Prevention of Cisplatin Ototoxicity Using Transtympanic N-Acetylcysteine and Lactate

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Molecular Characteristics of Cisplatin-Induced Ototoxicity and Therapeutic Interventions

Cisplatin is a commonly used chemotherapeutic agent with proven efficacy in treating various malignancies, including testicular, ovarian, cervical, breast, bladder, head and neck, and lung cancer. Cisplatin is also used to treat tumors in children, such as neuroblastoma, osteosarcoma, and hepatoblastoma. However, its clinical use is limited by severe side effects, including ototoxicity, nephrotoxicity, neurotoxicity, hepatotoxicity, gastrointestinal toxicity, and retinal toxicity. Cisplatin-induced ototoxicity manifests as irreversible, bilateral, high-frequency sensorineural hearing loss in 40-60% of adults and in up to 60% of children. Hearing loss can lead to social isolation, depression, and cognitive decline in adults, and speech and language developmental delays in children. Cisplatin causes hair cell death by forming DNA adducts, mitochondrial dysfunction, oxidative stress, and inflammation, culminating in programmed cell death by apoptosis, necroptosis, pyroptosis, or ferroptosis. Contemporary medical interventions for cisplatin ototoxicity are limited to prosthetic devices, such as hearing aids, but these have significant limitations because the cochlea remains damaged. Recently, the U.S. Food and Drug Administration (FDA) approved the first therapy, sodium thiosulfate, to prevent cisplatin-induced hearing loss in pediatric patients with localized, non-metastatic solid tumors. Other pharmacological treatments for cisplatin ototoxicity are in various stages of preclinical and clinical development. This narrative review aims to highlight the molecular mechanisms involved in cisplatin-induced ototoxicity, focusing on cochlear inflammation, and shed light on potential antioxidant and anti-inflammatory therapeutic interventions to prevent or mitigate the ototoxic effects of cisplatin. We conducted a comprehensive literature search (Google Scholar, PubMed) focusing on publications in the last five years.

Otologic safety of intratympanic N-acetylcysteine in an animal model

OBJECTIVE

N-acetylcysteine (NAC) is an anti-oxidant and mucolytic effective against bacterial biofilms, making it useful in the treatment of chronically discharging ears that are unresponsive to traditional treatment methods. The objective of this study was to evaluate the otologic safety of intratympanic NAC combined with Ciprodex® in an animal model.

METHODS

Baseline distortion product otoacoustic emissions (DPOAE) and auditory brainstem response (ABR) measurements were performed for both ears on thirteen guinea pigs from the animal care research facilities of the McGill University Health Center. This was followed by intratympanic administration of control solution (Ciprofloxacin 0.3%/Dexamethasone 0.1%) to the left ear and experimental solution (1.25% NAC/Ciprofloxacin 0.3%/Dexamethasone 0.1%) to the right ear. Three additional intratympanic injections were performed over the next fourteen days. DPOAE and ABR measurements were repeated 3-4 weeks after the initial procedure. Outcome measures included differences in DPOAE and ABR thresholds after intervention, clinical evidence of vestibular dysfunction and histological evidence of ototoxicity.

RESULTS

There were no significant differences in the ABR thresholds and DPOAE results of the control and experimental ears at baseline and after intervention. There was neither clinical manifestation of vestibular dysfunction nor histological evidence of ototoxicity.

CONCLUSION

Our study suggests that intratympanic 1.25% NAC with ciprofloxacin and dexamethasone is safe in guinea pigs and support its potential use in the treatment of chronically discharging ears. Further studies in humans are required to analyze its efficacy relative to conventional treatments.

LEVEL OF EVIDENCE

Animal Research.

Role of mitochondrial dysfunction and oxidative stress in sensorineural hearing loss

Sensorineural hearing loss (SNHL) can either be genetically inherited or acquired as a result of aging, noise exposure, or ototoxic drugs. Although the precise pathophysiological mechanisms underlying SNHL remain unclear, an overwhelming body of evidence implicates mitochondrial dysfunction and oxidative stress playing a central etiological role. With its high metabolic demands, the cochlea, particularly the sensory hair cells, stria vascularis, and spiral ganglion neurons, is vulnerable to the damaging effects of mitochondrial reactive oxygen species (ROS). Mitochondrial dysfunction and consequent oxidative stress in cochlear cells can be caused by inherited mitochondrial DNA (mtDNA) mutations (hereditary hearing loss and aminoglycoside-induced ototoxicity), accumulation of acquired mtDNA mutations with age (age-related hearing loss), mitochondrial overdrive and calcium dysregulation (noise-induced hearing loss and cisplatin-induced ototoxicity), or accumulation of ototoxic drugs within hair cell mitochondria (drug-induced hearing loss). In this review, we provide an overview of our current knowledge on the role of mitochondrial dysfunction and oxidative stress in the development of SNHL caused by genetic mutations, aging, exposure to excessive noise, and ototoxic drugs. We also explore the advancements in antioxidant therapies for the different forms of acquired SNHL that are being evaluated in preclinical and clinical studies.

Intratympanic Administration of Dieckol Prevents Ototoxic Hearing Loss

OBJECTIVE

Systemic administration of dieckol reportedly ameliorates acute hearing loss. In this study, dieckol was delivered to the inner ear by the intratympanic route. The functional and anatomic effects and safety of dieckol were assessed using the rat ototoxicity model.

MATERIALS AND METHODS

Dieckol in a high-molecular-weight hyaluronic acid vehicle (dieckol+vehicle group) or vehicle without dieckol (vehicle-only group) were randomly delivered into 12 ears intratympanically. Ototoxic hearing loss was induced by intravenous administration of cisplatin, gentamicin, and furosemide. The hearing threshold and surviving outer hair cells (OHC) were enumerated. Biocompatibility was assessed by serial endoscopy of the tympanic membrane (TM), and the histology of the TM and the base of bulla (BB) mucosa was quantitatively assessed.

RESULTS

The hearing threshold was significantly better (difference of 20 dB SPL) in the dieckol+vehicle group than in the vehicle-only group. The number of surviving OHCs was significantly greater in the dieckol+vehicle group than in the vehicle-only group. There were no signs of inflammation or infection in the ear. The thickness of the TM and the BB mucosa did not differ between the two groups.

CONCLUSION

Intratympanic local delivery of dieckol may be a safe and effective method to prevent ototoxic hearing loss.

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.

Optimal N-acetylcysteine concentration for intratympanic injection to prevent cisplatin-induced ototoxicity in guinea pigs

BACKGROUND

Cisplatin is a chemotherapy drug that can induce sensorineural hearing loss. At present, no otoprotective agent is approved for use.

OBJECTIVES

This study investigated the optimal concentration of intratympanic N-acetylcysteine (NAC) to prevent cisplatin-induced ototoxicity in a guinea pig model.

