Endothelial dysfunction in coronary artery disease

Cyclic stretch induces the expression of vascular endothelial growth factor in vascular smooth muscle cells

OBJECTIVE

Accumulating evidence links the release of vascular endothelial growth factor (VEGF) by vascular smooth muscle cells (VSMC) to normal endothelial cell (EC) function, repair and maintenance. Using an in vitro model we investigate the role of cyclic stretch on both the release of VEGF by VSMC and the phosphorylation of a VEGF receptor on EC.

METHODS

Bovine VSMC and EC were exposed to 10% cyclic strain for 4 hours. VEGF mRNA steady-state levels of VSMC were analysed by northern blot hybridisation. The presence of secreted VEGF from VSMC was determined by assaying the migration of EC. VEGF receptor phosphorylation on stretched EC was assayed by immunoblotting.

RESULTS

The steady-state level of VEGF mRNA in stretched VSMC increased 3.3 (+/- 0.6) fold above that of unstretched VSMC (p < 0.005). Migration of EC was stimulated 8.3 (+/- 1.1) and 14.6 (+/- 1.3) fold by media from unstretched and stretched VSMC respectively, demonstrating a 1.8 fold increase due to stretch alone (p < 0.05). Cyclic stretch resulted in phosphorylation of the VEGF receptor KDR.

CONCLUSION

Exposure of VSMC to physiological levels of stretch induces a biologically significant increase in VEGF secretion and may provide an arterial stimulus for maintenance of steady state levels of VEGF essential for EC survival.

Tissue-specific expression of human lipoprotein lipase in the vascular system affects vascular reactivity in transgenic mice

1. The role of smooth muscle-derived lipoprotein lipase (LPL) that translocates to the endothelium surface on vascular dysfunction during atherogenesis is unclear. Thus, the role of vascular LPL on blood vessel reactivity was assessed in transgenic mice that specifically express human LPL in the circulatory system. 2. Aortic free fatty acids (FFAs) were increased by 69% in the transgenic mice expressing human LPL in aortic smooth muscle cells (L2LPL) compared with their non-transgenic littermates (L2). 3. Contractility to KCl was increased by 33% in aortae of L2LPL mice. Maximal contraction to phenylephrine (PE) was comparable in L2 and L2LPL animals, while the frequency of tonus oscillation to PE increased by 104% in L2LPL mice. 4. In L2LPL animals, *NO mediated relaxation to acetylcholine (ACh) and ATP was reduced by 47 and 32%, respectively. In contrast, endothelium-independent relaxation to sodium nitroprusside (SNP) was not different in both groups tested. 5. ATP-initiated Ca(2+) elevation that triggers *NO formation was increased by 41% in single aortic endothelial cells freshly isolated from L2LPL animals. 6. In aortae from L2LPL mice an increased *O(2)(-) release occurred that was normalized by removing the endothelium and by the NAD(P)H oxidase inhibitor DPI and the PKC inhibitor GF109203X. 7. The reduced ACh-induced relaxation in L2LPL animals was normalized in the presence of SOD, indicating that the reduced relaxation is due, at least in part, to enhanced *NO scavenging by *O(2)(-). 8. These data suggest that despite normal lipoprotein levels increased LPL-mediated FFAs loading initiates vascular dysfunction via PKC-mediated activation of endothelial NAD(P)H oxidase. Thus, vascular LPL activity might represent a primary risk factor for atherosclerosis independently from cholesterol/LDL levels.

Cholesterol enrichment upregulates intercellular adhesion molecule-1 in human vascular endothelial cells

Hypercholesterolemia is a major risk factor for atherosclerosis, but the mechanism by which cholesterol activates the endothelium remains undocumented. The present investigation was undertaken to investigate the role of cholesterol, one of the bioactive moieties of the low-density lipoprotein (LDL) particle, in initiating of intracellular signaling in endothelial cells (ECs) and culminating in increased abundance of the intercellular adhesion molecule-1 (ICAM-1). Cholesterol was delivered to human umbilical vein ECs (HUVECs) via cholesterol-enriched liposomes. In HUVECs, the cellular cholesterol:phospholipid ratio increased after 1 h of exposure to cholesterol. The level of ICAM-1 increased in both mRNA and protein after 24 h of cholesterol exposure. ICAM-1 mRNA half-life was not affected by cholesterol exposure. Promoter studies showed greater than two-fold activation of the ICAM-1 gene expression after cholesterol exposure. Electrophoretic mobility shift assay showed that activator protein-1 (AP-1) activity substantially increased after 2 h of exposure to cholesterol. In contrast, cholesterol did not affect nuclear factor-kappaB (NF-kappaB) activity. Results of trans-reporting assay revealed 2.5-fold increased expression of the AP-1-dependent reporter gene after cholesterol exposure whereas NF-kappaB-dependent expression was not affected. The AP-1/Ets (-891 to -908) site, one of the three AP-1-like sites in the ICAM-1 promoter, was most responsive to cholesterol. These data demonstrate for the first time that cholesterol enrichment phenotypically modulates ECs by transcriptionally upregulating ICAM-1 expression.

Hyperglycemia inhibits endothelial nitric oxide synthase activity by posttranslational modification at the Akt site

Endothelial nitric oxide synthase (eNOS) is activated by phosphorylation of serine 1177 by the protein kinase Akt/PKB. Since hyperglycemia-induced mitochondrial superoxide overproduction increases O-linked N-acetylglucosamine modification and decreases O-linked phosphorylation of the transcription factor Sp1, the effect of hyperglycemia and the hexosamine pathway on eNOS was evaluated. In bovine aortic endothelial cells, hyperglycemia inhibited eNOS activity 67%, and treatment with glucosamine had a similar effect. Hyperglycemia-associated inhibition of eNOS was accompanied by a twofold increase in O-linked N-acetylglucosamine modification of eNOS and a reciprocal decrease in O-linked serine phosphorylation at residue 1177. Both the inhibition of eNOS and the changes in its post-translational modifications were reversed by antisense inhibition of glutamine:fructose-6-phosphate amidotransferase, the rate-limiting enzyme of the hexosamine pathway, or by blocking mitochondrial superoxide overproduction with uncoupling protein-1 (UCP-1) or manganese superoxide dismutase (MnSOD). Immunoblot analysis of cells expressing myc-tagged wild-type human eNOS confirmed the reciprocal increase in O-linked N-acetylglucosamine and decrease in O-linked serine 1177 phosphorylation in response to hyperglycemia. In contrast, when myc-tagged human eNOS carried a mutation at the Akt phosphorylation site (Ser1177), O-linked N-acetylglucosamine modification was unchanged by hyperglycemia and phospho-eNOS was undetectable. Similar changes in eNOS activity and covalent modification were found in aortae from diabetic animals. Chronic impairment of eNOS activity by this mechanism may partly explain the accelerated atherosclerosis of diabetes.

The coronary artery bypass conduit: I. Intraoperative endothelial injury and its implication on graft patency

Prevention of intraoperative injury to the vascular endothelium is of primary importance in maintaining viability and patency of the aorto-coronary saphenous vein graft. Surgical manipulation, ischemia, storage conditions, and distension before anastomosis can abnormally alter the antithrombogenic property of the endothelium leading to vasospasms, thrombogenesis, occlusive intimal hyperplasia, and stenosis. Endothelial injury can also form an initiation site for the formation of later-stage atheromas and graft failure. A multifactorial strategy aimed at prevention of endothelial injury and graft failure should include improved surgical techniques, optimal preservation conditions, avoidance of nonphysiologic distension pressures, and use of specific pharmacologic agents as the primary form of intervention. The successful application of this strategy, and the development of newer and more efficacious strategies that may impact on long-term graft patency, can now be aided by assessment of the structural and functional integrity of bypass conduits using multiphoton imaging techniques.

