Effect of acoustic stress on glucocorticoid receptor mRNA in the cochlea of the guinea pig

Protective effects and mechanisms of the Erzhi formula on glucocorticoid induced primary cortical neuron injury

High concentrations of glucocorticoids (GC) can cross the blood-brain barrier into the brain parenchyma, triggering a stress state that can lead to a range of physiological changes. This study investigated whether Erzhi formula has neuroprotective effects against glucocorticoid damage by establishing a dexamethasone-induced primary cortical neuron injury model in vitro. The results showed that Erzhi formula could reduce dexamethasone-induced apoptosis in primary cultured cortical neurons and improve synaptic damage. Further, network pharmacological analysis revealed that Erzhi formula may exert antidepressant effects by multi-component, multi-target, and multi-pathway characteristics, in which Salidroside, Biochanin-A and other ingredients are key components, HSD11B1, NR3C1, and other proteins are key targets, and steroid metabolism may be a key process in its action. Moreover, our study found that the neuroprotective effect of Erzhi formula might be related to the 11β-HSD1-GC/glucocorticoid receptor (GR) signaling pathway. The Erzhi formula could significantly inhibit the activity of 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in vitro using homogeneous time-resolved fluorescence. In addition to providing evidence for the pharmacological effects of the Erzhi formula, the present study lays down the foundation for subsequent experiments.

The circadian timing of noise exposure influences noise-induced inflammatory responses in the mouse cochlea

INTRODUCTION

Noise-induced hearing loss is one of the most common forms of sensorineural hearing loss. Nevertheless, the mechanisms of noise-induced hearing loss are still not fully understood.

OBJECTIVE

To investigate the dynamics of inflammatory responses in the mammalian cochlea following noise trauma at two different times, once during the light cycle and once during the dark.

METHODS

We challenged C57BL/6J mice with moderate, continuous noise trauma at either 9 a.m. or 9 p.m. Auditory function, histological changes in hair cells, and modifications in gene expression levels of inflammatory mediators were assessed at specific time points. Shifts in auditory brainstem response thresholds were measured at 1, 3, 7 and 14 days after noise exposure to measure potential noise-induced hearing loss. Cochlear basilar-membrane immunofluorescent staining was performed at 3 and 14 days after noise exposure. The mRNA levels of several inflammatory mediators were measured via quantitative real-time polymerase chain reaction before (pre) and after (0, 3, 12, 24 and 72 h) noise exposure.

RESULTS

We found that all noise-exposed mice developed a temporary threshold shift and that there were no significant differences between daytime and nighttime noise exposures in terms of inducing hearing-threshold shifts. Similarly, we did not detect significant histological changes in hair cells between these two groups. However, we discovered an interesting phenomenon in that the peak mRNA levels of IL-1β, IL-6, CCL2 and TNF-α were higher in day noise-exposed mice compared to those in night noise-exposed mice, and these mRNA levels subsided more slowly in day noise-exposed mice.

CONCLUSION

Overall, these observations suggest that the circadian timing of noise exposure has a significant effect on noise-induced inflammatory responses in the mouse cochlea and that a greater inflammatory response might occur after daytime exposure.

On the Role of Fibrocytes and the Extracellular Matrix in the Physiology and Pathophysiology of the Spiral Ligament

The spiral ligament in the cochlea has been suggested to play a significant role in the pathophysiology of different etiologies of strial hearing loss. Spiral ligament fibrocytes (SLFs), the main cell type in the lateral wall, are crucial in maintaining the endocochlear potential and regulating blood flow. SLF dysfunction can therefore cause cochlear dysfunction and thus hearing impairment. Recent studies have highlighted the role of SLFs in the immune response of the cochlea. In contrast to sensory cells in the inner ear, SLFs (more specifically type III fibrocytes) have also demonstrated the ability to regenerate after different types of trauma such as drug toxicity and noise. SLFs are responsible for producing proteins, such as collagen and cochlin, that create an adequate extracellular matrix to thrive in. Any dysfunction of SLFs or structural changes to the extracellular matrix can significantly impact hearing function. However, SLFs may prove useful in restoring hearing by their potential to regenerate cells in the spiral ligament.

