Protective effects of glucocorticoids on ischemia-reperfusion injury of outer hair cells

Preparation, characterization, and in vitro/vivo evaluation of dexamethasone/poly(ε-caprolactone)-based electrode coatings for cochlear implants

With dexamethasone as the model drug and polycaprolactone (PCL) as the carrier material, a drug delivery coating for cochlear electrodes was prepared, to control cochlear fibrosis caused by cochlear implantation. A dexamethasone/poly (ε-caprolactone)-based electrode coating was prepared using the impregnation coating method. Preparation parameters were optimized, yielding 1 impregnation instance, impregnation time of 10 s, and PCL concentration of 10%. The coating was characterized in vitro using scanning electron microscopy, a universal machine, high-performance liquid chromatography, and CCK-8. The surface was porous and uniformly thick (average thickness, 48.67 µm)—with good flexibility, long-term slow drug release, and optimal drug concentration—and was biologically safe. The experimental results show that PCL is an ideal controlled-release material for dexamethasone as a drug carrier coating for cochlear implants.

Immune Response After Cochlear Implantation

A cochlear implant (CI) is an electronic device that enables hearing recovery in patients with severe to profound hearing loss. Although CIs are a successful treatment for profound hearing impairment, their effectivity may be improved by reducing damages associated with insertion of electrodes in the cochlea, thus preserving residual hearing ability. Inner ear trauma leads to inflammatory reactions altering cochlear homeostasis and reducing post-operative audiological performances and electroacoustic stimulation. Strategies to preserve residual hearing ability led to the development of medicated devices to minimize CI-induced cochlear injury. Dexamethasone-eluting electrodes recently showed positive outcomes. In previous studies by our research group, intratympanic release of dexamethasone for 14 days was able to preserve residual hearing from CI insertion trauma in a Guinea pig model. Long-term effects of dexamethasone-eluting electrodes were therefore evaluated in the same animal model. Seven Guinea pigs were bilaterally implanted with medicated rods and four were implanted with non-eluting ones. Hearing threshold audiograms were acquired prior to implantation and up to 60 days by recording compound action potentials. For each sample, we examined the amount of bone and fibrous connective tissue grown within the scala tympani in the basal turn of the cochlea, the cochleostomy healing, the neuronal density, and the correlation between electrophysiological parameters and histological results. Detection of tumor necrosis factor alpha, interleukin-6, and foreign body giant cells showed that long-term electrode implantation was not associated with an ongoing inflammation. Growth of bone and fibrous connective tissue around rods induced by CI was reduced in the scala tympani by dexamethasone release. For cochleostomy sealing, dexamethasone-treated animals showed less bone tissue growth than negative. Dexamethasone did not affect cell density in the spiral ganglion. Overall, these results support the use of dexamethasone as anti-inflammatory additive for eluting electrodes able to protect the cochlea from CI insertion trauma.

Metabolomic analysis of urine with Nuclear Magnetic Resonance spectroscopy in patients with idiopathic sudden sensorineural hearing loss: A preliminary study

OBJECTIVE

Idiopathic sudden sensorineural hearing loss is a frequent emergency, with unknown aetiology and usually treated with empiric therapy. Steroids represent the only validated treatment but prognosis is unpredictable and the possibility to select the patients who will not respond to steroids could avoid unnecessary treatments. Metabolomic profiling of the biofluids target the analysis of the final product of genic expression and enzymatic activity, defining the biochemical phenotype of a whole biologic system.

METHODS

We studied the metabolomics of the urine of a cohort of patients with idiopathic sudden sensorineural hearing loss, correlating the metabolic profiles with the clinical outcomes. Metabolomic profiling of urine samples was performed by ¹H Nuclear Magnetic Resonance spectroscopy in combination with multivariate statistical approaches.

