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This study addresses the relationship between cochlear oxidative damage and auditory cortical injury in a rat model of repeated noise exposure. To test the effect of increased antioxidant defenses, a water-soluble coenzyme Q10analog (Qter) was used. We analyzed auditory function, cochlear oxidative stress, morphological alterations in auditory cortices and cochlear structures, and levels of coenzymes Q9and Q10(CoQ9and CoQ10, respectively) as indicators of endogenous antioxidant capability. We report three main results. First, hearing loss and damage in hair cells and spiral ganglion was determined by noise-induced oxidative stress. Second, the acoustic trauma altered dendritic morphology and decreased spine number of II–III and V–VI layer pyramidal neurons of auditory cortices. Third, the systemic administration of the water-soluble CoQ10analog reduced oxidative-induced cochlear damage, hearing loss, and cortical dendritic injury. Furthermore, cochlear levels of CoQ9and CoQ10content increased. These findings indicate that antioxidant treatment restores auditory cortical neuronal morphology and hearing function by reducing the noise-induced redox imbalance in the cochlea and the deafferentation effects upstream the acoustic pathway.

Background Although styrene is an established ototoxic agent at occupational exposure levels, the mechanisms of styrene toxicity in the auditory system are still unclear. Objectives The aim of this study was to identify the consequences of styrene chronic exposure in cochlear structures, looking for the mechanisms of ototoxicity of this organic compound and focusing on cell targets and oxidative stress/inflammatory processes. Methods Male adult Wistar rats were exposed to styrene (400 mg/kg by gavage for 5 days/week, 3 consecutive weeks). Hearing loss was evaluated by measuring auditory brainstem responses (ABR), morphological analysis were performed to evaluate hair cell and spiral ganglion neuron survival, as well as synaptic damage. Analysis of apoptotic (p53) and inflammatory (NF-κB, TNF-α, IL-1β and IL-10) mediators were performed by immunofluorescence analysis and western blot. Results Styrene ototoxic effects induced a hearing loss of about 35–40 dB. Immunofluorescence and western blotting analyses demonstrated that styrene administration induced redox imbalance and activated inflammatory processes, targeting sensory hair cell and neural dysfunction by a cross-talk between oxidative and inflammatory mediators. Discussion Major findings connect styrene ototoxicity to an interplay between redox imbalance and inflammation, leading to the intriguing assumption of a mixed sensory and neural styrene-induced ototoxicity. Thus, in a clinical perspective, data reported here have important implications for styrene risk assessment in humans.

Mutations in GJB2, the gene that encodes connexin 26 (Cx26), are the most common cause of sensorineural hearing impairment. The truncating variant 35delG, which determines a complete loss of Cx26 protein function, is the prevalent GJB2 mutation in several populations. Here, we generated and analyzed Gjb2+/− mice as a model of heterozygous human carriers of 35delG. Compared to control mice, auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs) worsened over time more rapidly in Gjb2+/− mice, indicating they were affected by accelerated age-related hearing loss (ARHL), or presbycusis. We linked causally the auditory phenotype of Gjb2+/− mice to apoptosis and oxidative damage in the cochlear duct, reduced release of glutathione from connexin hemichannels, decreased nutrient delivery to the sensory epithelium via cochlear gap junctions and deregulated expression of genes that are under transcriptional control of the nuclear factor erythroid 2-related factor 2 (Nrf2), a pivotal regulator of tolerance to redox stress. Moreover, a statistically significant genome-wide association with two genes (PRKCE and TGFB1) related to the Nrf2 pathway (p-value < 4 × 10−2) was detected in a very large cohort of 4091 individuals, originating from Europe, Caucasus and Central Asia, with hearing phenotype (including 1076 presbycusis patients and 1290 healthy matched controls). We conclude that (i) elements of the Nrf2 pathway are essential for hearing maintenance and (ii) their dysfunction may play an important role in the etiopathogenesis of human presbycusis., Graphical abstract fx1, Highlights • Partial loss of Cx26 accelerates hearing impairment progression in Gjb2+/- mice. • The auditory organ is affected by increased apoptosis due to redox imbalance. • The expression of several genes controlled by the Nrf2/ARE pathway is deregulated. • Genome-wide association detected two of these genes in humans with presbycusis. • This work sheds new light on the etiopathogenesis of presbycusis and its prevention.

