Expression of histamine receptors in the human endolymphatic sac: the molecular rationale for betahistine use in Menieres disease

Ménière's disease and allergy: Epidemiology, pathogenesis, and therapy

The etiology of Ménière's disease (MD) remains controversial. Allergies are potential extrinsic factors that, in conjunction with underlying intrinsic factors, may cause MD. The link between allergies and MD was first described in 1923. For nearly a century, studies have demonstrated a possible link between allergies and MD, even though a causal relationship has not been definitively determined. Previous reviews have mainly focused on clinical epidemiology studies of patients. In this review, we shed light on the association between allergies and MD not only in terms of its epidemiology, but also from an immunology, pathophysiology, and immunotherapy perspective in both patients and animal models. Patients with MD tend to have a high risk of comorbid allergies or an allergy history, showing positive allergy immunology characteristics. Other MD-related diseases, such as migraine, may also interact with allergies. Allergy mediators such as IgE may worsen the symptoms of MD. Deposits of IgE in the vestibular end organs indicate the ability of the inner ear to participate in immune reactions. Allergic challenges can induce vertigo in animals and humans. Anti-allergy therapy plays a positive role in patients with MD and animal models of endolymphatic hydrops.

Examination of betahistine bioavailability in combination with the monoamine oxidase B inhibitor, selegiline, in humans-a non-randomized, single-sequence, two-period titration, open label single-center phase 1 study (PK-BeST)

Background

Betahistine was registered in Europe in the 1970s and approved in more than 80 countries as a first-line treatment for Menière's disease. It has been administered to more than 150 million patients. However, according to a Cochrane systematic review of betahistine and recent meta-analyses, there is insufficient evidence to say whether betahistine has any effect in the currently approved dosages of up to 48 mg/d. A combination with the monoamine oxidase B (MAO-B) inhibitor, selegiline, may increase the bioavailability of betahistine to levels similar to the well-established combination of L-DOPA with carbidopa or benserazide in the treatment of Parkinson's disease. We investigated the effect of selegiline on betahistine pharmacokinetics and the safety of the combination in humans.

Methods

In an investigator-initiated prospective, non-randomized, single-sequence, two-period titration, open label single-center phase 1 study, 15 healthy volunteers received three single oral dosages of betahistine (24, 48, and 96 mg in this sequence with at least 2 days' washout period) without and with selegiline (5 mg/d with a loading period of 7 days). Betahistine serum concentrations were measured over a period of 240 min at eight time points (area under the curve, AUC0-240 min). This trial is registered with EudraCT (2019-002610-39) and ClinicalTrials.gov.

Findings

In all three single betahistine dosages, selegiline increased the betahistine bioavailability about 80- to 100-fold. For instance, the mean (±SD) of the area under curve for betahistine 48 mg alone was 0.64 (+/-0.47) h*ng/mL and for betahistine plus selegiline 53.28 (+/-37.49) h*ng/mL. The half-life time of around 30 min was largely unaffected, except for the 24 mg betahistine dosage. In total, 14 mild adverse events were documented.

Interpretation

This phase 1 trial shows that the MAO-B inhibitor selegiline increases betahistine bioavailability by a factor of about 80 to 100. No safety concerns were detected. Whether the increased bioavailability has an impact on the preventive treatment of Menière's disease, acute vestibular syndrome, or post-BPPV residual dizziness has to be evaluated in placebo-controlled trials.

Clinical trial registration

https://clinicaltrials.gov/study/NCT05938517?intr=betahistine%20and%20selegiline&rank=1, identifier: NCT05938517.

Histamine and Its Receptors in the Mammalian Inner Ear: A Scoping Review

BACKGROUND

Histamine is a widely distributed biogenic amine with multiple biological functions mediated by specific receptors that determine the local effects of histamine. This review aims to summarize the published findings on the expression and functional roles of histamine receptors in the inner ear and to identify potential research hotspots and gaps.

METHODS

A search of the electronic databases PubMed, Web of Science, and OVID EMBASE was performed using the keywords histamine, cochlea*, and inner ear. Of the 181 studies identified, 18 eligible publications were included in the full-text analysis.

