Endolymphatic hydrops induced by chronic administration of vasopressin

Vasopressin in definite Meniere's disease with positive electrocochleographic findings

CONCLUSION

There was no evidence of a mean raised vasopressin level in 80 subjects suffering from definite Meniere's disease with positive electrocochleographic findings. There was no correlation with stress. The only group with a mildly raised level comprised those who had had a vertigo attack within a day. The most likely cause is nausea, which is the most potent trigger for vasopressin release.

OBJECTIVE

It has been claimed that patients with Meniere's disease have raised vasopressin levels. This has been linked with a long-standing notion that that there is a link between stress and Meniere's disease, so that an increase in vasopressin could trigger a vertigo attack.

METHODS

Serum vasopressin concentrations were measured in 80 patients with Meniere's disease whose diagnosis was based on conventional symptom criteria plus electrocochleographic evidence of endolymphatic hydrops.

RESULTS

The community mean for vasopressin is 2.2 pmol/L (SD = 2.4). For all 80 Meniere's patients the mean vasopressin concentration was 2.1 pmol/L (SD = 1.6), and 2.8 pmol/L (SD = 0.9) when the last attack was within a day.

Endolymphatic hydrops: pathophysiology and experimental models

It is well established that endolymphatic hydrops plays a role in Ménière disease, even though the precise role is not fully understood and the presence of hydrops in the ear does not always result in symptoms of the disease. It nevertheless follows that a scientific understanding of how hydrops arises, how it affects the function of the ear, and how it can be manipulated or reversed could contribute to the development of effective treatments for the disease. Measurements in animal models in which endolymphatic hydrops has been induced have given numerous insights into the relationships between hydrops and other pathologic and electrophysiological changes, and how these changes influence the function of the ear. The prominent role of the endolymphatic sac in endolymph volume regulation, and the cascade of histopathological and electrophysiological changes that are associated with chronic endolymphatic hydrops, have now been established. An increasing number of models are now available that allow specific aspects of the interrelationships to be studied. The yclical nature of Ménière symptoms gives hope that treatments can be developed to maintain the ear in permanent state of remission, possibly by controlling endolymphatic hydrops, thereby avoiding the rogressive damage and secondary pathologic changes that may also contribute to the patient's symptoms.

Expression and translocation of aquaporin-2 in the endolymphatic sac in patients with Meniere's disease

Meniere's disease, characterised by episodic vertigo, fluctuating hearing loss and tinnitus, can occur under conditions of stress. Its pathology was first revealed to be inner ear hydrops through temporal bone studies in 1938. Although its pathogenesis has been proposed to be a disorder of water transport in the inner ear, subsequently, it remains unsolved, until now. A recent study revealed that both plasma stress hormone, vasopressin (pAVP) and its receptor, V2 (V2R) expression in the inner ear endolymphatic sac were significantly higher in Meniere's patients. In the present study, to link V2R-related molecules and inner ear hydrops, we examined V2R-linked water channel molecule, aquaporin-2 (AQP2) expression and translocation in human endolymphatic sac. AQP2 mRNA expression in the endolymphatic sac was significantly higher in Meniere's patients by using real-time polymerase chain reaction, as further confirmed by western blotting. AQP2-like immunoreactivity (-LIR) was translocated from luminal to basolateral side with endosomal trapping in the endolymphatic sac at the time of AVP exposure in human endolymphatic sac tissue culture. The similar AQP2-LIR translocation was also demonstrated by forskolin and blocked by vasopressin/V2R specific antagonist, OPC31260 and protein kinase A (PKA) specific antagonists, H-89 and KT-5720. We concluded that in the pathogenesis of inner ear hydrops resulting in Meniere's attacks, pAVP elevation as a result of stress and subsequent V2R-cAMP-PKA-AQP2 activation and endosomal trapping of AQP2 in the endolymphatic sac, might be important as a basis of this disease. Further experimental and clinical studies are needed to better clarify the neuroscientific relationship between stress and Meniere's disease.

Magnetic resonance imaging of guinea pig cochlea after vasopressin-induced or surgically induced endolymphatic hydrops

Objective: To investigate the ability to detect the in vivo cochlear changes associated with vasopressin-induced and surgically induced endolymphatic hydrops using MRI at 3 tesla (T).

Study Design: Prospective, animal model.

Setting: Animal laboratory.

Subjects and Methods: In group 1, five guinea pigs underwent post–gadolinium temporal bone MRI before and after seven and 14 days of chronic systemic administration of vasopressin by osmotic pump. In group 2, five guinea pigs underwent temporal bone MRI eight weeks after unilateral surgical ablation of the endolymphatic sac. Three-tesla high-resolution T1-weighted sequences were acquired pre- and postcontrast administration. Region of interest signal intensities of the perilymph and endolymph were analyzed manually. Quantitative evaluation of hydrops was measured histologically.

Results: Gadolinium preferentially concentrated in the perilymph, allowing for distinction of cochlear compartments on 3.0-T MRI. The T1-weighted contrast MRI of vasopressin-induced hydropic cochlea showed significant increases in signal intensity of the endolymph and perilymph. Surgically induced unilateral hydropic cochlea also showed increased signal intensity, compared with the control cochlea of the same animal, but less of an increase than the vasopressin group. The histological degree of hydrops induced in the vasopressin group was comparable to previous studies.

Conclusions: In vivo postcontrast MRI of the inner ear demonstrated cochlear changes associated with chronic systemic administration of vasopressin and surgical ablation of the endolymphatic sac. Understanding the MRI appearance of endolymphatic hydrops induced by various methods contributes to the future use of MRI as a possible tool in the diagnosis and treatment of Ménière's disease.

