title: Acoustic trauma increases cochlear and hair cell uptake of gentamicin.
abstract: BACKGROUND
  Exposure to intense sound or high doses of aminoglycoside antibiotics can increase hearing thresholds, induce cochlear dysfunction, disrupt hair cell morphology and promote hair cell death, leading to permanent hearing loss. When the two insults are combined, synergistic ototoxicity occurs, exacerbating cochlear vulnerability to sound exposure. The underlying mechanism of this synergism remains unknown. In this study, we tested the hypothesis that sound exposure enhances the intra-cochlear trafficking of aminoglycosides, such as gentamicin, leading to increased hair cell uptake of aminoglycosides and subsequent ototoxicity.
  
  
  METHODS
  Juvenile C57Bl/6 mice were exposed to moderate or intense sound levels, while fluorescently-conjugated or native gentamicin was administered concurrently or following sound exposure. Drug uptake was then examined in cochlear tissues by confocal microscopy.
  
  
  RESULTS
  Prolonged sound exposure that induced temporary threshold shifts increased gentamicin uptake by cochlear hair cells, and increased gentamicin permeation across the strial blood-labyrinth barrier. Enhanced intra-cochlear trafficking and hair cell uptake of gentamicin also occurred when prolonged sound, and subsequent aminoglycoside exposure were temporally separated, confirming previous observations. Acute, concurrent sound exposure did not increase cochlear uptake of aminoglycosides.
  
  
  CONCLUSIONS
  Prolonged, moderate sound exposures enhanced intra-cochlear aminoglycoside trafficking into the stria vascularis and hair cells. Changes in strial and/or hair cell physiology and integrity due to acoustic overstimulation could increase hair cell uptake of gentamicin, and may represent one mechanism of synergistic ototoxicity.
authors.affiliation: Department of Otolaryngology/Head and Neck Surgery, Oregon Hearing Research Center, Oregon Health and Science University, Portland, Oregon, United States of America. liho@ohsu.edu
authors.forename: Hongzhe
authors.initials: H
authors.lastname: Li
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Peter S
authors.initials: PS
authors.lastname: Steyger
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001692:Biological Transport; D005839:Gentamicins / Q000378:metabolism*; D006198:Hair Cells, Auditory / Q000378:metabolism*; D006317:Hearing Loss, Noise-Induced / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D013016:Sound / Q000009:adverse effects; D013316:Stria Vascularis / Q000378:metabolism / Q000473:pathology; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins