Immunogold TEM of otoconin 90 and otolin - relevance to mineralization of otoconia, and pathogenesis of benign positional vertigo

Cupulolithiasis: A Critical Reappraisal

Objective

To review the history and pathophysiologic theories for cupulolithiasis and canalith jam in benign paroxysmal positional vertigo.

Data Sources

PubMed, Google Scholar.

Review Methods

Three PubMed and Google Scholar searches were performed, keywords: "cupulolithiasis," "apogeotropic [and] benign," and "canalith jam," resulting in 187 unique full-text articles in English or with English translation. Figures-Labyrinthine photographs were obtained of fresh utricles, ampullae, and cupulae of a 37-day-old mouse.

Conclusions

Freely moving otoconial masses explain most cases (>98%) of benign paroxysmal positional vertigo. Evidence that otoconia adhere strongly or persistently to the cupula is lacking. Apogeotropic nystagmus in the horizontal canal form is often attributed to cupulolithiasis; however, periampullary canalithiasis explains self-limited nystagmus, and reversible canalith jam explains prolonged apogeotropic nystagmus. Treatment-resistant cases can be explained by entrapment of particles in the canals or ampullae, but persistent adherence to the cupula remains theoretical.

Implications for Practice

Apogeotropic nystagmus is usually due to freely moving particles and should not be used in studies of horizontal canal benign paroxysmal positional vertigo as the sole method to define entrapment or cupulolithiasis. Caloric testing and imaging may help differentiate jam from cupulolithiasis. Treatment for apogeotropic benign paroxysmal positional vertigo should include maneuvers that rotate the head through 270° to fully clear the canal of mobile particles, using mastoid vibration or head shaking if entrapment is suspected. Canal plugging can be used for treatment failures.

Association between otolin-1 and benign paroxysmal positional vertigo: A meta-analysis

Background

There is increasing research on the potential of inner ear proteins as serum biomarkers for the diagnosis and prognosis of various inner ear diseases. Among them, benign paroxysmal positional vertigo (BPPV) is the most common vestibular disease. Notably, otolin-1, an inner ear-specific protein, is detectable in the serum of most patients with BPPV patients. Therefore, we found a need to conduct this meta-analysis to determine the relationship between otolin-1 in serum and BPPV.

Methods

This meta-analysis was conducted by searching PubMed, EMBASE, Cochrane Library, Google Scholar, and China Network Knowledge Infrastructure databases for the eligible original studies in Chinese or English published between January 2010 and February 2022. Data were collected and pooled by using the mean differences (MDs) corresponding to 95% confidence intervals (CIs). Heterogeneity among these studies was assessed by using I² statistics and the adopted fixed or random-effect mode thereafter. Egger's and Begg's tests were also used to assess the publication bias.

Results

This meta-analysis included six articles with a total of 585 participants. Serum otolin-1 levels were remarkably increased in patients with BPPV as compared to that in healthy controls (MD: 165.38, 95% CI: 110.13-220.64, p < 0.00001). However, Egger's and Begg's tests have indicated no publication bias, and the results were reliable based on the sensitivity analysis.

Conclusion

This meta-analysis indicated that there is a higher serum level of otolin-1 in patients with BPPV than in healthy controls. Therefore, otolin-1 may serve as a biomarker for the onset of BPPV.

The Role of Intrinsically Disordered Proteins in Liquid–Liquid Phase Separation during Calcium Carbonate Biomineralization

Some animal organs contain mineralized tissues. These so-called hard tissues are mostly deposits of calcium salts, usually in the form of calcium phosphate or calcium carbonate. Examples of this include fish otoliths and mammalian otoconia, which are found in the inner ear, and they are an essential part of the sensory system that maintains body balance. The composition of ear stones is quite well known, but the role of individual components in the nucleation and growth of these biominerals is enigmatic. It is sure that intrinsically disordered proteins (IDPs) play an important role in this aspect. They have an impact on the shape and size of otoliths. It seems probable that IDPs, with their inherent ability to phase separate, also play a role in nucleation processes. This review discusses the major theories on the mechanisms of biomineral nucleation with a focus on the importance of protein-driven liquid–liquid phase separation (LLPS). It also presents the current understanding of the role of IDPs in the formation of calcium carbonate biominerals and predicts their potential ability to drive LLPS.

Second harmonic generation microscopy of otoconia

The origin of second harmonic generation (SHG) signal in otoconia was investigated. SHG signal intensity from otoconia was compared to pure calcite crystals, given calcite is the primary component of otoconia and is known to emit surface SHG. The SHG intensity from calcite was found to be ∼41× weaker than the SHG intensity from otoconia signifying that the SHG signal from otoconia is likely generated from the organic matrix. Furthermore, the SHG intensity from otoconia increased when treated with a chelating agent known to dissolve calcite which confirms that calcite is not the source of SHG. Additionally, polarization-resolved SHG microscopy imaging revealed that the arrangement of the SHG emitters is radial and can form highly ordered domains.

