The Experts below are selected from a list of 1416 Experts worldwide ranked by ideXlab platform
Alec N Salt - One of the best experts on this subject based on the ideXlab platform.
-
dexamethasone and dexamethasone phosphate entry into Perilymph compared for middle ear applications in guinea pigs
Audiology and Neuro-otology, 2018Co-Authors: Alec N Salt, J. J. Hartsock, Fabrice Piu, Jennifer HouAbstract:Dexamethasone phosphate is widely used for intratympanic therapy in humans. We assessed the pharmacokinetics of dexamethasone entry into Perilymph when administered as a dexamethasone phosphate solution or as a micronized dexamethasone suspension, with and without inclusion of poloxamer gel in the medium. After a 1-h application to guinea pigs, 10 independent samples of Perilymph were collected from the lateral semicircular canal of each animal, allowing entry at the round window and stapes to be independently assessed. Both forms of dexamethasone entered the Perilymph predominantly at the round window (73%), with a lower proportion entering at the stapes (22%). When normalized by applied concentration, dexamethasone phosphate was found to enter Perilymph far more slowly than dexamethasone, in accordance with its calculated lipid solubility and polar surface area properties. Dexamethasone phosphate therefore has a problematic combination of kinetic properties when used for local therapy of the ear. It is relatively impermeable and enters Perilymph only slowly from the middle ear. It is then metabolized in the ear to dexamethasone, which is more permeable through tissue boundaries and is rapidly lost from Perilymph. Understanding the influence of molecular properties on the distribution of drugs in Perilymph provides a new level of understanding which may help optimize drug therapies of the ear.
-
Perilymph pharmacokinetics of marker applied through a cochlear implant in guinea pigs
PLOS ONE, 2017Co-Authors: Alec N Salt, J. J. Hartsock, Ruth M Gill, Daniel Smyth, Jonathon Kirk, Kristien VerhoevenAbstract:Patients undergoing cochlear implantation could benefit from a simultaneous application of drugs into the ear, helping preserve residual low-frequency hearing and afferent nerve fiber populations. One way to apply drugs is to incorporate a cannula into the implant, through which drug solution is driven. For such an approach, Perilymph concentrations achieved and the distribution in the ear over time have not previously been documented. We used FITC-labeled dextran as a marker, delivering it into Perilymph of guinea pigs at 10 or 100 nL/min though a cannula incorporated into a cochlear implant with the outlet in the mid basal turn. After injections of varying duration (2 hours, 1 day or 7 days) Perilymph was collected from the cochlear apex using a sequential sampling technique, allowing dextran levels and gradients along scala tympani to be quantified. Data were interpreted quantitatively using computer simulations of the experiments. For injections of 2 hours duration, dextran levels were critically influenced by the presence or absence of fluid leakage at the cochleostomy site. When the cochleostomy was fluid-tight, substantially higher Perilymph levels were achieved at the injection site, with concentration declining along scala tympani towards the apex. Contrary to expectations, large dextran gradients along scala tympani persisted after 24 hours of sustained injection and were still present in some animals after 7 days injection. Functional changes associated with implantation and dextran delivery, and the histological state of the implant and cannula were also documented. The persistent longitudinal gradients of dextan along the ear were not readily explained by computer simulations of the experiments based on prior pharmacokinetic data. One explanation is that inner ear pharmacokinetics are altered in the period after cochlear implantation, possibly by a permeabilization of the blood-labyrinth barrier as part of the immune response to the implant.
-
Perilymph pharmacokinetics of locally applied gentamicin in the guinea pig
Hearing Research, 2016Co-Authors: Alec N Salt, J. J. Hartsock, Ruth M Gill, E King, F B Kraus, Stefan K PlontkeAbstract:Intratympanic gentamicin therapy is widely used clinically to suppress the vestibular symptoms of Meniere's disease. Dosing in humans was empirically established and we still know remarkably little about where gentamicin enters the inner ear, where it reaches in the inner ear and what time course it follows after local applications. In this study, gentamicin was applied to the round window niche as a 20 μL bolus of 40 mg/ml solution. Ten 2 μL samples of Perilymph were collected sequentially from the lateral semi-circular canal (LSCC) at times from 1 to 4 h after application. Gentamicin concentration was typically highest in samples originating from the vestibule and was lower in samples originating from scala tympani. To interpret these results, Perilymph elimination kinetics for gentamicin was quantified by loading the entire Perilymph space by injection at the LSCC with a 500 μg/ml gentamicin solution followed by sequential Perilymph sampling from the LSCC after different delay times. This allowed concentration decline in Perilymph to be followed with time. Gentamicin was retained well in scala vestibuli and the vestibule but declined rapidly at the base of scala tympani, dominated by interactions of Perilymph with CSF, as reported for other substances. Quantitative analysis, taking into account Perilymph kinetics for gentamicin, showed that more gentamicin entered at the round window membrane (57%) than at the stapes (35%) but the lower concentrations found in scala tympani were due to greater losses there. The gentamicin levels found in Perilymph of the vestibule, which are higher than would be expected from round window entry alone, undoubtedly contribute to the vestibulotoxic effects of the drug. Furthermore, calculations of gentamicin distribution following targeted applications to the RW or stapes are more consistent with cochleotoxicity depending on the gentamicin concentration in scala vestibuli rather than that in scala tympani.
