Vascular biology and medicine in the 1990s: scope, concepts, potentials, and perspectives

Sulfur dioxide induces vascular relaxation through PI3K/Akt/eNOS and NO/cGMP signaling pathways in rats

Sulfur dioxide (SO₂) is a common exogenous atmospheric pollutant. Studies have shown that SO₂ can cause vasodilation as a gas signaling molecule, but the specific signaling pathways are not well understood. This study aimed to explore the underlying mechanism behind the effects of SO₂ on vasodilation of isolated rat aorta. The results showed that when the dose of SO₂ was 30 μM, the vasodilation of endothelium-intact rings was partially suppressed by LY294002 and N^G-nitro-l-arginine methyl ester, and the protein levels of phosphoinositide 3-kinase (PI3K), p-Akt, and p-endothelial nitric oxide synthase (p-eNOS) were significantly increased. When the dose of SO₂ was 300 μM or 1500 μM, the vasodilation of endothelium-denuded rings did not change after application of the inhibitor, but the protein levels of PI3K, p-Akt, and p-eNOS were significantly decreased, and the activity of NOS and the level of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) were significantly increased. We speculate that the mechanism of SO₂-induced vasodilatation likely involved the endothelial PI3K/Akt/eNOS and NO/cGMP signal pathways. In addition, at the concentration of 1500 μM, SO₂ markedly increased the level of caspase-3 and caspase-9. The results suggest that high concentrations of SO₂ may cause damage to blood vessels. This study will help to further inform the etiologies of SO₂-related cardiovascular disease.

Molecular atherectomy for restenosis

Receptors for basic (b) and acidic (a) fibroblast growth factor (FGF) are upregulated in activated smooth muscle cells. These cells, which proliferate in response to bFGF, can thus be killed by a conjugate of bFGF and the ribosome-inactivating enzyme, saporin (which, by itself, does not enter the cells). Quiescent smooth muscle cells and other cells that have few FGF receptors are not killed. In vivo, bFGF-saporin transiently inhibits smooth muscle cell proliferation and neointimal accumulation after balloon injury to the rat carotid artery. Delivery of saporin, diagnostic imaging agents, or antisense oligodeoxynucleotides might be made even more selective by linking these substances to antibodies against the extracellular domains of the putative FGF receptor isoform specific for activated smooth muscle cells.

The role of nitric oxide in female reproduction

The cardiovascular system undergoes profound changes during pregnancy. Maternal intravascular volume begins to increase in the first trimester rising an average of 45% by term.1Cardiac output increases similarly2and is redistributed to organs whose functions are crucial for a successful pregnancy. In the guinea pig, uterine artery (UA) blood flow increases 3500%, while mesenteric and renal artery blood flows increase only 90% and 10% respectively.3Blood flow to the trunk actually diminishes. The mechanism underlying this redistribution is unknown. Coupled with the rise in cardiac output is a decrease in the systemic pressor response to angiotensin II (AII), norepinephrine(NE), and epinephrine.4–8There is also a decrease in the contraction response among some but not all vascular beds. For example, contraction of UA to NE and thromboxane is characteristically reduced by pregnancy, whereas the response of the carotid artery is unaltered8–10Since pregnancy does not alter neuroeffector mechanisms of NE such as release, receptor sensitivity, and accumulation11, changes in sympathetic control during pregnancy must be dependent on alterations at sites other than the neuroeffector junction. We have hypothesized that the mechanisms which alter vascular reactivity during pregnancy also mediate the redistribution of maternal cardiac output.9We have further hypothesized that many of these mechanisms involve endothelium-dependent factors which are modulated by sex hormones.

Different Effects of Atherogenic Lipoproteins and Blood Pressure on Arterial Structure and Function: The Bogalusa Heart Study

Differential impact of non-high-density lipoprotein cholesterol (total cholesterol minus high-density lipoprotein cholesterol) and blood pressure on arterial wall thickness and stiffness was examined in 900 black and white adults aged 24-43 years. Blacks compared with whites had greater values of pulse wave velocity (5.4 m/sec vs. 5.2 m/sec; p<0.01) and carotid artery intima-media thickness (0.83 mm vs. 0.80 mm; p<0.01). Non-high-density lipoprotein cholesterol was significantly associated with carotid intima-media thickness (standardized regression coefficient [b]=0.21; p<0.01), but not with pulse wave velocity (b=0.03; p=0.37), after adjusting for race, sex, age, body mass index, insulin, glucose, and smoking. Systolic blood pressure was associated significantly stronger with pulse wave velocity (b=0.36; p<0.01) than with carotid intima-media thickness (b=0.15; p<0.01). No race difference in these relationships was found. The results of this study indicate that atherogenic lipoproteins and blood pressure may play different roles in the development of arterial wall stiffness and atherosclerosis.

