Large-scale phenotyping of ABR P1-N1 amplitudes before and after exposure to noise in 69 strains of mice.

ABR wave I amplitude represents the synapse of auditory nerve fibers with the inner hair cell and is highly correlated with synapse counts. Cochlear synaptopathy, the loss of synaptic connections between inner hair cells and auditory nerve fibers, has been well-demonstrated in animal models of noise-induced hearing loss. The peak-to-peak wave I amplitude was determined at baseline and 2 weeks after noise exposure. We determined the ABR wave I amplitude at 80 dB SPL at the frequencies of 8, 12, 16, 24, and 32 kHz. A total of 69 strains (1-8 mice/strain) were analyzed. A statistically significant post-noise reduction in wave I amplitude was observed in all the tested frequencies (p < 0.00001). We identify distinct patterns of noise susceptibility and make this complete phenotypic dataset available for general use. This data establishes a new resource for the study of NIHL in mice and we hope this database will be a useful tool to expand the research in this field.

Role of Neuropilin-1/Semaphorin-3A signaling in the functional and morphological integrity of the cochlea.

Neuropilin-1 (Nrp1) encodes the transmembrane cellular receptor neuropilin-1, which is associated with cardiovascular and neuronal development and was within the peak SNP interval on chromosome 8 in our prior GWAS study on age-related hearing loss (ARHL) in mice. In this study, we generated and characterized an inner ear-specific Nrp1 conditional knockout (CKO) mouse line because Nrp1 constitutive knockouts are embryonic lethal. In situ hybridization demonstrated weak Nrp1 mRNA expression late in embryonic cochlear development, but increased expression in early postnatal stages when cochlear hair cell innervation patterns have been shown to mature. At postnatal day 5, Nrp1 CKO mice showed disorganized outer spiral bundles and enlarged microvessels of the stria vascularis (SV) but normal spiral ganglion cell (SGN) density and presynaptic ribbon body counts; however, we observed enlarged SV microvessels, reduced SGN density, and a reduction of presynaptic ribbons in the outer hair cell region of 4-month-old Nrp1 CKO mice. In addition, we demonstrated elevated hearing thresholds of the 2-month-old and 4-month-old Nrp1 CKO mice at frequencies ranging from 4 to 32kHz when compared to 2-month-old mice. These data suggest that conditional loss of Nrp1 in the inner ear leads to progressive hearing loss in mice. We also demonstrated that mice with a truncated variant of Nrp1 show cochlear axon guidance defects and that exogenous semaphorin-3A, a known neuropilin-1 receptor agonist, repels SGN axons in vitro. These data suggest that Neuropilin-1/Semaphorin-3A signaling may also serve a role in neuronal pathfinding in the developing cochlea. In summary, our results here support a model whereby Neuropilin-1/Semaphorin-3A signaling is critical for the functional and morphological integrity of the cochlea and that Nrp1 may play a role in ARHL.

The impact of erdosteine on cisplatin-induced ototoxicity: a proteomics approach.

Cisplatin is a commonly used chemotherapeutic agent and causes serious side effects, including progressive and irreversible hearing loss. No treatment is currently available for cisplatin-induced ototoxicity. We have previously demonstrated that erdosteine, a potent antioxidant, partially protected the cochlea against cisplatin toxicity in vivo. The aims of this study were to (1) evaluate the protein profiles of the cochlea following cisplatin administration and (2) evaluate the impact of erdosteine on the protein profile using a proteomics-based approach. Thirty Sprague-Dawley rats were injected intraperitoneally with saline (n = 10), cisplatin (n = 10) or with cisplatin and erdosteine (n = 10). The cisplatin dosage was 14 mg/kg and for erdosteine, 500 mg/kg. Following euthanasia, protein lysates were obtained from fresh-frozen cochleae and were processed for mass spectrometry and western blotting. We detected 445 proteins that exhibited a twofold change or greater in the cisplatin group as compared to the control group. Of these, 18 proteins showed a fourfold or greater change in expression associated with cisplatin administration, including ras-related protein Rab-2A, Rab-6A, cd81, ribosomal protein S5, and myelin basic protein, which were downregulated, while Ba1-647 and fibrinogen (alpha chain), amongst others, were upregulated. Co-administration of erdosteine revealed a reversal of these changes in the expression of ras-related protein Rab-2A, ribosomal protein S5, myelin basic protein, and fibrinogen (alpha chain); erdosteine also upregulated glutathione reductase. In this study, we identified various proteins that may play a role in cisplatin-induced ototoxicity. We also observed the changes resulting from co-treatment with an antioxidant.

