Leonard P. Rybak

Round window application of d-methionine provides complete cisplatin otoprotection☆

OBJECTIVE: Cisplatin is a widely used, very effective chemotherapeutic agent that can cause severe ototoxicity. In this study, D-methionine was tested as an otoprotectant via round window membrane (RWM) application in the chinchilla. METHODS: A minute amount of cisplatin alone, or D-methionine followed by cisplatin, was applied topically directly to the intact RWM of anesthetized adult chinchillas. Auditory brainstem responses were measured before and 1 week after topical round window application. Animals were killed, and the cochleas were examined. RESULTS: The ears pretreated with D-methionine were completely protected from hearing loss and hair cell loss in the organ of Corti compared with controls. The ears receiving cisplatin without D-methionine protection sustained nearly complete hearing loss with threshold shifts of >60 dB, with extensive outer hair cell loss throughout the organ of Corti but particularly in the basal turn. CONCLUSION: These results demonstrate that topical D-methionine provides excellent otoprotection against cisplatin-induced ototoxicity both electrophysiologically and structurally.

Combined effects of adrenalectomy and noise exposure on compound action potentials, endocochlear potentials and endolymphatic potassium concentrations

The effects of removal of endogenous corticosteroids via bilateral adrenalectomy in combination with noise exposure (30 min at 100 dB) were determined by recording compound action potential (CAP) and endocochlear potentials (EP), and by measuring potassium concentrations (K+e) within the endolymph. Thirty-eight Long-Evans rats were divided into groups according to experimental treatments: adrenalectomy (ADX) or non-ADX and noise exposure or non-noise exposure. CAP thresholds, EP and K+e values were subjected to repeated-measures analysis of variance with group and time as factors classifying the measurements. Noise exposure resulted in significant elevations of CAP thresholds in both the ADX and non-ADX animals, but had no effect on either EP or endolymphatic K+e. Recovery was noted during all post-exposure measurement periods and was significantly faster for ADX animals. EP and K+e did not change during or after noise exposure. ADX animals showed a non-significant reduction of EP and a statistically significant increase of K+e during all measurement periods as compared to non-ADX animals.

Quantification of furosemide from serum and tissues using high-performance liquid chromatography.

Since pharmacokinetics may play a significant role in furosemide (FSM) developmental ototoxicity, we developed an assay for the extraction and quantification of FSM in tissue and fluid from neonatal and adult rats. Rats from post-natal day (PND) 10, 30 and 50, were given an intravenous dose of FSM (35 mg/kg). Blood and tissues were analyzed by HPLC. FSM in serum, perilymph and liver was elevated in PND ten rats as was the body burden of FSM. Renal concentrations were higher in older rats. Altered clearance of FSM in developing rats may result in higher concentrations in the cochlea and ototoxicity.

Correlative evidence of hypertension and altered cochlear microhomeostasis: electrophysiological changes in the spontaneously hypertensive rat.

The spontaneously hypertensive rat model has been used to show that hypertension is an important pathophysiological risk factor in age-related hearing loss. In the present study, compound action potential (CAP), electrochemical potential (ECP), and potassium concentration (CK+) measurements were taken from the cochlea of genetically predisposed, spontaneously hypertensive rats (SHR) and from normotensive Wistar-Kyoto (WKY) rats. In the SHR model, as the duration of hypertension increased with the animals age (from 3 to 8 months), CAP thresholds increased, ECP increased in marginal cells only, and CK+ increased in both endolymph and marginal cells. Collectively, the data suggest that ionic alternations of cellular potentials are involved in hearing changes in the hypertensive state. Ultimately, such data may assist in understanding hearing loss in individuals who are diagnosed with hypertension.

Effects of organic acids on the edema of the stria vascularis induced by furosemide.

Furosemide is a loop diuretic which is ototoxic. Investigations have shown the stria vascularis to be the target tissue of this ototoxic drug. The purpose of the present study was to investigate the effects of furosemide on the stria vascularis in chinchillas, in controls and in animals pretreated with the above organic acids. Control animals were injected with 0.5 ml alkalinized saline followed by furosemide IV 30 min later. Experimental animals received probenecid, penicillin or sodium salicylate IV. Thirty minutes later, furosemide was injected in the same dose as in the controls. The basal turn of the stria vascularis was rapidly removed at various times from 10 to 30 min after furosemide administration and processed for transmission electron microscopy. Control animals were found to have reversible edema of the stria vascularis. Experimental animals had variable findings. Those animals pretreated with penicillin had virtually no edema of the stria vascularis at any time. Salicylate and probenecid pretreated animals had significantly less edema from one to 10 min after furosemide injection, but more edema than controls at later times. These findings suggest a discrepancy between ultrastructural pathology and functional status of the cochlea in experimental animals pretreated with probenecid or sodium salicylate followed by furosemide. On the other hand, good structure function correlations were seen in controls and in experimental animals pretreated with penicillin.

