Biomedical subjects

Timo Stöver

Publications and source records attributed to Timo Stöver.

17 recordsLinked to original sources

PubMed2006

Differential brain-derived neurotrophic factor and transforming growth factor-beta expression in the rat cochlea following deafness.

Brain derived neurotrophic factor (BDNF) and transforming growth factor-beta (TGFbeta) subtypes have demonstrated their importance in cochlear functions. The aim of this study was to determine gene and protein expression patterns of BDNF, TGFbeta1/2 and their main receptors trkB and TGFbetaR1/R2 in the auditory nerve and inferior colliculus of normal hearing and deafened rats by reverse-transcriptase polymerase chain reaction and immunohistochemistry. Deafening was performed by cochlear injection of neomycin (10%). Significant gene expression changes were not found in the inferior colliculus after deafness; however, in the auditory nerve, BDNF, TGFbeta1 and TGFbetaR1 mRNA in particular were upregulated. Additionally, BDNF protein and the cytokines were found to be expressed in the auditory nerve after hair cell loss. These data indicate the importance of BDNF and TGFbeta1 as endogenous survival factors.

Animals↗

PubMed2006

Upregulation of glial cell line-derived neurotrophic factor and artemin mRNA in the auditory nerve of deafened rats.

Nerve growth factors play key roles in spiral ganglion cells survival and excitability. Our aim was to determine gene expression patterns of glial cell line-derived neurotrophic factor family (GDNF) members and their receptors in the auditory nerve and inferior colliculus of deafened rats. The gene expression of GDNF, persephin, artemin and neurturin, and their receptors GFRalpha1, GFRalpha2, GFRalpha3 and Ret, was determined by semiquantitative reverse transcriptase-polymerase chain reaction using GAPDH expression as an internal standard. Following deafness, no significant changes in expression of GDNF family genes were found in inferior colliculus. In contrast, artemin, GDNF, GFRalpha1-3 and Ret RNA expression were strongly upregulated in the auditory nerve following deafness, indicating their importance in protecting the auditory nerve against cell damage.

Acoustic Stimulation↗

PubMed2006

p27(Kip1) deficiency causes organ of Corti pathology and hearing loss.

p27(Kip1) (p27) has been shown to inhibit several cyclin-dependent kinase molecules and to play a central role in regulating entry into the cell cycle. Once hair cells in the cochlea are formed, p27 is expressed in non-sensory cells of the organ of Corti and prevents their re-entry into the cell cycle. In one line of p27 deficient mice (p27(-/-)), cell division in the organ of Corti continues past its normal embryonic time, leading to continual production of cells in the organ of Corti. Here we report on the structure and function of the inner ear in another line of p27 deficient mice originating from the Memorial Sloan-Kettering Cancer Center. The deficiency in p27 expression of these mice is incomplete, as they retain expression of amino acids 52-197. We determined that mice homozygote for this mutation had severe hearing loss and their organ of Corti exhibited an increase in the number of inner and outer hair cells. There also was a marked increase in the number of supporting cells, with severe pathologies in pillar cells. These data show similarities between this p27(Kip1) mutation and another, previously reported null allele of this gene, and suggest that reducing the inhibition on the cell cycle in the organ of Corti leads to pathology and dysfunction. Manipulations to regulate the time and place of p27 inhibition will be necessary for inducing functionally useful hair cell regeneration.

Animals↗

PubMed2006

Determination of the clinical growth index in unilateral vestibular schwannoma.

