Enhanced endothelial adhesiveness in hypercholesterolemia is attenuated by L-arginine

Gene transfer of dimethylarginine dimethylaminohydrolase-2 improves the impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells induced by lysophosphatidylcholine

Dimethylarginine dimethylaminohydrolase (DDAH) is a key enzyme responsible for the metabolism of nitric oxide (NO) synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA), and DDAH2 is the predominant isoform in vascular endothelium. Lysophosphatidylcholine (LPC) and ADMA are implicated in endothelial dysfunction of atherosclerosis. This study was to examine changes in DDAH/ADMA/NOS/NO pathway in endothelial cells after exposure to LPC and investigate whether DDAH2 gene transfer could reverse LPC-induced changes. Human endothelial cell line ECV304 cells were transfected with recombinant pcDNA3.1-hDDAH2 plasmid and incubated with 3 micromol/L LPC for 48 h. Cells were harvested for assays of DDAH transcription, DDAH and NOS activities. The culture medium was collected for measurements of ADMA and nitrite/nitrate concentrations. LPC treatment suppressed DDAH2 transcription and DDAH activity in parallel with increased ADMA concentration, inhibited NOS activity and decreased NO metabolites content. DDAH2 gene transfer not only prevented the suppression of DDAH activity and the elevation of endogenous ADMA, but also attenuated the inhibition of NOS activity and the reduction of NO level induced by LPC in endothelial cells. These results suggest that LPC induces impairments of DDAH/ADMA/NOS/NO pathway, and DDAH2 gene transfer could improve the LPC-elicited impairments in endothelial cells.

Dimethylarginine dimethylaminohydrolase promotes endothelial repair after vascular injury

OBJECTIVES

We sought to determine if a reduction in asymmetric dimethylarginine (ADMA) enhances endothelial regeneration.

BACKGROUND

Asymmetric dimethylarginine is an endogenous inhibitor of nitric oxide synthase (NOS). Increased plasma levels of ADMA are associated with endothelial vasodilator dysfunction in patients with vascular disease or risk factors. Asymmetric dimethylarginine is eliminated largely by the action of dimethylarginine dimethylaminohydrolase (DDAH), which exists in 2 isoforms. Dimethylarginine dimethylaminohydrolase-1 transgenic (TG) mice manifest increased DDAH activity, reduced plasma and tissue ADMA levels, increased nitric oxide synthesis, and reduced systemic vascular resistance.

METHODS

The left femoral arteries of DDAH1 TG mice and wild-type (WT) mice were injured by a straight spring wire, and regeneration of the endothelial cell (EC) monolayer was assessed. Endothelial sprouting was assayed with growth factor-reduced Matrigel.

RESULTS

Regeneration of the EC monolayer was more complete 1 week after injury in TG mice (WT vs. TG: 40.0 +/- 6.5% vs. 61.2 +/- 6.4%, p < 0.05). The number of CD45 positive cells at the injured sites was reduced by 62% in DDAH TG mice (p < 0.05). Four weeks after injury, the neointima area and intima/media ratio were attenuated in DDAH TG mice (WT vs. TG: 0.049 +/- 0.050 mm2 vs. 0.031 +/- 0.060 mm2, 3.1 +/- 0.5 vs. 1.7 +/- 0.2, respectively, p < 0.05). Endothelial cell sprouting from vascular segments increased in TG mice (WT vs. TG: 24.3 +/- 3.9 vs. 39.0 +/- 2.2, p < 0.05).

CONCLUSIONS

We find for the first time an important role for DDAH in EC regeneration and in neointima formation. Strategies to enhance DDAH expression or activity might be useful in restoring the endothelial monolayer and in treating vascular disease.

Celiprolol, a Selective .BETA.1-Blocker, Reduces the Infarct Size Through Production of Nitric Oxide in a Rabbit Model of Myocardial Infarction

BACKGROUND

It is still unclear whether celiprolol, a beta(1)-selective blocker, reduces myocardial infarct size. This study will examine whether celiprolol reduces myocardial infarct size, as well as investigate the mechanisms for its infarct size-reducing effect in rabbits.

METHODS AND RESULTS

Japanese white rabbits underwent 30 min of ischemia and 48 h of reperfusion. Celiprolol (1 or 10 mg x kg (-1) x h(-1) for 60 min, iv) was administered 20 min before ischemia with or without pretreatment with N(omega)-nitro-L-arginine methylester (L-NAME, 10 mg/kg, iv, a nitric oxide synthase inhibitor) or 5-hydroxydecanoic acid sodium salt (5-HD, 5 mg/kg, iv, a mitochondrial K(ATP) channel blocker). The area at risk as a percentage of the left ventricle was determined by using Evans blue dye, and the infarct size was determined as a percentage of the area at risk by triphenyl tetrazolium chloride staining. Celiprolol 1 and 10 mg x kg(-1) x h(-1) significantly reduced the infarct size in a dose-dependent manner (36.4+/-1.7%, n=7 and 25.4+/-2.9%, n=7, respectively) compared with the control (46.2+/-3.1%, n=8). The infarct size-reducing effect of celiprolol was completely blocked by L-NAME (40.4 +/-2.8%, n=8) but not by 5-HD (27.3+/-1.0%, n=8). Celiprolol 1 mg x kg(-1) x h (-1) increased the myocardial interstitial levels of NOx, an indicator of nitric oxide, and reduced the intensity of dihydro-ethidium staining of myocardium, an indicator of superoxide, during reperfusion after 30 min of ischemia.

CONCLUSION

Celiprolol reduces myocardial infarct size and also increases nitric oxide production and reduces superoxide levels but not mitochondrial K(ATP) channels in rabbits.

Pravastatin Reduces Myocardial Infarct Size Via Increasing Protein Kinase C-Dependent Nitric Oxide, Decreasing Oxyradicals and Opening the Mitochondrial Adenosine Triphosphate-Sensitive Potassium Channels in Rabbits

BACKGROUND

Statins reportedly protect against myocardial infarction, but the precise mechanism is unclear.

METHODS AND RESULTS

Rabbits underwent 30 min of coronary occlusion followed by 48 h of reperfusion. Pravastatin (1 or 5 mg/kg) or saline was intravenously administered 10 min before ischemia. Pravastatin (5 mg/kg) was also administered 10 min before reperfusion. N(omega)-nitro-L-arginine methylester (L-NAME, 10 mg/kg), chelerythrine (5 mg/kg) or 5-hydroxydecanoic acid sodium salt (5-HD, 5 mg/kg) was intravenously administered 10 min before pravastatin injection. The infarct size was determined. The myocardial interstitial levels of 2,5-dihydroxybenzoic acid (DHBA) and nitrogen oxide (NOx), and the intensity of myocardial dihydroethidium staining were measured. Pre-ischemic treatment with pravastatin reduced the infarct size (34+/-5% and 24+/-4%, 1 and 5 mg/kg, respectively), but not pre-reperfusion treatment (42.1+/-3.7%), compared with the control (45+/-3%). This effect was blocked by L-NAME (42.6+/-4%), chelerythrine (50.9+/-3%) and 5-HD (52.7+/-2%). Pre-ischemic treatment with pravastatin increased myocardial NOx levels, and attenuated both the 2,5-DHBA level and the intensity of dihydroethidium staining during reperfusion. Chelerythrine abolished the increase in NOx levels by pravastatin.

CONCLUSION

Pre-ischemic treatment with pravastatin reduces the myocardial infarct size via protein kinase C-dependent nitric oxide production, decreasing hydroxyl radicals and superoxide, and opening the mitochondrial adenosine triphosphate-sensitive potassium channels.

Influence of chronic liver disease on coronary atherosclerosis vulnerability features

INTRODUCTION

A lower incidence of acute myocardial infarction was reported in patients with chronic liver disease.

OBJECTIVE

To analyze the impact of chronic liver disease on characteristics associated with vulnerability of human coronary artery atherosclerotic plaques.

METHODS

One hundred fourteen hearts were collected from 3 groups of individuals: A--38 chronic liver disease patients who died while on the waiting list for liver transplantation; B--38 individuals who died of natural causes; and C--38 individuals who died of accidental causes. The most obstructed portion of the initial 2-cm segment of coronary arteries was histologically evaluated regarding to plaque area, luminal area, inflammation, percentage of fat, and total vessel area.

RESULTS

The mean age (years) and male frequency in groups A, B and C were, respectively, 52+/-9 and 79%; 52+/-11 and 71%; and 54+/-18 and 89%. The mean area of the plaque and the incidence of severe plaque inflammation in group A were significantly lower (4.2+/-3.2; 13.2%) than those in the other two groups (6.6+/-4.3; 84.2%, and 6.3+/-4.4; 52.6%) p<0.01. The cross-sectional vessel measures were not statistically different regarding to vessel area (10.5+/-4.6; 12.1+/-4.6; 13.0+/-4.4) p=0.08, luminal obstruction (45%+/-15%; 60%+/-20%; 53%+/-20%) p=0.07, and fat area in the plaque (16%+/-17%; 30%+/-24%; 18%+/-18) p=0.37. In conclusion, compared with the general population, chronic liver disease patients have coronary arteries with smaller intimal plaque and less vessel inflammation. These findings favor the concept that hepatic disease patients are less prone to develop complicated coronary atherosclerosis.