Plasma vasopressin and V2 receptor in the endolymphatic sac in patients with delayed endolymphatic hydrops

OBJECTIVE

There are some kinds of sicknesses provoked by inadequate adaptation to physical and/or psychogenic stress in daily life. Delayed endolymphatic hydrops (DEH) is an inner ear disease like Ménière's disease (MD) characterized by episodic vertigo in the setting of preexisting unilateral deafness that especially occurs in civilized people with a stressful lifestyle. Its otopathologic finding was demonstrated to be inner ear endolymphatic hydrops through a temporal bone study in 1976, as in the case with MD in 1938. To elucidate the relationship between stress and the inner ear, we examined the plasma antidiuretic stress hormone vasopressin (pAVP) and its type 2 receptor (V2R) expression in the endolymphatic sac in patients with DEH.

STUDY DESIGN

A prospective molecular biological study.

METHODS

Between 1998 and 2007, we enrolled 20 patients with ipsilateral DEH to examine their pAVP during remission from vertigo attacks. Plasma vasopressin was also examined in 87 patients with unilateral MD and 30 control patients with chronic otitis media. Using the real-time polymerase chain reaction method with tissue samples obtained during surgery, we examined V2R mRNA expression in the endolymphatic sac in 6 patients with ipsilateral DEH, 9 patients with unilateral MD, and 6 control patients with acoustic neuroma.

RESULTS

Plasma vasopressin (1.5 times versus controls; unpaired t test, p = 0.140) and V2R mRNA expression in the endolymphatic sac (35.8 times versus controls; unpaired t test, p = 0.002) were higher in patients with DEH compared with those with acoustic neuroma. There were no significant differences in pAVP or V2R expression in the endolymphatic sac between DEH and MD. Patients with DEH showed a significantly negative correlation between pAVP and V2R (Pearson test, r = -0.92, p = 0.009) as in those with MD (Pearson test, r = -0.68, p = 0.043).

CONCLUSION

Civilized people are frequently exposed to stress in their daily life, and pAVP can easily become elevated at any time. Therefore, a negative feedback system between pAVP and V2R in the endolymphatic sac may function for inner ear fluid homeostasis against stress-induced increases in pAVP. For the pathogenesis of endolymphatic hydrops resulting in vertigo attacks in patients with DEH as well as MD, pAVP may represent a matter of consequence, but V2R overexpression in the endolymphatic sac could be much more essential as a basis for these diseases.

Expression of aquaporins, vasopressin type 2 receptor, and Na+₋K+₋Cl⁻ cotransporters in the rat endolymphatic sac

CONCLUSION

Since many water channels and pumps, such as aquaporin (AQP) 1-4, AQP6-9, vasopressin type 2 receptor (V(2)-R), Na(+)-K(+)-Cl(-) cotransporter (NKCC) 1, and NKCC2 were expressed in the rat endolymphatic sac, it should play an important role in the physiological function of acid-based metabolism and water balance in endolymphatic fluid homeostasis.

OBJECTIVE

To evaluate the expression and immunolocalization of AQP1-9, V(2)-R, NKCC1, and NKCC2 in the rat endolymphatic sac.

MATERIALS AND METHODS

Wistar rats were used. Expression of AQP1-9, V(2)-R, NKCC1, and NKCC2 mRNA in the rat endolymphatic sac was investigated using the reverse transcription-polymerase chain reaction (RT-PCR) method, and detailed immunolocalization of AQP1-9, V(2)-R, NKCC1, and NKCC2 was investigated using immunohistochemical methods, including immunofluorescence microscopy.

RESULTS

mRNAs and proteins of AQP1-4, AQP6-9, V(2)-R, NKCC1, and NKCC2 were expressed, but AQP5 was not expressed in the rat endolymphatic sac.

Time course changes of vasopressin-induced enlargement of the rat intrastrial space and the effects of a vasopressin type 2 antagonist

CONCLUSION

The intrastrial space was enlarged remarkably at 20 min after vasopressin (VP) injection, and this enlargement of the intrastrial space was reduced by administration of OPC-31260 before VP injection. These results suggest that VP increases the influx of water from the perlymph to the basal cells via aquaporin (AQP) 2 and causes the formation of endolymphatic hydrops.

OBJECTIVES

To investigate a time course of changes of the stria vascularis after VP injection and the influence of OPC-31260 on experimentally induced enlargement of the intrastrial space caused by VP injection.

MATERIALS AND METHODS

In the time course study, Wistar rats were injected with 50 microg/kg of VP subcutaneously. The stria vascularis specimens were harvested at 10, 20, 30, and 60 min after VP injection. For OPC-31260 administration, animals were administered 100 mg/kg of OPC-31260 orally 1 h before receiving 50 microg/kg of VP subcutaneously. The specimens were harvested 20 min after VP injection. These specimens were observed using transmission electron microscopy.

RESULTS

In the time course study, the incidence of intrastrial space enlargement was 50%, 100%, 25%, and 0% for 10, 20, 30, and 60 min, respectively. In the study with OPC-31260 administration, the stria vascularis showed no morphological changes.

Image evaluation of endolymphatic space in fluctuating hearing loss without vertigo

The objective of the present study was to investigate endolymphatic space images in patients with fluctuating hearing loss without vertigo, and to elucidate its underlying pathophysiology. Eight patients with fluctuating hearing loss without vertigo were included in this study. 3T MRI was taken, 24 h after intratympanic injection of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). Electrocochleography and VEMP tests were performed to evaluate cochlear and vestibular functions. Endolymphatic hydrops were observed both in the cochlea and in the vestibule of all eight patients. Three patients out of six whose summating potential/action potential (SP/AP) ratio was recordable showed an elevation of SP/AP ratio. In the two patients with remarkable endolymphatic hydrops in the vestibule, VEMP was absent from the affected ear. In conclusion, 3T MRI after intratympanic injection of Gd-DTPA revealed endolymphatic hydrops both in the cochlea and in the vestibule in the patients with fluctuating hearing loss without vertigo.

