AAV-Mediated Delivery of the Caspase Inhibitor XIAP Protects Against Cisplatin Ototoxicity:

Quercetin attenuates cisplatin-induced mitochondrial apoptosis via PI3K/Akt mediated inhibition of oxidative stress in pericytes and improves the blood labyrinth barrier permeability

Cisplatin (CDDP) is broadly employed to treat different cancers, whereas there are no drugs approved by the Food and Drug Administration (FDA) for preventing its side effects, including ototoxicity. Quercetin (QU) is a widely available natural flavonoid compound with anti-tumor and antioxidant properties. The research was designed to explore the protective effects of QU on CDDP-induced ototoxicity and its underlying mechanisms in male C57BL/6 J mice and primary cultured pericytes (PCs). Hearing changes, morphological changes of stria vascularis, blood labyrinth barrier (BLB) permeability and expression of apoptotic proteins were observed in vivo by using the auditory brainstem response (ABR) test, HE staining, Evans blue staining, immunohistochemistry, western blotting, etc. Oxidative stress levels, mitochondrial function and endothelial barrier changes were observed in vitro by using DCFH-DA probe detection, flow cytometry, JC-1 probe, immunofluorescence and the establishment in vitro BLB models, etc. QU pretreatment activates the PI3K/AKT signaling pathway, inhibits CDDP-induced oxidative stress, protects mitochondrial function, and reduces mitochondrial apoptosis in PCs. However, PI3K/AKT specific inhibitor (LY294002) partially reverses the protective effects of QU. In addition, in vitro BLB models were established by coculturing PCs and endothelial cells (ECs), which suggests that QU both reduces the CDDP-induced apoptosis in PCs and improves the endothelial barrier permeability. On the whole, the research findings suggest that QU can be used as a novel treatment to reduce CDDP-induced ototoxicity.

Protection from cisplatin-induced hearing loss with lentiviral vector-mediated ectopic expression of the anti-apoptotic protein BCL-XL

Cisplatin is a highly effective chemotherapeutic agent, but it can cause sensorineural hearing loss (SNHL) in patients. Cisplatin-induced ototoxicity is closely related to the accumulation of reactive oxygen species (ROS) and subsequent death of hair cells (HCs) and spiral ganglion neurons (SGNs). Despite various strategies to combat ototoxicity, only one therapeutic agent has thus far been clinically approved. Therefore, we have developed a gene therapy concept to protect cochlear cells from cisplatin-induced toxicity. Self-inactivating lentiviral (LV) vectors were used to ectopically express various antioxidant enzymes or anti-apoptotic proteins to enhance the cellular ROS scavenging or prevent apoptosis in affected cell types. In direct comparison, anti-apoptotic proteins mediated a stronger reduction in cytotoxicity than antioxidant enzymes. Importantly, overexpression of the most promising candidate, Bcl-xl, achieved an up to 2.5-fold reduction in cisplatin-induced cytotoxicity in HEI-OC1 cells, phoenix auditory neurons, and primary SGN cultures. BCL-XL protected against cisplatin-mediated tissue destruction in cochlear explants. Strikingly, in vivo application of the LV BCL-XL vector improved hearing and increased HC survival in cisplatin-treated mice. In conclusion, we have established a preclinical gene therapy approach to protect mice from cisplatin-induced ototoxicity that has the potential to be translated to clinical use in cancer patients.

Advancements and future prospects of adeno-associated virus-mediated gene therapy for sensorineural hearing loss

Sensorineural hearing loss (SNHL), a highly prevalent sensory impairment, results from a multifaceted interaction of genetic and environmental factors. As we continually gain insights into the molecular basis of auditory development and the growing compendium of deafness genes identified, research on gene therapy for SNHL has significantly deepened. Adeno-associated virus (AAV), considered a relatively secure vector for gene therapy in clinical trials, can deliver various transgenes based on gene therapy strategies such as gene replacement, gene silencing, gene editing, or gene addition to alleviate diverse types of SNHL. This review delved into the preclinical advances in AAV-based gene therapy for SNHL, spanning hereditary and acquired types. Particular focus is placed on the dual-AAV construction method and its application, the vector delivery route of mouse inner ear models (local, systemic, fetal, and cerebrospinal fluid administration), and the significant considerations in transforming from AAV-based animal model inner ear gene therapy to clinical implementation.

Current Advances in Adeno-Associated Virus-Mediated Gene Therapy to Prevent Acquired Hearing Loss

Adeno-associated viruses (AAVs) are viral vectors that offer an excellent platform for gene therapy due to their safety profile, persistent gene expression in non-dividing cells, target cell specificity, lack of pathogenicity, and low immunogenicity. Recently, gene therapy for genetic hearing loss with AAV transduction has shown promise in animal models. However, AAV transduction for gene silencing or expression to prevent or manage acquired hearing loss is limited. This review provides an overview of AAV as a leading gene delivery vector for treating genetic hearing loss in animal models. We highlight the advantages and shortcomings of AAV for investigating the mechanisms and preventing acquired hearing loss. We predict that AAV-mediated gene manipulation will be able to prevent acquired hearing loss.