OBJECTIVES: To analyze factors associated with the clinical growth index of sporadic unilateral vestibular schwannoma and to evaluate the validity of the index as an indicator of tumor growth. DESIGN: A retrospective case review study. PATIENTS AND METHODS: A series of 118 patients with unilateral vestibular schwannomas. Clinical growth index was calculated by dividing tumor size by the length of clinical history. Clinical growth index, tumor size, symptoms, and symptom duration were tested for a relationship with tumor location, patient sex, and age. All tests were performed for the total group and separately for three subgroups: intrameatal tumors (IT group, n = 46), intrameatal and extrameatal tumors (IET group, n = 60), and extrameatal tumors (ET group, n = 12). RESULTS: Vestibular schwannoma diameter ranged from 3 to 40 mm (mean size, 14.3 +/- 7.6 mm). The maximum tumor diameter was significantly greater for the IET group (17.9 +/- 6.5 mm) and the ET group (19.3 +/- 8.5 mm) than for the IT group (8.5 +/- 4.3 mm) (p < 0.001). The mean clinical growth index was determined as being 31.3 +/- 55.7 mm/yr for the total group. A significantly lower clinical growth index was found for the IT group (14.7 +/- 25.3 mm/yr) compared with the IET group (41.9 +/- 69.2 mm/yr) and the ET group (43.3 +/- 52.4 mm/yr) (p = 0.031). A significantly negative correlation between the clinical growth index and the age of the patients was noted for both the total group (p = 0.010) and the IET group (p = 0.017). A significantly negative correlation between the tumor size and the age of the patients was determined for the ET group (p = 0.22). CONCLUSIONS: This study demonstrates a lower clinical growth index and smaller tumors in the older population, supporting data previously presented by extensive radiological studies. Our findings might provide a rationale for the consideration of the clinical growth index to estimate vestibular schwannoma growth rate.

Journal Article↗

PubMed2006

Flat-panel volume computed tomography for cochlear implant electrode array examination in isolated temporal bone specimens.

HYPOTHESIS: Flat-panel based volume computed tomography could improve cochlear implant electrode evaluation in comparison with multislice computed tomography. BACKGROUND: Flat-panel based volume computed tomography offers higher spatial resolution and less metal artifacts than multislice computed tomography. Both characteristics could improve the evaluation of challenging but important questions in cochlear implantation assessment, such as an exact imaging of cochlea, osseous spiral lamina, electrode array position, and single electrode contacts. These questions are not currently fully answered by multislice computed tomography. METHODS: Four isolated temporal bone specimens were scanned in a current multislice computed tomography scanner and in two experimental flat-panel based volume computed tomography scanners before and after cochlea implantation. To compare flat-panel based volume computed tomography and multislice computed tomography, four features were rated according to the following criteria: 1) visibility of the cochlea; 2) visibility of the osseous spiral lamina; 3) discernibility of individual electrode contacts; and 4) the ability to determine the electrode array position relative to scala tympani and scala vestibuli. Layer-by-layer microgrinding pictures were used as the ground truth for verification of imaging findings. RESULTS: Flat-panel based volume computed tomography was superior to multislice computed tomography in all four features rated. The cochlea and facial nerve canal were much better delineated in flat-panel based volume computed tomography. The osseous spiral lamina and single electrode contacts were only visible in flat-panel based volume computed tomography. Assessment of implant position with regard to the cochlear spaces was considerably improved by flat-panel based volume computed tomography. CONCLUSION: Cochlear implantation assessment could be improved by flat-panel based volume computed tomography and, therefore, would be highly beneficial for cochlea implantation research and for clinical evaluation. However, these first results were shown by scanning isolated temporal bone specimens; scanning whole human skull bases might be more challenging.

Artifacts↗

PubMed2006

Elimination of facial nerve stimulation by reimplantation in cochlear implant subjects.

HYPOTHESIS: Perimodiolar intracochlear electrodes with contacts facing towards the modiolus have limited current flow towards the outer wall of the cochlea and therefore, may reduce the occurrence of facial nerve stimulation (FN) in cochlear implant subjects. BACKGROUND: Facial nerve stimulation is a well-known complication in cochlear implant treatment especially in the group of subjects with otosclerosis. The possible explanation of this side effect is a change of the electrical properties of the otosclerotic bone leading to leakage current and resulting in facial nerve stimulation. METHODS: Four CI subjects who had been implanted with a Nucleus Mini22 device with a Nucleus Straight electrode between 9 to 12 years ago suffered from severe FN stimulation. Electrode contacts had to be switched off so that they could only use 4, 11, 13, and 15 electrodes of their usual set of 22. The switch off resulted in deteriorating speech understanding over time. Therefore, all subjects were reimplanted with a Nucleus 24R device with a Contour electrode. Preoperatively, the threshold of FN stimulation was obtained on all electrodes subjectively. Intraoperatively, FN stimulation thresholds were measured objectively with both, the old and the new device and were compared. NRT and SRT thresholds were also obtained with the reimplanted device to assure effective electrical stimulation of the auditory nerve. RESULTS: In all four cases the postoperative fitting demonstrated no FN stimulation on all electrodes up to maximum comfortable level. The insertion of the Contour electrode array was complete in three cases, in one case the array could only be inserted partially similarly to the situation before the reimplantation. Speech perception tests showed a significant improvement in all subjects with the new device. CONCLUSION: Electrodes with modiolar facing contacts and perimodiolar position like the Nucleus Contour electrode reduce the possibility of facial nerve stimulation significantly due to more focused electrical stimulation.

