Experience with microaneurysm formation at the basilar terminus in the rabbit elastase aneurysm model

Endogenous animal models of intracranial aneurysm development: a review

The pathogenesis and natural history of intracranial aneurysm (IA) remains poorly understood. To this end, animal models with induced cerebral vessel lesions mimicking human aneurysms have provided the ability to greatly expand our understanding. In this review, we comprehensively searched the published literature to identify studies that endogenously induced IA formation in animals. Studies that constructed aneurysms (i.e., by surgically creating a sac) were excluded. From the eligible studies, we reported information including the animal species, method for aneurysm induction, aneurysm definitions, evaluation methods, aneurysm characteristics, formation rate, rupture rate, and time course. Between 1960 and 2019, 174 articles reported endogenous animal models of IA. The majority used flow modification, hypertension, and vessel wall weakening (i.e., elastase treatment) to induce IAs, primarily in rats and mice. Most studies utilized subjective or qualitative descriptions to define experimental aneurysms and histology to study them. In general, experimental IAs resembled the pathobiology of the human disease in terms of internal elastic lamina loss, medial layer degradation, and inflammatory cell infiltration. After the early 2000s, many endogenous animal models of IA began to incorporate state-of-the-art technology, such as gene expression profiling and 9.4-T magnetic resonance imaging (MRI) in vivo imaging, to quantitatively analyze the biological mechanisms of IA. Future studies aimed at longitudinally assessing IA pathobiology in models that incorporate aneurysm growth will likely have the largest impact on our understanding of the disease. We believe this will be aided by high-resolution, small animal, survival imaging, in situ live-cell imaging, and next-generation omics technology.

Comparison of Aneurysm Patency and Mural Inflammation in an Arterial Rabbit Sidewall and Bifurcation Aneurysm Model under Consideration of Different Wall Conditions

Background: Biological processes that lead to aneurysm formation, growth and rupture are insufficiently understood. Vessel wall inflammation and degeneration are suggested to be the driving factors. In this study, we aimed to investigate the natural course of vital (non-decellularized) and decellularized aneurysms in a rabbit sidewall and bifurcation model. Methods: Arterial pouches were sutured end-to-side on the carotid artery of New Zealand White rabbits (vital [n = 6] or decellularized [n = 6]), and into an end-to-side common carotid artery bifurcation (vital [n = 6] and decellularized [n = 6]). Patency was confirmed by fluorescence angiography. After 28 days, all animals underwent magnetic resonance and fluorescence angiography followed by aneurysm harvesting for macroscopic and histological evaluation. Results: None of the aneurysms ruptured during follow-up. All sidewall aneurysms thrombosed with histological inferior thrombus organization observed in decellularized compared to vital aneurysms. In the bifurcation model, half of all decellularized aneurysms thrombosed whereas the non-decellularized aneurysms remained patent with relevant increase in size compared to baseline. Conclusions: Poor thrombus organization in decellularized sidewall aneurysms confirmed the important role of mural cells in aneurysm healing after thrombus formation. Several factors such as restriction by neck tissue, small dimensions and hemodynamics may have prevented aneurysm growth despite pronounced inflammation in decellularized aneurysms. In the bifurcation model, rarefication of mural cells did not increase the risk of aneurysm growth but tendency to spontaneous thrombosis.

Preclinical Intracranial Aneurysm Models: A Systematic Review

Intracranial aneurysms (IA) are characterized by weakened cerebral vessel walls that may lead to rupture and subarachnoid hemorrhage. The mechanisms behind their formation and progression are yet unclear and warrant preclinical studies. This systematic review aims to provide a comprehensive, systematic overview of available animal models for the study of IA pathobiology. We conducted a systematic literature search using the PubMed database to identify preclinical studies employing IA animal models. Suitable articles were selected based on predefined eligibility criteria following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Included studies were reviewed and categorized according to the experimental animal and aneurysm model. Of 4266 returned results, 3930 articles were excluded based on the title and/or abstract and further articles after screening the full text, leaving 123 studies for detailed analysis. A total of 20 different models were found in rats (nine), mice (five), rabbits (four), and dogs (two). Rat models constituted the most frequently employed intracranial experimental aneurysm model (79 studies), followed by mice (31 studies), rabbits (12 studies), and two studies in dogs. The most common techniques to induce cerebral aneurysms were surgical ligation of the common carotid artery with subsequent induction of hypertension by ligation of the renal arteries, followed by elastase-induced creation of IAs in combination with corticosterone- or angiotensin-induced hypertension. This review provides a comprehensive summary of the multitude of available IA models to study various aspects of aneurysm formation, growth, and rupture. It will serve as a useful reference for researchers by facilitating the selection of the most appropriate model and technique to answer their scientific question.