Background Transcranial direct current stimulation (tDCS) is a non-invasive tool capable to modulate cortical functions by affecting neuronal excitability and synaptic plasticity. Objective Here we investigated the effects of anodal tDCS on auditory cortex (ACx) in normal-hearing rats and following a paradigm of noise-induced hearing loss (NIHL), that causes morphological alterations in ACx pyramidal neurons. Methods Male rats exposed to intense pure tone (10 kHz) were subsequently subjected to unilateral anodal tDCS of ACx and changes in dendritic morphology and spines were assessed by Golgi-Cox staining 30 days after the onset of the acoustic trauma. Molecular and functional changes were investigated by Western immunoblotting, immunofluorescence experiments and electrophysiological recordings in brain slices. Results We found that NIHL altered dendritic morphology by decreasing spine density, mostly in layer 2/3 pyramidal neurons. Interestingly, tDCS increased ACx spine density, targeting apical dendrites of layer 2/3 and 5/6 pyramidal neurons in rats with normal auditory function and both apical and basal arborizations in layer 2/3 of NIHL rats. Twenty-four hours after tDCS, Bdnf and synaptophysin levels in ACx increased both in normal-hearing and noise-exposed rats. Field recordings showed that basal synaptic transmission at layer 2/3 horizontal connections was significantly reduced in noise-exposed rats compared to normal-hearing animals and, notably, input-output curves of noise-exposed animals subjected to tDCS were similar to those of normal-hearing rats. Conclusions Our findings provide novel evidence that anodal tDCS affects structural plasticity in the ACx suggesting that it might be beneficial in treating cortical alterations due to cochlear damage.

Experimental and human investigations have raised the level of concern about the potential ototoxicity of organic solvents and their interaction with noise. The main objective of this study was to characterize the effects of the combined noise and styrene exposure on hearing focusing on the mechanism of damage on the sensorineural cells and supporting cells of the organ of Corti and neurons of the ganglion of Corti. The impact of single and combined exposures on hearing was evaluated by auditory functional testing and histological analyses of cochlear specimens. The mechanism of damage was studied by analyzing superoxide anion and lipid peroxidation expression and by computational analyses of immunofluorescence data to evaluate and compare the oxidative stress pattern in outer hair cells versus the supporting epithelial cells of the organ of Corti. The oxidative stress hypothesis was further analyzed by evaluating the protective effect of a Coenzyme Q10 analogue, the water soluble Qter, molecule known to have protective antioxidant properties against noise induced hearing loss and by the analysis of the expression of the endogenous defense enzymes. This study provides evidence of a reciprocal noise-styrene synergism based on a redox imbalance mechanism affecting, although with a different intensity of damage, the outer hair cell (OHC) sensory epithelium. Moreover, these two damaging agents address preferentially different cochlear targets: noise mainly the sensory epithelium, styrene the supporting epithelial cells. Namely, the increase pattern of lipid peroxidation in the organ of Corti matched the cell damage distribution, involving predominantly OHC layer in noise exposed cochleae and both OHC and Deiters' cell layers in the styrene or combined exposed cochleae. The antioxidant treatment reduced the lipid peroxidation increase, potentiated the endogenous antioxidant defense system at OHC level in both exposures but it failed to ameliorate the oxidative imbalance and cell death of Deiters' cells in the styrene and combined exposures. Current antioxidant therapeutic approaches to preventing sensory loss focus on hair cells alone. It remains to be seen whether targeting supporting cells, in addition to hair cells, might be an effective approach to protecting exposed subjects.