Molecular aspects of atherogenesis: new insights and unsolved questions

The development of atherosclerotic disease results from the interaction between environment and genetic make up. A key factor in atherogenesis is the oxidative modification of lipids, which is involved in the recruitment of mononuclear leukocytes to the arterial intima--a process regulated by several groups of adhesion molecules and cytokines. Activated leukocytes, as well as endothelial mitochondria, can produce reactive oxygen species (ROS) that are associated with endothelial dysfunction, a cause of reduced nitric oxide (NO) bioactivity and further ROS production. Peroxisome proliferator-activated receptors (PPAR) and liver X receptors (LXR) are nuclear receptors significantly involved in the control of lipid metabolism, inflammation and insulin sensitivity. Also, an emerging role has been suggested for G protein coupled receptors and for the small Ras and Rho GTPases in the regulation of the expression of endothelial NO synthase (eNOS) and of tissue factor, which are involved in thrombus formation and modulation of vascular tone. Further, the interactions among eNOS, cholesterol, oxidated LDL and caveola membranes are probably involved in some molecular changes observed in vascular diseases. Despite the relevance of oxidative processes in atherogenesis, anti-oxidants have failed to significantly improve atherosclerosis (ATS) prevention, while statins have proved to be the most successful drugs.

Genes and atherosclerosis: at the origin of the predisposition

Atherosclerosis (ATS) is a multifactorial disease caused by the interaction of established or emerging risk factors with multiple predisposing genes that regulate ATS-related processes. This review will discuss the current knowledge concerning the potential role of the genetic variations that could promote and/or accelerate ATS, in both animal models and humans. Allelic polymorphisms or variations of distinct genes that enhance the risk of ATS frequently occur in the general population, but only adequate gene-environment interactions will lead to the disease. The main genes so far studied are involved in the regulation of processes such as endothelial function, antioxidant potential, coagulation, inflammatory response, and lipid, protein and carbohydrate metabolism. The detection of candidate genes associated with ATS could allow, in the near future, earlier interventions in genetically susceptible individuals. Further, large-scale population studies are needed to obtain more information on the specific gene-environment and drug-gene interactions capable of influencing ATS progression.

Lipids: potential regulators of nitric oxide generation

The endothelium is a dynamic organ that secretes several biologically active substances and plays a major functional role in the health of an organism in both physiological and pathological conditions. For instance, the endothelium is involved in control of the exchange of plasma and tissue biomolecules, regulation of vessel tone, inflammation, lipid metabolism, vessel growth and remodeling, and modulation of coagulation and fibrinolysis. The endothelium generates nitric oxide, which is a key regulator of vasodilation and plays important roles in preventing, or in some cases promoting, numerous cardiovascular diseases. Several recent studies have examined the interplay between lipids and nitric oxide generation, especially in relation to atherosclerosis. The endothelium is continuously exposed to circulating lipids in the form of lipoproteins and protein carriers that may have a direct impact on nitric oxide synthesis and function. The purpose of this review is to illustrate some of the recent findings that link lipids (plasma and cellular) to nitric oxide generation (see Fig. 1).

Role of statin therapy in the coronary bypass patient

Statins have been proven to prevent or delay ischemic events in patients at risk for atherosclerotic coronary disease. Increasing evidence suggests that statin therapy is also beneficial to patients undergoing coronary revascularization. In this review statin therapy will be shown to improve vein graft patency, minimize recurrent ischemic events, and decrease the need for repeat revascularization procedures in patients who have undergone coronary artery bypass grafting.

Endothelium and the lipid metabolism: the current understanding

The endothelium is a dynamic organ and responds to various physical and humoral conditions. The endothelium secretes several biologically active substances, both vasoconstrictors and vasodilators, which control these processes. Endothelial function is most commonly assessed as the vasodilatory response to stimuli. Several endothelium-dependent agonists have been identified, each of which acts through a membrane receptor. Nitric oxide which is continuously synthesized by the endothelium has a wide range of biological properties that maintain vascular homeostasis. It is a potent vasodilator and inhibitor of platelet aggregation and thus has an important protective role. Endothelial dysfunction in hypercholesterolemic patients is in large part due to a reduced bioavailability of NO. Traditional coronary risk factors, especially hypercholesterolemia, produce endothelial dysfunction even in patients with normal blood vessels. The underlying mechanisms involve a local inflammatory response, release of cytokines and growth factors, activation of oxidation-sensitive mechanisms in the arterial wall, modulation of intracellular signaling pathways, increased oxidation of low-density lipoprotein cholesterol, and quenching of nitric oxide. Clinical studies have shown a significant improvement in endothelial dysfunction following lowering of serum cholesterol levels, infusion of nitric oxide donors like L-arginine and exercise training. Clinical trials are underway examining the role of endothelin-1 receptor antagonists like bosentan in the prevention of graft atherosclerosis.

Haemodynamic factors and the important role of local low static pressure in coronary wall thickening

BACKGROUND/STUDY OBJECTIVES: The purpose of our study was to investigate the possible correlation between blood flow physical parameters and the wall thickening in typical human coronary arteries.

METHODS

Digitized images of seven transparent arterial segments prepared post-mortem were adopted from a previous study in order to extract the geometry for numerical analysis. Using the exterior outline, reconstructed forms of the vessel geometries were used for subsequent computational fluid dynamic analysis. Data was input to a pre-processing code for unstructured mesh generation. The flow was assumed to be two-dimensional, steady, laminar with parabolic inlet velocity profile. The vessel walls were assumed to be smooth, inelastic and impermeable. Non-Newtonian power law was applied to model blood rheology. The arterial wall thickening was measured and correlated to the wall shear stress, static pressure, molecular viscosity, and near wall blood flow velocity.

