The lactoperoxidase system links anion transport to host defense in cystic fibrosis

Chronic respiratory infections in cystic fibrosis result from CFTR channel mutations but how these impair antibacterial defense is less clear. Airway host defense depends on lactoperoxidase (LPO) that requires thiocyanate (SCN−) to function and epithelia use CFTR to concentrate SCN− at the apical surface. To test whether CFTR mutations result in impaired LPO-mediated host defense, CF epithelial SCN− transport was measured. CF epithelia had significantly lower transport rates, did not accumulate SCN− in the apical compartment. The lower CF [SCN−] did not support LPO antibacterial activity. Modeling of airway LPO activity suggested that reduced transport impairs LPO-mediated defense and cannot be compensated by LPO or H2O2 upregulation

Antimicrobial proteins and polypeptides in pulmonary innate defence

Inspired air contains a myriad of potential pathogens, pollutants and inflammatory stimuli. In the normal lung, these pathogens are rarely problematic. This is because the epithelial lining fluid in the lung is rich in many innate immunity proteins and peptides that provide a powerful anti-microbial screen. These defensive proteins have anti-bacterial, anti- viral and in some cases, even anti-fungal properties. Their antimicrobial effects are as diverse as inhibition of biofilm formation and prevention of viral replication. The innate immunity proteins and peptides also play key immunomodulatory roles. They are involved in many key processes such as opsonisation facilitating phagocytosis of bacteria and viruses by macrophages and monocytes. They act as important mediators in inflammatory pathways and are capable of binding bacterial endotoxins and CPG motifs. They can also influence expression of adhesion molecules as well as acting as powerful anti-oxidants and anti-proteases. Exciting new antimicrobial and immunomodulatory functions are being elucidated for existing proteins that were previously thought to be of lesser importance. The potential therapeutic applications of these proteins and peptides in combating infection and preventing inflammation are the subject of ongoing research that holds much promise for the future

Effects of albuterol enantiomers on ciliary beat frequency in ovine tracheal epithelial cells

β2-Adrenergic agonists stimulate ciliary beat frequency (CBF), an integral part of mucociliary clearance. To evaluate the differential effects of albuterol enantiomers and their racemic mixture on ciliary function, CBF and intracellular calcium were measured at room temperature from single ovine airway epithelial cells with use of digital videomicroscopy. Baseline CBF was 7.2 ± 0.2 (SE) Hz ( n = 80 measurements). R-albuterol (10 μM to 1 mM) stimulated CBF in a dose-dependent manner to maximally 24.4 ± 5.4% above baseline. Racemic albuterol stimulated CBF to maximally 12.8 ± 3.6% above baseline, a significantly lower increase compared with R-albuterol alone, despite identical R-enantiomer amounts in both groups. Simultaneous recordings of intracellular calcium concentration and CBF from single cells indicated that the CBF increase in response to R-albuterol was mediated through β-receptors and stimulation of protein kinase A, in a calcium-dependent and -independent fashion. S-albuterol had a negligible effect on CBF and did not change intracellular calcium. Together, these results suggest that R-albuterol is more efficacious than racemic albuterol in stimulating CBF. Thus S-albuterol may interfere with the ability of R-albuterol to increase CBF

Lactoperoxidase and human airway host defense

The lactoperoxidase (LPO) antibiotic system is a well-characterized component of mammary and salivary gland secretions. Because LPO has been shown to function in ovine airways, human airway tissue and secretions were examined for the presence of LPO and its substrate, the anion thiocyanate (SCN �). In addition, human airway secretions were tested for LPO-mediated antibacterial activity, and LPO’s activity was assessed against some human airway pathogens. The data showed that normal human airway secretions contained LPO enzyme activity (0.65 � 0.09 �g/mg secreted protein; n � 17), and Western blots of secretions demonstrated bands of the expected sizes for LPO. LPO mRNA was detected in trachea by sequencing PCR-amplified cDNA. SCN � , LPO’s substrate, was present in undiluted airway secretions at concentrations sufficient for LPO catalysis (0.46 � 0.19 mM; n � 8), and dilute

Transcellular thiocyanate transport by human airway epithelia

Human airway mucosa synthesizes and secretes lactoperoxidase (LPO). As H(2)O(2) and thiocyanate (SCN(−)) are also present, a functional LPO antibacterial defence system exists in the airways. SCN(−) concentrations in several epithelial secretions are higher than in serum, although the mechanisms of transepithelial transport and accumulation in these secretions are unknown. To examine SCN(−) accumulation in secretions, human airway epithelial cells, re-differentiated at the air–liquid interface, were used in open-circuit conditions. [(14)C]SCN(−), in the basolateral medium, was transported across the epithelium and concentrated tenfold at the apical surface. Measurement of the transepithelial potential showed that the basolateral compartment was positive relative to the apical surface (13.7 ± 1.8 mV) and therefore unfavourable for passive movement of SCN(−). Transport was dependent on basolateral [SCN(−)] and saturable (K(m,app) = 69 ± 25 μm); was inhibited by increased apical [SCN(−)]; and was dependent on the presence of basolateral Na(+). Perchlorate (K(i,app) = 0.6 ± 0.05 μm) and iodide (K(i,app) = 9 ± 8 μm) in the basolateral medium reversibly inhibited transport, but furosemide did not. Iodide was also transported (K(m,app)= 111 ± 69 μm). RT-PCR and immunohistochemistry confirmed expression of Na(+)−I(−) symporter (NIS) in the airways. SCN(−) transport was insensitive to apical disulphonic acid Cl(−) channel blockers, but sensitive to apical glibenclamide and arylaminobenzoates. Forskolin and dibutyryl cAMP increased transport. These data suggest SCN(−) transport may occur through basolateral NIS-mediated SCN(−) concentration inside cells, followed by release through an apical channel, perhaps cystic fibrosis transmembrane conductance regulator