Pravastatin attenuates noise-induced cochlear injury in mice

Lipidomics profiling identifies β-oxidation as a key process in noise-induced hearing loss

Noise-induced hearing loss (NIHL) is the second leading cause of hearing loss worldwide, and the most common cause in young adults. Despite this burden, the molecular mechanisms by which noise causes damage are poorly understood, and there are no pharmacologic therapies to prevent or reduce noise-induced damage to the inner ear. Here, using targeted and untargeted lipidomics, we show that noise exposure induces changes in fatty acid (FA) and acylcarnitine (CAR) species in the inner ear, a metabolic profile indicative of noise-induced increases in β- oxidation. This conclusion is validated through treatment with Etomoxir, an inhibitor of carnitine palmitoyltransferase 1A, the rate-limiting enzyme of long-chain β-oxidation. Furthermore, we demonstrate that blocking β-oxidation with Etomoxir does not affect hearing in a normal acoustic environment but reduces the extent of hearing loss induced by an intense noise exposure (2 hours, 112 dB SPL, 8-16kHz). Together, our findings provide insights into cochlear energy metabolism and suggest that its modulation could be targeted to reduce NIHL.

Cisplatin-Induced Hearing Loss, Oxidative Stress, and Antioxidants as a Therapeutic Strategy-A State-of-the-Art Review

Cisplatin is an established component of treatment protocols for various solid malignancies but carries a significant potential for serious adverse effects. Ototoxicity from cisplatin treatment is an important dose-limiting toxicity that manifests as bilateral, progressive, irreversible, dose-dependent sensorineural hearing loss, ear pain, tinnitus, and vestibular dysfunction. Despite the recent approval of sodium thiosulphate for the prevention of cisplatin-induced hearing loss (CIHL) in pediatric patients, structured prevention programs are not routinely implemented in most hospitals, and reducing platinum-induced ototoxicity in adults remains an important clinical problem without established treatment options. Cochlear oxidative stress plays a fundamental role in CIHL. Here, we review the molecular mechanisms leading to oxidative stress in CIHL and the clinical and preclinical studies testing antioxidants in CIHL to guide future clinical trials in assessing the efficacy and safety of candidate antioxidant compounds in this clinical setting.

Hearing loss during chemotherapy: prevalence, mechanisms, and protection

Ototoxicity is an often-underestimated sequela for cancer patients undergoing chemotherapy, with an incidence rate exceeding 50%, affecting approximately 4 million individuals worldwide each year. Despite the nearly 2,000 publications on chemotherapy-related ototoxicity in the past decade, the understanding of its prevalence, mechanisms, and preventative or therapeutic measures remains ambiguous and subject to debate. To date, only one drug, sodium thiosulfate, has gained FDA approval for treating ototoxicity in chemotherapy. However, its utilization is restricted. This review aims to offer clinicians and researchers a comprehensive perspective by thoroughly and carefully reviewing available data and current evidence. Chemotherapy-induced ototoxicity is characterized by four primary symptoms: hearing loss, tinnitus, vertigo, and dizziness, originating from both auditory and vestibular systems. Hearing loss is the predominant symptom. Amongst over 700 chemotherapeutic agents documented in various databases, only seven are reported to induce hearing loss. While the molecular mechanisms of the hearing loss caused by the two platinum-based drugs are extensively explored, the pathways behind the action of the other five drugs are primarily speculative, rooted in their therapeutic properties and side effects. Cisplatin attracts the majority of attention among these drugs, encompassing around two-thirds of the literature regarding ototoxicity in chemotherapy. Cisplatin ototoxicity chiefly manifests through the loss of outer hair cells, possibly resulting from damages directly by cisplatin uptake or secondary effects on the stria vascularis. Both direct and indirect influences contribute to cisplatin ototoxicity, while it is still debated which path is dominant or where the primary target of cisplatin is located. Candidates for hearing protection against cisplatin ototoxicity are also discussed, with novel strategies and methods showing promise on the horizon.

Pathogenesis and New Pharmacological Approaches to Noise-Induced Hearing Loss: A Systematic Review

Noise-induced hearing loss (NIHL) is responsible for significant adverse effects on cognition, quality of life and work, social relationships, motor skills, and other psychological aspects. The severity of NIHL depends on individual patient characteristics, sound intensity, and mainly the duration of sound exposure. NIHL leads to the production of a reactive oxygen (ROS) inflammatory response and the activation of apoptotic pathways, DNA fragmentation, and cell death. In this situation, antioxidants can interact with free radicals as well as anti-apoptotics or anti-inflammatory substances and stop the reaction before vital molecules are damaged. Therefore, the aim of this study was to analyze the effects of different pharmacological treatments, focusing on exogenous antioxidants, anti-inflammatories, and anti-apoptotics to reduce the cellular damage caused by acoustic trauma in the inner ear. Experimental animal studies using these molecules have shown that they protect hair cells and reduce hearing loss due to acoustic trauma. However, there is a need for more conclusive evidence demonstrating the protective effects of antioxidant/anti-inflammatory or anti-apoptotic drugs' administration, the timeline in which they exert their pharmacological action, and the dose in which they should be used in order to consider them as therapeutic drugs. Further studies are needed to fully understand the potential of these drugs as they may be a promising option to prevent and treat noise-induced hearing loss.

Potential role of modulating autophagy levels in sensorineural hearing loss

In recent years, extensive research has been conducted on the pathogenesis of sensorineural hearing loss (SNHL). Apoptosis and necrosis have been identified to play important roles in hearing loss, but they cannot account for all hearing loss. Autophagy, a cellular process responsible for cell self-degradation and reutilization, has emerged as a significant factor contributing to hearing loss, particularly in cases of autophagy deficiency. Autophagy plays a crucial role in maintaining cell health by exerting cytoprotective and metabolically homeostatic effects in organisms. Consequently, modulating autophagy levels can profoundly impact the survival, death, and regeneration of cells in the inner ear, including hair cells (HCs) and spiral ganglion neurons (SGNs). Abnormal mitochondrial autophagy has been demonstrated in animal models of SNHL. These findings indicate the profound significance of comprehending autophagy while suggesting that our perspective on this cellular process holds promise for advancing the treatment of SNHL. Thus, this review aims to clarify the pathogenic mechanisms of SNHL and the role of autophagy in the developmental processes of various cochlear structures, including the greater epithelial ridge (GER), SGNs, and the ribbon synapse. The pathogenic mechanisms of age-related hearing loss (ARHL), also known as presbycusis, and the latest research on autophagy are also discussed. Furthermore, we underscore recent findings on the modulation of autophagy in SNHL induced by ototoxic drugs. Additionally, we suggest further research that might illuminate the complete potential of autophagy in addressing SNHL, ultimately leading to the formulation of pioneering therapeutic strategies and approaches for the treatment of deafness.

