Progressive loss of hearing and balance in superficial siderosis due to occult spinal dural defects.

PURPOSE: Superficial siderosis, a progressive, debilitating, neurological disease, often presents with bilateral impairment of auditory and vestibular function. We highlight that superficial siderosis is often due to a repairable spinal dural defect of the type that can also cause spontaneous intracranial hypotension. METHODS: Retrospective chart review of five patients presenting with moderate to severe, progressive bilateral sensorineural hearing loss as well as vestibular loss. All patients had developed superficial siderosis from spinal dural defects: three after trauma, one after spinal surgery and one from a thoracic discogenic microspur. RESULTS: The diagnosis was made late in all five patients; despite surgical repair in four, hearing and vestibular loss failed to improve. CONCLUSIONS: In patients presenting with progressive bilateral sensorineural hearing loss, superficial siderosis should be considered as a possible cause. If these patients also have bilateral vestibular loss, cerebellar impairment and anosmia, then the diagnosis is likely and the inevitable disease progress might be halted by finding and repairing the spinal dural defect.

Use of deep learning in the MRI diagnosis of Chiari malformation type I.

PURPOSE: To train deep learning convolutional neural network (CNN) models for classification of clinically significant Chiari malformation type I (CM1) on MRI to assist clinicians in diagnosis and decision making. METHODS: A retrospective MRI dataset of patients diagnosed with CM1 and healthy individuals with normal brain MRIs from the period January 2010 to May 2020 was used to train ResNet50 and VGG19 CNN models to automatically classify images as CM1 or normal. A total of 101 patients diagnosed with CM1 requiring surgery and 111 patients with normal brain MRIs were included (median age 30 with an interquartile range of 23-43; 81 women with CM1). Isotropic volume transformation, image cropping, skull stripping, and data augmentation were employed to optimize model accuracy. K-fold cross validation was used to calculate sensitivity, specificity, and the area under receiver operating characteristic curve (AUC) for model evaluation. RESULTS: The VGG19 model with data augmentation achieved a sensitivity of 97.1% and a specificity of 97.4% with an AUC of 0.99. The ResNet50 model achieved a sensitivity of 94.0% and a specificity of 94.4% with an AUC of 0.98. CONCLUSIONS: VGG19 and ResNet50 CNN models can be trained to automatically detect clinically significant CM1 on MRI with a high sensitivity and specificity. These models have the potential to be developed into clinical support tools in diagnosing CM1.

Externalization of Mitochondrial PDCE2 on Irradiated Endothelium as a Target for Radiation-Guided Drug Delivery and Precision Thrombosis of Pathological Vasculature.

Endothelial cells are highly sensitive to ionizing radiation, and exposure leads to multiple adaptive changes. Remarkably, part of this response is the translocation of normally intracellular proteins to the cell surface. It is unclear whether this ectopic expression has a protective or deleterious function, but, regardless, these surface-exposed proteins may provide unique discriminatory targets for radiation-guided drug delivery to vascular malformations or tumor vasculature. We investigated the ability of an antibody-thrombin conjugate targeting mitochondrial PDCE2 (E2 subunit of pyruvate dehydrogenase) to induce precision thrombosis on irradiated endothelial cells in a parallel-plate flow system. Click-chemistry was used to create antibody-thrombin conjugates targeting PDCE2 as the vascular targeting agent (VTA). VTAs were injected into the parallel-plate flow system with whole human blood circulating over irradiated cells. The efficacy and specificity of fibrin-thrombus formation was assessed relative to non-irradiated controls. The PDCE2-targeting VTA dose-dependently increased thrombus formation: minimal thrombosis was induced in response to 5 Gy radiation; doses of 15 and 25 Gy induced significant thrombosis with equivalent efficacy. Negligible VTA binding or thrombosis was demonstrated in the absence of radiation or with non-targeted thrombin. PDCE2 represents a unique discriminatory target for radiation-guided drug delivery and precision thrombosis in pathological vasculature.

Respiratory cerebrospinal fluid flow is driven by the thoracic and lumbar spinal pressures.

