Current Vascular Pharmacology - Volume 2, Issue 3, 2004

Hypercoagulability is widely associated with sepsis, inflammation, diabetes, cancers, aging, and many pathological conditions, resulting in life-threatening disseminated intravascular coagulation (DIC), venous thrombosis, thromboembolism, cardiovascular complications, or even deadly multiple organ failure. Relieving coagulation dysfunction is not only a task for research scientists but also a challenge for physicians. The development of effective anticoagulants is under way with the basic understanding of the pathophysiology of hypercoagulable state. In this overview, various anticoagulants will be discussed according to the proposed inhibitory target-sites along the extrinsic pathway that is believed to play an integral role in homeostasis. Anticoagulants generally fall into two broad categories as natural or pharmacological ones. Antithrombin (AT), activated protein C (APC), and tissue factor pathway inhibitor (TFPI) mainly constitute the natural anticoagulant system apart from the recently reported physiological components such as lipoproteins, sphingosine, thrombomodulin (TM) or cellular Marcks protein. Pharmacological anticoagulants include warfarin, FVIIa inhibitors, FXa inhibitors, and thrombin inhibition by its direct inhibitors or heparins. In addition, a group of novel compounds inhibiting TF-dependent FVII activation result in anticoagulation; such upstream downregulation in the extrinsic pathway awaits further research to establish their in vivo benefits. The molecular genetic approaches such as developing soluble TF, FVII and thrombin mutants provide unique downregulation. Anticoagulation also extends its significance to anti-inflammation, making broad impacts on the improvement of human health.

Oxidant stress [ OS ] is a condition in which cells are exposed to excessive levels of either molecular oxygen or chemical derivatives of oxygen called reactive oxygen species [ROS], principal amongst which is superoxide [O2 -]. It is becoming increasingly apparent that O2 - is a key risk factor for cardiovascular disease [CVD], including atherogenesis, reperfusion injury, angina, restenosis following balloon angioplasty and vein graft failure. When one considers the multiplicity of effects of O2 -, this is perhaps not surprising, as it promotes vascular smooth muscle cell proliferation, damages the endothelium, promotes lipid oxidation and activates blood cells. However, perhaps the key reaction of O2 - is that with nitric oxide [NO] to form peroxynitrite [ONOO] resulting in a depletion of endogenous vascular NO. Reduced NO formation is also now firmly associated with the aetiology of CVD and as such NO donors may become a major class of drugs. Furthermore, risk factors for CVD, in particular diabetes mellitus [DM], dyslipidaemia, and hyperhomocysteinaemia are all associated with OS. As such, it is becoming increasingly apparent that novel antioxidant therapies, including the gene transfer of antioxidant enzymes, are potentially valuable in the treatment of CVD. In this review, the aetiology of OS and CVD is discussed with particular emphasis on NO. The interactions of risk factors and how this pathophysiology relates to the design of effective novel strategies to treat CVD is also considered. Particular emphasis is also placed on OS and cardiovascular surgery.

Diabetic patients show a higher incidence of cardiac arrhythmias, including ventricular fibrillation and sudden death. However, although diabetic cardiomyopathy is a frequent and important complication of diabetes mellitus, its physiological basis is not completely known. The electrocardiogram of diabetic patients shows several alterations from normal patterns, most of them related to the QT interval and T wave. Recently, different alterations in cardiac ionic currents have been described in myocytes isolated from diabetic hearts, mainly a reduction in potassium repolarizing currents. Three different mechanisms could be involved in these alterations. First, direct metabolic alterations of the cardiac myocyte, such as impaired activity of protein kinases and phosphatases, intracellular pH regulation, intracellular calcium handling, and others. Second, impaired support of extra cardiac factors regulating cardiac activity, such as sympathetic regulation of heart rate and contractility. Thus, diabetic autonomic neuropathy leads to diminished noradrenaline release in cardiac ventricle in response to standing, exercise or cold stress. Besides, diabetic cardiomyopathy reduces cardiac myocyte response to acute noradrenaline exposure and finally, impairs support of different trophic factors responsible for the regulation of ionic channel expression. Thus, basal noradrenaline release in the ventricles, necessary to maintain adequate potassium channel expression, is reduced by sympathetic neuropathy. Moreover, the levels of insulin and other trophic factors required for the maintenance of adequate ionic channel expression are also altered in diabetic patients. Therefore, different physiopathological mechanisms are involved in diabetic cardiomyopathy. Thus, further research is needed in order to prevent the development of this long-term complication, and to improve the pharmacological management of diabetic patients.

The role of chronic inflammation in the pathogenesis of the acute coronary syndromes has received increasing attention since active plaques rich in macrophages (MfΦs) are more prone to rupture whereas plaques rich in myofibroblasts are considered to be stable. Functionally, active plaques show a locally enhanced vasoreactivity. Endothelin-1 (ET-1) a potent vasoconstrictor acts in a paracrine fashion to regulate vascular tone. ET-1 is also produced by inflammatory cells suggesting a role for ET-1 in inflammation. Additionally, ET-1 is a mitogen. Endothelin converting enzyme-1 (ECE-1) activates ET-1 and may thus contribute to the regulation of vascular tone and cell growth during atherosclerosis. We evaluated the presence of ECE-1 and big ET-1 / ET-1 and the activity of ECE-1 in different plaque types. Together with ET-1, ECE-1 is present in endothelial cells (ECs), vascular smooth muscle cells (VSMCs) and MfΦs. ECE-1 activity and ET-1-immunoreactivity (IR) both are upregulated during the progression of atherosclerosis from a non-inflammatory to an inflammatory stage. Thus, enhanced production of active ET-1 may contribute to cell growth and regulation of vascular tone in advanced plaques and also in very early stages of atherosclerosis. Furthermore, we examined the presence of ET-1 in coronary plaque tissue obtained by directional coronary atherectomy. ET-1 IR localized to plaque components indicative of chronic inflammation. Semiquantitative analysis of ET-1 IR revealed significantly higher staining grades in active coronary lesions compared with nonactive lesions. The increased ET-1 content in active coronary lesions may be beneficial to the stabilization of the vessel wall after plaque rupture and disadvantageous because it may lead to vasospasm and to the progression of atherosclerosis.