N'-terminal- and Ca2+-induced stabilization of high-order oligomers of full-length Danio rerio and Homo sapiens otolin-1

Otolin-1 is a C1q family member and a major component of the organic matrix of fish otoliths and human otoconia. To date, the protein molecular properties have not been characterized. In this work, we describe biochemical characterization and comparative studies on saccular-specific otolin-1 derived from Danio rerio and Homo sapiens. Due to the low abundance of proteins in the otoconial matrix, we developed a production and purification method for both recombinant homologues of otolin-1. Danio rerio and Homo sapiens otolin-1 forms higher-order oligomers that can be partially disrupted under reducing conditions. The presence of Ca²⁺ stabilizes the oligomers and significantly increases the thermal stability of the proteins. Despite the high sequence coverage, the oligomerization of Danio rerio otolin-1 is more affected by the reducing conditions and presence of Ca²⁺ than the human homologue. The results show differences in molecular behaviour, which may be reflected in Danio rerio and Homo sapiens otolin-1 role in otolith and otoconia formation.

High Serum Levels of Otolin-1 in Patients With Benign Paroxysmal Positional Vertigo Predict Recurrence

Background

Otolin-1 is an inner ear-specific protein that is exclusively expressed in otoconia and vestibule and cochlea cells. Recent investigations reported that otolin-1 can cross the blood-labyrinthine barrier and that the levels in serum well-reflected otolith status. Serum otolin-1 levels in patients with benign paroxysmal positional vertigo (BPPV) are significantly elevated compared with healthy controls. We aimed to explore whether otolin-1 can also serve as a biomarker for predicting BPPV recurrence.

Method

Patients at our institution with new-onset of idiopathic BPPV between May, 2017 and May, 2018 were recruited and followed up for 2 years. All demographic data of the patients were collected, and serum levels of otolin-1 and other laboratory indicators were measured and compared according to the recurrence status.

Results

A total of 74 patients, who met the inclusion criteria were enrolled in this study, of which 27 (36.5%) patients had suffered one or more episodes of recurrence after undergoing canal repositioning treatments during the study. The serum levels of otolin-1 in patients with recurrent BPPV were significantly higher than those in patients without recurrent BPPV (363.9 vs. 309.8 pg/ml, p = 0.001). In multivariate analysis comparing the second to fourth quartiles (Q2–Q4) against the first quartile (Q1) of otolin-1, the level of otolin-1 in Q4 could significantly predict BPPV recurrence, and the odds ratio (OR) was elevated by approximately 812% (OR = 9.12; 95% confidence interval [CI]: 1.44–57.9; p = 0.019).

Conclusion

High serum levels of otolin-1 were associated with an increased risk of BPPV recurrence, and further investigation is required to confirm this association and clarify the exact mechanism.

Climatic Variations as Indicators of Vitamin D Levels and Benign Paroxysmal Positional Vertigo

Objective

To investigate the possible correlation between benign paroxysmal positional vertigo (BPPV), seasonality, and climatic variations as indicators of vitamin D deficiency, since otoconia are calcium carbonate crystals.

Methods

This is a study of patients who received the diagnosis of BPPV from September 2015 to August 2019. Gender, age, and month of diagnosis were factors recorded and analyzed. The cut-off age of 50 years is used to include osteoporotic patients and postmenopausal women. Meteorological and climatic data of latitude, temperature, sunshine hours, humidity, precipitation, wind force, atmospheric pressure, and horizontal solar irradiance were collected.

Results

Four hundred and eighty-five patients were included in the study; 206 were male (42%) and 279 were female (58%). The mean age was 57.8±15.4 and 54.9±13.9, respectively; 192 patients were ≤50 years old (121 female and 71 male) and 293 patients were over 50 years old (135 male and 158 female). A statistical significance in seasonal variation during autumn months was demonstrated (p-value= 5.2 e-05, z-statistic: 9.8164). There was no statistical correlation between the median number of BPPV patients and the median sunshine hours per month, horizontal solar irradiance, or other climatic variables.

Conclusions

Our study demonstrates seasonality in BPPV patients in Greece but no correlation between BPPV and climatic variations as a proxy for Vitamin-D levels was documented.

Review of Post-embedding Immunogold Methods for the Study of Neuronal Structures

The post-embedding immunogold (PI) technique for immunolabeling of neuronal tissues utilizing standard thin-section transmission electron microscopy (TEM) continues to be a prime method for understanding the functional localization of key proteins in neuronal function. Its main advantages over other immunolabeling methods for thin-section TEM are (1) fairly accurate and quantifiable localization of proteins in cells; (2) double-labeling of sections using two gold particle sizes; and (3) the ability to perform multiple labeling for different proteins by using adjacent sections. Here we first review in detail a common method for PI of neuronal tissues. This method has two major parts. First, we describe the freeze-substitution embedding method: cryoprotected tissue is frozen in liquid propane via plunge-freezing, and is placed in a freeze-substitution instrument in which the tissue is embedded in Lowicryl at low temperatures. We highlight important aspects of freeze-substitution embedding. Then we outline how thin sections of embedded tissue on grids are labeled with a primary antibody and a secondary gold particle-conjugated antibody, and the particular problems encountered in TEM of PI-labeled sections. In the Discussion, we compare our method both to earlier PI methods and to more recent PI methods used by other laboratories. We also compare TEM immunolabeling using PI vs. various pre-embedding immunolabeling methods, especially relating to neuronal tissue.

