Oxidative stress causes vascular dysfunction in the placenta

Increased production of superoxide and nitric oxide may produce oxidative stress in the placenta by formation of the prooxidant peroxynitrite, which itself causes vascular dysfunction. Nitrotyrosine residues, which are a marker of peroxynitrite formation and action, are found in placental vessels of preeclamptic and diabetic pregnancies, indicating oxidative stress. Treatment of the placental vasculature with authentic peroxynitrite in vitro attenuates responses both to vasoconstrictors such as the thromboxane mimetic U46619 and to vasodilators, including glyceryl trinitrate and prostacyclin, indicating it has caused vascular dysfunction. Further, the responses of the fetal-placental vasculature of diabetic and preeclamptic placentae to these same vasoconstrictor and vasodilator agents are significantly attenuated when compared to responses in normal control placentae. Together these data suggest there may be a cause and effect relationship between formation and action of peroxynitrite and vascular dysfunction in the placenta of both preeclamptic and diabetic pregnancies. The presence of such attenuated vascular responses indicates that perhaps the placenta may not be able to adequately respond to demands for altered blood flow in situations where this is necessary in preeclamptic or diabetic pregnancies, thus leading to further fetal compromise.

Biomechanical-stress-induced signaling and gene expression in the development of arteriosclerosis

The vascular wall is an integrated functional component of the circulatory system that is continually remodeling or develops arteriosclerosis in response to hemodynamic or biomechanical stress. How vascular cells sense and transduce the extracellular mechanical signals into the cell nucleus resulting in quantitative and qualitative changes in gene expression is an interesting and challenging question. Based on recent progress in this field, this article attempts to formulate a biomechanical-stress hypothesis-that physical force initiates signal pathways, especially mitogen-activated protein kinases (MAPKs), leading to vascular cell death and inflammatory response followed by smooth muscle cell proliferation. Thus, mechanical stress, akin to cytokines or growth factors, can effectively activate signal transduction pathways, resulting in morphological and functional changes in vascular cells, which contribute to the development of arteriosclerosis.

A pivotal role of nitric oxide in endothelial cell dysfunction

The functional role of the vascular endothelium is a subject of growing interest and appreciation. Some of the key functions of the endothelium are modulated by the activity and expression of endothelial nitric oxide synthase (eNOS), suggesting a role for this enzyme in endothelial dysfunction. Several well-known angiogenic stimulators exert their effect only in the presence of the functional eNOS. In this setting NO production is responsible for the scalar podokinetic cell motility, which is a prerequisite for the acquisition of vectorial movement when guidance cues are applied. The mode of this NO action appears to lie in the accelerated turnover of focal adhesions through the process of activation/inactivation of protein tyrosine phosphatases. Localization of eNOS to the caveolar domains, in the proximity of clustered beta1 integrins, provides an additional level of regulatory complexity through the modulation of caveolar dynamics and the state of caveolin oligomerization. Therefore, eNOS serves various important functions in the endothelium and is a putative target for therapeutic interventions.

Inhibition of NOS enhances pulmonary vascular changes in stroke-prone spontaneously hypertensive rats

To determine the effects of chronic nitric oxide (NO) blockade on the pulmonary vasculature, 58-day-old spontaneously hypertensive rats of the stroke-prone substrain (SHRSP) and Wistar-Kyoto rats (WKY) received N(omega)-nitro-L-arginine (L-NNA; 15 mg. kg(-1). day(-1) orally for 8 days). Relaxation to acetylcholine (ACh) in hilar pulmonary arteries (PAs), the ratio of right ventricular (RV) to body weight (RV/BW) to assess RV hypertrophy (RVH), and the percent medial wall thickness (WT) of resistance PAs were examined. L-NNA did not alter the PA relaxation, RV/BW, or WT in WKY. Although the PA relaxation and RV/BW in control SHRSP were comparable to those in WKY, the WT was increased (31 +/- 2 vs. 19 +/- 1%). L-NNA-treated SHRSP showed two patterns: in one group, the relaxation, RV/BW, and WT were comparable to those in the control SHRSP; in the other, impaired relaxation (36 +/- 7 vs. 88 +/- 4% for WKY) was associated with an increase in WT (37 +/- 1%) and RV/BW (0. 76 +/- 0.05). Thus the abnormal pulmonary vasculature in SHRSP at <10 wk of age is not accompanied by impaired relaxation in PAs or RVH; however, impaired relaxation is associated with increased WT and RVH.

