Noise-Induced Hearing Loss: Permanent Versus Temporary Threshold Shifts and the Effects of Hair Cell Versus Neuronal Degeneration

Association of GRM7 Polymorphisms with Bilateral Auditory Regions Glutamate and Coupling with Glutathione in ARHL Patients

This study aimed to investigate the relationship between GRM7 polymorphisms and the levels of glutamate (Glu) and glutathione (GSH) in bilateral auditory regions (ARs) of ARHL patients. Seventy-eight ARHL patients (mean age, 65.94 years ± 3.37 [SD]; 44 men) and 46 normal hearing (NH) controls (mean age, 65.72 years ± 2.32 [SD]; 28 men) were enrolled. Glu and GSH levels in bilateral ARs of all participants were measured and estimated by using magnetic resonance spectroscopy (MRS) and LCModel. In addition, we collected peripheral venous blood samples from all participants for DNA extraction and investigated polymorphisms in the GRM7 gene using TaqMan SNP genotyping. The results showed that Glu and GSH levels in bilateral ARs were significantly lower in GRM7 high-risk group compared with GRM7 low-risk group, regardless of disease status (all pglu < 0.001; all pgsh = 0.001). Furthermore, GRM7 low-risk ARHL group had lower Glu levels in bilateral ARs than GRM7 low-risk NH group, whereas no difference was observed between NH and ARHL groups in high-risk (all pglu < 0.05; all pglu > 0.05). Finally, we found that Glu and GSH levels were positively correlated only in the low-risk NH group (rleft = 0.536 p = 0.007; rright = 0.545 p = 0.006). The glutamatergic dysfunction in ARs may be associated with GRM7 polymorphisms, and redox reactions are involved in regulating the glutamatergic abnormalities. The TT genotype of GRM7 rs11928865 SNP is more vulnerable to damage from the antioxidant and the glutamatergic system.

Deciphering Auditory Hyperexcitability in Otogl Mutant Mice Unravels an Auditory Neuropathy Mechanism

Auditory neuropathies affect the spiral ganglion neurons of the auditory nerve or their synapses with the sensory hair cells, distorting the sound information transmitted from the ear to the brain. Deciphering the underlying pathophysiological mechanisms remains challenging owing to the diversity of spiral ganglion neuron subtypes and associated central auditory circuits. An auditory neuropathy mechanism is unraveled by investigating the origin of auditory hyperexcitability in a mouse model for hereditary congenital deafness. Otogl encodes the large Otogelin-like protein, which is related to secreted epithelial mucins and is implicated in the mechanical stimulation of cochlear outer hair cells. Heterozygous Otogl+/- mutant mice display auditory hyperexcitability, highlighted by their susceptibility to audiogenic seizures induced by loud sounds. It is shown that Otogl is transiently expressed in a subpopulation of spiral ganglion neurons during cochlear development. Despite their apparently normal hearing, Otogl+/- mice display poor activation of the spiral ganglion neurons processing loud sounds and an elevation of the activation threshold of the middle the ear muscle reflex that attenuates loud sounds. The findings reveal how a neuropathy affecting spiral ganglion neurons specialized in loud sound processing and associated with the middle the ear muscle reflex can manifest itself as auditory hyperexcitability.

Interplay between noise-induced sensorineural hearing loss and hypertension: pathophysiological mechanisms and therapeutic prospects

More than 5% of the global population suffers from disabling hearing loss, primarily sensorineural hearing loss (SNHL). SNHL is often caused by factors such as vascular disorders, viral infections, ototoxic drugs, systemic inflammation, age-related labyrinthine membrane degeneration, and noise-induced hearing loss (NIHL). NIHL, in particular, leads to changes in blood-labyrinth-barrier (BLB) physiology, increased permeability, and various health issues, including cardiovascular disease, hypertension, diabetes, neurological disorders, and adverse reproductive outcomes. Recent advances in neuromodulation and vector-based approaches offer hope for overcoming biological barriers such as the BLB in the development of innovative treatments. Computational methods, including molecular docking, molecular dynamics simulations, QSAR/QSPR analysis with machine/deep learning algorithms, and network pharmacology, hold potential for identifying drug candidates and optimizing their interactions with BLB transporters, such as the glutamate transporter. This paper provides an overview of NIHL, focusing on its pathophysiology; its impact on membrane transporters, ion channels, and BLB structures; and associated symptoms, comorbidities, and emerging therapeutic approaches. Recent advancements in neuromodulation and vector-based strategies show great promise in overcoming biological barriers such as BLB, facilitating the development of innovative treatment options. The primary aim of this review is to examine NIHL in detail and explore its underlying mechanisms, physiological effects, and cutting-edge therapeutic strategies for its effective management and prevention.

Comparison of IL-1 Receptor Antagonist and Dexamethasone in Noise-Induced Hearing Loss: Animal Model

OBJECTIVE

This study aimed to attenuate cochlear inflammation following noise-induced hearing loss by targeting IL-1. We evaluated the effectiveness of IL-1 inhibition through auditory and histological assessments in an animal model.

STUDY DESIGN

Experimental animal study.

SETTING

Gazi University Faculty of Medicine, Ankara, Turkey.

METHODS

Twenty-four rats were randomly assigned into 3 groups: Anakinra, dexamethasone, and control groups. All animals were exposed to broadband noise (110 dB SPL, 8 hours), auditory brainstem response (ABR) tests were conducted before noise exposure, immediately after, and on Day 14. Anakinra, dexamethasone, and saline were administered intraperitoneally, cochlear tissues were harvested for histological and immunohistochemical evaluation.

RESULTS

On Day 14, ABR thresholds in Anakinra group were better than the control group across all frequencies, with a significant difference observed at 8 kHz (P = .036). The mean number of OHC was significantly higher in Anakinra group compared to the control group (P < .05). The mean number of IHC in the Anakinra group was greater than in the dexamethasone group. IL-1β immunopositivity in the stria vascularis and spiral ganglia was significantly higher in Anakinra group compared to dexamethasone group (P = .022 and P = .013, respectively). TNF-α immunopositivity in the stria vascularis and spiral ganglia was significantly greater in control group than in Anakinra group (P = .037 and P = .01, respectively).

CONCLUSION

The comparable efficacy of Anakinra and dexamethasone in both histological and auditory assessments suggests that Anakinra may serve as a promising therapeutic option for noise-induced hearing loss.

Metabolome modification and underlying biomarker of noise-induced hearing loss Guinea pig cochlear fluid

BACKGROUND

Noise-induced hearing loss (NIHL) is a kind of acquired sensorineural hearing loss and has shown an increasing incidence in recent years. Hence, elucidating the exact pathophysiological mechanisms and proposing effective treatment and prevention methods become the top priority. Though a great number of researches have been carried out on NIHL, few of them were focused on metabolites.

AIMS/OBJECTIVES

To reveal the metabolomic changes in cochlear fluid after noise injury and search for underlying inner ear biomarkers of NIHL.

MATERIAL AND METHODS

In this study, cochlea fluid extracted from guinea pigs after impulse noise exposure were subjected to GC-MS and LC-MS untargeted metabolomics analysis.

RESULTS

After impulse noise exposure, 62 significantly changed metabolites in guinea pig cochlea fluid were screened out and deoxyribose 1-phosphate was selected as the key metabolite and underlying biomarker for NIHL. KEGG pathway analysis showed that oxidative phosphorylation, glycerophospholipid metabolism, pyrimidine metabolism and pentose phosphate pathway were significantly changed at all observed time points after noise.

CONCLUSIONS AND SIGNIFICANCE

This study effectively promoted the application of metabolomics in hearing research. The pathophysiology process of NIHL in the inner ear was closely connected with oxidative phosphorylation, glycerophospholipid metabolism, pyrimidine metabolism and pentose phosphate pathway and deoxyribose 1-phosphate could be the biomarker for NIHL.

The Role of Connexin26 and Connexin30 in the Mouse Cochlea of Noise-Induced Hearing Loss

OBJECTIVE

We aimed to explore the role of connexin26 (Cx26) and connexin30 (Cx30) in the cochlea in noise-induced permanent threshold shifts (PTS) and temporary threshold shift (TTS).

STUDY DESIGN

Prospective, controlled.

SETTING

Laboratory.

METHODS

A mouse model of noise-induced PTS and TTS was constructed. Western blots were used to detect the expression of Cx26 and Cx30 in the cochlea. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were used to assess the potential biological pathways.