Adeno-Associated Viral Vectors as Versatile Tools for Neurological Disorders: Focus on Delivery Routes and Therapeutic Perspectives

It is without doubt that the gene therapy field is currently in the spotlight for the development of new therapeutics targeting unmet medical needs. Thus, considering the gene therapy scenario, neurological diseases in general and neurodegenerative disorders in particular are emerging as the most appealing choices for new therapeutic arrivals intended to slow down, stop, or even revert the natural progressive course that characterizes most of these devastating neurodegenerative processes. Since an extensive coverage of all available literature is not feasible in practical terms, here emphasis was made in providing some advice to beginners in the field with a narrow focus on elucidating the best delivery route available for fulfilling any given AAV-based therapeutic approach. Furthermore, it is worth nothing that the number of ongoing clinical trials is increasing at a breath-taking speed. Accordingly, a landscape view of preclinical and clinical initiatives is also provided here in an attempt to best illustrate what is ongoing in this quickly expanding field.

Mild Therapeutic Hypothermia and Putative Mechanisms of Hair Cell Survival in the Cochlea

Significance: Sensorineural hearing loss has significant implications for quality of life and risk for comorbidities such as cognitive decline. Noise and ototoxic drugs represent two common risk factors for acquired hearing loss that are potentially preventable. Recent Advances: Numerous otoprotection strategies have been postulated over the past four decades with primary targets of upstream redox pathways. More recently, the application of mild therapeutic hypothermia (TH) has shown promise for otoprotection for multiple forms of acquired hearing loss. Critical Issues: Systemic antioxidant therapy may have limited application for certain ototoxic drugs with a therapeutic effect on redox pathways and diminished efficacy of the primary drug's therapeutic function (e.g., cisplatin for tumors). Future Directions: Mild TH likely targets multiple mechanisms, contributing to otoprotection, including slowed metabolics, reduced oxidative stress, and involvement of cold shock proteins. Further work is needed to identify the mechanisms of mild TH at play for various forms of acquired hearing loss.

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.

Ultrasound-microbubble cavitation facilitates adeno-associated virus mediated cochlear gene transfection across the round-window membrane

The round window of the cochlea provides an ideal route for delivering medicines and gene therapy reagents that can cross the round window membrane (RWM) into the inner ear. Recombinant adeno-associated viruses (rAAVs) have several advantages and are recommended as viral vectors for gene transfection. However, rAAVs cannot cross an intact RWM. Consequently, ultrasound-mediated microbubble (USMB) cavitation is potentially useful, because it can sonoporate the cell membranes, and increase their permeability to large molecules. The use of USMB cavitation for drug delivery across the RWM has been tested in a few animal studies but has not been used in the context of AAV-mediated gene transfection. The currently available large size of the ultrasound probe appears to be a limiting factor in the application of this method to the RWM. In this study, we used home-made ultrasound probe with a decreased diameter to 1.5 mm, which enabled the easy positioning of the probe close to the RWM. In guinea pigs, we used this probe to determine that (1) USMB cavitation caused limited damage to the outer surface layer or the RWM, (2) an eGFP-gene carrying rAAV could effectively pass the USMB-treated RWM and reliably transfect cochlear cells, and (3) the hearing function of the cochlea remained unchanged. Our results suggest that USMB cavitation of the RWM is a good method for rAAV-mediated cochlear gene transfection with clear potential for clinical translation. We additionally discuss several advantages of the small probe size.

Direct cellular reprogramming and inner ear regeneration

INTRODUCTION

Sound is integral to communication and connects us to the world through speech and music. Cochlear hair cells are essential for converting sounds into neural impulses. However, these cells are highly susceptible to damage from an array of factors, resulting in degeneration and ultimately irreversible hearing loss in humans. Since the discovery of hair cell regeneration in birds, there have been tremendous efforts to identify therapies that could promote hair cell regeneration in mammals.

AREAS COVERED

Here, we will review recent studies describing spontaneous hair cell regeneration and direct cellular reprograming as well as other factors that mediate mammalian hair cell regeneration.

EXPERT OPINION

Numerous combinatorial approaches have successfully reprogrammed non-sensory supporting cells to form hair cells, albeit with limited efficacy and maturation. Studies on epigenetic regulation and transcriptional network of hair cell progenitors may accelerate discovery of more promising reprogramming regimens.

