Faculty Bibliography

Oxidative stress has been implicated as a cause of hair cell damage after ischemia reperfusion injury, noise trauma, and ototoxic injury. Oxidative stress can induce both apoptosis or necrosis depending on the degree of exposure. To study how reactive oxygen species (ROS) interacts with hair cells, we have developed an in vitro model of oxidative stress using organ of Corti cultures exposed to physiologically relevant concentrations of hydrogen peroxide (H(2) O(2) ). Treatment of organ of Corti cultures with low concentrations of H(2) O(2) results in loss of outer hair cells in the basal turn of the explant. Higher concentrations of peroxide result in more extensive outer hair cell injury as well as loss of inner hair cells. Early outer hair cell death appears to occur though apoptosis as demonstrated by staining of activated caspase. The effect of oxidative stress on mitochondrial function is a key determinant of degree of damage. Oxidative stress results in reduction of the mitochondrial membrane potential and reduction of mitochondrial produced antioxidants. Low doses of oxidative stress induce changes in mitochondrial gene expression and induce mitochondrial DNA deletions. Recurrent oxidative stress or inhibition of mitochondrial function significantly enhanced hair cell death. This tissue culture model of oxidative hair cell injury maintains a pattern of injury similar to what is observed in vivo after oxidative injury and can be used to study the effects of ROS on hair cells over the time period of the culture.

OBJECTIVE: The objective of this study was to review our pediatric emergency department's (ED's) utilization of computed tomography (CT) in the diagnosis of peritonsillar abscess (PTA) and treatment outcomes. METHODS: This study used case series with chart review. RESULTS: From January 2007 to January 2009, 148 patients were seen in our ED for possible PTA. Mean age at presentation was 11.8 years (range, 10 months to 18 years); 81 (54.7%) of 148 were females. Computed tomography was ordered in 96 (64.9%) of 148 patients, of which 73 (49.3%) 148 were confirmed to have PTA. Mean age of patients who underwent CT was younger when compared with those who did not have CT performed (mean, 11 vs 13 years; P = 0.02). Unilateral PTA was found in 65 (43.9%) of 148, bilateral in 8 (5.4%) of 148, and intratonsillar in 25 patients (16.9%). Concomitant CT findings of parapharyngeal space involvement were found in 19 (12.8%), and retropharyngeal space involvement in 11 (7.4%). Admission was necessary for 104 (71.2%) of 148 patients, whereas 42 were discharged from the ED. Transoral needle aspiration and/or incision and drainage were performed in the ED in 41 patients, with purulence identified in 33 (80.5%) of 41. Rapid strep testing was positive in 40 (32%) of 124 patients tested. Operative treatment was necessary in 44 patients (29.7%), 34 underwent incision and drainage, and 10 underwent quinsy tonsillectomy. CONCLUSIONS: Computed tomography is commonly utilized in the ED for the evaluation of PTA and is ordered more often in younger children.

CONCLUSION: Replacement of vestibular hair cells induced by atoh1 driven by the tissue-specific GFAP promoter was significantly more efficient than use of the cBA or hCMV promoter. OBJECTIVE: To test whether expression level, persistence, or selectivity from adenovirus vectors delivered in the inner ear can be altered by changing the adenovector backbone or by using different cellular and viral promoters. MATERIALS AND METHODS: Adenovector and promoter modifications were tested for differences in transgene expression in adult macular organs. The effect of using an E1/E3 deleted vector was compared to E1/E3/E4 deleted vectors. The effect of using viral and cellular promoters to modify transgene expression was tested in explanted adult mouse macular organs. Based on these results three different promoters were tested for efficacy of atonal gene. RESULTS: Use of adenovectors containing human CMV, the hybrid cBA and ubiquitin promoters driving transgene expression resulted in different types of transgene expression. While several viral and cellular promoters provided broad cell type expression, expression driven by the GFAP promoter was limited to vestibular supporting cells, demonstrating the specificity of this promoter.

Loss of auditory and vestibular hair cells is a common cause of hearing loss and balance disorders. A variety of strategies have been proposed to restore function to damaged inner ear neuroepithelium. Delivery of the atonal homolog, atoh1, has been demonstrated to induce recovery of auditory and vestibular hair cells using a variety of delivery methods and model systems. We have developed a mouse model of vestibular aminoglycoside ototoxicity and demonstrated that delivery of an advanced generation adenovector that expresses atoh1 results in the regeneration of vestibular hair cells. Additionally, mice treated with atoh1 recover balance function. Currently vestibular diseases have few treatment options and several lines of evidence suggest that regeneration of hair cells may be more easily accomplished in the vestibular system. Development of atoh1-based gene therapy for vestibular hair cell loss may provide an initial opportunity for developing gene therapy for inner ear disease.

