Cochlear Glucocorticoid Receptor and Serum Corticosterone Expression in a Rodent Model of Noise-induced Hearing Loss: Comparison of Timing of Dexamethasone Administration

Ototoxicity-Alleviating and Cytoprotective Allomelanin Nanomedicine for Efficient Sensorineural Hearing Loss Treatment

Sensorineural hearing loss (SNHL) represents a significant clinical challenge, predominantly attributed to oxidative stress-related mechanisms. In this work, we report an innovative antioxidant strategy for mitigating SNHL, utilizing synthetically engineered allomelanin nanoparticles (AMNPs). Empirical evidence elucidates AMNPs' profound capability in free radical neutralization, substantiated by a significant decrement in reactive oxygen species (ROS) levels within HEI-OC1 auditory cells exposure to cisplatin or hydrogen peroxide (H2O2). Comparative analyses reveal that AMNPs afford protection against cisplatin-induced and noise-induced auditory impairments, mirroring the effect of dexamethasone (DEX), a standard pharmacological treatment for acute SNHL. AMNPs exhibit notable cytoprotective properties for auditory hair cells (HCs), effectively preventing ototoxicity from cisplatin or H2O2 exposure, as confirmed by both in vitro assays and cultured organ of Corti studies. Further in vivo research corroborates AMNPs' ability to reverse auditory brainstem response (ABR) threshold shifts resulting from acoustic injury, concurrently reducing HCs loss, ribbon synapse depletion, and spiral ganglion neuron degeneration. The therapeutic benefits of AMNPs are attributed to mitigating oxidative stress and inflammation within the cochlea, with transcriptome analysis indicating downregulated gene expression related to these processes post-AMNPs treatment. The pronounced antioxidative and anti-inflammatory effects of AMNPs position them as a promising alternative to DEX for SNHL treatment.

Blood-Labyrinth Barrier in Health and Diseases: Effect of Hormetic Nutrients

Significance: The stria vascularis, located in the inner ear, consists of three layers, one of which is the blood-labyrinth barrier (BLB). It is formed by endothelial cells, sealed together to prevent the passage of toxic substances from the blood to the inner ear, by pericytes and perivascular-resident macrophage-like melanocyte. Recent Advances: There are various causes that lead to hearing loss, and among these are noise-induced and autoimmune hearing loss, ear disorders related to ototoxic medication, Ménière's disease, and age-related hearing loss. For all of these, major therapeutic interventions include drug-loaded nanoparticles, via intratympanic or intracochlear delivery. Critical Issues: Since many pathologies associated with hearing loss are characterized by a weakening of the BLB, in this review, the molecular mechanisms underlying the response to damage of BLB cellular components have been discussed. In addition, insight into the role of hormetic nutrients against hearing loss pathology is proposed. Future Directions: BLB cellular components of neurovascular cochlear unit play important physiological roles, owing to their impermeable function against all ototoxic substances that can induce damage. Studies are needed to investigate the cross talk occurring between these cellular components to exploit their possible role as novel targets for therapeutic interventions that may unravel future path based on the use of hormetic nutrients. Antioxid. Redox Signal. 40, 542-563.

Therapeutic effect of intraperitoneal dexamethasone on noise-induced permanent threshold shift in mice model

The purpose of the study was to which investigate whether dexamethasone, which has anti-inflammatory and immune response suppression roles, could treat noise-induced hearing loss caused by damage to hair cells in the cochlea. The experiment used 8-week-old CBA mice exposed to white noise at an intensity of 110 dB SPL for 2 h, with hearing loss confirmed by the auditory brainstem response test. Dexamethasone was administered by intraperitoneal injection for 5 days, and the therapeutic effect was investigated for 3 weeks. The experimental groups were 3 mg/kg of dexamethasone (3 mpk) and 10 mg/kg of dexamethasone (10 mpk), and the control group was a saline-administered group. The results showed that compared to the control group, the hearing threshold value was recovered by 10 dB SPL compared to the saline group from the 14th day in the 3 mpk group. In the 10 mpk group, thresholds were recovered from the 7th day compared to the saline group. This difference was similar at 4 kHz, and in the case of the 10 mpk group, the threshold was recovered by 20 dB SPL compared to the saline group. The study also confirmed the restoration of nerve cell activity and showed a recovery effect of about 20 µV in the amplitude value change in the 10 mpk group. In conclusion, the study suggests that dexamethasone has a therapeutic effect for noise-induced hearing loss by increasing the activity of nerve cells and showing a recovery effect from hair cells damaged by noise.

