Mechanisms of noise-induced hearing loss indicate multiple methods of prevention

Advances in the Study of Etiology and Molecular Mechanisms of Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL), a multifactorial progressive disorder, results from a complex interplay of genetic and environmental factors, with its underlying mechanisms remaining unclear. Several pathological factors are believed to contribute to SNHL, including genetic factors, ion homeostasis, cell apoptosis, immune inflammatory responses, oxidative stress, hormones, metabolic syndrome, human cytomegalovirus infection, mitochondrial damage, and impaired autophagy. These factors collectively interact and play significant roles in the onset and progression of SNHL. The present review offers a comprehensive overview of the various factors that contribute to SNHL, emphasizes recent developments in understanding its etiology, and explores relevant preventive and intervention measures.

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.

Effects of 90 dB pure tone exposure on auditory and cardio-cerebral system functions in macaque monkeys

Excessive noise exposure presents significant health risks to humans, affecting not just the auditory system but also the cardiovascular and central nervous systems. This study focused on three male macaque monkeys as subjects. 90 dB sound pressure level (SPL) pure tone exposure (frequency: 500Hz, repetition rate: 40Hz, 1 min per day, continuously exposed for 5 days) was administered. Assessments were performed before exposure, during exposure, immediately after exposure, and at 7-, 14-, and 28-days post-exposure, employing auditory brainstem response (ABR) tests, electrocardiograms (ECG), and electroencephalograms (EEG). The study found that the average threshold for the Ⅴ wave in the right ear increased by around 30 dB SPL right after exposure (P < 0.01) compared to pre-exposure. This elevation returned to normal within 7 days. The ECG results indicated that one of the macaque monkeys exhibited an RS-type QRS wave, and inverted T waves from immediately after exposure to 14 days, which normalized at 28 days. The other two monkeys showed no significant changes in their ECG parameters. Changes in EEG parameters demonstrated that main brain regions exhibited significant activation at 40Hz during noise exposure. After noise exposure, the power spectral density (PSD) in main brain regions, particularly those represented by the temporal lobe, exhibited a decreasing trend across all frequency bands, with no clear recovery over time. In summary, exposure to 90 dB SPL noise results in impaired auditory systems, aberrant brain functionality, and abnormal electrocardiographic indicators, albeit with individual variations. It has implications for establishing noise protection standards, although the precise mechanisms require further exploration by integrating pathological and behavioral indicators.

Association between oxidative balance score and hearing loss: a cross-sectional study from the NHANES database

Aim

The oxidative balance score (OBS), a composite score of dietary nutrients and lifestyles, reflects an individual's oxidative and antioxidant status. Evidence showed that oxidative stress levels were related to hearing loss. The relationship between OBS and hearing loss remains unclear. This study was to explore the association between OBS and hearing loss in adults.

Methods

In this cross-sectional study, data of participants aged 20-69 years who received hearing tests were extracted from the National Health and Nutrition Examination Survey (NHANES) database (2011-2012, 2015-2016). Hearing loss was defined as hearing threshold >25 dB in either ear. The OBS was composed of 16 dietary nutrients and 4 lifestyles. The covariates were screened using the backward stepwise regression analysis. The association of OBS and hearing loss was assessed with odds ratios (ORs) and 95% confidence intervals (CIs). Subgroups of age, gender, occupational noise exposure, recreational noise exposure, firearm noise exposure, and veteran status were further evaluated the associations. The importance ranking of OBS components was analyzed by the weighted random forest model.

Results

Of the total 3,557 adults, 338 (9.5%) suffered from hearing loss. High OBS levels were associated with lower odds of hearing loss (OR = 0.58, 95%CI: 0.41-0.82), after adjusting age, gender, race, hypertension, tinnitus, recreational noise exposure, and occupational noise exposure. Similar results were discovered in individuals aged50-59 years old (OR = 0.47, 95%CI: 0.24-0.93), aged 60-69 years old (OR = 0.31, 95%CI: 0.16-0.61), with female (OR = 0.44, 95%CI: 0.20-0.96), without occupational noise exposure (OR = 0.31, 95%CI: 0.16-0.62), recreational noise exposure (OR = 0.48, 95%CI: 0.30-0.76), firearm noise exposure (OR = 0.38, 95%CI: 0.19-0.77), and veteran status (OR = 0.57, 95%CI: 0.39-0.82). In OBS components, vitamin B12, total fat and physical activity were important for hearing loss.

Conclusion

Elevated OBS may be associated with hearing health in adults. Appropriate vitamin B12 supplementation, reduction of total fat intake, and increased physical activity may be beneficial to the prevention of hearing loss.

A single dose of AC102 restores hearing in a guinea pig model of noise-induced hearing loss to almost prenoise levels

Although sudden sensorineural hearing loss (SSNHL) is a serious condition, there are currently no approved drugs for its treatment. Nevertheless, there is a growing understanding that the cochlear pathologies that underlie SSNHL include apoptotic death of sensory outer hair cells (OHCs) as well as loss of ribbon synapses connecting sensory inner hair cells (IHCs) and neurites of the auditory nerve, designated synaptopathy. Noise-induced hearing loss (NIHL) is a common subtype of SSNHL and is widely used to model hearing loss preclinically. Here, we demonstrate that a single interventive application of a small pyridoindole molecule (AC102) into the middle ear restored auditory function almost to prenoise levels in a guinea pig model of NIHL. AC102 prevented noise-triggered loss of OHCs and reduced IHC synaptopathy suggesting a role of AC102 in reconnecting auditory neurons to their sensory target cells. Notably, AC102 exerted its therapeutic properties over a wide frequency range. Such strong improvements in hearing have not previously been demonstrated for other therapeutic agents. In vitro experiments of a neuronal damage model revealed that AC102 protected cells from apoptosis and promoted neurite growth. These effects may be explained by increased production of adenosine triphosphate, indicating improved mitochondrial function, and reduced levels of reactive-oxygen species which prevents the apoptotic processes responsible for OHC death. This action profile of AC102 might be causal for the observed hearing recovery in in vivo models.

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.

The association between dietary total antioxidant capacity and hearing loss: results from the Tehran employees Cohort Study

BACKGROUND

Despite numerous studies that have explored the association between individual antioxidants or specific combinations and the risk of hearing loss, there is lack of information regarding the relationship between dietary total antioxidant capacity (dTAC) and hearing loss. The conflicting results on this association further highlight the need for more research in this area. This study aims to investigate the association between overall dietary antioxidant intake and the risk of hearing loss among Iranian adults.

METHODS

This cross-sectional study recruited 3443 adult participants aged between 19 and 67 years (with an average age of 41.4 years ± 8.8) who were employed at Tehran University of Medical Sciences in Iran. Participants underwent dietary assessment using a validated Food Frequency Questionnaire (FFQ). The hearing status of each participant was evaluated by a licensed audiologist in a soundproof room, using diagnostic audiometry that adhered to American National Standards specifications and followed standard audiometric clinical procedures. The dietary total antioxidant capacity (dTAC) was calculated using the Ferric Reducing-Antioxidant Power (FRAP) values.

RESULTS

43.6% of male participants had hearing loss, while 26.8% among female participants. After accounting for various confounding factors, no significant association was observed between higher levels of dTAC and reduced odds of hearing loss in the overall population. However, among men under the age of 40, higher levels of dTAC were associated with decreased odds of hearing loss, even after adjusting for several covariates (OR: 0.56, 95% CI: 0.31-1.02, Ptrend = 0.02). This relationship was not evident in men over 40 years of age or among women.

CONCLUSION

The study found an inverse relationship between higher antioxidant intake in the diet and lower odds of hearing loss, specifically among men who were 40 years old or younger. However, this relationship was not observed in the overall population or among women. Additional prospective studies are necessary to validate these results.

