Oscar H. University of Bern. We present a clinical case that shows a year-old male diagnosed with plaque in the right internal carotid artery, the result of computerized axial tomography by an extension study of squamouscell carcinoma, shows a mural thrombosis. Ultrasound is performed in Primary Care shows a plaque that echographically looks like a thrombus and is referred to the vascular surgery service for study. No history of cardiovascular events or coagulation disorders. This patient came to our clinic with the results of computerized axial tomography CAT with neck contrast for the extension study of facial epidermoid carcinoma ordered by the otorhinolaryngology department OD.
Pulmonary auscultation: regular heart sounds, conserved vesicular murmur. Ultrasound is performed in our primary care centre PCC finding plaque in the right internal carotid []: Hypoechogenic, heterogeneous and calcified posterior shadow that echographically looks like a thrombus.
Figure 1. Following this finding we communicated with the reference department of VS and the patient is sent for we supraortic trunks ultrasound, which confirms the finding of the ultrasound performed at the PC.
Cerebral and aortoiliac CT scans are performed, without finding any alterations. Ultrasound image of hypoechoic, heterogeneous and calcified plaque posterior shadow in right internal carotid that echographically looks like a thrombus.
Figure 2. Plaque injury to make the atheroma complicated such as thrombosis or haemorrhage. At what stage does the fatty plaque become irreversible.
When it gets to the point of forming an early atheroma in which the medial layer of the blood vessel becomes involved. What are the components of an uncomplicated athermatous plaque. Foam cells fat containing macrophages , smooth muscle cells from the medial layer, lymphocytes, fibrosis and a fibrous cap. What is the difference between an early and late atheromatous plaque. In the early stages there is no involvement of the tunica media.
In the late stages smooth muscle cells from the medial layer become involved, however it is still uncomplicated. What can make a plaque "complicated". Ulceration, haemorrhage, thrombosis. Why is atherosclerosis more likely to be an issue in coronary arteries compared to the aorta. Because coronary arteries are narrower so less obstruction is required.
What are the local complications of atheroma. What are the systemic complications of atheroma. Infarction, stroke, ischaemia, gangrene. What is a thrombus. A solidification of blood constituents that forms within the vascular system during life. What is thrombosis. A pathological process. It is the formation of a thrombus in an uninterrupted vascular system.
When is it normal for thrombus formation to occur. In an interrupted vascular system when it is associated with injury. Indeed, large animal models present disadvantages which are primarily the reverse of the advantages of small animal models high cost, heightened ethical concerns, less precise genetic characterization, difficulties involved in maintaining the colonies and their handling and a scarcity of transgenic models, and antibodies ; however, their human-resemblance makes them an attractive tool to provide new insights into the atherothrombotic field.
Because of similarities between human and nonhuman primates [ 28 ], nonhuman primate animal models are believed to be better suited to investigate human cardiovascular pathology atherosclerosis, thrombus formation and dissolution, and therapeutic interventions.
In Malinov and Maruffo [ 29 ] published studies performed using the monkey as animal model to evaluate aortic atherosclerosis. More recently, familial LDL receptor deficiency with atherosclerosis has been reported in rhesus monkey [ 30 , 31 ]. Nonhuman primate thrombosis models, mainly arteriovenous shunt models are good models to evaluate novel thrombotic agents prior to administration of the drugs to human in clinical trials [ 32 ].
In fact, nonhuman primates platelet function, coagulation, and fibrinolytic system and drug pharmacokinetics resemble those in humans [ 28 ], and some immunologic overlap allows utilization of available assays. However, nowadays, the use of primates is constrained by obvious species specific risk of extinction and financial concerns, as well as the complexity, training and expertise required to perform this animal approach.
This has supported the use of a more accessible and less costly large animal models, such as the porcine model, which fairly reproduces human atherosclerotic and thrombotic disease as detailed below. The pig is a very good model because it develops spontaneous atherosclerotic lesions, has a human-like cardiovascular anatomy, and even may develop sudden death when under stress White Belgian breed [ 33 — 37 ]. In addition, swine offer the ability to evaluate their coronary arteries rather than larger central vessels mostly studied in smaller animals.
