Aminoglycoside ototoxicity is a common cause of drug-induced
hearing loss. Toxicity is dose related, but some patients may still develop
hearing loss even under safe dosage. Apart for genetic idiosyncrasy, indirect evidences imply that
ischemia may increase the
aminoglycoside ototoxic sensitivity because common clinical situations associated with cochlear
ischemia such as noise,
sepsis, and
shock are known to augment the development of
aminoglycoside ototoxicity. At present, a direct interaction of cochlear
ischemia and
aminoglycoside ototoxicity is still lacking. This study demonstrated a direct evidence of increased
gentamicin (GM) ototoxic sensitivity in chronic guinea pig models of transient cochlear
ischemia. No permanent auditory changes were observed after a single dose of GM (125 mg/kg) or after transient cochlear
ischemia for 30 min. Persistent and significant auditory threshold shift was detected when GM was given after transient cochlear
ischemia. Cochlear hair cells and spiral ganglion neurons are the major regions affected. Apoptosis contributes to hair cell death during acute interaction of
ischemia and GM
ototoxicity. Increased apoptotic cell death was also depicted when GM crossreacted with
hypoxia in vitro, using cochlear cell lines. Generation of
reactive oxygen species, loss of mitochondrial membrane potential,
calcium release, and
caspase-dependent apoptotic cell death were shown during the interaction of
hypoxia and GM
ototoxicity in vitro. This synergistic
ototoxicity may be critical to
aminoglycoside-induced
hearing loss in clinical scenarios. The results should improve our understanding of the interacting mechanism and potential preventive strategy to
aminoglycoside ototoxicity.