Mammalian respiratory mucociliary clearance

Evaluation of Second Generation Amiloride Analogs as Therapy for Cystic Fibrosis Lung Disease

Epithelial sodium channel (ENaC) blockers have been proposed as a therapy to restore mucus clearance (MC) in cystic fibrosis (CF) airways. The therapeutic effects of the first generation ENaC blocker, amiloride, in CF patients, however, were minimal. Because the failure of amiloride reflected both its low potency and short duration of action on airway surfaces, we investigated whether the increased potency of benzamil and phenamil would produce more favorable pharmacodynamic properties. In vitro potency, maximal efficacy, rate of recovery from maximal block of ENaC, and rate of drug absorption were compared for amiloride, benzamil, and phenamil in cultured human and ovine bronchial epithelial cells. In both human and ovine bronchial epithelia, the rank order of potency was benzamil > phenamil >> amiloride, the maximal efficacy was benzamil = phenamil = amiloride, the recovery to baseline sodium transport was phenamil < benzamil << amiloride, and the rate of drug absorption was phenamil > benzamil >> amiloride. Based on greater potency, benzamil was compared with amiloride in in vivo pharmacodynamic studies in sheep, including tracheal mucus velocity (TMV) and MC. Benzamil enhanced MC and TMV, but acute potency or duration of effect did not exceed that of amiloride. In conclusion, our data support the hypothesis that ENaC blocker aerosol therapy increases MC. However, rapid absorption of benzamil from the mucosal surface offset its greater potency, making it equieffective with amiloride in vivo. More potent, less absorbable, third generation ENaC blockers will be required for an effective aerosol CF pharmacotherapy.

Altering airway surface liquid volume: inhalation therapy with amiloride and hyperosmotic agents

The thin layer of liquid lining the entire respiratory tract is the first line of defense against the continuous insult of inhaled bacteria and noxious chemicals. Many chronic obstructive diseases of the airway may reflect decreased airway surface liquid, which results from imbalances in ion transport and mucus production. Reduction in the thickness of airway surface liquid leads to reduced mucociliary clearance rates, causing mucus accumulation and infection in the airway. In this chapter, two inhalation therapies to replenish airway surface liquid and enhance mucociliary clearance are discussed: (1) aerosolized hyperosmotic agents; and (2) aerosolized sodium channel blockers. The advantages and disadvantages of each therapy are discussed, as well as future directions for improving airway surface liquid volume by inhalation pharmacotherapy.

Nasal mucociliary clearance in Sjögren's syndrome. Dissociation in flow between sol and gel layers

Nasal mucociliary clearance was measured with two methods in 8 patients with Sjögren's syndrome and in 6 normal subjects. The movement of two different tracers placed 1.5 cm posterior to the inferior turbinate tip was measured respectively. The transport rate of a 500 microns anion resin particle tagged with 99mTc was measured. The clearance of 10 microliters saline labelled with 99mTc was monitored and the clearance rate was calculated. Whereas the measurement with the particle method revealed the lowered transport rate in Sjögren's syndrome, measurement with the saline method did not reveal any difference in clearance rate between the two groups. Since the former method measures the transport of particle in the gel phase (the outer mucous layer) and the latter measures the clearance of both gel and sol (periciliary fluid) layers, it is postulated that there is a dissociation of flow between sol and gel layers in Sjögren's syndrome.

Ultrastructure of mucous blanket in otitis media with effusion

We used transmission electron microscopy to study the mucous blanket of the promontory from children with otitis media with effusion. The vast majority of the epithelial cells were secretory, and the rest were ciliated. The mucous blanket consisted of the electron-lucent periciliary fluid and the mucous layer. In the mucous layer, two layers were identified: an inner layer with migrating cells, and an outer layer with specks. Moreover, there was a lucent zone over the nonciliated surface that was as high as the microvilli. The thickness of the periciliary layer was predominantly as great as that of the ciliary tips, which just make contact with the mucous layer; however, the mucous layer occasionally penetrated into the periciliary space. These findings indicated that there is a mucociliary dysfunction in the middle ear caused by a decrease in the number of ciliated cells, and an abnormal interaction between cilia and mucus that would interfere with ciliary movement. Thus, such a system would fail to transport the mucous blanket.

Nasal trigeminal chemoreception: responses to n-aliphatic alcohols

Odorant molecules can stimulate nasal trigeminal receptors, but the properties of such molecules which make them effective stimuli are largely unknown. In the present study, we obtained integrated multiunit responses from the ethmoid branch of the rat trigeminal nerve to a homologous series of aliphatic alcohols. Our aim was to determine whether lipid solubility might correlate with stimulus efficacy. Response thresholds (ranging from 3000 ppm for methanol to 3 ppm for octanol) decreased with increasing carbon chain length, suggesting that lipid solubility is important for stimulus effectiveness. One plausible explanation for the importance of lipophilicity is that the more lipid soluble a substance, the more easily it can penetrate epithelial layers to reach chemoreceptive trigeminal nerve endings. Since all stimuli at vapor saturation elicited responses within 0.5 s, and because diffusion of stimulus molecules through epithelium is slow, we speculate that trigeminal nerve endings lie closer to the epithelial surface than previously thought.

