Identification of FDA-Approved Drugs and Bioactives that Protect Hair Cells in the Zebrafish (Danio rerio) Lateral Line and Mouse (Mus musculus) Utricle

The hair cells of the larval zebrafish lateral line provide a useful preparation in which to study hair cell death and to screen for genes and small molecules that modulate hair cell toxicity. We recently reported preliminary results from screening a small-molecule library for compounds that inhibit aminoglycoside-induced hair cell death. To potentially reduce the time required for development of drugs and drug combinations that can be clinically useful, we screened a library of 1,040 FDA-approved drugs and bioactive compounds (NINDS Custom Collection II). Seven compounds that protect against neomycin-induced hair cell death were identified. Four of the seven drugs inhibited aminoglycoside uptake, based on Texas-Red-conjugated gentamicin uptake. The activities of two of the remaining three drugs were evaluated using an in vitro adult mouse utricle preparation. One drug, 9-amino-1,2,3,4-tetrahydroacridine (tacrine) demonstrated conserved protective effects in the mouse utricle. These results demonstrate that the zebrafish lateral line can be used to screen successfully for drugs within a library of FDA-approved drugs and bioactives that inhibit hair cell death in the mammalian inner ear and identify tacrine as a promising protective drug for future studies.     

Trafficking of Systemic Fluorescent Gentamicin into the Cochlea and Hair Cells

Aminoglycosides enter inner ear hair cells across their apical membranes via endocytosis, or through the mechanoelectrical transduction channels in vitro, suggesting that these drugs enter cochlear hair cells from endolymph to exert their cytotoxic effect. We used zebrafish to determine if fluorescently tagged gentamicin (GTTR) also enters hair cells via apically located calcium-sensitive cation channels and the cytotoxicity of GTTR to hair cells. We then examined the serum kinetics of GTTR following systemic injection in mice and which murine cochlear sites preferentially loaded with systemically administered GTTR over time by confocal microscopy. GTTR is taken up by, and is toxic to, wild-type zebrafish neuromast hair cells. Neuromast hair cell uptake of GTTR is attenuated by high concentrations of extracellular calcium or unconjugated gentamicin and is blocked in mariner mutant zebrafish, suggestive of entry via the apical mechanotransduction channel. In murine cochleae, GTTR is preferentially taken up by the stria vascularis compared to the spiral ligament, peaking 3 h after intra-peritoneal injection, following GTTR kinetics in serum. Strial marginal cells display greater intensity of GTTR fluorescence compared to intermediate and basal cells. Immunofluorescent detection of gentamicin in the cochlea also revealed widespread cellular labeling throughout the cochlea, with preferential labeling of marginal cells. Only GTTR fluorescence displayed increasing cytoplasmic intensity with increasing concentration, unlike the cytoplasmic intensity of fluorescence from immunolabeled gentamicin. These data suggest that systemically administered aminoglycosides are trafficked from strial capillaries into marginal cells and clear into endolymph. If so, this will facilitate electrophoretically driven aminoglycoside entry into hair cells from endolymph. Trans-strial trafficking of aminoglycosides from strial capillaries to marginal cells will be dependent on as-yet-unidentified mechanisms that convey these drugs across the intra-strial electrical barrier and into marginal cells.     

ototoxicity of styrene

Styrene is extensively used in industry,but its ototoxicity,in particular in the pregnant female and the offspring,is still not well understood.In the current study,young adult male rats and pregnant f...     

配伍使用赖氨匹林与庆大霉素对豚鼠的听力影响实验

 目的观察混合给药后的配伍安全以及豚鼠ABR检测和细胞形态学的变化。方法混合2种药物后,进行灯检,pH值、旋光度检测,两种药物均为临床使用剂量,观察两种药物在临床使用剂量下混合给药的安全性和有效性。健康杂色雄性豚鼠随机分为3组,GM组、GM+Aspirin-DL-Lysine组、对照组,采用听性脑干反应(ABR)、耳蜗铺片观察用药前后听阈及耳蜗毛细胞形态学改变,并检测庆大霉素血药浓度。结果混合后药物的pH值、颜色、及澄明度均无变化,混合试液与单纯药物溶液之间的旋光度无明显差异。①GM组不同频率下的ABR阈移分别为:1kHz15～18dB,8kHz17～20dB,GM+Aspirin-DL-Lysine组的阈移分别为:1kHz9～15dB,8kHz10～15dB。两组间差异显著(P<0.05);②耳蜗铺片结果显示:耳蜗铺片GM组底圈毛细胞有损伤,与正常组比较排列不整齐,毛细胞损伤向上逐渐减轻,提示与听阈升高的程度相平行。而GM+As-pirin-DL-Lysine组的毛细胞排列整齐,无损伤。结论赖氨匹林(来比林)与庆大霉素可以安全的配伍使用。单独注射正常量庆大霉素4周使豚鼠的高频ABR升高,混合注射GM+Aspirin-DL-Lysine后对豚鼠的ABR影响不明显。注射正常量庆大霉素使豚鼠耳蜗毛细胞有损伤,底圈比顶圈重,与正常组比较,毛细胞排列紊乱。而配伍使用GM+Aspirin-DL-Lysine可以减轻庆大霉素对毛细胞的损伤。与正常组比较无明显差别。     

Heat Shock Inhibits both Aminoglycoside- and Cisplatin-Induced Sensory Hair Cell Death

