Biomedical subjects

Mark Praetorius

Publications and source records attributed to Mark Praetorius.

9 recordsLinked to original sources

PubMed2006

Pharmacodynamics of adenovector distribution within the inner ear tissues of the mouse.

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.

Adenoviridae↗

PubMed2006

Alternobaric vertigo--really a hazard?

OBJECTIVE: To determine the prevalence of alternobaric vertigo (AV) in sport divers and to find out whether AV led to dangerous situations underwater. Furthermore, to examine whether objective neurootologic tests are associated with the manifestation of AV. DESIGN: Retrospective cohort study. PARTICIPANTS: Sixty-three sport divers with an average diving experience of 10 years and 650 dives were questioned regarding their medical and diving history and the manifestation of vertigo during diving. METHODS: Microscopic otoscopy, tympanometry, stapedius reflexes, hearing threshold for air and bone conduction, caloric video-oculography including analysis of the slow-phase velocity of the nystagmus, acoustic brain stem responses, and magnetic resonance imaging were performed to find possible differences between divers with and without AV. RESULTS: We found 17 divers with AV (27%). There was no significant difference in all measured parameters apart from sex and history of middle ear equalization difficulty in divers with AV. Ten (59%) of 17 female divers and 7 (15%) of 46 male divers experienced AV, representing a significant sex difference (p < 0.001). Correlation with our divers' outpatient clinic revealed that female divers had a significantly higher incidence of middle ear equalization disorders which could be an explanation for the predominance of female divers with symptoms of AV. None of the divers reported any dangerous or life-threatening situations following AV. Whether AV leads to dangerous situations underwater remains unclear, but this hypothesis is not supported by our data. CONCLUSION: Alternobaric vertigo is a common finding in divers. In our study group, female divers had a four-time higher risk to suffer AV. Our data do not support the thesis that AV is a life-threatening condition.

Acoustic Impedance Tests↗

PubMed2004

Increased noise sensitivity and altered inner ear MENA distribution in VASP-/- mice.

Vasodilator-stimulated phosphoprotein (VASP) and mammalian-enabled protein (MENA) share similar cellular localisation and functions (signal transduction pathways, regulation of actin cytoskeleton dynamics). Functional substitution and compensation among Ena/VASP proteins have been proposed as the reason for the absence of major morphological and functional deficits in VASP-/- mice. The aim of this study was to investigate VASP expression in the mouse cochlea, to analyse cochlear function in VASP-/- mice compared with wildtype mice, and to analyse cochlear MENA distribution taking into account that MENA protein might compensate VASP loss in the cochlea of VASP-/- mice. We confirmed specific VASP expression in the pillar cells of the mice organ of Corti as previously reported for rat cochlea. By analysing the hearing function in VASP-/- mice, we found no differences in auditory brainstem responses and distortion product otoacoustic emissions from those of wildtype mice but evidence for an increased noise sensitivity at lower frequencies. When MENA protein levels in cochlea tissue were tested in mutant and wildtype mice by Western blot analysis, no significant differences were found, as was also seen with regard to MENA mRNA levels in laser-microdissected single pillar cells. Most surprisingly, however, MENA protein was absent in pillar cells of VASP-/- mice, whereas it was detected in other cochlear cells. The finding of a cell-specific, and not organ-specific, redundancy of MENA protein expression noted for the first time in VASP-/- mice is proposed as the reason for the observed distinct cochlear phenotype.

Animals↗

PubMed2004

Drug delivery to the inner ear using gene therapy.

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.

Administration, Topical↗

PubMed2003

Expression of VASP and zyxin in cochlear pillar cells: indication for actin-based dynamics?

Vasodilator-stimulated phosphoprotein (VASP) is a member of the ENA/VASP-protein family. VASP is considered to be a crucial factor in the regulation of actin dynamics, which involves processes such as motility and cell adhesion, e.g. in filopodia or growth cones. In these processes zyxin acts as an important partner of VASP and is particularly concentrated at sites where VASP-dependent actin dynamics occur. Based on indirect evidence that actin-mediated dynamics may effect the mechanical properties of the cochlea, we have investigated expression of VASP and zyxin in the postnatal and adult rat cochlea using polymerase chain reaction and Western blot approaches, as well as immunohistochemistry and confocal microscopy. Besides an expected expression in vessels and fibroblasts, VASP and zyxin expression was also observed in pillar cells. Here, the staining was restricted to the head and foot plate of the pillar cells. Onset of VASP expression in pillar cells coincided with the beginning of hearing. In pillar cells, VASP and zyxin were co-localised with pan-actin, suggesting actin-based dynamics in these cochlear cells, which until now were rather presumed to form a highly rigid bridge between the inner and outer sensory cells. Thus, pillar cells may be more dynamically involved in controlling longer-lasting mechanical properties of the cochlea as hitherto presumed.

Actins↗

PubMed2003

Dural cell culture. A new approach to study duraplasty.

