Biomedical subjects

Hans-Peter Zenner

Publications and source records attributed to Hans-Peter Zenner.

At least 19 recordsLinked to original sources

PubMed2006

Cochlear pharmacokinetics with local inner ear drug delivery using a three-dimensional finite-element computer model.

HYPOTHESIS: Cochlear fluid pharmacokinetics can be better represented by three-dimensional (3D) finite-element simulations of drug dispersal. BACKGROUND: Local drug deliveries to the round window membrane are increasingly being used to treat inner ear disorders. Crucial to the development of safe therapies is knowledge of drug distribution in the inner ear with different delivery methods. Computer simulations allow application protocols and drug delivery systems to be evaluated, and may permit animal studies to be extrapolated to the larger cochlea of the human. METHODS: A finite-element 3D model of the cochlea was constructed based on geometric dimensions of the guinea pig cochlea. Drug propagation along and between compartments was described by passive diffusion. To demonstrate the potential value of the model, methylprednisolone distribution in the cochlea was calculated for two clinically relevant application protocols using pharmacokinetic parameters derived from a prior one-dimensional (1D) model. In addition, a simplified geometry was used to compare results from 3D with 1D simulations. RESULTS: For the simplified geometry, calculated concentration profiles with distance were in excellent agreement between the 1D and the 3D models. Different drug delivery strategies produce very different concentration time courses, peak concentrations and basal-apical concentration gradients of drug. In addition, 3D computations demonstrate the existence of substantial gradients across the scalae in the basal turn. CONCLUSION: The 3D model clearly shows the presence of drug gradients across the basal scalae of guinea pigs, demonstrating the necessity of a 3D approach to predict drug movements across and between scalae with larger cross-sectional areas, such as the human, with accuracy. This is the first model to incorporate the volume of the spiral ligament and to calculate diffusion through this structure. Further development of the 3D model will have to incorporate a more accurate geometry of the entire inner ear and incorporate more of the specific processes that contribute to drug removal from the inner ear fluids. Appropriate computer models may assist in both drug and drug delivery system design and can thus accelerate the development of a rationale-based local drug delivery to the inner ear and its successful establishment in clinical practice.

Animals↗

PubMed2006

Hyposmotic stimulation-induced nitric oxide production in outer hair cells of the guinea pig cochlea.

Nitric oxide (NO) production during hyposmotic stimulation in outer hair cells (OHCs) of the guinea pig cochlea was investigated using the NO sensitive dye DAF-2. Simultaneous measurement of the cell length and NO production showed rapid hyposmotic-induced cell swelling to precede NO production in OHCs. Hyposmotic stimulation failed to induce NO production in the Ca(2+)-free solution. L-N(G)-nitroarginine methyl ester (L-NAME), a non-specific NO synthase inhibitor and gadolinium, a stretch-activated channel blocker inhibited the hyposmotic stimulation-induced NO production whereas suramin, a P2 receptor antagonist did not. S-nitroso-N-acetylpenicillamine (SNAP), a NO donor inhibited the hyposmotic stimulation-induced increase in the intracellular Ca(2+) concentrations ([Ca(2+)](i)) while L-NAME enhanced it. 1H-[1,2,4]oxadiazole[4,3a]quinoxalin-1-one, an inhibitor of guanylate cyclase and KT5823, an inhibitor of cGMP-dependent protein kinase (PKG) mimicked effects of L-NAME on the Ca(2+) response. Transient receptor potential vanilloid 4 (TRPV4), an osmo- and mechanosensitive channel was expressed in the OHCs by means of immunohistochemistry. 4alpha-phorbol 12,13-didecanoate, a TRPV4 synthetic activator, induced NO production in OHCs. These results suggest that hyposmotic stimulation can induce NO production by the [Ca(2+)](i) increase, which is presumably mediated by the activation of TRPV4 in OHCs. NO conversely inhibits the Ca(2+) response via the NO-cGMP-PKG pathway by a feedback mechanism.

Animals↗

PubMed2006

Technical note on microcatheter implantation for local inner ear drug delivery: surgical technique and safety aspects.

