ROS-Induced Activation of DNA Damage Responses Drives Senescence-Like State in Postmitotic Cochlear Cells: Implication for Hearing Preservation

miR-130b-3p involved in the pathogenesis of age-related hearing loss via targeting PPARγ and autophagy

The study focuses on the underlying regulatory mechanism of age-related hearing loss (ARHL), which results from autophagy dysregulation mediated by miR-130b-3p targeting PPARγ. We constructed miR-130b-3p knockout (antagomir) and PPARγ over-expression (OE-PPARγ) mice model by injecting mmu-miR-130b-3p antagomir and HBAAV2/Anc80-m-Pparg-T2A-mCHerry into the right ear' round window of each mouse, respectively. In vitro, we introduced oxidative stress within HEI-OC1 cells by H2O2 and exogenously changed the miR-130b-3p and PPARγ levels. MiRNA level was detected by RT-qPCR, proteins by western blotting and immunohistochemistry. Morphology of autophagosomes was observed by electron microscopy. In vivo, the cochlea of aged mice showed higher miR-130b-3p expression and lower PPARγ expression, while exogenous inhibition of miR-130b-3p up-regulated PPARγ expression. Autophagy-related biomarkers expression (ATG5, Beclin-1 and LC3B II/I) decreased in aged mice, which reversely increased after the inhibition of miR-130b-3p. The elevation of PPARγ demonstrated similar effects. Contrarily, exogenous overexpression of miR-130b-3p resulted in the decrease of ATG5, Beclin-1 and LC3B II/I. We created oxidative stress within HEI-OC1 by H2O2, subsequently observed the formation of autophagosomes under electron microscope, so as the elevated cell apoptosis rate and weakened cell viability. MiR-130b-3p/PPARγ contributed to the premature senescence of these H2O2-induced HEI-OC1 cells. MiR-130b-3p regulated HEI-OC1 cell growth by targeting PPARγ, thus leading to ARHL.

Unveiling the Role of Oxidative Stress in Cochlear Hair Cell Death: Prospective Phytochemical Therapeutics against Sensorineural Hearing Loss

Hearing loss represents a multifaceted and pervasive challenge that deeply impacts various aspects of an individual's life, spanning psychological, emotional, social, and economic realms. Understanding the molecular underpinnings that orchestrate hearing loss remains paramount in the quest for effective therapeutic strategies. This review aims to expound upon the physiological, biochemical, and molecular aspects of hearing loss, with a specific focus on its correlation with diabetes. Within this context, phytochemicals have surfaced as prospective contenders in the pursuit of potential adjuvant therapies. These compounds exhibit noteworthy antioxidant and anti-inflammatory properties, which hold the potential to counteract the detrimental effects induced by oxidative stress and inflammation-prominent contributors to hearing impairment. Furthermore, this review offers an up-to-date exploration of the diverse molecular pathways modulated by these compounds. However, the dynamic landscape of their efficacy warrants recognition as an ongoing investigative topic, inherently contingent upon specific experimental models. Ultimately, to ascertain the genuine potential of phytochemicals as agents in hearing loss treatment, a comprehensive grasp of the molecular mechanisms at play, coupled with rigorous clinical investigations, stands as an imperative quest.

Probucol-bile acid based nanoparticles protect auditory cells from oxidative stress: an in vitro study

Aim: Excessive free radicals contribute to oxidative stress and mitochondrial dysfunction in sensorineural hearing loss (SNHL). The antioxidant probucol holds promise, but its limited bioavailability and inner ear barriers hinder effective SNHL treatment. Methodology: We addressed this by developing probucol-loaded nanoparticles with polymers and lithocholic acid and tested them on House Ear Institute-Organ of Corti cells. Results: Probucol-based nanoparticles effectively reduced oxidative stress-induced apoptosis, enhanced cellular viability, improved probucol uptake and promoted mitochondrial function. Additionally, they demonstrated the capacity to reduce reactive oxygen species through the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Conclusion: This innovative nanoparticle system holds the potential to prevent oxidative stress-related hearing impairment, providing an effective solution for SNHL.

Sirtuins in intervertebral disc degeneration: current understanding

BACKGROUND

Intervertebral disc degeneration (IVDD) is one of the etiologic factors of degenerative spinal diseases, which can lead to a variety of pathological spinal conditions such as disc herniation, spinal stenosis, and scoliosis. IVDD is a leading cause of lower back pain, the prevalence of which increases with age. Recently, Sirtuins/SIRTs and their related activators have received attention for their activity in the treatment of IVDD. In this paper, a comprehensive systematic review of the literature on the role of SIRTs and their activators on IVDD in recent years is presented. The molecular pathways involved in the regulation of IVDD by SIRTs are summarized, and the effects of SIRTs on senescence, inflammatory responses, oxidative stress, and mitochondrial dysfunction in myeloid cells are discussed with a view to suggesting possible solutions for the current treatment of IVDD.

PURPOSE

This paper focuses on the molecular mechanisms by which SIRTs and their activators act on IVDD.

METHODS

A literature search was conducted in Pubmed and Web of Science databases over a 13-year period from 2011 to 2024 for the terms "SIRT", "Sirtuin", "IVDD", "IDD", "IVD", "NP", "Intervertebral disc degeneration", "Intervertebral disc" and "Nucleus pulposus".

RESULTS

According to the results, SIRTs and a large number of activators showed positive effects against IVDD.SIRTs modulate autophagy, myeloid apoptosis, oxidative stress and extracellular matrix degradation. In addition, they attenuate inflammatory factor-induced disc damage and maintain homeostasis during disc degeneration. Several clinical studies have reported the protective effects of some SIRTs activators (e.g., resveratrol, melatonin, honokiol, and 1,4-dihydropyridine) against IVDD.

CONCLUSION

The fact that SIRTs and their activators play a hundred different roles in IVDD helps to better understand their potential to develop further treatments for IVDD.

NOVELTY

This review summarizes current information on the mechanisms of action of SIRTs in IVDD and the challenges and limitations of translating their basic research into therapy.

Connexins 30 and 43 expression changes in relation to age-related hearing loss

Age-related hearing loss (ARHL), also known as presbycusis, is the number one communication disorder for aging adults. Connexin proteins are essential for intercellular communication throughout the human body, including the cochlea. Mutations in connexin genes have been linked to human syndromic and nonsyndromic deafness; thus, we hypothesize that changes in connexin gene and protein expression with age are involved in the etiology of ARHL. Here, connexin gene and protein expression changes for CBA/CaJ mice at different ages were examined, and correlations were analyzed between the changes in expression levels and functional hearing measures, such as ABRs and DPOAEs. Moreover, we investigated potential treatment options for ARHL. Results showed significant downregulation of Cx30 and Cx43 gene expression and significant correlations between the degree of hearing loss and the changes in gene expression for both genes. Moreover, dose-dependent treatments utilizing cochlear cell lines showed that aldosterone hormone therapy significantly increased Cx expression. In vivo mouse treatments with aldosterone also showed protective effects on connexin expression in aging mice. Based on these functionally relevant findings, next steps can include more investigations of the mechanisms related to connexin family gap junction protein expression changes during ARHL; and expand knowledge of clinically-relevant treatment options by knowing what specific members of the Cx family and related inter-cellular proteins should be targeted therapeutically.

