الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 116 |  |  |
| | | from | 116 | | |
Abstract
Hearing loss is one of the major disabilities worldwide. Although conductive hearing loss is largely overcome by surgical treatment, therapeutic options for SNHL are limited to hearing aids and cochlear implants and sometimes pharmacotherapy in acute onset SNHL.
Sensorineural hearing loss is caused by degeneration of hair cells or auditory neurons. Hair cells (HCs) are easily damaged by aging as well as during episodes of ototoxicity and acoustic trauma. HCs damages typically occur in the early stage of injury and can result in a permanent hearing loss. Although some regeneration of vestibular hair cells has been reported in the mammalian inner ear, sensory hair cells of the organ of Corti do not regenerate.
Moreover, the loss of cochlear hair cells results in the secondary degeneration of spiral ganglion neurons (SGNs), most likely through loss of trophic factors that enhance SGNs survival. Also SGNs are not capable of postembryonic mitosis to produce new neurons, thus aggravating the hearing impairment and reducing the possibilities for rehabilitation.
Hearing aids can be used effectively for patients with moderate to severe hearing loss. A cochlear implant is the sole option for individuals with profound SNHL. While the
Summary
75
development of the cochlear implant has been remarkable, the prognosis for those individuals receiving an implant is still variable and, even with the best outcomes, normal hearing is not restored. Therefore patients with severe SNHL would welcome alternative strategies, and in particular, medical treatments for hearing rehabilitation.
Unlike birds and other vertebrates which have the ability to regenerate hair cells and auditory function, in the mature organ of Corti of mammals once a hair cell dies, it is not replaced. Instead, the loss of a hair cell leads to rapid changes in the morphology of the surrounding cells to seal the opening in the reticular lamina that results from the loss of a hair cell.
Stem cells (SCs) have been introduced to the search for new therapeutic strategies for mammalian cochlear cell regeneration in the past several years. Previous studies have suggested that inner ear neurons or hair cell like cells could be generated in vivo or in vitro from embryonic stem cells, from neural stem cells, from umbilical cord blood stem cells, from induced pluripotent stem cells, and from adult inner ear stem cells.
Different cochlear areas were targeted for SC application such as auditory epithelium, SGN and lateral canal wall with variable success.
Summary
76
In order to target the damaged area, difficult surgical routes of delivery are used via scala tympani, scala media and modiolus and cochlear nerve trunk
In our meta-analysis, we aimed at evaluation of the efficacy of SCs transplantation on treatment of SNHL, 4 articles included in our study included 34 guinea pigs all were transplanted by stem cells. Using the appropriate statistical methods, no statistically significant difference was found when comparing ABR threshold before and after SCs transplantation. In only two articles of the four, stem cells were transplanted in 18 guinea pigs while sham surgery was performed in 24 guinea pigs where ABR thresholds were found to be significantly better after SCs transplantation when compared to sham surgery.
Although success in humans has not yet been achieved, the use of stem cell seems to represent the future treatment for SNHL. Therefore further research in this field is a must.