STK33 alleviates gentamicin-induced ototoxicity in cochlear hair cells and House Ear Institute-Organ of Corti 1 cells

Ivacaftor attenuates gentamicin-induced ototoxicity through the CFTR-Nrf2-HO1/NQO1 pathway

OBJECTIVES

Gentamicin is one of the most common ototoxic drugs that can lower patients' quality of life. Oxidative stress is a key factors inducing sensory hair cell death during gentamicin administration. So far, there are no effective drugs to prevent or treat gentamicin- induced hearing loss. A recent study found cystic fibrosis transmembrane conductance regulator (CFTR) as a new target to modulate cellular oxidative balance. The objective of this study was to estimate the effect of the CFTR activator ivacaftor on gentamicin-induced ototoxicity and determine its mechanism.

METHODS

The hair cell count was analyzed by Myosin 7a staining. Apoptosis was analyzed by TUNEL Apoptosis Kit. Cellular reactive oxygen species (ROS) level was detected by DCFH-DA probes. The Nrf2 related proteins expression levels were analyzed by western blot.

RESULTS

An in vitro cochlear explant model showed that gentamicin caused ROS accumulation in sensory hair cells and induced apoptosis, and this effect was alleviated by pretreatment with ivacaftor. Western blotting showed that ivacaftor administration markedly increased the protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO1), and NAD(P)H:quinone oxidoreductase 1 (NQO1). The protective effect of ivacaftor was abolished by the Nrf2 inhibitor ML385.

DISCUSSION

Our results indicate the protective role of the CFTR-Nrf2-HO1/NQO1 pathway in gentamicin-induced ototoxicity. Ivacaftor may be repositioned or repurposed towards aminoglycosides-induced hearing loss.

Regulation of the p53/SLC7A11/GPX4 Pathway by Gentamicin Induces Ferroptosis in HEI-OC1 Cells

BACKGROUND

Gentamicin is a commonly used aminoglycoside antibiotic, with ototoxicity as a significant side effect. Ferroptosis, an iron-dependent form of cell death, has been implicated in a variety of disorders. Whether ferroptosis impacts gentamicin ototoxicity is not yet known. The current work used an in-vitro model to examine the influence of gentamicin-induced ferroptosis on cochlear hair cell damage and probable molecular biological pathways.

METHODS

House Ear Institute-Organ of Corti 1 (HEI-OC1) cells were treated with different concentrations of gentamicin for 24 hours, with or without ferrostatin-1 pretreatment, to observe gentamicin-induced ferroptosis. The role of p53/solute carrier family 7 member 11 (SLC7A11)/glutathione peroxidase 4 (GPX4) signaling in gentamicin-induced ferroptosis was explored by pretreating cells with the p53 inhibitor pifithrin-α (PFT-α). We investigated the effect of gentamicin on cells by assessing cell viability. Cellular proteins were isolated and Western blots were performed to detect changes in the expression of p53, SLC7A11, and GPX4. Fluorescence staining was used to assess levels of reactive oxygen species. An enzymatic detection kit was used to detect glutathione, Fe, and malondialdehyde markers.

RESULTS

Gentamicin reduced cell viability, glutathione content, and SLC7A11 and GPX4 protein levels, and increased levels of p53 protein, reactive oxygen species, malondialdehyde, and Fe. These effects were largely blocked by pretreatment with ferrostatin-1. Pretreatment with the p53 inhibitor PFT-α prevented the gentamicin-induced reduction in SLC7A11 and GPX4, which alleviated several features of ferroptosis including glutathione depletion, iron overload, and lipid peroxidation build-up.

CONCLUSION

Gentamicin induces ferroptosis in the HEI-OC1 cell line, and the mechanism may be related to the p53/SLC7A11/GPX4 signaling pathway.

Effects of Cross-linked Hyaluronic Acid in a Rat Model of Vestibular and Cochlear Toxicity

Objective

To investigate the effects of cross-linked hyaluronic acid (CLHA) in an experimental model of vestibulotoxicity and cochleotoxicity.

