The role of vascular endothelial growth factor and vascular stability in diseases of the ear

Correlation between genotype and phenotype with special attention to hearing in 14 Japanese cases of NF2-related schwannomatosis

NF2-related schwannomatosis (NF2) is an autosomal dominant genetic disorder caused by variants in the NF2 gene. Approximately 50% of NF2 patients inherit pathogenic variants, and the remainder acquire de novo variants. NF2 is characterized by development of bilateral vestibular schwannomas. The genetic background of Japanese NF2 cases has not been fully investigated, and the present report performed a genetic analysis of 14 Japanese NF2 cases and examined genotype-phenotype correlations. DNA samples collected from peripheral blood were analyzed by next-generation sequencing, multiplex ligation-dependent probe amplification analysis, and in vitro electrophoresis. Ten cases had pathogenic or likely pathogenic variants in the NF2 gene, with seven truncating variants and three non-truncating variants. The age of onset in all seven cases with truncating variants was < 20 years. The age of onset significantly differed among cases with truncating NF2 variants, non-truncating NF2 variants, and no NF2 variants. However, the clinical course of tumor growth and hearing deterioration were not predicted only by germline pathogenic NF2 variants. The rate of truncating variants was higher in the present study than that of previous reports. Genotype-phenotype correlations in the age of onset were present in the analyzed Japanese NF2 cases.

Targeted Therapies in the Treatment of Vestibular Schwannomas: Current State and New Horizons

Vestibular schwannomas continue to cause hearing loss, facial nerve paralysis, imbalance, and tinnitus. These symptoms are compounded by germline neurofibromatosis type 2 (NF2) gene loss and multiple intracranial and spinal cord tumors associated with NF2-related schwannomatosis. The current treatments of observation, microsurgical resection, or stereotactic radiation may prevent catastrophic brainstem compression but are all associated with the loss of cranial nerve function, particularly hearing loss. Novel targeted treatment options to stop tumor progression include small molecule inhibitors, immunotherapy, anti-inflammatory drugs, radio-sensitizing and sclerosing agents, and gene therapy.

Connexin 30 deletion exacerbates cochlear senescence and age-related hearing loss

Pathogenic mutations in the Gjb2 and Gjb6 genes, encoding connexin 26 (Cx26) and connexin 30 (Cx30), respectively, have been linked to the most frequent monogenic hearing impairment, nonsyndromic hearing loss, and deafness DFNB1. It is known that Cx26 plays an important role in auditory development, while the role of Cx30 in hearing remains controversial. Previous studies found that partial deletion of Cx26 can accelerate age-related hearing loss (ARHL), a multifactorial complex disorder, with both environmental and genetic factors contributing to the etiology of the disease. Here, we investigated the role of Cx30 in cochlear-aging processes using a transgenic mouse model with total deletion of Cx30 (Cx30 ΔΔ mice), in which Cx30 was removed without perturbing the surrounding sequences. We show that these mice are affected by exacerbated ARHL, with increased morphological cochlear damage, oxidative stress, inflammation, and vascular dysfunctions. Overall, our data demonstrate that Cx30 deletion can be considered a genetic risk factor for ARHL, making cochlear structures more susceptible to aging processes.

Effect of Angiogenesis and Lymphangiogenesis in Diesel Exhaust Particles Inhalation in Mouse Model of LPS Induced Acute Otitis Media

Lymphangiogenesis and angiogenesis might have significant involvement in the pathogenesis of otitis media with effusion. This study investigated the effect of diesel exhaust particles (DEP) on inflammation and lymphangiogenesis in a mouse model of acute otitis media (AOM). BALB/c mice were injected with LPS and exposed to 100 µg/m³ DEP. The mice were divided into four groups: control (no stimulation), AOM, AOM + DEP, and DEP + AOM.

