New understanding, diagnosis, and prognosis of atherothrombosis and the role of imaging

Anti-platelet Drug-loaded Targeted Technologies for the Effective Treatment of Atherothrombosis

Atherothrombosis results from direct interaction between atherosclerotic plaque and arterial thrombosis and is the most common type of cardiovascular disease. As a long term progressive disease, atherosclerosis frequently results in an acute atherothrombotic event through plaque rupture and platelet-rich thrombus formation. The pathophysiology of atherothrombosis involves cholesterol accumulation endothelial dysfunction, dyslipidemia, immuno-inflammatory, and apoptotic aspects. Platelet activation and aggregation is the major cause for stroke because of its roles, including thrombus, contributing to atherosclerotic plaque, and sealing off the bleeding vessel. Platelet aggregates are associated with arterial blood pressure and cardiovascular ischemic events. Under normal physiological conditions, when a blood vessel is damaged, the task of platelets within the circulation is to arrest the blood loss. Antiplatelet inhibits platelet function, thereby decreasing thrombus formation with complementary modes of action to prevent atherothrombosis. In the present scientific scenario, researchers throughout the world are focusing on the development of novel drug delivery systems to enhance patient's compliance. Immediate responding pharmaceutical formulations become an emerging trend in the pharmaceutical industries with better patient compliance. The proposed review provides details related to the molecular pathogenesis of atherothrombosis and recent novel formulation approaches to treat atherothrombosis with particular emphasis on commercial formulation and upcoming technologies.

Intelligent Platelet Morphometry

Technological advances in image-based platelet analysis or platelet morphometry are critical for a better understanding of the structure and function of platelets in biological research as well as for the development of better clinical strategies in medical practice. Recently, the advent of high-throughput optical imaging and deep learning has boosted platelet morphometry to the next level by providing a new set of capabilities beyond what is achievable with traditional platelet morphometry, shedding light on the unexplored domain of platelet analysis. This Opinion article introduces emerging opportunities in 'intelligent' platelet morphometry, which are expected to pave the way for a new class of diagnostics, pharmacometrics, and therapeutics.

A study of the ultrasound-targeted microbubble destruction based triplex-forming oligodexinucleotide delivery system to inhibit tissue factor expression

The efficiency of cellular uptake of triplex‑forming oligodexinucleotides (TFO), and the inhibition of tissue factor (TF) is low. The aim of the present study was to improve the absorption of TFO, and increase the inhibition of TF induced by shear stress both in vitro and in vivo, by using an ultrasound‑targeted microbubble destruction (UTMD)‑based delivery system. TFO‑conjugated lipid ultrasonic microbubbles (TFO‑M) were first constructed and characterised. The absorption of TFO was observed by a fluorescence‑based method, and the inhibition of TF by immunofluorescence and quantitative polymerase chain reaction. ECV304 human umbilical vein endothelial cells were subjected to fluid shear stress for 6 h after treatment with TFO conjugated lipid ultrasonic microbubbles without sonication (TFO‑M group); TFO alone; TFO conjugated lipid ultrasonic microbubbles, plus immediate sonication (TFO+U group and TFO‑M+U group); or mock treated with 0.9% NaCl only (SSRE group). The in vivo experiments were established in a similar manner to the in vitro experiments, except that TFO or TFO‑M was injected into rats through the tail vein. Six hours after the preparation of a carotid stenosis model, the rats were humanely sacrificed. The transfection efficiency of TFO in the TFO‑M+U group was higher as compared with the TFO‑M and TFO+U group (P<0.01). The protein and mRNA expression of TF in the TFO‑M+U group was significantly decreased both in vitro and in vivo (P<0.01), as compared with the TFO‑M, TFO+U and SSRE groups. The UTMD‑based TFO delivery system promoted the -absorption of TFO and the inhibition of TF, and was therefore considered to be favorable for preventing thrombosis induced by shear stress.

Limiting extensibility constitutive model with distributed fibre orientations and ageing of abdominal aorta

The abdominal aorta is susceptible to age-related pathological changes (arteriosclerosis, atherosclerosis, aneurysm, and tortuosity). Computational biomechanics and mechanobiology provide models capable of predicting mutual interactions between a changing mechanical environment and patho-physiological processes in ageing. However, a key factor is a constitutive equation which should reflect the internal tissue architecture. Our study investigates three microstructurally-motivated invariant-based hyperelastic anisotropic models suitable for description of the passive mechanical behaviour of the human abdominal aorta at a multiaxial state of stress known from recent literature. The three adopted models have also been supplemented with a newly proposed constitutive model (limiting extensibility with fibre dispersion). All models additively decouple the mechanical response of the isotropic (elastin and smooth muscle cells represented by the neo-Hookean term) and the anisotropic (collagen) parts. Two models use exponential functions to capture large strain stiffening ascribed to the engagement of collagen fibres into the load-bearing process. The other two models are based on the concept of limiting extensibility. Perfect alignment of reinforcing fibres with two preferred directions as well as fibre dispersion are considered. Constitutive models are calibrated to the inflation-extension response adopted from the literature based on the computational model of the residually-stressed thick-walled tube. A correlation analysis of determined material parameters was performed to reveal dependence on the age. The results of the nonlinear regression suggest that limiting fibre extensibility is the concept which is suitable to be used for the constitutive description of the aorta at multiaxial stress states and is highly sensitive to ageing-induced changes in mechanical response.