Altered Fhod3 expression involved in progressive high-frequency hearing loss via dysregulation of actin polymerization stoichiometry in the cuticular plate

Age-related hearing loss (ARHL) is a common sensory impairment with complex underlying mechanisms. In our previous study, we performed a meta-analysis of genome-wide association studies (GWAS) in mice and identified a novel locus on chromosome 18 associated with ARHL specifically linked to a 32 kHz tone burst stimulus. Consequently, we investigated the role of Formin Homology 2 Domain Containing 3 (Fhod3), a newly discovered candidate gene for ARHL based on the GWAS results. We observed Fhod3 expression in auditory hair cells (HCs) primarily localized at the cuticular plate (CP). To understand the functional implications of Fhod3 in the cochlea, we generated Fhod3 overexpression mice (Pax2-Cre+/-; Fhod3Tg/+) (TG) and HC-specific conditional knockout mice (Atoh1-Cre+/-; Fhod3fl/fl) (KO). Audiological assessments in TG mice demonstrated progressive high-frequency hearing loss, characterized by predominant loss of outer hair cells, and a decreased phalloidin intensities of CP. Ultrastructural analysis revealed loss of the shortest row of stereocilia in the basal turn of the cochlea, and alterations in the cuticular plate surrounding stereocilia rootlets. Importantly, the hearing and HC phenotype in TG mice phenocopied that of the KO mice. These findings suggest that balanced expression of Fhod3 is critical for proper CP and stereocilia structure and function. Further investigation of Fhod3 related hearing impairment mechanisms may lend new insight towards the myriad mechanisms underlying ARHL, which in turn could facilitate the development of therapeutic strategies for ARHL.

BubR1 controls starvation-induced lipolysis via IMD signaling pathway in Drosophila

Lipolysis, the key process releasing fat acids to generate energy in adipose tissues, correlates with starvation resistance. Nevertheless, its detail mechanisms remain elusive. BubR1, an essential mitotic regulator, ensures proper chromosome alignment and segregation during mitosis, but its physiological functions are largely unknown. Here, we use Drosophila adult fat body, the major lipid storage organ, to study the functions of BubR1 in lipolysis. We show that both whole body- and fat body-specific BubR1 depletions increase lipid degradation and shorten the lifespan under fasting but not feeding. Relish, the conserved regulator of IMD signaling pathway, acts as the downstream target of BubR1 to control the expression level of Bmm and modulate the lipolysis upon fasting. Thus, our study reveals new functions of BubR1 in starvation-induced lipolysis and provides new insights into the molecular mechanisms of lipolysis mediated by IMD signaling pathway.

Oxidative Stress Plays an Important Role in Glutamatergic Excitotoxicity-Induced Cochlear Synaptopathy: Implication for Therapeutic Molecules Screening

The disruption of the synaptic connection between the sensory inner hair cells (IHCs) and the auditory nerve fiber terminals of the type I spiral ganglion neurons (SGN) has been observed early in several auditory pathologies (e.g., noise-induced or ototoxic drug-induced or age-related hearing loss). It has been suggested that glutamate excitotoxicity may be an inciting element in the degenerative cascade observed in these pathological cochlear conditions. Moreover, oxidative damage induced by free hydroxyl radicals and nitric oxide may dramatically enhance cochlear damage induced by glutamate excitotoxicity. To investigate the underlying molecular mechanisms involved in cochlear excitotoxicity, we examined the molecular basis responsible for kainic acid (KA, a full agonist of AMPA/KA-preferring glutamate receptors)-induced IHC synapse loss and degeneration of the terminals of the type I spiral ganglion afferent neurons using a cochlear explant culture from P3 mouse pups. Our results demonstrated that disruption of the synaptic connection between IHCs and SGNs induced increased levels of oxidative stress, as well as altered both mitochondrial function and neurotrophin signaling pathways. Additionally, the application of exogenous antioxidants and neurotrophins (NT3, BDNF, and small molecule TrkB agonists) clearly increases synaptogenesis. These results suggest that understanding the molecular pathways involved in cochlear excitotoxicity is of crucial importance for the future clinical trials of drug interventions for auditory synaptopathies.

ROS-induced oxidative stress and mitochondrial dysfunction: a possible mechanism responsible for noise-induced ribbon synaptic damage

Evidence suggests that damage to the ribbon synapses (RS) may be the main cause of auditory dysfunction in noise-induced hearing loss (NIHL). Oxidative stress is implicated in the pathophysiology of synaptic damage. However, the relationship between oxidative stress and RS damage in NIHL remains unclear. To investigate the hypothesis that noise-induced oxidative stress is a key factor in synaptic damage within the inner ear, we conducted a study using mice subjected to single or repeated noise exposure (NE). We assessed auditory function using auditory brainstem response (ABR) test and examined cochlear morphology by immunofluorescence staining. The results showed that mice that experienced a single NE exhibited a threshold shift and recovered within two weeks. The ABR wave I latencies were prolonged, and the amplitudes decreased, suggesting RS dysfunction. These changes were also demonstrated by the loss of RS as evidenced by immunofluorescence staining. However, we observed threshold shifts that did not return to baseline levels following secondary NE. Additionally, ABR wave I latencies and amplitudes exhibited notable changes. Immunofluorescence staining indicated not only severe damage to RS but also loss of outer hair cells. We also noted decreased T-AOC, ATP, and mitochondrial membrane potential levels, alongside increased hydrogen peroxide concentrations post-NE. Furthermore, the expression levels of 4-HNE and 8-OHdG in the cochlea were notably elevated. Collectively, our findings suggest that the production of reactive oxygen species leads to oxidative damage in the cochlea. This mitochondrial dysfunction consequently contributes to the loss of RS, precipitating an early onset of NIHL.

Bile Acid Application in Cell-Targeting for Molecular Receptors in Relation to Hearing: A Comprehensive Review

Bile acids play important roles in the human body, and changes in their pool can be used as markers for various liver pathologies. In addition to their functional effects in modulating inflammatory responses and cellular survivability, the unconjugated or conjugated, secondary, or primary nature of bile acids accounts for their various ligand effects. The common hydrophilic bile acids have been used successfully as local treatment to resolve drug-induced cell damage or to ameliorate hearing loss. From various literature references, bile acids show concentration and tissue-dependent effects. Some hydrophobic bile acids act as ligands modulating vitamin D receptors, muscarinic receptors, and calcium-activated potassium channels, important proteins in the inner ear system. Currently, there are limited resources investigating the therapeutic effects of bile acid on hearing loss and little to no information on detecting bile acids in the remote ear system, let alone baseline bile acid levels and their prevalence in healthy and disease conditions. This review presents both hydrophilic and hydrophobic human bile acids and their tissue-specific effects in modulating cellular integrity, thus considering the possible effects and extended therapeutic applicability of bile acids to the inner ear tissue.

Optimized DOX Drug Deliveries via Chitosan-Mediated Nanoparticles and Stimuli Responses in Cancer Chemotherapy: A Review

Chitosan nanoparticles (NPs) serve as useful multidrug delivery carriers in cancer chemotherapy. Chitosan has considerable potential in drug delivery systems (DDSs) for targeting tumor cells. Doxorubicin (DOX) has limited application due to its resistance and lack of specificity. Chitosan NPs have been used for DOX delivery because of their biocompatibility, biodegradability, drug encapsulation efficiency, and target specificity. In this review, various types of chitosan derivatives are discussed in DDSs to enhance the effectiveness of cancer treatments. Modified chitosan-DOX NP drug deliveries with other compounds also increase the penetration and efficiency of DOX against tumor cells. We also highlight the endogenous stimuli (pH, redox, enzyme) and exogenous stimuli (light, magnetic, ultrasound), and their positive effect on DOX drug delivery via chitosan NPs. Our study sheds light on the importance of chitosan NPs for DOX drug delivery in cancer treatment and may inspire the development of more effective approaches for cancer chemotherapy.