Local activation of the complement system in endoneurial microvessels of diabetic neuropathy

Quantitative immunocytochemical analysis of complement proteins (CP) was performed on sural nerve biopsies from 15 patients with diabetic neuropathy (DN) and 18 nondiabetic patients with other forms of chronic neuropathy (ON). The mean age of the patients and the pathological severity of the neuropathy were similar in both groups. The percentage of patients that expressed strongly immunoreactive CP in the walls of endoneurial microvessels was significantly greater in DN than in ON for all proteins tested. C3d neoantigen was expressed in 100% of DN cases compared with 17% of ON; and membrane attack complex (MAC), C5b-9 neoantigen, in 93% of DN and 17% of ON. In the cases with DN, 81% of endoneurial microvessels, as identified by the endothelial marker, Ulex europaeus, contained C5b-9 neoantigen deposits, compared with 22% in those of ON, and the staining in DN was significantly more intense. Expression of the neoantigens of C3d and C5b-9 in nerve implies local activation of the complement system. In DN, activation of the complement pathway and formation of the MAC could injure blood vessels and adversely affect the circulation in the endoneurium.

Haemodynamics, wall mechanics and atheroma: a clinician's perspective

Atherosclerosis, leading to myocardial infarction and stroke, is the major cause of death and morbidity in Western societies. Atheromatous lesions characteristically occur in regions of branching and marked curvature. Low shear stress and increased mural tensile stress may be major determinants underlying atheroma formation at these sites. Furthermore, the distribution of circumferential tensile stresses may play a critical role in where, why and when advanced atheromatous plaques rupture, leading to catastrophic ischaemic events. Recent advances in the application of computational modelling to in vivo vascular ultrasound and magnetic resonance imaging data should further elucidate the roles of haemodynamic factors and vessel wall mechanics in atherosclerosis. In future this is likely to lead to better use of currently available anti-atherosclerosis strategies. It may also facilitate the discovery, evaluation and development of novel treatments.

Oxidative stress as a regulator of gene expression in the vasculature

Oxidative stress and the production of intracellular reactive oxygen species (ROS) have been implicated in the pathogenesis of a variety of diseases. In excess, ROS and their byproducts that are capable of causing oxidative damage may be cytotoxic to cells. However, it is now well established that moderate amounts of ROS play a role in signal transduction processes such as cell growth and posttranslational modification of proteins. Oxidants, antioxidants, and other determinants of the intracellular reduction-oxidation (redox) state play an important role in the regulation of gene expression. Recent insights into the etiology and pathogenesis of atherosclerosis suggest that this disease may be viewed as an inflammatory disease linked to an abnormality in oxidation-mediated signals in the vasculature. In this review, we summarize the evidence supporting the notion that oxidative stress and the production of ROS function as physiological regulators of vascular gene expression mediated via specific redox-sensitive signal transduction pathways and transcriptional regulatory networks. Elucidating, at the molecular level, the regulatory processes involved in redox-sensitive vascular gene expression represents a foundation not only for understanding the pathogenesis of atherosclerosis and other inflammatory diseases but also for the development of novel therapeutic treatment strategies.

Endothelial cell functions. Relationship to atherogenesis

The vascular endothelium plays a critical role in the preservation of normal vessel wall structure and function. In particular, endothelial cells control vascular permeability, vessel tone, coagulation, fibrinolysis, and inflammatory responses. These functions are accomplished by production of a variety of biologically active substances. However, endothelial cell-mediated reactions may also lead to the development of pathological stages within the vessel wall. The current review is focused on endothelial cell metabolism in relationship to the development of atherosclerosis.