Otoconia Structure After Short- and Long-Duration Exposure to Altered Gravity

Vertebrates use weight-lending otoconia in the inner ear otolith organs to enable detection of their translation during self or imposed movements and a change in their orientation with respect to gravity. In spaceflight, otoconia are near weightless. It has been hypothesized that otoconia undergo structural remodeling after exposure to weightlessness to restore normal sensation. A structural remodeling is reasoned to occur for hypergravity but in the opposite sense. We explored these hypotheses in several strains of mice within a Biospecimen Sharing Program in separate space- and ground-based projects. Mice were housed 90 days on the International Space Station, 13 days on two Shuttle Orbiter missions, or exposed to 90 days of hindlimb unloading or net 2.38 g via centrifugation. Corresponding flight habitat and standard cage vivarium controls were used. Utricular otoliths were visually analyzed using scanning electron microscopy and in selected samples before and after focused ion beam (FIB) milling. Results suggest a possible mass addition to the otoconia outer shell might occur after exposure to longer-duration spaceflight, but not short ones or hindlimb unloading. A destructive process is clearly seen after centrifugation: an ablation or thinning of the outer shell and cavitation of the inner core. This study provides a purely descriptive account of otoconia remodeling after exposures to altered gravity. The mechanism(s) underlying these processes must be identified and quantitatively validated to develop countermeasures to altered gravity levels during exploration missions.

Serum otolin-1 as a biomarker for benign paroxysmal positional vertigo: a case-control study

OBJECTIVES

This study aimed to evaluate serum otolin-1 levels in patients with benign paroxysmal positional vertigo and to compare these levels with healthy individuals.

METHOD

This was a case-control study. After obtaining institutional ethical committee clearance, the serum level of otolin-1 was calculated in adult individuals (18-75 years old) who were divided into group 1 (patients presenting with benign paroxysmal positional vertigo) and group 2 (healthy patients without benign paroxysmal positional vertigo as the control group). Data analysis was carried out to compare the serum levels in the cases and controls. A p-value less than 0.05 was considered significant.

RESULTS

A total of 70 age-matched individuals (cases, n = 40; controls, n = 30) were included in the study. The mean serum level of otolin-1 was 636.8 pg/ml (range, 259-981 pg/ml) in the group of patients with benign paroxysmal positional vertigo and 236.2 pg/ml (range, 189-370 pg/ml) in the control group. The difference was statistically significant (p = 0.0000).

CONCLUSION

The serum levels of otolin-1 in patients with benign paroxysmal positional vertigo are significantly higher compared with individuals without benign paroxysmal positional vertigo.

The Association Between Serum Vitamin D Levels and Benign Paroxysmal Positional Vertigo

OBJECTIVE

This study aimed to evaluate the association between serum vitamin D levels and benign paroxysmal positional vertigo (BPPV).

PARTICIPANTS AND METHODS

This prospective study consisted of 137 participants. There were 69 participants in the BPPV group compared with 68 healthy participants. Blood samples from both groups were collected from all participants to assess serum vitamin D levels.

RESULTS

No significant difference in demographic data between BPPV and control groups. The results showed that the mean serum vitamin D levels in the BPPV group was lower than that of the control group (P value = .001). Among BPPV participants, there was no statistically significant difference between mean serum vitamin D levels of participants with recurrent BPPV, and that of newly diagnosed BPPV participants (P value = .313).

CONCLUSION

A statistically significant association between lower mean serum vitamin D levels in the BPPV group compared with that of the control group. Therefore, low serum vitamin D levels may be one of the risk factors for BPPV.

Causes and treatment of idiopathic benign paroxysmal positional vertigo based on endocrinological and other metabolic factors

The genesis of the Benign Paroxysmal Positional Vertigo (BPPV) seems to be related to some metabolic factors. These factors, such as vitamin D, glucocorticoids, and even thyroid and growth hormones, can affect bone metabolism and the mineralization of otoconia. It also seems to link to factors related to aging or nutritional habits. Besides, since the incidence of BPPV is quantitatively higher in women than in men, female sex steroids could be associated with this process. It could be useful to understand how these factors act in otoconial mineralization if we want to develop treatments aimed at preventing or delaying BPPV recurrences. In this review, we will analyze the role of these metabolic and hormonal factors in otoconial mineralization and in the treatment of BPPV.

Nanostructure of mouse otoconia

Mammalian otoconia of the inner ear vestibular apparatus are calcium carbonate-containing mineralized structures critical for maintaining balance and detecting linear acceleration. The mineral phase of otoconia is calcite, which coherently diffracts X-rays much like a single-crystal. Otoconia contain osteopontin (OPN), a mineral-binding protein influencing mineralization processes in bones, teeth and avian eggshells, for example, and in pathologic mineral deposits. Here we describe mineral nanostructure and the distribution of OPN in mouse otoconia. Scanning electron microscopy and atomic force microscopy of intact and cleaved mouse otoconia revealed an internal nanostructure (~50 nm). Transmission electron microscopy and electron tomography of focused ion beam-prepared sections of otoconia confirmed this mineral nanostructure, and identified even smaller (~10 nm) nanograin dimensions. X-ray diffraction of mature otoconia (8-day-old mice) showed crystallite size in a similar range (73 nm and smaller). Raman and X-ray absorption spectroscopy - both methods being sensitive to the detection of crystalline and amorphous forms in the sample - showed no evidence of amorphous calcium carbonate in these mature otoconia. Scanning and transmission electron microscopy combined with colloidal-gold immunolabeling for OPN revealed that this protein was located at the surface of the otoconia, correlating with a site where surface nanostructure was observed. OPN addition to calcite growing in vitro produced similar surface nanostructure. These findings provide details on the composition and nanostructure of mammalian otoconia, and suggest that while OPN may influence surface rounding and surface nanostructure in otoconia, other incorporated proteins (also possibly including OPN) likely participate in creating internal nanostructure.