Methods

Twenty-eight female Wistar albino rats (200-250 g) were divided into four groups. Group A received 0.06 mL of 13.33 mg/mL gentamicin, Group B received 0.06 mL of CLHA, Group C received 0.03 mL of 26.66 mg/mL gentamicin and 0.03 mL CLHA, and Group D received 0.06 mL of 0.09% saline. All groups underwent auditory brainstem response testing at 4-32 kHz, signal-to-noise ratio of distortion product otoacoustic emission measurements at 1.5-8 kHz and vestibular tests on days 0,1,7,10. The rats were sacrificed, and their labyrinths were histologically assessed and scored.

Results

The hearing thresholds of Groups A and C were similar and significantly higher than those of the other groups at all frequencies, beginning from day 1. The vestibular and histological scores of Groups A and C were similar and significantly higher than those of the other groups from day 1. The audiological results, vestibular scores, and histological scores of Groups B and D were similar, except for a temporary middle ear effusion and hearing threshold shift in Group B. No significant deterioration was observed in the audiological, vestibular, and histological analyses of Groups B and D.

Conclusion

That both Group A and Group C similarly showed worsening audiological, vestibular, and histological tests suggests that CLHA did not alter the pharmacokinetics and histologic results of gentamicin.

DJ-1 Protects Auditory Cells from Cisplatin-induced Ototoxicity via Regulating Apoptosis and Autophagy

AIMS

DJ-1, a multifunctional protein encoded by the Park7 gene, is tightly related to mitochondrial dysfunction, oxidative stress, protein aggregation, and autophagy regulation. The current study was designed to investigate whether DJ-1 is expressed in auditory cells and, if so, to explore the possible correlation between DJ-1 and cisplatin-induced ototoxicity in this type of cells.

METHODS

The location and dynamic expression of DJ-1 in mouse cochlea hair cells (HCs) and House Ear Institute-Organ of Corti 1 (HEI-OC1 cells) were detected by immunofluorescence, real-time PCR, and western blot. The apoptosis of auditory cells was assessed by TUNEL staining and flow cytometry. The levels of ROS were evaluated by MitoSox red staining. The expression of protein cleaved caspase-9, cleaved caspase-3, and LC3B was examined by immunofluorescence and western blot. The expressions of certain key factors relevant to apoptosis (Bcl-2 and Bax) and autophagy (Beclin1, p-JNK, and p-c-Jun) were determined by western blot. The dynamic alterations of those factors in response to DJ-1 knockdown in HEI-OC1 cells (DJ-1-KD) were measured by western blotting and MitoSox red staining.

RESULTS

The expression of DJ-1 was clearly shown in both HCs and HEI-OC1 cells and cisplatin led to the reduction of DJ-1 expression in a concentration and time-dependent manner. Meanwhile, cisplatin-induced apoptotic process was implemented by promoting reactive oxygen species (ROS) production and activating the mitochondrial pathway. Furthermore, DJ-1 explicitly participated in cisplatin-trigged cell damage by regulating autophagy.

CONCLUSIONS

Findings from this work clearly reveal, for the first time, that DJ-1 is expressed in the cochlea. Of particular importance, DJ-1 exerts its protective action against cisplatin-elicited injury on auditory cells via regulating apoptosis and autophagy, which provides a new strategy for the prevention of cisplatin-induced ototoxicity.

Zwitterionic Polymer/Polydopamine Coating of Electrode Arrays Reduces Fibrosis and Residual Hearing Loss after Cochlear Implantation