RESULTS

Wall shear stress, static pressure and near wall velocity magnitude exhibit negative correlation to wall thickening, while molecular viscosity exhibits positive correlation to wall thickening.

CONCLUSION

There is a strong correlation between the development of vessel wall thickening and the blood flow physical parameters. Amongst these parameters the role of local low wall static pressure is predominant.

Molecular approaches for the treatment of atherosclerosis

Advances in vascular biology and the study of molecular pathophysiology have enabled the design and initial testing of therapeutic principles for cardiovascular intervention at the level of gene expression. This approach can offer an avenue to greatly impact the onset and progression of vascular disease at its roots. Early translations of basic research into human clinical protocols might provide novel alternatives for patients without traditional therapeutic options and might provide means of improving and prolonging the success of standard therapies. As the understanding of the genetic basis of vascular disease continues to grow and the tools for in vivo genetic manipulation continue to improve, vascular gene therapies might someday become a part of routine patient care.

Oxidative stress and vascular aging

In attempt to meet tissue demands for proper blood flow, the vasculature alters its structure, simultaneously responding to both physical and chemical stresses. Substantial information has emerged in this field of study, particularly concerning the roles of the endothelium and smooth muscle cells in relation to signaling pathways for mechanotransduction. As a first line of defense upon exposure to various stressors, the endothelium and smooth muscle cells respond with adaptive cellular modifications. One prime example of these modifications is the cellular response to oxidative stress as evidenced by accumulated data. A recent proposal of the inflammatory hypothesis of vascular aging emphasized that stress-induced vascular aging may be the primary event that underlies the general aging phenomenon of systemic dysfunction.

Acute effects of angiotensin II on myocardial performance

BACKGROUND

Specific angiotensin II (Ang II) receptors exist in many organs including peripheral blood vessels, cardiac myocytes and the central nervous system. This suggests multiple sites of actions for Ang II throughout the cardiovascular system. Cardiac effects of Ang II are not completely understood, though its prominent vasoconstrictor actions are well described. This study was designed to assess left ventricular function during administration of Ang II using relatively load-independent methods in a whole-animal model.

METHODS

Ang II was infused in incremental doses (0-200 microg x h(-1)) in anaesthetised instrumented pigs (n=10). Cardiac systolic and diastolic function were evaluated by analysis of the left ventricular pressure-volume relationship.

RESULTS

Heart rate (HR), mean arterial pressure (MAP) and systemic vascular resistance (SVR) increased dose-dependently with Ang II, while cardiac output (CO) remained unchanged. Systolic function indices, end-systolic elastance (Ees) and preload recruitable stroke work (PRSW), demonstrated dose-dependent increases. The diastolic function parameter tau (tau) did not change with increasing Ang II dose.

CONCLUSION

Ang II infusion caused increases in contractility indices in anaesthetised pigs in the doses used in this study. The mechanisms for these systolic function effects may be a direct myocardial effect or modulated through changes in autonomic nervous system activity.

Molecular genetics and gene expression in atherosclerosis

Although molecular cardiology is a relative young discipline, the impact of the new techniques on diagnosis and therapy in cardiovascular disease are extensive. Our insight into pathophysiological mechanisms is rapidly expanding and is changing our understanding of cardiovascular disease radically and irrevocably. Molecular cardiology has many different aspects. In this paper the importance of molecular cardiology and genetics for every day clinical practice are briefly outlined. It is expected that in the genetic predisposition for atherosclerotic disease multiple genes are involved (genetics). The role of only a minority of genes involved in the atherosclerotic process is known. Far less is known about particular gene-gene and gene-environment interactions. In some families disease can be explained mostly by a single, major gene (monogenic), of which the lipid disorder Familial Hypercholesterolemia is an example. In other cases, one or several variations in minor genes (multigenic) contribute to an atherosclerotic predisposition, for instance the lipoprotein lipase gene. Although mutations in this gene influence lipoprotein levels, disease development is predominantly depending on environmental influences. Recently several additional genetic risk factors were identified including elevated levels of lipoprotein (a) [Lp(a)], the DD genotype of angiotensin converting enzyme (ACE), and elevated levels of homocysteine. This illustrates the complexity of genetics in relation to atherosclerosis and the difficulty to assign predictive values to separate genetic risk factors. Furthermore, little attention has been given to protective genes thus far, explaining why some high risk patients are protected from vascular disease. Genetics based treatment or elimination of the genetic risk factor requires complete understanding of the pathogenic molecular basis. Once this requirement is fulfilled, disease management can be strived for, provided that adequate medical management is available. Recent studies suggest that such treatment should be genotype specific, as the genetic makeup can determine the outcome of a pharmacological intervention (pharmacogenetics). Once the trigger for atherosclerosis has initiated disease development, various genes are activated or silenced and contribute to lesion progression. Every stage of lesion development depends on a different gene expression programme (genomics). In this review paper an introduction is provided into genetics, pharmacogenetics and gene expression with respect to atherosclerotic disease.