Progress on mechanisms of age-related hearing loss

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

Altered Fhod3 Expression Involved in Progressive High-Frequency Hearing Loss via Dysregulation of Actin Polymerization Stoichiometry in The Cuticular Plate

Age-related hearing loss (ARHL) is a common sensory impairment with comlex underlying mechanisms. In our previous study, we performed a meta-analysis of genome-wide association studies (GWAS) in mice and identified a novel locus on chromosome 18 associated with ARHL specifically linked to a 32 kHz tone burst stimulus. Consequently, we investigated the role of Formin Homology 2 Domain Containing 3 (Fhod3), a newly discovered candidate gene for ARHL based on the GWAS results. We observed Fhod3 expression in auditory hair cells (HCs) and primarily localized at the cuticular plate (CP). To understand the functional implications of Fhod3 in the cochlea, we generated Fhod3 overexpression mice (Pax2-Cre+/-; Fhod3Tg/+) (TG) and HC-specific conditional knockout mice (Atoh1-Cre+/-; Fhod3fl/fl) (KO). Audiological assessments in TG mice demonstrated progressive high-frequency hearing loss, characterized by predominant loss of outer HCs and decrease phalloidin intensities of CP. Ultrastructural analysis revealed shortened stereocilia in the basal turn cochlea. Importantly, the hearing and HC phenotype in TG mice were replicated in KO mice. These findings indicate that Fhod3 plays a critical role in regulating actin dynamics in CP and stereocilia. Further investigation of Fhod3-related hearing impairment mechanisms may facilitate the development of therapeutic strategies for ARHL in humans.

D-galactose-induced mitochondrial oxidative damage and apoptosis in the cochlear stria vascularis of mice

BACKGROUND

Age-related hearing loss, known as presbycusis, is the result of auditory system degeneration. Numerous studies have suggested that reactive oxygen species (ROS) and mitochondrial oxidative damage play important roles in the occurrence and progression of aging. The D-galactose (D-gal)-induced aging model is well known and widely utilized in aging research. Our previous studies demonstrate that administration of D-gal causes mitochondrial oxidative damage and causes subsequent dysfunction in the cochlear ribbon synapses, which in turn leads to hearing changes and early stage presbycusis. Stria vascularis (SV) cells are vital for hearing function. However, it is unclear to what extent D-gal induces oxidative damage and apoptosis in the cochlear SV of mice. In addition, the source of the causative ROS in the cochlear SV has not been fully investigated.

METHODS

In this study, we investigated ROS generation in the cochlear SV of mice treated with D-gal. Hearing function was measured using the auditory brainstem response (ABR). Immunofluorescence was used to examine apoptosis and oxidative damage. Transmission electron microscopy was also used to investigate the mitochondrial ultrastructure. DNA fragmentation was determined using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) assay. Mitochondrial membrane potential (MMP) and ATP were also measured.

RESULTS

We found that D-gal-treated mice exhibited a significant shift in the mean amplitude and latency of the ABR; a remarkable increase in the levels of NADPH oxidase (NOX-2), Uncoupling protein 2 (UCP2) and cleaved caspase-3 (c-Cas3) was observed, as well as an increase in the number of TUNEL-positive cells were observed in the SV of mice. Both the expression of the DNA oxidative damage biomarker 8-hydroxy-2-deoxyguanosine (8-OHdG) and a commonly occurring mitochondrial DNA deletion were markedly elevated in the SV of mice that had been treated with D-gal to induce aging. Conversely, the ATP level and MMP were significantly reduced in D-gal-induced aging mice. We also found alterations in the mitochondrial ultrastructure in the SV of aging mice, which include swollen and distorted mitochondrial shape, shortened and thickened microvilli, and the accumulation of lysosomes in the SV.

CONCLUSION

Our findings suggest that the impairment of cochlear SV during presbycusis may be caused by mitochondrial oxidative damage and subsequent apoptosis.

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.

Association of Clinical Aspects and Genetic Variants with the Severity of Cisplatin-Induced Ototoxicity in Head and Neck Squamous Cell Carcinoma: A Prospective Cohort Study

Background: Cisplatin (CDDP) is a major ototoxic chemotherapy agent for head and neck squamous cell carcinoma (HNSCC) treatment. Clinicopathological features and genotypes encode different stages of CDDP metabolism, as their coexistence may influence the prevalence and severity of hearing loss. Methods: HNSCC patients under CDDP chemoradiation were prospectively provided with baseline and post-treatment audiometry. Clinicopathological features and genetic variants encoding glutathione S-transferases (GSTT1, GSTM1, GSTP1), nucleotide excision repair (XPC, XPD, XPF, ERCC1), mismatch repair (MLH1, MSH2, MSH3, EXO1), and apoptosis (P53, CASP8, CASP9, CASP3, FAS, FASL)-related proteins were analyzed regarding ototoxicity. Results: Eighty-nine patients were included, with a cumulative CDDP dose of 260 mg/m2. Moderate/severe ototoxicity occurred in 26 (29%) patients, particularly related to hearing loss at frequencies over 3000 Hertz. Race, body-mass index, and cumulative CDDP were independent risk factors. Patients with specific isolated and combined genotypes of GSTM1, GSTP1 c.313A>G, XPC c.2815A>C, XPD c.934G>A, EXO1 c.1762G>A, MSH3 c.3133A>G, FASL c.-844A>T, and P53 c.215G>C SNVs had up to 32.22 higher odds of presenting moderate/severe ototoxicity. Conclusions: Our data present, for the first time, the association of combined inherited nucleotide variants involved in CDDP efflux, DNA repair, and apoptosis with ototoxicity, which could be potential predictors in future clinical and genomic models.

Association of polymorphisms in the catalase gene with the susceptibility to noise-induced hearing loss: A meta-analysis

OBJECTIVES

The association between single nucleotide polymorphisms (SNPs) of the Catalase (CAT) gene and noise-induced hearing loss (NIHL) has been reported in several case-control studies. However, their conclusions are conflicting. This study aimed to determine the association between CAT genetic variants and NIHL susceptibility.

METHODS

We searched PubMed, Embase, CNKI, Wanfang, and Web of Science for eligible English and Chinese studies published up to September 26, 2021. Studies reporting primary data that assessed the association between CAT SNPs and NIHL susceptibility were included. The quality of the included studies was assessed using the Newcastle-Ottawa Scale (NOS). The odds ratio (OR), 95 % confidence interval (CI), and P value were calculated to assess the strength of the association. Publication bias was explored using funnel plots and Egger's test.

RESULTS

Our meta-analysis included six articles involving 1428 patients and 2162 healthy controls. For rs208679, a significant association was detected in the allele model (A vs. G: OR = 0.81 [95 % CI, 0.67-0.97], P = 0.02) and the dominant model (AA vs. GG + AG: OR = 0.78 [95 % CI, 0.62-0.98], P = 0.03), but not in the heterozygote model, homozygote model, or the recessive model. For rs769217, rs7943316, and rs769214, no significant association was found in any genetic model. No significant publication bias was observed.

CONCLUSIONS

The rs208679 may be used in the Chinese population as a risk predictor for NIHL. While the rs769217, rs7943316, and rs769214 polymorphisms were not found to be associated with susceptibility to NIHL. Further studies with a larger population and higher quality are required to update the results.

Doxorubicin-An Agent with Multiple Mechanisms of Anticancer Activity

Doxorubicin (DOX) constitutes the major constituent of anti-cancer treatment regimens currently in clinical use. However, the precise mechanisms of DOX's action are not fully understood. Emerging evidence points to the pleiotropic anticancer activity of DOX, including its contribution to DNA damage, reactive oxygen species (ROS) production, apoptosis, senescence, autophagy, ferroptosis, and pyroptosis induction, as well as its immunomodulatory role. This review aims to collect information on the anticancer mechanisms of DOX as well as its influence on anti-tumor immune response, providing a rationale behind the importance of DOX in modern cancer therapy.