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Risk-taking propensity as a risk factor for noise-induced hearing loss in the general population

OBJECTIVES

To examine general risk propensity in relation to perceptions of noise, risk behaviour, and hearing loss in the general population.

DESIGN

Participants completed an online survey using the Amazon Mechanical Turk crowdsourcing platform.

STUDY SAMPLE

The sample comprised 1274 adults from the United States.

RESULTS

Higher general risk propensity was associated with an increased likelihood to engage in noise-risk behaviours. Lower general risk propensity was associated with increased knowledge of noise risks and an increased perception of noise as risky. The frequency of self-reported exposures to hazardous noise resulted in estimated annual noise doses exceeding standard hazard limits in 40% of the surveyed population.

CONCLUSIONS

Results revealed limited knowledge of the risks and associated health consequences of noise exposure in the general population Results of this study suggest a high rate of self-exposure to hazardous noise by the general population. Those with higher general risk propensity are more likely to engage in risky noise behaviour. Risky noise behaviour is associated with age, gender, race, ethnicity, and general risk propensity. Intervention programs to modify risky noise behaviour in the general population should focus on both increasing knowledge and establishing accurate perceptions of risk.

Association of coffee consumption with the prevalence of hearing loss in US adults, NHANES 2003-2006

OBJECTIVE

This study aims to explore the association between coffee consumption and the prevalence of hearing loss in American adults based on a national population-based survey.

DESIGN

Cross-sectional analysis of reported audiometric status and coffee intake from the 2003-2006 National Health and Nutrition Examination Survey (NHANES). Multivariate logistic regression, forest plots and restricted cubic spline (RCS) analyses were used to explore the associations and dose-response relationships between coffee consumption frequency and hearing loss.

SETTING

The USA.

PARTICIPANT

This study included 1894 individuals aged ≥ 20 from the 2003-2006 NHANES.

RESULTS

In this study, the prevalence of speech-frequency hearing loss (SFHL) and high-frequency hearing loss (HFHL) among the participants was 35·90 % and 51·54 %, respectively. Compared with those who no consumed coffee, non-Hispanic White who consumed ≥ 4 cups/d had higher prevalence of SFHL (OR: 1·87; 95 % CI: 1·003. 3·47). And a positive trend of coffee consumption frequency with the prevalence of HFHL was found (Ptrend = 0·001). This association of HFHL was similar for participants aged 20-64 (Ptrend = 0·001), non-Hispanic White (Ptrend = 0·002), non-noise exposure participants (Ptrend = 0·03) and noise-exposed participants (Ptrend = 0·003). The forest plots analysis found that the association between 1 cup-increment of daily coffee consumption and the prevalence of HFHL was statistically significant in males. RCS model supported a positive linear association of coffee consumption with SFHL (P for overall association = 0·02, P for nonlinearity = 0·48) and a positive non-linear association of coffee consumption with HFHL (P for overall association = 0·001, P for nonlinearity = 0·001).

CONCLUSION

Our findings suggested that coffee consumption was associated with higher prevalence of hearing loss. Further cohort studies in larger population are needed to investigate these findings.

Audiological, Phonatory and Cardiac Correlates of Individuals Exposed to Low-Frequency Noise or at Risk of Vibroacoustic Disease

Introduction  Low-frequency noise (LFN) is hazardous to hearing. Long-term exposure to LFN may lead to vibroacoustic disease (VAD), which not only affects a specific organ but the physiological function of entire systems, such as the auditory, phonatory, respiratory, and cardiac systems. Moreover, VAD may lead to many psychological problems and hence affect the quality of life. Objective  To investigate the adverse effects of LFN on hearing, acoustic and perceptual correlates of the voice, blood pressure, cardiac rate, and anxiety level. Method  A total of 20 subjects exposed to LFN and 20 not exposed to LFN were included, and a detailed case history was recorded. The patients were submitted to pure tone audiometry, otoscopic examination, acoustic and perceptual analyses of the voice, maximum phonation time, and an assessment of the s/z ratio. We also assessed blood pressure, and the results of a voice-related quality of life questionnaire and of the Hamilton anxiety rating scale. Results  The results indicate that LFN had an adverse impact on the high-frequency threshold. The present study found a significant difference in shimmer and harmonics-to-noise ratio (HNR) values. Few subjects had high blood pressure and showed the sign of anxiety on the Hamilton anxiety rating scale. Conclusion  Low-frequency noise has adverse effects on entire systems of the body and causes many psychological issues, which, in turn negatively affect quality of life.

Preclinical prospects of investigational agents for hearing loss treatment

INTRODUCTION

: Hearing loss has a high prevalence, with aging, noise exposure, ototoxic drug therapies, and genetic mutations being some of the leading causes of hearing loss. Health conditions such as cardiovascular disease and diabetes are associated with hearing loss, perhaps due to shared vascular pathology in the ear and in other tissues.

AREAS COVERED

: Issues in the design of preclinical research preclude the ability to make comparisons regarding the relative efficacy of different drugs of interest for possible hearing loss prevention or hearing restoration. This has not slowed the advancement of candidate therapeutics into human clinical testing. There is a robust pipeline with drugs that have different mechanisms of action providing diverse candidate therapies and opportunities for combination therapies to be considered.

EXPERT OPINION

: Much of the preclinical research literature lacks standard study design elements such as dose response testing, and lack of standardization of test protocols significantly limits conclusions regarding relative efficacy. Nonetheless, the many positive results to date have supported translation of preclinical efforts into clinical trials assessing potential human benefits. Approval of the first hearing loss prevention therapeutic is a major success, providing a pathway for other drugs to follow.

Noise exposure in pediatric otolaryngology clinic: A sound survey of a single-institution tertiary care facility

BACKGROUND

The Occupational Safety and Health Administration (OSHA) considers acoustic exposure of 90 decibels (dB) an occupational risk for noise-induced hearing loss. Pediatric healthcare clinicians are exposed to considerable noise especially during invasive procedures, predisposing them to noise-induced hearing loss, increased work-related stress, and increased complications associated with intense noise exposure. While there has been extensive research in noise exposure in dentistry, to date there has been no research on noise exposure in the pediatric otolaryngology clinic setting. The objective of this study is to quantify the degree of noise exposure that pediatric otolaryngologists encounter in the clinical setting.

METHODS

A sound survey was performed of 420 pediatric otolaryngology clinic visits within a single-institution tertiary care facility from January 2022 to March 2022, with a total of 409 visits included. At each visit, noise was measured using a calibrated National Institute for Occupational Safety and Health (NIOSH) Sound Meter application, an iPad, and a microphone. The Equivalent Continuous Sound Pressure Level (LAeq), peak sound pressure level (SPL), C-weighted peak noise level (LCpeak), and the 8-hour time-weighted average (TWA) sound level were recorded.

RESULTS

The average LAeq was 61.1 dB, the median LAeq was 60.3 dB, and the average peak SPL was 80.5 dB. Only 0.5 % of visits reached an LAeq above 80 dB, however, 51 % were above 60 dB and 99 % were above 45 dB. No clinicians were exposed to noise exceeding established limits of safety. Patients younger than ten years old (p < 0.001) and those who underwent procedures such as cerumen removal (p < 0.001) elicited higher ranges of elevated noise. Multivariate analysis confirmed that increased age decreased acoustic exposure while procedures increased acoustic exposure.

CONCLUSIONS

The results of this study suggest that pediatric otolaryngology clinicians do not exceed hazardous noise limit exposure. However, they are exposed to levels above those which have been linked to stress, poor productivity, and stress-related disorders. This analysis also reports that patients who are younger and those that undergo procedures, specifically cerumen removal, tend to expose their providers to the highest levels of noise. This is the first study examining noise exposure in pediatric otolaryngology, and further research should evaluate the risks of noise exposure in this environment.

