Telmisartan Attenuates Kanamycin-Induced Ototoxicity in Rats.

Telmisartan (TM) has been proposed to relieve inflammatory responses by modulating peroxisome proliferator activator receptor-γ (PPARγ) signaling. This study aimed to investigate the protective effects of TM on kanamycin(KM)-induced ototoxicity in rats. Forty-eight, 8-week-old female Sprague Dawley rats were divided into four groups: (1) control group, (2) TM group, (3) KM group, and (4) TM + KM group. Auditory brainstem response was measured. The histology of the cochlea was examined. The protein expression levels of angiotensin-converting enzyme 2 (ACE2), HO1, and PPARγ were measured by Western blotting. The auditory threshold shifts at 4, 8, 16, and 32 kHz were lower in the TM + KM group than in the KM group (all p < 0.05). The loss of cochlear outer hair cells and spiral ganglial cells was lower in the TM + KM group than in the KM group. The protein expression levels of ACE2, PPARγ, and HO1 were higher in the KM group than in the control group (all p < 0.05). The TM + KM group showed lower expression levels of PPARγ and HO1 than the KM group.TM protected the cochlea from KM-induced injuries in rats. TM preserved hearing levels and attenuated the increase in PPARγ and HO1 expression levels in KM-exposed rat cochleae.

The effect of systemic administration of salicylate on the auditory cortex of guinea pigs.

OBJECTIVE: To investigate the effect of systemic administration of salicylate as a tinnitus inducing drug in the auditory cortex of guinea pigs. METHODS: Extracellular recording of spikes of the primary auditory cortex and dorsocaudal areas in healthy male albino Hartley guinea pigs was continuously performed (pre- and post-salicylate). RESULTS: We recorded 160 single units in the primary auditory cortex from five guinea pigs and 156 single units in the dorsocaudal area from another five guinea pigs. The threshold was significantly elevated after the administration of salicylate in both the primary auditory cortex and dorsocaudal areas. The Q10dB value was significantly increased in the primary auditory cortex, whereas it has significantly decreased in the dorsocaudal area. Spontaneous firing activity was significantly decreased in the primary auditory cortex, whereas it has significantly increased in the dorsocaudal area. CONCLUSION: Salicylate induces significant changes in single units of both stimulated and spontaneous activity in the auditory cortex of guinea pigs. The spontaneous activity changed differently depending on its cortical areas, which may be due to the neural elements that generate tinnitus.

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

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

Istradefylline Mitigates Age-Related Hearing Loss in C57BL/6J Mice.

Age-related hearing loss (ARHL) is the most common sensory disorder among older people, and yet, the treatment options are limited to medical devices such as hearing aids and cochlear implants. The high prevalence of ARHL mandates the development of treatment strategies that can prevent or rescue age-related cochlear degeneration. In this study, we investigated a novel pharmacological strategy based on inhibition of the adenosine A2A receptor (A2AR) in middle aged C57BL/6 mice prone to early onset ARHL. C57BL/6J mice were treated with weekly istradefylline (A2AR antagonist; 1 mg/kg) injections from 6 to 12 months of age. Auditory function was assessed using auditory brainstem responses (ABR) to tone pips (4-32 kHz). ABR thresholds and suprathreshold responses (wave I amplitudes and latencies) were evaluated at 6, 9, and 12 months of age. Functional outcomes were correlated with quantitative histological assessments of sensory hair cells. Cognitive function was assessed using the Morris water maze and the novel object recognition test, and the zero maze test was used to assess anxiety-like behaviour. Weekly injections of istradefylline attenuated ABR threshold shifts by approximately 20 dB at mid to high frequencies (16-32 kHz) but did not improve ABR suprathreshold responses. Istradefylline treatment improved hair cell survival in a turn-dependent manner, whilst the cognitive function was unaffected by istradefylline treatment. This study presents the first evidence for the rescue potential of istradefylline in ARHL and highlights the role of A2AR in development of age-related cochlear degeneration.

Early hearing threshold changes and peculiarities of audiometric assessments among patients in a drug-resistant tuberculosis treatment center.

