Prevention of cisplatin-induced ototoxicity by the inhibition of gap junctional intercellular communication in auditory cells

AdipoRon reduces cisplatin-induced ototoxicity in hair cells:possible relation to the regulation of mitochondrial biogenesis

AdipoRon (AR) can exert antidiabetic and anti-inflammatory effects by maintaining mitochondrial structure and function. The present study was designed to explore whether AR protects the auditory cells from cisplatin-induced damage and, if so, to probe the possible mechanisms underlying its action on this type of cells. Cell viability and apoptosis in House Ear Institute-Organization of Corti 1 (HEI-OC1 cells) and mouse cochlea hair cells (HCs) were detected by CCK8 and immunofluorescence. The expressions of apoptosis-related proteins (cleaved caspase-3 and Bcl-2), adiponectin receptor 1 (AdipoR 1) and the key factors relevant to mitochondrial biogenesis（SIRT1 and TFAM）were determined by Western blot and immunofluorescence. Changes in apoptotic rate and expression of SIRT1 and TFAM after silencing of AdipoR 1 (AdipoR 1-siRNA) in HEI-OC1 cells were measured by flow cytometry and Western blot. The levels of reactive oxygen species (ROS) were evaluated by MitoSox red staining. We found that 30 μM cisplatin exposure induced severe cellular damage, which resulted from activation of the mitochondrial apoptotic pathway. Cisplatin decreased the expression of AdipoR 1, SIRT1, and TFAM proteins, leading to impaired mitochondrial biogenesis and increased mitochondrial ROS production. 10 μM AR pre-treatment enhanced mitochondrial biogenesis, decreased mitochondrial ROS levels, alleviated imbalances in the mitochondrial apoptotic pathway, thus reducing cisplatin-induced apoptosis. Taken together, this work reveals that AR exerts anti-apoptotic effects, possibly via regulating mitochondrial biogenesis and function. Interestingly, AR might possess the promising potential to be a novel drug for the prevention and/ or treatment of cisplatin-induced ototoxicity.

Aucubin protects mouse cochlear hair cells from cisplatin-induced ototoxicity via activation of the PI3K/AKT/STAT3 pathway

Cisplatin is commonly used to treat cancers and is associated with a significant risk of irreversible sensorineural hearing loss. However, no effective preventive strategies are available for cisplatin-induced HL. Therefore, significant efforts have been made to discover new drugs protecting cochlear hair cells from cisplatin-induced damage. We found that a new phytochemical, aucubin, attenuated cisplatin-induced apoptosis, the production of reactive oxygen species, and mitochondrial dysfunction in House Ear Institute Organ of Corti 1 cells and cochlear hair cells. Moreover, aucubin attenuated cisplatin-induced sensorineural hearing loss and hair cells loss in vivo. Furthermore, RNA sequencing analysis revealed that the otoprotective effects of aucubin were mainly mediated by increased STAT3 phosphorylation via the PI3K/AKT pathway. Inhibition of the STAT3 signaling pathway with the inhibitor S3I-201 or siRNA disrupted the protective effects of aucubin on cisplatin-induced apoptosis. In conclusion, we identified an otoprotective effect of aucubin. Therefore, aucubin could be used to prevent cisplatin-induced ototoxicity.

Supporting Cells and Their Potential Roles in Cisplatin-Induced Ototoxicity

Cisplatin is a known ototoxic chemotherapy drug, causing irreversible hearing loss. Evidence has shown that cisplatin causes inner ear damage as a result of adduct formation, a proinflammatory environment and the generation of reactive oxygen species within the inner ear. The main cochlear targets for cisplatin are commonly known to be the outer hair cells, the stria vascularis and the spiral ganglion neurons. Further evidence has shown that certain transporters can mediate cisplatin influx into the inner ear cells including organic cation transporter 2 (OCT2) and the copper transporter Ctr1. However, the expression profiles for these transporters within inner ear cells are not consistent in the literature, and expression of OCT2 and Ctr1 has also been observed in supporting cells. Organ of Corti supporting cells are essential for hair cell activity and survival. Special interest has been devoted to gap junction expression by these cells as certain mutations have been linked to hearing loss. Interestingly, cisplatin appears to affect connexin expression in the inner ear. While investigations regarding cisplatin-induced hearing loss have been focused mainly on the known targets previously mentioned, the role of supporting cells for cisplatin-induced ototoxicity has been overlooked. In this mini review, we discuss the implications of supporting cells expressing OCT2 and Ctr1 as well as the potential role of gap junctions in cisplatin-induced cytotoxicity.

