A calcium channel blocker activates both ecto-5′-nucleotidase and NO synthase in HUVEC

Antiatherosclerotic and anti-insulin resistance effects of adiponectin: basic and clinical studies

Adiponectin is a protein secreted by adipose cells that may couple regulation of insulin sensitivity with energy metabolism and serve to link obesity with insulin resistance. Obesity-related disorders characterized by insulin resistance including the metabolic syndrome, diabetes, atherosclerosis, hypertension, and coronary artery disease are associated with both decreased adiponectin levels and endothelial dysfunction. Recent studies demonstrate that adiponectin has insulin-sensitizing effects as well as antiatherogenic properties. Lifestyle modifications and some drug therapies to treat atherosclerosis, hypertension, diabetes, and coronary heart disease have important effects in increasing adiponectin levels, decreasing insulin resistance, and improving endothelial dysfunction. In this review, we discuss insights into the relationships between adiponectin levels, insulin resistance, and endothelial dysfunction that are derived from various therapeutic interventions. The effects of lifestyle modifications and cardiovascular drugs on adiponectin levels and insulin resistance suggest plausible mechanisms that may be important for understanding and treating atherosclerosis and coronary heart disease.

Does reversal of oxidative stress and inflammation provide vascular protection?

Chronic inflammation is a pathogenic feature of atherosclerosis and cardiovascular disease mediated by substances including angiotensin II, proinflammatory cytokines, and free fatty acids. This promotes generation of reactive oxygen species in vascular endothelial cells and smooth muscle cells, which mediate injury through several mechanisms. Reciprocal relationships between endothelial dysfunction and insulin resistance as well as cross-talk between hyperlipidaemia and the renin-angiotensin-aldosterone system (RAAS) at multiple levels contribute importantly to a variety of risk factors. Therefore, combination therapy that simultaneously addresses multiple mechanisms for the pathogenesis of atherosclerosis is an attractive emerging concept for slowing progression of atherosclerosis. Combined therapy with statins, peroxisome proliferator-activated receptors, and RAAS blockade demonstrates additive beneficial effects on endothelial dysfunction and insulin resistance when compared with monotherapies in patients with cardiovascular risk factors due to both distinct and interrelated mechanisms. These additive beneficial effects of combined therapies are consistent with laboratory and recent clinical studies. Thus, combination therapy may be an important paradigm for treating and slowing progression of atherosclerosis, coronary heart disease, and co-morbid metabolic disorders characterized by endothelial dysfunction and insulin resistance.

Distinct vascular and metabolic effects of different classes of anti-hypertensive drugs

BACKGROUND

ASCOT-BPLA study demonstrates that in hypertensive subjects, atenolol+bendroflumethiazide therapy is associated with higher incidence of adverse cardiovascular outcomes and developing diabetes than an amlodipine+perindopril regimen. This is not explained by changes in blood pressure alone. We hypothesized that distinct vascular and metabolic effects of anti-hypertensive drugs may explain these differential effects.

METHODS

Either placebo or one class of anti-hypertensive drug (atenolol 100 mg, amlodipine 10 mg, hydrochlorothiazide 50 mg, ramipril 10 mg, or candesartan 16 mg) was given daily during 8 weeks to 31 patients in each of 6 arms of a randomized, single-blind, placebo-controlled, parallel study.

RESULTS

Atenolol, amlodipine, and candesartan therapies significantly reduced systolic blood pressure when compared with ramipril (P<0.05 by ANOVA). Atenolol and thiazide therapies increased triglycerides levels greater than ramipril or candesartan (P=0.005 by ANOVA). Amlodipine significantly increased HDL cholesterol levels greater than atenolol (P=0.011 by ANOVA). Ramipril and candesartan therapies improved FMD and increased adiponectin levels and insulin sensitivity to a greater extent than atenolol or thiazide therapies (P<0.001 and P<0.015 by ANOVA). Amlodipine therapy increased adiponectin levels greater than atenolol therapy (P<0.05 by ANOVA). Ramipril, candesartan, and amlodipine therapies significantly decreased leptin levels to a greater extent when compared with atenolol or thiazide therapies (P<0.001 by ANOVA). Amlodipine therapies significantly decreased resistin levels greater than ramipril or candesartan therapies (P=0.001 by ANOVA).

