title: Mannitol protects hair cells against tumor necrosis factor α-induced loss.
abstract: OBJECTIVE
  Mannitol has otoprotective effects against tumor necrosis factor (TNF) α-induced auditory hair cell (HC) loss.
  
  
  BACKGROUND
  Mannitol has been demonstrated to possess cytoprotective effects in several organ systems. Its protective effect on postischemic hearing loss has also been shown. Mannitol's otoprotective mechanism and site of action are at present unknown.
  
  
  METHODS
  Organ of Corti (OC) explants were dissected from 3 day-old rat pups. The safety (nonototoxicity) of mannitol was assessed at 4 different concentrations (1-100 mM). Three experimental arms were designed including: a control group, TNFα group, and TNFα + mannitol group. Cell viability was determined by counts of fluorescein isothiocyanate (FITC) phalloidin stained HC. Immunofluorescence assay of phospho-c-Jun and the proapoptotic mediators, cleaved caspase-3, apoptosis inducing factor (AIF), and endonuclease G (Endo G) were performed.
  
  
  RESULTS
  Analysis of HC density confirmed the safety of mannitol at concentration ranges of 1 to 100 mM. The ototoxic effect of TNFα was demonstrated (p < 0.05). The otoprotective effect of 100 mM mannitol in TNFα-challenged OC explants was also demonstrated (p < 0.001). Mannitol treatment reduced the high levels of phospho-c-Jun observed in the TNFα-challenged group. AIF cluster formation and EndoG translocation into the nuclei of HCs were also reduced by mannitol treatment.
  
  
  CONCLUSIONS
  Mannitol significantly reduces the ototoxic effects of TNFα against auditory HC's potentially by inhibiting c-Jun N terminal kinase (JNK) activation pathway and AIF, EndoG nuclear translocation. This local otoprotective effect may have therapeutic implications in inner ear surgery, for example, cochlear implants, protection of residual hearing, as well as implications for postischemic inner ear insults.
authors.affiliation: Cochlear Implant Research Program, University of Miami Ear Institute, Miami, Florida 33136-1015, USA.
authors.forename: Esperanza Bas
authors.initials: EB
authors.lastname: Infante
authors.forename: Guyan A
authors.initials: GA
authors.lastname: Channer
authors.forename: Fred F
authors.initials: FF
authors.lastname: Telischi
authors.forename: Chhavi
authors.initials: C
authors.lastname: Gupta
authors.forename: John T
authors.initials: JT
authors.lastname: Dinh
authors.forename: Ly
authors.initials: L
authors.lastname: Vu
authors.forename: Adrien A A
authors.initials: AA
authors.lastname: Eshraghi
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Van De Water
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004396:Coloring Agents; D005455:Fluorescent Antibody Technique; D006198:Hair Cells, Auditory / Q000187:drug effects* / Q000648:ultrastructure; D008353:Mannitol / Q000009:adverse effects / Q000494:pharmacology*; D018613:Microscopy, Confocal; D018696:Neuroprotective Agents; D009925:Organ of Corti / Q000166:cytology / Q000187:drug effects; D051381:Rats; D016707:Tissue Fixation; D014409:Tumor Necrosis Factor-alpha / Q000633:toxicity*
chemical_list: D004396:Coloring Agents; D018696:Neuroprotective Agents; D014409:Tumor Necrosis Factor-alpha; D008353:Mannitol