Evaluating calcium channel blockers and bisphosphonates as otoprotective agents in cochlear implantation hearing preservation candidates

OBJECTIVES

Evaluate potential effects of calcium channel blockers (CCB) and bisphosphonates (BP) on residual hearing following cochlear implantation.

METHODS

Medications of 303 adult hearing preservation (HP) candidates (low frequency pure tone average [LFPTA] of 125, 250, and 500 Hz ≤80 dB HL) were reviewed. Postimplantation LFPTA of patients taking CCBs and BPs were compared to controls matched by age and preimplantation LFPTA.

RESULTS

Twenty-six HP candidates were taking a CCB (N = 14) or bisphosphonate (N = 12) at implantation. Median follow-up was 1.37 years (range 0.22-4.64y). Among subjects with initial HP, 29% (N = 2 of 7) CCB users compared to 50% (N = 2 of 4) controls subsequently lost residual hearing 3-6 months later (OR = 0.40, 95% CI = 0.04-4.32, p = 0.58). None of the four BP patients with initial HP experienced delayed loss compared to 50% (N = 2 of 4) controls with initial HP (OR = 0.00, 95% CI = 0.00-1.95, P = 0.43). Two CCB and one BP patients improved to a LFPTA <80 dB HL following initial unaided thresholds that suggested loss of residual hearing.

DISCUSSION

There were no significant differences in the odds of delayed loss of residual hearing with CCBs or BPs.

CONCLUSION

Further investigation into potential otoprotective adjuvants for maintaining residual hearing following initial successful hearing preservation is warranted, with larger cohorts and additional CCB/BP agents.

Hear and Now: Ongoing Clinical Trials to Prevent Drug-Induced Hearing Loss

Each year over half a million people experience permanent hearing loss caused by treatment with therapeutic drugs with ototoxic side effects. There is a major unmet clinical need for therapies that protect against this hearing loss without reducing the therapeutic efficacy of these lifesaving drugs. At least 17 clinical trials evaluating 10 therapeutics are currently underway for therapies aimed at preventing aminoglycoside- and/or cisplatin-induced ototoxicity. This review describes the preclinical and clinical development of each of these approaches, provides updates on the status of ongoing trials, and highlights the importance of appropriate outcome measures in trial design and the value of reporting criteria in the dissemination of results.

Effect of statins on hearing outcome in patients with idiopathic sudden sensorineural hearing loss

Objective

Statins have been reported to improve vascular endothelial function and microcirculation, reduce oxidative stress, and exert anti-inflammatory and protective effects against inner ear damage. Therefore, this study aimed to investigate the effect of statins on hearing prognosis in patients with idiopathic sudden sensorineural hearing loss (ISSNHL).

Methods

We reviewed the medical records of 149 patients diagnosed with ISSNHL. Clinical characteristics, hearing thresholds, statin medications, and hematological findings were investigated. First, patients with ISSNHL were assigned to the good and poor outcome groups, and factors influencing their prognosis were analyzed. Furthermore, patients with dyslipidemia were investigated to determine whether statins have therapeutic effects on ISSNHL.

Results

Significant differences in age (p = .011), days from the onset of ISSNHL to the initiation of treatment (p = .04), and hematological total cholesterol (TC; p = .015) between the good and poor outcome groups were observed. Furthermore, when hearing outcomes were investigated in patients with dyslipidemia, TC was significantly lower in the good outcome group (p = .03). Although no significant therapeutic effects of statins were observed in participants with dyslipidemia, patients in the statin-treated group were significantly older and experienced more diabetic complications than those in the non-statin-treated group.

Conclusion

Although our study showed that dyslipidemia is a poor prognostic factor for ISSNHL, statins had no significant therapeutic effects on hearing recovery in ISSNHL patients with dyslipidemia. The patients that received statin medications were significantly older and experienced more diabetic complications, which may have affected their hearing prognosis.

Level of Evidence

Level 4.

Statins protect mice from high-decibel noise-induced hearing loss

No medical interventions for noise induced hearing loss (NIHL) are approved by the Food and Drug Administration (USA). Here, we evaluate statins in CBA/CaJ mice as potential drugs for hearing loss. Direct delivery of fluvastatin to the cochlea and oral delivery of lovastatin were evaluated. Baseline hearing was assessed using Auditory Brain Stem Responses (ABRs). For fluvastatin, a cochleostomy was surgically created in the basal turn of the cochlea by a novel, laser-based procedure, through which a catheter attached to a mini-osmotic pump was inserted. The pump was filled with a solution of 50 µM fluvastatin+carrier or with the carrier alone for continuous delivery to the cochlea. Mice were exposed to one octave band noise (8-16 kHz x 2 h x 110 dB SPL). In our past work with guinea pigs, fluvastatin protected in the contralateral cochlea. In this study in CBA/CaJ mice, hearing was also assessed in the contralateral cochlea 1-4 weeks after noise exposure. At two weeks post exposure, ABR thresholds at 4, 8, 12, 16, and 32 kHz were elevated, as expected, in the noise+carrier alone treated mice by approximately 9-, 17-, 41-, 29-, and 34-dB, respectively. Threshold elevations were smaller in mice treated with noise+fluvastatin to about 2-, 6-, 20-,12- and 12-dB respectively. Survival of inner hair cell synapses were not protected by fluvastatin over these frequencies. Lovastatin delivered by gavage showed lower threshold shifts than with carrier alone. These data show that direct and oral statin delivery protects mice against NIHL.