Hyperglycemia inhibits endothelial nitric oxide synthase activity by posttranslational modification at the Akt site

Endothelial nitric oxide synthase (eNOS) is activated by phosphorylation of serine 1177 by the protein kinase Akt/PKB. Since hyperglycemia-induced mitochondrial superoxide overproduction increases O-linked N-acetylglucosamine modification and decreases O-linked phosphorylation of the transcription factor Sp1, the effect of hyperglycemia and the hexosamine pathway on eNOS was evaluated. In bovine aortic endothelial cells, hyperglycemia inhibited eNOS activity 67%, and treatment with glucosamine had a similar effect. Hyperglycemia-associated inhibition of eNOS was accompanied by a twofold increase in O-linked N-acetylglucosamine modification of eNOS and a reciprocal decrease in O-linked serine phosphorylation at residue 1177. Both the inhibition of eNOS and the changes in its post-translational modifications were reversed by antisense inhibition of glutamine:fructose-6-phosphate amidotransferase, the rate-limiting enzyme of the hexosamine pathway, or by blocking mitochondrial superoxide overproduction with uncoupling protein-1 (UCP-1) or manganese superoxide dismutase (MnSOD). Immunoblot analysis of cells expressing myc-tagged wild-type human eNOS confirmed the reciprocal increase in O-linked N-acetylglucosamine and decrease in O-linked serine 1177 phosphorylation in response to hyperglycemia. In contrast, when myc-tagged human eNOS carried a mutation at the Akt phosphorylation site (Ser1177), O-linked N-acetylglucosamine modification was unchanged by hyperglycemia and phospho-eNOS was undetectable. Similar changes in eNOS activity and covalent modification were found in aortae from diabetic animals. Chronic impairment of eNOS activity by this mechanism may partly explain the accelerated atherosclerosis of diabetes.

Changes in coronary vessel resistance during postischemic reperfusion and effectiveness of nitroglycerin

OBJECTIVE

Microvascular incompetence after ischemia and reperfusion may compromise the normal postischemic coronary perfusion and additionally jeopardize the recovery of the myocytes. We investigated whether such a form of acute endothelial dysfunction occurs in the routine operative setting despite the use of protective measures. For this purpose, we measured pressure-flow relations in the coronary vasculature during heart operations before and after ischemia and after reperfusion and their reaction to the nitric oxide donor nitroglycerin.

METHODS

Forty-eight patients with a low risk profile scheduled for routine coronary artery bypass surgery were included. During normothermic extracorporeal circulation, the fibrillating heart was completely excluded from bypass by clamping of the ascending aorta and snaring of the caval veins. It was relieved of blood by opening the right atrium and venting the left atrium and ventricle to avoid distention. The coronary vessels were perfused under controlled flow, and the perfusion pressures were monitored. This protocol was performed in 24 patients before and immediately after ischemia and after a reperfusion period.

RESULTS

Compared with the preischemic control, vascular resistance was decreased by 17% (P <.003) immediately after ischemia but increased again by 46% (P <.0001) during an average of 25 minutes of reperfusion and, even more important, by 23% (P <.028) in comparison with the preischemic values. In two groups of 12 patients, nitroglycerin was added to the perfusate either in a dosage of 3 microg. kg. min(-1) or as a bolus injection of 2 mg. Low-dose nitroglycerin did not reduce the elevated postreperfusion resistances significantly, but bolus injection did (P <.0002). Coronary vessel resistance increased during reperfusion in particular in patients with a history of hypertension.

CONCLUSION

Coronary vasoconstriction during postischemic reperfusion is regularly present in the routine operative setting in cardiac surgery, despite myocardial protection measures. The amount of vasoconstriction varies considerably and is particularly increased in patients with hypertension. The nitric oxide donor nitroglycerin can normalize the elevated resistances, but only in high dosages. This demonstrates a preserved ability of vascular smooth muscle to relax. The phenomenon had no sequelae in our low-risk patients having elective operations. However, it may gain significance in the case of severe left heart hypertrophy and in patients at risk with both a postoperative low-output syndrome and reduced mean arterial pressures during reperfusion.

Menadione induces endothelial dysfunction mediated by oxidative stress and arylation

Our previous studies showed that menadione causes endothelial dysfunction which results in decreased relaxation and increased contraction of blood vessels. This investigation examined the role of two possible mechanisms (oxidative stress and arylation) in menadione-induced endothelial dysfunction. Menadione increased superoxide anion generation in aortic rings in a dose-dependent manner. Superoxide dismutase (SOD), reversed the inhibitory effects of menadione on vascular relaxation. The relaxation induced by the NO donor, sodium nitroprusside, was inhibited by menadione pretreatment in a dose-dependent manner. Endothelial nitric oxide synthase activity (eNOS) was suppressed by menadione. Menadione resulted in a dose-dependent reduction of cGMP levels accumulated by acetylcholine. This reduction of cGMP levels was blocked by SOD treatment, suggesting that superoxide anion generated by menadione could play a role in the inhibition of the nitric oxide pathway. Evidence supporting a possible role for arylation in impaired vascular relaxation was suggested by the observation that benzoquinone, which does not induce oxidative stress in aortic rings, inhibited acetylcholine-induced vascular relaxation to the same extent as menadione. Collectively, these results suggest that menadione can cause endothelial dysfunction in blood vessels by the inhibition of the nitric oxide pathway via superoxide anion generation and that arylation activity may also be another important mechanism.

Gene transfer of manganese superoxide dismutase reverses vascular dysfunction in the absence but not in the presence of atherosclerotic plaque

Impaired endothelium-dependent vasorelaxation (EDVR) is observed in hypercholesterolemia both in the presence and absence of morphological abnormalities and may be due to superoxide anions. Our aim was to assess the effect of gene transfer of manganese superoxide dismutase (MnSOD) to blood vessels from hypercholesterolemic animals with and without atherosclerotic plaque and to compare the effects of endothelial nitric oxide synthase (eNOS) and MnSOD over-expression on vascular dysfunction in the setting of atherosclerosis. Rabbits received a high-cholesterol diet for 10 weeks, resulting in abnormal EDVR in the absence of plaque in the carotids and the presence of plaque in the aorta. In Group 1, adenoviral vectors encoding MnSOD (AdMnSOD) or beta-galactosidase (Ad(beta)gal) were delivered to the carotid arteries in vivo. Four days later, transgene expression and vascular reactivity were assessed. In Group 2, segments of the aorta were transduced ex vivo with AdMnSOD, AdeNOS or both. Transgene expression and vascular reactivity were assessed 24 hr later. In Group 1, MnSOD expression was detected in AdMnSOD-ransduced vessels and impaired EDVR was reversed in the absence of atherosclerotic plaque. In Group 2 (with atherosclerotic plaque present), MnSOD and eNOS expression were detected by western analysis, and eNOS, but not MnSOD over-expression, improved EDVR whereas simultaneous over-expression of eNOS and MnSOD was no better than eNOS alone. Adenovirus-mediated gene transfer of MnSOD to nonatherosclerotic carotid arteries, but not atherosclerotic aorta, normalizes EDVR. eNOS gene transfer improves EDVR, even in the presence of plaque.