RESULTS

26 patients were included in the study: 5 healthy controls, 13 patients who did not recover after treatment at 6 months while the remaining 8 patients recovered from the hearing loss. The orthogonal partial least square-discriminant analysis score plot showed a significant separation between the two groups, responders and non-responders after steroid therapy, R²Y of 0.83, Q² of 0.38 and p value <0.05. The resulting metabolic profiles were characterized by higher levels of urinary B-Alanine, 3-hydroxybutyrate and Trimethylamine N-oxide, and lower levels of Citrate and Creatinine in patients with worst outcome.

CONCLUSION

Idiopathic sudden sensorineural hearing loss is a specific disease with unclear systemic changes, but our data suggest that there are different types of this disorder or patients predisposed to effective action of steroids allowing the recover after treatment.

Using the Implant Electrode Array to Conduct Real-time Intraoperative Hearing Monitoring During Pediatric Cochlear Implantation: Preliminary Experiences

OBJECTIVES

To present the preliminary experiences and findings from a pilot study evaluating a novel technique for monitoring cochlear electrophysiological function during electrode insertion in cochlear implantation surgery.

STUDY DESIGN

Prospective pilot cohort study.

SETTING

Tertiary academic neuro-otology center.

PATIENTS

Pediatric patients with residual hearing undergoing hearing preservation cochlear implant surgery.

INTERVENTION

Monitoring of intraoperative cochlear microphonics during cochlear implant surgery.

MAIN OUTCOME MEASURE

Intraoperative intracochlear microphonic measurement, preservation of these responses postoperatively and preservation of hearing as measured by audiometry.

RESULTS

Intracochlear microphonics could be identified in both patients presented and were preserved during the surgical procedure and postoperatively. The preservation of intracochlear microphonics correlates with preservation of hearing.

CONCLUSION

The novel approach using the electrode array to detect and measure intracochlear microphonics during cochlear implantation surgery shows promise as an instrument to alert the operating surgeon to hair cell damage during electrode insertion. Further refinement of the technique is required to better understand the measurements and correlate these with pre- and postoperative hearing and risk of hearing loss from surgery. Improvements in the software algorithm will reduce the time required for each measurement, leading to the development a more real-time monitoring technique.

Dexamethasone Is One of the Factors Minimizing the Inner Ear Damage from Electrode Insertion in Cochlear Implantation

The aim of this study was to investigate the efficacy of preoperative and intraoperative steroid administration for inner ear protection in cochlear implantation (CI). Nineteen subjects who underwent CI were included in the study, and 10 subjects were enrolled as controls (steroid-administered group, n = 19; control group, n = 10). Dexamethasone (dexamethasone sodium phosphate, 5 mg/ml) was systemically administered preoperatively (1 ml) and topically applied during CI (0.5 ml). The extent of hearing preservation (HP) after CI and the change in the bithermal caloric response were evaluated. Hearing level was calculated using mean thresholds [(250 Hz + 500 Hz + 1,000 Hz + 2,000 Hz)/4]. Preoperative hearing thresholds were similar in the steroid-administered and control groups (100.92 ± 12.60 vs. 103.29 ± 14.39 dB, p = 0.650). The mean thresholds significantly increased in both groups after surgery (108.46 ± 14.08 dB, p = 0.006, for the steroid-administered group; 117.50 ± 6.34 dB, p = 0.027, for the control group), and the difference between the groups was also significant (p = 0.027). The postoperative shift in the hearing thresholds at frequencies of 500 and 1,000 Hz was significant in the steroid-administered group and that at the frequencies of 500, 1,000 and 2,000 Hz was significant in the control group. However, the extent of the shift in hearing threshold levels at each frequency was not significantly different between the groups. Preservation of hearing thresholds was compared between the groups, and there were significantly more subjects with complete and partial HP in the steroid-administered group than in the control group (p = 0.008). The preoperative caloric response was maintained after CI in the steroid-administered group. This study suggests that the perioperative use of a steroid could minimize the inner ear damage after CI.

