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

Effects of fluoxetine on the gene expression of hippocampus and gap inhibition in noise-induced hearing loss rats

OBJECTIVE

Fluoxetine was reported to restore critical period-like neural plasticity via alleviating perineuronal nets (PNNs). This study aimed to investigate the effect of fluoxetine on auditory processing and PNNs in auditory cortex and hippocampus.

METHODS

Sprague-Dawley rats were exposed 2-20 kHz, 115 dB sound pressure level noise for 3 h per day from postnatal day 1-3 to postnatal day 21. After completion of noise exposure, 10 mg/kg/day of fluoxetine was administered for 19 days. There were four groups of rats according to the presence of noise exposure and fluoxetine treatment, vehicle, noise + vehicle, fluoxetine, and noise + fluoxetine rats. The gene expression changes of hippocampus were analyzed using RNA sequencing.

RESULTS

In the auditory cortex, the expression of aggrecan (ACAN) was lower in noise-exposed rats than vehicle rats, while the noise + fluoxetine rats presented higher expression levels of ACAN which was comparable with that of the vehicle rats (p = 0.01 in Mann-Whitney U test; 146 ± 15 vs. 100 ± 11). In the hippocampus, the expression of brain-derived neurotrophic factor (BDNF) was lower in noise + vehicle rats while noise + fluoxetine rats presented higher expression of BDNF than noise + vehicle rats (p < 0.001 in Mann-Whitney U test; 389 ± 21 vs. 249 ± 16). The RNA sequencing of the hippocampus predicted the down regulation of genes involving extracellular matrix organization when compared noise + vehicle vs. noise + fluoxetine rats.

CONCLUSION

The fluoxetine administration in noise exposed rats improved the gap inhibition ability. The noise exposure decreased expression of BDNF and modulated the expression of genes related with extracellular matrix organization which was partially reversed after fluoxetine treatment.

Advancements of ROS-based biomaterials for sensorineural hearing loss therapy

Sensorineural hearing loss (SNHL) represents a substantial global health challenge, primarily driven by oxidative stress-induced damage within the auditory system. Excessive reactive oxygen species (ROS) play a pivotal role in this pathological process, leading to cellular damage and apoptosis of cochlear hair cells, culminating in irreversible hearing impairment. Recent advancements have introduced ROS-scavenging biomaterials as innovative, multifunctional platforms capable of mitigating oxidative stress. This comprehensive review systematically explores the mechanisms of ROS-mediated oxidative stress in SNHL, emphasizing etiological factors such as aging, acoustic trauma, and ototoxic medication exposure. Furthermore, it examines the therapeutic potential of ROS-scavenging biomaterials, positioning them as promising nanomedicines for targeted antioxidant intervention. By critically assessing recent advances in biomaterial design and functionality, this review thoroughly evaluates their translational potential for clinical applications. It also addresses the challenges and limitations of ROS-neutralizing strategies, while highlighting the transformative potential of these biomaterials in developing novel SNHL treatment modalities. This review advocates for continued research and development to integrate ROS-scavenging biomaterials into future clinical practice, aiming to address the unmet needs in SNHL management and potentially revolutionize the treatment landscape for this pervasive health issue.

Neurovascular coupling dysfunction associated with inflammatory factors in sudden sensorineural hearing loss

PURPOSE

The neuropathologic mechanisms of sudden sensorineural hearing loss (SSNHL) are unknown. The aim of this study was to investigate the alterations of neurovascular coupling (NVC) in patients with SSNHL and its association with hematologic inflammatory factors.

METHODS

The amplitude of low-frequency fluctuations (ALFF), fractional amplitude of low-frequency fluctuations (fALFF), regional homogeneity (ReHo), and degree centrality (DC) were calculated in 48 patients with SSNHL and 54 age-, gender-, and education-matched healthy control (HC), and also utilized the arterial spin labeling imaging (ASL) to calculate cerebral blood flow (CBF). Four indices of NVC (CBF-ALFF, CBF-fALFF, CBF-ReHo, and CBF-DC) in the whole brain gray matter as well as the NVC ratio were compared between two groups. In addition, correlation analyses were performed with inflammatory factors for the NVC indexes at the global level and regional level, respectively.