Adult↗

PubMed2005

Brain-derived neurotrophic factor/glial cell line-derived neurotrophic factor survival effects on auditory neurons are not limited by dexamethasone.

Cochlear implant performance depends on the number of surviving excitable auditory neurons and prevention of degradation of nerve-electrode interaction caused by adverse tissue reactions. Glucocorticoids and neurotrophic factors are promising options for a possible therapeutic intervention. Neurons dissociated from the spiral ganglion of rats (3-5 days old) were cultivated with addition of brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor and the corticosteroid dexamethasone in various concentrations (25, 50, 100 ng/ml) and in combination with each other (100 ng/ml). The results suggest that a combination of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor does not enhance spiral ganglion cell survival significantly when compared with single brain-derived neurotrophic factor treatment (100 ng/ml). In addition, dexamethasone application did not interfere with the survival-promoting effects of brain-derived neurotrophic factor or glial cell line-derived neurotrophic factor.

Animals↗

PubMed2005

Substance distribution in a cochlea model using different pump rates for cochlear implant drug delivery electrode prototypes.

Several studies using animals have shown the protective effects of neurotrophic factors (NF) on spiral ganglion cells (SGC). This is of particular importance since the number of SGCs is considered to be among the factors defining the efficacy of cochlear implants. A device for local inner ear treatment is therefore of great interest. As described previously, we modified a Contour(TM) cochlear implant electrode, to examine the inbuilt canal to be used for fluid release [Paasche, G., Gibson, P., Averbeck, T., Becker, H., Lenarz, T., Stöver, T., 2003. Technical report: modification of a cochlear implant electrode for drug delivery to the inner ear. Otol. Neurotol. 24, 222-227]. In the present study, three different electrode prototypes with openings of the delivery channel at various locations along the electrode array were examined to determine distribution of dye in a cochlea model over time. We compared dye delivery with: (a) release of the dye at the tip, (b) release of the dye at the tip and the side of the electrode, and (c) release of the dye only at the side of the electrode (6 mm from the tip). A mechanical pump was used to drive the system at pump rates of 100, 10, and 1 microl/h. Dye concentration changes along the length of the whole cochlea were investigated. Mean values for all experimental conditions show that the distribution along the array is fastest with two outlets whereas the distribution via a single outlet at the side of the electrode array is not considered to be sufficient. The established experimental setup provides the possibility of investigating prototypes of a fluid based drug delivery system for the treatment of inner ear pathologies in combination with electrical stimulation.

Animals↗

PubMed2005

The use of buccal smears for a non-invasive screening of the 35delG mutation of the Connexin-26 gene in hearing impaired young children.

OBJECTIVES: Recent advances in genetic research indicate that about 50% of congenital deaf patients have a genetic background, with mutations in the Connexin-26 gene being the most frequent one. Screening methods for the genetic cause of deafness have so far mostly been based on the use of peripheral whole blood as DNA source. The use of buccal smears for the genetic screening of deaf patients presents an interesting alternative to drawing blood, especially in young children. In order to validate this method, we compared results from buccal smears from very young deaf children (age<or=3 years) and deaf patients older than 3 years with the results from blood samples deriving from the same patients. METHODS: The detection of the 35delG mutation in the Connexin-26 gene was chosen to demonstrate the method's feasibility. Blood and buccal smears were collected for genetic analysis from 29 very young deaf children (Group 1: age<or=3 years) and 31 deaf patients older than 3 years (Group 2) during their clinical pre-evaluation for cochlear implantation. Genomic DNA was isolated from blood as well as from buccal smears. Yield of both sources was determined by photometric evaluation of the isolated DNA concentration. Genomic DNA isolated from blood and buccal smears was then submitted to PCR-mediated site-directed mutagenesis followed by BS1 YI restriction and electrophoresis. The results for 35delG detection in DNA originating from blood were compared to those of buccal smears. RESULTS: Quantitative DNA analysis showed that both sources provided adequate amounts of DNA for PCR. No significant difference was found between Group 1 and Group 2 considering either the DNA amount isolated from blood or from buccal smears. In all 60 patients, DNA isolated from blood revealed the same results concerning the presence of the 35delG mutation as DNA originating from buccal smears. CONCLUSIONS: This study demonstrates that buccal smears are an adequate, reliable source of genomic DNA providing material for genetic tests that can especially help to avoid drawing blood from very young children for the genetic screening of deafness.

