Glucocorticosteroids increase sodium transport in middle ear epithelium

Divergent expression of α-ENaC in middle ear mucosa in the course of otitis media with effusion induced by barotrauma

CONCLUSION

Gene transcription and protein expression of α-ENaC showed a divergent expression in association with the development of OME induced by barotrauma.

OBJECTIVES

ENaC was identified to mediate the fluid absorption through epithelia of the middle ear. This study was designed to investigate the involvement of ENaC in otitis media with effusion (OME) induced by barotrauma.

METHODS

A rat model of otitis media with effusion was established using a pressure cabin. The dynamic expression of α-ENaC was detected by Real time-PCR and western blot in the course of otitis media.

RESULTS

Compared with the control, the volume of α-ENaC mRNA and protein increased significantly by 3.18-fold and 2.8-fold on the 3(rd) day, respectively, while decreased by 0.54-fold and 0.32-fold on the 7(th) day, respectively.

Is Dysregulation of the HPA-Axis a Core Pathophysiology Mediating Co-Morbid Depression in Neurodegenerative Diseases?

There is increasing evidence of prodromal manifestation of neuropsychiatric symptoms in a variety of neurodegenerative diseases such as Parkinson's disease (PD) and Huntington's disease (HD). These affective symptoms may be observed many years before the core diagnostic symptoms of the neurological condition. It is becoming more apparent that depression is a significant modifying factor of the trajectory of disease progression and even treatment outcomes. It is therefore crucial that we understand the potential pathophysiologies related to the primary condition, which could contribute to the development of depression. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signaling system involved in physiological homeostasis and stress response. Disturbances of this system lead to severe hormonal imbalances, and the majority of such patients also present with behavioral deficits and/or mood disorders. Dysregulation of the HPA-axis is also strongly implicated in the pathology of major depressive disorder. Consistent with this, antidepressant drugs, such as the selective serotonin reuptake inhibitors have been shown to alter HPA-axis activity. In this review, we will summarize the current state of knowledge regarding HPA-axis pathology in Alzheimer's, PD and HD, differentiating between prodromal and later stages of disease progression when evidence is available. Both clinical and preclinical evidence will be examined, but we highlight animal model studies as being particularly useful for uncovering novel mechanisms of pathology related to co-morbid mood disorders. Finally, we purpose utilizing the preclinical evidence to better inform prospective, intervention studies.

A randomized, double-blind, placebo-controlled clinical study to assess safety and clinical activity of OTO-104 given as a single intratympanic injection in patients with unilateral Ménière's disease

OBJECTIVE

To evaluate the safety, tolerability, and clinical activity of a single intratympanic injection of OTO-104, sustained-release dexamethasone formulation, in patients with unilateral Ménière's disease.

STUDY DESIGN

Prospective, double-blind, randomized, placebo-controlled, dose-escalation study of 16 weeks' (4-wk lead-in before dosing; 12-wk follow-up after dosing) duration for each patient.

SETTING

Fifteen centers (physician offices and academic or tertiary referral centers).

PATIENTS

Forty-four patients aged 22 to 75 years.

INTERVENTION

Single intratympanic injection of OTO-104 (3 or 12 mg) or placebo.

MAIN OUTCOME MEASURES

Safety and tolerability were assessed via adverse event reports, otoscopy, audiometry, and tympanometry. Clinical activity was assessed primarily as changes in vertigo frequency.

RESULTS

OTO-104 was well tolerated, with no impact on hearing function. Plasma levels were observed in a few patients and were barely quantifiable. The most frequently reported adverse event considered related to investigational product was tympanic membrane perforation; no clinical sequelae were associated with these perforations and all were graded mild or moderate. At Month 3, the observed mean ± standard deviation (SD) change from baseline in vertigo frequency was -0.124 ± 0.153, -0.147 ± 0.166, and -0.211 ± 0.153 for the placebo, 3-mg OTO-104, and 12-mg OTO-104 groups, respectively; corresponding to 42%, 56% and 73% reductions in vertigo frequency, respectively. Similar results were observed for tinnitus, measured by the Tinnitus Handicap Inventory (THI-25).

CONCLUSION

OTO-104 was safe and well tolerated. Although the sample size was small, the data suggest 12 mg of OTO-104 was associated with a clinically meaningful reduction in vertigo frequency compared to placebo 3 months after treatment.