RESULTS

The NVC at global level was lower in SSNHL group than in HC, except for CBF-ALFF. At the regional level, most of the brain regions with abnormal NVC in SSNHL patients involved auditory and sensorimotor language centers and limbic system compared to HC. In addition, both at the global and regional levels, NVC metrics were shown to correlate with partial inflammatory factors or hematologic parameters, including platelet-lymphocyte ratio (PLR), neutrophil-lymphocyte ratio (NLR), systemic immunoinflammatory index (SII), blood platelet count (PLT), and lymphocyte count (Lym).

CONCLUSION

From the view of the NVC metrics, these findings provide new perspectives on the neuropathologic mechanisms and clinical treatment of SSNHL.

Early transtympanic administration of rhBDNF exerts a multifaceted neuroprotective effect against cisplatin-induced hearing loss

BACKGROUND AND PURPOSE

Cisplatin-induced sensorineural hearing loss is a significant clinical challenge. Although the potential effects of brain-derived neurotrophic factor (BDNF) have previously been investigated in some ototoxicity models, its efficacy in cisplatin-induced hearing loss remains uncertain. This study aimed to investigate the therapeutic potential of recombinant human BDNF (rhBDNF) in protecting cells against cisplatin-induced ototoxicity.

EXPERIMENTAL APPROACH

Using an in vivo model of cisplatin-induced hearing loss, we investigated the beneficial effects of transtympanic administration of rhBDNF in a thermogel solution on hearing function and cochlear injury, using electrophysiological, morphological, immunofluorescence and molecular analyses.

KEY RESULTS

Our data showed that local rhBDNF treatment counteracted hearing loss in rats receiving cisplatin by preserving synaptic connections in the cochlear epithelium and protecting hair cells (HCs) and spiral ganglion neurons (SGNs) against cisplatin-induced cell death. Specifically, rhBDNF maintains the balance of its receptor levels (pTrkB and p75), boosting TrkB-CREB pro-survival signalling and reducing caspase 3-dependent apoptosis in the cochlea. Additionally, it activates antioxidant mechanisms while inhibiting inflammation and promoting vascular repair.

CONCLUSION AND IMPLICATIONS

Collectively, we demonstrated that early transtympanic treatment with rhBDNF plays a multifaceted protective role against cisplatin-induced ototoxicity, thus holding promise as a novel potential approach to preserve hearing in adult and paediatric patients undergoing cisplatin-based chemotherapy.

Rodent models in sensorineural hearing loss research: A comprehensive review

Sensorineural hearing loss (SNHL) constitutes a major global health challenge, affecting millions of individuals and substantially impairing social integration and quality of life. The complexity of the auditory system and the multifaceted nature of SNHL necessitate advanced methodologies to understand its etiology, progression, and potential therapeutic interventions. This review provides a comprehensive overview of the current animal models used in SNHL research, focusing on their selection based on specific characteristics and their contributions to elucidating pathophysiological mechanisms and evaluating novel treatment strategies. It discusses the most commonly used rodent models in hearing research, including mice, rats, guinea pigs, Mongolian gerbils, and chinchillas. Through a comparative analysis, this review underscores the importance of selecting models that align with specific research objectives in SNHL studies, discussing the advantages and limitations of each model. By advocating for a multidisciplinary approach that leverages the strengths of various animal models with technological advancements, this review aims to facilitate significant advancements in the prevention, diagnosis, and treatment of sensorineural hearing loss.

