Animal Model Of Arteriovenous Malformation Research Articles

In vivo imaging of endothelial cell adhesion molecule expression after radiosurgery in an animal model of arteriovenous malformation.

Focussed radiosurgery may provide a means of inducing molecular changes on the luminal surface of diseased endothelium to allow targeted delivery of novel therapeutic compounds. We investigated the potential of ionizing radiation to induce surface expression of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) on endothelial cells (EC) in vitro and in vivo, to assess their suitability as vascular targets in irradiated arteriovenous malformations (AVMs). Cultured brain microvascular EC were irradiated by linear accelerator at single doses of 0, 5, 15 or 25 Gy and expression of ICAM-1 and VCAM-1 measured by qRT-PCR, Western, ELISA and immunocytochemistry. In vivo, near-infrared (NIR) fluorescence optical imaging using Xenolight 750-conjugated ICAM-1 or VCAM-1 antibodies examined luminal biodistribution over 84 days in a rat AVM model after Gamma Knife surgery at a single 15 Gy dose. ICAM-1 and VCAM-1 were minimally expressed on untreated EC in vitro. Doses of 15 and 25 Gy stimulated expression equally; 5 Gy was not different from the unirradiated. In vivo, normal vessels did not bind or retain the fluorescent probes, however binding was significant in AVM vessels. No additive increases in probe binding were found in response to radiosurgery at a dose of 15 Gy. In summary, radiation induces adhesion molecule expression in vitro but elevated baseline levels in AVM vessels precludes further induction in vivo. These molecules may be suitable targets in irradiated vessels without hemodynamic derangement, but not AVMs. These findings demonstrate the importance of using flow-modulated, pre-clinical animal models for validating candidate proteins for vascular targeting in irradiated AVMs.

Phosphatidylserine Translocation after Radiosurgery in an Animal Model of Arteriovenous Malformation.

Phosphatidylserine (PS) is asymmetrically distributed across the plasma membrane, located predominantly on the inner leaflet in healthy cells. Translocation of PS to the outer leaflet makes it available as a target for biological therapies. We examined PS translocation after radiosurgery in an animal model of brain arteriovenous malformation (AVM). An arteriovenous fistula was created by end-to-side anastomosis of the left external jugular vein to the common carotid artery in 6-week-old, male Sprague Dawley rats. Six weeks after AVM creation, 15 rats underwent Gamma Knife stereotactic radiosurgery receiving a single 15 Gy dose to the margin of the fistula; 15 rats received sham treatment. Externalization of PS was examined by intravenous injection of a PS-specific near-infrared probe, PSVue-794, and in vivo fluorescence optical imaging at 1, 7, 21, 42, 63 and 84 days postirradiation. Fluorescent signaling indicative of PS translocation to the luminal cell surface accumulated in the AVM region, in both irradiated and nonirradiated animals, at all time points. Fluorescence was localized specifically to the AVM region and was not present in any other anatomical sites. Translocated PS increased over time in irradiated rats (P < 0.001) but not in sham-irradiated rats and this difference reached statistical significance at day 84 (P < 0.05). In summary, vessels within the mature rat AVM demonstrate elevated PS externalization compared to normal vessels. A single dose of ionizing radiation can increase PS externalization in a time-dependent manner. Strict localization of PS externalization within the AVM region suggests that stereotactic radiosurgery can serve as an effective priming agent and PS may be a suitable candidate for vascular-targeting approaches to AVM treatment.

Radiosurgery Alters the Endothelial Surface Proteome: Externalized Intracellular Molecules as Potential Vascular Targets in Irradiated Brain Arteriovenous Malformations.