Effect of ciprofloxacin/dexamethasone versus ciprofloxacin/hydrocortisone on lipopolysaccharide-induced experimental otitis media

OBJECTIVES

The purpose of this study is to compare the effect of topical ciprofloxacin/dexamethasone versus topical ciprofloxacin/hydrocortisone on the outcome of lipopolysaccharide (LPS)–induced otitis media with effusion in chinchillas.

STUDY DESIGN

A randomized experimental animal study.

SETTING

Jerry L. Pettis Veteran's Medical Center.

SUBJECTS AND METHODS

Otitis media with effusion was induced in 5 groups of chinchillas, 6 per group, by injecting 0.3 mL (1 mg/mL) of Salmonella enteric LPS into the superior bullae of each chinchilla with a venting needle in place. Each group was treated with 0.2 mL of test substance at –2, 24, 48, and 72 hours relative to the 0-hour LPS induction. Group 1 was treated with vehicle control. Groups 2 to 5 received 0.3% ciprofloxacin with either 0.1% dexamethasone (group 2), 1% dexamethasone (group 3), 0.1% hydrocortisone (group 4), or 1% hydrocortisone (group 5). The outcome of each treatment was measured by the amount of middle ear effusion present and mucosal thickness at 120 hours posttreatment.

RESULTS

Ciprofloxacin/dexamethasone 1% significantly (P = .0150) reduced middle ear effusion compared with control. Ciprofloxacin/dexamethasone 1% significantly reduced the mucosal thickness when compared with vehicle control (P = .0005), ciprofloxacin/dexamethasone 0.1% (P = .0240), and ciprofloxacin/hydrocortisone 0.1% (P = 1.00). Results also showed a dose-response effect between the ciprofloxacin/dexamethasone concentrations.

CONCLUSIONS

This study demonstrated that treatment with a combination of topical ciprofloxacin and corticosteroid decreased the middle ear effusion when compared with the control group and that ciprofloxacin/dexamethasone suspension reduced the severity of LPS-induced experimental otitis media more than ciprofloxacin/hydrocortisone did.

Drug-related nephrotoxic and ototoxic reactions : a link through a predictive mechanistic commonality

BACKGROUND

Drug-induced ototoxicity is a subject of interest because many diseases are treated with drugs that have potential toxic effects on the ear. There is evidence that both inner ear and kidney tissue are immunologically, biochemically and functionally related. It has been suggested that drugs that influence the transport of sodium and/or potassium change ionic homeostasis in the inner ear and, hence, induce functional disturbances such as hearing loss, tinnitus and vertigo.

OBJECTIVES

To assess whether renal suspected adverse drug reactions (sADRs) have predictive value for ear and labyrinth adverse drug reactions (ADRs) and whether drug classes involved have influence ion transport systems.

STUDY DESIGN

Data were obtained from the Netherlands Pharmacovigilance Centre Lareb. The study base comprised all reports of sADRs up until 1 January 2007. Cases were all sADRs for relevant renal disorders and all sADRs for relevant ear disorders. All other reported sADRs were selected as 'non-cases'. The relationship between drug classes and renal, ear and labyrinth sADRs was evaluated by calculating reporting odds ratios (RORs). An ROR > or = 1.50 was regarded as a cut-off value for an association. Drug classes were classified into four groups: (A) ROR kidney <1.50 and ROR ear <1.50 or no reports on ear sADRs (reference group); (B) ROR kidney <1.50 and ROR ear > or = 1.50; (C) ROR kidney > or = 1.50 and ROR ear <1.50 or no reports on ear sADRs; and (D) ROR kidney > or = 1.50 and ROR ear > or = 1.50. For each group, we calculated odds ratios (ORs) for the association between the group classification and the effect on ion channels/ion transport systems in kidney and ear tissues.

RESULTS

Of 193 drug classes with relevant ADRs for renal disorders, 120 drug classes also had reports on ototoxic reactions. Fourteen out of 120 drug classes had an ROR > or = 1.50 for the association between the drug class and both renal and ear sADRs. Among these drug classes were several with a well known ability to induce renal (adverse) effects and ear and labyrinth disorders, such as loop diuretics, aminoglycosides and quinine. We found that one mechanistic commonality of the drug classes mentioned in the reports was the ability to affect ion transport systems. The percentage of drugs having this property differed between the four groups. The ORs for groups D and B were significantly higher compared with the reference group (OR 12.2, 95% CI 3.0, 30.5 and OR 8.7, 95% CI 2.4, 18.7, respectively), whereas there was no association for group C.

