Age-related hearing loss in C57BL/6J mice is mediated by Bak-dependent mitochondrial apoptosis

The Role and Research Progress of Mitochondria in Sensorineural Hearing Loss

Hearing loss is one of the most common human diseases, seriously affecting everyday lives. Mitochondria, as the energy metabolism center in cells, are also involved in regulating active oxygen metabolism and mediating the occurrence of inflammation and apoptosis. Mitochondrial defects are closely related to hearing diseases. Studies have shown that mitochondrial DNA mutations are one of the causes of hereditary hearing loss. In addition, changes in mitochondrial homeostasis are directly related to noise-induced hearing loss and presbycusis. This review mainly summarizes and discusses the effects of mitochondrial dysfunction and mitophagy on hearing loss. Subsequently, we introduce the recent research progress of targeted mitochondria therapy in the hearing system.

The Role of Molecular and Cellular Aging Pathways on Age-Related Hearing Loss

Aging, a complex process marked by molecular and cellular changes, inevitably influences tissue and organ homeostasis and leads to an increased onset or progression of many chronic diseases and conditions, one of which is age-related hearing loss (ARHL). ARHL, known as presbycusis, is characterized by the gradual and irreversible decline in auditory sensitivity, accompanied by the loss of auditory sensory cells and neurons, and the decline in auditory processing abilities associated with aging. The extended human lifespan achieved by modern medicine simultaneously exposes a rising prevalence of age-related conditions, with ARHL being one of the most significant. While our understanding of the molecular basis for aging has increased over the past three decades, a further understanding of the interrelationship between the key pathways controlling the aging process and the development of ARHL is needed to identify novel targets for the treatment of AHRL. The dysregulation of molecular pathways (AMPK, mTOR, insulin/IGF-1, and sirtuins) and cellular pathways (senescence, autophagy, and oxidative stress) have been shown to contribute to ARHL. However, the mechanistic basis for these pathways in the initiation and progression of ARHL needs to be clarified. Therefore, understanding how longevity pathways are associated with ARHL will directly influence the development of therapeutic strategies to treat or prevent ARHL. This review explores our current understanding of the molecular and cellular mechanisms of aging and hearing loss and their potential to provide new approaches for early diagnosis, prevention, and treatment of ARHL.

Hearing Loss and Oxidative Stress: A Comprehensive Review

Hearing loss is a prevalent condition affecting millions of people worldwide. Hearing loss has been linked to oxidative stress as a major factor in its onset and progression. The goal of this thorough analysis is to investigate the connection between oxidative stress and hearing loss, with an emphasis on the underlying mechanisms and possible treatments. The review addressed the many forms of hearing loss, the role of reactive oxygen species (ROS) in causing damage to the cochlea, and the auditory system's antioxidant defensive mechanisms. The review also goes over the available data that support the use of antioxidants and other methods to lessen hearing loss brought on by oxidative stress. We found that oxidative stress is implicated in multiple types of hearing loss, including age-related, noise-induced, and ototoxic hearing impairment. The cochlea's unique anatomical and physiological characteristics, such as high metabolic activity and limited blood supply, make it particularly susceptible to oxidative damage. Antioxidant therapies have shown promising results in both animal models and clinical studies for preventing and mitigating hearing loss. Emerging therapeutic approaches, including targeted drug delivery systems and gene therapy, offer new possibilities for addressing oxidative stress in the auditory system. The significance of this review lies in its comprehensive analysis of the intricate relationship between oxidative stress and hearing loss. By synthesizing current knowledge and identifying gaps in understanding, this review provides valuable insights for both researchers and clinicians. It highlights the potential of antioxidant-based interventions and emphasizes the need for further research into personalized treatment strategies. Our findings on oxidative stress mechanisms may also affect clinical practice and future research directions. This review serves as a foundation for developing novel therapeutic approaches and may inform evidence-based strategies for the prevention and treatment of hearing loss, ultimately contributing to improved quality of life for millions affected by this condition worldwide.

Serum Prealbumin as a Potential Predictive Factor for Age-Related Hearing Loss: A Retrospective Study

Objectives: Age-related hearing loss (ARHL) is a complex disease associated with the interaction of multiple factors. Furthermore, indicators of liver function represent the body's metabolic, immune, and repair abilities. This study investigated correlations between liver function and ARHL. Methods: A total of 107 patients with ARHL and 107 age- and sex-matched healthy volunteers were included. Linear correlations, logistic regression, and receiving operator characteristic curves were used to assess the associations between liver function and ARHL. Results: Serum prealbumin (PAB) levels were significantly lower in the ARHL group compared to the control group. Logistic regression analysis indicated that low PAB levels may be an independent risk factor for ARHL. The ARHL was divided into 2 groups according to the degree of hearing loss (moderately severe-to-profound and mild-to-moderate); the median ages in the 2 groups were 70.48 and 66.85 years, respectively, with the difference being significant. Age was an independent risk factor for moderately severe-to-profound ARHL, as shown by the logistic regression analysis. Conclusions: Lower PAB levels in patients with ARHL suggested that PAB may be a risk factor for ARHL. Furthermore, higher age in patients with ARHL was associated with a greater degree of hearing loss.

L-Ergothioneine slows the progression of age-related hearing loss in CBA/CaJ mice

The naturally occurring amino acid, l-ergothioneine (EGT), has immense potential as a therapeutic, having shown promise in the treatment of other disease models, including neurological disorders. EGT is naturally uptaken into cells via its specific receptor, OCTN1, to be utilized by cells as an antioxidant and anti-inflammatory. In our current study, EGT was administered over a period of 6 months to 25-26-month-old CBA/CaJ mice as a possible treatment for age-related hearing loss (ARHL), since presbycusis has been linked to higher levels of cochlear oxidative stress, apoptosis, and chronic inflammation. Results from the current study indicate that EGT can prevent aging declines of some key features of ARHL. However, we found a distinct sex difference for the response to the treatments, for hearing - Auditory Brainstem Responses (ABRs) and Distortion Product Otoacoustic Emissions (DPOAEs). Males exhibited lower threshold declines in both low dose (LD) and high dose (HD) test groups throughout the testing period and did not display some of the characteristic aging declines in hearing seen in Control animals. In contrast, female mice did not show any therapeutic effects with either treatment dose. Further confirming this sex difference, EGT levels in whole blood sampling throughout the testing period showed greater uptake of EGT in males compared to females. Additionally, RT-PCR results from three tissue types of the inner ear confirmed EGT activity in the cochlea in both males and females. Males and females exhibited significant differences in biomarkers related to apoptosis (Cas-3), inflammation (TNF-a), oxidative stress (SOD2), and mitochondrial health (PGC1a).These changes were more prominent in males as compared to females, especially in stria vascularis tissue. Taken together, these findings suggest that EGT has the potential to be a naturally derived therapeutic for slowing down the progression of ARHL, and possibly other neurodegenerative diseases. EGT, while effective in the treatment of some features of presbycusis in aging males, could also be modified into a general prophylaxis for other age-related disorders where treatment protocols would include eating a larger proportion of EGT-rich foods or supplements. Lastly, the sex difference discovered here, needs further investigation to see if therapeutic conditions can be developed where aging females show better responsiveness to EGT.