Cochlear Glucocorticoid Receptor and Serum Corticosterone Expression in a Rodent Model of Noise-induced Hearing Loss: Comparison of Timing of Dexamethasone Administration

Glucocorticoid (GC) is a steroid hormone secreted from the adrenal cortex in response to stress, which acts by binding to cytoplasmic glucocorticoid receptors (GRs). Dexamethasone (DEX) is a synthetic GC exhibiting immunosuppressive effects in both human and rodent models of hearing loss. While clinical evidence has shown the effectiveness of DEX for treatment of various inner ear diseases, its mechanisms of action and the optimal timing of treatment are not well understood. In the present study, intergroup comparisons were conducted based on the time point of treatment with DEX: (1) pretreatment; (2) posttreatment; and (3) pre&post-noise. The pre&post DEX treatment group showed a significant improvement in threshold shift at 1 day post-noise exposure as compared to the TTS (transient threshold shift)-only group at 8 and 16 kHz. Both TTS and PTS (permanent threshold shift) significantly reduced cochlear GR mRNA expression and increased serum corticosterone and cochlear inflammatory cytokines. The pre&post DEX treatment group showed a significant decrease in serum corticosterone level as compared to other DEX treatment groups and TTS-treated group at 3 days after acoustic trauma. Our results suggest that the timing of DEX administration differentially modulates systemic steroid levels, GR expression and cochlear cytokine expression.

Expression and dexamethasone-induced nuclear translocation of glucocorticoid and mineralocorticoid receptors in guinea pig cochlear cells

Glucocorticoids (GC) are powerful anti-inflammatory agents frequently used to protect the auditory organ against damage associated with a variety of conditions, including noise exposure and ototoxic drugs as well as bacterial and viral infections. In addition to glucocorticoid receptors (GC-R), natural and synthetic GC are known to bind mineralocorticoid receptors (MC-R) with great affinity. We used light and laser scanning confocal microscopy to investigate the expression of GC-R and MC-R in different cell populations of the guinea pig cochlea, and their translocation to different cell compartments after treatment with the synthetic GC dexamethasone. We found expression of both types of receptors in the cytoplasm and nucleus of sensory inner and outer hair cells as well as pillar, Hensen and Deiters cells in the organ of Corti, inner and outer sulcus cells, spiral ganglion neurons and several types of spiral ligament and spiral limbus cells; stria vascularis cells expressed mostly MC-R whereas fibrocytes type IV were positive for GC-R only. GC-R and MC-R were also localized at or near the plasma membrane of pillar cells and outer hair cells, whereas GC-R were found at or near the plasma membrane of Hensen cells only. We investigated the relative levels of receptor expression in the cytoplasm and the nucleus of Hensen cells treated with dexamethasone, and found they varied in a way suggestive of dose-induced translocation. These results suggest that the oto-protective effects of GC could be associated with the concerted activation of genomic and non-genomic, GC-R and MC-R mediated signaling pathways in different regions of the cochlea.

Effects of hyperbaric oxygen and dexamethasone on proinflammatory cytokines of rat cochlea in noise-induced hearing loss

HYPOTHESIS

To investigate effects of dexamethasone and hyperbaric oxygen therapy (HBOT) on proinflammatory cytokines and hearing levels in the noise-exposed cochlea of rats.

BACKGROUND

There is an arising concern about negative effects of early initiation of HBOT on hearing in noise-induced hearing loss. Furthermore, effects of HBOT and dexamethasone on cochlear cytokines are not fully elucidated.

