In vivo observation of dynamic perilymph formation using 4.7 T MRI with gadolinium as a tracer

The Breakdown of Blood-Labyrinth Barrier Makes it Easier for Drugs to Enter the Inner Ear

PURPOSE

This study aimed to investigate dynamic change of permeability of blood-labyrinth barrier (BLB) after noise exposure and its effect on the drug delivery efficiency of systemic administration.

METHODS

Gadopentetate dimeglumine (Gd-DTPA) and dexamethasone (DEX) were used as tracers, and magnetic resonance imaging (MRI) and immunofluorescence were used to observe the change of the BLB after strong noise exposure in guinea pigs. High-performance liquid chromatography-mass spectrometry (LC-MS) was used to observe the effect of the breakdown of BLB after noise exposure on the drug delivery efficiency of intravenous DEX. The guinea pigs were divided into 6 groups: normal group (N), 1, 3, 5, 8, and 12 days after noise exposure groups (P1, P3, P5, P8, P12), with 5 animals in each group.

RESULTS

The BLB changes dynamically after noise exposure. Increased permeability of the blood-endolymph barrier, the endolymph-perilymph barrier, and the blood-nerve barrier was observed at days 1-3, 1-5, and 1-8, respectively, after noise exposure in guinea pigs. Higher drug concentration in the cochlear tissue was obtained by intravenous administration of DEX in guinea pigs during the time window of increased permeability of the BLB.

CONCLUSION

After noise exposure, the increased BLB permeability makes it easier for drugs to enter the inner ear from blood. In guinea pigs, 1-8 days after strong noise exposure, the drug delivery efficiency of systemic administration increased. After 8 days, the efficiency gradually returned to normal level. 1-8 days after noise exposure may be the best intervention time for systemic administration.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:2377-2386, 2024.

Preliminary Experience of 5.0 T Higher Field Abdominal Diffusion-Weighted MRI: Agreement of Apparent Diffusion Coefficient With 3.0 T Imaging

BACKGROUND

Recently, a prototype 5.0 T whole-body MRI scanner was developed. A 5.0 T diffusion-weighted imaging (DWI) may help overcome the issues that limit 3.0 T DWI.

PURPOSE

To evaluate the feasibility of 5.0 T high-field DWI in the upper abdomen and assess the agreement of the apparent diffusion coefficient (ADC) with that from 3.0 T abdominal DWI.

STUDY TYPE

Prospective proof of concept.

POPULATION

Nine volunteers (mean ± SD age: 37.3 ± 7.0 years, 8 M), eight healthy and one with liver and kidney cysts.

FIELD STRENGTH/SEQUENCE

3.0 T and 5.0 T; respiratory-triggered spin-echo echo-planar-imaging (SE-EPI)-based DWI sequence.

ASSESSMENT

Subjective image quality scores. The ADC values in abdominal organs (liver, pancreas, spleen, and kidney) were measured by two observers for evaluating the interobserver and interfield agreement.

STATISTICAL TESTS

Wilcoxon-rank sum test, Bland-Altman analysis, intraclass correlation coefficients (ICCs), and coefficients of variation (CVs).

RESULTS

The 5.0 T DWI displayed an increase in subjective image quality score compared to 3.0 T DWI without the significant difference (3.0 T DWI: 3.50 ± 0.47, 5.0 T DWI: 3.72 ± 0.42, P = 0.157). Both the interfield and interobserver agreements of ADC values were substantial to excellent (ICCs = 0.640-0.902). For all four upper abdominal organs, there were no significant differences between the ADC values measured by two observers and between the ADC values of 3.0 T and 5.0 T DWI (P = 0.134-1.000). The CVs of ADC measurements from 3.0 T and 5.0 T DWI were all less than 15.0% (6.7%-14.2%).

DATA CONCLUSION

The substantial to excellent agreements between the ADC values measured with 3.0 T and 5.0 T DWI for liver, pancreas, spleen, and kidney suggested that 5.0 T DWI can be applied for abdominal imaging. The ADC values from 5.0 T abdominal DWI hold the potential to serve as the quantitative markers for clinical investigations.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

Four-Hour Delayed Gadolinium-Enhanced 3D-FLAIR MR Imaging Highlights Intralabyrinthine Micro-Schwannomas

OBJECTIVE

To demonstrate the clinical significance of 4-hour delayed gadolinium-enhanced three-dimensional fluid-attenuated inversion recovery (delayed 3D-FLAIR) in patients with intralabyrinthine schwannoma (ILS).

PATIENTS

Three patients who were clinically diagnosed with ILS.

INTERVENTIONS

All patients underwent audiological examinations and magnetic resonance imaging (MRI) scans. The MR-protocol included axial MR cisternography, immediate gadolinium-enhanced T1-weighted sequence, and heavily T2-weighted 3D-FLAIR prior to and 4 hours after the intravenous administration of gadolinium contrast medium.

MAIN OUTCOME MEASURES

All MR images were visually inspected.

RESULTS

In all three patients with ILS, delayed 3D-FLAIR MRI demonstrated a strong signal of cochlear fluid surrounding the tumor, which highlighted a tumor region that lacked signals.

CONCLUSIONS

Delayed 3D-FLAIR MRI may serve as a novel diagnostic tool for the early detection of intralabyrinthine micro-schwannoma. The findings also shed light on the pathophysiology of ILS.

High-quality imaging of endolymphatic hydrops acquired in 7 minutes using sensitive hT2W-3D-FLAIR reconstructed with magnitude and zero-filled interpolation

Background

It is still challenging to detect endolymphatic hydrops (EH) in patients with Meniere’s disease (MD) using MRI. The aim of the present study was to optimize a sensitive technique generating strong contrast enhancement from minimum gadolinium–diethylenetriamine pentaacetic acid (Gd–DTPA) while reliably detecting EH in the inner ear, including the apex.

