Influence of noise exposure on antioxidant system and TEOAEs in rabbits

Effects of acute exposure to Al2O3-NPs (α and γ) and white noise and their combination on cochlea structure and function in Wistar rats

Hearing loss induced by noise and combinations of factors is a common occupational disease among workers. This study aimed to investigate the impact of acute exposure to white noise and Al2O3 NPs, alone and in combination, on changes in the hearing and structural functions of the cochlea in rats. Thirty-six rats were randomly assigned to one of six groups: Control, acute exposure to white noise, exposure to γ-Al2O3 NPs, exposure to noise plus γ-Al2O3 NPs, exposure to α-Al2O3 NPs, and exposure to the combination of noise plus α-Al2O3 NPs. TTS and PTS were examined using DPOAE, while oxidative index (MDA, GSH-Px), gene expression (NOX3, TGF-ß, CYP1A1), protein expression (ß-Tubulin, Myosin VII), and histopathological changes were examined in the cochlea. The morphology of Al2O3 NPs was examined by TEM. The results of the DPOAE test showed a significant increase in TTS in all groups and an increase in PTS in the groups exposed to noise, γ-Al2O3 NPs, and a combination of noise plus Al2O3 NPs (P < 0.05). In the group exposed to white noise plus Al2O3 NPs, the MDA levels increased, the level of GSH-Px decreased, and the expression percentage of ß-Tubulin and Myosin VII decreased, while the expression of NOX3, TGF-ß, and CYP1A1 (except for the α-Al2O3 NPs group) significantly increased (P < 0.05). Histopathological changes of the cochlea indicated damage to hair and ganglion cells, which was more severe in the combined exposure group. The combined and independent exposure to white noise and Al2O3 NPs damaged hair and ganglion cells for high-frequency perception, affecting the function and structure of the cochlea and leading to TTS and PTS.

Combined effects of the exposure to silver nanoparticles and noise on hearing function and cochlea structure of the male rats

AIMS

This study intended to investigate whether exposure to the combination of noise and Ag-NPs in rats induces cochlear damage and hearing dysfunction.

MAIN METHODS

A total of 24Wistar rats were divided into four treatment groups and received/exposed to saline (IP), Ag-NPs (100 mg/kg, 5d/w for 4 weeks), 8 kHz narrowband noise (104 dB SPL, 6 h/day, 5d/w for 4 weeks) and Ag-NPs plus noise. The DPOAE, serum levels of MDA and SOD and changes in body weight were assessed. The rat cochlea was further stained for investigating the mRNA expression (TL-6, NOX3, and TNF-), IHC (TUJ-1 and MHC7), and histological alterations. The Ag-NPs characteristics were also analysed by SEM and XRD.

KEY FINDINGS

DPOAE values were remarkably reduced (p < 0.05) among the exposed groups. Furthermore, exposure to noise and Ag-NPs significantly increased MDA levels and decreased the SOD activity in the serum. In comparison to the control group, the expression of IL-6, TNF-, and NOX3 was shown to be elevated in the Ag-NPs plus noise group. The body weight also increased significantly in all groups with the exception of the Ag-NPs plus noise group. IHC tests showed remarkable down-regulation of TUJ1 and MYO7A. Morphological changes confirmed our findings as well. SEM and XRD data validated the production of Ag-NPs.

SIGNIFICANCE

According to the findings of this study, sub-acute exposure to noise and Ag-NPs causes permanent damage to the hair cells that are in charge of high-frequency perception.

Correlation of SOD and MDA Expression in the Organ of Corti and Changes in the Function of Outer Hair Cells Measured by DPOAE Examination in Noise-Exposed Rat Cochlea

BACKGROUND

Hearing loss due to noise can cause the disturbances toward the quality of life and cause mechanical damage and metabolic decompensation. Distortion Product Otoacoustic Emission (DPOAE) is an examination to assess the sensory function of outer hair cells. Superoxide Dismutase (SOD) and Malondialdehyde (MDA) are markers of oxidative stress. The aim of this study was to identify the correlation between DPOAE examination and SOD and MDA expression in rats exposed to noise.

METHODS

This research was conducted on 27 rats which were divided into 3 groups, group 1 (control), group 2, and group 3 were groups with 100 dB and 110 dB noise exposure respectively.

RESULTS

Our findings show a decrease in SOD expression and DPOAE values as well as an increase in MDA expression in rats exposed to noise and there is a positive correlation between Signal to Noise Ratio (SNR) value with SOD expression (r= 0.733, p= 0.025) and a negative correlation between SNR value with MDA expression (r= -0.678, p= 0.045).

