In vitro effects of hydrogen peroxide on the cochlear neurosensory epithelium of the guinea pig.

Reactive oxygen species (ROS) have been postulated to be involved in drug ototoxicity and noise-induced hearing loss. Hydrogen peroxide (H(2)O(2))-induced cell damage in the inner ear was investigated using the neurosensory epithelium of a guinea pig cochlea. Hair cells and supporting cells of the epithelium incubated in Hanks' balanced salt solution were viable up to 6 h. After 2 h of treatment with 0.2 mM H(2)O(2) about 85% of the outer hair cells lost their viability. In contrast inner hair cells slowly began to die after 2 h of H(2)O(2) treatment. The Deiters cells and Hensen cells did not show any signs of damage in the presence of H(2)O(2). Nifedipine, a calcium channel blocker, Quin-2 AM, an intracellular calcium chelator, and 2,2'-dipyridyl, a membrane-permeable iron chelator, all provided partial protection against H(2)O(2)-induced outer hair cell death. The combination of both chelators showed an additional protective effect. The antioxidants N-acetylcysteine and glutathione-monoethyl ester completely protected against H(2)O(2) damage. These results suggest that calcium, iron, and thiol homeostasis play a crucial role in hair cell death caused by H(2)O(2).

[Hearing loss caused by high dose carboplatin therapy]. / Hörverlust durch Hochdosis-Carboplatintherapie.

BACKGROUND: Carboplatin is regarded as a non-ototoxic or low-grade ototoxic chemotherapeutic agent. METHOD: We report on three patients with a recurrence of testicular cancer after cisplatin chemotherapy who suffered hearing loss after subsequent high-dose carboplatin therapy. RESULTS: Audiometry demonstrated carboplatin-induced hearing loss primarily in the mid-range and high frequencies up to 45 dB at 3 kHz and up to 55 dB at 8 kHz. In two of three patients, transitory-evoked otoacoustic emissions were absent after carboplatin therapy. CONCLUSION: Following first-line cisplatin chemotherapy, salvage treatment with high-dose carboplatin can generate hearing loss in the middle and high frequencies.

[Case report of epithelioid hemangioendothelioma of the frontal region metastatic to the parotid gland]. / Fallbericht über ein in die Glandula parotis metastasierendes epithelioides Hämangioendotheliom der Regio frontalis.

BACKGROUND: The epithelioid hemangioendothelioma is a soft tissue tumor of vascular origin. Typical localisations are subcutis, cutis, liver, lungs and bones. It has been described in 1982 by Weiss and Enzinger as a separate tumor entity. Due to the unpredictable biological behaviour of the tumor, a borderline malignancy is assumed. CASE REPORT: We report on the case of a 44-year old woman with a metastasising epithelioid hemangioendothelioma in the head and neck area. The primary tumor was located in the subcutis of the left forehead. Due to local recurrences surgical treatment was performed three times after the initial removal in 1993. At the time of the last local recurrence in 1996, a tumor in the left parotid gland was diagnosed and was the reason for a lateral parotidectomy. Pathohistologically, a metastasis of the epithelioid hemangioendothelioma was found. Postoperative radiotherapy was performed and no recurrence occurred until now (22 months follow-up). CONCLUSION: Metastatic epithelioid hemangioendotheliomas are rarely found in the head and neck area. Literature has not yet reported on metastasis formation in the parotid gland. The case illustrates the potentially malignant behaviour of epithelioid hemangioendotheliomas. Hence, therapy should consist of a combination of radical tumor removal and post-operative radiotherapy.

[Diagnosis and therapy of thyroid tissue of the base of the tongue]. / Diagnostik und Therapie der Zungengrundstruma.

Lingual thyroid tissue is the most frequent ectopic location of the thyroid gland, although its clinical incidence is low with 1 in 100,000 cases occurring. We describe a 25-year-old woman who presented with dysphagia due to lingual thyroid tissue. Suppressive hormone therapy did not have a significant effect. Surgical therapy was used when obstructive symptoms increased. The lingual thyroid was resected partially while the remaining gland was transposed into a lateral submental region. Diagnostic procedures using such imaging techniques as scintigraphy, ultrasound, computed tomography and magnetic resonance imaging and therapeutic options are discussed.

Expression of Na, K-ATPase alpha and beta isoforms in the neonatal rat cochlea.