BACKGROUND: Hearing threshold changes occurred relative to baseline at both one and two weeks after onset of aminoglycoside therapy. OBJECTIVES: To assess changes in audiometric hearing thresholds between pre-treatment values and two weeks into therapy. To document observed changes, and occurrence of ototoxicity within the period. METHODS: Prospective analytical cohort study on drug-resistant tuberculosis patients. Basic demographic parameters were taken. Three-point audiometric assessments within two weeks into therapy were done. Percentage of patients with ototoxicity were calculated. Pure tone threshold changes between the three audiometric values were compared. RESULTS: Audiograms of 53 patients comprising 56.6% males; age range was 13 to 91 years. Both air and bone conduction hearing thresholds significantly worsened between baseline and one week into therapy (p=0.011, and 0.015 respectively), and between baseline and two weeks into therapy (p=0.003 and 0.042 respectively). Minimal insignificant reduction occurred between both air and bone conduction hearing values of week 1 and week 2 of therapy (p= 1.000 and 0.856 respectively). By audiometric criteria, 4 patients (7.5%) developed ototoxicity within two weeks of treatment. CONCLUSION: Audiometric assessments within two weeks into therapy with anti-tuberculous therapy may not represent baseline audiometry. 7.5% of the patients developed ototoxicity within two weeks of therapy.

Effects of Androgen Receptor Inhibition on Kanamycin-Induced Hearing Loss in Rats.

Megalin has been proposed as an endocytic receptor for aminoglycosides as well as estrogen and androgen. We aimed to investigate the otoprotective effects of antiandrogens (flutamide, FM) on kanamycin (KM)-induced hearing loss in rats. Rats were divided into four groups. The KM group was administered KM (20 mg/kg/day) for 5 days, while the FM group received FM (15 mg/kg/day) for 10 days. In the KM + FM group, KM and FM (15 mg/kg/day) were simultaneously injected for 5 days and then FM was injected for 5 days. Auditory brainstem responses were measured. Western blotting and/or quantitative reverse transcriptase-polymerase chain reaction were performed for megalin, cytochrome P450 1A1 (Cyp1a1), Cyp1b1, metallothionein 1A (MT1A), MT2A, tumor necrosis factor (TNF)-α, caspase 3, and cleaved caspase 3. The FM + KM group showed attenuated auditory thresholds when compared with the KM group at 4, 8, 16, and 32 kHz (all p < 0.05). The KM + FM group showed lower megalin and Cyp1b1 levels than the KM group (all p < 0.05). The KM + FM group revealed lower MT1A, TNFα, and caspase 3 protein levels, compared with those in the KM group (all p < 0.05). Androgen receptor inhibition protects against cochlear injuries in KM-induced hearing loss rats by attenuating megalin expression, revealing anti-inflammatory and anti-apoptotic effects.

Chronic Oral Selegiline Treatment Mitigates Age-Related Hearing Loss in BALB/c Mice.

Age-related hearing loss (ARHL), a sensorineural hearing loss of multifactorial origin, increases its prevalence in aging societies. Besides hearing aids and cochlear implants, there is no FDA approved efficient pharmacotherapy to either cure or prevent ARHL. We hypothesized that selegiline, an antiparkinsonian drug, could be a promising candidate for the treatment due to its complex neuroprotective, antioxidant, antiapoptotic, and dopaminergic neurotransmission enhancing effects. We monitored by repeated Auditory Brainstem Response (ABR) measurements the effect of chronic per os selegiline administration on the hearing function in BALB/c and DBA/2J mice, which strains exhibit moderate and rapid progressive high frequency hearing loss, respectively. The treatments were started at 1 month of age and lasted until almost a year and 5 months of age, respectively. In BALB/c mice, 4 mg/kg selegiline significantly mitigated the progression of ARHL at higher frequencies. Used in a wide dose range (0.15-45 mg/kg), selegiline had no effect in DBA/2J mice. Our results suggest that selegiline can partially preserve the hearing in certain forms of ARHL by alleviating its development. It might also be otoprotective in other mammals or humans.