CONCLUSION

our study find the correlation of oxidant and antioxidant status values in the organ of corti and changes in the function of outer hair cells in noise-exposed rat models.

Cigarette Smoking, Smoking Cessation, and Risk of Hearing Loss in Women

BACKGROUND

Previous studies demonstrated higher risk of hearing loss among cigarette smokers, but longitudinal data on whether the risk is influenced by smoking cessation are limited. We prospectively investigated relations between smoking, smoking cessation, and risk of self-reported moderate or worse hearing loss among 81,505 women in the Nurses' Health Study II (1991-2013).

METHODS

Information on smoking and hearing status was obtained from validated biennial questionnaires. Cox proportional hazards regression was used to estimate multivariable-adjusted relative risks (MVRR, 95% confidence interval).

RESULTS

During 1,533,214 person-years of follow-up, 2760 cases of hearing loss were reported. Smoking was associated with higher risk of hearing loss and the risk tended to be higher with greater number of pack-years smoked. Compared with never smokers, the MVRR (95% confidence interval) among past smokers with 20+ pack-years of smoking was 1.30 (1.09-1.55) and 1.21 (1.02-1.43) for current smokers. The magnitude of elevated risk diminished with greater time since smoking cessation. Compared with never smokers, the MVRR among smokers who quit <5 years prior was 1.43 (1.17-1.75); 5-9 years prior was 1.27 (1.03-1.56); 10-14 years prior was 1.17 (0.96-1.41); and plateaued thereafter. Additional adjustment for pack-years smoking attenuated the results.

CONCLUSIONS

The higher risk of hearing loss associated with smoking may diminish over time after quitting.

Effect of myricetin on the gene expressions of NOX3, TGF-β1, prestin, and HSP-70 and anti-oxidant activity in the cochlea of noise-exposed rats

Objective(s):

Noise-induced hearing loss is one of the most common occupational diseases in industrialized countries and can be affected by various environmental and genetic factors. This study was designed to examine the effect of myricetin in preventing this disorder.

Materials and Methods:

Twenty-one Wistar rats were randomly divided into five groups: Non-exposed, noise exposure only, noise exposure with vehicle, noise exposure with myricetin 5 mg/Kg, and noise exposure with myricetin 10 mg/kg. All animals were sacrificed after last noise exposure. The left cochlea was dissected from each rat. It was used for mRNA expression analysis (NOX3, TGF-β1, prestin, and HSP-70). Blood samples were collected to assess superoxide dismutase (SOD) activity, 1, 1 diphenyl picrylhydrazyl (DPPH), and malondialdehyde (MDA) measurements.

Results:

Real time-PCR assay revealed that noise decreased NOX3 and increased TGF-β1, prestin, and HSP-70 gene expressions. Administration of myricetin at the dose of 5 mg/kg, but not at 10 mg/kg, significantly reversed these changes. Noise also increased MDA levels and decreased SOD and DPPH scavenging activities. Myricetin at the doses of 5 and 10 mg/kg also reversed these changes.

Conclusion:

The findings of this study showed that myricetin at the dose of 5 mg/Kg was able to reverse noise-induced abnormalities in gene expression and oxidant/anti-oxidant balance. It is a possibility that myricetin via enhancement of anti-oxidant activity induced these effects.

Oxidative Damage and Inflammation Biomarkers: Strategy in Hearing Disorders

IMPORTANCE

Excess free radical-induced oxidative stress and inflammatory processes are increasingly recognized as causative factors in hearing and balance disorders. Antioxidant micronutrients neutralize free radicals and, at adequate doses, reduce inflammation and demonstrate benefits in animal models and human trials. Therefore, it is reasonable to expect that biomarkers of oxidative damage and inflammation are appropriate correlative biological outcome parameters in clinical hearing intervention studies.

OBJECTIVE

To provide the otology investigator a selected panel of biomarkers from the large universe of available tests that can be used as reasonable secondary endpoints in hearing and balance research.

BACKGROUND SETTING

The tenets of antioxidant science dictate that there are a great variety of free radicals and that they impact different cellular targets. They also demonstrate varying functions in different cellular environments. In addition, oxidative stress and inflammation may cause direct injury to tissues, cell membrane lipids, proteins and mitochondrial, and nuclear DNA. To accommodate these many pathways, the useful categories of potential biomarkers become extensive. The degree of injury is also reflected by separate markers of inflammation and measures of antioxidant levels. Therefore, to provide a reliable indication of oxidative damage, inflammation and antioxidant level, it is necessary to determine a broad spectrum of lipid peroxidation markers, adducts of DNA, oxidation levels of proteins and pro-inflammatory cytokines.