The postnatal expression of five Na, K-ATPase alpha (alpha 1, alpha 2, alpha 3) and beta (beta 1, beta 2) subunit isoforms in the rat cochlea was investigated by immunocytochemistry. High levels of expression of the alpha 1 and beta 2 isoforms were observed in stria vascularis (SV) at all developmental stages. alpha 1 and beta 1 isoforms showed a distinct time-dependent developmental expression pattern in tissues of the spiral ligament (SL) and spiral limbus (SLi). Limited, temporary expression of alpha 2 and alpha 3 subunit isoforms were found in SV and SL. Expression of each isoform was also seen in organ of Corti (OC), spiral ganglion (SG), cochlear nerve (CN) and Kölliker's Organ (KO). These observations suggest that individual isoforms may exert specific actions postnatally during final cochlear maturation.

Expression of Na+,K(+)-ATPase alpha 1 subunit mRNA in the developing rat cochlea.

The distribution of Na+,K(+)-ATPase alpha 1 subunit mRNA was identified using in situ hybridization in the developing rat cochlea. The expression of alpha 1 subunit mRNA in stria vascularis (SV) was observed in all time points studied, 1 to 30 postnatal day (pnd) rats. The adult expression level was attained between 11 to 14 pnd. Surprisingly, alpha 1 subunit mRNA in spiral ligament (SL) and spiral limbus (SLi) was expressed in a more distinct time-dependent manner. At 7 pnd, the alpha 1 subunit mRNA expression was observed initially in the tissues of the SL. At 11 pnd, alpha 1 subunit expression appeared in SLi. Between 11 and 14 pnd, an adult-like pattern of Na+,K(+)-ATPase alpha 1 subunit mRNA expression was attained in the SL and SLi. These data suggest that the expression of Na+,K(+)-ATPase alpha 1 subunit mRNA in these areas are closely related to the development of the rat EP, as its expression in the stria vascularis.

Na,K-ATPase subunit isoform expression in the guinea pig endolymphatic sac.

Na,K-ATPase subunit isoform expression was studied by immunocytochemistry in the guinea pig endolymphatic sac, using subunit isoform-specific polyclonal antibodies. Epithelial cells of the guinea pig endolymphatic sac were observed to contain the alpha 1- and beta 2-subunit isoforms, and to a lesser extent the beta 1-subunit isoform, of Na,K-ATPase. The alpha 1- and beta 2-subunit isoforms of Na,K-ATPase have been observed previously in other ion and fluid transporting regions of the membranous labyrinth, e.g., stria vascularis and vestibular dark cells. Combined data indicate that the alpha 1-, beta 2-form of Na,K-ATPase plays a role in the microhomeostasis of endolymph. The alpha 1 beta 2 Na,K-ATPase subunit isoform combination is different from typical ion and fluid transporting tissues, e.g., kidney and colon, and may reflect distinctive characteristics of inner ear Na,K-ATPase.

Na,K-ATPase alpha and beta subunit isoform distribution in the rat cochlear and vestibular tissues.

The distribution of five Na,K-ATPase subunit isoforms (alpha 1, alpha 2, alpha 3, beta 1 and beta 2) in rat cochlear and vestibular tissues was determined by immunocytochemical techniques using subunit isoform specific polyclonal antibodies. The expression of Na,K-ATPase alpha and beta subunit isoforms varied among different cell regions of the inner ear. The alpha 1 subunit isoform was more extensively distributed in all inner ear tissues than the alpha 2 or alpha 3 subunit isoforms. The beta 1 subunit isoform was distributed primarily in spiral ligament and inner hair cells of the cochlea, and in crista ampullaris and macula of the saccule. The beta 2 subunit isoform was most abundant in the stria vascularis, dark cells of the ampullae and utricle. The alpha 1 beta 1 subunit combination of Na,K-ATPase was most commonly found in the spiral ligament, while the alpha 1 beta 2 combination was most abundant in the stria vascularis. Similarly, alpha 1 beta 2 was confined more to the dark cells of the ampullae and utricle. The alpha 3 beta 1 subunit combination of Na,K-ATPase was identified in the inner hair cells of the cochlea and the sensory regions of the vestibular end organs. These observations may reflect functional diversity of Na,K-ATPase in the individual inner ear regions and may provide insight into the differences between fluid and ion transport in the inner ear and that of other transporting tissues. Overall, the distribution pattern further indicates that the different isoform combinations have specific roles.

Density of marginal cell basolateral membranes in basal, middle, and apical turns of the rat cochlea.

