Ototoxicity of sodium nitroprusside

Area of Science:

• Ototoxicity and neuroprotection
• Auditory hair cell biology
• Nitric oxide signaling in the inner ear

Background:

• Nitric oxide (NO) plays dual roles, mediating physiological functions and potentially causing neurodestruction in pathological states.
• The inner ear's vulnerability to oxidative stress and the role of NO in cochlear function remain areas of active investigation.

Purpose of the Study:

• To investigate the ototoxic effects of direct cochlear exposure to a NO donor (SNP) and a NO synthase inhibitor (L-NAME) on auditory hair cells.
• To determine if NO signaling pathways contribute to hair cell damage in the cochlea.

Main Methods:

• Guinea pigs were treated with sodium nitroprusside (SNP) or N(G)-nitro-L-arginine methyl ester (L-NAME) applied to the round window.
• Auditory hair cell counts (inner and outer) were performed using scanning electron microscopy at various survival periods (1-7 days).
• Experiments included controls and a subset with hydroxycobalamin to assess SNP metabolite contributions.

Main Results:

• Direct application of SNP led to a striking loss of inner and outer hair cells in the lower cochlear turns within 1 day.
• Outer hair cell damage progressed to the apical turn over time, while inner hair cells in the apex remained largely unaffected.
• L-NAME treatment at both tested concentrations did not result in significant hair cell loss in any cochlear region.

Conclusions:

• Excessive nitric oxide production in the inner ear, as induced by SNP, can cause extensive auditory hair cell damage.
• The findings suggest NO signaling plays a critical role in cochlear integrity and that NO donors may be ototoxic.
• Inhibition of NO synthesis did not appear to cause hair cell damage, highlighting the specific role of NO itself in ototoxicity.