Role of mitochondrial dysfunction and oxidative stress in sensorineural hearing loss

Sensorineural hearing loss (SNHL) can either be genetically inherited or acquired as a result of aging, noise exposure, or ototoxic drugs. Although the precise pathophysiological mechanisms underlying SNHL remain unclear, an overwhelming body of evidence implicates mitochondrial dysfunction and oxidative stress playing a central etiological role. With its high metabolic demands, the cochlea, particularly the sensory hair cells, stria vascularis, and spiral ganglion neurons, is vulnerable to the damaging effects of mitochondrial reactive oxygen species (ROS). Mitochondrial dysfunction and consequent oxidative stress in cochlear cells can be caused by inherited mitochondrial DNA (mtDNA) mutations (hereditary hearing loss and aminoglycoside-induced ototoxicity), accumulation of acquired mtDNA mutations with age (age-related hearing loss), mitochondrial overdrive and calcium dysregulation (noise-induced hearing loss and cisplatin-induced ototoxicity), or accumulation of ototoxic drugs within hair cell mitochondria (drug-induced hearing loss). In this review, we provide an overview of our current knowledge on the role of mitochondrial dysfunction and oxidative stress in the development of SNHL caused by genetic mutations, aging, exposure to excessive noise, and ototoxic drugs. We also explore the advancements in antioxidant therapies for the different forms of acquired SNHL that are being evaluated in preclinical and clinical studies.

Antioxidant Therapy as an Effective Strategy against Noise-Induced Hearing Loss: From Experimental Models to Clinic

Cochlear redox unbalance is the main mechanism of damage involved in the pathogenesis of noise-induced-hearing loss. Indeed, the increased free radical production, in conjunction with a reduced efficacy of the endogenous antioxidant system, plays a key role in cochlear damage induced by noise exposure. For this reason, several studies focused on the possibility to use exogenous antioxidant to prevent or attenuate noise-induce injury. Thus, several antioxidant molecules, alone or in combination with other compounds, have been tested in both experimental and clinical settings. In our findings, we tested the protective effects of several antioxidant enzymes, spanning from organic compounds to natural compounds, such as nutraceuticals of polyphenols. In this review, we summarize and discuss the strengths and weaknesses of antioxidant supplementation focusing on polyphenols, Q-Ter, the soluble form of CoQ10, Vitamin E and N-acetil-cysteine, which showed great otoprotective effects in different animal models of noise induced hearing loss and which has been proposed in clinical trials.

Oridonin employs interleukin 1 receptor type 2 to treat noise-induced hearing loss by blocking inner ear inflammation

NOD-like receptor protein 3 (NLRP3) inflammasomes trigger the inflammatory cascades and participate in various inflammatory diseases, including noise-induced hearing loss (NIHL) caused by oxidative stress. Recently, the anti-inflammatory traditional medicine oridonin (Ori) has been reported to provide hearing protection in mice after noise exposure by blocking the NLRP3-never in mitosis gene A-related kinase 7 (NEK7)-inflammasome complex assembly. Using RNA sequencing analysis, we further elucidated that interleukin 1 receptor type 2 (IL1R2) may be another crucial factor regulated by Ori to protect NIHL. We observed that IL1R2 expression was localized in spiral ganglion neurons, inner and outer hair cells, in Ori-treated mouse cochleae. Additionally, we confirmed that ectopic overexpression of IL1R2 in the inner ears of healthy mice using an adeno-associated virus delivery system significantly reduced noise-induced ribbon synapse lesions and hearing loss by blocking the "cytokine storm" in the inner ear. This study provides a novel theoretical foundation for guiding the clinical treatment of NIHL.

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.

Dietary magnesium and calcium intake is associated with lower risk of hearing loss in older adults: A cross-sectional study of NHANES

Aim

Dietary intake as a modifiable factor has been reported to be associated with hearing loss (HL). The relationship between magnesium (Mg) and calcium (Ca) as common dietary nutrients and HL in the elderly has rarely been reported. This study aimed to assess the association between Mg and Ca intake and HL in older adults.

Method

This cross-sectional study included participants aged ≥70 years from the National Health and Nutrition Examination Survey (NHANES) 2005–2006, 2009–2010, and 2017–2018. Outcomes were low-frequency [pure-tone averages (PTAs) at 500, 1000, and 2000 Hz &gt;25 dB] and speech-frequency (PTAs at 500, 1000, 2000, and 4,000 Hz &gt;25 dB) HL. Multivariate logistic analysis was utilized to explore the association between dietary Mg and Ca intake and their combined intake (Ca/Mg, Ca*Mg) and HL, and was described as odds ratio (OR) and 95% confidence interval (CI).

Results

A total of 1,858 participants were included, of which 1,052 (55.95%) had low-frequency HL and 1,349 (72.62%) had speech-frequency HL. Dietary Ca intakes [OR = 0.86, 95%CI: (0.74–0.99)] and Mg intakes [OR = 0.81, 95%CI: (0.68–0.95)] and Ca * Mg [OR = 0.12, 95%CI: (0.02–0.87)] were associated with lower odds of low-frequency HL after adjusting for confounders. Similar, dietary Ca intakes [OR = 0.85, 95%CI: (0.77–0.95)] and Mg intakes [OR = 0.78, 95%CI: (0.68–0.90)] and Ca * Mg [OR = 0.23, 95%CI: (0.05–0.78)] were related to lower odds of speech-frequency HL. For different levels of Mg and Ca intake, the combined intake of Ca (≥1,044 mg) and Mg (≥330 mg) was related to lower odds of low-frequency HL [OR = 0.02, 95%CI: (0.00–0.27)] and speech-frequency HL [OR = 0.44, 95%CI: (0.21–0.89)].

Conclusion

Dietary intakes of Mg and Ca were associated with lower odds of HL and are a promising intervention to be further explored in older adults with HL.

Noise-induced auditory damage affects hippocampus causing memory deficits in a model of early age-related hearing loss

Several studies identified noise-induced hearing loss (NIHL) as a risk factor for sensory aging and cognitive decline processes, including neurodegenerative diseases, such as dementia and age-related hearing loss (ARHL). Although the association between noise- and age-induced hearing impairment has been widely documented by epidemiological and experimental studies, the molecular mechanisms underlying this association are not fully understood as it is not known how these risk factors (aging and noise) can interact, affecting memory processes. We recently found that early noise exposure in an established animal model of ARHL (C57BL/6 mice) accelerates the onset of age-related cochlear dysfunctions. Here, we extended our previous data by investigating what happens in central brain structures (auditory cortex and hippocampus), to assess the relationship between hearing and memory impairment and the possible combined effect of noise and sensory aging on the cognitive domain. To this aim, we exposed juvenile C57BL/6 mice of 2 months of age to repeated noise sessions (60 min/day, pure tone of 100 dB SPL, 10 kHz, 10 consecutive days) and we monitored auditory threshold by measuring auditory brainstem responses (ABR), spatial working memory, by using the Y-maze test, and basal synaptic transmission by using ex vivo electrophysiological recordings, at different time points (1, 4 and 7 months after the onset of noise exposure, corresponding to 3, 6 and 9 months of age). We found that hearing loss, along with accelerated presbycusis onset, can induce persistent synaptic alterations in the auditory cortex. This was associated with decreased memory performance and oxidative-inflammatory injury in the hippocampus, the extra-auditory structure involved in memory processes. Collectively, our data confirm the critical relationship between auditory and memory circuits, suggesting that the combined detrimental effect of noise and sensory aging on hearing function can be considered a high-risk factor for both sensory and cognitive degenerative processes, given that early noise exposure accelerates presbycusis phenotype and induces hippocampal-dependent memory dysfunctions.

