To Örebro University

OBJECTIVE: Establishing methods for topical administration of drugs to the inner ear have great clinical relevance and potential even in a relatively short perspective. To evaluate the efficacy of sodium hyaluronate (HYA) as a vehicle for drugs that could be used for treatment of inner ear disorders.

METHODS: The cochlear hair cell loss and round window membrane (RWM) morphology were investigated after topical application of neomycin and HYA into the middle ear. Sixty-five albino guinea pigs were used and divided into groups depending on the type of the treatment. Neomycin was chosen as tracer for drug release and pharmacodynamic effect. HYA loaded with 3 different concentrations of neomycin was injected to the middle ear cavity of guinea pigs. Phalloidin stained surface preparations of the organ of Corti were used to estimate hair cell loss induced by neomycin. The thickness of the midportion of the RWM was measured and compared with that of controls using light and electron microscopy. All animal procedures were pe rformed in accordance with the ethical standards of Karolinska Institutet.

RESULT: Neomycin induced a considerable hair cell loss in guinea pigs receiving a middle ear injection of HYA loaded with the drug, demonstrating that neomycin was released from the gel and delivered to the inner ear. The resulting hair cell loss showed a clear dose-dependence. Only small differences in hair cell loss were noted between animals receiving neomycin solution and animals exposed to neomycin in HYA suggesting that the vehicle neither facilitated nor hindered drug transport between the middle ear cavity and the inner ear. One week after topical application, the thickness of the RWM had increased and was dependent upon the concentration of neomycin administered to the middle ear. At 4 weeks the thickness of the RWM had returned to normal.

CONCLUSION: HYA is a safe vehicle for drugs aimed to pass into the inner ear through the RWM. Neomycin was released from HYA and transported into the inner ear as evidenced by hair cell loss.

Development of efficient local delivery systems for the auditory organ has an important role in clinical practice for the management of inner ear disorders using pharmacological means. Chitosan, a biodegradable polymer, is a good drug carrier with bioadhesive properties. The aim of this study was to investigate the feasibility of using chitosan to deliver drugs to the inner ear across the round window membrane (RWM). Three structurally different chitosans loaded with a tracer drug, neomycin, were injected into the middle ear cavity of albino guinea pigs (n=35). After 7 days the effect of chitosans and neomycin was compared among the treatment groups. The hearing organ was analysed for hair cell loss and the RWM evaluated in term of thickness. All tested chitosan formulations successfully released the loaded neomycin which then diffused across the RWM, and exerted ototoxic effect on the cochlear hair cells in a degree depending on the concentrations used. Chitosans per se had no noxious effect on the cochlear hair cells. It is concluded that the chitosans, and especially glycosylated derivative, are safe and effective carriers for inner ear therapy.

Background: Sensorineural hearing loss is a significant problem worldwide and a condition that is not completely cured by currently available therapy. Gene therapy of the inner ear offers an exciting alternative and it has been suggested that this therapeutic modality could be used in treatment aiming at preventing, reversing or managing cochlear disorders. Because of their desired properties as an alternative to the viral vectors, non-viral vectors have been extensively explored for gene delivery. One example is chitosan, a biodegradable cationic polymer.

Objective: To evaluate the in vitro and in vivo transfection efficiency of chitosan as a non-viral gene carrier for gene delivery to cells of the inner ear.

Materials and Methods: Organotypic cultures of the hearing organ, the organ of Corti, were prepared from postnatal day 2 rats, and exposed to chitosan carrying plasmid DNA (pDNA) encoding for green fluorescent protein (GFP) for 24-48 hours. The in vivo transfection efficiency was tested at two time points, at one day or seven days after infusing chitosan/pDNA polyplexes through osmotic pumps into the cochlea of adult guinea pigs (n=41). The tissue was then processed for anti-GFP immunostaining (in vitro and in vivo) and RT-PCR (in vivo).

Results: The in vitro assessment showed prominent GPF transfection after 24-48 hours, while the in vivo GFP transfection in the inner ear was inconsistent and did not show good correlation with the in vitro transfection. Conclusion: It can be concluded that the using chitosan as a carrier for the in vivo transfection, is associated with varying and in consistent degree of transfection.