The heart of the pig is anatomically similar to humans except for the presence of the left azygous hemiazygous vein, which drains the intercostal system into the coronary sinus [ 38 ], and for the size, which tends to be a bit smaller.
Regarding the heart, blood supply is mostly right side dominant since it originates from the posterior septal artery [ 37 ] and both anatomy and function of the pig coronary system as well as the histological anatomy of the aorta are comparable to humans. However, on the other hand, pig blood vessels are more friable and prone to vasospasm during manipulation, and thus require careful handling during blood withdrawals [ 39 ].
In relation to pig hemodynamics, either physiological cardiac function or mechanically induced myocardial infarction and the subsequent arrhythmogenic activity in reperfusion is also analogous to humans as well as the wound healing process [ 40 ]. Pig atherosclerosis, diverging to small animal models, is generally quite slow and occurs both spontaneously i. Moreover, if allowed to develop over time, mild atherosclerotic lesions first appear in coronary arteries and both atherosclerotic plaque distribution and composition lipid, fibrinogen, smooth muscle cells, and macrophage content [ 43 ] follows a pattern comparable to that of humans [ 44 — 46 ].
Human-like pig lipoprotein metabolisms may help to explain, in part, the above mentioned similarities [ 47 ]. Finally, unlike other animal models, after gradual occlusion of the coronary vessels induced by both balloon injury and atherogenic diet, swine may develop the coronary restenosis syndrome as humans [ 40 , 44 , 45 , 48 , 49 ]. As mentioned above, swine can develop hypercholesterolemia and atherosclerotic lesions by diet induction high-cholesterol content diets , reaching plasma cholesterol levels similar to those in human.
After a day period with a standard hypercholesterolemic diet we have previously observed that almost all pigs developed early atherosclerotic lesions fatty streaks localized in the abdominal aorta and to a lesser extent in the coronary arteries [ 43 ]. In such cases, lesion composition was similar to early-stage human atherosclerosis [ 43 ]. As expected, increasing the diet induction period to and days was associated with a higher degree of lesion severity made evident when suitable fat stain was applied.
Notwithstanding, animals employed in these long-period studies tend to be within the prepuberty period, and in consequence their lesions are not as severe as those developed in adult humans over the years.
To overcome size-related problems, the minipigs are becoming increasingly used. Indeed, miniature swine are preferable to commercial swine as animal models because of their small size and small growth rate that allows them to maintain weight and size throughout adulthood. They are docile and easily handled and there are several miniature strains disposable to better fit scientific purposes. Miniature pigs have been used in several fields of biomedical research studies such as cardiovascular disease models of thrombosis and restenosis , obesity, diabetes, and transplantation, however, the principal disadvantage for using miniature pigs as a substitute of common pigs are the maintenance requirements and the high cost of the animals.
As a consequence, miniature pigs' breeders are not largely distributed in all countries. The ex vivo porcine model of thrombus formation e. Indeed, it has allowed to evaluate the thrombogenic effect of different atherosclerotic plaque constituents e. Furthermore, these ex vivo models of thrombosis offer the opportunity to evaluate, in an easy and reproducible manner, the interaction of a given compound with the blood and vascular compartment and consider any metabolic transformation.
Baumgartner developed the first popular annular perfusion chamber that helped to advance the knowledge and understanding of platelet adhesion to the subendothelium under laminar flow [ 61 ]. Since then, other ex vivo chamber systems have been developed for investigating prosthetic and biologics substrates surfaces over a broad range of flow conditions [ 62 , 63 ]. In fact, although atherosclerosis preferentially occurs in areas of turbulent blood flow and low fluid shear stress, thrombosis is induced by high shear stress.
Moreover, in atherosclerotic vessels, laminar flow conditions may not be maintained since stenotic narrowing induces flow disturbances that modify cell-cell and cell-vessel interactions as well as the local concentration of fluid-phase chemical mediators necessary for cell interaction. In this regard, we have developed an extracorporeal perfusion system the Badimon chamber [ 64 ] that allows to investigate the dynamics of platelet deposition and thrombus formation a on different surfaces biological and prosthetic materials [ 65 , 66 ]; b under a broad range of patho-physiological flow conditions including laminar and nonparallel streamline flows [ 54 , 67 , 68 ]; c with varying perfusing blood treatments.