Intratympanic steroid treatment can reduce ROS and immune response in human perilymph investigated by in-depth proteome analysis

Intratympanic (IT) steroid treatment is one of the most widely used and effective treatments for inner ear disorders such as sudden sensorineural hearing loss (SNHL). However, a clear mechanism of IT steroids in inner ear recovery has not yet been revealed. Therefore, we investigated proteome changes in extracted human perilymph after steroid treatment. In this study, we applied a tandem mass spectrometry (MS/MS)-based proteomics approach to discover global proteome changes by comparing human perilymph after steroid treatment with non-treated perilymph group. Using liquid chromatography-MS/MS analysis, we selected 156 differentially expressed proteins (DEPs) that were statistically significant according to Student's t-test. Functional annotation analysis showed that upregulated proteins after steroid treatment are related to apoptosis signaling, as well as reactive oxygen species (ROS) and immune responses. The protein-protein interaction (PPI) clusters the proteins associated with these processes and attempts to observe signaling circuitry, which mediates cellular response after IT steroid treatments. Moreover, we also considered the interactome analysis of DEPs and observed that those with high interaction scores were categorized as having equivalent molecular functions (MFs). Collectively, we suggest that DEPs and interacting proteins in human perilymph after steroid treatment would inhibit the apoptotic and adaptive immune processes that may lead to anti-inflammatory effects.

Association of dietary factors with noise-induced hearing loss in Korean population: A 3-year national cohort study

Noise-induced hearing loss (NIHL) is a hearing impairment (HI) caused by various clinical factors. Identifying the relationship between NIHL and nutrient consumption could help in reducing the prevalence of hearing loss. The aim of this study was to analyze the relationship between NIHL and dietary factors using data of the Korea National Health and Nutrition Examination survey (KNHANES). The data were collected from The Fifth KNHANES 2010-2012. The survey was taken by a total of 10,850 participants aged 20-65 years. Air conduction audiometry was measured at 500, 1000, 2000, and 4000 Hz in both ears. Metabolic syndrome, noise exposure, alcohol consumption, smoking, income level, marital status, and nutritional intake were evaluated. The differences between non-HI and HI participants in the noise-exposed group showed statistically significant differences in age, sex, marital and smoking status, alcohol consumption, and fasting glucose and triglyceride levels (p<0.05). In a multiple regression analysis of the noise-exposed group, age showed a significant association with HI (OR: 0.604; 95% CI: 0.538-0.678) after adjusting for confounders. In multivariate analysis for dietary factors affecting HI in noise-exposed groups, retinol (OR: 1.356; 95% CI: 1.068-1.722), niacin (OR: 1.5; 95% CI: 1.022-2.201), and carbohydrates (OR: 0.692; 95% CI: 0.486-0.985) showed a significant association with NIHL. Age was identified as the only factor significantly affecting NIHL. When the dietary factors of the noise-exposed group were analyzed, high intake of niacin and retinol and low intake of carbohydrates appeared to reduce the risk of hearing loss.

Age-related hearing loss was accelerated by apoptosis of spiral ganglion and stria vascularis cells in ApoE KO mice with hyperglycemia and hyperlipidemia

Age-related hearing loss (ARHL) is associated with diabetes and/or dyslipidemia in humans. However, the detailed mechanism for the development of ARHL by diabetes and/or dyslipidemia has not been elucidated. In this study, we investigated the etiology of ARHL in apolipoprotein E (ApoE)-deficient mice with diabetes and dyslipidemia. The atherosclerotic CD-STZ (mice fed with a control diet and received an STZ injection), WD-con (mice fed with a western diet), and WD-STZ (mice fed with a western diet and received an STZ injection) mice showed a 2.4-, 4.9-, and 6.8-fold larger area, respectively, occupied by lesions throughout the aorta compared with the CD-con mice. A significantly larger area under the curve (AUC) was observed in the STZ-treated groups than in the non-treated groups based on the oral glucose tolerance test (OGTT). At 20 weeks of age, HbA_1c levels were significantly higher in the CD-STZ and WD-STZ mice than in the CD-con and WD-con mice. In all the groups, the auditory brainstem response (ABR) thresholds of the 16-week-old mice were significantly higher compared with those of the 8-week-old mice. In particular, in the WD-STZ mice, the ABR thresholds of the left and right ears reached the maximum decibel peak equivalent sound pressure levels (130 dBpeSPL), which is a sign of deafness. The apoptotic spiral ganglion neurons (SGNs) of the WD-STZ mice were significantly increased compared with those of the other three groups, indicating that SGN apoptosis resulted in hearing loss in STZ-induced diabetic ApoE KO mice fed with a WD. A significant loss of the stria vascularis cells was observed in the WD-STZ group compared with the CD-con mice. In the organ of Corti, few apoptotic hair cells were found in all the groups; however, no significant difference was observed. Therefore, we consider that the reduced hearing ability in the STZ-treated and WD-fed groups was attributed to the damage to the SGN and stria vascularis in the cochlea. Thus, our results indicated that ototoxicity by diabetes and/or dyslipidemia accelerated ARHL in ApoE KO mice, thereby suggesting the importance of appropriate treatment of patients with diabetes and/or dyslipidemia to prevent ARHL.

Prevalence and global estimates of unsafe listening practices in adolescents and young adults: a systematic review and meta-analysis

INTRODUCTION

This study aimed to determine the prevalence of unsafe listening practices from exposure to personal listening devices (PLDs) and loud entertainment venues in individuals aged 12-34 years, and to estimate the number of young people who could be at risk of hearing loss from unsafe listening worldwide.

METHODS

We conducted a systematic review and meta-analysis to estimate the prevalence of unsafe listening practices from PLDs and loud entertainment venues. We searched three databases for peer-reviewed articles published between 2000 and 2021 that reported unsafe listening practices in individuals aged 12-34 years. Pooled prevalence estimates (95% CI) of exposed populations were calculated using random effects models or ascertained from the systematic review. The number of young people who could be at risk of hearing loss worldwide was estimated from the estimated global population aged 12-34 years, and best estimates of exposure to unsafe listening ascertained from this review.

RESULTS

Thirty-three studies (corresponding to data from 35 records and 19 046 individuals) were included; 17 and 18 records focused on PLD use and loud entertainment venues, respectively. The pooled prevalence estimate of exposure to unsafe listening from PLDs was 23.81% (95% CI 18.99% to 29.42%). There was limited certainty (p&gt;0.50) in our pooled prevalence estimate for loud entertainment venues. Thus, we fitted a model as a function of intensity thresholds and exposure duration to identify the prevalence estimate as 48.20%. The global estimated number of young people who could be at risk of hearing loss from exposure to unsafe listening practices ranged from 0.67 to 1.35 billion.

CONCLUSIONS

Unsafe listening practices are highly prevalent worldwide and may place over 1 billion young people at risk of hearing loss. There is an urgent need to prioritise policy focused on safe listening. The World Health Organization provides comprehensive materials to aid in policy development and implementation.

