**6. Pathophysiology of vascular remodeling in hypertension**

## **6.1. Hypothesis of inflammatory and endothelial dysfunction**

The traditional view of atherosclerosis as a lipid storage disease is crumbling with growing evidence that inflammation is involved during all stages, from the initial injury to the final stage of thrombotic complications. The narrowing of the arterial lumen is not necessarily a sign of myocardial infarction, and treating narrowed blood vessels does not prolong life. Although invasive procedures are needed in some cases, we understand that medical treatment and lifestyle modification (diet and physical activity) produce benefits that may result from reductions in inflammatory processes [49].

Usually, endothelial cells (EC) prevent leukocyte adhesion. However, the triggers of atherosclerosis can initiate the expression of adhesion molecules on EC, mediating leukocyte adhesion to the arterial wall. A key part of this interaction is VCAM-1. It is likely that oxidized lipids can induce gene expression via the pathway initiated by the nuclear transcription factor-kB (NF-kB), such as IL-1β and TNF-α [50].

This concept of vascular inflammatory disease allows a new approach for risk stratification and treatment. Increased levels of CAM are predictive of cardiac events and are an independent risk factor in men with coronary disease [51]. In our previous study, we demonstrated the presence of the endothelium as well as the products of NF-kB signaling and VCAM-1 in an experimental model of metabolic syndrome in hypertensive rats receiving a fructose-rich diet fructose-fed hypertensive rats (FFHR) [52].

Chemokines are low molecular weight cytokines responsible for mediating the maturation, differentiation, and migration of cells involved in the inflammatory response. In addition to this role, chemokines could promote reactive oxygen species (ROS) production and other cytokines during leukocyte infiltration of the vessel wall. Monocyte chemotactic protein-1 (MCP-1) is a chemokine that regulates the migration and infiltration of monocytes and macrophages into the site of inflammation. It is overexpressed in the presence of cardiovascular risk factors, especially in atherosclerotic lesions. Differential activation induces nuclear transcription factors such as NF-kB and AP-1, which leads to the release of IL-6 and the proliferation of VSMC [53].

Cytokines are soluble proteins that form a complex signaling network critical in the regulation of innate and adaptive inflammatory response. Cytokines modulate the inflammatory response through their influence on the growth, development and activation of leukocytes, and other inflammatory cells. TNF-α is a key mediator in systemic inflammation with a significant role in the Th1 inflammatory pathway. The activity of TNF-α is varied and includes the production of interleukin CAM expression, cell migration and activation, and activation of metalloproteinases (MMP) and COX activity, promoting the procoagulant state. TNF-α is detected in endothelial cells and smooth muscle cells at all stages of the formation of atheromatous plaques [54].

In summary, vascular wall remodeling is the result of changes in cellular and noncellular components, depending on the disease process causing the changes. Changes in the growth and migration of VSMC, endothelial dysfunction, inflammatory processes, and the synthesis or degradation of extracellular matrix components may be present during the disease process.

The traditional view of atherosclerosis as a lipid storage disease is crumbling with growing evidence that inflammation is involved during all stages, from the initial injury to the final stage of thrombotic complications. The narrowing of the arterial lumen is not necessarily a sign of myocardial infarction, and treating narrowed blood vessels does not prolong life. Although invasive procedures are needed in some cases, we understand that medical treatment and lifestyle modification (diet and physical activity) produce benefits that may result

Usually, endothelial cells (EC) prevent leukocyte adhesion. However, the triggers of atherosclerosis can initiate the expression of adhesion molecules on EC, mediating leukocyte adhesion to the arterial wall. A key part of this interaction is VCAM-1. It is likely that oxidized lipids can induce gene expression via the pathway initiated by the nuclear transcription fac-

This concept of vascular inflammatory disease allows a new approach for risk stratification and treatment. Increased levels of CAM are predictive of cardiac events and are an independent risk factor in men with coronary disease [51]. In our previous study, we demonstrated the presence of the endothelium as well as the products of NF-kB signaling and VCAM-1 in an experimental model of metabolic syndrome in hypertensive rats receiving a fructose-rich

Chemokines are low molecular weight cytokines responsible for mediating the maturation, differentiation, and migration of cells involved in the inflammatory response. In addition to this role, chemokines could promote reactive oxygen species (ROS) production and other cytokines during leukocyte infiltration of the vessel wall. Monocyte chemotactic protein-1 (MCP-1) is a chemokine that regulates the migration and infiltration of monocytes and macrophages into the site of inflammation. It is overexpressed in the presence of cardiovascular risk factors, especially in atherosclerotic lesions. Differential activation induces nuclear transcription factors such as NF-kB and AP-1, which leads to the release of IL-6 and the proliferation