Materials and methods

All imaging was performed using a 3.0 T MR system 24 h after intratympanic injection of low-dose Gd–DTPA. Heavily T2-weighted 3-dimensional fluid-attenuated inversion recovery reconstructed with magnitude and zero-filled interpolation (hT₂W–FLAIR–ZFI) was optimized and validated in phantom studies and compared with medium inversion time inversion recovery imaging with magnitude reconstruction (MIIRMR). The following parameters were used in hT₂W–FLAIR–ZFI: repetition time 14,000 ms, echo time 663 ms, inversion time 2900 ms, flip angle 120°, echo train length 271, and field of view 166 × 196 mm².

Results

MRI obtained using hT₂W–FLAIR–MZFI yielded high-quality images with sharper and smoother borders between the endolymph and perilymph and a higher signal intensity ratio and more homogenous perilymph enhancement than those generated with MIIRMR (p < 0.01). There were predominantly grade II EHs in the cochleae and grade III EHs in the vestibule in definite MD. EH was detected in the apex of 11/16 ipsilateral ears, 3/16 contralateral ears in unilateral definite MD and 3/6 ears in bilateral MD.

Conclusions

The novel hT₂W–FLAIR–MZFI technique is sensitive and demonstrates strong and homogenous enhancement by minimum Gd–DTPA in the inner ear, including the apex, and yields high-quality images with sharp borders between the endolymph and perilymph.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00405-021-06912-4.

MRI With Gadolinium as a Measure of Blood-Labyrinth Barrier Integrity in Patients With Inner Ear Symptoms: A Scoping Review

Objective: Capillaries within the inner ear form a semi-permeable barrier called the blood-labyrinth barrier that is less permeable than capillary barriers elsewhere within the human body. Dysfunction of the blood-labyrinth barrier has been proposed as a mechanism for several audio-vestibular disorders. There has been interest in using magnetic resonance imaging (MRI) with intravenous gadolinium-based contrast agents (GBCA) as a marker for the integrity of the blood labyrinth barrier in research and clinical settings. This scoping review evaluates the evidence for using intravenous gadolinium-enhanced MRI to assess the permeability of the blood-labyrinth barrier in healthy and diseased ears.

Methods: A systematic search was conducted of three databases: PubMed, EMBASE, CINAHL PLUS. Studies were included that used GBCA to study the inner ear and permeability of the blood-labyrinth barrier. Data was collected on MRI protocols used and inner ear enhancement patterns of healthy and diseased ears in both human and animal studies.

Results: The search yielded 14 studies in animals and 53 studies in humans. In healthy animal and human inner ears, contrast-enhanced MRI demonstrated gradual increase in inner ear signal intensity over time that was limited to the perilymph. Signal intensity peaked at 100 min in rodents and 4 h in humans. Compared to controls, patients with idiopathic sudden sensorineural hearing loss and otosclerosis had increased signal intensity both before and shortly after GBCA injection. In patients with Ménière's disease and vestibular schwannoma, studies reported increased signal at 4 h, compared to controls. Quality assessment of included studies determined that all the studies lacked sample size justification and many lacked adequate control groups or blinded assessors of MRI.

Conclusions: The included studies provided convincing evidence that gadolinium crosses the blood-labyrinth barrier in healthy ears and more rapidly in some diseased ears. The timing of increased signal differs by disease. There was a lack of evidence that these findings indicate general permeability of the blood-labyrinth barrier. Future studies with consistent and rigorous methods are needed to investigate the relationship between gadolinium uptake and assessments of inner ear function and to better determine whether signal enhancement indicates permeability for molecules other than gadolinium.

Towards precision nanomedicine for cerebrovascular diseases with emphasis on Cerebral Cavernous Malformation (CCM)

Introduction: Cerebrovascular diseases encompass various disorders of the brain vasculature, such as ischemic/hemorrhagic strokes, aneurysms, and vascular malformations, also affecting the central nervous system leading to a large variety of transient or permanent neurological disorders. They represent major causes of mortality and long-term disability worldwide, and some of them can be inherited, including Cerebral Cavernous Malformation (CCM), an autosomal dominant cerebrovascular disease linked to mutations in CCM1/KRIT1, CCM2, or CCM3/PDCD10 genes.Areas covered: Besides marked clinical and etiological heterogeneity, some commonalities are emerging among distinct cerebrovascular diseases, including key pathogenetic roles of oxidative stress and inflammation, which are increasingly recognized as major disease hallmarks and therapeutic targets. This review provides a comprehensive overview of the different clinical features and common pathogenetic determinants of cerebrovascular diseases, highlighting major challenges, including the pressing need for new diagnostic and therapeutic strategies, and focusing on emerging innovative features and promising benefits of nanomedicine strategies for early detection and targeted treatment of such diseases.Expert opinion: Specifically, we describe and discuss the multiple physico-chemical features and unique biological advantages of nanosystems, including nanodiagnostics, nanotherapeutics, and nanotheranostics, that may help improving diagnosis and treatment of cerebrovascular diseases and neurological comorbidities, with an emphasis on CCM disease.

Comparison of Speech Performance in Bimodal versus Bilateral Cochlear Implant Users

OBJECTIVE

To assess whether listening with two cochlear implants (bilateral) offers significant benefits in terms of speech perception over listening with one cochlear implant and one hearing aid (bimodal).

METHODS

Retrospective review of bilateral cochlear implant recipients (24 pediatric and 26 adult). Bimodal listening was compared to bilateral listening in terms of speech perception performance at 1-year post second implant under three listening conditions: 50 dBHL, 35 dBHL, and 50 dBHL+5 SNR. Changes in speech performance from bimodal (before second implant) to bilateral (after second implant) listening were determined within subjects and compared to a separate control group of bimodal users matched for age of first implantation who never received a second implant (10 pediatric and 20 adult).

RESULTS

In the pediatric group, compared to bimodal listening prior to a second implant, speech perception scores with bilateral implants increased significantly when measured at 50 dBHL, 35 dBHL, and 50 dBHL+5 SNR. By contrast, pediatric bimodal controls who never received a second implant failed to demonstrate similar improvement over 1 year's time. In the adult group, compared to bimodal listening prior to a second implant, speech perception scores with bilateral implants increased when measured at 50 dBHL, but were not significantly different at 35 dBHL and 50 dBHL + 5 SNR. Adult bimodal controls who never received a second implant failed to demonstrate significant improvement in all conditions over 1 year's time.