METHODS

Twenty-six rats were divided into 3 groups: control, noise, and treatment groups. Five rats served as control group. White noise at 115 dB sound pressure level was applied to the noise group of 4 rats for 10 days. This group was assigned to a positive control group as it was equivalent to treatment groups. The treatment group of 17 rats underwent the same noise exposure, and then, they were divided into 3 groups based on treatment protocol: 5 and 6 rats received HBOT at the third hour and 24th hour after the noise, respectively, and 6 rats received dexamethasone. Auditory brain stem response threshold was measured in all groups before being assigned to the groups, after the noise exposure and right before being killed. Cytokine levels at the cochlear soft tissues were measured using enzyme-linked immunoassay.

RESULTS

Final thresholds (10 dB and 5 dB nHL-normal hearing level) of HBOT-24th hour and dexamethasone groups were significantly better than that of untreated noise group (22.5 dB nHL) (p < 0.05). There was no significant difference between HBOT-24th hour group (10 dB nHL) and dexamethasone group (5 dB nHL) (p > 0.05). IL-6 and IL-1β of HBOT-third hour group (2.30 ng/mg and 185.43 pg/mg) were significantly higher than those of the noise group (0.91 ng/mg and 131.40 pg/mg), dexamethasone group (1.19 ng/mg and 112.29 pg/mg) and HBOT-24th hour group (1.34 ng/mg and 106.69 pg/mg) (p < 0.05). There was no significant difference in IL-6 and IL-1β of HBOT-24th hour group, dexamethasone group, noise group, and control group (p > 0.05). There was no significant difference in TNF-α of the 3 treatment groups, noise group, and control group (p > 0.05).

CONCLUSION

The results showed that the most effective method in the treatment of noise-induced hearing loss was early initiation of dexamethasone therapy. There could be negative effects of HBOT on hearing if it is commenced early after the noise (first 3 h). HBOT treatment, which was started at the 24th hour, was found to be an effective method.

Corticotropin-releasing hormone affects short immobilization stress-induced changes in lung cytosolic and membrane glucocorticoid binding sites

Glucocorticoids act via glucocorticoid receptors (GR), typically localized in the cytosol (cGR). Rapid action is probably mediated via membrane receptors (mGR). In corticotropin-releasing hormone knockouts (CRH-KO), basal plasma glucocorticoid levels do differ from wild type levels (WT), but are approximately ten times lower during exposure to immobilization stress (IMMO) in comparison to WT. We tested the following hypotheses: (1) the mice lung tissue GR basal numbers would not be changed in CRH-KO (because of similar glucocorticoid levels), (2) the number of GR would be changed in WT but not in KO during short (30, 90, and 120 min) IMMO (because of higher increase of glucocorticoid levels in WT). The basal levels of cGR were not changed in CRH-KO (compared to WT), while mGR were significantly lower (62 %) in CRH-KO. In WT, there was the only decrease (to 32 %) in cGR after 120 min when we also found an increase in mGR in WT (to 201 %). In CRH-KO, IMMO caused gradual decrease in cGR (to 52 % after 30 min, to 46 % after 90 min, and to 32 % after 120 min). In CRH-KO, the only increase in mGR appeared already at 30 min of IMMO. These data suggest, on the contrary to our hypotheses, that CRH-KO are more susceptible to GR changes in early phases of stress.

Environmental disturbance confounds prenatal glucocorticoid programming experiments in Wistar rats

Low birth weight in humans is predictive of hypertension in adult life, and while the mechanisms underlying this link remain unknown, fetal overexposure to glucocorticoids has been implicated. We have previously shown that prenatal dexamethasone (DEX) exposure in the rat lowers birth weight and programmes adult hypertension. This current study aimed to unravel the molecular nature of this hypertension. However, unknowingly, post hoc investigations revealed that our animals had been subjected to environmental noise stresses from an adjacent construction site, which were sufficient to confound our prenatal DEX-programming experiments. This perinatal stress successfully established low birth weight, hypercorticosteronaemia, insulin resistance, hypertension and hypothalamic-pituitary-adrenal axis dysfunction in vehicle (VEH)-treated offspring, such that the typical distinctions between both treatment groups were ameliorated. The lack of an additional effect on DEX-treated offspring is suggestive of a maximal effect of perinatal stress and glucocorticoids, serving to prevent against the potentially detrimental effects of sustained glucocorticoid hyper-exposure. Finally, this paper serves to inform researchers of the potential detrimental effects of neighbouring construction sites to their experiments.