Comparative analysis of markers for H2O2-induced senescence in renal tubular cells

To address what marker(s) is/are most suitable for determining renal cell senescence, cell area, granularity, cycle shift/arrest, SA-β-Gal, SIRT1 and p16 were evaluated after inducing senescence in HK-2 cells with 0.2-0.8 mM H₂O₂. Only cell area and granularity concentration-dependently increased at all time-points, whereas SA-β-Gal, SIRT1 and p16 showed significant coefficient of determination (R²) at two time-points. Cell granularity had significant correlation coefficient (R) with other six, whereas SA-β-Gal had significant R with five, and cell area, SIRT1 and p16 had significant R with four others. Comparing to SA-β-Gal, other markers had significantly lower fold-changes only at 72-h with 0.8 mM H₂O₂, whereas p16 provided greater fold-changes at 48-h with 0.4 and 0.8 mM H₂O₂. Therefore, cell area, granularity, SA-β-Gal and p16 may serve as the most suitable markers for determining H₂O₂-induced senescence in HK-2 renal cells, whereas other markers can be also used but with inferior quantitative precision.

Hearing and Ageing

Age-related hearing loss (ARHL), or presbycusis, occurs in most mammals, humans included, with a different age of onset and magnitude of loss. It is associated with two major symptoms: loss of sensitivity to sound, especially for high pitches, and a reduced ability to understand speech in background noise. This phenomenon involves both the peripheral structures of the inner ear and the central acoustic pathways. Several mechanisms have been identified as pro-ageing in the human cochlea. The main one is the oxidative stress. The inner ear physiological degeneration can be affected by both intrinsic conditions, such as genetic predisposition, and extrinsic ones, such as noise exposure. The magnitude of neuronal loss precedes and exceeds that of inner hair cell loss, which is also less important than the loss of outer hair cells. Patients with HL often develop atrophy of the temporal lobe (auditory cortex) and brain gliosis can contribute to the development of a central hearing loss. The presence of white matter hyperintensities (WMHs) on the MRI, which is radiologic representation of brain gliosis, can justify a central HL due to demyelination in the superior auditory pathways. Recently, the presence of WMHs has been correlated with the inability to correctly understand words in elderly with normal auditory thresholds.

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.

Network pharmacology and experimental evidence reveal the protective mechanism of Yi-Qi Cong-Ming decoction on age-related hearing loss

CONTEXT

Yi-Qi Cong-Ming (YQCM) decoction has been widely used to prevent age-related hearing loss (ARHL), the most prevalent neurodegenerative disease in the elderly.

OBJECTIVE

To explore the mechanism of YQCM decoction in the treatment of ARHL.

MATERIALS AND METHODS

The chemical constituents of YQCM were screened from the Traditional Chinese Medicine Systems Pharmacology Database. Potential targets of YQCM against ARHL were predicted by DrugBank, GeneCards, and OMIM database. Protein-protein network and enrichment analysis were used for exploring possible molecular mechanisms. Molecular docking and an in vitro model of ARHL by exposing auditory cells with 100 μM H₂O₂ for 3 h were applied. Cell viability and mitochondrial membrane potential (ΔΨM) were detected by CCK-8 and high-content analysis. γH2AX and cleaved caspase-3 were detected by Western blot.

RESULTS

The main compounds have good affinities with hub targets, especially AKT1, PTGS2, and CASP3. GO and KEGG analysis showed that the main biological process and key targets were related to negative regulation of the apoptotic process. H₂O₂ treatment could reduce the cell viability by 68% and impaired ΔΨM, while 90 μg/mL YQCM pre-treatment could restore the cell viability by 97.45% and increase ΔΨM (2-fold higher). YQCM pre-treatment also reduced γH2AX and cleaved caspase-3 protein levels.

CONCLUSIONS

Our study suggested that YQCM prevents ARHL by modulating the apoptosis process in auditory hair cells. Moreover, this study proved that bioinformatics analysis combined with molecular docking and cell model is a promising method to explore other possible pharmacological interventions of ARHL.

Effects of Diet and Lifestyle on Audio-Vestibular Dysfunction in the Elderly: A Literature Review

BACKGROUND

The world's age-related health concerns continue to rise. Audio-vestibular disorders, such as hearing loss, tinnitus, and vertigo, are common complaints in the elderly and are associated with social and public health burdens. Various preventative measures can ease their impact, including healthy food consumption, nutritional supplementation, and lifestyle modification. We aim to provide a comprehensive summary of current possible strategies for preventing the age-related audio-vestibular dysfunction.

METHODS

A PubMed, Embase, and Cochrane review databases search was conducted to identify the relationship between diet, lifestyle, and audio-vestibular dysfunction. "Diet", "nutritional supplement", "lifestyle", "exercise", "physical activity", "tinnitus", "vertigo" and "age-related hearing loss" were used as keywords.

RESULTS

Audio-vestibular dysfunction develops and progresses as a result of age-related inflammation and oxidative stress. Diets with anti-inflammatory and antioxidant effects have been proposed to alleviate this illness. A high-fat diet may induce oxidative stress and low protein intake is associated with hearing discomfort in the elderly. Increased carbohydrate and sugar intake positively correlate with the incidence of audio-vestibular dysfunction, whereas a Mediterranean-style diet can protect against the disease. Antioxidants in the form of vitamins A, C, and E; physical activity; good sleep quality; smoking cessation; moderate alcohol consumption; and avoiding noise exposure are also beneficial.

CONCLUSIONS

Adequate diet or nutritional interventions with lifestyle modification may protect against developing audio-vestibular dysfunction in elderly individuals.

Preventive Effect of Cocoa Flavonoids via Suppression of Oxidative Stress-Induced Apoptosis in Auditory Senescent Cells

Presbycusis or Age-related hearing loss (ARHL) is a sensorineural hearing loss that affects communication, leading to depression and social isolation. Currently, there are no effective treatments against ARHL. It is known that cocoa products have high levels of polyphenol content (mainly flavonoids), that are potent anti-inflammatory and antioxidant agents with proven benefits for health. The objective is to determine the protective effect of cocoa at the cellular and molecular levels in Presbycusis. For in vitro study, we used House Ear Institute-Organ of Corti 1 (HEI-OC1), stria vascularis (SV-k1), and organ of Corti (OC-k3) cells (derived from the auditory organ of a transgenic mouse). Each cell line was divided into a control group (CTR) and an H₂O₂ group (induction of senescence by an oxygen radical). Additionally, every group of every cell line was treated with the cocoa polyphenolic extract (CPE), measuring different markers of apoptosis, viability, the activity of antioxidant enzymes, and oxidative/nitrosative stress. The data show an increase of reactive oxidative and nitrogen species (ROS and RNS, respectively) in senescent cells compared to control ones. CPE treatment effectively reduced these high levels and correlated with a significant reduction in apoptosis cells by inhibiting the mitochondrial-apoptotic pathway. Furthermore, in senescence cells, the activity of antioxidant enzymes (Superoxide dismutase, SOD; Catalase, CAT; and Glutathione peroxidase, GPx) was recovered after CPE treatment. Administration of CPE also decreased oxidative DNA damage in the auditory senescent cells. In conclusion, CPE inhibits the activation of senescence-related apoptotic signaling by decreasing oxidative stress in auditory senescent cells.

A potassium channel agonist protects hearing function and promotes outer hair cell survival in a mouse model for age-related hearing loss

Age-related hearing loss (ARHL) is the most common sensory impairment mainly caused by degeneration of sensory hair cells in the cochlea with no causal medical treatment available. Auditory function and sensory hair cell survival critically depend on the Kv7.4 (KCNQ4) channel, a voltage-gated potassium channel expressed in outer hair cells (OHCs), with its impaired function or reduced activity previously associated with ARHL. Here, we investigated the effect of a potent small-molecule Kv7.4 agonist on ARHL in the senescence-accelerated mouse prone 8 (SAMP8) model. For the first time in vivo, we show that Kv7.4 activation can significantly reduce age-related threshold shifts of auditory brainstem responses as well as OHC loss in the SAMP8 model. Pharmacological activation of Kv7.4 thus holds great potential as a therapeutic approach for ARHL as well as other hearing impairments related to Kv7.4 function.