Cochlear implant and inflammation reaction: Safety study of a new steroid-eluting electrode

Dexamethasone is a common anti-inflammatory agent added to cochlear implants to reduce hearing loss due to electrode insertion trauma. We evaluated the safety of eluting silicone rods containing 10% dexamethasone in a Guinea pig model. Animals were implanted with a dexamethasone eluting silicone electrode (DER) or with a non-eluting electrode (NER). The control group only underwent a cochleostomy (CS). Prior to implantation and during the two weeks following implantation, the hearing status of the animals was assessed by means of Compound Action Potentials (CAPs) with an electrode placed near the round window. Two weeks after implantation, the mean click threshold shifts were 1 dB ± 10 dB in the DER group, 10 dB ± 10 dB in the NER group and -4 dB ± 10 dB in the control group. After two weeks the bullae of each animal were extracted to verify the presence of macrophages, the percent of tissue growth in the scala tympani and the tissue sealing around cochleostomy. Silicone electrodes samples were also explanted and examined for bacterial infection. Neither bacterial infection nor enhanced number of macrophages were observed. A limited, but not significant, tissue growth was found in the scala tympani between the experimental and the control group. The data suggest that, in the Guinea pig model, the use of DER is apparently safe as an anti-inflammatory slow-release additive to the cochlear implant.

Predictors of Hearing Preservation in the Management of Labyrinthine Fistulas Positioned on the Semicircular Canals

Objectives:

We sought to identify factors that would predict hearing preservation in the treatment of semicircular canal labyrinthine fistulas.

Methods:

Between 1990 and 2010, 97 patients with semicircular canal fistulas were operated on and enrolled in this retrospective study. In 62 patients the matrix was removed and the fistula was sealed, whereas in 35 patients the canal was drilled, the matrix was detached, and the canal was occluded. Perioperative corticosteroids were administered in 51 patients. The main outcome measures were the bone conduction thresholds evaluated at 1 year after the operation. Factors considered for possible association with hearing preservation included age, gender, site and size of the fistula, primary versus revision surgery, surgeon, perioperative corticosteroid treatment, and surgical management of the fistula.

Results:

The bone conduction hearing level was improved in 16 patients, remained unchanged in 73 patients, and had worsened in 11 patients. On the univariate analysis, good hearing was predicted by grade II fistula, canal plugging, and corticosteroid treatment. However, none of these factors attained significance in the logistic regression model.

Conclusions:

In surgery of semicircular canal fistulas, good hearing outcomes are to be expected if perioperative corticosteroids are administered, matrix removal and fistula sealing is performed in grade II fistulas, and canal occlusion is performed in grade III and IV fistulas.

The cochlea as an independent neuroendocrine organ: expression and possible roles of a local hypothalamic-pituitary-adrenal axis-equivalent signaling system

A key property possessed by the mammalian cochlea is its ability to dynamically alter its own sensitivity. Because hair cells and ganglion cells are prone to damage following exposure to loud sound, extant mechanisms limiting cochlear damage include modulation involving both the mechanical (via outer hair cell motility) and neural signaling (via inner hair cell-ganglion cell synapses) steps of peripheral auditory processing. Feedback systems such as that embodied by the olivocochlear system can alter sensitivity, but respond only after stimulus encoding, allowing potentially damaging sounds to impact the inner ear before sensitivity is adjusted. Less well characterized are potential cellular signaling systems involved in protection against metabolic stress and resultant damage. Although pharmacological manipulation of the olivocochlear system may hold some promise for attenuating cochlear damage, targeting this system may still allow damage to occur that does not depend on a fully functional feedback loop for its mitigation. Thus, understanding endogenous cell signaling systems involved in cochlear protection may lead to new strategies and therapies for prevention of cochlear damage and consequent hearing loss. We have recently discovered a novel cochlear signaling system that is molecularly equivalent to the classic hypothalamic-pituitary-adrenal (HPA) axis. This cochlear HPA-equivalent system functions to balance auditory sensitivity and susceptibility to noise-induced hearing loss, and also protects against cellular metabolic insults resulting from exposures to ototoxic drugs. This system may represent a local cellular response system designed to mitigate damage arising from various types of insult.

