Pharmacological influence on inner ear endothelial cells in relation to the pathogenesis of sensorineural hearing loss.

Despite an increasing incidence of acute sensorineural hearing loss, the pathogenesis of this disease remains uncertain. While viral infection of the stria vascularis, organ of Corti or spiral ganglion cells is discussed in the American literature, a vascular genesis with resulting impaired perfusion of the inner ear is favoured by European investigators. Although both hypotheses are supported by different therapeutic strategies to regain normal hearing, the influence of spontaneous remission remains unclear. This study aims at combining these seemingly opposing concepts with the assumption of an immunologically mediated vasculitis with consequent cochlear hypoperfusion. We already know from other organs that during viral vasculitis circulating immunoglobulins are deposited perivascularly, which leads to a local decrease in perfusion and tissue hypoxia. Also in autoimmune diseases, perivasculitis is common with the endothelium playing a major role at the initial stages of the disease. These endothelial cells promote vasculitis by secreting pro-inflammatory cytokines like IL-1, IL-6 or TNF-alpha in addition to the expression of adhesion molecules. Due to the persistence of these immunopathological mechanisms stenosis or atresia with ischaemic necrosis results. To examine whether this pathomechanism is also important in inner ear dysfunction, the immunological response after stimulation of the cochlear endothelium of guinea pigs was determined. In addition, the influence of corticosteroids on this immune cascade was examined.

Sudden sensorineural hearing loss: does application of glucocorticoids make sense?

BACKGROUND: Treatment of sudden sensorineural hearing loss (SSNHL) consists of administration of blood flow-promoting drugs with or without the addition of glucocorticoids. General guidelines based on scientific data do not currently exist. OBJECTIVE: To investigate the effect of glucocorticoids on the treatment of SSNHL. SETTING: Academic medical center. PATIENTS AND METHODS: We retrospectively analyzed the audiograms of 603 patients with SSNHL: 301 patients (cared for between January 1, 1986, and December 31, 1991) received intravenous blood flow-promoting drugs without glucocorticoids and 302 patients (cared for between January 1, 1992, and December 31, 1998) received intravenous blood flow-promoting drugs with glucocorticoids (intravenous +/- oral application). The age distribution of patients with SSNHL in lower, middle, and higher frequencies was similar in both groups. RESULTS: Patients with SSNHL in lower and middle frequencies (250-2000 Hz) who received glucocorticoids (prednisolone-21-hydrogen-succinate) showed significantly better recovery of hearing levels compared with those who did not receive glucocorticoids (P<.05). There was no significant difference at higher frequencies between the 2 groups. Patients with SSNHL throughout all frequencies (pancochlear hearing loss) who received glucocorticoids also had significantly better recovery of hearing levels compared with those who received blood flow-promoting drugs alone (P<.05). Also, patients with elevated blood sedimentation rates had better improvement of their hearing levels after receiving glucocorticoids. CONCLUSIONS: Administration of glucocorticoids should be recommended for treatment of patients with SSNHL. In particular, patients with SSNHL in the lower and middle frequency range and pancochlear hearing loss have significantly better recovery of hearing levels.

[Immunohistochemical detection of humoral autoantibodies in patients with hearing loss in the last hearing ear]. / Immunhistochemischer Nachweis von humoralen Auto-Antikörpern bei Patienten mit einer Hörminderung auf dem letzthörenden Ohr.

BACKGROUND: An autoimmune etiology similar to the sympathetic ophthalmia has been discussed for sensorineural hearing loss on the last hearing ear following deafness in the first ear. In sympathetic cochleolabyrinthitis inner ear proteins are thought to be released after laterobasal fracture, which may induce an autoimmune process in the last hearing ear. Animal models have failed to clearly demonstrate the location of the target in the labyrinth, attacked by immunologic processes. Furthermore, it is unclear whether the humoral or cellular pathway is initiating this process. METHODS AND PATIENTS: Serum was acquired from 15 patients with traumatic or post-inflammatory unilateral deafness and slowly progressive or sudden sensorineural hearing loss on the last hearing ear. Deparaffinized sections of rat temporal bones were incubated with patient serum and subjected to immunohistochemical examination. RESULTS: A specific but heterogeneous binding pattern of the labyrinth was found in 14 of 15 patients. CONCLUSION: Our results indicate different autoantibodies in the patient serum, which may be the cause of the hearing loss. Therefore, in patients with sensorineural hearing loss on the last hearing ear, we recommend a therapeutic trial with corticosteroids.

Role of S-100beta as potential autoantigen in an autoimmune disease of the inner ear.