Drug delivery in cochlear implantation.

Intra-cochlear fibrous tissue formation around the electrode following cochlear implantation affects the electrode impedance as well as electrode explantation during reimplantation surgeries. Applying corticosteroids in cochlear implantation is one way of minimizing the intra-cochlear fibrous tissue formation around the electrode. It were J. Kiefer, C. von Ilberg, and W. Gstöttner who proposed the first idea on drug delivery application in cochlear implantation to MED-EL in the year 2000. During the twenty years of translational research efforts at MED-EL in collaboration with several clinics and research institutions from across the world, preclinical safety and efficacy of corticosteroids were performed leading to the final formulation of the electrode design. In parallel to the drug eluting CI electrode development, MED-EL also invested research efforts into developing tools enabling delivery of pharmaceutical agents of surgeon's choice inside the cochlea. The inner ear catheter designed to administer drug substances into the cochlea was CE marked in 2020. A feasibility study in human subjects with MED-EL CI featuring dexamethasone-eluting electrode array started in June 2020. This article covers the milestones of translational research towards the drug delivery in CI application that took place in association with MED-EL.

Sudden hearing loss and coronavirus disease 2019: the role of corticosteroid intra-tympanic injection in hearing improvement.

BACKGROUND: Coronavirus disease 2019 was first seen in December 2019. Due to the insidious and complex nature of the disease, the list of symptoms is rapidly expanding. So far, few studies have reported sudden sensorineural hearing loss as a possible symptom of coronavirus disease 2019. CASE REPORT: A 60-year-old woman with a complaint of sudden sensorineural hearing loss and subjective severe tinnitus presented to the ENT clinic. Coronavirus disease 2019 was subsequently confirmed with a polymerase chain reaction test. At the time of presentation, she was treated with intra-tympanic dexamethasone. Improvements in hearing threshold and speech perception, and a subjective reduction in tinnitus, were observed after treatment. CONCLUSION: This case report supports evidence from other case reports of a possible association between coronavirus disease 2019 and sudden sensorineural hearing loss. Sudden sensorineural hearing loss may be a symptom of this disease that behaves as an underlying aggravating factor. Intra-tympanic injection of corticosteroids is recommended for managing these patients during the pandemic.

Salicylate decreases the spontaneous firing rate of guinea pig auditory nerve fibres.

Tinnitus has similarities to chronic neuropathic pain where there are changes in the firing rate of different types of afferent neurons. We postulated that one possible cause of tinnitus is a change in the distribution of spontaneous firing rates in at least one type of afferent auditory nerve fibre in anaesthetised guinea pigs. In control animals there was a bimodal distribution of spontaneous rates, but the position of the second mode was different depending upon whether the fibres responded best to high (> 4 kHz) or low (≤4 kHz) frequency tonal stimulation. The simplest and most reliable way of inducing tinnitus in experimental animals is to administer a high dose of sodium salicylate. The distribution of the spontaneous firing rates was different when salicylate (350 mg/kg) was administered, even when the sample was matched for the distribution of characteristic frequencies in the control population. The proportion of medium spontaneous rate fibres (MSR, 1≤ spikes/s ≤20) increased while the proportion of the highest, high spontaneous firing rate fibres (HSR, > 80 spikes/s) decreased following salicylate. The median rate fell from 64.7 spikes/s (control) to 35.4 spikes/s (salicylate); a highly significant change (Kruskal-Wallis test p < 0.001). When the changes were compared with various models of statistical probability, the most accurate model was one where most HSR fibres decreased their firing rate by 32 spikes/s. Thus, we have shown a reduction in the firing rate of HSR fibres that may be related to tinnitus.

A Randomized, Double-Blind, Placebo-Controlled, Multiple Dose Escalation Study to Evaluate the Safety and Pharmacokinetics of ELX-02 in Healthy Subjects.