The role of preoperative, intratympanic glucocorticoids for hearing preservation in cochlear implantation: a prospective clinical study

BACKGROUND

Hearing Preservation is becoming increasingly important in cochlear implantation as there is growing evidence that preserving the residual hearing, especially in the low frequencies in combination with the electric stimulation can significantly improve hearing and speech outcomes in noise. Besides the ongoing development of atraumatic implant electrodes and insertion techniques, the implementation of pharmacologic hair cell protection is thought to increase hearing preservation. This study investigates the effects of preoperative intratympanic glucocorticoid application on hearing preservation rates in cochlear implantation.

STUDY DESIGN

Prospective interventional study.

SETTING

Tertiary neurotology referral center.

PATIENTS

Patients undergoing cochlear implantation with measurable preoperative hearing thresholds using either a Flex soft electrode or a Flex EAS electrode depending on the degree of residual low frequency hearing.

INTERVENTION

Preoperative intratympanic steroid application during cochlear implantation via round window insertion.

MAIN OUTCOME MEASURES

Level of hearing preservation after cochlear implantation; electrode- and frequency-specific hearing preservation rates.

RESULTS

Preoperative hearing thresholds were comparable in the control group and the interventional Flex soft group (70.5 db±12.5 dB vs. 73.5 dB±10.5 dB, P=.27). As per selection criteria the low-frequency hearing thresholds were significantly lower in interventional Flex EAS groups when compared to the control group. Hearing preservation was significantly better in the interventional group with no case of complete hearing loss in this group (11 dB±2.5 dB vs. 19.5 dB 3.5 dB, P<.05). The interventional group displayed a higher stability of hearing preservation after implantation (r=.8, P=.03). Level of hearing preservation was higher when a specific hearing preservation electrode was used (r=.85, P<.05). Hearing preservation in the low frequencies was significantly higher than in the high frequencies.

CONCLUSIONS

Our study suggests that the additional preoperative use of intratympanic glucocorticoids improves and stabilizes hearing preservations rates in round window cochlear implantation for adults and children with residual hearing.

Preserving bone conduction in patients with labyrinthine fistula

The management of labyrinthine fistula is a controversial issue. Hearing preservation represents a major challenge. Retrospective study of 31 patients with labyrinthine fistula confirmed intra-operatively during cholesteatoma surgery. In all cases, total matrix removal was performed, and the fistula covered with bone dust, periostium and/or cartilage. Twenty-five patients received a high intra-operative dosage (500 mg) of intravenously applied steroids at least 15 min before handling the fistula. Outcome measurements included comparison of the pre-operative and post-operative bone conduction to assess inner ear function. The results were, the fistula was located in the lateral semicircular canal (LSC) in 22 patients (71.8%) and in the oval window in eight. One patient had a double localization in the superior and lateral semicircular canals. Out of the LSC fistulas, five patients (16.12%) had a fistula type I, 8 had type IIa (25.8%), four (12.9%) type IIb, and six patients type III (19.35%). Three out of eight patients with fistula located in the oval window had a total absence of the footplate, other four presented a partial anterior resorption at the level of the fissula antefenestram and the remaining one had a fractured platina. Pre-operatively, the bone conduction displayed a mean threshold of 35 dB. Twenty-two (85%) out of 26 patients treated intra-operatively with steroids showed preservation or improvement of bone conduction. Patients with fistulas of the oval window, type I, IIa and III fistulas in the LSC treated with cortisone presented good sensorineural hearing outcome (preservation or significant improvement of inner ear function in the majority of cases-91%); the auditory results for group IIb were inconclusive. Five patients did not receive steroids, four of them developed partial sensorineural hearing loss and one went deaf. To conclude, cholesteatoma surgery with a single-staged matrix removal on perilymphatic fistulas, after intra-operative intravenous administration of a high dosage of steroids followed by a multilayer closure of the fistula achieved a hearing preservation or improvement in 85% of our patients.