Early growth-response factor 1 and basic transcriptional element-binding protein 2 expression in cardiac allografts

Early growth-response factor 1 (Egr-1) and basic transcriptional element-binding protein 2 (BTEB2) are transcriptional factors that regulate multiple genes involved in phenotypic changes of smooth muscle cells (SMCs), one of the outstanding pathologic features of chronic cardiac allograft rejection. In this study, we used a heterotopic abdominal heart transplant model in monkeys to evaluate the roles of these molecules in graft coronary vasculopathy. We demonstrated that Egr-1 and BTEB2 are induced in vascular SMCs of rejected cardiac allografts well before morphologic changes, such as intimal thickening. These findings suggest that expression of Egr-1 and BTEB2 is one of the initial events in allograft angiopathy.

Antisense and gene therapy to prevent restenosis

A primary pathologic response to vascular injury is the proliferation and migration of vascular smooth muscle cells and the development of neointimal lesions. An increasing body of knowledge regarding the molecular and genetic basis of neointimal disease has created a unique opportunity for the treatment of this complex disorder. Gene therapy attempts to correct pathobiological processes by either inhibiting or correcting cellular functions at the level of gene expression. These endpoints are achieved by the delivery of either functional genes or oligonucleotides, capable of interfering with a cell's programmed machinery. Since the early 1990s, the evolution of this technology, along with an ever-expanding source of pathobiological information, has led to many novel approaches for the treatment of restenosis in arterial balloon injury as well as vein graft bypass failure. Using a variety of targets, inhibition of proliferation has predominantly been achieved through direct disruption of the cell cycle machinery. In addition, others have demonstrated successful inhibition by interfering with the signals for cellular proliferation or the enhancement of anti-proliferative stimuli. As this exciting therapeutic alternative evolves, improvements in safety, specificity and efficiency will enhance the likelihood of widespread clinical application.

Angiotensin II mesenteric and renal vasoregulation: dissimilar modulatory effects with nitroprusside

BACKGROUND

The role of systemic arterial pressure for the vascular effects of angiotensin II (Ang II) and the interactions between Ang II and perfusion pressure-dependent local vascular control mechanisms are not well understood. This study addresses these aspects of exogenous Ang II in the mesenteric and renal regional circulations.

METHODS

Ang II was infused in incremental doses (0-200 microg/h) in anesthetized instrumented pigs (n=10). Renal and portal blood flows were measured by perivascular ultrasound. In the second part of the study, sodium nitroprusside (SNP) was infused at doses titrated to keep mean arterial pressure constant, in spite of concurrent Ang II administration.

RESULTS

Powerful dose-dependent vasoconstrictions by Ang II were found in renal and mesenteric vascular beds (at highest Ang II doses vascular resistances increased by 109% and 88% respectively). Ang II-induced vasoconstriction was fully inhibited in the mesenteric, but not in the renal circulation, during conditions of constant mean arterial pressures achieved by SNP infusion.

CONCLUSIONS

Mesenteric, but not renal, vasoconstriction by Ang II was inhibited by pharmacological maintenance of perfusion pressure. This could reflect differences between these vascular beds as regards the importance of co-acting myogenic pressure-dependent vasoconstriction. Alternatively, as the drug chosen for pressure control, sodium nitroprusside, serves as a nitric oxide donor, the relative balance between nitric oxide-mediated vasodilation and Ang II-induced vasoconstriction could have regional differences.

Cholesterol lowering with pravastatin improves resistance artery endothelial function: report of six subjects with normal coronary arteriograms

STUDY OBJECTIVES

Improvement in coronary artery endothelial function has been demonstrated after cholesterol lowering in hypercholesterolemic patients with significant atherosclerosis. However, to our knowledge, no previous study has shown improvement in resistance artery function in subjects with normal coronary arteries after cholesterol lowering. The purpose of our study was to investigate the effect of cholesterol lowering with pravastatin on coronary resistance artery endothelial function in the setting of angiographically normal coronary arteries.

METHODS

Invasive testing of coronary endothelial and vasomotor function was performed at baseline and after 6 months of pravastatin treatment in six patients with normal coronary arteriograms.

RESULTS

After 6 months of pravastatin treatment, low-density lipoprotein cholesterol level dropped from 157+/-11 to 117+/-8 mg/dL (p = 0.02) and percent increase in coronary blood flow after acetylcholine improved from 97+/-13% to 160+/-16% (p = 0.01). There was a trend (p = 0.17) toward enhanced epicardial dilation in response to acetylcholine after pravastatin treatment when compared with the baseline study.

CONCLUSIONS

Our study demonstrates significant improvement in coronary resistance artery endothelial function after 6 months of cholesterol lowering with pravastatin in six subjects presenting with chest pain who were found to have normal coronary arteriograms. A trend toward improved epicardial vasomotion was also observed.

Gene therapy for peripheral arterial disease

Our understanding of the molecular biology of vascular disease is rapidly expanding, and this scientific growth has brought with it new opportunities for therapeutic intervention at the molecular and genetic levels. Although our tools for genetic manipulation in vivo and our knowledge of potential molecular targets are still crude and incomplete, the early application of these concepts to clinical problems is already underway, both in the pre-clinical and clinical arenas. The treatment of peripheral vascular disease, although greatly improved over recent decades by surgical and minimally-invasive techniques, remains limited by vascular proliferative lesions and by our inability to modulate the progression of native disease. This review explores some of the evolving concepts of therapeutic gene manipulation and their initial application in the peripheral circulation.