Coronary endothelial damage during off-pump CABG related to coronary-clamping and gas insufflation

OBJECTIVE

Although off-pump coronary artery bypass grafting (CABG) has been recognized less invasive than conventional CABG on cardiopulmonary bypass, off-pump CABG may be partly invasive especially to the coronary endothelium. The present study was designed to evaluate the adverse effects of coronary snaring with looped sutures and gas insufflation on the coronary endothelium. The protective efficacies on the coronary endothelium of coronary snaring with elastic sutures or humidified gas insufflation with/without heparin and dipyridamole-added were also tested.

METHODS

Thirty-six mongrel dogs were used. After systemic heparinization (150 U/kg), a 5 mm longitudinal coronary incision was made with looped non-elastic monofilament sutures or elastic sutures applied proximally and distally. The incised coronary artery was exposed to non-humidified carbon dioxide, humidified carbon dioxide with lactated Ringer solution, or humidified carbon dioxide with heparin and dipyridamole-added lactated Ringer solution for 10 or 20 min in each group. After gas insufflation, the incised coronary artery was repaired, then, the coronary was reperfused. Perfusion-fixation was done for observation of the coronary endothelium by scanning electron microscopy. The adverse effect on the endothelium was graded as follows: grade 1, appeared normal; grade 2, few blood cells deposited; grade 3, many blood cells deposited; grade 4, few endothelial cells delaminated with blood cells deposited; grade 5, many endothelial cells delaminated with blood cells deposited.

RESULTS

Non-elastic looping caused much more endothelial tears than elastic looping (P<0.00001). Non-humidified gas blowing for 20 min caused more endothelial cell damage than humidified gas blowing (P=0.00005). Non-humidified gas blowing for 10 min caused less damage than for 20 min (P=0.00326), but still caused more damage than humidified gas blowing (P=0.00253). Heparin and dipyridamole-added humidification reduced coronary endothelial area mottled by the deposited cells when compared with simple humidification (P=0.00120).

CONCLUSIONS

Coronary snaring resulted in coronary endothelial injury, which was ameliorated by using elastic sutures instead of non-elastic sutures. Non-humidified gas insufflation made blood cells deposited and endothelial cells delaminated with time. Humidified gas insufflation attenuated these adverse effects. Heparin and dipyridamole-added humidification had potential advantage in terms of reducing deposited blood cells on the endothelium over simple humidification.

Age-associated changes in nitric oxide metabolites nitrite and nitrate

Aging is an important determinant of vascular disease. Endothelial dysfunction accompanying vascular disease may be related to cardiovascular risk factors such as aging, hypertension, and atherosclerosis. Experimental models suggest that endothelium-derived nitric oxide is reduced with aging, and this reduction is implicated in atherogenesis. The aim of this study was to determine whether increased age resulted in altered serum nitrite and nitrate levels, end-products of nitric oxide, in healthy subjects. Sixty-nine healthy individuals were divided into five different age groups: group I (6-15 years), group II (16-30 years), group III (31-45 years), group IV (46-60 years), and group V (>61 years). In these subjects, serum nitrite was measured by the Griess reaction and nitrate by the nitrate reductase method. Statistical analysis showed that serum nitrite levels were not significantly different in any of the groups, while serum nitrate concentrations exhibited significant differences (P<0.001). These findings suggest that nitric oxide synthesis and/or secretion is reduced with age and consequently endothelium-dependent vasodilation is impaired.

Diabetes and endothelial dysfunction: a clinical perspective

The main etiology for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. A hypothesis for the initial lesion of atherosclerosis is endothelial dysfunction, defined pragmatically as changes in the concentration of the chemical messengers produced by the endothelial cell and/or by blunting of the nitric oxide-dependent vasodilatory response to acetylcholine or hyperemia. Endothelial dysfunction has been documented in patients with diabetes and in individuals with insulin resistance or at high risk for developing type 2 diabetes. Factors associated with endothelial dysfunction in diabetes include activation of protein kinase C, overexpression of growth factors and/or cytokines, and oxidative stress. Several therapeutic interventions have been tested in clinical trials aimed at improving endothelial function in patients with diabetes. Insulin sensitizers may have a beneficial effect in the short term, but the virtual absence of trials with cardiovascular end-points preclude any definitive conclusion. Two trials offer optimism that treatment with ACE inhibitors may have a positive impact on the progression of atherosclerosis. Although widely used, the effect of hypolipidemic agents on endothelial function in diabetes is not clear. The role of antioxidant therapy is controversial. No data have been published regarding the effects of hormonal replacement therapy on endothelial dysfunction in postmenopausal women with type 2 diabetes.

Rat Coronary Endothelial Cell Membrane Potential Responses During Hypertension

-The purpose of this study was to provide the first membrane potential profile in coronary endothelial cells from normotensive sham-operated control and 1-kidney, 1-clip renal hypertensive rats. Dilator responses were assessed in cannulated coronary arteries from control and 1-kidney, 1-clip rats, and the perforated patch-clamp method was used to compare membrane potential responses between the intact endothelial cells. Under these conditions, acetylcholine (100 pmol/L to 10 µmol/L) induced similar large dilations of coronary arteries from control and 1-kidney, 1-clip rats that were associated with endothelial cell hyperpolarizing responses of 16+/-3 and 18+/-2 mV, respectively. Substance P (10 fmol/L to 1 nmol/L) and bradykinin (100 fmol/L to 10 nmol/L) also substantially dilated coronary arteries from control rats but only induced small (2 to 4 mV) endothelial cell hyperpolarizing responses. These dilations, which appeared independent of membrane potential changes, were highly blunted or absent in arteries from 1-kidney, 1-clip rats. Thus, dilator responses to acetylcholine that are associated with large endothelial hyperpolarizing responses are normal in the small coronary arteries of 1-kidney, 1-clip rats. However, dilator response to substance P and bradykinin, which apparently are not heavily dependent on endothelial cell hyperpolarizations, are selectively targeted for impairment in the coronary arteries of this model of hypertension

Hepatocyte growth factor is upregulated by low-density lipoproteins and inhibits endothelin-1 release

Low-density lipoproteins (LDL) are known to cause endothelial injury and to promote the development of atherosclerotic lesions. This study demonstrates a significant concentration-dependent stimulatory effect of LDL on hepatocyte growth factor (HGF) synthesis (maximum release: 423 +/- 16% of control) and HGF receptor mRNA expression in cultured human coronary artery endothelial cells (HCAEC). HGF is a potent mitogen for endothelial cells but does not affect smooth muscle cell proliferation. In contrast, endothelin-1 (ET-1) acts as a mitogen on vascular smooth muscle cells and seems to be upregulated in coronary atherosclerosis. In this study, the basal ET-1 synthesis in HCAEC was concentration-dependently reduced by HGF (minimum: 54 +/- 3% of control). This inhibitory effect seems to be mediated via the tyrosine kinase activity of the HGF receptor c-met, since it was antagonized by the tyrosine kinase inhibitor lavendustin A. In addition, HGF also significantly reduced the LDL-stimulated ET-1 release. The LDL-induced upregulation of HGF synthesis in HCAEC and the inhibitory effect of HGF on ET-1 synthesis suggest a protective role of HGF in coronary atherosclerosis.

Regular aerobic exercise prevents and restores age-related declines in endothelium-dependent vasodilation in healthy men

BACKGROUND

In sedentary humans endothelium-dependent vasodilation is impaired with advancing age contributing to their increased cardiovascular risk, whereas endurance-trained adults demonstrate lower age-related risk. We determined the influence of regular aerobic exercise on the age-related decline in endothelium-dependent vasodilation.