Hearing Function and Nutritional Status in Aviation Pilots from Spain Exposed to High Acoustic Damage

Noise-induced hearing loss is the most frequent and preventable occupational disease. Aviation pilots are a vulnerable population, as they spend many hours exposed to noise pollution in their working environment. Different studies suggest that certain dietary compounds may play a key role in the etiology and prevention of this pathology. We aimed to study the relationship linking auditory function, dietary intake, and some serum biomarkers in pilots, exposed to noise in the work environment. A total of 235 pilots, who undergo a periodic medical examination at the Centro de Instrucción de Medicina Aeroespacial (Madrid, SPAIN), were evaluated. Auditory function was assessed by tonal audiometry. Energy and nutrient intakes were estimated by 24 h recall (DIALTM program). Serum homocysteine (Hcy) was determined in a Cobas 6000TM multi-analyzer while folate, vitamin B12, and D were analyzed in a Cobas e411TM. The prevalence of hearing loss (HL) was 64.3%. HL was significantly related to age (r = 0.588, p ≤ 0.001) and flight hours (r = 0.283, p ≤ 0.001). A multiple linear regression model was used to assess the relationship among HL, flight hours, serum folate, and Hcy serum levels. HL was significantly (p < 0.050) associated with flight hours (β = 0.246), serum folate (β = −0.143), and serum Hcy (β = 0.227). Nutritional interventions would be of great interest to monitor and slow down the HL progression in populations exposed to noise pollution in their workplace.

Effects of pyrroloquinoline quinone on noise-induced and age-related hearing loss in mice

We investigated whether the oxidoreductase cofactor pyrroloquinoline quinone (PQQ) prevents noise-induced and age-related hearing loss (NIHL and ARHL) in mice. To assess NIHL, 8 week-old mice with and without PQQ administration were exposed to noise for 4 h. PQQ was orally administered for one week before and after noise exposure and subcutaneously once before noise exposure. For ARHL evaluation, mice were given drinking water with or without PQQ starting at 2 months of age. In the NIHL model, PQQ-treated mice had auditory brainstem response (ABR) thresholds of significantly reduced elevation at 8 kHz, a significantly increased number of hair cells at the basal turn, and significantly better maintained synapses beneath the inner hair cells compared to controls. In the ARHL model, PQQ significantly attenuated the age-related increase in ABR thresholds at 8 and 32 kHz at 10 months of age compared to controls. In addition, the hair cells, spiral ganglion cells, ribbon synapses, stria vascularis and nerve fibers were all significantly better maintained in PQQ-treated animals compared to controls at 10 months of age. These physiological and histological results demonstrate that PQQ protects the auditory system from NIHL and ARHL in mice.

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.

Role of Oxidative Stress and Antioxidants in Acquired Inner Ear Disorders

Oxygen metabolism in the mitochondria is essential for biological activity, and reactive oxygen species (ROS) are produced simultaneously in the cell. Once an imbalance between ROS production and degradation (oxidative stress) occurs, cells are damaged. Sensory organs, especially those for hearing, are constantly exposed during daily life. Therefore, almost all mammalian species are liable to hearing loss depending on their environment. In the auditory pathway, hair cells, spiral ganglion cells, and the stria vascularis, where mitochondria are abundant, are the main targets of ROS. Excessive generation of ROS in auditory sensory organs is widely known to cause sensorineural hearing loss, and mitochondria-targeted antioxidants are candidates for treatment. This review focuses on the relationship between acquired hearing loss and antioxidant use to provide an overview of novel antioxidants, namely medicines, supplemental nutrients, and natural foods, based on clinical, animal, and cultured-cell studies.

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.

Inner Ear Drug Delivery for Sensorineural Hearing Loss: Current Challenges and Opportunities

Most therapies for treating sensorineural hearing loss are challenged by the delivery across multiple tissue barriers to the hard-to-access anatomical location of the inner ear. In this review, we will provide a recent update on various pharmacotherapy, gene therapy, and cell therapy approaches used in clinical and preclinical studies for the treatment of sensorineural hearing loss and approaches taken to overcome the drug delivery barriers in the ear. Small-molecule drugs for pharmacotherapy can be delivered via systemic or local delivery, where the blood-labyrinth barrier hinders the former and tissue barriers including the tympanic membrane, the round window membrane, and/or the oval window hinder the latter. Meanwhile, gene and cell therapies often require targeted delivery to the cochlea, which is currently achieved via intra-cochlear or intra-labyrinthine injection. To improve the stability of the biomacromolecules during treatment, e.g., RNAs, DNAs, proteins, additional packing vehicles are often required. To address the diverse range of biological barriers involved in inner ear drug delivery, each class of therapy and the intended therapeutic cargoes will be discussed in this review, in the context of delivery routes commonly used, delivery vehicles if required (e.g., viral and non-viral nanocarriers), and other strategies to improve drug permeation and sustained release (e.g., hydrogel, nanocarriers, permeation enhancers, and microfluidic systems). Overall, this review aims to capture the important advancements and key steps in the development of inner ear therapies and delivery strategies over the past two decades for the treatment and prophylaxis of sensorineural hearing loss.

Noise-induced hearing loss correlates with inner ear hair cell decrease in larval zebrafish

Anthropogenic noise can be hazardous for the auditory system and wellbeing of animals, including humans. However, very limited information is known on how this global environmental pollutant affects auditory function and inner ear sensory receptors in early ontogeny. The zebrafish (Danio rerio) is a valuable model in hearing research, including to investigate developmental processes of the vertebrate inner ear. We tested the effects of chronic exposure to white noise in larval zebrafish on inner ear saccular sensitivity and morphology at 3 and 5 days post fertilization (dpf), as well as on auditory-evoked swimming responses using the prepulse inhibition paradigm (PPI) at 5 dpf. Noise-exposed larvae showed significant increase in microphonic potential thresholds at low frequencies, 100 and 200 Hz, while PPI revealed a hypersensitisation effect and similar threshold shift at 200 Hz. Auditory sensitivity changes were accompanied by a decrease in saccular hair cell number and epithelium area. In aggregate, the results reveal noise-induced effects on inner ear structure-function in a larval fish paralleled by a decrease in auditory-evoked sensorimotor responses. More broadly, this study highlights the importance of investigating the impact of environmental noise on early development of sensory and behavioural responsiveness to acoustic stimuli.

Frailty Syndrome and Oxidative Stress as Possible Links Between Age-Related Hearing Loss and Alzheimer’s Disease

As it is well known, a worldwide improvement in life expectancy has taken place. This has brought an increase in chronic pathologies associated with aging. Cardiovascular, musculoskeletal, psychiatric, and neurodegenerative conditions are common in elderly subjects. As far as neurodegenerative diseases are concerned dementias and particularly, Alzheimer’s disease (AD) occupy a central epidemiological position given their high prevalence and their profound negative impact on the quality of life and life expectancy. The amyloid cascade hypothesis partly explains the immediate cause of AD. However, limited therapeutical success based on this hypothesis suggests more complex remote mechanisms underlying its genesis and development. For instance, the strong association of AD with another irreversible neurodegenerative pathology, without curative treatment and complex etiology such as presbycusis, reaffirms the intricate nature of the etiopathogenesis of AD. Recently, oxidative stress and frailty syndrome have been proposed, independently, as key factors underlying the onset and/or development of AD and presbycusis. Therefore, the present review summarizes recent findings about the etiology of the above-mentioned neurodegenerative diseases, providing a critical view of the possible interplay among oxidative stress, frailty syndrome, AD and presbycusis, that may help to unravel the common mechanisms shared by both pathologies. This knowledge would help to design new possible therapeutic strategies that in turn, will improve the quality of life of these patients.