A Comprehensive Overview of the Complex Role of Oxidative Stress in Aging, The Contributing Environmental Stressors and Emerging Antioxidant Therapeutic Interventions

Introduction

Aging is a normal, inevitable, irreversible, and progressive process which is driven by internal and external factors. Oxidative stress, that is the imbalance between prooxidant and antioxidant molecules favoring the first, plays a key role in the pathophysiology of aging and comprises one of the molecular mechanisms underlying age-related diseases. However, the oxidative stress theory of aging has not been successfully proven in all animal models studying lifespan, meaning that altering oxidative stress/antioxidant defense systems did not always lead to a prolonged lifespan, as expected. On the other hand, animal models of age-related pathological phenotypes showed a well-correlated relationship with the levels of prooxidant molecules. Therefore, it seems that oxidative stress plays a more complicated role than the one once believed and this role might be affected by the environment of each organism. Environmental factors such as UV radiation, air pollution, and an unbalanced diet, have also been implicated in the pathophysiology of aging and seem to initiate this process more rapidly and even at younger ages.

Aim

The purpose of this review is to elucidate the role of oxidative stress in the physiology of aging and the effect of certain environmental factors in initiating and sustaining this process. Understanding the pathophysiology of aging will contribute to the development of strategies to postpone this phenomenon. In addition, recent studies investigating ways to alter the antioxidant defense mechanisms in order to prevent aging will be presented.

Conclusions

Careful exposure to harmful environmental factors and the use of antioxidant supplements could potentially affect the biological processes driving aging and slow down the development of age-related diseases. Maybe a prolonged lifespan could not be achieved by this strategy alone, but a longer healthspan could also be a favorable target.

New Genetic Variants in CYP2B6 and SLC6A Support the Role of Oxidative Stress in Familial Ménière’s Disease

The objective was to study the genetic etiology of Ménière’s disease (MD) using next-generation sequencing in three families with three cases of MD. Whole exome sequencing was used to identify rare genetic variants co-segregating with MD in Finnish families. In silico estimations and population databases were used to estimate the frequency and pathogenicity of the variants. Variants were validated and genotyped from additional family members using capillary sequencing. A geneMANIA analysis was conducted to investigate the functional pathways and protein interactions of candidate genes. Seven rare variants were identified to co-segregate with MD in the three families: one variant in the CYP2B6 gene in family I, one variant in GUSB and EPB42 in family II, and one variant in each of the SLC6A, ASPM, KNTC1, and OVCH1 genes in family III. Four of these genes were linked to the same co-expression network with previous familial MD candidate genes. Dysfunction of CYP2B6 and SLC6A could predispose to MD via the oxidative stress pathway. Identification of ASPM and KNTC1 as candidate genes for MD suggests dysregulation of mitotic spindle formation in familial MD. The genetic etiology of familial MD is heterogenic. Our findings suggest a role for genes acting on oxidative stress and mitotic spindle formation in MD but also highlight the genetic complexity of MD.

Oxidative Stress and 4-hydroxy-2-nonenal (4-HNE): Implications in the Pathogenesis and Treatment of Aging-related Diseases

Oxidative stress plays an important role in the development of aging-related diseases by accelerating the lipid peroxidation of polyunsaturated fatty acids in the cell membrane, resulting in the production of aldehydes, such as malondialdehyde and 4-hydroxy-2-nonenal (4-HNE) and other toxic substances. The compound 4-HNE forms adducts with DNA or proteins, disrupting many cell signaling pathways including the regulation of apoptosis signal transduction pathways. The binding of proteins to 4-HNE (4-HNE-protein) acts as an important marker of lipid peroxidation, and its increasing concentration in brain tissues and fluids because of aging, ultimately gives rise to some hallmark disorders, such as neurodegenerative diseases (Alzheimer's and Parkinson's diseases), ophthalmic diseases (dry eye, macular degeneration), hearing loss, and cancer. This review aims to describe the physiological origin of 4-HNE, elucidate its toxicity in aging-related diseases, and discuss the detoxifying effect of aldehyde dehydrogenase and glutathione in 4-HNE-driven aging-related diseases.

Nitric oxide protects against cochlear hair cell damage and noise-induced hearing loss through glucose metabolic reprogramming

Nitric oxide (NO) is critically involved in the regulation of a wide variety of physiological and pathophysiological processes. However, the role of NO in the pathogenesis of noise-induced hearing loss (NIHL) is complex and remains controversial. Here we reported that treatment of CBA/J mice with l-arginine, a physiological precursor of NO, significantly reduced noise-induced reactive oxygen species accumulation in outer hair cells (OHCs), attenuated noise-induced loss of OHCs and NIHL consequently. Conversely, pharmacological inhibition of endothelial nitric oxide synthase exacerbated noise-induced loss of OHCs and aggravated NIHL. In HEI-OC1 cells, NO also showed substantial protection against H₂O₂-induced oxidative stress and cytotoxicity. Mechanistically, NO increased S-nitrosylation of pyruvate kinase M2 (PKM2) and inhibited its activity, which thus diverted glucose metabolic flux from glycolysis into the pentose phosphate pathway to increase production of reducing equivalents (NADPH and GSH) and eventually prevented H₂O₂-induced oxidative damage. These findings open new avenues for protection of cochlear hair cells from oxidative stress and prevention of NIHL through NO modulation of PKM2 and glucose metabolism reprogramming.

ROS-Induced Oxidative Damage and Mitochondrial Dysfunction Mediated by Inhibition of SIRT3 in Cultured Cochlear Cells

Sensorineural hearing loss (SNHL) is one of the most common causes of disability worldwide. Previous evidence suggests that reactive oxygen species (ROS) may play an important role in the occurrence and development of SNHL, while its mechanism remains unclear. We cultured dissected organs of Corti in medium containing different concentrations (0, 0.25, 0.5, 0.75, 1, and 1.25 mM) of hydrogen peroxide (H₂O₂) and established a four-concentration model of 0, 0.5, 0.75, and 1 mM to study different degrees of damage. We examined ROS-induced mitochondrial damage and the role of sirtuin 3 (SIRT3). Our results revealed that the number of ribbon synapses and hair cells appeared significantly concentration-dependent decrease with exposure to H₂O₂. Outer hair cells (OHCs) and inner hair cells (IHCs) began to be lost, and activation of apoptosis of hair cells (HCs) was observed at 0.75 mM and 1 mM H₂O₂, respectively. In contrast with the control group, the accumulation of ROS was significantly higher, and the mitochondrial membrane potential (MMP) was lower in the H₂O₂-treated groups. Furthermore, the expression of SIRT3, FOXO3A, and SOD2 proteins declined, except for an initial elevation of SIRT3 between 0 and 0.75 mM H₂O₂. Administration of the selective SIRT3 inhibitor 3-(1H-1,2,3-triazol-4-yl) pyridine resulted in increased damage to the cochlea, including loss of ribbon synapses and hair cells, apoptosis of hair cells, more production of ROS, and reduced mitochondrial membrane potential. Thoroughly, our results highlight that ROS-induced mitochondrial oxidative damage drives hair cell degeneration and apoptosis. Furthermore, SIRT3 is crucial for preserving mitochondrial function and protecting the cochlea from oxidative damage and may represent a possible therapeutic target for SNHL.