Effect of statin on age-related hearing loss via drug repurposing

Hearing loss in the elderly cause communication difficulties, decreased quality of life, isolation, loneliness and frustration. The aim of our study was to investigate the effect of drug repurposing candidates in aging mouse. The selected candidate drugs for age-related hearing loss (ARHL) included atorvastatin (AS) and sarpogrelate. Monotherapy or fixed dose combination (FDC) products were administered via oral gavage for 6 consecutive months. Auditory outcomes showed significant hearing preservation in AS-treated aging mice compared to aging control, especially in the early stages of ARHL in both 8 and 16 kHz frequencies. However, none of the FDC products were able to prevent ARHL regardless of AS involvement. In aging mice, damage and dysfunction of mitochondria was noted as well as reactive oxygen species overproduction leading to oxidative stress and intrinsic apoptosis. These processes of ARHL were significantly prevented with administration of AS. Normal structures of mitochondria were maintained, and antioxidant activity were proceeded by activation of HSF1/Sirt1 pathway. Our study suggests that AS is a promising drug repurposing candidate to delay the progression of ARHL.

Pitavastatin protects against neomycin-induced ototoxicity through inhibition of endoplasmic reticulum stress

Irreversible injury to inner ear hair cells induced by aminoglycoside antibiotics contributes to the formation of sensorineural hearing loss. Pitavastatin (PTV), a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, has been reported to exert neuroprotective effects. However, its role in aminoglycoside-induced hearing loss remains unknown. The objectives of this study were to investigate the beneficial effects, as well as the mechanism of action of PTV against neomycin-induced ototoxicity. We found that PTV remarkably reduced hair cell loss in mouse cochlear explants and promoted auditory HEI-OC1 cells survival after neomycin stimulation. We also observed that the auditory brainstem response threshold that was increased by neomycin was significantly reduced by pretreatment with PTV in mice. Furthermore, neomycin-induced endoplasmic reticulum stress in hair cells was attenuated by PTV treatment through inhibition of PERK/eIF2α/ATF4 signaling. Additionally, we found that PTV suppressed the RhoA/ROCK/JNK signal pathway, which was activated by neomycin stimulation in HEI-OC1 cells. Collectively, our results showed that PTV might serve as a promising therapeutic agent against aminoglycoside-induced ototoxicity.

Pravastatin Administration Alleviates Kanamycin-Induced Cochlear Injury and Hearing Loss

The effect of statins on aminoglycoside-induced ototoxicity is controversial. This study aimed to explore the role of pravastatin (PV) in kanamycin-induced hearing loss in rats. Adult rats were intraperitoneally treated with 20 mg/kg/day of kanamycin (KM) for 10 days. In the PV- and PV + KM-treated rats, 25 mg/kg/day of PV was intraperitoneally administered for 5 days. The auditory brainstem response (ABR) thresholds were measured before and after drug treatment using a smartEP system at 4, 8, 16, and 32 kHz. Cochlear changes in poly ADP-ribose (PAR) polymerase (PARP), PAR, and caspase 3 were estimated using Western blotting. PV administration did not increase the ABR thresholds. The KM-treated rats showed elevated ABR thresholds at 4, 8, 16, and 32 kHz. The PV + KM-treated rats demonstrated lower ABR thresholds than the KM-treated rats at 4, 8, and 16 kHz. The cochlear outer hair cells and spiral ganglion cells were relatively preserved in the PV + KM-treated rats when compared with that in the KM-treated rats. The cochlear expression levels of PARP, PAR, and caspase 3 were higher in the KM-treated rats. The PV + KM-treated rats showed lower levels of PARP, PAR, and caspase 3 than the KM-treated rats. PV protected cochleae from KM-induced hearing loss in rats. The regulation of autophagy and apoptosis mediated the otoprotective effects of PV.

Hearing Function, Degeneration, and Disease: Spotlight on the Stria Vascularis

The stria vascularis (SV) is a highly vascularized tissue lining the lateral wall of the cochlea. The SV maintains cochlear fluid homeostasis, generating the endocochlear potential that is required for sound transduction. In addition, the SV acts as an important blood-labyrinth barrier, tightly regulating the passage of molecules from the blood into the cochlea. A healthy SV is therefore vital for hearing function. Degeneration of the SV is a leading cause of age-related hearing loss, and has been associated with several hearing disorders, including Norrie disease, Meniere's disease, Alport syndrome, Waardenburg syndrome, and Cytomegalovirus-induced hearing loss. Despite the SV's important role in hearing, there is still much that remains to be discovered, including cell-specific function within the SV, mechanisms of SV degeneration, and potential protective or regenerative therapies. In this review, we discuss recent discoveries elucidating the molecular regulatory networks of SV function, mechanisms underlying degeneration of the SV, and otoprotective strategies for preventing drug-induced SV damage. We also highlight recent clinical developments for treating SV-related hearing loss and discuss future research trajectories in the field.

Effect of Electroacupuncture on Noise-Induced Hearing Loss in Rats

Acupuncture has long been used to relieve some inner ear diseases such as deafness and tinnitus. The present study examined the effect of electroacupuncture (EA) on noise-induced hearing loss (NIHL) in animals. A NIHL rat model was established. Electroacupuncture pretreatment at 2 Hz or posttreatment at the right Zhongzhu (TE3) acupoint was applied for 1 hour. Auditory thresholds were measured using auditory brainstem responses (ABRs), and histopathology of the cochlea was examined. The results indicated that the baseline auditory threshold of ABR was not significantly different between the control (no noise), EA-only (only EA without noise), noise (noise exposure only), pre-EA (pretreating EA then noise), and post-EA (noise exposure then posttreating with EA) groups. Significant auditory threshold shifts were found in the noise, pre-EA, and post-EA groups in the immediate period after noise exposure, whereas auditory recovery was better in the pre-EA and post-EA groups than that in the noise group at the three days, one week (W1), two weeks (W2), three weeks (W3), and four weeks(W4) after noise stimulation. Histopathological examination revealed greater loss of the density of spiral ganglion neurons in the noise group than in the control group at W1 and W2. Although significant loss of spiral ganglion loss happened in pre-EA and post-EA groups, such loss was less than the loss of the noise group, especially W1. These results indicate that either pretreatment or posttreatment with EA may facilitate auditory recovery after NIHL. The detailed mechanism through which EA alleviates NIHL requires further study.

