Ischemia-reperfusion injury of the cochlea: effects of an iron chelator and nitric oxide synthase inhibitors.

Release of free iron from cellular stores and activation of nitric oxide synthase (NOS) has been implicated in a wide variety of cochlear injuries. In order to evaluate the effects of deferoxamine (a iron chelator), 3-bromo-7-nitroindazole (a relatively selective neuronal NOS (nNOS) inhibitor) or aminoguanidine (a relatively selective inducible NOS (iNOS) inhibitor) on the post-ischemic cochlear dysfunction, albino guinea pigs were subjected to 30 min ischemia, and the threshold shifts of the compound action potential (CAP) from pre-ischemic values were compared with those of control animals 4 h after the onset of reperfusion. A statistically significant reduction in the post-ischemic CAP threshold shift was observed in the animals treated with deferoxamine or 3-bromo-7-nitroindazole. However, aminoguanidine did not affect the post-ischemic CAP threshold shift. These results suggest that free iron and nNOS play deleterious roles in the cochlear injury induced by transient ischemia.

Protection of outer hair cells from reperfusion injury by an iron chelator and a nitric oxide synthase inhibitor in the guinea pig cochlea.

To examine whether an active process of the cochlea was injured by ischemia-reperfusion, time courses of distortion-product otoacoustic emissions (DPOAEs) were examined before, during and after 30 min cochlear ischemia using albino guinea pigs. DPOAEs decreased to the minimum level when the animals were subjected to ischemia. When the cochlea was recirculated, DPOAEs initially recovered with time until 20 min after the onset of reperfusion. However, thereafter the amplitude of DPOAEs gradually decreased toward the noise level. Administration of deferoxamine (an iron chelator) or N-nitro-L-arginine (a nitric oxide synthase inhibitor) ameliorated this decrease of DPOAEs during reperfusion and significantly increased the DPOAE amplitudes 60 min after the onset of reperfusion as compared with those in non-treated animals. These results suggest that cochlear reperfusion as well as ischemia injured the active process of the cochlea and that free radicals and nitric oxide play important roles in this injury.

Does xanthine oxidase contribute to the hydroxyl radical generation in ischemia and reperfusion of the cochlea?

We investigated the effect of a hydroxyl radical scavenger, 1,3-dimethyl-2-thiourea (dimethylthiourea), and two xanthine oxidase inhibitors, oxypurinol and allopurinol, on the threshold shift of the compound action potential (CAP) after transient ischemia of the cochlea. Transient ischemia of 30 min duration was induced in albino guinea pigs via a skull base approach. The animals were treated with perilymphatic perfusion of dimethylthiourea, oxypurinol or allopurinol from 10 min before the onset of ischemia to 4 h after the termination of ischemia. Dimethylthiourea ameliorated the CAP threshold shifts at 4 h after the onset of reperfusion in a dose-dependent manner. However, oxypurinol and allopurinol did not affect the post-ischemic cochlear dysfunction. These results imply that the hydroxyl radical plays an important role in generation of cochlear dysfunction induced by ischemia-reperfusion and that xanthine oxidase may not be the primary source of this radical.

Poly(adenosine diphosphate-ribose) synthetase inhibitor 3-aminobenzamide alleviates cochlear dysfunction induced by transient ischemia.

The present study was undertaken to determine the possible deleterious role played by poly(adenosine diphosphate-ribose) synthetase (PARS) in cochlear ischemia-reperfusion injury. Transient ischemia of the cochlea was induced in albino guinea pigs for 15, 30, or 60 minutes by pressing the labyrinthine artery at the porus acusticus internus. The animals were given intravenous 3-aminobenzamide (a PARS inhibitor) or physiological saline solution I minute before the onset of reperfusion. The compound action potential thresholds were measured before the onset of ischemia and 4 hours after the onset of reperfusion. A statistically significant reduction in the postischemic compound action potential threshold shift was observed in the animals treated with 3-aminobenzamide after 15 or 30 minutes of ischemia, whereas no statistical difference was found after 60 minutes of ischemia. These results suggest that excessive activation of PARS exerts deleterious effects on the cochlear injury induced by transient ischemia.

Effect of acoustic overstimulation on regulation of glucocorticoid receptor mRNA in the cochlea of the guinea pig.