CONCLUSION

Bilateral listening with two cochlear implants improved speech perception performance relative to bimodal listening in the pediatric population. Improvement in the adult population was not as significant.

LEVEL OF EVIDENCE

4, Retrospective Chart Review. Laryngoscope, 131:E1322-E1327, 2021.

Missing perilymph but leaking blood-endolymph and vestibulocochlear nerve barriers in idiopathic sudden sensorineural hearing loss: A case study

Objectives

To evaluate the pathological changes in the blood-perilymph, blood-endolymph, and blood-nerve barriers of a patient with idiopathic sudden sensorineural hearing loss (SSNHL).

Methods

Potential ossification or fibrosis in the inner ear was evaluated using temporal bone CT and MRI acquired using the 3-dimensional T2-weighted sampling perfection with application-optimized contrasts using a flip angle evolution sequence. Pathological changes in the barriers were analyzed by MRI obtained 4 h after a single-dose intravenous injection of gadolinium chelate using a medium inversion-time inversion recovery imaging with magnitude reconstruction sequence.

Results

The perilymph was absent, while significant enhancements of the vestibulocochlear nerve and the endolymphatic compartments were detected.

Conclusion

Significant injuries in the blood-endolymph and blood-vestibulocochlear nerve barriers and disabled perilymph production may contribute to the development of SSNHL with poor response to treatments.

Ultra-high-field (9.4 T) MRI Analysis of Contrast Agent Transport Across the Blood-Perilymph Barrier and Intrastrial Fluid-Blood Barrier in the Mouse Inner Ear

HYPOTHESIS

Effective paramagnetic contrast agent for the penetration of the perilymphatic spaces of the scala tympani, scala vestibuli, and scala media of the mouse inner ear can be determined using intravenous injection of various gadolinium (Gd) complexes and ultra-high-field magnetic resonance imaging (MRI) at 9.4 Tesla.

BACKGROUND

A number of contrast agents have been explored in experimental high-field MRI to determine the most effective Gd complex for ideal signal-to-noise ratio and maximal visualization of the in vivo mammalian inner ear in analyzing the temporal and spatial parameters involved in drug penetration of the blood-perilymph barrier and intrastrial fluid-blood barrier in the mouse model using MRI.

METHODS

Gadoteric acid (Dotarem), Gadobutrol (Gadovist), Gadodiamide (Omniscan), Gadopent acid (Magnevist), and Mangafodipir (Teslascan) were administered intravenously using the tail vein of 60 Balb/C mice. High-resolution T1 images of drug penetration were acquired with a horizontal 9.4 T Agilent magnet after intravenously injection. Signal intensity was used as a metric of temporal and spatial parameters of drug delivery and penetration of the perilymphatic and endolymphatic spaces.

RESULTS

ANOVA analysis of the area under the curve of intensity enhancement in perilymph revealed a significant difference (p < 0.05) in the scalae uptake using different contrast agents (F (3,25) = 3.54, p = 0.029). The Gadoteric acid complex Dotarem was found to be the most effective Gd compound in terms of rapid, morphological enhancement for analysis of the temporal, and spatial distribution in the perilymphatic space of the inner ear.

CONCLUSION

Gadoteric acid (Dotarem) demonstrated efficacy as a contrast agent for enhanced visualization of the perilymphatic spaces of the inner ear labyrinthine in the mouse, including the scala tympani and scala vestibuli of the cochlea, and the semicircular canals of the vestibular apparatus. These findings may inform the clinical application of Gd compounds in patients with inner ear fluid disorders and vertigo.

Inner ear barriers to nanomedicine-augmented drug delivery and imaging

There are several challenges to inner ear drug delivery and imaging due to the existence of tight biological barriers to the target structure and the dense bone surrounding it. Advances in imaging and nanomedicine may provide knowledge for overcoming the existing limitations to both the diagnosis and treatment of inner ear diseases. Novel techniques have improved the efficacy of drug delivery and targeting to the inner ear, as well as the quality and accuracy of imaging this structure. In this review, we will describe the pathways and biological barriers of the inner ear regarding drug delivery, the beneficial applications and limitations of the imaging techniques available for inner ear research, the behavior of engineered nanomaterials in inner ear applications, and future perspectives for nanomedicine-based inner ear imaging.

Postaurical injection is a systemic delivery supported by symmetric distribution of Gd-DOTA in both the ipsilateral and contralateral ears

Postaurical injection of therapeutics was recently applied in clinical practice to treat inner ear diseases based on supposed existence of a direct channel from the postaurical area to the inner ear. Doubting on the associated reports and aiming to provide evidence on the inner ear uptake mechanism, the present study tracked the dynamic distribution of gadolinium-tetra-azacyclo-dodecane-tetra-acetic acid (Gd-DOTA) in rat inner ears after postaurical injection using MRI. A targeted tympanic medial wall delivery was utilized as control. The results showed that, at the early time points after postaurical injection, Gd-DOTA distributed mainly in tissues surrounding the bulla, temporal bone and skull and neck space. In the inner ear, there was gradual uptake of Gd-DOTA on both the ipsilateral and contralateral sides with equal signal intensities. There was no sign of direct channel carrying the agent from the postaurical area to the inner ear. Targeted tympanic medial wall delivery induced significantly greater uptake of Gd-DOTA in the inner ear than did postaurical injection. At 30 min post-administration, targeted tympanic medial wall delivery yielded 4.6-folds higher signal intensity than did postaurical injection. The total dose of Gd-DOTA delivered by the targeted tympanic medial wall approach was only 0.1% of that delivered by postaurical injection. In conclusion, postaurical injection is a systemic administration, which is similar to hypodermic injection, rather than a focal delivery method. By contraries, targeted tympanic medial wall delivery induces fast and abundant uptake of Gd-DOTA in the ipsilateral inner ear without significant distribution in unwanted areas.