Association between Statin Use and Sensorineural Hearing Loss in Type 2 Diabetic Patients: A Hospital-Based Study

Statins have emerged as protective agents against sensorineural hearing loss (SNHL) associated with dyslipidemia, but the effects of statins on SNHL are not consistent. The purpose of this study was to investigate the association between statin use and the risk of SNHL using a hospital cohort. This nested case-control study included type 2 diabetic patients over the age of 18 years without a history of hearing loss. Of these, 1379 patients newly diagnosed with SNHL or tinnitus were classified as cases, and 5512 patients matched to the cases based on age, sex, and index year were classified as controls. Chi-squared tests were used to compare categorical variables between the two groups. Odds ratios (ORs) and adjusted odds ratios (AOR) were calculated from univariate and multivariable unconditional logistic regression analyses, respectively. There was a significant difference in the prevalence of statin use between the cases and controls (53.7% vs. 61.2%, respectively; p < 0.001). The use of statins in type 2 diabetic patients significantly reduced the risk of SNHL or tinnitus by 24.8% (95% CI 14.2–34.1%, p < 0.001) after controlling for confounders. Similar results were found for the association between statin use and SNHL (AOR = 0.706; 95% CI 0.616–0.811, p < 0.001). The protective effects of statins against SNHL were consistent regardless of age and sex. The use of statins for type 2 diabetic patients was significantly associated with a reduced risk of SNHL, regardless of age and sex. Further studies are needed, especially large cohort studies, to evaluate the long-term protective effects of statins.

A cell-type-specific atlas of the inner ear transcriptional response to acoustic trauma

Noise-induced hearing loss (NIHL) results from a complex interplay of damage to the sensory cells of the inner ear, dysfunction of its lateral wall, axonal retraction of type 1C spiral ganglion neurons, and activation of the immune response. We use RiboTag and single-cell RNA sequencing to survey the cell-type-specific molecular landscape of the mouse inner ear before and after noise trauma. We identify induction of the transcription factors STAT3 and IRF7 and immune-related genes across all cell-types. Yet, cell-type-specific transcriptomic changes dominate the response. The ATF3/ATF4 stress-response pathway is robustly induced in the type 1A noise-resilient neurons, potassium transport genes are downregulated in the lateral wall, mRNA metabolism genes are downregulated in outer hair cells, and deafness-associated genes are downregulated in most cell types. This transcriptomic resource is available via the Gene Expression Analysis Resource (gEAR; https://umgear.org/NIHL) and provides a blueprint for the rational development of drugs to prevent and treat NIHL.

Atorvastatin is associated with reduced cisplatin-induced hearing loss

BACKGROUNDCisplatin is widely used to treat adult and pediatric cancers. It is the most ototoxic drug in clinical use, resulting in permanent hearing loss in approximately 50% of treated patients. There is a major need for therapies that prevent cisplatin-induced hearing loss. Studies in mice suggest that concurrent use of statins reduces cisplatin-induced hearing loss.METHODSWe examined hearing thresholds from 277 adults treated with cisplatin for head and neck cancer. Pretreatment and posttreatment audiograms were collected within 90 days of initiation and completion of cisplatin therapy. The primary outcome measure was a change in hearing as defined by the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE).RESULTSAmong patients on concurrent atorvastatin, 9.7% experienced a CTCAE grade 2 or higher cisplatin-induced hearing loss compared with 29.4% in nonstatin users (P < 0.0001). A mixed-effect model analysis showed that atorvastatin use was significantly associated with reduced cisplatin-induced hearing loss (P ≤ 0.01). An adjusted odds ratio (OR) analysis indicated that an atorvastatin user is 53% less likely to acquire a cisplatin-induced hearing loss than a nonstatin user (OR = 0.47; 95% CI, 0.30-0.78). Three-year survival rates were not different between atorvastatin users and nonstatin users (P > 0.05).CONCLUSIONSOur data indicate that atorvastatin use is associated with reduced incidence and severity of cisplatin-induced hearing loss in adults being treated for head and neck cancer.TRIAL REGISTRATIONClinicalTrials.gov identifier NCT03225157.FUNDINGFunding was provided by the Division of Intramural Research at the National Institute on Deafness and Other Communication Disorders (1 ZIA DC000079, ZIA DC000090).

Association between Statin Use and Meniere's Disease: Results from a National Health Screening Cohort

The protective effects of statins against inner ear diseases have been suggested. This study investigated the relationship between previous statin use and the occurrence of Meniere’s disease (MD). Participants ≥40 years old in the Korean National Health Insurance Service-Health Screening Cohort 2002–2015 were enrolled. A total of 7734 MD participants were matched with 38,670 comparison participants. The dates of statin prescriptions for the 2 years before the onset of MD were examined. A conditional logistic regression analysis was performed to estimate the odds ratios (ORs) of statin use for MD. Regarding the different types of statins, lipophilic statins, but not hydrophilic statins, were associated with lower odds of MD in the <65 year-old group (adjusted OR = 0.81, 95% CI = 0.68–0.97, p = 0.023). Prior statin use did not show association with MD in the adult population. Regarding the different types of statins, lipophilic statin use was related to a lower rate of MD in a middle-aged population.

Melatonin protects cochlear hair cells from nicotine-induced injury through inhibiting apoptosis, inflammation, oxidative stress and endoplasmic reticulum stress

Hearing loss positively links with cigarette smoking. However, the involved mechanism and treatment strategies are largely unrevealed. This study aimed to investigate the damaging effect of nicotine on cochlear hair cells, reveal the underlying mechanism and evaluate the therapeutic effect of melatonin on nicotine-induced injury. The results showed that nicotine induced cytotoxicity of House Ear Institute-Organ of Corti 1 (HEI-OC1) cochlear hair cells in a dose-dependent manner (0, 2.5, 5, 10, 20, 40 and 80 μM). Functional investigations showed that nicotine (10 μM) stimulation dramatically promoted apoptosis, inflammatory response, oxidative stress and endoplasmic reticulum stress in HEI-OC1 cells. Moreover, melatonin treatment dose-dependently alleviated the nicotine-induced cytotoxicity in HEI-OC1 cells (0, 10 25, 50 and 100 μM). Further investigation showed that melatonin (100 μM) effectively attenuated the nicotine-induced apoptosis, inflammation, oxidative stress and endoplasmic reticulum stress in HEI-OC1 cells. Collectively, we demonstrated that nicotine induced apoptosis, inflammation, oxidative stress and endoplasmic reticulum stress of cochlear hair cells in an in vitro cell model. Melatonin showed protective effect on these aspects, suggesting that melatonin may be a potential agent for treating smoking-induced hearing loss.