Coronary artery interventions, such as balloon angioplasty and stenting, have become established treatments for symptomatic coronary artery disease [ 76 ].
Many animal models have provided insights into the mechanisms of angioplasty and in-stent restenosis in different metabolic disorders obesity, diabetes, etc. Experience suggests, however, that porcine coronary stenting is a very suitable model because injury response is similar to human vessels with an adaptive response being more profound in animals fed a hypercholesterolemic diet [ 79 ]. Moreover, as stated above, since size and anatomic distribution of porcine coronary arteries are similar to those of the human, angiography, intravascular ultrasound, instrumentation, and stent deployment are all similar to the clinical situation.
On the other hand, a number of strategies have also been adopted in an effort to reduce both the acute thrombogenic potential of metallic stents and the stent-induced neointimal thickening [ 80 ].
As such, oral administration of endothelin receptor antagonists [ 81 ] or tranilast [ 82 ], capable of modulating the inflammatory tissue responses, has been demonstrated to be efficacious in preventing neointima formation after coronary stenting in swine.
Similarly, subcutaneous low-molecular-weight heparin administration on top of acetylsalicylic acid has also shown to reduce neointimal proliferation after coronary stent implantation in hypercholesterolemic minipigs [ 83 ].
In contrast, systemic pharmacological approaches in humans have been largely disappointing, possibly owing to insufficient local drug concentration. To solve this limitation, polymer coated stents were developed as a vehicle for local drug administration. To date, a number of diverse biological agents have been shown to elute slowly from polymer coatings and are associated with reduced neointima formation in pig models [ 84 , 85 ]. The dog, as described for rats, is not a good model for atherosclerosis because they do not develop spontaneous atherosclerosis even under a high-cholesterol diet [ 86 ].
As to canine models of thrombosis, Folts and colleagues [ 88 ] described in a model of repetitive thrombus formation, assessed by cyclic flow reductions by an electromagnetic flow probe, in stenosed coronary arteries of open-chest anesthetized dogs. The Folts model is based on the combination of severe, concentric stenosis, and focal intimal injury canine coronaries circumflex and left anterior descending [ 3 ]. The Folts model mainly induces platelet-rich thrombus formation.
In fact, the preclinical data obtained with this animal model has been further corroborated in clinical trials such as the EPIC abciximab [ 93 ] and PRISM tirofiban investigators trials [ 94 ]. Canine thrombosis can also be challenged by advancing a thrombogenic coil into a coronary artery in closed-chest animals [ 95 ].
The composition alloy and size of the coil determine the time to occlusive thrombus formation confirmed by a filling defect distal to the coil. This model, in contrast to the Folts model, induces platelet-poor and fibrin-rich thrombus and thus enables to test thrombolytic agents [ 96 ]. To overcome this disadvantages Bush and collaborators [ 97 ] developed a femoral artery version of this model that uses the same thrombogenicity coils but consists of Doppler flow probes placed proximal to the site of thrombosis and thus is also appropriate to use in rabbits.
Another model of coronary thrombosis in open-chest dogs is based on the local delivery of thrombin in the LAD coronary artery. This approach induces fibrin-rich clots amenable to lyse upon thrombolytic administration [ 98 ].
It is the most common inherited bleeding disorder in humans, and over the past years several animal species have also been described as suffering from this disease whether through spontaneous mutation pigs and dogs or through a genetically engineered mutation mice [ 6 ]. All these different animal models have been extremely useful in exploring the characteristics of VWd and in testing new treatments. Indeed, the interaction of platelets with VWF is crucial in the initiation and development of any thrombotic process since enables platelets, via its surface glycoprotein receptors, to adhere to exposed subendothelium and to respond to blood shear stress [ — ].
In fact, we and Fuster et al. The pig is a good model for studying VWd since VWF localization in endothelial cells and platelets mimics that of humans as do the clotting and platelet characteristics. Additionally, in normal pigs the level of VWF is close to the human level [ 6 ]. Canine VWd has also demonstrated to be similar to humans. Over the years, many dog breeds have been identified as suffering from this disease, making VWd the most common inherited bleeding disorder in dogs.
