Preclinical and clinical otoprotective applications of cell-penetrating peptide D-JNKI-1 (AM-111).

There is a growing interest in the auditory community to develop novel prophylactic and therapeutic drugs to prevent permanent sensorineural hearing loss following acute cochlear injury. The jun-N-terminal protein kinase (JNK) pathway plays a crucial role in acute sensory hearing loss. Blocking the JNK pathway using the cell-penetrating peptide D-JNKI-1 (AM-111/brimapitide) has shown promise as both a prophylactic and therapeutic agent for acute cochlear injury. A number of pre-clinical and clinical studies have determined the impact of D-JNKI-1 on acute sensorineural hearing loss. Given the inner-ear selective therapeutic profile, local route of administration, and ability to diffuse across cellular membranes rapidly using both active and passive transport makes D-JNK-1 a promising oto-protective drug. In this review article, we discuss the application of D-JNKI-1 in various auditory disorders as well as its pharmacological properties and distribution in the cochlea.

Activation of caspase-3 is associated with oxidative stress in the hydropic guinea pig cochlea.

The aim of this study was to investigate the involvement of oxidative stress and apoptosis in an animal model of Meniere's disease. Endolymphatic hydrops (ELH) is generally accepted as the decisive histological characteristic of Meniere's disease. Closure of the endolymphatic duct (Kimura's method) was used to induce endolymphatic hydrops in guinea pigs. Sham-operated animals served as controls. After 4 weeks the animals operated showed a significant elevation of the hearing thresholds as measured by audiometric brainstem responses (ABR) pre- and postoperatively. Immediately after the second ABR measurement, the animals were sacrificed for further immunohistological examinations of the inner ear with specific antibodies to active caspase-3 (cas-3) as a marker for apoptosis and antibodies to 8-isoprostane (8-iso) and nitrotyrosine (NT) as indicators of oxidative stress. Compared with the sham-operated controls, hydropic cochleae showed strong immunostaining for both oxidative stress markers in spiral ganglion cells, in the blood-vessels and fibrocytes of the lateral wall, as well as in supporting cells of the organ of Corti. Activation of cas-3 in spiral ganglion cells and the lateral wall was found exclusively in hydropic cochleae. Our findings suggest that oxidative stress is involved in the development of endolymphatic hydrops and may lead to cellular damage which induces apoptosis by activation of cas-3. Apoptotic cell death might contribute to the sensorineural hearing loss found in later stages of Meniere's disease.

Contributions of age, cochlear integrity, and auditory environment to avian cochlear nucleus metabolism.

Most commercially raised broiler chickens display progressive cochlear degeneration with age [Hear. Res. 166 (2002) 82]. Recent work examining the effects of age and cochlear degeneration on avian cochlear nucleus (nucleus magnocellularis, NM) metabolism showed that changes in metabolic activity occur with age and cochlear damage [Hear. Res. 175 (2003) 101]. The auditory environment also differed between facilities housing young and adult birds. The relative contributions of age, cochlear degeneration, and auditory environment to these changes in NM metabolism are unknown. Using cytochrome oxidase (CO) histochemistry, NM neuron metabolism is examined in several age groups of birds under varying conditions. When normal cochlear integrity and auditory environment are held constant, CO staining is significantly decreased in adult vs. young birds. When age and auditory environment are held constant, CO staining is significantly decreased in birds with damaged vs. normal cochleae. When age and normal cochlear integrity are held constant, CO staining is significantly decreased in birds living in a quiet vs. noisy environment. All factors examined cause changes in CO staining, which is indicative of NM metabolic activity. Results are discussed in the context of mitochondrial aging, afferent regulation, and auditory deprivation and enrichment.

Nuclear-factor kappa B (NF-kappa B)-inducible nitric oxide synthase (iNOS/NOS II) pathway damages the stria vascularis in cisplatin-treated mice.

BACKGROUND: Cisplatin is reported to damage the stria vascularis of the cochlea. Free radicals, especially large amounts of nitric oxide catalyzed by inducible nitric oxide synthase, are considered to have an important role in this toxicity. The induction of inducible nitric oxide synthase is regulated by nuclear-factor kappa B (NF-kappa B). We examined the damage of the stria vascularis by immunohistochemical techniques. MATERIALS AND METHODS: Cisplatin (15 mg/kg b.w.) was injected intraperitoneally into the mice. Three days after the injection, the cochleas were immunohistochemically-stained using specific antibodies for nuclear-factor kappa B (NF-kappa B), inducible nitric oxide synthase (iNOS) or single-stranded DNA. RESULTS: NF-kappa B was expressed in the cisplatin-treated cochlea, especially in the stria vascularis and the spiral ligament. iNOS was also expressed in the stria vascularis and the spiral ligament. Fragments of DNA were observed only in the stria vascularis. CONCLUSION: The large amounts of NO catalyzed by iNOS led to inner ear dysfunction. Our results indicate that apoptosis is triggered by iNOS and that it mediates the ototoxicity induced by cisplatin.

Effect of protective agents against cisplatin ototoxicity.