-
intracochlear drug injections through the round window membrane measures to improve drug retention
Audiology and Neuro-otology, 2016Co-Authors: Stefan K Plontke, J. J. Hartsock, Ruth M Gill, Alec N SaltAbstract:The goal of this study was to develop an appropriate methodology to apply drugs quantitatively to the Perilymph of the ear. Intratympanic applications of drugs to the inner ear often result in variable drug levels in the Perilymph and can only be used for molecules that readily permeate the round window (RW) membrane. Direct intracochlear and intralabyrinthine application procedures for drugs, genes or cell-based therapies bypass the tight boundaries at the RW, oval window, otic capsule and the blood-labyrinth barrier. However, perforations can release inner ear pressure, allowing cerebrospinal fluid (CSF) to enter through the cochlear aqueduct, displacing the injected drug solution into the middle ear. Two markers, fluorescein or fluorescein isothiocyanate-labeled dextran, were used to quantify how much of an injected substance was retained in the cochlear Perilymph following an intracochlear injection. We evaluated whether procedures to mitigate fluid leaks improved marker retention in Perilymph. Almost all procedures to reduce volume efflux, including the use of gel for internal sealing and glue for external sealing of the injection site, resulted in improved retention of the marker in Perilymph. Adhesive on the RW membrane effectively prevented leaks but also influenced fluid exchange between CSF and Perilymph. We conclude that drugs can be delivered to the ear in a consistent, quantitative manner using intracochlear injections if care is taken to control the fluid leaks that result from cochlear perforation.
-
Systemic Lipopolysaccharide Compromises the Blood-Labyrinth Barrier and Increases Entry of Serum Fluorescein into the Perilymph
Journal of the Association for Research in Otolaryngology, 2014Co-Authors: Keiko Hirose, J. J. Hartsock, Shane Johnson, Peter Santi, Alec N SaltAbstract: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.
Tsutomu Nakashima - One of the best experts on this subject based on the ideXlab platform.
-
imaging of meniere s disease after intravenous administration of single dose gadodiamide utility of multiplication of mr cisternography and hydrops image
Magnetic Resonance in Medical Sciences, 2013Co-Authors: Shinji Naganawa, Masahiro Yamazaki, Hisashi Kawai, Kiminori Bokura, Michihiko Sone, Tsutomu NakashimaAbstract:A HYDROPS (HYbriD of Reversed image Of Positive endolymph signal and native image of positive Perilymph Signal) image, created by subtracting a positive endolymph image from a positive Perilymph image after intravenous injection of single-dose gadodiamide, has been reported to facilitate recognition of endolymphatic hydrops. To further increase the contrast-to-noise ratio (CNR) of HYDROPS images, we multiplied a T2-weighted MR cisternographic image onto the HYDROPS image. Ten patients with suspected Meniere's disease were included. The average CNR of generated images increased to more than 200 times that of HYDROP images.
-
imaging of meniere s disease by subtraction of mr cisternography from positive Perilymph image
Magnetic Resonance in Medical Sciences, 2012Co-Authors: Shinji Naganawa, Masahiro Yamazaki, Hisashi Kawai, Kiminori Bokura, Michihiko Sone, Tsutomu NakashimaAbstract:To visualize endolymph, Perilymph, and bone separately in a single image after intravenous injection of single-dose gadodiamide, we generated a HYDROPS2 image (subtraction of MR cisternography from heavily T(2)-weighted 3-dimensional fluid-attenuated inversion recovery image) in 12 patients with suspected Meniere's disease. The contrast-to-noise ratio of endo- and Perilymph did not differ significantly between the HYDROPS2 and previously reported HYDROPS (hybrid of reversed image of positive endolymph signal and native image of positive Perilymph Signal) images, and scan time was 40% shorter for the HYDROPS2 than HYDROPS.