In Lewis rats, adoptive transfer of T cells specific for the calcium-binding protein S-100beta mediates experimental autoimmune encephalomyelitis, but surprisingly also induced a marked labyrinthitis associated with impairment of hearing. This suggests that transfer of S-100beta-specific T cells into susceptible animals could be a novel model to study autoimmunity of inner ear diseases. The investigation demonstrated in detail an inner ear involving, central nervous system (CNS)-specific autoimmune disease in order to identify a putatively shared autoantigen(s) in these pathologies. In fact, the model will be a useful tool to investigate in detail, the pathological mechanisms of the human inner ear disease associated with Vogt-Koyanagi-Harada disease.

A rat T-cell line that mediates autoimmune disease of the inner ear in the Lewis rat.

In various patterns of sensorineural hearing loss including Ménière's disease, which may show improvement in auditory function following immunosuppressive therapy, an isolated autoimmune disease of the inner ear has been postulated. Because of the lack of well-defined diagnostic criteria to identify autoimmune processes within the inner ear and the fact that the human inner ear is one of the few organs of the body not amenable to diagnostic biopsy, there has been great interest in developing animal models that mimic these clinical entities. Previous studies have found evidence that this process might be cell mediated and that the endolymphatic sac functions as an immunodefensive organ for the inner ear. By heterologous immunization of inbred Lewis rats with inner ear tissue, an autoreactive inner-ear-specific T helper cell line was established. After passive transfer of these cells a labyrinthitis was induced in recipient animals. Immunohistochemically, T helper cells were first identified in the cochlea suggesting that this cell type might carry the autoantigenic epitope. Autoantibodies against inner ear tissue were demonstrated in animals with histologically evident labyrinthitis. We conclude that this experimental design can serve as an animal model for cell-mediated autoimmune disease of the inner ear and could be used to explain the etiology of certain types of sensorineural hearing loss such as Ménière's disease. With this approach the identification of the causative autoantigen should be possible and will lead to the development of appropriate clinical tests to diagnose autoimmune diseases of the inner ear in humans.

The endolymphatic sac receives antigenetic information from the organs of the mucosa-associated lymphatic system.

The endolymphatic sac holds the entire arrangement of immunocompetent cells and functions as an immunological potent control organ for the inner ear. The evidence of secretory immunoglobulin A and other features of lymphocyte subtypes characterizes the endolymphatic sac as an organ of the mucosa-associated lymphatic system (MALT). In this system a permanent recirculation of sensitized memory lymphocytes from one organ to the other has been demonstrated experimentally as serving to dispose memory lymphocytes after renewed antigenetic stimulus. The aim of this study was to prove the possible recirculation of antigen-sensitized lymphocytes to the endolymphatic sac after antigenic stimulus of another part of the mucosa-associated lymphatic system. The results are evidence that the endolymphatic sac is provided with immunocompetent cells which derive from the lymphatic tissue of the nasopharynx. While the origin of immunocompetent cells in the endolymphatic sac still remains uncertain, this study underlines the role of lympho-epithelial tissue of the nasopharynx as a possible cell source for the endolymphatic sac. The results might explain the altered or disturbed function of the endolymphatic sac as a possible cause of certain inner ear diseases.

[Is the use of factor XIII for delayed wound healing in patients with head-neck tumors of value?]. / Ist der Einsatz von Faktor XIII bei Wundheilungsstörungen von Patienten mit Kopf-Hals-Tumoren sinnvoll?

BACKGROUND: Factor XIII is known to play an important role in wound healing. In patients with head and neck carcinomas there is an accumulation of risk factors for factor XIII deficiency such as chronic liver disease, extensive tissue lesions, and high intraoperative blood loss. METHOD: Serum levels of factor XIII in 22 patients who had undergone tumor surgery for head and neck carcinoma were measured preoperatively and daily up to 1 week following surgery. Factor XIII was measured with the Berichrome assay as part of our routine laboratory studies. The results were correlated with preoperative pseudocholinesterase (PChe). Factor XIII was substituted for 3 days in 8 patients with persistent wound healing problems that did not improve after two weeks of conservative treatment. RESULTS: We found that PChe levels are a predictor for the development of factor XIII levels during this period. In patients (n = 14) with normal PChe, factor XIII levels reached 86% of the preoperative values 1 week after operation (group 1). In patients (n = 8) with low PChe, the levels reached only 65% (group 2). The rate of wound healing problems was higher in group 2 (6/8) than in group 1 (2/14). In 6 patients treated with factor XIII, the wounds healed within 3 to 7 days. In two cases revision operation was necessary. CONCLUSION: We conclude that the therapy with factor XIII may be successful in patients with wound healing problems. Further studies will be necessary to find out whether prophylactic substitution of factor XIII in patients with low preoperative pseudocholinesterase levels is useful.

Induction of an inner-ear-specific autoreactive T-cell line for the diagnostic evaluation of an autoimmune disease of the inner ear.