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.

Use of the traditional Chinese medicine "compound healthy ear agent" to protect against age-related hearing loss in mice: A proteomics study

Background

Previous studies have shown that the traditional Chinese medicine (TCM) called "compound healthy ear agent" (CHEA) had anti-apoptosis effects in cochlear hair cells and spiral ganglion neurons, and could protect mice hearing against presbycusis or age-related hearing loss (AHL), as well as aminoglycoside antibiotic-induced ototoxicity. Because its mechanisms of action are still unclear, we investigated the mechanism of action of CHEA against AHL in mice using proteomics techniques.

Methods

Eighteen C57BL/6J mice at 1 month of age were randomly divided into three groups: (A) drinking water until 2 months of age, K2M); (B) drinking water until 7 months of age to induce AHL, K7M; (C) drinking water containing CHEA daily until 7 months of age as treatment group, Z7M. At 2 or 7 months mice were sacrificed and their cochleae were removed for proteomics analysis.

Results

The numbers of proteins with a false discovery rate (FDR) < 1% were respectively 5873 for qualitative and 5492 for quantitative statistics. The numbers of proteins with differential enrichment at least 1.5-fold (p < 0.05) were respectively 351 for K7M vs K2M groups, 52 for Z7M vs K7M groups, 264 for Z7M vs K2M groups. The differentially expressed proteins in the Z7M group were involved in synaptic molecular transmission, energy metabolism, immune response, antioxidant defenses, and anti-apoptosis.

Conclusion

The TCM CHEA played a protective role against AHL in mice by regulating the expression of specific proteins and genes in cochlear hair cells and spiral ganglion neurons. Besides the pathways expected to be involved (antioxidant and anti-apoptosis), proteins related to immune response is a new finding of the present study.

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.

Prosaposin is a novel coenzyme Q10-binding protein

Coenzyme Q10 (CoQ10) is essential for mitochondrial ATP production and functions as an important antioxidant in every biomembrane and lipoprotein. Due to its hydrophobicity, a binding and transfer protein for CoQ10 is plausible, and we previously described saposin B as a CoQ10-binding and transfer protein. Here, we report that prosaposin, the precursor of saposin B, also binds CoQ10. As prosaposin is both a secretory protein and integral membrane protein, it is ubiquitous in the body. Prosaposin was isolated from human seminal plasma, and CoQ10 was extracted from hexane solution into the water phase. It was additionally found that immunoprecipitates of mouse brain cytosol generated using two different anti-prosaposin antibodies contained coenzyme Q9. Furthermore, mouse liver cytosol and mouse kidney cytosol also contained prosaposin-coenzyme Q9 complex. These results suggest that prosaposin binds CoQ10 in human cells and body fluids. The significance and role of the Psap-CoQ10 complex in vivo is also discussed.

Age-related hearing loss: An updated and comprehensive review of the interventions

Aging causes progressive degenerative changes in many organs, particularly the auditory system. Several attempts have been conducted to investigate preventive and therapeutic strategy/strategies for age-related auditory dysfunction, such as maintaining a healthy lifestyle through good nutrition, lower anxiety levels, and noise exposure, different pharmacological approaches, gene and cell therapy, and other strategies. However, it is not clear which approach is the best to slow down these dysfunctions because several different underlying mechanistic pathways are associated with presbycusis which eventually leads to different types of this disease. A combination of several methods is probably required, whereas the effectiveness for some people needs to be monitored. The effectiveness of treatments will not be the same for all; therefore, we may need to have a unique and personalized approach to the prevention and treatment of ARHL for each person. In addition, each method needs to specify what type of presbycusis can prevent or treat and provide complete information about the extent, duration of treatment, persistency of treatment, side effects, and whether the approach is for treatment or prevention or even both. This paper reviews the updated literature, which targets current interventions for age-related hearing loss.

Sheep as a large animal model for hearing research: comparison to common laboratory animals and humans

Sensorineural hearing loss (SNHL), caused by pathology in the cochlea, is the most common type of hearing loss in humans. It is generally irreversible with very few effective pharmacological treatments available to prevent the degenerative changes or minimise the impact. Part of this has been attributed to difficulty of translating "proof-of-concept" for novel treatments established in small animal models to human therapies. There is an increasing interest in the use of sheep as a large animal model. In this article, we review the small and large animal models used in pre-clinical hearing research such as mice, rats, chinchilla, guinea pig, rabbit, cat, monkey, dog, pig, and sheep to humans, and compare the physiology, inner ear anatomy, and some of their use as model systems for SNHL, including cochlear implantation surgeries. Sheep have similar cochlear anatomy, auditory threshold, neonatal auditory system development, adult and infant body size, and number of birth as humans. Based on these comparisons, we suggest that sheep are well-suited as a potential translational animal model that bridges the gap between rodent model research to the clinical use in humans. This is especially in areas looking at changes across the life-course or in specific areas of experimental investigation such as cochlear implantation and other surgical procedures, biomedical device development and age-related sensorineural hearing loss research. Combined use of small animals for research that require higher throughput and genetic modification and large animals for medical translation could greatly accelerate the overall translation of basic research in the field of auditory neuroscience from bench to clinic.

Differential outcomes of high-fat diet on age-related rescaling of cochlear frequency place coding

Auditory frequency coding is place-specific, which depends on the mechanical coupling of the basilar membrane-outer hair cell (OHC)-tectorial membrane network. Prestin-based OHC electromotility improves cochlear frequency selectivity and sensitivity. Cochlear amplification determines the frequency coding wherein discrete sound frequencies find a 'best' place along the cochlear length. Loss of OHC is the leading cause of age-related hearing loss (ARHL) and is the most common cause of sensorineural hearing loss and compromised speech perception. Lipid interaction with Prestin impacts OHC function. It has been established that high-fat diet (HFD) is associated with ARHL. To determine whether genetic background and metabolism preserve cochlear frequency place coding, we examined the effect of HFD in C57BL/6J (B6) and CBA/CaJ (CBA) on ARHL.We found a significant rescuing effect on ARHL in aged B6 HFD cohort. Prestin levels and cell sizes were better maintained in the experimental B6-HFD group. We also found that distortion product otoacoustic emission (DPOAE) group delay measurement was preserved, which suggested stable frequency place coding. In contrast, the response to HFD in the CBA cohort was modest with no appreciable benefit to hearing threshold. Notably, group delay was shortened with age along with the control. In addition, the frequency dependent OHC nonlinear capacitance gradient was most pronounced at young age but decreased with age. Cochlear RNA-seq analysis revealed differential TRPV1 expression and lipid homeostasis. Activation of TRPV1 and downregulation of arachidonic acid led to downregulation of inflammatory response in B6 HFD, which protects the cochlea from ARHL. The genetic background and metabolic state-derived changes in OHC morphology and function collectively contribute to a redefined cochlear frequency place coding and improved age-related pitch perception.