RESULTS

All four types of histamine receptors were identified in the mammalian inner ear. The functional studies of histamine in the inner ear were mainly in vitro. Clinical evidence suggests that histamine and its receptors may play a role in Ménière's disease, but the exact mechanism is not fully understood. The effects of histamine on hearing development remain unclear.

CONCLUSIONS

Existing studies have successfully determined the expression of all four histamine receptors in the mammalian inner ear. However, further functional studies are needed to explore the potential of histamine receptors as targets for the treatment of hearing and balance disorders.

Cytokines and Inflammation in Meniere Disease

Meniere disease (MD) is a rare set of conditions associated with the accumulation of endolymph in the cochlear duct and the vestibular labyrinth with a decrease of endocochlear potential. It is considered a chronic inflammatory disorder of the inner ear with a multifactorial origin. The clinical syndrome includes several groups of patients with a core phenotype: sensorineural hearing loss, episodes of vertigo, and tinnitus with a non-predictable course. Genetic factors and the innate immune response seem to play a central role in the pathophysiology of the condition. Autoimmune MD should be diagnosed if a patient fulfills the diagnostic criteria for MD and one of the following autoimmune disorders: autoimmune thyroid disease, psoriasis, autoimmune arthritis, ankylosing spondylitis, or systemic lupus erythematosus. We summarize the evidence to support autoimmune MD as an endophenotype in bilateral MD associated with the allelic variant rs4947296 and nuclear factor-kappa B (NF-κB)-mediated inflammation, the role of cytokines (particularly interleukin-1β and tumor necrosis factor-α) in defining a subset of patients with autoinflammation, and the potential role of cytokines as biomarkers to distinguish between patients with MD and vestibular migraine. Finally, we also introduce a list of potential drugs that could regulate the immune response in MD with potential for repurposing in clinical trials.

Allergy, Immunotherapy, and Alternative Treatments for Dizziness

Allergic reactions may result in central symptoms of dizziness, including nonspecific chronic imbalance, Meniere's disease, and autoimmune inner ear disease. Excepting first-generation antihistamines, and short-term use of steroids, most pharmacotherapies used to treat allergic rhinitis have limited benefit in treating allergically induced or related dizziness. Allergy immunotherapy and/or an elimination diet for diagnosed food allergies have been found to be effective treatments. Individuals diagnosed with autoimmune inner ear disease remain challenging to treat and may require high-dose, long-term steroid treatment, biologics, or immunomodulators for symptom control.

High level of IgE in acute low-tone sensorineural hearing loss: A predictor for recurrence and Meniere Disease transformation

BACKGROUND

Autoimmunity may play an important role in sudden onset sensorineural hearing loss. However, little is known about the relationship between immunoglobulin E (IgE) and acute low-tone sensorinerual hearing loss (ALHL).

OBJECTIVES

To investigate the relationship between IgE level and endolymphatic hydrops and outcomes of ALHL.

METHODS

A total of 242 subjects with sudden onset hearing loss, including 115 with ALHL and 127 with idiopathic sudden sensorineural hearing loss (ISSHL), were included in this study. Peripheral venous blood samples of 242 subjects were collected for detection. Clinical data, IgE level, and distribution of allergens were compared between the ALHL and ISSHL groups. The ALHL group received an electrocochleogram (ECochG) test and a follow-up in the outpatient unit or by telephone to evaluate outcomes.

RESULTS

Compared to the values in the ISSHL group, a significantly younger onset age (42.30±14.33 years old), higher female onset proportion (72/115, 62.61%), increased total IgE level (median: 66.47, interquartile range: 24.56, 180.96, IU/mL) and specific IgE level (median: 9.42, interquartile range: 1.42, 22.23 IU/mL) were noted in the ALHL group. A clear difference in allergen distribution was noted between the ALHL and ISSHL groups (p=.001). Total IgE and specific IgE levels were factors that contributed to the SP/AP ratio in the electrocochleogram (ECochG) (R²=0.413) in ALHL group. Finally, during the follow-up (17.61±3.46 months) for the ALHL group, 37 subjects recurred, and 17 subjects developed Meniere Disease. In the ROC curve for ALHL recurrence, the area under the curve (AUC) of total IgE was 0.709 and that of specific IgE was 0.679. For MD transformation, the AUC of total IgE was 0.736 and that of specific IgE was 0.716.