The Na-K-ATPase activity within stria vascularis tissues has been observed to decrease from basal to apical cochlear turns. This reduction in Na-K-ATPase activity in more apical regions of the cochlea may be accounted for, at least in part, by a lower density of Na-K-ATPase-containing basolateral membranes of the marginal cells. This study was performed to compare the surface density of marginal cell basolateral membranes in standardized basal, middle, and apical turns of the rat cochlea. Montages of transmission electron microscopic micrographs of standardized regions of the rat stria vascularis were morphometrically analyzed. Surface area of marginal cell basolateral membrane was determined per unit stria vascularis volume and per unit marginal cell volume. Results demonstrated that the surface density of marginal cell basolateral membrane per stria vascularis volume of the standardized basal region increased 20 percent compared to that of the standardized apical region (p < or = .1). Surface density of marginal cell basolateral membranes per marginal cell volume was similar in all three standardized turns. The observed longitudinal differences in surface density of marginal cell basolateral membranes per stria vascularis volume may account, in part, for the biochemical cochlear Na-K-ATPase activity gradient from base to apex.

Effects of low-sodium, high-potassium dietary intake on cochlear lateral wall Na+,K(+)-ATPase.

The effect of a low Na+, high K+ diet on Na+,K(+)-ATPase levels in cochlear lateral wall tissues was investigated in laboratory rats by using an enzyme-linked immunosorbent assay. The low Na+, high K+ diet induced high aldosterone plasma levels in the animals as well as changes in plasma cation levels. Animals that received a low Na+, high K+ diet demonstrated a statistically significant (97%) increase in Na+,K(+)-ATPase levels in the stria vascularis when compared to animals that received a control diet. This increase in strial Na+,K(+)-ATPase levels was blocked only 70% by administration of the aldosterone antagonist, spironolactone. Findings therefore indicate that strial Na+,K(+)-ATPase may be modulated by both aldosterone and Na+,K+ plasma levels. Na+,K(+)-ATPase levels in the spiral ligament were not affected by the experimental treatment. These findings suggest that spiral ligament Na+,K(+)-ATPase levels may be regulated by factors other than aldosterone and Na+,K+ plasma levels. This study provides further insight into the mechanisms of the beneficial effects of salt restriction and potassium loading in patients with Méniére's disease.

Dynamics of Na,K-ATPase sites in lateral cochlear wall tissues of the rat.

The objective of this study was to determine whether varying levels of either the synthetic glucocorticoid, dexamethasone, or the mineralocorticoid, aldosterone, modulate the quantity of Na,K-ATPase sites in stria vascularis and spiral ligament tissues. Surgically adrenalectomized male rats were administered different dosages of dexamethasone or aldosterone for 7 days and subsequently were sacrificed. Na,K-ATPase alpha-subunits of stria vascularis and spiral ligament homogenates were determined quantitatively by enzyme-linked immunosorbent assay, using a monoclonal antibody shown to react with lateral wall Na,K-ATPase alpha-subunit. Elevated serum levels of dexamethasone were correlated with significantly increased Na,K-ATPase alpha-subunit levels in both the stria vascularis and spiral ligament (P < 0.05). Elevated serum levels of aldosterone were correlated with increased Na,K-ATPase alpha-subunits in the stria vascularis, but not in the spiral ligament (P < 0.1). These data further indicate a positive correlation between increased serum levels of adrenal steroids and induction of Na,K-ATPase synthesis by such steroids, particularly by dexamethasone.

Plasma membrane modulation of ampullar dark cells by corticosteroids.

Individual effects of corticosteroids on the ultrastructure of rat ampullar dark cells were quantitatively determined. Adrenalectomized rats subsequently received either aldosterone or dexamethasone or only hormone solvent via miniosmotic pumps for a period of 14 days. Ampullar tissues of the animals were processed for transmission electron microscopy, and standardized regions of ampullar dark cells were photographed and morphometrically analyzed. Surface density and boundary length of basolateral membrane increased significantly after hormone substitution with aldosterone, but not after replacement with dexamethasone, as compared with animals that received only solvent. No significant differences were observed for other morphological parameters between the groups. This response of ampullar dark cells to aldosterone appears similar to that of principal cells of the collecting duct in comparable experimental conditions. These morphological observations suggest that the mineralocorticoid, aldosterone, modulates ampullar dark-cell membranes.

Modulation of the rat stria vascularis in the absence of circulating adrenocorticosteroids.

Structural changes in the cellular morphology of the rat stria vascularis from a standardized region of the basal region and from a standardized region in the apical region of the rat cochlear duct were measured using stereological methods after removal of endogenous levels of adrenal steroids by bilateral adrenalectomy. Although there were some inconsistent and insignificant alterations in the volume density of intermediate and basal cells, a decreased volume density of marginal cells in both the basal region and in the apical region in adrenalectomized (ADX) animals as compared to sham animals was consistent with a concomitant significant increased (p less than or equal to 0.05) volume density of intercellular space as observed in both the basal and apical regions of the stria vascularis of ADX animals. Findings of this study indicate that the strial cells of the stria vascularis react differently and independently in response to the removal of adrenal steroids, and such strial responses occur uniform in both the base and apex.