Analysis of axial prestretch in the abdominal aorta with reference to post mortem interval and degree of atherosclerosis

It is a well-known fact that the length of an artery in situ and the length of an excised artery differs. Retraction of blood vessels is usually observed. This prestretch plays an important role in arterial physiology. We have recently determined that the decrease of axial prestretch in the human abdominal aorta is so closely correlated with age that it is suitable for forensic applications (estimation of the age at time of death for cadavers of unknown identity). Since post mortem autolysis may affect the reliability of an estimate based on axial prestretch, the present study aims to detail analysis of the effect of post mortem time. The abdominal aorta is a prominent site of atherosclerotic changes (ATH), which may potentially affect longitudinal prestretch. Thus ATH was also involved in the analysis. Axial prestretch in the human abdominal aorta, post mortem interval (PMI), and the degree of ATH were documented in 365 regular autopsies. The data was first age adjusted to remove any supposed correlation with age. After the age adjustment of the sample, the correlation analysis showed no significant PMI effects on the prestretch in non-putrefied bodies. Analysis of the prestretch variance with respect to ATH suggested that ATH is not a suitable factor to explain the prestretch variability remaining after the age adjustment. It was concluded that, although atherosclerotic plaques may certainly change the biomechanics of arteries, they do not significantly affect the longitudinal prestretch in the human abdominal aorta.

Imaging of atherosclerosis: magnetic resonance imaging

Atherosclerosis and its thrombotic complications are the major cause of morbidity and mortality in the industrialized countries. Despite advances in our understanding of the pathophysiology, pathogenesis, and new treatment modalities, the absence of an adequate non-invasive imaging tool for early detection limits both the prevention and treatment of patients with various degrees and anatomical localizations of atherothrombotic disease. An ideal clinical imaging modality for atherosclerotic vascular disease should be safe, inexpensive, non-invasive or minimally invasive, accurate, and reproducible, and the results should correlate with the extent of atherosclerotic disease and have high predictive values for future clinical events. High-resolution magnetic resonance imaging (MRI) has emerged as the most promising technique for studying atherothrombotic disease in humans in vivo. Most importantly, MRI allows for the characterization of plaque composition, i.e. the discrimination of lipid core, fibrosis, calcification, and intraplaque haemorrhage deposits. Magnetic resonance imaging also allows for the detection of arterial thrombi and in defining thrombus age. Magnetic resonance imaging has been used to monitor plaque progression and regression in several animal models of atherosclerosis and in humans. Emerging MRI techniques capable of imaging biological processes, including inflammation, neovascularization, and mechanical forces, may aid in advancing our understanding of the atherothrombotic disease. Advances in diagnosis do prosper provided they march hand-in-hand with advances in treatment. We stand at the threshold of accurate non-invasive assessment of atherosclerosis. Thus, MRI opens new strategies ranging from screening of high-risk patients for early detection and treatment as well as monitoring of the target lesions for pharmacological intervention. Identification of subclinical atherosclerosis and early treatment initiation has the potential to surpass conventional risk factor assessment and management in terms of overall impact on cardiovascular morbidity and mortality. Such strategy is currently under clinical investigation.

Noninvasive imaging of atherosclerotic vessels by MRI for clinical assessment of the effectiveness of therapy

Atherosclerosis and its thrombotic complications are the major cause of morbidity and mortality in the industrialized countries. Despite advances in our understanding of the mechanisms of pathogenesis and new treatment modalities, the absence of an adequate noninvasive method for early detection limits prevention or treatment of patients with various degrees and localizations of atherothrombotic disease. The ideal clinical imaging modality for atherosclerosis should be safe, inexpensive, noninvasive or minimally invasive, accurate, and reproducible, thus allowing longitudinal studies in the same patients. Additionally, the results should correlate with the extent of atherosclerotic disease and have high predictive values for clinical events. In vivo, high-resolution magnetic resonance imaging (MRI) has recently emerged as one of the most promising techniques for the noninvasive study of atherothrombotic disease in several vascular beds such as the aorta, the carotid arteries, and the coronary arteries. Most importantly MRI can be used to characterize plaque composition as it allows the discrimination of lipid core, fibrosis, calcification, and intra-plaque hemorrhage deposits. MRI findings have been extensively validated against pathology in ex vivo studies of carotid, aortic, and coronary artery specimens obtained at autopsy and using experimental models of atherosclerosis. In vivo MRI of carotid arteries of patients referred for endarterectomy has shown a high correlation with pathology and with previous ex vivo results. A recent study in patients with plaques in the thoracic aorta showed that compared with transesophageal echocardiography plaque composition and size are more accurately characterized and measured using in vivo MRI. The composition of the plaque rather than the degree of stenosis determines the patient outcome. Therefore, a reliable noninvasive imaging tool able to detect early atherosclerotic disease in the various regions and identify the plaque composition is clinically desirable. MRI has potential in the detection arterial thrombi and in the definition of thrombus age. MRI has been used to monitor plaque progression and regression in several animal model of atherosclerosis and more recently in human. Advances in diagnosis prosper when they march hand-in-hand with advances in treatment. We stand at the threshold of accurate noninvasive assessment of atherosclerosis. Thus, MRI opens new strategies ranging from screening of high-risk patients for early detection and treatment as well as monitoring the target areas for pharmacological intervention.

