Effect of exogenous surfactant on eustachian tube function in the rat

Otitis Media: Treatment With Intranasal Aerosolized Surfactant

OBJECTIVES/HYPOTHESIS

The objective was to determine the effect of intranasal surfactant alone and with other medications administered by metered dose inhaler aerosol on the function of the eustachian tube and on the resolution of experimentally induced otitis media with effusion (OME) and acute otitis media (AOM).

STUDY DESIGN

Randomized, experimental, controlled animal studies.

METHODS

Previously unreported (experiment 4) as well as published (experiments 1-3) data were detailed so that the reader could understand the continuum of information leading to the conclusions. In experiment 1, after a live-animal technique of measuring eustachian tube passive opening pressure was developed and validated, eustachian tube passive opening pressure was determined in 61 adult gerbils and 34 mice at baseline and 5 and 10 minutes after delivery of aerosolized intranasal metered dose inhaler surfactant. In experiments 2 and 3 (Klebsiella pneumoniae), lipopolysaccharide-induced OME was developed in gerbils. Thirty-five animals were randomly assigned to control, placebo, surfactant, surfactant with betamethasone, and surfactant with phenylephrine groups. Seventy animals were randomly assigned to control, placebo once daily (QD) and twice daily (BID), surfactant QD and BID, surfactant with betamethasone QD and BID, and surfactant with phenylephrine QD and BID groups. Intranasal aerosolized MDI medications were administered from postinfection day 2 until the effusion resolved. Otomicroscopy and tympanometry were performed on alternate days for 30 days. In experiment 4, AOM was developed in 39 chinchillas via transbullar injection of nontypeable Haemophilus influenzae on day 1. Thirteen animals each received placebo BID or surfactant BID, beginning on day 1. Thirteen animals received surfactant BID beginning on day 3. All administrations were continued for 10 days. Examinations were performed on seven occasions until day 27. Appropriate statistical measurements were employed, including one- and two-way ANOVA, strength-of-association measure (omega) calculation, chi, and Newman-Keuls post hoc multiple comparison tests. Significance was set as P value of less than.05.

RESULTS

In experiment 1, a significant reduction in passive opening pressure was seen in both 5- and 10-minute postsurfactant measurements. Propellant alone was not effective. In experiments 2 and 3, OME resolved after an average period of 16 to 16.5 days in control, placebo QD and BID, and surfactant with phenylephrine QD groups. A significant decrease in OME days was seen in the surfactant QD (10.57 d) and BID (8.57 d), and surfactant with betamethasone QD (8.57 d) and BID (6.3 d) groups. A significant increase was seen in the phenylephrine BID group (18.67 d). In experiment 4, tympanometry was normal or near-normal in 62% and 48% of treated ears and in only 24% of placebo ears on day 12. Sixty-seven percent of placebo ears were culture positive at day 27, compared with 10% and 16% in surfactant groups 1 and 2. Seventy-five percent of untreated animals developed severe labyrinthitis, compared with 15% in groups 1 and 2. On day 27, 58% of placebo group middle ears had fluid, whereas 61% and 62% of ears in groups 1 and 2, respectively, were dry. These findings were significant.

CONCLUSION

Intranasal application of aerosolized metered dose inhaler surfactant alone or with steroid reduced eustachian tube passive opening pressure in normal animals and duration of effusion in animals with experimental OME. Intranasal surfactant reduced the severity and duration of middle ear infection in AOM in this animal model.

Ultrastructural and ultracytochemical study of the middle ear epithelium in the chicken, Gallus gallus domesticus

The fine structure of the epithelium lining the tympanic cavity of the chicken was studied by TEM and SEM. In addition, the distribution of nonspecific esterase activity in the epithelium was investigated by TEM. Ultrastructural study revealed the presence of disk-like apical protrusions of the epithelial cells, previously not observed in other cell types. The protrusions contained some cytoplasmic organelles and were characterized by a ring-shaped thickening around their periphery. The ring was made up of a granulo-filamentous material. Our observations clearly indicate the existence of an apocrine secretory mechanism, consisting of a progressive detachment of disk-like protrusions from the apex of the epithelial cells. The ultracytochemical study demonstrated nonspecific esterase activity on the epithelial surface and in the secretory vesicles. We propose that nonspecific esterase is a marker for middle ear surfactant in birds.