Vasopressin induces endolymphatic hydrops in mouse inner ear, as evaluated with repeated 9.4 T MRI

From histopathological specimens, endolymphatic hydrops has been demonstrated in association with inner ear disorders. Recent studies have observed findings suggestive of hydrops using MRI in humans. Previous studies suggest that vasopressin may play a critical role in endolymph homeostasis and may be involved in the development of Ménière's disease. In this study we evaluate the effect of vasopressin administration in vivo in longitudinal studies using two mouse strains. High resolution MRI at 9.4 T in combination with intraperitoneally delivered Gadolinium contrast, was performed before and after chronic subcutaneous administration of vasopressin via mini-osmotic pumps in the same mouse. A development of endolymphatic hydrops over time could be demonstrated in C57BL6 mice (5 mice, 2 and 4 weeks of administration) as well as in CBA/J mice (4 mice, 2 weeks of administration; 6 mice, 3 and 4 weeks of administration). In most C57BL6 mice hydrops developed first after more than 2 weeks while CBA/J mice had an earlier response. These results may suggest an in vivo model for studying endolymphatic hydrops and corroborates the future use of MRI as a tool in the diagnosis and treatment of inner ear diseases, such as Ménière's disease. MRI may also be developed as a critical tool in evaluating inner ear homeostasis in genetically modified mice, to augment the understanding of human disease.

Toxicity of silver nanoparticle in rat ear and BALB/c 3T3 cell line

Background

Silver nanoparticles (AgNPs) displayed strong activities in anti-bacterial, anti-viral, and anti-fungal studies and was reportedly efficient in treating otitis media .The potential impact of AgNPs on the inner ear was missing.

Objective

Attempted to evaluate the potential toxicity of AgNPs in the inner ear, middle ear, and external ear canal after transtympanic injection in rats.

Results

In in vitro studies, the IC₅₀ for AgNPs in neutral red uptake assay was lower than that in NAD(P)H-dependent cellular oxidoreductase enzyme assay (WST-1) and higher than that in total cellular ATP and nuclear membrane integrity (propidium iodide) assessments. In in vivo experiments, magnetic resonance imaging (MRI) showed that significant changes in the permeability of biological barriers occurred in the middle ear mucosa, the skin of the external ear canal, and the inner ear at 5 h post-transtympanic injection of AgNPs at concentrations ranging from 20 μg/ml to 4000 μg/ml. The alterations in permeability showed a dosage-response relationship, and were reversible. The auditory brainstem response showed that 4000 μg/ml AgNPs induced hearing loss with partial recovery at 7 d, whereas 20 μg/ml caused reversible hearing loss. The functional change in auditory system was in line with the histology results. In general, the BALB/c 3T3 cell line is more than 1000 times more sensitive than the in vivo studies. Impairment of the mitochondrial function was indicated to be the mechanism of toxicity of AgNPs.

Conclusion

These results suggest that AgNPs caused significant, dose-dependent changes in the permeability of biological barriers in the middle ear mucosa, the skin of the external ear canal, and the inner ear. In general, the BALB/c 3T3 cell line is more than 1000 times more sensitive than the in vivo studies. The rat ear model might be expended to other engineered nanomaterials in nanotoxicology study.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-014-0052-6) contains supplementary material, which is available to authorized users.

Pathway and morphological transformation of liposome nanocarriers after release from a novel sustained inner-ear delivery system

Aim: To validate a novel sustained delivery system of liposome nanocarriers for inner-ear therapy and to investigate the transport pathway for their delivery. Materials & methods: Liposome nanocarriers containing gadolinium-tetra-azacyclo-dodecane-tetra-acetic acid (LPS+Gd-DOTA) were developed for MRI tracking the in vitro release profile and for in vivo uptake studies. Results: Encapsulating Gd-DOTA did not modify the liposomes. The LPS+Gd-DOTA nanocarriers were slowly released from a miniature osmotic pump. The LPS+Gd-DOTA moved along the ossicular chain toward the oval window after an epitympanic injection, whereas they traveled directly to the round window after a mesotympanic injection. However, the round window membrane was the major pathway for the LPS+Gd-DOTA to enter the inner ear. LPS+Gd-DOTA were visualized on both sides of the cochlea within 6 days of in vivo delivery via the osmotic pump. Discussion: The novel sustained inner-ear delivery system induced liposome nanocarriers into the inner ear efficiently without causing obvious adverse effect. There is the potential of using the system to administrate therapeutics in treating inner-ear diseases in the clinic.

Original submitted 25 April 2013; Revised submitted 3 September 2013

Systemic lipopolysaccharide compromises the blood-labyrinth barrier and increases entry of serum fluorescein into the perilymph

The blood vessels that supply the inner ear form a barrier between the blood and the inner ear fluids to control the exchange of solutes, protein, and water. This barrier, called the blood-labyrinth barrier (BLB) is analogous to the blood-brain barrier (BBB), which plays a critical role in limiting the entry of inflammatory and infectious agents into the central nervous system. We have developed an in vivo method to assess the functional integrity of the BLB by injecting sodium fluorescein into the systemic circulation of mice and measuring the amount of fluorescein that enters perilymph in live animals. In these experiments, perilymph was collected from control and experimental mice in sequential samples taken from the posterior semicircular canal approximately 30 min after systemic fluorescein administration. Perilymph fluorescein concentrations in control mice were compared with perilymph fluorescein concentrations after lipopolysaccharide (LPS) treatment (1 mg/kg IP daily for 2 days). The concentration of perilymphatic fluorescein, normalized to serum fluorescein, was significantly higher in LPS-treated mice compared to controls. In order to assess the contributions of perilymph and endolymph in our inner ear fluid samples, sodium ion concentration of the inner ear fluid was measured using ion-selective electrodes. The sampled fluid from the posterior semicircular canal demonstrated an average sodium concentration of 145 mM, consistent with perilymph. These experiments establish a novel technique to assess the functional integrity of the BLB using quantitative methods and to provide a comparison of the BLB to the BBB.

MRI evidence of endolymphatic impermeability to the gadolinium molecule in the in vivo mouse inner ear at 9.4 tesla

OBJECTIVE

Previous in vivo experimental magnetic resonance imaging (MRI) investigations of the mammalian inner ear at 4.7 Tesla have indicated that intravenously injected gadolinium (Gd) penetrates the perilymphatic labyrinth, but not the endolymphatic membranous labyrinth. In the present study, high field MRI at 9.4T was used to visualize the in vivo mouse vestibulo-cochlea system, and to determine whether the endolymphatic system is permeable to a Gd complex.