Systemic dexamethasone for the prevention of cisplatin-induced ototoxicity.

Ototoxicity is a common side effect of cisplatin chemotherapy. This study was undertaken to determine the potential protective effects of a systemic administration of dexamethasone against cisplatin-induced ototoxicity. A prospective controlled trial conducted in an animal model. The setting was Animal care research facilities of the Montreal Children's Hospital Research Institute. An experimental guinea pig model was used. The animals were divided as follows: group 1 (n = 10): 12 mg/kg intraperitoneal (IP) cisplatin, group 2 (n = 14): 15 mg/kg/day dexamethasone IP for 2 days followed by cisplatin 12 mg/kg IP, group 3 (n = 14): 10 mg/kg/day dexamethasone IP for 2 days, on day 3, they received cisplatin 12 mg/kg IP followed by 20 mg/kg/day dexamethasone for 2 days and group 4 (n = 5): 10 ml of saline IP twice a day for 3 days. Auditory brainstem response (ABR) threshold shifts were measured at four frequencies (8, 16, 20 and 25 kHz) for groups 1, 2 and 3. Histological changes in the organ of Corti, the stria vascularis, the spiral ligament and the spiral ganglion neurons as well as scanning electron microscopy for outer hair cells were completed. Immunohistochemistry for tumour necrosis factor-alpha (TNF-α) was performed. ABR threshold shifts were similar in all groups. Histological and scanning electron findings demonstrate that dexamethasone has greater protective effect on the stria vascularis. Systemic dexamethasone administration in a guinea pig model did not provide significant protection against cisplatin-induced ototoxicity. Dexamethasone may be useful in future applications as a complementary treatment.

The Genetics of Variation of the Wave 1 Amplitude of the Mouse Auditory Brainstem Response.

This is the first genome-wide association study with the Hybrid Mouse Diversity Panel (HDMP) to define the genetic landscape of the variation in the suprathreshold wave 1 amplitude of the auditory brainstem response (ABR) both pre- and post-noise exposure. This measure is correlated with the density of the auditory neurons (AN) and/or the compliment of synaptic ribbons within the inner hair cells of the mouse cochlea. We analyzed suprathreshold ABR for 635 mice from 102 HMDP strains pre- and post-noise exposure (108 dB 10 kHz octave band noise exposure for 2 h) using auditory brainstem response (ABR) wave 1 suprathreshold amplitudes as part of a large survey (Myint et al., Hear Res 332:113-120, 2016). Genome-wide significance levels for pre- and post-exposure wave 1 amplitude across the HMDP were performed using FaST-LMM. Synaptic ribbon counts (Ctbp2 and mGluR2) were analyzed for the extreme strains within the HMDP. ABR wave 1 amplitude varied across all strains of the HMDP with differences ranging between 2.42 and 3.82-fold pre-exposure and between 2.43 and 7.5-fold post-exposure with several tone burst stimuli (4 kHz, 8 kHz, 12 kHz, 16 kHz, 24 kHz, and 32 kHz). Immunolabeling of paired synaptic ribbons and glutamate receptors of strains with the highest and lowest wave 1 values pre- and post-exposure revealed significant differences in functional synaptic ribbon counts. Genome-wide association analysis identified genome-wide significant threshold associations on chromosome 3 (24 kHz; JAX00105429; p < 1.12E-06) and chromosome 16 (16 kHz; JAX00424604; p < 9.02E-07) prior to noise exposure and significant associations on chromosomes 2 (32 kHz; JAX00497967; p < 3.68E-08) and 13 (8 kHz; JAX00049416; 1.07E-06) after noise exposure. In order to prioritize candidate genes, we generated cis-eQTLs from microarray profiling of RNA isolated from whole cochleae in 64 of the tested strains.This is the first report of a genome-wide association analysis, controlled for population structure, to explore the genetic landscape of suprathreshold wave 1 amplitude measurements of the mouse ABR. We have defined two genomic regions associated with wave 1 amplitude variation prior to noise exposure and an additional two associated with variation after noise exposure.

Detection of single mRNAs in individual cells of the auditory system.