Cytokines are soluble proteins that form a complex signaling network critical in the regulation of innate and adaptive inflammatory response. Cytokines modulate the inflammatory response through their influence on the growth, development and activation of leukocytes, and other inflammatory cells. TNF-α is a key mediator in systemic inflammation with a significant role in the Th1 inflammatory pathway. The activity of TNF-α is varied and includes

**6. Pathophysiology of vascular remodeling in hypertension**

**6.1. Hypothesis of inflammatory and endothelial dysfunction**

202 Physiologic and Pathologic Angiogenesis - Signaling Mechanisms and Targeted Therapy

from reductions in inflammatory processes [49].

tor-kB (NF-kB), such as IL-1β and TNF-α [50].

diet fructose-fed hypertensive rats (FFHR) [52].

of VSMC [53].

There are over 30 members of the interleukin family. They are subdivided by the similar structure or homology of the receptor. The transformation from a vascular homeostasis inflammatory state is influenced by an imbalance between the pro-inflammatory and antiinflammatory activities of interleukins. The role of IL-1 includes the stimulation of CAM, chemokines, growth factors, tissue factor, and other cytokines. The expression levels of the receptor antagonist IL-1Ra significantly increase in unstable angina compared with stable angina. Decreased levels of IL-1Ra after coronary stent placement may be linked to a low association with recurrent ischemia [55]. IL-6 is a multifunctional cytokine with a central role in inflammation. Elevated levels of IL-6 increase the risk of myocardial infarction and mortality in patients with coronary heart disease [56].

IL-10 has pleiotropic properties and influences different cell populations. Its most important role is in inflammatory vascular disease as part of the Th2 response. The expression of IL-10 decreases the expression of inflammatory cytokines, decreasing the Th1 phenotype. IL-10 also decreases NF-kB signaling reducing synthesis of pro-inflammatory cytokines, CAM, chemoattractants, and growth factors [57, 58].

Endothelial dysfunction in FFHR causes an increase in the expression of NF-kB and AP-1 and the posttranscriptional product VCAM-1. The expression of NF-kB (p65) and AP-1 (c-fos) predominates throughout the vessel wall. Increased VCAM-1, as discussed in the literature, is a marker of vascular inflammation, vascular permeability, and endothelial dysfunction.

This experimental model produced an increased expression of several cytokines. This finding demonstrates that the vascular bed FFHR model presents a pro-inflammatory and proatherogenic microenvironment that favors vascular remodeling. C-reactive protein (CRP) was used to evaluate whether this local inflammatory process is also systemic and revealed significantly increased IL-6 expression in the liver.

The potential importance of vascular wall inflammation as a therapeutic target remains an area not yet fully explored, where understanding the involvement of inflammatory mediators in vascular remodeling is relevant. The data suggest that oxidative stress and the subsequent activation of genes involved in the inflammatory process are actively involved in organ damage at the vascular level.

## **6.2. Vascular remodeling and extracellular matrix metalloproteinases**

MMPs are tools for maintaining the homeostasis of extracellular structures. Their synthesis is induced by cytokines as well as cell-cell and cell-matrix interactions. Acute coronary syndromes are an example of an increase in clinical conditions, specifically in the vulnerable region of the plaque [59]. Exposure to oxidized low-density lipoproteins or TNF-α induces the expression of MT3-MMP, a protease that degrades atherosclerotic plaques and is expressed in macrophages [60, 61].

MMPs with accessory signaling molecules can modulate cell-cell interactions through the activation of signal transmission and release of cytokines and chemokines. By these effects, accessory signaling molecules can propagate the inflammatory response.

#### **6.3. Vascular remodeling and acute phase reactants**

The production of acute phase reactants is a normal physiological response to cytokine release in acute and chronic inflammatory conditions. Ultrasensitive quantification of CRP, when it is below the detection limits of the common assay, has a very important role in the detection of vascular inflammation and cardiovascular risk prediction. There is evidence that CRP is involved in atherosclerosis, especially during the early stages. It stimulates the production of pro-inflammatory cytokines in monocytes and macrophages [62] and mediates the expression of CAM, allowing for increased leukocyte adhesion and migration. Their increased expression suppresses endothelial nitric oxide synthase [34] and promotes a procoagulant state.