The cochlear CRF signaling systems and their mechanisms of action in modulating cochlear sensitivity and protection against trauma

A key requirement for encoding the auditory environment is the ability to dynamically alter cochlear sensitivity. However, merely attaining a steady state of maximal sensitivity is not a viable solution since the sensory cells and ganglion cells of the cochlea are prone to damage following exposure to loud sound. Most often, such damage is via initial metabolic insult that can lead to cellular death. Thus, establishing the highest sensitivity must be balanced with protection against cellular metabolic damage that can lead to loss of hair cells and ganglion cells, resulting in loss of frequency representation. While feedback mechanisms are known to exist in the cochlea that alter sensitivity, they respond only after stimulus encoding, allowing potentially damaging sounds to impact the inner ear at times coincident with increased sensitivity. Thus, questions remain concerning the endogenous signaling systems involved in dynamic modulation of cochlear sensitivity and protection against metabolic stress. Understanding endogenous signaling systems involved in cochlear protection may lead to new strategies and therapies for prevention of cochlear damage and consequent hearing loss. We have recently discovered a novel cochlear signaling system that is molecularly equivalent to the classic hypothalamic-pituitary-adrenal (HPA) axis. This cochlear HPA-equivalent system functions to balance auditory sensitivity and susceptibility to noise-induced hearing loss, and also protects against cellular metabolic insults resulting from exposures to ototoxic drugs. We review the anatomy, physiology, and cellular signaling of this system, and compare it to similar signaling in other organs/tissues of the body.

Ischemia-reperfusion injury of the cochlea: pharmacological strategies for cochlear protection and implications of glutamate and reactive oxygen species

A large amount of energy produced by active aerobic metabolism is necessary for the cochlea to maintain its function. This makes the cochlea vulnerable to blockade of cochlear blood flow and interruption of the oxygen supply. Although certain forms of human idiopathic sudden sensorineural hearing loss reportedly arise from ischemic injury, the pathological mechanism of cochlear ischemia-reperfusion injury has not been fully elucidated. Recent animal studies have shed light on the mechanisms of cochlear ischemia-reperfusion injury. It will help in the understanding of the pathology of cochlear ischemia-reperfusion injury to classify this injury into ischemic injury and reperfusion injury. Excitotoxicity, mainly observed during the ischemic period, aggravates the injury of primary auditory neurons. On the other hand, oxidative damage induced by hydroxyl radicals and nitric oxide enhances cochlear reperfusion injury. This article briefly summarizes the generation mechanisms of cochlear ischemia-reperfusion injury and potential therapeutic targets that could be developed for the effective management of this injury type.

Dexamethasone treatment of tumor necrosis factor-alpha challenged organ of Corti explants activates nuclear factor kappa B signaling that induces changes in gene expression that favor hair cell survival

The objective was to determine the role of nuclear factor kappa B (NFκB) in dexamethasone base (DXMb) protection of auditory hair cells from tumor necrosis factor-alpha (TNFα)-induced loss on gene expression and cell signaling levels. Organ of Corti (OC) explants from 3-day-old rats were cultured under one of the following conditions: (1) media only--no treatment; (2) media+TNFα; (3) media+TNFα+DXMb; (4) media+TNFα+DXMb+NFκB-Inhibitor (NFκB-I); or (5) media+TNFα+DXMb+NFκBI-Scrambled control (NFκBI-C). A total of 60 organ of Corti explants (OC) were stained with FITC-Phalloidin after 96 h in culture (conditions 1-5) for hair cell counts and imaging of surface characteristics. A total of 108 OC were used for gene expression studies (i.e. B-actin, Bax, Bcl-2, Bcl-xl, and TNFR1) after 0, 24, or 48 h in vitro (conditions 1-4). A total of 86 OC were cultured (conditions 1-3) for 48 h, 36 of which were used for phosphorylated NFκB (p-NFκB) ELISA studies and 50 for whole mount anti-p-NFκB immunostain experiments. TNFα+DXMb exposed cultures demonstrated significant upregulation in anti-apoptotic Bcl-2 and Bcl-xl genes and downregulation in pro-apoptotic Bax gene expression; DXMb treatment of TNFα explants also lowered the Bax/Bcl-2 ratio and inhibited TNFR1 upregulation. After inhibiting NFκB activity with NFκB-I, the gene expression profile following TNFα+DXMb treatment now mimics that of TNFα-challenged OC explants. The levels of p-NFκB and the degree of nuclear translocation are significantly greater in TNFα+DXMb exposed OC explants than observed in the TNFα and control groups in the middle+basal turns of OC explants. These findings were supported by the results of the hair cell counts and the imaging results obtained from the whole mount OC specimens. DXMb protects against TNFα-induced apoptosis of auditory hair cells in vitro via activation of NFκB signaling in hair cell nuclei, and regulation of the expression levels of anti- and pro-apoptotic genes and a pro-inflammatory gene.