KEY POINTS: Respiration plays a key role in the circulation of cerebrospinal fluid (CSF) around the central nervous system. During inspiration increased venous return from the cranium is believed to draw CSF rostrally. However, this mechanism does not explain why CSF has also been observed to move caudally during inspiration. We show that during inspiration decreased intrathoracic pressure draws venous blood from the cranium and lumbar spine towards the thorax. We also show that the abdominal pressure was associated with rostral CSF displacement. However, a caudal shift of cervical CSF was seen with low abdominal pressure and comparably negative intrathoracic pressures. These results suggest that the effects of epidural blood flow within the spinal canal need to be considered, as well as the cranial blood volume balance, to understand respiratory-related CSF flow. These results may prove useful for the treatment of CSF obstructive pathology and understanding the behaviour of intrathecal drug injections. ABSTRACT: It is accepted that during inspiration, cerebrospinal fluid (CSF) flows rostrally to compensate for decreased cranial blood volume, caused by venous drainage due to negative intrathoracic pressure. However, this mechanism does not explain observations of caudal CSF displacement during inspiration. Determining the drivers of respiratory CSF flow is crucial for understanding the pathophysiology of CSF flow disorders. To quantify the influence of respiration on CSF flow, real-time phase-contrast magnetic resonance imaging (MRI) was used to record CSF and blood flow, while healthy subjects (5:5 M:F, 25-50 years) performed either a brief expiratory or inspiratory effort between breaths. Transverse images were taken perpendicular to the spinal canal in the middle of the C3 and L2 vertebrae. The same manoeuvres were then performed after a nasogastric pressure catheter was used to measure the intrathoracic and abdominal pressures. During expiratory-type manoeuvres that elevated abdominal and intrathoracic pressures, epidural blood flow into the spinal canal increased and CSF was displaced rostrally. With inspiratory manoeuvres, the negative intrathoracic pressure drew venous blood from C3 and L2 towards the thoracic spinal canal, and cervical CSF was displaced both rostrally and caudally, despite the increased venous drainage. Regression analysis showed that rostral displacement of CSF at both C3 (adjusted R2  = 0.53; P < 0.001) and L2 (adjusted R2  = 0.38; P < 0.001) were associated with the abdominal pressure. However, with low abdominal pressure and comparably negative intrathoracic pressure, cervical CSF flowed caudally. These findings suggest that changes in both the cranial and spinal pressures need to be considered to understand respiratory CSF flow.

Radiation-Stimulated Translocation of CD166 and CRYAB to the Endothelial Surface Provides Potential Vascular Targets on Irradiated Brain Arteriovenous Malformations.

Vascular targeting with pro-thrombotic antibody-conjugates is a promising biological treatment for brain arteriovenous malformations (bAVMs). However, targeted drug delivery relies on the identification of unique or overexpressed markers on the surface of a target cell. In the absence of inherent biological markers, stereotactic radiosurgery may be used to prime induction of site-specific and targetable molecular changes on the endothelial surface. To investigate lumen-accessible, endothelial targets induced by radiation, we combined Gamma knife surgery in an AVM animal model with in vivo biotin-labeling and comparative proteomics. Two proteins, αB-crystallin (CRYAB)-a small heat shock protein that normally acts as an intracellular chaperone to misfolded proteins-and activated leukocyte cell adhesion molecule CD166, were further validated for endothelial surface expression after irradiation. Immunostaining of endothelial cells in vitro and rat AVM tissue ex vivo confirmed de novo induction of CRYAB following irradiation (20 Gy). Western analysis demonstrated that CRYAB accumulated intracellularly as a 20 kDa monomer, but, at the cell surface, a novel 65 kDa protein was observed, suggesting radiation stimulates translocation of an atypical CRYAB isoform. In contrast, CD166 had relatively high expression in non-irradiated cells, localized predominantly to the lateral surfaces. Radiation increased CD166 surface exposure by inducing translocation from intercellular junctions to the apical surface without significantly altering total protein levels. These findings reinforce the dynamic molecular changes induced by radiation exposure, particularly at the cell surface, and support further investigation of radiation as a priming mechanism and these molecules as putative targets for focused drug delivery in irradiated tissue.

Proteomics identification of radiation-induced changes of membrane proteins in the rat model of arteriovenous malformation in pursuit of targets for brain AVM molecular therapy.