The role of glucocorticoids for spiral ganglion neuron survival

Glucocorticoids, which are steroidal stress hormones, have a broad array of biological functions. Synthetic glucocorticoids are frequently used therapeutically for many pathologic conditions, including diseases of the inner ear; however, their exact functions in the cochlea are not completely understood. Recent work has clearly demonstrated the presence of glucocorticoid signaling pathways in the cochlea and elucidated their protective roles against noise-induced hearing loss. Furthermore, indirect evidence suggests the involvement of glucocorticoids in age-related loss of spiral ganglion neurons and extensive studies in the central nervous system demonstrate profound effects of glucocorticoids on neuronal functions. With the advancement of recent pharmacologic and genetic tools, the role of these pathways in the survival of spiral ganglion neurons after noise exposure and during aging should be revealed.

Dexamethasone and methylprednisolone do not inhibit neuritic outgrowth while inhibiting outgrowth of fibroblasts from spiral ganglion explants

CONCLUSION

Dexamethasone and methylprednisolone do not inhibit neuritic outgrowth while inhibiting fibroblastic outgrowth from spiral ganglion micro-explants.

OBJECTIVES

To demonstrate reduced fibroblastic outgrowth while maintaining neurite outgrowth for several corticosteroids using an in vitro test system of neonatal rat spiral ganglion micro-explants.

MATERIALS AND METHODS

The in vitro test system comprised 3-day-old rat spiral ganglion micro-explants. Dexamethasone, methylprednisolone, triamcinolone acetonide, and human recombinant brain-derived neurotrophic factor (hrBDNF) were tested in vitro. The control was ganglion micro-explants in supplemented Dulbecco's modified Eagle's medium. Areas of the ganglion explant, neurite and fibroblast outgrowth of ganglion explants after 10 days in vitro were imaged, digitized, and analyzed using Image Tool 3.00 on a PC workstation. Areas of neurite and fibroblast outgrowth from the experimental explants were compared against values obtained from control explants.

RESULTS

Dexamethasone gave the best result of the three corticosteroids tested for inhibiting fibroblast outgrowth while not inhibiting neurite outgrowth from the ganglion micro-explants. Media containing hrBDNF (10 ng/ml) stimulated significantly greater neurite outgrowth than outgrowth from control explants (p < 0.001). Ganglion micro-explants treated with dexamethasone (0.02 mg/ml) and methylprednisolone (0.5 mg/ml) provided the greatest inhibition of fibroblast outgrowth compared with control explants (p < 0.001).

Intratympanic injection of dexamethasone: time course of inner ear distribution and conversion to its active form

HYPOTHESIS

Intratympanically injected dexamethasone 21-phosphate is converted to its active form dexamethasone in the inner ear and follows the distribution of the glucocorticoid receptor.

BACKGROUND

Although dexamethasone is routinely delivered intratympanically for hearing loss, we know little of its inner ear pharmacokinetics. Dexamethasone 21-phosphate is the pharmaceutical compound available for injection, but it must be converted to its biologically active form (dexamethasone) to bind to the glucocorticoid receptor. Therefore, the current study was conducted to determine the time course of dexamethasone 21-phosphate movement from the middle ear into the inner ear, its conversion to dexamethasone, and the distribution of both forms relative to the glucocorticoid receptor.

METHODS

BALB/c mice were injected intratympanically with the prodrug dexamethasone 21-phosphate and inner ears collected at postinjection times ranging from 5 minutes to 7 days. Ears were immunohistochemically stained for dexamethasone 21-phosphate, dexamethasone, and the glucocorticoid receptor.

