Introduction
Cardiovascular disease is the leading global cause of death. According to the World Health Organization, 17.3 million deaths resulted from cardiovascular disease worldwide in 2008, and that number is expected to reach 23.3 million by 2030. The underlying pathology of cardiovascular disease is atherosclerosis and, depending on the artery affected, can manifest as CAD or as cerebrovascular or peripheral disease. Coronary artery disease (CAD) is responsible for 7.3 million deaths and is the second cause of death in people under the age of 59. It is also noteworthy that CAD is listed among the first causes for years of life lost due to premature death or disability, and thus has important social and economic impact. Low- and middle-income countries exhibit a continuous increase in the prevalence of CAD in contrast to developed countries. This discrepancy is attributed to the ineffective primary and secondary prevention measures in addition to poor healthcare systems in the low- and middle-income countries [1].
The mechanisms of atherosclerosis have gained increasing attention over recent decades. Many questions still remain concerning the heterogeneity that atherosclerosis displays in time (when?), in the areas affected (where?), in the factors triggering the initiation (how?), and in defining the natural history and evolution of the disease (why?). Atherosclerosis is a chronic systematic disease involving large and medium-sized arteries that initiates early in life [2]. As it progresses, the structure of normal arteries is modified, and atherosclerotic plaques are formed with consequent narrowing or dilation of the vessel. Atherosclerosis is a systematic disease with local manifestations, but the factors determining the preferential involvement of a vascular region over another (ie, coronary or carotid artery) as well as the development of atherosclerotic lesions in certain sites of a specific artery (eg, branches, curvatures, and proximal areas of left anterior descending) are unclear. In addition, regardless of tremendous research efforts, sparse data are available illuminating the factors responsible for the transition of a stable atherosclerotic plaque to a vulnerable plaque that can cause the acute complications of atherosclerosis (eg, myocardial infarction (MI) in CAD). Diversity also exists in the biological procedures and their clinical manifestations following rupture or erosion of unstable plaques (clinically silent MI, unstable angina, and MI with or without ST elevation).
The biggest question to be answered is why the human arteries are vulnerable to atherosclerotic changes. As most communicable diseases are now successfully treated and average life expectancy has increased, cardiovascular disease burden emerges as one of the most important health issues. It was some decades ago that the Framingham Heart Study provided valuable data regarding the primary prevention of atherosclerotic cardiovascular disease and established the cardiovascular risk factor as a new term. The identification of several risk factors associated with modern lifestyle such as hyperlipidemia, smoking, hypertension, obesity, diabetes mellitus, lack of exercise, anxiety, and depression supports the notion that atherosclerosis is a disease of urbanization [3]. However, well-known risk factors such as older age, family history of cardiovascular disease, male sex, and genetic abnormalities (familial hypercholesterolemia) indicate a genetic contribution to atherosclerosis. The report of atherosclerotic findings in mummies from populations of disparate regions with differences in dietary habits and certainly differences in dietary and lifestyle patterns compared to the present time suggests that human vessels are susceptible to atherosclerotic alterations regardless of the current environmental risk factors. Moreover, these observations underline the ongoing need for novel risk factors [4]. Therefore, both genetic and environmental factors are implicated in the pathogenesis of atherosclerosis, whereas their interaction may account for the heterogeneity that atherosclerosis displays.
Normal Artery Structures
The normal artery wall comprises three layers: the tunica intima, the tunica media, and the tunica adventitia.
• The tunica intima consists of the endothelium, connective tissue (collagen, laminin, fibronectin, and other extracellular matrix molecules), and a basal layer of elastic tissue called internal elastic lamina that separates the tunica intima from tunica media. Endothelium is a thin monolayer of cells that serves as the contact surface with blood. Due to its strategic location, the endothelium has emerged as the main regulator of vascular homeostasis with its structural and functional properties altered in response to...