METHODS AND RESULTS

In a cross-sectional study, 68 healthy men 22 to 35 or 50 to 76 years of age who were either sedentary or endurance exercise-trained were studied. Forearm blood flow (FBF) responses to intra-arterial infusions of acetylcholine and sodium nitroprusside were measured by strain-gauge plethysmography. Among the sedentary men, the maximum FBF response to acetylcholine was 25% lower in the middle aged and older compared with the young group (P:<0.01). In contrast, there was no age-related difference in the vasodilatory response to acetylcholine among the endurance-trained men. FBF at the highest acetylcholine dose was almost identical in the middle aged and older (17.3+/-1.3 mL/100 mL tissue per minute) and young (17.7+/-1.4 mL/100 mL tissue per minute) endurance-trained groups. There were no differences in the FBF responses to sodium nitroprusside among the sedentary and endurance- trained groups. In an exercise intervention study, 13 previously sedentary middle aged and older healthy men completed a 3-month, home-based aerobic exercise intervention (primarily walking). After the exercise intervention, acetylcholine-mediated vasodilation increased approximately 30% (P:<0.01) to levels similar to those in young adults and middle aged and older endurance-trained men.

CONCLUSIONS

Our results indicate that regular aerobic exercise can prevent the age-associated loss in endothelium-dependent vasodilation and restore levels in previously sedentary middle aged and older healthy men. This may represent an important mechanism by which regular aerobic exercise lowers the risk of cardiovascular disease in this population.

Evidence of the participation of peribiliary mast cells in regulation of the peribiliary vascular plexus along the intrahepatic biliary tree

Our pilot study disclosed that tryptase-positive mast cells (MC) were densely distributed around the intrahepatic bile ducts (peribiliary MC). In this study, the pathophysiologic roles of these MC were examined with respect to the microcirculation around the bile duct in 71 cases of histologically normal liver, 24 cases of chronic hepatitis, and 45 cases of liver cirrhosis. The tryptase-positive MC were very close to the microvessels of the peribiliary vascular plexus (PVP), which supply the intrahepatic biliary tree. The tryptase-positive MC were frequently found adjacent to vascular smooth muscle cells, including pericytes. The location of the tryptase-positive MC was confirmed by ultrastructural analysis. In cirrhosis, the numbers of both microvessels of PVP and peribiliary MC increased in parallel. Peribiliary MC were immunoreactive for endothelin 1 (ET-1), and were variably immunoreactive for histamine, chymase, inducible nitric oxide synthase (iNOS), and endothelin A and B (ET(A) and ET(B)) receptors, particularly in cirrhotic livers. On vascular endothelial cells of PVP, endothelial nitric oxide synthase (eNOS) and ET-1 were consistently detectable, and ET(A) receptors, ET(B) receptors, and iNOS were variably detectable. Pericytes of PVP expressed ET(A) and ET(B) receptors in addition to ET-1 and iNOS. Biliary epithelial cells also focally expressed iNOS, ET-1, and ET(A) and ET(B) receptors. These vasoactive substances were strongly expressed on the cellular components in cirrhotic liver. By in situ hybridization, iNOS mRNA signals were observed on iNOS-immunoreactive cell components, including peribiliary MC. These morphologic and immunohistochemical findings suggest that the cellular components displaying vasoactive substances in the milieu of the intrahepatic biliary tree are very dynamic in the vasoregulation of PVP in normal livers, even more so in cirrhosis, and that peribiliary MC exert local effects on the microcirculation of PVP, directly and indirectly.

The endothelium: a new target for therapy

At one time considered merely a monolayer of cells lining the vascular conduit, the endothelium has emerged recently as an organ with functions as complex as any in the body. A highly active regulatory organ, the endothelium senses and assesses the hemodynamic, humoral, and inflammatory signals to which it is constantly exposed by the blood and responds by secreting factors that affect vessel tone and structure. These interactions are not merely of academic interest. It has been increasingly recognized that endothelial dysfunction plays a pivotal role in the development and progression of atherosclerosis and coronary artery disease.

Transplantation of ex vivo expanded endothelial progenitor cells for therapeutic neovascularization

Animal studies and preliminary results in humans suggest that lower extremity and myocardial ischemia can be attenuated by treatment with angiogenic cytokines. The resident population of endothelial cells that is competent to respond to an available level of angiogenic growth factors, however, may potentially limit the extent to which cytokine supplementation enhances tissue neovascularization. Accordingly, we transplanted human endothelial progenitor cells (hEPCs) to athymic nude mice with hindlimb ischemia. Blood flow recovery and capillary density in the ischemic hindlimb were markedly improved, and the rate of limb loss was significantly reduced. Ex vivo expanded hEPCs may thus have utility as a "supply-side" strategy for therapeutic neovascularization.

In vivo gene transfer of endothelial nitric oxide synthase to carotid arteries from hypercholesterolemic rabbits enhances endothelium-dependent relaxations

BACKGROUND AND PURPOSE

Hypercholesterolemia is associated with abnormal endothelium-dependent vasorelaxation due to decreased nitric oxide bioavailability. Our aim was to examine the effect of adenovirus-mediated gene transfer of endothelial nitric oxide synthase (eNOS) to the hypercholesterolemic rabbit carotid artery in vivo. In addition, we examined whether adenovirus-mediated gene transfer was associated with vascular dysfunction.

METHODS

Rabbits were fed a 1% cholesterol diet for 4 weeks followed by a 0.5% cholesterol diet for 6 weeks. Vascular reactivity was assessed in nontransduced carotid arteries from chow- and cholesterol-fed animals. In addition, carotid arteries were surgically isolated, and 2 separate doses of adenoviral vectors encoding eNOS or beta-galactosidase (AdbetaGal) on the contralateral side were delivered to the lumen (1x10(10) and 5x10(10) pfu/mL).

RESULTS

Abnormal acetylcholine-mediated endothelium-dependent vasorelaxation was detected in the carotid artery from cholesterol-fed animals, whereas responses to calcium ionophore A23187 and diethylamine NONOate were normal. Vascular reactivity was similar in nontransduced and AdbetaGal-transduced hypercholesterolemic vessels. In vessels transduced with eNOS, transgene expression was demonstrated by immunostaining in both the endothelium and the adventitia and by Western blot analysis. High-dose but not low-dose eNOS gene transfer enhanced endothelium-dependent relaxation in vessels from cholesterol-fed rabbits.

CONCLUSIONS

Adenovirus-mediated gene transfer of eNOS to carotid arteries of cholesterol-fed animals improves endothelium-dependent relaxation when an optimal viral titer is administered.

Transplantation of ex vivo expanded endothelial progenitor cells for therapeutic neovascularization

Animal studies and preliminary results in humans suggest that lower extremity and myocardial ischemia can be attenuated by treatment with angiogenic cytokines. The resident population of endothelial cells that is competent to respond to an available level of angiogenic growth factors, however, may potentially limit the extent to which cytokine supplementation enhances tissue neovascularization. Accordingly, we transplanted human endothelial progenitor cells (hEPCs) to athymic nude mice with hindlimb ischemia. Blood flow recovery and capillary density in the ischemic hindlimb were markedly improved, and the rate of limb loss was significantly reduced. Ex vivo expanded hEPCs may thus have utility as a "supply-side" strategy for therapeutic neovascularization.

