Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection

Aminoglycoside-induced Hearing Loss Among Patients Being Treated for Drug-resistant Tuberculosis in South Africa: A Prediction Model

BACKGROUND

Individuals treated for drug-resistant tuberculosis (DR-TB) with aminoglycosides (AGs) in resource-limited settings often experience permanent hearing loss, yet there is no practical method to identify those at higher risk. We sought to develop a clinical prediction model of AG-induced hearing loss among patients initiating DR-TB treatment in South Africa.

METHODS

Using nested, prospective data from a cohort of 379 South African adults being treated for confirmed DR-TB with AG-based regimens we developed the prediction model using multiple logistic regression. Predictors were collected from clinical, audiological, and laboratory evaluations conducted at the initiation of DR-TB treatment. The outcome of AG-induced hearing loss was identified from audiometric and clinical evaluation by a worsened hearing threshold compared with baseline during the 6-month intensive phase.

RESULTS

Sixty-three percent of participants (n = 238) developed any level of hearing loss. The model predicting hearing loss at frequencies from 250 to 8000 Hz included weekly AG dose, human immunodeficiency virus status with CD4 count, age, serum albumin, body mass index, and pre-existing hearing loss. This model demonstrated reasonable discrimination (area under the receiver operating characteristic curve [AUC] = 0.71) and calibration (χ2[8] = 6.10, P = .636). Using a cutoff of 80% predicted probability of hearing loss, the positive predictive value of this model was 83% and negative predictive value was 40%. Model discrimination was similar for ultrahigh-frequency hearing loss (frequencies >9000 Hz; AUC = 0.81) but weaker for clinically determined hearing loss (AUC = 0.60).

CONCLUSIONS

This model may identify patients with DR-TB who are at highest risk of developing AG-induced ototoxicity and may help prioritize patients for AG-sparing regimens in clinical settings where access is limited.

Advances in the development of connexin hemichannel inhibitors selective toward Cx43

Gap-junction channels formed by two connexin hemichannels play diverse and pivotal roles in intercellular communication and regulation. Normally hemichannels at the plasma membrane participate in autocrine and paracrine signaling, but abnormal increase in their activity can lead or contribute to various diseases. Selective inhibitors toward connexin hemichannels are of great interest. Among more than 20 identified isoforms of connexins, connexin 43 (Cx43) attracts the most interest due to its prevalence and link to cell damage in many disorders or diseases. Traditional antibacterial kanamycin decorated with hydrophobic groups yields amphiphilic kanamycins that show low cytotoxicity and prominent inhibitory effect against Cx43. This review focuses on the development of amphiphilic kanamycins as connexin hemichannel inhibitors and their future perspective.

Dissociating antibacterial from ototoxic effects of gentamicin C-subtypes

Gentamicin is a potent broad-spectrum aminoglycoside antibiotic whose use is hampered by ototoxic side-effects. Hospital gentamicin is a mixture of five gentamicin C-subtypes and several impurities of various ranges of nonexact concentrations. We developed a purification strategy enabling assaying of individual C-subtypes and impurities for ototoxicity and antimicrobial activity. We found that C-subtypes displayed broad and potent in vitro antimicrobial activities comparable to the hospital gentamicin mixture. In contrast, they showed different degrees of ototoxicity in cochlear explants, with gentamicin C2b being the least and gentamicin C2 the most ototoxic. Structure-activity relationships identified sites in the C4'-C6' region on ring I that reduced ototoxicity while preserving antimicrobial activity, thus identifying targets for future drug design and mechanisms for hair cell toxicity. Structure-activity relationship data suggested and electrophysiological data showed that the C-subtypes both bind and permeate the hair cell mechanotransducer channel, with the stronger the binding the less ototoxic the compound. Finally, both individual and reformulated mixtures of C-subtypes demonstrated decreased ototoxicity while maintaining antimicrobial activity, thereby serving as a proof-of-concept of drug reformulation to minimizing ototoxicity of gentamicin in patients.

Systemic application of honokiol prevents cisplatin ototoxicity without compromising its antitumor effect

Cisplatin is a potent drug used in about 40% of cancer treatment but also leads to severe deafness in 60-80% of the cases. Although the mechanism is known to be related to the accumulation of reactive oxygen species (ROS), no drug or FDA approved treatment is currently available to prevent cisplatin ototoxicity. With this study, we show for the first time that honokiol (HNK), a pleiotropic poly-phenol prevents cisplatin-induced hearing loss. HNK also improves the wellbeing of the mice during the treatment, determined by the increase in the number of surviving animals. In a transgenic tumor mouse model, HNK does not hinder cisplatin's antitumor effect. The mechanism is related to the activation of sirtuin 3, a deacetylase in mitochondria essential for ROS detoxification. We expect a paradigm shift in cisplatin chemotherapy based on the current study and future clinical trials, where honokiol is applied to reduce side effects including hearing loss.

A new aminoglycoside etimicin shows low nephrotoxicity and ototoxicity in zebrafish embryos

Aminoglycoside antibiotics are widely used for many life-threatening infections. The use of aminoglycosides is often comprised by their deleterious side effects to the kidney and inner ear. A novel semisynthetic antibiotic, etimicin, has good antimicrobial activity against both gram-positive and gram-negative bacteria. But its toxicity profile analysis is still lacking. In the present study, we compared the in vivo toxic effects of three aminoglycosides, gentamicin, amikacin, and etimicin, in zebrafish embryos. We examined the embryotoxicity, nephrotoxicity, and the damage to the neuromast hair cells. Our results revealed that etimicin and amikacin exhibit more developmental toxicities to the young embryos than gentamicin. But at subtoxic doses, etimicin and amikacin show significantly reduced toxicities towards kidney and neuromast hair cells. We further demonstrated that fluorescently conjugated aminoglycosides (gentamicin-Texas red [GTTR], amikacin-Texas red [AMTR], and etimicin-Texas red [ETTR]) all enter the hair cells properly. Inside the hair cells, gentamicin, not etimicin and amikacin, displays robust reactive oxygen species generation and induces apoptosis. Our data support that the different intracellular cytotoxicity underlies the different ototoxicity of the three aminoglycosides and that etimicin is a new aminoglycoside with reduced risk of nephrotoxicity and ototoxicity.

A Novel Mouse Model of Aminoglycoside-Induced Hyperacusis and Tinnitus

Aminoglycosides (AG) such as amikacin are commonly used in cystic fibrosis patients with opportunistic pulmonary infections including multi-drug resistant mycobacterium tuberculous and non-tuberculous mycobacterium. Unfortunately, this class of drugs is known to cause peripheral damage to the cochlea leading to hearing loss that can fluctuate and become permanent over time or multiple exposures. However, whether amikacin can lead to central auditory dysfunction like hyperacusis (increased sensitivity to sound) or tinnitus (perception of sound in the absence of acoustic stimulation) is not well-described in the literature. Thus, an animal model needs to be developed that documents these side effects in order to develop therapeutic solutions to reduce AG-induced auditory dysfunction. Here we present pioneer work in mice which demonstrates that amikacin can lead to fluctuating behavioral evidence of hyperacusis and tinnitus as assessed by the acoustic startle reflex. Additionally, electrophysiological assessments of hearing via auditory brainstem response demonstrate increased central activity in the auditory brainstem. These data together suggest that peripheral AG-induced dysfunction can lead to central hyperactivity and possible behavioral manifestations of hyperacusis and tinnitus. Importantly, we demonstrate that ebselen, a novel investigational drug that acts as both an antioxidant and anti-inflammatory, can mitigate AG-induced hyperacusis.