Semi-quantitative reverse transcription polymerase chain reaction was performed to determine the distribution of mRNA levels of glucocorticoid receptor (GR) within the guinea pig cochlea and to examine the change in their expression after acoustic overstimulation. Using an original PCR primer for the guinea pig, the highest GR mRNA level was revealed in the modiolus and lowest in the medial portion including the organ of Corti. Total RNA was extracted from the whole cochlea of the guinea pig 0, 2, 6 and 24 h after exposure to a 2 kHz pure tone of 110, 120 or 130 dB SPL for 10 min. The level of GR mRNA significantly decreased immediately and 2 h after exposure to the sound of 120 dB SPL, and 2 and 6 h after exposure to that of 130 dB SPL. These results suggest the presence of a down-regulation of GR mRNA induced by acoustic overstimulation, although the exact mechanism of this phenomenon remains unsolved.

Effect of 7-nitroindazole upon cochlear dysfunction induced by transient local anoxia.

The purpose of the present study was to further elucidate how nitric oxide (NO) is involved in cochlear anoxia-reperfusion injury. Transient local anoxia of the cochlea was induced in albino guinea pigs for 15, 30, or 60 minutes by transiently compressing the labyrinthine artery through a skull base approach. 7-Nitroindazole (7NI), a relatively selective neuronal nitric oxide synthase (nNOS) inhibitor. was intraperitoneally administered to the guinea pigs 30 minutes before the onset of local anoxia. The compound action potential (CAP) thresholds were measured before the administration of 7NI and 4 hours after the onset of reperfusion. A statistically significant reduction in the postanoxic CAP threshold shift from the preadministration value was observed in the 7NI-administered animals as compared with the control animals after 15- and 30-minute periods of anoxia. These results confirm the involvement of NO and nNOS in the cochlear injury induced by transient local anoxia.

Evaluation of the vestibular aqueduct in vestibulocochlear disorders by magnetic resonance imaging.

The visibility of the vestibular aqueduct (VA) was examined using magnetic resonance imaging (MRI) in 95 patients: 15 patients with Meniere's disease, 4 with vestibular Meniere's disease, 4 with cochlear Meniere's disease and 72 patients with other vestibular and/or cochlear disorders. In order to visualize the VA, the T2-weighted image (T2WI) and the proton-density weighted image (PDWI) were obtained in the sagittal plane with a head coil. The visibility of the VA was classified into 4 grades, i.e. grade 0 (not visible), grade 1 (partially visible with PDWI), grade 2 (partially visible with T2WI) and grade 3 (clearly visible with T2WI). The visibility of the VA was significantly lower bilaterally in Meniere's disease, vestibular Meniere's disease, cochlear Meniere's disease and idiopathic bilateral sensorineural hearing loss (IBSNHL) than in the other diseases. The differences among Meniere's disease, vestibular Meniere's disease and cochlear Meniere's disease were not significant. The significance of decreased visibility in IBSNHL is unknown so far. The VA studies using MRI strongly suggest that the pathogenesis of Meniere's disease, vestibular Meniere's disease, cochlear Meniere's disease and IBSNHL is, at least in part, related to the findings of the VA.

The contribution of phospholipase A2 to the cochlear dysfunction induced by transient ischemia.

The objective of the present study was to examine whether mepacrine, a commonly used phospholipase A2 inhibitor, decreases ischemic damage to the cochlea. Transient ischemia of the cochlea was induced in albino guinea pigs for 15, 30 or 60 min by pressing the labyrinthine artery at the porus acusticus internus. The animals were intraperitoneally given mepacrine or physiological saline solution (PSS) 20 min prior to ischemia. Although mepacrine failed to alleviate the post-ischemic threshold shift of compound action potential (CAP) in case of 60 min ischemia, a statistically significant reduction in the CAP threshold shift was observed in the mepacrine-treated animals after 15 and 30 min ischemia. However, there was no statistically significant difference in the post-ischemic threshold shift of cochlear microphonic between the mepacrine-given and the PSS-given animals. Furthermore, mepacrine partially alleviated ischemia-induced swelling of radial afferent dendrites of primary auditory neurons. These results suggest that excessive activation of phospholipase A2 plays an injury-producing role at least by enhancing excitotoxicity in ischemia-reperfusion injury of the cochlea.

Effect of calmodulin antagonists on the compound action potential of the cochlea.