[Current aspects of vertigo and dizziness in advanced age]

Vertigo and dizziness in advanced age are common complaints in daily clinical practice. The otorhinolaryngologist holds a central position in the differential diagnostic clarification. Age-related disorders (e.g. benign positional vertigo, presbyvestibulopathy, otholith functional disorders) arise due to a physiological, individually distinct and objectively detectable reduction in the sensitivity of sensory and extrasensory elements of the vestibular system. They may reach pathological significance if these dysfunctions affect the physical and emotional well-being (e.g. gait disturbances and falls with subsequent morbidity). Disorders accompanying aging (e.g. neurological, cardiovascular or psychiatric) can occur simultaneously with age-related changes in sensory function. The identification, especially with respect to the risk of falling in older people and the development of individual therapeutic strategies is an interdisciplinary task. Besides a causative therapy, strength, coordination and balance training contribute to the treatment of equilibrium disorders and falls from the perspective of evidence-based medicine.

A Relationship Between Blood Levels of Otolin-1 and Vitamin D

OBJECTIVE

Low vitamin D levels have been associated with and could play a role in the pathogenesis of idiopathic benign paroxysmal positional vertigo (iBPPV). Since otoconia degeneration contributes to iBPPV and a lack of vitamin D may impact otoconia structure and integrity, we proposed a negative association between vitamin D levels and levels of a proposed circulatory biomarker for otolithic degeneration, otolin-1.

STUDY DESIGN

Cross-sectional clinical study.

SETTING

Clinical research center.

PATIENTS

Seventy-nine men and women ranging in age from 22 to 95 years old without known vertigo.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

Blood levels of 25-OH vitamin D and otolin-1.

RESULTS

Previously, we had reported higher otolin-1 levels in older age groups. The majority of the subjects (83%) had vitamin D levels that were below 40 ng/ml. Vitamin D level was lowest in the young and increased with age before declining in subjects 70 years of age and older (p = 0.005). There was a negative correlation between vitamin D and otolin-1 levels of subjects over 70 (r = -0.36, p = 0.036).

CONCLUSION

Our results demonstrate a relationship between vitamin D and otolin-1. The majority of our subjects had abnormally low vitamin D levels, but only those over 70 years of age showed a negative correlation with high otolin-1 levels. We postulate that a seasonal drop in vitamin D may not be sufficient for otoconia fragmentation and ultimately iBPPV, rather, chronically low vitamin D maybe required to induce otoconia degeneration.

Otopetrin-2 Immunolocalization in the Human Macula Utricle

BACKGROUND

In the present study, we investigated the localization of otopetrin-2-a member of the otopetrin family that encodes proton-selective ion channels-in the human macula utricle using immunohistochemistry.

METHODS

Macula utricle were acquired at surgery from patients who required transmastoid labyrinthectomy for intractable vertigo due to Meniere's disease (MD; n = 3) and/or vestibular drops attacks (VDA; n = 2) and from temporal bones (n = 2) acquired at autopsy from individuals with no balance disorders. Immunofluorescence staining with otopetrin-2 (rabbit affinity purified polyclonal antibody) and GFAP (mouse monoclonal antibody) to identify vestibular supporting cells was made in formalin fixed cryostat sections or whole microdissected utricle (for flat mount preparations). Secondary antibodies against rabbit and mouse were used for the identification of both proteins. Digital fluorescent images were obtained using a high-resolution laser confocal microscope.

RESULTS

Using cryostat sections and flat mount preparations otopetrin-2 immunofluorescence was seen as punctated signal throughout the supporting cells cytoplasm. GFAP immunofluorescence was present in the supporting cell cytoplasm. The distribution of otopetrin-2 was similar in the macula utricle obtained from MD, VDA, or autopsy normative patients.

CONCLUSIONS

Otopetrin-2 was localized in supporting cells in a similar fashion that otopetrin-1 previously reported in the mouse macula utricle. The differential expression of otopetrin-2 in the supporting cells of the human macula utricle suggest an important role in the vestibular sensory periphery homeostasis and otolith maintenance.

Benign paroxysmal positional vertigo in the elderly: current insights

Balance disorders, unsteadiness, dizziness and vertigo in the elderly are a significant health problem, needing appropriate treatment. One third of elderly patients with vertigo were diagnosed with benign paroxysmal positional vertigo (BPPV), the most common cause of dizziness in both primary care specialist Neurology and Ear Nose Throat settings. BPPV presents a specific paroxysmal positional nystagmus which can be obtained using the appropriate diagnostic positional test and can be treated effectively using specific therapeutic maneuvers. This review presents current insights into the diagnostic, pathogenetic and therapeutic aspects of BPPV in the elderly. BPPV in older patients does not differ significantly from BPPV in younger patients, with regard to pathogenesis, diagnosis and treatment. However, in older patients, its prevalence is higher and it responds less effectively to treatment, having a tendency for recurrence. Specific issues which should be considered in the elderly are: 1) difficulty in obtaining an accurate history; 2) difficulty in performing the diagnostic and therapeutic maneuvers, which should be executed with slow and gentle movements and extremely cautiously to avoid any vascular or orthopedic complications; and 3) the relation between BPPV and falls.