The role of oxidative stress in the susceptibility of noise-impaired cochleae to synaptic loss induced by intracochlear electrical stimulation

Intracochlear electrical stimulation (ES) generated by cochlear implants (CIs) is used to activate auditory nerves to restore hearing perception in deaf subjects and those with residual hearing who use electroacoustic stimulation (EAS) technology. Approximately 1/3 of EAS recipients experience loss of residual hearing a few months after ES activation, but the underlying mechanism is unknown. Clinical evidence indicates that the loss is related to the previous history of noise-induced hearing loss (NIHL). In this report, we investigated the impact of intracochlear ES on oxidative stress levels and synaptic counts in inner hair cells (IHCs) of the apical, middle and basal regions of guinea pigs with normal hearing (NH) and NIHL. Our results demonstrated that intracochlear ES with an intensity of 6 dB above the thresholds of electrically evoked compound action potentials (ECAPs) could induce the elevation of oxidative stress levels, resulting in a loss of IHC synapses near the electrodes in the basal and middle regions of the NH cochleae. Furthermore, the apical region of cochleae with NIHL were more susceptible to synaptic loss induced by relatively low-intensity ES than that of NH cochleae, resulting from the additional elevation of oxidative stress levels and the reduced antioxidant capability throughout the whole cochlea.

Association Between Sudden Sensorineural Hearing Loss and History of Statin Use: A Nested Case-Control Study

OBJECTIVE

The effect of statin on sudden sensorineural hearing loss (SSNHL) remains unclear. Thus, this study aimed to investigate the association between prior statin use and SSNHL.

STUDY DESIGN

A nested case-control study.

SETTING

Participants aged ≥40 years were enrolled from the 2002-2015 Korean National Health Insurance Service-Health Screening Cohort.

METHODS

A total of 5876 patients with SSNHL were matched with 23,504 control participants for age, sex, income, and region of residence. History of statin use for 2 years before SSNHL onset was investigated between the groups. The odds ratios (ORs) of the length of statin use for SSNHL stratified by age, sex, income, and region of residence were analyzed with conditional logistic regression. Dyslipidemia, total cholesterol, blood pressure, blood glucose, hemoglobin, obesity, smoking, alcohol consumption, and Charlson Comorbidity Index score were adjusted. The adjusted variables were subjected to subgroup analyses.

RESULTS

The SSNHL group had a longer duration of statin use than the control group (mean [SD], 81.9 [197.7] days vs 72.7 [188.0] days; P = .001). However, statin use was not associated with SSNHL after adjusting for the confounders (adjusted OR, 1.04; 95% CI, 0.98-1.11; P = .245). There was a positive correlation between statin use and SSNHL in the crude model (crude OR, 1.10; 95% CI, 1.04-1.16; P = .001). However, there was no association between statin use and SSNHL in all subgroup analyses.

CONCLUSION

Previous statin use was not associated with SSNHL.

Regeneration of Cochlear Synapses by Systemic Administration of a Bisphosphonate

Sensorineural hearing loss (SNHL) caused by noise exposure and attendant loss of glutamatergic synapses between cochlear spiral ganglion neurons (SGNs) and hair cells is the most common sensory deficit worldwide. We show here that systemic administration of a bisphosphonate to mice 24 h after synaptopathic noise exposure regenerated synapses between inner hair cells and SGNs and restored cochlear function. We further demonstrate that this effect is mediated by inhibition of the mevalonate pathway. These results are highly significant because they suggest that bisphosphonates could reverse cochlear synaptopathy for the treatment of SNHL.

Lovastatin protects against cisplatin-induced hearing loss in mice

Cisplatin is used to treat a variety of solid tumors in both children and adults. However, cisplatin has serious side-effects, some of which may permanently affect patients' quality of life following treatment, such as ototoxicity. There is currently no FDA-approved therapy for the prevention or treatment of cisplatin-induced hearing loss. Herein we examine the potential for statins to prevent cisplatin-induced ototoxicity. Statins, a class of drugs commonly used to prevent or manage hypercholesterolemia, have been of clinical utility for decades with dependable outcomes and reliable safety profiles in humans. Statins are known to be protective in animal models of noise-induced and age-related hearing loss. Moreover, studies have demonstrated an additive benefit of statins in cancer treatment. In the current study, lovastatin reduces cisplatin-induced hearing loss in adult mice. Lovastatin-mediated protection was significantly greater among female than male mice, and the dose of lovastatin required for protection was different between the sexes. Taken together our data indicate that lovastatin reduces cisplatin-induced hearing loss in mice and suggest that concurrent statin and cisplatin therapy may represent a feasible clinical strategy for reducing cisplatin-induced ototoxicity that should be explored for future clinical use.