MATERIALS AND METHODS

Guinea pigs (n = 64) were treated with a single intratympanic injection containing different NAC concentrations or saline (control) 3 days prior to intraperitoneal injection with cisplatin. The threshold change in the auditory brainstem response was assessed.

RESULTS

Four weeks after intraperitoneal cisplatin injection, only the group that received 2% NAC exhibited significant otoprotection (p < .05) compared with the control. Otoprotection was observed at all the frequencies tested (1k, 2k, 4k, and 8k Hz). The 2% NAC group also exhibited significant otoprotection (p < .05) compared with the other NAC groups (at 1k, 2k, 4k, and 8k Hz). The 4% NAC group exhibited significantly reduced hearing capacity (p < .05) in the fourth week compared with controls.

CONCLUSIONS AND SIGNIFICANCE

Intratympanic NAC administration is an efficient and safe means of preventing cisplatin-induced ototoxicity. In our animal model, the optimal intratympanic NAC concentration was 2%; concentrations of 4% loss of otoprotection.

Long-term auditory follow-up in the management of pediatric platinum-induced ototoxicity

PURPOSE

Irreversible bilateral sensorineural hearing loss is a common side effect of platinum compounds. Because of the extended overall survival, a prolonged hearing surveillance and management of hearing impairments are emerging concerns for pediatric oncology.

METHODS

In this retrospective observational study, we enrolled 38 children out of 116 treated at our institution by chemotherapy (cisplatin and/or carboplatin) with or without irradiation between 2007 and 2014, submitted to hearing monitoring before every cycle of chemotherapy, and who completed a 5-year long-term audiological follow-up. Chemotherapy regimens, demographic findings, cumulative doses, and cranial irradiation were compared.

RESULTS

At the end of 5-year follow-up, ototoxicity was significantly increased compared to that observed at the end of chemotherapy (52.5% vs 39.5%, p < 0.001). A late onset of hearing loss was experienced in 13.1% of children, while in 26.3% progressive hearing loss was measured. Deafness at the end of chemotherapy and irradiation were significant prognostic factors for late ototoxicity outcomes (Odds Ratio 7.2-CI 1.67-31.1-p < 0.01 and 5.25-CI 1.26-21.86-p < 0.01 respectively). No significant differences were found between cisplatin and combined treatment (i.e., cisplatin shifted to carboplatin during monitoring for the onset of ototoxicity) and ototoxicity was not associated with platinum compounds cumulative dose (p > 0.05). 13.1% of children needed hearing aids at the end of follow-up.

CONCLUSION

Long-term monitoring of at least 5 years prevents the harmful effects of hearing deprivation identifying late onset/progressive hearing loss after platinum compound chemotherapy in children thanks to early hearing rehabilitation, especially in those who underwent multimodal therapy or subjected to irradiation.

Transtympanic injection of a liposomal gel loaded with N-acetyl-L-cysteine: A relevant strategy to prevent damage induced by cochlear implantation in guinea pigs?

Patients with residual hearing can benefit from cochlear implantation. However, insertion can damage cochlear structures and generate oxidative stress harmful to auditory cells. The antioxidant N-acetyl-L-cysteine (NAC) is a precursor of glutathione (GSH), a powerful endogenous antioxidant. NAC local delivery to the inner ear appeared promising to prevent damage after cochlear implantation in animals. NAC-loaded liposomal gel was specifically designed for transtympanic injection, performed both 3 days before and on the day of surgery. Hearing thresholds were recorded over 30 days in implanted guinea pigs with and without NAC. NAC, GSH, and their degradation products, N,N'-diacetyl-L-cystine (DiNAC) and oxidized glutathione (GSSG) were simultaneously quantified in the perilymph over 15 days in non-implanted guinea pigs. For the first time, endogenous concentrations of GSH and GSSG were determined in the perilymph. Although NAC-loaded liposomal gel sustained NAC release in the perilymph over 15 days, it induced hearing loss in both implanted and non-implanted groups with no perilymphatic GSH increase. Under physiological conditions, NAC appeared poorly stable within liposomes. As DiNAC was quantified at concentrations which were twice as high as NAC in the perilymph, it was hypothesized that DiNAC could be responsible for the adverse effects on hearing.

Cisplatin-induced ototoxicity: Updates on molecular mechanisms and otoprotective strategies

Cisplatin is a highly effective antitumor drug generally used in the treatment of solid malignant tumors. However, cisplatin causes severe side effects such as bone marrow depression, nephrotoxicity, and ototoxicity, thus limiting its clinical application. The incidence of ototoxicity induced by cisplatin ranges from 20% to 70%, and it usually manifests as a progressive, bilateral and irreversible hearing loss. Although the etiology of cisplatin-induced ototoxicity remains unclear, an increasing body of evidence suggests that the ototoxicity of cisplatin is mainly related to the production of reactive oxygen species and activation of apoptotic pathway in cochlear tissues. Many drugs have been well proved to protect cisplatin-induced hearing loss in vitro and in vivo. However, the anti-tumor effect of cisplatin is also weakened by systemic administration of those drugs for hearing protection, especially antioxidants. Therefore, establishing a local administration strategy contributes to the otoprotection without affecting the effect of cisplatin. This review introduces the pathology of ototoxicity caused by cisplatin, and focuses on recent developments in the mechanisms and protective strategies of cisplatin-induced ototoxicity.

Antioxidant Therapy against Oxidative Damage of the Inner Ear: Protection and Preconditioning

Oxidative stress is an important mechanism underlying cellular damage of the inner ear, resulting in hearing loss. In order to prevent hearing loss, several types of antioxidants have been investigated; several experiments have shown their ability to effectively prevent noise-induced hearing loss, age-related hearing loss, and ototoxicity in animal models. Exogenous antioxidants has been used as single therapeutic agents or in combination. Antioxidant therapy is generally administered before the production of reactive oxygen species. However, post-exposure treatment could also be effective. Preconditioning refers to the phenomenon of pre-inducing a preventative pathway by subtle stimuli that do not cause permanent damage in the inner ear. This renders the inner ear more resistant to actual stimuli that cause permanent hearing damage. The preconditioning mechanism is also related to the induction of antioxidant enzymes. In this review, we discuss the mechanisms underlying antioxidant-associated therapeutic effects and preconditioning in the inner ear.

Strategies to reduce the risk of platinum containing antineoplastic drug-induced ototoxicity

INTRODUCTION

Cisplatin is a highly effective chemotherapeutic agent against a variety of solid tumors in adults and in children. Unfortunately, a large percentage of patients suffer permanent sensorineural hearing loss. Up to 60% of children and at least 50% of adults suffer this complication that seriously compromises their quality of life. Hearing loss is due to damage to the sensory cells in the inner ear. The mechanisms of cochlear damage are still being investigated. However, it appears that inner ear damage is triggered by reactive oxygen species (ROS) formation and inflammation 34.