Multiple studies have determined that increases in CRP are an independent risk factor for developing atherosclerosis. Data from clinical studies indicate that this association is less important when viewed in healthy subjects and controls inflammatory markers such as IL-6 and fibrinogen [63, 64], whereas another study identified CRP as a predictor of diabetes mellitus independent of established risk factors. CRP also indicated a correlation with the risk of cardiovascular events in women with metabolic syndrome [65].

#### **6.4. Vascular remodeling and the renin-angiotensin-aldosterone system**

Another important pillar in the vascular remodeling process is the renin-angiotensin-aldosterone system (RAAS) [66, 67]. To evaluate its participation, we studied the expression of AT1R and AT2R at the vascular level. In the experimental model of FFHR, we observed increased expression of AT1R and decreased expression of AT2R, promoting growth, vascular hypertrophy, and endothelial dysfunction. The release of ROS and initiation of vascular inflammation through different intracellular signaling cascades foster interconnections with other routes such as NAD(P)H oxidase and the growth factor receptor associated with insulin (IGFR).

**Figure 4** allows us to appreciate the AT1R-associated intracellular cascades. In this experimental model, the route associated with the satellite receptor and the IGFR subunit associated with NAD(P)H oxidase are the most important pathophysiological mechanisms. The FAK pathways PI3K and JAK2 generate stimuli and trigger contraction, migration and cell adhesion via intranuclear promoters that synthesize ICAM-1 and VCAM-1. Endothelial Growth Factor Receptor (EGFR) and Insulin Growth Factor Receptor (IGFR) amplified pathways are associated with cellular growth and hypertrophy as a result of insulinogenic stimuli and permit activation of collagenase, which modifies the extracellular matrix. Finally, the oxidative stress pathway stimulated by angiotensin activates redox-sensitive inflammatory molecules such as AP-1 and NF-kB, which amplify the inflammatory response by cytokines, chemokines, and lymphokines to ultimately induce more vascular inflammation.

Angiotensin II is the main effector of the RAAS in the homeostatic regulation of the cardiovascular system and in the pathogenesis of cardiovascular disease. Aldosterone interacts with mineralocorticoid receptors (MR), causing endothelial dysfunction, facilitating thrombosis,

MMPs with accessory signaling molecules can modulate cell-cell interactions through the activation of signal transmission and release of cytokines and chemokines. By these effects,

The production of acute phase reactants is a normal physiological response to cytokine release in acute and chronic inflammatory conditions. Ultrasensitive quantification of CRP, when it is below the detection limits of the common assay, has a very important role in the detection of vascular inflammation and cardiovascular risk prediction. There is evidence that CRP is involved in atherosclerosis, especially during the early stages. It stimulates the production of pro-inflammatory cytokines in monocytes and macrophages [62] and mediates the expression of CAM, allowing for increased leukocyte adhesion and migration. Their increased expression suppresses endothelial nitric oxide synthase [34] and promotes a procoagulant state.

Multiple studies have determined that increases in CRP are an independent risk factor for developing atherosclerosis. Data from clinical studies indicate that this association is less important when viewed in healthy subjects and controls inflammatory markers such as IL-6 and fibrinogen [63, 64], whereas another study identified CRP as a predictor of diabetes mellitus independent of established risk factors. CRP also indicated a correlation with the risk of

Another important pillar in the vascular remodeling process is the renin-angiotensin-aldosterone system (RAAS) [66, 67]. To evaluate its participation, we studied the expression of AT1R and AT2R at the vascular level. In the experimental model of FFHR, we observed increased expression of AT1R and decreased expression of AT2R, promoting growth, vascular hypertrophy, and endothelial dysfunction. The release of ROS and initiation of vascular inflammation through different intracellular signaling cascades foster interconnections with other routes such as NAD(P)H oxidase and the growth factor receptor associated with insulin (IGFR).

**Figure 4** allows us to appreciate the AT1R-associated intracellular cascades. In this experimental model, the route associated with the satellite receptor and the IGFR subunit associated with NAD(P)H oxidase are the most important pathophysiological mechanisms. The FAK pathways PI3K and JAK2 generate stimuli and trigger contraction, migration and cell adhesion via intranuclear promoters that synthesize ICAM-1 and VCAM-1. Endothelial Growth Factor Receptor (EGFR) and Insulin Growth Factor Receptor (IGFR) amplified pathways are associated with cellular growth and hypertrophy as a result of insulinogenic stimuli and permit activation of collagenase, which modifies the extracellular matrix. Finally, the oxidative stress pathway stimulated by angiotensin activates redox-sensitive inflammatory molecules such as AP-1 and NF-kB, which amplify the inflammatory response by cytokines, chemo-

Angiotensin II is the main effector of the RAAS in the homeostatic regulation of the cardiovascular system and in the pathogenesis of cardiovascular disease. Aldosterone interacts with mineralocorticoid receptors (MR), causing endothelial dysfunction, facilitating thrombosis,

accessory signaling molecules can propagate the inflammatory response.