Sound and Alzheimer's Disease-From Harmful Noise to Beneficial Soundscape Augmentation and Music Therapy

Exposure to sound energy may be a risk factor or a therapeutic intervention for Alzheimer's disease (AD). On one hand, noise has a harmful effect on people with AD by contributing to hearing loss, sleep disturbance, oxidative stress, inflammation, and excitotoxicity. But on the other hand, clinical trials and nursing home interventions with soundscape augmentation involving natural sounds have shown promising results in alleviating psychophysiological symptoms in people with AD. Music therapy, an emerging non-pharmacological treatment, can improve cognition, reduce anxiety and depression, and enhance self-awareness in patients with AD. To ensure that music does not become noise in clinical trials, only favorite music at levels safe for hearing should be used. From a public health standpoint, noise countermeasures, soundscape augmentation with natural sounds, and active or passive engagement with music may be regarded as potentially powerful strategies for the prevention of AD.

Gastrodin Ameliorates Learning and Memory Impairments Caused by Long-Term Noise Exposure

The developing brain is significantly affected by long-term exposure to noise at an early age, leading to functional disorders such as learning and memory impairments. Gastrodin (GAS), a natural organic compound, is an extraction of phenolic glycoside from the rhizome of Gastrodia elata. Clinically, GAS is extensively utilised for the treatment of neurological disorders. This study aimed to explore the effect and mechanism of GAS on noise exposure-induced learning and memory impairments. Rats aged 21 days were exposed to a 90 dB noise environment for 4 weeks and divided into the noise group, the noise + GAS group, and the control group to establish a noise exposure model. After noise exposure treatment, the improvement effect of GAS on the memory of rats was evaluated by Y-maze and Morris water maze. Enzyme-linked immunosorbent assay was utilised to determine the effect of GAS on neurotransmitter levels in the hippocampal tissue of noise-exposed rats. Western blot was applied for the detection of the protein levels of neurotrophic factors. The GAS treatment significantly improved spatial memory and increased the levels of key neurotransmitters (norepinephrine, dopamine and serotonin) and neurotrophic factors (neurotrophin-3 and brain-derived neurotrophic factor) in the hippocampal tissues of noise-exposed rats. These alterations correlate with enhanced cognitive functions, suggesting a neuroprotective effect of GAS against noise-induced cognitive impairments. This study supports the potential of GAS to treat noise-induced learning and memory impairments by modulating neurotransmitter secretion and enhancing the expression levels of neurotrophic factors. These findings offer potential therapeutic avenues for cognitive impairments induced by noise exposure.

Disturbance in the protein landscape of cochlear perilymph in an Alzheimer's disease mouse model

Hearing loss is a pivotal risk factor for dementia. It has recently emerged that a disruption in the intercommunication between the cochlea and brain is a key process in the initiation and progression of this disease. However, whether the cochlear properties can be influenced by pathological signals associated with dementia remains unclear. In this study, using a mouse model of Alzheimer's disease (AD), we investigated the impacts of the AD-like amyloid β (Aβ) pathology in the brain on the cochlea. Despite little detectable change in the age-related shift of the hearing threshold, we observed quantitative and qualitative alterations in the protein profile in perilymph, an extracellular fluid that fills the path of sound waves in the cochlea. Our findings highlight the potential contribution of Aβ pathology in the brain to the disturbance of cochlear homeostasis.

Oxidative stress and inflammation cause auditory system damage via glial cell activation and dysregulated expression of gap junction proteins in an experimental model of styrene-induced oto/neurotoxicity

BACKGROUND

Redox imbalance and inflammation have been proposed as the principal mechanisms of damage in the auditory system, resulting in functional alterations and hearing loss. Microglia and astrocytes play a crucial role in mediating oxidative/inflammatory injury in the central nervous system; however, the role of glial cells in the auditory damage is still elusive.

OBJECTIVES

Here we investigated glial-mediated responses to toxic injury in peripheral and central structures of the auditory pathway, i.e., the cochlea and the auditory cortex (ACx), in rats exposed to styrene, a volatile compound with well-known oto/neurotoxic properties.