AREAS COVERED

We discuss a number of potential therapeutic targets that can be addressed to provide hearing protection. These strategies include enhancing the endogenous antioxidant pathways, heat shock proteins, G protein coupled receptors and counteracting ROS and reactive nitrogen species, and blocking pathways that produce inflammation, including TRPV1 and STAT1 36.

EXPERT OPINION

Numerous potential protective agents show promise in animal models by systemic or local administration. However, clinical trials have not shown much efficacy to date with the exception of sodium thiosulfate. There is an urgent need to discover safe and effective protective agents that do not interfere with the efficacy of cisplatin against tumors yet preserve hearing 151.

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.

Ototoxicity and Platinum Uptake Following Cyclic Administration of Platinum-Based Chemotherapeutic Agents

Cisplatin is a widely used anti-cancer drug used to treat a variety of cancer types. One of the side effects of this life-saving drug is irreversible ototoxicity, resulting in permanent hearing loss in many patients. In order to understand why cisplatin is particularly toxic to the inner ear, we compared the hearing loss and cochlear uptake of cisplatin to that of two related drugs, carboplatin and oxaliplatin. These three drugs are similar in that each contains a core platinum atom; however, carboplatin and oxaliplatin are considered less ototoxic than cisplatin. We delivered these three drugs to mice using a 6-week cyclic drug administration protocol. We performed the experiment twice, once using equimolar concentrations of the drugs and once using concentrations of the drugs more proportional to those used in the clinic. For both concentrations, we detected a significant hearing loss caused by cisplatin and no hearing loss caused by carboplatin or oxaliplatin. Cochlear uptake of each drug was measured using inductively coupled plasma mass spectrometry (ICP-MS) to detect platinum. Cochlear platinum levels were highest in mice treated with cisplatin followed by oxaliplatin, while carboplatin was largely excluded from the cochlea. Even when the drug doses were increased, cochlear platinum remained low in mice treated with oxaliplatin or carboplatin. We also examined drug clearance from the inner ear by measuring platinum levels at 1 h and 24 h after drug administration. Our findings suggest that the reduced cochlear platinum we observed with oxaliplatin and carboplatin were not due to increased clearance of these drugs relative to cisplatin. Taken together, our data indicate that the differential ototoxicity among cisplatin, carboplatin, and oxaliplatin is attributable to differences in cochlear uptake of these three drugs.

Clinical trials evaluating transtympanic otoprotectants for cisplatin-induced ototoxicity: what do we know so far?

BACKGROUND

Cisplatin (CDDP) chemotherapy can cause serious side effects including irreversible and progressive hearing loss. Studies have aimed to assess potential protective strategies; however, systemic treatments have presented variable results, and potential interactions with CDDP have limited clinical trials.

METHODS

A review of the literature was performed in order to evaluate clinical trials that have studied a transtympanic approach as an otoprotectant strategy.

RESULTS

Six clinical trials were included. While a transtympanic approach can limit side effects and avoid interactions with CDDP, recurrent issues have been expressed including which otoprotectant to test, time delays between CDDP treatment and transtympanic injections, side effects such as pain and dizziness, concentrations, and number of injections. Clinical trials have used sodium thiosulfate, N-acetylcysteine and dexamethasone.

CONCLUSIONS

While a transtympanic approach seems like an attractive strategy, further research is needed to clarify which is the optimal otoprotectant, its dosage, and the number of injections.

Overview of cisplatin-induced neurotoxicity and ototoxicity, and the protective agents

Cisplatin has dramatically improved the survival rate of cancer patients, but it has also increased the prevalence of hearing and neurological deficits in this population. Cisplatin induces ototoxicity, peripheral (most prevalent) and central (rare) neurotoxicity. This review addresses the ototoxicity and the neurotoxicity associated with cisplatin-based chemotherapy, providing an integrated view of the potential protective agents that have been evaluated in vitro, in vivo and in clinical trials, their targets and mechanisms of protection and their effects on the antitumor activity of cisplatin. So far, the findings are insufficient to support the use of any oto- or neuroprotective agent before, during or after cisplatin chemotherapy. Despite their promising effects in vitro and in animal studies, many agents have not been evaluated in clinical trials. Additionally, the clinical trials have limitations concerning the sample size, controls, measurement, heterogeneous groups, several arms of treatment, short follow-up or no blinding. Besides that, for most agents, the effects on the antitumor activity of cisplatin have not been evaluated in tumor-bearing animals, which discourages clinical trials. Further well-designed randomized controlled clinical trials are necessary to definitely demonstrate the effectiveness of the oto- or neuroprotective agents proposed by animal and in vitro studies.

[Topical drug administration to the inner ear. Modern state of the problem and development perspectives]

The work assessed modern methods of drug delivery through biological barriers to the lesion, in particular, through the most studied - skin. The main advantages and disadvantages of the existing methods for the topical administration of drugs into the inner ear - intra-imperial and intra-labyrinth delivery are analyzed. A brief review of medicinal substances for topical administration to the inner ear, both widely used (for example, aminoglycosides, steroid drugs) and undergoing clinical trials, is given. An assessment is made of the prospects for the use of transmembrane drug delivery to the inner ear using an electric field, which has a combined electro-creative and iontophoretic effect.

Use of the guinea pig in studies on the development and prevention of acquired sensorineural hearing loss, with an emphasis on noise

Guinea pigs have been used in diverse studies to better understand acquired hearing loss induced by noise and ototoxic drugs. The guinea pig has its best hearing at slightly higher frequencies relative to humans, but its hearing is more similar to humans than the rat or mouse. Like other rodents, it is more vulnerable to noise injury than the human or nonhuman primate models. There is a wealth of information on auditory function and vulnerability of the inner ear to diverse insults in the guinea pig. With respect to the assessment of potential otoprotective agents, guinea pigs are also docile animals that are relatively easy to dose via systemic injections or gavage. Of interest, the cochlea and the round window are easily accessible, notably for direct cochlear therapy, as in the chinchilla, making the guinea pig a most relevant and suitable model for hearing. This article reviews the use of the guinea pig in basic auditory research, provides detailed discussion of its use in studies on noise injury and other injuries leading to acquired sensorineural hearing loss, and lists some therapeutics assessed in these laboratory animal models to prevent acquired sensorineural hearing loss.