-
imaging of meniere s disease after intravenous administration of single dose gadodiamide utility of subtraction images with different inversion time
Magnetic Resonance in Medical Sciences, 2012Co-Authors: Shinji Naganawa, Masahiro Yamazaki, Hisashi Kawai, Kiminori Bokura, Michihiko Sone, Tsutomu NakashimaAbstract:For the separate visualization of endolymph, Perilymph, and bone on a single image after intravenous injection of single-dose gadodiamide, we fused gray-scale inverted positive endolymph (PEI) with native positive Perilymph (PPI) images, that is, we subtracted PEI from PPI. Subtraction significantly improved the contrast noise ratio between endolymph and Perilymph and the subjective visibility score for endolymphatic space. The 24 patients with the suspect of Meniere's disease were included.
-
comparison of contrast effect on the cochlear Perilymph after intratympanic and intravenous gadolinium injection
American Journal of Neuroradiology, 2012Co-Authors: Masahiro Yamazaki, Shinji Naganawa, Hisashi Kawai, Mitsuhiko Tagaya, Mitsuru Ikeda, M Sone, Masaaki Teranishi, Hidenori Suzuki, Tsutomu NakashimaAbstract:BACKGROUND AND PURPOSE: 3D-FLAIR imaging 24 hours after intratympanic gadolinium injection (IT-method) or 4 hours after IV injection (IV-method) has been used to visualize the endolymphatic hydrops in Meniere disease. The purpose of this study was to compare the degree of Perilymph enhancement with the 2 methods and the Perilymph contrast-effect difference with the IV-method in both sides in patients with unilateral Meniere disease. MATERIALS AND METHODS: Sixty-one patients with Meniere disease or sudden SNHL were included in this study. Thirty-nine patients who underwent the unilateral IT-method (Gd-DTPA was diluted 8-fold with saline) and 22 patients who underwent the IV-method (a double-dose of Gd-HP-DO3A; 0.4 mL/kg body weight [ie, 0.2 mmol/kg body weight]) at 3T were analyzed retrospectively. Regions of interest of the cochlear Perilymph and the medulla oblongata were determined on each image, and the signal-intensity ratio between the 2 (CM ratio) was subsequently evaluated. The differences in the CM ratio between the 2 methods (Student t test) and the IV-method CM ratio between the affected and unaffected sides in patients with unilateral Meniere disease (paired t test) were evaluated. RESULTS: The IT-method CM ratio (2.98 ± 1.15, n = 39) was higher than the IV-method CM ratio (1.61 ± 0.60, n = 44; P CONCLUSIONS: In general, the IT-method provides higher Perilymph enhancement than the IV-method. In the patients with unilateral Meniere disease who underwent the IV-method, the affected side had a higher contrast effect.
-
detection of herpesvirus dnas in Perilymph obtained from patients with sensorineural hearing loss by real time polymerase chain reaction
Laryngoscope, 2004Co-Authors: Saiko Sugiura, Tetsushi Yoshikawa, Yukihiro Nishiyama, Yoshihiro Morishita, Eisuke Sato, Reiko Beppu, Taku Hattori, Tsutomu NakashimaAbstract:Objectives/Hypothesis: Perilymph and peripheral blood mononuclear cells (PBMCs) from patients with bilateral severe sensorineural hearing loss (SNHL) were evaluated for the presence of DNA from cytomegalovirus (CMV), herpes simplex virus (HSV), and human herpesvirus (HHV)6. Study Design: A prospective clinical study. Methods: The subjects were 14 patients who underwent cochlear implantation and 1 patient who underwent gentamicin injection in the inner ear. We attempted to detect viral DNA from Perilymph and PBMCs by real-time polymerase chain reaction (rtPCR). Results: CMV DNA was detected in two Perilymph specimens obtained from patients who were diagnosed as congenitally symptomatic CMV infection, although no CMV DNA was detected in PBMCs. Neither HSV DNA nor HHV6 DNA was detected in any other Perilymph specimens. CMV DNA was detected in three PBMC samples, HSV DNA was detected in two samples, and HHV6 DNA was detected in six samples. Conclusion: CMV may persistently infect the inner ear of patients with congenital CMV infection, and rtPCR analysis may prove to be a valuable tool for investigating the etiology of SNHL.