Photobiomodulation promotes adenoviral gene transduction in auditory cells

Gene therapy is the delivery of a therapeutic gene into target cells to treat disorders by replacing disease-causing mutated genes with healthy ones. Gene therapy of the inner ear has been recently described, with applications for sensorineural hearing loss. However, gene delivery to the location of the inner ear, and thus efficacy of therapy, is challenging. Photobiomodulation (PBM) with a low-level laser has been suggested to have a therapeutic effect and has the potential to augment gene therapy. To investigate whether PBM improves the rate of adenovirus (Ad)-mediated viral delivery, we compared low-level laser therapy (LLLT) and non-LLLT HEI-OC1 cells treated with an Ad viral vector carrying green fluorescent protein (GFP). Cultured HEI-OC1 cells were divided into six groups: no treatment control, LLLT only, 1 μL Ad-GFP, 3 μL Ad-GFP, 1 μL Ad-GFP + LLLT, and 3 μL Ad-GFP + LLLT (LLLT: 808 nm at 15 mW for 15 min). Cells were irradiated twice: at 2 h and again at 24 h. A nonparametric Mann-Whitney U test was used to statistically analyze differences between the control and treatment groups. The viral inoculations used in this study did not change the amount of viable HEI-OC1 cells (N = 4-8). The 1 μL Ad-GFP + LLLT and 3 μL Ad-GFP + LLLT groups showed an increased density of GFP-positive cells compared to 1 μL and 3 μL Ad-GFP cells (N = 5-8, 1 μL: p = 0.0159; 3 μL: p = 0.0168,). The quantitative analysis of the epifluorescence of the 1 μL Ad-GFP + LLLT, and 3 μL Ad-GFP + LLLT groups revealed increased GFP expression/cell compared to 1 μL and 3 μL Ad-GFP cells (N = 6-15, 1 μL: p = 0.0082; 3 μL: p = 0.0012). The RT-qPCR results were consistent (N = 4-5, p = 0.0159). These findings suggest that PBM may enhance the gene delivery of Ad-mediated viral transduction, and the combination of the two may be a promising tool for gene therapy for sensorineural hearing loss.

Potential of Gene and Cell Therapy for Inner Ear Hair Cells

Sensorineural hearing loss is caused by the loss of sensory hair cells (HCs) or a damaged afferent nerve pathway to the auditory cortex. The most common option for the treatment of sensorineural hearing loss is hearing rehabilitation using hearing devices. Various kinds of hearing devices are available but, despite recent advancements, their perceived sound quality does not mimic that of the "naïve" cochlea. Damage to crucial cochlear structures is mostly irreversible and results in permanent hearing loss. Cochlear HC regeneration has long been an important goal in the field of hearing research. However, it remains challenging because, thus far, no medical treatment has successfully regenerated cochlear HCs. Recent advances in genetic modulation and developmental techniques have led to novel approaches to generating HCs or protecting against HC loss, to preserve hearing. In this review, we present and review the current status of two different approaches to restoring or protecting hearing, gene therapy, including the newly introduced CRISPR/Cas9 genome editing, and stem cell therapy, and suggest the future direction.

PI3K and Inhibitor of Apoptosis Proteins Modulate Gentamicin- Induced Hair Cell Death in the Zebrafish Lateral Line

Inner ear hair cell death leads to sensorineural hearing loss and can be a direct consequence of aminoglycoside antibiotic treatment. Aminoglycosides such as gentamicin are effective therapy for serious Gram-negative bacterial infections such as some forms of meningitis, pneumonia, and sepsis. Aminoglycosides enter hair cells through mechanotransduction channels at the apical end of hair bundles and initiate intrinsic cell death cascades, but the precise cell signaling that leads to hair cell death is incompletely understood. Here, we examine the cell death pathways involved in aminoglycoside damage using the zebrafish (Danio rerio). The zebrafish lateral line contains hair cell-bearing organs called neuromasts that are homologous to hair cells of the mammalian inner ear and represents an excellent model to study ototoxicity. Based on previous research demonstrating a role for p53, Bcl2 signaling, autophagy, and proteasomal degradation in aminoglycoside-damaged hair cells, we used the Cytoscape GeneMANIA Database to identify additional proteins that might play a role in neomycin or gentamicin ototoxicity. Our bioinformatics analysis identified the pro-survival proteins phosphoinositide-dependent kinase-1 (PDK1) and X-linked inhibitor of apoptosis protein (Xiap) as potential mediators of gentamicin-induced hair cell damage. Pharmacological inhibition of PDK1 or its downstream mediator protein kinase C facilitated gentamicin toxicity, as did Xiap mutation, suggesting that both PI3K and endogenous Xiap confer protection. Surprisingly, aminoglycoside-induced hair cell death was highly attenuated in wild type Tupfel long-fin (TL fish; the background strain for the Xiap mutant line) compared to wild type ^∗AB zebrafish. Pharmacologic manipulation of p53 suggested that the strain difference might result from decreased p53 in TL hair cells, allowing for increased hair cell survival. Overall, our studies identified additional steps in the cell death cascade triggered by aminoglycoside damage, suggesting possible drug targets to combat hearing loss resulting from aminoglycoside exposure.

