Lipids and endothelial function: effects of lipid-lowering and other therapeutic interventions

Exploring the relationship between biomechanical stresses and coronary atherosclerosis

The pathophysiology of coronary atherosclerosis is multifaceted. Plaque initiation and progression are governed by a complex interplay between genetic and environmental factors acting through processes such as lipid accumulation, altered haemodynamics and inflammation. There is increasing recognition that biomechanical stresses play an important role in atherogenesis, and integration of these metrics with clinical imaging has potential to significantly improve cardiovascular risk prediction. In this review, we present the calculation of coronary biomechanical stresses from first principles and computational methods, including endothelial shear stress (ESS), plaque structural stress (PSS) and axial plaque stress (APS). We discuss the current experimental and human data linking these stresses to the natural history of coronary artery disease and explore the future potential for refining treatment options and predicting future ischaemic events.

Triglyceride to HDL-cholesterol ratio as an independent risk factor for the poor development of coronary collateral circulation in elderly patients with ST-segment elevation myocardial infarction and acute total occlusion

To determine the prognostic role of triglyceride (TG) to high-density lipoprotein cholesterol (HDL) ratio for poorly developed coronary collateral circulation (CCC) in elderly patients with ST-segment elevation myocardial infarction (STEMI) and acute total occlusion (ATO).As a retrospective case-control study, elderly patients (age ≥60 years) with both STEMI and ATO (n = 346) were classified as having either poorly- or well-developed CCC (Rentrop grades 0-1 and 2-3, respectively). The ratio of TG/HDL was calculated according to the detected levels of TG and HDL. The difference of TG/HDL ratio in those 2 groups was compared by Student t test, and multivariate logistic regression analysis indicating occurrence of poorly developed CCC was performed. Receiver operator characteristic curve (ROC) analysis of TG/HDL ratio which determine the optimal cut-off value of TG/HDL ratio was applied.The TG/HDL ratio was significantly higher in patients with poorly developed CCC than in those with well-developed CCC (2.88 ± 2.52 vs 1.81 ± 1.18, P < .001). In multivariate logistic regression analysis, higher TG/HDL ratio (OR 1.789, 95% CI 1 . 346-2.378, P < .001) and the presence of left circumflex branch of coronary artery (LCX) occlusion (OR6.235, 95% CI 2.220-17.510, P = .001) were emerged as independent positive predictors of poor development of CCC, whereas presence of right coronary artery (RCA) occlusion (OR 0.474, 95% CI 0.265-0.850, P = .002) and onset time (OR 0.693, 95% CI 0.620-0.775, P < .001) were found as negative indicators. The optimal cut-off value of TG/HDL ratio was found as 1.58 in ROC analysis, which yielded an area under the curve value of 0.716 (95% CI 0.654-0.778, P < .001) and demonstrated a sensitivity of 80.9% and a specificity of 59.3% for prediction of poorly developed CCC.TG/HDL ratio is an independent risk factor for predicting poor development of CCC in elderly patients with STEMI and ATO.

Cellular biomarkers of endothelial health: microparticles, endothelial progenitor cells, and circulating endothelial cells

Endothelial dysfunction, the shift from a healthy endothelium to a damaged pro-coagulative, pro-inflammatory, and pro-vasoconstrictive phenotype, is an early event in many chronic diseases that frequently precedes cardiovascular complications. Functional assessment of the endothelium can identify endothelial damage and predict cardiovascular risk; however, this assessment provides little information as to the mechanisms underlying development of endothelial dysfunction. Changes in plasma asymmetric dimethyl arginine levels, markers of lipid peroxidation, circulating levels of inflammatory mediators, indices of coagulation and cellular surrogates such as microparticles, circulating endothelial cells, and endothelial progenitor cells may reflect alterations in endothelial status and as such have been defined as "biomarkers" of endothelial function. Biomarkers may be chemical or cellular. This review examines some markers of endothelial dysfunction, with a particular focus on cellular biomarkers of endothelial dysfunction and their diagnostic potential.

Acute coronary syndromes: diagnosis and management, part I

The term acute coronary syndrome (ACS) refers to any group of clinical symptoms compatible with acute myocardial ischemia and includes unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). These high-risk manifestations of coronary atherosclerosis are important causes of the use of emergency medical care and hospitalization in the United States. A quick but thorough assessment of the patient's history and findings on physical examination, electrocardiography, radiologic studies, and cardiac biomarker tests permit accurate diagnosis and aid in early risk stratification, which is essential for guiding treatment. High-risk patients with UA/NSTEMI are often treated with an early invasive strategy involving cardiac catheterization and prompt revascularization of viable myocardium at risk. Clinical outcomes can be optimized by revascularization coupled with aggressive medical therapy that includes anti-ischemic, antiplatelet, anticoagulant, and lipid-lowering drugs. Evidence-based guidelines provide recommendations for the management of ACS; however, therapeutic approaches to the management of ACS continue to evolve at a rapid pace driven by a multitude of large-scale randomized controlled trials. Thus, clinicians are frequently faced with the problem of determining which drug or therapeutic strategy will achieve the best results. This article summarizes the evidence and provides the clinician with the latest information about the pathophysiology, clinical presentation, and risk stratification of ACS and the management of UA/NSTEMI.