Morphology of the utricular otolith organ in the toadfish, Opsanus tau

The utricle provides the vestibular reflex pathways with the sensory codes of inertial acceleration of self-motion and head orientation with respect to gravity to control balance and equilibrium. Here we present an anatomical description of this structure in the adult oyster toadfish and establish a morphological basis for interpretation of subsequent functional studies. Light, scanning, and transmission electron microscopy techniques were applied to visualize the sensory epithelium at varying levels of detail, its neural innervation and its synaptic organization. Scanning electron microscopy was used to visualize otolith mass and morphological polarization patterns of hair cells. Afferent nerve fibers were visualized following labeling with biocytin, and light microscope images were used to make three-dimensional (3-D) reconstructions of individual labeled afferents to identify dendritic morphology with respect to epithelial location. Transmission electron micrographs were compiled to create a serial 3-D reconstruction of a labeled afferent over a segment of its dendritic field and to examine the cell-afferent synaptic contacts. Major observations are: a well-defined striola, medial and lateral extra-striolar regions with a zonal organization of hair bundles; prominent lacinia projecting laterally; dependence of hair cell density on macular location; narrow afferent dendritic fields that follow the hair bundle polarization; synaptic specializations issued by afferents are typically directed towards a limited number of 7-13 hair cells, but larger dendritic fields in the medial extra-striola can be associated with > 20 hair cells also; and hair cell synaptic bodies can be confined to only an individual afferent or can synapse upon several afferents.

Age-Related Increase in Blood Levels of Otolin-1 in Humans

OBJECTIVE

To test the hypothesis that age-related demineralization of otoconia will result in an age-related increase in blood levels of otoconia matrix protein, otolin-1.

STUDY DESIGN

Cross-sectional observational clinical trial.

SETTING

Clinical research center.

PATIENTS

Seventy nine men and women ranging in age from 22 to 95 years old.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

Blood levels of otolin-1 in relation to age.

RESULTS

Levels of otolin-1 of subjects divided into four age groups (1: 20-30 [n = 20], 2: 50-65 [n = 20], 3: 66-80 [n = 20], 4: 81-95 [n = 19] years old) demonstrated an increasing trend with age. The difference between otolin levels of groups 2 and 3, as well as, (p = 0.04) and 2 and 4 (p = 0.031) were statistically significant, but there was no significant difference between the two oldest groups.

CONCLUSIONS

Otolin-1 blood levels are significantly higher in patients older than 65 years of age. This is consistent with previous scanning electron microscopy findings of age-related otoconia degeneration and increased prevalence of benign paroxysmal positional vertigo (BPPV) with age. Normative data provided here can serve as important reference values against which levels from BPPV patients can be compared with further evaluate otolin-1 as a circulatory biomarker for otoconia degeneration.

Idiopathic benign paroxysmal positional vertigo in the elderly: a long-term follow-up study

BACKGROUND

Benign paroxysmal positional vertigo (BPPV) is the most common cause of peripheral-type vertigo in the elderly. While some studies have investigated BPPV among the elderly, no study has focused on the isolated idiopathic BPPV (iBPPV) in the elderly.

AIMS

To investigate the clinical features and recurrence rate in elderly patients diagnosed with iBPPV.

METHODS

The authors prospectively reviewed the medical records of 627 patients diagnosed with BPPV, and a total of 370 patients fulfilled the inclusion criteria. The subjects were divided into two groups by age (experimental group ≥65 years and control group 17-64 years), and the gender, numbers of canalith reposition maneuver (CRM) for successful treatment, time elapsed from onset of symptoms to clinic visit, the affected semicircular canal, and the 1- and 5-year recurrence proportion were analyzed.

RESULTS

The gender, numbers of CRM for successful treatment, affected semicircular canal, and the 1- and 5-year recurrence proportion showed no statistically significant difference between two groups (p > 0.05). The only exception was the experimental group which took a longer duration from manifestation of symptoms to hospital visit than control group (student's t test, p = 0.021).

DISCUSSION

Several previous studies report that the elderly with iBPPV shows more protracted clinical course and much higher recurrence rate than younger adult. Unlike those reports, our study showed no significant differences about the clinical features and recurrence rate between age groups.

CONCLUSION

The elderly with iBPPV could be treated as effective as general population.

Amorphous polyphosphate, a smart bioinspired nano-/bio-material for bone and cartilage regeneration: towards a new paradigm in tissue engineering

Physiological amorphous polyphosphate nano/micro-particles, injectable and implantable, attract and stimulate MSCs into implants for tissue regeneration.

The Understanding of the Metazoan Skeletal System, Based on the Initial Discoveries with Siliceous and Calcareous Sponges

Initiated by studies on the mechanism of formation of the skeletons of the evolutionary oldest still extant multicellular animals, the sponges (phylum Porifera) have provided new insights into the mechanism of formation of the Ca-phosphate/hydroxyapatite skeleton of vertebrate bone. Studies on the formation of the biomineral skeleton of sponges revealed that both the formation of the inorganic siliceous skeletons (sponges of the class of Hexactinellida and Demospongiae) and of the calcareous skeletons (class of Calcarea) is mediated by enzymes (silicatein: polymerization of biosilica; and carbonic anhydrase: deposition of Ca-carbonate). Detailed studies of the initial mineralization steps in human bone-forming cells showed that this process is also controlled by enzymes, starting with the deposition of Ca-carbonate bio-seeds, mediated by carbonic anhydrases-II and -IX, followed by non-enzymatic transformation of the formed amorphous Ca-carbonate deposits into amorphous Ca-phosphate and finally hydroxyapatite crystals. The required phosphate is provided by enzymatic (alkaline phosphatase-mediated) degradation of an inorganic polymer, polyphosphate (polyP), which also acts as a donor for chemically useful energy in this process. These new discoveries allow the development of novel biomimetic strategies for treatment of bone diseases and defects.