Specific monocyte adhesion to endothelial cells induced by oxidized phospholipids involves activation of cPLA2 and lipoxygenase

Oxidized phospholipids stimulate endothelial cells to bind monocytes, but not neutrophils, an initiating event in atherogenesis. Here, we investigate intracellular signaling events induced by oxidized phospholipids in human umbilical vein endothelial cells (HUVECs) that lead to specific monocyte adhesion. In a static adhesion assay, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine and one of its components, 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine, stimulated HUVECs to bind U937 cells and human peripheral blood monocytes but not HL-60 cells or blood neutrophils. Monocyte adhesion was dependent on protein kinases A and C, extracellular signal-regulated kinase 1/2, p38 mitogen activated protein kinases (MAPKs), and cytosolic phospholipase A(2) (cPLA(2)). Inhibition of 12-lipoxygenase (12-LOX), but not cyclooxygenases, blocked monocyte adhesion, and addition of 12-hydroxyeicosatetraenoic acid (12-HETE) mimicked the effects of oxidized phospholipids. Peroxisome proliferator-activated receptor alpha (PPARalpha) was excluded as a possible target for 12-HETE, because monocyte adhesion was still induced in endothelial cells from PPARalpha null mice. Together, our results suggest that oxidized phospholipids stimulate HUVECs to specifically bind monocytes involving MAPK pathways, which lead to the activation of cPLA(2) and 12-LOX. Further analysis of signaling pathways induced by oxidized phospholipids that lead to specific monocyte adhesion should ultimately lead to the development of novel therapeutic approaches against chronic inflammatory diseases.

Endothelial dysfunction precedes atherosclerotic lesions and platelet activation in high fat diet-induced prothrombotic state

INTRODUCTION

Earlier we have demonstrated a prothrombotic state in spontaneously atherogenic rodents kept on Western-style high fat diet. The aim of the present study was to investigate the cellular mechanism of such prothrombotic state.

MATERIALS AND METHODS

Two kinds of diets, Western-style high fat diet containing 20% fat (w/w) and 0.05% cholesterol (w/w) and low fat diet containing 7% fat without cholesterol based on AIN93G, were added to diet-sensitive apolipoprotein E and low-density lipoprotein receptor double deficient male mice for 12 or 18 weeks from 6 weeks of age. Atherosclerosis was assessed by morphometry of the aortic wall or lipid-stained lesions. Endothelial function was measured by flow-mediated vasodilation (FMV) of the femoral artery. Platelet reactivity was measured ex vivo by a shear-induced platelet aggregation test.

RESULTS AND CONCLUSIONS

12 weeks feeding of mice with high fat diet significantly impaired FMV, as compared with mice fed with low fat diet (P<0.05). In contrast, there was no significant difference in the lipid-stained areas and in the reactivity of platelets between the two groups. 18 weeks feeding with high fat diet significantly impaired FMV (P<0.05) and enhanced both lipid-stained areas (P<0.05) and platelet reactivity (P<0.01). These findings show that in high fat diet-induced prothrombotic state, endothelial dysfunction precedes both the morphologically detectable lesions and the enhancement of platelet reactivity.

Diabetes mellitus-associated atherosclerosis: mechanisms involved and potential for pharmacological invention

While diabetes mellitus is most often associated with hypertension, dyslipidemia, and obesity, these factors do not fully account for the increased burden of cardiovascular disease in patients with the disease. This strengthens the need for comprehensive studies investigating the underlying mechanisms mediating diabetic cardiovascular disease and, more specifically, diabetes-associated atherosclerosis. In addition to the recognized metabolic abnormalities associated with diabetes mellitus, upregulation of putative pathological pathways such as advanced glycation end products, the renin-angiotensin system, oxidative stress, and increased expression of growth factors and cytokines have been shown to play a causal role in atherosclerotic plaque formation and may explain the increased risk of macrovascular complications. This review discusses the methods used to assess the development of atherosclerosis in the clinic as well as addressing novel biomarkers of atherosclerosis, such as low-density lipoprotein receptor-1. Experimental models of diabetes-associated atherosclerosis are discussed, such as the streptozocin-induced diabetic apolipoprotein E knockout mouse. Results of major clinical trials with inhibitors of putative atherosclerotic pathways are presented. Other topics covered include the role of HMG-CoA reductase inhibitors and fibric acid derivatives with respect to their lipid-altering ability, as well as their emerging pleiotropic anti-atherogenic actions; the effect of inhibiting the renin-angiotensin system by either ACE inhibition or angiotensin II receptor antagonism; the effect of glycemic control and, in particular, the promising role of thiazolidinediones with respect to their direct anti-atherogenic actions; and newly emerging mediators of diabetes-associated atherosclerosis, such as advanced glycation end products, vascular endothelial growth factor and platelet-derived growth factor. Overall, this review aims to highlight the observation that various pathways, both independently and in concert, appear to contribute toward the pathology of diabetes-associated atherosclerosis. Furthermore, it reflects the need for combination therapy to combat this disease.

Chronic L-arginine supplementation improves endothelial cell vasoactive functions in hypercholesterolemic and atherosclerotic monkeys

Chronic exposure to L-arginine results in regression of atherosclerotic lesions and reversal of endothelial dysfunction. We investigated whether chronic L-arginine supplementation induces regression of atherosclerotic lesions and reversal of endothelial dysfunction in atherogenic rhesus monkeys and the mechanism which leads to these effects. About 12 male rhesus monkeys were fed 1% cholesterol and 18 g butter for 6 months to create an experimental model of hypercholesterolaemia and atherosclerosis (Group I) and 12 monkeys were fed standard stock diet for 6 months (Group II). After, 6 months these two groups were further divided into 2 sub-groups which in addition to their respective diets were fed 2.5% L-arginine in drinking water for additional 6 months (Group III and Group IV). Systemic nitric oxide (NO) formation was assessed as plasma nitrite and cGMP formation every 3 months. Oxygen free radical (OFR) generation and malondialdehyde production as an index of lipid peroxidation were determined. Changes in isometric tension were compared in isolated ring segments of thoracic aorta from normal and hypercholesterolemic animals. Cholesterol feeding progressively reduced plasma nitrite and cGMP generation (p < 0.05). Dietary L-arginine partly restored the levels of plasma nitrite and cGMP (p < 0.05) but did not change plasma cholesterol levels. L-arginine significantly reduced aortic intimal thickening, blocked the production of carotid and coronary intimal plaques and completely preserved endothelium-dependent vasodilator function. Further, L-arginine significantly inhibited generation of the reactive oxygen species (ROS) generation and lipid peroxidation. Chronic oral supplementation with L-arginine blocks the progression of plaques via restoration of nitric oxide synthase substrate availability and reduction of vascular oxidative stress.

Endothelial cell dysfunction: can't live with it, how to live without it

Endothelial cell dysfunction is emerging as an ultimate culprit for diverse cardiovascular diseases and cardiovascular complications of chronic renal diseases, yet the definition of this new syndrome, its pathophysiology, and therapy remain poorly defined. Here, I summarize some molecular mechanisms leading from hyperhomocystinemia, elevated asymmetric dimethylarginine, and advanced glycolation end product-modified protein level to the proatherogenic, prothrombogenic, and proinflammatory endothelial phenotype and offer a model of endothelial dysfunction based on the interconnectedness of diverse functions. Finally, several therapeutic strategies to prevent and correct endothelial dysfunction are discussed in the light of uncertainty of their action modulated by the endothelial dysfunction per se.

Rosuvastatin Attenuates Monocyte-Endothelial Cell Interactions and Vascular Free Radical Production in Hypercholesterolemic Mice

One of the earliest observable events in atherogenesis is enhanced monocyte adhesion to the endothelium. In addition to reducing circulating levels of cholesterol, 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors (statins) are thought to have direct salutary effects upon vascular cells. We hypothesized that the new statin, rosuvastatin, would have anti-inflammatory effects on the vessel wall. Eight-week-old apolipoprotein E-deficient mice were fed a normal chow diet for a period of 12 weeks. During this time mice were administered vehicle or rosuvastatin at a dose of 0, 1, 5, or 20 mg/kg by subcutaneous injection at the same time daily for a period of 2 or 6 weeks prior to sacrifice. At the end of the study, rosuvastatin-treated animals displayed lower plasma total cholesterol levels, whereas showing little change in high-density lipoprotein cholesterol or triglycerides. Using a functional binding assay, we also demonstrated that endothelial adhesiveness for monocytes was significantly attenuated after 2 weeks of treatment with rosuvastatin. Quantitative real-time polymerase chain reaction determined that rosuvastatin reduced the expression of vascular cell adhesion molecule-1, monocyte chemotactic protein-1, and metalloproteinase-9 in the vessel wall. In addition, rosuvastatin inhibited vascular expression of p22(phox) and superoxide production, as well as diminishing plasma 8-isoprostanes concentrations. Thus, treatment with rosuvastatin has acute anti-inflammatory actions that likely participate in its beneficial actions during atherogenesis.

