Mechanisms Involved in Tandem Hypertension – Inflammation
Although precise mechanisms which link inflammation and hypertension are not well established, changes in mechanical stress associated with hypertension as well as humoral factors involved in the development and complications of hypertension have been proposed Endothelium is exposed to mechanical stress created by blood flow and the cardiac cycle. The pulsatile nature of arterial blood flow in combination with a complex geometric vascular network configuration determine endothelial shear stress patterns that can be complicated by changes in hemodynamic forces associated with high blood pressure levels. [16] Endothelial cells are able to sense mechanical stress because they are equipped with numerous mechanoreceptors.
Their activation triggers a cascade of intracellular pathways that interact among themselves through cross-talk, especially the mitogen-activated protein kinase (MAPKs). All of these signalling pathways lead to phosphorylation of several transcription factors such as NF-kB which modulate expression of mechanosensitive genes. These genes include ROS production from NADPH oxidase and other enzymes such as xanthine oxidase, as well as activation of modulators of cytoskeleton such as protein kinase C and Rho family small GTPases with subsequent structural changes in the arterial wall. NF-kB activation, at the same time, leads to an increased expression of several adhesion molecules (VCAM-1, ICAM-1, E-selectin), chemoattractant chemokines(MCP)-1, and pro-inflammatory cytokines such as TNF-α, and IL-1β Consequently, it not only favours an inflammatory process but also the development of atherosclerosis.
Mechanisms involved in the link between hypertension and atherosclerosis, which is the principal origin of cardiovascular disease
Figure: Mechanisms involved in the link between hypertension and atherosclerosis, which is the principal origin of cardiovascular disease
The renin-angiotensin-aldosterone system (RAAS) plays an important role in the regulation of the cardiovascular system through control of extracellular fluid volume, sodium balance, and functional and structural cardiac and vascular effects. In addition, RAAS overactivity is associated with development of hypertension, atherosclerosis, left ventricular hypertrophy and cardiovascular events such as myocardial infarction, stroke and congestive heart failure. Angiotensin II, the main effector of the RAAS, is not only a vasoconstrictor factor, but is also profibrotic and proinflammatory through its binding to the angiotensin type 1 (AT1) receptor. The proinflammatory effect of angiotensin II is mediated, in part, through the activation of NF-kB and subsequent production of a whole variety of inflammatory mediators. [17] This role has been clearly confirmed by the observation that angiotensin II antagonism results in a reduction of inflammatory markers.
Hypertension and hyperlipidemia exert many similar effects on the arterial wall. The increase in oxidative stress, a mechanism common to both conditions, may activate genes involved in generating an inflammatory response that, in the presence of hyperlipidemia, leads to the formation of atherosclerotic plaque. There is a great deal of interest in the use of antioxidants in the treatment of atherosclerosis. The possibility that members of this class of compounds might also ameliorate hypertensive vascular injury deserves further investigation.