Mattis Bertlich

Betahistine Exerts a Dose-Dependent Effect on Cochlear Stria Vascularis Blood Flow in Guinea Pigs In Vivo

Objective Betahistine is a histamine H1-receptor agonist and H3-receptor antagonist that is administered to treat Menière’s disease. Despite widespread use, its pharmacological mode of action has not been entirely elucidated. This study investigated the effect of betahistine on guinea pigs at dosages corresponding to clinically used doses for cochlear microcirculation. Methods Thirty healthy Dunkin-Hartley guinea pigs were randomly assigned to five groups to receive betahistine dihydrochloride in a dose of 1,000 mg/kg b. w. (milligram per kilogram body weight), 0.100 mg/kg b. w., 0.010 mg/kg b. w., 0.001 mg/kg b. w. in NaCl 0.9% or NaCl 0.9% alone as placebo. Cochlear blood flow and mean arterial pressure were continuously monitored by intravital fluorescence microscopy and invasive blood pressure measurements 3 minutes before and 15 minutes after administration of betahistine. Results When betahistine was administered in a dose of 1.000 mg/kg b. w. cochlear blood flow was increased to a peak value of 1.340 arbitrary units (SD: 0.246; range: 0.933–1.546 arb. units) compared to baseline (p<0.05; Two Way Repeated Measures ANOVA/Bonferroni t-test). The lowest dosage of 0.001 mg/kg b. w. betahistine or NaCl 0.9% had the same effect as placebo. Nonlinear regression revealed that there was a sigmoid correlation between increase in blood flow and dosages. Conclusions Betahistine has a dose-dependent effect on the increase of blood flow in cochlear capillaries. The effects of the dosage range of betahistine on cochlear microcirculation corresponded well to clinically used single dosages to treat Menière’s disease. Our data suggest that the improved effects of higher doses of betahistine in the treatment of Menière’s disease might be due to a corresponding increase of cochlear blood flow.

Betahistine metabolites, Aminoethylpyridine, and Hydroxyethylpyridine increase cochlear blood flow in guinea pigs in vivo

Abstract Objective: Betahistine is a histamine-like drug that is used in the treatment of Ménières disease. It is commonly believed that betahistine increases cochlear blood flow and thus decreases the endolymphatic hydrops that is the cause of Ménières. Despite common clinical use, there is little understanding of the kinetics or effects of its metabolites. This study investigated the effect of the betahistine metabolites aminoethylpyridine, hydroxyethylpyridine, and pyridylacetic acid on cochlear microcirculation. Design: Guinea pigs were randomly assigned to one of the groups: placebo, betahistine, or equimolar amounts of aminoethylpyridine, hydroxyethylpyridine, or pyridylacetic acid. Cochlear blood flow and mean arterial pressure were recorded for three minutes before and 15 minutes after treatment. Study sample: Thirty Dunkin-Hartley guinea pigs assigned to one of five groups with six guinea pigs per group. Results: Betahistine, aminoethylpyridine, and hydroxyethylpyridine caused a significant increase in cochlear blood flow in comparison to placebo. The effect seen under aminoethylpyridin was greatest. The group treated with pyridylacetic acid showed no significant effect on cochlear blood flow. Conclusion: Aminoethylpyridine and hydroxyethylpyridine are, like betahistine, able to increase cochlear blood flow significantly. The effect of aminoethylpyridine was greatest. Pyridylacetic acid had no effect on cochlear microcirculation.

Etanercept prevents decrease of cochlear blood flow dose-dependently caused by tumor necrosis factor alpha.

Objectives: Tumor necrosis factor alpha (TNF-alpha) is a mediator of inflammation and microcirculation in the cochlea. This study aimed to quantify the effect of a local increase of TNF-alpha and study the effect of its interaction with etanercept on cochlear microcirculation. Methods: Cochlear lateral wall vessels were exposed surgically and assessed by intravital microscopy in guinea pigs in vivo. First, 24 animals were randomly distributed into 4 groups of 6 each. Exposed vessels were superfused repeatedly either with 1 of 3 different concentrations of TNF-alpha (5.0, 0.5, and 0.05 ng/mL) or with placebo (0.9% saline solution). Second, 12 animals were randomly distributed into 2 groups of 6 each. Vessels were pretreated with etanercept (1.0 μg/mL) or placebo (0.9% saline solution), and then treated by repeated superfusion with TNF-alpha (5.0 ng/mL). Results: TNF-alpha was shown to be effective in decreasing cochlear blood flow at a dose of 5.0 ng/mL (p < 0.01, analysis of variance on ranks). Lower concentrations or placebo treatment did not lead to significant changes. After pretreatment with etanercept, TNF-alpha at a dose of 5.0 ng/mL no longer led to a change in cochlear blood flow. Conclusions: The decreasing effect that TNF-alpha has on cochlear blood flow is dose-dependent. Etanercept abrogates this effect.