CONCLUSIONS

We observed differential effects of anti-hypertensive drugs on endothelial dysfunction and plasma adipocytokines.

Nitric oxide and atherosclerosis: an update

Nitric oxide (NO) is a molecule that has gained recognition as a crucial modulator of vascular disease. NO has a number of intracellular effects that lead to vasorelaxation, endothelial regeneration, inhibition of leukocyte chemotaxis, and platelet adhesion. Endothelium damage induced by atherosclerosis leads to the reduction in bioactivity of endothelial NO synthase (eNOS) with subsequent impaired release of NO together with a local enhanced degradation of NO by increased generation of reactive oxygen species with subsequent cascade of oxidation-sensitive mechanisms in the arterial wall. Many commonly used vasculoprotective agents have their therapeutic actions through the production of NO. L-Arginine, the precursor of NO, has demonstrated beneficial effects in atherosclerosis and disturbed shear stress. Finally, eNOS gene polymorphism might be an additional risk factor that may contribute to predict cardiovascular events. However, further studies are needed to understand the possible clinical implications of these correlations.

Endothelial antioxidant actions of dihydropyridines and angiotensin converting enzyme inhibitors

Dihydropyridines and angiotensin converting enzyme inhibitor effects on superoxide and nitric oxide (NO) were compared in high glucose (20 mM, 24 h)-treated human Ea.hy 926 endothelial cells. High glucose stimulated superoxide both extracellularly (lucigenin chemiluminescence, cytochrome c reduction) and intracellularly (dihydrorhodamine 123 fluorescence). The dihydropyridines amlodipine, nisoldipine, BayK 8644 or the angiotensin converting enzyme inhibitors captopril and enalaprilat attenuated extra- and intracellular superoxide formation; nifedipine blocked extracellular increases only, ramiprilat was without antioxidant effect. Dihydropyridines and captopril also prevented NADPH-driven superoxide release. Antioxidant actions were blunted by a bradykinin B(2) receptor antagonist or an inhibitor of p38 mitogen activated protein kinase (MAPK), and were accompanied by improved NO release (amperometric sensor). p38MAPK inhibition prevented the NO-sparing actions of dihydropyridines but not angiotensin converting enzyme inhibitors. Thus, dihydropyridines and angiotensin converting enzyme inhibitors limit high glucose-induced superoxide formation and improve NO bioavailability in human endothelial cells, in part via bradykinin and p38MAPK.

Modulation of ecto-5'-nucleotidase by phospholipids in human umbilical vein endothelial cells (HUVEC)

Ecto-5'-nucleotidase, the major enzyme controlling extracellular adenosine production, can be activated by phospholipids, e.g. lysophosphatidylcholine (LPC). This study examined the structural requirements of phospholipids to evoke this enzyme activation and figured out two new activators of ecto-5'-nucleotidase: platelet activating factor (PAF) and sphingosylphosphorylcholine (SPC). Potential signal transduction pathways including an involvement of protein kinase C and PAF-receptor were evaluated on the model of human umbilical vein endothelial cells (HUVEC). Cells were pre-incubated with 10 microM of various phospholipids including lysophosphatidylcholine, beta-arachidonyl-gamma-palmityl-alpha-phosphatidylcholine, beta,gamma-dipalmityl-alpha-phosphatidyl-choline, beta,gamma-dipalmityl-alpha-phosphatidylethanolamine, beta,gamma-dipalmityl-alpha-phosphatidylserine, gamma-acyl-beta-lyso-alpha-phosphatidylethanolamine, beta-acetyl-gamma-O-hexadecyl-alpha-phosphatidylcholine (platelet activating factor), lysophosphatidylic acid, sphingosine-1-phosphate and sphingosylphosphorylcholine. In the cell supernatant the extracellular dephosphorylation rate of the fluorescent AMP-analogue 1,N6-etheno-5'AMP to 1,N6-etheno-adenosine was measured by HPLC. Out of these ten structurally related phospholipids only lysophosphatidylcholine, sphingosylphosphatidylcholine and platelet activating factor dose-dependently increased the activity of ecto-5'-nucleotidase. Pharmacological blocking experiments revealed that neither the activation of PAF-receptor nor of protein kinase C were important for mediating the activation of ecto-5'-nucleotidase. Thus, using information on the known molecular structures of tested phospholipids, a phosphatidylcholine residue in alpha-position and a short chain length fatty acid esterified in beta-position seem essential for activation of ecto-5'-nucleotidase by glycerophospholipids. Since all tested phospholipids have similar fatty acid chain lengths and residues in alpha-position, they should act similarly on membrane fluidity. It is concluded that the observed effects are not based on changes in membrane fluidity by the added phospholipids, but rather involve a yet to be determined phospholipid-receptor.

