway fluid acidification. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene leads to impaired bicarbonate secretion contributing to CF airway pathology. Chronic cigarette smoke (CS) -the major cause of COPD- is reported to induce acquired CFTR dysfunction underlying airway acidification and inflammation. We hypothesize that bicarbonate-containing aerosols could be beneficial for patients with CFTR dysfunctions. Thus, we investigated the safety of hypertonic sodium bicarbonate (NaHCO3) inhalation in CS-exposed guinea pigs. METHODS: Animals were divided into groups inhaling hypertonic NaCl (8.4%) or hypertonic NaHCO3 (8.4%) aerosol for 8 weeks. Subgroups from each treatment groups were further exposed to CS. Respiratory functions were measured at 0 and after 2, 4, 6 and 8 weeks. After 8 weeks blood tests and pulmonary histopathological assessment were performed. RESULTS: Neither smoking nor NaHCO3-inhalation affected body weight, arterial and urine pH, or histopathology significantly. NaHCO3-inhalation did not worsen respiratory parameters. Moreover, it normalized the CS-induced transient alterations in frequency, peak inspiratory flow, inspiratory and expiratory times. CONCLUSION: Long-term NaHCO3-inhalation is safe in chronic CS-exposed guinea pigs. Our data suggest that bicarbonate-containing aerosols might be carefully applied to CF patients.

Extracellular alkalinization stimulates calcium-activated chloride conductance in cystic fibrosis human airway epithelial cells.

BACKGROUND: The pH of the airway surface liquid (ASL) plays a pivotal role in maintaining the proper function of the respiratory epithelium. In patients with cystic fibrosis (CF) acidic ASL has been observed. Thus, alkalinization of ASL itself might be beneficial in CF. The aim of this study was to investigate the role of extracellular pH (pH(o)) on the alternative Ca(2+)-activated Cl(-) channels (CaCCs) in CF airway epithelial cells. METHODS: The [Ca(2+)](i) and viability of CF airway epithelial cells (IB3-1) were assessed using Fluo-3/AM and YO-PRO-1 fluorescent dyes, respectively. Ion currents were detected in whole-cell configuration using the patch clamp technique. RESULTS: Extracellular alkalinization (pH(o) 8.2) stimulated Ca(2+) entry and inward currents in low Na(+) containing medium. The inward currents were blocked by the removal of extracellular Ca(2+), chelating cytosolic Ca(2+), as well as by the application of niflumic acid and DIDS. While Zn(2+) promoted sustained Ca(2+) entry in pH(o)-dependent manner, it inhibited the anion conductance. The low external Na(+) concentrations and alkaline pH(o) were well tolerated by the cells. CONCLUSIONS: Stimulation of CaCCs could be achieved by alkalinization of the extracellular environment in CF airway epithelial cells. Zn(2+) directly blocked, however indirectly enhanced the activity of Cl(-) conductance.

Calcium entry is regulated by Zn2+ in relation to extracellular ionic environment in human airway epithelial cells.

The extracellular pH, sodium and divalent cation concentrations influence the ATP-induced changes in cytosolic Ca(2+) concentration ([Ca(2+)](i)). This elevation of [Ca(2+)](i) and activation of Ca(2+)-dependent Cl(-) channels represent a possible therapeutic approach in cystic fibrosis (CF). We investigated the changes of [Ca(2+)](i) in different external ionic environment, and P2X purinergic receptors (P2XRs) expression in the control and CF airway epithelial cells. The parallel removal of Na(+) and alkalinization of the extracellular solution increased the amplitude of sustained ATP-induced Ca(2+) signals independent of wild-type or mutant CFTR expression. The ATP-induced Ca(2+) entry was either inhibited or stimulated by Zn(2+) depending on the extracellular Na(+) concentration. In Na(+)-free environment, Zn(2+) and other divalent cations elicited a biphasic Ca(2+) signal. Immunohistochemical data suggest that, multiple subtypes of P2XRs are expressed in these airway epithelial cells. In conclusion, Ca(2+) entry is finely regulated by external ionic environment. Therefore, we speculate that properly compiled aerosols could influence efficacy of zinc-based therapy in CF.

Role of Ca2+ -activated ion transport in the treatment of cystic fibrosis.

Cystic fibrosis (CF) is caused by defective cyclic AMP-dependent cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. Therefore, CF epithelial cells fail to transport, Cl(-) and water. Furthermore, the cessation of Cl(-) efflux across the apical membrane of CF pancreatic and biliary duct cells reduces HCO(3) (-) secretion as well. In CF epithelial cells activation of calcium-dependent Cl(-) channels might substitute for impaired CFTR function and restore Cl(-) and/or HCO(3) (-) secretion. ATP-mediated stimulation of P2Y and P2X purinergic receptors causes an increase in cytosolic Ca(2+) concentration ([Ca(2+)](i)). Effects of ATP are influenced by external zinc, pH and Na(+) concentrations. In low Na(+), alkaline environment, ATP and zinc induce a sustained and reproducible Ca(2+) signal because of P2X receptor mediated Ca(2+) influx from the extracellular space. Importantly, the increase in [Ca(2+)](i) stimulates anion secretion of nasal epithelia in CF mouse models suggesting that targeting P2X receptors might have beneficial effects in CF therapy.