BACKGROUND: Rapid identification of novel targets and advancement of a vascular targeting strategy requires a comprehensive assessment of AVM endothelial membrane protein changes in response to irradiation. The aim of this study is to provide additional potential target protein molecules for evaluation in animal trials to promote intravascular thrombosis in AVM vessels post radiosurgery. METHODS: We employed in vivo biotinylation methodology that we developed, to label membrane proteins in the rat model of AVM post radiosurgery. Mass spectrometry expression (MSE) analysis was used to identify and quantify surface protein expression between irradiated and non irradiated rats, which mimics a radiosurgical treatment approach. RESULTS: Our proteomics data revealed differentially expressed membrane proteins between irradiated and non irradiated rats, e.g. profilin-1, ESM-1, ion channel proteins, annexin A2 and lumican. CONCLUSION: This work provides additional potential target protein molecules for evaluation in animal trials to promote intravascular thrombosis in AVM vessels post radiosurgery.

A Systematic Review of Cognition in Chiari I Malformation.

Displacement of the cerebellar tonsils in Chiari type I malformation (CMI) can affect functions controlled by the cerebellum and brainstem. While playing an integral role in the control of movement, the cerebellum also has widespread cortical connections, influencing a range of cognitive process. A systematic literature review was conducted to examine the relationship between cognition and CMI, assessing evidence for general or domain-specific cognitive change. The search protocol examined the AMED, CINAHL, Cochrane Library, EMBASE, MEDLINE, PsycINFO, and Scopus databases. Articles meeting the following criteria were included in this review (i) examined children or adults with a clinically defined diagnosis of CMI, (ii) assessed cognitive function with a prospective examination, (iii) included at least one standardized instrument designed to measure general or specific domains of cognitive function, and (iv) were published in English in a peer-reviewed journal. Twelve articles were identified, including 783 cases aged 3 months to 64 years. General cognition, processing speed, and learning and memory appeared less affected, while language deficits appeared to diminish with age. Executive dysfunction was the most commonly reported cognitive impairment, while attention and working memory, and visuospatial and perceptual skills also appeared vulnerable. Numerous methodological limitations were identified that should be considered in interpreting the impact of CMI and planning future investigations. Overall, there is currently insufficient evidence to describe a valid and reliable profile of cognitive impairment in CMI. Further research is required to confirm these preliminary psychometric results and integrate them with pathophysiological models.

De novo brain arteriovenous malformation after tumor resection: case report and literature review.

The congenital origin of brain arteriovenous malformations (bAVMs) has been increasingly challenged by reports of de novo bAVMs in patients previously confirmed to have no vascular malformation. We describe the oldest patient reported in the English language literature harboring a de novo bAVM. An uneventful frontal convexity meningioma resection was performed for a 60-year-old woman, and at 67 years of age, a bAVM was detected by MRI and confirmed by digital subtraction angiography at the site of the previous meningioma resection. This case adds to the growing literature that the etiology of bAVMs is most likely multifactorial.

Identification of protein targets in cerebral endothelial cells for brain arteriovenous malformation (AVMs) molecular therapies.

BACKGROUND: To develop a new molecular targeted treatment for brain (AVMs), identification of membrane proteins that are localised on the AVM endothelium is crucial. Current treatment methods are surgery and radiosurgery. However, complete occlusion post radiosurgery are achieved within 3 years, while patient remain at risk of haemorrhage. This study aims to identify potential protein targets in AVM endothelial cells that discriminate these vessels from normal vessels; these proteins targets will be investigated for the molecular therapy of brain AVMs to promote rapid thrombosis after radiosurgery. METHODS: We employed in vitro biotinylation that we developed, and mass spectrometry to detect cell surface-exposed proteins in cultures of murine cerebral endothelial cells (bEnd.3). Two forms of mass spectrometry were applied (iTRAQ-MS and MSE) to identify and quantify membrane protein expression at various time-points following irradiation which simulates a radiosurgical treatment approach. Immunocytochemistry was used to confirm the expression of selected membrane proteins. ProteinPilot V4.0 software was used to analyse the iTRAQ-MS data and the MSE data was analysed using ProteinLynx Global Server version 2.5 software. RESULTS: The proteomics data revealed several differentially expressed membrane proteins between irradiated and non-irradiated cells at specific time points, e.g. PECAM-1, cadherin-5, PDI, EPCR and integrins. Immunocytochemistry data confirmed the expression of these proteins. CONCLUSION: Cell surface protein biotinylation and proteomics analysis successfully identified membrane proteins from murine brain endothelial cells in response to irradiation. This work suggests potential target protein molecules for evaluation in animal models of brain-AVM.