Potential ergogenic effects of arginine and creatine supplementation

The rationale for the use of nutritional supplements to enhance exercise capacity is based on the assumption that they will confer an ergogenic effect above and beyond that afforded by regular food ingestion alone. The proposed or advertised ergogenic effect of many supplements is based on a presumptive metabolic pathway and may not necessarily translate to quantifiable changes in a variable as broadly defined as exercise performance. L-arginine is a conditionally essential amino acid that has received considerable attention due to potential effects on growth hormone secretion and nitric oxide production. In some clinical circumstances (e.g., burn injury, sepsis) in which the demand for arginine cannot be fully met by de novo synthesis and normal dietary intake, exogenous arginine has been shown to facilitate the maintenance of lean body mass and functional capacity. However, the evidence that supplemental arginine may also confer an ergogenic effect in normal healthy individuals is less compelling. In contrast to arginine, numerous studies have reported that supplementation with the arginine metabolite creatine facilitates an increase in anaerobic work capacity and muscle mass when accompanied by resistance training programs in both normal and patient populations. Whereas improvement in the rate of phosphocreatine resynthesis is largely responsible for improvements in acute work capacity, the direct effect of creatine supplementation on skeletal muscle protein synthesis is less clear. The purpose of this review is to summarize the role of arginine and its metabolite creatine in the context of a nutrition supplement for use in conjunction with an exercise stimulus in both healthy and patient populations.

Asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, explains the "L-arginine paradox" and acts as a novel cardiovascular risk factor

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO). Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of NO synthase. ADMA inhibits vascular NO production in concentrations found in pathophysiological conditions; ADMA also causes local vasoconstriction when it is infused intraarterially. Thus, elevated ADMA levels may explain the "L-arginine paradox," i.e., the observation that supplementation with exogenous L-arginine improves NO-mediated vascular functions in vivo, although its baseline plasma concentration is about 25-fold higher than the Michaelis-Menten constant K(m) of the isolated, purified endothelial NO synthase in vitro. The biochemical and physiological pathways related to ADMA are well understood: Dimethylarginines are the result of degradation of methylated proteins; the methyl group is derived from S-adenosylmethionine. Both ADMA and its regioisomer, symmetric dimethylarginine, are eliminated from the body by renal excretion, whereas only ADMA is metabolized via hydrolytic degradation to citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). DDAH activity and/or expression may therefore contribute to the pathogenesis of endothelial dysfunction in various diseases. Plasma ADMA levels are increased in humans with hypercholesterolemia, atherosclerosis, hypertension, chronic renal failure, and chronic heart failure. Increased ADMA levels are associated with reduced NO synthesis as assessed by impaired endothelium-dependent vasodilation. In several prospective and cross-sectional studies, ADMA evolved as a marker of cardiovascular risk. With increasing knowledge of the role of ADMA in the pathogenesis of cardiovascular disease, ADMA is becoming a goal for pharmacotherapeutic interventions. Among other potential strategies that are currently being tested, administration of L-arginine has been shown to improve endothelium-dependent vascular functions in subjects with high ADMA levels. Finally, ADMA has gained clinical importance recently because several studies have shown that ADMA is an independent cardiovascular risk factor.

Nitric oxide insufficiency and atherothrombosis

Nitric oxide (NO) is a structurally simple compound that participates in a wide range of biological reactions to maintain normal endothelial function and an antithrombotic intravascular milieu. Among its principal effects are the regulation of vascular tone, vascular smooth muscle cell proliferation, endothelial-leukocyte interactions, and the antiplatelet effects of the endothelium. Impaired NO bioavailability represents the central feature of endothelial dysfunction, the earliest stage in the atherosclerotic process, and also contributes to the pathogenesis of acute vascular syndromes by predisposing to intravascular thrombosis. The causes of NO insufficiency can be grouped into two fundamental mechanisms: inadequate synthesis and increased inactivation of NO. Polymorphisms in the endothelial NO synthase gene and decreased substrate or cofactor availability for this enzyme are the main mechanisms that compromise the synthesis of NO. Inactivation of NO occurs mainly through its interaction with reactive oxygen species and can be favored by a deficiency of antioxidant enzymes such as glutathione peroxidase. In this review, we present an overview of NO synthesis and biological chemistry, discuss the mechanisms of action of NO in regulating endothelial and platelet function, and explore the causes of NO insufficiency, as well as the evidence linking these causes to the pathophysiology of endothelial dysfunction and atherothrombosis.

Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in patients with chronic kidney diseases

BACKGROUND

NO synthesis is inhibited by the dimethylarginine (DMA) ADMA, which accumulates, similar to SDMA, in the plasma of patients suffering from chronic renal failure (CRF). ADMA and possibly SDMA contribute to hypertension and atherosclerosis in patients with chronic renal disease: ADMA inhibits directly eNOS, whereas SDMA competes with the NO precursor arginine for uptake into the cells.

METHODS

In 26 control persons and 221 patients with kidney diseases of different stage as were CRF, end stage renal disease (ESRD), and patients after renal transplantation (RT), the plasma concentrations of ADMA (c(ADMA)), SDMA (c(SDMA)) and 20 endogenous amino acids (AA) were measured by HPLC and correlated to blood pressure, cardiac events, endothelial dysfunction, and diabetes mellitus.

RESULTS

Both ADMA (1.04+/-0.04 vs. 0.66+/-0.04 microM) and SDMA (2.69+/-0.12 vs. 0.49+/-0.03 microM) were significantly (p<0.001) elevated in all patients compared to healthy controls, whereas arginine concentration (51.4+/-2.3 vs. 76.0+/-5.2 microM) was decreased in dependence on the degree of kidney disease. In RT patients, SDMA levels were significantly decreased, but c(ADMA) remained enhanced. A strong correlation was found between SDMA and both serum urea and creatinine in CRF and RT patients. A linear correlation was found between ADMA and cholesterol concentrations in RT patients. Hypertension in CRF was accompanied by a further increase in the concentration of DMAs. There was no relation between DMAs and the occurrence of peripheral arterial occlusive disease or cerebrovascular diseases. In patients with cardiac diseases, c(SDMA) was additionally increased only in the CRF group.

CONCLUSIONS

In patients with chronic kidney disease, c(ADMA) and c(SDMA) are significantly increased but cardiovascular diseases are evidently not correlated to changes in DMA concentrations in this group of patients.

Benidipine Reduces Myocardial Infarct Size Involving Reduction of Hydroxyl Radicals and Production of Protein Kinase C-Dependent Nitric Oxide in Rabbits

Japanese white rabbits underwent 30 minutes of ischemia and 48 hours of reperfusion. Benidipine (3 or 10 microg/kg, i.v.) was administered 10 minutes before ischemia with and without pretreatment with L-NAME (10 mg/kg, i.v., a NOS inhibitor), chelerythrine (5 mg/kg, i.v., a PKC blocker) or 5-HD (5 mg/kg, i.v. a mitochondrial KATP channel blocker), genistein (5 mg/kg, i.v. a protein tyrosin kinase blocker). SNAP (2.5 mg/kg/min x 70 minutes, i.v., an NO donor) was also administered 10 minutes before ischemia. Benidipine significantly reduced the infarct size in a dose-dependent manner (3 microg/kg: 29.0 +/- 2.7%, n = 8, 10 microg/kg: 23.0 +/- 2.4%, n = 10) compared with the control (41.6 +/- 3.3%, n = 10). This effect was completely blocked by L-NAME (39.9 +/- 3.6%, n = 8) and chelerythrine (35.5 +/- 2.4%, n = 8) but not by 5-HD (23.0 +/- 2.4%, n = 10) or genistein (24.6 +/- 3.1%, n = 10). SNAP also reduced the infarct size (24.6 +/- 3.1%, n = 8). Benidipine significantly increased the expression of eNOS mRNA at 30 minutes after reperfusion and significantly increased the expression of eNOS protein at 3 hours after reperfusion in the ischemic area of the left ventricle. Benidipine and SNAP significantly decreased myocardial interstitial 2,5-DHBA levels, an indicator of hydroxyl radicals, during ischemia and reperfusion. Benidipine increased myocardial interstitial NOx levels, which effect was blocked by chelerythrine, during 0 to 30 minutes and 150 to 180 minutes after reperfusion. Benidipine reduces the infarct size through PKC-dependent production of nitric oxide and decreasing hydroxyl radicals but not through involving protein tyrosine kinase or mitochondrial KATP channels in rabbits.