Since the first surgery 50 years ago, cochlear implantation (CI) is the major treatment for patients with severe sensorineural hearing loss. However, unexpected foreign body reactions (FBRs) after surgery are reported in 90% of CI recipients, resulting in the formation of fibrosis in the cochlea and progressive residual hearing loss. Zwitterion modification is universally used to reduce bio-fouling and suppress FBRs but never for CI. In the present study, a zwitterionic coating is developed, which is composed of poly sulfobetaine methacrylate (PSB) and polydopamine (PDA) for cochlear implants. The PSB-PDA coating shows a series of characters for an ideal anti-FBRs material, including super-hydrophilicity, low protein and cell adsorption, long-term stability, and high biocompatibility. Compared to the uncoated controls, PSB-PDA coating inhibits the activation of macrophages and reduces the release of inflammatory factors (TNF-α, IL-1β, NO) and fibrosis-related factors (TGF-β1, α-SMA, collagen I). PSB-PDA coated electrode arrays suppress fibrosis completely and preserve residual hearing significantly in rat CI models. These results suggest that PSB-PDA coating is a novel strategy for anti-fibrosis to improve the outcomes of CI.

Mesoporous silica nanoparticle-modified electrode arrays of cochlear implants for delivery of siRNA-TGFβ1 into the inner ear

Cochlear implants (CI) are widely used in patients to restore hearing function. Uncontrolled fibrosis in the cochleae induced by excess secretion of TGFβ1 seriously affects the effectiveness of CIs. siRNA is a potential therapeutic strategy to downregulate TGFβ1 specifically. However, treatment with siRNA in cochleae is difficult due to the poor penetration capability and instability of siRNA and the inaccessibility and vulnerability of cochleae. To address these challenges, we developed amino-functionalized mesoporous silica nanoparticle (MSN-NH2)-modified electrode arrays to deliver siRNA-TGFβ1 into the inner ear. The shape, diameter, pore diameter, and zeta potential of MSN-NH2 were investigated. siRNA loading capability and protective effect of MSN-NH2 were determined by agarose gel electrophoresis assay. The cytotoxicity, cellular uptake assay, and TGFβ1 knockdown efficiency of MSN-NH2 were studied by CCK-8 assay, flow cytometry, and real-time PCR, respectively. MSN-NH2-siTGFβ1 nanoparticles were absorbed into the electrode arrays and worked in the cochleae. MSN-NH2-siTGFβ1-modified CI electrode arrays may be an attractive therapeutic clinical intervention strategy to inhibit cochlear implantation fibrosis.

Identification of Target Proteins Involved in Cochlear Hair Cell Progenitor Cytotoxicity following Gentamicin Exposure

Given the non-labile, terminal differentiation of inner-ear sensory cells, preserving their function is critical since sensory cell damage results in irreversible hearing loss. Gentamicin-induced cytotoxicity is one of the major causes of sensory cell damage and consequent sensorineural hearing loss. However, the precise molecular mechanisms and target proteins involved in ototoxicity are still unknown. The objective of the present study was to identify target proteins involved in gentamicin-induced cytotoxicity to better characterize the molecular pathways involved in sensory cell damage following ototoxic drug administration using House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). We identified several unique proteins involved in gentamicin-induced cytotoxicity, expression of which were further confirmed using confocal microscopy. Further investigation of these pathways can inform the design and discovery of novel treatment modalities to prevent sensory cell damage and preserve their function.

Heme Oxygenase-1 Protects Hair Cells From Gentamicin-Induced Death

Gentamicin ototoxicity can generate free radicals within the inner ear, leading to permanent damage to sensory hair cells (HCs) and eventually hearing loss. The following study examined the alterations of oxidative damage-related genes in the cochlea and important molecules responsible for oxidation following gentamicin injury in vitro. The RT² Profiler polymerase chain reaction (PCR) array was used to screen candidate targets for treatment to prevent hearing loss caused by gentamicin. We found that during gentamicin-induced death in HCs, Heme oxygenase-1 (HO-1) had a high fold change in the HCs of the cochlea. Moreover, the use of CoPPIX to induce HO-1 inhibited gentamicin-induced HC death, while HO-1 inhibitors ZnPPIX after CoPPIX reversed this process. Furthermore, the inhibitors of NF-E2-related factor-2 (Nrf2) reduced the expression of HO-1 and inhibited the protective effect of HO-1 after gentamicin, thus suggesting that the Nrf2/HO-1 axis might regulate gentamicin-associated ototoxicity. We further demonstrated that induction of HO-1 up-regulated the expression of Nrf2 in both cochlear and HEI-OC1 cells. In summary, these findings indicated that HO-1 protects HCs from gentamicin by up-regulating its expression in HCs and interacting with Nrf2 to inhibit reactive oxygen species (ROS).