J. J. Hartsock - One of the best experts on this subject based on the ideXlab platform.
-
dexamethasone and dexamethasone phosphate entry into Perilymph compared for middle ear applications in guinea pigs
Audiology and Neuro-otology, 2018Co-Authors: Alec N Salt, J. J. Hartsock, Fabrice Piu, Jennifer HouAbstract:Dexamethasone phosphate is widely used for intratympanic therapy in humans. We assessed the pharmacokinetics of dexamethasone entry into Perilymph when administered as a dexamethasone phosphate solution or as a micronized dexamethasone suspension, with and without inclusion of poloxamer gel in the medium. After a 1-h application to guinea pigs, 10 independent samples of Perilymph were collected from the lateral semicircular canal of each animal, allowing entry at the round window and stapes to be independently assessed. Both forms of dexamethasone entered the Perilymph predominantly at the round window (73%), with a lower proportion entering at the stapes (22%). When normalized by applied concentration, dexamethasone phosphate was found to enter Perilymph far more slowly than dexamethasone, in accordance with its calculated lipid solubility and polar surface area properties. Dexamethasone phosphate therefore has a problematic combination of kinetic properties when used for local therapy of the ear. It is relatively impermeable and enters Perilymph only slowly from the middle ear. It is then metabolized in the ear to dexamethasone, which is more permeable through tissue boundaries and is rapidly lost from Perilymph. Understanding the influence of molecular properties on the distribution of drugs in Perilymph provides a new level of understanding which may help optimize drug therapies of the ear.
-
Perilymph pharmacokinetics of marker applied through a cochlear implant in guinea pigs
PLOS ONE, 2017Co-Authors: Alec N Salt, J. J. Hartsock, Ruth M Gill, Daniel Smyth, Jonathon Kirk, Kristien VerhoevenAbstract:Patients undergoing cochlear implantation could benefit from a simultaneous application of drugs into the ear, helping preserve residual low-frequency hearing and afferent nerve fiber populations. One way to apply drugs is to incorporate a cannula into the implant, through which drug solution is driven. For such an approach, Perilymph concentrations achieved and the distribution in the ear over time have not previously been documented. We used FITC-labeled dextran as a marker, delivering it into Perilymph of guinea pigs at 10 or 100 nL/min though a cannula incorporated into a cochlear implant with the outlet in the mid basal turn. After injections of varying duration (2 hours, 1 day or 7 days) Perilymph was collected from the cochlear apex using a sequential sampling technique, allowing dextran levels and gradients along scala tympani to be quantified. Data were interpreted quantitatively using computer simulations of the experiments. For injections of 2 hours duration, dextran levels were critically influenced by the presence or absence of fluid leakage at the cochleostomy site. When the cochleostomy was fluid-tight, substantially higher Perilymph levels were achieved at the injection site, with concentration declining along scala tympani towards the apex. Contrary to expectations, large dextran gradients along scala tympani persisted after 24 hours of sustained injection and were still present in some animals after 7 days injection. Functional changes associated with implantation and dextran delivery, and the histological state of the implant and cannula were also documented. The persistent longitudinal gradients of dextan along the ear were not readily explained by computer simulations of the experiments based on prior pharmacokinetic data. One explanation is that inner ear pharmacokinetics are altered in the period after cochlear implantation, possibly by a permeabilization of the blood-labyrinth barrier as part of the immune response to the implant.