Increased oxidative stress, inflammation, and glutamate: Potential preventive and therapeutic targets for hearing disorders

Hearing disorders constitute one of the major health concerns in the USA. Decades of basic and clinical studies have identified numerous ototoxic agents and investigated their modes of action on the inner ear, utilizing tissue culture as well as animal and human models. Current preventive and therapeutic approaches are considered unsatisfactory. Therefore, additional modalities should be developed. Many studies suggest that increased levels of oxidative stress, chronic inflammation, and glutamate play an important role in the initiation and progression of damage to the inner ear leading to hearing impairments. To prevent these cellular deficits, antioxidants, anti-inflammatory agents, and antagonists of glutamate receptor have been used individually or in combination with limited success. It is essential, therefore, to simultaneously enhance the levels of antioxidant enzymes by activating the Nrf2 (a nuclear transcriptional factor) pathway, dietary and endogenous antioxidant compounds, and B12-vitamins in order to reduce the levels of oxidative stress, chronic inflammation, and glutamate at the same time. This review presents evidence to show that increased levels of these cellular metabolites, biochemical or factors are involved in the pathogenesis of cochlea leading to hearing impairments. It presents scientific rationale for the use of a mixture of micronutrients that may decrease the levels of oxidative damage, chronic inflammation, and glutamate at the same time. The benefits for using oral administration of proposed micronutrient mixture in humans are presented. Animal and limited human studies indirectly suggest that orally administered micronutrients can accumulate in the inner ear. Therefore, this route of administration may be useful in prevention, and in combination with standard care, in improved management of hearing problems following exposure to well-recognized and studied ototoxic agents, such as noise, cisplatin, aminoglycoside antibiotics, and advanced age.

Evidence Supporting the Hypothesis That Inflammation-Induced Vasospasm Is Involved in the Pathogenesis of Acquired Sensorineural Hearing Loss

Sensorineural hearing loss is mainly acquired and affects an estimated 1.3 billion humans worldwide. It is related to aging, noise, infection, ototoxic drugs, and genetic defects. It is essential to identify reversible and preventable causes to be able to reduce the burden of this disease. Inflammation is involved in most causes and leads to tissue injury through vasospasm-associated ischemia. Vasospasm is reversible. This review summarized evidence linking inflammation-induced vasospasm to several forms of acquired sensorineural hearing loss. The link between vasospasm and sensorineural hearing loss is directly evident in subarachnoid haemorrhage, which involves the release of vasoconstriction-inducing cytokines like interleukin-1, endothelin-1, and tumour necrosis factor. These proinflammatory cytokines can also be released in response to infection, autoimmune disease, and acute or chronically increased inflammation in the ageing organism as in presbyacusis or in noise-induced cochlear injury. Evidence of vasospasm and hearing loss has also been discovered in bacterial meningitis and brain injury. Resolution of inflammation-induced vasospasm has been associated with improvement of hearing in autoimmune diseases involving overproduction of interleukin-1 from inflammasomes. There is mainly indirect evidence for vasospasm-associated sensorineural hearing loss in most forms of systemic or injury- or infection-induced local vascular inflammation. This opens up avenues in prevention and treatment of vascular and systemic inflammation as well as vasospasm itself as a way to prevent and treat most forms of acquired sensorineural hearing loss. Future research needs to investigate interventions antagonising vasospasm and vasospasm-inducing proinflammatory cytokines and their production in randomised controlled trials of prevention and treatment of acquired sensorineural hearing loss. Prime candidates for interventions are hereby inflammasome inhibitors and vasospasm-reducing drugs like nitric oxide donors, rho-kinase inhibitors, and magnesium which have the potential to reduce sensorineural hearing loss in meningitis, exposure to noise, brain injury, arteriosclerosis, and advanced age-related and autoimmune disease-related inflammation.

The efficacy of statins as otoprotective agents: A systematic review

OBJECTIVE

This systematic review examined current literature, summarised research findings and identified research gaps regarding the efficacy of statins on audiological outcomes.

METHODS

Systematic search of electronic databases and grey literature was performed. Eligibility criteria were the study of a statin drug with report of audiological outcomes such as hearing, tinnitus or balance in either human or animal studies. Data extraction and quality assessment were performed by two independently researchers. The characteristics of the study and research findings were collated and summarised. A narrative synthesis was conducted. Meta-analysis was not possible due to heterogeneity of the included studies.

RESULTS

Analysis of searches yielded 17 studies meeting the criteria. Included studies had variable drug type and dosage, outcome measures and associated inner ear conditions. Most animal experiments showed promising audiological outcomes after statin treatment, demonstrated by the results of auditory brainstem response, distortion product otoacoustic emissions and inner ear histology. However, no clear effect can be discerned in human trials due to the mixed results, and heterogeneity in research methodology and quality. Audiological outcomes were not always correlated with cholesterol levels.

CONCLUSIONS

Statins remain a potential candidate as otoprotective agents which warrant further investigation.

Effect of statins on hearing function and subjective tinnitus in hyperlipidemic patients

INTRODUCTION

It is known that hyperlipidemia reduces hearing functions. In this study, we aimed to study the effect of antihyperlipidemic drugs on hearing functions and tinnitus.

METHODS

Eighty-four patients aged 18 to 84, who were diagnosed with hyperlipidemia and started treatment with the statin group (atorvastatin 20 mg and 40 mg, rosuvastatin 10 mg and 20 mg, and simvastatin 20 mg) of antihyperlipidemic drugs, were included in this study. All patients underwent pure-tone audiometry before starting treatment with antihyperlipidemic drugs. Patients with tinnitus were evaluated by Tinnitus Severity Index and Visual Analogue Scale. In the 6th month of therapy, otologic examination, pure-tone audiometry and tinnitus evaluation of the patients were repeated.

RESULTS

No significant difference was found in the pure-tone averages of the patients before and after statin use (p > 0.05). However, it was found in the audiometry that, after statin use, all drugs caused to statistically significant decrease in the hearing thresholds at 6000 Hertz (p < 0.05). Also, a strong increase was found in the Speech Discrimination percentages after treatment in patients using rosuvastatin 10 mg (p = 0.022). A significant decrease was found in the tinnitus frequency, duration, severity and degree of annoyance in patients using rosuvastatin 10 mg and 20 mg (p < 0.05).

CONCLUSION

Statin group of drugs can have a positive effect on the hearing functions and subjective tinnitus. In particular, it is seen that rosuvastatin group of statins has a more notable effect on tinnitus. It was considered that further studies with larger patient groups are needed.