Programmed cell death pathways in hearing loss: A review of apoptosis, autophagy and programmed necrosis

Programmed cell death (PCD)—apoptosis, autophagy and programmed necrosis—is any pathological form of cell death mediated by intracellular processes. Ototoxic drugs, ageing and noise exposure are some common pathogenic factors of sensorineural hearing loss (SNHL) that can induce the programmed death of auditory hair cells through different pathways, and eventually lead to the loss of hair cells. Furthermore, several mutations in apoptotic genes including DFNA5, DFNA51 and DFNB74 have been suggested to be responsible for the new functional classes of monogenic hearing loss (HL). Therefore, in this review, we elucidate the role of these three forms of PCD in different types of HL and discuss their guiding significance for HL treatment. We believe that further studies of PCD pathways are necessary to understand the pathogenesis of HL and guide scientists and clinicians to identify new drug targets for HL treatment.

Protective effect of creatine on amikacin-induced ototoxicity

Introduction

Aminoglycosides are widely known for their ototoxic side effects. Nevertheless, they are potent antibiotics used in the treatment of life-threatening conditions because of the current concern for antibiotic resistance. We hypothesized that creatine supplements which are believed to improve mitochondrial antioxidant defense system and maintain optimal energy homeostasis may improve the ototoxic side effects.

Objective

This study aimed to investigate the protective effects of creatine monohydrate against ototoxicity induced by amikacin in rats in an experimental animal model, using distortion product otoacoustic emissions and auditory brainstem response.

Methods

Twenty healthy rats were assigned to four groups (5 rats in each): the control group, the creatine monohydrate group, the amikacin group and the amikacin + creatine monohydrate group. The creatine monohydrate group received creatine at a dose of 2 g/kg once daily via gastric gavage for 21 days. The amikacin group received amikacin at a dose of 600 mg/kg by intramuscular injections once daily for 21 days. The amikacin + creatine monohydrate group received intramuscular injections of amikacin (600 mg/kg) once daily for 21 days and creatine monohydrate (2 g/kg) once daily via gastric gavage for 21 days. The control group received nothing. The distortion product otoacoustic emissions and auditory brainstem response measurements were performed on all rats on days 0, 7, 21.

Results

Regarding auditory brainstem response values, a significant increase in the auditory threshold was observed in the amikacin group on day 21 (p <  0.001). The amikacin+creatine monohydrate group showed significantly lower levels of auditory brainstem response auditory thresholds on day 21 in comparison to the amikacin group (p <  0.001). Additionally, the control group and the amikacin+creatine monohydrate group did not differ significantly with respect to auditory brainstem response thresholds on treatment day 21 (p >  0.05). When we compare distortion product otoacoustic emissions values, there was no significant difference between the amikacin and amikacin+creatine monohydrate groups on day 7 (p >  0.05), However significantly greater distortion product otoacoustic emissions values were observed in the amikacin+creatine monohydrate group on day 21 compared to the amikacin group (p <  0.001).

Conclusion

Our findings demonstrate that creatine treatment protects against amikacin ototoxicity when given at a sufficient dose and for an adequate time period.

Saliva versus Plasma Therapeutic Drug Monitoring of Gentamicin in Jordanian Preterm Infants. Development of a Physiologically-Based Pharmacokinetic (PBPK) Model and Validation of Class II Drugs of Salivary Excretion Classification System

Gentamicin has proven to be a very successful treatment for bacterial infection, but it also can cause adverse effects, especially ototoxicity, which is irreversible. Therapeutic drug monitoring (TDM) in saliva is a more convenient non-invasive alternative compared to plasma. A physiologically-based pharmacokinetic (PBPK) model of gentamicin was built and validated using previously-published plasma and saliva data. The validated model was then used to predict experimentally-observed plasma and saliva gentamicin TDM data in Jordanian pediatric preterm infant patients measured using sensitive LCMS/MS method. A correlation was established between plasma and saliva exposures. The developed PBPK model predicted previously reported gentamicin levels in plasma, saliva and those observed in the current study. A good correlation was found between plasma and saliva exposures. The PBPK model predicted that gentamicin in saliva is 5-7 times that in plasma, which is in agreement with observed results. Saliva can be used as an alternative for TDM of gentamicin in preterm infant patients. Exposure to gentamicin in plasma and saliva can reliably be predicted using the developed PBPK model in patients.

Changes in Vestibular Function in Patients With Head-and-Neck Cancer Undergoing Chemoradiation

INTRODUCTION

While the cochleotoxicity of cisplatin has been well investigated, less is known about the effects of platinum-based chemotherapy on the vestibular system. In particular, there is a lack of prospective studies using modern laboratory vestibular testing that examine the effects of cisplatin on the semicircular canals and on the otolith organs. The aim of the present study was, therefore, to investigate the vestibulotoxic effect of cisplatin in patients with head and neck tumors who are undergoing chemoradiation.

METHODS

Forty-five patients undergoing cisplatin-based chemoradiation for head and neck cancer received a vestibular assessment consisting of anamnesis, a horizontal video head impulse test (vHIT), ocular and cervical vestibular evoked myogenic potential testing, as well as pure tone audiometry. This assessment was performed before therapy, 6 weeks after therapy, and 3 months after therapy.

RESULTS

Video head impulse test showed a significantly reduced median gain 6 weeks after chemoradiation. In addition, significantly more refixational saccades could be detected after therapy. Vestibular evoked myogenic potential testing results also revealed significant changes, whereas pure tone audiometry did not. None of the patients mentioned "dizziness" during the follow-up examinations.

CONCLUSION

We demonstrated a vestibulotoxic effect of cisplatin-based chemoradiation in patients with head and neck cancer. Future studies are needed to better understand cisplatin-induced vestibulotoxicity and to identify possible vestibuloprotective substances. Still, before and after chemoradiation, patients should undergo not only auditory testing but also vestibular testing in order to detect potential vestibular loss as soon as possible and to quickly initiate vestibular physiotherapy.

Potentiating aminoglycoside antibiotics to reduce their toxic side effects

The lack of new antibiotics necessitates the improvement of existing ones, many of which are limited by toxic side effects. Aminoglycosides, antibiotics with excellent activity and low bacterial resistance, are hampered by dose-dependent toxic effects in patients (nephrotoxicity, ototoxicity). High antibiotic concentrations are often required to treat dormant, non-dividing bacteria, though previous studies show that aminoglycosides can be activated against such bacteria by specific metabolites. Here, we employed this mechanism to greatly boost the activity of low concentrations of aminoglycosides against prevalent Gram-negative pathogens (Escherichia coli, Salmonella enterica, and Klebsiella pneumoniae), suggesting that less toxic drug concentrations might be used effectively in patients. We go on to show that this effect improved treatment of biofilms, did not increase aminoglycoside resistance, and was due to the generation of proton-motive force (PMF). By single-cell microscopy, we demonstrate that stationary-phase cells, while non-dividing, actively maintain a growth-arrested state that is not reversed by metabolite addition. Surprisingly, within starved populations, we observed rare cells (3%) that divided without added nutrients. Additionally, we discovered that mannitol could directly protect human kidney cells from aminoglycoside cytotoxicity, independent of the metabolite's effect on bacteria. This work forwards a mechanism-based strategy to improve existing antibiotics by mitigating their toxic side effects.

