Temporary hearing loss induced by combinations of intense sounds and nonsteroidal anti-inflammatory drugs

Long‑term treatment with salicylate enables NMDA receptors and impairs AMPA receptors in C57BL/6J mice inner hair cell ribbon synapse

Salicylate is widely used to produce animal models of tinnitus in mice and/or rats. The side effects on auditory function, including hearing loss and tinnitus, are considered the results of the auditory nerve dysfunction. A recent study indicated that chronic treatment with salicylate for several weeks reduces compressed action potential amplitude, which is contradictory to the studies reporting excessive activation of N-methyl-D-aspartate receptors (NMDAR) in tinnitus-induced animals. The specific aims of the experiment were to detect the effect of salicylate on the inner hair cells (IHCs), ribbon synapse, as well as the association between the hearing threshold and the number of mismatched ribbon synapses. In the present study, mice were injected intraperitoneally with a low dose of salicylate (200 mg/kg) for 14 days. The auditory brainstem response and otoacoustic emission were measured to assess auditory function of the mice. The postsynaptic regions of IHC were identified with two types of immunostaining targets: Postsynaptic density protein 95 and Glu2/3. The number of spheres was counted and the synapses were reconstructed in 3-dimensional images. Increases in distortion product otoacoustic emissions amplitudes of the salicylate group were detected, however, an elevation in the hearing threshold was also observed. A mismatch between pre-and post-ribbon synapses was observed. In addition, the cochlear components, including the numbers of outer hair cells and IHCs, were unlikely to be affected by salicylate. IHC ribbon synapses were more susceptible to salicylate stimuli. Furthermore, mismatch of pre- and post-ribbon synapses may indicate a competitive inhibition between NMDAR and α-amino-3-hydroxy-5-methyl-4-isoxa-zole-propionate receptors and dysfunction of ribbon synapses.

Duration of Analgesic Use and Risk of Hearing Loss in Women

Aspirin, nonsteroidal antiinflammatory drugs (NSAID), and acetaminophen are commonly used. Frequent use of analgesics has been associated with a higher risk of hearing loss. However, the association between duration of analgesic use and the risk of hearing loss is unclear. We investigated the relationship between duration of analgesic use and self-reported hearing loss among 55,850 women in the Nurses' Health Study. Cox proportional hazards regression was used to adjust for potential confounders. During 873,376 person-years of follow-up (1990-2012), longer durations of NSAID use (for >6 years of use compared with <1 year, multivariable-adjusted relative risk = 1.10, 95% confidence interval: 1.06, 1.15; P for trend < 0.001) and acetaminophen use (for >6 years of use compared with <1 year, multivariable-adjusted relative risk = 1.09, 95% confidence interval: 1.04, 1.14; P for trend < 0.001) were associated with higher risks of hearing loss. Duration of aspirin use was not associated with hearing loss (for >6 years of use compared with <1 year, multivariable-adjusted relative risk = 1.01, 95% confidence interval: 0.97, 1.05; P for trend = 0.35). In this cohort of women, longer durations of NSAID and acetaminophen use were associated with slightly higher risks of hearing loss, but duration of aspirin use was not. Considering the high prevalence of analgesic use, this may be an important modifiable contributor to hearing loss.

Central Nervous Activity upon Systemic Salicylate Application in Animals with Kanamycin-Induced Hearing Loss--A Manganese-Enhanced MRI (MEMRI) Study

This study investigated the effect of systemic salicylate on central auditory and non-auditory structures in mice. Since cochlear hair cells are known to be one major target of salicylate, cochlear effects were reduced by using kanamycin to remove or impair hair cells. Neuronal brain activity was measured using the non-invasive manganese-enhanced magnetic resonance imaging technique. For all brain structures investigated, calcium-related neuronal activity was increased following systemic application of a sodium salicylate solution: probably due to neuronal hyperactivity. In addition, it was shown that the central effect of salicylate was not limited to the auditory system. A general alteration of calcium-related activity was indicated by an increase in manganese accumulation in the preoptic area of the anterior hypothalamus, as well as in the amygdala. The present data suggest that salicylate-induced activity changes in the auditory system differ from those shown in studies of noise trauma. Since salicylate action is reversible, central pharmacological effects of salicylate compared to those of (permanent) noise-induced hearing impairment and tinnitus might induce different pathophysiologies. These should therefore, be treated as different causes with the same symptoms.