Vascular dementia: the role of changes in the vessels

The role of changes in the vessels in vascular dementia (VaD) was reviewed through histopathology. Because Binswanger's subcortical arteriosclerotic encephalopathy is a common type of VaD, and it forms a homogenous group among the subtypes of VaD, arteriopathy in the subcortical structure was the main focus. Fibrohyalinosis and fibrinoid necrosis with segmental arterial disorganization are the two cardinal features of arteriopathy in the subcortical structures. From the viewpoint of neuropathological changes in VaD, notes were made of the areas that need to be explored in future studies and revised clinical criteria for VaD were proposed.

Experimental and numerical study of pulsatile flows through stenosis: wall shear stress analysis

Different shapes of pulsatile flows through a model of stenosis are experimentally and numerically modeled to validate both methods and to determine the wall shear stress temporal evolution downstream from the stenosis. Two-dimensional velocity measurements are performed in a 75% severity stenosis using a pulsed Doppler ultrasonic velocimeter. Finite element package is employed for the transient numerical simulations. Polynomial method, based on the experimental velocity values, is proposed to determine the wall shear stress temporal evolution. There is a good agreement between the numerical and experimental results. The wall shear stress temporal analysis shows oscillating wall shear stress values during the cycle with high wall shear stress values at the throat of about 120 dyn/cm2, and low values downstream from the stenosis of about - 2.5 dyn/cm2. The key result of the study is that the presence of the stenosis leads the artery to work in a direction which is opposite to the direction of a healthy artery.

New model of tumor angiogenesis: dynamic balance between vessel regression and growth mediated by angiopoietins and VEGF

Our analyses in several different tumor settings challenge the prevailing view that malignancies and metastases generally initiate as avascular masses that only belatedly induce vascular support. Instead, we find that malignant cells rapidly co-opt existing host vessels to form an initially well-vascularized tumor mass. Paradoxically, the co-opted vasculature does not undergo angiogenesis to support the growing tumor, but instead regresses (perhaps as part of a normal host defense mechanism) via a process that involves disruption of endothelial cell/smooth muscle cell interactions and endothelial cell apoptosis. This vessel regression in turn results in necrosis within the central part of the tumor. However, robust angiogenesis is initiated at the tumor margin, rescuing the surviving tumor and supporting further growth. The expression patterns of Angiopoietin-2 (the natural antagonist for the angiogenic Tie2 receptor) and vascular endothelial growth factor (VEGF) strongly implicate these factors in the above processes. Angiopoietin-2 is highly induced in co-opted vessels, prior to VEGF induction in the adjacent tumor cells, providing perhaps the earliest marker of tumor vasculature and apparently marking the co-opted vessels for regression. Subsequently, VEGF upregulation coincident with Angiopoietin-2 expression at the tumor periphery is associated with robust angiogenesis. Thus, in tumors, Angiopoietin-2 and VEGF seem to reprise the roles they play during vascular remodeling in normal tissues, acting to regulate the previously underappreciated balance between vascular regression and growth.

Vascular alpha 1D-adrenoceptors: are they related to hypertension?

Heterogeneity of vascular alpha 1-adrenoceptor subtypes has been revealed by pharmacological and molecular biology studies (i.e., alpha 1A-, alpha 1B-, and alpha 1D-adrenoceptors). The alpha 1D-adrenoceptor subtype is predominantly involved in the contraction of a variety of vessels and its role in the control of blood pressure has been suggested, a phenomenon probably related to aging. Recent advances in the use of young pre-hypertensive rats and adult spontaneously hypertensive rats with one kidney and Grollman-type renal hypertension suggest vascular alpha 1D-adrenoceptor involvement in the increased blood pressure. The possible role of alpha 1D-adrenoceptors in the genesis/maintenance of hypertension is discussed in this review.