Berbamine Analogs Exhibit Differential Protective Effects From Aminoglycoside-Induced Hair Cell Death

Hearing loss is the third most common chronic health condition in the United States and largely results from damage to sensory hair cells. Major causes of hair cell damage include aging, noise exposure, and medications such as aminoglycoside antibiotics. Due to their potent antibacterial properties and low cost, aminoglycosides are often used for the treatment of gram-negative bacterial infections, surpassing expensive antibiotics with fewer harmful side effects. However, their use is coupled with permanent hearing loss in over 20% of patients requiring these life-sustaining antibiotics. There are currently no FDA-approved drugs that prevent hearing loss from aminoglycosides. A previous study by our group identified the plant alkaloid berbamine as a strong protectant of zebrafish lateral line hair cells from aminoglycoside damage. This effect is likely due to a block of the mechanotransduction channel, thereby reducing aminoglycoside entry into hair cells. The present study builds on this previous work, investigating 16 synthetic berbamine analogs to determine the core structure underlying their protective mechanisms. We demonstrate that nearly all of these berbamine analogs robustly protect lateral line hair cells from ototoxic damage, with ED₅₀ values nearing 20 nM for the most potent analogs. Of the 16 analogs tested, nine strongly protected hair cells from both neomycin and gentamicin damage, while one conferred strong protection only from gentamicin. These data are consistent with prior research demonstrating that different aminoglycosides activate somewhat distinct mechanisms of damage. Regardless of the mechanism, protection required the entire berbamine scaffold. Phenolic alkylation or acylation with lipophilic groups appeared to improve protection compared to berbamine, implying that these structures may be responsible for mitigating damage. While the majority of analogs confer protection by blocking aminoglycoside uptake, 18% of our analogs also confer protection via an uptake-independent mechanism; these analogs exhibited protection when delivered after aminoglycoside removal. Based on our studies, berbamine analogs represent a promising tool to further understand the pathology of aminoglycoside-induced hearing loss and can serve as lead compounds to develop otoprotective drugs.

Translational read-through promotes aggregation and shapes stop codon identity

Faithful translation of genetic information depends on the ability of the translational machinery to decode stop codons as termination signals. Although termination of protein synthesis is highly efficient, errors in decoding of stop codons may lead to the synthesis of C-terminally extended proteins. It was found that in eukaryotes such elongated proteins do not accumulate in cells. However, the mechanism for sequestration of C-terminally extended proteins is still unknown. Here we show that 3′-UTR-encoded polypeptides promote aggregation of the C-terminally extended proteins, and targeting to lysosomes. We demonstrate that 3′-UTR-encoded polypeptides can promote different levels of protein aggregation, similar to random sequences. We also show that aggregation of endogenous proteins can be induced by aminoglycoside antibiotics that promote stop codon read-through, by UAG suppressor tRNA, or by knokcdown of release factor 1. Furthermore, we find correlation between the fidelity of termination signals, and the predicted propensity of downstream 3′-UTR-encoded polypeptides to form intrinsically disordered regions. Our data highlight a new quality control mechanism for elimination of C-terminally elongated proteins.

Prevalence of Pre-Existing Hearing Loss Among Patients With Drug-Resistant Tuberculosis in South Africa

Purpose Hearing loss, resulting from aminoglycoside ototoxicity, is common among patients with drug-resistant tuberculosis (DR-TB). Those with pre-existing hearing loss are at particular risk of clinically important hearing loss with aminoglycoside-containing treatment than those with normal hearing at baseline. This study aimed to identify factors associated with pre-existing hearing loss among patients being treated for DR-TB in South Africa. Method Cross-sectional analysis nested within a cluster-randomized trial data across 10 South African TB hospitals. Patients ≥ 13 years old received clinical and audiological evaluations before DR-TB treatment initiation. Results Of 936 patients, average age was 35 years. One hundred forty-two (15%) reported pre-existing auditory symptoms. Of 482 patients tested by audiometry, 290 (60%) had pre-existing hearing loss. The prevalence of pre-existing hearing loss was highest among patients ≥ 50 years (adjusted prevalence ratio [aPrR] for symptoms 5.53, 95% confidence interval (CI) [3.63, 8.42]; aPrR for audiometric hearing loss 1.63, 95% CI [1.31, 2.03] compared to age 13-18 years) and among those with a prior history of second-line TB treatment (aPrR for symptoms 1.73, 95% CI [1.66, 1.80]; PrR for audiometric hearing loss 1.33, 95% CI [1.03, 1.73]). Having HIV with cluster of differentiation 4 cell count < 200 cells/mm³ and malnutrition were risk factors but did not reach statistical significance in adjusted analyses. Conclusion Pre-existing hearing loss is common among patients presenting for DR-TB treatment in South Africa, and those older than the age of 50 years or who had prior second-line TB treatment history were at highest risk.

Mutation-Directed Therapeutics for Neurofibromatosis Type I

Significant advances in biotechnology have led to the development of a number of different mutation-directed therapies. Some of these techniques have matured to a level that has allowed testing in clinical trials, but few have made it to approval by drug-regulatory bodies for the treatment of specific diseases. While there are still various hurdles to be overcome, recent success stories have proven the potential power of mutation-directed therapies and have fueled the hope of finding therapeutics for other genetic disorders. In this review, we summarize the state-of-the-art of various therapeutic approaches and assess their applicability to the genetic disorder neurofibromatosis type I (NF1). NF1 is caused by the loss of function of neurofibromin, a tumor suppressor and downregulator of the Ras signaling pathway. The condition is characterized by a variety of phenotypes and includes symptoms such as skin spots, nervous system tumors, skeletal dysplasia, and others. Hence, depending on the patient, therapeutics may need to target different tissues and cell types. While we also discuss the delivery of therapeutics, in particular via viral vectors and nanoparticles, our main focus is on therapeutic techniques that reconstitute functional neurofibromin, most notably cDNA replacement, CRISPR-based DNA repair, RNA repair, antisense oligonucleotide therapeutics including exon skipping, and nonsense suppression.

Exosomes mediate sensory hair cell protection in the inner ear

Hair cells, the mechanosensory receptors of the inner ear, are responsible for hearing and balance. Hair cell death and consequent hearing loss are common results of treatment with ototoxic drugs, including the widely used aminoglycoside antibiotics. Induction of heat shock proteins (HSPs) confers protection against aminoglycoside-induced hair cell death via paracrine signaling that requires extracellular heat shock 70-kDa protein (HSP70). We investigated the mechanisms underlying this non-cell-autonomous protective signaling in the inner ear. In response to heat stress, inner ear tissue releases exosomes that carry HSP70 in addition to canonical exosome markers and other proteins. Isolated exosomes from heat-shocked utricles were sufficient to improve survival of hair cells exposed to the aminoglycoside antibiotic neomycin, whereas inhibition or depletion of exosomes from the extracellular environment abolished the protective effect of heat shock. Hair cell-specific expression of the known HSP70 receptor TLR4 was required for the protective effect of exosomes, and exosomal HSP70 interacted with TLR4 on hair cells. Our results indicate that exosomes are a previously undescribed mechanism of intercellular communication in the inner ear that can mediate nonautonomous hair cell survival. Exosomes may hold potential as nanocarriers for delivery of therapeutics against hearing loss.