Ubiquitous aspirin: a systematic review of its impact on sensorineural hearing loss

OBJECTIVE

This systematic review evaluates the impact of aspirin on audiometric outcomes with respect to: (1) doses exceeding 325 mg daily, (2) doses of 325 mg daily or less, (3) studies applicable to the general populace, and (4) studies applicable to those with inflammatory conditions. It also assesses the impact of aspirin on (a) self-reported hearing loss, (b) noise-induced audiometric changes, and (c) the adverse otological effects of aminoglycoside therapy.

DATA SOURCES

Computerized searches of MEDLINE, PubMed, Cochrane, and EMBASE databases were performed, updated through January 2014, and supplemented by manual searches and inquiries to topic experts.

REVIEW METHODS

A systematic review was performed according to an a priori protocol. Data extraction was performed by 2 independent parties and focused on relevant audiological measurements, potential confounders, and study design elements associated with risk of bias, including utilization of randomization, prospective/retrospective data collection, and incorporation of blinding.

RESULTS

The 37 criterion-meeting studies included a combined total of 185,155 participants. Aspirin ingestion ≥ 1.95 g/d was associated with worse audiometric results (4-112 dB threshold shift); the effect was dose dependent and reversible in the short term. There were no audiometric data that confirm that long-term doses of 81 mg or 325 mg daily have no hearing consequences. Paradoxically, aspirin (in doses shown to be detrimental in isolation) had a protective effect when co-administered with intravenous gentamicin.

CONCLUSIONS

With the large-scale population utilization of aspirin for cardiovascular prophylaxis, the potential risks to hearing health should be considered for future longitudinal study, particularly given that short-term effects may be reversible.

Salicylate-induced cochlear impairments, cortical hyperactivity and re-tuning, and tinnitus

High doses of sodium salicylate (SS) have long been known to induce temporary hearing loss and tinnitus, effects attributed to cochlear dysfunction. However, our recent publications reviewed here show that SS can induce profound, permanent, and unexpected changes in the cochlea and central nervous system. Prolonged treatment with SS permanently decreased the cochlear compound action potential (CAP) amplitude in vivo. In vitro, high dose SS resulted in a permanent loss of spiral ganglion neurons and nerve fibers, but did not damage hair cells. Acute treatment with high-dose SS produced a frequency-dependent decrease in the amplitude of distortion product otoacoustic emissions and CAP. Losses were greatest at low and high frequencies, but least at the mid-frequencies (10-20 kHz), the mid-frequency band that corresponds to the tinnitus pitch measured behaviorally. In the auditory cortex, medial geniculate body and amygdala, high-dose SS enhanced sound-evoked neural responses at high stimulus levels, but it suppressed activity at low intensities and elevated response threshold. When SS was applied directly to the auditory cortex or amygdala, it only enhanced sound evoked activity, but did not elevate response threshold. Current source density analysis revealed enhanced current flow into the supragranular layer of auditory cortex following systemic SS treatment. Systemic SS treatment also altered tuning in auditory cortex and amygdala; low frequency and high frequency multiunit clusters up-shifted or down-shifted their characteristic frequency into the 10-20 kHz range thereby altering auditory cortex tonotopy and enhancing neural activity at mid-frequencies corresponding to the tinnitus pitch. These results suggest that SS-induced hyperactivity in auditory cortex originates in the central nervous system, that the amygdala potentiates these effects and that the SS-induced tonotopic shifts in auditory cortex, the putative neural correlate of tinnitus, arises from the interaction between the frequency-dependent losses in the cochlea and hyperactivity in the central nervous system.