HYPOTHESIS: Despite its invasiveness, the temporary implantation of a microcatheter into the middle ear cavity is an appropriately safe method for providing continuous drug delivery to the inner ear. BACKGROUND: For the application of drugs to the inner ear, different delivery strategies are available ranging from intratympanic injections to temporarily implanted microcatheters. It has recently been demonstrated that the choice of the drug delivery system influences the pharmacokinetics in the inner ear. If a continuous drug application over several weeks is required, a secure placement of the delivery device (i.e., the microcatheter) is necessary to guarantee efficient drug delivery and to avoid unwanted side effects. STUDY DESIGN: Retrospective chart review. MATERIALS AND METHODS: During 2000 to 2005, 25 patients with acute unilateral severe-to-profound hearing loss or anacusis and failure of systemic high-dose glucocorticoid and rheological therapy were offered an intratympanic delivery of glucocorticoids via a temporarily implanted catheter and an external pump for up to 4 weeks as a salvage treatment option. The standardized surgical implantation and fixation technique developed for the microcatheter were characterized by six elements: 1) a medial and a lateral tunnel connected by a groove in the posterior wall of the bony ear canal, 2) stabilization of the catheter with bone wax and soft tissue plugs in the tunnels, 3) an ear canal packing, 4) a series of fixating sutures along the catheter, 5) an adhesive dressing, and 6) additional tapes at the connecting line between pump and catheter. At the end of the implantation period, the catheter was removed by a second surgical procedure allowing for evaluation of the catheter position and the condition of the middle ear space. RESULTS: Adverse events included catheter dislocation, catheter obstruction, formation of mild granulation tissue in the middle ear cavity, tympanic membrane defects, and ear canal skin defects. With introduction of an improved implantation and fixation technique, the number of catheter dislocations could be significantly reduced. No complications were observed on long-term follow-up. CONCLUSION: If the pharmacokinetics or pharmacodynamics of a specific local inner ear therapy approach requires a continuous intratympanic drug application (e.g., to restore hearing in patients with severe or profound hearing loss), the temporary implantation of a microcatheter by a standardized surgical technique is a feasible and appropriately safe method for providing continuous drug delivery to the inner ear.

Catheterization↗

PubMed2005

Phenotypic characterization of a DFNA6 family showing progressive low-frequency sensorineural hearing impairment.

Only three autosomal dominant hearing loss loci (DFNA1, DFNA6/14/38 and DFNA54) have been reported to be associated with predominantly low-frequency (<2kHz) sensorineural hearing impairment (LFSNHI). The DFNA6 locus was previously mapped to chromosome 4p16.3. It was showed that WFS1 is located in this region. This study presents a six-generation family from Hungary with nonsyndromic, post-lingual, bilateral, symmetric, progressive LFSNHI, that discloses positive linkage to the DFNA6 region. Eleven genetically affected family members have LFSNHI. The HI is started before the age of 25 years. The severity of HI varies from mild to moderate, related to age. Progression was mild but significant at all frequencies causing a flat type audiogram. High-resolution temporal bone CT scan showed normal external, middle and inner ear without any osseus malformations in the temporal bone. Studying genotype-phenotype correlations will enhance our understanding of normal and disturbed hearing process.

Adolescent↗

PubMed2005

High frequency of ENG and ALK1/ACVRL1 mutations in German HHT patients.

Morbus Osler or HHT (hereditary hemorrhagic telangiectasia) is a disorder of the fibrovascular tissue that is inherited in an autosomal dominant way with frequency rates between 1:2,500 and 1:40,000. The disease provokes malformations of the blood vessels sometimes resulting in life-threatening complications. Presently, two genes involved in the development of HHT have been identified: ACVRL1 and ENG. Both of them encode proteins that belong to the TGF-beta receptor complex family and play an essential role in the formation of the vascular system. Recently, several mutations in ACVRL1 and ENG have been described in other European populations. However, no data concerning mutation frequencies in the German population have been reported so far. Therefore, we screened our collective of German HHT patients (28 single cases and 11 familial cases) for mutations in both genes by direct sequencing. We detected 11 mutations already described elsewhere and 19 novel ones. Furthermore, evidence for the pathogenic role of four new missense mutations was collected by screening a healthy control collective using RFLP analysis. Interestingly, the majority of ACVRL1 mutations represented missense mutations, whereas mutations in ENG mostly resulted in a shortened protein. Our results demonstrate the importance of ACVRL1 and ENG mutations in German HHT patients displaying mutation frequencies over 80%.