Immunohistochemical localization of glucocorticoid receptors in the human cochlea

In the present study we investigated the localization of glucocorticoid receptors (GCR) in the human inner ear using immunohistochemistry. Celloidin-embedded cochlear sections of patients with normal hearing (n = 5), patients diagnosed with MD (n = 5), and noise induced hearing loss (n = 5) were immunostained using GCR rabbit affinity-purified polyclonal antibodies and secondary fluorescent or HRP labeled antibodies. Digital fluorescent images were acquired using a light sheet laser confocal microscope. In celloidin-embedded sections GCR-IF was present in the cell nuclei of hair cells and supporting cells of the organ of Corti. GCR-IF was detected in cell nuclei of the Reisner's membrane. GCR-IF was seen in cell nuclei of the stria vascularis and the spiral ligament. GCR-IF was found in the spiral ganglia cell nuclei, however, spiral ganglia neurons showed no GCR-IF. Although GCRs were found in most cell nuclei of the cochlea, the intensity of IF was differential among the different cell types being more intense in supporting cells than in sensory hair cells. The differential expression of GCR receptors found in the human cochlea may help to understand the site of action of glucocorticoids in different ear diseases.

Conditional Ablation of Glucocorticoid and Mineralocorticoid Receptors from Cochlear Supporting Cells Reveals Their Differential Roles for Hearing Sensitivity and Dynamics of Recovery from Noise-Induced Hearing Loss

Endogenous glucocorticoids (GC) are known to modulate basic elements of cochlear physiology. These include both noise-induced injury and circadian rhythms. While GC signaling in the cochlea can directly influence auditory transduction via actions on hair cells and spiral ganglion neurons, evidence also indicates that GC signaling exerts effects via tissue homeostatic processes that can include effects on cochlear immunomodulation. GCs act at both the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). Most cell types in the cochlea express both receptors sensitive to GCs. The GR is associated with acquired sensorineural hearing loss (SNHL) through its effects on both gene expression and immunomodulatory programs. The MR has been associated with age-related hearing loss through dysfunction of ionic homeostatic balance. Cochlear supporting cells maintain local homeostatic requirements, are sensitive to perturbation, and participate in inflammatory signaling. Here, we have used conditional gene manipulation techniques to target Nr3c1 (GR) or Nr3c2 (MR) for tamoxifen-induced gene ablation in Sox9-expressing cochlear supporting cells of adult mice to investigate whether either of the receptors sensitive to GCs plays a role in protecting against (or exacerbating) noise-induced cochlear damage. We have selected mild intensity noise exposure to examine the role of these receptors related to more commonly experienced noise levels. Our results reveal distinct roles of these GC receptors for both basal auditory thresholds prior to noise exposure and during recovery from mild noise exposure. Prior to noise exposure, auditory brainstem responses (ABRs) were measured in mice carrying the floxed allele of interest and the Cre recombinase transgene, but not receiving tamoxifen injections (defined as control (no tamoxifen treatment), versus conditional knockout (cKO) mice, defined as mice having received tamoxifen injections. Results revealed hypersensitive thresholds to mid- to low-frequencies after tamoxifen-induced GR ablation from Sox9-expressing cochlear supporting cells compared to control (no tamoxifen) mice. GR ablation from Sox9-expressing cochlear supporting cells resulted in a permanent threshold shift in mid-basal cochlear frequency regions after mild noise exposure that produced only a temporary threshold shift in both control (no tamoxifen) f/fGR:Sox9iCre+ and heterozygous f/+GR:Sox9iCre+ tamoxifen-treated mice. A similar comparison of basal ABRs measured in control (no tamoxifen) and tamoxifen-treated, floxed MR mice prior to noise exposure indicated no difference in baseline thresholds. After mild noise exposure, MR ablation was initially associated with a complete threshold recovery at 22.6 kHz by 3 days post-noise. Threshold continued to shift to higher sensitivity over time such that by 30 days post-noise exposure the 22.6 kHz ABR threshold was 10 dB more sensitive than baseline. Further, MR ablation produced a temporary reduction in peak 1 neural amplitude one day post-noise. While supporting cell GR ablation trended towards reducing numbers of ribbon synapses, MR ablation reduced ribbon synapse counts but did not exacerbate noise-induced damage including synapse loss at the experimental endpoint. GR ablation from the targeted supporting cells increased the basal resting number of Iba1-positive (innate) immune cells (no noise exposure) and decreased the number of Iba1-positive cells seven days following noise exposure. MR ablation did not alter innate immune cell numbers at seven days post-noise exposure. Taken together, these findings support differential roles of cochlear supporting cell MR and GR expression at basal, resting conditions and especially during recovery from noise exposure.

