Permanent and transient effects of locally delivered n-acetyl cysteine in a guinea pig model of cochlear implantation

A preoperative dose of the pyridoindole AC102 improves the recovery of residual hearing in a gerbil animal model of cochlear implantation

Sensorineural hearing loss (SNHL) is the most common sensory deficit worldwide. Due to the heterogeneity of causes for SNHL, effective treatment options remain scarce, creating an unmet need for novel drugs in the field of otology. Cochlear implantation (CI) currently is the only established method to restore hearing function in profound SNHL and deaf patients. The cochlear implant bypasses the non-functioning sensory hair cells (HCs) and electrically stimulates the neurons of the cochlear nerve. CI also benefits patients with residual hearing by combined electrical and auditory stimulation. However, the insertion of an electrode array into the cochlea induces an inflammatory response, characterized by the expression of pro-inflammatory cytokines, upregulation of reactive oxygen species, and apoptosis and necrosis of HCs, putting residual hearing at risk. Here, we characterize the small molecule AC102, a pyridoindole, for its protective effects on residual hearing in CI. In a gerbil animal model of CI, AC102 significantly improves the recovery of hearing thresholds across multiple frequencies and confines the cochlear trauma to the directly mechanically injured area. In addition, AC102 significantly preserves auditory nerve fibers and inner HC synapses throughout the whole cochlea. In vitro experiments in an ethanol challenged HT22 cell-line revealed significant and dose-responsive anti-apoptotic effects following the treatment of with AC102. Further, AC102 treatment resulted in significant downregulation of the expression of pro-inflammatory cytokines in an organotypic ex vivo model of electrode insertion trauma (EIT). These results suggest that AC102's effects are likely elicited during the inflammatory phase of EIT and mediated by anti-apoptotic and anti-inflammatory properties, highlighting AC102 as a promising compound for hearing preservation during CI. Moreover, since the inflammatory response in CI shares similarities to that in other etiologies of SNHL, AC102 may be inferred as a potential general treatment option for various inner ear conditions.

Mild therapeutic hypothermia protects against inflammatory and proapoptotic processes in the rat model of cochlear implant trauma

OBJECTIVE

Mild therapeutic hypothermia (MTH) has been demonstrated to prevent residual hearing loss from surgical trauma associated with cochlear implant (CI) insertion. Here, we aimed to characterize the mechanisms of MTH-induced hearing preservation in CI in a well-established preclinical rodent model.

APPROACH

Rats were divided into four experimental conditions: MTH-treated and implanted cochleae, cochleae implanted under normothermic conditions, MTH only cochleae and un-operated cochleae (controls). Auditory brainstem responses (ABRs) were recorded at different time points (up to 84 days) to confirm long-term protection and safety of MTH locally applied to the cochlea for 20 min before and after implantation. Transcriptome sequencing profiling was performed on cochleae harvested 24 h post CI and MTH treatment to investigate the potential beneficial effects and underlying active gene expression pathways targeted by the temperature management.

RESULTS

MTH treatment preserved residual hearing up to 3 months following CI when compared to the normothermic CI group. In addition, MTH applied locally to the cochleae using our surgical approach was safe and did not affect hearing in the long-term. Results of RNA sequencing analysis highlight positive modulation of signaling pathways and gene expression associated with an activation of cellular inflammatory and immune responses against the mechanical damage caused by electrode insertion.

SIGNIFICANCE

These data suggest that multiple and possibly independent molecular pathways play a role in the protection of residual hearing provided by MTH against the trauma of cochlear implantation.

Cochlear implants: Causes, effects and mitigation strategies for the foreign body response and inflammation

Cochlear implants provide effective auditory rehabilitation for patients with severe to profound sensorineural hearing loss. Recent advances in cochlear implant technology and surgical approaches have enabled a greater number of patients to benefit from this technology, including those with significant residual low frequency acoustic hearing. Nearly all cochleae implanted with a cochlear implant electrode array develop an inflammatory and fibrotic response. This tissue reaction can have deleterious consequences for implant function, residual acoustic hearing, and the development of the next generation of cochlear prosthetics. This article reviews the current understanding of the inflammatory/foreign body response (FBR) after cochlear implant surgery, its impact on clinical outcome, and therapeutic strategies to mitigate this response. Findings from both in human subjects and animal models across a variety of species are highlighted. Electrode array design, surgical techniques, implant materials, and the degree and type of electrical stimulation are some critical factors that affect the FBR and inflammation. Modification of these factors and various anti-inflammatory pharmacological interventions have been shown to mitigate the inflammatory/FBR response. Ongoing and future approaches that seek to limit surgical trauma and curb the FBR to the implanted biomaterials of the electrode array are discussed. A better understanding of the anatomical, cellular and molecular basis of the inflammatory/FBR response after cochlear implantation has the potential to improve the outcome of current cochlear implants and also facilitate the development of the next generation of neural prostheses.

The Effect of Pluronic-Coated Gold Nanoparticles in Hearing Preservation Following Cochlear Implantation-Pilot Study