Low-intensity ultrasound activates vestibular otolith organs through acoustic radiation force

The present study examined the efficacy of 5 MHz low-intensity focused ultrasound (LiFU) as a stimulus to remotely activate inner ear vestibular otolith organs. The otolith organs are the primary sensory apparati responsible for detecting orientation of the head relative to gravity and linear acceleration in three-dimensional space. These organs also respond to loud sounds and vibration of the temporal bone. The oyster toadfish, Opsanus tau, was used to facilitate unobstructed acoustic access to the otolith organs in vivo. Single-unit responses to amplitude-modulated LiFU were recorded in afferent neurons identified as innervating the utricle or the saccule. Neural responses were equivalent to direct mechanical stimulation, and arose from the nonlinear acoustic radiation force acting on the otolithic mass. The magnitude of the acoustic radiation force acting on the otolith was measured ex vivo. Results demonstrate that LiFU stimuli can be tuned to mimic directional forces occurring naturally during physiological movements of the head, loud air conducted sound, or bone conducted vibration.

Clinical characteristics and treatment outcomes for benign paroxysmal positional vertigo comorbid with hypertension

CONCLUSIONS

Patients with BPPV comorbid with hypertension (h-BPPV) tend to receive a delayed diagnosis of BPPV. Comorbidity with hypertension did not influence the efficacy of the repositioning maneuver; however, comorbidity with hypertension was associated with an increased recurrence rate of BPPV.

OBJECTIVES

To determine the clinical characteristics and outcomes of h-BPPV, as well as the clinical differences between h-BPPV and idiopathic BPPV (i-BPPV).

METHODS

The authors reviewed the medical records of 41 consecutive patients with h-BPPV (the h-BPPV group) from March to December 2014 and 47 patients with i-BPPV (the i-BPPV group) during the same period.

RESULTS

There were no significant differences in age, sex ratio, or the affected side between the h-BPPV and i-BPPV groups. The proportion of patients reporting an initial episode of positional vertigo was significantly lower in the h-BPPV group (51.22% vs 74.47%; p = .024). Patients in the h-BPPV group reported a longer median episode duration than did those in the i-BPPV group (60 days vs 15 days; p = .017). The results of treatment using repositioning maneuvers were similar between the two groups. At follow-up, 13 patients in the h-BPPV group were diagnosed with recurrent BPPV compared with six in the i-BPPV group (p = .031).

The sense of balance in humans: Structural features of otoconia and their response to linear acceleration

We explored the functional role of individual otoconia within the otolith system of mammalians responsible for the detection of linear accelerations and head tilts in relation to the gravity vector. Details of the inner structure and the shape of intact human and artificial otoconia were studied using environmental scanning electron microscopy (ESEM), including decalcification by ethylenediaminetetraacetic acid (EDTA) to discriminate local calcium carbonate density. Considerable differences between the rhombohedral faces of human and artificial otoconia already indicate that the inner architecture of otoconia is not consistent with the point group -3m. This is clearly confirmed by decalcified otoconia specimen which are characterized by a non-centrosymmetric volume distribution of the compact 3+3 branches. This structural evidence for asymmetric mass distribution was further supported by light microscopy in combination with a high speed camera showing the movement of single otoconia specimen (artificial specimen) under gravitational influence within a viscous medium (artificial endolymph). Moreover, the response of otoconia to linear acceleration forces was investigated by particle dynamics simulations. Both, time-resolved microscopy and computer simulations of otoconia acceleration show that the dislocation of otoconia include significant rotational movement stemming from density asymmetry. Based on these findings, we suggest an otolith membrane expansion/stiffening mechanism for enhanced response to linear acceleration transmitted to the vestibular hair cells.

Biocalcite and Carbonic Acid Activators

Based on evolution of biomineralizing systems and energetic considerations, there is now compelling evidence that enzymes play a driving role in the formation of the inorganic skeletons from the simplest animals, the sponges, up to humans. Focusing on skeletons based on calcium minerals, the principle enzymes involved are the carbonic anhydrase (formation of the calcium carbonate-based skeletons of many invertebrates like the calcareous sponges, as well as deposition of the calcium carbonate bioseeds during human bone formation) and the alkaline phosphatase (providing the phosphate for bone calcium phosphate-hydroxyapatite formation). These two enzymes, both being involved in human bone formation, open novel not yet exploited targets for pharmacological intervention of human bone diseases like osteoporosis, using compounds that act as activators of these enzymes. This chapter focuses on carbonic anhydrases of biomedical interest and the search for potential activators of these enzymes, was well as the interplay between carbonic anhydrase-mediated calcium carbonate bioseed synthesis and metabolism of energy-rich inorganic polyphosphates. Beyond that, the combination of the two metabolic products, calcium carbonate and calcium-polyphosphate, if applied in an amorphous form, turned out to provide the basis for a new generation of scaffold materials for bone tissue engineering and repair that are, for the first time, morphogenetically active.