Effect of MMF Immunosuppression Based on CNI Reduction on CNI-Related Renal Damage after Lung Transplantation

In this paper, numerous effects of immunosuppressive regimen of mycophenolate mofetil (MMF) on CNI-related renal damage after lung transplantation are evaluated thoroughly. For this purpose, 110 lung transplant recipients who were treated in our hospital from March 2016 to January 2018 were randomly selected. All patients took prednisone acetate tablets or rapamycin at the same time or not at the same time. MMF is 1 g every time, twice a day, and adjusted according to the re-examination. According to the different drugs taken by 110 patients, they were divided into cyclosporine A group and tacrolimus group. Among them, 92 patients in cyclosporine A group took cyclosporine A; 18 patients in tacrolimus group took tacrolimus. The clinical data of age and gender of the two groups were collected, To observe and compare the occurrence of CNI-related renal damage in lung transplant recipients and different immunosuppressants. The CNI dosage of tacrolimus group and cyclosporine A group was compared before and after MMF. The changes of serum creatinine level and serum creatinine clearance rate were measured before MMF administration and 30, 60, and 90 days after MMF administration, to observe the complications of CNI-related renal damage after lung transplantation. Experimental results showed that there were 16 cases (14.55%) of CNI-related renal damage in lung transplant recipients and different immunosuppressants, including 10 cases (11.36%) in males, 6 cases (27.27%) in females, 11 cases (12.09%) in tacrolimus group, and 5 cases (26.32%) in cyclosporine A group. There was no significant difference between the two groups (P > 0.05). Compared with MMF before and after administration, CNI dosage of cyclosporine A group and tacrolimus group decreased significantly (P < 0.01). Compared with MMF before administration, serum creatinine level decreased and serum creatinine clearance rate increased significantly (P < 0.05). In the follow-up, 16 patients with CNI-related renal damage were found to be immune rejection before the adjustment of immunosuppression program, no complications such as immune rejection, myelosuppression, and infection occurred within 15 months after the adjustment of immunosuppression program, blood glucose increased in 3 patients within 2 years after operation, blood lipid increased in 1 patient, urea increased in 1 patient, and uric acid increased in 1 patient. MMF immunosuppressive therapy based on CNI reduction is a safe and effective immunosuppressive therapy, which can significantly reduce immune rejection, improve renal function, and play an important role in improving CNI-related renal damage after lung transplantation.

Design, Synthesis, and Biological Evaluation of Dexamethasone-Salvianolic Acid B Conjugates and Nanodrug Delivery against Cisplatin-Induced Hearing Loss

Cisplatin (CDDP) is an extensively used chemotherapeutic agent but has a high incidence of severe ototoxicity. Although a few molecules have entered clinical trials, none have been approved to prevent or treat CDDP-induced hearing loss by the Food and Drug Administration. In this study, an amphiphilic drug-drug conjugate was synthesized by covalently linking dexamethasone (DEX) and salvianolic acid B (SAL) through an ester or amide bond. The conjugates could self-assemble into nanoparticles (NPs) with ultrahigh drug loading capacity and favorable stability. Compared with DEX, SAL, or their physical mixture at the same concentrations, both conjugates and NPs showed enhanced otoprotection in vitro and in vivo. More importantly, the conjugates and NPs almost completely restored hearing in a guinea pig model with good biocompatibility. Immunohistochemical analyses suggested that conjugates and NPs activated the glucocorticoid receptor, which may work as one of the major mechanisms for their protective effects.