Metastatic thymoma to the head and neck

Malignant thymoma is a mediastinal tumor which spreads primarily by local invasion. Spread to regional lymph nodes and distant organs is variable. The most common sites of metastasis in the head and neck region are the supraclavicular nodes and the brain. Cervical lymph node metastasis as the presenting symptom of malignant thymoma has not yet been reported in the otolaryngologic literature. We present three cases of metastatic thymoma to the neck from a series of 28 thymomas, ten of which were malignant. The clinical presentation, histopathological features, therapy, and prognosis of malignant thymomas are discussed.

Electrochemical potentials and potassium concentration profiles recorded from perilymph, endolymph and associated inner ear tissues in adrenalectomized rats

This study evaluated the electrochemical potentials and potassium concentration (Ck+) profiles in the perilymph, endolymph, marginal cells, and spiral ligament of adrenalectomized rats in which endogenous corticosteroids had been removed. Electrochemical potentials recorded at the four cochlear sites were not affected by adrenalectomy (ADX). Ck+ was greater in the endolymph of the ADX animals as compared to control animals. Additionally, there was an increase of Ck+ in the marginal cells, perilymph, and spiral ligament tissues of the ADX animals as compared to control animals, although the observed increases were not statistically significant. In a previous study (Ma et al., 1995a), it was found that potassium levels in the blood plasma of ADX animals were higher than those identified in normal rats; thus, ADX may have a systemic effect on Ck+ that is detectable in both tissues and fluids within the cochlea. Even though Ck+ was elevated within the cochlea in the ADX model, the functional response of the inner ear, as assessed electrophysiologically, was not altered.

Role of STAT1 and Oxidative Stress in Gentamicin-Induced Hair Cell Death in Organ of Corti.

Rationale: Oxidative stress plays a critical role in gentamicin-induced hair cell death. Previous work has implicated the cytoplasmic transcription factor signal transducer and activator of transcription 1 (STAT1) as a potential mediator of drug-induced ototoxicity, but role in aminoglycosides is largely unknown. This study investigated aminoglycosides-induced cell death, exploring contributions of reactive oxygen species and STAT1 pathway in injury and protection. Methods: Neonatal murine organ of Corti explants from 2 to 3 day postnatal pups (nu200a=u200a96) were treated with gentamicin at (4u200a&mgr;M, 50u200a&mgr;M) for 4 to 72 hours, with/without protectants. Effects on STAT1 pathway and gentamicin-induced hair cell death were measured with 50u200a&mgr;M Epigallocatechin gallate (EGCG, a STAT1 inhibitor) and all-trans retinoic acid (atRA, a STAT1 activator). Hair cell morphology was evaluated and hair cell loss was quantified with cytocochleograms. Mitochondrial membrane potential was assayed and superoxide generation and suppression was measured with dihydroethidium (DHE) staining. Results: Co-administration of 50u200a&mgr;M EGCG conferred protection from 4u200a&mgr;M gentamicin toxicity (pu200a<u200a0.001), whereas atRA potentiated gentamicin-induced hair cell death (pu200a<u200a0.001). On immunohistochemistry, STAT1 phosphorylation at theserine 727 (Ser727) residues was increased at 72 hours with 4u200a&mgr;M gentamicin. With administration of 50u200a&mgr;M gentamicin, there was activation of STAT1 Tyr701 at 4 hours and STAT1 Ser727 at 16u200ahours. Gentamicin dissipated mitochondrial membrane potentials, and EGCG attenuated gentamicin-induced oxidative stress at 72u200ahours. Conclusion: EGCG protected outer hair cells from gentamicin toxicity in a cochlear explant model, with the underlying mechanism involving both reactive oxygen species (ROS) suppression and STAT1 inhibition.

Altered calcium homeostasis in the rat cochlear duct and endogenous corticosteroid insufficiency

AbstractFree calcium concentration (n