ELX-02 is an investigational compound being developed as a therapy for genetic diseases caused by nonsense mutations such as cystic fibrosis. Structurally, ELX-02 is an aminoglycoside analogue that induces read-through of nonsense mutations through interaction with the ribosome, resulting in the production of full-length functional proteins. This phase 1 multiple-ascending-dose trial evaluated the safety and pharmacokinetics of ELX-02 in 62 healthy volunteers. ELX-02 plasma exposure was dose proportional, with no apparent accumulation, and followed by renal elimination. The most reported adverse event was injection site reactions that were mild to moderate in severity. At the top dose of 5.0 mg/kg, 1 of 6 subjects experienced auditory threshold changes in which ototoxicity could not be clearly ruled out, and 2 of 6 had hearing threshold changes consistent with possible ototoxicity. Two of 3 subjects receiving placebo in the 5.0 mg/kg group also had significant hearing threshold changes. All observed hearing threshold changes resolved or were trending toward resolution after withdrawal of the study drug. No severe or serious adverse events were reported.The results of this study support the evaluation of ELX-02 in phase 2 clinical trials with patients that have genetic diseases caused by nonsense mutations.

Melatonin reduces radiation damage in inner ear.

The purpose of this study was to use a murine model to determine if melatonin can protect the inner ear from radiation-induced damage. A total of 81 4-week-old Balb/c mice were randomly divided into five groups: control group; 50 mg/kg melatonin group; 5 mg/kg melatonin+radiotherapy group; 50 mg/kg melatonin+radiotherapy group; radiotherapy group. The radiotherapy groups received 16 Gy irradiation and melatonin was administered by intraperitoneal injection 30 min before radiotherapy. On days 3 and 7 after irradiation the function of outer hair cells was determined by auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs) testing, pathological changes of inner ear cells were observed by light microscopy, and the expression of prestin mRNA was determined. ABR thresholds were increased and wave I latencies were extended after radiotherapy; however, the increases were lower in the groups that received melatonin (P < 0.05). DPOAEs showed radiotherapy-induced hearing loss at 8-12 kHz, and hearing loss was greater on day 7 than day 3. However, hearing loss was less in the melatonin groups (P < 0.05). Histopathological examination showed irradiation resulted in breaks and distortion of the cochlear basement membrane, disruption of the stria vascularis, and swelling of outer hair cells. Melatonin reduced these changes. Radiotherapy upregulated prestin mRNA expression. Radiotherapy-induced upregulation of prestin was decreased in the melatonin groups (P < 0.05), and the decrease was greater in the 50 mg/kg melatonin group (P < 0.05). Melatonin protects against radiation-induced cochlear damage by reducing damage to outer hair cells.

Trk agonist drugs rescue noise-induced hidden hearing loss.

TrkB agonist drugs are shown here to have a significant effect on the regeneration of afferent cochlear synapses after noise-induced synaptopathy. The effects were consistent with regeneration of cochlear synapses that we observed in vitro after synaptic loss due to kainic acid-induced glutamate toxicity and were elicited by administration of TrkB agonists, amitriptyline, and 7,8-dihydroxyflavone, directly into the cochlea via the posterior semicircular canal 48 hours after exposure to noise. Synaptic counts at the inner hair cell and wave 1 amplitudes in the auditory brainstem response (ABR) were partially restored 2 weeks after drug treatment. Effects of amitriptyline on wave 1 amplitude and afferent auditory synapse numbers in noise-exposed ears after systemic (as opposed to local) delivery were profound and long-lasting; synapses in the treated animals remained intact 1 year after the treatment. However, the effect of systemically delivered amitriptyline on synaptic rescue was dependent on dose and the time window of administration: it was only effective when given before noise exposure at the highest injected dose. The long-lasting effect and the efficacy of postexposure treatment indicate a potential broad application for the treatment of synaptopathy, which often goes undetected until well after the original damaging exposures.

Comparison of 2 Different Intratympanic Methylprednisolone Injection Schedules in Combination With Intravenous Dexamethasone for Unilateral Sudden Sensorineural Hearing Loss.