Effect of Ataluren on dystrophin mutations

Duchenne muscular dystrophy is a severe muscle wasting disease caused by mutations in the dystrophin gene (dmd). Ataluren has been approved by the European Medicines Agency for treatment of Duchenne muscular dystrophy. Ataluren has been reported to promote ribosomal read‐through of premature stop codons, leading to restoration of full‐length dystrophin protein. However, the mechanism of Ataluren action has not been fully described. To evaluate the efficacy of Ataluren on all three premature stop codons featuring different termination strengths (UAA > UAG > UGA), novel dystrophin‐deficient zebrafish were generated. Pathological assessment of the muscle by birefringence quantification, a tool to directly measure muscle integrity, did not reveal a significant effect of Ataluren on any of the analysed dystrophin‐deficient mutants at 3 days after fertilization. Functional analysis of the musculature at 6 days after fertilization by direct measurement of the generated force revealed a significant improvement by Ataluren only for the UAA‐carrying mutant dmd^ta222a. Interestingly however, all other analysed dystrophin‐deficient mutants were not affected by Ataluren, including the dmd^pc3 and dmd^pc2 mutants that harbour weaker premature stop codons UAG and UGA, respectively. These in vivo results contradict reported in vitro data on Ataluren efficacy, suggesting that Ataluren might not promote read‐through of premature stop codons. In addition, Ataluren had no effect on dystrophin transcript levels, but mild adverse effects on wild‐type larvae were identified. Further assessment of N‐terminally truncated dystrophin opened the possibility of Ataluren promoting alternative translation codons within dystrophin, thereby potentially shifting the patient cohort applicable for Ataluren.

How do cyclic antibiotics with activity against Gram-negative bacteria permeate membranes? A machine learning informed experimental study

All antibiotics have to engage bacterial amphiphilic barriers such as the lipopolysaccharide-rich outer membrane or the phospholipid-based inner membrane in some manner, either by disrupting them outright and/or permeating them and thereby allow the antibiotic to get into bacteria. There is a growing class of cyclic antibiotics, many of which are of bacterial origin, that exhibit activity against Gram-negative bacteria, which constitute an urgent problem in human health. We examine a diverse collection of these cyclic antibiotics, both natural and synthetic, which include bactenecin, polymyxin B, octapeptin, capreomycin, and Kirshenbaum peptoids, in order to identify what they have in common when they interact with bacterial lipid membranes. We find that they virtually all have the ability to induce negative Gaussian curvature (NGC) in bacterial membranes, the type of curvature geometrically required for permeation mechanisms such as pore formation, blebbing, and budding. This is interesting since permeation of membranes is a function usually ascribed to antimicrobial peptides (AMPs) from innate immunity. As prototypical test cases of cyclic antibiotics, we analyzed amino acid sequences of bactenecin, polymyxin B, and capreomycin using our recently developed machine-learning classifier trained on α-helical AMP sequences. Although the original classifier was not trained on cyclic antibiotics, a modified classifier approach correctly predicted that bactenecin and polymyxin B have the ability to induce NGC in membranes, while capreomycin does not. Moreover, the classifier was able to recapitulate empirical structure-activity relationships from alanine scans in polymyxin B surprisingly well. These results suggest that there exists some common ground in the sequence design of hybrid cyclic antibiotics and linear AMPs.

Protective Mechanisms of Avocado Oil Extract Against Ototoxicity

Despite the excellent antimicrobial activity of aminoglycoside antibiotics, permanent inner ear damage associated with the use of these drugs has resulted in the need to develop strategies to address the ototoxic risk given their widespread use. In a previous study, we showed that avocado oil protects ear hair cells from damage caused by neomycin. However, the detailed mechanism by which this protection occurs is still unclear. Here, we investigated the auditory cell-protective mechanism of enhanced functional avocado oil extract (DKB122). RNA sequencing followed by pathway analysis revealed that DKB122 has the potential to enhance the expression of detoxification and antioxidant genes associated with glutathione metabolism (Hmox4, Gsta4, Mgst1, and Abcc3) in HEI-OC1 cells. Additionally, DKB122 effectively decreased ROS levels, resulting in the inhibition of apoptosis in HEI-OC1 cells. The expression of the inflammatory genes that encode chemokines and interleukins was also downregulated by DKB122 treatment. Consistent with these results, DKB122 significantly inhibited p65 nuclear migration induced by TNF-α or LPS in HEI-OC1 cells and THP-1 cells and the expression of inflammatory chemokine and interleukin genes induced by TNF-α was significantly reduced. Moreover, DKB122 treatment increased LC3-II and decreased p62 in HEI-OC1 cells, suggesting that DKB122 increases autophagic flux. These results suggest that DKB122 has otoprotective effects attributable to its antioxidant activity, induction of antioxidant gene expression, anti-inflammatory activity, and autophagy activation.

2,3,4',5-Tetrahydroxystilbene-2-O-β-D-Glucoside (THSG) Activates the Nrf2 Antioxidant Pathway and Attenuates Oxidative Stress-Induced Cell Death in Mouse Cochlear UB/OC-2 Cells

Oxidative stress plays a critical role in the pathogenesis of hearing loss, and 2,3,4′,5-tetrahydroxystilbene-2-O-β-D-glucoside (THSG) exerts antioxidant effects by inhibiting reactive oxygen species (ROS) generation. With the aim of developing new therapeutic strategies for oxidative stress, this study investigated the protective mechanism of THSG in vitro using a normal mouse cochlear cell line (UB/OC-2). The THSG and ascorbic acid have similar free radical scavenger capacities. H₂O₂, but not THSG, reduced the UB/OC-2 cell viability. Moreover, H₂O₂ might induce apoptosis and autophagy by inducing morphological changes, as visualized by microscopy. As evidenced by Western blot analysis and monodansylcadaverine (MDC) staining, THSG might decrease H₂O₂-induced autophagy. According to a Western blotting analysis and Annexin V/PI and JC-1 staining, THSG might protect cells from H₂O₂-induced apoptosis and stabilize the mitochondrial membrane potential. Furthermore, THSG enhanced the translocation of nucleus factor erythroid 2-related factor 2 (Nrf2) into the nucleus and increased the mRNA and protein expression of antioxidant/detoxifying enzymes under H₂O₂-induced oxidative stress conditions. Collectively, our findings demonstrate that THSG, as a scavenging agent, can directly attenuate free radicals and upregulate antioxidant/detoxifying enzymes to protect against oxidative damage and show that THSG protects UB/OC-2 cells from H₂O₂-induced autophagy and apoptosis in vitro.

Analysis of behavioral changes in zebrafish (Danio rerio) larvae caused by aminoglycoside-induced damage to the lateral line and muscles

Zebrafish behavior is influenced by the lateral line hair cells and muscles. Drug-induced behavioral changes can serve as indicators in the evaluation of drug toxicity. The aminoglycoside family of antibiotics comprise a number of agents, including neomycin (NM) and gentamicin (GM). We hypothesized that NM and GM exert different effects on zebrafish larvae through their action on the lateral line and muscle fibers, inducing different swimming behavioral patterns such as locomotor behavior and the startle response. In this study, 125 μM NM and 5, 10, 20 μM GM induced hair cell damage in the anterior and posterior lateral lines of zebrafish larvae. However, unlike GM, 125 μM NM also caused muscle damage. Locomotor behavior was decreased in the 125 μM NM-exposed group compared to the group exposed to GM. Furthermore, 125 μM NM exposure induced significantly different patterns of various indices of startle behavior compared with the GM exposure groups. Additionally, the larvae exhibited different startle responses depending on the concentration of GM. These results suggest that GM may be the drug-of-choice for analyzing behavioral changes in zebrafish caused by damage to the lateral line alone. Our study highlights the importance of confirming muscle damage in behavioral analyses using zebrafish.