The effects of DEP inhalation pre- and post-DEP induction were estimated based on measurements of the auditory brainstem response, mRNA levels of lymphangiogenesis-related genes and cytokines, and histology of the middle ear. Cell viability of human middle ear epithelial cells decreased in a dose-response manner at 24 and 48 hours post-DEP exposure. DEP alone did not induce AOM. AOM-induced mice with pre- or post-DEP exposure showed thickened middle ear mucosa and increased expression of TNF-α and IL1-β mRNA levels compared to the control group, but increased serum IL-1β levels were not found in the AOM + Post DEP. The mRNA expression of TLR4, VEGFA, VEGFAC, and VEGFR3 was increased by pre-AOM DEP exposure.

The expression of VEFGA protein was stronger in the AOM + Post DEP group than in any other group. The expression of CD31 and CD45 markers in the mouse middle ear tissue was higher in the Pre DEP + AOM group than in the AOM group. This result implies that pre-exposure to DEP more strongly increases inflammation and lymphangiogenesis in a mouse model of acute otitis media.

Early Noise-Induced Hearing Loss Accelerates Presbycusis Altering Aging Processes in the Cochlea

Several studies identified hearing loss as a risk factor for aging-related processes, including neurodegenerative diseases, as dementia and age-related hearing loss (ARHL). Although the association between hearing impairment in midlife and ARHL has been widely documented by epidemiological and experimental studies, the molecular mechanisms underlying this association are not fully understood. In this study, we used an established animal model of ARHL (C57BL/6 mice) to evaluate if early noise-induced hearing loss (NIHL) could affect the onset or progression of age-related cochlear dysfunction. We found that hearing loss can exacerbate ARHL, damaging sensory-neural cochlear epithelium and causing synaptopathy. Moreover, we studied common pathological markers shared between hearing loss and ARHL, demonstrating that noise exposure can worsen/accelerate redox status imbalance [increase of reactive oxygen species (ROS) production, lipid peroxidation, and dysregulation of endogenous antioxidant response] and vascular dysfunction [increased expression of hypoxia-inducible factor-1alpha (HIF-1α) and vascular endothelial growth factor C (VEGFC)] in the cochlea. Unveiling the molecular mechanisms underlying the link between hearing loss and aging processes could be valuable to identify effective therapeutic strategies to limit the effect of environmental risk factors on age-related diseases.

Past and Future Biologics for Otologic Disorders

Biologic therapies have the ability to fundamentally change the management of hearing loss; clinicians need to familiarize themselves with their prospective applications in practice. This article reviews the current application of 4 categories of biological therapeutics-growth factors, apoptosis inhibitors, monoclonal antibodies, and gene therapy-in otology and their potential future directions and applications.

Vascular endothelial growth factor and transforming growth factor β in hypertrophic adenoids in children suffering from otitis media with effusion

OBJECTIVES

The study objective was to assess the levels of VEGF-A and TGF-β cytokines in the children with adenoid hypertrophy concomitant with exudative otitis media (OME) and in children with adenoid hypertrophy (HA) alone.

METHODS

The study material consisted of hypertrophic adenoids removed during adenoidectomy from 39 children (20 girls and 19 boys), aged 2-7 years suffering from OME. The reference group included 41 children (19 girls and 22 boys), aged from 3 to 9 years with adenoid hypertrophy. The levels of VEGF-A and TGF-β were determined in supernatants obtained from phytohemagglutinin-stimulated cell cultures of the adenoids using a commercial enzyme-linked immunosorbent assay kit.

RESULTS

The median VEGF-A and mean TGF-β concentrations in the study group were significantly higher than those in the reference group (503 pg/mL versus 201 pg/mL, P < 0.001 and 224 pg/mL versus 132 pg/mL, P < 0.001, respectively). ROC analysis revealed that the area under the curve (AUC) for VEGF-A was 0.952 with diagnostic sensitivity and specificity of 95%, whereas for TGF-β it was 0.902 with 60% sensitivity and the same specificity as for VEGF-A. There was no significant difference between the AUC for VEGF-A and TGF-β (P = 0.573).