CONCLUSION

Our data suggest that renal sADRs as such are not a marker for drug-induced ear and labyrinth disorders. However, the ability of drugs to act on ion channels or ion transport systems and, therefore, have an influence on ionic homeostasis in the kidney and ear might be a predictor for the possible occurrence of drug-related ototoxicity.

Activation of epithelial sodium channel in human middle ear epithelial cells by dexamethasone

The middle ear epithelium functions to maintain a fluid-free middle ear cavity. Dysfunction of the middle ear epithelial ion and fluid transport is implicated in the pathogenesis of fluid collection in the middle ear cavity, characteristic of otitis media with effusion. The efficacy of steroid therapy for the treatment of otitis media with effusion remains controversial, and postulated modulation of transepithelial transport function in middle ear epithelia has yet to be demonstrated. The effect of dexamethasone on Na(+) transport and fluid absorption capacity was investigated in cultured normal human middle ear epithelial (NHMEE) cells. Dexamethasone produced a significant increase in amiloride-sensitive short-circuit current (Isc). Dexamethasone significantly increased expression levels of mRNAs and proteins of Epithelial Sodium Channel (ENaC)-alpha and -beta subunits. In addition, the ENaC-dependent fluid absorption was significantly increased after dexamethasone treatment. In summary, we have shown that dexamethasone stimulates ENaC activity and ENaC-dependent fluid absorption in NHMEE cells. These findings suggest glucocorticosteroids may be beneficial in treatment of otitis media with effusion by stimulating Na(+) transport and fluid clearance in the middle ear epithelia.

Control of chronic otitis media and sensorineural hearing loss in C3H/HeJ mice: glucocorticoids vs mineralocorticoids

OBJECTIVE

The impact of glucocorticoids and mineralocorticoids on chronic otitis media (COM) in toll-like receptor 4-deficient C3H/HeJ mice was investigated.

STUDY DESIGN

To evaluate control of COM by steroids with differences in their anti-inflammatory (prednisolone, dexamethasone), and fluid absorption functions (fludrocortisone, aldosterone). A minimum sample size of five animals for each group was required based on power analysis calculations. Sample sizes ranged from 7 to 17 mice per treatment group.

SUBJECTS AND METHODS

Auditory brain stem response (ABR) thresholds were performed at baseline, 2 weeks and 4 weeks. Histopathologic test results were evaluated on all mice ears at the end of the study.

RESULTS

Analysis of variance (ANOVA) of ABR threshold change showed significant treatment effects (P < 0.05) by both steroid types at all time intervals and ABR frequencies except 4 weeks/8 kHz. Histologic assessment showed prednisolone-treated mice (62%) had a higher rate of clearance of middle and inner ear inflammation than control mice (4%).

CONCLUSION

It was concluded that steroid treatments can improve the physiology of chronic middle and inner ear disease seen with COM.

Effect of topical dexamethasone versus rimexolone on middle ear inflammation in experimental otitis media with effusion

CONCLUSION

The lipopolysaccharide (LPS)-induced chinchilla otitis media (OM) model was proven useful in screening anti-inflammatory agents for topical use. Both 1% rimexolone and 1% dexamethasone are effective in reducing the volume of middle ear effusion and mucosal thickness compared with control groups. Topical corticosteroid therapy was efficacious in reducing middle ear mucosal inflammation.

OBJECTIVE

OM is one of the most common diseases in the pediatric population. Our previous studies have shown that treatment with systemic antibiotics and corticosteroids was more efficacious than antibiotics alone. The purpose of this study was to determine the effectiveness of topically applied corticosteroids on the outcome of OM. The long-term goal of this study was to develop a better method of OM treatment by demonstrating effectiveness of topically applied anti-inflammatory agents, such as corticosteroids, avoiding systemic side effects.