Systemic Fluorescent Gentamicin Enters Neonatal Mouse Hair Cells Predominantly Through Sensory Mechanoelectrical Transduction Channels

Systemically administered aminoglycoside antibiotics can enter inner ear hair cells and trigger apoptosis. However, the in vivo route(s) by which aminoglycoside antibiotics enter hair cells remains controversial. Aminoglycosides can enter mouse hair cells by endocytosis or by permeation through transmembrane ion channels such as sensory mechanoelectrical transduction (MET) channels, transient receptor potential (TRP) channels, P2X channels, Piezo2-containing ion channels, or a combination of these routes. Transmembrane channel-like 1 (TMC1) and TMC2 are essential for sensory MET and appear to be the pore-forming components of sensory MET channels. The present study tested the hypothesis that systemic fluorescent gentamicin enters mouse hair cells predominantly through sensory MET channels. We employed Tmc1^Δ, Tmc2^Δ, and Tmc1::mCherry mice. In Tmc1::mCherry mice, the transgene was integrated on the X chromosome, resulting in mosaic expression of TMC1-mCherry in the hair cells of female heterozygous mice. After systemic administration of gentamicin-conjugated Texas Red (GTTR) into Tmc1^Δ;Tmc2^Δ mice and wild-type mice at postnatal day 4 (P4), robust GTTR fluorescence was detected in wild-type hair cells, whereas little or no GTTR fluorescence was detected in Tmc1^Δ;Tmc2^Δ hair cells. When GTTR was injected into developing mice at P0, P2, P4, or P6, the GTTR fluorescent intensity gradually increased from P0 to P4 in wild-type hair cells, whereas the intensity was stably low from P0 through P6 in Tmc1^Δ;Tmc2^Δ hair cells. The increase in the GTTR intensity coincided with the spatio-temporal onset of sensory MET in wild-type hair cells. In Tmc1::mCherry cochleae, only hair cells that showed a significant uptake of systemic GTTR took up FM1-43. Transmission electron microscopy could detect no disruption of normal endocytosis at the apical surface of Tmc1^Δ;Tmc2^Δ hair cells in vitro. These results provide substantial novel evidence that in vivo gentamicin enters neonatal mouse hair cells predominantly through sensory MET channels and not via endocytosis.

Ebselen attenuates tobramycin-induced ototoxicity in mice

BACKGROUND

Cystic fibrosis patients are often adminstered tobramycin to treat pulmonary infections. Unfortunately, a common side effect is hearing loss, which can fluctuate. Ebselen has known anti-inflammatory properties and could reduce the incidence and severity of tobramycin-induced hearing loss.

METHODS

In vitro: neonatal cochlear cultures were treated with tobramycin or cotreated with tobramycin and ebselen for 3 days. In vivo: adult mice were injected with tobramycin or tobramycin and ebselen for 14 days. ABRs were collected in a repeated measures design until 56 days after treatments. ABR threshold shifts were analyzed and a novel cochleotoxic criteria applied to determine the incidence of ototoxicity. Cochlear immunohistology was analyzed for IHC and OHC loss.

RESULTS

Tobramycin leads to significant IHC and OHC loss in cochlear explant cultures. Ebselen co-treatment at 1:20 concentrations resulted in significant otoprotection. Tobramycin leads to significant ABR threshold shifts that are ameliorated by ebselen co-treatment. Hearing loss did not correlate with significant IHC or OHC loss.

CONCLUSIONS

This mouse model of tobramycin-induced ototoxicity is clinically relevant in that it results in an incidence and severity of hearing loss recently documented in clinic. The in vitro experiments show that tobramycin kills hair cells and that ebselen co-treatment can attenuate this ototoxicity. The in vivo model shows tobramycin-induced hearing loss is ameliorated by ebselen co-treatment, but this is not explained by concomitant hair cell loss. These preclinical data support the testing of ebselen in CF patients receiving tobramycin treatment.

Intravenously delivered aminoglycoside antibiotics, tobramycin and amikacin, are not ototoxic in mice

Many drugs on the World Health Organization's list of critical medicines are ototoxic, destroying sensory hair cells within the ear. These drugs preserve life, but patients can experience side effects including permanent hearing loss and vestibular dysfunction. Aminoglycoside ototoxicity was first recognised 80 years ago. However, no preventative treatments have been developed. In order to develop such treatments, we must identify the factors driving hair cell death. In vivo, studies of cell death are typically conducted using mouse models. However, a robust model of aminoglycoside ototoxicity does not exist. Previous studies testing aminoglycoside delivery via intraperitoneal or subcutaneous injection have produced variable ototoxic effects in the mouse. As a result, surgical drug delivery to the rodent ear is often used to achieve ototoxicity. However, this technique does not accurately model clinical practice. In the clinic, aminoglycosides are administered to humans intravenously (i.v.). However, repeated i.v. delivery has not been reported in the mouse. This study evaluated whether repeated i.v. administration of amikacin or tobramycin would induce hearing loss. Daily i.v. injections over a two-week period were well tolerated and transient low frequency hearing loss was observed in the aminoglycoside treatment groups. However, the hearing changes observed did not mimic the high frequency patterns of hearing loss observed in humans. Our results indicate that the i.v. delivery of tobramycin or amikacin is not an effective technique for inducing ototoxicity in mice. This result is consistent with previously published reports indicating that the mouse cochlea is resistant to systemically delivered aminoglycoside ototoxicity.

Protective effects of pharmacological agents against aminoglycoside-induced nephrotoxicity: A systematic review

Introduction: Aminoglycosides have been long used for antibacterial treatment and are still commonly used in clinical practice. Despite their extensive application and positive effects, drug-related toxicity is considered as the main obstacle for aminoglycosides. Aminoglycosides induce nephrotoxicity through the endocytosis and accumulation of the antibiotics in the epithelial cells of proximal tubule. Most importantly, however, a number of pharmacological agents were demonstrated to have protective activities against nephrotoxicity in experimental animals.Areas covered: In the present systematic review, the authors provide and discuss the mechanisms and epidemiological features of aminoglycoside-induced nephrotoxicity, and focus mainly on recent discoveries and key features of pharmacological interventions. In total, 39 articles were included in this review.Expert opinion: The majority of studies investigated gentamicin-induced nephrotoxicity in animal models. Antioxidants, chemicals, synthetic drugs, hormones, vitamins, and minerals showed potential values to prevent gentamicin-induced nephrotoxicity. Indicators used to evaluate the effectiveness of nephroprotection included antioxidative indexes, inflammatory responses, and apoptotic markers. Among the nephroprotective agents studied, herbs and natural antioxidant agents showed excellent potential to provide a protective strategy against gentamicin-induced nephrotoxicity.

Apralogs: Apramycin 5-O-Glycosides and Ethers with Improved Antibacterial Activity and Ribosomal Selectivity and Reduced Susceptibility to the Aminoacyltranserferase (3)-IV Resistance Determinant

Apramycin is a structurally unique member of the 2-deoxystreptamine class of aminoglycoside antibiotics characterized by a monosubstituted 2-deoxystreptamine ring that carries an unusual bicyclic eight-carbon dialdose moiety. Because of its unusual structure, apramycin is not susceptible to the most prevalent mechanisms of aminoglycoside resistance including the aminoglycoside-modifying enzymes and the ribosomal methyltransferases whose widespread presence severely compromises all aminoglycosides in current clinical practice. These attributes coupled with minimal ototoxocity in animal models combine to make apramycin an excellent starting point for the development of next-generation aminoglycoside antibiotics for the treatment of multidrug-resistant bacterial infections, particularly the ESKAPE pathogens. With this in mind, we describe the design, synthesis, and evaluation of three series of apramycin derivatives, all functionalized at the 5-position, with the goals of increasing the antibacterial potency without sacrificing selectivity between bacterial and eukaryotic ribosomes and of overcoming the rare aminoglycoside acetyltransferase (3)-IV class of aminoglycoside-modifying enzymes that constitutes the only documented mechanism of antimicrobial resistance to apramycin. We show that several apramycin-5-O-β-d-ribofuranosides, 5-O-β-d-eryrthofuranosides, and even simple 5-O-aminoalkyl ethers are effective in this respect through the use of cell-free translation assays with wild-type bacterial and humanized bacterial ribosomes and of extensive antibacterial assays with wild-type and resistant Gram negative bacteria carrying either single or multiple resistance determinants. Ex vivo studies with mouse cochlear explants confirm the low levels of ototoxicity predicted on the basis of selectivity at the target level, while the mouse thigh infection model was used to demonstrate the superiority of an apramycin-5-O-glycoside in reducing the bacterial burden in vivo.