Sudden sensorineural hearing loss is a common otologic disease in clinic. Systemic and intratympanic steroid treatment have been proved to be effective, but the regimens vary from center to center. The purpose of the study is to analyze the effects of the combined application of intravenous dexamethasone and intratympanic methylprednisolone injection in different time strategies for the treatment of unilateral sudden sensorineural hearing loss. A retrospective chart review was performed for the period from March 2016 to June 2018 at our Department of Otorhinolaryngology-Head and Neck Surgery. A total number of 61 patients who met the academy criteria for unilateral sudden hearing loss were included and grouped based on the time to introduce intratympanic methylprednisolone. All the patients received intravenous dexamethasone 10 mg once daily for 5 days, followed 5 mg once daily for the next 7 days. Intratympanic methylprednisolone (40 mg) was injected every other day 4 times into all patients. This regimen was commenced on day 1 in group 1 and on day 6 in group 2. The pre and posttreatment pure-tone audiograms were analyzed. Sixty-one patients met our inclusion criteria. No significant differences were observed between patients' demographics or pretreatment hearing thresholds. In the 3 months posttreatment pure-tone audiogram assessment, the mean hearing threshold improvement were similar between groups with no frequency specificity. The curative rate in both groups were similar and satisfying. Two patients with diabetes mellitus had persistent small perforations. Some patients had other transient discomfort that disappeared before discharge. The different timing of initiation of intratympanic methylprednisolone injection does not significantly affect the outcome of the treatment for sudden sensorineural hearing loss. Thus, we suggest that intratympanic steroid injection should not be applied as a first-line method except for patients who do not respond early to systemic steroid therapy.

Intratympanal administration of lidocaine in the management of Ménière's Disease.

BACKGROUND: Ménière's Disease (MD) is a chronic condition where patients suffer recurrent vertigo attacks. Evidence for treatment concepts are to this date low. AIMS/OBJECTIVE: To evaluate the therapeutic effect of intratympanic lidocaine injections to reduce the number of attacks. METHODS: Twenty patients diagnosed with definitive MD that were treated with 34 intratympanic lidocaine injections were included. Main outcome measures were the number of vertigo attacks in the previous four weeks, the attack free period and the subjective improvement of the condition. RESULTS: Mean follow up after first lidocaine injection was 25.3 months (±22.2; range 1.9-79.7). Patients expressed subjective improvement in overall situation, vertigo, and aural fullness. The number of vertigo attacks before each assessment decreased from 7.1 (±5.9; range 2-20) per months at baseline to 1.9 (±3.8; range 0-15). 25% of the patients suffered no further attacks, the other patients had an average attack free period of 7.8 months (±15.4; range 0.2-58.4). Hearing thresholds remained unaffected. Repetitive injections proved effective. CONCLUSION AND SIGNIFICANCE: Intratympanic lidocaine is an effective nonsurgical and non-ablative therapy for MD. When patients experience an increase of attacks repetitive injections promise improvement.

Regulator of G Protein Signalling 4 (RGS4) as a Novel Target for the Treatment of Sensorineural Hearing Loss.

We and others have previously identified signalling pathways associated with the adenosine A1 receptor (A1R) as important regulators of cellular responses to injury in the cochlea. We have shown that the "post-exposure" treatment with adenosine A1R agonists confers partial protection against acoustic trauma and other forms of sensorineural hearing loss (SNHL). The aim of this study was to determine if increasing A1R responsiveness to endogenous adenosine would have the same otoprotective effect. This was achieved by pharmacological targeting of the Regulator of G protein Signalling 4 (RGS4). RGS proteins inhibit signal transduction pathways initiated by G protein-coupled receptors (GPCR) by enhancing GPCR deactivation and receptor desensitisation. A molecular complex between RGS4 and neurabin, an intracellular scaffolding protein expressed in neural and cochlear tissues, is the key negative regulator of A1R activity in the brain. In this study, Wistar rats (6-8 weeks) were exposed to traumatic noise (110 dBSPL, 8-16 kHz) for 2 h and a small molecule RGS4 inhibitor CCG-4986 was delivered intratympanically in a Poloxamer-407 gel formulation for sustained drug release 24 or 48 h after noise exposure. Intratympanic administration of CCG-4986 48 h after noise exposure attenuated noise-induced permanent auditory threshold shifts by up to 19 dB, whilst the earlier drug administration (24 h) led to even better preservation of auditory thresholds (up to 32 dB). Significant improvement of auditory thresholds and suprathreshold responses was linked to improved survival of sensorineural tissues and afferent synapses in the cochlea. Our studies thus demonstrate that intratympanic administration of CCG-4986 can rescue cochlear injury and hearing loss induced by acoustic overexposure. This research represents a novel paradigm for the treatment of various forms of SNHL based on regulation of GPCR.