Activin Receptors, Type II↗

PubMed2005

Outcomes research analysis of continuous intratympanic glucocorticoid delivery in patients with acute severe to profound hearing loss: basis for planning randomized controlled trials.

CONCLUSIONS: The data presented herein form the basis for conducting randomized placebo-controlled clinical trials evaluating the safety and efficacy of salvage treatment in patients with idiopathic sudden severe sensorineural hearing loss (but not anacusis) refractory to initial systemic therapy. Comparison of different application protocols and drug delivery systems will allow assessment of the value of continuous versus intermittent intratympanic glucocorticoid drug delivery. OBJECTIVES: To describe and critically evaluate the results of continuous intratympanic glucocorticoid delivery in patients with acute unilateral severe and profound sensorineural hearing loss refractory to initial systemic therapy and to compare the outcome with a historical control group. MATERIAL AND METHODS: In a retrospective chart review, treatment results were analyzed in 23 patients with acute severe and profound hearing loss and failure of systemic standard therapy who received a continuous intratympanic delivery of glucocorticoids as a salvage treatment. Audiological results were compared within the local therapy group and with the results of an historical control group who did not receive salvage treatment. The study and control groups were matched with respect to hearing loss after initial systemic treatment failure. RESULTS: The average pure-tone threshold after intratympanic salvage treatment showed a statistically significant improvement of 15 dB (95% CI 7-24 dB; p<0.001). After exclusion of patients with complete anacusis, i.e. a non-measurable hearing threshold, the local therapy group showed a significantly better improvement (mean 19 dB; 95% CI 6-32 dB) than the historical control group (mean 5 dB; 95% CI -2-11 dB; p<0.05).

Adolescent↗

PubMed2004

Chromosome 11 monosomy in conjunction with a mutated SDHD initiation codon in nonfamilial paraganglioma cases.

Paragangliomas of the head and neck region are a group of rare, usually benign, slow-growing tumors developing from paraganglionic chemoreceptors in most patients. Mutations in a subunit of the mitochondrial enzyme II complex (succinate dehydrogenase [SDHD]) were shown to be responsible for the formation of paragangliomas. In addition, loss of heterozygosity (LOH) on chromosome 11, mainly in 11q23 (PGL1), was observed recently. We analyzed DNA derived from tumor sections of three unrelated paraganglioma patients (one case with multiple paragangliomas, two cases with single tumors; all of them sporadic cases) for mutations in the SDHD gene by direct sequencing. Microsatellite-based LOH was performed, and events of chromosomal loss were validated by fluorescence in situ hybridization (FISH) on paraffin-embedded tumor and normal tissue by using centromeric satellite DNA. Sequence analysis revealed mutations in SDHD exon 1 in all patients, affecting the initiation codon (M1V). Another alteration was detected in exon 2 but was lacking in tumor DNA and therefore classified as polymorphism (H50R). LOH and FISH analyses demonstrated partial/total monosomy for chromosome 11 in the tumor samples tested. A common genetic mechanism appears to be the pathophysiologic basis for sporadic tumor development because the proposed two-hit model comprising both LOH and point mutation is manifest in our patients. Loss of chromosome 11 regions, including the deletion of PGL1 and PGL2 loci, may result in a more severe phenotype, as exemplified by the development of multiple tumors in one of the patients.

Adult↗

PubMed2004

Nonmuscle myosin heavy-chain gene MYH14 is expressed in cochlea and mutated in patients affected by autosomal dominant hearing impairment (DFNA4).

Myosins have been implicated in various motile processes, including organelle translocation, ion-channel gating, and cytoskeleton reorganization. Different members of the myosin superfamily are responsible for syndromic and nonsyndromic hearing impairment in both humans and mice. MYH14 encodes one of the heavy chains of the class II nonmuscle myosins, and it is localized within the autosomal dominant hearing impairment (DFNA4) critical region. After demonstrating that MYH14 is highly expressed in mouse cochlea, we performed a mutational screening in a large series of 300 hearing-impaired patients from Italy, Spain, and Belgium and in a German kindred linked to DFNA4. This study allowed us to identify a nonsense and two missense mutations in large pedigrees, linked to DFNA4, as well as a de novo allele in a sporadic case. Absence of these mutations in healthy individuals was tested in 200 control individuals. These findings clearly demonstrate the role of MYH14 in causing autosomal dominant hearing loss and further confirm the crucial role of the myosin superfamily in auditive functions.