TMT-Based Quantitative Proteomics Reveals Cochlear Protein Profile Alterations in Mice with Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) is a global occupational disease affecting health. To date, genetic polymorphism studies on NIHL have been performed extensively. However, the proteomic profiles in the cochleae of mice suffering noise damage remain unclear. The goal of this current study was to perform a comprehensive investigation on characterizing protein expression changes in the cochlea based on a mouse model of NIHL using tandem mass tag (TMT)-labeling quantitative proteomics, and to reveal the potential biomarkers and pathogenesis of NIHL. Male C57BL/6J mice were exposed to noise at 120 dB SPL for 4 h to construct the NIHL mouse model. The levels of MDA and SOD, and the production of proinflammatory cytokines including TNF-α and IL-6 in the mice cochleae, were determined using chemical colorimetrical and ELISA kits. Moreover, differentially expressed proteins (DEPs) were validated using Western blotting. The mouse model showed that the ABR thresholds at frequencies of 4, 8, 12, 16, 24 and 32 kHz were significantly increased, and outer hair cells (HCs) showed a distinct loss in the noise-exposed mice. Proteomics analysis revealed that 221 DEPs were associated with NIHL. Bioinformatics analysis showed that a set of key inflammation and autophagy-related DEPs (ITGA1, KNG1, CFI, FGF1, AKT2 and ATG5) were enriched in PI3K/AKT, ECM-receptor interaction, and focal adhesion pathways. The results revealed that the MDA level was significantly increased, but the activity of SOD decreased in noise-exposed mice compared to the control mice. Moreover, TNF-α and IL-6 were significantly increased in the noise-exposed mice. Western blotting revealed that the expression levels of ITGA1, KNG1, and CFI were upregulated, but FGF1, AKT2, and ATG5 were significantly downregulated in noise-exposed mice. This study provides new scientific clues about the future biomarkers and pathogenesis studies underlying NIHL. Furthermore, the findings suggest that the validated DEPs may be valuable biomarkers of NIHL, and inflammation and autophagy may be pivotal mechanisms that underlie NIHL.

Investigational Medicinal Products for the Inner Ear: Review of Clinical Trial Characteristics in ClinicalTrials.gov

BACKGROUND

The previous 30 years have provided information on the mechanisms of cell death in the inner ear after noise exposure, ototoxic drug injury, and during aging, and clinical trials have emerged for all of these acquired forms of hearing loss. Sudden hearing loss is less well understood, but restoration of hearing after sudden hearing loss is also a long-standing drug target, typically using steroids as an intervention but with other agents of interest as well.

PURPOSE

The purpose of this review was to describe the state of the science regarding clinical testing of investigational medicinal products for the inner ear with respect to treatment or prevention of acquired hearing loss.

DATA COLLECTION AND ANALYSIS

Comprehensive search and summary of clinical trials listed in the National Library of Medicine (www.

CLINICALTRIALS

gov) database identified 61 clinical trials.

RESULTS

Study phase, status, intervention, and primary, secondary, and other outcomes are summarized for studies assessing prevention of noise-induced hearing loss, prevention of drug-induced hearing loss, treatment of stable sensorineural hearing loss, and treatment of sudden sensorineural hearing loss.

CONCLUSION

This review provides a comprehensive summary of the state of the science with respect to investigational medicinal products for the inner ear evaluated in human clinical trials, and the current challenges for the field.

Hearing loss in Africa: current genetic profile

Hearing impairment (HI) is highly heterogeneous with over 123 associated genes reported to date, mostly from studies among Europeans and Asians. Here, we performed a systematic review of literature on the genetic profile of HI in Africa. The study protocol was registered on PROSPERO, International Prospective Register of Systematic Reviews with the registration number “CRD42021240852”. Literature search was conducted on PubMed, Scopus, Africa-Wide Information, and Web of Science databases. A total of 89 full-text records was selected and retrieved for data extraction and analyses. We found reports from only 17/54 (31.5%) African countries. The majority (61/89; 68.5%) of articles were from North Africa, with few reports found from sub-Saharan Africa. The most common method used in these publications was targeted gene sequencing (n = 66/111; 59.5%), and only 13.5% (n = 15/111) used whole-exome sequencing. More than half of the studies were performed in families segregating HI (n = 51/89). GJB2 was the most investigated gene, with GJB2: p.(R143W) founder variant only reported in Ghana, while GJB2: c.35delG was common in North African countries. Variants in MYO15A were the second frequently reported in both North and Central Africa, followed by ATP6V1B1 only reported from North Africa. Usher syndrome was the main syndromic HI molecularly investigated, with variants in five genes reported: USH2A, USH1G, USH1C, MYO7A, and PCDH15. MYO7A: p.(P1780S) founder variant was reported as the common Usher syndrome variant among Black South Africans. This review provides the most comprehensive data on HI gene variants in the largely under-investigated African populations. Future exomes studies particularly in multiplex families will likely provide opportunities for the discovery of the next sets of novel HI genes, and well as unreported variants in known genes to further our understanding of HI pathobiology, globally.

Noise induced epigenetic effects: A systematic review

Background:

Noise-induced hearing loss (NIHL) is one of the leading causes of acquired sensorineural hearing loss. However, molecular mechanisms responsible for its pathogenesis remain to be elucidated. Epigenetic changes, i.e. DNA methylation, histone and microRNA expression modifications may function as a link between noise exposure and hearing loss. Therefore, the aim of the present review was to assess whether epigenetic alterations may serve as biomarkers of noise exposure or early effect.

Materials and Methods:

A systematic review of studies available in Pubmed, Scopus, and ISI Web of Science databases was performed.

Results:

Noise exposure was able to induce alterations in DNA methylation levels in workers and animal models, resulting in expression changes of genes related to hearing loss and also to extra-auditory effects. Differently expressed microRNAs were determined in NIHL workers compared to noise-exposed subjects with normal hearing, supporting their possible role as biomarkers of effect. Acoustic trauma affected histon acethylation and methylation levels in animals, suggesting their influence in the pathogenesis of acute noise-induced damage and their role as targets for potential therapeutic treatments.

Conclusions:

Although preliminary data suggest a relationship between noise and epigenetic effects, the limited number of studies, their different methodologies and the lack of adequate characterization of acoustic insults prevent definite conclusions. In this context, further research aimed to define the epigenetic impact of workplace noise exposure and the role of such alterations in predicting hearing loss may be important for the adoption of correct risk assessment and management strategies in occupational settings.

Multifunctional Redox Modulators Protect Auditory, Visual, and Cognitive Function

Significance: Oxidative stress contributes to vision, hearing and neurodegenerative disorders. Currently, no treatments prevent these disorders; therefore, there is an urgent need for redox modulators that can prevent these disorders. Recent Advances: Oxidative stress is associated with the generation of reactive oxygen species (ROS) and reactive nitrogen species, metal dyshomeostasis, and mitochondrial dysfunction. Here, we discuss the role that oxidative stress and metal dyshomeostasis play in hearing loss, visual impairments, and neurodegeneration and discuss the benefits of a new class of multifunctional redox modulators (MFRMs) that suppress sensory and neural degeneration. MFRMs not only reduce free radicals but also independently bind transition metals associated with the generation of hydroxyl radicals. The MFRMs redistribute zinc from neurotoxic amyloid beta zinc (Aβ:Zn) complexes to the cytoplasm, facilitating the degradation of Aβ plaques by matrix metalloprotease-2 (MMP-2). Although MFRMs bind copper (Cu1+, Cu2+), iron (Fe2+, Fe3+), zinc (Zn2+), and manganese (Mn2+), they do not deplete free cytoplasmic Zn+2 and they protect mitochondria from Mn+2-induced dysfunction. Oral administration of MFRMs reduce ROS-induced cataracts, protect the retina from light-induced degeneration, reduce neurotoxic Aβ:Zn plaque formation, and protect auditory hair cells from noise-induced hearing loss. Critical Issues: Regulation of redox balance is essential for clinical efficacy in maintaining sensory functions. Future Directions: Future use of these MFRMs requires additional pharmacokinetic, pharmacodynamics, and toxicological data to bring them into widespread clinical use. Additional animal studies are also needed to determine whether MFRMs can prevent neurodegeneration, dementia, and other forms of vision and hearing loss.