Nerve repair: toward a sutureless approach.

Peripheral nerve repair for complete section injuries employ reconstructive techniques that invariably require sutures in their application. Sutures are unable to seal the nerve, thus incapable of preventing leakage of important intraneural fluids from the regenerating nerve. Furthermore, sutures are technically demanding to apply for direct repairs and often induce detrimental scarring that impedes healing and functional recovery. To overcome these limitations, biocompatible and biodegradable glues have been used to seal and repair peripheral nerves. Although creating a sufficient seal, they can lack flexibility and present infection risks or cytotoxicity. Other adhesive biomaterials have recently emerged into practice that are usually based on proteins such as albumin and collagen or polysaccharides like chitosan. These adhesives form their union to nerve tissue by either photothermal (tissue welding) or photochemical (tissue bonding) activation with laser light. These biomaterial adhesives offer significant advantages over sutures, such as their capacity to unite and seal the epineurium, ease of application, reduced invasiveness and add the potential for drug delivery in situ to facilitate regeneration. This paper reviews a number of different peripheral nerve repair (or reconstructive) techniques currently used clinically and in experimental procedures for nerve injuries with or without tissue deficit.

Cerebellar Tonsillar Descent Mimicking Chiari Malformation.

Chiari I malformation has been defined as cerebellar tonsillar descent greater than 5 mm below the foramen magnum. Suboccipital decompression remains the mainstay of treatment for symptomatic patients. Other conditions sometimes have imaging features that mimic Chiari I malformation. These patients are at risk of misdiagnosis and mismanagement, including surgery that may be unnecessary or may even worsen the underlying condition. The aim of this study was to analyse a series of Chiari I malformation mimics and identify differentiating imaging features. The mimics are categorised as post-traumatic cranio-cervical junction arachnoiditis, dural band, spontaneous intracranial hypotension, idiopathic intracranial hypertension, and cysts. Better understanding of these conditions will assist with diagnosis and optimal management, including avoiding unnecessary surgery.

Aquaporin-4 expression and modulation in a rat model of post-traumatic syringomyelia.

Aquaporin-4 (AQP4) has been implicated in post-traumatic syringomyelia (PTS), a disease characterised by the formation of fluid-filled cysts in the spinal cord. This study investigated the expression of AQP4 around a mature cyst (syrinx) and the effect of pharmacomodulation of AQP4 on syrinx size. PTS was induced in male Sprague-Dawley rats by computerized spinal cord impact and subarachnoid kaolin injection. Immunofluorescence of AQP4 was carried out on mature syrinx tissue 12 weeks post-surgery. Increased AQP4 expression corresponded to larger, multiloculated cysts (R2 = 0.94), yet no localized changes to AQP4 expression in perivascular regions or the glia limitans were present. In a separate cohort of animals, at 6 weeks post-surgery, an AQP4 agonist (AqF026), antagonist (AqB050), or vehicle was administered daily over 4 days, with MRIs performed before and after the completion of treatment. Histological analysis was performed at 12 weeks post-surgery. Syrinx volume and length were not altered with AQP4 modulation. The correlation between increased AQP4 expression with syrinx area suggests that AQP4 or the glia expressing AQP4 are recruited to regulate water movement. Given this, further investigation should examine AQP4 modulation with dose regimens at earlier time-points after PTS induction, as these may alter the course of syrinx development.

A novel method to quantify perivascular space enlargement near the syrinx in a rodent model of post-traumatic syringomyelia.

Posttraumatic syringomyelia (PTS) is an enigmatic condition characterized by the development of fluid-filled cysts (syrinxes) within the spinal cord. Perivascular spaces (PVS) are a critical component of fluid transport within the central nervous system (CNS), with dilated PVSs variably implicated in the pathogenesis of syringomyelia. The extent and spatial distribution of dilated PVSs in syringomyelia, however, remains unclear. This study aims to develop a method to assess PVS dimensions across multiple spinal cord segments in rats with PTS. Syrinxes were induced in two Sprague-Dawley rats at C6/7 with computer-controlled motorized spinal cord impaction; two control rats underwent sham laminectomies. Spinal cord segments were obtained at C4, C6 and C8, cleared via tissue clearing protocols, stained with immunofluorescent antibodies and imaged under confocal microscopy. Qualitative and quantitative analyses of PVS size were performed. Arteriolar PVSs were enlarged in the perisyringeal region of the spinal cord, compared to the control cord. No PVS enlargement was observed above or below the syrinx. These results confirm previous incidental findings of enlarged PVSs in the perisyringeal region, providing new insights into PVS dimensions across multiple spinal segments, and providing a novel method for quantifying spinal cord perivascular space size distributions.