Superparamagnetic Nanoparticle Delivery to the Cochlea Through Round Window by External Magnetic Field: Feasibility and Toxicity

Introduction. The objective of this study was to evaluate the feasibility and toxicity of superparamagnetic iron oxide nanoparticles (SPIONs) administered into the cochlea through the round window (RW) by an external magnetic field. Materials and Methods. In 5 Wistar rats, the left RW was punctured. SPIONs suspended in hyaluronic gel (5 mg/mL) were applied in the RW niche and covered by a muscle graft. The nanoparticles were mobilized using a rare earth magnet (0.54 T) held in 4 consecutive positions around the head. The right ear served as control. Hearing function was monitored by auditory brainstem responses (4-32 kHz tone bursts). Results. The auditory thresholds remained unchanged 1 month after the administration. The histological study of the cochleae showed that SPIONs were driven into the scala tympani in the basal turn, the second turn, and the apex. Conclusion. Superparamagnetic nanoparticles can be driven inside the cochlea toward the apex with a preserved hearing up to 1 month in rats.

Local Drug Delivery for Prevention of Hearing Loss

Systemic delivery of therapeutics for targeting the cochlea to prevent or treat hearing loss is challenging. Systemic drugs have to cross the blood-labyrinth barrier (BLB). BLB can significantly prevent effective penetration of drugs in appropriate concentrations to protect against hearing loss caused by inflammation, ototoxic drugs, or acoustic trauma. This obstacle may be obviated by local administration of protective agents. This route can deliver higher concentration of drug compared to systemic application and preclude systemic side effects. Protective agents have been administered by intra-tympanic injection in numerous preclinical studies. Drugs such as steroids, etanercept, D and L-methionine, pifithrin-alpha, adenosine agonists, melatonin, kenpaullone (a cyclin-dependent kinase 2 (CDK2) inhibitor) have been reported to show efficacy against cisplatin ototoxicity in animal models. Several siRNAs have been shown to ameliorate cisplatin ototoxicity when administered by intra-tympanic injection. The application of corticosteroids and a number of other drugs with adjuvants appears to enhance efficacy. Administration of siRNAs to knock down AMPK kinase, liver kinase B1 (LKB1) or G9a in the cochlea have been found to ameliorate noise-induced hearing loss. The local administration of these compounds appears to be effective in protecting the cochlea against damage from cisplatin or noise trauma. Furthermore the intra-tympanic route yields maximum protection in the basal turn of the cochlea which is most vulnerable to cisplatin ototoxicity and noise trauma. There appears to be very little transfer of these agents to the systemic circulation. This would avoid potential side effects including interference with anti-tumor efficacy of cisplatin. Nanotechnology offers strategies to effectively deliver protective agents to the cochlea. This review summarizes the pharmacology of local drug delivery by intra-tympanic injection to prevent hearing loss caused by cisplatin and noise exposure in animals. Future refinements in local protective agents provide exciting prospects for amelioration of hearing loss resulting from cisplatin or noise exposure.

Prevention of cisplatin-induced hearing loss by extended release fluticasone propionate intracochlear implants

OBJECTIVE

Cisplatin is a chemotherapeutic drug known to induce hearing loss. Although corticosteroids may help to mitigate the ototoxic side effects of cisplatin, there are complications associated with their systemic and prolonged use. The goal of this study is to test the efficacy of extended-release fluticasone propionate intracochlear implant particles to protect against cisplatin-induced hearing loss.

METHODS

We used guinea pigs (n = 9) injected with cisplatin (IP, 12 mg/kg weight). Fluticasone particles were delivered to the cochlear scala tympani through the round window membrane into the right ears of the guinea pigs (left ears being used as a control) two weeks prior to cisplatin administration, and hearing function was evaluated by ABR and DPOAE before implantation, immediately before cisplatin administration, and 2 weeks after the challenge with cisplatin. Data was statistically evaluated using paired t-test analysis.

RESULTS

No significant differences were observed in ABR threshold between control and implanted ears on day 14 (23.9 ± 2.3 dB vs. 25.6 ± 1.3 dB, P = 0.524), whereas the significant cisplatin-induced hearing loss in control animals (23.9 ± 2.3 dB at day 14 vs. 40.7 ± 2.5 dB at day 28, P ≤ 0.0001) was prevented in implanted animals (25.6 ± 1.3 dB at day 14 vs. 25.0 ± 3.1 at day 28, P ≥ 0.85). A similar, though not statistically significant, trend was observed in DPOAE responses in untreated ears (7.9 ± 5.8 dB at day14 vs. -0.5 ± 5.3 dB at day 28, P = 0.654) as compared to treatment (11.1 ± 3.4 dB at day 14 vs. 13.6 ± 4.8 dB at day 28, P = 0.733).

CONCLUSION

These results suggest that fluticasone intracochlear implants are safe and able to provide effective otoprotection against cisplatin-induced hearing loss in the guinea pig model.

A Review of Cisplatin-Associated Ototoxicity

Cisplatin, an effective antineoplastic drug used in the treatment of many cancers, has ototoxic potential, thus placing cancer patients, receiving this treatment, at risk of hearing loss. It is therefore important for health care professionals managing these patients to be aware of cisplatin's ototoxic properties and its clinical signs to identify patients at risk of developing a hearing impairment. Eighty-five English peer-reviewed articles and two books, from January 1975 to July 2015, were identified from PubMed, ScienceDirect, and EBSCOhost. An overview of cisplatin-associated ototoxicity, namely its clinical features, incidence rates, molecular and cellular mechanisms, and risk factors, is presented in this article. This review further highlights the importance of a team-based approach to complement an audiological monitoring program in reducing any further loss in the quality of life of affected patients, as there is currently no otoprotective agent routinely recommended for the prevention of cisplatin-associated ototoxicity.

Mitochondria-Targeted Antioxidants for Treatment of Hearing Loss: A Systematic Review

Mitochondrial dysfunction is associated with the etiologies of sensorineural hearing loss, such as age-related hearing loss, noise- and ototoxic drug-induced hearing loss, as well as hearing loss due to mitochondrial gene mutation. Mitochondria are the main sources of reactive oxygen species (ROS) and ROS-induced oxidative stress is involved in cochlear damage. Moreover, the release of ROS causes further damage to mitochondrial components. Antioxidants are thought to counteract the deleterious effects of ROS and thus, may be effective for the treatment of oxidative stress-related diseases. The administration of mitochondria-targeted antioxidants is one of the drug delivery systems targeted to mitochondria. Mitochondria-targeted antioxidants are expected to help in the prevention and/or treatment of diseases associated with mitochondrial dysfunction. Of the various mitochondria-targeted antioxidants, the protective effects of MitoQ and SkQR1 against ototoxicity have been previously evaluated in animal models and/or mouse auditory cell lines. MitoQ protects against both gentamicin- and cisplatin-induced ototoxicity. SkQR1 also provides auditory protective effects against gentamicin-induced ototoxicity. On the other hand, decreasing effect of MitoQ on gentamicin-induced cell apoptosis in auditory cell lines has been controversial. No clinical studies have been reported for otoprotection using mitochondrial-targeted antioxidants. High-quality clinical trials are required to reveal the therapeutic effect of mitochondria-targeted antioxidants in terms of otoprotection in patients.