The viral anti-inflammatory chemokine-binding protein M-T7 reduces intimal hyperplasia after vascular injury

Chemokines and IFN-gamma function as central regulators of inflammatory responses to vascular injury. Both classes of cytokines are upregulated during restenosis, a response to vascular injury that leads to recurrent atherosclerotic plaque growth, but the relative impact of each class of cytokines remains undetermined. M-T7 is a secreted myxoma viral immunomodulatory glycoprotein that functions both as a species-specific inhibitor of rabbit IFN-gamma and as a chemokine-binding protein, interacting with a wide range of C, C-C, and C-X-C chemokines in a species-nonspecific fashion. We wished to (a) assess the efficacy of purified M-T7 protein in inhibiting intimal hyperplasia after angioplasty injury and (b) exploit unique species-specific functions of M-T7 in order to judge the relative importance of each cytokine class on plaque growth. Anesthetized New Zealand white rabbits and Sprague-Dawley rats received either M-T7 or control at the time of arterial angioplasty injury. Histological analysis at 28 days demonstrated significant reductions in intimal hyperplasia with M-T7 treatment in both models, with an associated early inhibition of inflammatory cell invasion. Purified M-T7 protein inhibits intimal hyperplasia after angioplasty injury in a species-nonspecific fashion, thus implicating the chemokine-binding activity as more critical for prevention of plaque growth after vascular injury.

Transcriptional regulation of smooth muscle phenotypic modulation

Phenotypic modulation of vascular smooth muscle cell plays a pivotal role in the development of vascular pathology, such as atherosclerosis and restenosis after angioplasty. We have identified the zinc finger protein BTEB2 as a DNA binding protein that regulates the nonmuscle myosin heavy chain (SMemb) promoter. BTEB2 is expressed in fetal aorta but not in adult aorta and is induced in the neointima in response to vascular injury. BTEB2 also activates a number of vascular disease-associated genes, such as tissue factor, PAI-1 (plasminogen activator inhibitor-1), and Egr-1 gene. We have further isolated and characterized the human BTEB2 gene. Functional studies using 5'-deletion and site-directed mutation constructs demonstrated that phorbol ester induces Egr-1, which can activate the BTEB2 promoter through binding to -32 from the transcription start site. These results suggest that phenotypic modulation of vascular smooth muscle cells occurring in response to mitogen stimulation may be mediated by BTEB2 through Egr-1 induction.

Oxidized-LDL and atherosclerosis. Role of LOX-1

The accumulation of substantial numbers of monocyte/macrophages and activated T lymphocytes in focal areas of the arterial intima appears to be a hallmark of atherosclerosis. Our report demonstrated that lysophosphatidylcholine (lyso-PC), a polar phospholipid component that is increased in atherosclerotic lipoproteins, such as oxidized LDL and remnant lipoproteins in diabetic and Type 3 hyperlipidemia, can upregulate adhesion molecules for monocytes and T lymphocytes, and growth factors, such as heparin-binding epidermal growth factor-like growth factor and PDGF A and B chains. Recently, we identified the novel receptor for oxidized LDL, named LOX-1. We summarize the importance of the interaction between oxidized LDL and its receptor, LOX-1, in terms of early stage atherogenesis.

Cholesterol lowering and endothelial function

The pathophysiology of the association between cholesterol and atherosclerosis has been thought to involve the deposition, modification, and cellular uptake of cholesterol. We now believe that the process begins with vascular injury and involves inflammation and vessel remodeling. The vascular endothelium actively regulates vascular tone, lipid breakdown, thrombogenesis, inflammation, and vessel growth, all of which are important factors in the development of atherosclerosis. Endothelial dysfunction promotes atherosclerosis through vasoconstriction, monocyte and platelet adhesion, thrombogenesis, and cytokine and growth factor stimulation and release. An important component of endothelial dysfunction is reduced availability of nitric oxide, which is caused by low-density lipoproteins, especially if they are oxidized. This reduced availability appears to occur through a combination of decreased production, abnormal signaling, and increased destruction by oxygen-free radicals. Concurrently, endothelium-mediated vasoconstrictors, adhesion molecules, cytokines, growth factors, and thrombogenic factors, such as endothelin, are increased by oxidized low-density lipoprotein. Several studies have shown improvements in endothelial function with cholesterol lowering, which may explain the early and substantial reductions in major cardiovascular events associated with cholesterol lowering.

The renin-angiotensin system in essential hypertension: associations with cardiovascular risk

The importance of the renin-angiotensin system (RAS) in blood pressure regulation is well established. High RAS activity has also been implicated in connection with elevated cardiovascular risk in patients with essential hypertension. Data from epidemiological studies have related high plasma renin levels in essential hypertensive patients to cardiovascular complications. However, whether renin itself is a risk factor of cardiovascular events or just acts as a marker for other risk factors still remains to be elucidated. Several possible mechanisms that could be responsible for the association between elevated RAS activity and cardiovascular risk are reviewed. The concept of high RAS activity being a cardiovascular risk factor is strongly supported by results from large clinical studies showing the beneficial effects of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers in congestive heart failure and hypertension. Knowing more about the exact mechanisms of the association between high RAS activity and cardiovascular complications would enable us to profile the treatment of high blood pressure more specifically to improve outcome in individuals or groups of patients.