Adolescent↗

PubMed2005

Evaluation of the advance off-stylet insertion technique and the cochlear insertion tool in temporal bones.

OBJECTIVE: The concept and design of new cochlear implant electrodes is a challenging process. To evaluate new electrode designs, we present a study that uses a microgrinding procedure to evaluate damage to the microstructures of the cochlea resulting from the insertion procedure. In this study, we compared different insertion techniques with the Contour electrode with Softip for placement inside the cochlea and any resulting damage. METHODS: Twenty-five fresh frozen human temporal bones were used to compare electrode insertion characteristics with three insertion techniques (i.e., conventional insertion, Advance Off-Stylet performed manually, and Advance Off-Stylet performed with insertion tool) and two prototype variants of the Contour electrode with Softip (referred as Softip I and Softip II in this article). Five temporal bones were used for each arm of the study: Softip I electrode and conventional insertion; Softip I electrode and manual Advance Off-Stylet insertion; Softip I electrode and Advance Off-Stylet insertion with an early experimental insertion tool; Softip II prototype electrode and manual Advance Off-Stylet insertion; and Softip II prototype and Advance Off-Stylet insertion with a prototype insertion tool. The temporal bones were dehydrated and embedded in epoxy and used for the microgrinding procedure. Resulting images were documented and compared with conventional radiographic images. RESULTS: Our results showed that, especially when using the conventional insertion technique with Softip I electrode arrays, basilar membrane perforations were observable. Using the prototype insertion tool, good placement of the electrode array but also two basilar membrane perforations (one with each type of electrode) were observed. In contrast, the Advance Off-Stylet insertion technique did not show basilar membrane perforation with Softip I and II electrodes and resulted in reliable perimodiolar placement of the arrays. CONCLUSION: Using microgrinding of temporal bones, the Advance Off-Stylet insertion technique was proven to enable more atraumatic insertions of Contour electrodes with Softip and to provide very reliable perimodiolar placements.

Basilar Membrane↗

PubMed2004

Diagnostic relevance of beta2-transferrin for the detection of cerebrospinal fluid fistulas.

OBJECTIVE: The beta(2)-transferrin assay is a specific method to identify cerebrospinal fluid (CSF). Hitherto, this test has not been widely used for the routine screening of patients with suspected CSF leakage. The purpose of this study was to investigate the clinical relevance of the identification of beta(2)-transferrin by comparing the test results with other diagnostic measures and intraoperative findings. DESIGN: Case series. PATIENTS: Retrospective analysis of 182 patients tested once or multiple times for beta(2)-transferrin. MAIN OUTCOME MEASURES: Information was obtained regarding different diagnostic procedures applied to diagnose CSF leakage. The effectiveness of those diagnostic measures was compared. RESULTS: The main indication to test for beta(2)-transferrin was posttraumatic rhinorrhea (25%), followed by spontaneous (22%) and postsurgical (22%) rhinorrhea. In 35 of 205 cases, beta(2)-transferrin was detected in the tested specimens. Thirteen of these required surgical intervention for treatment of the CSF fistula, and the leakage site was identified in all of them. Taking all results into consideration, the highest correlation was observed between the beta(2)-transferrin assay, intrathecal fluorescein application, and surgical exploration. CONCLUSIONS: The beta(2)-transferrin assay is a reliable method for confirming suspected CSF and should be used as a primary screening method in all patients with suspected CSF leakage. Although less invasive, the beta(2)-transferrin assay almost matches the high sensitivity achieved by exploratory surgery and intrathecal application of fluorescein. However, the possibility of bias should be carefully considered, and in particular, negative results should be critically compared with clinical symptoms and with results from other diagnostic procedures.