Glucose regulates interleukin-8 production in aortic endothelial cells through activation of the p38 mitogen-activated protein kinase pathway in diabetes

We have shown that chronic elevated glucose (25 mm) increases monocyte adhesion to human aortic endothelial cells (EC). This increased adhesion is mediated primarily through induction of interleukin (IL)-8 via activation of the transcription factor AP-1 (Srinivasan, S., Yeh, M., Danziger, E. C., Hatley, M. E., Riggan, A. E., Leitinger, N., Berliner, J. A., and Hedrick, C. C. (2003) Circ. Res. 92, 371-377). In the current study, we identified the elements in the AP-1 transcriptional complex that are activated by glucose. These elements include c-Jun, c-Fos, and Fra-1. AP-1 is activated by cellular oxidative stress, and we have reported significant production of ROS by high glucose-cultured cells. We examined signaling pathways upstream of AP-1 in EC that lead to AP-1 activation by HG. EC cultured in 25 mm glucose had a 2-fold increase in p38 phosphorylation compared with control normal glucose-cultured EC. Inhibition of the p38 pathway using 5 microm SB203580 significantly reduced glucose-mediated IL-8 mRNA production by 60%. Furthermore, blocking p38 pathway activation using a dominant-negative p38 construct significantly reduced glucose-mediated monocyte adhesion by 50%. Thus, glucose-stimulated monocyte adhesion is primarily regulated through phosphorylation of p38 with subsequent activation of AP-1, leading to IL-8 production. To study this pathway in the setting of diabetes, we used the db/db mouse. P38 phosphorylation was increased in diabetic db/db mice compared with control mice. We found a dramatic elevation in plasma levels of KC, the mouse ortholog of IL-8 in diabetic db/db mice (1800 +/- 100 pg/ml KC in db/db versus 300 +/- 75 pg/ml in C57BL/6J control mice, p < 0.0001). Inhibition of the p38 pathway in diabetic db/db mice significantly reduced monocyte adhesion by 50%. Taken together, these data indicate that chronic elevated glucose in diabetes activates the p38 MAP kinase pathway to increase inflammatory IL-8 gene induction and monocyte/endothelial adhesion.

12/15-Lipoxygenase activity mediates inflammatory monocyte/endothelial interactions and atherosclerosis in vivo

We have shown that the 12/15-lipoxygenase (12/15-LO) product 12S-hydroxyeicosatetraenoic acid increases monocyte adhesion to human endothelial cells (EC) in vitro. Recent studies have implicated 12/15-LO in mediating atherosclerosis in mice. We generated transgenic mice on a C57BL/6J (B6) background that modestly overexpressed the murine 12/15-LO gene (designated LOTG). LOTG mice had 2.5-fold elevations in levels of 12S-hydroxyeicosatetraenoic acid and a 2-fold increase in expression of 12/15-LO protein in vivo. These mice developed spontaneous aortic fatty streak lesions on a chow diet. Thus, we examined effects of 12/15-LO expression on early events leading to atherosclerosis in these mice. We found that, under basal unstimulated conditions, LOTG EC bound more monocytes than B6 control EC (18 +/- 2 versus 7 +/- 1 monocytes/field, respectively; p < 0.0001). Inhibition of 12/15-LO activity in LOTG EC using a 12/15-LO ribozyme completely blocked monocyte adhesion in LOTG mice. Thus, 12/15-LO activity is required for monocyte/EC adhesion in the vessel wall. Expression of ICAM-1 in aortic endothelia of LOTG mice was increased severalfold. VCAM-1 expression was not changed. In a series of blocking studies, antibodies to alpha(4) and beta(2) integrins in WEHI monocytes blocked monocyte adhesion to both LOTG and B6 control EC. Inhibition of ICAM-1, VCAM-1, and connecting segment-1 fibronectin in EC significantly reduced adhesion of WEHI monocytes to LOTG EC. In summary, these data indicate that EC from LOTG mice are "pre-activated" to bind monocytes. Monocyte adhesion in LOTG mice is mediated through beta(2) integrin and ICAM-1 interactions as well as through VLA-4 and connecting segment-1 fibronectin/VCAM-1 interactions. Thus, 12/15-LO mediates monocyte/EC interactions in the vessel wall in atherogenesis at least in part through molecular regulation of expression of endothelial adhesion molecules.

Adhesion molecules, catecholamines and leucocyte redistribution during and following exercise

The circulating blood normally contains no more than 1-2% of the body's population of leucocytes. The numbers and phenotypes of circulating leucocyte subsets can change dramatically during and immediately following exercise. The surface expression of adhesion molecules makes an important contribution to such responses by changing patterns of cell trafficking. Alterations in the surface expression of adhesion molecules could reflect a shedding of molecules, selective apoptosis or differential trafficking of cells with a particular phenotype, effects from mechanical deformation of the cytoplasm, active biochemical processes involving cytokines, catecholamines, glucocorticoids or other hormones, or changes in the induction of adhesion molecules. The expression of adhesion molecules changes with maturation and activation of leucocytes. Typically, mature cells express lower densities of L-selectin (CD62L), the homing receptor for secondary lymphoid organs, and higher densities of LFA-1 (CD11a), the molecule associated with trafficking to non-lymphoid reservoir sites. The neutrophils and natural killer cells that are mobilised during exercise also express high levels of Mac-1 (CD11b), a marker associated with cellular activation. Possibly, exercise demarginates older cells that are awaiting destruction in the spleen. Plasma concentrations of catecholamines rise dramatically with exercise, and there is growing evidence that catecholamines, acting through a cyclic adenosine monophosphate second messenger system, play an important role in modifying the surface expression of adhesion molecules. Analogous changes can be induced by other forms of stress that release catecholamines or by catecholamine infusion, and responses are blocked by beta(2)-blocking agents. Catecholamines also modify adherence and expression of adhesion molecules in vitro. Cell trafficking is modified by genetic deficiencies in the expression of adhesion molecules, but leucocyte responses to exercise and catecholamines are generally unaffected by splenectomy. A number of clinical conditions including atherogenesis and metaplasia are marked by an altered expression of adhesion molecules. The effects of exercise on these molecules could thus have important health implications.

NOS inhibition accelerates atherogenesis: reversal by exercise

In this study, we assessed the effects of chronic exercise training (12 wk) on atherosclerotic lesion formation in hypercholesterolemic apolipoprotein E-deficient mice (n = 31). At the age of 9 wk, mice were assigned to the following groups: sedentary (Sed; n = 9); exercise (Ex; n = 12); sedentary and oral NG-nitro-L-arginine (L-NNA, Sed-NA; n = 4), or exercise and oral L-NNA (Ex-NA; n = 6). Chronic exercise training was performed on a treadmill for 12 wk (6 times/wk and twice for 1 h/day) at a final speed of 22 m/min, and an 8 degrees grade. L-NNA was discontinued 5 days before final treadmill testing. The farthest distance run to exhaustion was observed in Ex-NA mice (Sed: 306 +/- 32 m; Ex: 640 +/- 87; Sed-NA: 451 +/- 109 m; Ex-NA: 820 +/- 49 m; all P < 0.05). Lesion formation was assessed in the proximal ascending aorta by dissection microscopy after oil red O staining. The aortas of Sed-NA mice manifested a threefold increase in lesion formation compared with the other groups. This L-NNA-induced lesion formation was reduced by chronic exercise training (Sed, 786 +/- 144; Ex, 780 +/- 206; Sed-NA, 2,147 +/- 522; Ex-NA, 851 +/- 253; Sed-NA vs. all other groups: P < 0.001). In conclusion, treatment with oral L-NNA (an nitric oxide synthase antagonist) leads to accelerated atherogenesis in genetically determined hypercholesterolemic mice. This adverse effect can be overcome by chronic exercise training.

Increased production of 12/15 lipoxygenase eicosanoids accelerates monocyte/endothelial interactions in diabetic db/db mice

Atherosclerosis is a major complication of diabetes. Up to 16 weeks of age, the db/db mouse is insulin-resistant and hyperglycemic and is a good model of Type 2 diabetes. After approximately 16 weeks of age, the mice develop pancreatic beta cell failure that can progress to a Type 1 diabetes phenotype. We have previously shown that glucose increases production of endothelial 12/15 lipoxygenase (12/15LO) products in vitro. In young 10-week-old Type 2 diabetic db/db mice, we found significant elevations in levels of urinary 12/15LO products, 12S-hydroxyeicosatetraenoic acid (12S-HETE) and 13S-hydroxyoctadecaenoic acid (13S-HODE) in vivo compared with C57BLKS/J mice. Using isolated primary aortic endothelial cells (ECs) from db/db mice and WEHI78/24 mouse monocyte cells in static adhesion assays, we found increased WEHI monocyte adhesion to db/db ECs (14 +/- 2 monocytes/field for db/db ECs versus 4 +/- 1 monocytes/field for C57BLKS/J ECs, p < 0.002). Thus, ECs from db/db mice appear to be "pre-activated" to bind monocytes. Analysis of db/db ECs revealed a 2-fold elevation in 12/15LO protein compared with C57BLKS/J EC. To determine that 12/15LO products were responsible for the increased monocyte adhesion observed with db/db ECs, we inhibited expression of murine 12/15LO using either an adenovirus expressing a ribozyme to 12/15LO (AdRZ) or with the 12/15LO inhibitor cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate. Treatment of db/db ECs for 48 h with AdRZ or 4 h with 10 microm cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate significantly reduced monocyte adhesion to db/db endothelium (p < 0.009). Thus, inhibition of the murine 12/15LO in db/db mice significantly reduced monocyte/endothelial interactions. We also found that adhesion of monocytes to diabetic db/db ECs was mediated by interactions of alpha4beta1 integrin on monocytes with endothelial vascular cell adhesion molecule 1 and connecting segment 1 fibronectin and interactions of beta2 integrins with endothelial intercellular adhesion molecule 1. In summary, regulation of the 12/15LO pathway is important for mediating early vascular changes in diabetes. Modulation of the 12/15LO pathway in the vessel wall may provide therapeutic benefit for early vascular inflammatory events in diabetes.