Introduction: During cochlear implantation, electrode insertion can cause cochlear damage, inflammation, and apoptosis, which can affect the residual hearing. Nanoparticles are increasingly studied as a way to increase the availability of inner ear protective factors. We studied the effect on rats of Pluronic-coated gold nanoparticles (Plu-AuNPs) containing dexamethasone, which were applied locally in the rat’s middle ear following the implant procedure. Methods: Seven rats were used in the study. The right ear served as a model for the Dex-Plu-AuNP group. Following the intracochlear dummy electrode insertion through the round window, Dex-Plu-AuNPs were placed in the round window niche. In the right ear, following the same insertion procedure, free dexamethasone (Dex) was placed in the same manner. Auditory brainstem response thresholds (click stimulus, pure tones at 8 kHz, 16 kHz, 24 kHz, and 32 kHz) were measured before and one week after the procedure. A two-tailed T-test was used for the variables. Statistical significance was set as p < 0.05. Results: In the Dex-Plu-AuNP group, the threshold shift was less than that in the free dexamethasone group, but no statistical significance was noted between the groups. When compared individually, only the 8 kHz frequency showed statistically significant, better results after one week, in favor of the Dex-Plu-AuNP group. The mean postoperative 8 kHz threshold in the Dex-Plu-AuNPs was significantly lower than that of the control group (p = 0.048, t-test). For the other frequencies, statistical analysis showed no significant differences between the mean threshold shifts of the two cohorts. Conclusions: The local application of Plu-AuNPs containing dexamethasone following cochlear implantation may better protect the residual hearing than dexamethasone alone, but a larger sample size is needed to reach a possible statistical significance. Dex-Plu-AuNPs do not seem to cause ototoxicity and may be used as a carrier for other agents. In a clinical setting, Dex-Plu-AuNPs may have the effect of protecting lower frequencies in patients with partial deafness who are candidates for electric acoustic stimulation (EAS). If we consider this tendency, Dex-Plu-AuNPs may also be beneficial for patients with Ménière’s disease.

Enhanced Antioxidant Ability of PEG-Coated Ce0.5Zr0.5O2-Based Nanofluids for Scavenging Hydroxyl Radicals

The antioxidant therapy to preserve residual hearing is relatively recent, and the search for effective antioxidants is still ongoing. Though nanoceria has shown promising radical-scavenging capability, improving its antioxidant ability and the dispersion stability of its nanofluid, which is critical to the desired site, i.e., cochlea, still remains a major challenge. The objective of the present work is to study the radical-scavenging capability of poly(ethylene glycol) (PEG)-coated CeO₂ and Ce_0.5Zr_0.5O₂ nanoparticles in water and the biologically relevant fluid (PBS buffer). Nanoparticles in the size range of 4.0-9.0 nm are synthesized using the coprecipitation method and characterized using suitable techniques. The scavenging and dispersion stability of the synthesized nanofluid are analyzed using a UV-vis spectrophotometer. It is found that the addition of PEG during the synthesis process promoted the generation of finer nanoparticles with a narrow size distribution and the doping of zirconium produced a large number of defects in the crystallite structure. The PEG coating over the nanoparticles improved the dispersion stability of nanofluids without affecting their surface reactivity, and it is found to be 94 and 80% in water and PBS, respectively, at 500 μM and 60 min, which is maintained till 90 min. The highest scavenging of hydroxyl radicals by PEG-coated Ce_0.5Zr_0.5O₂ is found to be 60%, which is significantly superior to that of CeO₂. The scavenging capability is found to be increased with the concentration of nanoparticles, showing the best scavenging activity at 190 and 150 μM for PEG-coated CeO₂ and Ce_0.5Zr_0.5O₂, respectively, and the scavenging in water is at par with that of PBS, indicating that these nanoparticles are suitable to be used in sites where a biologically relevant fluid is present, e.g., the cochlea. It is proposed that PEG-coated Ce_0.5Zr_0.5O₂ having an average size of ∼ 4 nm can be a potential antioxidant in relevant biomedical applications.

Current Concepts and Future Trends in Increasing the Benefits of Cochlear Implantation: A Narrative Review

Hearing loss is the most common neurosensory disorder, and with the constant increase in etiological factors, combined with early detection protocols, numbers will continue to rise. Cochlear implantation has become the gold standard for patients with severe hearing loss, and interest has shifted from implantation principles to the preservation of residual hearing following the procedure itself. As the audiological criteria for cochlear implant eligibility have expanded to include patients with good residual hearing, more attention is focused on complementary development of otoprotective agents, electrode design, and surgical approaches. The focus of this review is current aspects of preserving residual hearing through a summary of recent trends regarding surgical and pharmacological fundamentals. Subsequently, the assessment of new pharmacological options, novel bioactive molecules (neurotrophins, growth factors, etc.), nanoparticles, stem cells, and gene therapy are discussed.

Advances in hearing preservation in cochlear implant surgery

PURPOSE OF REVIEW

Advancements in cochlear implant surgical approaches and electrode designs have enabled preservation of residual acoustic hearing. Preservation of low-frequency hearing allows cochlear implant users to benefit from electroacoustic stimulation, which improves performance in complex listening situations, such as music appreciation and speech understanding in noise. Despite the relative high rates of success of hearing preservation, postoperative acoustic hearing outcomes remain unpredictable.

RECENT FINDINGS

Thin, flexible, lateral wall arrays are preferred for hearing preservation. Both shortened and thin, lateral wall arrays have shown success with hearing preservation and the optimal implant choice is an issue of ongoing investigation. Electrocochleography can monitor cochlear function during and after insertion of the electrode array. The pathophysiology of hearing loss acutely after cochlear implant may differ from that involved in delayed hearing loss following cochlear implant. Emerging innovations may reduce cochlear trauma and improve hearing preservation.

SUMMARY

Hearing preservation is possible using soft surgical techniques and electrode arrays designed to minimize cochlear trauma; however, a subset of patients suffer from partial to total loss of acoustic hearing months to years following surgery despite evidence of residual apical hair cell function. Early investigations in robotic-assisted insertion and dexamethasone-eluting implants show promise.

Transtympanic injection of a liposomal gel loaded with N-acetyl-L-cysteine: A relevant strategy to prevent damage induced by cochlear implantation in guinea pigs?