Actually, canine VWd can vary in genetic transmission, clinical severity and diagnostic laboratory findings. Thus, in contrast to pigs, VWd dogs have not been used extensively for research purposes [ ].
Finally, it deserves to be mentioned that VWd has also been reported in other animal species such as murine [ , ], rabbits [ ], and cats [ ]. However, caution must be taken in extrapolating such results to the human clinical conditions. By its very nature, rupture of an atherosclerotic plaque is difficult to study in humans. Moreover, since rupture of an atherosclerotic plaque occurs in a stochastic fashion, it is also difficult to identify triggering factors and equally hard to investigate treatments addressed towards plaque stabilization.
Thus, the appropriate animal model, not only should help to better understand the mechanisms behind plaque rupture but also test treatments to prevent it from happening. Despite the development of porcine models of advanced human-like coronary atherosclerosis, no suitable large animal model of high-risk vulnerable plaque exists.
In fact, spontaneous hemorrhage and rupture is considered an extremely rare event in large animal models and has only been found in the coronary arteries of pigs with inherited hyper-low-density lipoprotein cholesterolemia or in cholesterol-fed pigs with streptozotocin-induced diabetes [ , ].
Lack of such a model has hampered studies designed to validate imaging technologies and to scrutinize the effects of therapeutic interventions in atherosclerotic arteries. Yet, the relevance of these mice models of plaque rupture on the final events precipitated by plaque disruption of human atherosclerotic lesions is controversial, especially in animals surprisingly resistant to formation of thrombi at sites of atherosclerosis [ ].
On the other hand, other investigators have evaluated the harmful effect of combining several risk factors. As such, it has been reported that either in double knockout mice with homozygous null mutations in the Apo E and the high-density lipoprotein HDL receptor, scavenger receptor class B, or combination of hypertension and dislipemia hypertensive rats transgenic from human cholesteryl ester transfer protein increase plaque vulnerability and thrombi formation.
Rabbits have been used as a model of plaque instability and rupture [ , ], besides their extended use in animal models of atherogenesis [ , ], myocardial infarction [ ], and to evaluate the efficacy of new antithrombotic and anti-atherosclerotic drugs [ ].
Moreover, transgenic rabbits have also been developed to obtain models of hereditary hyperlipidemia WHHL-rabbit. Rabbits are easy to handle and cost-effective and there are three breeds of rabbits that have been commonly used in biomedical research: New Zealand White, Dutch Belted and Flemish Giant.
Although rabbits do not develop spontaneous atherosclerosis, as they are vegetarian, we and others have robustly demonstrated that they can rapidly develop foam-cell-rich fatty steaks plaques after the administration of a rich atherosclerotic diet 0. Yet, rabbit atherosclerotic lesions differ from human atheroma since their lipid and macrophage content is much higher as it is their hypercholesterolemic index [ ]. Conversely, intermittent cycles of fat feeding with periods of normal diet has shown to induce plaques at more advanced stages that resemble human atheroma [ ].
In addition, we have shown that combining cholesterol-rich feeding with arterial wall injury e. The addition of pharmacological triggering at the end of the atherogenic diet has provided the first evidence of thrombosis associated with plaques in this experimental animal model, the Constantinides New Zealand white CNZW rabbit model, with similarities to thrombosis seen in human coronary arteries [ ].
Furthermore, these observations have been supported by in vivo magnetic resonance imaging [ ] and molecular-targeted imaging, using a fibrin binding peptide conjugated to gadolinium, which have clearly shown thrombus superimposition to the atherosclerotic lesion [ ]. In counterpart, CNZW rabbit model similarity to human atherothrombosis has been questioned either because rabbits' atherosclerotic lesion composition i.
Other more simplistic approaches e. Thrombogenesis in veins is mainly attributed to some combination of hypercoagulability, stasis, and vascular injury.
All these triggering factors induce tissue thromboplastin tissue factor release to the flowing blood forming thrombin and fibrin that trap red blood cells. Animal models for venous thrombosis appear to be particularly useful for studying the pathophysiology of blood coagulation in vivo and the pathogenesis of venous thrombosis. For instance, this model has helped to define the role of activated protein C, the interplay between inflammatory and procoagulant mediators, and the regulatory role of PAI-1 in thrombolysis besides therapeutic approaches [ ].