Protein transduction therapy into cochleae via the round window niche in guinea pigs

Cell-penetrating peptides (CPPs) are short sequences of amino acids that facilitate the penetration of conjugated cargoes across mammalian cell membranes, and as such, they may provide a safe and effective method for drug delivery to the inner ear. Simple polyarginine peptides have been shown to induce significantly higher cell penetration rates among CPPs. Herein, we show that a peptide consisting of nine arginines ("9R") effectively delivered enhanced green fluorescent protein (EGFP) into guinea pig cochleae via the round window niche without causing any deterioration in auditory function. A second application, 24 hours after the first, prolonged the presence of EGFP. To assess the feasibility of protein transduction using 9R-CPPs via the round window, we used "X-linked inhibitor of apoptosis protein" (XIAP) bonded to a 9R peptide (XIAP-9R). XIAP-9R treatment prior to acoustic trauma significantly reduced putative hearing loss and the number of apoptotic hair cells loss in the cochleae. Thus, the topical application of molecules fused to 9R-CPPs may be a simple and promising strategy for treating inner ear diseases.

On the Distant Horizon--Medical Therapy for Sensorineural Hearing Loss

Hearing loss is the most common sensory deficit in developed societies. Hearing impairment in children, particularly of prelingual onset, has been shown to negatively affect educational achievement, future employment and earnings, and even life expectancy. Sensorineural hearing loss (SNHL), which refers to defects within the cochlea or auditory nerve itself, far outweighs conductive causes for permanent hearing loss in both children and adults. The causes of SNHL in children are heterogeneous, including both congenital and acquired causes. This article identifies potential mechanisms of intervention both at the level of the hair cell and the spiral ganglion neurons.

An integrated view of cisplatin-induced nephrotoxicity and ototoxicity

Cisplatin is one of the most widely-used drugs to treat cancers. However, its nephrotoxic and ototoxic side-effects remain major clinical limitations. Recent studies have improved our understanding of the molecular mechanisms of cisplatin-induced nephrotoxicity and ototoxicity. While cisplatin binding to DNA is the major cytotoxic mechanism in proliferating (cancer) cells, nephrotoxicity and ototoxicity appear to result from toxic levels of reactive oxygen species and protein dysregulation within various cellular compartments. In this review, we discuss molecular mechanisms of cisplatin-induced nephrotoxicity and ototoxicity. We also discuss potential clinical strategies to prevent nephrotoxicity and ototoxicity and their current limitations.

Gene transfection mediated by polyethyleneimine-polyethylene glycol nanocarrier prevents cisplatin-induced spiral ganglion cell damage

Polyethyleneimine-polyethylene glycol (PEI-PEG), a novel nanocarrier, has been used for transfection and gene therapy in a variety of cells. In our previous study, we successfully carried out PEI-PEG-mediated gene transfer in spiral ganglion cells. It remains unclear whether PEI-PEG could be used for gene therapy with X-linked inhibitor of apoptosis protein (XIAP) in the inner ear. In the present study, we performed PEI-PEG-mediated XIAP gene transfection in the cochlea of Sprague-Dawley rats, via scala tympani fenestration, before daily cisplatin injections. Auditory brainstem reflex tests demonstrated the protective effects of XIAP gene therapy on auditory function. Immunohistochemical staining revealed XIAP protein expression in the cytoplasm of cells in the spiral ganglion, the organ of Corti and the stria vascularis. Reverse transcription-PCR detected high levels of XIAP mRNA expression in the cochlea. The present findings suggest that PEI-PEG nanocarrier-mediated XIAP gene transfection results in XIAP expression in the cochlea, prevents damage to cochlear spiral ganglion cells, and protects hearing.

Cochlear protection against cisplatin by viral transfection of X-linked inhibitor of apoptosis protein across round window membrane

We have previously demonstrated that both age-related and noise-induced hearing loss are reduced in transgenic mice that ubiquitously overexpress X-linked inhibitor of apoptosis protein (XIAP). In view of the therapeutic implications of these findings, we have developed a minimally invasive surgical method to deliver adenoid-associated virus (AAV) across the round window membrane (RWM) of the cochlea, enabling efficient gene transfer to hair cells and sensory neurons in this enclosed structure. This RWM approach was used in the present study to evaluate the effectiveness of AAV-mediated XIAP overexpression in protecting against cisplatin-induced ototoxicity. Two weeks following surgery, AAV-derived XIAP was detected in the majority of inner and outer hair cells, resulting in a threefold elevation of this antiapoptotic protein in the cochlea. The protection of AAV-mediated XIAP overexpression was evaluated in animals treated with cisplatin at a dose of 4 mg kg(-1) per day for 4-7 consecutive days. The XIAP overexpression was found to attenuate cisplatin-induced hearing loss by ~22 dB. This was accompanied by a reduction of the loss of vulnerable hair cells and sensory neurons in the cochlea by 13%.