Patients with residual hearing can benefit from cochlear implantation. However, insertion can damage cochlear structures and generate oxidative stress harmful to auditory cells. The antioxidant N-acetyl-L-cysteine (NAC) is a precursor of glutathione (GSH), a powerful endogenous antioxidant. NAC local delivery to the inner ear appeared promising to prevent damage after cochlear implantation in animals. NAC-loaded liposomal gel was specifically designed for transtympanic injection, performed both 3 days before and on the day of surgery. Hearing thresholds were recorded over 30 days in implanted guinea pigs with and without NAC. NAC, GSH, and their degradation products, N,N'-diacetyl-L-cystine (DiNAC) and oxidized glutathione (GSSG) were simultaneously quantified in the perilymph over 15 days in non-implanted guinea pigs. For the first time, endogenous concentrations of GSH and GSSG were determined in the perilymph. Although NAC-loaded liposomal gel sustained NAC release in the perilymph over 15 days, it induced hearing loss in both implanted and non-implanted groups with no perilymphatic GSH increase. Under physiological conditions, NAC appeared poorly stable within liposomes. As DiNAC was quantified at concentrations which were twice as high as NAC in the perilymph, it was hypothesized that DiNAC could be responsible for the adverse effects on hearing.

Randomized placebo-controlled clinical trial investigating the effect of antioxidants and a vasodilator on overall safety and residual hearing preservation in cochlear implant patients

BACKGROUND

The standard therapy for patients suffering from sensorineural hearing loss is cochlear implantation. The insertion of the electrode array into the cochlea, with potential mechanical trauma and the presence of this foreign body inside the cochlea, may lead to free radical formation and reduced blood perfusion of the cochlea which can result in a loss of residual hearing. Studies have suggested that a particular combination of the antioxidants vitamins A, C and E as well as the vasodilator magnesium (together: ACEMg) may protect the residual hearing.

METHODS

The potential protective effect of ACEMg on residual hearing preservation in cochlear implant (CI) patients was investigated in a single-centre, randomized, placebo-controlled, double-blind phase II clinical trial. CI candidates with some residual hearing in low frequencies receiving MED-EL implants of different FLEX electrode array lengths were treated with ACEMg tablets or placebo respectively 2 days preoperatively and up to 3 months postoperatively. The study objective was to demonstrate that ACEMg is more efficacious than placebo in preserving residual hearing during cochlear implantation by comparing the hearing loss (change in hearing thresholds at 500 Hz from baseline) 3 months after the first fitting between the two treatment groups and to investigate the treatments' safety.

RESULTS

Fifty-one patients were included in the study, which had to be terminated before the recruitment goal was reached because of IMP-resupply mismanagement of one partner. In the intention-to-treat population, 25 patients were treated with ACEMg and 24 patients with placebo. The mean hearing loss at 500 Hz was (± 15.84) 30.21 dB (placebo) or (± 17.56) 26.00 dB (ACEMg) 3 months after the initial fitting. Adjusting the postoperative hearing loss for the baseline residual hearing, planned electrode length and surgeon results in 8.01 dB reduced hearing loss in ACEMg-treated patients compared to placebo-treated ones. The safety analysis revealed that ACEMg was generally well-tolerated with adverse event frequencies below the placebo level.

CONCLUSION

This is the first clinical trial investigating a drug effect on residual hearing in CI patients. These first-in-man data may suggest that a perioperative oral administration of ACEMg is safe and may provide protection of residual hearing in CI patients.

TRIAL REGISTRATION

EU Clinical Trial Register No. 2012-005002-22 . Registered on 6 December 2013.

FUNDING

European Commission FP7-HEALTH-2012-INNOVATION-2.

Evaluating the Efficacy of L-N-acetylcysteine and Dexamethasone in Combination to Provide Otoprotection for Electrode Insertion Trauma

BACKGROUND

Electrode insertion trauma (EIT) during cochlear implantation (CI) can cause loss of residual hearing. L-N-acetylcysteine (L-NAC) and dexamethasone (Dex) have been individually shown to provide otoprotection albeit at higher concentrations that may be associated with adverse effects. Objective/Aims: The aim of this study is to determine whether L-NAC and Dex could be combined to decrease their effective dosage.

MATERIALS AND METHODS

The organ of Corti (OC) explants were divided into various groups: 1) control; 2) EIT; 3) EIT treated with different concentrations of Dex; 4) EIT treated with different concentrations of L-NAC; 5) EIT treated with L-NAC and Dex in combination. Hair cell (HC) density, levels of oxidative stress, proinflammatory cytokines and nitric oxide (NO) was determined.

RESULTS

There was a significant loss of HCs in explants subjected to EIT compared to the control group. L-NAC and Dex in combination was able to provide significant otoprotection at lower concentrations compared to individual drugs.

CONCLUSIONS AND SIGNIFICANCE

A combination containing L-NAC and Dex is effective in protecting sensory cells at lower protective doses than each compound separately. These compounds can be combined allowing a decrease of potential side effects of each compound and providing significant otoprotection for EIT.

Intracochlear fibrosis and the foreign body response to cochlear implant biomaterials

OBJECTIVE

To report current knowledge on the topic of intracochlear fibrosis and the foreign body response following cochlear implantation (CI).

METHODS

A literature search was performed in PubMed to identify peer-reviewed articles. Search components included "cochlear implant," "Foreign body response (FBR)," and "fibrosis." Original studies and review articles relevant to the topic were included.

RESULTS

Ninety peer-reviewed articles describing the foreign body response or intracochlear fibrosis following CI were included.

CONCLUSIONS

Intracochlear fibrosis following CI represents a significant limiting factor for the success of CI users. Several strategies have been employed to mitigate the foreign body response within the cochlea including drug delivery systems and modifications in surgical technique and electrode design. A better understanding of the FBR has the potential to improve CI outcomes and the next generation of cochlear prostheses.