Different patterns of sensorineural hearing loss with a potential improvement in auditory function following immunosuppressive therapy might be caused by an isolated autoimmune disease of the inner ear. Because of the lack of well-defined detection methods to identify autoimmune processes within the inner ear and the fact that the human inner ear is one of the few organs of the body not amenable to diagnostic biopsy, there has been great interest in developing animal models. Previous studies found evidence that this entity might be cellular mediated. By heterologeous immunization of inbred Lewis rats with inner-ear tissue, an autoreactive inner-ear-specific T-cell line was established. After passive transfer of these cells, a labyrinthitis was induced in recipient animals. The experimental design can serve as an animal model for a cellular-mediated autoimmune disease of the inner ear. Further studies have to split the cochlear proteins and to identify the protein with the strongest autoimmunological potency. After biotechnical production of this protein, a clinical test to diagnose an autoimmune disease of the inner ear in man should be possible.

Role of adhesion molecules for the immunological defense of the inner ear.

Previous experiments demonstrated an organ-specific migration of sensitized lymphocytes to the inner ear and enabled us to establish an animal model for an autoimmunological labyrinthitis in the guinea pig. For a nonrandom emigration from capillaries into tissues of their immunological destination, memory lymphocytes need homing receptors on their cell surface to interact with specialized postcapillary venules, the so-called high endothelial venules. These molecules were already demonstrated in organs of the mucosa-associated lymphatic system (MALT). This study was performed to demonstrate these adhesion molecules on endothelial cells and lymphocytes of the inner ear by using two monoclonal antibodies: MECA-325 and MEL-14. Special interest was directed to the posterior spiral modiolar vein as a known port of entry for lymphocytes during an immune response. Emphasis was placed on the development of new or additional binding sites for lymphocytes on the above-mentioned structures using immunohistochemistry during an immune response of the inner ear. The results suggest a constant recirculation of memory lymphocytes through the endolymphatic sac as known for other organs of the MALT. The acquisition of high endothelial venules in the cochlea during an immune response could serve for the cellular requirements of a sympathetic cochleolabyrinthitis with the spiral modiolar vein as port of entry for lymphocytes. Furthermore, this study supports the hypothesis of the endolymphatic sac as central immunological control organ of the inner ear and as the primary place for antigen processing.

Adoptive transfer of an autoimmunological labyrinthitis in the guinea pig; animal model for a sympathetic cochleolabyrinthitis.

Sensorineural hearing loss is a common problem in the otolaryngologist's practice, with autoimmune disease of the inner ear being one possible cause. The restoration of auditory function in some patients following immunosuppressive therapy has created a desire to define and understand this disease better. Because of the lack of a well defined detection method to identify this entity clinically, this study was undertaken in order to provide an animal model for autoimmune disease of the inner ear. Previous studies with guinea pigs have demonstrated that sensitized lymphocytes from the systemic circulation migrate to the labyrinth during an immune response in the inner ear. The aim of this study was to prove the capacity of sensitized lymphocytes to transfer autoimmune inner ear disease, and to describe the resulting morphological and physiological changes. Therefore two groups of sensitized lymphocytes partially labelled with a radioactive marker from inbred guinea pigs with an immune response within the inner ear were injected into the bloodstream of naive recipient animals. Most of the labelled cells were observed in the apical turn of the experimental cochlea, while only few cells were detectable in the control cochleas. In addition, the absence of otoacoustic emissions and the loss of outer hair cells observed by electron microscopy were interpreted as a sign of damage caused by the provoked immunopathologic mechanism. The results are discussed as a possible model for a sympathetic cochleolabyrinthitis.

Detection of cochlear dysfunction by the measurement of transiently evoked otoacoustic emissions in guinea pigs with autoimmune-induced labyrinthitis.

For the evaluation of functional inner ear lesions caused by an autoimmune-induced labyrinthitis, transiently evoked otoacoustic emissions (TEOAEs) were detected in guinea pigs before and after transfer of sensitized lymphocytes from animals suffering from a labyrinthitis induced by the foreign protein keyhole limpet hemocyanin (KLH). Initially TEOAEs were detectable from 47 of 62 ears (76%) in healthy guinea pigs. These animals then were used as recipients for sensitized lymphocytes from donors exclusively. Three months after cell transfer the incidence of TEOAEs was reduced to 48% in animals receiving lymphocytes from donors sensitized with KLH intradermally and intracochlearly. In recipients of lymphocytes from donors sensitized only intradermally and in untreated animals no significant alteration of the TEOAE incidence was found. These findings showed strong correlation with those from scanning electron microscopy of the organ of Corti, indicating that the measurement of TEOAE is a useful, time-saving tool for the detection of cochlear dysfunction caused by sensitized lymphocytes in experimental animal. The present findings also show that the migration of sensitized lymphocytes actually leads to functional lesions in the cochlea.