Amino Acid Sequence↗

PubMed2004

GJB2 mutations in patients with non-syndromic hearing loss from Northeastern Hungary.

Mutations in the GJB2 gene encoding the gap-junction protein connexin 26 have been identified in many patients with childhood hearing impairment (HI). One single mutation, c.35delG, accounts for the majority of mutations in Caucasian patients with HI. In the present study we screened 500 healthy control individuals and a group of patients with HI from Northeastern Hungary for GJB2 mutations. The patients' group consisted of 102 familial from 28 families and 92 non-familial cases. The most common mutation in the Hungarian population is the c.35delG, followed by the c.71G>A (p.W24X) mutation. 34.3% of the patients in the familial group were homozygous, and 17.6% heterozygous for 35delG. In the non-familial group the respective values were 37% and 18% (allele frequency: 46.2%). In the general population an allele frequency of 2.4% was determined. Several patients were identified with additional, already described or new GJB2 mutations, mostly in heterozygous state. The mutation c.380G>A (p.R127H) was formerly found only in heterozygous state and its disease relation was controversial. We demonstrated the presence of this mutation in a family with three homozygous patients and 4 heterozygous unaffected family members, a clear indication of recessively inherited HI. Furthermore, we provided evidence for the pathogenic role of two new mutations, c.51C>A (p.S17Y) and c.177G>T (p.G59V), detected in the present study. In the latter case the pattern of inheritance might be dominant. Our results confirm the importance of GJB2 mutations in the Hungarian population displaying mutation frequencies that are comparable with those in the Mediterranean area.

Adolescent↗

PubMed2004

Cognitive tinnitus sensitization: behavioral and neurophysiological aspects of tinnitus centralization.

OBJECTIVE: Acquired centralized tinnitus (ACT) is the most frequent type of chronic tinnitus. We introduce a cognitive neurophysiological ACT hypothesis based on centralized cognitive sensitization processes. MATERIAL AND METHODS: Published cognitive sensitization processes were reviewed using PubMed. Furthermore, a Cochrane analysis was performed. RESULTS: Patients frequently perceive tinnitus as being extremely loud although audiological tinnitus-matching measures reveal that its loudness levels are low. An important principle of central tinnitus processing is that individual tinnitus appraisal is directly linked to neuronal networks in the brain responsible for the production of emotions and cognitions. Cognitive processes may be associated with a reduction in the tinnitus cognition threshold, resulting in hypersensitivity of cognition. The underlying mechanism is known as sensitization and is suggested to be a specific learning process. CONCLUSIONS: ACT may be associated with a specific learning process allowing increased tinnitus awareness and continuous appraisal. The underlying mechanism, the cognitive tinnitus sensitization process, is associated with a decrease in the tinnitus cognition threshold. The sensitization contributes to the extremely loud cognition of the tinnitus signal. The associated audiological cognitive discrepancy can be used clinically and diagnostically to identify patients for cognitive testing. The sensitization model does not require tinnitus hyperactivity.

Attention↗

PubMed2004

A genotype-phenotype correlation with gender-effect for hearing impairment caused by TECTA mutations.

BACKGROUND: Alpha-tectorin is a noncollagenous component of the tectorial membrane which plays an essential role in auditory transduction. In several DFNA12 families mutations in TECTA, the gene encoding alpha-tectorin, were shown to cause hearing impairment (HI) with different phenotypes depending on the location of the mutation. METHODS/RESULTS: Here we report a Turkish family displaying autosomal dominant inherited HI. Linkage analysis revealed significant cosegregation (LOD score: 4.6) of the disease to markers on chromosome 11q23.3- q24. This region contains the TECTA gene which was subsequently sequenced. A nucleotide change in exon 13, 4526T>G, was detected leading to a substitution from cysteine to glycine at codon 1509 of the TECTA protein. This cysteine is located in vWFD4 domain, a protein domain which is supposed to be involved in disulfide bonds and protein-protein interactions. CONCLUSIONS: It is conspicuous that the phenotype in this family correlates with other families, also displaying mutations involving conserved cysteines. In all three families these mutations result in progressive HI involving high frequencies. In contrast, mutations which are not affecting the vWFD domains seem to provoke mid-frequency sensorineural HI. Furthermore, evaluation of clinical data in our family revealed a gender effect for the severity of hearing impairment. Males were significantly more affected than females. The identification of the third family displaying a missense mutation in the vWFD domain of alpha-tectorin underlines the phenotype-genotype correlation based on different mutations in TECTA.