Hypertension and insulin resistance: role of peroxisome proliferator-activated receptor gamma

1. Insulin resistance has been highlighted as a common causal factor for hypertension, hyperlipidaemia, diabetes mellitus and obesity, all of which are recognized to occur simultaneously, and a distinct clinical entity is defined as 'multiple risk factor syndrome'. 2. Recently, a new class of antidiabetic agents, thiazolidinediones (TZD) has been developed and has been shown to improve insulin resistance by binding and activating a nuclear receptor, peroxisome proliferator-activated receptor (PPAR) gamma. 3. cDNA of rat PPAR gamma 1 and gamma 2 were cloned and gene regulation of PPAR gamma in rat mature adipocytes was examined. Hydrogen peroxide, an oxygen radical, which is recognized to be the common intracellular signal for multiple risk factors, potently down-regulated PPAR gamma mRNA expression in rat mature adipocytes. 4. Tumour necrosis factor (TNF)-alpha, which is considered to play a role in obesity-induced non-insulin-dependent diabetes mellitus and to augment oxidative stress, also suppressed PPAR gamma expression. 5. Thiazolidinediones dose-dependently recovered TNF-alpha-induced down-regulation of PPAR gamma mRNA expression. 6. The modulation of PPAR gamma expression by TZD can be one mechanism for the improvement of insulin resistance by TZD. 7. Vascular tone and remodelling are controlled by several vasoactive autocrine/paracrine factors produced by endothelial cells in response to several vascular injury stimuli, including hypertension. The PPAR gamma gene transcript was detected in cultured endothelial cells. 8. The administration of TZD stimulated the endothelial secretion of type-C natriuretic peptide, which is one of the natriuretic peptide family and is demonstrated by us to act as a novel endothelium-derived relaxing peptide. 9. Concomitantly, TZD significantly suppressed the secretion of endothelin, a potent endothelium-derived vasoconstricting peptide. 10. Thiazolidinediones can affect vascular tone and growth by modulating the production of endothelium-derived vasoactive substances to influence occurrence and progression of hypertension and atherosclerosis.

Postmenopausal hormone replacement, risk estimators for coronary artery disease and cardiovascular protection

Menopause, regardless of age at onset, is associated with a marked increase in coronary artery disease (CAD) risk. A large body of observational clinical studies repeatedly demonstrated favorable associations between postmenopausal hormone replacement therapy (HRT) and cardiovascular morbidity, mortality, and risk factors. Estrogens may act in a gender-specific way on vascular endothelial cells and other components of the vessel wall, enhancing the synthesis and release of nitric oxide (NO) and other vasodilators, and by inhibiting the synthesis and release of vasoconstricting agents, thus favoring vasodilation. Menopause-related changes in metabolic cardiovascular risk factors are identifiable, as are HRT-related changes in these factors. The metabolic effects include changes in lipoprotein (a), coagulation and fibrinolysis as well as homocysteine metabolism. The various actions of estrogen alone and combined with progestogen on the vascular system are reviewed. Furthermore, the outcome of the recently published Heart and estrogen/progestin replacement study (HERS) data are put in perspective. In addition, we outline the present data on the effects of raloxifene, a new second generation selective estrogen receptor modulator (SERM), which has been shown to favorably alter several markers of cardiovascular risk in postmenopausal women.

Effects of hyperinsulinemia on vascular blood flows in experimental obesity

Human obesity, which is very common in Polycystic Ovaries Syndrome and in "X Syndrome", constitutes an insulin-resistance state in which multiple clinical, biochemical and hemodynamic alterations coexist. Insulin resistance in the obese has been recently associated with an endothelial dysfunction. To investigate the possibility that clinical and metabolic derangements related to insulin resistance could induce changes in vascular blood flows, we have studied the levels of mesenteric (MBF), renal (RBF) and femoral (FBF) blood flows in Beagle dogs kept for 2 years on a normal (control group) or high fat diet (obese group). This experimental model exhibits many of the abnormalities with the human syndrome. In addition, we have tested the effects of chronic treatment with captopril (capto group) in monotherapy or in association with pravastatin (prava+capto group) on the hemodynamic changes associated with this diet. After the two year follow-up, Transonic flow probes were placed around the three arteries to measure basal blood flows and their response to a hyperinsulinemic-normoglycemic test in anesthetized animals. During this test the degree of insulin sensitivity was estimated. In association with higher body weight, blood pressure, insulin resistance, and fasting levels of insulin and total cholesterol, the obese group exhibited decreased basal levels of FBF and a greater femoral vasoconstriction during hyperinsulinism (P < 0.05 vs control). Combined therapy with captopril and pravastatin ameliorated the reduction in basal FBF and hyperinsulinism-induced vasoconstriction (P < 0.05), in addition to the beneficial effects on insulin sensitivity, and clinical and metabolic parameters. Synergistic beneficial effects of both drugs on lipid and carbohydrate profiles may account for this positive outcome, by attenuating the atherogenic process associated with this model.

Short-term estrogen administration improves abnormal endothelial function in women with systemic sclerosis and Raynaud's phenomenon

BACKGROUND

Morphologic changes of the vascular endothelium are common in patients with systemic sclerosis and Raynaud's phenomenon. The aim of this study was to evaluate the endothelium-dependent vasodilatation and endothelium-independent vasodilatation and to examine the effects of short-term estrogen administration on vascular responses in these patients.