This study aimed to evaluate the effect of calmodulin antagonists on the threshold of the compound action potential (CAP) and the functional recovery of the cochlea after transient ischemia. When trifluoperazine and W-7 were administered to albino guinea pigs with perilymphatic perfusion, these drugs did not significantly affect the CAP thresholds. Transient cochlear ischemia of 30-min duration was obtained via a skull base approach. Although trifluoperazine significantly ameliorated the post-ischemic CAP threshold shifts 4 h after the onset of reperfusion, 1 to 50 microM W-7 did not affect the CAP threshold shifts. These results suggest that the action antagonizing calmodulin has no effect on the CAP threshold, while the role that calmodulin plays in cochlear ischemia-reperfusion injury still remains unclear.

Steroid-sensitive nephrotic syndrome associated with Kimura disease.

We report an 11-year-old Japanese boy with Kimura disease and associated nephrotic syndrome. Before the diagnosis of Kimura disease was established, the patient had three episodes of swelling on the left cheek with subsequent nephrotic syndrome. Steroids were effective for both conditions. However, both conditions recurred within months of discontinuation of steroids. For the fourth episode of swelling on the left cheek, cyclosporine (CsA) was used. The subcutaneous tumor responded to CsA and disappeared within a few days. There has been no subsequent relapse of the nephrotic syndrome to date.

Hydroxyl radical formation in the perilymph of asphyxic guinea pig.

To elucidate the role of hydroxyl radical (.OH) species in the generation mechanism of the cochlear pathology induced by transient asphyxia and subsequent re-ventilation, the concentrations of 2,3-hydroxybenzoic acid (DHBA) and 2,5-DHBA, major products arising from the attack of .OH upon salicylate, were measured in the perilymph of the guinea pig by the high performance liquid chromatography-electrochemical/UV method. The mean value of 2, 3-DHBA concentration in the perilymph significantly increased from the pre-asphyxic level (6.4 microM) to 7.6 microM and 8.8 microM during asphyxia of 3 min duration and at 5 min after the onset of re-ventilation, respectively. The 2,5-DHBA concentration was 7.9 microM before asphyxia, and also significantly increased to 11.5 microM and 16.2 microM during and after asphyxia, respectively. These results strongly indicated that .OH was generated in the perilymph of the asphyxic and re-ventilated guinea pig cochlea, and the significance of this increased .OH in generating anoxia and re-perfusion injury is discussed with respect to iron and oxygen-derived free radicals.

Effect of A1 adenosine receptor agonist upon cochlear dysfunction induced by transient ischemia.

The present study was undertaken to determine whether 2-chloro-N6-cyclopentyladenosine (CCPA), a highly selective A1 adenosine receptor agonist, attenuated cochlear dysfunction induced by transient ischemia or not. Ischemia of different durations (15, 30 or 60 min) was induced in 46 albino guinea pigs by transiently pressing the labyrinthine artery. CCPA or physiological saline solution was intraperitoneally administered to the animals 15 min prior to ischemia. The post-ischemic CAP threshold shift from the pre-administration value was measured 4 h after the onset of reperfusion to assess post-ischemic cochlear dysfunction. A statistically significant reduction in the CAP threshold shift was seen in CCPA-given animals after 15- and 30-min ischemia, whereas there was no statistical difference after 60-min ischemia. These results suggest that A1 adenosine receptor agonist exerts a protective effect on the cochlear injury induced by transient ischemia of intermediate duration.

Effect of nitric oxide synthase inhibitor on cochlear dysfunction induced by transient local anoxia.

To evaluate whether nitric oxide (NO) plays a role in the mechanism of generation of cochlear dysfunction induced by anoxia and reperfusion, the effects of a nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine, were examined using 71 albino guinea pigs. Transient cochlear anoxia of different duration (15, 30 or 60 min) was induced by pressing the labyrinthine artery and compound action potential (CAP) was measured before and 4 h after anoxia. N-nitro-L-arginine (1-30 mg/kg) administered intraperitoneally 1 h before the onset of anoxia alleviated the cochlear dysfunction when the anoxic period was 15 or 30 min. No beneficial effect was observed, however, in the 60-min anoxia. These results indicate that NO contributes to the generation of anoxia-induced cochlear dysfunction and that NOS inhibitor has a protective effect on the cochlear injury induced by anoxia of moderate duration.

Metastatic lymph-node clearance from head and neck epidermoid carcinomas following radiotherapy.

