Gentamicin differentially alters cellular metabolism of cochlear hair cells as revealed by NAD(P)H fluorescence lifetime imaging

Abstract

Aminoglycoside antibiotics are implicated as culprits of hearing loss in more than 120,000 individuals annually. Research has shown that the sensory cells, but not supporting cells, of the cochlea are readily damaged and/or lost after use of such antibiotics. High-frequency outer hair cells (OHCs) show a greater sensitivity to antibiotics than high- and low-frequency inner hair cells (IHCs). We hypothesize that variations in mitochondrial metabolism account for differences in susceptibility. Fluorescence lifetime microscopy was used to quantify changes in NAD(P)H in sensory and supporting cells from explanted murine cochleae exposed to mitochondrial uncouplers, inhibitors, and an ototoxic antibiotic, gentamicin (GM). Changes in metabolic state resulted in a redistribution of NAD(P)H between subcellular fluorescence lifetime pools. Supporting cells had a significantly longer lifetime than sensory cells. Pretreatment with GM increased NAD(P)H intensity in high-frequency sensory cells, as well as the NAD(P)H lifetime within IHCs. GM specifically increased NAD(P)H concentration in high-frequency OHCs, but not in IHCs or pillar cells. Variations in NAD(P)H intensity in response to mitochondrial toxins and GM were greatest in high-frequency OHCs. These results demonstrate that GM rapidly alters mitochondrial metabolism, differentially modulates cell metabolism, and provides evidence that GM-induced changes in metabolism are significant and greatest in high-frequency OHCs.

The Severity of Infection Determines the Localization of Damage and Extent of Sensorineural Hearing Loss in Experimental Pneumococcal Meningitis

“…This finding is in line with a previously observed higher vulnerability of OHCs versus IHCs to ototoxic compounds, i.e., aminoglycoside antibiotics, due to differences in mitochondrial metabolism in inner and outer hair cells (Zholudeva et al, 2015). Despite the substantial loss of SGNs and OHCs, the majority of IHCs were still present in the OC even after infecting the animals with the high INO.…”

Multiphoton NAD(P)H FLIM reveals metabolic changes in individual cell types of the intact cochlea upon sensorineural hearing loss

“…The quantities τ bound and α bound have been observed to differ in response to metabolic perturbation and the onset of disease, prompting diagnostic tools to be designed based on time-resolved autofluorescence methods 26 . Indeed, these techniques have previously been applied to investigate the metabolism of the cochlea 19,27 . However, their full potential has yet to be realised as the interpretation of the nanoscale properties reported by the NAD(P)H fluorescence decay in terms of the underlying physiological or biochemical state of the tissue has not yet been unambiguously defined 14–17 .…”

ROS Scavenger, Ebselen, Has No Preventive Effect in New Hearing Loss Model Using a Cholesterol-Chelating Agent

“…However, an effect on ubiquitous lipid components cannot easily explain the specificity of injury to the OHCs. OHCs show heightened sensitivity to other ototoxic agents, such as cisplatin and aminoglycosides, compared to other cochlear cell types, possibly due to differences in uptake mechanisms [7] and mitochondrial metabolism [8]. Indeed, increased reactive oxygen species (ROS) production is a common cause in otopathology from several forms of acquired hearing loss [9].…”