Statistical shape models of the posterior cranial fossa and hindbrain volumes may provide a more robust clinical metric for Chiari malformation.

Chiari malformation is characterised by the herniation of the cerebellar tonsils through the foramen magnum. However, tonsillar herniation and other 2D morphometric measurements of the posterior cranial fossa (PCF) have a weak association with patients' symptoms and clinical outcomes. This study aimed to contrast current 2D metrics with a novel 3D shape analysis of the PCF and the hindbrain, to determine if 3D measurements provides further insight into the pathophysiology of Chiari. The cranium of 12 controls and 21 Chiari malformation patients with (N = 9) and without (N = 12) a syrinx were scanned. The morphology of the PCF was quantified with typical 2D measurements. Additionally, a correspondence-based shape model that normalised the PCF volume, was used to find 3D differences in the shape of the PCF, and the distance of the hindbrain from the inner surfaces of the PCF. Shape analysis showed that, compared to controls, the caudal (p = 0.007; 2.3 mm, IQR: 1.6-3.3 mm) and anterior (p = 0.027; 1.3 mm,IQR: 1.1-1.6 mm) surfaces of the hindbrain were closer to the PCF in patients with and without a syrinx, respectively. However, there were negligible differences in the shape of the PCF between patient groups (p > 0.39). Current morphometric measures should be normalised for variation in PCF volume, so that shape measures are not biased. The reduced CSF space between the hindbrain and PCF will alter CSF dynamics, which may compress cerebellar vasculature and contribute to patient symptomatology.

Treatment of ruptured aneurysms of the choroidal collateral system in moyamoya disease: a systematic review and data analysis.

OBJECTIVE: Moyamoya disease (MMD) is a chronic, progressive steno-occlusive condition of the distal internal carotid arteries of unknown etiology. Collateral arterial networks typically develop in MMD, bypassing the steno-occlusion. Aneurysms arising on the collateral networks are a known source of hemorrhage. The choroidal collateral system is the most common location for collateral pathway aneurysms in MMD and associated hemorrhage. The authors performed data collection and analysis to further elucidate the best treatment approaches for ruptured aneurysms of the choroidal collateral system in MMD, which as yet remain unclear. METHODS: A comprehensive data collection and analysis of case reports and case series with ruptured choroidal collateral artery aneurysms (CCAAs) was performed. PRISMA guidelines for systematic reviews were followed and the Medline, Embase, and Scopus databases were searched for relevant studies. A database was created including patients with ruptured CCAA in MMD. Original data from case series were included whenever possible. A previously unreported case of a ruptured choroidal artery aneurysm in MMD treated by the authors was also included. RESULTS: The database comprised 72 patients with ruptured CCAA in MMD. The most common clinical symptoms were headache, nausea, and vomiting (39%). Initially, a conservative treatment approach was chosen in 29% of cases but led to rehemorrhage in 40% of cases; 63% of these rehemorrhages occurred during the first 35 days. Endovascular treatment seemed a safe option for aneurysm exclusion, mainly through parent vessel sacrifice, but had a treatment failure rate of 21%, due to inadequate access. Aneurysm treatment with revascularization as the initial treatment strategy led to aneurysm regression in 82% with no reported rehemorrhage. Aneurysm exclusion through open surgery was effective but was associated with a relatively high complication rate (25%). Outcome after rupture of CCAA was poor, with 41% of patients deceased or permanently disabled. Overall, patient outcomes were better in the endovascular and revascularization treatment group than in the conservative treatment group. CONCLUSIONS: Rupture of CCAA in MMD is associated with high morbidity and rerupture rate requiring urgent treatment.

Changes in intrathoracic pressure, not arterial pulsations, exert the greatest effect on tracer influx in the spinal cord.