RESULTS

Both the expression of Cx26 and Cx30 showed a trend of first rising and then falling in noise-induced PTS. The expression of Cx26 increased greatly in the 24 hours noise exposure (P < .05) and reached the highest level in the 4 hours after noise exposure (P < .05), then decreased gradually and returned to the control level on the seventh day after the noise exposure, when compared with the control group. The expression of Cx30 showed a similar trend in noise-induced PTS. However, both the expression of Cx26 and Cx30 showed a trend of first falling and then rising in noise induced TTS. The expression of Cx26/Cx30 reached its lowest level in the 4 hours after noise exposure (P < .05), and then increased to the control level on the second day after noise exposure (P > .05), compared with the control group. The first KEGG and GO pathway may be related with oxidative phosphorylation.

CONCLUSION

Cx26 and Cx30 may have an effect in noise induced PTS and TTS. Future studies are needed to confirm the results.

Lateral olivocochlear neurons modulate cochlear responses to noise exposure

The sense of hearing originates in the cochlea, which detects sounds across dynamic sensory environments. Like other peripheral organs, the cochlea is subjected to environmental insults, including loud, damage-inducing sounds. In response to internal and external stimuli, the central nervous system directly modulates cochlear function through olivocochlear neurons (OCNs), which are located in the brainstem and innervate the cochlear sensory epithelium. One population of OCNs, the lateral olivocochlear (LOC) neurons, target spiral ganglion neurons (SGNs), the primary sensory neurons of the ear. LOCs alter their transmitter expression for days to weeks in response to noise exposure (NE), suggesting that they could tune SGN excitability over long time periods in response to auditory experience. To examine how LOCs affect auditory function after NE, we characterized OCN transcriptional profiles and found transient LOC-specific gene expression changes after NE, including upregulation of multiple neuropeptide-encoding genes. Next, by generating intersectional mouse lines that selectively target LOCs, we chemogenetically ablated LOCs and assayed auditory responses at baseline and after NE. Compared to controls, mice with reduced LOC innervation showed greater NE-induced functional deficits 1 d later and had worse auditory function after a 2-wk recovery period. The number of remaining presynaptic puncta at the SGN synapse with inner hair cells did not differ between control and LOC-ablated animals, suggesting that the primary role of LOCs after NE is likely not to protect but instead to compensate, ensuring that SGN function is enhanced during periods of need.

An Exploratory Study of Peripheral Vestibular System in Users of Personal Listening Devices

BACKGROUND AND OBJECTIVES

The widespread use of mobile phones and personal listening devices (PLDs) poses potential health risks, particularly noise-induced hearing loss. Among younger generations, high-volume PLD use is associated with auditory and vestibular system changes. Clinical vestibular testing, including vestibular-evoked myogenic potentials (VEMP) and the video head impulse test (vHIT), may reveal peripheral vestibular impacts from prolonged PLD exposure at volumes over 60%. This study examines VEMP and vHIT results in individuals with normal hearing who have had extended high-volume PLD exposure. Subjects and.

METHODS

A cross-sectional comparative study was conducted on individuals aged 15-24 years. All the participants had normal pure tone thresholds with "A" type tympanogram, present acoustic reflexes, and history of PLD usage. Participants were divided into groups according to PLD exposure of <1 year (group A), 1.1-2 years (group B), 2.1-3 years (group C), and 3.1-4 years (group D). The output sound pressure level (dB SPL) near the tympanic membrane was measured. Furthermore, cervical VEMP, ocular VEMP, and vHIT were assessed.

RESULTS

The VEMP and vHIT findings were statistically analyzed and compared across groups. The peak-to-peak amplitudes of VEMP showed a statistically significant difference between groups A and D.

CONCLUSIONS

Potential subclinical damage to the otolith organs can be associated with increased PLD exposure. No damage to the semi-circular canals was observed as the participants used lower dBA values by the PLDs.

IL-1β promotes glutamate excitotoxicity: indications for the link between inflammatory and synaptic vesicle cycle in Ménière's disease

Ménière's disease (MD) is a complex inner ear disorder characterized by a range of symptoms, with its pathogenesis linked to immune-related mechanisms. Our previous research demonstrated that IL-1β maturation and release can trigger cell pyroptosis, exacerbating the severity of the endolymphatic hydrops in a mouse model; however, the specific mechanism through which IL-1β influences MD symptoms remains unclear. This study conducted on patients with MD examined changes in protein signatures in the vestibular end organs (VO) and endolymphatic sac (ES) using mass spectrometry. Gene ontology and protein pathway analyses showed that differentially expressed proteins in the ES are closely related to adhesion, whereas those in the VO are related to synapse processes. Additionally, the study found elevated expression of Glutaminase (GLS) in the VO of MD patients compared to controls. Further investigations revealed that IL-1β increased glutamate levels by upregulating GLS expression in HEI-OC1 cells. Treatment with a GLS inhibitor or an IL-1β receptor antagonist alleviated auditory-vestibular dysfunction and reduced glutamate levels in mice with endolymphatic hydrops. These findings collectively suggest that imbalanced neurotransmitter release and immune responses contribute to the pathology of MD, potentially explaining the hearing loss and vertigo associated with the disease and offering new avenues for therapeutic interventions.

Hearing Loss in the Unoperated Ear After High-Speed Drilling in Otologic and Skull Base Surgery

OBJECTIVE

To evaluate if permanent hearing loss occurred in the unoperated ear of patients undergoing otologic and skull base surgery with high-speed otologic drilling.

STUDY DESIGN

We retrospectively studied 250 patients (mean age 57.8 yr; 120 males, and 130 females) undergoing otologic or skull base surgery with high-speed drilling between 2013 and 2019.

SETTING

The University of Pittsburgh Medical Center.

PATIENTS

We evaluated preoperative and postoperative audiograms for patients undergoing surgery for cochlear implantation (95 patients, 38.0%), cholesteatoma or chronic ear disease (88 patients, 35.2%), repair of lateral skull base encephalocele (26 patients, 10.4%), resection of vestibular schwannoma or meningioma of the cerebellopontine angle (23 patients, 9.2%), lateral temporal bone resection (8 patients, 3.2%), microvascular decompression (7 patients, 2.8%), or other operations involving a high-speed otologic drill (3 patients, 1.2%).

MAIN OUTCOME MEASURES

Hearing threshold shift, measured as the difference between postoperative threshold and preoperative threshold for each frequency. The association of age, gender, tested frequency, and surgery type with hearing threshold shift was investigated with analysis of covariance.

RESULTS

A total of 102 patients (40.8%) had a 10-dB or greater worsening of their hearing in at least one frequency on their postoperative audiogram in the contralateral, unoperated ear. One hundred six subjects (42.4%) had no change in hearing of 10 dB or greater at any frequency. Among patients with longitudinal postoperative audiograms, accelerated age-related hearing loss was observed in low frequencies.

CONCLUSIONS

A significant number of patients demonstrated poorer hearing thresholds in the contralateral, unoperated ear after otologic and skull base surgery.

Tissue engineering strategies for spiral ganglion neuron protection and regeneration

Cochlear implants can directly activate the auditory system's primary sensory neurons, the spiral ganglion neurons (SGNs), via circumvention of defective cochlear hair cells. This bypass restores auditory input to the brainstem. SGN loss etiologies are complex, with limited mammalian regeneration. Protecting and revitalizing SGN is critical. Tissue engineering offers a novel therapeutic strategy, utilizing seed cells, biomolecules, and scaffold materials to create a cellular environment and regulate molecular cues. This review encapsulates the spectrum of both human and animal research, collating the factors contributing to SGN loss, the latest advancements in the utilization of exogenous stem cells for auditory nerve repair and preservation, the taxonomy and mechanism of action of standard biomolecules, and the architectural components of scaffold materials tailored for the inner ear. Furthermore, we delineate the potential and benefits of the biohybrid neural interface, an incipient technology in the realm of implantable devices. Nonetheless, tissue engineering requires refined cell selection and differentiation protocols for consistent SGN quality. In addition, strategies to improve stem cell survival, scaffold biocompatibility, and molecular cue timing are essential for biohybrid neural interface integration.