METHODS

A 9.4 T Varian magnet equipped with a 12 cm inner diameter gradient system with maximum gradient strength of 600 mT/m, a millipede coil (Varian design) and a Gd contrast agent were used for image acquisition in the normal C57 BL-6 mouse.

RESULTS

High-resolution 2D and 3D images of the mouse cochlea were acquired within 80 minutes following intravenous injection of Gd. Gd initially permeated the perilymphatic scala tympani and scala vestibuli, and permitted visualization of both cochlear turns from base to apex. The superior, inferior and lateral semicircular canals were subsequently visualized in 3 planes. The membranous endolymphatic labyrinth was impermeable to intravenously injected Gd, and thus showed no apparent uptake of Gd at 9.4T.

CONCLUSION

The 9.4T field strength MRI permitted acquisition of high resolution images of anatomical and physiological features of the normal, wild type mouse perilymphatic inner ear in vivo, and provided further evidence that the endolymphatic system is impermeable to intravenously injected Gd.

Postauricular hypodermic injection to treat inner ear disorders: experimental feasibility study using magnetic resonance imaging and pharmacokinetic comparison

Background:

To investigate the feasibility of postauricular hypodermic injection for treating inner ear disorders, we compared perilymph pharmacokinetics for postauricular versus intravenous injection, using magnetic resonance imaging, in an animal model.

Methods:

Twelve albino guinea pigs were divided randomly into two groups and administered gadopentetate dimeglumine via either a postauricular or an intravenous bolus injection. A 7.0 Tesla magnetic resonance imaging system was used to assess the signal intensities of gadolinium-enhanced images of the cochlea, as a biomarker for changes in gadopentetate dimeglumine concentration in the perilymph. Pharmacokinetic parameters were calculated based on these signal intensity values.

Results:

Guinea pigs receiving postauricular injection showed longer times to peak signal intensity, longer elimination half-life, longer mean residence time and a greater area under the signal–time curve (from pre-injection to the last time point) (p < 0.05).

Conclusion:

Postauricular injection shows potential as an efficient drug delivery route for the treatment of inner ear disorders.

Novel multiple agents loaded PLGA nanoparticles for brain delivery via inner ear administration: in vitro and in vivo evaluation

The aim of this study was to develop novel multiple agents loaded poly (D,L-lactide-co-glycolide acid) (PLGA) nanoparticles (NPs) and evaluate their potential for brain delivery via inner ear administration. PLGA NPs loaded with salvianolic acid B (Sal B), tanshinone IIA (TS IIA) and panax notoginsenoside (PNS) were prepared by double emulsion/solvent evaporation method. It was observed that optimized NPs displayed satisfactory encapsulation efficiency and desired sustained-release characteristics. NPs following intratympanic administration (IT) in guinea pigs greatly improved drug distribution within the inner ear, cerebrospinal fluid (CSF) and brain tissues compared with intravenous administration (IV). Pharmacodynamic studies demonstrated that NPs following IT markedly inhibited oxidizing reactions and protected the brain from cerebral ischemia reperfusion (I/R) injury by upregulating superoxide dismutase (SOD) activity both in serum and brain tissues, simultaneously significantly reducing the levels of malondialdehyde (MDA) and nitric oxide synthase (NOS). Moreover intratympanic delivery did not cause injury of cochlear function by preliminary study on the toxicity. These findings suggested that PLGA NPs-based delivery system via inner ear administration was a promising candidate to brain delivery for the treatment of brain diseases.

Variability in the perilymphatic diffusion of gadolinium does not predict the outcome of intratympanic gentamicin in patients with Ménière's disease

OBJECTIVES/HYPOTHESIS

To assess the utility of imaging in planning intratympanic (IT) gentamicin (Gent) treatment in Ménière's disease (MD), we compared the dosage and outcomes of ITGent with the severity and extent of endolymphatic hydrops (EH), as evaluated by three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) sequence in a 3-T magnetic resonance imaging (MRI) unit, after IT gadolinium administration.

STUDY DESIGN

Retrospective review.

METHODS

A total of 18 patients (10 males and 8 females; age, 28-78 years; median age, 53.2 years) with definite MD participated in the investigation. The duration of the disease ranged from 8 months to 9 years (median, 2 years), with a prevalence of vertigo spells ranging from 0.8 to 8 per month (median, 2.2), as calculated in the last 6 months. A 3D-FLAIR MRI was performed 24 hours after IT injection of diluted gadobutrol. ITGent injection was performed within a variable period of time, from 1 week to 3 weeks after 3D-FLAIR MRI. The degree and extension of EH as evaluated by 3D-FLAIR MRI were compared with the number of injections necessary to cure vertigo attacks. Vertigo results, functional level scale modifications, variations in caloric excitability, and pure-tone average modifications.

RESULTS

No statistically significant correlation was observed between severity of EH and outcomes of ITGent administration.

CONCLUSIONS

The hypothesis of a reduced effect of Gent administered intratympanically in the presence of severe EH, owing to obstacled diffusion along the perilymphatic compartments, has not been confirmed in the present investigation.

Comparison of the distribution pattern of PEG-b-PCL polymersomes delivered into the rat inner ear via different methods

CONCLUSION

Cochleostomy is the most efficient approach in delivering PEG-b-PCL polymersomes (PMs) to the inner ear. PMs can be delivered to the vestibule by transtympanic injection or cochleostomy.

OBJECTIVE

To evaluate the efficiency of delivering PEG-b-PCL PMs into the inner ear using different approaches.

METHODS

The PEG-b-PCL PMs were administered either by sustained topical round window membrane (RWM) delivery using gelatin sponge pledgets in combination with an osmotic pump, transtympanic injection, or cochleostomy. The distribution of the PMs in the inner ear was observed by confocal microscopy using either whole mount specimens or cryosections.

RESULTS

Cochleostomy resulted in distribution of the PMs in the spiral ligament (SL), mesothelial cells beneath the organ of Corti, supporting cells in the organ of Corti, and spiral ganglion cells (SGCs). Transtympanic injection induced uptake of the PMs in the SL and mesothelial cells beneath the organ of Corti. Topical administration showed distribution of the PMs only in the SL. In the vestibulum, transtympanic injection and cochleostomy induced more distribution of the PMs than did topical RWM delivery (p < 0.05, Kruskal-Wallis test).