Background: In oncology, an emerging paradigm emphasises molecularly targeted approaches for cancer prevention and therapy and the use of adjuvant chemotherapeutics to overcome cisplatin limitations. Owing to their safe use, some polyphenols, such as curcumin, modulate important pathways or molecular targets in cancers. This paper focuses on curcumin as an adjuvant molecule to cisplatin by analysing its potential implications on the molecular targets, signal transducer and activator of transcription 3 (STAT3) and NF-E2 p45-related factor 2 (Nrf-2), in tumour progression and cisplatin resistance in vitro and the adverse effect ototoxicity in vivo. Methods: The effects of curcumin and/or cisplatin treatment have been evaluated in head and neck squamous cell carcinoma as well as in a rat model of cisplatin-induced ototoxicity by using immunofluorescence, western blot, and functional and morphological analysis. Results: This study demonstrates that curcumin attenuates all stages of tumour progression (survival, proliferation) and, by targeting pSTAT3 and Nrf-2 signalling pathways, provides chemosensitisation to cisplatin in vitro and protection from its ototoxic adverse effects in vivo. Conclusions: These results indicate that curcumin can be used as an efficient adjuvant to cisplatin cancer therapy. This treatment strategy in head and neck cancer could mediate cisplatin chemoresistance by modulating therapeutic targets (STAT3 and Nrf2) and, at the same time, reduce cisplatin-related ototoxic adverse effects.

Noise induced hearing loss depends on the progressive increase of reactive oxygen species and lipoperoxidative damage in conjunction with the imbalance of antioxidant defenses. The redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) plays a critical role in the regulation of cellular defense against oxidative stress including heme oxygenase-1 (HO-1) activation. In this work we describe a link between cochlear oxidative stress damage, induced by noise exposure, and the activation of Nrf2/HO-1 pathway. In our model, noise induces superoxide production and overexpression of the lipid peroxidation marker, 4-hydroxy-nonenals (4-HNE). To face the oxidative stress, the endogenous defense system is as well activated as shown by the slight activation of superoxide dismutases (SODs). In addition, we also observed the activation of the Nrf2/HO-1 pathway after noise exposure. In doing so, Nrf2 appears to promote the maintenance of cellular homeostasis under stress conditions. However, in this model the endogenous antioxidant system fails to counteract noise-induced cell damage and its activation is not enough effective in preventing the cochlear damage. The herb-derived phenol rosmarinic acid (RA) attenuates noise-induced hearing loss reducing threshold shift and promotes hair cell survival. In fact, RA enhances the endogenous antioxidant defenses as shown by the decreased superoxide production, the reduced expression of 4-HNE and the up-regulation of SODs. Interestingly, RA potentiates the Nrf2/OH-1 signaling pathway as shown by immunohistochemical and western blot analyses. Thus, protective effects of RA are associated with the induction/activation of Nrf2-ARE signaling pathway in addition to RA direct scavenging capability.