Age Factors↗

PubMed2004

[1D-and 3D- computer simulation for experimental planning and interpretation of pharmacokinetic studies in the inner ear after local drug delivery].

The local delivery of drugs to the cochlea is a promising alternative to systemic treatment of inner ear disorders. Whilst new drugs are being developed for this purpose, it is important to determine the time course and total dose required for the various target regions within the inner ear. Due to the small fluid spaces of the inner ear and the resulting experimental and analytical difficulties, many animal studies have only obtained one sample per animal. This results in limited information about drug time courses at specific locations in the inner ear. We show here how computer models considering general pharmacokinetic principles and inner ear geometry are used for application of the 3R-principle in animal research while avoiding experimental sampling artefacts. This can be achieved by: (1) careful planning and interpretation of experiments to study pharmacokinetics in the inner ear, (2) optimising volume sampling techniques, (3) facilitating the use of advantageous, continuous sampling methods like microdialysis and (4) developing a 3D-model that will permit consideration of the complex geometry of the inner ear when transferring results from one species to another.

Animal Testing Alternatives↗

PubMed2003

Aquaporin-mediated fluid regulation in the inner ear.

1. The sensory functions of the inner ear (hearing and balance) critically depend on the precise regulation of two fluid compartments of highly desparate ion composition, i.e., the endolymph and the perilymph. 2. The parameters volume, ion composition, and pH need to be held at homeostasis irrespective of the hydration status of the total organism. 3. Specific cellular water channels, aquaporins, have been shown to be essential for the fluid regulation of several organs, e.g., kidney, lung, and brain. 4. Because of functional similarities of water regulation in the kidney and inner ear this review initially summarizes some aquaporin functions in the kidney and then focuses on 6 out of 11 mammalian aquaporins that are present in the inner ear (AQP1-6). 5. Their potential role in the inner ear fluid control will be discussed on the basis of the respective expression patterns and individual pore properties. 6. Further, a working model is presented of how the endolymphatic sac may contribute to inner ear fluid regulation.

Animals↗

PubMed2003

Tracheal stenosis and obliteration above the tracheostoma after percutaneous dilational tracheostomy.

Percutaneous dilational tracheotomy (PDT) as opposed to the conventional surgical tracheostomy is a procedure that allows airway control in critically ill patients without surgical exposure of the trachea. Based on the Seldinger technique, dilators are passed along a guiding wire through a small neck incision into the trachea under endoscopic surveillance. This separates the tracheal rings and results in a stoma. As opposed to the regular surgical tracheostoma, a PDT-stoma is not epithelialized. The procedure is cost effective and little time consuming. Considering the increasing number of performed PDTs in the last few years, we feel a need to be aware of possible long-term complications. Thus, in this report, we describe three cases of tracheal stenosis/obliteration after a PDT procedure. In all cases, tracheal narrowing occurred above the level of the stoma. This suggests a procedure-related mechanism, i.e., tracheal ring invagination and the consecutive development of granulation tissue, rather than a mechanism based on the duration of the cannula's placement, which would normally produce the stenosis below the stoma in the area of the cuff. Toward the end of the article, we provide evidence for this hypothesis and thus present a new subset of long-term complications after PDT.

Adolescent↗

PubMed2002

A patient database application for Hereditary Deafness Epidemiology and Clinical Research (H.E.A.R.): an effort for standardization in multiple languages.