Analgesic use and the risk of hearing loss in women

Use of analgesics is common and is associated with increased risk of hearing loss in men; however, the relation has not been examined prospectively in women. The authors prospectively examined the relation between frequency of aspirin, ibuprofen, and acetaminophen use and risk of hearing loss among 62,261 women aged 31-48 years at baseline (1995) in Nurses' Health Study II. The outcome was self-reported hearing loss (n = 10,012), and the follow-up period was 1995-2009. Cox proportional hazards regression was used to adjust for potential confounders. During 764,247 person-years of follow-up, ibuprofen use and acetaminophen use were independently associated with increased risk of hearing loss, but aspirin use was not. For ibuprofen, the multivariate-adjusted relative risk of hearing loss was 1.13 (95% confidence interval (CI): 1.06, 1.19) for use 2-3 days/week, 1.21 (95% CI: 1.11, 1.32) for use 4-5 days/week, and 1.24 (95% CI: 1.14, 1.35) for use ≥6 days/week (P-trend < 0.0001), compared with use less than once per week. For acetaminophen, the corresponding relative risks were 1.11 (95% CI: 1.02, 1.19), 1.21 (95% CI: 1.07, 1.37), and 1.08 (95% CI: 0.95, 1.22), respectively (P-trend = 0.0007). In this study, use of ibuprofen or acetaminophen (but not aspirin) 2 or more days per week was associated with an increased risk of hearing loss in women.

Salicylate-induced degeneration of cochlea spiral ganglion neurons-apoptosis signaling

Aspirin, whose active ingredient is sodium salicylate, is the most widely used drug worldwide, but it is not recommended for children because it may cause Reye's syndrome. High doses of salicylate also induce temporary hearing loss and tinnitus; while these disorders are believed to disappear when treatment is discontinued some data suggest that prolonged treatment may be neurotoxic. To investigate its ototoxicity, immature, postnatal day 3 rat cochlear organotypic cultures were treated with salicylate. Salicylate did not damage the sensory hair cells, but instead damaged the spiral ganglion neurons (SGN) and their peripheral fibers in a dose-dependent manner. The cross-sectional area of SGN decreased from 205 microm(2) in controls to 143, 116, and 91 microm(2) in cultures treated with 1, 3, or 5 mM salicylate, respectively. Morphological changes and caspase upregulation were indicative of caspase-mediated apoptosis. A quantitative RT-PCR apoptosis array identified a subset of genes up- or down regulated by salicylate. Eight genes showed a biologically relevant change (P<0.05, > or =2 fold change) after 3 h treatment with salicylate; seven genes (Tp53, Birc3, Tnfrsf5, Casp7, Nfkb1, Fas, Lta, Tnfsf10) were upregulated and one gene (Pycard) was downregulated. After 6 h treatment, only one gene (Nol3) was upregulated and two genes were downregulated (Cideb and Lhx4) while after 12 h treatment, two genes (Il10, Gadd45a) were upregulated and 4 (Prok2, Card10, Ltbr, Dapk1) were downregulated. High doses of salicylate in a physiologically relevant range can induce caspase-mediated cell death in immature SGN; changes in the expression of apoptotic genes particularly among members of the tumor necrosis factor (TNF) family appear to play an important role in the degeneration.