High CA repeat numbers in intron 13 of the endothelial nitric oxide synthase gene and increased risk of coronary artery disease

Endothelial nitric oxide synthase (eNOS) plays a key role in vascular homeostasis. Because its product, nitric oxide, possesses vasodilatory and antiatherogenic properties, an altered eNOS function might promote atherosclerosis. We investigated the association between variations in CA repeat copy number [(CA), polymorphism] in intron 13 of the eNOS gene and the risk of coronary artery disease. (CA), polymorphism was investigated in 1000 consecutive patients with angiographically confirmed coronary artery disease and 1000 age- and gender-matched control subjects by a PCR-based fragment length calculation. Twenty-eight different alleles were identified containing 17-44 CA repeats. The presence of one allele containing > or = 38 repeats was associated with an excess risk of coronary artery disease (odds ratio 1.94, 95% confidence interval 1.31-2.86, P = 0.001). Carriers of alleles containing > or = 38 CA repeats were, in particular, overrepresented in the subgroup without common cardiovascular risk factors (odds ratio 3.39, 95% confidence interval 1.30-8.86, P = 0.009). Logistic regression analysis revealed that the (CA), polymorphism proved to be an independent risk factor (relative risk 2.17, 95% confidence interval 1.44-3.27, P = 0.0002). Our findings indicate that high numbers of CA repeats in intron 13 of the eNOS gene are associated with an excess risk of coronary artery disease.

Nitric oxide in the pathogenesis of vascular disease

Nitric oxide (NO) is synthesized by at least three distinct isoforms of NO synthase (NOS). Their substrate and cofactor requirements are very similar. All three isoforms have some implications, physiological or pathophysiological, in the cardiovascular system. The endothelial NOS III is physiologically important for vascular homeostasis, keeping the vasculature dilated, protecting the intima from platelet aggregates and leukocyte adhesion, and preventing smooth muscle proliferation. Central and peripheral neuronal NOS I may also contribute to blood pressure regulation. Vascular disease associated with hypercholesterolaemia, diabetes, and hypertension is characterized by endothelial dysfunction and reduced endothelium-mediated vasodilation. Oxidative stress and the inactivation of NO by superoxide anions play an important role in these disease states. Supplementation of the NOS substrate L-arginine can improve endothelial dysfunction in animals and man. Also, the addition of the NOS cofactor (6R)-5,6,7, 8-tetrahydrobiopterin improves endothelium-mediated vasodilation in certain disease states. In cerebrovascular stroke, neuronal NOS I and cytokine-inducible NOS II play a key role in neurodegeneration, whereas endothelial NOS III is important for maintaining cerebral blood flow and preventing neuronal injury. In sepsis, NOS II is induced in the vascular wall by bacterial endotoxin and/or cytokines. NOS II produces large amounts of NO, which is an important mediator of endotoxin-induced arteriolar vasodilatation, hypotension, and shock.

SERCA pump isoform expression in endothelium of veins and arteries: every endothelium is not the same

Endothelium from rat aorta expresses sarco/endoplasmic reticulum Ca2+(SERCA) pump gene SERCA3 where as the smooth muscle expresses SERCA2. This has led to the postulate that vascular endothelium expresses SERCA3. To test this postulate, we examined the SERCA2 and SERCA3 mRNA expression in endothelium and smooth muscle dissected from coronary artery, coronary vein, aorta and vena cava of pig. Smooth muscle from all arteries and veins expressed only the SERCA2 mRNA. Endothelium from coronary artery, coronary vein and aorta expressed both SERCA2 and SERCA3 mRNA but the endothelium from vena cava did not express SERCA3 mRNA although it expressed SERCA2. These observations support the postulate that vascular endothelium expresses SERCA3 but the affirmation is equivocal because vena cava endothelium does not express SERCA3.

Low-density lipoprotein-independent effects of statins

Statins have pleiotropic properties that complement their cholesterol-lowering effects. These properties may partly account for their established benefit in the prevention of coronary artery disease beyond the reduction of LDL-cholesterol levels. The most widely recognized properties are reviewed here. They include: (i) nitric oxide-mediated improvement of endothelial dysfunction and upregulation of endothelin-1 expression; (ii) antioxidant effects; (iii) anti-inflammatory properties; (iv) inhibition of cell proliferation with anticarcinogenic actions in animals; (v) stabilization of atherosclerotic plaques; (vi) anticoagulant effects; and (vii) inhibition of graft rejection after heart and kidney transplantation. As advances are made in our knowledge, new properties are steadily being uncovered. Pleiotropic effects are currently being given consideration when instituting combination therapy for patients at high cardiovascular risk. Some pleiotropic effects are negative, and may account for occasional untoward drug interactions. For many of these new properties, the clinical relevance has not been established. The challenge for the future will be to design and carry out appropriate clinical trials to establish their relative importance in the prevention of coronary artery disease.

Menadione-induced vascular endothelial dysfunction and its possible significance

Although several studies have shown that treatment with menadione leads to endothelial cell cytotoxicity, investigations of menadione's effects on blood vessels are limited. Our previous studies have shown that menadione can indirectly induce alterations in vasomotor tone through platelet cytotoxicity. To determine if menadione affects vascular function, we investigated the effect of menadione on blood vessels using the isolated rat aortic rings in vitro organ bath system. Treatment with menadione directly resulted in contraction of aortic rings with endothelium but did not cause any effect on aortic rings without endothelium. Menadione irreversibly inhibited the acetylcholine- and histamine-induced relaxation of aortic rings with endothelium in a time- and concentration-dependent manner. Menadione treatment potentiated phenylephrine- and serotonin-induced vasoconstriction in aortic rings with endothelium. These in vitro results were observed at concentrations of menadione that are highly relevant to human therapeutics with menadione. When menadione was administrated intravenously to rats, blood pressure increased significantly in a concentration-dependent manner. Furthermore, menadione infusion suppressed the blood pressure reduction induced by acetylcholine. By demonstrating that menadione caused in vitro endothelial dysfunction (i.e., decreased relaxation and increased vasoconstriction in the organ bath experiments) and confirming that these results were consistent with in vivo observations, we have provided evidence suggesting that a quinone such as menadione can alter vasomotor tone through endothelial dysfunction. Such dysfunction could possibly contribute to vascular diseases.

Mechanisms of MAPK activation by bradykinin in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is a prominent feature of the atherosclerotic process occurring after endothelial injury. A vascular wall kallikrein-kinin system has been described. The contribution of this system to vascular disease is undefined. In the present study we characterized the signal transduction pathway leading to mitogen-activated protein kinase (MAPK) activation in response to bradykinin (BK) in VSMC. Addition of 10(-10)-10(-7) M BK to VSMC resulted in a rapid and concentration-dependent increase in tyrosine phosphorylation of several 144- to 40-kDa proteins. This effect of BK was abolished by the B(2)-kinin receptor antagonist HOE-140, but not by the B(1)-kinin receptor antagonist des-Arg(9)-Leu(8)-BK. Immunoprecipitation with anti-phosphotyrosine antibodies followed by immunoblot revealed that 10(-9) M BK induced tyrosine phosphorylation of focal adhesion kinase (p125(FAK)). BK (10(-8) M) promoted the association of p60(src) with the adapter protein growth factor receptor binding protein-2 and also induced a significant increase in MAPK activity. Pertussis and cholera toxins did not inhibit BK-induced MAPK tyrosine phosphorylation. Protein kinase C downregulation by phorbol 12-myristate 13-acetate and/or inhibitors to protein kinase C, p60(src) kinase, and MAPK kinase inhibited BK-induced MAPK tyrosine phosphorylation. These findings provide evidence that activation of the B(2)-kinin receptor in VSMC leads to generation of multiple second messengers that converge to activate MAPK. The activation of this crucial kinase by BK provides a strong rationale to investigate the mitogenic actions of BK on VSMC proliferation in disease states of vascular injury.