CONCLUSIONS

The changes in the levels of VEGF-A and TGF-β may indicate bacterial pathogen as one of the causes of exudative otitis media in children. Determination of VEGF-A and TGF-β could be used as additional and objective tests to confirm the clinical diagnosis.

The inflammatory microenvironment in vestibular schwannoma

Vestibular schwannomas are tumors arising from the vestibulocochlear nerve at the cerebellopontine angle. Their proximity to eloquent brainstem structures means that the pathology itself and the treatment thereof can be associated with significant morbidity. The vast majority of these tumors are sporadic, with the remainder arising as a result of the genetic syndrome Neurofibromatosis Type 2 or, more rarely, LZTR1-related schwannomatosis. The natural history of these tumors is extremely variable, with some tumors not displaying any evidence of growth, others demonstrating early, persistent growth and a small number growing following an extended period of indolence. Emerging evidence now suggests that far from representing Schwann cell proliferation only, the tumor microenvironment is complex, with inflammation proposed to play a key role in their growth. In this review, we provide an overview of this new evidence, including the role played by immune cell infiltration, the underlying molecular pathways involved, and biomarkers for detecting this inflammation in vivo. Given the limitations of current treatments, there is a pressing need for novel therapies to aid in the management of this condition, and we conclude by proposing areas for future research that could lead to the development of therapies targeted toward inflammation in vestibular schwannoma.

Hearing impairment and associated morphological changes in pituitary adenylate cyclase activating polypeptide (PACAP)-deficient mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a regulatory and cytoprotective neuropeptide, its deficiency implies accelerated aging in mice. It is present in the auditory system having antiapoptotic effects. Expression of Ca²⁺-binding proteins and its PAC1 receptor differs in the inner ear of PACAP-deficient (KO) and wild-type (WT) mice. Our aim was to elucidate the functional role of PACAP in the auditory system. Auditory brainstem response (ABR) tests found higher hearing thresholds in KO mice at click and low frequency burst stimuli. Hearing impairment at higher frequencies showed as reduced ABR wave amplitudes and latencies in KO animals. Increase in neuronal activity, demonstrated by c-Fos immunolabeling, was lower in KO mice after noise exposure in the ventral and dorsal cochlear nuclei. Noise induced neuronal activation was similar in further relay nuclei of the auditory pathway of WT and KO mice. Based on the similar inflammatory and angiogenic protein profile data from cochlear duct lysates, neither inflammation nor disturbed angiogenesis, as potential pathological components in sensorineural hearing losses, seem to be involved in the pathomechanism of the presented functional and morphological changes in PACAP KO mice. The hearing impairment is probably concomitant with the markedly accelerated aging processes in these animals.

Cognitive Decline, Dementia, Alzheimer's Disease and Presbycusis: Examination of the Possible Molecular Mechanism

The incidences of presbycusis and dementia are high among geriatric diseases. Presbycusis is the general term applied to age-related hearing loss and can be caused by many risk factors, such as noise exposure, smoking, medication, hypertension, family history, and other factors. Mutation of mitochondrial DNA in hair cells, spiral ganglion cells, and stria vascularis cells of the cochlea is the basic mechanism of presbycusis. Dementia is a clinical syndrome that includes the decline of cognitive and conscious states and is caused by many neurodegenerative diseases, of which Alzheimer’s disease (AD) is the most common. The amyloid cascade hypothesis and tau hypothesis are the two major hypotheses that describe the AD pathogenic mechanism. Recent studies have shown that deposition of Aβ and hyperphosphorylation of the tau protein may cause mitochondrial dysfunction. An increasing number of papers have reported that, on one hand, the auditory system function in AD patients is damaged as their cognitive ability declines and that, on the other hand, hearing loss may be a risk factor for dementia and AD. However, the relationship between presbycusis and AD is still unknown. By reviewing the relevant literature, we found that the SIRT1-PGC1α pathway and LKB1 (or CaMKKβ)-AMPK pathway may play a role in the preservation of cerebral neuron function by taking part in the regulation of mitochondrial function. Then vascular endothelial growth factor signal pathway is activated to promote vascular angiogenesis and maintenance of the blood–brain barrier integrity. Recently, experiments have also shown that their expression levels are altered in both presbycusis and AD mouse models. Therefore, we propose that exploring the specific molecular link between presbycusis and AD may provide new ideas for their prevention and treatment.