Stress axis plasticity during vestibular compensation in the adult cat

The postural, ocular motor, perceptive and neurovegetative syndromes resulting from unilateral vestibular neurectomy (UVN) symptoms could generate a stress and thereby activate the hypothalamo-pituitary-adrenal (HPA) axis. This study was aimed at determining whether UVN causes changes in the activity of the HPA axis, and if so, evaluating the time course of changes associated with UVN syndrome. At the cellular level, corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) immunoreactivity (Ir) were analyzed and quantified in the paraventricular nucleus (PVN) and the vestibular nuclei (VN) complex of cats killed early (1 and 7 days) or late (30 and 90 days) after UVN. Dopamine-beta-hydroxylase (DbetaH), the enzyme synthesizing noradrenaline was examined in the locus coeruleus (LC) in these same cats. At the behavioral level, the time course of recovery of the postural and locomotor functions was quantified at the same postoperative delays in another group of UVN cats. Results showed a significant bilateral increase in the number of both AVP-Ir and CRF-Ir neurons in the PVN and an increase of DbetaH-Ir neurons in the LC at 1, 7 and 30 days after UVN. This increased number of neurons was no longer observed at 90 days. Conversely, a significant bilateral decrease of CRF-Ir neurons was observed in the VN at these same postlesion times, with a similar return to control values at 90 days. Our behavioral observations showed strong posturo-locomotor functional deficits early after UVN (1 and 7 days), which had recovered partially at 30 days and completely by 90 days postlesion. We demonstrate a long-lasting activation of the HPA axis, which likely reflects a chronic stress, experienced by the animals, which corresponds to the time course of full vestibular compensation, and which is no longer present when the animals are completely free of posturo-locomotor symptoms at 90 days.

Effect of inner ear blood flow changes in Ménière's model mice

CONCLUSIONS

The endolymphatic sac (ES) is important for inner ear fluid homeostasis. A dysfunctional ES can cause vertigo attacks following additional stress such as a sudden change in endolymphatic volume and/or pressure, or restricted inner ear blood flow.

OBJECTIVE

The purpose of this study was to elucidate the mechanism of vertigo attacks in Ménière's disease.

MATERIALS AND METHODS

Adult CBA/J mice were given an intratympanic injection of lipopolysaccharide and an intraperitoneal injection of aldosterone. These 'model' animals had epinephrine or sodium nitroprusside (SNP) instilled into the middle ear cavity. Cochleae, vestibules, and endolymphatic sacs were studied morphologically by light microscopy.

RESULTS

The injection of epinephrine into the model animals reduced the endolymphatic hydrops in the cochlea, but also produced mild hydrops in the vestibule, which was never observed in untreated (control) animals. The ES did not react to epinephrine in the normal way. Injection of SNP did not cause any changes.

Aquaporins as potential drug targets for Meniere's disease and its related diseases

The homeostasis of water in the inner ear is essential for maintaining function of hearing and equilibrium. Since the discovery of aquaporin water channels, it has become clear that these channels play a crucial role in inner ear fluid homeostasis. Indeed, proteins or mRNAs of AQP1, AQP2, AQP3, AQP4, AQP5, AQP6, AQP7 and AQP9 are expressed in the inner ear. Many of them are expressed mainly in the stria vascularis and the endolymphatic sac, which are the main sites of secretion and/or absorption of endolymph. Vasopressin type2 receptor is also expressed there. Water homeostasis of the inner ear is regulated in part via the arginine vasopressin-AQP2 system in the same fashion as in the kidney, and endolymphatic hydrops, a morphological characteristic of Meniere's disease, is thought to be caused by mal-regulation of this system. Therefore, aquaporins appear to be important for the development of novel drug therapies for Meniere's disease and related disorders.

Meniere's attacks occur in the inner ear with excessive vasopressin type-2 receptors

Meniere's disease is peculiar to humans and is characterised by episodic vertigo, fluctuating hearing loss and tinnitus, and attacks of the affliction occurring under conditions of stress. Its pathology was first revealed to be inner ear hydrops through temporal bone studies in 1938. Although subsequently proposed as a disorder of water metabolism in the inner ear, its pathogenesis remains unsolved. The present study aimed to assess the link between the inner ear pathology in Meniere's disease and vasopressin, an anti-diuretic stress hormone with a potential role in inner ear fluid homeostasis. Blood samples were obtained from Meniere's disease patients in the morning, before any surgical treatment, to examine plasma vasopressin (pAVP) levels, and then from inner ear tissue during surgical treatment, to examine vasopressin type-2 receptor (V2R) in the endolymphatic sac. pAVP and the relative V2R mRNA expression in the endolymphatic sac were examined using a real-time polymerase chain reaction. Relative cAMP activity in the endolymphatic sac was also examined using tissue culture and cAMP assay. Both pAVP (1.6-fold versus controls; P = 0.048) and inner ear V2R mRNA expression (41.5-fold versus controls; P = 0.022) were significantly higher in Meniere's patients. cAMP activity was basally up-regulated (2.1-fold versus controls) and cAMP sensitivity to vasopressin application was largely elevated (4.9-fold versus controls) in Meniere's patients. We conclude that, in the pathogenesis of inner ear hydrops, resulting in Meniere's attacks, elevation of pAVP levels (probably as a result of stress) may present as a matter of consequence, but susceptibility of the V2R-overexpressed and cAMP-hypersensitized inner ear to pAVP elevation might be essential as the basis of this disease. Further experimental and clinical studies are needed to better clarify the relationship between Meniere's disease and stress.

Effect of inner ear blood flow changes on the endolymphatic sac

CONCLUSIONS

That the endolymphatic sac (ES) reacts to changes in inner ear blood flow may be important for homeostasis of the inner ear fluid volume and pressure.

OBJECTIVES

To elucidate the effect of changes in inner ear blood flow on the ES and to learn more about the volume and pressure regulatory function of the ES.

MATERIALS AND METHODS

Epinephrine or sodium nitroprusside (SNP) was injected into the middle ear cavity of adult CBA/J mice. The ES were analyzed morphologically by light microscopy.

RESULTS

Epinephrine reduced the luminal size of the ES leading to an accumulation of intraluminal homogeneous substance. Injection of SNP increased the size of the ES lumen, accompanied by a collapse of the lateral intercellular space (LIS) and dense perisaccular tissue. These changes were almost reversed 4 h after injection.