-
Perilymph pharmacokinetics of locally applied gentamicin in the guinea pig
Hearing Research, 2016Co-Authors: Alec N Salt, J. J. Hartsock, Ruth M Gill, E King, F B Kraus, Stefan K PlontkeAbstract:Intratympanic gentamicin therapy is widely used clinically to suppress the vestibular symptoms of Meniere's disease. Dosing in humans was empirically established and we still know remarkably little about where gentamicin enters the inner ear, where it reaches in the inner ear and what time course it follows after local applications. In this study, gentamicin was applied to the round window niche as a 20 μL bolus of 40 mg/ml solution. Ten 2 μL samples of Perilymph were collected sequentially from the lateral semi-circular canal (LSCC) at times from 1 to 4 h after application. Gentamicin concentration was typically highest in samples originating from the vestibule and was lower in samples originating from scala tympani. To interpret these results, Perilymph elimination kinetics for gentamicin was quantified by loading the entire Perilymph space by injection at the LSCC with a 500 μg/ml gentamicin solution followed by sequential Perilymph sampling from the LSCC after different delay times. This allowed concentration decline in Perilymph to be followed with time. Gentamicin was retained well in scala vestibuli and the vestibule but declined rapidly at the base of scala tympani, dominated by interactions of Perilymph with CSF, as reported for other substances. Quantitative analysis, taking into account Perilymph kinetics for gentamicin, showed that more gentamicin entered at the round window membrane (57%) than at the stapes (35%) but the lower concentrations found in scala tympani were due to greater losses there. The gentamicin levels found in Perilymph of the vestibule, which are higher than would be expected from round window entry alone, undoubtedly contribute to the vestibulotoxic effects of the drug. Furthermore, calculations of gentamicin distribution following targeted applications to the RW or stapes are more consistent with cochleotoxicity depending on the gentamicin concentration in scala vestibuli rather than that in scala tympani.
-
intracochlear drug injections through the round window membrane measures to improve drug retention
Audiology and Neuro-otology, 2016Co-Authors: Stefan K Plontke, J. J. Hartsock, Ruth M Gill, Alec N SaltAbstract:The goal of this study was to develop an appropriate methodology to apply drugs quantitatively to the Perilymph of the ear. Intratympanic applications of drugs to the inner ear often result in variable drug levels in the Perilymph and can only be used for molecules that readily permeate the round window (RW) membrane. Direct intracochlear and intralabyrinthine application procedures for drugs, genes or cell-based therapies bypass the tight boundaries at the RW, oval window, otic capsule and the blood-labyrinth barrier. However, perforations can release inner ear pressure, allowing cerebrospinal fluid (CSF) to enter through the cochlear aqueduct, displacing the injected drug solution into the middle ear. Two markers, fluorescein or fluorescein isothiocyanate-labeled dextran, were used to quantify how much of an injected substance was retained in the cochlear Perilymph following an intracochlear injection. We evaluated whether procedures to mitigate fluid leaks improved marker retention in Perilymph. Almost all procedures to reduce volume efflux, including the use of gel for internal sealing and glue for external sealing of the injection site, resulted in improved retention of the marker in Perilymph. Adhesive on the RW membrane effectively prevented leaks but also influenced fluid exchange between CSF and Perilymph. We conclude that drugs can be delivered to the ear in a consistent, quantitative manner using intracochlear injections if care is taken to control the fluid leaks that result from cochlear perforation.
-
Perilymph Kinetics of FITC-Dextran Reveals Homeostasis Dominated by the Cochlear Aqueduct and Cerebrospinal Fluid
Journal of the Association for Research in Otolaryngology, 2015Co-Authors: A. N. Salt, R. M. Gill, J. J. HartsockAbstract:Understanding how drugs are distributed in Perilymph following local applications is important as local drug therapies are increasingly used to treat disorders of the inner ear. The potential contribution of cerebrospinal fluid (CSF) entry to Perilymph homeostasis has been controversial for over half a century, largely due to artifactual contamination of collected Perilymph samples with CSF. Measures of Perilymph flow and of drug distribution following round window niche applications have both suggested a slow, apically directed flow occurs along scala tympani (ST) in the normal, sealed cochlea. In the present study, we have used fluorescein isothiocyanate-dextran as a marker to study Perilymph kinetics in guinea pigs. Dextran is lost from Perilymph more slowly than other substances so far quantified. Dextran solutions were injected from pipettes sealed into the lateral semicircular canal (SCC), the cochlear apex, or the basal turn of ST. After varying delays, sequential Perilymph samples were taken from the cochlear apex or lateral SCC, allowing dextran distribution along the Perilymphatic spaces to be quantified. Variability was low and findings were consistent with the injection procedure driving volume flow towards the cochlear aqueduct, and with volume flow during Perilymph sampling driven by CSF entry at the aqueduct. The decline of dextran with time in the period between injection and sampling was consistent with both a slow volume influx of CSF (∼30 nL/min) entering the basal turn of ST at the cochlear aqueduct and a CSF-Perilymph exchange driven by pressure-driven fluid oscillation across the cochlear aqueduct. Sample data also allowed contributions of other processes, such as communications with adjacent compartments, to be quantified. The study demonstrates that drug kinetics in the basal turn of ST is complex and is influenced by a considerable number of interacting processes.
