Different uptake of gentamicin through TRPV1 and TRPV4 channels determines cochlear hair cell vulnerability

Jeong-Han Lee,Se-Jin Kim,Hyung-Jin Kim,Gi-Su Oh,Raekil Park,Aihua Shen,Hong-Seob So,Channy Park

doi:10.1038/emm.2013.25

Abstract

Hair cells at the base of the cochlea appear to be more susceptible to damage by the aminoglycoside gentamicin than those at the apex. However, the mechanism of base-to-apex gradient ototoxicity by gentamicin remains to be elucidated. We report here that gentamicin caused rodent cochlear hair cell damages in a time- and dose-dependent manner. Hair cells at the basal turn were more vulnerable to gentamicin than those at the apical turn. Gentamicin-conjugated Texas Red (GTTR) uptake was predominant in basal turn hair cells in neonatal rats. Transient receptor potential vanilloid 1 (TRPV1) and 4 (TRPV4) expression was confirmed in the cuticular plate, stereocilia and hair cell body of inner hair cells and outer hair cells. The involvement of TRPV1 and TRPV4 in gentamicin trafficking of hair cells was confirmed by exogenous calcium treatment and TRPV inhibitors, including gadolinium and ruthenium red, which resulted in markedly inhibited GTTR uptake and gentamicin-induced hair cell damage in rodent and zebrafish ototoxic model systems. These results indicate that the cytotoxic vulnerability of cochlear hair cells in the basal turn to gentamicin may depend on effective uptake of the drug, which was, in part, mediated by the TRPV1 and TRPV4 proteins.

Highlights

Aminoglycoside antibiotics such as gentamicin are a class of polybasic compounds used for Gram-negative bacterial infections
The involvement of Transient receptor potential vanilloid 1 (TRPV1) and TRPV4 in gentamicin trafficking of hair cells was confirmed by exogenous calcium treatment and TRPV inhibitors, including gadolinium and ruthenium red, which resulted in markedly inhibited Gentamicin-conjugated Texas Red (GTTR) uptake and gentamicin-induced hair cell damage in rodent and zebrafish ototoxic model systems. These results indicate that the cytotoxic vulnerability of cochlear hair cells in the basal turn to gentamicin may depend on effective uptake of the drug, which was, in part, mediated by the TRPV1 and TRPV4 proteins
Basal turn inner hair cells (IHCs) and outer hair cells (OHCs) showed the greatest degree of damage, Figure 1 Hair cell death caused by gentamicin in a time- and dose-dependent manner. (A) Cochlear explant cultures from postnatal day 3 rats were maintained in the absence (a, c) or presence (b, d) of 300 mM gentamicin for 24 h

Summary

Introduction

Aminoglycoside antibiotics such as gentamicin are a class of polybasic compounds used for Gram-negative bacterial infections. Rapid uptake and long exposure of the cochlea to gentamicin accounts for the development of ototoxicity as assessed by cochlear hair cell death. Hair cells at the base of the cochlea appear to be more susceptible to damage by gentamicin than those at the apex. The base-to-apex gradient of aminoglycoside ototoxicity can be, in part, attributed to the difference of intrinsic susceptibility of cochlea to aminoglycosides. Considering that hair cells at the basal turn are severely affected, whereas hair cells at the apex are not affected when exposed to an equal amount of aminoglycosides,[1,3] a particular underlying difference in intrinsic susceptibility toward drugs may exist. Sha et al.[4] supported this possibility by demonstrating that the levels of reduced glutathione, a critical reactive oxygen species scavenger, are higher at the apex than those of OHCs at the base; thereby, OHCs at the apex are intrinsically more resistant

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