CONCLUSION

This report highlights some of the most clinically relevant and well-studied biomarkers in each category of tissue damage. It also includes those markers with which the authors have had direct positive clinical experience. The outcome from these studies is intended to provide a list of adjunctive measures that can be recommended as a relevant biomarker panel in hearing disorder clinical trials.

Sex-Related Cochlear Impairment in Cigarette Smokers

Background

A number of studies have documented the influence of cigarette smoking on hearing. However, the association between sex and hearing impairment in smokers as measured by otoacoustic emissions (OAEs) has not been clearly established. The aim of this study was to analyze sex-specific effects of smoking on hearing via conventional and ultra-high-frequency pure tone audiometry (PTA), and OAEs, specifically spontaneous OAEs, click-evoked OAEs, and distortion-product OAEs.

Material/Methods

The study included 84 healthy volunteers aged 25–45 years (mean 34), among them 46 women (25 non-smokers and 21 smokers) and 38 men (16 non-smokers and 22 smokers). The protocol of the study included otoscopic examination, tympanometry, low-, moderate-, and ultra-high-frequency PTA, evaluation of spontaneous click-evoked (CEAOEs) and distortion-product otoacoustic emissions (DPOAEs), assessment of the DP-grams for 2f₁-f₂ (f₁ from 977 to5 164 Hz), and input/output function at L₂ primary tone level of 40–70 dB SPL.

Results

Smokers and non-smokers did not differ significantly in terms of their hearing thresholds assessed with tone audiometry. Male smokers presented with significantly lower levels of CEAOEs and DPOAEs than both male non-smokers and female smokers.

Conclusions

Smoking does not modulate a hearing threshold determined with PTA at low, moderate, and ultra-high frequencies, but causes a significant decrease in OAE levels. This effect was observed only in males, which implies that they are more susceptible to smoking-induced hearing impairment. Sex-specific differences in otoacoustic emissions level may reflect influences of genetic, hormonal, behavioral, and/or environmental factors.

Is rosuvastatin protective against on noise-induced oxidative stress in rat serum?

Noise, one of the main components of modern society, has become an important environmental problem. Noise is not only an irritating sound, but also a stress factor leading to serious health problems. In this study, we have investigated possible effects of rosuvastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, thought to have an antioxidant effect, on noise-induced oxidative stress in the serum of rat models. Thirty-two male Wistar albino rats were used. In order to ease their adaptation, 2 weeks before the experiment, the rats were divided into four groups (with eight rats per each group): Noise exposure plus rosuvastatin usage, only noise exposure, only rosuvastatin usage and control. After the data had been collected, oxidant (Malondialdehyde, nitric oxide [NO], protein carbonyl [PC]) and antioxidant (superoxide dismutase [SOD], glutathione peroxidase [GSH-PX], catalase [CAT]) parameters were analyzed in the serum. Results indicated that SOD values were found to be significantly lower, while PC values in serum were remarkably higher in the group that was exposed to only noise. GSH-Px values in serum dramatically increased in the group on which only rosuvastatin was used. During noise exposure, the use of rosuvastatin caused significantly increased CAT values, whereas it resulted in reduced PC and NO values in serum. In conclusion, our data show that noise exposure leads to oxidative stress in rat serum; however, rosuvastatin therapy decreases the oxidative stress caused by noise exposure.

Effects of Ascorbic Acid on Oxidative System and Transient Evoked Otoacoustic Emissions in Rabbits Exposed to Noise

OBJECTIVES/HYPOTHESIS

The objective was to investigate the effects of both noise exposure and ascorbic acid on oxidative status and hearing thresholds of rabbits.

STUDY DESIGN

Randomized prospective animal study comparing oxidative parameters and otoacoustic emissions in two rabbit groups exposed to noise. One group was given ascorbic acid, the other group was not given any treatment.

METHODS

Two groups of rabbits were used in the study; each group had six rabbits. The six rabbits in the first group were not given any treatment, whereas 500 mg intramuscular ascorbic acid twice daily for 2 1/2 days was given to the six rabbits in the second group. Transient evoked otoacoustic emissions were recorded in all animals before and after noise exposure. Total protein sulfhydryl groups, carbonyl contents, and malondialdehyde levels, as well as erythrocyte glutathione, superoxide dismutase, and catalase enzyme levels, were measured in all rabbits. All the rabbits were exposed to noise (100 dB sound pressure level, 1000 Hz, 1 h), and transient evoked otoacoustic emissions were recorded again.