Anti-PD-1 Therapy Does Not Influence Hearing Ability in the Most Sensitive Frequency Range, but Mitigates Outer Hair Cell Loss in the Basal Cochlear Region.

The administration of immune checkpoint inhibitors (ICIs) often leads to immune-related adverse events. However, their effect on auditory function is largely unexplored. Thorough preclinical studies have not been published yet, only sporadic cases and pharmacovigilance reports suggest their significance. Here we investigated the effect of anti-PD-1 antibody treatment (4 weeks, intraperitoneally, 200 µg/mouse, 3 times/week) on hearing function and cochlear morphology in C57BL/6J mice. ICI treatment did not influence the hearing thresholds in click or tone burst stimuli at 4-32 kHz frequencies measured by auditory brainstem response. The number and morphology of spiral ganglion neurons were unaltered in all cochlear turns. The apical-middle turns (<32 kHz) showed preservation of the inner and outer hair cells (OHCs), whilst ICI treatment mitigated the age-related loss of OHCs in the basal turn (>32 kHz). The number of Iba1-positive macrophages has also increased moderately in this high frequency region. We conclude that a 4-week long ICI treatment does not affect functional and morphological integrity of the inner ear in the most relevant hearing range (4-32 kHz; apical-middle turns), but a noticeable preservation of OHCs and an increase in macrophage activity appeared in the >32 kHz basal part of the cochlea.

[Inner hair cells loss by carboplatin and the changes of cochlear compound action potential in chinchillas].

Objective: To measure the cochlear compound action potential (CAP) and the densities of hair cells (HCs) along the whole length of the basilar membrane (BM) in adult chinchillas. And to investigate the relationship between the severity of inner hair cells (IHCs) loss and the changes of CAP by using carboplatin-cochlear lesion model. Methods: Totally 18 chinchillas were recruited after ontological evaluation. They were randomly divided into three groups (with 6 subjects in each), A: control, B and C: legion groups treated with one or two shot(s) of carboplatin respectively (76 mg/kg in one shot, i.p., one-week interval between the two shots). Endpoint tests were performed 30 days after the carboplatin treatment in groups B and C, and matched time in group A. A sliver-ball electrode was placed into round window niche via hypotympanic approach in anesthetized chinchilla. CAP was measured in response to clicks and tone burst of 0.5, 1, 2, 4, 8, 16 kHz respectively under anesthesia. CAP amplitudes and thresholds were measured and compared across the groups. After the recording, the whole cochlea surface preparation was made and the HCs were stained in histochemistry against substrate of succinate dehydrogenase (SDH). Images were taken with high-resolution digital camera under light microscope and across the whole cochlea. The length of the basilar membrane (BM) and the number of both IHCs and OHCs were counted. The HC density was calculated as the number of HCs per 10% BM length. Results: The CAP thresholds were (7.1±2.6), (25.4±5.0), (24.6±5.4), (10.4±5.0), (0.4±1.4), (4.2±6.3) and (17.1±14.1) dB SPL (from 6 subjects in group A, n=12 ears) corresponding to stimuli of Click and 0.5, 1, 2, 4, 8, 16 kHz tone bursts respectively. The total number of cochlear HCs were measured as (8 936±643) (x±s) and the average length of the BMs was (17.73±1.012) mm from the six subjects in the group A (n=12 ears). The HC density was found to be varied slightly across the BM. There was no significant CAP threshold difference between the control (group A) and the group B, which received one shot of carboplatin. However, the maximal CAP amplitude was reduced by 40% in the group B and compared with group A. Correspondingly, approximately 40% loss of IHCs were seen. In contrast, a significant CAP threshold shift was seen in subjects receiving two shots of carboplatin (group C), which was accompanied by a loss of 90% IHCs. Conclusions: The CAP thresholds of adult chinchillas show typical open-V shape with the lowest values at 2, 4, and 8 kHz. IHC loss by carboplatin in certain degree is well correlated with CAP amplitude reduction, but does not change the threshold when inner hair cell loss reaches 40%, however, if inner hair cell loss exceeds 80%, the threshold shift of CAP will be inevitable.