Too much of a good thing: long-term treatment with salicylate strengthens outer hair cell function but impairs auditory neural activity

Aspirin has been extensively used in clinical settings. Its side effects on auditory function, including hearing loss and tinnitus, are considered as temporary. A recent promising finding is that chronic treatment with high-dose salicylate (the active ingredient of aspirin) for several weeks enhances expression of the outer hair cell (OHC) motor protein (prestin), resulting in strengthened OHC electromotility and enhanced distortion product otoacoustic emissions (DPOAE). To follow up on these observations, we carried out two studies, one planned study of age-related hearing loss restoration and a second unrelated study of salicylate-induced tinnitus. Rats of different strains and ages were injected with salicylate at a dose of 200 mg/kg/day for 5 days per week for 3 weeks or at higher dose levels (250-350 mg/kg/day) for 4 days per week for 2 weeks. Unexpectedly, while an enhanced or sustained DPOAE was seen, permanent reductions in the amplitude of the cochlear compound action potential (CAP) and the auditory brainstem response (ABR) were often observed after the chronic salicylate treatment. The mechanisms underlying these unexpected, permanent salicylate-induced reductions in neural activity are discussed.

Analgesic use and the risk of hearing loss in men

BACKGROUND

Hearing loss is a common sensory disorder, yet prospective data on potentially modifiable risk factors are limited. Regularly used analgesics, the most commonly used drugs in the US, may be ototoxic and contribute to hearing loss.

METHODS

We examined the independent association between self-reported professionally diagnosed hearing loss and regular use of aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and acetaminophen in 26,917 men aged 40-74 years at baseline in 1986. Study participants completed detailed questionnaires at baseline and every 2 years thereafter. Incident cases of new-onset hearing loss were defined as those diagnosed after 1986. Cox proportional hazards multivariate regression was used to adjust for potential confounding factors.

RESULTS

During 369,079 person-years of follow-up, 3488 incident cases of hearing loss were reported. Regular use of each analgesic was independently associated with an increased risk of hearing loss. Multivariate-adjusted hazard ratios of hearing loss in regular users (2+ times/week) compared with men who used the specified analgesic <2 times/week were 1.12 (95% confidence interval [CI], 1.04-1.20) for aspirin, 1.21 (95% CI, 1.11-1.33) for NSAIDs, and 1.22 (95% CI, 1.07-1.39) for acetaminophen. For NSAIDs and acetaminophen, the risk increased with longer duration of regular use. The magnitude of the association was substantially higher in younger men. For men younger than age 50 years, the hazard ratio for hearing loss was 1.33 for regular aspirin use, 1.61 for NSAIDs, and 1.99 for acetaminophen.

CONCLUSIONS

Regular use of aspirin, NSAIDs, or acetaminophen increases the risk of hearing loss in men, and the impact is larger on younger individuals.

Cochlear Compression: Perceptual Measures and Implications for Normal and Impaired Hearing

This article provides a review of recent developments in our understanding of how cochlear nonlinearity affects sound perception and how a loss of the nonlinearity associated with cochlear hearing impairment changes the way sounds are perceived. The response of the healthy mammalian basilar membrane (BM) to sound is sharply tuned, highly nonlinear, and compressive. Damage to the outer hair cells (OHCs) results in changes to all three attributes: in the case of total OHC loss, the response of the BM becomes broadly tuned and linear. Many of the differences in auditory perception and performance between normal-hearing and hearing-impaired listeners can be explained in terms of these changes in BM response. Effects that can be accounted for in this way include poorer audiometric thresholds, loudness recruitment, reduced frequency selectivity, and changes in apparent temporal processing. All these effects can influence the ability of hearing-impaired listeners to perceive speech, especially in complex acoustic backgrounds. A number of behavioral methods have been proposed to estimate cochlear nonlinearity in individual listeners. By separating the effects of cochlear nonlinearity from other aspects of hearing impairment, such methods may contribute towards identifying the different physiological mechanisms responsible for hearing loss in individual patients. This in turn may lead to more accurate diagnoses and more effective hearing-aid fitting for individual patients. A remaining challenge is to devise a behavioral measure that is sufficiently accurate and efficient to be used in a clinical setting.