Gene expression analysis is essential for understanding the rich repertoire of cellular functions. With the development of sensitive molecular tools such as single-cell RNA sequencing, extensive gene expression data can be obtained and analyzed from various tissues. Single-molecule fluorescence in situ hybridization (smFISH) has emerged as a powerful complementary tool for single-cell genomics studies because of its ability to map and quantify the spatial distributions of single mRNAs at the subcellular level in their native tissue. Here, we present a detailed method to study the copy numbers and spatial localizations of single mRNAs in the cochlea and inferior colliculus. First, we demonstrate that smFISH can be performed successfully in adult cochlear tissue after decalcification. Second, we show that the smFISH signals can be detected with high specificity. Third, we adapt an automated transcript analysis pipeline to quantify and identify single mRNAs in a cell-specific manner. Lastly, we show that our method can be used to study possible correlations between transcriptional and translational activities of single genes. Thus, we have developed a detailed smFISH protocol that can be used to study the expression of single mRNAs in specific cell types of the peripheral and central auditory systems.

Otoprotective Effects of Stephania tetrandra S. Moore Herb Isolate against Acoustic Trauma.

Noise is the most common occupational and environmental hazard, and noise-induced hearing loss (NIHL) is the second most common form of sensorineural hearing deficit. Although therapeutics that target the free-radical pathway have shown promise, none of these compounds is currently approved against NIHL by the United States Food and Drug Administration. The present study has demonstrated that tetrandrine (TET), a traditional Chinese medicinal alkaloid and the main chemical isolate of the Stephania tetrandra S. Moore herb, significantly attenuated NIHL in CBA/CaJ mice. TET is known to exert antihypertensive and antiarrhythmic effects through the blocking of calcium channels. Whole-cell patch-clamp recording from adult spiral ganglion neurons showed that TET blocked the transient Ca2+ current in a dose-dependent manner and the half-blocking concentration was 0.6 + 0.1 µM. Consistent with previous findings that modulations of calcium-based signaling pathways have both prophylactic and therapeutic effects against neural trauma, NIHL was significantly diminished by TET administration. Importantly, TET has a long-lasting protective effect after noise exposure (48 weeks) in comparison to 2 weeks after noise exposure. The otoprotective effects of TET were achieved mainly by preventing outer hair cell damage and synapse loss between inner hair cells and spiral ganglion neurons. Thus, our data indicate that TET has great potential in the prevention and treatment of NIHL.

The Genetic Architecture of Noise-Induced Hearing Loss: Evidence for a Gene-by-Environment Interaction.

The discovery of environmentally specific genetic effects is crucial to the understanding of complex traits, such as susceptibility to noise-induced hearing loss (NIHL). We describe the first genome-wide association study (GWAS) for NIHL in a large and well-characterized population of inbred mouse strains, known as the Hybrid Mouse Diversity Panel (HMDP). We recorded auditory brainstem response (ABR) thresholds both pre and post 2-hr exposure to 10-kHz octave band noise at 108 dB sound pressure level in 5-6-wk-old female mice from the HMDP (4-5 mice/strain). From the observation that NIHL susceptibility varied among the strains, we performed a GWAS with correction for population structure and mapped a locus on chromosome 6 that was statistically significantly associated with two adjacent frequencies. We then used a "genetical genomics" approach that included the analysis of cochlear eQTLs to identify candidate genes within the GWAS QTL. In order to validate the gene-by-environment interaction, we compared the effects of the postnoise exposure locus with that from the same unexposed strains. The most significant SNP at chromosome 6 (rs37517079) was associated with noise susceptibility, but was not significant at the same frequencies in our unexposed study. These findings demonstrate that the genetic architecture of NIHL is distinct from that of unexposed hearing levels and provide strong evidence for gene-by-environment interactions in NIHL.

Large-scale phenotyping of noise-induced hearing loss in 100 strains of mice.

A cornerstone technique in the study of hearing is the Auditory Brainstem Response (ABR), an electrophysiologic technique that can be used as a quantitative measure of hearing function. Previous studies have published databases of baseline ABR thresholds for mouse strains, providing a valuable resource for the study of baseline hearing function and genetic mapping of hearing traits in mice. In this study, we further expand upon the existing literature by characterizing the baseline ABR characteristics of 100 inbred mouse strains, 47 of which are newly characterized for hearing function. We identify several distinct patterns of baseline hearing deficits and provide potential avenues for further investigation. Additionally, we characterize the sensitivity of the same 100 strains to noise exposure using permanent thresholds shifts, identifying several distinct patterns of noise-sensitivity. The resulting data provides a new resource for studying hearing loss and noise-sensitivity in mice.