Although tumor clearance is a common criterion in assessing the impact of radiotherapy (RT), it is not always reliable. Patterns of tumor clearance were determined using 91 metastatic lymph nodes (LNs) from 51 patients with head and neck tumors treated by definitive RT (61-80 Gy) or preoperative RT (43-65 Gy). Clearance rate (CR) was estimated as a daily volume decrement expressed as a ratio to the pre-RT LN volume. CR was greater for the so-called radioresponsive nasopharyngeal subgroups and more poorly differentiated than those of oral cavity and well-differentiated, respectively. Histologically, LNs that were removed following RT consisted mainly of fibrous tissues, necrotic tissues, and few cancer cells. There was no difference in CR between the cancer-cell-positive group (n = 21) and the cancer-cell-negative group (n = 31). Although the CR may reflect inherent radiosensitivity of tumor cells, tumor persistence predicts the amount of oncologically inactive materials rather than that of remaining cancer cells.

The effect of mannitol upon cochlear dysfunction induced by transient local anoxia.

Transient local anoxia of the cochlea was induced by pressing the labyrinthine artery, and compound action potential (CAP) or endocochlear potential (EP) was measured before and after transient local anoxia ranging from 5 to 60 min using 106 albino guinea pigs. The complete interruption of the cochlear blood flow by this procedure and its full restoration after releasing the pressure on the artery was confirmed by a laser-Doppler flowmeter. The anoxia of less than 10 min induced no post-anoxic cochlear dysfunction, whereas the anoxia of a longer duration induced an irreversible dysfunction of the cochlea. It was evident that the post-anoxic recovery of the CAP threshold was worse as the anoxia period was prolonged, and CAP was almost completely abolished after 60-min anoxia. In animals which were administered mannitol intravenously just after the restoration of the cochlear blood circulation, the recovery of the CAP threshold was significantly better than that in the control animals, when the animals were subjected to local anoxia of 15- to 30-min duration. No beneficial effect, however, was observed in the 60-min anoxia group. In conclusion, local anoxia of 10 min or longer caused cochlear dysfunction, which was partially but significantly alleviated by mannitol.

Dominant hereditary conductive hearing loss due to an ossified stapedius tendon.

Familial conductive deafness is rare. This report confirms the existence of a lineage with congenital conductive hearing loss in 3 generations. The results of otologic evaluations, including pure-tone audiometry, tympanometry, acoustic reflex test, and liquid test, in 14 patients in this family were consistent with the findings of ossicular fixation in 10 patients. Tympanotomies performed in both ears of 4 patients indicated stapes ankylosis caused by ossification of the stapedius tendon. The patients gained normal hearing levels using a simple surgical procedure.

Effect of isosorbide on distortion-product otoacoustic emissions and endocochlear DC potential in experimentally induced hydropic ears.

The effects of isosorbide on distortion-product otoacoustic emissions (DPOAEs) and endocochlear DC potential (EP) were examined in experimentally induced endolymphatic hydropic ears and untreated control ears using 20 albino guinea pigs. DPOAEs and EP in the hydropic ears decreased after obliteration of the endolymphatic duct and sac. The administration of isosorbide restored DPOAEs to the normal level, whereas EP was further reduced. In control ears there was no significant change in DPOAEs and EP after the administration of isosorbide. The results obtained in the present study indicate that the effect of isosorbide on DPOAEs is different from that on EP, and the recovery of DPOAEs in hydropic ears is not a secondary phenomenon due to the recovery of EP.

The effect of methylprednisolone on acoustic trauma.

The effect of methylprednisolone (mPSL) upon acoustic trauma was studied using albino guinea pigs which were exposed to 2 kHz pure tone of 110, 115 or 120 dB SPL for 10 min. After the exposure to intense sound, mPSL of 6, 12 or 40 mg/kg was intraperitoneally given daily for 7 days and the threshold of the compound action potential (CAP) was examined on the 8th day. Compared with CAP of the control animals given physiological saline solution, no significant difference was observed in the CAP threshold shift between the mPSL group and the controls following exposures to the sound of 115 and 120 dB SPL, respectively. However, when the animals were exposed to the sound of 110 dB SPL, the CAP threshold shift was significantly smaller in the mPSL animals than in the controls. The present results indicate that mPSL possesses a therapeutic effect in cases of mild acoustic overstimulation.