Transcriptomic characterization of dying hair cells in the avian cochlea

Sensory hair cells are prone to apoptosis caused by various drugs including aminoglycoside antibiotics. In mammals, this vulnerability results in permanent hearing loss because lost hair cells are not regenerated. Conversely, hair cells regenerate in birds, making the avian inner ear an exquisite model for studying ototoxicity and regeneration. Here, we use single-cell RNA sequencing and trajectory analysis on control and dying hair cells after aminoglycoside treatment. Interestingly, the two major subtypes of avian cochlear hair cells, tall and short hair cells, respond differently. Dying short hair cells show a noticeable transient upregulation of many more genes than tall hair cells. The most prominent gene group identified is associated with potassium ion conductances, suggesting distinct physiological differences. Moreover, the dynamic characterization of >15,000 genes expressed in tall and short avian hair cells during their apoptotic demise comprises a resource for further investigations toward mammalian hair cell protection and hair cell regeneration.

A metal-organic framework based inner ear delivery system for the treatment of noise-induced hearing loss

Noise-induced hearing loss (NIHL) is associated with both acute and chronic noise exposure. The application of steroid hormones is the first-line treatment for NIHL. However, a high dose of steroid hormone in the body is necessary to maintain its efficacy and causes side effects, such as headache and osteoporosis. In this work, we prepared a zeolitic imidazolate framework (ZIF)-based system for steroid hormone delivery in the inner ear. Methylprednisolone (MP), a typical steroid hormone, was encapsulated into ZIF-90 nanoparticles (NPs) using one-pot synthesis method. The obtained MP@ZIF-90 NPs are negatively charged and 120 nm in size and showed good biocompatibility and stability at a pH value of 7.4. After intraperitoneal injection, ZIF-90 could efficiently protect drugs during peripheral blood circulation, enter the inner ear via the blood labyrinthine barrier (BLB) and slowly release the drugs. Auditory brainstem response (ABR) tests indicated that MP@ZIF-90 exhibits better protection of mice from noise than those using the free MP and ZIF-8 with encapsulated MP (MP@ZIF-8). More importantly, MP@ZIF-90 showed no defects to the inner ear after being treated for noise and low nephrotoxicity during therapy, which demonstrates the biocompatibility of this material. We believe the ZIF-90 based delivery system is an efficient strategy for inner ear therapy of NIHL.

Differential Effects of Low- and High-Dose Dexamethasone on Electrically Induced Damage of the Cultured Organ of Corti

An increased number of patients with residual hearing are undergoing cochlear implantation. A subset of these experience delayed hearing loss post-implantation, and the aetiology of this loss is not well understood. Our previous studies suggest that electrical stimulation can induce damage to hair cells in organ of Corti (OC) organotypic cultures. Dexamethasone has the potential to protect residual hearing due to its multiple effects on cells and tissue (e.g., anti-inflammatory, free radical scavenger). We therefore hypothesized that dexamethasone treatment could prevent electrical stimulation induced changes in the OC. Organ of Corti explants from neonatal rats (P2–4) were cultured for 24 h with two different concentrations of dexamethasone. Thereafter, OC were subjected to a charge-balanced biphasic pulsed electrical stimulation (0.44–2 mA) for a further 24 h. Unstimulated dexamethasone-treated OC served as controls. Outcome analysis included immunohistochemical labelling of ribbon synapses, histochemical analysis of free reactive oxygen species and morphological analysis of stereocilia bundles. Overall, the protective effects of dexamethasone on electrically induced damage in cochlear explants were moderate. High-dose dexamethasone protected bundle integrity at higher current levels. Low-dose dexamethasone tended to increase ribbon density in the apical region.