Advances and Challenges in Pharmaceutical Therapies to Prevent and Repair Cochlear Injuries From Noise

Noise induces a broad spectrum of pathological injuries to the cochlea, reflecting both mechanical damage to the delicate architecture of the structures of the organ of Corti and metabolic damage within the organ of Corti and lateral wall tissues. Unlike ototoxic medications, the blood-labyrinth barrier does not offer protection against noise injury. The blood-labyrinth barrier is a target of noise injury, and can be weakened as part of the metabolic pathologies in the cochlea. However, it also offers a potential for therapeutic intervention with oto-protective compounds. Because the blood-labyrinth barrier is weakened by noise, penetration of blood-borne oto-protective compounds could be higher. However, systemic dosing for cochlear protection from noise offers other significant challenges. An alternative option to systemic dosing is local administration to the cochlea through the round window membrane using a variety of drug delivery techniques. The review will discuss noise-induced cochlear pathology, including alterations to the blood-labyrinth barrier, and then transition into discussing approaches for delivery of oto-protective compounds to reduce cochlear injury from noise.

Recent Advancements in Gene and Stem Cell-Based Treatment Modalities: Potential Implications in Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) poses a significant burden on not only the economics of health care but also the quality of life of an individual, as we approach an unprecedented age of longevity. In this article, we will delineate the current landscape of management of NIHL. We discuss the most recent results from in vitro and in vivo studies that determine the effectiveness of established pharmacotherapy such as corticosteroid and potential emerging therapies like N-acetyl cysteine and neurotrophins (NTs), as well as highlight ongoing clinical trials for these therapeutic agents. We present an overview of how the recent advancements in the field of gene-based and stem cell-based therapies can help in developing effective therapeutic strategies for NIHL. Gene-based therapies have shown exciting results demonstrating cochlear cellular regeneration using Atoh1, NRF2 as well as NT gene therapy employing viral vectors. In addition, we will discuss the recent advancements in genome-editing technologies, such as CRISPR/Cas9, and its potential role in NIHL therapy. We will further discuss the current state of stem cell therapy as it pertains to treating neurodegenerative conditions including NIHL. Embryonic stem cells, adult-derived stem cells, and induced pluripotent stem cells all represent an enticing reservoir of replacing damaged cells as a result of NIHL. Finally, we will discuss the barriers that need to be overcome to translate these promising treatment modalities to the clinical practice in pursuit of improving quality of life of patients having NIHL. Anat Rec, 303:516-526, 2020. © 2019 American Association for Anatomy.

Electric and Acoustic Stimulation in Cochlear Implant Recipients with Hearing Preservation

Hearing loss affects 30 million people in the United States, and a subset of these patients have normal low-frequency hearing and ski-sloped high-frequency hearing loss. For these patients, hearing aids alone may not provide adequate benefit. Cochlear implantation alone has been utilized to improve speech perception. The addition of high-frequency electric hearing to low-frequency acoustic hearing in these patients is beneficial. Technical improvements have allowed preservation of low-frequency hearing in cochlear implant recipients, allowing for electric and acoustic stimulation in the same ear with significant improvements in speech perception, sound localization, music appreciation, and quality of life.

l-N-acetylcysteine protects outer hair cells against TNFα initiated ototoxicity in vitro

OBJECTIVE

The present study is aimed at determining the efficacy and exploring the mechanisms by which l-N-acetylcysteine (l-NAC) provides protection against tumor necrosis factor-alpha (TNFα)-induced oxidative stress damage and hair cell loss in 3-day-old rat organ of Corti (OC) explants. Previous work has demonstrated a high level of oxidative stress in TNFα-challenged OC explants. TNFα can potentially play a significant role in hair cell loss following an insult to the inner ear. l-NAC has shown to provide effective protection against noise-induced hearing loss in laboratory animals but mechanisms of this otoprotective effect are not well-defined.

DESIGN

Rat OC explants were exposed to either: (1) saline control (N = 12); (2) TNFα (2 μg/ml, N = 12); (3) TNFα+l-NAC (5 mM, N = 12); (4) TNFα+l-NAC (10 mM, N = 12); or (5) l-NAC (10 mM, N = 12). Outer hair cell (OHC) density, levels of reactive oxygen species (ROS), lipid peroxidation of cell membranes, gluthathione activity, and mitochondrial viability were assayed.

RESULTS

l-NAC (5 and 10 mM) provided protection for OHCs from ototoxic level of TNFα in OC explants. Groups treated with TNFα+l-NAC (5 mM) showed a highly significant reduction of both ROS (p < 0.01) and 4-hydroxy-2-nonenal immunostaining (p < 0.001) compared to TNFα-challenged explants. Total glutathione levels were low in TNFα-challenged explants compared to control and TNFα+l-NAC (5 mM) treated explants (p < 0.001).

CONCLUSIONS

l-NAC is a promising treatment for protecting auditory HCs from TNFα-induced oxidative stress and subsequent loss via programmed cell death.

Perilymph pharmacokinetics of marker applied through a cochlear implant in guinea pigs

Patients undergoing cochlear implantation could benefit from a simultaneous application of drugs into the ear, helping preserve residual low-frequency hearing and afferent nerve fiber populations. One way to apply drugs is to incorporate a cannula into the implant, through which drug solution is driven. For such an approach, perilymph concentrations achieved and the distribution in the ear over time have not previously been documented. We used FITC-labeled dextran as a marker, delivering it into perilymph of guinea pigs at 10 or 100 nL/min though a cannula incorporated into a cochlear implant with the outlet in the mid basal turn. After injections of varying duration (2 hours, 1 day or 7 days) perilymph was collected from the cochlear apex using a sequential sampling technique, allowing dextran levels and gradients along scala tympani to be quantified. Data were interpreted quantitatively using computer simulations of the experiments. For injections of 2 hours duration, dextran levels were critically influenced by the presence or absence of fluid leakage at the cochleostomy site. When the cochleostomy was fluid-tight, substantially higher perilymph levels were achieved at the injection site, with concentration declining along scala tympani towards the apex. Contrary to expectations, large dextran gradients along scala tympani persisted after 24 hours of sustained injection and were still present in some animals after 7 days injection. Functional changes associated with implantation and dextran delivery, and the histological state of the implant and cannula were also documented. The persistent longitudinal gradients of dextan along the ear were not readily explained by computer simulations of the experiments based on prior pharmacokinetic data. One explanation is that inner ear pharmacokinetics are altered in the period after cochlear implantation, possibly by a permeabilization of the blood-labyrinth barrier as part of the immune response to the implant.