Expression and immunolocalization of aquaporin-6 (Aqp6) in the rat inner ear

CONCLUSION

Since aquaporin-6 (Aqp6) protein was located in the membrane of intracellular vesicles of the stria vascularis, endolymphatic sac, and vestibule, Aqp6 might be involved in some distinct physiological function of acid-base metabolism and water balance in endolymphatic fluid homeostasis. However, its lack of expression on the plasma membrane indicates that Aqp6 does not have a direct role in water flux via the plasma membrane.

OBJECTIVE

To evaluate the expression and immunolocalization of Aqp6 in the rat inner ear.

MATERIALS AND METHODS

Wistar rats were used. Aqp6 mRNA expression in the rat inner ear was investigated in the vestibulum as well as in the cochlea and endolymphatic sac using the reverse transcription-polymerase chain reaction (RT-PCR) method, and detailed immunolocalization of Aqp6 in the rat inner ear was investigated using immunohistochemical methods including immunofluorescence microscopy and immunoelectron microscopy.

RESULTS

We obtained novel data showing that not just Aqp6 mRNA but also Aqp6 protein is expressed in the cochlea, endolymphatic sac, and vestibule. Immunoelectron microscopic studies revealed that the immunolabelled gold was diffusely seen in the intracellular area of the stria vascularis, endolymphatic sac, and vestibule, but never in the plasma membranes.

Decompression effects of erythritol on endolymphatic hydrops

OBJECTIVE

The effect of the uptake of erythritol with and without the addition of pectin on fecal condition, p-OSM and p-AVP levels, and the endolymphatic volume was investigated to consider the possibility that erythritol is applicable as a therapeutic agent for Meniere's disease.

MATERIALS AND METHODS

Two experiments were performed using 100 female Hartley guinea pigs. Experiment 1 was designed to morphologically investigate the influence of the uptake of erythritol with or without the addition of pectin on the endolymphatic volume. Experiment 2 was designed to investigate changes in p-OSM and p-AVP levels after the uptake of erythritol with or without the addition of pectin.

RESULTS

(1) Endolymphatic hydrops significantly decreased after the uptake of a mixture of erythritol and pectin, but did not decrease after the uptake of pectin or erythritol (p<0.001). (2) The fecal condition was muddy in all animals with the uptake of erythritol alone, but muddy or very soft feces were not observed in animals with a mixture of pectin and erythritol. p-AVP and p-OSM levels were significantly elevated in animals with the uptake of erythritol alone or a mixture of erythritol and pectin. Notably, the increase in p-AVP and p-OSM levels was significantly more evident in animals with the uptake of erythritol alone (one-way ANOVA, p<0.001).

CONCLUSIONS

The addition of pectin almost completely suppressed erythritol-induced diarrhea. Consequently, the secondary elevation of p-AVP and p-OSM due to diarrhea was also reduced. The uptake of a mixture of erythritol and pectin markedly decompressed endolymphatic hydrops, although the uptake of erythritol alone did not. The difference of the decompression effect between animal groups with the uptake of erythritol alone and a mixture of erythritol and pectin seemed to be attributable to the difference of p-AVP levels due to diarrheal state.

Expression of aquaporin1, 3, and 4, NKCC1, and NKCC2 in the human endolymphatic sac

OBJECTIVE

To locate aquaporin (AQP) 1, 3, and 4, Na-K-2Cl cotransporter (NKCC) 1 and 2 in the human endolymphatic sac (ES).

METHODS

A sample of human ES was harvested during the removal of vestibular schwannoma via the translabyrinthine approach. The sample was immediately fixed in 4% paraformaldehyde and embedded in OCT compound. Immunohistochemistry was performed with AQP1, 3, and 4, NKCC1, and NKCC2 polyclonal antibodies.

RESULTS

AQP1, AQP3, and NKCC2 were strongly expressed in the epithelial layer of the ES. AQP4 and NKCC1 were weakly expressed in the epithelial layer of the ES.

CONCLUSIONS

As it is impossible to perform quantitative analysis based on the fluorescence intensity of each immunoreactivity, we have presented the existence of AQP1, 3, and 4, NKCC1, and NKCC2 in the ES. The expression of NKCC1 and 2 indicated that the ES may have both secretory and adsorptive functions to maintain the homeostasis of endolymph.

Effect of acute endolymphatic hydrops overload on the endolymphatic sac

CONCLUSIONS

Homeostasis of endolymph volume is a complex mechanism, in which the endolymphatic sac (ES) may play an important role.

OBJECTIVES

To elucidate the effect of acute endolymphatic hydrops (EH) on the ES and to gain further information about the volume and pressure regulative function of the ES.

MATERIALS AND METHODS

Distilled water was injected into the middle ear cavity of adult CBA/J mice. The ESs were studied morphologically by light and transmission electron microscopy.

RESULTS

Mild EH was found, particularly in the upper turn of the cochlea. Acute EH led to an increase in the size of the ES lumen, accompanied by collapse of the lateral intercellular spaces and dense perisaccular tissue, changes which had reversed 2 h after the injection.

A new animal model for Ménière's disease

CONCLUSION

A new murine model for the study of Ménière's disease has been developed by treatment with both lipopolysaccharide (LPS) and aldosterone. Induction of vestibular dysfunction in the hydropic animal model may entail additional stress such as reduced inner ear blood flow, and sudden acute changes in endolymph volume and/or pressure.

OBJECTIVE

The purpose of this study was to develop a more suitable animal model, showing closer resemblance to the pathophysiological process in Ménière's disease.

MATERIALS AND METHODS

Adult CBA/J mice were treated by intratympanic injection of LPS, intraperitoneal injection of aldosterone, or injection of both LPS and aldosterone. Morphological analyses were performed in the cochlea and endolymphatic sac.

RESULTS

All experimental animals showed mild to moderate endolymphatic hydrops. Those treated with both LPS and aldosterone showed reversible vestibular dysfunction after the intratympanic injection of epinephrine.