BACKGROUND: Cerebrospinal fluid (CSF) circulation in the brain has garnered considerable attention in recent times. In contrast, there have been fewer studies focused on the spine, despite the expected importance of CSF circulation in disorders specific to the spine, including syringomyelia. The driving forces that regulate spinal CSF flow are not well defined and are likely to be different to the brain given the anatomical differences and proximity to the heart and lungs. The aims of this study were to determine the effects of heart rate, blood pressure and respiration on the distribution of CSF tracers in the spinal subarachnoid space, as well as into the spinal cord interstitium. METHODS: In Sprague Dawley rats, physiological parameters were manipulated such that the effects of spontaneous breathing (generating alternating positive and negative intrathoracic pressures), mechanical ventilation (positive intrathoracic pressure only), tachy/bradycardia, as well as hyper/hypotension were separately studied. To investigate spinal CSF hydrodynamics, in vivo near-infrared imaging of intracisternally infused indocyanine green was performed. CSF tracer transport was further characterised with in vivo two-photon intravital imaging. Tracer influx at a microscopic level was quantitatively characterised by ex vivo epifluorescence imaging of fluorescent ovalbumin. RESULTS: Compared to mechanically ventilated controls, spontaneous breathing animals had significantly greater movement of tracer in the subarachnoid space. There was also greater influx into the spinal cord interstitium. Hypertension and tachycardia had no significant effect on spinal subarachnoid spinal CSF tracer flux and exerted less effect than respiration on tracer influx into the spinal cord. CONCLUSIONS: Intrathoracic pressure changes that occur over the respiratory cycle, particularly decreased intrathoracic pressures generated during inspiration, have a profound effect on tracer movement after injection into spinal CSF and increase cord parenchymal tracer influx. Arterial pulsations likely drive fluid transport from perivascular spaces into the surrounding interstitium, but their overall impact is less than that of the respiratory cycle on net tracer influx.

The Evolution of Safe and Effective Coaguligands for Vascular Targeting and Precision Thrombosis of Solid Tumors and Vascular Malformations.

In cardiovascular and cerebrovascular biology, control of thrombosis and the coagulation cascade in ischemic stroke, myocardial infarction, and other coagulopathies is the focus of significant research around the world. Ischemic stroke remains one of the largest causes of death and disability in developed countries. Preventing thrombosis and protecting vessel patency is the primary goal. However, utilization of the body's natural coagulation cascades as an approach for targeted destruction of abnormal, disease-associated vessels and tissues has been increasing over the last 30 years. This vascular targeting approach, often termed "vascular infarction", describes the deliberate, targeted delivery of a thrombogenic effector to diseased blood vessels with the aim to induce localized activation of the coagulation cascade and stable thrombus formation, leading to vessel occlusion and ablation. As systemic delivery of pro-thrombotic agents may cause consternation amongst traditional stroke researchers, proponents of the approach must suitably establish both efficacy and safety to take this field forward. In this review, we describe the evolution of this field and, with a focus on thrombogenic effectors, summarize the current literature with respect to emerging trends in "coaguligand" development, in targeted tumor vessel destruction, and in expansion of the approach to the treatment of brain vascular malformations.

Tachycardia and hypertension enhance tracer efflux from the spinal cord.

BACKGROUND: Disruption of cerebrospinal fluid (CSF)/interstitial fluid (ISF) exchange in the spinal cord is likely to contribute to central nervous system (CNS) diseases that involve abnormal fluid accumulation, including spinal cord oedema and syringomyelia. However, the physiological factors that govern fluid transport in the spinal cord are poorly understood. The aims of this study were to determine the effects of cardiac pulsations and respiration on tracer signal increase, indicative of molecular movement following infusion into the spinal cord grey or white matter. METHODS: In Sprague Dawley rats, physiological parameters were manipulated such that the effects of spontaneous breathing (generating alternating positive and negative intrathoracic pressures), mechanical ventilation (positive intrathoracic pressure only), tachycardia (heart atrial pacing), as well as hypertension (pharmacologically induced) were separately studied. Since fluid outflow from the spinal cord cannot be directly measured, we assessed the molecular movement of fluorescent ovalbumin (AFO-647), visualised by an increase in tracer signal, following injection into the cervicothoracic spinal grey or white matter. RESULTS: Tachycardia and hypertension increased AFO-647 tracer efflux, while the concomitant negative and positive intrathoracic pressures generated during spontaneous breathing did not when compared to the positive-pressure ventilated controls. Following AFO-647 tracer injection into the spinal grey matter, increasing blood pressure and heart rate resulted in increased tracer movement away from the injection site compared to the hypotensive, bradycardic animals (hypertension: p = 0.05, tachycardia: p < 0.0001). Similarly, hypertension and tachycardia produced greater movement of AFO-647 tracer longitudinally along the spinal cord following injection into the spinal white matter (p < 0.0001 and p = 0.002, respectively). Tracer efflux was strongly associated with all blood vessel types. CONCLUSIONS: Arterial pulsations have profound effects on spinal cord interstitial fluid homeostasis, generating greater tracer efflux than intrathoracic pressure changes that occur over the respiratory cycle, demonstrated by increased craniocaudal CSF tracer movement in the spinal cord parenchyma.