Antioxidant and nitric oxide-sparing actions of dihydropyridines and ACE inhibitors differ in human endothelial cells

The effects of dihydropyridine Ca2+ channel blockers (DHP) and ACE inhibitors on superoxide formation and nitric oxide (NO) bioavailability were compared in human EA.Hy926 endothelial cells (EC). EC were stimulated 4 h with angiotensin II (Ang II, 10 nM) +/- study drugs. Specific superoxide formation was measured by lucigenin-enhanced chemiluminescence, reduction of cytochrome c and rhodamine-123 fluorescence. Free NO release was determined with an amperometric NO sensor. NADPH oxidase subunits expression was examined with Western Blot. In untreated EC the intracellular superoxide is -64.3 +/- 6.0% decreased compared to Ang II stimulated EC. Elevated extracellular superoxide formation was on a -43.0 +/- 1.7% lower level in untreated EC. The DHP Ca2+-channel agonist BayK8644 and ACE inhibitors captopril and ramiprilat led extracellular superoxide concentration to control level. Enalaprilat blocked extracellular superoxide, the DHP amlodipine and nisoldipine prevented intracellular increases only (n = 8-9, p < 0.05). Icatibant (HOE 140), a kinin-B2 receptor antagonist, attenuated antioxidant actions of all tested agents except of nisoldipine. Ang II-induced superoxide was elevated by the phorbolester PMA and blocked by the protein kinase C (PKC) inhibitor chelerythrine. Suppression of substance P-evoked NO release by Ang II (>70%, n = 6) was reversed by the PKC inhibitor chelerythrine, the DHP amlodipine and nisoldipine and the ACE inhibitor ramiprilat. Further, Ang II reduces Nox-4 expression by 34.5 +/- 4.9. Nox-2 expression was not regulated. DHP and ACE inhibitors exert different antioxidant effects in human EC stimulated with Ang II, but both improve NO bioavailability via bradykinin and modulation of redox-regulating enzymes.

A calcium channel blocker amlodipine increases coronary blood flow via both adenosine- and NO-dependent mechanisms in ischemic hearts

Amlodipine reduces oxidative stress that decreases NO and adenosine release. This study was undertaken to examine whether amlodipine mediates coronary vasodilation and improves myocardial metabolism and contractility in ischemic hearts via either adenosine- or NO-dependent mechanisms. In open-chest dogs, amlodipine (2 mug kg per min) was infused at the minimum dose that caused maximal coronary vasodilation. The perfusion pressure was reduced in the left anterior descending coronary artery so that coronary blood flow (CBF) decreased by 50%. Amlodipine increased the difference of the adenosine level (VAD (Ado): 119+/-14 to 281+/-46 nM) and the nitrate+nitrite level (VAD (NOx): 7.8+/-1.3 to 16.1+/-1.1 muM) between coronary venous and coronary arterial blood, and also increased CBF (50+/-3 to 69+/-6 ml/100 g/min). These changes were partially reversed by either 8-sulfophenyeltheophylline (8SPT) or l(omega)-nitro arginine methyl ester (l-NAME), and were completely blocked by both 8SPT and l-NAME. The reduction of CBF increased VAD (8-iso-prostaglandin F(2alpha)), and this increase was reduced by amlodipine (10.8+/-1.1 to 5.0+/-0.5 pg/ml). In addition, pretreatment with superoxide dismutase mimicked the coronary effects of amlodipine and blunted the response to amlodipine administration. Amlodipine-induced coronary vasodilation via both adenosine- and NO-dependent mechanisms. Adenosine and NO may interact in ischemic hearts to mediate coronary vasodilation by amlodipine.