Clinical observations provide the substrate to build up pathophysiological hypotheses, but for obvious ethical reasons our ability to test these hypotheses in humans is very limited. Cell biology-related studies have helped to answer mechanistic questions, but lack complexity of a real disease thus limiting the scope of testable hypotheses.
On the other hand, studies using rodent or large animal models have proved to be essential for proof of concept since they yield in vivo approaches to confirm critical hypotheses previously evaluated in relevant in vitro models.
Experience over many decades has established that a single, naturally available model of human vascular disease does not exist. The advent of genetic engineering and the availability of transgenic and knockout animals have allowed pinpointing the relative functional importance of single changes in specific gene products.
These approaches have permitted uncovering specific gene functions and have facilitated the formulation of new strategies for cardiovascular protection and the prevention and treatment of atherothrombosis.
However, their utility as models of human disease and to prove the validity of products for human pharmacological use has not been demonstrated. Animal models have helped to accelerate the rate of new target identification and validation leading to improved therapeutics for the atherothrombotic disease. However, while small animal models provide experimental convenience and easiness to manipulate, more clinically relevant models are necessary to study the mechanisms involved in human atherothrombogenesis.
Large animal models, although associated to a higher cost and handling-related difficulties, have shown an atherothrombotic pattern more comparable to that of humans. To date, considering all models, the porcine model is one of the most useful currently available atherothrombotic models.
Indeed, pig animal models have shown to address specific questions related to blood and atherosclerotic vessel mechanisms involved in thrombus formation that have been eventually translated to clinical situations. National Center for Biotechnology Information , U. Journal List J Biomed Biotechnol v. J Biomed Biotechnol. Published online Jan 2.
Author information Article notes Copyright and License information Disclaimer. Received Sep 23; Accepted Dec 9. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article has been cited by other articles in PMC. Abstract Atherosclerosis and its thrombotic complications are responsible for remarkably high numbers of deaths. Animal Models as a Tool for Preclinical Translation Atherosclerotic plaques may appear early in life and their advance into severe, symptomatic plaques, depends on the coexistence of risk factors.
Table 1 Differences between large animal models and humans in the thrombotic system and other parameters that may influence antithrombotic effectiveness.
Specie Differences with humans Human similarities Reference Nonhuman primates Platelet function, coagulation, fibrinolysis and therapeutic interventions arteriovenous vascular graft or surgical endarterectomy Harker et al. Open in a separate window.
Small versus Large Animal Models Small animals, primarily rodents and rabbits, have been used extensively for atherosclerosis and thrombosis research [ 15 ]. The Pig as a Tool for Atherothrombotic Disease The pig is a very good model because it develops spontaneous atherosclerotic lesions, has a human-like cardiovascular anatomy, and even may develop sudden death when under stress White Belgian breed [ 33 — 37 ]. Diet-Induced Atherosclerosis As mentioned above, swine can develop hypercholesterolemia and atherosclerotic lesions by diet induction high-cholesterol content diets , reaching plasma cholesterol levels similar to those in human.
Extracorporeal Arteriovenous Shunts The ex vivo porcine model of thrombus formation e. Intravascular Interventions Coronary artery interventions, such as balloon angioplasty and stenting, have become established treatments for symptomatic coronary artery disease [ 76 ]. Canine Models of Atherosclerosis and Thrombosis The dog, as described for rats, is not a good model for atherosclerosis because they do not develop spontaneous atherosclerosis even under a high-cholesterol diet [ 86 ].
Animal Models of Plaque Rupture By its very nature, rupture of an atherosclerotic plaque is difficult to study in humans. Animal Models of Venous Thrombosis Thrombogenesis in veins is mainly attributed to some combination of hypercoagulability, stasis, and vascular injury.
Conclusions and Future Perspectives Clinical observations provide the substrate to build up pathophysiological hypotheses, but for obvious ethical reasons our ability to test these hypotheses in humans is very limited. References 1. Lipoproteins, platelets and atherothrombosis.
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