METHODS AND RESULTS

The study included 12 female patients with systemic sclerosis and Raynaud's phenomenon (aged 49+/-14 years) and 12 age- and sex-matched healthy control subjects. With the use of high-resolution ultrasound imaging, brachial artery diameter was measured at rest, during reactive hyperemia (endothelium-dependent response), and after administration of sublingual nitroglycerin (endothelium-independent dilatation). Intima-media thickness of the common carotid artery was also measured. Baseline diameter was similar in patients and control subjects; intima-media thickness was significantly higher in patients (0.83+/-0.3 vs 0.46+/-0.2 mm, P= .002) than in control subjects. Flow-mediated dilatation was reduced in patients (3.6%+/-7% vs 11.9%+/- 4.6%, P = .003); endothelium-independent dilatation also was reduced in patients with Raynaud's phenomenon (14%+/-7% vs 23%+/-6%, P= .003). Vascular responses in 10 patients were examined 15 minutes after administration of conjugated estrogens (25 mg intravenously); there was a significant increase of endothelium-dependent dilatation after estrogen administration (1.7%+/-4% to 6.3%+/-4%, P= .01), whereas endothelium-independent dilatation did not change (13.4%+/-8% to 15.5%+/-7%, not significant).

CONCLUSIONS

Endothelium-dependent vasodilatation and endothelium-independent vasodilatation are impaired in patients with Raynaud's phenomenon secondary to systemic sclerosis, whereas intima-media thickness is increased. Short-term estrogen administration can improve endothelial dysfunction in this group of patients.

Assessing the coronary circulation in hypertension

Systemic arterial hypertension is one of the major risk factors for coronary artery disease, coronary microangiopathy, and left ventricular hypertrophy, all of which can potentially lead to cardiac failure and sudden cardiac death. Coronary flow reserve is defined as the maximal increase in coronary flow above its resting, autoregulated level for a given perfusion pressure. In arterial hypertension functional and structural alterations are observed at the level of epicardial vessels as well as in resistive vessels requiring sophisticated approaches to assess coronary flow reserve and thus myocardial perfusion. Electrocardiographic tests and echocardiography can be regarded as monitoring and screening methods. Myocardial scintography is useful to semiquantitatively estimate hypertension-associated perfusion abnormalities, whereas positron emission tomography provides the only quantitative approach of a non-invasive technique for myocardial blood flow measurement. Invasive methods for the assessment of coronary blood flow need cardiac catheterization procedures, such as techniques requiring catheterization of the coronary sinus, angiographic methods, and guidewire based methods. Thermodilution and venous oxymetry in the coronary sinus systematically underestimate coronary flow reserve and are thus considered as only semiquantitative approaches. In contrast, the gas chromatographic argon method allows a quantitative measurement of coronary blood flow at baseline and during maximum vasodilation; thus it is possible to distinguish between an altered autoregulated and maximal flow as the major cause of a reduced coronary flow reserve and to evaluate long-term therapeutic interventions in hypertensive hearts. Videodensitometric and angiographic methods should be restricted only to patients with coronary microangiopathy or with coronary single-vessel disease. Guidewire-based Doppler techniques are suitable to semiquantitatively assess coronary flow reserve with a considerable spatial and time resolution. Myocardial biopsies may gain insight into hypertension-associated structural alterations in small arterioles. Long-term treatment of hypertensive heart disease aims to normalize blood pressure, to reduce left ventricular hypertrophy and to achieve cardioreparation including reversal of the abnormal structure and function of coronary circulation. Based on the different methods for assessment of coronary circulation the therapeutic value of different classes of antihypertensive therapeutics will be evaluated in this overview.

Site-specific delivery of iloprost during experimental angioplasty suppresses smooth muscle cell proliferation

PURPOSE

The authors have previously reported that intramural delivery of iloprost during angioplasty suppresses local platelet aggregation at 1 hour in undiseased porcine arteries. In this study, the authors sought to quantify the effect of such treatment on medial vascular smooth muscle cell proliferation, an event implicated in the development of intimal hyperplasia.

MATERIALS AND METHODS

Three Yorkshire pigs underwent percutaneous transluminal angioplasty with hydrogel-coated balloons for a total of 10 iloprost-treated (experimental) and 10 saline-treated (control) arterial sites. The balloons were prepared with previously reported techniques and loaded with 2.25 microg of iloprost for the experimental sites. On the eighth day after angioplasty, these sites were harvested and prepared for immunohistochemical staining. Thin (4 microm) sections of the specimens were stained with use of monoclonal antibody to proliferating cell nuclear antigen (PCNA). Appropriate positive and negative controls were used. Approximately 350-500 vascular smooth muscle cells were randomly counted under high power (100x) by an experienced physician who was blinded to the origin of the specimen. A PCNA index (%) was calculated as follows: [(#PCNA [+] cells)/(#PCNA [+] cells + #PCNA [-] cells)]x 100. A paired t test was used for statistical comparison.

RESULTS

The PCNA indices for eight (n = 8) paired large vessels (iliac, carotid, subclavian) were 7.98 (+/- 1.8)%, for the iloprost-treated experimental sites, and 14.58 (+/- 3.8)% for the saline-treated control sites. This difference was statistically significant (P = .003). One large vessel pair was not available for analysis. When the pair of renal arteries of animal 3 were included (n = 9), the PCNA indices were 8.32 (+/- 2.3)% for the experimental sites, and 13.79 (+/- 4.2)% for the control sites. The differences were again significant (P = .01).