Advancing noise management in aviation: Strategic approaches for preventing noise-induced hearing loss

As urbanization and population growth escalate, the challenge of noise pollution intensifies, particularly within the aviation industry. This review examines current insights into noise-induced hearing loss (NIHL) in aviation, highlighting the risks to pilots, cabin crew, aircraft maintenance engineers, and ground staff from continuous exposure to high-level noise. It evaluates existing noise management and hearing conservation strategies, identifying key obstacles and exploring new technological solutions. While progress in developing protective devices and noise control technologies is evident, gaps in their widespread implementation persist. The study underscores the need for an integrated strategy combining regulatory compliance, technological advances, and targeted educational efforts. It advocates for global collaboration and policy development to safeguard the auditory health of aviation workers and proposes a strategic framework to enhance hearing conservation practices within the unique challenges of the aviation sector.

Role of Oxidative Stress in Sensorineural Hearing Loss

Hearing is essential for communication, and its loss can cause a serious disruption to one's social life. Hearing loss is also recognized as a major risk factor for dementia; therefore, addressing hearing loss is a pressing global issue. Sensorineural hearing loss, the predominant type of hearing loss, is mainly due to damage to the inner ear along with a variety of pathologies including ischemia, noise, trauma, aging, and ototoxic drugs. In addition to genetic factors, oxidative stress has been identified as a common mechanism underlying several cochlear pathologies. The cochlea, which plays a major role in auditory function, requires high-energy metabolism and is, therefore, highly susceptible to oxidative stress, particularly in the mitochondria. Based on these pathological findings, the potential of antioxidants for the treatment of hearing loss has been demonstrated in several animal studies. However, results from human studies are insufficient, and future clinical trials are required. This review discusses the relationship between sensorineural hearing loss and reactive oxidative species (ROS), with particular emphasis on age-related hearing loss, noise-induced hearing loss, and ischemia-reperfusion injury. Based on these mechanisms, the current status and future perspectives of ROS-targeted therapy for sensorineural hearing loss are described.

Redox homeostasis dysregulation in noise-induced hearing loss: oxidative stress and antioxidant treatment

Noise exposure is an important cause of acquired hearing loss. Studies have found that noise exposure causes dysregulated redox homeostasis in cochlear tissue, which has been recognized as a signature feature of hearing loss. Oxidative stress plays a pivotal role in many diseases via very complex and diverse mechanisms and targets. Reactive oxygen species are products of oxidative stress that exert toxic effects on a variety of physiological activities and are considered significant in noise-induced hearing loss (NIHL). Endogenous cellular antioxidants can directly or indirectly counteract oxidative stress and regulate intracellular redox homeostasis, and exogenous antioxidants can complement and enhance this effect. Therefore, antioxidant therapy is considered a promising direction for NIHL treatment. However, drug experiments have been limited to animal models of NIHL, and these experiments and related observations are difficult to translate in humans; therefore, the mechanisms and true effects of these drugs need to be further analyzed. This review outlines the effects of oxidative stress in NIHL and discusses the main mechanisms and strategies of antioxidant treatment for NIHL.

Pre-Existing Audiometric Hearing Loss is a Predictor of Significant Threshold Shift Following Injury During Combat Deployment

OBJECTIVES

Military personnel are exposed to multiple risk factors for hearing loss, particularly on the battlefield. The objective of this study was to determine whether pre-existing hearing loss predicted hearing threshold shift in male U.S. military personnel following injury during combat deployment.

DESIGN

This was a retrospective cohort study with 1573 male military personnel physically injured in Operations Enduring and Iraqi Freedom between 2004 and 2012. Audiograms before and after injury were analyzed and used to calculate significant threshold shift (STS), defined as a 30 dB or greater change in the sum of hearing thresholds at 2000, 3000, and 4000 Hz in either ear on the postinjury audiogram, relative to the same frequencies on the preinjury audiogram.

RESULTS

Twenty-five percent (n = 388) of the sample had preinjury hearing loss, which mostly occurred in the higher frequencies (i.e., 4000 and 6000 Hz). The prevalence of postinjury STS ranged from 11.7% to 33.3% as preinjury hearing level moved from better to worse. In multivariable logistic regression, preinjury hearing loss was a predictor of STS, and there was a dose-response relationship between severity of preinjury hearing threshold and postinjury STS, specifically for preinjury hearing levels of 40 to 45 dBHL (odds ratio [OR] = 1.99; 95% confidence interval [CI] = 1.03 to 3.88), 50 to 55 dBHL (OR = 2.33; 95% CI = 1.17 to 4.64), and >55 dBHL (OR = 3.77; 95% CI = 2.25 to 6.34).

CONCLUSIONS

These findings suggest that better preinjury hearing provides increased resistance to threshold shift than impaired preinjury hearing. Although STS is calculated using 2000 to 4000 Hz, clinicians must closely attend to the pure-tone response at 6000 Hz and use this test frequency to identify service members at-risk for STS prior to combat deployment.

Acoustic differences in tinnitus between noise-induced and non-noise-induced hearing loss

BACKGROUND

Tinnitus, the perception of sound without external stimuli, varies across hearing loss types. The present study compared the acoustic characteristics of tinnitus in patients with noise-induced hearing loss (NIHL) and in those with hearing loss unrelated to noise exposure.

OBJECTIVE

This study compared the acoustic characteristics of tinnitus in patients with noise-induced and non-noise-induced hearing loss.

METHODS

A total of 403 patients with tinnitus were divided into those with noise-induced and non-noise-induced hearing loss. Patients were evaluated by pure tone audiometry (PTA), tinnitogram, transient evoked otoacoustic emission (TEOAE), distortion product otoacoustic emission (DPOAE), and auditory brainstem evoked response (ABR) tests.

RESULTS

Patients with NIHL exhibited significantly higher hearing thresholds across all frequencies (125-8000 Hz) (p < .05) and reported significantly higher tinnitus intensity (p < .05). Otoacoustic emission tests showed that response rates were significantly lower (p < .05), and ABR tests found that latency periods were significantly more prolonged (p < .05), in patients with NIHL.

CONCLUSIONS

Tinnitus differs acoustically between patients with NIHL and those with non-noise-induced hearing loss, with specific patterns of intensity and auditory responses. These findings emphasize the need for tailoring the management of tinnitus according to the underlying type of hearing loss.

Progress on mechanisms of age-related hearing loss

Age-related hearing loss, or presbycusis, is a common cause of hearing loss in elderly people worldwide. It typically presents as progressive, irreversible, and usually affects the high frequencies of hearing, with a tremendous impact on the quality of life. Presbycusis is a complex multidimensional disorder, in addition to aging, multiple factors including exposure to noise, or ototoxic agents, genetic susceptibility, metabolic diseases and lifestyle can influence the onset and severity of presbycusis. With the aging of the body, its ability to clean up deleterious substances produced in the metabolic process is weakened, and the self-protection and repair function of the body is reduced, which in turn leads to irreversible damage to the cochlear tissue, resulting in the occurrence of presbycusis. Presently, oxidative stress (OS), mitochondrial DNA damage, low-grade inflammation, decreased immune function and stem cell depletion have been demonstrated to play a critical role in developing presbycusis. The purpose of this review is to illuminate the various mechanisms underlying this age-related hearing loss, with the goal of advancing our understanding, prevention, and treatment of presbycusis.

Cell-type-specific plasticity of inhibitory interneurons in the rehabilitation of auditory cortex after peripheral damage

Peripheral sensory organ damage leads to compensatory cortical plasticity that is associated with a remarkable recovery of cortical responses to sound. The precise mechanisms that explain how this plasticity is implemented and distributed over a diverse collection of excitatory and inhibitory cortical neurons remain unknown. After noise trauma and persistent peripheral deficits, we found recovered sound-evoked activity in mouse A1 excitatory principal neurons (PNs), parvalbumin- and vasoactive intestinal peptide-expressing neurons (PVs and VIPs), but reduced activity in somatostatin-expressing neurons (SOMs). This cell-type-specific recovery was also associated with cell-type-specific intrinsic plasticity. These findings, along with our computational modelling results, are consistent with the notion that PV plasticity contributes to PN stability, SOM plasticity allows for increased PN and PV activity, and VIP plasticity enables PN and PV recovery by inhibiting SOMs.

Defining Hearing Loss Severity Based on Pure-Tone Audiometry and Self-Reported Perceived Hearing Difficulty: National Health and Nutrition Examination Survey

BACKGROUND

 There is a well-known metric to describe average/normal vision, 20/20, but the same agreed-upon standard does not exist for hearing. The pure-tone average has been advocated for such a metric.

PURPOSE

 We aimed to use a data-driven approach to inform a universal metric for hearing status based on pure-tone audiometry and perceived hearing difficulty (PHD).