MATERIALS AND METHODS

Three experimental groups were studied in chinchillas. OM with effusion was induced in all groups by injecting LPS. Group 1 consisted of controls in three subgroups as follows. Control-LPS alone, vehicle of dexamethasone (control-dexa), vehicle of rimexolone (control-rimex). Group 2 was treated with dexamethasone and included subgroups of separate concentrations of dexamethasone: 0.1% and 1% suspensions. Group 3 was treated with rimexolone and included subgroups of separate concentrations of rimexolone: 0.1% and 1% suspensions. A total of 58 animals were used: 18 for controls and 40 for experimental groups. All test substances (saline, control-dexa, control-rimex, dexamethasone and rimexolone, 200 microl) were injected at -2, 48 and 60 h; LPS was injected at 0 h. Animals were monitored by daily otomicroscopy. After 4 days, samples of middle ear effusion (MEE) were collected for analysis and temporal bones were harvested for histopathological studies.

RESULTS

At the end of 4 days, only in five ears (3/20 with 1% dexamethasone, 1/20 with 1% rimexolone, and 1/20 with 0.1% rimexolone) had the fluid diminished to the point of being unobservable. The volume of MEE, thickness of mucoperiosteum, and the degree of inflammation of middle ear mucosa with 1% dexamethasone and 1% rimexolone was significantly less compared with other groups.

Dexamethasone increases fluid absorption via Na+/H+ exchanger (NHE) 3 activation in normal human middle ear epithelial cells

The proper homeostasis of the liquid lining the surface of the middle ear cavity is vitally important for maintaining a fluid-free middle ear cavity. Disruption of this homeostasis leads to fluid collection in the middle ear cavity and results in otitis media with effusion. We demonstrated the molecular and functional expression of the Na+/H+ exchanger (NHE)s in normal human middle ear epithelial (NHMEE) cells. We also evaluated the role of NHEs in fluid absorption and the effect of dexamethasone on NHE function and NHE-dependent fluid absorption in NHMEE cells. Western blot analysis was performed for NHE1, -2, and -3 in NHMEE cells. The fluid absorption rate was measured after liquid application on the luminal surface of the cells. Intracellular pH (pHi) was measured using the pH-sensitive fluorescent probe bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-AM. NHE activity was determined as Na+-induced pHi recovery from an acid load achieved by luminal exposure to 40 mmol/l NH4Cl. NHE1, -2 and -3 were all expressed in the NHMEE cells. The pHi recovery rate was suppressed by inhibition of NHE2 and -3 with HOE694 at concentrations greater than 50 microM. Inhibition of NHE3 with 650 microM of HOE694 or S3226 significantly decreased the fluid absorption rate. Dexamethasone increased the Na+-induced pHi recovery rate which was reversed by the inhibition of NHE3 with 650 microM of HOE694. Dexamethasone treatment up-regulated NHE3 expression in a dose-dependent manner. The fluid absorption rate was increased by treatment with dexamethasone (10(-7) M) and reversed by the inhibition of NHE3. In summary, we have shown that NHE3 are involved in the regulation of both pHi and fluid absorption on the luminal surface of NHMEE cells. Dexamethasone stimulates NHE3 expression and NHE3-dependent fluid absorption in NHMEE cells. These findings provide a new insight into mechanisms that regulate periciliary fluid and the therapeutic mechanisms behind steroid treatment of otitis media with effusion.

In vivo demonstration of the absorptive function of the middle ear epithelium

The present study investigated in vivo fluid and ion transport across the middle ear epithelium. The tympanic membrane of rats was punctured under general anesthesia. A capillary tube was fitted to the external auditory canal and the bulla filled with various solutions. Middle ear (ME) fluid volume variations were then measured at constant pressure. When saline was used, a linear decrease of fluid volume was apparent. Replacement of sodium with a non-permeable cation (N-methyl-D-glucamin) reduced the absorption rate from 0.065+/-0.008 to 0.019+/-0.003 microl/min (P<0.05, n=6). Similarly, amiloride (10(-3)M), a sodium channel antagonist, reduced the absorption rate to 0.027+/-0.006 microl/min (P<0.05, n=6). Net absorption was abolished when chloride was substituted with gluconate: -0.008+/-0.004 microl/min (P<0.02, n=6), which might have been related (i) to the role of chloride as a diffusible anion through the paracellular pathway, or (ii) to the secretion of chloride through apical channels. However in this condition, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, a chloride channel blocker, did not affect the rate of fluid exchange -0.008+/-0.007 microl/min (P=0.75, n=6). This model provides the first in vivo evidence for the absorptive function of the ME. Fluid introduced into the ME cavity disappears due to active transport through the mucosa. This process is sodium-dependent and can be hindered by high concentration of amiloride. The rate of absorption is high enough to allow total clearance of fluid from the cavity of the middle ear within 13 h. This process might play a role in the maintaining a fluid-free and gas-filled middle ear cavity.