Emerging Therapies for Sensorineural Hearing Loss

OBJECTIVE

To critically review and evaluate the proposed mechanisms and documented results of the therapeutics currently in active clinical drug trials for the treatment of sensorineural hearing loss.

DATA SOURCES

US National Institutes of Health (NIH) Clinical Trials registry, MEDLINE/PubMed.

STUDY SELECTION & DATA EXTRACTION

A review of the NIH Clinical Trials registry identified candidate hearing loss therapies, and supporting publications were acquired from MEDLINE/PubMed. Proof-of-concept, therapeutic mechanisms, and clinical outcomes were critically appraised.

DATA SYNTHESIS

Twenty-two active clinical drug trials registered in the United States were identified, and six potentially therapeutic molecules were reviewed. Of the six molecules reviewed, four comprised mechanisms pertaining to mitigating oxidative stress pathways that presumably lead to inner ear cell death. One remaining therapy sought to manipulate the cell death cascade, and the last remaining therapy was a novel cell replacement therapy approach to introduce a transcription factor that promotes hair cell regeneration.

CONCLUSION

A common theme in recent clinical trials registered in the United States appears to be the targeting of cell death pathways and influence of oxidant stressors on cochlear sensory neuroepithelium. In addition, a virus-delivered cell replacement therapy would be the first of its kind should it prove safe and efficacious. Significant challenges for bringing these bench-to-bedside therapies to market remain. It is never assured that results in non-human animal models translate to effective therapies in the setting of human biology. Moreover, as additional processes are described in association with hearing loss, such as an immune response and loss of synaptic contacts, additional pathways for targeting become available.

ACEMg-mediated hearing preservation in cochlear implant patients receiving different electrode lengths (PROHEARING): study protocol for a randomized controlled trial

BACKGROUND

The indications for a cochlear implant (CI) have been extended to include patients with some residual hearing. Shorter and thinner atraumatic electrodes have been designed to preserve the residual hearing in the implanted ear. However, the insertion of the electrode array into the cochlea, with potential mechanical trauma and the presence of this foreign body inside the cochlea, may lead to free radical formation and reduced blood perfusion of the cochlea which can result in the loss of residual hearing.

METHODS/DESIGN

In this single-center, randomized, placebo-controlled, double-blind phase II clinical trial the effect of free radical scavengers and a vasodilator on the residual hearing of 140 CI patients will be evaluated. The formulation is composed of β-carotene (vitamin A), ascorbic acid (vitamin C), dl-α-tocopherol acetate (vitamin E) and the vasodilator magnesium (Mg), or ACEMg. Medication is administered twice daily per os for approximately 3 months. The primary measure is based upon the reduction in postoperative low-frequency air-conducted pure-tone thresholds compared to preoperative thresholds in ACEMg-treated patients compared to those of a placebo group. Additionally, the effect of different electrode lengths (20, 24 and 28 mm) is analyzed. Study visits are scheduled 2 days before surgery, at first fitting, which is the adjustment and start of stimulation via CI 4 weeks after surgery and 3, 6, 9 and 12 months after first fitting. The primary endpoint is the air-conduction hearing loss at 500 Hz 3 months after first fitting. Additionally, speech recognition tests, hearing aid benefit in the implanted ear and electrophysiological measurements of implant function are assessed. Since this is a blinded clinical trial and recruitment is still ongoing, data continue to accrue and we cannot yet analyze the outcome of the ACEMg treatment.

DISCUSSION

There is an unfulfilled need for new strategies to preserve acoustic hearing in CI patients. This study will provide first-in-man data on ACEMg-mediated protection of residual hearing in CI patients. Performing all surgeries and patient follow-up at one study site improves consistency in diagnosis and therapy and less variability in surgery, audiological test techniques and fitting. This approach will allow investigation of the influence of ACEMg on residual hearing in CI patients.

TRIAL REGISTRATION

The German Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM) application number 4039192, was registered on 6 December 2013 with protocol amendment version 3.0 from 19 August 2014. EudraCT number: 2012-005002-22 .

Prevention of trauma-induced cochlear fibrosis using intracochlear application of anti-inflammatory and antiproliferative drugs

Cochlear fibrosis is a common finding following cochlear implantation. Evidence suggests that cochlear fibrosis could be triggered by inflammation and epithelial-to-mesenchymal cell transition (EMT). In this study, we investigate the mechanisms of cochlear fibrosis and the risk/benefit ratio of local administration of the anti-inflammatory drug dexamethasone (DEX) and antimitotic drug aracytine (Ara-C). Cochlear fibrosis was evaluated in cochlear fibrosis models of rat cochlear slices in vitro and in KLH-induced immune labyrinthitis and platinum wire cochlear implantation-induced fibrosis in vivo. Cochleae were invaded with tissue containing fibroblastic cells expressing α-SMA (alpha smooth muscle actin), which along with collagen I, fibronectin, and laminin in the extracellular matrix, suggests the involvement of a fibrotic process triggered by EMT in vitro and in vivo. After perilymphatic injection of an adenoviral vector expressing GFP in vivo, we demonstrated that the fibroblastic cells derived from the mesothelial cells of the scalae tympani and vestibuli. Activation of inflammatory and EMT pathways was further assessed by ELISA analysis of the expression of IL-1β and TGF-β1. Both markers were elevated in vitro and in vivo, and DEX and Ara-C were able to reduce IL-1β and TGF-β1 production. After 5days of culture in vitro, quantification of calcein-positive cells revealed that Ara-C was 30-fold more efficient in preventing fibrosis, and provoked less sensory hair cell loss, than DEX. In KLH-induced immune labyrinthitis and platinum wire-implanted models, Ara-C was more efficient in preventing proliferation of fibrosis with less side effects on hair cells and neurons than DEX. In conclusion, DEX and Ara-C both prevent fibrosis in the cochlea. Analysis of the risk/benefit ratio favors the use of Ara-C for preventing cochlear fibrosis.