In vivo overexpression of X-linked inhibitor of apoptosis protein protects against neomycin-induced hair cell loss in the apical turn of the cochlea during the ototoxic-sensitive period

Aminoglycoside-induced cochlear ototoxicity causes hair cell (HC) loss and results in hearing impairment in patients. Previous studies have developed the concept of an ototoxicity-sensitive period during which the cochleae of young mice are more vulnerable to auditory trauma than adults. Here, we compared neomycin-induced ototoxicity at the following four developmental ages in mice: postnatal day (P)1–P7, P8–P14, P15–P21, and P60–P66. We found that when neomycin was administered between P8 and P14, the auditory brainstem response threshold increase was significantly higher at low frequencies and HC loss was significantly greater in the apical turn of the cochlea compared to neomycin administration during the other age ranges. Quantitative real-time PCR (qPCR) data revealed that the expression of apoptotic markers, including Casp3 and Casp9, was significantly higher when neomycin was injected from P8 to P14, while the expression of the X-linked inhibitor of apoptosis protein (XIAP) gene was significantly higher when neomycin was injected from P60 to P66. Because XIAP expression was low during the neomycin-sensitive period, we overexpressed XIAP in mice and found that it could protect against neomycin-induced hearing loss at low frequencies and HC loss in the apical turn of the cochlea. Altogether, our findings demonstrate a protective role for XIAP against neomycin-induced hearing loss and HC loss in the apical turn of the cochlea during the ototoxic-sensitive period, and suggest that apoptotic factors mediate the effect of neomycin during the ototoxic-sensitive period.

Effects of microbubble size on ultrasound-mediated gene transfection in auditory cells

Gene therapy for sensorineural hearing loss has recently been used to insert genes encoding functional proteins to preserve, protect, or even regenerate hair cells in the inner ear. Our previous study demonstrated a microbubble- (MB-)facilitated ultrasound (US) technique for delivering therapeutic medication to the inner ear. The present study investigated whether MB-US techniques help to enhance the efficiency of gene transfection by means of cationic liposomes on HEI-OC1 auditory cells and whether MBs of different sizes affect such efficiency. Our results demonstrated that the size of MBs was proportional to the concentration of albumin or dextrose. At a constant US power density, using 0.66, 1.32, and 2.83 μm albumin-shelled MBs increased the transfection rate as compared to the control by 30.6%, 54.1%, and 84.7%, respectively; likewise, using 1.39, 2.12, and 3.47 μm albumin-dextrose-shelled MBs increased the transfection rates by 15.9%, 34.3%, and 82.7%, respectively. The results indicate that MB-US is an effective technique to facilitate gene transfer on auditory cells in vitro. Such size-dependent MB oscillation behavior in the presence of US plays a role in enhancing gene transfer, and by manipulating the concentration of albumin or dextrose, MBs of different sizes can be produced.

Inner ear symptoms and disease: pathophysiological understanding and therapeutic options

In recent years, huge advances have taken place in understanding of inner ear pathophysiology causing sensorineural hearing loss, tinnitus, and vertigo. Advances in understanding comprise biochemical and physiological research of stimulus perception and conduction, inner ear homeostasis, and hereditary diseases with underlying genetics. This review describes and tabulates the various causes of inner ear disease and defines inner ear and non-inner ear causes of hearing loss, tinnitus, and vertigo. The aim of this review was to comprehensively breakdown this field of otorhinolaryngology for specialists and non-specialists and to discuss current therapeutic options in distinct diseases and promising research for future therapies, especially pharmaceutic, genetic, or stem cell therapy.

Possible protective effect of sertraline against cisplatin-induced ototoxicity: an experimental study

Background/Objective. Cisplatin is a widely used chemotherapeutic agent, but its ototoxicity side effect can occur in the majority of patients. Lots of agents were tried to prevent this, but there is not a routine treatment modality yet. The aim of this study was to evaluate the otoprotective effect of sertraline, which is an antidepressant with neuroprotective effects, against cisplatin, in rats. Design. Experimental animal study. Material and Methods. Forty-eight rats were randomly separated in two groups as groups I and II. Group I was identified as the control group and only a single dose of intraperitoneal cisplatin was administered. In group II, in addition to cisplatin, sertraline was administered to the rats through an oral cannula for ten-day period. Distortion product otoacoustic emission measurements were performed at the first day and the 10th day. Results. When the ototoxicity rates after cisplatin in group I and group II in distortion product otoacoustic emission measurements were compared, it was statistically significantly lower in group II in frequencies of 5652, 6165, 6726, 7336, and 7996 Hz (P < 0.05). Conclusion. Sertraline seems to have a protective effect on cisplatin ototoxicity and could be used to prevent the ototoxicity and also to treat the depression that occurred in cancer patients together.

Cisplatin-induced ototoxicity: transporters playing a role in cisplatin toxicity

Cisplatin is a potent antineoplastic agent widely used for a variety of cancer types. Unfortunately, its use leads to dose limiting side effects such as ototoxicity. Up to 93% of patients receiving cisplatin chemotherapy will develop progressive and irreversible sensorineural hearing loss which leads to a decreased quality of life in cancer survivors. No treatment is currently available for cisplatin-induced ototoxicity. It appears that cisplatin causes apoptosis by binding DNA, activating the inflammatory cascade as well as generating oxidative stress in the cell. Various studies have aimed to assess the potential protective effects of compounds such as antioxidants, anti-inflammatories, caspase inhibitors, anti-apoptotic agents and calcium channel blockers against the toxicity caused by cisplatin in the inner ear with variable degrees of protection. Nevertheless, the pathophysiology of cisplatin-induced ototoxicity remains unclear. This review summarizes all of the known transporters that could play a role in cisplatin influx, leading to cisplatin-induced ototoxicity. The following were evaluated: copper transporters, organic cation transporters, the transient receptor potential channel family, calcium channels, multidrug resistance associated proteins, mechanotransduction channels and chloride channels.