Stefan K Plontke - One of the best experts on this subject based on the ideXlab platform.
-
Perilymph pharmacokinetics of locally applied gentamicin in the guinea pig
Hearing Research, 2016Co-Authors: Alec N Salt, J. J. Hartsock, Ruth M Gill, E King, F B Kraus, Stefan K PlontkeAbstract:Intratympanic gentamicin therapy is widely used clinically to suppress the vestibular symptoms of Meniere's disease. Dosing in humans was empirically established and we still know remarkably little about where gentamicin enters the inner ear, where it reaches in the inner ear and what time course it follows after local applications. In this study, gentamicin was applied to the round window niche as a 20 μL bolus of 40 mg/ml solution. Ten 2 μL samples of Perilymph were collected sequentially from the lateral semi-circular canal (LSCC) at times from 1 to 4 h after application. Gentamicin concentration was typically highest in samples originating from the vestibule and was lower in samples originating from scala tympani. To interpret these results, Perilymph elimination kinetics for gentamicin was quantified by loading the entire Perilymph space by injection at the LSCC with a 500 μg/ml gentamicin solution followed by sequential Perilymph sampling from the LSCC after different delay times. This allowed concentration decline in Perilymph to be followed with time. Gentamicin was retained well in scala vestibuli and the vestibule but declined rapidly at the base of scala tympani, dominated by interactions of Perilymph with CSF, as reported for other substances. Quantitative analysis, taking into account Perilymph kinetics for gentamicin, showed that more gentamicin entered at the round window membrane (57%) than at the stapes (35%) but the lower concentrations found in scala tympani were due to greater losses there. The gentamicin levels found in Perilymph of the vestibule, which are higher than would be expected from round window entry alone, undoubtedly contribute to the vestibulotoxic effects of the drug. Furthermore, calculations of gentamicin distribution following targeted applications to the RW or stapes are more consistent with cochleotoxicity depending on the gentamicin concentration in scala vestibuli rather than that in scala tympani.
-
intracochlear drug injections through the round window membrane measures to improve drug retention
Audiology and Neuro-otology, 2016Co-Authors: Stefan K Plontke, J. J. Hartsock, Ruth M Gill, Alec N SaltAbstract:The goal of this study was to develop an appropriate methodology to apply drugs quantitatively to the Perilymph of the ear. Intratympanic applications of drugs to the inner ear often result in variable drug levels in the Perilymph and can only be used for molecules that readily permeate the round window (RW) membrane. Direct intracochlear and intralabyrinthine application procedures for drugs, genes or cell-based therapies bypass the tight boundaries at the RW, oval window, otic capsule and the blood-labyrinth barrier. However, perforations can release inner ear pressure, allowing cerebrospinal fluid (CSF) to enter through the cochlear aqueduct, displacing the injected drug solution into the middle ear. Two markers, fluorescein or fluorescein isothiocyanate-labeled dextran, were used to quantify how much of an injected substance was retained in the cochlear Perilymph following an intracochlear injection. We evaluated whether procedures to mitigate fluid leaks improved marker retention in Perilymph. Almost all procedures to reduce volume efflux, including the use of gel for internal sealing and glue for external sealing of the injection site, resulted in improved retention of the marker in Perilymph. Adhesive on the RW membrane effectively prevented leaks but also influenced fluid exchange between CSF and Perilymph. We conclude that drugs can be delivered to the ear in a consistent, quantitative manner using intracochlear injections if care is taken to control the fluid leaks that result from cochlear perforation.