Acute coronary syndromes: diagnosis and management, part I

The term acute coronary syndrome (ACS) refers to any group of clinical symptoms compatible with acute myocardial ischemia and includes unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). These high-risk manifestations of coronary atherosclerosis are important causes of the use of emergency medical care and hospitalization in the United States. A quick but thorough assessment of the patient's history and findings on physical examination, electrocardiography, radiologic studies, and cardiac biomarker tests permit accurate diagnosis and aid in early risk stratification, which is essential for guiding treatment. High-risk patients with UA/NSTEMI are often treated with an early invasive strategy involving cardiac catheterization and prompt revascularization of viable myocardium at risk. Clinical outcomes can be optimized by revascularization coupled with aggressive medical therapy that includes anti-ischemic, antiplatelet, anticoagulant, and lipid-lowering drugs. Evidence-based guidelines provide recommendations for the management of ACS; however, therapeutic approaches to the management of ACS continue to evolve at a rapid pace driven by a multitude of large-scale randomized controlled trials. Thus, clinicians are frequently faced with the problem of determining which drug or therapeutic strategy will achieve the best results. This article summarizes the evidence and provides the clinician with the latest information about the pathophysiology, clinical presentation, and risk stratification of ACS and the management of UA/NSTEMI.

Rosuvastatin protects against angiotensin II-induced renal injury in a dose-dependent fashion

OBJECTIVE

We showed earlier that statin treatment ameliorates target-organ injury in a transgenic model of angiotensin (Ang) II-induced hypertension. We now test the hypothesis that rosuvastatin (1, 10, and 50 mg/kg/day) influences leukocyte adhesion and infiltration, prevents induction of inducible nitric oxide synthase (iNOS), and ameliorates target-organ damage in a dose-dependent fashion.

METHODS

We treated rats harboring the human renin and human angiotensinogen genes (dTGR) from week 4 to 8 (n = 20 per group). Untreated dTGR developed severe hypertension, cardiac hypertrophy, and renal damage, with a 100-fold increased albuminuria and focal cortical necrosis. Mortality of untreated dTGR at age 8 weeks was 59%.

RESULTS

Rosuvastatin treatment decreased mortality dose-dependently. Blood pressure was not affected. Albuminuria was reduced dose-dependently. Interstitial adhesion molecule (ICAM)-1 expression was markedly reduced by rosuvastatin, as were neutrophil and monocyte infiltration. Immunohistochemistry showed an increased endothelial and medial iNOS expression in small vessels, infiltrating cells, afferent arterioles, and glomeruli of dTGR. Immunoreactivity was stronger in cortex than medulla. Rosuvastatin markedly reduced the iNOS expression in both cortex and medulla. Finally, matrix protein (type IV collagen, fibronectin) expression was also dose- dependently reduced by rosuvastatin.

CONCLUSION

Our findings indicate that rosuvastatin dose- dependently ameliorates angiotensin II-induced-organ damage and almost completely prevents inflammation at the highest dose. The data implicate 3-hydroxy-3-methylglutaryl coenzyme A function in signaling events leading to target-organ damage.

Should standard medical therapy for angina include a statin?

Although a wealth of evidence supports the use of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) in patients with clinically evident coronary artery disease, these agents are still underutilized. Statins are the most effective agents in reducing low-density lipoprotein-cholesterol among lipid-lowering drugs, and studies have recently shown that they improve endothelial function and plaque stabilization, and induce regression of atherosclerotic lesions. This article reviews the most recent evidence and guideline recommendations supporting the use of statins in chronic stable angina pectoris and acute coronary syndromes.

Relevance of different apolipoprotein content in binding of homocysteine to plasma lipoproteins

BACKGROUND AND AIMS

In plasma the atherogenic thiol homocysteine (Hcy) circulates either free or bound to proteins (Pb-Hcy). The present study sets out to evaluate the lipoprotein-Hcy (LP-Hcy) binding in vivo and the possible influence of different apolipoprotein content in this binding, being lipoprotein oxidation a possible mechanism of Hcy-induced damage.