Potential roles for lncRNA Mirg/Foxp1 in an ARHL model created using C57BL/6J mice

Age-related hearing loss (ARHL) is associated with hair cell apoptosis, but the underlying mechanism of hair cell apoptosis remains unclear. Here, we investigated the expression profiles of long noncoding RNAs (lncRNAs) and mRNAs in an ARHL model created with C57BL/6 J mice using RNA sequencing and found that the expression of several lncRNAs was significantly correlated with apoptosis-associated mRNAs in the cochlear tissues of old mice compared to young mice. We found that lncRNA Mirg was upregulated in the cochlear tissues of old mice compared to young mice and its overexpression promoted apoptosis in House Ear Institute-Organ of Corti 1 (HEI-OC1). H2O2-induced oxidative stress increased HEI-OC1 cell apoptosis by upregulating lncRNA Mirg. Furthermore, the expression of lncRNA Mirg and Foxp1 showed the highest correlation coefficient in the cochlear tissues of old mice, and lncRNA Mirg promoted HEI-OC1 cell apoptosis by increasing Foxp1 expression. In conclusion, our findings suggest that lncRNA Mirg expression correlates with cell apoptosis-associated mRNAs in the ARHL model created using C57BL/6 J mice and that oxidative stress-induced lncRNA Mirg promotes HEI-OC1 cell apoptosis by increasing Foxp1 expression. These data suggest the potential therapeutic significance of targeting lncRNA Mirg/Foxp1 signaling in ARHL.

Coenzyme Q10 exhibits anti-inflammatory and immune-modulatory thereby decelerating the occurrence of experimental cerebral malaria

Cerebral Malaria (CM) is associated with the complex neurological syndrome, whose pathology is mediated by severe inflammatory processes following infection with Plasmodium falciparum. Coenzyme-Q10 (Co-Q10) is a potent anti-inflammatory, anti-oxidant, and anti-apoptotic agent with numerous clinical applications. The aim of this study was to elucidate the role of oral administration of Co-Q10 on the initiation or regulation of inflammatory immune response during experimental cerebral malaria (ECM). For this purpose, the pre-clinical effect of Co-Q10 was evaluated in C57BL/6 J mice infected with Plasmodium berghei ANKA (PbA). Treatment with Co-Q10 resulted in the reduction of infiltrating parasite load, greatly improved the survival rate of PbA-infected mice that occurred independent of parasitaemia and prevented PbA-induced disruption of the blood-brain barrier (BBB) integrity. Exposure to Co-Q10 resulted in the reduction of infiltration of effector CD8 + T cells in the brain and secretion of cytolytic Granzyme B molecules. Notably, Co-Q10-treated mice had reduced levels of CD8 +T cell chemokines CXCR3, CCR2, and CCR5 in the brain following PbA-infection. Brain tissue analysis showed a reduction in the levels of inflammatory mediators TNF- α, CCL3, and RANTES in Co-Q10 administered mice. In addition, Co-Q10 modulated the differentiation and maturation of both splenic and brain dendritic cells and cross-presentation (CD8α+DCs) during ECM. Remarkably, Co-Q10 was very effective in decreasing levels of CD86, MHC-II, and CD40 in macrophages associated with ECM pathology. Exposure to Co-Q10 resulted in increased expression levels of Arginase-1 and Ym1/chitinase 3-like 3, which is linked to ECM protection. Furthermore, Co-Q10 supplementation prevented PbA-induced depletion of Arginase and CD206 mannose receptor levels. Co-Q10 abrogated PbA-driven elevation in pro-inflammatory cytokines IL-1β, IL-18, and IL-6 levels. In conclusion, the oral supplementation with Co-Q10 decelerates the occurrence of ECM by preventing lethal inflammatory immune responses and dampening genes associated with inflammation and immune-pathology during ECM, and offers an inimitable opening for developing an anti-inflammatory agent against cerebral malaria.

Ageing-associated phenotypes in mice

Ageing is a continuous process in life featuring progressive damage accumulation that leads to physiological decline, functional deterioration and ultimately death of an organism. Based on the relatively close anatomical and physiological similarity to humans, the mouse has been proven as a valuable model organism in ageing research over the last decades. In this review, we survey methods and tools currently in use to assess ageing phenotypes in mice. We summarize a range of ageing-associated alterations detectable at two major levels of analysis: (1) physiology and pathophysiology and (2) molecular biomarkers. Age-sensitive phenotypes provided in this article may serve to inform future studies targeting various aspects of organismal ageing in mice. In addition, we discuss conceptual and technical challenges faced by previous ageing studies in mice and, where possible, provide recommendations on how to resolve some of these issues.

Phytosterols reverse antiretroviral-induced hearing loss, with potential implications for cochlear aging

Cholesterol contributes to neuronal membrane integrity, supports membrane protein clustering and function, and facilitates proper signal transduction. Extensive evidence has shown that cholesterol imbalances in the central nervous system occur in aging and in the development of neurodegenerative diseases. In this work, we characterize cholesterol homeostasis in the inner ear of young and aged mice as a new unexplored possibility for the prevention and treatment of hearing loss. Our results show that cholesterol levels in the inner ear are reduced during aging, an effect that is associated with an increased expression of the cholesterol 24-hydroxylase (CYP46A1), the main enzyme responsible for cholesterol turnover in the brain. In addition, we show that pharmacological activation of CYP46A1 with the antiretroviral drug efavirenz reduces the cholesterol content in outer hair cells (OHCs), leading to a decrease in prestin immunolabeling and resulting in an increase in the distortion product otoacoustic emissions (DPOAEs) thresholds. Moreover, dietary supplementation with phytosterols, plant sterols with structure and function similar to cholesterol, was able to rescue the effect of efavirenz administration on the auditory function. Altogether, our findings point towards the importance of cholesterol homeostasis in the inner ear as an innovative therapeutic strategy in preventing and/or delaying hearing loss.

Curcumin protects against the age-related hearing loss by attenuating apoptosis and senescence via activating Nrf2 signaling in cochlear hair cells

Age-related hearing loss (ARHL) is a most widespread neurodegenerative disease affecting the elderly population, but effective pharmacological treatments remain limited. Curcumin is a bioactive compound of Curcuma longa with antioxidant properties. Herein, we looked into the effects of curcumin on the H₂O₂-induced oxidative stress in cochlear hair cells and hearing function in an ARHL animal model (C57BL/6J mice). We found that pretreatment of curcumin could attenuate H₂O₂-induced apoptosis and cell senescence in auditory hair cells and prevent mitochondrial function dysfunction. More specifically, Western blot and luciferase activity assay showed that curcumin activated the nuclear translocation of Nrf2, which in turn triggered the activation of its downstream target gene Heme Oxygenase1 (HO-1). The enhanced Nrf2 and HO-1 activity by curcumin was blocked by the AKT inhibitor LY294002, indicating the protective effect of curcumin was mainly achieved by activating Nrf2/HO-1 through the AKT pathway. Furthermore, the knockdown of Nrf2 with siRNA diminished the protective effects of Nrf2 against apoptosis and senescence, consolidating the pivotal role of Nrf2 in the protective effect of curcumin on auditory hair cells. More importantly, curcumin (10 mg/kg/d) could attenuate progressive hearing loss in C57BL/6J mice, as evident from the reduced threshold of auditory nerve brainstem response. Administration of curcumin also elevated the expression of Nrf2 and reduced the expression of cleaved-caspase-3, p21, and γ-H2AX in cochlear. This study is the first to demonstrate that curcumin can prevent oxidative stress-induced auditory hair cell degeneration through Nrf2 activation, highlighting its potential therapeutic value in preventing ARHL.