Inhibition of KDM5A attenuates cisplatin-induced hearing loss via regulation of the MAPK/AKT pathway

The study aimed to investigate the potential role of lysine-specific demethylase 5A (KDM5A) in cisplatin-induced ototoxicity. The effect of the KDM5A inhibitor CPI-455 was assessed by apoptosis assay, immunofluorescence, flow cytometry, seahorse respirometry assay, and auditory brainstem response test. RNA sequencing, qRT-PCR, and CUT&Tag assays were used to explore the mechanism underlying CPI-455-induced protection. Our results demonstrated that the expression of KDM5A was increased in cisplatin-injured cochlear hair cells compared with controls. CPI-455 treatment markedly declined KDM5A and elevated H3K4 trimethylation levels in cisplatin-injured cochlear hair cells. Moreover, CPI-455 effectively prevented the death of hair cells and spiral ganglion neurons and increased the number of ribbon synapses in a cisplatin-induced ototoxicity mouse model both in vitro and in vivo. In HEI-OC1 cells, KDM5A knockdown reduced reactive oxygen species accumulation and improved mitochondrial membrane potential and oxidative phosphorylation under cisplatin-induced stress. Mechanistically, through transcriptomics and epigenomics analyses, a set of apoptosis-related genes, including Sos1, Sos2, and Map3k3, were regulated by CPI-455. Altogether, our findings indicate that inhibition of KDM5A may represent an effective epigenetic therapeutic target for preventing cisplatin-induced hearing loss.

Prediction of the Molecular Mechanisms Underlying Erlong Zuoci Treatment of Age-Related Hearing Loss via Network Pharmacology-Based Analyses Combined with Experimental Validation

Background: The traditional Chinese medicine formula ErLong ZuoCi (ELZC) has been extensively used to treat age-related hearing loss (ARHL) in clinical practice in China for centuries. However, the underlying molecular mechanisms are still poorly understood.

Objective: Combine network pharmacology with experimental validation to explore the potential molecular mechanisms underlying ELZC with a systematic viewpoint.

Methods: The chemical components of ELZC were collected from the Traditional Chinese Medicine System Pharmacology database, and their possible target proteins were predicted using the SwissTargetPrediction database. The putative ARHL-related target proteins were identified from the database: GeneCards and OMIM. We constructed the drug-target network as well as drug-disease specific protein-protein interaction networks and performed clustering and topological property analyses. Functional annotation and signaling pathways were performed by gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis. Finally, in vitro experiments were also performed to validate ELZC’s key target proteins and treatment effects on ARHL.

Results: In total, 63 chemical compounds from ELZC and 365 putative ARHL-related targets were identified, and 1860 ARHL-related targets were collected from the OMIM and GeneCards. A total of 145 shared targets of ELZC and ARHL were acquired by Venn diagram analysis. Functional enrichment analysis suggested that ELZC might exert its pharmacological effects in multiple biological processes, such as cell proliferation, apoptosis, inflammatory response, and synaptic connections, and the potential targets might be associated with AKT, ERK, and STAT3, as well as other proteins. In vitro experiments revealed that ELZC pretreatment could decrease senescence-associated β-galactosidase activity in hydrogen peroxide-induced auditory hair cells, eliminate DNA damage, and reduce cellular senescence protein p21 and p53. Finally, Western blot analysis confirmed that ELZC could upregulate the predicted target ERK phosphorylation.