Effect of exogenous surfactant on ventilatory and clearance function of the rat's eustachian tube

HYPOTHESIS AND BACKGROUND

The Eustachian tube has three important functions with respect to the middle ear: ventilation, clearance, and protection. Surfactants are assumed to be important to maintain these functions. The administration of exogenous surfactant may therefore be effective to improve the function of the Eustachian tube. This randomized, double-blind, placebo-controlled study was designed to investigate the effect of exogenous surfactant on the function of the Eustachian tube in rats.

MATERIALS AND METHODS

Exogenous surfactant was administered into the middle ear of 10 otologically healthy rats, and 10 other rats received placebo. The effect on the opening and closing pressure (passive ventilatory function) and the dye clearance time (clearance function) of the rat's Eustachian tube was measured.

RESULTS

A significant decrease in the opening pressure was seen after the administration of surfactant. Both surfactant and placebo caused an increase in the closing pressure. A serious disturbance of the dye clearance time was induced in 13 rats, and the test failed in 1 rat. In the remaining 6 rats, no significant differences in the dye clearance time were observed between the two groups.

CONCLUSIONS

Exogenous surfactant decreased the closing forces of the Eustachian tube even in otologically healthy rats. No significant effect on the mucociliary clearance was observed, but this may have resulted from the small number of rats. Additional randomized, double-blind, placebo-controlled trials should be conducted to determine the clinical relevance of these changes and to further assess the effect of surfactant on the function of the Eustachian tube.

A model of active Eustachian tube function in the rat: effect of modulating parasympathetic innervation

The effect of altering secretion into the Eustachian tube by modulating cholinergic innervation was studied in the anaesthetized rat. Active properties of the Eustachian tube were determined by measuring the ability of reflex-induced swallowing to equalize against an increased pressure level in the bulla. Reflex-induced swallowing was initiated by electrically stimulating the superior laryngeal nerve. Passive properties of the Eustachian tube were determined by increasing middle ear pressure until the Eustachian tube spontaneously opened. Blocking cholinergic neurotransmission with atropine had no effect on active or passive properties of the Eustachian tube. Potentiating cholinergic neurotransmission with neostigmine significantly impaired the ability of active swallowing to equilibrate middle ear pressure, but had no effect on passive properties of the Eustachian tube. The findings show that cholinergic nerve transmission, most likely from the parasympathetic division of the autonomic nervous system, can influence Eustachian tube function. We hypothesize that this effect is due to changes in surface tension in the Eustachian tube as a result of changes in secretion.

Therapeutic improvement of Eustachian tube function: a review

An impaired Eustachian tube is assumed to be an important factor in the pathogenesis of different middle ear diseases. Therefore, several investigators have studied different treatment strategies to improve Eustachian tube function. The aim of this review is to provide a comprehensive summary of the results of these studies on improvement of tubal function. The English language literature was searched systematically to identify all articles that described the effect of different interventions on Eustachian tube function. Although the results were not uniform throughout the different studies and despite several restrictions of the reviewed studies, the results of this review indicate that the function may be improved by medical intervention. However, it seems premature to recommend any of the interventions reviewed in this paper to improve function in humans. More studies, preferably randomized, placebo-controlled trials, should be conducted to assess the efficacy of different interventions.

Intranasal metered dose aerosolized surfactant reduces passive opening pressure of the eustachian tube: comparison study in two animal models

HYPOTHESIS

Intranasal metered dose aerosolized inhaler surfactant will reduce opening pressure of the eustachian tube in gerbils and mice.

BACKGROUND

Eustachian tube opening pressure necessary to allow ventilation of the middle ear must exceed the contractile force exerted by the tension on the curved surface of the eustachian tube. When the active function of opening the eustachian tube is inefficient, functional collapse of the tube persists, resulting in negative middle ear pressure. Such dysfunction is the primary cause of otitis media with effusion in children.

METHODS

Surfactant in a metered dose aerosolized intranasal delivery system was administered to 61 healthy Mongolian gerbils and 34 albino mice. In the first arm of the experiment, measurements of eustachian tube passive opening pressure were taken at baseline, after the delivery of propellant, and then at 5 and 10 minutes after surfactant administration. In the second arm of the experiment, the animals were divided into control, propellant, and experiment groups. At zero minutes, propellant was administered to the propellant group and intranasal surfactant was administered to the experiment group. Measurements of eustachian tube passive opening pressure were taken at 0, 5, and 10 minutes.