Genome-Wide Association Analysis Identifies Dcc as an Essential Factor in the Innervation of the Peripheral Vestibular System in Inbred Mice.

This study aimed to investigate the genetic causes of vestibular dysfunction. We used vestibular sensory-evoked potentials (VsEPs) to characterize the vestibular function of 35 inbred mouse strains selected from the Hybrid Mouse Diversity Panel and demonstrated strain-dependent phenotypic variation in vestibular function. Using these phenotypic data, we performed the first genome-wide association study controlling for population structure that has revealed two highly suggestive loci, one of which lies within a haplotype block containing five genes (Stard6, 4930503L19Rik, Poli, Mbd2, Dcc) on Chr. 18 (peak SNP rs29632020), one gene, deleted in colorectal carcinoma (Dcc) has a well-established role in nervous system development. An in-depth analysis of Dcc-deficient mice demonstrated elevation in mean VsEP threshold for Dcc (+/-) mice (-11.86 dB) compared to wild-type (-9.68 dB) littermates. Synaptic ribbon studies revealed Dcc (-/-) (P0) and Dcc (+/-) (6-week-old) mice showed lower density of the presynaptic marker (CtBP2) as compared to wild-type controls. Vestibular ganglion cell counts of Dcc (-/-) (P0) was lower than controls. Whole-mount preparations showed abnormal innervation of the utricle, saccule, and crista ampullaris at E14.5, E16.5, and E18.5. Postnatal studies were limited by the perinatal lethality in Dcc (-/-) mice. Expression analyses using in situ hybridization and immunohistochemistry showed Dcc expression in the mouse vestibular ganglion (E15.5), and utricle and crista ampullaris (6-week-old), respectively. In summary, we report the first GWAS for vestibular functional variation in inbred mice and provide evidence for the role of Dcc in the normal innervation of the peripheral vestibular system.

Assessment of ototoxicity of intratympanic administration of Auralgan in a chinchilla animal model.

OBJECTIVES/HYPOTHESIS: Auralgan (benzocaine and antipyrine) is an over-the-counter otic drug commonly used for otalgia. Nevertheless, there is limited evidence about the effects of the drug on hearing function and cochlear morphology in the presence of a tympanic membrane perforation. The aim of the present study was to assess the cytotoxicity of Auralgan using cultured auditory cells (HEI-OC1) and to examine its effects on hearing function and cochlear morphology after intratympanic administration in a chinchilla model. STUDY DESIGN: Animal experiment. METHODS: Cell viability and DNA labeling assays were conducted to investigate the cytotoxic effect of the drug on cultured auditory cells (HEI-OC1). To examine the possible drug ototoxic effect in vivo, chinchillas received intratympanic injection of Auralgan in one ear, whereas the contralateral control ear received saline. Outcome measures included auditory brainstem response and postmortem cochlear morphology. RESULTS: A dose-dependent toxic effect of Auralgan was noted on cultured cells. Animal experiments showed an inflammatory reaction in the experimental ears and facial paralysis in 80% of the animals on the side receiving transtympanic injection of Auralgan (P < .05). Auditory brainstem response testing demonstrated a 30- to 50-dB hearing threshold shift across all frequencies tested (P < .05). Control ears showed no inflammation or significant threshold shift. Microscopy showed damage to the hair cells and stria vascularis with bleeding in the perilymphatic space in the experimental ears and damage to the hair cells. CONCLUSIONS: Auralgan was cytotoxic to cultured auditory cells. It promoted an inflammatory reaction and seemed to be ototoxic when given via transtympanic injection in an animal model. LEVEL OF EVIDENCE: NA

Safety and otoprotection of metformin in radiation-induced sensorineural hearing loss in the guinea pig.