Auditory sensori-neural alterations induced by salicylate

Early after the development of aspirin, almost 150 years ago, its auditory toxicity has been associated with high doses employed in the treatment of chronic inflammatory diseases. Tinnitus, loss of absolute acoustic sensitivity and alterations of perceived sounds are the three auditory alterations described by human subjects after ingestion of large doses of salicylate. They develop over the initials days of treatment but may then level off, fluctuate or decrease, and are reversible within a few days of cessation of treatment. They may also occur within hours of ingestion of an extremely large dose. Individual subjects vary notably as to their susceptibility to salicylate-induced auditory toxicity. Tinnitus may be the first subjective symptom, and is often described as a continuous high pitch sound of mild loudness. The hearing loss is slight to moderate, bilaterally symmetrical and affects all frequencies with often a predominance at the high frequencies. Alterations of perceived sounds include broadening of frequency filtering, alterations in temporal detection, deterioration of speech understanding and hypersensitivity to noise. Behavioral conditioning of animals provides evidence for mild and reversible hearing loss and tinnitus, similar to those observed in humans. Anatomical examinations revealed significant alterations only at outer hair cell lateral membrane. Electrophysiological investigations showed no change in endocochlear resting potential, and small changes in the compound sensory potentials, cochlear microphonic and summating potential, at low acoustic levels. Measures of cochlear mechanical responses to sounds indicated a clear loss of absolute sensitivity and an associated broadening of frequency filtering, both of a magnitude similar to audiometric alterations in humans, but at extremely high salicylate levels. Otoacoustic emissions demonstrated changes in the mechano-sensory functioning of the cochlea in the form of decrease of spontaneous emissions and reduced nonlinearities. In vitro measures of isolated outer hair cells showed reduction of their fast motile responses which are thought to be at the origin of cochlear absolute sensitivity and associated fine filtering. Acoustically evoked neural responses from the eighth nerve to the auditory cortex showed reversible and mild losses of absolute sensitivity and associated broadening of frequency filtering. There is no evidence of a direct alteration of cochlear efferent innervation. Evidence was obtained for decreases in cochlear blood supply under control of autonomous innervation. Spontaneous neural activity of the auditory nerve revealed increases in firings and/or in underlying temporal synchronies. Similar effects were found at the inferior colliculus, mostly at the external nucleus, and at the cortex, mostly at the anterior and less at the secondary auditory cortex but not at the primary auditory cortex. These changes in spontaneous activity might underlie tinnitus as they affect mostly neural elements coding high frequencies, can occur without a loss of sensitivity, are dose dependent, develop progressively, and are reversible. Biochemical cochlear alterations are poorly known. Modifications of oxydative phosphorylation does not seem to occur, involvement of inhibition of prostaglandin synthesis appears controversial but could underlie changes in blood supply. Other biochemical alterations certainly also occur at outer hair cells and at afferent nerve fibers but remain unknown.

Effects of aspirin on psychophysical measures of frequency selectivity, two-tone suppression, and growth of masking

Three psychophysical measures of nonlinearity were evaluated before and during a course of aspirin ingestion to investigate the role of outer hair cells (OHCs) in these measures, as aspirin is thought to alter the functioning of OHCs. Six normal-hearing individuals received a moderate dose (3.9 g/day) of aspirin for four days, producing essentially flat, temporary hearing losses that ranged from 5-20 dB. The losses were about 2 dB greater for a 300-ms signal than for a 15-ms signal, indicating reduced temporal integration with aspirin. On the final three days of aspirin use, three experiments were completed; each was designed to measure one aspect of nonlinear behavior: (1) the effects of level on frequency selectivity in simultaneous masking using notched-noise maskers, (2) two-tone suppression using forward maskers at the signal frequency (fs) and suppressor tones above fs, and (3) growth-of-masking functions in forward masking using a masking tone below fs. Signal frequencies of 750 and 3000 Hz were used to evaluate the effects of aspirin at relatively low- and high-frequency regions of the cochlea. In experiment 1, aspirin broadened the auditory filters and reduced the effect of level on frequency selectivity. In experiment 2, aspirin reduced or eliminated two-tone suppression. And, in experiment 3, aspirin reduced the slopes of the growth-of-masking functions. Thus, the aspirin was effective in reducing nonlinearity in all three experiments, suggesting that these measures reflect the same (or a similar) active, nonlinear mechanism, namely the compressive nonlinearity provided by the OHCs. In all experiments, aspirin tended to have larger detrimental effects on the nonlinear measures at 3000 Hz than at 750 Hz, which can be explained in terms of greater involvement of nonlinear processing at higher frequencies. Finally, these effects of aspirin were found to be similar to those observed in preliminary measurements in two subjects with mild, permanent hearing loss.