Anti-atherogenic effect of soya and rice-protein isolate, compared with casein, in apolipoprotein E-deficient mice

Our objective was to determine whether dietary plant proteins such as soya-protein isolate (SPI) and rice-protein isolate (RPI) compared with animal proteins, such as casein, could afford beneficial effects on atherosclerosis development in apolipoprotein E-deficient mice. In experiment 1, male and female mice were fed on a purified diet containing either casein, SPI or RPI for 9 weeks. The en face lesion area in the aorta (P<0.05) and the lesion size in the aortic root (P<0.05) in mice fed the casein-based diet were greater than those in the SPI or RPI groups. The plant protein groups had an increased concentration of serum l-arginine (P<0.05) and NO metabolites (NO2 plus NO3) (P<0.05) than did the casein group. The inhibitory effect of the plant proteins on the lesion formations was unrelated to gender and total serum cholesterol. In experiment 2, the l-arginine and l-methionine contents were the same in the l-arginine-supplemented casein-based and SPI-based diets, and between the l-methionine-supplemented SPI-based and the casein-based diets. Male mice were fed on the diets for 15 weeks. There were no significant differences in the en face lesion area and the lesion size between the casein group and the l-arginine-supplemented group, although the serum l-arginine (P<0.05) and NO2 plus NO3 (P<0.05) concentrations in the supplemented group were higher than those in the casein group. There were no significant effects of l-methionine supplementation on the lesion formations. In experiment 3, male mice were given the casein-based diet or the l-arginine-supplemented casein-based diet together with water or water containing an NO synthesis inhibitor for 9 weeks. When given the casein-based diet, the inhibitor drinking, compared with water drinking, resulted in a reduction of the serum NO2 plus NO3 concentration (P<0.01) and an increase in the en face lesion area (P<0.05) and the lesion size (P<0.01). When given the l-arginine-supplemented diet, the inhibitor drinking, compared with water drinking, resulted in no increase in the lesion area and size. These results demonstrate anti-atherogenic potentials of SPI- as well as RPI-derived proteins, but their l-arginine and l-methionine contents were not sufficient enough to explain the underlying mechanism(s).

Quinaprilat reduces myocardial infarct size involving nitric oxide production and mitochondrial KATP channel in rabbits

This study examined whether quinaprilat, an angiotensin-converting enzyme inhibitor, reduces the infarct size, and investigated the mechanisms for its infarct size-reducing effect, in rabbits. Japanese white rabbits underwent 30 min of ischemia and 48 h of reperfusion. Quinaprilat (100 microg/kg/h or 300 microg/kg/h for 70 min, IV) was administered 20 min before ischemia with or without pretreatment with Nomega-nitro-l-arginine methyl ester (l-NAME) (10 mg/kg, IV, a nitric oxide synthase inhibitor), 5-hydroxydecanoic acid sodium salt (5-HD) or posttreatment with 5-HD (5 mg/kg, IV, a mitochondrial KATP channel blocker). The area at risk as a percentage of the left ventricle was determined by Evans blue dye and the infarct size was determined as a percent of the area at risk by triphenyl tetrazolium chloride staining. Using a microdialysis technique, myocardial interstitial levels of 2,5-dihydroxybenzoic acid (2,5-DHBA), an indicator of hydroxyl radicals, and NOx, an indicator of nitric oxide, were measured before, during, and after 30 min of ischemia. Quinaprilat significantly reduced the infarct size in a dose-dependent manner (30.1 +/- 3%, n = 10, and 27.6 +/- 2%, n = 7, respectively) compared with the control (46.5 +/- 4%, n = 10). The infarct size-reducing effect of quinaprilat was completely blocked by pretreatment with l-NAME (43.8 +/- 2%, n = 8) and 5-HD (50.1 +/- 3%, n = 8) and posttreatment with 5-HD (50.3 +/- 2%, n = 8), respectively. Quinaprilat did not affect the myocardial interstitial 2,5-DHBA level but significantly increased the NOx level during ischemia and reperfusion. Quinaprilat reduces myocardial infarct size involving NO production and mitochondrial KATP channels in rabbits without collateral circulation.

Minireview: adiposity, inflammation, and atherogenesis

Adipose tissue is a dynamic endocrine organ that secretes a number of factors that are increasingly recognized to contribute to systemic and vascular inflammation. Several of these factors, collectively referred to as adipokines, have now been shown regulate, directly or indirectly, a number of the processes that contribute to the development of atherosclerosis, including hypertension, endothelial dysfunction, insulin resistance, and vascular remodeling. Several adipokines are preferentially expressed in visceral adipose tissue, and the secretion of proinflammatory adipokines is elevated with increasing adiposity. Not surprisingly, approaches that reduce adipose tissue depots, including surgical fat removal, exercise, and reduced caloric intake, improve proinflammatory adipokine levels and reduce the severity of their resultant pathologies. Systemic adipokine levels can also be favorably altered by treatment with several of the existing drug classes used to treat insulin resistance, hypertension, and hypercholesterolemia. Greater understanding of adipokine regulation, however, should result in the design of improved treatment strategies to control disease states associated with increase adiposity, an important outcome in view of the growing worldwide epidemic of obesity.

Platelet-activating factor synthesis by neutrophils, monocytes, and endothelial cells is modulated by nitric oxide production

Nitric oxide (NO) and platelet-activating factor (PAF) can modulate the interaction between endothelial lining and circulating leukocytes. Several studies implicated the production of PAF and NO in the pathogenesis of microcirculatory alterations occurring in septic shock. However, the reciprocal interaction between PAF and NO has not been fully elucidated. In the present study, we evaluated whether the basal synthesis of NO could modulate the production of PAF by neutrophils (PMN), monocytes (MO), and endothelial cells (EC) unstimulated or stimulated with lipopolysaccharides (LPS) or tumor necrosis factor (TNF). PMN, MO, and EC, when incubated with N(omega)-nitro-L-arginine methyl ester (L-NAME) spontaneously synthesized PAF, with an early peak at 30 min. The effective inhibition of NO production was visualized on MO cells as generation of fluorescence reactivity by cell-permeable NO reactive dye DAF-2 DA. Also, monomethyl-L-arginine (L-NMMA) induced PAF synthesis by PMN, whereas the biologically inactive D-enantiomers of NAME (D-NAME) and of NMMA (D-NMMA) did not. Stimulation of PMN with L-NAME in presence of the exogenous NO donor nitroprusside, of the NO secondary mediator cGMP, or of the NO synthase substrate L-arginine reduced PAF synthesis, suggesting the involvement of an NO-dependent pathway on the modulation of PAF synthesis. The synthesis of PAF was enhanced by combined treatment with L-NAME and TNF or LPS. These results indicate an inhibitor effect of NO on the spontaneous and TNF or LPS-induced synthesis of PAF by human PMN, MO, and EC.

The effects of L-arginine on atherosclerosis and heart disease

L-arginine, a semi-essential amino acid, can enhance the synthesis of nitric oxide (NO) via the nitric oxide synthase pathway. Enhanced bioavailability of NO may prevent activation of pro-inflammatory endothelial genes by the inhibition of nuclear transcription factor NF 3B, thus preventing the expression of adhesion molecules on endothelial surfaces. Animal studies have demonstrated that the chronic administration of L-arginine reduces the extent of atherosclerosis and prevents xanthoma development in LDL receptor knockout mice. Human studies have demonstrated improvement in endothelium vasodilator function both in coronary arteries and forearm flow responses. In addition oral L-arginine reverses an increased monocyte-endothelial adhesion in men with coronary artery disease and normalizes platelet aggregation in hypercholesterolemic humans. L-arginine may be a promising drug in the therapy of atherosclerosis. (Int J Cardiovasc Interventions

Protective role of endothelial nitric oxide synthase

Nitric oxide is a versatile molecule, with its actions ranging from haemodynamic regulation to anti-proliferative effects on vascular smooth muscle cells. Nitric oxide is produced by the nitric oxide synthases, endothelial NOS (eNOS), neural NOS (nNOS), and inducible NOS (iNOS). Constitutively expressed eNOS produces low concentrations of NO, which is necessary for a good endothelial function and integrity. Endothelial derived NO is often seen as a protective agent in a variety of diseases. This review will focus on the potential protective role of eNOS. We will discuss recent data derived from studies in eNOS knockout mice and other experimental models. Furthermore, the role of eNOS in human diseases is described and possible therapeutic intervention strategies will be discussed.