Innovative pharmaceutical approaches for the management of inner ear disorders

The sense of hearing is essential for permitting human beings to interact with the environment, and its dysfunctions can strongly impact on the quality of life. In this context, the cochlea plays a fundamental role in the transformation of the airborne sound waves into electrical signals, which can be processed by the brain. However, several diseases and external stimuli (e.g., noise, drugs) can damage the sensorineural structures of cochlea, inducing progressive hearing dysfunctions until deafness. In clinical practice, the current pharmacological approaches to treat cochlear diseases are based on the almost exclusive use of systemic steroids. In the last decades, the efficacy of novel therapeutic molecules has been proven, taking advantage from a better comprehension of the pathological mechanisms underlying many cochlear diseases. In addition, the feasibility of intratympanic administration of drugs also permitted to overcome the pharmacokinetic limitations of the systemic drug administration, opening new frontiers in drug delivery to cochlea. Several innovative drug delivery systems, such as in situ gelling systems or nanocarriers, were designed, and their efficacy has been proven in vitro and in vivo in cochlear models. The current review aims to describe the art of state in the cochlear drug delivery, highlighting lights and shadows and discussing the most critical aspects still pending in the field.

Protective effect of N-acetylcysteine against cisplatin ototoxicity in rats: a study with hearing tests and scanning electron microscopy

INTRODUCTION

Ototoxicity is a health problem appearing after powerful treatments in serious health conditions. It is sometimes inevitable when treatment of the serious disease is required. Cisplatin is an antineoplastic agent which was investigated previously to reveal increased nitrogen and reactive oxygen radicals that damages hair cells, resulting in ototoxicity. N-acetylcysteine, previously shown to decrease ototoxicity caused by different agents, is known to be a powerful in vitro antioxidant. Probably N-acetylcysteine, in addition to its antioxidant effect, blocks a cascade where reactive oxygen species result in apoptosis in the cochlea.

OBJECTIVES

The possible preventive effect of N-acetylcysteine in cisplatin ototoxicity was studied with auditory brain stem responses, otoacoustic emissions, and histopathological investigation of the cochlea in a scanning electron microscopy.

METHODS

This study was conducted on 21 Wistar Albino rats in four groups. 1mL/kg/day three times in total intraperitoneal (i.p.) Saline (n=5), 500mg/kg/day i.p. three times in total N-acetylcysteine (n=5), i.p. 15mg/kg cisplatin alone (single dose) (n=5) and i.p. 15mg/kg cisplatin plus 500mg/kg/day N-acetylcysteine (n=6) were administered. The rats were anesthetized to study the hearing tests before and after the experiment. The rats were sacrificed to investigate the cochleas by scanning electron microscopy.

RESULTS

Auditory brain stem responses and otoacoustic emissions values were attenuated in the cisplatin group. The group that received N-acetylcysteine in addition to cisplatin had better auditory brain stem responses thresholds and otoacoustic emissions. The samples obtained from the cisplatin group showed surface irregularities, degeneration areas, and total or partial severe stereocilia losses. The changes were milder in the cisplatin+N-acetylcysteine group.

CONCLUSION

Cisplatin ototoxicity can be detected by auditory brain stem responses and otoacoustic emissions testing in rats. N-acetylcysteine may protect the cochlear cells from histopathological changes. We concluded that N-acetylcysteine given 4h after cisplatin injection has a potential otoprotective effect against cisplatin ototoxicity. which suggests it could be used in clinical trials.

Research protocol: Cisplatin-associated ototoxicity amongst patients receiving cancer chemotherapy and the feasibility of an audiological monitoring program

Background

Cisplatin is an anti-cancer chemotherapy drug classified as an alkylating agent. It is used for the treatment of a variety of cancers such as cervical, breast, stomach, prostate, bladder and oesophageal, to name a few. However due to its expansive toxicity profile, patients receiving cisplatin can experience high frequency hearing loss, a side effect known as ototoxicity. The dearth of information on the extent and severity of cisplatin-associated ototoxicity in South Africa prevents the implementation of a context-specific audiological monitoring programme.

Methods

This study aims to determine the extent and severity of ototoxicity amongst patients with cervical cancer, receiving cisplatin-based chemotherapy and hence the feasibility of an ototoxicity monitoring program in the province of KwaZulu-Natal, South Africa. A concurrent mixed methods design will be employed in the study. This longitudinal study will involve interviewing oncology nurses, oncologists, pharmacists and audiologists to assess the level of awareness to ototoxicity, as well as conducting diagnostic audiological evaluations at regular intervals on 78 patients with cervical cancer to ascertain the progression of hearing loss during and after chemotherapy. The feasibility of the monitoring program will be assessed as a parallel process to the audiological evaluations, where patient outcomes and cost implications to the patient and the health sector will be considered. Data will be subjected to statistical analyses so as to strengthen knowledge in the field and inform appropriate policies, and healthcare providers.

Discussion

This study is the first longitudinal study in South Africa to determine the ototoxic effects of cisplatin therapy on patients diagnosed with cervical cancer. Thus, the results generated from this study is likely to bring novel information to the fore using an evidence-based approach that will influence policy and clinical practice which can vastly improve the quality of life of patients undergoing chemotherapy. Mitigation of any further loss in the quality of life of affected patients is of paramount importance and the data generated from this project can lay the basis for further effective dialogue towards policy formulation on an ototoxic monitoring programme and the resultant strengthening of health systems in limited resource settings.

Electronic supplementary material

The online version of this article (10.1186/s12905-017-0486-8) contains supplementary material, which is available to authorized users.

Mechanisms of Cisplatin-Induced Ototoxicity and Otoprotection

Evidence of significant hearing loss during the early days of use of cisplatin as a chemotherapeutic agent in cancer patients has stimulated research into the causes and treatment of this side effect. It has generally been accepted that hearing loss is produced by excessive generation of reactive oxygen species (ROS) in cell of the cochlea, which led to the development of various antioxidants as otoprotective agents. Later studies show that ROS could stimulate cochlear inflammation, suggesting the use of anti-inflammatory agents for treatment of hearing loss. In this respect, G-protein coupled receptors, such as adenosine A₁ receptor and cannabinoid 2 receptors, have shown efficacy in the treatment of hearing loss in experimental animals by increasing ROS scavenging, suppressing ROS generation, or by decreasing inflammation. Inflammation could be triggered by activation of transient receptor potential vanilloid 1 (TRPV1) channels in the cochlea and possibly other TRP channels. Targeting TRPV1 for knockdown has also been shown to be a useful strategy for ensuring otoprotection. Cisplatin entry into cochlear hair cells is mediated by various transporters, inhibitors of which have been shown to be effective for treating hearing loss. Finally, cisplatin-induced DNA damage and activation of the apoptotic process could be targeted for cisplatin-induced hearing loss. This review focuses on recent development in our understanding of the mechanisms underlying cisplatin-induced hearing loss and provides examples of how drug therapies have been formulated based on these mechanisms.