Conclusion: We provide an integrative network pharmacology approach, in combination with in vitro experiments to explore the underlying molecular mechanisms governing ELZC treatment of ARHL. The protective effects of ELZC against ARHL were predicted to be associated with cellular senescence, inflammatory response, and synaptic connections which might be linked to various pathways such as JNK/STAT3 and ERK cascade signaling pathways. As a prosperous possibility, our experimental data suggest phosphorylation ERK is essential for ELZC to prevent degeneration of cochlear.

Puerarin alleviates the ototoxicity of gentamicin by inhibiting the mitochondria‑dependent apoptosis pathway

Gentamicin (GM) is a commonly used antibiotic, and ototoxicity is one of its side effects. Puerarin (PU) is an isoflavone in kudzu roots that exerts a number of pharmacological effects, including antioxidative and free radical scavenging effects. The present study investigated whether PU could protect against GM-induced ototoxicity in C57BL/6J mice and House Ear Institute-Organ of Corti 1 (HEI-OC1) cells. C57BL/6J mice and HEI-OC1 cells were used to establish models of GM-induced ototoxicity in this study. Auditory brainstem responses were measured to assess hearing thresholds, and microscopy was used to observe the morphology of cochlear hair cells after fluorescent staining. Cell viability was examined with Cell Counting Kit-8 assays. To evaluate cell apoptosis and reactive oxygen species (ROS) production, TUNEL assays, reverse transcription-quantitative PCR, DCFH-DA staining, JC-1 staining and western blotting were performed. PU protected against GM-induced hearing damage in C57BL/6J mice. PU ameliorated the morphological changes of mouse cochlear hair cells and reduced the apoptosis rate of HEI-OC1 cells after GM-mediated damage. GM-induced ototoxicity may be closely related to the upregulation of p53 expression and the activation of endogenous mitochondrial apoptosis pathways, and PU could protect cochlear hair cells from GM-mediated damage by reducing the production of ROS and inhibiting the mitochondria-dependent apoptosis pathway.

XIAP inhibits gentamicin-induced hair cell damage and ototoxicity through the caspase-3/9 pathway

Gentamicin (GM), an aminoglycoside antibiotic, is one commonly used clinical drugs with ototoxic side effects. One of the most principal mechanisms of its ototoxicity is that GM can activate caspase-mediated cell death pathways in the cochlea. Since the anti-apoptotic protein known as X-linked Inhibitor of Apoptosis Protein (XIAP) has been reported to directly bind to activated caspase protein and inhibit their activities, we hypothesized that it might protect cochlea hair cells from GM ototoxicity. To evaluate this hypothesis, postnatal day 2-3 (P2-3) transgenic (TG) mice, in which XIAP gene is over-expressed under a pure C57BL/6J genetic background was constructed. We first extracted the cochlea tissue of normal mice and treated them with different concentrations of GM, and the number of hair cells were observed to determine the concentration of GM used in subsequent experiments. Next, we used Western Blot experiment to examine the effect of GM on XIAP protein expression in normal mouse cochlea, and then Western Blot and RT-PCR experiments were used to identify the transgenic mice. Finally, immunofluorescence assays were used to detect the effect of GM on the expression of caspase protein and verify the protective effect of XIAP. We found that GM at a concentration of 0.5 mM significantly affected the function of cochlea hair cells, up-regulating the expression of cleaved-caspase-3 and cleaved-caspase-9 protein but down-regulating XIAP protein. In the cochlea tissues of TG mice, this effect of GM was suppressed, and the destruction of hair cells was significantly reduced, and the cleaved-caspase-3 and cleaved-caspase-9 proteins were significantly suppressed. These results suggested that XIAP reduces GM-induced ototoxicity and caspase-3/9 pathway is associated with this process.

