Free Radicals in the Guinea Pig Inner Ear following Gentamicin Exposure

Abstract

The purpose of this study was to investigate the occurrence of free radicals, nitric oxide (NO), superoxide (O^–₂) and peroxynitrite, in the inner ear of the guinea pig following intratympanic injection with 5 mg of gentamicin (GM). Forty-eight hours after GM injection, varying degrees of degeneration of the inner ear were observed. Immunohistochemical study revealed immunoreactivity to NO synthase II (which generates NO) and to xanthine oxidase (which generates O^–₂) in both the vestibular organ and the organ of Corti. Immunohistochemical investigation, using a specific antinitrotyrosine antibody, also showed intense staining, suggesting formation of peroxynitrite in the inner ear through the reaction of NO with O^–₂. Scanning electron-microscopic study showed that the ototoxic effects could be blocked with N-nitro-L-arginine methylester, a competitive inhibitor of NO synthase, with superoxide dismutase, an O^–₂ scavenger, and with ebselen, a scavenger of peroxynitrite. On the basis of these findings, it can be concluded that NO together with O^–₂, which form more reactive peroxynitrite, play an important role in GM ototoxicity in the guinea pig.

Simultaneous Detection of Both Nitric Oxide and Reactive Oxygen Species in Guinea Pig Vestibular Sensory Cells

“…ROS scavengers and glutamate antagonists have been shown to provide protection from cochlear and vestibular damage by aminoglycoside, cisplatin or noise [1,6,7,9,16]. Furthermore, such damage is prevented by NOS inhibitors or scavengers of peroxynitrite [3,[8][9][10]. As already reported, L-NAME inhibits the production of NO [9,13], while D-met reduced the production of ROS [7].…”

Gentamicin-Induced Cytotoxicity Involves Protein Kinase C Activation, Glutathione Extrusion and Malondialdehyde Production in an Immortalized Cell Line from the Organ of Corti

“…In gentamicin cytotoxicity, depletion of intracellular GSH levels may be associated with an increase in reactive oxygen species. Many authors have suggested the participation of free oxygen radicals and nitric oxide in the adverse renal and cochlear effects of aminoglycosides [Lopez-Gonzalez et al, 1998Priuska and Schacht, 1995;Schacht, 1998, 1999b;Takumida et al, 1999]. The involvement of free radicals has been proven by the attenuation of gentamicin cytotoxicity and ototoxicity by antioxidants and iron chelators [Lopez-Gonzalez et al, 2000;Schacht, 1999c, 2000;Song et al, 1997].…”

“…There is increasing evidence that free radical generation plays a central role in this toxicity [Priuska and Schacht, 1995;Baliga et al, 1997;Lopez-Gonzalez et al, 1999;Sha and Schacht, 1999a, b;Walker et al, 1999]. In particular, hair cell death occurs by apoptosis [Takumida et al, 1999;Forge, 1985;Nakagawa et al, 1998], probably induced by a mechanism involving free radical formation and lipid peroxidation [Forge and Schacht, 2000]. Accordingly, in vivo and in vitro experiments confirmed that several radical scavengers [Garetz et al, 1994a, b] and iron chelators attenuate aminoglycoside-induced ototoxicity and nephrotoxicity [Conlon et al, 1998[Conlon et al, , 1999Sha and Schacht, 2000;Song and Schacht, 1996;Song et al, 1997].…”

Mitochondrial calcium uptake underlies ROS generation during aminoglycoside-induced hair cell death

“…Within the avian and rodent cochlea, elevated ROS levels have been detected within hair cells following aminoglycoside exposure (6)(7)(8)(9)(10)(11). Augmentation with various antioxidants in vitro and in vivo has proven to be partially effective at ameliorating aminoglycoside ototoxicity (12)(13)(14)(15)(16)(17)(18), suggesting a causal link between ROS production and hair cell death. However, antioxidants generally do not protect across a wide range of antibiotic doses and do not distinguish between the origins of ROS, leaving the source of ROS production during aminoglycoside-induced hair cell death an open question.…”