Effects of peroxide on contractility of coronary artery rings of different sizes

Reactive oxygen species (ROS, free radicals) produced during cardiac ischemia and reperfusion can damage the contractile functions of arteries. The sarcoplasmic reticulum (SR) Ca2+ pump in coronary artery smooth muscle is very sensitive to ROS. Here we show that contractions of de-endothelialized rings from porcine left coronary artery produced by the hormone Angiotensin II and by the SR Ca2+ pump inhibitors cyclopiazonic acid and thapsigargin correlate negatively with the tissue weight. In contrast, the contractions due to membrane depolarization by high KCl correlate positively. Peroxide also produces a small contraction which correlates negatively with the tissue weight. When artery rings are treated with peroxide and washed, their ability to contract with Angiotensin II, cyclopiazonic acid and thapsigargin decreases. Thus, the SR Ca2+ pump may play a more important role in the contractility of the smaller segments of the coronary artery than in the larger segments. These results are consistent with the hypothesis that ROS which damage the SR Ca2+ pump affect the contractile function of the distal segments more adversely than of the proximal segments.

Vasospasm, vascular injury, and atherogenesis: a perspective

It is generally believed that injury of the vessel wall is an important condition for the development of atherosclerosis. The nature of this injury and its relationship to lesion origin, however, are not clearly understood. Based on early work by the author and a selective review of the literature, evidence is presented to show how a common cardiovascular event, vasospasm, may be one of the factors responsible for this tissue damage, because it produces a substantial arteriopathy in the very vessel in which it occurs.

Endothelin ETA receptor blockade restores NO-mediated endothelial function and inhibits atherosclerosis in apolipoprotein E-deficient mice

This study investigated whether endothelin-1 (ET-1), a potent vasoconstrictor, which also stimulates cell proliferation, contributes to endothelial dysfunction and atherosclerosis. Apolipoprotein E (apoE)-deficient mice and C57BL/6 control mice were treated with a Western-type diet to accelerate atherosclerosis with or without ETA receptor antagonist LU135252 (50 mg/kg/d) for 30 wk. Systolic blood pressure, plasma lipid profile, and plasma nitrate levels were determined. In the aorta, NO-mediated endothelium-dependent relaxation, atheroma formation, ET receptor-binding capacity, and vascular ET-1 protein content were assessed. In apoE-deficient but not C57BL/6 mice, severe atherosclerosis developed within 30 wk. Aortic ET-1 protein content (P < 0.0001) and binding capacity for ETA receptors was increased as compared with C57BL/6 mice. In contrast, NO-mediated, endothelium-dependent relaxation to acetylcholine (56 +/- 3 vs. 99 +/- 2%, P < 0.0001) and plasma nitrate were reduced (57.9 +/- 4 vs. 93 +/- 10 micromol/liter, P < 0.01). Treatment with the ETA receptor antagonist LU135252 for 30 wk had no effect on the lipid profile or systolic blood pressure in apoE-deficient mice, but increased NO-mediated endothelium-dependent relaxation (from 56 +/- 3 to 93 +/- 2%, P < 0.0001 vs. untreated) as well as circulating nitrate levels (from 57.9 +/- 4 to 80 +/- 8.3 micromol/liter, P < 0.05). Chronic ETA receptor blockade reduced elevated tissue ET-1 levels comparable with those found in C57BL/6 mice and inhibited atherosclerosis in the aorta by 31% without affecting plaque morphology or ET receptor-binding capacity. Thus, chronic ETA receptor blockade normalizes NO-mediated endothelial dysfunction and reduces atheroma formation independent of plasma cholesterol and blood pressure in a mouse model of human atherosclerosis. ETA receptor blockade may have therapeutic potential in patients with atherosclerosis.

In vivo gene transfer of nitric oxide synthase enhances vasomotor function in carotid arteries from normal and cholesterol-Fed rabbits

BACKGROUND

The vascular endothelium is anatomically intact but functionally abnormal in preatherosclerotic states, and an early deficit in the bioavailability of nitric oxide (NO) or related molecules has been described in both humans and animal models. We hypothesized that the targeted gene transfer of NO synthase (NOS) isoforms might ameliorate or reverse the deficit.

METHODS AND RESULTS

We constructed a recombinant adenovirus, Ad.nNOS, that expresses the neuronal isoform of NOS (nNOS) and used it for in vivo endovascular gene transfer to carotid arteries (CA) from normal and cholesterol-fed rabbits. Vessels were harvested 3 days after gene transfer. In CA from normal rabbits, Ad.nNOS generated high levels of functional nNOS protein predominantly in endothelial cells and increased vascular NOS activity by 3.4-fold relative to sham-infected control CA. Ad.nNOS gene transfer also significantly enhanced endothelium-dependent vascular relaxation to acetylcholine; at 3 micromol/L acetylcholine, Ad.nNOS-treated arteries showed an 86+/-4% reduction in precontracted tension, whereas control CA showed a 47+/-6% reduction in tension. Contraction in response to phenylephrine and relaxation in response to nitroprusside were unaffected in both control and Ad.nNOS-treated CA. To determine the effect of Ad.nNOS in atherosclerotic arteries, 10 male New Zealand White rabbits maintained on a 1% cholesterol diet for 10 to 12 weeks underwent gene transfer according to the same protocol used in normal rabbits. Ad.nNOS-treated arteries showed a 2-fold increase in NADPH-diaphorase staining intensity relative to sham-infected and Ad. betaGal-treated arteries. The CA from cholesterol-fed rabbits showed impaired acetylcholine-induced relaxation, but this abnormality was almost entirely corrected by Ad.nNOS gene transfer.

CONCLUSIONS

In vivo adenovirus-mediated endovascular delivery of nNOS markedly enhances vascular NOS activity and can favorably influence endothelial physiology in the intact and atherosclerotic vessel wall.

Endothelial response to cardiopulmonary bypass surgery

BACKGROUND

The vascular endothelium has been shown to actively participate in maintaining normal cardiovascular homeostasis by influencing the regulation of membrane permeability, lipid transport, vasomotor tone, coagulation, fibrinolysis, and inflammation. Endothelial cells are very responsive to a wide range of local and systemic stimuli that occur during cardiopulmonary bypass (CPB) operation. Major pathologic conditions result from impaired vascular function secondary to CPB, including vasospasm, coagulopathy, and widespread neutrophil adhesion secondary to a systemic inflammatory response. Additionally, more chronic responses to endothelial cell injury include the development of intimal hyperplasia and arteriosclerosis, both of which limit the long-term success of coronary artery bypass grafting.

METHODS

Because of the increasingly recognized role of the endothelium in the maintenance of normal cardiovascular function, this article will review the normal structure and function of the endothelium, as well as the major pathologic conditions that result in response to CPB.

RESULTS

Potential treatments to counteract endothelial cell dysfunction secondary to CPB are under active investigation. Strategies may be directed toward blocking single cytokines, integrins, or adhesion molecules involved in endothelial dysfunction or, alternatively, toward targeting a molecular event that governs the expression of these proinflammatory, procoagulant, and vasoactive genes. In our laboratory, we have used both strategies to study the pathologic response to CPB. We blocked neutrophil adhesion in subhuman primates with a monoclonal antibody. Alternatively, we targeted the transcriptional activation of multiple genes involved in the endothelial cell's response to CPB.

CONCLUSIONS

Although both therapies help elucidate the multiple, redundant pathways involved in the pathologic response to CPB, it is through molecular biology that we are beginning to understand the mechanics of transcriptional control and translational expression that occurs in the endothelial cell in response to CPB. This knowledge will allow the development of therapies that inhibit not a single cytokine or adhesion molecule, but rather an array of substances that result in the endothelial cell's pathologic response to CPB.