Changes in guinea pig cochlea after transient cochlear ischemia

Perturbation of cochlear microcirculation, that is, ischemia is a major cause of hearing impairment. Earlier studies examined the short-term (≤7 days) effect of cochlear ischemia. This study characterized the long-term (4 weeks) functional and morphological changes in adult guinea pig cochleae subject to transient ischemia by clamping the labyrinthine artery for 0.25-3 h. Notably, cochlear ischemia for over 1 h caused an increase of auditory brainstem response thresholds and loss of high-frequency hearing, basal-turn hair cells, and spiral ganglions. Auditory recovery may be possible after 30-min ischemia. The extent of the functional and morphological changes depended on the ischemia period, and the changes progressed in extent from the apical to the basal turn in an orderly fashion.

[Glucocorticoid treatment for cochlear ischemic and acoustic injuries]

The effect of glucocorticoids on sensorineural hearing loss of sudden onset remains to be controversial although glucocorticoids have been used for treatment of sudden sensorineural hearing loss. We review recent findings about the effect of glucocorticoids on cochlear ischemic and acoustic injuries obtained from animal experiments. Systemically administered glucocorticoids penetrate the blood-cochlear barrier well. Glucocorticoids ameliorated the cochlear ischemic and acoustic injuries at a relatively wide range of doses, and they protect cochlear hair cells in these types of injury. The therapeutic actions of glucocorticoids in cochlear injuries were considered to be mediated via both genomic and non-genomic pathways. Based on the results obtained in acoustic injury, therapeutic time window of glucocorticoids is considered to be short after the onset of injury. These findings obtained from animal experiments are important in considering clinical usage of glucocorticoids for the treatment of sensorineural hearing loss.

Preventing hearing damage using topical dexamethasone during reversible cochlear ischemia: an animal model

HYPOTHESIS

Local application of dexamethasone to the round window (RW) niche prevents cochlear damage caused by local reversible ischemia.

BACKGROUND

Cochlear ischemia induced by internal auditory artery (IAA) compression/stretching is thought to cause postoperative sensory hearing loss after attempted hearing preservation removal of acoustic neuroma tumors. Dexamethasone administered to the RW niche traveling through the membrane to the cochlear fluids may prevent ischemic damage.

MATERIALS AND METHODS

Ten young albino rabbits were used for this study. Ischemic episodes were induced by compressing the IAA. Laser Doppler cochlear blood flow was measured using a probe positioned at the RW niche. Transtympanic electrocochleography was measured at 4, 8, and 12 kHz. In 5 test ears, dexamethasone was administered topically at the RW for approximately 50 minutes before the IAA compressions, whereas in 5 control ears, saline was applied in the same way. Each ear underwent one 10-minute IAA compression with a 60-minute postischemic period of transtympanic electrocochleography monitoring.

RESULTS

In both control- and dexamethasone-treated ears, ischemic episodes measured by Laser Doppler cochlear blood flow were comparable. Fifty minutes after IAA decompression, in dexamethasone-pretreated ears, cochlear microphonic and compound action potential amplitudes at all test frequencies were 10 to 15% less reduced than those in control ears. Compound action potential latencies in dexamethasone-pretreated ears resulted in shorter latency delay than in control ears.