RESULTS

Surfactant administration in the gerbil reduced eustachian tube passive opening pressure from a basal measurement of 40.5 mm Hg to 32.5 mm Hg after 5 minutes and to 30.1 mm Hg after 10 minutes. In mice, eustachian tube passive opening pressure reduced from a basal level of 41.8 mm Hg to 31.3 mm Hg after 5 minutes and to 31.2 mm Hg after 10 minutes in the surfactant group. Propellant placebo resulted in no change from basal level in both animal models and in both arms of the experiment.

CONCLUSION

Intranasal metered dose inhaler aerosolized surfactant is effective in reducing eustachian tube passive opening pressure.

Surfactant proteins in the digestive tract, mesentery, and other organs: evolutionary significance

For years, the so-called surfactant proteins (SPs) that were discovered in the phospholipid-rich material designated pulmonary surfactant, were considered to be lung-specific. The fact that surfactant-like materials composed of phospholipids are secreted by a number of other organs recently prompted several groups to search for SP expression in these organs also. The hydrophilic proteins SP-A and SP-D and their transcripts have been found in a number of tissues, including gastric and intestinal mucosae, mesothelial tissues (mesentery, peritoneum, and pleura), synovial cells, Eustachian tube and sinus, and possibly in salivary glands, pancreas, and urinary tract. By contrast, the hydrophobic proteins SP-B and SP-C actually appear to be expressed in lung epithelium only. SP-A and SP-D belong to the innate defence system against pathogens and play a role as opsonins for facilitating phagocytosis. Their expression appears as a general feature of organs exposed to pathogens because they present an interface with the external milieu. Although this function has thus far been investigated in the lung only through the gene-targeting approach, increased expression of SP-A in the infected middle ear and of SP-D in the Helicobacter-infected antrum argues for such a function also in other organs. In organs that are not exposed to external pathogens, their role is likely to exert anti-inflammatory and immunomodulatory functions, as suggested by increased SP-A immunoreactivity in rheumatoid disease. SP-A and SP-B have been found in association with phospholipids in the lung of all air-breathing vertebrates, including the most primitive forms represented by lungfish, which implies that the surfactant system had a single evolutionary origin. Immunochemical proximity of the proteins among vertebrates indicates considerable conservation during evolution. Moreover, the finding of an SP-A-like protein in intestine and swim bladder of actinopterygian fish implies that the ancestral form of the protein was already present before the emergence of lung structures.

Dosage regimens of intranasal aerosolized surfactant on otitis media with effusion in an animal model

OBJECTIVE

To determine optimal dosage regimens of intranasal metered dose aerosolized surfactant with and without other medications in the treatment of otitis media with effusion (OME).

STUDY DESIGN

Resolution of experimental OME in gerbils was determined based on otomicroscopy and tympanometry. Experimental intranasal drugs were: surfactant, surfactant with betamethasone, surfactant with phenylephrine, and a normal saline solution placebo. Medications were administered once or twice daily via a metered dose inhaler.

RESULTS

For twice-daily dosing, mean days to OME resolution were 8.5 for the aerosolized surfactant, 6.3 for the surfactant with betamethasone, 18.7 for the surfactant with phenylephrine, and 16 each for control and placebo. Resolution with the once-daily dosage was longer for all conditions. Results were comparable using tympanometry.

CONCLUSION

OME resolved faster than the natural course when treated with intranasal surfactant with and without steroids. Twice-daily dosing was statistically superior.

SIGNIFICANCE

This study reiterates the effectiveness of OME treatment with an aerosolized synthetic surfactant with and without steroids and establishes a superior twice-daily dosage schedule.