Characterization of quinoxaline derivatives for protection against iatrogenically induced hearing loss

Hair cell loss is the leading cause of hearing and balance disorders in humans. It can be caused by many factors, including noise, aging, and therapeutic agents. Previous studies have shown the therapeutic potential of quinoxaline against drug-induced ototoxicity. Here, we screened a library of 68 quinoxaline derivatives for protection against aminoglycoside-induced damage of hair cells from the zebrafish lateral line. We identified quinoxaline-5-carboxylic acid (Qx28) as the best quinoxaline derivative that provides robust protection against both aminoglycosides and cisplatin in zebrafish and mouse cochlear explants. FM1-43 and aminoglycoside uptake, as well as antibiotic efficacy studies, revealed that Qx28 is neither blocking the mechanotransduction channels nor interfering with aminoglycoside antibacterial activity, suggesting that it may be protecting the hair cells by directly counteracting the ototoxin’s mechanism of action. Only when animals were incubated with higher doses of Qx28 did we observe a partial blockage of the mechanotransduction channels. Finally, we assessed the regulation of the NF-κB pathway in vitro in mouse embryonic fibroblasts and in vivo in zebrafish larvae. Those studies showed that Qx28 protects hair cells by blocking NF-κB canonical pathway activation. Thus, Qx28 is a promising and versatile otoprotectant that can act across different species and toxins.

Liproxstatin-1 Protects Hair Cell-Like HEI-OC1 Cells and Cochlear Hair Cells against Neomycin Ototoxicity

Ferroptosis is a recently discovered iron-dependent form of oxidative programmed cell death distinct from caspase-dependent apoptosis. In this study, we investigated the effect of ferroptosis in neomycin-induced hair cell loss by using selective ferroptosis inhibitor liproxstatin-1 (Lip-1). Cell viability was identified by CCK8 assay. The levels of reactive oxygen species (ROS) were determined by DCFH-DA and cellROX green staining. The mitochondrial membrane potential (ΔΨm) was evaluated by TMRM staining. Intracellular iron and lipid peroxides were detected with Mito-FerroGreen and Liperfluo probes. We found that ferroptosis can be induced in both HEI-OC1 cells and neonatal mouse cochlear explants, as evidenced by Mito-FerroGreen and Liperfluo staining. Further experiments showed that pretreatment with Lip-1 significantly alleviated neomycin-induced increased ROS generation and disruption in ΔΨm in the HEI-OC1 cells. In parallel, Lip-1 significantly attenuated neomycin-induced hair cell damage in neonatal mouse cochlear explants. Collectively, these results suggest a novel mechanism for neomycin-induced ototoxicity and suggest that ferroptosis inhibition may be a new clinical intervention to prevent hearing loss.

Inhibition of ferroptosis protects House Ear Institute-Organ of Corti 1 cells and cochlear hair cells from cisplatin-induced ototoxicity

Ferroptosis is a recently recognized form of non‐apoptotic cell death caused by an iron‐dependent accumulation of lipid hydroperoxides, which plays important roles in a wide spectrum of pathological conditions. The present study was aimed to investigate the impact of ferroptosis on cisplatin‐induced sensory hair cell damage. Cell viability was determined by Cell Counting Kit‐8 and lactase dehydrogenase assays. The reactive oxygen species (ROS) levels were evaluated by 2,7‐Dichlorodi‐hydrofluorescein diacetate (DCFH‐DA) and MitoSox‐Red staining. Mitochondrial membrane potential (MMP) was measured by tetramethylrhodamine methyl ester (TMRM) staining. Lipid peroxidation, intracellular and mitochondrial iron were detected by Liperfluo, C11‐BODIPY^581/591, FerroOrange and Mito‐FerroGreen, respectively. We found that cisplatin treatment not only markedly augmented ROS accumulation, decreased the MMP, but increased lipid peroxidation and iron accumulation in House Ear Institute‐Organ of Corti 1 (HEI‐OC1) cells. Of note, treatment with the specific ferroptosis inhibitor ferrostatin‐1 could effectively abrogate the cisplatin‐induced toxicity and subsequent cell death. Specifically, the improvement of mitochondrial functions is important mechanisms for protective action of ferroptosis inhibitor against cisplatin‐induced damages in HEI‐OC1 cells. Moreover, inhibition of ferroptosis significantly protected murine cochlear hair cells against cisplatin damage. In addition, treatment murine cochlear hair cells with ferroptosis inducer, RSL3, significantly exacerbated cisplatin‐induced damage, which could be alleviated by ROS inhibitor N‐acetyl‐L‐cysteine. Collectively, our study indicated that ferroptosis inhibition could alleviate the cisplatin‐induced ototoxicity via inactivation of lipid peroxide radical and improvement of mitochondrial function in hair cells.