High-flow gas insufflation to facilitate MIDCABG: effects on coronary endothelium

BACKGROUND

During less invasive coronary bypass operations on the beating heart, as well as conventional operations using continuous warm cardioplegia, a precise anastomosis is facilitated by a bloodless field. To maintain a clear field, many surgeons use high-flow gas insufflation. However, the potentially damaging effects of gas insufflation on coronary endothelium have not been elucidated.

METHODS

Seven pigs underwent median sternotomy. Between two coronary occluders, an arteriotomy in the mid left anterior descending coronary artery (LAD) was performed. In the experimental group (n = 5), the operative field was kept clear by exposing the arteriotomy to a catheter-directed stream of carbon dioxide at 15 L/min. In the control group (n = 2), the arteriotomy was left open to room air. After 20 minutes, the segments of LAD exposed to carbon dioxide or room air, and the unexposed proximal LAD and right coronary artery, were processed, sectioned, and stained together. A murine anti-human tie-2 monoclonal antibody was used to identify endothelium.

RESULTS

All unexposed LAD and right coronary artery segments and all LAD segments exposed only to room air demonstrated normal, contiguous staining of endothelium with the murine anti-human tie-2 monoclonal antibody. In contrast, all LAD segments exposed to high-flow carbon dioxide gas insufflation demonstrated near-complete loss of endothelium.

CONCLUSIONS

These data demonstrate that high-flow carbon dioxide gas insufflation denudes the coronary artery of its endothelium. This exposes blood elements to the subendothelium and promotes clotting, and endothelial loss may promote smooth muscle cell migration and proliferation. These events set the stage for early and late graft failure.

Control of risk factors in peripheral vascular disease. Management of hypertension

Hypertension is a highly prevalent disorder and a potent factor in promoting atherosclerosis. Identifying and controlling high blood pressure are major goals in caring for the vascular patient. A focused history and physical examination and selected laboratory studies will identify potential underlying (and remediable) causes of hypertension, target organ effects, and other risk factors for vascular disorders. Lifestyle changes and pharmacologic therapy tailored for this patient population are discussed, along with the importance of considering whether renovascular hypertension is present.

Effects of peroxide on endothelial nitric oxide synthase in coronary arteries

Reactive oxygen species (ROS) are produced in ischemia and reperfusion. Since endothelial nitric oxide synthase (eNOS) is key to the endothelium-dependent vasodilation, we examined the effects of peroxide on this enzyme. We treated cells cultured from pig coronary artery endothelium with different concentrations of hydrogen peroxide, washed them, solubilized them and measured NOS activity by arginine to citrulline conversion. Hydrogen peroxide inhibited the eNOS activity with an IC50 value of 0.85 +/- 0.39 mM. In another experiment, we perfused arteries with solutions containing 0 or 1 mM hydrogen peroxide, washed them, removed the endothelium using a cotton swab, centrifuged and solubilized the endothelium and monitored its NOS activity. Hydrogen peroxide (1 mM) did not affect the NOS activity significantly (p > 0.05) in this assay. We conclude that the inactivation of eNOS by hydrogen peroxide does not play a major role in the ischemia-reperfusion damage because the peroxide concentrations attained during ischemia-perfusion are much lower than those affecting the eNOS activity.

Characterization of the stress-inducing effects of homocysteine

The mechanism by which homocysteine causes endothelial cell (EC) injury and/or dysfunction is not fully understood. To examine the stress-inducing effects of homocysteine on ECs, mRNA differential display and cDNA microarrays were used to evaluate changes in gene expression in cultured human umbilical-vein endothelial cells (HUVEC) exposed to homocysteine. Here we show that homocysteine increases the expression of GRP78 and GADD153, stress-response genes induced by agents or conditions that adversely affect the function of the endoplasmic reticulum (ER). Induction of GRP78 was specific for homocysteine because other thiol-containing amino acids, heat shock or H2O2 did not appreciably increase GRP78 mRNA levels. Homocysteine failed to elicit an oxidative stress response in HUVEC because it had no effect on the expression of heat shock proteins (HSPs) including HSP70, nor did it activate heat shock transcription factor 1. Furthermore homocysteine blocked the H2O2-induced expression of HSP70. In support of our findings in vitro, steady-state mRNA levels of GRP78, but not HSP70, were elevated in the livers of cystathionine beta-synthase-deficient mice with hyperhomocysteinaemia. These studies indicate that the activation of stress response genes by homocysteine involves reductive stress leading to altered ER function and is in contrast with that of most other EC perturbants. The observation that homocysteine also decreases the expression of the antioxidant enzymes glutathione peroxidase and natural killer-enhancing factor B suggests that homocysteine could potentially enhance the cytotoxic effect of agents or conditions known to cause oxidative stress.

LDL induces transcription factor activator protein-1 in human endothelial cells

Low density lipoprotein (LDL) has been shown to perturb endothelial cells, with manifestations ranging from alterations in free radicals and arachidonate metabolism to stress fiber formation and monocyte recruitment. Some of these changes are regulated by LDL at the transcriptional level. Using mobility shift assays with consensus sequences for various transcription factors, we have detected an increase in activator protein 1 (AP-1), but not nuclear factor-kappaB (NF-kappaB), binding in human umbilical vein endothelial cells exposed to LDL. Following transfection, AP-1-driven chloramphenicol acetyltransferase and AP-1-driven-luciferase are upregulated by LDL. In contrast, there is no effect on NF-kappaB-driven chloramphenicol acetyltransferase. AP-1 increases in a biphasic fashion, with the first peak occurring 6 hours after and the second 48 hours after exposure to LDL. This AP-1 binding increase involves c-Jun, but not c-Fos, as shown by gel supershift, Northern hybridization, and Western blotting analyses. c-Jun mRNA levels are elevated by 9 hours after and remain so until at least 24 hours after exposure to LDL. c-Jun protein levels increase at 12 hours and continue to rise for 24 hours after exposure to LDL. Moreover, this LDL-increased AP-1 binding is suppressed by several protein kinase (PK) inhibitors: the PKC inhibitor calphostin C, the cAMP-dependent PK inhibitor H89, and the tyrosine PK inhibitors genistein and lavendustin A. This study demonstrates that (1) LDL is an endothelial agonist distinct from other cell stimulators, such as cytokines, endotoxin, and phorbol 12-myristate 13-acetate, because LDL appears to activate human umbilical vein endothelial cells predominantly through the transcription factor AP-1 and not NF-kappaB; and (2) LDL increases AP-1 via mechanisms involving multiple kinase activities and c-Jun transcription.

Effects of peroxide on the fluorescence of the Ca2+ probe Fluo 3 and the pH probe BCECF

Fluorescence probes are invaluable tools in monitoring intracellular ion concentrations. They have also been used for studying how reactive oxygen species alter these concentrations and yet there are no studies indicating how reactive oxygen species directly affect the characteristics of the probes. Our concern was that if reactive oxygen were to affect characteristics of these probes, these measurements would be inconsequential. Therefore, we examined the effects of peroxide on the Ca2+-sensitive dye Fluo 3 and the pH sensitive dye BCECF. Peroxide concentrations below 10 mM did not alter fluorescence or binding characteristics of either dye. Since the concentrations of peroxide used in most pathophysiological experiments are in the micromolar range, we conclude that these probes are appropriate for monitoring the effects of peroxide on intracellular ion concentrations.