CONCLUSION

The RW seems to be an efficacious route for the administration of dexamethasone into the inner ear. Dexamethasone showed a protective effect on cochlear function after local ischemia. Transtympanic electrocochleography was found to be a sufficient and effective tool in monitoring hearing.

Biopolymer-released dexamethasone prevents tumor necrosis factor alpha-induced loss of auditory hair cells in vitro: implications toward the development of a drug-eluting cochlear implant electrode array

HYPOTHESIS

Polymer-eluted dexamethasone (DXM) will retain its ability to protect against tumor necrosis factor alpha (TNFalpha)-induced hair cell (HC) loss.

BACKGROUND

TNFalpha has been shown to be associated with trauma-induced hearing loss. DXM has been demonstrated to protect the cochlea against trauma-induced hearing loss. DXM is currently administered either systemically or locally to treat patients with sudden hearing loss of unknown cause.

METHODS

P-3 organ of Corti explants challenged with an ototoxic level of TNFalpha was the experimental system, and the base form of DXM (DXMb) incorporated into a biorelease polymer (i.e., SIBS) was the otoprotection molecule tested. The efficacy of otoprotection was determined by counts of fluorescein isothiocyanate-phalloidin-stained HCs and changes in gene expression.

RESULTS

HC counts show 1) SIBS alone did not protect HCs from TNFalpha ototoxicity (SIBS versus SIBS + TNFalpha; p < 0.001), and 2) SIBS with DXMb provides a significant level of protection against TNFalpha-induced loss of HCs (TNFalpha + SIBS versus TNFalpha + SIBS/DXMb, 299 mug; p < 0.001). Gene expression results show that polymer-eluted DXMb 1) upregulates antiapoptotic genes (i.e., Bcl-2, Bcl-xl) and downregulates a proapoptotic gene (i.e., Bax) in TNFalpha-challenged explants and 2) downregulates TNFR1 in these explants.

CONCLUSION

Polymer-eluted DXMb retains its otoprotection capabilities in our in vitro test system of TNFalpha-challenged organ of Corti explants by altering the pattern of gene expression to favor survival of TNFalpha-exposed HCs. These results, although in vitro, support the application of polymer containing DXMb to electrode arrays for the conservation of hearing during cochlear implantation.

Cochlear blood flow during occlusion and reperfusion of the anterior inferior cerebellar artery--effect of topical application of dexamethasone to the round window

CONCLUSION

Topical application of dexamethasone may support autoregulation of cochlear blood flow (CBF), although it had no direct effect on CBF.

OBJECTIVES

Although intratympanic steroid therapy for patients with inner ear disorders is common, the mechanism by which steroids exert their effect is unclear. We investigated the response of CBF to topical application of dexamethasone onto the round window.

MATERIALS AND METHODS

Two concentrations of dexamethasone (3.3 mg/ml and 33 mg/ml dexamethasone in 0.5 microl saline) were applied to the round windows of rats, and CBF responses were measured using a laser Doppler flowmeter. The effects on CBF of a 2 h occlusion of the anterior inferior cerebellar artery (AICA) and subsequent release of the clamp with or without previous dexamethasone application were investigated.

RESULTS

No significant change in CBF was observed after topical application of dexamethasone, and it did not affect the decrease in CBF caused by AICA occlusion. However, recovery of CBF after release of the AICA clamp was better in animals treated with dexamethasone than in those that did not receive dexamethasone.

Issues, indications, and controversies regarding intratympanic steroid perfusion

PURPOSE OF REVIEW

Office-based intratympanic inner ear steroid perfusion (ITPs) treatment for Ménière's disease, autoimmune inner ear disease, and sudden sensorineural hearing loss has been expanding over the past 10-15 years, yet remains controversial. The purpose of this review is to examine the current literature of basic science and human studies of ITPs treatment.