Attenuation of Age-Related Hearing Impairment in Senescence-Accelerated Mouse Prone 8 (SAMP8) Mice Treated with Fatty Acid Synthase Inhibitor CMS121

In the senescence-accelerated mouse prone 8 (SAMP8) mouse model, oxidative stress leads to premature senescence and age-related hearing impairment (ARHI). CMS121 inhibits oxytosis/ferroptosis by targeting fatty acid synthase. The aim of our study was to determine whether CMS121 is protective against ARHI in SAMP8 mice. Auditory brainstem responses (ABRs) were used to assess baseline hearing in sixteen 4-week-old female SAMP8 mice, which were divided into two cohorts. The control group was fed a vehicle diet, while the experimental group was fed a diet containing CMS121. ABRs were measured until 13 weeks of age. Cochlear immunohistochemistry was performed to analyze the number of paired ribbon-receptor synapses per inner hair cell (IHC). Descriptive statistics are provided with mean ± SEM. Two-sample t-tests were performed to compare hearing thresholds and paired synapse count across the two groups, with alpha = 0.05. Baseline hearing thresholds in the control group were statistically similar to those of the CMS121 group. At 13 weeks of age, the control group had significantly worse hearing thresholds at 12 kHz (56.5 vs. 39.8, p = 0.044) and 16 kHz (64.8 vs. 43.8, p = 0.040) compared to the CMS121 group. Immunohistochemistry showed a significantly lower synapse count per IHC in the control group (15.7) compared to the CMS121 group (18.4), p = 0.014. Our study shows a significant reduction in ABR threshold shifts and increased preservation of IHC ribbon synapses in the mid-range frequencies among mice treated with CMS121 compared to untreated mice.

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.

The association of food intake on the development of hearing impairment after middle age among Japanese community dwellers

OBJECTIVES

This study aimed to determine whether food intake modifies the risk of developing hearing impairment (HI) in Japanese adults in their 40s.

METHODS

Data for individuals who were in their 40s with no HI at baseline and had participated in the survey multiple times were extracted from the National Institute for Longevity Sciences, Longitudinal Study of Aging. A total of 1846 samples observed for up to 11.5 years in 421 participants were included in the analyses. The average 3-day food intake was calculated. HI is defined as a pure-tone average of the better ear at frequencies of 0.5, 1, 2, and 4 kHz greater than 25 dB. The risk of developing HI in the 18 food groups was calculated longitudinally using multivariable cumulative data analyses.

RESULTS

Even after adjusting basic confounding factors, food groups, and baseline hearing level, significant associations were found between beverage consumption and risk increments for HI (odds ratio [OR] = 2.374, 95% confidence interval [CI]:1.141-4.940) and also between mushroom intake and risk reduction (OR = 0.215, 95% CI:0.069-0.667). Other foods did not consistently show significant results when the combination of analysis variables were changed.

CONCLUSIONS

Although the effect of food on hearing is modest to the extent that the significance varies with the variables used in the analysis, the intake of beverages and mushrooms could potentially modify the risk of developing HI after middle age.

Presbycusis and balance disorders in the elderly. Bibliographical review of ethiopathogenic aspects, consequences on quality of life and positive effects of its treatment

At this time, we still do not have adequate knowledge and awareness of the consequences of hearing loss in the elderly on quality of life. Similarly, there is also insufficient information on the relationship of presbycusis and balance disorders with other comorbidities. Such knowledge can contribute to improve both prevention and treatment of these pathologies, to reduce their impact on other areas such as cognition or autonomy, as well as to have more accurate information on the economic impact they generate in society and in the health system. Therefore, with this review article we aim to update the information on the type of hearing loss and balance disorders in people over 55 years of age, and their associated factors; to analyze the impact on the quality of life of these people and the one which can be generated at a personal and population level (both sociological and economic) if an early intervention in these patients is pursued.

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.

Protein Susceptibility to Peroxidation by 4-Hydroxynonenal in Hereditary Hemochromatosis

Iron overload caused by hereditary hemochromatosis (HH) increases free reactive oxygen species that, in turn, induce lipid peroxidation. Its 4-hydroxynonenal (HNE) by-product is a well-established marker of lipid peroxidation since it reacts with accessible proteins with deleterious consequences. Indeed, elevated levels of HNE are often detected in a wide variety of human diseases related to oxidative stress. Here, we evaluated HNE-modified proteins in the membrane of erythrocytes from HH patients and in organs of Hfe^-/- male and female mice, a mouse model of HH. For this purpose, we used one- and two-dimensional gel electrophoresis, immunoblotting and MALDI-TOF/TOF analysis. We identified cytoskeletal membrane proteins and membrane receptors of erythrocytes bound to HNE exclusively in HH patients. Furthermore, kidney and brain of Hfe^-/- mice contained more HNE-adducted protein than healthy controls. Our results identified main HNE-modified proteins suggesting that HH favours preferred protein targets for oxidation by HNE.

Taurine, Coenzyme Q10, and Hydrogen Water Prevents Germanium Dioxide-Induced Mitochondrial Dysfunction and Associated Sensorineural Hearing Loss in mouse

Mitochondrial dysfunction has been implicated in numerous common diseases as well as aging and plays an important role in the pathogenesis of sensorineural hearing loss (SNHL). In the current study, we showed that supplementation with germanium dioxide (GeO2) in CBA/J mice resulted in SNHL due to the degeneration of the stria vascularis and spiral ganglion, which were associated with down-regulation of mitochondrial respiratory chain associated genes and up-regulation in apoptosis associated genes in the cochlea. Supplementation with taurine, coenzyme Q10, or hydrogen-rich water, attenuated the cochlear degeneration and associated SNHL induced by GeO2. These results suggest that daily supplements or consumption of antioxidants, such as taurine, coenzyme Q10, and hydrogen-rich water, may be a promising intervention to slow SNHL associated with mitochondrial dysfunction.

Redox Imbalance as a Common Pathogenic Factor Linking Hearing Loss and Cognitive Decline

Experimental and clinical data suggest a tight link between hearing and cognitive functions under both physiological and pathological conditions. Indeed, hearing perception requires high-level cognitive processes, and its alterations have been considered a risk factor for cognitive decline. Thus, identifying common pathogenic determinants of hearing loss and neurodegenerative disease is challenging. Here, we focused on redox status imbalance as a possible common pathological mechanism linking hearing and cognitive dysfunctions. Oxidative stress plays a critical role in cochlear damage occurring during aging, as well as in that induced by exogenous factors, including noise. At the same time, increased oxidative stress in medio-temporal brain regions, including the hippocampus, is a hallmark of neurodegenerative disorders like Alzheimer's disease. As such, antioxidant therapy seems to be a promising approach to prevent and/or counteract both sensory and cognitive neurodegeneration. Here, we review experimental evidence suggesting that redox imbalance is a key pathogenetic factor underlying the association between sensorineural hearing loss and neurodegenerative diseases. A greater understanding of the pathophysiological mechanisms shared by these two diseased conditions will hopefully provide relevant information to develop innovative and effective therapeutic strategies.