RESULTS

When oxidative parameters before noise exposure were compared, erythrocyte glutathione and catalase enzyme levels were detected to be higher in the second group (P <.05). In the first group of rabbits after noise exposure, total protein sulfhydryl groups were found to be reduced (P <.05), whereas plasma carbonyl contents and malondialdehyde levels were elevated significantly (P <.05). In this group, erythrocyte glutathione, superoxide dismutase, and catalase enzyme levels were low (P <.05). In the second group, which was given ascorbic acid, total protein sulfhydryl groups were reduced (P <.05), whereas plasma carbonyl contents and malondialdehyde levels did not change (P >.05) following noise exposure. In the second group, erythrocyte glutathione and catalase enzyme levels were reduced (P <.05), but superoxide dismutase levels did not change (P >.05). Transient evoked otoacoustic emissions after noise exposure were weak in both groups, but reproducibility and signal-to-noise ratios were higher in the second group (P <.05).

CONCLUSION

Ascorbic acid treatment inhibited both lipid peroxidation and oxidative damage of proteins in rabbits exposed to noise. The study data suggest, at least, that oxidative status should be included in the physiopathology of noise-induced hearing loss; in addition, a brief application of ascorbic acid before noise exposure appeared to play a protective role for cochlea.

Intratympanic dexamethasone injection effects on transient-evoked otoacoustic emission

PURPOSE

To investigate the effects of intratympanic dexamethasone injection, which is done because of tinnitus, on transient evoked otoacoustic emission (TEOAE) and so determine whether given dexamethasone cause any damage in the inner ear.

PATIENTS AND METHODS

Twenty-six patients, aged between 32 and 75, with subjective tinnitus, were randomly selected. The selected patients were the ones whose improvement had not been achieved through minimum 6 months' medical therapy (eg, Ginkgo biloba extract EGb 761, betahistidine, and trimetazidin) and who were free of systemic or otolaryngologic disease (hypertension, diabetes mellitus, hypo/hypertyroidi, hypercholesterolemia, Meniere disease, and otosclerosis). Before and after the injections, audiometry including high-frequency tinnitus matching and TEOAE tests were done. The injections of 4 mg/mL dexamethasone were done 5 times in fixed protocols on days 0, 2, 4, 6, and 8. After each injection, the patients were kept supine for 60 minutes with the head turned 45 degrees to opposite ear. Paired t test was used to compare the beginning and final measurements.

RESULTS

Temporary pain and vertigo attacks which lasted at most for 15 minutes occurred in some patients only during injections. Neither infection nor persistent perforation occurred in any patients. After the management, there was no significant difference on patient's pure tone averages ( P = .067) and high-frequency averages ( P = .592). When the obtained TEOAE results before and after management were compared, the only significant increase was detected in the reproducibility values ( P = .042). There was no significant difference in other TEOAE parameters which are stimulus stability, stimulus intensity, and overall signal-to-noise ratio ( P > .05). There is no fixed criteria for rejecting a response solely on the reproducibility. However, a high value of the reproducibility (or increase in reproducibility) is always meaningful.

CONCLUSION

Intratympanic dexamethasone used for management in many indications, primarily in Meniere and tinnitus patients, was found to increase the reproducibility values of otoacoustic emission. Despite the fact that there was not a reasonable increase in the responses coming from the outer hair cells, the result was considered positive for the study as the responses did not decrease. It is found out that 4 mg/mL dexamethasone given intratympanically does not adversely affect the outer hair cell function as measured by otoacoustic emission. Within the limits of this study, dexamethasone appears to be safe when given intratympanically.

Effect of SOD1 overexpression on age- and noise-related hearing loss

Reactive oxygen species (ROS) have been implicated in hearing loss associated with aging and noise exposure. Superoxide dismutases (SODs) form a first line of defense against damage mediated by the superoxide anion, the most common ROS. Absence of Cu/Zn SOD (SOD1) has been shown to potentiate hearing loss related to noise exposure and age. Conversely, overexpression of SOD1 may be hypothesized to afford a protection from age- and noise-related hearing loss. This hypothesis may be tested using a transgenic mouse model carrying the human SOD1 gene. Contrary to expectations, here, we report that no protection against age-related hearing loss was observed in mice up to 7 months of age or from noise-induced hearing loss when 8 week old mice were exposed to broadband noise (4-45 kHz, 110 dB for 1 h). Mitochondrial DNA deletion, an index of aging, was elevated in the acoustic nerve of transgenic mice compared to nontransgenic littermates. The results indicate the complexity of oxidative metabolism in the cochlea is greater than previously hypothesized.