Loss of Cochlear Ribbon Synapse Is a Critical Contributor to Chronic Salicylate Sodium Treatment-Induced Tinnitus without Change Hearing Threshold.

Tinnitus is a common auditory disease worldwide; it is estimated that more than 10% of all individuals experience this hearing disorder during their lifetime. Tinnitus is sometimes accompanied by hearing loss. However, hearing loss is not acquired in some other tinnitus generations. In this study, we injected adult rats with salicylate sodium (SS) (200 mg/kg/day for 10 days) and found no significant hearing threshold changes at 2, 4, 8, 12, 14, 16, 20, or 24 kHz (all p > 0.05). Tinnitus was confirmed in the treated rats via Behaviour Testing of Acoustic Startle Response (ASR) and Gap Prepulse Inhibition Test of Acoustic Startle Reflex (GPIAS). A immunostaining study showed that there is significant loss of anti-CtBP2 puncta (a marker of cochlear inner hair cell (HC) ribbon synapses) in treated animals in apical, middle, and basal turns (all p < 0.05). The ABR wave I amplitudes were significantly reduced at 4, 8, 12, 14, 16, and 20 kHz (all p < 0.05). No significant losses of outer HCs, inner HCs, or HC cilia were observed (all p > 0.05). Thus, our study suggests that loss of cochlear inner HC ribbon synapse after SS exposure is a contributor to the development of tinnitus without changing hearing threshold.

Otoprotective Effects of Zingerone on Cisplatin-Induced Ototoxicity.

Previous studies have described the effects of zingerone (ZO) on cisplatin (CXP)-induced injury to the kidneys, liver, and other organs but not to the cochlea. This study aimed to investigate the effects of ZO on CXP-induced ototoxicity. Eight-week-old Sprague-Dawley rats were used and divided into a control group, a CXP group, and a CXP + ZO group. Rats in the CXP group received 5 mg/kg/day CXP intraperitoneally for five days. Rats in the CXP + ZO group received 5 mg/kg/day CXP intraperitoneally for five days and 50 mg/kg/day ZO intraperitoneally for seven days. Auditory brainstem response thresholds (ABRTs) were measured before (day 0) and after (day 10) drug administration. Cochlear histology was examined using hematoxylin and eosin (H&E) staining and cochlear whole mounts. The expression levels of cytochrome P450 (CYP)1A1, CYP1B1, inducible nitric oxide synthase (iNOS), nuclear factor kappa B (NFκB), tumor necrosis factor alpha (TNFα), and interleukin 6 (IL6) were estimated using quantitative reverse transcription-polymerase chain reaction. The expression levels of heme oxygenase 1 (HO1) and caspase 3 were analyzed via Western blotting. The auditory thresholds at 4, 8, and 16 kHz were attenuated in the CXP + ZO group compared with the CXP group. The mRNA expression levels of CYP1A1, CYP1B1, iNOS, NFκB, TNFα, and IL6 were lower in the CXP + ZO group than in the CXP group. The protein expression levels of HO1 and caspase 3 were lower in the CXP + ZO group than in the CXP group. Cotreatment with ZO exerted otoprotective effects against CXP-induced cochlear injury via antioxidative and anti-inflammatory activities involving CYPs, iNOS, NFκB, and TNFα.