Association between individual, household, and area-level socioeconomic status indicators and sensorineural hearing loss in adults in southwest Iran: a population-based study

Introduction

Hearing loss is the fourth most common chronic disease, but studies on the relationship between hearing loss and socioeconomic factors are limited. We aimed to examine the association between hearing loss and socioeconomic factors among 35-70 year adults in southwest Iran.

Materials and methods

This population-based cross-sectional study was conducted in the baseline of Hoveyzeh cohort study in adults aged 35-70 in southwest Iran between 2017 and 2021. Information on socioeconomic factors, demographic characteristics, comorbidities, family history of hearing loss, and noise exposure was collected. We assessed the relationship between three levels of socioeconomic factors (individual, household, and area level) with sensorineural hearing loss (SNHL). Multiple logistic regression was used to adjust the potential confounders.

Results

Among a total of 1,365 assessed participants, 485 patients were diagnosed as having hearing loss, and the other 880 individuals were diagnosed without hearing loss, which is considered the case and the control group, respectively. At the individual level of socioeconomic, the odds of having hearing loss in the participants with high school education and diploma, [OR = 0.51 (95%CI:0.28-0.92)], and the individuals with university education [OR = 0.44 (95%CI:0.22-0.87)] were significantly lower than the illiterate participants. At the household socioeconomic level, the odds of having hearing loss were lower for those with poor [OR = 0.63 (95%CI:0.41-0.97)] and moderate [OR = 0.62 (95%CI:0.41-0.94)] wealth status vs. those with the poorest wealth status. In the area level socioeconomic, although the odds of hearing loss in the residents of affluent areas were slightly lower than the residents of deprived areas, there was no significant difference among the groups.

Conclusion

The individuals with hearing loss may have insufficient education and income.

The roles of NADPH and isocitrate dehydrogenase in cochlear mitochondrial antioxidant defense and aging

Hearing loss is the third most prevalent chronic health condition affecting older adults. Age-related hearing loss affects one in three adults over 65 years of age and is caused by both extrinsic and intrinsic factors, including genetics, aging, and exposure to noise and toxins. All cells possess antioxidant defense systems that play an important role in protecting cells against these factors. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) serves as a co-factor for antioxidant enzymes such as glutathione reductase and thioredoxin reductase and is produced by glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase 1 (IDH1) or malic enzyme 1 in the cytosol, while in the mitochondria, NADPH is generated from mitochondrial transhydrogenase, glutamate dehydrogenase, malic enzyme 3 or IDH2. There are three isoforms of IDH: cytosolic IDH1, and mitochondrial IDH2 and IDH3. Of these, IDH2 is thought to be the major supplier of NADPH to the mitochondrial antioxidant defense system. The NADP+/NADPH and NAD+/NADH couples are essential for maintaining a large array of biological processes, including cellular redox state, and energy metabolism, mitochondrial function. A growing body of evidence indicates that mitochondrial dysfunction contributes to age-related structural or functional changes of cochlear sensory hair cells and neurons, leading to hearing impairments. In this review, we describe the current understanding of the roles of NADPH and IDHs in cochlear mitochondrial antioxidant defense and aging.

Aging and aging-related diseases: from molecular mechanisms to interventions and treatments

Aging is a gradual and irreversible pathophysiological process. It presents with declines in tissue and cell functions and significant increases in the risks of various aging-related diseases, including neurodegenerative diseases, cardiovascular diseases, metabolic diseases, musculoskeletal diseases, and immune system diseases. Although the development of modern medicine has promoted human health and greatly extended life expectancy, with the aging of society, a variety of chronic diseases have gradually become the most important causes of disability and death in elderly individuals. Current research on aging focuses on elucidating how various endogenous and exogenous stresses (such as genomic instability, telomere dysfunction, epigenetic alterations, loss of proteostasis, compromise of autophagy, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing) participate in the regulation of aging. Furthermore, thorough research on the pathogenesis of aging to identify interventions that promote health and longevity (such as caloric restriction, microbiota transplantation, and nutritional intervention) and clinical treatment methods for aging-related diseases (depletion of senescent cells, stem cell therapy, antioxidative and anti-inflammatory treatments, and hormone replacement therapy) could decrease the incidence and development of aging-related diseases and in turn promote healthy aging and longevity.

Deep phenotyping and lifetime trajectories reveal limited effects of longevity regulators on the aging process in C57BL/6J mice

Current concepts regarding the biology of aging are primarily based on studies aimed at identifying factors regulating lifespan. However, lifespan as a sole proxy measure for aging can be of limited value because it may be restricted by specific pathologies. Here, we employ large-scale phenotyping to analyze hundreds of markers in aging male C57BL/6J mice. For each phenotype, we establish lifetime profiles to determine when age-dependent change is first detectable relative to the young adult baseline. We examine key lifespan regulators (putative anti-aging interventions; PAAIs) for a possible countering of aging. Importantly, unlike most previous studies, we include in our study design young treated groups of animals, subjected to PAAIs prior to the onset of detectable age-dependent phenotypic change. Many PAAI effects influence phenotypes long before the onset of detectable age-dependent change, but, importantly, do not alter the rate of phenotypic change. Hence, these PAAIs have limited effects on aging.

AAV-ie-mediated UCP2 overexpression accelerates inner hair cell loss during aging in vivo

BACKGROUND

Uncoupling protein 2 (UCP2), activated by excessive reactive oxygen species (ROS) in vivo, has the dual effect of reducing ROS to protect against oxidative stress and reducing ATP production to regulate cellular metabolism. Both the UCP2 and ROS are increased in cochleae in age-related hearing loss (ARHL). However, the role of UCP2 in sensory hair cells in ARHL remains unclear.

METHODS

Male C57BL/6 J mice were randomly assigned to an 8-week-old group (Group 1), a 16-week-old group (Group 2), a 16-week-old + adeno-associated virus-inner ear (AAV-ie) group (Group 3), and a 16-week-old + AAV-ie-UCP2 group (Group 4). Mice aged 8 weeks were administrated with AAV-ie-GFP or AAV-ie-UCP2 via posterior semicircular canal injection. Eight weeks after this viral intervention, hearing thresholds and wave-I amplitudes were tested by auditory brainstem response (ABR). Subsequently, the cochlear basilar membrane was dissected for investigation. The number of hair cells and inner hair cell (IHC) synapses, the level of ROS, and the expression of AMP-activated protein kinase α (AMPKα), were assessed by immunofluorescence staining. In addition, mitochondrial function was determined, and the expression of AMPKα and UCP2 proteins was further evaluated using western blotting.