Treating hearing disorders with cell and gene therapy

Hearing loss is an increasing problem for a substantial number of people and, with an aging population, the incidence and severity of hearing loss will become more significant over time. There are very few therapies currently available to treat hearing loss, and so the development of new therapeutic strategies for hearing impaired individuals is of paramount importance to address this unmet clinical need. Most forms of hearing loss are progressive in nature and therefore an opportunity exists to develop novel therapeutic approaches to slow or halt hearing loss progression, or even repair or replace lost hearing function. Numerous emerging technologies have potential as therapeutic options. This paper details the potential of cell- and gene-based therapies to provide therapeutic agents to protect sensory and neural cells from various insults known to cause hearing loss; explores the potential of replacing lost sensory and nerve cells using gene and stem cell therapy; and describes the considerations for clinical translation and the challenges that need to be overcome.

High-frequency hearing, tinnitus, and patient satisfaction with stapedotomy: A randomized prospective study

Otosclerosis is a common disorder that leads to conductive hearing loss. Most patients with otosclerosis also have tinnitus, and surgical treatment is known to improve hearing as well as tinnitus. Some patients however experience worsening of tinnitus after the operation, but there are no known factors that allow surgeons to predict who will be at risk. In this prospective observational study on 133 patients undergoing stapedotomy, we show that postoperative air conduction thresholds at very high stimulus frequencies predict improvement of tinnitus, as assessed with proportional odds logistic regression models. Young patients were significantly more likely to experience reduction of tinnitus and patients whose tinnitus became better were also more satisfied with the outcome of the operation. These findings have practical importance for patients and their surgeons. Young patients can be advised that surgery is likely to be beneficial for their tinnitus, but a less positive message should be conveyed to older patients.

Application of a TNF-alpha-inhibitor into the scala tympany after cochlear electrode insertion trauma in guinea pigs: preliminary audiologic results

OBJECTIVE

Cochlear implantation trauma causes both macroscopic and inflammatory trauma. The aim of the present study was to evaluate the effectiveness of the TNF-alpha inhibitor etanercept applied after cochlear implantation trauma on the preservation of acoustic hearing.

DESIGN

Guinea pigs were randomly assigned to three groups receiving cochlear implantation trauma by cochleostomy. In one group, the site was sealed by bone cement with no further treatment. A second group was additionally implanted with an osmotic minipump delivering artificial perilymph into the scala tympani for seven days. In the third group, etanercept 1 mg/ml was added to artificial perilymph. Hearing was assessed by auditory brainstem responses at 2, 4, 6, and 8 kHz prior to and after surgery and on days 3, 5, 7, 14, 28.

STUDY SAMPLE

Fifteen healthy guinea pigs.

RESULTS

The trauma led to threshold shifts from 50.3 dB ± 16.3 dB to 68.0 dB ± 19.3 dB. Hearing thresholds were significantly lower in etanercept-treated animals compared to controls on day 28 at 8 kHz and from day 3 onwards at 4 and 2 kHz (p < 0.01; two-way RM ANOVA / Bonferroni t-test).

CONCLUSION

The application of etanercept led to preservation of acoustic hearing after cochlear implantation trauma.

Recent advances in local drug delivery to the inner ear

Inner ear diseases are not adequately treated by systemic drug administration mainly because of the blood-perilymph barrier that reduces exchanges between plasma and inner ear fluids. Local drug delivery methods including intratympanic and intracochlear administrations are currently developed to treat inner ear disorders more efficiently. Intratympanic administration is minimally invasive but relies on diffusion through middle ear barriers for drug entry into the cochlea, whereas intracochlear administration offers direct access to the colchlea but is rather invasive. A wide range of drug delivery systems or devices were evaluated in research and clinic over the last decade for inner ear applications. In this review, different strategies including medical devices, hydrogels and nanoparticulate systems for intratympanic administration, and cochlear implant coating or advanced medical devices for intracoclear administration were explored with special attention to in vivo studies. This review highlights the promising systems for future clinical applications as well as the current hurdles that remain to be overcome for efficient inner ear therapy.

A randomised, double blind trial of N-Acetylcysteine for hearing protection during stapes surgery

Background

Otosclerosis is a disorder that impairs middle ear function, leading to conductive hearing loss. Surgical treatment results in large improvement of hearing at low sound frequencies, but high-frequency hearing often suffers. A likely reason for this is that inner ear sensory cells are damaged by surgical trauma and loud sounds generated during the operation. Animal studies have shown that antioxidants such as N-Acetylcysteine can protect the inner ear from noise, surgical trauma, and some ototoxic substances, but it is not known if this works in humans. This trial was performed to determine whether antioxidants improve surgical results at high frequencies.

Methods

We performed a randomized, double-blind and placebo-controlled parallel group clinical trial at three Swedish university clinics. Using block-stratified randomization, 156 adult patients undergoing stapedotomy were assigned to intravenous N-Acetylcysteine (150 mg/kg body weight) or matching placebo (1:1 ratio), starting one hour before surgery. The primary outcome was the hearing threshold at 6 and 8 kHz; secondary outcomes included the severity of tinnitus and vertigo.