The Link between Gut Dysbiosis Caused by a High-Fat Diet and Hearing Loss

This review aims to provide a conceptual and theoretical overview of the association between gut dysbiosis and hearing loss. Hearing loss is a global health issue; the World Health Organisation (WHO) estimates that 2.5 billion people will be living with some degree of hearing loss by 2050. The aetiology of sensorineural hearing loss (SNHL) is complex and multifactorial, arising from congenital and acquired causes. Recent evidence suggests that impaired gut health may also be a risk factor for SNHL. Inflammatory bowel disease (IBD), type 2 diabetes, diet-induced obesity (DIO), and high-fat diet (HFD) all show links to hearing loss. Previous studies have shown that a HFD can result in microangiopathy, impaired insulin signalling, and oxidative stress in the inner ear. A HFD can also induce pathological shifts in gut microbiota and affect intestinal barrier (IB) integrity, leading to a leaky gut. A leaky gut can result in chronic systemic inflammation, which may affect extraintestinal organs. Here, we postulate that changes in gut microbiota resulting from a chronic HFD and DIO may cause a systemic inflammatory response that can compromise the permeability of the blood-labyrinth barrier (BLB) in the inner ear, thus inducing cochlear inflammation and hearing deficits.

A Screen of Autophagy Compounds Implicates the Proteasome in Mammalian Aminoglycoside-Induced Hair Cell Damage

Introduction: Autophagy is a degradative pathway to safely break down and recycle dysfunctional cellular components. There is prior evidence of autophagy participation during hair cell (HC) damage. Our goal was to screen compounds targeting different aspects of autophagy for their effects on HC loss due to an ototoxic aminoglycoside, gentamicin (GM).

Methods: The SELLECKChem autophagy compound library, consisting of 154 compounds with defined autophagy inducing or inhibitory activity, was used for targeted screening in vitro model of ototoxicity. Organ of Corti from postnatal days 3–5 pou4f3/GFP transgenic mice (HCs express green fluorescent protein) were utilized. The organs were micro-dissected, and basal and middle turns divided into micro-explants individually placed into the single wells of a 96-well plate. Samples were treated with 200 μM of GM plus three dosages of tested compound and cultured for 72 h. Negative controls were treated with media only; positive ototoxicity controls were treated with GM only.

Results: The majority of the library compounds had no effect on GM-induced HC loss. However, 18 compounds exhibited a significant, protective effect, two compounds were protective at low dosage but showed enhanced GM toxicity at higher doses and one compound was toxic to HCs in the absence of GM.

Conclusions: This study evaluated many autophagy compounds that have not been tested previously on HCs. The disparate results obtained underscore the complexity of autophagy events that can influence HC responses to aminoglycosides, but also implicate the proteosome as an important damage mechanism. The screening results can serve as basis for further studies with protective compounds as potential drug targets.

Metformin protects against inflammation, oxidative stress to delay poly I:C-induced aging-like phenomena in gut of an annual fish

Metformin, a clinical agent of type 2 diabetes, is reported as a potential geroprotector. Viral infection induces phenotypes of senescence in human T cells, and polyinosinic:polycytidylic acid (poly I:C), a viral mimic, induces upregulation of SA-β-gal activity in ovary of the annual fish Nothobranchius guentheri. However, the effects and mechanisms of metformin on poly I:C-induced aging-like phenomena are poorly understood in vertebrates. In this study, the activity of SA-β-gal increased in gut of 12-month-old fish and poly I:C-injected 6-month-old fish, compared to 6-month-old control fish, indicating that poly I:C induces aging-like phenomena in gut of the fish. Metformin supplementation retarded accumulation of SA-β-gal in gut of old fish and poly I:C-treated young fish. The results of q-PCR analysis showed that metformin reduced NF-κB mediated inflammatory response including decreased level of pro-inflammatory cytokine IL-8 and increased expression of anti-inflammatory cytokine IL-10 in gut of the fish with natural aging and poly I:C-injected 6-month-old fish. Metformin also exhibited antioxidant effects, as it reduced ROS production which is associated with the upregulation of FoxO3a and PGC-1α in gut of 6-month-old fish with poly I:C-injection. Expression of AMPK and SIRT1 was reduced in gut of 6-month-old fish with poly I:C-treatment, and feeding metformin reversed these declines. Taken together, the present study suggested that poly I:C-injection led to aging-like phenomena in gut and metformin activated AMPK and SIRT1 to reduce NF-κB mediated inflammation and resist oxidative stress via enhanced expression of FoxO3a and PGC-1α, and finally delayed gut aging in vertebrates.

Quercetin Prevents Oxidative Stress-Induced Injury of Periodontal Ligament Cells and Alveolar Bone Loss in Periodontitis

Purpose

Emerging evidence has indicated that oxidative stress (OS) contributes to periodontitis. Periodontal ligament cells (PDLCs) are important for the regeneration of periodontal tissue. Quercetin, which is extracted from fruits and vegetables, has strong antioxidant capabilities. However, whether and how quercetin affects oxidative damage in PDLCs during periodontitis remains unknown. The aim of this study was to assess the effects of quercetin on oxidative damage in PDLCs and alveolar bone loss in periodontitis and underlying mechanisms.

Materials and Methods

The tissue block culture method was used to extract human PDLCs (hPDLCs). First, a cell counting kit 8 (CCK-8) assay was used to identify the optimal concentrations of hydrogen peroxide (H₂O₂) and quercetin. Subsequently, a 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) probe, RT-qPCR, Western blotting and other methods were used to explore the effects of quercetin on OS in hPDLCs and the underlying mechanism. Finally, quercetin was administered to mice with periodontitis through gavage, and the effect of quercetin on the level of OS and alveolar bone resorption in these mice was observed by immunofluorescence, microcomputed tomography (micro-CT), hematoxylin and eosin staining (H&E) staining and so on.

Results

Quercetin at 5 μM strongly activated NF-E2-related factor 2 (NRF2) signaling, alleviated oxidative damage and enhanced the antioxidant capacity of hPDLCs. In addition, quercetin reduced cellular senescence and protected the osteogenic ability of hPDLCs. Finally, quercetin activated NRF2 signaling in the periodontal ligaments, reduced the OS level of mice with periodontitis, and slowed the absorption of alveolar bone in vivo.

Conclusion

Quercetin can increase the antioxidant capacity of PDLCs and reduce OS damage by activating the NRF2 signaling pathway, which alleviates alveolar bone loss in periodontitis.

Auditory Threshold Variability in the SAMP8 Mouse Model of Age-Related Hearing Loss: Functional Loss and Phenotypic Change Precede Outer Hair Cell Loss

Age-related hearing loss (ARHL) is the most common sensory deficit in aging society, which is accompanied by increased speech discrimination difficulties in noisy environments, social isolation, and cognitive decline. The audiometric degree of ARHL is largely correlated with sensory hair cell loss in addition to age-related factors not captured by histopathological analysis of the human cochlea. Previous studies have identified the senescence-accelerated mouse prone strain 8 (SAMP8) as a model for studying ARHL and age-related modifications of the cochlear redox environment. However, the SAMP8 population exhibits a large variability in auditory function decline over age, whose underlying cause remains unknown. In this study, we analyzed auditory function of SAMP8 mice by measuring auditory brainstem response (ABR) thresholds at the age of 6 weeks (juvenile), 12 weeks (young adult), and 24 weeks (adult). Consistent with previous studies, SAMP8 mice exhibit an early progressive, age-related decline of hearing acuity. However, a spatiotemporal cytohistological analysis showed that the significant increase in threshold variability was not concurrently reflected in outer hair cell (OHC) loss observed in the lower and upper quartiles of the ABR threshold distributions over age. This functional loss was found to precede OHC loss suggesting that age-related phenotypic changes may be contributing factors not represented in cytohistological analysis. The expression of potassium channels KCNQ4 (K_V7.4), which mediates the current I_K,n crucial for the maintenance of OHC membrane potential, and KCNQ1 (K_V7.1), which is an essential component in potassium circulation and secretion into the endolymph generating the endocochlear potential, showed differences between these quartiles and age groups. This suggests that phenotypic changes in OHCs or the stria vascularis due to variable oxidative deficiencies in individual mice may be predictors of the observed threshold variability in SAMP8 mice and their progressive ARHL. In future studies, further phenotypic predictors affected by accumulated metabolic challenges over age need to be investigated as potentially underlying causes of ARHL preceding irreversible OHC loss in the SAMP8 mouse model.