Short-term tinnitus develops shortly after the administration of a high dose of salicylate. Since salicylate selectively potentiates N-methyl- D-aspartate (NMDA) currents in spiral ganglion neurons, it may play a vital role in tinnitus by amplifying NMDA-mediated neurotransmission. The aim of this study was to determine whether systemic treatment with a NMDA channel blocker, memantine, could prevent salicylate-induced tinnitus in animals. Additional experiments were performed to evaluate the effect of memantine on the auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) to test for changes in hearing function. Thirty-six rats were divided into 3 groups and treated daily for four consecutive days. One group (n = 12) was injected with salicylate (300 mg/kg/d, IP), the second (n = 12) was treated with memantine (5 mg/kg/d, IP) and the third group (n = 12) was injected with salicylate and memantine. All rats were tested for tinnitus and hearing loss at 2, 24, 48 and 72 h after the first drug administration and 24 h post treatment; tinnituslike behaviour was assessed with gap prepulse inhibition of acoustic startle (GPIAS), and hearing function was measured with DPOAE, ABR and noise burst prepulse inhibition of acoustic startle (NBPIAS). Rats in the salicylate group showed impaired GPIAS indicative of transient tinnitus-like behaviour near 16 kHz that recovered 24 h after the last salicylate treatment. Memantine did not cause a significant change in GPIAS. Combined injection of salicylate and memantine significantly attenuated GPIAS tinnitus-like behaviour at 48 hours after the first injection. None of the treatments induced permanent threshold shifts in the ABR and DPOAE, which recovered completely within one day post treatment. Animals treated with salicylate plus memantine showed results comparable to animals treated with salicylate alone, confirming that there is no effect of memantine on DPOAE which reflects OHC function. The present study confirms the role of cochlear NMDA receptors in the induction of salicylate-induced tinnitus.Il sodio salicilato, principio attivo dell'aspirina, è una molecola in grado di indurre un acufene transitorio mediante l'attivazione dei recettori N-metil-D-aspartato (NMDA) a livello periferico e centrale. L'obiettivo primario di questo studio è di valutare la potenzialità della memantina, inibitore selettivo dei recettori NMDA, nel contrastare l'insorgenza e la persistenza dell'acufene indotto da salicilato in un modello animale. Obiettivo secondario è lo studio degli effetti della memantina sulla funzione uditiva e sulle cellule ciliate esterne. Nel nostro studio sono stati utilizzati 36 ratti divisi in tre gruppi: nel primo gruppo (n = 12) gli animali sono stati trattati con salicilato (300 mg/kg/d, IP), nel secondo (n = 12) con memantina (5 mg/kg/d, IP), nel terzo (n = 12) con entrambi. In tutti gli animali è stato studiato l'acufene con la tecnica GPIAS ad intervalli di 2, 24, 48, 72 e 96 ore dalla prima somministrazione e la funzione uditiva mediante i prodotti di distorsione (DPOAE) ed i potenziali evocati uditivi (ABR). Negli animali trattati con salicilato la nostra metodica ha evidenziato la presenza di un acufene con frequenza vicina ai 16 kHz insorto dopo la prima somministrazione e risoltosi spontaneamente 24 ore dopo l'ultima. Negli animali trattati con salicilato e memantina l'acufene, seppur presente, è risultato significativamente attenuato, prevalentemente durante il secondo giorno di trattamento. Né il salicilato né la memantina hanno causato alterazioni permanenti della funzione uditiva; le variazioni registrate mediante i prodotti di distorsione sono regredite al termine del trattamento. Il nostro studio conferma il ruolo dei recettori NMDA nell'acufene da salicilato e le potenzialità della memantina nel contrastarne l'insorgenza e la persistenza. Data la facile reperibilità del farmaco, già utilizzato nel trattamento della malattia di Alzheimer e del morbo di Parkinson, ed i risultati incoraggianti ottenuti nel modello animale, sono auspicabili ulteriori approfondimenti nell'uomo.

Background. Implantation of autologous skin fibroblasts transduced ex vivo with a replication-defective adenoviral vector, carrying the LIM mineralization protein-3 (Ad-LMP-3), and adsorbed on a hydroxyapatite/collagen (HA/COL) scaffold. Methods. Twenty-seven Wistar rats were used. A 5- × 5-mm full-thickness defect was created in the exposed mandible. All animals were randomized into 3 experimental groups: (1) autologous dermal fibroblasts transduced with Ad-LMP-3 and adsorbed on the HA/COL; (2) nontransduced dermal fibroblasts adsorbed on the HA/COL scaffold; and (3) HA/COL scaffold without cells. Three-dimensional micro-CT (3DmicroCT or 3DμCT) and histological analysis were performed. Results. Efficient neoosteogenesis was observed in animals treated with LMP-3–expressing cells (group 1) as soon as 4 weeks after surgery. Conversely, nonsignificant bone formation was detected in control animals (groups 2 and 3) at all time points tested. Conclusion. These results suggest that the experimental approach based on transplantation of genetically modified autologous cells could provide an alternative treatment for cranio-maxillo-facial defects. Nonetheless, additional data from the study on larger bone defects must follow to foresee a clinical application in the near future. © 2009 Wiley Periodicals, Inc. Head Neck, 2010