Direct entry of gadolinium into the vestibule following intratympanic applications in Guinea pigs and the influence of cochlear implantation

Although intratympanic (IT) administration of drugs has gained wide clinical acceptance, the distribution of drugs in the inner ear following IT administration is not well established. Gadolinium (Gd) has been previously used as a marker in conjunction with magnetic resonance imaging (MRI) to visualize distribution in inner ear fluids in a qualitative manner. In the present study, we applied gadolinium chelated with diethylenetriamine penta-acetic acid (Gd-DTPA) to the round window niche of 12 guinea pigs using Seprapack(TM) (carboxlmethylcellulose-hyaluronic acid) pledgets which stabilized the fluid volume in the round window niche. Gd-DTPA distribution was monitored sequentially with time following application. Distribution in normal, unperforated ears was compared with ears that had undergone a cochleostomy in the basal turn of scala tympani and implantation with a silastic electrode. Results were quantified using image analysis software. In all animals, Gd-DTPA was seen in the lower basal scala tympani (ST), scala vestibuli (SV), and throughout the vestibule and semi-circular canals by 1 h after application. Although Gd-DTPA levels in ST were higher than those in the vestibule in a few ears, the majority showed higher Gd-DTPA levels in the vestibule than ST at both early and later time points. Quantitative computer simulations of the experiment, taking into account the larger volume of the vestibule compared to scala tympani, suggest most Gd-DTPA (up to 90%) entered the vestibule directly in the vicinity of the stapes rather than indirectly through the round window membrane and ST. Gd-DTPA levels were minimally affected by the implantation procedure after 1 h. Gd-DTPA levels in the basal turn of scala tympani were lower in implanted animals, but the difference compared to non-implanted ears did not reach statistical significance.

Effect of aspiration of perilymph during stapes surgery on the endocochlear potential of guinea pig

OBJECTIVE

Suction applied to the vestibule through the oval window during stapes surgery is considered a primary risk for postoperative sensorineural hearing impairment. This study investigated the mechanism of acute phase change in cochlear function caused by aspiration of the opened oval window.

STUDY DESIGN

Guinea pig model.

SETTING

Academic hospital laboratory.

SUBJECTS AND METHODS

Guinea pigs were divided into 3 groups: stapes footplate removed without suctioning (6 animals), with indirect suctioning (5 animals), and with direct suctioning of the vestibular perilymph (6 animals). Endocochlear potentials (EPs) were measured at the second turn of the cochlea, and temporal bones were examined histologically.

RESULTS

Removal of the stapes footplate without suctioning caused little change in the EP (original value, 80.12 ± 3.52 mV), indirect suctioning caused minor decline of the EP of 9.14 ± 1.84 mV, and partial recovery ensued, whereas direct but gentle suctioning, resulting in dry vestibule, caused reduction in the EP of 16.38 ± 6.63 mV. Recovery was not observed or incomplete. No animals showed profound decrease in the EP.

CONCLUSION

Gentle suctioning and removal of the vestibular perilymph can cause a mild decrease in the EP even without damaging the inner ear structures. Therefore, suctioning of the perilymph should be avoided during stapes surgery because acute hearing loss can result even without damaging the inner ear structures. However, hearing loss may not be profound, if suctioning is not vigorous enough to cause damage to the inner ear structures.

Transport augmentation through the blood-inner ear barriers of guinea pigs treated with 3-nitropropionic acid and patients with acute hearing loss, visualized with 3.0 T MRI

OBJECTIVE

To visualize the permeability changes in the blood-inner ear barriers of guinea pigs with acute mitochondria dysfunction and in patients with acute hearing loss using contrast agent-enhanced MRI.

MATERIALS AND METHODS

An animal model of acute mitochondria dysfunction-induced hearing loss was created by introducing 3-nitropropionic acid (3-NP) intratympanically in guinea pigs. Vestibular disorder and hearing loss were evaluated. An MRI was performed at 2 h after either intravenous (IV) or intratympanic administration of dimeglumine gadopentetate (Gd-DTPA), using 3D fast-recovery fast spin-echo (FRFSE) and 3D fluid-attenuated inversion recovery (FLAIR) sequences. The inner ears of patients with acute hearing loss were imaged using a 3D-FLAIR sequence with a 3 T MRI machine at 2 h post-IV injection with Gd-DTPA at a routine dosage.

RESULTS

Guinea pigs treated with 3-NP showed severe hearing loss and vestibular dysfunction. MR imaging with a 3D-FLAIR sequence at 2 h post-IV injection of Gd-DTPA was an optimal method for visualizing transport augmentation through the blood-inner ear barriers. Apoptosis appeared in the stria vascularis and Reissner's membrane of cochleae treated with 3NP. Similar MRI changes were observed in patients with SSHL and Ménière's disease 2 h post-IV injection with Gd-DTPA using the 3D-FLAIR sequence.

CONCLUSION

Variations of Gd-DTPA transport through the blood-inner ear barriers induced by mitochondria toxin was visualized in guinea pigs using a clinical 3.0 T machine. IV injection of Gd-DTPA with 2 h of waiting time and imaging with 3D-FLAIR are optimal methods. The MRI observation of the inner ear in the animal model was translatable to patients with acute hearing loss, using an IV injection of Gd-DTPA at the routine dosage.