RESEARCH DESIGN

 This is a cross-sectional national representative survey of the civilian noninstitutionalized population in the United States.

STUDY SAMPLE

 Data from the 2011-2012 and 2015-2016 cycles of the National Health and Nutrition Examination Survey (NHANES) were used in our analysis. Of 9,444 participants aged 20 to 69 years from the 2011-2012 and 2015-2016 cycles, we excluded those with missing self-reported hearing difficulty (n = 8) and pure-tone audiometry data (n = 1,361). The main analysis sample, therefore, included 8,075 participants. We completed a subanalysis limited to participants with "normal" hearing based on the World Health Organization (WHO) standard (pure-tone average, PTA of 500, 1000, 2000, 4000 Hz < 20 dBHL).

ANALYSIS

 Descriptive analyses to calculate means and proportions were used to describe characteristics of the analysis sample across PHD levels relative to PTA. Four PTAs were compared, low frequency (LF-PTA, 500, 1,000, 2,000 Hz), four-frequency PTA (PTA4, 500, 1,000, 2,000, 4,000 Hz), high frequency (HF-PTA, 4,000, 6,000, 8,000 Hz), and all frequency (AF-PTA, 500, 1,000, 2,000, 4,000, 6,000, 8,000 Hz). Differences between groups were tested using Rao-Scott χ2 tests for categorical variables and F tests for continuous variables. Logistic regression was used to plot receiver operating characteristic curves with PHD as a function of PTA. The sensitivity and specificity for each PTA and PHD were also calculated.

RESULTS

 We found that 19.61% of adults aged 20 to 69 years reported PHD, with only 1.41% reporting greater than moderate PHD. The prevalence of reported PHD increased with higher decibel hearing levels (dBHL) categories reaching statistical significance (p < 0.05 with Bonferroni correction) at 6 to 10 dBHL for PTAs limited to lower frequencies (LF-PTA and PTA4) and 16 to 20 dBHL when limited to higher frequencies (HF-PTA). The prevalence of greater than moderate PHD reached statistical significance at 21 to 30 dBHL when limited to lower frequencies (LF-PTA) and 41 to 55 dBHL when limited to higher frequencies (HF-PTA). Forty percent of the sample had high-frequency loss with "normal" low-frequency hearing, representing nearly 70% of hearing loss configurations. The diagnostic accuracy of the PTAs for reported PHD was poor to sufficient (<0.70); however, the HF-PTA had the highest sensitivity (0.81).

CONCLUSION

 We provide four basic recommendations based on our analysis: (1) a PTA-based metric for hearing ability should include frequencies above 4,000 Hz; (2) the data-driven dBHL cutoff for any PHD/"normal" hearing is 15 dBHL; (3) when considering greater than moderate PHD, the data-driven cutoffs were more variable but estimated at 20 to 30 dBHL for LF-PTA, 30 to 35 dBHL for PTA4, 25 to 50 dBHL for AF-PTA, and 40 to 65 dBHL for HF-PTA; and (4) clinical recommendations and legislative agendas should include consideration beyond pure-tone audiometry such as functional assessment of hearing and PHD.

Targeting CXCL1 chemokine signaling for treating cisplatin ototoxicity

Cisplatin is chemotherapy used for solid tumor treatment like lung, bladder, head and neck, ovarian and testicular cancers. However, cisplatin-induced ototoxicity limits the utility of this agent in cancer patients, especially when dose escalations are needed. Ototoxicity is associated with cochlear cell death through DNA damage, the generation of reactive oxygen species (ROS) and the consequent activation of caspase, glutamate excitotoxicity, inflammation, apoptosis and/or necrosis. Previous studies have demonstrated a role of CXC chemokines in cisplatin ototoxicity. In this study, we investigated the role of CXCL1, a cytokine which increased in the serum and cochlea by 24 h following cisplatin administration. Adult male Wistar rats treated with cisplatin demonstrated significant hearing loss, assessed by auditory brainstem responses (ABRs), hair cell loss and loss of ribbon synapse. Immunohistochemical studies evaluated the levels of CXCL1 along with increased presence of CD68 and CD45-positive immune cells in cochlea. Increases in CXCL1 was time-dependent in the spiral ganglion neurons and organ of Corti and was associated with progressive increases in CD45, CD68 and IBA1-positive immune cells. Trans-tympanic administration of SB225002, a chemical inhibitor of CXCR2 (receptor target for CXCL1) reduced immune cell migration, protected against cisplatin-induced hearing loss and preserved hair cell integrity. We show that SB225002 reduced the expression of CXCL1, NOX3, iNOS, TNF-α, IL-6 and COX-2. Similarly, knockdown of CXCR2 by trans-tympanic administration of CXCR2 siRNA protected against hearing loss and loss of outer hair cells and reduced ribbon synapses. In addition, SB225002 reduced the expression of inflammatory mediators induced by cisplatin. These results implicate the CXCL1 chemokine as an early player in cisplatin ototoxicity, possibly by initiating the immune cascade, and indicate that CXCR2 is a relevant target for treating cisplatin ototoxicity.

Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) is the second most common cause of sensorineural hearing loss, after age-related hearing loss, and affects approximately 5% of the world's population. NIHL is associated with substantial physical, mental, social, and economic impacts at the patient and societal levels. Stress and social isolation in patients' workplace and personal lives contribute to quality-of-life decrements which may often go undetected. The pathophysiology of NIHL is multifactorial and complex, encompassing genetic and environmental factors with substantial occupational contributions. The diagnosis and screening of NIHL are conducted by reviewing a patient's history of noise exposure, audiograms, speech-in-noise test results, and measurements of distortion product otoacoustic emissions and auditory brainstem response. Essential aspects of decreasing the burden of NIHL are prevention and early detection, such as implementation of educational and screening programs in routine primary care and specialty clinics. Additionally, current research on the pharmacological treatment of NIHL includes anti-inflammatory, antioxidant, anti-excitatory, and anti-apoptotic agents. Although there have been substantial advances in understanding the pathophysiology of NIHL, there remain low levels of evidence for effective pharmacotherapeutic interventions. Future directions should include personalized prevention and targeted treatment strategies based on a holistic view of an individual's occupation, genetics, and pathology.

Loss of Pex1 in Inner Ear Hair Cells Contributes to Cochlear Synaptopathy and Hearing Loss

Peroxisome Biogenesis Disorders (PBD) and Zellweger syndrome spectrum disorders (ZSD) are rare genetic multisystem disorders that include hearing impairment and are associated with defects in peroxisome assembly, function, or both. Mutations in 13 peroxin (PEX) genes have been found to cause PBD-ZSD with ~70% of patients harboring mutations in PEX1. Limited research has focused on the impact of peroxisomal disorders on auditory function. As sensory hair cells are particularly vulnerable to metabolic changes, we hypothesize that mutations in PEX1 lead to oxidative stress affecting hair cells of the inner ear, subsequently resulting in hair cell degeneration and hearing loss. Global deletion of the Pex1 gene is neonatal lethal in mice, impairing any postnatal studies. To overcome this limitation, we created conditional knockout mice (cKO) using Gfi1^Creor VGlut3^Cre expressing mice crossed to floxed Pex1 mice to allow for selective deletion of Pex1 in the hair cells of the inner ear. We find that Pex1 excision in inner hair cells (IHCs) leads to progressive hearing loss associated with significant decrease in auditory brainstem responses (ABR), specifically ABR wave I amplitude, indicative of synaptic defects. Analysis of IHC synapses in cKO mice reveals a decrease in ribbon synapse volume and functional alterations in exocytosis. Concomitantly, we observe a decrease in peroxisomal number, indicative of oxidative stress imbalance. Taken together, these results suggest a critical function of Pex1 in development and maturation of IHC-spiral ganglion synapses and auditory function.

