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Biomedical subjects

J A Leopold

Publications and source records attributed to J A Leopold.

9 recordsLinked to original sources
PubMed2001

Catheter-based revascularization strategies for acute coronary syndromes in women.

Women with acute coronary syndromes who present for percutaneous revascularization have clinical characteristics that place them at higher risk for adverse events. These women are older with an increased incidence of hypertension, diabetes, and congestive heart failure. At angiography, women with epicardial coronary disease tend to have smaller diameter vessels, which predict an increase in procedural complications. Recent observations suggest that in the new device era, women with unstable angina/non-Q myocardial infarction may have clinical outcomes similar to their male counterparts; however, women who present with acute ST-elevation myocardial infarction and undergo catheter-based revascularization procedures remain at increased risk for adverse events. Although adjunctive glycoprotein IIb/IIIa antagonists may improve procedural outcomes, women undergoing catheter-based revascularization procedures are at increased risk for hemorrhagic complications. Despite these high-risk features, catheter-based reperfusion therapies remain an effective treatment strategy in women with acute coronary syndromes.

Aged↗
PubMed2000

Roles of endothelial dysfunction in coronary artery disease.

Endothelial dysfunction is an early and persistent vascular abnormality in the evolution of atherothrombotic disease. Risk factors for atherosclerosis promote an inflammatory oxidative environment in the vasculature that induces pathologic changes in endothelial function, including the support of enhanced smooth muscle tone, thrombosis, and smooth muscle proliferation. This article provides an overview of the molecular basis of endothelial dysfunction and of its diagnosis and treatment.

Antioxidants↗
PubMed2000

Cyclic strain modulates resistance to oxidant stress by increasing G6PDH expression in smooth muscle cells.

Vascular smooth muscle cells (VSMC) may be subjected to mechanical forces, such as cyclic strain, that promote the formation of reactive oxygen species (ROS). We hypothesized that VSMC modulate this adverse milieu by increasing the expression of glucose-6-phosphate dehydrogenase (G6PDH) to maintain or restore intracellular glutathione (GSH) levels. Cyclic strain increased superoxide formation, which resulted in diminished GSH because of an increase in oxidized glutathione formation; there was also an increase in glutathione peroxidase and glutathione reductase activities. G6PDH activity and protein expression were enhanced concomitant with decreases in GSH levels and remained elevated until intracellular GSH levels were restored. To confirm the role of G6PDH in repleting GSH stores, we inhibited G6PDH activity with DHEA or inhibited enzyme expression with an antisense oligodeoxynucleotide. Diminished G6PDH activity or expression was associated with persistently depleted GSH levels and inhibition of the cyclic strain-mediated increase in glutathione reductase activity. These observations demonstrate that cyclic strain promotes oxidant stress in VSMC, which, in turn, induces G6PDH expression. When G6PDH is inhibited, GSH levels are not restored because of impaired glutathione reductase activity. These data suggest that G6PDH is a critical determinant of the response to oxidant stress in VSMC.

Animals↗
PubMed2000

Endothelial dysfunction in a murine model of mild hyperhomocyst(e)inemia.

Homocysteine is a risk factor for the development of atherosclerosis and its thrombotic complications. We have employed an animal model to explore the hypothesis that an increase in reactive oxygen species and a subsequent loss of nitric oxide bioactivity contribute to endothelial dysfunction in mild hyperhomocysteinemia. We examined endothelial function and in vivo oxidant burden in mice heterozygous for a deletion in the cystathionine beta-synthase (CBS) gene, by studying isolated, precontracted aortic rings and mesenteric arterioles in situ. CBS(-/+) mice demonstrated impaired acetylcholine-induced aortic relaxation and a paradoxical vasoconstriction of mesenteric microvessels in response to superfusion of methacholine and bradykinin. Cyclic GMP accumulation following acetylcholine treatment was also impaired in isolated aortic segments from CBS(-/+) mice, but aortic relaxation and mesenteric arteriolar dilation in response to sodium nitroprusside were similar to wild-type. Plasma levels of 8-epi-PGF(2alpha) (8-IP) were somewhat increased in CBS(-/+) mice, but liver levels of 8-IP and phospholipid hydroperoxides, another marker of oxidative stress, were normal. Aortic tissue from CBS(-/+) mice also demonstrated greater superoxide production and greater immunostaining for 3-nitrotyrosine, particularly on the endothelial surface. Importantly, endothelial dysfunction appears early in CBS(-/+) mice in the absence of structural arterial abnormalities. Hence, mild hyperhomocysteinemia due to reduced CBS expression impairs endothelium-dependent vasodilation, likely due to impaired nitric oxide bioactivity, and increased oxidative stress apparently contributes to inactivating nitric oxide in chronic, mild hyperhomocysteinemia.