Gene expression profiles of early pneumococcal otitis media in the rat

OBJECTIVE

To define the gene expression patterns during the early phases of a bacterial middle ear infection in the rat model.

METHOD

Using cDNA gene array technology, we profiled the mRNA expression of 1176 genes in a rat model of acute otitis media. We identified changes in gene expression two-fold or greater 12 and 48 h after bilateral ME inoculation with either tryptic soy broth (TSB) or Streptococcus pneumoniae in TSB.

RESULTS

Transcripts of cytokines and cell adhesion molecules were up-regulated by 12 h, but returned to placebo transcription levels by 48 h. Three of six stress-response genes, including inducible nitric oxide synthase, GADD45 and heat shock protein 27 (HSP27) were up-regulated by 12 h, with HSP27 transcription levels continuing to rise through 48 h. All assayed transcription factors were up-regulated by 12 h, but only c-fos and c-jun up-regulation persisted to the 48-h time point. Up-regulation of apoptosis-related genes, except for bcl-x, was not evident until 48 h. These gene expression patterns reflected an early proinflammatory response consisting of cytokines, cell adhesion and stress-response molecules at 12 h followed by an up-regulation of apoptosis-related genes at 48 h.

CONCLUSION

Downstream targets of several transcription factors, up-regulated transiently at 12 h, control secondary effects of S. pneumoniae infection, including apoptosis of neutrophils and mucosal epithelial cells, bone proliferation and promotion of leukocyte differentiation. These observations lead to a greater understanding of the early events in the pathogenesis of an AOM episode and highlight therapeutic targets, which may play a roll in the sequelae of AOM.

Modulation of epithelial sodium channel (ENaC) expression in mouse lung infected with Pseudomonas aeruginosa

Background

The intratracheal instillation of Pseudomonas aeruginosa entrapped in agar beads in the mouse lung leads to chronic lung infection in susceptible mouse strains. As the infection generates a strong inflammatory response with some lung edema, we tested if it could modulate the expression of genes involved in lung liquid clearance, such as the α, β and γ subunits of the epithelial sodium channel (ENaC) and the catalytic subunit of Na⁺-K⁺-ATPase.

Methods

Pseudomonas aeruginosa entrapped in agar beads were instilled in the lung of resistant (BalB/c) and susceptible (DBA/2, C57BL/6 and A/J) mouse strains. The mRNA expression of ENaC and Na⁺-K⁺-ATPase subunits was tested in the lung by Northern blot following a 3 hours to 14 days infection.

Results

The infection of the different mouse strains evoked regulation of α and β ENaC mRNA. Following Pseudomonas instillation, the expression of αENaC mRNA decreased to a median of 43% on days 3 and 7 after infection and was still decreased to a median of 45% 14 days after infection (p < 0.05). The relative expression of βENaC mRNA was transiently increased to a median of 241%, 24 h post-infection before decreasing to a median of 43% and 54% of control on days 3 and 7 post-infection (p < 0.05). No significant modulation of γENaC mRNA was detected although the general pattern of expression of the subunit was similar to α and β subunits. No modulation of α₁Na⁺-K⁺-ATPase mRNA, the catalytic subunit of the sodium pump, was recorded. The distinctive expression profiles of the three subunits were not different, between the susceptible and resistant mouse strains.

Conclusions

These results show that Pseudomonas infection, by modulating ENaC subunit expression, could influence edema formation and clearance in infected lungs.

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.

Oral budesonide significantly improves water absorption in patients with ileostomy for Crohn disease

BACKGROUND

In addition to their anti-inflammatory effects, steroids influence electrolyte and water transport systems in the intestinal mucosa. This study analysed the effect of the topically acting glucocorticoid budesonide on ileostomy output in patients with Crohn disease.