METHODS AND RESULTS

In 34 healthy subjects we assayed fasting plasma lipoprotein and correspondent apolipoprotein (apo A-I, apo A-II, apo C-II, apo C-III, apo B, apo(a) and apo E content, and Hcy bound to different plasma protein fractions; moreover ten subjects underwent an oral methionine load in order to evaluate possible "dynamic" modifications of Pb-Hcy and LP-Hcy after induction of hyperhomocysteinemia. Pb-Hcy (mean values 9.22 +/- 1.7 mumol/L) represented about 78% of total plasma Hcy (mean values 11.8 +/- 1.8 mumol/L). Pb-Hcy distribution between the different fractions was as follows (mumol/L): VLDL = 0.25 +/- 0.08 (2.7%); LDL = 0.88 +/- 0.22 (9.5%); HDL = 1.40 +/- 0.36 (15.2%); fractions with density greater than 1.21 g/mL (Lipoprotein-Free Protein Fraction, LPDS) = 6.7 +/- 1.2 (72.6%). Hcy/protein ratios (nmol/mg of protein) in each protein fraction were: VLDL = 0.32 +/- 0.19, LDL = 0.43 +/- 0.37, HDL = 0.26 +/- 0.18, LPDS < 0.1, thus suggesting a higher binding capacity for Hcy by VLDL and LDL. These data were confirmed by the higher increase in Hcy content in LDL and VLDL (76 and 90%, respectively vs 36% and 3.1% for HDL and LPDS fractions) after hyperhomocysteinemia. Lp-Hcy binding significantly correlated with the apo B content of VLDL and LDL and Apo A-I content of HDL.

CONCLUSIONS

An important fraction of plasma Hcy circulates bound to LP (about 27% of Pb-Hcy); VLDL and LDL show the highest binding capacity for Hcy, probably due to their content in Apo B, a possible high capacity binding site for Hcy.

Pathogenetic concepts of acute coronary syndromes

The propensity of plaque to disrupt is a major determinant of future ischemic events. Although they are distinct from one another, the atherosclerotic and thrombotic processes appear to be interdependent and may be integrated under the term "atherothrombosis." It is now clear that plaque composition, rather than the percent stenosis, is a major determinant of plaque vulnerability. Plaque disruption seems to depend on both passive and active phenomena and is not purely mechanical. Inflammation (activation of monocytes/macrophages) is a major determinant of both plaque vulnerability and thrombogenicity as they relate to plaque disruption. In one-third of acute coronary syndromes, there is, however, no plaque disruption but only superficial erosion of a markedly stenotic, fibrotic plaque. In these cases, thrombus formation may be exacerbated by a hyperthrombogenic state present in patients with certain systemic risk factors. The endothelium plays a pivotal role in vascular homeostasis and hemostasis. This dynamic organ regulates blood thrombogenicity as well as contractile, secretory, and mitogenic activities in the vessel wall. Some classic risk factors induce endothelial dysfunction by reducing the bioavailability of nitric oxide, increasing tissue endothelin-1, and activating pro-inflammatory signaling pathways. Vascular hemostasis, which is the maintenance of blood fluidity and vascular integrity, is achieved by counter-balancing the intrinsic clotting tendency of blood. As a consequence of the central role of endothelial cells in hemostatic control, a dysfunctional endothelium will generate a pro-thrombotic environment favoring development of atherosclerotic lesions and thrombotic complications.

Biologic aspects of vulnerable plaque

Atherosclerosis and its thrombotic complications are the major cause of morbidity and mortality in the industrialized world. The progression of atherosclerotic plaques in coronary circulation is modulated by several risk factors. It is now clear that plaque composition is a major determinant of plaque disruption and superimposed thrombosis. Plaque vulnerability, defined as the propensity of plaques to disrupt, is further determined by intrinsic and extrinsic triggering factors. After disruption, the fatty core of the plaque and its high content of tissue factor provide a powerful substrate for the activation of the coagulation cascade. Plaque disruption can be clinically silent or cause symptoms of ischemia depending on thrombus burden and the degree of vessel occlusion. In addition, plaque disruption and subsequent healing are recognized to play key roles in the rapid plaque progression. This review looks at the mechanisms underlying the development and progression of atherosclerotic plaques, factors leading to plaque rupture and subsequent thrombosis, and their clinical consequences as potential targets for future research.

Statins modulate oxidized low-density lipoprotein-mediated adhesion molecule expression in human coronary artery endothelial cells: role of LOX-1