A model of the regional uptake of gaseous pollutants in the lung. I. The sensitivity of the uptake of ozone in the human lung to lower respiratory tract secretions and exercise

An ozone (O3) dosimetry model is presented that takes into account convection and diffusion of O3 in the lumen and airspaces of the lower respiratory tract and transport and chemical reactions in the mucous and surfactant layers and in the underlying tissue and capillaries. The model was applied to human airway morphometric data. Values for the chemical and physical parameters that define the liquid tissue and blood compartments were based on reported experimental data. Simulation results illustrate the variability of results due to an uncertainty in the knowledge of transport parameters, liquid, tissue, and blood compartment thicknesses, and chemical reaction rates. Results were most sensitive to mucous compartment thickness and reaction rate constant and least sensitive to transport and blood parameters. Exercise was simulated, showing little effect on tracheobronchial uptake but a pronounced effect on pulmonary uptake.

Physicochemical processes and the formulation of dosimetry models

The major physical and chemical processes involved in the transport and absorption of O3 or NO2 in the lower respiratory tract are discussed. This includes the development of respiratory tract models, flow patterns, and transport in tube networks, the mucous, surfactant, and tissue layers, and chemical reactions and transport of O3 or NO2 within these layers. Descriptions of the individual processes are simplified and integrated to illustrate the formulation of dosimetry models. Data from a dosimetry model, formulated from the concepts discussed, are used to illustrate the types of information obtained by modeling.

Cilia in the human kidney

Utilizing transmission electron microscopy we have found multiple cilia with a 9 + 2 microtubular pattern (the same type found in the bronchial tree) in the renal tubules of four adults with the nephrotic syndrome. Each patient had a different pathologic diagnosis: amyloidosis, lipoid nephrosis, membranoproliferative glomerulonephritis, and focal segmental glomerulosclerosis. Previously, multiple renal tubular cilia with 9 + 2 architecture had been reported in patients with Burnett's syndrome, systemic lupus erythematosus, and congenital nephrotic syndrome. Additionally, we found multiple cilia in the metanephric tubules of 4 of 4 human fetuses. Pathologists should be aware that cilia with various microtubular patterns occur in human adult kidneys.

Oxidant-induced enhanced sensitivity to infection in animal models and their extrapolations to man

Animal studies have provided the toxicologist with useful and scientifically sound information indicating that exposure to oxidant gases can alter the functioning of the host's normal pulmonary defense system, resulting in an increased risk to infectious disease. Since the basic mechanisms of action of the human and the animal pulmonary defenses are similar, it is reasonable to relate these animal's biological responses to human exposures. This paper examines the possibility of quantitatively extrapolating such animal dose-response data to humans.

Influence of steroid aerosol treatments on the clearance of inhaled gold particles

Female Long Evans rats were used to test the hypothesis that in haled triamcinolone acetonide accelerates the rate of clearance of particles from the lung. Three groups of animals inhaled a radioactive gold aerosol, which functioned as a tracer of respiratory tract clearance, and then were subjected to various inhalation treatments. The group treated with triamcinolone acetonide aerosol showed a significant acceleration in the rate of early clearance, but the total amount of tracer particles cleared in the first day was not significantly increased. Inhaled triamcinolone acetonide appears to accelerate the translocation of foriegn particles from small airways to larger ones, but stimulation of clearance does not appear to be a large effect.

Measurement of frequency of ciliary beats of human respiratory epithelium

A method for accurate measurement of beats on ciliated respiratory epithelial cells in vitro is described. The technique allows the frequency of ciliary beats to be recorded directly on minute specimens of human respiratory epithelium obtained by bronchoscopic brushing. A "hanging-drop" preparation of the scraped material is placed on a thin, flat welled slide and is viewed with a phase-contrast microscope at a magnification of x450. Light transmitted through the specimen is deflected in varying intensities due to the beating action of the cilia and is detected by a photomultiplier cell, amplified and transduced as peaks on an oscilloscope. Due to the relatively high magnification, a small group of cilia may be focused upon and their activity measured. Specimens from two groups totaling 53 patients were measured; in the first group the frequency of ciliary beats was measured at 23 degrees C and ranged from 9.1 to 12.9 beats per second with a mean and standard deviation of 11.0 +/- 1.3 beats per second. The second group was measured at 37 degrees C, and values ranged from 10.3 to 16.8 beats per second, with a mean and standard deviation of 13.8 +/- 1.8 beats per second. These values are interpreted to reflect the autonomous frequency of ciliary beats of the isolated respiratory cells. This simple method may be applied to screen for abnormalities of ciliary beating in patients with altered respiratory mucous clearance, as well as to examine the specific effects in vitro of chemicals, drugs, or pollutants on human ciliary activity.