METHODS

Oral budesonide (3 mg/three times daily for 8 days; n = 20) was compared to placebo (n = 20) in a double-blind design using matched-pair randomization according to ileal resection length in patients without detectable inflammatory activity. Under controlled hospital conditions, absolute output volumes were measured and response was defined as a reduction in intestinal output of > 25% compared to pretreatment conditions.

RESULTS

In the treatment group, we observed an absolute decrease in median intestinal output from 1,240 ml to 865 ml (30.2%), compared to 0.3% under placebo (from 950 ml to 947.5 ml). Response was documented in 60% (12/20 patients) in the treatment group compared to no response under placebo (P < 0.0001). While both treatment groups showed similar absolute median reductions (400 ml with ileal resection < or = 20 cm and 405 ml with ileal resection > 20 cm), the relative reduction (response rate) was lower in the subgroup of an ileal resection > 20 cm (36%) due to the greater increase in output secondary to the loss of ileum.

CONCLUSIONS

These data support the assumption that the absorptive capacity of the intestinal mucosa for water may be improved by topically acting steroids and suggest that this occurs independently of their anti-inflammatory effect.

Spironolactone blocks glucocorticoid-mediated hearing preservation in autoimmune mice

HYPOTHESIS

Although autoimmune sensorineural hearing loss can be effectively treated with corticosteroids, little is known about how these drugs affect cochlear function. MRL/MpJ-Faslpr autoimmune mice treated with a mineralocorticoid (aldosterone) have previously been shown to have hearing improvement equal to those treated with a glucocorticoid (prednisolone). This suggested that the restoration of hearing with steroids was the result of an effect on sodium transport rather than an antiinflammatory or immunosuppressive role. We hypothesized that corticosteroids reverse autoimmune hearing loss through the mineralocorticoid receptor and that blocking the mineralocorticoid receptor will prevent glucocorticoid effects.

METHODS

Spironolactone, a mineralocorticoid receptor antagonist, was administered to MRL/MpJ-Faslpr autoimmune mice alone or in combination with corticosteroids. The four treatment groups were: spironolactone, spironolactone + aldosterone, spironolactone + prednisolone, and untreated water controls. Auditory brainstem response (ABR) thresholds were recorded before and during treatment (2, 3, and 4 mo) to measure the effect of steroids on hearing decline.

RESULTS

Hearing in spironolactone and spironolactone + prednisolone mice showed progressive decline in hearing similar to water controls. The hearing was preserved in spironolactone + aldosterone mice, presumably as a result of the fact that aldosterone has a higher affinity for the mineralocorticoid receptor than spironolactone. Thus, aldosterone was able to maintain cochlear function with autoimmune disease progression, similar to previous reports of aldosterone treatment effects.

CONCLUSIONS

Spironolactone effectively blocked prednisolone from improving hearing in MRL/MpJ-Faslpr autoimmune mice. This offers evidence that the inner ear mineralocorticoid receptor is the therapeutic target for corticosteroids used to treat autoimmune and sudden sensorineural hearing loss. Pharmacologic treatments that selectively target the mineralocorticoid receptor may provide greater clinical benefit with fewer systemic side effects than prednisone in patients with autoimmune sensorineural hearing loss.

Modulation of alpha-ENaC and alpha1-Na+-K+-ATPase by cAMP and dexamethasone in alveolar epithelial cells