-
gentamicin concentration gradients in scala tympani Perilymph following systemic applications
Audiology and Neuro-otology, 2013Co-Authors: Hartmut Hahn, Alec N Salt, Ulrike Schumacher, Stefan K PlontkeAbstract:It has been shown in prior studies that round window membrane (RWM) application of gentamicin produced a robust basal-apical concentration gradient in the Perilymph of scala tympani (ST) with peak concentrations in the basal turn of ST. These gradients potentially contribute to the clinical efficacy and safety of intratympanic gentamicin applications for the treatment of Meniere's disease. The present study aimed to establish the distribution of gentamicin along ST Perilymph after systemic applications. Gentamicin sulfate was applied intravenously in the amounts of 100, 300 and 600 mg/kg body weight (BW) over a period of 3 h or as a 300 mg/kg BW subcutaneous bolus injection. At 3 and 5 h after the start of the application Perilymph of ST was aspirated from the cochlea apex of the right and left cochlea, respectively, and 10 sequential 1-µl Perilymph samples from the apex of each cochlea were quantitatively analyzed using a fluorescence polarization immunoassay. In contrast to local RWM delivery, systemic application of gentamicin resulted in the highest Perilymph levels in the apex of the cochlea with decreasing concentrations towards the basal regions of ST. The absolute gentamicin concentrations increased with the amount of drug applied and time before sampling. While it is likely that the basal-apical gradient measured after local drug applications to the round window niche is the result of the direct uptake of drugs into the Perilymph of the ST, distribution by diffusion and a very low Perilymph flow towards the cochlear apex, computer simulations suggested that the apical-basal gradient observed with these systemic applications can be explained by higher entry rates of gentamicin in the apex compared to the basal turns of the cochlea. It is also possible that gentamicin enters Perilymph indirectly from the blood via the endolymph. In this case the faster kinetics in apical turns could be due to the smaller cross-sectional area of ST relative to endolymph in the apical turns.
-
marker retention in the cochlea following injections through the round window membrane
Hearing Research, 2007Co-Authors: Alec N Salt, J. J. Hartsock, Ruth M Gill, Davud B Sirjani, Stefan K PlontkeAbstract:Local delivery of drugs to the inner ear is increasingly being used in both clinical and experimental studies. Although direct injection of drugs into Perilymph appears to be the most promising way of administering drugs quantitatively, no studies have yet demonstrated the pharmacokinetics in Perilymph following direct injections. In this study, we have investigated the retention of substance in Perilymph following a single injection into the basal turn of scala tympani (ST). The substance injected was a marker, trimethylphenylammonium (TMPA) that can be detected in low concentrations with ion-selective microelectrodes. Perilymph pharmacokinetics of TMPA was assessed using sequential apical sampling to obtain Perilymph for analysis. The amount of TMPA retained in Perilymph was compared for different injection and sampling protocols. TMPA concentrations measured in fluid samples were close to those predicted by simulations when the injection pipette was sealed into the bony wall of ST but were systematically lower when the injection pipette was inserted through the round window membrane (RWM). In the latter condition, it was estimated that over 60% of the injected TMPA was lost due to leakage of Perilymph around the injection pipette at a rate estimated to be 0.09 μL/min. The effects of leakage during and after injections through the RWM were dramatically reduced when the round window niche was filled with 1% sodium hyaluronate gel before penetrating the RWM with the injection pipette. The findings demonstrate that in order to perform quantitative drug injections into Perilymph, even small rates of fluid leakage at the injection site must be controlled.
-
Demonstration of a Longitudinal Concentration Gradient Along Scala Tympani by Sequential Sampling of Perilymph from the Cochlear Apex
Journal of the Association for Research in Otolaryngology, 2006Co-Authors: Robert Mynatt, Ruth M Gill, Stefan K Plontke, Shane A. Hale, Alec N SaltAbstract:Local applications of drugs to the inner ear are increasingly being used to treat patients' inner ear disorders. Knowledge of the pharmacokinetics of drugs in the inner ear fluids is essential for a scientific basis for such treatments. When auditory function is of primary interest, the drug's kinetics in scala tympani (ST) must be established. Measurement of drug levels in ST is technically difficult because of the known contamination of Perilymph samples taken from the basal cochlear turn with cerebrospinal fluid (CSF). Recently, we reported a technique in which Perilymph was sampled from the cochlear apex to minimize the influence of CSF contamination ( J. Neurosci. Methods , doi: 10.1016/j.jneumeth.2005.10.008 ). This technique has now been extended by taking smaller fluid samples sequentially from the cochlear apex, which can be used to quantify drug gradients along ST. The sampling and analysis methods were evaluated using an ionic marker, trimethylphenylammonium (TMPA), that was applied to the round window membrane. After loading Perilymph with TMPA, 10 1-μL samples were taken from the cochlear apex. The TMPA content of the samples was consistent with the first sample containing Perilymph from apical regions and the fourth or fifth sample containing Perilymph from the basal turn. TMPA concentration decreased in subsequent samples, as they increasingly contained CSF that had passed through ST. Sample concentration curves were interpreted quantitatively by simulation of the experiment with a finite element model and by an automated curve-fitting method by which the apical–basal gradient was estimated. The study demonstrates that sequential apical sampling provides drug gradient data for ST Perilymph while avoiding the major distortions of sample composition associated with basal turn sampling. The method can be used for any substance for which a sensitive assay is available and is therefore of high relevance for the development of preclinical and clinical strategies for local drug delivery to the inner ear.