Occlusion of Animal Model Arteriovenous Malformations Using Vascular Targeting.

Brain arteriovenous malformations (AVMs) are a significant cause of intracerebral hemorrhage in children and young adults. Currently, one third of patients have no viable treatment options. Vascular targeting agents (VTAs) are being designed to deliver pro-thrombotic molecules to the abnormal AVM vessels for rapid occlusion and cure. This study assessed the efficacy of a pro-thrombotic VTA targeting phosphatidylserine (PS) in a radiation-primed AVM animal model. The model AVM was surgically created in rats by anastomosis of the left external jugular vein to the adjacent common carotid artery. After 6 weeks, the AVM was irradiated (20 Gy) using gamma knife surgery (GKS). A PS-targeting VTA was created by conjugation of annexin V with human thrombin and administered intravenously 3 weeks post-GKS or sham. Unconjugated thrombin was used as a non-targeting control. AVM thrombosis and occlusion was monitored 3 weeks later by angiography and histology. Preliminary experiments established a safe dose of active thrombin for systemic administration. Subsequently, a single dose of annexin V-thrombin conjugate (0.77 mg/kg) resulted in angiographic AVM occlusion in sham (75%) and irradiated (63%) animals, while non-targeted thrombin did not. Lowering the conjugate dose (0.38 mg/kg) decreased angiographic AVM occlusion in sham (13%) relative to irradiated (80%) animals (p = 0.03) as did delivery of two consecutive doses of 0.38 mg/kg, 2 days apart (sham (0%); irradiated (78%); p = 0.003). These findings demonstrate efficacy of the PS-targeting VTA and the feasibility of a vascular targeting approach for occlusion of high-flow AVMs. Targeting specificity can be enhanced by radiation-sensitization and VTA dose modification.

Targeting of externalized αB-crystallin on irradiated endothelial cells with pro-thrombotic vascular targeting agents: Potential applications for brain arteriovenous malformations.

BACKGROUND: Vascular targeting uses molecular markers on the surface of diseased vasculature for ligand-directed drug delivery to induce vessel occlusion or destruction. In the absence of discriminatory markers, such as in brain arteriovenous malformations (AVMs), stereotactic radiosurgery may be used to prime molecular changes on the endothelial surface. This study explored αB-crystallin (CRYAB) as a radiation induced target and pre-tested the specificity and efficacy of a CRYAB-targeting coaguligand for in vitro thrombus induction. METHODS: A parallel-plate flow system was established to circulate human whole blood over a layer of human brain endothelial cells. A conjugate of anti-CRYAB antibody and thrombin was injected into the circuit to compare binding and thrombus formation on cells with or without prior radiation treatment (0-25 Gy). RESULTS: Radiation increased CRYAB expression and surface exposure in human brain endothelial cells. In the parallel-plate flow system, the targeted anti-CRYAB-thrombin conjugate increased thrombus formation on the surface of irradiated cells relative to non-irradiated cells and to a non-targeting IgG-thrombin conjugate. Fibrin deposition and accumulation of fibrinogen degradation products increased significantly at radiation doses at or above 15 Gy with conjugate concentrations of 1.25 and 2.5 µg/mL. CONCLUSIONS: CRYAB exposure can be detected at the surface of human brain endothelial cells in response to irradiation. Pro-thrombotic CRYAB-targeting conjugates can bind under high flow conditions and in the presence of whole blood induce stable thrombus formation with high specificity and efficacy on irradiated surfaces. CRYAB provides a novel radiation marker for potential vascular targeting in irradiated brain AVMs.