RESULTS

Both forms of dexamethasone were seen in the inner ear within 15 minutes, reaching their highest staining intensity at 1 hour. Neither drug was seen after 24 hours. The strongest staining occurred in the spiral ligament, organ of Corti, spiral ganglion, and vestibular sensory epithelia. Distribution of the drug paralleled locations of the glucocorticoid receptor except in the stria vascularis marginal cells, which stained heavily for the receptor but not the drug.

CONCLUSION

Dexamethasone rapidly travels from the middle ear into the inner ear and converts to its active form. The drug distribution follows that of the glucocorticoid receptor. However, it probably has little impact on ear tissues after 24 hours.

Nitric oxide production from cultured spiral ligament fibrocytes: effects of corticosteroids

CONCLUSION

This is the first report of nitric oxide (NO) production by cultured spiral ligament (SL) fibrocytes. The data suggest that dexamethasone (Dex) suppresses NO production by SL fibrocytes. Given that SL fibrocytes play a role in cochlear fluid and ion homeostasis, glucocorticoids may suppress cochlear malfunction caused by NO production in SL fibrocytes.

OBJECTIVE

To investigate NO production by cultured SL fibrocytes and regulation of NO production by Dex in mouse secondary cell cultures.

MATERIALS AND METHODS

Cultured SL fibrocytes were stimulated with tumor necrosis factor-alpha (TNF-alpha), and NO production was visualized with membrane-permeable 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM diacetate). Inducible nitric oxide synthase (NOSII) messenger RNA (mRNA) was measured by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

After TNF-alpha stimulation, the fluorescence intensity increased in a time-dependent manner. This increase in fluorescence intensity was suppressed by a nonspecific NOS inhibitor, N(G)-nitro L-arginine methyl ester (L-NAME), and Dex. After TNF-alpha stimulation, expression of NOSII mRNA was observed. Expression of NOSII mRNA was inhibited by Dex.

Therapeutic efficacy of intra-cochlear administration of methylprednisolone after acoustic trauma caused by gunshot noise in guinea pigs

The therapeutic efficacy of cochlear infusion of methylprednisolone (MP) after an impulse noise trauma (170dB SPL peak) was evaluated in guinea pigs. The compound action potential threshold shifts were measured over a 14 days recovery period after the gunshot exposure. For each animal, one of the cochlea was perfused directly into the scala tympani with MP during 7 days via a mini-osmotic pump, whereas the other cochlea was not pump-implanted. The functional study of hearing was supplemented by histological analysis. Forty eight hours after the trauma, significant differences between auditory threshold shifts in the implanted and non-implanted ears were observed for frequencies above 8kHz. At day 7, the difference was significant for only one frequency and no difference was observed after 14 days recovery. Cochleograms showed that the hair cell losses were significantly lower in the MP treated ears. This work indicates that direct infusion of MP into perilymphatic space accelerates hearing recovery, reduces hair cell losses after impulse noise trauma but does not limit permanent threshold shifts.

Triamcinolone acetonide protects auditory hair cells from 4-hydroxy-2,3-nonenal (HNE) ototoxicity in vitro

CONCLUSION

Triamcinolone acetonide crystalline suspension (e.g. Volon A) was not ototoxic to the auditory hair cells present within organ of Corti explants and protected them from an ototoxic molecule, i.e. 4-hydroxy-2,3-nonenal (HNE), that is produced within the organ of Corti as a result of oxidative stress-induced damage.

OBJECTIVES

To test the corticosteroid, triamcinolone acetonide, for ototoxicity and otoprotective capacity in organ of Corti explants.

MATERIALS AND METHODS

Organ of Corti explants excised from 4-day-old rats were the test system, HNE was the ototoxin challenge. Hair cell integrity counts were performed with fluorescent microscopy on fixed explants stained with FITC-labeled phalloidin. Statistical significance was set at p<0.05.