Vestibular regeneration--experimental models and clinical implications

Therapies aimed at the protection and/or regeneration of inner ear hair cells are of great interest, given the significant monetary and quality of life impact of balance disorders. Different viral vectors have been shown to transfect various cell types in the inner ear. The past decade has provided tremendous advances in the use of adenoviral vectors to achieve targeted treatment delivery. Several routes of delivery have been identified to introduce vectors into the inner ear while minimizing injury to surrounding structures. Recently, the transcription factor Atoh1 was determined to play a critical role in hair cell differentiation. Adenoviral-mediated overexpression of Atoh1 in culture and in vivo has demonstrated the ability to regenerate vestibular hair cells by causing transdifferentiation of neighbouring epithelial-supporting cells. Functional recovery of the vestibular system has also been documented following adenoviral-induced Atoh1 overexpression. Experiments demonstrating gene transfer in human vestibular epithelial cells reveal that the human inner ear is a suitable target for gene therapy.

Gene therapy for the inner ear

Animal studies on inner ear development, repair and regeneration provide understanding of molecular pathways that can be harnessed for treating inner ear disease. Use of transgenic mouse technology, in particular, has contributed knowledge of genes that regulate development of hair cells and innervation, and of molecular players that can induce regeneration, but this technology is not applicable for human treatment, for practical and ethical reasons. Therefore other means for influencing gene expression in the inner ear are needed. We describe several gene vectors useful for inner ear gene therapy and the practical aspects of introducing these vectors into the ear. We then review the progress toward using gene transfer for therapies in both auditory and balance systems, and discuss the technological milestones needed to advance to clinical application of these methods.

Caspase inhibition with XIAP as an adjunct to AAV vector gene-replacement therapy: improving efficacy and prolonging the treatment window

Purpose

AAV-mediated gene therapy in the rd10 mouse, with retinal degeneration caused by mutation in the rod cyclic guanosine monophosphate phosphodiesterase β-subunit (PDEβ) gene, produces significant, but transient, rescue of photoreceptor structure and function. This study evaluates the ability of AAV-mediated delivery of X-linked inhibitor of apoptosis (XIAP) to enhance and prolong the efficacy of PDEβ gene-replacement therapy.

Methods

Rd10 mice were bred and housed in darkness. Two groups of animals were generated: Group 1 received sub-retinal AAV5-XIAP or AAV5-GFP at postnatal age (P) 4 or 21 days; Group 2 received sub-retinal AAV5-XIAP plus AAV5- PDEβ, AAV5-GFP plus AAV5- PDEβ, or AAV- PDEβ alone at age P4 or P21. Animals were maintained for an additional 4 weeks in darkness before being moved to a cyclic-light environment. A subset of animals from Group 1 received a second sub-retinal injection of AAV8-733-PDEβ two weeks after being moved to the light. Histology, immunohistochemistry, Western blots, and electroretinograms were performed at different times after moving to the light.

Results

Injection of AAV5-XIAP alone at P4 and 21 resulted in significant slowing of light-induced retinal degeneration, as measured by outer nuclear thickness and cell counts, but did not result in improved outer segment structure and rhodopsin localization. In contrast, co-injection of AAV5-XIAP and AAV5-PDEβ resulted in increased levels of rescue and decreased rates of retinal degeneration compared to treatment with AAV5-PDEβ alone. Mice treated with AAV5-XIAP at P4, but not P21, remained responsive to subsequent rescue by AAV8-733-PDEβ when injected two weeks after moving to a light-cycling environment.

Conclusions

Adjunctive treatment with the anti-apoptotic gene XIAP confers additive protective effect to gene-replacement therapy with AAV5-PDEβ in the rd10 mouse. In addition, AAV5-XIAP, when given early, can increase the age at which gene-replacement therapy remains effective, thus effectively prolonging the window of opportunity for therapeutic intervention.