Vascular endothelial growth factor: a neurovascular target in neurological diseases

Brain function critically relies on blood vessels to supply oxygen and nutrients, to establish a barrier for neurotoxic substances, and to clear waste products. The archetypal vascular endothelial growth factor, VEGF, arose in evolution as a signal affecting neural cells, but was later co-opted by blood vessels to regulate vascular function. Consequently, VEGF represents an attractive target to modulate brain function at the neurovascular interface. On the one hand, VEGF is neuroprotective, through direct effects on neural cells and their progenitors and indirect effects on brain perfusion. In accordance, preclinical studies show beneficial effects of VEGF administration in neurodegenerative diseases, peripheral neuropathies and epilepsy. On the other hand, pathologically elevated VEGF levels enhance vessel permeability and leakage, and disrupt blood-brain barrier integrity, as in demyelinating diseases, for which blockade of VEGF may be beneficial. Here, we summarize current knowledge on the role and therapeutic potential of VEGF in neurological diseases.

The redox protein p66(shc) mediates cochlear vascular dysfunction and transient noise-induced hearing loss

p66^shc, a member of the ShcA protein family, is essential for cellular response to oxidative stress, and elicits the formation of mitochondrial Reactive Oxygen Species (ROS), thus promoting vasomotor dysfunction and inflammation. Accordingly, mice lacking the p66 isoform display increased resistance to oxidative tissue damage and to cardiovascular disorders. Oxidative stress also contributes to noise-induced hearing loss (NIHL); we found that p66^shc expression and serine phosphorylation were induced following noise exposure in the rat cochlea, together with markers of oxidative stress, inflammation and ischemia as indicated by the levels of the hypoxic inducible factor (HIF) and the vascular endothelial growth factor (VEGF) in the highly vascularised cochlear lateral region and spiral ganglion. Importantly, p66^shc knock-out (p66 KO) 126 SvEv adult mice were less vulnerable to acoustic trauma with respect to wild type controls, as shown by preserved auditory function and by remarkably lower levels of oxidative stress and ischemia markers. Of note, decline of auditory function observed in 12 month old WT controls was markedly attenuated in p66KO mice consistent with delayed inner ear senescence. Collectively, we have identified a pivotal role for p66^shc -induced vascular dysfunction in a common pathogenic cascade shared by noise-induced and age-related hearing loss.

Low-dose bevacizumab induces radiographic regression of vestibular schwannomas in neurofibromatosis type 2: A case report and literature review

The current case study aimed to explore the efficacy of a low-dose bevacizumab regimen in inhibiting tumor growth and minimizing adverse effects. A 55-year-old man with neurofibromatosis type 2 (NF2) suffered bilateral vestibular schwannomas (VS) measuring 5.25 and 2.54 cm³ on the left and right, respectively. His capacity for bilateral language recognition was impaired. However, the patient refused microsurgical tumor resection and gamma knife therapy. Low-dose bevacizumab regimen (3.3–2.2 mg/kg every 2–4 weeks) was administered by intravenous injection for ~1.5 years to inhibit tumor growth and avoid further deterioration of hearing. Compared with baseline measurements prior to treatment, the bilateral VS regressed to 3.59 cm³ (68%) and 2.08 cm³ (82%) on the left and right, respectively. No hearing improvement was detected; however, the patient subjectively experienced a significant hearing improvement as his ability to communicate with people and distinguish voices was restored. No adverse effects were observed. Bevacizumab provides an alternative treatment option for those who refuse surgical intervention. Given the adverse effects commonly induced by bevacizumab, the use of a low-dose regimen would appear to be promising with regard to tumor regression and hearing preservation for patients with VS in NF2. However, the minimum dose required to sustain a response to bevacizumab in NF2 patients remains unknown. Finding the minimum effective dose sufficient to sustain hearing and/or volumetric response for individual patients is required.