LOX-1, a receptor for oxidized low-density lipoprotein (ox-LDL), plays a critical role in endothelial dysfunction and atherosclerosis. LOX-1 activation also plays an important role in monocyte adhesion to endothelial cells. A number of studies show that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) reduce total LDL cholesterol and exert a cardioprotective effect. We examined the modulation of LOX-1 expression and its function by two different statins, simvastatin and atorvastatin, in human coronary artery endothelial cells (HCAECs). We observed that ox-LDL (40 microg/ml) treatment up-regulated the expression of E- and P-selectins, VCAM-1 and ICAM-1 in HCAECs. Ox-LDL mediated these effects via LOX-1, since antisense to LOX-1 mRNA decreased LOX-1 expression and subsequent adhesion molecule expression. Pretreatment of HCAECs with simvastatin or atorvastatin (1 and 10 microM) reduced ox-LDL-induced expression of LOX-1 as well as adhesion molecules (all P < 0.05). A high concentration of statins (10 microM) was more potent than the low concentration (1 microM) (P < 0.05). Both statins reduced ox-LDL-mediated activation of the redox-sensitive nuclear factor-kappaB (NF-kappaB) but not AP-1. These observations indicate that LOX-1 activation plays an important role in ox-LDL-induced expression of adhesion molecules. Inhibition of expression of LOX-1 and adhesion molecules and activation of NF-kappaB may be another mechanism of beneficial effects of statins in vascular diseases.

Inhibition of LOX-1 by statins may relate to upregulation of eNOS

LOX-1, a receptor for oxidized low-density lipoprotein (ox-LDL), plays a critical role in endothelial dysfunction and atherosclerosis; both of these conditions are associated with diminished expression of constitutive endothelial nitric oxide synthase (eNOS). Recent studies show that HMG CoA reductase inhibitors (statins) exert cardioprotective effect. We examined the role of LOX-1 in eNOS expression and modulation of this relationship by two different statins, simvastatin and atorvastatin in human coronary artery endothelial cells (HCAECs). Ox-LDL (40 microg/ml) upregulated the expression of LOX-1; simultaneously, there was a reduction in eNOS expression. Pretreatment of HCAECs with simvastatin or atorvastatin (1 and 10 microM) reduced ox-LDL-induced upregulation of LOX-1 and downregulation of eNOS (both P < 0.05). High concentration of statins (10 microM) was more potent than the low concentration (1 microM) (P < 0.05). Both statins also attenuated ox-LDL-mediated activation of MAP kinase. These observations indicate that statins attenuate the effect of ox-LDL on eNOS expression. Inhibitory effect on LOX-1 and subsequently MAP kinase activity provides a potential mechanism of beneficial effects of statins beyond lowering cholesterol.

Can the potential benefits of statins in general medical practice be extrapolated to liver transplantation?

Hypercholesterolemia is a common complication of liver transplantation and is a risk factor for cardiovascular disease after renal and heart transplant. The effect of hyperlipidemia after liver transplantation is less certain, but a less favorable outcome is to be expected. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors or statins have proven efficacy in reducing serum cholesterol and mortality from cardiovascular disease in the general population. Early evidence shows that statins are safe and effective in treating hypercholesterolemia after liver transplantation. Studies in cardiovascular disease have shown that statins exhibit beneficial properties independent of lipid-lowering. These include anti-inflammatory effects and improvement in endothelial function. Recently, statins were shown to repress induction of major histocompatibility complex class II complexes by interferon-gamma, which in turn suppresses activation of T lymphocytes. Such effects may assume significance when using statins after solid-organ transplants. Pravastatin has been shown to reduce acute rejection after cardiac and renal transplantation and to also reduce natural killer cell cytotoxicity in these populations. It remains to be seen whether statins will demonstrate similar benefits after liver transplantation.

Involvement of oxidation-sensitive mechanisms in the cardiovascular effects of hypercholesterolemia

Hypercholesterolemia is a common clinical metabolic and/or genetic disorder that promotes functional and structural vascular wall injury. The underlying mechanisms for these deleterious effects involve a local inflammatory response and release of cytokines and growth factors. Consequent activation of oxidation-sensitive mechanisms in the arterial wall, modulation of intracellular signaling pathways, increased oxidation of low-density lipoprotein cholesterol, and quenching of nitric oxide can all impair the functions controlled by the vascular wall and lead to the development of atherosclerosis. This cascade represents a common pathological mechanism activated by various cardiovascular risk factors and may partly underlie synergism among them as well as the early pathogenesis of atherosclerosis. Antioxidant intervention and restoration of the bioavailability of nitric oxide have been shown to mitigate functional and structural arterial alterations and improve cardiovascular outcomes. Elucidation of the precise nature and role of early transductional signaling pathways and transcriptional events activated in hypercholesterolemia in children and adults, including mothers during pregnancy, and understanding their downstream effects responsible for atherogenesis may help in directing preventive and interventional measures against atherogenesis and vascular dysfunction.

Cerivastatin prevents angiotensin II-induced renal injury independent of blood pressure- and cholesterol-lowering effects

BACKGROUND

Statins are effective in prevention of end-organ damage; however, the benefits cannot be fully explained on the basis of cholesterol reduction. We used an angiotensin II (Ang II)-dependent model to test the hypothesis that cerivastatin prevents leukocyte adhesion and infiltration, induction of inducible nitric oxide synthase (iNOS), and ameliorates end-organ damage.