Cisplatin-Associated Ototoxicity: A Review for the Health Professional

Cisplatin is an effective drug used in the treatment of many cancers, yet its ototoxic potential places cancer patients, exposed to this drug, at risk of hearing loss, thus negatively impacting further on a patient's quality of life. It is paramount for health care practitioners managing such patients to be aware of cisplatin's ototoxic properties and the clinical signs to identify patients at risk of developing hearing loss. English peer-reviewed articles from January 1975 to July 2015 were assessed from PubMed, Science Direct, and Ebscohost. Seventy-nine articles and two books were identified for this review, using MeSH terms and keywords such as "ototoxicity", "cisplatin", "hearing loss", and "ototoxicity monitoring". This review provides an up-to-date overview of cisplatin-associated ototoxicity, namely, its clinical features, incidence rates, and molecular and cellular mechanisms and risk factors, to health care practitioners managing the patient with cancer, and highlights the need for a team-based approach to complement an audiological monitoring programme to mitigate any further loss in the quality of life of affected patients, as there is currently no otoprotective agent recommended routinely for the prevention of cisplatin-associated ototoxicity. It also sets the platform for effective dialogue towards policy formulation and strengthening of health systems in developing countries.

Mitochondria-Targeted Antioxidant Mitoquinone Reduces Cisplatin-Induced Ototoxicity in Guinea Pigs

Objective To determine if mitoquinone (MitoQ) attenuates cisplatin-induced hearing loss in guinea pigs. Study Design Prospective and controlled animal study. Setting Academic, tertiary medical center. Subjects and Methods Guinea pigs were injected subcutaneously with either 5 mg/kg MitoQ (n = 9) or normal saline (control, n = 9) for 7 days and 1 hour before receiving a single dose of 10 mg/kg cisplatin. Auditory brainstem response thresholds were measured before MitoQ or saline administration and 3 to 4 days after cisplatin administration. Results Auditory brainstem response threshold shifts after cisplatin treatment were smaller by 28 to 47 dB in guinea pigs injected with MitoQ compared with those in the control group at all tested frequencies (4, 8, 16, and 24 kHz, P = .0002 to .04). Scanning electron microscopy of cochlear hair cells showed less outer hair cell loss and damage in the MitoQ group. Conclusion MitoQ reduced cisplatin-induced hearing loss in guinea pigs. MitoQ appears worthy of further investigation as a means of preventing cisplatin ototoxicity in humans.

Antibacterial effect of N-acetylcysteine on common canine otitis externa isolates

BACKGROUND

N-Acetylcysteine (NAC) has the potential to be a useful therapeutic agent for the treatment of otitis externa due to its antimicrobial and mucolytic properties, as well as its ability to disrupt bacterial biofilm.

HYPOTHESIS/OBJECTIVES

To determine the antibacterial activity of NAC against common bacterial isolates associated with canine otitis externa.

ANIMALS

Twenty two isolates from canine clinical cases of otitis externa were identified and tested, including five Staphylococcus pseudintermedius, six Pseudomonas aeruginosa, five Corynebacterium spp. and six β-haemolytic Streptococcus spp. isolates.

METHODS

Each isolate was grown on blood agar for 24 h and transferred to Mueller Hinton Broth (MHB) to achieve a final concentration of 5 × 10(5)  CFU/mL. NAC was diluted in MHB to a starting concentration of 160 mg/mL and serial two-fold microdilution assays were performed in triplicate with negative controls for all isolates tested. Concentrations of NAC tested ranged from 0.125 to 80 mg/mL. A 50 μL volume of bacterial suspension was used to inoculate each well.

RESULTS

The minimum inhibitory concentration (MIC) of NAC for all isolates tested ranged from 5 to 20 mg/mL.

CONCLUSIONS AND CLINICAL RELEVANCE

N-Acetylcysteine inhibits clinically relevant and drug resistant bacteria in vitro, and has potential for use as a novel agent for treatment of otitis externa.

The Sustained-Exposure Dexamethasone Formulation OTO-104 Offers Effective Protection against Cisplatin-Induced Hearing Loss

The otoprotective effects of OTO-104 were investigated following both acute and chronic administration of cisplatin. The acute administration of cisplatin to guinea pigs resulted in profound hearing loss (70-80 dB SPL) across all frequencies tested. A single intratympanic injection of 6% OTO-104, but not of lower doses, almost completely protected against cisplatin ototoxicity. In contrast, a dexamethasone solution administered under the same experimental conditions offered no otoprotection. OTO-104 was also very effective in protecting against the progressive hearing loss observed with the chronic administration of cisplatin (3 injections at a weekly interval). The otoprotection was found to be dependent upon the activation of dexamethasone-dependent classical nuclear receptor pathways.

Cisplatin-Induced Ototoxicity: Effects, Mechanisms and Protection Strategies

Cisplatin is a highly effective chemotherapeutic agent that is widely used to treat solid organ malignancies. However, serious side effects have been associated with its use, such as bilateral, progressive, irreversible, dose-dependent neurosensory hearing loss. Current evidence indicates that cisplatin triggers the production of reactive oxygen species in target tissues in the inner ear. A variety of agents that protect against cisplatin-induced ototoxicity have been successfully tested in cell culture and animal models. However, many of them interfere with the therapeutic effect of cisplatin, and therefore are not suitable for systemic administration in clinical practice. Consequently, local administration strategies, namely intratympanic administration, have been developed to achieve otoprotection, without reducing the antitumoral effect of cisplatin. While a considerable amount of pre-clinical information is available, clinical data on treatments to prevent cisplatin ototoxicity are only just beginning to appear. This review summarizes clinical and experimental studies of cisplatin ototoxicity, and focuses on understanding its toxicity mechanisms, clinical repercussions and prevention strategies.

Investigation of protective role of curcumin against paclitaxel-induced inner ear damage in rats

OBJECTIVES/HYPOTHESIS

The aim of this study was to investigate the potential protective effect of curcumin on paclitaxel-induced ototoxicity in rats by means of immunohistochemical and histopathological analysis and distortion product otoacoustic emissions (DPOAEs).

STUDY DESIGN

Animal study.

METHODS

Forty Sprague-Dawley rats were randomized into five groups. Group 1 was administered no paclitaxel and curcumin during the study. Groups 2, 3, 4 and 5 were administered 5 mg/kg paclitaxel; 200 mg/kg curcumin; 5 mg/kg paclitaxel, followed by 200 mg/kg curcumin; 200 mg/kg curcumin and a day later 5 mg/kg paclitaxel followed intraperitoneally by 200 mg/kg curcumin once a week for 4 consecutive weeks, respectively. After the final DPOAEs test, the animals were sacrificed and their cochlea were prepared for hematoxylin and eosin and caspase-3 staining.