Anil K Lalwani - One of the best experts on this subject based on the ideXlab platform.
-
impact of systemic versus intratympanic dexamethasone administration on the Perilymph proteome
Journal of Proteome Research, 2021Co-Authors: Betsy Szeto, Aykut Aksit, Chris Valentini, Emily G Werth, Shahar Goeta, Lewis M Brown, Elizabeth S Olson, Jeffrey W Kysar, Anil K LalwaniAbstract:Glucocorticoids are the first-line treatment for sensorineural hearing loss, but little is known about the mechanism of their protective effect or the impact of route of administration. The recent development of hollow microneedles enables safe and reliable sampling of Perilymph for proteomic analysis. Using these microneedles, we investigate the effect of intratympanic (IT) versus intraperitoneal (IP) dexamethasone administration on guinea pig Perilymph proteome. Guinea pigs were treated with IT dexamethasone (n = 6), IP dexamethasone (n = 8), or untreated for control (n = 8) 6 h prior to aspiration. The round window membrane (RWM) was accessed via a postauricular approach, and hollow microneedles were used to perforate the RWM and aspirate 1 μL of Perilymph. Perilymph samples were analyzed by liquid chromatography-mass spectrometry-based label-free quantitative proteomics. Mass spectrometry raw data files have been deposited in an international public repository (MassIVE proteomics repository at https://massive.ucsd.edu/) under data set # MSV000086887. In the 22 samples of Perilymph analyzed, 632 proteins were detected, including the inner ear protein cochlin, a Perilymph marker. Of these, 14 proteins were modulated by IP, and three proteins were modulated by IT dexamethasone. In both IP and IT dexamethasone groups, VGF nerve growth factor inducible was significantly upregulated compared to control. The remaining adjusted proteins modulate neurons, inflammation, or protein synthesis. Proteome analysis facilitated by the use of hollow microneedles shows that route of dexamethasone administration impacts changes seen in Perilymph proteome. Compared to IT administration, the IP route was associated with greater changes in protein expression, including proteins involved in neuroprotection, inflammatory pathway, and protein synthesis. Our findings show that microneedles can mediate safe and effective intracochlear sampling and hold promise for inner ear diagnostics.
-
novel 3d printed hollow microneedles facilitate safe reliable and informative sampling of Perilymph from guinea pigs
Hearing Research, 2021Co-Authors: Betsy Szeto, Aykut Aksit, Chris Valentini, Emily G Werth, Shahar Goeta, Chuanning Tang, Lewis M Brown, Elizabeth S Olson, Jeffrey W Kysar, Anil K LalwaniAbstract:Abstract Background Inner ear diagnostics is limited by the inability to atraumatically obtain samples of inner ear fluid. The round window membrane (RWM) is an attractive portal for accessing Perilymph samples as it has been shown to heal within one week after the introduction of microperforations. A 1 µL volume of Perilymph is adequate for proteome analysis, yet the total volume of Perilymph within the scala tympani of the guinea pig is limited to less than 5 µL. This study investigates the safety and reliability of a novel hollow microneedle device to aspirate Perilymph samples adequate for proteomic analysis. Methods The guinea pig RWM was accessed via a postauricular surgical approach. 3D-printed hollow microneedles with an outer diameter of 100 µm and an inner diameter of 35 µm were used to perforate the RWM and aspirate 1 µL of Perilymph. Two Perilymph samples were analyzed by liquid chromatography-mass spectrometry-based quantitative proteomics as part of a preliminary study. Hearing was assessed before and after aspiration using compound action potential (CAP) and distortion product otoacoustic emissions (DPOAE). RWMs were harvested 72 h after aspiration and evaluated for healing using confocal microscopy. Results There was no permanent damage to hearing at 72 h after perforation as assessed by CAP (n = 7) and DPOAE (n = 8), and all perforations healed completely within 72 h (n = 8). In the two samples of Perilymph analyzed, 620 proteins were detected, including the inner ear protein cochlin, widely recognized as a Perilymph marker. Conclusion Hollow microneedles can facilitate aspiration of Perilymph across the RWM at a quality and volume adequate for proteomic analysis without causing permanent anatomic or physiologic dysfunction. Microneedles can mediate safe and effective intracochlear sampling and show great promise for inner ear diagnostics.
