Cu/Zn superoxide dismutase and age-related hearing loss

Mice, in which the genetics can be manipulated and the life span is relatively short, enable evaluation of the effects of specific gene expression on cochlear degeneration over time. Antioxidant enzymes such as Cu/Zn superoxide dismutase (SOD I) protect cells from toxic, reactive oxygen species and may be involved in age-related degeneration. The effects of SODI deletion and over-expression on the cochlea were examined in Sodl-null mice, Sodl transgenic mice and in age- and genetics-matched controls. Auditory brainstern responses (ABR) were measured and cochleae were histologically examined. The absence of SOD] resulted in hearing loss at an earlier age than in wildtype or heterozygous mice. The cochleae of the null mice had severe spiral ganglion cell degeneration at 7-9 months of age. The stria vascularis in the aged, null mice was thinner than in the heterozygous or wildtype mice. Over-expression of SODI did not protect against hearing loss except at 24 months of age. In conclusion, SOD] seems important for survival of cochlear neurons and the stria vascularis, however even half the amount is sufficient and an over abundance does not provide much protection from age-related hearing loss. (c) 2005 Elsevier B.V. All rights reserved.