Effect of Korean Red Ginseng on Noise-Induced Hearing Loss

Objective:

Noise-induced hearing loss (NIHL) is one of the most important problems affecting both social and professional life of patients. There is no treatment method considered to be successful on the hearing loss that has become a permanent nature. Aim of this study is to evaluate protective effect of Korean Red Ginseng (KRG) against NIHL in an animal model.

Methods:

Twenty-eight rats were separated into four groups [control saline (group I), control KRG (group II), saline + noise (group III), KRG + noise (group IV)]. Rats in the saline and KRG groups were fed via oral gavage with a dose of 200 mg/kg/day throughout for 10 days. Fourteen rats (group III and IV) were exposed to 4 kHz octave band noise at 120 dB SPL for 5 hours. Hearing levels of rats were evaluated by distortion product otoacoustic emissions (DPOAE) and auditory brainstem responses (ABR) at 4, 8, 12, 16 and 32 kHz frequencies prior to and on days 1, 7 and 10 after the noise exposure. Rats were sacrificed on 10th day, after the last audiological test. Cochlea and spiral ganglion tissues were evaluated by light microscopy.

Results:

Audiological and histological results demonstrated that after noise the group IV showed better results than group III. In the noise exposed groups, the most prominent damage was seen at the 8 kHz frequency region than other regions. After the noise exposure, DPOAE responses were lost in 1st, 7th and 10th measurements in both group III and IV. Thus, we were not able to perform any statistical analyses for DPOAE results.

Conclusion:

Our findings suggest that KRG seems to be an efficient agent against NIHL. There is need for additional research to find out about the mechanisms of KRG’s protective effect.

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.

Oridonin ameliorates noise-induced hearing loss by blocking NLRP3 - NEK7 mediated inflammasome activation

Inflammation is involved in noise-induced hearing loss (NIHL), but the mechanism is still unknown. The NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, which triggers the inflammatory cascade, has been implicated in several inflammatory diseases in response to oxidative stress. However, whether the NLRP3 inflammasome is a key factor for permanent NIHL is still unknown. In this study, quantitative real-time polymerase chain reaction (qPCR), western blot, and enzyme-linked immunosorbent assays (ELISAs) demonstrated that the expression levels of activated caspase-1, interleukin (IL)-1β, IL-18, and NLRP3 were significantly increased in the cochleae of mice exposed to broadband noise (120 dB) for 4 h, compared with the control group. These results indicate that the activation of inflammasomes in the cochleae of mice during the pathological process of NIHL as well as NLRP3, a sensor protein of reactive oxygen species (ROS), may be key factors for inflammasome assembly and subsequent inflammation in cochleae. Moreover, many recent studies have revealed that NEK7 is an important component and regulator of NLRP3 inflammasomes by interacting with NLRP3 directly and that these interactions can be interrupted by oridonin. Here, we further determined that treatment with oridonin could indeed interrupt the interaction between NLRP3 and NEK7 as well as inhibit the downstream inflammasome activation in mouse cochleae after noise exposure. Furthermore, we tested anakinra, another inflammatory inhibitor, and it was shown to partially alleviate the degree of hearing impairment in some frequencies in an NIHL mouse model. These discoveries suggest that inhibiting NLRP3 inflammasomes and the downstream signaling pathway may provide a new strategy for the clinical treatment of NIHL.

Epac1 Signaling Pathway Mediates the Damage and Apoptosis of Inner Ear Hair Cells after Noise Exposure in a Rat Model

To investigate the role of the exchange protein directly activated by cAMP (Epac) signaling pathway in inner ear hair cell damage and apoptosis after noise exposure, we analyzed the expression level of Epac1 in a rat model of noise-induced hearing loss (NIHL), based on rat exposure to a 4-kHz and 106-dB sound pressure level (SPL) for 8 h. Loss of outer hair cells (OHCs), mitochondrial lesions, and hearing loss were examined after treatment with the Epac agonist, 8-CPT, or the Epac inhibitor, ESI-09. The effects of 8-CPT and ESI-09 on cell proliferation and apoptosis were examined by CCK-8 assays, holographic microscopy imaging, and Annexin-V FITC/PI staining in HEI-OC1 cells. The effects of 8-CPT and ESI-09 on Ca²⁺ entry were evaluated by confocal Ca²⁺ fluorescence measurement. We found that the expression level of Epac1 was significantly increased in the cochlear tissue after noise exposure. In NIHL rats, 8-CPT increased the loss of OHCs, mitochondrial lesions, and hearing loss compared to control rats, while ESI-09 produced the opposite effects. Oligomycin was used to induce HEI-OC1 cell damage in vitro. In HEI-OC1 cells treated with oligomycin, 8-CPT and ESI-09 increased and reduced cell apoptosis, respectively. Moreover, 8-CPT promoted Ca²⁺ uptake in HEI-OC1 cells, while ESI-09 inhibited this process. In conclusion, our data provide strong evidence that the Epac1 signaling pathway mediates early pathological damage in NIHL, and that Epac1 inhibition protects from NIHL, identifying Epac1 as a new potential therapeutic target for NIHL.

The DNA methylation inhibitor RG108 protects against noise-induced hearing loss

Background

Noise-induced hearing loss represents a commonly diagnosed type of hearing disability, severely impacting the quality of life of individuals. The current work is aimed at assessing the effects of DNA methylation on noise-induced hearing loss.

Methods

Blocking DNA methyltransferase 1 (DNMT1) activity with a selective inhibitor RG108 or silencing DNMT1 with siRNA was used in this study. Auditory brainstem responses were measured at baseline and 2 days after trauma in mice to assess auditory functions. Whole-mount immunofluorescent staining and confocal microcopy of mouse inner ear specimens were performed to analyze noise-induced damage in cochleae and the auditory nerve at 2 days after noise exposure.

Results

The results showed that noise exposure caused threshold elevation of auditory brainstem responses and cochlear hair cell loss. Whole-mount cochlea staining revealed a reduction in the density of auditory ribbon synapses between inner hair cells and spiral ganglion neurons. Inhibition of DNA methyltransferase activity via a non-nucleoside specific pharmacological inhibitor, RG108, or silencing of DNA methyltransferase-1 with siRNA significantly attenuated ABR threshold elevation, hair cell damage, and the loss of auditory synapses.

Conclusions

This study suggests that inhibition of DNMT1 ameliorates noise-induced hearing loss and indicates that DNMT1 may be a promising therapeutic target.

Graphical abstract

Treatment With Calcineurin Inhibitor FK506 Attenuates Noise-Induced Hearing Loss

Attenuation of noise-induced hair cell loss and noise-induced hearing loss (NIHL) by treatment with FK506 (tacrolimus), a calcineurin (CaN/PP2B) inhibitor used clinically as an immunosuppressant, has been previously reported, but the downstream mechanisms of FK506-attenuated NIHL remain unknown. Here we showed that CaN immunolabeling in outer hair cells (OHCs) and nuclear factor of activated T-cells isoform c4 (NFATc4/NFAT3) in OHC nuclei are significantly increased after moderate noise exposure in adult CBA/J mice. Consequently, treatment with FK506 significantly reduces moderate-noise-induced loss of OHCs and NIHL. Furthermore, induction of reactive oxygen species (ROS) by moderate noise was significantly diminished by treatment with FK506. In agreement with our previous finding that autophagy marker microtubule-associated protein light chain 3B (LC3B) does not change in OHCs under conditions of moderate-noise-induced permanent threshold shifts, treatment with FK506 increases LC3B immunolabeling in OHCs after exposure to moderate noise. Additionally, prevention of NIHL by treatment with FK506 was partially abolished by pretreatment with LC3B small interfering RNA. Taken together, these results indicate that attenuation of moderate-noise-induced OHC loss and hearing loss by FK506 treatment occurs not only via inhibition of CaN activity but also through inhibition of ROS and activation of autophagy.