Flow cytometric determination of cell proliferation in hypertensive blood vessels

BACKGROUND

Measurement of vascular cell proliferation in animal models of hypertension is currently accomplished by demonstrating [(3)H]-thymidine ([(3)H]-dT) incorporation into DNA using autoradiography. This method, however, is labor intensive, requires radioactivity, and is limited by the inherent difficulty in discriminating labeled and unlabeled cells. To address these limitations, a flow cytometric-based method is described utilizing incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA of nuclei isolated from blood vessels.

METHODS

Pulmonary hypertension was induced in rats by exposure to 10% O(2) (hypoxia) for varying periods of time. Pulmonary arteries and aorta from rats injected with BrdU prior to sacrifice were isolated, fixed with 10% formalin, and digested with Protease XIV. The intact nuclei liberated by this treatment were successively treated with HCl/Triton X-100 and sodium borate. Processed nuclei were probed with a BrdU-specific fluorescein-conjugated antibody, and the percentage of BrdU staining cells was determined using flow cytometry.

RESULTS

An approximately 20-fold increase in BrdU-positive cells at 3 days of hypoxia in pulmonary arteries (relative to control) with no change in aorta was observed. These results were similar to previous studies using [(3)H]-dT labeling.

CONCLUSIONS

Flow cytometric determination of cell proliferation in blood vessels is a simple, objective technique that may facilitate measurement of cell proliferation in animal models of vascular disease.

Vascular stress response and endothelial vasoactive factors for vascular remodelling

In response to several vascular stresses caused by hyperglycaemia, hypertension or hyperlipidemia, endothelial cells (EC) sense these stresses as oxidative stress to secrete several autocrine/paracrine factors, including growth factors/cytokines and vasoactive peptides to regulate vascular tone and remodelling. Vascular stresses induce co-ordinate gene regulation of endothelial vasoactive substances and their related enzymes to cause vasorelaxation and vascular growth inhibition. We speculate that prolonged and excessive vascular stresses impair endothelial function, which results in the imbalance of endothelial production of vasoactive substances and leads to the formation of proliferative vascular lesions.

New evidence for the spasm-of-resistance-vessel concept of ischemic diseases

The spasm of resistance vessel (S-RV) concept of ischemic diseases avers that S-RV representing vascular autoregulatory dysfunction directly induces symptoms in ischemic diseases. The most important ischemic diseases, ischemic heart disease (IHD) and stroke, generally are not attributed to S-RV, and new evidence will be provided in this communication that S-RV induces IHD and stroke. Hypertension and the ischemic disorders of migraine and Raynaud's disease have been attributed to S-RV and to vascular dysregulation, and this information was used to help structure the study. It was found that these disorders are closely associated with IHD and stroke, and this is consistent with S-RV and vascular dysregulation as the mechanism for IHD and stroke. Also, it was found that multiple risk factors for IHD foster S-RV and are risk factors for hypertension, migraine, Raynaud's disease, and stroke, and this supports S-RV as the mechanism for IHD and stroke.

Fluid shear stress as a regulator of gene expression in vascular cells: possible correlations with diabetic abnormalities

Diabetes mellitus is associated with increased frequency, severity and more rapid progression of cardiovascular diseases. Metabolic perturbations from hyperglycemia result in disturbed endothelium-dependent relaxation, activation of coagulation pathways, depressed fibrinolysis, and other abnormalities in vascular homeostasis. Atherosclerosis is localized mainly at areas of geometric irregularity at which blood vessels branch, curve and change diameter, and where blood is subjected to sudden changes in velocity and/or direction of flow. Shear stress resulting from blood flow is a well known modulator of vascular cell function. This paper presents what is currently known regarding the molecular mechanisms responsible for signal transduction and gene regulation in vascular cells exposed to shear stress. Considering the importance of the hemodynamic environment of vascular cells might be vital to increasing our understanding of diabetes.