HYPOTHESIS: The goals of this investigation were to compare the efficacy of three protective agents against cisplatin-induced elevation of auditory brainstem response (ABR) thresholds and to examine whether these protective agents prevent cisplatin-induced alterations of the antioxidant defense system in the cochlea of the rat. BACKGROUND: Cisplatin is an ototoxic antitumor agent. Previous animal studies have shown that cisplatin administration causes an elevation of ABR thresholds. These auditory changes are accompanied by alterations in the concentration of glutathione and the antioxidant enzymes in the cochlea. The authors' previous work has indicated that the protective agent diethyldithiocarbamate (DDTC) prevents decrease in glutathione (GSH), alteration of antioxidant enzyme activity, and disruption of cochlear function with cisplatin administration. METHODS: Wistar rats were sedated and underwent pretreatment ABR testing using clicks and tone burst stimuli at 8, 16, and 32 kHz. Control rats received saline by intraperitoneal (i.p.) injection. Positive control rats were administered cisplatin 16 mg/kg i.p. Three groups of rats received protective agents in combination with cisplatin. The DDTC-protected rats were given 600 mg/kg of DDTC subcutaneously 1 hour after cisplatin. Animals protected by 4-methylthiobenzoic acid (MTBA) were given 250 mg/kg of this agent i.p. 30 minutes before cisplatin. Animals protected with ebselen were given 16 mg/kg i.p. one hour before cisplatin. The ABR thresholds were recorded 72 hours after cisplatin administration in all groups. Cochleas were removed, and extracts of the tissues were analyzed for GSH, activities of antioxidant enzymes (superoxide dismutase [SOD], catalase, glutathione peroxidase, and glutathione reductase) and malondialdehyde (MDA) (as an index of lipid peroxidation). RESULTS: Cisplatin-treated rats had significant ABR threshold shifts, ranging from 27 to 40 dB. Rats administered each of the three protective agents in combination with cisplatin had ABR threshold shifts of <10 dB. The cochleae of rats administered cisplatin alone had nearly a 50% depletion of glutathione and about a 50% reduction in the activities of SOD, glutathione peroxidase, and glutathione reductase, while catalase activity was reduced to 70% of control values. These changes were accompanied by a reciprocal elevation of MDA of 165%. These changes, namely, the depletion of GSH and antioxidant enzyme activity and the elevation of MDA in the cochlea, were largely attenuated by the administration of the protective agents tested. CONCLUSION: These findings suggest that cisplatin ototoxicity is related to lipid peroxidation and that the use of protective agents prevents hearing loss and lipid peroxidation by sparing the antioxidant system in the cochlea. These results suggest the possibility that the clinical use of protective agents could effectively reduce or prevent damage to the inner ear of patients receiving cisplatin chemotherapy, provided that the antitumor effect is not altered.

Changes of the compound action potential (CAP) and the expression of inducible nitric oxide synthase (iNOS/NOS II) in the cochlea under the inflammatory condition(1).

In this study, the effect of endotoxin on the guinea pig cochlea has been examined electrophysiologically and immunohistochemically. Bacterial lipopolysaccharide (LPS, 5 mg/ml, 0.2 ml) was injected into the middle ear trans-tympanically. The electrocochleograms were measured before, immediately upon, and 3, 6 and 12 h after the injection continuously with an electrode inserted into the facial canal. After each measurement, some of the animals were killed with an intracardiac perfusion of fixative, temporal bones were removed and were immunohistochemically examined for inducible nitric oxide synthase (iNOS/NOS II). On serial paraffin section, iNOS could be detected first after 3 h in the lateral wall, the supporting cells of the organ of Corti and in cells of the spiral ganglion and was observed up to 12 h. After the injection of LPS, the threshold of compound action potential became significantly worse after 12 h in the LPS group. These changes became evident first at higher frequency (8 kHz). These results suggest that iNOS-generated NO is involved in the cochlea dysfunction under inflammatory conditions.

[Effect of electroacupuncture on succinate dehydrogenase of gentamycin induced ototoxic cochlear hair cells in guinea pigs].

OBJECTIVE: To observe the effect of electroacupuncture (EA) on succinate dehydrogenase (SDH) of gentamycin (GE) induced ototoxic cochlear hair cells. METHODS: Preyer's reflex normal guinea pigs were selected and divided randomly into three groups: GE group, EA group, control group. Brainstem auditory evoked potential (BAEP) and SDH in the cochlear hair cells were taken as indexes. In the animals of GE group GE was alone injected intramuscularly 80 mg.kg-1.d-1 for 20 days, while in the animals of EA group GE and additional EA was applied once a day on Tinggong (SI19), Yifeng(SJ17) and Shenshu (UB23) points. EA lasted for 15 minutes. RESULTS: In the GE group BAEP reaction threshold rose markedly, while that rose slightly in EA group. The difference was significant between two groups (P < 0.05). The change of SDH within cochlear hair cells and degree of hair cells injury in the EA group were lower than those in GE group. CONCLUSIONS: EA therapy could relieve GE ototoxicity, protect SDH in cochlear hair cells and might be a possible mechanism of action of EA.