Otoprotective Effect of 2,3,4',5-Tetrahydroxystilbene-2-O-β-d-Glucoside on Gentamicin-Induced Apoptosis in Mouse Cochlear UB/OC-2 Cells

Excessive levels of reactive oxygen species (ROS) lead to mitochondrial damage and apoptotic cell death in gentamicin-induced ototoxicity. 2,3,4',5-Tetrahydroxystilbene-2-O-β-d-glucoside (THSG), a bioactive constituent, isolated from Polygonum multiflorum Thunb., exhibits numerous biological benefits in treating aging-related diseases by suppressing oxidative damage. However, its protective effect on gentamicin-induced ototoxicity remains unexplored. Therefore, here, we aimed to investigate the otoprotective effect of THSG on gentamicin-induced apoptosis in mouse cochlear UB/OC-2 cells. We evaluated the effect of gentamicin and THSG on the ROS level, superoxide dismutase (SOD) activity, mitochondrial membrane potential, nuclear condensation, and lactate dehydrogenase (LDH) release, and the expression of apoptosis-related proteins was assessed to understand the molecular mechanisms underlying its preventive effects. The findings demonstrated that gentamicin increased ROS generation, LDH release, and promoted apoptotic cell death in UB/OC-2 cells. However, THSG treatment reversed these effects by suppressing ROS production and downregulating the mitochondrial-dependent apoptotic pathway. Additionally, it increased the SOD activity, decreased the expression of apoptosis-related proteins, alleviated the levels of the apoptotic cells, and impaired cytotoxicity. To the best of our knowledge, this is the first study to demonstrate that THSG could be a potential therapeutic option to attenuate gentamicin-induced ototoxicity.

STK33 alleviates gentamicin-induced ototoxicity in cochlear hair cells and House Ear Institute-Organ of Corti 1 cells

Serine/threonine kinase 33 (STK33), a member of the calcium/calmodulin‐dependent kinase (CAMK), plays vital roles in a wide spectrum of cell processes. The present study was designed to investigate whether STK33 expressed in the mammalian cochlea and, if so, what effect STK33 exerted on aminoglycoside‐induced ototoxicity in House Ear Institute‐Organ of Corti 1 (HEI‐OC1) cells. Immunofluorescence staining and western blotting were performed to investigate STK33 expression in cochlear hair cells (HCs) and HEI‐OC1 cells with or without gentamicin treatment. CCK8, flow cytometry, immunofluorescence staining and western blotting were employed to detect the effects of STK33 knockdown, and/or U0126, and/or N‐acetyl‐L‐cysteine (NAC) on the sensitivity to gentamicin‐induced ototoxicity in HEI‐OC1 cells. We found that STK33 was expressed in both mice cochlear HCs and HEI‐OC1 cells, and the expression of STK33 was significantly decreased in cochlear HCs and HEI‐OC1 cells after gentamicin exposure. STK33 knockdown resulted in an increase in the cleaved caspase‐3 and Bax expressions as well as cell apoptosis after gentamicin damage in HEI‐OC1 cells. Mechanistic studies revealed that knockdown of STK33 led to activated mitochondrial apoptosis pathway as well as augmented reactive oxygen species (ROS) accumulation after gentamicin damage. Moreover, STK33 was involved in extracellular signal‐regulated kinase 1/2 pathway in primary culture of HCs and HEI‐OC1 cells in response to gentamicin insult. The findings from this work indicate that STK33 decreases the sensitivity to the apoptosis dependent on mitochondrial apoptotic pathway by regulating ROS generation after gentamicin treatment, which provides a new potential target for protection from the aminoglycoside‐induced ototoxicity.