Enhanced mitochondrial membrane potential and ATP synthesis by photobiomodulation increases viability of the auditory cell line after gentamicin-induced intrinsic apoptosis

Photobiomodulation (PBM) has been suggested to have a therapeutic effect on irreversible hearing loss induced by aminoglycosides, including gentamicin (GM). However, its intracellular mechanism(s) in GM-induced ototoxicity remain poorly understood. In the present study, we investigated the effect of PBM in GM-induced ototoxicity in auditory cells. We tried to characterize the downstream process by PBM, and the process that triggered the increased cell viability of auditory cells. As a result, the effects of PBM against GM-induced ototoxicity by increasing ATP levels and mitochondrial membrane potential was confirmed. These results suggest a theory to explain the therapeutic effects and support the use of PBM for aminoglycoside-induced hearing loss.

Synergistic Ototoxicity of Gentamicin and Low-Dose Irradiation: Molecular Basis and Clinical Significance

BACKGROUND

Inner ear structures may be included in the radiation fields when irradiation is used to treat patients with head and neck cancers. These patients may also have concurrent infections that require gentamicin treatment. Radiation and gentamicin are both potentially ototoxic, and their combined use has been shown to result in synergistic ototoxicity in animals.

OBJECTIVE

We aimed to confirm the synergistic ototoxicity of combined gentamicin and low-dose irradiation treatment and identify the underlying molecular mechanisms using an in vitro model.

METHOD

We compared the ototoxic effects of gentamicin, low-dose irradiation, and their combination in the OC-k3 mouse cochlear cell line using cell viability assay, live/dead stain, apoptosis detection assay, oxidative stress detection, and studied the molecular mechanisms involved using immunoblot analysis.

RESULTS

Combined treatment led to prolonged oxidative stress, reduced cell viability, and synergistic apoptosis. Gentamicin induced the concurrent accumulation of LC3b-II and SQSTM1/p62, suggesting an impairment of autophagic flux. Low-dose irradiation induced transient p53 phosphorylation and persistent Akt phosphorylation in response to DNA damage. In combined treatment, gentamicin attenuated irradiation-induced Akt activation.

CONCLUSIONS

Besides increased oxidative stress, synergistic apoptosis observed in combined treatment could be attributed to gentamicin-induced perturbation of autophagic flux and attenuation of Akt phosphorylation, which led to an impairment of radiation-induced DNA repair response.

Combination of antioxidants and NFAT (nuclear factor of activated T cells) inhibitor protects auditory hair cells from ototoxic insult

Hair cell (HC) degeneration causes hearing loss in millions of people worldwide. Aminoglycoside exposure is one major cause of sensory HC damage. Aminoglycosides generate free radicals within the inner ear, permanently damaging sensory cells, and thus causing hearing loss. Hearing protection requires strategies to overcome the apparently irreversible loss of HCs in mammals. The nuclear factor of activated T cells (NFAT) inhibitor 11R-VIVIT reportedly protects HCs from gentamicin toxicity. Here we investigated whether the combination of 11R-VIVIT with the antioxidant L-carnitine or N-acetylcysteine could protect mouse cochlear HCs from gentamicin damage. Compared to single-component treatment, combined treatment with 11R-VIVIT plus L-carnitine yielded significant protection from gentamicin, and 11R-VIVIT plus N-acetylcysteine provided almost complete protection of HCs from gentamicin. Caspase activity in organ of Corti was significantly reduced by combined treatment with 11R-VIVIT + N-acetylcysteine + gentamicin, compared to 11R-VIVIT + gentamicin or gentamicin alone. Analysis of relative gene expression by qPCR revealed down-regulation of the pro-apoptotic genes Fasl and Casp9, and up-regulation of the antioxidant genes Hmox1 and Nrf2 after treatment with 11R-VIVIT + N-acetylcysteine + gentamicin, compared to single-compound treatment or gentamicin alone in cultures. Selective NFAT inhibition by 11R-VIVIT may be a good strategy for preventing gentamicin-induced HC damage. L-carnitine and N-acetylcysteine, with their ROS-reducing properties, contribute to the synergistic effectiveness with 11R-VIVIT by decreasing ROS-induced NFAT translocation. Our data suggest that a combined approach of NFAT inhibition together with an antioxidant, like N-acetylcysteine, could be useful for hearing loss treatment and/or prevention. Cover Image for this issue: https://doi.org/10.1111/jnc.14759.

Antibiotic regimens for neonatal sepsis - a protocol for a systematic review with meta-analysis

BACKGROUND

Sepsis is a major cause of morbidity and mortality among neonates and infants. Antibiotics are a central part of the first line treatment for sepsis in neonatal intensive care units worldwide. However, the evidence on the clinical effects of the commonly used antibiotic regimens for sepsis in neonates remains scarce. This systematic review aims to assess the efficacy and harms of antibiotic regimens for neonatal sepsis.

METHODS

Electronic searches will be conducted in MEDLINE, Embase, The Cochrane Library, CINAHL, ZETOC and clinical trial registries (clinicaltrials.gov and ISRCTN). We will include randomised controlled trials of different antibiotic regimens for sepsis of neonates and infants. Eligible interventions will be any antibiotic regimen. Two reviewers will independently screen, select, and extract data. The methodological quality of individual studies will be appraised following Cochrane methodology. Primary outcomes will be 'all-cause mortality' and 'serious adverse events'. Secondary outcomes will be 'need for respiratory support', 'need for circulatory support', 'neurodevelopmental impairment', ototoxicity, nephrotoxicity and necrotizing enterocolitis. We plan to perform a meta-analysis with trial sequential analysis.

DISCUSSION

This is the study protocol for a systematic review on the effects of different antibiotic regimens for neonatal sepsis. The results of this systematic review intent to adequately inform stakeholders or health care professionals in the field of neonatal sepsis, and to aid appropriate development of treatment guidelines.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO reference number: CRD42019134300.

The Novel Peptide Vaccine GV1001 Protects Hearing in a Kanamycin-induced Ototoxicity Mouse Model

HYPOTHESIS

We tested whether GV1001 has any ototoxic side effects at different doses and whether it protects hearing in an aminoglycoside-induced ototoxicity mouse model.

BACKGROUND

GV1001, a novel peptide vaccine currently being examined in a Phase 3 clinical trial to treat pancreatic cancer, also has anti-inflammatory and antioxidant effects.

METHODS

In the first experiment, C57/BL6 mice were injected with GV1001 preparations at concentrations of 0.1 to 100 mg/kg for 7 days to evaluate the toxicity of GV1001 on the inner ear and kidneys. In the second experiment, the protective effect of GV1001 was tested in an ototoxicity mouse model that was generated by injecting 800 mg/kg kanamycin (KM) for 2 weeks. The hearing threshold and hair cell loss were compared between the KM + GV1001 group (treated with 10 mg/kg GV1001 for 2 wk) and the KM + saline group. The hearing threshold was measured before, and 7, 14, and 21 days after the initial treatment. The blood urea nitrogen level was measured.

RESULTS

No ototoxicity or renal toxicity was found following treatment with different doses of GV1001 (0.1-100 mg/kg). The KM + saline group showed impaired auditory function and markedly disoriented and missing cochlear hair cells, while the KM + GV1001 group showed significant hearing and hair cell preservation in comparison (p < 0.05).