Puerarin attenuates cisplatin-induced apoptosis of hair cells through the mitochondrial apoptotic pathway

Puerarin, one of the main components of Pueraria lobata, has been reported to possess a wide range of pharmacological activities, including anti-inflammatory, antioxidative and anti-apoptotic effects. However, the role of puerarin in ototoxic drug-induced hair cell injury has not been well characterized. This study explored whether puerarin protects against cisplatin-induced hair cell damage and its potential mechanisms. The viability of puerarin-treated HEI-OC1 cells was assessed by CCK8 assay. Reactive oxygen species (ROS) was estimated with flow cytometric analysis using Cellrox Green fluorescent probe. Apoptosis-related protein levels were detected by western blot analysis. Immunostaining of the organ of Corti was performed to determine mice cochlear hair cell survival. Our results showed that puerarin improved cell viability and suppressed apoptosis in the cisplatin-damaged HEI-OC1 cells and cochlear hair cells. Mechanistic studies revealed that puerarin attenuated mitochondrial apoptosis pathway by regulating apoptotic related proteins, such as Bax and cleaved caspase-3, and attenuated ROS accumulation after cisplatin damage. Moreover, puerarin was involved in regulating the Akt pathway in HEI-OC1 cells in response to cisplatin. Our results demonstrated that puerarin administration decreased the sensitivity to apoptosis dependent on the mitochondrial apoptotic pathway by reducing ROS generation, which could be used as a new protective agent against cisplatin-induced ototoxicity.

Inhibiting DNA methylation alleviates cisplatin-induced hearing loss by decreasing oxidative stress-induced mitochondria-dependent apoptosis via the LRP1-PI3K/AKT pathway

Cisplatin-related ototoxicity is a critical side effect of chemotherapy and can lead to irreversible hearing loss. This study aimed to assess the potential effect of the DNA methyltransferase (DNMT) inhibitor RG108 on cisplatin-induced ototoxicity. Immunohistochemistry, apoptosis assay, and auditory brainstem response (ABR) were employed to determine the impacts of RG108 on cisplatin-induced injury in murine hair cells (HCs) and spiral ganglion neurons (SGNs). Rhodamine 123 and TMRM were utilized for mitochondrial membrane potential (MMP) assessment. Reactive oxygen species (ROS) amounts were evaluated by Cellrox green and Mitosox-red probes. Mitochondrial respiratory function evaluation was performed by determining oxygen consumption rates (OCRs). The results showed that RG108 can markedly reduce cisplatin induced damage in HCs and SGNs, and alleviate apoptotic rate by protecting mitochondrial function through preventing ROS accumulation. Furthermore, RG108 upregulated BCL-2 and downregulated APAF1, BAX, and BAD in HEI-OC1 cells, and triggered the PI3K/AKT pathway. Decreased expression of low-density lipoprotein receptor-related protein 1 (LRP1) and high methylation of the LRP1 promoter were observed after cisplatin treatment. RG108 treatment can increase LRP1 expression and decrease LRP1 promoter methylation. In conclusion, RG108 might represent a new potential agent for preventing hearing loss induced by cisplatin via activating the LRP1-PI3K/AKT pathway.

Gap Junction-Mediated Intercellular Communication of cAMP Prevents CDDP-Induced Ototoxicity via cAMP/PKA/CREB Pathway

In the cochlea, non-sensory supporting cells are directly connected to adjacent supporting cells via gap junctions that allow the exchange of small molecules. We have previously shown that the pharmacological regulation of gap junctions alleviates cisplatin (CDDP)-induced ototoxicity in animal models. In this study, we aimed to identify specific small molecules that pass through gap junctions in the process of CDDP-induced auditory cell death and suggest new mechanisms to prevent hearing loss. We found that the cyclic adenosine monophosphate (cAMP) inducer forskolin (FSK) significantly attenuated CDDP-induced auditory cell death in vitro and ex vivo. The activation of cAMP/PKA/CREB signaling was observed in organ of Corti primary cells treated with FSK, especially in supporting cells. Co-treatment with gap junction enhancers such as all-trans retinoic acid (ATRA) and quinoline showed potentiating effects with FSK on cell survival via activation of cAMP/PKA/CREB. In vivo, the combination of FSK and ATRA was more effective for preventing ototoxicity compared to either single treatment. Our study provides the new insight that gap junction-mediated intercellular communication of cAMP may prevent CDDP-induced ototoxicity.