RESULTS

Mice with early-onset ARHL exhibited enhanced oxidative stress and loss of outer hair cells and IHC synapses, while UCP2 overexpression aggravated hearing loss and cochlear pathophysiological changes in mice. UCP2 overexpression resulted in a notable decrease in the number of IHCs and IHC synapses, caused ATP depletion and excessive ROS generation, increased AMPKα protein levels, and promoted IHC apoptosis, especially in the apical and middle turns of the cochlea.

CONCLUSION

Collectively, our data suggest that UCP2 overexpression may cause mitochondrial dysfunction via energy metabolism, which activates mitochondrion-dependent cellular apoptosis and leads to IHC loss, ultimately exacerbating ARHL.

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.

Effect of N-acetyl-cysteine treatment on sensorineural hearing loss: a meta-analysis

N-acetyl-cysteine (NAC) is an efficacious treatment for sensorineural hearing loss in animal models, such as noise-induced hearing loss (NIHL), however previous research into the effect of NAC on patients with hearing loss produced contradictory results. In this study, we investigated the effect of NAC treatment on sensorineural hearing loss. PubMed, Web of Science and Embase databases were searched in their entirety using the key words: hearing loss, NAC, N-acetylcysteine, and sensorineural hearing loss. Studies which included assessment of hearing loss with pure-tone threshold (PTA) data were selected. Eligible studies regarding the effects of NAC treatment on patients with hearing loss were collected by two independent reviewers. A total of 1197 individuals were included from seven published studies. Two studies reported data for a sudden idiopathic sensorineural hearing loss (SISNHL) group. Three studies reported data for a NIHL group. Other studies reported data for drug-induced hearing loss. The meta-analysis demonstrated that the overall effect of NAC treatment on sensorineural hearing loss was invalid. However, NAC treatment was linked with improved patient outcomes of hearing tests in cases of sudden hearing loss, but did not prevent hearing loss induced by noise or ototoxicity. However, there is a need for better-designed studies with larger samples to further prove the correlation between the effect of NAC and hearing loss.

Connexin 30 deletion exacerbates cochlear senescence and age-related hearing loss

Pathogenic mutations in the Gjb2 and Gjb6 genes, encoding connexin 26 (Cx26) and connexin 30 (Cx30), respectively, have been linked to the most frequent monogenic hearing impairment, nonsyndromic hearing loss, and deafness DFNB1. It is known that Cx26 plays an important role in auditory development, while the role of Cx30 in hearing remains controversial. Previous studies found that partial deletion of Cx26 can accelerate age-related hearing loss (ARHL), a multifactorial complex disorder, with both environmental and genetic factors contributing to the etiology of the disease. Here, we investigated the role of Cx30 in cochlear-aging processes using a transgenic mouse model with total deletion of Cx30 (Cx30 ΔΔ mice), in which Cx30 was removed without perturbing the surrounding sequences. We show that these mice are affected by exacerbated ARHL, with increased morphological cochlear damage, oxidative stress, inflammation, and vascular dysfunctions. Overall, our data demonstrate that Cx30 deletion can be considered a genetic risk factor for ARHL, making cochlear structures more susceptible to aging processes.

Analyzing efficacy, stability, and safety of AAV-mediated optogenetic hearing restoration in mice

AAV-mediated optogenetic neural stimulation has become a clinical approach for restoring function in sensory disorders and feasibility for hearing restoration has been indicated in rodents. Nonetheless, long-term stability and safety of AAV-mediated channelrhodopsin (ChR) expression in spiral ganglion neurons (SGNs) remained to be addressed. Here, we used longitudinal studies on mice subjected to early postnatal administration of AAV2/6 carrying fast gating ChR f-Chrimson under the control of the human synapsin promoter unilaterally to the cochlea. f-Chrimson expression in SGNs in both ears and the brain was probed in animals aged 1 mo to 2 yr. f-Chrimson was observed in SGNs at all ages indicating longevity of ChR-expression. SGN numbers in the AAV-injected cochleae declined with age faster than in controls. Investigations were extended to the brain in which viral transduction was observed across the organ at varying degrees irrespective of age without observing viral spread-related pathologies. No viral DNA or virus-related histopathological findings in visceral organs were encountered. In summary, our study demonstrates life-long (24 mo in mice) expression of f-Chrimson in SGNs upon single AAV-dosing of the cochlea.

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.

Garland chrysanthemum consumption ameliorates age-related hearing loss in C57BL/6 mouse; model system to explore hearing loss prevention foods in a short period

Garland chrysanthemum (Glebionis coronaria L.) is an antioxidant-rich leafy vegetable. We found that garland chrysanthemum consumption ameliorated age-related hearing loss (AHL) in C57BL/6J mice, an early onset model. We also found that AHL progression was significantly ameliorated by three of ten products. Metabolome analysis of the 10 products using nuclear magnetic resonance (NMR) spectroscopy indicated that phytosterols may be involved in the amelioration of AHL. However, the direct inhibitory effect of phytosterol mixture on mouse AHL progression was not identified. These results suggest that garland chrysanthemum consumption delays AHL development in mice and its efficiency varies depending on the source of product. Our findings also suggest that phytosterol content in garland chrysanthemum function as an evaluation marker for the efficiency. Furthermore, to accelerate the search for foods that prevent AHL, we have used these data to develop an automatic threshold determination method for auditory brainstem response using machine learning.

Exploring the Association of Leukocyte Telomere Length and Hearing Threshold Shifts of Adults in the United States

Background

Although telomere length has a significant relationship with various age-related diseases, studies on its relationship with hearing status in adults are limited and equivocal. This study investigated the associations between mean telomere length (MTL) and low-, speech-, and high-frequency hearing threshold shifts of adults in the United States.

Methods

A total of 2,027 adults, aged 20-69 years, from the National Health and Nutrition Examination Surveys (NHANES, 1999-2002) were included in the analytic sample. The quantitative polymerase chain reaction method was used for the MTL assay, and MTL was expressed using the telomere-to-single copy gene (T/S) ratio. Hearing loss was defined as a pure-tone average (PTA) for the better ear at ≥ 20 dB HL at frequencies 500, 1,000, 2,000, and 4,000 Hz. Univariate and multivariate linear regression analyses and smooth curve fittings were conducted to evaluate the correlation between MTL and low-, speech-, and high-frequency hearing levels.

Results

The mean age of the participants was 40.60 ± 12.76 years, including 952 men (weighted, 48.67%) and 303 (weighted, 12.88%) participants with hearing loss. After adjusting for potential confounders in the multivariate linear regression model, the relationship between MTL and hearing thresholds was not statistically significant. Smooth curve fittings indicated a non-linear relationship between MTL and high-frequency PTA hearing threshold shifts. MTL was inversely related to high-frequency PTA to the turning point (T/S ratio = 0.82) (adjusted β-21.45, 95% CI -37.28, -5.62; P = 0.008). When the T/S ratio exceeded0.82, MTL was not associated with high-frequency PTA (adjusted β0.18, 95% CI -2.21, 2.57; P = 0.8809).