Oral L-arginine prevents murine coxsackievirus B3 myocarditis

We have previously demonstrated that administration of nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), aggravated murine coxsackievirus B3 myocarditis. In the present study, we evaluated the effects of L-arginine, a precursor of NO, upon acute and chronic myocarditis. Dietary L-arginine and L-arginine plus L-NAME (L-arginine+L-NAME group) were administered to coxsackievirus B3 (CB3)-infected C(3)H/He mice for 2 weeks (experiment I), and to CB3-infected mice from the second week until the fourth week after virus inoculation (experiment II). Infected control was prepared in each experiment. In experiment I, survival was higher in the L-arginine group compared with the other two groups, and cardiac damage was less. In addition, plasma concentrations of L-arginine and NO were elevated in the L-arginine group. In experiment II, cardiomyopathic lesion in the L-arginine group was less prominent associated with lower plasma catecholamine and lower myocardial collagen concentrations compared with the other two groups. Thus, L-arginine treatment may be effective not only in preventing the development of acute CB3 myocarditis but in ameliorating cardiac dysfunction in chronic myocarditis.

Oral L-arginine improves endothelial dysfunction in patients with essential hypertension

BACKGROUND

L-Arginine is a nitric oxide precursor, which augments endothelium-dependent vasodilatation in hypercholesterolemic humans and animals. Endothelium-dependent vasodilation is attenuated in patients with hypertension; however the effects of oral L-arginine on endothelial function of the conduit arteries in patients with essential hypertension have not previously been investigated.

METHODS

In a prospective randomized double blind trial, 35 patients with essential hypertension received either 6 g L-arginine (18 subjects) or placebo (17 subjects). Patients were examined for flow-mediated endothelium-dependent dilatation of the brachial artery before and 1.5 h after administration of L-arginine or placebo. At the end of the protocol the nitrate-induced, endothelium-independent vasodilatation was evaluated.

RESULTS

Two groups of L-arginine and placebo were similar regarding age, sex, blood lipids, smoking, diabetes, coronary artery disease, body mass index, intima-media thickness of the common carotid artery, clinics blood pressure and baseline brachial artery parameters. Administration of L-arginine or placebo did not change significantly heart rate, blood pressure, baseline diameter, blood flow or reactive hyperemia. L-Arginine resulted in a significant improvement of flow-mediated dilatation (1.7+/-3.4 vs. 5.9+/-5.4%, P=0.008) while placebo did not significantly change this parameter (3.0+/-2.7 vs. 3.1+/-2.2%, P=ns). The effect of L-arginine on flow-mediated dilatation was significantly different from the effect of placebo (P=0.05). L-Arginine did not significantly influence nitrate-induced dilatation (16+/-6.9 vs. 17.7+/-6.7%, P=ns).

CONCLUSIONS

Oral administration of L-arginine acutely improves endothelium-dependent, flow-mediated dilatation of the brachial artery in patients with essential hypertension. The long-term effects of L-arginine in these patients require further investigation.

L-arginine and antineutrophil serum enable venular control of capillary perfusion in hypercholesterolemic rats

OBJECTIVE

The purpose of this study was to investigate and counteract dysfunctional control of capillary flow in hypercholesterolemia. Capillary flow is controlled by arteriolar tone, which in turn is influenced by mediators released from closely paired venules in a mechanism that involves nitric oxide (NO). However, venular control of capillary flow is altered with hypercholesterolemia.

METHODS

Rats were given a normal or high-cholesterol diet before measurements of mesenteric capillary red blood cell velocity. The arteriolar pathway leading to the capillary was videotaped to measure the percent of the surrounding area (within 15 |gmm) that was occupied by a venule (% pairing).

RESULTS

Venule-paired arterioles were significantly smaller in hypercholesterolemia compared with normocholesterolemia, corresponding to slower capillary flow. A positive correlation between capillary velocity and % pairing observed in normocholesterolemia was not observed during NO synthase inhibition or in hypercholesterolemic rats. However, positive correlations between the two parameters were found in hypercholesterolemia when the rats were given drinking water supplementation of L-arginine or an injection of antineutrophil serum, both of which tended to improve velocity in capillaries branching from venule-paired arteriolar pathways.

CONCLUSIONS

Dysfunctional venular control of capillary perfusion in hypercholesterolemia may be a consequence of a neutrophil-mediated deficiency of NO.

Native LDL and minimally oxidized LDL differentially regulate superoxide anion in vascular endothelium in situ

Low-density lipoprotein (LDL) and its oxidized derivatives are hypothesized to impair vascular function by increasing superoxide anion (O.). To investigate mechanisms in situ, isolated carotid arteries were incubated with native LDL (nLDL) or minimally oxidized LDL (mmLDL). With the use of en face fluorescent confocal microscopy and hydroethidine, an oxidant-sensitive fluorescent probe, we found that nLDL increased O. in vascular endothelium greater than fourfold by an N(omega)-nitro-L-arginine methyl ester (L-NAME)-inhibitable mechanism. In contrast, mmLDL increased O. in vascular endothelium greater than eightfold by mechanisms that were partially inhibited by L-NAME and allopurinol and essentially ablated by diphenyleneiodium. These data indicate that both nLDL and mmLDL uncouple endothelial nitric oxide synthase (eNOS) activity and that mmLDL also activates xanthine oxidase and NADPH oxidoreductase to induce greater increases in O. generation than nLDL. Western analysis revealed that both lipoproteins inhibited A-23187-stimulated association of heat shock protein 90 (HSP90) with eNOS without inhibiting phosphorylation of eNOS at serine-1179 (phospho-eNOS), an immunological index of electron flow through the enzyme. As HSP90 mediates the balance of.NO and O. generation by eNOS, these data provide new insight into the mechanisms by which oxidative stress, induced by nLDL and mmLDL, uncouple eNOS activity to increase endothelial O. generation.

Inhibition of major histocompatibility complex class II gene transcription by nitric oxide and antioxidants

Interferon (IFN)-gamma facilitates cellular immune response, in part, by inducing the expression of major histocompatibility complex class II (MHC-II) molecules. We demonstrate that IFN-gamma induces the expression of HLA-DRA in vascular endothelial cells via mechanisms involving reactive oxygen species. IFN-gamma-induced HLA-DRA expression was inhibited by nitric oxide (NO) and antioxidants such as superoxide dismutase, catalase, pyrrolidine dithiocarbamate, and N-acetylcysteine. Nuclear run-on assays demonstrated that NO and antioxidants inhibited IFN-gamma-induced HLA-DRA gene transcription. Transient transfection studies using a fully functional HLA-DRA promoter construct ([-300]DR alpha.CAT) showed that inhibition of endogenous NO synthase activity by N(omega)-monomethyl-l-arginine or addition of exogenous hydrogen peroxide (H(2)O(2)) augmented basal and IFN-gamma-stimulated [-300]DR alpha.CAT activity. However, H(2)O(2) and N(omega)-monomethyl-l-arginine could induce HLA-DRA expression suggesting that H(2)O(2) is a necessary but not a sufficient mediator of IFN-gamma-induced HLA-DRA expression. Electrophoretic mobility shift assay and Western blotting demonstrated that NO and antioxidants had little or no effect on IFN-gamma-induced IRF-1 activation or MHC-II transactivator (CIITA) expression but did inhibit IFN-gamma-induced activation of STAT1 alpha (p91) and Y box transcription factors, NF-Y(A) and NF-Y(B). These results indicate that NO and antioxidants may attenuate vascular inflammation by antagonizing the effects of intracellular reactive oxygen species generation by IFN-gamma, which is necessary for MHC-II gene transcription.

Oral administration of L-arginine prevents congestive heart failure in murine viral myocarditis

It was previously demonstrated that administration of the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) aggravated viral myocarditis in mice. In the current study, the effects of l-arginine, a precursor of nitric oxide, on congestive heart failure (CHF) in myocarditis were evaluated. Dietary l-arginine and l-arginine plus l-NAME (l-arginine + l-NAME group) were administered to encephalomyocarditis virus-infected BALB/c mice over 4 weeks (experiment I) and to encephalomyocarditis virus-infected DBA/2 mice from the 4th through 12th weeks after the virus inoculation (experiment II). An infected control was prepared in each experiment. In experiment I, survival was higher in the l-arginine group compared with the other two groups, and cardiac damage was less, as was incidence of CHF. In addition, extravasated fibrin was less prominent in the l-arginine group. Plasma concentrations of l-arginine and nitric oxide were elevated in the l-arginine group. In experiment II, plasma cardiomyopathic lesions in the l-arginine group were less prominent and were associated with lower plasma catecholamine and lower myocardial collagen concentrations compared with the other two groups. l-arginine treatment may be effective in preventing the development of CHF in viral myocarditis by modifying postmyocarditic architectural remodeling.