Fluvastatin protects cochleae from damage by high-level noise

Exposure to noise and ototoxic drugs are responsible for much of the debilitating hearing loss experienced by about 350 million people worldwide. Beyond hearing aids and cochlear implants, there have been no other FDA approved drug interventions established in the clinic that would either protect or reverse the effects of hearing loss. Using Auditory Brainstem Responses (ABR) in a guinea pig model, we demonstrate that fluvastatin, an inhibitor of HMG-CoA reductase, the rate-limiting enzyme of the mevalonate pathway, protects against loss of cochlear function initiated by high intensity noise. A novel synchrotron radiation based X-ray tomographic method that imaged soft tissues at micrometer resolution in unsectioned cochleae, allowed an efficient, qualitative evaluation of the three-dimensional internal structure of the intact organ. For quantitative measures, plastic embedded cochleae were sectioned followed by hair cell counting. Protection in noise-exposed cochleae is associated with retention of inner and outer hair cells. This study demonstrates the potential of HMG-CoA reductase inhibitors, already vetted in human medicine for other purposes, to protect against noise induced hearing loss.

Current insights in noise-induced hearing loss: a literature review of the underlying mechanism, pathophysiology, asymmetry, and management options

BACKGROUND

Noise-induced hearing loss is one of the most common forms of sensorineural hearing loss, is a major health problem, is largely preventable and is probably more widespread than revealed by conventional pure tone threshold testing. Noise-induced damage to the cochlea is traditionally considered to be associated with symmetrical mild to moderate hearing loss with associated tinnitus; however, there is a significant number of patients with asymmetrical thresholds and, depending on the exposure, severe to profound hearing loss as well.

MAIN BODY

Recent epidemiology and animal studies have provided further insight into the pathophysiology, clinical findings, social and economic impacts of noise-induced hearing loss. Furthermore, it is recently shown that acoustic trauma is associated with vestibular dysfunction, with associated dizziness that is not always measurable with current techniques. Deliberation of the prevalence, treatment and prevention of noise-induced hearing loss is important and timely. Currently, prevention and protection are the first lines of defence, although promising protective effects are emerging from multiple different pharmaceutical agents, such as steroids, antioxidants and neurotrophins.

CONCLUSION

This review provides a comprehensive update on the pathophysiology, investigations, prevalence of asymmetry, associated symptoms, and current strategies on the prevention and treatment of noise-induced hearing loss.

The Effect of Atorvastatin on Preventing Noise-Induced Hearing Loss: An Experimental Study

Background:

Noise-induced hearing loss (NIHL) is a common, irreversible occupational disease. Statins have recently been proposed to prevent NIHL.

Objective:

To assess the effect of atorvastatin for the prevention of NIHL in rats.

Methods:

In this experimental study, forty 2–3-month-old Wistar male rats were divided into 5 groups of 8 animals. 3 groups of rats received atorvastatin at doses of 5, 25, and 50 mg/kg daily for 14 days. The 4^th group of rats received normal saline; another group was the control group. After 2 weeks of treatment, the rats were exposed to broad-band noise (125– 20 000 Hz) at 110 dB-SPL intensity for 2 hours. Response amplitude of all ears at 5 frequencies was assessed by distortion product otoacoustic emissions (DP-OAE) at baseline, 2 hours, and 2 weeks after the exposure.

Results:

Response amplitude was significantly decreased at all frequencies immediately after exposure to noise in all studied groups. The amplitude increased after 72 hours to a level higher than temporary threshold shift (TTS); this change was only significant in the group received 5 mg/kg atorvastatin.

Conclusion:

Low dose atorvastatin (5 mg/kg) used before exposure to noise can probably prevent NIHL in rats. This effect was not observed with higher doses of the drug.

NRF2 Is a Key Target for Prevention of Noise-Induced Hearing Loss by Reducing Oxidative Damage of Cochlea

Noise-induced hearing loss (NIHL) is one of the most common sensorineural hearing deficits. Recent studies have demonstrated that the pathogenesis of NIHL is closely related to ischemia-reperfusion injury of cochlea, which is caused by blood flow decrease and free radical production due to excessive noise. This suggests that protecting the cochlea from oxidative stress is an effective therapeutic approach for NIHL. NRF2 is a transcriptional activator playing an essential role in the defense mechanism against oxidative stress. To clarify the contribution of NRF2 to cochlear protection, we examined Nrf2^–/– mice for susceptibility to NIHL. Threshold shifts of the auditory brainstem response at 7 days post-exposure were significantly larger in Nrf2^–/– mice than wild-type mice. Treatment with CDDO-Im, a potent NRF2-activating drug, before but not after the noise exposure preserved the integrity of hair cells and improved post-exposure hearing levels in wild-type mice, but not in Nrf2^–/– mice. Therefore, NRF2 activation is effective for NIHL prevention. Consistently, a human NRF2 SNP was significantly associated with impaired sensorineural hearing levels in a cohort subjected to occupational noise exposure. Thus, high NRF2 activity is advantageous for cochlear protection from noise-induced injury, and NRF2 is a promising target for NIHL prevention.

Macrophage Migration Inhibitory Factor Deficiency Causes Prolonged Hearing Loss After Acoustic Overstimulation

HYPOTHESIS

Macrophage migration inhibitory factor plays an important role in noise-induced hearing loss.

BACKGROUND

Macrophage migration inhibitory factor is an essential factor in axis formation and neural development. Macrophage migration inhibitory factor is expressed in the inner ear, but its function remains to be elucidated.

METHODS

Macrophage migration inhibitory factor-deficient mice (MIF(-/-) mice) were used in this study. Wild-type and MIF(-/-) mice received noise exposure composed of octave band noise. Auditory brainstem response thresholds were examined before (control) and at 0, 12, and 24 hours and 2 weeks after the intense noise exposure. Morphological findings of cochlear hair cells were investigated using scanning electron microscopy. Histopathological examination with hematoxylin and eosin staining and TUNEL assay were also performed.

RESULTS

In both the wild-type and MIF(-/-) mice, acoustic overstimulation induced significant hearing loss compared with the control level. Two weeks after the intense noise exposure, the MIF(-/-) mice had an increased hearing threshold compared with the wild-type mice. Scanning electron microscopy demonstrated that the outer hair cells in the MIF(-/-) mice were affected 2 weeks after noise exposure compared with the wild-type mice. TUNEL-positive cells were identified in the organ of Corti of the MIF(-/-) mice.