OBJECTIVE: There is currently no treatment available to prevent radiation-induced sensorineural hearing loss. Metformin has antineoplastic effects and is able to regulate the mitochondrial production of reactive oxygen species after cellular stress, which is one of the mechanisms involved in apoptosis after radiation damage. The objective of this study was to determine the safety and radioprotective properties of metformin against radiation-induced cochlear damage both in vitro and in vivo. STUDY DESIGN: In vitro and prospective animal study. SETTING: Animal Care Facilities of the Montreal Children's Hospital Research Institute. METHODS: Cultured auditory hair cells (HEI-OC1) were exposed to different concentrations of metformin to determine its safety. Cells were incubated with different metformin concentrations and subjected to radiation. Cell viability after experiments was determined with the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. Sixteen guinea pigs were divided in 2 groups: drinking tap water (n = 8) and drinking water containing metformin (n = 8). The animals were unilaterally irradiated for 20 days (total dose 70 Gy), and the ears were divided in 4 groups: control (n = 8), irradiated (n = 8), metformin (n = 8), and experimental (n = 8). Auditory brainstem responses were assessed before and 1, 6, and 16 weeks after completion of radiotherapy. RESULTS: Metformin was not cytotoxic or radioprotective in cultured auditory hair cells. Experimental ears had less hearing loss than radiated ones; however, differences were not statistically significant (P > .05). CONCLUSION: Metformin is not ototoxic or radioprotective in vitro or in vivo. Ears solely subjected to metformin had better hearing thresholds than the rest of the groups.

Attenuation of cisplatin ototoxicity by otoprotective effects of nanoencapsulated curcumin and dexamethasone in a guinea pig model.

OBJECTIVES: Cisplatin, one of the most effective and widely used chemotherapeutic agents in the treatment of head and neck malignancies, has severe dose-limiting side effects including ototoxicity. This study evaluates the effectiveness of nanoencapsulated curcumin and dexamethasone in preventing degenerative changes in inner ear cells caused by cisplatin. STUDY DESIGN: Prospective study, animal experiment. METHODS: Cultured auditory cells [House Ear Institute Organ of Corti-1 (HEI-OC1)] and a guinea pig model were used for in vitro and in vivo experiments, respectively. Cell viability assays were conducted to compare the direct toxicity of cisplatin against auditory cells in the presence or absence of pretreatment with nanoencapsulated curcumin and dexamethasone. To recapitulate these effects in vivo, 68 guinea pigs received cisplatin either alone, or along with dexamethasone, nanoencapsulated curcumin, or the combination of both products. Outcome measures included auditory brainstem response, cochlear morphology under both light and scanning electron microscopy, and antioxidant enzyme assays. RESULTS: Pretreatment of auditory cells with naonoencapsulated curcumin and dexamethasone resulted in significant attenuation of cisplatin toxicity. Similarly, in the corresponding animal model (guinea pig), cisplatin caused an average hearing loss of 50 dB, which was attenuated by nanoencapsulated curcumin and dexamethasone across all of the hearing frequencies. There was also greater preservation of histologic structures in this group. Superoxide dismutase and catalase activities were increased in cisplatin-treated animals, whereas the nanoencapsulated curcumin with dexamethasone led to a diminution of this effect. CONCLUSION: Nanoencapsulated curcumin administered in combination with dexamethasone provides a partial but marked protection against cisplatin-induced hearing loss, likely because of reduced toxic damage to auditory cells.

Curcumin loaded NIPAAM/VP/PEG-A nanoparticles: physicochemical and chemopreventive properties.

This study aims at modifying the synthesis method of preparing N-isopropylacrylamide (NIPAAM)/N-vinyl-2-pyrrolidone (VP)/Polyethylene glycol monoacrylate (PEG-A) polymeric nanoparticles encapsulating curcumin as a model drug. The optimal concentration of nanoparticle reagents was determined using Fourier Transform Infrared Spectroscopy. Curcumin nanoparticles mean hydrodynamic size was found to be 104 nm with zeta potential of 3 ± 13 mV. The release kinetic study of curcumin nanoparticles indicates that a maximum release of curcumin at 24 h positively correlates with increase in temperature; however, change in pH did not produce any substantial drug release. In vitro cell viability assay performed on cancer cells exposed to various concentrations of model compound displayed the IC50 ranging between 100 and 200 µg/mL for human prostate cancer cells (PC3 cells) and 50 and 200 µg/mL for epidermoid carcinoma (A431 cell line). The Hoechst staining and phase contrast micrographs for 48 h exposure of curcumin nanoparticles at a concentration of 400 µg/mL resulted in almost 92% of cells death in both cell lines. This study concludes that the physiochemical characteristics of NIPAAM/VP/PEG-A polymer with key features of water solubility, sustained drug release, small particle size make these nanoparticles a prominent drug delivery device.