Stereotactic radiosurgery (SRS) is an established treatment for brain arteriovenous malformations (AVMs) that drives blood vessel closure through cellular proliferation, thrombosis and fibrosis, but is limited by a delay to occlusion of 2-3 years and a maximum treatable size of 3 cm. In this current study we used SRS as a priming tool to elicit novel protein expression on the endothelium of irradiated AVM vessels, and these proteins were then targeted with prothrombotic conjugates to induce rapid thrombosis and vessel closure. SRS-induced protein changes on the endothelium in an animal model of AVM were examined using in vivo biotin labeling of surface-accessible proteins and comparative proteomics. LC-MS/MS using SWATH acquisition label-free mass spectrometry identified 280 proteins in biotin-enriched fractions. The abundance of 56 proteins increased after irradiation of the rat arteriovenous fistula (20 Gy, ≥1.5-fold). A large proportion of intracellular proteins were present in this subset: 29 mitochondrial and 9 cytoskeletal. Three of these proteins were chosen for further validation based on previously published evidence for surface localization and a role in autoimmune stimulation: cardiac troponin I (TNNI3); manganese superoxide dismutase (SOD2); and the E2 subunit of the pyruvate dehydrogenase complex (PDCE2). Immunostaining of AVM vessels confirmed an increase in abundance of PDCE2 across the vessel wall, but not a measurable increase in TNNI3 or SOD2. All three proteins co-localized with the endothelium after irradiation, however, more detailed subcellular distribution could not be accurately established. In vitro, radiation-stimulated surface translocation of all three proteins was confirmed in nonpermeabilized brain endothelial cells using immunocytochemistry. Total protein abundance increased modestly after irradiation for PDCE2 and SOD2 but decreased for TNNI3, suggesting that radiation primarily affects subcellular distribution rather than protein levels. The novel identification of these proteins as surface exposed in response to radiation raises important questions about their potential role in radiation-induced inflammation, fibrosis and autoimmunity, but may also provide unique candidates for vascular targeting in brain AVMs and other vascular tissues.

Focused post mortem dissection technique for harvest of rete mirabile in domestic swine (Sus scrofa)

BackgroundRete mirabile (RM) of the domestic pig is a popular animal model of arteriovenous malformations. The RM (Latin for ‘wonderful net)’ comprises the arterioarterial portal connecting ascending pharyngeal arteries and...

Durable thrombosis in a rat model of arteriovenous malformation treated with radiosurgery and vascular targeting

Radiosurgical treatment of brain arteriovenous malformations (AVMs) has the significant shortcomings of being limited to lesions smaller than 3 cm in diameter and of a latency-to-cure time of up to 3 years. A possible method of overcoming these limitations is stimulation of thrombosis by using vascular targeting. Using an animal model of AVM, the authors examined the durability of the thrombosis induced by the vascular-targeting agents lipopolysaccharide and soluble tissue factor conjugate (LPS/sTF). Stereotactic radiosurgery or sham radiation was administered to 32 male Sprague-Dawley rats serving as an animal model of AVM; 24 hours after this intervention, the rats received an intravenous injection of LPS/sTF or normal saline. The animals were killed at 1, 7, 30, or 90 days after treatment. Immediately beforehand, angiography was performed, and model AVM tissue was harvested for histological analysis to assess rates of vessel thrombosis. Among rats that received radiosurgery and LPS/sTF, induced thrombosis occurred in 58% of small AVM vessels; among those that received radiosurgery and saline, thrombosis occurred in 12% of small AVM vessels (diameter < 200 μm); and among those that received LPS/sTF but no radiosurgery, thrombosis occurred at an intermediate rate of 43%. No systemic toxicity or intravascular thrombosis remote from the target region was detected in any of the animals. Vascular targeting can increase intravascular thrombosis after radiosurgery, and the vessel occlusion is durable. Further work is needed to refine this approach to AVM treatment, which shows promise as a way to overcome the limitations of radiosurgery.

Endothelial Gene Expression and Molecular Changes in Response to Radiosurgery inIn VitroandIn VivoModels of Cerebral Arteriovenous Malformations

Radiosurgery for cerebral arteriovenous malformations (AVMs) is limited to 2-year latency. There is no early marker to monitor whether the lesion is responsive to radiosurgery. In this study, we examined endothelial gene expression and molecular changes in response to radiosurgery. Gene expression of E- and P-selectin, ICAM-1, PECAM-1, VCAM-1, tissue factor, and vWF in human cerebral microvascular endothelial cells was quantified by RT-qPCR at different radiation doses and time points. Soluble E- and P-selectin, ICAM-1, VCAM-1, and tissue factor in an animal model of AVMs were quantified by ELISA at different time after radiosurgery. We found that gene expression of E- and P-selectin, ICAM-1, PECAM-1, and VCAM-1 was upregulated by radiation in a dose-dependent manner (P < .05). Gene expression of E- and P-selectin and ICAM-1 was more sensitive to irradiation than that of PECAM-1 and VCAM-1. Radiosurgery induced gene expression of P-selectin, ICAM-1, PECAM-1, and VCAM-1 was linearly correlated with time (P < .05). Radiosurgery induced elevation of soluble E- and P-selectin, ICAM-1, VCAM-1, and tissue factor in a rat model of AVMs (P < .05). Thus, a combination of these molecules measured at different time points may serve as an early predictor of responsiveness of AVMs to radiosurgery.