KATP and TRPM2-like channels couple metabolic status to resting membrane potential of octopus neurons in the mouse ventral cochlear nucleus

ATP-sensitive potassium (K_ATP) channels and transient receptor potential melastatin 2 (TRPM2) channels are commonly expressed both pre- and postsynaptically in the central nervous system (CNS). We hypothesized that K_ATP and TRPM2 may couple metabolic status to the resting membrane potential of octopus neurons of the mouse ventral cochlear nucleus (VCN). Therefore, we studied the expression of K_ATP channels and TRPM2 channels in octopus cells by immunohistochemical techniques and their contribution to neuronal electrical properties by the electrophysiological patch clamp technique. In immunohistochemical staining of octopus cells, labelling with Kir6.2 and SUR1 antibodies was strong, and labelling with the SUR2 antibody was moderate, but labelling with Kir6.1 was very weak. Octopus cells had intense staining with TRPM2 antibodies. In patch clamp recordings, bath application of K_ATP channel agonists H₂O₂ (880 μM), ATZ (1 mM), cromakalim (50 μM), diazoxide (200 μM), NNC 55-0118 and NN 414 separately resulted in hyperpolarizations of resting potential to different extents. Application of 8-Bro-cADPR (50 μM), a specific antagonist of TRPM2 channels, in the presence of H₂O₂ (880 μM) resulted in further hyperpolarization by approximately 1 mV. The amplitudes of H₂O₂-induced outward K_ATP currents and ADPR-induced inward currents were 206.1 ± 31.5 pA (n = 4) and 136.8 ± 22.4 pA, respectively, at rest. Their respective reversal potentials were -77 ± 2.6 mV (n = 3) and -6.3 ± 2.9 (n = 3) and -6.3 ± 2.9 (n = 3). In conclusion, octopus cells appear to possess both K_ATP channels and TRPM2-like channels. K_ATP might largely be constituted by SUR1-Kir6.2 subunits and SUR2-Kir6.2 subunits. Both K_ATP and TRPM2-like channels might have a modulatory action in setting the membrane potential.

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.

Role of cochlear synaptopathy in cytomegalovirus infected mice and in children

OBJECTIVES

Determine whether a murine model of cytomegalovirus (CMV) and CMV- infected children show evidence of synaptopathy.

STUDY DESIGN

Murine model of CMV infection and case series.

SUBJECTS AND METHODS

C57 BL/6 mice were inoculated with murine-CMV (mCMV). Auditory function was assessed using Auditory Brainstem Response (ABR) and distortion product otoacoustic emission (DPOAE) testing. Temporal bones from mCMV-infected mice were used for both ribbon synapse and hair cell quantification. Four groups of children (non-CMV normal hearing, non-CMV hearing impaired, CMV normal hearing and CMV hearing impaired) underwent ABRs between 2014 and 2018. The outcomes included raw amplitude, wave I:V amplitude ratio, absolute latency, and interpeak latency.

RESULTS

Mice at 8 weeks post mCMV infection had higher ABR and DPOAE (P < 0.05) thresholds and increased outer hair cell loss compared to uninfected mice and mCMV-infected mice at 4 and 6 weeks post infection, indicating progressive hearing loss. A reduction in the wave I amplitude and synaptic counts were noted earlier at 4 weeks in CMV-infected mice (P < 0.05). The human data indicated that the wave I:V amplitude ratio was lower on average in CMV-infected groups when compared to the uninfected cohorts. The wave I:V amplitude ratio for the click and 4k stimuli were not significantly different between the congenital CMV-infected and uninfected children with normal or with hearing loss.

CONCLUSION

This study suggests mCMV infection results in a synaptopathy before hair cell damage. Additional studies need to be performed to determine whether this effect is also observed in CMV-infected children.

LEVEL OF EVIDENCE

Animal studies and basic science- NA; human studies: level 4.

Constant Light Dysregulates Cochlear Circadian Clock and Exacerbates Noise-Induced Hearing Loss

Noise-induced hearing loss is one of the major causes of acquired sensorineural hearing loss in modern society. While people with excessive exposure to noise are frequently the population with a lifestyle of irregular circadian rhythms, the effects of circadian dysregulation on the auditory system are still little known. Here, we disturbed the circadian clock in the cochlea of male CBA/CaJ mice by constant light (LL) or constant dark. LL significantly repressed circadian rhythmicity of circadian clock genes Per1, Per2, Rev-erbα, Bmal1, and Clock in the cochlea, whereas the auditory brainstem response thresholds were unaffected. After exposure to low-intensity (92 dB) noise, mice under LL condition initially showed similar temporary threshold shifts to mice under normal light-dark cycle, and mice under both conditions returned to normal thresholds after 3 weeks. However, LL augmented high-intensity (106 dB) noise-induced permanent threshold shifts, particularly at 32 kHz. The loss of outer hair cells (OHCs) and the reduction of synaptic ribbons were also higher in mice under LL after noise exposure. Additionally, LL enhanced high-intensity noise-induced 4-hydroxynonenal in the OHCs. Our findings convey new insight into the deleterious effect of an irregular biological clock on the auditory system.

The effect of noise and dust exposure on oxidative stress among livestock and poultry feed industry workers

INTRODUCTION

Simultaneous exposure to noise and dust may have detrimental health effects. This study was conducted to determine the effect of exposure to noise and dust on oxidative stress.

METHODS

In this cross-sectional study, 82 employees of two livestock and poultry feed factories in Golestan Province, Iran, were selected as the exposed group and 82 office workers were selected as the control group. Occupational noise and dust exposure were measured using a dosimeter, sampling pump, and vinyl chloride filter. Oxidative stress was determined by measuring the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) in blood samples. T-tests, one-way analysis of variance, and multivariate linear regression were used to analyze the data.

RESULTS

The levels of MDA and SOD in the exposed group were significantly higher and lower than the control group (p < 0.001), respectively. The results showed the subgroup with both over the threshold dust and noise exposure had the highest MDA levels. The SOD level among those exposed to noise more than the recommended level, in the subgroup with more dust exposure, was significantly less than the subgroup with low noise exposure (p = 0.017).

CONCLUSION

Noise and dust exposure probably increase the level of oxidative stress by increasing the level of lipid peroxidation (MDA) and reducing the level of antioxidant enzymes (SOD).

The impact of carbon monoxide inhalation on developing noise-induced hearing loss in guinea pigs

Carbon monoxide (CO) poisoning is one of the most common types of fatal poisonings worldwide. Acute exposure to high levels of CO as well as chronic exposure to low levels of CO and excessive noise can lead to high frequency hearing loss. In this study, twelve guinea pigs were randomly divided into two groups: (1) exposed to noise and (2) exposed to noise plus CO. Auditory brainstem responses (ABRs) were measured prior to the experiment and immediately, 5, 10 and 15 days post exposures. There was a significant difference between the ABR thresholds before and immediately after exposure to noise at frequencies of 4, 8, and 16 kHz and the most threshold shift was observed at 8 kHz. There was also a significant difference between the ABR thresholds before and immediately after exposure to noise and CO at frequencies of 2, 4, 8, and 16 kHz which demonstrated a temporary hearing loss after exposure to noise and CO and the major impact of CO on developing noise induced hearing loss occurred at 8 kHz. No significant difference was observed between the ABR thresholds recorded before conducting the experiments and the ones obtained 5, 10 and 15 days after simultaneous exposure to noise and CO at none of frequencies. Simultaneous exposure to noise and CO contributes to transient hearing loss in guinea pigs with the most evident temporary shift at 8 kHz. The methods were accepted in the Ethics Committee of Iran University of Medical Science (registration No. CTRI/2016/01/017170) on January 18, 2016.