RESULTS

The DPOAEs thresholds and histopathological and immunohistochemical findings were substantially correlated in all groups. The histopathologic findings in the cochlea of the paclitaxel-treated animals showed not only changes in the organ of Corti, but also damage to the stria vascularis and spiral limbus, including nuclear degeneration, cytoplasmic vacuolization, and atrophy of intermediate cells. Additionally, cochlear changes in group 2, such as intense apoptosis, were confirmed by caspase-3 immunohistochemical staining. In group 4, coreceiving curcumin could not sufficiently prevent paclitaxel-induced ototoxicity, and the results in group 5 were similar to the control group.

CONCLUSIONS

In our study, we have concluded that pre- and coreceiving curcumin can significantly protect the cochlear morphology and functions on paclitaxel-induced ototoxicity in rats. Curcumin might be considered as a potential natural product that, used as a dietary supplement, could be easily given to patients undergoing paclitaxel chemotherapy.

LEVEL OF EVIDENCE

NA

The Safety Pharmacology of Auditory Function

Safety pharmacology satisfies a key requirement in the process of drug development. Safety pharmacology studies are required to assess the impact of a new chemical entity (NCE) or biotechnology-derived product for human use on vital systems, such as those subserving auditory function. Safety pharmacology studies accordingly are defined as those studies that investigate the potential undesirable effects of a substance on auditory functions in relation to exposure in and above the therapeutic range. Auditory safety studies should be designed with the primary objective of determining how administration of a compound influences normal hearing. If an effect on hearing is identified, then it is necessary to determine through histopathology the underlying mechanism for the observed hearing loss. Since the auditory system contains a heterogeneous mixture of structural and cellular components that are organized in a very complex and integrated manner, it is necessary to clearly identify the underlying primary mechanism or target of the new chemical entity that produced the hearing loss. This chapter will highlight major components of auditory function with regard to potential opportunities for drug interaction. Aspects of designing ototoxicity studies will be discussed with an emphasis on standards deemed necessary by the US Food and Drug Administration. Additionally, classes of ototoxic compounds and their proposed mechanisms of action are described in depth.

Early investigational drugs for hearing loss

INTRODUCTION

Sensorineural hearing loss (HL) is becoming a global phenomenon at an alarming rate. Nearly 600 million people have been estimated to have significant HL in at least one ear. There are several different causes of sensorineural HL included in this review of new investigational drugs for HL. They are noise-induced, drug-induced, sudden sensorineural HL, presbycusis and HL due to cytomegalovirus infections.

AREAS COVERED

This review presents trends in research for new investigational drugs encompassing a variety of causes of HL. The studies presented here are the latest developments either in the research laboratories or in preclinical, Phase 0, Phase I or Phase II clinical trials for drugs targeting HL.

EXPERT OPINION

While it is important that prophylactic measures are developed, it is extremely crucial that rescue strategies for unexpected or unavoidable cochlear insult be established. To achieve this goal for the development of drugs for HL, innovative strategies and extensive testing are required for progress from the bench to bedside. However, although a great deal of research needs to be done to achieve the ultimate goal of protecting the ear against acquired sensorineural HL, we are likely to see exciting breakthroughs in the near future.

Targeted Amelioration of Cisplatin-Induced Ototoxicity in Guinea Pigs

This pilot study compared otoprotection provided by trans-tympanic formulations and systemic intraperitoneal administration of L-N-acetylcysteine from cisplatin-induced cochlear oxidative stress. Protection was assessed by measures of hearing loss and cochlear glutathione levels. All groups received an equivalent single dose of L-N-acetylcysteine followed by cisplatin.

Cisplatin was administered subcutaneously for 3 days (5.5 mg/kg/day). Two hours prior to day 1 cisplatin, L-N-acetylcysteine was administered either intraperitoneally (250 mg/kg), trans-tympanic as 2% L-N-acetylcysteine in gel, or trans-tympanic as L-N-acetylcysteine–loaded nanocapsules in gel. Hearing was assessed prior to and 3 days after cisplatin followed by microdissection of cochlear tissue. The levels of reduced (GSH) and oxidized (GSSG) glutathione in homogenized tissue supernatants were determined via luminometry.

Intraperitoneal L-N-acetylcysteine administration preceding cisplatin resulted in less hearing loss and a higher GSH/GSSG ratio than either trans-tympanic formulation. This suggests that for equivalent doses of L-N-acetylcysteine, systemic rather than targeted cochlear delivery provides increased otoprotection from cisplatin ototoxicity.

Prevention and restoration of hearing loss associated with the use of cisplatin

Background. Cisplatin is a well known platinum-based chemotherapeutic agent used for the treatment of various malignant tumours. A frequent side effect of cisplatin therapy is ototoxicity. Unfortunately, currently there are no available treatments. Material and Methods. Experimental, clinical studies and reviews published between 2004 and 2014 in the English medical literature concerning ototoxicity were selected using Medline, PubMed, and Google Scholar databases. Inclusion criteria were cisplatin-induced ototoxicity and therapy aimed at preventing or curing this disorder. Molecular mechanisms and clinical, audiological, and histological markers of cisplatin-induced ototoxicity are described. Moreover, experimental and clinical strategies for prevention or treatment of hearing loss were also reviewed. Results and Discussion. Experimental studies demonstrate a wide range of otoprotective molecules and strategies efficient against cisplatin-induced hearing loss. However, only dexamethasone proved a slight otoprotective effect in a clinical study. Conclusion. Further research must be completed to bring future therapeutic options into clinical setting.

In vitro efficacy of N-acetylcysteine on bacteria associated with chronic suppurative otitis media

Background

The safety and efficacy of Ciprodex® has been demonstrated for treatment of chronic suppurative otitis media (CSOM). However, symptoms fail to resolve in 9-15% of patients. The objective of this study is to evaluate the efficacy of N-acetylcysteine (NAC) on S. aureus, and planktonic and sessile (biofilm forming) P. aeruginosa in vitro using clinical isolates from patients with CSOM.

Methods

1) Stability was assessed using liquid chromatography-mass spectrometry for each component in a prepared mixture of Ciprodex® and NAC over 15 days. Sterility was assessed by measuring bacterial growth on a blood agar plate. Efficacy was assessed using a disc diffusion method by inoculating plates with S. aureus ATCC 29513 and P. aeruginosa ATCC 27853, and measuring the clearance zone.

2) Fifteen P. aeruginosa strains were isolated from patients with CSOM and tested in vitro using the bioFILM PA™ antimicrobial susceptibility assay. Treatment solutions included Ciprodex® & ciprofloxacin +/- NAC, and NAC alone (0.25%, 0.5% & 1.25%).