Magnetic resonance imaging of the inner ear in Meniere's disease

Recent magnetic resonance imaging (MRI) techniques have made it possible to examine the compartments of the cochlea using gadolidium-chelate (GdC) as a contrast agent. As GdC loads into the perilymph space without entering the endolymph in healthy inner ears, the technique provides possibilities to visualize the different cochlear compartments and evaluate the integrity of the inner ear barriers. This critical review presents the recent advancements in the inner ear MRI technology, contrast agent application and the correlated ototoxicity study, and the uptake dynamics of GdC in the inner ear. GdC causes inflammation of the mucosa of the middle ear, but there are no reports or evidence of toxicity-related changes in vivo either in animals or in humans. Intravenously administered GdC reached the guinea pig cochlea about 10 minutes after administration and loaded the scala tympani and scala vestibuli with the peak at 60 minutes. However, the perilymphatic loading peak was 80 to 100 minutes in mice after intravenous administration of GdC. In healthy animals the scala media did not load GdC. In mice in which GdC was administered topically onto the round window, loading of the cochlea peaked at 4 hours, at which time it reached the apex. The initial portions of the organ to be filled were the basal turn of the cochlea and vestibule. In animal models with endolymphatic hydrops (EH), bulging of the Reissner's membrane was observed as deficit of GdC in the scala vestibuli. Histologically the degree of bulging correlated with the MR images. In animals with immune reaction-induced EH, MRI showed that EH could be limited to restricted regions of the inner ear, and in the same inner ear both EH and leakage of GdC into the scala media were visualized. More than 100 inner ear MRI scans have been performed to date in humans. Loading of GdC followed the pattern seen in animals, but the time frame was different. In intravenous delivery of double-dose GdC, the inner ear compartments were visualized after 4 hours. The uptake pattern of GdC in the perilymph of humans between 2 hours and 7 hours after local delivery needs to be clarified. In almost all patients with probable or suspected Ménière's disease, EH was verified. Specific algorithms with a 12-pole coil using fluid attenuation inversion recovery sequences are recommended for initial imaging in humans.

CTP (Cochlin-tomoprotein) detection in the profuse fluid leakage (gusher) from cochleostomy

CONCLUSIONS

By testing 125 samples, we confirmed that Cochlin-tomoprotein (CTP) is present in the perilymph, not in cerebrospinal fluid (CSF). Perilymph and CSF exist in two distinct compartments, even in the case of a malformed inner ear with a bony defect in the lamina cribrosa, as described here. Cochleostomy might have suddenly decreased the perilymph pressure, allowing the influx of CSF into the inner ear resulting in profuse fluid leakage, first perilymph then CSF.

OBJECTIVES

The first purpose of this study was to further confirm the specificity of the perilymph-specific protein CTP that we reported recently. Secondly, we assessed the nature of the fluid leakage from the cochleostomy using the CTP detection test.

METHODS

A standardized CTP detection test was performed on 65 perilymph and 60 CSF samples. Samples of profuse fluid leakage collected from cochleostomy during cochlear implantation surgery of one patient with branchio-oto-renal (BOR) syndrome were also tested by the CTP detection test.

RESULTS

CTP was detected in 60 of 65 perilymph samples but not in any of the CSF samples. The leaked fluid was shown to contain CTP, i.e. perilymph, at the outset, and then the CTP detection signals gradually disappeared as time elapsed.

Round window delivery of dexamethasone ameliorates local and remote hearing loss produced by cochlear implantation into the second turn of the guinea pig cochlea

Application of dexamethasone to the round window has been shown to ameliorate high frequency hearing loss resulting from the trauma of cochlear implantation in experimental animals, but elucidation of the factors influencing protection of the high frequencies has been confounded by the local trauma from electrode array insertion. In this experiment, a second turn cochleostomy and implantation was performed on guinea pigs, to examine protection in the basal turn without the confounding effect of local trauma, as well as to test the efficacy of hearing protection in the second cochlear turn. The implantation resulted in an increase in hearing thresholds across all frequencies examined (2-32 kHz). Local delivery of dexamethasone to the round window prior to implantation protected hearing across frequencies from 2 to 32 kHz. Auditory thresholds improved over the first week after surgery, and then remained stable for the month of the experiment. The protection of hearing in the basal turn increased with longer periods of drug application prior to implantation. The level of hearing protection in the second turn was similar irrespective of the time that the drug was applied, but was greater when a higher steroid concentration was used. It was concluded that steroids protect hearing in the basal turn of the cochlea even when there was no local trauma. The level of hearing protection in the second turn exceeded that expected from models of steroid diffusion through the cochlea, suggesting that inner ear surgery alters the distribution of dexamethasone within the cochlea.

Resistance to learning binaurally mismatched frequency-to-place maps: implications for bilateral stimulation with cochlear implants

Simulations of monaural cochlear implants in normal hearing listeners have shown that the deleterious effects of upward spectral shifting on speech perception can be overcome with training. This study simulates bilateral stimulation with a unilateral spectral shift to investigate whether listeners can adapt to upward-shifted speech information presented together with contralateral unshifted information. A six-channel, dichotic, interleaved sine-carrier vocoder simulated a binaurally mismatched frequency-to-place map. Odd channels were presented to one ear with an upward frequency shift equivalent to 6 mm on the basilar membrane, while even channels were presented to the contralateral ear unshifted. In Experiment 1, listeners were trained for 5.3 h with either the binaurally mismatched processor or with just the shifted monaural bands. In Experiment 2, the duration of training was 10 h, and the trained condition alternated between those of Experiment 1. While listeners showed learning in both experiments, intelligibility with the binaurally mismatched processor never exceeded, intelligibility with just the three unshifted bands, suggesting that listeners did not benefit from combining the mismatched maps, even though there was clear scope to do so. Frequency-place map alignment may thus be of importance when optimizing bilateral devices of the type studied here.

Role of binaural hearing in speech intelligibility and spatial release from masking using vocoded speech

A cochlear implant vocoder was used to evaluate relative contributions of spectral and binaural temporal fine-structure cues to speech intelligibility. In Study I, stimuli were vocoded, and then convolved through head related transfer functions (HRTFs) to remove speech temporal fine structure but preserve the binaural temporal fine-structure cues. In Study II, the order of processing was reversed to remove both speech and binaural temporal fine-structure cues. Speech reception thresholds (SRTs) were measured adaptively in quiet, and with interfering speech, for unprocessed and vocoded speech (16, 8, and 4 frequency bands), under binaural or monaural (right-ear) conditions. Under binaural conditions, as the number of bands decreased, SRTs increased. With decreasing number of frequency bands, greater benefit from spatial separation of target and interferer was observed, especially in the 8-band condition. The present results demonstrate a strong role of the binaural cues in spectrally degraded speech, when the target and interfering speech are more likely to be confused. The nearly normal binaural benefits under present simulation conditions and the lack of order of processing effect further suggest that preservation of binaural cues is likely to improve performance in bilaterally implanted recipients.