METHODS

We analyzed intracellular targets, such as mitogen-activated protein kinase and transcription factor (nuclear factor-kappaB and activator protein-1) activation. We used immunohistochemistry, immunocytochemistry, electrophoretic mobility shift assays, and enzyme-linked immunosorbent assay techniques. We treated rats transgenic for human renin and angiotensinogen (dTGR) chronically from week 4 to 7 with cerivastatin (0.5 mg/kg by gavage).

RESULTS

Untreated dTGR developed hypertension, cardiac hypertrophy, and renal damage, with a 100-fold increased albuminuria and focal cortical necrosis. dTGR mortality at the age of seven weeks was 45%. Immunohistochemistry showed increased iNOS expression in the endothelium and media of small vessels, infiltrating cells, afferent arterioles, and glomeruli of dTGR, which was greater in cortex than medulla. Phosphorylated extracellular signal regulated kinase (p-ERK) was increased in dTGR; nuclear factor-kappaB and activator protein-1 were both activated. Cerivastatin decreased systolic blood pressure compared with untreated dTGR (147 +/- 14 vs. 201 +/- 6 mm Hg, P < 0.001). Albuminuria was reduced by 60% (P = 0.001), and creatinine was lowered (0.45 +/- 0.01 vs. 0.68 +/- 0.05 mg/dL, P = 0. 003); however, cholesterol was not reduced. Intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression was diminished, while neutrophil and monocyte infiltration in the kidney was markedly reduced. ERK phosphorylation and transcription factor activation were reduced. In addition, in vitro incubation of vascular smooth muscle cells with cerivastatin (0.5 micromol/L) almost completely prevented the Ang II-induced ERK phosphorylation.

CONCLUSION

Cerivastatin reduced inflammation, cell proliferation, and iNOS induction, which led to a reduction in cellular damage. Our findings suggest that 3-hydroxy-3-methylglutaryl coenzyme (HMG-CoA) reductase inhibition ameliorates Ang II-induced end-organ damage. We suggest that these effects were independent of cholesterol.

Lipids, cardiovascular disease and atherosclerosis in systemic lupus erythematosus

Systemic lupus erythematosus is commonly associated with early onset cardiovascular disease and is often associated with hyperlipidaemia. This review examines the evidence for an increased prevalence of both CHD and hyperlipidaemia in SLE and mechanisms by which autoimmunity in SLE could accelerate the progression of atheroma. It postulates how lipid lowering therapies used in cardiological disease might help reduce the incidence of CHD in SLE.

Rapid restoration of normal endothelial functions in genetically hyperlipidemic mice by a synthetic mediator of reverse lipid transport

Endothelial dysfunction is a major pathophysiological consequence of hypercholesterolemia and other conditions. We examined whether a synthetic mediator of lipid transport from peripheral tissues to the liver (ie, the "reverse" pathway) could restore normal endothelial function in vivo. Using assays of macrovascular and microvascular function, we found that genetically hypercholesterolemic apolipoprotein E knockout mice exhibited key endothelial impairments. Treatment of the mice for 1 week with daily intravenous bolus injections of large "empty" phospholipid vesicles, which accelerate the reverse pathway in vivo, restored endothelium-dependent relaxation, leukocyte adherence, and endothelial expression of vascular cell adhesion molecule-1 to normal or nearly normal levels. These changes occurred despite the long-standing hyperlipidemia of the animals and the persistence of high serum concentrations of cholesterol-rich atherogenic lipoproteins during the treatment. Our results indicate that dysfunctional macrovascular and microvascular endothelium in apolipoprotein E knockout mice can recover relatively quickly in vivo and that accelerated reverse lipid transport may be a useful therapy.

The effect of fenofibrate treatment on endothelium-dependent relaxation induced by oxidative modified low density lipoprotein from hyperlipidemic patients

The objective of the research project was to investigate whether fenofibrate treatment may alter the biochemical content of the oxidized LDL and consequently its ability to impair the endothelium-dependent relaxation in hyperlipidemic patients. We hypothesized that fenofibrate treatment of hyperlipidemic patients may attenuate the ability of their oxidized LDL to impair the endothelium-dependent relaxation of the blood vessels as a consequence of fenofibrate-induced changes to the content and composition of lysoPC in the LDL molecule. Hyperlipidemic patients (Type IIb and Type IV) were recruited from the Lipid Clinic, HSC, Winnipeg, Canada, for this study. A blood sample was taken immediately after the recruitment, a second sample was taken after 6 weeks of dietary treatment, and a third sample was taken after 8 weeks of fenofibrate treatment. LDL was isolated from the plasma and oxidized by copper sulfate. Fenofibrate was shown to be highly effect in the reduction of total cholesterol, LDL cholesterol and triglycerides in these patients. Fenofibrate treatment also caused the attenuation of impairment of endothelium-dependent relaxation by the oxidized LDL from these patients. A slight reduction of lysophosphatidylcholine level was also found in the oxidized LDL of the fenofibrate treated patients, relative to LDL isolated after dietary treatment. In addition there were no changes in the fatty acid levels of the lysophosphatidylcholine isolated from LDL. Taken together, our results suggest that while the reduced lysophosphatidylcholine levels may contribute to the attenuated impairment of the endothelium-dependent relaxation of the aortic ring, other unidentified factors impacted by fenofibrate are likely to contribute to the attenuated effects.