CONCLUSIONS

High IgE levels correlated with an enhanced SP/AP ratio in ALHL. High IgE levels could be used as a predictor of ALHL recurrence and MD transformation.

Pathophysiological mechanisms at the sources of the endolymphatic hydrops, and possible consequences

The mechanisms of ion exchanges and water fluxes underlying the endolymphatic hydrops phenomenon, remain indeterminate so far. This review intends to reposition the physical environment of the endolymphatic compartment within the inner ear, as well as to recall the molecular effectors present in the membranous labyrinth and that could be at the source of the hydrops.

Evaluation of Serum Immunoreactivity to Common Indigenous Iranian Inhalation and Food Allergens in Patients with Meniere's Disease

Background: A few studies investigated the relationship between allergy and Meniere disease considering complete allergen panel. We aimed to evaluate the serum immunoreactivity in patients with Meniere's disease (MD) compared with healthy people according to common indigenous Iranian inhalation and food allergens.Methods: Thirty-nine patients with MD referred to Rasoul Akram Hospital (Tehran, Iran) were evaluated and compared with a 41 membered control group. A panel of common inhalation and food allergens (using an immunoblotting method), as well as total immunoglobulin E (IgE) level (using the sandwich enzyme-linked immunosorbent assay method), were checked on the patients' serum.Results: The mean total IgE level was 193.85 ± 175.43 IU/ml in the patients with MD and 117.61 ± 138.05 IU/ml in the control group, which was significantly higher than the other subjects in the control group (P = .016). There was a significant difference between the two groups regarding inhalation allergens such as; sweet vernal grass, cultivated rye, cultivated oat, Russian thistle, goosefoot, and rough pigweed (P = .01-0.038). Patients with MD reported more reactive to food allergens such as; rye flour, hazelnut, pepper, citrus mix 2, potato, strawberry, and celery allergens. There was a significant relationship between Meniere and serum immunoreactivity to inhalation and food allergens (both P = .001).Conclusion: Serum total IgE level in patients with MD (in both inhalation and food allergens groups) was higher than the control group, and there was a relationship between MD and immunoreactivity to common indigenous inhalation and food allergens of Iran.

Mast Cells in the Auditory Periphery of Rodents

Mast cells (MCs) are densely granulated cells of myeloid origin and are a part of immune and neuroimmune systems. MCs have been detected in the endolymphatic sac of the inner ear and are suggested to regulate allergic hydrops. However, their existence in the cochlea has never been documented. In this work, we show that MCs are present in the cochleae of C57BL/6 mice and Wistar rats, where they localize in the modiolus, spiral ligament, and stria vascularis. The identity of MCs was confirmed in cochlear cryosections and flat preparations using avidin and antibodies against c-Kit/CD117, chymase, tryptase, and FcεRIα. The number of MCs decreased significantly during postnatal development, resulting in only a few MCs present in the flat preparation of the cochlea of a rat. In addition, exposure to 40 µM cisplatin for 24 h led to a significant reduction in cochlear MCs. The presence of MCs in the cochlea may shed new light on postnatal maturation of the auditory periphery and possible involvement in the ototoxicity of cisplatin. Presented data extend the current knowledge about the physiology and pathology of the auditory periphery. Future functional studies should expand and translate this new basic knowledge to clinics.