Efficient cochlear gene transfection in guinea-pigs with adeno-associated viral vectors by partial digestion of round window membrane

The auditory portion of the inner ear, the cochlea, is an ideal organ for local gene transfection owing to its relative isolation. Various carriers have been tested for cochlear gene transfection. To date, viral vectors appear to have much higher transfection efficacy than non-viral mechanisms. Among these vectors, recombinant adeno-associated virus (rAAV) vectors have several advantages such as being non-pathogenic and the ability to produce prolonged gene expression in various cell types. However, rAAV vectors cannot pass through the intact round window membrane (RWM), otherwise a very attractive approach to access the human inner ear. In this study, performed in guinea-pigs, we describe a method to increase the permeability of RWM to rAAV vectors by partial digestion with collagenase solution. Elevated delivery of rAAV across the partially digested RWM increased transfection efficacy to a satisfactory level, even though it was still lower than that achieved by direct cochleostomy injection. Functional tests (auditory brainstem responses) showed that this enzymatic manipulation did not cause permanent hearing loss if applied appropriately. Morphological observations suggested that the damage to RWM caused by partial digestion healed within four weeks. Taken together, these findings suggest that partial digestion of the RWM is a safe and effective method for increasing the transfection of cochlear sensory cells with rAAV.

Current status and prospects of gene therapy for the inner ear

Inner ear diseases are common and often result in hearing disability. Sensorineural hearing loss is the main cause of hearing disability. So far, no effective treatment is available although some patients may benefit from a hearing aid equipped with a hearing amplifier or from cochlear implantation. Inner ear gene therapy has become an emerging field of study for the treatment of hearing disability. Numerous new discoveries and tremendous advances have been made in inner ear gene therapy including gene vectors, routes of administration, and therapeutic genes and targets. Gene therapy may become a treatment option for inner ear diseases in the near future. In this review, we summarize the current state of inner ear gene therapy including gene vectors, delivery routes, and therapeutic genes and targets by examining and analyzing publications on inner ear gene therapy from the literature and patent documents, and identify promising patents, novel techniques, and vital research projects. We also discuss the progress and prospects of inner ear gene therapy, the advances and shortcomings, with possible solutions in this field of research.

Adeno-associated virus-mediated gene delivery into the scala media of the normal and deafened adult mouse ear

Murine models are ideal for studying cochlear gene transfer, as many hearing loss-related mutations have been discovered and mapped within the mouse genome. However, because of the small size and delicate nature, the membranous labyrinth of the mouse is a challenging target for the delivery of viral vectors. To minimize injection trauma, we developed a procedure for the controlled release of adeno-associated viruses (AAVs) into the scala media of adult mice. This procedure poses minimal risk of injury to structures of the cochlea and middle ear, and allows for near-complete preservation of low and middle frequency hearing. In this study, transduction efficiency and cellular specificity of AAV vectors (serotypes 1, 2, 5, 6 and 8) were investigated in normal and drug-deafened ears. Using the cytomegalovirus promoter to drive gene expression, a variety of cell types were transduced successfully, including sensory hair cells and supporting cells, as well as cells in the auditory nerve and spiral ligament. Among all five serotypes, inner hair cells were the most effectively transduced cochlear cell type. All five serotypes of AAV vectors transduced cells of the auditory nerve, though serotype 8 was the most efficient vector for transduction. Our findings indicate that efficient AAV inoculation (via the scala media) can be performed in adult mouse ears, with hearing preservation a realistic goal. The procedure we describe may also have applications for intra-endolymphatic drug delivery in many mouse models of human deafness.

Cisplatin ototoxicity and protection: clinical and experimental studies

Cisplatin is a chemotherapeutic agent that is widely used to treat a variety of malignant tumors. Serious dose-limiting side effects like ototoxicity, nephrotoxicity and neurotoxicity occur with the use of this agent. This review summarizes recent important clinical and experimental investigations of cisplatin ototoxicity. It also discusses the utility of protective agents employed in patients and in experimental animals. The future strategies for limiting cisplatin ototoxicity will need to avoid interference with the therapeutic effect of cisplatin in order to enhance the quality of life of patients receiving this important anti-tumor agent.

Over-expression of X-linked inhibitor of apoptosis protein slows presbycusis in C57BL/6J mice

Apoptosis of cochlear cells plays a significant role in age-related hearing loss or presbycusis. In this study, we evaluated whether over-expression of the anti-apoptotic protein known as X-linked Inhibitor of Apoptosis Protein (XIAP) slows the development of presbycusis. We compared the age-related hearing loss between transgenic (TG) mice that over-express human XIAP tagged with 6-Myc (Myc-XIAP) on a pure C57BL/6J genetic background with wild-type (WT) littermates by measuring auditory brainstem responses. The result showed that TG mice developed hearing loss considerably more slowly than WT littermates, primarily within the high-frequency range. The average total hair cell loss was significantly less in TG mice than WT littermates. Although levels of Myc-XIAP in the ear remained constant at 2 and 14 months, there was a marked increase in the amount of endogenous XIAP from 2 to 14 months in the cochlea, but not in the brain, in both genotypes. These results suggest that XIAP over-expression reduces age-related hearing loss and hair cell death in the cochlea.