The relevance of an elevation in the plasma vasopressin levels to the pathogenesis of Meniere's attack

An elevation of plasma vasopressin levels has been frequently observed in Meniere's disease patients. However, little is known regarding the mechanism behind this elevation. The plasma vasopressin levels and plasma osmolality were therefore determined in 18 diagnosed Meniere's disease patients and 20 patients with other types of vertigo, who required admission for severe vertigo attacks. All participants were given questionnaires regarding their clinical and psychological status, including their stress levels and depression status, to evaluate environmental stress events. The plasma vasopressin levels of Meniere's disease patients in the acute phase (4.1 +/- 1.37 pg/ml) were significantly higher compared with with those of other vertigo patients in the acute phase (2.1 +/- 0.41 pg/ml) (P < 0.01). The average plasma osmolality of the Meniere's disease group was higher than that of the other vertigo patients group (P < 0.05). No significant difference in reported stress levels, depression status and prevalence of primary headache between the groups was observed. The plasma vasopressin showed no significant correlation with the patients' clinical data (occurrence of emesis or nausea, prevalence of primary headache, depression status and stress). No correlation between the plasma vasopressin and the plasma osmolarity was observed in the Meniere's disease group. These results suggest that the elevation of plasma vasopressin in the acute phase of Meniere's disease is therefore related to the pathogenesis of Meniere's attacks, and the results obtained may provide helpful information for distinguishing between Meniere's disease and other various inner ear diseases.

Protective effect of edaravone against endolymphatic hydrops

CONCLUSION

Our findings suggest that edaravone prevented the production of reactive oxygen species (ROS). Edaravone also delayed the formation of endolymphatic hydrops in guinea pigs, but had no effect on endolymphatic hydrops.

OBJECTIVE

To analyse the protective effect of a free radical scavenger, edaravone, on endolymphatic hydrops.

MATERIALS AND METHODS

Guinea pigs were subjected to surgical obliteration of the endolymphatic duct (ED). For the detection of ROS, group 1 received intraperitoneal injections of edaravone (3 mg/kg/day) for 2 days, group 2 received edaravone for 2 weeks, group 3 saline for 2 days, and group 4 saline for 2 weeks. ROS production by the organ of Corti and stria vascularis was examined by using dihydrotetramethylrosamine. For the morphological analysis, guinea pigs were divided into five groups, i.e. 2 or 4 weeks after ED obliteration, 2 weeks with edaravone, first or last 2 weeks with edaravone and sacrificed 4 weeks after ED obliteration. Increases in the ratios of the cross-sectional area of scala media were analysed quantitatively to assess the degree of endolymphatic hydrops among the above-mentioned five groups of the hydropic cochlea.

RESULTS

ROS was detected both in the organ of Corti and in the lateral wall of cochleae 2 days after ED obliteration. Edaravone prevented the production of ROS and also attenuated the formation of endolymphatic hydrops in the acute hydrops group.

Expressions of Aquaporin-2, Vasopressin Type 2 Receptor, Transient Receptor Potential Channel Vanilloid (TRPV)1, and TRPV4 in the Human Endolymphatic Sac

OBJECTIVE

To localize aquaporin (AQP)2, vasopressin type 2 receptor (V2-R), and transient receptor potential channel vanilloid subfamily 1, 4 (TRPV1, TRPV4) in the human endolymphatic sac (ES).

METHODS

Three samples of human ES were sampled during the removal of vestibular schwannoma by way of the translabyrinthine approach. The samples were immediately fixed in 4% paraformaldehyde and embedded in OCT compound; immunohistochemistry was performed with AQP2, V2-R, TRPV1, and TRPV4 polyclonal antibodies.

RESULTS

AQP2, V2-R, TRPV1, and TRPV4 proteins were detected in the epithelial layer of the ES but were not observed in connective tissue around the ES. TRPV1 was also expressed in blood vascular endothelial cells of the connective tissue of ES.

CONCLUSIONS

AQP2, V2-R, and TRPV4 were expressed in the luminal epithelium of human ES. The same characteristic distribution of water and ion channels is seen in the kidney, where a significant amount of fluid is filtrated and resorbed. ES probably plays an active role in the homeostasis of the endolymph.

Effects of vasopressin on gene expression in rat inner ear

Vasopressin regulates water excretion from the kidney by increasing water permeability of the collecting duct as a hormone secreted from the posterior pituitary. A clinical study reported that plasma levels of arginine vasopressin were significantly higher in patients suffering from Meniere's disease. It was histologically confirmed that chronic administration of vasopressin induced endolymphatic hydrops in guinea pigs. However, the mechanism of endolymphatic hydrops induced by vasopressin is still unclear. We use cDNA microarray to study the effects of vasopressin on gene expression profiles in rat inner ear to elucidate the possible mechanism of the induced hydrolabyrinth. Wistar rats were intraperitoneally injected with 50 microg/kg arginine vasopressin once a day for one week. Hydrolabyrinth in rat inner ear induced by administration of vasopressin was detected by HE stain. The bullae were dissected out for total RNA extraction. cDNAs were synthesized by reverse transcription and labeled with Cyanine3 (Cy3) or Cyanine5 (Cy5). The BiostarR-40s cDNA microarray was hybridized with the above cDNAs and the changes of mRNA expression intensity were showed by data analysis. Furthermore, the changes of aquaporins expression level were measured by reverse transcription polymerase chain (RT-PCR). Endolymphatic hydrops were present in rats intraperitoneally injected with vasopressin. 226 known differentially expressed genes were screened out in rat inner ear induced by vasopressin injection. Of the 226 genes, 18 transcripts were increased by 5-fold or more, and 7 transcripts were decreased to 0.2-fold or less. Ten differentially expressed genes were identified that associate with cell signal transduction, 14 differentially expressed genes were identified that relate to ion transport, 7 differentially expressed genes were involved in vesicle-mediated transport, and 2 differentially expressed genes were aquaporin 2 (AQP2) and aquaporin 7 (AQP7). The expression level of AQP2 was significantly higher and AQP7 was significantly lower. These results suggest that there are obvious differences in gene expression profiles in inner ear between vasopressin injected rats and normal control rats. Vasopressin may disturb fluid homeostasis in inner ear by way of signal transduction, ion transport, vesicle-mediated transport and aquaporins. It is likely that up-regulated expression of AQP2 mRNA and down-regulated expression of AQP7 mRNA in the rat inner ear caused by vasopressin induce an increased production and a decreased absorption of endolymph, resulting in endolymphatic hydrops.