Acetylcholine↗
PubMed1997

New developments in nitrosovasodilator therapy.

Under basal conditions, nitric oxide (NO) modulates vascular tone, serves as an antithrombotic agent, and inhibits vascular smooth muscle cell proliferation. NO deficiency has been implicated in the pathophysiology of several vascular disorders, including hypertension, atherosclerosis, and restenosis, and provides a plausible biologic basis for the use of NO replacement therapy in these conditions. Treatment with conventional nitrate preparations is limited by a short therapeutic half-life, systemic absorption with potentially adverse hemodynamic effects, and drug tolerance. To overcome these limitations, novel delivery systems and novel NO donors have been developed that offer selective effects, a prolonged half-life, and a reduced incidence of tolerance.

Humans↗
PubMed1986

Short- and long-term interactions of endothelium and vascular smooth muscle in coculture: effects on cyclic GMP production.

In intact blood vessels, many vasodilators act by stimulating the release from endothelium of factor(s) that relax vascular smooth muscle and stimulate increases in cGMP. To investigate how endothelium regulates cGMP production in vascular smooth muscle, bovine aortic endothelial cells and rat aortic smooth muscle cells were cultured both separately and together in cocultures for 48 hr. Nitroprusside (1 mM) increased intracellular cGMP concentration 30-fold in smooth muscle cells (from a basal level of 103 +/- 54 fmol/mg of cell protein to 2920 +/- 1800 fmol/mg) but only 2-fold in endothelial cells (from 41 +/- 7 fmol/mg to 93 +/- 23 fmol/mg). When endothelial and smooth muscle cells were cocultured as a mixed cell population (1:1 cell ratio), both basal and nitroprusside-stimulated cGMP levels were significantly increased (550 +/- 250 and 13,240 +/- 9950 fmol/mg of total cell protein, respectively). The calcium ionophore A23187 (10 microM) caused no increase in cGMP concentration in either cell type cultured alone but produced a 6-fold increase in cocultures. Neither aspirin nor 5,8,11,14-icosatetraynoic acid influenced these results. No changes in cAMP levels were detected. Using cocultures in which one cell type was grown on microcarrier beads, we have shown that cGMP increased only in vascular smooth muscle cells and was not dependent upon the formation of junctions between endothelium and smooth muscle cells. In long-term (48-hr) mixed-cell cocultures, but not in short-term microcarrier cocultures, amplification of the nitroprusside-induced increase in cGMP was observed. These results show that responses associated with endothelium-dependent relaxation can be reconstituted in cultured endothelial and vascular smooth muscle cells and that endothelium generates a humoral factor(s) that stimulates accumulation of smooth muscle cGMP and has a longer-term effect that amplifies guanylate cyclase stimulation by nitroprusside, a drug acting directly upon smooth muscle to stimulate formation of the cyclic nucleotide. Cultured cells provide a valuable model system for the study of endothelium-vascular smooth muscle interactions.

Animals↗
PubMedDate not supplied

Clinical importance of understanding vascular biology.

A comprehensive understanding of the biology of the vessel wall has fostered the discovery of novel therapeutic interventions. The vascular endothelium, smooth muscle cells, and adventitial fibroblasts exist in a tightly regulated milieu in which extravascular stimuli produce coordinated physiologic actions in each cell type, which, in turn, modulate integrative responses in the vessel wall. When vascular injury occurs as a result of biochemical or mechanical forces, such as in hypertension, atherosclerosis, or restenosis, normal homeostatic mechanisms are perturbed, and if compensatory mechanisms are overwhelmed, the vessel becomes dysfunctional. These states are characterized by changes in regulatory molecules that stimulate aberrant responses. Recent advances in molecular biology, including gene transfer and antisense technology, have been used successfully to replete or diminish these factors and restore vascular homeostasis. We present an overview of basic vascular biology as it relates to relevant clinical vascular pathobiology and molecular therapeutics.

Coronary Artery Disease↗