Histaminergic H3-Heteroreceptors as a Potential Mediator of Betahistine-Induced Increase in Cochlear Blood Flow.

Objective: Betahistine is a histamine-like drug that is considered beneficial in Ménières disease by increasing cochlear blood flow. Acting as an agonist at the histamine H1-receptor and as an inverse agonist at the H3-receptor, these receptors as well as the adrenergic α2-receptor were investigated for betahistine effects on cochlear blood flow. Materials and Methods: A total of 54 Dunkin-Hartley guinea pigs were randomly assigned to one of nine groups treated with a selection of H1-, H3- or α2-selective agonists and antagonists together with betahistine. Cochlear blood flow and mean arterial pressure were recorded for 3 min before and 15 min after infusion. Results: Blockage of the H3- or α2-receptors caused a suppression of betahistine-mediated typical changes in cochlear blood flow or blood pressure. Activation of H3-receptors caused a drop in cochlear blood flow and blood pressure. H1-receptors showed no involvement in betahistine-mediated changes of cochlear blood flow. Conclusion: Betahistine most likely affects cochlear blood flow through histaminergic H3-heteroreceptors.

Tumor Necrosis Factor-induced Decrease of Cochlear Blood Flow Can Be Reversed by Etanercept or JTE-013

Hypothesis: This study aimed to quantify the effects of tumor necrosis factor (TNF) inhibitor Etanercept and sphingosine-1-phosphate receptor 2 antagonist JTE-013 on cochlear blood flow in guinea pigs after TNF-induced decrease. Background: Sudden sensorineural hearing loss is a common cause for disability and reduced quality of life. Good understanding of the pathophysiology and strong evidence-based therapy concepts are still missing. In various inner ear disorders, inflammation and impairment of cochlear blood flow (CBF) have been considered factors in the pathophysiology. A central mediator of inflammation and microcirculation in the cochlea is TNF. S1P acts downstream in one TNF pathway. Methods: Cochlea lateral wall vessels were exposed surgically and assessed by intravital microscopy in guinea pigs in vivo. Twenty-eight animals were randomly distributed into four groups of seven each. Exposed vessels were superfused by TNF (5.0 ng/ml) and afterward repeatedly either by Etanercept (1.0 &mgr;g/ml), JTE-013 (10 &mgr;mol/L), or vehicle (0.9 % NaCl solution or ethanol: phosphate-buffered saline buffer, respectively). Results: After decreasing CBF with TNF (p <0.001, two-way RM ANOVA), both treatments reversed CBF, compared with vehicle (p <0.001, two-way RM ANOVA). The comparison of the vehicle groups showed no difference (p = 0.969, two-way RM ANOVA), while there was also no difference between the treatment groups (p = 0.850, two-way RM ANOVA). Conclusion: Both Etanercept and JTE-013 reverse the decreasing effect of TNF on cochlear blood flow and, therefore, TNF and the S1P-signalling pathway might be targets for treatment of microcirculation-related hearing loss.

Two-Photon Microscopy Allows Imaging and Characterization of Cochlear Microvasculature In Vivo

Impairment of cochlear blood flow has been discussed as factor in the pathophysiology of various inner ear disorders. However, the microscopic study of cochlear microcirculation is limited due to small scale and anatomical constraints. Here, two-photon fluorescence microscopy is applied to visualize cochlear microvessels. Guinea pigs were injected with Fluorescein isothiocyanate- or Texas red-dextrane as plasma marker. Intravital microscopy was performed in four animals and explanted cochleae from four animals were studied. The vascular architecture of the cochlea was visualized up to a depth of 90.0 ± 22.7 μm. Imaging yielded a mean contrast-to-noise ratio (CNR) of 3.3 ± 1.7. Mean diameter in vivo was 16.5 ± 6.0 μm for arterioles and 8.0 ± 2.4 μm for capillaries. In explanted cochleae, the diameter of radiating arterioles and capillaries was measured with 12.2 ± 1.6 μm and 6.6 ± 1.0 μm, respectively. The difference between capillaries and arterioles was statistically significant in both experimental setups (P < 0.001 and P = 0.022, two-way ANOVA). Measured vessel diameters in vivo and ex vivo were in agreement with published data. We conclude that two-photon fluorescence microscopy allows the investigation of cochlear microvessels and is potentially a valuable tool for inner ear research.