Findings

One year after surgery, high-frequency hearing had improved 2.7 ± 3.8 dB in the placebo group (67 patients analysed) and 2.4 ± 3.7 dB in the treated group (72 patients; means ± 95% confidence interval, p = 0.54; linear mixed model). Surgery improved tinnitus, but there was no significant intergroup difference. Post-operative balance disturbance was common but improved during the first year, without significant difference between groups. Four patients receiving N-Acetylcysteine experienced mild side effects such as nausea and vomiting.

Conclusions

N-Acetylcysteine has no effect on hearing thresholds, tinnitus, or balance disturbance after stapedotomy.

Trial Registration

ClinicalTrials.gov NCT00525551

Electroacoustic stimulation: now and into the future

Cochlear implants have provided hearing to hundreds of thousands of profoundly deaf people around the world. Recently, the eligibility criteria for cochlear implantation have been relaxed to include individuals who have some useful residual hearing. These recipients receive inputs from both electric and acoustic stimulation (EAS). Implant recipients who can combine these hearing modalities demonstrate pronounced benefit in speech perception, listening in background noise, and music appreciation over implant recipients that rely on electrical stimulation alone. The mechanisms bestowing this benefit are unknown, but it is likely that interaction of the electric and acoustic signals in the auditory pathway plays a role. Protection of residual hearing both during and following cochlear implantation is critical for EAS. A number of surgical refinements have been implemented to protect residual hearing, and the development of hearing-protective drug and gene therapies is promising for EAS recipients. This review outlines the current field of EAS, with a focus on interactions that are observed between these modalities in animal models. It also outlines current trends in EAS surgery and gives an overview of the drug and gene therapies that are clinically translatable and may one day provide protection of residual hearing for cochlear implant recipients.

In vitro efficacy of N-acetylcysteine on bacteria associated with chronic suppurative otitis media

Background

The safety and efficacy of Ciprodex® has been demonstrated for treatment of chronic suppurative otitis media (CSOM). However, symptoms fail to resolve in 9-15% of patients. The objective of this study is to evaluate the efficacy of N-acetylcysteine (NAC) on S. aureus, and planktonic and sessile (biofilm forming) P. aeruginosa in vitro using clinical isolates from patients with CSOM.

Methods

1) Stability was assessed using liquid chromatography-mass spectrometry for each component in a prepared mixture of Ciprodex® and NAC over 15 days. Sterility was assessed by measuring bacterial growth on a blood agar plate. Efficacy was assessed using a disc diffusion method by inoculating plates with S. aureus ATCC 29513 and P. aeruginosa ATCC 27853, and measuring the clearance zone.

2) Fifteen P. aeruginosa strains were isolated from patients with CSOM and tested in vitro using the bioFILM PA™ antimicrobial susceptibility assay. Treatment solutions included Ciprodex® & ciprofloxacin +/- NAC, and NAC alone (0.25%, 0.5% & 1.25%).

Results

1) NAC combined with Ciprodex® demonstrated stability, sterility, and efficacy over a two-week period

2) P. aeruginosa strains in the sessile (33%-40%) and planktonic (13%) state demonstrated resistance to Ciprodex® and ciprofloxacin. When NAC ≥0.5% was used in isolation or as an adjunct to either of these medications, no resistance was found in the sessile or planktonic state among all 15 strains.

Conclusion

1) Ciprodex® combined with NAC has a shelf life of at least two weeks given the documented preservation of stability, sterility, and clinical efficacy of the mixed compounds.

2) P. aeruginosa strains demonstrated resistance to both Ciprodex® and ciprofloxacin. NAC ≥0.5% overcomes issues with resistance and shows promise in the treatment of CSOM.

Development of an ototoxicity model in the adult CBA/CaJ mouse and determination of a golden window of corticosteroid intervention for otoprotection

OBJECTIVE

To investigate the effect of timing of dexamethasone administration on auditory hair cell survival following an ototoxic insult with kanamycin and furosemide.

STUDY DESIGN

Controlled experimental study.

SETTING

Translational science experimental laboratory.

METHODS

5-6 week old CBA/CaJ mice, divided into 6 groups, were injected with kanamycin (1 mg/g SC) followed by furosemide (0.5 mg/g IP). Dexamethasone (0.1 mg/g IP) was injected at either 1 hour prior to insult, +1 hr, +6 hr, +12 hr, or +72 hr post insult. Temporal bones harvested on day 7 underwent Organ of Corti dissection. Immunohistochemical staining was performed using antibodies to myosin 7a, phalloidin, and TO-PRO.

RESULTS

Hair cell counts demonstrate a uniform ototoxicity model with total loss of outer hair cells (OHCs) and near-total loss of inner hair cells (IHCs). The group pre-treated with dexamethasone showed a statistically significant improvement in counts compared to controls (p = 0.004). Counts from the other experimental groups given dexamethasone after the insult were highly variable but demonstrated some apical and middle turn inner hair cell survival.

CONCLUSION

Treatment of systemic dexamethasone prior to ototoxic insult attenuates hair cell loss in a reliable, novel, ototoxicity model using kanamycin and furosemide in CBA/CaJ mice. Dosing with dexamethasone following ototoxic insult shows promising yet variable response in hair cell survival.

Influence of cochleostomy and cochlear implant insertion on drug gradients following intratympanic application in Guinea pigs

Locally applied drugs can protect residual hearing following cochlear implantation. The influence of cochlear implantation on drug levels in the scala tympani (ST) after round window application was investigated in guinea pigs using the marker trimethylphenylammonium (TMPA) measured in real time with TMPA-selective microelectrodes. TMPA concentration in the upper basal turn of the ST rapidly increased during implantation and then declined due to cerebrospinal fluid entering the ST at the cochlear aqueduct and exiting at the cochleostomy. The TMPA increase was found to be caused by the cochleostomy drilling if the burr tip partially entered the ST. TMPA distribution in the second turn was less affected by implantation procedures. These findings show that basal turn drug levels may be changed during implantation and the changes may need to be considered in the interpretation of therapeutic effects of drugs in conjunction with implantation.