Spatiotemporal differences in otoconial gene expression

Otoconia are minute biocrystals composed of glycoproteins, proteoglycans, and CaCO₃ , and are indispensable for sensory processing in the utricle and saccule. Otoconia abnormalities and degeneration can cause or facilitate crystal dislocation to the ampulla, leading to vertigo and imbalance in humans. In order to better understand the molecular mechanism controlling otoconia formation and maintenance, we have examined the spatial and temporal expression differences of otoconial genes in the mouse inner ear at developmental, mature and aging stages using whole transcriptome sequencing (RNA-Seq) and quantitative RT-PCR. We show that the expression levels of most otoconial genes are much higher in the utricle and saccule compared with other inner ear tissues before postnatal stages in C57Bl/6J mice, and the expression of a few of these genes is restricted to the embryonic utricle and saccule. After the early postnatal stages, expression of all otoconial genes in the utricle and saccule is drastically reduced, while a few genes gain expression dominance in the aging ampulla, indicating a potential for ectopic debris formation in the latter tissue at old ages. The data suggest that the expression of otoconial genes is tightly regulated spatially and temporally during developmental stages and can become unregulated at aging stages. Birth Defects Research (Part A) 106:613-625, 2016. © 2016 Wiley Periodicals, Inc.

Preliminary Report on the Investigation of the Association Between BPPV and Osteoporosis Using Biomarkers

OBJECTIVE

To test the hypothesis that levels of a BPPV biomarker, otolin-1, correlate with those of osteoporosis markers, aminoterminal propeptide of protocollagen type I (P1NP), and aminoterminal telopeptides of collagen (NTX), thus further supporting a link between the two diseases.

STUDY DESIGN

Prospective pilot clinical trial (Level of Evidence: 2b).

PATIENTS

Postmenopausal women with BPPV.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

Serum levels of otolin-1, P1NP, NTX, vitamin D, and calcium were examined in relation to each other, age, and DEXA scan T-scores.

RESULTS

There was a strong, negative correlation between T-scores and otolin-1 levels. Although P1NP and NTX levels were strongly correlated, neither had statistical correlations with otolin-1.

CONCLUSIONS

Despite a strong correlation between DEXA scan results and otolin-1 levels, there were no significant correlations between otolin-1 and P1NP or NTX. This suggests that the association between osteoporosis and BPPV is complex, but not likely to be causal. Although more work is needed to elucidate these relationships, this preliminary finding has important practical implications for BPPV in that proactive management of osteoporosis, per se, would not be expected to have benefits in management of BPPV.

A Geriatric Perspective on Benign Paroxysmal Positional Vertigo

Benign paroxysmal positional vertigo (BPPV) is the most common cause of vertigo in older adults. Beyond the unpleasant sensation of vertigo, BPPV also negatively affects older adults' gait and balance and increases their risk of falling. As such it has a profound effect on function, independence, and quality of life. Otoconia are the inner ear structures that help detect horizontal and vertical movements. Aging contributes to the fragmentation of otoconia, whose displacement into the semicircular, most commonly posterior canals, can produce rotatory movement sensations with head movement. BPPV is more commonly idiopathic in older adults than in younger individuals, can present atypically, and has a more-protracted course and higher risk of recurrence. Medications such as meclizine that are commonly prescribed for BPPV can be associated with significant side effects. Dix-Hallpike and Head Roll tests can generally identify the involved canal. Symptoms resolve as otoconia fragments dissolve into the endolymph, but appropriate canalith repositioning (e.g., Epley maneuver) can expedite recovery and reduce the burden of this disorder. Observations suggesting an association between idiopathic BPPV and vitamin D deficiency and osteoporosis indicate that BPPV may share risk factors with other common geriatric conditions, which highlights the importance of moving beyond purely otological considerations and addressing the needs of older adults with vertigo through a systems-based multidisciplinary approach.

Otolith tethering in the zebrafish otic vesicle requires Otogelin and α-Tectorin

Otoliths are biomineralised structures important for balance and hearing in fish. Their counterparts in the mammalian inner ear, otoconia, have a primarily vestibular function. Otoliths and otoconia form over sensory maculae and are attached to the otolithic membrane, a gelatinous extracellular matrix that provides a physical coupling between the otolith and the underlying sensory epithelium. In this study, we have identified two proteins required for otolith tethering in the zebrafish ear, and propose that there are at least two stages to this process: seeding and maintenance. The initial seeding step, in which otolith precursor particles tether directly to the tips of hair cell kinocilia, fails to occur in the einstein (eis) mutant. The gene disrupted in eis is otogelin (otog); mutations in the human OTOG gene have recently been identified as causative for deafness and vestibular dysfunction (DFNB18B). At later larval stages, maintenance of otolith tethering to the saccular macula is dependent on tectorin alpha (tecta) function, which is disrupted in the rolling stones (rst) mutant. α-Tectorin (Tecta) is a major constituent of the tectorial membrane in the mammalian cochlea. Mutations in the human TECTA gene can cause either dominant (DFNA8/12) or recessive (DFNB21) forms of deafness. Our findings indicate that the composition of extracellular otic membranes is highly conserved between mammals and fish, reinforcing the view that the zebrafish is an excellent model system for the study of deafness and vestibular disease.

Inner Ear Protein as a Biomarker in Circulation?