Cochlear Pericytes Are Capable of Reversibly Decreasing Capillary Diameter In Vivo After Tumor Necrosis Factor Exposure

OBJECTIVE The aim of this work was to evaluate the effect of tumor necrosis factor (TNF) and its neutralization with etanercept on the capability of cochlear pericytes to alter capillary diameter in the stria vascularis. METHODS Twelve Dunkin-Hartley guinea pigs were randomly assigned to one of three groups. Each group was treated either with placebo and then placebo, TNF and then placebo, or TNF and then etanercept. Cochlear pericytes were visualized using diaminofluorescein-2-diacetate and intravasal blood flow by fluorescein-dextrane. Vessel diameter at sites of pericyte somas and downstream controls were quantified by specialized software. Values were obtained before treatment, after first treatment with tumor necrosis factor or placebo and after second treatment with etanercept or placebo. RESULTS Overall, 199 pericytes in 12 animals were visualized. After initial treatment with TNF, a significant decrease in vessel diameter at sites of pericyte somas (3.6 ±4.3%, n = 141) compared with placebo and downstream controls was observed. After initial treatment with TNF, the application of etanercept caused a significant increase (3.3 ±5.5%, n = 59) in vessel diameter at the sites of pericyte somata compared with placebo and downstream controls. CONCLUSION We have been able to show that cochlear pericytes are capable of reducing capillary diameter after exposition to TNF. Moreover, the reduction in capillary diameter observed after the application of TNF is revertible after neutralization of tumor necrosis factor by the application of etanercept. It seems that contraction of cochlear pericytes contributes to the regulation of cochlear blood flow.

Drug-induced Defibrinogenation as New Treatment Approach of Acute Hearing Loss in an Animal Model for Inner Ear Vascular Impairment

OBJECTIVE Disturbance of cochlear microcirculation is considered to be the final common pathway of various inner ear diseases. Hyperfibrinogenemia causing increased plasma viscosity is a known risk factor for sudden sensorineural hearing loss and may lead to a critical reduction of cochlear blood flow. The aim of this study was to evaluate the effect of a substantial reduction of plasma fibrinogen levels by drug-induced defibrinogenation for the treatment of acute hearing loss in vivo. METHODS Acute hearing loss was induced by hyperfibrinogenemia (i.v. injection of 330 mg/kg BW fibrinogen), using a guinea pig animal model. Parameters of cochlear microcirculation and hearing thresholds were quantified by intravital microscopy and evoked response audiometry. After obtaining baseline values, the course of hearing loss and disturbances of microcirculation were investigated under influence of intravenous defibrinogenation therapy (ancrod), corticosteroid, or placebo treatment, using 5 animals/group. RESULTS Acute hyperfibrinogenemia caused hearing loss from 10 ± 7 to 26 ± 10 dB SPL at baseline. Drug-induced reduction of fibrinogen levels showed a significant increase of cochlear microcirculation (1.6-fold) and recovered hearing threshold (11 ± 6 dB SPL). Placebo or corticosteroid treatment had no effect on hearing loss (35 ± 7 dB SPL and 32 ± 18 dB SPL, respectively). CONCLUSION Acute hyperfibrinogenemia resulted in hearing loss. Drug-induced reduction of elevated fibrinogen levels caused an increase in cochlear blood flow and a decrease in hearing thresholds. Placebo or corticosteroid treatment had no effect. Reduction of plasma fibrinogen levels could serve as a clinical treatment option for acute hearing loss.

Transoral laser microsurgery or total laryngectomy for recurrent squamous cell carcinoma of the larynx: Retrospective analysis of 199 cases.

Surgical treatment options for local recurrences of laryngeal cancer can be either organ‐preserving surgery or total laryngectomy. The purpose of this study was to present our evaluation of the treatment with transoral laser microsurgery (TLM) in comparison to laryngectomy.

Role of capillary pericytes and precapillary arterioles in the vascular mechanism of betahistine in a guinea pig inner ear model

Aims: Betahistine is a histamine analogue that is used for the treatment of Menières disease. Animal studies showed that it increases local blood flow in the stria vascularis. In terms of its mode of action, recent studies have prompted discussion of whether betahistine actively affects cochlear microcirculation by dilations of pericytes or of precapillary arterioles or by mere downstream effects. Hence, we investigated the effects of betahistine on cochlear capillary pericytes and precapillary arterioles. Main methods: The stria vascularis was visualized in 12 guinea pigs by in vivo fluorescence microscopy. In these, 152 pericytes were stained and local diameter at sites of pericyte somas and downstream controls as well as intravascular blood flow were measured before and after betahistine application. Moreover, in two guinea pigs the precapillary arterioles were visualized by 2‐photon‐microscopy before and after betahistine application. Key findings: There was no significant change in capillary diameter at sites of pericyte somas after betahistine application compared to controls, baseline or downstream controls, even though cochlear blood flow increased significantly. The two‐photon measurements indicated an active dilation of precapillary arterioles. Significance: Since we found no evidence that betahistine affects cochlear microcirculation by cochlear pericytes, its main mode of action is evidently active dilation of pre‐capillary arterioles. These findings are in line with similar effects reported in the central nervous system and indicate an active effect on cochlear microcirculation.