Human hearing and balance impairments are often attributable to the death of sensory hair cells in the inner ear. These cells are hypersensitive to death induced by noise exposure, aging, and some therapeutic drugs. Two major classes of ototoxic drugs are the aminoglycoside antibiotics and the antineoplastic agent cisplatin. Exposure to these drugs leads to hair cell death that is mediated by the activation of specific apoptotic proteins, including caspases. The induction of heat shock proteins (HSPs) in response to cellular stress is a ubiquitous and highly conserved response that can significantly inhibit apoptosis in some systems by inhibiting apoptotic proteins. Induction of HSPs occurs in hair cells in response to a variety of stimuli. Given that HSPs can directly inhibit apoptosis, we hypothesized that heat shock may inhibit apoptosis in hair cells exposed to ototoxic drugs. To test this hypothesis, we developed a method for inducing HSP expression in the adult mouse utricle in vitro. In vitro heat shock reliably produces a robust up-regulation of HSP-70 mRNA and protein, as well as more modest up-regulation of HSP-90 and HSP-27. The heat shock does not result in death of hair cells. Heat shock has a significant protective effect against both aminoglycoside- and cisplatin-induced hair cell death in the utricle preparation in vitro. These data indicate that heat shock can inhibit ototoxic drug-induced hair cell death, and that the utricle preparation can be used to examine the molecular mechanism(s) underlying this protective effect.     

Application of antioxidants and other agents to prevent cisplatin ototoxicity

OBJECTIVE/HYPOTHESIS: To review the recent data from experiments performed in this laboratory to test the hypothesis that cisplatin ototoxicity is related to depletion of glutathione and antioxidant enzymes in the cochlea and that the use of antioxidants or protective agents would protect the cochlea against cisplatin damage and prevent hearing loss. STUDY DESIGN/METHODS: Data were reviewed from experiments performed in this laboratory. Control rats were treated intraperitoneally with cisplatin 16 mg/kg. Experimental rats were given cisplatin in combination with one of the following protective agents: diethyldithiocarbamate, 4-methylthiobenzoic acid, ebselen, or lipoic acid. Animals in each group underwent auditory brainstem response (ABR) threshold testing before and 3 days after treatment. Cochleae were removed after final ABR testing and analyzed for glutathione and activities of the enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and malondialdehyde. RESULTS: Rats in the control group receiving cisplatin were found to have significant ABR threshold shifts. This was accompanied by a reduction of glutathione and the activity of antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase, and glutathione reductase) and an elevation of malondialdehyde. Experimental animals had preservation of ABR thresholds and levels of glutathione, antioxidant enzyme activity, and malondialdehyde that were similar to untreated animals. CONCLUSION: Cisplatin ototoxicity appears to be initiated by fee-radical production, which causes depletion of glutathione and antioxidant enzymes in the cochlea, and lipid peroxidation, manifested by an increase in malondialdehyde. These effects were blocked by each of a series of antioxidant compounds given in combination with cisplatin. A mechanism for cisplatin ototoxicity is elaborated with a proposed plan of chemoprevention using agents with different mechanisms of action. These substances could be used alone or in combination to reduce the severity of cisplatin ototoxicity in patients.     

Erythromycin ototoxicity in liver transplant patients

We reprot on three liver transplant patients who developed erythromycin-related ototoxicity. This complication has been described in renal transplant patients and in patients with liver dysfunction, but to our knowledge it has not yet been reported in liver transplant patients. The influence of hepatic dysfunction, common renal failure, and the interaction between cyclosporin and erythromycin in the development of erythromycin ototoxicity are discussed.     

Comparative Ototoxicity of Dibekacin and Netilmicin in Guinea Pigs

Abstract: The cochleo- and vestibulotoxicity of dibekacin and netilmicin were compared in a guinea pig model. Both aminoglycosides were administered subcutaneously for 21 days at the dose level of 150 mg/kg/day. Control animals were injected with saline. Dibekacin-treated animals showed a significant (P<0.05) increase in the thresholds of the Preyer pinna reflex and the VIIIth nerve compound action potential in response to sound click stimulation. Moreover, a deterioration of the electrophysiologic auditory response and an almost complete suppression of the post-rotatory nystagmus were detected. In contrast, netilmicin did not induce any significant change in auditory and vestibular functions as compared to the control group. Our results demonstrated that netilmicin was devoid of ototoxicity in the guinea pig, while dibekacin provoked mild cochlear and severe vestibulotoxicity.     

Structural abnormalities in the stria vascularis following chronic gentamicin treatment

Freeze-fracture and thin-sectioning have been used to examine the stria vascularis of albino guinea pigs chronically treated with gentamicin. Immediately following the end of treatment, most marginal cells showed lipid bodies in the cell body region and freeze-fracture revealed alterations to the marginal cell plasma membrane. Intermediate cells also showed peculiarities including a dilation of the rough endoplasmic reticulum. A co-incidence was noted in the location in the cochlea in which effects in the stria and in outer hair cells occurred. At 4 weeks post-treatment, the stria was significantly thinner than normal and appeared less structurally complex. A minority of marginal cells degenerated. Some morphological features associated with degeneration resembled those of apoptosis, a process of controlled, cellular self-destruction. There were also indications of turnover of gap-junctions throughout the post-treatment period examined. The results indicate significant ototoxic effects of gentamicin occur in the stria and that changes to plasma membranes are one of the initial alterations.