Mitochondrial Damage and Necroptosis in Aging Cochlea

Age-related hearing loss (ARHL) is an irreversible, progressive neurodegenerative disorder and is presently untreatable. Previous studies using animal models have suggested mitochondrial damage and programmed cell death to be involved with ARHL. Thus, we further investigated the pathophysiologic role of mitochondria and necroptosis in aged C57BL/6J male mice. Aged mice (20 months old) exhibited a significant loss of hearing, number of hair cells, neuronal fibers, and synaptic ribbons compared to young mice. Ultrastructural analysis of aged cochleae revealed damaged mitochondria with absent or disorganized cristae. Aged mice also showed significant decrease in cochlear blood flow, and exhibited increase in gene expression of proinflammatory cytokines (IL-1β, IL-6, and TNF-α), receptor-interacting serine/threonine-protein kinase 1 and 3 (RIPK1 and RIPK3) and the pseudokinase mixed-lineage kinase domain-like (MLKL). Immunofluorescence (IF) assays of cytochrome C oxidase I (COX1) confirmed mitochondrial dysfunction in aged cochleae, which correlated with the degree of mitochondrial morphological damage. IF assays also revealed localization and increased expression of RIPK3 in sensorineural tissues that underwent significant necroptosis (inner and outer hair cells and stria vascularis). Together, our data shows that the aging cochlea exhibits damaged mitochondria, enhanced synthesis of proinflammatory cytokines, and provides new evidence of necroptosis in the aging cochlea in in vivo.

Evaluating the Efficacy of L-N-acetylcysteine and Dexamethasone in Combination to Provide Otoprotection for Electrode Insertion Trauma

BACKGROUND

Electrode insertion trauma (EIT) during cochlear implantation (CI) can cause loss of residual hearing. L-N-acetylcysteine (L-NAC) and dexamethasone (Dex) have been individually shown to provide otoprotection albeit at higher concentrations that may be associated with adverse effects. Objective/Aims: The aim of this study is to determine whether L-NAC and Dex could be combined to decrease their effective dosage.

MATERIALS AND METHODS

The organ of Corti (OC) explants were divided into various groups: 1) control; 2) EIT; 3) EIT treated with different concentrations of Dex; 4) EIT treated with different concentrations of L-NAC; 5) EIT treated with L-NAC and Dex in combination. Hair cell (HC) density, levels of oxidative stress, proinflammatory cytokines and nitric oxide (NO) was determined.

RESULTS

There was a significant loss of HCs in explants subjected to EIT compared to the control group. L-NAC and Dex in combination was able to provide significant otoprotection at lower concentrations compared to individual drugs.

CONCLUSIONS AND SIGNIFICANCE

A combination containing L-NAC and Dex is effective in protecting sensory cells at lower protective doses than each compound separately. These compounds can be combined allowing a decrease of potential side effects of each compound and providing significant otoprotection for EIT.

Acoustic Trauma Modulates Cochlear Blood Flow and Vasoactive Factors in a Rodent Model of Noise-Induced Hearing Loss

Noise exposure affects the organ of Corti and the lateral wall of the cochlea, including the stria vascularis and spiral ligament. Although the inner ear vasculature and spiral ligament fibrocytes in the lateral wall consist of a significant proportion of cells in the cochlea, relatively little is known regarding their functional significance. In this study, 6-week-old male C57BL/6 mice were exposed to noise trauma to induce transient hearing threshold shift (TTS) or permanent hearing threshold shift (PTS). Compared to mice with TTS, mice with PTS exhibited lower cochlear blood flow and lower vessel diameter in the stria vascularis, accompanied by reduced expression levels of genes involved in vasodilation and increased expression levels of genes related to vasoconstriction. Ultrastructural analyses by transmission electron microscopy revealed that the stria vascularis and spiral ligament fibrocytes were more damaged by PTS than by TTS. Moreover, mice with PTS expressed significantly higher levels of proinflammatory cytokines in the cochlea (e.g., IL-1β, IL-6, and TNF-α). Overall, our findings suggest that cochlear microcirculation and lateral wall pathologies are differentially modulated by the severity of acoustic trauma and are associated with changes in vasoactive factors and inflammatory responses in the cochlea.