CONCLUSION

GV1001 itself did not have any detrimental effects on the inner ear or kidney. In the KM induced ototoxicity model, concomitant administration of GV1001 protected against cochlear hair cell damage and preserve hearing.

Aminoglycoside- and Cisplatin-Induced Ototoxicity: Mechanisms and Otoprotective Strategies

Ototoxicity refers to damage of inner ear structures (i.e., the cochlea and vestibule) and their function (hearing and balance) following exposure to specific in-hospital medications (i.e., aminoglycoside antibiotics, platinum-based drugs), as well as a variety of environmental or occupational exposures (e.g., metals and solvents). This review provides a narrative derived from relevant papers describing factors contributing to (or increasing the risk of) aminoglycoside and cisplatin-induced ototoxicity. We also review current strategies to protect against ototoxicity induced by these indispensable pharmacotherapeutic treatments for life-threatening infections and solid tumors. We end by highlighting several interventional strategies that are currently in development, as well as the diverse challenges that still need to be overcome to prevent drug-induced hearing loss.

Unresolved gustatory, olfactory and auditory adverse drug reactions to antibiotic drugs: a survey of spontaneous reporting to Eudravigilance

Objectives: Sensory adverse drug reactions (ADRs) are generally expected to be transient in nature. However, spontaneous reports describe frequently these events as long-lasting or unresolved. In this study, the authors reviewed the Eudravigilance publicly accessible database to describe the volume and expectedness of potentially unresolved outcomes for gustatory, olfactory and auditory (GOA) suspected ADRs associated with antibiotics for systemic use.Methods: 'Overall' and 'GOA' suspected ADRs were extracted from Eudravigilance to estimate the distribution of their outcomes among different antibiotic groups. Then, the authors identified the drugs contributing to at least 15% of all suspected GOA ADRs observed for the antibiotic groups, and evaluated the expectedness.Results: The frequency of persistent/permanent outcomes was higher for GOA suspected ADRs, as compared to the overall ones. Unresolved and undetermined outcomes for antibiotic-associated GOA ADRs in Eudravigilance might hide a large number of events with underestimated clinical consequences. Several persistent/permanent antibiotic-associated GOA reactions could be classified as serious and unexpected.Conclusion: Potential long-lasting or irreversible GOA reactions are often reported for all antibiotics drugs. Further studies are warranted to clarify whether this is an actual safety issue or simply it reflects a general difficulty in outcomes assessment for such reactions.

Modification at the 2'-Position of the 4,5-Series of 2-Deoxystreptamine Aminoglycoside Antibiotics To Resist Aminoglycoside Modifying Enzymes and Increase Ribosomal Target Selectivity

A series of derivatives of the 4,5-disubstituted class of 2-deoxystreptamine aminoglycoside antibiotics neomycin, paromomycin, and ribostamycin was prepared and assayed for (i) their ability to inhibit protein synthesis by bacterial ribosomes and by engineered bacterial ribosomes carrying eukaryotic decoding A sites, (ii) antibacterial activity against wild type Gram negative and positive pathogens, and (iii) overcoming resistance due to the presence of aminoacyl transferases acting at the 2′-position. The presence of five suitably positioned residual basic amino groups was found to be necessary for activity to be retained upon removal or alkylation of the 2′-position amine. As alkylation of the 2′-amino group overcomes the action of resistance determinants acting at that position and in addition results in increased selectivity for the prokaryotic over eukaryotic ribosomes, it constitutes an attractive modification for introduction into next generation aminoglycosides. In the neomycin series, the installation of small (formamide) or basic (glycinamide) amido groups on the 2′-amino group is tolerated.

Aminoglycoside drugs induce efficient read-through of CDKL5 nonsense mutations, slightly restoring its kinase activity

The X-linked CDKL5 gene codes for a kinase whose mutations have been associated with a suite of neurodevelopmental disorders generally characterized by early-onset epileptic encephalopathy and severe intellectual disability. The impact of these mutations on CDKL5 functions and brain development remain mainly unknown, although the importance of maintaining the catalytic activity is generally recognized. Since no cure exists for CDKL5 disorders, the demand for innovative therapies is a real emergency. The recent discovery that CDKL5 is dosage sensitive poses concerns on conventional protein and gene augmentative therapies. Thus, RNA-based therapeutic approaches might be preferred. We studied the efficacy of read-through therapy on CDKL5 premature termination codons (PTCs) that correspond roughly to 15% of all mutations. Our results provide the first demonstration that all tested CDKL5 nonsense mutations are efficiently suppressed by aminoglycoside drugs. The functional characterization of the restored full-length CDKL5 reveals that read-through proteins fully recover their subcellular localization, but only partially rescue their catalytic activity. Since read-through can cause amino acid substitution, CDKL5 patients carrying the PTC outside the catalytic domain might benefit more from a nonsense suppression therapy. Eventually, we demonstrate that non-aminoglycoside drugs, such as Ataluren (PTC124) and GJ072, are unable to induce read-through activity on CDKL5 PTCs. Although these drugs might be more effective in vivo, these results question the validity of the Ataluren phase 2 clinical trial that is currently ongoing on CDKL5 patients.

A new active peptide from Neptunea arthritica cumingii exerts protective effects against gentamicin-induced sensory-hair cell injury in zebrafish

Gentamicin is commonly used for effective treatment of severe Gram-negative bacterial infections. However, its use is being increasingly restricted owing to the ototoxic effects attributed to it. Gentamicin-induced ototoxicity is thought to be related with apoptosis induced by reactive oxygen species (ROS). In this study, we found a novel active peptide from Neptunea arthritica cumingii with otoprotective effects and no significant embryotoxic effects. The combined application of gentamicin and this novel active peptide helped sensory-hair cells to protect themselves from lethal ROS accumulation. This, in turn, reduced the expression of three genes (caspase-3, caspase-9, Bax), and thereby, the sensory-hair cell apoptosis promoted by ROS accumulation upon gentamicin administration. Our findings provided new insights into the prevention of gentamicin-induced hearing loss.

Inner ear organoids: new tools to understand neurosensory cell development, degeneration and regeneration

The development of therapeutic interventions for hearing loss requires fundamental knowledge about the signaling pathways controlling tissue development as well as the establishment of human cell-based assays to validate therapeutic strategies ex vivo Recent advances in the field of stem cell biology and organoid culture systems allow the expansion and differentiation of tissue-specific progenitors and pluripotent stem cells in vitro into functional hair cells and otic-like neurons. We discuss how inner ear organoids have been developed and how they offer for the first time the opportunity to validate drug-based therapies, gene-targeting approaches and cell replacement strategies.

Transcriptomic analysis of mouse cochleae suffering from gentamicin damage reveals the signalling pathways involved in hair cell regeneration

There is a strong capacity for hair cell regeneration after damage in the inner ear of non-mammals. However, mammalian hair cells are substantially unable to regenerate. To obtain insights into the mechanism of this difference, we analyzed the transcriptomic changes in the mouse cochleae suffered from gentamicin damage and compared them with those in the chick cochleae suffered from the same damage. The results indicated that 2,230 genes had significantly differential expression between the gentamicin- and saline-treated mouse cochleae. Some of the differentially expressed genes were grouped into 265 signaling pathways, including the Notch, Wnt (Wingless and INT-1), Bmp (bone morphogenetic protein), FGF (fibroblast growth factor) and Shh (sonic hedgehog) pathways. Using pharmacological inhibitors or agonists of these pathways, the effects of these pathways on hair cell regeneration were further studied. The results indicated that Bmp alone and its coregulation with the Notch or Wnt signaling pathways increased the numbers of generated cells from transdifferentiation or proliferation in the mouse cochlea after damage, in addition to the reported coregulation of Notch and Wnt. Thus, this work indicates a new signaling pathway (Bmp) and its synergetic coregulation in mammalian hair cell regeneration, providing potential therapeutic targets to increase mammalian hair cell regeneration.