Cholesterol-induced upregulation of angiotensin II and its effects on monocyte-endothelial interaction and superoxide production

Atherogenesis involves an early endothelial dysfunction hallmarked by elevated free radical production and increased adhesiveness for monocytes. It was hypothesized that activation of the tissue renin angiotensin system may contribute to the endothelial alteration. To test this hypothesis, thoracic aortae were isolated from normocholesterolemic (NC; n = 6) and hypercholesterolemic (HC; n = 6; diet: 0.5% cholesterol; 6 weeks) New Zealand white rabbits, and incubated for 2 h with the angiotensin II (Ang II) receptor antagonist Sar-1,Ile-8-Ang II, the antioxidant pyrolidine dithiocarbamate (PDTC) and the protein kinase C (PKC) antagonist staurosporin. Superoxide production from aortic segments was measured by lucigenin-enhanced chemiluminescence. In comparison to the normocholesterolemic state, hypercholesterolemia led to a significant increase in superoxide production (221 +/- 44%, p < 0.02); this was reduced by ex vivo treatment of the vessel segment with Ang II-antagonist (to 130 +/- 29%; p < 0.04 vs HC), or PKC-antagonist (to 86 +/- 26%; p < 0.001 vs HC), or PDTC (to 103 +/- 27%; p < 0.02 vs HC). Monocyte-endothelial interaction was assessed by functional binding assay. When compared to normocholesterolemic rabbits, hypercholesterolemia led to a twofold increase in monocyte binding (74 +/- 13 vs 37 +/- 4 monocytoid cells per high power field (m/hpf); p < 0.03). The Ang II-antagonist and the PKC-antagonist led to a normalization of monocyte-endothelial binding (Ang II-antagonist: 37 +/- 9 m/hpf; PKC-antagonist: 41 +/- 17 m/hpf; p < 0.05). In conclusion, these results indicate that hypercholesterolemia activates the tissue renin angiotensin system, which results in an increased endothelial production of superoxide and monocyte adhesiveness. Ang II-antagonist inhibits free radical production and monocyte adhesion through a mechanism which may include PKC.

Obesity, atherosclerosis and the vascular endothelium: mechanisms of reduced nitric oxide bioavailability in obese humans

It is now well established that obesity is an independent risk factor for the development of coronary artery atherosclerosis. The maintenance of vascular homeostasis is critically dependent on the continued integrity of vascular endothelial cell function. A key early event in the development of atherosclerosis is thought to be endothelial cell dysfunction. A primary feature of endothelial cell dysfunction is the reduced bioavailability of the signalling molecule nitric oxide (NO), which has important anti atherogenic properties. Recent studies have produced persuasive evidence showing the presence of endothelial dysfunction in obese humans NO bioavailability is dependent on the balance between its production by a family of enzymes, the nitric oxide synthases, and its reaction with reactive oxygen species. The endothelial isoform (eNOS) is responsible for a significant amount of the NO produced in the vascular wall. NO production can be modulated in both physiological and pathophysiological settings, by regulation of the activity of eNOS at a transcriptional and post-transcriptional level, by substrate and co-factor provision and through calcium dependent and independent signalling pathways. The present review discusses general mechanisms of reduced NO bioavailability including factors determining production of both NO and reactive oxygen species. We then focus on the potential factors responsible for endothelial dysfunction in obesity and possible therapeutic interventions targetted at these abnormalities.

Vascular effects of dietary L-arginine supplementation

The vascular endothelium is acknowledged to play an important role in vascular physiology. Attention has focused on endothelial production of nitric oxide as a key element in many of the processes associated with the development of atherosclerosis. L-arginine is the substrate for the enzyme nitric oxide synthase (NOS), which is responsible for the endothelial production of nitric oxide. Therefore, many investigators have been interested in whether dietary L-arginine supplementation can augment nitric oxide production and thereby improve vascular health. The effects of oral L-arginine on vascular health and disease have been examined both in human beings and in various animal models. In this review, we summarize the results of studies of oral L-arginine supplementation on atherosclerotic lesion formation, as well as markers of endothelial function (e.g. macrophage function, platelet aggregation and adhesion, and in vitro vascular ring studies). Although results of oral L-arginine supplementation in hypercholesterolemic animals have generally shown beneficial effects, the data in humans are varied, possibly because of small sample sizes and brief periods of study. Long-term randomized clinical trials are needed to more definitively address whether oral L-arginine supplementation could be advantageous for vascular health.

Increased cardiomyocyte apoptosis following ischemia and reperfusion in diet-induced hypercholesterolemia: relation to Bcl-2 and Bax proteins and caspase-3 activity

It has been reported that apoptosis is a significant contributor to myocardial cell death as a result of reperfusion injury. However, whether the extent of cardiomyocyte apoptosis following ischemia and reperfusion varies in different pathophysiological backgrounds is still uncertain. In this study, we examined whether hypercholesterolemia increases the extent of myocardial reperfusion injury by aggravating cardiomyocyte apoptosis and the effects of hypercholesterolemia on the expression of Bcl-2 and Bax proteins and the activation of caspase-3. Twenty-eight male New Zealand white rabbits were fed standard chow (control, n = 14) or chow supplemented with 10% cholesterol (hypercholesterolemic, n = 14) for 8 wk. Anesthetized rabbits were then subjected to 30 min of left circumflex artery occlusion followed by 4 h of reperfusion. Apoptosis was identified as "DNA ladders" by gel electrophoresis and confirmed histologically using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. The infarct size (% of risk region) was significantly greater in hypercholesterolemic rabbits than in controls (39 +/- 6 vs. 23 +/- 2%, P = 0.02). Very few TUNEL-positive cardiomyocytes could be identified in the nonischemic regions in both groups, consistent with an absence of DNA laddering. In contrast, TUNEL-positive cardiomyocytes were significantly displayed in the ischemic, nonnecrotic myocardium, and DNA ladder occurred in all animals. The percentage of TUNEL-positive cardiomyocytes in the ischemic nonnecrotic myocardium was significantly higher in hypercholesterolemic rabbits compared with controls (40 +/- 5 vs. 17 +/- 11%, P < 0.001). Western blot analysis showed that, in the nonischemic myocardium, hypercholesterolemic rabbits exhibited an approximately 50% increase in the expression of Bcl-2 (P < 0.05), but not Bax, than control rabbits. However, compared with controls, hypercholesterolemic rabbits exhibited a more pronounced decrease in the expression of Bcl-2 (42 +/- 4 vs. 26 +/- 2%, P < 0.01) and a similar extent of increase in the expression of Bax in the ischemic myocardium. Furthermore, hypercholesterolemic rabbits were associated with a markedly increased activation of caspase-3 within the ischemic myocardium compared to control rabbits. This study demonstrates that although hypercholesterolemia is associated with an increased myocardial Bcl-2/Bax ratio at baseline, it still significantly exacerbates cardiac reperfusion injury, not only by increasing the infarct size but also by increasing the extent of cardiomyocyte apoptosis.

Maintaining the endothelium: preventive strategies for vessel integrity

The endothelium is a diaphanous membrane, only one cell layer thick, that lines all of our blood vessels. Despite its apparent fragility, it exerts profound control over vascular tone, structure, and intersection with circulating blood elements. One of the factors that the endothelium synthesizes is nitric oxide, which is the most potent endogenous vasodilator known. In addition to its blood flow regulating effects, nitric oxide also inhibits key processes in atherosclerosis, including monocyte adherence, platelet aggregation, and proliferation of vascular smooth muscle cells. Nitric oxide synthesis is impaired, and its degradation is accelerated, in many of the conditions associated with atherosclerosis, including hypercholesterolemia. Restoration of nitric oxide synthesis and activity in these disorders can improve blood flow, relieve symptoms, and perhaps reduce the progression of atherosclerosis.(c) 2001 by CHF, Inc.

Oral L-arginine administration attenuates postprandial endothelial dysfunction in young healthy males

BACKGROUND

Endothelial dysfunction is considered the earliest stage of atherosclerosis. Postprandial phase is associated with a transient impairment of endothelial function concomitantly with the triglyceride-rich lipoprotein increase. This phenomenon may be explained by the oxidative burden induced by triglyceride-rich lipoproteins, reducing nitric oxide bioavailability.

OBJECTIVE

To investigate the effect of a diet enriched with L-arginine, the substrate for nitric oxide synthesis on endothelial function in healthy volunteers.

METHODS

Endothelial function (expressed as flow-mediated vasodilation (FMV) of the brachial artery), total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, LDL-size, Lp (a) and reduced glutathione (GSH) were evaluated in seven healthy males (mean age 23 +/- 3 years) without cardiovascular risk factors. Measurements were made at baseline and 2, 4 and 6 h after a standardized oral fat load. L-arginine (6 g daily) was administered for 10 days. On the 11th day the oral fat load and the parameters examined previously at entry were repeated.