Effect of atorvastatin on endothelium-dependent constrictor factors in dyslipidemic rabbits

Relaxations to acetylcholine and contractions to acetylcholine in the presence of the nitric oxide (NO) synthesis inhibitor (L-N(G)-nitroarginine methyl ester, L-NAME) were studied in aortic rings from rabbits fed either a control or a diet containing 0.5% cholesterol+14% coconut oil for 14 weeks and treated or not with atorvastatin (2.5 mg kg(-1) day(-1)). Rings were incubated with the endothelin (ET(A)) receptor antagonist BQ123, and/or the thromboxane A(2) (TXA(2))/prostaglandin H(2) (PGH(2)) receptor antagonist ifetroban. In rabbits, high cholesterol and triglyceride plasma levels were associated with intimal thickening and blunted acetylcholine-relaxation as compared with controls. By contrast, acetylcholine+L-NAME response was higher. Incubation with either ifetroban or BQ123 increased acetylcholine-relaxation in both diet groups and it reduced the constrictor response only in dyslipidemic rabbits. Removal of endothelium reduced acetylcholine+L-NAME contraction in dyslipidemic rabbits, although increased it in control animals. Atorvastatin treatment reduced plasma lipid levels and lesion size in dyslipidemic animals. Likewise, it prevented acetylcholine-relaxation reduction. In addition, atorvastatin reduced constrictor response in dyslipidemic rabbits but only in rings with endothelium. Incubation with either ifetroban or BQ123 did not further modify these responses in atorvastatin-treated animals in any group. These data suggest that ET and TXA(2) availabilities seem to participate in the endothelial dysfunction associated with dyslipidemia. Atorvastatin treatment reduces intimal thickening and improves endothelial dysfunction in rabbits. This effect seems to be a consequence of its ability to act on ET and TXA(2) systems.

Abnormalities of endothelial function in patients with predialysis renal failure

BACKGROUND

Endothelial dysfunction plays an important role in the development of atherosclerotic vascular disease, which is the leading cause of mortality in patients with chronic renal failure.

OBJECTIVE

To examine the relation between predialysis renal failure and endothelial function.

DESIGN

Two groups were studied: 80 patients with non-diabetic chronic renal failure and 26 healthy controls, with similar age and sex distributions. Two indices of endothelial function were assessed: high resolution ultrasonography to measure flow mediated endothelium dependent dilatation of the brachial artery following reactive hyperaemia, and plasma concentration of von Willebrand factor. Endothelium independent dilatation was also assessed following sublingual glyceryl trinitrate. The patients were divided into those with and without overt atherosclerotic vascular disease.

RESULTS

Although patients with chronic renal failure had significantly impaired endothelium dependent dilatation compared with controls (median (interquartile range), 2.6% (0.7% to 4.8%) v 6.5% (4.8% to 8.3%); p < 0.001) and increased von Willebrand factor (254 (207 to 294) v 106 (87 to 138) iu/dl; p < 0.001), there was no difference between renal failure patients with and without atherosclerotic vascular disease. Within the chronic renal failure group, endothelium dependent dilatation and von Willebrand factor were similar in patients in the upper and lower quartiles of glomerular filtration rate (2.7% (0.7% to 6.7%) v 2.8% (1.1% to 5.0%); and 255 (205 to 291) v 254 (209 to 292) iu/dl, respectively). Endothelium independent dilatation did not differ between the renal failure or control groups and was also similar in patients with renal failure irrespective of the degree of renal failure or the presence of atherosclerotic vascular disease.

CONCLUSIONS

Endothelial function is abnormal in chronic renal failure, even in patients with mild renal insufficiency and those without atherosclerotic vascular disease, suggesting that uraemia may directly promote the development of atherosclerosis early in the progression of chronic renal failure.

