In Vitro Ototoxicity of aminoglycosides and platin derivatives. A semi-automatic assay for sensory hair cell damage in explanted rat organ of corti

Growth factors have a protective effect on neomycin-induced hair cell loss

We have demonstrated that selected growth factors are involved in regulating survival and proliferation of progenitor cells derived from the neonatal rat organ of Corti (OC). The protective and regenerative effects of these defined growth factors on the injured organ of Corti were therefore investigated. The organ of Corti dissected from the Wistar rat pups (P3-P5) was split into apical, middle, and basal parts, explanted and cultured with or without neomycin and growth factors. Insulin-like growth factor-1 (IGF-1), fibroblast growth factor-2 (FGF-2), and epidermal growth factor (EGF) protected the inner hair cells (IHCs) and outer hair cells (OHCs) from neomycin ototoxicity. Using EGF, IGF-1, and FGF-2 alone induced no protective effect on the survival of auditory hair cells. Combining 2 growth factors (EGF + IGF-1, EGF + FGF-2, or IGF-1 + FGF-2) gave statistically protective effects. Similarly, combining all three growth factors effectively protected auditory hair cells from the ototoxic insult. None of the growth factors induced regeneration of hair cells in the explants injured with neomycin. Thus various combinations of the three defined factors (IGF-1, FGF-2, and EGF) can protect the auditory hair cells from the neomycin-induced ototoxic damage, but no regeneration was seen. This offers a possible novel approach to the treatment of hearing loss.

Identification of factors that maintain mammalian outer hair cells in adult organ of Corti explants

Both outer hair cells (OHCs) and inner hair cells (IHCs) survive and mature in 3 days old rat organ of Corti explants cultured for 1 month in a minimal essential medium. In contrast, under the same culture conditions, only IHCs survive in explants from adult guinea pig organ of Corti while many of the OHCs are lost within the first 48 h. Hair cell counts show OHCs loss to be greater in the lower portion (i.e. middle turn) of the cochlea than at the apex. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) indicates that there is DNA damage in adult OHCs within 8 h of explantation. Treatment of the adult organ of Corti explants with either actinomycin D (10(-7) M) or cycloheximide (10(-6) M) prevents most OHC losses. According to these results apoptosis may be the mechanism of OHC loss in adult organ of Corti explants. Stable membrane potentials recorded from the OHCs in both uncultured and actinomycin D-treated organ of Corti explants cultured for 72 h demonstrate the functional integrity of these hair cells. OHC losses in the adult guinea pig organ of Corti cultures can also be prevented by treatment with several of the growth factors tested, i.e. acidic fibroblast growth factor (aFGF), insulin-like growth factor-1 (IGF-1), epidermal growth factor (EGF), transforming growth factor-beta1 (TGF-beta1), and glial cell-derived neurotrophic factor (GDNF). The results of this study suggest that growth factor therapy may be applicable to the treatment of some hearing disorders.