Hearing Loss Caused by HCMV Infection through Regulating the Wnt and Notch Signaling Pathways

Hearing loss is one of the most prevalent sensory disabilities worldwide with huge social and economic burdens. The leading cause of sensorineural hearing loss (SNHL) in children is congenital cytomegalovirus (CMV) infection. Though the implementation of universal screening and early intervention such as antiviral or anti-inflammatory ameliorate the severity of CMV-associated diseases, direct and targeted therapeutics is still seriously lacking. The major hurdle for it is that the mechanism of CMV induced SNHL has not yet been well understood. In this review, we focus on the impact of CMV infection on the key players in inner ear development including the Wnt and Notch signaling pathways. Investigations on these interactions may gain new insights into viral pathogenesis and reveal novel targets for therapy.

Resveratrol protects against cisplatin-induced ovarian and uterine toxicity in female rats by attenuating oxidative stress, inflammation and apoptosis

Cisplatin is an important antineoplastic drug used in multiple chemotherapeutic regimens but unfortunately causes serious toxic effects as ovarian and uterine toxicity. This study aimed to investigate the potential protective effect of resveratrol (RSV) against cisplatin-induced ovarian and uterine toxicity in female rats. Thirty-two female Wistar rats were divided randomly into four groups (n = 8 in each). Control group received oral normal saline for 28 days; RSV group received RSV (10 mg/kg; daily) via oral gavage; CIS group received a single dose of CIS (7 mg/kg; i.p.) on the 21st day; (CIS + RSV) group received both RSV and CIS by the same schedules and doses of RSV and CIS groups, respectively. Results demonstrated a significant decrease in MDA level and a significant increase in both glutathione content and activity of the antioxidant enzymes GPx, SOD, and CAT in the tissues of the ovary and uterus of CIS + RSV group in comparison to that of CIS group (P<0.05), also there are significantly decreased tissue levels of the proinflammatory cytokines and enzymes (NF-κB, IL-1β, IL-6, TNF-α, COX-2, and iNOS), increased estradiol, progesterone, prolactin and decreased FSH serum levels in CIS + RSV group compared to CIS group (P < 0.05). Moreover, there is downregulation of tissues Cleaved Caspase-3, NF-κB and Cox-2 proteins as shown in Western blot analysis, also apoptosis was significantly inhibited, evidenced by downregulation of Bax and upregulation of Bcl-2 proteins, and the ovarian and uterine histological architecture and integrity were maintained in CIS + RSV group compared to CIS group. In conclusion, these findings indicate that RSV has beneficial effects in ameliorating cisplatin-induced oxidative stress, inflammation, and apoptosis in the ovarian and uterine tissues of female rats.

Cisplatin-induced ototoxicity in organotypic cochlear cultures occurs independent of gap junctional intercellular communication

Cisplatin is a very effective chemotherapeutic, but severe and permanent hearing loss remains a prevalent side effect. The processes underpinning cisplatin-induced ototoxicity are not well understood. Gap junction channels composed of connexin (Cx) subunits allow for the passage of small molecules and ions between contacting neighboring cells. These specialized channels have been postulated to enhance cisplatin-induced cell death by spreading “death signals” throughout the supporting cells of the organ of Corti. This study sought to investigate the role of Cx43 in cisplatin-induced ototoxicity using organotypic cochlear cultures from control and two Cx43-mutant mouse strains harboring either a moderate (Cx43^I130T/+) or severe (Cx43^G60S/+) reduction of Cx43 function. Cochlear cultures from Cx43-mutant mice with a severe reduction in Cx43-based gap junctional intercellular communication (GJIC) had an enhanced number of hair cells that were positive for cleaved caspase 3, a marker of active apoptosis, after cisplatin treatment. In cisplatin-treated organotypic cochlear cultures, there was a decrease in the co-localization of Cx26 and Cx30 compared with untreated cultures, suggesting that cisplatin causes reorganization of connexin composition in supporting cells. Both Cx26 and Cx30 protein expression as well as GJIC were decreased in organotypic cochlear cultures treated with the gap-junction blocker carbenoxolone. When cisplatin and carbenoxolone were co-administered, there were no differences in hair cell loss compared with cisplatin treatment alone. Using cisplatin-treated control and Cx43-ablated organ of Corti derived HEI-OC1 mouse cells, we found that greatly reducing GJIC led to preferential induction of an ER stress pathway. Taken together, this study strongly suggests that inhibition of GJIC in organ of Corti cells does not lead to differential susceptibility to cisplatin-induced ototoxicity. Although cisplatin causes the same degree of cell death in gap junction competent and incompetent cochlear cells, the engagement of the mitochondrial dysregulation and ER stress differs.