204 Physiologic and Pathologic Angiogenesis - Signaling Mechanisms and Targeted Therapy

**6.3. Vascular remodeling and acute phase reactants**

cardiovascular events in women with metabolic syndrome [65].

**6.4. Vascular remodeling and the renin-angiotensin-aldosterone system**

kines, and lymphokines to ultimately induce more vascular inflammation.

**Figure 4.** Associated intracellular cascades to physiopathology of vascular remodeling. In FFHR experimental model, the route associated with the satellite receptor and the IGFR subunit associated with NAD(P)H oxidase are the most important pathophysiological mechanisms. Also, the oxidative stress pathway stimulated by angiotensin activates redox-sensitive inflammatory molecules such as AP-1 and NF-kB, which amplify vascular inflammatory response.

reducing complacence, causing vascular hypertrophy and cardiac fibrosis, and generating pathological remodeling. Aldosterone also induces the growth and proliferation of VSMC. A classical genomic action of aldosterone on MR is the translocation of this Aldo-MR complex into the nucleus, where it interacts with promoters to post-transcriptionally regulate gene and protein expression. For this path, increased Ki-ras2A expression (small and monomeric GTPbinding protein), which is associated with cardiac remodeling, generates fibrosis, and cell proliferation by ERK1/2 possibly [68]. Recently, some authors have demonstrated that aldosterone stimulates EGFR intracellularly in CHO cells. The transactivation of this receptor has also been described as a crucial step in the cascade of MAPK signaling activated by angiotensin II. This pathway allows for "cross-talk" and mutual activation that allows the development of cardiovascular injury and subsequent remodeling. The latter route is via "fast" activation, which is different from genomic stimulation and stimulates MKP-1 and Ki-generated ras2A proliferation and vascular remodeling; this discovery explains the changes previously observed in other studies [69].

Noting the role of aldosterone in vascular remodeling in FFHR, we observed that chronic administration of spironolactone did not change the variables of metabolic syndrome that were partially reversed by oxidative stress. This can be explained by the relationship between aldosterone and the angiotensin II receptor AT1R, which sensitizes the effects and increased the post-receptor response [67].

In summary, abundant evidences indicate the involvement of the RAAS in the pathophysiology of vascular remodeling; our observations in experimental pathology highlight the structural and functional changes.

In this special issue, different authors have tried to demonstrate the involvement of different pathophysiological mechanisms to clarify the vascular changes associated with hypertension and metabolic syndrome.

## **7. Clinical data**

The most feasible possibility for studies of resistance vessels in humans relies on the examination of small muscular arteries from biopsies of subcutaneous gluteal fat. Small arteries can also be obtained from omental fat [70–73]. The dissected vessels are mounted in a wire or pressure myograph, but due to the invasive character of these procedures, most relevant studies are of modest size [74–76]. In other cases, untreated hypertensives in place of patients newly diagnosed. In this studies, a data indicate that small subcutaneous arteries of nondiabetic hypertensives undergo inward eutrophic remodeling. Evidence suggests that diabetes, on top of essential hypertension, is associated with media hypertrophy (eutrophy remodeling). The same hypertrophy was also shown by one of these studies in normotensive diabetics, supporting a pressure-independent effect.

Finally, hypertension secondary as renovascular disease could promote media growth in arteries [77–80].

When evaluating the clinical data, there are two problems.


## **Author details**

Nicolás F. Renna1,2\*, Rodrigo Garcia<sup>2</sup> , Jesica Ramirez<sup>3</sup> and Roberto M. Miatello1,2

\*Address all correspondence to: nicolasfede@gmail.com

1 Department of Pathology, School of Medicine, National University of Cuyo, Mendoza, Argentina

2 Institute of Experimental Medicine and Biology of Cuyo (IMBECU), CONICET, Mendoza, Argentina

3 Genetics Institute, School of Medicine, National University of Cuyo, Mendoza, Argentina