CONCLUSION

Intraarterial site-specific delivery of iloprost during angioplasty with drug-loaded, hydrogel-coated balloons significantly suppresses medial smooth muscle cells in swine at the expected peak period of proliferation of 7 days after angioplasty.

Boundary layer drug delivery using a helical catheter

BACKGROUND

A catheter-based approach for local endovascular drug delivery has been developed. The catheter is deployed percutaneously, while the end of the catheter is in the form of a helix that is placed just proximal to the vascular site to be treated. The helices are in contact with the vessel wall. A number of small holes is drilled in the coils of the catheter through which drug is infused, so that the infused drug remains within the blood fluid 'boundary layer' adjacent to the vessel wall. This approach is expected to be highly efficient for administration of antithrombotic and antiproliferative agents that target processes leading to vascular occlusion, heart attacks, and strokes.

METHODS

The helical catheter was qualitatively evaluated using optical dye density measurements of Evans blue dye infused using an in vitro steady flow system under a physiologic range of conditions. To further demonstrate the efficiency of the technique, its capacity to inhibit thrombosis was evaluated in a baboon thrombosis model. The catheter was inserted into a femoral arteriovenous shunt (blood flow rate = 100 ml/min) and placed proximal to a segment of highly thrombogenic Dacron vascular graft (4.0 mm i.d.). Integrelin (an inhibitor of platelet glycoprotein IIb/IIIa; doses: 0.25-1.0 microg/min) and hirudin (an antithrombin; doses: 10-100 microg/min) were used to inhibit thrombus formation.

RESULTS

Experimental flow visualization studies demonstrated that high concentrations of the infused Evans blue dye were retained near the vessel wall. In the animal experiments, platelet deposition on the Dacron graft surface was reduced by 82-97% (Integrelin) and 68-92% (hirudin) over 1-2 h of blood exposure. The local antithrombotic effects produced were found to be 200-fold and 30-fold more efficient than systemic administration of the same agents.

CONCLUSIONS

Local drug infusion using the helical catheter approach can achieve high drug concentration levels at target sites, may avoid systemic effects, and can reduce cost of therapy by reducing total drug requirements.

Claudication as an 'orphan disease': rationale and goals of drug therapy for peripheral arterial disease

Patients with peripheral arterial disease are often perceived to suffer from a disorder whose pathogenesis and symptoms are not amenable to drug therapies. This clinical misperception remains prevalent despite an abundance of data suggesting that diverse pharmacotherapies may modulate the natural history of this disease. Patients with chronic limb arterial occlusive disease suffer from a disease that is characterized by: (1) a prolonged asymptomatic state that can be identified by simple physical examination and confirmed by measurement of the ankle brachial index; (2) a multi-year period of symptomatic claudication; and (3) a variable rate of progression to critical limb ischemia or acute arterial occlusion. This stage-dependent disease progression is mediated via the dynamic, but as yet incompletely understood, interaction of factors that elicit endothelial dysfunction, atherogenesis, and thrombosis. Current data suggest that each of these contributory disease processes can be modulated by extant pharmacotherapies. Additionally, many novel pharmacotherapeutic agents that are currently under investigation may further improve the ability of clinicians to modulate these fundamental biologic processes. Pharmacologic therapies should be targeted to decrease the rate of limb arterial disease progression, to improve limiting symptoms, and to prolong life. Symptoms of claudication can be objectively assessed via both exercise testing and disease-specific questionnaires. The presence of lower extremity atherosclerotic disease is predictive of the presence of coronary heart disease and a foreshortened five-year survival. Current data suggest that clinical investigations should be able to effectively stratify this relative risk via use of both clinical variables (e.g., age, diabetes mellitus, tobacco use, etc.) or by measurement of the ankle brachial index (ABI). The role of the physician is to decrease suffering and to prolong life. Judicious administration of medical therapies can play a critical role in helping the vascular practitioner accomplish these goals.

Heterogeneous smooth muscle cell population derived from small and larger arteries

Vascular lesion formations in such disease states as hypertension and atherosclerosis occur in a district-specific manner. Large conduit and small resistance arteries play district-specific roles in the regulation of organ perfusion. Using a culture method, we studied the morphology and growth of smooth muscle cells derived from small arteries (S-SMCs, less than 90 microm in internal diameter) and from larger arteries (L-SMCs, ranging from 800 to 900 microm) of the rat mesenteric arterial bed. S-SMCs showed a hill-and-valley pattern, whereas L-SMCs showed sheet or whorl formation. The majority of S-SMCs were smaller, bipolar-shaped; in contrast, the majority of L-SMCs were larger, polygonal-shaped. Actin fibers within S-SMCs were oriented in a bipolar manner from the nuclei, whereas those within L-SMCs had a radial appearance. [3H]Thymidine incorporation induced by serum, platelet-derived growth factor-AB (PDGF), or mechanical stretch was greater in S- vs L-SMCs. The population doubling time measured after the addition of serum or PDGF was shorter in S- vs L-SMCs. Thus, distinct morphological and growth phenotypes of SMCs exist in small and larger arteries of the same vascular bed.