RESULTS

After the first oral fat load, FMV significantly decreased at 2 and 4 h, and overlapped with the basal levels at 6 h. After L-arginine treatment, FMV significantly decreased at 2 h and normalized after 4 and 6 h. Triglycerides increased at 2 and 4 h and decreased after 6 h in both sets of observations relating to before and after L-arginine administration. GSH dropped 2 h after the fat load, both before and after L-arginine. Before L-arginine, FMV exhibited a significant correlation with triglycerides (r= -0.426, P= 0.024) and GSH (r=0.48; P=0.009). After L-arginine, FMV was related to GSH (r=0.39; P=0.03) but not to triglycerides (r= -0.12; P=0.52).

CONCLUSION

Postprandial endothelial impairment is partly abolished by L-arginine administration. These data, which require confirmation, suggest the importance of dietary choice for atherosclerosis prevention even in young healthy subjects.

Atherosclerotic lesions are associated with increased immunoreactivity for inducible nitric oxide synthase and endothelin-1 in thoracic aortic intimal cells of hyperlipidemic Watanabe rabbits

The development and progression of atherosclerotic lesions in Watanabe heritable hyperlipidemic rabbits is associated with increases in inducible nitric oxide synthase (NOS2) and endothelin-1 (ET-1) immunoreactivity. In contrast, there is a reduction of immunoreactivity for neuronal NOS (NOS1) in aortic endothelial cells, but no change in endothelial NOS (NOS3) immunoreactivity. However, subendothelial macrophages and smooth muscle showed a different pattern of immunoreactivity of NADPH-diaphorase (NADPH-d), NOS2, ET-1, and NOS1. The lipid-rich macrophages in the intima were positively labeled for NADPH-d, NOS1, NOS2, NOS3, and ET-1. Smooth muscle cells in the subendothelium and the medial layers of the vascular wall were also positive for these markers. These results are consistent with the reduction of endothelium-dependent vasorelaxation that is known to occur during the development and progression of atherosclerosis in familial hypercholesterolemia. The data suggest a key role for vasoactive substances in the development of atherosclerosis.

Endothelium-dependent vasodilation is independent of the plasma L-arginine/ADMA ratio in men with stable angina: lack of effect of oral L-arginine on endothelial function, oxidative stress and exercise performance

OBJECTIVES

This study was designed to determine the effect of two weeks' treatment with L-arginine on the ratio of plasma L-arginine to asymmetric dimethylarginine (ADMA), oxidative stress, endothelium-dependent vasodilatation to acetylcholine, exercise performance and heart rate variability in men with stable angina.

BACKGROUND

The ratio of plasma L-arginine:ADMA has been proposed as a determinant of endothelium-dependent dilation; dietary supplementation with L-arginine has been shown to improve endothelium-dependent vasodilation and symptoms in some conditions.

METHODS

Men (n = 40) with stable angina, at least one epicardial coronary artery with a stenosis >50% and a positive exercise test were randomized to receive L-arginine (15 g daily) or placebo for two weeks according to a double-blind parallel-group design. Plasma L-arginine, ADMA, 8-epi-prostaglandin F2alpha (a marker of oxidative stress) and forearm vasodilator responses to brachial artery infusion of nitroprusside and acetylcholine (+/-L-arginine) were measured. A standard Bruce protocol exercise test was performed before and at the end of the treatment period.

RESULTS

Plasma L-arginine increased after oral L-arginine, whereas ADMA remained unchanged, leading to an increase in the L-arginine/ADMA ratio of 62 +/- 11% (mean +/- SE, p < 0.01). Despite a significant enhancement in acetylcholine response by intra-arterial L-arginine at baseline, this response remained unchanged after oral L-arginine. Measures of oxidative stress and exercise performance after L-arginine/placebo were similar in placebo and active groups.

CONCLUSIONS

In men with stable angina, an increase in plasma L-arginine/ADMA ratio after two weeks' oral supplementation with L-arginine is not associated with an improvement in endothelium-dependent vasodilatation, oxidative stress or exercise performance.

The clinical pharmacology of L-arginine

L-Arginine (2-amino-5-guanidinovaleric acid) is the precursor of nitric oxide, an endogenous messenger molecule involved in a variety of endothelium-mediated physiological effects in the vascular system. Acute and chronic administration of L-arginine has been shown to improve endothelial function in animal models of hypercholesterolemia and atherosclerosis. L-Arginine also improves endothelium-dependent vasodilation in humans with hypercholesterolemia and atherosclerosis. The responsiveness to L-arginine depends on the specific cardiovascular disease studied, the vessel segment, and morphology of the artery. The pharmacokinetics of L-arginine have recently been investigated. Side effects are rare and mostly mild and dose dependent. The mechanism of action of L-arginine may involve nitric oxide synthase substrate provision, especially in patients with elevated levels of the endogenous NO synthase inhibitor asymmetric dimethylarginine. Endocrine effects and unspecific reactions may contribute to L-arginine-induced vasodilation after higher doses. Several long-term studies have been performed that show that chronic oral administration of L-arginine or intermittent infusion therapy with L-arginine can improve clinical symptoms of cardiovascular disease in man.

Atherogenesis and the arginine hypothesis

In patients who have elevated levels of plasma ADMA, a relative deficiency of L-arginine has been found to contribute to the pathophysiology of athersclerosis, causing vasoconstriction, and accelerating atherogenesis. This finding--that there is a relative deficiency of L-arginine in atherosclerotic disease--is a breakthrough that will open new avenues of therapy.

L-arginine polymers inhibit the development of vein graft neointimal hyperplasia

OBJECTIVE

We sought to determine whether L -arginine polymer treatment of vein grafts enhances vascular production of nitric oxide and inhibits the development of neointimal hyperplasia.

METHODS

External jugular veins of New Zealand White rabbits (n = 42) were harvested; treated intraluminally for 15 minutes with phosphate-buffered saline solution or L -arginine polymer 5, 7, or 9 at either 10 or 100 micromol/L; and then grafted into the contralateral carotid artery. Rabbits were killed after 28 days, and 5-microm sections of vessels were stained with hematoxylin and scored for intima/media ratio by using computerized morphometric analysis. Separate veins were treated in a similar fashion with biotinylated polymers and phosphate-buffered saline solution to assess for translocation efficiencies. Finally, vein segments pretreated with either phosphate-buffered saline solution or L -arginine polymers were cultured in Dulbecco's modified Eagle's medium containing lipopolysaccharide (100 microg/mL) and interferon gamma (200 U/mL) for 48 hours before measuring nitric oxide levels by means of the Griess reaction.

RESULTS

Biotinylated L -arginine polymers demonstrated a dose- and length-dependent uptake into intimal and medial cells of treated vessels. Nitric oxide levels were significantly higher in vein segments treated with 100 micromol/L of L -arginine polymer 9 compared with control segments. Finally, the intima/media ratio also reflected both length- and concentration-dependent inhibition of neointimal hyperplasia.intima/media ratio PBS R5 R7 R9 10 micromol/L 0.909 +/- 0.072 0.920 +/- 0.073 0.861 +/- 0.138 0.710 +/- 0.122 100 micromol/L 0.924 +/- 0.061 0.581 +/- 0.089* 0.529 +/- 0.093* PBS, Phosphate-buffered saline solution; R, L -arginine polymer. *P <.001 versus phosphate-buffered saline solution and L -arginine polymer 5 controls (Bonferroni-corrected value).

CONCLUSIONS

Arginine polymers of sufficient length and concentration were effective in increasing nitric oxide levels and reducing neointimal hyperplasia in this vein graft model.

Long-term oral L-arginine administration improves peripheral and hepatic insulin sensitivity in type 2 diabetic patients

The aim of this study was to evaluate whether long-term administration of arginine acting through a normalization of NO/cyclic-guanosine-3' 5'-cyclic monophosphate (cGMP) pathway was able to ameliorate peripheral and hepatic insulin sensitivity in 12 lean type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

A double-blind study was performed for 3 months. In the first month, patients were treated with their usual diet. Then they were randomly allocated into to groups. In group 1, patients were treated with diet plus placebo (orally three times per day) for 2 months. In group 2 patients were treated for 1 month with diet plus placebo orally, three times per day) and then for 1 month with diet plus L-arginine (3 g three times per day). At the end of the first and the second month of therapy, patients underwent a euglycemic-hyperinsulinemic clamp combined with [6,6-2H2] glucose infusion. A total of 10 normal subjects underwent the same test as control subjects.

RESULTS

In group 1, no changes in basal cGMP levels, systolic blood pressure, forearm blood flow, glucose disposal, and endogenous glucose production were observed throughout. In group 2, L-arginine normalized basal cGMP levels and significantly increased forearm blood flow by 36% and glucose disposal during the clamp by 34% whereas it decreased systolic blood pressure and endogenous glucose production by 14 and 29%, respectively. However, compared with normal subjects, L-arginine treatment was not able to completely overcome the defect in glucose disposal.

CONCLUSIONS

L-Arginine treatment significantly improves but does not completely normalizc peripheral and hepatic insulin sensitivity in type 2 diabetic patients.