Molecular and cellular mechanisms of loss of residual hearing after cochlear implantation

OBJECTIVES

We describe the various molecular and cellular pathways that lead to early and delayed loss of residual hearing after cochlear implantation.

METHODS

We performed a systematic review using the Medline database with the key words cochlear implant, residual hearing, inflammation, apoptosis, and necrosis.

RESULTS

The mechanisms underlying the loss of residual hearing after cochlear implantation are multiple. Early hearing loss may be provoked by the surgical access to the inner ear spaces and by trauma caused by insertion of the electrode array. After the initial trauma, an acute inflammatory response promotes elevated levels of cytokines and reactive oxygen species, which in turn promote sensory cell loss by apoptosis, necrosis, and necrosis-like programmed cell death. Treatments that counteract such an inflammatory reaction, production of reactive oxygen species, and apoptosis are effective at preventing hair cell degeneration. However, delayed hearing loss appears to be a consequence of chronic inflammation with development of fibrotic tissue. The mechanisms that lead to fibrosis are poorly understood, and standard antiinflammatory drugs are insufficient for preventing its development.

CONCLUSIONS

Cochlear implantation is followed by an inflammatory response involving several pathways that lead to either short-term or long-term sensory hair cell degeneration. Future studies should focus on revealing the precise molecular mechanisms induced by cochlear implantation to allow the discovery of new targets for the effective prevention and treatment of loss of residual hearing.

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.

Protective effect of systemic administration of erythropoietin on auditory brain stem response and compound action potential thresholds in an animal model of cochlear implantation

OBJECTIVES

An animal model of cochlear implantation has been developed, and the hearing threshold was evaluated after different surgical procedures. The effect of perioperative systemic administration of erythropoietin on the hearing loss induced by cochlear implantation was tested.

METHODS

Twenty-nine guinea pigs with normal hearing underwent implantation of a 254-microm-diameter array through a cochleostomy. The effects on hearing of cochleostomy and transient and long-term array implantation (21 days) were assessed by testing of the auditory brain stem responses and compound action potentials. Eleven implanted animals received intraperitoneal administration of erythropoietin. Selected computed tomographic scans and cochlear histologic studies were performed 1 month after implantation to confirm proper placement of the array. The erythropoietin concentration at the time of surgery was assessed in samples of perilymph, cerebrospinal fluid, and blood.

RESULTS

The cochleostomy and transient array insertion had no effect on hearing thresholds. Long-term array implantation induced a stable decrease of hearing threshold (30 dB), a decrease that was reduced by 12 dB in erythropoietin-treated animals. The erythropoietin-treated animals had better hearing preservation at higher frequencies. Fibrosis surrounding the array was seen in both groups.

CONCLUSIONS

The hearing loss observed was probably due to the presence of the array in the cochlea. The intraperitoneal injection of erythropoietin improved the hearing threshold shift induced by implantation.

Direct entry of gadolinium into the vestibule following intratympanic applications in Guinea pigs and the influence of cochlear implantation

Although intratympanic (IT) administration of drugs has gained wide clinical acceptance, the distribution of drugs in the inner ear following IT administration is not well established. Gadolinium (Gd) has been previously used as a marker in conjunction with magnetic resonance imaging (MRI) to visualize distribution in inner ear fluids in a qualitative manner. In the present study, we applied gadolinium chelated with diethylenetriamine penta-acetic acid (Gd-DTPA) to the round window niche of 12 guinea pigs using Seprapack(TM) (carboxlmethylcellulose-hyaluronic acid) pledgets which stabilized the fluid volume in the round window niche. Gd-DTPA distribution was monitored sequentially with time following application. Distribution in normal, unperforated ears was compared with ears that had undergone a cochleostomy in the basal turn of scala tympani and implantation with a silastic electrode. Results were quantified using image analysis software. In all animals, Gd-DTPA was seen in the lower basal scala tympani (ST), scala vestibuli (SV), and throughout the vestibule and semi-circular canals by 1 h after application. Although Gd-DTPA levels in ST were higher than those in the vestibule in a few ears, the majority showed higher Gd-DTPA levels in the vestibule than ST at both early and later time points. Quantitative computer simulations of the experiment, taking into account the larger volume of the vestibule compared to scala tympani, suggest most Gd-DTPA (up to 90%) entered the vestibule directly in the vicinity of the stapes rather than indirectly through the round window membrane and ST. Gd-DTPA levels were minimally affected by the implantation procedure after 1 h. Gd-DTPA levels in the basal turn of scala tympani were lower in implanted animals, but the difference compared to non-implanted ears did not reach statistical significance.

Effects of systemic administration of methylprednisolone on residual hearing in an animal model of cochlear implantation

CONCLUSION

Delivery of intramuscular injection of methylprednisolone around the implantation surgery improved the hearing threshold shift induced by cochlear implantation.

OBJECTIVES

During electroacoustic cochlear implantation surgery, the residual hearing is not preserved in about 15% of cases. In this study, we tested the effects of intramuscular administration of methylprednisolone on the hearing loss induced by cochlear implantation in a model of guinea pig cochlear implantation.

METHODS

Eleven guinea pigs with normal hearing were implanted with a 254 μm diameter silicone array through a cochleostomy, and the effects on hearing of longstanding array insertion (21 days) were assessed. Six of the implanted animals received intramuscular administration of methylprednisolone. Auditory brainstem response recordings were performed before and up to 21 days after the cochlear implantation. CT scans were performed in some animals 1 month after implantation.

RESULTS

CT scans confirmed that the array was well positioned in tested animals. From days 3 to 21, a hearing loss of about 30 dB on all frequencies was observed in the implanted nontreated group. This hearing loss remained stable during the whole follow-up period. Compared with implanted nontreated animals, the hearing threshold shift decreased by 12 dB in animals treated with methylprednisolone.