The impact of targeted ablation of one row of outer hair cells and Deiters' cells on cochlear amplification

The mammalian cochlea contains three rows of outer hair cells (OHCs) that amplify the basilar membrane traveling wave with high gain and exquisite tuning. The pattern of OHC loss caused by typical methods of producing hearing loss in animal models (noise, ototoxic exposure, or aging) is variable and not consistent along the length of the cochlea. Thus, it is difficult to use these approaches to understand how forces from multiple OHCs summate to create normal cochlear amplification. Here, we selectively removed the third row of OHCs and Deiters' cells in adult mice and measured cochlear amplification. In the mature cochlear epithelia, expression of the Wnt target gene Lgr5 is restricted to the third row of Deiters' cells, the supporting cells directly underneath the OHCs. Diphtheria toxin administration to Lgr5DTR-EGFP/+ mice selectively ablated the third row of Deiters' cells and the third row of OHCs. Basilar membrane vibration in vivo demonstrated disproportionately lower reduction in cochlear amplification by about 13.5 dB. On a linear scale, this means that the 33% reduction in OHC number led to a 79% reduction in gain. Thus, these experimental data describe the impact of reducing the force of cochlear amplification by a specific amount. Furthermore, these data argue that because OHC forces progressively and sequentially amplify the traveling wave as it travels to its peak, the loss of even a relatively small number of OHCs, when evenly distributed longitudinally, will cause a substantial reduction in cochlear amplification.NEW & NOTEWORTHY Normal cochlear physiology involves force production from three rows of outer hair cells to amplify and tune the traveling wave. Here, we used a genetic approach to target and ablate the third row of outer hair cells in the mouse cochlea and found it reduced cochlear amplification by 79%. This means that the loss of even a relatively small number of OHCs, when evenly distributed, causes a substantial reduction in cochlear amplification.

A PRMT5 inhibitor protects against noise-induced hearing loss by alleviating ROS accumulation

The aim of this study was to investigate the effect of LLY-283, a selective inhibitor of protein arginine methyltransferase 5 (PRMT5), on a noise-induced hearing loss (NIHL) mouse model and to identify a potential target for a therapeutic intervention against NIHL. Eight-week-old male C57BL/6 mice were used. The auditory brainstem response was measured 2 days after noise exposure. The apoptosis of hair cells (HCs) was detected by caspase-3/7 staining, whereas the accumulation of reactive oxygen species (ROS) was measured by 4-HNE staining. We demonstrated that the death of HCs and loss of cochlear synaptic ribbons induced by noise exposure could be significantly reduced by the presence of LLY-283. LLY-283 pretreatment before noise exposure notably decreased 4-HNE and caspase-3/7 levels in the cochlear HCs. We also noticed that the number of spiral ganglion neurons (SGNs) was notably increased after LLY-283 pretreatment. Furthermore, we showed that LLY-283 could increase the expression level of p-AKT in the SGNs. The underlying mechanism involves alleviation of ROS accumulation and activation of the PI3K/AKT pathway, indicating that LLY-283 might be a potential candidate for therapeutic intervention against NIHL.

The Use of Antioxidants in the Prevention and Treatment of Noise-Induced Hearing Loss

As of today, there are no therapeutic measures for the prevention or treatment of noise-induced hearing loss (NIHL). The current preventative measures, including avoidance and personal protective hearing equipment, do not appear to be sufficient because there is an increasing number of people with NIHL, especially in the adolescent population. Therefore, we must find a therapy that prevents the impact of noise on hearing. Antioxidants are a promising option in preventing the damaging effects of noise by targeting free radicals but further studies are needed to confirm their efficacy in humans.

The Role of Genetic Variants in the Susceptibility of Noise-Induced Hearing Loss

Noised-induced hearing loss (NIHL) is an acquired, progressive neurological damage caused by exposure to intense noise in various environments including industrial, military and entertaining settings. The prevalence of NIHL is much higher than other occupational injuries in industrialized countries. Recent studies have revealed that genetic factors, together with environmental conditions, also contribute to NIHL. A group of genes which are linked to the susceptibility of NIHL had been uncovered, involving the progression of oxidative stress, potassium ion cycling, cilia structure, heat shock protein 70 (HSP70), DNA damage repair, apoptosis, and some other genes. In this review, we briefly summarized the studies primary in population and some animal researches concerning the susceptible genes of NIHL, intending to give insights into the further exploration of NIHL prevention and individual treatment.

Hearing loss drug discovery and medicinal chemistry: Current status, challenges, and opportunities

Hearing loss is a severe high unmet need condition affecting more than 1.5 billion people globally. There are no licensed medicines for the prevention, treatment or restoration of hearing. Prosthetic devices, such as hearing aids and cochlear implants, do not restore natural hearing and users struggle with speech in the presence of background noise. Hearing loss drug discovery is immature, and small molecule approaches include repurposing existing drugs, combination therapeutics, late-stage discovery optimisation of known chemotypes for identified molecular targets of interest, phenotypic tissue screening and high-throughput cell-based screening. Hearing loss drug discovery requires the integration of specialist therapeutic area biology and otology clinical expertise. Small molecule drug discovery projects in the global clinical portfolio for hearing loss are here collated and reviewed. An overview is provided of human hearing, inner ear anatomy, inner ear delivery, types of hearing loss and hearing measurement. Small molecule experimental drugs in clinical development for hearing loss are reviewed, including their underpinning biology, discovery strategy and activities, medicinal chemistry, calculated physicochemical properties, pharmacokinetics and clinical trial status. SwissADME BOILED-Egg permeability modelling is applied to the molecules reviewed, and these results are considered. Non-small molecule hearing loss assets in clinical development are briefly noted in this review. Future opportunities in hearing loss drug discovery for human genomics and targeted protein degradation are highlighted.

Effects of alprostadil combined with hyperbaric oxygen on hearing recovery and hemorheology in patients with sudden sensorineural hearing loss and analysis of related influencing factors

The causes of sudden sensorineural hearing loss (SSNHL) are unclear, and the condition cannot be treated with specific regimens. The present study was designed to explore the effects of alprostadil combined with hyperbaric oxygen (HBO) on hearing recovery and hemorheology in patients with SSNHL, and to analyze factors influencing treatment efficacy. in total, 104 patients with SSNHL were enrolled between January 2015 and July 2018 in a randomized controlled trial. Group A (n=52) received alprostadil treatment and Group B (n=52) were treated with HBO plus alprostadil. Following treatment, the overall recovery rates of tinnitus, aural fullness and vertigo in Group B were significantly higher than those in Group A (P<0.05). Low-, middle- and high-shear whole blood viscosity and whole blood viscosity in the two groups significantly decreased, and those in Group B were significantly lower than those in Group A (P<0.05). The present results indicated that the combination of alprostadil with HBO can improve the therapeutic effect on SSNHL, reduce blood viscosity and improve coagulation function, thus significantly promoting hearing recovery. Further, SSNHL treatment efficacy was influenced by age, time of onset, hearing threshold, presence or absence of tinnitus, plasma viscosity and serum C-reactive protein levels. The trial registration number for the present study was: NCT02563872.

Impulse Noise Induced Hidden Hearing Loss, Hair Cell Ciliary Changes and Oxidative Stress in Mice

Recent studies demonstrated that reversible continuous noise exposure may induce a temporary threshold shift (TTS) with a permanent degeneration of auditory nerve fibers, although hair cells remain intact. To probe the impact of TTS-inducing impulse noise exposure on hearing, CBA/J Mice were exposed to noise impulses with peak pressures of 145 dB SPL. We found that 30 min after exposure, the noise caused a mean elevation of ABR thresholds of ~30 dB and a reduction in DPOAE amplitude. Four weeks later, ABR thresholds and DPOAE amplitude were back to normal in the higher frequency region (8–32 kHz). At lower frequencies, a small degree of PTS remained. Morphological evaluations revealed a disturbance of the stereociliary bundle of outer hair cells, mainly located in the apical regions. On the other hand, the reduced suprathreshold ABR amplitudes remained until 4 weeks later. A loss of synapse numbers was observed 24 h after exposure, with full recovery two weeks later. Transmission electron microscopy revealed morphological changes at the ribbon synapses by two weeks post exposure. In addition, increased levels of oxidative stress were observed immediately after exposure, and maintained for a further 2 weeks. These results clarify the pathology underlying impulse noise-induced sensory dysfunction, and suggest possible links between impulse-noise injury, cochlear cell morphology, metabolic changes, and hidden hearing loss.

