Drug-induced hearing loss: Infection raises the odds

Detecting Novel Ototoxins and Potentiation of Ototoxicity by Disease Settings

Over 100 drugs and chemicals are associated with permanent hearing loss, tinnitus, and vestibular deficits, collectively known as ototoxicity. The ototoxic potential of drugs is rarely assessed in pre-clinical drug development or during clinical trials, so this debilitating side-effect is often discovered as patients begin to report hearing loss. Furthermore, drug-induced ototoxicity in adults, and particularly in elderly patients, may go unrecognized due to hearing loss from a variety of etiologies because of a lack of baseline assessments immediately prior to novel therapeutic treatment. During the current pandemic, there is an intense effort to identify new drugs or repurpose FDA-approved drugs to treat COVID-19. Several potential COVID-19 therapeutics are known ototoxins, including chloroquine (CQ) and lopinavir-ritonavir, demonstrating the necessity to identify ototoxic potential in existing and novel medicines. Furthermore, several factors are emerging as potentiators of ototoxicity, such as inflammation (a hallmark of COVID-19), genetic polymorphisms, and ototoxic synergy with co-therapeutics, increasing the necessity to evaluate a drug's potential to induce ototoxicity under varying conditions. Here, we review the potential of COVID-19 therapies to induce ototoxicity and factors that may compound their ototoxic effects. We then discuss two models for rapidly detecting the potential for ototoxicity: mammalian auditory cell lines and the larval zebrafish lateral line. These models offer considerable value for pre-clinical drug development, including development of COVID-19 therapies. Finally, we show the validity of in silico screening for ototoxic potential using a computational model that compares structural similarity of compounds of interest with a database of known ototoxins and non-ototoxins. Preclinical screening at in silico, in vitro, and in vivo levels can provide an earlier indication of the potential for ototoxicity and identify the subset of candidate therapeutics for treating COVID-19 that need to be monitored for ototoxicity as for other widely-used clinical therapeutics, like aminoglycosides and cisplatin.

The relationship between the structure and toxicity of aminoglycoside antibiotics

Aminoglycoside antibiotics, used to treat persistent gram-negative infections, tuberculosis, and life-threatening infections in neonates and patients with cystic fibrosis, can infer acute kidney injury and irreversible hearing loss. The full repertoire of cellular targets and processes leading to the toxicity of aminoglycosides is not fully resolved, making it challenging to devise rational directions to circumvent their adverse effects. As a result, there has been very limited effort to rationally address the issue of aminoglycoside-induced toxicity. Here we provide an overview of the reported effects of aminoglycosides on cells of the inner ear and on kidney tubular epithelial cells. We describe selected examples for structure–toxicity relationships established by evaluation of both natural and semisynthetic aminoglycosides. The various assays and models used to evaluate these antibiotics and recent progress in development of safer aminoglycoside antibiotics are discussed.

Chemical Modifications Reduce Auditory Cell Damage Induced by Aminoglycoside Antibiotics

Although aminoglycoside antibiotics are effective against Gram-negative infections, these drugs often cause irreversible hearing damage. Binding to the decoding site of the eukaryotic ribosomes appears to result in ototoxicity, but there is evidence that other effects are involved. Here, we show how chemical modifications of apramycin and geneticin, considered among the least and most toxic aminoglycosides, respectively, reduce auditory cell damage. Using molecular dynamics simulations, we studied how modified aminoglycosides influence the essential freedom of movement of the decoding site of the ribosome, the region targeted by aminoglycosides. By determining the ratio of a protein translated in mitochondria to that of a protein translated in the cytoplasm, we showed that aminoglycosides can paradoxically elevate rather than reduce protein levels. We showed that certain aminoglycosides induce rapid plasma membrane permeabilization and that this nonribosomal effect can also be reduced through chemical modifications. The results presented suggest a new paradigm for the development of safer aminoglycoside antibiotics.

Monitoring neonates for ototoxicity

OBJECTIVES

Neonates admitted to the neonatal intensive care unit (NICU) are at greater risk of permanent hearing loss compared to infants in well mother and baby units. Several factors have been associated with this increased prevalence of hearing loss, including congenital infections (e.g. cytomegalovirus or syphilis), ototoxic drugs (such as aminoglycoside or glycopeptide antibiotics), low birth weight, hypoxia and length of stay. The aetiology of this increased prevalence of hearing loss remains poorly understood.

DESIGN

Here we review current practice and discuss the feasibility of designing improved ototoxicity screening and monitoring protocols to better identify acquired, drug-induced hearing loss in NICU neonates.

STUDY SAMPLE

A review of published literature.

CONCLUSIONS

We conclude that current audiological screening or monitoring protocols for neonates are not designed to adequately detect early onset of ototoxicity. This paper offers a detailed review of evidence-based research, and offers recommendations for developing and implementing an ototoxicity monitoring protocol for young infants, before and after discharge from the hospital.