Pivotal role of Harakiri in the induction and prevention of gentamicin-induced hearing loss

Gilda M. Kalinec ^* , Martin E. Fernandez-Zapico ^, , Raul Urrutia , Nora Esteban-Cruciani , Shanping Chen ^*, and Federico Kalinec ^*, ¶, ||

^*Gonda Department of Cell and Molecular Biology, House Ear Institute, Los Angeles, CA 90057; Gastroenterology Research Unit, Mayo Clinic College of Medicine, Rochester, MN 55905; Children's Hospital at Montefiore and Albert Einstein College of Medicine, Bronx, NY 10461; and ^¶Departments of Otolaryngology and Cell and Neurobiology, University of Southern California, Los Angeles, CA 90089

Received for publication January 5, 2005.

Abstract: Gentamicin is a widely used ototoxic agent. In this study, we shed light on the mechanisms underlying gentamicin-induced hearing loss. More importantly, we demonstrate in vivo and in vitro the effectiveness of a strategy for preventing drug-induced hearing loss using L-carnitine (LCAR), a safe micronutrient that plays a key role in energy metabolism and detoxification [Rebouche, C. J. & Seim, H. (1998) Annu. Rev. Nutr. 18, 39-61]. We show that LCAR prevents changes in hearing threshold and cochlear damage in newborn guinea pigs exposed to gentamicin in utero. Mechanistically, gentamicin-induced apoptosis of auditory cells is mediated by the extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase (MAPK) pathway through up-regulation of the proapoptotic factor Harakiri (Hrk). Most important, small interfering RNA (siRNA) experiments demonstrate that Hrk up-regulation is crucial for gentamicin-induced apoptosis. LCAR, in contrast, prevents both gentamicin-induced Hrk up-regulation and apoptosis acting by means of c-Jun N-terminal kinase (JNK). Together, these results outline pathways for gentamicin-induced hearing loss and its prevention and assign a key role to Hrk in these processes. Thus, our data offer a conceptual framework for designing clinical trials using a safe micronutrient, LCAR, as a simple preventive strategy for iatrogenically induced ototoxicity.

Key Words: apoptosis • ototoxicity • L-carnitine • extracellular signal-regulated kinase 1/2 • HEI-OC1 cells

Conflict of interest statement: No conflicts declared.

Abbreviations: LCAR, L-carnitine; Hrk, Harakiri; ABR, auditory brainstem response; SEM, scanning electron microscopy; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; siRNA, small interfering RNA; OHC, outer hair cell; MAPK, mitogen-activated protein kinase; p, phosphorylated; I, inhibitor.

G.M.K. and M.E.F.-Z. contributed equally to this work.

^|| To whom correspondence should be addressed at: Department of Cell and Molecular Biology, House Ear Institute, 2100 West Third Street, Los Angeles, CA 90057. E-mail: fkalinec{at}hei.org.

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