Clinical implications and mechanisms of plaque rupture in the acute coronary syndromes

Coronary atherosclerosis complicated by plaque rupture or disruption and thrombosis is primarily responsible for the development of acute coronary syndromes. Plaques with a large extracellular lipid-rich core, a thin fibrous cap due to reduced collagen content and smooth muscle density, and increased numbers of activated macrophages and mast cells appear to be vulnerable to rupture. Plaque disruption tends to occur at points at which the plaque surface is weakest and most vulnerable, which coincide with points at which stresses resulting from biomechanical and hemodynamic forces acting on plaques are concentrated. Reduced matrix synthesis as well as increased matrix degradation predisposes vulnerable plaques to rupture in response to extrinsic mechanical or hemodynamic stresses. Modification of endothelial dysfunction and reduction of vulnerability to plaque rupture and thrombosis may lead to plaque stabilization. These concepts have significant clinical implications that are just beginning to be explored and incorporated into clinical practice. This article reviews the mechanism of coronary atherosclerosis development and the pathophysiology of acute coronary syndromes to provide a framework for understanding how plaque passivation might be accomplished in clinical medicine.

Angiogenesis: A link to Thrombosis in Athero-thrombotic Disease

New insights to explain the clinical manifestations of atherosclerosis have resulted in a paradigm in which thrombosis is the major cause of acute coronary syndromes, peripheral arterio-vascular disease and stroke. Major efforts have been directed toward developing drugs to reduce thrombin and fibrin formation. Recent studies support a central role for angiogenesis of the atherosclerotic plaque in promoting atherothrombosis. The findings, in the face of efforts to use angiogenic agents to enhance vascular function, underline the challenge in treating atherothrombotic disease.

Noninvasive atherosclerosis imaging for predicting cardiovascular events and assessing therapeutic interventions

Noninvasive assessment of atherosclerosis offers an opportunity to provide individual cardiovascular risk management and an opportunity to monitor the efficacy of therapy targeted toward atherosclerosis. The three imaging modalities that currently hold the most promise at the clinical and research levels are ultrasound for carotid intima-media thickness, computed tomography for coronary artery calcification, and magnetic resonance imaging for carotid and aortic plaque imaging. The following review describes the evidence that validates each technique as a surrogate marker of atherosclerosis, with an emphasis on cardiovascular events and the progression of disease. Both the particular strengths and limitations of each imaging modality are discussed.

Evaluation of ischemic heart disease with cardiac magnetic resonance and computed tomography

Ischemic heart disease is the most common cardiac problem encountered by physicians in their daily practice. In the last few years, computed tomography and magnetic resonance have emerged as robust imaging modalities with great potential for the comprehensive evaluation of patients with this disorder. This article reviews current evidence of the applications where these techniques have demonstrated their usefulness and provides guidance for their use in the clinical management of coronary artery disease.

Atherothrombosis: Epidemiology, Pathophysiology, and Prevention

OBJECTIVES

To review the pathophysiology of atherothrombosis (atherosclerosis with superimposed platelet-rich thrombus formation) and the measures that can be taken to prevent its clinical sequelae through lifestyle modifications and pharmacotherapy, with emphasis on the role of antiplatelet agents.

DATA SOURCES

Recent (1995-2003) published scientific literature, as identified by the authors through Medline searches using the terms atherothrombosis, pathophysiology, risk factors, prevention, and reviews on treatment.

STUDY SELECTION

Recent systematic English-language review articles were screened for relevant material.

DATA SYNTHESIS

Atherothrombosis is a generalized and diffuse progressive process affecting multiple vascular beds; its clinical consequences, including acute coronary syndromes (unstable angina, acute myocardial infarction, and sudden cardiac death), ischemic stroke, and peripheral arterial disease, are unpredictable in their time course and potentially life-threatening. Atherothrombosis rather than arterial stenosis appears to account for most of the acute ischemic manifestations of the atherosclerotic process. Interventions that can favorably influence atherosclerotic progression include lifestyle modifications (dietary control, exercise, and smoking cessation) and pharmacotherapy (lipid-lowering, antihypertensive, antiglycemic, and antiplatelet drugs). The pivotal role played by the platelet in thrombus formation provides the rationale for employing antiplatelet drugs with complementary modes of action (e.g., aspirin, clopidogrel) to prevent atherothrombosis.

CONCLUSION

Ischemic cerebrovascular, coronary, and peripheral arterial disease can be regarded as diverse manifestations of a common underlying systemic pathology, namely atherothrombosis. Secondary prevention of an ischemic event in an affected arterial bed confers the added benefit of primary prevention against potential ischemic events in other arterial beds.