Peroxide resistance of ER Ca2+ pump in endothelium: implications to coronary artery function

We examined the effects of peroxide on the sarco(endo)plasmic reticulum Ca2+ (SERCA) pump in pig coronary artery endothelium and smooth muscle at three organizational levels: Ca2+ transport in permeabilized cells, cytosolic Ca2+ concentration in intact cells, and contractile function of artery rings. We monitored the ATP-dependent, azide-insensitive, oxalate-stimulated 45Ca2+ uptake by saponin-permeabilized cultured cells. Low concentrations of peroxide inhibited the uptake less effectively in endothelium than in smooth muscle whether we added the peroxide directly to the Ca2+ uptake solution or treated intact cells with peroxide and washed them before the permeabilization. An acylphosphate formation assay confirmed the greater resistance of the SERCA pump in endothelial cells than in smooth muscle cells. Pretreating smooth muscle cells with 300 microM peroxide inhibited (by 77 +/- 2%) the cyclopiazonic acid (CPA)-induced increase in cytosolic Ca2+ concentration in a Ca2+-free solution, but it did not affect the endothelial cells. Peroxide pretreatment inhibited the CPA-induced contraction in deendothelialized arteries with a 50% inhibitory concentration of 97 +/- 13 microM, but up to 500 microM peroxide did not affect the endothelium-dependent, CPA-induced relaxation. Similarly, 500 microM peroxide inhibited the angiotensin-induced contractions in deendothelialized arteries by 93 +/- 2%, but it inhibited the bradykinin-induced, endothelium-dependent relaxation by only 40 +/- 13%. The greater resistance of the endothelium to reactive oxygen may be important during ischemia-reperfusion or in the postinfection immune response.

Nitric oxide and platelet function: implications for neonatology

Nitric oxide (NO) is a mediator that modulates vessel wall tone and hemostatic-thrombotic balance. Platelet function is regulated by NO generated from platelets, endothelial cells and leukocytes. Nitric oxide has been shown to inhibit platelet adhesion, aggregation, and stimulate disaggregation of preformed platelet aggregates. Many of the effects of NO are mediated by its stimulation of guanylate cyclase and the formation of cyclic GMP and its subsequent transduction mechanism. In vivo, NO is likely to interact with prostacyclin, metabolites of ecto-nucleotidase, and lipoxygenase to modulate platelet function in a synergistic manner. An imbalance of NO production (deficiency or overproduction) has been implicated in the pathogenesis of various vascular disorders including thrombosis, atherosclerosis, septicemia, and ischemia-reperfusion injury. It is likely that some of detrimental effects of NO are mediated through its reaction with superoxide anion to form the potent oxidant, peroxynitrite. Nitric oxide gas and NO donors are used for the pharmacological treatment of various vascular disorders. Because inhaled NO has been documented to improve systemic oxygenation and reduce the need for extracorporeal membrane oxygenation, it has been widely used in neonates with severe hypoxemia. An inhibition of platelet function, resulting in a prolonged bleeding time, has been shown in adults receiving inhaled NO. Because bleeding complications may occur in high-risk infants, it is important to evaluate the effect of inhaled NO on platelet function and its correlation with clinical consequences such as intracranial hemorrhage. For these reasons, hemostasis should be carefully monitored during the administration of inhaled NO to critically ill neonates.

Reciprocal relation between VEGF and NO in the regulation of endothelial integrity

Balloon angioplasty disrupts the protective endothelial lining of the arterial wall, rendering arteries susceptible to thrombosis and intimal thickening. We show here that vascular endothelial growth factor (VEGF), an endothelial cell mitogen, is upregulated in medial smooth muscle cells of the arterial wall in response to balloon injury. Both protein kinase C (PKC) and tyrosine kinase pp60src mediate augmented VEGF expression. In contrast, nitric oxide (NO) donors inhibit PKC-induced VEGF upregulation by interfering with binding of the transcription factor activator protein-1 (AP-1) to the VEGF promoter. Inhibition of VEGF promoter activation suggests that NO secreted by a restored endothelium functions as the negative feedback mechanism that downregulates VEGF expression to basal levels. Administration of a neutralizing VEGF antibody impaired reendothelialization following balloon injury performed in vivo. These findings establish a reciprocal relation between VEGF and NO in the endogenous regulation of endothelial integrity following arterial injury.

Role of endothelium in angiotensin II formation by the rat aorta and mesenteric arterial bed

We investigated the angiotensin II (Ang II)-generating system by analyzing the vasoconstrictor effect of Ang II, angiotensin J (Ang I), and tetradecapeptide (TDP) renin substrate in the absence and presence of inhibitors of the renin-angiotensin system in isolated rat aortic rings and mesenteric arterial beds with and without functional endothelium. Ang II, Ang I, and TDP elicited a dose-dependent vasoconstrictor effect in both vascular preparations that was completely blocked by the Ang II receptor antagonist saralasin (50 nM). The angiotensin converting enzyme (ACE) inhibitor captopril (36 microM) completely inhibited the vasoconstrictor effect elicited by Ang I and TDP in aortic rings without affecting that of Ang II. In contrast, captopril (36 microM) significantly reduced (80-90%) the response to bolus injection of Ang I, without affecting those to Ang II and TDP in mesenteric arteries. Mechanical removal of the endothelium greatly potentiated (70-95%) the vasoconstrictor response to Ang II, Ang I, and TDP in aortic rings while these responses were unaffected by the removal of the endothelium of mesenteric arteries with sodium deoxycholate infusion. In addition, endothelium disruption did not change the pattern of response elicited by these peptides in the presence of captopril. These findings indicate that the endothelium may not be essential for Ang II formation in rat mesenteric arteries and aorta, but it may modulate the response to Ang II. Although Ang II formation from Ang I is essentially dependent on ACE in both vessels, our results suggest the existence of an alternative pathway in the mesenteric arterial bed that may play an important role in Ang II generation from TDP in resistance but not in large vessels during ACE inhibition.

Passivation of metallic stents after arterial gene transfer of phVEGF165 inhibits thrombus formation and intimal thickening

OBJECTIVES

This study sought to test the hypothesis that direct gene transfer of an endothelial cell mitogen could passivate metallic stents by accelerating endothelialization of the prosthesis.

BACKGROUND

Thrombosis and restenosis comprise the principal clinical manifestations of compromised biocompatibility of endovascular stents. Previous studies have demonstrated that endothelial recovery at sites of balloon injury is a critical determinant of consequent intimal thickening and mural thrombus. We therefore investigated the potential for an endothelial cell mitogen delivered as plasmid DNA to optimize stent biocompatibility.

METHODS

Naked plasmid DNA encoding vascular endothelial growth factor (VEGF)/vascular permeability factor (VPF) (phVEGF165) was delivered locally using a hydrogel-coated balloon angioplasty catheter to 16 rabbit iliac arteries in which metallic stents had been placed at the site of balloon injury; the contralateral iliac artery of each rabbit was balloon injured and stented but not transfected.

RESULTS

Stent endothelialization was accelerated by phVEGF165 gene transfer (87.38 +/- 5.06% vs. 33.13 +/- 9.73% [mean +/- SEM] of the planimetered stent surface in the treated vs. contralateral limb, p = 0.005). This was associated with a significant reduction in mural thrombus (3.7 +/- 2.4% vs. 32.7 +/- 9.7%, p = 0.01) at day 7 and intimal thickening (maximal intimal area 0.61 +/- 0.09 vs. 1.44 +/- 0.12 mm2, p < 0.0001) at day 28. No benefit was observed from pCMV-luciferase in 14 similarly instrumented control rabbits.

CONCLUSIONS

These findings indicate that arterial gene transfer of naked plasmid DNA encoding for an endothelial cell mitogen may successfully passivate endovascular stents by accelerating stent endothelialization, thereby reducing in-stent thrombus and obstruction due to intimal thickening.