| Sensorineural hearing loss is the most common sensory deficit in humans. Despite the enormity of this problem, there is no effective therapy for the correction of it. A variety of growth factors have been shown to can prevent or reduce degenerative responses of the adult mammalian cochleae to a variety of injuries. The basic fibroblast growth factor ( bFGF ) is one of fibroblast growth factor family. It plays important roles in the development and functional activity of inner ear. bFGF is an active promoter of neuron survival and neurite extension in vitro and in vivo, and has been shown to protect cochlear hair cells from ototoxin- and noise-induced trauma. However, delivery of polypeptide growth factors to inner ear is problematic because their plasmatic half-life are very short and their ability to cross the blood-labyrinth barrier are theoretically null. Gene therapy may overcome these problems by deliver bFGF gene into inner ear. Utilizing the semipermeable property of round wind membrane ( RWM ), in the present study we investigated the feasibility of a vector transgene-soaked gelatin sponge for bFGF gene delivery into rat cochlea through an intact RWM, and investigated the protection and treatment of bFGF on cochlear damage induced by intensive impulse noise. The study was divided into follow two parts:Part one: Cochlear EGFP gene expression through an intact round window membrane in ratThe object of this part is to investigate the expression of cationic liposome mediated EGFP gene into the rat cochlea through an intact RWM, and to assess the effect of the operation on hearing. Twenty-four adult SD rats were used for the study: eighteen were implanted with gelatin sponge soaked with cationicliposome-pEGFP in the bony groove of the round window niche, six were implanted with gelatin sponge soaked with normal saline. All the animals measured auditory brainstem response (ABR) thresholds before and after surgery, respectively. On postoperative day 3, day 7 and day 14, the animals were sacrificed, the bilateral cochleae were harvested and the surface preparation of basilar membrane were observed. ABR showed that the operation had no significant effect on the ABR thresholds. Bright green fluorescence in the cochleae was observed in test groups. Gene expression was in the highest level three days after operation and reduced thereafter. However, the contralateral cochleae and control groups were free of fluorescence. The technique of transgene delivery into the inner ear through an intact RWM proved to be feasible, atraumatic, and effective.Part two: The protection and treatment ofbFGFgene transfer into cochlea on explosive deafness in ratIn order to test the feasibility of gene therapy for sensorineural hearing loss, we introduced bFGF gene mediated by cationic liposome into the cochlea of rat with placement of vector-soaked gelatin sponge against the RWM. Thirty SD adult rats were divided into four groups: (1) noise group: only accepted 155 dB SPL impulse noise 20 times (n=6); (2) EGFP control group: cationic liposome-pEGFP complex administered immediately after impulse noise (n=8); (3) bFGF rescue group: cationic liposome-pEGFP-bFGF complex administered immediately after impulse noise (n=8); (4) bFGF protection group: cationic liposome-pEGFP-bFGF complex administered 3 days before impulse noise (n=8). All the animals measured ABR thresholds before and after noise on day 1, day 3, day 7 and day 14, respectively. On postoperative day 14, all the animals were sacrificed, the bilateral cochleae were harvested and the surface preparation ofbasilar membrane were observed. The expression of bFGF in hair cells was detected by immunofluorescent staining. ABR showed that hearing thresholds in bFGF rescue and protection groups were significantly better than those measured in the noise and EGFP control groups after noise exposure. In the bFGF rescue and protection groups, bFGF afforded significant preservation of cochlear hair cells. The results of this study suggest that cationic liposome me...
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