Adenoviral-mediated up-regulation of Otos, a novel specific cochlear gene, decreases cisplatin-induced apoptosis of cultured spiral ligament fibrocytes via MAPK/mitochondrial pathway

Previous reports have implicated Otos, a novel specific gene expressed by spiral ligament fibrocytes (SLFs) with unclear functions, as a protective gene for cochlea. However, whether Otos gene could protect SLFs against cisplatin (DDP)-induced apoptosis remains largely unknown. In the present study, we utilized Adenoviral-mediated gene transfection to up-regulate Otos expression in cultured SLFs and further assessed the cell viability and apoptosis as well as possible MAPK and mitochondrial pathways. As expected, the data showed that Otos up-regulation significantly decreased apoptosis of SLFs induced by DDP possibly through activation of ERK and partial inhibition of JNK and mitochondrial pathway but not p-38 pathway, suggesting Otos as a potential protective gene for cochlea and raising the possibility of Otos up-regulation as a promising approach to DDP-induced deafness therapy.

X-linked inhibitor of apoptosis protein as a therapeutic target

Dysregulation of apoptosis has been shown to contribute to many diseases, including cancer formation, development and resistance, as well as neurodegenerative and autoimmune disorders. One mechanism through which tumour cells are believed to acquire resistance to apoptosis is by overexpression of X-linked inhibitor of apoptosis protein (XIAP), which belongs to a family of inhibitor of apoptosis proteins. When XIAP is overexpressed, cancer cells are rendered resistant to apoptosis, both intrinsically and in response to chemotherapy and radiotherapy. Significant progress has been made in targeting XIAP therapeutically, both directly and indirectly through the modulation of other molecules involved in the apoptotic pathway. This review introduces XIAP from its molecular origins, discusses its modulation and potential as a novel drug target, and considers future therapeutic perspectives.

Role of inhibitor of apoptosis protein in gentamicin-induced cochlear hair cell damage

Apoptotic cell death is considered to play a key role in gentamicin-induced cochlear hair cell loss. Inhibitor of apoptosis proteins (IAPs) are important regulators of apoptosis that can prevent activation of effector caspases. This study was designed to investigate the possible involvement of X-linked inhibitor of apoptosis protein (XIAP) in hair cell death due to gentamicin. Basal turn organ of Corti explants from postnatal day (p) p3 or p4 rats were maintained in tissue culture and were exposed to 35 muM gentamicin for up to 48 h. Effects of specific XIAP inhibitors on gentamicin-induced hair cell loss and caspase-3 activation were examined. XIAP inhibitors increased gentamicin-induced hair cell loss but an inactive analog had no effect. Caspase-3 activation was primarily observed at 36 or 48 h in gentamicin-treated hair cells, whereas caspase-3 activation peaked at 24-36 h when explants were treated with gentamicin and an XIAP inhibitor. The inhibitors alone had no effect on hair cells. Finally, a caspase-3 inhibitor decreased caspase-3 activation and hair cell loss induced by gentamicin and an XIAP inhibitor, but caspase-8 and -9 inhibitors did not. The results indicate that XIAP normally acts to decrease caspase-3 activation and hair cell loss during gentamicin ototoxicity, as part of a protective response to potentially damaging stimuli.

XIAP protection of photoreceptors in animal models of retinitis pigmentosa

BACKGROUND

Retinitis pigmentosa (RP) is a blinding genetic disorder that is caused by the death of photoreceptors in the outer nuclear layer of the retina. To date, 39 different genetic loci have been associated with the disease, and 28 mutated genes have been identified. Despite the complexity of the underlying genetic basis for RP, the final common pathway is photoreceptor cell death via apoptosis.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, P23H and S334ter rhodopsin transgenic rat models of RP were used to test the neuroprotective effects of anti-apoptotic gene therapy. Adeno-associated viruses (AAV) carrying the X-linked inhibitor of apoptosis (XIAP) or green fluorescent protein (GFP) were delivered subretinally into the eye of transgenic rat pups. Histological and functional measures were used to assess neuroprotection. XIAP is known to block apoptosis by inhibiting the action of caspases-3, -7 and -9. The results show that XIAP gene therapy provides long-term neuroprotection of photoreceptors at both structural and functional levels.

CONCLUSIONS/SIGNIFICANCE

Our gene therapy strategy targets the apoptotic cascade, which is the final common pathway in all forms of retinitis pigmentosa. This strategy holds great promise for the treatment of RP, as it allows for the broad protection of photoreceptors, regardless of the initial disease causing mutation.

Mechanisms of cisplatin-induced ototoxicity and prevention

Cisplatin is a widely used chemotherapeutic agent to treat malignant disease. Unfortunately, ototoxicity occurs in a large percentage of patients treated with higher dose regimens. In animal studies and in human temporal bone investigations, several areas of the cochlea are damaged, including outer hair cells in the basal turn, spiral ganglion cells and the stria vascularis, resulting in hearing impairment. The mechanisms appear to involve the production of reactive oxygen species (ROS), which can trigger cell death. Approaches to chemoprevention include the administration of antioxidants to protect against ROS at an early stage in the ototoxic pathways and the application of agents that act further downstream in the cell death cascade to prevent apoptosis and hearing loss. This review summarizes recent data that shed new light on the mechanisms of cisplatin ototoxicity and its prevention.