Conclusion

Our findings revealed that MTL was associated with high-frequency PTA hearing threshold shifts of adults in the United States in a non-linear manner.

Urolithin A attenuates auditory cell senescence by activating mitophagy

Aging of sensory organs is associated with a decline in mitochondrial function and the accumulation of dysfunctional mitochondria. Impaired mitophagy blocks the turnover of dysfunctional mitochondria and leads to their accumulation. Urolithin A (UA) induces mitophagy in various mammalian cells. This study was aimed at investigating the effect of the mitophagy activator, UA, on premature senescent auditory cells. The levels of cellular senescence-associated p53 and p21 significantly increased in H₂O₂-induced senescent House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and cochlear explants. However, the levels of mitophagy-related molecules significantly decreased. UA significantly decreased the expression of senescence-associated p53 and p21, and increased the expression of mitophagy-related proteins, in H₂O₂-induced senescent cells and cochlear explants. The percentage of β-galactosidase-stained senescent cells also reduced in H₂O₂-treated cells and cochlear explants upon UA pre-treatment. The formation of mitophagosomes and mitophagolysosomes was restored upon UA pre-treatment of H₂O₂-induced senescent cells. The knockdown of mitophagy-related genes (Parkin and Bnip3) resulted in annulment of UA-induced anti-senescent activity. UA significantly increased the ATP content, mitochondrial DNA (mtDNA) integrity, and mitochondrial membrane potential in senescent HEI-OC1 cells. These findings indicate that UA counteracted mitophagy decline and prevented premature senescence in auditory cells. Hence, UA administration might be a promising strategy for preventing mitochondrial dysfunction in patients with age-related hearing loss.

Early Noise-Induced Hearing Loss Accelerates Presbycusis Altering Aging Processes in the Cochlea

Several studies identified hearing loss as a risk factor for aging-related processes, including neurodegenerative diseases, as dementia and age-related hearing loss (ARHL). Although the association between hearing impairment in midlife and ARHL has been widely documented by epidemiological and experimental studies, the molecular mechanisms underlying this association are not fully understood. In this study, we used an established animal model of ARHL (C57BL/6 mice) to evaluate if early noise-induced hearing loss (NIHL) could affect the onset or progression of age-related cochlear dysfunction. We found that hearing loss can exacerbate ARHL, damaging sensory-neural cochlear epithelium and causing synaptopathy. Moreover, we studied common pathological markers shared between hearing loss and ARHL, demonstrating that noise exposure can worsen/accelerate redox status imbalance [increase of reactive oxygen species (ROS) production, lipid peroxidation, and dysregulation of endogenous antioxidant response] and vascular dysfunction [increased expression of hypoxia-inducible factor-1alpha (HIF-1α) and vascular endothelial growth factor C (VEGFC)] in the cochlea. Unveiling the molecular mechanisms underlying the link between hearing loss and aging processes could be valuable to identify effective therapeutic strategies to limit the effect of environmental risk factors on age-related diseases.

Age-related Activation of Cyclic GMP-AMP synthase-Stimulator of Interferon Genes Signaling in the Auditory System is Associated with Presbycusis in C57BL/6J Male Mice

Presbycusis, or age-related hearing loss (ARHL), is primarily associated with sensory or transduction nerve cell degeneration in the peripheral and/or central auditory systems. During aging, the auditory system shows mitochondrial dysfunction and increased inflammatory responses. Mitochondrial dysfunction promotes leakage of mitochondrial DNA (mtDNA) into the cytosol, which activates the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway to induce type I interferon and inflammatory responses. However, whether this pathway is involved in the occurrence and development of ARHL is unknown. This study aimed to determine whether there are age-related changes in the levels of cytosolic mtDNA and cGAS-STING pathway activation in the auditory pathway and to explore their relationship with ARHL. The results showed that cGAS-positive immunoreactive cells were observed in the cochlea, inferior colliculus, and auditory cortex. Levels of cytosolic mtDNA, cGAS, STING, phosphorylated interferon regulatory factor 3, and cytokines were significantly increased in the cochlea, inferior colliculus, and auditory cortex of 6-, 9-, and 12-month-old mice compared with 3-month-old mice. These findings suggested that cytosolic mtDNA may play an important role in the pathogenesis of ARHL by activating cGAS-STING-mediated type I interferon and inflammatory responses.

Long noncoding RNA Gm44593 attenuates oxidative stress from age-related hearing loss by regulating miR-29b/WNK1

Long noncoding RNA has been reported to play important role in various disease. However, the function of lncRNA in age-related hearing loss still unclear. The aim of our study is to investigate the function and mechanism of lncRNA Gm44593 in AHL. ATP content, JC-1 assay, mitochondrial content, cell death rates and dual-luciferase reporter assay were performed to assess the function of lncRNA Gm44593 in HEI-OC1 cells. The expression of lncRNA Gm44593 was significantly upregulated upon H₂O₂ and starvation treatment. Overexpression of lncRNA Gm44593 manifestly reduced the cell death rates. The ATP content, mtDNA content and mitochondrial membrane potential were alleviated upon overexpression of lncRNA Gm44593. We also proved that miR-29b is the direct target of lncRNA Gm44593. Overexpression of miR-29b completely restored the effect induced by lncRNA Gm44593. In addition, we provided evidences that WNK1 is the direct target of miR-29b. Our research uncovers a potential role of lncRNA Gm44593 in age-related hearing loss. We provide new insights into potential therapeutic targets for the amelioration of age-related hearing loss.

Deletion of Oncomodulin Gives Rise to Early Progressive Cochlear Dysfunction in C57 and CBA Mice

Ca²⁺ signaling is a major contributor to sensory hair cell function in the cochlea. Oncomodulin (OCM) is a Ca²⁺ binding protein (CaBP) preferentially expressed in outer hair cells (OHCs) of the cochlea and few other specialized cell types. Here, we expand on our previous reports and show that OCM delays hearing loss in mice of two different genetic backgrounds: CBA/CaJ and C57Bl/6J. In both backgrounds, genetic disruption of Ocm leads to early progressive hearing loss as measured by auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE). In both strains, loss of Ocm reduced hearing across lifetime (hearing span) by more than 50% relative to wild type (WT). Even though the two WT strains have very different hearing spans, OCM plays a considerable and similar role within their genetic environment to regulate hearing function. The accelerated age-related hearing loss (ARHL) of the Ocm KO illustrates the importance of Ca²⁺ signaling in maintaining hearing health. Manipulation of OCM and Ca²⁺ signaling may reveal important clues to the systems of function/dysfunction that lead to ARHL.