Binding sites of atrial natriuretic peptide (ANP) in the mammalian cochlea and stimulation of cyclic GMP synthesis.

The distribution of binding sites for atrial natriuretic peptide (ANP) has been examined in frozen sections of the guinea pig inner ear by means of autoradiography. The highest density was found in the stria vascularis of all cochlear turns. In membrane preparations of stria vascularis in vitro, the production of the second messenger cGMP was strongly stimulated by synthetic ANP in a dose dependent manner. Adenylate cyclase was neither stimulated nor inhibited by ANP, thus suggesting, that the binding sites coincide with an ANP receptor, which is coupled to guanylate cyclase but not negatively coupled to an adenylate cyclase molecule. The production of cyclic GMP could not be reduced by GDP-beta S, a strong inhibitor of the Gs protein. We conclude the existence of an ANP receptor-guanylate cyclase signal transfer system, similar to the beta 2 receptor-adenylate cyclase system in the inner ear, without coupling to a G protein. ANP might play a role in sodium and water regulation of the endolymph and might antagonize the action of vasopressin.

Influence of middle ear immune response on the immunological state and function of the inner ear.

According to clinical experience, a causative correlation between otitis media and sensorineural hearing loss is likely. During an otitis media, inflammatory mediators should be released and diffuse through the round window membrane to cause an immune response of the inner ear. Using 20 guinea pigs, an immunologically caused otitis media was induced. Auditory evoked potentials were registered by means of electrocochleography and electric response audiometry from day 0 to day 7. Each time, before and after starting the immune response serum, middle ear effusion and perilymph were sampled and the concentration of interleukin-2 (IL-2) analyzed. Decalcified temporal bones were examined immunohistochemically. In this study, IL-2 was found in the middle ear effusion and perilymph, and there was evidence of an immune response of the inner ear during an otitis media. Histological results were in close correlation with this event. Electrophysiological data showed conduction deafness and signs of sensorineural hearing loss with a maximum at day 3.

Homing of lymphocytes to the inner ear.

The migration of lymphocytes to the inner ear was studied during an immune response in the cochlea. Sensitized lymphocytes from peripheral blood, neck lymph nodes and spleen from strain 13 inbred guinea pigs were labelled with 51Cr and injected intravenously into strain 13 recipients undergoing an inner ear immune response. Eighteen hours later the temporal bones and immune organs of the recipients were assayed for radioactivity to detect the infiltration of labelled cells. In addition autoradiography was performed to localize labelled cells in the inner ear. More lymphocytes from the peripheral blood entered the inner ear during the immune response than spleen or lymph node cells. This indicates that the inner ear comes under the immuno-surveillance of the peripheral circulation in response to antigenic stimulation. Most labelled lymphocytes were observed in the basal turn of the scala tympani and in and around the spiral modiolar vein of the challenged cochlea. A few cells were seen also in the control cochleas but almost all where inside the blood vessels. This pattern suggests that the blood vessels of the spiral modiolar vein are the initial site through which lymphocytes entered the inner ear.

Inhibition of adenylate-cyclase-coupled G protein complex by ototoxic diuretics and cis-platinum in the inner ear of the guinea pig.

The enzyme adenylate cyclase produces the second messenger cAMP and is located in the mammalian inner ear, predominantly in the stria vascularis and to a lesser extent in the organ of Corti. It is coupled to hormone receptors and regulating G proteins in the outer cell membrane. By means of immunofluorescence in cryostat sections of the guinea pig cochlea, we could demonstrate the G proteins Gs and Gi, which belong to the adenylate cyclase complex. These proteins had their highest density in the stria vascularis. In membrane preparations of this tissue, the adenylate cyclase complex was inhibited by ototoxic drugs (furosemide, ethacrynic acid and cis-platinum). Stimulation at different sites of the enzyme system showed that the target of these drugs was probably the regulating G protein complex and not the enzyme molecule itself. Inhibition depended on the concentration of the drug and the incubation time.

Role of lymphokines in the immune response of the inner ear.

In secondary inner ear responses against keyhole limpet hemocyanin (KLH), the characterization of interleukin-2 levels in perilymph and serum developing over 5 days in Hartley guinea pigs was investigated using an immunoassay. No interleukin-2 levels were detectable at Day 0 in serum and perilymph. The earliest perilymph IL-2 levels were observed after 6 h, peaking at 18 h and decreasing to zero by Day 5. In contrast, during this observation period, no IL-2 was detectable in serum or perilymph from control ears. Since previous work has identified T-helper cells in the endolymphatic sac, this site appears to be the probable source of interleukins. This study provides further support for the existence of an inner ear immune response which is regulated by lymphokines. Furthermore, interleukins may be a chemoattractant for cells entering the cochlea during the immune response.