CONCLUSION

The MIF(-/-) mice had prolonged hearing loss and significant loss of cochlear hair cells after intense noise exposure. Macrophage migration inhibitory factor may play an important role in recovery from acoustic trauma. Management of macrophage migration inhibitory factor may be a novel therapeutic option for noise-induced hearing loss.

Caspase-mediated apoptosis in the cochleae contributes to the early onset of hearing loss in A/J mice

A/J and C57BL/6 J (B6) mice share a mutation in Cdh23 (ahl allele) and are characterized by age-related hearing loss. However, hearing loss occurs much earlier in A/J mice at about four weeks of age. Recent study has revealed that a mutation in citrate synthase (Cs) is one of the main contributors, but the mechanism is largely unknown. In the present study, we showed that A/J mice displayed more severe degeneration of hair cells, spiral ganglion neurons, and stria vascularis in the cochleae compared with B6 mice. Moreover, messenger RNA accumulation levels of caspase-3 and caspase-9 in the inner ears of A/J mice were significantly higher than those in B6 mice at 2 and 8 weeks of age. Immunohistochemistry localized caspase-3 expression mainly to the hair cells, spiral ganglion neurons, and stria vascularis in cochleae. In vitro transfection with Cs short hairpin RNA (shRNA) alone or cotransfection with Cs shRNA and Cdh23 shRNA significantly increased the levels of caspase-3 in an inner ear cell line (HEI-OC1). Finally, a pan-caspase inhibitor Z-VAD-FMK could preserve the hearing of A/J mice by lowering about 15 decibels of the sound pressure level for the auditory-evoked brainstem response thresholds. In conclusion, our results suggest that caspase-mediated apoptosis in the cochleae, which may be related to a Cs mutation, contributes to the early onset of hearing loss in A/J mice.

Protection from noise-induced hearing loss with Src inhibitors

Noise-induced hearing loss is a major cause of acquired hearing loss around the world and pharmacological approaches to protecting the ear from noise are under investigation. Noise results in a combination of mechanical and metabolic damage pathways in the cochlea. The Src family of protein tyrosine kinases could be active in both pathways and Src inhibitors have successfully prevented noise-induced cochlear damage and hearing loss in animal models. The long-term goal is to optimize delivery methods into the cochlea to reduce invasiveness and limit side-effects before human clinical testing can be considered. At their current early stage of research investigation, Src inhibitors represent an exciting class of compounds for inclusion in a multifaceted pharmacological approach to protecting the ear from noise.

Role of cysteinyl leukotriene signaling in a mouse model of noise-induced cochlear injury

Noise-induced hearing loss is one of the most common types of sensorineural hearing loss. In this study, we examined the expression and localization of leukotriene receptors and their respective changes in the cochlea after hazardous noise exposure. We found that the expression of cysteinyl leukotriene type 1 receptor (CysLTR1) was increased until 3 d after noise exposure and enhanced CysLTR1 expression was mainly observed in the spiral ligament and the organ of Corti. Expression of 5-lipoxygenase was increased similar to that of CysLTR1, and there was an accompanying elevation of CysLT concentration. Posttreatment with leukotriene receptor antagonist (LTRA), montelukast, for 4 consecutive days after noise exposure significantly decreased the permanent threshold shift and also reduced the hair cell death in the cochlea. Using RNA-sequencing, we found that the expression of matrix metalloproteinase-3 (MMP-3) was up-regulated after noise exposure, and it was significantly inhibited by montelukast. Posttreatment with a MMP-3 inhibitor also protected the hair cells and reduced the permanent threshold shift. These findings suggest that acoustic injury up-regulated CysLT signaling in the cochlea and cochlear injury could be attenuated by LTRA through regulation of MMP-3 expression. This study provides mechanistic insights into the role of CysLTs signaling in noise-induced hearing loss and the therapeutic benefit of LTRA.

Attenuation of noise-induced hearing loss using methylene blue

The overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) has been known to contribute to the pathogenesis of noise-induced hearing loss. In this study, we discovered that in BALB/c mice pretreatment with methylene blue (MB) for 4 consecutive days significantly protected against cochlear injury by intense broad-band noise for 3 h. It decreased both compound threshold shift and permanent threshold shift and, further, reduced outer hair cell death in the cochlea. MB also reduced ROS and RNS formation after noise exposure. Furthermore, it protected against rotenone- and antimycin A-induced cell death and also reversed ATP generation in the in vitro UB-OC1 cell system. Likewise, MB effectively attenuated the noise-induced impairment of complex IV activity in the cochlea. In addition, it increased the neurotrophin-3 (NT-3) level, which could affect the synaptic connections between hair cells and spiral ganglion neurons in the noise-exposed cochlea, and also promoted the conservation of both efferent and afferent nerve terminals on the outer and inner hair cells. These findings suggest that the amelioration of impaired mitochondrial electron transport and the potentiation of NT-3 expression by treatment with MB have a significant therapeutic value in preventing ROS-mediated sensorineural hearing loss.

A novel QTL underlying early-onset, low-frequency hearing loss in BXD recombinant inbred strains

The DBA/2J inbred strain of mice has been used extensively in hearing research as it suffers from early-onset, progressive hearing loss. Initially, it mostly affects high frequencies, but already at 2-3 months hearing loss becomes broad. In search for hearing loss genes other than Cadherin 23 (otocadherin) and fascin-2, which make a large contribution to the high-frequency deficits, we used a large set of the genetic reference population of BXD recombinant inbred strains. For frequencies 4, 8, 16 and 32 kHz, auditory brainstem response hearing thresholds were longitudinally determined from 2-3 up to 12 weeks of age. Apart from a significant, broad quantitative trait locus (QTL) for high-frequency hearing loss on chromosome 11 containing the fascin-2 gene, we found a novel, small QTL for low-frequency hearing loss on chromosome 18, from hereon called ahl9. Real-time quantitative polymerase chain reaction of organs of Corti, isolated from a subset of strains, showed that a limited number of genes at the QTL were expressed in the organ of Corti. Of those genes, several showed significant expression differences based on the parental line contributing to the allele. Our results may aid in the future identification of genes involved in low-frequency, early-onset hearing loss.