Adolescent↗

PubMed2003

Hearing and hair cells are protected by adenoviral gene therapy with TGF-beta1 and GDNF.

Glial cell line-derived neurotrophic factor (GDNF) overexpression in the inner ear can protect hair cells against degeneration induced by aminoglycoside ototoxicity. The protective efficiency of GDNF increases when it is combined with co-factors such as transforming growth factor beta1 (TGF-beta1), a ubiquitous cytokine. The aim of this study was to determine whether TGF-beta1 receptors are expressed in the inner ear and whether a cocktail of GDNF and TGF-beta1 transgenes provides enhanced protection of the inner ear against ototoxic trauma. Using RT-PCR analysis, we determined that both TGF-beta1 receptors, type 1 and 2 are present in rat cochlea. We co-inoculated two adenoviral vectors, one encoding human TGF-beta1 gene (Ad.TGF-beta1) and the other encoding human GDNF gene (Ad.GDNF) into guinea pig cochleae 4 days prior to injecting an ototoxic dose of aminoglycosides. Inoculated ears had better hearing and fewer missing inner hair cells after exposure to the aminoglycoside ototoxicity, as compared with controls and ears treated only with Ad.GDNF. Cochleae with TGF-beta1 overexpression exhibited fibrosis in the scala tympani regardless of the presence of GDNF. Our results suggest that the adenovirus-mediated overexpression of GDNF and TGF-beta1 can be used in combination to protect cochlear hair cells and hearing from ototoxic trauma.

Adenoviridae↗

PubMed2002

Glial cell line-derived neurotrophic factor and chronic electrical stimulation prevent VIII cranial nerve degeneration following denervation.

As with other cranial nerves and many CNS neurons, primary auditory neurons degenerate as a consequence of loss of input from their target cells, the inner hair cells (IHCs). Electrical stimulation (ES) of spiral ganglion cells (SGCs) has been shown to enhance their survival. Glial cell line-derived neurotrophic factor (GDNF) has also been shown to increase survival of SGCs following IHC loss. In this study, the combined effects of the GDNF transgene delivered by adenoviral vectors (Ad-GDNF) and ES were tested on SGCs after first eliminating the IHCs. Animal groups received Ad-GDNF or ES or both. Ad-GDNF was inoculated into the cochlea of guinea pigs after deafening, to overexpress human GDNF. ES-treated animals were implanted with a cochlear implant electrode and chronically stimulated. A third group of animals received both Ad-GDNF and ES (GDNF/ES). Electrically evoked auditory brainstem responses were recorded from ES-treated animals at the start and end of the stimulation period. Animals were sacrificed 43 days after deafening and their ears prepared for evaluation of IHC survival and SGC counts. Treated ears exhibited significantly greater SGC survival than nontreated ears. The GDNF/ES combination provided significantly better preservation of SGC density than either treatment alone. Insofar as ES parameters were optimized for maximal protection (saturated effect), the further augmentation of the protection by GDNF suggests that the mechanisms of GDNF- and ES-mediated SGC protection are, at least in part, independent. We suggest that GDNF/ES combined treatment in cochlear implant recipients will improve auditory perception. These findings may have implications for the prevention and treatment of other neurodegenerative processes. .

Animals↗

PubMed2002

Gene expression profiles of the rat cochlea, cochlear nucleus, and inferior colliculus.

High-throughput DNA microarray technology allows for the assessment of large numbers of genes and can reveal gene expression in a specific region, differential gene expression between regions, as well as changes in gene expression under changing experimental conditions or with a particular disease. The present study used a gene array to profile normal gene expression in the rat whole cochlea, two subregions of the cochlea (modiolar and sensorineural epithelium), and the cochlear nucleus and inferior colliculus of the auditory brainstem. The hippocampus was also assessed as a well-characterized reference tissue. Approximately 40% of the 588 genes on the array showed expression over background. When the criterion for a signal threshold was set conservatively at twice background, the number of genes above the signal threshold ranged from approximately 20% in the cochlea to 30% in the inferior colliculus. While much of the gene expression pattern was expected based on the literature, gene profiles also revealed expression of genes that had not been reported previously. Many genes were expressed in all regions while others were differentially expressed (defined as greater than a twofold difference in expression between regions). A greater number of differentially expressed genes were found when comparing peripheral (cochlear) and central nervous system regions than when comparing the central auditory regions and the hippocampus. Several families of insulin-like growth factor binding proteins, matrix metalloproteinases, and tissue inhibitor of metalloproteinases were among the genes expressed at much higher levels in the cochlea compared with the central nervous system regions.