Surfactant protein A (SP-A): the alveolus and beyond

Surfactant protein A (SP-A) is the major protein component of pulmonary surfactant, a material secreted by the alveolar type II cell that reduces surface tension at the alveolar air-liquid interface. The function of SP-A in the alveolus is to facilitate the surface tension-lowering properties of surfactant phospholipids, regulate surfactant phospholipid synthesis, secretion, and recycling, and counteract the inhibitory effects of plasma proteins released during lung injury on surfactant function. It has also been shown that SP-A modulates host response to microbes and particulates at the level of the alveolus. More recently, several investigators have reported that pulmonary surfactant phospholipids and SP-A are present in nonalveolar pulmonary sites as well as in other organs of the body. We describe the structure and possible functions of alveolar SP-A as well as the sites of extra-alveolar SP-A expression and the possible functions of SP-A in these sites.

Classification of otitis media and surgical principles

Otitis media is an important disease of children and adults and is caused by multiple interrelated factors, including infection, eustachian tube dysfunction, allergy, and barotrauma. This article includes a pertinent review of the literature regarding otitis media. The pathogenesis, classification, and treatment of otitis media in children and adults are also reviewed in this article. Additionally, therapy is discussed with emphasis on the surgical options appropriate at each stage.

Surfactant protein-A: new insights into an old protein--II

Pulmonary surfactant is a lipoprotein substance that lines the lungs and helps reduce surface tension. Surfactant associated protein-A (SP-A) is the most abundant non-serum protein in pulmonary surfactant. This complex glycoprotein aids in the synthesis, secretion and recycling of surfactant phospholipids, and facilitates the reduction of surface tension by surfactant phospholipids. Recent evidence has highlighted the role of SP-A in the innate immune system present in the lung. SP-A may play a major role in defense against pathogens by interacting with both infectious agents and the immune system. Factors that affect fetal lung maturation, e.g. gestational age and hormones regulate SP-A gene expression. Mediators of immune function also regulate SP-A levels. A number of lung disorders, including infectious diseases and respiratory distress syndrome are associated with abnormal alveolar SP-A levels. SP-A can no longer be called a lung-specific protein, since it has recently been detected in other tissues. In most species, SP-A is encoded by a single gene, however in humans it is encoded by two, very similar genes. Models for the structure of the human SP-A protein molecule have been proposed, suggesting that the mature alveolar SP-A molecule is composed of both gene products. The study of SP-A may provide information helpful in understanding disease processes and formulating new treatment modalities.

Drug-Induced Changes in Eustachian Tube Function

Many studies have shown that antihistamines and decongestants are of little use in the treatment of acute otitis media and otitis media with effusion, or in the prophylaxis of these disorders.1 However, because some drugs can improve otitis media with effusion (glycocorticosteroids)2–4 and some can impair the opening function of the eustachian tube (atropine),5 it seems justified to continue studies of eustachian tube function and medication.

Nebulized Surfactant for Experimentally Induced Otitis Media with Effusion

Eustachian tube dysfunction frequently results in clinical evidence of otitis media with effusion (OME). Surface active substances, surfactants, are hypothesized to play a role in normal eustachian tube function. Recent work in a rodent model has demonstrated improved eustachian tube function with topical application of surfactants to the middle ear. A novel, noninvasive, and clinically practical method of delivering surfactant to the eustachian tube was studied in a gerbil model of OME. Otitis media with effusion was experimentally induced in 20 gerbils by transtympanic inoculation of heat-killed Streptococcus pneumoniae. This represents a well established model for creating a serous effusion in the gerbil that significantly increases eustachian tube opening pressure. Effusion developed in 27 of 40 ears (67.5%) after inoculation. An inhaled nebulized surfactant was used to treat the animals with microscopically confirmed OME in one or both ears. The treatment period was 5 days. Eustachian tube opening studies were performed on both affected and nonaffected animals. Successful eustachian tube opening pressures were obtained in 30 of 36 ears (83.3%). The mean opening pressure for ears without effusion (healthy ears) was 42.8 mmHg. The mean opening pressure for ears with effusion in animals treated with nebulized surfactant was 41.4 mmHg. The difference between these mean values was not statistically significant ( t = 0.32; p > 0.50). This pilot study suggests that inhaled nebulized surfactant may be efficacious in treating eustachian tube dysfunction when manifested in disorders such as OME.