MGluR7 is a presynaptic metabotropic glutamate receptor at ribbon synapses of inner hair cells

Glutamate is the most pivotal excitatory neurotransmitter in the central nervous system. Metabotropic glutamate receptors (mGluRs) dimerize and can couple to inhibitory intracellular signal cascades, thereby protecting glutamatergic neurons from excessive excitation and cell death. MGluR7 is correlated with age-related hearing deficits and noise-induced hearing loss; however its exact localization in the cochlea is unknown. Here, we analyzed the expression and localization of mGluR7a and mGluR7b in mouse cochlear wholemounts in detail, using confocal microscopy and 3D reconstructions. We observed a presynaptic localization of mGluR7a at inner hair cells (IHCs), close to the synaptic ribbon. To detect mGluR7b, newly generated antibodies were characterized and showed co-localization with mGluR7a at IHC ribbon synapses. Compared to the number of synaptic ribbons, the numbers of mGluR7a and mGluR7b puncta were reduced at higher frequencies (48 to 64 kHz) and in older animals (6 and 12 months). Previously, we reported a presynaptic localization of mGluR4 and mGluR8b at this synapse type. This enables the possibility for the formation of homo- and/or heterodimeric receptors composed of mGluR4, mGluR7a, mGluR7b and mGluR8b at IHC ribbon synapses. These receptor complexes might represent new molecular targets suited for pharmacological concepts to protect the cochlea against noxious stimuli and excitotoxicity.

Effect of Phlorofucofuroeckol A and Dieckol Extracted from Ecklonia cava on Noise-induced Hearing Loss in a Mouse Model

One of the well-known causes of hearing loss is noise. Approximately 31.1% of Americans between the ages of 20 and 69 years (61.1 million people) have high-frequency hearing loss associated with noise exposure. In addition, recurrent noise exposure can accelerate age-related hearing loss. Phlorofucofuroeckol A (PFF-A) and dieckol, polyphenols extracted from the brown alga Ecklonia cava, are potent antioxidant agents. In this study, we investigated the effect of PFF-A and dieckol on the consequences of noise exposure in mice. In 1,1-diphenyl-2-picrylhydrazyl assay, dieckol and PFF-A both showed significant radical-scavenging activity. The mice were exposed to 115 dB SPL of noise one single time for 2 h. Auditory brainstem response(ABR) threshold shifts 4 h after 4 kHz noise exposure in mice that received dieckol were significantly lower than those in the saline with noise group. The high-PFF-A group showed a lower threshold shift at click and 16 kHz 1 day after noise exposure than the control group. The high-PFF-A group also showed higher hair cell survival than in the control at 3 days after exposure in the apical turn. These results suggest that noise-induced hair cell damage in cochlear and the ABR threshold shift can be alleviated by dieckol and PFF-A in the mouse. Derivatives of these compounds may be applied to individuals who are inevitably exposed to noise, contributing to the prevention of noise-induced hearing loss with a low probability of adverse effects.

Noise-Induced Hearing Loss: Updates on Molecular Targets and Potential Interventions

Noise overexposure leads to hair cell loss, synaptic ribbon reduction, and auditory nerve deterioration, resulting in transient or permanent hearing loss depending on the exposure severity. Oxidative stress, inflammation, calcium overload, glutamate excitotoxicity, and energy metabolism disturbance are the main contributors to noise-induced hearing loss (NIHL) up to now. Gene variations are also identified as NIHL related. Glucocorticoid is the only approved medication for NIHL treatment. New pharmaceuticals targeting oxidative stress, inflammation, or noise-induced neuropathy are emerging, highlighted by the nanoparticle-based drug delivery system. Given the complexity of the pathogenesis behind NIHL, deeper and more comprehensive studies still need to be fulfilled.

Cochlin-cleaved LCCL is a dual-armed regulator of the innate immune response in the cochlea during inflammation

The inner ear is a complex and delicate structure composed of the cochlea and the vestibular system. To maintain normal auditory function, strict homeostasis of the inner ear is needed. A proper immune response against infection, thus, is crucial. Also, since excessive immune reaction can easily damage the normal architecture within the inner ear, the immune response should be fine regulated. The exact mechanism how the inner ear’s immune response, specifically the innate immunity, is regulated was unknown. Recently, we reported a protein selectively localized in the inner ear during bacterial infection, named cochlin, as a possible mediator of such regulation. In this review, the immunological function of cochlin and the mechanism behind its role within inner ear immunity is sum-marized. Cochlin regulates innate immunity by physically en-trapping pathogens within scala tympani and recruiting innate immune cells. Such mechanism enables efficient removal of pathogen while preserving the normal inner ear structure from inflammatory damage.

Ultrasonic bone removal from the ossicular chain affects cochlear structure and function

INTRODUCTION

Ultrasonic bone removal devices (UBD) are capable of cutting through bony tissue without injury to adjacent soft tissue. The feasibility and safety of using this technology for removal of bone from an intact ossicular chain (as might be required for otosclerosis or congenital fixation) was investigated in an animal model.

METHODS

This was a prospective animal study conducted on seven anesthetised adult chinchillas. An UBD was used to remove bone from the malleus head in situ. Pre and post-operative distortion product otoacoustic emission (DPOAE) levels and auditory brainstem response (ABR) thresholds were recorded. Scanning electron microscopy (SEM) was used to assess cochlear haircell integrity.

RESULTS

Precise removal of a small quantity of bone from the malleus head was achieved by a 30s application of UBD without disruption of the ossicular chain or tympanic membrane. DPOAEs became undetectable after the intervention with signal-to-noise ratios (SNR) < 5 dB SPL in all ears. Furthermore, ABR thresholds were elevated > 85 dB SPL in 13 ears. SEM showed significant disruption of structural integrity of the organ of Corti, specifically loss and damage of outer haircells.

CONCLUSIONS

Although UBD can be used to reshape an ossicle without middle ear injury, prolonged contact with the ossicular chain can cause structural and functional injury to the cochlea. Extensive cochlea pathology was found, but we did not investigate for recovery from any temporary threshold shift. In the authors' opinion, further study should be undertaken before consideration is given to use of the device for release of ossicular fixation.

The Relationship Between Blast-related Hearing Threshold Shift and Insomnia in U.S. Military Personnel

INTRODUCTION

Hearing loss and insomnia emerged as preeminent sources of morbidity among military service members and veterans who served in the recent Iraq and Afghanistan conflicts. Significant threshold shift (STS), an early indicator of hearing loss, has not been studied in relation to insomnia. This study's objective was to examine the co-occurrence of STS and insomnia among U.S. military personnel with blast-related injury.

MATERIALS AND METHODS

A total of 652 service members who were blast-injured during military operations in Iraq or Afghanistan between 2004 and 2012 were identified from the Blast-Related Auditory Injury Database. Pre- and post-injury audiometric data were used to ascertain new-onset STS, defined as 30 dB or greater increase for the sum of thresholds at 2,000, 3,000, and 4,000 Hz for either ear. Insomnia diagnosed within 2 years post-injury was abstracted from electronic medical records. Multivariable logistic regression analysis examined the relationship between STS and insomnia, while adjusting for age, year of injury, occupation, injury severity, tinnitus and concussion diagnosed in-theater, and PTSD.

RESULTS

A majority of the study sample was aged 18-25 years (79.9%) and sustained mild-to-moderate injuries (92.2%). STS was present in 21.1% of service members. Cumulative incidence of diagnosed insomnia was 22.3% and 11.1% for those with and without STS, respectively. After adjusting for covariates, those with STS had nearly 2-times higher odds of insomnia (odds ratio (OR) = 1.91, 95% CI = 1.12-3.24) compared with those without STS. In multivariable modeling, the strongest association was between PTSD and insomnia (OR = 5.57, 95% CI = 3.35-9.26). A secondary finding of note was that military personnel with STS had a significantly higher frequency of PTSD compared with those without STS (28.1% vs. 15.2%).

CONCLUSIONS

Hearing threshold shift was associated with insomnia in military personnel with blast-related injury and could be used to identify service members at risk. Multidisciplinary care is needed to manage the co-occurrence of both conditions during the post-deployment rehabilitation phase. Future research should evaluate the specific mechanisms involved in this relationship and further explore the association between hearing threshold shift and PTSD.

Contributions and limitations of using machine learning to predict noise-induced hearing loss

Purpose

Noise-induced hearing loss (NIHL) is a global issue that impacts people’s life and health. The current review aims to clarify the contributions and limitations of applying machine learning (ML) to predict NIHL by analyzing the performance of different ML techniques and the procedure of model construction.

Methods

The authors searched PubMed, EMBASE and Scopus on November 26, 2020.

Results

Eight studies were recruited in the current review following defined inclusion and exclusion criteria. Sample size in the selected studies ranged between 150 and 10,567. The most popular models were artificial neural networks (n = 4), random forests (n = 3) and support vector machines (n = 3). Features mostly correlated with NIHL and used in the models were: age (n = 6), duration of noise exposure (n = 5) and noise exposure level (n = 4). Five included studies used either split-sample validation (n = 3) or ten-fold cross-validation (n = 2). Assessment of accuracy ranged in value from 75.3% to 99% with a low prediction error/root-mean-square error in 3 studies. Only 2 studies measured discrimination risk using the receiver operating characteristic (ROC) curve and/or the area under ROC curve.