Antisense Oligonucleotides for the Treatment of Inner Ear Dysfunction

Antisense oligonucleotides (ASOs) have shown potential as therapeutic molecules for the treatment of inner ear dysfunction. The peripheral sensory organs responsible for both hearing and equilibrium are housed within the inner ear. Hearing loss and vestibular balance problems affect a large portion of the population and limited treatment options exist. Targeting ASOs to the inner ear as a therapeutic strategy has unique pharmacokinetic and drug delivery opportunities and challenges. Here, we review ASO technology, delivery, disease targets, and other key considerations for development of this therapeutic approach.

Lower ototoxicity and absence of hidden hearing loss point to gentamicin C1a and apramycin as promising antibiotics for clinical use

Spread of antimicrobial resistance and shortage of novel antibiotics have led to an urgent need for new antibacterials. Although aminoglycoside antibiotics (AGs) are very potent anti-infectives, their use is largely restricted due to serious side-effects, mainly nephrotoxicity and ototoxicity. We evaluated the ototoxicity of various AGs selected from a larger set of AGs on the basis of their strong antibacterial activities against multidrug-resistant clinical isolates of the ESKAPE panel: gentamicin, gentamicin C1a, apramycin, paromomycin and neomycin. Following local round window application, dose-dependent effects of AGs on outer hair cell survival and compound action potentials showed gentamicin C1a and apramycin as the least toxic. Strikingly, although no changes were observed in compound action potential thresholds and outer hair cell survival following treatment with low concentrations of neomycin, gentamicin and paromomycin, the number of inner hair cell synaptic ribbons and the compound action potential amplitudes were reduced. This indication of hidden hearing loss was not observed with gentamicin C1a or apramycin at such concentrations. These findings identify the inner hair cells as the most vulnerable element to AG treatment, indicating that gentamicin C1a and apramycin are promising bases for the development of clinically useful antibiotics.

Tramadol attenuates the sensitivity of glioblastoma to temozolomide through the suppression of Cx43‑mediated gap junction intercellular communication

Analgesics and antineoplastic drugs are often used concurrently for cancer patients. Our previous study reported that gap junctions composed of connexin32 (Cx32) was implicated in the effect of analgesics on cisplatin cytotoxicity. However, the effect of analgesic on the most widely expressed connexin (Cx), connexin43 (Cx43), and whether such effect mediates the influence on chemotherapeutic efficiency remain unknown. By manipulation of Cx43 expression or gap junction function, we found that there were gap junction-dependent and independent effect of Cx43 on temozolomide (TMZ) sensitivity in U87 glioblastoma cells. Studies on survival and apoptosis showed widely used analgesic tramadol significantly reduced TMZ-induced cytotoxicity in control and negative control cells but not shCx43-transfected cells. Proliferation assay demonstrated tramadol suppressed TMZ-induced cytotoxicity only on high density (with gap junction formation) but not on low density (without gap junction formation). Tramadol inhibited dye-coupling through gap junctions between U87 cells. Tramadol treatment for 72 h did not alter Cx43 expression, but decreased Cx43 phosphorylation accompanied with reduced p-ERK and p-JNK. Our results indicated that long-term treatment with tramadol reduced TMZ cytotoxicity in U87 cells by suppressing Cx43-composed gap junctions, suggesting identification and usage of antinociceptive drugs which do not downregulate connexin activity should have beneficial therapeutic consequences.