Hydrogen peroxide toxicity on auditory cells: An in vitro study

In recent decades, interest has increased in the role of reactive oxygen species (ROS) in health and disease. The ROS are key causative factors in several hearing loss pathologies including ototoxicity, noise trauma, cochlear ageing and ischemic injury. In order to investigate ROS effects on inner ear cells and counteract them, we developed an in vitro model of oxidative stress by exposing the inner ear cell line OC-k3 to hydrogen peroxide (H₂O₂) at concentrations able to affect in vivo cellular components but allowing cell survival. The treatment with high concentrations (20 and 30 μM) resulted in reduction of cell viability, activation of apoptosis/necrosis and alteration of morphology, cell cycle progression and antioxidant defences. The ROS effects in inner ear cells are difficult to assess in vivo. Organocultures may provide preservation of tissue architecture but involve ethical issues and can be used only for a limited time. An in vitro model that could be commercially available and easy to handle is necessary to investigate inner ear oxidative stress and the ways to counteract it. The OC-k3 line is a suitable in vitro model to study ROS effects on inner ear cells because the observed cell alterations and damages were similar to those reported in studies investigating ROS effects of ototoxic drugs, noise trauma and cochlear ageing.

Autophagy-Based Unconventional Secretory for AIM2 Inflammasome Drives DNA Damage Resistance During Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) is the primary cause of low back pain. Stress-induced DNA damage is closely relevant to the pathogenesis of IDD; however, the underlying mechanisms remain unclear. This study investigated the role of the absent in melanoma 2 (AIM2) inflammasome as a DNA damage sensor in nucleus pulposus (NP) cells. We found that the level of AIM2 increased in degenerated discs and was correlated to the degree of IDD. Knockdown of AIM2 ameliorated H₂O₂-induced DNA damage and apoptosis in NP cells in vitro, and retarded the progression of IDD in vivo. Furthermore, the induction of autophagy protected against cellular DNA damage via the unconventional secretion of AIM2. We further identified the Golgi re-assembly and stacking protein 55 (GRASP55) as mediator of the transport and secretion of AIM2 via an autophagic pathway. Taken together, our researches illustrate the role and regulatory mechanism of the AIM2 inflammasome during IDD. Targeting the AIM2 inflammasome may offer a promising therapeutic strategy for patients with IDD.

SAMP8 Mice as a Model of Age-Related Cognition Decline with Underlying Mechanisms in Alzheimer's Disease

Alzheimer's disease (AD) is a highly age-related cognitive decline frequently attacking the elderly. Senescence-accelerated mouse-prone 8 (SAMP8) is an ideal model to study AD, displaying age-related learning and memory disorders. SAMP8 mice exhibit most features of pathogenesis of AD, including an abnormal expression of anti-aging factors, oxidative stress, inflammation, amyloid-β (Aβ) deposits, tau hyperphosphorylation, endoplasmic reticulum stress, abnormal autophagy activity, and disruption of intestinal flora. SAMP8 mice, therefore, have visualized the understanding of AD, and also provided effective ways to find new therapeutic targets. This review focused on the age-related pathogenesis in SAMP8 mice, to advance the understanding of age-related learning and memory decline and clarify the mechanisms. Furthermore, this review will provide extensive foundations for SAMP8 mice used in therapeutics for AD.

Mitochondrial Dysfunction and Sirtuins: Important Targets in Hearing Loss

Mitochondrial dysfunction has been suggested to be a risk factor for sensorineural hearing loss (SNHL) induced by aging, noise, ototoxic drugs, and gene. Reactive oxygen species (ROS) are mainly derived from mitochondria, and oxidative stress induced by ROS contributes to cochlear damage as well as mitochondrial DNA mutations, which may enhance the sensitivity and severity of hearing loss and disrupt ion homeostasis (e.g., Ca2+ homeostasis). The formation and accumulation of ROS further undermine mitochondrial components and ultimately lead to apoptosis and necrosis. SIRT3–5, located in mitochondria, belong to the family of sirtuins, which are highly conserved deacetylases dependent on nicotinamide adenine dinucleotide (NAD+). These deacetylases regulate diverse cellular biochemical activities. Recent studies have revealed that mitochondrial sirtuins, especially SIRT3, modulate ROS levels in hearing loss pathologies. Although the precise functions of SIRT4 and SIRT5 in the cochlea remain unclear, the molecular mechanisms in other tissues indicate a potential protective effect against hearing loss. In this review, we summarize the current knowledge regarding the role of mitochondrial dysfunction in hearing loss, discuss possible functional links between mitochondrial sirtuins and SNHL, and propose a perspective that SIRT3–5 have a positive effect on SNHL.

Senescence in Post-Mitotic Cells: A Driver of Aging?

Significance: Cell senescence was originally defined by an acute loss of replicative capacity and thus believed to be restricted to proliferation-competent cells. More recently, senescence has been recognized as a cellular stress and damage response encompassing multiple pathways or senescence domains, namely DNA damage response, cell cycle arrest, senescence-associated secretory phenotype, senescence-associated mitochondrial dysfunction, autophagy/mitophagy dysfunction, nutrient and stress signaling, and epigenetic reprogramming. Each of these domains is activated during senescence, and all appear to interact with each other. Cell senescence has been identified as an important driver of mammalian aging. Recent Advances: Activation of all these senescence domains has now also been observed in a wide range of post-mitotic cells, suggesting that senescence as a stress response can occur in nondividing cells temporally uncoupled from cell cycle arrest. Here, we review recent evidence for post-mitotic cell senescence and speculate about its possible relevance for mammalian aging. Critical Issues: Although a majority of senescence domains has been found to be activated in a range of post-mitotic cells during aging, independent confirmation of these results is still lacking for most of them. Future Directions: To define whether post-mitotic senescence plays a significant role as a driver of aging phenotypes in tissues such as brain, muscle, heart, and others. Antioxid. Redox Signal. 34, 308-323.

Glucose Protects Cochlear Hair Cells Against Oxidative Stress and Attenuates Noise-Induced Hearing Loss in Mice

Oxidative stress is the key determinant in the pathogenesis of noise-induced hearing loss (NIHL). Given that cellular defense against oxidative stress is an energy-consuming process, the aim of the present study was to investigate whether increasing energy availability by glucose supplementation protects cochlear hair cells against oxidative stress and attenuates NIHL. Our results revealed that glucose supplementation reduced the noise-induced formation of reactive oxygen species (ROS) and consequently attenuated noise-induced loss of outer hair cells, inner hair cell synaptic ribbons, and NIHL in CBA/J mice. In cochlear explants, glucose supplementation increased the levels of ATP and NADPH, as well as attenuating H₂O₂-induced ROS production and cytotoxicity. Moreover, pharmacological inhibition of glucose transporter type 1 activity abolished the protective effects of glucose against oxidative stress in HEI-OC1 cells. These findings suggest that energy availability is crucial for oxidative stress resistance and glucose supplementation offers a simple and effective approach for the protection of cochlear hair cells against oxidative stress and NIHL.