Management of peripheral vertigo with antihistamines: New options on the horizon

Vertigo is associated with a wide range of vestibular pathologies. It increasingly affects the elderly, with a high cost to society. Solutions include vestibular suppressants and vestibular rehabilitation, which form the mainstay of therapy. Antihistamines represent the largest class of agents used to combat vestibular vertigo symptoms. Agents targeting the H₁ and H₃ receptors have been in clinical use for several decades as single agents. Nonetheless, effective management of vertigo proves elusive as many treatments largely address only associated symptoms, and with questionable efficacy. Additionally, the primary and limiting side effect of sedation is counterproductive to normal functioning and the natural recovery process occurring via central compensation. To address these issues, the timing of administration of betahistine, the mainstay H₃ antihistamine, can be fine-tuned, while bioavailability is also being improved. Other approaches include antihistamine combination studies, devices, physical therapy and behavioural interventions. Recently demonstrated expression of H₄ receptors in the peripheral vestibular system represents a new potential drug target for treating vestibular disorders. A number of novel selective H₄ antagonists are active in vestibular models in vivo. The preclinical potential of SENS-111 (Seliforant), an oral first-in-class selective H₄ antagonist is the only such molecule to date to be translated into the clinical setting. With an excellent safety profile and notable absence of sedation, encouraging outcomes in an induced vertigo model in healthy volunteers have led to ongoing clinical studies in acute unilateral vestibulopathy, with the hope that H₄ antagonists will offer new effective therapeutic options to patients suffering from vertigo.

Efficacy of betahistine plus cognitive behavioral therapy on residual dizziness after successful canalith repositioning procedure for benign paroxysmal positional vertigo

BACKGROUND

Some patients still complain of residual dizziness after successful canalith repositioning procedure (CRP) for benign paroxysmal positional vertigo (BPPV). Previous study found that compared to the low-dose betahistine, the high-dose betahistine could yield better efficacy in treating residual dizziness. Therefore, this study was conducted to assess whether the addition of cognitive behavioral therapy (CBT) could make low-dose betahistine produce similar results to high-dose betahistine in treating residual dizziness.

METHODS

The recruited patients were randomly assigned to receive either low-dose betahistine (6 mg/time, three times/day) or high-dose betahistine (12 mg/time, three times/day). Patients in the low-dose group also received CBT (twice a week, 1 hour per time). The treatment was continued for 4 weeks. The duration of residual dizziness, 25-item Dizziness Handicap Inventory (DHI), Hamilton Anxiety Rating Scale (HARS), and Hamilton Depression Rating Scale (HDRS) were recorded and analyzed. The duration of residual dizziness and DHI score were the primary outcomes, and the HARS and HDRS scores were the secondary outcomes.

RESULTS

Each group had 50 patients. After treatment, the average DHI scores, HDRS scores, and HARS scores were significantly decreased in both groups. The duration of residual dizziness and average DHI score were nonsignificantly different (P=0.08; P=0.06) between the two groups, although they were lower in the low-dose group. Compared to the high-dose group, the low-dose group had the significantly lower average HDRS score (P=0.007) and HARS score (P=0.02). Meanwhile, four patients in the high-dose group experienced intolerable stomach upset.

CONCLUSION

These results demonstrated that the addition of CBT could make low-dose beta-histine produce similar results to high-dose betahistine in treating residual dizziness. Moreover, the low-dose betahistine plus CBT showed some advantages over high-dose betahistine in relieving depressive and anxiety symptoms and should be further explored.

Betahistine Treatment in a Cat Model of Vestibular Pathology: Pharmacokinetic and Pharmacodynamic Approaches