Conclusion

In spite of high accuracy and low prediction error of machine learning models, some improvement can be expected from larger sample sizes, multiple algorithm use, completed reports of model construction and the sufficient evaluation of calibration and discrimination risk.

Regulator of G Protein Signalling 4 (RGS4) as a Novel Target for the Treatment of Sensorineural Hearing Loss

We and others have previously identified signalling pathways associated with the adenosine A₁ receptor (A₁R) as important regulators of cellular responses to injury in the cochlea. We have shown that the “post-exposure” treatment with adenosine A₁R agonists confers partial protection against acoustic trauma and other forms of sensorineural hearing loss (SNHL). The aim of this study was to determine if increasing A₁R responsiveness to endogenous adenosine would have the same otoprotective effect. This was achieved by pharmacological targeting of the Regulator of G protein Signalling 4 (RGS4). RGS proteins inhibit signal transduction pathways initiated by G protein-coupled receptors (GPCR) by enhancing GPCR deactivation and receptor desensitisation. A molecular complex between RGS4 and neurabin, an intracellular scaffolding protein expressed in neural and cochlear tissues, is the key negative regulator of A₁R activity in the brain. In this study, Wistar rats (6–8 weeks) were exposed to traumatic noise (110 dBSPL, 8–16 kHz) for 2 h and a small molecule RGS4 inhibitor CCG-4986 was delivered intratympanically in a Poloxamer-407 gel formulation for sustained drug release 24 or 48 h after noise exposure. Intratympanic administration of CCG-4986 48 h after noise exposure attenuated noise-induced permanent auditory threshold shifts by up to 19 dB, whilst the earlier drug administration (24 h) led to even better preservation of auditory thresholds (up to 32 dB). Significant improvement of auditory thresholds and suprathreshold responses was linked to improved survival of sensorineural tissues and afferent synapses in the cochlea. Our studies thus demonstrate that intratympanic administration of CCG-4986 can rescue cochlear injury and hearing loss induced by acoustic overexposure. This research represents a novel paradigm for the treatment of various forms of SNHL based on regulation of GPCR.

Noise Exposures Causing Hearing Loss Generate Proteotoxic Stress and Activate the Proteostasis Network

Exposure to excessive sound causes noise-induced hearing loss through complex mechanisms and represents a common and unmet neurological condition. We investigate how noise insults affect the cochlea with proteomics and functional assays. Quantitative proteomics reveals that exposure to loud noise causes proteotoxicity. We identify and confirm hundreds of proteins that accumulate, including cytoskeletal proteins, and several nodes of the proteostasis network. Transcriptomic analysis reveals that a subset of the genes encoding these proteins also increases acutely after noise exposure, including numerous proteasome subunits. Global cochlear protein ubiquitylation levels build up after exposure to excess noise, and we map numerous posttranslationally modified lysines residues. Several collagen proteins decrease in abundance, and Col9a1 specifically localizes to pillar cell heads. After two weeks of recovery, the cochlea selectively elevates the abundance of the protein synthesis machinery. We report that overstimulation of the auditory system drives a robust cochlear proteotoxic stress response.

Changes in microRNA Expression in the Cochlear Nucleus and Inferior Colliculus after Acute Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) can lead to secondary changes that induce neural plasticity in the central auditory pathway. These changes include decreases in the number of synapses, the degeneration of auditory nerve fibers, and reorganization of the cochlear nucleus (CN) and inferior colliculus (IC) in the brain. This study investigated the role of microRNAs (miRNAs) in the neural plasticity of the central auditory pathway after acute NIHL. Male Sprague–Dawley rats were exposed to white band noise at 115 dB for 2 h, and the auditory brainstem response (ABR) and morphology of the organ of Corti were evaluated on days 1 and 3. Following noise exposure, the ABR threshold shift was significantly smaller in the day 3 group, while wave II amplitudes were significantly larger in the day 3 group compared to the day 1 group. The organ of Corti on the basal turn showed evidence of damage and the number of surviving outer hair cells was significantly lower in the basal and middle turn areas of the hearing loss groups relative to controls. Five and three candidate miRNAs for each CN and IC were selected based on microarray analysis and quantitative reverse transcription PCR (RT-qPCR). The data confirmed that even short-term acoustic stimulation can lead to changes in neuroplasticity. Further studies are needed to validate the role of these candidate miRNAs. Such miRNAs may be used in the early diagnosis and treatment of neural plasticity of the central auditory pathway after acute NIHL.

Cochlear protein biomarkers as potential sites for targeted inner ear drug delivery

The delivery of therapies to the cochlea is notoriously challenging. It is an organ protected by a number of barriers that need to be overcome in the drug delivery process. Additionally, there are multiple sites of possible damage within the cochlea. Despite the many potential sites of damage, acquired otologic insults preferentially damage a single location. While progress has been made in techniques for inner ear drug delivery, the current techniques remain non-specific and our ability to deliver therapies in a cell-specific manner are limited. Fortunately, there are proteins specific to various cell-types within the cochlea (e.g., hair cells, spiral ganglion cells, stria vascularis) that function as biomarkers of site-specific damage. These protein biomarkers have potential to serve as targets for cell-specific inner ear drug delivery. In this manuscript, we review the concept of biomarkers and targeted- inner ear drug delivery and the well-characterized protein biomarkers within each of the locations of interest within the cochlea. Our review will focus on targeted drug delivery in the setting of acquired otologic insults (e.g., ototoxicity, noise-induce hearing loss). The goal is not to discuss therapies to treat acquired otologic insults, rather, to establish potential concepts of how to deliver therapies in a targeted, cell-specific manner. Based on our review, it is clear that future of inner ear drug delivery is a discipline filled with potential that will require collaborative efforts among clinicians and scientists to optimize treatment of otologic insults.

The limitation of risk factors as a means of prognostication in auditory neuropathy spectrum disorder of perinatal onset

OBJECTIVE

The management of hearing loss due to auditory neuropathy spectrum disorder (ANSD) in neonates and infants is challenging because speech and language development prognosis cannot be directly inferred from early audiometric hearing thresholds. Consequently, appropriate intervention with hearing aids or cochlear implantation (CI) can be delayed. Our objective was to determine whether any features of patient history could be used to identify CI candidates with ANSD at an earlier age.

METHOD

A database was maintained over 11 years to monitor cases of perinatal onset ANSD. Risk factors associated with the perinatal time period considered pertinent to hearing outcomes were assessed, including prematurity, birth weight, APGAR score, ototoxic drugs, and hyperbilirubinemia. Children with cochlear nerve aplasia and genetic mutations were excluded. Hearing outcome was determined according to mode of auditory rehabilitation beyond 30 months of age: A) no hearing device; B) hearing aid; C) CI.

RESULTS

Of twenty-eight children with ANSD, nine (32%) had behavioural thresholds and language development sufficient to require no assistive device, 9 (32%) were fitted with hearing aids and 10 (36%) had CIs. The average age at CI (3.45 ± 2.07 years) was significantly older than the age at CI of other children in our program with prelingual hearing loss (2.05 ± 1.14 years; p = 0.01 Mann-Witney U Test). None of the putative risk factors for hearing loss reliably predicted the need for subsequent CI.

CONCLUSION

The small sample size in this study is sufficient to confirm that clinical history alone does not reliably predict which young children with perinatal-onset ANSD will require CI. Consequently, timing for CI remains delayed in these children, potentially affecting speech and language outcome. The pathogenesis of perinatal-onset ANSD remains undetermined and novel means of assessment are required for prognostication in affected infants.

Cochlear synaptopathy: new findings in animal and human research

In animal models, prolonged exposure (2 h) to high-level noise causes an irreparable damage to the synapses between the inner hair cells and auditory nerve fibers within the cochlea. Nevertheless, this injury does not necessarily alter the hearing threshold. Similar findings have been observed as part of typical aging in animals. This type of cochlear synaptopathy, popularly called "hidden hearing loss," has been a significant issue in neuroscience research and clinical audiology scientists. The results obtained in different investigations are inconclusive in their diagnosis and suggest new strategies for both prognosis and treatment of cochlear synaptopathy. Here we review the major physiological findings regarding cochlear synaptopathy in animals and humans and discuss mathematical models. We also analyze the potential impact of these results on clinical practice and therapeutic options.