Increased risk of aminoglycoside-induced hearing loss in MDR-TB patients with HIV coinfection

SETTING

A high proportion of individuals with multidrug-resistant tuberculosis (MDR-TB) develop permanent hearing loss due to ototoxicity caused by injectable aminoglycosides (AGs). The prevalence of AG-induced hearing loss is greatest in tuberculosis (TB) and human immunodeficiency virus (HIV) endemic countries in sub-Saharan Africa. However, whether HIV coinfection is associated with a higher incidence of AG-induced hearing loss during MDR-TB treatment is controversial.

OBJECTIVE

To evaluate the impact of HIV coinfection on AG-induced hearing loss among individuals with MDR-TB in sub-Saharan Africa.

DESIGN

This was a meta-analysis of articles published in PubMed, Embase, Scopus, Cumulative Index to Nursing and Allied Health Literature, Web of Science, Cochrane Review, and reference lists using search terms 'hearing loss', 'aminoglycoside', and 'sub-Saharan Africa'.

RESULTS

Eight studies conducted in South Africa, Botswana and Namibia and published between 2012 and 2016 were included. As the included studies were homogeneous (χ2 = 8.84, df = 7), a fixed-effects model was used. Individuals with MDR-TB and HIV coinfection had a 22% higher risk of developing AG-induced hearing loss than non-HIV-infected individuals (pooled relative risk 1.22, 95%CI 1.10-1.36) during MDR-TB treatment.

CONCLUSION

This finding is critical for TB programs with regard to the expansion of injectable-sparing regimens. Our findings lend credibility to using injectable-sparing regimens and more frequent hearing monitoring, particularly in resource-limited settings for HIV-coinfected individuals.

Why study inner ear hair cell mitochondria?

In several systems of the body (muscle, liver, nerves), new studies have examined the internal structure of mitochondria and brought to light striking new findings about how mitochondria are constructed and how their structure affects cell function. In the inner ear field, however, we have little structural knowledge about hair cell and supporting cell mitochondria, and virtually none about mitochondrial subtypes or how they function in health and disease. The need for such knowledge is discussed in this short review.

Aminoglycoside ribosome interactions reveal novel conformational states at ambient temperature

The bacterial 30S ribosomal subunit is a primary antibiotic target. Despite decades of discovery, the mechanisms by which antibiotic binding induces ribosomal dysfunction are not fully understood. Ambient temperature crystallographic techniques allow more biologically relevant investigation of how local antibiotic binding site interactions trigger global subunit rearrangements that perturb protein synthesis. Here, the structural effects of 2-deoxystreptamine (paromomycin and sisomicin), a novel sisomicin derivative, N1-methyl sulfonyl sisomicin (N1MS) and the non-deoxystreptamine (streptomycin) aminoglycosides on the ribosome at ambient and cryogenic temperatures were examined. Comparative studies led to three main observations. First, individual aminoglycoside–ribosome interactions in the decoding center were similar for cryogenic versus ambient temperature structures. Second, analysis of a highly conserved GGAA tetraloop of h45 revealed aminoglycoside-specific conformational changes, which are affected by temperature only for N1MS. We report the h44–h45 interface in varying states, i.e. engaged, disengaged and in equilibrium. Third, we observe aminoglycoside-induced effects on 30S domain closure, including a novel intermediary closure state, which is also sensitive to temperature. Analysis of three ambient and five cryogenic crystallography datasets reveal a correlation between h44–h45 engagement and domain closure. These observations illustrate the role of ambient temperature crystallography in identifying dynamic mechanisms of ribosomal dysfunction induced by local drug-binding site interactions. Together, these data identify tertiary ribosomal structural changes induced by aminoglycoside binding that provides functional insight and targets for drug design.

Effects of Ageing on the Mitochondrial Genome in Rat Vestibular Organs

Background:

Deterioration in vestibular function occurs with ageing and is linked to age-related falls. Sensory hair cells located in the inner ear vestibular labyrinth are critical to vestibular function. Vestibular hair cells rely predominantly on oxidative phosphorylation (OXPHOS) for ener-gy production and contain numerous mitochondria. Mitochondrial DNA (mtDNA) mutations and perturbed energy production are associated with the ageing process.

Objective:

We investigated the effects of ageing on mtDNA in vestibular hair and support cells, and vestibular organ gene expression, to better understand mechanisms of age-related vestibular deficits.

Methods:

Vestibular hair and supporting cell layers were microdissected from young and old rats, and mtDNA was quantified by qPCR. Additionally, vestibular organ gene expression was analysed by microarray and gene set enrichment analyses.

Results:

In contrast to most other studies, we found no evidence of age-related mtDNA deletion mu-tations. However, we found an increase in abundance of major arc genes near the mtDNA control re-gion. There was also a marked age-related reduction in mtDNA copy number in both cell types. Ves-tibular organ gene expression, gene set enrichment analysis showed the OXPHOS pathway was down regulated in old animals.

Conclusion:

Given the importance of mtDNA to mitochondrial OXPHOS and hair cell function, our findings suggest the vestibular organs are potentially on the brink of an energy crisis in old animals

Applications of photobiomodulation in hearing research: from bench to clinic

Hearing loss is very common and economically burdensome. No accepted therapeutic modality for sensorineural hearing loss is yet available; most clinicians emphasize rehabilitation, placing hearing aids and cochlear implants. Photobiomodulation (PBM) employs light energy to enhance or modulate the activities of specific organs, and is a popular non-invasive therapy used to treat skin lesions and neurodegenerative disorders. Efforts to use PBM to improve hearing have been ongoing for several decades. Initial in vitro studies using cell lines and ex vivo culture techniques have now been supplanted by in vivo studies in animals; PBM protects the sensory epithelium and triggers neural regeneration. Many reports have used PBM to treat tinnitus. In this brief review, we introduce PBM applications in hearing research, helpful protocols, and relevant background literature.

Novel compounds protect auditory hair cells against gentamycin-induced apoptosis by maintaining the expression level of H3K4me2

Aminoglycoside-induced hair cell (HC) loss is a major cause of hearing impairment, and the effective prevention of HC loss remains an unmet medical need. Epigenetic mechanisms have been reported to be involved in protecting cochlear cells against ototoxic drug injury, and in this study we developed new bioactive compounds that have similar chemical structures as the epigenetics-related lysine-specific demethylase 1 (LSD1) inhibitors. LSD1 inhibitors have been reported to protect cochlear cells by preventing demethylation of dimethylated histone H3K4 (H3K4me2). To determine whether these new compounds exert similar protective effects on HCs, we treated mouse cochlear explant cultures with the new compounds together with gentamycin. There was a severe loss of HCs in the organ of Corti after gentamycin exposure, while co-treatment with the new compounds significantly protected against gentamycin-induced HC loss. H3K4me2 levels in the nuclei of HCs decreased after exposure to gentamycin, but H3K4me2 levels were maintained in the presence of the new compounds. Apoptosis is also involved in the injury process, and the new compounds protected the inner ear HCs against apoptosis by reducing caspase-3 activation. Together, our findings demonstrate that our new compounds prevent gentamycin-induced HC loss by preventing the demethylation of H3K4me2 and by inhibiting apoptosis, and these results might provide the theoretical basis for novel drug development for hearing protection.