Intense physical training decreases circulating antioxidants and endothelium-dependent vasodilatation in vivo

Physical training increases free radical production and consumes antioxidants. It has previously been shown that acute exercise markedly increases the susceptibility of LDL to oxidation but whether such changes are observed during physical training is unknown. We measured circulating antioxidants, lipids and lipoproteins, and blood flow responses to intrabrachial infusions of endothelium-dependent (acetylcholine, ACh, L-N-monomethyl-arginine, L-NMMA) and -independent (sodium nitroprusside, SNP) vasoactive agents, before and after 3 months of running in 9 fit male subjects. Maximal aerobic power increased from 53 +/- 1 to 58 +/- 2 ml/kg min (P < 0.02). All circulating antioxidants (uric acid, SH-groups, alpha-tocopherol, beta-carotene, retinol) except ascorbate decreased significantly during training. Endothelium-dependent vasodilatation in forearm vessels decreased by 32-35% (P < 0.05), as determined from blood flow responses to both a low (10.8 +/- 2.1 vs. 7.3 +/- 1.5 ml/dl min, 0 vs. 3 months) and a high (14.8 +/- 2.6 vs. 9.6 +/- 1.8) ACh dose. The % endothelium-dependent blood flow (% decrease in basal flow by L-NMMA), decreased through training from 37 +/- 3 to 22 +/- 7% (P < 0.05). Blood flow responses to SNP remained unchanged. The decrease in uric acid was significantly correlated with the change in the % decrease in blood flow by L-NMMA (r = 0.74, P < 0.05). The lag time for the susceptibility of plasma LDL to oxidation in vitro, LDL size and the concentration of LDL cholestetol remained unchanged. We conclude that relatively intense aerobic training decreases circulating antioxidant concentrations and impairs endothelial function in forearm vessels.

Endogenous nitric oxide synthase inhibitor: a novel marker of atherosclerosis

BACKGROUND

Exposure to risk factors such as hypertension or hypercholesterolemia decreases the bioavailability of endothelium-derived nitric oxide (NO) and impairs endothelium-dependent vasodilation. Recently, a circulating endogenous NO synthase inhibitor, asymmetric dimethylarginine (ADMA), has been detected in human plasma. The purpose of this study was to examine the relationship between plasma ADMA and atherosclerosis in humans.

METHODS AND RESULTS

Subjects (n=116; age, 52+/-1 years; male:female ratio, 100:16) underwent a complete history and physical examination, determination of serum chemistries and ADMA levels, and duplex scanning of the carotid arteries. These individuals had no symptoms of coronary or peripheral artery disease and were taking no medications. Univariate and multivariate analyses revealed that plasma levels of ADMA were positively correlated with age (P<0.0001), mean arterial pressure (P<0.0001), and Sigma glucose (an index of glucose tolerance) (P=0.0006). Most intriguingly, stepwise regression analysis revealed that plasma ADMA levels were significantly correlated to the intima-media thickness of the carotid artery (as measured by high-resolution ultrasonography).

CONCLUSIONS

This study reveals that plasma ADMA levels are positively correlated with risk factors for atherosclerosis. Furthermore, plasma ADMA level is significantly correlated with carotid intima-media thickness. Our results suggest that this endogenous antagonist of NO synthase may be a marker of atherosclerosis.

Heme oxygenase isozymes in bone: induction of HO-1 mRNA following physiological levels of mechanical loading in vivo

Heme oxygenases (HO) are responsible for the production of carbon monoxide, which has been suggested to act similarly to nitric oxide as a signaling molecule. Inducible HO-1 and constitutive HO-2 were located in sections of weight-bearing ulnae of the rat by immunocytochemistry. Intense HO-1 localization was restricted to peri- and endosteal sites, whereas HO-2 staining occurred in osteoblasts and osteocytes throughout the cortex. Northern blot hybridization of mRNA levels for HO-1 and HO-2 extracted from bones was also performed. Six hours after a single 10 min period of noninvasive mechanical loading of the ulna in vivo, generating physiological levels of strain sufficient to initiate an osteogenic response, the level of mRNA for the inducible HO-1 isoform was increased, but that of HO-2 was unchanged. The presence of a constitutive and strain-related upregulation of an inducible enzyme capable of producing carbon monoxide suggests that carbon monoxide may participate not only in bone cells' basal metabolism but also in their adaptive response to mechanical load.

Pathogenesis of atherosclerosis: a possible relation to infection

Atherosclerosis is the main underlying cause of coronary heart disease, which in turn is the most common cause of death in the industrialized world. An acute event in coronary heart disease is typically precipitated by thrombosis occurring at the site of atherosclerotic plaque disruption. Atherosclerotic plaques consist of a fibrous cap overlying a lipid-rich core. Many cell types are involved in their formation, including platelets, endothelial cells, activated monocytes, macrophages derived from monocytes and smooth muscle cells. The currently accepted hypothesis is that atherosclerosis develops as a response to injury and that it is primarily a chronic inflammatory condition. The endothelium plays an important role in regulating vascular blood flow and it is now apparent that endothelial dysfunction is an important contributor to the pathogenesis of atherosclerosis. There is growing evidence that infection may be a risk factor for atherosclerosis and myocardial infarction. Numerous studies have reported associations between human coronary heart disease (CHD) and bacterial and viral infections. At present, interest is focused on the potential aetiological role of C. pneumoniae which has been repeatedly identified, using various diagnostic techniques, in atherosclerotic lesions. There is also increasing seroepidemiological evidence of the association between C. pneumoniae and CHD. The role of this organism in atherosclerosis may be analogous to that of chronic C. trachomatis infection in trachoma.