This study is a pharmacokinetic (PK) and pharmacodynamics (PD) approach using betahistine doses levels in unilateral vestibular neurectomized cats (UVN) comparable to those used in humans for treating patients with Menière's disease. The aim is to investigate for the first time oral betahistine administration (0.2 and 2 mg/kg/day) with plasma concentrations of betahistine and its major metabolite 2-pyridylacetic acid (2-PAA) (N = 9 cats), the time course of posture recovery (N = 13 cats), and the regulation of the enzyme synthesizing histamine (histidine decarboxylase: HDC) in the tuberomammillary nuclei (TMN) of UVN treated animals (N = the same 13 cats plus 4 negative control cats). In addition the effect of co-administration of the lower betahistine dose (0.2 mg/kg/day) and selegiline (1 mg/kg/day), an inhibitor of the monamine oxidase B (MAOBi) implicated in betahistine catabolism was investigated. The PK parameters were the peak concentration (C_max), the time when the maximum concentration is reached (T_max) for both betahistine and 2-PAA and the area under the curve (AUC). The PD approach consisted at quantifying the surface support area, which is a good estimation of posture recovery. The plasma concentration-time-profiles of betahistine and 2-PAA in cats were characterized by early C_max-values followed by a phase of rapid decrease of plasma concentrations and a final long lasting low level of plasma concentrations. Co administration of selegiline and betahistine increased values of C_max and AUC up to 146- and 180-fold, respectively. The lowest dose of betahistine (0.2 mg/kg) has no effects on postural function recovery but induced an acute symptomatic effect characterized by a fast balance improvement (4–6 days). The higher dose (2 mg/kg) and the co-administration treatment induced both this acute effect plus a significant acceleration of the recovery process. The histaminergic activity of the neurons in the TMN was significantly increased under treatment with the 2 mg/kg betahistine daily dose, but not with the lower dose alone or in combination with selegiline. The results show for the first time that faster balance recovery in UVN treated cats is accompanied with high plasma concentrations of betahistine and 2-PAA, and upregulation of HDC immunopositive neurons in the TMN. The higher betahistine dose gives results similar to those obtained with the lower dose when co-administrated with an inhibitor of betahistine metabolism, selegiline. From a clinical point of view, the study provides new perspectives for Menière's disease treatment, regarding the daily betahistine dose that should be necessary for fast and slow metabolizers.

Menière's disease: combined pharmacotherapy with betahistine and the MAO-B inhibitor selegiline-an observational study

OBJECTIVES

Since oral betahistine has a very high first-pass effect (ca. 99%), metabolized by monoamine oxidases (MAO), the benefits of a high-dosage betahistine monotherapy were compared with those of a lower dosage of betahistine in combination with the MAO-B inhibitor (MAO-B) selegiline on the frequency of acute attacks of vertigo in patients with Menière's disease (MD).

METHODS

Thirteen adults aged 40-75 years (mean 58.9 years; six females) had initially been treated with a high dosage of betahistine dihydrochloride for at least 1 year. Under this therapy, all of them had ≤ 1 attack for ≥ 3 months prior to the combination pharmacotherapy. Subsequently, they received 5 mg/day selegiline and the dosage of betahistine was reduced to about one tenth and then individually adjusted to the dosage needed to achieve the same treatment response (≤ 1 per 3 months, observational period of at least 6 months).

RESULTS

The initial dosage for the long-term "titration" of the attacks of vertigo was 9-80 24-mg tablets/day (mean 37.3), i.e. 216-1920 mg/day (mean 895.4 mg/day). After the combination with selegiline, the dosage needed to achieve the same benefit for ≥ 3 months was 3-36 24-mg tablets (mean 8.5), i.e., 72-864 mg/day [mean 204.9 mg/day, p < 0.001 (paired t test)]. One patient transiently stopped the treatment with selegiline, another one reduced the dosage to 2.5 mg/day and the attacks re-occurred after 2-4 weeks. Six out of 13 patients reported transient fullness of the head during the combined treatment; in 2 of them this went away when they switched to 2.5 mg bid. In the longer term (> 9 months), one patient had to increase the selegiline dosage to 5 mg bd, one patient stopped the treatment with selegiline.

CONCLUSIONS

The achievement of the same clinical effect with a significantly lower (about 1/5) dosage of betahistine can be explained by the inhibition of the MAO-B by selegiline leading to higher serum concentrations of betahistine. This approach is in line with recent developments to bypass the first-pass effect of betahistine by transbuccal or intranasal application. Despite the substantial methodological limitations of such an observational study, this combined pharmacotherapy could be an alternative to a high-dosage monotherapy with betahistine of MD.