Animals↗

PubMed2001

Gene-based therapy for inner ear disease.

Environmental inner ear insults often lead to hair cell injury and loss. Therapeutic measures for the prevention of hair cell loss are currently limited. Several reports have demonstrated the applicability of growth factors for hair cell protection. The goal of the experiments presented here was to assess the protective capability of the human GDNF transgene against noise trauma in the guinea pig cochlea. The left ears of guinea pigs were inoculated with a recombinant adenovirus with a human GDNF insert (Ad.GDNF). Four days later, animals were exposed to noise trauma. One week later, animals were sacrificed and hair cells counted in the left (inoculated) and right (non-inoculated) ears. Auditory brainstem thresholds were measured before the inoculation and just prior to sacrifice. Control groups included inoculation with a reporter gene vector (Ad.lacZ) and Ad.GDNF in normal ears with no noise exposure. The results show that intracochlear inoculation with adenovirus into normal ears does not compromise hair cell counts and ABR thresholds. Both Ad.GDNF and Ad.lacZ vectors can protect the cochlear hair cells and hearing from the noise insult. The difference between the protection afforded by Ad.GDNF and that of the Ad.lacZ vector is not statistically significant. The mechanism of Ad.lacZ protection needs to be elucidated. The data demonstrate the general feasibility of gene therapy for over-expression of neurotrophic factors against noise trauma, and emphasize the complexity of the technique and the problems of variability between subjects.

Journal Article↗

PubMedDate not supplied

From gene identification to gene therapy.

Inner ear disease due to hair cell loss is common, and no restorative treatments for the balance and hearing impairment are currently available. To develop clinical means for enhancing protection and regeneration in the inner ear, it is necessary to understand the molecular basis for hereditary and acquired deafness and vestibular disorders. One approach is to identify and characterize genes that regulate protection or repair in other systems. For that purpose, we have used the differential display assay and compared gene expression between normal and acoustically traumatized inner ears of chicks. Several chick cDNAs that were identified are considered as candidates for roles in the reparative process that follows trauma in the basilar papilla. The mammalian vestibular epithelium has a limited regenerative capability. To identify genes that may participate in the regenerative response, we have used gene arrays profiling, comparing normal to drug-traumatized vestibular epithelia. We identified several genes that are differentially expressed in traumatized vestibular epithelium, including several insulin-like growth factor-I binding proteins. To use this molecular knowledge for enhancing protection and repair in the organ of Corti, it is necessary to overexpress the genes of choice in the inner ear. Using viral-mediated gene transfer, we overexpressed transgenic glial cell line-derived neurotrophic factor and demonstrated a robust protective effect against acoustic and ototoxic inner ear trauma. Future identification of the genes that are important for protection and regeneration, along with improved gene transfer technology, will allow the use of gene therapy for treating hereditary and environmental inner ear disease.

Animals↗

PubMedDate not supplied

A glucocorticoid reduces adverse effects of adenovirus vectors in the cochlea.

Gene transfer using a recombinant adenovirus is a powerful tool for research and clinical applications, but its cytotoxicity and immune response limit its use, especially when repeated application of the vector is necessary. This study investigated the effects of dexamethasone (DEX)-induced immunosuppression on the outcome of adenovirus gene transfer in guinea pig inner ears. Animals received DEX for 29 days. Their inner ear was inoculated with 5 micro l of adenovirus vector twice, on days 5 and 26. Auditory brainstem response was measured on days 1, 8 and 29. The animals were sacrificed on day 29, and reporter gene expression was evaluated. In control animals that received no DEX, postinoculation threshold shifts and lesions in the organ of Corti were observed and reporter gene expression was absent. In contrast, DEX-treated ears were largely protected, and transduction of inner ear cells was readily apparent. These data demonstrate that immunosuppressive treatment can reduce the negative consequences of repeated adenovirus-mediated gene therapy.

Adenoviridae Infections↗