Differential passage of gadolinium through the mouse inner ear barriers evaluated with 4.7T MRI

Magnetic resonance imaging (MRI), supplemented by contrast agents, is a powerful tool that can be used to visualise the structures of the inner ear in vivo and assess some aspects of physiology, such as the permeability of agents through membranes. The mouse is an excellent animal species for investigating human diseases, including hearing loss but detailed MRI studies with contrast have not been reported. In this work, we aimed to demonstrate the limits of MR imaging resolution of the fine inner ear structures in the mouse and to explore the permeability of the intracochlear barriers to gadolinium-tetra-azacyclo-dodecane-tetra-acetic acid (Gd-DOTA) administered by intravenous injection (IV) or intratympanic (IT) routes. Twenty-three female FVB mice were imaged with a 4.7-T MR scanner using both 2D and high resolution 3D sequences. Inner ear region of interest (ROI) signal intensities and perilymph volumes were evaluated. Finer structures were studied using 3D acquisition and reconstruction techniques and comparisons were made to similarly oriented histological sections that were examined by light microscopy. Gd-DOTA enhancement occurred in the perilymphatic compartment and highlighted the contiguous inner ear structures, but enhancement did not appear within the endolymph. The dynamic uptake of Gd-DOTA in the perilymphatic compartments reached an initial plateau 80min after IV administration and continued to slightly increase to a maximum level by 100min. The perilymph volume demonstrated by Gd-DOTA uptake was statistically significantly larger in the IV group (1.72mm(3)) than in the IT group (1.28mm(3)) (p<0.05).

Visualization of inner ear disorders with MRI in vivo: from animal models to human application

CONCLUSION

The inner ear membranous permeability and leakiness and endolymphatic hydrops can be visualized using gadolinium-enhanced MRI in both rodents and man. Intratympanic administration of contrast agent gives greater perilymphatic loading of gadolinium.

OBJECTIVES

Visualization of different types of inner ear dysfunction in MRI with intravenous or intratympanic administration of contrast agent.

MATERIALS AND METHODS

In the animal study, gadolinium was administered intravenously or intratympanically and imaged with 4.7 T MRI. In man, gadolinium was delivered intratympanically and studied with 1.5 T or 3 T MRI.

RESULTS

In the animals, intravenous delivery of gadolinium demonstrated uptake in the perilymph of normal inner ears. The cochlear modiolus appeared to be a critical site for the secretion of perilymph and the location of fluid communication between the perilymphatic scalae. Intense noise exposure and immune reaction caused cochlear injury and accelerated gadolinium passage through the blood-perilymph and blood-endolymph barriers. In man, perilymphatic uptake of gadolinium was only observed in the impaired inner ear when administered intravenously. However, the signal-to-noise ratio of images was improved when gadolinium was delivered intratympanically. MRI demonstrated endolymphatic hydrops in both animal models and patients with Meniere's disease.

Inner ear drug delivery for auditory applications

Many inner ear disorders cannot be adequately treated by systemic drug delivery. A blood-cochlear barrier exists, similar physiologically to the blood-brain barrier, which limits the concentration and size of molecules able to leave the circulation and gain access to the cells of the inner ear. However, research in novel therapeutics and delivery systems has led to significant progress in the development of local methods of drug delivery to the inner ear. Intratympanic approaches, which deliver therapeutics to the middle ear, rely on permeation through tissue for access to the structures of the inner ear, whereas intracochlear methods are able to directly insert drugs into the inner ear. Innovative drug delivery systems to treat various inner ear ailments such as ototoxicity, sudden sensorineural hearing loss, autoimmune inner ear disease, and for preserving neurons and regenerating sensory cells are being explored.

Perilymph/Modiolar Communication Routes in the Human Cochlea

OBJECTIVES

To analyze communication routes between perilymph spaces and the modiolus in the human cochlea. Such pathways are of potential importance with regard to local inner ear drug delivery and pharmacokinetics.

DESIGN

We analyzed the surface structure of the human cochlea, using high-resolution scanning electron microscopy (SEM) in macerated and freshly obtained specimens together with light microscopy of celloidin-embedded temporal bones.

RESULTS

Combined SEM and light microscopy showed that perilymph and fluid spaces in the modiolar periphery form a common system. The modiolar wall of the scala vestibuli and tympani in the first and second turn is porous, forming a perilymphatic communication route to the perivascular and perineural spaces in the modiolus. A "perimodiolar lymph" or fluid space can be identified in the modiolar periphery. It communicates through a trabecular meshwork of porous membrane and web of connective tissue with the perilymph. The thin mesothelial cell sheets showed pores and displayed signs of vesicular activity.

CONCLUSIONS

This canalicular system may play a role in the circulation of perilymph in the human cochlea. We suggest that this system may represent an important fluid communication route between modiolus and perilymph and may represent a pathway for future drug and cell-based therapy to the inner ear.

Communication between the perilymphatic scalae and spiral ligament visualized by in vivo MRI

We evaluated the transport of Gadolinium-diethylenetriaminepentaacetate-bismethylamide (Gd-DTPA-BMA) through the round window (RW) membrane into the perilymphatic space with 4.7-T MRI in an animal study and 1.5-T MRI in humans. After administration of Gd-DTPA-BMA onto the intact RW membrane of guinea pig, Gd-DTPA-BMA uptake was observed in the basal turn and part of the second turn within 40 min. The scala tympani, scala vestibuli, the fibrous part of the spiral ligament and semicircular canal all showed uptake of Gd-DTPA-BMA. All turns of the cochlea were filled with Gd within 10 min in the perforated RW membrane administration group and within 30 min in the intravenous administration group. In patients who accepted middle ear injection of Gd-DTPA-BMA, uptake was observed within 2 h in the basal turn and semicircular canal. After 12 h the apex did still not show any uptake. Gd-DTPA-BMA is transported from the RW to the semicircular canal, the scala tympani and scala vestibuli without passing the helicotrema.