Recent studies have demonstrated that delivery of genes to the inner ear can achieve a variety of effects ranging from support of auditory neuron survival to protection and restoration of hair cells, demonstrating the utility of vector based gene delivery. Translation of these findings to useful experimental systems or even clinical applications requires a detailed understanding of the pharmacokinetics of gene delivery in the inner ear. Ideal gene delivery systems will employ a well tolerated vector which efficiently transduces the appropriate target cells within a tissue, but spare non-target structures. Adenovectors based on serotype 5 (Ad 5) are commonly used vectors, are easy to construct and have a long track record of efficacious gene transfer in the inner ear. In this study we demonstrate that distribution of Ad5 vector occurs in a basal to apical gradient with rapid distribution of vector to the vestibule after delivery via a round window cochleostomy. Transduction of the vector and expression of the delivered transgene occurs by 10 min post vector delivery. At 24 h post delivery only 16% of vector that was initially detectable within the inner ear by quantitative PCR remained. Perilymph sampling was used to determine that vector concentrations in perilymph peaked at 30 min post delivery and then declined rapidly. Understanding these basic distribution patterns and parameters for delivery are important for the design of gene delivery vectors and vital for modeling dose responses to achieve safe efficacious delivery of a therapeutic agent.

HYPOTHESIS: Delivery of math1 using an adenovector (Admath1.11D) results in vestibular hair cell regeneration and recovery of balance function in ototoxin-treated adult mice. BACKGROUND: Loss of peripheral vestibular function is associated with disease processes such as vestibular neuronitis, aminoglycoside ototoxicity, and aging. Loss of vestibular hair cells is one of the mechanisms underlying balance dysfunction in all of these disorders. Currently, recovery from these diseases relies on central vestibular compensation rather than on local tissue recovery. Overexpression of the mammalian atonal homologue math1 has been demonstrated to induce generation of hair cells in neonatal organ of Corti cultures and in the guinea pig cochlea in vivo and could thus provide an approach to local tissue recovery. METHODS: Admath1.11D was applied to cultures of aminoglycoside-treated macular organs or in vivo in a mouse aminoglycoside ototoxicity model. Outcome measures included histologic examination, immunohistochemistry, swim testing, and evaluation of the horizontal vestibulo-ocular reflex. RESULTS: Delivery of math1 resulted in the generation of vestibular hair cells in vitro after aminoglycoside-mediated loss of hair cells. Math1-treated mice showed recovery of the vestibular neuroepithelium within 8 weeks after Admath1.11D treatment. Assessment of animals after vector infusion demonstrated a recovery of vestibular function compared with aminoglycoside-only-treated mice. CONCLUSION: Molecular replacement of math1 may provide a therapeutic means of restoring vestibular function related to vestibular hair cell loss.

The last 10 years have seen the development of numerous strategies for the delivery of genes to the inner ear. Besides being a useful research tool,gene therapy has significant promise as a potential clinical treatment. The human inner ear is easily accessible through either the round window or the stapes footplate. It is now possible to choose a variety of vectors to target a variety of different tissues. Modification of promoters yields different expression patterns as well as differences in degree of expression. Several animal studies have also demonstrated that expression of exogenous genes in the cochlea does not result in loss of hearing function. A variety of potential clinical applications are already evident from these early studies. Protective strategies such as prevention of neuronal degeneration and protection of auditory hair cells from oxidative stress are potential examples where gene therapy may be useful. As the understanding of gene therapy improves, investigators will be able to move toward targeted single-gene replacement to treat disorders such as connexin mutations and applying gene therapy to sensory cell replacement.

Objective: To develop and validate a mouse model of implantation trauma. Study design: Adult CBA mice were anesthetized and a basal turn cochleostomy created. Using a micromanipulator varying amounts of sterile phosphate-buffered saline were injected into the cochleostomy. The cochleostomy was sealed and bearing was then tested by ABR. Animals were also treated with cell death inhibitors prior to injection. Hearing was tested after 24 h allowing the elucidation of cell death pathways after cochlear trauma. Results: Volume changes under 4% of the perilymph volume of the mouse cochlea were well tolerated. Greater volume injections resulted in progressively larger hearing losses with profound bearing loss occurring at 30% of perilymph volume injection. There was a correlation between volume delivered, hearing loss, and histological findings with higher volumes resulting in tears of Reisner's membrane and blood in the perilymph. Addition of caspase inhibitors to the injection mix significantly improved hearing outcomes in high volume injections. Conclusion: This animal model allows evaluation of a cochlear injury in a quantitative fashion. Use of cell death pathway inhibitors significantly improved hearing outcome, suggesting that these substances may play a role in cases where bearing preservation is planned in implant surgery. This mouse model of hydraulic trauma may be used to test a variety of potential protective substances. (c) 2004 Elsevier B.V. All rights reserved.