METHODS

Male adult Wistar rats were treated with styrene (400 mg/kg daily for 3 weeks, 5/days a week). Electrophysiological, morphological, immunofluorescence and molecular analyses were performed in both the cochlea and the ACx to evaluate the mechanisms underlying styrene-induced oto/neurotoxicity in the auditory system.

RESULTS

We showed that the oto/neurotoxic insult induced by styrene increases oxidative stress in both cochlea and ACx. This was associated with macrophages and glial cell activation, increased expression of inflammatory markers (i.e., pro-inflammatory cytokines and chemokine receptors) and alterations in connexin (Cxs) and pannexin (Panx) expression, likely responsible for dysregulation of the microglia/astrocyte network. Specifically, we found downregulation of Cx26 and Cx30 in the cochlea, and high level of Cx43 and Panx1 in the ACx.

CONCLUSIONS

Collectively, our results provide novel evidence on the role of immune and glial cell activation in the oxidative/inflammatory damage induced by styrene in the auditory system at both peripheral and central levels, also involving alterations of gap junction networks. Our data suggest that targeting glial cells and connexin/pannexin expression might be useful to attenuate oxidative/inflammatory damage in the auditory system.

Dysregulations of metabolites and gut microbes and their associations in rats with noise induced hearing loss

Background

Noise exposure could lead to hearing loss and disorders of various organs. Recent studies have reported the close relations of environmental noise exposure to the metabolomics dysregulations and gut microbiota disturbance in the exposers. However, the associations between gut microbial homeostasis and the body metabolism during noise-induced hearing loss (NIHL) were unclear. To get a full understanding of their synergy in noise-associated diseases, it is essential to uncover their impacts and associations under exposure conditions.

Methods

With ten male rats with background noise exposure (≤ 40 dB) as controls (Ctr group), 20 age- and weight-matched male rats were exposed to 95 dB Sound pressure level (SPL) (LN group, n = 10) or 105 dB SPL noise (HN group, n = 10) for 30 days with 4 h/d. The auditory brainstem response (ABR) of the rats and their serum biochemical parameters were detected to investigate their hearing status and the potential effects of noise exposure on other organs. Metabolomics (UPLC/Q-TOF-MS) and microbiome (16S rDNA gene sequencing) analyses were performed on samples from the rats. Multivariate analyses and functional enrichments were applied to identify the dysregulated metabolites and gut microbes as well as their associated pathways. Pearson correlation analysis was performed to investigate the associations of the dysregulations of microbiota and the metabolites.

Results

NIHL rat models were constructed. Many biochemical parameters were altered by noise exposure. The gut microbiota constitution and serum metabolic profiles of the noise-exposed rats were also dysregulated. Through metabolomics analysis, 34 and 36 differential metabolites as well as their associated pathways were identified in LN and HN groups, respectively. Comparing with the control rats, six and 14 florae were shown to be significantly dysregulated in the LN group and HN group, respectively. Further association analysis showed significant correlations between differential metabolites and differential microbiota.

Conclusion

There were cochlea injuries and abnormalities of biochemical parameters in the rats with NIHL. Noise exposure could also disrupt the metabolic profiles and the homeostatic balance of gut microbes of the host as well as their correlations. The dysregulated metabolites and microbiota might provide new clues for prevention of noise-related disorders.

Research progress on the treatment and nursing of sensorineural hearing loss

This article provides a comprehensive review of the progress in the treatment and care of sensorineural hearing loss (SNHL), which is a common disease in the field of otolaryngology. In recent years, the incidence of SNHL has been on the rise due to factors such as fast-paced lifestyles, work pressure, and environmental noise pollution, which have a significant impact on the quality of life of patients. Therefore, the study of the treatment and care of SNHL remains a hot topic in the medical community. Despite significant advances in this field, there are still some challenges and limitations. For example, there is currently no single method that can completely cure SNHL, and the effectiveness of treatment may vary significantly among individuals. In addition, due to the complex etiology of SNHL, the prognosis of patients may vary greatly, requiring the development of personalized treatment plans and care strategies. To address these challenges, continuous research is needed to explore new treatment methods and care models to improve the quality of life of patients. In addition, there is a need for health education programs for the general public to raise awareness of SNHL and promote preventive measures to reduce its incidence. The ultimate goal is to ensure the sustainable development of the field of SNHL treatment and care, thus ensuring the health and well-being of affected individuals.