Results

1) NAC combined with Ciprodex® demonstrated stability, sterility, and efficacy over a two-week period

2) P. aeruginosa strains in the sessile (33%-40%) and planktonic (13%) state demonstrated resistance to Ciprodex® and ciprofloxacin. When NAC ≥0.5% was used in isolation or as an adjunct to either of these medications, no resistance was found in the sessile or planktonic state among all 15 strains.

Conclusion

1) Ciprodex® combined with NAC has a shelf life of at least two weeks given the documented preservation of stability, sterility, and clinical efficacy of the mixed compounds.

2) P. aeruginosa strains demonstrated resistance to both Ciprodex® and ciprofloxacin. NAC ≥0.5% overcomes issues with resistance and shows promise in the treatment of CSOM.

Inhibitory effect of N-acetyl cysteine and ascorbic acid on the development of myringosclerosis: an experimental study

OBJECTIVES

This study investigated the effects of ascorbic acid and N-acetyl cysteine (NAC) antioxidants on the development of myringosclerosis (MS) in an experimental model.

METHODS

Myringotomies were performed in the ears of 15 guinea pigs, and Spongostan pieces were placed on the perforated regions of the tympanic membrane. The subjects were divided randomly into three groups and treated with three different solutions on the Spongostan-group 1: (control, 0.9% saline), group 2 (ascorbic acid), and group 3 (NAC). On day 15 after treatment, specimens from the tympanic membranes were obtained and examined via light microscopy. Sclerosis and inflammation scores and the tympanic membrane thicknesses were evaluated. Immunohistochemical methods were used to evaluate the expression of VEGF, TGF-β, iNOS, and IL1-β in all groups.

RESULTS

Lower sclerosis and inflammation scores and reduced tympanic membrane thicknesses were observed in groups treated with NAC or ascorbic acid compared with the control group. Immunohistochemical studies revealed significantly less expression of VEGF, TGF-β, and iNOS in groups 2 and 3 compared with group 1. Additionally, IL1-β expression was significantly less in group 3 than in group 1. Compared with group 1, group 2 animals exhibited reduced inflammation in the lamina propria, fewer active fibroblasts, less leukocyte infiltration, and decreased thickness of the vessels; group 3 animals exhibited decreased numbers of active fibroblasts and collagen fibers in the lamina propria.

CONCLUSIONS

Inflammation scores, cellular infiltration, and expression of VEGF, TGF-β, and iNOS were reduced by ascorbic acid and/or NAC treatments, thereby decreasing MS development. Decreased expression of IL1-β was observed only in animals treated with NAC.

Assessing cisplatin-induced ototoxicity and otoprotection in whole organ culture of the mouse inner ear in simulated microgravity

Cisplatin is a widely used anti-cancer drug. Ototoxicity is a major dose-limiting side-effect. A reproducible mammalian in-vitro model of cisplatin ototoxicity is required to screen and validate otoprotective drug candidates. We utilized a whole organ culture system of the postnatal mouse inner ear in a rotating wall vessel bioreactor under "simulated microgravity" culture conditions. As previously described this system allows whole organ culture of the inner ear and quantitative assessment of ototoxic effects of aminoglycoside induced hair cell loss. Here we demonstrate that this model is also applicable to the assessment of cisplatin induced ototoxicity. In this model cisplatin induced hair cell loss was dose and time dependent. Increasing exposure time of cisplatin led to decreasing EC50 concentrations. Outer hair cells were more susceptible than inner hair cells, and hair cells in the cochlear base were more susceptible than hair cells in the cochlear apex. Initial cisplatin dose determined the final extent of hair cell loss irrespective if the drug was withdrawn or continued. Dose dependant otoprotection was demonstrated by co-administration of the antioxidant agent N-acetyl l-cysteine. The results support the use of this inner ear organ culture system as an in vitro assay and validation platform for inner ear toxicology and the search for otoprotective compounds.

Protective effect of metformin against cisplatin-induced ototoxicity in an auditory cell line

Metformin, an antidiabetic drug with potent anticancer activity, is known to prevent oxidative stress-induced cell death in several cell types through a mechanism dependent on the mitochondria. In the present study, we investigated the influence of metformin on cisplatin ototoxicity in an auditory cell line. Cell viability was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (Sigma, St. Louis, MO, USA) cell proliferation assay. Oxidative stress and apoptosis were assessed by flow cytometry analysis, Hoechst 33258 staining, reactive oxygen species (ROS) measurement, and western blotting. Intracellular calcium concentration changes were detected using calcium imaging. Pretreatment with 1 mM metformin prior to the application of 20 μM cisplatin significantly decreased the frequency of late apoptosis in HEI-OC1 cells and also significantly attenuated the cisplatin-induced increase in ROS. In addition, metformin inhibited the activation of caspase-3 and levels of poly-ADP-ribose polymerase (PARP). Pretreatment with metformin prevented the cisplatin-induced elevation in intracellular calcium concentrations. We propose that metformin protects against cisplatin-induced ototoxicity by inhibiting the increase in intracellular calcium levels, preventing apoptosis, and limiting ROS production.

The Protective Effect of Chrysin Against Cisplatin İnduced Ototoxicity in Rats

Ototoxicity is a common side effect of cisplatin chemotherapy. The aim of this study was to investigate the potential protective effect of chrysin against cisplatin-induced ototoxicity. Thirty-four adult female Wistar albino rats were separated into four groups: a cisplatin group (Group A), with cisplatin administered to ten rats once daily for three consecutive days at doses of 8 mg/kg body weight intraperitoneally (i.p.); a cisplatin plus chrysin group (Group B), with 8 mg/kg of cisplatin administered i.p. daily to ten rats for three consecutive days and 25 mg/kg of chrysin administered via oral gavage in a corn oil for 5 days: a chrysin group (Group C), with 25 mg/kg of chrysin administered via oral gavage in corn oil for 5 days to seven rats; and a control group (Group D), with 5 ml/kg of corn oil administered to seven rats via oral gavage for 5 days. Distortion product otoacoustic emission measurements were performed in the same ear of the rats under general anesthesia at baseline and on the first and fifth days after drug administration. No significant differences were noted between the measurements either in the chrysin group or in the control group. In the cisplatin group, there was a significant worsening of hearing compared to baseline and the measurements on the fifth day at all frequencies. In the statistical analysis, a statistically significant difference was observed at 5039, 6351, 8003, and 10078 Hz frequencies between the measurements on the first and fifth days. In the cisplatin plus chrysin group, there were statistically significant differences at frequencies of 2,003 and 5,039 Hz between the measurements at baseline and on the fifth day, at 3,175 and 5,039 Hz between the measurements on the first and fifth days, and at 8,003 and 100,078 Hz between the measurements at baseline and on the first day. According to these results, this study demonstrates that cisplatin-related ototoxicity can be prevented in rats by the administration of chrysin.