Aquaporins and Meniere's disease

PURPOSE OF REVIEW

Review of the role of aquaporins in inner ear homeostasis and potential role in the pathogenesis of Meniere's disease.

RECENT FINDINGS

Recent findings include the immunolocalization of aquaporins in the inner ear of mouse, rat, and human to cell types that are likely to undergo high ionic perturbances (e.g. potassium flux) and to putative areas of endolymph resorption or cycling.

SUMMARY

The expression of aquaporins and related proteins in the human cochlea and vestibular periphery resembles the distribution found in animal models, suggesting a critical role of aquaporins in inner ear water homeostasis and their potential role in the pathogenesis of Meniere's disease.

Antidiuretic Hormone and Osmolality in Isosorbide Therapy and Glycerol Test

Changes in plasma antidiuretic hormone (p-ADH) and plasma osmolality (p-Osm) levels were studied in 63 patients with Ménière's disease before and after isosorbide administration and a glycerol test. Increments in both p-ADH and p-Osm levels were observed after isosorbide administration and the glycerol test. The p-ADH secretion appeared to be secondarily stimulated by an increase in the p-Osm level. This p-ADH level increase affects cochlear fluid homeostasis. Based on these results, we must consider both the p-Osm and p-ADH levels when treating patients with Ménière's disease by osmotic diuretics.

Water may cure patients with Meniere disease

OBJECTIVES/HYPOTHESIS

We examined whether sufficient water intake is effective in the long-term control of vertigo and hearing activity in patients with Meniere disease (MD) for whom conventional therapy has proven unsuccessful.

STUDY DESIGN

The authors conducted a time-series study with historical control.

METHODS

Eighteen patients with MD in group 1 drank 35 mL/kg per day of water for 2 years. Twenty-nine patients with MD treated with the conventional dietary and diuretic therapy for more than 2 years during 1992 to 1999 at the same hospital were enrolled in a historical control of group 2.

RESULTS

Patients in group 1 dramatically relieved vertigo and significantly improved in the hearing of the worst pure-tone average of three frequencies (0.125, 0.25, and 0.5 kHz) (low PTA) during the last 6 months of the study period. In contrast, patients in group 2 became worse in both the four- (0.5, 1, 2, and 4 kHz) frequency PTA and the low PTA, although their vertigo did improve. The number of patients whose hearing were improved, unchanged, and worse were 4, 12, and 2 in group 1 and 2, 11, and 16 in group 2, respectively.

CONCLUSION

Deliberate modulation of the intake of water may be the simplest and most cost-effective medical treatment for patients with MD. Larger studies will be needed to confirm these results in a larger patient cohort.

The association of antidiuretic hormone levels with an attack of Meniere's disease

OBJECTIVES

An elevation of the plasma antidiuretic hormone (ADH) levels has frequently been observed in Meniere's disease patients. However, little is known regarding the mechanism behind such an elevation of ADH level in Meniere's disease patients. Therefore, we measured the plasma ADH in Meniere's disease patients and other vertigo patients to elucidate the association between the ADH levels, stress levels and the development of Meniere's symptom.

DESIGN AND SETTING

The plasma ADH levels and plasma osmotic pressure were determined in 23 definite Meniere's disease patients and 160 patients with other types of vertigo/dizziness. All participants were administered questionnaire regarding their psychological status including their stress levels.

RESULTS

The ADH levels of Meniere's disease patients in the acute phase (5.80 +/- 1.37 pg/mL) were significantly higher in comparison with that of Meniere's disease patients in the remission phase (2.26 +/- 0.41 pg/mL) (P < 0.05). In other peripheral vertigo patients, the ADH level in the acute phase (1.71 +/- 0.23 pg/mL) was not significantly different from that in the remission phase (1.45 +/- 0.15 pg/mL). Meniere's disease patients in the acute phase had a significantly higher stress score (114 +/- 23) than Meniere's disease patients in the remission phase (56 +/- 13) (P < 0.05). However, there was no significant correlation between their stress score and the ADH levels.

CONCLUSIONS

These results suggest that the elevation of the plasma ADH levels in Meniere's disease patients in the acute phase is, therefore, associated with the pathogenesis of Meniere's disease attacks rather than with stress.

A comparison of dehydration effects of V2-antagonist (OPC-31260) on the inner ear between systemic and round window applications

V2-antagonist (OPC-31260 (OPC)) application to the scala tympani reduced endolymphatic hydrops. In the present study, we investigated whether systemic administration or local infusion via the round window (RW application) of OPC would be more suitable for clinical use. In Experiment 1, the increase ratios of the cross-sectional area of the scala media of experimentally induced endolymphatic hydrops were quantitatively assessed among four groups of non-OPC application, RW application of xanthan gum, systemic application of OPC and RW application of OPC. In Experiment 2, the effects of systemic and RW applications of OPC on plasma vasopressin (p-VP) concentrations and plasma osmolality (p-OSM) were investigated. In Experiment 3, endocochlear DC potential (EP) was measured in guinea pigs with the RW application of OPC. Electron microscopic observations of the stria vascularis and the hair cells were also made. Both systemic and RW applications of OPC significantly reduced endolymphatic hydrops. However, systemic application resulted in the distension of the Reissner's membrane in the non-operated ear, which seemed to be caused by elevated p-VP levels resulting from the systemic application of OPC. In contrast, RW application of OPC produced no apparent toxic effects in the inner ear, as indicated electrophysiological or morphological changes. Thus, drug delivery via the round window is more useful for the clinical application of OPC for medical decompression.