Prophylactic etanercept treatment in cisplatin ototoxicity

The aim of our study was to evaluate the audiological protective effects of etanercept using distortion product otoacoustic emission (DPOAE) in rats with hearing loss due to cisplatin ototoxicity. The study began with 36 healthy female albino rats; 31 rats had good measurements in DPOAE and were included in the study. On day 0, a single dose of etanercept was given by intraperitoneal administration to 15 rats (etanercept group). No medication was given to the control group. After 24 h, 16 mg/kg cisplatin was given to all rats. DPOAE measurements were performed on the 3rd, 7th, and 21st day. After the DPOAE test on the 21st day, the animals were killed by decapitation. Between-group and intra-group comparisons were made using the data of the two groups. A statistically significant difference was observed on the 3rd day at 4921 Hz and higher frequencies, on the 7th day at 6064 Hz and higher frequencies, and on the 21st day at 6494 Hz and higher frequencies (p < 0.05). We observed 10% ototoxicity in the etanercept group and 56% ototoxicity in the control group. A single dose of etanercept 1 day before cisplatin administration decreases cisplatin ototoxicity in the early period. This effect comes to the fore especially over 4500 Hz frequencies at 65 dB and higher.

NLRX1 accelerates cisplatin-induced ototoxity in HEI-OC1 cells via promoting generation of ROS and activation of JNK signaling pathway

Nucleotide-binding domain and leucine-rich-repeat-containing family member X1 (NLRX1), located in mitochondria, can recognize cytoplasmic pattern recognition receptors and is tightly related to reactive oxygen species (ROS) production, mitochondrial function, apoptosis and inflammation. The present study was designed to explore whether NLRX1 expresses in HEI-OC1 cells and, if so, to investigate the possible correlations between NLRX1 and cisplatin-induced ototoxity in vitro. Here, we report that NLRX1 was specifically localized to mitochondria in the cytoplasm of HEI-OC1 cells and its expression was increased concurrent with the increase of ROS production and occurrence of apoptosis in HEI-OC1 cells in response to cisplatin stimulus. NLRX1 overexpression led to a higher apoptosis in HEI-OC1 cells treated with cisplatin, whereas, NLRX silencing decreased cisplatin induced apoptosis. Mechanistic studies showed that NLRX1 activated mitochondrial apoptosis pathway as well as promoted ROS generation and JNK activation. Either inhibition of ROS generation or JNK signaling significantly prevented NLRX1-mediated mitochondrial apoptosis in HEI-OC1cells. In addition, NLRX1 expression was confirmed in cochlear explants. The findings from this work reveal that NLRX1 sensitizes HEI-OC1 cells to cisplatin-induced apoptosis via activation of ROS/JNK signaling pathway, suggesting that NLRX1 acts as an important regulator of the cisplatin-elicited ototoxity.

Connexin 43 Acts as a Proapoptotic Modulator in Cisplatin-Induced Auditory Cell Death

AIMS

Gap junction coupling is known to play a role in intercellular communication by the Good Samaritan effect or bystander effect. Nonjunctional connexins (Cxs) may also play certain gap junction-independent roles in cell death or survival. The purpose of the present study was to investigate the role of junctional and nonjunctional Cxs in ototoxic drug-induced auditory cell death by focusing on Cx43 in the cochlea.

RESULTS

Nonjunctional Cx43 conditions were prepared by low confluence culture (5 × 10³/cm²) or a trafficking inhibitor, brefeldin A (BFA), in auditory cells, and short lengthened Cx43s with amino-terminal (NT; amino acids 1-256) or carboxy-terminal (CT; amino acids 257-382) were transfected into Cx-deficient HeLa cells to avoid gap junction formation. Knockdown of nonchannel Cx43 (small interfering RNA [siRNA]) inhibited Cis-diamminedichloroplatinum (cisplatin)-induced cell death regardless of gap junction formation; however, a gap junction blocker, 18 alpha-glycyrrhetinic acid (18α-GA), showed inhibitory effect only under the junctional condition. BFA did not show any additive influence on the inhibitory effect of siRNA Cx43. Shortened Cx43-transfected HeLa cells also resulted in a significant increase in cell death under cisplatin. In the animal studies with cisplatin-treated rats, hearing thresholds of auditory brainstem response were significantly preserved by a gap junction blocker, carbenoxolone, showing much more preserved stereocilia of hair cells in scanning electron microscopic findings. Innovation and Conclusion: Cx43 plays a proapoptotic role in cisplatin-induced auditory cell death in both junctional and nonjunctional conditions. Targeting the Cx-mediated signaling control may be helpful in designing new therapeutic strategies for drug-induced ototoxicity. Antioxid. Redox Signal. 25, 623-636.

Investigation of an SPR biosensor for determining the influence of connexin 43 expression on the cytotoxicity of cisplatin

The real-time and label free detection abilities of surface plasmon resonance (SPR) biosensors provide a way of evaluating the influence of some genes’ expression on anti-tumor drug cytotoxicity.