Alleviation of mortality induced by salicylate and stress

Protection from the deleterious effects of the interaction of environmental stress and salicylate by calcium supplement was investigated in 96 pigmented rats. Within a 2 x 2 x 4 factorial design, rats were assigned to groups defined by: A) ad lib access to 1) plain tap water, or 2) 50 mM calcium chloride solution; B) exposure to stressors consisting of daily 10 h periods of 1) 98 dB SPL noise, or 2) confinement precluding movements; C) daily injections of 233, 350, or 410 mg/kg of sodium salicylate or the saline vehicle. For subjects maintained on tap water, weight loss and mortality increased with salicylate levels, with all subjects dying in the group drinking water and injected with 410 mg/kg. Calcium protected all of the subjects in the noise stress group but not in the confined group.

Effects of aspirin on human auditory filters

Auditory filter shapes were measured in eight male volunteers with normal hearing, using a notched-noise forward-masking paradigm and a signal frequency of 4 kHz. The measurements were made under three conditions: after listeners had taken eight doses of three 320 mg aspirin tablets every six hours; after an identical schedule of placebo ingestion; and one week after testing in the first two conditions had been completed. Half of the listeners did the placebo condition first, and half did the aspirin condition first. Aspirin and placebo were administered double-blind, and testing took place approximately one hour after the last dose. Filter shapes were significantly broader in the aspirin condition than in the placebo and post-test conditions, indicating that even a modest dose affects auditory frequency selectivity. Two-point measures of growth of masking did not differ significantly between conditions.

Interaction of salicylate and noise results in mortality of rats

Survival as a function of salicylate dose and the intensity of environmental noise was investigated in 150 adult female pigmented rats. Rats were assigned to groups (n = 6/group) defined by combinations of salicylate levels from 0-(saline) to 300 mg/kg, injected subcutaneously, and noise levels from ambient noise to 98 dB SPL, presented daily for 10-h periods for up to 17 days. Mortality occurred in groups exposed to the higher combinations of salicylate and noise.

Aspirin-induced hearing loss as a model of sensorineural hearing loss

Performance in forward-masking, temporal-integration, and gap-detection tasks was measured in five normal-hearing subjects before and during a five-day period of aspirin use. The drug regimen was 3.9 g per day, taken in four equal doses at 6-h intervals. In the subjects showing substantial temporary hearing loss induced by the aspirin, (1) forward masking declined at about a normal rate as the masker-to-signal interval was increased, (2) the temporal-integration functions were flatter than normal, and (3) detection of a temporal gap was worse than normal at low sound-pressure levels (SPLs) but was essentially normal at levels above about 60 dB SPL. These aspirin-induced changes in performance are similar to the differences observed between normal listeners and listeners with mild sensorineural hearing loss. Thus, temporary, aspirin-induced hearing loss offers promise as a model condition for sensorineural hearing loss. The advantages offered by this model include all those typically attributed to within-subjects experimental designs, as well as the ability to manipulate the amount of hearing loss. Its primary disadvantages are that the hearing loss is not asymmetrically distributed toward the high-frequency region, as it typically is with sensorineural deafness, and there are large individual differences in the amount of temporary hearing loss induced by fixed doses of aspirin.