Disorder of the saliva melatonin circadian rhythm in patients with Meniere's disease

OBJECTIVES

Stress is involved in the development of symptoms of Meniere's disease (MD). Stress-related disease has been reported to be associated with disorders in the circadian rhythm of melatonin (MEL) which regulates that rhythm. We therefore investigated MEL circadian rhythm of patients with MD.

PATIENTS AND METHODS

A comparison of 13 MD patients was made with age-matched controls. Saliva samples were collected every 3 h. A statistical analysis of the circadian rhythm of saliva MEL was performed for a circadian rhythm by the fit of a 24- and 12-h composite cosine model. In addition, we assessed the stress and depression status of the two groups.

RESULTS

The rhythmic amplitude of MEL in the MD group was significantly lower than that in the control group (P < 0.05). The acrophase in the MD group was significantly earlier than that in the control group (P < 0.05). MD patients had significantly higher stress score and depression score than control subjects (P < 0.05). The amplitude in MD patients had no significant correlation with their otologic clinical data.

CONCLUSIONS

These results suggest that MD patients have a MEL deficiency, which is related to their stress and depression status rather than the otologic pathological status of MD.

Hyperprolactinemia in some Ménière patients even in the absence of incapacitating vertigo

Stress can be a significant factor influencing ear pathologies and is often reported to trigger the symptoms of Meniere's disease. Both physiological and psychological stress provokes the release of prolactin from the pituitary thus allowing the classification of prolactin as a major stress hormone. We investigated the level of the stress hormone prolactin in a Swedish population with early symptoms of Meniere's disease. The median prolactin level in the Meniere patients (n=33) was not significantly different from that of non-Meniere patients (n=23). However, in the Meniere group one female (90 year old) had prolactin levels in the upper normal range for women, one male (77 year old) had prolactin levels above the normal limit for men, and a third patient (76 year old female) presented hyperprolactinemia with more than twice the normal level. MRI confirmed a pituitary adenoma in this patient. This study provides further support for the recent report of hyperprolactinemia in some patients with long-standing Meniere's disease and presenting incapacitating vertigo in France. The data emphasize the likely implication of stress in this pathology where the stress hormone prolactin is likely to represent one actor in a complex hormonal imbalance affecting the inner ear.

Stress hormones in Ménière's disease and acoustic neuroma

Stress has been postulated to trigger or contribute to inner ear pathologies but there is little objective evidence. We investigated stress hormones in Ménière's patients and patients with acoustic neuroma. Data were compared with those from a control group of patients with facial spasm. We assayed classic stress hormones including adrenocorticotropic hormone, cortisol, growth hormone and prolactin. We found a strong positive correlation between cortisol and adrenocorticotropic hormone in Ménière patients and patients with acoustic neuroma but no correlation in patients with facial spasm. The data also revealed in female patients with Ménière's disease or with acoustic neuroma an unexpected significant positive correlation between cortisol and prolactin. The data showed the expected negative correlation or no correlation between cortisol and prolactin associated with males and females in the other patient groups. Both cortisol and prolactin increases are known to represent alternative strategies to cope with stress, and our data point to prolactin being possibly more dominant in Ménière's disease and cortisol in acoustic neuroma. These data provide further evidence for modification of different stress hormones in audiovestibular pathologies, which might provide a valuable diagnostic or prognostic tool in the future.

Intralabyrinthine fluid dynamics: Meniere disease

PURPOSE OF REVIEW

Meniere disease has long been postulated to be a disorder of intralabyrinthine fluid dynamics.

RECENT FINDINGS

More recent developments in this field indicate that the control of fluid movement may be at a cellular level and that hormonal influence may be important.

SUMMARY

The control of fluid and ion movements through aquaporins and gap junctions in the cell membranes are creating new perspectives in the mechanism of development of endolymphatic hydrops as well as potential methods for treatment. Intralabyrinthine fluid dynamics also play a role in the ability to locally deliver drugs to the inner ear through the middle ear.

Time Course of Dehydrating Effects of Isosorbide on Experimentally Induced Endolymphatic Hydrops in Guinea Pigs

Osmotic diuretics are therapeutic agents used to reduce endolymphatic hydrops. However, glycerol-induced change in endolymph volume is followed by a rebound phenomenon. In this study, we investigated the rebound phenomenon occurring with isosorbide, an osmotic diuretic used as a therapeutic agent for Ménière's disease in Japan. Forty guinea pigs underwent surgical obliteration of the endolymphatic sac. Thirty received isosorbide orally 1 month after surgery. These animals were sacrificed 3, 6, or 12 h after isosorbide intake. The remaining 10 animals served as controls. Quantitative assessment of changes in the endolymphatic space was performed light-microscopically. Isosorbide reduced cochlear endolymph volume, with a peak reduction 6 h after intake. Thereafter, no prominent rebound phenomenon was noted. Clinically, since isosorbide is orally administered every 8 h, rebound phenomenon need not be considered in the treatment with isosorbide.

The emotional ear in stress

Stress of some kind is encountered everyday and release of stress hormones is essential for adaptation to change. Stress can be physical (pain, noise exposure, etc.), psychological (apprehension to impending events, acoustic conditioning, etc.) or due to homeostatic disturbance (hunger, blood pressure, inner ear pressure, etc.). Persistent elevated levels of stress hormones can lead to disease states. The aim of the present review is to bring together data describing morphological or functional evidence for hormones of stress within the inner ear. The present review describes possible multiple interactions between the sympathetic and the complex feed-back neuroendocrine systems which interact with the immune system and so could contribute to various inner ear dysfunctions such as tinnitus, vertigo, hearing losses. Since there is a rapidly expanding list of genes specifically expressed within the inner ear this clearly allows for possible genomic and non-genomic local action of steroid hormones. Since stress can be encountered at any time throughout the life-time, the effects might be manifested starting from in-utero. These are avenues of research which remain relatively unexplored which merit further consideration. Progress in this domain could lead towards integration of stress concept into the overall clinical management of various inner ear pathologies.