Vascular biomarkers derived from dynamic contrast-enhanced MRI predict response of vestibular schwannoma to antiangiogenic therapy in type 2 neurofibromatosis

BACKGROUND

Antiangiogenic therapy of vestibular schwannoma (VS) in type 2 neurofibromatosis can produce tumor shrinkage with response rates of 40%-60%. This study examines the predictive value of parameter-derived MRI in this setting.

METHODS

Twelve patients with 20 VSs were recruited. Each had at least one rapidly growing tumor. Patients were treated with bevacizumab, 5 mg/kg every 2 weeks. Patients with stable or reduced VS volume were maintained at 2.5-5 mg every 4 weeks after 6 months. Those who failed treatment had their bevacizumab discontinued. Dynamic contrast-enhanced (DCE) MRI performed prior to treatment using a high temporal resolution technique, and data were analyzed to allow measurement of contrast transfer coefficient (K(trans)), vascular fraction (v(p)), extravascular-extracellular fraction (v(e)). Relaxation rate (R1(N)) was measured using a variable flip angle technique. Apparent diffusional coefficient (ADC) was calculated from diffusion-weighted imaging. The predictive power of microvascular parameters and ADC were examined using logistic regression modeling.

RESULTS

Responding tumors were larger (P < .001), had lower R1(N) (P < .001), and higher K(trans) (P < .05) and ADC (P < .01). They showed increases in R1(N) (P < .01) and reduction of K(trans) (P < .01) and ADC (P < .01). Modeling to predict response demonstrated significant independent predictive power for R1(N) (Β = - 0.327, P < .001), and K(trans) (Β = 0.156, P < .05). Modeling to predict percentage change in tumor volume at 90 days identified baseline tumor volume (Β = 5.503, P < .05), R1(N) (Β = - 5.844, P < .05), and K(trans) (Β = 5.622, P < .05) as independent significant predictors.

CONCLUSIONS

In patients with type 2 neurofibromatosis, biomarkers from DCE-MRI are predictive of VS volume response to inhibition of vascular endothelial growth factor inhibition.

Secreted Factors from Human Vestibular Schwannomas Can Cause Cochlear Damage

Vestibular schwannomas (VSs) are the most common tumours of the cerebellopontine angle. Ninety-five percent of people with VS present with sensorineural hearing loss (SNHL); the mechanism of this SNHL is currently unknown. To establish the first model to study the role of VS-secreted factors in causing SNHL, murine cochlear explant cultures were treated with human tumour secretions from thirteen different unilateral, sporadic VSs of subjects demonstrating varied degrees of ipsilateral SNHL. The extent of cochlear explant damage due to secretion application roughly correlated with the subjects' degree of SNHL. Secretions from tumours associated with most substantial SNHL resulted in most significant hair cell loss and neuronal fibre disorganization. Secretions from VSs associated with good hearing or from healthy human nerves led to either no effect or solely fibre disorganization. Our results are the first to demonstrate that secreted factors from VSs can lead to cochlear damage. Further, we identified tumour necrosis factor alpha (TNFα) as an ototoxic molecule and fibroblast growth factor 2 (FGF2) as an otoprotective molecule in VS secretions. Antibody-mediated TNFα neutralization in VS secretions partially prevented hair cell loss due to the secretions. Taken together, we have identified a new mechanism responsible for SNHL due to VSs.