One of the most challenging and neglected issues in medicine is the effective recording of the data obtained from the patients. The "European Work Group on the Genetics of Hearing Impairment," which has been working since 1996, proposed a few questionnaires to collect data regarding the phenotype, ENT findings, audiological examination findings and other special investigations. In this study, a computerized patient database application named "Izmir H.E.A.R version 1.0," written in Delphi 4.0 for Windows for recording the patients with hearing problems, is presented. The application consists of a modular form, including information about identity, genetic condition, proband query, audiology and vestibular tests, phenotype, pedigree and special examinations, which allows data entry on all these issues. It has been developed by using the guidelines of Hereditary Deafness Epidemiology and Clinical Research (H.E.A.R.) and by the experience gained within the last 10 years by the authors. The target population of the program is the ENT clinicians, audiologists, epidemiologists, geneticists and researchers in the field. The main idea is to create a program serving the needs of both the daily routine work and research purposes and to distribute this program to the above-mentioned specialists, to encourage them to try the first version and to find a standard and/or better way to collect data. For this reason, the program aims to be multilingual, and the currently available languages are English, German, Spanish and Turkish.

Biomedical Research↗

PubMed2002

The incidence of acoustic trauma due to New Year's firecrackers.

While occupational noise is tightly regulated by various noise protection programs, some kinds of leisure noise have been poorly addressed. The aim of this study was to estimate prospectively the incidence of blast and explosion trauma due to the use of New Year's firecrackers in a western industrialized society. The results are based on 562 centers in Germany, including the otorhinolaryngology departments of 31 university hospitals and of 87 city hospitals as well as a random sample of specialized otorhinolaryngology private practices (n=444). After extrapolation of the number of reported cases to the number of hospitals and practices on duty, a total of 8,160 cases (95% confidence interval 7,515-8,805) was estimated giving an incidence of 9.9 per 100,000 inhabitants. There were three times as many men affected as woman. The incidence for the age group of 6 to 25 years was much higher: 28 per 100,000 with a maximum of 107 per 100,000 for 19-year-old men. These incidences suggest that firecrackers may pose a momentous public health risk. Because of the medical and economic importance of incurable sensorineural hearing loss, it is the task of public health services to promote the effective prevention of irreversible damage to the hearing organ.

Adolescent↗

PubMed2002

Thyroid hormone is a critical determinant for the regulation of the cochlear motor protein prestin.

The most impressive property of outer hair cells (OHCs) is their ability to change their length at high acoustic frequencies, thus providing the exquisite sensitivity and frequency-resolving capacity of the mammalian hearing organ. Prestin, a protein related to a sulfate/anion transport protein, recently has been identified and proposed as the OHC motor molecule. Homology searches of 1.5 kb of genomic DNA 5' of the coding region of the prestin gene allowed the identification of a thyroid hormone (TH) response element (TRE) in the first intron upstream of the prestin ATG codon. Prestin(TRE) bound TH receptors as a monomer or presumptive heterodimer and mediated a triiodothyronine-dependent transactivation of a heterologous promotor in response to triiodothyronine receptors alpha and beta. Retinoid X receptor-alpha had an additive effect. Expression of prestin mRNA and prestin protein was reduced strongly in the absence of TH. Although prestin protein typically was redistributed to the lateral membrane before the onset of hearing, an immature pattern of prestin protein distribution across the entire OHC membrane was noted in hypothyroid rats. The data suggest TH as a first transcriptional regulator of the motor protein prestin and as a direct or indirect modulator of subcellular prestin distribution.

5' Flanking Region↗

PubMed2002

Mutation A1555G in the 12S rRNA gene and its epidemiological importance in German, Hungarian, and Polish patients.

The A1555G mutation in the 12SrRNA gene has been associated with aminoglycoside induced and nonsyndromic sensorineural hearing impairment. In this study we analyzed Hungarian, Polish and German patients with nonsyndromic severe to profound hearing impairment of unknown origin for this mutation. The frequency of the A1555G mutation in the Hungarian hearing impaired population was below 1.8 %. Three out of 125 Polish patients carrying the A1555G mutation were identified. Among German patients one carrier was found (0.7 %) revealing a homoplastic A1555G mutation, whereas no mutation was detected in control individuals with normal hearing (frequency < 0.6%). In summary the frequencies of the A1555G mutation are low in the hearing impaired as well as in the normal population in Hungary, Poland and Germany. Since the importance of this mutation and its relationship with aminoglycoside exposure is not well understood yet, patients with nonsyndromic hearing impairment should be routinely screened for this mutation to avoid aminoglycoside induced hearing impairment due to increased sensitivity of maternal relatives.

Adult↗