A network-based method using a random walk with restart algorithm and screening tests to identify novel genes associated with Menière's disease

As a chronic illness derived from hair cells of the inner ear, Menière’s disease (MD) negatively influences the quality of life of individuals and leads to a number of symptoms, such as dizziness, temporary hearing loss, and tinnitus. The complete identification of novel genes related to MD would help elucidate its underlying pathological mechanisms and improve its diagnosis and treatment. In this study, a network-based method was developed to identify novel MD-related genes based on known MD-related genes. A human protein-protein interaction (PPI) network was constructed using the PPI information reported in the STRING database. A classic ranking algorithm, the random walk with restart (RWR) algorithm, was employed to search for novel genes using known genes as seed nodes. To make the identified genes more reliable, a series of screening tests, including a permutation test, an interaction test and an enrichment test, were designed to select essential genes from those obtained by the RWR algorithm. As a result, several inferred genes, such as CD4, NOTCH2 and IL6, were discovered. Finally, a detailed biological analysis was performed on fifteen of the important inferred genes, which indicated their strong associations with MD.

Dizziness in the Outpatient Care Setting

PURPOSE OF REVIEW

This article summarizes an approach to evaluating dizziness for the general neurologist and reviews common and important causes of dizziness and vertigo.

RECENT FINDINGS

Improved methods of diagnosing patients with vertigo and dizziness have been evolving, including additional diagnostic criteria and characterization of some common conditions that cause dizziness (eg, vestibular migraine, benign paroxysmal positional vertigo, chronic subjective dizziness). Other uncommon causes of dizziness (eg, superior canal dehiscence syndrome, episodic ataxia type 2) have also been better clarified. Distinguishing between central and peripheral causes of vertigo can be accomplished reliably through history and examination, but imaging techniques have further added to accuracy. What has not changed is the necessity of obtaining a basic history of the patient's symptoms to narrow the list of possible causes.

SUMMARY

Dizziness and vertigo are extremely common symptoms that also affect function at home and at work. Improvements in the diagnosis and management of the syndromes that cause dizziness and vertigo will enhance patient care and cost efficiencies in a health care system with limited resources. Clinicians who evaluate patients with dizziness will serve their patient population well by continuing to manage patients with well-focused workup and attentive care.

Multiple Targeting Approaches on Histamine H3 Receptor Antagonists

With the very recent market approval of pitolisant (Wakix®), the interest in clinical applications of novel multifunctional histamine H₃ receptor antagonists has clearly increased. Since histamine H₃ receptor antagonists in clinical development have been tested for a variety of different indications, the combination of pharmacological properties in one molecule for improved pharmacological effects and reduced unwanted side-effects is rationally based on the increasing knowledge on the complex neurotransmitter regulations. The polypharmacological approaches on histamine H₃ receptor antagonists on different G-protein coupled receptors, transporters, enzymes as well as on NO-signaling mechanism are described, supported with some lead structures.

Meniere's disease

Meniere's disease (MD) is a disorder of the inner ear that causes vertigo attacks, fluctuating hearing loss, tinnitus and aural fullness. The aetiology of MD is multifactorial. A characteristic sign of MD is endolymphatic hydrops (EH), a disorder in which excessive endolymph accumulates in the inner ear and causes damage to the ganglion cells. In most patients, the clinical symptoms of MD present after considerable accumulation of endolymph has occurred. However, some patients develop symptoms in the early stages of EH. The reason for the variability in the symptomatology is unknown and the relationship between EH and the clinical symptoms of MD requires further study. The diagnosis of MD is based on clinical symptoms but can be complemented with functional inner ear tests, including audiometry, vestibular-evoked myogenic potential testing, caloric testing, electrocochleography or head impulse tests. MRI has been optimized to directly visualize EH in the cochlea, vestibule and semicircular canals, and its use is shifting from the research setting to the clinic. The management of MD is mainly aimed at the relief of acute attacks of vertigo and the prevention of recurrent attacks. Therapeutic options are based on empirical evidence and include the management of risk factors and a conservative approach as the first line of treatment. When medical treatment is unable to suppress vertigo attacks, intratympanic gentamicin therapy or endolymphatic sac decompression surgery is usually considered. This Primer covers the pathophysiology, symptomatology, diagnosis, management, quality of life and prevention of MD.