Occupational Noise Exposure and Risk for Noise-Induced Hearing Loss Due to Temporal Bone Drilling

BACKGROUND

Noise-induced hearing loss is one of the most common occupational hazards in the United States. Several studies have described noise-induced hearing loss in patients following mastoidectomy. Although otolaryngologists care for patients with noise-induced hearing loss, few studies in the English literature have examined surgeons' occupational risk.

METHODS

Noise dosimeters and sound level meters with octave band analyzers were used to assess noise exposure during drilling of temporal bones intraoperatively and in a lab setting. Frequency specific sound intensities were recorded. Sound produced using burrs of varying size and type were compared. Differences while drilling varying anatomic structures were assessed using drills from two manufacturers. Pure tone audiometry was performed on 7 to 10 otolaryngology residents before and after a temporal bone practicum to assess for threshold shifts.

RESULTS

Noise exposure during otologic drilling can exceed over 100 dB for short periods of time, and is especially loud using large diameter burrs > 4 mm, with cutting as compared with diamond burrs, and while drilling denser bone such as the cortex. Intensity peaks were found at 2.5, 5, and 6.3 kHz. Drilling on the tegmen and sigmoid sinus revealed peaks at 10 and 12.5 kHz. No temporary threshold shifts were found at 3 to 6 kHz, but were found at 8 to 16 kHz, though this did not reach statistical significance.

CONCLUSION

This article examines noise exposure and threshold shifts during temporal bone drilling. We were unable to find previous descriptions in the literature of measurements done while multiple people drilling simultaneously, during tranlabyrinthine surgery and a specific frequency characterization of the change in peach that appears while drilling on the tegmen. Hearing protection should be considered, which would still allow the surgeon to appreciate pitch changes associated with drilling on sensitive structures and communication with surgical team members. As professionals who specialize in promoting the restoration and preservation of hearing for others, otologic surgeons should not neglect hearing protection for themselves.

Localization of group II and III metabotropic glutamate receptors at pre- and postsynaptic sites of inner hair cell ribbon synapses

Glutamate is the major excitatory neurotransmitter in the CNS binding to a variety of glutamate receptors. Metabotropic glutamate receptors (mGluR1 to mGluR8) can act excitatory or inhibitory, depending on associated signal cascades. Expression and localization of inhibitory acting mGluRs at inner hair cells (IHCs) in the cochlea are largely unknown. Here, we analyzed expression of mGluR2, mGluR3, mGluR4, mGluR6, mGluR7, and mGluR8 and investigated their localization with respect to the presynaptic ribbon of IHC synapses. We detected transcripts for mGluR2, mGluR3, and mGluR4 as well as for mGluR7a, mGluR7b, mGluR8a, and mGluR8b splice variants. Using receptor-specific antibodies in cochlear wholemounts, we found expression of mGluR2, mGluR4, and mGluR8b close to presynaptic ribbons. Super resolution and confocal microscopy in combination with 3-dimensional reconstructions indicated a postsynaptic localization of mGluR2 that overlaps with postsynaptic density protein 95 on dendrites of afferent type I spiral ganglion neurons. In contrast, mGluR4 and mGluR8b were expressed at the presynapse close to IHC ribbons. In summary, we localized in detail 3 mGluR types at IHC ribbon synapses, providing a fundament for new therapeutical strategies that could protect the cochlea against noxious stimuli and excitotoxicity.-Klotz, L., Wendler, O., Frischknecht, R., Shigemoto, R., Schulze, H., Enz, R. Localization of group II and III metabotropic glutamate receptors at pre- and postsynaptic sites of inner hair cell ribbon synapses.

Transcriptomic and epigenetic regulation of hair cell regeneration in the mouse utricle and its potentiation by Atoh1

The mammalian cochlea loses its ability to regenerate new hair cells prior to the onset of hearing. In contrast, the adult vestibular system can produce new hair cells in response to damage, or by reprogramming of supporting cells with the hair cell transcription factor Atoh1. We used RNA-seq and ATAC-seq to probe the transcriptional and epigenetic responses of utricle supporting cells to damage and Atoh1 transduction. We show that the regenerative response of the utricle correlates with a more accessible chromatin structure in utricle supporting cells compared to their cochlear counterparts. We also provide evidence that Atoh1 transduction of supporting cells is able to promote increased transcriptional accessibility of some hair cell genes. Our study offers a possible explanation for regenerative differences between sensory organs of the inner ear, but shows that additional factors to Atoh1 may be required for optimal reprogramming of hair cell fate.

[Hidden hearing loss-damage to hearing processing even with low-threshold noise exposure?]

BACKGROUND

New research in animal models indicates that even at lower intensities, noise exposure can induce defects in the synapses of the auditory pathway. However, only very high levels of noise exposure lead to mechanical hair cell damage with lesions of the inner ear and measurable hearing loss (audiogram; distortion product otoacoustic emissions, DPOAE). This paper revises the literature, starting with a case study.

CASE HISTORY

A 41-year-old patient suffered from hearing loss and tinnitus in the right ear following a car accident with airbag deployment. Hearing loss recovered partially, tinnitus and difficulties in speech discrimination persisted. Audiometry showed typical high-frequency hearing loss (40 dB) and tonal tinnitus (8 kHz). Although DPOAE and ABR potentials (auditory brainstem response, wave III and V) were completely normal 6 months after the accident, there was no detectable cochlear action potential (CAP) in electrocochleography (ECochG).

DISCUSSION

These findings indicate recovery of initial hair cell damage, whereas synaptic transformation remains reduced and slight hearing loss and poor speech perception in complex listening situations persist. This phenomenon has been described as "hidden hearing loss" in newer literature. Although similar retrocochlear lesions in the auditory pathway could be detected in animal models, valid data in humans are currently lacking because no adequate diagnostic methods are available.

CONCLUSION

Noise trauma initially results in hair cell damage. After recovery, hearing loss may persist, which can be due to synaptic lesions in the first neuron. An adequate testbattery has to be developped.

Otoprotective Effects of Stephania tetrandra S. Moore Herb Isolate against Acoustic Trauma

Noise is the most common occupational and environmental hazard, and noise-induced hearing loss (NIHL) is the second most common form of sensorineural hearing deficit. Although therapeutics that target the free-radical pathway have shown promise, none of these compounds is currently approved against NIHL by the United States Food and Drug Administration. The present study has demonstrated that tetrandrine (TET), a traditional Chinese medicinal alkaloid and the main chemical isolate of the Stephania tetrandra S. Moore herb, significantly attenuated NIHL in CBA/CaJ mice. TET is known to exert antihypertensive and antiarrhythmic effects through the blocking of calcium channels. Whole-cell patch-clamp recording from adult spiral ganglion neurons showed that TET blocked the transient Ca2+ current in a dose-dependent manner and the half-blocking concentration was 0.6 + 0.1 μM. Consistent with previous findings that modulations of calcium-based signaling pathways have both prophylactic and therapeutic effects against neural trauma, NIHL was significantly diminished by TET administration. Importantly, TET has a long-lasting protective effect after noise exposure (48 weeks) in comparison to 2 weeks after noise exposure. The otoprotective effects of TET were achieved mainly by preventing outer hair cell damage and synapse loss between inner hair cells and spiral ganglion neurons. Thus, our data indicate that TET has great potential in the prevention and treatment of NIHL.

Tonotopy in calcium homeostasis and vulnerability of cochlear hair cells

Ototoxicity, noise overstimulation, or aging, can all produce hearing loss with similar properties, in which outer hair cells (OHCs), principally those at the high-frequency base of the cochlea, are preferentially affected. We suggest that the differential vulnerability may partly arise from differences in Ca²⁺ balance among cochlear locations. Homeostasis is determined by three factors: Ca²⁺ influx mainly via mechanotransducer (MET) channels; buffering by calcium-binding proteins and organelles like mitochondria; and extrusion by the plasma membrane CaATPase pump. We review quantification of these parameters and use our experimentally-determined values to model changes in cytoplasmic and mitochondrial Ca²⁺ during Ca²⁺ influx through the MET channels. We suggest that, in OHCs, there are two distinct micro-compartments for Ca²⁺ handling, one in the hair bundle and the other in the cell soma. One conclusion of the modeling is that there is a tonotopic gradient in the ability of OHCs to handle the Ca²⁺ load, which correlates with their vulnerability to environmental challenges. High-frequency basal OHCs are the most susceptible because they have much larger MET currents and have smaller dimensions than low-frequency apical OHCs.