Fistulas of the cerebrospinal fluid are often repaired by insertion of grafts of various kinds. However, current knowledge of wound healing after graft insertion is limited, and only a few animal studies are available. The objective of this study is to test whether an in vitro model is suited to analyze cellular healing aspects after duraplasty and to assess dura substitutes in such conditions in regard to their surface attractiveness for cellular migration from the dura margins. Harvested dura pieces from minipigs were perforated to mimic central dura lesions, placed on various coated surfaces (collagen, laminin, poly-L-lysine) or grafts, and investigated in a cell culture for cellular closure of the perforation. Cellular migration from the dura into the central perforation was noted on collagen-coated surfaces and when defects were filled with collagen gels, but there was no cell growth on surfaces with poly-L-lysine or laminin coating. Immunocytochemistry identified the migrating cells mainly as fibroblasts with some intermingled epithelial cells. Scanning electron microscopy proved cellular closure of defects after dura placement on allogenic non-crosslinked collagen transplants. Less cellular migration was observed on poly-P-dioxanon sheets, while no cells migrated into the central dura perforation after placement on a cartilage substitute. Cell counting indicated enhanced cellular closure of the dura opening after introduction of insulin or fibroblast growth factor (sign test for both: 0.031). Our study succeeded in establishing a cell culture model for duraplasty and indicated cellular migration from the dura borders at the site of the defect during the wound healing process. The cell culture model presented in this report shows that collagen grafts are best suited for duraplasty. In accordance with the immunocytological finding of fibroblast migration from the dura borders additional application of fibroblast-stimulating growth factors accelerated cellular defect closure.

Animals↗

PubMed2002

First evidence of genetic imbalances in angiofibromas.

OBJECTIVE/HYPOTHESIS: Angiofibromas are clinically well characterized by their origin at the posterior lateral nasal wall close to the sphenopalatine foramen, their occurrence in male adolescent patients, and the histological findings of a benign fibrovascular neoplasm with irregular, endothelium-lined vascular spaces in a fibrous stroma. However, their etiology and genetic causes remain unknown. The present study addresses genetic imbalances in angiofibromas. STUDY DESIGN: The present pilot study compared genomic hybridization in three angiofibromas to search for chromosomal abnormalities in this rare tumor. METHODS: Fluorescence-marked normal DNA and angiofibroma DNA were compared using genomic hybridization screening to detect chromosomal abnormalities. Their binding ratio to metaphase chromosomes were analyzed by special digital image analysis. RESULTS: Chromosomal gains and losses showing a high level of agreement were detected in all three angiofibromas. Specifically, DNA gains were observed on chromosomes 3q, 4q, 5q, 6q, 7q, 8q, 12p, 12q, 13q, 14q, 18q, 21q, and X, and DNA losses were screened on chromosomes 17, 19p, 22q, and Y. Finding chromosomal abnormalities at the sex chromosomes X and Y of this rare tumor is remarkable. Concurrent chromosomal gain on 8q12q22 was noted in all three tumor specimens. CONCLUSIONS: Comparative genomic hybridization is suitable for screening angiofibromas on a genetic level. The results on these screens indicate that further genetic investigations of this rare benign tumor may provide more details about the tumor's genetic abnormalities and perhaps clarify the etiology of angiofibromas.

Angiofibroma↗

PubMedDate not supplied

A novel vestibular approach for gene transfer into the inner ear.

The aim of gene transfer to the cochlea and vestibular organ is to protect the inner ear from different disorders. Although various vectors for gene delivery have been used with some success, there remains a need for a reliable transfer of genes into the inner ear without damaging cochlear function. Here, we have tested a novel application method for gene transfer into the rat inner ear in vivo using herpes simplex virus type-1(HSV-1)-based amplicon vectors. Our goal was to find an entry route into the inner ear that leaves its function intact. Besides other non-invasive and invasive application techniques, we applied the viral vector via injection through a small opening of the utriculus. Using this method, efficient -galactosidase reporter gene expression was achieved in nearly all neurons in the vestibulum and cochlea, without functional hearing deficits. At the time point of maximal expression 5 days after injection, -galactosidase activity was also observed in axonal fibres and synaptic endings close to inner and outer hair cells. Our results thus describe an efficient and reliable protocol for short-term expression of potential therapeutic genes in the neuronal compartment of the inner ear.

Animals↗

PubMedDate not supplied

Hearing preservation after inner ear gene therapy: the effect of vector and surgical approach.

Over seventy studies have examined the potential of gene therapy in the inner ear. For the most part, they have focused on adenoviral vectors and delivery into the cochlea. Most studies have emphasized looking at the expression of marker genes driven by a CMV promoter and have used first-generation adenoviral constructs. E1/E3/E4 deleted adenoviral vectors carrying the green fluorescent protein (GFP) gene were injected into the round window, the basal turn of the cochlea (via a cochleostomy) or into the superior semicircular canal. Hearing was then tested 24 h after viral gene transfer. Large vector titers in small volumes of fluid were well tolerated with the round window approach resulting in complete hearing preservation with transfer of GFP to hair cells and spiral ganglion cells. Injection of comparable doses of vector into a basal turn cochleostomy resulted in high-frequency hearing loss. Addition of a pancaspase inhibitor protected hearing when larger volumes of fluid were administered to the inner ear.

Adenoviridae↗