Influence of surface condition of mucosa of eustachian tube on tubal compliance

To clarify the influence of the mucosal condition of the eustachian tube (ET) upon its collapsibility, three experimental studies were performed by using the forced response test. First, by washout of the mucous blanket of ET, the tubal compliance index (TCI), the ratio of passive tubal resistances at two different airflow rates, significantly increased in all the 6 ETs of 5 cats, and all returned to the baseline within 50 min. Second, the TCIs significantly decreased in all the 7 ETs of 5 cats after application of Triton X (surfactant) into the ET washed out by saline. Third, the increased TCIs of a tubal model by application of saline significantly decreased after application of Triton X. These results seem to support our hypothesis that compliance of the ET, which means its collapsibility, may depend upon the mucosal condition as well as on the property of the cartilaginous framework of ET.

The effect of surfactant on eustachian tube function in a gerbil model of otitis media with effusion

The relationship of eustachian tube surfactant and otitis media with effusion on eustachian tube opening pressure was studied in a gerbil model. Injection of killed Streptococcus pneumoniae bacteria created a serous effusion that increased eustachian tube opening pressure. The introduction of exogenous surfactant to this system resulted in a dramatic decrease in eustachian tube opening pressure in both normal ears and those with effusion. Identifying means to increase surfactant in the eustachian tube could be beneficial in reducing persistent otitis media with effusion.

The fate of tumour rests following removal of acoustic neuromas: an MRI Gd-DTPA study

The fate of capsular fragments left attached to vital structures at the time of otherwise total tumour removal was studied in 14 of 21 such patients who underwent acoustic neuroma surgery. Imaging using magnetic resonance Gd-DTPA at post-operative intervals of 6 months-12 years (mean 70 months) showed evidence of persistent tumour in half the patients. None of the patients had developed new symptoms and computed tomography had failed to demonstrate tumour recurrence. Persistence of the tumour was more likely if the residual fragments were not cauterized at the time of operation. Four of the seven persisting tumour rests showed evidence of gradual enlargement. The implications for patient management, particularly if an attempt is made to preserve hearing, are discussed.

Implication of surfactant apoprotein in otitis media with effusion

A two-site simultaneous immunoassay using monoclonal antibodies against human surfactant apoprotein (SAP) was used to measure SAP in middle ear effusions (MEEs). In 130 MEE samples from children with otitis media with effusion, SAP was detected in 54 samples (SAP-positive cases, 41.5%). In the remainder, the SAP concentration was below the sensitivity of the immunoassay (SAP-negative cases, 58.5%). A significant difference in periods of observation was found between the SAP-positive cases (17.3 +/- 16.8 months) and the SAP-negative cases (26.2 +/- 22.5 months) (p less than .01). The percentage of positive cases was highest in the serous MEE group (81.2%) and decreased in the purulent MEE group (57%), the mucoid MEE group (30%), and the hyperviscous MEE group (13.6%), in that order. In the purulent MEE group and the mucoid MEE group, the period of observation was significantly shorter in the SAP-positive cases (18.3 +/- 20.4 months and 20.2 +/- 19.4 months) than in the SAP-negative cases (35.9 +/- 24.5 months and 25.4 +/- 18.7 months) (p less than .05). These results suggest that SAP is present in the middle ear cleft and may be a good prognostic predictor of otitis media with effusion in children.

Surfactant and isoprenaline effect on eustachian tube opening in rats with acute otitis media

Purulent otitis media was induced in 12 middle ears of Sprague-Dawley rats by inoculation of pneumococci type 3. The pressure required to open the eustachian tube was recorded 4 days later and was found to be 3.05 +/- 0.10 kPa (mean +/- SEM), which was 1.08 +/- 0.15 kPa lower than the mean value obtained in a control group of healthy rats (P less than or equal to .001). We also measured the effects of pulmonary surfactant instilled into the middle ear as well as isoprenaline injected intravenously. The presence of surfactant further reduced the pressure opening level by 0.72 +/- 0.05 kPa; this reduction did not differ from that found in the control group (P greater than .8). Isoprenaline reduced the pressure opening level in the control group by 0.20 +/- 0.03 kPa (P less than or equal to .001), and no reduction was found in the rats with otitis media. Although the part played by surface tension-lowering factors in eustachian tube function is still uncertain, such factors apparently also exert an effect in the inflamed tube. However, isoprenaline, which is considered to act by the secretion of surface tension-lowering substances, did not facilitate opening of the eustachian tube in rats with acute otitis media.