RESULTS

Triamcinolone acetonide did not affect hair cell integrity in the organ of Corti explants and it provided a high level of protection of hair cells against the ototoxic effects of a damaging level of HNE as determined by hair cell density counts.

Effect Of Intratympanic Dexamethasone on Noise-Induced Temporary Threshold Shift

OBJECTIVE

To evaluate the effects of intratympanic treatment of dexamethasone (IT-DEX) and combination of DEX and hyaluronic acid (DEX/HA) for noise-induced temporary threshold shift (NITTS).

MATERIALS AND METHODS

NITTS was experimentally performed in 60 rats. Electrophysiologic hearing thresholds of the rats were measured before and right after noise exposure. Then, the rats were placed into two groups, the first 30 rats in an IT-DEX group and the second in an IT-DEX/HA group. Treatments were performed in the two subgroups (30 ears in one subgroup) of each group. In the IT-DEX group, one ear of each rat was treated with 0.02 mL IT-DEX, and the other ear was treated with IT 0.02 mL physiologic solution of serum saline. In the IT-DEX/HA group, one ear of each rat was treated with combination of 0.01 mL IT-DEX and 0.01 mL HA, and the other ear was treated with IT 0.02 mL of physiologic solution of serum saline. One week after the treatments, electrophysiologic hearing thresholds of all rats were measured again.

RESULTS

No statistically significant difference was observed in recovery values of electrophysiologic hearing thresholds between IT-DEX and serum saline (P = .641) in the IT-DEX group. Also, we found no statistically significant difference in the recovery values of electrophysiologic hearing thresholds between IT-DEX/HA and serum saline (P = .344) in the IT-DEX/HA group.

CONCLUSION

There is no effect of either IT-DEX and DEX/HA for NITTS.

Down-regulation of otospiralin mRNA in response to acoustic stress in guinea pig

Noise over-stimulation will induce or influence molecular pathways in the cochlea; one approach to the identification of the components of these pathways in the cochlea is to examine genes and proteins that change following different types and levels of stress. Quantitative reverse transcription polymerase chain reaction provides a method to look at differential expression of genes in the acoustic stress response. By using this technique we have revealed a down-regulation of the level of otospiralin mRNA in the cochlea of guinea pigs after white noise over-stimulation for 2 h at 108 dB SPL. Otospiralin represents an inner ear specific protein found in fibrocytes of spiral limbus and spiral ligament in the cochlea, and some regions of the vestibule as the stroma underlying the utricle and crista sensory epithelia and the subepithelial layer of the walls of semicircular canals and maculae. It has been recently reported that transient down-regulation of otospiralin in guinea pigs causes vestibular syndrome and deafness. Our results suggest a possible role of this gene in response to acoustical stress, although the exact mechanism remains to be resolved.

Direct inner ear infusion of dexamethasone attenuates noise-induced trauma in guinea pig

The protective effect of dexamethasone (DEX) against noise-induced trauma, as reflected in hair cell destruction and elevation in auditory brainstem response (ABR) sensitivity, was assessed in guinea pigs. The animals were administered DEX (1, 10, 100, and 1000 ng/ml) or artificial perilymph (AP) via a mini-osmotic pump directly into scala tympani and, on the fourth day after pump implantation, exposed to 120 dB SPL octave band noise, centered at 4 kHz, for 24 h. Animals receiving DEX demonstrated a dose-dependent reduction in noise-induced outer hair cell loss (significant at 1, 10 and 100 ng/ml DEX animals compared to AP control animals) and a similar attenuation of the noise-induced ABR threshold shifts, observed 7 days following exposure (significant at 100 ng/ml DEX animals compared to AP control animals). These physiological and morphological results indicate that direct infusion of DEX into the perilymphatic space has protective effects against noise-induced trauma in the guinea pig cochlea.