Stable experimental model of carotid artery saccular aneurysm in swine using the internal jugular vein

OBJECTIVE

To develop an experimental model of stable saccular aneurysm in carotid of pigs using the internal jugular vein.

METHODS

In 12 healthy pigs, weighing between 25 and 5 0kg, five males and seven females, we made a right common carotid artery aneurysm. After elliptical arteriotomy, we carried out a terminolateral anastomosis with the distal stump of the internal jugular vein. Aneurysm volume was calculated so that the value did not exceed 27 times the area of the arteriotomy. After six days angiography and microscopic examination were performed to assess patency of the aneurysm and the presence of total or partial thrombosis.

RESULTS

There was a significant weight gain of pigs in the time interval between the manufacture of the aneurysm and angiography (p = 0.04). Aneurysmal patency was observed in ten pigs (83%). Operative wound infections occurred in two animals (16.6%), both with early onset, three days after the making of the aneurysm. Histological analysis showed aneurysm thrombus partially occluding the light in nine pigs (75%). In these animals, it was observed that on average 9% of the aneurysmal diameter was filled with thrombi.

CONCLUSION

It was possible to develop a stable experimental model of saccular aneurysms in pig carotid artery by use of the internal jugular vein.

Monitoring of the heparinization in the rabbit animal model during endovascular interventions

INTRODUCTION

The purpose of this study was to monitor and to optimize heparinization during endovascular procedures in the New Zealand White Rabbit (NZWR) model.

METHODS

Right common carotid artery aneurysms were surgically created in 43 NZWR, with an average weight of 4,330 g (range 3,500-5,430 g). The activated partial thromboplastin time (aPTT) was measured during different stages of the interventional procedures. Blood samples were taken before and 10 min after administration of heparin and at the end of each endovascular procedure. We compared three different experimental groups: 100 U heparin, 500 U heparin and 100 U heparin plus pretreatment with aspirin and clopidogrel. The individual aPTT values were measured using a ball coagulometer.

RESULTS

The average baseline aPTT in the rabbit is 75.2 ± 18.9 s compared to a mean of 33 s (range 26-40 s) in humans. The dosages of heparin used achieved anticoagulation in all cases. Five hundred units of heparin increased the aPTT significantly more than 100 U. No difference was found between the aPTT obtained from the 100 U and the 100 U plus pretreatment group, as aspirin and clopidogrel do not affect the coagulation cascade.

CONCLUSION

One hundred units of heparin can achieve anticoagulation in a similar magnitude as needed in interventional procedures in humans. This fact enhances suitability of the rabbit animal model for the testing of intravascular devices.

Lack of aneurysm formation after carotid artery ligation in rabbits: a polymer MICROFIL® study

INTRODUCTION

Previous studies have noted formation of saccular aneurysms along the distal basilar artery/P1 segments after carotid ligation in rabbits. In this prospective study we employed MICROFIL®, a polymer, which was used to fill the entire arterial tree, to examine the incidence of microaneurysm formation following right common carotid artery (RCCA) ligation in rabbits.

METHODS

RCCA ligation was performed in 18 New Zealand White rabbits for 0 day (n = 2), 3 weeks (n = 6), or 16 weeks (n = 10). Three control rabbits without carotid surgery were sacrificed at 4 weeks. At the time of sacrifice, MICROFIL® MV-122 yellow was injected through left CCA to fill cerebral vasculature. After gross photographs were taken, specimens were embedded, sectioned, and stained for histopathological evaluation. Tissue and sections were carefully evaluated for microaneurysm formation, defined as a localized dilatation of the vessel wall, associated with fragmentation or complete loss of the internal elastic lamina (IEL), and/or medial degeneration.

RESULTS

Gross examination with MICROFIL® opacification demonstrated no evidence of saccular aneurysm formation, but prominent perforating vessels were present in all 19 cases at, or adjacent to, the basilar terminus. Branches noted upon gross examination corresponded histologically to small, saccular contour defects, which demonstrated apparent loss of the IEL and apparent medial thinning. These observations, however, were a consequence of sectioning through the bases of perforating arteries, which simulated microaneurysm formation.

CONCLUSIONS

Unilateral carotid ligation does not induce microaneurysm formation at the basilar terminus in rabbits. Prominent perforating arteries as well as tissue injury from the processing may simulate "aneurysms" histologically.