Efficiency of resveratrol in the prevention and treatment of age-related hearing loss

Age-related hearing loss (ARHL) is a major public health concern, which is characterized by gradual, progressive sensorineural hearing loss and deterioration of sound localization, with no effective treatment available to date. The aim of the present study was to evaluate the efficacy of resveratrol to prevent and treat ARHL. For this purpose, 32 male C57BL/6 mice were assigned to four groups: Early treatment, late treatment, control and sham control. The experiment lasted for 15 months. Treatment was started at three months of age in the early treatment group and at sixth months in the late treatment group. The auditory brainstem response test was performed once every three months. At the end of the study period, inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2, NF-κB, Bcl-2, Bcl-xL, Bax, Bcl-2 homologous antagonist/killer (Bak), caspase-3 and caspase-9 levels in the cochlear tissues of the animals were analyzed by reverse transcription-quantitative PCR. Hearing thresholds of the mice in the early treatment group were better than those in the other groups (P<0.001) at the end of the study. However, hearing levels in the late treatment group were not significantly different from those in the control groups (P>0.05), although mean thresholds were lower. The threshold shift in the early treatment group was significantly lower at all frequencies when compared with those in the control groups (P<0.001). The mRNA expression levels of pro-apoptotic genes Bax and Bak were lower (P<0.05), anti-apoptotic genes Bcl-2 and Bcl-xL were higher (P<0.05), NF-κB, COX-2 and iNOS as genes that have a role in inflammation and caspase-3 and caspase-9 as genes with a vital role in apoptosis were lower (P<0.05) in the early treatment group when compared with the late treatment and control groups. These results suggested that resveratrol is effective in the prevention of ARHL, particularly when started prior to the beginning of hearing loss.

Thymoquinone ameliorates age-related hearing loss in C57BL/6J mice by modulating Sirt1 activity and Bak1 expression

Age-related hearing loss (AHL) is the most common sensory disorder of aged population. Currently, one of the most important sources of experimental medicine for AHL is medicinal plants. This study performed the first investigation of the effect of thymoquinone (TQ), a potent antioxidant, on AHL. Here, we used inbred C57BL/6J mice (B6 mice) as a successful experimental model of the early onset of AHL. The behavioral assessment of hearing revealed that the injection of a high dose of TQ (40 mg/kg; TQ40) significantly improved the auditory sensitivity of B6 mice at all tested frequencies (8, 16 and 22 kHz). Histological sections of cochlea from B6 mice injected with a low dose (20 mg/kg; TQ20) and high dose showed relatively less degenerative signs in the modiolus, hair cells and spiral ligaments, the main constituents of the cochlea. In addition, TQ40 completely restored the normal pattern of hair cells in B6 mice, as shown in scanning electron micrographs. Our data indicated that TQ20 and TQ40 reduced levels of Bak1-mediated apoptosis in the cochlea of B6 mice. Interestingly, the level of Sirt1, a positive regulator of autophagy, was significantly increased in B6 mice administered TQ40. In conclusion, TQ relieves the symptoms of AHL by downregulating Bak1 and activating Sirt1 in the cochlea of B6 mice.

Cochlear Inflammaging in Relation to Ion Channels and Mitochondrial Functions

The slow accumulation of inflammatory biomarker levels in the body-also known as inflammaging-has been linked to a myriad of age-related diseases. Some of these include neurodegenerative conditions such as Parkinson's disease, obesity, type II diabetes, cardiovascular disease, and many others. Though a direct correlation has not been established, research connecting age-related hearing loss (ARHL)-the number one communication disorder and one of the most prevalent neurodegenerative diseases of our aged population-and inflammaging has gained interest. Research, thus far, has found that inflammatory markers, such as IL-6 and white blood cells, are associated with ARHL in humans and animals. Moreover, studies investigating ion channels and mitochondrial involvement have shown promising relationships between their functions and inflammaging in the cochlea. In this review, we summarize key findings in inflammaging within the auditory system, the involvement of ion channels and mitochondrial functions, and lastly discuss potential treatment options focusing on controlling inflammation as we age.

Hearing Status of Low-Income, Middle-Aged and Elderly Women in Northern China: A Population-Based, Cross-Sectional Study

Objective

Hearing impairment (HI) has become one of the most common causes of disability worldwide. To date, few studies have examined the hearing of women in these frequently rural regions. Thus, we explored the HI prevalence and risk factors among low-income, middle-aged, and elderly women in Tianjin, China.

Methods

Between October and November 2013, female residents aged ≥45 years of rural Tianjin, China were recruited into the study. The participants completed questionnaire surveys, physical examinations, and hearing tests. The hearing at frequencies of 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz was used to analyze the hearing characteristics of specific frequency bands, and HI was defined as the better ear pure tone averages (PTA) >25 dB HL.

Results

Among the 1416 participants, the prevalence of HI was 46.0%. Among those aged 45-54-years, most (65.3%) demonstrated normal hearing; in other age groups, slight HI accounted for the largest proportions of individuals. Compared with women who did not drink, the odds ratio (OR) of HI among women who consumed alcohol was 4.2 (95% confidence interval [CI]: 1.844-9.574; P = 0.001). Compared with pre-menopausal women, the OR of HI among postmenopausal women was 1.8 (95% CI: 1.261-2.667; P = 0.001). Further, each 1-year increase in age in women resulted in a 7.1% increase in HI risk (P < 0.001).

Conclusion

The burden of HI among women is heavy in rural northern China, especially among those who experienced menopause. Additionally, the results suggest that to further reduce the risk of developing HI, women in rural areas should stop consuming alcohol. The problem of HI among women in rural areas should be taken seriously; moreover, the measures implemented to prevent HI in high-risk women should be strengthened.

Antioxidant supplementation partially rescues accelerated ovarian follicle loss, but not oocyte quality, of glutathione-deficient mice†

The tripeptide thiol antioxidant glutathione (GSH) has multiple physiological functions. Female mice lacking the modifier subunit of glutamate cysteine ligase (GCLM), the rate-limiting enzyme in GSH synthesis, have decreased GSH concentrations, ovarian oxidative stress, preimplantation embryonic mortality, and accelerated age-related decline in ovarian follicles. We hypothesized that supplementation with thiol antioxidants, N-acetyl cysteine (NAC), or α-lipoic acid (ALA) will rescue this phenotype. Gclm-/- and Gclm+/+ females received 0 or 80 mM NAC in drinking water from postnatal day (PND) 21-30; follicle growth was induced with equine chorionic gonadotropin (eCG) on PND 27, followed by an ovulatory dose of human CG and mating with a wild type male on PND 29 and zygote harvest 20 h after hCG. N-acetyl cysteine supplementation failed to rescue the low rate of second pronucleus formation in zygotes from Gclm-/- versus Gclm+/+ females. In the second study, Gclm-/- and Gclm+/+ females received diet containing 0, 150, or 600 mg/kg ALA beginning at weaning and were mated with wild type males from 8 to 20 weeks of age. α-Lipoic acid failed to rescue the decreased offspring production of Gclm-/- females. However, 150 mg/kg diet ALA partially rescued the accelerated decline in primordial follicles, as well as the increased recruitment of follicles into the growing pool and the increased percentages of follicles with γH2AX positive oocytes or granulosa cells of Gclm-/- females. We conclude that ovarian oxidative stress is the cause of accelerated primordial follicle decline, while GSH deficiency per se may be responsible for preimplantation embryonic mortality in Gclm-/- females.