Serum biomarkers detect the earliest events in disease, monitor management, and provide insight into disease pathogenesis. At this time, there are no biomarkers available for otologic disorders. Otolin-1 is a scaffolding protein exclusively expressed in otoconia and cells of the vestibule and the cochlea; therefore, it may be a biomarker candidate for assessing the health of the inner ear. As a proof of concept, we used serum samples from controls without otologic history and subjects with a history of benign paroxysmal positional vertigo (BPPV), performed enzyme-linked immunosorbent assay for otolin-1, and measured the optical density of the substrate. Otolin-1 was detectable and quantifiable in all subjects, indicating that this inner ear protein crosses the blood-labyrinthine barrier. Furthermore, subjects with BPPV had significantly higher levels, with about one-third being above the control range. This promising preliminary result suggests that inner ear–specific proteins have the potential to serve as biomarkers for otologic disease processes.

Principles of calcite dissolution in human and artificial otoconia

Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (calcite gelatin nanocomposits) and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV.

Benign Paroxysmal Positional Vertigo: An Integrated Perspective

Benign paroxysmal positional vertigo (BPPV), the most common cause of dizziness, occurs in all age groups. It presents with vertigo on head movement, but in older patients presentation may be typical and thus accounting for a low recognition rate in the primary care setting. It may be recurrent in up to 50% of cases. BPPV is associated with displacement of fragments of utricular otoconia into the semicircular canals, most commonly the posterior semicircular canal. Otoconia are composed of otoconin and otolin forming the organic matrix on which calcium carbonate mineralizes. Otoconia may fragment with trauma, age, or changes in the physiology of endolymph (e.g., pH and calcium concentration). Presentation varied because otoconia fragments can be displaced into any of the semicircular canals on either (or both) side and may be free floating (canalolithiasis) or attached to the cupula (cupulolithiasis). Most cases of BPPV are idiopathic, but head trauma, otologic disorders, and systemic disease appear to be contributory in a subset. Positional maneuvers are used to diagnose and treat the majority of cases. In rare intractable cases surgical management may be considered. A strong association with osteoporosis suggests that idiopathic BPPV may have diagnostic and management implications beyond that of a purely otologic condition.

Modulation of the initial mineralization process of SaOS-2 cells by carbonic anhydrase activators and polyphosphate

Ca-phosphate/hydroxyapatite (HA) crystals constitute the mineral matrix of vertebrate bones, while Ca-carbonate is the predominant mineral of many invertebrates, like mollusks. Recent results suggest that CaCO₃ is also synthesized during early bone formation. We demonstrate that carbonic anhydrase-driven CaCO₃ formation in vitro is activated by organic extracts from the demosponge Suberites domuncula as well as by quinolinic acid, one component isolated from these extracts. Further results revealed that the stimulatory effect of bicarbonate (HCO₃ (-)) ions on mineralization of osteoblast-like SaOS-2 cells is strongly enhanced if the cells are exposed to inorganic polyphosphate (polyP), a linear polymer of phosphate linked by energy-rich phosphodiester bonds. The effect of polyP, administered as polyP (Ca²⁺ salt), on HA formation was found to be amplified by addition of the carbonic anhydrase-activating sponge extract or quinolinic acid. Our results support the assumption that CaCO₃ deposits, acting as bio-seeds for Ca-carbonated phosphate formation, are formed as an intermediate during HA mineralization and that the carbonic anhydrase-mediated formation of those deposits is under a positive-negative feedback control by bone alkaline phosphatase-dependent polyP metabolism, offering new targets for therapy of bone diseases/defects.

In vitro calcite crystal morphology is modulated by otoconial proteins otolin-1 and otoconin-90

Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia.

Induction of carbonic anhydrase in SaOS-2 cells, exposed to bicarbonate and consequences for calcium phosphate crystal formation

Ca-phosphate/hydroxyapatite crystals constitute the mineralic matrix of vertebrate bones, while Ca-carbonate dominates the inorganic matrix of otoliths. In addition, Ca-carbonate has been identified in lower percentage in apatite crystals. By using the human osteogenic SaOS-2 cells it could be shown that after exposure of the cells to Ca-bicarbonate in vitro, at concentrations between 1 and 10 mm, a significant increase of Ca-deposit formation results. The crystallite nodules formed on the surfaces of SaOS-2 cells become denser and larger in the presence of bicarbonate if simultaneously added together with the mineralization activation cocktail (β-glycerophosphate/ascorbic acid/dexamethasone). In parallel, with the increase of Ca-deposit formation, the expression of the carbonic anhydrase-II (CA-II) gene becomes upregulated. This effect, measured on transcriptional level is also substantiated by immunohistological studies. The stimulatory effect of bicarbonate on Ca-deposit formation is prevented if the carbonic anhydrase inhibitor acetazolamide is added to the cultures. Mapping the surface of the Ca-deposit producing SaOS-2 cells by scanning electron microscopy coupled with energy-dispersive X-ray analysis revealed an accumulation of the signals for the element carbon and, as expected, also for phosphorus. Finally, it is shown that ortho-phosphate and hydrolysis products of polyphosphate inhibit CA-II activity, suggesting a feedback regulatory system between the CA-driven Ca-carbonate deposition and a subsequent inactivation of this process by ortho-phosphate. Based on the presented data we suggest that Ca-carbonate deposits act as bioseeds for a downstream Ca-phosphate deposition process. We propose that activators for CA, especially for CA-II, might be beneficial for the treatment of bone deficiency diseases.