Age-related hearing loss pertaining to potassium ion channels in the cochlea and auditory pathway

Age-related hearing loss (ARHL) is the most prevalent sensory deficit in the elderly and constitutes the third highest risk factor for dementia. Lifetime noise exposure, genetic predispositions for degeneration, and metabolic stress are assumed to be the major causes of ARHL. Both noise-induced and hereditary progressive hearing have been linked to decreased cell surface expression and impaired conductance of the potassium ion channel K_V7.4 (KCNQ4) in outer hair cells, inspiring future therapies to maintain or prevent the decline of potassium ion channel surface expression to reduce ARHL. In concert with K_V7.4 in outer hair cells, K_V7.1 (KCNQ1) in the stria vascularis, calcium-activated potassium channels BK (KCNMA1) and SK2 (KCNN2) in hair cells and efferent fiber synapses, and K_V3.1 (KCNC1) in the spiral ganglia and ascending auditory circuits share an upregulated expression or subcellular targeting during final differentiation at hearing onset. They also share a distinctive fragility for noise exposure and age-dependent shortfalls in energy supply required for sustained surface expression. Here, we review and discuss the possible contribution of select potassium ion channels in the cochlea and auditory pathway to ARHL. We postulate genes, proteins, or modulators that contribute to sustained ion currents or proper surface expressions of potassium channels under challenging conditions as key for future therapies of ARHL.

G6PD overexpression protects from oxidative stress and age-related hearing loss

Aging of the auditory system is associated with the incremental production of reactive oxygen species (ROS) and the accumulation of oxidative damage in macromolecules, which contributes to cellular malfunction, compromises cell viability, and, ultimately, leads to functional decline. Cellular detoxification relies in part on the production of NADPH, which is an important cofactor for major cellular antioxidant systems. NADPH is produced principally by the housekeeping enzyme glucose‐6‐phosphate dehydrogenase (G6PD), which catalyzes the rate‐limiting step in the pentose phosphate pathway. We show here that G6PD transgenic mice (G6PD‐Tg), which show enhanced constitutive G6PD activity and NADPH production along life, have lower auditory thresholds than wild‐type mice during aging, together with preserved inner hair cell (IHC) and outer hair cell (OHC), OHC innervation, and a conserved number of synapses per IHC. Gene expression of antioxidant enzymes was higher in 3‐month‐old G6PD‐Tg mice than in wild‐type counterparts, whereas the levels of pro‐apoptotic proteins were lower. Consequently, nitration of proteins, mitochondrial damage, and TUNEL⁺ apoptotic cells were all lower in 9‐month‐old G6PD‐Tg than in wild‐type counterparts. Unexpectedly, G6PD overexpression triggered low‐grade inflammation that was effectively resolved in young mice, as shown by the absence of cochlear cellular damage and macrophage infiltration. Our results lead us to propose that NADPH overproduction from an early stage is an efficient mechanism to maintain the balance between the production of ROS and cellular detoxification power along aging and thus prevents hearing loss progression.

Pursuing the Elixir of Life: In Vivo Antioxidative Effects of Manganosalen Complexes

Manganosalen complexes are coordination compounds that possess a chelating salen-type ligand, a class of bis-Schiff bases obtained by condensation of salicylaldehyde and a diamine. They may act as catalytic antioxidants mimicking both the structure and the reactivity of the native antioxidant enzymes active site. Thus, manganosalen complexes have been shown to exhibit superoxide dismutase, catalase, and glutathione peroxidase activities, and they could potentially facilitate the scavenging of excess reactive oxygen species (ROS), thereby restoring the redox balance in damaged cells and organs. Initial catalytic studies compared the potency of these compounds as antioxidants in terms of rate constants of the chemical reactivity against ROS, giving catalytic values approaching and even exceeding that of the native antioxidative enzymes. Although most of these catalytic studies lack of biological relevance, subsequent in vitro studies have confirmed the efficiency of many manganosalen complexes in oxidative stress models. These synthetic catalytic scavengers, cheaper than natural antioxidants, have accordingly attracted intensive attention for the therapy of ROS-mediated injuries. The aim of this review is to focus on in vivo studies performed on manganosalen complexes and their activity on the treatment of several pathological disorders associated with oxidative damage. These disorders, ranging from the prevention of fetal malformations to the extension of lifespan, include neurodegenerative, inflammatory, and cardiovascular diseases; tissue injury; and other damages related to the liver, kidney, or lungs.

Biocompatibility of Bone Marrow-Derived Mesenchymal Stem Cells in the Rat Inner Ear following Trans-Tympanic Administration

Recent advancements in stem cell therapy have led to an increased interest within the auditory community in exploring the potential of mesenchymal stem cells (MSCs) in the treatment of inner ear disorders. However, the biocompatibility of MSCs with the inner ear, especially when delivered non-surgically and in the immunocompetent cochlea, is not completely understood. In this study, we determined the effect of intratympanic administration of rodent bone marrow MSCs (BM-MSCs) on the inner ear in an immunocompetent rat model. The administration of MSCs did not lead to the generation of any oxidative stress in the rat inner ear. There was no significant production of proinflammatory cytokines, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-12, due to BM-MSCs administration into the rat cochlea. BM-MSCs do not activate caspase 3 pathway, which plays a central role in sensory cell damage. Additionally, transferase dUTP nick end labeling (TUNEL) staining determined that there was no significant cell death associated with the administration of BM-MSCs. The results of the present study suggest that trans-tympanic administration of BM-MSCs does not result in oxidative stress or inflammatory response in the immunocompetent rat cochlea.

Probiotic bacteria as modulators of cellular senescence: emerging concepts and opportunities

Probiotic bacteria are increasingly gaining importance in human nutrition owing to their multifaceted health beneficial effects. Studies have also shown that probiotic supplementation is useful in mitigating age-associated oxi-inflammatory stress, immunosenescence, and gut dysbiosis thereby promoting health and longevity. However, our current understanding of the process of aging suggests a strong interrelationship between the accumulation of senescent cells and the development of aging phenotype, including the predisposition to age-related disorders. The present review studies the documented pro-longevity effects of probiotics and highlights how these beneficial attributes of probiotics could be related to the mitigation of cellular senescence. We present a perspective that to fully understand and comprehend the anti-aging characteristics of probiotic bacteria; it is imperative that probiotics or their synbiotic amalgamation with plant polyphenols, be studied under the purview of cellular senescence, that may ultimately help devise probiotic-based anti-senescence strategies.

D-Galactose-induced oxidative stress and mitochondrial dysfunction in the cochlear basilar membrane: an in vitro aging model

The cochlear basilar membrane (CBM) contains inner hair cells and outer hair cells that convert sound waves into electrical signals and transmit them to the central auditory system. Cochlear aging, the primary reason of age-related hearing loss, can reduce the signal transmission capacity. There is no ideal in vitro aging model of the CBM. In this study, we cultured the CBM, which was dissected from the cochlea of the C57BL/6 mice 5 days after birth, in a medium containing 20 mg/mL, 40 mg/mL, or 60 mg/mL D-galactose (D-gal). Compared with the control group, the levels of senescence-associated β-galactosidase were increased in a concentration-dependent manner in the CBM of the D-gal groups. In addition, levels of the mitochondrial superoxide and patterns of an age-related mitochondrial DNA3860-bp deletion were significantly increased. The ATP levels and the membrane potential of the mitochondrial were significantly decreased in the CBM of the D-gal groups compared with the control group. Furthermore, in comparison with the control group, damaged hair cell stereocilia and a loss of inner hair cell ribbon synapses were observed in the CBM of the D-gal groups. A loss of hair cells and activation of caspase-3-mediated outer hair cell apoptosis were also observed in the CBM of the high-dose D-gal group. These insults induced by D-gal in the CBM in vitro were similar to the ones that occur in cochlear natural aging in vivo. Thus, we believe that this is a successful in vitro aging model using cultured CBM. These results demonstrate the effects of mitochondrial oxidative damage on presbycusis and provide a reliable aging model to study the mechanisms of presbycusis in vitro.