Homocysteine stimulates the production and secretion of cholesterol in hepatic cells

Homocysteinemia and hypercholesterolemia are important risk factors associated with the occurrence of arteriosclerotic vascular diseases. A positive correlation between plasma levels of homocysteine and cholesterol was found in homocysteinemic patients as well as in experimental animals. In the present study, the effect of homocysteine on the production and secretion of cholesterol in human hepatoma cell line HepG2 cells was investigated. When cells were incubated with 4 mM homocysteine, the amounts of total cholesterol produced as well as the cholesterol secreted by these cells were significantly increased (from 32 +/- 5 to 74 +/- 5 nmol/mg cellular protein). Further biochemical analyses revealed that the increase in cholesterol was resulted from an enhancement in the production and secretion of the unesterified cholesterol with no concomitant change in the level of cholesteryl esters. The activity of intracellular 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was markedly elevated by 131% and 190% after cells were incubated with homocysteine for 24 and 48 h. Homocysteine also stimulated the secretion of apo B100 by HepG2 cells (from 0.84 +/- 0.11 to 1.37 +/- 0.12 micrograms apolipoprotein B/mg cellular protein). Our results demonstrate that homocysteine stimulates the production and secretion of cholesterol and apolipoprotein B100 in HepG2 cells. The increase in the production of cholesterol induced by homocysteine may contribute to the pathogenesis of arteriosclerosis.

Extrahepatic cytochrome P450: role in in situ toxicity and cell-specific hormone sensitivity

It is clear that members of the Cytochrome P450 supergene family are responsible for the majority of activations of procarcinogens to ultimate carcinogens in the body. These procarcinogens include the food mutagens (heterocyclic amines), pesticides, polycyclic aromatic hydrocarbons and nitrosamines. The Cyp P450 profile in a cell can indicate the capacity of that cell to form reactive metabolites. Furthermore, environmental factors, through their action on P450s, influence the fate of procarcinogens in a cell. This is because different isoforms of P450 are regulated differently by ethanol, diet and environmental inducers, have different substrate specificities and different propensity to be inhibited or activated by dietary components. Cyp P450 (through steroid inactivation), can also influence sensitivity of cells to hormones. Age and hormone related regulation of P450 isoforms such as 1A1, 2B1 and 2A3 in the breast suggest that in situ activation of carcinogens and hormone inactivation can occur in the breast. In the brain and endometrium most of the #P450 isoforms remain to be identified.

Effects of lipid-lowering agents in the Dahl salt-sensitive rat

Inducing renal cytochrome P4504A (P4504A) activity with clofibrate prevents the development of hypertension in Dahl salt-sensitive (Dahl S) rats. To determine if this also occurs with other antilipidemic agents, we compared the effects of a related drug, fenofibrate, with those of an unrelated agent, pravastatin, on blood pressure, renal histology, and P4504A activity. Dahl S rats were pretreated with fenofibrate (95 mg/kg per day), pravastatin (70 mg/kg per day), or vehicle for 7 days before and after being switched from a low-salt (0.1% NaCl) to a high-salt (8.0% NaCl) diet. After 3 weeks on the high-salt diet, mean arterial pressures averaged 183+/-13 (n=9), 126+/-10 (n=9), and 148+/-11 mm Hg (n=8), respectively, in vehicle-, fenofibrate-, and pravastatin-treated animals. Both drugs reduced the degree of proteinuria and glomerular injury. P4504A protein levels and the synthesis of 20-hydroxyeicosa-5,8,11,14-tetraenoic acid (20-HETE) were increased in the liver and kidney of fenofibrate-treated, but not pravastatin-treated rats. We also administered these agents to Dahl S rats in which hypertension had previously been induced by a high-salt diet. Mean arterial pressures averaged 164+/-10, 113+/-23, and 160+/-15 mm Hg in rats treated with vehicle, fenofibrate, or pravastatin for 3 weeks. Fenofibrate-treated rats exhibited a natriuresis. Proteinuria and glomerular injury were reduced by pravastatin but not by fenofibrate. These results indicate that fenofibrate prevented the development of hypertension and reduced subsequent glomerular injury in Dahl S rats, probably secondary to increased renal production of 20-HETE. Although pravastatin did not induce renal P4504A activity in these animals, it reduced the severity of hypertension and renal damage through some other mechanism.