Tumor targeting therapy, that is “Missile therapy”, using a complex composed of a tumor suppressive drug and a whole antibody against tumor cells, is expected to become an attractive chemotherapy strategy. However, clinically convincing results have not yet been obtained mainly due to poor transport from the circulation to tumor tissue and marked toxicity. Recently, recombinant immunotoxins, composed of an Fv fragment of an antibody to a tumor-related antigen fused to various truncated toxins have been developed to overcome the distribution of immunotoxins in tumors. These recombinant immunotoxins have shown encouraging clinical results for some hematopoietic malignancies. However, there were no significant anti-tumor responses to many tumors, especially solid tumors, probably due to their rapid clearance from the circulation and their immunogenicity and antigenicity. More recently, PEGylation of recombinant immunotoxins has been attempted to overcome these drawbacks. It was found that PEGylation of recombinant immunotoxins improves their effectiveness. We discuss the recent progress in tumor missile therapy. In contrast to others, we developed “Missile therapy against tumor blood vessels” by using specific monoclonal antibodies against tumor endothelial cells rather than actual tumor cells. The complex between antibodies to tumor vascular endothelial cells and anti-tumor drugs can freely access the target cells without concern for their vascular permeability. These preparations have exhibited excellent anti-tumor effects for solid tumors. In this review, we also discuss this vascular targeting therapy as an attractive new strategy for tumor chemotherapy.

Gene polymorphisms of components of the renin-angiotensin system, angiotensinogen, angiotensin I-converting enzyme (ACE) and angiotensin II type 1 receptor (AT-1), have been considered to contribute to inherited predisposition towards coronary artery disease (CAD). The best analyzed is the insertion / deletion (I / D) gene polymorphism of the ACE gene. Several studies suggest that the ACE D allele is associated with the occurrence of CAD and myocardial infarction. Moreover, the I / D polymorphism of the ACE gene has been thought to be related to diverse responses to drugs. Modern gene technologies may therefore provide the information, which may help to identify disease-associated genes and determine the responsiveness to a given drug.

Vascular endothelium plays strategic roles in many drug delivery paradigms, both as an important therapeutic target itself and as a barrier for reaching tissues beyond the vascular wall. Diverse means are being developed to improve vascular drug delivery including stealth liposomes and polymer carriers. Affinity carriers including antibodies or peptides that specifically bind to endothelial surface determinants, either constitutive or pathological, enhance targeting of drugs to endothelial cells (EC) in diverse vascular areas. In many cases, binding to endothelial surface determinants facilitates internalization of the drug / carrier complex. There are several main endocytic pathways in EC, including clathrin- and caveoli-mediated endocytosis, phagocytosis and macropinocytosis (these two are less characteristic of generic EC) and the recently described Cell Adhesion Molecule (CAM)-mediated endocytosis. The latter may be of interest for intracellular drug delivery to EC involved in inflammation or thrombosis. The metabolism and effects of internalized drugs largely depend on the routes of intracellular trafficking, which may lead to degrading lysosomal compartments or other organelles, recycling to the plasma membrane or transcytosis to the basal surface of endothelium. The latter route, characteristic of caveoli-mediated endocytosis, may serve for trans-endothelial drug delivery. Paracellular trafficking, which can be enhanced under pathological conditions or by auxiliary agents, represents an alternative for transcytosis. Endothelial surface determinants involved in endocytosis, mechanisms of the latter and trafficking pathways, as well as specific characteristics of EC in different vascular areas, are discussed in detail in the context of modern paradigms of vascular drug delivery.

Diastolic heart failure (DHF) is characterized by the clinical presentation of heart failure in the setting of preserved left ventricular systolic function and evidence of diastolic dysfunction. It is estimated to be present in at least one-third of patients, who represent the signs and symptoms of heart failure, and is especially prevalent among the elderly population. Despite an increasing understanding of the pathophysiology of this disease and the improvement of diagnostic and prognostic assessment, the management of DHF remains to be established. Medical therapy consists of the cautious use of diuretics, and some studies suggested the beneficial role of beta-blockers and calcium antagonists. The rationale of current therapy is largely dependent on understanding the pathophysiology of DHF and observations from clinical trials that included relatively small numbers of patients. Large, multicenter, randomized, controlled studies are needed to define the role of various therapeutic agents in DHF, and whether the prognosis of the disease will be altered. The SWEDIC trial observed that carvedilol treatment in patients with DHF was associated with an improvement in diastolic indices measured by Doppler echocardiography. The CHARM-Preserved trial reported a non-significant reduction of cardiovascular death or admission for heart failure. Other studies which are underway include PEP-CHF and the Hong Kong Diastolic Heart Failure study. They will play a pivotal role in ascertaining the therapeutic efficacy of various agents and will help experts to set up treatment guidelines for this common condition.