The Method of Establishing a Xenograft Animal Model

Objective: 1) Establish a xenograft animal model of arteriovenous malformation (AVM), an uncommon and often incurable vascular anomaly. 2) Observe the morphological alterations and histological characteristics of xenograft AVM. Method: AVM specimens harvested from 4 patients were sectioned (5x5x5mm) and implanted in the subcutaneous dorsum of 5-Athymic Nude-Foxn1nu mice. 4 implants per animal were placed (N = 20). Specimens were harvested monthly and stained for hematoxylin and eosin (H&amp;E). Immunohistochemistry for anti-human nuclear antigen and Ki-67 was performed. Histologic observations were recorded by 2-blinded pathologists. Results: Clinical characteristics and pathologic diagnosis of AVM was confirmed in each donor patient. A total of 85% (n = 17) of AVM xenografts survived the xenograft implantation. Survival was unrelated to date of harvest. The majority of implants slightly decreased in size by date of harvest (1-2mm). Pathologic diagnosis of a vascular anomaly was confirmed in each implant and demonstrated numerous small and medium-size vessels. A total of 76.5% (n = 13) of implants of surviving xenografts were positive for Ki-67 and anti-human nuclear antigen, confirming survival of the human derived tissue. Conclusion: We herein describe an animal model for AVM that may provide the first step for examining the pathophysiology and potential treatment of these difficult to treat lesions in vivo.

Expression of Endothelial Adhesion Molecules After Radiosurgery in an Animal Model of Arteriovenous Malformation

Endothelial adhesion molecules may be important in the response of brain arteriovenous malformations (AVMs) to radiosurgery. In addition to a putative role in the occlusive process after radiosurgery, they may serve as potential targets for biological strategies to accelerate intravascular thrombosis. To determine the temporal expression of E-selectin and vascular cell adhesion molecule-1 in an animal model of AVMs. Forty-one Sprague-Dawley rats underwent surgical creation of a carotid-to-jugular anastomosis. Radiosurgery (25 Gy) was delivered to the model "nidus" after 6 weeks, and the tissue was harvested 1 to 84 days after radiosurgery. Control groups received sham irradiation. Immunofluorescence was used to study the expression of E-selectin and vascular cell adhesion molecule-1. Endothelial E-selectin expression was limited to regions receiving radiosurgery. E-selectin expression reached maximal expression at 24 hours after radiosurgery and was sustained for another 24 hours before gradually reducing to baseline at 84 days post-radiosurgery (P < .01). Vascular cell adhesion molecule-1 expression remained at the baseline level for the first week; a 50% increase was observed at 21 days after radiosurgery, which was sustained for another 3 weeks before returning to the baseline at 84 days after radiosurgery (P < .05). Radiosurgery stimulates early expression of E-selectin and delayed up-regulation of vascular cell adhesion molecule-1 on the endothelial surface of the AVM model nidus. Cell adhesion molecule expression may play an important role in the process leading to vascular obliteration after irradiation. These molecular alterations may be harnessed to promote thrombosis in the irradiated vasculature using a vascular targeting agent.

Comparison of an animal model of arteriovenous malformation with human arteriovenous malformation

This study assessed the blood flow and histological changes of an animal model of arteriovenous malformation (AVM) over 84 days in 71 rats, and compared the histological findings to 17 specimens of human AVM. Carotid–jugular fistula blood flow positively correlated with time. The maximum flow rate occurred at 42 days, at which time the nidus was considered mature and was histologically similar to human AVMs. Morphological similarities between the model and human AVM vessels included heterogeneously thickened walls, splitting of the elastic lamina, thickened endothelial layers, endothelial cushions, lack of tight junctions, loss of endothelial continuity, endothelial–subendothelial adherent junctions, and luminally directed filopodia. These findings support the theory that vascular changes in human AVMs are secondary to increased flow and provide a basis for using this model in studies of AVMs.