RECENT FINDINGS

Animal studies exist regarding the delivery, distribution, biochemical, and microbiological changes in the inner ear post ITPs. However, few clinical studies exist on ITPs treatment in sudden sensorineural hearing loss and even less in treating Ménière's disease. There are no consistent studies regarding drug delivery methods, type, and concentration of steroids. Moreover, there are no studies comparing ITPs results to the natural history of Ménière's disease.

SUMMARY

ITPs has impacted otology and neurotology practice due to increased utilization. A sound understanding of the basic science and clinical studies is needed to establish long-term efficacy of ITPs in controlling hearing loss in Ménière's disease by comparison to its natural history, as well as, potential application to other disorders.

Dexamethasone and methylprednisolone do not inhibit neuritic outgrowth while inhibiting outgrowth of fibroblasts from spiral ganglion explants

CONCLUSION

Dexamethasone and methylprednisolone do not inhibit neuritic outgrowth while inhibiting fibroblastic outgrowth from spiral ganglion micro-explants.

OBJECTIVES

To demonstrate reduced fibroblastic outgrowth while maintaining neurite outgrowth for several corticosteroids using an in vitro test system of neonatal rat spiral ganglion micro-explants.

MATERIALS AND METHODS

The in vitro test system comprised 3-day-old rat spiral ganglion micro-explants. Dexamethasone, methylprednisolone, triamcinolone acetonide, and human recombinant brain-derived neurotrophic factor (hrBDNF) were tested in vitro. The control was ganglion micro-explants in supplemented Dulbecco's modified Eagle's medium. Areas of the ganglion explant, neurite and fibroblast outgrowth of ganglion explants after 10 days in vitro were imaged, digitized, and analyzed using Image Tool 3.00 on a PC workstation. Areas of neurite and fibroblast outgrowth from the experimental explants were compared against values obtained from control explants.

RESULTS

Dexamethasone gave the best result of the three corticosteroids tested for inhibiting fibroblast outgrowth while not inhibiting neurite outgrowth from the ganglion micro-explants. Media containing hrBDNF (10 ng/ml) stimulated significantly greater neurite outgrowth than outgrowth from control explants (p < 0.001). Ganglion micro-explants treated with dexamethasone (0.02 mg/ml) and methylprednisolone (0.5 mg/ml) provided the greatest inhibition of fibroblast outgrowth compared with control explants (p < 0.001).

Local Dexamethasone Therapy Conserves Hearing in an Animal Model of Electrode Insertion Trauma-Induced Hearing Loss

HYPOTHESIS

The progressive loss of hearing that develops after electrode insertion trauma (EIT) can be attenuated by local dexamethasone (DXM) therapy.

BACKGROUND

Hearing loss (HL) that develops after cochlear implant EIT occurs in two stages in laboratory animals, that is, an immediate loss followed by a progressive loss. Direct infusion of DXM into the guinea pig cochlea can attenuate both ototoxin- and noise-induced HL.

MATERIALS AND METHODS

Auditory-evoked brainstem responses (ABRs) of guinea pigs were measured for 4 frequencies (i.e., 0.5, 1, 4, and 16 kHz) before, immediately after, and more than 30 days post-EIT for experimental (EIT,EIT + artificial perilymph, and EIT + DXM) and for the contralateral unoperated cochleae of each group. An electrode analog of 0.14-mm diameter was inserted through a basal turn cochleostomy for a depth of 3 mm and withdrawn. DXM in artificial perilymph was delivered immediately post-EIT into the scala tympani via a miniosmotic pump for 8 days.

RESULTS

The ABR thresholds of EIT animals increased progressively post-EIT. Contralateral unoperated cochleae had no significant changes in ABR thresholds. Immediately post-EIT, that is, Day 0, the DXM-treated animals exhibited a significant HL at 1, 4, and 16 kHz, but this HL was no longer significant by Day 30 compared with contralateral control ears.

CONCLUSION

The results from immediate local treatment of the cochlea with DXM in an animal model of EIT-induced HL suggest a novel therapeutic strategy for hearing conservation by attenuating the progressive HL that can result from the process of electrode array insertion during cochlear implantation.