cAMP and dexamethasone are known to modulate Na+ transport in epithelial cells. We investigated whether dibutyryl cAMP (DBcAMP) and dexamethasone modulate the mRNA expression of two key elements of the Na+ transport system in isolated rat alveolar epithelial cells: alpha-, beta-, and gamma-subunits of the epithelial Na+ channel (ENaC) and the alpha1- and beta1-subunits of Na+-K+-ATPase. The cells were treated for up to 48 h with DBcAMP or dexamethasone to assess their long-term impact on the steady-state level of ENaC and Na+-K+-ATPase mRNA. DBcAMP induced a twofold transient increase of alpha-ENaC and alpha1-Na+-K+-ATPase mRNA that peaked after 8 h of treatment. It also upregulated beta- and gamma-ENaC mRNA but not beta1-Na+-K+-ATPase mRNA. Dexamethasone augmented alpha-ENaC mRNA expression 4.4-fold in cells treated for 24 h and also upregulated beta- and gamma-ENaC mRNA. There was a 1.6-fold increase at 8 h of beta1-Na+-K+-ATPase mRNA but no significant modulation of alpha1-Na+-K+-ATPase mRNA expression. Because DBcAMP and dexamethasone did not increase the stability of alpha-ENaC mRNA, we cloned 3.2 kb of the 5' sequences flanking the mouse alpha-ENaC gene to study the impact of DBcAMP and dexamethasone on alpha-ENaC promoter activity. The promoter was able to drive basal expression of the chloramphenicol acetyltransferase (CAT) reporter gene in A549 cells. Dexamethasone increased the activity of the promoter by a factor of 5.9. To complete the study, the physiological effects of DBcAMP and dexamethasone were investigated by measuring transepithelial current in treated and control cells. DBcAMP and dexamethasone modulated transepithelial current with a time course reminiscent of the profile observed for alpha-ENaC mRNA expression. DBcAMP had a greater impact on transepithelial current (2.5-fold increase at 8 h) than dexamethasone (1.8-fold increase at 24 h). These results suggest that modulation of alpha-ENaC and Na+-K+-ATPase gene expression is one of the mechanisms that regulates Na+ transport in alveolar epithelial cells.

Aldosterone (mineralocorticoid) equivalent to prednisolone (glucocorticoid) in reversing hearing loss in MRL/MpJ-Fas1pr autoimmune mice

HYPOTHESIS

Although the glucocorticoid prednisone is the standard therapy for autoimmune sensorineural hearing loss, what this hormone does in the ear to restore hearing is not known. MRL/MpJ-Fas(lPr) autoimmune mice consistently have shown only stria vascularis disease, implying that abnormal ion balances in the endolymph underlie cochlear dysfunction. Previously we have shown that hearing loss in these mice is reversed with prednisolone treatment. This, coupled with the complete lack of cochlear inflammation, suggests that the restoration of hearing with prednisolone is due to its sodium transport function and not to its anti-inflammatory or immune suppression effects. Therefore the hypothesis of this study was that the mineralocorticoid aldosterone, which only increases sodium transport, would be as effective as prednisolone in reversing autoimmune hearing loss.

STUDY DESIGN

MRL/MpJ-Fas(lPr) autoimmune mice were treated with either prednisolone or aldosterone to compare steroid effects on auditory brainstem response (ABR) thresholds and stria morphology.

METHODS

After baseline ABR audiometry, autoimmune mice were given prednisolone (5 mg/kg per day), aldosterone (15 microg/kg per day), or water in their drinking bottles. After 2 months of treatment the ABR thresholds were remeasured, and ears collected for histological examination.

RESULTS

The untreated controls showed continued elevation of ABR thresholds and edematous stria. However, thresholds in most steroid mice were improved or unchanged and their stria morphology improved, particularly with aldosterone treatment.

CONCLUSIONS

Restoration of hearing with steroid treatment is due to increased sodium transport to re-establish cochlear ionic balances. Aldosterone therapy may offer advantages over prednisone for long-term management of not only autoimmune hearing loss, but also other forms of nonimmune-related deafness for which steroids are currently prescribed.

Oxygen modulates Na+ absorption in middle ear epithelium

The physiology of the middle ear is primarily concerned with keeping the cavities air filled and fluid free to allow transmission of the sound vibrations from the eardrum to the inner ear. Middle ear epithelial cells are thought to play a key role in this process, since they actively transport Na+ and water. The PO2 of the middle ear cavities varies from 44 to 54 mmHg in healthy human ears but may be lower in the course of secretory otitis media. The effect of chronic hypoxia on ion transport was investigated on a middle ear cell line using the short-circuit current technique. Chronic hypoxia reversibly decreased the rate of Na+ absorption across the MESV cell line. Although a decrease in cellular ATP content was observed, the decrease of Na+ absorption seemed related to a primary modulation of apical Na+ entry. As revealed by RNase protection assay, the decrease in the rate of apical Na+ entry strictly paralleled the decrease in the expression of transcripts encoding the alpha-subunit of the epithelial Na+ channel. This effect of oxygen on Na+ absorption might account for 1) the presence of fluid in the middle ear in the course of secretory otitis media and 2) the beneficial effect of the ventilation tube in treating otitis media that allows the PO2 to rise and restores the fluid clearance.