Adult mice with noise-induced hearing loss exhibited temporal ordering memory deficits accompanied by microglia-associated neuroplastic changes in the medial prefrontal cortex

Acquired peripheral hearing loss in midlife is considered the primary modifiable risk factor for dementia, while the underlying pathological mechanism remains poorly understood. Excessive noise exposure is the most common cause of acquired peripheral hearing loss in modern society. This study was designed to investigate the impact of noise-induced hearing loss (NIHL) on cognition, with a focus on the medial prefrontal cortex (mPFC), a brain region that is involved in both auditory and cognitive processes and is highly affected in patients with cognitive impairment. Adult C57BL/6 J mice were randomly assigned to a control group and seven noise groups: 0HPN, 12HPN, 1DPN, 3DPN, 7DPN, 14DPN, and 28DPN, which were exposed to broadband noise at a 123 dB sound pressure level (SPL) for 2 h and sacrificed immediately (0 h), 12 h, or 1, 3, 7, 14, or 28 days post-noise exposure (HPN, DPN), respectively. Hearing assessment, behavioral tests, and neuromorphological studies in the mPFC were performed in control and 28DPN mice. All experimental animals were included in the time-course analysis of serum corticosterone (CORT) levels and mPFC microglial morphology. The results illustrated that noise exposure induced early-onset transient serum CORT elevation and permanent moderate-to-severe hearing loss in mice. 28DPN mice, in which permanent NIHL has been verified, exhibited impaired performance in temporal order object recognition tasks concomitant with reduced structural complexity of mPFC pyramidal neurons. The time-course immunohistochemical analysis in the mPFC revealed significantly higher morphological microglial activation at 14 and 28 DPN, preceded by a remarkably higher amount of microglial engulfed postsynaptic marker PSD95 at 7 DPN. Additionally, lipid accumulation in microglia was observed in 7DPN, 14DPN and 28DPN mice, suggesting a driving role of lipid handling deficits following excessive phagocytosis of synaptic elements in delayed and sustained microglial abnormalities. These findings provide fundamentally novel information concerning mPFC-related cognitive impairment in mice with NIHL and empirical evidence suggesting the involvement of microglial malfunction in the mPFC neurodegenerative consequences of NIHL.

The Role of BDNF as a Biomarker in Cognitive and Sensory Neurodegeneration

Brain-derived neurotrophic factor (BDNF) has a crucial function in the central nervous system and in sensory structures including olfactory and auditory systems. Many studies have highlighted the protective effects of BDNF in the brain, showing how it can promote neuronal growth and survival and modulate synaptic plasticity. On the other hand, conflicting data about BDNF expression and functions in the cochlear and in olfactory structures have been reported. Several clinical and experimental research studies showed alterations in BDNF levels in neurodegenerative diseases affecting the central and peripheral nervous system, suggesting that BDNF can be a promising biomarker in most neurodegenerative conditions, including Alzheimer's disease, shearing loss, or olfactory impairment. Here, we summarize current research concerning BDNF functions in brain and in sensory domains (olfaction and hearing), focusing on the effects of the BDNF/TrkB signalling pathway activation in both physiological and pathological conditions. Finally, we review significant studies highlighting the possibility to target BDNF as a biomarker in early diagnosis of sensory and cognitive neurodegeneration, opening new opportunities to develop effective therapeutic strategies aimed to counteract neurodegeneration.

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.