The effects of V2 antagonist (OPC-31260) on endolymphatic hydrops

In the present study, two experiments were performed to investigate the influence of OPC-31260 on experimentally induced endolymphatic hydrops in guinea pigs and the regulation of aquaporin-2 (AQP2) mRNA expression in the rat inner ear. In morphological studies, the increases in the ratios of the length of Reissner's membrane (IR-L) and the cross-sectional area of the scala media (IR-S) were quantitatively assessed among normal guinea pigs (normal ears) and three groups with hydropic ears: hydropic ears with no infusion (non-infusion hydropic ears), hydropic ears with an infusion of physiological saline into the scala tympani (saline-infused hydropic ears) and hydropic ears with infusion of 0.3% OPC-31260 into the scala tympani (OPC-infused hydropic ears). IR-Ls in the experimental groups were markedly larger than in the normal ear group, but there was no significant difference among the groups of non-infusion hydropic ears, saline-infused hydropic ears and OPC-infused hydropic ears. The IR-Ss of non-infusion hydropic ears and saline-infused hydropic ears (48.8-49.3%) were statistically different from that of normal ears (6.5%) (Dunnet multiple comparison test, P<0.01). However, IR-S of the OPC-infused hydropic ears (-14.8%) was significantly smaller than those of non-infusion hydropic ears and saline-infused hydropic ears (one-way ANOVA, P<0.01). In the quantitative polymerase chain reaction study, a comparison of the ratio of AQP2 and beta-actin mRNA (MAQP2/Mbeta-actin) was made between water-injected and OPC-31260-injected rats. An intravenous injection of OPC-31260 resulted in a significant decrease in MAQP2/Mbeta-actin both in the cochlea and in the endolymphatic sac (t-test, P<0.001). These results indicate that water homeostasis in the inner ear is regulated via the vasopressin-AQP2 system, and that the vasopressin type-2 antagonist OPC-31260 is a promising drug in the treatment of Meniere's disease.

Serum antidiuretic hormone levels in patients with unilateral Meniere's disease

OBJECTIVES/HYPOTHESIS

Prior studies have indicated a possible role of antidiuretic hormone (ADH) in the pathogenesis of Meniere's disease. Animal studies have shown presence of ADH receptors in the inner ear, and chronic vasopressin administration has been shown to induce endolymphatic hydrops. Furthermore, elevation of serum ADH levels in human has been noted in patients with Meniere's disease. The goal of the study report was to analyze ADH levels in a series of patients with definite unilateral Meniere's disease to further investigate this relationship.

STUDY DESIGN

Retrospective analysis

METHODS

Antidiuretic hormone levels were obtained from 26 consecutive patients with a diagnosis of definite Meniere's disease as defined by the 1995 guidelines from the Committee of Hearing and Equilibrium (American Academy of Otolaryngology-Head and Neck Surgery). The ADH levels were drawn for each patient within one week of an acute episode of vertigo. These values were compared to ADH levels from 31 healthy volunteers. Statistical analysis was performed using a two-tailed t test.

RESULTS

Mean ADH level for patients with Meniere's disease was 4.07 pg/mL (SD = 2.82 pg/mL) and for the control group, 3.37 pg/mL (SD = 1.48 pg/mL). The difference in ADH levels was not statistically significant (P >.05).

CONCLUSIONS

Although previous reports have demonstrated a possible role of ADH in the pathogenesis of Meniere's disease, the study did not show a statistically significant elevation of ADH levels in patients with unilateral Meniere's disease. Before excluding an ADH-inner ear pathogenic relationship, ADH levels in patients with bilateral Meniere's disease should be investigated.

Aquaporin-2 regulation by vasopressin in the rat inner ear

Our previous studies have suggested a close relationship between vasopressin and endolymphatic hydrops, or the increased volume of endolymph in the inner ear. Endolymphatic hydrops is also thought to occur in Ménière's disease patients. In the kidney collecting duct, vasopressin induces the expression of aquaporin-2 (AQP2), resulting in increased water reabsorption. We explored the possibility, using a quantitative PCR method, that vasopressin regulates the expression of AQP2 mRNA in the rat inner ear, as it does in the kidney. The levels of AQP2 mRNA in the cochlea and endolymphatic sac were significantly higher in rats treated with vasopressin than the levels in control animals. We speculate that over-expression of AQP2 may be involved in the formation of endolymphatic hydrops.

Etiology, pathophysiology of symptoms, and pathogenesis of Meniere's disease

Endolymphatic hydrops is the pathologic feature associated with Meniere's disease. The development of endolymphatic hydrops appears to arise from multifactorial inheritance with alteration of endolymphatic homeostasis. Various factors associated with the phenomenon of hydrops include functional or anatomic obstruction of endolymphatic flow, malabsorption of endolymph, genetic anomalies, vasodilation, allergy, viral infection, and autoimmunity.

The endocrine system, vertigo and balance

Steroid, amine and peptide hormones affect the peripheral vestibular system. Vasopressin hypersensitivity of the endolymphatic sac may be implicated in the pathogenesis of Meniere's disease. Specific vasopressin antagonists will help define the role of vasopressin in Meniere's disease. The modulation of central vestibular pathways by neuroactive steroids may involve effects on gamma-aminobutyric acid-ergic and glutaminergic pathways. The vestibular nuclei also express enzymes that are important in the synthesis of steroids and the modulation of their activity. Steroids mediate both facilitatory and deleterious effects of stress on vestibular compensation. The quality and quantity of stressor that determines the pattern of hormonal output, may be important. Clinical observation suggests that episodic ataxia type 2, a P/Q calcium channelopathy, may be phenotypically modulated by endocrine fluctuations. Steroid hormones may affect the episodic ataxia type 2 phenotype by modulation of voltage-gated calcium channel activity via second messenger systems and ion channel subunit expression. Despite evidence to support the link, the role of the endocrine system in vestibular function and disease is as yet virtually unexplored.